December 25, 2011

When did plate tectonics begin? Not necessarily associated with commencement of significant continent formation?

Filed under: Letters from Ionia — Tags: , , — zankaon @ 2:00 am

When did plate tectonics begin? The early Archean was essentially shallow seas, salty water early on from rifting, shield volcanoes (no viscous silicates, since no oxygen) etc. There were no deep oceans, no mountain building, nor continents, since there was no plate tectonics, nor significant oxygenation. Could one still have uplifting oceanic like plateau (like Ontong java?), but no terranes drifting together, since no plates? How long would it take a crust to cool sufficiently so that it becomes rigid enough for plates? (1) The earth was fully energized from mass aggregation, collisional energy, and core drop from planetesimal to proto-earth. Perhaps 1 billion years or more to cool sufficiently? Stromatolites are present at 3.5 Byrs ago, consistent with shallow seas. If they were wide spread, might this indicate that deep oceans, high mountains, and early continent formation had not yet commenced? Continental material requires oxygenation and resultant differentiation; ~2.5 Byr ago? Did plate tectonics start earlier (1)? Even if so, still significant continental formation might have required oxygenation of sedimentary layers, in addition to cooling and subduction. Thus the start of plate tectonics might not have been the start of significant continent formation; they could have commenced at significantly different times. So was the early and middle Archean, and origin of life, largely just associated with shallow seas; very different from present day plate tectonics, continents, and deep oceanic environments? TMM

1. Shirey Steven, Richardson Stephen, Start of Wilson cycle 3Ga [ago], shown by diamonds from subcontinental mantle, Science Vol 333, July22,2011, and references therein.


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