Abstract:

The volcanic rocks of the Shuangxiwu Group of Mesoproterozoic in Zhangcun, Zhejiang Province are the important part of the Jiangnan orogen. The Beiwu Group in the bottom mainly consists of intermediate-basic to intermediate-acid tuff, the Yanshan Group in the middle is made of sedimentary tuff, and the Zhangcun Group in the top consists mainly of the intermediate-acid and acid ignimbrites, which together compose a complete evolvement sequences from intermediate-basic to acid volcanic rocks. It is proved that they were formed in an island-arc environment by the evidence of petrochemistry and geochemistry of trace and rare elements, and the arc shows growing and maturing gradually from bottom to top. According to the analysis and survey results, it is concluded that the volcanic rock series of the Shuangxiwu Group maybe undergo the 3 processes. The first was Beiwu period of volcanic arc continental eruption, and the second was Yanshan period of the intermittent intra-arc basin sedimentation, and the third was Zhangcun period of continental volcanic arc extrusion and explosion. After the continuing volcanic activities, the Longmenshan island arc was undergone the compaction and folding orogeny, related to the Rodinia supercontinental assemblage orogeny.

Key words: volcanic rock of Shuangxiwu Group, island arc setting, geochemistry, orogeny belt, Rodinia supercontinent assemblage, Mesoproterozoic, Zhangcun of Zhejiang Province