HR: 0800h
AN: T51D-1387    [Abstracts]
TI: U/Pb Geochronology of the Maya Block, Guatemala
AU: * Martens, U
EM: umartens@stanford.edu
AF: Dept Environmental & Geological Sciences Stanford University, 450 Serra Mall, Bldg 320, Stanford, CA 94305 United States
AU: Ratschbacher, L
EM: lothar@geo.tu-freiberg.de
AF: Institut für Geowissenschaften Technische Universität Bergakademie Freiberg, Bernhard-von-Cottastr. 2 , Freiberg/Sachsen, D-09596 Germany
AU: McWilliams, M
EM: mcwilliams@stanford.edu
AF: Dept Environmental & Geological Sciences Stanford University, 450 Serra Mall, Bldg 320, Stanford, CA 94305 United States
AB: The Maya Block can be defined as Guatemala north of the Motagua transform fault, Belize, and part of southern Mexico. The absence of radiometric ages has hindered an understanding of the geologic evolution of the Maya Block and its connections with adjacent blocks in North America, South America and the Caribbean. We present an exploratory study of SHRIMP U/Pb ages from zircons collected in central and western Guatemala that shows ubiquitous Grenvillian inheritance, magmatism at ~ 1020 Ma, ~ 975 Ma and ~ 175 Ma, Devonian-Silurian and Triassic tectonomagmatic events, and Cretaceous metamorphism. Grenvillian orthogneisses were identified in the northern flank of the Sierra de Chuac'{u}s whose magmatic ages are 1020 ± 35 Ma and 975 ± 15 Ma with possible Pb-loss at ~ 420 Ma. Zircons of the Rabinal Granite show an important ~ 975 Ma inheritance and concordant ages in the 400-500 Ma range. We interpret the Devonian-Silurian ages as magmatic and correlate the peraluminous Rabinal Granite with similar intrusions in the Maya Mountains of Belize. Coeval events recorded in Chuac'{u}s orthogneisses and the Rabinal Granite suggest connections since Early Paleozoic time between the Chuac'{u}s complex and the Maya Block north of the Baja Verapaz shear zone that separates rocks of contrasting metamorphic grade. The magmatic age for deformed granites south of Sacapulas in central-western Guatemala is 174 ± 3 Ma. Migmatitic paragneisses collected south of Huehuetenango yield Triassic metamorphic ages at 223 ± 4 Ma, coeval with anatexis in the basement of Chiapas, Mexico. Medium to high-grade metasedimentary rocks on the southern flank of the Sierra de Chuac'{u}s do not record a Silurian-Devonian provenance. Instead, they yield clear Grenvillian and Triassic (240-210 Ma) components. Dating of zircon rims at 74 ± 1 Ma yields a precise age for the peak Cretaceous epidote-amphibolite metamorphic event in the Chuac'{u}s complex. Ductile structures exhibiting at least 4 tectonic phases and relic eclogite-facies metamorphism of unknown age in the Chuac'{u}s complex indicate a polymetamorphic history that has been greatly obliterated during this latest event. The ubiquitous Grenvillian provenance of Maya Block zircons indicates a Oaxaquia-Maya connection. Connections with the Chortis Block and the basement of the Eastern Cordillera of Colombia require further evaluation.
DE: 1115 Radioisotope geochronology
DE: 8106 Continental margins: transform
DE: 8125 Evolution of the Earth (0325)
DE: 9350 North America
SC: Tectonophysics [T]
MN: Fall Meeting 2005