Constraining Lithospheric Delamination on Venus with Flexural Topography and Trench Geometry

Andrea Adams, Suzanne Smrekar, Michael Gurnis, Dave Stegman , Paul Tackley

Rollback-style lithospheric recycling has been proposed for a subset of Venusian coronae and other tectonic features based on the presence of trench-outer-rise systems, but the mechanism and conditions required to initiate recycling remain poorly understood. Peel-back delamination (PBD) is a proposed mechanism in which dense lithospheric mantle decouples and peels away from a thin layer of overlying crust, resulting in slab rollback. PBD has only been modeled in 2D, and therefore its 3D surface expression is unknown. Here, we present the first three-dimensional models of peel-back delamination on Venus and compare their predicted trench geometry and flexural topography with observations from Artemis Corona, Atahensik Corona, and Derceto Plateau. PBD initiation is facilitated by increasing lithosphere thickness which enhances the negative buoyancy of the lithospheric mantle and drives decoupling from the weak, buoyant crust. Once initiated, rift geometry, lithosphere structure around the rift, and maximum yield strength control the evolution of trench geometry throughout PBD. Elastic thickness (Te) provides an independent constraint on lithospheric thickness, increasing with thermal lithospheric thickness. Comparisons with observations indicate that models of Artemis and Atahensik Corona best satisfy both trench geometry and flexural topography constraints, whereas the Derceto Plateau model reproduces trench geometry but not flexural topography. At Artemis Corona, along-trench variation in Te may reflect differences in subsurface slab morphology and plate bending. Te estimates from the southeastern trench at Artemis Corona favor a thermal lithospheric thickness of approximately 200-250 km for a 1700 K mantle.