中国西藏南部珠穆朗玛峰地区构造特征

中华人民共和国成立以来,在中国共产党的领导下,曾几次派遣科学考察队到西藏地区进行考察。在无产阶级文化大革命期间,中国科学院组织了一支科学考察队,于1966-1968年在东起亚东西到吉隆我国喜马拉雅地区大约50,000平方公里的范围内进行了考察。在地质方面,根据地层发育、变质程度和构造变形的不同考察地区可以分成南、北两条东西向构造带。南带的地层层序非常完全,而北带则只有石炭-二迭纪和中生代地层出露。在南带发现了奥陶纪、志留纪和泥盆纪化石,对中生代和新生代沉积地层进行了较详细的划分,从而初步建立了珠穆朗玛峰(以下简称珠峰)地区比较完整的地层系统。

TECTONIC FEATURES OF THE MOUNT JOLMO LUNGMA REGION IN SOUTHERN TIBET, CHINA

This paper presents a brief account of the regional geology of the Jolmo Lungma region which lies south of the Yalutsangpo (Tsangpo) Eiver and between longitudes 85°30′E and 89°30′E.In view of the regional stratigraphy and tectonic history of the region, two belts could be recognized. Rocks of the southern belt lie upon a crystalline and metamor-phic basement, being a thick sequence of essentially unmetarnorphosed sediments, mainly marine, ranging in age from early Ordovician to early Tertiary, with many horizons rich in fossils. Rocks are generally of shallow and stable water origin and seem to have nothing to do with geosynclines.So far as we know, the oldest fossiliferous beds in the northern belt belong to the Permo-Carboniferous. From the Permian on, the deposits differ from those of the southern belt and the difference becomes more distinguished during the Mesozoic. Here the rock types are highly varied, including flysch, graywackes, basic volcanics and radiolarian cherts. This thick series of geosynclinal origin is intensely folded and often thoroughly metamorphosed.From gravimetric and seismological data, it is estimated that the crustal thickness of the main Himalayas, including the Mount Jolmo Lungma and other lofty peaks, amounts to about 55 km while along the Yalutsangpo Valley a maximum thickness over 70 km is deduced.Near and roughly parallel to the above mentioned valley, a long, narrow, intermediate belt of ultramafic rocks occurs. This is the eastern continuation of the so-called "Indus Suture" and probably marks the line of collision, as postulated by some authors, where the northward drifting Indian Plate was thrusted under the Eurasian Plate. Northward, the Tahglha, the Kunlun and the Altyn Tagh ranges might be also outcomes of successive stages of subduction. In each case, a smaller southern plate impinged against and plunged beneath the ancient Eurasian Plate.