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Cobertura geogràfica
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The basement of eastern Mexico comprises Grenvillian-age granulite-facies metamorphic
rocks. The Oaxacan Complex represents the largest outcrop belt of this basement in Mexico. In
this work, southwestern Oaxacan Complex garnets are studied from a petrographical, geochemical,
and geothermobarometrical perspective for the first time. The studied garnets display different
grain sizes nucleated in a polyphase evolution. The almandine end member proportion is similar
in all of the studied lithotypes. The highest pyrope concentrations are found in Qz Fsp paragenesis
and ultramafic rocks and the lowest pyrope concentrations are found in amphibolite. The highest
grossular and spessartine concentrations are found in the amphibolite lithotype. Southwestern
Oaxacan Complex garnets from paraderivate samples are more enriched in Rb, Ba, Pb, Ni, and Zn
than those from orthoderivate samples enriched in Ti and V. This fact is related to the nature of the
protoliths and the mineral phases that fractionate the same minor and trace elements. Garnets from
para- and orthoderivate samples display 0.02–1.1 Eu/Eu* anomalies. This fact indicates that almost
all of the garnets formed while the plagioclase was stable, and it does not rule out the interpretation
that some garnets were peritectic. The pressure obtained using a Grt-Opx-Pl-Qz geobarometer in
the southwestern Oaxacan Complex is higher than the pressure obtained in the northern part of
the Complex, and it is consistent with the pressure obtained in the Grenvillian-age granulites of the
Novillo Gneiss from northeastern Mexico. Geothermobarometric studies reveal different P-T features
at the study site, so different structural levels of the orogen are inferred.
Citació
Minerals 2021, 11, 805