zankaon

February 20, 2012

Further continental formation? Pacific Ocean permanence?

Filed under: Letters from Ionia — Tags: , — zankaon @ 3:18 am

Continents are lighter than oceanic crust. Oceanic plates tend to subduct under continental crust. The crust is highly oxygenated, such as for silicates. Such oxygenation of crust was not possible until after the great oxygenation stage, when banded iron formation (BIF) occurred ~2.5 byrs ago. Therefore continental formation could not occur until such oxygenation occurred. However could associated cooling over 2 byrs have led to earlier commencement of plate tectonics, without any continent formation? Over the last ~2.5 Byrs fully oxygenated duration, has all lighter crustal material accumulated in continental blocks? Did this process essentially proceed ‘rapidly’ and fully, geologically speaking? Hence then subsequently no significant further continental block growth? Would this seem consistent with only ~24 % earth surface area for over a long geological time, and indefinitely for the future?

Perhaps also consistent with the long persistence of paleoPacific Ocean, and with it’s future long term permanence? Have continental blocks (but not terranes) stayed out of paleo-Pacific for a long time – for ever? Why? Upwelling? Is south Pacific plate portion(s) older, cooler, and thus stiffer? Also might shear stress between upper and lower mantle contribute to early continent formation, directly or indirectly? Or just significance of ~ 400-650 km transition zone? see paleo-Pacific blog. TMM

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