90-3 Multi-Stage Lithospheric Drips Drive Topographic Evolution of Sedimentary Basins and Orogenic Plateaus: Insights from Analogue and Numerical Modelling

Abstract:

Seismic tomography surveys reveal regions of  “missing” continental lithosphere that manifest as slow seismic wave speed in gaps of seismically fast mantle lithosphere or columns of seismically fast, cold/dense mantle lithosphere descending into the sub-lithospheric mantle. Such findings have been interpreted as evidence of lithospheric “dripping” whereby gravitationally unstable, high density anomalies in the mantle lithosphere sink or “drip” into the underlying sub-lithospheric mantle. As the mantle lithosphere drips, it thins, removing a portion and leaving a gap that is filled by upwelling sub-lithospheric mantle. This produces crustal tectonics where the dripping lithosphere induces surface subsidence, and horizontal tractions causing thickening, folding/faulting of the crust above the drip. Lithospheric dripping has been  linked to the topographic evolution of sedimentary basins within orogenic plateaus, while simultaneously large-scale lithospheric removal has been linked to uplift of the plateaus themselves. Thus far, our understanding of the surface manifestations of deeper mantle processes remains unresolved. Furthermore, the link (if any) between basin scale deformation and plateau scale uplift through lithospheric dripping processes has not been established. Three dimensional, scaled, analogue models and high-resolution optical image correlation techniques are used in conjunction with two dimensional numerical models to demonstrate that basin topographic evolution and plateau scale uplift may be linked through a process of multi-stage dripping. Furthermore, the models demonstrate that lithospheric drips differ in their surface manifestations where some drips induce significant shortening in the crust, while others do not and are further differentiated by the scale (small or large) of lithosphere removed. These deeper mantle lithosphere processes may be identified by the topographic changes over time in the crust. This research provides insight into the dynamics between the mantle and upper crust and the tectonics that drive topographic evolution of orogenic plateaus.

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