Multiple Collisions in the East African-Antarctica Orogen: Constraints from Timing of Metamorphism in the Filchnerfjella and Hochlinfjellet Terranes in Central Dronning Maud Land

Sensitive high-resolution ion microprobe (SHRIMP) U-Pb zircon age dating was applied to several types of cordierite-bearing gneisses and orthopyroxene-bearing gneiss from the basement rocks in central Dronning Maud Land, East Antarctica, to clarify the timing of tectonothermal events during the amalgamation of East and West Gondwana. The zircon ages of ca. 522-525 and 598-599 Ma were obtained in Filchnerfjella and Hochlinfjellet, respectively, and the cathodoluminescence images of analyzed zircons suggest that these were formed during high-temperature metamorphism. These two sets of ages are interpreted to represent periods that immediately followed the peak metamorphism. The dating results reveal an age gap of 80 Myr between the two areas, indicating different collisional events. In the cordierite-bearing samples in Filchnerfjella, zircon cores with oscillatory zoning have concordia ages that range from 1800 to 650 Ma. These are considered to represent the ages of detrital zircons derived over a long time from different source materials. In Hochlinfjellet, the inherited detrital zircons with oscillatory zoning have concordia ages of ca. 930, 780, and 730 Ma, indicating sedimentary protoliths derived from differently aged igneous source rocks, possibly formed in a subduction zone as an accretionary prism before the collision. According to previous age results, previously documented shear zones are now interpreted as representing a major tectonic boundary. The obtained age results imply that different allochthonous metamorphic terranes were assembled along the collisional zone of the East African-Antarctica Orogen during the period from 650 to 500 Ma.