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

花岗岩类侵入岩构成了地壳的大部分，并且大多数显示出岩浆叶理和线理（即组构）。虽然构造地质学家在量化岩浆组构和解释其在岩体侵位背景下的意义方面取得了很大进展，但在使用组构来理解构造和岩浆过程、识别组构叠加或修改以及整合不同尺度的观察方面仍然存在问题。组构是在岩浆房过程中形成的，如在岩浆房底板上沉积晶体泥，还是在构造过程中形成的，如在活动剪切带中变形，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中的组构形成，并且一个岩体中组构形成的机制可能与另一个岩体中的组构形成的机制不同，但很少有被广泛接受的标准存在于测试组构形成的不同模型之间。该项目综合了构造学和岩石学方法，以检验关于缅因州沿海两个志留纪浅岩体（Cadillac Mountain和Vinalhaven侵入杂岩）中组构形成和侵位的假设。这两个岩体都显示出岩浆结构的可量化变化，也没有显示出固态变形的证据。除了开发新的方法来量化花岗岩中的岩浆组构，该建议采取假设检验的方法来解释组构的起源。它还支持六名女大学生在她们人数不足的领域进行研究。研究目标有三个方面：目标1：通过量化花岗岩织物，纹理和成分中的露头尺度梯度来进行织物开发和修改的测试模型。PI将使用最先进的组构分析技术，对花岗岩大型定向手制样品的相互正交面进行研究，以量化每种矿物种群所定义的组构强度和对称性。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：对构造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。重点是梯度在三个设置：（a）与保存的岩浆房地板，因为它是夹层与镁铁质片，（B）典型的均匀花岗岩，（c）花岗岩与镁铁质纹影。目标2：进行岩体尺度的岩浆组构研究，以进一步限制我们对两个岩体中岩浆组构的起源和意义的解释。利用磁化率的各向异性（AMS），PI将绘制岩浆叶理和线理相对于围岩接触和花岗岩相之间的主要边界的方向。AMS研究将伴随着磁性矿物学和AMS椭球体与岩石组构的关系的详细工作。目标3：检验岩浆房底板在岩体侵位期间凹陷的假设。以前的工作，根据映射的极性标准和古水平指标保存在镁铁质和长英质层，产生了一个可测试的模型，这些岩体的侵位向下凹陷的岩体底板。通过对目标#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岩体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.