HR: 0800h
AN: U51A-03    [Abstracts]
TI: Petrological, Structural and Geochemical Characteristics of the Cuicateco Terrane, Southern Tehuantepec Isthmus, Oaxaca, Mexico
AU: * Perez, R
EM: perezr@geologia.unam.mx
AF: Posgrado en Ciencias de la Tierra, Instituto de Geología, UNAM, Ciudad Universitaria, Delegación Coyoacán, México, DF, 04510, Mexico
AU: Solari, L
EM: solari@servidor.unam.mx
AF: Centro de Geociencias, Campus Juriquilla, Querétato, Qro 76001, Mexico
AU: Gomez, A
EM: tuena@geociencias.unam.mx
AF: Centro de Geociencias, Campus Juriquilla, Querétato, Qro 76001, Mexico
AU: Sole, J
EM: Jsole@geologia.unam.mx
AF: Instituto de Geología, UNAM, Ciudad Universitaria, Delegación Coyoacán, México, DF, 04510, Mexico
AB: The southeastern portion of Cuicateco terrane in southern Mexico is composed of a low grade volcanosedimentary sequence interbedded with phyllites, and are generally considered be pre-Cretaceous. This sequence is overlain by Albian, rudist-bearing limestones. The volcanic rocks mainly correspond to amphibolites with fine-grained porphyritic to phaneritic textures made of plagioclase, hornblende, epidote and quartz phenocrysts set in a microlitic matrix. The phyllites display lepidoblastic texture made of muscovite, quartz, graphite, zircon and iron oxides, as well as lithic fragments. The rocks of the Cuicateco terrane display at least three deformational events: D1) Reclined to isoclinal F1 folding of the S0 bedding surface, with a general vergence toward northeast and producing a penetrative, moderately SW-dipping S1 axial plane foliation with development of hornblende, epidote, chlorite, muscovite and quartz. D2) Moderately dipping, NE-directed thrusting of the entire sequence, and F2 folding of S1 axial surfaces without development of new minerals along the axial plane. D3) Left-lateral to normal faulting, affecting all rocks. We consider that the D1 event predates the deposition of the Cretaceous fossiliferous limestones, whereas D2 also affects such rocks and it can be associated to the Laramide Orogeny. D3 is possibly a Tertiary feature, similarly to what is observed farther to W along the Chacalapa - La Venta fault system. The chemical compositions of amphibolite rocks of the Cuicateco terrane are similar to oceanic tholeiitic basalts (SiO2 of 45 to 50 wt%, light REE depleted and flat HREE patterns). A possible interpretation of these results suggests a basic volcanism in a backarc environment during the Mesozoic, which proposes an interesting debate on the tectonic implications of the Cuicateco terrane in the evolution of southern Mexico.
DE: 1000 GEOCHEMISTRY
DE: 1100 GEOCHRONOLOGY
DE: 8000 STRUCTURAL GEOLOGY
DE: 8100 TECTONOPHYSICS
SC: Union [U]
MN: 2007 Joint Assembly