Collaborative Research: Quantifying the thermal effects of fluid circulation in oceanic crust on temperatures in the southern Mexico subduction zone

University Of New Mexico, Albuquerque NM

Investigators

Abstract

Subduction zones are where one tectonic plate moves under another. They generate the largest earthquakes and tsunamis. Earthquake size is affected by temperatures on a fault. In subduction zones, temperatures also affect magma generation. To understand earthquake and volcano hazards in subduction zones, accurate temperature estimates are needed. Seawater flowing within subducting tectonic plates can affect temperatures. For the hazardous subduction zone of southern Mexico, the effects of this fluid flow are unknown. This causes large uncertainty in temperature estimates. This study will measure temperature in seafloor sediments and map sediment distribution off Mexico. The goals are to improve estimates of subduction zone temperatures and understand their controls. This study will benefit society by informing hazard estimates. Additionally, the project will enhance education at two Hispanic-serving institutions. Students at New Mexico Tech and the University of New Mexico will participate in the study. They will work with a researcher and student from an Earth science research center in Mexico. 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. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.