Plagioclase Crystal Networks in Partly Crystallized Basalt: Their Formation and Role in Magmatic Differentiation

[805269] philpottp .]在厚的洪水玄武岩流上进行的部分熔融实验表明，当熔岩结晶不超过25%时，存在一个显著的斜长石-晶体链的三维网络。一旦形成，这个网络允许在流体的下三分之一处发生晶体糊状物的压实，而排出的液体向上移动到流体的中心部分，在那里它聚集成水平片状的分化液体。由压实引起的网络变形是通过部分熔化的玄武岩样品的连续剖面构建的三维模型来测量的。这些测量提供了确定火成岩凝固过程中发生的压实量的第一个直接方法。继续进行的研究项目的主要目标是确定这种压实是如何在最简单的火成岩体中发生的——一种厚厚的、池塘状的熔岩流。这将通过确定斜长石网络的变形如何随流动高度和流动厚度而变化来实现。这些信息将与现有的化学数据相结合，以创建晶体-浆糊压实和岩浆分选的定量模型。虽然这项研究将在地表熔岩流上进行，但其结果将广泛应用于地球内部更大、更复杂的岩浆体。

9805269PhilpottsPartial melting experiments on a thick flood basalt flow have revealed that a remarkable 3-D network of plagioclase-crystal chains is present when the lava is no more than 25% crystallized. Once formed, this network allows compaction of the crystal mush to take place in the lower third of the flow and the expelled liquid moves upward into the central part of the flow where it accumulates as horizontal sheets of differentiated liquid. Deformation of the network resulting from compaction is measured from 3-D models constructed from serial sections through partially melted basalt samples. These measurements provide the first direct means of determining the amount of compaction occurring during solidification of an igneous body. The main goal of the continued research program is to determine how this compaction takes place in the simplest of igneous bodies - a thick, ponded lava flow. This will be done by determining how the deformation of the plagioclase network varies with height in the flow and with flow thickness. This information will be combined with existing chemical data to create a quantitative model for crystal-mush compaction and resulting magmatic differentiation. Although this study will be carried out on a surface lava flow, the results will have wide application to much larger and more complicated magma bodies within the Earth.