Are the western Mogollon-Datil mid-Cenozoic ash flows cogenetic? Pearce element ratios and isotopic aspects of the question
The three major ash flows in the western Mogollon-Datil volcanic field, the Davis Canyon Tuff, Shelley Peak Tuff, and Bloodgood Canyon Tuff, and the flow-banded rhyolites with which they are associated, were produced in a period of about 1 Ma from two interlocking calderas — the Gila Cliff Dwellings (source of Davis Canyon and Shelley Peak Tuffs), and the Bursum (source of Bloodgood Canyon Tuff). Magmas parent to the tuffs could have been produced by assimilation of existing crust by a mantle-derived basaltic magma, and fractional crystallization of the resultant mix. Fractionation of pyroxene and plagioclase in varying proportions from more mafic magmas produced the present ash flows. The proportions calculated from the use of Pearce element ratios were 80:20 plagioclase:pyroxene for ash flows from the Gila Cliff Dwellings caldera and 55:45 for the Bursum caldera- derived Bloodgood Canyon Tuff.
- Bikerman, Michael, 1994, Are the western Mogollon-Datil mid-Cenozoic ash flows cogenetic? Pearce element ratios and isotopic aspects of the question, in: Mogollon Slope, west-central New Mexico, Chamberlin, Richard M.; Kues, Barry S.; Cather, Steven M.; Barker, James B.; McIntosh, William C., New Mexico Geological Society, Guidebook, 45th Field Conference, pp. 187-192.