PETROLOGY AND GEOCHEMSITRY OF VOLCANIC ROCKS FROM THE WESTERN MOGOLLON DATIL VOLCANIC FIELD, NEW MEXICO: INSIGHTS IN TO THE EVOLUTION OF A LONG LIVED CRUSTAL MAGMA RESERVOIR

Southern New Mexico magmatism in the Miocene and Oligocene was strongly influenced by the thermal state of the lithosphere. From the Miocene to the present volcanic rocks record a shift in magma source from subduction contaminated lithospheric mantle to the asthenosphere and the source of contamination from the lower crust to the upper crust and finally too little or no contamination. Intermediate volcanism between 45-36 Ma followed by bimodal volcanism from 33-24Ma gave rise to Oligocene ignimbrites of the Mogollon Datil Volcanic Field (MDVF). This regionally extensive volcanic field is composed of more than 30 caldera forming volcanic centers and numerous smaller volcanoes. Three fundamental features exist for ignimbrite sources in the MDVF. First, three distinct phases of volcanism occurred as episodic pulses, each separated by 1-3 m.y. Second, two distinct clusters occur: a northern cluster active during all three phases and a second wider band of calderas towards the south which migrates northwest-west over time with a culmination of activity in what is now the Mogollon Mountains. Finally, caldera forming eruptions were prevalent during each pulse, but only in pulse three were large volume effusive eruptions produced. These volcanic rocks suggest the presences of a regional underlying magma body or MASH zone that persisted throughout magmatism in the MDVF with remobilization triggering ignimbrite eruptions. Here we present major and trace element and isotopic data along with petrographic and field descriptions from the volcanic products in the western MDVF. Rhyolites tuffs erupted from the Gila Cliff Dwellings, Mogollon and Bursum calderas that span phases 2 and 3 include: the Bloodgood Canyon, Davis Canyon, Shelley Peak and Cooney tuffs. Large volume intermediate composition lava flows from three units from pulse 3 include: the Last Chance, Mineral Creek and Bearwallow andesites. These rocks are used to evaluate the petrogenic processes operating in the magmatic plumbing system feeding the volcanic vents in the southwest MDVF. Further, we use this data to estimate rates of magma accumulation and conditions of magma storage in the crust. These data are compared to data from basaltic lava flows from the Sierra de la Uvas which represents the end of rhyolitic volcanism in the southern MDVF.