Igor Ashchepkov - Academia.edu (original) (raw)

Papers by Igor Ashchepkov

EGU General Assembly Conference Abstracts, Apr 1, 2013

ABSTRACT Dalnaya pipe is one of the largest in Daldyn field, Yakutia is composed of autolite brec... more ABSTRACT Dalnaya pipe is one of the largest in Daldyn field, Yakutia is composed of autolite breccia (AKB) and porphyric kimberlite (PK). Minerals from concentrates of both phases were compared and with the peridotite xenoliths minerals. Cpx from Dalnyaya are showing common tendencies Fe--Ti rise and Cr, Al, Na decrease. Garnets belong to lherzolite field with more deviation to harzbuirgitic one for (PK) . The chromites show two subtrends for Cr Fe, Ni vs TiO2. In general the variations of the AKB minerals and dispersion are higher but amount of depleted varieties is higher in PK. We used >50 xenoliths and ~1200 concentrate minerals for PT reconstructions. Combine PTX diagram show deep SCLM root beneath Dalnyaya with the main heating ~7 GPa. The HT 45mwm-2 branch is traced by some xenoliths from base to 2GPa. Essential inflection and heating detected by PT for OPx ~3GPa referring to Ca- enriched pyroxenitic garnets . Small Fe enrichment for Cpx and Gar found near 6 GPa referring to heated porhyroclastic varieties. Continuous and irregular growth of Fe# for Gar and low Fe Cpx Fe# 6 to 12# suggest that primary mantle layering beneath this pipe was smoothed by the high scale interaction with melts. The refertilization trend with Fe#9-15% rising upward in two branches refer to the Ilm and Cpx parental melt evolutions produced the intergrowth sometimes with garnets. In the PFO2 diagrams garnets and Cpx show continuous reduction to the lithosphere base to 4QMF higher for Cpx. Ilm - garnet trend is rising upward between -2 -0 QMF. The PT diagram for the AKB minerals from Dalnyaya pipe is nearly the same with the high dispersion to Fe rich varieties and smaller amount o f Mg rich minerals. Since the diamond grade is often determined by the amount of depleted varieties it is higher for the PK. Trace elements determined for Gar and Cpx from 13 xenoliths from the middle part of mantle section reveal very similar patterns in general. Supported by RBRF grant 11-05-00060.

<p&amp... more <p>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.</p><p>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.</p><p><em>This work was supported by the Russian Science Foundation under Grant No 16-17-10067.</em></p><p>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.</p><p>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.</p><p>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).</p><p>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.</p>

Ofioliti, Jan 3, 1999

Bartoy volcanoes (Dzhida, Trans Baikal, 1.5-0.8 Ma) are located in the southern peripheral margin... more Bartoy volcanoes (Dzhida, Trans Baikal, 1.5-0.8 Ma) are located in the southern peripheral margin of the Trans Hamar Daban zone within the Miocene alkaline-basalt lava plateau. Abundant xenoliths are here found in every scoria cones. Petrography and chemistry of xenoliths and lavas vary between the sites. The youngest and most alkaline Krich Bolshoi volcano contains the most variable set of inclusions, including spinel lherzolites with mica or/and amphibole megacrysts, their intergrowths and various cumulates. Megacrysts are pyrope nodules (up to 20 cm) with rutile, Tiaugites rarely in intergrowth with Ti-biotite, kaersutites with the feldspars between grains; anorthoclases with inclusions of Ti-biotites and oxides; common ilmenite and Ti magnetite nodules and rare sapphires and zircons. Clinopyroxene megacrysts reveal also four or five temperature and compositional intervals, with the more Cr-rich varieties found in contact with peridotites. Different inclinations of trend lines in Fe- or T oC- Ti, Al, Na diagrams correspond to the changes of the associated phases from pyrope to phlogopite and probably alkali feldspar (see figure). Kaersutites that are more magnesian than augite megacrysts form the large veins with druses on the lherzolite walls and are the result of the AFC of the HT hydrous melts. The more ferriferous group continues the augite crystallization line further followed by Ti-biotites and Ti-magnetites with anorthoclases. This range of the megacrystalline assemblages reflects the T-P descending crystallization line in the chain of the connected vein-magma chamber system at the pre-eruption stage, which later served as the conductor for the erupted melts. The polymineral cumulates forming clusters of Cpx compositions on the T axes seem to be connected with the megacrystalline descending line being the apophyses from the main magmatic system. More Fe-rich Pl-Cpx-pyrope cumulates form two varieties: i) the HT coarse-grained; ii) the LT layered fine grained. The descending line of augite-pyrope cumulates with Phl and later Amph derived from the beginning of the Phl-augite group represent the thick veins in contact with the hydrated lherzolite. Special varieties of hydrous hybrid polymineral peridotites with magmatic mineral zoning likely result from low viscous melt percolation through the lherzolites. The green LT-MT Low-Cr cumulates sometimes with garnet were subjected to fracturing and metasomatism. The lherzolite metasomatic column is separated into intervals: 1) HT sheared Fe- lherzolites; 2) HT deformed porphyroclastic phlogopite lherzolite; 3) microvein intergranular phlogopite-amphibole lherzolite; 4) amphibole equi- and protogranular lherzolites and 5) protogranular anhydrous lherzolites. Na fluctuates within each group revealing two tendencies with descending T: 1) decrease (Jd) with pressure and 2) increase (Eug) with the intergranular differentiation. The K/Na ratio, Ti, F in amphiboles decrease together with the temperatures, which demonstrates the infiltration nature of metasomatism but Ba and Na increase what may suggest a preceding mantle wedge stage. In each group of metasomatics two (or three) modes of Na, Al, Ti depletion and Cr enrichment in minerals suggest hydration on the protolith. The bulk rock composition demonstrates Fe, Na, Ti growth in bottom (interaction) and top (differentiation and melt accumulation) of the mantle column. Two lower parts reveal the thermal excitation. The metasomatic minerals always reveal LREE-rich Gd/YbN>1 patterns which suggests derivation of fluids from OIB melts generated in garnet facies. The question is whether the hydrated mantle column results from the preceding mantle metasomatism later reactivated with the intruded plume magmas saturating in water when interacting with wall rocks or the initial juvenile water abundance produced the hydrous cumulative assemblages and peridotite hydration. The absence of hydrous cumulates in the earlier formed nearest volcanoes is in favour of the first assumption. But the Barun Hobol volcanic group, 15 km southward also contains phlogopite and pyrope as megacrysts. It is possible to suggest that the main magmatic chamber feeding all this volcanoes was located beneath the lithospheric mantle and produced a series of pulses with different saturation in water. One can suppose that they had the same feeding channels and the megacrysts were created not in a rising evolving system but as a succession of melt intrusions. Detailed comparison of the megacrysts from the nearest volcanoes will help solve this problem. The ore mineralization in Dzhida was produced by hydrous magmas generated from the Ordovician collision. The mineral isochrones for hydrous mantle lherzolites (Ionov et al., 1992) give also Paleozoic ages for the primary water enrichment of the Dzhida mantle domain. However nearest xenoliths localities in Hamar-Daban are anhydrous (Ashchepkov, 1991; Ionov et al., 1995). More likely the water…

Geodinamika i Tektonofizika, Oct 12, 2022

<p>The Morkoka pipe belonging to the territory of West Daldyn terra... more <p>The Morkoka pipe belonging to the territory of West Daldyn terrane but It has all the features which are characteristic to the Malo- Botuobinsky or Upper MunaThe lower part of mantle section is represented by the depleted lower part of mantle section with the high amount of sub  Ca garnets with the high amount like in Mir pipe and rather long lineal ilmenite trend from the LAB at 7.5 GPA to the Moho at 2 GPA which is also the common feature of most pipe from the Magan terrane an happens in the Upper Muna field  Though the Morkoka pipe itself is barren the nearest territories around contain similar indicator minerals which shot ha there is a group pf pipes and some of them may be diamondiferous. The TRE patterns show mainly S- type which is perspective for the prospecting of diamonds.  But the HFSE for the garnets reveal rather high Zr>Hf peaks which became higher with the HREE level, (Ta>Nb) and higher than La. The LILE and Ba are typically low  but Th U sometimes higher than Nb. The ilmenites reveal slightly concave patterns with the minima near Gd  or  reveal  opposite inclination  similar to garnets but with the elevated LREE part.  The HFSE are rather high an Ta-Nb are higher that Zr Hf Some samples with the high LREE also reveal elevated Th and U, indicating influence of the essentially carbonatitic melts.</p><p>It seems that the mantle beneath the Morkoka pipe wre originally depleted but regenerated but the H2O bearing melts possibly rather oxidized and this may be the reason of the rather low diamond grade.  The ilmenites were generated by the essentially carbonatitic protokimberlite melts which passed through the matrix where garnets prevail  Reaction of the maters with the different REE inclination produced concave REE  patterns</p><p>Grant RBRF 19- 05-00788</p>

Acta Geologica Sinica-english Edition, Nov 1, 2021

EGU General Assembly Conference Abstracts, Apr 1, 2012

ABSTRACT Calculated oxygen fugacity conditions for ilmenites and chromites were obtained using th... more ABSTRACT Calculated oxygen fugacity conditions for ilmenites and chromites were obtained using the monomineral version of the Taylor (1998) oxygen barometers with the calculation of Fe#Ol according to (Ashchepkov et al., 2010). The monomineral version of the Gar- Ol- Opx method (Gudmundsson & Wood, 1995) was obtained using the regression between FO2 and Fe3 in garnet and additional correlation to P and T. F5=Fe#Gar/FeGar; Fo2= 2030.2*Ff5**3-1061.4*F5**2+190.89*F5-12.644 Fo2 = (Fo2-0.01*P (kbar)+(ToC-500)/(3500 -05.)*0.9 The obtained values wee regression and the new Cpx method constructed by the cross correlations of the Fe3+ in Cpx with the oxygen fugacity values obtained for garnets were used for the additional characterization of the mantle SCLM section. The statistical between regression obtained from the work (Gudmundsson, Wood , 1995) and corrections for the temperature and pressure justified by the comparisons obtained with the Ol- Sp and Ilm- Ol oxybarometers (Taylor et al., 1998) allow to estimate the FO2 (Δ log QMF) by following simple equations: For clinopyroxene the cross calibration allow to receive the following regression. Fo2=-186.71*Fe3**2+48.617*Fe3 - 2.3262; Fo2 = Fo2+(T0-500)/3500-0.01*P Fo2 = (Fo2-0.01*P (kbar)+(ToC-500)/3500 -05.)*0.7 For clinopyroxene the cross calibration allow to receive the following regression. Fo2=-186.71*Fe3**2+48.617*Fe3 - 2.3262; Fo2 = Fo2+(T0-500)/3500-0.01*P Fo2=(Fo2-0.5)*0.8 For the orthopyroxene the correlating with the CPx parameter was calculated as following The Fe3'Opx was corrected as Fe3Opx-0.03;Fo2=23.882*Fe3'Opx*(Fe1*15)**2-1.8805 Fo2= Fo2+((T0-400)/1000)*(Fe1*20)-0.0175*P; Fo2=(Fo2*(Fe1*15)**2-0.9*P/70)*0.9 Fo2=(Fo2-0.5)*0.9 Despite on the rather low resolution of the Fe3+ EPMA estimates statistically the determined parameters are rather useful and mark major levels in the SCLM beneath Siberian and other cratons. The rise of FO2 is marked in the three major intervals - in the lithosphere base near the base of lithosphere marking cumulates and shearing peridotites. Near the boundary of the upper and lower mantle at 40 kbar marking so called pyroxenite layer and within basaltic trap - cresponding to the level of water bearing malt interaction , Despite there several layer corresponding to the mantle layering and levels of polybaric hydraulic shearing coused by the protokimberlite melt intrusion. The garnets commonly give some additional trends of joined rising of Fo2 and decreasing of the pressures. There amount in the lower part of the mantle columns is reaching 5-6 units. They are very often correlating with the values determined for the Cpx but later are generally more oxidized. The diamond bearing associations including eclogites are commonly less oxidized belonging to the diamond stability field found by (McCammon et al ., 2001) . Sometimes these values are as low as -5.5 log u. Δ log QMF. Interesting feature the upper part of the SCLM is sometimes less oxidized then pyroxenite lens and even lower part of SCLM. The trends of the ilmenites commonly are just marking the line of diamong stability in DSCLM od became higher and (even SCLM) in the upper part . The Ti- bearing spinel are commonly marking slightly lower values then ilmenites while Ti-less chromites are commonly less oxidized marking major units in mantle layering. RBRF grant 11-05-00060.

EGU General Assembly Conference Abstracts, Apr 1, 2013

ABSTRACT Several xenoliths of the unusual fine grained essentially Phl-Ol rocks there were found ... more ABSTRACT Several xenoliths of the unusual fine grained essentially Phl-Ol rocks there were found in the Udachnaya Vostochnaya kimberlite pipe. There two varieties. The fist type ids composed mainly from Phl, and Ol and Chromites with Phl-Ol, Chromite while the other contain more ilmenites and phlogopites and rare. Among the xenocrysts the rounding Ol xenocrysts and mantle xenoliths including dunite, sheared peridotites, Mg- ilmenites, prevail. In the second type Ol -pyroxenites and xenocrysts of low Cr garnets occur (surrounded by thick kelyphite). The first type contain Ol (Fe#~15), Na -Ti-rich kersutite and low. In intergranular space Sr -apitite, Ba selestine as well as barites. Sulfides are pyrotites . chalcopyrite, pentlandite. Such a mineralogy are typical of the lamproite but the bulk rock composition gives relatively low Na (1.3%) and K (2.8%) and Al2O3 contents with ~32% of MgO and 11 % Fe due to abundant Ol xenocrysts. This allow to interpreted rock Ol breccia cemented by the lamprorite magma. the Ol xenocryst are zonal with Mg - rich cores 8-10% and Fe(14%) rims. The Chromite xenocrysts and phenocrsts show 50 -22 % Cr2O3 compositional range. and pressure range 5.0 -2.0 GPa The second type represent the zonal rocks with the Cpx outer xone the essentally Phl zone and then fine grained material of Phl. Ol, Cr-low Cpx, and ilmenites. Variation o Cpx from the contact to the inner part show an essential increase of Fe (4 - 7 %) TiO2 And Al2O3 as well as CaO suggesting the crystallization differentiation of magma. Starting parameters of the xenocrysts crystallization of the Ilm-Phl-Ol rock refer to the basement of the lithosphere beneath Udachnaya ~6.0 -5.5 GPa. But the final stage of crystallization was near Moho 1.2 -1.5 GPa according to Cpx barometry Ashchepkov et al ., 2011. and T 1100-1250 oC. The Ol-Chr sample possibly was crystallizing upper. The trace elements were measured by the LAM ICP MS method in IGM SD RAS using Finnigan ELEMENT with the YAG Nd 266 Laser Probe laser system (analyst S.V. Palessky). The Cpx from the contact zone from the last sample show the incline REE pattern with LREE to 100 and hump near Pr. The incompatible element (IK) are more plat near 70 C1 with depression in Nb -Ta. The REE patterns for phlogopite are more inclined. Phls as well as bulk rock demonstrate inflected in Gd patterns consisting from two highly inclined parts suggesting mixing of two highly evolved liquids. Spiderdiagrams show continuous PhlL enrichment in IK (smaller in HFSE and Pb) and extremely high Ba, Rb (1000C1). The Cr- low garnet megacryst show elevated LREE and high HREE and moderate enrichment in IK. Phl-Ol rocks represent the last stage dyke stage of H2O rich melts evolution close to kimberlite II which produced Phl metasomatism in the lithosphere base (Ashchepkov et al., 2012, 2013). RBRF grant 11-05-00060.

AGU Spring Meeting Abstracts, May 1, 2004

Layered mantle sequences beneath kimberlite pipes influences on melt- fluid percolation. Units re... more Layered mantle sequences beneath kimberlite pipes influences on melt- fluid percolation. Units recognized from top: 1. Sp- and Sp-garnet facies primitive or Si-enriched. 10-20 kbar (I) heated to 70-90 mv/m2 similar to alkali basalt xenoliths; 2. Upper garnet facie -coarse enriched lherzolites 20-35 kbar (I-II) are diapiric rising from submelted (II) 3.Pyroxenite lens 35-45 kbar (III) 35-55 mv/m2 accumulated water

EGU General Assembly Conference Abstracts, Apr 1, 2013

ABSTRACT Pleistocene Bartoy volcanoes 1.5-0.8 Ma (Ashchepkov et al., 2003) represent variable set... more ABSTRACT Pleistocene Bartoy volcanoes 1.5-0.8 Ma (Ashchepkov et al., 2003) represent variable set of hydrous cumulates and megacrysts and peridotite mantle xenoliths from spinel facies (Ashchepkov, 1991; Ionov, Kramm, 1992). Hydrous peridotites give series of the temperature groups: 1) deformed Fe - lherzolites (1200-1100o) , 2) Phl porhyroclastiμ (1100-1020o), 3) Amph -Phl (1020-940o), 4) Dry protogranular (1020-940o), 5)Amph equigranular (940-880o) and 6) dry and fine grained (880-820o). and Fe-rich poikilitic (700-600o) (Ashchepkov, 1991). T according (Nimis, Taylor, 2000) The sequence of the megacrysts crystallized on the wall of basaltic feeder in pre - eruption stage is starting from HT dark green websterites (1300-1200o), black Cpx- Gar varieties (1250-1200o) evolved to Phl -CPx (1200-1130o) and Cpx - Kaers (1130-1020o) - Cpx low in TiO2., Ilm and San (<1000o) like in Vitim (Ashchepkov et la., 2011). The differentiation trends looks branched but the question if they. Differentiation ain relatively large magma bodies p produced Ga- Cpx (+Amph-Phl- Ilm +-San) and then Cpx-Gar -Pl cumulates in( ~8-12 kbar) interval. In the ToC-Fe# diagram the Intermediate trend between lherzolites and megacrysts sub parallel to lherzolitic is correspondent to the fractionation of the hydrous alkali basalt melts in vein network created from the highly H2O bearing basaltic derivates formed in intermediate magma chambers. The interaction of the peridotites with the pulsing rising and evolving basaltic system produced the wall rock metasomatism and separate groups of peridotites in different levels of mantle column. PT calculations show two PT path and probably melt intrusion events. Trace elements in glass from crystalline basalts show Zr, Pb dips and Ta, Nb, Sr enrichment for the black megacrystalline Cpx , Gar series. They show link with evolved basalts by HFSE, Ba enrichment but Cpx from kaersutite and further Gar - Cpx cumulates show depressions in Ta, Nb, Zr, and Pb moderate enrichment in LILE and Sr. Pl - Gar cumulates show even jugged TRE spidergrams with Eu peaks and dips. The green Cpx from green series have now humps in TRE related to the garnet in meting source and are depleted in HFSE especially in Zr suggesting H2O- induced melting. Lherzolitic Cpx show enrichment in LREE and LILE but decrease in HFSE. The Cpx in contacts with basaltic derivates show U shaped REE and flattened patterns with Zr dips . The interaction is not highly pronounced and the distance of 3-4 sm. Most probably that metasomatism in lherzolitic column was produced by melts more rich fluids. The interaction with HT basalts produced the Fe lherzolites with the TRE patterns showing hump garnet signatures The model of the developing of the mantle column beneath Bartoy volcanoes suggest pulsing interaction with the basalts are checking using TRE components of all studied samples. Grant 11-05-00060.

EGU General Assembly Conference Abstracts, Apr 1, 2018

EGUGA, Apr 1, 2012

ABSTRACT Pyropes from the tributaries of Tumanshet r. (Birysa basin) were studied by EPMA and LAM... more ABSTRACT Pyropes from the tributaries of Tumanshet r. (Birysa basin) were studied by EPMA and LAM ICP methods. It Saranchet and Kharyuzovka placers rounded and pyropes (to 13% Cr2O3) are associated with Ti -chromites, rare picroilmenites (to 9% MgO and Cr-1-4%), Mn - ilmenites, low Na- Cr diopsides, hydro- garnets ( to 2% Cr2O3). In Slyudyanka in addition Cr- ruby (to 2.5%) and chromites to 60% Of cr2O3 are associated with pyropes. All placers are located within Poima - Buryusa paleo gulf constituted by carboniferous limestones. Pyropes from the upper stretches of small tributaries became fine grained less rounded and less in Cr2O3 (to 8%). Finding of diamonds locates at the boundaries of limestone deposits including the Shelehovo placer. Basal conglomerations contain only Cr-low pyropes and Mg- rich(7- 9%) almandines. LowNa Cr- diopside common in this area are from alnoites like those form Bushkanayskay dyke (Minaeva Egorov, 2009 )/ The Pyropes in placers possibly came from the phreatic kimberlite or lamproitic magamtism in paleo gulf which started close in time to the kimberlites in Central Yakutia (D-C boundary) and continued to 300 ma (Ingashisky lamproites) and possibly to Jurassic (alnoites). The trends P (kbar)- Fe# differ for three localities of pyropes: Muro Kovinsky - 200 to north reveal the typical Paleozoic trend with slight increasing of Fe to the top and bottom of sublithospheric mantle (SCLM). Judging by abundance of ilmenites and TRE of garnets - source of placer was typical for the D-C kimberlites. The pyropes from Tumanshet locality show unic trend Mg -rich in basement (typical for the diamond inclusions) and increasing in upper part which is common for Jurassic post superplume kimberlites in Northern part of Siberian platform with inflection near 40 kbar. The garnet trend from Ingashi lamproites reveal gentle decrease of Fe# (10%) starting from the basement to the top (7%). The rarity of picroilmenites and frequency of Ti - enrichment in chromites in Tumanshet placer evidences that the source was essentially H2O rich magmas kimberlite II or lamproites. Trace elements for all these localities in southern part of Siberian craton essentially differ (Egorov et al in press). The garnets from Muro- Kovinkoe shows typical primive mantle lherzolitic rounded distributions. The garnets from Ingashi lamproites show LREE enrichment. And the Tumanshet garnets reveal motley distributions from S- type (basement) to magmatic HFSE enriched in middle part of SCLM. Thermo-barometric reconstruction reveal that mantle in deepest part of SCLM (80-60 kbar) was not subjected to essential malt interaction. The intraction with H2O bearing plume melts starts from 60 kbar to the 40 kbar boundary/ And upper part was subjected to the refertillizarion within the trap for picro basaltic magmas Thlithospheric keel which, was excited by proto-kimberlitic magma at level 65 -75 kbar. Grants of Russian Basic Research Fund 11-05-00060a; 11-05-91060-PICS

EGU General Assembly Conference Abstracts, Apr 1, 2015

Springer eBooks, 1991

Tectonized harzburgites constituting the ultramafic basement of inter-arc and back-arc basins and... more Tectonized harzburgites constituting the ultramafic basement of inter-arc and back-arc basins and forming the lower part of corresponding ophiolites provide textural and mineralogical evidences that some veins and other local mineral segregations resulted from crystallization from infiltrated basicultrabasic melt and the reaction of that melt with harzburgites. Veins of dunite are found by reaction. Veins of pyroxenite and gabbro may be formed by disequilibrium crystallization from infiltrated melts during the general cooling. These vein assemblages occur in many ophiolites including Upper Precambrian and Palaeozoic ophiolites of the Urals and southern Siberia. The evolution of the upper mantle beneath Baikal Rift Zone (BRZ) in the Cenozoic was estimated based on the studies of a great number of mantle xenoliths from the basaltic lavas and tuffs of three stages of volcanic activity (about 30 m.y., 18-9 m.y. and 5-2 m.y.). The xenoliths of the first stage are composed of Mg-and Cr-rich minerals whereas those of the second and the third stages are enriched in AI, Fe, Ti, Na. Magma segregation was deepest at the early stage, shifted upwards at the second stage and went down again at the third stage. These changes may be correlated with the compositions of lavas and the scale of volcanic activity. The geotherms plotted using garnet-bearing assemblages show that the temperatures for the same depth levels increased by about 100-150°C from the first to the last stage. We suppose that the heating and alteration of mantle was started by the intrusion of the picritic magma at the depth of 100-120 km. Green pyroxenites crystallized from picritic melts while black pyroxenites and amphibole-phlogopite cumulites were formed from basaltic liquids. A direct evidence of infiltration of such melts is glass-bearing veins in the mantle lherzolites. The composition of these glasses from the Cenozoic mantle xenoliths of BRZ includes olivinerich to felsic differentiated liquids. The composition of rocks and minerals show the same similarities and differences between the processes in oceanic and continental upper mantle. The main differences can be related to composition of migrating melt and

Geochimica et Cosmochimica Acta, Mar 1, 1994

Spine1 and garnet facies peridotites from the Vitim Volcanic Field in Siberia comprise a suite of... more Spine1 and garnet facies peridotites from the Vitim Volcanic Field in Siberia comprise a suite of fertile mantle xenoliths, which are LREE depleted and have strongly depleted strontium and neodymium isotopic compositions. Determination of '*O/ I60 ratios by conventional and laser-assisted fluorination techniques yield a very restricted range of whole-rock 6'*0 values for both spine1 peridotites (+5.4 to +5.8%0) and garnet lherzolites (+5.5 to +5.8%0) equivalent to that observed for lunar rocks and midocean ridge basalts (MORB). Mineral 6'*0 values for the xenoliths are: olivine = $5.1 to +5.8%0, orthopyroxene = +5.7 to +6.0%0, clinopyroxene = +5.5 to +6.2%0, garnet = f5.5 to +6.0%0, and spine1 = +4.9 to +5.5%0. Similarly, 6'*0 ranges for silicate mineral pairs vary from only 0.5 to 0.7%0. The sixteen peridotite xenoliths studied exhibit equilibrium O-isotope fractionations between minerals of a magnitude expected from theoretical and experimental considerations, in particular a temperature-controlled I80 distribution between olivine and pyroxenes in spinel-bearing peridotites. Because the Vitim garnet and spine1 peridotites are rich in basaltic components and show long-term depletion in incompatible elements, they are derived from a MORB-like mantle source which makes up, according to current geochemical models, a predominant part of the Earth's upper mantle. The Vitim xenolith suite may, therefore, reflect its bulk O-isotope character. With increasing temperature and degree of partial melting, such a mantle source could generate basaltic liquids with 6 I80 values varying from c.+6.1 to +5.7%0. Thus, the broad 6180 range of c.+4.5 to +7.5%0 reported in the literature for spine1 peridotite xenoliths is probably a very restricted disequilibrium phenomenon that likely reflects recent metasomatic overprinting in highly localized zones of the uppermost continental mantle affected by basaltic magmatism and, therefore, should not be considered as representative of the upper mantle, in general. _

Contributions to Mineralogy and Petrology, Nov 21, 1995

Lherzolite xenoliths in Miocene to Pleistocene basalts from five sites in the Hamar-Daban range i... more Lherzolite xenoliths in Miocene to Pleistocene basalts from five sites in the Hamar-Daban range in southern Siberia provide sampling of the mantle close to the axis of the Baikal rift. These anhydrous spinel lherzolites commonly have foliated fabrics and spongy rims around clinopyroxene, and many contain accessory feldspar. The feldspar occurs in reaction zones adjacent to spinel and orthopyroxene (where it appears to have been formed by the reaction: splϩopxϩcpxϩfluid → fsϩol) and less commonly as thin, irregular veins. The feldspars have variable compositions but are generally alkali-rich; their K 2 O content ranges from 0.3 to 11.2% and is much higher than in plagioclase from orogenic lherzolites (usually Ͻ0.1% K 2 O). The temperature range for the Hamar-Daban xenolith suite (950-1010Њ C) is more restricted than for spinel peridotite xenoliths from other occurrences in the Baikal area. The feldspar-bearing lherzolites yield equilibration temperatures similar to or slightly lower than feldspar-free ones. The majority of the Hamar-Daban lherzolites are fertile and clinopyroxene-rich, as for most other occurrences in the Baikal region. Trace element compositions of selected xenoliths and their clinopyroxenes were determined by ICP-MS, INAA and proton microprobe. Feldspar-bearing xenoliths are enriched in alkalies indicating that feldspar formation is associated with addition of material and is not simply due to isochemical phase changes. Most xenoliths and their clinopyroxenes studied are depleted in light REE and have contents of Sr, Zr and Y common for fertile or moderately depleted mantle peridotites. Few are moderately enriched in LREE, Sr, Th and U. Sr-Nd isotope compositions of clinopyroxenes indicate long-term depletion in incompatible elements similar to unmetasomatised xenoliths from other occurrences south and east of Lake Baikal. The formation of feldspar and of spongy aggregates after clinopyroxene, and the enrichment in alkalies appear to be recent phenomena related to infiltration of an alkali-rich, H 2 O-poor fluid into spinel peridotites.

EGU General Assembly Conference Abstracts, Apr 1, 2013

ABSTRACT Dalnaya pipe is one of the largest in Daldyn field, Yakutia is composed of autolite brec... more ABSTRACT Dalnaya pipe is one of the largest in Daldyn field, Yakutia is composed of autolite breccia (AKB) and porphyric kimberlite (PK). Minerals from concentrates of both phases were compared and with the peridotite xenoliths minerals. Cpx from Dalnyaya are showing common tendencies Fe--Ti rise and Cr, Al, Na decrease. Garnets belong to lherzolite field with more deviation to harzbuirgitic one for (PK) . The chromites show two subtrends for Cr Fe, Ni vs TiO2. In general the variations of the AKB minerals and dispersion are higher but amount of depleted varieties is higher in PK. We used >50 xenoliths and ~1200 concentrate minerals for PT reconstructions. Combine PTX diagram show deep SCLM root beneath Dalnyaya with the main heating ~7 GPa. The HT 45mwm-2 branch is traced by some xenoliths from base to 2GPa. Essential inflection and heating detected by PT for OPx ~3GPa referring to Ca- enriched pyroxenitic garnets . Small Fe enrichment for Cpx and Gar found near 6 GPa referring to heated porhyroclastic varieties. Continuous and irregular growth of Fe# for Gar and low Fe Cpx Fe# 6 to 12# suggest that primary mantle layering beneath this pipe was smoothed by the high scale interaction with melts. The refertilization trend with Fe#9-15% rising upward in two branches refer to the Ilm and Cpx parental melt evolutions produced the intergrowth sometimes with garnets. In the PFO2 diagrams garnets and Cpx show continuous reduction to the lithosphere base to 4QMF higher for Cpx. Ilm - garnet trend is rising upward between -2 -0 QMF. The PT diagram for the AKB minerals from Dalnyaya pipe is nearly the same with the high dispersion to Fe rich varieties and smaller amount o f Mg rich minerals. Since the diamond grade is often determined by the amount of depleted varieties it is higher for the PK. Trace elements determined for Gar and Cpx from 13 xenoliths from the middle part of mantle section reveal very similar patterns in general. Supported by RBRF grant 11-05-00060.

<p&amp... more <p>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.</p><p>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.</p><p><em>This work was supported by the Russian Science Foundation under Grant No 16-17-10067.</em></p><p>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.</p><p>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.</p><p>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).</p><p>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.</p>

Ofioliti, Jan 3, 1999

Bartoy volcanoes (Dzhida, Trans Baikal, 1.5-0.8 Ma) are located in the southern peripheral margin... more Bartoy volcanoes (Dzhida, Trans Baikal, 1.5-0.8 Ma) are located in the southern peripheral margin of the Trans Hamar Daban zone within the Miocene alkaline-basalt lava plateau. Abundant xenoliths are here found in every scoria cones. Petrography and chemistry of xenoliths and lavas vary between the sites. The youngest and most alkaline Krich Bolshoi volcano contains the most variable set of inclusions, including spinel lherzolites with mica or/and amphibole megacrysts, their intergrowths and various cumulates. Megacrysts are pyrope nodules (up to 20 cm) with rutile, Tiaugites rarely in intergrowth with Ti-biotite, kaersutites with the feldspars between grains; anorthoclases with inclusions of Ti-biotites and oxides; common ilmenite and Ti magnetite nodules and rare sapphires and zircons. Clinopyroxene megacrysts reveal also four or five temperature and compositional intervals, with the more Cr-rich varieties found in contact with peridotites. Different inclinations of trend lines in Fe- or T oC- Ti, Al, Na diagrams correspond to the changes of the associated phases from pyrope to phlogopite and probably alkali feldspar (see figure). Kaersutites that are more magnesian than augite megacrysts form the large veins with druses on the lherzolite walls and are the result of the AFC of the HT hydrous melts. The more ferriferous group continues the augite crystallization line further followed by Ti-biotites and Ti-magnetites with anorthoclases. This range of the megacrystalline assemblages reflects the T-P descending crystallization line in the chain of the connected vein-magma chamber system at the pre-eruption stage, which later served as the conductor for the erupted melts. The polymineral cumulates forming clusters of Cpx compositions on the T axes seem to be connected with the megacrystalline descending line being the apophyses from the main magmatic system. More Fe-rich Pl-Cpx-pyrope cumulates form two varieties: i) the HT coarse-grained; ii) the LT layered fine grained. The descending line of augite-pyrope cumulates with Phl and later Amph derived from the beginning of the Phl-augite group represent the thick veins in contact with the hydrated lherzolite. Special varieties of hydrous hybrid polymineral peridotites with magmatic mineral zoning likely result from low viscous melt percolation through the lherzolites. The green LT-MT Low-Cr cumulates sometimes with garnet were subjected to fracturing and metasomatism. The lherzolite metasomatic column is separated into intervals: 1) HT sheared Fe- lherzolites; 2) HT deformed porphyroclastic phlogopite lherzolite; 3) microvein intergranular phlogopite-amphibole lherzolite; 4) amphibole equi- and protogranular lherzolites and 5) protogranular anhydrous lherzolites. Na fluctuates within each group revealing two tendencies with descending T: 1) decrease (Jd) with pressure and 2) increase (Eug) with the intergranular differentiation. The K/Na ratio, Ti, F in amphiboles decrease together with the temperatures, which demonstrates the infiltration nature of metasomatism but Ba and Na increase what may suggest a preceding mantle wedge stage. In each group of metasomatics two (or three) modes of Na, Al, Ti depletion and Cr enrichment in minerals suggest hydration on the protolith. The bulk rock composition demonstrates Fe, Na, Ti growth in bottom (interaction) and top (differentiation and melt accumulation) of the mantle column. Two lower parts reveal the thermal excitation. The metasomatic minerals always reveal LREE-rich Gd/YbN>1 patterns which suggests derivation of fluids from OIB melts generated in garnet facies. The question is whether the hydrated mantle column results from the preceding mantle metasomatism later reactivated with the intruded plume magmas saturating in water when interacting with wall rocks or the initial juvenile water abundance produced the hydrous cumulative assemblages and peridotite hydration. The absence of hydrous cumulates in the earlier formed nearest volcanoes is in favour of the first assumption. But the Barun Hobol volcanic group, 15 km southward also contains phlogopite and pyrope as megacrysts. It is possible to suggest that the main magmatic chamber feeding all this volcanoes was located beneath the lithospheric mantle and produced a series of pulses with different saturation in water. One can suppose that they had the same feeding channels and the megacrysts were created not in a rising evolving system but as a succession of melt intrusions. Detailed comparison of the megacrysts from the nearest volcanoes will help solve this problem. The ore mineralization in Dzhida was produced by hydrous magmas generated from the Ordovician collision. The mineral isochrones for hydrous mantle lherzolites (Ionov et al., 1992) give also Paleozoic ages for the primary water enrichment of the Dzhida mantle domain. However nearest xenoliths localities in Hamar-Daban are anhydrous (Ashchepkov, 1991; Ionov et al., 1995). More likely the water…

Geodinamika i Tektonofizika, Oct 12, 2022

<p>The Morkoka pipe belonging to the territory of West Daldyn terra... more <p>The Morkoka pipe belonging to the territory of West Daldyn terrane but It has all the features which are characteristic to the Malo- Botuobinsky or Upper MunaThe lower part of mantle section is represented by the depleted lower part of mantle section with the high amount of sub  Ca garnets with the high amount like in Mir pipe and rather long lineal ilmenite trend from the LAB at 7.5 GPA to the Moho at 2 GPA which is also the common feature of most pipe from the Magan terrane an happens in the Upper Muna field  Though the Morkoka pipe itself is barren the nearest territories around contain similar indicator minerals which shot ha there is a group pf pipes and some of them may be diamondiferous. The TRE patterns show mainly S- type which is perspective for the prospecting of diamonds.  But the HFSE for the garnets reveal rather high Zr>Hf peaks which became higher with the HREE level, (Ta>Nb) and higher than La. The LILE and Ba are typically low  but Th U sometimes higher than Nb. The ilmenites reveal slightly concave patterns with the minima near Gd  or  reveal  opposite inclination  similar to garnets but with the elevated LREE part.  The HFSE are rather high an Ta-Nb are higher that Zr Hf Some samples with the high LREE also reveal elevated Th and U, indicating influence of the essentially carbonatitic melts.</p><p>It seems that the mantle beneath the Morkoka pipe wre originally depleted but regenerated but the H2O bearing melts possibly rather oxidized and this may be the reason of the rather low diamond grade.  The ilmenites were generated by the essentially carbonatitic protokimberlite melts which passed through the matrix where garnets prevail  Reaction of the maters with the different REE inclination produced concave REE  patterns</p><p>Grant RBRF 19- 05-00788</p>

Acta Geologica Sinica-english Edition, Nov 1, 2021

EGU General Assembly Conference Abstracts, Apr 1, 2012

ABSTRACT Calculated oxygen fugacity conditions for ilmenites and chromites were obtained using th... more ABSTRACT Calculated oxygen fugacity conditions for ilmenites and chromites were obtained using the monomineral version of the Taylor (1998) oxygen barometers with the calculation of Fe#Ol according to (Ashchepkov et al., 2010). The monomineral version of the Gar- Ol- Opx method (Gudmundsson & Wood, 1995) was obtained using the regression between FO2 and Fe3 in garnet and additional correlation to P and T. F5=Fe#Gar/FeGar; Fo2= 2030.2*Ff5**3-1061.4*F5**2+190.89*F5-12.644 Fo2 = (Fo2-0.01*P (kbar)+(ToC-500)/(3500 -05.)*0.9 The obtained values wee regression and the new Cpx method constructed by the cross correlations of the Fe3+ in Cpx with the oxygen fugacity values obtained for garnets were used for the additional characterization of the mantle SCLM section. The statistical between regression obtained from the work (Gudmundsson, Wood , 1995) and corrections for the temperature and pressure justified by the comparisons obtained with the Ol- Sp and Ilm- Ol oxybarometers (Taylor et al., 1998) allow to estimate the FO2 (Δ log QMF) by following simple equations: For clinopyroxene the cross calibration allow to receive the following regression. Fo2=-186.71*Fe3**2+48.617*Fe3 - 2.3262; Fo2 = Fo2+(T0-500)/3500-0.01*P Fo2 = (Fo2-0.01*P (kbar)+(ToC-500)/3500 -05.)*0.7 For clinopyroxene the cross calibration allow to receive the following regression. Fo2=-186.71*Fe3**2+48.617*Fe3 - 2.3262; Fo2 = Fo2+(T0-500)/3500-0.01*P Fo2=(Fo2-0.5)*0.8 For the orthopyroxene the correlating with the CPx parameter was calculated as following The Fe3'Opx was corrected as Fe3Opx-0.03;Fo2=23.882*Fe3'Opx*(Fe1*15)**2-1.8805 Fo2= Fo2+((T0-400)/1000)*(Fe1*20)-0.0175*P; Fo2=(Fo2*(Fe1*15)**2-0.9*P/70)*0.9 Fo2=(Fo2-0.5)*0.9 Despite on the rather low resolution of the Fe3+ EPMA estimates statistically the determined parameters are rather useful and mark major levels in the SCLM beneath Siberian and other cratons. The rise of FO2 is marked in the three major intervals - in the lithosphere base near the base of lithosphere marking cumulates and shearing peridotites. Near the boundary of the upper and lower mantle at 40 kbar marking so called pyroxenite layer and within basaltic trap - cresponding to the level of water bearing malt interaction , Despite there several layer corresponding to the mantle layering and levels of polybaric hydraulic shearing coused by the protokimberlite melt intrusion. The garnets commonly give some additional trends of joined rising of Fo2 and decreasing of the pressures. There amount in the lower part of the mantle columns is reaching 5-6 units. They are very often correlating with the values determined for the Cpx but later are generally more oxidized. The diamond bearing associations including eclogites are commonly less oxidized belonging to the diamond stability field found by (McCammon et al ., 2001) . Sometimes these values are as low as -5.5 log u. Δ log QMF. Interesting feature the upper part of the SCLM is sometimes less oxidized then pyroxenite lens and even lower part of SCLM. The trends of the ilmenites commonly are just marking the line of diamong stability in DSCLM od became higher and (even SCLM) in the upper part . The Ti- bearing spinel are commonly marking slightly lower values then ilmenites while Ti-less chromites are commonly less oxidized marking major units in mantle layering. RBRF grant 11-05-00060.

EGU General Assembly Conference Abstracts, Apr 1, 2013

ABSTRACT Several xenoliths of the unusual fine grained essentially Phl-Ol rocks there were found ... more ABSTRACT Several xenoliths of the unusual fine grained essentially Phl-Ol rocks there were found in the Udachnaya Vostochnaya kimberlite pipe. There two varieties. The fist type ids composed mainly from Phl, and Ol and Chromites with Phl-Ol, Chromite while the other contain more ilmenites and phlogopites and rare. Among the xenocrysts the rounding Ol xenocrysts and mantle xenoliths including dunite, sheared peridotites, Mg- ilmenites, prevail. In the second type Ol -pyroxenites and xenocrysts of low Cr garnets occur (surrounded by thick kelyphite). The first type contain Ol (Fe#~15), Na -Ti-rich kersutite and low. In intergranular space Sr -apitite, Ba selestine as well as barites. Sulfides are pyrotites . chalcopyrite, pentlandite. Such a mineralogy are typical of the lamproite but the bulk rock composition gives relatively low Na (1.3%) and K (2.8%) and Al2O3 contents with ~32% of MgO and 11 % Fe due to abundant Ol xenocrysts. This allow to interpreted rock Ol breccia cemented by the lamprorite magma. the Ol xenocryst are zonal with Mg - rich cores 8-10% and Fe(14%) rims. The Chromite xenocrysts and phenocrsts show 50 -22 % Cr2O3 compositional range. and pressure range 5.0 -2.0 GPa The second type represent the zonal rocks with the Cpx outer xone the essentally Phl zone and then fine grained material of Phl. Ol, Cr-low Cpx, and ilmenites. Variation o Cpx from the contact to the inner part show an essential increase of Fe (4 - 7 %) TiO2 And Al2O3 as well as CaO suggesting the crystallization differentiation of magma. Starting parameters of the xenocrysts crystallization of the Ilm-Phl-Ol rock refer to the basement of the lithosphere beneath Udachnaya ~6.0 -5.5 GPa. But the final stage of crystallization was near Moho 1.2 -1.5 GPa according to Cpx barometry Ashchepkov et al ., 2011. and T 1100-1250 oC. The Ol-Chr sample possibly was crystallizing upper. The trace elements were measured by the LAM ICP MS method in IGM SD RAS using Finnigan ELEMENT with the YAG Nd 266 Laser Probe laser system (analyst S.V. Palessky). The Cpx from the contact zone from the last sample show the incline REE pattern with LREE to 100 and hump near Pr. The incompatible element (IK) are more plat near 70 C1 with depression in Nb -Ta. The REE patterns for phlogopite are more inclined. Phls as well as bulk rock demonstrate inflected in Gd patterns consisting from two highly inclined parts suggesting mixing of two highly evolved liquids. Spiderdiagrams show continuous PhlL enrichment in IK (smaller in HFSE and Pb) and extremely high Ba, Rb (1000C1). The Cr- low garnet megacryst show elevated LREE and high HREE and moderate enrichment in IK. Phl-Ol rocks represent the last stage dyke stage of H2O rich melts evolution close to kimberlite II which produced Phl metasomatism in the lithosphere base (Ashchepkov et al., 2012, 2013). RBRF grant 11-05-00060.

AGU Spring Meeting Abstracts, May 1, 2004

Layered mantle sequences beneath kimberlite pipes influences on melt- fluid percolation. Units re... more Layered mantle sequences beneath kimberlite pipes influences on melt- fluid percolation. Units recognized from top: 1. Sp- and Sp-garnet facies primitive or Si-enriched. 10-20 kbar (I) heated to 70-90 mv/m2 similar to alkali basalt xenoliths; 2. Upper garnet facie -coarse enriched lherzolites 20-35 kbar (I-II) are diapiric rising from submelted (II) 3.Pyroxenite lens 35-45 kbar (III) 35-55 mv/m2 accumulated water

EGU General Assembly Conference Abstracts, Apr 1, 2013

ABSTRACT Pleistocene Bartoy volcanoes 1.5-0.8 Ma (Ashchepkov et al., 2003) represent variable set... more ABSTRACT Pleistocene Bartoy volcanoes 1.5-0.8 Ma (Ashchepkov et al., 2003) represent variable set of hydrous cumulates and megacrysts and peridotite mantle xenoliths from spinel facies (Ashchepkov, 1991; Ionov, Kramm, 1992). Hydrous peridotites give series of the temperature groups: 1) deformed Fe - lherzolites (1200-1100o) , 2) Phl porhyroclastiμ (1100-1020o), 3) Amph -Phl (1020-940o), 4) Dry protogranular (1020-940o), 5)Amph equigranular (940-880o) and 6) dry and fine grained (880-820o). and Fe-rich poikilitic (700-600o) (Ashchepkov, 1991). T according (Nimis, Taylor, 2000) The sequence of the megacrysts crystallized on the wall of basaltic feeder in pre - eruption stage is starting from HT dark green websterites (1300-1200o), black Cpx- Gar varieties (1250-1200o) evolved to Phl -CPx (1200-1130o) and Cpx - Kaers (1130-1020o) - Cpx low in TiO2., Ilm and San (<1000o) like in Vitim (Ashchepkov et la., 2011). The differentiation trends looks branched but the question if they. Differentiation ain relatively large magma bodies p produced Ga- Cpx (+Amph-Phl- Ilm +-San) and then Cpx-Gar -Pl cumulates in( ~8-12 kbar) interval. In the ToC-Fe# diagram the Intermediate trend between lherzolites and megacrysts sub parallel to lherzolitic is correspondent to the fractionation of the hydrous alkali basalt melts in vein network created from the highly H2O bearing basaltic derivates formed in intermediate magma chambers. The interaction of the peridotites with the pulsing rising and evolving basaltic system produced the wall rock metasomatism and separate groups of peridotites in different levels of mantle column. PT calculations show two PT path and probably melt intrusion events. Trace elements in glass from crystalline basalts show Zr, Pb dips and Ta, Nb, Sr enrichment for the black megacrystalline Cpx , Gar series. They show link with evolved basalts by HFSE, Ba enrichment but Cpx from kaersutite and further Gar - Cpx cumulates show depressions in Ta, Nb, Zr, and Pb moderate enrichment in LILE and Sr. Pl - Gar cumulates show even jugged TRE spidergrams with Eu peaks and dips. The green Cpx from green series have now humps in TRE related to the garnet in meting source and are depleted in HFSE especially in Zr suggesting H2O- induced melting. Lherzolitic Cpx show enrichment in LREE and LILE but decrease in HFSE. The Cpx in contacts with basaltic derivates show U shaped REE and flattened patterns with Zr dips . The interaction is not highly pronounced and the distance of 3-4 sm. Most probably that metasomatism in lherzolitic column was produced by melts more rich fluids. The interaction with HT basalts produced the Fe lherzolites with the TRE patterns showing hump garnet signatures The model of the developing of the mantle column beneath Bartoy volcanoes suggest pulsing interaction with the basalts are checking using TRE components of all studied samples. Grant 11-05-00060.

EGU General Assembly Conference Abstracts, Apr 1, 2018

EGUGA, Apr 1, 2012

ABSTRACT Pyropes from the tributaries of Tumanshet r. (Birysa basin) were studied by EPMA and LAM... more ABSTRACT Pyropes from the tributaries of Tumanshet r. (Birysa basin) were studied by EPMA and LAM ICP methods. It Saranchet and Kharyuzovka placers rounded and pyropes (to 13% Cr2O3) are associated with Ti -chromites, rare picroilmenites (to 9% MgO and Cr-1-4%), Mn - ilmenites, low Na- Cr diopsides, hydro- garnets ( to 2% Cr2O3). In Slyudyanka in addition Cr- ruby (to 2.5%) and chromites to 60% Of cr2O3 are associated with pyropes. All placers are located within Poima - Buryusa paleo gulf constituted by carboniferous limestones. Pyropes from the upper stretches of small tributaries became fine grained less rounded and less in Cr2O3 (to 8%). Finding of diamonds locates at the boundaries of limestone deposits including the Shelehovo placer. Basal conglomerations contain only Cr-low pyropes and Mg- rich(7- 9%) almandines. LowNa Cr- diopside common in this area are from alnoites like those form Bushkanayskay dyke (Minaeva Egorov, 2009 )/ The Pyropes in placers possibly came from the phreatic kimberlite or lamproitic magamtism in paleo gulf which started close in time to the kimberlites in Central Yakutia (D-C boundary) and continued to 300 ma (Ingashisky lamproites) and possibly to Jurassic (alnoites). The trends P (kbar)- Fe# differ for three localities of pyropes: Muro Kovinsky - 200 to north reveal the typical Paleozoic trend with slight increasing of Fe to the top and bottom of sublithospheric mantle (SCLM). Judging by abundance of ilmenites and TRE of garnets - source of placer was typical for the D-C kimberlites. The pyropes from Tumanshet locality show unic trend Mg -rich in basement (typical for the diamond inclusions) and increasing in upper part which is common for Jurassic post superplume kimberlites in Northern part of Siberian platform with inflection near 40 kbar. The garnet trend from Ingashi lamproites reveal gentle decrease of Fe# (10%) starting from the basement to the top (7%). The rarity of picroilmenites and frequency of Ti - enrichment in chromites in Tumanshet placer evidences that the source was essentially H2O rich magmas kimberlite II or lamproites. Trace elements for all these localities in southern part of Siberian craton essentially differ (Egorov et al in press). The garnets from Muro- Kovinkoe shows typical primive mantle lherzolitic rounded distributions. The garnets from Ingashi lamproites show LREE enrichment. And the Tumanshet garnets reveal motley distributions from S- type (basement) to magmatic HFSE enriched in middle part of SCLM. Thermo-barometric reconstruction reveal that mantle in deepest part of SCLM (80-60 kbar) was not subjected to essential malt interaction. The intraction with H2O bearing plume melts starts from 60 kbar to the 40 kbar boundary/ And upper part was subjected to the refertillizarion within the trap for picro basaltic magmas Thlithospheric keel which, was excited by proto-kimberlitic magma at level 65 -75 kbar. Grants of Russian Basic Research Fund 11-05-00060a; 11-05-91060-PICS

EGU General Assembly Conference Abstracts, Apr 1, 2015

Springer eBooks, 1991

Tectonized harzburgites constituting the ultramafic basement of inter-arc and back-arc basins and... more Tectonized harzburgites constituting the ultramafic basement of inter-arc and back-arc basins and forming the lower part of corresponding ophiolites provide textural and mineralogical evidences that some veins and other local mineral segregations resulted from crystallization from infiltrated basicultrabasic melt and the reaction of that melt with harzburgites. Veins of dunite are found by reaction. Veins of pyroxenite and gabbro may be formed by disequilibrium crystallization from infiltrated melts during the general cooling. These vein assemblages occur in many ophiolites including Upper Precambrian and Palaeozoic ophiolites of the Urals and southern Siberia. The evolution of the upper mantle beneath Baikal Rift Zone (BRZ) in the Cenozoic was estimated based on the studies of a great number of mantle xenoliths from the basaltic lavas and tuffs of three stages of volcanic activity (about 30 m.y., 18-9 m.y. and 5-2 m.y.). The xenoliths of the first stage are composed of Mg-and Cr-rich minerals whereas those of the second and the third stages are enriched in AI, Fe, Ti, Na. Magma segregation was deepest at the early stage, shifted upwards at the second stage and went down again at the third stage. These changes may be correlated with the compositions of lavas and the scale of volcanic activity. The geotherms plotted using garnet-bearing assemblages show that the temperatures for the same depth levels increased by about 100-150°C from the first to the last stage. We suppose that the heating and alteration of mantle was started by the intrusion of the picritic magma at the depth of 100-120 km. Green pyroxenites crystallized from picritic melts while black pyroxenites and amphibole-phlogopite cumulites were formed from basaltic liquids. A direct evidence of infiltration of such melts is glass-bearing veins in the mantle lherzolites. The composition of these glasses from the Cenozoic mantle xenoliths of BRZ includes olivinerich to felsic differentiated liquids. The composition of rocks and minerals show the same similarities and differences between the processes in oceanic and continental upper mantle. The main differences can be related to composition of migrating melt and

Geochimica et Cosmochimica Acta, Mar 1, 1994

Spine1 and garnet facies peridotites from the Vitim Volcanic Field in Siberia comprise a suite of... more Spine1 and garnet facies peridotites from the Vitim Volcanic Field in Siberia comprise a suite of fertile mantle xenoliths, which are LREE depleted and have strongly depleted strontium and neodymium isotopic compositions. Determination of '*O/ I60 ratios by conventional and laser-assisted fluorination techniques yield a very restricted range of whole-rock 6'*0 values for both spine1 peridotites (+5.4 to +5.8%0) and garnet lherzolites (+5.5 to +5.8%0) equivalent to that observed for lunar rocks and midocean ridge basalts (MORB). Mineral 6'*0 values for the xenoliths are: olivine = $5.1 to +5.8%0, orthopyroxene = +5.7 to +6.0%0, clinopyroxene = +5.5 to +6.2%0, garnet = f5.5 to +6.0%0, and spine1 = +4.9 to +5.5%0. Similarly, 6'*0 ranges for silicate mineral pairs vary from only 0.5 to 0.7%0. The sixteen peridotite xenoliths studied exhibit equilibrium O-isotope fractionations between minerals of a magnitude expected from theoretical and experimental considerations, in particular a temperature-controlled I80 distribution between olivine and pyroxenes in spinel-bearing peridotites. Because the Vitim garnet and spine1 peridotites are rich in basaltic components and show long-term depletion in incompatible elements, they are derived from a MORB-like mantle source which makes up, according to current geochemical models, a predominant part of the Earth's upper mantle. The Vitim xenolith suite may, therefore, reflect its bulk O-isotope character. With increasing temperature and degree of partial melting, such a mantle source could generate basaltic liquids with 6 I80 values varying from c.+6.1 to +5.7%0. Thus, the broad 6180 range of c.+4.5 to +7.5%0 reported in the literature for spine1 peridotite xenoliths is probably a very restricted disequilibrium phenomenon that likely reflects recent metasomatic overprinting in highly localized zones of the uppermost continental mantle affected by basaltic magmatism and, therefore, should not be considered as representative of the upper mantle, in general. _

Contributions to Mineralogy and Petrology, Nov 21, 1995

Lherzolite xenoliths in Miocene to Pleistocene basalts from five sites in the Hamar-Daban range i... more Lherzolite xenoliths in Miocene to Pleistocene basalts from five sites in the Hamar-Daban range in southern Siberia provide sampling of the mantle close to the axis of the Baikal rift. These anhydrous spinel lherzolites commonly have foliated fabrics and spongy rims around clinopyroxene, and many contain accessory feldspar. The feldspar occurs in reaction zones adjacent to spinel and orthopyroxene (where it appears to have been formed by the reaction: splϩopxϩcpxϩfluid → fsϩol) and less commonly as thin, irregular veins. The feldspars have variable compositions but are generally alkali-rich; their K 2 O content ranges from 0.3 to 11.2% and is much higher than in plagioclase from orogenic lherzolites (usually Ͻ0.1% K 2 O). The temperature range for the Hamar-Daban xenolith suite (950-1010Њ C) is more restricted than for spinel peridotite xenoliths from other occurrences in the Baikal area. The feldspar-bearing lherzolites yield equilibration temperatures similar to or slightly lower than feldspar-free ones. The majority of the Hamar-Daban lherzolites are fertile and clinopyroxene-rich, as for most other occurrences in the Baikal region. Trace element compositions of selected xenoliths and their clinopyroxenes were determined by ICP-MS, INAA and proton microprobe. Feldspar-bearing xenoliths are enriched in alkalies indicating that feldspar formation is associated with addition of material and is not simply due to isochemical phase changes. Most xenoliths and their clinopyroxenes studied are depleted in light REE and have contents of Sr, Zr and Y common for fertile or moderately depleted mantle peridotites. Few are moderately enriched in LREE, Sr, Th and U. Sr-Nd isotope compositions of clinopyroxenes indicate long-term depletion in incompatible elements similar to unmetasomatised xenoliths from other occurrences south and east of Lake Baikal. The formation of feldspar and of spongy aggregates after clinopyroxene, and the enrichment in alkalies appear to be recent phenomena related to infiltration of an alkali-rich, H 2 O-poor fluid into spinel peridotites.