塔里木南缘煌斑岩的时代及其地质意义

^(40)Ar-^(39)Ar DATING OF LAMPROITE ALONG SOUTH MARGIN OF THE TARIM PLATFORM AND ITS GEOLOGIC SIGNIFICANCE

在塔里木南缘皮山县境内发现东西向煌斑岩带 ,它们呈脉状产出 ,围岩为前寒武纪绢云绿泥石英片岩、变质粉砂岩及石炭纪玄武岩、结晶灰岩等。岩石地球化学特征与典型地区的钾镁煌斑岩相似。从煌斑岩中挑选的金云母经Ar Ar测年 ,获得理想的坪年龄为 2 1 7.65± 0 .39Ma ,40 Ar/36Ar 39Ar/36Ar等时线年龄为 2 1 7.2 7± 1 .38Ma,与坪年龄一致。这一年龄值代表了煌斑岩的形成时代 ,与阿尔金断裂形成时代基本一致 ,它代表了塔里木南缘在这一时期重要的走滑事件。煌斑岩带的发现 。

A lamproite belt was found along south margin of the Tarim platform. The lamproite outcroped as dyke occurring in the Precambrian schists and the Carboniferous limestone and basalt. The phlogopite from the lamproite yielded a plateau age of 217.65±0.39 Ma and 40 Ar/ 36 Ar 39 Ar/ 36 Ar isochron age of 217.27±1.38 Ma . The both represented forming age of the Altyn fault (220～240 Ma ago), namely, an important strike slipping event related to collision between the Qiangtang Block and west Kunlun. The discovery of the lamproite belt might be helpful to exploration of diamond deposits in the southern margin of Tarim.