Earth Sciences 1022A/B Lecture Notes - Lecture 3: Porphyritic, Igneous Textures, Oceanic Crust
9 Apr 2018
School
Department
Course
Professor
Document Summary
Igneous rocks crystalize from molten silicate material called magma that forms at high temperatures and pressures deep in the earth. Magma rises through the crust and either reaches the surface by volcanoes (extrusive) or cools below surface (intrusive) Through bowen"s reaction series in which crystals settle in a magma chamber: earlier dark crystals remove heavy elements, leaving melt with lighter ones (magmatic differentiation) Also assimilation (host rock melts in magma), magma mixing. Igneous compositions: dark versus light mineral content (i. e. fe, mg vs silica) Igneous textures: size, shape, arrangement of mineral crystals. Pyroclastic (airborne pieces of magma fell to the ground)\ Felsic (~70% silica: granite (in core of mountains, rhyolite (volcanic) Intermediate (~60% silica: andesite (from volcanoes above subduction zones, diorite (in intrusive rocks above subduction zones) Mafic (~50% silica: basalt (most abundant rock, forms oceanic crust, gabbro (in lower oceanic crust) Ultramafic (~40% silica: peridotite (in upper mantle)
