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Fluids in the Crust. Experimental constraints on fluid-rock reactions during incipient serpentinization of harzburgite

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Published/Copyright: April 3, 2015
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American Mineralogist
From the journal American Mineralogist Volume 100 Issue 4

Abstract

The exposure of mantle peridotite to water at crustal levels leads to a cascade of interconnected dissolution-precipitation and reduction-oxidation reactions-a process referred to as serpentinization. These reactions have major implications for microbial life through the provision of hydrogen (H2). To simulate incipient serpentinization under well-constrained conditions, we reacted centimeter-sized pieces of uncrushed harzburgite with chemically modified seawater at 300 °C and 35 MPa for ca. 1.5 yr (13 441 h), monitored changes in fluid chemistry over time, and examined the secondary mineralogy at the termination of the experiment. Approximately 4 mol% of the protolith underwent alteration forming serpentine, accessory magnetite, chlorite, and traces of calcite and heazlewoodite. Alteration textures bear remarkable similarities to those found in partially serpentinized abyssal peridotites. Neither brucite nor talc precipitated during the experiment. Given that the starting material contained ~4 times more olivine than orthopyroxene on a molar basis, mass balance requires that dissolution of orthopyroxene was significantly faster than dissolution of olivine. Coupled mass transfer of dissolved Si, Mg, and H+ between olivine and orthopyroxene reaction fronts was driven by steep activity gradients and facilitated the precipitation of serpentine. Hydrogen was released in significant amounts throughout the entire experiment; however, the H2 release rate decreased with time. Serpentinization consumed water but did not release significant amounts of dissolved species (other than H2) suggesting that incipient hydration reactions involved a volume increase of ~40%. The reduced access of water to fresh olivine surfaces due to filling of fractures and coating of primary minerals with alteration products led to decreased rates of serpentinization and H2 release. While this concept might seem at odds with completely serpentinized seafloor peridotites, reaction-driven fracturing offers an intriguing solution to the seemingly self-limiting nature of serpentinization. Indeed, the reacted sample revealed several textural features diagnostic of incipient reaction-driven fracturing. We conclude that fracturing must have far reaching impacts on the rates of serpentinization and H2 release in peridotite-hosted hydrothermal systems.

Keywords : Serpentinization; phase relations; reaction rates; reaction pathways; fracturing; hydrogen; hydrothermal experiment
Received: 2014-7-3
Accepted: 2014-10-15
Published Online: 2015-4-3
Published in Print: 2015-4-1

© 2015 by Walter de Gruyter Berlin/Boston

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https://doi.org/10.2138/am-2015-5112
Keywords for this article
Serpentinization; phase relations; reaction rates; reaction pathways; fracturing; hydrogen; hydrothermal experiment

Articles in the same Issue

  1. Highlights and Breakthroughs. Clays are messy—also on Mars
  2. Highlights and Breakthroughs. Tweed, Twins, and Holes: A link between mineralogy and materials science
  3. Highlights and Breakthroughs. Bursting the bubble of melt inclusions
  4. Review. Mineralogy, materials science, energy, and environment: A 2015 perspective
  5. Crossroads in Earth and Planetary Materials. Block-by-block and layer-by-layer growth modes in coral skeletons
  6. Roebling Medal Paper. Toward theoretical mineralogy: A bond-topological approach
  7. Investigating Petrologic Indicators of Magmatic Processes in Volcanic Rocks. Petalite under pressure: Elastic behavior and phase stability
  8. Investigating Petrologic Indicators of Magmatic Processes in Volcanic Rocks. Pre-eruptive magma mixing and crystal transfer revealed by phenocryst and microlite compositions in basaltic andesite from the 2008 eruption of Kasatochi Island volcano
  9. What Lurks in the Martian Rocks and Soil? Investigations of Sulfates, Phosphates, and Perchlorates. Akaganéite and schwertmannite: Spectral properties and geochemical implications of their possible presence on Mars
  10. Special Collection: Mechanisms, Rates, and Timescales of Geochemical Transport Processes in the Crust and Mantle. Timescales of exhumation and cooling inferred by kinetic modeling: An example using a lamellar garnet pyroxenite from the Variscan Granulitgebirge, Germany
  11. Special Collection: Glasses, Melts, and Fluids, as Tools for Understanding Volcanic Processes and Hazards. Constraints on the origin of sub-effusive nodules from the Sarno (Pomici di Base) eruption of Mt. Somma-Vesuvius (Italy) based on compositions of silicate-melt inclusions and clinopyroxene
  12. Special Collection: Glasses, Melts, and Fluids, as Tools for Understanding Volcanic Processes and Hazards. Experiments and models on H2O retrograde solubility in volcanic systems
  13. Special Collection: Glasses, Melts, and Fluids, as Tools for Understanding Volcanic Processes and Hazards. Melt inclusion CO2 contents, pressures of olivine crystallization, and the problem of shrinkage bubbles
  14. Special Collection: Glasses, Melts, and Fluids, as Tools for Understanding Volcanic Processes and Hazards. Spatio-temporal constraints on magma storage and ascent conditions in a transtensional tectonic setting: The case of the Terceira Island (Azores)
  15. Special Collection: Glasses, Melts, and Fluids, as Tools for Understanding Volcanic Processes and Hazards. Bubbles matter: An assessment of the contribution of vapor bubbles to melt inclusion volatile budgets
  16. The origin and implications of clay minerals from Yellowknife Bay, Gale crater, Mars
  17. The whole-block approach to measuring hydrogen diffusivity in nominally anhydrous minerals
  18. Atom probe tomography of isoferroplatinum
  19. Structural investigation of (130) twins and rutile precipitates in chrysoberyl crystals from Rio das Pratinhas in Bahia (Brazil)
  20. Carbon speciation in silicate-C-O-H melt and fluid as a function of redox conditions: An experimental study, in situ to 1.7 GPa and 900 °C
  21. Kinetic behavior of partially dehydroxylated kaolinite
  22. The fall and rise of metamorphic zircon
  23. Eckermannite revised: The new holotype from the Jade Mine Tract, Myanmar—crystal structure, mineral data, and hints on the reasons for the rarity of eckermannite
  24. In-situ oxygen isotope and trace element geothermometry of rutilated quartz from Alpine fissures
  25. Synchrotron micro-spectroscopic examination of Indonesian nickel laterites
  26. Density functional investigation of the thermo-physical and thermo-chemical properties of 2M1 muscovite
  27. Complex IR spectra of OH– groups in silicate glasses: Implications for the use of the 4500 cm–1 IR peak as a marker of OH– groups concentration
  28. Versatile Monazite: Resolving Geological Records and Solving Challenges in Materials Science. Monazite, zircon, and garnet growth in migmatitic pelites as a record of metamorphism and partial melting in the East Humboldt Range, Nevada
  29. The Second Conference on the Lunar Highlands Crust and New Directions. Revised mineral and Mg# maps of the Moon from integrating results from the Lunar Prospector neutron and gamma-ray spectrometers with Clementine spectroscopy
  30. The Second Conference on the Lunar Highlands Crust and New Directions. Low-pressure crystallization of a volatile-rich lunar basalt: A means for producing local anorthosites?
  31. Fluids in the Crust. Experimental constraints on fluid-rock reactions during incipient serpentinization of harzburgite
  32. Minerals in the human body. Crystal chemical and structural modifications of erionite fibers leached with simulated lung fluids
  33. Letter. Competition between two redox states in silicate melts: An in-situ experiment at the Fe K-edge and Eu L3-edge
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