Boris Belyatsky

Geochemical features of the quaternary lamproitic lavas of Gaussberg Volcano, East Antarctica: Result of the impact of the Kerguelen plume

Petrological-geochemical data were obtained on the lamproites of the Gaussberg Volcano located at the eastern Antarctic coast and compared with data on the magmatic rocks developed in the East Antarctica and Indian Ocean in relation with the Kerguelen plume. It was shown that the lamproites were derived from the ancient Gondwana lithosphere repeatedly modified at the early stages of its evolution, including significant enrichment in volatiles, lithophile elements, and radiogenic Sr and Pb isotopes.The Gaussberg Volcano located on the eastern Antarctic continental margin falls in the distribution field of the Kerguelen plume, which formed 130 Ma within the incipient Indian Ocean and is continuing to operate at present, forming volcanic rocks of Heard Island in the last ka. Manifestations of alkaline magmatism at the Antarctic margin around 56 ka (Mt. Gaussberg) indicate a sublithospheric spreading of mantle plume in the southwestern direction.

Isochron Re-Os age of gold from mayskoe gold-quartz vein deposit (Northern Karelia, Baltic Shield)

54 In contrast to most of the isotope systems of litho phile elements widely abundant in geochronological investigations (Rb, Sr, K, Ca, Sm, Nd, Hf, Lu, U, and Pb), the behavior of the rhenium–osmium system is mainly controlled by the chalcophile and siderophile properties of these elements [1]. This makes it possible to apply the Re–Os system for direct dating of ore mineralization of various genetic types and origins [2].

Geochemical and Petrological Characteristics of Mesozoic Dykes from Schirmacher Oasis (East Antarctica)

Olivine-bearing dolerite and gabbro-dolerite dykes intruded host Precambrian metamorphic rocks of oasis Schirmacher most likely represented Jurassic trap activities in this region of Antarctica. Olivine shows a wide composition range between Fo91.5 to Fo55, which proves strong influence of accumulation processes during melt differentiation. Most common olivine compositions correspond to Fo88 – Fo89, which are close to some olivine compositions reported for less-evolved Jurassic basalts in Vestfjella, western Dronning Maud Land. Relative deviations from the QWM buffer are about 1–1.2. Clinopyroxene crystallization followed precipitation of olivine and plagioclase. Clinopyroxene has wide mg# variation range between 81 and 69 and low Cr/Al (0.01–0.14) and Na/Al (0.1–0.15) ratios. Using clinopyroxene composition Schirmacher Oasis dyke samples yield pressure estimations at 2 kbar (by mean temperature – 1,100°C), which points out to a shallow crystallization environment. Similar crystallization pressure was also calculated for western Dronning Maud Land magmas. The isotope compositions of Schirmacher Oasis dolerites demonstrate clearly radiogenic signatures: 87Sr/86Sr: 0.7045–0.7047, 208Pb/204Pb: 37.98–38.2; 207Pb/204Pb: 15.45–15.52; and reflect the crust contamination process, which took place during plume upwelling and emplacement into crust level. The studied plume-related magmatism within the Schirmacher oasis proves the distribution of Karoo-Maud plume in Antarctica, which is determined by the splitting of Gondwana continent and formation of the Indian Ocean, to the east – from Queen Maud Land towards Schirmacher oasis during the period of 10 m.y.

Peculiarities of the osmium isotopic composition of basaltic glass from the western termination of the Southwest Indian Ridge

1126 Detailed isotopic-geochemical study of tholeiitic magmas from midocean ridges (MOR) in recent years revealed that basaltic magmatism is character� ized by largescale acrosssegment (tens and hundreds of kilometers) variations along the ridge and small� scale heterogeneity within separate seamounts and volcanoes. Wide isotopic variations were presumably caused by compositional heterogeneities within the ascending mantle diapir and by delamination of con� tinental areas in the asthenospheric mantle (1-3). Osmium isotopic systematics ( 187 Os/ 188 Os) of basalts provides not only additional information on the man� tle source of spreading magmas, but also makes it pos� sible to estimate the age of mantle material, admixture of crustal material, and its origin. Unlike mainly litho� phile elements traditionally used in isotopic- geochemical studies, rhenium and osmium are typical siderophile and chalcophile elements; in addition, osmium behaves as a highly compatible element dur� ing mantle melting. Unlike osmium, radiogenic rhe� nium is a moderately incompatible element. Hence, the isotopic composition of highradiogenic osmium can be used as a sensitive tracer of crustal-mantle dif� ferentiation. Previous study (4) of tholeiitic basalts from the western termination of the Southwest Indian Ridge discovered a prominent geochemical anomaly equal to similar one known in the Quaternary volcanoes of west Antarctica. At the same time, basalts in the

Origin, Distribution and Evolution of Plume Magmatism in East Antarctica

According to current models (Dalziel et al., 2000; Lawver et al., 1985; Morgan, 1981), the formation of oceanic crust in the South Atlantic and Indian Ocean was affected by large mantle plumes, such as the Karoo–Maud, Kerguelen, and Parana–Etendeka plumes. The penetration of the Karoo–Maud plume into the upper lithosphere at about 180 Ma affected the southern end of Africa and western part of the East Antarctica and was among the main factors that caused the subsequent breakup of the Gondwana supercontinent (Duncan et al., 1997; Jokat et al., 2003; Storey, 1995; Storey & Kyle, 1997). Later, at about 130 Ma, the Kerguelen plume formed near the spreading zone of the opening Indian Ocean (Coffin et al., 2002; Mahoney et al., 1995; Storey et al., 1989, 1992; Weis et al., 1996) which had a considerable impact on the character of oceanic magmatism and resulted in the formation of numerous volcanic rises (Ninetyeast Ridge, Afanasy Nikitin Rise, Naturaliste Plateau, and, probably, Conrad Rise) (Borisova et al., 1996; Frey et al., 2002; Sushchevskaya et al., 1998). Moreover, it affected the continental margins of India (Rajmahal traps) and Australia (Bunbury basalts) (Curray & Munasinghe, 1991; Frey et al., 1996; Kent et al., 1997, 2002). The plume magmatism of South America and Central Africa was assigned to the activity of another mantle plume, Parana–Etendeka, which caused the formation of a seamount chain, the Walvis Ridge, within the South Atlantic at 130–90 Ma (Renne et al., 1996; Stewart et al., 1996). It is obvious that the interaction of plume and oceanic magmatism has a grate sense for resolving many important problems of marine geology and, primarily, the evolution of the oceanic lithosphere. In addition, plume magmatism provides evidence for deciphering the spatio-temporal spreading of plume materials in the lithosphere (in general sense), determining the timing of plume activity and its evolution under lithospheric conditions, and estimating the influence of plumes on the processes of lithospheric plate disintegrations. In this context, an interesting occurrence of plume activity is the Jurassic magmatism of Antarctica, which has been extensively studied in the past few years (Brewer et al., 1996; Elliot et al., 1999; Elliot & Fleming, 2000; Harris et al., 1990; Hergt et al., 1991; etc.). It is supposed that the Mesozoic plume magmatism of Antarctica propagated along the weakened zones of the Earth’s crust at the margins of the East Antarctica, along the

The 3.98–3.63 Ga zircons as indicators of major processes operating in the ancient continental crust of the east Antarctic shield (Enderby Land)

This study presents new results on zircons from the enderbite-charnockite rocks of Enderby Land, East Antarctica. U-Pb age of 3981 ± 8 Ma (SIMS SHRIMP II), which was first obtained for a protolith of massive enderbites from Aker Peaks, eastern Napier Mts, suggests that the existence of sialic crust in the study area at 4 Ga. Although there was only one magmatic zircon (of 150 grains analyzed) in the study area known with the oldest age, its significance cannot be overestimated, since it may indirectly evidence the existence of an Early Archean crustal block with a minimum age of 4 Ga, which extends for over 300 km across Enderby Land from its western to eastern part. Based on the U-Pb systematics, REE and trace element distributions in zircons from charnockite and enderbite gneisses, high-aluminous gneisses, and basic granulites, we first revealed that an early high-temperature metamorphic event accompanied by the emplacement of granodiorite intrusions occurred in the vicinity of Aker Peaks at 3620–3630 Ma. Although the 2850–3050 metamorphic overprints are clearly observed in some other areas of Enderby Land and are widely considered to be of critical importance on a regional scale, their metamorphic signatures are apparently absent from the U-Pb systematics of the studied zircon, thus suggesting the presence of similar old zircons in the study area. At the same time, all samples in this study record a 2480–2550 Ma granulite-amphibolite facies overprint represented as new zircon growths or recrystallization of earlier phases.

Isotopic systematics of He, Ar, S, Cu, Ni, Re, Os, Pb, U, Sm, Nd, Rb, Sr, Lu, and Hf in the rocks and ores of the Norilsk deposits

This paper reports the first results of a study of 11 isotope systems (3He/4He, 40Ar/36Ar, 34S/32S, 65Cu/63Cu, 62Ni/60Ni, 87Sr/86Sr, 143Nd/144Nd, 206–208Pb/204Pb, Hf–Nd, U–Pb, and Re–Os) in the rocks and ores of the Cu–Ni–PGE deposits of the Norilsk ore district. Almost all the results were obtained at the Center of Isotopic Research of the Karpinskii All-Russia Research Institute of Geology. The use of a number of independent genetic isotopic signatures and comprehensive isotopic knowledge provided a methodic basis for the interpretation of approximately 5000 isotopic analyses of various elements. The presence of materials from two sources, crust and mantle, was detected in the composition of the rocks and ores. The contribution of the crustal source is especially significant in the paleofluids (gas–liquid microinclusions) of the ore-forming medium. Crustal solutions were probably a transport medium during ore formation. Air argon is dominant in the ores, which indicates a connection between the paleofluids and the atmosphere. This suggests intense groundwater circulation during the crystallization of ore minerals. The age of the rocks and ores of the Norilsk deposits was determined. The stage of orebody formation is restricted to a narrow age interval of 250 ± 10 Ma. An isotopic criterion was proposed for the ore-bearing potential of mafic intrusions in the Norilsk–Taimyr region. It includes several interrelated isotopic ratios of various elements: He, Ar, S, and others.

Evolution of the Kerguelen plume and its impact upon the continental and oceanic magmatism of East Antarctica

Petrological–geochemical study showed that the alkaline-ultramafics of the Jetty Oasis (rift zone of the Lambert glacier, East Antarctica) are similar in the age (117–110 Ma) and geochemistry to the ultrapotassic alkali basalts of eastern India (Jharia and Raniganj intrusions). Alkaline magmatism in India and Antarctica is related to the activity of the Kerguelen plume, which significantly affected the evolution of the entire eastern Indian Ocean, in particular, determined geodynamic peculiarities of the ocean opening (existence of non-spreading blocks, fragments of the Gondwana lithosphere in oceanic areas) and geochemical characteristics of erupted tholeiitic magmas. Enriched magma sources related to the Kerguelen plume were formed by melting of ancient Gondwana-derived continental fragments, which experienced multiple transformations during its evolution up to the formation of metasomatized mantle under the impact of the Kerguelen plume on the Antarctic and India margins.

Regional and local magmatic anomalies and tectonics of rift zones between the Antarctic and South American plates

The study provides new understanding of magmatism at extinct and modern spreading zones around the western margin of East Antarctica from Bransfield Strait to the Bouvet Triple Junction (BTJ) in the Atlantic Ocean and reveals causes of geochemical heterogeneity of mantle magmatism during the early opening of the Southern Ocean. The results indicate the involvement of an enriched source component in the generation of parental melts, which was formed in several tectonic stages. The enriched (metasomatized) mantle generated at rift zones has geochemical characteristics typical of the western Gondwana lithosphere (with isotopic compositions similar to those inferred for the enriched HIMU and EM-2 sources). This mantle source may have been produced by the thermal erosion of the continental mantle during the early stages of the Karoo–Maud–Ferrar superplume activity. This enriched mantle generated in the apical parts of the plume (sub-oceanic) began to melt during tectonic displacement and fragmentation of Gondwana. The Bouvet Triple Junction, located along modern spreading zones between the Antarctic and South American plate, is characterized by a greater depth of melting and a higher degree of enrichment of primary tholeiitic magmas. The highest enrichment of magmas in this region is controlled by a contribution from a pyroxenite-rich component, which was also identified in the extinct spreading center in Powell Basin.

U-Pb SHRIMP-II Baddeleyite and Zircon Dating of the Early Proterozoic Monchegorsk Layered Mafite-Ultramafite Complex (Kola Peninsula): Evidence of Synchronous Magmatism

exposed over an area of 550 km and comprises two layered mafite–ultramafite intrusions: the Monchepluton of ultramafic and mafic rocks and the predominantly gabbroid Main Range Massif (or Monchetundra), which are separated by a fault. Both massifs were produced by similar melts of siliceous high-Mg series but differ sharply in their cumulative prevalence: while the Monchepluton is dominated by ultramafites, the Monchetundra Massif consists mostly of gabbroids (Sharkov, 2006). The Complex is located in the southern part of the transform zone connecting Imandra and Pechenga segments of PechengaImandra-Varzuga rift system and intrudes the Archean gneisses and is overlapped by the middle Proterozoic volcanogenic-sedimentary rocks. The Complex is spatially restricted to the Middle Paleoproterozoic regional Central Kola Fault and is now a tectonic collage of variably affected by overprinted metamorphism rocks (Sharkov et al., 2006). Geological position and structure of individual blocks from the Monchetundra fault zone are not well understood and there is no consensus as to the identity tectonized blocks of rhythmically layered rocks from junction zone to a particular massif (Smolkin et al., 2004). Today it has been considered the time of Monchegorsk Layered Complex formation to be 2450-2510 Myr ago, but geological character and age relationships between Monchepluton and Monchetundra have been interpreted differently. The first researchers on the base of strongly metamorphosed rocks of the Main Range Massif and fresh appearance of the most rocks of Monchepluton believed that the Main Range is older. Later isotope-dating has shown that both massifs have Early Proterozoic age of 2501 ± 3 to 2453 ± 4 Ma (Smolkin et al, 2004). Least altered rocks from the upper zone of the Monchetundra have been recently dated by zircon and baddeleyite multigrain U-Pb isotope dilution analysis and the existence of closely spaced in time but independent intrusive phases within massif is assumed: gabbronorites (2476-2471 Ma) and gabbroanorthosites (2456-2453 Ma), while the most young anorthosite injections could be as later as 2420 Ma (Bayanova et al., 2010). However, the age of zircons from Monchetundra gabbronorite previously has been identified as 2505-2501 Ma (Smolkin et al., 2004) and U-Pb zircon age of the Monchepluton corresponds to 2493 ± 7 Ma (Balashov et al., 1993). Thus, simultaneous formation of both magmatic massifs remains debatable. To resolve this contradiction, we have studied by U-Pb SHRIMP-II zircon and baddeleyite separated from 3 gabbroid hard-rocks sampled from the same outcrops as (Bayanova et al., 2010)–two samples from the Monchepluton: (1) melanocratic coarse-grained noritegabbronorite (M-64) and (2) olivine-gabbronorite (M-61) from regional dyke synchronous with Monchepluton outcropped at Olenegorsky open-pit; and one sample from middle zone of Monchetundra: gabbronorite-anorthosite (MT-1, mainly plagioclase cumulate) (3). One of the studied gabbroid sample (M-61) had enough (>20) grains of baddeleyite while other two contained a few zircon (2 grains in M-64 and 30 grains in MT-1) only (Fig.1). Analytical method: Analysis of samples made possible during the continuous session to eliminate the problem of mutual correlation between the various sessions measurements and intercalibration of standard data. Baddeleyite studied grains randomly oriented with respect to the surface and mounted with 91500 standard zircon and baddeleyite «Phalaborwa» standard with the average age of 2060 Ma. Thus obtained for the standard error 1.2% (2s) was generally comparable to those obtained for zircon measurements. Results and Conclusions: 26 SHRIMP-II analyses for 20 baddeleyite grains of olivine gabbro (M-61) from regional dyke have been obtained but only 20 or 18 measurements were used for 208Pb-corrected age calculation: 2491.4 ± 3.9 Ma Pb/Pb averaged age or 2490.5 ± 8.9 Ma concordant age (Fig.2). Up to 8 analyses have a very large Nickolay V. Rodionov, Anton A. Antonov, Boris V. Belyatsky, and Sergey A. Sergeev, 2016. U-Pb SHRIMP-II Baddeleyite and Zircon Dating of the Early Proterozoic Monchegorsk Layered Mafite-Ultramafite Complex (Kola Peninsula): Evidence of Synchronous Magmatism. Acta Geologica Sinica (English Edition), 90(supp. 1): 79-80.