HR: 0800h
AN: T11B-0578    [Abstracts]
TI: New Geochronologic, Stratigraphic and Structural Data Constraining the Cretaceous Evolution of Southwestern Mexico
AU: * Martini, M
EM: ziggystardust_@infinito.it
AF: Centro de Geociencias UNAM, Campus Juriquilla, Queretaro, Qro 76230, Mexico
AU: Ferrari, L
EM: luca@servidor.unam.mx
AF: Centro de Geociencias UNAM, Campus Juriquilla, Queretaro, Qro 76230, Mexico
AU: Cerca, M
EM: mcerca@geociencias.unam.mx
AF: Centro de Geociencias UNAM, Campus Juriquilla, Queretaro, Qro 76230, Mexico
AU: Valencia, V
EM: victorv@email.arizona.edu
AF: Department of Geosciences, The University of Arizona, Gould-Simpson Building 1040 East Fourth St Room 548, Tucson, AZ 85721-0077, United States
AB: The Mesozoic volcano-sedimentary successions of southwestern Mexico have been often interpreted to represent the record of a single or multi-arc system (Guerrero Terrane), built on oceanic crust far away from the continent, which was subsequently accreted to the continental margin of the North American plate in Late Cretaceous time after a prolonged period of W-directed subduction. An alternative model proposes that the Guerrero island arc was built partly on oceanic crust and partly on continental crust and later collided with the continent (Tardy et al., 1994). However, no solid data exist to support either a true accretionary process or the collision of two continental masses in southern Mexico during Laramide deformation. Furthermore, the occurrence of Paleozoic and Precambrian terrigenous sediments at various stratigraphic levels of the Cretaceous sedimentary succession of the southern Guerrero Terrane indicates that it formed relatively close to a continent. This is also supported by the Grenvillian inherited component recognized in zircons of the ~120 Ma Placeres del Oro pluton, which resulted from partial assimilation of either a lower crustal continental basement or of upper crustal detrital zircons recycled from Grenvillian basement. Models considering the accretion of intraoceanic insular arcs to nuclear Mexico during Late Cretaceous time cannot explain such continental influence and need to be revisited. We suggest that the Cretaceous volcano-sedimentary successions were deposited directly on the thinned continental margin of the North American plate, and were deformed in Late Cretaceous time to form a thrust-and- fold belt. The apparent litho-stratigrahic incompatibilities of the Mesozoic successions can be completely explained in terms of spatial and temporal variations of facies on a heterogeneous crust with a migrating continental arc, and its back-arc and fore-arc basins. The arc was related to eastward subduction of the Farallon oceanic plate. In this way, the Laramide deformation of southern Mexico is definitively unrelated to accretion of allochtonous terranes, and the intervention of another driving force is required to explain the Late Cretaceous- Early Tertiary shortening of the southern margin of the North American plate.
DE: 8104 Continental margins: convergent
DE: 8108 Continental tectonics: compressional
DE: 8413 Subduction zone processes (1031, 3060, 3613, 8170)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting