Investigating the Relative Absence of Volcanism Around Coronae

Introduction:

Coronae are ovoid tectonic and magmatic features that are unique to Venus. Because Venus is likely to be geologically active in the present day, yet lacks an apparent system of plate tectonics, understanding the relationship between coronae, volcanism, and tectonism is important to characterize Venus’s geology and geophysical state over its history. At long spherical harmonic wavelengths volcanoes and coronae often associated [1] but at regional scales there is a general anti-correlation related to spatial separation of volcanoes and coronae. A contextual view of this pattern is needed to understand the structures and processes underlying coronae formation and evolution.

Taking advantage of recently produced global datasets for Venusian volcanoes [2] and coronae [3], we investigate the population density of volcanoes in and around coronae and for different geological units. The stand-out result is the lack of volcanoes in the region surrounding coronae relative to the population within coronae and other geological units, especially those of the plains which dominate the planet’s surface (Fig. 1). A possible interpretation of this pattern of volcanism is that the development of coronae erases preexisting geological features in their surroundings. 

Figure 1: Mean volcano densities, calculated for different geological units on Venus [4]. Rift zones exhibit the least volcanoes per unit area. It is likely that ongoing tectonic activity at rift zones erodes any volcanic edifice as fast or faster than they are formed. This contrasts with the plains units where any volcanism is likely preserved due to lesser impact of mechanical erosion or tectonic activity [5, 6]. Coronae and the circum-coronal regions (50% means the ring around the corona up to 1.5 times its radius from the center, 100% means the same but up to 2 times its radius) lie between these extremes, with more volcanoes in the corona than in its vicinity.

 

Methods:

If corona activity is erasing evidence of ongoing volcanism, then putatively active coronae (as defined by local gravity anomalies) should correlate with decreased volcano population densities in their vicinity compared to older, extinct coronae. To test this, we use Boolean statistical methods [7] to develop correlation indices between corona characteristics, geological context, and volcano populations (Fig. 2). 

 

Figure 2: Correlation indices between corona characteristics (rows) and volcano populations (columns), showing how the likelihood of a corona to have an area “clean” of volcanoes relative to its interior varies with corona morphology and geological context. Topographic Groups (TG) describe topographic profiles across coronae [8] and volcano population density is recorded in units of volcanoes per 100 km². “Ring (100%)” refers to the thickness of the ring around the corona being 100% of the radius of the corona. Coronae in plains units are the most likely to exhibit a “clean” region in around them, while those in rifts and in deformed belts the least likely. If the morphology of a corona is domal or plateau-like (TGs 1, 2, 3,) or lacks a trough at its boundary than that corona is less likely to exhibit a clean cicrum-coronal region. These morphologies are strong correlated with being in a rift setting, suggesting a link between rifts, coronae, and patterns of volcanism.

We also use terrestrial eruption rates to predict patterns of volcanism for different geological settings on Venus. By comparing predicted volcano populations to observed populations, as well as populations of volcanoes in and around coronae to the geological unit the corona is embedded in, the degree of volcanic activity can be characterized across Venus’ surface. If volcanic populations in the clean regions around coronae are reduced proportionally to the background rate of volcanism for that specific geological unit across all of Venus, than the suppression of volcanism is likely a result of coronae destroying evidence of volcanism in their vicinity. If not, then other factors, such as the thermal state and structure of the lithosphere, control the interactions between volcano populations and coronae. To further test this, we also look for evidence of deformed and embayed volcanoes in the vicinity of coronae in Magellan imagery.

 

Results:

We present the results of these analyses to constrain the degree of volcanic and tectonic activity for different geological settings, inside coronae, and in the coronal regions on Venus. Correlations between volcano populations, corona morphologies, and rift zones suggest that extensional, geodynamic processes may be interfering with the expression of volcanism around coronae. Outside of these zones, however, coronae generally lack evidence of volcanism in their vicinity, likely as a result of erosion or burial by tectonic and volcanic activity originating from the corona itself or by a geodynamic process that suppresses volcanism. Future work characterizing the geophysical properties of coronae (especially gravitational anomalies) and higher resolution maps will be able to definitely distinguish between these possibilities.

 

References:

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[2] Hahn R. M. and Byrne P. K. (2023) JGR: Planets, 128.4, e2023JE007753. 

[3] Gülcher A. J. P., et al. (2025). LPI Contributions, 1944.

[4] Ivanov M. A. & Head J. W. (2011). Planetary and Space Science, 59(13), 1559-1600.

[5] Carter L. M. et al. (2023).Space Science Reviews, 219(8), 85.

[6] Herrick R. R. et al. (2023). Space Science Reviews, 219(4), 29.

[7] De Toffoli B. et al. (2024). Earth and Space Science, 11, e2024EA003854. 

[8] Smrekar S. E., & Stofan E. R. (1997). Science, 277(5330), 1289-1294.