青、藏、川、滇地区印支期太平洋型古大陆边缘的特征

THE CHARACTERISTICS OF THE INDOSINIAN PACIFIC-TYPE ANCIENT CONTINENTAL MARGIN IN THE QINGHAITIBET-SICHUAN-YUNNAN REGION

青藏高原和“三江”地区,广泛发育着特堤斯型的海相三叠系和印支期构造变动及岩浆活动,成为研究中国大地构造演化和印支运动的重要地区,也是研究中国境内冈瓦纳与劳亚古陆界线和特堤斯洋壳时空分布特征的地区。长期以来,不少学者对该区大地构造和区域地质演化做过大量研究和不同观点的探讨。本文根据近来一些新资料和作者的野外观察,结合板块构造研究方法,认为青海中南部、西藏东北部、四川西部和西北部以及云南西部地区,在晚二叠世到三叠纪时曾经发育了一个南临古特堤斯大洋(或北特堤斯大洋)的太平洋型(活动性)古大陆边缘。它的特征基本代表了该区印支期大地构造的演化。

A pacific-type ancient continental margin developing during the lndosinian period can be recognized in the region of southern Qinghai, northeastern Tibet, northwestern Sichuan and western Yunnan provinces of China. It consists mainly of the following tectonic and sedimentary settings typical of the trench-arc-basin system: 1. the Karakorum-Amdo-Dengqen-Lancang River ancient trench or subduction zone; 2. the Tanggula fore-arc basin; 3. the Zadio-Yushu-Qamdo-Yidong island-arc uplift zone; 4. the Jiaza-Dege-Baiyu-Zhongdian-Simao intraarc basin; 5. the Bayan Har-Songpan-Garz back-arc basin; 6. the Tongde-Gonghe back-arc continental-margin sea basin; 7. the Western Qinlin-Upper Yangtze back-arc continental shelf; 8. the Eastern Kunlun-Southern Qilian continental-margin uplift zone. The formation and evolution of the active continental margin were related to the global plate tectonic events such as breakup of Gongwanaland and northward subduction or closure of Palaeo-Tethys (or North Tethys) oceanic crust during the Late Permian to Triassic period. The ancient continental margin was tectonically located on the southwestern margin of the Chinese palaeo-plate belonging to Laurasia, or was bordering Palaeo-Tethys on the south, and palaeogeographically situated near the equator. The evolutionary features of the continental margin reflect the upper and lower time limits and nature of the lndosinian movement in the Qinghai-Tibet—Sichuan-Yunnan border region of China and its adjacent regions. The features of each tectonicsedimentary setting on the margin and evolutionary model of the entire ancient continental margin are analysed and discussed from a plate tectonic point of view in this paper.