ODE Exam 3- Metamorphism and Metamorphic Processes

Metamorphism

Changes in mineral chemistry and textures in solid state due to changes in pressure, temperature, or fluids

Protolith

The original rock from which a metamorphic rock forms

Foliation

Layering in metamorphic rocks caused by a parallel alignment of sheet-like minerals (micas, biotite, muscovite)

Index Minerals

Minerals sensitive to temperature and pressure changes that indicate the grade of metamorphism

Contact Metamorphism

Metamorphism that occurs when hot magma heats surrounding rocks in a limited area.

no foliation

low pressure and temp

Regional Metamorphism

occurs over large areas due to tectonic forces, radioactive decay, and magma often resulting in higher and directed foliated textures

Lithostatic Pressure

Uniform pressure exerted in all directions by the weight of overburden.

Directed Pressure

Non-uniform pressure that arises from tectonic activity, leading to foliation.

Hydrothermal Metamorphism

occurs due to the action of hot fluids, enhancing ion migration and altering rock chemistry.

low grade metamorphism

metamorphism at lower temperatures and pressures, typically producing finer-grained rocks like slate.

high grade

Metamorphism at higher temperatures and pressures, resulting in coarser-grained rocks like gneiss.

Marble

A non-foliated metamorphic rock formed from limestone, primarily composed of calcite.

Quartzite

A non-foliated metamorphic rock formed from sandstone, primarily composed of quartz.

Garnet

An index mineral used to determine the grade of metamorphism, often found in schist

Schist

A medium-grade metamorphic rock with visible mica minerals, formed from shale

Anthracite

A high-grade coal that forms under high temperatures and pressures

Slaty Cleavage

A type of foliation in slate characterized by thin, flat layers

temperature main heat sources

original heat- from when earth formed

radioactive decay- adds new heat

magmas- may release heat to surrounding rock

temperature effects

stability of minerals (the pressure and temp at which given mineral is stable)

reaction rates (kinetics)- migration rates of ions

bedding plane does or does not equal foliation

does not

sedimentary bedding

horizontal foliation

slaty cleavage

vertical foliation

schist minerals- examples

biotite, muscovite, garnet, chlorite, kyanite, staurolite

gneiss minerals

biotite, hornblende

prolith for shale, phyllite, schist, gneiss

shale

marble dominate minerals

calcite

quartzite dominate minerals

quartz

anthracite coal dominate minerals

carbon, plant material

sources of fluids

trapped in pore spaces between grains

structurally bound in minerals

magmas may release water to surrounding when the magmas crystallize

fluid characteristics

increase migration rates of ions

alter rocks chemistry

mobile

leach ions out of minerals

hydrothermal metamorphasis of seafloor

hot water rises reacts with rock

metamorphism occurs

water heats up

cold water sinks into crust

longer duration of metamorphism allows more ____ for minerals to reach equilibrium (stability)

time

what causes regional-scale metamorphism

burial and plate tectonics

why are high grade rocks found at earths surface (why don’t they react back to lower temp minerals during uplift and cooling)

decreasing temps during uplift and cooling, so reaction rates are slowed ~exponentially as temp decreases