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Lithospheric structure of the Rio Grande rift

机译：大里奥裂谷的岩石圈结构

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摘要

A high-resolution, regional passive seismic experiment(1-6) in the Rio Grande rift region of the southwestern United States has produced new images of upper-mantle velocity structure and crust-mantle topography. Synthesizing these results with geochemical(7-9) and other geophysical(10-13) evidence reveals highly symmetric lower-crustal and upper-mantle lithosphere extensional deformation, suggesting a pure-shear rifting mechanism for the Rio Grande rift. Extension in the lower crust is distributed over a region four times the width of the rift's surface expression. Here we propose that the laterally distributed, pure shear extension is a combined effect of low strain rate and a regionally elevated geotherm, possibly abetted by pre-existing lithospheric structures, at the time of rift initiation. Distributed extension in the lower crust and mantle has induced less concentrated vertical mantle upwelling and less vigorous small-scale convection(14) than would have arisen from more localized deformation. This lack of highly focused mantle upwelling may explain a deficit of rift-related volcanics in the Rio Grande rift compared to other major rift systems such as the Kenya rift(15,16).
机译：美国西南部里奥格兰德大裂谷地区的高分辨率区域被动地震实验（1-6）产生了上地幔速度结构和地壳幔地形的新图像。将这些结果与地球化学（7-9）和其他地球物理（10-13）的证据进行综合后，揭示出高度对称的下地壳和上地幔岩石圈伸展变形，这暗示了里奥格兰德裂谷的纯剪切裂谷机制。下地壳的延伸分布在一个区域，其范围是裂谷表面表情宽度的四倍。在这里，我们提出，在裂谷开始时，横向分布的纯剪切扩展是低应变率和局部升高的地热的综合作用，可能由先前存在的岩石圈结构教a。下部地壳和地幔中的分布延伸引起的集中地幔上升流较少，而小尺度对流强度较小（14），这比局部变形引起的要少。与其他主要的裂谷系统如肯尼亚裂谷相比，里奥格兰德裂谷缺乏高度集中的地幔上升流可能解释了裂谷相关火山的不足（15,16）。

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