Stress-driven fluid flow controls long-term megathrust strength and deep accretionary dynamics

Armel Menant,Samuel Angiboust,Taras Gerya

doi:10.1038/s41598-019-46191-y

Abstract

The heterogeneity of frictional strength along the megathrust earthquake zone critically controls plate coupling and long-term subduction dynamics. However, the persistence and distribution of high-friction segments through space and time remain poorly constrained. Here, we show that accretion processes, such as tectonic underplating (i.e., basal accretion of material below the fore-arc region), can be used as a proxy to characterize the long-term frictional zonation of the subduction interface. We carry out numerical thermo-mechanical experiments, which predict a first-order control of tectonic-stress variations on fluid transport in deep fore-arc regions. Accordingly, positive feedback between fluid distribution and effective stress favours the stability of the interface frictional properties at Myr-scale which, in turn, controls the deep accretionary dynamics. We propose that the recognition of thick duplex structures resulting from successive underplating events over tens of Myr, allows for tracking subduction segments exhibiting an increasing frictional behaviour. Our numerical results help ascertain the long-term hydro-mechanical properties and distribution of coupling/decoupling segments of megathrust earthquake zones worldwide where active tectonic underplating is recognized.

Highlights

Subduction fluids are intricately linked to tectonic processes[1,2] and have paramount effects on the frictional strength of subduction interfaces and, on the seismogenic behaviour of megathrust faults[3,4,5]
The model takes into account hydration and dehydration processes by implementing compaction and thermodynamically constrained metamorphic reactions[16], as well as fluid transport driven by fluid buoyancy and dynamic pressure gradients[11,17]
The reference experiment cold[-1] reproduces the subduction of an old and cold oceanic lithosphere below a 30-km-thick continental lithosphere at a convergence rate of 5 cm yr−1. Accretion dynamics of this long-lived subduction zone is dominated by a succession of tectonic underplating events of sedimentary and basaltic material inserted at the base of the fore-arc crust as discrete tectonic slices (Fig. 1 and Supplementary Movie S1)

Summary

Introduction

Subduction fluids are intricately linked to tectonic processes[1,2] and have paramount effects on the frictional strength of subduction interfaces and, on the seismogenic behaviour of megathrust faults[3,4,5]. The exact connection between interface properties, deformation mechanisms and detachments of tectonic slices remains elusive and requires to deal with pore fluid pressure and effective stress interrelations In this context, we assess for the first time the relations between long-term fluid flow, stress regime and tectonic underplating events in deep fore-arc regions, using high-resolution, two-dimensional, thermo-mechanical experiments. Www.nature.com/scientificreports plate convergence rate (i.e., from 4 to 8 cm yr−1) and the overriding continental crust thickness (i.e., 30 and 40 km thick; Supplementary Table S1) Aside from these parameters, the main uncertainty on fluid transport calculation is the reference percolation velocity (vperc; see Methods). Additional experiments have been carried out by varying vperc to explore the effect of fluid drainage on plate interface strength and accretion processes (Supplementary Table S1)

Methods

Results

Conclusion