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Published December 2011 | public
Journal Article

Acigöl rhyolite field, Central Anatolia (part 1): high-resolution dating of eruption episodes and zircon growth rates

Abstract

Protracted pre-eruptive zircon residence is frequently detected in continental rhyolites and can conflict with thermal models, indicating briefer magma cooling durations if scaled to erupted volumes. Here, we present combined U-Th and (U-Th)/He zircon ages from the Acigöl rhyolite field (Central Anatolia, Turkey), which is part of a Quaternary bimodal volcanic complex. Unlike other geochronometers, this approach dates crystallization and eruption on the same crystals, allowing for internal consistency testing. Despite the overall longevity of Acigöl rhyolite volcanism and systematic trends of progressive depletion in compatible trace elements and decreasing zircon saturation temperatures, we find that zircon crystallized in two brief pulses corresponding to eruptions in the eastern and western part of the field during Middle and Late Pleistocene times, respectively. For Late Pleistocene zircon, resolvable differences exist between interior (average: 30.7 ± 0.9 ka; 1σ error) and rim (21.9 ± 1.3 ka) crystallization ages. These translate into radial crystal growth rates of ~10^(−13) to 10^(−14) cm/s, broadly consistent with those constrained by diffusion experiments. Rim crystallization and (U-Th)/He eruption ages (24.2 ± 0.4 ka) overlap within uncertainty. Evidence for brief zircon residence at Acigöl contrasts with many other rhyolite fields, suggesting that protracted zircon crystallization in, or recycling from, long-lived crystal mushes is not ubiquitous in continental silicic magma systems. Instead, the span of pre-eruptive zircon ages is consistent with autochthonous crystallization in individual small-volume magma batches that originated from basaltic precursors.

Additional Information

© 2011 Springer-Verlag. Received: 22 January 2011. Accepted: 3 May 2011. Published online: 24 May 2011. We thank Felix Wicke for photographic documentation of fieldwork, Simone Jahn for assistance in zircon separation, as well as Cam Scadding and Allen Thomas at TSW Analytical, Perth, for assistance with ICP MS. Erkan Aydar and Vedat Toprak are thanked for insightful discussions during a field trip to the area. Erkan Aydar also provided samples for the regional comparison, and Lütfiye Akın is thanked for additional zircon sample preparation. Constructive reviews by Calvin Miller and Jonathan Miller are acknowledged. We thank Jochen Hoefs for editorial handling. This study was supported by a grant from the German Science Foundation (Si 718/9-1). The ion microprobe facility at UCLA is partly supported by a grant from the Instrumentation and Facilities Program, Division of Earth Sciences, National Science Foundation.

Additional details

Created:
August 19, 2023
Modified:
October 24, 2023