龙首山古裂谷带及河西走廊的大地构造

TECTONICS OF THE LONGSHOUSHAN ANCIENT RIFT AND HEXI CORRIDOR

本文基于沉积建造及岩浆岩的研究,确定龙首山是阿拉善地块南缘的古裂谷带。裂谷型建造以中-晚元古带的墩子沟群和韩母山群为代表;岩浆岩组合则是富含Bi—Cu矿产的超镁铁岩及镁铁岩。河西走廊可分为东西两段;东段是阿拉善南缘的造山带,由永昌—武威冒地斜和冷龙岭—古浪优地斜2个单元构成;西段是祁连造山带北祁连优地斜的一部分。二者分别属于2个古板块,其间的缝合线位于高台至民乐一带。笔者在该区(包括祁连山)共识别出7个构造—地层地体,其中1个具外来属性,其余均为增生地体。

On the basis of recent investigations in Gansu Province and tectono-Stratigraphical analysis the authors consider that there is a Proterozoic rift of WNW trend along the Longshoushan Mountains on the southern margin of the Alxa massif. The Dunzigou Group and Hanmushan Group of closed lagoon facies or neritic facies were deposited in the rift during the Middle-Late Proterozoic. Along the rift a series of ultramafic-mafic intrusions conlainning Ni-Cu ore deposits are scattered in the area of Jinchuang. The whole Hexi Corridor of Gansu Province may be divided into two halves. The eastern half is an orogenic zone along the southern continental margin of the Alxa massif and consists of the Yongchang-Wuwei miogeocline and the Lenglongling-Gulang eugeocline from north to south. In the Early Paleozoic, it belonged to the North China-Korea Paleoplate. The western half is a part of the northern Qilian eugeocline and belonged to the Qaidam-Qilian paleoplate in the Early Paleozoic. The suture line between the two halves lies from Gaotai to Minle. Through the authors' repeated investigations, the tectonic evolution of the Qilian Mts, and Hexi Corridor between the two paleoplates has been established. At least seven tectonostratigraphic terranes can be recongnized in this region. Among them, the northermost one occurs on the southwestern margin of the North China-Korea Paleoplate, and the other six terranes occur on the northern-continental margin of the Qaidam massif.