HR: 0800h
AN: U51A-02    [Abstracts]
TI: Gravity and Magnetic Survey of the Oaxaca-Juarez Terrane Boundary (Oaxaca Fault), Southern Mexico: Evidence for three Half Grabens
AU: * Campos-Enriquez, J O
EM: ocampos@geofisica.unam.mx
AF: Instituto de Geofisica, UNAM, Ciudad Universitaria Delegacion Coyoacan, Mexico, D.F., 04510, Mexico
AU: Belmonte-Jimenez, S I
EM: amigochava@yahoo.com.mx
AF: CIIDIR-IPN/Oaxaca, Calle Hornos 1003 Santa Cruz Jojocotlan, Oaxaca, Oax 71230, Mexico
AU: Ortega-Gutierrez, F
EM: fortega@servidor.unam.mx
AF: Instituto de Geologia, UNAM, Ciudad Universitaria Delegacion Coyoacan, Mexico, D.F., 04510, Mexico
AU: Keppie-Moorhouse, J D
EM: duncan@servidor.unam.mx
AF: Instituto de Geologia, UNAM, Ciudad Universitaria Delegacion Coyoacan, Mexico, D.F., 04510, Mexico
AU: Martinez-Silva, J
EM:
AF: Instituto de Geofisica, UNAM, Ciudad Universitaria Delegacion Coyoacan, Mexico, D.F., 04510, Mexico
AU: Martinez-Silva, J
EM:
AF: Ciencias de la Tierra, ESIA-IPN, Ave. Ticoman 600 Col. San Jose Ticoman, Mexico, D.F., 07340, Mexico
AU: Martinez-Serrano, R
EM: rms@geofisica.unam.mx
AF: Instituto de Geofisica, UNAM, Ciudad Universitaria Delegacion Coyoacan, Mexico, D.F., 04510, Mexico
AU: Martinez-Serrano, R
EM: rms@geofisica.unam.mx
AF: Instituto de Geofisica, UNAM, Ciudad Universitaria Delegacion Coyoacan, Mexico, D.F., 04510, Mexico
AB: A geophysical survey of the Oaxaca Fault boundary between the Oaxaca (Oaxaquia) (Zapoteco) and Juarez (Cuicateco) terranes along the Etla and Zaachila valleys area, southern Mexico shows a series of NW-SE Bouguer and magnetic anomalies with stronger gradients towards the east. The basement from the Oaxaca terrane has a high density (2.8 gr/cm3 ) and magnetic susceptibility of up to 0.0051 cgs units, which contrast with the Juarez basement that has a lower density (2.67 gr/cm3) and a higher magnetic susceptibility (values ranging between 0.0025 to 0.0045 cgs units). The magnetic susceptibility is similar south of the Donaji fault. Interpretation of six combined gravity and magnetic NE-SW profiles perpendicular to the valleys indicates the presence of a composite depression comprising three N-S sub-basins with the Etla and Zachila sub-basins located at the northern and southern portions, respectively, separated by a third sub-basin relatively displaced westwards. They are bounded on the east by the steeply W-dipping Oaxaca master fault, and on the west by the gently E-dipping Huitzo-Zimatlan fault. Two interpretations are suggested for the southward continuation of the Oaxaca Fault: 1) it continues southwards at depth with the same strike. Together the Bouguer and total field magnetic anomalies suggest that the Oaxaca fault is continuous from Etla via Oaxaca City and Ocotlán de Morelos probably to Miahuatlán de Porfirio Díaz, and 2) it continues with the same strike but is displaced eastwards ~20 km along a sinistral transfer fault, which forms the northern boundary of the Zaachila sub-basin.
DE: 0905 Continental structures (8109, 8110)
DE: 0920 Gravity methods (1219)
DE: 8102 Continental contractional orogenic belts and inversion tectonics
DE: 8109 Continental tectonics: extensional (0905)
DE: 8111 Continental tectonics: strike-slip and transform
SC: Union [U]
MN: 2007 Joint Assembly