Chain Cruise 1

This collaborative project is to explore the structure, seismicity, rheology, and magmatism within the slow-slipping Chain Transform Fault in the equatorial Atlantic. The formation of localized zones of deformation is a key attribute of plate tectonics. Oceanic transform faults are ideal laboratories for studying the mechanisms of localized deformation due to their relatively uniform composition and predictable motion. Many aspects of strain accommodation remain poorly understood, including (1) the extent to which cracking and seawater-driven reactions cause fault weakening deep into the fault, (2) the role of serpentine and other phyllosilicates in accommodating aseismic creep, and (3) the importance of melt infiltration and weakening within the fault zone. While existing samples of transform faults provide constraints on strain weakening mechanisms, very little sampling has been done in concert with the collection of structural and seismicity data to directly link fault behavior to rheology. An interdisciplinary field program to study the structure, composition, and seismicity of the Chain Transform Fault will be conducted through two research cruises. The first cruise, aboard the R/V Langseth, will collect multi-channel seismics to image sub-surface fault structures and the extent of magmatism in the fault domain. An ocean bottom seismometer array will be deployed during the cruise to determine the depth extent of microseismicity and the relationship between fault structures and seismicity. The second cruise will occur one year later to recover the OBS array. This cruise will dredge the fault zone to determine the composition and rheology of the fault and conduct surveys using AUV Sentry to identify the surface expression of the fault.