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Petrology of high-grade metapelitic xenoliths in an Oligocene rhyodacite plug--Precambrian crust beneath the southern Guerrero terrane, Mexico?

Abstract:

The Guerrero terrane in southern Mexico (Figure l) is considered a major tectonostratigraphic accretion to the Mesozoic continental crust of Mexico, and essentially lacking an old continental basement (Campa and Coney, 1993; Centeno-Garcia et al,, 1993). One of the main reasons for this hypothesis is the virtual absence of outcrops of highgrade metamorphic rocks in the terrane such as those profusely found in the adjacent Mixteco and Zapoteco terranes of Paleozoic and Precambrian ages, respectively. Nevertheless, some geological data (Elias-Herrera and Sanchez-Zavala, 1990) indicate the possible presence of evolved crustal rocks beneath parts of the volcanic-sedimentary units that make up most of the southern Guerrero terrane. Moreover, in contrast to the region of northern Mexico, Cenozoic volcanic rocks in southern Mexico are of calcalkaline character and apparently do not contain xenoliths from the …