Depth estimation to crystalline basement in the valley of La Paz, Baja California Sur, Mexico

Abstract

Based on gravity data, the depth to crystalline basement in the valley of La Paz, Baja California Sur was estimated. Geometry of the tectonic depression that underlies the valley was interpreted with support of the aeromagnetic anomaly. For regional-residual separation of gravity data, regional effect was considered as a horizontal plane. In order to estimate depth to basement, the formula for the calculation of gravity in a point over a horizontal layer of infinite extension was used. A density contrast of 0.66 g/cm³ was used, based on the general characteristics of basement and sedimentary infill. Estimated depths were normalized to a depth to basement obtained in a magnetic profile from another study. Two sections were modeled to evaluate the procedure. The depth to basement in the valley of La Paz ranges from 100 to 500 m on the east and the center-south, to more than 1500 m to the NNE, NW and west. A graben delimited by two main lineaments is evident, one lineament extends on the east with a N-S direction, and the other on the west with a SSE-NNW orientation, which are respectively attributed to the La Paz and El Carrizal faults. The graben is tilted towards the WNW.