摘要
通过横穿青藏高原近 80 0 0km长的 4条天然地震层析剖面 ,获得 4 0 0km深度以上的地壳和地幔速度图像及地震波各向异性 ,揭示了青藏高原 4 0 0km深度范围内的地壳和地幔结构特征。地幔速度图像显示 ,青藏高原腹地的深地幔中存在以大型低速异常体为特征的地幔羽 ,其可能通过热通道与大面积分布的可可西里新生代高钾碱性火山作用有成因联系 ;阿尔金、康西瓦、金沙江、嘉黎及雅鲁藏布江等走滑断裂可下延至 30 0～ 4 0 0km深度 ,显示了低速高热物质组成的垂向低速异常带特征及大型超岩石圈或地幔剪切带的产出 ;发现康西瓦、东昆仑—金沙江、班公湖—怒江和雅鲁藏布缝合带下部存在不连续的高速异常带 ,可以解释为青藏高原地体拼合及碰撞过程中可能保留的加里东、古特提斯和中特提斯大洋岩石圈“化石”残片 ,是“拆沉”的地球物理证据。印度大陆岩石圈的巨厚俯冲板片以 15～ 2 0°倾角向北插入唐古拉山下 30 0km深处 ,并被高热物质组成的地幔剪切带分开。结合新的横穿喜马拉雅及青藏高原的地幔层析资料 ,提出青藏高原碰撞动力学新模式 :青藏高原南部印度岩石圈板片的翻卷式陆内超深俯冲 ,北缘克拉通向南的陆内俯冲 ,腹地深部的地幔羽上涌 ,以及地幔范围内的高原“右旋隆升”及物质向东及北东方向运动及挤出。
By using four seismic tomographic profiles of nearly 8 000 km long across the Qinghai-Tibet Plateau, we obtained the crustal and mantle velocity images and seismic wave anisotropy over the depth down to 400 km, which revealed significant characteristics of the crust and mantle structure in the region. The mantle velocity images indicate the presence of a mantle plume characterized by a large low-velocity anomalous body beneath the interior of the Qinghai-Tibet Plateau; this feature shows its genetic relationship to the widespread Hoh-Xil Cenozoic potassic and alkaline volcanism through a thermal channel. The Altyn Tagh, Kangxiwa, Jinshajiang, Jiali and Yaluzangbu strike-slip faults extend downward to the depth of 300～400 km, which demonstrate the characteristics of a vertical low-velocity anomalous zone composed of high temperature material and the existence of large-scale translithospheric or mantle shear zones. The discontinuous anomalous high-velocity zones under the Kangxiwa, East Kunlun- Jinsha River , Bangong Lake-Nu River and Yaluzangbu sutures are tentatively interpreted as the “fossil” slab remnants of Caleodonian, Paleo-Tethyan and Meso-Tethyan oceanic lithosphere preserved during the terrane amalgamation and collision; they formed several slab remnants separating the anomalous low-velocity zones, and can be the geophysical evidence for “delamination”. The Indian lithospheric slab, which is marked by a gigantic, discontinuous anomalous high-velocity zone, was subducted gently northward to a depth of 300～400 km beneath the Tanggula Mountains. Based on the new tomographic data across the Himalaya and Tibet plateau, we proposed a new collisional model for the uplift of the Tibet plateau, which involves the “roll over” of the subducted Indian lithospheric slab beneath the south of the Tibetan Plateau, the southward intracontinental subduction of the cratonic lithosphere in the northern margin of the plateau, the upwelling of the deep mantle plume in the interior of the plateau, and the “dextral uplift” of the plateau within the limits of the deep mantle, as well as the motion and the extrusion of material toward the east and the northeast.
出处
《地学前缘》
EI
CAS
CSCD
2004年第4期329-343,共15页
Earth Science Frontiers
基金
国土资源部(原地质矿产部)重点基础项目"东昆仑造山带的构造演化"
"祁连山阿尔金山地质演化及岩石圈剪切作用"[编号9501106]
国土资源部科技专项"青藏高原演化与资源"的课题""地体边界和岩石圈断裂对青藏高原形成的贡献"[编号2001010201]
国家自然科学基金重点
关键词
青藏高原
地震层析剖面
地幔羽
地幔剪切带
岩石圈板片拆沉
Qinghai-Tibet Plateau
seismic tomographic profile
mantle plume
mantle shear zones
delamination of lithospheric slab
