The Preliminary Discussion On The Era Of Neoproterozoic Glaciations In Quruqtagh And The Precambrian Crustal Evolution Of The Tarim Craton

The Quruqtagh area is located in the northeastern of the Tarim Craton. The Precambrain outcrops in Quruqtagh can be subdivided into a pre-Nanhua metamorphic basement and a Nanhua-Sinian sedimentary cover. The Nanhua-Sinian Quruqtagh Group has four tillite units in the Bayisi, Altungol, Tereeken and Hankalchough Formations. To constrain the age and duration of the Altungol tillite and to show a new evidence for the Chronostratigraphy profile of Neoproterozoic glaciations in Quruqtagh, we dated the tillite and volcanic units in the Altungol Formation using the LA-ICP-MS (Laser ablation-inductively coupled plasma-mass spectrometer) zircon U-Pb method. Our U-Pb dating results suggest a maximum deposition age of681±16Ma for the Altungol tillite and a weighted-mean age of642±8Ma for the rhyolite unit in the upper part of the Altungol Formation. These data suggest that the Altungol tillite was deposited between681±16Ma and642±＋8Ma. The Altungol glaciation may be consistent with the720Ma～660Ma Sturtian glaciation.On the other hand, in order to reveal the magmatic activity and crustal evolution of the Tarim Craton, we performed detrital zircon U-Pb dating and in situ Hf isotopic analysis of the Altungol tillite. A total of163detrital zircon analyses yield three age populations:late Neoarchean to early Paleoproterozoic group (2800Ma～2350Ma, weak peaks at2426Ma,2518Ma and2587Ma), indicates the presence of late Neoarchean to early Paleoproterozoic magmatism in the Tarim Craton, and probably correlates with the similar ages reported for Neoarchean global continental growth. Paleoproterozoic group (2050Ma-1800Ma, peaks at1845Ma and1960Ma), probably is response to the amalgamation of the Columbia supercontinent, and may also correlates with the high-grade metamorphism and anatexis events in the Tarim Craton. Neoproterozoic group (900Ma～700Ma, peak at850Ma), probably implies the time of the breakup of the Rodinia supercontinent. The age populations of Mesoproterozoic (1.6Ga～1.4Ga) and Grenville (1.3Ga～1.0Ga) have not been found in this study, revealing the fact that the breakup of Columbia and the Grenville-age Orogenic activity have little influence along the northern margin of the Tarim Craton. The detrital zircon Hf model age (TDMC) data suggest three major stages of crustal evolution at3600Ma～3550Ma,3400Ma～3050Ma and3000Ma～2500Ma in the Tarim Craton. Only a few Neoarchean detrital zircons exhibit positive εHf(t) values, suggesting juvenile crust input took place during the Neoarchean times. All Neoproterozoic, Paleoproterozoic and most of Neoarchean detrital zircons show negative εHf(t) values, indicating they may come from the reworked older crustal materials.