Early Neoproterozoic sedimentary basin evolution in the Micangshan area,northwestern Yangtze Block:Constraints from the depositional sequence and zircon U-Pb chronology
Early Neoproterozoic sedimentary basin evolution in the Micangshan area,northwestern Yangtze Block:Constraints from the depositional sequence and zircon U-Pb chronology
The Huodiya Group and the Zhengyuan-Yingcui volcanic-sedimentary rocks(formerly known as the Houhe Group)from the Micangshan area of the northwestern Yangtze Block provide significant records of the mid-Neoproterozoic tectonic evolution related to the assembly of the Rodinia supercontinent.However,their evolutionary history and tectonic characteristics remain uncertain.This paper presents a systematic analysis of sedimentary sequences within typical sections of the Huodiya Group,complemented by detrital zircon U-Pb geochronology of the Zhengyuan-Yingcui volcanic-sedimentary rocks.This integrated approach aims to elucidate their tectonic-sedimentary evolution processes and establish a precise timeframe for these events.Our comprehensive investigations reveal that the Huodiya Group comprises a complex assemblage of sedimentary rocks,characterized by interbedded clastic,carbonatite,and volcanic rocks.The evolution history of the basin can be divided into three stages:(1)subduction of oceanic crust and the formation of an arc-basin system;(2)back-arc extension and the construction of a carbonate ramp/platform;(3)flexural subsidence in the basin and rapid infilling.Detrital zircon analysis indicates that the Zhengyuan-Yingcui volcanic-sedimentary rocks were deposited in the early Neoproterozoic and sourced from both the northwestern and east/southeastern sides of the basin.This finding,coupled with the contemporaneous yet spatially distinct nature of the Zhengyuan-Yingcui volcanic-sedimentary rocks and the Huodiya Group,suggests that they developed in different parts of the basin,which could be the response of the assemblage of the Rodinia supercontinent.
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