Chapter 20 Mountain building the evolution of continents

Chapter 20 Mountain building & the evolution of continents 1. Mountain belts 2. Mountain building 3. Continental accretion 4. Uplift, Basin and Range , Southern Rocky mountains

Study questions üWhat is the geologic history of the Basin and Range province and southern Rocky mountains? üWhat is an accreted terrane and where do they originate? What is the connection with plate tectonics? üWhat is the geologic history of the Himalayas and Appalachians?

1) Mountain belts “Orogeny” = 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

1) Mountain belts u many “young” mountain belts ( < 100 million years - Western Americas old) - Himalayas (45 million yrs ago) - NW Pacific, etc u. Paleozoic and Precambrian-age mountains (> 250 million Yrs old) - Appalachians - Urals u mountain belts usually parallel folded/faulted ridges u sedimentary or volcanic rocks, usually intruded by igneous bodies Fig. 20. 1+19

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

2) Mountain building Subduction zones (convergent plate boundaries) Continental collisions (examples: Himalayas, Appalachians) Himalayas Fig. 20. 13, 14, 15

2) Mountain building Subduction zones (convergent plate boundaries) Continental collisions (examples: Himalayas, Appalachians) Himalayas Fig. 20. 15

2) Mountain building Subduction zones (convergent plate boundaries) Continental collisions Appalachians Valley and Ridge Province in Pennsylvania Fig. 20. 4

Formation of the Appalachians

3) Continental accretion “Continental accretion” Small island arcs or “mini-continents” can be added to continents Accreted crustal blocks= terranes Example: Western N. America Fig. 20. 11 Fig. 20. 12

4. Uplift, Basin and Range, Southern Rockies Fig. 20. 5 See Fig. 20. 6

Northern Rocky Mountains, British Columbia Deformed sedimentary rock from continental shelf deposits displaced by low angle thrust faults toward the interior of Canada.

Basin and Range Fault-block mountain ranges and rift valleys

4. Uplift, Basin and Range, Southern Rockies Current uplift or subsidence in the U. S.

Sample MC Where are the oldest rocks in North America located? A. B. C. D. in the Appalachian Mountains in the Basin and Range province in the Canadian Shield in the Rocky Mountains

Sample MC In which of the following settings were most of the rocks of the interior platform of North America deposited? A. B. C. D. in a continental rift in a deep ocean basin in an extensive shallow sea in a volcanic island arc

Sample MC Why is the North American Cordillera topographically higher than the Appalachians? A. because the Appalachians have undergone less erosion B. because the Cordillera formed by continent-continent collision C. because the main orogeny in the Cordillera was more recent D. because the spreading rate of the East Pacific Rise is greater than the spreading rate of the Mid-Atlantic Ridge

Sample MC Which of the following processes is responsible for the topography of the Basin and Range province in western North America? A. B. C. D. normal faulting strike-slip faulting thrust faulting upwarping

Sample MC In which of the following regions is new material currently being added to the crust? A. B. C. D. Appalachian Mountains Canadian Shield Cascade Range Rocky Mountains

Sample MC Which of the following mountain belts formed as a result of a collision between two continents? A. B. C. D. Appalachians Himalayas Urals all of these

Sample MC What type of faults are depicted in the cross section? A. B. C. D. normal faults strike-slip faults thrust faults cannot tell from the information given