Abstract

Previous attempts to explain Paleoproterozoic post-tectonic magmatism in the Penokean and southern Trans-Hudson orogens inadequately account for the entire tectonic setting and geologic history of these areas. Key characteristics of post-tectonic plutonism in both orogens include the similar time-lag of emplacement after orogenesis (50–60 m.y.), the close association in both time and space between post-orogenic uplift and intrusion, the depth of emplacement, and the long-lived tectonic quiescence (crustal stabilization) that followed magma emplacement. Post-tectonic magmatism appears closely associated with post-orogenic uplift (collapse) and crustal stabilization. I propose that convective removal of the mantle lithospheric root may best explain post-tectonic magma genesis. Such a model suggests that there is a simple and related evolutionary history that began with construction of the Penokean and southern Trans-Hudson orogens (crustal thickening, metamorphism, plutonism, etc.) and ended with their destruction (crustal thinning, widespread uplift/cooling, plutonism, etc.), thus stabilizing the crust. Post-tectonic plutons may be an indelible mark of orogenic demise, not the culmination of terminal collision. Delamination-magmatism probably played a key role in the differentiation and stabilization of crust after orogenesis and may have promoted its transformation into craton.

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