Evidence of Topographic Change Recorded by Lava Flows at Atete and Aruru Coronae on Venus

Coronae are quasi‐circular volcano‐tectonic features on Venus. Four critical observations have been identified within the coronae population, including fracture annuli, a wide range of diameters, complex and varied topography, and various types of associated volcanic features. Geophysical models have attempted to replicate their formation from a variety of lithospheric processes but struggle to recreate all four of the critical observations. Volcanism is an often overlooked characteristic in corona formation models. Paleotopographic techniques are applied to lava flows associated with Atete Corona and Aruru Corona in the Beta‐Atla‐Themis region to investigate post‐emplacement changes in topography. Our results indicate marked divergence between lava flow orientation and the modern slope within the fracture annuli of the coronae. Intra‐annular flows at Atete Corona were emplaced on a surface that was reoriented by up to ∼180°. Intra‐annular flows at Aruru Corona were emplaced on a surface that was reoriented between 90° and 145°. Lava flows on the flanks of both coronae diverge less than those within the fractures. This finding suggests a progression of volcanism that starts at the interior of the corona and migrates outward to the fracture annuli. The role of volcanism, both intrusive and extrusive, is likely to play a more substantial role in the corona formation. Incorporating melt migration into geophysical models could significantly enhance our comprehension of the processes underlying the formation of coronae.

A "standard" model of corona evolution that results from a thermally buoyant diapir can be simplified to three main stages (e.g., DeLaughter & Jurdy, 1999;Gerya, 2014;Grindrod et al., 2006;Gülcher et al., 2020;Janes & Squyres, 1995;Janes et al., 1992;Pronin & Stofan, 1990;Smrekar & Stofan, 1997;Squyres et al., 1992;Stofan & Head, 1990).First, a buoyant diapir rises through the mantle exerting stresses on the lithosphere.In response, the lithosphere domes, and radial extensional fractures form from the domal center.Next, as the diapir impinges on the base of the lithosphere, it flattens and spreads laterally.The topographic signature evolves from a dome to a plateau-like feature.Finally, as the diapir cools, the surface relaxes, forming an interior depression.The various topographic signatures observed at coronae have been interpreted as evolutionary stages from domal to circular to calderic with two transitional stages, with more complex topographic morphologies considered to be representations of coronae in a late evolutionary stage (e.g., DeLaughter & Jurdy, 1999;Smrekar & Stofan, 1997;Stofan et al., 1997).Moreover, detailed mapping of coronae in Guinevere and Sedna Planitia has shown the evolution to be more complex with a multi-stage annulus formation (Copp et al., 1998).More recent modeling of coronae formation has considered that mechanisms of formation are constrained by limiting factors such as size (e.g., Davaille et al., 2017) or proximity to rift zones (e.g., Piskorz et al., 2014).Furthermore, the wide variety of corona morphologies might be due to a continuum of processes rather than a singular formation mechanism (McGovern et al., 2013).
In this paper, we first discuss four critical observations of coronae and examine their implications for models of formation and evolution.In doing so, we will update the review of corona formation models from Dombard et al. (2007).We then discuss the geologic setting of two coronae of interest, Atete and Aruru, before applying paleotopographic techniques to the associated lava flows.We will assess the topographic divergence of mapped lava flows, which is the difference between the azimuthal orientation of the apparent flow direction and the modern slope facing direction.We will show that volcanism is a crucial and under studied, component of corona formation, and using surface observations, we will constrain the timing of volcanic and tectonic events associated with the formation of coronae.

Corona Critical Observations
The global view of coronae allows for four critical observations of the population: a wide range of diameters, distinctive annular fractures, varied topographic profiles, and associated volcanism.As reviewed by Dombard et al. (2007), geophysical models of corona formation have been able to reproduce only some of the features associated with coronae (Table 1).In the following sections, we will update the review of these critical observations from Dombard et al. (2007).These critical observations provide a comprehensive backdrop against which the influence of volcanism can be better understood.Volcanism, with its potential to reshape topographies and influence geophysical processes, offers a unique lens through which we can understand the intricacies of corona formation.
In discussing the various corona formation models, it is essential to recognize the inherent complexities and challenges associated with comparing models that employ different techniques, assumptions, and resolutions.While some models utilize two-dimensional geometries, others employ three-dimensional setups, and each has unique implications for plume buoyancy, lithospheric stresses, and other geophysical phenomena.Additionally, the resolution of these models can influence their ability to accurately capture small-scale processes, such as individual volcanic flows and surface interactions.While certain models might appear to overlook processes such as partial 10.1029/2023JE007971 3 of 15 melting and volcanism, it is crucial to understand that many incorporate these elements, albeit in a simplified manner due to computational constraints.The diversity in model approaches and assumptions underscores the intricate nature of corona formation and the challenges in drawing direct comparisons.

Fracture Annulus
The fracture annulus may be the most distinctive corona feature, and therefore, the most necessary characteristic for the reconstruction of formation models.The Venusian crust is able to withstand stresses that are much higher than Earth's crust, with faulting occurring once stresses get to ∼80 MPa (Foster & Nimmo, 1996).To produce concentric fractures, stresses must be both properly oriented and of sufficient magnitude.Fluid-flow based formation models of thermally buoyant plumes (e.g., Gülcher et al., 2020;Koch & Manga, 1996;Smrekar & Stofan, 1997) are unlikely to produce the necessary stresses to account for the concentric fracturing (Dombard et al., 2007), because of the relatively small density contrasts associated with thermal buoyancy.
To overcome the high stresses required to create the characteristic fractures, Gerya (2014) suggested that a hot and brittle upper crust could be fractured by the buoyancy of large volumes of magmas emplaced in a ductile lower crust.The magmas could rise as convection cells and fracture the weak upper layer.Furthermore, resolution limits of newer three-dimensional thermomechanical models inhibit direct comparison of simulated deformation with observed fracturing, although surface-strain rates of simulations suggest that concentric and stellate deformation features develop under certain scenarios of plume-lithosphere interaction (Gülcher et al., 2020).However, newer numerical models that account for melt-induced crustal weakening may intensify the amount of fracturing produced in simulations, as these models do not account for elasticity (e.g., Gülcher et al., 2020).Similarly, flexure of the lithosphere in response to volcanic loading could also overcome this stress barrier (e.g., Dombard et al., 2007;McGovern et al., 2013).

Wide Diameter Ranges
Corona diameters are the only quantitative data available for the four critical observations discussed here.A total of 545 coronae have been identified from the combined databases of Stofan et al. (2001) and the USGS corona data base (planetarynames.wr.usgs.gov).They span a wide range of diameters, from ∼60 km to over 1,000 km, and they are well fit to a lognormal distribution (Figure 2).The largest suspected corona, Artemis Corona (35°N, 135°E), has a diameter of more than 2,600 km, making it twice the size of the next largest corona, 255°E).Artemis Corona's immense size and complex geology could allude to a unique formation mechanism and evolution (Glaze et al., 2002).The arcuate annulus morphology of large corona, such as Artemis, has been presented as evidence for the presence of subduction zones on Venus (e.g., Brown & Grimm, 1996;Davaille et al., 2017;McKenzie et al., 1992;Sandwell & Schubert, 1992).Ascribing a subduction zone mechanism for coronae to the entire range of observed diameters is unlikely.Schubert and Sandwell (1995) suggested Latona Corona (22°S, 172°E), with an interior of 600 km, provides the strongest evidence for subduction.It is morphologically similar to the South Sandwich trench in the South Atlantic Ocean (see Sandwell & Schubert, 1992; Figure 1), and shares the same topographic and flexural signatures.Although subduction had been linked previously to the thinning and weakening of the lithosphere by a mantle plume (Sandwell & Schubert, 1992), the geographic association with chasmata and observed subduction morphologies provided a compelling argument for a rift induced origin of subduction.Modeling of plume induced subduction has been achieved experimentally (e.g., Davaille et al., 2017).However, since these models focused on plume sizes associated with large coronae and evidence of subduction morphologies has only been observed at a few coronae, subduction mechanisms for coronae formation might only occur under specific conditions.
Most models reproduce coronae with sizes greater than the average diameter of 250 km (e.g., Gülcher et al., 2020;Hoogenboom & Houseman, 2006;Smrekar & Stofan, 1997).This outcome is a consequence of the initial conditions of the plume diameter being roughly equal to the diameter of the resultant corona for numerical simulation.Under this scenario, the Venusian mantle convection regime would need to generate plumes from tens to thousands of kilometers across.Large, long-lived mantle plumes are thought to reside below large volcanic rises that span well over 1,000 km and may be analogous to terrestrial hotspots (Kiefer & Hager, 1991;Smrekar et al., 1997).Johnson and Richards (2003) proposed that coronae are the result of smaller transient thermal plumes.The flow of these smaller thermals is focused by large, long-lived plumes that result in volcanic rises.If a smaller thermal ascends too close to a large plume, then it gets absorbed by the plume, which possibly explains why coronae tend to be relatively absent from regions of major upwellings such as rises and downwellings such as planitiae.Gerya (2014) modeled the evolution of small coronae (<200 km) from plume-induced crustal convection.In their three-dimensional (3D) numerical model, an upwelling plume causes a "pre-nova dome" to form on the surface, and subsequent stages of evolution result in various topographic forms before the final "fossil" corona where the crustal convective cell cools and the previously molten crustal rock solidifies.This model again relates the size of the plume to the size of the corona.Additionally, smaller plumes and diapirs only resulted in a nova structure, and the crustal convection cells could not pierce the brittle upper crust.Further, models with a smaller plume temperature or stronger crust did not result in the formation of a corona.Gülcher et al. (2020) proposed that for coronae between 300 and 1,000 km, the way a plume interacts with the lithosphere results from specific formation mechanisms that depend on variables unrelated to the size of the plume; however, the size of the resultant corona does still relate to the size of the initial plume head.
To summarize, most models of corona formation relate the diameter of a corona to the width of the ascending plume/transient.This corollary is problematic for the width range of corona diameters, however, as boundary layer theory suggests a range of plume sizes (typically a factor of 2-3) smaller than the more the order of magnitude difference seen in corona widths.In contrast, Dombard et al. (2007) suggested that the size of the corona does not necessarily relate to the size of the plume head, but rather to the pocket of partial melt caused by an impinged thermal.The size of the partial melt is more sensitive to the local variables, and thus does not necessarily represent the size of the plume.

Complex and Varied Topography
Coronae have been classified into nine topographic groups based on the morphology of their topographic profiles (see Smrekar & Stofan, 1997; Table 1).Coronae from group 3, for example, include an elevated rim surrounding an inner trough, and irregular shaped interiors (e.g., Figure 3).Models of formation that presume a single evolutionary mechanism struggle to reproduce the variety of topographic shapes that have been observed for coronae.Ultimately, a single mechanism formation model must evolve through each of the topographic 10.1029/2023JE007971 5 of 15 groups in order to resolve the variety.Of the models discussed here (see Table 1), only Smrekar and Stofan (1997) have suggested that their model can resolve the range of observed topographic profiles.It is not implausible that other models could recreate the variety of topographic profiles given more thorough testing (e.g., Dombard et al., 2007), though these models did not do so.
It is thus unclear if a topographic profile can be attributed to an evolutionary stage of coronae.Furthermore, there is disagreement on the topographic evolution between various models (e.g., Gülcher et al., 2020;Janes & Squyres, 1995;Smrekar & Stofan, 1997).Gülcher et al. (2020) attributed the topographic morphology to the type of plume-lithosphere interaction and whether the coronae are active (i.e., presently underlain by a thermal).For example, a corona that is formed by either lithospheric dripping or ephemeral subduction displays an outer rise, trench, and inner high while they are active and during their inactive stage displays just a rim and interior depression.Contrast this scenario with the plume underplating regime that shows an elevated plateau for the length of the simulation (Gülcher et al., 2020).
Differences in local variables may also affect the resulting topography of a coronae.The ability of a plume to penetrate the lithosphere could result in markedly different surface expressions (e.g., Gülcher et al., 2020).Statistical analysis of the corona data set showed no significant correlation between the topographic shape of coronae and the geologic setting (Glaze et al., 2002).This finding has been interpreted as evidence that the evolutionary stage dictates the shape of coronae more than lithosphere or plume properties (e.g., Smrekar & Stofan, 1997).However, fluid-flow models (e.g., Gerya, 2014;Gülcher et al., 2020;Smrekar & Stofan, 1997) disregard the mechanical lithosphere and predict surface topography from vertical flow stresses that are isostatically balanced.Additionally, surface stresses differ depending on the thickness of the lithosphere.
A range of elastic thickness estimates have been predicted for Venus: anywhere from 0 to 100 km (Anderson & Smrekar, 2006).Further, the estimated range of elastic thickness near coronae is not substantially reduced.Estimates are as low 2-9 km from localized thinning (Russell & Johnson, 2021) and as much as 15-40 km (Barnett et al., 2002;Johnson & Sandwell, 1994;Sandwell & Schubert, 1992;Smrekar et al., 1997).McGovern et al. (2013) suggested that the thickness of the lithosphere may result in edifice growth that produces coronae due to changes in magma ascent pathways from changing stress regimes.Previous work found a correlation between lithospheric thickness and the various topographic groups assigned to the corona population (Smrekar & Stofan, 2003).A range of topographic profiles is to be expected, though, when considering the many geologic processes associated with coronae formation, including volcanic emplacement, crustal flow, and density anomalies.It is plausible that the addition to and deformation of the mechanical lithosphere associated with these loads could produce any one of the topographic classes observed in the corona population.

Associated Volcanism
The role of volcanism in corona formation and evolution is unclear.Only a limited number of coronae display any observable associated volcanism, and the extent of volcanism associated with a corona is variable even along geographically similar regions such as chasmata (e.g., Martin et al., 2007).Despite this, there is evidence for large-scale volcanism associated with coronae on the scale of terrestrial flood basalts (Roberts & Head, 1993).In the "standard" model of coronae formation, volcanism is thought to occur during the initial domical uplift stage before shifting to extra-annulus volcanism as the concentric fractures form and again shift toward the interior during the last evolutionary stage (Squyres et al., 1992).Roberts and Head (1993) used cross-cutting and stratigraphic relationships to determine when flow fields were emplaced relative to corona evolution.The authors noted that the majority of flow fields were emplaced prior to the annulus formation; small shields and interior flooding were associated more localized events within the annulus during the late stages of formation.Processing power has previously limited the ability of models to include melt production in simulations.In contrast, newer three-dimensional thermomechanical simulations can include melt production as newly formed crust, which is formed within the interior of the coronae during initial stages; however, these models do not simulate lava flows or produce extra-annulus volcanism (e.g., Gerya, 2014;Gülcher et al., 2020).With various plume-lithosphere interaction models being the most prevalent class of corona formation hypotheses, volcanism and magmatism are often predicted side effects of corona formation and rarely considered a mechanism that leads to corona formation.There are, though, exceptions.Dombard et al. (2007) showed that crustal loading from melt produced by an impinged thermal upwelling could form coronae and produce the required surface stresses to form the observed radial and concentric fractures.By not directly tying corona and plume sizes together, this model seemingly best explains the range of corona diameters (cf., Section 1.1.2).McGovern et al. (2013) proposed that some coronae are the result of volcanic edifice construction, their unique morphologies arising from specific lithospheric thicknesses and stress states.Additionally, Lang and López (2015) mapped the volcanic and structural features of three coronae and concluded that their morphologies were the result of a collapsing shallow magma chamber.Regardless of the exact mechanism for formation, the evidence indicates that volcanism, both intrusive and extrusive, has the potential to play a significant role during and after the formation of coronae.

Atete Corona and Aruru Corona Geologic Setting
To investigate in more detail the relationship between corona formation and associated volcanism, we explore 2 coronae with extensive mappable discrete volcanic flows within and exterior to the fracture annuli.This abundance of lava flows makes these coronae particularly suitable sites for our investigation.Specifically, we will look for evidence of topographic change at these coronae, with implications for how they formed.Atete Corona (16°S, 243.5°E) and Aruru Corona (9°N, 262°E) are located in the Beta-Atla-Themis (BAT) region (Figure 4), which spans from 50°N to 50°S and 180°E to 300°E.Spatial analyses of the global corona distribution have identified the BAT region to have a higher concentration of coronae (e.g., Squyres et al., 1993;Stofan et al., 1992Stofan et al., , 2001)).The abundance of coronae in addition to the volcanic highlands is indicative of long-term mantle upwelling (Johnson & Richards, 2003;Smrekar & Stofan, 1999).
Aruru Corona is an asymmetric, rimmed plateau corona located in the Hecate Chasma quadrangle (V-28).Volcanic materials associated with Aruru Corona extend radially in the form of digitate and sheet-like emplacements (Stofan et al., 2012).These extra-annulus flows may have sources on the flanks of the corona, but exact edifices are not resolvable.Volcanic flows from Aruru Corona are locally some of the youngest materials and units associated with neighboring coronae and tholi.However, there is little relative age information regarding the volcanic events in the region, which comes from the flows farthest from their sources, providing limited observational evidence.Therefore, it is possible that the features of this region formed concurrently (Stofan et al., 2012).
Without observational evidence, various techniques to assess whether coronae are active have been implemented.Aruru corona sits on positive regional topography and geoid anomalies while simultaneously positioned on a negative Bouguer anomaly suggesting a thermally buoyant upwelling is presently impinged on the base of the lithosphere (Dombard et al., 2007).Additionally, the uncompensated state of Aruru Corona could make it a candidate for presently active coronae (Johnson & Richards, 2003).Gülcher et al. (2020) interpreted the state of coronae activity based on numerical models of formation.Assuming that mantle-lithosphere interactions play a key role in the surface expression, the stage of corona evolution was related to the topographic profile.Aruru Corona's raised rims surrounded by lower elevations were attributed to an inactive plume.Kiefer and Peterson (2003) also interpreted Aruru to be geologically inactive based on the lack of mantle thermal anomalies from gravity inversion models despite the thickened crust.
Atete Corona is a ∼600 km wide corona whose northern rim forms a cliff above Parga Chasma, where sections have been proposed as potential subduction sites (Schubert & Sandwell, 1995).Considering that Atete Corona shares its trough with Parga Chasma, these two features may have formed contemporaneously (Chapman, 2000;Martin et al., 2007).Atete Corona has a high number of associated lava flows both within and exterior to its annulus.Indeed, this region is densely populated with coronae and their associated lava flows.To the north, flows from Atete Corona are interbedded with flows associated with Dhorani Corona, and to the east, Atete Corona flows overlie flows from an unnamed asymmetric corona.South and southeast of Atete Corona, its flows are superposed by flows from Lalohonua Corona and Dilga Corona, respectively.As with the mapping of Aruru Corona, age relations are difficult with the resolution of available data; determining the relative ages of events within units is difficult and subjective at best.The relationships between units, identified by the outermost flows, may only suggest events were coeval.Gülcher et al. (2020) interpreted Atete Corona, with its partial trench, rim, and inclined interior, to indicate the presence of ongoing plume activity.Furthermore, Atete Corona's uncompensated state (Johnson & Richards, 2003) and negative Bouguer anomaly (Dombard et al., 2007) provide additional evidence of being active.

Methods
The comparison of surface features with the current orientation of topography has been used to interpret the topographic change since the formation of the features, and to reconstruct timelines of geologic events (e.g., Conrad et al., 2021;Isherwood et al., 2013;Mouginis-Mark & Wilson, 2019).These previous studies looked for non-orthogonality between a surface feature with an inherent directionality (e.g., a lava flow) and topographic contour lines.This approach can be implemented on planetary bodies where the resolution of surface imagery and topographic data are relatively high, such as Mars.However, without careful analysis of the flow path and surrounding features, variations in the flow direction interpreted as large-scale changes in topography may be caused by local topographic variations.These directional changes are not representative of topographic changes since the feature was formed.We compare the direction of lava flows associated with coronae with the regional slope direction that does not rely on the intersection of a flow feature with contour lines.A similar approach has been successfully implemented for valley networks on Mars (Bahia et al., 2022;Grau Galofre et al., 2020;Luo & Stepinski, 2012) and lava flows on the flanks of Olympus Mons and Arsia Mons on Mars (Chadwick et al., 2015(Chadwick et al., , 2017)).
Lava flows associated with the coronae of interest were mapped using Magellan SAR images at 75 m per pixel (astrogeology.usgs.gov)imported into ESRI ArcGIS.Identification of discrete lobate and digitate flows is achieved by favorably stretching SAR data to accentuate flow margins (e.g., Figure 5) (Zimbelman, 2003).Flow directions are determined by the morphology of lobate flow fronts and distributaries.The center line of individual flow units is mapped, and the azimuthal orientation (ϕ) of each flow is calculated from their geographic start and end points.The line azimuth data are compared to the topographic aspect or slope facing direction.The aspect is determined by identifying the maximum amount of change in pixel values from Magellan global topographic data records (GTDR) mosaics at a resolution of 4.6 km per pixel (Pettengill, 1991).Vertical resolution of topography derived from Magellan altimeter data has an inherent absolute vertical error due to uncertainties in the spacecraft orbit.Importantly, the relative accuracy of smooth surfaces is approximately 5-10 m (Pettengill et al., 1992).The aspect calculation's reliance on the amount of change between neighboring pixels is therefore affected by relative error rather than absolute error of the planetary radius.Still, we include absolute error of the topography at the start and end points of each mapped flow in Tables S1 and S2.The regional slope direction is identified by the mean aspect   from a buffer polygon with a 25 km radius created along the length of the center line of each flow.The ArcMap Spatial Analyst aspect geoprocessing tool outputs a raster with the directional degree, measured from the north, of each pixel.To determine the mean regional aspect (i.e., slope direction), α, of the buffer area, the aspect of each pixel in the buffer, α j , are converted to Cartesian coordinates: Subtracting the flow line azimuth from the slope direction provides data on the changes in topography since the time of flow emplacement.

Results
A total of 191 lava flows were digitized: 91 at Atete Corona and 100 at Aruru Corona (Tables S1 and S2).Both coronae have flows within and exterior to their fracture annuli that diverge from the modern topographic slope direction.
Mapped lava flows within the fracture annulus of Atete Corona show marked differences between their original direction of flow and the current topographic gradient, while flows that are exterior to the annulus vary in the amount of topographic divergence (Figure 5).The flows within the annulus are seen radiating from a region of radial fractures near the southern part of the corona, extending to the northern limit of the concentric fractures (Figure 6).This cluster of mapped flows in the center of the corona interior appears to be flowing uphill.The slope they were emplaced on has flipped orientation, with some flows showing a change in the slope direction of nearly 180° (Figure 7).
To the north of the corona annulus lies another cluster of flow features with an apparent northward flow, but they are situated on a slope facing in the opposite direction.On Atete's eastern flank are flows exhibiting divergence with the modern topographic slope adjacent to flows that conform to the current topography (Figure 6).Flows on the eastern flank of Atete can be divided into two groups: the northern set of flows that follow the current topography, and the adjacent southern cluster that are emplaced on a surface that has since rotated counterclockwise from its original orientation.Roberts and Head (1993; Figure 1) posits that the emplacement of lava flows on the corona's eastern flank and interior took place after the annulus formation.However, this hypothesis contradicts the obvious topographic divergence of the interior flows that now seemingly "flow" uphill.Moreover, the differences in the topographic divergence of flows on the eastern flank imply multiple volcanic events.The southern flows might be related to the initial volcanism associated with the area of radial fractures, but the northern flows' lack of topographic divergence and their perpendicular orientation to the annulus suggest a later emplacement, possibly originating from the annulus itself.
Aruru Corona, similar to Atete Corona, shows the greatest amount of discrepancy between the slope facing direction and the lava flow azimuth for flows within the fracture annulus (Figure 8).Additionally, the interior flows extend to the southeast from an area of radial fractures, as seen in Atete (cf., Figures 7 and 9).The mean divergence of the interior flows, which is the mean of the absolute value of change in slope facing direction, is ∼98°.One flow within the interior recorded a slope change direction of around −75° (Figure 8), and despite Varying amounts of topographic divergence can be seen in the exterior flows of Aruru Corona.The highest point of elevation at Aruru is its northwestern rim (Figure 9), and the topographically elevated region extends beyond the fractures toward the corona's exterior (Figure 4).The flows situated at 11.5°N, 260.5°E slope directly from this topographic high, and as such, do not record any topographic change.The flows on the western side (from 9° to 11°N, 260°E) and the eastern side (from 10.5° to 11.5°N, 264°E) of the elevated area reveal variations in the slope direction greater than 45°.The topographic divergence of these flows implies emplacement prior to the uplift of Aruru's northwest rim.This observation is likely true for the flows directly to the northwest with no divergence as well, although their orientation relative to the uplift might be indicative of post-uplift emplacement.
All exterior flows at Aruru south of 9°N exhibit minimal or no divergence from the modern slope direction.The southeast rim of the corona, while not as high as the northwest rim, still rises over 500 m above the surrounding area (Figure 3).Consequently, the absence of divergence from the modern slope direction suggests that these flows were emplaced after the formation of the annulus.

Discussion
Lava flows that diverge from modern topographic slope direction can be used as relative dating markers to link the volcanic and tectonic events of corona formation.These observations can then be used to assess various models of formation that were discussed in Section 1.Initial domical uplift and radial fracturing as an early or first stage is observed in corona models of varying formation mechanisms (e.g., Gerya, 2014;Gülcher et al., 2020;Janes et al., 1992;Koch & Manga, 1996;Smrekar & Stofan, 1997;Squyres et al., 1992).This scenario is consistent with the results found for the lava flows within the fracture annuli of Atete and Aruru Corona.Both coronae have flows within their annuli whose apparent flow directions diverge from the modern topography.Furthermore, these flows appear to be sourced from an area of radial fracturing (Figures 5-8).The initial thermal upwelling could have produced a zone of partial melt (e.g., Dombard et al., 2007;Lang & López, 2015) causing an initial pulse of volcanism that, if topography allows, extends radially from the edifice.The formation of the fracture annulus and topographic rim led to the current orientation of the slope face and the resulting divergence of the flows since their emplacement.
Some models of corona evolution attempt to explain the timing of deformation and volcanism (e.g., Janes et al., 1992;Smrekar & Stofan, 1997).Intra-annulus volcanism is thought to occur after the initial domal uplift.Subsequently, as the impinged plume flattens, volcanism transitions to the area outside the fracture annuli.In the final stage, volcanism shifts back to the interior of the corona (e.g., Janes et al., 1992;Smrekar & Stofan, 1997;Squyres et al., 1992;Stofan et al., 1992).However, this straightforward sequence can be deceptive as volcanism occurring before the formation of the annuli might extend beyond the corona's diameter.Roberts and Head (1993) found that, on average, flow fields can extend radially up to 300 km from the central source, but the average diameter of coronae on Venus is approximately 220 km (Figure 2).As found at both Atete and Aruru Corona, lava flows exterior to the fracture annuli can be representative of volcanic events from early in the formation of the coronae or subsequent to the annulus formation.
Indeed, both coronae showed similar age progression.The interior flows are apparently from an early stage, as evidenced by the lack of flows that follow the modern topography.In contrast, the flows on and exterior to the annuli show a range of inferred ages, with some showing topographic change and others following the modern topography.These different generations can even be spatially coincident.Lava flows within the fracture annuli at Atete and Aruru corona can pre-date the formation of the fracture annulus.This finding contradicts other observations (e.g., Roberts & Head, 1993) and does not align with discussions of volcanism in corona formation models discussed above (see Section 1.1.4).However, small-scale local volcanism may have occurred within the annuli after their formation.Both coronae discussed here have small shield volcanoes.Atete Corona, in particular, has many small shield volcanoes near the radial fractures in the southern part of its interior (Figure 6).It is not possible, at present, to identify the timing of these shields relative to other volcanic features here, or if they are related to the coronae in any way except geographically.
The observation of the substantial volcanism occurring prior to the formation of the fracture annulus is in contrast to the findings of Lang and López (2015), who investigated the magmatic and structural evolution of three coronae.In their study, they concluded that the most extensive volcanism occurred after the formation of the fracture annuli.Furthermore, Copp et al. (1998) mapped the geology associated with five coronae and noted various amounts and styles of volcanism, particularly regarding early-stage volcanism.In addition, this late-stage volcanism may be intrinsically linked to fracture annuli.Large lithospheric loads can redirect magma from a central source to circumferential regions (McGovern et al., 2013).The lower flexural stresses near the fracture annuli can produce narrow zones of magma ascent.Indeed, volcanic constructs, such as tholi, have been observed directly on top of fracture annuli, suggesting that late-stage volcanism may utilize the fractures as pathways for magma (e.g., Russell & Johnson, 2021).We do not consider the results of these previous studies to conflict with our findings; rather, they reinforce the argument that volcanism plays a crucial role in the formation and growth of certain coronae.
These findings suggest why models have difficulty capturing more than one or two characteristic observations: coronae, like most geological features, are messy and do not exactly follow textbook models of formation.Given the variety in corona morphologies, volcanism, and geographic setting (e.g., Glaze et al., 2002;Roberts & Head, 1993;Stofan et al., 1992), it is evident that a singular formation mechanism might not be sufficient to explain all observations.This complexity, combined with the range of the proposed mechanisms, further supports the idea of a continuum formation process, emphasizing the non-uniqueness of corona formation.Therefore, a range of deviations are seen from the schematic models.At Atete Corona and Aruru Corona, the northward surface inflation and extension of the annulus from an initial center violate the axisymmetry of these simple models, and it is difficult to reconcile these models with Atete's initial northward slope across the whole of the annulus interior followed by a wholescale flip in the slope direction, for example.What is clearer is that volcanism played a significant role in the evolution, with it occurring at early to late stages.
Indeed, changing centers of volcanic activity with associated surface inflation/deflation could serve as an explanation for the observed topographic change.Thus, discrepancies between flow direction and downslope direction would indicate tectonic events after the lava was emplaced and suggest more complex evolutionary stages than have been previously proposed, with volcanism more intimately tied to the corona formation.Relying on large-scale lithospheric processes, as most geophysical models of corona formation do, underestimates how intrusive and extrusive volcanism can impact morphology on the scale of coronae.This source of change could be from migrating magma sources (e.g., McGovern et al., 2013) or additional volcanic construction that can alter the heat flow and stress regimes (e.g., Lang & López, 2015;Russell & Johnson, 2021).Moreover, intrusive magmatism may be the primary source of volcanic activity on Venus, which would have significant impacts on the surface expression above magma sources (Lourenço et al., 2020).This oversight regarding the influence of volcanism is where many geophysical models of corona formation fall short.Further implementation of melt intrusion and migration into numerical models, a resource intensive task, would provide an increased understanding of how volcanism impacts corona formation.
In addition, further implementation of paleotopographic techniques to lava flows on Venus will provide invaluable insight into the formation of coronae.Future studies would benefit from the improved SAR imagery and topographic resolution of NASA's VERITAS mission and the European Space Agency's EnVision mission.Specifically, the VISAR instrument on VERITAS will provide radar images with a resolution of ∼30 m/pixel, a marked improvement over the 75-100 m/pixel resolution of the Magellan SAR images used in our study.This superior resolution would facilitate more detailed identification of discrete lava flows and their intricate interactions with the modern topography.Moreover, the topographic data from VISAR, with a spatial resolution of 250 m, will be vastly superior to Magellan's altimetry data, enabling a clearer depiction of surface features and elevations.This enhanced resolution, the capability to detect active deformation with interferometry, and the potential to identify decadal changes through comparison with Magellan data, would offer invaluable insights into coronae and the underlying geophysical processes.

Conclusions
Coronae are best described using four critical observations: fracture annuli, a wide range of diameters, complex and varied topography, and associated volcanism.Geophysical models of corona formation need to be able to replicate these observations, but often struggle to do so.This is especially true regarding the role of volcanism in formation models.Here, we evaluated the orientation of lava flows and the current downhill direction at Atete and Aruru Corona.We identified flows that diverge from the modern topography, indicating post-emplacement alteration of the topography.Flows within the fracture annuli at both coronae displayed a greater degree of divergence than flows exterior to the annuli.This discrepancy suggests that large-scale volcanism occurred prior to the formation of the fractures, likely at an area of domal uplift, and migrated toward the fracture annuli during later stages of corona formation.The migration of volcanism affects the morphologies of coronae, which in turn suggests a more complex stage of evolution.Fluid flow models (e.g., Gerya, 2014;Gülcher et al., 2020;Smrekar & Stofan, 1997) rely on the interaction between thermal upwellings and the lithosphere.The resulting topographic changes do not account for partial melt above an impinged thermal, which could vary in size, location, and composition depending on variations in the lithosphere.In contrast, these volcanic processes may be driving coronae morphologies (e.g., Dombard et al., 2007).

Data Availability Statement
GIS shapefiles of the mapped center lines and Python scripts for use with ESRI ArcGIS Pro are available on Zenodo (Tucker & Dombard, 2023).NASA Magellan mission data are available from the NASA Planetary Data System, including the full-resolution SAR images (Pettengill, 1991) and global topography data (Ford, 1992).The locations of Atete Corona and Aruru Corona are available through the USGS Venus nomenclature database from the International Astronomical Union Working Group for Planetary System Nomenclature (2023) (https:// planetarynames.wr.usgs.gov).

Figure 1 .
Figure 1.Perspective view of the 450 km wide Aruru Corona (9°N, 262°E) from Magellan SAR and altimeter data.The view is from the southeast looking northwest with a vertical exaggeration of 40x.Lava flows coming off the flank are apparent on the nearer side.

Figure 2 .
Figure 2. Histogram of corona diameters binned every 100 km.The dashed line is the lognormal probability distribution shown for comparison.Data is the combined USGS corona database and the Type 1 and Type 2 database of Stofan et al. (2001).Artemis corona, with a diameter of 2,600 km, is excluded from this distribution.

Figure 3 .
Figure 3. Topographic profiles and reference map with profile line locations for Aruru Corona.Profiles derived from Magellan altimetry data.A-A′ runs from northwest to southeast and B-B′ runs from southwest to northeast.

Figure 4 .
Figure 4. Beta-Atla-Themis region with Magellan altimetry-derived elevation (low elevation is blue and high elevation is red) overlying SAR image mosaic in Mollweide projection.Bounding boxes indicate the location of Aruru Corona (right inset) and Atete Corona (left inset).

Figure 5 .
Figure 5. Examples of mapped lava flows on (a) the southeast flank and (b) within the annulus of Atete Corona.The white arrows are the center line of the flows and the dashed line is the outline of the flow.

Figure 6 .
Figure 6.Lava flow divergence for flows mapped at Atete Corona.Azimuthal flow directions that differ from the slope aspect by close to 180° or −180° are on surfaces that have reversed orientation since the flow was emplaced.Negative values represent a counterclockwise rotation of the surface and positive values represent a clockwise rotation of the surface.

Figure 7 .
Figure 7.The topography of Atete Corona overlying full resolution Magellan SAR image.Red is high elevation and blue is low elevation.Arrows indicate apparent direction of flow of mapped lava flows.Inset is an SAR image of an area of radial fractures that is likely the location of the initial domal uplift during an early stage of corona formation.

Figure 8 .
Figure 8. Lava flow divergence for flows mapped at Aruru Corona.Azimuthal flow directions that differ from the slope aspect by close to 180° or −180° are on surfaces that have reversed orientation since the flow was emplaced.Negative values represent a counterclockwise rotation of the surface and positive values represent a clockwise rotation of the surface.

Figure 9 .
Figure 9.The topography of Aruru Corona overlying full resolution Magellan SAR image.Areas are high elevation blue is low elevation.Arrows indicate apparent flow direction of mapped lava flows.Inset is an SAR image of an area of radial fractures and potential collapsed vent.

Table 1
Critical Observations of Coronae Produced by Models of Formation