Evaluating the Substrate for Mantle Hosted Hydrothermal Activity At the Mid-Cayman Rise



This proposal is to evaluate the substrate for ultramafic-hosted hydrothermal activity at the Mid-Cayman Rift.  We propose to characterize the petrography, including the inter-relationships among metamorphic and igneous assemblages in thin section, and to analyze with the electron microprobe at MIT representative examples of the major mineral phases in existing Cayman samples in the WHOI collections and any new samples collected on a forthcoming cruise.  This will permit an initial characterization of the geochemical fluxes involved in hydrothermal alteration of the substrate, and aid in understanding the controls on the composition of the resulting hydrothermal fluids.

The Mid-Cayman Rise is the deepest known example of a mid-ocean ridge, and an ultraslow spreading ridge - the newly recognized end-member for seafloor spreading.  They are characterized by unique tectonics, exceptional exposures of mantle rock where the tectonic plates split at the ridge and the mantle is pulled directly to the seafloor, and an extraordinary abundance of what are likely to be the longest lived hydrothermal systems on the ocean ridge system.  With the greatest depths of any ocean ridge and unusual crustal structure these ridges represent a unique geologic and biologic environment that can extend our understanding of life and crustal evolution to the most extreme possible environment on the global ridge system.  While these ridges comprise some 30% of the global ridge system, they largely lie in the remotest and most inaccessible portions of the planet.  The Mid-Cayman Rise, however, lays a few hours transit from the Cayman Islands in the Caribbean: a popular and readily accessible tourist destination a few hours flight from the US mainland.  As a consequence a team of scientists and engineers led by WHOI's Chris German will deploy WHOI's new hybrid ROV Nereus in the Cayman Rise this October to locate hydrothermal systems at the Mid-Cayman Rise.  This represents a pioneering engineering and scientific enterprise to establish a new marine laboratory for the study of life, hydrothermal systems, and the evolution of the ocean crust and mantle at an ultraslow spreading ridge that will be uniquely accessible to the US scientific community.  This proposal seeks to support this effort by documenting the substrate for the hydrothermal systems to be studied there, and to lay the ground work for future work at the Mid-Cayman Rift.