Metamorphic Rocks

Marble

Protolith: Limestone

Texture: Massive, unfoliated

Minerals: calcite, dolomite

Diagnostic: Sugary, massive, will fizz

Phyllite

Protolith: mudstone

Texture: foliated

Minerals: chlorite, muscovite

Diagnostic: wavy foliation, more surface sheen than slate

Gneiss

Protolith: igneous or sedimentary

Texture: banded

Minerals:quartz, feldspar, biotite, garnet, hornblende

Diagnostic: augens are the big crystals, banded

Grey Slate

Protolith: Mudstone

Texture: slaty cleavage

Minerals: clays and chlorite, indistinguishable

Diagnostic: slateiness, plated

Greenstone

Protolith: basalt, mafic volcanic rocks

Texture: massive, weakly foliated

Minerals: indistinguishable chlorite, actinolite, epidote?

Diagnostic: green and massive, weak foliation

Mica Schist

Protolith: mud rich sed. rock

Texture: foliated (schistose)

Minerals: muscovite, biotite, chlorite, quartz, garnet, feldspar

Diagnostic: wavy texture, glittery

Quartzite

Protolith: sandstone

Texture: massive, unfoliated

Minerals: quartz

Diagnostic: sugary, unfoliated, won’t fizz, hardness of 7

Red Slate

Protolith: mudstone

Texture: slaty, foliated

Minerals: clay minerals

Diagnostic: platey, no visible minerals

Amphibolite

Protolith: basalt, andesite or gabbro

Texture: foliated, liniated

Minerals: amphiboles, hornblende, plagioclase, quartz

Diagnostic: dark, foliated, hornblende abundant

Chlorite Schist

Protolith: mudstone

Texture: foliated

Minerals: chlorite

Diagnostic: green chlorite masses

Andalusite Schist

Protolith: mudstone

Texture: foliated

Minerals: andalusite,

Diagnostic: andalusite porphyroblasts

porphyroblasts

large chunky mineral in a rock (like garnet)

Metamorphism

solid state transformation, starts with a protolith

Agents of metamorphism

heat, pressure, chemically active fluids

Foliation

planar alignment of minerals, also the cleavage planes

Cleavage Forming Processes

1) mechanical rotation

2) flattening and elongation

3) new mineral growth

4) pressure dissolution

2 Main metamorphism environments

Contact Metamorphism: contact with an igneous body adds heat

Regional Metamorphism: tectonics, usually continental collision

2 ways gneiss forms

Transposition: folded rocks break under intense pressure and become parallel

Metamorphic differentiation: minerals arrange themselves into light and dark bands

index minerals: least to most metamorphosed

chlorite

biotite

garnet

staurolite

kyanite

silliminite

2 ways metamorphic rocks are exhumed

erosion: deep erosion and uplift (isostacy)

gravitational collapse: normal faults, no large pressure force anymore

what is a vein

a sealed crack

Closure temperature minerals to tell time of metamorphism

Ar40 to Ar39 concentrations in:

hornblende (480*C)

muscovite (350*C)

biotite (300*C)