Publication Date:
2015-02-06
Description:
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 waves, 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 degrees 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.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Stern, T A -- Henrys, S A -- Okaya, D -- Louie, J N -- Savage, M K -- Lamb, S -- Sato, H -- Sutherland, R -- Iwasaki, T -- England -- Nature. 2015 Feb 5;518(7537):85-8. doi: 10.1038/nature14146.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Institute of Geophysics, Victoria University, Salamanca Road, Wellington 6140, New Zealand. ; Institute of Geological and Nuclear Sciences, 1 Fairway Drive, Lower Hutt 5010, New Zealand. ; Department of Earth Sciences, University of Southern California, 3651 Trousdale Parkway, Los Angeles, California 90210, USA. ; Seismological Observatory, University of Nevada, 1664 North Virginia Street, Reno, Nevada 90210, USA. ; Earthquake Research Institute, Tokyo University, 1-1-1 Yoyoi, Tokyo 113-0032, Japan. ; 1] Institute of Geophysics, Victoria University, Salamanca Road, Wellington 6140, New Zealand [2] Institute of Geological and Nuclear Sciences, 1 Fairway Drive, Lower Hutt 5010, New Zealand.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/25653000" target="_blank"〉PubMed〈/a〉
Print ISSN:
0028-0836
Electronic ISSN:
1476-4687
Topics:
Biology
,
Chemistry and Pharmacology
,
Medicine
,
Natural Sciences in General
,
Physics
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