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Are the lower planes of double seismic zones caused by serpentine dehydration in subducting oceanic mantle?

Simon M. Peacock
Are the lower planes of double seismic zones caused by serpentine dehydration in subducting oceanic mantle?
Geology (Boulder) (April 2001) 29 (4): 299-302

Abstract

In a number of subduction zones, earthquakes at 50-200 km depth define two dipping planes, separated by 20-40 km, that appear to merge downdip. Upper plane earthquakes are inferred to occur within the subducting oceanic crust, whereas lower plane earthquakes occur in the subducting oceanic mantle. Beneath northeast Japan, the results of a new finite-element heat-transfer model suggest that the lower seismic plane cuts across isotherms at a shallow angle. Lower plane earthquakes occur at approximately 550-800 degrees C at 100 km depth and at approximately 350-600 degrees C at 160 km depth. These conditions coincide with the dehydration reaction antigorite (serpentine)-->forsterite+enstatite+H (sub 2) O, which suggests that lower plane earthquakes may be triggered by dehydration embrittlement, which in turn suggests that the subducting oceanic mantle is partially hydrated. Serpentinization may occur in the trench-outer rise region, where faulting may promote infiltration of seawater several tens of kilometers into the oceanic lithosphere. If this hypothesis is correct, current subduction-zone H (sub 2) O budgets may significantly underestimate the amount of bound H (sub 2) O entering the "subduction factory."


ISSN: 0091-7613
EISSN: 1943-2682
Coden: GLGYBA
Serial Title: Geology (Boulder)
Serial Volume: 29
Serial Issue: 4
Title: Are the lower planes of double seismic zones caused by serpentine dehydration in subducting oceanic mantle?
Author(s): Peacock, Simon M.
Affiliation: Arizona State University, Department of Geological Sciences, Tempe, AZ, United States
Pages: 299-302
Published: 200104
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 35
Accession Number: 2001-030984
Categories: Solid-earth geophysics
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. sketch maps
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2018, American Geosciences Institute. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 200110
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