The Process Of Rodinia Supercontinent Breakup,constrains From Deposite Records Of Nanhua System In Quruqtagh,Xinjiang

The Nanhua System in Quruqtagh area could record the synchronous volcanic-sedimentary events along the northern margin of the Tarim craton and could be used to answer the question about the tectonic evolution of the northern margin of the Tarim basin during the Nanhua-Sinian.Besides,it could also be used to research the tectonic evolution of the basin as well as could constrain the model of Rodinia supercontinent break up.Firstly,in this study,we analysed the stratigraphy characters and sedimentary environment of Nanhua System by the basal boundary,growth fault,and its petrology,sedimentary structures and grain size analysis etc.The results indicated that the basal boundary and the stratigraphy characters of both sides of Xinger fault has a significant difference.Generally speaking,the bottom of the north side of Xinger fault developed onlap structures,growth fault,fall breccias and terrestrial deposit,whereas,the bottom of the south side of Xinger fault only developed angular unconformity and effusive rock.From the base up,Bayisi Formation could be principally divided into residual slope facies,alluvial pluvial fan facies,fan delta facies,coastal and shallow sea facies,reflect a transgression process and indicated this basin was in an extensional setting.The depositional sequences are same to rift basin,but it has a highly extensional rate.Its depositional environment varies from land to marine quickly and lacks lacustrine facies,combined with previous data we can draw the conclusion that Quruqtagh sited at the margin of Rodinia supercontinent at early Nanhua.Meanwhile,Altungol formation has the sedimentary structures that developed characteristically in storm deposits,includes hummocky cross stratifications and gutter casts.Three types of storm deposits are recognized,indicating that it's a storm-dominated shallow clastic sea depositional environment with a warm and wide paleogeographic environment at low latitudes.It is a robust evidence to that the Tereeken and Altungol diamictites not belongs to the same Ice Age and Quruqtagh sited at the margin of Rodinia supercontinent at early Nanhua.From Zhaobishan Formation up to Tereeken Formation,it is different environments that could be recognized,such as,slope facies,shelf facies and so forth.It is a sedimentary response to rift breakup.At the same time,the characters of the detrital components of Nanhua System sandstones from various sections indicate that sandstones from Bayisi Formation in different sections have different detrital components.In Xishankou section,litharenites are the key components,which the rock fragments are volcanic rocks and sedimentary rocks,obviously,indicate a recycled sedimentary provenance.Whereas,in Yigezitage section,the key components are arkoses and lithic arkoses,the rock fragments are metamorphic rocks while there are lots of mineral inclusions in quartz,that all indicate a metamorphic provenance.Vertical variation of sandstone's detrital components recorded a transform event at the boundary of Bayisi Formation and Zhaobishan Formation(725Ma±),which causes Zhaobihsan,Altungol and Tereeken Formation have a uniform sandstone component.Converted to a typical arkose composition those represent a basement uplift-transitional continental provenance.The detrital component of Nanhua System sandstones and temporal-spatial variation demonstrates a continental rift setting of Nanhua System at Quruqtagh area.Meanwhile,shows a successive provenance evolution from pre-rift sedimentary successions to transitional rift-shoulder to dissected rift-shoulder to transitional continental and craton interior.Consequently,the petrography of sandstones in Quruqtagh area records the early breakup of Quruqtagh-Mangar aulacogen.Additional,the well textural maturity of sandstones and the shallow clastic sea depositional environment and the geochemical characteristics with V-Cr-Ni-Sc negative anomaly,Ti-Hf-Zr-Y positive anomaly all indicate a passive margin tectonic setting.Provenance discrimination diagrams,the transition elements and REE patterns all show that the detrital materials of Altungol Formation were derived from felsic rocks and old recycled sediments which mainly came from southern Tarim craton.The CIA,A-CN-K diagram and Th/U ratio all suggest that the source area underwent a lower-moderate weathering and sediment recycling and K mobility are significant,whose characteristics were in accordance with the passive margin tectonic.Combining previous research results,it can be summarized that the continental rifting began on Nanhua Beiyisi Formation,then Altungol Formation evolved into a passive margin and last until Sinian system Zhamoketi Formation in the Quruqtagh area.Based on the sedimentary records which we analysed above,the evolution process of Nanhua sedimentary basin,i.e.the rift process of northern margin of Rodinia superconitent,could be divided into four stages: initiation stage,rapid chasmic stage,further chasmic stage and initially passive margin stage.