Metamorphism

Spitsbergen, Arctic Norway

Rock folding

Scotland

Antarctica

Mineral Alignment: Foliation

Contact Metamorphism

Heat from magmaalters surroundingcountry rock. Nopressure.

Regional Metamorphism

Heat and pressureon a regional scale.

With increasing heat and pressure, minerals break down and recrystallize.As this happens, rock types change.

Metamorphic Grade

Certain minerals are stable only at specific temperaturesand pressures.

Appalachians: Coreof ancient mountainrange is exposed.

Metamorphic Facies

Facies Definitive Mineral Assemblage in Mafic Rocks

Zeolite zeolites: especially laumontite, wairakite, analcime

Prehnite-Pumpellyite prehnite + pumpellyite (+ chlorite + albite)

Greenschist chlorite + albite + epidote (or zoisite) + quartz ± actinolite

Amphibolite hornblende + plagioclase (oligoclase-andesine) ± garnet

Granulite orthopyroxene (+ clinopyrixene + plagioclase ± garnet ±

hornblende)

Blueschist glaucophane + lawsonite or epidote (+albite ± chlorite)

Eclogite pyrope garnet + omphacitic pyroxene (± kyanite)

Contact Facies

After Spear (1993)

Table 25-1 . Definitive Mineral Assemblages of Metamorphic Facies

Mineral assemblages in mafic rocks of the facies of contact meta-morphism do not differ substantially from that of the corresponding regional facies at higher pressure.

Suites of minerals indicate specific range of T & P.

Shelf Sediments

Accumulation of sands and muds. 10,000-15,000 feet thick.

Folded Appalachians

Under stress and strain, rocks behave in two different ways:

1) Brittle deformation. Low temperature, high pressure.Rocks fracture: faults

2) Ductile (plastic) deformation. High temperature, lowto medium pressure. Rocks deform: folds

Types of Deformation

Folded Rocks

Anticlines and Synclines

Plunging Folds

Plunging folds

Dome and Basin

Michigan Basin

Fault Definitions

Normal Fault

Hanging wallmoves downrelative to thefootwall.

Creates gentle mountain front, not steep

Horst and Graben

Basin and Range Province

Normal faults

Result of tensional stress -- crustal extension. The crust in this part of the world is beingpushed up on from below.

Horst Photo

Reverse Fault

Hanging wall moves uprelative to the footwall.

Wasatch Fault

Very steep imposing mountain front

Thrust Fault

Low-angle (<20o)reverse fault.

Many thrust faults do not outcrop at the surface -- they remain underground -- and aremapped seismically. Most recent ‘quakes in LA were from slippage along previously-unknownthrust faults.

San Andreas Fault

Strike-Slip Fault

No vertical movement

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San Andreas Fault

Fault

Offset stream

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Putting it all together ---Brittle and ductile deformation of rocksduring the formation of the AppalachianMountains.

World Mountain Chains

Geologic Time Scale

Mass Extinctions75% of species extinct

90% of species extinct

Why?

ELE

Impact Crater