Tectonic evolution of core zones of orogenic belts (Canadian Cordillera and Grenville Province)

为了建立和验证碰撞山带形成的模型，必须了解内部带整个垂直地壳剖面的构造演化、压力(P) -温度(T)历史以及变形和变质作用的相对和绝对时间。在BC省南部的科迪勒拉（Cordillera）暴露了这样一段剖面，在那里对造山活动最后阶段的构造历史、时间和P-T条件有很好的了解。在建造的早期阶段，对P-T历史进行年龄限制会出现困难，因为易于确定年代的矿物不包含直接的P-T信息。第一个目标是建立一种新技术，使用Sm-Nd同位素来确定石榴石晶内区域的年代，石榴石是一种化学成分和质地变化可能记录其生长和变形历史中环境P-T条件的矿物。因此，在不同阶段形成的P-T条件和结构可以直接确定年代，这是一种应用于广泛地质研究的最有力的工具。第二个目标是将该技术与其他领域、岩石学和地质年代学研究相结合，应用于缺乏早期变形和P-T条件直接日期的Cordillera和Ontario Grenville。研究结果将为地壳中部过程和山带构造与崩塌模型提供检验，并应用于解释加拿大地盾的古代地质地体和完善资源勘探模型。第三，根据矿物的化学成分来确定岩石的P-T条件的方法是基于热力学原理的，没有考虑变形的影响。变形和变质过程之间的相互作用将通过在岩石中进行详细的研究来评估，我们可以跟踪变质作用的差异，作为微观结构变化的函数。本研究结果将对变形岩石中P-T结果的意义产生广泛的影响。本科生和研究生的研究涉及项目设计、实地考察、分析技术和构造综合的各个方面，是拟议研究计划的组成部分。

In order to formulate and test models for the formation of collisional mountain belts, it is essential to know the structural evolution, pressure (P) - temperature (T) history, and relative and absolute timing of deformation and metamorphism throughout a vertical crustal section in the internal zone. Such a section is exposed in the Cordillera of southern BC where the structural history, timing and P-T conditions of the last stages of mountain building events are well understood. Difficulties arise in placing age constraints on the P-T history during the early stages of construction, because minerals that are readily dated do not contain direct P-T information. The first goal is to set up a new technique that uses Sm-Nd isotopes to date intracrystalline domains of garnet, a mineral whose variations in chemical composition and textures may record the ambient P-T conditions during its growth and deformation history. Thus P-T conditions and structures that formed at different stages may be dated directly, a most powerful tool with applications to a wide spectrum of geological studies. The second goal is to apply this technique, in conjunction with other field, petrology and geochronology studies, to the Cordillera and Ontario Grenville where direct dates on early-stage deformation and P-T conditions are missing. Results will provide a test of models about mid-crustal processes and the construction and collapse of mountain belts, with applications to interpreting ancient geologic terranes in the Canadian Shield and refining models for resource exploration. Thirdly, methods used to determine P-T conditions of rocks from chemical compositions of minerals are based on thermodynamic principles, and do not account for the effects of deformation. The interplay between deformation and metamorphic processes will be evaluated by carrying out detailed studies in rocks where we can track differences in metamorphism as a function of variation in microstructures. The results of this study will have broad reaching implications for significance of P-T results in deformed rocks. Undergraduate and Graduate Student research involving all aspects of project design, fieldwork, analytical techniques and tectonic synthesis is an integral part of the proposed research program.