Low differential stress during high-pressure metamorphism: The microstructural record of a metapelite from the Eclogite Zone, Tauern Window, Eastern Alps
Low differential stress during high-pressure metamorphism: The microstructural record of a metapelite from the Eclogite Zone, Tauern Window, Eastern Alps
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高压变质作用期间的低差应力：来自东阿尔卑斯山陶恩窗榴辉岩带的变泥岩的微观结构记录
DOI：
10.1016/s0024-4937(97)82007-5
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发表时间：
1997
期刊：
影响因子：
3.5
通讯作者：
Elke Ursula Nowlan
中科院分区：
文献类型：
--
作者：
B. Stöckhert;H. Massonne;Elke Ursula Nowlan
在折返过程中保持不变的前提下，可以从高压变质岩的微构造记录中获得收敛板块边界深部应力状态的约束条件。东阿尔卑斯山Tauern窗榴辉岩带中变闪长石榴石的包裹体模式揭示了受晶界自由能控制的石英泡沫微结构。石榴石爆炸显示同心化学分带。根据与蓝晶石、金红石和石英共生的石榴石、绿泥石和多硅白云母的组成区域之间的相关性进行的温压测量表明，石榴石的生长在接近25kbar和600°C的峰值P-T条件之前就开始了，并在减压早期持续。这表明石英的微结构受晶界自由能控制，在埋藏末期至约80公里深度和折返早期持续存在，包括从下行板剥离并释放到俯冲通道中。复生石英的泡沫结构表明，在此期间，当岩石穿过板块之间的界面时，差异应力太低，不足以驱动位错蠕变，高的差异应力导致构造超压或显著的剪切加热被排除在外。在保护性石榴石之外，由于位错蠕变变形过程中的动态再结晶，界面自由能控制的石英微结构被完全破坏。这发生在地壳切片被挖掘到大约45公里深的时候。这种同运动学石英显微结构的保存表明了一种构造情景，即最终冷却迅速，脆塑性转变没有明显的应力峰值。
Constraints on the state of stress at deep levels of convergent plate boundaries can be obtained from the microstructural record of high-pressure metamorphic rocks, provided that this record has remained unchanged during exhumation. The inclusion patterns in poikiloblastic garnet of a metapelite from the Eclogite Zone of the Tauern Window, Eastern Alps, reveal a foam microstructure of quartz controlled by grain boundary free energy. The garnet blasts show concentric chemical zonation. Thermobarometry based on correlation between compositional domains in garnet, chloritoid and phengite coexisting with kyanite, rutile and quartz shows that garnet growth commenced before peak P-T conditions close to 25 kbar and 600°C had been reached and continued during the early stage of decompression. This implies that the microstructure of quartz, controlled by grain boundary free energy, persisted continuously during the latest stage of burial to ca. 80 km depth and the early stage of exhumation, involving detachment from the downgoing slab and release into the subduction channel. The foam structure of the overgrown quartz indicates that the differential stress was too low to drive dislocation creep during that period, when the rock crossed the interface between the plates, with a high differential stress resulting in ‘tectonic overpressure’ or significant shear heating being ruled out. Outside the protective garnet the interfacial free energy controlled quartz microstructure has been destroyed completely due to dynamic recrystallization during deformation by dislocation creep. This happened while the crustal slice was exhumed to a depth of about 45 km. The preservation of this synkinematic quartz microstructure indicates a tectonic scenario where the final cooling was rapid and no marked stress peak was associated with the brittle-plastic transition.