Structure, and geothermal potential of the Laguna Salada Basin, BCN, Mexico

Abstract

Based on gravity and vertical magnetic field data we established the structure of the sediment-basement interface of the Laguna Salada basin. A three-dimensional inversion for the gravity was carried out in the wavenumber domain using an iterative scheme. The maximum density contrast of -400 kg/m and the mean depth of 3 km constrained the inversion. The resulting model indicated that the sedimentary infill is up to 4.2 km thick at its deepest point. Vertical magnetic field measurements available were interpreted on four selected two-dimensional profiles. The magnetic anomalies were interpreted successfully using the gravity derived basement-sedimentary infill interface as top of the magnetic bodies. An elongated N-S to NW-SE trending highly magnetized body running from south to north along the basin is observed to the west of the basin. This magnetic anomaly has no gravity signature, and can be interpreted as an intrusive body emplaced along a fault running through Laguna Salada Basin. Two-dimensional thermal modeling was carried out in three profiles across the Laguna Salada basin. We used a finite difference scheme to solve the coupled Darcy and Fourier differential equations. Computed models showed fluid flow in the sedimentary layers and a redistribution of heat flow from the basin axis toward its rims (Sierra de Juarez and Sierra Cucapah). The numerical and chemical analyses support the hypothesis of fluid circulation between the clay-lutite layer and the fractured granitic basement. Thermal modeling shows low heat flow values along the Laguna Salada basin. Deep fluid circulation patterns were observed that redistribute such flow at depth. Two patterns were distinguished; one displays the heat flow increasing from the basin axis towards its borders (temperature increases at 20o). The second pattern shows an increasing heat flow from south to north of the basin. Such behavior is confirmed by the temperature measurements in the thermometric boreholes.