Evolution of fracture permeability of ultramafic rocks undergoing serpentinization at hydrothermal conditions: An experimental study

Farough, A.; Moore, Diane E.; Lockner, D. A.; Lowell, R. P.

doi:10.1002/2015gc005973

Cited by 52 publications

(44 citation statements)

References 43 publications

(79 reference statements)

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“…For example, it is likely that tectonic and / or flexural stresses related to plate separation and footwall exhumation (e.g., deMartin et al, ) could help drive grain‐scale cracking and the formation of permeable pathways. In addition, alteration reactions such as serpentinization could provide both a source of heat and volumetric stress (Farough et al, ; Germanovich et al, ; Plumper et al, ; Rudge et al, ). While not accounted for in our analytical framework, additional driving stresses could be described as an effective decrease in the critical fracture toughness of the material ( K IC in equation , meaning that for the same amount of cooling at a given pressure, it would be mechanically easier to drive stable cracking.…”

Section: Discussionmentioning

confidence: 99%

Smoke Without Fire: How Long Can Thermal Cracking Sustain Hydrothermal Circulation in the Absence of Magmatic Heat?

Olive

Crone

2018

JGR Solid Earth

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Long‐lived hydrothermal circulation is now well documented along slow and ultraslow spreading mid‐ocean ridges, even though these settings only receive a moderate and intermittent supply of magma. This challenges the notion that hydrothermal convection must be sustained by a continuously replenished magma body. Here we investigate the possibility of sustaining hydrothermal circulation by infrequent magmatic intrusions separated by episodes of downward propagation of small cracks enabling fluids to tap heat from deep hot rocks. We focus on cracks nucleating from grain boundary flaws in response to the buildup of cooling stresses at the base of the convection system. We develop an analytical model describing the stable propagation of a percolation front and the associated heat transfer through hydrothermal circulation. Convection ceases when thermoelastic stresses can no longer overcome lithostatic pressure and hydrothermal circulation can no longer mine heat from underlying units. For lithospheric permeabilities greater than ∼10−15 m2 and over a wide range of grain and flaw sizes, this occurs within ∼100 kyr to ∼1 Myr from the onset of cracking, after the cracking front has moved by a few kilometers. We validate this analytical prediction by developing two‐dimensional numerical models of porous convection subjected to a lower boundary condition representing the dynamics of the cracking front. These models suggest that moderate‐ to low‐temperature hydrothermal venting in off‐axis, ultramafic‐hosted sites does not require an underlying magma sill at all times, but instead repeated sill intrusions every ∼10–100 kyr, which periodically reinvigorate hydrothermal convection without building a continuous crustal section.

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Section: Discussionmentioning

confidence: 99%

Smoke Without Fire: How Long Can Thermal Cracking Sustain Hydrothermal Circulation in the Absence of Magmatic Heat?

Olive

Crone

2018

JGR Solid Earth

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“…The coefficient of internal friction from Eq. 7for a dry mantle decreases from f s = 0.65 (Byerlee, 1978) to f s ∼ 0.35 or 0.45 if peridotite is partly serpentinized (Raleigh and Paterson, 1965;Escartín et al, 1997), leading to γ m between 2.8 and 0.8. However, assuming γ m = 2.8 would lead to an extremely high lithospheric strength (∼ 1 GPa at only 11 km depth) since our rheological model neglects other deformation mechanisms.…”

Section: Parametric Study Derived From Force Balancementioning

confidence: 99%

“…Rocks forming the fault "gouge" are likely to be vertically highly variable in composition, possibly rich in buoyant phases such as serpentine and talc close to the surface (e.g., Cannat et al, 1991) and more depleted in hydrous phases at the deeper level. Below the Moho, down to its deepest portion, the fault may be compounded of a mix between oceanic crust and altered mantle (Cannat et al, 1991;Escartín and Cannat, 1999). The density of the fault gouge is thus likely to increase from the surface toward the deeper part of the fault, from a hydrated gabbro density to a mantle density.…”

Section: Crust and Transform Fault Densitiesmentioning

confidence: 99%

Can subduction initiation at a transform fault be spontaneous?

et al. 2020

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Abstract. We present an extensive parametric exploration of the feasibility of “spontaneous” subduction initiation, i.e., lithospheric gravitational collapse without any external forcing, at a transform fault (TF). We first seek candidates from recent subduction initiation events at an oceanic TF that could fulfill the criteria of spontaneous subduction and retain three natural cases: Izu–Bonin–Mariana, Yap, and Matthew and Hunter. We next perform an extensive exploration of conditions allowing for the spontaneous gravitational sinking of the older oceanic plate at a TF using 2-D thermomechanical simulations. Our parametric study aims at better delimiting the ranges of mechanical properties necessary to achieve the old plate sinking (OPS). The explored parameter set includes the following: crust and TF densities, brittle and ductile rheologies, and the width of the weakened region around the TF. We focus on characterizing the OPS conditions in terms of (1) the reasonable vs. unrealistic values of the mechanical parameters and (2) a comparison to modern cases of subduction initiation in a TF setting. When modeled, OPS initiates following one of two distinct modes, depending mainly on the thickness of the overlying younger plate. The asthenosphere may rise up to the surface above the sinking old plate, provided that the younger plate remains motionless (verified for ages ≥5 Myr, mode 1). For lower younger plate ages (typically ≤2 Myr), the younger plate is dragged toward the older plate, resulting in a double-sided subduction (mode 2). When triggered, spontaneous OPS is extremely fast. The parameters that exert the strongest control over whether OPS can occur or not are the brittle properties of the shallow part of the lithosphere, which affect the plate resistance to bending, the distance away from the TF over which weakening is expected, and the crust density. We find that at least one mechanical parameter has to be assigned an unrealistic value and at least two other ones must be set to extreme ranges to achieve OPS, which we do not consider realistic. Furthermore, we point out inconsistencies between the processes and consequences of lithospheric instability, as modeled in our experiments and geological observations of subduction infancy, for the three natural candidates of subduction initiation by spontaneous OPS. We conclude that spontaneous instability of the thick older plate at a TF evolving into mature subduction is an unlikely process of subduction initiation in modern Earth conditions.

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“…S1 in the supporting information) for which OPS is modelled for a broad ranges of plate ages (see for instance diagrams 6g-h), in agreement with Dymkova and 10 Gerya's results. However the low permeabilities assumed by Dymkova and Gerya (2013) are questioned by recent experiments of mantle hydration at ridge or water percolation in a peridotite, and by estimates from a peridotite aquifer (Godard et al, 2013;Farough et al, 2016;Dewandel et al, 2004). These studies rather infer permeabilities encompassed between 10 −19 and 10 −16 m 2 , that would hamper high pore fluid pressures and eventually, plate bending.…”

Section: Model Limitationsmentioning

confidence: 99%

Can subduction initiation at a transform fault be spontaneous?

Arcay¹,

Lallemand²,

Abecassis³

et al. 2019

Preprint

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Abstract. We propose a new exploration of the concept of spontaneous subduction, i.e., lithospheric gravitational collapse without any external forcing, at a transform fault (TF). We first seek candidates in recent subduction initiations at a TF that could fulfill the criteria of spontaneous subduction and retain 3 natural cases: Izu-Bonin-Mariana (IBM), Yap, and Matthew & Hunter. We next perform an extensive exploration of conditions allowing spontaneous gravitational sinking of the older plate in a oceanic TF using 2D thermo-mechanical simulations. Our parametric study aims at better deliminating the ranges of mechanical properties necessary to achieve the old plate sinking (OPS). The explored parameter set includes: crust and TF densities, brittle and ductile rheologies, and width of the weakened region around the TF. We focus on characterising OPS conditions in terms on (1) reasonable vs unrealistic values of mechanical parameters and (2) comparison to modern cases of subduction initiation in a TF setting. When modelled, OPS initiates following one of two distinct modes, depending mainly on the thickness of the overlying younger plate (YP). Asthenosphere may rise up to the surface above the sinking old plate provided that the YP remains motionless (verified for ages ≥ 5 Myr, mode 1). For lower YP ages (typically ≤ 2 Myr), the YP is dragged towards the OP resulting in a double-sided subduction (mode 2). When triggered, spontaneous OPS is extremely fast. The basic parameters to simulate OPS are the brittle properties of the shallow part of the lithosphere, controlling the plate resistance to bending, the distance away from the TF over which weakening is expected, and crust density. We find that all mechanical parameters have to be assigned extreme values to achieve OPS, that we consider as irrelevant. Furthermore, we point out inconsistencies between the processes and consequences of lithospheric instability as modelled in our experiments and geological observations of subduction infancy for the 3 natural candidates of subduction initiation by spontaneous OPS. We conclude that spontaneous instability of the thick OP at a TF evolving into mature subduction is an unlikely process of subduction initiation at modern Earth conditions.

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Evolution of fracture permeability of ultramafic rocks undergoing serpentinization at hydrothermal conditions: An experimental study

Cited by 52 publications

References 43 publications

Smoke Without Fire: How Long Can Thermal Cracking Sustain Hydrothermal Circulation in the Absence of Magmatic Heat?

Smoke Without Fire: How Long Can Thermal Cracking Sustain Hydrothermal Circulation in the Absence of Magmatic Heat?

Can subduction initiation at a transform fault be spontaneous?

Can subduction initiation at a transform fault be spontaneous?

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