关键词: 塔里木地块, 侏罗, 白垩系, 古地磁

Abstract: 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.

Key words: Tarim block, Jurassic, Cretacious, Paleomagnetism