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53 Cards in this Set
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Phaneritic |
igneous rock; crystal size can be seen with the naked eye; intrusive(cooled slowly underground)
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Aphanitic |
igneous rock; crystals are to small to see or rock is glass; extrusive(cooled quickly in air or underwater) |
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Igneous Minerals |
Mostly silicates; Olivine, Pyroxene, Amphibole, Micas, Feldspar, Quartz |
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Names for Igneous Rocks |
Based on texture(intrusive/extrusive) and Mineral assemblage(how much silica, Fe, Mg, Na, Ca and K) |
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5 types of Igneous rocks |
Granite, Granodiorite, Diorite, Gabbro, Peridotite |
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Why and Where Rock Melts |
temp increases with depth, but so does melting point of rock; melting is rare; 4 concepts, partial melting, pressure and melting, water and melting melt density |
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Partial Melt |
rocks don't melt at one temp; partially molten rock is mostly solid; Melt is higher in silica; Melt is more felsic |
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Felsic/Mafic |
felsic rocks have little Fe and Mg, lots of silica, and are usually light in color; Mafic rocks are the opposite(rich in Fe and Mg, silica poor and dark in color |
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Pressure and Melting |
The melting point of rock increases with pressure |
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Water and Melting |
Water lowers the melting point of rock, like salt on ice, very little(>1%) can make a big change; Presence of water makes melt more felsic |
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Melt Density |
Melt is less dense than solid rock; opposite of ice and water; melt will rise through cracks or burn a path- magmas can ascend tens of km or more |
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Where melt is made? |
Mid-Ocean ridges(and rifts)-most productive source of magma, responsible for production of all oceanic crust Subduction Zones- major geologic hazard Hot Spots- Make great resorts, cool deep interior of planet, pose enormous, but exceedingly rare, hazard |
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Mid-Ocean Ridges |
Pressure-release melting-magma ascends adiabatically, doesn't exchange heat, cools only by release of pressure Produces 1 to 20% partial melts Mantle peridotite melts to form basalt/gabbro |
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Subduction Zones |
Subduction hydrates the mantle wedge- hydrous minerals breakdown and release water Water lowers melting point Partial melts ascend to form volcanic arcs Many kinds of igneous rock; andesite is common |
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Hot Spots |
Hot material rises from deep mantle-part of convection Pressure-release melting Produces basalts- close, but not identical, to MORB Cools planet(brings up hot material) Major geologic hazard?
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Magmatic Intrusions |
Magma can be placed in variety of ways: -Vertical Sheets(dykes) Horizontal sheets(sills) -Near-vertical conduits(necks) wart-like bumps(laccoliths) Huge bodies(plutons and batholiths)
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Igneous rock summary |
Mantle melts are basalt/gabbro Oceanic crust is basalt/gabbro Hotspot islands are usually basalt/gabbro subduction zones also basalt/gabbro, but if continental crust is involved, andesite, dacite, and rhyolites also can occur |
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Magmatic Eruptions |
Explosive and non explosive Depending on gas content and viscosity Mafic are less viscous and have less dissolved gas, Felsic are more viscous and more dissolved gas Mid ocean ridges and hot spots are rarely explosive subduction zones are often explosive |
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Shield Volcanoes |
low sloping and usually basaltic; nonexplosive
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Strato (composite) volcano |
Mixed rock and tephra; Steep sided, Explosive, cascades in Oregon and Washington |
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Tephra |
unconsolidated accumulations of pyroclastic grains(pieces of rock blown from volcano during eruption): ash(dust) Lapilli(marbles) Bombs(baby heads to fridges) |
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Tuff |
rock consisting of welded pyroclastic material(pieces bound to each other) example: bishop tuff-long valley caldera in cali erupted 140 times as much as st.helens |
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In the oceans |
magnetite in the oceanic crust records field; when same as present field the sum is high when reversed the sum(present and rock) is low |
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Assumptions |
Dipole is the stronges part of the field Dipole aligned with north pole over long time scales |
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Clastic Sediments |
Broken pieces, clay to boulder size |
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Chemical Sediments |
precipitated from water |
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Biogenetic Sediments |
shells and casts of organisms; coral reefs |
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Transport |
Sediment moves down slope Primary agents are water, ice and air; water being most important Transport results in: sorting by size shaping- sediment matures with transport making grains rounder chemical weathering |
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Deposition |
Sediments usually deposited on top of crust, not within sediments usually deposited in horizontal layers younger sediments deposited onto tolder sediments sediments deposited at one time can vary horizontally |
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Tectonic setting |
two settings that frequently result in large accumulations(sedimentary basins) subduction zones-trench and fore-arc basins; abundant supply, topographic lows Continental rift zones- subsidence due to cooling |
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Stratification or bedding |
Sedimentary structure; gravity produces horizontal layering |
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Graded bedding |
Sedimentary structure; coarse sediment on bottom, grading up to fine; deposition from water
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Cross bedding |
Sedimentary structure; bedding planes not parallel to stratification; deposition from moving water or air; structures dip in the down wind direction |
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Lithification |
compaction from deposition and burial; reduction in porosity; cementation(CaCO3 or SiO2 deposited from fluids in pore space |
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Clastic Classification |
Based primarily on texture(clast size and shape) Four size bins, gravel(conglomerate or breccia) sand(sandstone) silt(siltstone) clay(mudstone or shale)
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Carbonates |
chiefly limestone(CaCO3); reefs, foraminifera, precipitation |
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evaporites |
sea water evaporation and supersaturation; calcite, gypsum, halite, Mg and K, chlorides, sulfates fresh water; evaporites such as borax and various nitrates |
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Siliceous sediments |
diatoms and radiolara(freshwater) chert and flint(SiO2) and opal (siO2 x nH2O) cold water (upwelling) |
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Peat, coal, oil and gas |
deposition under reducing environments(low oxygen) various amounts and durations of heat and pressure |
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Metamorphism |
the process of changing the characteristics of a rock by changes in temperature and pressure -usually doesn't change rock composition -alters minerals and texture -no melting, but fluids can be important |
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Pressure and Temperature |
increases in the two cause metamorphism pressure- increases at 30mPa/km Temperature- increases at 30degrees/km rocks formed at or near surface are not in equilibrium at depth |
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Two types of Pressure |
confining pressure(uniform) stress pressure(directional pressure) can cause; growth or dissolution of crystals change in crystalline structure texture or "fabric"
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Metamorphic grade |
refers to the combination of pressure and temperature low grade <10km high grade> 20 km |
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Water in metamorphism |
facilitates mineral growth by easing movement of ions when it moves through system, composition can change- metasomatism |
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Regional Metamorphism |
widespread(most common) medium to high grade differential pressures-> fabric cores of mountains |
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contact metamorphism |
high T, low P "halo" around intrusions grade decreases away from intrusion |
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Hydrothermal metamorphism |
moving hot water metasomatism common near mid-ocean ridges produces important resources(sulfides and ore bodies, origin of life(ore refuge)) |
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Naming Metamorphic rocks |
based on minerals, texture, and source rock or protolith 4 common protoliths: shales and mudstones basalts quartz rich sandstones, limestones
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Shales and Mudstones |
produce unique textures: foliation- sets of flat or wavy parallel planes in rock; formed by alignment of platy minerals(micas and clays) slaty cleavage; planes along which rock easily cleaves(splits) |
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Low to high grade shales and mudstones |
Slate-slaty cleavage, aphanitic materials Phyllite- slaty cleavage, visible minerals, shiny Schist-wavy foliation and large crystals gneiss- color banding and weak foliation |
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Limestone and Sandstone |
Marble- chiefly calcite(CaCO3); sedimentary structure usually lost Quartzite- little or no remaining porosity; interlocking quartz grains |
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Basalt |
based on mineral assemblage(little foliation): greenschist-low grade; has chlorite Amphibolite- intermediate grade; amphibole Granulite- high grade; garnet and sillimanite |
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Metamorphic Minerals |
Chlorite: bright green mica(no Cl) Glaucophane: rich blue amphibole Zeolites: hydrous silicates Garnet: silicates, moderate to high grade Alumino-Silicates(Al2SiO5)- andalusite (low T low P), Kyanite (high P low T), sillimanite |
