Study on Paleomagnetism and Plate Tectonics of Indian Plate

通过对印度半岛东部沿着孟加拉湾沿岸古地磁的研究，阐明印度次大陆在冈瓦纳超大陆中的古地理位置，特别是与南极洲的相对位置，并追踪其位置随时间的变化。古地磁和地球物理岩石样品是1991年从Godavari和MahanadiGrabens地区的各种岩层中获得的。样品的初步古地磁测量结果表明，太古代、元古代等古老时代的岩石大多具有非常复杂的多次反射成分。因此，1992年和1993年的古地磁采样主要集中在古生界和中生代的圈闭玄武岩和冈瓦纳沉积物中。1992年和1993年分别在Rajimahal丘陵、Mahanadi地堑、Godavari地堑和泰米尔纳德邦地区的35个和24个地点采集了岩石样品，虽然古地磁和年龄测定研究仍在进行中，但已取得了一些初步结果。用Ar-Ar法测定了6个年龄。戈达瓦里地堑中21号测点太古代脉岩年龄为574 Ma，34号测点下元古代孔兹岩年龄为520 Ma，0号测点元古代粗玄岩脉岩年龄为510-520 Ma，1号测点元古代片麻状花岗岩年龄为510 Ma，38号测点和59号测点太古代花岗质片麻岩年龄分别为560和680 Ma。在马哈纳迪地堑在38号站太古代花岗质片麻岩、39号站太古代紫苏花岗岩、0号站元古宙粗玄岩脉和80、82、101号站白垩纪Rajmahl圈闭玄武岩流中获得了6个可靠的古地磁恢复方向。

The aim of this survey is to clarify the paleogeographic position of the Indian subcontinent in the Gondwana super-continent, especially relative position to the Antarctica, and to trace its change of the position with time by the paleomagnetic studies of the eastern regions of the Indian Peninsula along the coast of the Bengal Bay.As a reconnaissance survey, the paleomagnetic and geophysical rock samples were obtained from various rock formations in the region of the Godavari and the Mahanadi Grabens in 1991. The preliminary paleomagnetic measurements of the samples show that most of the rocks of old ages such as Archean and Proterozoic have very complex multiple remanent components. So that, the paleomagnetic samplings were concentrated to the rocks of the trap basalt and the Gondwana sediments of the Paleozoic and Mesozoic in 1992 and 1993. Rock samples were collected from 35 sites in 1992 and from 24 sites in 1993 in the regions of Rajimahal hills, the Mahanadi Graben, the Godavari Graben and the Tamil-Nadu.Although the paleomagnetic and age dating studies are still on going, we got some preliminary results. 6 ages are determined by the Ar-Ar method. The ages obtained are 574 Ma for the Archean dike of Site 21, 520 Ma for the lower Proterozoic khondalite of Site 34, 510-520 Ma for the Proterozoic dolerite dike of Site 0, and 510 Ma for the Proterozoic gneissose granite of Site 1 in the Godavari graben, and 560 and 680 Ma for the Archean granitic gneiss of Site 38 and 59, in the Mahanadi Graben. And 6 reliable paleomagnetic remanent directions are obtained from the Archean granitic gneiss of Site 38, the Archean charnokite of Site 39, the Proterozoic dolerite dike of Site 0, and the Cretaceous Rajmahl trap basalt flows of Sites 80, 82 and 101.