DOC PREVIEW
WOU ES 104 - Continental Drift

This preview shows page 1 out of 3 pages.

Save
View full document
View full document
Premium Document
Do you want full access? Go Premium and unlock all 3 pages.
Access to all documents
Download any document
Ad free experience
Premium Document
Do you want full access? Go Premium and unlock all 3 pages.
Access to all documents
Download any document
Ad free experience

Unformatted text preview:

I. Continental Drift a. Alfred Wegener—German meteorologist i. Suspected continents were once joined across the Atlantic Ocean—hypothesis suggested by obvious fit of coastlines ii. Supported by restricted range of coastal swamp reptile Mesosaurus— 1. appearing on both South America and Southern Africa, in Permian age rocks, but not elsewhere in the same age rocks 2. if it could swim the Atlantic Ocean to get to the other continent, why was it not more widespread? iii. Set out to find additional evidence to support hypothesis 1. 2.2 billion year old granite in Brazil and Africa 2. similar aged mountain belts from North America to Europe 3. Glacial deposits in tropical areas 4. Equatorial swamp deposits in temperate areas iv. Rejoined land masses into Pangaea in the early Jurassic Period b. Challenged to find a mechanism for continents to plow through the ocean basins i. Suggested tidal forces, but this was easily countered by physicists ii. But just because there were holes, and some misconceptions (plowing through ocean basin) doesn’t make the supporting evidence wrong. II. Plate Tectonics a. Additional data about the nature of our world came to be known throughout the middle of the twentieth century i. Sonar mapped the sea floor 1. showed oceanic ridge system, crossed by fracture zones, and presence of deep arcuate trenches ii. Earthquake studies showed distinct patterns of locations and depths of earthquakes iii. Magnetic data from continents and the sea floor 1. sea floor showed parallel bands of greater and lesser magnetism symmetric across the mid-ocean ridge 2. continents showed location of North Pole relative to the land area had changed through time: Polar Wandering. Each continent had a different path of polar wandering unique to itself. b. Plate Tectonics Paradigm is a ‘super theory’: so well supported and able to explain large amounts of apparently unrelated data i. Earth’s surface is composed of rigid lithospheric plates—from a few km to a few hundred km thick1. These move as coherent units with respect to one another 2. Each plate has little to no internal deformation 3. i.e.: New York moves with respect to London, but the distance between New York and Denver remains essentially the same. ii. There are seven major lithospheric plates, most of which contain both continental crust and oceanic crust, and numerous smaller plates 1. Lithospheric plates a. Contain both crust and uppermost rigid mantle b. Slide over the asthenosphere, which is composed of rocks that are nearly melted 2. crust types a. continental crust is granitic, less dense, more silicic (about 80%) b. oceanic crust is basaltic, more dense, about ½ silica 3. seven major plates a. Pacific b. North American c. South American d. Eurasian e. Australian-Indian f. Antarctic 4. intermediate plates a. Juan de Fuca b. Cocos c. Nazca d. Caribbean e. Scotia f. Philippine g. Arabian 5. over a dozen small plates have been identified of local significance 6. Plate boundaries are defined by earthquake locations iii. plates interact on their edges 1. divergent boundaries—move apart a. mantle material partially melts and magma fills in the gap remaining b. constructive, because building new plate 2. convergent boundaries—move toward one another a. oceanic plate can be overridden and subducted—destructive margin b. continental plate remains buoyant i. will subduct oceanic plateii. two continental plates collide to create mountain range 3. transform boundaries—slide past one another 4. each plate is bounded by a combination of these types of margins—Example: Juan de Fuca Plate a. eastward margin—Cascadia Subduction zone b. western edges—Gorda Ridge, JdF Ridge c. southern sides (connecting ridges to ridges or to trench) are transform boundaries— i. Mendocino Fault: most southerly ii. Blanco Fault: between Gorda and JdF III. Divergent Boundaries a. Moving apart b. Sea Floor spreading at Oceanic Ridges i. Ridge is a relative term 1. 2000-3000 m higher than surrounding sea floor 2. 1000-4000 km wide 3. often contain central ‘rift valley’ ii. ridge exists because of newly created lithosphere 1. made from upwelling, hot melt from mantle 2. hotter things are less dense 3. as sea floor moves away from ridge, it cools a. contracts as it cools, becomes more dense b. increase in lithosphere thickness because cooling strengthens underlying mantle iii. spreading occurs from 2 to 15 cm/yr: average ~5 cm/yr 1. could have created all ocean basins in existence in 200 million years 2. no oceanic crust has been discovered that is over 180 million years old c. divergent boundaries can occur on continents also i. examples 1. East African Rift Valley 2. Rio Grande Rift ii. Characterized by volcanism, faulting, down-dropped areas within uplifted area iii. Continued rifting results in splitting of continent 1. fill with mantle-derived material—dense 2. new lithosphere created becomes oceanic a. floats at level below ocean surface b. Red Sea, for example, or Gulf of


View Full Document

WOU ES 104 - Continental Drift

Documents in this Course
Rocks

Rocks

6 pages

Volcanoes

Volcanoes

65 pages

Minerals

Minerals

61 pages

VolcanoeS

VolcanoeS

81 pages

Minerals

Minerals

45 pages

Minerals

Minerals

61 pages

Volcanoes

Volcanoes

14 pages

Minerals

Minerals

10 pages

Rocks

Rocks

34 pages

Volcanoes

Volcanoes

66 pages

Volcanoes

Volcanoes

10 pages

Volcanoes

Volcanoes

10 pages

Volcanoes

Volcanoes

11 pages

Rocks

Rocks

52 pages

Minerals

Minerals

30 pages

Volcanoes

Volcanoes

56 pages

Volcanoes

Volcanoes

68 pages

Load more
Download Continental Drift
Our administrator received your request to download this document. We will send you the file to your email shortly.
Loading Unlocking...
Login

Join to view Continental Drift and access 3M+ class-specific study document.

or
We will never post anything without your permission.
Don't have an account?
Sign Up

Join to view Continental Drift 2 2 and access 3M+ class-specific study document.

or

By creating an account you agree to our Privacy Policy and Terms Of Use

Already a member?