造山带中古洋壳核杂岩的识别与地质意义

发布时间：2018-02-04 14:02

本文关键词： 洋壳核杂岩拆离断层带变质底板蛇绿岩造山带　出处：《中国科学:地球科学》2017年01期 　论文类型：期刊论文

【摘要】：洋壳核杂岩是由低角度正断层的大规模拆离作用而形成的大型洋底穹窿状凸起构造.其大规模拆离作用产生的韧性构造现象,最终会随着洋盆的闭合保存在造山带的蛇绿岩中.本文以将今论古的思路,系统总结现今洋壳核杂岩的岩石-构造特征.现今洋壳核杂岩包括了上盘火山熔岩与深海沉积、拆离断层带和下盘地幔橄榄岩与辉长岩侵入体等三部分.造山带中古洋壳核杂岩在全球造山带不同程度被揭示出来,我们较为系统地总结了(西阿尔卑斯Chenaillet蛇绿岩、阿尔巴尼亚Mirdita、伊朗扎格罗斯造山带Kermanshah、西藏普兰和加拿大阿帕拉契亚的Thetford-Mine)蛇绿岩中可能的古洋壳核杂岩及其特征.通过系统的对比,我们认为古洋壳核杂岩较为普遍,其有如下鉴别特征:超基性岩-基性岩单元规模较大、直接出露洋底导致发育一定规模的蛇绿质角砾岩;基性熔岩少或缺失,一般相对是晚期产物;深海沉积物(硅泥质岩、灰岩)或枕状熔岩直接覆盖在超基性岩之上;发育强韧性剪切变形拆离断层带,局部可发育高角度正断层;蛇绿岩中发育辉长岩、斜长花岗岩等侵入脉体.总之,造山带中的蛇绿岩有相当一部分是古洋壳核杂岩,是洋底拆离断层作用形成的.蛇绿岩中的韧性变形带不一定都是就位在造山带时的变质底板成因,极有可能是初始形成洋中脊时的拆离断层成因.然而,蛇绿岩中发育的韧性变形,以前普遍被认为是蛇绿岩在仰冲就位过程中形成的.两种不同成因的韧性变形代表截然不同的地质意义,前者形成于拆离断层的伸展环境、伴随一系列伸展构造,代表新生洋盆的形成;而后者则形成于逆冲就位的挤压背景,表示蛇绿岩的就位、洋盆的消亡.造山带中含蛇绿岩质的角砾岩不一定是造山阶段隆升剥蚀的产物,也可能是初始形成洋中脊时的产物.
[Abstract]:Oceanic crust core complex is a large bulge of ocean floor dome formed by the large-scale detachment of low-angle normal faults. Eventually, the ocean basin will be preserved in the ophiolite of the orogenic belt with the closure of the ocean basin. The petro-structural characteristics of the present oceanic crust core complex are systematically summarized. The present oceanic crust core complex includes upper plate volcanic lava and deep-sea sediments. The detachment fault zone and mantle peridotite and gabbro intrusions are three parts. The Middle Paleo-oceanic crust core complex in the orogenic belt has been revealed in different degrees in the global orogenic belt. We have systematically summarized (Chenaillet ophiolite in the West Alps, Mirdita in Albania, Kermanshah in the Zagros orogenic belt in Iran). The possible paleo-oceanic crust-core complex and its characteristics in the ophiolite of Plain, Tibet, and Thetford-Mineia, Canada. Based on the systematic comparison, we think that the paleo-oceanic crust complex is relatively common. It has the following distinguishing characteristics: the ultrabasic rock-basic rock unit is large in scale, and the direct outcrop of the ocean floor leads to the development of ophiolite breccia of a certain scale; The basic lava is rare or absent, and generally is a relatively late product. Deep-sea sediments (silicalite, limestone) or pillow lava are directly overlaid on ultrabasic rocks; The strong and tough shear deformation detachment fault zone is developed, and the high angle normal fault can be developed locally. The ophiolites are developed into intrusive veins such as gabbro and plagioclase granite. In short some of the ophiolite in the orogenic belt are paleo-oceanic crust-core complex. The ductile deformation zone in ophiolite is not always the origin of metamorphic floor in the orogenic belt, but most likely the origin of the detachment fault during the initial formation of the mid-ocean ridge. The ductile deformation developed in ophiolite was generally considered to be formed in the process of upsetting and emplacement of ophiolite. The two types of ductile deformation of different genesis represent distinct geological significance. The former formed in the extensional environment of the detachment fault, accompanied by a series of extensional structures, representing the formation of the new oceanic basin. The latter is formed in the compressional setting of thrusting position, indicating the location of ophiolite and the extinction of oceanic basin. The breccia containing ophiolite in the orogenic belt is not necessarily the product of uplift and denudation in orogenic stage. It may also be the product of the initial formation of the mid-ocean ridge.
【作者单位】：中国科学院地质与地球物理研究所岩石圈演化国家重点实验室;中国科学院新疆生态与地理研究所新疆矿产资源中心;中国科学院青藏高原地球科学卓越创新中心;中国科学院大学地球科学学院;
【基金】：国家自然科学基金项目(批准号:41390441,41472192,41230207) 中国科学院战略性先导科技专项项目(B类)(编号:XBD03010801)资助
【分类号】：P542
【正文快照】： 1引言造山带中古洋壳核杂岩,指的是洋壳核杂岩随着洋盆闭合而构造就位于造山带中的大洋残片,是一类独特的蛇绿岩.洋壳核杂岩(O c e a n i c c o r e c o m p l e x),指的是形成于大西洋和西南印度洋等慢速或超慢速扩展洋脊与转换断层内侧角区域的大型穹窿状凸起构造(图1

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