GEO 303 Chapter Notes - Chapter 6: Lithosphere, Stratovolcano, Basalt

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10 May 2016
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Geo Chapter 6 Notes:
Introduction
oIgneous rocks: produced when melted rock material, magma,
solidifies
oLava: magma that flows out of the earth’s surface
oRock texture (sizes, shapes, arrangements of mineral grains)
oMafic: magnesium and ferric iron
oFelsic: rock rich in feldspar
oUltramafic: exceptionally mafic
Igneous Rock Types
oClassified according to two factors
Magma composition and where it solidifies
Plutonic: intrusive rocks, formed when magma solidifies below
the Earth’s surface large enough to see with our own eyes
Pegmatite: huge crystals growth is not only at depth but also
from a silicate magma charged with dissolved H20.
Volcanic: solidify quickly on the earth surface, small crystals
Obsidian: and its frothy equivalent, pumice, have no crystals at
all
Tuff: fine grained product of volcanism so explosive that the
rock material has completely shattered
Porphyry: igneous texture in which a few larger crystals are set
in a matrix of much smaller crystals
Plenocrysts: large crystals in a porphyry, variety of mineral
species
Plutonic Rock Bodies
oPlutonic rocks occur as several types of intrusive bodies, categorized
on the basis of their size, shape, and geometric relationship to rock
present in the area prior to igneous invasion
Volcanic Landforms
oPyroclastic debris: felsic magmas with considerable water content,
generated where continental lithosphere melts, are associated with
explosive volcanic events
oComposite volcanoes form as the pyroclastic alternate with lava flows
oFissure flows: basalt lavas on land will first fill in topographic
irregularities, and then continue to build great thicknesses of nearly
horizontal flows called plateau basalts
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