中天山早古生代离散地体构造的讨论

中天山造山带的基底性质长期以来是天山大地构造研究中最有争议的问题之一。本文在比较研究中天山及塔里木北缘中晚元古代至古生代地层的基础上,认为中天山不存在连续的“前寒武系隆起带(或结晶轴)”,它是由寒武纪后从塔里木大陆北缘离散出来的若干地体组成。由于早古生代时期中天山地体的离散,形成了具洋壳性质的南天山边缘海盆地。库米什北夹于蛇绿混杂岩带中间的片麻状——眼球状花岗岩块体,是一个残留于边缘海盆地中的陆壳碎块(地体)。

On the Early Paleozoic Dispersed Terranes in Mid-Tianshan

The Middle Tianshan has been tranditionally considered as a geoanticline whcih formed an east-west trending barrier between South Tianshan and North Tianshan in geological history. In the text of this paper, the basement of Mid-Tiansban is divided into a few dispersed terranes, the west segment is Yili terrane, the east segment is Xingxingxia terrane. The Pre-Ordovician sequences on these terranes are similar to those on Tarim. For example, the Sinian System contains tillite horizons. During Ordovician and Silurian, Tarim platform sedimentary are interlayered limestones, siltstones, and sand-stones, while the records of Mid-Tianshan have a great amount of calc-alkaline volcanoclastics and granites. So this paper proposes that the dispersed terranes in Mid-Tianshan began to rift away from Tarim craton at the beginning of Ordovician. The Silurian sedimentary sequences of South Tianshan are deep oceanic basin deposits consisting of cherts and bathyal elastics associated with ophiolites and containing minor limestones. These evidences reveal that Mid-Tianshan was alreday separated from Tarim by a widespread ocean during Silurian. The Kumishi granitoid terrane in South Tianshan confined around by ophiolitic zones may be a relict of continental fragment in South Tianshan marginal sea. In late Paleozoic, Mid-Tianshan composite terranes collided with Tarim craton, the suture was south Tianshan ophiolitic melange zones.