Prevalent thickening and local thinning of the mantle transition zone beneath the Baikal rift zone and its dynamic implications  

作　　者：SI ShaoKun TIAN XiaoBo ZHANG HongShuang TENG JiWen 

机构地区：[1]Institute of Geology and Geophysics, Chinese Academy of Sciences [2]Graduate University of Chinese Academy of Sciences

出　　处：《Science China Earth Sciences》2013年第1期31-42,共12页中国科学（地球科学英文版）

基　　金：supported by National Natural Science Foundation of China(Grant Nos. 40974025 and 40721003);Innovative Research Group Science Foundation (Grant No. 41021063);National Key Project (Grant No.2008ZX05008-006)

摘　　要：The Baikal rift is the most seismically active continental rift in the world and is significant for studying the dynamics of continental rifts, although its precise dynamic mechanisms remain controversial. We calculated receiver functions (1748) from Global Seismographic Network seismic stations TLY and ULN and stacked receiver functions in different bins. Here we present discontinuities at depths of 410km and 660km and thickness of the mantle transition zone (MTZ) beneath the study area. The MTZ structure shows an obvious thickening (292km) in the Baikal rift zone except for an area of limited thinning (230km), whereas it is basically normal (250km) beneath the Mongolian area, to the southeast of the Baikal rift. Combining these results with previous findings, we propose that the large-scale thickening beneath the Baikal rift zone is likely to be caused by the Mesozoic collision between the Siberian Platform and the Mongolia-North China Block or magmatic intrusion into the lower crust, which would result in crust and lithosphere thickening. Thus, the lower crust becomes eclogitized and consequently detached into the deep mantle because of negative buoyancy. The detachment not only induces asthenosphere upwelling but also accelerates mantle convection of water detached from the subducted slab, which would increase mantle melting, while both processes promote the development of the rift. Our preliminary results indicate that the detachment and the consequent hot upwelling have an important influence on the development of the Baikal rift, and a small-scale mantle upwelling indicated by the located thinning may have destroyed the lithosphere and promoted this development.The Baikal rift is the most seismically active continental rift in the world and is significant for studying the dynamics of conti- nental rifts, although its precise dynamic mechanisms remain controversial. We calculated receiver functions （1748） from Global Seismographic Network seismic stations TLY and ULN and stacked receiver functions in different bins. Here we pre- sent discontinuities at depths of 410 km and 660 km and thickness of the mantle transition zone （MTZ） beneath the study area. The MTZ structure shows an obvious thickening （292 km） in the Baikal rift zone except for an area of limited thinning （230 km）, whereas it is basically normal （250 km） beneath the Mongolian area, to the southeast of the Baikal rift. Combining these results with previous findings, we propose that the large-scale thickening beneath the Baikal rift zone is likely to be caused by the Mesozoic collision between the Siberian Platform and the Mongolia-North China Block or magmatic intrusion into the lower crust, which would result in crust and lithosphere thickening. Thus, the lower crust becomes eclogitized and conse- quently detached into the deep mantle because of negative buoyancy. The detachment not only induces asthenosphere upwelling but also accelerates mantle convection of water detached from the subducted slab, which would increase mantle melting, while both processes promote the development of the rift. Our preliminary results indicate that the detachment and the consequent hot upwelling have an important influence on the development of the Baikal rift, and a small-scale mantle upwelling indicated by the located thinning may have destroyed the lithosphere and promoted this development.

关 键 词：Baikal rift zone mantle transition zone P wave receiver function 

分 类 号：P542.5[天文地球—构造地质学]