A five-day workshop held on the island of Porquerolles off the southern French coast in September 2012 brought together ninety scientists from twelve countries to discuss the role of serpentinization in carbon fluxes and as an energy source for deep ecosystems. Serpentinization occurs along mid-ocean ridges, in ophiolites, and also in geological settings where warm water reacts with ultramafic rocks. This process has been also observed in subduction zones, along active faults, within terrains more than three billion years old, in meteorites, and more recently on the surface of Mars. The presence of serpentinite minerals has even been hypothesized in other extraterrestrial bodies like the core of icy satellites like Titan.
In recent years, the consequences of serpentinization, a process that releases large amounts of hydrogen, methane, and other complex organic carbon molecules, have been recognized to be much greater than previously thought, both now and in the geologic past. The effects of this process on physical properties, geodynamics, and chemical cycles – especially carbon cycles – have led some to describe serpentinization as the most important reaction in the solar system.
The Serpentine Days workshop featured presentations of the most recent results on serpentinization, serpentine minerals, serpentinites, and associated organic matter and fluids.
Some highlights of the workshop:
• Serpentinites are recognized as the major component of the oceanic lithosphere formed at slow spreading ridges, and are therefore significant contributors to chemical and heat transfer through hydrothermal activity at mid-ocean ridges, and to the input budget in subduction zones. Ocean serpentinites are associated with a large and varied number of organic and inorganic, biotic and abiotic carbon species in both the oxidized and reduced forms. Investigating the component of Earth’s carbon cycle associated with serpentinization from mid-ocean ridges to subduction zones is a great geological and instrumental challenge.
• Serpentinites are abundant in subduction zones; they have density and viscosity that is low enough to facilitate the exhumation of high-pressure and ultra high-pressure metamorphic rocks and to accommodate silent earthquake, slow slip events, and post-seismic creep. Still, the serpentine channel is probably thin, less that 2km wide, and possibly below seismic resolution. Studies of serpentinite geochemistry show that they originate from serpentinization of the mantle rocks and act like sponges for the fluid mobile elements that circulate in subduction zones.
• The Lost City hydrothermal vent field was the first site at which researchers studied the affinity of primordial ecosystems for hydrothermal sites sustained by serpentinization and subsequent hydrogen gas (H2) and methane (CH4) production. Since then, this research has been extended to almost all types of continental and oceanic ultramafic exposures from the Precambrian shields to active ridges. Those ecosystems are generally characterized by a low biomass and a low biodiversity, with closely related microorganisms that may be as old as 2 billion years old. The early serpentinizing environments observed on Mars are envisioned as propitious for the emergence of Life. Serpentine minerals and serpentinization may also catalyze a series of prebiotic reactions over a large range of pH and redox conditions. A detailed investigation of those reactions should enlighten our understanding of the origin of Life.
• The research community identified two locations that are likely to be most relevant as natural laboratories: 1) the Atlantis Massif, located 30°N along the Mid-Atlantic, hosting the Lost City hydrothermal (IODP proposal 758), and 2) the Oman ophiolite, displaying evidences for active, alkaline, H2 and CH4 seepages in low temperature springs, where CO2 is also efficiently mineralized.
The Serpentine Days workshop was supported by:
• The Deep Carbon Observatory
• Mineralogy and Crystallography Society of France (SFMC)
• National Science Foundation for Earth & Planetary Sciences (INSU)
• Institute of Mineralogy and Physics of Condensed Matter (IMPMC)
• University Claude Bernard Lyon 1
• International Ocean Drilling Program (IODP)