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

超高压变质岩金红石和辉石中的纳米相和微观结构研究：TEM 研究和计算机建模

• 批准号: 0810150
• 负责人: Huifang Xu
• 金额: $ 13.24万
• 依托单位: University of Wisconsin-Madison
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-07-15 至 2011-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0810150&HistoricalAwards=false
• 关键词: Study; Nano; phases; Microstructures; Rutile

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.

纳米相和纳米沉淀物在高温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，因为随着晶体变小，界面能对其稳定性的贡献变得巨大。我们将结合联合收割机TEM观察，从充分表征的超高压（UHP =柯石英和/或金刚石轴承）变质岩和计算机建模，使用密度泛函理论的超高压纳米沉淀物的尺寸和变化之间的关系，在他们的稳定领域相对于宏观相。中国东部大别-苏鲁超高压变质岩中的超高压岩石（榴辉岩）和波希米亚地块的摩尔达努比亚推覆体中的幔源超高压石榴辉石岩和榴辉岩将用于拟议的研究。采用高分辨透射电子显微镜（HRTEM）和X射线能谱仪（EDS）、电子能量损失谱仪（EELS）以及扫描透射电子显微镜（STEM）模式下的Z衬度成像技术，研究辉石和金红石中纳米沉淀物和纳米相的微观结构。辉石矿物中的棒状富硅沉淀物、斜顽辉石片晶和反相畴界;金红石中的针状沉淀物和高压TiO_2相的片晶，具有_-PbO_2型结构。使用密度泛函理论，计算将进行对纳米相稳定性的尺寸的影响。推测斜顽火辉石和_-PbO_2型TiO_2纳米相薄片在其主体矿物中的稳定性与其体相的稳定性有很大的不同。微相的结构和化学性质以及它们之间的关系可以提供大陆板块俯冲和折返过程中寄主矿物的P-T历史。威斯康星州-麦迪逊大学刚刚购买了一个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，具有X射线EDS和EELS功能，由NSF MRI计划支持。该系统能够获得1µ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，并有望提供有关纳米相，界面结构和矿物缺陷的丰富新的和重要的知识，以及它们如何记录其形成条件和寄主岩石的历史。更广泛的影响这项工作的结果将被纳入PI教授的课程，并通过UW-Madison地质博物馆进行各种推广活动，每年为约13，000名K-12学生提供导游图尔斯，每年吸引超过40，000名游客。该项目还将支持研究生的研究。