LATE PALEOZOIC VERTICAL GROWTH OF CONTINENTAL CRUST AROUND THE JUNGGAR BASIN, XINJIANG, CHINA (PART I): TIMING OF POST-COLLISIONAL PLUTONISM

Abstract

As an important part of the Paleozoic orogonic belt in northern Xinjiang, the Junggar is characterized by intense and extensive development of Late Paleozoic granitoid plutons together with minor mafic plutons, and it is one of the representative regions for the Phanerozoic continental crustal growth in the Central Asian Orogenic Belt. On the basis of new SHRIMP zircon U-Pb dating on the plutons in the East and West Junggar, in association with the zircon U-Pb ages from the literature, an attempt is made in this study to establish the timing of the late Paleozoic post-collisional plutonism in the region. It is concluded that the late Paleozoic post-collisional plutonism occurred from middle-late Visean of Carboniferous to the end of Early Permian in accordance to the Geological Time Scale (Gradstein et al., 2004). Temporally, the plutons in the East and West Junggar formed in a period of 65Ma, from 330 to 265Ma and from 340 to 275Ma, respectively. However, the plutonism in the East Junggar showed two peaks of 330 to 310Ma and 305 to 280Ma, whereas most plutons in the West Junggar were emplaced from 310 to 295Ma. Spatially, the plutonism occurred in all tectonic units separated by ophiolite belts and even some granitoid plutons intruded in ophiolites. Furthermore, the post-collisional plutons can be found not only in the Junggar, but also in the Altai orogenic belt to the north and in the Tianshan orogenic belt to the south.