3 - Fluids + Textures

volatile content _____ (increases/decreases) with increasing metamorphic grade

decreases

what is LOI

loss of ignition (h2o, co2, so3)

what temperature and pressure are the critical end points at for h2o?

P = 2MPa

T = 374 C

what temperature and pressure are the critical end points at for CO2

P = 3 MPa

T = 31.1 C

above the h2o critical point, it is a _______ fluid

supercritical

what is an isochore

lines of constant density

what happens to a fluid inclusion during cooling and exhumation?

the mass/volume of the inclusion is constant, so density is constant

it will follow the isochore until it intersects the LV curve then the phases will separate (boiling),

Then it fully follows the LV curve

what is the LV curve?

liquid-vapour curve

whats the symbol for stress

sigma σ

definition of stress

an applied force acting on a rock over a cross-sectional area

what is strain

the response of a rock to an applied stress (deformation)

how do rocks beneath the earths surface experience stressed

uniform in all directions

what does the equilibrium mineral assemblage depend on

the pressure of the lithosphere (as well as the T, fluid and protolith)

how to find differential stress

σ1-σ3 (mohrs circles!!!!)

what is the mohr failure criterion

where shear failure occurs

what caused shear failure

increasing fluid pressure

x and y axis of a mohr circle diagram

y = shear stress τ

x = normal stress σN

what is σ1_eff (an equation)

(σ1 minus pressure of fluid)

what is σ3_eff (an equation)

(σ3 minus pressure of fluid)

what reduces effective stresses and what kind of failure does it cause

increasing pore fluid, causes brittle failure

what is deviatoric stress and what does it result in

unequal stresses, results in rock deformation and development of metamorphic foliation

describe the order of principle stresses (___>___>___)

σ1 > σ2 > σ3

what is the maximum stress?

σ1'

what is the intermediate stress?

σ2

what is the minimum stress?

σ3

how do the 3 principle stresses act on a unit? like what direction do they face

like dis

what is simple shear

parallel to surfaces, pushing like a deck of cards

what is pure shear

acts at right angles to surfaces, compression/extension

how does deviatoric stress result in metamorphic foliations (4 ways)

1. Platy minerals growing perpendicular to σ1 = slaty cleavage

2. Rotation of mineral grains

3. Pressure solution

4. Dislocation glide

what is pressure solution

dissolution-precipitation (minerals dissolve at grain contacts under high stress—> then reprecipitate in lower stress areas)

higher temperatures tend to _____ (increase/decrease) grain size

increase

how does slow heating impact grain size

fewer nuclei, coarser grained

how does rapid heating impact grain size

many nuclei, fine grained textures

deformation tends to _____ (increase/decrease) grain size

decrease

how do low strain rates impact grain size

more time to reduce accumulated strain energy

how do high strain rates impact grain size

less time to reduce accumulated strain energy

what does the final grain size depend on? (6 reasons)

the protolith, temperature, rate of heating, strain, strain rate, and ability to reduce strain energy

rocks will ____ (fine/coarsen) if high temperatures outlast high strain rates

coarsen

what are the 5 categories we can put rock names into

• foliated (planar fabric)

• non foliated

• metabasalts

• monomineralic rocks

• other special names

4 examples of foliated (planar fabric) rocks

slate, phyllite, schist, gneiss

2 examples of non-foliated rocks

hornfels, granulite (granofels)

4 examples of metabasalts

greenschist, blueschist, amphibole, eclogite

3 examples of monomineralic rocks

quartzite, marble, serpentinite

3 examples other “special” named rocks

migmatite, mylonite, pseudotachylite

from low to high metamorphic grade, rank the foliated rocks

slate, phyllite, schist, gneiss

in the foliated rocks, what do we call them if there are important minerals like garnet or staurolite in them?

just call them garnet-schist or staurolite schist

what is a hornfel and how does it form

fine grained, non foliated rock formed by contact metamorphism

what is a granofel and what do we typically call it

coarse grained non foliated rock, usually call it gneiss or granulite

how are metabasaltic rocks named

based on their metamorphic facies

what mineral dominated in blueschist

glaucophane

what mineral dominated in greenschist

epidote, chlorite, actinolite

what mineral dominated in eclogite

garnet, omphacite

what mineral dominated in amphibolite

hornblende and plag

what mineral dominated in mafic granulite/gneiss

hornblende, clinopyroxene, plag

what is a migmatite

underwent partial melting

what is a mylonite

shear zone rock, highly deformed, indicative of ductile stress

what is a pseudotachlite

a frictional melt layer, indicative of a brittle regime