Effect of water activity on rates of serpentinization of olivine

Hector M Lamadrid,Sarah Ulrich,Esther M Schwarzenbach,Robert J Bodnar,Frieder Klein,Andrei Dolocan,J Donald Rimstidt

doi:10.1038/ncomms16107

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.

Highlights

The hydrothermal alteration of mantle rocks occurs in submarine environments extending from mid-ocean ridges to subduction zones
Serpentinization encompasses a series of hydration reactions that occur when ultramafic rocks are exposed to circulating aqueous fluids at temperatures lower than B400 °C, leading to the formation of serpentine phases±brucite±talc±magnetite, among other minerals[1]
Despite the pivotal role that serpentinization plays in a number of geological and biological processes and its central role in current origin of life hypotheses[16,17,18,19], few experimental studies have attempted to determine the rates of serpentinization reactions and the rates that have been reported diverge widely[20,21,22,23,24,25]

Summary

Introduction

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. 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. Serpentinization affects the chemical composition, rheology, magnetic properties, seismic structure and habitability of the shallow lithosphere at slow- and ultraslow-spreading mid-ocean ridges, continental margins and forearc settings of subduction zones[2,3,4,5,6,7,8]. The micro-reactor technique presents several advantages and permits monitoring mineral precipitation and water activity in situ and in real time

Methods

Results

Conclusion