Delineating the ocean-continent crustal boundary in the Gulf of Mexico using heat flow measurements
Characterization of the igneous basement of the ocean-continent transition zone is important in reconstructing the early opening history of sedimentary basins. However, the transition zone is usually buried under a thick sediment cover, inhibiting detailed characterization of the basement by conventional seismic techniques or drilling. Previous studies have proposed use of heat flow observations to locate the ocean-continent crustal boundary in the Gulf of Mexico and elsewhere. Because continental crustal rocks produce more radiogenic heat than oceanic crustal rocks, the crustal boundary may be detected by closely spaced, marine heat flow measurements in the transition zone. This study tests such a possibility in the eastern margin of the Gulf of Mexico, using ~160 seafloor heat flow measurements obtained by TDI Brooks International. In a narrow (~25-km width), northwest-southeast trending, zone along the northeastern Gulf of Mexico margin, the seafloor heat flow values increase abruptly from ~20 mW/m2 to ~40 mW/m2. This zone roughly coincides with the Gulf of Mexico ocean-continent crustal boundary proposed by recent seismic and gravity gradiometry studies. There is no obvious coincidental change in the sedimentary stratigraphy and structure across this zone. 20 numerical heat flow models for the lithosphere in the eastern Gulf are generated to constrain the basal heat flow. In these models, the opening of the Gulf of Mexico and the sediment burial history of the study area are reconstructed using 2D seismic data, wire-line logs, biostratigraphic data, and previously published stratigraphic studies. The heat flow models were calibrated by comparing the modeled seafloor heat flow values to the corresponding measured seafloor heat flow. The heat flow models account for the thermal effects of sediment accumulation and radiogenic heat production within sediments. The basal heat flow values for the oceanic crustal groups are consistent at 38 to 39 mW/m^2. While, the average of the basal heat flow values in the transitional continental crustal section is 50 mW/m^2, with a standard deviation of 2 mW/m^2. This large difference, of 11-12 mW/m^2, between the average basal heat flow for the two sets of groups, oceanic and transitional continental, is attributed to a difference in radiogenic heat produced within the crustal basement, thus, implying a change in crustal lithology.