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26 Cards in this Set
- Front
- Back
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How rocks respond to stress
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Stress – force exerted against an object
Factors affecting response Nature of rock Elastic deformation Fracture Plastic deformation Temperature Pressure Time |
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Geologic structure
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Folds – a bend
Anticline – arch upwards Syncline – arch downwards Dome – circular anticline Basin – circular syncline |
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Faults
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Faults – fracture with displacement
Slip – the distance of motion Fault zone – numerous, closely spaced fractures Hanging wall – miner’s reference, the side of a fault “overhead” in a mine Footwall – (as above) the fault side underfoot |
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Faults (CONT)
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Normal fault – pulling apart of landscape causes hanging wall to move downward
Graben – a down-dropped, wedge-shaped block Horst – the blocks between grabens Reverse fault – compression of landscape forces hanging wall up relative to footwall Thrust fault – low angle reverse fault Strike-slip fault – fracture close to vertical, motion horizontal (transform) |
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Folds, Faults & plate boundaries
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Convergent – compression
Divergent – extension (pulling) Transform – strike-slip |
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Orogeny –
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- the process of mountain building
Crustal thickening Subduction zones Sub-plate magmatic activity Continental collision Compressive forces “squeeze” crust together Thickening leads to isostatic adjustment Rising of less-dense continental crust Rising increases erosion, redistributes mass |
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Island arcs
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Island arcs – volcanic mountain chain
Ocean-ocean convergent zone Subduction complex – “squeegeed” sediments and fractured rock Underthrusting – subduction complex grows from bottom, forced up Forearc basin – down dip area between arc and complex |
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the andes
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190 mya (Jurassic) South America moves west
By 140 mya, Pacific plate had subducted to accommodate motion By 130 mya, descending plate creates lots of basaltic magma Rising magma Some rises to form volcanoes Some cools inside forming plutons Thickening leads to isostatic rise Once thick enough, soft rock beneath oozed outwards creating thrust faults Sediments eroding from risen landscape makes sedimentary rocks on both sides of mountains |
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the Himalayas
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80 mya, India lithosphere fragment splits from South Polar landmass
India “gallops” (20 cm/yr) north, creates subduction zone beneath Asia Creates “Andean” margin – granitic plutons, stratovolcanoes, etc. 40 mya – oceanic lithosphere between landmasses consumed. Continents collide. Velocity decreases to ~5 cm/yr Both continental crust, neither can sink. India thrusts beneath Asia, crustal thickness doubles |
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the himalayas today
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Today:
Contains all three rock types Many sedimentary rocks from old sea-floor Plateau is ~4000m, mountains rise from this Crustal mass caused faulting as it spread Extensional (normal) faults in mountains Compressional (reverse/thrust) faults in foothills India still moving north Alps, Urals, Appalachians all happened under similar circumstances |
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Mountains and Earth Systems
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Mountains rise due to tectonic forces
Once risen, they interact with hydrosphere, atmosphere, biosphere Air rises over mt – moisture rains out Rise of Himalayas coincides with global cooling period – connected? Mountains make unique habitat for plants, animals and more recently - humans |
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1. A cool rock near the Earth’s surface is more likely to __________ than a similar rock that is hot and under great pressure.
a. deform plastically b. undergo pressure-release melting c. undergo brittle fracture d. metamorphose |
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2. A/an __________ is any feature produced by rock deformation.
a. anticline b. geologic structure c. syncline d. limb |
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3. Rock that is caught at the junction of two converging plates is deformed by __________ stress.
a. divergent b. tensional c. compressive d. shear |
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4. A/an __________ is a fold that arches upward.
a. anticline b. syncline c. hanging wall d. horst |
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5. A circular syncline is called a __________.
a. dome b. basin c. mountain d. valley |
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6. In a __________ fault, the hanging wall has moved downward relative to the footwall.
a. normal b. reverse c. thrust d. joint |
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7. A reverse fault occurs as a result of __________.
a. extensional stress stretching the Earth’s crust b. crustal shortening c. pressure-release fracturing d. the plastic behavior of rock |
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8. A/an __________ is a wedge-shaped block of rock that has dropped downward between two normal faults.
a. horst b. graben c. slip d. joint |
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9. The term __________ refers to the process of mountain building.
a. orogeny b. origami c. orology d. originy |
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10. A sedimentary basin between a trench and an island arc is called a __________.
a. forearc basin b. backarc basin c. middle-arc basin d. double-trench |
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11. Sea floor sediment and oceanic crust pieces are scraped off a subducting plate and accumulate in the __________ complex.
a. forearc b. subduction c. island arc d. orogeny |
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12. Subduction of oceanic crust at a continental margin creates __________.
a. underthrusting b. a Himalayan margin c. an Andean margin d. an island arc |
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13. The Andes Mountains were formed by convergence of a plate carrying __________ crust with a plate carrying __________ crust.
a. oceanic, oceanic b. oceanic, continental c. continental, continental d. peridotitic, oceanic |
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14. The underthrusting of __________ beneath Tibet caused the rise of the Himalayas.
a. Japan b. Indonesia c. India d. Antarctica |
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15. The Himalayas were formed by convergence of the __________ plate and the __________ plate.
a. Antarctic, Indian b. Pacific, Eurasian c. Indian, Eurasian d. Antarctic, Pacific |
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