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Physical Geology Midterm Notes
notes ranging from sedimentary, igenous, and metamorphic rocks and other basic principles
72
Geology
Undergraduate 1
10/19/2007

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Term
Magma
Definition
Molten material in the Earth's interior...plutonic (intrsuive) rocks. Magma intrudes towards the surface.
Term
Lava
Definition
Molten material at Earth's surface. Lava extrudes onto Earth's surface,
Term
Decompression Melting
Definition
Lower pressure can induce melting. Deeper in Earth pressure and temperature increase. Pressure changes faster than temp. Rocks are poor conductors.
Term
Heat Transfer Melting
Definition
Typically involves upwelling and/or intrusion of mantle material into overlying crust; hot fidge on ice-cream analogy.
Term
Felsic
Definition
Silica rich. Felsic rocks are rich in quartz and feldspar and are light in color. Coarse felsic rock: granite. Fine felsic rock: rhyolite.  Last to crystallize. Felsic lavas tend to errupt explosively and form thick ash deposits (greater viscosity.) Felsic melts first.
Term
Intermediate (Magma)
Definition
Neither light nor dark colored. Coarse intermediate rock: diorite. Fine intermediate rock: andesite.
Term
Mafic (Magma)
Definition
Silica poor. Mafic rocks are rich in olivine and pyroxene and are dark in color.  Coarse mafic rock: gabbro. Fine mafic rock: basalt. First to crystallize. Melts last. Mafic lavas have low viscosity and spreads easily.
Term
Factors in Differences of Magma
Definition

1. source rock composition

2. partial melting

3. assimilation

4.magma mixing

5.fractional crystallization 

Term
Dike
Definition
Tabular intrusions of rock that cuts across the layering of the country rock
Term
Silt
Definition
nearly horizontal, tabletop-shaped tabular intrusions
Term
Laccolith
Definition
intrusions inject between layers, dome upwards
Term
Plutons
Definition
irregular or blob-shaped intrusions that range in size
Term
Batholiths
Definition
numerous plutons that do not extend all the way down to the base of the crust
Term
Factors that Control Cooling Time
Definition

1. depth of intrusion

2. shape and size of magma body

3. presence of circulating ground water 

Term
Three Types of Magma Texture
Definition

1. glassy texture- more common in felsic rocks because silica inhibits crystal growth

2. interlocking texture

3. fragmental texture

Term
Basalt Characteristics
Definition
occurs in oceans and continents, very high temps, typically very fluid lava, not prone to explosive erruptions, can spread out to cover wide lateral extent, low silica
Term
Rhyolite Characteristics
Definition
only in large volumes on continents, realtively low temp, explosive erruptions, high in silica therefore the gas gets stuck, most silic
Term
Andesite Characteristics
Definition
typical of stratovolcanoes located at convergent margins, typically intermediate, locally occurs with basalt/rhyolite, eruption style varies
Term
Basaltic Volcanoes
Definition
can be either Aa lava flow, which is runny, or pahoehoe lava, which is high in volatiles and can move very fast, basalt is the common lava type on Earth, occurs in a variety of settings, tends to be relatively nonviolent, typically nonexplosive but widespread lava flows. Basalt lava makes shield volcanoes.
Term
Vesicles
Definition
evidence of magmatic gases, semi-spherical voids in rock, results when there's a significant amount of gas in the lava and low pressure, usually at the top of the flow
Term
Columnar Jointing
Definition
evidence of subaerial cooling, always indicate crystallization, exposed to air
Term
Pyroclastic Deposits
Definition
release of volatile constituents, often occurs in magmas near the surface. This may result in explosive erruptions which are more characteristic of rhyolite and andesite types than basalt.
Term
Volcanic Ash
Definition
fien grained tephra, volcanic glass
Term
Volcanic Bomb
Definition
large spindle shaped pyroclasts
Term
Nuee Ardent/Ignimbrite
Definition
very fast moving flow of ash and hot gas that is moving at 60mph, it's made of new eruptive material, unpredicatble
Term
Plateau Flood Basalts
Definition
characteristics include enormous volumes, high erruptive rates, wide lateral extent, errupted by extensional forces. No volcanoes formed, lavas often low in viscosity (runny), spread laterally, usually attain great thickness through accumulation
Term
Mid-Ocean Ridges
Definition
characteristics include large volumes, high erruptive rates, very high heat flow, wide lateral extent
Term
Black Smokers
Definition
mineral deposits formed at mid-ocean ridges by precipitation from superheated water, rich in important minerals
Term

Composite/

Stratovolcanoes

Definition
andesite typically constitute the major component of the erruptive products, usually occuring with basalt and/or rhyolite. Such basalts typically forms flows that help give rise to the characteristic shape of the cone, ash is weak part of volcanoes makes soil loose, extremely common to have multiple volcanic episodes, one goes dormant and new one forms
Term
Cinder Cones
Definition
accumlation of loose ash and cinders, smaller than stratovolcanoes, lava comes out of bottom, nonviolent, typically occur in clusters
Term
Shield Volcanoes
Definition
broad, gentle domes formed from either low-viscosity basaltic lava or large pyroclastic sheets, only one with an effusive erruption: lava flows, low viscosity, basaltic lava
Term
Calderas
Definition
large, typically circular volcanic depressions, several miles wide but can be much larger, usually formed by a collapse of a previous volcano, gas escapes
Term
Tephra
Definition
unconsolidated deposits of pyroclastic grains
Term
Tuff
Definition
formed from debris
Term
Weathering
Definition
general process by which rocks are broken down at the Earth's surface. It involves little or no movement of material. The products of weathering are loose gravel, sand, clay, soils, and components dissolved in aqueous solutions.
Term
Chemical Weathering
Definition
occurs as a result of interactions with atmosphere and hydrosphere and involves chemical processes, usually leads to changes in the mineralogic and geochemical composition of parent material. Final products are different than originals.
Term
Physical Weathering
Definition
fragmentation by physical processes that do not change chemical composition, reduce size to individual particles, grain-size reduction greatly increases the total surface are available for chemical reactions and thus might enhance the chemical process.
Term
Factors Controlling Weathering
Definition

property of parent rock, climate-temp and abundance of water change the chemical process:

warm and wet- chemical

warm and dry- not much weathering

cool and wet- physical 

cool and dry- not much weathering 

 

 

Term
Sediment
Definition
loose fragments of rocks and minerals broken off bed rock, mineral crystals that precipitate directly out of water, and shells.
Term
Sedimentary Rock
Definition
forms at or near the surface of the earth by the precipitation of minerals from water solutions, by the growth of skeletal materials from water solutions, by the cementing together of shell fragments or loose grains derived from preexisting rock. occur only in the upper part of the crust.
Term
Horizons
Definition
soil developed into distinct zones
Term
Clastic
Definition
composed of clasts/pieces of weathered preexisting rocks. constitute over 85% of all sedimentary rock
Term
Bioclastic
Definition
composed of broken shell and skeletal fragments derived from organisms. many limestones
Term
Classification of Sedimentary Rocks
Definition

Particle Name

Size

Rock Name

Gravel

> 2mm

Conglomerate or breccia

Sand

See pieces and feel them

Sandstone

Silt

Can’t see, can feel pieces

Siltstone

Clay

Can’t see or feel pieces

Shale/mudstone

Term
Calcium and Carbonate=
Definition
calcite, reacts with HcL
Term
Breccia
Definition
rock broken down into angular fragments
Term
Conglomerate
Definition
rock broken down into rounded clasts
Term
Arkose
Definition
buried and lithified quartz and feldspar
Term
Limestone
Definition
any rock composed of calcitte
Term
Bioturbation
Definition
organisims  that destruct the layering of sedimentary rocks
Term
Stratographic Formation
Definition
a sequence of strata distinctive enough to be traced across a fairly large region
Term
Crossbeds
Definition
internal laminations of ripples or dunes that are inclined at an angle to the boundrary of the main sedimentary layer
Term
Principle of Uniformitarianism
Definition
present is the key to the past. (what happened a billion years ago still happens today)
Term
Correlation
Definition
the process of defining the age relations between the strata at one locality and the strata at another
Term
Original Horizontality
Definition
all sedimentary rocks are formed as sheets that are originally horizontal
Term
Superposition
Definition
sedimentary rocks are formed by material that accumulates primarily under the influence of gravity: oldest layers on the bottom
Term
Original Continuity
Definition
rocks exposed on either side of canyon match in both appearance and sequence reflect that strata was originally deposited as a continous sheet
Term
Cross-Cutting Relations
Definition
any igneous rock that intrudes another rock must be younger
Term
Fossils
Definition
any remains of ancient life; usually preserved in rocks
Term
Intrusion
Definition
igneous magma
Term
Fossil Correlation
Definition
broad areas, relative age of sedimentary rocks based on fossils
Term
Cambrian Explosion
Definition
sudden diversification in life with many new species appearing over short interval
Term
Radiometric Dating
Definition
radioactive elements decay at a constant rate that can be measured in the lab and specified in years, used to date rocks
Term
Homogeneous
Definition
the same through and throughout, cannot be broken down into smaller components
Term
Crystal
Definition
a single, continous piece of a crystalline said bounded by flat suraces called crystal faces
Term
Euhedral Crystal
Definition
mineral with uninhibited growth
Term
Anhedral Growth
Definition
minerals without well-formed crystal faces
Term
Mineral Classes
Definition
silicates, oxides, sulfides, sulfates, hallides, carbonates, native metals
Term
Igneous Rocks
Definition
molten, interlocking crystals, tough rocks, might look glassy/frothy, no layering, no fossils
Term
Sedimentary Rocks
Definition
layers and fossils, particles, weather preexistng rocks, erosionm mass wasting, biology, fluids evaporate and precipitate minerals, salt, gypsum, dolomite, calcite
Term
Metamorphic Rocks
Definition
"protolith", agents of change: heat, pressure, chemically reactive fluids. foliating or not foliating, often hard, mica, flakey, garnite, calcite in marble and limestone
Term
Foliation
Definition

alignment, aligned crystals or grains, grains generally fused

 

 

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