Collaborative Research: Little Devils Postpile Revisited: Intercalibration of Thermochronometer Kinetics in a Contact Aureole

在地壳上部几公里的岩石热历史的约束的需求驱动下，中低温热年代学在过去的二十年中在构造和地貌应用中激增。尽管这种增长，每一个热年代学的应用是有限的基本动力学校准和样品内的变化，在一定程度上或另一个地质解释提出了问题，从他们的不确定性。这些不确定性来自许多来源，但也许最重要的是来自经验实验室步进加热扩散和退火实验的解释和外推，这些实验通常在与相关自然条件不同的许多数量级的速率和温度下进行。几条线的证据，包括从头算动力学模型，从理想化的配置自然样品的偏差，和简单的观察“耐人寻味的复杂性”在许多冷却年龄，光谱，剖面和轨道长度的数据集，表明存在显着的差距，在我们的理解常规使用的基本热年代学动力学校准。需要对来自控制良好的天然实验室的多个热时计进行仔细和深思熟虑的基准测试和相互校准研究，以阐明这些问题，并最终建立对动力学模型和地质解释的更大信心。建议重新采样和分析13个不同的稀有气体和裂变径迹温度计的详细行为，在剖面附近的小魔鬼Postpile，一个经典的天然实验室研究的Calk和Naeser在1973年，其中一个约100米的玄武岩塞子侵入约80-Ma花岗岩类岩石在~8 Ma。虽然可能会因热液循环和其他影响而变得复杂，但这一自然实验的相对简单的配置将允许构建与侵入体相关的热历史的现实模型，从而预测年龄剖面和其他热年代学特性作为与接触点距离的函数。围岩中许多不同矿物的丰度可通过惰性气体和裂变径迹方法测定，这将允许根据许多参数（包括：整体年龄、轮廓、光谱和轨迹长度等）。 良好校准的测年系统的相互组合将作为基准，以确定解释的问题，并推断出潜在的改进，以提高其他测年系统的校准。智力优点：这集中和合作研究将提供一个相对罕见的和需要的机会来测试，完善，并在某些情况下建立动力学校准使用的许多地球和行星科学家每年数百个应用程序。这将通过在实验室无法实现的条件下进行的自然实验来实现，通过相对简单的接触关系，允许直接建模，但有合理的机会揭示复杂性（如样品内变化），这在许多地质应用中可能会经常遇到。除了有助于地质学界广泛使用的热年代学校准，并可能建立一个对测试其他系统有用的热年代学“典型地点”外，这项工作将为一些本科生和研究生提供培训和支持，建立新的裂变径迹测年能力（锆石，钛铁矿和绿帘石），并将提供外展机会，游客在约塞米蒂国家公园，通过我们与公园地质学家格雷戈里·斯托克博士的合作

Thermochronometer Kinetics in a Contact AureoleDriven by the demand for constraints on thermal histories of rocks in the upper few kilometers of the Earth's crust, intermediate- and low-temperature thermochronology has proliferated in tectonic and geomorphic applications in the last two decades. Despite this growth, every thermochronologic application is limited by uncertainties in fundamental kinetic calibrations and intra-sample variation that to one degree or another raise questions about geologic interpretations derived from them. These uncertainties arise from many sources, but perhaps most importantly from the interpretation and extrapolation of empirical laboratory step-heating diffusion and annealing experiments that are usually performed at rates and temperatures many orders of magnitude different from relevant natural conditions. Several lines of evidence, including ab initio kinetic models, deviations of natural samples from idealized configurations, and simply observations of "intriguing complexities" in many cooling-age, -spectra, -profile and track-length data sets, suggest the existence of significant gaps in our understanding of routinely used fundamental thermochronologic kinetic calibrations. A careful and deliberate benchmarking and intercalibration study of multiple thermochronometers from a well-controlled natural laboratory is needed to illuminate these issues and to ultimately establish more confidence in kinetic models and geologic interpretations derived from them. It is proposed to resample and analyze the detailed behavior of 13 different noble-gas and fissiontrack thermochronometers in profiles adjacent to Little Devils Postpile, a classic natural laboratory studied by Calk and Naeser in 1973, where a ~100 m basalt plug intruded ~80-Ma granitoid rock at ~8 Ma. Although possibly complicated by hydrothermal circulation and other effects, the relatively simple configuration of this natural experiment will allow construction of realistic models of the thermal histories associated with the intrusion, hence prediction of profiles of age and other thermochronometric properties as a function of distance from the contacts. The abundance of many different minerals dateable by both noble gas and fission-track methods in the country rock will then allow comparison between and predicted the observed thermochronologic patterns based on many parameters (incl. bulk ages, profiles, spectra, and track lengths, etc.). Inter-combinations of well-calibrated dating systems will serve as benchmarks to identify interpretive problems and to infer potential refinements needed to improve calibrations of other dating systems.Intellectual Merit: This focused and collaborative study will provide a relatively rare and needed opportunity to test, refine, and in some cases establish kinetic calibrations used by many Earth and planetary scientists for hundreds of applications each year. This will be accomplished using a natural experiment performed under conditions not achievable in the laboratory, through a relatively simple contact relationship that allows for straightforward modeling, but with reasonable opportunity for revealing complexities (such as intrasample variations) that are likely to be commonly encountered in many geologic applications.Broader Impacts: Besides contributing to thermochronologic calibrations widely used in the geologic community, and potentially establishing a thermochronologic "type locality" useful for testing other systems, this work will provide training and support for several undergraduate and graduate students, establish new fission-track dating capabilities (in zircon, titanite, and epidote) at UT, and will provide for outreach opportunities to visitors at Yosemite National Park, through our collaboration with Park Geologist Dr. Gregory Stock.