Mountain building & the Mountain building & the evolution of continentsevolution of continents

Chapter 20Chapter 20

1) Mountain belts1) Mountain belts

““OrogenesisOrogenesis”” = mountain building = mountain building

Mountain beltsMountain belts = continuous mountain ranges = continuous mountain ranges

Huge horizontal forces in the crust build mountainsHuge horizontal forces in the crust build mountains

Signs of such forces: folding, faulting, metamorphism, igneous activitySigns of such forces: folding, faulting, metamorphism, igneous activity

Huge horizontal forces in the crust build mountainsHuge horizontal forces in the crust build mountains

Signs of such forces: folding, faulting, metamorphism, igneous activitySigns of such forces: folding, faulting, metamorphism, igneous activity

2) Isostacy and crustal uplift2) Isostacy and crustal uplift

Abundant evidence for uplift exists

2) Isostacy and crustal uplift2) Isostacy and crustal uplift

Let’s talk about gravity.

“isostacy” = gravitational balance

3) Mountain building3) Mountain building

many “young” mountain belts ( < 100 million years old)

mountain belts usually parallel folded/faulted ridges

sedimentary or volcanic rocks, usually intruded by igneous bodies

- Western Americas- Himalayas- NW Pacific, etc

3) Mountain building3) Mountain building

Subduction zones (convergent plate boundaries)

Ocean-ocean boundaries (Aleutian-type)

Ocean-continent boundaries (Andean-type)

Generates avolcanic arc

1st: a passive continental margin (like east coast of US)2nd: turns into an active margin, subduction initiates3rd: deformation, metamorphism: 2 parallel zones: accretionary wedge and volcanic arc

3) Mountain building3) Mountain building

Subduction zonesSubduction zones (convergent plate boundaries) (convergent plate boundaries)

Continental collisionsContinental collisions

Appalachians

Formation of the AppalachiansFormation of the Appalachians

3) Mountain building3) Mountain building

““Continental accretion”Continental accretion”

Small island arcs or “mini-continents”can be added to continents

Example: Western N. America

Endicott Mtns, Alaska

4) Evolution of continental crust4) Evolution of continental crust

Not well known. Different ideas:

Continents evolved early in Earth’s history

Gradual evolution of the continents

During Earth formation, light stuff quickly rose to surface and formed crust

Continents slowly grow in the process of recyclingoceanic crust

4) Evolution of continental crust4) Evolution of continental crust

T&L Figure 20.19

Current uplift or subsidence in the U.S.Current uplift or subsidence in the U.S.