Abstract:

In this paper we reported the 40 Ar 39 Ar dating results of hornblendes in Grt Pl bearing Amphibolite from the Larsemann Hills, East Antarctica. Their apparent ages respectively are 1586Ma, 1011-1080Ma, 761Ma, 529-582Ma. Their plateau ages of 1036Ma and 554Ma as well as an Ar Ar isochron age of 1010Ma have also been obtained respectively. These isotopic dating results for the first time by the Ar Ar method for hornblendes completely record almost all the structural metamorphic thermal events that this region experienced, and provide an answer to the controversial question on the structural metamorphic thermal events of this region in recent several years, namely, the late Proterozoic 1000Ma event (Grenvillian) and the early Palaeozoic 500Ma event (Pan African) which one is more important than another, as well as whether the former exists or not. The 40 Ar 39 Ar dating results of hornblendes show that the Larsemann Hills experienced a complicated poly metamorphic evolutionary history, and their protoliths probably formed in early to mid Proterozoic. The late Proterozoic 1000Ma event (Grenvillian) has been confirmed to be a predominant tectonothermal event whilst the early Palaeozoic 500Ma event (Pan African) has been confirmed just to be the last strong tectonothermal event in this region.