Subduction factory - 2. Are intermediate-depth earthquakes in subducting slabs linked to metamorphic dehydration reactions?

Publication Type  Journal Article
Year of Publication  2003
Authors  Hacker, B. R.; Peacock, S. M.; Abers, G. A.; Holloway, S. D.
Journal Title  Journal of Geophysical Research-Solid Earth
Volume  108
Issue  B1
Pages  -
Journal Date  Jan 18
ISBN Number  0148-0227
Accession Number  ISI:000181799800003
Key Words  subduction; seismicity; intermediate-depth earthquake; dehydration; transformation; double seismic zone; deep-focus earthquakes; northeastern japan arc; wave velocity structure; pacific plate beneath; pore pressure excess; phase-changes; oceanic-crust; sp
Abstract  

[1] New thermal-petrologic models of subduction zones are used to test the hypothesis that intermediate-depth intraslab earthquakes are linked to metamorphic dehydration reactions in the subducting oceanic crust and mantle. We show that there is a correlation between the patterns of intermediate-depth seismicity and the locations of predicted hydrous minerals: Earthquakes occur in subducting slabs where dehydration is expected, and they are absent from parts of slabs predicted to be anhydrous. We propose that a subducting oceanic plate can consist of four petrologically and seismically distinct layers: (1) hydrated, fine-grained basaltic upper crust dehydrating under equilibrium conditions and producing earthquakes facilitated by dehydration embrittlement; (2) coarse-grained, locally hydrated gabbroic lower crust that produces some earthquakes during dehydration but transforms chiefly aseismically to eclogite at depths beyond equilibrium; (3) locally hydrated uppermost mantle dehydrating under equilibrium conditions and producing earthquakes; and (4) anhydrous mantle lithosphere transforming sluggishly and aseismically to denser minerals. Fluid generated through dehydration reactions can move via at least three distinct flow paths: percolation through local, transient, reaction-generated high-permeability zones; flow through mode I cracks produced by the local stress state; and postseismic flow through fault zones.

Notes  

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URL  <Go to ISI>://000181799800003
DOI  Doi 10.1029/2001jb001129