HIGH-GRADE CONTACT METAMORPHISM IN THE KOCHUMDEK RIVER VALLEY (Podkamennaya Tunguska basin, East Siberia): EVIDENCE FOR MAGMA FLOW
E.V. Sokol1, O.P. Polyansky1, A.N. Semenov1, V.V. Reverdatto1, S.N. Kokh1, A.S. Devyatiyarova1, V.Yu. Kolobov1, P.V. Khvorov2, A.V. Babichev1
1V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptuga 3, Novosibirsk, 630090, Russia 2Institute of Mineralogy, Ural Branch of the Russian Academy of Sciences, Miass, 456317, Russia
Keywords: Contact metamorphism, spurrite-merwinite facies, Kuzmovka complex traps, simulation, indicator minerals, East Siberia
Abstract
Spurrite-merwinite marbles on the right bank of the Kochumdek River in the Podkamennaya Tunguska basin formed along the top margin of a flood basalt intrusion (Kuzmovka complex) from a marly limestone protolith of the Rhuddanian Lower Kochumdek Subformation, at a pressure of ~200 bars. The contact aureole comprises four zones of successively decreasing temperatures marked by the respective mineral assemblages: T ≥ 900 °C (merwinite, spurrite, and gehlenite (± rankinite, bredigite); T ≥ 750 °C (spurrite); T ≥ 700 °C (tilleyite, wollastonite, and melilite (Gehl<50)); and ~500-550 °C (diopside, amphibole, and grossular). Very high temperatures at the contact ( T cont > 2/3 T melt) result from magma flow along a conduit. The temperature profiles for the Kochumdek metamorphic complex show good fit between measured and geothermometer-derived values at a magma temperature of 1200 °C, an intrusion thickness of ≥40 m, a heating time of six months, and a magma flow lifespan within one month. Stagnant magma in a conduit of any thickness cools down and crystallizes rapidly and fails to heat up sediments to the temperatures required for spurrite-merwinite metamorphism (above 790 °C).
DOI: 10.15372/RGG2019088
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