TECTONIC EVOLUTION OF SUBDUCTIVE COMPLEX BELTS IN THE NORTH QILIAN MOUNTAINS
TECTONIC EVOLUTION OF SUBDUCTIVE COMPLEX BELTS IN THE NORTH QILIAN MOUNTAINS
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DOI：
10.11867/j.issn.1001-8166.1997.04.0351
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发表时间：
1997-08
期刊：
影响因子：
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通讯作者：
Song Shuguang
中科院分区：
文献类型：
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作者：
Song Shuguang
北祁连山位于中祁连柴达木地块和新朝鲜半岛西部的阿拉斯加地块之间。它是中国最典型的大陆造山带之一。该造山带发育震旦纪-中寒武纪裂谷火山岩、晚寒武世-奥陶世蛇绿岩、中-晚奥陶世岛弧火山岩、晚奥陶世拉张盆地火山沉积岩、志留纪残留海盆复理石和泥盆纪磨拉石。蛇绿岩主要分布在三个带中，其地球化学特征相似（大岔大坂蛇绿岩除外），且有由南向北年轻化的趋势。北祁连山中段肃南祁连地区发育加里东期两条不同的俯冲杂岩带，即南部深层次俯冲杂岩带和北方浅层次俯冲杂岩带。南带由海沟滑积岩和杂砂岩、蛇绿岩块、裂谷火山岩等组成，部分经高压变质作用转变为榴辉岩和高级蓝片岩，呈三个构造岩片分布于深层次俯冲杂岩带。变形和变质分析表明，不仅顺时针，倒退的PTt-D路径，但也板块运动的动力学变化从俯冲走滑剪切上推。北方浅部俯冲杂岩带由杂砂岩、蛇绿岩和低级蓝片岩组成，夹有岛弧火山岩。低品位蓝片岩的P-T条件为150~250℃，0.4~0.7GPa，反映了浅部或浅部的高压变质作用。这两个杂岩带可能形成于同一俯冲带的不同深度，其岩石学、变质和变形特征揭示了一个从裂谷-洋化-俯冲-弧陆碰撞-造山的构造演化历史。
The North Qilian Mountains are located between the Middle Qilian Qaidam Massif and the Alaskan Massif which is the west part of Sin korea Craton. It is one of the most typical continent orogenic belt in China. In this orogenic belt, there are rift volcanic rocks from Sinian to Middle Cambrain, ophiolites from late Cambrain to Ordovician, island arc volcanic rocks from middle to late Ordovician, extensional basin volcanic sedimentary rocks of late Ordovician, residual sea basin flysh of Silurian and Devonian molasse. The ophiolites, which mainly distribute in three belts, show similar geochemical characteristics( except for Dachadaban ophiolite), with the tendency of becoming younger from south to north. In Sunan Qilian region, the middle part of the North Qilian Mountains, two different Caledonian subductive complex belts, namely, the southern deep level subductive complex belt and the northern shallow level subductive complex belt, occur parallelly. The southern belt consists of trench olistostrome and graywacke, ophiolitic blocks,and rift volcanic rocks, etc., with some been transformed into eclogites and high grade blueschists by high pressure metamorphism and distributing as three tectonic slices in the deep level subductive complex belt. Deformation and metamorphic analysis suggest not only a clockwise, retrogressive P T t D path, but also a kinetic variation of plate movements from subduction to strike slip shear to upthrusting. The northern shallow level subductive complex belt consists of graywacke, ophiolite and low grade blueschists, mixed with some island arc volcanic rocks. The P T condition of low grade blueschists is 150～250℃, 0.4～0.7GPa, reflecting high pressure metamorphism at shallow level or anchi surface. The two complex belts were probably formed at different depth of the same subduction zone, and the characteristics of petrology, metamorphism and deformation reveal a tectonic evolution history of transition from rift to oceanization to subduction to arc continent collision to orogenesis.