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

中新世摩门峰滑脱是内华达州南部盆岭省Sevier造山带前缘的一条低角度正断层。它经常被认为是世界上最好的大位移(20公里)正断层之一，它在倾角小于25度时形成并滑动，因此它的起源与与最大主应力成大角度的平面如何发生脆性断裂和滑动有关。近年来，该滑脱又被解释为一套灾难性侵位的重力滑动块体系统(两个独立的研究小组)或一个大规模的溶蚀和有限的构造滑动的带(第三个研究小组)。这些假说挑战了大位移伸展拆离是S地壳中重要构造元素的观点。该项目的目标是继续检验滑脱、滑坡和溶解模式的预测，方法是充分描述沿断层保存的流体的温度和来源，包括矿脉、角砾岩和断层泥，利用新的“块状同位素”碳酸盐温度计区分滑坡模式(冷底盘脉系统、断裂面热泥)和滑脱模式(热底盘脉和热泥)的预测。不管对各种构造假说的这些和其他测试的结果如何，断层岩和脉系的低温碳酸盐测温是一个从未被应用于构造地质学问题的新领域，因此拟议的工作具有潜在的变革影响。这将是与上地壳断层有关的结晶温度和流体来源的首次表征。阻碍我们理解地震和断层机制的主要障碍之一，非正式地被称为“应力悖论”。应力悖论简单地说就是，沿断层面的地力太低，既不允许破裂，也不允许持续的摩擦滑动，但很明显，断层移动并产生地震。关于为什么会这样，目前还没有达成共识，因此这个问题是地质学和地球物理学的一个主要研究重点领域。这种应力悖论对于一类被称为“低角度正断层”的断层最为尖锐，这种断层适应了地球的水平伸展--S地壳。该项目旨在检验关于位于内华达州南部的摩门峰支队的世界上暴露最好的低角度正断层之一的起源的相互竞争的假说。几个研究小组已经提出了证据，他们声称证明了摩门峰滑脱根本不是一个低角度的正断层，从而质疑任何这样的断层存在的想法。我们将使用最先进的地球化学技术来研究沿滑脱带变形的时间、深度和温度，我们预计这将证伪一个或多个提出的假说。除了该项目的研究目标外，它还支持对研究生的培训；正在促进未被充分代表的群体更广泛地参与地球科学；正在促进一种新的同位素温度计的开发和应用，该温度计具有广泛学科的变革潜力，包括岩石力学、构造地质学、地震学、地震灾害分析、经济地质学等。

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.