2010

U.S. Department of the Interior

U.S. Geological Survey

Prepared for the National Aeronautics and Space Administration

Geologic Map of the Greenaway Quadrangle (V–24), Venus

By Nicholas P. Lang and Vicki L. Hansen

Pamphlet to accompany

Scientific Investigations Map 3089

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0° 30° 60° 90° 120° 150° 180°

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–50° –50°

–75° –75°

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V–23 V–24 V–22

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V–62

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V–33 V–36

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V–45 V–48

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Contents

The Magellan Mission ..................................................................................................................................1

Magellan Radar Data ..........................................................................................................................1

Introduction ....................................................................................................................................................1

Data ....................................................................................................................................................2

Terminology ...........................................................................................................................................2

Mapping Techniques and SAR Image Interpretation ....................................................................2

Geology of the Greenaway Quadrangle (V–24) ..............................................................................3

Geologic Overview ...............................................................................................................................3

Geologic Units ......................................................................................................................................3

Terrain and Flow Materials .......................................................................................................3

Ribbon-Tessera Terrain .....................................................................................................3

Intratessera Basin Material .............................................................................................5

Lineated Terrain .................................................................................................................5

Shield Terrain ......................................................................................................................5

Coronae-Sourced Flow Material .....................................................................................6

Impact Craters ......................................................................................................................................6

Channels ................................................................................................................................................7

Simple Channels .........................................................................................................................7

Complex Channels ......................................................................................................................7

Tectonic Features ................................................................................................................................7

Wrinkle Ridges ............................................................................................................................7

Linear Features ............................................................................................................................7

Coronae ........................................................................................................................................8

Dorsa ...........................................................................................................................................9

Discussion .............................................................................................................................................9

Geologic History..................................................................................................................................10

References Cited..........................................................................................................................................11

Table

1. Crater data for the Greenaway quadrangle (V–24), Venus ..............................................................15

1

The Magellan Mission

The Magellan spacecraft orbited Venus from August 10, 

1990, until it plunged into the Venusian atmosphere on October 

12, 1994. Magellan Mission objectives included (1) improving 

the knowledge of the geological processes, surface properties, 

and geologic history of Venus by analysis of surface radar characteristics, topography, and morphology and (2) improving the 

knowledge of the geophysics of Venus by analysis of Venusian 

gravity.

The Magellan spacecraft carried a 12.6-cm radar system to 

map the surface of Venus. The transmitter and receiver systems 

were used to collect three data sets: (1) synthetic aperture radar 

(SAR) images of the surface, (2) passive microwave thermal 

emission observations, and (3) measurements of the backscattered power at small angles of incidence, which were processed 

to yield altimetric data. Radar imaging and altimetric and radiometric mapping of the Venusian surface were accomplished in 

mission cycles 1, 2, and 3 from September 1990 until September 1992. Ninety-eight percent of the surface was mapped with 

radar resolution on the order of 120 m. The SAR observations 

were projected to a 75-m nominal horizontal resolution, and 

these full-resolution data compose the image base used in 

geologic mapping. The primary polarization mode was horizontal-transmit, horizontal-receive (HH), but additional data for 

selected areas were collected for the vertical polarization sense. 

Incidence angles varied between about 20° and 45°.

High-resolution Doppler tracking of the spacecraft took 

place from September 1992 through October 1994 (mission 

cycles 4, 5, 6). Approximately 950 orbits of high-resolution 

gravity observations were obtained between September 1992 

and May 1993 while Magellan was in an elliptical orbit with a 

periapsis near 175 km and an apoapsis near 8,000 km. An additional 1,500 orbits were obtained following orbit-circularization 

in mid-1993. These data exist as a 75° by 75° harmonic field.

Magellan Radar Data

Radar backscatter power is determined by (1) the morphology of the surface at a broad range of scales and (2) the intrinsic 

reflectivity, or dielectric constant, of the material. Topography at 

scales of several meters and larger can produce quasi-specular 

echoes, and the strength of the return is greatest when the local 

surface is perpendicular to the incident beam. This type of 

scattering is most important at very small angles of incidence, 

because natural surfaces generally have few large tilted facets 

at high angles. The exception is in areas of steep slopes, such as 

ridges or rift zones, where favorably tilted terrain can produce 

very bright signatures in the radar image. For most other areas, 

diffuse echoes from roughness at scales comparable to the radar 

wavelength are responsible for variations in the SAR return. In 

either case, the echo strength is also modulated by the reflectivity of the surface material. The density of the upper few wavelengths of the surface can have a significant effect. Low-density 

layers, such as crater ejecta or volcanic ash, can absorb the incident energy and produce a lower observed echo. On Venus, a 

rapid increase in reflectivity exists at a certain critical elevation 

above which high-dielectric minerals or coatings are thought to 

be present. This leads to very bright SAR echoes from virtually 

all areas above that critical elevation.

The measurements of passive thermal emission from 

Venus, though of much lower spatial resolution than the SAR 

data, are more sensitive to changes in the dielectric constant 

of the surface than to roughness. They can be used to augment 

studies of the surface and to discriminate between roughness 

and reflectivity effects. Observations of the near-nadir backscatter power, collected using a separate smaller antenna on 

the spacecraft, were modeled using the Hagfors expression 

for echoes from gently undulating surfaces to yield estimates 

of planetary radius, Fresnel reflectivity, and root-mean-square 

(rms) slope. The topographic data produced by this technique 

have horizontal footprint sizes of about 10 km near periapsis 

and a vertical resolution on the order of 100 m. The Fresnel 

reflectivity data provide a comparison to the emissivity maps, 

and the rms slope parameter is an indicator of the surface tilts, 

which contribute to the quasi-specular scattering component.

Introduction

The Greenaway quadrangle (V–24; lat 0°–25° N., long 

120°–150° E.), Venus, derives its name from the impact crater 

Greenaway, centered at lat 22.9° N., long 145.1° E., in the 

northeastern part of the quadrangle. Greenaway was a wellnoted writer and illustrator of children’s books in Britain during 

the nineteenth century. In Greenaway’s honor, the Library Association of Great Britain presents the annual Kate Greenaway 

Medal to an illustrator living and publishing in Britain who has 

produced the most distinguished children’s book illustrations for 

that year.

The Greenaway quadrangle occupies an 8,400,000 km2

equatorial swath of lowlands and highlands (fig. 1). The map 

area is bounded by the crustal plateau, Thetis Regio, to the 

south and Gegute Tessera to the west. The rest of the quadrangle 

consists of part of Llorona Planitia, which is part of the vast 

lowlands that cover about 80 percent of Venus’ surface (Masursky and others, 1980). The southern map area marks the north 

edge of Aphrodite Terra, including Thetis Regio, that includes 

the highest topography in the quadrangle with elevations reaching >1 km above the Mean Planetary Radius (MPR; 6,051.84 

km). Northern Aphrodite Terra abruptly slopes north to Llorona 

Planitia. A broad northeast-trending topographic arch pocked 

with coronae separates two northeast-trending elongate basins, 

Llorona Planitia on the east, that form depositional centers 

for shield and coronae-sourced materials; both basins drop to 

elevations of <–1 km. In addition to these major features, the 

map area hosts thousands of small volcanic constructs (shields); 

seven coronae; ribbon-tessera terrain; suites of faults, fractures, and wrinkle ridges; 23 impact craters; and one craterless 

splotch.

Our goal for mapping the geology of the Greenaway quadrangle was to determine the geologic history for this region, 

which in turn provides insights into volcanic and tectonic processes that shaped the Venusian surface. Map relations illustrate 
2

that aerially expansive shield terrain (unit st; see Aubele, 1996; 

Hansen, 2005) played a primary role and coronae played a secondary role in volcanic resurfacing across the map area.

Data

Mapping was conducted using cycles 1, 2, and 3 of NASA 

Magellan synthetic aperture radar (SAR) imagery and Magellan 

altimetry datasets. We compiled the map on a digital C-1MIDR 

(Compressed Once Mosaiced Image Data Record) 225-m/pixel 

SAR base, however we mapped using full-resolution, hard-copy 

images and full-resolution digital (~100 m/pixel) normal and 

inverted (negative) SAR image bases. Synthetic stereo imagery, 

created by merging altimetry data with cycle 1 SAR (Kirk and 

others, 1992), using NIH-Image macros developed by D.A. 

Young, proved useful in resolving the interactions of flows, primary and secondary structures, and topography. In addition, we 

incorporated emissivity, reflectivity, and rms-slope data sets for 

V–24 to aid in mapping as necessary (fig. 2). Adobe IllustratorTM 

9 and 10, in association with Avenza MAPublisherTM 4, comprised the primary mapping and GIS tools; we enhanced radar 

images using Adobe PhotoshopTM 5. We obtained digital fullresolution SAR image bases from the U.S. Geological Survey 

MAP-A-PLANET website (http://www.mapaplanet.org). 

Terminology

Because terminology can carry stated and unstated 

assumptions that may vary with the reader or through time, we 

use this section to define terminology used herein.

We use the term “geologic unit” to mean a body of rock 

that consists of dominant, unifying features recognizable in 

the Magellan SAR imagery and mappable at the 1:5,000,000 

scale. Primary and secondary structures play critical roles in 

geologic-unit identification. Primary structures form during unit 

emplacement and include channels, flow boundaries, and volcanic edifices (shields). Secondary, or tectonic (strain), structures 

form after unit emplacement and include deformation features 

such as faults, fractures, ridges, folds, lineaments, and ribbon 

structures—parallel, paired, radar-bright and radar-dark lineaments that define a periodic fabric marked by parallel extensional troughs and ridges and have large length:width aspect 

ratios (Hansen and Willis, 1996, 1998; Ghent and Hansen, 

1999).

We separate geologic units into material units and terrains. 

The term "material unit" describes a sequence of materials 

interpreted to have been emplaced during a specific period of 

geologic time or representing a specific process. For example, 

corona-related flow material represents specific material 

emplaced during one or multiple volcanic eruptions; impactcrater ejecta deposits represent a specific process. The term 

"terrain" describes a texturally defined region (Hansen, 2005). 

The texture could include primary or secondary structures and 

imply that a particular region experienced at least one event 

that melded possibly previously unrelated material units (any 

combination of igneous, metamorphic, and sedimentary rocks) 

into a new package; this new package may be a larger collection 

of preserved material units (shield terrain, unit st) or a region 

characterized by secondary (tectonic) structures (Llorona Planitia lineated terrain, unit lL). There is no implication of a unique 

history prior to the event(s) that melded potentially separate 

units into the textural terrain. Events prior to terrain formation 

are unconstrained unless specifically noted. Gneissic terrain 

represents an analogous terrestrial unit.

Terrains in the map area include shield terrain, ribbontessera terrain, and a lineated terrain. Ribbon-tessera terrain and 

lineated terrain are each defined by secondary structures indicating that the host material(s) forming each terrain underwent 

a shared deformation history that completely inhibits original 

unit identification (Wilhelms, 1990). Shield terrain differs from 

ribbon-tessera terrain and lineated terrain in that it represents 

a shared emplacement mechanism (represented by primary 

structures). Shield terrain is comparable, for example, to a terrestrial sedimentary formation comprised of turbidite deposits 

from multiple source regions. Absolute time involved in shield 

terrain formation is unconstrained, whereas a terrestrial turbidite 

terrain might have many accessible clues to temporal evolution. 

Terrains, whether marked by shared tectonic histories or depositional histories, may represent multiple, time transgressive, 

events; timing across an entire terrain cannot be assumed.

The term “lowland” is used in a topographic sense in 

reference to broad, regional, long-wavelength (approximately 

hundreds of kilometers) basins. The terms “planitia” (singular) 

or “planitiae” (plural), used in a geomorphic sense, refer to individual basins or lowland regions (Llorona Planitia).

Mapping Techniques and SAR Image

Interpretation

The first order task in mapping geologic units is to determine their spatial distribution and to examine their contact 

relations with adjacent units (Wilhelms, 1990). Using Magellan SAR imagery, we identify geologic units on Venus using 

the following criteria: patterns in SAR, identification of sharp 

continuous contacts, interaction with or truncation of underlying structures, and (or) the presence of primary structures. These 

criteria allow determination of a reasonable geologic history 

and hint at a three-dimensional geometry (for further discussion 

see Wilhelms, 1990; Tanaka and others, 1994; Hansen, 2000; 

Zimbelman, 2001; Skinner and Tanaka, 2003). The radar dataset, 

however, may inhibit unique distinction between geologic units 

because radar backscatter is sensitive to surface roughness at the 

scale of radar wavelength (Ford and others, 1993). Such roughness differences could be attributed to facies changes within a 

single unit, such as the transition from pahoehoe to aa facies 

within an individual terrestrial lava flow; pahoehoe facies exhibit 

low-radar backscatter, whereas aa facies may display high-radar 

backscatter. Mapping geologic units solely on radar backscatter would incorrectly delineate such a flow into two separate 

geologic units. Hence, the truncation of structures and (or) the 

presence of distinctive patterns in primary structures are the most 

reliable criteria for identifying geologic units. Where possible, 

we indicate flow direction; arrows indicate both the interpreted 

flow direction and the location of flows, providing locations 
3

of substantive evidence for minimum limits of flow units. 

Hachured lines indicate the extent of a flow front. Thin dashed 

lines indicate that unit contacts are approximately located due to 

vague outcrop expression. Thick dashed lines indicate a gradational boundary where the transition between units may exist 

over several tens to hundreds of kilometers. Radar boundaries 

indicate the locations of sharp, radar-backscatter transitions in 

the lowlands. Based on caveats discussed above, it is unclear if 

the radar boundary represents a geologic boundary. When mapping secondary structures, we do not map every single structure 

observed on the SAR imagery. Instead, we map a representative 

amount of each structure to convey the density and distribution 

of individual suites. In many cases, the exact location of a unit 

contact or the total number of structures is most important within 

the context of specific questions. Thus, we encourage users of 

this map to examine such contacts and distribution of structures 

in detail with specific questions in mind.

One major limitation in interpreting the geologic history of 

Venus’ surface is the uncertainty of rock types. We assume that 

Venus could host only the three basic rock types observed on 

Earth: igneous, metamorphic, and sedimentary. The extremely 

dehydrated state of the lower atmosphere (Donahue and others, 

1997) and lithosphere (Mackwell and others, 1998), as well as 

the high current surface temperature of approximately 460°C 

(Crisp and Titov, 1997), precludes the current presence of 

surface water, dismissing the idea that many surface rocks are 

sedimentary. In addition, the apparent absence of widespread 

erosion suggests that surface rocks are not likely exposed 

crustal metamorphic rocks or intrusive igneous rocks. Thus, surface rocks most likely originated as extrusive igneous (volcanic) 

rocks (Banerdt and others, 1997), an interpretation consistent 

with the abundance of volcano-like features on Venus (Head and 

others, 1992) and geochemical measurements of a basaltic surface composition (Grimm and Hess, 1997). Exceptions to volcanic rocks on Venus include impact-related materials (Schultz, 

1992; Campbell and others, 1992), eolian deposits (Arvidson 

and others, 1992; Greeley and others, 1992), and atmospheric 

chemical precipitates (Fegley and others, 1997). Although 

these materials are present on Venus, their aerial extent appears 

limited. However, given the uncertainty of past Venus climatic 

conditions (Bullock and Grinspoon, 1996; Donahue and others, 

1997; Phillips and others, 2001) and our nascent understanding of Venusian surface processes, it is best to keep an open 

mind when interpreting Venus’ rock record. Venus could indeed 

have hosted vast oceans in the past (Donahue and others, 1982; 

Donahue and Russell, 1997; Donahue, 1999; Hunten, 2002; see 

also Jones and Pickering, 2003; Hamilton, 2005).

Geology of the Greenaway

Quadrangle (V–24)

Geologic Overview

Geologic units in the Greenaway quadrangle include three 

terrain units and 11 material units. Terrain units characterize 

most of the map area and include a regionally expansive shielddominated terrain (unit st), a ribbon-tessera terrain (unit rtGH), 

and a potentially regionally extensive lineated terrain (unit lL) 

characterized by closely spaced (<<1 km), northwest-trending 

lineaments. Interspersed with the terrains are material units 

separated into flow materials (presumed volcanic and associated mostly with individual coronae) and materials associated 

with impact craters. Coronae-related materials include coronaesourced flow materials. Impact-crater materials are mapped 

as undivided ejecta (unit cu), fluidized outflow (unit co), and 

crater fill (unit cf). One terrain unit (unit st) and one of the 

material units (unit fu) are composite units composed of multiple flows emplaced over an unknown period of geologic time; 

we considered them stratigraphically discontinuous units.

The map area also hosts an array of secondary structures. 

Secondary structures occur at a variety of scales and include 

fractures, folds, ridges, and lineaments. Multiple suites of 

structures locally occur together to structurally define larger 

scale features, such as coronae, as well as individual suites 

defining features such as fracture zones. Wrinkle ridges trend 

mostly east-northeast across the northern one-third of the quadrangle, where they deform a majority of the map units located 

in the lowlands. Local deviations from the dominant northeast 

trend occur and are apparently associated with local features. 

For example, wrinkle ridges near lat 18.5° N., long 131.5° E. 

make an arcuate bend along the northwest margin of a coronalike feature.

The geology and topography in the map area are grossly 

linked. Crustal-plateau (high-standing, flat-topped, quasi-circular regions interpreted as isostatically supported by relatively 

shallow low-density material [Bindschadler and others, 1992; 

Phillips and Hansen, 1994; Hansen and others, 1997]), ribbontessera terrain characterizes the highlands along the west and 

south boundaries of the map area. Local topographic highs as 

much as approximately hundreds of meters in elevation occur 

across the quadrangle and mark kipukas of ribbon-tessera terrain and unit lL. Shield terrain dominates most of the lowland 

where it embays units rtGH and lL (fig. 3). A northeast-trending 

topographic arch marked by four coronae divides the lowland 

into two topographic basins. The western basin hosts local 

outcroppings of unit lL, as well as three separate units of flow 

material (units fcA, fcR, fcS) that broadly parallel the basin 

trend. The eastern basin hosts extensive outcrops of unit lL. 

Corona-sourced flow material is present along the northeast 

margin of the eastern basin (unit fcI). Coronae along the topographic arch produced flow material that has embayed kipukas 

of unit rtGH located along the arch flanks.

Geologic Units

Terrain and Flow Materials

Ribbon-Tessera Terrain

Ribbon-tessera terrain is defined as deformed crust 

containing multiple suites of intersecting tectonic structures 

including folded-ribbon structures (Hansen and Willis, 1996). 

Ribbon-tessera terrain includes two large ribbon-tessera inliers 

(Gegute and Haattse-baad Tesserae) and kipukas that crop out 
4

across the map area. Gegute Tessera, located along the west 

boundary of V–24, is a large arcuate inlier that reflects a broad, 

north-trending warp; the inlier grades into smaller outcrops, or 

kipukas, along its margins. Haasttse-baad Tessera occurs along 

the south margin of the map and marks the northeast edge of 

Aphrodite Terra. This region includes numerous blocks separated by topographic lows marked with low-backscatter material 

mapped as unit st and flow material associated with Blai and 

Rosmerta Coronae (units fcB, fcR). We map ribbon-tessera terrain (unit rtGH) as a single unit, based on the similarity of structure trends present in all tessera outcrops. However, unit rtGH

should not be viewed as a synchronously formed geologic unit 

but as an indeterminate (one or many) number of pre-existing 

materials subsequently deformed one or multiple times.

Numerous secondary structures recognized as ribbon 

structures, folds, and lineaments characterize unit rtGH in the 

map area. The structures occur at scales from an effective image 

resolution of about 1 km to tens of kilometers (fig. 4) across 

all of unit rtGH and have erased the original character of the 

predeformation materials (Wilhelms, 1990). Clues to the type 

of material and emplacement style of the pre-ribbon-tessera 

materials are subsequently indeterminate due to ribbon-tessera 

deformation. Because structure wavelengths extend to effective 

image resolution, it is conceivable that they may extend below 

effective image resolution (Zimbelman, 2001). Figure 4 highlights the southwest corner of the Haasttse-baad Tessera region 

and serves as an example of both the abundance of ribbontessera structures and the various wavelengths at which they can 

occur within unit rtGH. Six types of secondary structures characteristic of unit rtGH are highlighted in figure 4. These structures include a northeast-trending background fabric, a suite of 

northwest-trending ribbon structures (wavelength approximately 

2.5 km), northwest-trending parallel folds or warps (wavelength 

approximately 15–20 km) that occur at oblique angles to ribbon 

structures, two types of ribbon-tessera lineaments, and structural troughs associated with basin and dome terrain (Hansen 

and Willis, 1996). Ribbon structures occur across all of unit 

rtGH and have both northwest and orthogonal northeast trends. 

Long-wavelength folds or warps also locally occur within the 

northwestern (northwest-trending folds with wavelengths of 

15–25 km) and eastern (north-northeast-trending folds with 

wavelengths of 15–20 km) expanses of the Haasttse-baad Tessera region. The structural troughs associated with basin dome 

terrain consist of linear and curvilinear ridges and troughs 

that deform earlier formed ribbon fabrics (fig. 4C) and occur 

mostly within the central region of the Haasttse-baad Tessera 

region. Curvilinear ridges and troughs display variable trends 

and rounded, gentle slopes similar to a fold. It is not clear if the 

linear and curvilinear ridges and troughs record contractional 

or extensional strain. However, the curvilinear nature implies 

multiple episodes of deformation.

Of the secondary structures identified in figure 4, the background fabric and the two types of ribbon-tessera lineaments are 

worth discussing further.

The background fabric consists of lineaments that are penetrative at image resolution and that appear to be constrained to 

the Haattse-baad Tessera region of unit rtGH. The character of 

individual lineaments is undefined: lineaments trend northeast 

with lengths as much as hundreds of kilometers and are overprinted by later-forming tessera structures.

The two distinct suites of ribbon-tessera lineaments are 

distinguished based on structure spacing and are termed ribbontessera lineament a and ribbon-tessera lineament b. Ribbon-tessera lineament a occurs within suites of tightly spaced (<<1 km) 

lineaments that define variable trends across unit rtGH. Within 

figure 4 and kipukas in eastern V–24, these lineaments define 

northwest and orthogonal northeast trends, however within the 

Gegute Tessera region, they define mostly northwest trends. 

Tessera lineament a is similar to the S-type structures identified by Tuckwell and Ghail (2003) and Kumar (2005) along the 

boundary between southeastern Ovda Regio and northwestern 

Thetis Regio. In some regions, suites of ribbon-tessera lineament a appear to wrap around some ribbon-tessera blocks and 

may represent a zone of high strain (for example, near lat 5° N., 

long 137° E.). At these locations, the fabric might indicate local 

shearing within regions of unit rtGH. Ribbon-tessera lineament 

b has 1–10 km spacing and broadly parallels the trends of the 

long-wavelength folds or warps in unit rtGH. The nature of 

ribbon-tessera lineament b is indeterminate, although this lineament suite may be similar to short-wavelength folds identified 

by Nordberg and others (2005) in Alpha Regio and by Hansen 

(2006) in Ovda Regio.

One other type of secondary structure, which is not 

observed in figure 4, also occurs in unit rtGH. Steep-walled 

structural troughs that have rectangular cross sections and a 

consistent width of approximately 2 km cut northern Haasttsebaad Tessera and several tessera kipukas in the central map area. 

The troughs cut all pre-existing structures and maintain a spacing of approximately 10–50 km. Within northern Haasttse-baad 

Tessera, these troughs describe an arcuate pattern, whereas they 

describe variable trends within tessera-terrain kipukas north of 

Haasttse-baad Tessera.

Temporal relations between the various structural suites 

that contain ribbon-tessera terrain fabrics are constrained based 

on mechanical arguments. Based on figure 4B, ribbons cut 

the background fabric, which implies that the fabric predates 

ribbon structures. However, other temporal relations are not 

as straightforward. Ribbon-structure wavelengths, marked by 

ribbon-ridge width (2.5 km), suggest a shallow depth, possibly 

between 0.6 and 2.9 km deep (see Ghent and Tibuleac, 2002), 

to the brittle-ductile transition (BDT) at the time of ribbon 

formation (Hansen and Willis, 1998). In turn, fold wavelengths 

between 15 to 25 km imply a depth to BDT of approximately 

6 km (Brown and Grimm, 1997; Ghent and Hansen, 1999). 

Northwest-trending graben with wavelengths of approximately 

15–25 km (fig. 4A, C) that cut across all structures, as well as 

the basin and dome terrain, also imply a relatively deeper depth 

to BDT at the time of their formation. Based on the interpreted 

depth to BDT required to form the various tessera structures, it 

seems plausible that the structures reflect a progressive thickening of the lithosphere as the BDT moved downward with 

time. Therefore, ribbons and, thus, the background fabric likely 

formed before tessera folds, graben, and basin and dome terrain. 

If ribbons and the background fabric formed after the folds, the 

shallow BDT would not support the folds, and they would have 

disappeared by viscous relaxation (Hansen and Willis, 1998). 
5

Relative timing between the formation of folds and basin and 

dome terrain is unconstrained. The northwest-trending graben 

crosscut and, therefore, postdate all the other structures. Hansen 

(2006) also presents a detailed discussion of ribbon-tesseraterrain evolution derived from detailed mapping of a portion 

of Ovda Regio. For a different view of the evolution of ribbontessera-terrain fabric, see Gilmore and others (1998).

Intratessera Basin Material

Intratessera basins, marked by local topographic lows as 

deep as several hundred meters, reside locally within tracts of 

ribbon-tessera terrain (Bindschadler and Head, 1991; Banks 

and Hansen, 2000). In the map area, these basins occur within 

Gegute and Haasttse-baad Tesserae and are floored with lowradar-backscatter material (unit ibGH) assumed to be volcanic 

in origin following previous interpretations (Bindschadler and 

others, 1992; Gilmore and Head, 1994; Banks and Hansen, 

2000; Bleamaster and Hansen, 2005). Intratessera basins in 

Gegute Tessera broadly mimic the inlier’s arcuate nature; 

whereas basin shapes in Haasttse-baad Tessera mimic local 

tectonic trends. Unit ibGH commonly preserves primary shield 

edifices and typically does not exhibit tessera-related structure, 

implying that unit ibGH postdated tessera-related tectonism. 

Lumping of spatially disparate unit ibGH, as we have done, 

is not meant to imply that all intratessera basins, or basin fill, 

formed at the same time.

Lineated Terrain

Tightly spaced (<<1 km spacing) northwest-trending 

lineaments characterize unit lL. Lineaments are predominantly 

fractures marked by linear topographic lows, although local 

ridges exist. Unit lL crops out across the lowland, occurring as 

10- to 1,000-km2 patches; the largest expanses are exposed in 

the eastern basin in spatial association with Barbale and Lumo 

Dorsa. The topographic arch hosts approximately 10 km2

patches of unit lL in the vicinity of Kamadhenu Corona, and 

the western basin hosts approximately 100 km2 patches in the 

vicinity of Gegute Tessera. Lineament trends are parallel within 

all unit lL outcrops. In addition, where unit lL crops out near 

ribbon-tessera-terrain units, lineament trends broadly parallel 

ribbon fabrics and tessera lineament a trends within unit rtGH. 

Based on this parallelism in all unit lL outcrops, we map the 

lineated terrain as a single, undivided terrain that represents 

materials that have experienced at least one episode of deformation. Presumably, deformation destroyed the nature of the original unit(s) and created a tectonic fabric that characterizes the 

lineated terrain unit. The consistent northwest trend, preserved 

across spatially separate exposures, indicates that unit lL may 

form a regionally expansive unit that underlies much of unit st

and coronae-sourced flow materials.

Outcrops of unit lL are related to the unit’s low local relief 

that ranges from below the resolution of Magellan radar altimetry to as much as approximately hundreds of meters. Flow material associated with units st and fu flood much of unit lL, locally 

covering the topographically lowest portions and preserving 

the topographically highest portions of the unit. In many cases, 

this results in variable exposures of unit lL over distances of 

as much as hundreds of kilometers (for example, see fig. 3). In 

such cases, we map the boundary between unit lL and embaying 

flow materials as a gradational contact (in plan view); we place 

the contact at the first exposure of unit lL that is mappable at the 

1:5,000,000 scale. Because the contact is gradational between 

unit lL and units st and fu, flow material associated with units st

and fu flood low-lying regions within areas mapped as unit lL. 

To delineate the degree of such flooding, we divided unit lL into 

two facies: facies a and facies b. Facies a includes extensively 

flooded portions of unit lL, whereas facies b includes lessflooded portions of the unit where flow material associated with 

units st and fu locally flood some fractures (see fig. 3B).

Shield Terrain

Unit st, shield terrain, collectively consists of shield edifices and erupted products. Shield edifices, or shields, are circular to quasi-circular features that are flat-topped or cone, dome, 

or shield shaped, generally <<1 km in height, and typically 1–2 

km in diameter (Guest and others, 1992; Crumpler and others, 

1997). A few shields range to approximately 20 km in diameter. 

Shields may or may not contain a summit pit. Shield size is 

difficult to constrain, because shield bases are typically poorly 

defined; shields appear to blend into the erupted products of 

other shields. The erupted products represent material potentially emplaced from any combination of lava flows, air-fall 

deposits, or pyroclastic flows (Guest and others, 1992). The 

erupted products, collectively called “shield paint” (Hansen, 

2005), appear to have coalesced to form a coherent, mechanical 

layer that variably covers pre-existing materials and structures 

(fig. 3). The shield paint contains windows that expose the local 

underlying geology. Individual flows within shield paint are 

typically indistinguishable; based on radar caveats discussed 

above and the limited spatial extent of individual radar domains, 

we do not attempt to divide distinct individual flow units or 

shield clusters, even though sharp radar backscatter transitions 

within unit st may reflect flow boundaries. However, we should 

note that shields located within coronae interiors could represent shield fields that could be associated with the evolution of 

individual coronae (Crumpler and others, 1997).

Shield terrain displays three types of relations with other 

map units and features in the Greenaway quadrangle. First, 

units that are topographically higher than unit st (unit rtGH) 

display definite, abrupt boundaries with shield terrains. Second, 

units that have low local relief (unit lL) display contacts with 

unit st that exist over tens to hundreds of kilometers; there 

is a gradation in plan view from unit st to the other unit, a 

phenomenon illustrated in figure 3. Figure 3 illustrates shield 

paint that flowed into local topographic lows and around local 

topographic obstacles, resulting in a tight, digitate contact 

between younger shield paint and older lineated terrain (unit lL). 

The detail of the boundary between unit lL and shield terrain 

indicates an extremely shallow contact that is characteristic of 

the boundary between the two units. The complex contact also 

indicates that shield terrain forms a thin layer, possibly on the 

order of meters to tens of meters, an interpretation consistent 

with Guest and others (1992), who estimated shield-associated 

deposits as likely tens of meters or less in thickness (see also, 
6

Hansen, 2005). The third type of relation is a time-transgressive 

relation, which unit st displays with other flow units and tectonic structures. For example, Rosmerta Corona flow material 

(unit fcR) locally covers unit st at lat 11° N., long 124° E. In 

turn, scattered shields variably occur across much of unit fcR. 

In addition, fractures locally cut unit st in some areas, presumably because of structural reactivation; shields and associated 

materials, in turn, locally cover fractures. For example, near lat 

8° N., long 139° E., lineaments associated with unit lL cut unit 

st. In turn, the lineaments terminate along a radar-backscatter 

boundary.

Shield terrain is an aerially expansive unit that covers 

much of the map area and extends into adjoining quadrangles. 

Unit st covers >70 percent of the map area and extends north 

into Shimti Tessera quadrangle (V–11) and Vellamo Planitia quadrangle (V–12), where it is equivalent with the shield 

plains of Aubele (1996). Shield terrain also extends westward 

into Niobe Planitia quadrangle (V–23; Hansen, 2005, 2006), 

and shield densities along the borders with Rusalka Planitia 

quadrangle (V–25; between lats 3°–16° N.) and Thetis Regio 

qudrangle (V–36; between longs 142°–148° E.) suggest that 

unit st extends into these two quadrangles. However, Young 

and Hansen (2003) did not describe shield terrain within V–25 

but instead identified several shield fields along its west border. 

Perhaps regionally extensive shield terrain in the map area 

grades into localized shield fields within V–25. Further, shield 

density seems to decrease dramatically in the southeast corner 

of the map area (near lat 1° N., long 149° E.) and gradually 

in the northeast corner. In the southeastern map area, unit fC

appears to mark the boundary with unit st; unit fC may locally 

cover shields and related deposits associated with unit st. There 

is no obvious reason for the decrease in shield density in the 

northeastern map area, although the gradual decrease in shield 

density suggests that shield terrain grades into materials that 

come from other sources; as such, we map a gradational boundary from unit st to unit fu. However, it is also possible that the 

apparent decrease in shields can be attributed to the regional, 

impact-crater haloes obscuring the shields and (or) the diameters of shields in this region being below the effective resolution 

of Magellan imagery (Zimbelman, 2001).

Coronae-Sourced Flow Material

Corona-sourced flows in the map area vary in aerial extent. 

For example, units fcA and fcB form relatively localized flows 

that extend a few hundred kilometers or less from their sources. 

High-standing tracts of unit rtGH locally limit the extent of 

unit fcB. In contrast, units fcR, fcS, and fcI define relatively 

extensive corona-sourced flows that extend greater than 300 km 

from their source. Unit fcR, the most expansive corona flow in 

the map area, floods much of the Haasttse-baad Tessera region 

of unit rtGH and spills into three adjoining quadrangles: Niobe 

Planitia (V–23; Hansen, 2009), Ovda Regio (V–35; Bleamaster 

and Hansen, 2005), and Thetis Regio (V–36). Flow directions 

and flow fronts preserve a record of flow directions within unit 

fcR. Rosmerta Corona flows may have traversed through a 

fracture zone north of Rosmerta Corona and into the western 

basin where flow limits become difficult to define. A possible 

flow-front limit is indicated on the map, although changes in 

radar backscatter characteristics north of this boundary indicate 

that the flow might extend farther north. Unit fcS, forming a 

relatively narrow lobate flow approximately 700 km long within 

the map area, extends from Vellamo Planitia quadrangle (V–12) 

and broadly parallels the trend of the western basin; the source 

of unit fcS is uncertain, but it may be Boann Corona in V–12. 

Lobate flow fronts associated with unit fcI, sourced from Ituana 

Corona (V–25), marks the northeast corner of the Llorona Planitia basin; one flow lobe of unit fcI embays unit lL.

Impact Craters

The Greenaway quadrangle (V–24) hosts 23 impact 

craters (table 1). Thirteen craters have diameters <20 km, eight 

range from 20 to 90 km diameter, and two show diameters 

>90 km. Only one crater (unnamed crater b, table 1) is tectonized; the rest of the craters do not appear deformed. Outflow 

material extending from Vigée-Lebrun crater flows around 

wrinkle ridges, clearly indicating that this crater postdates 

local wrinkle-ridge formation and regional contractional strain. 

Greenaway, Maria Celeste, and Vigée-Lebrun form multiring 

craters (Schaber and others, 1992); each contains segments of a 

discontinuous topographic ring composed of high-backscatter 

material located within the main crater basins. Other impact 

craters within the map area contain a central peak composed of 

high-radar-backscatter material. Fifteen craters have low-radarbackscatter interiors interpreted as interior fill (unit cf), five 

craters have high-radar-backscatter floors, and the backscatter 

within two craters is indeterminate.

Although all impact craters within the map area contain 

continuous ejecta blankets (unit cu), six craters also contain 

fluidized outflow material (unit co) (Asimow and Wood, 1992; 

Herrick and others, 1997). Outflow materials extending from 

craters Bourke-White, Maria Celeste, Vigée-Lebrun, and Wilder 

show low-radar backscatter and are segmented into complex 

channels approximately 1–2 km wide. Shield edifices and 

deposits associated with unit st locally cover outflow material associated with Wilder crater near lat 17° N., long 123° E. 

Outflow material extending from craters Ban Zhao and Himiko 

occurs as approximately 2–3 km wide, high-radar-backscatter 

lobate flows that extend as far as approximately 75 km from the 

respective ejecta blankets.

Extensive halos, including parabolas and splotches, are 

associated with some impact craters in the map area. Impact 

haloes are generally accepted as representing the distal, finegrained component of impact ejecta, whereas parabolas represent material entrained by the prevailing easterly winds of 

the upper atmosphere (Campbell and others, 1992). Ban Zhao, 

Budveska, Himiko, and Olena craters are associated with welldeveloped, east-trending, low-radar-backscatter, parabolic halos. 

The Ban Zhao crater halo is superimposed on a second approximately 600 km diameter irregular halo that could be related to 

any of the five other impact craters located in the northeastern 

map area. In addition, Hwangcini and Phyllis craters show 

irregular, low-radar-backscatter halos. The one craterless 

splotch, located near lat 7° N., long 144° E., probably represents 
7

a shock feature formed by the airburst of a meteor that failed to 

reach the surface (McKinnon and others, 1997). Although the 

paucity of impact craters on Venus inhibits dating of geologic 

units, the decay of crater halos may serve as an approximate 

index for the relative ages of individual craters (Izenberg and 

others, 1994; Basilevsky and Head, 2002). In addition, crater 

halos obscure local geologic relations in specific areas in the 

map area. For example, the Himiko crater halo hinders the identification of wrinkle ridges and possible flow material extending 

from Abundia and Nintu Coronae in the western map area.

Channels

Greenaway quadrangle (V–24) hosts both simple and complex channels (Baker and others, 1992). Simple channels, which 

consist of a long, single main channel, occur within units st and 

fu. Complex channels form anastomosing, braided, or distributary patterns and are associated with fluidized outflow (unit co) 

extending from some impact craters.

Simple Channels

Simple channels can be further subdivided into sinuous 

rilles and canali. Sinuous rilles are approximately 1–2 km wide, 

tens to hundreds of kilometers long, and extend from small 

(approximately kilometers in diameter) quasi-circular collapse 

regions (Baker and others, 1992). Sinuous rilles in the map area 

occur along a broad ridge associated with Rosmerta Corona and 

are discussed further in the Rosmerta Corona section. Canali, 

channels with consistent widths of 1–2 km for lengths as much 

as several hundred kilometers, occur across the lowland of 

V–24. The canali lack obvious sources, termini, and levee structures and appear to be negative topographic features. Ikhwezi 

Vallis, which extends into eastern Rusalka Planitia quadrangle 

(V–25), is a north-trending, segmented canale located in 

Llorona Planitia; segments are approximately 1 km wide and 

tens to hundreds of kilometers long. The segmented nature of 

Ikwhezi Vallis may be due to (1) covering by local volcanic 

flows, (2) subsurface fluid flow that eroded overlying surface 

materials (Lang and Hansen, 2006), or (3) partial roof collapse 

of a constructional lava tube (Gregg and Greeley, 1993). Kinsei 

Vallis, an approximately 50 km wide, east-west-trending canale, 

occurs in the vicinity of western Barbale Dorsa. Neither Ikwhezi 

nor Kinsei Valles are associated with definitive sources, termini, 

or any apparent flow material. Other unnamed canali in the map 

area are approximately hundreds of meters wide and as much as 

tens of kilometers long.

Complex Channels

Complex channels in the map area are associated with fluidized outflow material (unit co) extending from the impact craters Bourke-White, Maria Celeste, Vigée-Lebrun, and Wilder. 

Channels associated with these impact craters maintain relatively constant widths of 1–2 km and range in length from tens 

to hundreds of kilometers; each apparently facilitated transport 

of unit co. Low-radar-backscatter material marks the channel 

floors, which are bounded by moderate-radar-backscatter walls 

or levees composed of unit co. These relations are consistent 

with at least a partial constructional origin for these complex 

channels.

Tectonic Features

Secondary structures including faults, fractures, ridges, 

and warps occur across the map area and display widely diverse 

scales, ranging from individual suites of linear to curvilinear 

features a few kilometers long to multiple suites of tectonic 

structures that define larger scale tectonic features such as 

coronae.

Wrinkle Ridges

Wrinkle ridges, low sinuous ridges 1–2 km wide and tens 

to hundreds of kilometers long that record a small degree of 

regional contractional strain occur on most terrestrial worlds, 

especially on large expanses of volcanic plains (Watters, 1988). 

At map scale, wrinkle ridges in the map area (V–24) describe 

a broad, east-northeast pattern across the north one-third of the 

map area, broadly paralleling Thetis Regio, and are interpreted 

as a response to loading of the lithosphere by Aphrodite Terra 

(Sandwell and others, 1997; Bilotti and Suppe, 1999). Wrinkle 

ridges within this northeastern trend typically contain wavelengths between approximately 25 and 50 km; however, shorter 

wavelengths of approximately 5 km are common within some 

coronae interiors. Based on mechanical considerations, shorterwavelength suites likely reflect deformation of a thinner layer, 

and longer-wavelength suites likely reflect deformation of a 

thicker layer. Local variations from the east-northeastern trend 

exist at the ten- to hundred-kilometer scale. For example, at lat 

18.5° N., long 131°E., wrinkle ridges define an arc around a 

quasi-circular topographic low northwest of Kubebe Corona.

In contrast to the rest of the map area, wrinkle ridges 

are rare in southeastern V–24. Only local east-west-trending, 

wrinkle-ridge suites occur over areas of approximately hundreds 

of kilometers. The relatively low strain preserved in southeastern V–24 may be attributed to strain partitioning or to burial 

by later-stage volcanic flows. Wrinkle ridges are also notably 

absent within exposures of unit rtGH, although wrinkle ridges 

extend to the boundary between the underlying ribbon-tessera 

terrain and the overlying shield terrain. These relations presumably indicate that unit rtGH is not rheologically amenable to 

wrinkle-ridge formation, whereas the thin layer of overlying 

shield terrain (unit st) can be readily deformed into wrinkleridge structures. Thus, the presence or absence of wrinkle ridges 

in the map area is likely related to rheological criteria rather 

than temporal considerations.

Linear Features

The Greenaway quadrangle (V–24) hosts numerous highradar-backscatter, linear to curvilinear features. Although some 

of these features are too narrow to allow robust characterization, many contain parallel, low-radar-backscatter segments 
8

indicating a trough-like character. We interpret most linear and 

curvilinear features as graben and fractures; where we cannot 

characterize the features as graben or fractures, we map the 

features as regional lineaments. Individual graben and fractures 

range in length from effective resolution (approximately 1–2 

km) to hundreds of kilometers. Graben and fractures describe 

linear, radial, concentric, and anastomosing patterns. Radial 

and concentric fractures occur within coronae. Rosmerta and 

Blai Coronae, for example, display prominent suites of radial 

fractures and graben, whereas Abundia and Nintu Coronae host 

concentric fracture patterns. Coronae along the topographic arch 

are linked by a northerly trending, approximately 1,500 km long 

and approximately 500 km wide, anastomosing zone of fractures and graben.

Three other zones of linear features crop out in local topographic highs (approximately 100 m high) in the northwestern, 

central, and southeastern map area. The northwestern zone hosts 

northerly trending lineaments and fractures, approximately 

hundreds of kilometers long, immediately north of Abundia 

Corona. The central zone occurs in an approximately 200- by 

250-km patch in the central map area along the east margin 

of the topographic arch. This zone consists of two suites of 

near orthogonal northwest- and northeast-trending fractures 

(wavelengths approximately 5–20 km). The southeastern zone 

is approximately 1,000 km wide and consists of northeasttrending lineaments, fractures, and graben, each having lengths 

of approximately tens to hundreds of kilometers, that cut the 

eastern extent of unit rtGH and extend from northeastern Thetis 

Regio quadrangle (V–36) to southwestern Rusalka Planitia 

quadrangle (V–25).

Coronae

Coronae are circular to quasi-circular features broadly 

defined by an annulus of fractures or ridges, an interior topographic depression or bulge, and possible radial fractures (Janes 

and others, 1992; Squyres and others, 1992; Stofan and others, 

1992). “Corona” is a morphologic term stemming from the 

Latin word for crown (Stofan and others, 1997). However, the 

term “corona” has taken on a genetic connotation implying that 

any circular to elongate structure defined by an annulus of concentric fractures and (or) ridges is the result of the interaction of 

a diapir with the lithosphere (Squyres and others, 1992; Stofan 

and others, 1992; Koch and Manga, 1996; Smrekar and Stofan, 

1997; Stofan and others, 1997; Chapman and Zimbelman, 1998; 

Chapman, 1999; DeLaughter and Jurdy, 1999; Hansen, 2003). 

Some studies, though, suggest that at least some coronae may 

result from other processes such as impact cratering (Schultz, 

1992, 1993; Hamilton, 1993, 2005; Stewart and others, 1993; 

Vita-Finizi and others, 2005; McDaniel and Hansen, 2005). We 

do not endorse any particular model of corona formation. We 

qualitatively describe features in the map area that fit the morphologic description of a corona and visit the idea of various 

corona formation hypotheses in the Discussion section.

The Greenaway quadrangle (V–24) hosts seven coronae. 

Four coronae lie along the northeast-trending topographic arch 

and three coronae occur as isolated features in the west half of 

the map area. An eighth corona (Blai Corona) lies mostly within 

the Thetis Regio quadrangle (V–36) to the south but extends 

into the southern map area. Rosmerta and Blai Coronae exhibit 

well-developed radial fractures, positive topography, and extensive radial flows. The other coronae are similar to old coronae 

of Chapman and Zimbelman (1998), consisting of low circular 

basins locally surrounded by raised rims and generally lacking obvious radial fractures or extensive volcanic flows. Each 

corona is discussed below.

Abundia Corona (lat 18° N., long 125° E.; approximately 

300 km diameter) includes an approximately 75–100 km wide 

annulus of concentric fractures (fracture spacing approximately 

1–2 km), locally covered by low-backscatter material. Along 

the north arc of the annulus, a suite of approximately 10–100 

km long, north-trending lineaments and fractures (wavelength 

approximately 1–5 km) trend approximately perpendicular 

to the concentric fractures and are preserved in a broad topographic high. Relative timing between these two fracture suites 

is unconstrained, and it is unclear if the north-trending fractures 

and lineaments are associated with the formation of Abundia 

Corona. The annulus surrounds an approximately 150 km 

diameter circular basin. The basin contains shields and associated materials of unit st and a centrally located, approximately 

100 km diameter dome. Wrinkle ridges that are approximately 

50–100 km long and have wavelengths of approximately 10–15 

km trend northeast through the basin, which is consistent with 

the regional trend, although wrinkle ridges within the basin 

exhibit shorter wavelengths. The large dome lacks wrinkle 

ridges. Two approximately 20 km diameter, steep-sided tholi, 

previously called “pancake domes” (McKenzie and others, 

1992; Pavri and others, 1992), occur within the vicinity of 

Abundia Corona. One tholus lies superposed on the west edge 

of the annulus, whereas the second dome lies approximately 50 

km east of the outer edge of the annulus.

Blai Corona (lat –0.4° N., long 134.5° E.) occurs predominantly within Thetis Regio quadrangle (V–36) south of the map 

area. Graben, >100 km long, radiate from the corona center and 

cut unit rtGH; the graben broadly parallel local ribbon-structure 

trends. Flow material sourced from Blai Corona (unit fcB) 

embays unit rtGH and floods local topographic lows, including 

ribbon structures, for as much as hundreds of kilometers.

Kamadhenu Corona (lat 20° N., long 136° E.; approximately 400 km diameter) includes a 30-km-wide, horseshoeshaped ridge that has parallel fractures approximately 100 km 

long and approximately 1–5 km wide. The ridge is cut by an 

approximately 25 km diameter pit at lat 19.5° N., long 136.5° E. 

that is marked by an approximately 15 km wide annulus of concentric fractures. Local topographic highs as much as approximately 100 km2 within the corona interior preserve two distinct 

lineament sets. One set consists of northeast-trending fractures 

approximately 1 km wide and 50–75 km long that have 10–15 

km spacing. The second set consists of tightly spaced (<<1 km), 

northwest-trending lineaments similar to those within unit lL. 

Wrinkle ridges that are approximately 50–100 km long and have 

wavelengths of approximately 5–10 km trend northeast through 

the corona interior and parallel the regional wrinkle-ridge trend.

Kubebe Corona (lat 15° N., long 132° E.; approximately 

150 km diameter) includes an approximately 50–75 km wide 

annulus of factures that surround an approximately 75 km 
9

diameter circular basin. Kubebe Corona corresponds with a 

northwest bend in the fracture zone along the topographic arch. 

Low-radar-backscatter material composed of shields and associated deposits of unit st mark the floor of the basin and locally 

cover north-trending fractures. High-radar-backscatter material, 

presumably volcanic flow material, extends from the east and 

west margins of the corona down the flanks of the topographic 

arch. Complete boundaries for the flow materials are obscured 

and difficult to trace in many locales, which makes identifying 

entire flow units difficult. As a result, we indicate flow boundaries and flow directions where possible. Adjacent to the northwest edge of Kubebe Corona is an approximately 25 km wide, 

quasi-circular ridge that surrounds an approximately 200 km 

wide circular basin that contains low-radar-backscatter material 

composed of shields and associated deposits. Approximately 

100 km2 patches of <1 km-spaced, north-trending lineaments 

crop out within the basin. The relation between Kubebe Corona 

and the adjacent corona-like feature is unclear. The adjacent 

feature may be genetically related to, or completely independent 

of, Kubebe Corona.

Nintu Corona (lat 19.5° N., long 123.5° E.; approximately 

100 km diameter), located about 100 km west-northwest of 

Abundia Corona, consists of an approximately 30 km wide 

annulus of concentric fractures surrounding a 50-km-diameter, 

circular basin. The basin hosts an approximately 25 km diameter, low-backscatter, steep-sided, flat-topped dome resembling 

a tholus. A quasi-circular, approximately 15 km diameter dome 

crosscuts the annulus near lat 19° N., long 123° E.

Rosmerta Corona (lat 0.5° N., long 124° E.; approximately 

300 km diameter) represents the best developed corona in the 

map area; Rosmerta Corona includes an approximately 25 km 

wide trough surrounding an approximately 125 km diameter, 

quasi-circular plateau covered with low- and moderate-backscatter material. A northerly trending fracture zone extends from 

Thetis Regio quadrangle (V–36) to the south and cuts through 

the trough, but it diverges around and surrounds the plateau 

and continues north, cutting unit rtGH. In western Rosmerta 

Corona, low- and moderate-radar-backscatter material fills the 

trough, locally covering parts of the fracture zone. A 50-kmwide, 200-km-long ridge occurs northwest of Rosmerta Corona. 

Three sinuous rilles occur on the northwest side of the ridge 

and are associated with minor amounts of flow material. Two of 

the rilles begin as a single conduit about 1 km wide and several 

kilometers long but branch into two <1-km-wide segments 

that are several kilometers long. A suite of northwest-trending 

fractures radiate from an area near lat 1.5° N., long 123° E. and 

extend about 400 km into unit rtGH.

Unnamed Corona a (lat 11.5° N., long 135.5° E.; approximately 150 km diameter) consists of a highly degraded, approximately 25 km wide, quasi-circular annulus that surrounds an 

interior topographic low. Moderate-radar-backscatter material 

extends radially for approximately 300 km from the annulus and 

embays a kipuka of unit lL near lat 11° N., long 138° E.

Unnamed corona b (lat 15° N., long 134.5° E.; approximately 100 km diameter) includes a 15-km-wide annulus of 

concentric fractures surrounding a 60-km-wide circular basin. 

Low-radar-backscatter material extends northeast from the topographic basin locally covering part of the annulus.

Dorsa

Dorsa define long-wavelength, linear topographic warps as 

much as thousands of kilometers long. The map area hosts three 

such features: Barbale Dorsa, Lumo Dorsa, and the northeasttrending topographic arch. Kipukas of unit lL decorate Barbale 

and Lumo Dorsa, whereas the northeast-trending topographic 

arch contains kipukas of unit rtGH, coronae fragments, and 

lineaments associated with unit lL.

Barbale Dorsa, northwest-trending dorsa in Llorona Planitia, exposes unit lL and is locally covered by unit st. Barbale 

Dorsa’s low topographic expression, which extends to the resolution of the Magellan altimetry, makes accurately determining 

the margins and dimensions of Barbale Dorsa difficult.

Northwest-trending Lumo Dorsa occurs along the northeast 

slope of Llorona Planitia, where it extends into Vellamo Planitia 

quadrangle (V–12) and Rusalka Planitia quadrangle (V–25). 

Lumo Dorsa contains a core of unit lL. Northeast-trending 

wrinkle ridges that have wavelengths of 10–25 km cut Lumo 

Dorsa, whereas wrinkle ridges that have wavelengths of 5–10 

km parallel the kipukas of unit lL. Unit fcI, sourced in adjacent 

V–25, embays Lumo Dorsa along its northeast edge. Young and 

Hansen (2003) suggested that the interaction of Lumo Dorsa 

with successive members of unit fcI records an extended progressive history of warp growth in the region.

The northeast-trending topographic arch has poorly defined 

margins but extends a total distance of approximately 2,500 km 

from about lat 9° N., long 133° E. in the map area to about lat 

34° N., long 137° E. in V–12. The arch spans approximately 

800 km and is covered by unit st and coronae-related flow 

material. As discussed above, fragments of four coronae connected by a northerly trending fracture zone occur along the 

arch. Kipukas of unit rtGH crop out as local topographic highs 

(approximately tens to hundreds of meters high) along the arch 

flanks and crest. Northwest-trending lineaments associated with 

unit lL also crop out along the arch.

Discussion

Geologic relations derived from mapping the Greenaway 

quadrangle (V–24) bear on some issues of global interest: 

ribbon-tessera terrain, coronae development, and the style and 

sources of volcanic resurfacing.

A major question in the map area is the genetic relation and 

spatial extent of ribbon-tessera terrain. Although ribbon-tessera 

terrain occurs as geographically isolated patches within the map 

area, the consistent structural trends among outcrops imply that 

all patches are remnants of the same unit, although we cannot 

robustly constrain its lateral extent. In addition, it is premature 

to state that ribbon-tessera terrain in the map area is part of a 

globally extensive unit as predicted by Basilevsky and Head 

(1998), Head and Basilevsky (1998), and Ivanov and Head 

(2001). Lineament trends within unit lL are broadly consistent 

across the map area with northwest structural trends within unit 

rtGH. The nature of this consistent trend is uncertain, but in 

some localities (near lat 22° N., long 123° E.), unit lL lineaments appear to grade into ribbon-tessera trends. In addition, 
10

the area between lats 6°–11° N. and longs 136°–142° E. exhibits 

northwest-trending lineaments associated with unit lL (but outcrop within unit st) that parallel ribbon-tessera structure trends. 

Both cases reflect a possible genetic relation between ribbontessera terrain and unit lL, which suggests that unit lL represents 

either a structural facies within ribbon-tessera terrain or local 

reactivation of buried or veiled ribbon-tessera-related structures. 

These hypotheses may be tested by future mapping; it is possible that units rtGH and lL form a continuous unit across much 

of the map area, where they are obscured by a thin veil of shield 

terrain and other flow materials.

Coronae in the map area show variability in their morphology and range of associated structures, signifying that more 

than one mechanism might be responsible for the formation 

of coronae-like features. Structure patterns and topographic 

profiles of Rosmerta and Blai Coronae and the arch corona are 

consistent with current models that attribute coronae formation 

to Rayleigh-Taylor instabilities (Tackley and Stevenson, 1991) 

or mantle diapirs (Stofan and Head, 1990; Squyres and others, 

1992; Stofan and others, 1992). Abundia and Nintu Coronae, 

however, are strikingly different from other coronae in the map 

area. Both coronae have amphitheater-like topographic profiles 

and lack obvious radial fractures, making them similar to circular lows (McDaniel and Hansen, 2005), although the possibility that the north-trending fractures located north of Abundia 

Corona may reflect locally preserved radial fractures cannot be 

excluded. The absence of obvious or at least extensive radial 

fractures may be attributed to burial by subsequently emplaced 

material and (or) the impairment of radial fracture formation 

due to a horizontal regional stress field (Withjack and Scheiner, 

1982). However, if radial fractures formed during Abundia and 

(or) Nintu Coronae formation, the fractures would be expected 

to cut Gegute Tessera, yet no such structures are observed. 

Furthermore, if radial fracture formation is impaired due to an 

imposed stress field, the resulting structure should be elongate 

rather than circular (Withjack and Scheiner, 1982). Both Abundia and Nintu Coronae form almost perfectly circular structures. 

Therefore, we suggest that the formation of these two coronae is 

difficult to accommodate within the diapiric hypothesis. Instead, 

Abundia and Nintu Coronae may have formed from different 

processes, including caldera formation (Squyres and others, 

1992; McDaniel and Hansen, 2005) or bolide impact (Schultz, 

1992, 1993; Hamilton, 1993, 2005; Stewart and others, 1993; 

Vita-Finizi and others, 2005; McDaniel and Hansen, 2005), 

where the rheology of the target material has varied over time.

Shields and coronae are the two contributors to volcanic 

resurfacing in the map area. Shields associated with shield 

terrain (unit st) are the dominant volcanic source for resurfacing >70 percent of the map area. Coronae-sourced materials 

resurface only about 5 percent of the map area. Shield-sourced 

resurfacing is distinct from resurfacing styles in the adjacent 

quadrangles (V–25, Young and Hansen, 2003; V–35, Bleamaster and Hansen, 2005; V–37, Hansen and DeShon, 2002), 

where volcanic activity is associated with coronae and chasmata evolution. Stofan and others (2005) recognized shields 

as a major contributor to volcanic resurfacing in other lowland 

regions of Venus, which, when combined with Hansen (2005) 

and this study, suggests that shield-sourced volcanism may 

play a significantly larger role in Venus resurfacing than previously recognized. Further, volcanic resurfacing in the map 

area appears to be inconsistent with the proposed catastrophic 

resurfacing event of Strom and others (1994; see Hansen, 2005, 

and Hansen and Young, 2006, for a more complete discussion). According to the catastrophic resurfacing hypothesis, 

Venus’ lowlands, including the map area, were resurfaced with 

flood-type lava flows approximately 750 Ma. The basis for 

this proposal is the paucity of impact craters on Venus’ surface 

(Strom and others, 1994). Specifically, in order to erase or 

bury pre-existing impact craters, volcanic material (Banerdt 

and others, 1997) approximately 1–3 km thick must have been 

emplaced in Venus’ lowlands at a geologically rapid (10–100 

m.y.) rate (Ivanov and Head, 1996; Basilevsky and others, 

1997; Head and Coffin, 1997; Head and Basilevsky, 1998). 

If 1- to 3-km-thick lavas were emplaced, then map relations 

should show abrupt, steep contacts between resurfacing material and pre-existing topography; the flood lavas also should 

reside unconformably on basement materials (units rtGH, lL). 

Although volcanic flow materials in the map area do appear to 

reside unconformably on basement materials (units rtGH, lL), 

they appear to be relatively thin layers (as much as hundreds 

of meters?) that maintain extremely shallow contacts with the 

basement materials. The thin nature of the volcanic materials in the map area, therefore, suggests that they could not 

have erased pre-existing impact craters, which makes it seem 

unlikely that catastrophic resurfacing occurred within the map 

area. However, the observation that the majority of impact 

craters in the map area occur on units located within the lowlands and not on the higher-standing unit rtGH suggests that 

resurfacing may have been relatively rapid, although it would 

not have been specifically voluminous. If pre-existing impact 

craters have been erased in the map area, it may have been 

through processes other than burial (Hansen, 2006).

Geologic History

Geologic unit correlation is the process of interpreting mutual time relations of local stratigraphic sections, and 

it attempts to synthesize local stratigraphic sections into a 

composite time scheme applicable to a wider region (Dunbar 

and Rogers, 1957). The surest means to correlate units involves 

one or more criteria: fossil content, isotopic data, stratigraphic 

position in relation to a widespread geologically instantaneous 

marker bed (Compton, 1985; Prothero, 1990), and significant 

and robust impact crater statistics (Hauck and others, 1998; 

Campbell, 1999). The inability to robustly ascertain any of 

these criteria on Venus makes geologic unit correlation highly 

suspect. Therefore, we developed a Sequence of Map Units 

(SOMU) for the Greenaway quadrangle (V–24), using embayment and crosscutting relations to constrain relative timing and 

allow an interpretation of a geologic history. Because of the 

widespread occurrence of many units in the map area (notably the terrains), we do not divide the SOMU into geographic 

regions.

The geologic history of the map area supports the interpretation that, as is the case on most of Venus, volcanism and 
11

tectonism are the two dominant processes that have shaped the 

map area, although determining the timing of specific events in 

the map area is nontrivial. Based on embayment and crosscutting relations, ribbon-tessera terrain (unit rtGH) and lineated 

terrain (unit lL) appear to be two of the oldest recorded units 

in the Greenaway quadrangle (V–24), where the emplacement 

history and timing of deformation of these two units is unconstrained. The temporal relation between the two units is also 

unconstrained, but, as discussed earlier, it is possible that units 

rtGH and lL are genetically related, which would infer that these 

two units are closely related in time. The occurrence of unit 

ibGH in intratessera basins implies that unit ibGH cannot be 

older than ribbon-tessera terrain formation. In turn, the absence 

of tessera-related structures that cut unit ibGH suggests that the 

emplacement of unit rtGH material continued after the formation of unit ibGH. Because unit ibGH is only in contact with 

unit rtGH, the temporal relation of unit ibGH to other map 

units is unconstrained. Where units st and fu are in contact with 

ribbon-tessera terrain and lineated terrain, they are stratigraphically younger than units rtGH and lL. Thus, units st and fu at 

any one location postdate the formation of units rtGH and (or) 

lL at that same location. However, given the uncertainty of the 

extent of units rtGH and lL in the subsurface across the map 

area, we cannot robustly state (or deny) that all of units st and 

fu postdate the formation of all of units rtGH and lL. In addition, units st and fu appear to have time-transgressive relations 

with the other map units. Warping of the Gegute Tessera inlier 

postdated unit rtGH and unit lL formation, but timing cannot be 

further constrained because there is no evidence that any other 

map units were concurrently warped. Scattered outcrops of 

units rtGH and lL along the topographic arch indicate that they 

predate arch formation, suggesting that the uplift of the arch 

is responsible for local preservation of the two terrain units. 

The topographic arch and the arch-related coronae (including 

the anastomosing fracture zone linking the coronae) probably 

formed synchronously. To suggest differently would require 

an explanation for the parallelism of the arch and coronae 

along the arch crest. Initiation of arch coronae volcanism is 

unconstrained, however. Some coronae flow material extends 

down the arch flanks, indicating that coronae-related volcanism 

occurred, at least locally, after arch formation.

Because material flow units are not in contact with each 

other, their temporal relations cannot be constrained. However, 

their interactions with units rtGH and lL and (or) topography 

do provide some time constraints. The parallelism of units fcA, 

fcR, and fcS with the trend of the western basin implies that 

these three flow units postdate formation of the topographic 

arch and, therefore, units rtGH and lL, which is an interpretation 

that is consistent with unit fcS embayment of units rtGH and 

lL and unit fcR embayment of unit rtGH. Because unit rtGH

is similarly embayed by unit fcB, Blai Corona flow material is 

likely younger than ribbon-tessera terrain, although the possibility that Rosmerta and Blai Coronae occurred (and initially 

emplaced flow material) synchronously with ribbon-tessera 

terrain formation cannot be excluded. Embayment relations also 

indicate that unit fcI is younger than unit lL. The timing of unit 

fC cannot be robustly constrained based on direct observations 

of the surface geology but, instead, requires inferences regarding the subsurface geology. For example, if unit rtGH and (or) 

unit lL extend in the subsurface to the southeast corner of the 

map area, then unit fC must be younger than one or both of 

these terrain units. However, if neither terrain unit exists in the 

subsurface in the southeast corner, then the timing of unit fC is 

unconstrained and it may be younger than, concurrent with, or 

older than units rtGH and (or) lL.

Formation of the fracture zone in the southeastern map 

area appears to have occurred time transgressively with unit st. 

However, because the fracture zone cuts unit rtGH near lat 1° 

N., long 139° E., it must locally postdate unit rtGH.

Wrinkle ridges and impact craters are some of the youngest features within the map area. This interpretation is based 

on the observations that wrinkle ridges deform, and most 

impact craters occur on, units in the lowlands; the impact crater 

Wilder is embayed by shield-related deposits, suggesting that 

Wilder is locally younger than unit st. However, initiation of 

wrinkle-ridge formation is difficult to constrain. The initial age 

of imposition of a wrinkle-ridge fabric may predate its current geomorphic expression, implying that there is ideally no 

stratigraphic constraint on wrinkle-ridge timing; material units 

can only be said to predate the very last phase of wrinkle-ridge 

formation. Further, the observation that, with the exception of 

unnamed crater b, impact craters are not deformed suggests that 

impact craters in this map area are younger than wrinkle ridges. 

This observation also suggests that relatively little tectonism has 

occurred in the map area since impact-crater formation.

The Greenaway quadrangle (V–24) records a rich geologic history for parts of Venus’ lowland and highland regions. 

The geologic history is constrained by observed contact and 

structural interactions, which resulted in the construction of a 

Sequence of Map Units consistent with the 1:5,000,000 scale of 

mapping. Mapping at a larger scale that shows a higher degree 

of detail may lead to the discovery of new relations inconsistent 

with our mapping. Map users are encouraged to analyze regions 

of interest with specific questions in mind.

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15

Table 1. Crater data for the Greenaway quadrangle (V–24), Venus.

Crater name

Unit

label

Center

latitude

(deg N.)

Center

longitude

(deg E.)

Diameter

(km) Floor1 Halo2 Deformation3

Afua st, ItL 15.5 124 0.011 LBS N N

Aimee fcA 16.1 127.2 16.8 LBS N N

Ban Zhao fu, rtGH, ItL 17.2 146.9 38.3 HBS Y N

Bourke-White fu 21.1 147.9 34.4 LBS N N

Budevska st 0.5 143.2 18.7 HBS Y N

Callirhoe st 21.2 140.7 32.9 LBS IND N

Escoda fu, fcI 18.2 149.5 19.5 HBS IND N

Greenaway fu 22.9 145.1 92.3 HBS IND N

Himiko fu 19 124.3 36.7 HBS Y N

Hwangcini st 6.3 141.7 30.8 LBS Y N

Jutta st 0.0 142.6 7.0 LBS N N

Maria Celeste st 23.4 140.4 96.6 LBS IND N

Neeltje st 12.4 124.5 10.3 IND N N

Němcová fcR 5.9 125.1 21.4 LBS N N

Ogulbek st 2.4 145.1 6.6 LBS N N

Olena fu 10.9 149 0.007 LBS Y N

Phyllis st 12.2 132.4 10.6 LBS Y N

Tinyl st 9.7 132.1 11.7 LBS N N

Vigée-Lebrun st, ltL 17.3 141.4 57.6 LBS IND N

Wilder rtGH, st 17.4 122.6 35.3 LBS N N

Unnamed crater a st 8.0 148 <1 IND N N

Unnamed crater b st 2.1 148.1 <1 LBS N Y

Unnamed crater c st 11.9 132.4 <1 IND N N

1

Indicates the radar characteristic of the floor: HBS, high backscatter

2

Indicates whether halo is evident: N, no; Y, yes; IND, indeterminate

3

Indicates whether ejecta, rim, or outflow are cut by later tectonic structures: N, no; Y, yes