Quiz 2 extended- due tonight before midnight I sent an to everyone on the class roster last night. My address: This is correct- “o” was taken out.

Classes 7 and 8 (combined and condensed because of the snow day) PLATE BOUNDARY TYPES MORE EVIDENCE FOR THE PLATE TECTONICS MODEL FEATURES OF THE OCEAN BOTTOM

1. Evidence existing in early 60’s Distribution of earthquakes Heat flow from the sea floor 2. Testable Hypotheses Generated by Hess and Others “Age of the ocean floor must increase steadily with increasing distance from a mid-ocean ridge.” Thickness and age of sediments on the sea floor –Deep Sea Drilling Program tested this Magnetization of ocean crust- predictions for older areas away from the mid-ocean ridges Evidence for sea-floor spreading and plate tectonics

Earthquakes No Earthquakes

Earthquakes at all plate boundaries Deep (>100km) earthquakes only in subduction zones

x x x x x x Earthquakes occur in zones that follow subducting slabs

Mid- Ocean Ridge Oceanic Plain Central Rift Valley High Heat Flow Lower Heat Flow

Testable Hypothesis: Age of Oceanic Crust and Sediment

Age and thickness of sedimentsAge and thickness of sediments Volcanic featuresVolcanic featuresSeamounts Guyots- flat-topped seamounts Coral atolls Chains of volcanic islands (e.g., Hawaii) Ocean basins - Many features explained by plate tectonics theory

The mantle is NOT liquid!The mantle is NOT liquid! But over many thousands of years, and because the distances are so great, the mantle deforms in a plastic mannerBut over many thousands of years, and because the distances are so great, the mantle deforms in a plastic manner If the earth’s crust gets loaded down (e.g., by a glacier) it will sink lowerIf the earth’s crust gets loaded down (e.g., by a glacier) it will sink lower Similar to a cargo shipSimilar to a cargo ship LESS DENSE MATERIAL “FLOATS” HIGHERLESS DENSE MATERIAL “FLOATS” HIGHER DENSER MATERIAL FORMS DEPRESSIONSDENSER MATERIAL FORMS DEPRESSIONS Isostatic adjustment

Young Oceanic Lithosphere is hotter, and therefore less dense…..“FLOATS” HIGHERYoung Oceanic Lithosphere is hotter, and therefore less dense…..“FLOATS” HIGHER As the lithosphere ages and cools, it “sinks” lowerAs the lithosphere ages and cools, it “sinks” lower This is why mid-ocean ridges are “up” relative the other parts of the ocean floorThis is why mid-ocean ridges are “up” relative the other parts of the ocean floor Isostatic Adjustment and the Ocean Floor

Depth to the Ocean Crust as a Function of Age or Distance from the Mid-Ocean Ridge

Guyots

Guyots 1.Islands 2.Subsidence 3.Waves erode high parts- flattened 4.Subsidence below surface

??????? Coral Atolls

Stationary plume of rising hot mantle material Plate migrates over plume Active volcanoes- over plume Extinct volcanoes- moved away from plume, forming a chain The Hot Spot Theory