Collaborative Research: Origin of Long-lived Crustal Shear Zones as Transforms or Subduction Zones?

合作研究：作为转换带或俯冲带的长寿地壳剪切带的起源？

• 批准号: 1549902
• 负责人: William McClelland
• 金额: $ 11.2万
• 依托单位: University of Iowa
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-04-01 至 2019-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1549902&HistoricalAwards=false
• 关键词: Collaborative; Research; Origin; Long; lived

Large-scale faults (1000 kilometer) are first-order features observed at Earth's active and ancient plate boundaries. Active faults, such as the San Andreas, accommodate relative motion between tectonic plates. Ancient plate boundary faults now within plates, such as the New Madrid fault in Missouri, can also continue to be active, as demonstrated by major earthquakes on them. Why some plate boundary faults remain the locus of crustal deformation and uplift 100s of millions of years after they form has remained a topic of debate. This study will provide ideas on how and why some major faults that form at plate boundaries persist as zones of weakness in the crust, prone to reactivation. The results will ultimately inform a broad group of scientists on deep crustal processes that control the location of seismicity, high heat flow, and hydrothermal systems that may have implications for the understanding of geologic hazards and resources. In addition to the scientific goals of the project, important societal relevant outcomes of the project will include the training of graduate and undergraduate students in an important STEM (Science, Technology, Engineering and Mathematics) discipline. The project will facilitate collaborative research between three U.S. research institutions, thus contributing to support of scientific infrastructure. It will provide research funding for two early career gescientists. The project will contribute to the broadening of participation of underrepresented groups in STEM. Importantly, the project will foster international collaboration and exchange between U.S. and Argentine scientists. Results of the research will be broadly disseminated through presentations at professional society meetings and in peer-reviewed scientific publications. The presence of major fault zones within continental crust which show evidence for reactivation over 100s of millions of years defies models for continuum deformation of the continents, wherein faults are viewed as passive features responding to mantle flow. Large-scale faults occur on every continent and many long-lived intracontinental fault systems record complex histories of reactivation, in particular localizing convergent and strike-slip deformation. This research will test competing models for the origin of persistent large-scale faults by studying the tectonic history of exhumed middle and lower crust sections of an ancient fault zone. End member models predict that such fault zones originate either as: 1) convergent-collisional boundaries between blocks of different strength, 2) transform boundaries along pre-existing zones of weakness, or 3) strike-slip boundaries within the arc-forearc region of oblique subduction settings. The Valle Fertil fault zone of western Argentina is an approximately 1200-kilometer-long major crustal lineament that records at least 400 million years of intermittent deformation and is an ideal location to test the above models because of excellent geophysical constraints on crustal strength contrasts, variable depths of exposure along strike, a well constrained tectonic evolution, and ideal mineral assemblages for dating the history of deformation within the fault. The results from the Valle Fertil fault can be applied to other intracontinental faults to address what factors determine the origin of major structures within complex orogens and the processes by which they ultimately become large-scale faults with complex histories of continued reactivation.

大规模断层（1000公里）是在地球活动板块和古代板块边界观察到的一级特征。活动断层，例如圣安德烈亚斯断层，适应构造板块之间的相对运动。现在板块内的古代板块边界断层，例如密苏里州的新马德里断层，也可能继续活跃，这些断层上发生的大地震就证明了这一点。为什么一些板块边界断层在形成数百年或数百万年后仍然是地壳变形和隆起的场所，这仍然是一个争论的话题。这项研究将为板块边界形成的一些主要断层如何以及为何作为地壳薄弱区持续存在、易于重新激活提供思路。研究结果最终将为广大科学家提供关于控制地震活动、高热流和热液系统位置的深部地壳过程的信息，这些过程可能对地质灾害和资源的理解产生影响。除了该项目的科学目标外，该项目的重要社会相关成果将包括对研究生和本科生进行重要的 STEM（科学、技术、工程和数学）学科的培训。该项目将促进三个美国研究机构之间的合作研究，从而为科学基础设施的支持做出贡献。它将为两名早期职业基因科学家提供研究经费。该项目将有助于扩大代表性不足的群体对 STEM 的参与。重要的是，该项目将促进美国和阿根廷科学家之间的国际合作和交流。研究结果将通过在专业协会会议和同行评审的科学出版物上的演讲来广泛传播。大陆地壳内存在的主要断层带显示了数百年或数百万年重新活动的证据，这违背了大陆连续变形的模型，其中断层被视为响应地幔流的被动特征。每个大陆都会出现大规模断层，许多寿命较长的陆内断层系统记录了复杂的再活动历史，特别是局部汇聚和走滑变形。 这项研究将通过研究古代断层带挖掘出的中下地壳部分的构造历史来测试持续性大型断层起源的竞争模型。端元模型预测，此类断层带起源于：1）不同强度块体之间的汇聚碰撞边界，2）沿先前存在的薄弱带转换边界，或3）弧前区域内的走滑边界倾斜俯冲设置。 阿根廷西部的 Valle Fertil 断裂带是一条大约 1200 公里长的主要地壳线，记录了至少 4 亿年的间歇性变形，并且由于对地壳强度对比、变量的地球物理约束极好，是测试上述模型的理想地点。沿走向的暴露深度、受到良好约束的构造演化以及用于测定断层内变形历史的理想矿物组合。 Valle Fertil断层的结果可以应用于其他陆内断层，以解决哪些因素决定复杂造山带内主要结构的起源，以及它们最终成为具有复杂的持续再活动历史的大规模断层的过程。