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: 1550110
• 负责人: Sean Mulcahy
• 金额: $ 13.41万
• 依托单位: Western Washington University
• 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 2020-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1550110&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）是在地球活动和古老板块边界观察到的一级特征。活动断层，如圣安德烈亚斯，适应构造板块之间的相对运动。现在位于板块内部的古代板块边界断层，如密苏里州的新马德里断层，也可以继续活跃，这一点可以通过发生在它们上面的大地震来证明。为什么一些板块边界断层在形成后的几十亿年里仍然是地壳变形和隆升的场所，这仍然是一个有争议的话题。这项研究将提供一些想法，如何以及为什么在板块边界形成的一些主要断层持续作为地壳中的薄弱区，易于重新激活。这些结果最终将为一大批科学家提供有关地壳深部过程的信息，这些过程控制着地震活动、高热流和热液系统的位置，可能对理解地质灾害和资源产生影响。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在重要的STEM（科学，技术，工程和数学）学科中培训研究生和本科生。该项目将促进美国三个研究机构之间的合作研究，从而有助于支持科学基础设施。它将为两名早期职业gescientist提供研究资金。该项目将有助于扩大STEM中代表性不足的群体的参与。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上的介绍和同行评审的科学出版物广泛传播。大陆地壳内主要断裂带的存在，显示了在数十亿年内重新活化的证据，这与大陆连续变形的模型不符，其中断裂被视为对地幔流动的被动特征。大规模的断层发生在每个大陆上，许多长期存在的陆内断层系统记录了复杂的复活历史，特别是局部会聚和走滑变形。 这项研究将通过研究一个古老断裂带的中地壳和下地壳部分的构造历史来检验持续性大规模断层起源的竞争模型。端元模型预测，这样的断层带起源于：1）不同强度的块体之间的会聚碰撞边界，2）转换边界沿着预先存在的薄弱地带，或3）走滑边界内的弧-弧前区域的斜俯冲设置。 阿根廷西部的瓦莱费尔蒂尔断裂带是一个大约1200公里长的主要地壳线性构造，记录了至少4亿年的间歇变形，是测试上述模型的理想地点，因为对地壳强度对比的极好的地球物理约束，暴露深度沿着走向变化，构造演化受到很好的约束，以及确定断层变形历史的理想矿物组合。瓦莱费尔蒂尔断层的结果可以应用于其他陆内断层，以解决什么因素决定了复杂造山带内主要构造的起源，以及它们最终成为具有复杂持续活化历史的大规模断层的过程。