The buried southern continuation of the Oaxaca-Juarez terrane boundary and Oaxaca Fault,southern Mexico: Magnetotelluric constraints |
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| Institution: | 1. CICESE, División de Ciencias de la Tierra, Departamento de Geofísica Aplicada, Carretera Ensenada-Tijuana No 3918, Fraccionamiento Zona Playitas, Ensenada, Baja California Postal Code 22818, Mexico;2. Estación Regional del Noroeste, Instituto de Geología, Universidad Nacional Autónoma de Mexico, Blvd L.D. Colosio S/N y Madrid, A.P. 1039, Hermosillo, Sonora Postal Code 83240, Mexico;1. ADECAL Technopole, ZoNéCo Research Program, Nouméa, New Caledonia;2. Geological Survey of New Caledonia, DIMENC, BP 465, 98845 Nouméa, New Caledonia;3. Ifremer, Géosciences Marines, CS 10070, 29280 Plouzané, France |
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| Abstract: | Thirty magnetotelluric soundings were made along two NW–SE profiles to the north and south of Oaxaca City in southern Mexico. The profiles crossed the N–S Oaxaca Fault and the Oaxaca-Juarez terrane boundary defined by the Juarez mylonitic complex. Dimensionality analysis of the MT data showed that the subsurface resistivity structure is 2D or 3D. The Oaxaca and correlative Guichicovi terranes consist of ca. 1–1.4 Ga granulitic continental crust overlain by Phanerozoic sedimentary rocks, characterized by high and low resistivities, respectively. The Juarez terrane consists of oceanic Mesozoic metavolcanic and metasedimentary rocks, characterized by a low to medium resistivity layer, that is approximately 10 km thick. The Oaxaca Fault is a Cenozoic aged, normal fault that reactivated the dextral and thrust Juarez mylonitic complex north of Oaxaca City: its location south of Oaxaca City is uncertain. In the southern profile, the MT data show a ca. 20–50 km wide, west-dipping, relatively low resistivity zone material that extends through the entire crust. This is inferred to be the Juarez terrane bounded on either side by the ca. 1–1.4 Ga granulites. The Oaxaca Fault is imaged only by a major electrical resistivity discontinuity (low to the west, high to the east) along both the western border of the Juarez mylonitic complex (northern profile) and the San Miguel de la Cal mountains (southern profile) suggesting continuity. |
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