GPS资料对青藏高原现今下地壳粘性特征的约束  

Viscous characteristics of the present Tibetan lower crust:From the constraint of the GPS velocity field

作　　者：陆诗阔[1,2] 丁林[2] 刘金朝[3] 

机构地区：[1]中国石油大学(华东)地球科学与技术学院地质系,山东青岛266555 [2]中国科学院青藏高原研究所,北京100085 [3]中国铁道科学研究院,北京100081

出　　处：《地学前缘》2011年第3期22-32,共11页Earth Science Frontiers

基　　金：国家自然科学基金项目(40504015);中国科学院知识创新工程重要方向项目(KZCX3-SW-143);中国博士后科学基金项目(200503743)

摘　　要：假定GPS速度场在很大程度上受震间期地壳浅部发震层弹性应变积累的影响,文中以青藏地区现有GPS观测资料为约束,在较高精度地形数据和全球板块相对运动的NUVEL-1 A模型基础上,借助数值模拟方法通过构建粘弹性动力学模型,分析了用下地壳介质流动和大陆深部断裂带内的延性应变集中等两种不同的大陆岩石圈深部变形机制对青藏地区现今地壳运动解释的合理性。研究表明,对于青藏高原内部不同地区,现今地壳运动可能受不同的深部动力学机制控制。在青藏高原的东南部地区,尽管模型结果本身不能排除该区下地壳可能存在着延性应变相对集中的深部断裂带,但为了减小对GPS观测资料的预测误差,模拟试验明确表明该地区下地壳介质粘度偏低。在青藏高原的中北部和东北部地区,用中下地壳断裂带内延性应变相对集中来解释GPS观测资料更好,暗示在青藏高原的这两个地区活动断裂可能向下切割很深。忽略青藏高原下地壳介质粘度的横向差异,为了对GPS观测资料的预测做到一级近似,要求青藏高原下地壳平均粘度为（1~5）×1022Pa.s,同时在青藏高原活动断裂向深部的延伸带内介质的粘度约为1021Pa.s。受青藏高原高海拔和下地壳低粘度的控制,重力作用对青藏高原现今地壳运动有着极为重要的影响。Assuming that the GPS velocity field is greatly affected by the interseismic elastic deformation of the upper crust,under the constraints of the existing GPS data,and referring to the elevation data and the NUVEL-1A model of global plate movement,we have constructed the viscoelastic mechanical models to analyze the rationality of the explanation to the Tibetan present-day crustal movement by two different deformation mechanisms in the deep continental lithosphere,including the viscous flow in the lower crust and the ductile strain localization in the deep fault zones.Numerical experiments show that the present-day crustal movement in different regions of the Tibet may be attributed to different geodynamic mechanisms.In the Tibetan southeast area,although the lower crustal ductile strain localization could not be excluded,the viscosity of the lower crust should be much lower in order to reduce the model＇s prediction error.In the middle-north and northeast areas of the Tibet,the GPS velocity field is interpreted much better by the ductile strain localization in the deep fault zones,implying that the actual active faults may incise down deeply in these areas.Ignoring the lateral change of the viscosity in the lower crust,the model whose prediction of the movement has a first-order similarity with the GPS data yields an estimate of（1-5）×1022 Pa·s for the average viscosity of the Tibetan lower crust,and about 1021 Pa·s for that of the deep fault zones.Due to the high elevation and the lower viscosity of the lower crust,the gravity plays an important role in the present-day movement of the Tibetan plateau.

关 键 词：青藏高原 GPS资料 下地壳介质流动 深部断裂带延性应变集中 数值模型 

分 类 号：P227[天文地球—大地测量学与测量工程] P315.725[天文地球—测绘科学与技术]