NSF-BSF: Quantifying climate-dependent subcritical cracking and mechanical weathering over geologic time

机械风化作用——地球表面岩石因开裂而发生的物理破坏——是地球生物、水文、大气和地质系统中至关重要的一环，影响着从碳循环到生命赖以生存的土壤，再到含水层形成的方方面面。然而，控制机械风化的环境和岩石力学特征仍然不清楚，裂缝本身的长期演化尚未观察到。这项工作汇集了来自美国、以色列、日本和英国的多学科团队，收集了一些有史以来第一个地质时间尺度（10^3-10^5年）的机械风化数据集，以及一套特殊岩石力学特性的数据集——那些与气候相关的亚临界开裂。该项目将与北卡罗来纳大学夏洛特艺术与建筑学院开展科学艺术合作，将项目成果传达给不同的公众受众。研究人员将在美国地质学会举办一个讲习班，讨论在这项工作中探索的亚临界开裂的基本概念，并将指导学生，重点是扩大妇女和代表性不足的少数民族的参与。研究人员将测试的假设包括：a)地质时期的机械风化速率主要由岩石亚临界开裂速率控制；B)与化学风化相似，机械风化速率随地质年代的变化而减小；c)在不同的环境条件下，机械风化速率更高的气候条件有利于更快的亚临界开裂-分离，除了之前认识到的气候对应力加载机制的影响。将测量以下内容：1)在加利福尼亚州内华达山脉和以色列内盖夫沙漠的不同年龄的晚第四纪沉积物中发现的岩石（花岗岩和石灰石）的机械风化（开裂）速率和特征。2)在不同环境条件下测量来自同一地点的样品的亚临界开裂参数。然后将实验室数据纳入数值模型，计算不同环境条件下长期亚临界裂纹驱动的裂纹速率。模型结果将使用现场数据进行验证和改进。该项目将揭示地质时期的机械风化以及控制它的因素。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Mechanical weathering - the physical breakdown of Earth's surface rocks by cracking - is a vital cog in the wheel of Earth's biologic, hydrologic, atmospheric and geologic systems, influencing everything from carbon cycling, to the soils in which life thrives, to aquifer formation. Yet the environmental and rock mechanical features that control mechanical weathering remain poorly characterized, and the long-term evolution of cracking itself has not been observed. This work brings together a multidisciplinary team from the United States, Israel, Japan and the United Kingdom to collect some of the first ever geologic time scale (10^3-10^5 years) data sets for both mechanical weathering as well as for a suite of special rock mechanical properties - those related to climate-dependent subcritical cracking. The project will develop a Science-Art collaboration with the UNC Charlotte College of Arts + Architecture to communicate the project results to diverse public audiences. The investigators will conduct a workshop at the Geological Society of America on the basic subcritical cracking concepts explored in this work and will mentor students with a focus on broadening participation of women and underrepresented minorities.The investigators will test hypotheses including: a) mechanical weathering rates over geologic time are primarily controlled by rock subcritical cracking rates; b) similar to chemical weathering, mechanical weathering rates decrease through geologic time; and c) under different environmental conditions, mechanical weathering rates are higher in climates where conditions favor faster subcritical cracking - separate, and in addition to, the previously recognized influence of climate on stress loading mechanisms. The following will be measured: 1) Mechanical weathering (cracking) rates and characteristics for boulders (granite and limestone) found on different aged late Quaternary deposits, in the Sierra Nevada, CA, and the Negev Desert of Israel. 2) Subcritical cracking parameters - measured under different environmental conditions - for samples from the same locations. Laboratory data will then be incorporated into numerical models that will calculate long-term subcritical cracking-driven cracking rates under different environmental conditions. Model results will be validated and refined using field data. The project will shed new light on mechanical weathering, and the factors controlling it, over geologic time.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.