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Effect of water activity on rates of serpentinization of olivine.

ABSTRACT: The hydrothermal alteration of mantle rocks (referred to as serpentinization) occurs in submarine environments extending from mid-ocean ridges to subduction zones. Serpentinization affects the physical and chemical properties of oceanic lithosphere, represents one of the major mechanisms driving mass exchange between the mantle and the Earth's surface, and is central to current origin of life hypotheses as well as the search for microbial life on the icy moons of Jupiter and Saturn. In spite of increasing interest in the serpentinization process by researchers in diverse fields, the rates of serpentinization and the controlling factors are poorly understood. Here we use a novel in situ experimental method involving olivine micro-reactors and show that the rate of serpentinization is strongly controlled by the salinity (water activity) of the reacting fluid and demonstrate that the rate of serpentinization of olivine slows down as salinity increases and H₂O activity decreases.

SUBMITTER: Lamadrid HM

PROVIDER: S-EPMC5594423 | biostudies-literature | 2017 Jul

REPOSITORIES: biostudies-literature

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Effect of water activity on rates of serpentinization of olivine.

Lamadrid Hector M HM Rimstidt J Donald JD Schwarzenbach Esther M EM Klein Frieder F Ulrich Sarah S Dolocan Andrei A Bodnar Robert J RJ

Nature communications 20170714

The hydrothermal alteration of mantle rocks (referred to as serpentinization) occurs in submarine environments extending from mid-ocean ridges to subduction zones. Serpentinization affects the physical and chemical properties of oceanic lithosphere, represents one of the major mechanisms driving mass exchange between the mantle and the Earth's surface, and is central to current origin of life hypotheses as well as the search for microbial life on the icy moons of Jupiter and Saturn. In spite of ...[more]

PMID: 28706268

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Project description:We report the results of experiments designed to separate the effects of temperature and pressure from liquid composition on the partitioning of Ni between olivine and liquid, [Formula: see text]. Experiments were performed from 1300 to 1600 °C and 1 atm to 3.0 GPa, using mid-ocean ridge basalt (MORB) glass surrounded by powdered olivine in graphite-Pt double capsules at high pressure and powdered MORB in crucibles fabricated from single crystals of San Carlos olivine at one atmosphere. In these experiments, pressure and temperature were varied in such a way that we produced a series of liquids, each with an approximately constant composition (~12, ~15, and ~21 wt% MgO). Previously, we used a similar approach to show that [Formula: see text] for a liquid with ~18 wt% MgO is a strong function of temperature. Combining the new data presented here with our previous results allows us to separate the effects of temperature from composition. We fit our data based on a Ni-Mg exchange reaction, which yields [Formula: see text] Each subset of constant composition experiments displays roughly the same temperature dependence of [Formula: see text] (i.e.,[Formula: see text]) as previously reported for liquids with ~18 wt% MgO. Fitting new data presented here (15 experiments) in conjunction with our 13 previously published experiments (those with ~18 wt% MgO in the silicate liquid) to the above expression gives [Formula: see text] = 3641 ± 396 (K) and [Formula: see text] = - 1.597 ± 0.229. Adding data from the literature yields [Formula: see text] = 4505 ± 196 (K) and [Formula: see text] = - 2.075 ± 0.120, a set of coefficients that leads to a predictive equation for [Formula: see text] applicable to a wide range of melt compositions. We use the results of our work to model the melting of peridotite beneath lithosphere of varying thickness and show that: (1) a positive correlation between NiO in magnesian olivine phenocrysts and lithospheric thickness is expected given a temperature-dependent [Formula: see text] and (2) the magnitude of the slope for natural samples is consistent with our experimentally determined temperature dependence. Alternative processes to generate the positive correlation between NiO in magnesian olivines and lithospheric thickness, such as the melting of olivine-free pyroxenite, are possible, but they are not required to explain the observed correlation of NiO concentration in initially crystallizing olivine with lithospheric thickness.

Dataset Information

Effect of water activity on rates of serpentinization of olivine.

Publications

Effect of water activity on rates of serpentinization of olivine.

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