Deformation of Asian continent

印度与亚洲的碰撞是新生代最突出的构造事件之一。印度大陆在约52 Ma时与亚洲大陆发生碰撞，并继续向亚洲大陆渗透。印度向北的侵位引起了亚洲大陆的构造变形。本次调查的目的是从古地磁的角度探测亚洲大陆东部的构造剥蚀作用。我们选择了中国地区的云南和四川作为印度大陆碰撞变形的可能区域。将中国的内蒙古和俄罗斯的锡霍特阿里木地区视为未发生变形的地区，对这四个地区进行了古地磁研究。我们重点研究了侏罗纪焊接凝灰岩、侏罗纪红砂岩、上白垩世红砂岩和古新世褶皱凝灰岩，因为晚中生代地层保存了印度碰撞时晚于52 Ma的变形证据。从这四个地区收集了750多个样本。在一个地点，用磁罗盘定位的三到十个手部样本被分布在长达15米的距离内。地点的位置是由便携式导航仪器确定的。目前采样点的偏差值是根据1994年国际地磁参考场的计算得出的。在实验室里，从样品中制备了直径25 mm，长23 mm的单个样品。用2G低温磁强计测量了自然剩余磁化强度。每个样品中的一个样品进行高达690*710*的逆热退磁。现在对测量数据进行分析。

Collision of India and Asia is one of the most prominent tectonic events in Cenozoic time. The Indian continent collided to Asia at about 52 Ma and continued to penetrate into the Asian continent. The northward penetration of the India gave rise to tectonic deformation in the Asian continent.The present program of investigation aims to detect tectonic defonriation on eastern part of Asian continent from paleomagnetic view points. We chose the Yunnan and Sichuan in China areas as possible areas which was subjected to deformation due to collision of Indian continent. Inner Mongolia of China and Sikhote Alim area in Russia are regarded as areas without any deformation.We carried out our paleomagnetic study in these four areas. We focused the Jurassic welded tuffs, the Jurassic red sandstones, the Upper Cretaceous red sandstones and the Paleocene wefded tuffs, because late Mesozoic formation preserves evidence of deformation later than 52 Ma when India collided. More than 750 samples were collected from these four areas. Three to ten hand samples, oriented with a magnetic compass, were distributed over a distance ranging up to 15m in a site. Localities of sites were determined by a portable navigational instrument. The present declination value at the sampling point was estimated from the calculation using the International Geomagnetic Reference Field of 1994.In the laboratory, individual specimens, 25mm in diameter and 23mm long, were prepared from samples. Natural remanent magnetizations were measured with a 2G cryogenic magnetometer. One specimen from each sample was subjected to stcpwise thermal demagnetization up to 690* 710*. Measurement data are now analyzed.