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

EAR-0003574EAR-0003463本项目旨在通过比较简单的自然实例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。该项目涉及的数据收集使用：1)磁化率各向异性(AMS)，2)形状择优取向(SPO)，3)计算机X射线断层扫描(X-射线CT)，4)与犹他州亨利山脉的岩床、熔岩和杂岩有关的岩浆组构和应变的现场测量，以及5)人工流动中颗粒的实验室测量。亨利山脉侵入岩为奥里戈西世-中新世，侵入科罗拉多高原的上地壳，科罗拉多高原是晚古生代和中生代的一段平坦的砂岩和页岩。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，而亨利山脉的侵入岩提供了了解这一基本过程的最佳机会。这些侵入物的地板、墙壁、内部和屋顶在犹他州南部的沙漠高原上都暴露得很好。这些深成岩块通过弯曲覆盖层或使侵入体上方的覆盖层发生断层而抬高了覆盖层。侵入体的形状代表了岩床和漆石之间的完全渐变。通过记录这些岩体中的岩浆组构，解释了侵入体的时间组构发展，并将其与物理模型中流动演化的步骤相关联。侵入的边界条件被很好地理解：岩浆岩、杂砂岩和岩床侵入科罗拉多高原未变形的水平地层。地层作为标志，记录岩浆侵入引起的平移、旋转和内部应变。此外，深成岩侵入了科罗拉多高原的一部分，没有经历过区域变形。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。该项目涉及详细的实地研究，以记录这些侵入体中的面理和线理。此外，还记录了斑晶的三维SPO，并对侵入体进行了AMS采样。AMS技术将得到X射线CT技术的证实，这将使记录相同样品上磁铁矿的取向和空间分布成为可能。现场研究正在与非均匀流的物理实验同步进行。这些侵入岩是可以模拟的完美例子，因为它们的形状简单而已知，而且岩浆的低晶体含量受到很好的约束。被模拟的流动包括减速流动和圆柱流，它们分别提供了岩浆侵入岩浆层和副岩层的一级近似。在这些实验中放置了被动的、中性浮力的标记，以获得与流入腔室的不同数量的流体相关的定量应变。这一结果正在与亨利山脉侵入岩的布料进行比较，后者布满了不同数量的岩浆。利用这种多样化的技术，以及亨利山脉提供的理想环境，人们将了解与强烈侵位岩浆侵入有关的三维结构。

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.