南沙海槽前陆盆地热流变结构  

Lithospheric Thermal-Rheological Structure of Nansha Trough Foreland Basin in South China Sea

作　　者：马辉[1,2] 许鹤华[1] 施小斌[1] 陈爱华[1,2] 刘唐伟[1,2] 

机构地区：[1]中国科学院南海海洋研究所边缘海地质重点实验室,广东广州510301 [2]中国科学院研究生院,北京100049

出　　处：《地球科学（中国地质大学学报）》2011年第5期939-948,共10页Earth Science-Journal of China University of Geosciences

基　　金：中国科学院知识创新工程重要方向项目群项目(No.KZCX2-YW-Q05-04);国家重点基础研究发展计划"973"项目(No.2007CB41170405);国家高技术研究发展计划"863"课题(No.2008AA09Z306)

摘　　要：为了研究南沙海槽前陆盆地深部岩石圈的热力学性质,在前人所做的地质与地球物理研究工作的基础上,结合各种岩石热力学流变参数,采用有限元分析方法,计算了现今构造逆冲之后和中中新世-全新世逆冲过程活跃时两种状态下的深部岩石圈二维温度场和流变结构.模拟计算表明,南沙海槽前陆盆地地幔热流贡献达60%～70%,大地热流受深部地幔控制.逆冲推覆构造作用使盆地逆冲推覆带地表热流显著升高了15%～25%,达到70～75mW/m2.盆地沉积层温度在200℃以内,莫霍面温度420～500℃,地壳地温梯度25～30℃/km,盆地热岩石圈厚度为80km左右,横向上变化幅度不大.南沙海槽前陆盆地深部岩石圈流变性质具有明显的分层特性,为典型的"三明治"结构.盆地岩石圈综合强度由南沙海槽向逆冲推覆带方向呈下降趋势,盆地力学岩石圈厚度50km左右,有效弹性厚度为30～32km.通过模拟盆地深部岩石圈热流变结构,揭示了盆地深部岩石圈具有强地幔、弱地壳的流变学特征,表现为高强度块体.同时南沙海域地震活动与深部岩石圈热结构、热活动和岩石圈综合强度密切相关.地壳内热构造活动弱、岩石圈强度大可能是区域地震很少发生的重要原因.In order to study the lithospheric thermodynamic properties of Nansha trough foreland basin,we simulate the deep lithosphere temperature field and rheological structure during the thrust faults tectonic activities from Middle Miocene to Holocene and after thrusting（static） in the basin using the finite element method,based on previous studies of geological and geophysical data together with a variety of rock thermodynamic parameters.Simulation results indicate that heat flow contribution from mantle reaches 60%-70% of surface heat flow which is controlled by deep mantle in Nansha trough foreland basin.Thrusting movements increase the surface heat flow in thrust-slip fault belts by 15%-25% to 70-75 mW/m2.Our results also show that the temperature of sedimentary layer is less than 200 ℃,while the temperature at Moho varies from 420 to 500 ℃;crust geothermal gradient ranges from 25 to 30 ℃/km.And calculated thickness of thermal lithosphere is about 80 km,which varies slightly laterally.The lithosphere in Nansha waters shows obvious rheological stratification properties,as a typical ＂sandwich＂ structure.Horizontally,lithosphere strength decreases in the direction from Nansha trough to thrust belt（NW to SE）.The thickness of mechanical lithosphere is about 50 km and the effective elastic thickness ranges from 30 to 32 km.The simulated thermal lithosphere rheological structure also reveals that lithosphere of Nansha basin has rheological characteristics of strong mantle and weak crust,acting as high-strength block.Earthquake activities of Nansha waters are closely related to thermal structure,thermal activity and integrated strength of lithosphere.The weak thermal activity in the crust and high lithosphere strength may be important reasons for rare earthquake occurrence in this area.

关 键 词：南沙海槽 岩石圈 温度场 流变结构 地震 有效弹性厚度 海洋地球物理. 

分 类 号：P738.6[天文地球—海洋地质]