Earth Sciences 1022A/B Lecture 7: Earth Science Lecture January 28 2016

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JANUARY 28 2016 LECTURE
METAMORPHIC ROCKS
Rocks can be deeply buried, intruded by magma or squeezed
oThey are subjected to heat, pressure, and chemically active fluids
These agents result in metamorphism
Controlling Factors
Parent Rock
oMetamorphic rock retains much the same chemistry at the parent
Heat
oDrives chemical reactions that crystallize mineral in the parent rock as it bakes
Heat from magma intrusion and from deep I the Earth
Geothermal gradient
Pressure
oConfining pressure or directed pressure under which minerals realign to form a
new texture
From all directions, by colliding lithospheric pates, foliation
Chemical Activity
oWater is important in mineral transformations
Commonly loaded with ions in the rock’s pore spaces and water is also
released from minerals on heating to react with minerals in the parent
rock to form new minerals
Metamorphic Grade
The intensity of metamorphism
oIncreases mainly with temperature as indicated by index minerals in
metamorphic rocks
Contact Metamorphism
Caused by magma intrusion into cooler parent rocks
oResults in metamorphic aureoles with decreasing effect away from the intrusion
Host rock minerals recrystallize to new minerals but are not reoriented
Nonfoliated
oe.g. Marble from baking limestone, quartzite from baking
sandstone
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