Shallow Miocene basaltic magma reservoirs in the Bahia de Los Angeles basin, Baja California, Mexico |
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| Authors: | Luis A Delgado-Argote Juan García-Abdeslem |
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| Institution: | 1. Applied and Environmental Geophysics Group, University of Lausanne, 1015 Lausanne, Switzerland;2. G360 Centre for Applied Groundwater Research, University of Guelph, Guelph, ON, Canada;1. Centro de Nanociencias y Nanotecnologia, Universidad Nacional Autónoma de México, Apartado Postal 14, Ensenada, Baja California Codigo Postal 22800, Mexico;2. Instituto de Investigaciones Oceanologicas, Doctorado en Medio Ambiente y Desarrollo, Universidad Autonoma de Baja California, Codigo Postal 22860, Mexico |
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| Abstract: | The basement in the Bahía de Los Angeles basin consists of Paleozoic metamorphic rocks and Cretaceous granitoids. The Neogene stratigraphy overlying the basement is formed, from the base to the top, by andesitic lava flows and plugs, sandstone and conglomeratic horizons, and Miocene pyroclastic flow units and basaltic flows. Basaltic dikes also intrude the whole section. To further define its structure, a detailed gravimetric survey was conducted across the basin about 1 km north of the Sierra Las Flores. In spite of the rough and lineal topography along the foothills of the Sierra La Libertad, we found no evidence for large-scale faulting. Gravity data indicates that the basin has a maximum depth of 120 m in the Valle Las Tinajas and averages 75 m along the gravimetric profile. High density bodies below the northern part of the Sierra Las Flores and Valle Las Tinajas are interpreted to be part of basaltic dikes. The intrusive body located north of the Sierra Las Flores is 2.5 km wide and its top is about 500 m deep. The lava flows of the top of the Sierra Las Flores, together with the distribution of basaltic activity north of this sierra, suggests that this intrusive body continues for 20 km along a NNW-trending strike. Between the sierras Las Flores and Las Animas, a 0.5-km-wide, 300-m-thick intrusive body is interpreted at a depth of about 100 m. This dike could be part of the basaltic activity of the Cerro Las Tinajas and the small mounds along the foothills of western Sierra Las Animas. The observed local normal faulting in the basin is inferred to be mostly associated with the emplacement of the shallow magma reservoirs below Las Flores and Las Tinajas. |
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| Keywords: | Bahia de Los Angeles basin Miocene basaltic magma reservoir Paleozoic metamorphic rocks |
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