Philpotts Partial 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.
