Heat Flow survey offshore Guerrero, southern Mexico (8-G cruise in 2025) #
Jeffrey Poort, Glenn Spinelli, Raquel Negrete-Aranda
Abstract #
During an oceanographic cruise of the R/V Marcus G. Langseth offshore southern Mexico 148 new marine heat flux data have been acquired in and near the trench of the offshore Guerrero subduction zone. The cruise was organized in the framwork of the project "Oceanic Crust Hydrothermal circulation Offshore Guererro (8-G)". The high-quality heat flux determinations were made on the Cocos plate across plate bending normal faults and adjacent to several seamounts. The heat flux ranged from exceptionally low <30 mW/m² to high heat flow of >300 mW/m², and appears to be indicative of lateral heat redistribution within the basaltic basement aquifer and potentially thermally-significant fluid flow along normal bending faults and seamounts. Overall, heat flux is substantially lower than the expected values for conductively cooled oceanic lithosphere are consistent with the extraction of heat from the crust by ventilated hydrothermal circulation. This affects the thermal state of the subducting crust, and ultimately the temperature distribution in the subduction zone.
Introduction #
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. 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 goal of this study is to assess the thermal regime of the Cocos plate entering the subduction zone offshore southern Mexico by collecting seismic reflection profiles and heat flux measurements.
Background #
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.
Objectives #
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.