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Mountain building & the evolution of continents Chapter 20.

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1 Mountain building & the evolution of continents Chapter 20

2 1) Mountain belts “Orogenesis” = mountain building Mountain belts = continuous mountain ranges v Huge horizontal forces in the crust build mountains v Signs of such forces: folding, faulting, metamorphism, igneous activity v Huge horizontal forces in the crust build mountains v Signs of such forces: folding, faulting, metamorphism, igneous activity

3 2) Isostacy and crustal uplift Abundant evidence for uplift exists

4 2) Isostacy and crustal uplift Let’s talk about gravity. “isostacy” = gravitational balance

5 3) Mountain building u many “young” mountain belts ( < 100 million years old) u mountain belts usually parallel folded/faulted ridges u sedimentary or volcanic rocks, usually intruded by igneous bodies - Western Americas - Himalayas - NW Pacific, etc

6 3) Mountain building Subduction zones (convergent plate boundaries) Ocean-ocean boundaries (Aleutian-type) Ocean-continent boundaries (Andean-type) Generates a volcanic arc 1st: a passive continental margin (like east coast of US) 2nd: turns into an active margin, subduction initiates 3rd: deformation, metamorphism: 2 parallel zones: accretionary wedge and volcanic arc

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8 3) Mountain building Subduction zones (convergent plate boundaries) Subduction zones (convergent plate boundaries) Continental collisions Appalachians

9 Formation of the Appalachians

10 3) Mountain building “Continental accretion” “Continental accretion” Small island arcs or “mini-continents” can be added to continents Example: Western N. America

11 Endicott Mtns, Alaska

12 4) Evolution of continental crust Not well known. Different ideas: l Continents evolved early in Earth’s history l Gradual evolution of the continents During Earth formation, light stuff quickly rose to surface and formed crust Continents slowly grow in the process of recycling oceanic crust

13 4) Evolution of continental crust T&L Figure 20.19

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15 Current uplift or subsidence in the U.S.


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