Geodynamic Modeling On The Formation Mechanism Of Linxi Basin: New Constraints On The Closure Time Of The Paleo-Asian Ocean

The Linxi Basin is situated 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. The Linxi Basin has the best preserved Permian sediments and its formation mechanism is much debated. Two controversial Permian tectonic backgrounds are proposed for this basin, i.e., oceanic-continental convergence (hence an arc basin related to subduction) versus post-orogenic extension (hence a crustal/lithospheric subsidence basin). Oceanic-continental convergence indicates subduction of oceanic lithosphere beneath the continental boundary of the North China Craton, whereas post-orogenic extension implies a thickened continental lithosphere experienced a drip-like gravitational instability. To address this controversy, we conduct subduction and drip (lithospheric instability) numerical experiments to calculate model predictions of surface topography for the Linxi Basin across the Solonker suture. Comparisons between the model predictions and the Permian sedimentary records in the Linxi Basin are made to determine which model can better explain the sedimentation. The persistent accumulation of Permian sediments indicates continuous crustal subsidence, which fits better the predicted subsidence from our drip model. By contrast, our modelled subduction-induced surface evolution in the 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 to explain the Linxi Basin development during the Permian. In addition, the spatial and temporal distribution of magmatic activities is consistent with drip process. Our preferred Permian basin formation induced by drip model favors an early closure of the Paleo-Asian Ocean before the Permian.