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

大型断层(1000公里)是在地球活动板块和古板块边界观察到的第一级特征。活动断层，如圣安德烈亚斯，适应了构造板块之间的相对运动。现在板块内的古老板块边界断层，如密苏里州的新马德里断层，也可以继续活跃，正如它们上的大地震所证明的那样。为什么一些板块边界断裂在形成后百年仍是地壳形变和隆升的中心，这一直是一个争论的话题。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作为地壳中的薄弱地带持续存在，容易重新激活。这些结果最终将为广大科学家提供关于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，这些系统可能对了解地质灾害和资源产生影响。除了该项目的科学目标外，该项目与社会相关的重要成果将包括对一门重要的STEM(科学、技术、工程和数学)学科的研究生和本科生进行培训。该项目将促进美国三个研究机构之间的合作研究，从而为科学基础设施提供支持。它将为两名早期职业地质科学家提供研究资金。该项目将有助于扩大代表人数不足的群体在科技教育管理中的参与。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学会会议上的发言和同行评议的科学出版物广泛传播。大陆地壳内主要断裂带的存在表明有证据表明在数亿年后重新活动，这与大陆连续变形的模型背道而驰，在大陆连续变形模型中，断裂被视为对地幔流动作出反应的被动特征。每个大陆都有大规模的断裂，许多长寿的陆内断裂系统记录了复杂的再活动历史，特别是局部化的会聚变形和走滑变形。这项研究将通过研究一个古老断裂带出土的中、下地壳段的构造史，来检验持续大型断裂起源的相互竞争的模型。末端成员模型预测，这种断裂带起源于：1)不同强度块体之间的会聚-碰撞边界，2)沿先前存在的薄弱带的转换边界，或3)斜俯冲环境的弧前区内的走滑边界。阿根廷西部的Valle Fertil断裂带是一条长约1200公里的主要地壳线条，记录了至少4亿年的间歇性变形，是检验上述模型的理想地点，因为它对地壳强度对比具有极好的地球物理约束，沿走向的暴露深度可变，构造演化受到很好的约束，并且断层内的变形历史具有理想的矿物组合。Valle Fertil断裂的研究结果可以应用于其他陆内断裂，以解决决定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的持续重新活动历史的大型断裂的过程。

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.