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Russian Geology and Geophysics

2016 year, number 5

1.
TECTONIC ACTIVITY OF THE EARLY EARTH (4.56-3.4(2.7?) Ga)

M.I. Kuzmin1, V.V. Yarmolyuk2, R. E. Ernst3,4
1A.P. Vinogradov Institute of Geochemistry, Siberian Branch of the Russian Academy of Sciences, ul. Favorskogo 1a, Irkutsk, 664033, Russia
2Institute of the Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry (IGEM), Russian Academy of Sciences, Staromonetnyi per. 35, Moscow, 109017, Russia
3Department of Earth Sciences, Carleton University, Ottawa, ON K1S 5B6, Canada
4Faculty of Geology and Geography, Tomsk State University, pr. Lenina 36, Tomsk, 634050, Russia
Keywords: Мантийные перевороты, метеоритно-астероидные бомбардировки, мантийная конвекция, сагдукция, Mantle overturns, meteorite-asteroid bombardments, mantle convection, sagduction

Abstract >>
The paper discusses a possible model of the ancient (Hadean-Archean) Earth’s geodynamic evolution. We believe that the early Earth was characterized by a stagnant lid regime and whole-mantle convection suggesting cells that convect through the whole mantle (from the core-mantle boundary to the lithosphere base). The lid tectonics was perturbed by asteroid-meteorite bombardments that destroyed the primary terrestrial partly granitoid crust. The destroyed crust together with the residual enriched mantle reservoirs sank into the lower mantle. In addition to the crust destruction, the bombardments led to emplacement of a huge proportion of basalt-komatiitic melts, which can be interpreted as mantle overturn events. In the Hadean, the Earth survived frequent large-scale asteroid-meteorite bombardments, which resulted in almost a complete destruction of the primary terrestrial crust. In the Early Archean, the Earth still experienced the same tectonic processes, as in the Hadean; however, meteorite impact was small-scale and the bombardments influenced only a limited area of a common, as it seems to us, subequatorial supercontinent. Those bombardments led to the sagduction of the Archean basalt-komatiiic terrestrial crust, which sank into the mantle, transforming into amphibolite-eclogite rocks giving rise to a tonalite-troondhjemite-granodiorite suite. As preserved in the zircon record, the formation of the Archean mantle-derived magmas occurred as pulses at 4.5, 4.2-4.3, 3.8-3.9, and 3.3-3.4 Ga. These peaks, most likely, correspond to the Hadean-Archean meteorite bombardments. There is evidence of formation of the subcontinental lithospheric mantle (SCLM) beneath the cratons between 3.3 and 3.5 Ga. This SCLM was markedly different from peridotites of modern ophiolites. However, the existence of ophiolitic peridotites indicates that modern style plate tectonic processes were in operation at that time, as we will discuss below. The transition from the early Earth (Hadean-Archean) tectonic style to the recent tectonics occurred between 3.4 (2.7?) and 2.0 Ga.



2.
THE 1501 MA KUONAMKA LARGE IGNEOUS PROVINCE OF NORTHERN SIBERIA: U-Pb GEOCHRONOLOGY, GEOCHEMISTRY, AND LINKS WITH COEVAL MAGMATISM ON OTHER CRUSTAL BLOCKS

R.E. Ernst1,2, A.V. Okrugin3, R.V. Veselovskiy4, S.L. Kamo5, M.A. Hamilton5, V.E. Pavlov4, U. Sцderlund6, K.R. Chamberlain7, C. Rogers8
1Department of Earth Sciences, Carleton University, pr. Lenina 36, Tomsk, 634050, Russia
2Faculty of Geology and Geography, Tomsk State University
3Diamond & Precious Metal Geology Institute, Russian Academy of Sciences, pr. Lenina 39, Yakutsk, 677000, Russia
4Institute of Physics of the Earth, Russian Academy of Sciences, ul. Bol'shaya Gruzinskaya 10, build. 1, 123995, Moscow, Russia
5Jack Satterly Geochronology Laboratory, University of Toronto, Toronto, ON, M5S 3B1, Canada
6Department of Geology, Lund University, Lund, 223 62, Sweden
7Department of Geology and Geophysics, University of Wyoming, Laramie, Wyoming, 82071, USA
8Department of Earth Sciences, Carleton University, Ottawa, ON, K1S 5B6, Canada
Keywords: Магматизм, дайки, силлы, крупная изверженная провинция, север Сибири, Magmatism, dikes, sill, igneous province, northern Siberia

Abstract >>
A new large igneous province (LIP), the 1501 ± 3 Ma Kuonamka LIP, extends across 700 km of northern Siberia and is linked with coeval dykes and sills in the formerly attached São Francisco craton (SFC)-Congo craton to yield a short-duration LIP event 2000 km across. The age of the Kuonamka LIP can be summarized as 1501 ± 3 Ma (95% confidence), based on 7 U-Pb ID-TIMS ages (six new herein) from dolerite dikes and sills extending across the Anabar shield and within western Riphean cover rocks for a distance of 270 km. An additional sill yielded a SIMS (CAMECA) age of 1483 ± 17 Ma and sill in the Olenek uplift several hundred kilometers farther east, a previous SIMS (SHRIMP) age of ca. 1473 Ma was obtained on a sill; both SIMS ages are within the age uncertainty of the ID-TIMS ages. Geochemical data indicate a tholeiitic basalt composition with low MgO (4-7 wt.%) within-plate character based on trace element classification diagrams and source between E-MORB and OIB with only minor contamination from crust or metasomatized lithospheric mantle. Two subgroups are distinguished: Group 1 has gently sloping LREE ((La/Sm)PM = 1.9) and HREE ((Gd/Yb)PM = 1.8) patterns, slightly negative Sr and moderate TiO2 anomalies (2.2 wt.%), and Group 2 has steeper LREE ((La/Sm)PM = 2.3) and HREE ((Gd/Yb)PM = 2.3), strong negative Sr anomaly, is higher in TiO2 (2.7 wt.%), and is transitional from tholeiitic to weakly alkaline in composition. The slight differences in REE slopes are consistent with Group 2 on average melting at deeper levels. Proposed reconstructions of the Kuonamka LIP with 1500 Ma magmatism of the SFC-Congo craton are supported by a geochemical comparison. Specifically, the chemistry of the Chapada Diamantina and Curaça dikes of the SFC can be linked to that of Groups 1 and 2, respectively, of the Kuonamka LIP and are consistent with a common mantle source between EMORB and OIB and subsequent differentiation history. However, the coeval Humpata sills and dikes of the Angola block of the Congo craton represent a different magma batch.



3.
MESOPROTEROZOIC MANTLE PLUME BENEATH THE NORTHERN PART OF THE SIBERIAN CRATON

D.P. Gladkochub1, T.V. Donskaya1, A.M. Mazukabzov1, S.A. Pisarevsky2,3, R.E. Ernst4,5,6, A.M. Stanevich1
1Institute of the Earth's Crust, Siberian Branch of the RAS, ul. Lermontova 128, Irkutsk, 664033, Russia
2Australian Research Council Centre of Excellence for Core to Crust Fluid Systems (CCFS) and the Institute for Geoscience Research (TIGeR), Department of Applied Geology, Curtin University, GPO Box U1987, Perth, WA 6845, Australia
3School of Earth and Environment, University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia
4Department of Earth Sciences, Carleton University, 1125 Colonel By Drive, Ottawa, ON K1S 5B6, Canada
5Tomsk State University, pr. Lenina 36, Tomsk, 634050, Russia
6Ernst Geosciences, 43 Margrave Ave., Ottawa, ON K1T 3Y2, Canada
Keywords: Долериты, геохимия, мантийный плюм, мезопротерозой, Оленекский выступ, Сибирский кратон, суперконтинент Нуна (Колумбия), Dolerites, geochemistry, mantle plume, Mesoproterozoic, Olenek uplift, Siberian craton, Nuna supercontinent (Columbia)

Abstract >>
The study of the Mesoproterozoic (1473 ± 24 Ma) dolerites of the Olenek uplift of the Siberian craton basement has shown their petrologic and geochemical similarity to typical OIB produced with the participation of a mantle plume. The dolerites are characterized by variations in geochemical composition explained by different degrees of melting of the same source. A conclusion is drawn that the parental melts of the rocks were slightly modified by crustal contamination, as evidenced from their Nd isotope composition (εNd(T) = +0.6 to -0.8) and the presence of inherited zircons of four ages (2564, 2111, 2053, and 1865 Ma). Since the Siberian craton in the structure of the Nuna supercontinent (Columbia) was located relatively close to the Baltic continent and the Congo and Saõ Francisco cratons, we assume that the Early Mesoproterozoic mafic intrusions (1500-1470 Ma) of all these cratons belong to the same large igneous province (LIP). The province formation was related to the activity of superplume (or mantle hot field), which supplied mantle matter to the lithosphere basement. The superplume core was probably located beneath the northern part of the Siberian craton, where basites are compositionally most similar to the primary mantle source.



4.
PHYSICOCHEMICAL PARAMETERS OF DEEP-SEATED MANTLE PLUMES

I.D. Ryabchikov1, L.N. Kogarko2
1Institute of Geology of Ore Deposits, Petrography, Mineralogy and Geochemistry, Russian Academy of Sciences, Staromonetnyi per. 35, Moscow, 119017, Russia
2V.I. Vernadsky Institute of Geochemistry and Analytical Chemistry, ul. Kosygina 19, Moscow, 119991, Russia
Keywords: Мантийные плюмы, фугитивность кислорода, геооксометр, магма, шпинель, нижняя мантия, углеродсодержащие соединения, алмаз, Mantle plumes, oxygen fugacity, oxygen barometer, magma, spinel, lower mantle, carbon-containing compounds, diamond

Abstract >>
Thermodynamic analysis of experimental data has demonstrated that FeO activity in silicate melts identical in composition to natural magmas can be described by the regular-solution model, which takes into account interactions of all cations with Si and interaction of Ca with Al. Using this model, we propose an oxygen barometer for spinel + magma phase association. In contrast to the earlier proposed methods for estimation of oxygen chemical potential, this barometer can work in the PT-domain close to the liquidus of magmatic process. The new oxygen barometer has been applied to magmas related to mantle plume activity, including Siberian meimechites, Hawaiian picrites, and picrites from the Emeishan large igneous province (LIP) and Greenland. We have shown that most magmas related to the activity of deep-seated mantle plumes are characterized by a higher relative chemical potential of oxygen than magmas of mid-ocean ridges. Thermodynamically calculated stability fields of rocks with different carbon-containing phases show that under PT-conditions of the lower mantle, the material of ascending mantle plumes is characterized by relatively elevated oxygen fugacity. Formation of diamond in the lower mantle requires more oxidizing conditions as compared with the major part of this geosphere, where the presence of Fe-Ni alloy is predicted. We have put forward a hypothesis that the main reason for the oxygen fugacity increase in particular domains of the lower mantle is a shift of redox equilibria toward a decrease in the amount of Fe-Ni alloy, up to its disappearance, with temperature growth.



5.
GENESIS AND CRYSTALLIZATION OF ULTRAMAFIC ALKALINE CARBONATITE MAGMAS OF SIBERIA: ORE POTENTIAL, MANTLE SOURCES, AND RELATIONSHIP WITH PLUME ACTIVITY

N.V. Vladykin
A.P. Vinogradov Institute of Geochemistry, Siberian Branch of the Russian Academy of Sciences, ul. Favorskogo 1a, Irkutsk, 664033, Russia
Keywords: Петрология щелочных пород, рудоносность, геохимия редких элементов и изотопов, мантийные источники, модель зарождения магм, Petrology of alkaline rocks, ore potential, trace element and isotope geochemistry, mantle sources, magma genesis model

Abstract >>
This paper discusses the genesis of large Siberian alkaline massifs hosting major ore deposits. These reference massifs are grouped based on the predominance of alkalies (K or Na) and their agpaitic index (miaskitic and agpaitic). We proposed new emplacement schemes for the Tomtor, Murun, Burpala, Synnyr, and Bilibino massifs supported by petrochemical and geochemical data, as well as new age estimates. Types of their ore potential and genesis of rare-metal mineralization are discussed. The formational types of carbonatites as the main ore-bearing rocks are given. The depth of magma generation and types of mantle sources are determined using isotopic data from previous studies. A model of plume-related generation of ultramafic alkaline magmas is proposed.



6.
Origin of high-velocity anomalies beneath the Siberian craton: A fingerprint of multistage magma underplating since the Neoarchean

Qin Wang1, N. Bagdassarov2, V.S. Shatsky3,4,5
1State Key Laboratory for Mineral Deposits Research, Department of Earth Sciences, Nanjing University, Nanjing, 210046, China
2Institute for Geosciences, University Frankfurt, Frankfurt am Main, 60438, Germany
3Vinogradov Institute of Geochemistry, Siberian Branch of the Russian Academy of Sciences, ul. Favorskogo 1A, Irkutsk, 664033, Russia
4V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
5Novosibirsk State University, ul. Pirogova 2, Novosibirsk, 630090, Russia
Keywords: Плюм, литосфера, кратоны, скорость сейсмических волн, Siberian craton, Siberian Traps, seismic velocities, eclogites, Moho

Abstract >>
Despite the violent eruption of the Siberian Traps large igneous province at ~250 Ma, the Siberian craton has an extremely low heat flow (18-25 mW/m2) and a very thick lithosphere (300-350 km), which makes it an ideal place to study the influence of mantle plumes on the long-term stability of cratons. Compared with seismic velocities of rocks, the lower crust of the Siberian craton is composed mainly of mafic granulites and could be rather heterogeneous in composition. The very high vP (>7.2 km/s) in the lowermost crust can be fit by a mixture of garnet granulites, two-pyroxene granulites, and garnet gabbros as a result of magma underplating. The high-velocity anomaly in the upper mantle ( vP = 8.3-8.6 km/s) can be interpreted by a mixture of eclogites and spinel peridotites. Combined with the study of lower crustal and mantle xenoliths, we recognized multistage magma underplating at the crust-mantle boundary beneath the Siberian craton, including the Neoarchean growth and Paleoproterozoic assembly of the Siberian craton beneath the Markha terrane, the Proterozoic collision along the Sayan-Taimyr suture zone, and the Triassic Siberian Trap event beneath the central Tunguska basin. The Moho becomes a metamorphism boundary of mafic rocks between granulite facies and eclogite facies rather than a chemical boundary that separates the mafic lower crust from the ultramafic upper mantle. Therefore, multistage magma underplating since the Neoarchean will result in a seismic Moho shallower than the petrologic Moho. Such magmatism-induced compositional change and dehydration will increase viscosity of the lithospheric mantle and finally trigger lithospheric thickening after mantle plume activity. Hence, mantle plumes are not the key factor for craton destruction.



7.
LATE MESOZOIC-EARLY CENOZOIC RIFTING MAGMATISM IN THE UDA SECTOR OF WESTERN TRANSBAIKALIA

A.A. Vorontsov1, V.V. Yarmolyuk2, T.Yu. Komaritsyna1
1Vinogradov Institute of Geochemistry, Siberian Branch of the Russian Academy of Sciences, ul. Favorskogo 1A, Irkutsk, 664033, Russia
2Institute of Geology of Ore Deposits, Petrography and Geochemistry, Russian Academy of Sciences, Staromonetnyi per. 35, Moscow, 119017, Russia
Keywords: Внутриплитный магматизм, рифтогенез, эволюция магматизма, магматические источники, Западное Забайкалье, Within-plate magmatism, rifting, evolution of magmatism, magma sources, Western Transbaikalia

Abstract >>
Magmatism of the Uda sector enclosed within the West Transbaikalian rift zone (WTRZ) is discussed in this paper. Seven stages of the Late Mesozoic-Cenozoic volcanism have been recognized within span 174-51 Ma. On the border about 135 Ma the nature of volcanism changed noticeably: (a) the volume of volcanic rocks essentially reduced; (b) transition from differentiated to basaltic associations proceeded with the disappearance of volcanics containing SiO2 over 54 wt.%; (c) alkali and subalkaline basaltoids appeared in the associations, their volume increasing at later stages. Geochemical features of the Uda volcanics are determined by participation in their formation of the mantle source close in composition to the source with OIB parameters. They are responsible for high concentrations of incompatible elements in magmatic products. The isotope characteristics of rocks indicate conformity of this mantle source to the varying behavior of EMII and PREMA with the role of the latter strengthening in time. The basaltoids of initial stages show the deficit of Ti, Nb, and Ta caused by involvement of water-saturated lithosphere mantle in magma formation. The main specifics of the Uda volcanics composition and the pattern of their variability in time correspond to those in WTRZ, as well as in the other Late Mesozoic-Cenozoic rift zones of Central Asia. This evidence suggests similar geodynamic settings for origination and development of rifting processes, when continuously evolving mantle plume affects the regional lithosphere. The magmatism of the Uda sector, as in the entire WTRZ, differs considerably from magmatic processes developing over the convergent boundaries of the Mongol-Okhotsk belt; their products are represented by differentiated magmatic associations with geochemical properties are common for the rocks of suprasubduction zones.



8.
MANTLE DIAPIRISM AT CONVERGENT BOUNDARIES (Sea of Japan)

Yu.A. Martynov, V.V. Golozubov, A.I. Khanchuk
Far Eastern Geological Institute, Far Eastern Branch of the Russian Academy of Sciences, pr. 100-letiya Vladivostoka 159, Vladivostok, 690022, Russia
Keywords: Тектоника, микроэлементы, изотопы, мантийная геодинамика, Японское море, Восточный Сихотэ-Алинь, Tectonics, trace elements, isotopes, mantle geodynamics, Sea of Japan, East Sikhote-Alin

Abstract >>
New data on geology, geochemistry, and isotope systematics of lavas in the East Sikhote-Alin area, along with earlier published evidence for the Sea of Japan, provide insights into the dynamics of back-arc basins and their role in the tectonic and magmatic history of continental margins. Right-lateral strike-slip faulting, the key event in the Cenozoic history of East Sikhote-Alin, apparently had no relation with the subduction in post-Eocene time. At that time, the Late Cretaceous subduction ended and oceanic asthenosphere with Pacific-type MORB isotope signatures injected into the subcontinental mantle through slab windows. The Sea of Japan opening began in the Eocene with formation of small rift basins in the Tatar Strait, which accumulated coastal facies. During the main Miocene phase of activity, the zone affected by oceanic asthenosphere moved eastward, i.e., to the modern deepwater Sea of Japan. The effect of oceanic asthenosphere on the continental margin ended in the Late Miocene after the Sea of Japan had opened and new subduction initiated east of the Japan Islands.



9.
SHOSHONITE-LATITE SERIES OF THE EASTERN TRANSBAIKALIA: 40Ar/39Ar AGE, GEOCHEMISTRY, AND Sr-Nd ISOTOPE COMPOSITION OF ROCKS FROM THE AKATUI VOLCANOPLUTONIC ASSOCIATION OF THE ALEKSANDROVSKII ZAVOD DEPRESSION

S.A. Sasim1, S.I. Dril1, A.V. Travin2,3,4, T.A. Vladimirova1, N.S. Gerasimov1, Yu.V. Noskova1
1A.P. Vinogradov Institute of Geochemistry, Siberian Branch of the Russian Academy of Sciences, ul. Favorskogo 1a, Irkutsk, 664033, Russia
2V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
3Novosibirsk State University, ul. Pirogova 2, Novosibirsk, 630090, Russia
4Tomsk State University, pr. Lenina 36, Tomsk, 634050, Russia
Keywords: Ar/Ar датирование , Акатуевский массив, кайласская свита, Восточное Забайкалье, внутриплитовый магматизм, шошонит-латитовая серия, 40Ar/39Ar dating, Akatui massif, Kailas Formation, Eastern Transbaikalia, within-plate magmatism, shoshonite-latite series

Abstract >>
The paper presents new data on age, geochemistry, and Sr and Nd isotope composition of rocks from the Akatui massif and comagmatic rocks from the lower unit of the Kailas Formation (Akatui volcanoplutonic association), localized within the Aleksandrovskii Zavod depression. The amphibole 40Ar/39Ar age date the monzogabbro of the early phase of the Akatui massif at 154.8 ± 4.4 Ma; the monzonite of the main phase yields a 40Ar/39Ar age of 160.7 ± 3.9 Ma, and the shoshonite basalt of the lower unit of the Kailas Formation yields a 40Ar/39Ar age of 161.5 ± 1.7 Ma. The leading petrogenetic mechanism for the Akatui volcanoplutonic association is crystal fractional differentiation of melts with minor crustal contamination, which can be suggested from the mineralogical and petrographic features and geochemical and isotope characteristics of rocks. The geochemical data for the Akatui volcanoplutonic association show LILE, LREE, U, Th, and Pb enrichment with a characteristic depletion in high-field strength elements (HFSE), such as Nb and Ti. They are also depleted in P. Sr-Nd isotope data (87Sr/86Sr(160 Ma) = 0.70642-0.70688 and εNd(160 Ma) = -0.6 to -2.2) suggest an EMII-type mantle source and could also indicate a negligible degree of crustal contamination in the evolved melts.



10.
LATE PALEOZOIC GRANITOID MAGMATISM OF EASTERN KAZAKHSTAN AND WESTERN TRANSBAIKALIA: PLUME MODEL TEST

S.V. Khromykh1,2, A.A. Tsygankov3,4, P.D. Kotler1,2, O.V. Navozov5, N.N. Kruk1, A.G. Vladimirov1,2, A.V. Travin1, D.S. Yudin1, G.N. Burmakina3, V.B. Khubanov3,4, M.D. Buyantuev3, T.N. Antsiferova3,4, G.S. Karavaeva5
1V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
serkhrom@mail.ru
2Novosibirsk State University, ul. Pirogova 2, Novosibirsk, 630090, Russia
3Geological Institute, Siberian Branch of the Russian Academy of Sciences, ul. Sakh'yanovoi 6a, Ulan-Ude, 670047, Russia
4Buryat State University, ul. Smolina 24a, Ulan-Ude, 670000, Russia
5Topaz Geological Exploration Company Ltd, ul. Geologicheskaya 1, Ust'-Kamenogorsk, 070001, Kazakhstan
Keywords: Гранитоидные батолиты, крупные магматические провинции, плюм-литосферное взаимодействие, Центрально-Азиатский складчатый пояс, Granitoid batholiths, large igneous provinces, Central Asian Orogenic Belt, plume-lithosphere interaction

Abstract >>
We present results of a comparative study of Late Paleozoic granitoids of Eastern Kazakhstan and Western Transbaikalia composing the large Kalba-Narym and Angara-Vitim batholiths. We have established that despite the different geologic history of these regions, granitoid magmatism there proceeded nearly synchronously at the Carboniferous-Permian boundary (330-280 Ma) and was accompanied by mantle magmatism. The regularities of its evolution are considered in terms of the plume model and different stages of interaction of mantle plumes with the lithosphere. The major principles of plume-lithosphere interaction in accretion-collision fold belts have been formulated: (1) Plume-lithosphere interaction results in large-scale melting of sublithospheric mantle, lower lithosphere, and crustal substrates warmed by the preceding orogenic process; (2) The processes last 30 to 50 Myr and produce large volumes of igneous rocks, mostly granitoids; (3) The sequence of formation of granitoid and basic igneous complexes and the metallogenic specialization can be different and depend on the lithosphere structure and preceding geologic history of the region.



11.
LATE PALEOZOIC GABBROIDS OF WESTERN TRANSBAIKALIA: U-Pb and Ar-Ar ISOTOPIC AGES, COMPOSITION, AND PETROGENESIS

A.A. Tsygankov1,2, V.B. Khubanov1,2, A.V. Travin3,4,5, E.N. Lepekhina6, G.N. Burmakina1, T.N. Antsiferova1,2, O.V. Udoratina7
1Geological Institute, Siberian Branch of the Russian Academy of Sciences, ul. Sakh'yanovoi 6a, Ulan-Ude, 670047, Russia
2Buryat State University, ul. Smolina 24a, Ulan-Ude, 670000, Russia
3V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
4, pr. Lenina 36, Tomsk, 634050, Russia
5Tomsk State University
6A.P. Karpinsky Russian Geological Research Institute, Srednii pr. 74, St. Petersburg, 199106, Russia
7Institute of Geology, Komi Science Center, Ural Branch of the Russian Academy of Sciences, ul. Pervomaiskaya 54, Syktyvkar, 167982, Russia
Keywords: Западное Забайкалье, базитовый магматизм, изотопный возраст, источники магм, мантийный плюм, Basic magmatism, isotopic age, magma sources, mantle plume, Western Transbaikalia

Abstract >>
We provide new isotope-geochronological evidence for the synchronous occurrence of Late Paleozoic basic and granitoid magmatism in Western Transbaikalia; this is a strong argument for the contribution of mantle magmas to granitoid petrogenesis. The Late Paleozoic basic rocks originated from the phlogopite-garnet-bearing lherzolitic mantle, which melted under «hydration conditions». The specific features of Late Paleozoic magmatism in Western Transbaikalia were determined by the combination of the activity of a low-energy mantle plume with the final stage of the Hercynian orogeny in space and time. At the early stage of magmatism, during the formation of the Barguzin granites, the plume had only a thermal influence on the crustal rocks heated as a result of Hercynian fold-thrust deformations. The mixing of mantle basic and crustal salic magmas at different levels marked the transition from crustal to mixed (mantle-crustal) granites, which include all post-Barguzin complexes (probably, except for alkali granites). In the geologic evolution of Transbaikalia, the Late Paleozoic magmatism was postorogenic, but it was initiated and influenced by the mantle plume.



12.
DISTRIBUTION OF PGE IN PERMO-TRIASSIC BASALTS OF THE SIBERIAN LARGE IGNEOUS PROVINCE

A.E. Izokh1,2, A.Ya. Medvedev3, G.S. Fedoseev1,2, G.V. Polyakov1, I.V. Nikolaeva1, S.V. Palesskii1
1V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
2Novosibirsk State University, ul. Pirogova 2, Novosibirsk, 630090, Russia
3A.P. Vinogradov Institute of Geochemistry, Siberian Branch of the Russian Academy of Sciences, ul. Favorskogo 1a, Irkutsk, 664033, Russia
Keywords: Ультрамафит-мафитовые интрузивы, элементы платиновой группы, крупные изверженные провинции, геохимия, Ultramafic-mafic intrusions, PGE, Large Igneous Provinces, geochemistry

Abstract >>
We have revealed the spatio-temporal regularities of distribution of platinum group elements (PGE) in basaltoids related to the activity of the Siberian mantle plume. As objects of study, we chose rift and flood basalts from the Norilsk district (sampled from the SD-9 borehole), flood basalts from the central part of the Tunguska syneclise (Lower Tunguska), Kuznetsk Basin traps, and subalkalic basalt from the Semeitau volcanoplutonic structure in eastern Kazakhstan. Based on the PGE patterns of basaltoids related to the activity of the Permo-Triassic Siberian plume, we have shown that the rocks that formed in the central part of the Siberian Large Igneous Province (LIP) at the early rift stage have low contents of PGE, whereas picrites and tholeiitic flood basalts have high contents. The rift (Semeitau structure) and flood (Kuznetsk Basin traps) basalts from the peripheral regions are characterized by extremely low PGE contents. The high PGE contents in magmas of the plume head are responsible for the high productivity of ultramafic-mafic trap magmatism. The elevated K contents in magmas and the high PGE contents in the mantle plume head are probably due to the assent of deep-seated material from the core-lower-mantle boundary, as follows from the thermochemical model of the Siberian plume.



13.
RELATIONSHIP BETWEEN PLATINUM-BEARING ULTRAMAFIC-MAFIC INTRUSIONS AND LARGE IGNEOUS PROVINCES (exemplified by the Siberian Craton)

A.S. Mekhonoshin1,2, R.E. Ernst3,4, U. Sцderlund5, M.A. Hamilton6, T.B. Kolotilina1,2, A.E. Izokh7,8, G.V. Polyakov7, N.D. Tolstykh7
1Vinogradov Institute of Geochemistry, Siberian Branch of the Russian Academy of Sciences, ul. Lermontova 83, Irkutsk, 664074, Russia
2Irkutsk Research Technical University
3Department of Earth Sciences, Carleton University, Ottawa, ON K1S 5B6, Canada
4Tomsk State University, ul. Lenina 36, Tomsk, 634050, Russia
5Lund University, 12 Sulvegatan, Lund, 223 62, Sweden
6J. Sutterlay Geochronology Laboratory, Toronto University, Toronto, ON N5S 3B1, Canada
7V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
8Novosibirsk State University, ul. Pirogova 2, Novosibirsk, 630090, Russia
Keywords: ЭПГ-Cu-Ni месторождения, ультрамафит-мафитовые интрузии, крупные изверженные провинции, PGE-Ni-Cu deposits, ultramafic-mafic intrusions, large igneous provinces

Abstract >>
This study aims at summarizing available geological and geochemical data on known Proterozoic platinum-bearing ultramafic-mafic massifs in the south of Siberia. Considering new data on geochemistry and geochronology of some intrusions, it was feasible to compare ore-bearing complexes of different time spans and areas and to follow their relationships with the recognized large igneous provinces. In the south of Siberia, the platinum-bearing massifs might be united into three age groups: Late Paleoproterozoic (e.g., Chiney complex, Malozadoisky massif), Late Mesoproterozoic (e.g., Srednecheremshansky massif), and Neoproterozoic (e.g., Kingash complex, Yoko-Dovyren massif, and massifs in the center of the East Sayan Mts.). In most massifs but Chiney the initial magmas are magnesium-rich. On paleogeodynamic reconstructions, the position of the studied massifs is the evidence that three most precisely dated events in North Canada continued into southern Siberia: In the period 1880-1865 Ma, it was the Ghost-Mara River-Morel LIP; at 1270-1260 Ma, the Mackenzie LIP; and at 725-720 Ma, the Franklin LIP. In Siberia, the mostly productive massifs with respect to PGE-Ni-Cu mineralization are those linked with the Franklin LIP: Verkhnii Kingash, Yoko-Dovyren, and central part of the Eastern Sayan Mountains, e.g., Tartay, Zhelos, and Tokty-Oy.



14.
PLATINUM-GROUP MINERALS IN DOLERITES FROM ALEXANDRA LAND ISLAND (Franz Josef Land Archipelago)

E.V. Sklyarov1, Yu.V. Karyakin2, N.S. Karmanov3, N.D. Tolstykh3
1Far Eastern Federal State University, ul. Sukhanova 8, Vladivostok, 690950, Russia
2Geological Institute, Russian Academy of Sciences, Pyzhevsky per. 7, Moscow, 119017, Russia
3V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
Keywords: Мантийный плюм, крупная изверженная провинция, базальтовый магматизм, золото-медно-палладиевая минерализация, Земля Франца-Иосифа, Mantle plume, large igneous province, basaltic magmatism, Cu-PGE-Au mineralization, Franz Josef Land Archipelago

Abstract >>
Lavas in Alexandra Land Island of the Franz Josef Land Archipelago bear Au-Cu-Pd-type mineralization. The found mineral species belong to the Cu-Au-Pd and Pd-Cu-(Te + Sb + S + As) systems being, respectively, (i) cuproauride (Au(Cu, Pd)) and auricupride (Au(Cu,Pd)3) and (ii) phases similar to skaergaardite (PdCu), nielsenite (PdCu3), and numerous S-Te-Sb-Pd-Cu phases of various compositions. The morphology of PGM existing as tiny grains and films along the boundaries of plagioclase and clinopyroxene and in cracks, their crystallization at low temperatures predicted by experimental data, and the presence of native copper with sulfur impurity are signatures of postmagmatic origin. The Alexandra Land tholeiitic basalts and dolerites were, most likely, produced by the hotspot which may be the source of PGE-bearing intrusions in eastern Greenland that contain PGM similar to those discussed in the paper.