Melilitites are ultramafic magmas characterized by normative Ca₂SiO₄, larnite, high FeO* and TiO₂. Liquids compositionally close to melilitites were experimentally reproduced from carbonated lherzolites in alkali, Fe and Ti-free model systems at 3.2-3.3 GPa, approx.  1500 °C (Gudfinnsson & Presnall, 2005), at relatively high melt proportions. In complex compositions, MORB-eclogite derived, carbonated, partial melts reacted with a fertile peridotite were proposed at the origin of melilitites (Mallik & Dasgupta, 2013, 2014). The experimental reconstruction of phase relationships along a join olivine melilitite - carbonate revealed that at 3 GPa, clinopyroxene and olivine or garnet are stable on the liquidus (Brey & Ryabchikov, 1994), suggesting that carbonated wehrlites are potential sources for the genesis of melilitites.

Here, we explore phase relationships on the high pressure melting of a model wehrlite, initially composed of a mechanical mixture of San Carlos olivine, diopside, aegirine, dolomite, rutile and kyanite. Starting materials were loaded in graphite capsules, inserted in sealed platinum capsules. Vitreous carbon spheres and synthetic diamond grains were adopted for liquid traps. 

Preliminary experimental results show that at 3 GPa the solidus is located at temperatures lower than 1200 °C. A thick, orthopyroxene-rich layer, with polygonal microstructure, forms at contact with aggregates resulting from quenched liquids, both at 1200 °C and 1400 °C. Estimates of liquid composition are melilititic, with TiO₂ approx. 2.5 wt.% on a volatile free basis.

Currently available experiments suggest that the solidus is controlled by the reaction dolomite + olivine + clinopyroxene = orthopyroxene + liquid, as suggested in Eggler (1976). This is feasible only if the liquid composition is located on the CaO-rich side of the plane diopside-forsterite-dolomite in the model system CaO-MgO-SiO₂-CO₂, i.e. on the normative larnite (akermanite) portion of the tetrahedron.

Brey G.P. & Ryabchikov I.D. (1994). Carbon-dioxide in strongly silica undersaturated melts and origin of kimberlite magmas. Neues Jahrbuch Fur Mineralogie-Monatshefte, (10), 449-463.

Eggler D.H. (1976). Does CO₂ cause partial melting in the low-velocity layer of the mantle?. Geology, 4(2), 69-72

Gudfinnsson G.H. & Presnall D.C. (2005). Continuous gradations among primary carbonatitic, kimberlitic, melilititic, basaltic, picritic, and komatiitic melts in equilibrium with garnet lherzolite at 3–8 GPa. Journal of Petrology, 46(8), 1645-1659.

Mallik A. & Dasgupta R. (2013). Reactive infiltration of MORB-eclogite-derived carbonated silicate melt into fertile peridotite at 3 GPa and genesis of alkalic magmas. Journal of Petrology, 54(11), 2267-2300

How to cite: Poli, S. and Melluso, L.: The origin of melilitites: preliminary results on melting of a carbonated wehrlite, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16571, https://doi.org/10.5194/egusphere-egu24-16571, 2024.

Venus and Mars have operated as one-plate planets for some or all of their history and intraplate magmatic activity on Earth has been suggested as an analogue for the observed volcanic activity on these bodies. Flipping the question around, what can we learn about intraplate magmatism on Earth from other planets?

Volcanic features, including extensive lava flows and vast lava plains, cover large portions of the Martian surface. Mars has two large volcanic provinces: Tharsis and Elysium. While the continent-sized region of elevated terrain called the Tharsis rise receives most of the attention, Elysium—the second largest volcanic province on Mars—is larger than the Ontong-Java plateau—the largest LIP on Earth. Activity detected by the InSight seismometer near Cerberus Fossae (located in Elysium Planitia, southeast of the Elysium volcanic province) is consistent with fluid flow at depth. Cerberus Fossae is among the youngest tectonic structures on Mars and large discharges of water and lava have been proposed to explain the geomorphic structures observed at Cerberus Fossae. The regional gravity and topography, volcanic history, and seismic activity at Cerberus Fossae are consistent with a present-day 2,000-km-radius plume head beneath Elysium Planitia. The characteristics of the Elysium Planitia plume are comparable to terrestrial plumes proposed to explain the formation of terrestrial LIPs. Plumes on Mars appear to be spatially stable for long periods of time, reflecting the stabilizing influence of a thick stagnant lid and sluggish mantle convection.

While Venus is nearly the same size as Earth, there is no evidence supporting Earth-like plate tectonics for the past 250-750 Myrs. The similarity in size invites comparison of present-day volcanic activity between the two planets. This is complicated by the presence of plate tectonics where volcanic activity at ridges and subduction zones has no clear analogue on Venus. Expanding intraplate volcanism on Earth suggests as many as 100 active volcanic events per year on Venus. While detecting surface changes is one goal of the upcoming NASA and ESA Venus missions, surface change associated with volcanic activity has already been found in the Magellan image archive. Herrick and Hemsley identified a 2 km² volcanic vent that changed shape in the eight months between two Magellan radar images. While sulfuric acid clouds obscure our view of the surface, those same clouds provide the best evidence for ongoing volcanic activity. Assuming the primary mechanism removing atmospheric SO₂ is a reaction between calcium minerals on the surface and SO₂, an SO₂ residence time of ~2 Myrs is required. This requires an outgassing rate of ~6x10¹⁰ kg SO₂/year—about the same yearly SO₂ outgassing rate measured on Earth over the past decade. Converting this outgassing rate to erupted lava, an eruption rate on Venus of ~1 km³/yr is obtained.

How to cite: King, S., Duncan, M., Euen, G., Murphy, J., Parrish, S., and Weller, M.: Can Venus and Mars Inform Us About Intraplate Magmatism on Earth?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5761, https://doi.org/10.5194/egusphere-egu24-5761, 2024.

The Tibetan lateral mantle flow bears considerable significance in deciphering the material movement mechanisms within global plate convergence zones. However, the front edge of this mantle flow is unclear. Here we conduct petrological, geochronological, mineralogical, geochemical and Sr-Nd-Pb isotopic investigations on Quaternary intracontinental alkali basalts from the southwestern Yunnan (the south of 27°N), to determine the source characteristics and geodynamic mechanisms of the Quaternary alkali basalts in southeastern Tibetan Plateau and to trace the recent Tibetan mantle flow. Alkali basalts in the region are mainly basanite and trachybasalt with eruptions during the Pleistocene epoch. They possess a highly incompatible elemental and radiogenic Sr-Nd-Pb isotopic composition similar to those of the Ocean Island Basalts, consistent with melts derived from asthenospheric mantle with low-degree partial melting. Calculated magma-water contents of regional alkali basalts range from 1.32 ± 0.48 wt.% to 2.23 ± 0.18 wt.%, corresponding to 269 ppm to 3591 ppm water contents of their mantle source, which are significantly higher than that of the normal upper mantle (i.e., 50–250 ppm). Quantitative trace-element modelling and dramatic variations in oceanic crust-sensitive indicators such as Eu/Eu*, Sr/Sr*, Ce/Pb, (Nb/Th)_N-PM and (Ta/U)_N-PM indicate variable contributions of upper and lower oceanic crust to magma sources. Systematic examinations of petrological, geochemical, and geophysical evidence reveal that the temporary small-volume Quaternary volcanism in southeastern Tibetan Plateau is not related to Tibetan southeastward mantle flow but is primarily attributed to stagnant Neo-Tethyan slab in the mantle transition zone.

How to cite: Kang, H., Zhao, Y., Zhang, X., Zhang, L., Zhang, H., and Zou, H.: Quaternary volcanism in southeastern Tibetan Plateau: A record of stagnant oceanic slab in the mantle transitional zone, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7403, https://doi.org/10.5194/egusphere-egu24-7403, 2024.

The geodynamic regime driving formation of Archean felsic continent crust is still an ongoing debated and unsolved fundamental issue. The episodic Archean TTGs and associated granitoids, with emplacement ages of ca. 2.9, 2.7 and 2.5 Ga, occurred in the Jiaobei Terrane, North China Craton (NCC), provide prolonged continuous records of formation processes of Meso-Neoarchean felsic continental crust. To track patterns of crust-mantle differentiation, crustal reworking and recycling, and accordingly, constrain underlying geodynamic regimes associated with formation of the Meso-Neoarchean felsic continental crust, we present comprehensive zircon U-Pb dating, Hf-O isotopes and whole-rock major- and trace-element geochemical data for the episodic Archean TTGs and associated granitoids. The comprehensive dataset decodes the generation of the episodic Archean TTGs over wide-range pressure conditions from amphibolite to eclogite facies and Meso-Neoarchean coupled crust-mantle differentiation, which was likely driven by episodic hot mantle (plume) upwelling. In addition, the ca. 2.9 and 2.7 Ga TTGs shared identical Mesoarchean juvenile crust source and exhibit consistent mantle-like zircon δ¹⁸O values, whereas the ca. 2.5 Ga TTGs mainly derived from distinctly younger Neoarchean juvenile crust, implying removal and replacement of the Mesoarchean juvenile lower crust. Importantly, some ca. 2.5 Ga TTGs, granitic gneisses and sanukitoids exhibit significantly higher zircon δ¹⁸O values than mantle δ¹⁸O values, demonstrating occurrence of Neoarchean supracrustal recycling. Consequently, the combined geochemical dataset with geological evidence allow us to track the geodynamic processes for the formation of the Meso-Neoarchean felsic continent crust in the Jiaobei Terrane, NCC: Episodic hot upwelling mantle (plume)-lithosphere interactions at ca. 2.9, 2.7 and 2.5 Ga resulted in the coupled crust-mantle differentiation over different depths to produce the spatial-temporally coexisted various-pressure-type TTGs, juvenile crust and voluminous dense lower crustal restite, respectively. Subsequently, dense lithospheric delamination triggered by gravitational instability occurred, followed by continental uplifting, subduction of altered oceanic crust, and asthenosphere and mantle-derived mafic melts upwelling, resulting in extensive occurrences of anatexis and metamorphism with anticlockwise P-T paths in the medium-lower crust at ca. 2.5 Ga. Along with large-scale melting and cooling of mantle, thick stable craton lithosphere with strong rigidity and viscosity had likely developed by the end of Neoarchean. The geodynamic processes in Meso-Neoarchean were likely diverse, especially episodic hot upwelling mantle (plume) -lithosphere interaction could be a favored geodynamic regime responsible for formation of Archean felsic continental crust in the Jiaobei Terrane, NCC.

How to cite: Liu, J.: Meso-Neoarchean coupled crust-mantle differentiation followed by gravity-driven lithospheric delamination and subduction initiation in the North China Craton, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4864, https://doi.org/10.5194/egusphere-egu24-4864, 2024.

A low-velocity layer atop the mantle transition zone has been extensively observed worldwide, which may play an important role in mantle dynamics and Earth habitability. In subduction zones, this layer is widely explained as partial melting triggered by slab subduction on a regional or global scale. However, direct observational evidence is still absent, and the response of the layer to slab subduction is not well known. Here, we image the seismic velocity around the mantle transition zone by matching synthetic and observed triplicated seismic P and sP waveforms in the Indian–Eurasian continental subduction zone. Our observations reveal a laterally varied low-velocity layer atop the mantle transition zone beneath the Hindu Kush, where a subducted slab extends to the mantle transition zone. It is characterized by thickness of 56-94 km and P-wave velocity drop of -2.8~-4.7%. The geometric morphology of the low-velocity layer indicates that it is a partially molten layer induced by the subducted slab on a regional scale. Interestingly, our observations also support that the layer has a low viscosity. The decreased viscosity possibly facilitates slab motion in the deep domain; however, the buoyant continental crust in the shallow domain likely resists downwards movement of the slab. This differential movement is more likely to cause slab stretching, tearing and break-off in the middle region, which may contribute to explaining rare recurring large intermediate-depth earthquakes in an intracontinental setting.

How to cite: Li, G.: Seismic evidence of upper mantle melt caused by a subducted slab in the Indian-Eurasian continental subduction zone, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7577, https://doi.org/10.5194/egusphere-egu24-7577, 2024.

Based on the analysis of the tectonophysical characteristics of the actual seismofocal zone (SFZ) in the lithosphere of the Kuril-Kamchatka region and adjacent Oceanic areas,  we estimated the boundary conditions necessary for constructing the quantitative models of heat and mass transfer dynamics in compacted heterophase media under active volcanoes located over the mantle and crustal magmatic   sources of the ocean–continent transition regions of the northwestern sector of the Pacific Ocean.

The methodology of obtaining the information  used for developing of the mathematical models of magmatogenic processes includes: 1) the study of individual porphyry deposits associated with active fluid volcanogenic systems; 2) the study of morphological structures using cosmic satellite images (Sharapov et al., 1980); 3) the study of mantle and crust xenoliths of volcanics (Kutyev, Sharapov, 1979; Sharapov et al., 2009, 2017, 2020); 4) parametric tectono-physical analysis of the modern SFZ of the studied region (Sharapov et al., 1984, 1992); 5) experimental modeling of the  processes of deformation   Earth's crust and lithospheric mantle rocks of modern SFZ (Sharapov et al., 1984, 1992); 6) construction of mathematical models of the petrogenesis under volcanoes (Sharapov et al., 2007, 2020)

According to data on the structure of the Earth's crust under the Avacha volcano; (Koulakov et al., 2014), permeable zones are linear fractures 2-4 km wide, which are conductors of melts and magmatogenic fluids coming from magmatic systems (Koloskov et al., 2014).

An analysis of the time characteristics of formation porphyric deposits in the active margins of the Pacific Ocean (Sharapov et al., 2013) showed that more than 70% of the described deposits are formed during the evolution of fluid mantle-crustal ore-magmatic systems. This study analyzes the data on the structure of the modern SFZ of Kamchatka and the Kuril Island arc, used in constructing a model of heat and mass transfer under volcanoes.

Based on the analysis of the tectonophysical characteristics of the actual seismofocal zone (SFZ) in the lithosphere of the Kuril-Kamchatka region and adjacent Oceanic areas,  we estimated the boundary conditions necessary for constructing the quantitative models of heat and mass transfer dynamics in compacted heterophase media under active volcanoes located over the mantle and crustal magmatic   sources of the ocean–continent transition regions of the northwestern sector of the Pacific Ocean.

T

An analysis of the time characteristics of formation porphyric deposits in the active margins of the Pacific Ocean (Sharapov et al., 2013) showed that more than 70% of the described deposits are formed during the evolution of fluid mantle-crustal ore-magmatic systems. This study analyzes the data on the structure of the modern SFZ of Kamchatka and the Kuril Island arc, used in constructing a model of heat and mass transfer under volcanoes.

RNF grant  24-27-00411

How to cite: Sharapov, V., Perepechko, Y., Mikheeva, A., Vasilevsky, A., Sorokin, K., Ashchepkov, I., and Kuznetsov, G.: Analyze of the structural conditions of heat and mass transfer under volcanoes of the northwestern sector of the Pacific ocean- Eurasian continent transition, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4048, https://doi.org/10.5194/egusphere-egu24-4048, 2024.

The problem of the introduction of heterophase magmatic melts into the conducting channels of the lithospheric mantle under the cratons of the Siberian platform has been studied numerically. The analysis of the features of the introduction of melts was carried out on the basis of a hydrodynamic model of the evolution of magmatic and fluid-magmatic systems. The mathematical model describes the two-speed dynamics of the redistribution of hot heterophase melts and magmatogenic fluids in the flow during their movement from the generation zones to the platform cover, as well as the processes of heat and mass transfer between melts and rocks in permeable zones of the lithosphere. The nature of the flow of mixtures of liquid fractions of aluminosilicate, sulfide, native and oxide liquids, in which a sub-liquid solid phase appears during movement and decompression boiling occurs, the features of heat and mass transfer processes determine the type of magmatic and magmatogenic deposits of the trap formation of the Siberian platform. The flow of magmatic melts in a wide temperature range of 300-1200 °C, the viscosity of the melt phases of 101-106 N, as well as the rate of penetration and the degree of stratification of the heterophase magmatic flow were studied.

The figure shows an example of the randomization of an intrusive flow. (a) (b) An example of the development of heterogeneity in the distribution of the concentration of particles of the dispersed phase (a, m-3) and temperature (b, °C) in an initially stratified magmatic flow embedded in the host rocks. The temperature of the introduced flow is 500 °C, in the channel at the initial moment standard thermodynamic conditions; the dynamic viscosity of the melt is 102 P. The work was carried out with the financial support of the Russian Science Foundation, grant No. 24-27-00411.

How to cite: Perepechko, Y., Sorokin, K., and Imomnazarov, S.: Features of the introduction of magmatic melts in permeable zones of the platform cover, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14538, https://doi.org/10.5194/egusphere-egu24-14538, 2024.

The influence of the hot spot for the AVB was assumed by (Kuzmin and Yarmolyuk, 2011). It may be the same hot spot that cause the creation of the kimberlites at 420 Ma at the north of Siberian craton (Sun et al,, 2014; 2018) than in the central part of Yakutian kimberlite province 350- 370 Ma. and transferred to the Prisayanie forming kimberlite fields covered by Carboni ferrous Permian sedimentary sequences in the basins of Tumanshet, Biryusa and Chuna rivers. Than it produced the Ingashi kimberlites - lamproites 310 -300 Ma (Kostrovitsly et al., 2022).

Granites of Angara-Vitim batholith were caused and influenced by this huge thermal event. The A-type granitoid magmatism and acid and mafic magmatism accompanied by mingling between these magmas suggest influence of the mantle plume (Litvinovsky et al., 2002; Tsygankov et al., 2019). This explains the K-nature of the granitoid magmatism, corresponding to the selective melting of the K-feldspars (Litvinovsky et al., 2000). This is the reason of the alkaline magmatism widely distributed among the  AVB magmas (Tsygankov et al., 2010-2021).

The huge amount of the volatiles that accompany plumes are responsible for melting in the mantle and crust (White and McKenzie, 1995). But essential parts of plume volatiles are CO₂ and CH gases (Marty and Tolstikhin, 1998).. The H₂O fluxes correspond to the starting and final stages of plume impulses (Ivanov et al., 2013). The periods of such pulses are nearly close to 30- Ma what is regulated by the Cosmic forces (Abbott, and Isley, 2002). Boundaries of the geological periods correspond to plume events In Transbaikalia, the H₂O-rich flux was designated by transition to more acid magmas at 270 Ma. The CO₂-rich flux at the maximum was manifested by the generation of the Burpala alkali-carbonatite massif (Vladykin et al., 2017).

Further, numerous already granitic and associated magmas and massifs were found in Eastern Sayan and Southern Pribaikalie. In Svyatoi Nos in Baikal 310 Ma (Kruk et al., 2023). 

The simultaneously and later the hot spot  created the main massifs of the AVB at the time span 275 -320 Ma (Khubanov et al., 2016; 2021).  The further continuation could be found in Khangai  batholith (270-240 Ma) (Yarmolyuk et al., 2013).

Than at the eastern margin, the plume turned to the NNW again and created the Siberian large igneous province- Permo-Triassic traps (Kuzmin and Yarmolyuk, 2011) 260-240 Ma.  the development of the plume magmatism in Early Triassic and later  in Jurassic time probably was transformed to the Island hot spot (Kuzmin and Yarmolyuk, 2010).

RNF grant 23-17-00030

Kostrovitsky  S.I. ea  2021.  Special Publications 513, 45 - 70.

Khubanov V.B ea 2021.   Russian Geology  Geophysics. 62, 1331-1349.

Kuzmin, M.I. , Yarmolyuk,   2014.   Russian Geology and Geophysics, 55, 120-143.

Kuzmin M.I. ea 2010.   Earth-Science Reviews, 102, 29-59.

Yarmolyuk V.V ea 2013,   Petrologiya , 21/2, 115–142.

How to cite: Tsygankov, A., Ashchepkov, I., and Galina, B.: The influence of the Siberian plume to the formation of Angaro-Vitim batholiths, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3630, https://doi.org/10.5194/egusphere-egu24-3630, 2024.

The lower crust and Moho pyroxenites and xenocrysts from Cenozoic volcanoes studied with the EPMA, SEM and LA ICP MS for trace elements evidence about the structure and composition of the transitional zone from the crust to mantle in Cenozoic volcanic regions In Vitim (picrite basalts), Dzhida, (Bartoy volcanoes) and Tunka valley (Karierny volcano). For the comparisons the lower crust xenocrysts from the Angara Vitim batholite were studied. The calculated PT conditions show the PT estimates are localizing within the Moho –and just beneath giving the vast range of temperatures. Lower they trace 90 mw/m2 geotherm. Within the crust the variation of temperature regime are varying from the conductive to advective. Xenocrysts and pyroxenite xenoliths mainly trace 90 mw/m2  SEA plume geotherm the area of the intrusions is over heated to 1350oC.

Fig.1 PT diagram for the xenoliths from Vitim Miocene  Picrite basalts

Fig.2 PT diagram for the xenoliths from Bartoy Pleistocene basalts

Fig.3 PT diagram for the xenoliths from Tunka Pliocene basalts

Fig.4 PT diagram for the xenocrysts from  Magmas of Angara-Vitim batholite

The granulites are typically represent the more colder conditions than SEA geotherm.  Xenocrysts from Angara Vitim batholith magmas reveal more depleted material of lower crust than those found in Cenozoic lavas and possibly are skialites. The xenocrysts and granulate xenoliths in Cenozoic lavas are mainly basic cumulates. The lower crust became more acid to the upper part. The lateral variations in the lower crust sampled material show enrichment in K2O at the boundary with the Siberian craton in Tunka, more metasomatic and hydrous nature in Dzhida zone and more basic and CaO rich characteristic in Vitim area.  These data give the evidence for the conditions of the creation of magmas of Angara-Vitim Batholiths.  It was created by the hot spot created kimberlites and basalts in north and Center of Yakutia in Silurian- Devonian time and Ingashi lamproites,  than it turned in Transbaikalia and after returned to central and Northern Siberia.   

 Supported by Ministry of Science and Higher Education of the Russian Federation. Supported by Russian Science Foundation (23-17-00030). Work is done on state assignment of IGM SB RAS, Geological institute SB RAS Ulan Ude and Institute of Earth crust SB RAS, Irkutsk

How to cite: Ashchepkov, I., Tsygankov, A., Burmakina, G., Rasskazov, S., Ailow, Y., and Karmanov, N.: Thermal state and nature of the low crust in the Baikal Rift zone according to the lower crust xenoliths of Cenozoic volcanics and Paleozoic magmas. , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1231, https://doi.org/10.5194/egusphere-egu24-1231, 2024.

Small-volume alkaline magmatism has now garnered due attention in geosciences, wherein these rocks provide essential information about deep mantle processes, geochemical composition, and the prevailing geodynamics. The continental alkaline magmatism of deep-seated ultramafic lamprophyres (UML) is spatially and temporally linked with continental breakup and rifting. Additionally, they have gained significant attention in terms of mineralization.

Deccan hosts one of the most extensive and peculiar suites of lamprophyre complexes in India, and this magmatism holds valuable geological information to unveil the geodynamic processes and provide significant implications on the enrichment/depletion processes of SCLM during Deccan times. The present research delves into the mineral and whole-rock geochemical compositions and paleomag dating of lamprophyres from the West Coast Alkaline Complex (WCAC) of the Deccan Large Igneous Province. The study has implications for the relation of lamprophyre magmatism with the Réunion mantle plume, the associated main phase of Deccan tholeiite magmatism, the initiation of rifting in the western Indian subcontinental margin, the separation of Seychelles from the Indian subcontinent, as well as the role of lithosphere thinning in triggering lamprophyre magmatism. WCAC lamprophyres are principally composed of olivine and phlogopite phenocrysts/ macrocryst embedded in a mesostasis of carbonate, clinopyroxene, olivine, nepheline, spinel, and melilite groundmass. The presence of titanian aluminous phlogopite, clinopyroxene, and Al-enriched spinels with high Fe²⁺/(Fe+Mg) ratios are the characteristic features of WCAC lamprophyres. They are primitive, undersaturated in silica (SiO₂: 38.43 – 38.99), and rich in MgO (up to 10 wt. %), TiO₂ (up to 4.2 wt. %), and light rare earth elements. Mineral genetic classification schemes and geochemical compositions demonstrate a resemblance with ultramafic lamprophyres. 

High LREE/HREE (La/Yb= 75-82) ratios, similar to UMLs reported globally, and low Ba/Rb and Rb/Sr ratios exhibit the predominance of phlogopite and amphibole in the mantle source. Geochemical investigations inarguably trace their genesis back to the enriched garnet lherzolite mantle, metasomatised by silicate and carbonate veins. They show compositional similarity with global damtjernites and derivation from moderate pressure depth (3-4 GPa) corresponding to 90-100 km thick lithospheric mantle. Paleomagnetic studies support the intrusion of lamprophyres, predominantly during the chron C29n, thereby substantiating their radiometric eruption age at ~65 Ma. Seismic tomography models reveal a current lithospheric thickness of approximately 50 km beneath the WCAC, suggesting delamination of the lithosphere after the intrusion of lamprophyres at 65 Ma. UML magmatism in WCAC resulted from the initiation of a rift, which ultimately led to the separation of the Indian subcontinent and the Seychelles. The impetus behind the emplacement of UML dykes is intricately tied to passive rifting and external plate boundary forces, surpassing the influence of the Reunion mantle plume. The lithospheric thinning presumably occurred after the emplacement of lamprophyres and other alkaline rocks and continued with continental rifting in response to greater plate-tectonic stresses in the region of persistent lithospheric weakness.

How to cite: Singh, A. and Dongre, A.: Post-tholeiite rifting and genesis of ultramafic lamprophyres at ~65 Ma in the Deccan Large Igneous Province, India, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4288, https://doi.org/10.5194/egusphere-egu24-4288, 2024.

An alkaline magma undergoes significant modification during its ascent to the surface due to assimilation of mantle and crustal material, exsolution of volatiles, trapping of crystals from earlier crystallized melt batches, fractional differentiation and explosive processes, making a thorough understanding of the petrogenesis of the magma and the nature of its mantle source in large igneous provinces difficult. The dikes and pipes of ultramafic lamprophyres, picrites and nephelinites are characterised by rapid rise of melt batches that could provide a high chance of preserving unworked mantle and crustal material. A study of olivine from these rocks may help to resolve some issues of their mantle sources and melt evolution.

The Namuaive pipe located in the northern part of the nepheline syenite Khibina Massif, Kola alkaline province. The pipe is filled by pyroclastic alkaline picrite (melanephelenite). The rock is texturally heterogeneous, consisting of 30-40 vol % magmaclasts and lapilli, phenocrysts and macrocrysts (up to 40 vol %) of phlogopite, olivine and clinopyroxene, xenoliths of Khibina Massif rocks, and fine grained matrix composed of phlogopite, apatite, perovskite, spinel, Ti-magnetite, nepheline, sodalite, high-Ti garnet.

Olivine is one of the most abundant macrocrysts in alkaline picrite, ranging up to 30 vol %; it is fresh or slightly replaced by serpentine or clinopyroxene-phlogopite intergrowth. Three groups of olivine based on core-to-rim zonation were observed:

• Euhedral-to-subhedral olivine grains up to 5 mm are phenocrysts. Some grains have spinel inclusions. Phenocrysts show normal Mg#-zonation. They consist of a more magnesian core (Mg# = 0.90-0.89) with Ni content from 1595 to 3058 ppm and a thin marginal ferruginous zone (Mg# = 0.89-0.83) with Ni content from 363 to 2663 ppm.
• Antecrysts have rounded and often corroded edges. Their size ranges from the first few hundred µm to 1 mm. They are characterised by Fe-rich cores (Mg# = 0.84-0.87) with a wide range of Ni contents from 1200 to 3200 ppm, surrounded by a transitional zone with a gradual increase in magnesium (Mg# = 0.86-0.89) and Fe-rich rind (Mg# = 0.89-0.86) with Ni contents from 1500 to 605 ppm. They have a small clinopyroxene-phlogopite rim and spinel along cracks.
• The xenocrysts have been divided into two subgroups according to their Mg# and Ni contents. The cores of the first subgroup have Mg# 0.90-0.91 and Ni contents from 2800 to 3200 ppm, the cores of the second subgroup have Mg# 0.91-0.93 and Ni content about 2000 ppm. The rims of both subgroups have Mg# 0.83-0.85 and Ni contents from 1236 to 433 ppm. Some olivine grains are intergrown with high-Cr clinopyroxene and high Mg phlogopite.

The antecrysts reflect mixing of the evolved lamprophyric melts during previous pulses with the partial melt batch that formed the Namuaive pipe. Phenocrysts and other olivine rims formed during fractional crystallization. Antecrysts and phenocrysts equilibrated to melts from wehrlite sources.

The study was supported by the Russian Science Foundation under Grant No 23-77-01052

How to cite: Lebedeva, N., Nosova, A., Sazonova, L., Kargin, A., Shaikhutdinova, D., Yapaskurt, V., and Shcherbakov, V.: The alkaline rocks olivine variety: a case study of Namuaive Pipe, Kola alkaline province, Russia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8338, https://doi.org/10.5194/egusphere-egu24-8338, 2024.

Petrological investigations of large alkaline provinces with carbonatites are very important to understanding the generation and evolution of alkaline melts, as well as processes provided generation of related ore deposits. Most often, generation of large alkaline massifs with carbonatites accompanied by intrusion of related ultramafic alkaline and related alkaline-ultramafic melts as dykes swarms and explosive pipes. These melts could be generated on the initial stages of magmatic activities of alkaline province magmatism, or fix the final stages of alkaline magmatism, after the formation of large alkaline massifs with carbonatites. Studying of these melts could provide insights into the composition of primary melts for large alkaline province, as well as understanding their evolution during magmatic activities. Moreover, the latest melts forming dykes and explosive pipes could provide information about the evolution of the mantle source of these rocks including of processes of lithospheric mantle transformations (enrichment, depleting, mantle metasomatism etc.).

The Kola alkaline province (KAP) with carbonatites is a good natural laboratory for investigation petrology of alkaline melts and their evolutions. KAP includes large alkaline massifs with carbonatites, the early dyke swarms of ultramafic and alkaline lamprophyres and late explosive pipes of the alkaline rocks (Arzamastsev et al., 2005). To investigate the composition of alkaline melts at the late stages of the province's magmatic activity, we have studied the petrography and mineralogy (olivine composition) of the Namuaiv pipe rocks.

The Namuaiv pipe (363 ± 3 Ma; Arzamastsev et al., 2005) erupted the alkaline rocks of the north part Khibiny massif (377± 3 Ma). The detailed petrographical studied suggested, that the pipe breccia was formed during mixing of two portions of alkaline melts close in composition to alkaline picrite and melanephelinite.

The Namuaiv rocks contain several types of olivine grains: (1) picritic melt phenocrysts; (2) antecrysts of ultramafic lamprophyres of the Kandalaksha Bay (Vozniak et al., 2023) that traced the first stages of the province magmatism; and (3) disintegrated fragments of the lithospheric mantle peridotites (mantle xenocrysts). The composition of olivine phenocrysts suggests that in the final stage of KAP activity, the alkaline melts have not fractionated in deep magmatic chambers and their composition is close to primary melts. That is in contrast to the first stages of KAP magmatism, where lamprophyre dikes were formed as fractionated melts (Vozniak et al., 2023). The present of the olivine antecrysts assumes that the Namuaiv melts ascent trough magmatic channels modified by previous portions of alkaline melts, that consistent with the presence metasomatic clinopyroxene-phlogopite xenoliths within the pipe.

The study was supported by the Russian Science Foundation under Grant No 23-77-01052.

Arzamastsev A.A., Belyatsky B.V., Travin A.V. et al. 2005. Dyke rocks in the Khibiny massif: relation to plutonic series, age, and characterization of mantle sources // Petrology. V.42. N3. P.1-23.

Vozniak A.A., Kopylova M.G., Peresetskaya E.V. et al. 2023. Olivine in lamprophyres of the Kola Alkaline Province and the magmatic evolution of olivine in carbonate melts // Lithos 448–449, 107149. doi:10.1016/j.lithos.2023.107149

How to cite: Shaikhutdinova, D., Kargin, A., Sazonova, L., Lebedeva, N., Nosova, A., and Vasiliy, Y.: The Namuaiv picrite-melanephelinite pipe, Kola alkaline province, Russia: petrography and evolution of late alkaline melts during forming large alkaline province with carbonatites., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-616, https://doi.org/10.5194/egusphere-egu24-616, 2024.

Massif-type anorthosite intrusions are enigmatic and significant crustal components widespread worldwide. They occur either as individual massifs or accompanied by mangerite, charnockite, and granite (AMCG suite). This Proterozoic phenomenon has been studied in numerous complexes, generating long-lasting discussions regarding the magmatic source and the tectonic setting where these rocks form. This controversy is still a matter of debate after decades of scientific research. In this sense, Mexico represents a unique and new opportunity to explore such petrological issues because its exposures of massive anorthosite and associated lithologies are mainly unstudied. These rocks are better exposed in the Oaxacan Complex, the most extensive Mexican inlier of Grenvillian rocks. This work is focused on its northern portion. This area is characterized by 1.4-1.1 Ga metamorphic rocks from the El Catrín and El Marquez units that were later intruded by anorthosite, gabbro, leucogabbro, oxide-apatite gabbronorites (OAGN), and granite bodies from the Huitzo suite. New LA-ICP-MS U-Pb zircon data revealed similar crystallization age ranges in the gabbro-anorthositic (1013-960 Ma) and granitic (1012-964 Ma) rocks. Their zircon Hf-O isotopic composition was compared with previous and new data from the older units of the area to assess the possible interaction between mantle- and crustal-derived melts during their generation. The intrusions of massive anorthosite and gabbro exhibit ε_Hf(t) values of -2.54-4.79 and δ¹⁸O = 6.84-8.03‰. The granitic rocks have ε_Hf(t) values of -0.79-2.87 and δ¹⁸O = 7.80-8.42‰. The lack of mantle-like ε_Hf(t) and δ¹⁸O values suggests the participation of high-δ¹⁸O supracrustal material with more radiogenic Hf signatures during their generation. Simple binary mixing modeling indicates that the gabbro-anorthositic intrusions incorporated ~20-30% of metasedimentary country rocks, supporting a mantle-dominated origin. A slightly higher crustal component is recognized in the studied granitic intrusion. We also propose that these rocks permit an alternative model where Oaxaquia is paleogeographical relocated close to the eastern margin of Laurentia during the final stages of Rodinia amalgamation due to the resemblance in age to the late- to post-Grenvillian AMCG rocks (1016-956 Ma) outcropping there (e.g., Roseland, Mattawa, Labrieville, and Vieux Fort). This new tectonic view challenges the classical Amazonia-Oaxaquia-Baltica connection.

How to cite: Elizondo Pacheco, L. A., Solari, L., He, H., Ramírez Fernández, J. A., and Maldonado, R.: Geochronological, petrological and tectonic implications of the Proterozoic massif-type anorthosite intrusions and related rocks from the northern Oaxacan Complex, southern Mexico, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4770, https://doi.org/10.5194/egusphere-egu24-4770, 2024.

While heavy molybdenum (Mo) isotope compositions in arc-related rocks have been linked to slab-derived fluids, the origins of arc lavas with light isotopic Mo compositions remain enigmatic. The two potential sources for the origin of light Mo isotopes in arc rocks are (1) dehydrated oceanic crust ^{1, 2} and (2) subducting sediments ^{3, 4}. Although the former has been extensively recognized, the latter still poses an enigma. We present the Mo-Sr-Nd-Hf isotope compositions and elemental data of a suite of Jiang Tso andesites to elucidate the chemical compositions of sediment-derived melts in the central Tibetan Plateau. The andesites from the Jiang Tso area show elevated Mg# values, along with trace element characteristics reminiscent of melts derived from sediments. Their Sr-Nd-Hf isotope compositions (⁸⁷Sr/⁸⁶Sri = 0.710260–0.710671, ε_Nd(t) = –10.63 to –8.97, and ε_Hf(t) = –9.38 to –8.02) closely resemble those of contemporaneous sediments in the central Tibetan Plateau. In addition, these andesites exhibit higher Ce/Mo ratios (396–587) and extremely lighter δ^98/95Mo values (−1.62‰ to −0.69‰) compared to the depleted mantle (δ^98/95Mo = –0.21‰ ± 0.02‰) ^{5, 6} and the majority of arc lavas (δ^98/95Mo = –0.07‰ ± 0.04‰) ³, suggesting a more plausible explanation lies in the involvement of subducting sediments rather than dehydrated oceanic crust in the source. Our latest findings, integrated with previous studies, indicate that the arc-related rocks exhibiting light Mo isotopes may not solely originate from the rutile-breakdown oceanic crust source but could also result from sediment melting at various sub-arc depths. Consequently, sediment-derived melts play a crucial role in Mo isotope cycling and the formation of arc magmas in subduction zones.

¹ Chen, S., et al., Nat. Comm. 10, 4773 (2019). ² Freymuth, H., et al., EPSL 432, 176-186 (2015). ³ Huang, F., et al., GCA 341, 75-89 (2023). ⁴ König, S., et al., EPSL 447, 95-102 (2016). ⁵ McCoy-West, A.J., et al., Nat. Geos.12, 946-951 (2019). ⁶ Willbold, M. & Elliott T., CG 449, 253-268 (2017).

How to cite: Huang, F., Li, J., Xu, J., and Zeng, Y.: Role of sediment-derived melts in Mo cycling of subduction zone, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4498, https://doi.org/10.5194/egusphere-egu24-4498, 2024.

Redox state of parental magma would have undergone significant changes from partial melting in the mantle to emplacement in the shallow crust, which might play a critical role in the genesis of magmatic Ni-Cu sulfide deposits in convergent tectonic settings. In this study, we present mineralogy, petrology, and fO₂ calculations of the Xiarihamu Ni-Cu deposit and the Shitoukengde non-mineralized intrusion in the East Kunlun orogenic belt. Olivine-spinel pairs in different magmatic stages were chosen to estimate the magma fO₂ (olivine-spinel oxybarometer), track the changes in oxygen fugacity during magmatic evolution, and reveal its influence on the metallogenic mechanism of the Ni-Cu sulfide deposit. Spinel Fe³⁺/ΣFe ratios determined by a secondary standard calibration method using electron microprobe. Those ratios of the Xiarihamu Ni-Cu deposit vary from 0.32±0.09 to 0.12±0.01, corresponding to magma fO₂ values ranging from ΔQFM+2.2±1.0 to ΔQFM-0.6±0.2. By contrast, those of the Shitoukengde mafic-ultramafic intrusion increase from 0.07±0.02 to 0.23±0.04, corresponding to magma fO₂ varying from ΔQFM-1.3±0.3 to ΔQFM+1.0±0.5. A positive correlation between fO₂ and Cr-spinel Fe³⁺/ΣFe ratios suggests that the Cr-spinel Fe³⁺/ΣFe ratios can be used as an indicator for magma fO₂. The high fO₂ (QFM+2.2) of the harzburgite in the Xiarihamu Ni-Cu deposit suggests that the most primitive magma was characterized by relatively oxidized conditions, and then became reduced during magmatic evolution, causing S saturation and sulfide segregation to form the Xiarihamu Ni-Cu deposit. The evolution trend of the magma fO₂ can be reasonably explained by metasomatism in mantle source by subduction-related fluid and addition of external reduced sulfur from country gneisses (1.08–1.14 wt.% S) during crustal processes. Conversely, the primitive magma of the Shitoukengde intrusion was reduced and gradually became oxidized (from QFM-1.3 to QFM+1.0) during crystallization. Fractional crystallization of large amounts of Cr-spinel can reasonably explain the increasing magma fO₂ during magmatic evolution, which would hamper sulfide precipitation in the Shitoukengde intrusion. We propose that the temporal evolution of oxygen fugacity of the mantle-derived magma can be used as one of the indicators for evaluating metallogenic potential of Ni-Cu sulfide deposits, and reduction processes from mantle source to shallow crust play an important role in the genesis of magmatic Ni-Cu sulfide deposits.

How to cite: Jia, L., Chen, Y., Su, B., Mao, Q., and Zhang, D.:  Oxygen-fugacity evolution of magmatic Ni-Cu sulfide deposits in East Kunlun: Insights from Cr-spinel composition , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-103, https://doi.org/10.5194/egusphere-egu24-103, 2024.

Joint analysis of tectonics, magmatism, metallogeny, and hydrocarbons (HC – oil-gas) for the South Caspian - west Baluchestan, Middle East (Alpine time mainly) was made. Different anomalies and degassing here are of interest too.  Specific anomalous deep regime and degassing of CH4, H2 etc. due to a giant African superPlume activity are noted too. Such points discussed as follows:

1.      Alpine North-Eastern (NE) tectonic zoning exists in this region up to Present (Q4). Anomalous long-lived African superPlume activity influences on regional tectonics, related magmatism and fluid regime (Fig.). There are different anomalies in this region on gravity, hydrocarbons (HC), degassing etc.

2. Miocene – Recent (N1-Q) intraplate magmatism with: different subalkaline- alkaline rocks directly relates to superPlume mentioned. There are data about Sr, Ca etc. input in upper younger Caspian Sea sediments from the lower older magmatites. Such magmatic trend exists as: Quaternary carbonatites, Hanneshin, Helmand block (Afghanistan) - Ca-rich volcanites with CaO up to 34.8% -  trachyandesites with CaO = 7.2%.  

• Oligocene-Recent (Pg3-Q) calk-alkaline subduction-related rocks are as antipodes to mentioned intraplate rocks (intrusive, extrusive and volcaniclastic ones). Relation with African superplume is not formally necessary, but there are our data about warmer calk-alkaline rocks here, ex., warm melt inclusions in them with T crystallization as 1180oC.
• Decreasing of earthquakes activity from South to the Middle Caspian Sea, at

least (Khain, Bogdanov, 2003 etc.). HC resources decreasing from Persian Gulf to North Caspian Sea

• Lesser order HC zoning (west to east: oil - gas) in the S-M Caspian Sea exists. Is Great Caucasus a barrier for HC in lesser order?
• A regional tectonic - HC correlation in Iraq - South Caspian- Turkmenistan exists: more compression and oil in west of region versus less compression and gas in the east of region up to the east Turkmenistan with, however, non-deep sea conditions (transitional facies) in the latter. Moreover, unusual several times repeating of oil - gas - gas-condensate in a stratigraphic section is revealed in west Turkmenistan. Is it a result of deep fluids input too? HC behavior and zoning is not quite clear in this unique economic and geological region.
• Other HC north-south (N-S) zoning is as follows: HC in the old rocks - since Devonian up to Paleogene (D-Pg) – North Caspian Sea vs. HC in Triassic-Jurassic, Paleogene rocks in the Middle Caspian Sea, and in Low Pliocene (N2) rocks - South Caspian Sea. It could be in agreement with northeastern (NE) superplume activity decreasing. Giant HC resources in Saudi Arabia – Caspian region could be related with this hot regime. HC localizations are in agreement with a regional general geology. Surely, the oil genesis is traditional – organic one.

There is a good correlation as detailed HC structural map - HC maximum. It is in agreement with a young concrete HC localization despite the different age of host rocks.  Mud volcanoes (Kholodov, 2012 etc.) – HC – Salt – magmatism - tectonics in this region studied is the one system.    

This work was made due to the State program of the Geological Institute RAS.

How to cite: Romanko, A., Imamvderdiyev, N., Vikentiev, I., Rashidi, B., Heidari, M., and Poleshchuk, A.: On a tectonics, magmatism and hydrocarbons (HC, oil-gas) of the South Caspian - West Baluchestan, Middle East: some problems and constraints, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20570, https://doi.org/10.5194/egusphere-egu24-20570, 2024.

Finding of the giant diamond in Ebelyakh of CLIPPIR type of IIa type (Moor, 2014) suggest that similar diamonds should be found in the source kimberlites in Anabar basing and nearest Northern fields located within collision Khapchan terrain. To predict the finding authors are using the method of 5E diagrams based on the principle of analogy of the compositions Fe/(Fe+Mg) – Cr/(Cr+Al) – (Mn,Na) (Mitchell, 1986) for satellite minerals (Gar, Cpx, Chr and Ilmenites) of diamond (DSM) comparing with the etalon diagram for Karowe pipe (reference) and any other pipe. The forecast is quantified by the probability of convergence of these compositions using the division to the cluster groups. It was shown that the convergence of the DSM compositions of the Karowe and Grib pipes is 74%, which can be regarded as an indicator of the possible presence of diamonds in the predicted CLIPPIR pipe (Zinchenko et al., 2021).

 The application of this technique to two weakly diamondiferous kimberlite pipes of the Anabar region is demonstrated that the Leningrad pipe (Lower Devonian) have probability (75%) and Malokuonamskaya (Lower Triassic) (20%). Methods of constructing 5E diagrams and complementary PTXfO₂ diagrams by I.V. Ashchepkov (2010-2023) of reconstructed lithospheric mantle sections (SCLM) to predict the crystallization of CLIPPIR diamonds. The petrological meaning of such characteristic suggest diamond formation in pipe in permeable mantle within protokimberlite magmatic chamber located near the lithosphere boundary and  connected with the asthenospheric source supplying by low oxidized magma, sulfides and extra pressure. The pipe should be surrounded by the low oxidized mantle eclogites rich C and dunites with the high pressure-temperature and Mg-rich ilmenite-chromite metasomatites.

A.

B.

Fig.1.  Mitchels’s diagram for minerals from Leningrad  and Malokuhamskay (B) pipes in comporisond with the Karowe pipe (contur lines) Cr- pyropes, Cr-diopsides, Ilmenites, Cr -spinels together. B. Triangle Na-Mn-Ti and C. Triangle Na-Al-Cr for Cr-diopsides and pyropes. D. distributions of the cluster groups for different minerals. E. Correltions of diamond grade with TiO₂ in garnest, Cr-diopsides and Cr-spinels and Fe₂O₃ in ilmenites

The application of this technique to two weakly diamondiferous kimberlite pipes of the Anabar region is demonstrated that the Leningrad pipe (Lower Devonian) have probability (75%) and Malokuonamskaya (Lower Triassic) (20%). Methods of constructing 5E diagrams and complementary PTXfO₂ diagrams by I.V. Ashchepkov (2010-2023) of reconstructed lithospheric mantle sections (SCLM) to predict the crystallization of CLIPPIR diamonds. The petrological meaning of such characteristic suggest diamond formation in pipe in permeable mantle within protokimberlite magmatic chamber located near the lithosphere boundary and  connected with the asthenospheric source supplying by low oxidized magma, sulfides and extra pressure. The pipe should be surrounded by the low oxidized mantle eclogites rich C and dunites with the high pressure-temperature and Mg-rich ilmenite-chromite metasomatites.

A.

B.

C.

Fig.2. PTXFO₂ diagram for all xenocrysts from Leningrad (A), Malokuonamskaya (B) and Karowe AK-6 pipes. Symboles see legend

Russian Science Foundation grant 23-17-00030

How to cite: Ivanov, A., Zinchenko, V., Ashchepkov, I., Babushkina, S., Oleinikov, O., and Shelkov, P.: The perspectives of finding of giant CLIPPIR-type diamonds in weakly diamondiferous kimberlites of the north of Yakutia (Western Anabar region) using method of 5E Mitchells’s diagrams and cluster analyses, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3574, https://doi.org/10.5194/egusphere-egu24-3574, 2024.

The modal metasomatic alteration for lithosphere mantle may be investigated using mantle xenoliths from kimberlite pipes. The pyroxenite xenoliths from diamondiferous upper-Devonian Udachnaya kimberlite pipe (Daldyn field, Yakutia) were studied, mineral chemical composition was researched. The several stages of metasomatic processes were observed in the lithospheric mantle under the Udachnaya kimberlite pipe.

The most garnets from studied xenoliths demonstrated so-called “normal” trace element distribution that closed to the element coefficients the basalt - silicate melt. All garnets are characterized by a maximum in Ta, a minimum in La-Ce, and a minimum in Ti. Eclogites (especially with a mosaic texture) are characterized by a small minimum in Eu, which may indicate the presence of Pl in the initial rock. The presence of eclogitic xenoliths (with Eu-minimum in garnet) indicates the influence of the subduction component. The pyroxenite xenoliths with narrow variations in the composition of minerals indicates their crystallization from melts, accompanied later by metamorphic recrystallization. The 10% studied xenoliths are observed the secondary metasomatic amphibole (pargasite - taramite) - the evidence of modal Amph metasomatism. The Ti/Eu – La/Yb distribution for clinopyroxene and amphibole demonstrate the influence of silicate (not carbonatite) melts.The increasing concentrations of HFSE and REE group elements can also be traced by the Cpx and Grt chemical composition, it may be indicating the asthenospheric melts. Several garnet samples from high-Zr (80–100 ppm) eclogites demonstrated the features of fluid metasomatism (fluid-produced, accompanied by phlogopite crystallization). Another sign of the alkaline melts influence is secondary Na silicates crystallization (according reaction Grt + Omphacite + K - Fluid = Amph + Сpx2 ± Cal ± Sodalite).

Thus, several stages of metasomatic processes were observed in the lithospheric mantle under the Udachnaya kimberlite pipe. The presence of eclogite xenoliths (with a Eu minimum) indicates the influence of a subduction component. The presence of pyroxenite xenoliths with narrow variations in mineral composition indicates their crystallization from melts - the second stage of metasomatic processes, subsequently be accompanied by metamorphic recrystallization. The content of trace elements in garnets indicates the asthenospheric nature of the melts. Such melts brought elements of the HFSE and REE groups, as well as Pt, Pd and Re. The last stage is most clearly traced using modal Amph metasomatism. The presence of secondary amphibole indicates widespread occurrence of silicate pre-kimberlite metasomatism in the lithospheric mantle beneath the center of the Siberian craton.

The research was supported by Russian Science Foundation grant № 22-77-10073.

How to cite: Kalashnikova, T. and Kostrovitsky, S.: The silicate and carbonatite metasomatic alterations in lithospheric mantle under Siberian craton (the evidence of mantle xenoliths from Udachnaya pipe), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11448, https://doi.org/10.5194/egusphere-egu24-11448, 2024.

Comparative study of the mantle xenocrysts from Anabar region (Ary-Mastakh, Dyuken, Orto-Yargyn fields) and Boomerang kimberlites and pipe show essential differences with the mantle in surrounding area from Olenek (Chomurdakh field)

The PTX diagram show presence of the rare lherzolitic pyrope and abundant eclogitic almandines to 6 GPa. In suture zone of Daldyn and Magan terranes (Boomerang pipe) eclogitic omphacites and Cr less pyroxenites and Cr diopsides occurs mainly in the middle mantle part the pyroxenite layer possibly formed after eclogites due to plume melt interaction. Long ilmenite fractionation trend extends from the lithosphere base to the GPa 2.5, which is typical. Geochemistry of minerals vary from most depleted pyropes with V-U shaped REE patterns typical of arc mantle and Ba, U peaks and HFSE minima of subduction type. The fertilization produced the increase of the incompatible elements and sometimes LILE and The marginal parts of the SCLM of Anabar shield are extremely enriched in eclogitic deep-seated material located in lower SCLM part and demonstrating similar thermobarometric trends and features to the diamond inclusions from the Ebelyakh (Mayat) placers. Mantle column beneath several pipes (Losi, Universitetskaya, Kuranakh) contain Cr amphiboles distributes from lithosphere base to Moho. Comparison of reconstructed SCLM beneath Anabar and Chomurdakh field reveal more fertile compositions of the mantle rocks and simpler structure for later field. Abundance of eclogites in Kuranakh and Orto-Yargyn kimberlite in the lower mantle lithosphere part and their PTX trends are similar to the eclogitic diamond inclusions from the Ebelyakh placers. This increase the possibility of finding of diamonds deposits in Anabar shield kimberlites.

RNF grant No. 24-27-00411

How to cite: Kostrovitsky, S., Ashchepkov, I., Babushkina, S., and Mdevedev, N.: Reconstructions of mantle structure beneath kimberlites of Anabar shield and surroundings – similarities and differences., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14806, https://doi.org/10.5194/egusphere-egu24-14806, 2024.