Far-travelled 3700 km lateral magma propagation just below the surface of Venus

Domain: earth_science
Published: 2024-02-26
Editorial outcome: minor_revision

Abstract
The Great Dyke of Atla Regio (GDAR) is traced for ~3700 km on Venus, as a surface graben (narrow trough) interpreted to overlie a continuous laterally-emplaced underlying mafic dyke (vertical magma-filled crack). The GDAR belongs to a giant radiating dyke swarm associated with Ozza Mons (volcano), Atla Regio plume, and was fed from a magma reservoir ~600 km south of the Ozza Mons centre. A 50-degree counter-clockwise swing of the GDAR at 1200 km from the centre is consistent with a 1200 km radius for the underlying Ozza Mons plume head, and a stress link to the 10,000 km long Parga Chasmata rift system. Our discovery of the GDAR, should spur the search for additional long continuous single dykes on Venus (and Earth), with implications for estimating plume head size, locating buffered magma reservoirs, mapping regional stress variation at a geological instant, and revealing relative ages (through cross-cutting relationships) over regional-scale distances.

Introduction
Dyke swarms are the dominant mode of transport of mafic magma on planetary bodies including Earth, and the largest swarms have giant radiating or circumferential patterns that can be linked to mantle plume centres1–9. Radiating swarms are interpreted to be laterally emplaced from their plume centre regions whereas giant circumferential swarms are likely fed both vertically and in part laterally. The longest radiating swarms on Earth have a maximum known radius of 2000 km (for the 1270 Ma Mackenzie of northern Canada2,3) and perhaps up to nearly 3000 km (for the 201 Ma Central Atlantic Magmatic Province (CAMP) LIP10). It is interpreted in such cases that the magma is generated and ascends vertically in the plume centre region (potentially up to a distance of a few hundred km out from the plume centre), and then is laterally emplaced for the entire remaining distance3,11,12. Given this lateral emplacement interpretation, it can be predicted that individual dykes of these giant swarms must extend the length of the swarm (e.g. up to ~3000 km). However, the longest distance that individual dykes have actually been traced so far on Earth is much shorter: the 1140 Ma Great Abitibi dyke of the Canadian shield is traced for 700 km13, a Red Sea dyke for about 1000 km14, and the Great Dyke of Zimbabwe for 550 km15. On Earth it is difficult to track the full extent of individual dykes for at least three reasons: (1) a dense dyke swarm prevents continuous tracking of individual dykes, (2) continental breakup can fragment swarms, and (3) younger sedimentary or volcanic units can mask the distribution of dykes.

Due to the current hot surface temperature (ca. 450 °C), there is an absence of fluvial erosion (and wind erosion is relatively minor) on Venus e.g. 16–18. extending back at least hundreds of myr (based on cratering age constraints of ~300–1250 Myr18, cf. 19, or ~240 Ma20, and back to about 700 Ma based on climate modelling21. As a consequence, the primary surface of geological units and structures is preserved except where covered by younger lava flows, obscured by superimposed tectonics, or covered by rare sand dunes or talus associated with rift zones.

The relatively minor role of erosion17 means that intrusive units such as dykes are not exposed; however, their presence can be inferred from their surface expression as narrow grabens, and also pit chains and chains of shield volcanoes inferred to overlie blind dykes (dykes not reaching the surface) that are, for the most part, interpreted to be laterally emplaced9,22–24. There have been detailed studies of graben systems (interpreted in the context of dykes) in multiple regions of Venus9,25–27 and other planetary bodies, notably Mars4,6,28–30. In the global reconnaissance study by ref. 22, 163 radiating systems were identified on Venus, with maximum radii ranging from 40 to ≥2000 km, and with an average radius of ~325 km. This study22 used the Magellan SAR (synthetic aperture radar) data, which had been compressed once to produce images (with a resolution of 225 m/pixel31). Subsequent regional studies using the full resolution Magellan SAR images (~125 m/pixel) reveal a greater number of radiating systems. For instance, 5 times as many were recognized in the Guinevere Planitia region where a 3800 km long radiating graben system was reported by 24, consisting of a 1000 km radiating portion focussed on Theia Mons, Beta Regio, that transitions outward into a linear 2000 km long N-S swarm24. Similarly, a radiating graben system with a radius of 6000 km has been associated with the 1200 km radius Artemis Corona magmatic centre32. In these cases, it is typically interpreted that these grabens overlie dykes which were emplaced laterally for up to these full distances, away from the magmatic centres (as on Earth, as discussed above). However, no single dyke of these swarms has been continuously traced for such distances. Herein, through detailed analysis using full resolution Magellan SAR images we track a single graben (interpreted as a dyke) for at least 3700 km.

Part of the BAT (Beta-Atla-Themis) region, Atla Regio is recognized as a major plume centre, on the basis of gravity, topography, geoid and other criteria favouring deep dynamic support, and being the locus of triple junction rifting with the largest rifts extending to the ENE, SW and SE to connect with other Regios, and also associated an radiating dyke swarm (Fig. 1 inset)9,33–36.

In this work, we identify the longest individual graben (interpreted as overlying a dyke), traced so far, on Venus (and indeed in the solar system) and discuss the implication of this discovery, and more generally, the importance of identifying other long individual dykes.

Results
Tracing of the Great Dyke of Atla Regio (GDAR)
We have traced a single graben nearly continuously for 3700 km using the full resolution (~75–150 pixel37,38. left-look and right-look Magellan SAR images (Fig. 1, images 1 and 3). A 1700 km portion of this graben structure was previously mapped as Penthesilea Fossa (i.e. a long, narrow depression (trough), interpreted as a graben) in Taussig Quadrangle V-3939. Our mapping has confirmed the extent of this single graben, and also traced this graben west of Taussig Quadrangle back to the interpreted source associated with Ozza Mons. As with other grabens (as discussed above) we interpret this particular graben to represent a single mafic dyke.

However, given the significance of our proposed recognition of a single mafic dyke of such length, we also consider other origins for a long and narrow geological feature. Could this represent a fault (strike slip or thrust), or purely tectonic extensional structure? If it were strike-slip fault then the boundaries of older host units should be offset across the feature, which is not observed. If it were a thrust fault then given the minor role of erosion (see discussion above) there should be a topographic change across the feature, which is also not observed. A purely extensional feature without a dyke underneath would imply regional extension, but the result would be rift zone, with a complex pattern of rifting40, not a single narrow graben several thousand km long.

This leaves a dyke interpretation as the most likely. Another point to discuss is whether the dyke is fed vertically or horizontally. If fed vertically then this would require an underlying source co-extensive with the entire length of the dyke (and indeed co-extensive with the full extent of the Ozza Mons radiating swarm). On Earth, using flow fabric (magnetic fabric) and geochemical studies it has been shown that such large dyke swarms are mainly fed horizontally except near their plume centre resource, where emplacement is vertical3,11,41. It is also typically interpreted that major radiating graben systems on Venus and Mars are also underlain by laterally emplaced dykes5,6,22,23.

Our final point is that the underlying dykes must be mafic (mainly basaltic) in composition rather than intermediate or felsic. Two reasons are relevant, (1) nearly all the volcanism that extends across 80% of Venus is interpreted to be basaltic based on flow morphology (e.g. 42, and also from measurements by Soviet lander data43; so if dyke feeders are present they should dominantly be mafic rather than felsic; (2) more specifically there are many examples of flows with basaltic morphology, emanating from individual graben (e.g. 24). Thus, we interpret that this 3700 km long graben (fossa) is a single mafic dyke (likely equivalent to a large dolerite-gabbro dyke on Earth) which we have termed the Great Dyke of Atla Regio (GDAR).

We note that there are some breaks and gaps in the continuity of the GDAR. Small breaks along this graben are also associated with en echelon offsets (e.g. detailed image 2 in Fig. 1) which are common in regional mafic dyke swarms on Earth and typically interpreted to represent a continuous laterally propagating dyke at depth, for which the upper portions ascend into slightly different stress regime causing local rotation and segmentation of the dyke44.

Also, four gaps in the tracing of the GDAR were observed due to superimposed younger events: (1) a 213 km gap is covered by lava flows of Oduduwa Corona (from 10.160S, 210.715E to 11.163S, 212.501 E; location B in Fig. 1), (2) an intensely fractured radar bright zone (older or younger is not clear) obscures the GDAR for a distance of 166 km (from 13.240S, 216.036E to 14.155S, 217.430E; location C in Fig. 1), (3) a 139 km gap is obscured by grabens (dykes) of Onenhste Corona (from 16.127S, 220.963E to 17.090S, 222.188E, location D in Fig. 1), and (4) a 66 km gap is obscured by radar dark material, likely dust from Felicia impact (or radar dark lava flows) (from 19.334S, 226.177E to 19.627S, 226.762E, location E in Fig. 1). In each case, the continuity of the GDAR across the gaps is clear (based on matching of trend and width of the graben). The last position to which the GDAR can be reliably traced is 20.878S, 229.299E.

The width of the graben along the GDAR (measured using the Magellan SAR images) is typically 2±1 km which using the scaling ratios of 3.5±0.5 [after 6, using data from 45), and with error propagation would translate to a depth to the top of the underlying dyke of 600±300 m.

Topographic profiles using Magellan altimetry data across the graben reveal no discernable trough indicating that the maximum depth of the graben must be less than the vertical resolution (50-100 m) of the Magellan altimetry data31,46. The cross-section area of the surface graben should equal the rectangular area given by the distance from the top of the dyke to the surface, multiplied by the dyke width. Therefore, multiplying graben width (2±1 km) times inferred graben depth <75±25 m) should equal the estimated depth to the top of the dyke (0.6±0.3 km) times the dyke width. Using the above numbers, and with error propagation, the dyke width can be determined as <250±195 m. Obviously, there is considerable uncertainty in our estimate of dyke thickness, but we note that the range of values overlaps with measured widths (20 to >200 km) for terrestrial mafic dykes associated with mantle plumes2,10. Also, our outlined approach will yield better estimates (of the depth to the top of the dyke and dyke width) using the expected higher resolution altimetry of future Venus missions.

Link to Ozza Mons
The GDAR is part of the giant radiating swarm focused on Ozza Mons (Fig. 1 ref. 9), and is therefore linked to Ozza Mons. The GDAR appears to begin at a NNW-trending steep-sided elongate trough basin (72 km long, 18 km wide and up to 900 m deep) starting ~600 km from the Ozza Mons centre (Fig. 2) (see discussion below).

Control on trend of dykes
An individual dyke represents a single lateral emplacement event potentially emplaced in hours, days or weeks1,6,45,47,48. Recognition of such a long continuous dyke provides a rare opportunity to understand regional stress variation across a large region of Venus, at a geological instant. Regional mafic dyke swarms are emplaced as Mode 1 fractures, with trend perpendicular to the minimum compressive stress, and parallel to the maximum compressive stress47–50. They can have giant radiating and circumferential patterns associated with mantle plumes8. For radiating swarms, the radius of the domal uplift is linked to the size of the radiating portion of the swarm. However, given continued magma supply, the radial swarm will continue to propagate outward but then swing into a regional stress trend beyond the area of domal uplift3,51.

Swing in trend at Ningyo Fluctus
The GDAR trends initially to the SSE, then, at a distance of about 1200 km from the plume centre (blue star in Fig. 1) swings 50 degrees counter-clockwise (over a distance of about 300 km) when crossing Ningyo Fluctus (location A in Fig. 1). This change in trend is consistent with similar swings in other parts of the Ozza Mons radiating swarm9, and is interpreted to indicate a plume head radius for Ozza Mons of 1200 km9 (blue line in Fig. 1). The criteria for interpreting the transition from fully radiating to a swing in trend, as marking the edge of the underlying mantle plume, is discussed in 9, 52; it is linked to the extent of domal uplift associated with flattening of the plume head against the lithosphere. This approach derives from terrestrial literature on using a radiating dyke swarm to interpret plume head size, first done by 3 for the interpretation of the outer edge of the 1270 Ma Mackenzie plume head in northern Canada.

Consistent SW trend parallel to Parga Chasmata
Beyond 1200 km, the GDAR has an approximately linear trend which is parallel to the trend of the 10,000 km long rift system of Parga Chasmata. This indicates that the plume-generated uplift of Ozza Mons (which produced the radiating swarm including the GDAR) was coeval with active extension along the 10,000 km Parga Chasmata—at least for the 3000 km that is paralleled by the GDAR. This is reasonable since Parga Chasmata represents one arm of the 4-armed ‘triple’ junction rifting associated with Ozza Mons (Fig. 1 inset). Previous studies of local radiating swarms along Parga Chasmata had recognized some with trends locally swinging into parallelism to the Parga Chasmata rift zone22,27,53, but the remarkable continuity of the GDAR confirms a link between the timing of Ozza Mons (and its >3700 km long GDAR) and active extensional stresses along Parga Chasmata as a whole.

Geologically instantaneous regional time marker
The continuity of the GADR allows its use as a precise time marker to indicate relative ages along its length, based on cross-cutting relationships. The GADR appears to cut all geological units, both those associated with Ozza Mons, and along its path parallel to Parga Chasmata, except in three cases mentioned above: the GDAR is obscured by lava flow units on the north side of Oduduwa Corona (as mentioned above) indicating that Oduduwa Corona is younger (location B in Fig. 1). Multiple grabens of the radiating dyke swarm of Onenhtse Corona cross cut the GDAR, indicating that Onenhtse Corona is also younger than the GDAR (location D in Fig. 1). Radar dark (and hence fine-grained) material from Felicia impact crater obscures the dyke at location E in Fig. 1).

Characterizing the magma reservoir source
Given the current lack of significant erosion on Venus at the time of the GDAR (as discussed above), the surface expression of dykes as graben-fissure lineaments is visible unless covered by younger flows. A closer look at the entire length of the GDAR using the high-resolution Magellan SAR images (apart from the gaps mentioned above), confirms that nowhere along its 3700 km length did any significant lava spill out of the GDAR. We cannot rule out very small insignificant flows emanating from the dyke, having areal extents on the order of 6000–22,000 m2 on the order of a single Magellan SAR pixel (75–150 m37,38). Therefore, our conclusion is that the entire volume (or at least essentially the entire volume) of magma injected laterally into the GDAR is still preserved within the dyke.

We estimate the volume of magma injected into the GDAR, by multiplying dyke length by its width and vertical extent. A key question is the vertical extent of magma in a dyke. Models for dyke injection indicate that the dyke is ‘floating’ in the crust at a level of neutral buoyancy that matches the cumulative density of the vertical blade of mafic dyke magma against that of the host rocks over the same vertical distance6,10,47,54. An earlier estimate by 2 suggested that such laterally-emplaced terrestrial dykes bottom out in the lower crust. As summarized in 47 the maximum vertical height of a terrestrial dyke is likely between 10 and 20 km, although the analysis of 6 suggests vertical extents of >50 km. Estimates for the thickness of Venusian crust vary, and average values typically vary between 8 and 25 km55–57, with larger values for highlands e.g. 56. In the calculation below we use both 50 and 20 km for the GDAR’s vertical extent.

Widths of dykes in major regional swarms on Earth can range between 20 and 60 m, but the largest can reach more than 200 m6,10. Based on these values, the maximum and minimum volumes of the GDAR would be: 37,000 km3 (=3700 km × 200 m × 50 km) and 1480 km3 (=3700 km × 20 m × 20 km).

These values are compared with a very approximate estimate of the volume of the interpreted source magma reservoir, located about 600 km south of the Ozza Mons plume centre. We hypothesize that this steep sided trough basin (1200 km3 = 72 km long × 18 km wide × 900 m deep) (Figs. 1 and 2) represents roof collapse above an underlying dyke-like magma reservoir. On Earth some radiating swarms have been linked to lateral emplacement from major intrusions3, and on Venus we are also identifying source magma reservoirs through topographic depressions marking roof collapse as magma is expelled as flows or dykes (e.g. in 58). Lateral emplacement of the entire extent of the GDAR from the proposed reservoir would require multiple cycles (of filling and emptying of this reservoir). Using the above volume estimates for the GDAR this would suggest between 1 and 37 cycles (1480 km3/1200 km3 to 37,000/1200) to emplace the GDAR. This would indicate that the shallow magma reservoir (marked by the trough basin) was likely buffered with regular input of magma from another reservoir59, at greater depth or perhaps closer to the centre of Ozza Mons (Fig. 1).

Lessons for long dykes in other radiating swarms on Venus
The implications of our discovery of the 3700 km long Great Dyke of Atla Regio, should spur the search for additional long continuous single dykes on Venus, with implications for plume head size, buffered magma reservoirs, mapping regional stress variation across a large region of Venus at a geological instant, and revealing relative ages (through crosscutting relationships) over regional distances. Recognition of the GDAR and other long dykes will be valuable as observation targets for the new Venus missions planned over the next couple of decades including (VERITAS, DAVINCI, EnVision, Venera-D, Shukrayaan-1, VOICE).

On Venus, such long dyke swarms are particularly likely in the other major Regios on Venus that are interpreted to mark major plumes33–35,60, such as Beta, Bell, Eistla, and Imdr regios.

Lessons for dyke swarms on Earth
The radius of the plume head of Ozza Mons (1200 km) is in line with modelling, tomography, and dyke swarm radii for plume head size on Earth61, and supports the matching of plume head characteristics between Earth and Venus. Therefore, the great length of the GDAR indicates that terrestrial LIPs could have individual dykes of similar length. This is an important conclusion since the difficulty of tracing individual dykes leads to much shorter (and incorrect) estimates of maximum individual dyke lengths for LIPs, typically on the order of 10s of kms. However, lateral emplacement indicates that the individual dykes of a radiating swarm should track back to a magma reservoir source near or at the plume/diapir centre, with implication for much longer dyke lengths.

On Earth giant radiating swarms are observed in continental crust, but have so far not been recognized in Earth oceanic crust. However, since the composition of Venusian crust appears mainly basaltic (in contrast to the major continental area on Earth that host giant dyke swarms) then this result from Venus suggests that the tracing of such long individual dyke swarms could also be associated with terrestrial oceanic plumes/oceanic plateaus cutting basaltic oceanic crust.

Methods
We used full-resolution (~125 m/pixel) Magellan SAR images and altimetry data from USGS Astrogeology Science Center (https://astrogeology.usgs.gov/search?pmi-target=venus) and mapped in ArcGIS ArcMap v. 10.3. JMARS (Java Mission-planning and Analysis for Remote Sensing)62 was used for reconnaissance and generation of topographic profiles.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "Review of “The Great Dyke of Atla Regio, Venus: The Longest Traced Individual Dyke in the Solar System” for Nature Communicafions. April 29, 2023\nIn this study, the authors traced surface graben on Venus for over ~3700 km. They claimed that these graben are the surface manifestafion of a single dyke that is confinuous, except for several breaks (the largest of which is ~200 km). They inferred that this “confinuous laterally-emplaced underlying mafic dyke (verfical sheet of magma)” was “fed from a buffered magma reservoir” located south of a putafive mantle plume at Ozza Mons. They discussed implicafions of this conclusion for understanding the regional volcanic and tectonic acfivity. My comments below are quite crifical, so I want to emphasize first that this study is very interesfing. Venus is a superlafive sefting to study volcanic and tectonic processes. The conclusions of this manuscript, if convincingly established, would have many important implicafions. However, the stronger the conclusions, the stronger the scrufiny that a reviewer has a duty to apply…\nUnfortunately, I recommend rejecfing this manuscript because virtually all the major conclusions are not convincingly established—and, in fact, many of them seem to be in doubt. Overall, the manuscript relies on qualitafive analogies (and arguably excessive self-citafions) to establish its conclusions, which are not supported here by other types of data analysis or substanfial quanfitafive modeling. Many statements in the manuscript merit heavy caveats. Finally, the proposed acronym (“Great Dyke of Atla Regio (GDAR)”) and epithet (“longest traced individual dyke in the Solar System”) seem over-hyped. As discussed below, the GDAR has *not* been established as confinuous—and the manuscript acknowledges mulfiple fimes that there could be longer dykes on Venus and elsewhere.\nI elaborate on my concerns in order of appearance in the manuscript:\n- Line 13: The manuscript claims that the dyke is confinuous, laterally-emplaced, and mafic. However, the manuscript does not include sufficient evidence to prove these claims. The graben that allegedly are the surface manifestafion of the GDAR are *not* confinuous. There are mulfiple breaks, one as large as ~200 km. The manuscript claims (lines 141–152) that, because the dyke is allegedly confinuous, it must be older than Oduduwa Corona. However, this seems like circular logic? If the GDAR is not confinuous (e.g., if it were mulfiple dykes of different ages that happen to line up), then we cannot use cross-cufting analyses as simple as those presented here. Finally, the claims that the dyke was laterally-emplaced and (especially) mafic seem to rely on qualitafive analogies to dyke swarms on Earth. But there are, in principle, ways to idenfify the composifion of rocks besides drawing lines on a map. I do not believe that the analyses in this manuscript uniquely constrain the putafive magma to a mafic composifion.\n- Lines 18–19: The last sentence of this abstract relies on a very simple calculafion that has substanfial uncertainfies that are not addressed (discussed toward the end of my comments). I think it is hazardous to the unwary reader to have things stated as fact when they are quite speculafive.\n- Line 57: The “at least back to about 1 Ga” claim is wildly overstated. The surface might not be nearly that old, on average. The canonical Venus II book chapter by McKinnon et al. (1997) esfimate the surface age as ~300–1250 Myr. Le Feuvre & Wieczorek (2011, Icarus) derived a cratering age of ~240 Myr for the surface of Venus. So, giving a number like 1 Ga with total certainty might mislead readers. Furthermore, the citafion here is inappropriate—and is, alas, an example of this manuscript’s habit of self-citafion. Reference 17 by Way, Ernst, & Scargle is a very interesfing study, but it focuses on the fiming of large-scale volcanism on Earth. It does not report, as far as I can tell, substanfial new analyses of the age of the surface of Venus or possible rates of erosion. I recommend cifing works that establish the stated claims (in this case, after modifying the claim appropriately). Finally, “significant” is doing a lot of work in this sentence. There is some sedimentary acfivity on Venus today. Venera landers observed stuff moving; there are dunes; craters produce sediment that is clearly moved around over fime; etc. What counts as “significant”?\n- Lines 66–67: The resolufion of the SAR images is overstated throughout the manuscript. The available mosaics are presented at a pixel scale of 75 meters per pixel, but they are over-sampled. The real resolufion is ~125 meters per pixel (e.g., Saunders et al. 1992).\n- Lines 72–74: The hypothesis that the GDAR is laterally-emplaced is one of the major claims of this manuscript. However, again the main evidence seems to be qualitafive analogy to other locafions on Venus and Earth. Specifically, how “can [it] be inferred” that individual dykes are laterally emplaced? How was this done for the radiafing swarm around Artemis? Can those same methods be applied here? Incidentally, this is also the place in the manuscript that highlights why calling the GDAR “longest” might seem like puffery—dykes around Artemis could be much longer.\n- Lines 80–81: The claim that “Atla Regio is recognized as a major plume centre” needs a reference (not a self-citafion, please) and elaborafion. On what basis do folks infer the presence of a mantle plume? Are there compefing hypotheses?\n- Line 98: “72 km”?\n- Line 106–107: “The recognifion of the GDAR” is stated as a fact here (and elsewhere) and used to support many further claims. However, the “GDAR” has several breaks in confinuity, and the authors have not mustered sufficient proof that these breaks are not real gaps between different dykes. In any case, all these statements need caveats. If the GDAR is one confinuous dyke, then we can make certain claims.\n- Line 126: “Confirming” seems way too strong here. Maybe “consistent with...”? Determining the plume head size would probably require geophysical data like seismology, high-resolufion gravity, etc.\n- Line 137: Again, “the remarkable confinuity of the GDAR provides a conclusive link” is way too strong. It’s not enfirely confinuous.\n- Lines 142–152: Again, the topic sentence of this paragraph is way too strong. Also, “GADR”? The dyke could be used as a precise fime marker if it were confinuous. However, that seems to be an *assumpfion* because there is no specific proof that the breaks in visible confinuity do not correspond to the real end of a dyke. Line 145 says that “the only significant break in the confinuity of the GDAR is for 200 km” but “significant” is in the eye of the beholder (and I believe disallowed in Nature journals unless one has performed a stafisfical test with a quanfitafive threshold). Confinuity is the sine qua non of this manuscript, so I believe that proving the stated conclusions would require evaluafing every single break in confinuity observed along the trace.\n- Lines 160–161: “the surface expression… is visible unless covered by younger flows” implies that the depth of the dyke does not change along its length, correct? If the dyke were verfically emplaced or laterally emplaced but at different depths along track, then the surface expression could change even if the surface were everywhere the same age?\n- Lines 162–165: Apologies that I sound like a broken record, but I do not believe that it is possible to draw such a strong conclusion from the evidence presented in this manuscript. Specifically, the authors state “nowhere along its 3700 km length did any lava flow spill out of the GDAR. Our conclusion is that the enfire volume of magma injected laterally to form the GDAR is sfill preserved within the dyke.” Let me draw a qualitafive analogy. Balfis Vallis is the longest lava (almost certainly lava) channel on Venus. However, scienfists debate whether lava flowed from north to south or from south to north. That’s because it’s not obvious where lava spilled out of Balfis Vallis. However, I would not thus conclude that all the lava that formed Balfis Vallis is *sfill inside* Balfis Vallis. Our available data are limited (e.g., the radar images have low-resolufion; we do not have composifional data; we haven’t yet done sub-surface radar sounding that could idenfify individual flows). I could make similar arguments about over a hundred other lava channels on Venus. So, can the authors prove that *their failure to observe* lava spilling out of the dyke means that *no lava at all* spilled out of the dyke? Surely there is some amount of lava (maybe a huge amount) that could have spilled out but escaped detecfion? Maybe EnVision and/or VERITAS will find some? In an extreme case, perhaps nearly the *enfire* volume of lava spilled out of the end of the dyke, but then the end of the dyke was covered by a younger flow? Overall, the stated conclusion seems like an extreme upper bound on reality—and the manuscript should acknowledge other possibilifies.\n- Lines 165–184: Here is the quanfitafive part of the manuscript, which underlies the central conclusion that the GDAR was fed from a buffered magma reservoir. However, once again, this conclusion depends on an assumpfion that was not well-jusfified. The calculafion of the magma volume includes an uncertainty analysis related to measurements of the width of the dyke. However, the verfical extent of the dyke is even more uncertain—but no such uncertainty is included in the calculafion. Specifically, the manuscript uses 20 km as the verfical extent. If the verfical extent is <10 km, then only one cycle of magma from the reservoir is (maybe) required to fill the dyke—meaning that the conclusion of a “buffered magma reservoir” goes away. How do we know that the verfical extent is not <10 km? Cited references 33 and 9 seem to focus on Mars and Earth. Reference 33 admits verfical heights <10 km—and condifions on Venus could be different than on Earth. In parficular, the relevant calculafion would require assumpfions about the density of the magma and the host rocks. The manuscript does not provide esfimates for those densifies, which must be considered uncertain in the absence of much relevant geophysical data for Venus. Similarly, one number is used for the volume of the volume of the source magma reservoir, but that number is uncertain. As with virtually all the conclusions in this manuscript, the scenario described by the authors seems *possible* but is by no means the only possibility that is consistent with the data.\n- Lines 197–201: To support transparent and reproducible science, I believe that the authors should make available, in an accessible digital format, all the data used to generate the figures in the manuscript (e.g., all traces and topographic profiles).\n- References. By my count, almost half of the citafions are self-citafions, which seems a bit excessive. I recommend reconsidering these self-citafions. As with the “1 Ga” “[17]” example discussed above, there might be many cases where it would be more appropriate to cite a paper that directly performed the relevant analysis, rather than a study, which included the senior author, that simply menfioned the issue.", "reviewer_2": "Review of Nature Communicafions Manuscript: The Great Dyke of Atla Region, Venus: The Longest Traced Individual Dyke in the Solar System\nGeneral comments:\nThis manuscript presents a strong case for idenfifying the longest single dyke in the Solar System on the planet Venus. This idenfificafion could have extremely important implicafions for our interpretafion of stress regimes on Venus, as well as our ability to determine relafive ages across large regions. This manuscript is well wriften and lays out its case carefully. However, it would benefit from some slight restructuring and some addifional clarificafion to befter support its argument.\nSpecific Comment:\nThe authors frequently say that they are observing (or mapping, or measuring) dykes when what they really mean is that they are observing graben that they are interprefing to overlie dykes. This is a prefty important disfincfion to make. The papers the authors are cifing to support their interpretafion of dykes beneath the graben all assume that it is the emplacement of the dykes that forms the overlying graben. There is sfill quite a considerable amount of debate about this issue. For all of the literature that supports the contenfion that graben form above dykes, there is an equal number of papers showing that dykes don’t necessarily form overlying graben. Not every graben on Earth has a dyke beneath it, so it is odd that planetary researchers seem to assume that there is a dyke beneath every graben on Venus (or Mars). And there are mulfiple locafions on Earth where exposed cross-secfions of dykes show no fracturing (or deformafion of any kind) above them. Physical models have also shown that dyking does not necessarily form graben.\nTo be fair, the authors do state that they are making this interpretafion in several places in the manuscript. But it doesn’t make it any less jarring when they then talk about measuring the length of a dyke when what they really mean is they measured the length of the graben that they are interprefing to overlie a dyke. And to be clear, I am not trying to suggest that there are no dykes beneath the graben radial to Ozza Mons. I just think that the authors could be more precise and accurate in their wrifing. Such clarity would only strengthen their arguments and support their case for the presence of a 3700 km long dyke on Venus.\nMinor Comments:\nI have made some suggesfions in an aftached annotated PDF that I believe would strengthen the paper.", "reviewer_3": "In this short paper, El Bilali & Ernst analyze Magellan radar images of Venus’ Atla Regio to map a giant dyke that is described as the longest dyke traced so far on Venus and the enfire solar system. The authors demonstrate a length of least 3700 km and potenfially almost 4500 km, which substanfially exceeds the longest dyke traces on Earth. The authors trace the dyke based on its graben signature and use elevafion data to idenfify major troughs. I found this lefter relevant and interesfing to read and it is relafively easy to follow the manuscript even without being an expert on dyke swarms and/or geological mapping. In this sense, I feel this work is on interest for publicafion in a journal such as Nature Communicafions.\nI have not spofted any major flaw in the way the results are obtained and interpreted. However, I was a liftle disappointed about the discussion of broader implicafions and significance of the detecfion of such a long dyke. Some issues that I would have liked to see discussed a bit more:\n1.) Could such a long dyke imply that Venusian dykes may be longer than on Earth’s or does it just demonstrate that terrestrial dykes are much more overprinted and we can trace their original length? Are there implicafions of such a long dyke on the properfies and state of the interior (which are thought to be different and probably have been for substanfial fime for Earth and Venus)? For instance, could the place constraints on local crustal thickness and strength?\n2.) What is a feasible tectonic regime that may support such long dykes? Is this more in line with classical end-members such as the stagnant or mobile lid tectonics, or could that be befter explained by some more recent suggesfions for Venus’ tectonic regime, such as the plutonic-squishy lid?\n3.) I understand that the 1200-km-distance at which the direcfional swing of the dyke occurs is here used as a proxy for the source plume head below Ozza Mons, but I would have liked a short discussion whether this is indicates an unusually large plume or not, perhaps by comparison to befter-studied terrestrial seftings. In other words, is a very long dyke indicafive of an unusually large or hot plume head? Or is the length of dyke swarm thought to be controlled mostly by other factors?\n4.) The last paragraph (line 190++) points towards searching for other long confinuous dykes on Venus. But what are regions on Venus which may display such features more likely than others? Also, in what sense may be upcoming Venus missions – Veritas, DaVinci, and EnVision – help to idenfify more such dykes and/or provide more details about the structure of the GDAR and its implicafions?\nI think, some elaborafion of points 1.) - 4.) would improve the manuscript and its impact on the Venus’ science community the most, but I do have some addifional minor comments, following below. Overall, I think this paper can be made suitable for publicafion with minor-to-moderate revision.\nAddifional comments:\nLine 11++: The abstract lacks a statement of the broader significance for our understanding of either dykes or of Venus’ tectonics. It would be good to add one if the word limit allows.\nLine 17: Remove the comma after “1200 km”.\nLine 29: “It is inferred ...” Inferred based on what? Also, the word “inferred” seemed to appear quite often throughout the manuscript. Please check and think about alternafives.\nLine 40/41: Where has been the longest dyke in the solar system before your detecfion of GDAR? Readers may wonder about this (well, I did ...).\nLine 57: “...at least back to about 1 Ga ...” Why 1 Ga? Is that supposed to be linked to Venus’ mean surface age? This is unknown and, yes, 1 Ga is in the range of esfimates. But at the very upper end, and the most recent esfimates tend to suggest younger surface ages perhaps as young as 100-200 Myr. Please clarify, why you write “at least 1 Ga” if actually have very liftle clue of how Venus’ operated at this fime (it may or may not had more acfive tectonics etc.)\nLine 59: “... inferred to overlie blind dykes ...” I do not understand how such blind dykes can be recognized from radar images such as those used here? Would that not need some rather high-resolufion gravity data at least? Or is this inference actually just used in analogy to terrestrial dykes for we may know about these blind dykes?\nLine 64: I am puzzle by the word “once-compressed”. Could it be also twice-compressed? Does it effecfively mean that the compressed images have coarser resolufion (225m/px) than the uncompressed (75m/px)?\nLine 69: “In this study [20] ...” should be “In that study [20] ...”!?\nLine 185++: This short paragraph falls a bit short compared to the others. Would you expect similarly long dykes extending outwards from Ozza Mons in various direcfions (at least unfil the 1200 km-limit up to which the regional stresses seem to be less significant)? Or could there be some preferenfial direcfions? In Figure 1, it seems that there is at least one quadrant (SW) of the blue circle without any radiafing graben systems (orange line)? Why?\nLine 203++: DOI’s seem to be missing consistently in the reference. These are always useful to have. It seems references 4 and parficularly 30 are earlier (reduced) versions of the contents presented here, so consider delefing these ref’s, especially as they are conference abstracts without peer-review.\nFigure 1: I am not sure what the color coding in the large-scale inset (upper right corner of the figure) is meant to represent!?\nFigure 2: It was not clear to me immediately what the 500 m label in the left panel is supposed to mean. While I got it on a second look, consider adding a note in the capfion to make it clear right away. Also, it seems that you show here a ~100-200 km long secfion from the beginning of the GDAR, that is close to Ozza Mons, I suppose. It would be interesfing to see, for comparison, how this compares to a secfion further away, perhaps at around the 1200-km boundary or even further out. This could potenfially indicate structural changes along the dyke"}, "author_response": "REPONSE TO REVIEWER COMMENTS (in red font)\nReviewer #1 (Remarks to the Author):\nReview of “The Great Dyke of Atla Regio, Venus: The Longest Traced Individual Dyke in the Solar System”\nfor Nature Communications. April 29, 2023\nIn this study, the authors traced surface graben on Venus for over ~3700 km. They claimed that these\ngraben are the surface manifestation of a single dyke that is continuous, except for several breaks (the\nlargest of which is ~200 km). They inferred that this “continuous laterally-emplaced underlying mafic\ndyke (vertical sheet of magma)” was “fed from a buffered magma reservoir” located south of a putative\nmantle plume at Ozza Mons. They discussed implications of this conclusion for understanding the\nregional volcanic and tectonic activity. My comments below are quite critical, so I want to emphasize\nfirst that this study is very interesting. Venus is a superlative setting to study volcanic and tectonic\nprocesses. The conclusions of this manuscript, if convincingly established, would have many important\nimplications. However, the stronger the conclusions, the stronger the scrutiny that a reviewer has a duty\nto apply…\nUnfortunately, I recommend rejecting this manuscript because virtually all the major conclusions are not\nconvincingly established—and, in fact, many of them seem to be in doubt. Overall, the manuscript relies\non qualitative analogies (and arguably excessive self-citations) to establish its conclusions, which are not\nsupported here by other types of data analysis or substantial quantitative modeling. Many statements in\nthe manuscript merit heavy caveats.\nFinally, the proposed acronym (“Great Dyke of Atla Regio (GDAR)”) and epithet (“longest traced\nindividual dyke in the Solar System”) seem over-hyped.\nREE: the use of the term “Great Dyke…” is common on earth for individual mafic (-ultramafic) dykes that\nare particularly long and significant. The text refers to examples such as the Great Dyke of Zimbabwe,\nand the Great Abitibi dyke. Other examples can be added if necessary.\nREE: perhaps we have over hyped this--- but it is certainly the longest TRACED individual dyke in the\nSolar System—I am very knowledgeable on the terrestrial and planetary literature on dykes, and there is\nno longer individual dyke yet traced. So the hype is justified, but we have toned it down. In particularly\nwe have changed the title to:\n“FAR-TRAVELLED (4000 KM) MAGMA PROPOGATION JUST BELOW THE SURFACE OF\nVENUS”\nAs discussed below, the GDAR has *not* been established as continuous—and the manuscript\nacknowledges multiple times that there could be longer dykes on Venus and elsewhere.\nREE: We explain below why the interpretation of a continuous dyke is correct, and our explanation for\ngaps. We certainly indicate that the careful tracing of dykes in other swarms may yield longer dykes.\nBut until this work yields a longer individual dyke, then the GDAR remains the record holder for the longest\nTRACED individual dyke.\nThe Artemis radiating swarm of (Hansen and Olive 2010 Geology) is the largest radiating swarm with the\nswarm extending up to 6000 km away from the Artemis centre. It is sensible to consider that these have\nbeen laterally emplaced for the entire 5000 km distance from the edge of corona ring (at about 1000 km\nradius) to the full extent of swarm—and thus 5000 km long individual dykes can be expected—but this\nwill need to be confirmed by detailed mapping of the type we have done. Thus, our approach is also a\ntemplate for how to approach identifying other very long individual dykes\nI elaborate on my concerns in order of appearance in the manuscript:\n- Line 13: The manuscript claims that the dyke is continuous, laterally-emplaced, and mafic. However,\nthe manuscript does not include sufficient evidence to prove these claims.\nREE: the continuity of the GDAR is based on its distinct width and appearance (see images in Figure 1)\nwhich allow it to be traced reliably across such gaps. We would be happy to ‘walk’ with the reviewer\n(using Magellan images) showing that our tracing of this dyke is unambiguous. We also noted in the text\nthat the 1700 km long Penthesilea Fossa portion was previously recognized as a single dyke in Brian et al\n(2005).\nThe graben that allegedly are the surface manifestation of the GDAR are *not* continuous. There are\nmultiple breaks, one as large as ~200 km. The manuscript claims (lines 141–152) that, because the dyke\nis allegedly continuous, it must be older than Oduduwa Corona. However, this seems like circular logic?\nIf the GDAR is not continuous (e.g., if it were multiple dykes of different ages that happen to line up),\nthen we cannot use cross-cutting analyses as simple as those presented here.\nREE: Our logic is partly based on extensive terrestrial experience mapping dyke swarms including the\n700 km long Great Abitibi Dyke for my PhD (Ernst and Bell 1992 J. Petrology). The GDAR is so distinctive\nin its graben width, that it is not reasonable to hypothesize multiple separate dykes (with similar wide\ngrabens) just happening to line up.\nFinally, the claims that the dyke was laterally-emplaced and (especially) mafic seem to rely on qualitative\nanalogies to dyke swarms on Earth.\nREE: The interpretation that regional dyke swarms on Earth (and Venus and Mars) are mainly laterally\nemplaced is so well established in the literature (as referenced in the manuscript); it is not really open to\ndebate any more. We included some of the key papers, but could add at least 20 more in support lateral\ninjection of regional dyke swarms on Earth and Venus and Mars.\nBut there are, in principle, ways to identify the composition of rocks besides drawing lines on a map. I do\nnot believe that the analyses in this manuscript uniquely constrain the putative magma to a mafic\ncomposition.\nREE: On Earth the major regional dyke swarms are dominantly mafic. Dykes of ultramafic (e.g. kimberlite\ndykes) and silicic composition tend to have much narrower widths. Given the similar regional scale of\ninterpreted dyke swarms on Venus and Mars it is entirely reasonable to also infer their\nmafic compositions. Modelling by Wilson and Head (2002 JGR) also supports mafic compositions. In\nfact, there is no literature that I am aware of that interprets the dykes underlying graben (on Mars and\nVenus) to be anything other than mafic in composition.\nREE: A further point: On Venus, there is a consensus that about 80% of the planet is covered by basaltic\nvolcanism and the only potential area of silicic magma is in the older tesserae areas. In some\ncases, graben (interpreted to overlie dykes) are observed to feed flows (that are interpreted to be\nbasaltic), and for these examples the dykes (feeding the flows) must also be mafic in composition.\n- Lines 18–19: The last sentence of this abstract relies on a very simple calculation that has substantial\nuncertainties that are not addressed (discussed toward the end of my comments). I think it is hazardous\nto the unwary reader to have things stated as fact when they are quite speculative.\nREE: Agreed. The calculation has significant uncertainties, which we discuss more completely in the text,\nbut the observation of the remarkable topographic trough, and its interpretation as a collapsed magma\nchamber at the start of the GDAR--- is consistent with the abundant literature linking the source of\nregional radiating dyke swarms to such buffered magma chambers. We have revised the text to\nconsider the range possible refilling values, and have add more justification of the values used for the\ncalculation.\n- Line 57: The “at least back to about 1 Ga” claim is wildly overstated. The surface might not be nearly\nthat old, on average. The canonical Venus II book chapter by McKinnon et al. (1997) estimate the surface\nage as ~300–1250 Myr. Le Feuvre & Wieczorek (2011, Icarus) derived a cratering age of ~240 Myr for the\nsurface of Venus. So, giving a number like 1 Ga with total certainty might mislead readers. Furthermore,\nthe citation here is inappropriate—and is, alas, an example of this manuscript’s habit of self-citation.\nReference 17 by Way, Ernst, & Scargle is a very interesting study, but it focuses on the timing of large-\nscale volcanism on Earth. It does not report, as far as I can tell, substantial new analyses of the age of\nthe surface of Venus or possible rates of erosion. I recommend citing works that establish the stated\nclaims (in this case, after modifying the claim appropriately). Finally, “significant” is doing a lot of work in\nthis sentence. There is some sedimentary activity on Venus today. Venera landers observed stuff\nmoving; there are dunes; craters produce sediment that is clearly moved around over time; etc. What\ncounts as “significant”?\nREE: We thank this reviewer for this useful and correct point. 1 Ga was added as a shorthand for the\ntiming, but we have revised the text to include the suggested new references (McKinnon et al. (1997)\nand Le Feuvre & Wieczorek (2011, Icarus), to better reflect the uncertainties in timing.\nTo add these uncertainties to the timing of the formation of the Venusian surface. we also note that\nthere is an emerging consensus that the Venusian surface formed over a range of time in a number of\nseparate, not in a single volcanic resurfacing event.\nREE: The word significant is used in four places in the manuscript and given Nature’s policy of restricting\nits use to statistical cases, then we have changed the word in each of the four cases.\n- Lines 66–67: The resolution of the SAR images is overstated throughout the manuscript. The available\nmosaics are presented at a pixel scale of 75 meters per pixel, but they are over-sampled. The real\nresolution is ~125 meters per pixel (e.g., Saunders et al. 1992).\nREE: minor point—and in fact the actual resolution varies across the planet (because of the changing\ndistance to the surface in each pass of the Magellan spacecraft), but we indicate that the resolution\nvaries across the planet but with an average of 125 m – as suggested by this reviewer.\n- Lines 72–74: The hypothesis that the GDAR is laterally-emplaced is one of the major claims of this\nmanuscript. However, again the main evidence seems to be qualitative analogy to other locations on\nVenus and Earth. Specifically, how “can [it] be inferred” that individual dykes are laterally emplaced?\nREE: There is extensive literature on lateral emplacement of regional (mafic) dyke swarms on Earth,\nVenus and Mars from a variety of scientific constraints including on the basis of theoretical modelling,\nmagnetic and petrographic fabric analysis of samples, geochemistry and paleomagnetic studies along\nindividual dykes. I could easily add many more references in support of this consensus view.\nHow was this done for the radiating swarm around Artemis? Can those same methods be applied here?\nREE: Actually, the interpretation of lateral emplacement of the giant radiating swarm associated with\nArtemis (Hansen and Olive 2010, Geology), does use the same ‘method’ as we have done--- and refers to\na number of terrestrial and planetary papers—including several from the Corresponding Author for this\nGDAR manuscript, Ernst.\nIncidentally, this is also the place in the manuscript that highlights why calling the GDAR “longest” might\nseem like puffery—dykes around Artemis could be much longer.\nREE: We are very precise in our statement that this individual graben (interpreted as overlying a dyke)\nis TRACED for such a distance, giving it the current record for maximum TRACED length of a individual\ndyke. We certainly anticipate that our record may be broken by similar studies on other long\nswarms. For instance, the Artemis dykes extend from the rim (at 1000 km radius) out to 6000 km,\nmeaning that individual Artemis dykes have the POTENTIAL to be directly INDIVIDUALLY TRACED up to\n5000 km in length. But until this is successfully done, then our GDAR does hold the length record.\n- Lines 80–81: The claim that “Atla Regio is recognized as a major plume centre” needs a reference (not\na self-citation, please) and elaboration. On what basis do folks infer the presence of a mantle plume?\nAre there competing hypotheses?\nREE: Reference added to key newly-accepted paper in Commun Earth and Environment (El Bilali et al.\n2023). This reference summarizes the existing literature and provides new conclusive evidence from the\nradiating graben systems in support of a plume origin for Atla Regio.\n- Line 98: “72 km”?\nREE: thanks--- the missing “km” has been added\n- Line 106–107: “The recognition of the GDAR” is stated as a fact here (and elsewhere) and used to\nsupport many further claims. However, the “GDAR” has several breaks in continuity, and the authors\nhave not mustered sufficient proof that these breaks are not real gaps between different dykes. In any\ncase, all these statements need caveats. If the GDAR is one continuous dyke, then we can make certain\nclaims.\nREE: It is so well established in the terrestrial literature (since initial key papers of Halls et al.. 1982, and\nFahrig, 1985) that major radiating swarms are laterally emplaced. This requires a lateral continuity of\ndykes (which has been supported in the terrestrial literature, from paleomagnetic and geochemical\narguments). Even the observation of en echelon offsets is not an issue with interpreted continuity of\ndyke at depth (as referenced in our manuscript). See the text below for a more complete discussion of\nthe reasons that dykes of radiating swarms are laterally emplaced (except near the plume centre\nregion).\nWe could include such text (with references) as a Supplementary File if recommended by the Editor.\nActually, there is much evidence AGAINST vertical emplacement and IN FAVOUR of lateral emplacement\nin giant radiating swarms.\n1) There is no geophysical evidence for a widespread magma chamber underneath the entire\nextent of radiating swarms (the extent of a magmatic underplate can be recognized from\ngeophysics, is only the central part of radiating swarms.--- for some swarms that would require a\nmagma reservoir over millions of square km at the base of the crust.\n2) Another issue is that many swarms are emplaced in crustal blocks with thick lithospheric roots—\nsufficiently thick that mafic magma could not be generated from beneath--- the simplest\nsolution is lateral emplacement of the magma from regions of thinner lithosphere at the edge of\nthe craton via lateral dyke emplacement\n3) Geochemical study indicates separate dykes of a swarm can have a distinct incompatible trace\nelement chemistry along their length, but the unique incompatible trace element chemistry\ncharacteristic of each dyke is different from that of nearby dykes of the same swarm. A good\nexample is the 700 km long Great Abitibi dyke of the Canadian shield and its companion long\ndykes (hundreds of km in length which are separate from the Great Abitibi dyke by only 10s of\nkm. This implies that each individual dyke represents a single distinct magmatic pulse that could\nextend 100s of km long but be different than the geochemical pulse that is characteristic of a\nneighboring dyke 100s of km in length. How is this possible to producing such consistent\nchemistry for linear features (dykes 100s of km along), but be different for adjacent linear\nfeatures (dykes) in the swarm. This is not consistent with derivation of a giant radiating swarm\nfrom a coextensive underlying magma chamber\n4) Magmatic fabric studies in radiating swarms typically indicate lateral emplacement except near\nthe plume centre\n5) The surface expression of radiating dyke swarms on Venus and Mars is as graben--- meaning\nthat the magma is not vertically emplaced except locally.\nREE: So if a major (distinctive) individual dyke ends and then reappears further along trend, that can\nonly mean (based on the evidence of lateral emplacement of regional-scale radiating dyke swarms) that\nthe intervening portion of the dyke has been obscured—by younger units.\nREE: Our argument is not circular-----given that we can see the interpreted same major graben (dyke)\nreappearing further away. Key to this argument is distinct width and appearance of the GDAR graben\n(see images in Figure 1) which is so unlike any of the other nearby graben.\n- Line 126: “Confirming” seems way too strong here. Maybe “consistent with...”? Determining the plume\nhead size would probably require geophysical data like seismology, high-resolution gravity, etc.\nREE: We have changed to “consistent with” Again our newly published paper on the Atla Regio\nSuperplume (El Bilali et al., 2023, Commun: Earth and Environment) fully answers this question of\nplume size of Ozza Mons\n- Line 137: Again, “the remarkable continuity of the GDAR provides a conclusive link” is way too strong.\nIt’s not entirely continuous.\nREE: We have commented on this above.\n- Lines 142–152: Again, the topic sentence of this paragraph is way too strong. Also, “GADR”? The dyke\ncould be used as a precise time marker if it were continuous. However, that seems to be an\n*assumption* because there is no specific proof that the breaks in visible continuity do not correspond\nto the real end of a dyke.\nREE: The key criterion for assessing dyke continuity is this particular graben is so distinct (by its width\nand appearance) that it can be reliably traced across gaps (even the 200 km gap). We would be happy\nhave a Zoom call to ‘walk’ along the dyke using the Magellan SAR image and show that a single dyke is a\nreasonable interpretation.\nREE: By the way, my PhD was on the Great Abitibi Dyke (GAD) that we traced for 700 km using both\ngeology maps and aeromagnetic images. However, in a few areas the aeromagnetic maps were busy,\nleading to small breaks in the continuity of GAD. But since this dyke (GAD) was so wide (90-250 m in\nthickness) then it was confidently traced across these gaps. Furthermore, geochemistry and\npaleomagetic data confirm that the Great Abitibi Dyke (despite some aeromagnetic gaps) was indeed a\nsingle dyke: chemistry showed a distinct trace element geochemistry at sites along the dyke (which was\ndifferent from adjacent dykes) and similarly the paleomagnetic data showed a distinct palaeomagnetic\ndirection along the dyke that differed from that along other adjacent dykes of the swarm (representing\nemplacement and cooling of the Great Abitibi dyke as a single event in a short time (<1000 years) )\nLine 145 says that “the only significant break in the continuity of the GDAR is for 200 km” but\n“significant” is in the eye of the beholder (and I believe disallowed in Nature journals unless one has\nperformed a statistical test with a quantitative threshold). Continuity is the sine qua non of this\nmanuscript, so I believe that proving the stated conclusions would require evaluating every single break\nin continuity observed along the trace.\nREE: We have replaced the word “significant” per the guidance in Nature journals, in which this term\nshould only be used in a statistical sense. In the text we have added more information on each of the\nbreaks (and giving the coordinates of the start and end of each break)\n- Lines 160–161: “the surface expression… is visible unless covered by younger flows” implies that the\ndepth of the dyke does not change along its length, correct? If the dyke were vertically emplaced or\nlaterally emplaced but at different depths along track, then the surface expression could change even if\nthe surface were everywhere the same age?\nREE: current understanding of large radiating dyke swarms, indicates that they are emplaced vertically\nnear the plume centre (within a few hundred km) but then emplaced laterally out to the full extent of\nthe swarm, e.g out to 2300 km in the Mackenzie dyke swarm of Canada (e.g. Ernst and Baragar 1992,\nNature, and other more recent references)--- see my more detailed comment above.\nREE: however, dominant vertical emplacement may occur in linear swarms, particularly those associated\nwith a rift zone--- but lateral emplacement dominates in giant radiating swarms\nREE: There is very little known about the surface expression of dykes on Earth because the surface\ngraben are only rarely observed (due to widespread erosion on Earth). So we don’t really know the\nmagma level (depth below surface) on Earth nor Venus. We can speculate (as done by Baragar et al.\n1996, J. Petrol.) that dykes will be travelling laterally away from the plume centre and perhaps at a\nrelatively constant level below the surface. In any case, further work that analyzes the width and other\ncharacteristics of graben above the GADR on Venus can potentially help address the above question.\nWe have added some text with some estimate of the characteristic width of the GDAR graben and\nestimates of the depth to the top of the dyke\n- Lines 162–165: Apologies that I sound like a broken record, but I do not believe that it is possible to\ndraw such a strong conclusion from the evidence presented in this manuscript. Specifically, the authors\nstate “nowhere along its 3700 km length did any lava flow spill out of the GDAR. Our conclusion is that\nthe entire volume of magma injected laterally to form the GDAR is still preserved within the dyke.”\nREE: But this is exactly what we expect on Earth—part of the recognition of long distance lateral\nemplacement of dykes on Earth is assuming that the magma is not spilling out. If magma does spill out\nthen this would likely cause the dyke to end or reduce the distance that the dyke could continue to\npropagate laterally.\nLet me draw a qualitative analogy. Baltis Vallis is the longest lava (almost certainly lava) channel on\nVenus. However, scientists debate whether lava flowed from north to south or from south to north.\nThat’s because it’s not obvious where lava spilled out of Baltis Vallis. However, I would not thus\nconclude that all the lava that formed Baltis Vallis is *still inside* Baltis Vallis. Our available data are\nlimited (e.g., the radar images have low-resolution; we do not have compositional data; we haven’t yet\ndone sub-surface radar sounding that could identify individual flows). I could make similar arguments\nabout over a hundred other lava channels on Venus. So, can the authors prove that *their failure to\nobserve* lava spilling out of the dyke means that *no lava at all* spilled out of the dyke? Surely there is\nsome amount of lava (maybe a huge amount) that could have spilled out but escaped detection? Maybe\nEnVision and/or VERITAS will find some? In an extreme case, perhaps nearly the *entire* volume of lava\nspilled out of the end of the dyke, but then the end of the dyke was covered by a younger flow? Overall,\nthe stated conclusion seems like an extreme upper bound on reality—and the manuscript should\nacknowledge other possibilities.\nREE: Yes, it is our robust conclusion that along its traced length that the GDAR does not spill any\nlava. We have a lot of experience identifying flows coming out of graben (dykes) on Venus. Our\nInternational Venus Research Group has about 40 students from 5 countries doing detailed mapping of\nlava flows and grabens all over Venus, having produced 28 abstracts for the Lunar and Planetary Science\nConference (LPSC) in 2023 and 34 abstracts for LPSC 2022. So, we can easily recognize flows fed from\ngrabens. Thus, it is remarkable to us that the GDAR does not anywhere along its traced length exhibit\nflows sourced from the grabens. Also, we do not see any flow emanating from the end of the dyke. We\nmaintain that these are robust observations. This also could be demonstrated via a Zoom tour of\nMagellan SAR images along the dyke.\nREE: Reviewer 3 does make the point that the dyke could actually extend further and feed flows; but\nthat these are obscured by younger cover. We did look for a considerable distance beyond the traced\nend of the GDAR for any resumption of this dyke—so we think that we have indeed reached the end of\nthe GDAR.\nREE: It certainly is also possible that in the 200 km gap where we interpret the dyke to be overlain by a\nyounger flow unit, that there is lava-spilling from this hidden portion of the dyke.. But since along nearly\n3500 km of traced dyke we so no spilling, then it is more probable that there is no spilling in the 200 km\nlong hidden portion of the GDAR In any case we have added text to indicate acknowledge that we can\nprove the absence of feeding of flows in the gaps\nREE: this analysis of long lava channels (canali) is sensible but is not a relevant analogy to dykes.\n- Lines 165–184: Here is the quantitative part of the manuscript, which underlies the central conclusion\nthat the GDAR was fed from a buffered magma reservoir. However, once again, this conclusion depends\non an assumption that was not well-justified. The calculation of the magma volume includes an\nuncertainty analysis related to measurements of the width of the dyke. However, the vertical extent of\nthe dyke is even more uncertain—but no such uncertainty is included in the calculation. Specifically, the\nmanuscript uses 20 km as the vertical extent. If the vertical extent is <10 km, then only one cycle of\nmagma from the reservoir is (maybe) required to fill the dyke—meaning that the conclusion of a\n“buffered magma reservoir” goes away. How do we know that the vertical extent is not <10 km? Cited\nreferences 33 and 9 seem to focus on Mars and Earth. Reference 33 admits vertical heights <10 km—\nand conditions on Venus could be different than on Earth. In particular, the relevant calculation would\nrequire assumptions about the density of the magma and the host rocks. The manuscript does not\nprovide estimates for those densities, which must be considered uncertain in the absence of much\nrelevant geophysical data for Venus. Similarly, one number is used for the volume of the volume of the\nsource magma reservoir, but that number is uncertain. As with virtually all the conclusions in this\nmanuscript, the scenario described by the authors seems *possible* but is by no means the only\npossibility that is consistent with the data.\nREE: It is correct that there are significant uncertainties in the width and vertical extent of the Dyke and\nso the volume estimate has large uncertainties. Indeed, we have used the range in plausible values to\nbracket the volume and conclude a range in refilling from 1 time to 37 times.\n- Lines 197–201: To support transparent and reproducible science, I believe that the authors should\nmake available, in an accessible digital format, all the data used to generate the figures in the\nmanuscript (e.g., all traces and topographic profiles).\nREE: Our interpretation is entirely reproducible. The Magellan SAR image data are available via the USGS\nAstropedia site and also on the JMARS site--- and the map shows the location of the line work which can\nallow anyone to confirm our tracing of the GDAR. We have also added coordinates all the labelled places\nalong the GDAR in Figure 1 (nos. 1, 2, 3 and letters, B, C, D, and E) as well as for the end of the dyke. So\nany reader with access to JMARS can easily confirm our results\n- References. By my count, almost half of the citations are self-citations, which seems a bit excessive. I\nrecommend reconsidering these self-citations. As with the “1 Ga” “[17]” example discussed above, there\nmight be many cases where it would be more appropriate to cite a paper that directly performed the\nrelevant analysis, rather than a study, which included the senior author, that simply mentioned the\nissue.\nREE: we have added more references to other authors. However, it should be noted that many key\npapers on mafic dyke swarms on Earth and Venus have been done by our co-authors\nReviewer #2 (Remarks to the Author):\nReview of Nature Communications Manuscript: The Great Dyke of Atla Region, Venus: The Longest\nTraced Individual Dyke in the Solar System\nGeneral comments:\nThis manuscript presents a strong case for identifying the longest single dyke in the Solar System on the\nplanet Venus. This identification could have extremely important implications for our interpretation of\nstress regimes on Venus, as well as our ability to determine relative ages across large regions. This\nmanuscript is well written and lays out its case carefully. However, it would benefit from some slight\nrestructuring and some additional clarification to better support its argument.\nREE: we thank this reviewer for providing an annotated PDF with editorial and other suggestions that we\nhave implemented\nSpecific Comment:\nThe authors frequently say that they are observing (or mapping, or measuring) dykes when what they\nreally mean is that they are observing graben that they are interpreting to overlie dykes. This is a pretty\nimportant distinction to make. The papers the authors are citing to support their interpretation of dykes\nbeneath the graben all assume that it is the emplacement of the dykes that forms the overlying graben.\nThere is still quite a considerable amount of debate about this issue.\nREE: additional support of our dyke swarm interpretation of the graben we are mapping in the Atla\nRegio superplume area comes from the newly published (El Bilali et al. 2023, Communications Earth and\nEnvironment,\nFor all of the literature that supports the contention that graben form above dykes, there is an equal\nnumber of papers showing that dykes don’t necessarily form overlying graben. Not every graben on\nEarth has a dyke beneath it, so it is odd that planetary researchers seem to assume that there is a dyke\nbeneath every graben on Venus (or Mars). And there are multiple locations on Earth where exposed\ncross-sections of dykes show no fracturing (or deformation of any kind) above them. Physical models\nhave also shown that dyking does not necessarily form graben.\nREE: the discussion of the argument for interpretating the families of cross cutting graben sets on Venus\nas overlying dykes is further discussed in the newly published paper (El Bilali et al. 2023,\nCommunications Earth and Environment, ). Although generally difficult to observe because of\nerosion, there are terrestrial examples of graben above dykes on Earth; we could add additional\nreferences on this point if necessary---\nTo be fair, the authors do state that they are making this interpretation in several places in the\nmanuscript. But it doesn’t make it any less jarring when they then talk about measuring the length of a\ndyke when what they really mean is they measured the length of the graben that they are interpreting\nto overlie a dyke. And to be clear, I am not trying to suggest that there are no dykes beneath the graben\nradial to Ozza Mons. I just think that the authors could be more precise and accurate in their writing.\nSuch clarity would only strengthen their arguments and support their case for the presence of a 3700\nkm long dyke on Venus.\nREE: We have modified our text to refer to graben and follow this with text such as the following\n“interpreted to overlie dykes”\nMinor Comments:\nI have made some suggestions in an attached annotated PDF that I believe would strengthen the paper.\nREE: we have accepted the suggested changes in the annotated PDF\nReviewer #3 (Remarks to the Author):\nIn this short paper, El Bilali & Ernst analyze Magellan radar images of Venus’ Atla Regio to map a giant\ndyke that is described as the longest dyke traced so far on Venus and the entire solar system. The\nauthors demonstrate a length of least 3700 km and potentially almost 4500 km, which substantially\nexceeds the longest dyke traces on Earth. The authors trace the dyke based on its graben signature and\nuse elevation data to identify major troughs. I found this letter relevant and interesting to read and it is\nrelatively easy to follow the manuscript even without being an expert on dyke swarms and/or geological\nmapping. In this sense, I feel this work is on interest for publication in a journal such as Nature\nCommunications.\nI have not spotted any major flaw in the way the results are obtained and interpreted. However, I was a\nlittle disappointed about the discussion of broader implications and significance of the detection of such\na long dyke. Some issues that I would have liked to see discussed a bit more:\n1.) Could such a long dyke imply that Venusian dykes may be longer than on Earth’s or does it just\ndemonstrate that terrestrial dykes are much more overprinted and we can trace their original length?\nAre there implications of such a long dyke on the properties and state of the interior (which are thought\nto be different and probably have been for substantial time for Earth and Venus)? For instance, could\nthe place constraints on local crustal thickness and strength?\n2.) What is a feasible tectonic regime that may support such long dykes? Is this more in line with\nclassical end-members such as the stagnant or mobile lid tectonics, or could that be better explained by\nsome more recent suggestions for Venus’ tectonic regime, such as the plutonic-squishy lid?\n3.) I understand that the 1200-km-distance at which the directional swing of the dyke occurs is here\nused as a proxy for the source plume head below Ozza Mons, but I would have liked a short discussion\nwhether this is indicates an unusually large plume or not, perhaps by comparison to better-studied\nterrestrial settings. In other words, is a very long dyke indicative of an unusually large or hot plume\nhead? Or is the length of dyke swarm thought to be controlled mostly by other factors?\n4.) The last paragraph (line 190++) points towards searching for other long continuous dykes on Venus.\nBut what are regions on Venus which may display such features more likely than others? Also, in what\nsense may be upcoming Venus missions – Veritas, DaVinci, and EnVision – help to identify more such\ndykes and/or provide more details about the structure of the GDAR and its implications?\nI think, some elaboration of points 1.) - 4.) would improve the manuscript and its impact on the Venus’\nscience community the most, but I do have some additional minor comments, following below. Overall, I\nthink this paper can be made suitable for publication with minor-to-moderate revision.\nREE: We appreciate the suggestion of this review, and have added more text on the implications of our\ndiscovery, but in the limitations of space we could not go into detail on all the points suggested\nAdditional comments:\nLine 11++: The abstract lacks a statement of the broader significance for our understanding of either\ndykes or of Venus’ tectonics. It would be good to add one if the word limit allows.\nREE: We have added some text on the significance of our discovery\nLine 17: Remove the comma after “1200 km”.\nREE: done\nLine 29: “It is inferred ...” Inferred based on what? Also, the word “inferred” seemed to appear quite\noften throughout the manuscript. Please check and think about alternatives.\nREE: agreed “Inferred” is used to much and alternative wording are used\nLine 40/41: Where has been the longest dyke in the solar system before your detection of GDAR?\nReaders may wonder about this (well, I did ...).\nREE: The longest traced individual dykes were those mentioned in the paragraph. Probably the longest\nTRACED individual dyke was 1000 km (Red Sea), but the longest INFERRED length assuming lateral\nemplacement on Earth is probably the Central Atlantic radiating swarm with dykes going out to 2800 km\naway from the plume centre (hence the individual (laterally emplaced) dykes that reach the end of the\nswarm might be up to 2800 km long. The longest on Mars is likely about 4000 km (based on the\nmaximum length of the Tharsis radiating graben systems (e.g. Mege and Ernst 2001). On Venus the\nlargest known swarm is the Artemis radiating swarm which has dykes extending out to nearly 6000 km,\nbut since they appear to start at the edge of the Artemis corona (radius 1000 km) then may be starting\nfrom magma reservoirs at the edge of the corona-- in which case their maximum length could be about\n5000 km.\nLine 57: “...at least back to about 1 Ga ...” Why 1 Ga? Is that supposed to be linked to Venus’ mean\nsurface age? This is unknown and, yes, 1 Ga is in the range of estimates. But at the very upper end, and\nthe most recent estimates tend to suggest younger surface ages perhaps as young as 100-200 Myr.\nPlease clarify, why you write “at least 1 Ga” if actually have very little clue of how Venus’ operated at\nthis time (it may or may not had more active tectonics etc.)\nREE: good point and also made by reviewer 1. We are adding these estimates of these ages, citing\nadditional references.\nLine 59: “... inferred to overlie blind dykes ...” I do not understand how such blind dykes can be\nrecognized from radar images such as those used here? Would that not need some rather high-\nresolution gravity data at least? Or is this inference actually just used in analogy to terrestrial dykes for\nwe may know about these blind dykes?\nREE: yes, this is reference to the model (applied to both Mars, Venus and Earth) in which graben are\ninferred to overlie blind dykes. The graben sets (radiating, circumferential and linear) on Venus\ninterpreted to overlie dykes for all the reasons given in the cited references and the most relevant\nmanuscript is our just-published paper on the Atla Regio radiating dyke swarms (El Bilali et al. 2023,\nCommun: Earth and Environment)\nLine 64: I am puzzle by the word “once-compressed”. Could it be also twice-compressed? Does it\neffectively mean that the compressed images have coarser resolution (225m/px) than the\nuncompressed (75m/px)?\nREE: yes, this is the term that was used for these lower resolution datasets. We have provided a\nreference for these once-compressed data\nLine 69: “In this study [20] ...” should be “In that study [20] ...”!?\nREE: Thanks – I have made that correction.\nLine 185++: This short paragraph falls a bit short compared to the others. Would you expect similarly\nlong dykes extending outwards from Ozza Mons in various directions (at least until the 1200 km-limit up\nto which the regional stresses seem to be less significant)? Or could there be some preferential\ndirections? In Figure 1, it seems that there is at least one quadrant (SW) of the blue circle without any\nradiating graben systems (orange line)? Why?\nREE: we expect that the swarms are radiating (due to domal uplift above the plume) out to the edge of\nthe plume beyond which they have trend controlled by the regional stress field.\nREE: The absence of radiating dykes in the SW quadrant is due to the presence of younger flows of Maat\nMons and Unnamed Mons\nLine 203++: DOI’s seem to be missing consistently in the reference. These are always useful to have. It\nseems references 4 and particularly 30 are earlier (reduced) versions of the contents presented here, so\nconsider deleting these ref’s, especially as they are conference abstracts without peer-review.\nREE: Reference 4 has now been replaced by the newly published El Bilali et al. (2023)\nREE: Yes, reference 30 can be dropped.\nREE: regarding adding the DOIs. I agree they are useful, and we will add them if the journal requests.\nREE: We have added and removed some references and renumbered accordingly\nFigure 1: I am not sure what the color coding in the large-scale inset (upper right corner of the figure) is\nmeant to represent!?\nREE: thanks for catching that. We have added text to the caption to explain the colour coding in the\ninset\nFigure 2: It was not clear to me immediately what the 500 m label in the left panel is supposed to mean.\nWhile I got it on a second look, consider adding a note in the caption to make it clear right away. Also, it\nseems that you show here a ~100-200 km long section from the beginning of the GDAR, that is close to\nOzza Mons, I suppose. It would be interesting to see, for comparison, how this compares to a section\nfurther away, perhaps at around the 1200-km boundary or even further out. This could potentially\nindicate structural changes along the dyke\nREE: In response to this reviewer comment we have experimented with adding an image closer to the\ncentre, but in this area the geology seems very complicated with multiple graben and areas that are\ncovered by younger flows. There is no obvious way to trace the GDAR closer to the plume centre. We\nare planning to undertake a more detailed mapping of the central region of Ozza Mons (including the\nflows) and perhaps that will yield some insights on this point, for a future paper."}, {"round": 2, "reviewer_comments": {"reviewer_1": "Re-review of “Far-Travelled (4000 km) Magma Propogafion [sic?] Just Below the Surface of Venus” for Nature Communicafions. September 26, 2023.\nI reviewed the new manuscript and the authors’ response to the original reviews. I also read the new manuscript by the authors: “Dyke swarms record the plume stage evolufion of the Atla Regio superplume on Venus” by El Bilali et al. (2023) in Communicafions Earth & Environment.\nI leave it to the editors to judge the overall significance of this manuscript, especially given the very similar results presented in El Bilali et al. (2023). Regardless, I have many technical concerns with the manuscript that I believe should be addressed regardless of where it is ulfimately published. Some of these concerns are carried over from my first review, but several of my comments relate to new text and numbers that were added for this submission.\nComments (in order of appearance):\n- Should “Propogafion” be “Propagafion” in the fitle of this manuscript?\n- Lines 16, 46–48: I think these sentences need a “so far” or a comparable caveat to avoid giving unwary readers the impression that all long graben on Venus have been traced.\n- Figure 1: The subpanel in the top-right corner is basically idenfical to Figure 1d in El Bilali et al. (2023). In my opinion, this duplicafion should be acknowledged.\n- Lines 70–71: The statement “wind erosion is minor” is rather vague—“minor” by what metric? Overall, the extent of sedimentary acfivity on the surface of Venus is debated but could be substanfial. Even if wind speeds are low, the thick atmosphere can transport small parficles. Mass wasfing could be common on the steep slopes of graben.\n- Line 118: The manuscript asserts “the confinuity of the GDR across the gap is unambiguous (based on matching of trend and width of the graben).” The response to reviewers likewise states that “this parficular graben is so disfinct (by its width and appearance) that it can be reliably traced across gaps.” I wish these statements were specific and quanfitafive. How does the width of this graben compare to the distribufion of widths observed for nearby graben? As noted in the response, we simply do not have the types of datasets (geochemistry, paleomagnefism, etc.) that have been used to prove the confinuity of Great Dykes on Earth.\n- Lines 121–123: This scaling rafio has substanfial uncertainty. Cited reference 9 adopts the value of 3.5 as a rough average from a study of only two dyke-induced graben in Iceland by Rubin (1992). In that study, the specific values were 1.9 and 4. So, the depth to the underlying dyke could be anywhere from ~250 m to 1,600 km based on the 2 ± 1 km width measured in this study. This uncertainty should propagate through to the next calculafion in this paragraph—and to the calculafions later in the manuscript.\n- Lines 123–125: I am not convinced that this depth esfimate is robust. What is the horizontal resolufion of the Magellan alfimetry along the graben? Is the stereo-derived topography available here? If the horizontal resolufion is much worse than the width of the graben (it might be an order of magnitude worse…), then the verfical resolufion of the Magellan alfimetry data is not a strict limit. A deeper depth would be “smoothed out” (i.e., look less deep) in poorly resolved alfimetry data.\n- Lines 188–189: The last sentence of the preceding paragraph seems to contradict the first sentence of this paragraph. That is, I’m not sure that “flow” describes fine-grained material from an impact? So, it seems possible that, besides (lava) flows, sediment (which can form on Venus from impact or other processes) could pile up in certain locafions and obscure graben.\n- Lines 190–192: Again, I believe the word “any” is inappropriate in this sentence. The radar images of Venus are simply insufficient to exclude “any” volume of lava flowing out of the GDAR. In response to my previous comment, the authors pointed out that they have submifted >50 abstracts to the Lunar and Planetary Science Conference. However, I maintain that lava could have spilled out at spafial scales that are not resolvable in the available imagery (e.g., <10,000 m^2). Alternafively, the spilled lava could have radar properfies that make it difficult to disfinguish from the surrounding plains. I believe that the authors “did not observe lava flows spilling out of the GDAR.” Therefore, there is probably a (non-zero!) upper limit to the amount of lava that could have spilled out. They should say that, recognizing that absence of evidence is not always evidence of absence.\n- Line 201 states that “Venusian crust is typically 20-25 km thick, thick.” (Maybe one “thick” is enough.) However, Maia & Wieczorek (2022, JGR) found that, under some assumpfions, “the global average crustal thickness of Venus is about 20 km.” Previously, James et al. (2013, JGR) found that “the mean thickness of the crust is constrained to a range of 8–25 km.” So, I wouldn’t be surprised if Venusian crust were thinner than considered here, at least over half or more of the surface.\n- Lines 226–228: The phrase \"will be valuable for contribufing to target selecfion by the fleet of new missions to Venus planned over the next decade (VERITAS, DAVINCI, EnVision, Venera-D, Shukrayaan-1, VOICE)\" also appears verbafim in El Bilali et al. (2023). This verges on self-plagiarism. I recommend that the authors double-check the enfire manuscript for similar problems.", "reviewer_4": "In my opinion, this manuscript is interesfing, well structured, and the science is quite sound, although I have a few minor concerns that I believe the authors should address before this paper can be published in a high-end journal such as Nature Communicafions. These minor concerns fall in line with the concerns raised by reviewer #1, whose comments are, in my opinion, often replied to in the “reply to reviewers” but then not thoroughly taken into the revised manuscript, and also (importantly) about the data availability. The detailed review (a couple of points) can be found int he aftached PDF.\n[Editorial Note: The contents of the PDF have been included below]\nThis is a very interesfing study and detailed mapping of the Venusian surface, with an excifing new feature thoroughly analyzed, and interpreted to be an extremely far-travelled magmafic dyke. As is an external review in the second round of this manuscript’s review, below, I assessed both the manuscript as the comments to concerns raised by previous reviewers.\nIn my opinion, this manuscript is interesfing, well structured, and the science is quite sound, although I have a few minor concerns that I believe the authors should address before this paper can be published in a high-end journal such as Nature Communicafions. These minor concerns fall in line with the concerns raised by reviewer #1, whose comments are, in my opinion, often replied to in the “reply to reviewers” but then not thoroughly taken into the revised manuscript. I quite am certain that many readers would have similar concerns, even when they appear “stupid” to the authors. The editor and authors should consider the factors summarized here:\n• The interpretafion of the surface structure as a laterally confinuous dyke should be befter described, it is not a given. What may seem “obvious” to the author does not come across as such in the manuscript. I would urge the authors to address, in the paper or in a supplement, the details behind recognizing GDAR as a laterally confinuous dyke, and to also discuss some alternafive interpretafions (e.g., as one of the reviewers menfioned, there is a wealth of literature showing that dykes don’t necessarily form overlying graben; not every graben on Earth overlies a dyke).\n• Throughout the authors excessively make use of self-citafion. I agree that one of the authors has long-standing research output in the field of (dyke) mapping and that many papers on mafix dyke swarms on Venus/Earth include this author. Yet this is not the case in the field of Venus science, tectonics, geodynamics, or past mission observafions. Any statement about interpretafions of Venusian research should be supported by the original works, not only by the author’s latest paper. I urge the editor to take important note of this.\n• I see absolutely no reason for the authors not to accompany the datasets of their mapped structures (e.g., a shape file or other file, to be opened in GIS software or JMARS), and the topographic profiles of the structures, with this manuscript. Especially since these files should not be extremely large or sensifive, I so nee reason to leave them out. I do not request this for interpretafion reproducibility per se, but for the FAIR data principles that allows for reusability and for other scienfists to include the mapped structures in their own future mapping endeavors (with obviously the appropriate references to this paper). Nature’s data ethics include “authors are required to make materials, data, code, and associated protocols promptly available to readers without undue qualificafions” and making available the “minimum dataset necessary to extend the research in the arficle”.\nYou can find some more details with line numbers below:\nLines 71-72: This sentence is quite complex maybe since it misses a “)”? Also, I would suggest a recent review to be added as reference regarding the present-day knowledge on the surface age of Venus (few 100 Myr to ~1 Gyr, or widely distributed if the surface age is in fact not uniform but formed in a so-called “equilibrium” resurfacing model):\nhftps://doi.org/10.1007/s11214-023-00966-y\nLines 95-99 (and concern reviewer #1): the claim that “Atla Regio is recognized as a major plume center” should have an original citafion of key Venus papers rather than a self-citafion their recent paper. The earliest and most convincing argument for a plume center beneath Atla Regio (and for that mafter, the BAT region) comes from gravity studies that reveal a deep dynamic support at these regions. These original sources have to be cited and ideally, in the paper, it should even be discussed why the Atla Regio is inferred to be a “hotspot” region:\nhftps://doi.org/10.1111/j.1365-246X.1997.tb00593.x\nhftps://doi.org/10.1006/icar.1994.1166\nhftps://doi.org/10.1029/95JE01834\nLines 161-162 “and consistent with a plume head radius for Ozza Mons of 1200 km diameter”\nthis one-on-one correlafion comes with assumpfions that should be briefly menfioned. This is assuming that the plume head completely reaches the edge of the “purely radiafing paftern”. Couldn’t radiafing paftern extend far beyond the lateral plume head size (e.g. numerical models)? Please discuss or, if convinced, menfion why this one-on-one correlafion is correct with appropriate references.\nThroughout the paper (and concern reviewer #1) The confident use of the “recognized GDAR” can, in my opinion, only be valid in this manuscript when the authors befter address their interpretafion and assumpfion. Not all grabens on Earth overly dykes, so why are you so convinced this one does? Please clarify or add a supplement with a paragraph of details, for the reader who may be unaware of this.\nHere, the authors can also go in depth on exactly why the minor lateral disconfinuifies are not affecfing their interpretafion of the dyke being laterally confinuous and the result of lateral emplacement rather than verfical. The authors have replied to this concern in detail (albeit, also dismissive) to reviewer #1 but not so much in the paper."}, "author_response": "RESPONSE TO REVIEWS\nAll responses in red font\nRE-REVIEW BY ORIGINAL REVIEWER 1\nI reviewed the new manuscript and the authors’ response to the original reviews. I also read the\nnew manuscript by the authors: “Dyke swarms record the plume stage evolution of the Atla Regio\nsuperplume on Venus” by El Bilali et al. (2023) in Communications Earth & Environment.\nI leave it to the editors to judge the overall significance of this manuscript, especially given the very\nsimilar results presented in El Bilali et al. (2023).\nRESPONSE: We appreciate that the editor assessed that this Great Dyke paper represents a distinct\ncontribution with respect to our earlier paper (El Bilali et al. 2023) on the Atla Regio Superplume\nRegardless, I have many technical concerns with the manuscript that I believe should be addressed\nregardless of where it is ultimately published. Some of these concerns are carried over from my first\nreview, but several of my comments relate to new text and numbers that were added for this\nsubmission.\nRESPONSE: We have endeavored to accommodate all the comments of this review—see response\nbelow\nComments (in order of appearance):\n- Should “Propogation” be “Propagation” in the title of this manuscript?\n- RESPONSE: First of all thank you to the reviewer for catching the spelling error. We have added\nthe word “Lateral “ FAR-TRAVELLED (4000 KM) LATERAL MAGMA PROPAGATION JUST BELOW THE\nSURFACE OF VENUS. Our interpretation is clearer now by adding the word lateral, since our point\nthat such a long single dyke would be emplaced laterally from the plume centre region.\n-\n- Lines 16, 46–48: I think these sentences need a “so far” or a comparable caveat to avoid giving\nunwary readers the impression that all long graben on Venus have been traced.\n- RESPONSE: We thank the reviewer for this suggestion. “so far” has been added.\n- Figure 1: The subpanel in the top-right corner is basically identical to Figure 1d in El Bilali et al.\n(2023). In my opinion, this duplication should be acknowledged.\nRESPONSE: we have acknowledged that this subpanel is after El Bilali et al. (2023). This is an ideal\nlocation diagram for any part of the BAT region and so we think it makes sense to also use it here.\n- Lines 70–71: The statement “wind erosion is minor” is rather vague—“minor” by what metric?\nOverall, the extent of sedimentary activity on the surface of Venus is debated but could be\nsubstantial. Even if wind speeds are low, the thick atmosphere can transport small particles. Mass\nwasting could be common on the steep slopes of graben.\n- RESPONSE: Yes, there a few areas of recognized sand dunes and plenty of examples of mass\nwasting associate rift zones, and apart from these local areas of erosion, in a general way the level\nof erosion has to be minor. The morphology of lava flows is so well preserved in most areas that\nthe cumulative effect of any cumulative erosion has to be minor. There is also the observation of\ndark parabolic haloes caused by dust from bolide impacts and these are modelled to persist some\n40 myr before they are successfully degraded and removed by wind erosion. We could have added\nadditional references for all these points but this would have added about 5 references and we\nalready needed to add references in response to other reviewer comments.\n- Line 118: The manuscript asserts “the continuity of the GDR across the gap is unambiguous (based\non matching of trend and width of the graben).” The response to reviewers likewise states that “this\nparticular graben is so distinct (by its width and appearance) that it can be reliably traced across\ngaps.” I wish these statements were specific and quantitative. How does the width of this graben\ncompare to the distribution of widths observed for nearby graben? As noted in the response, we\nsimply do not have the types of datasets (geochemistry, paleomagnetism, etc.) that have been used\nto prove the continuity of Great Dykes on Earth.\n- RESPONSE: This is an easy point to respond to: We have now provided the line work (ARCGIS shape\nfile) that will allow anyone to duplicate our work--- to see exactly how distinctive this particular\nfeature is. We have reiterated that for 1700 km of its length this feature is named as Penthesilea\nFossa, fossa (as the singular of fossae) indicating a single graben. This individual graben is traced\nacross Taussig Quadrangle V-39 (see quadrangle map of Brian et al. 2005). Our mapping confirms\nthe observation in Brian et al. (2005) and tracing the single graben outside the side area, to the\nwest to be able to connect it with Ozza Mons. We added new text to make this point.\n- Lines 121–123: This scaling ratio has substantial uncertainty. Cited reference 9 adopts the value of\n3.5 as a rough average from a study of only two dyke-induced graben in Iceland by Rubin (1992). In\nthat study, the specific values were 1.9 and 4. So, the depth to the underlying dyke could be\nanywhere from ~250 m to 1,600 km based on the 2 ± 1 km width measured in this study. This\nuncertainty should propagate through to the next calculation in this paragraph—and to the\ncalculations later in the manuscript.\nRESPONSE: We have now used error propagation to develop our final number which indicates a\nwidth of 250 +/- 195 m.\n- Lines 123–125: I am not convinced that this depth estimate is robust. What is the horizontal\nresolution of the Magellan altimetry along the graben? Is the stereo-derived topography available\nhere? If the horizontal resolution is much worse than the width of the graben (it might be an\norder of magnitude worse…), then the vertical resolution of the Magellan altimetry data is not a strict\nlimit. A deeper depth would be “smoothed out” (i.e., look less deep) in poorly resolved altimetry\ndata.\n- RESPONSE: The stereo topography is not going to help since the vertical resolution of the stereo-\ntopography is still only 100-50 km and with the horizontal resolution having been reduced to a few\nkm rather than 20 km, this will still be insufficient to resolve the depth of the graben. We now\nacknowledge the uncertainties in our calculation, and make that the point that a similar analysis will\nbe useful when the new Venus missions provide higher resolution altimetry and imagery.\n- Lines 188–189: The last sentence of the preceding paragraph seems to contradict the first sentence\nof this paragraph. That is, I’m not sure that “flow” describes fine-grained material from an impact?\nSo, it seems possible that, besides (lava) flows, sediment (which can form on Venus from impact or\nother processes) could pile up in certain locations and obscure graben.\nRESPONSE: It is widely recognized that graben can be obscured by lots of younger processes:\nyounger lava flows, impact ejecta and dust (the parabolic haloes mentioned above). However, our\nkey point is that the Penthesilea and its continuation to the west (to the inferred source at Ozza\nMons--is that the feature is traceable--- i.e. is therefore NOT covered by any younger material. This\nis our basic and key observation and is consistent with the cross-cutting relationships that clearly\nindicate that the GDAR is younger than most features and thus cuts across them.\n- Lines 190–192: Again, I believe the word “any” is inappropriate in this sentence. The radar images\nof Venus are simply insufficient to exclude “any” volume of lava flowing out of the GDAR. In\nresponse to my previous comment, the authors pointed out that they have submitted >50 abstracts\nto the Lunar and Planetary Science Conference. However, I maintain that lava could have spilled out\nat spatial scales that are not resolvable in the available imagery (e.g., <10,000 m^2).\nAlternatively, the spilled lava could have radar properties that make it difficult to distinguish from\nthe surrounding plains. I believe that the authors “did not observe lava flows spilling out of the\nGDAR.” Therefore, there is probably a (non-zero!) upper limit to the amount of lava that could have\nspilled out. They should say that, recognizing that absence of evidence is not always evidence of\nabsence.\n- REPONSE: We have added this point – that given the pixel size of about 100 m, then a minimum\nestimate that would be expelled in any one spot that would be unresolveable would be 100 x 100\nequals 10,000 km2. While acknowledging this point (that we cannot rule out very small volumes\nbeing expelled) our main point still stands, that there is no major expulsion of magma observed\nanywhere along the length of the GDAR\n- Line 201 states that “Venusian crust is typically 20-25 km thick, thick.” (Maybe one “thick” is\nenough.) However, Maia & Wieczorek (2022, JGR) found that, under some assumptions, “the global\naverage crustal thickness of Venus is about 20 km.” Previously, James et al. (2013, JGR) found that\n“the mean thickness of the crust is constrained to a range of 8–25 km.” So, I wouldn’t be surprised if\nVenusian crust were thinner than considered here, at least over half or more of the surface.\n- RESPONSE: We add these other estimates of crustal thickness. However, the thickness of the crust\nis not the only consideration, as the analysis of Wilson and Head (2002) suggested dyke heights\nextending through the crust into the mantle lithosphere.\n- Lines 226–228: The phrase \"will be valuable for contributing to target selection by the fleet of new\nmissions to Venus planned over the next decade (VERITAS, DAVINCI, EnVision, Venera-D,\nShukrayaan-1, VOICE)\" also appears verbatim in El Bilali et al. (2023). This verges on self-plagiarism. I\nrecommend that the authors double-check the entire manuscript for similar problems.\nRESPONSE: We have edited this sentence to avoid any self-plagiarism.\nReviewer #4 (Remarks to the Author):\nIn my opinion, this manuscript is interesting, well structured, and the science is quite sound,\nalthough I have a few minor concerns that I believe the authors should address before this paper can\nbe published in a high-end journal such as Nature Communications. These minor concerns fall in line\nwith the concerns raised by reviewer #1, whose comments are, in my opinion, often replied to in the\n“reply to reviewers” but then not thoroughly taken into the revised manuscript, and also\n(importantly) about the data availability. The detailed review (a couple of points) can be found int he\nattached PDF.\nRESPONSE: We have now fully addressed each point from the re-review of Review 1 above (see above)\nand the responded to the specific comments of new Reviewer 4 below\nTitle: Far-Travelled (4000 km) magma propagation just below the surface of Venus\nJournal: Nature Communications\nThis is a very interesting study and detailed mapping of the Venusian surface, with an exciting new\nfeature thoroughly analyzed, and interpreted to be an extremely far-travelled magmatic dyke. As is an\nexternal review in the second round of this manuscript’s review, below, I assessed both the manuscript\nas the comments to concerns raised by previous reviewers.\nRESPONSE: Thank you for the positive comments\nIn my opinion, this manuscript is interesting, well structured, and the science is quite sound, although I\nhave a few minor concerns that I believe the authors should address before this paper can be published\nin a high-end journal such as Nature Communications. These minor concerns fall in line with the\nconcerns raised by reviewer #1, whose comments are, in my opinion, often replied to in the “reply to\nreviewers” but then not thoroughly taken into the revised manuscript. I quite am certain that many\nreaders would have similar concerns, even when they appear “stupid” to the authors.\nRESPONSE: Thank you for the positive comments. We see the importance of better explaining and\ndemonstrating to the broad readership what we have recognized from our detailed work.\nThe editor and authors should consider the factors summarized here:\n• The interpretation of the surface structure as a laterally continuous dyke should be better\ndescribed, it is not a given. What may seem “obvious” to the author does not come across as such\nin the manuscript. I would urge the authors to address, in the paper or in a supplement, the details\nbehind recognizing GDAR as a laterally continuous dyke, and to also discuss some alternative\ninterpretations (e.g., as one of the reviewers mentioned, there is a wealth of literature showing\nthat dykes don’t necessarily form overlying graben; not every graben on Earth overlies a dyke).\nRESPONSE: We have now added a section that fully considers alternative geological interpretations of\nsuch an amazing long narrow feature.\n• Throughout the authors excessively make use of self-citation. I agree that one of the authors has\nlong-standing research output in the field of (dyke) mapping and that many papers on mafix dyke\nswarms on Venus/Earth include this author. Yet this is not the case in the field of Venus science,\ntectonics, geodynamics, or past mission observations. Any statement about interpretations of\nVenusian research should be supported by the original works, not only by the author’s latest\npaper. I urge the editor to take important note of this.\nRESPONSE: We acknowledge this concern and have now added more referencing to the original work,\nand only cited our work where our contribution was relevant and significant.\n• I see absolutely no reason for the authors not to accompany the datasets of their mapped\nstructures (e.g., a shape file or other file, to be opened in GIS software or JMARS), and the\ntopographic profiles of the structures, with this manuscript. Especially since these files should not\nbe extremely large or sensitive, I so nee reason to leave them out. I do not request this for\ninterpretation reproducibility per se, but for the FAIR data principles that allows for reusability\nand for other scientists to include the mapped structures in their own future mapping endeavors\n(with obviously the appropriate references to this paper). Nature’s data ethics include “authors\nare required to make materials, data, code, and associated protocols promptly available to\nreaders without undue qualifications” and making available the “minimum dataset necessary to\nextend the research in the article”.\nRESPONSE: We have now included the ArcGIS shape files for that the linework shown. The generalized\nlinework for the Ozza Mons system and the detailed linework for the GDAR. This will allow any reader to\nreproduced our mapping. We are not adding the topographic profiles since the profiles were generated\nin the on-line software JMARS and we exported the profile images—and there were no data tables to\nexport.\nYou can find some more details with line numbers below:\nLines 71-72: This sentence is quite complex maybe since it misses a “)”?\nRESPONSE: Parenthesis added\nAlso, I would suggest a recent\nreview to be added as reference regarding the present-day knowledge on the surface age of Venus (few\ncalled\n“equilibrium” resurfacing model):\nhttps://doi.org/10.1007/s11214-023-00966-y\nRESPONSE: We have added this reference, as a useful review, but the timing of resurfacing is not\nimportant to our paper—the key point is the absence of erosion which indicates why we see the surface\nexpression of dykes.\nLines 95-99 (and concern reviewer #1): the claim that “Atla Regio is recognized as a major plume\ncenter” should have an original citation of key Venus papers rather than a self-citation their recent\npaper.\nThe earliest and most convincing argument for a plume center beneath Atla Regio (and for that matter,\nthe\nBAT region) comes from gravity studies that reveal a deep dynamic support at these regions. These\noriginal\nsources have to be cited and ideally, in the paper, it should even be discussed why the Atla Regio is\ninferred\nto be a “hotspot” region:\nhttps://doi.org/10.1111/j.1365-246X.1997.tb00593.x\nhttps://doi.org/10.1006/icar.1994.1166\nhttps://doi.org/10.1029/95JE01834\nRESPONSE: we have added the Smrekar and Stofan references but also kept El Bilali et al. 2023 since\nthat provides new insights into the specifics of the plume history\nLines 161-162 “and consistent with a plume head radius for Ozza Mons of 1200 km diameter”\nthis one-on-one correlation comes with assumptions that should be briefly mentioned. This is assuming\nthat the plume head completely reaches the edge of the “purely radiating pattern”. Couldn’t radiating\npattern extend far beyond the lateral plume head size (e.g. numerical models)? Please discuss or, if\nconvinced, mention why this one-on-one correlation is correct with appropriate references.\nRESPONSE: We can now reference the paper by Chadda et al. 2024 (Icarus) in which we discuss the\nbasis for this interpretation.\nThroughout the paper (and concern reviewer #1) The confident use of the “recognized GDAR” can,\nin my opinion, only be valid in this manuscript when the authors better address their interpretation and\nassumption. Not all grabens on Earth overly dykes, so why are you so convinced this one does? Please\nclarify or add a supplement with a paragraph of details, for the reader who may be unaware of this.\nHere,\nthe authors can also go in depth on exactly why the minor lateral discontinuities are not affecting their\ninterpretation of the dyke being laterally continuous and the result of lateral emplacement rather than\nvertical. The authors have replied to this concern in detail (albeit, also dismissive) to reviewer #1 but not\nso much in the paper.\nRESPONSE: We have expanded the text that discusses the reasons that Venusian graben are typically\nthought to overlie dykes. We have also included a specific new section that discuss the GDAR graben\nand all possible origins: fault (strike slip or vertical), or zone of pure extension, before concluding that\nunderlying dyke is most logical. Also we have discussed why the dyke composition should be mafic and\nalso why an interpretation of lateral emplacement of the dyke from the plume centre region is\nreasonable.\nREVIEWERS' COMMENTS\nReviewer #4 (Remarks to the Author):\nI believe that the authors have responded to my comments quite well:\n(a) They have added more original references (although some are in my opinion missing, see below)\n(b) They made the source data available\n(c) They included a much befter discussion for their interpretafion of a GDAR\nSome minor comments (some with a reoccurring theme of erosion) prevail, that are stated below:\nLine 71 “Due to the current hot atmosphere (ca. 450° C)” note that only the lowermost\natmosphere/surface temperature reaches this value, and that there is a steep gradient in temperature\nonly at the boftom few 10km of the atmosphere. This is confusing, I’d suggest replacing “hot\natmosphere” by “hot surface temperature”\nLine 72: this relates to my point in my previous review about lines 71-72 about adding the reference\nhftps://doi.org/10.1007/s11214-023-00966-y. The authors claim they have added this reference but\ninstead I see a reference to an older paper. I suggest to sfill include (or replace) this more recent\nreference since it provides a befter overview of our present-day knowledge of Venus’ resurfacing, several\ndecades after Magellan.\nLine 78 “The absence of erosion” This is contradicfing with the previous paragraph: you argue that fluvial\nerosion is absent, and that wind erosion is minor (but sfill present). As discussed in Carter et al. (2023)\nhftps://doi.org/10.1007/s11214-023-01033-2 (which in my opinion also needs to be cited for here and\nlines 71-72) , erosion is indeed present in various forms on Venus. Please rephrase (e.g. “absence” into\n“relafively minor role”\nLine 118 and 223: Similar comment on “absence/lack of erosion”: erosion may be minor compared to on\nEarth, but it is not 100% absent (see Carter et al. 2023). Rephrase into either something more nuanced\nor suggesfive.\nMinor editorial comments (could also be handled by editorial team):\nLine 160: I suggest replacing “so” by “therefore”\nLine 180 odd phrasing. I suggest “on this basis is linked to” to be rephrased to “is therefore linked to”\nLine 181: Odd long sentence, I suggest to break this sentence and start a new one after “Ozza Mons”.\nLines 249-250: Could the authors make one confinuously flowing sentence of this? The two different\nsentences read a bit odd. Suggesfion: something along the lines of “Esfimates for the thickness of\nVenusian crust vary, and average values typically vary between 8-25 km [53,54,55], with larger values for\nhighlands [e.g. 54]”.\nLine 271: Remove “Basically” and define “it”\nREPONSE TO REVIEWERS: IN RED FONT\n(2024 January 21\nREVIEWERS' COMMENTS\nReviewer #4 (Remarks to the Author):\nI believe that the authors have responded to my comments quite well:\nRESPONSE: Thank you\n(a) They have added more original references (although some are in my opinion missing, see\nbelow)\n(b) They made the source data available\n(c) They included a much better discussion for their interpretation of a GDAR\nSome minor comments (some with a reoccurring theme of erosion) prevail, that are stated\nbelow:\nLine 71 “Due to the current hot atmosphere (ca. 450° C)” note that only the lowermost\natmosphere/surface temperature reaches this value, and that there is a steep gradient in\ntemperature only at the bottom few 10km of the atmosphere. This is confusing, I’d suggest\nreplacing “hot atmosphere” by “hot surface temperature”\nRESPONSE: Revised as suggested\nLine 72: this relates to my point in my previous review about lines 71-72 about adding the\nreference https://doi.org/10.1007/s11214-023-00966-y. The authors claim they have added this\nreference but instead I see a reference to an older paper. I suggest to still include (or replace)\nthis more recent reference since it provides a better overview of our present-day knowledge of\nVenus’ resurfacing, several decades after Magellan.\nRESPONSE: the new Carter et al. (2023) paper has been added here, but the Herrick et al. (2023)\nresurfacing paper was already added later in the sentence\nLine 78 “The absence of erosion” This is contradicting with the previous paragraph: you argue\nthat fluvial erosion is absent, and that wind erosion is minor (but still present). As discussed in\nCarter et al. (2023) https://doi.org/10.1007/s11214-023-01033-2 (which in my opinion also\nneeds to be cited for here and lines 71-72) , erosion is indeed present in various forms on\nVenus. Please rephrase (e.g. “absence” into “relatively minor role”\nRESPONSE: the excellent Carter et al. (2023) reference has been added. Thank you for bringing\nthis reference to our attention. We have made the suggested edit of replacing “absence” with\n“relatively minor role”\nLine 118 and 223: Similar comment on “absence/lack of erosion”: erosion may be minor\ncompared to on Earth, but it is not 100% absent (see Carter et al. 2023). Rephrase into either\nsomething more nuanced or suggestive.\nRESPONSE: change to “minor erosion”, and “lack of significant erosion”\nMinor editorial comments (could also be handled by editorial team):\nLine 160: I suggest replacing “so” by “therefore”\nRESPONSE: Revised as suggested\nLine 180 odd phrasing. I suggest “on this basis is linked to” to be rephrased to “is therefore\nlinked to”\nRESPONSE: Revised as suggested\nLine 181: Odd long sentence, I suggest to break this sentence and start a new one after “Ozza\nMons”.\nRESPONSE: This section is rewritten for improved clarity and flow\nLines 249-250: Could the authors make one continuously flowing sentence of this? The two\ndifferent sentences read a bit odd. Suggestion: something along the lines of “Estimates for the\nthickness of Venusian crust vary, and average values typically vary between 8-25 km\n[53,54,55], with larger values for highlands [e.g. 54]”.\nRESPONSE: Revised as suggested\nLine 271: Remove “Basically” and define “it”\nRESPONSE: Revised as suggested"}]

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