A LOOK AT THE SERI-TAHUE TERRANE BOUNDARY SINALOA, NORTHWESTERN MEXICO: GEOBAROMETRIC AND THERMOBAROMERIC CONSTRAINTS OF THE SINALOA BATHOLITH

The accretionary history of northwestern Mexico is a subject of debate. The object of this study is to better determine the nature of the Seri-Tahue terrane boundary. The place where it is being studied is near the 27th parallel Mexico, just south of the Sinaloa, Sonora, and Chihuahua tri-state triple junction. The boundary is believed to be a tectonic divide between the North American Craton and an accreted late Triassic volcanic arc. Determining the nature the boundary is difficult due Paleocene to mid-Tertiary andesite and granitic batholith emplacement which was followed by Tertiary ignimbrite cover. Recent isotopic studies (87Sr/86Sr, åNd) and REE of the batholith suites in northwestern Mexico support the existence of the terrane boundary. However, the exact nature of the boundary remains unresolved. To further constrain the boundary, this study will focus on the Sinaloa batholith. The batholith is found in outcrops at the base of the canyons in the study area. This study employs geobarometry, thermobarometry and petrographic analysis of Sinaloa batholith. Preliminary Al-in-hornblende barometer results from samples of the Sinaloa batholith suggest a shallow emplacement depth. Investigations of geobarometry and thermobarometry are important and will allow for future comparisons between the Northern, Central, and Southern granites of Northwestern Mexico (Valencia et al. 2001). Currently there is a lack of published geobarometry and or geothermometry data to constrain the crystallization conditions of the southern granites which include the Sinaloa batholith. Pressure and temperature constraints are useful tools that tell what the conditions were at the time of emplacement.