Earth Sciences 1022A/B Lecture 13: Earth Science Lecture March 1 2016

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MARCH 1 2016 LECTURE
MOUNTAIN BUILDING AND CONTINENTAL FRAMEWORKS
Continents rise above oceans due to isostasy
oBuoyant continental lithosphere floats on dense asthenosphere
Thicker lithosphere creates higher mountains with deeper roots
Mountain building processes are collectively called oogenesis
Mountains and Plate Tectonic Environments
Mountain (orogenic) belts parallel plate boundaries in three main settings of continental
margins
Divergent
oMantle plumes, rises, uplifts and splits continental lithosphere to form rift valley
with blocks dropped along normal faults and volcanoes along valley sides
Passive
oRift widens, sea water invades and a new ocean basin forms whose sides
experience no seismic activity but gradually subside under the weight of
sediment load
Convergent
oAs mountains grown, they undergo isostatic adjustments
oAndean-type
Oceanic crust subducts beneath continental crust
Develops accretionary wedge, continental volcanic arc and
plutons in the core of deformed mountain belts
oAleutian-type
Oceanic crust subducts under oceanic crust to form volcanic island arc
oContinental collision
Ocean basins close, subduction stops
This leads to the highest mountains forming
oAccreted terranes
Foreign pieces of crust forcefully attached to continental margin
Wilson cycle
oOceans opened and closed, mountains built and rebuilt repeatedly
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