Dating Metamorphism with Accessory Minerals - Integrated In-situ Geochronology and Trace Element Budgeting of Metamorphic Reactions

该提案寻求资金来研究岩石学研究的两个基本方面，即通过辅助矿物对变质过程定年的改进理解和“麻粒岩之谜”。地质年代学仍然面临的挑战之一是了解用于U-Th-Pb定年的辅助矿物在变质作用中何时以及通过何种反应生长和修饰。问题是：在变质的P-T路径的哪一部分，我们可以用一种特殊的辅助矿物来确定年代？最先进的成像和激光烧蚀ICP-MS技术将用于进行现场地质年代学、微量元素测温和指纹、微量元素预算，所有这些都是在详细的纹理背景下进行的。“麻粒岩之谜”关注的是如何在大陆地壳中形成麻粒岩相条件（高T和中等P）。知识价值。提出的研究将解决变质岩石学和地质年代学中的三个基本问题：1)变质路径的哪一部分可以通过不同的附属相来确定年代？2)夹杂物纹理是配件相的可靠的相对时间标记吗？3)高山型造山带麻粒岩变质的热源可能是什么？研究对象为阿尔卑斯中部格鲁夫杂岩造山带中一个年轻（30 Ma）的高温麻粒岩相岩产状。利用激光烧蚀ICP-MS法测定富u - th辅助矿物（xenotime、monazite、锆石）的年龄，可获得1- 2%的精度，从而将瞬变变质事件与区域地质历史进行对比。以往的PI研究已经确定了格鲁夫杂粒岩中的副矿物结构，它们具有将矿物结构和包裹体关系与变质反应的微量元素收支和副相生长的平衡反应结合起来的潜力，例如石榴石破碎结构中的xenotime可能是由高温石榴石中储存的HREE和Y产生的，有或没有monazite和/或磷灰石的参与。石榴石或金红石的分解可能使Zr参与变质锆石的生长。更广泛的影响。这项研究将有助于解决上述非常基本的科学问题。此外，该项目将支持一名博士生，并为该博士生提供与变质岩石学建模领域专家进行国际合作的机会，从而提高堪萨斯大学的专业知识。这将为研究生未来在工业界或学术界的职业生涯提供重要的国际经验。该项目还涉及本科生的活动，将发展他们的教学和领导技能，并提供深入了解研究，最先进的分析设施和国际合作科学。与PI和KU实验室的其他学者的合作将把学习扩展到课堂之外。

This proposal seeks funding to investigate two fundamental aspects of petrological research, namely an improved understanding of dating metamorphic processes by accessory minerals and the "granulite enigma". One of the remaining challenges to geochronology is to understand when and by which reactions accessory minerals used for U-Th-Pb dating grow and are modified during metamorphism. The question is: which part of a metamorphic P-T path are we dating with a particular accessory mineral? State-of-the-art imaging and laser-ablation ICP-MS techniques will be used to carry out in-situ geochronology, trace element thermometry and fingerprinting, trace element budgeting, all in a detailed textural context. The "granulite enigma" concerns how granulite facies conditions (high T at moderate P) are attained in the continental crust.Intellectual merit. The proposed research will address three fundamental questions in metamorphic petrology and geochronology: 1) Which part of the metamorphic path can be dated by different accessory phases? 2) Are inclusion textures reliable relative time markers for accessory phases? 3) What is the likely heat source responsible for granulite metamorphism in an alpine style orogen? The target area to be investigated is a young (30 Ma) occurrence of high temperature granulite facies rocks in orogenic belts, the Gruf complex in the Central Alps. Ages can determined with 1-2 % precision by laser ablation ICP-MS dating of U-Th-rich accessory minerals (xenotime, monazite, zircon), enabling correlation of the transient metamorphic event with the regional geological history. Previous studies of the PI have identified accessory mineral textures in the Gruf complex granulites that have the potential to combine mineral textures and inclusion relationships with trace element budgeting of metamorphic reactions and balancing reactions of accessory phase growth, e.g. xenotime found in breakdown-textures of garnet may be produced from HREE and Y stored in high temperature garnet, with or without involvement of monazite and/or apatite. Garnet- or rutile-breakdown may contribute Zr to metamorphic zircon growth.Broader impacts. This study will contribute to the very fundamental scientific questions outlined above. In addition, the project will support one PhD student and provides that student an opportunity for international collaboration with an expert in the field of metamorphic petrological modeling, which enhances the expertise at KU. This will provide the graduate student with important international experience for a future career either in industry or academia. The project also involves undergraduate students in activities that will develop their teaching and leadership skills and provide insight into research, state-of-the-art analytical facilities and international collaborative science. Work with the PI and other academics in the KU laboratories will extend learning beyond the classroom.