10 Cretaceous and Paleogene Magmatism in the Western Cordillera

Tuesday, 1 April 2003
8:25 AM - 12:05 PM

PETROLOGIC AND GEOCHEMICAL CONSTRAINTS FROM LA ENCARNACION GRANITOIDS, HIDALGO STATE (MEXICO)

Paper number: 10-8
Program: THEME SESSIONS
Time: 10:25 AM – 10:45 AM

Authors

Abstract

Granitoid rock exposures are scarce in Hidalgo State (Mexico). They occur at the northwestern side of the state in the Sierra Madre Oriental Province, related to the late Laramide deformation, where the level of erosion has been more intense. In La Encarnacion area, granitoids form discrete stocks in the core of an NW-SE trending anticline. They intrude pelitic and calcareous Mesozoic formations ranging from late Jurassic to upper Cretaceous age. They are partially covered by tertiary volcanic products of Transmexican Volcanic Axe.

Petrographic types of the granitoids include quartzdiorite, monzodiorite, quartzmontzodiorite and granodiorite. Their distinctive mineralogy is represented by plagioclase (oligoclase-andesine), perthitic K-feldspar (orthoclase), subordinated mafic minerals dominated by hornblende, scarse biotite, diopside and titanite, abundant magnetite – ilmenite association, and apatite.

These rocks belong to high-K calc-alkaline magmatic series with a shoshonitic trends. The 87Sr/86Sr ratio values show that the source of magmatism corresponds to the lower crust. The emplacement pressures from 1.5 to 2.5 kbar were determined by AlT in hornblende geobarometer. K/Ar age of the granitoids are obtained in hornblende and biotite, and is related to the Eocene (50 Ma).

Petrologic and geochemical constraints are discussed and related to the geological evolution of central Mexico.