西准噶尔南部玛依勒洋盆开启、闭合时限:来自中泥盆统与下伏地质体之间角度不整合关系的证据

新疆西准噶尔南部地区出露多条蛇绿岩,其中玛依勒蛇绿岩是该地区比较重要的蛇绿岩之一,其所代表的古洋盆的开启、闭合时限一直是地学界争论的焦点。详细的野外调查发现:玛依勒蛇绿混杂岩呈构造岩块的形式就位于中-上志留统玛依拉山岩群复理石基质中或与寒武纪杂岩体在空间上密切共生,表明玛依勒蛇绿岩所代表的古洋盆至少在寒武纪时期就已经开启,一直持续到中-晚志留世;中泥盆统库鲁木迪组分别角度不整合于中-上志留统玛依拉山岩群和寒武纪杂岩体之上,从而限定了玛依勒洋盆闭合时限的上限为中泥盆世之前。地层剖面分析发现库鲁木迪组与玛依拉山岩群之间在岩性特征、地层序列、沉积环境等方面均存在显著差异,表明晚古生代早期是西准噶尔地区构造演化发展的重要转换时期,库鲁木迪组下部的陆相沉积序列是对玛依勒早古生代洋盆闭合过程的沉积学响应。这将对进一步研究西准噶尔的构造演化和古生代中亚地区的构造格局提供了重要的制约。

The timing of opening and closure of the Mayile oceanic basin: Evidence from the angular unconformity between the Middle Devonian and its underlying geological body in the southern West Junggar

Mayile ophiolitic mélange belt is one of the important Early Paleozoic ophiolite suites in the southern West Junggar, Xinjiang. It is controversial concerning the timing of opening and closure of the Mayile ancient oceanic basin. Based on detailed field investigations, Mayile ophiolitic mélange emplaced in Middle-Upper Silurian Mayilashan Group flysch matrix or coexistenced closely with the Cambrian intrusive rocks in space. This indicates that Mayile ancient oceanic basin opened at least in the Cambrian. Observation along stratigraphic profiles suggest that there is angular unconformity between the Middle Devonian Kulumudi Formation and Mayilashan Group in lithologic characteristics, basic sequence, sedimentary environment. These reflect that early Late Paleozoic is a major transition period in the development of tectonic evolution of the West Junggar, and the deposition of continental sedimentary sequence in the lower part of Kulumudi Formation is a sedimentary response to the closure of Mayile Early Paleozoic ocean basin. Furthermore, this will provide important constraints on the tectonic evolution of the West Junggar orogenic belt and the tectonic framework of the Central Asian Orogenic Belt (CAOB) during the Paleozoic period.