01:460:101 Lecture Notes - Lecture 3: Porphyritic, Partial Melting, Plagioclase
28 Sep 2016
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Forms: dykes: shallow, tubular structure that cuts across any layering in country rock (discordant, sills: shallow, tabular intrusive structure that cuts across any layering in country rock (discordant, laccoliths: concordant body, with flat bottom and convex upward. It is dome shaped: bysmaliths: cylindrical shaped body. Intrusive rock bodies: plutons: deep, large, blob-shaped intrusive body formed of coarse-grained igneous rock, commonly granitic in composition. This can reduce the melting point of rocks: mineral mixtures: certain minerals can mix together (quartz and feldspar) lowering the melting temperatures of both minerals. In terms of continuous, plagioclase feldspar chemical composition evolves from ca-rich to na-rich with decreasing temperature. Pegmatitic- extremely coarse-grained: glassy- contains no crystals at all. Small formed from cooling at surface: compositional classification, mafic rocks (50% silica) (gabbro-basalt) contain dark colored ferromagnesian minerals. Intermediate rocks (between 50-65%) (diorite-andesite) contain roughly equal amounts of dark- and light-colored minerals.
