摘要
对青藏高原拉萨地块早白垩纪火山岩15个采点的古地磁测定,揭示了一组高温特征剩磁分量。实验结果表明采样剖面获得的早白垩统卧荣沟组的古地磁结果全部为正极性,显示与早白垩纪正极性超静带的极性特征相似。对岩石的显微镜观察表明岩石未受后期热液化学交代作用和风化作用,这表明所获得的高温分量很可能代表岩石形成时的原生剩磁,其特征剩磁方向为:偏角 D=18.4°,倾角 I=26.5°,α_(95)=8.6°;相应的极位置为:经度■_p=220.3°E,纬度λ_p=66.4°N,dp=9.3°,dm=6.9°,古纬度 plat=14.0°。通过对比拉萨地块以北诸地块早白垩纪古地磁结果,认为拉萨地块在早白垩纪已与芜塘地块碰撞拼合在一起,而自早白垩纪以来相对欧亚大陆发生了1500±600km 的构造缩短。结合拉萨地块已有的晚白垩纪和古新纪古地磁数据,认为欧亚大陆的最南缘(拉萨地块)在印度/欧亚大陆发生碰撞前自早白垩纪—始新纪一直处于北纬12.8°～14°N低纬度位置,并未发生明显的纬向运动。
We present paleomagentic results on the Early Cretaceous volcanic sequences in the eastern Lhasa block near localities of Deqing （30.5°N/90. I°E）. A total 15 sites have been sampled from rhyolitic tuff. The stepwise thermal demagnetizating has successfully isolated high unblocking temperature characteristic directions. Only normal polarity observed in all sites is consistent with magnetization within the Cretaceous long Normal Superchron. Microscopic observation indicates an essentially original volcanic texture with no chemical alteration. These finds indicates the primary magnetization. The tilt-corrected mean directions for the Early Cretaceous is D/I = 18.4°/26.5° with a95 = 8.6° and N = 15 sites, corresponding to a paleopole at 65.3°N, 221.4°E. Compared with the Early Cretaceous poles from the Eurasia block, significant post-Early Cretaceous northward motion may have occurred between Lhasa block and the Eurasia block. On the basis of the existing Late Cretaceous and Palocene paleomagnetic data from the Lhasa block, the Lhasa block stood at 12.8° - 14.0°N since Early Cretaceous, thus, confirming the limited displacement of the margin of Eurasia between Paleocene and the Early Cretaceous.
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2008年第7期1621-1626,共6页
Acta Petrologica Sinica
基金
地质力学所基本科研业务费项目(编号:DZLXJK200712)
地调项目(编号:1212010610105)
“地质过程与矿产资源国家重点实验室开放课题(编号:GPMR200606)”联合资助的成果
关键词
早白垩世
拉萨地块
古地磁
纬向运动
Early Cretaceous
Lhasa block
Paleomagnetic
Displacement
