岩石圈—软流圈物质循环促进大陆增生的新方式  

A new mode for continental accretion induced by interaction between the lithosphere and asthenosphere

作　　者：杨文采 YANG Wencai(Zhejiang University,Hangzhou,310027)

机构地区：[1]浙江大学地球科学学院

出　　处：《地质论评》2019年第5期1039-1053,共15页Geological Review

基　　金：中国地质调查局资助的基础研究项目(编号:#12120113093800)的成果~~

摘　　要：大陆动力学研究地球内能量和物质的运动和伴随的信息传播,上地幔中的软流圈是地球内部的物质运动的关键部位之一。由于观测的技术方法少,人类对软流圈内部的地质作用过程所知甚少。在青藏高原,过去地震波三维层析成像的分辨率不高,难以对地壳上地幔构造进行准确的定位。我们收集和整理了地方地震台的数字化观测数据,使地震体波三维层析成像的准确度大大提高,为解决软流圈的地质构造准确成像提供了新的可能性。根据地震体波三维层析的成像结果,在古特提斯洋和特提斯洋俯冲板块前沿的软流圈底部410 km间断面上方,存在反映古大洋俯冲板块的高速体,它们在青藏高原、苏鲁和伊朗都有出现。清晰和稳定的高波速异常的位置表明,特提斯洋俯冲板块现在已经拆沉在软流圈的底部,古特提斯洋俯冲板块也可能曾经拆沉在软流圈的底部。对比青藏高原和苏鲁的地壳上地幔波速结构推测,拆沉造成软流圈中的轻元素物质上涌,进入大陆岩石圈,造成岩浆活动。上涌还使碰撞造山带地壳厚度减小,而岩石圈厚度增加。大约100 Ma后,俯冲下去的大洋残块会被软流圈物质磨蚀交代,使岩石圈厚度增加,形成大陆下方的大陆根,造成大陆克拉通化和体积增生。大洋板块俯冲后在软流圈拆沉是岩石圈—软流圈物质循环的一种重要方式,对软流圈中物质均衡和体积稳定也起重要作用。Objectives:Continental dynamics studies the motion of energy and matter in the earth and the accompanying information propagation,and the asthenosphere in the upper mantle is one of the key parts of the material motion inside the earth.Because of lack of precise methods,little is known about the geological action process of the asthenosphere.In the Qinghai—Xizang(Tibet)Plateau,the resolution of three-dimensional tomography of seismic waves in the past was not high,and it is difficult to accurately locate the mantle structures.Methods:We collect and organize the digital observation data from hundreds of local seismic stations,select more than 260000 rays and their travel-time for the 3 D seismic inversions,obtaining 3 D velocity images of scale of1°×1°×20 km,and greatly improves the accuracy of 3 D seismic velocity images.Thus the work provides new possibilities for correct positioning of the geological structures of the lithosphere and asthenosphere.Results:According to the imaging results of the seismic 3 D velocity tomography,there are high-velocity bodies exist on the bottom of the asthenosphere,corresponding to the ancient or new Tethys-Ocean subduction plate,which appear in the Qinghai—Xizang(Tibet)Plateau,Sulu and Iran.They lay on the 410 km discontinuity in the bottom of the asthenosphere along the front of the corresponding suture lines.The clear and stable position of the high velocity anomalies indicate that the old Ocean Subduction Plates occurred delamination down to the bottom of the asthenosphere after they subducted into the asthenosphere.Comparing the velocity structures of the mantle between the Qinghai—Xizang(Tibet)Plateau and Sulu orogenic belt,it is speculated that the delamination caused the light elements mass of the asthenosphere upwelling onto the continental lithosphere,resulting in magma and volcanic activity.The upwelling also reduces the thickness of the crust of the collisional orogeny and increases the thickness of the continental lithosphere.After about 100 Ma,the subducti

关 键 词：软流圈 地震层析成像 古特提斯洋 特提斯洋板块 俯冲板块拆沉 大陆增生 

分 类 号：P315.7[天文地球—地震学]