评熊耳群和西洋河群形成的构造背景

1850—1400Ma的熊耳群及西洋河群火山岩建造形成的构造背景,是认识华北古板块南缘构造发展的关键。近年的研究产生了两种认识,即孙枢等提出的裂谷观点和胡受奚等提出的山弧观点。本文基于对秦岭山系的长期研究,对两种观点作了较详细的评述,且提出了山弧与裂谷并存的新认识,即熊耳群为山弧火山岩建造,西洋河群为裂谷火山岩建造。裂谷与山弧同时发育,裂谷与山弧垂直,属被动型裂谷。

THE TECTONIC ENVIRONMENT FOR THE FORMATION OF THE XIONGER GROUP AND THE XIYANGHE GROUP

The tectonic setting of the Xionger Group (1 850--1 400 Ma) and xiyangheGroup (1850--1400 Ma) is the key to study the tectonic evolution of the southernmargin of the North China paleo--plate. The knowledge about the Xionger Groupand Siyanghe Group leads to two controversial ideas. One of them is the rift modeladvanced by Sun et al., and the other is the volcanic are model presented by Huet al. In this paper, these two models are reviewed in detail based on a long--termstudy in the Qinlin area. A new model--coexistence of volcanic arc and continentalrift, is proposed to outline the tectonic setting. The Xionger Group is recognizedas an assemblage of arc volcanics, and the Xiyanghe Group is marked by an assem-blage of rift volcanics. The rift is a passive rift which developed contempora-neously with and perpendicularly to the volcanic arc.