Titanium concentration in quartz as a record of multiple deformation mechanisms in an extensional shear zone
Titanium concentration in quartz as a record of multiple deformation mechanisms in an extensional shear zone
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石英中的钛浓度作为拉伸剪切带中多种变形机制的记录
DOI：
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发表时间：
2014
期刊：
影响因子：
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通讯作者：
A. Mulch
中科院分区：
文献类型：
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作者：
W. O. Nachlas;D. Whitney;C. Teyssier;B. Bagley;A. Mulch
通过对一套渐进变形石英岩糜棱岩中不同重结晶微结构石英中Ti含量（[Ti]）的高精度分析，揭示了重结晶对石英中Ti分布的影响。岩相学观察和离子探针分析揭示了糜棱岩中三种结构和地球化学上不同的石英微结构：（1）再结晶的石英带的芯保持最高的[Ti]并且被解释为已经通过晶界迁移再结晶而再结晶，（2）再结晶边缘和晶界保持较低和更易变的[Ti]反映了亚晶旋转和膨胀重结晶的综合影响;（3）在膨胀部位析出的新固结石英[Ti]较低（~ 1 ppm），反映了同变形流体的Ti含量。白云母nonmylonitic石英岩（在采样导线的基础）的成分分区，而白云母在糜棱岩石英岩显示了一个逐步减少分区在较高的应变样品。岩石样品的X射线计算机断层扫描分析的三维相分布图显示，与非糜棱岩石英岩相比，含Ti副相在高应变糜棱岩中的含量较低，且更分散。本研究证明了动态重结晶对石英中Ti置换的影响，并评估了含水流体（流星与变质/岩浆）的Ti缓冲能力以及变形石英岩中含Ti副相的分布和反应性。本研究结果表明，变形石英的钛石英温压法是解决地壳剪切带中石英变形和重结晶的多阶段历史的敏感技术。
Results of high precision analysis of Ti concentration ([Ti]) in quartz representing different recrystallization microstructures in a suite of progressively deformed quartzite mylonites show the effect of recrystallization on distribution of Ti in quartz. Petrographic observations and ion microprobe analysis reveals three texturally and geochemically distinct quartz microstructures in mylonites: (1) cores of recrystallized quartz ribbons preserve the highest [Ti] and are interpreted to have recrystallized via grain boundary migration recrystallization, (2) recrystallized rims and grain margins preserve a lower and more variable [Ti] and are interpreted to reflect the combined influence of subgrain rotation and bulging recrystallization, and (3) neocrystallized quartz precipitated in dilatancy sites has low (∼1 ppm) [Ti], reflecting the Ti content of the syndeformational fluid. Muscovite in nonmylonitic quartzite (at the base of the sampling traverse) is compositionally zoned, whereas muscovite in mylonitic quartzite shows a progressive decreasing in zoning in higher strain samples. Three‐dimensional phase distribution mapping using X‐ray computed tomography analysis of rock hand samples reveals that Ti‐bearing accessory phases are less abundant and more dispersed in higher strained mylonites compared to nonmylonitic quartzite. This study demonstrates the influence of dynamic recrystallization on Ti substitution in quartz and evaluates the Ti buffering capacity of aqueous fluids (meteoric versus metamorphic/magmatic) as well as the distribution and reactivity of Ti‐bearing accessory phases in a deforming quartzite. Results of this study suggest that Ti‐in‐quartz thermobarometry of deformed quartz is a sensitive technique for resolving the multistage history of quartz deformation and recrystallization in crustal shear zones.