THE ANAKIT CONTACT AUREOLE: SPURRITE-MERWINITE METAMORPHISM AND RETROGRADE PROCESSES
E.V. Sokol1, S.N. Kokh1, A.S. Polovykh1, 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 of the Russian Academy of Sciences, Novosibirsk, Russia
2South Urals Federal Research Center of Mineralogy and Geoecology, Urals Branch of Russian Academy of Science, Miass, Russia
Keywords: Contact metamorphism, spurrite-merwinite marble, metasomatism, stable isotopes, Cl-silicates
Abstract
The Anakit intrusion had a multistage effect on the host sediments, manifested as spurrite-merwinite metamorphism, early retrograde processes and associated formation of a uniquely diverse Cl-silicate mineralization (with a Cl content of up to 7-15 wt.%), skarn formation, and low-temperature hydrothermal processes. At the eastern contact of the Anakit massif, high-temperature spurrite-merwinite marbles were studied and characterized. The major and trace element and mineral composition of the rocks and the compositions of all rock-forming, accessory, and retrograde minerals has been determined. Under peak metamorphic conditions, the temperature in the near-contact zone (0.3-5 m) exceeded 900 °C, and X CO2 reached 0.3. The δ13C-δ18O trend determined for the first time is similar to those at contacts with a minimum metasomatic influence. The small difference between the δ13C and δ18O values of the Anakit marbles and their protoliths (Δδ13C ≤ 2.0‰ and Δδ18O ≤ 4.0‰) proves the predominant contribution of metamorphic decarbonation to carbon and oxygen isotope fractionation. Along with mineral indicators, it testifies to the limited infiltration of magmatogenic fluids into the host strata.
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