Petrographic studies of the multi-textured layered gabbro series of the lower crustal section recovered from U1415P were conducted to determine the mechanism of orthopyroxene formation in lower crustal gabbros drilled in the Hess Deep rift near the East Pacific Rise. In a particular horizon of the series (U1415P 6R-1 to 6R-2), homogeneous medium-grained troctolite and fine-grained spinel-bearing heterogeneous olivine gabbro occur in proximity.

The samples from the Hole1415P 6R are divided into homogeneous troctolite parts with medium-grained equigranular textures and spinel-bearing heterogeneous olivine gabbro parts with poikilitic textures (irregularly shaped fine-grained plagioclase characrysts enclosed in Ol-oikocrysts and Cpx-oikocrysts). The wide variation in TiO₂ content against nearly constant Mg# and Cr₂O₃ of clinopyroxene in these rocks is quite different from the compositional trend of clinopyroxene in layered mafic intrusions explained by the fractional crystallization of magma.

Recently, Yang et al. (2019) conducted a reaction experiment between MORB melts and troctolite and reported microtextures and mineral chemical compositions of the experimental products. In the experiment, fine-grained plagioclase was found to be poikilitically enclosed in olivine and clinopyroxene in the melt infiltration zone within troctolite near the boundary between troctolite and melt. The poikilitic textures and the oikocristic clinopyroxene compositional variations in the Hess Deep spinel-bearing olivine gabbro are very similar to those in the reaction experiment by Yang et al. (2019). These indicate that the heterogeneous olivine gabbro of the Hess Deep was formed by a melt-rock (or crystal mush) reaction.

              In addition, the multiphase solid inclusions of Cpx-Pl assemblage with basaltic magma composition and Opx-bearing multiphase solid inclusions with composition of high-Mg basaltic-andesite to andesite are enclosed in Cr-spinel from the spinel-bearing heterogeneous olivine gabbro. The presence of Opx-bearing multiphase solid inclusions indicate that the injection of SiO2-rich melt different in composition from the troctolite-forming magma has occurred. The SiO₂-rich melt reacted with the troctolite to form spinel-bearing heterogeneous olivine gabbro. Our results may suggest that the sheeted sills model, in which magma of various compositions intrudes into the crust, is a more appropriate mechanism for the formation of the lower oceanic crust.

How to cite: Hoshide, T. and Kondo, K.: Formation of spinel-bearing layered gabbros by the reaction between the basaltic crystal mush and high-Mg andesitic melts in the lower oceanic crust, East Pacific Rise (IODP Exp. 345 U1415P) , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4328, https://doi.org/10.5194/egusphere-egu24-4328, 2024.

In order to understand the cause of a caldera-forming eruption, it is crucial to study the pre-eruptive processes, from build-up to the collapse. In recent years, the cyclicity of large-scale magmatic systems and their corresponding caldera collapses has been described through various geochemical and petrological studies. Numerical modelling studies have investigated the collapse stage using a pressurised cavity or gas-filled chamber, studying the evolution of the surrounding lithosphere by inflating and deflating the chamber. Another modelling approach involves investigating the displacement effects of moving a piston-shaped object.

In this study, we use a multi-physical numerical modelling approach to investigate different aspects of the caldera cycle, including the accumulation of magma, the evolution of stress, the strain rate and the dynamics within the forming magmatic system. To achieve this, we couple an open-source thermal evolution magma intrusion code with a Stokes solver. The coupling allows for the evaluation of thermal and volumetric changes in the magmatic system, taking into account the complex interaction between magma dynamics and the surrounding host rock. The use of nonlinear visco-elasto-plastic rheology enables the assessment of fracturing and thermal effects on the lithosphere, which create downward propagating weak zones that are later utilised as eruption channels. These faults not only provide pathways but are also associated with the caldera collapse stage of the eruption cycle, which leads to geomorphological transformations of the surface.

Our approach is also applicable for assessing the evolution of current magmatic systems taking into account their topography. The model is applied to the well-studied area of the Toba caldera in Sumatra. The magma is injected into areas where seismic inversion studies have identified a melt phase. This allows for an assessment of the system's evolution and provides insights into an active magmatic system. Additionally, it serves as a reference for correlating and referencing our model with observational data.

How to cite: Aellig, P., de Montserrat, A., and Kaus, B.: From build-up to caldera collapse: High resolution modelling of large scale magmatic systems, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5290, https://doi.org/10.5194/egusphere-egu24-5290, 2024.

Geophysical, geochemical, and petrological studies indicate that magma storage and chemical differentiation can occur at various depths in the continental crust. Examination of exposed ancient magmatic systems reveal a continuum from a refractory lower crust to a silica-rich upper crust, prompting a debate on the mechanisms governing magma storage and differentiation in vertically extensive magmatic systems.

Conceptual models for magma storage and chemical differentiation within the crust range from (i) a low crystallinity magma body, where differentiation occurs primarily by fractional crystallisation and partial melting of the crust, to (ii) a trans-crustal high crystallinity ‘mush’ reservoir consisting of a porous crystal matrix with melt in the pore space. Chemical differentiation in these mush reservoirs is driven by the compaction of the crystal matrix, buoyant upward reactive flow of melt, and partial melting of the surrounding crust.

We use a numerical model to investigate magma storage and chemical differentiation in the continental crust. The model assumes a magmatic system sustained by the intrusion of mantle-derived basalt into the lower crust.  We find that intrusion of basalt creates a high crystallinity reservoir in the lower crust. Reactive flow and compaction cause melt to accumulate at the top of the reservoir, creating a layer of low crystallinity, chemically differentiated magma.  Buoyancy overpressure causes this magma to  evacuate via dikes and we assume the magma intrudes the mid-crust to form a second high crystallinity mush reservoir. Reactive flow and compaction once again lead to the accumulation of low-crystallinity, evolved magma at the top of the reservoir that can evacuate and intrude the upper crust, driving volcanic eruptions or forming shallow plutons.

The compositional evolution of magma as it ascends through the system is influenced by the flux of the parental basalt and the fertility of the crust. A higher basalt flux leads to warmer reservoirs that evacuate less evolved magma. Reservoirs in infertile crust that cannot melt are formed only of hot, parental magma, and also evacuate less evolved magma. Partial melting of fertile crust allows melt to percolate upwards and accumulate in cooler crust, leading to the evacuation of evolved (silicic) magma.

In most of our simulation cases, the reservoirs remain as discrete bodies in the lower- and mid-crust, with magma transfer occurring via dikes; a trans-crustal reservoir does not form. The lower-crust reservoir evacuates mafic to intermediate magma, whilst the cooler mid-crust reservoir primarily evacuates evolved, silicic magma, consistent with vertical compositional trends in exposed, ancient magmatic systems. Both reservoirs comprise primarily low-melt fraction mush, consistent with geophysical imaging of contemporary systems.  Layers of accumulated low-crystallinity magma are transient and likely too thin to resolve in geophysical data. The predicted volume, composition, and frequency of episodic magma intrusions into the upper crust are consistent with observed data from large volcanic eruptions. Our results suggest that reactive flow in multiple mush reservoirs controls magma storage and differentiation.

How to cite: Booth, C., Jackson, M., Sparks, S., and Rust, A.: Magma Storage, Differentiation and Transfer in Vertically Extensive Magmatic Systems, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11344, https://doi.org/10.5194/egusphere-egu24-11344, 2024.

The maim objective of this work is to investigate the structure of the superficial portion of the plumbing system at Mt. Etna in terms of interconnection among the conduits and internal variations linked to eruptive activity. For this purpose, the lava fountains that occurred in the years from 2011 to 2015 were taken into consideration, for a total of 51 events, and the infrasonic signals recorded by two stations were analysed. We extracted the infrasonic events, and analysed the evolution in time of the spectral content by using normalized and non-normalized pseudospectrograms, peak and mean frequency values. In addition, the sources of the events were located. We noted how, although the eruptions took place at South-East and Voragine craters, the infrasonic events recorded before and after the lava fountains are mostly generated by the North-East Crater. Most of the energy of these events is comprised in the frequency range 0.1 – 2 Hz. Furthermore, in most of the lava fountain episodes, we observed a decrease in the frequency peaks of the infrasonic events after the eruptions. To interpret the variations of the plumbing system responsible for these spectral changes, as well as the interconnection among the conduits feeding the main craters, we model the infrasonic events from the North-East Crater as an acoustic resonance of the crater and conduit, whose length changes with time as magma ascends or descends in the conduit.

How to cite: Amato, G., Minio, V., Sciotto, M., Spina, L., Watson, L. M., and Cannata, A.: Study of the variations of the feeding system at Mt. Etna during the paroxysmal activities by using infrasonic data., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11411, https://doi.org/10.5194/egusphere-egu24-11411, 2024.

Conical Seamount is an active submarine volcano of the Tabar-Lihir-Tanga-Feni island chain (TLTF) in north-eastern Papua New Guinea. This island chain is located within the New Ireland Basin and the related alkaline to shoshonitic magmas are ascending through a thick sedimentary sequence. The TLTF hosts several Cu-Au mineralized volcanic centers. Conical Seamount is a rare example of a submarine epithermal-style mineralization and is considered to be a juvenile analogue of the Ladolam world-class gold deposit located on the nearby island of Lihir.

Recent research assessed important crustal magmatic processes as precursors for the mineralization at Conical Seamount. More specifically, the presence of a degassing crustal magma chamber has been found to be critical for the metal concentration and transfer into the epithermal system. This may explain why other seamounts in the TLTF island chain remain barren (unmineralized).

Here we present new volatile (H₂O, CO₂, F, Cl, S) as well as major and trace element data of clinopyroxene-hosted melt inclusions. These data along with fluid inclusion data allow us to further constrain the volcanic plumbing system, more specifically the pressure (i.e., depth) of the crustal magma chamber, the degassing stage and sulfide saturation processes. Chalcophile elements and Au in particular are scavenged within sulfides concomitant with the magmatic fluid exsolution, leading to ideal conditions for the transfer of metals into the ore-forming system.

How to cite: Gautreau, L.-M., Hansteen, T., Portnyagin, M., and Brandl, P.: The importance of magmatic degassing at a mineralized, submarine volcano: The case of Conical Seamount, Papua New Guinea, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13201, https://doi.org/10.5194/egusphere-egu24-13201, 2024.

On the Korean Peninsula, located in the eastern region of East Asia, the Gyeongsang Basin, a representative sedimentary basin formed during the Cretaceous Period, occupies about a fourth of South Korea. In the Gyeongsang Basin, the Kusandong Tuff (ca. 103 Ma; Kim et al., 2013), a representative marker bed, is distributed across approximately 200 km from north to south. About 2.5 m-thick tuff layer also develops in Sinsu and Changseon islands, located in the southern part of the basin. There is controversy as to whether it is the southernmost extension of the Kusandong Tuff or a separate tuff body. To resolve this, a total of 4 samples were collected from two islands, and LA-MC-ICP-MS zircon U-Pb dating was performed. As a result, all samples were slightly contaminated with common lead, and lower intercept ages of ca. 99 Ma were calculated, indicating a systematically younger than the reported ages of Kusandong Tuff (ca. 103 Ma). And zircons used in age calculations are largely divided into two domains accoring to the significant differences in brightness in cathodoluminescence (CL) images. Based on the combination of these domains, zircons show: 1) dark overall, 2) dark in the core with bright rims (known as reverse zoning), and 3) only bright oscillatory zoning with/without some inherited cores. In general, dark domains have a uranium content of ca. 3000-7000 ppm, while bright ones range from 34-541 ppm. And in the CL image, some boundary of the dark domains in the cores had melted and infiltrated by bright ones. To understand the evolutionary history of the magma that formed these zircons, trace and rare earth elements were analyzed using LA-ICP-MS. The results indicate that the dark domains of zircons were formed in relatively highly evolved and cooler magma, while the bright domains of zircons were formed in less evolved and hotter magma. To summarize the magma evolution model, crystallization of dark domains occurred first in relatively highly evolved magma, and then domains showing bright and distinct oscillatory zoning were formed with the injection of less evolved magma from deeper sources. At the same time, bright domains grew on the rims of existing dark zircons due to the injected magma. It is thought that the new magma injected into the existing magma chamber caused an increase in internal pressure, which ultimately led to the volcanic eruption. Considering the dating results, it is believed that all of these processes occurred over a short period of time, roughly limited to about 99 Ma on the geological time scale.

How to cite: Chae, Y.-U., Jeong, Y.-J., Kim, J.-S., Ha, S., Joo, Y. J., Shin, S., and Lim, H. S.: Eruption age and magma evolution history of the Sinsudo Tuff in the Cretaceous Gyeongsang Basin, Korea, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13454, https://doi.org/10.5194/egusphere-egu24-13454, 2024.

The North Volcanic Zone of the Andes is the result of an overall uniform subduction of the Nazca Plate beneath the South American Plate in Ecuador and Colombia; however, age, composition, and thickness of the continental crust and the distance between the trench and arc, among other components of this subduction system, vary significantly along this segment of the Andes (Stern, 2004). Those changes are most likely responsible for differences in the geochemical characteristics of volcanic products in different parts of the Colombian arc as discussed in Monsalve (2020). Although several works related to the isotopic geochemistry of the volcanic products have been carried out in Ecuador (Bryan et al., 2006; Chiaradia et al., 2009, references therein), there are few records of the same type of data for Colombia and those available focus on the SW part of the arc (Marín-Cerón, 2007). This study seeks to fill the gap and use this new data to elucidate processes of magma generation and differentiation currently occurring under the northern Andes. Whole rock major elements, trace elements, and ¹⁷⁶Hf/¹⁷⁷Hf analyses from main volcanic centers along the Colombian arc are used to track lithospheric and crustal processes of mixing, assimilation, and fractional crystallization as well as the main source materials and contributions in magma generation in the subduction zone. From a broader view, this new data helps to discuss regional comparisons of the geochemical expressions in the Andean arcs caused by different tectono-magmatic processes.

Bryant, J.A., Yogodzinski, G.M., Hall, M.L., Lewicki, J.L. & Bailey, D.G. (2006). Geochemical constraints on the origin of volcanic rocks from the Andean Northern Volcanic Zone, Ecuador. Journal of Petrology, 47(6): 1147–1175.

Chiaradia, M., Müntener, O., Beate, B., & Fontignie, D. (2009). Adakite-like volcanism of Ecuador: lower crust magmatic evolution and recycling. Contributions to Mineralogy and Petrology, 158, 563-588.

Marín–Cerón, M.I. (2007). Major, trace element and multi–isotopic systematics of SW Colombian volcanic arc, northern Andes: Implication for the stability of carbonate–rich sediment at subduction zone and the genesis of andesite magma. Doctoral thesis, Okayama University, 140 p. Okayama, Japan.

Monsalve–Bustamante, M.L. (2020). The volcanic front in Colombia: Segmentation and recent and historical activity. In: Gómez, J. & Pinilla–Pachon, A.O. (editors), The Geology of Colombia, 97–159.

Stern, C.R. (2004). Active Andean volcanism: its geologic and tectonic setting. Revista geológica de Chile, 31(2), 161-206.

How to cite: Marroquín-Gómez, M. P., Ibañez-Mejía, M., and Johnson, A. C.: Geochemistry of the Northern Andean Volcanic Zone, Colombia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14492, https://doi.org/10.5194/egusphere-egu24-14492, 2024.

The modern view of magmatic systems includes transport and storage of melt at depths within the solid crust. Parameters that control the depths and duration of magma storage include the rheology (especially the depth of the brittle-ductile transition) and chemistry of the melt and solid, the crustal heat budget, and the tectonic setting. Understanding the large spatio-temporal variation in the magmatic output of volcanic arcs, therefore, requires consideration of solid deformation, melt transport, and chemical differentiation in transcrustal magmatic systems.

We present preliminary reactive transport models of transcrustal magmatic systems in the ductile limit. The model couples deformation of a compressible solid and Darcy-flow of melt through the solid matrix to phase equilibria calculations. The thermomechanical solver is self-developed in the Julia language and employs a matrix-free pseudo transient solution technique (e.g., Raess et al. 2022). Julia solves the two-language problem and allows for rapid transition from the development stage to massively parallelized production simulations. The thermomechanical two-phase flow equations are numerically discretized on 1D and 2D cartesian finite difference grids. Two different approaches of thermodynamic-thermomechanical coupling are implemented: (i) On-the-fly calculation of stable mineral phases using the Gibbs energy minimization software MAGEMin (Riel et al. 2022) and (ii) interpolation from a precompiled phase diagram.

MAGEMin is parallelized and shipped with a Julia wrapper. These features allow near seamless integration of thermodynamic calculations into the newly-developed geodynamic algorithm. The following workflow is applied: (1) Stable mineral phases are calculated at each numerical grid point as a function of local pressure and temperature values using MAGEMin. A starting bulk rock composition characteristic to arc magmas is used for the first time step. (2) The densities as well as the predicted major-oxide fractions of the solid and melt are used in the two-phase flow algorithm to solve for solid deformation, porosity evolution, and major-oxide transport. (3) The local major-oxide fractions predicted by the thermomechanical solver are used as new starting compositions in MAGEMin for the next time step. 

For the second approach, we compiled data from published fractional crystallization experiments at relevant pressure and temperature conditions. The data set contains the major-oxide fractions as well as calculated melt and solid densities. During the thermomechanical solution procedure, the data is interpolated from this phase diagram according to local pressure and temperature conditions at each grid point. A detailed comparison of the two approaches and potential implications for natural systems are presented.

References:

Räss, L., Utkin, I., Duretz, T., Omlin, S., & Podladchikov, Y. Y. (2022). Assessing the robustness and scalability of the accelerated pseudo-transient method. Geoscientific Model Development, 15(14), 5757-5786.

Riel, N., Kaus, B. J., Green, E. C. R., & Berlie, N. (2022). MAGEMin, an efficient Gibbs energy minimizer: application to igneous systems. Geochemistry, Geophysics, Geosystems, 23(7), e2022GC010427.

How to cite: Candioti, L. G., Nathwani, C. L., and Chelle-Michou, C.: Towards fully-coupled thermodynamic-thermomechanical two-phase flow models of transcrustal magmatic systems, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16936, https://doi.org/10.5194/egusphere-egu24-16936, 2024.

Subduction zones are key regions of mass exchange between the Earth’s crust and mantle, and magmas in the sub-arc mantle form as a result of the release of volatiles from the subducting slab, i.e. fluid-flux melting. Introducing unique geochemical tracers (e.g., Large Ion Lithophile Elements) into the depleted mantle wedge allows tracing of the flow of material underneath the island arcs. Back arc spreading centres form as a result of slab-rollback, and here melts form due to decompression melting similar to those forming at mid-ocean ridges. Back arc systems situated angular to their adjacent island arc encompass a range of slab depths and provide a unique means to assess the compositional changes as a function of distance to the active arc and above the subducting slab. The Valu Fa Ridge (VFR), Eastern Lau (ELSC) and Central Lau (CLSC) spreading centres are situated at an increasing distance from the active Tonga arc from south to north. Here, we present new major, trace and volatile element data along with radiogenic isotope and U-Th-Ra disequilibria along the VFR and ELSC and across the VFR. A systematic change of, e.g., Ba/Nb, Nb/La, H₂O contents and Pb isotopes with increasing distance between the back arc and the Tonga arc could be interpreted to reflect the slab-related metamorphic dehydration reactions. However, we do not observe a gradual change in geochemical compositions at a distance <100 km between the arc and the backarc, suggesting that the decompression and fluid-fluxed melting regimes overlap. At distances of >100 km between the arc and back arc, the occurrence of (²³⁰Th/²³⁸U) excess suggests that melting is due to decompression and that the systematic decrease in subduction influence observed with increasing distance is likely the result of melting of hydrous, ancient slab remnants during rollback. We conclude that the melting regimes between the ELSC and Tonga island arc separate at ~100 km total distance, as evident from the stepwise change in trace element and isotope geochemistry. The decrease in subduction-related signatures along the VFR and ELSC results from an overlap of the melting regimes and melt mixing between the arc and back arc in which the melting of the depleted mantle underneath the back arc becomes more prominent with increasing distance.

How to cite: Beier, C., Turner, S., Brandl, P. A., and Haase, K. M.: Fluid-flux versus decompression melting – the Tonga arc – Lau back arc system, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3818, https://doi.org/10.5194/egusphere-egu24-3818, 2024.

South Shetland Islands (western Antarctica) host widespread magmatism through the Meso-Cenozoic as a result of the subduction of the Phoenix plate along the South Shetland trench. With the logistical support of the Czech Antarctic Research Center and in-kind assistance from TÜBİTAK MAM Polar Research Institute, geological fieldwork was conducted on the Fildes Peninsula in order to understand the magma evolution beneath western Antarctica. This study presents preliminary results from field, petrographic and geochemical studies obtained from the volcanic and intrusive rocks in Fildes Peninsula- King George Island.

Fildes Peninsula represents the southwestern parts of King George Island which is located at the northeastern tip of the South Shetland Islands. The dominant lithologies in the study area are Paleocene- Eocene volcanic and intrusive rocks, with a minor presence of sedimentary rocks. The volcanic rocks cropping out on Fildes Peninsula are referred to as the Jasper Hill, Agate Beach, Block Hill and Long Hill formations. They mostly display similar compositions changing from basalt to basaltic andesite lavas and accompanied by pyroclastic rocks (tuffs and volcanic breccias). Intrusive rocks are composed of gabbro-micro gabbro stocks and diabase dykes. Petrographic investigations show that volcanic and intrusive rocks in the area mostly display disequilibrium textures such as sieve textures and embayments in plagioclase and pyroxenes, patchy and oscillatory zoning in different generations of plagioclases. Geochemically, all volcanic rocks show similar characteristics; they are represented by basic rocks that mostly display tholeiitic affinity. Their MgO and SiO₂contents range from 3.04 to 6.18 and 44.80 to 48,47wt. %, respectively. The samples are slightly enriched in large ion lithophile elements (LILE) and light rare earth elements (LREE) compared to N-MORB and they display depletions in Nb and Ti elements which are the typical indicators of subduction zone magmatism. All volcanic rocks display low Y and high Sr/Y contents which are typical for adakites.  These adakites are specifically represented by “low-silica adakites” due to their low SiO₂ (<48 wt. %). They also have low Zr and high Zr/Y abundances suggesting garnet in their source. These major- trace element characteristics and published Sr-Nd-Pb isotope compositions may collectively suggest that the adakites of Fildes Peninsula were originated from the partial melting of the mantle-wedge which was metasomatized by subduction processes along the South Shetland trench.

How to cite: Ünal, A., Altunkaynak, Ş., and Nývlt, D.: Source characteristics of the adakitic lavas and intrusions in Fildes Peninsula, King George Island (South Shetland Islands, Antarctica), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8392, https://doi.org/10.5194/egusphere-egu24-8392, 2024.

The composition of MgO-rich basalt produced during the six-months long 2021 eruption at Fagradalsfjall, Reykjanes Peninsula, varied from those with low K₂O/TiO₂ and incompatible element contents to basalt enriched in incompatible elements with high K₂O/TiO₂ over a timespan of a month, explained by binary mixing of different mantle melts (Halldórsson et al., 2022). For the rest of the eruption, the basalt composition varied in a periodic manner as illustrated by long-lived radiogenic isotope ratios. For example, the periodicity of ⁸⁷Sr/⁸⁶Sr from early May to middle of September 2021 was 52 days, likely representing the time elapsed from the final melt mixing at depth (the moment of acquiring the measured isotope composition) until eruption at surface. Preliminary results on Th isotope ratios in the 2021 Fagradalshraun yield relatively high Th isotope ratios [(²³⁰Th/²³²Th) = 1.30] in the first lava emitted (the low K₂O/TiO₂ basalt) relative to basalt erupted at the end of the eruption [(²³⁰Th/²³²Th) = 1.18]. While this observation could be explained by slower mantle melting, excellent correlation between Th and Nd isotope ratios confirms the importance of binary mixing of melts from a depleted mantle source (with high Th and Nd, and low Sr isotope ratios) with melt(s) from enriched mantle lithology (having lower Th and Nd, and higher Sr isotope ratios) before magma ascent and eruption. Consequently, mantle heterogeneity, melt aggregations and mixing dominate the composition of the erupted basalt, rather than the duration of mantle melting. Correlation between Sr isotope ratios and time-averaged discharge rate indicate mantle source fertility control on the discharge rate during the 2021 eruption.  Both the 2022 and the summer 2023 eruptions started with a stronger discharge rate than that of 2021 and produced basalt of similar composition as that emitted in September 2021, interpreted as a result of an establishment of crustal magma accumulation zone since at the end of the 2021 eruption. Moreover, whether the exhaustion of the low K₂O/TiO₂ and ⁸⁷Sr/⁸⁶Sr magma reservoir led to the end of the 2021 eruption remains to be explored.

How to cite: Sigmarsson, O.: Basaltic magma dynamics during the 2021-2023 eruptions at Reykjanes Peninsula, Iceland, constrained by Sr, Nd and Th isotope ratios, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12434, https://doi.org/10.5194/egusphere-egu24-12434, 2024.

The origin and extent of crustal material in arc magmas are critical for tracing the crust-mantle interaction at subduction zones. Arc volcanic rocks often have a characteristic range of trace elements and isotopic compositions that constrain the influx of crustal material, such as hydrous fluids derived from slab dehydration, melts of the subducted plate's veneer sediments, or heterogeneous mélange. Especially, the traditional geochemical proxies struggle to investigate the contribution of tectonic melange into the enriched subarc mantle source. Lithium and molybdenum isotope compositions provide a potential means of tracing the different components to the mantle wedge in subduction zones.

Here, we report Li-Mo isotope compositions of the Fushui mafic complex in the Qinling orogen, central China, to trace their source nature and to constrain metasomatic component(s) transferred during the early Paleozoic subduction event. The Fushui mafic rocks exhibit typical arc-type trace element features and enriched radiogenic isotope compositions, suggesting a mantle source had incorporated subducted compenents. The Fushui rocks also exhibit a light Li isotope composition providing direct evidence for the contribution of dehydrated serpentinites and eclogite. The variable Mo isotope values further suggest the mantle source has been metasomatized by aqueous fluid and hydrous melt. This study, therefore, confirms the transportation of dehydrated oceanic plates from footwall to hanging wall and its critical role in the subarc mantle source. The interpretation provides a new perspective to study the recycling of subducted oceanic lithosphere and associated petrogenesis of arc magmatism.

How to cite: Hu, P.: Lithium and molybdenum isotope systematic for Fushui complex and implications for the recycled oceanic crust in the source of arc magmatism, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15179, https://doi.org/10.5194/egusphere-egu24-15179, 2024.

Tertiary migmatizations are pivotal events in the geologic history of the Menderes Massif, one of the world's most extensively studied core complexes. In northern Menderes Massif (Gördes Submassif) several granitic intrusions were emplaced into the migmatitic core rocks. They are mostly monzogranitic and granodioritic in composition and cut by associated pegmatitic dikes. These granitoids exhibit holocrystalline granular and porphyritic textures, characterized by plagioclase and, occasionally, biotite phenocrysts. The mineral composition of the granodiorites comprises 35–45% plagioclase, 30–35% quartz, 15–25% K-feldspar, and 5–10% biotite, with ± 5–8% muscovite. In contrast, the monzogranites are distinguished by a reduced plagioclase/K-feldspar ratio. Secondary phases include opaque minerals and sericite, with muscovite also observed. Accessory phases are zircon minerals. The granites exhibit an ASI index between 1 and 1.1, classifying them as slightly peraluminous I-type granites. They predominantly display high-K calc-alkaline characteristics and, less frequently, calc-alkaline nature. The Eu/Eu* ratio of these granites varies from 0.8 to 1.4. Trace element patterns suggest a possible derivation from basaltic and greywacke source rocks. Notably, high LaN/YbN ratios (reaching up to 107 ppm) and elevated Sr/Y ratios (up to 108 ppm) imply the presence of garnet or amphibole in the source. DyN/YbN and LaN/YbN ratios and their relationships specifically indicate the presence of garnet, rather than amphibole in the mafic source region. These data imply the crucial role of lower crustal melting in the formation of granitoids and the evolutionary history of the Menderes Core Complex.

How to cite: Kamacı, Ö., Ünal, A., and Altunkaynak, Ş.: Geochemical Implications for Tertiary Lower Crustal Melting in Northern Menderes Massif (Western Anatolia): Preliminary results, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9011, https://doi.org/10.5194/egusphere-egu24-9011, 2024.