Collaborative Research: The role of Grain Boundary Migration in Water Weakening of Naturally Deformed Quartz

这项研究旨在了解矿物中亚微观量的水是如何影响其强度的。在岩石中，这种微量水的整体效果对板块如何相互作用具有重大意义。例如，印度板块正在与亚洲板块碰撞，形成喜马拉雅山脉，但强大的印度板块没有变形，而较弱的亚洲板块正在褶皱、断层、经历地震，并上升形成地球上最高的山脉。青藏高原(面积是法国的五倍)海拔超过3英里(4.8公里)，这是值得注意的。造成这种巨大板块强度差异的一种可能性是，印度板块的深层岩石是“干的”(没有亚微观水)，而亚洲板块的深层岩石是“湿的”(它们包含一些亚微观水)。因此，重要的是要了解这些微量的水是如何以及何时进入岩石的。这项研究项目涉及在加利福尼亚州的山区收集岩石，沿着一条5公里长的横断面，在那里人们已经知道岩石经历了从强到弱的转变。将利用先进的显微成像技术进行详细的化学分析，以准确地确定水如何以及在哪里沿着横断面进入和离开受影响的矿物。这项研究将支持1名博士后研究员、4-6名本科生研究员以及12名底特律市中心高中(César Chávez Academy High School)学生和3名高中教师的教育，他们将与研究团队一起前往加利福尼亚州，采样和了解水如何影响山体建筑和板块构造。水对塑造地球这一部分的影响在视觉上是显而易见的(以前的冰川、史前和历史上的湖床)，气候变化、干旱和火灾以及人类干预(通过管道输送到洛杉矶的水)的影响也将被研究。这个项目的目标是确定晶界迁移是否允许水进入石英晶格并导致弱化。氧同位素数据将作为追踪水入渗的主要指标。Harkless地层石英岩样品将沿着一条5公里的横断面采集，该横断面垂直于加利福尼亚州怀特-因约山脉的尤里卡山谷-约书亚平坦-比尔克里克岩体的接触点。接触变质作用在距离岩体2.9公里处首次观察到，在距离岩体1.1公里处突然出现整合，Harkless褶皱90°，强烈衰减。这种突然的转变被认为是一个“滚动的铰链”，在侵位过程中随着岩体的膨胀而向外发展。将在区域结构和围岩与侵入体的强烈一致性之间的这种过渡过程中收集样本。将使用标准岩相学和扫描电子显微镜技术以及包括电子背散射衍射和阴极发光在内的高级分析技术来记录：1)晶界迁移确切地从哪里开始，在哪里变得普遍，以及，2)在哪里晶体择优取向开始发展，以及它是如何在转变过程中发展的。使用小光斑尺寸(6-10微米凹坑尺寸)的聚焦二次离子质谱仪光束，将分析颗粒未迁移部分和迁移部分之间的晶界，以确定氧同位素特征，以跟踪水的渗透并描绘水的潜在来源。傅里叶变换红外光谱还将被用来记录在微观尺度上伴生矿物中水(OH)的总浓度。微量元素数据将被输入到几个TianiQ模型中，以确定变形期间的温度和冷却历史期间整个钛扩散部分再平衡。这一总体战略将有助于将岩石/矿物强度和变形行为与造山过程中强烈加热和压力下矿物中的亚微观水现象相关联。该奖项反映了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。

This research is designed to understand how sub-microscopic amounts of water, in minerals, can affect their strength. The overall effect of this tiny amount of water, in rocks, can have a big significance to how plates interact. For example, the Indian plate is colliding with the Asian plate to produce the Himalayas, but the strong Indian plate is not deforming while the weaker Asian plate is folding, faulting, experiencing earthquakes, and rising to produce the tallest mountains on Earth. The uplift of the Tibetan Plateau (which is five times the area of France) to an elevation of over 3 miles high (4.8 km) is remarkable. One possibility for this huge difference in plate strength is that deep rocks of the Indian plate are “dry” (no sub-microscopic water) whereas deep rocks of the Asian plate are “wet” (they contain some sub-microscopic water). Therefore, it is important to understand how and when this tiny amount of water gets into the rocks. This research project involves collecting rocks, in the mountains of California, along a 5 km transect where it is already known that rocks undergo the transition from strong to weak behavior. Detailed chemical analyses with advanced micro-imaging techniques will be conducted to determine exactly how and where along the transect the water gets into and out of the effected minerals. This research will support the education of one post-doctoral researcher, 4-6 undergraduate researchers, as well as 12 inner city Detroit High School (César Chávez Academy High School) students and three High School teachers who will travel to California with the research team to sample and learn about how water affects mountain building and plate tectonics. The effects of water on shaping this part of Earth are visually evident (previous glaciers, pre-historic and historic lake beds) and the effects of climate change, drought and fires, and human intervention (water piped to Los Angeles) will also be examined. The goal of this project is to determine if grain boundary migration allows water to enter the quartz crystal lattice and cause weakening. Oxygen isotope data will be used as the main proxy for tracking water infiltration. Harkless Formation quartzite samples will be collected along a 5 km transect, oriented perpendicular to the contact with the Eureka Valley-Joshua Flat-Beer Creek pluton in the White-Inyo Range of California. Contact metamorphism is first observed at 2.9 km from the pluton and concordancy occurs abruptly at 1.1 km where the Harkless folds 90° and is intensely attenuated. This abrupt transition is assumed to be a “rolling hinge”, that progressed outward as the pluton expanded during emplacement. Samples will be collected across this transition between regional structures and the forceful concordance of country rocks with the intrusion. Standard petrography and scanning electron microscopy techniques with advanced analysis including electron backscatter diffraction and cathodoluminescence, will be used to document; 1) where exactly grain boundary migration begins, where it becomes pervasive and, 2) where the crystallographic preferred orientation begins to develop and how it develops across the transition. Using a focused Secondary Ion Mass Spectrometer beam with a small spot size (6-10µm pit size), grain boundaries will be analyzed between unmigrated and migrated parts of the grains to determine the oxygen isotope signatures for tracking water infiltration and delineating the potential sources of this water. Fourier-transform infrared spectroscopy will also be used to document the overall concentrations of water (OH) on a microscopic scale in associated minerals. Trace element data will be input into several TitaniQ models to determine the temperatures during deformation and the overall Ti diffusional partial re-equilibration during the cooling history. This overall strategy will help correlate rock/mineral strength and deformation behavior with sub-microscopic water phenomena in minerals from intense heating and pressure during mountain building processes.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.