中文摘要：

采用二维有限元数值模拟的方法研究了岩石圈的对流减薄过程,特别是克拉通岩石圈的对流减薄过程.模型的主要参数包括增厚岩石圈的宽度x、增厚倍数γ、以及与岩石圈组分变化导致的黏性和密度变化密切相关的黏性比（ηc）和浮力数（B）或等效密度变化（Δρtc）.数值计算结果显示,地幔对流将逐渐减薄增厚的岩石圈部分,（1）当B=0和ηc=1时,即对一般地幔岩石圈,增厚岩石圈对流减薄的时间可表示为0.0073γ^0.70 x^0.26.将数值结果应用于地球,意味着增厚到300km的岩石圈,如宽度为300km,对流移除增厚部分回到初始平衡厚度120km大约需要225 Ma;如宽度为1500km,移除增厚部分大约需要342 Ma.（2）当B和ηc较小,克拉通岩石圈对流减薄过程与一般加厚岩石圈的对流减薄过程类似,但减薄时间受克拉通组分浮力和黏性比的影响而显著增长,克拉通岩石圈对流减薄的时间可表示为0.0057ηc^0.52Δρtc^-0.21γ^0.78ηc0.36 x^0.04.因而,对300km厚的克拉通岩石圈,如克拉通岩石圈的密度比周围地幔的密度低0.4%（即B=0.1）,宽度1500km,若克拉通岩石圈黏性因组分影响比普通地幔岩石圈大10倍,其被对流减薄到120km大约需要1.18Ga.（3）当B和ηc增大到一定量时（如B≥0.2且ηc〉10）,克拉通岩石圈被移除的过程将发生变化,由于组分浮力的影响,对流主要不是将克拉通岩石圈带到软流圈地幔中,而主要是将较厚的岩石圈物质向两边推送.在此情况下,克拉通岩石圈能长时间（〉3Ga）保持稳定.

英文摘要：

Convective removal on lithospheric root,especially on cratonic lithosphere root is studied via numerical simulations in 2Dmodels.The control parameters in the models include the width,x,stretching factor,γ,viscosity ratio,ηc,and chemical buoyancy number,B,or effective density contrast,Δρtc.Numerical results show that mantle convection thins the thickened lithosphere,and（1）when B=0andηc=1,i.e.,for general lithosphere,the root removal duration is scaled as 0.0073γ^0.70 x^0.26,which means,for a 300 km thickness lithosphere with an initially equilibrium thickness of 120 km,and a root width of 300 km or 1500 km,it takes 225 Ma or 342 Ma to thin by sublithospheric convection to its equilibrium;（2）for small Bandηc,theprocess to thin cratonic lithosphere is similar to that to thin general lithosphere,but the root removal duration is increased significantly,and the root removal duration is scaled as0.0057ηc^0.52Δρtc^-0.21γ^0.78ηc-0.36 x^0.04.With this scaling law,for a 300 km thickness lithosphere with an initially equilibrium thickness of 120 km,and a root width of 1500 km,the root removal duration is1.18 Ga ifηc=10;and（3）for large Bandηc（B≥0.2and ηc〉10）,the process to thin cratonic lithosphere is very different.Because of the influences of chemical buoyancy and viscosity,the cratonic lithosphere is spread to adjacent lithosphere instead of mixing with underneath mantle.In these cases,the root removal duration is very long（〉3Ga）.