The previous posts have highlighted some rather awkward questions for the current paradigm of Plate Tectonics (PT). The clearly cyclic nature of the regionally extensive ups and downs, experienced well beyond what is now the Colorado Plateau over at least the past 540Ma, does not appear to have an explanation within the current PT modelling. This is especially a problem given the well documented observations that these vertical movements have also been experienced and are largely synchronised with similar vertical movements across much of the N American craton.
Perhaps the most credible PT model for regionally
experienced vertical motions of the lithosphere is that of “dynamic topography”.
This relies upon temporal and spatial changes in the nature of the convective
motions within the underlying lower mantel. To explain just one of the up and
down cycles observed over the Colorado Plateau would require a convective
motion to be reversed so that a hot up-welling zone, considered in the dynamic
topography model to be the cause of uplift, would need to be transformed into a
cold down-welling zone within the mantle’s convective dynamics. But this would
not seem to be compatible with the observations that whatever is happening in
the region of the Colorado Plateau has also been experienced on a craton wide
basis. In addition, the consideration that similar ups and downs have been recorded
to have occurred synchronously over other continental areas makes it even less
likely that a dynamic topography explanation could be the answer. It does not
seem feasible within any conceivable convective geometry that an upward welling
convective motion could be simultaneously occurring over such widespread areas.
It also seems most unlikely that in what appears to be a regular periodicity of
the ups and downs the convective motion would experience phased reversals to
allow the upwelling to be transformed into a cold down-welling zone – as
required by the reversal of the lithosphere motion.
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