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

Description

In order to understand the tectonic behaviour of a stabilized Neoarchaean continental crust during subsequent tectonic activity,we investigated the compositemetamorphic basement along the Terre Adélie and George Vth Land coastline, also known as the Terre Adélie Craton (East Antarctica). Two domains are recognized: (1) a Neoarchaean basement, composed of granulite rocks to the east and overlain to thewest by amphibolites, and (2)two Paleoproterozoic detrital basins overly theNeoarchaean crust and extend further west.Newgeochronological data fromthe Terre Adélie Craton define a tectonic evolution with threemajor peaks' activity. Th­U­Pb 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. 1.7Ga along hydrated anastomozing metre-scale shear zones. New 40Ar/39Ar ages obtained by stepwise 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 1.7Ga transpressive event. A final event at ca. 1.55­1.50 Ga is only recognized close to the Mertz Shear Zone (145.E) bounding the Terre Adélie Craton to the East. The new data allow us to propose detailed geological pictures of the Terre Adélie Craton geodynamic evolution, from the Neoarchaean to the Mesoproterozoic.

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