New data on the metamorphism of Neoproterozoic Sodruzhestvo group in the southern Prince Charles Mountains. East Antarctica

Gulbin Yu. L., Egorova K. V., Mikhalsky E. V., Tkacheva D. А., Galankina O. L.

Zapiski RMO (Proceedings of the Russian Mineralogical Society). 2015. V. 144. N 5. P. 15-32

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Language: Russian


A thermobarometric study was carried out for metasedimentary rocks from the northern part of Cumpston massif in the southern Prince Charles Mountains of East Antarctica. These rocks are represented by metapsammites, quartzite schists and metapelites containing the Qtz—Bt—Ms—Pl—Grt assemblage. The peak conditions for the Cambrian metamorphic event were estimated with use of conventional and multiequilibrium thermobarometry. Moreover, metamorphic paths during the Cambrian have been determined from zoned garnets and pressure-temperature pseudosections modeling in the MnNCKFMASHT system with Theriak/Domino. These paths are arranged clockwise within the Grt—Bt—Pl—Ms field. They are characterized by pressure and temperature increasing from 6.5—8.5 kbar, 490—510 °C up to peak conditions of 10—11 kbar, 580—610 °C followed by cooling and decompression down to the limits of the chlorite stability field (7 kbar, 550 °C). The composition of white micas serves as an additional indicator of the high pressure. The thermobarometry evolution of garnet amphibolites sills intruded along the shear zone in the gneissic crystalline basement is comparable to that of metasedimentary rocks. Garnet zoning, plagioclase compositional variations and thermobarometric calculations indicate for metabasites the record peak conditions of 10—11 kbar and 620—650 °C, with the following near-isothermal decompression down to 6—7 kbar. These results show with evidence the importance of the collision orogeny during the tectonothermal event caused metamorphism of Sodruzhestvo series rocks.

Key words: metapelite, metabasite, P—T path, Theriak/Domino, TWQ, continental collision, Sodruzhestvo group, East Antarctica.