南设得兰群岛早第三纪火山岩古地磁学及其构造意义

PALAEOMAGNETISM OF EARLY TERTIARY VOLCANIC ROCKS FROM SOUTH SHETLAND ISLANDS AND ITS TECTONIC SIGNIFICANCE

从南极半岛南设得兰群岛地区的４３个采样点采集了３３４个定向火山岩样品进行古地磁研究。火山岩层的地质时代为早第三纪。火山岩样品的古地磁学研究表明，早第三纪时，南设得兰群岛及南极半岛已经处于或接近于现今的地理位置。早第三世以来，本区未有明显的相对运动。古地磁资料还表明，古新世南极半岛的北缘出现了小规模的逆时针转动（约１５°）。这与南美板块与南极板块的相对移动有关。随着南大西洋的扩张，南美板块向西漂移，南极半岛北部受此西向漂移的带动。

A total of 334 oriented rock samples collected from 43 sites in Fildes Peninsula,Keller Peninsula and Barton Peninsula of King George Island, Greewich Island and Lunar Island have been studied for palaeomagnetism. The geological age of whole samples are assigned to be Palaeocene and Eocene, including 4 stratigraphic units. They are Block Hill Fr.,Fossil Hill Fr., Agate beach Fr. and Jaskper Hill Fr.. The palaeomagnetic results indicate that the South Shetland Islands and Antarctic Peninsula has already been in situation as they now are, or geographically appreach to the present location during the early Tertiary period. No evidences show the present area has relative movements since that time. Furthermore, the palaeomagnetic data of ours also suggest that anticlockwise rotation has took place in small scale with the north margin of Antarcitc Peninsula during the Palaeocene Eocene period. The rotational direction is about 15 degrees, which may related with the events of South America plate moving away from the Antarctic plate and the opening of Drake Passage. The separating of Antarcitc Peninsula from South America plate may result from the spreading of Drake Passage.