Tarim and North China cratons linked to northern Gondwana through switching accretionary tectonics and collisional orogenesis

Accretionary and collisional orogenesis in the Tarim and North China cratons during Paleozoic time can be correlated with events associated with the assembly and subsequent incipient dispersal of Gondwana. Zircon U-Pb and Hf isotopic data from the northern margins of the two cratons and neighbors have revealed comparable epsilon(Hf)(t)-time patterns. Zircons with magmatic ages of 500-400 Ma display a large spread and decreasing epsilon(Hf)(t) values with time, whereas 400-310 Ma zircons have dominantly positive epsilon(Hf)(t) values and an overall increasing trend. The marked shift of the zircon Hf array at ca. 400 Ma was most likely related to a major tectonic switch from advancing to retreating accretionary orogenesis, corresponding to the development of regional extension. The commencement of subduction at 500 Ma and establishment of an advancing accretionary orogen along the preexisting passive margin was synchronous with early Paleozoic continental collisional events along the southern margins of the two cratons. The temporal agreement of these events, and their accordance with collision and/or accretion events during Gondwana assembly, suggest that the Tarim and North China cratons likely collided with the northern Australia margin of East Gondwana at ca. 500 Ma. They subsequently dispersed from Gondwana in the Early Devonian, coinciding with switching accretionary tectonics along the northern margins of the two cratons that were possibly induced by the slab rollback of the subducting paleo-Asian Ocean plate.