Collaborative Research: Three Dimensional Magmatic Strain within Laccoliths, Bysmaliths, and Sills in the Henry Mountains, Utah

合作研究：犹他州亨利山脉的 Laccoliths、Bysmaliths 和 Sills 内的三维岩浆应变

• 批准号: 0003574
• 负责人: Sven Morgan
• 金额: $ 5.6万
• 依托单位: Central Michigan University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2001
• 资助国家: 美国
• 起止时间: 2001-01-01 至 2003-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0003574&HistoricalAwards=false
• 关键词: Collaborative; Research; Three; Dimensional; Magmatic

EAR-0003574EAR-0003463This project is designed to understand the three-dimensional fabrics and strain associated with magmatic forceful expansion by comparing simple natural and experimental examples. The project involves data collection using: 1) anisotropy of magnetic susceptibility (AMS), 2) shape preferred orientations (SPO), 3) computed X-ray tomography (X-ray CT), 4) field measurements on the magmatic fabrics and strains associated with sills, laccoliths, and bysmaliths in the Henry Mountains, Utah, and 5) lab measurements on particles within artificial flows. The Henry Mountains intrusives are Oliogocene - Miocene age and intruded the upper crust of the Colorado Plateau, which is a late Paleozoic and Mesozoic section of flat-lying sandstones and shales.The goal is to relate magmatic fabrics to the displacement of the wallrocks caused by magmatic intrusion (inflation), and the intrusives in the Henry Mountains provide the best opportunity to understand this fundamental process. The floors, walls, interiors, and roofs of these intrusions are all very well exposed in the desert plateau of southern Utah. These plutons have raised the overburden by either bending the overburden or faulting the overburden immediately above the intrusion. The shapes of the intrusions represent a complete gradation between sills and laccoliths. By documenting the magmatic fabric in these bodies, the temporal fabric development of the intrusions is being interpreted and related to steps in the evolution of flow in the physical models.The boundary conditions of intrusion are well understood: laccoliths, bysmaliths, and sills intruded into the undeformed, horizontal strata of the Colorado Plateau. The strata act as markers to record the translation, rotation, and internal strain caused by magma intrusion. Moreover, the plutons intruded into a part of the Colorado plateau that has not experienced regional deformation. This setting precludes tectonic forces being involved with emplacement and allows an interpretation that unambiguously describes fabrics in terms of magmatic processes.The project involves a detailed field study to document the foliation and lineation within these intrusions. In addition, the three-dimensional SPO of the phenocrysts is being recorded and the intrusions are being sampled for AMS. The AMS technique will be corroborated by X-ray CT techniques, which will allow the documentation of the orientation and spatial distribution of magnetite on the same samples. The field studies are being conducted in tandem with physical experiments of non-uniform flows. These intrusives are the perfect examples to be modeled since their shapes are simple and known, and the low crystal content of the magmas is well constrained. The flows that are being modeled include decelerating flow and cylindrical flow, which provide a first-order approximation of magma intruding a laccolith and a bysmalith, respectively. Passive, neutrally-buoyant markers are being placed in these experiments in order to obtain quantitative strain associated with various amounts of fluid flow into a chamber. The results are being compared with the fabrics from the Henry Mountains intrusives, which were emplaced with varying amounts of magma. Using this variety of techniques, and the ideal setting provided by the Henry Mountains, the three-dimensional fabric associated with forceful emplacement of magmatic intrusions will be understood.

该项目旨在通过比较简单的自然和实验实例来了解与岩浆强力膨胀相关的三维组构和应变。该项目包括使用以下方法收集数据：1）磁化率各向异性（AMS），2）形状优选取向（SPO），3）计算机X射线断层扫描（X射线CT），4）犹他州亨利山脉岩浆组构和与岩床、岩盖岩和岩基岩相关的应变的现场测量，以及5）人工流内颗粒的实验室测量。亨利山侵入岩的时代为渐新世-中新世，侵入科罗拉多高原的上地壳，这是一个晚古生代和中生代的平坦砂岩和页岩段。目的是将岩浆组构与岩浆侵入（膨胀）引起的围岩位移联系起来，亨利山的侵入岩为了解这一基本过程提供了最好的机会。这些侵入物的地面、墙壁、内部和屋顶都很好地暴露在犹他州南部的沙漠高原上。这些侵入岩通过弯曲覆盖层或在侵入体正上方使覆盖层断裂而抬高覆盖层。侵入体的形状代表岩床和岩盖之间的完整渐变。通过记录这些岩体中的岩浆组构，对侵入体的时间组构发展进行了解释，并将其与物理模型中流体演化的步骤联系起来。侵入体的边界条件得到了很好的理解：岩盖岩、岩盖岩和岩床侵入到科罗拉多高原未变形的水平地层中。地层作为标志物记录了岩浆侵入引起的平移、旋转和内部应变。此外，侵入岩体侵入了科罗拉多高原的一部分，而这一部分并没有经历区域变形。这一背景排除了与侵位有关的构造力，并允许根据岩浆过程明确描述组构的解释。该项目涉及详细的实地研究，以记录这些侵入体内的叶理和线理。 此外，正在记录斑晶的三维SPO，并对侵入体进行AMS取样。AMS技术将得到X射线CT技术的证实，这将有助于记录相同样品上磁铁矿的方向和空间分布。 实地研究与非均匀流动的物理实验同时进行。 这些侵入岩是建模的完美例子，因为它们的形状简单且已知，并且岩浆的低晶体含量受到很好的限制。被模拟的流动包括减速流和圆柱流，它们分别提供了岩浆侵入岩盖岩和岩盖岩的一阶近似。在这些实验中放置了被动的中性浮力标记物，以获得与流入腔室的各种量的流体相关的定量应变。这些结果正与亨利山侵入岩的结构进行比较，后者是由不同数量的岩浆侵位的。利用这些不同的技术，以及亨利山脉提供的理想环境，我们将了解与岩浆侵入体强有力的侵位有关的三维结构。