Acigöl rhyolite field, Central Anatolia (part 1): high-resolution dating of eruption episodes and zircon growth rates Axel K. Schmitt, Martin Danišík, Noreen J. Evans, Wolfgang Siebel, Elena Kiemele, Faruk Aydin & Janet C. Harvey Contributions to Mineralogy and Petrology ISSN 0010-7999 Volume 162 Number 6 Contrib Mineral Petrol (2011) 162:1215-1231 DOI 10.1007/s00410-011-0648-x 1 23 Your article is protected by copyright and all rights are held exclusively by Springer- Verlag. This e-offprint is for personal use only and shall not be self-archived in electronic repositories. If you wish to self-archive your work, please use the accepted author’s version for posting to your own website or your institution’s repository. You may further deposit the accepted author’s version on a funder’s repository at a funder’s request, provided it is not made publicly available until 12 months after publication. 1 23 Author's personal copy Contrib Mineral Petrol (2011) 162:1215–1231 DOI 10.1007/s00410-011-0648-x ORIGINAL PAPER Acigo¨l rhyolite field, Central Anatolia (part 1): high-resolution dating of eruption episodes and zircon growth rates Axel K. Schmitt • Martin Danisˇ´ık • Noreen J. Evans • Wolfgang Siebel • Elena Kiemele • Faruk Aydin • Janet C. Harvey Received: 22 January 2011 / Accepted: 3 May 2011 / Published online: 24 May 2011 Ó Springer-Verlag 2011 Abstract Protracted pre-eruptive zircon residence is fre- crystallized in two brief pulses corresponding to eruptions quently detected in continental rhyolites and can conflict in the eastern and western part of the field during Middle with thermal models, indicating briefer magma cooling and Late Pleistocene times, respectively. For Late Pleis- durations if scaled to erupted volumes. Here, we present tocene zircon, resolvable differences exist between interior combined U-Th and (U-Th)/He zircon ages from the Aci- (average: 30.7 ± 0.9 ka; 1r error) and rim (21.9 ± 1.3 ka) go¨l rhyolite field (Central Anatolia, Turkey), which is part crystallization ages. These translate into radial crystal of a Quaternary bimodal volcanic complex. Unlike other growth rates of *10-13 to 10-14 cm/s, broadly consistent geochronometers, this approach dates crystallization and with those constrained by diffusion experiments. Rim eruption on the same crystals, allowing for internal con- crystallization and (U-Th)/He eruption ages (24.2 ± sistency testing. Despite the overall longevity of Acigo¨l 0.4 ka) overlap within uncertainty. Evidence for brief zir- rhyolite volcanism and systematic trends of progressive con residence at Acigo¨l contrasts with many other rhyolite depletion in compatible trace elements and decreasing fields, suggesting that protracted zircon crystallization in, zircon saturation temperatures, we find that zircon or recycling from, long-lived crystal mushes is not ubiq- uitous in continental silicic magma systems. Instead, the span of pre-eruptive zircon ages is consistent with Communicated by J. Hoefs. autochthonous crystallization in individual small-volume magma batches that originated from basaltic precursors. Electronic supplementary material The online version of this article (doi:10.1007/s00410-011-0648-x) contains supplementary material, which is available to authorized users. A. K. Schmitt (&) W. Siebel Á E. Kiemele Department of Earth and Space Sciences, Institute of Geosciences, Universita¨tTu¨bingen, University of California, Los Angeles, 595 Charles Young Drive Wilhelmstr. 56, 72074 Tu¨bingen, Germany East, Los Angeles, CA 90095-1567, USA e-mail: [email protected] F. Aydin Department of Geological Engineering, Karadeniz Technical M. Danisˇ´ık Á N. J. Evans University, 61010 Campus Trabzon, Turkey John de Laeter Centre for Isotope Research, Applied Geology, Curtin University, GPO Box U1987, Perth, WA 6845, Australia J. C. Harvey Geological and Planetary Sciences, California Institute Present Address: of Technology, MC 170-25, 1200 E California Blvd, M. Danisˇ´ık Pasadena, CA 91125, USA Department of Earth and Ocean Sciences, Faculty of Science & Engineering, The University of Waikato, Private Bag 3105, Hamilton 3240, New Zealand N. J. Evans CSIRO Earth Science and Resource Engineering, PO Box 1130, Bentley, WA 6102, Australia 123 Author's personal copy 1216 Contrib Mineral Petrol (2011) 162:1215–1231 Keywords Zircon Á (U-Th)/He Á Uranium series Á continental rhyolite fields (e.g., Yellowstone, Long Val- Calderas Á Rhyolite domes ley), Acigo¨l lacks a giant caldera and therefore excellently preserves evidence of most of its eruptive history. More- over, Acigo¨l is one of the youngest known rhyolite fields, Introduction similar to or even younger than Coso (California) which is also dominated by small-volume effusive eruptions (e.g., Continental rhyolite fields are the surface expression of Bacon et al. 1981; Duffield et al. 1980; Simon et al. 2009). intra-crustal hot zones capable of producing protracted Because of its young age, dating of the eruptive stratigra- (over hundred of thousands or million years) and cumula- phy and pre-eruptive crystallization can be achieved at high tively voluminous outpourings of differentiated magma, as absolute temporal precision approaching millennial time- well as batholith-sized intrusive bodies. They are often scales, which is precluded in older rhyolite fields (e.g., temporally and spatially associated with basaltic eruptions Duffield and Dalrymple 1990). Combined U-Th and forming bimodal complexes. Absence of basaltic vents in (U-Th)/He dating of individual zircon crystals provides a rhyolite-dominated regions has been interpreted as evi- detailed chronostratigraphic record with the advantage over dence for an underlying partially molten crustal density other Quaternary geochronometers (e.g., 14C, 40Ar/39Ar) of filter preventing mantle-derived magmas from reaching the using the same crystals for dating crucial events in the surface (Bacon 1985; Druitt et al. 1995). Models empha- evolution of the system (i.e., crystallization and eruption). sizing fractional crystallization of mafic magmas at shallow This allows for an internal consistency check of the ages. depth (*5 km) can explain first-order chemical charac- Our data permit testing of several hypotheses regarding teristics of continental rhyolites (e.g., Fowler and Spera rhyolite fields as an important end-member in the spectrum 2010), but crystal-chemical evidence from major and of continental magmatism: (1) dome clusters have multiple accessory phases (e.g., Reid et al. 2011) is frequently at vents tapping a large underlying melt zone vs. individual odds with simple monotonic cooling scenarios and suggest feeding dikes that extend from a central magma body (e.g., episodic re-heating and mixing events. Moreover, the Bacon 1985); (2) magmas are extracted from intra-crustal longevity of rhyolite fields and the explanation as to why hot zones undergoing thermal cycling rather than thermally some rhyolite systems oscillate between protracted small- retrograde liquid-dominated reservoirs (e.g., Annen 2009; volume monogenetic lava dome effusion and catastrophic Fowler and Spera 2010); and (3) the presence of evolved caldera-forming eruptions remain poorly understood. melts in intra-crustal mush zones is protracted (e.g., To better constrain the magmatic evolution of conti- Bachmann and Bergantz 2004; 2008) vs. rhyolitic magmas nental rhyolite fields and associated intra-crustal hot zones, accumulating rapidly via re-melting of solidified rocks or we initiated a comprehensive investigation into the Acigo¨l rapid differentiation of basalts (Bacon and Lowenstern complex in Cappadocia (Central Anatolia, Turkey; Fig. 1; 2005; Bindeman et al. 2001; Lowenstern et al. 2000; see also Siebel et al. 2011). Unlike many other intra- Schmitt et al. 2003). In a companion paper (Siebel et al. Fig. 1 Neotectonic overview 30°E 40°E map of Turkey with the location of the Cappadocian Volcanic Province (CVP) and its EURASIANE RASIAN PLP ATE Holocene volcanoes (red IstanbuIstanbulbu triangles), as well as the distribution of basement rocks Ankara of the Central Anatolian 40°N Crystalline Complex (CACC; hatched). Red dashed line CACACCCACACCC P outlines low Pn velocity region A CAC in the upper mantle (Dilek and Fig.g 2 Sandvol 2009; Gans et al. 2009) ANAANANATOLIAN MICROMICROPMICROPLROPLROR ATE low Pn ARABIAN PLATE 200 km 35°N AFRICAN PLATE N 123 Author's personal copy Contrib Mineral Petrol (2011) 162:1215–1231 1217 Fig. 2 Quaternary volcanic 34°35’E 34°40’E rocks (MTA 2005) overlay onto Ò KAR (22.3±1.1 ka) ASTER global digital 34°30’E elevation model at 30-m lateral 10 km ALA4 (117±4 ka) resolution. Sample locations and N LAT (206±17 ka) (U-Th)/He eruption ages are main map indicated. Inset: location of the N ’ A Acigo¨l complex and the extent 0 3 ° of the Lower and Upper Acigo¨l 8 KUZ (26.0±1.5 ka) Nev ehir Tuffs (LAT and UAT, 3 N TEP (25.9±0.6 ka) respectively) in relation to other Late Cenozoic volcanic units of G the CVP (yellow: dominantly C KAL (23.2±3.0 ka) rhyolitic centers; red triangles: N ’ T 0 H K basaltic vents): A Acigo¨l, 0 ° N Nenezi, G Go¨llu¨dag˘, 8 M ACI (20.3±0.6 ka) TAS (147±8 ka) 3 C Cinarli, T Tepeko¨y, GÜN (23.8±0.9 ka) UAT (163±7 ka) M Melendiz, K Kec¸iboyduran, Aksaray and H Hasan Dag˘ı (after: Druitt KOC (190±11 ka) BOG (190±9 ka) et al. 1995; Gencalioglu-Kuscu maar rhyolite lava (W Acigöl) and Geneli 2010) basaltic lava/cinder KOR (24.9±0.9 ka) tuffs (undifferentiated) 05 km rhyolite lava (E Acigöl) 38°30’N 2011), we present geochemical data (including radiogenic 1998b; Toprak 1998; Toprak and Go¨ncu¨og˘lu 1993; Vie- and oxygen isotope data) in support of evidence from zir- reck-Goette et al. 2010). The eruptive centers of Miocene– con crystal-scale dating that precludes a seemingly Pliocene ignimbrites inferred from field mapping and straightforward crystal fractionation lineage between sub- geophysical surveys are in close proximity to Quaternary sequently erupted rhyolites at Acigo¨l.