GEOL 256 Lecture Notes - Lecture 29: Accretionary Wedge, Spilite, Chabazite
13 Nov 2020
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Lecture 28: metamorphism 3 (11/11/20) hydrothermal metamorphism chart. Mid-ocean ridge spreading centers (and other volcanic regions) Metasomatism : altering rocks (specifically basalt here) with hydrothermal fluids. Oceanic crust + quenched glass on pillow lavas. Primary minerals =anhydrous olivine, pyroxene, plagioclase, fe and ti oxide. 2- , and interaction with basalt dissolves ca, fe, and si. Zeolites, epidote, p-p, chlorite, chabazite, replace primary minerals in amygdules. Hydrous alteration of ultramafic rock with olivine and pyroxene. Mostly composed of green mg-rich serpentine group minerals. Higher pressures but lower temperatures bc slab doesn"t heat up. Subducted oceanic slab minerals are destabilized by pressure. Garnet porphyroblasts, green omphacite, white coesite (high p quartz), occasionally blue. Slab pull - gravity on lowest parts of slab. Metamorphosing the basalt makes the slab heavier. Process of subduction and formation of eclogite leads to water in the mantle. Water in sediment (terrigenous and biogenous) and rock. Pulverized rock, near faults or areas with shear.
