Toward the global tectonic model: A new hope (part 2)
We all sense that ultimately ‘nature’ knows best. While we have tried to impose simple models and ordered processes on the world’s geology, we actually continue to encounter nature’s myriad uniqueness. As a result, we have grown comfortable with the butterfly effect of multiple influences randomly expressed at any scale from hand-sample to plate. We observe subsidence occurring offshore Argentina or Somalia while uplift occurs offshore Namibia and assume this is due to local tectonics acting ineffably and unconnectedly. That a sequence is deposited in a stable depositional regime in Angola while shelf collapse and instability produces the geology observed offshore Namibia is more troubling, but such contrasting tectonics acting simulta-neously is again an expression of local plate stresses acting on local geology with non-linear results. This is our experience, so we understand our basin geologies on an isolated basin scale. With no common glue of a process we rely on an understanding of local basin tectonics. And this works but are we missing something? There is hope of finding a glue to hold together our basin models. In the preceding article published in First Break (March, 2017), Hodgson and Rodriguez suggested that the potential for an overarching control on passive margin stability lies in the under¬lying convection patterns in the mantle. A revolutionary method for identifying present-day convection patterns in the mantle has been identified in an extraordinary paper by Hoggard et. al., 2016, which proposes to use deviations of the depth-to-oceanic crust of a given age from a model subsidence curve to indicate crust being uplifted or depressed by underlying convecting mantle. Their observed convection varies dramatically from previous mantle models. In this second article, we explore the potential consequences of this rebel mantle convection model for changing our understanding of geological processes on all the world’s passive margins.