Field-Based Analysis of Subduction Petrofabrics

俯冲岩石结构的现场分析

• 批准号: 0711263
• 负责人: Donna Whitney
• 金额: --
• 依托单位: University of Minnesota-Twin Cities
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2007
• 资助国家: 美国
• 起止时间: 2007-07-01 至 2011-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0711263&HistoricalAwards=false
• 关键词: Field; Based; Analysis; Subduction; Petrofabrics

This project, carried out by a team of researchers from the University of Minnesota, determines the high-pressure petrofabrics of an exhumed subduction complex characterized by pervasive, syn-kinematic high-pressure assemblages preserved in metasedimentary (marble, quartzite) and metabasaltic (eclogite, blueschist) rocks. Field mapping in the Sivrihisar Massif, Turkey, coupled with microstructural, petrologic, and stable isotope analyses are used to determine large-scale flow, deformation mechanisms, flow laws, and fluid-rock interaction at a range of depths in a subduction zone (40-75 km). Microstructural techniques include electron back-scattered diffraction (EBSD) to determine crystallographic orientation of the rheology-controlling phases clinopyroxene in eclogite, (fibrous) calcite in marble, and quartz in quartzite; field and petrographic analysis of kinematics, including determination of kinematic vorticity using lawsonite shape and orientation; and determination of sense of shear. Petrologic investigation includes microprobe analysis of mineral compositions and zoning, and evaluation of factors influencing the degree of preservation of high-pressure assemblages at different field sites in the massif. The extent, conditions, and pathways of fluid-rock interaction is assessed via oxygen isotope analyses, including mineral-whole rock analyses and in situ ion probe analysis of compositionally and texturally zoned grains from blueschist-eclogite transition zones.The deformation behavior of subducted crust strongly influences the geophysical and geochemical evolution of convergent plate boundaries, including the interaction of deformation, metamorphism, and fluid-rock reaction during subduction and return of deeply buried rocks to the Earth's surface, and the rates of subduction processes. This research addresses questions of the mechanisms of large-magnitude transport of high-pressure rocks in subduction zones by characterizing deformation characteristics from the map scale to the grain-scale using high-pressure minerals. The Sivrihisar Massif contains the one of the world's best-preserved and most extensive outcropping of lawsonite eclogite, a rock type predicted to be common at depth in subduction zones, but rarely exposed at the surface owing to the ease with which lawsonite is destroyed during exhumation. There have been no previous microstructural studies of this important rock type, which may be the dominant lithology in subducted oceanic crust between 45-300 km.

该项目由明尼苏达大学的一组研究人员实施，确定了一个折返俯冲杂岩的高压岩组，其特征是普遍存在的、同向运动的高压组合，保存在变沉积(大理石、石英岩)和变基性(榴辉岩、蓝片岩)岩石中。使用土耳其Sivrihisar地块的野外测绘，结合显微构造、岩石学和稳定同位素分析，确定了俯冲带(40-75公里)一定深度范围内的大规模流动、变形机制、流动规律和流体-岩石相互作用。微结构技术包括：电子背散射衍射(EBSD)，以确定榴辉岩中的单斜辉石、大理岩中的(纤维状)方解石和石英岩中的石英的流变学控制相的晶体取向；运动学的现场和岩石学分析，包括利用劳钠铝石的形状和取向确定运动涡度；以及剪切感的确定。岩石学研究包括矿物成分和分带的微探针分析，以及影响地块不同野外地点高压组合保存程度的因素评估。通过氧同位素分析，包括矿物-全岩分析和原位离子探针分析，评价了流体-岩石相互作用的程度、条件和途径。俯冲地壳的变形行为强烈影响收敛板块边界的地球物理和地球化学演化，包括俯冲和深埋岩石返回地球表面过程中变形、变质和流体-岩石反应的相互作用，以及俯冲过程的速率。本研究通过利用高压矿物表征从地图尺度到颗粒尺度的变形特征，探讨了俯冲带高压岩石的大规模运移机制。Sivrihisar地块包含世界上保存最完好和露头最广的劳钠辉石榴辉岩之一，据预测，这种岩石类型在俯冲带深处很常见，但由于在折返过程中很容易被破坏，因此很少在地表露出。这种重要的岩石类型可能是45-300公里之间俯冲洋壳的主要岩性，以前还没有对其进行显微构造研究。