Subduction | EPFL Graph Search

Subduction is a geological process in which the oceanic lithosphere and some continental lithosphere is recycled into the Earth's mantle at convergent boundaries. Where the oceanic lithosphere of a tectonic plate converges with the less dense lithosphere of a second plate, the heavier plate dives beneath the second plate and sinks into the mantle. A region where this process occurs is known as a subduction zone, and its surface expression is known as an arc-trench complex. The process of subduction has created most of the Earth's continental crust. Rates of subduction are typically measured in centimeters per year, with rates of convergence as high as 11 cm/year. Subduction is possible because the cold oceanic lithosphere is slightly denser than the underlying asthenosphere, the hot, ductile layer in the upper mantle underlying the cold, rigid lithosphere. Once initiated, stable subduction is driven mostly by the negative buoyancy of the dense subducting lithosphere. The slab s

Plasticity of the dense hydrous magnesium silicate phase A at subduction zones conditions

Elodie Adeline Amiguet, Yi Wang

The plasticity of the dense hydrous magnesium silicate (DHMS) phase A, a key hydrous mineral within cold subduction zones, was investigated by two complementary approaches: high-pressure deformation experiments and computational methods. The deformation experiments were carried out at 11 GPa, 400 and 580 degrees C, with in situ measurements of stress, strain and lattice preferred orientations (LPO). Based on viscoplastic self-consistent modeling (VPSC) of the observed LPO, the deformation mechanisms at 580 degrees C are consistent with glide on the (00 01) basal and (01 1 0) prismatic planes. At 400 degrees C the deformation mechanisms involve glide on (211 0) prismatic, (0001) basal and {1 1 21} pyramidal planes. Both give flow stresses of 2.5-3 GPa at strain rates of 2-4 x 10(-5) s(-1). We use the Peierls-Nabarro-Galerkin (PNG) approach, relying on first-principles calculations of generalized stacking fault (gamma-surface), and model the core structure of potential dislocations in basal and prismatic planes. The computations show multiple dissociations of the 1/3 [2 (1) over bar(1) over bar0] and [01 (1) over bar0] dislocations (< a >) and < b > dislocations) in the basal plane, which is compatible with the ubiquity of basal slip in the experiments. The gamma-surface calculations also suggest 1/3 [2 (1) over bar(1) over bar3] and [0 (1) over bar 11] dislocations (< a + c > or < c - b > directions) in prismatic and pyramidal planes, which is also consistent with the experimental data. Phase A has a higher flow strength than olivine. When forming at depths from the dehydration of weak and highly anisotropic hydrated ultramafic rocks, phase A may not maintain the mechanical softening antigorite can provide. The seismic properties calculated for moderately deformed aggregates suggest that S-wave seismic anisotropy of phase A-bearing rocks is lower than hydrous subduction zone lithologies such as serpentinites and blueschists. (C) 2015 The Authors. Published by Elsevier B.V.

Elsevier2015

Deformation mechanisms and rheology of serpentines in experiments and in nature

Elodie Adeline Amiguet

Microstructures in serpentine samples recovered from deformation experiments performed at high pressure (1-8 GPa), high temperature (150-500 degrees C), and laboratory strain rates (4 10(-4)-10(-6)s(-1)) were studied using transmission electron microscopy on thin sections prepared by focused ion beam. Lizardite crystals deform by easy glide along the basal planes associated with microkink. This mechanism is associated with a plastic strength of similar to 100MPa that defines the upper bound of lizardite strength in natural conditions. Antigorite crystals deform essentially by conjugated slip along (101) and (10 (1) over bar) planes observed in sections close to (010). This conjugate system results in an apparent global slip system akin to 100. In all samples, delamination and comminution produce fine-grained interconnected regions at grain boundaries because intracrystalline deformation mechanisms are insufficient to satisfy the von Mises criterion. The deformation laws of lizardite (plastic flow) and antigorite (strain rate dependent) differ because of their differing intracrystalline deformation mechanisms. Subgrain boundary geometry in natural samples and 100 crystal preferred orientations indicate the activation of slip systems similar to those observed in experimentally deformed samples, suggesting that the strain rate-dependent rheology of antigorite derived from experiments applies to subduction zone conditions. Delamination of antigorite crystals of a few tens to hundreds of nanometers is not observed in natural samples from subduction zones, suggesting plastic deformation of serpentinites at natural low strain rates and stresses is likely accompanied by recrystallization through dissolution-precipitation processes that act as a low-temperature equivalent of dynamic recrystallization through diffusion at high temperature.

Amer Geophysical Union2014

Coupling and Kinematic properties of Slow Slip Events in the Guerrero Gap, Mexico

Mathilde Edmée Lucette Radiguet de la Bastaie

Large slow slip events (SSEs) occur in the so-called Guerrero Gap, a segment of the Mexican subduction zone where no large earthquake occurred for more than one century. Analyzing the relations between slow slip and earthquakes in this region is a key question to assess the seismic potential of this gap. Permanent GPS networks (IG-UNAM, SSN, GGAP) supplied continuous recordings of three large SSEs in 2001-2002, 2006 and 2009-2010. Each event lasted about one year. Spaceborne radar interferometry (InSAR) is also used for the 2006 event, increasing the spatial constraint on the slip distribution. We perform kinematic inversions of GPS time series for the three slow slip events, including InSAR data for the 2006 SSE. We are using a linearized least-squares inversion procedure assuming a functional form for the slip function. We can thus retrieve the time evolution of slip on the subduction interface. We compare the location and time evolution of the recurrent slow slip events in the Guerrero Gap. We also assess the inter-SSE coupling of this region, inverting the linear inter-SSE GPS displacements. Resolution analyses are performed to assess the reliability of our inversion results. The three analyzed slow slip events have equivalent moment magnitude around 7.5, and stress drops of 0.1-0.2 MPa. The slip propagates with a velocity around 1km/day (2006 SSE). The slip also appears to be shallower than what is observed in most slow slip regions (Cascadia, Nankai…), propagating in the highly coupled part of the subduction zone.

2011

Plasticity of the dense hydrous magnesium silicate phase A at subduction zones conditions

Elodie Adeline Amiguet, Yi Wang

Elsevier2015