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Crustal Deformation

Graduate course at Columbia University

Question	Answer
Protomylonite	<50% dynamically recrystallized rock
Ultramylonite	>90% dynamically recrystallized rock
Mylonite	fine grained, banded, cohesive rock
Porphyroblasts	Grains that have grown in the rock during ductile deformation & metamorphism (e.g. garnet and pyrite)
Porphyroclasts	relict earlier grains that have survived ductile deformation (e.g. feldspar). These decrease in size with metamorphosis.
Augen type(s) that can't give you sense of motion	θ-type and Φ-type (symmetric)
Ductile sense of motion indicators	strain shadow/sigmoid, Augen: δ-object, σ-object, mineral fish, fractured grains, c-type shear bands, stair stepping
Mylonite protolith	any geologic material can be mylonitized, but granite is most common (deepest buried)
Mylonite formation mechanisms	Formed by local plastic flow and dynamic recrystallization (50-90% dynamic recrystallization)
Microcracks	mode-1 fractures, often FIPs (fluid inclusion planes)
FIP (Fluid Inclusion Plane) - What are they and what are they useful for?	Often fluids flow through and then the cracks collapse, leaving behind bubbles that lead to an optical discontinuity. Useful for measuring stress orientation.
Deformation Lamellae	Movement on crystal planes. Often mistaken for microcracks but are much smaller due to crystal orientation.
Shock Lamellae	Very high strain rates from impacts cause movements on crystal planes and turn the grain to glass.
Undulose extinction	Different parts of a grain in thin section go dark at different angles of polarized light.
Cause of undulose extinction	Bent crystals (elastic, recoverable) and crystal lattice defects (permanent dislocations) manifest this way in quartz.
Pseudotachylites	A dense rock produced in the compression and shear associated with intense fault movements (earthquakes) involving extreme mylotinization and/or partial melting.
Grenville Orogeny date and location	0.9-1.1 Ga, east coast tectonic event
Taconic Orogeny date and location	460±20 Ma (Late Ordivician), east coast of N. America
Ammonoosuc Island Arc	Collided with East coast of N. America, causing the Taconic Orogeny, part of "Gander Terrane"
Acadian Orogeny date and location	380±20 Ma (Devonian), east coast of N. America
Alleghenian Orogeny date and location	300±20 Ma (Mississippian/Permian), east coast of N. America
Avalon Terrane	Island arc or microcontinent that collided with N. America causing the Acadian Orogeny
Alleghanian Orogeny	Collision between the east coast of N. America and Africa
Flysch	interbedded sandstone/shale associated with turbidites
Molasse	an extensive post-orogenic sedimentary formation, partly marine and partly continental or deltaic. Results from the wearing down of elevated mountain ranges, during and after the main phase of rapid uplift.
Manhattan Schist protolith	shale including volcanic ash (as indicated by amphibolite), and turbidites (flysch)
Inwood Marble protolith	passive margin carbonate shelf
Taconic Sequence Rocks	Cambrian and Ordovician rocks found in the Taconic allochthons. They are the same age and often have the same lithology as rocks in the passive margin to the west. However, most often have higher metamorphic grade and contain more volcanic material.
Slices	Sometimes a name for Taconic Allochthons. Lower grade metamorphic thrust sheets.
Olistostromes	Melange deposits formed by submarine landslides that didn't completely dissociate.
Red Indian Line	Newfoundland's equivalent of Cameron's Line, except there's an extra arc (Notre Dame Arc, peri-laurentian). The Red Indian Line separates the Notre Dame Arc from the Gander Arcs.
Newfoundland's equivalent of Cameron's Line	Red Indian Line
Hayesville Fault	Southern Appalachian equivalent of Red Indian Line and Cameron's Line (separates Perilaurentian vs Perigondwanan)
Deformation Bands	A type of cataclasis found only in high porosity rock (like aeolian SS). Some calcite may precipitate out?
Brevard Thrust	major Alleghenian thrust in the southern Appalachians
Kings Mountain Belt	Acadian suture zone (margin to accreted terrane). Melange, metavolcanic/sedimentary. ~360Ma
West Coast Rifting	850-750 Ma
West Coast Passive Margin	750-360 Ma
Antler Orogeny	360±20 Ma
Sonoman Orogeny	250±30 Ma
Nevadan Orogeny	150±10 Ma
Sevier Orogeny	130±50 Ma
Laramide Orogeny	80-40 Ma
.704 line	An igneous rock has 87Sr/86Sr > 0.706 came through Precambrian N. American crust
Windermere supergroup	turbidites associated with west coast rifting (850-750 Ma)
Roberts Mountain Allochthon	Rock thrust onto N. America during the Antler Orogeny
Golconda Allochthon	Rock thrust onto N. America during the Sonoman Orogeny
Franciscan Melange	rocks pulled down by subducting plate, metamorphosed at high-P/low-T, and brought back to the surface (2-way street?). Contains lots of serpentine and blueschist
Key evidence for Nevadan Orogeny	Klamath Mountains (Josephine Ophiolite) and the Foothill Complex (Smartville Ophiolite)
What happened in the Nevadan orogeny?	Back-arc basin develops and is pushed up onto the continent
Manifestation of the Sevier Orogeny	volcanic arc along entire W. margin of N. America
Feeder plutons in Sevier Orogeny	Seirra Nevada, Peninsular Range, Coast Range Batholiths & Idaho Batholith
Laramide orogeny	Foreland orogeny (relatively rare)
Mechanisms controlling accretionary wedge critical taper angle	The angle of subduction, shape of wedge, rock strength, friction, density and pore fluid pressure
Blueschist	High-P/low-T metamorphism. Melange matrix formation, formed far away from batholiths.
Greenschist	Low-P/higher-T metamorphism. Mountain building events, formed closer to batholiths.
Catskill Delta	Molasse shed from Acadian Orogeny
Bellvale formation	Devonian stream deposits, the same stuff the Catskills are made of (debris from Acadian Orogeny). This was observed on one of the field trips in a large dropped-down graben folded into a syncline
Grenville formation	gneiss/schist, E. coast basement
Poughquag formation	The basal conglomerate of Cambrian transgression. Observed on the fieldtrip in Pete's backyard. Unconformably overlies the Grenville (this is the Cambrian-Ordovician unconformity)
Typical Andersonian thick-skinned thrust fault dip	30°
Reverse fault dip	>45°
Thin-skinned thrust fault dip	~10°
Klippen	thrust fault erosional remnants (isolated by erosion), map symbol has teeth pointing IN.
Fenster or Window	An area of erosion in an overthrust sheet in which the rocks beneath the overthrust are exposed. Map symbol has teeth pointing OUT.
Cutoff angle	the angle when a fault originally moved, helps in reconstruction
Classic example of thick-skinned thrusting	Laramide uplifts of western N. America
flat-irons	morphology formed by tilted erosion-resistant bed.
Typical Andersonian normal fault dip	60°
Low angle normal fault dip	<20°-30°
The best way to determine the dip of a fault	earthquake data (with nearby seismometers and good velocity model)
tip line	point of propagation of a fault
relay ramp	between two normal faults that are parallel but offset from one another
Rolling Hinge Model	Normal faults are only active in the brittle field at high angles. Isostatic response rolls the fault over after extension
Roll and Chop Model	Normal faults start at high angles then rotate until they reach their lock-up angles and a new (high angle) fault forms. No movement is required at low angles.
Paradox of Low-Angle Normal Faults	despite over 100 years of recorded earthquakes, there is no clear record of an earthquake on a low-angle normal fault.

Created by: eferguson on 2012-05-08

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Crustal Deformation

Graduate course at Columbia University