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: 1119039
• 负责人: Harold Stowell
• 金额: $ 32.45万
• 依托单位: University of Alabama Tuscaloosa
• 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 2015-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1119039&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.

该项目正在提供有关造山带崩塌期间加厚的下地壳如何伸展和减薄的新信息。野外研究和数值模型表明，下陆壳的强度、厚度和力学性质是影响造山作用期间整个岩石圈行为的关键因素，包括应变在剪切带中的局部化。然而，关于这些性质在造山旋回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。新西兰的菲奥德兰为解决这些问题提供了一个天然的实验室，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-中间岩浆作用、地壳熔融、变质作用和变形对这一下地壳段演化的时间尺度、物理尺寸和影响。这项工作将野外测绘与变形、岩石压力-温度-时间-变形路径以及铀-铅和钐-钕同位素年代学的三维分析结合在一起。这些工具正在帮助解决菲奥德兰下地壳2500万年来、35-50公里深处从缩短和地壳增厚向伸展和地壳减薄过渡过程中的热和机械结构。它们还揭示了应变局部化过程的变化性质，包括在高级变质岩穹隆边缘形成对称样式的伸展断层。这项研究的中心假设是，岩浆作用和变质作用导致的温度、成分、强度和地壳厚度的变化，形成了由弱变形区分隔的大片(1000平方公里)相对未变形的区域。在最年轻的深成岩体就位后不久，就形成了抵抗变形的强区域。最初，伸展广泛分布在弥漫剪切带中，反映了软弱区域的大小。后来，火成岩的快速冷却和熔体的移除或结晶加强了大段，改变了薄弱区域的位置和大小。在冷却过程中，深成岩体的干燥核变得比富含水的富石英寄主岩石更坚固，导致变形从深成岩体内部迁移到较软的寄主岩石中。这里支持的研究是佛蒙特州大学和阿拉巴马州塔斯卡卢萨大学科学家合作项目的一部分。除了研究目标外，该项目还支持两所大学的STEM学科的研究生和本科生培训。学生们参与了该项目的方方面面，并通过使用来自各种来源的最先进的分析设施获得了经验，这些来源包括他们的主办机构北卡罗来纳大学教堂山分校和美国地质调查局。该项目正在加强美国和新西兰科学机构之间的合作。与新西兰科学家的密切合作提供了访问未发表的数据和样本档案的机会，这些数据和样本档案是最近一个以1：25万比例尺绘制菲奥德兰地图的项目产生的。学生参与这些合作有助于推进发现并加强这些伙伴关系。学生们从文化和科学交流中受益，并在一些最好的研究设施中获得重要经验。正在将研究成果纳入课堂课程，通过在专业科学会议上的发言和同行评审的地质文献进行传播，并将由此产生的数据存档到各种社区数据库中。