Earth Science Department, Rice University, Houston, Texas 77005-1892, USA.
1] Department of Geological Sciences, University of Oregon, Eugene, Oregon 97043, USA [2] Department of Earth Sciences, University of Minnesota, Minneapolis, Minnesota 55455-0231, USA.
Nature. 2014 Nov 13;515(7526):253-6. doi: 10.1038/nature13878.
Whereas subduction recycling of oceanic lithosphere is one of the central themes of plate tectonics, the recycling of continental lithosphere appears to be far more complicated and less well understood. Delamination and convective downwelling are two widely recognized processes invoked to explain the removal of lithospheric mantle under or adjacent to orogenic belts. Here we relate oceanic plate subduction to removal of adjacent continental lithosphere in certain plate tectonic settings. We have developed teleseismic body wave images from dense broadband seismic experiments that show higher than expected volumes of anomalously fast mantle associated with the subducted Atlantic slab under northeastern South America and the Alboran slab beneath the Gibraltar arc region; the anomalies are under, and are aligned with, the continental margins at depths greater than 200 kilometres. Rayleigh wave analysis finds that the lithospheric mantle under the continental margins is significantly thinner than expected, and that thin lithosphere extends from the orogens adjacent to the subduction zones inland to the edges of nearby cratonic cores. Taking these data together, here we describe a process that can lead to the loss of continental lithosphere adjacent to a subduction zone. Subducting oceanic plates can viscously entrain and remove the bottom of the continental thermal boundary layer lithosphere from adjacent continental margins. This drives surface tectonics and pre-conditions the margins for further deformation by creating topography along the lithosphere-asthenosphere boundary. This can lead to development of secondary downwellings under the continental interior, probably under both South America and the Gibraltar arc, and to delamination of the entire lithospheric mantle, as around the Gibraltar arc. This process reconciles numerous, sometimes mutually exclusive, geodynamic models proposed to explain the complex oceanic-continental tectonics of these subduction zones.
虽然俯冲洋壳的再循环是板块构造学的核心主题之一，但大陆岩石圈的再循环似乎要复杂得多，也了解得更少。拆沉作用和对流下沉是两种广泛认可的过程，用于解释造山带下或附近岩石圈地幔的去除。在这里，我们将大洋板块俯冲与某些板块构造环境中相邻大陆岩石圈的去除联系起来。我们从密集的宽带地震实验中发展出远震体波图像，这些图像显示与俯冲的大西洋板块下的异常快的地幔相关的体积高于预期，该异常位于南美洲东北部和直布罗陀弧区下方的阿尔伯兰海板块下，并且在 200 公里以上的深度与大陆边缘对齐。瑞利波分析发现，大陆边缘下的岩石圈地幔明显比预期的薄，而且薄岩石圈从俯冲带相邻的造山带向附近克拉通核心的边缘延伸。综合这些数据，我们在这里描述了一个可以导致俯冲带附近大陆岩石圈损失的过程。俯冲的大洋板块可以粘性地夹带并从相邻大陆边缘的大陆热边界层岩石圈底部去除。这会导致地表构造，并通过在岩石圈-软流圈边界沿线形成地形来为进一步变形做好准备。这可能导致在南美和直布罗陀弧下方以及整个岩石圈地幔下形成次下沉，就像直布罗陀弧下方一样。这个过程调和了许多相互排斥的地球动力学模型，这些模型被用来解释这些俯冲带复杂的海洋-大陆构造。
