Acigöl rhyolite field, Central Anatolia (part 1): high-resolution dating of eruption episodes and zircon growth rates
Acigöl rhyolite field, Central Anatolia (part 1): high-resolution dating of eruption episodes and zircon growth rates
复制标题
DOI：
10.1007/s00410-011-0648-x
复制
发表时间：
2011-05
影响因子：
3.5
通讯作者：
A. Schmitt;M. Danišík;N. Evans;W. Siebel;Elena Kiemele;F. Aydın;Janet Harvey
中科院分区：
文献类型：
--
作者：
A. Schmitt;M. Danišík;N. Evans;W. Siebel;Elena Kiemele;F. Aydın;Janet Harvey
在大陆流纹岩中经常检测到长期的喷发前锆石停留，并可能与热模型相冲突，这表明如果按喷发量衡量，岩浆冷却持续时间更短。在这里，我们给出了来自土耳其中安纳托利亚AcigöL流纹岩油田的U-Th和(U-Th)/He锆石联合年龄，该流纹岩油田是第四纪双峰式火山杂岩的一部分。与其他地质计时器不同的是，这种方法确定了同一晶体的结晶和喷发的时间，从而允许进行内部一致性测试。尽管L流纹岩火山作用的总体寿命和相容微量元素的逐渐亏损和锆石饱和温度下降的系统趋势，我们发现锆石结晶在中更新世和晚更新世分别对应于油田东部和西部的两个短暂的脉冲喷发。晚更新世锆石的内部结晶年龄(平均值：30.70±10.9ka；1σ误差)与边缘结晶年龄(21.9m±1.3ka)存在可分辨的差异。这些换算为~10−13~10−14 cm/S的径向晶体生长速率，与扩散实验所限制的结果基本一致。边缘结晶年龄和(U-Th)/He喷发年龄(24.2±100.4 ka)在不确定范围内重叠。AcigöL的锆石短暂停留的证据与许多其他流纹岩领域的对比表明，在大陆硅质岩浆系统中，长期结晶的锆石结晶或从长寿命晶体泥中回收的锆石并不普遍。相反，喷发前锆石年龄的跨度与来自玄武岩前体的个别小体积岩浆批次的原地结晶一致。
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; 1σerror) and rim (21.9 ± 1.3 ka) crystallization ages. These translate into radial crystal growth rates of ~10−13to 10−14cm/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.