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Nature:来自一个构造板块下面的图像

摘要 : Tim Stern及本文共同作者利用爆炸产生的地震波来形成正在向新西兰北岛底下潜没的一个海洋板块底部的高分辨率图像。他们在100公里深度处发现厚度不到一公里、倾角为15°的一个地震波速度突变带。

 

Tim Stern及本文共同作者利用爆炸产生的地震波来形成正在向新西兰北岛底下潜没的一个海洋板块底部的高分辨率图像。他们在100公里深度处发现厚度不到一公里、倾角为15°的一个地震波速度突变带。

一个平行的、深度比前者要大10公里的反射事件的存在表明,压缩波速度的降低被限于这个板块底部的一个通道,作者将该通道理解为由阻塞的部分熔融物或挥发物构成的一个剪切区域。

他们得出结论认为,这是证明在岩石圈-软流圈边界处存在一个将板块与下面的地幔流脱离、使板块构造得以发生的低粘度通道的独立证据。

原文链接:

A seismic reflection image for the base of a tectonic plate

Plate tectonics successfully describes the surface of Earth as a mosaic of moving lithospheric plates. But it is not clear what happens at the base of the plates, the lithosphere–asthenosphere boundary (LAB). The LAB has been well imaged with converted teleseismic waves1, 2, whose 10–40-kilometre wavelength controls the structural resolution. Here we use explosion-generated seismic waves (of about 0.5-kilometre wavelength) to form a high-resolution image for the base of an oceanic plate that is subducting beneath North Island, New Zealand. Our 80-kilometre-wide image is based on P-wave reflections and shows an approximately 15° dipping, abrupt, seismic wave-speed transition (less than 1 kilometre thick) at a depth of about 100 kilometres. The boundary is parallel to the top of the plate and seismic attributes indicate a P-wave speed decrease of at least 8 ± 3 per cent across it. A parallel reflection event approximately 10 kilometres deeper shows that the decrease in P-wave speed is confined to a channel at the base of the plate, which we interpret as a sheared zone of ponded partial melts or volatiles. This is independent, high-resolution evidence for a low-viscosity channel at the LAB that decouples plates from mantle flow beneath, and allows plate tectonics to work.(doi:10.1038/nature14146)

Earth science: The slippery base of a tectonic plate

High-resolution imaging of the base of the Pacific plate as it descends beneath New Zealand discloses a 10-kilometre-thick channel that decouples the plate from underlying upper mantle.(doi:10.1038/518039a)

对应Nature杂志: 2015年02月05日Nature杂志精选

来源: T. A. Stern 浏览次数:36

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