北祁连山古生代和中生代岩石古地磁的初步研究

THE PRELIMINARY PALEOMAGNETIC RESULTS OF THEUPPER PALEOZOIC AND THE MESOZOIC ROCKS OFTHE NORTH QILIAN MTS. TERRANE

本文通过对北祁连山近90个上古生代和中生代岩石样品的热退磁、交变退磁和剩余磁性的初步测定,认为石炭纪、二叠纪和侏罗纪岩石的剩余磁化强度已被现代地磁重新磁化;而上泥盆纪和三叠纪的剩余磁性可能是原生的,说明这一时期北祁连山地体有较大的北向移动,但三叠纪时尚未达到目前的地理位置。

If has been suggested that the north Qilian Mts. terrane was Accreted to the Sino-Korea craton some time around Upper Paleozoic from geological evidence. However, where was the north Qilian Mts. terrane before it accreted to the craton ? What were the paleolatitudes of the north Qilian Mts. terrane during the upper paleozoic and the Mesozoic? What was the exact accretion time of the north Qilian Mts. terrane. to the craton ? These questions have not yet been answered and are expected to be answered by paleomagnetic study. We conducted a pilot paleomagnetic study of the upper Paleozoic and the Mesozoic rocks in Yanniou Valley of Qilian county in Qinghai Province in 1982. No previous paleomagnetic data is available in this area before.The paleomagnetic results from this study shows that the remnant magnetizations of the Carboniferous.the Permian and the Jurassic have been overprinted by the present earth magnetic field. However, the remnant magnetizations of the upper Devonian and the Triassic are possibly original. The paleolatitudes of the site in the upper Devonina and the Triassic are 7° North (or South) and 25° North. These paleomagnetic results suggest (1) a large northward motion of the north Qilian Mts. terrane occured between the upper Devonian and the Triassic; (2) the north Qilian Mts. terrane probably had not yet reached to its present position in the Triassic.