Quartz in post-caldera rhyolites of Valles Caldera, New Mexico: ESR finger printing and discussion of ESR ages
Shin Toyoda and Fraser Goff
The eruption ages and stratigraphic sequence of the youngest members of the Valles Rhyolite are of interest for understanding the Quaternary volcanic history of the Valles caldera and for investigating volcanic hazards. ESR signals due to three types of Ti centers in quartz were employed to clarify the debated stratigraphic sequence found in the VC-1 core. Samples of xenocrystic quartz from the Banco Bonito, El Cajete and Battleship Rock Members have distinctive signal patterns, indicating that each magma had captured quartz grains from different sources, although the major and trace chemical composition of the magmas are similar. Comparing the patterns observed in the samples from the VC-1 core with those in the samples from outcrops, our results generally support the stratigraphic assignments of volcanic units made by Goff and Gardner (1987). The possible problems of ESR ages recently published by Toyoda et al. (1995) are also discussed, concluding that ESR ages of 53±6 ka for the El Cajete Member and 59±6 ka for the Battleship Rock Member, supported by the recent TL age on the El Cajete Member, are presently the best estimates of the eruption ages of these units.
- Toyoda, Shin; Goff, Fraser, 1996, Quartz in post-caldera rhyolites of Valles Caldera, New Mexico: ESR finger printing and discussion of ESR ages, in: The Jemez Mountains Region, Goff, Fraser; Kues, Barry S.; Rogers, Margaret Ann; McFadden, Les D.; Gardner, Jamie N., New Mexico Geological Society, Guidebook, 47th Field Conference, pp. 303-309.