EESA06 Lecture 3
How continents Break Up and Oceans Open
๎€Mantle movement creates - Triple junctions โ€“ 3 major fractures
oMiddle of continent, dome forms above plume,
oOutward flow from plume creates rifts
oOnly one rift develops into an ocean
๎€Failed rifts are preserved in modern continents from the breakup of Pangea โ€“ they
just sit there and may fill up with sediments
๎€Example of failed rifts in Canada: Ottawa river valley and St. Lawrence river valley
oControl river flow, generate earthquakes
Stage 1: East African Rift
๎€Continent undergoes extension, the crust is thinned and a rift valley forms
Stage 2: Red Sea
๎€Continent tears in two, continent edges are fractured and uplifted, Basalt eruptions
form oceanic crust
Stage 3: Atlantic Ocean
๎€Continental sediments blackout the subsiding โ€œpressureโ€ margins to keep
continental shelves, the ocean widens and a mid-ocean ridge develops as in the
Atlantic Ocean
Difference between a Sea and an Ocean
๎€Ocean has a mid-ocean ridge, and always widening
๎€Seas do not widen
East African Rift System
๎€Continental breakup and birth of a new ocean
๎€Somalian plate โ€“ the โ€œhornโ€ of Africa will break away and become an ocean
๎€Triple Junction - Gulf of Aden, Red Sea, Lake Turhana (one of these will become an
ocean)
Arabian Plate
๎€Pushed north by the widening of the red sea
Fissures โ€“ cracks in the earthโ€™s crust
๎€Basaltic magma comes out thru the fissures, generates flood basalts
Ash layers โ€“ can put an age on it
Early hominids started in East African Rifts โ€“ Kariandusi (layer of ash founder hammers)
๎€Homohabilis โ€“ tool maker hominids
Where is an ocean opening today?
๎€When there are lots of oceans there is lots of food โ€“ rich ecosystem, key step of
human evolution took place when there were large oceans
Afar Triangle โ€“ Rift widening, famous for human evolution (Lucy โ€“ australopicthin)
www.notesolution.com
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Document Summary

mantle movement creates - t r iple junctions 3 major fractures: middle of continent, dome forms above plume, outward flow from plume creates rifts, only one rift develops into an ocean. Failed rifts are preserved in modern continents from the breakup of pangea they just sit there and may fill up with sediments. example of failed rifts in canada: ottawa river valley and st. lawrence river valley: control river flow, generate earthquakes. continent undergoes extension, the crust is thinned and a rift valley forms. continent tears in two, continent edges are fractured and uplifted, basalt eruptions form oceanic crust. continental sediments blackout the subsiding pressure margins to keep continental shelves, the ocean widens and a mid-ocean ridge develops as in the. ocean has a mid-ocean ridge, and always widening. continental breakup and birth of a new ocean. somalian plate the horn of africa will break away and become an ocean.

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