Multistage Evolution of Proterozoic Crust of East Antarctica by the Example of the Filla Terrane (Rauer Islands): New Geological and Isotope Data

Abstract

Abstract —The paper presents new data on the Rauer Islands, one of the unique objects of the East Antarctic Shield. The interest in this area is triggered by its complex geologic structure, including both Archean and Proterozoic fragments of the Earth’s crust, and by its multiphase formation. A detailed scheme of the geologic structure of the area is proposed, new petrologic complexes are revealed, and the stages of tectonomagmatic activity at ~1400–1320 Ma and 1150 Ma are reliably dated. This serves as a factual basis for comparison the study area with other regions of East Antarctica. Based on the geological and isotope data obtained, the Meso–Neoproterozoic Filla Terrane in the area of the Rauer Islands is recognized. It is composed of metamorphic and primarily intrusive rocks, whose protoliths formed in the time interval 1400–950 Ma. Three periods of tectonothermal activity have been established in the Filla Terrane: Mid-Mesoproterozoic (1400–1320 Ma), Meso–Neoproterozoic (1150–886 Ma), and early Cambrian (536–504 Ma). The first period is the formation time of Mesoproterozoic crust, and it is time-correlated with the tectonogenesis phase in the adjacent Rayner province. The second period corresponds to the later phase of tectonothermal activity in the Rayner province. In the Filla Terrane, this period can be divided into two intervals, 1150–1100 Ma and 1010–886 Ma. The former interval is treated as intense crustal growth in the course of granitoid and mantle magmatism. The latter interval is a period of tectonothermal processes accompanied by intense deformations, high-temperature metamorphism, and intrusion of porphyritic granitoids. Apparently, the gap between the first and the second intervals is the time of deposition of the sedimentary protolith of paragneisses, which, together with the surrounding rocks, underwent high-temperature metamorphism and deformations at 950–914 Ma. The synchronous evolution of the Archean block and the Filla Terrane began at least within 1100–1000 Ma. The youngest, early Cambrian period of tectonic activity coincides with the development of local low-temperature mylonite zones and the intrusion of synkinematic pegmatite veins. Thus, the tectonothermal evolution of the Filla Terrane includes almost the same main phases of crustal growth and transformation as the Rayner province. This indicates that the Filla Terrane is a fragment of the Rayner province, which accreted to the Archean terrane at least in the late Mesoproterozoic.