Edge-driven convection and thinning of craton lithosphere:Two-dimensional thermal-mechanical modeling  

作　　者：Danhong LIU Lin CHEN 

机构地区：[1]State Key Laboratory of Lithospheric Evolution,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China [2]College of Earth and Planetary Sciences,University of Chinese Academy of Sciences,Beijing 100049,China

出　　处：《Science China Earth Sciences》2019年第12期2106-2120,共15页中国科学（地球科学英文版）

基　　金：supported by the National Key Research and Development of China (Grant No. 2016YFC0600406);the Strategic Priority Research Program (B) of the Chinese Academy of Sciences (Grant No. XDB18000000)

摘　　要：There are usually abrupt changes in lithospheric thickness at the boundaries between ancient cratons and adjacent young mobile belts.Lateral variations in temperature and density between the two can trigger small-scale mantle convection(edge-driven convection,EDC).Here,we use two-dimensional thermal-mechanical simulations to explore the EDC caused by the lithospheric step between a craton and a mobile belt,and its role in the thinning of the craton lithosphere.The results show that the impact of EDC on a craton depends on the properties of the craton lithosphere and on their contrasts with the adjacent mobile belt,given the same initial condition.When the craton lithospheric density is relatively large,a high-strength craton has strong ability to resist EDC,and craton lithospheric thinning is limited to the edge.In contrast,the ability of a low-strength craton to resist EDC is weak,and the craton lithosphere is gradually eroded by the downward flow,eventually leading to large-scale thinning of the cratonic lithosphere.When the craton lithospheric density is relatively small,regardless of the strength of the cratonic lithosphere,the craton can well withstand the impacts of EDC.In this case,upwelling flow drives cratonic lithosphere materials to the base of the mobile belt,and lithospheric thinning only occurs at the edge of the craton lithosphere.The Archean North China Craton(NCC)was surrounded by Phanerozoic mobile belts,and its lithospheric thinning first occurred on the northern and eastern margins,a process that lasted for a long time.We suggest that EDC has played an important role in lithospheric thinning of the NCC,in particular the initiation of lithospheric thinning,but we cannot rule out the additional contributions from other mechanisms.There are usually abrupt changes in lithospheric thickness at the boundaries between ancient cratons and adjacent young mobile belts.Lateral variations in temperature and density between the two can trigger small-scale mantle convection(edge-driven convection,EDC).Here,we use two-dimensional thermal-mechanical simulations to explore the EDC caused by the lithospheric step between a craton and a mobile belt,and its role in the thinning of the craton lithosphere.The results show that the impact of EDC on a craton depends on the properties of the craton lithosphere and on their contrasts with the adjacent mobile belt,given the same initial condition.When the craton lithospheric density is relatively large,a high-strength craton has strong ability to resist EDC,and craton lithospheric thinning is limited to the edge.In contrast,the ability of a low-strength craton to resist EDC is weak,and the craton lithosphere is gradually eroded by the downward flow,eventually leading to large-scale thinning of the cratonic lithosphere.When the craton lithospheric density is relatively small,regardless of the strength of the cratonic lithosphere,the craton can well withstand the impacts of EDC.In this case,upwelling flow drives cratonic lithosphere materials to the base of the mobile belt,and lithospheric thinning only occurs at the edge of the craton lithosphere.The Archean North China Craton(NCC) was surrounded by Phanerozoic mobile belts,and its lithospheric thinning first occurred on the northern and eastern margins,a process that lasted for a long time.We suggest that EDC has played an important role in lithospheric thinning of the NCC,in particular the initiation of lithospheric thinning,but we cannot rule out the additional contributions from other mechanisms.

关 键 词：Edge-driven CONVECTION LITHOSPHERIC steps LITHOSPHERIC thinning Numerical MODELING CRATON 

分 类 号：P54[天文地球—构造地质学]