PETROLOGY OF THE LAMPROITE AND GRANITE-SYENITE SERIES ROCKS OF THE BILIBINSKY (LOMAM) MASSIF, ALDAN-STANOVOY SHIELD
Chayka I.F.1,2, Izokh A.E.1,3, Sotnikova I.A.4, Alymova N.V.4, Kolotilina T.B.4, Karimov A.A.5, Shcherbakov V.D.6, Lobastov B.M.7
a:2:{s:4:"TEXT";s:685:"1V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia
2Institute of Experimental Mineralogy, Russian Academy of Sciences, Chernogolovka, Russia
3Novosibirsk State University, Novosibirsk, Russia
4Vinogradov Institute of Geochemistry, Siberian Branch of the Russian Academy of Sciences, Irkutsk, Russia
5Institute of the Earth’s Crust, Siberian Branch of the Russian Academy of Sciences, Irkutsk, Russia
6Lomonosov Moscow State University, Moscow, Russia
7Institute of Mining, Geology and Geotechnology. Krasnoyarsk, Russia
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Keywords: Aldan-Stanovoy shield, Bilibinsky massif, lamproites, differentiation, geochemistry, isotope geochemistry
Abstract
The Bilibisky massif is a Mesozoic intrusion located in the southeastern part of the Aldan high-potassic magmatic province of the Aldan-Stanovoy shield of the Siberian platform. This massif consists of alkali-mafic-ultramafic and granite-syenite phases, which form a concentric structure with the rocks becoming more silica-rich from edges to the center. Earlier studies proposed that these phases have been either formed from different parental magmas or derived from a common lamproitic magma via magmatic differentiation. In this study, we examined a representative set of rock samples from the Bilibinsky massif: phlogopite clinopyroxenites, melashonkinites, shonkinites, alkali syenites, quartz syenites, granites. Mineralogical-petrographic, geochemical and isotope-geochemical data implies that the differentiation series of lamproitic magma includes rocks from clinopyroxenites to shonkinites and, possibly, alkaline syenites. Quartz syenites and granites, which form the second phase, belong to a separate magmatic series. According to geochemical data and the isotopic composition of Nd, Sr and O in quartz syenites and granites, the magmas, which formed the syenites and granites, were rather derived from the lower crust than from lithospheric mantle and originated due to either crustal melting during the mantle-derived magmatism or collisional tectonics at the Southern margin of Siberian platform in Mesozoic. Rocks of the lamproite series allows us to consider it as an example of complete differentiation of lamproite melt, which presents the stages of cotectic crystallization: olivine + chromite, olivine + clinopyroxene + chromite, olivine + clinopyroxene + phlogopite, clinopyroxene + phlogopite + leucite, clinopyroxene + phlogopite + K-feldspar. Spot analyses of trace elements in clinopyroxene, phlogopite, leucite and apatite allowed for estimation of melt-mineral partitioning coefficients in such a system.
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