新疆东准噶尔卡拉麦里蛇绿岩带两侧志留系—石炭系沉积和构造特征分析及其意义

卡拉麦里蛇绿岩带位于新疆准噶尔盆地东北缘,查明卡拉麦里蛇绿岩所代表的古洋盆形成和闭合时代,是新疆东准噶尔乃至古亚洲洋演化历史的关键地质问题之一。本文通过对蛇绿岩带两侧志留—石炭系的岩石组合、结构构造、接触关系以及生物化石等沉积-构造特征的对比分析,揭示卡拉麦里构造带古生代的构造演化。在卡拉麦里蛇绿岩带北侧,广泛发育上志留统、下泥盆统与中—上奥陶统和加里东期花岗岩的角度不整合,普遍缺失下志留统,不整合面之下的奥陶系为变质达绿片岩相的安山岩为主,而在蛇绿岩带南北两侧的中、上志留统—泥盆系—下石炭统沉积体系特征相似,可以对比:地层间整合接触,产状平缓,褶皱、断裂构造和变质作用均不发育,主要为开阔的短轴背斜、向斜,与卡拉麦里蛇绿混杂岩带中的强变形构造明显不同;岩石组合都以火山碎屑岩为主,多见交错层理等沉积构造,产门类众多的动植物化石,反映了滨—浅海相的沉积环境。以上说明,卡拉麦里构造带晚古生代并不存在一个开阔的大洋,卡拉麦里蛇绿岩所代表的古洋盆在中志留世之前已经闭合。

An analysis of Silurian-Carboniferous sedimentary and structural characteristics on both sides of Karamaili ophiolitic belt of Xinjiang and its significance

The Karamaili ophiolite belt is located on the northeastern margin of Junggar Basin, which is a very important tectonic unit in northern Xinjiang and Central Asia area. The evolution of Karamaili oceanic basin remains controversial due to hot-debated issues on the ages and characteristics of Karamaili ophiolite. This study focuses on the Paleozoic tectonic setting in the Karamaili tectonic zone revealed by a comparative study of the Silurian-Carboniferous tectono-sedimentation on its north and south sides. To the north of the Karamaili ophiolitic belt, the angular unconformities are widely developed between Upper Silurian, Lower Devonian and underlying Middle-Upper Ordovician strata and Caledonian granitoids. The Lower Silurian strata are generally absent and the underlying Middle-Upper Ordovician strata mainly consist of andesite with greenschist facies. The Middle, Upper SilurianDevonian-Lower Carboniferous sedimentary deposition system to the north of Karamaili ophiolitic belt is similar to that to the south, including conformable contact, flat occurrence and undeveloped folds, faults and metamorphism. Anticlines or synclines are mainly of short axis, which is apparently different from strong deformation shown in the Karamaili ophiolitic mélange. Besides, pyroclastics-dominated rock associations, widely existent inclined beddings and cross-beddings and abundant kinds of animals and plants fossils indicate a littoral-shallow marine environment. Therefore, during Late Paleozoic, no ocean existed in the Karamaili tectonic zone and the oceanic basin represented by the Karamaili ophiolitic mélange had been closed before Middle Silurian.