Geodynamic Modeling on the Formation Mechanism of Linxi Basin: New Constraints on the Closure Time of the Paleo-Asian Ocean

Abstract:

The Paleo-Asian Ocean in Late Paleozoic era was developed and inherited by the Paleo-Tethys Ocean. Some studies suggested that Early Paleozoic Proto-Tethys Ocean and Paleo-Asian Ocean were one ocean. To understand the relationship between Paleo-Tethys Ocean and Paleo-Asian Ocean, it is essential to figure out the evolution history of Paleo-Asian Ocean. Linxi Basin situates at the eastern portion of the Tianshan-Solonker suture where the Paleo-Asian Ocean closed and represents the key region to understand the tectonic evolution of the Solonker suture. Linxi Basin is fulfilled with Permian sediments and its formation mechanism is in a big debate. Two controversial Permian tectonic backgrounds are proposed for this basin, i.e., oceanic-continental convergence versus post-orogenic extension. An oceanic-continental convergence indicates subducting of oceanic lithosphere beneath the continental boundary of the North China Craton, whereas a post-orogenic extension reflects a converged continental lithosphere has gone through thickening followed by a drip-like gravitational flow. To address this controversy, we conduct two geodynamic models, subduction and drip, and calculate two representative surface undulations for Linxi Basin along the Solonker suture. These two topography trends are compared with the Permian sedimentary records in Linxi Basin to determine which model can better explain the sedimentation. The Permian sedimentary records show the persistent accumulation indicating continuous crust subsidence, which fits better to the prediction of monotonic subsidence topography from our drip model. By contrast, our modelled subduction-induced surface undulation in Linxi Basin generally shows a switch from subsidence to uplift. The better fitting of the drip tectonics indicates that the post-orogenic extension rather than subduction tectonic setting would be more suitable for Linxi Basin during the Permian. In addition, the dominance of Permian symmetrical alkaline-magmatism across Linxi Basin is consistent with the drip-induced symmetrical upwellings of asthenosphere. Our preferred Permian basin formation induced by drip model favors an early closure of the Paleo-Asian Ocean before Permian.