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新疆东准噶尔卡拉麦里蛇绿岩是一套由以镁铁-超镁铁岩为主的构造岩块和不同岩性的基质组成的蛇绿混杂带,被认为是哈萨克斯坦板块和西伯利亚板块之间的缝合带。由于其特殊的大地构造位置,该蛇绿岩对恢复区域构造演化具有重要意义。然而,在过去20多年里,有关其形成及就位时代的争议一直很大,其原因在于不同学者采用来自化石资料和同位素年龄方面的不同证据。本文选择该蛇绿岩套中保存相对完整的辉长岩进行了LA-ICP-MS锆石U-Pb年龄测定,获得了3个峰值年龄:406±1.8 Ma,514±5.1Ma和332±6.4 Ma。结合该区野外地质特征和前人资料分析,本文认为除514±5.1 Ma的年龄可能来自古老围岩中的残余锆石之外,另外两组年龄分别与蛇绿岩的形成和就位有关,前者代表卡拉麦里蛇绿岩的形成时间,后者则代表卡拉麦里蛇绿岩的构造侵位时间,即卡拉麦里洋盆形成于泥盆纪初期,最终闭合于早石炭世早期。
The Kalamaili ophiolite in East Junggar, Xinjiang is a complex of ophiolitic complexes composed of mafic-ultramafic-hosted tectonic blocks and lithologically different matrices that are considered as Kazakhstan and Siberian plates Between the suture. Due to its special tectonic location, the ophiolite is of great importance to the tectonic evolution of the restoration area. However, the controversy over the age of more than two decades about its formation and its place has been high because of the different scholars’ differing evidence of fossil data and isotopic age. In this paper, LA-ICP-MS zircon U-Pb ages were selected to preserve relatively intact gabbro in this ophiolite suite and three peak ages were obtained: 406 ± 1.8 Ma, 514 ± 5.1Ma and 332 ± 6.4 Ma. Based on the field geological characteristics and previous data analysis, we consider that the age of 514 ± 5.1 Ma may come from the residual zircons in the ancient wall rocks, and the other two groups are related to the formation and placement of ophiolite respectively. The former represents the formation time of the Kalamaili ophiolite and the latter represents the tectonic emplacement time of the Kalamaili ophiolite. That is, the Kalamaili Ocean Basin was formed in the early Devonian and finally closed in the Early Carboniferous.