Refinement of Measurement of Crystal-Mush Compaction in the Palisades Sill, New Jersey

Philpotts/Gray EAR-0106538这项研究的目标是直接确定新泽西州Palisade Sill的固化过程中发生的压实量，Palisade Sill是最简单、研究最深入的侵入型火成岩之一。以前的研究表明，通过这个岩床的化学变化的一个可能的解释是晶体泥浆的压实和残余液体的向上排出。然而，证据完全是化学的，可以有其他解释。最近的研究表明，在岩浆结晶早期，斜长石晶体连接在一起，形成了一个三维的链状网络，这是一种厚重的溢流玄武岩流动。如果晶体碎屑在凝固过程中发生压实，斜长石晶体的网状结构就会发生变形，其各向异性程度是压实量的直接量度。在熔岩流较厚的情况下，由斜长石网络的各向异性和通过熔岩流的化学变化独立确定的压实量非常吻合。对Palisade Sill岩石组构的初步测量表明，它们确实是各向异性的，从化学证据推断的压实确实发生了。已经开发出三种独立的新方法来测量岩石组构的各向异性。这些方法包括在定向薄片中测量斜长石网络的各个方面。一种是基于斜石链之间沿相互垂直的导线的平均截距长度；另一种是将链中的链接视为矢量，可以分析其分布的各向异性；第三种是确定可以拟合到链之间间隙块的平均力矩椭圆。每种方法都可以对压实度和方位估计的标准误差进行彻底的统计分析。这些技术将用于从一系列定向样品中通过窗台切割出的三个相互垂直的薄片。这些测量将使我们能够为每个样品确定岩石组构各向异性的三维椭球体，并由此计算出压实量和方向。三种独立的压实测量方法之间的差异可以用来阐明压实过程的机理及其与窗台分层的关系。磁化率的各向异性通常被用来间接测量岩石组构的各向异性，它将在每个样品中进行测量，以确定它与斜长石链网络的各向异性之间的关系。直接测量晶体中的压实作用非常重要，因为它将提供对岩浆体分异和从部分熔融的地幔来源中提取岩浆所涉及的化学和物理过程的洞察。

Philpotts/Gray EAR-0106538 The goal of this research is to determine directly the amount of compaction that occurred during the solidification of the Palisades Sill, New Jersey, one of the simplest and best studied intrusive igneous bodies. Previous studies revealed that a possible explanation for the chemical variation through this sill involved compaction of crystal mush with upward expulsion of the residual liquid. The evidence, however, is entirely chemical and open to other interpretations. Recent studies of a thick flood-basalt flow have shown that plagioclase crystals link together to form a three-dimensional network of chains early in the crystallization of the magma. If compaction of crystal mush occurs during solidification, the network of plagioclase crystals is deformed, and its degree of anisotropy is a direct measure of the amount of compaction. In the case of the thick lava flow, the compaction amounts independently determined from the anisotropy of the plagioclase network and from the chemical variation through the flow agree remarkably well. Initial measurements of the fabric of rocks in the Palisades Sill document that they are indeed anisotropic and that the compaction inferred from the chemical evidence did occur. Three new, independent methods have been developed for measuring the anisotropy of a rock's fabric. The methods involve measuring various aspects of the plagioclase network in oriented thin sections. One is based on the average intercept length between plagioclase chains along mutually perpendicular traverses; another considers links in the chains as vectors whose distribution can be analyzed for anisotropy; and the third determines the average moment ellipse that can be fitted to the interstitial patches between the chains. Each of the methods is amenable to a thorough statistical analysis of the standard errors for the degree of compaction and orientation estimates. These techniques will be used on sets of three mutually perpendicular thin sections cut from a series of oriented samples through the sill. These measurements will allow us to determine, for each sample, the 3-D ellipsoid of the anisotropy of the rock1s fabric, from which will be calculated the amount and direction of compaction. Differences between the three independent methods of measuring compaction can be used to shed light on the mechanism of the compaction process and its relation to layering in the sill. The anisotropism of magnetic susceptibility, which has commonly been used as an indirect measure of the anisotropy of a rock1s fabric, will be measured in each sample to determine how it relates to the anisotropy of the plagioclase-chain network. The direct measurement of compaction in a crystal mush is of importance, because of the insight it will provide into the chemical and physical processes involved in the differentiation of magma bodies and in the extraction of magma from partly melted mantle sources.