Abstract

Zircons extracted from five chemically diverse granulite-facies crustal xenoliths from La Olivina cinder cone, Chihuahua, Mexico, were analyzed by SHRIMP ion microprobe in order to determine the age of the deep crust in northern Mexico. The results demonstrate the extreme age diversity of the deep crust in this region: zircon populations of ca. 1, 25-37, ca. 200, 350, 1100, and 1370 Ma are present. Nearly all samples contain 0-20 Ma zircons, reflecting recent granulite-facies conditions in the deep crust. In addition, high-grade metamorphism may also have occurred at 200 Ma and 1.10 Ga (Grenville). The paucity of Carboniferous-Permian ages in the xenoliths suggests that the Ouachita collision event provided little thermal input to the deep crust beneath La Olivina.

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