Precambrian tectonism,magmatiam,deformation and geochronology of igneous rocks in the Xingdi fault zone,Xinjiang.

Abstract

This paper analyzed the polyphase tectono-magmatism features,the LA-ICP-MS zircon U-Pb ages on the Precambrian igneous rocks and cinematic sense of ductile shear for the Xingdi fault zone.Results suggest that four-phase tectonic evolution took placed in the Xingdi fault zone including two phases of Precambrian tectonism.The first event took place in pre-Nanhua Period that is characterized by strong folding,ductile shearing and magmatism.The second event occurred in the Nanhua-Sinian Period when bimodal magmatism,composite magmatic flow and basic dyke swarm were widely developed,followed by a large-scale glacier and depressions, which is corresponded with the Rodinia supercontinental breakup.The LA-ICP-MS zircon U-Pb dating data reveal that a Meso- Neoarchean and Paleoproterozoic basement is likely buried under the deep part of studied area,dating at 3114±20Ma,2509±42Ma and 1916±36Ma on the captured zircons from gabbro.The dating results on the bimodal igneous rocks show that a peak bimodal magmatism took place during the 820～800Ma(798±7Ma for granitic dyke and 816±15Ma for diabase dyke).Cinematic analysis suggests that two phases of pre-Nanhua ductile deformation occurred in the Xingdi fault zone whereas the deformed age is not clear.The first belongs to a top-to-the north thrusting and the second-phase is a dextral strike-slip deformation along a sub-E-W direction.Since Nanhua Period,regional metamorphism and ductile shearing were very weak,only ductile-brittle deformation was widely developed.