Mountain building & the evolution of continents Chapter 20 Mountain building & the evolution of continents

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

2) Isostacy and crustal uplift Abundant evidence for uplift exists

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

3) 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 building Subduction zones (convergent plate boundaries) Ocean-ocean boundaries (Aleutian-type) Generates a volcanic arc Ocean-continent boundaries (Andean-type) 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

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

Formation of the Appalachians

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

Endicott Mtns, Alaska

4) 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 recycling oceanic crust

4) Evolution of continental crust T&L Figure 20.19

Current uplift or subsidence in the U.S.