Collaborative Research: Record of UHP Terrain Exhumation Preserved in Shear Zones of the Western Gneiss Region (Norway)

合作研究：西部片麻岩地区剪切带保存的超高压地形剥露记录（挪威）

• 批准号: 1827198
• 负责人: Stacia Gordon
• 金额: $ 22.04万
• 依托单位: Board of Regents, NSHE, obo University of Nevada, Reno
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2018
• 资助国家: 美国
• 起止时间: 2018-07-01 至 2024-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1827198&HistoricalAwards=false
• 关键词: Collaborative; Research; Record; UHP; Terrain

According to the theory of plate tectonics, continents can collide against others or dive under another plate (subduction) to depths of over 100 km. The existence of rocks at the Earth's surface that have minerals that can only be formed at great depths in the Earth?s interior suggests that continental subduction is a common process. The geological processes that are able to bring rocks from considerable depth back to the surface, also known as exhumation, remain enigmatic. This project focuses on a study of one of the largest and best-exposed area in the world (the Western Gneiss Region of Norway) where these so-called ultrahigh pressure rocks (UHP) are exposed. This study will examine how this process of exhumation may have occurred in the past. Because large blocks of UHP rocks have yet to be discovered in North America, they are typically not readily available in teaching collections at U.S. colleges and universities. This education activities in this project will be to create a teaching module centered on UHP rocks that includes rock and thin section sets to be used in petrology and related courses. The collections and teaching module will be disseminated to 15 schools in collaboration with geoscience education specialists in order to optimize impact and diversity and help manage teaching effectiveness and assessment. The project also includes a display and activities using field photos and rock samples from the Western Gneiss Region to explain plate tectonics and subduction zones to K-12 students visiting the Earth Science and Mineral Engineering Museum housed at University of Nevada - Reno. In addition, graduate and undergraduate students are trained in both research and outreach activities. The rates and mechanisms of exhumation of UHP terranes are still poorly known because the preservation of UHP mineral assemblages is sporadic, and it is also a function of how reactive the exhumed crust was. Two end-member modes of exhumation of UHP terranes have been proposed: 1) education of a coherent and thus poorly reactive lithospheric slab; and 2) return flow of a body of highly reactive UHP rocks along the subduction channel. The Western Gneiss Region of Norway is an ideal terrane to study these processes because it is transected by numerous 10-100 m scale shear zones that offer a clear history of progressive exhumation based on outcrop-scale crosscutting relationships and metamorphic overprinting in both the mafic (eclogite/amphibolite) bodies and the host quartzofeldspathic gneiss. These largely unstudied shear zones preserve the best record of pressure-temperature-time-deformation (P-T-t-D) conditions during exhumation from mantle to crustal depths and are therefore prime candidates for evaluating the proposed exhumation models. Methods that investigate the petrologic and geochemical record within the shear zones include: (1) detailed field mapping, from outcrop to regional scale, incorporating microstructural analyses within shear zones from across the Western Gneiss Region to determine progressive deformation-recrystallization of minerals, including datable minerals; (2) Titanium-in-quartz thermobarometry to trace conditions during ascent and decompression; and (3) petrochronology based on high- and medium-temperature chronometers based on U-Pb dating using zircon and monazite for the (U)HP part of the path and rutile and titanite for the HP to amphibolite-facies portion of the path. Results provide significant new insight into the P-T-t-D paths that are preserved in the geologic record of exhumed UHP terranes, and more generally into the rates and mechanisms of UHP terrane exhumation.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

根据板块构造的理论，大陆可以与他人碰撞或在另一个板块下潜水（俯冲）到超过100 km的深度。地球表面的岩石的存在只能在地球内部深处形成矿物质，这表明大陆俯冲是一个共同的过程。能够将岩石从深度带回到地面的地质过程（也称为挖掘）仍然是神秘的。该项目着重于对这些所谓的超高压力岩石（UHP）暴露的世界上最大，最暴露的地区之一（挪威西部地区）的研究。这项研究将研究过去如何发生这种挖掘过程。由于在北美尚未发现大量的UHP岩石，因此在美国大学和大学的教学收藏中，它们通常不容易获得。该项目中的这项教育活动将是创建一个以UHP岩石为中心的教学模块，其中包括岩石和薄片集，用于岩石学和相关课程。收集和教学模块将与地球科学教育专家合作将15所学校传播到15所学校，以优化影响和多样性，并帮助管理教学效率和评估。该项目还包括使用现场照片和岩石样品的展示和活动，向访问内华达大学 - 里诺大学的地球科学和矿产工程博物馆的K -12学生解释板块构造和俯冲区。此外，研究生和本科生接受了研究和外展活动的培训。 UHP地层挖掘的速率和机制仍然鲜为人知，因为UHP矿物质组合的保存是零星的，并且它也是散发性壳的反应性的函数。已经提出了两种末端成员的UHP地层挖掘模式：1）对连贯性且反应性岩石圈板的教育； 2）沿俯冲通道的高反应性UHP岩石体的返回流。挪威西部片麻岩地区是研究这些过程的理想地形，因为它是由许多10-100 m的剪切带过渡的，这些剪切区提供了基于露台横切关系和变质过高印刷（Eclogite/Amphibogolite）的身体的清晰渐进式灌输史，并提供了变质的过电。这些在很大程度上未研究的剪切区保留了从地幔到地壳深度的挖掘过程中压力 - 温度实时变形（P-T-T-D）条件的最佳记录，因此是评估拟议挖掘模型的主要候选者。研究剪切区域内岩石学和地球化学记录的方法包括：（1）从露头到区域尺度的详细田间映射，在整个西部Gneiss地区的剪切区域内纳入了微观结构分析，以确定逐步的矿物质矿物质矿物质矿物质，包括数据矿物质，包括数据矿物质； （2）在上升和减压期间，Quartz中钛热量计到痕量条件； （3）基于在路径的（U）HP部分的（U）HP部分以及HP将HP的（u）HP部分的（u）HP部分的氧化锆和单纳济基基于U-PB日期的高温和中等温度的石化学。结果提供了对P-T-T-D路径的重大见解，这些路径保留在挖掘的UHP地层的地质记录中，更笼统地介绍了UHP Terrane挖掘的速度和机制。该奖项反映了NSF的法定任务，并通过评估该基金会的知识分子优点和广泛的影响来评估NSF的法定任务。

项目成果

Deformation-enhanced recrystallization of titanite drives decoupling between U-Pb and trace elements

钛矿的形变强化再结晶驱动 U-Pb 与微量元素之间的解耦

• DOI: 10.1016/j.epsl2021.116810
• 发表时间: 2021
• 期刊: Earth and planetary science letters
• 影响因子: 5.3
• 作者: Gordon, S.M.;Kirkland, C.L.;Reddy, S.M.;Blatchford, H.J.;Whitney, D.L.;Teyssier, C.;Evans, N.J.;McDonald, B.J.
• 通讯作者: McDonald, B.J.

LEVERAGING SHEAR ZONE-HOSTED TITANITE, RUTILE, AND QUARTZ TO EXTRACT A DETAILED EXHUMATION HISTORY OF THE NORDØYANE UHP DOMAIN, WESTERN GNEISS REGION, NORWAY

利用剪切带中的钛铁矿、金红石和石英提取挪威西部片麻岩地区 Nordäyane UHP 域的详细挖掘历史

• DOI: 10.1130/abs/2023am-395646
• 发表时间: 2023
• 期刊: Geological Society of America
• 作者: Blatchford, Hannah;Whitney, Donna;Teyssier, Christian;Gordon, Stacia;Dektar, Emily C.
• 通讯作者: Dektar, Emily C.

COMBINED ZIRCON PETROCHRONOLOGY AND MICROSTRUCTURAL ANALYSIS: INSIGHT INTO LONG-LIVED SHEAR ZONE ACTIVITY IN THE WESTERN GNEISS REGION, NORWAY

结合锆石岩石年代学和微观结构分析：深入了解挪威西部片麻岩地区长期存在的剪切带活动

• DOI: 10.1130/abs/2022cd-373689
• 发表时间: 2022
• 期刊: Geological Society of America Abstracts with Programs
• 作者: Gordon, Stacia;Dektar, Emily C.;Blatchford, Hannah;Lim, Luz
• 通讯作者: Lim, Luz