ANAKIT CONTACT AUREOLE: SPURRITE-MERWINITE METAMORPHISM AND RETROGRADE PROCESSES
E.V. Sokol1, S.N. Kokh1, A.S. Polovykh, V.V. Sharygin1, V.V. Reverdatto1, P.V. Khvorov2, K.A. Filippova2, Yu.V. Seryotkin1, A.N. Pyryaev1
1V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch, Russian Academy of Sciences,Novosibirsk, Novosibirsk, Russia
2South Ural Federal Scientific Center of Mineralogy and Environmental Geology, Ural Branch of the Russian Academy of Sciences, Miass, Ilmen Nature Reserve territory, Russia
Keywords: contact metamorphism, spurrite-merwinite marble, metasomatism, stable isotopes, chlorine-bearing silicates
Abstract
The Anakit intrusion had a multi-stage effect on the host sediments: spurrite-merwinite metamorphism, early retrograde processes and linked formation of a uniquely diverse Cl-silicate mineralization (with Cl content up to 7-15 wt.%), skarn formation, and low-temperature hydrothermalism. In the eastern contact, the high-temperature spurrite-merwinite marbles were characterized; main, trace element and mineral composition of the rocks as well as the compositions of all rock-forming, accessory and retrograde minerals were determined. The first set of isotope characteristics (δ18O and δ13C) of carbonate-bearing rocks was obtained. At the peak metamorphic conditions, the temperature in the near-contact zone (0.3-5 m) exceeded 900°C, and XCO2 reached 0.3. The δ13C-δ18O trend revealed for the first time is similar to those in contacts with minimal metasomatic influence. Small difference between δ13C and δ18O values for the Anakit marbles and their protoliths (Δδ13C ≤ 2.0 ‰ and Δδ18O ≤ 4.0 ‰) proves the predominant contribution of metamorphic decarbonation into C and O isotope fractionation.
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