How the Earth Works Exam 3

Metamorphic Rocks, Structural Geology, and Earthquakes

Geothermal Gradient

Temperature increases 25 ° C per kilometer of depth into the Earth

Pressure

from overlying rocks or from collision of plates

Heat

Agent of metamorphism

Plutonic Heat

Heat from a pluton can metamorphose surrounding rocks

Directed pressure

comes from tectonic activity like mountain building and earthquakes

lithostatic pressure

present on buried rock; comes from all directions

Contact Metamorphism

Magma comes into contact with country rock (surrounding rock, pre-exisitng rock) and bakes it; higher degree of metamorphism closer to a pluton

Hot Fluids

super hot water saturated with ions move through rocks and alters them

Regional Metamorphism

occurs over broad geographic areas from large scale events like mountain building

Metamorphic Grade

A measure of how intensely the rock has been metamorphosed

Index Minerals

Minerals that can be used to determine metamorphic grade

Foliation

Another means of determining the metamorphic grade by looking at layering

Slaty Clevage

lowest grade of foliation

Phyllitic Clevage

low grade foliation

Schistosity

intermediate grade of foliation

Gneissic Banding

high grade foliation

Nonfoliated Metamorphic Rock

metamorphic rocks without obvious layering

Marble

Metamorphised limestone

Quartzite

metamorphised quartz sandstone

Metaconglomerate

metamorphic rock whose parent was a conglomerate

Jadelite/Nephrite

metamorphized sodium rich rock or dolomitic marble

Parent rock of marble

Limestone

Parent rock of quartzite

sandstone

Parent rock of amiphibole

Basalt

Parent rock of gneiss

granite

Parent rock of slate

Shale

Chlorite

lowest grade index mineral

Biotite

low-medium grade index mineral

Garnet

medium grade index mineral

Staurolite

higher grade index mineral

Kyanite and Sillimanite

high grade index minerals

Compressive Stress

pushing together

Shortening strains

Makes rock shorter horizontally and taller vertically; can also be bending

Tensional Stress

pulling apart

Stretching or Extensional Strain

makes rocks longer horizontally and shorter vertically

Shearing

displacing; moving rocks to a different position

Elastic strains

rocks that return to normal after being stressed; non-permanent stresses

Dip

the angle between the effect plane and the horizontal plane

Strike

perpendicular to the dip; the direction the rocks are going (length wise)