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8-G: Oceanic Crust Hydrothermal-circulation Offshore Guerrero

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Accurate estimates of subduction zone temperatures are required to understand a variety of critical processes, including controls on seismogenic and aseismic behavior on subduction megathrusts. The region of flat-slab subduction in Mexico has been a focus of seismic and geodetic studies because it hosts an interesting range of behaviors on the plate interface (e.g., tremor, slow slip, presence of an ultra-slow layer postulated to be generated by fluid overpressure). Attempting to better understand physical conditions within the subduction zone, various studies predict temperatures and the distribution of slab alteration in this system. However, thermal models for the margin remain largely unconstrained due to insufficient heat flux observations on the incoming plate. Specifically, the potential presence and effects of fluid circulation in the basaltic basement aquifer of crust entering the southern Mexico subduction zone are unknown. The subduction zone in southern Mexico is among the warmest globally and the extent to which fluid circulation redistributes heat has profound implications for temperature distributions and subduction processes. This observational and modeling study will assess the thermal regime of the Cocos plate entering the subduction zone offshore southern Mexico by collecting ~650 km of seismic reflection profiles and ~200 heat flux measurements. This will provide a process-based understanding of the thermal structure of the incoming Cocos plate.

The central hypotheses are:

1) hydrothermal circulation advects substantial quantities of heat in oceanic crust near the deformation front offshore southern Mexico, and

2) bending-related normal faults play an important role in hydrothermal circulation and the thermal structure of the incoming plate in this system.

Analyzing and interpreting the controls on the thermal state of the Cocos plate near the deformation front will allow for the development of improved predictive models of subduction zone temperatures.