Southern and Central Mexico: Basement Framework, Tectonic Evolution, and Provenance of Mesozoic–Cenozoic Basins

This volume furthers our understanding of key basins in central and southern Mexico, and establishes links to exhumed sediment source areas in a plausible paleogeographic framework. Authors present new data and models on the relations between Mexican terranes and the assembly and breakup of western equatorial Pangea, plate-tectonic and terrane reconstructions, uplift and exhumation of source areas, the influence of magmatism on sedimentary systems, and the provenance and delivery of sediment to Mesozoic and Cenozoic basins. Additionally, authors establish relationships between basement regions (sediment source) in the areas that supplied sediment to Mesozoic rift basins, Late Cretaceous foreland systems, and Cenozoic basins developed in response to Cordilleran events.
Metamorphic evolution of Proterozoic ultramafic rocks from the Oaxacan Complex (Oaxaca State, southern Mexico): Tectonic implications
*corresponding author: [email protected]
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Published:December 09, 2021
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CiteCitation
Laura Culí*, Jesús Solé, Fernando Ortega-Gutiérrez, 2021. "Metamorphic evolution of Proterozoic ultramafic rocks from the Oaxacan Complex (Oaxaca State, southern Mexico): Tectonic implications", Southern and Central Mexico: Basement Framework, Tectonic Evolution, and Provenance of Mesozoic–Cenozoic Basins, Uwe C. Martens, Roberto S. Molina Garza
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ABSTRACT
The Oaxacan Complex represents the largest outcrop of Grenvillian basement in Mexico. Broadly, it consists of pelitic gneisses, quartzofeldspathic gneisses, metasomatic calc-silicates, orthoamphibolites, and marbles, all intruded by anorthosites, orthocharnockites, and orthogneisses. The entire assemblage underwent granulite-facies metamorphism ca. 1 Ga. We studied for the first time the ultramafic rocks of the Oaxacan Complex, represented by six different samples, all corresponding to ultramafic granulites. Their igneous equivalents are orthopyroxenites, websterites, and clinopyroxenites, and they occur as metric-scale lenses or centimetric layers in paragneisses, or in mingling textures with anatectic marbles. We studied their petrography, geochemistry, geochronology, and geothermobarometry to elucidate their genesis and tectonic implications. Our samples have enriched mid-ocean-ridge basalt and oceanic-island-arc affinities, both tholeiitic and calc-alkaline. Rare earth element patterns normalized to chondritic uniform reservoir from whole rock or single minerals define two or three main groups related to their origin and metamorphic history. Based on their protoliths, these rocks can be divided into: (1) ortho-derived pyroxenites (pre–Grenvillian orogeny), the origin of which was a magmatic cumulate or mafic melt or a mantle rock that had undergone metasomatism; and (2) para-derived pyroxenites (syn- or post-Grenvillian orogeny), the origin of which was a calc-silicate rock undergoing pervasive anatectic and metasomatic processes. The geothermobarometry revealed different stages in the syn- and post-Grenvillian granulitic metamorphic history of the Oaxacan Complex. The high temperature calculated from one sample (~945 °C), in the ultrahigh-temperature metamorphic field, is probably closer to the granulitic metamorphism peak than those obtained in previous studies, although a relict igneous temperature cannot be ruled out with the present data.
- basement
- chemical composition
- eclogite
- electron microscopy data
- gneisses
- granulites
- Grenvillian Orogeny
- ICP mass spectra
- igneous rocks
- isotope ratios
- laser ablation
- laser methods
- mass spectra
- metals
- metamorphic rocks
- metamorphism
- Mexico
- Oaxaca Mexico
- P-T conditions
- plutonic rocks
- Precambrian
- Proterozoic
- pyroxenite
- rare earths
- Rb/Sr
- SEM data
- Sm/Nd
- spectra
- tectonics
- trace elements
- Trans-Mexican volcanic belt
- ultramafic composition
- ultramafics
- upper Precambrian
- X-ray fluorescence spectra
- X-ray spectra
- Oaxacan Complex