The Origin And Geochronology Of Zircons From Kuhai Group In Southern East Kunlun Terrane

The East Kunlun Orogenic Belt (EKOB) is a composite orogenic belt, which has undergone multi-stage tectonic evolution, and locates in the western of Central Orogenic Belt. A lot of researches have indicated that the EKOB mainly experienced the ocean-land tectonic cycles of Proto-Tethys Ocean and Paleo-Tethys Ocean. The East Kunlun is divided into the southern East Kunlun Terrane (SEKT) and the northern East Kunlun Terrane (NEKT) by the Central East Kunlun Fault, and the metamorphic basement are Kuhai group and Jinshuikou group, respectively. The zircon U-Pb chronology and statistics are applied to investigate the nature of the Kuhai group and its relationship wih the Jinshuikou group in this article.K This study presents 107 in-situ zircon U-Pb analyses (LA-ICP-MS) of three paragneisses from the Kuhai Group in the SEKT. Our results suggest that the earliest sedimentary age of Kuhai Group is Late Mesoproterozoic-Neoproterozoic (Pt2-3) (768?1169Ma); The paragneisses of Kuhai group underwent the metamorphic event in Silurian (425Ma) and they have different sedimentary ages and metamorphic degrees in different regions. Hf isotopic data of paragneiss from the Kuhai Group shows that it has the erosion source areas of 1900?2100 Ma and 2600 Ma, and the SEKT has good affinity to the the Yangtze plate.2?Comparing the zircon U-Pb dating of the Kuhai group in SEKT with that of the Jinshuikou group in NEKT, the earliest sedimentary ages of them are Late Mesoproterozoic-Neoproterozoic; The ages of their source materials all have the records of 1550?1750Ma?1900?2100Ma and 2350?2600Ma, suggesting that they might have had similar source; Peak age of the youngest member in the age spectrum with metamorphism origin is 400?450 Ma, indicating that they all underwent the metamorphism in Silurian. It can therefore be inferred that the oldest metamorphosed basement in SEKT and NEKT have the similar evolution history during pre-Silurian and the Jinshuikou group and Kuhai group are the same group with diferent names. Even if the paleo-Ocean basin between the SEKT and the NEKT existed in early Paleozoic, the ocean basin must have been a small one.3?According to the granite Nd,Hf isotopic analysis of NEKT and SEKT in Late Devonian and Early Ordovian, the source of them are partial melting of Kuhai group in SEKT and Jinshuikou group in NEKT. The characteristic of ancient crust can be reflected by the Nd,Hf isotopic analysis of granites. Compared with the Nd,Hf isotopic data of the granite from the SEKT and the NEKT, they have great similarity on the value of??Nd(t),TDM1(Nd),?Hf(t),TDM2(Hf), which means that they might be the same terrane before Early Palaeozoic. Hf isotopic data can be regarded as a further evidence that the SEKT has the record of 950?1250Ma, and the SEKT and the NEKT all have the same erosion source area of 1550?1750 Ma.