Geology Test 2- Mayne – Flashcards
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Each bed of sedimentary rock is older than the one above it and younger than the one below it.
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Law of Superposition
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Layers of sediment are generally deposited in a horizontal position. Deviation from this implies the rocks are not in their original state.
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Original Horizontality
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The first person to recognize a sequence of historical events in an outcrop of sedimentary rock layers.
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Nicolas Steno
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Faults always occur LAST where a fault or igneous intrusion cuts through other rock we can assume that the fault or intrusion is younger than that rock.
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Cross Cuttings
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A batholith that crosscuts a fault is younger than the fault.
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Batholith in Cross Cutting
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When rocks have been deposited without interruption.
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Conformable
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A period of deposition interrupted. Where erosion has removed the sediments that were deposited. Types: angular, disconformity.
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Unconformity
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Easiest unconformity to spot. The rock beds deposited above are at different angles than the ones they're deposited over.
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Angular Unconformity
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An erosional contact, where a chunk of the rock is missing because erosion has taken it away. A chunk of time is missing.
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Disconformity
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Separates older, metamorphic rocks or igneous rocks from sedimentary ones.
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Non Conformity
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Traces or remains of prehistoric life now preserved by a rock. Usually found in sedimentary rocks, are rare in metamorphic rocks, and never found in igneous rock.
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Fossils
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They aid in the interpretation of past life. They serve as time indicators. They allow for correlation of rocks from different places.
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Why are fossils important?
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Entire animals, flesh included (rare) Petrified remains molds casts carbonisation
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Types of direct evidence
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Tracks (footprints) Burrows Coprolites (fossilized poop) Gastroliths (stomach stones)
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Types of indirect evidence
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1st thing that has to happen is the rapid burial of a fossil because oxygen will decay a fossil.
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Fossil preservation
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Fossil organisms succeed one another in a definite and determinable order.
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principle of fossil succession
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examines the forces that deform rocks and the rock structures that result. We can use geological structures to help us reconstruct the geological history of an area.
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Structural Geology
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Every rock has a point at which it will fracture or flow. Refers to all changes in shape, position, or orientation of a rock mass.
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Deformation
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applied force over a rock's area that deforms a rock.
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Stress
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The magnitude of stress is a function of ----- and the area on which the force is applied.
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Applied force
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Compressional stress (forces pushing in) Tensional stress (forces pulling out on each side) Sheer stress (forces pushing side by side)
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stress types
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the result f the stress applied to the rock. distortion or change in shape that occurs. can tell you about the type of stress that occurred and the original shape of the rock.
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strain
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Elastic Deformation Ductile Deformation
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Deformation types
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Recoverable deformation, the rock will return to it's original size and shape when stress is removed. Ex. like a rubber band
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Elastic Deformation
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Solid state flow, object changes shape without fracturing. Some bonds break, others form allowing minerals to change shape.
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Ductile Deformation
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Temperature Confining pressure rock type
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Factors affecting rock strength
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When heated, an increase in --------- causes objects that would otherwise break, to flow (cold cookie, versus a warm cookie)
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Temperature
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Forces equally applied in all directions. Pressure increases with depth.
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Confining pressures
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Mineral composition and texture greatly influence deformation.
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Rock type
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Ductile Deformation (fold and flow)
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Type of deformation weak structures are subject to face
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Time affects of deformation
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Rocks respond to small stresses applied over geologic time periods, millions of years.
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longer, slower deformation
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Ductile deformation
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sudden deformation of a rock can result in fracture.
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Brittle Deformation
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A type of deformation, a result of compressional forces that cause a shortening and thickening of crust. A strain resulting from compressional stress.
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Folds
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The max angle that arises from the subsequent fold.
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Hinge line
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the angle the hinge is inclined at.
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Plunge
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The imaginary surface that divides the fold in half, as symmetrically as possible.
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Axial plane
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Up-folding or arching (ants build hills), younger rocks on the outside, older rocks in the middle.
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Anticline fold
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Down-folding, trough fold. Older rocks on the bottom, younger rocks on top.
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Syncline fold
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Upward structure of ductile deformation
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Dome
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Downward structure of ductile deformation. A large accumulation of sediments, that weight causes the crust to subside.
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Basin
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Rocks located in the upper crust tend to exhibit brittle behavior by fracturing or faulting.
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Brittle Structures
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Fractured surface which shear stress causes the rocks on one side to move relative to the rocks on its other side.
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Faults
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Fractured surfaces formed by stretching.
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Joints
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Faults in which movement is primarily parallel to the dip of the fault surface.
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Dip-slip faults
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The rock surface above the fault.
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Hanging wall
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The rock surface below the wall.
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Foot wall
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Accommodate the lengthening and extension of crusts.
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Normal faults
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Hanging wall moves upward relative to footwall. Occurs in strong compressional environments.
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Reverse faults
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Faults with a dip less than 45 degrees.
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Thrust faults
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Fault where both horizontal and parallel forces strike the fault surface.
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Strike-slip faults
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Lowering weighted lines off boats was how depth was originally measured. Now sonar is used, time taken to receive the reflected signal.
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How was the depth of the ocean floor measured- then and now?
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Vibration charts used to tell us about the sea floor and what's beneath it.
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Seismic
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Continental margins Deep-ocean basins Oceanic ridges
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The provinces of the ocean floor
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margins not associated with plate boundaries
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Passive continental margins
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margins associated with subduction zones.
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Active continental margins
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continental shelf continental slope continental rise
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Types of passive continental margins
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a submerged horizontal surface of the continent extending from a shoreline to a deep-ocean basin. a flooded extension of the continent.
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Continental shelf
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furthermost edge in the sea between continental and oceanic crust.
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Continental slope
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occurs from the thick accumulation of sediment that has moved down the continental slope onto the deep ocean floor.
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Continental rise
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Form at the site of convergence between subducting continental plate and oceanic crust. The deepest part of the ocean.
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Deep ocean trenches
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Submarine volcanoes that (rarely) become oceanic islands.
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Seamounts
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Form when an island sinks below the surface and waves erode and flatten the top of it after volcanic activity has stopped.
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Guyots
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Formed from vast outpourings of lava on the sea floor, form relatively quickly and produce a lot of sulfur and carbon dioxide.
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Oceanic plateaus
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Form at a divergent plate boundary in the ocean, site of extensive faulting with a high heat flow and produce 60% of the total magma on earth per year.
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Oceanic ridges
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Occurs along rift zones as plates move apart, magma wells up into newly created fractures and generates new seafloor.
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Seafloor spreading
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poorly developed magma chamber and a well-developed rift valley (deep).
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Slow spreading ridge characteristics
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well-developed magma chamber and an elevated surface replaces rift valley (no rift valley).
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fast spreading ridge characteristics
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Unconsolidated sediment Pillow lavas Sheet dikes Gabbro
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Layers of oceanic crust
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Made up of dead organisms and sediments coming off of a continent.
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Unconsolidated sediment
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Lava extruded onto the sea floor.
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Pillow lavas
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Pathways lava took to the surface.
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Sheet dikes
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Plutonic version of basalt.
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Gabbro
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Slab pull and suction.
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What causes rifting?
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Mountain building
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Ogenisis
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Convergent
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What type of plate boundaries form mountains?
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Volcanic arc, deep ocean trench, fore arc, back arc
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What are the 4 regions of convergent plate boundaries?
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The area between trench and volcanic island arc
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Fore arc
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Arc behind the island arc
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Back arc
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Can be in the ocean or on a continent. Occurs from the partial melting of slab. High volatile content.
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Island arc
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Oceanic lithosphere bends as it subducts. Trench depth is related to the AGE of the subducting slab.
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How do trenches form
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Cold slab
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What type of slab is easier to subduct, hot or cold?
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Older & colder crust that is less buoyant.
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What type of crust forms deep trenches?
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Younger & warmer crust means it's more buoyant.
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What type of crust form shallow trenches?
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The age of the crust.
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What determines the angle of subduction?
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a cold, dense slab sinks vertically as it descends.
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What causes "trench rollback"?
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An upper plate pulls towards a retreating plate causing extension of the slab, upwelling, and decompression melting.
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What occurs during slab suction?
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a change in tectonic regime, and emplacement of massive plutons within the crust.
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What produces an active continental margin?
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subduction stops entirely and mass is completely built upward.
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what occurs during continent/continent collides?
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fragment of oceanic crest that has scraped off and been deposited on a continent.
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ophiolite
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gradual up and down motions of continental crust that occur at many locations.
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vertical movements of continental crust
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less dense crust "floats" on top of the denser and deformable rocks of the mantle.
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isostasy
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The sudden and rapid movement of a large volume of rock.
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What causes earthquakes
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The origin of the earthquake from within the ground.
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Focus or hypocenter
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The guy who saw horizontal surface displacement along the San Andres fault after the earthquake.
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H.F. Reid
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stresses acting over many years to deform rocks on either side of a fault.
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Tectonic Stresses
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___________occurs when frictional resistance holding rocks in place exceeds its limit causing an earthquake.
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Slippage
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______________ are generated by rock elastically returning to its original shape.
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Vibrations
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Small tremors that often follow strong earth quakes.
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After shocks
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most studied fault system in the world.
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San Andres Fault
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The motion caused by the release of elastic energy stored within a fault for many years before rupturing.
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Slip-stick motion
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Where the initial rupture occurs.
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Focus
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When strain is finally less than frictional resistance.
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When does an earthquake finally stop?
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What people developed the first primitive seismographs?
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The Chinese
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waves that only travel along the outer parts of the earth. have an up and down and side to side motion.
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Surface waves
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Both compressional (P) and shear (S) waves
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Two types of body waves
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waves that travel through all materials and temporarily change the volume of the material it travels through.
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Compressional (P) Waves
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Change the shape of the material it travels through.
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Shear (S) Waves
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Large waves that are very damaging to buildings.
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Love waves
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P waves..... S waves
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Seismographs pick up ____ waves first and _____ waves second
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The further away from the source of the earthquake you are difference of time between P and S waves ___________________.
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Increases
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Measurements of earthquake size
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Intensity and magnitude
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What is the scale we use today to measure earthquake intensity
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Richter Scale
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What type of energy is measured by the Richter Scale?
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Strain energy
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What effects the level of destruction an earthquake produces?
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distance from populated area
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How to judge the damage to man-made structures after an earthquake?
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Intensity Duration of vibration Nature of the material the structure rests on Nature of the building material of the structure.
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this type of sediment can amplify vibrations and surface waves more than other types of sediments.
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Soft sediments
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When unconsolidated sediments become saturated with water and the vibrations turn stable soil into mobile fluid it's called _________________
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Liquefaction
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Name for the rhythmic sloshing of water producing large waves that can destroy dams.
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Seiches
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cracks in the bed rocks are activated as faults and a _____________________ occurs causing a whole area of land to slide towards the coast.
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Land slides
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Occur as more frequent waves are produced as water depth decreases.
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Tsunami
