Serpentinization processes in modern and ancient environments

The quantification of hydration processes of the mantle is critical to understanding the

physical and chemical consequences of serpentinization on the structure and tectonics of the oceanic crust and the chemical budgets of the oceans. Hydration of the oceanic mantle directly influences geophysical properties in that serpentinisation is accompanied by a decrease in bulk density, which directly affects the physical properties of the mantle, gravity signatures and seismic velocities, and may have important tectonic consequences. Furthermore, the process of serpentinization may have major implications on the overall chemical budget of the oceans, for example by producing H₂ and CH₄ and providing Ca, Mg, Ni, B, etc. to phases formed during subsequent alteration of the oceanic crust. We are investigating serpentinization processes in different tectonic environments along mid-ocean ridges; at oceanic fracture zones; and in arc-subduction zone environments, which includes field and laboratory studies of the recently discovered Lost City Hydrothermal Field.

Lost City: Understanding a peridotite-hosted hydrothermal system on the seafloor

SNF Project No. 20020-107620 (2005-2007). Principle Investigators: G.L. Früh-Green, S.M. Bernasconi. PhD student: Adélie Delacour
ETH Project No. 0-20890-01 (2001-2005). Principle Investigator: G.L. Früh-Green; PhD student: Chiara Boschi

Our research is part of a multidisciplinary investigation of the Lost City Hydrothermal Field (LCHF) that involves scientists from the ETH-Zürich, the University of Washington, Syracuse University, Woods Hole Oceanographic Institution, and Massachusetts Institute of Technology. A highly successful oceanographic mapping and sampling program was completed in April-May, 2003 and new imagery and samples were collected in 2005. The LCHF is distinct from all other known marine hydrothermal systems and is the product of reactions between seawater and ultramafic rocks that produce high alkaline (pH 10 to 11), 40 to 90°C fluids that form up to 60m tall carbonate-brucite towers. The fluids are enriched in H₂, CH₄ and other hydrocarbons, produced abiotically through Fischer-Tropsch type reactions, and support dense microbial communities that include anaerobic CH₄- and S-cycling thermophiles. Collectively, our multidisciplinary investigations highlight the complex interplay between deformation, fluid flow, mass transfer and microbial activity and indicate that high fluid fluxes and temperatures of ~100°-150°C have likely been sustained in the basement for many tens of thousands of years.

Links:
lostcity, washington
ocean explorer
immersion presents

Serpentinization, Fluids and Life: Comparing Carbon and Sulfur Cycles in Modern and Ancient Environments

SNF Project No. 200020-116226 (2007-2009). Principle Investigators: G.L. Früh-Green, S.M. Bernasconi. PhD student: Esther Schwarzenbach

This project is a comparative bio-geochemical and isotopic study of the Lost City hydrothermal system (North Atlantic) with modern and ancient serpentinite-carbonate systems. The Lost City hydrothermal system is distinctly different than all other known marine hydrothermal systems and represents an important analogue for ancient ophicalcite deposits. This study builds on an immense data set produced through multidisciplinary collaboration between the ETH Zurich, University of Washington, Syracuse University, and WHOI/MIT over the past six years. Our project focuses on understanding the links between inorganic reactions that produce hydrogen and hydrocarbons, biogeochemical cycling of carbon and sulfur, and microbial activity in high pH systems associated with serpentinization. In addition to conducting follow-up geochemical analyses on samples from Lost City, we will investigate high alkaline Ca-OH springs associated with present-day serpentinization and carbonate deposition in Liguria and Oman and compare these with studies of Jurassic ophicalcites. The overall goal of our project is to quantify carbon and sulfur pools in active serpentinite-carbonate systems and to model their changes over time. Furthermore, our investigations of the Lost City system and the comparative studies of similar systems on land has the potential to provide important information about the mass of CO₂ locked into serpentinite-dominated environments and the viability of variably serpentinized rocks to sequester anthropogenic CO₂.

Boron isotope geochemistry of serpentine-hosted hydrothermal systems

In collaboration with C. Boschi and A. Dini (CNR, Pisa), G. Zandomeneghi and B. Meier (Physical Chemistry, ETH Zürich)

We are conducting boron concentration, NMR, and boron isotope studies of the Lost City hydrothermal fluids and hydrothermal carbonates to better understand fluid-rock interaction and mixing processes during fluid discharge at seafloor. Our studies also aim at better understanding the (paleo)hydrology of the Lost City system and the role of early precipitates of brucite in controlling the chemical and isotopic composition of the venting fluids. These studies should particularly provide important constraints for understanding the fate of Mg in peridotite-hosted hydydrothermal systems and the role of brucite as a sink for Mg and B.