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

用副矿物测定变质作用 - 综合原位地质年代学和变质反应的微量元素预算

• 批准号: 0911633
• 负责人: Andreas Moeller
• 金额: $ 18.78万
• 依托单位: University of Kansas Center for Research Inc
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-08-01 至 2015-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0911633&HistoricalAwards=false
• 关键词: Dating; Metamorphism; Accessory; Minerals; Integrated

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.

这项建议寻求资金，以调查岩石学研究的两个基本方面，即改善对副矿物的变质作用年代测定过程的理解和“麻粒岩之谜”。地质年代学的剩余挑战之一是了解用于U-Th-Pb测年的副矿物在变质过程中何时以及通过哪些反应生长和修改。问题是：我们是在变质P-T路径的哪一部分与一种特殊的副矿物进行测年？将使用最先进的成像和激光消融电感耦合等离子体质谱技术进行现场地质年代学、微量元素测温和指纹、微量元素预算，所有这些都将在详细的背景下进行。“麻粒岩之谜”涉及大陆地壳如何获得麻粒岩相条件(高T、中P)。这项研究将解决变质岩石学和年代学中的三个基本问题：1)变质路径的哪一部分可以由不同的副相确定年龄？2)包裹体结构是副相的可靠相对时间标志吗？3)高山造山带麻粒岩变质的可能热源是什么？研究的目标区是中央阿尔卑斯山Gruf杂岩造山带中一种年轻的(30 Ma)高温麻粒岩相岩石。利用激光烧蚀电感耦合等离子体质谱(ICPMS)测定富U-Th副矿物(辉石、独居石、锆石)的年龄，精度可达1-2%，从而实现了瞬变变质事件与区域地质历史的对比。之前对PI的研究已在Gruf杂岩麻粒岩中发现了副矿物结构，这些副矿物结构可能将矿物结构和包裹体关系与变质反应的微量元素预算和副相生长的平衡反应结合在一起，例如，石榴石分解结构中发现的辉石可能来自储存在高温石榴石中的HREE和Y，有或没有独居石和/或磷灰石的参与。石榴石或金红石的分解可能有助于变质锆石的生长。这项研究将有助于解决上述最基本的科学问题。此外，该项目将支持一名博士生，并为该学生提供与变质岩石学建模领域的专家进行国际合作的机会，这将增强KU的专业知识。这将为研究生未来在工业或学术界的职业生涯提供重要的国际经验。该项目还包括本科生参与的活动，这些活动将发展他们的教学和领导技能，并提供对研究、最先进的分析设施和国际协作科学的见解。与KU实验室的PI和其他学者合作，将把学习延伸到课堂之外。