Preliminary Geochemical and Petrologic Assessment of the Fanney Rhyolite and the Bloodgood Canyon and Apache Springs tuffs, Mogollon-Datil Volcanic Field, New Mexico

Abstract:

Continental arc volcanoes represent a dramatic expression of a significant and fundamental phenomena in global tectonics: the subduction of an oceanic plate beneath a more buoyant continental plate. The subduction of an oceanic plate results in recycling of crustal material into the convecting mantle, partial melting, and primary basalt production. Moreover, during passage through thick continental crust, subduction zone magmas may substantially differentiate and melt crustal rocks giving rise to the great diversity of igneous lithologies characteristic of earth. These are important processes that must be understood in detail in order to interpret the long-term evolution of the earth and continental crust.

Here we present variations in the isotopic and trace element composition of volcanic rocks from Bloodgood Canyon and Apache Springs tuffs, and the Fanney Rhyolite located in the western Mogollon-Datil Volcanic Field (MDVF). The project will address several questions. First, are the Bloodgood and Apache Springs tuffs and Fanney Rhyolite petrogenically related, and are these rhyolites expressions of a continental arc ignimbrite flare-up? Second, what petrogenic processes affected differentiation and where is the magma sourced? Finally, to what extent do these units represent a manifestation of the MDVF and the transition from arc magmatism to rifting?

The Bloodgood Canyon is a crystal-rich rhyolite tuff containing quartz>k-feldspar>plagioclase>biotite, and pumice and lithic fragments. Rb ranges from 230-330ppm, Sr from 14-83ppm, and ⁸⁷Sr/⁸⁶Sr_m from 0.71619-0.72477.The Apache Springs Tuff is a rhyolite tuff containing quartz>k-feldspar>plagioclase>biotite, and lithics. Rb (228-233ppm) and ⁸⁷Sr/⁸⁶Sr_m (0.71025-0.71056) are restricted, while Sr (105-399ppm) is more variable in composition. The Fanney Creek is a massive rhyolite lava with flow banding and contains quartz phenocryst clusters and k-feldspars. Currently, no data exists for the Apache Springs Tuff.