RUI: Fabric in Granite: the Vinalhaven and Cadillac Mountain Intrusive Complexes, Maine

花岗岩类岩体构成了地壳的大部分，大多数显示岩浆的叶理和线理（即构造）。虽然构造地质学家在岩浆组构的定量化和解释其在岩体侵位背景下的意义方面取得了很大进展，但在利用组构理解构造和岩浆过程、识别组构叠印或变质、整合不同尺度的观测等方面仍存在问题。织物是在岩浆室过程中形成的，如岩浆室底部的结晶沉积，在构造过程中形成的，如活动剪切带的变形，还是作为多个事件的复合记录？虽然许多过程可能有助于花岗岩的组构形成，而且一个岩体中组构形成的机制可能与另一个岩体中的不同，但很少有被广泛接受的标准来检验不同的组构形成模型。本项目结合构造学和岩石学方法，对缅因州沿海地区两个志留系浅层岩体——凯迪拉克山和维纳尔黑文侵入杂岩的构造形成和侵位进行了假设。这两个岩体都显示出岩浆结构的可量化变化，但都没有显示出固态变形的证据。除了开发量化花岗岩岩浆结构的新方法外，本提案还采用假设检验方法来解释结构的起源。它还支持六名本科女性在她们代表性不足的领域进行的研究。研究目标有三个方面：目标1：通过量化花岗岩织物、纹理和成分的露头尺度梯度，测试织物发展和修改的模型。在大型、定向的花岗岩手工样品相互正交的表面上工作，PI将使用最先进的织物分析技术来量化每种矿物种群所定义的织物的强度和对称性。他们还将使用一种从未被整合到结构研究中的岩石学技术：对织物发育过程中存在的积云晶体和熔体的相对体积进行定性评估。重点是在三种情况下的梯度：(a)花岗岩与保存完好的岩浆室底部有关，因为它与基性片层之间；(b)典型的均质花岗岩；(c)花岗岩与基性纹纹有关。目标2：进行岩浆构造的岩体尺度研究，以进一步限制我们对两个岩体中岩浆构造的起源和意义的解释。利用磁化率的各向异性（AMS）， PI将根据岩体接触和花岗岩相之间的主要边界绘制岩浆面理和线理的方向。AMS研究将伴随着详细的磁矿物学研究和AMS椭球体与岩石组构的关系。目标3：验证岩浆房底部在岩体就位时下沉的假设。先前的工作，基于在基性和长英质地层中保存的极性标准和古水平指示的映射，已经产生了一个可测试的模型，说明这些岩体的侵位是由岩体底部向下下垂引起的。通过对为目标2收集的所有岩心进行交变磁场退磁测量，PI将使用古地磁研究来尝试量化冥王星不同部分的相对旋转。

Granitoid plutons constitute much of the earth's crust, and most show magmatic foliation and lineation (i.e. fabric). Although structural geologists have made great strides in quantifying magmatic fabric and interpreting its significance in the context of pluton emplacement, problems remain in using fabric to understand tectonic and magmatic processes, identifying fabric overprinting or modification, and integrating different scales of observation. Does fabric form during magma chamber processes such as deposition of crystal mush on the magma chamber floor, during tectonic processes such as deformation in an active shear zone, or as a composite record of multiple events? Although many processes probably contribute to fabric formation in granites, and the mechanisms by which fabric forms in one pluton may be different from those in another, few widely accepted criteria exist for testing the different models of fabric formation against one another. This project integrates structural and petrological methods in order to testhypotheses about fabric formation in and emplacement of two shallow Silurian plutons in coastal Maine: the Cadillac Mountain and Vinalhaven Intrusive Complexes. Both plutons show quantifiable variations in magmatic fabric, and neither shows evidence for solid-state deformation. In addition to developing new methods for quantifying magmatic fabric in granite, this proposal takes a hypothesis-testing approach to interpreting the origins of fabric. It also supports research by six undergraduate women in a field in which they are under-represented. The research goals are three-fold:Goal 1: Test models for fabric development and modification by quantifying outcrop-scale gradients in granite fabric, texture, and composition. Working on mutually orthogonal faces of large, oriented hand samples of granite, the PI's will use a state-of-the-art fabric analysis technique to quantify the strength and symmetry of fabric defined by each mineral population. They will also use a petrological technique that has never been integrated into a structural study: qualitative assessment of the relative volumes of cumulus crystals and melt present during fabric development. The focus is on gradients in three settings: (a) granite that is associated with a preserved magma chamber floor because it is interlayered with mafic sheets, (b) typical homogeneous granite, and (c) granite associated with mafic schlieren. Goal 2: Conduct pluton-scale studies of magmatic fabric in order to further constrain ourinterpretations of the origin and the significance of magmatic fabric in both plutons. Using the anisotropy of magnetic susceptibility (AMS), the PI's will map the orientations of magmatic foliation and lineation with respect to both the wall-rock contact and major boundaries between granite facies. The AMS study will be accompanied by detailed work on magnetic mineralogy and the relation of the AMS ellipsoid to rock fabric.Goal 3: Test the hypothesis that the magma chamber floor sagged during pluton emplacement. Previous work, based on mapping of polarity criteria and paleo-horizontalindicators preserved in mafic and felsic layers, has generated a testable model for theemplacement of these plutons by the downward sagging of the pluton floor. With alternating field demagnetization measurements on all cores collected for Goal #2, the PI's will use a paleomagnetic study to attempt to quantify the relative rotation of different parts of the pluton.