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listelement.badge.dso-typeЭлемент, GEOCHEMISTRY AND GEOCHRONOLOGY OF THE NEOPROTEROZOIC PAN-AFRICAN TRANSCAUCASIAN MASSIF (REPUBLIC OF GEORGIA) AND IMPLICATIONS FOR ISLAND ARC EVOLUTION OF THE LATE PRECAMBRIAN ARABIAN-NUBIAN SHIELD(2007) Zakariadze G.S.; Karpenko S.F.; Bazylev B.A.; Solov'eva N.; Dilek Y.; Adamia S.A.; Oberhänsli R.E.The Transcaucasian Massif (TCM) in the Republic of Georgia includes Neoproterozoic–Early Cambrian ophiolites and magmatic arc assemblages that are reminiscent of the coeval island arc terranes in the Arabian–Nubian Shield (ANS) and provides essential evidence for Pan-African crustal evolution in Western Gondwana. The metabasite–plagiogneiss–migmatite association in the Oldest Basement Unit (OBU) of TCM represents a Neoproterozoic oceanic lithosphere intruded by gabbro–diorite–quartz diorite plutons of the Gray Granite Basement Complex (GGBC) that constitute the plutonic foundation of an island arc terrane. The Tectonic Mélange Zone (TMZ) within the Middle-Late Carboniferous Microcline Granite Basement Complex includes thrust sheets composed of various lithologies derived from this arc-ophiolite assemblage. The serpentinized peridotites in the OBU and the TMZ have geochemical features and primary spinel composition (0.35) typical of mid-ocean ridge (MOR)-type, cpx-bearing spinel harzburgites. The metabasic rocks from these two tectonic units are characterized by low-K, moderate-to high-Ti, olivine-hypersthene-normative, tholeiitic basalts representing N-MORB to transitional to E-MORB series. The analyzed peridotites and volcanic rocks display a typical melt-residua genetic relationship of MOR-type oceanic lithosphere. The whole-rock Sm–Nd isotopic data from these metabasic rocks define a regression line corresponding to a maximum age limit of 804 ± 100 Ma and εNdint = 7.37 ± 0.55.listelement.badge.dso-typeЭлемент, SPINEL-GROUP MINERALS IN ROCKS OF THE KHIBINY ALKALINE PLUTON, KOLA PENINSULA(2007) Ivanyuk G.Yu.; Pakhomovsky Ya.A.; Konopleva N.G.; Yakovenchuk V.N.; Men'shikov Yu.P.; Mikhailova Yu.A.Seven spinel-group minerals in various geological settings have been revealed in the rocks of the Khibiny pluton. Hercynite, gahnite, and vuorelainenite occur only in xenoliths of hornfels after volcanic and sedimentary rocks, whereas spinel and magnesiochromite occur in alkaline ultramafic rocks of dike series. Franklinite has been discovered in a low-temperature hydrothermal vein. Ubiquitous magnetite is abundant in foyaite, foidolites, alkaline ultrabasic rocks, and pegmatite and hydrothermal veins and may even be the main mineral in some foidolite varieties. The spinel-group minerals are characterized by various chemical compositions due to the fractionation of nepheline syenites resulting in formation of the Main ring of foidolites and apatite-nepheline ore. Like most other minerals found throughout the pluton, magnetite is characterized by variation in the chemical composition along the radial line from the contact with country Proterozoic volcanic rocks to the geometric center of the pluton. Toward the center, the total Ti and Mn contents in magnetite increase from 5–15 up to 40 at %.listelement.badge.dso-typeЭлемент, THE CAMBRIAN 'BASEMENT' OF GASTROPOD EVOLUTION(2007) Parkhaev P.Y.The oldest gastropods are known from the uppermost Nemakit-Daldynian to lowermost Tommotian deposits. However, to trace ancestry before this time, when most metazoans did not possess shells, is difficult. Study of the oldest gastropods, diagnosed and discussed here, sheds some light on the earliest stages of evolution of major gastropod branches. It appears that the subclass Archaeobranchia served as the base for this early radiation.listelement.badge.dso-typeЭлемент, REDISTRIBUTION OF Au IN VOLCANIC ASHES IN THE COURSE OF THEIR POSTSEDIMENTARY ALTERATIONS(2007) Felitsyn S.B.The redistribution of Au in Late Precambrian volcanic ashes from the Vendian section of the East European Platform and the Sinian section of the South China Platform is characterized by high Au concentration (up to >20 ng/g) in Fe3+-rich samples. The Au content decreases to ∼2 ng/g in Fe2+-rich volcanic ashes from the Vendian section of the East European Platform. This distribution pattern suggests the mobility of Au-bearing compounds in postsedimentary processes.listelement.badge.dso-typeЭлемент, SEDIMENT PROVENANCE OF LATE QUATERNARY MORAINIC, FLUVIAL AND LOESS-LIKE DEPOSITS IN THE SOUTHWESTERN VERKHOYANSK MOUNTAINS (EASTERN SIBERIA) AND IMPLICATIONS FOR REGIONAL PALAEOENVIRONMENTAL RECONSTRUCTIONS(2007) Popp S.; Belolyubsky I.; Lehmkuhl F.; Prokopiev A.; Siegert C.; Spektor V.; Stauch G.; Diekmann B.A provenance analysis of late Quaternary deposits from tributaries of the Aldan and Lena rivers in Central Yakutia (eastern Siberia) was carried out using analysis of heavy minerals and clay mineralogy. Cluster analysis revealed one assemblage that is characterized by relatively high proportions of amphibole, orthopyroxene and garnet as well as pedogenic clay minerals, reflecting a sediment provenance from the wide catchment area of the Lena and Aldan rivers. In contrast, the three other clusters are dominated by stable heavy minerals with varying amounts of clinopyroxene, apatite and garnet, as well as high percentages of illite and chlorite that are indicative of source rocks of the Verkhoyansk Mountains. Glacial moraines reveal the local mountain source signal that is overprinted by the Lena-Aldan signal in the oldest moraines by reworking processes. Alluvial sediments in the Verkhoyansk Foreland show a clear Lena source signal through intervals of the middle and late Pleistocene, related to a stream course closer to the mountains at that time. Loess-like cover sediments are characterized by the dominant Lena provenance with increasing proportions of local mountain sources towards the mountain valleys. Aeolian sands in an alluvial terrace section at the mountain margin covering the time between 30 ka and 10 ka BP reflect temporarily dominant inputs of aeolian materials from the Lena Plains.