松潘—阿坝地块三叠系古地磁结果及运动学意义

Paleomagnetism Characteristics of Triassic in Songpan-Aba Block and Its Kinematic Indication

迄今为止,位于扬子地块的西北缘,夹持于扬子、华北、塔里木和羌塘—昌都地块之间呈倒三角形构造区块的巴颜喀拉褶皱带尚未有构造古地磁研究成果报导。为配合该区油气勘查与油气资源评价,并对构造区块定位提供定量数据,开展了松潘—阿坝地块的古地磁研究。采样区集中在西秦岭构造区南亚带(摩天岭和若尔盖)、中亚带(洮河)和巴颜喀拉构造区的马尔康复向斜带(巴颜喀拉褶皱区)4个微地块。采样地层单元主要为三叠系。共采集57个采点,376块岩心标本。通过对岩石样品测试数据的分析和计算,获得洮河、巴颜喀拉、摩天岭和若尔盖(后两者夹于前两者之间)4个微地块古地磁极极点位置:经度为191.4°E^202.9°E,纬度为49.5°N^58.5°N。洮河和巴颜喀拉两微地块在晚三叠世的古纬度同为26.2°N,表明晚三叠世这4个被断裂相隔的微地块已构成一个统一的较大的地块。洮河和巴颜喀拉地块在三叠纪时的古纬度变化分别从早三叠世的13.4°N和11.3°N向北移动到晚三叠世的26.2°N,同时在北向移动过程中从早三叠世至晚三叠世分别发生了约40°和16°的逆时针旋转。

Up to now, no paleomagnetic data has been reported on the Bayankala folded belt, which is an upside-down triangle area located among the Yangze, North China, Tarim, and Qiangtang-Changdu blocks. The paleomagnetic study on Songpan-Aba continental block is to provide with quantitative data for its localization during geological history and to be a basis for oil and gas resources evaluation. The sampling spots are around the four micro-blocks such as the southern structural belt（ Motianling area and Ruo＇ergai area）, and the central structural belt （Taohe area） of west Qinling structural zone , the Markang composite syncline belt of the Bayankala structural zone（ Bayankala folded zone）. The sampling is centered around the Triassic rocks. There are 57 sampling spots and 376 core samples in all. By the analysis and calculation of the measured data of the core samples, the paleomagnetic pole location for the Taohe, Bayankala, Motianling, and Ruo＇ergai blocks（with the later two blocks located between the former two blocks） has been acquired. These micro-blocks are located at north latitude 49.5° to 58.5° and east longitude 191.4° to 202. 9°. The paleo-latitude of the Taohe and the Bayankala micro-blocks in Late Triassic is the same as north 26.2°, which indicates that the four micro-blocks separated by the faults had combined to be a larger block in Late Triassic. The variation in the paleo-latitudeduring Triassic for the Taohe and the Bayankala micro-blocks shows the north 13.4° and north 11.3° of the two blocks respectively in Early Triassic have changed to the same north 26. 2° in Late Triassic. Meanwhile, the two blocks have anti-clockwise rotated approximately 40° and 16° respectively from Early Triassic to Late Triassic with their northward movement.