Paleoproterozoic assembly of the North and South Tarim terranes: New insights from deep seismic profiles and Precambrian granite cores

The basement of the Tarim Craton in NW China is divided into northern and southern terranes by the central 1500 km long Central Tarim Terrain (CTT) demarcated by a high aeromagnetic anomaly. However, the nature of the CTT remains enigmatic because of sparse data from basement below the deep basin. In this contribution we report new U-Pb ages from Precambrian granites from boreholes in the CTT to constrain the timing of the assembly of the northern and southern Tarim terranes. Zircon U-Pb ages from four samples of metagranite yielded four U-Pb ages of 1927.3 +/- 7.5 Ma and 1920.4 +/- 9.8 Ma, 1915.3 +/- 5.4 Ma and 1968 +/- 8.4 Ma along the CTT. Geochemically, the granitoids display high K2O and high K2O/Na2O ratios, showing their high-potassium calc-alkaline nature. They are rich in Ba, Sr, LREE and LILE, and depleted in Nb, Ta, Ti and Nd, Zr, Y, with variable negative Eu anomaly. The zircons have a large range of epsilon Hf(t) values (-14.6-16.1). Geochemical and isotopic characteristics suggest that the granites were derived from partial melting of crust and partial of the depleted mantle, and are geodynamically related to subduction in an arc setting. Collectively, our study argues that the assembly of the northern and southern Tarim terranes took place in the late Paleoproterozoic rather than the Neoproterozoic. We suggest that the amalgamation between the southern and northern terranes was completed by similar to 1.91 Ga, which led to extensive contemporaneous magmatism rather than the assembly with the Columbia supercontinent.