Ultraslow crustal accretion at the Mid-Cayman Spreading Center: Mantle exhumation or magmatism?

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The seismic structure of the Mid-Cayman Spreading Center (MCSC) will be investigated to determine the extent to which magmatism contributes to crustal structure of an ultra-slow oceanic rift segment. As part of a larger international project, seismic data will be acquired along five profiles, from the ridge axis to ~10 Myr old flank, and from the spreading segment center to the transform walls. Two main ideas will be addressed: (1) Whether the MCSC hosts oceanic core complexes of exhumed crustal or mantle materials; (2) Whether crustal thickness variations in the MCSC reflect inhibition of magmatism as the spreading-segment ends are approached. Ocean bottom seismograph data will constrain tomographic models of velocity structure, from which crustal thickness, its variability, and/or mantle properties can be inferred. Recently acquired bathymetry and gravity data will be combined with prior trackline data and used as the basis for integrated seismic, gravity, and morphologic interpretation.Up to 20-30% of the world's oceanic spreading centers rift at ultraslow rates of less than 20 mm/yr, and expose a range of lower-crustal and upper mantle rock. These ultraslow systems host hydrothermal fields with chemical and biological activity that are distinct from faster spreading chemosynthetic systems, and have relevance for understanding the development of early life on Earth. This joint US-German-UK project strengthens international collaboration on studies of seafloor spreading. A graduate student will participate in all phases of the US portion of the study, receiving training in a range of marine geophysical techniques.