Cascadia subducting plate fluids channelled to fore‐arc mantle corner: ETS and silica deposition

Hyndman, R. D.; McCrory, Patricia A.; Wech, A.; Kao, H.; Ague, Jay J.

doi:10.1002/2015jb011920

Cited by 116 publications

(129 citation statements)

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“…This flux of fluids is inferred from low Vp/Vs values found above the mantle wedge corner within the overlying crust, which may be explained by the precipitation of silica into quartz veins. This model is also consistent with the bulk of tremor activity occurring near the mantle wedge corner in most subduction zones studied here (i.e., Cascadia, southwest Japan, Costa Rica and Alaska), producing a gap in seismogenic behaviour of the megathrust as opposed to a smooth transition from unstable to stable sliding (Hyndman et al, 2015). Alternatively, serpentinites (in particular antigorites) have much lower viscosity than that of major mantle-…”

Section: Accepted M Manuscriptsupporting

confidence: 64%

“…updip edge of the main ETS zone also appears to be located approximately 70 km downdip of the seismogenic zone and around the mantle wedge corner (Hyndman et al, 2015), which suggests that fluids rising above the forearc mantle corner and along the plate interface may be responsible for ETS.…”

Section: Accepted M Manuscriptmentioning

confidence: 98%

“…Both deep slow slip and tremor generally occur near but downdip of the brittle-ductile transition, approximately coinciding with the transition from unstable to stable sliding in a region of conditional stability (e.g., Scholz, 1998;Fig. 1), although there may be a gap between the slow earthquake source region and the seismogenic zone in some cases (Hyndman et al, 2015). Their occurrence may be induced by fluid flow and fluid processes at the plate interface and within the overlying plate (Rubinstein et al, 2010, and references therein).…”

Section: Accepted M Manuscriptmentioning

confidence: 99%

“…Cascadia the segmentation of ETS along strike correlates qualitatively with the overriding forearc A C C E P T E D M A N U S C R I P T crust Vp/Vs with increasing depth to the plate interface, interpreted as a progressive enrichment in quartz content due to the strong temperature-dependent solubility of silica in slab-derived fluids (Manning, 1994) and its the precipitation into quartz veins into the upper continental crust (Hyndman et al, 2015). Such quartz enrichment requires significant amounts of silica-rich sediments that are entrained into the subduction zone.…”

Section: Structural Controls On Deep Slow Earthquake Recurrencementioning

confidence: 99%

“…Serpentinites, in particular lizardite that is stable at low pressure and temperature conditions, incorporate significant amounts of water in their crystal structure, and may act to focus fluids near the mantle wedge corner in close proximity to the slow earthquake source region (Katayama et al, 2012). In a related but contrasting model, Hyndman et al (2015) propose that the low permeability of sheared serpentinites blocks the vertical expulsion of fluids from the dehydrating oceanic crust and restricts flow along the plate interface. Upon reaching the mantle wedge corner, the fluids are released into the more permeable overlying forearc crust.…”

Section: Accepted M Manuscriptmentioning

confidence: 99%

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Teleseismic constraints on the geological environment of deep episodic slow earthquakes in subduction zone forearcs: A review

2016

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More than a decade after the discovery of deep episodic slow slip and tremor, or slow earthquakes, at subduction zones, much research has been carried out to investigate the structural and seismic properties of the environment in which they occur. Slow earthquakes generally occur on the megathrust fault some distance downdip of the great earthquake seismogenic zone in the vicinity of the mantle wedge corner, where three major structural elements are in contact: the subducting oceanic crust, the overriding forearc crust and the continental mantle. In this region, thermo-petrological models predict significant fluid production from the dehydrating oceanic crust and mantle due to prograde metamorphic reactions, and their consumption by hydrating the mantle wedge. These fluids are expected to affect the dynamic stability of the megathrust fault and enable slow slip by increasing pore-fluid pressure and/or reducing friction in fault gouges.Resolving the fine-scale structure of the deep megathrust fault and the in situ distribution of fluids where slow earthquakes occur is challenging, and most advances have been made using A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPTteleseismic scattering techniques (e.g., receiver functions). In this paper we review the teleseismic structure of six well-studied subduction zones (three hot, i.e., Cascadia, southwest Japan, central Mexico, and three cool, i.e., Costa Rica, Alaska, and Hikurangi) that exhibit slow earthquake processes and discuss the evidence of structural and geological controls on the slow earthquake behavior. We conclude that changes in the mechanical properties of geological materials downdip of the seismogenic zone play a dominant role in controlling slow earthquake behavior, and that near-lithostatic pore-fluid pressures near the megathrust fault may be a necessary but insufficient condition for their occurrence.

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Section: Accepted M Manuscriptsupporting

confidence: 64%

Section: Accepted M Manuscriptmentioning

confidence: 98%

Section: Accepted M Manuscriptmentioning

confidence: 99%

Section: Structural Controls On Deep Slow Earthquake Recurrencementioning

confidence: 99%

Section: Accepted M Manuscriptmentioning

confidence: 99%

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Teleseismic constraints on the geological environment of deep episodic slow earthquakes in subduction zone forearcs: A review

2016

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Helium as a tracer for fluids released from Juan de Fuca lithosphere beneath the Cascadia forearc

McCrory

Constantz

Hunt

et al. 2016

Geochem Geophys Geosyst

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Helium isotopic ratios (3He/4He) observed in 25 mineral springs and wells above the Cascadia forearc provide a marker for fluids derived from Juan de Fuca lithosphere. This exploratory study documents a significant component of mantle‐derived helium within forearc springs and wells, and in turn, documents variability in helium enrichment across the Cascadia forearc. Sample sites arcward of the forearc mantle corner generally yield significantly higher ratios (∼1.2–4.0 RA) than those seaward of the corner (∼0.03–0.7 RA). 3He detected above the inner forearc mantle wedge may represent a mixture of both oceanic lithosphere and forearc mantle sources, whereas 3He detected seaward of the forearc mantle corner likely has only an oceanic source. The highest ratios in the Cascadia forearc coincide with slab depths (∼40–45 km) where metamorphic dehydration of young oceanic lithosphere is expected to release significant fluid and where tectonic tremor occurs, whereas little fluid is expected to be released from the slab depths (∼25–30 km) beneath sites seaward of the corner. These observations provide independent evidence that tremor is associated with deep fluids, and further suggest that high pore pressures associated with tremor may serve to keep fractures open for 3He migration through the ductile upper mantle and lower crust.

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Modeling slow‐slip segmentation in Cascadia subduction zone constrained by tremor locations and gravity anomalies

Liu

2017

JGR Solid Earth

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Along‐strike segmentation of slow‐slip events (SSEs) and nonvolcanic tremors in Cascadia may reflect heterogeneities of the subducting slab or overlying continental lithosphere. However, the nature behind this segmentation is not fully understood. We develop a 3‐D model for episodic SSEs in northern and central Cascadia, incorporating both seismological and gravitational observations to constrain the heterogeneities in the megathrust fault properties. The 6 year automatically detected tremors are used to constrain the rate‐state friction parameters. The effective normal stress at SSE depths is constrained by along‐margin free‐air and Bouguer gravity anomalies. The along‐strike variation in the long‐term plate convergence rate is also taken into consideration. Simulation results show five segments of ∼Mw6.0 SSEs spontaneously appear along the strike, correlated to the distribution of tremor epicenters. Modeled SSE recurrence intervals are equally comparable to GPS observations using both types of gravity anomaly constraints. However, the model constrained by free‐air anomaly does a better job in reproducing the cumulative slip as well as more consistent surface displacements with GPS observations. The modeled along‐strike segmentation represents the averaged slip release over many SSE cycles, rather than permanent barriers. Individual slow‐slip events can still propagate across the boundaries, which may cause interactions between adjacent SSEs, as observed in time‐dependent GPS inversions. In addition, the moment‐duration scaling is sensitive to the selection of velocity criteria for determining when SSEs occur. Hence, the detection ability of the current GPS network should be considered in the interpretation of slow earthquake source parameter scaling relations.

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Cascadia subducting plate fluids channelled to fore‐arc mantle corner: ETS and silica deposition

Cited by 116 publications

References 115 publications

Teleseismic constraints on the geological environment of deep episodic slow earthquakes in subduction zone forearcs: A review

Teleseismic constraints on the geological environment of deep episodic slow earthquakes in subduction zone forearcs: A review

Helium as a tracer for fluids released from Juan de Fuca lithosphere beneath the Cascadia forearc

Modeling slow‐slip segmentation in Cascadia subduction zone constrained by tremor locations and gravity anomalies

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