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

机械风化--地球表面岩石因破裂而发生物理分解--是地球生物、水文、大气和地质系统中的一个重要齿轮，影响着从碳循环到生命繁衍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没有得到很好的描述，而且还没有观察到裂缝本身的长期演化。这项工作汇集了来自美国、以色列、日本和英国的一个多学科团队，收集了一些有史以来第一个地质时间尺度(10^3-10^5年)的数据集，用于机械风化以及一套特殊的岩石力学性质--那些与气候相关的亚临界破裂有关的数据集。该项目将与北卡罗来纳大学夏洛特艺术建筑学院开展科学-艺术合作，向不同的公众受众传达项目成果。研究人员将在美国地质学会就这项工作中探索的基本亚临界破裂概念进行研讨会，并将指导学生，重点是扩大妇女和代表性较低的少数民族的参与。调查人员将测试假设，包括：a)地质时期的机械风化速率主要由岩石亚临界裂解速率控制；b)与化学风化类似，机械风化速率随着地质时间的推移而下降；c)在不同的环境条件下，机械风化速率在有利于更快的亚临界破裂的气候条件下更高-单独的，此外，先前已经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不同年代的晚第四纪矿床中发现的巨石(花岗岩和石灰岩)的机械风化(破裂)速率和特征。2)同一地点样品的亚临界裂化参数--在不同环境条件下测量。然后，实验室数据将被合并到数值模型中，该模型将计算不同环境条件下的长期亚临界裂化驱动裂解速率。模型结果将使用现场数据进行验证和改进。该项目将对机械风化以及控制风化的因素进行新的揭示。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.