Collaborative Research: Time Scales and Dimensions of Rheological Heterogeneity and Fabric Evolution in the Lower Continental Crust during Extensional Orogenic Collapse

合作研究：伸展造山塌陷期间下陆壳流变异质性和结构演化的时间尺度和维度

• 批准号: 1119248
• 负责人: Keith Klepeis
• 金额: $ 29.06万
• 依托单位: University of Vermont & State Agricultural College
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-09-01 至 2016-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1119248&HistoricalAwards=false
• 关键词: Collaborative; Research; Time; Scales; Dimensions

This project is providing new information on how thickened lower crust in mountain belts extends and thins during orogenic collapse. Field studies and numerical models demonstrate that the strength, thickness, and mechanical properties of the lower continental crust are key factors that influence the behavior of the entire lithosphere during orogenesis, including the localization of strain into shear zones. However, there still is uncertainty about how these properties change during orogenic cycles and how they influence patterns of deformation. Fiordland, New Zealand provides a natural laboratory for resolving these questions because it exposes over 3000 square kilometers of ancient Mesozoic lower crust. This project is determining the time scales, physical dimensions, and effects of mafic-intermediate magmatism, crustal melting, metamorphism, and deformation on the evolution of this lower crustal section. The work integrates field mapping with three-dimensional analyses of deformation, pressure-temperature-time-deformation paths for rocks, and uranium-lead and samarium-neodymium isotope geochronology. These tools are helping to resolve the thermal and mechanical structure of Fiordland's lower crust over 25 million years and at depths of 35-50 kilometers during a transition from shortening and crustal thickening to extension and crustal thinning. They also are revealing the changing nature of strain localization processes, including the formation of a symmetric style of extensional faults that border domes of high grade metamorphic rocks.The central hypothesis of this research is that variations in temperature, composition, strength, and crustal thickness, resulting from magmatism and metamorphism, created a patchwork of large (1000 square kilometers) relatively undeformed regions separated by weak deforming regions. Strong regions resisting deformation develop shortly after the emplacement of the youngest plutons. Initially, extension was broadly distributed in diffuse shear zones that reflected the large size of weak areas. Later, rapid cooling of the igneous rocks and removal or crystallization of melt strengthened large sections, changing the location and size of weak areas. During cooling, the dry cores of plutons became stronger than the hydrous, quartz-rich host rocks, resulting in the migration of deformation out of pluton interiors and into softer host rock. The research supported here is part of a collaborative project between scientists at the University of Vermont and the University of Alabama Tuscaloosa. In addition to the research objectives, the project is supporting graduate and undergraduate student training in a STEM discipline at both institutions. The students are involved in all aspects of the project, and are gaining experience from using state-of-the-art analytical facilities from a variety of sources, including those of their host institutions, the University of North Carolina Chapel Hill, and the U.S. Geological Survey. The project is enhancing collaborations among U.S. and New Zealand scientific institutions. A strong partnership with New Zealand scientists provides access to unpublished data and sample archives resulting from a recent program to map Fiordland at a 1:250,000 scale. Student participation in these collaborations is helping to advance discovery and strengthen these partnerships. Students are benefiting from cultural and scientific exchanges and are gaining important experience in some of the best research facilities. Research results are being integrated into classroom curricula, disseminated via presentations at professional science meetings and the peer-reviewed geologic literature, and resulting data is being archived in a variety of community databases.

该项目提供了有关山地皮带中下层地壳变厚的新信息，在造山造成的过程中延伸和薄薄。 现场研究和数值模型表明，下大陆壳的强度，厚度和机械性能是影响整个岩性造成过程中整个岩石圈行为的关键因素，包括将应变定位到剪切区中。 但是，关于这些特性如何在造山循环中如何变化以及它们如何影响变形模式仍然存在不确定性。新西兰菲德兰（Fiordland）提供了一个自然实验室来解决这些问题，因为它暴露了超过3000平方公里的古代中生代下地壳。该项目正在确定镁铁质中间岩浆，地壳融化，变质和变形的时间尺度，物理尺寸以及对此下层地壳截面的演变的变形。 该工作将场映射与三维变形，岩石的压力 - 温度时间变形路径以及铀铅和samarium-neodymium同位素地质学的整合。这些工具有助于解决fiordland的下地壳的热和机械结构，超过2500万年，在从缩短和地壳增厚到延伸和地壳稀疏期的过渡期间，深度为35-50公里。他们还揭示了应变定位过程的不断变化的性质，包括形成了高级变质岩石的边界域的对称形式。这项研究的中心假设是，温度，成分，强度和地壳厚度的变化是由岩浆和变质造成的，较弱的（1000千分钟）的斑点，导致了岩浆和变质的分离。地区。抗变形的强区域后不久就会在最年轻的岩体埋入后不久就会发展出来。最初，扩展在弥漫性剪切区域中广泛分布，反映了较大的弱区域。后来，火成岩岩石的快速冷却以及熔体的去除或结晶增强了较大的部分，改变了弱区域的位置和大小。在冷却过程中，岩石的干芯变得比含水，富含石英的宿主岩石强，从而导致变形从岩内部内部迁移并进入较软的宿主岩石。这里支持的研究是佛蒙特大学科学家与阿拉巴马大学Tuscaloosa的一项合作项目的一部分。除了研究目标外，该项目还支持两个机构的STEM学科的毕业生和本科生培训。这些学生参与了该项目的各个方面，并从使用各种来源的最先进的分析设施（包括其东道机构，北卡罗来纳大学教堂山和美国地质调查局）获得了经验。该项目正在加强美国和新西兰科学机构之间的合作。与新西兰科学家的牢固合作伙伴关系可访问未发表的数据和示例档案，这是由于最近的计划，以1：250,000的比例绘制Fiordland。学生参与这些合作有助于提高发现并加强这些伙伴关系。学生正在从文化和科学交流中受益，并在一些最佳研究设施中获得重要的经验。研究结果正在集成到课堂课程中，在专业科学会议和同行评审的地质文献中通过演示进行传播，并在各种社区数据库中存档了结果数据。