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66 Cards in this Set
- Front
- Back
Porphyritic |
Large phenocrysts in a fine ground mass. |
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Flow Banding |
Light and dark bands contorted by plastic flow. Typical of viscous lavas, usually find grained |
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Vesicular |
Gas bubbles developed under low pressure. |
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Amygdaloidal |
Vesicles which have become I filled by minerals at a later date. Usually distinguished from phenocrysts by rounded and irregular outlines. |
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What crystal size does slow cooling result in? |
Big crystals as they have plenty of time to grow. Grow further away from their origin. |
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Crystal size that occurs from fast cooling? |
Small crystals, little time to grow and form close to origin. |
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Leucocratic (silcic) |
Acidic igneous rocks are light coloured. |
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Mesocratic |
Medium coloured intermediate rocks. |
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Diorite |
1 stage of slow cooling in a pluton. Intermediate colour, feldspars, horneblende, mica and some quartz. |
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Obsidian |
Very fast cooling, no crystals, glassy texture, formed on the surface in lava flow. |
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Vesicular Basalt |
Fast cooling, on surface in lava flow, mica, Augite, Olivine. Mafic, fine, vesicular. |
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Equicrystalline Basalt |
Fast cooling, on surface in lava flow, mafic and fine. Augite, Olivine, minor flecksdol of P. feld and mica. |
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Dolerite |
Medium cooling, 1 stage underground in a sill or dyke. Mafic, equicrystalline. P felds, Augite, Olivine. |
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Basalt (Amygdaloidal) |
Fast cooling, on surface underwater. Feldspar, Augite, Olivine, infilled with calcite. |
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Pumice |
Very fast cooling under pressure on land. Vesicular, silicic/intermediate. |
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Andesite |
Slow cooling- 2 stages on surface in lava flow. Hornblende and P feldspar. Fine grain mass. |
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Mid Ocean Hotspots e.g Hawaii and Constructive plate margins |
Basalt (Gabbro) magma produced by partial melting of mantle peridotite. |
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Destructive plate margin (subduction zones) |
Andesite (Diorite) magma produced by partial melting of subducted ocean crust. |
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Destructive plate margin (continental collision zone) |
Granite magma is produced from partial melting of dry granite continental crust. |
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Which magma is explosive? |
Andesitic- magma is full of steam due to subduction zone and basaltic wet ocean plate. |
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Ultra basic (peridotite) |
Green due to olivine. |
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Euhedral |
Well formed crystals. |
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Subhedral |
Poorly developed with few crystal faces. |
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Anhedral |
Irregular outlines. |
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How many stages of cooling for grain sizes to be roughly the same size? |
One. |
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How many stages of cooling for the grain sizes to be differing? |
Two. |
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Granite |
Slow: Two stages of cooling, formed in a pluton. Contains quartz, mica, feldspar. Porphyritic. |
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Gabbro |
Slow- one stage of cooling. Formed deep underground in a pluton. Feldspars, mica, augite, olivine. Usually equicrystalline and Melanocratic (mafic) |
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Mesocratic |
Medium coloured intermediate rocks. |
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Melanocratic (mafic) |
Basic rocks are dark coloured. |
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Obsidian |
Very fast cooling, no crystals, glassy texture, formed on the surface in lava flow. |
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Vesicular Basalt |
Fast cooling, on surface in lava flow, mica, Augite, Olivine. Mafic, fine, vesicular. |
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Equicrystalline Basalt |
Fast cooling, on surface in lava flow, mafic and fine. Augite, Olivine, minor flecksdol of P. feld and mica. |
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Dolerite |
Medium cooling, 1 stage underground in a sill or dyke. Mafic, equicrystalline. P felds, Augite, Olivine. |
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Andesite |
Slow cooling- 2 stages on surface in lava flow. Hornblende and P feldspar. Fine grain mass. |
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Mid Ocean Hotspots e.g Hawaii and Constructive plate margins |
Basalt (Gabbro) magma produced by partial melting of mantle peridotite. |
|
Destructive plate margin (subduction zones) |
Andesite (Diorite) magma produced by partial melting of subducted ocean crust. |
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Eu |
Basic rocks are dark coloured. |
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Destructive plate margin (continental collision zone) |
Granite magma is produced from partial melting of dry granite continental crust. |
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Which magma is explosive? |
Andesitic- magma is full of steam due to subduction zone and basaltic wet ocean plate. |
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Which magma is less dangerous? |
Basaltic- uplift of the ocean ridge causes lowering pressure. |
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Pillow Lava |
Under glaciers, in oceans.. The rind ruptures, the skin stretches and the next pillow forms. Shattered glassy breccia. |
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Pumice. |
Very fast cooling under pressure on land. Vesicular, silicic/intermediate. |
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Baked and Cooled Margins. |
Baked margins- at rim of heat altered rock. Contact metamorphism. Included fragments of mudstone and sandstone. Chilled margins- Magma at contact that cooled rapidly. Grain size always increases in the centre. |
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Lava flows in stratified rocks |
Eroded fragments of lava in new rock. Reddened erosional surface. Might get vesicles from gas in lava flow. |
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Phenocrysts within a pluton |
Stage 1: Phenocrysts form. Slow cooling pluton deep underground. Stage 2: Bouyant pluton rises. |
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Dykes |
Discordant- cuts through country rock. Thin dykes: fine grained basalt Thick dykes: medium grained dolerite. |
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Sills |
Concordant- follows boundaries of country rock. Generally thicker than dykes as they cool slower. |
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Ultra basic (peridotite) |
Green due to olivine. |
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Volcanic |
Hhh |
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Euhedral |
Well formed crystals. |
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Subhedral |
Poorly developed with few crystal faces. |
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Anhedral |
Irregular outlines. |
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Gran |
One. |
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Gabbr |
Two. |
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Granite |
Slow: Two stages of cooling, formed in a pluton. Contains quartz, mica, feldspar. Porphyritic. |
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Andesitic volcanoes |
-high viscosity (thick and sticky) -pressure builds- slow lava -big eruptions (explosive)- higher gas content makes it more bouyant. |
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Shield volcano |
Lower viscosity (free flowing) decrease in gas content, higher temperature. |
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Basaltic magmas (e.g Hawaiian Islands) |
- partial melting of mantle peridotite -low viscosity magma(free flowing) -low gas content (non explosive) -less likely to block the vent leading to pressure build up -easier to predict and more regular. -most scary due to free flowing magma. |
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Andesitic magmas e.g Mt Etna |
- harder to predict -high gas content -higher viscosity than basalt -violent explosions and steep sided volcanoes -pyroclastic flows, lahars and explosions limited to steep sides of volcano |
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Granitic magma e.g Yellowstone |
-high gas content -high viscosity -may explode violently -formed by partial melting of continental crust in mountain roots -not scary |
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Monitoring technique: Seismometers |
Magma moves and causes seismic disturbances. Rising magma fractures the surrounding cold, brittle rock and forces its way upward causing pressure build up and release, generating small earthquakes. More seismic data=volcano eruption imminent. |
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Ground Deformation |
As magma rises, the volcano inflates. Tiltmeters are used to measure changes in the angle of slope which increases as the rising magma causes uplift. Allows us to see how close it is to surface as greater tilt=more pressure. |
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Managing the risks: concrete spillways in Japan |
Used to channel lahars and steer them from vulnerable areas. Concrete and steel pillars in the channels filter out the large debris, reducing potentials of mudflows. Cameras and electronic sensors give early warning of movement in the channels. |
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Hazard Mapping |
Studying lavas and pyroclastic deposits of historical eruptions to predict the future activity of a volcano to identify areas most at risk of lava flows, pyroclastic flows and lahars. |
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Done |
Yay |