Precambrian Tectonic Evolution And Crust Growth Of Southern Tarim Terrane, Xinjiang, NW China

The Tarim Craton, one of the main Precambrian Cratons in China, where the inside Precambrian basement rocks outcrop along its margins. The Paleoproterozoic intrusive complex, Meso-to Neoproterozoic volcanic-sedimentary sequences and the latest Mesoproterozoic igneous rocks play an important role in Precambrian tectonic evolution and continental crust growth of the southwestern Tarim terrane. In this study, we investigated geochronology, geochemistry of the Precambrian igneous rocks and sedimentary sequences, together with the previous works, also in aiming to evaluate Precambrian tectonic evolution and the growth of the continental crust of the southwestern Tarim terrane.Heluositan Complex emplaced at 2.4-2.3 Ga, can roughly subdivide into A-and S-type granites. Furthermore, ca.1.9 Ga high-grade metamorphism was recorded in the intrusive complex. Geochemical data imply that the A-and S-type granites were likely derived from partial melting of Archean mafic rocks while felsic and/or metagreywackes recycled from Neoarchean TTG materials, respectively. The Azibailedi pluton emplaced at ca.1.4 Ga and mainly composed of biotite monzogranite. Both major and trace elements features defined its A-type affinities. Integrating geological, geochemical and Nd-Hf-O isotope data, we suggest that the Azibailedi A-type granites were derived from pre-existing early Paleoproterozoic mafic lower crust involving with variable amount of Paleoproterozoic juvenile crust.Geochronological data indicate the greenschist-facies metamorphic and tightly folded Sailajiazitage Group (SG) volcanic-sedimentary sequence deposited during 860-830 Ma, the Ailiankate Group (AG) clastic rocks, of low greenschist facies metamorphism and intensive deformation, deposited during 820-800 Ma while the unmetamorphosed and undeformed late Neoproterozoic carbonate-calstic-tillite sequences, including the Silu Group and the Qiakemakelieke Group (QG), deposited after 760 Ma. Two phases of glaciation from the QG in SW Tarim could be equivalent to the Beiyixi glaciation and the Altungol-Tereeken glaciation in north Tarim, respectively.Geochronology, geochemistry, spectrum of detrital zircon ages, rock association and features of transformation in these rocks suggests that Heluositan Complex may represent a rifting event in early Paleoproterozoic in southwestern Tarim terrane, the following ca.1.9 Ga high-grade metamorphism was considered to be related to the assembly of the Columbia supercontinent. It suggests that the southwestern Tarim terrane has been a fragment of the Paleo-to Mesoproterozoic supercontinent and was likely close to Laurentia, Siberia and Baltica, then the supercontinent broken up at ca.1.4 Ga. During 1.0-0.9 Ga, the late-Mesoproterozoic northward subduction along the southern margin of STT induced the formation of the Kalakashi Group (KG) volcanic arc and then STT and Australia assemblaged together. The southward subduction along the northern margin of the Southern Tarim Terrane led to the formation of the backarc basin during 860 Ma to 830 Ma. As the closure of the backarc basin, the foreland basin was formed at 820-800 Ma. According to the ages of the Aksu blueschist, the Neoproterozoic assemblage of the Tarim basement could have lasted till to 760 Ma.U-Pb geochronology and Hf isotopic analyses of zircons from the Precambrian plutons and sedimentary in SW Tarim show crustal growth episodes during 3.8-3.6 Ga、2.4-2.2 Ga and 1.0-0.7 Ga, distinct from the other Precambrian terranes of the Tarim Craton. A comprehensive synthesis of the records of assembly and breakup of Columbia supercontinent from different Precambrian terranes in the Tarim Craton reveals their individual significance. The temporal distinction in tectonothermal events and the marked difference in the continental crust growth processes suggest that the early Precambrian basement of the Tarim Craton was possibly composed of discrete terranes which were fragmented from different ancient cratonic nuclei and these terranes did not unify until Neoproterozoic during the assemblage of the Rodinia supper continent.