Regional‐Scale Lithospheric Recycling on Venus Via Peel‐Back Delamination

• Published in: Journal of geophysical research. Planets Vol. 127; no. 10
• Main Authors: Adams, A. C., Stegman, D. R., Smrekar, S. E., Tackley, P. J.
• Format: Journal Article
• Language: English
• Published: Washington Blackwell Publishing Ltd 01-10-2022
• Subjects: Asthenosphere; Bend strength; Buoyancy; Coupling; Decoupling; Deformation; Delamination; Isotopes; Lava; Lithosphere; Mathematical models; Numerical models; Plates (tectonics); Recycling; Resurfacing; Rift zones; Subduction (geology); Tectonics; Two dimensional models; Venus; Venus surface; Volcanic activity
• ISSN: 2169-9097; 2169-9100
• DOI: 10.1029/2022JE007460

We currently have a limited understanding of the tectonic framework that governs Venus. Schubert and Sandwell (1995, https://doi.org/10.1006/icar.1995.1150) identified over 10,000 km of possible subduction sites at both coronae and chasmata rift zones. Previous numerical and experimental studies have shown the viability of regional‐scale lithospheric recycling via plume‐lithosphere interactions at coronae, yet little work has been done to study the possibility of resurfacing initiated at Venusian rift zones. We created 2D numerical models to test if and how regional‐scale resurfacing could be initiated at a lateral lithospheric discontinuity. We observed several instances of peel‐back delamination—a form of lithospheric recycling in which the dense lithospheric mantle decouples and peels away from the weak, initially 30 km‐thick crust, leaving behind a hot, thinned layer of crust at the surface. Delamination initiation is driven by the negative buoyancy of the lithospheric mantle and is resisted by the coupling of the plate across the Moho, the significant positive buoyancy of the crust arising from a range of crustal densities, and the viscous strength of the plate. Initial plate bending promotes yielding and weakening in the crust, which is crucial to allow decoupling of the crust and lithospheric mantle. When there is sufficient excess negative buoyancy in the lithospheric mantle, both positively and negatively buoyant plates may undergo delamination. Following a delamination event, the emplacement of hot, buoyant asthenosphere beneath the crust may have consequences for regional‐scale volcanism and local tectonic deformation on Venus within the context of the regional equilibrium resurfacing hypothesis.
Plain Language Summary
The tectonic forces that have shaped Venus' surface over time are currently not well understood. Over 10,000 km of possible subduction sites have been identified on Venus, many of which are located near groupings of rift‐zone trenches called chasmata. Until now, no studies have tested the viability of subduction initiation at a rift zone on Venus. Here, we created 2D numerical models to determine if and how regional‐scale lithospheric recycling events could be initiated at a Venusian rift zone. We observed several cases of a tectonic regime called peel‐back delamination, which occurs when dense lithospheric mantle decouples from the crust and peels away, leaving behind a hot, thinned layer of crust at the surface. Delamination initiation is driven by the negative buoyancy of the sub‐crustal lithospheric mantle, and is inhibited by the coupling of the plate across the Moho, the positive compositional buoyancy of the crust, and the strength of the plate. Unlike subduction, both positively and negatively buoyant plates may undergo delamination if there is sufficient negative buoyancy in the lithospheric mantle. Following a delamination event, the emplacement of hot, buoyant asthenosphere beneath the crust may have consequences for localized volcanism and regional‐scale tectonic deformation on Venus.
Key Points
Dense lithospheric mantle on Venus can decouple from crust at the surface and be recycled into the interior
A regime diagram provides the conditions when peel‐back delamination is favored over stagnant‐lid despite having net‐positive plate buoyancy
Peel‐back delamination may be a source of tectonic/volcanic resurfacing within the framework of regional equilibrium resurfacing