Africa Flashcards
What lake formed in Africa? Why?
Lake Malawi- formed as part of mechanical stretching in South Africa. Somalian plate and African plate formed lake Malawi as plate went down and formed a lake. Lots of stress as the plate is being pulled apart
What was created by plate extension?
Afar lowlands- created by plate extension
What formed Tanzanian craton?
Rift zones splits into two parts-western and eastern branch- all this has formed as a consequence of continental divergence
What occurs frequently?
Lots of earthquakes around Lake Malawi, Wester and Eastern brands. Bigger earthquakes occur mainly in central Africa and in the South
What increases from south to north?
Maturity increases from the south to the north:
Rifting progresses in maturity as you go from south to north along the rift
Youngest part of rift is the south and oldest is the North
Why do melt intrusions make the central basin heavy?
Melt intrusions make the central basin heavy because (i) they add extra mass; and (ii) that mass is made up of mafic material from the asthenosphere that is heavier than the more silicic crust. There will therefore be substantial extra gravitational pull downwards
What happened in the first stage?
The rise of the asthenosphere heats, strains and stretches the overlying lithosphere, making a surface basin.
Strain alleviated by creation of large normal fault
Decompression melting meant that heat rose to the surface creating a bulge
Melt intrusions make the basin heavy and cause it to sink isostatically
Isostasy makes the rift move downwards, enhancing asymmetry making the basin heavy and slip along the fault zone. Led to accumulation and formation of lakes
What happened in the second stage?
Asthenosphere continued to rise and lithosphere was too thin so more melt intruded the central basin, creating volcanoes. Melt accumulated at the base. The melt escaped and accumulated between the crust and lithospheric mantle. Strain localized at magmatic intrustions and normal fault became inactive. More volcanoes and less earthquakes
What happened at the third stage?
Seafloor spreading commenced as plates moved apart. Now there is a mid-ocean ridge fuelled by magma from the asthenosphere
What do slower p-wave velocities imply?
Slower p-wave velocities imply that anomalously high temperature, which agrees with the presence of a mantle super plume beneath Africa that extends all the way from the upper mantle to the surface.
What is the plume near Lake Malawi?
One you proceed north to Lake Malawi, the plume gets closer to the surface and causes the asthenosphere to rise upwards, causing early stage rifting dominated by mechanical stretching as explained in Stage (a) in Ebinger’s (2005) model.
