Exam Flashcards

Question

k - na system - role solvus phase

Answer 1

2 loops joined at eutectic Solvus Curve: at high temps, k and na mix (a) At higher Temperatures the (b) at low temps separate so K and Na = Exsolution Lamellae or Perthitic Textures

Answer 2

melt contains H 2O i. The leucite field disappears with increasing H2O pressure. ii. Crystallization temperatures are reduced. iii. Composition changes continuously along liquidus-solidus during cooling.

Answer 3

Added SiO2 to Ca plag and heated result: -much of the plag had converted to albite. -in many low temperature and metamorphic rocks, albite is a stable end member. Ca plag is the high temperature end member

Answer 4

* Felsic rock: dominated by felsic minerals – Generally leucocratic: light-colored * Mafic rock: dominated by mafic minerals – Melanocratic: dark-colored – Ultramafic rock: >90% mafic minerals – Volume % of dark minerals – < 30% = leucocratic, 30-60% = mesotype, >60% = melanocratic

Answer 5

Acidic rocks are usually felsic rocks -Basic rocks are usually mafic rocks Ultrabasic rocks are usually ultramafic rocks this is determined by SiO2 %

Answer 6

undersaturated with respect to SiO2: -minerals can react with free silica to form more silica-rich minerals. -minerals can stably co-exist with free silica -oversaturated with respect to SiO2

Answer 7

Peraluminous: Al2O3 exceeds the sum of CaO, Na2O, and K2O. Peralkaline: Al2O3 is less than the sum of Na2O and K2O. Metaluminous: Al2 O3 exceeds the sum of Na2O and K2O, but is less than the sum of Na2 O, K2O, and CaO. Subaluminous: molecular proportion of Al2O3 is approximately equal to the sum of Na2O and K2O.

Answer 8

-alkalinity of the rocks. -CaO vs SiO2 -Na2 O+K2O vs SiO2 -CaO usually decreases as Na2O+K2O and SiO2 increase, the curves cross. The SiO2 content at the point where the curves cross indicates the alkalinity of the rock suite

Answer 9

Phaneritic Anorthosite – >90% plagioclase Diorite – <35% mafic minerals (hornblende, biotite) – Lighter colored Gabbro – >35% mafic minerals (olivine, pyroxene) – Darker colored

Answer 10

* Andesite – Has >52% SiO2 – lighter colored: color index < 35% * Basalt – Has <52% SiO2 – darker colored: color index > 35% andesite and basalt plot near p trachyte near a

Answer 11

triangle top pyroclastic breccia left lapillistone right tuff Tuff = consolidated/cemented ash

Answer 12

Contact -Heating during igneous intrusion or beneath thick flows -mineral growth random orientations. -Energy imparted to host intruded rock. main agent: heat regional a)Orogenic: -Batholith (large) scalemetamorphism -mountain belts and shield areas -result of tectonism Main agent: deformation then p/t b)burial: -post diagenetic -sedimentary rocks during burial main agent: pressure hydrothermal ->result of circulating fluids a) Sea floor spreading: b) Porphyry systems: main agent: fluids dynamic (faults, etc) -high strain -foliated, extremely sheared/streaked and re-crystallized grains main agent: deformation then pressure shock -Impact of high velocity meteorites, creates high P/T minerals at surface or shatter cones main agent: deformation and pressure then t

Answer 13

main point: can increase and decrease in grade, and do this multiple times Prograde: -progressive increase grade -increase p and/or t Retrograde: -decreasing grade as rock cools -after metamorphic/igneous event * Prograde metamorphism is typically of greater significance than retrograde metamorphism.

Answer 14

foliated Usually results in textural change of a rock as it reacts to accommodate stress/ strain Cataclasite – Mylonite - Gneiss Impactite: -category of high- strain rocks, -extremely high- pressure silica polymorphs (eg. coesite and stishovite) -macroscopic nested cone-like structures (shatter cones)

Answer 15

* Metamorphism is marked by the formation of new minerals: Lower limit : Diagenesis * Upper limit : Migmatites – Onset of Melting * However, the boundary between diagenesis and metamorphism is somewhat arbitrary * Some minerals are considered both diagenetic and metamorphic

Answer 16

Zones: -area subdivided into zones of different metamorphic conditions. -zone boundaries ->index mineral -new mineral that appears with a new metamorphic grade -> based on pelitic (metamorphosed shaly) rocks pros: -used worldwide -easily mappable boundaries (convenient in field) -can be used for different protoliths cons: -mostly applies to pelitic rocks -hard to relate p/t between protoliths -doesnt account for fluid, stress/strain Zones were defined from Pelitic rock -Zone is very protolith composition dependent facies: -closed system (equilibrium) -bulk chemistry of protolith = bulk chemistry of rock -a set of mineral assemblages for all bulk chemistries which occur in the same narrow P/T range (regardless of protolith) -corresponding P-T conditions -what reactions take place

Answer 17

polymorphs kyanite, sillimanite, andalusite phase diagram: kyanite - low t high p andalusite - low p med t sillimanite - high t

Answer 18

1.Formation of sediment – weathering, mineral grains, hard parts of organisms, or chemical precipitation 2. Transport of sediment – water, wind, ice = energy for physical weathering 3. Deposition in a variety of environments eg. basin – Formed by plate tectonic processes 4. Lithification – compaction/cementation

Answer 19

lithification is the process of forming and rock and involves compaction and sedimentation diagenesis is more general and describes all processes affecting sediment after deposition (during and after lithification) compaction refers to sediments being squeezed by weight of overlying layer cementation occurs material precipitates in pore spaces and glues rock together

Answer 20

Terrigenous allochemical orthochemical

Answer 21

1. Terrigenous terrigenous rocks occur from erosion outside depositional area and are transported – Transported as solids (clastic) -60% 2. Allochemical – Chemical precipitate outside depositional area – But also transported as solid -10% 3. Orthochemical – Chemical precipitate within depositional area -5% * Combination of (1) and (2) = siliciclastic * Combination of (2) and (3) = chemical siliciclastic rocks are a combination of terriginous and allochemical triangle: T at top A at left O at right

Answer 22

DISTANCE Greater transport distance ->better rounding & sorting Wind transport: rounding of sediment * Water transport: ->slower abrasion/rounding compared with wind * Glacial transport: ->least sorting and rounding MATURITY 1. Immature – >5% clay, sand poorly sorted, angular 2. Submature – <5% clay, sand poorly sorted, not well rounded 3. Mature – No clay, sand well sorted, not well rounded 4. Supermature – No clay, sand well sorted, well rounded

Answer 23

Terrigenous Sedimentary Rocks often classified as Grain or Matrix Supported Folk (Mineralogy) grains Q = Quartz = Orthoquartzite (90% Qtz) F = Feldspar = Arkose (Feldspathic) (~25%) R = Rock Fragments (volcanic/metamorphic) arkokes are feldpathic rocks by folk class arenites have fine sand, well sorted matrix by gilbert class Gilbert (Matrix) Wacke = appreciable fine mud, poorly sorted Arenite = clean eg. fine sand , well sorted

Answer 24

Classification of Limestones 1. Allochems (transported) 2. Microcrystalline ooze → Micrite (carbonate mud) 3. Sparry calcite → Sparite * Pore filling cement or recrystallization of micrite

Answer 25

Allochems 1. Intraclasts erosion of seafloor carbonate sediments, then transported and re-deposited 2. Oolites * Spherical/elliptical, carbonate accretes around central particle while being rolled around by currents 3. Fossils * Broken fragments of fossils 4. Pellets * Fecal pellets, well-rounded and sorted aggregates of fine carbonate (+ organics) with no internal structure

Answer 26

folk: Good for thin section classification -intraclasts, oolites,fossils,pellets -micrite to sparite dunham: good for hand samples -mudstones, wackes

Answer 27

salt rocks formed in evaporating water bodies Evaporate seawater, the sequence would be: 1. Calcite (not much) * Possibly dolomite if ancient seawater was Mg-rich 2. Gypsum, anhydrite (most abundant) CaSO4 2H2O 3. Halite (rare, requires 90% evaporation) 4. Sylvite (Potash minerals Cl – SO 4) (very rare)

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