Study on Nano-phases and Microstructures in Rutile and Pyroxene From Ultrahigh-pressure Metamorphic Rocks: TEM Investigation and Computer Modeling

纳米相和纳米沉淀物在高温和/或高压下形成的造岩矿物中非常常见。纳米相的稳定性场不同于相同宏观相的稳定性场，这是因为晶体越小，界面能对其稳定性的贡献就越大。我们将结合表征良好的超高压（UHP =钴矿和/或含金刚石）变质岩的透射电镜观测结果，并利用密度泛函理论建立计算机模型，将超高压纳米沉淀物的尺寸与其稳定场的变化与宏观相联系起来。中国东部大别-苏鲁超高压变质地体的超高压岩石（榴辉岩）和波希米亚地块Moldanubian推覆体的幔源超高压石榴石辉石岩和榴辉岩将被用于拟研究。知识的优点。利用高分辨率透射电子显微镜（HRTEM）和相关的x射线能谱（EDS）、电子能量损失谱（EELS）和扫描透射电子显微镜（STEM）模式下的z -对比成像技术，研究辉石和金红石中纳米沉淀物和纳米相的微观结构。研究的特征包括：(1)辉石矿物中的棒状富硅析出物、斜辉石片层和反相畴边界；(2)金红石中针状析出物和具有_pbo2型结构的高压TiO2相片层。利用密度泛函理论，计算尺寸对纳米相稳定性的影响。假设斜辉辉石和_-PbO2型TiO2纳米相片层在其宿主矿物中的稳定性与其体相的稳定性有很大不同。微相的结构和化学性质及其相互关系可以提供大陆板块俯冲和掘出过程中寄主矿物的P-T史。威斯康星大学麦迪逊分校刚刚购买了一套最先进的像差校正场发射枪（FEG） TEM / STEM（扫描透射电子显微镜）成像系统，该系统具有x射线EDS和EELS功能，由NSF MRI项目提供支持。该系统能够获得1 μ分辨率的空间分辨EELS光谱。使用STEM模式的z对比成像可以提供原子尺度的化学图像。这些系统将用于拟议的研究，并有望提供丰富的关于纳米相、界面结构和矿物缺陷的新知识，以及它们如何记录它们的形成条件和宿主岩石的历史。更广泛的影响这项工作的结果将被纳入通过威斯康星大学麦迪逊分校地质博物馆的PI和各种外展活动所教授的课程，该博物馆每年为大约13,000名K-12学生提供导游服务，每年吸引超过40,000名游客。该项目还将支持研究生的研究。

Nano-phases and nano-precipitates are very common in rock-forming minerals formed at high temperature and/or high pressure. The stability fields for the nano-phases differ from those of the same macroscopic phases, because as crystals get smaller, contributions to their stabilities from interface energies become tremendous. We will combine TEM observations from well characterized ultrahigh-pressure (UHP = coesite and/or diamond-bearing) metamorphic rocks and computer modeling using Density Functional Theory to correlate the relationship between sizes of ultrahigh-pressure nano-precipitates and changes in their stability fields with respect to the macroscopic phases. UHP rocks (eclogite) from the Dabie-Sulu UHP metamorphic terrane in eastern China and mantle-derived UHP garnet pyroxenite and eclogite from the Moldanubian Nappe of the Bohemian Massif will be used for the proposed studies.Intellectual merits. Microstructures of nano-precipitates and nano-phases in pyroxene and rutile will be investigated using high-resolution transmission electron microscopy (HRTEM) and associated techniques of X-ray EDS, electron energy-loss spectroscopy (EELS), and Z-contrast imaging under scanning transmission electron microscopy (STEM) mode. Features to be investigated include: (1) rod-like silica-rich precipitates, clinoenstatite lamellae, and anti-phase domain boundaries in the pyroxene minerals, and (2) needlelike precipitates, and lamellae of a high-pressure TiO2 phase with _-PbO2 type structure in rutile. Using Density Functional Theory, calculations will be carried out on the effects of size on nano-phase stabilities. It is hypothesized that the stabilities of nano-phase lamellae of clinoenstatite and _-PbO2 type TiO2 within their host minerals will be greatly different from the stabilities of their bulk phases. The structure and chemistry of the micro-phases and their relationships can provide P-T history of the host minerals during subduction and exhumation of a continental plate.The University of Wisconsin - Madison has just purchased a state-of-the-art aberration-corrected field emission-gun (FEG) TEM / STEM (Scanning Transmission Electron Microscope) imaging system with X-ray EDS and EELS capabilities that is supported by the NSF MRI program. This system is capable of getting spatially-resolved EELS spectra at 1µ resolution. Z-contrast imaging using STEM mode can provide chemical images at the atomic scale. These systems will be used in the proposed study and are expected to provide a wealth of new and significant knowledge about nano-phases, interface structures, and defects in the minerals, and how they record their formation condition and history of their host rocks.Broader impactResults of this work will be incorporated into courses taught by the PI and invarious outreach activities through the UW-Madison Geology Museum, which provides guided tours to about 13,000 K-12 students each year and attracts more than 40,000 visitors every year. The project will also support graduate student research.