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

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.

Thermal structure and intermediate-depth seismicity in the Tohoku-Hokkaido subduction zones

“…Cross sections are labeled following Kita (2009) plane of seismicity is not only confined to the descending oceanic crust, but also related to the presence of fluids that are liberated by the transformation of blueschist to eclogite. Support for this idea is provided in the qualitative sense by the deepening of the seismic belt below Kanto and western Hokkaido (Hasegawa et al, 2007;Kita et al, 2010a). Thermal shielding of the slab by an anomalous overriding plate structure is supported by heat flow data ( Fig.…”

Distribution of hydrous minerals in the subduction system beneath Mexico

“…Based on this analysis, we note that the gabbro-toeclogite transformation has not occurred in southern Mexico. As a comparison, Cascadia, the youngest and warmest slab in the world (Hyndman and Wang, 1993), has the formation of nearly anhydrous eclogite at 80-90 km (Hacker et al, 2003b).…”

“…As oceanic plates subduct, mineral-bound H 2 O is transported down into the deep mantle (Abers, 2000;Hacker et al, 2003b;Jacobsen and van der Lee, 2006;Maruyama and Okamoto, 2007;Mainprice and IIdefonse, 2009). The evidence has been seismically detected via tomography and receiver function (RF) based on teleseismic P-to-S converted (hereafter Ps) phases in various subduction environments as a lowvelocity layer atop of the subducting plate (e.g, Alaska-Ferris et al, 2003, Cascadia-Nicholson et al, 2005Abers et al, 2009;Audet et al, 2009;Peacock et al, 2011, central Andes-Yuan et al, 2000, southwest Japan-Shelly et al, 2006, northeast Japan-Kawakatsu and Watada, 2007Tsuji et al, 2008, andcentral Mexico-Pérez-Campos et al, 2008;Kim et al, 2010).…”

A community benchmark for subduction zone modeling

“…This thermomechanical approach should yield a reasonable prediction of the temperatures in the slab, which then can be linked to the metamorphic processes leading to slab dehydration, arc volcanism and seismogenesis. High accuracy of the thermal models is needed since thermodynamic, field-based and experimental predictions of the relevant metamorphic phase changes predict relatively narrow pressure-temperature ranges for the key phase changes (Schmidt and Poli, 1998;Connolly and Kerrick, 2002;Hacker et al, 2003;Forneris and Holloway, 2004;Abers et al, 2006).…”