华北陆块、秦岭地块和扬子陆块构造演化的古地磁证据

PALEOGEOGRAPHIC HISTORY OF NORTH CHINA CONTINENTAL BLOCK, QINLING GEOLOGICAL BLOCK AND YANGTZE CONTINENTAL BLOCK SINCE THE PALEOZOIC ERA

通过对河北井陉和湖北宜昌、兴山的39个采样点、392个样品进行的古地磁测试,以及7个采样点、71个样品中的原生剩磁以及笔者前期研究结果,系统分析了三大块体的古地磁极位置、古地磁偏角以及古纬度自寒武纪以来的变化特征,并进行了古地理复原。研究表明,三块体为不同地质构造单元,寒武纪时,华北陆块、秦岭地块以及扬子陆块自北到南顺序排列于北纬2.9°、南纬5.5°以及南纬17.0°。秦岭地块北侧和南侧分别存在一古洋盆,此时华北陆块和扬子陆块相距约1400Km左右;三块体向北漂移的过程中伴随着旋转运动;三块体开始拼合的时间为晚二叠纪至早三叠纪之间,华北陆块和秦岭地块完全拼合的时间为早三叠纪至中三叠纪之间,三块体完全拼合的时间为中三叠纪至晚白垩纪之间;晚白垩纪以后,一体化的三块体继续向北漂移,并于第四纪到达现今地理位置。

This paper introduces the results studying on paleomagnetism of 392 specimens from 39 sites from Jingxing in Hebei,Yichang and Xingshan in Hubei and the primary rema-nent magnetization of 71 specimens of 7 sites. Combining with our previous studies, the pale-ogeographic history of North China Continental Block (NCB), Qinling Geological Block (QGB)and Yangtze Continental Block(YZB)is demonstrated as follows: (1)The three zones have different geologic evolution from each other and are of different tectonic units. (2)The three zones have situated in the same order as the present from the geographic north to south since the Cambriam: North China Continental Block, Qinling Geological Block and Yangtze Continental Block(2. 9°N, 5. 5°S and 17°S respectively). There was a paleo-oceanic basin respectively at both sides (north and south) of Qinling Geological Block. (3)The three zones have drifted northward with tectonic rotation. (4) At first, the three zones partly collided with each other during the late Permian to the early Triassic. Next, NCB and QGB were united during the early to the middile Triassic. At last, fusion of the three zones occurred during the middle Triassic to the late Cretaceous. (5)The resultant united block has drifted northward to the present position since the late Cretaceous.