Porous fluid flow enables oceanic subduction initiation on Earth

Abstract

[1] Although most of the presently active intra-oceanic subduction zones are relatively young and initiated during the Cenozoic, subduction initiation process remains poorly understood. Previous models of subduction initiation assumed excessive weakening of tectonic plate boundaries that does not reconcile with laboratory rock strength measurements. The weakening was assumed to be caused by fluids present along tectonic fractures; however no selfconsistent solid-fluid model of subduction initiation has been developed so far. Here we present new numerical hydrothermo-mechanical model of spontaneous intra-oceanic subduction initiation where solid rock deformation and fluid percolation are fully coupled. Based on 2-D numerical experiments, we demonstrate that although subduction fails to initiate under fluid-absent conditions, it can naturally start when porous fluid is present inside oceanic crust and along the plate boundaries. Fluid percolation is localized along spontaneously forming faults where high fluid pressure compensates lithostatic pressure, thus dramatically decreasing friction along the incipient subduction zone. Through the parametric study, we conclude that the most important parameter for subduction initiation is the solid matrix permeability. Paradoxical at first, lowering the permeability indeed favors subduction initiation by maintaining high fluid pressure and thus decreasing friction along active faults.

New parametric implementation of metamorphic reactions limited by water content, impact on exhumation along detachment faults

“…The impact of bending stresses on fluid flow was already demonstrated for subduction settings (Faccenda and Mancktelow, 2010;Faccenda et al, 2012;Dymkova and Gerya, 2013) and strike-slip settings (Le Pourhiet and Saleeby, 2013). Our new implementation is consistent with these studies and our result shows that bending stresses also play key roles in terms of the fluid-suction capacity of the bending layers and of the direction of fluid flow in the deeper crust.…”

“…Evans and Chester, 1995;Macdonald et al, 1979) are beyond the scope of our study. These would require full two-phase flow approximation (e.g., Dymkova and Gerya, 2013;Keller et al, 2013;McKenzie, 1984) rather than simple Darcy law. However, taking into account the uncertainties on the flow parameters, the assumption of Darcy law is largely sufficient to test the idea of water-induced controls for detachment fault development.…”

2D thermomechanical modelling of continent–arc–continent collision

“…This prescribed factor is introduced in a way that the pore fluid pressure Pfluid reduces the yield strength σyield of fractured or fluid-containing rock (Dymkova and Gerya, 2013, and references therein). For the dry rocks λfluid = 1.…”

Subduction initiation from a stagnant lid and global overturn: new insights from numerical models with a free surface

“…These mechanisms include, for example, nucleation from an existing rupture produced either by a meteorite impact (Hansen 2007), by a transform fault Hall et al 2003;Nikolaeva et al 2010), by an oceanic plateau (Nair and Chacko 2008;Niu et al 2003) or by a major episode of delamination (Toth and Gurnis 1998). Different weakening mechanisms like the addition of water or melt into the lithosphere (Dymkova and Gerya 2013;Hirth and Kohlstedt 2003), grain-size reduction (e.g. Bercovici and Ricard 2005Karato et al 1980Karato et al , 1986Rozel et al 2011), void generation (Bercovici 1998;RegenauerLieb 1998) or shear-heating (Crameri and Kaus 2010;Lu et al 2015;Thielmann and Kaus 2012;Yuen et al 1978) have been proposed to be a key in subduction initiation by providing a necessary weak and localised, lithosphericscale shear zone.…”