GMPV2.1 | Evolution of the Earth's upper mantle: a petrological, geochemical and geodynamic perspective on lithospheric mantle xenoliths, orogenic and ophiolitic peridotites
Evolution of the Earth's upper mantle: a petrological, geochemical and geodynamic perspective on lithospheric mantle xenoliths, orogenic and ophiolitic peridotites
Co-organized by GD2
Convener: Jacek Puziewicz | Co-conveners: Federico CasettaECSECS, Michel Grégoire, Costanza Bonadiman
Orals
| Tue, 25 Apr, 10:45–12:30 (CEST)
 
Room -2.47/48
Posters on site
| Attendance Tue, 25 Apr, 16:15–18:00 (CEST)
 
Hall X2
Orals |
Tue, 10:45
Posters on site
Tue, 16:15
The nature of Earth’s lithospheric mantle is largely constrained from the petrological and geochemical studies of xenoliths. They are complemented by studies of orogenic peridotites and ophiolites, which show the space relationships among various mantle rocks, missing in xenoliths. Mantle xenoliths from cratonic regions are distinctly different from those occurring in younger non-cratonic areas. Percolation of melts and fluids through the lithospheric mantle significantly modifies its petrological and geochemical features, which is recorded in mantle xenoliths brought to the surface by oceanic and continental volcanism. Basalts and other mantle-derived magmas provide us another opportunity to study the chemical and physical properties the mantle. These various kinds of information, when assembled together and coupled with experiments and geophysical data, enable the understanding of upper mantle dynamics.
This session’s research focus lies on mineralogical, petrological and geochemical studies of mantle xenoliths, orogenic and ophiolitic peridotites and other mantle derived rocks. We strongly encourage the contributions on petrology and geochemistry of mantle xenoliths and other mantle rocks, experimental studies, the examples and models of mantle processes and its evolution in space and time.

Orals: Tue, 25 Apr | Room -2.47/48

Chairpersons: Jacek Puziewicz, Costanza Bonadiman
10:45–10:50
5-minute convener introduction
10:50–11:00
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EGU23-17587
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On-site presentation
Crustal rhyolite melts at mantle depths 
Luigi Dallai, Gianluca Bianchini, Riccardo Avanzinelli, Mario Gaeta, Etienne Deloule, Claudio Natali, Andrea Cavallo, and Sandro Conticelli

Melts with rhyolite compositions originate from partial melting of crustal rocks or extensive differentiation of basaltic melts, at temperatures in the range of 800 °C. Accordingly, they are confined to the shallow continental crust. Nevertheless, experimental studies have demonstrated that dacite-rhyolite melts can be generated at higher temperature (> 1000°c) and pressure (>2 GPa), by partial melting of continental crustal lithotypes, but direct evidence for their occurrence has never been found. This implies that rhyolite melts may be produced at mantle conditions either by subduction of sedimentary material or exhumation of subducted continental crust.

Ephemeral rhyolite melt inclusions were found preserved in peridotite xenoliths from Tallante (Betic Cordillera, southern Spain) that are remnants of a supra-subduction mantle wedge. Here, the interaction of silica-rich melts with peridotite generated hybrid mantle domains, characterized by the occurrence of millimetre-sizes felsic veins with crust-like Sr-Nd-Pb-O- isotope compositions. The “Tallante” composite xenoliths were found among a wide population of peridotitic xenoliths, and display extreme compositional and isotopic heterogeneities both within the ambient peridotite and within the felsic veins. The latter consist of orthopyroxene, plagioclase, and quartz, and they are separated from the surrounding peridotite by an orthopyroxene-rich reaction zone. In their mineral phases, rhyolite glass inclusions and interstitial films associated to quartz crystals were observed. Petrological evidence and thermodynamic modelling indicate that rhyolite melts were originated by partial melting of near an-hydrous garnet-bearing metapelites at temperatures above 1000 °C. Partial melting was likely triggered by near-isothermal decompression during rapid exhumation of previously subducted crustal slivers. The melts reacted with the ambient lithospheric mantle at lower temperature (900 °C) and produced orthopyroxene, followed by plagioclase, quartz, and phlogopite. On the basis of chemical characteristics, it is hypothesized that potassic (HK-calc-alkalic to shoshonitic) and  ultrapotassic magmas may originate from metasomatic mantle sources generated from the interaction of crustal rhyolitic melts with mantle peridotite.

How to cite: Dallai, L., Bianchini, G., Avanzinelli, R., Gaeta, M., Deloule, E., Natali, C., Cavallo, A., and Conticelli, S.: Crustal rhyolite melts at mantle depths, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17587, https://doi.org/10.5194/egusphere-egu23-17587, 2023.

11:00–11:10
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EGU23-2720
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On-site presentation
Preservation of the water concentration in mantle xenoliths. The cases of Peylenc & Ray Pic volcanoes (FMC) 
Jannick Ingrin, Konstantinos Thomaidis, and Maria Drouka

The ability of xenoliths to preserve water lithospheric signatures remains an unsolved question for many years. We report water content in olivine and pyroxenes of peridotite xenoliths from Peylenc and Ray Pic volcanoes (French Massif central, FMC). On each site xenoliths were sampled from products of an explosive eruption (volcanic breccia and pyroclastic deposit) and an effusive eruption (frozen magma chamber and a lava flow).

In Peylenc, the xenoliths from the breccia have systematically more water than the xenoliths from the basalt quarry: ol 1-9, opx 60-95 and cpx 250-380 wt. ppm H2O versus ol <0.2, opx 20-55 and cpx 110-240 wt. ppm H2O.

In Ray Pic, water content in xenoliths from the lava flow is independent of its location in the lava: ol < 1, opx 190-270 and cpx 430-640 wt. ppm H2O. Results suggest that the cooling and solidification of the lava had no impact on water content.

The xenoliths from the pyroclastic deposit have systematically more water: ol 3-12, opx 330-460 and cpx 810-890 wt. ppm H2O. These values are either comparable with or lower than the values reported previously from the same locality1.

The study shows that xenoliths recovered from explosive eruptions have higher water content than the ones from effusive eruptions, but also that water content can be different from one explosive event to another.

Conclusion is that water content can rapidly be reset during magma degassing prior to eruption. Degassing controls water content of xenoliths.

Among the xenoliths studied, several have spectral signatures different from others. This different spectral signature has also been reported from other volcanoes2, 3. The coexisting of different spectral signatures, which have not been erased during degassing, are probably the only OH signatures fully preserved from depth.

1 Azevedo-Vannson S.,et al. Chemical Geology 575 120257 (2021)

2 Denis C.M.M. et al. Lithos 226 256-274 (2015)

3 Patkó L. et al. Chemical Geology 507 23-41 (2019)

How to cite: Ingrin, J., Thomaidis, K., and Drouka, M.: Preservation of the water concentration in mantle xenoliths. The cases of Peylenc & Ray Pic volcanoes (FMC), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2720, https://doi.org/10.5194/egusphere-egu23-2720, 2023.

11:10–11:20
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EGU23-16798
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On-site presentation
Combining volatiles measurements in fluid inclusions with petrology of ultramafic xenoliths from the Massif d'Ambre: unravelling the nature and evolution of the northern Madagascar Sub-Continental Lithospheric Mantle 
Barbara Faccini, Luca Faccincani, Andrea Luca Rizzo, Federico Casetta, and Massimo Coltorti

Integrating petrography and mineral chemistry data with the determination of volatiles concentration and isotopic fingerprint in fluid inclusions (FI) in ultramafic xenoliths is a novel approach which provides crucial information on the nature and evolution of the lithospheric mantle, together with important insight into how and where volatiles are stored and/or migrate through the lithosphere.

In this work, we investigated a new suite of ultramafic peridotite xenoliths from the Massif d’Ambre by integrating petrography, mineral and glass chemistry and the concentrations of volatiles [CO2 and noble gases (He, Ne and Ar)] in fluid inclusions (FI) hosted in olivine (Ol), orthopyroxene (Opx) and clinopyroxene (Cpx). The Massif d’Ambre is a Cenozoic stratovolcano located in northern Madagascar originated upon intense volcanic activity from ~12 to ~0.85 Ma, and the area is characterized by the widespread occurrence of mantle xenoliths, mostly, but not restricted to, spinel lherzolites and subordinately pyroxenites, which are hosted in mafic volcanic rocks. The new suite comprises 18 lherzolites, 11 harzburgites, 2 dunites, 3 wehrlites and 1 Ol-clinopyroxenite. Based on their petrographic and textural features, the suite was divided into five distinct groups: group 1A (protogranular to porphyroclastic textures), group 1B (large and porphyroclastic olivines), group 2 (infiltrated dunites and wehrlites), group 3 (cumulate-textured wehrlites) and group 4 (Ol-clinopyroxenite). Xenoliths are modally and compositionally heterogeneous and a clear separation can be observed between groups 1A-1B and groups 2-3, as testified by the large forsterite range of olivine (Fo88.4 – 93.2 vs Fo78.7 – 89.1, respectively), the Mg# of orthopyroxene (89.5 – 93.2 vs 82.7 – 87.3, respectively) and clinopyroxene (90.9 – 95.2 vs 81.4 – 89.9, respectively). This systematics corroborates the distinct origin of the groups, with xenoliths belonging to 1A-1B having the most refractory character and reflecting high extents (up to 30%) of melt extraction, while groups 3-4 xenoliths reflecting less depleted or re-fertilized mantle portions. Based on glass analyses, we propose that a carbonatitic or carbonated alkaline agent may have interacted with some portion of the source mantle, in agreement with Coltorti et al. (2000). The noble gases in FI hosted in Ol, Opx and Cpx exhibit 3He/4He ratio corrected for air contamination (Rc/Ra values) ranging from 5.90 Ra to 7.05 Ra, which is below the typical MORB-like upper-mantle value (8 ± 1 Ra). Furthermore, the great majority of xenoliths exhibits 4He/40Ar* ratios between ca. 0.2 to 0.8.

The major element distribution in mineral phases together with the systematic variations in FI composition will be used to place constraints on the origin and evolution (in terms of melting and metasomatism) of this portion of the mantle below the Massif d’Ambre and will be exploited to obtain a possible timeline for the petrological events that have characterized this lithospheric mantle portion.

Coltorti M., Beccaluva L., Bonadiman C., Salvini L. & Siena F. 2000. Glasses in mantle xenoliths as geochemical indicators of metasomatic agents. Earth Planet Sc. Lett., 183, 303–320.

Keywords: mantle xenoliths; lithospheric mantle; metasomatism; Massif d’Ambre

How to cite: Faccini, B., Faccincani, L., Rizzo, A. L., Casetta, F., and Coltorti, M.: Combining volatiles measurements in fluid inclusions with petrology of ultramafic xenoliths from the Massif d'Ambre: unravelling the nature and evolution of the northern Madagascar Sub-Continental Lithospheric Mantle, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16798, https://doi.org/10.5194/egusphere-egu23-16798, 2023.

11:20–11:30
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EGU23-4404
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ECS
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On-site presentation
First noble gases measurements in lherzolites from Mt Vulture volcano: new constraints on the mantle below Italy 
Laura Italiano, Antonio Caracausi, Gabriele Carnevale, Michele Paternoster, and Silvio G. Rotolo

Mount Vulture is a stratovolcano (age 0.75-0.14 Myr) located in southern Italy, which despite being at the same latitude of Vesuvius and Phlegreian Fields, has several peculiarities about its setting and erupted magma composition. Indeed, if compared to other Italian Quaternary volcanoes, it is the only one located east of the Apennine Front, about 100 km off the axis of the Campanian Magmatic Province (Peccerillo et al., 2017). Furthermore, although being a quiescent volcano (last eruption dated 0.14 Myr), previous studies (e.g., Caracausi et al., 2015, Bragagni et al., 2022) have shown extremely high CO2 emissions (4.85 × 108 mol yr-1), which are likely related to the carbonatitic volcanism of its final phase of activity, as well as some petrological aspects in the erupted products pointing to a mantle source metasomatism.

Recently, investigations on Vulture mantle xenoliths (Carnervale et al., 2022) revealed CO2-rich fluid inclusions (FIs) that indicate a primary depth of bubbles entrapment in olivine and pyroxene phenocrysts coinciding with the regional crust-mantle boundary (27-30km).

This research focuses for the first-time noble gases isotopes (He, Ne, Ar) in FIs from lherzolite enclaves from Mt. Vulture tephra. The He isotopic ratios (as R/Ra; R is the 3He/4He ratio of the sample and Ra the same ratio in air), are between 6.2 and 5.4 ± 0.08. These values are lower than the signatures of the MORB upper mantle (8 ± 1Ra) and overlap the values of the Sub Continental Lithospheric Mantle (SCLM, 6.1 ± 0.9Ra). The Ne isotopic signatures (20Ne/22Ne and 21Ne/22Ne) are in the field of the MORB values.

The He-Ne-Ar systematics is consistent with a SCLM source feeding the magmatism of the Vulture volcano. However, considering the noble gases He-Ne-Ar, in Vulture xenolites this mantle source has affinities with that feeding the volcanic activities of Mt. Etna (Nakai et al., 1997; Correale et al., 2014). This inference bears some evidence about the similitudes of the mantle below these two volcanic systems that is affected by mantle metasomatism, which is likely also responsible for the large CO2 fluxes and the carbonatitic magmatism (Bragagni et al., 2022). New measurements of the noble gases in free gases from the two volcanoes together with a detailed comparison between the geochemistry and petrography of the Vulture and Etna most primitive products will provide new constraints on the mantle typology below the two volcanoes and its relationship with the geodynamical evolution of the central Mediterranean.

References

Bragagni et al., 2021, Geology

Carnevale et al. (2022). Geophys. Res. Lett.

Caracausi et al. (2015). Earth Planet. Sci Lett.

Correale et al., 2014. Lithos

Nakai et al., (1997). Earth Planet. Sci Lett.

Peccerillo, A. (2017). Advances in Volcanology. Springer, Cham.

How to cite: Italiano, L., Caracausi, A., Carnevale, G., Paternoster, M., and Rotolo, S. G.: First noble gases measurements in lherzolites from Mt Vulture volcano: new constraints on the mantle below Italy, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4404, https://doi.org/10.5194/egusphere-egu23-4404, 2023.

11:30–11:40
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EGU23-12712
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ECS
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On-site presentation
Peridotite xenoliths from the Udachnaya-East kimberlite: windows onto the evolution of the Siberian sub-cratonic lithospheric mantle 
Federico Casetta, Igor Ashchepkov, Luca Faccincani, Rainer Abart, and Theodoros Ntaflos

Peridotite xenoliths from kimberlites are useful tools for exploring the architecture and composition of the thick sub-cratonic lithosphere, and thus understanding the long-term evolution of the Earth’s mantle. However, the continuous infiltration of kimberlite-related melts and fluids prior to - and during - the transport of mantle-derived fragments towards the surface makes it difficult to extract information about the original texture and chemistry of the mantle rocks and the deep-seated metasomatic processes.

In this study, fresh spinel- to garnet-bearing peridotite xenoliths from Udachnaya-East were studied to unveil the nature and composition of the lithospheric mantle beneath the Siberian craton. The studied samples have mostly harzburgitic to dunitic composition, even though lherzolites and rare wehrlites are also found. Occasionally, harzburgites are orthopyroxene-rich (up to 40 vol.%) or garnet-rich (up to 30 vol.%). The texture of the peridotites is extremely variable, ranging from protogranular to highly recrystallized and/or sheared. In spinel-bearing rocks, primary olivine is Mg- and Ni-rich (Fo90-93; NiO = 0.34-0.46 wt%), orthopyroxene has Mg# of 92-94 and Al2O3 in the range of 0.3-3.0 wt%, while clinopyroxene is Mg-rich (Mg# 94-96), with Al2O3 comprised between 1.0 and 3.5 wt%. In garnet-bearing peridotites, olivine ranges from Mg- and Ni-rich (Fo92; NiO = 0.45 wt%) to Fe-rich and Ni-poor (Fo87; NiO = 0.25 wt%), while pyroxenes have Mg# from 93 to 87-88 and comparatively low Al2O3 contents (orthopyroxene: 0.5-1.1 wt%; clinopyroxene: 0.8-2.2 wt%). High-precision electron microprobe analyses complemented by thermo- and oxy-barometric models were used to reconstruct the thermo-chemical log of the Siberian sub-cratonic mantle, in comparison to what proposed by Liu et al. (2022). Textural-compositional studies of the reaction zones enabled to discriminate the secondary-formed minerals with composition ascribable to the liquid line of descent of kimberlite-related melts at Udachnaya (Casetta et al. 2023) from those formed during melt/fluid-rock reactions taking place in the mantle before xenoliths’ entrainment by the host kimberlites. Altogether, our results enable to trace the P-T-X evolution experienced by the Siberian mantle, opening a window onto the comprehension of the interactions between kimberlitic-related fluid/melts and the sub-cratonic lithosphere.

 

Casetta, F., Asenbaum, R., Ashchepkov, I., Abart, R., & Ntaflos, T. (2023). Mantle-Derived Cargo vs Liquid Line of Descent: Reconstructing the P–T–fO2–X Path of the Udachnaya–East Kimberlite Melts during Ascent in the Siberian Sub-Cratonic Lithosphere. Journal of Petrology, 64(1), egac122.

 Liu, Z., Ionov, D. A., Nimis, P., Xu, Y., He, P., & Golovin, A. V. (2022). Thermal and compositional anomalies in a detailed xenolith-based lithospheric mantle profile of the Siberian craton and the origin of seismic midlithosphere discontinuities. Geology.

How to cite: Casetta, F., Ashchepkov, I., Faccincani, L., Abart, R., and Ntaflos, T.: Peridotite xenoliths from the Udachnaya-East kimberlite: windows onto the evolution of the Siberian sub-cratonic lithospheric mantle, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12712, https://doi.org/10.5194/egusphere-egu23-12712, 2023.

11:40–11:50
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EGU23-9276
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ECS
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On-site presentation
Unlocking the secrets of the Archean cratonic mantle through garnet Lu-Hf geochronology 
Kira Musiyachenko, Matthijs Smit, Maya Kopylova, and Andrey Korsakov

The sub-continental lithospheric mantle (SCLM) of Archean cratons represents the depleted and buoyant residue left behind after crust extraction. The history of the SCLM is notably complex in all cratons, often recording multiple episodes of melting and metasomatism. Garnet is a prime target for studying this history, as it provides thermobarometric constraints and hosts incompatible trace elements that can help identify melting and refertilization. Placing the rich geological record of mantle garnet in time is crucial for resolving cratonic evolution. Robust age constraints from garnet have nevertheless been difficult to obtain. Isolating enough analyte material for Lu-Hf or Sm-Nd chronometry is challenging for small xenoliths of highly depleted mantle rock. Age estimates are typically based on external or two-point isochrons with limited statistical robustness and geological interpretability. Moreover, chronometer systematics are principally not well constrained for the conditions and processes of the mantle. The question of which assemblages and chemical features of the Archean SCLM are actually of the Archean age is often left unanswered. To address this, we used ultralow-blank Lu-Hf chronometry, in concert with trace element analysis, on a targeted analysis of texturally and compositionally different mantle xenoliths from three Archean cratons (Slave, Kaapvaal, and Siberian Cratons).

The samples analyzed in this study represent a variety of garnet-bearing lithologies: clinopyroxene-rich fertile lherzolite, harzburgite (both granular and sheared), and orthopyroxenite with pyrope in exsolution lamellae. These samples were chosen, as they capture various stages of mantle evolution, from initial melting and subsolidus equilibration to shearing and metasomatic re-equilibration. We were able to obtain multi-point internal Lu-Hf isochrons for all lithologies, including those with extremely depleted compositions. The Lu-Hf ages span the history of the SCLM, from the Mesoarchean to the ages of kimberlite eruption. The oldest ages were obtained from lithologies depleted in Ca and clinopyroxene, i.e., exsolved orthopyroxenites and harzburgites from the Kaapvaal and Siberian Cratons. Lherzolites provided younger ages corresponding to metasomatic events, some of which could be linked to synchronous magmatic episodes in the overlying crust.

The data show that compositional and geochronological signatures in garnet can be retained on billion-year time scales. Static and dynamic recrystallization, and metasomatism – rather than temperature alone – control these signatures in garnet. The exsolution of pyrope in Ca-depleted Kaapvaal and Siberian orthopyroxenites is now confirmed to have occurred in the Archean. The geochemistry and petrology of these particular samples thus can constrain the P-T evolution that led to the development of the early continents.

How to cite: Musiyachenko, K., Smit, M., Kopylova, M., and Korsakov, A.: Unlocking the secrets of the Archean cratonic mantle through garnet Lu-Hf geochronology, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9276, https://doi.org/10.5194/egusphere-egu23-9276, 2023.

11:50–12:00
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EGU23-243
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ECS
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On-site presentation
Reappraisal of the geodynamic evolution of the mantle massifs of the Ivrea-Verbano Zone based on new field, petrochemical and geochronological data 
Abimbola Chris Ogunyele, Mattia Bonazzi, Alessio Sanfilippo, Alessandro Decarlis, and Alberto Zanetti

The Ivrea-Verbano Zone (IVZ) is the westernmost sector of the Southern Alps. It is constituted by granulite-to-amphibolite-facies continental crust representing the basement of the Adria plate. The IVZ contains many orogenic mantle peridotites. The largest mantle bodies are aligned along the Insubric Line at the lowest stratigraphic units, in contact with mafic-ultramafic crustal intrusives. Mantle bodies in the central and southern sectors of IVZ are spinel lherzolites with spinel dunites and variable amount of clinopyroxenite, websterite and subordinate anhydrous/hydrous gabbroic bodies (e.g. the Baldissero, Balmuccia, Premosello peridotites). Conversely, modally-metasomatised spinel harzburgites with large dunite bodies and phlogopite-and-amphibole-bearing websterites (e.g. the Finero peridotite) crop out in the northern IVZ.

The constant association of the IVZ mantle peridotites with High-T shear zones suggests that none of them was emplaced into the crust by mantle diapirism. Alternative hypotheses involve emplacement at the crustal level at the onset of the Mesozoic extensional regime or tectonic addition to accretionary wedges of Paleozoic subduction zones. Recent gravimetric and seismic data converge in indicating that high-density rocks are very close to the surface near the Insubric Line, thus supporting the possibility that the largest mantle peridotites may be a direct expression of the underlying subcontinental mantle.

This contribution focuses on new field, petrographic, geochemical and geochronological data, to address some relevant issues, such as the nature of the spinel lherzolite (refractory residue vs. refertilised mantle), the origin of pyroxenites and gabbros, the relationships with the associated crustal intrusives and the record of Mesozoic tectono-magmatic events.

The final goal is to provide new insights into the geodynamic evolution of the mantle bodies and the mantle-crust systems at the Laurasia-Gondwana margin, defining in particular how the mantle heterogeneity acquired during Paleozoic may have governed the rifting process of the Adria margin in Jurassic times.

How to cite: Ogunyele, A. C., Bonazzi, M., Sanfilippo, A., Decarlis, A., and Zanetti, A.: Reappraisal of the geodynamic evolution of the mantle massifs of the Ivrea-Verbano Zone based on new field, petrochemical and geochronological data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-243, https://doi.org/10.5194/egusphere-egu23-243, 2023.

12:00–12:10
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EGU23-4252
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On-site presentation
Evidence for the effects of subduction in Triassic lavas from the Northern Peloponnese (Greece): A mineralogical, geochemical and isotopic (Sr-Nd) approach 
Petros Koutsovitis, Konstantinos Soukis, Sotirios Kokkalas, Andreas Magganas, Theodoros Ntaflos, Yirang Jang, and Sanghoon Kwon

Triassic volcanism in Greece is mainly associated with the rift phase of the Neotethys that resulted in the formation of E-MORB and OIB alkali basalts, which are widespread throughout the Hellenic mainland[1]. In most of the outcrop localities (e.g. Pindos, Koziakas, Othris, Argolis) these basalts are closely related in the field with other more differentiated volcanics that display a clear subduction signature [1,2]. In the Northern Peloponnese and specifically from the localities of Drakovouni, Palaiohouni and Perachora, three types of lavas were identified: basaltic andesites, andesites and rhyodakites, which are fine to medium grained and displaying either porphyritic or even equigranular textures in the more felsic varieties. These lavas were classified based on their Si, Na and K contents, as well as their Nb/Y vs. Zr/Ti ratios, which were subjected to rather restricted metasomatic processes (LOI:1.1-3.7, partial albitization and uratilization). Based on their potassium contents, as well as upon the AFM geochemical ternary plot and their FeO/MgO ratios, they are geochemically classified as calc-alkaline volcanics, clearly being affected by subduction-related processes. The latter is confirmed by: presence of magmatic magnesiohornblende in all types of lavas at variable amounts, enhanced Th/Yb contents (2.4-4.1), LREE enrichments [(La/Yb)CN=6.2-10.0], lower normalized values of Th and U compared to Nb and Ta, positive K and Pb anomalies, negative Ti anomalies in the PM-normalized diagrams, noticeable LILE enrichments (e.g. Cs, Rb, Ba).

Fractional crystallization played a significant role in the differentiation processes. This is confirmed by: presence of primary clinopyroxene and amphibole in the basaltic andesites whose modal composition significantly decreases in the andesites and rhyodakites (only accessory amphibole), relatively strong correlation between Sc/Y with CaO/Al2O3 (R2 = 0.91), positive correlation between P2O5/TiO2 and (La/Yb)N (R2 = 0.87), higher Cr and Ni contents in the least differentiated lavas, increase of Nb/Yb in the highly fractionated lavas, increasing Eu negative anomalies from the compositionally basic to the felsic varieties (basaltic andesites EuCN/Eu*= 0.73-0.80; andesites EuCN/Eu* = 0.63-0.74, rhyodakites EuCN/Eu* = 0.51-0.61). Apart from fractional crystallization, crustal assimilation (AFC processes) likely played an additional role during differentiation, shown by the strongly positive correlation between SiO2 and Nb/Yb (R2 = 0.92). The Sr-Nd isotopic data further confirm the effect of crustal contamination and AFC processes, with lower 143Nd/144Nd and higher 87Sr/86Sr ratios for the rhyodakites compared to the andesites and basaltic andesites.

References: [1]Koutsovitis, P., Magganas, A., Ntaflos, T., Koukouzas, N., Rassios, A.E., Soukis, K., 2020. Petrogenetic constraints on the origin and formation of the Hellenic Triassic rift-related lavas. Lithos 368-369, 105604, [2] Pe-Piper, G., Piper, D.J.W., 2002. The Igneous Rocks of Greece. Borntraeger, Stuttgart, pp. 1–645.

How to cite: Koutsovitis, P., Soukis, K., Kokkalas, S., Magganas, A., Ntaflos, T., Jang, Y., and Kwon, S.: Evidence for the effects of subduction in Triassic lavas from the Northern Peloponnese (Greece): A mineralogical, geochemical and isotopic (Sr-Nd) approach, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4252, https://doi.org/10.5194/egusphere-egu23-4252, 2023.

12:10–12:20
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EGU23-15786
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On-site presentation
The  evidences of deep melting from the  xenolith bearing mafic rocks in Southern Thrace region: The significance of the peridotite and the  pyroxenite source melting.
(withdrawn)
Biltan Kurkcuoglu, Tekin Yürür, Berivan Günes, Tanya Furman, and Barry Hanan
12:20–12:30
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EGU23-293
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ECS
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Virtual presentation
Evolution of the lithospheric mantle beneath Eastern Dharwar craton of Southern India: constraints from peridotite xenoliths from P3 kimberlite pipe of the Wajrakarur 
Zeeshan Daimi and Ashish Dongre

Even though the southern Indian Dharwar craton hosts several kimberlites, lamproite, and lamprophyre fields of the Mesoproterozoic age, mantle-derived peridotitic xenoliths are very rare and are often highly altered and poorly preserved. Due to these constraints, xenolith-based direct mantle investigations have been limited beneath the Indian cratons. In this study, we report extensive geochemical analyses on peridotite xenoliths from the P3 kimberlite pipe of the Wajrakarur kimberlite field from the Eastern Dharwar craton (EDC). With the help of major and trace element compositions of the garnets and clinopyroxenes, this study aims to characterize the mantle below EDC and to comment on its evolution.

During this study, 57 peridotite xenoliths were identified. P-T estimates were carried out using garnet compositions. Based on the vertical distribution of garnets on a projected depth, it is observed that the upper part of the lithosphere is composed mostly of lherzolites(G9) with few harzburgites (G10), whereas the base of the lithosphere is dominated by Ti-Metasomatized garnets(G11).

Garnet compositions show an anomaly in the TiO2 content, which is marked by a sudden increase in TiO2 at ~160 km of depth. This depth coincides with an increased concentration of G11 garnets. Zr/Hf vs Ti/Eu plot for garnets shows that carbonatitic and kimberlitic fluids are involved in metasomatizing the SCLM. The Mg# and Cr# values suggest that the lithosphere gets more depleted with increasing depth. Clinopyroxene compositions show the presence of two types. Type 1 is enriched in LREE than the Type 2 clinopyroxenes showing the metasomatic enrichment.

The depth range of the studied peridotite xenoliths indicates sampling of the mantle from ~170 to 190 km of depth, indicating a 190 km thick LAB at 1.1 Ga. However, geophysical studies show a present-day estimate of a ~110 to 120 km thick lithosphere. This further indicates about 70-80 km of delamination of the lithospheric keel in post-Mesoproterozoic times. Such large-scale delamination of the lithosphere might be possible due to the increased frequency of mantle plumes, convective erosion, and the heavily metasomatized nature of the SCLM.

How to cite: Daimi, Z. and Dongre, A.: Evolution of the lithospheric mantle beneath Eastern Dharwar craton of Southern India: constraints from peridotite xenoliths from P3 kimberlite pipe of the Wajrakarur, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-293, https://doi.org/10.5194/egusphere-egu23-293, 2023.

Posters on site: Tue, 25 Apr, 16:15–18:00 | Hall X2

Chairpersons: Federico Casetta, Michel Grégoire
X2.141
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EGU23-2878
Peridotite xenoliths from Stöpfling in Hessian Depression (Germany) revisited 
Jacek Puziewicz, Sonja Aulbach, Magdalena Matusiak-Małek, Theodoros Ntaflos, and Małgorzata Ziobro-Mikrut

The Hessian Depression in Germany represents the northern continuation of the Upper Rhine Graben and is known for Cenozoic alkaline basaltic lavas. Many of these carry peridotite xenoliths of mantle origin, which were studied mainly in the  80-ies of the XX century (Hartmann & Wedepohl 1990 and references therein). These studies documented mantle lithosphere melting followed by metasomatism. Here we describe the xenoliths from the Stöpfling quarry near Homberg upon Efze. The quarry has been recultivated and sampling is not possible now, our samples come from the archival collection of the Department of Geochemistry of the University of Göttingen. In this abstract, we give an overview of newly collected major- and trace-element mineral-chemical data from 11 xenoliths.

The xenoliths from Stöpfling are spinel-facies lherzolites and harzburgites. They consist of aggregates of few coarse (typically 4-6 mm across) grains of olivine and orthopyroxene embedded in fine-grained matrix of olivine, ortho- and clinopyroxene and spinel. Coarse-grained aggregates represent fragments of protogranular texture and are volumetrically prevailing. Spinel is commonly interstitial and has amaeboidal morphology. Locally, centimetre-thick layers of websterites cross-cut the peridotites. Hartmann & Wedepohl (1990) report traces  (<1 vol. %) of phlogopite in 2 of 12 lherzolites they studied.

The major element composition of olivine is strikingly homogeneous in all studied rocks (91±0.5 % forsterite and 0.40 wt. %. NiO), Ca content is < 500 ppm. Orthopyroxene is mildly aluminous (0.10-0.17 atoms of Al per formula unit, [pfu]) as is clinopyroxene (0.12-0.25 atoms Al pfu). Spinel Cr# [= Cr/(Cr+Al)] varies from 0.18 to 0.46. Clinopyroxene coexisting with spinel of low Cr# is Al-rich and contains 1600-2200 ppm Ti, whereas that coexisting with spinel of higher Cr# is less aluminous and contains 600-1200 ppm Ti. Clinopyroxene coexisting with spinel of Cr# 0.46 is extremely impoverished in Ti (50 ppm). The REE patterns of clinopyroxene in most samples are above the primitive-mantle (PM) level, are LREE-enriched and flat at MREE-HREE. Those extremely depleted in Ti show a decrease from HREE towards MREE, the contents of which are below PM level, and are strongly LREE-enriched.

Peridotites from Stöpfling consist of olivine which chemical homogeneity  across the xenolith suite supposedly records melt depletion. The variable content of Al in orthopyroxene from different samples probably is due to subsequent refertilization event(s) involving silicate melt, whereas the REE characteristics of clinopyroxene suggests that it was additionally cryptically  metasomatized. The unaffected olivine composition indicates low ratio of metasomatic agent to protolith.

Acknowledgements. JP is grateful to G. Wörner for enabling access to the xenoliths from Stöpfling that were originally collected by H. Wedepohl and are now archived at the Geochemistry and Isotope Geology Division of the Geoscience Center at University Göttingen (GZG).

Funding. This study originated thanks to the project of Polish National Centre of Research 2021/41/B/ST10/00900 to JP.

References:

Hartmann G., Wedepohl. K.H. (1990): Metasomatically altered peridotite xenoliths from the Hessian Depression (Nortwest Germany). Geochim. Cosmochim. Acta 54: 71-86.

How to cite: Puziewicz, J., Aulbach, S., Matusiak-Małek, M., Ntaflos, T., and Ziobro-Mikrut, M.: Peridotite xenoliths from Stöpfling in Hessian Depression (Germany) revisited, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2878, https://doi.org/10.5194/egusphere-egu23-2878, 2023.

X2.142
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EGU23-14795
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ECS
The lithospheric mantle beneath Devès volcanic field – case study of mantle xenoliths from Mt. Briançon (Massif Central, France) 
Małgorzata Ziobro-Mikrut, Jacek Puziewicz, Sonja Aulbach, and Theodoros Ntaflos

The 3.5-0.5 Ma Devès volcanic field is located in the “southern” mantle domain of the French Massif Central (MC), which originated by partial melting, likely followed by refertilization by melts from the upwelling asthenosphere [1, 2]. However, the extent of melting versus degree of refertilization remains unclear. In order to obtain new insights into this fundamental question, we studied a large mantle xenolith population (n – 21) from a cinder cone in the NW of Devès, the Mt. Briançon nepheline basanite. Extensive use of EMPA and LA-ICP-MS allowed us to gather a comprehensive and representative dataset. Here, we present preliminary interpretations. Ongoing EBSD analyses will provide further data to confirm or correct our hypothesis.

The lithospheric mantle (LM) beneath the Devès is heterogeneous. It contains lherzolite with clinopyroxene (cpx) exhibiting REE patterns with relatively flat Lu-Eu and variable LREE-depletion. The coexisting spinel (spl) is highly aluminous (Cr# 0.09-0.15). By analogy with prior work [2], we suggest that cpx and spl were added to the rock by a MORB-type melt [2]. Those lherzolites probably represent refertilized LM similar to the Lherz massif [3], which obscures the original degree of depletion.

A distinct mantle region below the Devès is represented by harzburgites and cpx-poor lherzolites containing cpx with REE patterns that show moderately increasing Lu-Sm and steeply increasing towards La. The coexisting spl has medium to high Cr# (0.17-0.28). We suggest that this lithology was not refertilized by MORB-like melts, but records some other metasomatic event(s).

A single harzburgite xenolith contains LREE-enriched cpx similar to those described above, but of significantly lower element abundances. This harzburgite is the most magnesian in the entire suite, with olivine Fo ~91.2% and Mg# in pyroxenes ~0.92 (vs Fo 88.5-90.4% and Mg# 0.88-0.91 for other peridotites). Pyroxenes have the lowest Al, Fe, Ti, Na contents in the whole suite and spinel is the most chromian (Cr# ~0.43). This rock resembles harzburgites from the northern domain of the MC, interpreted as a relatively depleted residue of partial melting [4].

This study was funded by Polish National Science Centre to MZM (UMO-2018/29/N/ST10/00259).

References:

[1] Lenoir et al. (2000). EPSL 181, 359-375.

[2] Puziewicz et al. (2020). Lithos 362–363, 105467.

[3] Le Roux et al. (2007). EPSL 259, 599–612.

[4] Downes et al. (2003). Chem Geol 200, 71–87.

How to cite: Ziobro-Mikrut, M., Puziewicz, J., Aulbach, S., and Ntaflos, T.: The lithospheric mantle beneath Devès volcanic field – case study of mantle xenoliths from Mt. Briançon (Massif Central, France), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14795, https://doi.org/10.5194/egusphere-egu23-14795, 2023.

X2.143
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EGU23-13627
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ECS
The impact of melt impregnation on the genesis of mantle peridotites from Puke Massif (Mirdita Ophiolite, Albania) revealed by geochemical data 
Jakub Mikrut, Magdalena Matusiak-Małek, Michel Gregoire, Georges Ceuleneer, Kujtim Onuzi, and Jacek Puziewicz

The Mirdita Ophiolite (N Albania) consists of two meridional belts of different geochemical affinities: supra-subduction zone for the Eastern belt and mid-ocean ridge (MOR) for the western belt. Puke Massif described in this study is a mantle dome belonging to the MOR belt.

Structurally, the Puka Massif is interpreted as an Oceanic Core Complex formed of harzburgites cross-cut by dunitic channels grading to mylonitized plagioclase and amphibole bearing lherzolites with minor dunites and chromitites at the top of the section. The massif experienced an intense magmatic activity evidenced by gabbroic and pyroxenitic dykes. Field and petrographic evidences revealed that plagioclase, clinopyroxene and amphibole in lherzolitic mylonites crystallized from impregnating melts (Nicolas et al. 1999, 2017). Scientific question behind our study is whether this conclusion is confirmed by geochemical data.

Clinopyroxene from magmatic veins cross-cutting mylonites, has trace elements (TE) composition identical to that from the host peridotite. In general, 3 types of TE patterns can be identified in the veins and mylonites: 1. Strongly depleted (Yb=0.3-0.6x primitive mantle, PM, McDonough & Sun 1995); 2. Intermediate (Yb=1.1-4xPM); 3. Enriched (Yb=5-11xPM). The group 1 comprises only pyroxenites. Two relatively undeformed harzburgites occurring in the lowermost section of the mantle dome contain TE-poor clinopyroxene. One, which is amphibole-bearing, exhibits TE pattern resembling that in group 1, while the other one shows even more depleted signature, with Yb=0.8-1.3xPM and La <0.001xPM. Intrusive rocks from groups 2 and 3 are widespread in the whole massif while the occurrences of the depleted group are restricted to the lowermost sections. Rocks from different groups may occur within a single outcrop.

The TiO2 content in clinopyroxene mimics the TE-based division of the rocks. Clinopyroxene in the group 1 and harzburgites has TiO2<0.1 wt.%, whereas that from group 2 and 3 has 0.1<TiO2<0.5 wt.% and TiO2>0.5 wt.%, respectively. Similar relationships are observed in the composition of spinel, which has TiO2<0.1 wt.% in group 1 rocks, 0.1 - 0.25 wt.% in group 2 and between 0.1 and 2.0 wt.% in the group 3 rocks.

As magmatic rocks and deformed peridotites share common clinopyroxene TE trends, as well as similar Ti variations in clinopyroxene and spinel, geochemical data support impregnating origin of mylonites. Impregnating melts, differing in enrichment level, were active within whole massif; only the most depleted seem to be restricted to some of its parts. Only internal or easternmost harzburgites could have escape magmatic impregnations; these samples are relatively undeformed and have depleted melting-like TE trends. These findings are in agreement with melt impregnation origin of mylonites. Presence of the depleted lithologies supports primarily harzburgitic origin of the massif, later followed by mylonitization of some of its part. 

This study was financed as a project within program “Diamond Grant” (DI 024748).

How to cite: Mikrut, J., Matusiak-Małek, M., Gregoire, M., Ceuleneer, G., Onuzi, K., and Puziewicz, J.: The impact of melt impregnation on the genesis of mantle peridotites from Puke Massif (Mirdita Ophiolite, Albania) revealed by geochemical data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13627, https://doi.org/10.5194/egusphere-egu23-13627, 2023.

X2.144
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EGU23-16528
Megacryst suites in kimberlite 
Daniel Schulze

Large, single crystals (> 1cm) are a familiar component of mantle xenolith suites of many kimberlites.  Confusion between different suites exists in the literature, however, which affects petrogenetic models, and some clarification is warranted.  Megacrysts of the Cr-poor suite[1] are most common.  Cr-poor silicates (garnet, clinopyroxene, orthopyroxene, olivine) are characterized by lower Mg/(Mg+Fe) and Cr2O3 and higher TiO2 values than typical mantle peridotite minerals.  Strong geochemical trends in most occurrences of Cr-poor megacryst suites (e.g., concomitant decrease in Mg/(Mg+Fe) and Cr2O3) are interpreted by most authors as the result of fractional crystallization of a kimberlite, or kimberlite-like, magma.   

The Cr-rich megacryst suite, comprising garnet, clinopyroxene, orthopyroxene and olivine, but not ilmenite, was described from the Sloan/Nix kimberlites in northern Colorado[1].  Constituent minerals, all four of which are essential to the definition of the suite, are characterized, in part, by high and restricted values of Mg/(Mg+Fe) and wt% Cr2O3 (e.g., 0.791 to 0.837 and 6.1 to 13.0, respectively, in garnet [2]).  Elsewhere, large crystals with Mg/(Mg+Fe) and Cr2O3 values higher than Cr-poor suite minerals do occur, but none correspond to the Sloan-Nix Cr-rich suite in paragenesis, size and/or composition[2].  For example, almost no garnet megacrysts described as “Cr-rich” or “high-Cr” from other localities (e.g., refs 3-6) contain >6 wt% Cr2O3 and even garnets with <2 wt% Cr2O3 are termed “Cr-rich” or “high-Cr”.  Most, or all, of these so-called “Cr-rich garnet megacrysts” are simply xenocrysts from coarse-grained peridotite. 

The “Granny Smith” suite, first described from Kimberley and Jagersfontein [7], is dominated by Cr-clinopyroxene associated with phlogopite (and ilmenite at Kimberley), with uncommon olivine or rutile.  Garnet and orthopyroxene do not occur in this suite, which is neither equivalent to nor a subset of the Cr-rich megacryst suite.  Other suites dominated by Cr-clinopyroxene, also not shown to coexist with garnet and orthopyroxene, have been described from Orapa and Bobbejaan [6] and Grib [8], though analogies have been drawn with the Cr-rich megacryst suite despite compositional and paragenetic differences.  A similar megacrystalline assemblage (Cr-cpx, ilmenite, phlogopite, olivine) has been described from Attawapiskat [9] and at Balmoral megacrysts of Cr-cpx occur with ilmenite, Nb-Cr rutile and zircon [10].

All of these suites of Cr-cpx +/- ilmenite, rutile, phlogopite, olivine, zircon (lacking garnet/opx), though varied, have more in common with each other than with the Cr-rich megacryst suite.  All might be best termed “Granny Smith”, and may have common origins.  The only feature they share with the Sloan-Nix Cr-rich megacryst suite is the presence of large chromian clinopyroxene.  Use of such populations as equivalents of the Sloan-Nix Cr-rich megacryst suite in mantle petrogenetic schemes can lead to faulty conclusions. 

References:  1) Eggler et al. (1979) The Mantle Sample, 2) Schulze (2022) Goldschmidt Conf. Abstr., 3) Hunter and Taylor (1984) Am. Min., 4) Kopylova et al. (2009) Lithos, 5) Bussweiller et al. (2018) Min. Pet., 6) Nkere et al. (2021) Lithos, 7) Boyd et al. (1984) GCA, 8) Kargin et al. (2017) Lithos, 9) Hetman (1996) MSc., 10) Schulze, unpub. data. 

How to cite: Schulze, D.: Megacryst suites in kimberlite, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16528, https://doi.org/10.5194/egusphere-egu23-16528, 2023.

X2.145
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EGU23-4995
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ECS
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The composition and origin of sulfides in peridotitic xenoliths from Ruddon’s Point (Fife, Scotland) 
Hubert Mazurek, Magdalena Matusiak-Małek, Hannah S.R. Hughes, and Brian J.G. Upton

Permian mafic volcanic rocks occurring in southern terrains of Scotland (United Kingdom) are rich in peridotitic xenoliths providing insight into the composition of the Subcontinental Lithospheric Mantle (SCLM) beneath this area. Peridotites from the Ruddon’s Point (Fife) xenolith suite form four textural groups: (1) protogranular and (2) porphyroclastic lherzolites, (3) equigranular wehrlites and (4) lherzolites transitional between protogranular and equigranular peridotites. The SCLM beneath southern Scotland was affected by reaction with an alkaline melt resulting in clinopyroxene crystallization (wehrlitization) and decrease of Fo in olivine from primary (protogranular and porphyroclastic) lherzolites (Fo88.5-90.0) through transitional to equigranular (Fo80.0-85.0) peridotites (Matusiak-Małek et al., 2022).

The sulfides occurring in the peridotites form oval, elongated or irregular grains enclosed in pyroxenes and olivine, or interstitial between these phases. The abundance of sulfides  increases from the transitional lherzolites (mean = 0.009 vol.‰), through equigranular and porphyroclastic peridotites (0.026 and 0.029 vol.‰, respectively) to protogranular lherzolites (0.050 vol.‰). Sulfide minerals present in all textural groups are pentlandite (Pn) and chalcopyrite (Ccp). There is generally an absence of pyrrhotite (Po), but protogranular and “transitional” lherzolites contain minor amounts. Porphyroclastic lherzolites occasionally contain millerite (Mlr) and covellite (Cv). The sulfides from the equigranular and protogranular peridotites are more enriched in Cu-, and depleted in Ni-phases (Po0Pn71Ccp29 and Po4Pn68Ccp27, respectively) in comparison to sulfides from the porphyroclastic and transitional peridotites (Po0Pn80Ccp20 and Po6Pn83Ccp12, respectively). The Cu/(Cu+Fe) is homogenous in sulfides of all the textural types, whereas Ni/(Ni+Fe) in pentlandite is homogenous only in transitional and equigranular peridotites (0.64–0.65 and 0.55–0.59, respectively) in contrast to porphyroclastic and protogranular ones (0.54–0.68 and 0.52–0.64, respectively). The only significant difference in trace element composition of sulfides appears in the concentrations of Co and Zn which  are  4894 ppm and 2214 ppm, respectively, in the protogranular peridotites, compared to 30090 ppm and 1391 ppm, respectively, in the transitional peridotites.

The more primitive protogranular and porphyroclastic lherzolites  are characterized by the highest sulfide abundances in comparison to the sulfides from melt-metasomatized equigranular wehrlites, with no significant differences  in sulfide mineral and chemical (major and trace elements) composition between groups. Thus, activity of the alkaline silicate melts responsible for wehrlitization of the primary lherzolites seems not to influence the sulfide enrichment in the SCLM beneath S Scotland. The presence of Cv and Mlr in lherzolites suggests alteration by hydrothermal, post-volcanic activity, affecting the xenoliths after the exhumation to the surface by basaltic lavas.

Matusiak-Małek, M., Kukuła, A., Matczuk, P., Puziewicz, J., Upton, B.J.G., Ntaflos, T., Aulbach, S., Grégoire, M., Hughes H.S.R. (2022). Evolution of upper mantle and lower crust beneath Southern Uplands and Midland Valley Terranes (S Scotland) as recorded by peridotitic and pyroxenitic xenoliths in alkaline mafic lavas. 4th EMAW TOULOUSE 2021 Book of Abstracts.

How to cite: Mazurek, H., Matusiak-Małek, M., Hughes, H. S. R., and Upton, B. J. G.: The composition and origin of sulfides in peridotitic xenoliths from Ruddon’s Point (Fife, Scotland), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4995, https://doi.org/10.5194/egusphere-egu23-4995, 2023.

X2.146
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EGU23-10026
Geochemical characteristics of mafic rocks from the Edessa ophiolite (North Greece): Implications for their petrogenesis 
Aikaterini Rogkala, Petros Petrounias, Petros Koutsovitis, Panagiota P. Giannakopoulou, Panagiotis Pomonis, and Konstantin Hatzipanagiotou

The Edessa ophiolite complex represents remnants of oceanic lithosphere which was thrust out of one or more ocean basins during Upper Jurassic to Lower Cretaceous time. Petrographic, geological and geochemical evidences indicate that this ophiolite complex consists of both mantle and crustal suites. It includes lherzolites, serpentinised harzburgites with high degree of serpentinisation, diorites, gabbros, diabase dolerites and basalts. We present here new data on mineral compositions and geochemistry in mafic rocks. The basalt displays N-MORB composition, having enhanced TiO2 (1.9-2.4 wt.%) and flat REE patterns, whereas the gabbros show E-MORB affinities, having moderate to high Ti content (TiO2 = 1.1-1.2 wt.%) with strong LREE-HREE fractionations. Such geochemical enrichment from N-MORB to E-MORB composition indicates mixing of melts derived from a depleted mantle and fertile mantle source at the spreading centre. On the other hand, diorites and partially diabase dolerites display SSZ-type composition with low Ti content (TiO2 = 0.1-0.7 wt.%) and depleted LREE pattern with respect to HREE. They also display high Ba/Zr, Ba/Nb and Ba/Th ratios relative to primitive mantle, which strongly represents the melt composition generated by partial melting of depleted lithospheric mantle wedge influenced by hydrous fluids derived from subducting oceanic lithosphere in a forearc setting. Based on these geochemical evidence, we suggest that mid ocean ridge (MOR) type mafic rocks (basalts and gabbros) from the Edessa ophiolite represent the section of older oceanic crust which was generated during the opening of the Axios Ocean. Conversely, the diorites and diabase dolerites represent the younger oceanic crust which was formed at the forearc region by partial melting of the depleted mantle wedge modified by hydrous fluids released from the subducting oceanic slab.

How to cite: Rogkala, A., Petrounias, P., Koutsovitis, P., Giannakopoulou, P. P., Pomonis, P., and Hatzipanagiotou, K.: Geochemical characteristics of mafic rocks from the Edessa ophiolite (North Greece): Implications for their petrogenesis, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10026, https://doi.org/10.5194/egusphere-egu23-10026, 2023.

X2.147
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EGU23-2760
Geology, geochemical typification and petrogenic model of formation of Middle Paleozoic metabasites of the Khrami crystalline massif (Georgia) 
David Shengelia, Tamara Tsutsunava, Giorgi Beridze, and Irakli Javakhishvili

The Khrami crystalline massif is located in the northern part of the Lesser Caucasus, in the Black Sea - Transcaucasian terrane. The massif outcrops Middle Paleozoic metabasites, which crosscut the Precambrian gneiss-migmatite complex and, in turn, are cut by Late Variscan granites. These metabasites have not experienced Precambrian prograde HT/LP (720-770°C, P<1.5 kbar) regional metamorphism, although retrograde LT/LP (T≈430-5100C, P≈0.6-1 kbar) metamorphism, associated with the Sudetian orogeny has been recorded. According to the presented geological data, the age of metabasites is within the Cambrian and Upper Paleozoic. Considering the analogy between the metabasites spread in the Dzirula crystalline massif, which is exposed in the same terrane, and the metabasites of the Khrami massif, the age of the latter is most likely Middle Paleozoic (Shengelia et al., 2022). The metabasites of the Khrami massif are represented by veins (1-60 m) and stock-shaped bodies (80-800 m) of fine-grained ophitic gabbro, gabbro-diabases and diabases of various thicknesses. They are cut by numerous granite veins and penetrated by thin quartz-feldspar injections. The paragenesis of the high-temperature magmatic stage - Cpx+Pl78-84 has been preserved in metabasites in some places; Further, under the conditions of greenschist facies, the paragenesis Ab+Act(Tr)+Chl+Ep±Qz develops. According to the petrogenic diagrams Na2O+K2O – SiO2, the metabasites of the Khrami massif belong to the formations of the subalkaline series (Irvine and Baragar, 1971), correspond to basalts and andesite-basalts (Le bas et al., 1986) and basalts and picrites (Cox et al., 1979). This is confirmed by the data of diagrams Zr/Ti-Nb/Y (Pearce, 1996) and Zr/TiO2 – Yb/Y (Winchester, Floyd, 1977). According to the Na2O+K2O–FeO*-MgO (Irvine and Baragar, 1971), a great part of the metabasites is of tholeiitic composition, and only a small part is of calc-alkaline composition. On the diagram Fe*-SiO2 (Frost et al., 2008) the dots denoting metabasites are completely disposed in the magnesian field. According to the TiO2 - Zr/(P2O5*104) diagram (Winchester, Floyd, 1976), the metabasites correspond to tholeiite basalts. According to the diagram V-Ti/1000 (Shervias, 1982), the metabasites belong to the MORB genetic formation, and according to the diagram Cr-Y (Pearce, 1982), they belong mainly to the VAB, and also to the MORB. According to the ratio MnO-TiO2/10-P2O5 (Mullen, 1983), dots of mafic rocks are located in the island-arc tholeiitic field. Thus, the Middle Paleozoic metabasites of the Khrami crystalline massif are represented by shallow subvolcanic magmatites predominantly of andesite-basalt and tholeiite-basalt groups of the tholeiitic series. They correspond to the MORB and VAB genetic groups.

How to cite: Shengelia, D., Tsutsunava, T., Beridze, G., and Javakhishvili, I.: Geology, geochemical typification and petrogenic model of formation of Middle Paleozoic metabasites of the Khrami crystalline massif (Georgia), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2760, https://doi.org/10.5194/egusphere-egu23-2760, 2023.

X2.148
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EGU23-4569
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ECS
The origin of hydrous amphibole in the subcontinental lithospheric mantle beneath the Southern Alps of New Zealand 
Nadine Cooper, James Scott, Marco Brenna, Marshall Palmer, Malcolm Reid, Claudine Stirling, and Petrus le Roux

Peridotite xenoliths provide valuable insight into lithospheric mantle conditions, composition, and evolution. The origin of amphibole in the lithospheric mantle and whether amphibole melts to produce alkaline intraplate magmas is a highly debated topic. Large areas of the lithospheric mantle forming Earth’s youngest continent, Zealandia, have chemical compositions comparable to Archean mantle lithosphere but Re-Os isotope and bulk rock data indicate that lithosphere stabilisation occurred in the Mesozoic. Some areas of this refractory lithospheric mantle have been metasomatized, with one of the clearest occurrences being MARID-like veins in xenoliths in alkaline intraplate magmas in the Southern Alps of New Zealand. These xenoliths contain abundant veinlets composed of amphibole, phlogopite, clinopyroxene and apatite in rocks that have average olivine compositions exceeding Mg# 92 and spinel Cr# 70. The latter indicates that these peridotites have undergone >25% partial melting prior to metasomatism.

Using a combination of quantitative scanning electron beam methods, trace element and in-situ laser ablation inductively coupled mass spectrometry (LA-ICP-MS) analysis, and conventional 87Sr/86Sr isotope analysis by solution, we seek to establish the origin of hydrous phases in this mantle lithosphere. The benefit of inspecting formerly highly depleted peridotites is that the chemistry of the metasomatic agent, which is typically enriched in incompatible elements, is less diluted than in the cases where melts infiltrate fertile lithosphere. Although minor Fe-diffusion has occurred within the studied host rock, the bulk compositions of the veins are picro-basaltic. The mica separates, measured by solution chemistry, are today more radiogenic than the in-situ diopside and amphibole analyses, however, we find that the age-corrected ~25 Ma, 87Sr/86Sr initials fall in a tight cluster of very depleted mantle-like ratios from 0.7027 to 0.7056. Although the fluids appear to have sub-alkaline bulk compositions, the amphibole trace elements are enriched in HFSE and lack depleted Nb components.

The data suggests that these basaltic veins are not arc-related and do not derive from melting of subducted sediment, but also have no direct genetic link to the host alkaline melts. If this latter interpretation is correct, then the injection of hydrous veins was not part of a continuous process that resulted in alkaline magmatism, although they may have been subsequently melted to give rise to alkaline magmas with depleted mantle-like isotopic characters. 

How to cite: Cooper, N., Scott, J., Brenna, M., Palmer, M., Reid, M., Stirling, C., and le Roux, P.: The origin of hydrous amphibole in the subcontinental lithospheric mantle beneath the Southern Alps of New Zealand, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4569, https://doi.org/10.5194/egusphere-egu23-4569, 2023.

X2.149
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EGU23-4686
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ECS
Evolution of the African Mantle Domain and its enriched signal: perspective from pre-200 Ma ophiolites 
Piero Azevedo Berquo de Sampaio, Zheng-Xiang Li, Luc Serge Doucet, and Hamed Gamaleldien

Earth’s mantle is highly heterogeneous, with mantle-derived rocks sampling depleted and enriched domains both in intraplate settings and along spreading ridges. The most notorious isotopic anomaly is the DUPAL anomaly, where an overall strong recycled isotopic signature occurs. Studies on Tethyan and Paleo-Tethyan ophiolites have shown the persistence of “DUPAL signature” in those oceans, which paleogeographic reconstructions place on approximately the same position as the present-day Indian Ocean and thus argue for a long-lived “DUPAL signature” in the mantle. The origin of the DUPAL anomaly is controversial, with many studies pointing to it being a primordial feature. More recently, however, it has been shown that plume products in the African Mantle Domain (AMD), of which the DUPAL anomaly region is a part of, generally bear a more enriched signal than plume-related rocks in the Pacific Mantle Domain. This observation has been hypothesized to be related to the formation of the Pangea supercontinent above the present-day AMD, and therefore offering a geodynamic scenario capable of explaining the origin of the enriched isotopic signature of the AMD. However, present-day ocean crust record is limited in time, extending to 200 Ma at maximum, younger than the formation of Pangea at ca. 320 Ma. To investigate the oceanic record of mantle enrichment further back in time and test the influence of supercontinent cycle on the composition of the AMD, it is necessary to utilise preserved oceanic terranes in orogenic belts. In this study we compiled isotopic data from preserved oceanic terranes related both to the formation of the AMD, starting from the assembly of Gondwana till the duration of Pangea, including that of the Mozambique, Adamastor, Goias-Pharusian, Iapetus, Rheic, Qilian-Shangdan, Paleo-Tethys, Meso-Tethys and Neo-Tethys paleo-oceans. Neodymium isotopic data is the most widely available for these ophiolites. The Nd isotopic data indicates a progressively more depleted signal before Gondwana formation until it reaches a maximum and stays relatively stable until shortly after Pangea break-up, where noticeable decrease in depletion occurs. Lead isotopic data is less readily available, existing data nevertheless allow to observe an increase in Th/U ratio during Gondwana formation. Taken together, these observations indicate an increase in recycled continental components in the mantle source of the AMD ophiolites. We envisage this to be evidence for mantle enrichment during the formation of Gondwana and Pangea within the AMD. New isotopic analyses are still needed to paint a clearer picture of the interplay between the supercontinent cycle and mantle geochemistry.

How to cite: Azevedo Berquo de Sampaio, P., Li, Z.-X., Doucet, L. S., and Gamaleldien, H.: Evolution of the African Mantle Domain and its enriched signal: perspective from pre-200 Ma ophiolites, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4686, https://doi.org/10.5194/egusphere-egu23-4686, 2023.

X2.150
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EGU23-10058
A monazite- and REE-rich apatite-bearing mantle xenolith from Pleiku, central Vietnam 
Christoph Hauzenberger, Jürgen Konzett, Bastian Joachim-Mrosko, and Hoang Nguyen

Primitive mantle rocks usually contain rare earth elements (REE) in very low concentrations. Here we report an occurrence of monazite associated with REE-rich apatites in a carbonate-bearing wehrlite xenolith from Pleiku, central Vietnam. The sampled xenolith displays an equigranular matrix of rounded olivine grains. Texturally primary orthopyroxene, clinopyroxene and spinel are notably absent. Scattered within the olivine matrix two types of domains are present: domain-I contains numerous blocky clinopyroxene grains within a matrix of quenched silicate melt and is associated with a second generation of olivine, small euhedral spinel and rare grains of carbonates. Both apatite and monazite may be present. Domain-II typically contains abundant irregularly shaped patches of carbonate associated with quenched silicate melt, secondary olivine, spinel, and clinopyroxene. No phosphate phases are observed within type-II domains. Monazite occurs in different generations: monazite I is found as very small rounded to elongate grains included in primary olivine, partly crosscut by fine melt veinlets, monazite II as large grains up to 300 x 200 µm in size with embayed grain boundaries and monazite III as very small euhedral and needle-like crystals in silicate melt pools. For apatite two textural types occur: apatite I forms lath-shaped to rounded crystals up to 200 x 50 µm in size, apatite II is present within silicate melt pools of type-I domains where it forms euhedral needle-like to equant grains. Some of the apatite II crystals may have cores of monazite III. Monazites show compositional variation mainly with respect to ∑REE2O3 (63-69 wt%) and ThO2 (1.1-5.3 wt%) and only minor variations in P2O5 (29-32 wt%) SiO2 (<0.05-0.4 wt%) and CaO (0.2-0.4 wt%) Apatites are characterized by strongly variable and high REE2O3 and SiO2 contents (4-27 wt% ∑REE2O3,0.6-6.8 wt% SiO2) as well as with significant Na2O (0.3-1.5 wt%), FeO (0.1-1.8 wt%), MgO (0.2-0.6 wt%) and SrO (0.2-0.9 wt%) contents. F and Cl contents are in the range 1.9-3.0 wt% and 0.2-0.8 wt%, respectively. Based on textural evidence and chemical composition of the metasomatized mineral phases an initial stage of metasomatism is proposed which was triggered by a P-REE-CO2-rich agent with low aH2O resulting in the co-precipitation of carbonates as patches and along micro-veins and of phosphates in a peridotite assemblage. A subsequent second stage is characterized by pervasive infiltration of an alkali-rich basaltic melt into the carbonate + phosphate-bearing assemblage. The presence of monazite prior to silicate melt infiltration is indicated by narrow melt veins crosscutting monazite I grains. Reactions of the silicate melt with the pre-existing phases led to the formation of domains-I and -II and changed the composition of the infiltrating melt towards phonolitic-trachytic composition. The second stage led to partial breakdown and recrystallization of monazite and apatite.

How to cite: Hauzenberger, C., Konzett, J., Joachim-Mrosko, B., and Nguyen, H.: A monazite- and REE-rich apatite-bearing mantle xenolith from Pleiku, central Vietnam, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10058, https://doi.org/10.5194/egusphere-egu23-10058, 2023.