EPSC 201 Lecture Notes - Lecture 13: Extrusive Rock, Xenolith, Source Rock
26 Jan 2017
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Document Summary
Source rock dictates initial magma composition: mantle source ultra-mafic and mafic magmas, crustal source mafic, intermediate and felsic magmas. Instead, only a portion of the rock melts: si-rich minerals melt first; si-poor minerals melt last. Partial melting, therefore yields a silica-rich magma. Removing a partial melt from its source creates: felsic magma, mafic residue. Magma melts the wall rock it passes through. Blocks of wall rock (xenoliths) fall into magma. Assimilation of these rocks alters magma composition. Different magmas may blend in a magma chamber. The result combines the characteristics of the two. Often magma mixing is incomplete, resulting in blobs of one rock type (xenolith) suspended within the other. Cooling rate how fast does magma cool: depth deeper is hotter; shallower is cooler. Deep plutons lose heat very slowly; take a long time to cool. Shallow flows lose heat more rapidly; cool quickly: shape spherical bodies cool slowly; tabular faster, groundwater circulating water removes heat.
