Metamorphic Rocks

Question 1

Metamorphism

Answer 1

Metamorphic changes occur when a rock is subjected to new temperatures and pressures. Over millions of years, rocks will change mineralogically and texturally until in equilibrium again.

Question 2

Main types of metamorphism

Answer 2

Contact, burial, and regional

Question 3

Contact Metamorphism

Answer 3

When hot magma rises to the surface fo the crust and heats adjacent cooler rocks transforming them.

Question 4

Burial Metamorphism

Answer 4

When sediment is buried ad accumulates under moderate temperatures and pressures transforming them.

Question 5

Regional Metamorphism

Answer 5

When a rock is buried deep into the crust, the elevated pressures and temperatures cause metamorphism. This takes place during mountain building and occurs at much larger scales than a simple intrusion.

When at convergent plate boundaries, it occurs at moderate to deep levels under moderate to ultra-high pressure and temperatures.

Question 6

Types of metamorphism

Answer 6

Regional, high-pressure, contact, seafloor, burial, shock, and regional

Question 7

High-pressure metamorphism

Answer 7

Along linear belts of volcanic arcs, rocks are produced by continent-continent collision and occur at high pressure.

Question 8

Seafloor Metamorphism

Answer 8

Occurs at mid-ocean ridges, where intruding magma drives seawater circulation through extruded basalts.

Question 9

Shock metamorphism

Answer 9

Results from the heat and shock waves of a meteorite impact, transforming rocks at the site.

Question 10

Theory of Techtonics provides a unified view for what types of metamorphism?

Answer 10

contact, regional, and burial

Question 11

Geothermal gradient

Answer 11

The increase in temperature with increasing depth is called the geothermal gradient. On average, it is 20 degrees per km.

Question 12

Plate tectonics affect metamorphic reactions as the processes move ____ rocks from the earth’s surface to the interior where temperatures are ___.

Answer 12

sedimentary

higher

Question 13

As a parent rock is metamorphosed, it progresses from ____ to ____ metamorphic rock.

Answer 13

from low-grade to high-grade

Question 14

Because fo different minerals crystallizing at different temperatures and pressures, a geologist can use a rock’s composition as a _________ to gauge the conditions at which the rock recrystallized.

Answer 14

Geothermometer/geobarometer

Question 15

Metasomatism

Answer 15

Hydrothermal fluids produced during metamorphism can carry dissolved ions and metals. As this water percolates upwards, they react with overlaying rocks they penetrate, changing their chemical and mineral composition.

Question 16

Foliated rocks

Answer 16

Metamorphic rocks show an alignment of minerals, which arises when directed stresses cause minerals to align.

Question 17

How foliated rocks form

Answer 17

1. direct pressure causes sedimentary rocks to form cleavage planes
2. original bedding in a sample is marked by thin sandstone layers
3. regionally metamorphic rock shows foliation by compressive forces
4. Rocks develop foliation when they contain platy of minerals aligning in a preferred orientation (caused by compression).

Question 18

As the intensity of metamorphism increases, so does ____ size and coarseness of _____.

Answer 18

crystalization

foliation

Question 19

Why a number of rocks do not form foliation

Answer 19

They are not initially composed of minerals that naturally align, or the rocks were not subjected to regional metamorphism

Question 20

An example of non-foliated rock formation

Answer 20

contact metamorphism

Question 21

Granoblastic rocks

Answer 21

non-foliated rocks

Question 22

Examples of non-foliated rocks

Answer 22

Hornfel, quartzite, marble, argillite,greenstone, amphibolite, and granulite

Question 23

Hornfel

Answer 23

a high temperature rock derived from shales of uniform grain size that has crystals randomly oriented

Question 24

Quartzine

Answer 24

very hard, dense rocks derived from sandstones

Question 25

Marble

Answer 25

heat and pressure acting on limestone

Question 26

greenstone

Answer 26

low-grade metamorphosed mafic volcanic rocks that tend to form when lavas and ash deposits react with percolating seawater

Question 27

amphibolite

Answer 27

a medium- to high-grade metamorphic product of mafic volcanic rocks

Question 28

granulite

Answer 28

a high grade metamorphic rock formed by the metamorphism of sandstone and many kinds of igneous rocks

Question 29

Porphyroblasts

Answer 29

Some metamorphic minerals may grow into large crystals, surrounded by a much finer-grained matrix. The large crystals called porphyroblasts are found in both contact and regionally metamorphosed rocks. The minerals that grow as the chemical components of the matrix are dissolved or re-organized.

Question 30

Examples of minerals that form porphyroblasts

Answer 30

staurolite and garnet

Question 31

Characteristic of foliated rock

Answer 31

slaty cleavage, schistosity, or gneissic foliation; mineral grains show preferred orientation

Question 32

Characteristics of granoblasts (non-foliated)

Answer 32

granular, characterized by coarse or fine interlocking grains; little or no preferred orientation

Question 33

Metamorphic Facies

Answer 33

a set of mineral assemblages in metamorphic rocks formed under similar pressures and temperatures. Additionally, the kind of metamorphic rocks that results from a given grade of metamorphism depends partly on the mineral composition of the parent rock.

Question 34

Examples of metamorphic facies (from graph)

Answer 34

Zeolite (lowest pressure and temperature), Eclogite and Granulite (highest temperature and pressures)

Question 35

Two essential points of metamorphic facies

Answer 35

1. different kinds of metamorphic rocks form from parent rocks of different compositional the same grade of metamorphism
2. Different kinds of metamorphic rocks form at different grades of metamorphism from parent rocks of the same composition.

Question 36

Isograds

Answer 36

Isograds based on index minerals can be used to plot metamorphic grades over a regional metamorphic belt. This can help us identify where a mountain used to be based on the grades of rocks.