Ocean Floor - Plate Tectonics Lecture Notes

Early mapmakers noticed the apparent fit of continents on either side of ocean (matching coastlines)Early mapmakers noticed the apparent fit of continents on either side of ocean (matching coastlines) Continental drift (Wegener)- Earth’s continents had once been joined as PangaeaContinental drift (Wegener)- Earth’s continents had once been joined as Pangaea

Similar fossils of plants and animals found on separated continents with different climates, proves that these continents were once closer to equatorSimilar fossils of plants and animals found on separated continents with different climates, proves that these continents were once closer to equator

Most scientists rejected Wegener's hypothesis-Most scientists rejected Wegener's hypothesis- –Could not explain how or why continents moved

Studies of ocean floor discovered vast, underwater mountain chains and ocean ridgesStudies of ocean floor discovered vast, underwater mountain chains and ocean ridges Rock samples taken from areas near ocean ridges were younger than samples taken from areas near deep sea trenchesRock samples taken from areas near ocean ridges were younger than samples taken from areas near deep sea trenches Oldest seafloor is 180 million years oldOldest seafloor is 180 million years old

Magnetic reversal- change in earth’s magnetic fieldMagnetic reversal- change in earth’s magnetic field –Same as present field- normal polarity –Opposite to present- reversed

Magnetic pattern on one side of a ridge is mirror image of pattern on other sideMagnetic pattern on one side of a ridge is mirror image of pattern on other side

Seafloor spreading- new ocean crust is formed at ocean ridges and destroyed at deep sea trenchesSeafloor spreading- new ocean crust is formed at ocean ridges and destroyed at deep sea trenches –Magma forced toward crust –Fills gaps and hardens –Forms new ocean floor

Theory of plate tectonics- earths crust and upper mantle are broken into slabs called platesTheory of plate tectonics- earths crust and upper mantle are broken into slabs called plates –Plates interact at boundaries

Divergent boundary-Divergent boundary- –Moving apart –Most are found on seafloor –Form ocean ridges –When on continent, form rift valley

Convergent boundary-Convergent boundary- –Moving toward each other –Classified according to type of crust involved –Oceanic crust mostly basalt –Continental crust granite and sedimentary rock –Oceanic-oceanic- subduction occurs (one plate descends) creates deep sea trench, forms arc of volcanic islands: Mariana trench and islands

Oceanic-continental: oceanic is subducted, volcanoes erupt- Peru- Chile trenchOceanic-continental: oceanic is subducted, volcanoes erupt- Peru- Chile trench

Continental- continental: mountains form (Himalayas)Continental- continental: mountains form (Himalayas)

Transform boundary- plates sliding past each otherTransform boundary- plates sliding past each other –Crust is deformed or fractured –Long faults –Shallow earthquakes

Pliocene 4 mya Pleistocene 0.6 mya Late Miocene 10 mya Early Miocene 21 mya Early Eocene 52 mya Late Paleocene 59 mya SJVRocks!! CSUBakersfield Department of Geological Sciences

San Andreas Fault Convection- transfer of energy between Earth’s hot interior and cooler exteriorConvection- transfer of energy between Earth’s hot interior and cooler exterior –Hot mantle less dense than cooler mantle –Hot mantle forced upward to crust –Cooler parts sink back down towards the core

Rising part of convection current spreads out as it reaches the upper mantle and causes both upward and side to side forcesRising part of convection current spreads out as it reaches the upper mantle and causes both upward and side to side forces –Lift and split the lithosphere at divergent boundaries, Material rising from mantle hardens forms new crust –Downward part occurs where a sinking force pulls plates downward at convergent boundary

Mantle Convection

Ridge push- forces in mantle cause asthenoshere to riseRidge push- forces in mantle cause asthenoshere to rise –Pushes oceanic plate toward trench –Could create drag on lithosphere Slab pull- sinking region of mantle convection sucks oceanic plate downwardSlab pull- sinking region of mantle convection sucks oceanic plate downward