METAMORPHIC PROCESSES

Question 1

• Comment on the 4 driving factors of metamorphism

Answer 1

pressure, temp, fluids, time

Question 2

pressure

Answer 2

 Lithostatic (equal in all direction) increases with depth
 Differential (directional stress, which may be compressive or shear) usually a result of plate tectonics (or meteorites)
 Greater pressure= higher density minerals
 Affects minerals stability and texture

Question 3

o Temperature

Answer 3

avg geothermal gradient 25C/km depth- mid ocean ridges = higher temp

Question 4

o Fluids-

Answer 4

h2O and other fluids in the pore spaces of rock
 Facilitates transfers of ions within rock and minerals
 Water increase rates o reactions and metamorphism
 Form veins (typically quartz or calcite) metals are possible as trace constituents

Question 5

o Time

Answer 5

 Metamorphism is a chemical reaction
 Time can lead to slow reactions
 Metamorphic minerals formation: 1mm per 1 million years
* Greens tone = basalt + time

Question 6

o Foliation:

Answer 6

: layers in rock, pervasive- start at the molecular level

Question 7

o Foliated metamorphic rocks

Answer 7

 Formed in an environment with directed or shear stress
 Crystallization allignes perpendicular to pressure

Question 8

o Non foliated metamorphic rocks

Answer 8

 Formed close to the surface whith minimal pressure
 Mostly by heat
 Limestone  marble
 Sandstone  quartzite(does not align with pressure)
* Clay turns into mica

Question 9

isostasy

Answer 9

why we see metamorphic rocks at earths surface

Question 10

o Sedimentary protoliths (parent rocks)

Answer 10

 Shale  slate phyllite schist  gneiss

Question 11

 Slate

Answer 11

• Low grade metamorphism of shale microscopic clay and mica

Question 12

 Phyllite

Answer 12

• Product of increased metaphormism of slate – can be wavy
• Larger micas grow – giving sheen/ shine on foliation

Question 13

 Schist

Answer 13

• Increased metamorphism of phyllite- metamorphic minerals and micas are clear

Question 14

gneiss

Answer 14

• No mica (at higher temp)
• Visible big crystals with alternating layers of mafic and felsic material

Question 15

• Correlate a metamorphic rock with a tectonic setting

Answer 15

o Most regional metamorphism – within continental crust in the roots of mountain ranges
 High temp/high pressure
 Large area
 Recrystallization and new mineral form foliated rocks
o Dynamic metamorphism
 Low temp/ high pressure
 Occur around fault zones
 Rocks grind against eachother creating friction/ heat
o Contact aureoles
 Larger the body the longer metamorphism takes time
 Metasomatism
* Heating groundwater making convection system
* Alteration of surrounding rocks: hydrothermal alteration
o Skarn

Question 16

o Divergent boundaries geothermal gradient

Answer 16

 Basalt and gabbro are formed at ocean ridges. Sea water is drawn in and creates a convective system, heating the waer up to 300 degrees, allowing for metamorphic reactions
 Pyroxene  chlorite/ serpentine
 Greenstone metamorphism is called retrograde metamorphism

Question 17

subduction geothermal gradient

Answer 17

 High pressure, low temp
 Blue color mineral forms: glaucophane, a rock called blueschist

Question 18

magma chambers

Answer 18

 1000C- heats 10m of surroundings