Abstract:

In this paper we reported the ⁴⁰Ar-³⁹Ar dating results of hornblendes in Grt-P1-bearing amphibolite from the Larsemann Hills, East Antarctica. Their apparent ages respectively are 1586 Ma, 1011-1080 Ma, 761 Ma, 529-582 Ma. Their plateau ages of 1036 Ma and 554 Ma as well as an Ar-Ar isochron age of 1010 Ma 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, which one is more important, the late Proterozoic 1000 Ma event (Grenvillian) or the early Palaeozoic 500 Ma event ( Pan African), as well as whether the former exists or not. The ⁴⁰Ar-³⁹Ar dating results of hornblendes show that the Larsemann Hills experienced a complicated poly metamorphic evolutionary history, and their protoliths were probably formed in early to mid Proterozoic. The late Proterozoic 1000 Ma event (Grenvillian) has been confirmed to be a predominant tectonothermal event whilst the early Palaeozoic 500 Ma event (Pan-African) has been confirmed just to be the last strong tectonothermal event in this region.

Key words: East Antarctica, Grt-P1-bearing amphibolite, hornblendes, ⁴⁰Ar-³⁹Ar ages, tectonothermal events