Ch.4Notes

Plate Tectonics

Continental Drift

• 400 years ago

• Magellan and Columbus mapping info

• Similar shoreline

• 1912 Alfred Wegener hypothesized

• Pangaea – 1 land mass

• Panthalassa – all seas

World Map

Evidence of Continental Drift

• Coastlines• Fossils• Mesosaurus – lived 270 million years ago• They cannot swim well• Age and type of rocks Brazil = Africa• Mountain ranges• Coal deposits• Continents joined over South Pole• No force making this happen? • Still not accepted 1930’s

Continental Drift

Sea floor spreading

• 1947

• Out of a ridge in the ocean floor magma flows creating new crust.

• Pushing old crust outward.

• Harry Hess – Princeton, MidAtlantic Ridge

• Arthur Holmes hypothesis in 1930 to put Wegener hypothesis back on map

Sea floor spreading

Sea Floor Spreading

Mid-Ocean Ridges

• Go around the earth

• 80,000 km long

• Undersea mountain range with a valley in the middle.

Mid Atlantic Ridge

Iceland

Earth layers

layers

Paleomagnetism of the ocean floor

• Magma has iron in it.

• Iron aligns with the poles like a magnet

• Reverse polarity in layers 1965

Paleomagnetism of the ocean floor

1960

• Hypothesis of continental drift and seafloor spreading turned into a theory.

The theory of Plate Tectonics

• Explanation of how and why the continents broke apart.

• Construction = tectonics• Crust • 1. oceanic crust• 2 continental crust• Lithosphere – upper mantle• Asthenosphere – solid rock that is under

pressure• 30 different plates

Microplate Terranes

Lithospheric Plate Boundaries

• Boundaries can be anywhere

• Divergent – moving away

• Convergent – moving toward

• Transform Boundaries – moving across

Divergent – moving away

• Plates moving away from each other

• Asthenosphere flows upward to fill in

• Mid-ocean ridge

• Rift valley – center of plate boundary

• Red sea is one

Sea floor spreading

Convergent – moving toward

• Opposite side of divergent• 1. Oceanic crust vs continental crust oceanic is

denser so subduction – goes under, continental crust goes up

• Forms deep ocean trenches• Often forms volcanoes on land• 2. If continental crust plates are even both

crumple and go up (Himalayas)• 3. oceanic and oceanic crusts one is subducted• Deep trench and island arc of volcanoes

Crust layers

Transform Boundaries – moving across

• 2 plates grinding past each other

• Not smooth so many spurts

• San Andreas Fault in California

Causes of Plate Motion

• Movement of lithospheric plates by convection (transfer of heat)

• Convectional current – boiling rice• Ex. Lake turning over• Arthur Holmes

• Radioactivity• thermalconvection

Plate Tectonics

Microplate Terranes

• Theory of plate tectonics refines continental drift theory• Theory of microplate terranes• Scraping of ocean floor materials to land crust

• Separate from other plates (neighbors)• 1. Contains rock and fossils unique• 2. major faults are the boundaries• 3. magnetic properties differ

• Palo Alto – fossils of coral reef• Ocean floor sediments in California mountains• Petosky stones

• FORMATION

Silicification of Paleozoic Era corals such as the Devonian age (416 to 359 million years ago) “Petosky Stone” of the Lake Michigan region (FIGURE 3) or on Prince of Wales Island, Alaska, are attributed to the large amount of siliceous sponges which flourished in the ancient warmer shallow waters. The sponges represent a likely source of mobile silica in the sedimentary pile. As the sponges decomposed, the silica was freed to replace the carbonate rich coral skeletons. Specimens are dominantly gray colored and exhibit a hexagonal pattern typical of primitive coral species

Assignment

• Pg. 71 4.1 Questions 1-4

• Page 77• Sec. 4.2 Questions 1-5

• Page 78-79• Question 1-14

• Testbank• Crossword puzzle

• Assigned • Due • Explain how Sea Floor spreading occurs.• You must include:• - rift valley• - magma• - asthenosphere• iron• magnetism• north and south poles• use a diagram to help explain• where the old rock and new rock is located• why is this important to Alfred Wegeners idea of continental drift• It should take at least 2 paragraphs to explain it in detail.