Geochemistry of exposed granulite facies terrains and lower crustal xenoliths in Mexico

The trace element compositions of 13 samples from exposed granulite facies terrains and 17 granulitic lower crustal xenoliths were determined using an inductively coupled plasma-mass spectrometer to constrain the composition and evolution of the Mexican lower crust. Most xenoliths found are pyroxene-plagioclase orthogneisses, although quartzo-feldspathic paragneisses form up to 50% of the xenolith population in some areas. Lithologies in the exposed terrains consist of pelitic and carbonate-rich paragneisses, charnockites, and less abundant basic, intermediate, and felsic orthogneisses. The differences observed between the xenoliths and exposed granulites indicate that there may be chemical and lithologic zonation in the Mexican lower crust. The lowermost crust in Mexico consists of crystallized basaltic liquids, cumulates, and/or residue after the removal of a partial melt as well as garnet-rich metasediments. -from Authors