IMS 4 - Plate Tectonics

Ocean bottom moves 1 ½ to 6 inches / year

Continental Drift Theory (Alfred Wegener)

-          All land masses grouped in 1 supercontinent Pangaea, global ocean Panthalassa

-          North America & Eurasia (Northern) split form Laurasia, Africa, South America, India, Australia, Antarctica (Southern) form Gondwanaland

-          Move over surface by slow current of molten rocks; 35 million years ago alike now

-          Pacific shrink, Atlantic & Indian Ocean inches wider / year

-          Red Sea: 25 million yrs widening, width of Atlantic in 200 million yrs

Mid-Ocean Ridges

-          Tectonic plates gradually part, gap filled by magma (seafloor hot springs & chemical heat source)

Plates

-          7 major: Indian-Australian, Eurasian, Pacific, African, Antarctic, North American, South American

-          7 minor: Cocos, Nazca, Arabian, Philippine, Caribbean, Scotia, Juan de Fuca

Plate boundaries

-          Divergent: new volcano/sea floor, continental breaking

(Crust sinks when stretched thin; usually in deep seafloor)

-          Convergent: Wider trench, mountain building

ü  Oceanic-continental: Light continental crust rides over denser oceanic crust (subduction zone)

Volcanic/trench, Eg: Peru-Chile Trench, Andes Mt.

ü   Oceanic-oceanic: Denser oceanic plate subducts

Eg: Mariana trench

ü  Continental-continental: No subduction, Collision form uplifted mountain range (massive deformation)

Eg: Himalayan Mt. (Indian & Eurasian plates meet) 1cm growth/year

-          Transform: Seafloor conserved

Eg: San Andreas fault between Pacific & North American plate

-          Hotspots exudes lava

-          Plate boundary zones

Hydrothermal vent

-          Seafloor geyser, super hot, mineral rich (dissolved metals) water gushes

-          Along mid-ocean ridge seafloor with volcanic activity avr. depth 2100m

-          Water enter seafloor cracks heated by molten rock to 400°C

Ocean	Area (million square km)	Average Depth (m)	Deepest depth (m)
Pacific Ocean	166.241	4,638	Mariana Trench 11,034
Atlantic Ocean	86.557	3,926	Puerto Rico Trench 8,605
Indian Ocean	73.426	3,963	Java Trench 7,725
Southern Ocean	20.327	4,000 – 5,000	The southern end of the South Sandwich Trench 7,235
Arctic Ocean	13.224	1,200	Eurasia Basin 5,450