HR: 09:45h
AN: T11D-08    [Abstracts]
TI: Petrotectonic Evolution of the Chuac\'us Complex, Central Guatemala, by U/Pb Geochronology
AU: * Martens, U
EM: umartens@stanford.edu
AF: Dept. Geological & Env. Sciences, Stanford University, 450 Serra Mall, Bldg 320, Stanford, CA 94305, United States
AU: Liou, J
EM: jliou@stanford.edu
AF: Dept. Geological & Env. Sciences, Stanford University, 450 Serra Mall, Bldg 320, Stanford, CA 94305, United States
AU: Solari, L
EM: solari@servidor.unam.mx
AF: Centro de Geociencias, UNAM, Campus Juriquilla, Queretaro, QRO 76001, Mexico
AU: Mattinson, C
EM: mattinson@stanford.edu
AF: Dept. Geological & Env. Sciences, Stanford University, 450 Serra Mall, Bldg 320, Stanford, CA 94305, United States
AU: Wooden, J
EM: jwooden@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield road, Menlo Park, CA 94025, United States
AB: Amphibolite-facies metamorphic rocks in the Sierra de Chuac\'us, Central Guatemala, can be divided into two units based on structure and U/Pb geochronology. The El Tumbadero unit is composed of orthogneisses with Triassic U/Pb igneous ages, and pelitic schists, paragneisses, marbles and quartzites. Detrital U/Pb zircon geochronology of two metasedimentary samples implies post-Ordovician and post-Pennsylvanian deposition. The fabric of El Tumbadero unit consists of a single foliation parallel to axial planes of scarce isoclinal folds. Partial melting of orthogneisses generated pegmatites that are in part concordant and in part cut the dominant foliation. Metamorphic zircon rims from orthogneisses have ~75Ma U/Pb ages, and trace element patterns consistent with amphibolite-facies zircon recrystallization. Minor amphibolitized eclogites occur as m-sized lenses and interfoliated bands within Triassic orthogneisses. These are interpreted as mafic dikes metamorphosed to near-UHP conditions (~700-750°C, ~22-24kbar) before crustal metamorphism and anatexis. In contrast, the El Chol unit exposes at least 3 generations of folds and foliations within banded gneisses, migmatites, and multiple generations of pegmatites; their latest foliation is parallel to the fabric of the El Tumbadero unit. Zircon U-Pb geochronology of El Chol mafic rocks reveals Pan-African protolith and Silurian- Devonian metamorphic rims. Refolded felsic bands have discordant U/Pb lower intercept ages of ~300Ma. The El Chol unit also contains eclogites as cm-scale irregular domains in amphibolite bands. A poorly constrained U/Pb age of an eclogitic zircon rim yielded a Late Cretaceous age. In summary, in the early Mesozoic the El Chol unit of the Chuacús complex constituted a metamorphosed basement over which the protoliths of the El Tumbadero unit were deposited and intruded. A late Cretaceous collision, possibly with the Cuban arc or the Chort\'is block, subducted both continental rock units to mantle depth. Subsequent exhumation to crustal level caused partial anatexis and ubiquitous amphibolite-facies overprint.
DE: 1100 GEOCHRONOLOGY
DE: 3613 Subduction zone processes (1031, 3060, 8170, 8413)
DE: 8104 Continental margins: convergent
SC: Tectonophysics [T]
MN: 2007 Fall Meeting