3-D Analysis of Lithospheric 'Super-Drips': Insights From High Resolution Analog Models

Various geodynamic hypotheses have been put forward to explain the evolution of felsic and mafic crust and the underlying mantle lithosphere that evolved since Archean. The continental crust is deformed through large scale epeirogenic plate motions including plateau uplifts, basin formations which may also be formed on planets that contain no significant record of plate tectonics (e.g Venus). The age of the beginning of modern style plate tectonics on Earth is uncertain where global stagnant lid tectonics may have been operating through mantle overturns, super-plumes and 'super-viscous drips' in which mantle upwellings and downwellings also occur simultaneously with orogenesis. In this work, our focus is on the —viscous drip (instability) models—where mantle upwellings develop in response to the descent of the gravitationally unstable lithosphere. We perform 3-D scaled laboratory (analog) experiments with high resolution Particle Image Velocimetry (PIV) to quantitatively analyze the interplay between the dynamic evolution of the lithospheric drips, its associated mantle counter-flow and subsequent surface elevation response. The first set of experiments investigates the role of these instabilities for the geodynamic evolution of the non-plate tectonics planetary environments (e.g. Venus), possibly the Archean earth and continental interiors. The model design includes the upper and lower crust, underlain by sub-crustal mantle lithosphere and asthenospheric mantle. The dripping lithospheric mantle into the asthenosphere pulls the crust down and thickens/shortens it while surface basin develops with drainage patterns towards the basin centre. The surface elevation increases when the drip evolves in the necking/thinning stage. In conjunction with the main lithospheric instability, small-scale secondary instabilities develop and they also show similar surface manifestations in the model box. In the second set of experiments we examine the role of lower crustal flow and thickening above the mantle lithosphere on the initiation of mantle lithosphere instabilities, specifically under the magmatic arcs. These experiments consider nearly the full width of plate subduction including accretionary complex, arc roots, and the imposed plate convergence on the margin of the model domain.