The effects of the thermal state of overriding continental plate on subduction dynamics: Two-dimensional thermal-mechani
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e effects of the thermal state of overriding continental plate on subduction dynamics: Two-dimensional thermal-mechanical modeling Jiaxuan TANG 1
1,2,3
, Lin CHEN
1,2*
, Qingren MENG
1,2,3
& Guoli WU
1,2
State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China; 2 Innovation Academy for Earth Science, Chinese Academy of Sciences, Beijing 100029, China; 3 College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing 100049, China Received December 3, 2019; revised April 14, 2020; accepted April 29, 2020; published online June 12, 2020
Abstract The dynamic process of ocean-continent subduction depends on not only the properties of the subducting oceanic plate, but also the characteristics and state of the overriding continental plate. Numerical models conducted to date have mostly focused on the oceanic lithosphere in this regard; research on the properties of overriding continental lithosphere remains relatively limited, especially the influence of its thermal state on subduction dynamics. Here we explored the performance of continental lithosphere with different thermal states during the subduction process using two-dimensional thermal-mechanical modeling and systematically investigated the effects of the thermal state of overriding continental plate, the age of subducting oceanic plate, and relative convergence rate on subduction dynamics. Modeling results show that: (1) When the geothermal −1 gradient of continental crust is low (between 10 and 15 °C km ), the oceanic plate first subducts at a low angle. As subduction continues, the slab dip gradually increases and the slab begins to retreat rapidly driven by its negative buoyancy, opening an ocean basin ranging from 600 to 1100 km in width. This leads to the decoupling between the overriding continental plate and oceanic plate. As the trench retreat continues, the horizontal deviatoric stress inside the overriding continental crust alternates between being positive and negative in a local area. Thinning of the overriding lithosphere mainly occurs at the region adjacent to the subduction zone, where the surface experiences significant subsidence. (2) When the geothermal gradient of continental crust −1 is higher (greater than 15 °C km ), oceanic plate retreat causes the overriding continental plate to be strongly stretched. In this case, the trench retreat distance decreases and the width of the ocean basin also reduces by between 100 and 1000 km. The horizontal deviatoric stress inside the whole overriding continental crust first manifests as compression and then changes into extension, which causes the surface to first uplift and then slowly subside. (3) Increasing the age of oceanic lithosphere accelerates trench retreat and promotes overriding plate thinning. (4) An advancing overriding continental plate slows down −1 trench retreat. In cases where the geothermal gradient of continental crust is greater than 17.5 °C km , the hot continental crust
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