New petrochronology tools and approaches for reconstructing high-temperature crustal process.

地壳保存了近40亿年来板块构造对地球的改造和分化的记录。在板块碰撞和造山(造山)期间，这两个过程都导致地壳岩石在数千万年的时间尺度上局部加热。这些古老碰撞的记录在岩石的埋葬、居住和挖掘过程中形成的矿物中留下了明显的结构、化学和同位素特征，回到了地表。破译古代高温地壳作用的印记是变质岩“岩石年代学”的重点。这一领域最近经历了复兴，因为有了新的分析工具，能够以以前无法达到的空间分辨率测量同位素比率。第一个项目将由一名硕士研究生完成，他的任务是记录公元前东南部中元古代变质杂岩中暴露的两个明确地壳区块之间的构造并置的绝对年龄。该项目将测试新的原位Rb-Sr测年技术在云母上的适用性，这些技术也以其微量元素分带模式为特征。这一结果有望为北美祖先边缘的中元古代活动边缘过程提供新的线索，并将为其他变质背景下更雄心勃勃的项目提供一个起点。第二个项目将由一名博士研究生在北半球布雷顿角高地西部约400 Ma的岩石中进行。这里暴露了从绿泥石到蓝晶石带岩石的完整变质序列，并显示了历时U-Pb独居石和Lu-HF石榴石年龄的升温。这里的目标将是使用运动式的原位Rb-sr测年和微量元素作图来识别变质序列沿其叠加的构造走廊。这些结果将有助于我们全面了解中地壳对板块碰撞的响应，以及变形和变质作用的时间是如何相互关联的。这项建议的最后一个组成部分旨在建立一种新的激光烧蚀液体取样系统(LASIL)，以充分利用对溶液进行的电感耦合等离子体质谱测量的高得多的灵敏度。其基本概念是将激光消融过程中从样品中喷出的纳米颗粒夹带到液体中。这将需要3D设计、计算流体流动建模、多喷口3D打印和原型测试。根据液体体积、烧蚀气溶胶释放体积和估计的分析物浓度进行的一级计算表明，与传统的激光消融相比，灵敏度至少有可能提高两个数量级。如果成功，这种LASIL方法将为原位同位素测量带来革命性的变化，并使加拿大处于现代激光烧蚀界面开发的前沿。

Earth's crust preserves a nearly 4.0 billion year record of our planet's modification and differentiation by plate tectonics. Both processes lead to localized heating of crustal rocks over timescales of tens of millions of years during episodes of plate collision and mountain building (orogenesis). The record of these ancient collisions leave tell-tale textural, chemical, and isotopic features in minerals that form in rocks during their burial, residence, and exhumation back to the surface. Deciphering the imprints of ancient high-temperature crustal processes is the focus of metamorphic `petrochronology'. This field has undergone a recent renaissance because of new analytical tools capable of measuring isotope ratios at spatial resolutions previously unattainable. The first project will be carried out by a MSc graduate student tasked with documenting the absolute age of structural juxtaposition between two well-defined crustal blocks exposed in a Mesoproterozoic metamorphic complex in southeastern BC. This project will test the applicability of new in situ Rb-Sr dating techniques on micas that also characterized in terms of their trace-element zoning patterns. The results are expected to shed new light on Mesoproterozoic active margin processes along the ancestral margin of North America and will provide a starting point for more ambitious projects in other metamorphic settings. The second project will be carried out by a PhD graduate student in ~400 Ma rocks in the western Cape Breton Highlands, NS. Here a complete metamorphic sequence from chloritoid- to kyanite-zone rocks is exposed and displays diachronous U-Pb monazite and Lu-Hf garnet ages moving up-temperature. The goal here will be to use campaign-style in situ Rb-Sr dating and trace-element mapping to identify structural corridors along which the metamorphic sequences were imbricated. The results will contribute to our overall understanding of how the middle-crust responds to plate collisions and how the timing of deformation and metamorphism are interlinked. The final component of this proposal aims to build a novel new laser ablation sampling in liquid (LASIL) to take full advantage of the much higher sensitivity of ICP-MS measurements performed on solutions. The basic concept is to entrain in a liquid the nanoparticles ejected from a sample during laser ablation. This will require the 3D design, computational fluid-flow modeling, multi-jet 3D printing, and prototype testing. First-order calculations based on volumes of liquid, volume of ablated aerosol liberated, and estimated concentrations of analytes suggest that an increase in sensitivity of at least two orders of magnitude, relative to conventional laser ablation, is possible. If successful, this LASIL method will revolutionize in situ isotope measurements and place Canada at the forefront of modern laser ablation interface development.