Lithospheric Decoupling Links Dripping to Delamination Beneath Venusian Coronae: Dynamically Scaled Laboratory Experiments

Introduction
Coronae are among the most characteristic tectonic features on Venus, with more than 740 examples catalogued from Magellan data [1,2]. Their formation has been attributed to plume-induced uplift, Rayleigh–Taylor dripping, coupled upwelling and delamination, and plume-induced subduction [1–4]. Recent analyses combining Magellan free-air gravity, Bouguer gravity, and topography show that coronae record a spectrum of formation regimes, including a subset whose gravity signatures cannot be reproduced by plume-based models [5]. Demeter Corona, located at 295.2°E and 54.2°N, is the clearest example. It combines a −18.5 mGal free-air anomaly with a positive Bouguer anomaly and an elongated asymmetric trough. The mechanical process that produces this signal remains unresolved.

Here, using dynamically scaled three-dimensional laboratory analogue experiments performed at the Planetary Analogue Laboratory, University of Freiburg, Germany, we investigate whether dense lithospheric downwelling can evolve into lateral peeling beneath Venus coronae. The experiments reproduce an upper crust made of sand overlying four polydimethylsiloxane (PDMS) layers that represent the Venus lower crust, mantle lithosphere, asthenosphere, and a hemispherical eclogitic density anomaly at the crust–mantle boundary. The viscosity ratio across the simulated Moho, η_lc / η_lith = 0.93, and the buoyancy number, B = 0.094, are scaled to Venus conditions. Internal deformation is tracked with synchronous side-view and top-view particle image velocimetry, while surface topography is reconstructed at each time step by multi-view stereo photogrammetry. Side-view neck width is extracted automatically from 1.4 × 10⁵ continuously recorded frames.

Results
The experiment evolves continuously from drip nucleation to fully developed lateral peeling. The viscous neck connecting the drip head to the overlying plate thins from a scaled width of about 163 km to about 45 km, corresponding to a 72% reduction over a scaled time of about 12 Myr. The ratio of drip-head diameter to neck width increases monotonically and reaches about 3.5 at the onset of lateral peeling. This provides a geometry-based criterion for the drip-to-peeling transition under Venus-relevant scaling.

As the neck narrows, stress transmission across the weak lower-crustal Moho decreases. The overlying plate progressively decouples from the drip head, and removal migrates laterally as a peeling front along the lower crust. The resulting evolution is compared with two Venus coronae. Eithinoha Corona represents an intermediate stage of the analogue model, expressed by a dual-wavelength swath topographic profile. However, Magellan gravity at this latitude cannot distinguish between plume-driven and plume-independent downwelling. Demeter Corona shows the full peeling signature. It combines an elongated planform, an asymmetric trough annulus, a −18.5 mGal free-air anomaly, and a positive Bouguer anomaly. This combination is not reproduced by any plume model in [5].

A morphological screening of 179 elongated coronae from the updated Gülcher et al. [2] catalogue places 44 candidates within the peeling-stage region of elongation–asymmetry space. These candidates have the deepest trench depths in the catalogue systematically and are broadly distributed across the Venus surface rather than clustered near known tectono-magmatic provinces.

Implications
Our results suggest that coronae with Demeter-like signatures can form by progressive neck thinning and lateral peeling of a dense lower lithosphere. This mechanism requires only a thermally decoupled Moho and a dense lower lithosphere, both consistent with the Venus geotherm and the crustal metamorphism framework of Semprich et al. [6]. EnVision and VERITAS will provide gravity and SAR data at the resolution needed to test the 44 screened candidates against the Demeter benchmark. These observations will determine whether lithospheric downwelling represents a major class of corona formation on Venus. Because comparable rheological conditions may also apply to the Archaean Earth, progressive neck thinning provides a candidate geometric mechanism linking eclogitic dripping to large-scale delamination during early terrestrial lithospheric evolution.

References [1] Stofan E.R. et al., 1991, JGR 96, 20933. [2] Gülcher A.J.P. et al., 2025, JGR Planets 130, e2024JE008749. [3] Smrekar S.E. & Stofan E.R., 1997, Science 277, 1289. [4] Davaille A. et al., 2017, Nature Geoscience 10, 349. [5] Cascioli G. et al., 2025, Science Advances 11, eadt5932. [6] Semprich J. et al., 2025, Nature Communications 16, 2905.