Coupled reactions and silica diffusion during serpentinization

Ogasawara, Yuichi; Okamoto, Atsushi; Hirano, Nobuo; Tsuchiya, Noriyoshi

doi:10.1016/j.gca.2013.06.001

Cited by 47 publications

(29 citation statements)

References 53 publications

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“…The XRD and EDS analyses show that the products were composed of serpentine + brucite + magnetite at 1.3 GPa and 400°C (Figures a and a). The serpentine occurred predominantly as fine (<∼5 μm) massive or platy grains that had a close resemblance to previously reported lizardite [ Ogasawara et al ., ]. A subordinate amount of conical crystals (∼5 μm in length) was also present (Figure a); this shape is characteristic of chrysotile.…”

Section: Resultsmentioning

confidence: 94%

Experimental constraints on the serpentinization rate of fore‐arc peridotites: Implications for the upwelling condition of the slab‐derived fluid

Nakatani

Nakamura

2016

Geochem Geophys Geosyst

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To constrain the water circulation in subduction zones, the hydration rates of peridotites were investigated experimentally in fore‐arc mantle conditions. Experiments were conducted at 400–580°C and 1.3 and 1.8 GPa, where antigorite is expected to form as a stable serpentine phase. Crushed powders of olivine ± orthopyroxene and orthopyroxene + clinopyroxene were reacted with 15 wt % distilled water for 4–19 days. The synthesized serpentine varieties were lizardite and aluminous lizardite (Al‐lizardite) in all experimental conditions except those of 1.8 GPa and 580°C in the olivine + orthopyroxene system, in which antigorite was formed. In the olivine + orthopyroxene system, the reactions were interface‐controlled except for the reaction at 400°C, which was transport‐controlled. The corresponding reaction rates were 7.0 × 10−12 to 1.5 × 10−11 m s−1 at 500–580°C and 7.5 × 10−16 m2 s−1 at 400°C for the interface and transport‐controlled reactions, respectively. Based on a simple reaction‐transport model including these hydration rates, we infer that penetration of the slab‐derived fluid all the way through a water‐unsaturated fore‐arc mantle is allowed only when focused flow occurs with a spacing larger than 77–229 km in hot subduction zones such as Nankai and Cascadia. However, the necessary spacing is only 2.3–4.6 m in intermediate‐temperature subduction zones such as Kyushu and Costa Rica. These calculations imply that fluid leakage in hot subduction zones may occur after the fore‐arc mantle is totally hydrated, whereas in intermediate‐temperature subduction zones, leakage through a water‐unsaturated fore‐arc mantle may be facilitated.

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Section: Resultsmentioning

confidence: 94%

Experimental constraints on the serpentinization rate of fore‐arc peridotites: Implications for the upwelling condition of the slab‐derived fluid

Nakatani

Nakamura

2016

Geochem Geophys Geosyst

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“…The example of serpentinization (Figure b), explored more fully in the following section, is illuminating in this respect because treating Al 2 O 3 as immobile results in a

f = 1

whereas an immobile TiO 2 results in an

f

∼ 0.75. Experiments and microstructural evidence show that the serpentinization leads to a volume increase and density decrease [ Evans et al ., ; Kelemen and Hirth , ], but the P‐M diagram shows a loss of most mobile elements what is also supported by laboratory experiments on olivine and pyroxene [ Gresen , 1967; Ogasawara et al ., ]. The magnitude of the volume or density change is thus reflected in the different f ‐values for the immobile elements.…”

Section: Methodsmentioning

confidence: 99%

Tracing mantle‐reacted fluids in magma‐poor rifted margins: The example of Alpine Tethyan rifted margins

Pinto

Manatschal

Karpoff

et al. 2015

Geochem Geophys Geosyst

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The thinning of the crust and the exhumation of subcontinental mantle in magma‐poor rifted margins is accompanied by a series of extensional detachment faults. We show that exhumation along these detachments is intimately related to migration of fluids leading to changes in mineralogy and chemistry of the mantle, crustal, and sedimentary rocks. Using field observation and analytical methods, we investigate the role of fluids in the fossil distal margins of the Alpine Tethys. Using Cr‐Ni‐V, Fe, and Mn as tracers, we show that fluids used detachment faults as pathways and interacted with the overlying crust and sediments. These observations allow us to discuss when, where, and how this interaction happened during the formation of the rifted margin. The results show that: (i) serpentinization of mantle rocks during their exhumation results in the depletion of elements and migration of mantle‐reacted fluids that are channeled along active detachment system; (ii) in earlier‐stages, these fluids affected the overlying syntectonic sediments by direct migration from the underlying detachments;(iii) in later‐stages, these fluids arrived at the seafloor, were introduced into, or “polluted” the seawater and were absorbed by post tectonic sediments. We conclude that a significant amount of serpentinization occurred underneath the hyperextended continental crust, and that the mantle‐reacted fluids might have modified the chemical composition of the sediments and seawater. We propose that the chemical signature of serpentinization related to mantle exhumation is recorded in the sediments and may serve as a proxy to date serpentinization and mantle exhumation at present‐day magma‐poor rifted margins.

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“…For near‐surface serpentinization of olivine it is observed that Ω∼10 7 (Kelemen & Hirth, ), which is large due to the fact that olivine is very far out of equilibrium with water under these conditions. Using the fact that the affinity A =−Δ r G , we may write

\frac{A}{R_{s} T} = \ln normalΩ \sim \ln false(1 0^{7} false) .

Experimentally derived rates of serpentinization in the literature are highly variable (Lafay et al, ; Lamadrid et al, ; Malvoisin et al, ; Martin & Fyfe, ; McCollom et al, ; Ogasawara et al, ; Wegner & Ernst, ) and temperature dependent. Rates in the aforementioned studies range from 10 −10 to 10 −7 mol·m −2 ·s −1 for temperatures in the range of 200–400 °C.…”

Section: Model Setupmentioning

confidence: 99%

A Poroelastic Model of Serpentinization: Exploring the Interplay Between Rheology, Surface Energy, Reaction, and Fluid Flow

2018

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The interactions between reactive fluids and solids are critical in Earth dynamics. Implications of such processes are wide ranging: from earthquake physics to geologic carbon sequestration and the cycling of fluids and volatiles through subduction zones. Peridotite alteration is a common feature in many of these processes, which—despite its obvious importance—is relatively poorly understood from a geodynamical perspective. In particular, although frequently observed in nature, it is still unknown how rocks can undergo 100% hydration/carbonation. One potential explanation of this observation is the mechanism of reaction‐driven cracking: that volume changes associated with these reactions are large enough to fracture the surrounding rock, leading to a positive feedback where new reactive surfaces are exposed and fluid pathways are created. The purpose of this study is to investigate the relative roles of reaction, elastic stresses, and surface tension in alteration reactions. In this regard, we derive a system of equations describing reactive fluid flow in elastically deformable porous media, which we apply to a model of serpentinization in a subseafloor environment. The stoichiometry of the serpentinization reaction predicts net volume reduction of the multiphase system, which, according to our numerical simulations, can lead to failure in tension. We also explore a parameterization of surface energy in the model, which allows fluid to infiltrate regions of dry peridotite, significantly changing the stresses and potentially leading to growing crack fronts.

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Coupled reactions and silica diffusion during serpentinization

Cited by 47 publications

References 53 publications

Experimental constraints on the serpentinization rate of fore‐arc peridotites: Implications for the upwelling condition of the slab‐derived fluid

Experimental constraints on the serpentinization rate of fore‐arc peridotites: Implications for the upwelling condition of the slab‐derived fluid

Tracing mantle‐reacted fluids in magma‐poor rifted margins: The example of Alpine Tethyan rifted margins

A Poroelastic Model of Serpentinization: Exploring the Interplay Between Rheology, Surface Energy, Reaction, and Fluid Flow

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