HR: 1400h
AN: V53B-13    [Abstracts]
TI: Petrological and Structural Setting of Mafic to Intermediate Dykes in the Xolapa Complex: Tierra Colorada-Acapulco Area, Southern Mexico
AU: * Hernandez, G A
EM: nnemon@prodigy.net.mx
AF: Instituto de Geologia, UNAM, Ciudad Universitaria, Coyoacan, Mexico, DF 04510, Mexico
AU: Solari, L A
EM: solari@servidor.unam.mx
AF: Centro de Geociencias, UNAM, Campus Juriquilla, Juriquilla, Qro 76230, Mexico
AB: The south of Mexico is conformed by a mosaic of suspect terranes. Three of them, characterized by different crystalline basements (Guerrero, Mesozoic; Mixteco, Paleozoic; Zapoteco Precambrian), are bordered toward the trench by the Chatino terrane, with the Xolapa Complex representing its basement, made up of amphibolite facies metamorphic rocks, affected by repeated granitic and granodioritic intrusions, with or without deformation. Several mafic dike intrusions are associated to the felsic magmatism. Felsic intrusions in the Tierra Colorada-Acapulco area show a volcanic arc geochemical signature. They range from I-type to S-type granites with different ages since Jurassic time. All intrusives were previously dated at ~165Ma, ~130Ma, ~55-65Ma and ~30-35 Ma. Mafic dykes could be arranged in three groups according to their structural pattern, mineral association and field relationships: (1) Group one dikes intrude basement units like migmatites, and gneisses. They are made up of plagioclase-biotite-hornblende. They are foliated and open to closely folded. Commonly biotite and hornblende define foliation planes, which share the same orientation as the regional foliation domain in orthogneisses and migmatites of the Xolapa Complex (WNW-ESE). (2) Group two dikes is represented by two kinds, the first one is of intermediate composition and affected by 45-50 Ma ductile shearing near Tierra Colorada. It bears plagioclase, k-feldspar and minor quartz, as well as biotite, hornblende, garnet and pyroxene as accessory minerals. NNW- SSE trending, NNE dipping foliation is defined by biotite and hornblende. The second type is not affected by mylonitization and consists of open to close folded and foliated mafic dykes, showing abundant plagioclase and accessory minerals such as biotite, muscovite, hornblende and titanite. Muscovite often is developed as coronitic texture surrounding biotite. Hornblende defines NNW-SSE to WNW-ESE trending, NNE dipping foliation planes. This type of dikes cuts only migmatitic gneisses units. (3) Group three dikes generally consists of intermediate dykes with subvolcanic textures. They cut all units in the central and northern area, and are affected by brittle normal faulting near Tierra Colorada. This group show two mineral and textural association, plagioclase and k- feldspar, with amphibole and rutile phenocrysts, and a microcrystalline matrix of plagioclase and k-feldspar, with some xenocrysts of quartz surrounded by hornblende.
DE: 1065 Major and trace element geochemistry
DE: 3619 Magma genesis and partial melting (1037)
DE: 3625 Petrography, microstructures, and textures
DE: 3640 Igneous petrology
DE: 3642 Intrusive structures and rocks
SC: Volcanology, Geochemistry, and Petrology [V]
MN: 2007 Joint Assembly