HR: 14:45h
AN: U53A-04    [Abstracts]
TI: Kinematics and age of Early Tertiary trench parallel volcano-tectonic lineaments in southern Mexico: Tectonic implications
AU: * Martini, M
EM: ziggystardust_ @infinito.it
AF: Centro de Geociencias UNAM, Campus Juriquilla, Queretaro, Qro 76230, Mexico
AU: Ferrari, L
EM: luca@geociencias.unam.mx
AF: Centro de Geociencias UNAM, Campus Juriquilla, Queretaro, Qro 76230, Mexico
AU: Lopez Martinez, M
EM: marlopez@cicese.mx
AF: Departamento de Geologia, CICESE, Ensenada, BC , Mexico
AU: Cerca Martinez, M
EM: mcerca@geociencias.unam.mx
AF: Centro de Geociencias UNAM, Campus Juriquilla, Queretaro, Qro 76230, Mexico
AU: Serrano Duran, L
EM: lserrano@geociencias.unam.mx
AF: Centro de Geociencias UNAM, Campus Juriquilla, Queretaro, Qro 76230, Mexico
AB: We present new geological, structural, and geochronological data that constrain the timing and geometry of Early Tertiary strike slip deformation in southwestern Mexico and its relation with the concurrent magmatic activity. Geologic mapping in Guerrero and Michoacan States documented two regional WNW trending volcano-tectonic lineaments sub parallel to the present trench. The southernmost lineament runs for ~140 km from San Miguel Totolapan area (NW Guerrero) to Sanchiqueo (SE Michoacan), and passes through Ciudad Altamirano. Its southeastern part is marked by the alignment of at least eleven silicic to intermediate major domes as well as by the course of the Balsas River. The northwestern part of the lineament is characterized by ductile left lateral shear zones in Early Tertiary plutonic rocks observed in the Rio Chiquito valley. Domes near Ciudad Altamirano are unaffected by ductile shearing and yielded a ~42 Ma 40Ar/39Ar age, setting a minimum age for this deformation. The northern volcano-tectonic lineament runs for ~190 km between the areas of Huitzuco in northern Guerrero and the southern part of the Tzitzio fold in eastern Michoacan. The Huautla, Tilzapotla, Taxco, La Goleta and Nanchititla silicic centers (all in the range 37-34 Ma) are emplaced along this lineament, which continues to the WNW trough a mafic dike swarm exposed north of Tiquicheo (37-35 Ma) and the Purungueo subvolcanic body (~42 Ma). These rocks, unaffected by ductile shearing, give a minimum age of deformation similar to the southern Totolapan-Sanquicheo lineament. Post ~42 Ma deformation is essentially brittle and is characterized by several left lateral and right lateral transcurrent faults with typical Riedel patterns. Other trench-parallel left lateral shear zones active in pre-Oligocene times were recently reported in western Oaxaca. The recognizing of Early Tertiary trench-parallel and left-lateral ductile shearing in internal areas of southern Mexico suggest a field of widely distributed flow and shear zones with relatively small individual displacement that might represent an immature stage of the developing North American-Caribbean plate boundary. The documented transition from ductile to brittle deformation and the localization of shearing and volcanism in the Late Eocene may be related to the focusing of inter-plate deformation in a discrete left lateral transcurrent North America-Caribbean boundary. The opening of the Cayman Through at ~49 Ma may have accelerated this process.
DE: 8111 Continental tectonics: strike-slip and transform
DE: 8150 Plate boundary: general (3040)
DE: 8178 Tectonics and magmatism
SC: Union [U]
MN: 2007 Joint Assembly