The Study Of Neoproterozoic Tectonic-magmatic Events In The Northern Margin Of The Yangtze Continental

The northern margin of the Yangtze continent is one of the important geological units in China, which has undertaken a long and complicated geological evolution.Previous researches on neoproterozoic igneous rocks are mainly focused in the Xixiang-Chenggu area in Hanzhong, and the study about the igneous rocks located in Daba Mountains of Wangchang county in Sichuan Province-Beiba area of Nanzheng county in Shanxi Province is a little deficient. Therefore, more attention on this region should be paid. By general study of basic rocks in Mengzi of Wangchang county (e.g. gabbronorite, amphibole gabbro) and intermediate-acidic magmatic rocks in Guangwu mountain in Nanjiang county (e.g. moyite, quartz diorite and granodiorite) in neoproterozoic era, the author has revealed that the temporal and spatial evolution framework of magmatic activities and its tectonic setting in Beiba area. And thus, provide more constraints on the evolution process in the northern margin of the Yangtze continent. The paper comes to the following conclusions:1. The formation age of moyite, quartz diorite, gabbronorite and amphibole gabbro is 745±11 Ma,764±38Ma,766±34 Ma,774±37 Ma, respectively. The formation age of magmatic rock is in agreement within the error limit, and they all formed in final phase of neoproterozoic. The result is similar with supercontinent breakup events discovered in Australia and other countries.2. According to petrological and geochemical characteristics, the moyite is A-type granite, the quartz diorite is adakite. The major elements, trace elements and rare earth elements of two the kinds are far different, so this reveals that the source regions of the rocks are different.3. The Hf isotope analytical technique is applied in the paper, and suggests that:A-type granite is crust source granite with contamination of mantle materials. The adakite is created by the melting of a new formed crust, with a mixing of the two source regions'magma in different degree.4. The study on the source region, genesis and the dynamic mechanism of the two kinds of rocks in the research area reveals that the plutonic rocks may be the result of the mantle plume activities. The intrusive rocks developed in Mengzi-Beiba area and Hannan Complex should be the product of the same dynamic background, constituting the huge intrusive complex together at the northern part of Yangtze block.