HR: 16:35h
AN: U54A-02    [Abstracts]
TI: Provenance Ages of Protoliths From the Chiapas Massif Complex and Adjacent Strata of the Southern Maya Block - Implications on the Paleozoic Reconstruction of Middle America.
AU: * Weber, B
EM: bweber@cicese.mx
AF: Depto. de Geología, CICESE, km. 107 carr. Tijuana-Ensenada, Ensenada, BC 22860, Mexico
AU: Schaaf, P
EM: pschaaf@geofisica.unam.mx
AF: Inst. de Geología, UNAM, Ciudad Universitaria, Coyoacan, Mexico, DF 04510, Mexico
AU: Valencia, V A
EM: victorv@email.arizona.edu
AF: Dep. of Geosciences, University of Arizona, 1040 East Fourth St., Tucson, AZ 857210077, United States
AU: Lopez-Martinez, M
EM: marlopez@cicese.mx
AF: Depto. de Geología, CICESE, km. 107 carr. Tijuana-Ensenada, Ensenada, BC 22860, Mexico
AU: Ortega-Gutierrez, F
EM: fortega@servidor.unam.mx
AF: Inst. de Geología, UNAM, Ciudad Universitaria, Coyoacan, Mexico, DF 04510, Mexico
AB: The basement of the Maya block is exposed in the Maya Mountains of Belize, the Chuacús Complex of Guatemala, and in the Chiapas Massif Complex (CMC) of SE Mexico. In the CMC medium- to high-grade metasedimentary rocks occur as isolated domains in mostly metaigneous crystalline rocks. The most important tectonothermal event in the entire CMC is of late Permian age, culminating in partial anatexis and the intrusion of the Chiapas batholith. In this work we present U-Pb data obtained by LA-MC-ICPMS from detrital zircon cores of metasediments from the CMC and from detrital zircons of Paleozoic strata exposed in SE Chiapas. The Pennsylvanian-Permian Santa Rosa Formation (SRF) contains mostly Pan-African (500-650 Ma) zircons, minor populations of Silurian-Early Devonian (400-420 Ma) and Grenville (1.0-1.25 Ga) zircons, and few Paleoproterozoic and Archean grains. The maximum sedimentation age is documented by ~320 Ma old zircons. Metagreywacke and metasandstones of the central CMC have inherited detrital zircon cores with age distributions indistinguishable from those of the SRF. High-grade metapelites and para-amphibolites from the CMC, instead, have inherited zircon cores with one single population of 1.0 Ga or with populations at 1.0, 1.2, and 1.5 Ga. In the southern part of the CMC leucocratic granites intrude sedimentary rocks whose detrital zircons yielded mostly 1.53 Ga ages with some grains in the range of 1.6-1.7 Ga, but no younger zircons. White mica grown in contact with the leucogranite has a ⁴⁰Ar- ³⁹Ar age of 406 ± 4 Ma, defining a minimum age for both deposition of the sediments and intrusion of the leucogranite. Our data indicate that the CMC has a composite pre-metamorphic basement, containing sedimentary protoliths from the Pennsylvanian-Permian SRF and from early Paleozoic strata intruded by Silurian-Early Devonian granites. This favors a similar pre-Permian geologic history for the CMC as for the Maya Mountains of Belize. The early Paleozoic sediments were shed from a Mesoproterozoic landmass with ages typically observed from the SW Amazon craton; however, it seems more likely that during the Silurian-Early Devonian the Maya block was situated close to the southern Grenville Province of Laurentia where ancestors from the SW Amazon craton, but no Pan-African belts, are present. By initiating the collision between Gondwana and Laurentia during the Carboniferous, the sediments were shed mostly from the newly formed orogens close to West Africa, which contains mainly Pan-African crust.
DE: 1115 Radioisotope geochronology
DE: 8102 Continental contractional orogenic belts and inversion tectonics
DE: 8169 Sedimentary basin processes
DE: 8178 Tectonics and magmatism
DE: 9614 Paleozoic
SC: Union [U]
MN: 2007 Joint Assembly