塔里木陆块晚古生代以来古地磁特征研究

S TUDY ON PALAEOMAGNETISM OF TARIM CRATON SINCE LATE PALAEOZOIC

塔里木陆块晚古生代以来极移曲线具有相似的规律,二叠纪以来塔里木陆块是一个稳定的整体.经统计各时代古地磁极位置:晚石炭世:184.9°,56.0°N;二叠纪:194.4°,64.4°N;三叠纪:206.0°,78.2°N;侏罗纪:251.6°,75.9°N;白垩纪:296.3°,75.8°N;老第三纪:223.4°,75.3°N;新第三纪:268.3°,79.9°N.

The Tarim Craton is one of three main cratons of China. Its developmental history and tectonic evolution are very interesting to geologians. Study on the ploblems is very useful not only to approach of structural framework and developmental history of the earth but also to study on formation of some mineral resources and ore-controlling tectonic system. In the nouthern ( Hotan ) and the northwestern borders (Baicheng) of the Tarim Craton the palaeomagnetic polar curves of each age are similar. The result shows clearly that tectonic developmental history of the Hotan and the Baicheng regions is identical. Since Permian the Hotan and the Baicheng regions are a stable whole. Statistical results of palaeomagnetic pole location of each age are as follows: Late Carboniforous; 185.9°, 56.0°N; Permian: 194.4°, 64.4°N; Tr.iassic: 206.0°. 78.2°N; Jurassic, 251.6°, 75.9°N; Cretaceous: 296.3°, 75.8°N; Paleogene, 223.4°, 75.3°N; Neogene: 268.3°, 79.9°N. According to comparesion of palaeomagnetic results the authors consider that the Tarim Craton,Sino-Korean Block,Yangtze Block,Qiangtang massif were independent mass from each other during Early Permian . from Late Permian to Eaely Triassic the Sino-Korean Block, the Yangtze Block and the Tarim Craton began to be close to each other, and then collision and convergence took place. But during the Late Triassic,the Qiangtang massif just split from the India plate. There was a paleotethys sea between the Tarim Craton and the Qiangtang massif. In the mid of the Middle Jurassic the Qiangtang massif had collided with the Tarim Craton. The authors consider boundary between Goudwana land and Eurasian land should be put at the Kengxiwar-Kalamilan megafault dividing the Tarim Craton and the Qiangtang massif. According to magnetostratigraphic study the divisions of the Cretaceous in the Baicheng region are basically identical with magnetostratigraphic column of the Cretaceous in the area. The bottom of the Cretaceous is about 144 Ma and the top about 65 Ma in age should the Lower Cretaceons strata of the original division in the Hotan region Collect to Triassic ( Uzunsayi grup ) . The boundary between Permian and Triassic was put at top of the Kiaman reverse polarity member by our precursors. According to magnetostratigraphic palaeontologic and petrostratigraphic data the authors consider that the boundary should be at the top of the first positive polarity member after the Kiaman reversed polarity member. According to palaeomagnetic and palaeontologic data the authors consider there sxist strata of Triassic in the Hotan region. In the period from Permian to Tertiary palaeolatitude of the Tarim Craton moved about from 23°N to 30°N, only seven degrees towards the north. But each block of the India plate ( they were located in the south of the Tarim Craton) moved towards the north and collided with the Tarim Craton. The Kunlun Mts., the Altun Mts. and the Himalayas were succesivcly formed. That made the Pa-laeotethes Sea to be closed. It is not only a decisive factor controlling paleoclimate and palaeoenvironment of the Tarim Craton but also one of control factors for some sedimentary mineral deposits in the area. According to results of the analysis of paleolatitude and pala oenvironment the authors have evaluated the prospects of coal, petroleum, gas and evaporites in the Tarim Craton.