Geology of the Sivorg Terrane, Heimefrontfjella, (East Antarctica), and new U-Pb zircon provenance analyses of metasedimentary rocks.

摘要

The Sivorg Terrane is the largest crustal block of the Heimefrontfjella.udIt consists of a thick supracrustal sequence of metavolcanic and metasedimentaryudrocks that are intruded by a wide range of predominantly graniticudplutonic rocks. The protolith ages of the metavolcanic rocks have been datedudat ~1170-1140 Ma and the granitoid intrusions at ~1110-1050 Ma. The bestudestimate for Grenville-age metamorphism in the Sivorg Terrane is 1090-1060udMa. Unlike the other two terranes in the Heimefrontfjella, the Sivorg Terraneudrecords intense reworking of Mesoproterozoic rocks during the Late Neoproterozoic-udCambrian East African – Antarctic Orogeny. U-Pb detrital zirconudprovenance analyses from two samples indicate that at least two age-groups ofuddifferent supracrustal sequences crop out in the Sivorg Terrane. The older,udpreorogenic sequence gave youngest detrital ages of ~1140 Ma, which areudinterpreted as dating the maximum deposition age of the original sediment.udThese rocks also provide evidence of a Palaeoproterozoic to Archaean foreland.udThe second sample is dominated by Mesoproterozoic to late Neoproterozoicuddetrital zircons, with a significant proportion of ages ranging from 1100udto 980 Ma. The youngest ages significantly postdate the Grenville-age metamorphism,udso the sediments must have been deposited after or during the LateudMesoproterozoic orogenesis and, as such, might represent remnants of audmolasse deposit of the orogen.