High-grade crystalline basement of the northwestern Wilson Terrane at Oates Coast: new petrological and geochronological data and implications for its tectonometamorphic evolution

The high-grade basement of the northwestern Wilson Terrane at Oates Coast is subdivided into three roughly north-south trending zones on the basis of tectonic thrusting and differences in metamorphic petrology. New results of detailed petrological investigations show that metamorphic rocks of the central zone were formed in course of one single, clockwise directed P-T evolution including a medium-pressure and high-temperature granulite-facies stage at about 8 kbar and >800° C, a subsequent isothermal decompression and a final stage with retrograde formation of biotite + muscovite gneisses. In the eastern and western zones the majority of metamorphic rocks experienced clockwise oriented metamorphism at somewhat lower P-T conditions of about 4-5.5 kbar and 700-800°C. While some rocks in both zones did not reach the upper stability limit of muscovite + quartz, granulite-facies rocks detected in parts of the western zone were formed under P-T conditions similar to those of the central zone. New SHRIMP data support an age for the metamorphic peak of 496-500 Ma in the central zone (Henjes-Kunst et al., 2004). 40Ar-39Ar dating of amphiboles and micas indicate a general trend to younger ages from the west to the east of the basement complex, i.e. from 488-486 Ma to 472-469 Ma for amphiboles and from 484-482 Ma to 466 Ma for micas. This is explained by temporal differences in the retrograde metamorphic evolution of the three zones in the course of the late-Ross-orogenic thrust-related uplift of the basement complex, with the western zone being exhumed earlier than the eastern zone.