Structure and serpentinization of the subducting Cocos plate offshore Nicaragua and Costa Rica

Avendonk, H. J. Van; Holbrook, W. S.; Lizarralde, D.; Denyer, Percy

doi:10.1029/2011gc003592

Cited by 138 publications

(204 citation statements)

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“…Extensional earthquakes in the Western Aleutians and Southern Bonin subduction zones can occur at 20 km below the crust, suggesting partial serpentinization at this depth (29). Seismic exploration has found a 12-km-thick serpentinized mantle beneath the Cocos plate offshore Costa Rica (30), although it is still unclear whether this amount of hydration layer is universal or not. We, therefore, tested three cases with different degrees of hydration.…”

Section: Resultsmentioning

confidence: 99%

Hydration-reduced lattice thermal conductivity of olivine in Earth’s upper mantle

Chang

Hsieh

Tan

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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Earth's water cycle enables the incorporation of water (hydration) in mantle minerals that can influence the physical properties of the mantle. Lattice thermal conductivity of mantle minerals is critical for controlling the temperature profile and dynamics of the mantle and subducting slabs. However, the effect of hydration on lattice thermal conductivity remains poorly understood and has often been assumed to be negligible. Here we have precisely measured the lattice thermal conductivity of hydrous San Carlos olivine (Mg 0.9 Fe 0.1 ) 2 SiO 4 (Fo90) up to 15 gigapascals using an ultrafast optical pump−probe technique. The thermal conductivity of hydrous Fo90 with ∼7,000 wt ppm water is significantly suppressed at pressures above ∼5 gigapascals, and is approximately 2 times smaller than the nominally anhydrous Fo90 at mantle transition zone pressures, demonstrating the critical influence of hydration on the lattice thermal conductivity of olivine in this region. Modeling the thermal structure of a subducting slab with our results shows that the hydration-reduced thermal conductivity in hydrated oceanic crust further decreases the temperature at the cold, dry center of the subducting slab. Therefore, the olivine−wadsleyite transformation rate in the slab with hydrated oceanic crust is much slower than that with dry oceanic crust after the slab sinks into the transition zone, extending the metastable olivine to a greater depth. The hydration-reduced thermal conductivity could enable hydrous minerals to survive in deeper mantle and enhance water transportation to the transition zone.hydration | thermal conductivity | geodynamics | metastable olivine | subducting slab H 2 O plays a critical role in driving and affecting many geophysical phenomena and dynamic processes in Earth's interior (1-3). It has been suggested that olivine, a primary mineral in the upper mantle, and its high-pressure polymorphs (wadsleyite and ringwoodite) could store a large amount of water (hydrogen ions) in their crystalline defects and act as a major water reservoir within Earth (2-4). Incorporation of water in these mantle minerals has been shown to influence their physical properties (5-12) and the dynamics of the mantle and subducting slabs (13). In particular, water enrichment could influence the minerals' thermal transport properties, which, in turn, alters the temperature gradient in the mantle and subducting slabs. At the center of subducting slabs, the cold temperature inhibits the olivine−wadsleyite/ringwoodite phase transformation (14). A thin wedge of olivine could therefore persist in a metastable state far below the 410-km depth. Previous experiments on transformation kinetics have shown that the presence of water inside the slabs greatly enhances the olivine−wadsleyite/ ringwoodite transformation rate under the same pressure and temperature conditions (15-18). However, the hydration effect on the lattice thermal conductivity of mantle minerals and its consequential influence on the temperature inside the slabs that also contro...

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Section: Resultsmentioning

confidence: 99%

Hydration-reduced lattice thermal conductivity of olivine in Earth’s upper mantle

Chang

Hsieh

Tan

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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“…However, an additional water source can be provided by the dehydration of hydrous minerals in the oceanic mantle lithosphere. Seismic exploration has found evidence of serpentinite under the oceanic Moho in the Central America subduction zone (Van Avendonk et al 2011). The sub-Moho serpentinite is subjected to less heating and remains stable at greater depth.…”

Section: Deep Hydrationmentioning

confidence: 99%

Mantle wedge serpentinization effects on slab dips

Tan¹

2017

Terr. Atmos. Ocean. Sci.

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The mechanical coupling between a subducting slab and the overlying mantle wedge is an important factor in controlling the subduction dip angle and the flow in mantel wedge. This paper investigates the role of the amount of mantle serpentinization on the subduction zone evolution. With numerical thermos-mechanical models with elasto-visco-plastic rheology, we vary the thickness and depth extent of mantle serpentinization in the mantle wedge to control the degree of coupling between the slab and mantle wedge. A thin serpentinized mantle layer is required for stable subduction. For models with stable subduction, we find that the slab dip is affected by the down-dip extent and the mantle serpentinization thickness. A critical down-dip extent exists in mantle serpentinization, determined by the thickness of the overriding lithosphere. If the down-dip extent does not exceed the critical depth, the slab is partially coupled to the overriding lithosphere and has a constant dip angle regardless of the mantle serpentinization thickness. However, if the down-dip extent exceeds the critical depth, the slab and the base of the overriding lithosphere would be separated and decoupled by a thick layer of serpentinized peridotite. This allows further slab bending and results in steeper slab dip. Increasing mantle serpentinization thickness will also result in larger slab dip. We also find that with weak mantle wedge, there is no material flowing from the asthenosphere into the serpentinized mantle wedge. All of these results indicate that serpentinization is an important ingredient when studying the subduction dynamics in the mantle wedge.

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“…Offshore central Nicaragua, a velocity decrease of 5-7% in the uppermost 3-4 km of the mantle was found seaward of the outer trench rise, indicating increasing crack density and/or systematic serpentinization of 12-17% (1.55-2.17 wt% water) [Ivandic et al, 2008]. On a trench parallel (15-20 km from the trench) profile over the Cocos plate, van Avendonk et al [2011] estimate ~1 wt% water content in the lower crust offshore Nicaragua, and uppermost mantle serpentinization of up to 30% (3.5 wt% water) offshore central and northwestern Nicaragua and 8-17% (1-2 wt% water) in the southeast. South-Central Chile similarly displays a decrease in upper mantle velocities in the trench and outer-rise area.…”

Section: Introductionmentioning

confidence: 99%

“…Low seismic velocities near the Chile and Nicaragua trenches have been used to estimate the extent of hydration of the incoming mantle [e.g., Contreras-Reyes et al, 2007;Ivandic et al, 2008;van Avendonk et al, 2011]. Offshore central Nicaragua, a velocity decrease of 5-7% in the uppermost 3-4 km of the mantle was found seaward of the outer trench rise, indicating increasing crack density and/or systematic serpentinization of 12-17% (1.55-2.17 wt% water) [Ivandic et al, 2008].…”

Section: Introductionmentioning

confidence: 99%

“…As the plate descends, metamorphic dehydration reactions resulting from increasing pressure and temperature [van Keken et al, 2011] provide a mechanism for significant delivery of water at depth [Kawakatsu and Watada, 2007]. Free water and the presence of hydrous phases in the subducting slab both affect a number of subduction zone processes such as [Hacker et al, 2003]: (1) The presence of serpentine decreases the shear strength of peridotite [Escartín et al, 2001], affecting the rheology of the mantle wedge [Billen and Gurnis, 2001]; (2) Episodic tremor and slip (ETS) events have been linked to fluid overpressures at and above the plate interface [Obara, 2002;Rogers and Dragert, 2003];…”

Section: Introductionmentioning

confidence: 99%

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Geophysical and geochemical constraints on the evolution of oceanic lithosphere from formation to subduction

Horning¹

2017

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This thesis investigates the evolution of the oceanic lithosphere in a broad sense from formation to subduction, in a focused case at the ridge, and in a focused case proximal to subduction. In general, alteration of the oceanic lithosphere begins at the ridge through focused and diffuse hydrothermal flow, continues off axis through low temperature circulation, and may occur approaching subduction zones as bending related faulting provides fluid pathways. In Chapter 2 I use a dataset of thousands of microearthquakes recorded at the Rainbow massif on the Mid-Atlantic Ridge to characterize the processes which are responsible for the long-term, high-temperature, hydrothermal discharge found hosted in this oceanic core complex. I find that the detachment fault responsible for the uplift of the massif is inactive and that the axial valleys show no evidence for faulting or active magma intrusion. I conclude that the continuous, low-magnitude seismicity located in diffuse pattern in a region with seismic velocities indicating ultramafic host rock suggests that serpentinization may play a role in microearthquake generation but the seismic network was not capable of providing robust focal mechanism solutions to constrain the source characteristics. In Chapter 3 I find that the Juan de Fuca plate, which represents the young/hot end-member of oceanic plates, is lightly hydrated at upper crustal levels except in regions affected by propagator wakes where hydration of lower crust and upper mantle is evident. I conclude that at the subduction zone the plate is nearly dry at upper mantle levels with the majority of water contained in the crust. Finally, in Chapter 4 I examine samples of cretaceous age serpentinite sampled just before subduction at the Puerto Rico Trench. I show that these upper mantle rocks were completely serpentinized under static conditions at the Mid-Atlantic Ridge. Further, they subsequently underwent 100 Ma of seafloor weathering wherein the alteration products of serpentinization themselves continue to be altered. I conclude that complete hydration of the upper mantle is not the end point in the evolution of oceanic lithosphere as it spreads from the axis to subduction. Chapter 1: IntroductionThe total water content of the oceanic lithosphere is the sum of the free water in pore spaces in the sedimentary cover and highly porous upper crust, chemically bound water in sediment clay minerals, chemically bound water in the upper and lower crust resulting from the precipitation of secondary hydrous alteration products, free water in fault zones, and bound water of hydrous minerals in the uppermost mantle resulting from serpentinization of peridotite. This thesis is focused on characterizing the location, extent, and timing of the processes that result in this alteration of the lithosphere.In Chapter 2 I focus on the alteration that occurs in the near axis region at an oceanic core complex located on the slow spreading Mid-Atlantic Ridge. At the Rainbow massif long-lived high-T hydrothermal venting h...

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Structure and serpentinization of the subducting Cocos plate offshore Nicaragua and Costa Rica

Cited by 138 publications

References 120 publications

Hydration-reduced lattice thermal conductivity of olivine in Earth’s upper mantle

Hydration-reduced lattice thermal conductivity of olivine in Earth’s upper mantle

Mantle wedge serpentinization effects on slab dips

Geophysical and geochemical constraints on the evolution of oceanic lithosphere from formation to subduction

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