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Deformation behaviour of feldspar in greenschist facies granitoide shear zones

绿片岩相花岗岩剪切带中长石的变形行为

基本信息

批准号：
277689670
负责人：
Professorin Dr. Claudia Trepmann
金额：
--
依托单位：
Institut des Sciences de la Terre (ISTerre)
依托单位国家：
德国
项目类别：
Research Grants
财政年份：
2015
资助国家：
德国
起止时间：
2014-12-31 至 2018-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/277689670?language=en
关键词：
Deformation behaviour feldspar greenschist facies

项目摘要

Objective of the proposed study is to elucidate the feldspar deformation behaviour at greenschist facies conditions relevant for the rheological properties of continental crust. Uncertainties in models for the rheological properties are partly due to a poor knowledge of the deformation mechanisms that are actually taking place in granitoid rocks at inaccessible depth. The deformation behaviour of feldspar, the most abundant mineral in the continental crust, is characterized by an interaction of brittle, dissolution-precipitation and crystal-plastic processes, which is difficult to evaluate in experiments given the problematic extrapolation of experimental conditions to reasonable natural conditions. However, microfabrics of metamorphic granitoid rocks record the grain-scale deformation mechanisms and involved chemical reactions proceeding during their geological history. This usually includes deformation and modification through several stages in space (depth, i.e., P, T conditions) and/or time. For deciphering the rock record this implies both, challenge and chance to resolve these different stages. Here, we propose to use the deformation record of mylonitic pegmatites from the Austroalpine basement south to the western Tauern window. The pegmatites represent a relatively simple Ca-poor granitoid system mineralogically dominated by albite-rich plagioclase, K-feldspar and quartz. The structural, crystallographic and chemical characteristics of the feldspar microfabrics will be determined via micro-analytical techniques to identify the deformation mechanisms. To constraint deformation conditions (stress, temperature) and to infer the relative sequence of processes, the feldspar microfabrics will be correlated to the microfabrics of quartz and REE-minerals that grew contemporaneously with or after deformation. In-situ U-Th-Pb dating of the REE-minerals will be performed in cooperation with Dr. Emilie Janots to identify different deformation stages with respect to time. The inferred age of REE-minerals allows a correlation to the Alpine deformation history, i.e., to the tectonometamorphic eoalpine event (Cretaceous) or to the activity of the DAV shear zone (Paleogene). The findings will be used to address the following key questions: Which role do brittle mechanisms, dissolution-precipitation creep and crystal-plastic processes play on the feldspar deformation behaviour? Are different deformation stages in space (depth, i.e. P, T conditions) and/or time recorded? What are the rheological implications (e.g., stress history, episodic deformation at transient high stresses, (re)activations of shear zones at different metamorphic conditions)? The findings contribute to elucidate the rheological properties of continental crust.

这项研究的目的是阐明与大陆地壳流变性有关的绿片岩相条件下的长石变形行为。流变性质模型中的不确定性部分是由于对花岗岩类岩石在难以接近的深度实际发生的变形机制知之甚少。长石是陆壳中最丰富的矿物，它的变形行为具有脆性、溶解-沉淀和晶体-塑性过程的相互作用，这在实验中很难评估，因为实验条件很难外推到合理的自然条件。而变质花岗岩类岩石的显微组构记录了其地质历史过程中的颗粒尺度变形机制和化学反应过程。这通常包括在空间(深度，即P、T条件)和/或时间上的几个阶段的变形和修改。对于破译摇滚唱片来说，这既意味着挑战，也意味着解决这些不同阶段的机会。这里，我们建议使用从奥斯特拉尔山基底南侧到陶恩窗口西侧的糜棱伟晶岩的变形记录。伟晶岩代表了一种相对简单的贫钙花岗岩系，矿物学上以富钠长石、钾长石和石英为主。将通过微观分析技术确定长石微结构的结构、结晶学和化学特征，以确定变形机制。为了约束变形条件(应力、温度)并推断相对的过程序列，长石微组构将与变形时或变形后同时生长的石英和稀土矿物的微组构进行对比。将与艾米丽·贾诺茨博士合作进行稀土矿物的原位U-Th-Pb测年，以确定不同的时间变形阶段。REE矿物的推断年龄可以与阿尔卑斯变形历史，即构造变质古阿尔卑斯事件(白垩纪)或DAV剪切带的活动(古近纪)进行对比。这些发现将被用来解决以下关键问题：脆性机制、溶解-沉淀蠕变和晶体塑性过程对长石变形行为起到什么作用？是否记录了空间(深度，即P、T条件)和/或时间上的不同变形阶段？流变学的含义是什么(例如，应力历史、瞬间高应力下的幕式变形、不同变质条件下剪切带的(重新)激活)？这些发现有助于阐明陆壳的流变性。