Geol 101L

Front 1

plane of the ecliptic

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earth's axis tilted at about 23.5 degrees to the plane in which it orbits the sun

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principle of uniformitarianism

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most ancient geologic features are formed by the same processes as modern ones

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pressure

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the pull on earth's gravity

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hydrostatic pressure

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pressure due to the weight of water

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lithostatic pressure

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pressure due to the weight of overlying rock

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asthenosphere

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zone in the upper mantle that has low rigidity and flows like soft plastic

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triple junction

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when three plates come together

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element

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a substance that cannot be broken down chemically into other substances

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atom

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the smallest piece of an element that still has all the properties of that element

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compounds

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atoms that combine with one another chemically

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molecule

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smallest possible piece of a compound

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cryosphere

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sphere made up with frozen water

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geosphere

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sphere made up of the solid earth

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bedrock

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a solid aggregate of minerals and rocks attached to those below

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sediment

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unattached boulders, sand, and clay

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soil

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sediment and rock modified by interactions with the atmosphere, hydrosphere, and organisms so that it can support plant life

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flux

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movement of materials from one reservoir to another

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heat energy

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measure of the degree to which atoms or molecules move about in matter

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density

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mass / volume (mass over volume)

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geobaric gradient

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rate at which lithostatic pressure increases

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lithosphere

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earth's crust to 100-150km of the mantle and is relatively rigid and is the outermost layer

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active continental margin

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where earthquakes and volcanic eruptions are common (US west coast)

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passive continental margin

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where earthquakes and volcanic eruptions are not common (US east coast)

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mineral

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naturally occurring, homogeneous, inorganic solid with an ordered internal arrangement of atoms and a distinctive chemical composition

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grain

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an irregular piece of mineral

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rock

Back 26

naturally occurring, inorganic solid consisting of an aggregate of mineral grains, pieces of older rocks, or a mass of natural glass

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luster

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the way light interacts with a mineral's surface

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crystal habit

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preferred crystal shape that forms when it grows unimpeded by other grains

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fracture

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occurs when there are no zones of particularly weak bonding within a mineral

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cleavage

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occurs when bonds holding atoms together are weaker in some directions than in others

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specific gravity

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a comparison of its density with the density of water

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elastic

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return to their original, unbent shape

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flexible

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retain their new shape

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rock composition

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the identity of minerals or glass that make up a rock

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rock texture

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the dimensions and shape of grains and the way in which grains are arranged, oriented, and held together

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igneous rocks

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form through the cooling and solidification of molten rock, which is created by the melting of preexisting rock in the mantle or lower crust

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sedimentary rocks

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form at or near the surface of the earth in two ways: when grains of preexisting rocks accumulate or when minerals precipitate out of water

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metamorphic rocks

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form when preexisting rocks are subjected to physical and chemical conditions within the earth that are significantly different from those under which they first formed

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course sized

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grains big enough to be identified easily

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medium sized

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grains can be seen as separate grains but can't be easily identified

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fine sized

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grains can barely be recognized

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very fine sized

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grains are so small they cannot even be seen with a magnifying glass

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equant

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grains have the same dimension in all directions

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inequant

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grain dimension in different directions is different

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crystalline texture

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crystallizing minerals interfere with one another and interlock

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foliation

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if the grains are aligned parallel to one another

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plutons

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massive intrusive blobs

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dikes

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intrusions that form thin sheets cutting across layering in the wall rock

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sills

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intrusions that form thin sheets parallel to the layers of wall rock

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viscosity

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ability to flow

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phaneritic texture

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texture of igneous rocks with coarse grains

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aphanitic texture

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texture of igneous rocks with fine grains

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porphyritic texture

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texture of igneous rocks with two different grain sizes

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pyroclastic debris

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enormous amounts of material blasted into the air by volcanic eruptions

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ash fall

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fine grain volcanic debris that falls quietly and blankets the ground

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pyroclastic flows

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avalanches of ash that rush down the side of a volcano while so hot that the fragments weld together immediately to form rock

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felsic igneous rocks

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have the most silica and the least iron and magnesium, contain a lot of potassic feldspar and plagioclase, light colored, low specific gravity

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intermediate igneous rocks

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between felsic and mafic rocks

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mafic igneous rocks

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have less silica and sodium but more calcium, iron, and magnesium, dark green or black, high specific gravities

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ultramafic igneous rocks

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least silica and most iron and magnesium, very dark colored and have the highest specific gravities

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decompression melting

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once pressure decreases, the heat already present in the rock is sufficient to overcome the bonds and cause melting

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flux melting

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water and volatiles are released when the subducted plate reaches critical depth and rise into the asthenosphere where they help melt the asthenosphere in

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heat transfer melting

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some very hot magmas that rise into continental crust from the mantle bring enough heat to start melting the crust

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partial melting

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magmas form by melting some of the preexisting rock

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magmatic differentiation

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early formed minerals may separate from a magma, usually by sinking, because they are denser than the liquid

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assimilation

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as a magma rises, it may add ions by melting some of the surrounding rocks

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magma mixing

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intermediate rocks crystallize from this magma which is when felsic and mafic magmas mix

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mineralogically immature

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sediments that still contain nonresistant minerals and rock fragments

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mineralogically mature

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sediments in which all minerals have weathered to produce stable minerals

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lithification

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accumulations of clasts that are buried and the weight of overlying sediment squeezes out air and water, fitting the clasts more tightly together

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cementation

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when ion rich groundwater passes through the compacted sediment, minerals precipitate and bind the clasts together

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diagenesis

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any chemical or physical change that happens in a sedimentary environment subsequent to the original deposition of the sediment

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biogenic sedimentary rock

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rock composed primarily of the remains of living organisms

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sorting

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the measure of the uniformity of grain size in clastic sedimentary rocks

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beds

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layers of sediment

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graded beds

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layers in which the clast size decreases progressively from the bottom to the top

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asymmetric ripply marks

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have systematically oriented steep and gentile sides and are produced by a current that flowed from the gentle side toward the steep side

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symmetric ripple marks

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have steep slopes on both sides and form from oscillating currents

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cross beds

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subtle curving surfaces that lie at an angle to the main bedding surfaces and form when sediment moves up the up-current side and then slips down the lee side as dunes and ripples build

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protolith

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metamorphic rock parent rock

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diffusion

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when freed atoms migrate slowly through the solid rock

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differential stress

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the type of pressure in such rock due to squeezing and/or shear as directed pressure; can flatten or elongate them rock on one direction

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metasomatism

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when the chemical composition of a metamorphic rock changes significantly due to the reaction with hydrothermal fluids

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contact metamorphism

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occurs where rocks are subjected to elevated heat without a change in pressure and without the application of differential stress; happens where an igneous rock comes in contact with a rock

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regional metamorphism

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occurs where rocks in a large region of crust are subjected to increases in temperature and pressure and are subjected to differential stress; happens during mountain building processes

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burial metamorphism

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happens when rocks are buried very deeply by overlying sediment

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dynamic metamorphism

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occurs where rock undergoes differential stress in response to shear along a fault zone but does not undergo a change in temperature or lithostatic pressure

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preferred orientation

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the alignment of parallism of grains

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granoblastic texture

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metamorphic rocks with random grain orientations

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mylonite

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a very fine grained rock with a strong foliation and lineation

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porphyroclasts

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leftover grains of feldspar

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metamorphic grade

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the approximate degree to which a rock has changed during dynamothermal or thermal metamorphism

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porphyroblasts

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large grains grown during metamorphism

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gneissic texture

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compositional banding, defined by the alternation of light colored and dark colored layers