Displays

Many processes in the earth involve the melting of rocks and the percolation of the produced melt through the residuum. These processes have been extensively studied but there is still much left what is not completely understood. In this work we focus on the emergence of solitary porosity waves, which can emerge from disturbances in regions where melt is allowed to percolate relatively to the matrix. These waves are regions of higher melt fractions that ascend with a constant velocity while not changing their shape during this ascending process. The size of these waves depends on the compaction length, which depends on just poorly known parameters such as the permeability and the viscosity of the matrix. As they can vary over several orders of magnitudes it might have a strong influence on porosity waves and their emergence from local disturbances with higher porosities than the background.

In this work we start with a 2D Gaussian-bell shaped disturbance with a certain porosity amplitude and vary the initial radius which is non-dimensionized by the characteristic compaction length. For some cases this disturbance results in an ascending solitary wave and for others it rises upwards as a diapir. For a few cases a kind of fingering can be observed which  looks like a small emerging porosity wave which is just slightly faster than the following melt of the initial larger disturbance. This leads to a melt ascent with a strongly focused front.

Comparison of porosity wave dispersion curves with analytical ascent rates of a Stokes sphere helps explaining this transition of diapirs to solitary waves via a melt ascent with a strongly focused front.

How to cite: Dohmen, J. and Schmeling, H.: The transition between solitary wave and diapir emergence from a high porosity disturbance in two-phase flow, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7959, https://doi.org/10.5194/egusphere-egu2020-7959, 2020.

Noble gas isotopes have been used to argue that hotspot volcanism taps a deep reservoir in the mantle that has remained largely isolated since the accretion of the Earth.  In order to evaluate the viability of this theory, it is important to understand how noble gases are stored at high pressure, and how processes such as melt separation may influence their transport.  Previous work (eg. Heber et al. 2007) has investigated the partitioning of noble gases in upper mantle minerals (olivine and pyroxenes), but as yet no data are available for other important phases, including garnet and higher-pressure minerals.  This study presents data collected from multi-anvil experiments at 6 GPa and 1700 °C – 1900 °C on artificial basalt compositions similar to those found at ocean island hotspots.  This composition has garnet on the liquidus at these conditions, and we have successfully quenched the melt to a glass.  The partitioning of noble gases between liquidus garnets and co-existing melts has been evaluated using a microprobe and laser ablation mass spectrometry to analyse the gas contents of the two phases.  These results shed light on the behaviour of noble gases in the presence of minerals that have, as yet, not been investigated for their ability to store such volatiles, and on the likelihood of the deep-untapped-reservoir theory.

How to cite: Flanigan, M., Frost, D., Withers, T., and Keppler, H.: Garnet-melt noble gas partitioning and its relevance to the deep isolated reservoir hypothesis, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9256, https://doi.org/10.5194/egusphere-egu2020-9256, 2020.

Sulphide inclusions in diamonds are commonly used for determining both the timing and lithology of diamond formation. Most sulphide inclusions were trapped as melts which then crystallized as Fe-Ni rich monosulphide solid solutions (MSS). Upon cooling below ~1000°C the inclusions recrystallize to phases such as pyrrhotite, Fe_(1-x)S (x = 0 to 0.2), and pentlandite, (Fe,Ni)₉S₈, and sometimes pyrite (FeS₂) depending on the bulk composition. Previous experimental studies have shown that oxygen can also partition into sulphide melts. Moreover, measurements of natural sulphide inclusions in diamonds show measurable oxygen concentrations. A systematic parameterization of factors that control the oxygen concentration of sulphide melts in the mantle could be potentially used to understand formation conditions of diamonds.

We performed a series of high pressure (3-15 GPa) and high temperature (1373 - 2000 K) multi anvil experiments to equilibrate a fertile peridotite (KLB-1) mixture with molten sulphide (FeS). The effects of pressure, temperature, oxygen fugacity and composition (both silicate and sulphide) on oxygen content in sulphide melt have been investigated. We also examined the effect of Ni content in sulphide on the oxygen concentration. Iridium was also added in some experiments in sufficient quantities to saturate the sulphides and produce Fe-Ir alloy, which was used to determine the oxygen fugacity of the experiments. Run products consisted of mantle silicate minerals and quenched sulphide melts. Chemical compositions were analyzed using the electron microprobe.

Our experiments show up to 16 mole% of FeO in the sulphide melts at relevant mantle conditions. Moreover, the oxygen content of the sulphides was found to be relatively independent of changes in fO₂ or fS₂, which is in contrast with experimental studies conducted at ambient pressures. Results indicate that the oxygen concentration is primarily controlled by the FeO activity in coexisting silicate phases and the temperature.

By fitting the experimental data, we have developed a thermodynamic model using an end-member equilibrium between olivine, pyroxene and FeO in the sulphide melt. The standard state Gibbs free energy change (ΔG⁰) of the equilibrium is calculated using known activity composition relations for the silicates and by refining non-ideal interaction parameters for the sulphide melt in the system FeO-FeS-NiS system. The ΔG⁰ is well determined as a function of temperature and shows no discernible dependence on pressure. The resulting relationship was used to calculate equilibrium temperatures of natural sulphide inclusions in diamonds. Using our new geo-thermometer, previously measured oxygen concentrations in natural sulphide inclusions in diamonds from the Slave craton reveal temperatures for lithospheric diamond formation generally in the range of 1200 – 1300°C

How to cite: Abeykoon, S., Frost, D. J., Laurenz, V., and Miyajima, N.: The oxygen content of sulphide inclusions in diamonds and its use as a mantle geothermometer, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22685, https://doi.org/10.5194/egusphere-egu2020-22685, 2020.

Whether in gases or fluids, as solid or liquid carbonates, dissolved in magma or precipitated in its elemental form, carbon is present in every domain on Earth. The pathways of carbon across atmospheric-, surface-, subduction- and deeper reservoirs of our planet are complex, but can be illuminated by tracing stable carbon isotope ratios. Carbonates take a key role in connecting the surface to the deep carbon cycle. At moderate temperatures, carbon compounds dissolve in fluids, above 1000 °C, carbonates dissolve in or form melts and mobilize carbon inside the Earth. Towards the crust, carbon compounds tend to be oxidized (e.g. CO₂, CO₃^2-) while in the deeper mantle (> 6-8 GPa), reduced states are dominant and cause carbonate reduction to CH₄, FeC or C dissolved in metal, graphite or diamond.^[1]

Recent experimental studies show large carbon isotope fractions at temperatures relevant for the mantle and early Earth environments (i.e. magma ocean surfaces). High temperature equilibrium fractionations have been constrained for CH₄-CO₂-CO^[2], carbonate - graphite^[3], and FeC - graphite^[4] systems, most pairs amounting to a few ‰ at 1000 ^oC. The recognition of kinetic carbon isotope fractionation during elemental carbon precipitation from C-O-H fluids revealed an unexpected high-temperature fractionation mechanism of ~5 ‰ for lower crust and mantle temperatures^[5]. In this light, carbon isotope fractionation may yield surprises in other experimentally underexplored processes. 

We present internally consistent experimental data on high temperature carbon isotope fractionation between carbonate or silicate melts, carbonate, C-O-H-fluids, carbide and graphite. Our results suggest that at high temperatures (>1000 °C) the bonding environment of CO₃-groups (i.e. either in depolymerized silicate- or carbonate melt, in which carbon is anionic CO₃^2-, or as calcite) causes no resolvable differences leading to a universal ∆¹³C (CO₂ -CO₃^2-) fractionation function. Similarly, we suggest that granitic melts with all carbon as molecular CO₂will show no isotope fractionation with an oxidized high temperature fluid. We further discuss challenges of experimental setups under reducing fO₂conditions and the intent of equilibrating silicate melt with reduced C-O-H-fluids, which is experimentally unconstrained and required to understand on one hand the magmatic outgassing of the Earth and how to reconstruct the source isotope composition, on the other hand in a magma-ocean setting, where reduced species are key for the evolution of primitive carbon reservoirs and their isotopic ratios (i.e. mantle carbon).

^[1] Rohrbach, A., Schmidt, M. (2011). Nature 472, 209–212.^[2] Kueter, N., Schmidt, M. W., Lilley M. D., Bernasconi, S.M. (2019b). EPSL 506, p.64-75. ^[3] Kueter, N., Lilley, M.D., Schmidt, M.W., Bernasconi, S.M. (2019a). GCA253, 290–306. ^[4] Satish-Kumar, M., So, H., Yoshino, T., Kato, M., Hiroi, Y. (2011). EPLS 310, 340–348. ^[5]Kueter, N., Schmidt, M. W., Lilley M. D., Bernasconi, S.M. (2020). EPSL 529,115848

How to cite: Petschnig, P., Kueter, N., and Schmidt, M.: Fractionation of Carbon Isotopes Between C-O-H Fluids and Melts in High Temperature Systems - Experimental Developments and Outlook, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21481, https://doi.org/10.5194/egusphere-egu2020-21481, 2020.

The Madiapala syenite massif is situated within the host Alldays TTG gneisses in the western part of the Central Zone(CZ) of the Limpopo Complex (South Africa). The age of the massif 2010.3±4.5 Ma corresponds to the period of Paleoproterozoic tectono-thermal event(D3/M3) in the CZ, which was characterized by fluid activity along regional and local shear-zones.

The model for the syenite rocks formation within the TTG gneisses was suggested in [1] on the basis of experiments on the interaction of a biotite-amphibole tonalite gneiss with H₂O-CO₂-(K,Na)Cl fluids at 750 and 800^oC and 5.5 kbar. These experiments demonstrated that the leading factor for formation of the syenite assemblages in a tonalite gneiss is an increase of potassium activity in a fluid. Thus, the Madiapala syenites could be a product of the syenitization of the TTG gneisses. ICP-MS and ICP-AES for the syenite rocks, syenitized gneisses and host TTG gneisses reveal two varieties of syenite rocks in the massif (syenites and syeno-diorites), confirm the crustal source of the syenites and their close genetic relationship with the Alldays tonalite gneisses. The REE pattern for the syenite rocks indicate active crystallization differentiation within the syenite massif.

The earliest assemblage of the syenite rocks is K-feldspar + clinopyroxene + titanite ± apatite. The latter assemblage is albite+amphibole. In order to estimate the conditions for formation of the earliest assemblage, we constructed the P-T pseudosections for syenite assemblage and isopleths of Na and #Mg in clinopyroxene coexisting with K-feldspar and titanite using the PERPLE_X software. It showed that the earliest assemblage was formed in the temperature range 800-850^oC and pressures between 6 and 9 kbar. The lg(a_H2O) – lg(a_K2O) pseudosections for the Alldays gneiss composition showed that the formation of the syenite assemblage proceeds via the increase of the K₂O activity at constant P and T.

In order to reproduce the syenite mineral assemblage, experiments on the interaction of a biotite tonalite Alldays gneiss with a H₂O-CO₂-(K,Na)Cl fluid with variable salt concentrations were performed at 850^oC and 6 kbar for 10 days using an internally heated gas pressure vessel. The starting materials were cylinder fragments of the Alldays gneiss and a mixture of oxalic acid with KCl and NaCl as a fluid.

Run products of experiments with KCl contain the assemblage of clinopyroxene + K-feldspar + titanite formed by reactions of Ti-bearing biotite with quartz and plagioclase, initiated by the alkali-bearing aqueous-carbonic fluid. At the run temperature, the assemblage coexists with a syenitic melt enriched in F, Cl and H₂O, which was confirmed by Raman spectroscopy of studies of quenched glasses. Amphibole was formed only in the experiments with NaCl. Thus, the formation of amphiboles can be attributed to a later stage of the massif evolution, which was characterized by an increase in chemical potential of sodium. This result is consistent with the suggested model for the formation of the Madiapala syenite rocks.

This study is supported by RSCF project No18-17-00206

Literature
1. Safonov O. G., Aranovich L. Y. Alkali control of high-grade metamorphism and granitization//Geoscience Frontiers. 2014. Vol.5. pp.711-727.

How to cite: Seliutina, N., Safonov, O., and Varlamov, D.: Syenite formation after TTG gneiss: evidence from the Madiapala massif (Limpopo complex, South Africa) and experiment, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-137, https://doi.org/10.5194/egusphere-egu2020-137, 2020.

The aim of the research is to construct a mathematical model of the formation of a fracture system in magma intrusion in the permeable zones of the lithosphere and on this basis to study the formation of magmatic channels in the lithosphere and crust. The lithosphere substrate is modeled by a saturated porous medium in which the processes of small-scale destruction in the mantle magma intrusion lead to the formation of faults and, consequently, to a magmatic channel. Destruction and occurrence of micro-fracture fields can be associated with both magma flow and external seismic effect leading to the rock breaking. The process of small-scale destruction is described within the framework of the dynamics of the elastoplastic fracture-porous medium and causes variations in the rheological properties of the lithosphere substrate. A feature of this process is the destruction substrate in the compression zone represented by a narrow area with a sharply changing concentration of micro-fractures. The micro-fracture accumulation provides the conversion of the broken area into a macro-fissure. The elastoplastic porous matrix in the destruction zone contains both broken and intact substrate, the relative content of which is determined by relaxation of deformations, the speed of which depends on stress and yield stress point according to the power law. The obtained mathematical model provides investigation of currents in fractured-porous media and their effect on the small-scale destruction. Based on the TVD-Runge Kutta method numerical simulation of the compressible fluid infiltration into the fracture-porous permeable channel has shown that stresses in the compression domain can reach stress limits of breaking and result in fracture formation. Change in relaxation time does not result in a marked change in stress fields. The concentration of maximum stresses is observed in the channel center leading to an increase in its fracture porosity. The computational results show the appearance of high stress values in the compression domain in the process of a liquid phase injection, for instance, magma, into a low-permeable fracture-porous layer. The introduction of the destruction criterion will help to associate the occurrence of such regions to the local breaking of the porous matrix. Thus, the proposed micro-fracture generation mechanism can be used to describe the formation of fracture or channels in micro-fracture porous media. Work is done on state assignment of IGM SB RAS with partial support from the Russian Foundation for Basic Research, grants No. 16-29-15131, 19-05-00788.

How to cite: Perepechko, Y., Sorokin, K., and Vasilyev, G.: Modeling of magmatic channel formation in thin lithosphere areas, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19839, https://doi.org/10.5194/egusphere-egu2020-19839, 2020.

We investigated the processes beneath the Avacha volcano using mantle peridotite xenoliths  the with the EPMA, electronic microscope and ICP methods and  numeric modeling of the mass transfer accounting the melt fluid reactions with peridotites

The decompression melting processes  in peridotites beneath Avachinsky volcano (Kamchatka) are associated with seismic events. After the reactions with the Si, Ca, Na, K  from partial  melts associated  with  the  subduction related fluids the spinel and orthopyroxene were melted and essentially clinopyroxene veins were formed. Secondary crystals growth in the mantle xenoliths (with melt and fluid inclusions) are associated possibly with  the fluids appeared  due to retrograde boiling of the magma chamber beneath the volcano.

The processes of sublimation and recrystallization of  Avacha harzburgites was investigated at the facility in the Institute of  Nuclear Physics (Novosibirsk, Russia), which generates high-density electron beams and makes it possible to obtain boiling ultrabasic and basic liquids and condensates of magmatic gas on the surface of  harzburgite.

Results of  experiments provides a satisfactory explanation for the observed local heterophase alterations within ultramafic rocks that have experienced multistage deformation beneath volcanoes of the Kamchatka volcanic front.

Mathematical model of convective heating and metasomatic reactions in harzburgites were modeled using the  Selector PC thermodynamic software. The obtained virtual dynamic patterns of metasomatic zoning across the mantle wedge show   how   composition   variations   of   fluids   and  PT  conditions   at   their   sources   influence   the   facies   of   metasomatized   mantle   wedge harzburgite.   Such processes are apparently common to seismically  deformed   permeable   lithosphere   above   magma   reservoirs.  

There are two regions fluid filtration conditions under the Avachinsky volcano which are regulated by the tectonic conditions. The lower field where compression conditions prevail. And the upper field, where the prevailing tensile conditions and intense seismic destruction of the rocks of the crust and upper mantle. The heat flux distribution shows the manifestation of the convective heating mechanism in the earth's crust over the most permeable fault zones.

The study of the composition of the gas phases and melt inclusions suggests that the partial melting of metasomatized ultrabasites occurs in the range of 1150 ° C <T <1200 ° C.

In accord with the composition of the glassy phase in the melt inclusions of spinel crystals, the harzburgite metasomatism in the local melting sites is associated with brine melts that bringing Ca, K, Na, Si. C. The work was financially supported by the Russian Foundation for Basic Research, Grants No. 16-29-15131, 16-01-00729.

References

Arai S., Ishimaru S. Insights into Petrologycal Characteristics of the Lithosphere Mantle Wedge beneath Arcs through Peridotite Xenoliths: a Review.// J. Petrol., 2008. V.49(4), 359-395.

Tomilenko A.A., Kovyazin S.V., Sharapov V.N., Timina T.Yu., Kuzmin D.V. Metasomatic recrystallization and melting of ultrabasic rocks of mantle wedge beneath Avacha Volcano, Kamchatka // ACROFI III and TBG XIV Abstracts Volume / SB RAS IGM, Novosibirsk: Publishing House of SB RAS, 2010, p. 248-249.

How to cite: Kuznetsov, G. and Sharapov, V.: Features of heat and mass transfer processes under the Avachinsky volcano (Kamchatka), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-362, https://doi.org/10.5194/egusphere-egu2020-362, 2020.

Deep sourced magmas play a key role in distribution of carbon in the Earth’s system. Oceanic hotspots rooted in deep mantle usually produce CO₂-rich magmas. However, the association of CO₂ with the origin of these magmas remains unclear. Here we report geochemical analyses of a suite of volcanic rocks from the Caroline Seamount Chain formed by the deep-rooted Caroline hotspot in the western Pacific. The most primitive magmas have depletion of SiO₂ and high field strength elements and enrichment of rare earth elements that are in concert with mantle-derived primary carbonated melts. The carbonated melts show compositional variations that indicate reactive evolution within the overlying mantle lithosphere and obtained depleted components from the lithospheric mantle. The carbonated melts were de-carbonated and modified to oceanic alkali basalts by precipitation of perovskite, apatite and ilmenite that significantly decreased the concentrations of rare earth elements and high field strength elements. These magmas experienced a stage of non-reactive fractional crystallization after the reactive evolution was completed. Thus, the carbonated melts would experience two stages, reactive and un-reactive, of evolution during their transport through in thick oceanic lithospheric mantle. We suggest that the mantle lithosphere plays a key role in de-carbonation and conversion of deep-sourced carbonated melts to alkali basalts. This work was financially supported by the National Natural Science Foundation of China (91858206, 41876040).

How to cite: Zhang, G.: Evolution of deep mantle sourced carbonated melt in the mantle lithosphere, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13055, https://doi.org/10.5194/egusphere-egu2020-13055, 2020.

On the diagram of uranogenic leads, we define 1.88 Byr locus of lithospheric sources for low-Mg rocks from Wudalianchi and a non-lithospheric recently homogenized material (referred to the Molabu source) for moderate-Mg rocks. Lithosphere-derived liquids were characteristic of the initial Laoshantou and Old Gelaqiushan lava flows erupted along a north-south volcanic line 2.5–2.0 Myr ago. Due to eastward expansion of the Wudalianchi melting anomaly, its NNE limit was designated by lithosphere-derived liquids erupted in North Gelaqiushan and Weishan volcanoes between 0.6 and 0.4 Myr ago. In the evolution of the melting anomaly, other volcanoes showed compositions derived due to mixing lithospheric and non-lithospheric components. The only exception was moderate-Mg rocks from East Longmenshan volcano that yielded peculiar compositions modified after liquids from the Molabu source. Decreasing Pb, S, and Ni abundances, Ni/Co, Ni/MgO ratios as well as increasing ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb, ²⁰⁸Pb/²⁰⁴Pb, Ce/Pb, Th/Pb, and U/Pb ratios are indicative for liquids likely affected by segregating small amounts of sulfide droplets. We infer that the Wudalianchi melting anomaly was firstly generated in the lithosphere and was evolved to melting of the sub-lithospheric medium.

This work is supported by the RSF grant 18-77-10027.

How to cite: Chuvashova, I., Yasnygina, T., Saranina, E., Sun, Y., and Rasskazov, S.: Evolution from lithospheric to sub-lithospheric potassic liquids with sulfide droplets in Wudalianchi, NE China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12311, https://doi.org/10.5194/egusphere-egu2020-12311, 2020.

On the one hand, Pb isotope data on 18–13 Myr volcanic rocks from the eastern part of the Tunka Valley yield age estimate of garnet-bearing source region in the viscous mantle of ca. 2.2 Byr that might correspond to the age of the Siberian craton mantle. On the other hand, inclusions from basanites show the pressure range that overlaps the pressure estimates for rocks of the Slyudyanka Ordovician collision zone. The lithospheric material corresponds to the transition from spinel-pyroxene to olivine-plagioclase facies of peridotites in the uppermost part of the mantle and lower-middle crust. V_S-data show a low-speed zone dipping from the central Tunka valley eastwards under Southern Baikal to a depth of 70 km. This zone ends at the South Baikal – Tunka Valley junction. We suggest that the eastern parts of the Tunka Valley has inherited the Early Paleozoic collision zone between the Hamar-Daban Terrane and Siberian Paleo-Continent and that the lithosphere of the collision zone overlays the viscous mantle related to the Siberian craton.

This work is supported by the RSF grant 18-77-10027.

How to cite: Yasnygina, T., Rasskazov, S., Ailow, Y., Chuvashova, I., Saranina, E., Mordvinova, V., and Khritova, M.: Accommodation of the Cenozoic Tunka Rift Valley at the Ordovician Slyudyanka Collision Zone: insight into volcanic sources, deep-seated inclusions, and seismic tomography models, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19714, https://doi.org/10.5194/egusphere-egu2020-19714, 2020.

The Late Triassic basaltic rocks that are dispersed as several lava sheets in a number of different tectonic slices within the Antalya nappes in SW Turkey represent the remnants of widespread oceanic magmatism with strong intra-plate geochemical signatures. The largest exposures are observed around the Antalya Bay, where pillow structured or massif lava flows are interlayered with Upper Triassic pelagic or carbonate platform sediments. Based on bulk-rock geochemical characteristics, the rocks mostly classify as alkaline basalts and display distinctive OIB-type trace element distributions characterized by significant enrichments in LILE and HFSE abundances, as well as LREE/HREE ratios, with respect to average N-MORB. Quantitative modeling of trace element data suggest that the primary melts that produced the alkaline lavas are largely the products of variable proportions of mixing between melts generated by variable, but generally low (<10) degrees of partial melting of more than one compositionally distinct mantle source. The samples, as a whole, display large variations in radiogenic isotope ratios with ⁸⁷Sr/⁸⁶Sr = 0.703021–0.70553, ¹⁴³Nd/¹⁴⁴Nd = 0.51247–0.51279, ²⁰⁶Pb/²⁰⁴Pb = 18.049–20.030, ²⁰⁷Pb/²⁰⁴Pb = 15.544–15.723 and ²⁰⁸Pb/²⁰⁴Pb = 38.546–39.530. Such variations in isotopic ratios correlate with the change in incompatible trace element relative abundances and reflect the involvement of a number of compositionally distinct mantle end-members. These include EMI and EMII type enriched mantle components both having lower ¹⁴³Nd/¹⁴⁴Nd than typical depleted MORB source with their contrasting low and high ²⁰⁶Pb/²⁰⁴Pb and ²⁰⁷Pb/²⁰⁴Pb ratios respectively, as well as a high time-integrated ²³⁸U/²⁰⁴Pb component with high ²⁰⁶Pb/²⁰⁴Pb at relatively low ⁸⁷Sr/⁸⁶Sr and εNd values. The results from trace element and radiogenic isotope data are consistent with the view that the initial melt generation was likely related to partial melting of the shallow convecting upper mantle in response to Triassic rifting events, while continued mantle upwelling resulted in progressively increased melting of mantle lithosphere that contained compositionally contrasting lithological domains with strong isotopic heterogeneities.

How to cite: Aldanmaz, E., Güçtekin, A., and Yıldız-Yüksekol, Ö.: Mantle source characteristics of Triassic alkaline lavas within the Antalya Nappes, SW Turkey , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6775, https://doi.org/10.5194/egusphere-egu2020-6775, 2020.

In Mongolia, East Asia, intraplate magmatism has occurred intermittently from the late Cretaceous to present day. During the Mesozoic, basaltic volcanism was widespread across much of the southern and eastern parts of Mongolia. In contrast, the Cenozoic magmatism mainly extends in central parts of the country in a band trending north to south. This magmatism occurs in small, diffusely dispersed and relatively small volume (<30km²) plateaus (Barry et al., 2003). An exception to this is the Dariganga plateau in the southeast of Mongolia with >200 volcanic cones, covering an area of >10,000km². Windley et al., (2010) and Sheldrick et al., (2018), proposed that the Mesozoic magmatism was caused by widespread but patchy removal of lithospheric mantle from beneath parts of Mongolia, NE China and Russia. Although several models have tried to explain the Cenozoic magmatism in Mongolia, there is no clear evidence for the cause of the volcanic activity. Isotopic studies on volcanic rocks from the Hangai Dome in central Mongolia revealed an asthenospheric origin for the melts (Barry et al., 2003). Could the Cenozoic volcanism be the result of melts that originated during a Mesozoic event? These melts could have been trapped in the lithospheric mantle since the Mesozoic and variably remobilised more recently. Or is there a mechanism causing melting during the Cenozoic, which can give insights into present-day conditions in the underlying mantle? Here, we examine the possibilities of (a) a direct link between the late Mesozoic and Cenozoic volcanic events in Mongolia leading to a multistage modification of the melt composition and (b) mechanism(s) in the asthenosphere/lithosphere causing present-day melting. In order to assess these possibilities we will compare the melt sources of the magmatism, focusing on three contrasting regions. (1) In central Mongolia, Cenozoic basalts occur on the flanks of the uplifted Hangai Dome, which is thought to have been uplifted in the Mesozoic (McDannell et al., 2018) but did not experience any volcanism at the time. (2) The Gobi Altai, which experienced both Mesozoic and Cenozoic magmatism, separated by ~40-50 Ma gap, but did not undergo any Mesozoic uplift. And finally, (3) the Dariganga plateau, which has experienced extensive volcanism during the late Cenozoic but not during the Mesozoic and in contrast to Hangai, underwent Mesozoic basin development rather than uplift. We will compare and contrast mantle sources of these regions to determine whether Mesozoic events have influenced the composition of the Cenozoic magmatism. Additionally, study of tomographic images from the upper mantle below central Mongolia will help us identify possible mechanisms that could have contributed towards the present-day melting of the upper mantle.

How to cite: Papadopoulou, M., Barry, T., and Rutson, A.: Unravelling intraplate Cenozoic magmatism in Mongolia: Reflections from the present-day mantle or a legacy from the past? , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12002, https://doi.org/10.5194/egusphere-egu2020-12002, 2020.

The ultramafic xenoliths and megacrysts in the intraplate alkali basalts are one of the most important information sources about the composition of substance of the Earth’s mantle and the lower part of lithosphere outside the cratons. We studied alkali basalts of Shavaryn Tsaram Paleovolcano (Mongolia), which extraordinarily enriched with the different types of megacrysts and ultrabasic inclusions. We found large (up to 5 cm in diameter) garnet megacryst hosting an aggregate in its core. The aggregate is complex and consists of porous glass and crystallized minerals, such as biotite, orthopyroxene, spinel, clinopyroxene, olivine, and ilmenite. The question arises - Was it a captured substance of the Earth’s mantle/upper crust? Or it was a zone of partial melting inside the garnet megacryst, so-called ‘melt pocket’.

The composition of each phase of the garnet megacryst with inclusion was studding with microprobe and ion probe. The data of oxygen isotopy as well as X-Ray images of host garnet and mica from partly-crystallized inclusion were obtained. In addition, we used WinTWQ 2.32 in order to describe PT conditions of minerals forming.

The careful study showed that the system was not completely closed: the crystallization inside the host garnet megacryst occurred not only due to the garnet's own substance, but also due to supply of the magmatic material. There were at least two acts of receipt of the new substance. 1 portion penetrated into the fractured (probably, during the explosion) crystal of garnet and formed Mica, Spinel, Orthopyroxene, and Clinopyroxene. 2 portion had a basically different composition as evidenced ilmenite frosting on the spinel crystals, along with recrystallization of the orthopyroxenes peripheral parts.

WinTWQ 2.32 allowed us to reconstruct conditions of some phases of the garnet transformation. Some point after the formation this garnet megacryst becomes fractured. At T 1120-11400C, P 0.75-0.8 GPA it is captured by basaltic melt and basaltic melt penetrated into it. For some time the aggregate existed at stable conditions, during this time the idiomorphic crystals Mica, Spinel, and Opx (T 1000-11200C, P 0.6-0.7 GPA) were crystallized. At the final stage (metasomatic), symplectites were formed (at T 950-10300C, P 0.55-0.65 GPA).

Thus, the megacryst under consideration was a trap for the Earth’s upper crust substances. This rare finding contains evidence of both magmatic events (in secondary melt inclusion) and subsequent metasomatic events (in symplectites). Oxygen isotopy investigation showed that the host garnet and biotite, crystallized in the melt inclusion, has the same values of δ18O, indicating a common mantle source. However geochemical evidence registered supply of the material, which is alien to the garnet and the host alkali basalts.

How to cite: Aseeva, A. and Avchenko, O.: Unusual Garnet Megacryst with a partly-crystallized melt inclusion from Cenozoic alkali basalts of Shavaryn Tsaram Paleovolcano (Mongolia): a captured material of the Earth’s interior or a ‘melt pocket’, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1989, https://doi.org/10.5194/egusphere-egu2020-1989, 2020.

We proposed an assessment of the intensity of metasomatic processes in mantle sampled by kimberlites on the example of samples of pyrope compositions from kimberlites with a known diamond grade. The intensity of metasomatic dissolution was estimated on the Ti correlations,  for low and high- Cr  pyropes.

For the titanium content in the pyrope compositions, positive high correlation coefficients were determined for such elements as  Hf, Zr, .Na  typical for the processes of alkaline H₂O metasomatism. Binary diagrams makes it possible to determine the main relationship between the mineral-forming elements in the compositions of pyropes and its mineral impurities. Weconcluded that this metasomatism leads to the dissolution of low-chromic pyropes but diamonds still remain and may continue to grow. A higher degree of metasomatism the pyropes are characterized by a high content of titanium,  for pyropes with high chromium contents. High degree of metasomatosis, brings to dissolution of pyropes and diamonds.

Burren  kimberlite pipe Dennis, Pobeda, and Zarnotsa  contains more than 14 %  pyrope grains ad diamond affinity according to  to N. V. Sobolev . Dennis ans dimond bearing thhe Pobeda is burren and Zarnitsa ~0.3 crt/t 

It is considered [1-5] that if the sample contains grains from diamond-bearing eclogical parageneses, or creased percentage of grains from diamond-bearing parageneses according to N. V. Sobolev [1],should contain diamonds.  But  for pyropes containing chromium oxides, Cr pyropes with TIO₂ > 0.6 weight  %, should be burren.  As well  even if  there is  high grain content o from th cluster group G10 according to the classification Dawson J. B., Stephens W. E. [2] . Grant RFBR 19-05-00788.

1. Sobolev N. V., on mineralogical criteria of diamond-bearing kimberlites / / Geology and Geophysics. 1971. No. 3. - Pp. 70-80.
2. Garanin V. K., Kudryavtseva G. P., Marfunin A. S., Mikhailichenko O. A. Inclusions in diamond and dia-mond-bearing rocks. // Moscow, Moscow state University Publishing house, 1991, 240 p.
3. Dawson J. B., Stephens W. E. Statistical classification of garnets from kimberlites and xenoliths. J. Geol. 1975. Vol. 83. No. 5. P. 589-607
4. J. Gurney, R. O. Moore. Geochemical correlation between the minerals of kimberlites and diamonds of the Kalahari Craton, Journal. Geology and Geophysics, Moscow, 1994, p. 12-24
5. Ivanov A. S., a New criterion for diamond-bearing kimberlites. Proceedings of the XII all-Russian (with in-ternational participation) Fersman session. KSC RAS Apatity, p. 268 -270, 2015.

How to cite: Ivanov, A., Spetsius, Z., and Vavilov, M.: Criteria of the mantle metasomatism intensity and diamond grades of kimberliotes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2151, https://doi.org/10.5194/egusphere-egu2020-2151, 2020.

Most researchers believe that large igneous provinces (LIPs) are formed by adiabatic melting of heads of ascending mantle plumes. Because the LIPs have existed throughout the geological history of the Earth (Ernst, 2014), their rocks can be used to probe the plume composition and to decipher the evolution of deep-seated processes in the Earth’s interior.

The early stages of the LIPs evolution are discussed by the example of the eastern Fennoscandian Shield, where three major LIP types successively changed each other during the early Precambrian: (1) Archean LIP composed mainly of komatiite-basaltic series, (2) Early Paleoproterozoic LIP made up mainly of siliceous high-Mg series, and (3) Mid-Paleoproterozoic LIP composed of picrites and basalts similar to the Phanerozoic LIPs (Sharkov, Bogina, 2009). The two former types of LIPs derived from high-Mg depleted ultramafic material practically were extinct after the Mid-Paleoproterozoic, whereas the third type is survived till now without essential change. The magmas of this LIP sharply differed in composition. Like in Phanerozoic LIPs, they were close to E-MORB and OIB and characterized by the elevated and high contents of Fe, Ti, P, alkalis, LREE, and other incompatible elements (Zr, Ba, Nb, Ta, etc.), which are typical of geochemically enriched plume sources.

According to modern paradigm (Maruyama, 1994; Dobretsov, 2010; French, Romanowiсz, 2015, etc.), formation of such LIPs is related to the ascending thermochemical mantle plumes, generated at the mantle-liquid core boundary due to the percolation of the core’s fluids into overlying mantle. Thus, these plumes contain two types of material, which provide two-stage melting of the plume’s heads: adiabatic and fluid-assisted incongruent melting of peridotites of upper cooled margins (Sharkov et al., 2017).

These data indicate that the modern setting in the Earth’s interior has existed since the Mid Paleoproterozoic (~2.3 Ga) and was sharply different at the early stages of the Earth’s evolution. What was happened in the Mid Paleoproterozoic? Why thermochemical plumes appeared only at the middle stages of the Earth’s evolution? It is not clear yet. We suggest that this could be caused by the involvement of primordial core material in the terrestrial tectonomagmatic processes.  This core survived from the Earth’s heterogeneous accretion owing to its gradual centripetal warming accompanied by cooling of outer shells (Sharkov, Bogatikov, 2010).

References

Dobretsov, N.L. (2008). Geological implications of the thermochemical plume model. Russian Geology and Geophysics, 49 (7), 441-454.

Ernst, R.E. (2014). Large Igneous Provinces. Cambridge Univ. Press, Cambridge, 653 p.

French, S.W., Romanowicz, B. (2015). Broad plumes rooted at the base of the Earth’s mantle beneath major hotspots. Nature, 525, 95-99.

Maruyama, S. (1994). Plume tectonics. Journal of Geological Society of Japan, 100, 24-49.

Sharkov, E.V., Bogina, M.M. (2009). Mafic-ultramafic magmatism of the Early Precambrian (from the Archean to Paleoproterozoic). Stratigraphy and Geological Correlation, 17, 117-136.

Sharkov, E.V., Bogatikov, O.A. (2010). Tectonomagmatic evolution of the Earth and Moon // Geotectonics 44(2), 83-101.

Sharkov, E., Bogina, M., Chistyakov, A. (2017). Magmatic systems of large continental igneous provinces. Geoscience Frontiers 8(4), 621-640

How to cite: Sharkov, E., Bogina, M., and Chistyakov, A.: Development of deep-seated magma sources throughout the Earth’s history: Evidence from evolution of the large igneous provinces (LIPs), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4445, https://doi.org/10.5194/egusphere-egu2020-4445, 2020.

Geochemical, isotope-geochemical, geochronolochical and thermobarometric study showed that the Badzhal, Mayo-Chan and Kavalerovo zones from Sikhote-Alin-Northern Sakhalin orogenic belt comprise: (1) oldest and geochemically and isotopically distinctive alkali mafic rocks, whose formation was related to mantle (asthenospheric) diapir. The possible regional distribution of the diapir is likely marked by subalkaline rocks (monzonites) having mantle Sr (0,7050) and Nd (0,5125) isotopic compositions at the Central (Tigrinoe deposit) and Southern (Kavalerovo district) Sikhote-Alin; (2) Tin-bearing ore-magmatic systems of the studied zones at the “ore region” level have similar intricate multi-root structure of generation area. 3) Magmatic evolution accompanying by increasing ore-bearing potential results in the final appearance of Li-F granites in the Badzhal Complex, and tourmaline granites in the Silinka Complex of the Myao-chan zone (Gonevchuk, 2002).

The elevated F and Cl contents and high water content as parameters responsible for ore potential of melt were confirmed by thermobarometric data (Bortnikov et al, 2019). Some associations of fluid and melt inclusions indicate that magma crystallization was accompanied by degassing with exsolution of water-rich fluids, which is required to form ore bodies in OMS. These data confirm significant role of mantle in the formation of the Myao-Chan and Badzhal zones, as well as early cassiterite—stannite—sulfide stage of the Arsen’evskoe deposit of the Kavalerovo district.

Numerical simulation of granitoids of the studied zones performed using logical-information method by I.A. Chizhova (2010) confirms crustal-mantle nature of magmatic complexes formed under transform continental margin and subduction settings. These systems are characterized by different geochemical features, in particular, different proportions of high-field strength (Sc, Y, Zr, Hf, Pb, U, Th, Nb), REE, and siderophile (Co, Ni, Cr, V, Cu) elements.

Obtained results in combination with previous data indicate that the Badzhal, Myao-Chain, and Kavalerovo zones were formed through several episodes of the growth and reworking of the Sikhote Alin’ Mesozoic continental crust, which were triggered by underplating. Granitoids and genetically related tin—base metal deposits were formed at final stage. The revealed difference in Sr-Nd composition of the granitoids could be caused by both initial geochemical crustal heterogeneity and the different degree of crustal contamination.

Geochemical and isotopic characteristics of the studied granitoids show that they were mainly derived through melting of juvenile metamafic crust, with subordinate contribution of metasedimentary rocks.

The ore-bearing magmatic complexes were formed during a change of transform margin setting by accretion of Early Cretaceous terranes of the Sikhote Alin—North Sakhalin orogenic belt.

Observed petrogeochemical diversirty of the granitoids from different zones could be caused by variations of sedimentary material, as well as by contamination of magmas by upper crustal material during emplacement, different contribution of mantle source, and diverse mechanisms of mantle-crustal interaction (Khanchuk et al, 2019). 

Obtained petrochemical, geochemical, and isotopic-geochemical data on the granitoids from the studied zones provide better understanding of diversity of tin-bearing magmatism and conditions of magma generation and evolution in transform margin setting at the continent-ocean boundary.

How to cite: Gorelikova, N., Bortnikov, N., Khanchuk, A., Gonevchuk, V., Chizhova, I., Ratkin, V., and Sharkov, E.: Crust-mantle systems of magmatic complexes of Sikhote-Alin' (Far East, Russia), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22099, https://doi.org/10.5194/egusphere-egu2020-22099, 2020.

The Korvatundra complex is situated between the granite gneisses of the White Sea complex and the rocks of the Tana belt the Kola region (Kozlov et al., 1990; Priyatkina&Sharkov, 1979) and composed of  mica gneisses, schists and quartzite schists. The metamorphism of the complex increases from south to north from the staurolite-muscovite zone to kyanite-garnet-biotite (Map of the mineral facies, 1992; Perchuk&Krotov, 1998).

The U-Pb age of igneous zircon from the metavolcanite is 2101±21 Ma (Kaulina et al., 2003). The early stages of the progressive metamorphism reflected in relict paragenesis in the southern part were under the conditions of the staurolite-chloritoid and staurolite-garnet-two-mica subfacies with 385-570^оС and 4.6-7.6  kbar (Belyaev&Petrov, 2002).  The prograde metamorphism were under the conditions of the kyanite-garnet-micas and kyanite-garnet-biotite subfacies and are reflected in the composition of newly formed, chemically non-zonal garnets, or in the similar composition newly formed garnet rim. The metamorphism stage parameters determined by the garnet indicate increasing of the temperatures and pressures to 575-615^оС и 7.5-9.1 kbar  (Belyaev&Petrov, 2002) or to 650^оС  и 7.5 kbar (Perchuk&Krotov, 1998). The time of prograde metamorphism of the Korvatundra is in the interval 1940 and 1917 Ma. Within the Korvatundra the processes of superimposed tectonometamorphism occur under conditions of the kyanite-garnet-biotite subfacies and in the north of the Korvatundra their temperatures and pressures reach of 700-750 ° C and 13-14 kbar, correspondingly. 

This research was funded by GI KSC RAS program 0226-2019-0052 and Fundamental Program of the Presidium of RAS section “Fundamental geological and geophysical research of the lithosphere processes”.

Belyaev O.A, Petrov V.P. // Apatity: GI KSC RAS. 2002. P. 195-208.

Map of the metamorphic rock mineral facies of the Baltic Shield. S.-Pb.: VSEGEI. 1992.

Kaulina T.V., Dlenizin A.A., Belyaev O.A., Kozlova N.E., Apanasevich E.A. // S.-Pb.: IPG RAS. 2003. 189-193 p.

Kozlov N.E., Ivanov A.A., Nerovich L.I. // Apatity: KSC RAS, 1990. 172 p.

Perchuk L.L.., Krotov A.V. // Petrologia. 1998. V.7. №4. P. 356-381.

Priyatkina L.A., Sharkov E.V. // Leningrad: Nauka. 1979. 127 с.

How to cite: Nitkina, E., Belyaev (Ϯ), O., Kozlova, N., Kaulina, T., Sharkov, E., and Kozlov, N.: The timescale of the endogenous processes and PT conditions of garnet, biotite, and plagioclase equilibrium in the mica schists and gneisses of the Korvatundra complex (Kola region), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1559, https://doi.org/10.5194/egusphere-egu2020-1559, 2020.

The Pados-Tundra massif is located in the western Kola Peninsula and included in the Notozero ultrabasic rock complex (Vinogradov, 1971). The intrusion occurs as a body of ca. 13 km² stretched out to the north-east. Enclosing rocks are Archaean granite- and granodiorite-gneisses. There are three major areas in the massif structure (Mamontov, Dokuchaeva, 2005): endocontact area, rhythmically layered series, and upper area. The endocontact area with thickness of 10-20 m occurs as schistose amphibole rocks formed during the metamorphism of main rocks. The rhythmically layered series occurs as a number of rocks from dunites to orthopyroxenites and composes most of the massif. There are 7 rhythms in total, each of which starts with dunites and ends with orthopyroxenites. Dykes of mezo- and leucocratic gabbro, diorites, and hornblendites are developed in the series rocks. The upper gabbronorite area can be partially observed in the north-eastern massif. Presumably, its major volume has been overlapped by enclosing rocks as a result of the overthrust. In the massif, there are 4 horizons of disseminated stratiform chromite ores, which are confined to dunites and serpentinites, as well as to a number of lens- and column-like bodies (podiform type) of chromite ores (Mamontov, Dokuchaeva, 2005; Barkov et al., 2017). Previous isotope-geochronological studies have determined the massif rock age of 2.15 Ga (Shapkin et al., 2008). However, further geological field observations and analysis of the obtained data assume that the intrusive is much older.

New Sm-Nd geochronological data indicate that the massif rocks and its rhythmically layered series are of Paleoproterozoic age, which is similar to the age of the Cu-Ni-Co-Cr-PGE ore-magmatic system of the Fennoscandian Shield (Amelin et al., 1995; Bayanova et al., 2014, 2017, 2019; Hanski et al., 2001; Huhma et al., 1990, 1996; Layered intrusions ...; 2004; Maier, Hanski, 2017; Mitrofanov et al., 2019; Peltonen, Brugmann, 2006; Puchtel et al., 2001; Serov, 2008; Serov et al., 2014; Sharkov, 2006; Sharkov, Smolkin, 1997). Complex Sm-Nd and U-Pb isotope-geochronological studies have allowed determining the major formation and alteration stages of the Pados-Tundra complex rocks:

–  formation of the rhythmically layered series rocks of the intrusive 2485±77 Ma, harzburgites of the layered series – 2475±38 Ma;

– metamorphism of the massif rocks at the turn of 1.95 - 1.9 Ga;

– postmetamorphic cooling of the complex rocks tо 650°-600°С at the turn of 1872±76 Ma (Sm-Nd for metamorphic minerals) and then to 450°-400°С (U-Pb for rutile, 1804±10 Ma).

Therefore, the study results expand geography the East-Scandinavian large Palaeoproterozoic igneous province and are prospective for further study of analogous ultramafite-mafite complexes.

All investigations and were supported by the RFBR 18-05-70082, 18-35-00246, Presidium RAS Program #48 and are in frame of the Theme of Scientific Research 0226-2019-0053.

How to cite: Serov, P., Bayanova, T., Steshenko, E., Kunakkuzin, E., and Borisenko, E.: Evolution and metallogenic settings of the Pados-Tundra chrome-bearing ultramafic complex, Kola Peninsula: isotope Sm-Nd and U-Pb evidence, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4978, https://doi.org/10.5194/egusphere-egu2020-4978, 2020.

The Petyayan-Vara area of the alkaline-ultramafic carbonatite complex Vuoriyarvi, located in Kola region (NW Russia; N 66°47’, E 30°05’), hosts abundant REE-Sr-Ba-rich magnesiocarbonatite veins. Magnesiocarbonatites containing burbankite are primary magmatic. These rocks underwent alterations during several magmatic-metasomatic events, which resulted in the formation of other varieties of carbonatites, including ancylite-dominant and bastnäsite-dominant magnesiocarbonatites (ores). We studied the Sr-Nd-C-O isotopic characteristics of both the most common varieties of carbonatites of the Petyayan-Vara area and calciocarbonatites (søvites) of its nearest surroundings. The isotopic composition of the least altered magnesiocarbonatites (ε_Sr³⁷⁰=-13.9, ε_Nd³⁷⁰=5.2, δ¹³C_PDB=-3.8‰, δ¹⁸O_SMOW=9.9‰) is close to that of søvites (ε_Sr³⁷⁰=-13.5±0.1, ε_Nd³⁷⁰=4.95±0.05, δ¹³C_PDB=-3.85±0.25‰, δ¹⁸O_SMOW=7.9±0.7‰). Analysis of other Petyayan-Vara carbonatites (including ancylite and bastnäsite ores) showed wide variations in signatures of all studied isotopic systematics. All altered carbonatites are enriched with crustal strontium (ε_Sr³⁷⁰ of -12.8 to -2.0), and an increase in ε_Sr³⁷⁰ is accompanied by an increase in the content of heavy isotopes of carbon (up to -1.0‰) and oxygen (up to 23.8‰). Most Petyayan-Vara carbonatites (including ancylite ores) have close values of ε_Nd³⁷⁰=5.1±0.2. Isochron dating based on the figurative points of these rocks yielded an age of 365 Ma, indicating that the Sm-Nd radiogenic isotope system in the studied samples was unperturbed after carbonatites were crystallized. The similarity of the obtained ε_Nd³⁷⁰ value with estimates of this parameter for different (both carbonate and silicate) rocks of the Vuoriyarvi complex indicates the isotopic homogeneity of the mantle source and its small contamination with the crustal material. Samples with a disturbed Sm-Nd system (ε_Nd³⁷⁰ of -1.1 to 4.7) have petrographic signs of alterations during later processes (e.g., superimposed silicification, crystallization of the late strontianite, etc.). Bastnäsite ores also exhibit severely disturbed Sm-Nd system (ε_Nd³⁷⁰=2.9). The change in ε_Nd³⁷⁰ can be explained by either (1) an addition of crustal Nd or (2) chemical fractionation of Sm and Nd during events that occurred much later than the crystallization of Petyayan-Vara carbonatites. The obtained isotope data refine the sequence of the magmatic-metasomatic events that led to the formation of the Petyayan-Vara REE deposit, which we proposed earlier. They also clarify the contribution of the sources of elements and the scale of their redistribution at different formation stages of Petyayan-Vara carbonatites.

This research was funded by the Russian Science Foundation, grant number 19-77-10039. Field work was supported by the Geological Institute KSC RAS, state order number 0226-2019-0053.

How to cite: Kozlov, E. and Fomina, E.: Sr-Nd-C-O isotope composition of carbonatites of the Petyayan-Vara REE deposit (Vuoriyarvi, Kola Region, NW Russia): Insight to the origin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13114, https://doi.org/10.5194/egusphere-egu2020-13114, 2020.

The paper provides new U-Pb, Sm-Nd and Nd-Sr isotope-geochronological data on rocks of the Paleoproterozoic Kandalaksha-Kolvitsa gabbro-anorthosite complex. REE contents in zircons from basic rock varieties of the Kandalaksha-Kolvitsa area have been defined in situ using LA-ICP-MS. Plots of REE distribution have been constructed, confirming the magmatic origin of zircon. Temperatures of zircon crystallization have been estimated, using a Ti-in-zircon geochronometer. For the first time, the U-Pb method with ²⁰⁵Pb artificial tracer has been applied to date single zircon grains (2448±5 Ma) from metagabbro of the Kolvitsa massif. The U-Pb analysis of zircon from anorthosites of the Kandalaksha massif has dated the early stage of the granulite metamorphism at 2230±10 Ma. The Sm-Nd isotope age has been estimated on metamorphic minerals (apatite, garnet, sulfides) and the rock at 1985±17 Ma (granulite metamorphism) for the Kolvitsa massif, 1887±37 Ma (high-temperature metasomatic transformations) and 1692±71 Ma (regional fluid reworking) for the Kandalaksha massif. The Sm-Nd model age of metagabbro is 3.3 Ga with negative value εNd=4.6, which corresponds either with processes of crustal contamination, or with primary enriched mantle reservoir of primary magmas.

This research was funded by the Scientific Research Contract of GI KSC RAS No. 0226-2019-0053, grants of the Russian Foundation for Basic Research NoNo. 18-05-70082 «Arctic Resources», 18-35-00246 mol_a, and the Presidium RAS Program No. 8.

How to cite: Steshenko, E., Bayanova, T., Serov, P., and Ekimova, N.: The Paleoproterozoic Kandalaksha-Kolvitsa gabbro-anorthosite complex (Fennoscandian Shield): new U-Pb, Sm-Nd and Nd-Sr (ID-TIMS) isotope data on the age of formation, metamorphism and geochemical features of zircon (LA-ICP-MS), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6800, https://doi.org/10.5194/egusphere-egu2020-6800, 2020.

In the Olkhon area of the Baikal Region, the Early Paleozoic magmatism derived diverse granitoids within a narrow time span of 500–465 Ma. The pegmatoid granites and pegmatites encompassed by gneiss-granitoids and leucogranites are similar to granitoids in mineral and chemical composition, as well as in the distribution of many rare elements; and their formation is best explained by the magmatic differentiation of the collisional granitoid massifs.

The zoned Ilixin pegmatite vein containing different rare-metal mineralization. The vein contains apographic pegmatite with protolithionite, and the schlieren includes microcline-plagioclase pegmatite with mineralization of samarskite, lepidolite, tourmaline, vorobyevite, bismuthtotantalite and bismuthocolumbite associated with albite, microcline, lepidolite and polychrome tourmaline. The schlieren containing rare-metal minerals is enriched in F, B, Li, Rb, Cs, Ta and Nb (Makagon, Belozerova, 2013). The other pegmatite veins of the Olkhon area (Naryn-Kunta, Ulan-Nur, Aya) belong to the same mineral-geochemical type, they contain characteristic minerals: amazonite, Li-micas (protolithionite, zinnwaldite and lepidolite), as well as topaz, fluorite, monazite, microlite, zircon, cassiterite, apatite, tantaloniobaty, wolframite.

In the Olkhon area, the Tashkinei pegmatite belongs to Be-REE geochemical series (U-Pb age of zircon 390 Ma). This is where the ore and rare-metal minerals appear. They are monazite, xenotime, euxenite, zircon, thortveitite, ittrowolframite, Nb-Ta wolframite, cassiterite. Unlike F-Ta-Y type, the Tashkinei  pegmatite is enriched in many lithophile and HFSE elements like W, U, Th, Sn, Sc, however they are strongly depleted in F, B, Li, Ba, Sr and Eu.

The post-collision pegmatites have neither spatial nor genetic affinity to the granites of the same age in the Olkhon area. The mineral-geochemical types of rare-metal pegmatites  specify the transition to the Hercynian within-plate magmatism related to the  processes of mantle-crustal interaction.     

The study was performed with RFBR funding (Grant 19-05-00172).                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      

How to cite: Viktor, A., Olga, B., Natalya, S., and Larisa, K.: Mineralogical and geochemical types of pegmatites, their origin within different geodynamic settings in the Olkhon area, Baikal Region of Russia , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4503, https://doi.org/10.5194/egusphere-egu2020-4503, 2020.

 The article describes geological structure of Jidoi massif and its age. The scheme of the massif magmatism has been constructed. Double correlation plots of petrogenic elements of rocks of the massif in which the unified trend of rock structures is observed, are given for verification of correctness of the scheme of magmatism. Spectra of TR and spider diagrams of concentrations of rare elements in rocks of the massif are given. Piroxenites, early rocks of the massif are ores on titanium. Titanium concentrates in three minerals: titanomagnetite, ilmenite and perovskite. The main type of titanium ores is perovskitic type, it is known only in Jidoi massif. Mantle sources of primary magma of the massif is concluded on the basic of geochemistry of isotopes of Sr and Nd. 

How to cite: Vladykin, N. and Alymova, N.: The Zhidoy massif of ultrabasic-alkaline rocks and carbonatites: its geochemical features, sources and ore potential., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8776, https://doi.org/10.5194/egusphere-egu2020-8776, 2020.

The ore specialization of carbonatite complexes of Urals-Timan region has been established: niobium and rare earth-niobium – for the Urals’ carbonatite complexes, the rare-earth – for carbonatites of Timan. The carbonatites of Il'menо- Vishnevogorsky miaskite-carbonatite complex (Southern Urals) are industrial niobium type deposits (pyrochlore type of ores). The Buldym ultrabasic-carbonatite complex (Southern Urals) are rare earth-niobium type deposits (monazite-aeschynite-columbite-pyrochlore type of ores). The Chetlassky carbonatite complex (Middle Timan) are cerium type deposits of bastnesite carbonatites (with monazite-bastnesite type of ores). The Rb-Sr и Sm-Nd isotope characteristics of the Ural carbonatite complexes conrm their mantle source and are similar to those of the ultrabasic-alkaline- carbonatite complexes located in the marginal parts of the platforms (with mantle sources of the moderately depleted DM and FOZO types) and in Precambrian cratons (with the deepest mantle sources of the EM1 type). The Chetlassky carbonatite complex (Middle Timan) has a mantle source with an insignicant addition of a recycled crust component.

Fig.1. Diagram εNd vs. Sr/ Sr of carbonatites and alkaline rocks of the Urals Fold Belt (Ilmeno-Vishnevogorsky and Buldym complexes (A)) and Timan Chetlassky complex (B)) in respect to the mantle sources DM, HIMU, FOZO, EM1, EM2, MORB and OIB [Zindler, Hart, 1986], as well as Kola (KCL)  Kramm, 1993], Eastern African (EACL) [Bell, Petersen, 1991], Siberia [Kogarko et al, 1999; Vladykin, 2005], Aldan [Vladykin, 2005] carbonatite complex of  latforms and shields and Himalayas, Tian Shan, Altai, Mongolia collision carbonatite complex of fold regions [Vladykin, 2005; Vrublewsky, Gertner, 2005; Hou et al, 2006].

How to cite: Nedosekova, I. and Vladykin, N.: Ore-geochemical specialization and sources of Ural and Timan carbonatite complexes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12889, https://doi.org/10.5194/egusphere-egu2020-12889, 2020.

The multi-compositional carbonatite body of Storkwitz is one of several purported diatremes of the Late Cretaceous Delitzsch Complex, which comprises carbonatites and ultramafic lamprophyres emplaced into a heterogeneous series of volcanic and sedimentary rocks of Precambrian to Early Permian age (Krüger et al., 2013; Seifert et al., 2000). The Late Cretaceous peneplain is covered with about one hundred meters of Tertiary soft rock. According to Röllig et al. (1990), the Delitzsch Complex developed in six stages: (i) hidden intrusion of a dolomite carbonatite (rauhaugite) that led to the formation of a fenite aureole; (ii) ultramafic and alkaline lamprophyre intrusion (alnöite, aillikite, monchiquite); (iii) formation of beforsitic diatremes (intrusive breccias), including xenoliths of dolomite carbonatite and ultramafic lamprophyre; (iv) ultramafic and alkali lamprophyres (dykes within diatremes of 3^rd stage); (v) formation of beforsite and (vi) alvikite dykes.

The Storkwitz carbonatite is mainly characterized by beforsitic breccias containing abundant angular xenoliths of metasediments form the complete underlying stratigraphic succession, metamorphic and igneous rocks, as well as rounded xenoliths of ultramafic lamprophyre, rauhaugite, fenite, and glimmerite, which suggest the existence of a deep-seated carbonatite pluton (Seifert et al., 2000). It is remarkable that the fenites exhibit a different degree of fenitization and show occurrence of phlogopite in the strongly fenitized samples. The matrix of the Storkwitz carbonatite is mainly composed of ankerite and calcite/siderite, which corresponds to ferro- or silico-carbonatites.

Detailed petrographical observations on extensive drill core material, new analyses and a reinterpretation of published data confirm the existence of compositional variation and zonation within the carbonatite body that reflect independent crystallization history and formation due to multiple magmatic events. The different generations of apatite and phlogopite from the early stage of the plutonic dolomite carbonatite through the late-stage beforsite dykes and fine-grained calcite carbonatite veins shed light on the crystallization history and magma development of carbonatites.

References

Krüger, J.C., Romer, R.L., Kämpf, H., 2013. Late Cretaceous ultramafic lamprophyres and carbonatites from the Delitzsch Complex, Germany. Chemical Geology, 353, 140-150.

Röllig, G., Viehweg, M., Reuter, N., 1990. The ultramafic lamprophyres and carbonatites of Delitzsch/GDR. Zeitschrift für Angewandte Geologie, 36, 49-54.

Seifert, W., Kämpf, H., Wasternack, J., 2000. Compositional variation in apatite, phlogopite and other accessory minerals of the ultramafic Delitzsch complex, Germany: implication for cooling history of carbonatites. Lithos, 53, 81-100.

How to cite: Gevorgyan, H., Schmidt, S., Kogan, I., and Lapp, M.: Mineral assemblages and xenolith cargo in the Storkwitz carbonatite (Delitzsch Complex, Germany), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10678, https://doi.org/10.5194/egusphere-egu2020-10678, 2020.

In Eastern Sayan mountains (E Siberia), ophiolite complexes form three extended branches: 1 - Ilchir (MOR ophiolites), 2 - Ospa-Khara-Nur (suprasubduction zone (SSZ) and volcanic arc (VA) ophiolites) and 3 - Shishkhid-Yehe-Shignin (back-arc ophiolites).

Lamprophyre (L) dykes or mica peridotites (Shestopalov, 1938) were found in brecciation zone of ophiolites (dunites, harzburgites, serpentinites) of the Ospa-Khara-Nur peridotite complex. They form bodies to 1m thick, and vein-like fragments in intensively deformed and altered (serpentinized, tremolitized) ultramafic rocks.

Dark gray massive porphyric L correspond to the range between ultramafic (UML), alkaline (AL), and Ca alkaline lamprophyre (CAL), and lamproite lamprophyres (LL) according to (Rock, 1991) and show compositional range in MgO-CaO, - Al₂O₃, - Na₂O, - P₂O₅ diagrams. Lamprophyre rocks consist of feldspar, phlogopite, orto- and clinopyroxene, amphibole, with relics of olivine (Fo=45-50, rarely 22-30) and large (up to 1 cm) porphyric phlogopite. In more acid L of CAL type with prevailing hypersthene and fieldspars are associated by amphiboles metasomatic type (ferro-eckermannite, actinolite, tremolite) and rarely metamorphic glaucophane. Micas grains from phlogopite to biotite (0.2-1.7% and 2.1-2.8% TiO₂) are surrounded by sericite. Feldspar vary albite to anorthite, and rare grains of orthoclase and Ba-feldspar. Fluorine-apatite (Cl to 0.3%), ilmenite, rutile are common in L but zircon, monazite and Ce-La-epidote are rare. Mineral thermometry range from 1300^oC to 950^oC for LL then 850^oC -560^oC and low metamorphic stage.

TRE from L shows inclined REE with flat La-Sm, HFSE troughs but high LILE. The acid CL reveal Eu peak (Eu*=3,2; (La/Yb)_n=9). Spider and REE diagram reveal elevated HFSE, Sr, Pb the same high LILE closer to anorthosites and pegmatiod charnokites. This suggests that high extremely high temperature ML reacted with acid rocks and produced Ca-alkaline L type.

Age spectra were obtained for phlogopites from lamprophyres by ⁴⁰Ar/³⁹Ar step heating method. In sample VS-66-2, spectrum reveal intermediate plateaus of 3 stages (32%, 35%, 33%) of cumulative ³⁹Ar with ages 950 ± 6 and 976 ± 6 Ma, respectively. In the spectrum VS-57 a good plateau 902 ± 9 Ma is distinguished (79% of cumulative ³⁹Ar). Most discordant spectrum VS-52 reveals 4 stages of creation. Most likely the age of L formation is - 976 ± 6 Ma and corresponds to ocean stage. Most likely, and 902 ± 9 corresponds to the age of the intensive deformation later event in subduction zone. Further deformation suggests the complex tectonic-thermal history.

We suggest that late Proterozoic ophiolites which refer to oceanic stage of 1100 Ma were later incorporated to arc complex with the acid base. At 980 Ma they were subjected to plume event with the creation of UML due to reaction with crust and the they were hybridized with acid rocks to produce CAL. Late alteration produced series of secondary minerals. Thus the UML, and AL, and CAL give more information about the history of ophiolites of the Eastern Sayan.

This work supported by RFBR grants: No. 19-05-00764 and the Russian Ministry of Education and Science.

References:

1. Shestopalov M.F. // In: Gemstone workbook. V. 4. 1938. P.84-100.
2. Rock N.M.S. Lamprophyres. Springer Science+Business Media, LLC. 1991.

How to cite: Kovalev, S., Zhmodik, S., Belyanin, D., Airiyants, E., Kiseleva, O., Kulikov, Y., and Travin, A.: Lamprophyres from Ospa ophiolite of the East Sayan (Russia), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-926, https://doi.org/10.5194/egusphere-egu2020-926, 2020.

Ultrabasic Ulan-Saridag massif is part of the Eastern Sayan ophiolite belts, lying between the ophiolites of the southern and northern branches. It was suggested that ophiolites of the southern branch were created in mid-oceanic ridges, and southern one – in island arcs environment. Recent data indicate the formation of Ulan- Saridag ophiolites in supra-subduction conditions of ensimatic island arcs.

Ore podiform chromitites consist of alumochromite, chromite, and chrompicotite (first finding for this region). Cr-spinelides are divided into three groups according to geochemistry. They refer to the MORB-peridotite, supra-subduction peridotites to the complexes of Ural-Alaska type.

PGE mineralization in this massif is represented by Os-Ir-Ru solid solutions, native Os, Ru, laurite-erlichmanite (Ru, Os)S₂, laurite (RuS₂), irarsite (IrAsS), zaccarinite (RhNiAs).

Solid solutions of Os-Ir-Ru were found as idiomorphic inclusions in Cr-spinel and xenomorphic grains in intergrowths with laurite. They correspond to the early high-temperature magmatic solid-solution Os-Ir-Ru. Also, the phases (Os-Ir-Ru) of varying composition are common in the form of numerous micro - and nano-size inclusions in laurite-erlichmanite with osmium or ruthenium. Native Os^o (Os> 80 wt.%) is recognized in polyphase aggregates, together with chalcocite, laurite, laurite-erlichmanite. Native Ru (Ru=93 wt.%) – occur in the polyphase, together with heazlewoodite, zaccarinite, Os-Ir-Ru solid solutions. Laurite and laurite- erlichmanite RuS₂ – (Ru, Os)S₂ are represented most widely.

There are two groups: 1) laurite-erlichmanite (Ru, Os)S₂; 2) laurite RuS₂- phase of variable composition. (Ru, Os)S₂ rarely forming independent grains, occurring more often in multi-component aggregates,  together with the laurites and contains a large number of rounded and rectangular micro-inclusions of native Os, (Os-Ir), and native Ru. Laurite has the reveal  stoichiometric composition (Ru=61,2 wt.%, S = 38.2 wt.%). It forms individual grains in chlorite and serpentine in association with irarsite, sulfides of Ni, Cu and rims around laurite-erlichmanite.

Solid solutions of (Os-Ir-Ru) and laurite-erlichmanite are forming before or simultaneously with Cr- spinel in the upper mantle at T=1200^oC and P= 5-10 kbar.

Sulfoarsenides and arsenides of Ru, Ir, Rh, Ni are formed from the residual fluid phase at a post-magmatic stage, together with heazlewoodite. It is possible that in chromitites from Ulan-Saridag there are two generations of sulfides. 1-st PGM generation – magmatic solid solutions of laurite-erlichmanite. 2 -nd generation – the newly formed laurite, with primary laurite-erlichmanite or intergrowths with chalcocite, heazlewoodite and millerite confined to zones of chloritization. The predominance of  Os, Ru sulfides over the solid solutions of Os-Ir-Ru indicates a higher sulfur fugacity in the mantle source of Ulan-Sardag ultramafic-mafic massif. These results indicate the distinctive characteristics of PGM of Ulan-Sardag massif compared to PGM from the chromitites of the Northern and Southern branches of the ophiolites.

Ulan-Sardag ultrabasic massif occurred in three different geodynamic settings: mid-ocean ridges, primitive ensimatic and ensialic island arcs, subduction zone, and belongs to the Alaska type basic formation.

Mineral chemistry was determined at the Analytical Centre for multi-elemental and isotope research SB RAS. This work supported by RFBR grants: No. 16-05-00737a, 15-05-06950, 19-05-00764 and the Russian Ministry of Education and Science. 

How to cite: Kiseleva, O., Airiyants, E., Belyanin, D., and Zhmodik, S.: Origin and alteration of platinum group minerals in chromite deposits of the Ulan-Sardag ophiolite, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-789, https://doi.org/10.5194/egusphere-egu2020-789, 2020.

The Yllymakh massif belongs to a number of ring massifs of the Mesozoic age typical for the Aldan shield. Being formed in an intraplate environment, the Yllymakh massif is characterized by specific features of intraplate rocks in general and a number of coeval intrusions of the Aldan magmatic province in particular. These include a potassium-sodium slope, an extremely low eNd value (-13--14), a specific distribution of rare-earth elements with almost or with a weakly developed Eu minimum.

The range of rocks composing the Yllymakh massif is very wide. It consists of up to 20 species of rocks. The most melanocratic are olivine schonkinites. The most widespread and diverse are the rocks average in SiO2 content. These include feldsparless syenites, feldspar syenites with nepheline, feldspar syenites with quartz, syenites with phoid (nepheline or leucite) in various quantities, alkaline granites. Of course, the question arises of the processes that led to such diversity.

Previous geochronological studies of the Ar-Ar method [Vasyukova et al, 2020] three stages of the massif formation were determined: 140 ± 1.9 Ma, 130 ± 1.9 - 131 ± 2.4 Ma and 125 ± 1.9 Ma. And geochemical studies showed that the Yllymakh massif was formed in several stages due to the pulsed introduction of successive portions of magma.

The analysis of petrochemical and geochemical diagrams showed the impossibility of the formation of the rock spectrum by fractionation of the melt. The critical fractionating phases were different: pyroxene in first and plagioclase in the second group. So they gave different trends in the coordinates CaO-, Na2O-, Al2O3-SiO2 and MgO-, Fe2O3-SiO2. apatite also plays an important role in the formation of the spectrum of rocks, as can be seen in P2O5-SiO2. However, it is not a rock-forming mineral, but it is a good marker of the fluid and geochemical conditions of the melt.

The isotopic composition of oxygen showed the predominance of mantle material in the source. The Nd and Sr isotopic data show that the rocks of the Yllymakh massif were formed in an enriched source. Sharply negative values of the eNd of the studied rocks fit into the overall picture of the region – similar characteristics are determined for other objects of similar age (Inagli, Ryabinovy, etc.).

Supported by RFBR grant 19-05-00788

Vasyukova E.A., Ponomarchuk V.A, Doroshkevich A.G. Petrology and age boundaries of Yllymakh massif. Russian Geology and Geophysics, 2020 in press

How to cite: Vasyukova, E. and Medvedev, N.: Mafic alkaline ring Yllymakh massif , Aldan shield, Yuakutia, geochemistry and geochronology, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21145, https://doi.org/10.5194/egusphere-egu2020-21145, 2020.

Predictive and prospecting research is the example of «inverse geological task» according to preliminary spatial localization of specific region of a plume activity, prediction and estimation of ore potential of one region in a middle part of the Russian platform. The Ustyansky potential region is characterized by coinciding of all the advantageous regional and local searching suppositions in space (morphostructural, tectonic, geologic-stratigpaphical, geophysical, morphometrical, mineralogical) and search features. It can be caused by implementing of mantle diapir (plume) and can be accompanied by diamong-bearing kimberlitemagmatism. Heavy diamond concentrate contents (most of all of pirop (1206 grains), not so many
of pycroilmenite, chromespinelide, olivine, chromedyopside) in alluvion of the region is 3-5 times higher than in the ZimnyBereg diamond-bearing region. Furthermore, contents of pirop of diamond paragenesis of the G10 group is about 10%. In stream sediment samples of minimum amounts, taken from alluvial and quaternary deposits, nine diamond crystals had been founded. Six of them (octahedrons and dodecahedrons with sizes up to 3,8 mm and weight up to 52 mg) had been founded in «Severnoe» kimberlite potential field. According to a complex of morphological and physical features all diamonds of the Ustyansky region occupy a completely outlier position and have almost no analogues among the diamonds of
large known deposits and mineral occurrences of Arkhangelsk, Finland, Urals and Timan, This might indicate to crystals flowing from a new, still unknown native source (or sources) of kimberlite. This new native source of kimberlite may be heightened diamond potential and may contain high-quality and big-size diamonds. Detection of this new native source will be a final confirmation of predictable selection of the Ustyansky region as a region of a plume activity. Features of possible similarity of the Arkhangelsk diamond-bearing province to the Yakutsk diamondbearing province in relation to patterns of kimberlite position and morphological features of diamond crystals, confirm great prospects of diamond-bearance of central
regions of the European part of Russia at all, and particularly of the Ustyansky region with «Severnoye» kimberlite potential field. 

How to cite: Sablukov, S., Sablukova, L., and Belov, A.: The characteristics of the plume magmatic activity in middle part The Russian platform (Ust diamondiferous district), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8662, https://doi.org/10.5194/egusphere-egu2020-8662, 2020.

The experimental study indicates that high-K magmas and kimberlites are in equilibrium with metasomatic minerals, such as phlogopite, richterite, and apatite during their formation in the mantle; i.e., metasomatic processes played a decisive role in their genesis.

In the uppermost part of the mantle, K is entirely concentrated in plagioclase. With increasing depth the K budget is determined mainly by clinopyroxene and, to a lesser extent, garnet A further increase in pressure causes pyroxene and garnet to react to form majorite, which has K and Na partition coefficients equal to 0.015 and 0.39, respectively [1]. In the depth interval of 410–660 km, majorite is associated with wadsleyite (410–500 km) and ringwoodite (500–660 km), neither of which incorporate K or Na into their structures. At deeper levels, below 660 km, the majorite–ringwoodite assemblage is replaced by the ferropericlase–bridgmanite–Ca-perovskite paragenesis. Here, the modal content of Ca-perovskite  is ~8%. The K partition coefficient for Ca-perovskite is relatively high (0.39), and that of Na is even higher (2.0) [2].The.hexagonal NAL phase content up to 1.1 and  6.2wt% K2O and Na2O respectively Thus, practically all K and Na will be concentrated in Ca-perovskite and  the NALphase in the upper parts of the lower mantle. When a mantle diapir ascends from a depth  more then of ~660 km, Ca-perovskite and NAL becomes unstable and reacts with bridgmanite and ferripericlase to produce majorite and ringwoodite, and, with a further decrease in pressure wadsleyite becomes stable. The K partition coefficient in Ca-perovskite is 26 times higher compared with that of majorite The K partition coefficient of NAL is unknown. The remaining K likely remains excluded from the lattices of minerals in this mantle zone .Majorite may be an important concentrator of Na in the uppermost part of the lower mantle and transition zone. Experimental data indicate that 12 molar % sodium can be incorporated in majorite solid solutions. The chemical composition of the natural majorite contains 0.27-1.12 wt % Na₂O Taking into consideration values of the K partition coefficient for Ca-perovskite and majorite, it can be confidently stated that the thermodynamic activity of K₂O in the system increases by more than an order of magnitude with the transition of the bridgmanite–Ca-perovskite–ferripericlase – NAL association to the majorite–ringwoodite paragenesis. This is evidence that majorite will markedly fractionate K and Na, resulting in conditions favorable for the transfer of K into a melt or fluid phase at the boundary between the lower mantle and the transition zone.

1 Corgne A. and Wood B.J., Trace element partitioning between majoritic garnet and silicate melt at 25 GPa. Physics of the Earth and Planetary Interiors, 2004, 143–144, 407-419.

2 Liebske C., Wood B.J., Rubie D.C., Frost D.J., Silicate perovskite-melt partitioning of trace elements and geochemical signature of a deep perovskitic reservoir. Geochimica et Cosmochimica Acta, 2005, 69(2), 485-496. 

How to cite: Kogarko, L.: Kimberlite magmatism and origin of K-rich metasomatic melt-fluid, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1698, https://doi.org/10.5194/egusphere-egu2020-1698, 2020.

The study of water content in the rock-forming minerals of mantle xenoliths, entrained in kimberlites, provides information about the water storage of the lithospheric mantle of ancient cratons. In mantle xenoliths, the water can be identified as several percentages by weight in hydrous minerals (e.g. phlogopite and amphibole) and up to 2000 ppm in nominally anhydrous minerals (NAMs; olivine, pyroxene, and garnet). Since the hydrous phases occur sporadically in mantle xenoliths, their NAMs reserve the main water content in the lithospheric mantle.

The water content in garnet and clinopyroxene from the mantle eclogites from the V. Grib kimberlite pipe (Arkhangelsk Diamondiferous Province, NW Russia) was analysed using Fourier transform infrared spectrometry. The studied samples are coarse-grained (grain sizes from 0.5–1.3 cm) bimineralic (garnet and clinopyroxene) eclogites with accessories of phlogopite, ilmenite, and rutile. The samples include high-MgO (three samples) and low-MgO (six samples) groups. The eclogites are interpreted as metamorphosed fragments of oceanic crustal rocks (basalt and gabbro for low-MgO eclogites and picritic/MgO basalt and troctolite for high-MgO eclogites) emplaced into the lithospheric mantle via a subduction event at 2.8 Ga. Based on pressure-temperature estimates (44–78 kbar; 940°C–1275°C), eclogites were transported by kimberlite from the range of depths of about 160 to >200 km.

The results show that all clinopyroxene grains contain structural water in the amount of 39 to 111 ppm, whereas only two garnet samples have detectable water in the amount of 211 and 337 ppm. The water incorporation into the clinopyroxene is mostly linked to M2 sites and aluminium in the tetrahedral position. The water content in the majority of eclogite clinopyroxene positively correlates with the jadeite component. The low-MgO eclogites with oceanic gabbro precursor contain significantly higher water concentrations in omphacites (70–111 ppm) and whole rock (35–224 ppm) compared to those with the oceanic basalt protolith (49–73 ppm and 20–36 ppm, respectively). The proposed observation is also confirmed by the negative correlations of water content in clinopyroxenes with a La/Yb ratio in clinopyroxene and WR water content versus the WR Yb concentration. The equilibrium pressure could be an additional factor that controls the water incorporation into the clinopyroxene of the high-MgO group.

Our results show that water content in the V. Grib pipe eclogites is not from the mantle metasomatism and therefore can reflect the water saturation of their protoliths. The eclogite portion of the lithospheric mantle beneath the V. Grib kimberlite pipe can have at least twice the water enrichment compared to peridotite sections, indicating that an Archean subduction event played an essential role in the water saturation of the mantle.

This work was supported by the Russian Science Foundation under grant no. 16-17-10067

How to cite: Shchukina, E., Kolesnichenko, M., Malygina, E., Agashev, A., and Zedgenizov, D.: Origin of water in the mantle eclogites from the V. Grib kimberlite pipe, NW Russia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-298, https://doi.org/10.5194/egusphere-egu2020-298, 2020.

Compared to xenoliths, kimberlite xenocrysts provide, although less accurate, more complete information about the deep structure and processes in the subcratonic lithospheric mantle (SCLM). This work is devoted to the study the composition of xenogenic olivine from kimberlites as the main mineral constituting SCLM. Olivine in kimberlites has a different origin, including those not related to depleted rocks of the lithosphere. It can crystallize directly from kimberlite or belong to the so-called Cr-poor megacryst association. In this regard, for the correct interpretation of data on its composition, it is necessary to have sufficiently clear criteria for the separation of olivine xenocrysts from kimberlites into various genetic types. In order to remove olivines crystallizing directly from kimberlite from consideration, in our study we used only central homogeneous parts of crystals larger than 0.5 mm in size [Giuliani, 2018].

Based on unique and literature data on the composition of olivines from 230 xenoliths of peridotites from 12 kimberlites of the North American, South African and Siberian cratons we proposed a general division into 4 genetic types: olivines of ultrahigh-temperature (HTP-1), high-temperature (HTP-2), low-temperature (LTP) peridotites, olivines of low-chromium megacrystal association (MCA). The separation scheme uses the CaO content as an indicator of the temperature of formation and the ratio Mg/Mg+Fe as an indicator of the degree of enrichment.

A study of more than 1,500 olivines from a number of kimberlite bodies of the Siberian platform according to this scheme revealed three characteristic distributions of olivine types in kimberlite bodies: 1) without high-temperature differences (Obnazhennaya pipe), 2) with significant development of HTP-2 (Olivinovaya and Vtorogodnitsa pipes) and 3) with significant development of HTP-1 (Dianga pipe). Only the latter type is characterized by the presence of a noticeable amount of olivines of the megaryst association.

In general, variations in the composition of LTP olivines correspond to granular ones, while HTP-1 and HTP-2 correspond to deformed (shared) peridotites. Interestingly, the enrichment of olivines with incompatible components in these three types does not correlate directly with the formation temperature. Olivines of ultrahigh-temperature peridotites (HTP-1) have unexpectedly small compositional variations and occupy an intermediate position between low-temperature and high-temperature in content of incompatible elements.

A study of the content of impurity elements (TiO2, NiO) in olivines made it possible to propose the way of formation of two different types of high-temperature olivines. It belongs to the model [Harte et al., 1993; Burgess and Harte, 1999; Burgess and Harte, 2004] where megacrystal melt of various stages of fractionation [Moore et al., 1992] effects depleted rocks of lithospheric mantle. According to it, HTP-2 olivines arose upon exposure to a fractionated melt characteristic of late crystallization stages, and HTP-1 olivines due to unfractionated (less enriched with incompatible components) megacrystal melt at higher temperatures characteristic of the initial crystallization stage.

Funded by RFBR grant 18-05-01143, T.V.A. was supported by RSF grant 16-17-10067.

How to cite: Tychkov, N., Agashev, A., Pokhilenko, N., Tsykh, V., and Sobolev, N.: Xenogenic olivine from Siberian kimberlites: types and features of origin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21143, https://doi.org/10.5194/egusphere-egu2020-21143, 2020.

Inclusion assemblages within Cr-pyrope xenocrysts from the Aldanskaya and Ogonek lamprophyres (Chompolo field, Aldan shield of Siberian craton, Yakutia) are characterized by the wide list of minerals. Partially the inclusion assemblages with graphite within Cr-pyropes in Chompolo lamprophyres were previously described (Nikolenko et al., 2017).

Here we present the results of a trace-elements study of 54 pyrope grains with Cr-spinel inclusions. The majority of studied pyropes are lherzolitic with small amount of wherlitic and harzburgitic ones, according to the classification schemes (Sobolev et al 1973; Grutter et al., 2004). The concentration of Cr₂O₃ ranges from 1.58 to 7.56 wt% at Mg # = 69.6-84.4 and Ca # = [100Ca / (Ca + Mg + Fe + Mn)] = 8.6-26.3. The TiO₂ content does not exceed 0.36 wt%. The MnO contents in the pyropes studied is in the range of 0.35–0.69 wt%, which indicates rather low temperature conditions (Grutter at al., 2004).

Studied mineral inclusions can be divided in two groups by their morphology and position within the host pyrope grain. Majority of the studied Cr-spinels within pyropes are represented by the single-mineral inclusions (CrSp-I), which have clear octahedral morphology but some of them can be described by more complex morphology that looks as irregular or rounded. Single Cr-spinel inclusions are commonly large and range in size from 100 to 500 µm. Another inclusions type represents joint associations of Cr-spinels (CrSp-II) with silicates, carbonates, sulphides, graphite, volatile-bearing minerals and series of Ti-oxides. Size of Cr-spinels II in this samples is usually 10-50 µm and rarely reaches 100 µm.

The distribution of the rare earth elements (REE) for pyropes containing CrSp-I inclusions in chondrite-normalized REE-diagram has a sinusoidal pattern and is characterized by the chondrite-normalized ratio Sm_N/Er_N > 1 at low Ti/Eu values, which is a sign of carbonatite metasomatism (Shchukina et al., 2017). Pyropes containing complex polyphase inclusions with CrSp-II carry signs of silicate (melt) metasomatism, expressed in elevated contents of Y (up to 20.5 ppm) and Zr (9.5–44.6 ppm) and an increased Ti impurity. Pyropes with CrSp-II inclusions have typical for lherzolites distribution of REE with  Sm_N/Er_N ratio in the range of 0.5-1.

Cr-spinel inclusions within pyropes were also studied in detail and revealed some differences in the chemical composition between two groups.

Temperatures estimated for the pyropes containing mineral inclusions using Ni-in-garnet thermometer ranges from 640-910 °C. Temperatures were also estimated for Cr-spinel inclusions by use the Zn-in-spinel thermometer (Ryan et al., 1996). The temperature distribution for CrSp-I and CrSp-II groups shows different values with maximum frequency at 650-700 and 750-800 °C respectively.

The geochemical features, the composition of inclusions and the results of thermometry of the two described pyrope populations with Cr-spinel inclusions indicate different metasomatic processes associated with their formation.

Complex studies of mineral inclusions in Cr-pyropes and major element analyses of Cr-pyropes and Cr-spinels were supported by the Russian Science Foundation, grant No 18-77-10062. Trace-elements studies of Cr-pyropes were supported by the Russian Science Foundation, grant No 18-17-00249.

How to cite: Nikolenko, E., Sharygin, I., Malkovets, V., Rezvukhin, D., and Afanasiev, V.: Mineralogy and geochemistry of the inclusion-bearing Cr-pyropes from the Chompolo lamprophyres, Aldan shield, Siberian сraton, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12823, https://doi.org/10.5194/egusphere-egu2020-12823, 2020.

Water plays a key role in evolution and dynamic of the Earth. It can change physical and chemical properties of mantle minerals, or the part of the mantle, for instance, the effect on mineral deformation and its impact on mantle rheology (Miller et al., 1987). Mantle xenoliths from kimberlites are one of direct source of information on the petrology and geochemistry of the deep mantle rocks.

Sytykanskaya pipe located in the central part of Yakutian diamondiferous province is characterized by a large amount of deep-seated xenoliths which contain relics of fresh minerals, e.g. clinopyroxenes, garnets, olivines, phlogopites, amphiboles, chromites, ilmenites and some other rare phases (Ashchepkov et al., 2015). Moreover it is known that there are several processes which can affect the mantle xenoliths, including metasomatism. Five peridotite xenoliths have been studied in order to indentify water enrichment. Using calibration coefficients (Bell et al., 2003) we calculated water content in the olivines. Water contents in olivine range from 12 to 92 ppm. In previous research (Kolesnichenko et al., 2017) we have studied peridotites from Udachnaya kimberlite pipe and found similar water content in olivines (2-95 ppm). So, the variably low water contents suggest a heterogeneous distribution of water beneath the mantle, which can be connected with metasomatism of essentially dry diamondiferous cratonic roots by hydrous and carbonatitic agents, and its related hydration and carbonation of peridotite accompanied by oxidation and dissolution of diamonds.

This work was supported by the Russian Science Foundation under Grant No 16-17-10067.

Miller, G. H., Rossman, G. R., & Harlow, G. E. (1987). The natural occurrence of hydroxide in olivine. Physics and chemistry of minerals, 14(5), 461-472.

Ashchepkov, I. V., Logvinova, A. M., Reimers, L. F., Ntaflos, T., Spetsius, Z. V., Vladykin, N. V., & Palesskiy, V. S. (2015). The Sytykanskaya kimberlite pipe: Evidence from deep-seated xenoliths and xenocrysts for the evolution of the mantle beneath Alakit, Yakutia, Russia. Geoscience Frontiers, 6(5), 687-714.

Bell, D. R., Rossman, G. R., Maldener, J., Endisch, D., & Rauch, F. (2003). Hydroxide in olivine: A quantitative determination of the absolute amount and calibration of the IR spectrum. Journal of Geophysical Research: Solid Earth, 108(B2).

Kolesnichenko, M. V., Zedgenizov, D. A., Litasov, K. D., Safonova, I. Y., & Ragozin, A. L. (2017). Heterogeneous distribution of water in the mantle beneath the central Siberian Craton: Implications from the Udachnaya Kimberlite Pipe. Gondwana Research, 47, 249-266.

How to cite: Kolesnichenko, M., Zedgenizov, D., and Ashchepkov, I.: Water contents of mantle xenoliths from Sytykanskaya kimberlite pipe (Yakutian diamondiferous province, Russia), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21023, https://doi.org/10.5194/egusphere-egu2020-21023, 2020.

            In the mantle column beneath the Leningrad pipe W Ukukit, the Cr-bearing amphiboles prevail on the clinopyroxenes. The amphiboles are varying from the Cr hornblendes  near the Moho to  Cr pargasites (to more Cr- bearing in the middle part of mantle columns and to K-Na near the lithosphere base. All amphiboles  from hornblendes to  richterites form nearly continuous range. With the inflection (Peak in Cr in pargasited and growth of K. Fe at the lithosphere base.

            The single grain thermobarometry for the garnets suggest the division to at least 7 horizons which from paleo subduction slabs. The ilmenite trend from 7.5 GPa suggest the vast range of metasomatism in the lower part and continuous trend to 3 GPA. Amphiboles compiles the HT branch from 3.5 GPA typical for basaltic melts and with the most Cr rich beginning and decreasing of Cr to the MOHO. Cr pargasites refer to 40mw/m2 geotherm together with the prevailing eclogites. An opposite the trend for the richterites also is dividing in to LT and HT branches. The eclogites compile dense MT branch in the middle part of mantle column with the highly inclined P-Fe# trend.

            The richterites in the LAB show the highly inclined and enriched TRE patterns with high LILE, SRSR and troughs in Nb Pb. The Na- rich have Rb, Ba, variable Th peaks and essentially lower REEE with the MREE depressions (created in harzburgites).  The pargasites and Hornblendes show contrasting Eu peaks (for enriched) and troughs (for depleted varieties in REE). They real subduction related Ba, U, Sr peaks and troughs in HFSE.

CPX are variable mostly showing TH, U Sr peaks related to plume carbonatitic melts

Abundance of unremelted subduction material  s suggests that in Khapchan zone the growth of the continents was accompanied by subduction fluids and possibly with nearly   sub vertical subductions. Khapchan terrane as a collision terrane and contain anomalous amount of eclogitic material which was not hybridized with peridotites like in in common granite-green-stone protocontinents. RFBR grant 19-05-00788

How to cite: Ashchepkov, I. and Babushkina, S.: Amphibole bearing mantle beneath Leningrad kimberlite pipe, West Ukukit field, NE Yakutia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2843, https://doi.org/10.5194/egusphere-egu2020-2843, 2020.

      The PT estimates and geochemistry minerals for 50 xenoliths from Zapolyarnaya pipe, Upper Muna field, Yakutia were obtained fist. This pipe contain good quality diamonds and now extensively mining. The garnet geotherm for the pipe is relatively high temperature and extends to 8 GPa as well as Cpx referring mainly to refertillization type give more HT^o geotherm tracing convective branch, HT^o also exists.  Deeper part SCLM is essentially more oxidized in upper mantle section which accompany heating and fertilization of the lower part of the mantle column. Cpx refer to the garnet trend (10-20%CO₃ in melt). Mantle section is layered according to garnets showing 6 Ca-rich jets in P-CaO trend and the same for subCa garnets starting from 2 GPa in mantle section. Cr-rich (to 5% ) ilmenites found from 6 to 3 GPa suggest intensive protokimberlite metasomatism n mantle column. The structure of Novinka pipe despite on similarity contain more fertile material. Cr-Di samples show Mg# from 0.92 to 0.84. and Al –Cr-NA as well giving Ht and Lt branches. Garnets demonstrated also depletion sturting from 2 to 8 GPA and mostly LAB level. Spectra REE for garnets from xenoliths determined by (LA ICP MS) of Zapolyarnaya pipe show S type for 50 % and rarely pyroxenitic concave up patterns. The have HFSE enrichment  (mainly Zr>Hf and asynchronous Nb, Ta) LILE) for those with high REE level suggesting hydrous Phl bearing metasomatism accompanied (and before) protokimberlites. Garnets from concentrate show less HFSE enrichments. HFSE enrichment of garnets heavy concentrate and S specrums is less suggesting Cpx growth in originally dunitic varieties serving as melt feeders. Clinopyroxenes are characterized by conform REE spectrums dividing in 3 groups in REE level (100 to 10/C1). half of TRE spectra have Zr Hf, Nb maxima and often Pb Ba peaks and varying Pb. The parental melts are closer to protokimberlites. The first low REE Zr-Hf, Pb,Cr and were oxidized and high T Cr diopsides  which indicates the reduction in FO₂ during risinf and reaction of protokimberlite with the mantle.  The TERE patterns from concentrates are more variable and contain Rb, Ba,Th U peaks suggesting alkaline carbonatitic metasomatism. Amph and mica show Rb, Ba,Sr, U peaks. Garnets from Novinka pipe show less variation in HFSE and sometimes U peaks suggesting less reactions with the protokimberlites and more subduction related features. There much more hydrous metasomatic clinopyroxenes also. General, this reflects the process of polybaric interaction of the evolving proto-kimberlite melt with the depleted peridotite mantle. The focus of the interaction was in Upper Muna beneath the Zapolyarnaya pipe. Supported by  RFBR grant 19-05-00788 

How to cite: Ashchepkov, I., Ivanov, A., Medvedev, N., and Vladykin, N.: Mantle xenoliths from Zapolyarnayay pipe comparison to Novinka pipe Upper Muna freld Yakutia , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1770, https://doi.org/10.5194/egusphere-egu2020-1770, 2020.

The Bumerang kimberlite pipe is unusual for the Anabar shield because it  contain great amount of the pyroxene both of Cr  diopside and  eclogite type and commonly in Anabar region the mantle is ultra-depleted and even garnets occurs rarely in kimbelrites (Ashchepkov et al (2010, 2014; 2015;).  This is because the pipe is close to the Margin of Anabar shield in the transition permeable zones   

The PTX diagram show presence of the rare pyrope garnets to 6 GPa of lherzolitic pipe and grate amount of the eclogitic garnets mainly of Fe of type

Both eclogitic and Cr diopside garnets occurs mainly in the middle part of the SCLM within the in the pyroxenite layer.

The ilmenite give long fractionation trend.  From the LAB to the GPa 2.5  which is typical of the Magan terrane (Mir, Internationalnaya pipes etc.).

The pyroxenes mostly have straight-line REE patterns, which create the fan - as series .They most depleted, have some Ba, U peaks of subduction type but deep Pb minima evidencing about the fractionations.  

The garnets  of subduction type reveals the U peaks and all have EU, Sr, minima and varying Ba  The HFSE minima are common But Ta>>Nb  and Zr>Hf/

All this features evidences about possibility of finding of diamond bearing kimbertites within the suture zone between Magan terrane and Anabar shoed in the west part of Yakutian kimberlite province. Grant RFFI 19-05-00788

How to cite: Kostrovitsky, S. and Ashchepkov, I.: Bumerang pipe Ary Mastakh field Upper Anabar region Yakutia – relatively fertile mantle in the transitional part between Anabar shield and Magan trerrane , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4994, https://doi.org/10.5194/egusphere-egu2020-4994, 2020.

Sulfide inclusions in Neoproterozoic West African diamonds have revealed mass-independently fractionated sulfur isotopes in them [Smit et.al., 2019]. This feature is a sign of Archean surface changes traced in the mantle. Here we present an S isotope study of the unique fresh mantle deep-seated peridotites, eclogites and pyroxenites with rare or without any secondary alterations from the Udachnaya-East pipe. This research will give better understanding the role of subduction in the formation of the lithospheric mantle under the Siberian craton. Sulfur isotopes (³⁴S/³²S which is denoted as δ³⁴S) were measured in the sulfides from eclogites, peridotites and pyroxenites using an Isoprime isotope ratio mass spectrometer (IRMS) with classic configuration with 4 collectors. The sulfides from eclogites are pyrrotite, pentlandites and chalcopyrites. They have δ³⁴S values from +0,67 to +3,08 per mil (‰). Sulfides in peridotites are pyrrotite-pentlandite-chalcopyrites assemblages and they have δ³⁴S values from +0,22 to +3,55 ‰. These δ³⁴S values from eclogites and peridotites are broadly overlap with the field for depleted mantle and chondrites (-1,9 to +0,35‰) [Labidi et.al., 2013; 2014]. Sulfides from pyroxenites are pyrrotite and they have δ³⁴S values from -3,62 to +1,49 ‰. These δ³⁴S values have a wider range than the estimates for depleted mantle. The δ³⁴S values in our samples are close to those in the depleted mantle, but still have deviation from it and do not fractionated. Our data did not detect mass-independently fractionated sulfur isotopes in the mantle samples from the Udachnaya pipe. Thus subduction of the earth’s crust did not play role in the values of sulfur isotopes of the lithospheric mantle sampled by Udachnaya kimberlite pipe. The source of sulfur in these rocks probably was the astenospheric mantle.

References

1. Smit et. al., 2019
2. Labidi et. al., 2013; 2014

This study was supported by the Russian Foundation for Basic Research № 18-05-70064

How to cite: Ilyina, O., Agashev, A., and Moine, B.: Sulfur isotopic compositions of the lithospheric mantle sulfides from the Udachnaya pipe (Yakutia), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21171, https://doi.org/10.5194/egusphere-egu2020-21171, 2020.

About  >50 zicons from the kimbelite and carbonatite small bodied were analyzed  Nikolaev Institute of Inorganic Chemistry SB RAS, Novosibirsk, Russi by  LAM ICP MS method  They shoes variation of the TYRE and REE levels and  altitude of the  naximunu of Zr Hf and Ta NB /  The similarity of the  Lu/Hf isotopy sygggest that all kimberlites and  carbonatite in general are coherent  but derived from the different levals in mantle columns. The ages from zircons are varying from Upper triasssic to prevailing Late Jurassic  Mostrly they are transparent and have now fractures beein edial for the geochemical studioes

 Graant RFBR  19-05-00788.

How to cite: Babushkina, S., Mevedev, N., and Ashchepkov, I.: Kimberlitic Zircons from the Northern Rianabarie, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16215, https://doi.org/10.5194/egusphere-egu2020-16215, 2020.

In this paper are summarized investigation results on the chemistry, petrography and mineralogy of kimberlitic rocks of the upper and deep levels of the Yubileynaya pipe. There are given original data on mineral phases contents in kimberlite ground mass,distribution of indicator minerals and olivine and its pseudomorphoses as well as autoliths (pyroclasts) in kimberlite drill cores of different levels (-)280 – (-)680m.

Petrologic evidence suggest that for the kimberlites of the Yubileynaya pipe is characteristic the prevalence garnet association of indicator minerals with the relatively low their whole content, predominance oflherzolitic pyropes, low content of titanium garnets, two types of ilmenites and chromespinelides.The particularity of this pipe is the presence, both eclogite and garnet websterite xenoliths as well as their diamondiferous varieties. This evidence is confirmed also by the composition of the paragenic associations of indicator minerals that is indicative of essential difference of lithospheric mantle under this given pipe in contrast with nearby kimberlitic pipes. It is possible to speculate that these peculiarities are specific for the kimberlite pipes of the middle diamond productivity.

Results of the garnets chemistry and the data of the distribution of eclogitic and ultramafic garnets in kimberlite concentrate of this pipe with the taking in account quantity of garnet variety potentially associated with diamonds suggest anincreased prevalence of eclogitic garnets among indicator minerals. This allowed making a statement about essential input of eclogitic paragenesis diamonds in the whole diamond production of this pipe. In our opinion these peculiarities also determine the increased content of large diamond crystals in kimberlites of the Yubileynaya pipe.    

How to cite: Spetsius, Z. and Ivanov, A.: Petrology of the Yubileynaya kimberlite pipe: application to the variation of kimberlites composition with the depth, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8541, https://doi.org/10.5194/egusphere-egu2020-8541, 2020.