November 2024 LIP of the Month
Radiating dyke swarms associated with the Atla Regio Plume / LIP on Venus
Hafida El Bilali 1, Richard E. Ernst 1, Kenneth L. Buchan 2, James W. Head 3
1 Department of Earth Sciences, Carleton University, Ottawa, Ontario, Canada; hafidaelbilali@cunet.carleton.ca,
2 273 Fifth Ave., Ottawa, Ontario, Canada,
3 Department of Earth, Environmental and Planetary Sciences, Brown University, Providence, RI 02912, U.S.A.
Extracted and modified from: El Bilali, H., Ernst, R.E., Buchan, K.L., Head, J.W. (2023). Dyke swarms record the plume stage evolution of the Atla Regio superplume on Venus. Communications: Earth and Environment, 4, 235, https://doi.org/10.1038/s43247-023-00901-7
Given the absence of plate tectonics (at least since ~1 Ga ago) all volcanism on Venus is intraplate and the largest events are considered analogous to terrestrial Large Igneous Provinces (LIPs) generated by large mantle plumes. An important question is the timing of Atla Regio, Venus (Fig. 1), is interpreted as a LIP associated with a major mantle plume centre and is considered to be young. We address whether it is at plume head or plume tail stage.
Our approach uses graben-fissure lineaments, interpreted as the surface expression of dykes (note the absence of erosion on Venus at this time). Mapping >40,000 such lineaments (Fig. 2) reveal giant radiating dyke swarms associated with major volcanic centres of Maat (>1500 km dyke swarm radius), Ozza (>2000 km), Ongwuti (>1100 km) and Unnamed montes (>1100 km) (Fig. 3), indicating that each is due to plume head magmatism rather than plume tail magmatism (maximum swarm length ~100 km).The size of an underlying flattened plume head for each centre is estimated by the radius where the swarm transitions from a radiating to linear pattern (Fig. 3).
Atla Regio is at the plume head stage with coeval triple-junction rifting, which on Earth would typically precede attempted continental breakup (see interpreted geological history in Fig. 4). Full details and referencing are available in El Bilali et al. (2023).
Figure 1: Atla Regio study area. a) NASA Magellan SAR (synthetic aperture radar) image annotated with features discussed in the text. b) location of Atla Regio and associated triple-junction rift arms in BAT (Beta-Atla-Themis) region. B = Beta Regio, T = Themis Regio, D = Devana Chasma. Basemap showing rift zones (chasma) in red, large volcanoes in green and coronae in yellow, and superimposed on geoid level (grey scale with value increasing from dark to light).
Figure 2: More than 40,000 graben-fissure lineaments mapped and interpreted as underlain by mafic dykes. Background is NASA Magellan SAR (synthetic aperture radar) image.
Figure 3: Generalized graben-fissure systems (from Fig. 2) associated with the four main magmatic centres on background of NASA Magellan SAR images. Circles indicate the inferred plume head size based on the radius (R) of transition in the dyke swarms, from radiating to linear; dashed where unconstrained (see text for discussion). The maximum radius of each swarm is: a) Ongwuti Mons = >1100 km, b) Ozza Mons = >2000 km, c) Unnamed Mons = >1100 km, d) Maat Mons = >1500 km.
Figure 4: Geological history inferred from graben-fissure mapping. DD = Dali-Diana Chasma, P = Parga Chasma, H = Hecate Chasma, G = Ganis Chasma.