Superimposed Neoarchaean and Paleoproterozoic tectonics in the Terre Adelie Craton (East Antarctica): Evidence from Th-U-Pb ages on monazite and Ar-40/Ar-39 ages

摘要

In order to understand the tectonic behaviour of a stabilized Neoarchaean continental crust during subsequent tectonic activity, we investigated the composite metamorphic basement along the Terre Adelie and George Vth Land coastline, also known as the Terre Adelie Craton (East Antarctica). Two domains are recognized: (1) a Neoarchaean basement, composed of granulite rocks to the east and overlain to the west by amphibolites, and (2) two Paleoproterozoic detrital basins overly the Neoarchaean crust and extend further west. New geochronological data from the Terre Adelie Craton define a tectonic evolution with three major peaks' activity. Th-U-Pb electron probe analyses of monazite from the Neoarchaean granulites constrain the main structuration event at ca. 2.45 Ga in agreement with zircon ages from throughout the Neoarchaean domain. Local resetting together with low temperature recrystallization of monazites occurred at ca. 1.7 Ga along hydrated anastomozing metre-scale shear zones. New Ar-40/Ar-39 ages obtained by step-wise heating techniques on amphibole, biotite and muscovite from both the Neoarchaean basement and the Paleoproterozoic basins, illustrate the differential evolutions of basement and its sedimentary cover during the major 1.7 Ga transpressive event. A final event at ca. 1.55-1.50 Ga is only recognized close to the Mertz Shear Zone (145 degrees E) bounding the Terre Adelie Craton to the East. The new data allow us to propose detailed geological pictures of the Terre Adelie Craton geodynamic evolution, from the Neoarchaean to the Mesoproterozoic.