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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
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