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

9805269 Philpotts在厚的溢流玄武岩流上进行的部分熔融实验表明，当熔岩的结晶度不超过25%时，就会出现斜长石晶体链的显著三维网络。一旦形成，该网络允许晶体糊状物的压实在流的下三分之一中发生，并且排出的液体向上移动到流的中心部分中，在那里它作为分化液体的水平片聚集。变形的网络所造成的压实测量从3-D模型构建的连续部分通过部分熔融的玄武岩样品。这些测量提供了确定火成岩体凝固过程中发生的压实量的第一个直接手段。继续研究计划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-一种厚的积水熔岩流。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完成。这些信息将与现有的化学数据相结合，以创建一个定量模型的晶体泥压实和由此产生的岩浆分异。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.