东南极拉斯曼丘陵石榴斜长角闪岩中角闪石的^(40)Ar-^(39)Ar年龄及其地质意义

THE 40 Ar 39 Ar AGES OF HORNBLENDES IN GRT PL BEARING AMPHIBOLITE FROM THE LARSEMANN HILLS, EAST ANTARCTICA AND THEIR GEOLOGICAL IMPLICATIONS

本文对东南极拉斯曼丘陵出露的石榴斜长角闪岩中的角闪石进行了４０Ａｒ－３９Ａｒ年龄测定，分别得到角闪石视年龄１５８６Ｍａ、１０１１～１０８０Ｍａ、７６１Ｍａ和５２９～５８２Ｍａ，角闪石坪年龄１０３６Ｍａ和５５４Ｍａ，角闪石Ａｒ－Ａｒ等时线年龄１０１０Ｍａ，这些同位素年龄证据，首次完整地记录了该区所经历的几乎所有构造变质热事件，为近几年国内外地质学家关于该区构造变质热事件争论的焦点问题，即晚元古代的１０００Ｍａ格林维尔事件（Ｇｒｅｎｖｉｌｉａｎ）与早古生代的５００Ｍａ泛非事件（Ｐａｎ－Ａｆｒｉｃａｎ）孰轻孰重以及前者是否存在，提供了答案。角闪石的４０Ａｒ－３９Ａｒ年龄测定结果表明，拉斯曼丘陵地区经历了复杂的多期变质演化历史，其原岩可能形成于早－中元古代，占主导地位的应该是晚元古代的１０００Ｍａ格林维尔事件，而５００Ｍａ泛非事件则是晚期较强烈的变质热事件。

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.