Strain partitioning and possible block-scale motion in Vinmara Planitia, Venus

Introduction

Venus does not show an unambiguous global network of plate boundaries, yet its surface preserves widespread evidence for tectonic deformation, volcanism, and possible lithospheric mobility. Recent work has suggested that parts of the Venusian lowlands may be divided into relatively coherent crustal blocks, or campi, bounded by deformation belts and tectonically disrupted margins¹. Such domains may be compatible with localized lithospheric mobility within a stagnant-lid or plutonic-squishy-lid planet, without requiring Earth-like plate tectonics². Here we investigate a tectonically complex lowland domain in Vinmara Planitia, previously identified as part of a Venusian campus¹, to assess whether its structural architecture is consistent with localized boundary-like deformation and strain partitioning.

Data and approach

We analyzed Magellan Synthetic Aperture Radar images, radar altimetry, gravity, microwave emissivity, and meter-scale roughness data across three tectonic sectors of the Vinmara domain: the contractional ridge belt of Ahsonnutli Dorsa, the extensional groove belt of Surupa Dorsa, and a faulted tessera terrain located southwest of Ahsonnutli Dorsa. SAR and altimetry data were used for structural mapping and topographic analysis³. Gravity data were derived from the Magellan gravity field, truncated to the reliable degree strength of the study region⁴, while emissivity and roughness data were used as ancillary constraints on the surface properties of Surupa Dorsa⁵,⁶. Topographic profiles across Ahsonnutli Dorsa were compared with a two-dimensional elastic flexure model to evaluate whether the long-wavelength relief is compatible with lithospheric bending⁷. In the tessera terrain, piercing points and structural markers were restored across fault zones to estimate lateral displacements. The resulting fault geometries were then compared with a first-order Euler-pole reconstruction⁸ to evaluate whether contraction, extension, and lateral displacement can be described as part of the same kinematic system.

General interpretation

The main result of this study is that deformation within the Vinmara domain is spatially organized. Ahsonnutli Dorsa forms a narrow, slightly arcuate contractional belt, Surupa Dorsa forms a broad extensional groove belt, and the southwestern tessera terrain records measurable lateral displacement along west-southwest to east-northeast trending faults. Restoring matched markers across four sectors of the tessera terrain yields offsets of 1.8 to 4.2 km, with a mean displacement of about 2.8 km and a cumulative displacement of approximately 11.3 km. All restored displacement vectors indicate a coherent northeastward sense of motion. Together, these observations suggest that deformation was partitioned along different margins of a relatively coherent crustal block.

A first-order Euler-pole reconstruction is consistent with this interpretation. The mapped tessera-cutting faults are compatible with transform-like motion, Surupa Dorsa is oriented approximately as an extensional boundary, and Ahsonnutli Dorsa occupies the contractional side of the inferred system. This configuration does not imply Earth-like plate tectonics on Venus. Rather, it suggests that localized lithospheric mobility may occur within a planet that lacks a global plate-boundary network.

End-member geodynamic scenarios

Within this kinematic interpretation, Ahsonnutli Dorsa and Surupa Dorsa can be evaluated through more specific end-member scenarios. Ahsonnutli Dorsa is associated with thrust-related structures, a trench-like topographic low, a broad elevated sector to the west, flexure-compatible long-wavelength topography, and a volcanic trend located landward of the contractional front. Flexural modeling of six topographic profiles reproduces the broad observed relief, with an average coefficient of determination of 0.86 and effective elastic thickness values of about 0.8 to 8.8 km. These observations are consistent with an end-member underthrusting or subduction-like interpretation, although they do not uniquely demonstrate subduction.

Surupa Dorsa is characterized by extensional faulting, an elongated axial topographic high, local syn-belt volcanism, relatively low Bouguer anomaly values where the belt broadens, and increased emissivity and meter-scale roughness along the groove system. This combination of observations is compatible with a focused tectono-magmatic extensional system and supports a spreading-like end-member interpretation. However, as for Ahsonnutli Dorsa, this interpretation remains non-unique because of the spatial resolution limits of the available Magellan datasets.

Implications

The Vinmara domain indicates that some Venusian lowland blocks may have undergone localized relative motion accompanied by contraction, extension, and lateral displacement. The results do not require a global plate tectonic regime, but they show that boundary-like deformation may develop locally within the Venusian lithosphere. Future VERITAS and EnVision observations will provide higher-resolution topography, radar imaging, gravity, interferometric measurements, and compositional data with which to reassess the origin, timing, and possible activity of structures such as those in Vinmara Planitia⁹,¹⁰.

Acknowledgments

G.M., D.S  acknowledge support from the Italian Space Agency (Grant No. 2022-15-HH.0). 

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