Temperatures and Fluids on Faults Based on Carbonate Clumped-isotope Thermometry

基于碳酸盐聚集同位素测温的断层温度和流体

• 批准号: 1250565
• 负责人: Brian Wernicke
• 金额: $ 17.57万
• 依托单位: California Institute of Technology
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2013
• 资助国家: 美国
• 起止时间: 2013-09-01 至 2015-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1250565&HistoricalAwards=false
• 关键词: Temperatures; Fluids; Faults; Based; Carbonate

The Miocene Mormon Peak detachment is a low-angle normal fault along the Sevier orogenic front in the Basin and Range province in southern Nevada. It is often cited as one of the best examples in the world of a large-displacement (20 km) normal fault that both formed and slipped at dips of less than 25 degrees, and therefore its origin is relevant to the problem of how brittle fracture and slip can occur on planes oriented at a high angle to the maximum principal stress. In recent years, the detachment has alternatively been interpreted as a system of catastrophically emplaced gravity slide blocks (two independent research teams) or a zone of large-scale dissolution with limited tectonic slip (a third research team). These hypotheses challenge the notion that large-displacement extensional detachments are important tectonic elements in the earth?s crust. The objective of this project is to continue to test predictions of the detachment, landslide and dissolution models by fully characterizing the temperature and origin of fluids preserved along the fault in veins, breccias and fault gouge, using the new "clumped isotope" carbonate thermometer to distinguish between predictions of the landslide model (cold footwall vein systems, hot gouge on the fault surface) and detachment model (warm footwall veins and warm gouge). Regardless of the outcome of these and other tests for various structural hypotheses, low-temperature carbonate thermometry of fault rocks and vein systems is a new field that has never been applied to a problem in structural geology, and the proposed work accordingly has the potential for transformative impact. It will represent the first characterization of both the temperatures of crystallization and the fluid sources associated with an upper crustal fault. One of the primary obstacles to our understanding of the mechanics of earthquakes and faulting is informally referred to as the "stress paradox." The stress paradox is simply that the forces in the earth along fault planes are too low to permit either fracture or continued frictional sliding, yet obviously the faults move and generate earthquakes. There is at present no consensus as to why this is the case, and hence the problem is a major research focus area in geology and geophysics. The stress paradox is most acute for a class of faults known as "low-angle normal faults," which accommodate horizontal extension of the earth?s crust. This project is designed to test competing hypotheses for the origin of one of the best-exposed low-angle normal faults in the world known as the Mormon Peak detachment, located in southern Nevada. Several research teams have presented evidence they claim demonstrate that the Mormon Peak detachment is not a low-angle normal fault at all, and thereby question the notion that any such faults even exist. We will use state-of-the-art geochemical techniques to investigate the timing, depth and temperature of deformation along the detachment, which we expect will falsify one or more of the proposed hypotheses. In addition to the research objectives of this project, it is supporting the training of a graduate student; is contributing to the broadening of participation of underrepresented groups in the earth sciences; is contributing to the development and application of a new isotopic thermometer that has transformative potential for a wide range of disciplines, including rock mechanics, structural geology, seismology, seismic hazards analysis, economic geology, and others.

中新世摩门峰拆离断层是沿着内华达州南部盆岭省塞维尔造山带前缘的一条低角度正断层。 它经常被引用为世界上大位移（20公里）正断层的最佳例子之一，该断层在小于25度的倾角下形成和滑动，因此其起源与脆性断裂和滑动如何在与最大主应力成高角度的平面上发生的问题有关。 近年来，拆离被交替解释为灾难性的重力滑动块体系统（两个独立的研究团队）或具有有限构造滑动的大规模溶解区（第三个研究团队）。 这些假说对大位移伸展构造是地球重要构造要素的观点提出了挑战。的外壳。 该项目的目标是继续测试对脱离、滑坡和溶解模型的预测，充分说明沿着断层保存在矿脉、角砾岩和断层泥中的流体的温度和来源，使用新的“凝聚同位素”碳酸盐温度计区分滑坡模型的预测（冷下盘脉系、断层面热断层泥）和拆离模式（热下盘脉系、热断层泥）。 无论这些和其他各种结构假设的测试结果如何，断层岩和脉系统的低温碳酸盐测温是一个从未应用于结构地质学问题的新领域，因此，拟议的工作具有潜在的变革性影响。 它将代表与上地壳断层有关的结晶温度和流体来源的第一个表征。我们理解地震和断层力学的主要障碍之一被非正式地称为“应力悖论”。“应力悖论简单地说，地球上沿着断层面的力太小，不允许断裂或继续摩擦滑动，但显然断层移动并产生地震。 目前还没有达成共识，为什么会这样，因此这个问题是地质学和地球物理学的一个主要研究焦点领域。 应力悖论对于一类被称为“低角度正断层”的断层最为尖锐，这种断层适应地球的水平延伸。的外壳。 该项目旨在测试位于内华达州南部的摩门峰拆离断层的起源，该断层是世界上暴露最好的低角度正断层之一。 几个研究小组提出了他们声称的证据，证明摩门教峰脱离根本不是一个低角度的正断层，从而质疑任何这样的断层甚至存在的概念。 我们将使用最先进的地球化学技术来调查沿着拆离带变形的时间、深度和温度，我们预计这将证伪一个或多个提出的假设。除了该项目的研究目标外，它还支持培训一名研究生;帮助扩大代表性不足的群体参与地球科学;正在为开发和应用一种新的同位素温度计做出贡献，这种温度计具有广泛学科的变革潜力，包括岩石力学、结构地质学、地震学、地震灾害分析、经济地质学，等人