Deformation behaviour of feldspar in greenschist facies granitoide shear zones

研究的目的是阐明绿片岩相条件下长石的变形行为与大陆地壳流变特性的关系。流变特性模型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了解不足。长石是大陆地壳中最丰富的矿物，其变形行为具有脆性、溶解-沉淀和结晶-塑性相互作用的特点，由于实验条件与合理自然条件的外推存在问题，因此难以在实验中进行评价。变质花岗质岩石的微组构记录了其在地质历史过程中的颗粒级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。对于破译岩石记录来说，这意味着解决这些不同阶段的挑战和机会。在这里，我们建议使用从奥阿尔卑斯基底向南至西部陶伦窗的糜棱质伟晶岩的变形记录。伟晶岩代表一个相对简单的贫钙花岗岩体系，矿物学上以富钠长石斜长石、钾长石和石英为主。通过显微分析技术确定长石微织物的结构、晶体学和化学特征，以确定其变形机制。为了约束变形条件（应力、温度）和推断过程的相对顺序，长石微织体将与与变形同时或之后生长的石英和ree矿物的微织体进行对比。将与Emilie Janots博士合作，对稀土矿物进行原位U-Th-Pb定年，以确定不同时间的变形阶段。ree矿物的推断年龄可以与高寒变形史进行对比，即与构造变质古高寒事件（白垩纪）或DAV剪切带（古近纪）的活动进行对比。这些发现将用于解决以下关键问题：脆性机制、溶解-沉淀蠕变和晶体-塑性过程在长石变形行为中起什么作用？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？流变学含义是什么（例如，应力历史，瞬态高应力下的幕式变形，不同变质条件下剪切带的（再）激活）？这些发现有助于阐明大陆地壳的流变特性。

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.