残留板块及地幔柱:怀俄明克拉通的上地幔地震图像(英文)

介绍了近年来天然地震体波和面波层析成像以及接收函数在怀俄明克拉通地区的应用。怀俄明克拉通地区的地壳和上地幔结构可以归结为克拉通成型时期的残存高速度异常以及进行中Yellowstone低速地幔柱。在克拉通南部边界缝合带地区以及在中部和北部下地壳中保存着一些高速度结构。南部边界缝合带地区的高速度倾斜上地幔结构与人工地震剖面LithoProbe在北美各个克拉通边界所记录的上地幔倾斜反射体一致。作为一个可能的上地幔消减板块残留体,这个倾斜上地幔结构显示出板块叠加可能是一个普遍的克拉通成型过程。在克拉通缝合带的莫霍面和上地幔深度,人工地震的研究结果显示板块叠加过程形成一个楔形体,体现出克拉通上地幔的较高粘度系数。接收函数的转换波共转换点叠加技术显示出这种楔形体存在于整个怀俄明克拉通的南部边界。接收函数和基于噪声的瑞利波层析成像图像显示出在克拉通地壳增厚地区存在下地壳高速体。作为早期岩石圈分裂过程残留的火成岩侵入体,这种下地壳高速体存在于较早成型的克拉通北部和中部地区,显示出南部克拉通地区不同的形成机制。克拉通的西部地区受到Yellowstone地幔柱的影响。层析成像显示低速的地幔柱从黄石地区向下延伸到至少500km。在消蚀岩石圈的同时,岩浆侵入体沿着hotspottrack在中地壳大量的形成,并引起下地壳岩石的横向流动。

Relict slab and young plume: Seismic view of the present time Wyoming lithosphere

Since nearly two decades ago, many temporary arrays have been deployed in the Archean Wyoming province and its neighboring areas. Due to the small station spacing (up to 2 km) of these array deployments, it is now possible to image the seismic structure in the Wyoming crust and upper mantle with a resolution scale comparable to active source profiling studies. Remarkable agreements between the passive and active source studies are found in the crust and shallow upper mantle. A high velocity dipping structure down to >150 km is revealed from tomography at the southern craton edge. Supported by other lines of evidence, a frozen-in fossil subduction slab model at the craton margin is preferred, which indicates that lateral slab accretion may be an important mechanism during the early craton assembly. High velocity lower crust magmatic underplates are present in the northern and central craton, but are perhaps inexistent in the south, indicating that they are related to possible different cratonization processes among the craton subprovinces. The spatial coincidence of these relict seismic structures with the surface sutures suggests the early lithospheric responses to various mantle deformation processes have been well preserved. Young tectonisms, for example the Yellowstone hotspot, have significantly altered the crust and lithosphere in the western side of the craton.