Collaborative Research: Dating Deformation with Titanite

我们对地球地质历史的大部分了解来自于对地球过程的辐射测年。目前，地球科学家很难对地壳深处断层发生的准确时间进行严格的限制。该项目结合了两种最先进的技术，可以直接测定阿拉斯加东南部一个关键断裂带的断裂时间，从而确定古代地震发生的时间。这种新的分析技术的发展将使未来对地球材料如何变形的大量研究和理解成为可能。此外，该研究项目将为一名女研究生和几名本科生提供培训和研究机会。对当地小学的访问将使未来的潜在科学家能够体验到地球科学研究的方法和结果，这对地震灾害具有直接影响。该合作项目包括两个主要目标：1)利用显微构造和显微地质年代学相结合的方法，开发矿物钛铁矿作为测定高温变形年龄的工具，以及2)将这一工具应用于阿拉斯加东南部海岸山脉造山带中壮观的海岸剪切带和大英云母山丘的演化。研究方法将包括实地考察，以定性地了解阿拉斯加和加拿大海岸剪切带中至深地壳弧内剪切带和同动席床杂岩的演化。钛矿分析将包括钛矿微结构的电子背向散射衍射图，以及包含U-Pb数据的钛矿成分的激光烧蚀分流电感耦合等离子体图。这些数据将允许评估影响晶体的物理和化学过程，并识别其U-Pb分布反映高温变形的晶体。由于钛铁矿是一种广泛的地壳矿物，这项技术应该在全球范围内得到广泛的应用，并加强我们对地壳变形和造山带如何随着时间的推移而聚集和变化的理解。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。

Much of our understanding of the geologic history of the Earth comes from radiometric dating of Earth processes. Currently, Earth scientists have a difficult time placing narrow constraints on the precise time that a fault occurs deep within the crust of the Earth. This project combines two state-of-the-science techniques to directly date the time of faulting along a key fault zone in southeast Alaska, and thereby date when ancient earthquakes occurred. Development of this new analytical technique will enable considerable future research and understanding of how Earth materials deform. In addition, this research project will provide training and research opportunities for a female graduate student and several undergraduate students. Visits to local elementary schools will enable potential future scientists to experience the methods and results of Earth science research, with direct implications for earthquake hazards. This collaborative project consists of two principal objectives: 1) develop the mineral titanite as a tool for dating high-temperature deformation by a combined microstructural and microgeochronology approach, and 2) apply this tool to the evolution of the spectacular Coast Shear Zone and Great Tonalite Sill in the Coast Mountains orogen of southeast Alaska. Research methods will incorporate a field study to understand qualitatively the evolution of a mid- to deep crustal intra-arc shear zone and synkinematic sheeted-sill complex exposed in the Coast shear zone of Alaska and Canada. Titanite analyses will include electron-backscatter diffraction maps of titanite microstructure, and laser-ablation split-stream inductively coupled plasma maps of titanite composition that incorporate U-Pb dates. These data will allow assessment of the physical and chemical processes that affected the crystal, and the identification of crystals whose U-Pb distribution reflects high-temperature deformation. Because titanite is a widespread crustal mineral, this technique should have broad application globally and enhance our understanding of how crust deforms and orogens assemble and change through 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.