南天山榆树沟遭受麻粒岩相变质改造的蛇绿岩套研究

 新疆南天山榆树沟高压麻粒岩地体的原岩是一层序基本完整的蛇绿岩套。该岩套主要由变质橄榄岩、超镁铁质-镁铁质堆晶岩、下部洋脊拉斑玄武岩、以及上部洋脊拉斑玄武岩等四个岩石单元构成。其岩石学和REE与相对惰性微量元素的地球化学特征表明,该蛇绿岩中的玄武岩属洋脊型;结合区域地质背景分析,初步认为榆树沟蛇绿岩可能形成于具相当规模的洋盆构造环境。锆石U-Pb年龄表明其形成时代为早古生代中晚期,证实西南天山早古生代蛇绿岩确已延伸至库米什一带。榆树沟麻粒岩相蛇绿岩套的确定以及对其独特的形成和俯冲-折返过程进行深入研究,不仅对进一步探讨天山构造带的形成和演化有重要意义,而且对发展大陆动力学理论也具重要参考价值。

STUDY ON YUSHUGOU OPHIOLITE SUITE MODIFIED WITH THE METAMORPHISM OF GRANULITE FACIES IN SOUTHERN TIANSHAN

The protolith of Yushugou terrane of high-pressure granulite facies in south Tianshan is a prefect ophiolite suite. The suite consists of 4 basic units which a remetamorphic peridotite, ultra-mafic and mafic accumulate, tholeiite of lower ridge and tholeiite of upper ridge, respectively. Based on petrological and geochemical characters of REE and some inert miner elements, it is suggested here that the basalt’s of the ophiolite suite is of oceanic ridge type. It is prelimin a rily considered from tectonic setting that the suite is probably formed in a quite large-scale small oceanic basin. The U-Pb ages of zircons show that the suite is formed in medium-late early Paleozoic, which suggests that the Paleozoic ophiolite in the west part of southern Tianshan does extend to the Kumishi area. The ophiolite in these two areas may be undertaken different tectonic deformation in different depth of the same collision-orogency process. Thus, the study on the unique formation and uplifting mechanism of Yushugou ophiolite is helpful for the discussion of not only formation and evolution of Tianshan tectonic belt but also the theory of continental dynamics.