Dyke swarm history of the northeastern margin of Central Ovda Regio, Venus: Evidence for mantle plume arrival and triple junction rifting

: Tesserae on Venus, the planet’s oldest geological units, record complex tectonic and magmatic histories. This study focuses on the tessera terrain of the northeastern central region of Ovda Regio (∼800,000 km 2 ), where we mapped lineaments (interpreted mainly as grabens, fissures and fractures) using full-resolution Magellan SAR imagery at a 1:500,000 scale. We identify 26 distinct lineaments systems — 10 radiating, 12 circumferential, and 4 linear — that are interpreted as the surface expression of underlying mafic dyke swarms linked to mantle plume activity. We interpret the cross-cutting relationships to reveal the following sequence of events: (1) arrival of a mantle plume (∼250 km radius); (2) emplacement of a radiating dyke swarm and triple junction rifting; (3) volcanic flooding of central and rifted regions; (4) a shift of ∼300 km in the centre of magmatic activity, marked by a second radiating swarm and second centre of triple junction rifting; and (5) emplacement of coronae and radiating swarms localized along thinned crust in the rifts. Our analysis supports the interpretation that tesserae record two major geological phases. The first “Tessera Formation” phase, possibly extending back to ∼4 Ga, involved tectonic deformation and lateral accretion of crustal blocks. The second “Post-Tessera Formation” phase is characterized by magmatic and tectonic activity in the absence of significant erosion, including dyke swarm emplacement and rifting associated with mantle plumes.