摘要
本文对塔里木地块西北缘库车、拜城一带中新生代剖面进行了古地磁研究。库车与拜城两剖面具有不同方向产状,经产状校正之后,均为同一方向,表明磁性是在第三系褶皱之前获得的。热退磁结果表明500℃之前为现代地磁场方向,解阻温度为675℃,说明磁性载体为赤铁矿。 古地磁结果表明,塔里木地块在晚侏罗—晚白垩世之间没有经历大规模的构造运动。有可能自晚白垩世之后相对西伯利亚地块向北东方向移动过。
Two Mesoxoic sections along the northern margin of the Tarim block of China were studied paleomagnetically. One Late Cretaceous redbed section of 180 meters, lying 100 km north of Kuche (lat. =41.5°N, long. =83.5°E)gives a mean paleomagnetic pole position at lat.=63.0°, long. = 210°(N = 5, α95 = 16°). The two lower sites within the section show reversed magnetic polarity. Another Late Jurassic to Early Cretacious sandstone section of 75 meters, lying northwest of Baicheng (lat.=41.8°N, long. =82°. E), yields a mean paleomagnetic pole at lat. =65°, long. =:209°(N = 6, α95 = 9°.). Although the poles from two sections are significantly different before tilt corrections, they become superimposed each other after tilt corrections, suggesting a positive fold test at 99% confidence level. Thermal demagnetization experiments remove the present earth field components in temperature ranges before 500℃ and exhibit unblocking temperatures around 675℃, indicating the main magnetic mineral in samples to be hematite.The new paleomagnetic results suggest that the Tarim block does not experience large tectonic movement between Late Jurassic and Late Cretacious. The new Cretacious poles of the Tarim block are in good agreement with the Cretacious poles for North and South China Blocks (Lin, 1984), and South Korea (Lee et al., 1987) , suggesting no post-Cretacious relative motion between the Tarim block and eastern Asia. However, the Cretacious ploes of the Tarim block are significantly different from those of the Siberian block, suggssting that there is a post-Cretacious relative motion. This relative motion can be explained, in one way, as the northeastward motion of the Tarim block with respect to the Siberian block since Late Cretacious.
出处
《地震地质》
EI
CSCD
北大核心
1989年第3期9-16,共8页
Seismology and Geology
关键词
古地磁
白垩纪
侏罗
塔里木地块
Tarim block, Jurassic, Cretacious, Paleomagnetism
