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Schistosity
Geological foliation (metamorphic arrangement in layers) with medium to large grained flakes in a preferred sheetlike orientation
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Gneissic banding
Banding exhibited by certain igneous rocks of heterogeneous composition
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Porphyroblasts
a larger recrystallized grain occurring in a finer groundmass in a metamorphic rock.
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Parent rock
the original rock from which something else was formed
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Continental drift
the gradual movement of the continents across the earth's surface through geological time.
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Sea-floor spreading
the formation of new areas of oceanic crust, which occurs through the upwelling of magma at midocean ridges and its subsequent outward movement on either side.
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Convergent plate boundaries
an actively deforming region where two (or more) tectonic plates or fragments of the lithosphere move toward one another and collide.
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Divergent plate boundaries
a linear feature that exists between two tectonic plates that are moving away from each other.
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Transform plate boundaries
a type of fault whose relative motion is predominantly horizontal
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Fault
a crack in the Earth's crust
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Normal fault
where two blocks of rock are pulled apart, as by tension
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Reverse fault
a geological fault in which the hanging wall appears to have been pushed up along the footwall
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Strike-slip/transform fault
a fault in which rock strata are displaced mainly in a horizontal direction, parallel to the line of the fault.
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Footwall
the block of rock that lies on the underside of an inclined fault or of a mineral deposit.
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Hanging wall
the block of rock that lies above an inclined fault or an ore body.
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Lithosphere
the rigid outer part of the earth, consisting of the crust and upper mantle.
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Asthenosphere
the upper layer of the earth's mantle, below the lithosphere, in which there is relatively low resistance to plastic flow and convection is thought to occur.
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Decompression melting
the upward movement of the earth's mantle to an area of lower pressure
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Geologic record
the history of Earth as recorded in the rocks that make up its crust
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Relative age dating
the science of determining the relative order of past events, without necessarily determining their absolute age
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Absolute age dating
the process of determining an age on a specified time scale in archaeology and geology
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Disconformity
a break in a sedimentary sequence that does not involve a difference of inclination between the strata on each side of the break.
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Angular unconformity
an unconformity where horizontally parallel strata of sedimentary rock are deposited on tilted and eroded layers, producing an angular discordance with the overlying horizontal layers
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Nonconformity
the sedimentary rock lies above and was deposited on the pre-existing and eroded metamorphic or igneous rock.
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