HR: 0800h
AN: U51A-01    [Abstracts]
TI: Tectonic Significance of Cretaceous to Tertiary Magmatic and Structural Evolution of the Northern Portion of the Xolapa Complex, Tierra Colorada-Acapulco Area, Southern Mexico
AU: * Torres De Leon, R
EM: torresdeleonr@yahoo.com.mx
AF: Instituto de Geologia, UNAM, Ciudad Universitaria Delegacion Coyoacan, Mexico, 04510, Mexico
AU: Perez, R
EM: perez_rosalva@yahoo.com.mx
AF: Instituto de Geologia, UNAM, Ciudad Universitaria Delegacion Coyoacan, Mexico, 04510, Mexico
AU: Solari, L
EM: solari@servidor.unam.mx
AF: Centro de Geociencias, UNAM, Campus Juriquilla Juriquilla, Qro, Queretaro, 76230, Mexico
AU: Hernandez, G
EM: gahp@hotmail.com
AF: Instituto de Geologia, UNAM, Ciudad Universitaria Delegacion Coyoacan, Mexico, 04510, Mexico
AU: Sole, J
EM: jsole@geologia.unam.mx
AF: Instituto de Geologia, UNAM, Ciudad Universitaria Delegacion Coyoacan, Mexico, 04510, Mexico
AU: Solis, G
EM: gsolis@geofisica.unam.mx
AF: Instituto de Geologia, UNAM, Ciudad Universitaria Delegacion Coyoacan, Mexico, 04510, Mexico
AU: Hernandez, T
EM: tht@geofisica.unam.mx
AF: Instituto de Geofisica, UNAM, Ciudad Universitaria Delegacion Coyoacan, Mexico, 04510, Mexico
AB: This work presents combined structural and geochronological data from Tierra Colorada to Acapulco area that show evidence of five deformational events and four episodes of arc related magmatism during Mesozoic and Cenozoic times. The oldest sequence correspond to metasedimentary units (paragneisses and marbles) metamorphosed in amphibolite facies that are affected by a penetrative foliation and mineral lineation (D1). This sequence is intruded by a first magmatic pulse (M1) that is represented by ~165 Ma metagranitoids that are affected by metamorphism and migmatization (D2). The second magmatic pulse (M2) corresponds to the intrusion of the El Pozuelo granite (129 +/- 0.5 Ma: concordant U-Pb zircon analysis), which postdates high grade metamorphism and migmatization. The next magmatic episode (M3) is represented by the peraluminous, deformed El Salitre granite (55.3 +/- 3.3 Ma: mineral-whole rock Rb-Sr isochron), and the protomylonitic Las Pi\hbaras I-type granite (54.2 +/- 5.8 Ma: lower intercept U-Pb zircon). Las Pi\hbaras granite is characterized by D3 ductile sheared fabric with normal, top-to-the NNW sense of shear, deformed at 45 - 50 Ma (Rb-Sr and K-Ar ages). D3 also affects the El Pozuelo granite and the lower Cretaceous metavolcanic rocks of the Chapolapa Formation. The 34 Ma undeformed granites (M4) corresponds to the last intrusive pulse in the area, post-dating D4 SSW-verging thrusting of the Cretaceous Morelos Formation over sheared granites and metavolcanic rocks. The last deformational event (D5) corresponds to brittle lateral features that affects all the units. These four pulses of subduction related magmatism in the Tierra Colorada-Acapulco area indicate a regular, northeastward subduction at the Mesoamerican trench since Jurassic time, alternated with contractile and/or extensional deformational events. The gap in magmatic activity at about 90-100 Ma roughly coincides with deposition of platformal limestones of the Morelos Formation during the middle Cretaceous. The stable conditions during deposition of the Morelos Formation may have resulted from a combination of back-arc extension and development of a passive margin during the Middle Cretaceous, which postdated the accretion of an exotic block, either the Guerrero terrane or the Chortís block. Following the Laramide Orogeny in southern Mexico (roughly during the Late Cretaceous) the Paleocene to Miocene tectonic evolution is represented by an alternation of magmatic pulses with contractile and extensional events, which are the result of a combination of several factors such as the geometry of the subducted slab, convergence rate, stress transmission between subducting and overlying plate, as well as to the rate of subduction erosion.
DE: 1090 Field relationships (3690, 8486)
DE: 1100 GEOCHRONOLOGY
DE: 1115 Radioisotope geochronology
DE: 3625 Petrography, microstructures, and textures
DE: 3690 Field relationships (1090, 8486)
SC: Union [U]
MN: 2007 Joint Assembly