U-Pb zircon geochronology of calc-alkaline ash-flow tuff units in the Mogollon-Datil volcanic field, southern New Mexico

Abstract

The Mogollon-Datil volcanic field is a 40–24 Ma cluster of calderas that formed during ignimbrite flare-up eruptions in southern New Mexico associated with sub-duction, and possible delamination, of the Farallon plate beneath the North American plate. This study uses magmatic zircon sampled from four ignimbrites from a nested caldera system and an additional ignimbrite located outside of the nested system to compare the processes and timing of magma accumulation in southern New Mexico. These ignimbrites include: the Whitewater Tuff, the Cooney Canyon Tuff, the Davis Canyon Tuff, and the Shelley Peak Tuff from the Mogollon Mountains and the Bell Top 4 Tuff from the Uvas volcanic field. The ignimbrites range from crystal-poor, high-silica rhyolite to crystal-rich, low-silica rhyolite. We compare previous 40Ar/39Ar sanidine eruption ages to new U-Pb crystallization ages and trace-element compositions of zircon. Weighted mean zircon ages define two magmatic groups. Group one includes the Bell Top Tuff (34.5 ± 0.5 Ma), the Cooney Canyon Tuff (34.8 ± 0.8 Ma), and the Whitewater Creek Tuff (36.2 ± 0.4 Ma). The second group includes the Davis Canyon Tuff (28.7 ± 0.5 Ma) and the Shelley Peak Tuff (29.6 ± 0.5 Ma). Weighted mean zircon ages are within published 40Ar/39Ar ages, with the exception of the Shelley Peak Tuff, which is ~1 m.y. older. Hafnium contents and Th/U and Yb/Gd ratios suggest the dominant mechanism that produced eruptible melt was rejuvenation or remobilization of a crystal mush accompanied by minimal partial melting of the continental crust.

Petrology and Geochemistry of the Bearwallow Mountain Andesite, Mogollon-Datil Volcanic Field, New Mexico

“…At the first appearance of mafic magmatism during bimodal magmatism at 32 Ma, both Sr/Y and (La/Yb)N ratios suggest the crust underwent a dramatic thinning event. Sr/Y and (La/Yb)N ratios of intermediate volcanic rocks between 28 and 20 Ma suggest a trend of crustal thinning consistentwith the timing of crustal extension in the area(Mack, 2004), and coincides with the end of bimodal magmatismRentz et al, 2019).While Sr/Y and (La/Yb)N ratios combined with structural estimates of paleo-crustal thickness provide a compelling argument, across-strike geochemical studies of thick crust continental arcs have suggested alternative hypotheses. Alternative models suggest that high Sr/Y and (La/Yb)N ratios are related to crustal composition and not depth of magma formation/ differentiation Michelfelder et al (2013).…”

“…; Wernicke et al, 1987;Chamberlin, 2002. Furthermore, the physical conditions of magma storage, magma remobilization, and reservoir timescales remain poorly constrained (Cooper and Kent, 2014;Rentz et al, 2019).…”