马尼拉海沟俯冲带热结构的模拟研究

俯冲带热结构的数值模拟研究是对地表观测研究的重要补充,也是验证地球动力学模型的重要方法.本文沿马尼拉海沟俯冲带东火山链(EVC)和西火山链(WVC)各取一条剖面,依据地质、地球物理条件,进行了有限元热模拟计算.计算过程中,分析了摩擦和剪切热对俯冲带热结构的影响,模拟了EVC和WVC两条测线下俯冲带的热结构,并结合岩石学实验结果预测了俯冲板块发生脱水和部分熔融的位置.模拟结果表明,在100 km深度处,考虑摩擦和剪切热时,俯冲板块表面的温度约为865 ℃;而不考虑摩擦和剪切时,俯冲板块表面的温度仅为770 ℃,二者温差可达95 ℃.在相同深度处,考虑摩擦和剪切热时,在EVC和WVC测线下俯冲板块表面的温度分别为865 ℃和895 ℃,俯冲洋壳底部温度分别为560 ℃和605 ℃.俯冲板块表面少量矿物开始脱水的深度小于50 km,但大量脱水和部分熔融主要发生在深度100 km左右,这与地表观测的火山活动位置一致.

A simulation study on the thermal structure of Manila trench subduction zone

Numerical simulation study of thermal structure is a supplement to field observations and an important method to verify geodynamic models.In this study,based on geological and geophysical conditions,we construct two thermal models across the East Volcano Chain(EVC) and the West Volcano Chain(WVC) along the Manila trench subduction zone and do the thermal simulations using finite-element numerical method.During these simulations,we study the thermal structure of the subduction zones affected by the frictional and shear heating and simulate the thermal structure of the subduction zones beneath the seismic lines at EVC and WVC.We also employ the results of rock experiments to predict the regions of dehydration and partial melting in the subducting slab.The simulation results show that,at 100 km depth,at the slab interface with frictional and shear heating the temperature is 865 ℃,about 95 ℃ warmer than temperature without frictional and shear heating.Considering the frictional and shear heating,the temperatures at the slab interface are 865 ℃ and 895 ℃ and at the base of subducting oceanic crust are 560 ℃ and 605 ℃ at 100 km beneath the seismic lines of EVC and WVC.At slab surface,the depth of dehydration onset is less than 50 km.However,partial melting and dehydration may mainly occur at about 100 km depth,which is well associated to the observed location of the volcanic activity.