Chapter 8 - Metamorphic Rocks

Calcite is the main mineral constituent of the sedimentary rock limestone and of the metamorphic rock marble. True False

True

Hydrothermal metamorphism involves chemical reactions between hot fluids and surrounding rocks such as occurs beneath mid-ocean ridges True False

True

Rank the following metamorphic rocks in order of increasing grade of metamorphism: schist, granulite, phyllite, slate, gneiss.

slate phyllite schist gneiss granulite

Describe how foliation is produced in a metamorphic rock (3 mechanisms)

1. preferred mineral orientation - perpendicular to stress 2. alternating mineral bands - compositional layers (light and dark) 3. mineral flattening - grains elongate and flatten

What is cataclastic metamorphism?

A high-pressure metamorphism resulting from the crushing and shearing of rock during tectonic movement, mostly along faults. Cataclastic metamorphism is generally localized along fault planes (areas of detachment where rocks slide past one another). Cataclastic Metamorphism produces sheared, highly deformed rocks called mylonites.

During metamorphism, what is the major effect of chemically active fluids? Increase the pressures in deeply buried, regional-metamorphic zones Aid in the movement of dissolved silicate constituents and facilitate growth of the mineral grains Prevent partial melting so solid rocks can undergo very high temperature regional metamorphism Inhibit the formation of schistosity in hornfels and quartzite

Aid in the movement of dissolved silicate constituents and facilitate growth of the mineral grains

What are index minerals?

An index mineral is used in geology to determine the degree of metamorphism a rock has experienced. Depending on the original composition of and the pressure and temperature experienced by the protolith (parent rock), chemical reactions between minerals in the solid state produce new minerals.

In which setting would regional metamorphism be most likely? At shallow depths adjacent to an igneous intrusion At shallow depths along major transform faults in the continental crust At great depths in the crust where two continents are colliding At shallow depths beneath the seafloor where water pressures are immense

At great depths in the crust where two continents are colliding

What term describes the zone of contact metamorphism surrounding an intrusive magma body? Schistosity Migmatite Metasomatism Aureole

Aureole

Which of the following metamorphic rocks forms at very high pressures but moderately low temperatures associated with subduction of oceanic crust and sediments? Mylonite Migmatite Marble Blueschist

Blueschist

Which one of the following is not likely to be genetically associated with impact of an asteroid or large meteorite? Tektites Blueschists Coesite Impact crater

Blueschists

Amphibolite is a foliated metamorphic rock composed principally of hornblende and plagioclase. How does it form? By contact metamorphism of sandstone adjacent to a granitic batholith By regional metamorphism of volcanic rocks such as andesite and basalt By gouging and crushing of limestone along a fault By the impact of a meteor on interbedded sandstone and shale

By regional metamorphism of volcanic rocks such as andesite and basalt

What is hydrothermal metamorphism?

Chemical reactions between the heated seawater and basalt result in metamorphism of the basalt. Hydrothermal metamorphism can also occur on continents where crustal rocks are metamorphosed by invading, hot fluids associated with igneous intrusions.

Name two common platy minerals that produce foliation in metamorphic rocks. Can non-platy minerals exhibit foliation (think metaconglomerate)?

Chlorite, Mica Yes

What are the differences between burial and regional metamorphism?

Contact metamorphism is a type of metamorphism where rock minerals and texture are changed, mainly by heat, due to contact with magma. Regional metamorphism is a type of metamorphism where rock minerals and texture are changed by heat and pressure over a wide area or region.

What type of stress is most likely to produce foliation in metamorphic rock?

Differential stress

Foliated metamorphic rocks are composed largely of equidimensional grains of minerals such as quartz and calcite. True False

False

Which of the following terms describes the strong, parallel alignment of coarse mica flakes and/or of different mineral bands in a metamorphic rock? Rock cleavage Foliation Stress streaking Marbleizing

Foliation

Which of the following metamorphic rocks is characterized by the segregation of light- and dark-colored minerals into thin layers or bands? Garnet hornfels Gneiss Slate Quartzite

Gneiss

Which of the following metamorphic rocks forms at the highest grade of regional metamorphism? Hornfel Granulite Schist Slate

Granulite

What metamorphic rock forms by contact metamorphism of mudstones and shales? Hornfels Marble Gneiss Schist

Hornfels

Which of the following metamorphic rocks forms from the metamorphism of limestone or dolostone? Migmatite Amphibolite Marble Quartzite

Marble

What platy, parallel, mineral grains are the most visual aspect of foliated metamorphic rocks? Micas Feldspars Calcite Quartz

Micas

What metamorphic rock is thought to form by partial melting and in situ crystallization of the melted portion? Blueschist Eclogite Migmatite Amphibolite

Migmatite

How do migmatites form?

Migmatites are found in high-grade metamorphic terrains where a sequence from high-grade metamorphic rocks through migmatites to granite bodies is often seen in the field. The granite component is thought to form by partial melting of the rock during extreme metamorphism.

Which of the following best describes the conditions of contact metamorphism? Pressures are low, the rocks are shallow, and geothermal fluids are the source of metamorphic reactions Pressures are fairly low, the rock is in the upper part of the crust, and heat is supplied from a nearby magma body Heat is generated by shearing and mechanical movements along faults Occurs deep within a subduction zone where temperatures are moderate but pressures are high enough to cause intense deformation

Pressures are fairly low, the rock is in the upper part of the crust, and heat is supplied from a nearby magma body

Which of the following metamorphic rocks typically forms by metamorphism of a sandstone? Marble Slate Amphibolite Quartzite

Quartzite

What type of foliation results from the parallel alignment of abundant, coarse-grained mica flakes in a metamorphic rock? Gneissic banding Slaty cleavage Phyllitic structure Schistosity

Schistosity

Which low-grade metamorphic rock, composed of extremely fine-sized mica and other mineral grains, typically exhibits well-developed rock cleavage? Marble Hornfels Quartzite Slate

Slate

What are the agents of metamorphism?

The agents of metamorphism include heat, pressure (stress), and chemically active fluids.

What are migmatites?

a rock composed of two intermingled but distinguishable components, typically a granitic rock within a metamorphic host rock.

Which of the Following would exhibit sheared and mechanically fragmented rocks? a. Fault movements at shallow depths b. Hydrothermal metamorphism at a mid-ocean ridge c. Heating of shale and mudstone near an igneous intrusion d. Burial metamorphism of volcanic rocks

a. Fault movements at shallow depths

What is the difference between differential stress and confining pressure?

confining pressure

What is the difference between differential stress and confining pressure?

confining pressure - Pressure applied equally on all surfaces of a body. differential stress - stress applied unequally and predominates in one direction

In what tectonic environment do blueschists and eclogites form?

progressive metamorphism of basalt blueschist - very high pressures, relatively low temperatures eclogites - extremely high pressures, moderate-high temperatures

Identify the parent rock for each of the following metamorphic rocks: slate, quartzite, marble, greenstone, and anthracite.

slate ---> shale quartzite ---> sandstone marble ---> limestone greenstone ---> basalt anthracite ---> bituminous coal

What is Contact Metamorphism?

usually occurs where high temperatures are restricted to a small area, generally around the margins of an igneous intrusion. Geothermal gradients are high.