Origin of Ti-rich rims in quartz phenocrysts from the Upper Bandelier Tuff and the Tunnel Spring Tuff, southwestern USA
Origin of Ti-rich rims in quartz phenocrysts from the Upper Bandelier Tuff and the Tunnel Spring Tuff, southwestern USA
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DOI：
10.1016/j.chemgeo.2013.10.015
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发表时间：
2013-12-18
期刊：
影响因子：
3.9
通讯作者：
Audetat, Andreas
中科院分区：
文献类型：
--
作者：
Audetat, Andreas
四个组成分区，熔融包裹体轴承石英斑晶从上Bandelier凝灰岩，新墨西哥州和隧道泉凝灰岩，犹他州进行了详细的阴极射线发光，激光烧蚀ICP-MS，和石英中的钛（TitaniQ）热压法，以重建石英结晶的条件。温度和TiO 2活性通过锆石饱和测温法和实验校准的TiO 2溶解度模型，从熔融包裹体成分估计岩浆中的α TiO 2（α TiO 2），而压力是通过最近校准的TitaniQ温压计对分析的熔融包裹体旁边的主石英进行估计的。所有四种研究的石英斑晶都显示出低发光，贫钛核心被高发光富钛边缘过度生长。重建的P-T-α TiO 2的条件表明，从上Bandelier凝灰岩的两个石英晶体的Ti含量的rimward增加是由于温度升高，增加α TiO 2和压力降低的组合，与温度的影响是占主导地位的一个晶体和α TiO 2的影响是占主导地位的其他晶体。在隧道泉凝灰岩的两个晶体中，Ti含量的边缘增加主要是由于温度升高，但在其中一个晶体中，负压变化起着同样重要的作用。这项研究表明，在快速冷却的过铝质或变铝质流纹中，石英斑晶的结晶条件可以在单个生长带的尺度上重建，这使得可以非常详细地研究这种岩浆的起源和演化。(C)2013爱思唯尔有限公司版权所有。
Four compositionally zoned, melt inclusion-bearing quartz phenocrysts from the Upper Bandelier Tuff, New Mexico and the Tunnel Spring Tuff, Utah were examined in detail by cathodoluminescence, laser-ablation ICP-MS, and titanium-in-quartz (TitaniQ) thermobarometry in order to reconstruct the conditions of quartz crystallization. Temperature and TiO2 activity (alpha TiO2) in the magma were estimated from melt inclusion compositions by means of zircon saturation thermometry and an experimentally calibrated TiO2 solubility model, whereas pressure was estimated with the most recent calibration of the TitaniQ thermobarometer on the host quartz next to the analyzed melt inclusions.All four investigated quartz phenocrysts display a low-luminescent, Ti-poor core overgrown by a high-luminescent, Ti-rich rim. Reconstructed P-T-alpha TiO2 conditions suggest that the rimward increase in the Ti content of the two quartz crystals from the Upper Bandelier Tuff is due to a combination of increasing temperature, increasing alpha TiO2 and decreasing pressure, with the temperature effect being dominant in one crystal and the alpha TiO2 effect being dominant in the other crystal. In the two crystals from the Tunnel Spring Tuff the rimward increase in Ti content is mostly due to increasing temperature, but in one of them a negative pressure change played an equally important role.This study demonstrates that in rapidly cooled, peraluminous or metaluminous rhyolites the crystallization conditions of quartz phenocrysts can be reconstructed at the scale of individual growth zones, which allows to investigate the origin and evolution of such magmas in great detail. (C) 2013 Elsevier B.V. All rights reserved.