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97 Cards in this Set
- Front
- Back
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Rock definition:
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Back (Definition) |
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Rock types |
Igneous, sedimentary, metamorphici |
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Igneous rocks definition |
Formed by cooling and solidification of magma |
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Cohesive |
Materials hang together. Term used is lithified |
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Aggregate |
Means more than one crystal |
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Aggregate |
Means more than one crystal |
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First rocks of the rock cycle |
Igneous |
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Aggregate |
Means more than one crystal |
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First rocks of the rock cycle |
Igneous |
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Extrusive textures and their definitions |
1. Aphanitic: uniformly fine grained with interlocking equigranular crystals that are too small to see.
2. Porphyritic: matrix of ground mass aphanitic material with layers of crystals called phenocrysts that exhibit well formed crystal faces.
3. Glassy: extremely rapid cooling produces highly viscous, felsic lavas and no crystal formation.
4. Vesicular: (bubbly rock) dissolved gassed or volatiles bubble out as lava cools producing spherical cavities.
5. Pyroclastic/Fragmental: when lava is cooling gases explode causing previously formed rock make angular fragments in all sizes.
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Cooling of porphyritic material |
Formed by slow, intrusive cooling. Then the magma (containing the phenocrysts) is erupted and cools quickly to produce aphanitic matrix |
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Scoria |
Highly vesicular magic rock/basalt |
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Scoria |
Highly vesicular magic rock/basalt |
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Pumice |
Frothy felsic rock/rhyolite |
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Amygdules |
Minerals deposited in vesicular cavities |
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Intrusive textures |
1. Phaneritic: uniform crystals of equigranular and interlocking, but are course-grained, easily seen with eye.
Concentration on dissolved volatiles, great mobility of atoms and course crystals=pegmattitic rocks
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Volatiles in igneous rocks |
1. Vesicles: already noted 2. Fluid inclusions: trapped vapour of their condensates in bubbles 3. Bound volatiles: H2O in the form of OH in amphiboles, micas and clays of f in lepidolite. Some are incorporated in the crystals of the minerals.
4. Volatile rich deposits: pegmatites. Already noted
5. Pyroclasts: already noted. Shattering process aka brecciation.
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Mafic rocks |
High in Mg and or Fe. Low in silica( less than 50%) |
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Mafic rocks |
-High in Mg and or Fe. Low in silica( less than 50%)
-darker and denser than felsic
-richer in Ca
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Felsic rock |
-High in silica( out to 70%) and low in fe and mg
-richer in Na and K
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Classification of igneous rocks |
Back (Definition) |
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SiO2 concentration |
Less than 55: no quartz Greater than 56: no pyroxene Greater than 51: no olivine
So quartz will never appear with pyroxene or olivine |
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Genesis of magma |
1. Geothermal Gradient: temp increases 2-3 degrees per 100m. Melting usually begins 25 km down.
2. Pressure: melting point increases with pressure. Which also increases with depth.
3. Water content: water lowers melting point.
4. Composition: felsic rocks have lower melting points than mafic.
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Bowen’s reaction series |
-2 series -Bowen raise temp of Mafic and felsic materials and cooled them to watch them crystallize. -equilibrium between crystals and remaining magma was maintained. |
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Genesis of magma |
1. Geothermal Gradient: temp increases 2-3 degrees per 100m. Melting usually begins 25 km down.
2. Pressure: melting point increases with pressure. Which also increases with depth.
3. Water content: water lowers melting point.
4. Composition: felsic rocks have lower melting points than mafic.
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Bowen’s reaction series |
-2 series -Bowen raise temp of Mafic and felsic materials and cooled them to watch them crystallize. -equilibrium between crystals and remaining magma was maintained. |
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Bowen’s reaction series: discontinuous or mafic |
(Olivine, pyroxene, amphibole, biotite) -At 1200 degrees olivine is the first to crystallize. Crystallizing with more and more Fe and less mg until Fe:mg less than original composition of melt -at a certain decrease in temp pyroxene starts to form instead of olivine and olivine crystals are corroded. -discontinuous because new mineral had dif structure -at a lower temp amphibole crystallizes -then biotite crystallizes
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Genesis of magma |
1. Geothermal Gradient: temp increases 2-3 degrees per 100m. Melting usually begins 25 km down.
2. Pressure: melting point increases with pressure. Which also increases with depth.
3. Water content: water lowers melting point.
4. Composition: felsic rocks have lower melting points than mafic.
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Bowen’s reaction series |
-2 series -Bowen raise temp of Mafic and felsic materials and cooled them to watch them crystallize. -equilibrium between crystals and remaining magma was maintained. |
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Bowen’s reaction series: discontinuous or mafic |
(Olivine, pyroxene, amphibole, biotite) -At 1200 degrees olivine is the first to crystallize. Crystallizing with more and more Fe and less mg until Fe:mg less than original composition of melt -at a certain decrease in temp pyroxene starts to form instead of olivine and olivine crystals are corroded. -discontinuous because new mineral had dif structure -at a lower temp amphibole crystallizes -then biotite crystallizes
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Bowen’s series continuous or plagioclase feldspar series |
-at 1200 degrees plag felds begins to crystallize and is Ca rich -as temp decreases it becomes more Na rich. Eventually more than Ca. -continuous bc crystal structure is not affected -at 600 both reaction series are done and the remaining melt crystallizes to yield k felds, muscovite, and quartz. - if all igneous rocks followed this pattern we would not expect to find olivine, pyroxene and Ca-plagioclase
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Factors that affect Bowen’s continuous reaction series |
1. Cooling rate: if lava cools too quickly things get frozen and locked in the mafic/ basalt end
2. Fractional crystallization: if crystals are separated from magma(settling gravity) they can’t react and are preserved.
3. Magma source: different source rocks melt to yield different magmas
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Forms of igneous intrusions |
-Rocks that solidify under surface. -shallow intrusive rocks are called hypabyssal(mafic called diabase felsic called aplite)
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Forms of igneous intrusions |
-Rocks that solidify under surface. -shallow intrusive rocks are called hypabyssal(mafic called diabase felsic called aplite)
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Classification of Igneous intrusions |
1. Non-tabular intrusions: i. Discordant: cut across or truncate features of country rock a. Batholith. Areal extent greater than 100 square km b. Stock. Areal less than 100 c. Volcanic neck. Magma dries in volcano and volcano is eroded. Neck is left ii. Concordant. Displaces but is harmonious with the fabric of country rock a. Laccolith: upper surface convex, shroom b. Lower surface convex, sag
2. Tabular intrusions: sheet like i. Discordant. Called a dike, multiple emplaced in regional fracture systems ii. Concordant. Called sill. Can see layer on mountain.
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Products of volcanism |
A. Lava: mafic/basaltic lava: low viscosity. Low sio2. 1000-1200 degree erupted. Felsic/rhyolite lava: high viscosity. 800-1000 degrees. 1/10 flow rate of mafic.
B. Pryroclastics: intermediate felsic composition. Viscous silica rich lava. Long eruption-intermediate composition volcanos. Ash aka nuee ardent. Lahars are flow of wet ash debris like avalanche.
C. Gases in magma escape when eruption. They contribute to earth atmosphere. Form vesicles. Can cause atmospheric disturbances
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Styles of volcanism |
A. Fissure eruptions. Lava erupted through linear fractures i. Mid ocean ridges-mor: long belts of fissure eruptions that mark lithospheric plates. Few cm per year, makes sheeted dikes, thin dense mafic. Production of pillow basalts ii. Intercontinental: thick felsic crust fissure allow flood basalt. Multiple thin flows covering vast surfaces. Ex columbia river. Rapid cooling causes cracking.
B. Central eruptions: i. Shield volcanos: low viscosity basalts spread out due to gravity. Ex Hawaii ii. Volcanic domes: more viscos lava doesnt spread out as nice. Usually in craters. Ex mt St. Helens. iii. Cinder cones: pyroclasts that are steep and not overly stable. Ex wizard island. iv. Composite volcanos: stratovolcanos. Alternating eruptions. Related to convergent plate boundaries.
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Setting of volcanism |
A. Divergent plate boundaries. Over mantle convection cells. Melting by pressure drop. Mor system and intercontinental are sub settings. B. Convergent plate boundaries. Ocean lithosphere is subducted under ocean plate for volcanic isl of continental plate for cont. volcano arc. Ex japan. Explosive activity and partial melting of mafic.
C. Hot spots/ mantle plumes. Near mantle core boundary. Flood basalt eruptions like Colombia river plateau.
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Weathering |
Physical and chemical breakdown of rocks |
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Weathering |
Physical and chemical breakdown of rocks |
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Types of weathering |
A. Physical/mechanical: no alter to mineralogy. Uses planes of weakeneses like bedding planes or joints/fractures. Ex. First, salt, temp, moisture, sheeting.
B. Chemical weathering: composition changes. Loss of ions. Like. i. Solution/ dissolution: dissolve in acid. ii. Hydrolysis: ex: feldspar hydrolyzes in acid water to make clay n dissolved silica. iii. Hydration: take in water molecule to crystal structure. iv. Oxidation:
C. Biogenic Weathering: organic activity or influence of organisms.
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How climate effects weathering |
-In tropics (hot and humid) chemical weathering is very intense -In deserts, arid weathering and soil replacements are slow -in humid sub arctic regions, physical weathering is strong when its cold and moist - frost action |
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Silicate Mineral Stability |
-Silicate minerals are more stable the further along bowens reaction series they are, i.e. lower temp -So mafic rocks(like basalt) are less stable -Felsic rocks(greanite) are more stable |
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Rocks that came out of solution are more or less stable |
-They are less stable/ resistant to weathering -these include halite, gypsum, and calcite |
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Already weathered products are more or less stable |
-More stable -these include clays, oxides, and hydroxides |
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What happens to minerals that weather rapidly |
They are destroyed and don't end up in clastic sedimentary rock |
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What dominates Clastic sedimentary rocks |
Quartz, feldspares, and micas |
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Examples of soils formed and transported |
-Floodplain deposits (silts and clays) -glacial deposits - till -wind blown sediments ( silt sized sediment called loess) |
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Soil Profile Horizons |
1. O: Organic litter 2. A: mixed minerals and organic matter, in reach of plant roots, (O and A make topsoil) 3. E: Eluviation or leaching zone, most strongly weathered horizon, most minerals are removed 4. B: Zone of accumulation, Minerals removed from E accumulate in horizon B 5. C: Physically weathered bedrock, chemically unaltered. Specifics depend on Six SOIL FORMING FACTORS |
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Six Soil Forming Factors |
i. Climate - temperature and precipitation ii. Relief (topography) - drainage and surface water movement, thus leaching and accumulation iii. Parent Materials - composition iv. Time v. Organisms - speeds up weathering vi. Drainage - are dissolved materials removed |
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Sedimentary Rocs |
Made of pre existing rocks and minerals, carried in fluid and deposited |
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Clastic Rocks |
clasts or fragments produced without organic activity |
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Siliclastic |
Clastic fragments predominently of silicate minerals |
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Process of forming siliclastics |
WETSL W: weathering - produces clasts E: erosion - seperates grains T: transport - to lower area, grains are modified by atrition(loss of material) and sorting S: sedimentation - deposits grains L: lithifcation - unconsolidated rocks turned into sediments |
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Processes of lithification |
Compaction: grains compacted and water expelled (volume reduced up to 80%) Binding: weak surface charges of clay Cementation: growth or precipitation that attatches grains, commonly in silica, calcites, clays, or hematites |
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Sedimentation stops and Metamorphosis begins at what tempurature |
aprx 200 degress celcius |
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Mineralogy of sedimentary rocks |
dominated by stable silicates, quartz, feldspares, biotite, muscovite, and lesser rock fragments |
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Size classifiation of sedimentary rocks |
grain size correlates with transport or environment energy -Coarse particles (<2mm) gravel sized -division between sand and mud is .062mm (1/16) -within fine particle sizes division between silt and clay is .0039 or 1/256 -silt rock = siltstone -clay rock = claystone -if you cant tell if its < or >1/256mm it is called mudstone |
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Conglomerate vs breccia (sedimentary rocks) |
Conglomerate = round clasts Breccia = angular clasts |
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Arenite |
another name for sandstone |
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Mudstone and Shale |
Mudstone - thick blocky blocks Shale - fissile, breaks into sheets |
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Sedimentary textures |
Sorting - how many size classes Roundness - presence of corners or not in grains Sphericity - equidiimensional or not higher values in these catagories = high kinetic energy applied to making them |
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Biochemical Sedimentary rocks ex: carbonates |
Come from biological activity/ remains -mostly carbonates(like calcite or dolomite) and some cherts |
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Chemistry of sedimentary rocks |
-As co2 increases, ph decrease, and calcite dissolves -most carbonates in marine environments(also saline lakes and caves) -photosynthesis = equilibrium to left=calcite -temp decrease = solubility of calcite increases - more soluble in deep water |
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Calcite Compensation Depth (CCD) |
at a few 1000m (5250m near equador) the supply of carbonate=amount lost by dissolution, below this carbonate sediments do not accumulate on sea floor |
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Biochemical Sources |
-Much of the carbonate in limestone(calcite) and dolostone(dolomite) come from shells -much carbonates come from agae |
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Low chemical stability of carbonates= |
Prone to diagenisis |
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Biochemical environments |
2 modern environments: 1. Tropical shelf seas: shallow(above base of photic zone=photosynthesis), warm(less soluble in warm), marine waters on continental shelf or crust, also clear water to allow photosynthesis 2. Deep Ocean Floor: rain of shells and organisms accumulate down to CCD |
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Chemical Sedimentary Rocks |
significant as halite, gypsum, potash and environmental indicator evaporation of seawater in subtropical, high pressure, low rain areas -need basin or depression filled with seawater -also in saline lake ( can form tropa and borax) |
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Metamorphic rocks |
Undergo recrystillization WITHOUT melting, stable at new conditions |
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Originial minerology of metamorphiv rocks |
Given the nature of earths crust: Silicates with lots of Al, Ca, Na, and K. Not much Fe, Mg but lots of H2O |
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Argillite |
Typical mudstone or shale, lots of silicates with Na, Ca, and K (earth crust ish) |
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What does quartz Arenite metamorphise to |
Quartzstone |
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What does limestone or dolomite metamorphie to |
Marble (Calcite or dolomite) |
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Crystal size __________ with increasing GRADE or INTENSITY of metamorphism but there is no _________________ |
Increases, Allignment of minerals (fabric) |
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Onset of metamorphism, first growing mineral |
Chlorite at 200 degrees celcius |
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Porphyroblasts |
larger, well formed crystal, usually in a matrix of micas |
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Why are temp and pressure considered together while talking about metamorphism |
many minerals form at certin combinations of the, |
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What happens to ARGILLITE with inceaseing metamorphic grade |
Succession of texture developp |
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why are texture changes found with increasing metamorphic grade |
produced by the responce of elongated OR platty/flat minerals directed to stree, they orient their axes or faces perpendicular to the stress by a)rotation b)recrystillizaztion |
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Slate |
low grade rock with slaty cleavage, rocks splits along cleavage, which is not the same as mineral cleavage, parrellel to bedding |
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Phyllite |
appreciable grain growth and recrystillization, cleavages have SHEEN OF LUSTRE (from chlorite) (higher grade than slate but still low grade) |
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Schist |
Grain size continues to increase, rock splits along irregular faces, PORPHYROBLAST MINERALS APPEAR, embedded in biotie or muscovite matrix (medium grade metamorphism) -May be folliated or lineated |
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Gneiss |
High grade metamorphism -dark bands of biotite or amphibole, and light bands with quartz or feldspares |
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Metamorphic Facies |
eclogite facies rocks, with garnet and pyroxene, are from the UPPER MANTLE |
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Thermal or Contact Metamorphism |
High temp and low pressure -heat from ingenous intrusions -Contact zone (aureole) has no fabric/allignment -Rock is typically dark, fine grained, and called HORNFELS, often with porphyroblasts(large crystals) -fluids and volatiles from intrusions, altering country rock ormineral deposists, called HYDROTHERMAL DEPOSISTS |
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Skarn |
silicate fluids flushing carbonate country rocks |
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Subduction Metamorphises |
-High pressure, low temp -wedge of sediments between volcanic arc and trench - |
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Rocks that develop in subduction metamorphises |
-Blueshists, facies rocks develop with glaucophane, blue mineral |
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Presence of Blueshist rock in cnotinental crust indicates |
sature where intervening ocean basin has been conumed by subduction as 2 smaller continental blocks converge |
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Regional metamorphism |
High temp and pressure -convergance and collision to produce mountains -as metamorphic grade increases we pass through greenshsist, amphible, and granular facies |
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Cataclastic Metamorphism |
Fault movement crushes rocks between displaced rock masses, producing mylonite or fault gauge |
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Shock/Impact Metamorphism |
extremely rapid application of extreme pressure: BIOTITE IMPACT, to produce shocked quartz grains, or cohesive geochemical anomalies and microtektites, may also impact cratering |
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Silicate minerals are ______________ stable the further along the bowens reaction they are |
More |
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Minerals (like halite, gypsum, and calcites) out of solution are _____________ stable |
Less |
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Minerals (like clays, oxides, and hydroxides) that have already been weathered are _____________ stable |
more |
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Classification of clastic sedimentary rocks |
-Conglomerate rounded clasts -Breccia angular clasts -Both of these have grains > 2mm -Sandstone/arenite - Between 1/16 and 2 mm -Siltstone - Between 1/16 and 1/256 mm -Claystone less than 1/256 mm -Mudstone blocky -Shale fissile -Expect to see quartz, potassium feldspar,as best choices (muscovite, biotite okay) because they are chemically stable but not olivine, pyroxene as best choices (use one, 1)because they are chemically unstableand destroyed by weathering |
