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Russian Geology and Geophysics

2016 year, number 5

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.