This textbook provides a basic understanding of the formative processes of igneous and metamorphic rock through quantitative applications of simple physical and chemical principles. The book encourages a deeper comprehension of the subject by explaining the petrologic principles rather than simply presenting the student with petrologic facts and terminology. Assuming knowledge of only introductory college-level courses in physics, chemistry, and calculus, it lucidly outlines mathematical derivations fully and at an elementary level, and is ideal for intermediate and advanced courses in igneous and metamorphic petrology. The end-of-chapter quantitative problem sets facilitate student learning by working through simple applications. They also introduce several widely-used thermodynamic software programs for calculating igneous and metamorphic phase equilibria and image analysis software. With over 350 illustrations, this revised edition contains valuable new material on the structure of the Earth's mantle and core, the properties and behaviour of magmas, recent results from satellite imaging, and more.
Melting experiments on samples of basaltic rock from a thick lava flow reveal that when this lava originally began to crystallize, feldspar crystals linked together to form a continuous three-dimensional network of chains when the lava was no more than 25% crystallized. Formation of this network has profound implications for the behaviour and differentiation of basaltic magma. Much of the compositional variation of igneous rocks results from the separation of liquid from crystals, a process that is dramatically affected according to whether crystals occur separately or are linked together in networks.Many thick flood-basalt flows 1-7 and lava lakes 8-11 contain horizontal sheets of coarse-grained rock whose composition corresponds to liquid formed by approximately one-third fractional crystallization of the host basalt. Several mechanisms have been proposed for separating this liquid from the basalt, one of which involves expulsion of liquid from a crystal mush that undergoes compaction in the lower part of the flow 7 . Compaction can occur only after crystals interconnect to form a network but before the network grows too strong to be deformed. Previous partial melting experiments 12 on the thick Jurassic Holyoke flood basalt of Connecticut and Massachusetts indicate that such a network forms when this basalt is only 25% crystallized.Here we present the results of experiments that indicate that the crystal mush in the Holyoke basalt owed its strength to the presence of a remarkable three-dimensional (3D) network of plagioclase crystal chains. We have determined the shape of this network from 3D models constructed from serial sections through partially melted samples of the basalt. The deformation of the network that resulted from compaction during solidification of the lava can be measured from the chain distribution in the serial sections. These measurements provide a direct means of determining the amount of compaction that has occurred during the solidification of an igneous body. Partial melting experimentsSamples of the Holyoke basalt have been partially melted so that the textural relations between the refractory minerals involved in compaction could be studied. By partly melting and then rapidly quenching the samples, the low-melting, late-crystallizing minerals are converted to glass in which the refractory minerals are embedded. One-centimetre cubes of the rock were heated in graphite crucibles under a reducing atmosphere. Graphite is not wetted by silicate melts and therefore does not wick away the liquid from the partially melted rock. The furnace atmosphere was not controlled precisely, but the cores of the rock cubes remained close to their intrinsic oxygen fugacity (quartz-fayalite-magnetite buffer) for the duration of the experiments (Ͻ24 hours).Previous melting experiments 12 reveal that cubes of basalt from the central (slowly cooled) part of this flow retain their cubic shape when at least 70% melted, which indicates that a continuous network of crystals still exists at this high degree of melt...
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