| 中国的混杂地质体 |
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| 引用本文：冯益民,汤耀庆.1984.中国的混杂地质体[J].地球学报,6(3):77-92. |
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| 中文摘要:<正> 随着板块构造学说的问世和发展,混杂地质体愈来愈引起构造地质学者的浓厚兴趣,因为它是古俯冲带或缝合带的主要标志之一。最早研究混杂地质体的当推Griesbash、Diener 和Middlemiss(1883),Kaufmann(1886)在描述阿尔卑斯复理石中的杂乱堆积物时,启用了“野复理石”(Wildflysch),Greenly(1919)首次将“melange”一词引入混杂地质体的研究中,Flores(1955)提出了滑混堆积(Olistostrome)的概念。板块构造学说问世以后,许靖华(1 |
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| CHAOTIC GEOLOGICAL BODIES IN CHINA |
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| Abstract:Chaotic geological bodies, an important indication for finding paleo-subduction zone and paleo-suture zone within continents, are the products of plates moving from each other. They may be divided into three types, i. e. ophiolitic melange (or serpentinite melange), tectonic melange (or argillo-arenaceous melange), and olistostrome. This paper describes in detail the chaotic geological bodies along the Yarlung Zangbo River, the Jinsha River, the West Qinling Mountains and Western Junggar which serve as examples to delineate the characteristics of the three types. They share a character in common of consisting of three parts, i. e. exotic blocks, autoclastic blocks and matrix. The fossil chaos are usually present in them.In China chaotic geological bodies are distributed chiefly in four greattectonic belts, i. e. Ancient Asian, Central China, Tethyan and the Circum-Pacific Ocean Tectonic Belts which are located among several rigid massives(median massives). Moreover, chaotic geological bodies concentrically occuralong paleo-subduction zones, suture zones and transform faults.The distribution of the three types reveals that they were all formed in subduction trench. The differences in the distances away from the central line of the trench and in the geological processes brought about various formative fashions.Ophiolitic melange belongs to a pure tectonic origin. It was formed in the central line of the trench. During or after the oceanic crust in the form of a young foldbelt fringed on a continental margin, an ophiolite nappe occurred along the subduction zone or collision zone between plates, and then was destroyed by overthrusting, thrusting and imbrication, resulting in the formation of ophiolitic melanges. Therefore, the ophiolitic melanges are a polytectonic product, in which the ophiolite is exotic, or high allochthon. But terrigenous sediments or shelf neritic deposits, which are younger than the tectonically overlying ophiolite, are autochthonous.Olistostrome was mainly formed by deposition further away from the central line of the trench. The important factors for its formation are the offscraping of the overriding plates to the sediments on the subduction oceanic crust, the self-collapsing of fore margin of the overriding plate, and the transportation of the products of collapsing by turbidity current. The components of blocks depend upon the location of a trench subduction zone. When the trench is located on the oceanic crust, ophiolitic olistostrome will be formed. Its embed ment in turbidite also proved its depositional origin.During subduction-collision of plates, tectonic melange was formed from olistostrome reworked by strong tectonism rather near the central line of the trench. In addition it may be also formed in such a way that normal sequences were broken up under strong tectonic compression. Its overlying and underlying beds are both marked by tectonic contact, i. e. thrusting (or fault) contact. The matrix of tectonic melange was intensively sheared, and pressed into fissures on the edge of the blocks in a plastic manner, thus indicating its close relation with a tectonic genesis.The location of paleo-subduction zone and paleo-suture zone might be identified based on the distribution of chaotic geological bodies. The location of a suture is generally marked by the youngest ophiolitic melange in region. Besides, the tendency of migration of subduction of an ancient ocean can be found out by combining with other regional geological data, and then the tectonic evolution of an ancient ocean might be finally reconstructed, thus offering a convincing regional geological background for mineral prospecting. And detailed investigation of ophiolitic melange may serve directly the exploration of mineral resources. |
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