March 2026 LIP of the Month

Dyke swarm history of Eastern Eistla Regio, Venus and implications for its plume origin

A. Hasanaine^a, H. El Bilali^b, R.E. Ernst^{b, *}, K.L. Buchan^c

^a Department of Geology, Faculty of Sciences-Semlalia, Cadi Ayyad University, Marrakesh, Morocco

^b Department of Earth Sciences, Carleton University, Ottawa, Ontario, Canada

^c 273 Fifth Ave., Ottawa, Ontario, Canada

Based on Hasanaine et al 2026 (see this publication for full details)

Importance of Venus for understanding terrestrial plume-generated Large Igneous Provinces (LIPs)

Our neighboring planet Venus is of similar size and interior structure to Earth, and has a robust intraplate magmatic history, including the presence of analogues to terrestrial LIPs (Head and Coffin, 1997; Buchan and Ernst, 2021; El Bilali and Ernst, 2024). Furthermore, given the absence of plate tectonics and the absence of surface erosion (due to the hot surface and absence of a water cycle), Venus provides the opportunity to improve our understanding of plume-generated LIPs, with lessons for those on Earth.

Here we focus on a major magmatic center on Venus, Eastern Eistla Regio, and use detailed geological mapping of its complex dyke swarm record to develop its geological history and understand the variety of discrete magmatic centers (four coronae in this case) as the product of a large mantle plume rising from the deep mantle.

Eastern Eistla Regio plume /LIP

Eistla Regio on Venus comprises three east–west–aligned regional topographic highs interpreted as products of mantle plume activity (e.g., Stofan et al., 1995; Senske et al., 1992; Ernst et al., 2007) (Fig. 1). Western Eistla generally peaks between 0.5 and 1.0 km, with the Sif and Gula mountains reaching elevations of 2 to 3 km. Central Eistla Regio rises to 1 km, this elevation being dominated by Irnini Mons/Sappho Patera and Anala Mons. Eastern Eistla is dominated by Ninmah, Isong, Pavlova and Didilia coronae. We selected Eastern Eistla Regio as the focus of this research (Hasanaine et al., 2026) in order to investigate the setting and age relationships of four well-developed similar-sized coronae above a single large mantle plume (Fig. 2).

Our study area includes portions of two quadrangle-scale (1:5,000,000) geological maps, Mead Quadrangle V-21 (Campbell and Clark, 2006) and Bell Regio Quadrangle, V-9 (Campbell and Campbell, 2002). Our study reconstructs the geological evolution of Eastern Eistla Regio with 1:500,000-scale mapping using NASA Magellan SAR imagery focused on extensional lineaments of the four principal coronae: Isong, Ninmah, Pavlova, and Didilia (Fig. 2, Hasanaine et al., 2026). A fifth corona, Calakomana, predates and is unrelated to Eastern Eistla Regio. Tepev Mons and Nyx Mons belong to the separate Bell Regio.

We mapped 70,000 extensional lineaments (grabens and fissures) (Fig. 3) and grouped them into radiating, circumferential and linear systems, which we interpreted as surface expressions of mafic dyke swarms (cf., Grosfils and Head, 1994; Ernst et al., 2003; Buchan and Ernst, 2021; El Bilali et al., 2023). Radiating and circumferential dyke swarms are closely associated with the four coronae and their underlying plumes or diapirs (Fig. 4). Twenty radiating systems are identified, including eight with radii >400 km and four >1000 km. Ninmah, Pavlova, and Didilia each host multiple radiating centers, whereas Isong exhibits a single center (Fig. 4). Circumferential swarms occur at Ninmah and Isong. Seven linear dyke swarms are also recognized, of which at least three likely originated by lateral emplacement from magmatic centers outside the study area (for full details see Hasanaine et al., 2026).

The size of the plume heads responsible for each radiating swarm can be determined from the distance at which a radiating swarm deviates from radiality (e.g., Buchan and Ernst, 2021; El Bilali et al. 2023). As illustrated in Figure 5 the radiating swarms associated with each center vary in size, but the inferred plume center sizes for all four coronae fit within the overall ~1300 km-radius region interpreted as the Eastern Eistla Regio mantle plume.

Relative chronology based on cross-cutting relationships and dyke trend changes indicates overlapping magmatic activity among the coronae, with principal radiating swarm development progressing from Isong to Ninmah, Pavlova, and Didilia. Pavlova also records late-stage activity (Fig. 6).

Bouguer gravity and crustal thickness anomalies (see Hasanaine et al., 2026) link Isong and Ninmah and also link Pavlova and Didilia, and suggest that each of these pairs of coronae are linked to an underlying zone of approximately similar trending (25^◦W and 10^◦W) lithospheric weakness spaced ~800 km apart that locally focused plume-related uplift and magmatism from the overall Eastern Eistla Regio plume (Fig. 7).

References