METAMORPHISM. Fig. Ta 7.1 Definition of Metamorphism The alteration of a pre- existing igneous,...

44
METAMORPHISM METAMORPHISM

Transcript of METAMORPHISM. Fig. Ta 7.1 Definition of Metamorphism The alteration of a pre- existing igneous,...

Page 1: METAMORPHISM. Fig. Ta 7.1 Definition of Metamorphism The alteration of a pre- existing igneous, sedimentary, or metamorphic rock (called the “parent.

METAMORPHISMMETAMORPHISM

Page 2: METAMORPHISM. Fig. Ta 7.1 Definition of Metamorphism The alteration of a pre- existing igneous, sedimentary, or metamorphic rock (called the “parent.

Fig. Ta 7.1

Page 3: METAMORPHISM. Fig. Ta 7.1 Definition of Metamorphism The alteration of a pre- existing igneous, sedimentary, or metamorphic rock (called the “parent.

Definition of MetamorphismThe alteration of a pre-existing igneous, sedimentary, or metamorphic rock (called the “parent rock” or “protolith”) by the application of heat and/or pressure. Complete melting does not occur.

Page 4: METAMORPHISM. Fig. Ta 7.1 Definition of Metamorphism The alteration of a pre- existing igneous, sedimentary, or metamorphic rock (called the “parent.

Metamorphism depends on:

Parent Rock

Equilibrium Exchange

Change in P-T-X

Geothermal Gradient

Confining/lithostatic pressure

Differential Stress: Shearing & Compression

TIME

Page 5: METAMORPHISM. Fig. Ta 7.1 Definition of Metamorphism The alteration of a pre- existing igneous, sedimentary, or metamorphic rock (called the “parent.

Confining Pressure

Page 6: METAMORPHISM. Fig. Ta 7.1 Definition of Metamorphism The alteration of a pre- existing igneous, sedimentary, or metamorphic rock (called the “parent.

CompressiveStress

Shearing

Page 7: METAMORPHISM. Fig. Ta 7.1 Definition of Metamorphism The alteration of a pre- existing igneous, sedimentary, or metamorphic rock (called the “parent.

Metamorphosed Conglomerate

Page 8: METAMORPHISM. Fig. Ta 7.1 Definition of Metamorphism The alteration of a pre- existing igneous, sedimentary, or metamorphic rock (called the “parent.

Effects of MetamorphismMineralogical: - change minerals to reflect new P-T (equilibrium) conditions.

Recrystallization: change of existing crystal size and shape to form layers (e.g., shale to schist), interlocking crystals (e.g., sandstone to quartzite).

Recombination: Recombination of elements in pre-existing minerals to form stable new ones. Addition/subtraction of ions common when fluid is present.

Page 9: METAMORPHISM. Fig. Ta 7.1 Definition of Metamorphism The alteration of a pre- existing igneous, sedimentary, or metamorphic rock (called the “parent.

Effects of Metamorphism

Textural: Re-orientation of mineral grains, especially platy (micaceous) grains in response to differential stress.

Non-foliated: random orientation – either no platy minerals or no directed stress (isotropic); Granoblastic (equigranular or isotropic) or Porphyroblastic (metamorphic porphyritic texture).

Foliated: fabric developed through directed pressure and/or shearing.

Page 10: METAMORPHISM. Fig. Ta 7.1 Definition of Metamorphism The alteration of a pre- existing igneous, sedimentary, or metamorphic rock (called the “parent.

Development of Foliation

Page 11: METAMORPHISM. Fig. Ta 7.1 Definition of Metamorphism The alteration of a pre- existing igneous, sedimentary, or metamorphic rock (called the “parent.

Non-Foliated

Page 12: METAMORPHISM. Fig. Ta 7.1 Definition of Metamorphism The alteration of a pre- existing igneous, sedimentary, or metamorphic rock (called the “parent.

Foliated

Page 13: METAMORPHISM. Fig. Ta 7.1 Definition of Metamorphism The alteration of a pre- existing igneous, sedimentary, or metamorphic rock (called the “parent.

FoliationOriented Minerals: platy or needle-like minerals growing in a plane either re-orientation or existing or growing of new.

Gives cleavage or planes of weakness.

Slate: oriented clay minerals allows the rock to be easily cleaved.

Phyllite: growth of microscopic micas to give strong foliation – rock is “shiny”.

Schist: strongly foliated with visible micas and feldspars.

Gneiss: strongly banded rock with dark bands of micas & pyroxenes, light bands of feldspars & quartz.

Migmatite: strongly veined rock as it has partially melted.

Page 14: METAMORPHISM. Fig. Ta 7.1 Definition of Metamorphism The alteration of a pre- existing igneous, sedimentary, or metamorphic rock (called the “parent.

Table 07.01

Page 15: METAMORPHISM. Fig. Ta 7.1 Definition of Metamorphism The alteration of a pre- existing igneous, sedimentary, or metamorphic rock (called the “parent.

Typical Metamorphic Minerals

Chlorite: Hydrous Fe-Mg-Al silicate

Talc: Hydrous Mg-silicate

Serpentine: Hydrous Mg silicate

Graphite: Carbon

Garnet: Ca-Mg-Fe-Al silicate

Staurolite: Fe-Al silicate

Also: Quartz, muscovite, biotite, feldspar, amphibole, calcite.

Page 16: METAMORPHISM. Fig. Ta 7.1 Definition of Metamorphism The alteration of a pre- existing igneous, sedimentary, or metamorphic rock (called the “parent.

Metamorphic GradeDegree of parent rock alteration, mostly dependent on increasing temperature for increasing grade.

Prograde: slate-phyllite-schist-gneiss-migmatite (melting).

Prograde metamorphic Reaction:

CaCO3 + SiO2 CaSiO3 + CO2

Calcite Quartz Wollastonite Fluid

Page 17: METAMORPHISM. Fig. Ta 7.1 Definition of Metamorphism The alteration of a pre- existing igneous, sedimentary, or metamorphic rock (called the “parent.

Classification

Mineralogical and textural if foliated:“garnet-mica schist”

“quartz-feldspar gneiss”

If non-foliated, named on compositional basis (and often color):

“(white) quartzite” or “(pink) marble”

Page 18: METAMORPHISM. Fig. Ta 7.1 Definition of Metamorphism The alteration of a pre- existing igneous, sedimentary, or metamorphic rock (called the “parent.

Types of Metamorphism: ContactThermal, local, around intrusions. Size of aureole depends on:Size of intrusion

Heat (composition)Fluid content of magmaFluid content of country rockCountry rock type

Page 19: METAMORPHISM. Fig. Ta 7.1 Definition of Metamorphism The alteration of a pre- existing igneous, sedimentary, or metamorphic rock (called the “parent.

Types of Metamorphism: ContactProduces non-foliated, granoblastic rocks:

Hornfels (if clastic - shale)Quartzite (if sandstone) Marble (if carbonate)

Page 20: METAMORPHISM. Fig. Ta 7.1 Definition of Metamorphism The alteration of a pre- existing igneous, sedimentary, or metamorphic rock (called the “parent.

Types of Metamorphism: RegionalAlso known as dynamothermal - produces both foliated and non-foliated metamorphic rocks.

Heat & directed pressure on rocks buried deep within the Earth - Prograde or Retrograde.

Associated with mountain belts - affects very large areas.

Prograde metamorphic reactions liberate a fluid.

Retrograde is difficult – pore spaces decrease during prograde so getting fluid back in is not easy.

Page 21: METAMORPHISM. Fig. Ta 7.1 Definition of Metamorphism The alteration of a pre- existing igneous, sedimentary, or metamorphic rock (called the “parent.

RegionalMetamorphism

Page 22: METAMORPHISM. Fig. Ta 7.1 Definition of Metamorphism The alteration of a pre- existing igneous, sedimentary, or metamorphic rock (called the “parent.

Types of Metamorphism: ShockMeteorite impact – sudden and intense deformation.

See www.meteorcrater.com

Page 23: METAMORPHISM. Fig. Ta 7.1 Definition of Metamorphism The alteration of a pre- existing igneous, sedimentary, or metamorphic rock (called the “parent.

Types of Metamorphism: ShockHigh-pressure polymorph of quartz – coesite – can form.Impact melt can form.Lots of rock fragmentation & mineral deformation.

Moon – no atmosphere so lots of meteorite impacts (micro and macro!). Produces regolith, rock flour, impact melt, breccias.

Page 24: METAMORPHISM. Fig. Ta 7.1 Definition of Metamorphism The alteration of a pre- existing igneous, sedimentary, or metamorphic rock (called the “parent.

Water in MetamorphismProvides transport mechanism and can promote reactions.Hydrothermal metamorphism: hot water streams add/remove ions. May promote ore formation.

Page 25: METAMORPHISM. Fig. Ta 7.1 Definition of Metamorphism The alteration of a pre- existing igneous, sedimentary, or metamorphic rock (called the “parent.

Metasomatism: addition of ions from external source.

Water in Metamorphism

Page 26: METAMORPHISM. Fig. Ta 7.1 Definition of Metamorphism The alteration of a pre- existing igneous, sedimentary, or metamorphic rock (called the “parent.

Water in Metamorphism

Metamorphic aureole is greater around granitic plutons than around gabbroic plutons, even though the magma temperature is lower.

Page 27: METAMORPHISM. Fig. Ta 7.1 Definition of Metamorphism The alteration of a pre- existing igneous, sedimentary, or metamorphic rock (called the “parent.

Ore-bearing veins in a mine

Page 28: METAMORPHISM. Fig. Ta 7.1 Definition of Metamorphism The alteration of a pre- existing igneous, sedimentary, or metamorphic rock (called the “parent.

Metamorphic Grade:

Degree of parent rock alteration, mostly dependent on increasing temperature for increasing grade

Prograde: SLATE -phyllite-schist-gneiss-migmatite (melting).

SLATE: oriented clay minerals allows the rock to be easily cleaved.

Page 29: METAMORPHISM. Fig. Ta 7.1 Definition of Metamorphism The alteration of a pre- existing igneous, sedimentary, or metamorphic rock (called the “parent.

Foliation can be deformed

Page 30: METAMORPHISM. Fig. Ta 7.1 Definition of Metamorphism The alteration of a pre- existing igneous, sedimentary, or metamorphic rock (called the “parent.

Prograde: slate-PHYLLITE-schist-gneiss-migmatite (melting).

PHYLLITE: growth of microscopic micas to give strong foliation – rock is

“shiny”.

Page 31: METAMORPHISM. Fig. Ta 7.1 Definition of Metamorphism The alteration of a pre- existing igneous, sedimentary, or metamorphic rock (called the “parent.

Prograde: slate-phyllite-SCHIST-gneiss-migmatite.

SCHIST: strongly foliated with visible micas & feldspars.

Page 32: METAMORPHISM. Fig. Ta 7.1 Definition of Metamorphism The alteration of a pre- existing igneous, sedimentary, or metamorphic rock (called the “parent.

Garnet Schist

Page 33: METAMORPHISM. Fig. Ta 7.1 Definition of Metamorphism The alteration of a pre- existing igneous, sedimentary, or metamorphic rock (called the “parent.

Fig. 07.14

Prograde: slate-phyllite-schist-

GNEISS-migmatite.

GNEISS: strongly banded rock with dark bands of micas

& pyroxenes and light bands of feldspars and quartz.

Page 34: METAMORPHISM. Fig. Ta 7.1 Definition of Metamorphism The alteration of a pre- existing igneous, sedimentary, or metamorphic rock (called the “parent.

Gneissose Banding

Page 35: METAMORPHISM. Fig. Ta 7.1 Definition of Metamorphism The alteration of a pre- existing igneous, sedimentary, or metamorphic rock (called the “parent.

Prograde: slate-phyllite-schist-gneiss-MIGMATITE.

MIGMATITE: strongly veined rock as it has partially melted.

Page 36: METAMORPHISM. Fig. Ta 7.1 Definition of Metamorphism The alteration of a pre- existing igneous, sedimentary, or metamorphic rock (called the “parent.

0065

Page 37: METAMORPHISM. Fig. Ta 7.1 Definition of Metamorphism The alteration of a pre- existing igneous, sedimentary, or metamorphic rock (called the “parent.
Page 38: METAMORPHISM. Fig. Ta 7.1 Definition of Metamorphism The alteration of a pre- existing igneous, sedimentary, or metamorphic rock (called the “parent.

Metamorphic Facies:

Rocks having broadly similar mineral assemblages = same metamorphic facies – analogous to climatic zones.

The metamorphic facies is determined by the specific mineral assemblage present.

The facies is defined as a mineral assemblage that may only occur over a relatively narrow range of P-T conditions.

Formed under broadly similar P-T conditions.

Mineralogy dependent upon protolith composition.

Page 39: METAMORPHISM. Fig. Ta 7.1 Definition of Metamorphism The alteration of a pre- existing igneous, sedimentary, or metamorphic rock (called the “parent.

Metamorphic Facies:

Page 40: METAMORPHISM. Fig. Ta 7.1 Definition of Metamorphism The alteration of a pre- existing igneous, sedimentary, or metamorphic rock (called the “parent.

Plate Tectonics and Metamorphism

Page 41: METAMORPHISM. Fig. Ta 7.1 Definition of Metamorphism The alteration of a pre- existing igneous, sedimentary, or metamorphic rock (called the “parent.

Plate Tectonics and MetamorphismGravitational collapse & spreading – central part of mountain becomes too high & collapses. Rock forced downward.

Foliation developed parallel to collapse & spreading.

Page 42: METAMORPHISM. Fig. Ta 7.1 Definition of Metamorphism The alteration of a pre- existing igneous, sedimentary, or metamorphic rock (called the “parent.

Index MineralsForm over a restricted range of pressure & temperatures (determined in the laboratory).

When found in rocks, the P-T of formation can be reasonably estimated.

Page 43: METAMORPHISM. Fig. Ta 7.1 Definition of Metamorphism The alteration of a pre- existing igneous, sedimentary, or metamorphic rock (called the “parent.

Index MineralsKyanite, Andalusite, Sillimanite: all Al2SiO5, different crystal structures - polymorphs.Andalusite - low P & T; Kyanite - high P; Sillimanite - high T.

Page 44: METAMORPHISM. Fig. Ta 7.1 Definition of Metamorphism The alteration of a pre- existing igneous, sedimentary, or metamorphic rock (called the “parent.

0062