From wide rifts to orogens: A new perspective for Proterozoic tectonics

The thermal structure of the lithosphere influences both the extensional and contractional phases of rift-inversion orogenesis. During the Proterozoic, elevated geotherms likely favored wide rift formation, yet examples of wide rift-inversion orogens are absent from the literature. Using 2-D thermo-mechanical models, we show that narrow rifts formed under colder initial geotherms invert into localized orogenic wedges flanked by foreland basins, largely utilizing rift architecture. Wide rifts formed under warmer initial geotherms, representing Proterozoic conditions, invert into broad, low-relief orogenic plateaus through distributed upper crustal faulting and ductile flow in the underlying lithosphere. Importantly, postrift tectonic quiescence modestly affects narrow rift inversion, primarily widening the orogenic wedge, but fundamentally alters wide rift inversion by promoting lithospheric cooling, embrittlement, and the development of deep contractional shear zones offsetting the Moho by 10−20 km. This wide rift-inversion framework may provide an explanation for distributed shortening and low topographic relief in Proterozoic orogens.