北祁连造山带中—西段陆壳残块群的构造—地层特征

TECTONO-STRATIGRAPHIC CHARACTERISTICS OF CONTINENT CRUSTAL REMNANTS IN CENTRAL-WESTERN SECTOR OF THE NORTH QILIAN OROGEN

北祁连造山带是一条多旋回的造山带 ,其最大特点是早古生代岩系中镶嵌有众多大小不一的由前震旦系变质岩系所组成的陆壳残块群 ,它们源于晋宁期末 ,统一的巨型华北古大陆早古生代初的裂解。寒武 奥陶纪西段演化为裂谷系 ,陆壳残块群组成裂谷系的正性隆起构造单元 ;中段发育微洋盆沟弧盆体系 ,在南缘的陆壳残块群处于奥陶纪活动大陆边缘张裂带上 ,并构成被晚期弧后盆地及裂谷分开后的陆壳基底部位 ,少数陆壳残块为沟弧盆体系中的孤岛隆起。它们不是由中祁连推覆来的飞来峰或是外来移置的滑覆体 ,而是由统一的巨型华北古大陆西南缘古阿拉善地块于早古生代初裂解后向洋或裂谷演化过程中残留其中的大小不一的陆壳残块。北祁连早奥陶世海域与现在加拿大北部巴芬湾及伊丽莎白女王群岛的构造格局相似。

The North Qilian Orogen was a multi cycle orogenic belt, with an obvious feature of some large to small blocks of continent crustal remnants composed of the Pre Sinian metamorphic rocks scattered in the Early Paleozoic rock series. The main characteristics of 9 tectono stratigraphic units were described in this paper, which demonstrated that these continent crustal remnants were parts of giant unified continent of the North China plate, rifted and drifted away during the Early Paleozoic. In the western sector of the orogen a rift system (including rift, taphrogen and submarine volcanic belt) occurred during the Cambro Ordovician. In the central sector of the orogen some rifts developed further and opened a micro oceanic basin. Both the Middle Qilian Block and these large or small continent crustal remnants in North Qilian were rifted from the Paleo Alaxa Block which was southwestern marginal part of the North China plate during Early Paleozoic; in other words, these continent crustal remnants were not nappe outliers or allochthones units. The tectonic framework of North Qilian in Early Ordovician should be similar to that of the Bafin Bay and the Queen Elizabeth Islands.