GMPV2.3 | Archives of Earth Processes - Advances in Geochronology, Trace Element and Isotope Geochemistry
EDI
Archives of Earth Processes - Advances in Geochronology, Trace Element and Isotope Geochemistry
Convener: Johannes RembeECSECS | Co-conveners: Aratz Beranoaguirre, Aileen DoranECSECS, Dawid SzymanowskiECSECS, Lorenzo TavazzaniECSECS, Caroline Lotout, Goran Andjic
Orals
| Mon, 15 Apr, 08:30–12:25 (CEST)
 
Room D3
Posters on site
| Attendance Mon, 15 Apr, 16:15–18:00 (CEST) | Display Mon, 15 Apr, 14:00–18:00
 
Hall X1
Posters virtual
| Attendance Mon, 15 Apr, 14:00–15:45 (CEST) | Display Mon, 15 Apr, 08:30–18:00
 
vHall X1
Orals |
Mon, 08:30
Mon, 16:15
Mon, 14:00
Geochronology and geochemistry are useful tools in geoscience research, covering all geological environments in the Earth`s crust. They are giving us different information about earth surface processes (e.g., biogenic, diagenetic, sedimentary), and processes at deeper levels of earth`s crust (e.g., hydrothermal, magmatic, metamorphic). Therefore, refining our understanding of rock-forming processes can contribute towards addressing important geological and societal problems, such as the Earth`s past and present carbon cycle or the exploration of critical raw materials. Carbonates, for instance, are forming in a wide range of geological settings and are nearly ubiquitous on earth. They are capable of aiding in understanding past climate evolution, as well as tectonic or metamorphic processes by providing time and temperature constraints.
Recent analytical developments allow for the application of geochronological, trace element and isotope geochemical techniques across a wide range of scales and sample materials. Currently, we are able to analyze and date more precisely and accurately than ever before, as well as to work with isotopic systems that were unimaginable in the past. Consequently, geochronological and geochemical studies are blooming in a variety of fields and in many cases could revolutionize our understanding of rates of fundamental natural processes.
This session aims to bring together an interdisciplinary community working both on method development (sample preparation, analytical techniques, interpretation and modelling approaches) and on the application of such methods to a variety of problems across the Earth sciences, across the geological time and scales. We invite geoscientists from all fields (e.g., paleo-oceanology, economic geology, igneous/metamorphic petrology, carbon storage) to contribute to this session by presenting their research in geochronology and geochemistry.

This session is a merge of two sessions: "Carbonate Geochronology, Trace Element and Stable Isotope Geochemistry — Applications and Advances" and "Temporal Framework of Geological Processes: Methods and Applications of Geochronology"

Orals: Mon, 15 Apr | Room D3

Chairpersons: Aratz Beranoaguirre, Caroline Lotout
08:30–08:35
Methods and Applications of Geochronology
08:35–08:45
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EGU24-14940
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ECS
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solicited
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On-site presentation
Patrick Carr, Rolf Romer, David Chew, Richard Wirth, and Julien Mercadier

Geochronological data on ore-bearing minerals can constrain the absolute ages and duration mineralising processes. Of the tungsten-bearing minerals, wolframite is the most promising geochronometer for these mineral systems, but high precision ages are hampered by common Pb and intra-grain heterogeneity. We present ID-TIMS and LA-ICP-MS U-Pb isotope data of wolframite , combined with milli scale (SEM-EDS) and microscale (LA-ICP-MS) element maps and nanoscale (FIB-TEM) chemical and structural images to elucidate the complex geochemical behaviour of this mineral and the implications for U-Pb geochronology.

During this study, three new U-Pb reference materials have been developed with ages of ca 158 Ma, 289 Ma and 325 Ma; these are available to interested laboratories. The best precision obtained by ID-TIMS was 1.24%, whilst we estimate the best possible precision for LA-ICP-MS ages to be ca 1.8%. Apart for analytical uncertainties, the main contributor to age uncertainty is the poor dispersion in U-Pb data (for Discordia fitting) and unknown common Pb composition for ID-TIMS data, and micron-scale heterogeneity for LA-ICP-MS data.

Microscale (LA-ICP-MS maps) to nanoscale (FIB-TEM) imaging techniques show large chemical and structural heterogeneity of wolframite related to the complex geological environments in which it is precipitated and altered. Trace element mapping highlights oscillatory and sector zoning not typically observed when using traditional SEM-based techniques. The variable distribution of the analysed elements (Fe, Mn, Sc, Nb, Ta, Y, Pb, Th and U for this study) can be explained both by coupled substitution and changing fluid chemistry recorded within a single wolframite crystal. The nano-scale structure of a strongly altered wolframite is characterised by rare ca 10x10 nm non-symmetric zones of amorphous crystal structure, and bands of elongate (ca 100 x 20 nm oval-shaped) low density zones that we consider representing porosity developed during rapid crystallisation of wolframite.

Although no real intra-grain age dispersion is observed in the analysed samples, the precision of U-Pb ages is strongly affected by the local chemical and structural characteristics of the wolframite. Most notably, the concentration of 238U and 238U/204Pb can vary by an order of magnitude within a zone smaller than a typically laser ablation spot (e.g., 100 µm).

 

How to cite: Carr, P., Romer, R., Chew, D., Wirth, R., and Mercadier, J.: Nano to milli scale characteristics of wolframite ([Fe,Mn]WO4)  and their implications for U-Pb geochronology of tungsten-bearing mineral deposits, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14940, https://doi.org/10.5194/egusphere-egu24-14940, 2024.

08:45–08:55
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EGU24-13231
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ECS
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On-site presentation
Johannes E. Pohlner, Siqi Hao, Richard Albert, Axel Gerdes, Daniel J. Schulze, Herwart Helmstaedt, and Sonja Aulbach

Intrusions of the Navajo Volcanic Field (NVF) contain eclogite xenoliths that record processes related to the subduction of the Farallon plate beneath the Colorado Plateau. Previous geochronological work sparked controversies about their origin, especially whether they are derived from oceanic crust of the Farallon plate, or from older continental lithosphere, based on occasional Proterozoic zircon U-Pb ages. Moreover, the mechanisms and timescales of the recorded high-pressure processes, including several stages of fluid metasomatism, are largely unknown. We study the U-Pb systematics of garnet, zircon and rutile by LA-ICP-MS in order to achieve a refined petrochronologic interpretation of the NVF eclogites.

The eclogite xenoliths are hosted by serpentinized ultramafic microbreccia (SUM) which intruded the Colorado Plateau at ~30 Ma as a consequence of extensive hydration of the lithospheric mantle by Farallon slab-derived fluids. In contrast to kimberlite-borne eclogite xenoliths, which often contain garnet and omphacite only, those of the NVF additionally contain ubiquitous rutile, and often pyrite, phengite, zoisite pseudomorphs after lawsonite (with rare lawsonite relics), accessory monazite, and rare coesite. Based on this assemblage, peak P-T conditions around 4 GPa and 600°C are estimated. Subsequent rapid uplift in the sub-solidus SUM is not thought to have caused significant further heating. Except for a few instances where a mid-ocean ridge basalt-like bulk chemical composition is essentially preserved, the xenoliths are strongly overprinted by several metasomatic events in the eclogite facies. Most notably, this involved interaction with a Na-Si-S-rich fluid, probably of crustal origin, and a later (just prior to exhumation) serpentinite-derived fluid.

All our U-Pb rutile data as well as published U-Pb monazite data (~29 Ma) agree with the ~30 Ma SUM formation age. The majority of the U-Pb zircon analyses predate the rutile data by not more than several Myr, with a minority of older ages forming a continuum to the late Cretaceous. Unlike some earlier studies, we did not obtain any Proterozoic U-Pb zircon ages. The garnet U-Pb dates, which are mostly from pre-metasomatic zones, partly agree with the zircon dates within uncertainty, but sometimes predate the zircon dates from the same sample by up to several tens of Myr.

Despite moderate peak metamorphic temperatures (~600°C), rutile remained an open system for Pb until exhumation. Garnet and zircon are resistant to Pb volume diffusion at these temperatures, however, the zircon ages appear to be largely reset during fluid metasomatism, as also indicated by often high common Pb contents. Due to the absence of preserved igneous zircon ages, the protolith origin remains uncertain. Garnet, which grew mostly before metasomatism, seems to provide robust ages of initial eclogitization, which may have been diachronous in our sample suite. Geochronological evidence implies that several tens of Myr passed between initial eclogitization and exhumation of the xenoliths.

How to cite: Pohlner, J. E., Hao, S., Albert, R., Gerdes, A., Schulze, D. J., Helmstaedt, H., and Aulbach, S.: Garnet, zircon and rutile U-Pb systematics of eclogite xenoliths from the Navajo Volcanic Field (USA), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13231, https://doi.org/10.5194/egusphere-egu24-13231, 2024.

08:55–09:05
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EGU24-15171
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ECS
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Highlight
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On-site presentation
Christopher Barnes, Thomas Zack, Axel Gerdes, Renelle Dubosq, Alfredo Camacho, Delia Rösel, and Michał Bukała

A schist and a marble are used to investigate 40Ar and Sr behaviour in white mica that show distinct records of deformation and fluid-mediated chemical exchange. The rocks were obtained from the upper level of the Middle Allochthon in the northern Scandinavian Caledonides. They underwent eclogite-facies metamorphism (2.4-2.6 GPa/590-660°C) at c. 486-481 Ma and were deformed during juxtaposition with the overlying Upper Allochthon in lower amphibolite/greenschist facies conditions at c. 430-420 Ma. Deformation of the schist is recorded by anastomosing shear bands that delimit polymineralic lenses of white mica, quartz, garnet, and apatite. White mica are only locally deformed along shear bands but show irregular zoning indicative of dissolution-reprecipitation, with high-celadonite zones (XCel: 0.22) generally enveloped by low-celadonite zones (XCel: 0.09). Fluid activity during rock deformation is evinced by the presence of chlorite in shear bands and surrounding partially retrogressed garnet, as well as dissolution-reprecipitation of plagioclase. Mobilization of trace elements is evident, with low-celadonite zones enriched in V, Sr, Nb, Ba and depleted in Li, Ti, Co, Zn relative to high-celadonite zones. The former also shows slight enrichment of average B (35.9 µg/g) compared to the latter (27.2 µg/g), but δ11B values are the same for both zones (-13.5 and -13.6 ‰), suggesting locally-derived fluids. Deformation and foliation development of the marble is characterized by shape preferred orientation of calcite and white mica. The mica show variable grain size and are all deformed, highlighted by electron channeling contrast imaging that reveals abundant µm-scale kink bands within individual grains, a feature that is significantly less apparent in the schist mica. The marble mica show uniform high-celadonite content (XCel: 0.28), representing preservation of high-pressure mica chemistry during deformation. They show no trace element variations, except for a decrease B content with δ11B values (36.3 µg/g and -18.1 ‰ to 15.5 µg/g and -22.0 ‰), which may be explained by heterogeneous devolatilization and preferential loss of 11B during high-grade metamorphism. Thus, it is evident the mica remained closed to chemical exchange during deformation. The white mica 40Ar/39Ar dates from the schist are dispersed (491 ± 4 Ma to 427 ± 4 Ma), with the older dates typically provided by high-celadonite zones, and vice versa. The marble mica yielded a similar range of dates (486 ± 4 Ma to 428 ± 4 Ma), with finer-grains yielding younger dates. Weighted averages of single-spot Rb/Sr dates show a similar pattern for the schist (high-celadonite: 485 ± 8 Ma; low-celadonite: 427 ± 15 Ma). However, Rb/Sr dates from the marble mica only reproduce the older population of dates (481 ± 4 Ma) regardless of grain size. These results demonstrate that loss of 40Ar from white mica can be facilitated by either fluid-mediated chemical exchange or deformation, but re-equilibration of Sr isotopes to reset Rb/Sr dates requires fluid-driven processes in lower amphibolite/upper greenschist facies conditions.

Research funded by NCN grant no. UMO-2021/40/C/ST10/00264 (C.J. Barnes), supported by “Juan de la Cierva” Fellowship JFJC2021-047505-I by MCIN/AEI/10.13039/501100011033 and CSIC (M. Bukała)

How to cite: Barnes, C., Zack, T., Gerdes, A., Dubosq, R., Camacho, A., Rösel, D., and Bukała, M.: Examining the behaviour of Sr and 40Ar in white mica in response to deformation and fluid-mediated chemical exchange, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15171, https://doi.org/10.5194/egusphere-egu24-15171, 2024.

09:05–09:15
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EGU24-11149
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ECS
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On-site presentation
Xin Chen and Yu Wang

Temperature is recognized as the only dominant factor that affects the opening and closing of isotope system, based on which thermochronology has well developed. However, there are some research shows that stress could also matter. The muscovite K-Ar ages of Sanbagawa (Japan) schists are consistently younger with increasing deformation extent (Tetsumaru, 1988), which revealed that tectonic deformation can have influence on isotopic ages. On a microscopic scale, elements like Pb can redistribute in zircon lattice during dislocation (Piazolo,2015). The behaviors of isotopic systems in dating minerals under stress involve the fundamental problem of isotopic chronology. The application of it can be very wide, it allows us to get the deformation age directly if we choose the right deformed minerals in the right way. Some of the works such as fault, fold and ductile shear zone dating by our lab has been published (Yu Wang, 2010, 2016, 2020). What role does stress play in isotope diffusion which in turn affects ages is what we are eager to know. We designed a set of experiments using three axles press to work on undeformed K-feldspars with known age (126Ma) to test the effects. Rock mechanics experiments, field observation and isotopic dating are combined to give us an insight to it.

How to cite: Chen, X. and Wang, Y.: Effect of tectonic stress on isotopic systems in dating minerals, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11149, https://doi.org/10.5194/egusphere-egu24-11149, 2024.

09:15–09:25
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EGU24-19715
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On-site presentation
Kathryn Cutts, Krisztian Szentpeteri, Seppo Karvinen, Stijn Glorie, Asko Käpyaho, and Hugh O'Brien

Understanding fluid processes is crucial for understanding the magmatic and metamorphic evolution of rocks, as well as mineral transport and deposition. Targeted in situ geochronology of minerals which have interacted with fluids allow us to investigate the temporal evolution of these fluid systems. Combined with trace element analysis or stable isotope analysis it is possible to gain insight into the nature of source of mineralising fluids. These results contribute to modelling and understanding of mineral systems which can be used for targeting mineral deposits.

Early results of this work are presented based on situ Lu-Hf geochronology applied to garnet and apatite associated with a variety of mineral deposits from Finland. The mineral deposits are hosted in rocks are variable age (Archean to Proterozoic) and all were affected by the Svecofennian orogeny (1.92-1.78 Ga) causing deformation, metamorphism and/or remobilisation.

The Siilinjärvi P deposit hosted in a 2.61 Ga carbonatite (Karhu et al., 2001) presents apatite ages ranging from 2050 to 2260 Ma and calcite ages of 1800 to 1920 Ma indicating potentially several phases of fluid remobilisation which may be prior to or during the Svecofennian orogeny.

The Kiviniemi Sc deposit is hosted in a garnet bearing ferrodiorite (1857 ± 2 Ma, U-Pb zircon; Halkoaho et al 2020). In situ Lu-Hf analysis of garnet produces an age of 1824 ± 18 Ma and for apatite an age of 1835 ± 19 Ma.

Garnet and apatite geochronology has also been applied to Li bearing pegmatites in the Somera-Tammela pegmatite province in Southern Finland. Garnet gave an age of 1801 ± 53 Ma and apatite gives 1835 ± 26 Ma. A second sample produced a nearly identical apatite age of 1835 ± 15 Ma.

Two garnets were sampled from inferred Archean deposits, the Sotkamo silver Mine is hosted in the Tipasjärvi Greenstone Belt and the Hosko gold deposit hosted in the Ilomantsi Greenstone Belt. In Sotkamo garnet from a quartz vein hosting base metal mineralisation produced a Lu-Hf age of 1870 ± 27 Ma. Two garnet samples were dated from the Hosko gold deposit, in mineralised sediments, garnet associated with vein quartz produced an age of 1837 ± 4 Ma. A granitic vein cross-cutting the ore hosting sediments gave an age of 2620 ± 7 Ma, although this sample clearly recorded a resetting event with younger ages obtained from the rim.

Despite only have the age results so far, it is clear that the Svecofennian orogeny had a strong impact on mineral systems, reworking of deposits thought to be Archean.

 

Halkoaho, T., Ahven, M., Rämö, O.T., Hokka, J., Huhma, H., 2020, https://doi.org/10.1007/s00126-020-00952-2

Karhu, J.A., Mänttäri, I., Huhma, H., 2001. Radiometric ages and isotope systematic of some Finnish carbonatites. University Oulu, Res. Terrea, Ser. A. No. 19.8.

How to cite: Cutts, K., Szentpeteri, K., Karvinen, S., Glorie, S., Käpyaho, A., and O'Brien, H.: In situ Lu-Hf dating of garnet and apatite as a means to understand fluid processes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19715, https://doi.org/10.5194/egusphere-egu24-19715, 2024.

09:25–09:35
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EGU24-17149
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ECS
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On-site presentation
Sava Markovic, Jörn-Frederik Wotzlaw, Dawid Szymanowski, and Cyril Chelle-Michou

High-precision (CA-ID-TIMS) U-Pb geochronology of individual growth zones of zircon has been a long-awaited milestone in the geochronological community. Focused ion beam (FIB) and femtosecond (fs) laser machining monitored in real time by CL-SEM both show promise as techniques for physical extraction of target zircon domains in preparation for spatially resolved ID-TIMS dating. In this contribution, we test a novel laboratory protocol for zircon microsampling using an in-house multi-ion plasma (Ar-Xe) FIB and fs laser, and showcase first µID-TIMS zircon dates. We first examine the chemical impacts of protective metal coatings (Cr, Pt-Pd and C) used for ion milling on the U-Pb systematics of a low-Pb and a low-U zircon. We then present high-resolution transmission electron microscope (TEM) images of a zircon surface irradiated by ion and fs laser beams to show the contrasting extent of structural damage induced by the two techniques at standard microsampling conditions. Potential Pb-loss/U-gain in the nanometer-wide ion damaged layer in zircon is mapped by atom probe tomography (APT). Subsequently, we showcase the FIB workflow for extracting a number of microsamples of the Mud Tank and GZ-7 reference zircon spanning the sizes expected in future applications using natural zircon. We present first results of spatially resolved high resolution (µID-TIMS) dating of the Mud Tank and GZ-7 microsamples, and explore the achieved analytical accuracy and precision. Finally, we discuss the feasibility of conducting a µID-TIMS study on natural zircon given zircon features (i.e., age, U content, and volume of target domain) and research objective, and discuss benefits and limits to our approach.

How to cite: Markovic, S., Wotzlaw, J.-F., Szymanowski, D., and Chelle-Michou, C.: µID-TIMS: A Focused Ion Beam (FIB)–Femtosecond (Fs) Laser Microsampling Protocol for Spatially Resolved High-Precision Zircon Geochronology , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17149, https://doi.org/10.5194/egusphere-egu24-17149, 2024.

09:35–09:45
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EGU24-15969
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ECS
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On-site presentation
Chetan Nathwani, Lorenzo Tavazzani, Dawid Szymanowski, Adrianna Virmond, Sava Markovic, and Cyril Chelle-Michou

U–Pb and U–Th geochronology of zircon in igneous rocks provides key information about the age, longevity, and assembly rates of magma reservoirs. Historically, the available analytical resolution limited these insights to an averaged “age” of a magmatic system. With dramatic improvements in analytical techniques over the last two decades, it has become possible to resolve extended records of zircon crystallisation within a single igneous sample, which can extend prior to its eruption or subsurface solidification by as much as a million years. In some magmatic systems these age spectra mirror those produced in zircon solubility models, reflecting monotonous cooling of a magma reservoir, whilst in others they may take other shapes indicative of a more complex interplay of processes [1,2]. Isolating the effect of these processes can be challenging since many analytical and geological factors also play a role. Such geological processes may include magma recharge or truncation of zircon crystallization by melt extraction.

In this study, we compiled high-precision zircon U-Pb dates from volcanic, plutonic and porphyry copper systems. We use the Wasserstein metric as a dissimilarity measure to compare distributions between all compiled age spectra. Dimensionality reduction of the resulting dissimilarity matrix reveals that plutonic systems have contrasting age spectra to volcanic and porphyry copper systems. Plutonic systems typically exhibit age spectra skewed towards older ages whereas volcanic and porphyry systems are skewed towards younger ages.

We adopt a bootstrap modelling approach to explain these differences, which allows the modelling of the effects of the number of sampled zircons, analytical uncertainties, magmatic recharge, mixed age domains and a truncation of crystallisation. The effects of multiple magmatic recharge events combined with truncation by volcanic eruption/dyke formation appear to be the most likely explanation for the young skew of volcanic and porphyry copper age spectra. Truncation of zircon crystallization alone appears to be incapable of explaining the full difference. Recognising the contrasting zircon age spectra between volcanic and plutonic systems is critical to improve eruption age estimation and interpretations of zircon compositions in petrological studies.

[1] Keller, C.B., et al., GPL, 2018. 31–35.

[2] Tavazzani, L., et al., EPSL, 2023. 623, 118432.

How to cite: Nathwani, C., Tavazzani, L., Szymanowski, D., Virmond, A., Markovic, S., and Chelle-Michou, C.: Controls on high precision zircon U-Pb age spectra in magmatic systems, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15969, https://doi.org/10.5194/egusphere-egu24-15969, 2024.

09:45–09:55
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EGU24-16158
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ECS
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On-site presentation
Anne Sturm, Axel K. Schmitt, Martin Danišík, and István Dunkl

Geochronological methods play a pivotal role in unraveling the evolution of volcanic fields, providing insights into eruption timescales and recurrence. In the Quaternary Eifel volcanic field, with >300 maars and scoria cones, dating volcanic events remains challenging due to the scarcity of suitable materials for conventional dating methods. A promising approach to determine accurate eruption ages is to apply (U-Th)/He geochronology to zircon extracted from partially re-melted crustal xenoliths1,2, which in case of Eifel maars are co-deposited with country-rock derived lithics and juvenile lapilli. However, the reproducibility of the method, if applied to xenoliths of different origin, age, composition, and texture, has not been studied for a single explosive eruption.

We collected >250 crustal xenoliths from >35 centers of the East and West Eifel volcanic fields. Coupled petrological investigation and zircon geochronology (U-Pb and U-Th) of a subset of these xenoliths reveal their diversity regarding protolith types (plutonic vs. low- to high-grade metamorphic), zircon crystallization ages (200 ka to 3 Ga) and degree of pyrometamorphic overprint (variable abundances of glass and vesicles, and crystal breakdown reaction textures). (U-Th)/He dating of the previously U-Th-Pb dated crystals (zircon-double-dating, ZDD) was performed to determine eruption ages for these centers.

Here, we focus on a xenolith suite (n = 8) from the Gemündener Maar and E-Schalkenmehrener Maar, two vents within a maar cluster known as Dauner Maar group. Tentative eruption ages of 20 to 30 ka were estimated from considerations on paleoclimate and crater morphology3,4, and ESR xenolithic quartz dates of 30 ± 4 ka5. The pyroclastic deposits are rich in diverse zircon-bearing crustal xenoliths and thus, offer an ideal testbed to investigate how critical parameters such as xenolith rock type, zircon crystallization age, grain morphology, structure and chemical composition determined by Raman analysis and cathodoluminescence imaging, among others, could influence the measured (U-Th)/He ages. The investigated xenoliths comprise both magmatic and metamorphic protoliths with varying degree of pyrometamorphic overprint. Zircon U-Pb ages range from 115 ± 4 Ma to 2731 ± 66 Ma. Preliminary (U-Th)/He dates of individual xenoliths agree with the expected eruption age range, underscoring the feasibility of the method. A detailed analysis of parameters potentially affecting (U-Th)/He systematics in zircon ages is ongoing.

 

[1] Blondes, M.S., Reiners, P.W., Edwards, B.R., Biscontini, A., 2007, Dating young basalt eruptions by (U-Th)/He on xenolithic zircons: Geology, 35, 17–20.
[2] Ulusoy, İ., Sarıkaya, M.A., Schmitt, A.K., Şen, E., Danišík, M., Gümüş, E., 2019, Volcanic eruption eye-witnessed and recorded by prehistoric humans: Quat Sci Rev, 212, 187–198.
[3] Büchel, G., 1993, Maars of the Westeifel, Germany: Paleolimnology of European Maar Lakes, 49, 1–13.
[4] Lange, T., Cieslack, M., Lorenz, V., Büchel, G., 2022, Chronological sequence of volcanic eruptions in the SE part of the Westeifel Volcanic Field during the Weichselian Glaciation: Jber Mitt Oberrhein Geol Ver, 104, 313– 365.
[5] Woda, C., Mangini, A., A. Wagner, G., 2001, ESR dating of xenolithic quartz in volcanic rocks: Quat Sci Rev, 20, 993–998.

How to cite: Sturm, A., Schmitt, A. K., Danišík, M., and Dunkl, I.: Assessing the reproducibility of (U-Th)/He geochronology of xenolithic zircon: Insights from the Quaternary Eifel intraplate volcanic field, Germany, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16158, https://doi.org/10.5194/egusphere-egu24-16158, 2024.

09:55–10:05
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EGU24-9818
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Highlight
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On-site presentation
Chris Mark, Roland Neofitu, Gary O'Sullivan, Stijn Glorie, Thomas Zack, Delia Rösel, Dan Barfod, David Chew, J. Stephen Daly, Peter Clift, and Yani Najman

Detrital geochronology is a powerful tool to interrogate the sedimentary archive of (paleo-)hinterland tectonism, metamorphism, and exhumation, and can also be applied to modern river sediment as a first-pass tool to establish regional bedrock ages. The popular zircon U-Pb detrital geochronometer has seen widespread adoption for these tasks (4,173/5,100 results for the search term detrital geochronology also contain the term zircon U-Pb; Clarivate Analytics Web of Science). However, zircon fertility is strongly biased to intermediate to felsic source rocks. Moreover, zircon crystallization is volumetrically limited in metamorphic terranes which do not achieve anataxis (e.g., Moecher & Samson, 2006), and is typically restricted to rim overgrowths which are vulnerable to mechanical destruction during fluvial transport, and which are challenging to detect and analyse (e.g., Campbell et al., 2005).

Therefore, it is desirable to develop complementary provenance tools for sub-anatectic settings, as well as tools targeting more abundant rock-forming minerals for use with small-volume samples (e.g., drillcore). Established alternative detrital phases include the U-Pb system in apatite, monazite, titanite, and garnet. The advent of LA-ICPMS systems equipped with mass-filtered online reaction cells now also permits the routine use of β-decay systems by overcoming parent-daughter isobaric interferences. These include Lu-Hf in garnet and apatite, and Rb-Sr in K-phases including K-feldspar and mica (Rösel & Zack, 2022; Woods 2016). K-phases are also amenable to conventional Ar-Ar detrital geochronology.

Here, we present case studies of emerging detrital provenance techniques, with particular application to modern and past orogenic systems.

Campbell, I., et al., 2005. Earth Planet. Sci. Lett. 237, 402-432,  doi: 10.1016/j.epsl.2005.06.043

Moecher, D., & Samson, S., 2006, Earth Planet. Sci. Lett. 247, 252–266, doi: 10.1016/j.epsl.2006.04.035

Rösel, D., & T. Zack, 2022. Geostandards and Geoanalytical Research 46.2, 143-168, doi: 10.1111/ggr.12414.

Woods, G. 2016. Agilent Application Note. Agilent Technologies, Cheadle.

How to cite: Mark, C., Neofitu, R., O'Sullivan, G., Glorie, S., Zack, T., Rösel, D., Barfod, D., Chew, D., Daly, J. S., Clift, P., and Najman, Y.: Mountains from sand grains: Advances in detrital provenance applied to orogens, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9818, https://doi.org/10.5194/egusphere-egu24-9818, 2024.

10:05–10:15
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EGU24-14298
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ECS
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On-site presentation
Darwinaji Subarkah, Alan Collins, Stefan Löhr, Angus Nixon, Morgan Blades, Juraj Farkas, Jarred Lloyd, Robert Klaebe, Sarah Gilbert, and Georgina Virgo

The Cryogenian period represents a critical interval in Earth’s history, characterized by drastic tectonic and environmental changes. Evidence of low-altitude glacial deposits from this time has been recognized globally, alluding to the most extensive icehouse regimes known on our planet. These conditions of successive global freezing and warming during the Neoproterozoic have been dubbed as ‘Snowball Earth’ events. Importantly, the Cryogenian may have played a key role in the accelerated evolution of early life, as microorganisms became more complex and abundant after this period. Consequently, it is important to constrain the absolute timing, duration, and termination of these glacial and interglacial events. Despite their significance, robust, direct dating of Cryogenian sections remains challenging. The most accurate way to constrain these units is through dating of interbedded volcanics. However, they are not present across all sections globally, making correlations difficult to establish.

As such, we present a novel strategy to address this issue by directly dating a broad array of Cryogenian carbonates through an in situ U-Pb mapping approach. Our case study includes inter-glacial and post-glacial carbonates from sections in Australia, Oman, and Greenland. We show that this method allows for the concurrent collection of geochemical, petrographic, and geochronological information at sufficient precision to address key geological questions. Geochemical proxies such as elevated Mn/Sr ratios and Al or Si can be used to filter areas affected by alteration or detrital input, respectively. Secondary phases such as veins and overgrowths can also be petrographically avoided as an advantage of the spatially coherent mapping technique. Regions that yield enrichment in U and best spread in U–Pb ratios can be preferentially selected. Triaging such datasets and spatial information can help identify subdomains within a sample that is most suitable for dating, maximizing the success rate of this approach. The technique is capable of yielding age precision of ±1% depending on the concentration of U, the range in radiogenic isotopes, and the number of pixels that make up an analytical point.  

How to cite: Subarkah, D., Collins, A., Löhr, S., Nixon, A., Blades, M., Farkas, J., Lloyd, J., Klaebe, R., Gilbert, S., and Virgo, G.: Direct dating of global Cryogenian sections by in situ U–Pb mapping of carbonates, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14298, https://doi.org/10.5194/egusphere-egu24-14298, 2024.

Coffee break
Chairpersons: Aileen Doran, Johannes Rembe
10:45–10:55
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EGU24-11865
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On-site presentation
Joe Connolly, Mark Anderson, Catherine Mottram, Gregory Price, and David Sanderson

The Bristol Channel Basin (BCB) is a small continental rift basin that developed along the eastern margin of the North-Atlantic during the Mesozoic. Relatively minor basin inversion occurred during the Cenozoic. It has been extensively studied due to the exceptional exposure of faults along both margins of the basin. Widespread calcite mineralisation of overprinting fracture networks documents fluid partitioning along these structures over time. However, the temporal evolution of deformation has been constrained solely from the relative timing of structures in the field and through comparisons with other basins in the region. This has made detailed modelling of how structures have evolved during basin development and later inversion problematic. In this study we succesfully use U-Pb carbonate geochronology on low U samples (<1ppm) to constrain the absolute timing of fault development, whilst also assessing fluid source evolution with stable isotope and fluid inclusion data. Absolute dating of calcite slickenfibres in the fault cores of extensional, thrust and strike-slip faults in the East-Quantoxhead - Kilve region reveals the precise timing of different phases of deformation within the BCB for the first time.

New age data show that extensional faulting occurred from ca. 154-118 Ma. Strike-slip faults formed ca. 47-21 Ma, with thrust faults forming ca. 46-35 Ma. The results show Late Jurassic – Early Cretaceous E-W extension with a vertical σ1, followed by Eocene – Miocene N-S contraction with σ1 now being ~horizontal. New age determinations provide much greater insight into the longevity of these structural phases, as well as how fluid nature and composition has evolved over time. Stable isotope data captures fluid source evolution, with δ13C & δ18O values being more negative in the older extensional faults, and becoming more positive over time in the later contractional features. Reactivated structures show evidence for deeper fluid sources, shown by relatively hotter fluid inclusion temperatures within these faults.

Constraining the development of different fault populations within the BCB increases our understanding of the evolution of regional stress within southern England and can be extrapolated to nearby basins. Understanding the historical partitioning of fluid flow through different fault populations has practical applications for understanding where produced and/or injected fluids will flow when a reservoir is exploited today, such as in an Enhanced Geothermal System (EGS).

How to cite: Connolly, J., Anderson, M., Mottram, C., Price, G., and Sanderson, D.: Using U-Pb Carbonate Geochronology to constrain the timing of fault development and fluid source evolution in an inverted continental rift basin., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11865, https://doi.org/10.5194/egusphere-egu24-11865, 2024.

10:55–11:05
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EGU24-15293
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ECS
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On-site presentation
Martina Rocca, Stefano Zanchetta, Xavier Mangenot, Marta Gasparrini, Fabrizio Berra, Pierre Deschamps, Abel Guihou, and Andrea Zanchi

Faults and related fractures have been studied for decades due to their potential in providing insights into past and present crustal deformation processes, climate evolution, seismology, and hydrology among others. Carbonates are very common syn-tectonic minerals that occur along fault planes or in fault-related fractures forming slickenfibres and veins (Roberts and Holdsworth, 2022). The ability of carbonates to incorporate uranium during their precipitation allows the application of in-situ carbonate U-Pb radioisotopic dating via LA-ICP-MS (Roberts et al., 2020). The integration of this method with the more conventional petrography and biostratigraphy holds strong potential in resolving the timing of brittle structure development. A robust pre-dating screening protocol using a multi-disciplinary approach, including structural, microstructural, petrographic, and isotopic characterization has been implemented to link carbonate precipitation event to fault kinematics.

This approach has been applied to the central Southern Alps (Northern Italy), where Early Jurassic rift-related faults are preserved despite their later involvement in the Alpine orogeny. Fieldwork and sampling focused on the Amora Fault (Bergamo, Italy), a rift-related N-S normal fault of the Jurassic Lombardian basin. Structural and paleostress analysis led to the identification of several mesoscopic N-S trending normal faults and veins both in the hanging wall and footwall of the Amora Fault, indicating an E-W extension. The fault is cross-cut by middle Eocene E-W trending magmatic bodies, which, in turn, are cross-cut by Alpine thrust faults. The Amora Fault and related minor faults also show strike-slip reactivation related to N-S Alpine compression.  

Sampling focused on the Norian to Lower Jurassic succession in the hangingwall and footwall of the main fault plane, where carbonate syn-tectonic veins and slickenfibres are present. Structural analysis allowed relating the structures to either the rifting or the Alpine reactivation.

Microstructural and petrographic analyses assisted by cathodoluminescence on 21 samples revealed the occurrence of several carbonate phases. Elemental analyses (Ca, Mg, Fe, Sr) and O-C stable isotope analyses confirmed the circulation of different fluids. U-Pb dating on the carbonate phases provided four age clusters, each connected to a tectonic phase: (1) Early to Middle Jurassic carbonates precipitated in rift-related structures from a fluid with a δ13C buffered by the host-rock. (2) Early Cretaceous carbonates possibly related to the late stage of rifting activity. (3) Late Cretaceous carbonates precipitated from a meteoric fluid during the early stages of the Alpine orogeny. (4) Oligo-Miocene carbonates connected to the strike-slip reactivation of rift-related normal faults.

The integration of field-based and stratigraphic observations with carbonate geochemistry and geochronology allowed the recognition of a complex reactivation history for the Amora Fault.

References

Roberts, N.M.W., Drost, K., Horstwood, M.S., Condon, D.J., Chew, D., Drake, H., Milodowski, A.E., McLean, N.M., Smye, A.J., Walker, R.J., and Haslam, R., 2020. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U–Pb carbonate geochronology: strategies, progress, and limitations. Geochronology 2, 33–61.

Roberts, N.M.W, and Holdsworth, R.E., 2022. Timescales of faulting through calcite geochronology: A review. Journal of Structural Geology, 158, 104578.

How to cite: Rocca, M., Zanchetta, S., Mangenot, X., Gasparrini, M., Berra, F., Deschamps, P., Guihou, A., and Zanchi, A.: Carbonate U-Pb geochronology as a tool to unravel complex fault evolution: an example from the central Southern Alps (Italy), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15293, https://doi.org/10.5194/egusphere-egu24-15293, 2024.

11:05–11:15
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EGU24-2777
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ECS
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Highlight
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On-site presentation
Aizimaiti Maimaiti, Jingqiang Tian, Fuyun Cong, and Qi Wang

Magmatic activities in sedimentary basins provides abnormal heat sources and exert significant impact on the regional temperature field. In previous studies, the anomalous thermal effects of magmatic activities of multiple scales were studied. Small-scale intrusions (cm-m) can conduct high-temperature thermal baking of surrounding strata within tens to hundreds of meters. Basin-scale heat flow anomalies caused by mantle plume upwelling have also received increasing attention. In contrast, the thermal effects of large igneous plutons (several km to tens of km) have received little attention. A few studies have shown that the large intrusive bodies can affect the temperature field within a range of tens of kilometers. The Permian large igneous province is widely distributed in the Tarim Basin, forming several large plutons. The Manalik pluton is a large intrusive body in the northwestern Tarim, with a long diameter of up to 40 km. We have measured the clumped isotope of different calcite fabrics from the Ordovician carbonate intervals surrounding the contact aureoles of Manalik pluton. In-situ U-Pb dating will be applied to these fabrics to provide starting anchors for thermal history modeling using solid-state reordering models of carbonate clumped isotope. In addition, Silurian sandstones from the same area were collected for zircon (U-Th)/He age measurement and subsequent thermochronological thermal history inversion. Compared with conventional thermal indicators applied in deeply buried strata (e.g., vitrinite reflectance), the integration of the two thermochronological tools (Δ47/U-Pb and zircon U-TH/He) holds the advantage in more accurately quantifying the abnormal thermal effects of kilometer-scale intrusive bodies. The experimental results show that zircon (U-Th)/He and clumped isotope jointly constrain temperatures exceeding 200°C in Well Shengli 1 and Well Yingmai 35, which are closest to the Manalik pluton; the thermal anomalies identified in Well Yudong 2 are as high as 220°C; Well Yingmai 2 Well and Yingmai 34, which are far away from the igneous intrusion, were not affected by the thermal contact aureoles of Manalik pluton during the Permian period, and the current burial temperature is the highest paleogeothermal temperature experienced in historical periods. Based on the zircon (U-Th)/He and U-Pb/Δ47 simulation results, we reveal that the Manalik pluton has a significant thermal baking effect on the area within 20km, and the maximum temperature in the area close to the igneous pluton can exceed 220°C. The results of this study provide typical cases and inspiration for identifying and quantifying the thermal effects of contact aureoles in other basins where large igneous pluton are developed.

How to cite: Maimaiti, A., Tian, J., Cong, F., and Wang, Q.: Quantifying the anomalous thermal effects of contact aureoles of a large pluton in the Tarim Basin: Constraints from clumped isotope thermometry, in situ calcite U-Pb dating, and zircon U-Th/He thermochronology, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2777, https://doi.org/10.5194/egusphere-egu24-2777, 2024.

11:15–11:25
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EGU24-5861
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ECS
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Highlight
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On-site presentation
João Carlos Cerqueira, Nick M. W Roberts, Giancarlo Scardia, Fabio Parenti, Francisco Ladeira, and Walter Neves

Dating Quaternary carbonates and phosphates beyond the range of U-series geochronology is challenging, but recent studies have shown potential using the method of LA-ICP-MS U-Pb geochronology. Terrestrial materials altered and produced by pedogenic processes are particularly challenging, as they are usually rich in common Pb and poor in U; however, they provide some of the rare opportunities to directly date important archaeological artefacts. Our aim is to advance the age constraints of the hominin presence in the Zarqa Valley, Jordan, an important geomorphological feature with the oldest hominin artefact outside Africa. Along with new Ar-Ar geochronology of sequence-bounding basalts and new palaeomagnetic constraints, our approach is to: (1) review published U-Pb data of 2019; (2) conduct LA-ICP-MS U-Pb analyses in various pedogenic carbonates (calcrete) that cap the artefact-bearing deposits along with mammoth fossil remains; and (3) review the regional 234U/238U activity ratio estimate required for calculation of accurate U-Pb ages.

A previous attempt to date hominin artifacts in the valley yielded an age of 1.98 ± 0.20 Ma for calcrete material, which is a weighted mean of several individual U-Pb isochrons derived from laminated calcretes, cracks, pore spaces and cement, and corrected by an initial 234U/238U activity ratio of 1.5 ± 0.5. We calculated an alternative, statistically favourable, age based on pooling the data into a single Tera-Wasserburg regression, resulting in 1.93 ± 0.44 Ma.

Our LA-ICP-MS analysis thus far has not yielded a new significant age, but we have focussed on understanding the U and Pb compositions in a range of materials, including calcretes, rhizoliths, fossil coatings and Mammalian fossils. Biogenic spherulite laminae in laminar calcrete have higher U (0.56 ± 0.064 ppm) and lower Pb contents (0.61 ± 0.15 ppm) compared to abiogenic cracks and cement (0.33 ± 0.084 and 0.9 ± 2 ppm, respectively). Although far from desirable for U-Pb geochronology, for now, the spherulite laminae seems to be the most suitable micromorphology to date calcrete. Coarse spar of rhizoconcretions have very low U contents (0.07 ± 0.35 ppm), leading to unfavourable U/Pb ratios. Two fragments of a mammoth molar from an artefact-bearing deposit have been analysed; one is part of the crown having dentine and enamel, and the other one is dentine of the root. The crown and root fragments have high U concentrations of 33 ± 11 and 13.7 ± 9.9 ppm, respectively, but with their high Pb contents they still yield a low spread in U/Pb ratios and very imprecise lower intercept ages. Using LA-ICP-MS mapping to better identify areas of alteration, we pooled U-Th-Pb spot data from regions with low Y (<5 ppm), Mn (<50 ppm), Al (<100 ppm), Th (< 0.05 ppm) and high P (> 7200 ppm), which correlated with the central portion of the dentine. These data yielded an age, using the combined U-Pb and Th-Pb calculation, of 1.9 ± 1.1 Ma; although very imprecise, it shows potential for further refinement.

How to cite: Cerqueira, J. C., Roberts, N. M. W., Scardia, G., Parenti, F., Ladeira, F., and Neves, W.: U-Pb geochronology of Quaternary pedogenic carbonates and teeth from archaeological sites of Zarqa Valley, Jordan, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5861, https://doi.org/10.5194/egusphere-egu24-5861, 2024.

Geochemistry — Applications and Advances
11:25–11:35
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EGU24-3567
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solicited
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Highlight
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On-site presentation
Wenhao Sun

Crystals grow in supersaturated solutions. A mysterious counterexample is dolomite CaMg(CO3)2, a geologically-abundant sedimentary mineral that does not readily grow at ambient conditions, not even under highly supersaturated solutions. Using atomistic simulations, we show that dolomite initially precipitates a cation-disordered surface, where high surface strains inhibit further crystal growth. However, mild undersaturation will preferentially dissolve these disordered regions, enabling increased order upon reprecipitation. Our simulations predict that frequent cycling of a solution between supersaturation and undersaturation can accelerate dolomite growth by up to seven orders of magnitude. We validate our theory with in situ liquid cell TEM—directly observing bulk dolomite growth following pulses of dissolution. This mechanism explains why modern dolomite is primarily found in natural environments with pH or salinity fluctuations. More generally, it reveals that the growth and ripening of defect-free crystals can be facilitated by deliberate periods of mild dissolution. [Kim et al., Science: adi3690 (2023)]

How to cite: Sun, W.: Dissolution enables dolomite growth near ambient conditions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3567, https://doi.org/10.5194/egusphere-egu24-3567, 2024.

11:35–11:45
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EGU24-18595
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ECS
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On-site presentation
Melanie J. Sieber, Hans Josef Reichmann, Robert Farla, and Monika Koch-Müller

Understanding the stability of carbonates under high pressure and temperature is essential for modelling the carbon balance and cycle in the deep Earth. In the presence of an H2O-containing fluid, the melting curve of carbonates can be strongly reduced to a lower temperature. Since magnesite is an important carbonate host in the Earth's mantle, the melting curve of magnesite in the presence of an H2O-containing fluid is of particular interest.

Here we report results from in situ synchrotron energy dispersive X-ray diffraction experiments and use texture observations from ex situ falling sphere experiments in the brucite-magnesite system between 1 and 12 GPa. We define the dehydration and melting curve of brucite and elucidate the stability of magnesite in the presence of a liquid and periclase.

The observed liquidus provides information on the fate of magnesite-bearing rocks in subduction zones. Our results show that magnesite remains stable under typical subduction zone gradients even when infiltrated by hydrous fluids released by dehydration reactions during subduction. We conclude that magnesite can be subducted to depths below the arc and beyond. Our results therefore have important implications for the carbon budget of the Earth's mantle and its role in the regulation of the carbon cycle.

How to cite: Sieber, M. J., Reichmann, H. J., Farla, R., and Koch-Müller, M.: Stability of magnesite (MgCO3) in the presence of a hydrous fluid in the upper mantle, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18595, https://doi.org/10.5194/egusphere-egu24-18595, 2024.

11:45–11:55
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EGU24-791
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ECS
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On-site presentation
Ariela Mazoz, Gary Stevens, Jean-François Moyen, Guilherme Gonçalves, Alanielson Ferreira, and Roberto Ventura Santos

The behaviour of rare earth elements (REE), U-Pb, Sm-Nd, and Sr-Sr isotope compositions in accessory minerals provides a unique opportunity to track fluid sources and investigate trace element mobilization during fluid-assisted metamorphism. Metapelites of the Southern Marginal Zone (SMZ), Limpopo Belt (Bandelierkop formation), South Africa, experienced a ca. 2.7 Ga granulite-facies event in which the rocks underwent anatexis. The southern portion of the SMZ contains dispersed fragments of retrogressed metapelites with ubiquitous amphibolite facies assemblages including biotite, orthoamphibole, kyanite and a 2nd generation of garnet replacing cordierite, equilibrated under 660-600ºC and ≥ 0.6GPa. The hydrated metapelites contain graphite intergrown with the retrograde assemblages, indicating a mixed H2O-CO2 fluid and a rock-dominated system. However, the source of the fluids that caused the retrogression remains unclear. Previous studies suggested that hydrating fluids were originally internally derived from the crystallizing in-situ melts, in sediments containing biogenic graphite, or that an externally derived CO2 and H2O-bearing fluid infiltrated the metapelites through shear zone systems. For the latter, some studies have proposed that this occurred during uplift of the granulite directly after Neo-Archean peak metamorphism, while others have used rutile U-Pb ages of ca. 2.1 Ga to argue for Paleoproterozoic retrogression.

This study investigated the geochemistry of garnet, apatite, and monazite from the hydrated zone metapelites to understand the origin of the fluids. Garnet trace elements show two distinct populations described as Grt1 (Eu/Eu*=0.36) and Grt2 (Eu/Eu*=1.55). Monazite shows relatively homogeneous REE pattern for distinct samples with a slight variation in HREE and negative Eu anomaly (Eu/Eu*=0.20-0.38). As for apatite the REE pattern is variable and distinct within and between samples (Eu/Eu*=0.36-0.37). 2741 Ma to 2707 Ma U-Pb monazite ages suggest that the amphibolite-facies assemblages are mainly related to the ca. 2.7 Ga granulite-facies event. U-Pb apatite dating yielded younger ages ranging from ca. 2057 Ma to 2047 Ma. Sm-Nd isochron of apatite yielded an initial 143Nd/144Nd (0.50950 ± 0.00100; 2s; n = 21; MSWD = 4.6) equivalent, within uncertainties, to the monazite initial 143Nd/144Nd (0.50882 ± 0.00030; 2s; n = 30; MSWD = 0.81). Monazite and apatite preserved its primary 2.7 Ga Sm-Nd isotope signature, but the U-Pb apatite system was reset at ca. 2.05Ga by solid-state diffusion. Thus, apatite reacted in the presence of a disequilibrium fluid in the Neo-Archean, as evidenced by the REE chemical variation, but did not experience dissolution/reprecipitation processes.  

We propose that the retrogressed zone of the SMZ experienced a Neo-Archean peak granulite-facies followed by amphibolite-facies retrogression, in which an internally derived fluid interacted with the metapelites. This is supported by published Sm-Nd bulk rock compositions that follow the same evolution trend as these samples, indicating a closed system history in the retrogressed zone of the SMZ. The rocks also record a Paleoproterozoic, lower-temperature, amphibolite-facies re-heating event, responsible for the resetting of the apatite. Initial 87Sr/88Sr = 0.7130±0.0014 (2s; n = 19; MSWD = 13) indicates a continental origin for the fluids that crystallized the apatite.

How to cite: Mazoz, A., Stevens, G., Moyen, J.-F., Gonçalves, G., Ferreira, A., and Santos, R. V.: Unravelling fluid-rock interaction in the hydrated zone of the Southern Marginal Zone of the Limpopo Belt - South Africa: a geochemical investigation based on U-Pb geochronology and Sm-Nd isotope composition of monazite and apatite in metapelites , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-791, https://doi.org/10.5194/egusphere-egu24-791, 2024.

11:55–12:05
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EGU24-14613
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ECS
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On-site presentation
Fengchun Li, Qingdong Zeng, Hongrui Fan, and Kuifeng Yang

Carbonatite has enormous potential for rare earth element resources, typically enriched in light rare earth elements, and has attracted increasing attention from geologists and economists. However, there are a small number of documented instances of carbonatite-related heavy rare earth elements enrichment. The Jialu carbonatites in the Qinling orogenic belt (central China) are characterized by the enrichment of heavy rare earth elements compared with typical global carbonatites. The carbonatites are dominantly comprised of calcite, quartz, sulfate, K-feldspar, minor sulfides, and rare earth minerals such as monazite, bastnäsite, parisite, and xenotime, with two mineralization stages including the early quartz-K-feldspar-calcite stage (Stage I) and the late sulfide-rare earth mineral-calcite stage (Stage II). The rare earth element contents of Stage I calcite are higher than those of the Stage II, especially heavy rare earth elements. Calcite from the different mineralization stages exhibits variable chondrite-normalized REE patterns, with the heavy rare earth elements and rare earth element abundances (134–1023 ppm) decreasing from the early to the late stage owing to the crystallization of xenotime. The δ13C (−5.39‰ to −6.68‰) and slightly higher δ18O (10.77‰ to 12.60‰) values for calcite from the Jialu carbonatites generally deviate from the values observed in the primary carbonatite field, which may be a result of Rayleigh-type fractionation. LA–ICP–MS U–Pb dating shows the lower-intercept ages of 243.8 ± 5 and 237.6 ± 1.3 Ma for the monazite and xenotime, respectively, with the weighted average 206Pb/238U ages of 240.9 ± 6 and 239.2 ± 1.3 Ma. These results indicate that the Jialu deposit was concurrent with Triassic carbonatite magmatism and rare earth element mineralization observed on the southern margin of the North China Craton. This implies that this region may have great rare earth element mineralization potential.

How to cite: Li, F., Zeng, Q., Fan, H., and Yang, K.: Unusual heavy rare earth elements enrichment and mineralization age in the Jialu deposit from the Qinling Orogen, central China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14613, https://doi.org/10.5194/egusphere-egu24-14613, 2024.

12:05–12:15
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EGU24-1982
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ECS
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On-site presentation
Giulia Schirripa Spagnolo, Stefano Bernasconi, Luca Aldega, Francesca Castorina, Fabrizio Agosta, Andrea Billi, Giacomo Prosser, Luca Smeraglia, and Eugenio Carminati

Calcite is a common syn-kinematic precipitate in upper crustal fault zones coating slickensides, forming slickenfibers, and infilling veins. Structural and geochemical analyses of fault-related calcites can be used to unravel the source, distribution, and mixing of parental fluids in association with past fault activity. Identifying deeply sourced fluids through syn-kinematic calcites is of paramount importance, as the correlation of the ascent of deep sourced fluids with strong earthquakes, may allow using hydrogeochemical modifications in groundwater as potential seismic precursors. In this study, we investigate the origin of syn-kinematic paleo-fluids that circulated along the Val d’Agri faults, in southern Italy. These faults bound an intermontane basin topping the largest onshore oil field in Western Europe. Since the Val d’Agri Basin is affected by natural seismicity and low magnitude oil production induced earthquakes, it is necessary to assess the potential threats of hydrocarbon fault leakage at shallow crustal levels. With this aim, we collected about 350 syn-tectonic calcites along high-angle extensional-transtensional fault zones. By combining macro- and micro- scale structural observations with carbonate isotopes (C, O, clumped, and Sr) and rare earth elements and yttrium (REY) geochemistry, we identified 5 fluid sources: (1) meteoric waters in geochemical and thermal disequilibrium with the host rocks, which interacted with superficial soil; (2) meteoric waters in geochemical disequilibrium and thermal equilibrium with the host rocks, which had limited interaction with the host rocks; (3) buffered fluids in geochemical and thermal equilibrium with the host rocks; (4) high temperature fluids in geochemical equilibrium and thermal disequilibrium with the host rocks, which ascended from the carbonate hydrocarbon reservoir; (5) hot meteoric waters in thermal and geochemical disequilibrium with the host rocks, which mixed with the deeply sourced fluids. The presence of multiple fluids is consistent with an open fault-related circulation system, which allowed mixing of shallow and deep fluids through the high-angle extensional-transtensional Val d’Agri faults. Given the societal and economic issues of this area, the recognized involvement of deep fluids during past fault activity is crucial for the context of oil exploration and production as well as for environmental monitoring. Furthermore, this suggests that the Val d’Agri Basin is an ideal region to explore fluid-fault relationships throughout the entire seismic cycle through local seismicity records and continuous groundwater monitoring.

How to cite: Schirripa Spagnolo, G., Bernasconi, S., Aldega, L., Castorina, F., Agosta, F., Billi, A., Prosser, G., Smeraglia, L., and Carminati, E.: The Isotope and REY geochemistry of fault-related calcites document syn-kinematic fluid distribution along the Val d’Agri faults (southern Italy), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1982, https://doi.org/10.5194/egusphere-egu24-1982, 2024.

12:15–12:25
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EGU24-2875
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Virtual presentation
Ana Fociro, Hüseyin Öztürk, Agim Sinojmeri, Zeynep Cansu, Lavdie Moisiu, Yakup Çelik, Shaqir Nazaj, and Irakli Prifti

The Tethyan Phosphogenic Province is one of the widest of its kind, representing an outstanding period of phosphate deposition principally in the Upper Cretaceous-Eocene period. The main aim of this study is to compare the Turkish phosphorites occurring along the southern side of the Neo Tethyan Ocean due to suitable seawater temperature and upwelling oceanic currents with Albanian phosphorites were deposited in higher latitudes and colder climates, in the same ocean. The Şemikan (Türkiye) phosphorites consist mainly of cream-coloured (CCP) and locally reddish phosphorites (RP) occurring as lenses or concordant blankets within high-grade cream phosphorites. Based on microscopic examination, cream-coloured phosphorites consist of phosphatic pellets, intraclasts, bioclasts (fossilized shark teeth, ostracods etc.) and nonphosphatic components, with texture changing from wackestone to packstone, testifying shallow marine depositional environment. Whereas, Gusmari (Albania) phosphorites consist of laminated phosphorites (LP), of mudstone/wackestone texture, with planktonic foraminifera Globotruncanidae, where the phosphate is sedimentary, and alternating laminae of phosphate and pelagic carbonate. Besides this, under SEM-EDS, 5µm crystals of the major ore of uranium, UO2, were evidenced for the first time in LP. The mineralogical analyses showed that the CCP consisted of carbonate-rich fluorapatite, minor calcite and quartz. The RP consisted predominantly of carbonate-rich fluorapatite, hydroxyapatite, montmorillonite, and minor quartz. The LP consisted predominantly of calcite, carbonate-rich fluorapatite, hydroxyapatite, and traces of quartz. The mean P2O5 content of the CCP is 29%, RP and LP 14%, which is lower than that of other well-known global phosphorite deposits. The CaO content of the CCP, RP and LP ore is also higher than that of other global deposits because of a calcite matrix between phosphorite pellets. Based on preliminary results of trace elements CCP, RP and LP show a general trace element scarcity compared to the trace element averages of the world’s average phosphorites. The main reason for this deficiency is the rapid sedimentation or high burial rate in the sedimentary basin, which prevents the replacement of carbonate-rich fluorapatite by trace elements.

How to cite: Fociro, A., Öztürk, H., Sinojmeri, A., Cansu, Z., Moisiu, L., Çelik, Y., Nazaj, S., and Prifti, I.: Petrographic and Geochemical Analysis of Upper Cretaceous Phosphorites in Şemikan, Turkey and Gusmari, Albania: Insights into Depositional Environments and Palaeoceanographic Conditions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2875, https://doi.org/10.5194/egusphere-egu24-2875, 2024.

Posters on site: Mon, 15 Apr, 16:15–18:00 | Hall X1

Display time: Mon, 15 Apr 14:00–Mon, 15 Apr 18:00
Chairpersons: Aileen Doran, Dawid Szymanowski
Geochemistry — Applications and Advances
X1.93
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EGU24-17192
Ciprian Stremtan, Jan Wozniak, Cristina Montana Puscas, and Tudor Tamas

Elemental analyzers (EA) are the go-to sample introduction instrument for light stable isotope analyses of solid materials. Sample preparation is labor intensive and time consuming, with high associated consumable and equipment cost. Sample recovery is impossible in case of malfunctioning, i.e., no repeat analysis when sample amount is restricted.

In the same way, Laser ablation (LA) is traditionally considered a sample introduction technique for Inductively Coupled Plasma Mass Spectrometry (ICP MS) where plasma-based instrumentation will ionize and measure with a high degree of accuracy and precision the aerosol generated during the ablation process.

In this contribution we present an innovative method of measuring C stable isotopic ratios of carbonates by hyphening two instruments that are not usually found in the same lab. We coupled a laser ablation system (Teledyne Photon Machines Fusions CO2) equipped with a specially designed ablation chamber (Terra Analitic isoScell Δ100) to a Cavity Ring Down Spectrometer (Picarro G2201-i) to perform spatially resolved, highly accurate and precise measurements of both inorganic (stalagmite) and bioaccumulated (freshwater bivalve) carbonate samples. This novel system requires minimal sample preparation, allows for in-situ sequential and repeat sampling, all while eliminating the need to individually prepare samples.

How to cite: Stremtan, C., Wozniak, J., Puscas, C. M., and Tamas, T.: Laser Ablation – Cavity Ring Down Spectrometry, a new method for the in-situ analysis of δ13C of organic and inorganic carbonates, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17192, https://doi.org/10.5194/egusphere-egu24-17192, 2024.

X1.94
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EGU24-15680
Grant Craig, Markus Pfeifer, Neil Williams, Lionnel Mournier, Claudia Bouman, and Nicholas Lloyd

               Within the first five years of the initial introduction of multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS) with the VG Elemental Plasma 54 the potential for the technique to be applied to Isotope Cosmochemistry applications had already been recognized1. Early work focused on the 182Hf-182W chronometer, which had up until the introduction of MC-ICP-MS, been extremely difficult to measure with existing thermal ionization mass spectrometry (TIMS) techniques due to the extremely high first ionization potential of W.

In the following 25 years the use of MC-ICP-MS for Isotope Cosmochemistry applications has expanded to numerous other isotopic systems, including, but not limited to 26Al-26Mg, 146Sm-142Nd and 60Fe-60Ni, not just 182Hf-182W.  A general feature of these measurements is typically a reliance on excellent precision, on the order of a few ppm, 2RSD [2]. The high count rates required to achieve such excellent precision take time in order to achieve. Excellent precision over such time scales require a high performance mass spectrometer, capable of high sensitivity, stable throughout the course of the measurement and equipped with a low-noise detection array.

For over 20 years Thermo Fisher Scientific has pioneered developments in multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS). The latest generation Thermo Scientific™ Neoma™ MC-ICP-MS, blends cutting-edge and field proven technology from the Ultra™ HR-IRMS and iCAP Qnova™ Series ICP-MS [3] and has the capability to complement and enhance Isotope Cosmochemistry applications [4]. Here we report our investigations into using the Neoma MC-ICP-MS and Neoma MS/MS MC-ICP-MS for a selection of Isotope Cosmochemistry application, including high precision Mg, Fe, Cu, Zn and W measurements.

[1] A. Halliday, D. Lee, J. Christensen, M. Rehkämper, W. Yi, X. Luo, C. Hall, C. Ballentine, T. Pettke, C. Stirling, Geochimica et Cosmochimica Acta, 1998, 62, 919-940.

[2] S. Goderis, R. Chakrabarti, V. Debaille, J. Kodolányi, 2016, J. Anal. At. Spectrom., 2016, 31, 841-862.

[3] Thermo Fisher Scientific, 2020, BR30600-EN 0520C: Neoma Multicollector ICP-MS [pdf], Thermo Fisher Scientific.

[4] Z. Deng, M. Schiller, M. G. Jackson, M-A. Millet, L. Pan, K. Nikoljsen, N. S. Saji, D. Huang, M. Bizzarro, Nature, 2023, 621, 100-104

How to cite: Craig, G., Pfeifer, M., Williams, N., Mournier, L., Bouman, C., and Lloyd, N.: High precision isotope ratio analysis for Cosmochemistry applications using the Thermo Scientific Neoma MC-ICP-MS., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15680, https://doi.org/10.5194/egusphere-egu24-15680, 2024.

X1.95
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EGU24-11910
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Highlight
Matthieu Clog, Paula Lindgren, Martin R Lee, and Sevasti Modestou

Carbonates (calcite, aragonite, dolomite) are a minor component (often below 4 vol. %) of CM carbonaceous chondrites and formed during the aqueous alteration of their asteroidal parent bodies in the first few million years of Solar System history. The chemical and isotopic composition of these minerals are a valuable source of information on the conditions of alteration, potentially providing information on the composition and temperature of asteroidal fluids.

We report the carbon triple oxygen and carbonate clumped isotope compositions of six CM chondrites (Allan Hills 83100, Cold Bokkeveld, LaPaz Icefield 031166, Lonewolf Nunataks 94101, Murchison, Scott Glacier 06043), which span a range of degrees of aqueous alteration. To avoid issues due to the brecciated nature of these meteorites, gas aliquots produced by a single acid digestion were used to measure both the clumped isotopes and the triple oxygen isotope compositions. Where both calcite and dolomite are present, stepped acid dissolution allows us to measure their isotopic compositions separately.

We found that the Δ17O values range from -1 to -2.6‰, with a 0.6‰ difference between coexisting calcite and dolomite that indicates precipitation from distinct fluids. Crystallization temperatures range from 5 to 50⁰C for calcite and 75 to 100⁰C for dolomite. CM chondrites often contain several generations of carbonates with ranges in isotopic compositions that can be determined by ion probe. Because our method relies on the bulk extraction of carbonate phases, the measured values are the modes of the distributions for each meteorite, which has to be considered carefully in their interpretation. The isotopic composition of the alteration fluids can also be calculated for each meteorite and carbonate phase. We find that their δ18OvsSMOW ranges from -6.6 to +2.3‰, with no clear relationship with temperature or the δ13C of the carbonates, indicating a variety of starting isotopic compositions for the alteration fluids.

The main pattern that emerges is that chondrites with a higher degree of alteration (based on their petrology) have carbonates with lower Δ17O and higher crystallization temperatures, which is consistent with a prograde reaction in a largely closed system, and with dolomite forming after calcite in our samples.

How to cite: Clog, M., Lindgren, P., Lee, M. R., and Modestou, S.: The thermal and aqueous evolution of CM carbonaceous chondrite meteorites revealed by triple oxygen and clumped isotope compositions of their carbonates, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11910, https://doi.org/10.5194/egusphere-egu24-11910, 2024.

X1.96
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EGU24-11037
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ECS
Błażej Cieślik, Anna Pietranik, Jakub Kierczak, Alicja Lacinska, and Vojtěch Ettler

The mantle section of the ophiolite sequence is composed of ultramafic rocks, abundant in magnesium silicates. When exposed to crustal depths, these minerals become thermodynamically unstable and often interact with fluids of different provenance and chemistry. Ophiolite-hosted carbonates are one of the most widespread secondary phases resulting from interactions between silicates and CO2-rich fluids. There is ample evidence that carbonation of ultramafic rocks can occur in various geological settings and across a broad range of P-T conditions (Plümper & Matter, 2023). Therefore, accurately identifying the source of the fluids responsible for carbonation could contribute to a more comprehensive understanding of the long and complex evolution of the ophiolites.

In this study, we investigate carbonates hosted by the two ultramafic massifs (Szklary and Braszowice) of the Central Sudetic Ophiolite (CSO) (NE Bohemian Massif). This ophiolitic complex represents a late Devonian oceanic lithosphere formed in the slow-spreading regime. The complex story of the CSO includes prograde metamorphism, reaching its climax within the amphibolite facies, emplacement of syn- and post-Variscan magmas, as well as tropical weathering event(s) in the Cenozoic. Carbonate mineralization appears mostly as extensive veins and vein-like structures within partially serpentinized peridotites and serpentinites. The vast majority of veins in both localities exhibit a high modal abundance of cryptocrystalline magnesite accompanied by chalcedony or quartz. Field investigations revealed that carbonate veins containing magnesite-dolomite and calcite-dolomite are comparatively less common occurrences and they are mostly seen in the Braszowice ophiolitic fragment. In some samples, hydrous magnesium silicates co-occur with the studied carbonates. Based on both bulk and single-spot chemical composition (ICP-MS/ES and LA-ICP-MS) of carbonates, discrepancies and similarities have been observed between two ultramafic massifs. The concentrations of several trace elements (Ni, Al, Mn, Sr, Ba, Fe) noticeably vary between Szklary and Braszowice. Moreover, varied chemical compositions have been pinpointed among veins sampled at different depths. Strontium isotope composition was analyzed for fraction dissolved in HCl. At least two groups of carbonate veins can be distinguished based on their 87Sr/86Sr ratios. Veins sampled from the Braszowice pit floor, exhibiting Mgs or Mgs ± Dol or Cal ± Dol paragenesis, consistently display 0.7064 - 0.7065 values. Carbonate veins located at shallow depths in Braszowice and Szklary, primarily composed of cryptocrystalline Mgs or Mgs ± Qz, show 87Sr/86Sr values ranging from 0.7070 to 0.7113 suggesting input from fluids derived from the continental crust. Our research indicates a level of complexity in the formation of ophiolite-hosted carbonates including several stages of their formation as well as several sources of carbonating fluids.

Plümper, O., & Matter, J. (2023). Olivine—the alteration rock star. Elements, 19(3), 165-172.

Funding: Research financially supported by NCN PRELUDIUM project 2022/45/N/ST10/00879

 

How to cite: Cieślik, B., Pietranik, A., Kierczak, J., Lacinska, A., and Ettler, V.: Multistage carbonation of the Variscan ophiolite? Insights from geochemical and isotopic diversity of ophiolite-hosted carbonates, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11037, https://doi.org/10.5194/egusphere-egu24-11037, 2024.

X1.97
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EGU24-5704
Xudong Chen and Qilu Xu

Microbialite development in the Ediacaran Qigebrak Formation of the Tarim Basin, Northwest China: An examination of characteristics, distribution, and paleoceanographic reconstruction

Xudong Chen1,2, Qilu Xu1,2

  • National Key Laboratory of Deep Oil and Gas, China University of Petroleum (East China), Qingdao 266580, China;
  • School of Geosciences, China University of Petroleum (East China), Qingdao, 266580, China

 

The Upper Ediacaran Qigebrak Formation in the Tarim Basin of NW China preserves abundant and well-preserved microbialites with primary textures. These provide valuable insights into Precambrian sedimentology and paleoceanography. Our study focuses on elucidating the relationship between paleoceanic conditions and the development of these microbialites to understand their Precambrian origin.

A comprehensive analysis of Ediacaran outcrops in the northwestern Tarim Basin identified 12 distinct microbialite types, ranging from mafic (F1) to flat-laminated stromatolite (F12). These comprise F2 (micrite dolomite), F3 (granular dolomite), F4 (bonded sand debris dolomite), and spongiomicrobialite variants (F5-F7). Additionally, we observed F8 (fenestral tectonic thrombolites), F9 (micrite thrombolites), and diverse stromatolite dolomites (F10-F12). Their occurrence is spatially distributed: F1 and F2 in the nearshore supratidal low-energy zone; F3, F4, and F7 in granular beach and microbial mound zones; F5 and F8 in the environmental transition zone; F6 and F11 in the lower intertidal high-energy zone; F10 predominantly in the upper subtidal high-energy zone; and F9 and F12 in both upper intertidal and lower subtidal low-energy zones.The shale-normalized REE patterns of these microbialites exhibit weak negative Ce anomalies, weak positive Eu anomalies, and positive La anomalies, suggestive of suboxic seawater deposition. Their chemical signatures, characterized by low V, Ni, and Co concentrations, high Sr content, and Sr/Cu ratios exceeding 50, collectively indicate warm and arid paleoclimatic conditions. Compared to F9, F6, F10, and F11 show lower V/(V+Ni) values, higher Mg/Ca ratios, and stronger LREE and MREE deficits, suggesting formation in shallower, more dynamic, saline, and oxygenated waters.

Our findings offer fresh perspectives on the formation mechanisms of Precambrian microbial rocks and paleo-oceanic reconstruction.

How to cite: Chen, X. and Xu, Q.: Microbialite development in the Ediacaran Qigebrak Formation of the Tarim Basin, Northwest China: An examination of characteristics, distribution, and paleoceanographic reconstruction, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5704, https://doi.org/10.5194/egusphere-egu24-5704, 2024.

X1.98
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EGU24-5609
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ECS
Irakli Javakhishvili, Tamara Tsutsunava, and Giorgi Beridze

The Dizi series formed on the southern passive margin of a small oceanic basin on the Southern Slope of the Greater Caucasus and is exposed in the structural zone of the same name. The series is composed of metaterrigenous phyllite-like and volcanogenic rocks of the Devonian-Triassic age; marbles also are quite widespread in the series. During the Variscan orogeny, all rocks of the series underwent low-temperature regional metamorphism; later, in the Middle Jurassic time, intensive contact metamorphism took place. The object of presented research is marble, found in the rocks of the series both in the form of lenses and blocks. Interest in the study of marbles spread in the Dizi series is caused by several factors, namely, there is still no consensus on the position of marbles in the series, their detailed geochemical study has not been carried out, and the conditions of their formation have not been determined. There is an opinion that the Dizi series represents part of the Triassic Upper Karakaya complex, which was probably deposited in the forearc of the southern margin of Laurasia. The marbles are included in the series as exotic blocks of shallow marine Carboniferous and Permian limestone, most likely formed in Gondwana. During the study of the Dizi series marbles petrographic and geochemical research methods were applied. Petrographic characteristics of the marbles from all outcrops show a similar mineral composition, and structure and texture as well. The authors analyzed the main components, RE, and REE of the Dizi series marbles. The ratios Ca VS Mg, Mg/Ca VS SiO2, and Sr VS Mg/Ca show that the protolith of the marbles was pure limestone. The reconstruction   of the deposition conditions of the marble protolith, based on the concentrations of Sr, Rb, and Ba, indicates the formation of limestones in the conditions of the continental margin. The Ce-negative anomaly observed in the marble samples is possibly due to the existence of an oxygenated marine environment, probably of shallow water conditions. These conditions fully correspond to the tectonic interpretation of geochemical data from other metasedimentary rocks of the series. The results of the presented studies confirm that the marbles under consideration were formed in situ, together with the other rocks of the Dizi series in the conditions of the continental slope and its foot on the southern passive margin of a small oceanic basin of the Southern Slope of the Greater Caucasus.

How to cite: Javakhishvili, I., Tsutsunava, T., and Beridze, G.: About the marbles of the Dizi series (Greater Caucasus): geochemical features, the nature of the protolith, and paleoecological conditions of their formation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5609, https://doi.org/10.5194/egusphere-egu24-5609, 2024.

Methods and Applications of Geochronology
X1.99
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EGU24-16536
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ECS
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Highlight
Lorenzo Tavazzani, Dawid Szymanowski, Patrick Carr, Marcel Guillong, Yannick Buret, Edgar A. Cortes-Calderon, Julien Mercadier, and Cyril Chelle-Michou

Cassiterite (SnO2) is one of the dominant ore phases in tin-tungsten bearing magmatic-hydrothermal deposits. It can contain high uranium contents and usually hosts low levels of common Pb, making it one of the best U-Pb geochronometers among ore minerals [1]. The widespread use of in-situ techniques to obtain crystallization ages for cassiterite, however, is limited by a paucity of accurately characterized reference materials (RMs). Such shortage is mostly caused by the difficulty of achieving closed-system acid decomposition of this mineral, which represents the foundation of isotope dilution techniques, necessary for accurate and precise determination of U-Pb isotopic composition using thermal ionization mass spectrometry (TIMS) techniques.

In this contribution, we present a new set of U-Pb isotopic compositions of two cassiterite samples from the archetypal Variscan Sn-W greisen deposits of Panasqueira (Portugal) and Krasno (Czechia) obtained with an updated protocol of complete HBr decomposition of cassiterite in the presence of a U-Pb tracer, followed by U and Pb purification, and TIMS analyses. Previous to dissolution, the U-Pb isotopic compositions of the same cassiterite aliquots are characterized via laser-ablation-inductively coupled-mass spectrometry (LA-ICP-MS) and each cassiterite fragment is imaged with an ultra-fast washout laser ablation system to obtain high-resolution maps of the content and distribution of key trace elements (e.g. U, Pb, Fe, REE).

These two samples show variable but high U concentrations (2-20 ppm) and produce U-Pb isochron ages with 1% precision and low dispersion. We compare these new materials with established RMs (Yankee [2]; AY-4 [3]) and discuss their usability as primary reference materials for microbeam applications.

[1] Neymark, L. A., et al., Chemical Geology. 2018, 483, 410-425.

[2] Carr, P.A., et al., Chemical Geology. 2020, 539, 119539.

[3] Yuan, S., et al., Ore Geology Reviews. 2011, 43, 235–242.

How to cite: Tavazzani, L., Szymanowski, D., Carr, P., Guillong, M., Buret, Y., Cortes-Calderon, E. A., Mercadier, J., and Chelle-Michou, C.: Two new cassiterite reference materials for in-situ U-Pb dating from the European Variscan metallogenic belt, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16536, https://doi.org/10.5194/egusphere-egu24-16536, 2024.

X1.100
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EGU24-16896
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ECS
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Highlight
Dawid Szymanowski, Nico Kueter, Marcel Guillong, Lorenzo Tavazzani, and Ismay Vénice Akker

Recent years have seen a rise in applications of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to elemental and isotopic analysis of a wide range of geological materials, with a true explosion of in situ geochronology. Standardising such analyses relies on a homogeneous matrix-matched primary reference material (RM) whose ablation, transport and ionisation characteristics will result in fractionating elements and isotopes in the same way as in the unknown of interest.

One of the current frontiers of LA-ICP-MS geochronology – U–Pb dating of carbonates – suffers from a lack of such a material. Because the currently used primary RMs (e.g. WC-1 [1]) are heterogeneous in both age and U/Pb ratio, isotopic ratios are corrected on an isochron (whole-sample) basis rather than for each individual analytical spot, which imposes excess uncertainty on all U–Pb ages obtained this way. The U–Pb carbonate geochronology community is thus in urgent need of homogeneous reference materials for wide distribution. Ideally, such a RM should match the ablation behaviour of the unknown carbonate and consequently all matrix effects, including the amount and depth progression of inter-element laser induced elemental fractionation (LIEF), can be corrected directly, as is standard in e.g. zircon U–Pb geochronology.

We present a method for preparing synthetic RMs that uses a natural rock starting material which is milled to nano-powder, homogenised, and recrystallised using high-pressure, high-temperature apparatuses. In this way, natural sample heterogeneity is removed through milling, while textural coarsening is aimed at generating ablation behaviour similar to that of routine unknown samples.

Initial tests of synthetic calcite materials demonstrate the ability to achieve homogeneity at the spatial scale of a typical LA-ICP-MS laser spot size (80–110 µm typical for calcite U–Pb), while the ablation rate and LIEF are comparable to those of a range of commonly used calcite RMs. This suggests that experimental manufacturing of recrystallised carbonate is a promising avenue to obtain primary RMs that will allow spot-by-spot correction of LIEF in U–Pb analyses, thereby significantly reducing the reliance on heterogenous natural calcite RMs and improving the precision and accuracy of this analytical method.

Finally, this approach may serve as a blueprint for larger-scale production of primary RMs for a variety of matrices and isotopic systems for which there are no natural RMs characterised by the necessary homogeneity or availability.

[1] Roberts, N.M.W., et al., Geochemistry Geophysics Geosystems, 2017, 18(7): 2807-2814.

How to cite: Szymanowski, D., Kueter, N., Guillong, M., Tavazzani, L., and Akker, I. V.: Synthesising homogeneous carbonate reference materials for in situ U–Pb calcite geochronology, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16896, https://doi.org/10.5194/egusphere-egu24-16896, 2024.

X1.101
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EGU24-18378
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Highlight
Aratz Beranoaguirre, Leo J. Millonig, Maria V. Stifeeva, Richard Albert, Horst Marschall, and Axel Gerdes

Well-characterized matrix-matched reference materials are an indispensable requisite for mineral dating by LA-ICPMS. Recently, the in-situ U-Pb dating of low-U minerals (<20 µg/g) has emerged as a cutting-edge technique in the field of geochronology. The methodology has especially been applied to carbonate and garnet, although other minerals such as sulfate, ilmenite, staurolite, etc., are likely dateable by the same technique. However, the ability to expand this technique to such phases is hampered by the scarcity of reliable reference materials, creating a strong need for investigating and developing appropriate materials with well-constraint ages and homogeneous isotopic compositions.

During the last few years, the FIERCE laboratory has been investigating reference materials for garnet dating. Analysing garnet crystals from different localities and of various U and Pb contents, we found that four garnet localities have the potential to become reference materials for in-situ U-Pb studies. On the one hand, the availability of garnet crystals is sufficient to be distributed to laboratories worldwide. On the other hand, the garnet crystals analysed at FIERCE are relatively homogeneous, except for specific domains like rims, which showed slightly different ages (Millonig et al., 2023). The studied specimens come from Balochistan, with an approximate age of 45 Ma; Mongolia (ca. 130 Ma); Mali (black variety, different to the popular “Red-Mali”, age of ca. 200 Ma) and the Lake Jaco district in Mexico (pink variety, ca. 35 Ma). For this contribution, we have done an intra-crystal, inter-crystal and inter-session comparative study of the different localities, analysing multiple crystals from each locality over multiple analytical sessions. The potential reference materials analyses have been cross-calibrated against garnet crystals of known age (ID-TIMS age) and yield reproducible ages between different analytical sessions. Furthermore, garnet from the four localities will also be analysed by TIMS to provide independent age constraints.

How to cite: Beranoaguirre, A., Millonig, L. J., Stifeeva, M. V., Albert, R., Marschall, H., and Gerdes, A.: Potential matrix-matched reference material for in-situ garnet U-Pb dating, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18378, https://doi.org/10.5194/egusphere-egu24-18378, 2024.

X1.102
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EGU24-13041
Christoph Schmidt, Aurélie Germa, Xavier Quidelleur, Georgina King, and Rocío Jaimes Gutiérrez

In south-western Martinique (Lesser Antilles), the Pointe Burgos Basaltic monogenetic strombolian cone and lava flow cut through a porphyritic dacitic lava dome (Morne Champagne) dated at 617 ± 52 ka (Germa et al., 2011). An exceptional feature of the basaltic lava flow is the occurrence of about 4% of large (up to 2 cm) quartz crystals. Previous studies suggested that quartz xenocrysts had been added to the basaltic magma upon mechanical magma mixing with the cooled shallow dacitic reservoir, with a 9:1 ratio. Indeed, plagioclase phenocrysts (>1 cm) present resorbed surface and reaction rims, a well-known evidence of crystal remobilization. However, no other textural evidence of magma mixing is visible in the basaltic edifice. Moreover, the quartz crystals present unusual habits, are heavily cracked, and appear as filling voids in the basalt. This led us to investigate the age of the basaltic eruption and of the quartz crystals to propose a scenario for the xenocrysts’ origin.

The groundmass of the basaltic lava flow was K-Ar dated at 379 ± 25 ka, therefore ~240 ka after the eruption of the dacitic dome that it cuts through. Such a long time difference suggests that magma in the shallow reservoir was completely solidified when the basaltic magma ascended through it. Therefore, we would have expected to see also enclaves of dacite included in the basalt. Thermoluminescence (TL) dating allows for estimating the time since mineral formation or the last heating of a mineral above ~350 °C, thus representing an ideal tool to test whether the quartz xenocrysts formed synchronously with lava flow, or if they were formed later as substitutional minerals or void fillings. Here, we used red TL in combination with several protocols for dose determination, yielding consistent results. For assessing the dose rate, we took into account the quartz xenocrysts’ size distribution, the radioelement concentration of the basaltic matrix and the sites’ erosive evolution. The latter is particularly important because the basaltic matrix is comparatively poor in radioactivity so that the share of the cosmic dose rate becomes important. We obtain preliminary TL ages of 345 ka (with a total erosion of 20 m) and 377 ka (with an erosion of 50 m), each with a ~7% uncertainty. This result emphasizes the importance of reconstructing the lava flow geometry for answering the research question. As we believe that scenario (1) is more plausible, our results indicate the xenocrysts were likely formed post-eruption, challenging the initially suggested model of magma mixing and favouring secondary precipitation or mineral substitution. In case of TL resetting through geothermal activity, the age would represent the cooling following its cessation. However, given the xenocrysts’ pseudomorphic habit, it appears more likely that they represent secondary precipitates from hydrothermal fluids in voids left by strong geothermal alteration of the basaltic host rock.    

 

References

Germa, A., Quidelleur, X., Lahitte, P., Labanieh, S., Chauvel, C., 2011. The K–Ar Cassignol–Gillot technique applied to western Martinique lavas: a record of Lesser Antilles arc activity from 2 Ma to Mount Pelée volcanism. Quat. Geochronol. 6, 341-355.

 

How to cite: Schmidt, C., Germa, A., Quidelleur, X., King, G., and Jaimes Gutiérrez, R.: Age and origin of quartz xenocrysts in a basaltic lava flow in Martinique , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13041, https://doi.org/10.5194/egusphere-egu24-13041, 2024.

X1.103
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EGU24-4508
Oliver Nebel, Zarin Ali, and Massimo Raveggi

The Rb-Sr dating system has long been recognised as being susceptible to thermal perturbation. Its so-called closure temperature (TC) in biotite, the lowermost temperature at which interstitial diffusion of radiogenic 87Sr is no longer facilitated, is ca. 400 ˚C, much lower than e.g., the commonly used U-Pb system in zircon in excess of 900 ˚C. Newly developed in-situ analyses or Rb-Sr isotope systematics in biotite using a collision cell mass spectrometer (ICP-MS/MS) have now enabled rapid dating using multiple grains and with high spatial resolution (on a single grain scale). This now allows making use of the thermal characteristics of this dating tool. However, the modes and degrees of isotope reset are still poorly understood. Here, we analyse rocks from the Kohler Range in Antarctica for their Rb-Sr systematics in biotite. The plutonic rocks formed as part of the active Permian Gondwana margin (ca. 280-260 Ma). Whilst two samples record their original Permian age, two other samples yield cretaceous ages (~100 Ma), consistent with regional magmatic activity during the breakup of Gondwana. Two samples with mixed populations of micas confirmed a partial reset in this rock, and thereby the full reset for the Cretaceous ages. An intriguing aspect is that reset is predominant in spot analyses with higher Rb/Sr, making these sections apparently more prone to thermal reset, likely through higher diffusion potentials. We interpret the resetting of the system as a response to thermal perturbation of the igneous rocks with no apparent petrographic footprint. It is demonstrated that in-situ Rb-Sr dating of igneous micas in plutons can be used to date magmatic flare-ups in rocks that can be hundreds of millions of tears older. The technique thus holds immense potential to decipher the thermal histories of terranes that otherwise remain undetected and may be used to shed new light on a large number of suspect Rb-Sr (mixed?) ages with no apparent geologic meaning.

How to cite: Nebel, O., Ali, Z., and Raveggi, M.: Magmatic flare-up recorded in Rb-Sr reset-ages during Gondwana break-up, Kohler Range, Marie Byrd Land, Antarctica , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4508, https://doi.org/10.5194/egusphere-egu24-4508, 2024.

X1.104
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EGU24-19239
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ECS
Derya Gürer, Matthew M. Jones, Steve M. Bohaty, Stefano M. Bernasconi, Lucien Nana Yobo, and Andrew P. Roberts

Continental breakup leads to formation of new oceanic gateways, evolution of ocean bathymetry, and, in many cases, emplacement of large igneous provinces (LIPs). Changes in ocean circulation, volcanic CO2 emissions, and alteration of freshly emplaced ocean crust associated with these events were likely drivers of global-scale Cretaceous climate change. Yet, the precise timing and nature of Cretaceous continental rifting and submarine LIP eruptions remain largely unconstrained. The Agulhas Plateau (AP), along with Maud Rise (MR) and Northeast Georgia Rise (NEGR), are thought to constitute a once contiguous submarine LIP that was emplaced in the gateway between the incipient South Atlantic, Southern Ocean, and Indian Ocean basins during the breakup of Africa and East Antarctica. International Ocean Discovery Program (IODP) Expedition 392 recovered sedimentary and igneous rocks from the Agulhas Plateau, southwest Indian Ocean, including basaltic pillow lavas at IODP Site U1582, located on the northernmost edge of the plateau. Calcite veins and infills hosted in pillow lavas can provide insights into the timing and chemical environment of post-magmatic fracturing, fluid circulation, submarine weathering and carbonation of the LIP. We present in-situ U/Pb ages (n=12) of the calcite veins determined via laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), clumped isotope (Δ47) compositions (n=6) and 87Sr/86Sr ratios to investigate the timing and temperature of calcite precipitation. U/Pb geochronologic dates for vein calcite and infill are reproducible and yield Cenomanian to Turonian ages, consistent with shipboard nannofossil biostratigraphic age constraints for sediments intercalated between the pillows. Reproducible clumped isotopic paleotemperatures range from ~19 to 26°C, with a calculated δ18O value for precipitating fluids of ~-2 to +1‰ Vienna Standard Mean Ocean Water (VSMOW). The ranges of both these values are consistent with ambient mid-Cretaceous marine waters and, when combined with the age constraints for the basalt and sediments, support rapid weathering and carbonation of the submarine LIP following post-eruptive cooling. U/Pb geochronology of calcites at IODP Site U1582, refined by Sr isotope stratigraphy, provide a minimum age for the Agulhas Plateau. These data constrain the timing of the formation of a paleobathymetric restriction at the gateway between several incipient Cretaceous ocean basins, and have implications for geochemical interactions between mafic igneous rocks and seawater through the life cycle of a Cretaceous LIP.

How to cite: Gürer, D., Jones, M. M., Bohaty, S. M., Bernasconi, S. M., Nana Yobo, L., and Roberts, A. P.: Agulhas Plateau large igneous province emplacement and carbonation constrained by in-situ U-Pb dating, Sr isotope geochemistry and clumped isotope thermometry of calcite veins in basaltic basement at IODP Site U1582, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19239, https://doi.org/10.5194/egusphere-egu24-19239, 2024.

X1.105
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EGU24-10059
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ECS
Honglei Xie and Jinqiang Tian

The fault system within petroliferous basins plays a pivotal role in governing the migration, accumulation, and preservation of oil and gas resources. Accurate determination of the timing of fault activities is critical for reconstructing the history of tectonic evolution and for the analysis of hydrocarbon systems. Conventionally, this determination is achieved through the analysis and interpretation of seismic data. However, this method's effectiveness is often constrained by the quality of the seismic data, typically yielding only an approximate timeframe for fault activity. This limitation poses significant challenges in precisely identifying the periods of fault activity, which is essential for the analysis of their impact on hydrocarbon accumulation. Calcite, a commonly developed vein mineral in response to fault activities, is noteworthy in this context. The use of LA-ICP-MS U-Pb dating for fault vein calcite has been established as an effective technique to reveal time information of fault activity. The Tuoputai area, situated within the Tarim Basin, is recognized as one of the exploration hotspots with a complex tectonic evolution history. In particular, the strike-slip faults connecting Lower Cambrian source rocks with Ordovician carbonate reservoirs are instrumental in hydrocarbon migration and accumulation. In this study, the TP39 fault zone in the Tuoputai area, recognized for its rich hydrocarbon content, was selected for detailed analysis. We initially analyzed seismic data to obtain the approximate period of fault activity, followed by LA-ICP-MS U-Pb dating of calcite veins from core samples, to precisely determine the fault activity time. Additionally, the study incorporated the analysis of oil fluid inclusions in the calcite veins to comprehensively analysis the impact of fault activities on hydrocarbon accumulation. The seismic data indicated that the TP39 fault zone has mainly experienced three activity periods, including the Caledonian (542-416 Ma) to Hercynian (416-251 Ma), Indosinian (251-199.6Ma) and Himalayan (65.5 Ma-present) periods. In situ U-Pb dating of calcite veins from Ordovician reservoir cores in two wells within the fracture zone yielded ages of 446.79±2.67 Ma, 443.63±1.31 Ma, and 278.23±2.11 Ma, defining two significant active events in the TP39 fault zone during the Late Caledonian (~440 Ma) and Late Hercynian (~280 Ma), respectively. Furthermore, fluid inclusion analysis in calcite veins revealed a high prevalence of yellowish-green and bluish-green fluorescent oil inclusions, followed by blue fluorescent oil inclusions. The corresponding Th results from coexisting water inclusions indicated that the mainly phases of crude oil charging occurred during the Late Caledonian and Late Hercynian periods, followed by the Himalayan period, correlating well with the U-Pb dating results. This indicated that the fault activity during the Late Caledonian and Late Hercynian periods opened pathways for crude oil migration from the source rocks to the reservoirs. This study used the absolute dating method to constrain the activity time of the fault, demonstrating its impact on hydrocarbon accumulation, which is of great significance to basin structural research and oil and gas exploration.

How to cite: Xie, H. and Tian, J.: Fault activity history under absolute age constraints and its impact on hydrocarbon accumulation: A case study of the Tuoputai area in the Tarim Basin, China , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10059, https://doi.org/10.5194/egusphere-egu24-10059, 2024.

X1.106
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EGU24-14745
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ECS
Constantin Lazar, Relu Dumitru Roban, and Mihai Ducea

In the northernmost part of the Romanian Carpathians, the Maramureș region exposes several tectonic units comprising remnants of the Mesozoic Ceahlău - Severin Ocean. The “Black Flysch” unit contains a mafic complex extended in the Middle – Late Jurassic interval. These are covered by Upper Jurassic–Lower Cretaceous sediments, which include deep-water carbonates and siliciclastic deposits in the “Black Flysch” Nappe and mainly turbidites in the Ceahlău unit, which belong to the Outer Dacide nappe system.

The U-Pb age distribution spectra of detrital zircons obtained from the samples collected from the “Black Flysch” and Ceahlău tectonic units exhibit similarities within the range of 180–3,000 Ma. Significant peaks have been noticed at around ~460, 580–620, ~320, 180–200, and 950–1,100 Ma. Within the ‘Black Flysch’ Nappe prevail Ordovician ages (~460 Ma) associated with the Bucovinian Nappe basement. Conversely, in the Ceahlău Nappe, the Late Neoproterozoic peak (~600 Ma) holds greater significance, corresponding to the sediments of the Eastern European Platform and the paragneiss of the Bucovinian Nappe. The East European Craton contributes insignificantly as source area, given the minimal percentage of inherited ages surpassing 1 Ga.

How to cite: Lazar, C., Roban, R. D., and Ducea, M.: Provenance of the North Eastern Carpathian thrust sheet deposits based on geochronology, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14745, https://doi.org/10.5194/egusphere-egu24-14745, 2024.

X1.107
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EGU24-16928
Eastern North China Craton–North Australia Craton connection at 1.0 Ga through detrital zircon modelling
(withdrawn)
Wen Zhang, Wang Xu, Pinghua Liu, Chaohui Liu, and Fulai Liu
X1.108
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EGU24-136
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ECS
Amit Mondal, Smruti Prakash Mallick, and Kamal Lochan Pruseth

The Mahakoshal Supracrustal Belt (MSB) marks the northern margin of the Central Indian Tectonic Zone (CITZ) along which are sutured the northern and southern crustal blocks of India. Monazite U-Th-Pb total ages in the Dudhi granite from a sample at the southern margin of the MSB are reported here. Although the age of the MSB was constrained between 1.8 and 2.2 Ga, a more precise upper age limit of ~2.1 Ga was proposed later. The present sample shows signatures of extensive hydrothermal alteration resulting in the replacement of orthoclase by oligoclase accompanied by precipitation of carbonate and microcrystalline silica. The monazites yield seven age peaks starting from 2053±65 Ma to 1457±39 Ma, suggesting multiple resetting of the ages. The most intense peaks are at 1951±19 Ma (n=29), 1851±20 Ma (n=20) and 1787±25 Ma (n=12), with only three points in the 2053±65 Ma population. Most likely, the Dudhi granite represents partial melting of the basement to the MSB at 2053±65 Ma and constrains the maximum age of the MSB, corroborating the upper age limit suggested earlier.

How to cite: Mondal, A., Mallick, S. P., and Pruseth, K. L.: Monazite age constraint on the Mahakoshal Supracrustal Belt, India, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-136, https://doi.org/10.5194/egusphere-egu24-136, 2024.

Posters virtual: Mon, 15 Apr, 14:00–15:45 | vHall X1

Display time: Mon, 15 Apr 08:30–Mon, 15 Apr 18:00
Chairperson: Lorenzo Tavazzani
vX1.7
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EGU24-14937
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ECS
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Ankita Nandi, Ravikant Vadlamani, and Melinda Kumar Bera

Chemical composition heterogeneity in carbonate rocks ranging from the microscale to several meters preclude their direct age determination. Therefore, stepwise dissolution of several bulk rock samples or subsamples of an individual specimen can provide information on the primary composition of the carbonate material and refine the resulting Pb–Pb age. A millimetre-thick carbonate-rich (white) and shale-rich (black) layer from the Rohtas Formation, Lower Vindhyan Group, was divided into eight subsamples each and subjected to three leaching steps. The first leachate (L1) was discarded, and subsequent leachates, L2 and L3, were obtained after 24 hours of leaching in 0.6M HBr. A Pb-Pb isochron age of 1666±25 Ma (n=23, MSWD=13) is obtained by regressing L2 and L3 leachates from both layers. Since initial leachates (e.g., L2) contain epigenetically altered carbonate material, data points in the 207Pb/204Pb vs 206Pb/204Pb plot are well correlated but show a large scatter. In contrast, regressing only the L3 leachates of both layers yielded a Pb-Pb isochron age of 1644±49 Ma (n=12, MSWD=7), with a reduced scatter and comparable with earlier published work. Increasing the number of leaching steps minimizes the degree of scatter and significantly improves the precision of the obtained Pb-Pb age. Two subsamples from phosphoritic stromatolite-bearing carbonate rocks of the Tirohan Dolomite from the Jankikund river section, Lower Vindhyan Group, were subjected to seven leaching steps, of one hour each, in 0.5M HBr. The Pb isotopic composition of the carbonate material dissolved in five steps (L3 to L7) was regressed to yield an isochron age of 1579±16 Ma (n=10, MSWD=1.3). The Pb-Pb age of the Tirohan Dolomite Member obtained by multi-step leaching in this study is indistinguishable within error from an earlier reported age [1] of 1650±89 Ma (n=5, MSWD=89), moreover shows a better correlation of the 207Pb/204Pb vs 206Pb/204Pb data. All the analyses were performed in static mode on a Thermo-Fisher Neptune Plus MC-ICPMS. The instrumental mass fractionation was corrected using both thallium-spiking and sample-standard bracketing. Furthermore, a generalized power law correction was applied to the 204Pb-corrected ratios of unknown samples using the 205Tl/203Tl ratios of the bracketing NBS-981 standards. The two-stage mass bias corrected ratios were then normalized by the ratios of NBS-981 during each analytical session. The long-term isotopic ratios of NBS-981 standard (n=71) are 206Pb/204Pb= 16.9371±0.0026 (2σ), 207Pb/204Pb= 15.4906±0.0046 (2σ), 208Pb/204Pb= 36.7042±0.0113 (2σ).

 

[1] Bengtson, S., Belivanova, V., Rasmussen, B., Whitehouse, M. (2009). The controversial “Cambrian” fossils of the Vindhyan are real but more than a billion years older. Proceedings of the National Academy of Sciences, 106(19), 7729-7734.

How to cite: Nandi, A., Vadlamani, R., and Bera, M. K.: Improving the precision of Pb-Pb ages of carbonate rocks by implementing stepwise dissolution techniques: A case study from the Lower Vindhyan Group, India, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14937, https://doi.org/10.5194/egusphere-egu24-14937, 2024.

vX1.8
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EGU24-5344
Agim Sinojmeri, Ana Fociro, Giovanna Della Porta, Giovanni Grieco, and Sajmir Beqiraj

Phosphorites are well-known, worldwide, for accommodating a significant amount of U relative to other sedimentary rocks, due to the crystal structure of apatite where U substitutes Ca. In Albania, uranium-bearing Lower Jurassic phosphorites form a distinctive horizon identified across the entire Ionian zone. Two different types of U-bearing phosphatic deposits are identified within the Lower Jurassic carbonate succession in Albania; one, stratigraphically younger, layered and parallel to carbonate strata and the other due to infiltration in older, brecciated carbonates. The first type consists of lenticular shape deposits of limited lateral extension intercalated in thin-shelled bivalve packstone/rudstone, possibly corresponding to the Toarcian Bositra-rich organic rich “Posidonia” shales of Austria and Germany. The phosphatic horizon is confined by dark gray J2 limestone on the top, while the bottom shows signs of an early erosion. Their extent varies from 5-10 m to 100-160 m, while their thickness varies from 0.3 to 6 m. The radioactivity measurements indicate that the intensity of gamma radiation varies from 0.6 to 1.66 µSv/h, while the uranium content varies from 50 to 230 ppm, the highest values corresponding to the P2O5 peak of 32.66%. The second type of phosphorite mineralization developed in a widespread horizon throughout the Ionian zone. Its extension varies from 1.5 to 8 km, composed of continuous zones up to 0.5-1 km with some small interruptions. Uranium-bearing phosphatic deposits occur as the infiltrated matrix of breccias (caused by hydraulic or tectonic stress, not of sedimentary origin) made of angular clasts of Pliensbachian inner carbonate platform facies of the J1 (peloidal and oncoidal packstone/grainstone with Siphovalvulina foraminifers and Palaeodasycladus mediterraneous dasyclad algae). The intensity of gamma radiation varies from 0.5 to 1.1 µSv/h, uranium content varies from 50 to 150 ppm and the P2O5 highest peak is 15%. In accordance to the first data achieved, the uranium-bearing phosphorites of Early Jurassic age in Albania formed in deep, oxygen-depleted marine conditions as suggested by the abundance of thin-shelled bivalves. The well-documented early Toarcian Oceanic Anoxic Event driven by an increase in nutrients linked to high volcanic emissions of CO2 may have favoured the formation of the phosphate deposits. The intensive tectonic events associated with the Alpine Tethys Ocean opening during the Early and Middle Jurassic should be the main factor causing the brecciation and controlling the formation of later infiltration mineralization.

How to cite: Sinojmeri, A., Fociro, A., Della Porta, G., Grieco, G., and Beqiraj, S.: Preliminary insights on uranium-bearing Jurassic phosphorites of the Ionian zone, Albania, their distribution and genesis, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5344, https://doi.org/10.5194/egusphere-egu24-5344, 2024.