2011

U.S. Department of the Interior

U.S. Geological Survey

Prepared for the National Aeronautics and Space Administration

Geologic Map of the Metis Mons Quadrangle (V–6), Venus

By James M. Dohm, Kenneth L. Tanaka, and James A. Skinner

Pamphlet to accompany

Scientific Investigations Map 3158

75°

50°

25°

75°

25°

–25°

0°

50°

0°

180° 210° 240° 270° 300° 330° 360°

–25°

–50° –50°

–75° –75°

V–1

V–29 V–30 V–28

V–40

V–62

V–41

V–27

V–26

V–15

V–14

V–16

V–39 V–42

V–18

V–51 V–54

V–17

V–52 V–53

V–60

V–6

V–5

V–19

V–50 V–55

V–31

V–38 V–43

V–7

V–59 V–61

i

Contents

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

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

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

Physiographic Setting ..................................................................................................................................2

Data and Methodology .................................................................................................................................2

Stratigraphy ...................................................................................................................................................3

Tessera Material ..................................................................................................................................3

Corona Material ...................................................................................................................................3

Plains Material .....................................................................................................................................4

Mons Material ......................................................................................................................................5

Impact Crater Material .......................................................................................................................6

Tectonic Structures ......................................................................................................................................6

Surficial Features ..........................................................................................................................................7

Geologic History ............................................................................................................................................8

Tessera Stage .......................................................................................................................................8

Corona Stage ........................................................................................................................................8

Plains Stage ..........................................................................................................................................9

Mons Stage ...........................................................................................................................................9

Summary .........................................................................................................................................................9

Acknowledgments ......................................................................................................................................10

References Cited .........................................................................................................................................10

Tables

1. Location and description of coronae and corona-like features of the Metis Mons 

quadrangle (V–6), Venus. ...........................................................................................................13

2. Location and description of large volcanos of the Metis Mons quadrangle (V–6), Venus. ......13

3. Location and description of impact craters (21) of the Metis Mons quadrangle (V–6), 

Venus. ............................................................................................................................................14

4. Elevation, emissivity, reflectivity, and rms-slope data of map units in the Metis Mons 

quadrangle (V–6), Venus. ...........................................................................................................15

5. Description of geologic map units of the Metis Mons quadrangle (V–6), Venus, including 

relative-age relations with adjoining map units. ....................................................................16

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 Metis Mons quadrangle (V–6) in the northern hemisphere of Venus (lat 50° to 75° N., long 240° to 300° E.; figs. 

1A and 1B) includes a variety of coronae, large volcanoes, ridge 

and fracture (structure) belts, tesserae, impact craters, and other 

volcanic and structural features distributed within a plains setting, affording study of their detailed age relations and evolutionary development. Coronae in particular have magmatic, 

tectonic, and topographic signatures that indicate complex evolutionary histories (Barsukov and others, 1986; Basilevsky and 

others, 1986; Stofan and Head, 1990; Head and others, 1992; 

Janes and others, 1992; Sandwell and Schubert, 1992; Squyres 

and others, 1992; Stofan and others, 1992; Smrekar and Stofan, 

1997; Chapman and Zimbelman, 1998).

Previously, the geology of the map region has been 

described either in general or narrowly focused investigations. 

Based on Venera radar mapping, a 1:15,000,000-scale geologic 

map of part of the northern hemisphere of Venus (Sukhanov and 

others, 1989) included the V–6 map region and identified larger 

features such as tesserae, smooth and hummocky plains materials, ridge belts, coronae, volcanoes, and impact craters but 

proposed little relative-age information. Global-scale mapping 

from Magellan data (Price and Suppe, 1994; Price and others, 

1996) identified similar features and also determined their mean 

global ages with crater counts. However, the density of craters 

on Venus is too low for meaningful relative-age determinations 

at local to regional scales (Campbell, 1999). Several of the 

coronae in the map area have been described using Venera data 

(Stofan and Head, 1990), while Crumpler and others (1992) 

compiled detailed identification and description of volcanic and 

tectonic features from Magellan data.

The main purpose of this map is to reconstruct the geologic history of the Metis Mons quadrangle at a level of detail 

commensurate with a scale of 1:5,000,000 using Magellan data. 

We interpret four partly overlapping stages of geologic activity, 
2

which collectively resulted in the formation of tesserae, coronae 

(oriented along structure belts), plains materials of varying ages, 

and four large volcanic constructs. Scattered impact craters, 

small shields and pancake-shaped domes, and isolated flows 

superpose the tectonically deformed materials and appear to be 

the most youthful materials in the map region.

Physiographic Setting

The Metis Mons quadrangle (V–6) is in the northern hemisphere of Venus and extends from lat 50° to 75° N. and from 

long 240° to 300° E. (fig. 1A). The quadrangle includes a backdrop of volcanic plains, mostly in the south half of the quadrangle (Kawelu, Libuše, and Guinevere Planitiae), whose mean 

elevation is within a few hundred meters of the mean planetary 

radius of 6,051.84 km (Ford and Pettengill, 1992) (fig. 2). Topographic highs are collectively produced by eight named ovoid 

tectonic centers known as coronae (from north to south: Bachue, 

Feronia, Otau, Azham, Coatlicue, Rananeida, Demeter, and Bau 

Coronae); two unnamed coronae features (one in the western 

plains and one forming an oblong ring in Mokosha Mons); four 

named broad volcanic shields (Metis, Bagbartu, Mokosha, and 

Atira Montes); one unnamed feature in east-central plains; and 

ridge and fracture belts (Ben, Okipeta, Varma-Ava, ChrykhKeyok, Hemera, and Iyele Dorsa). These topographic highs 

range from hundreds of meters to >2.5 km in relief (tables 1 and 

2; Stofan and Head, 1990) and extend >3.5 m above the mean 

planetary radius. Ridge and fracture belts generally define coronae boundaries, as well as systems of mostly aligned fractures 

(Ilbis and Minerva Fossae and Lampedo Linea), that extend 

for hundreds of kilometers. Outcrops of tessera material rise 

hundreds of meters above the low-lying plains in the northeast 

and southeast corners (Atropos and Senectus Tesserae, respectively) and along the west margin (Virilis Tesserae) of the map 

region. Small shield volcanoes, steep-sided domes (including 

Ale, Upunusa, and Nerthus Tholi), pitted cones, isolated lava 

flows, channel-form features (including Utrenitsa Vallis), and 21 

impact craters (table 3) occur throughout the map area.

Data and Methodology

The Magellan mission to Venus acquired SAR backscatter, emissivity, reflectance, and topographic data for most of 

the planet. Image mosaics of radar backscatter (fig. 1A) were 

the primary data set used to delineate the boundaries of discrete 

geologic units and characterize their appearance, morphology, and distribution. Topographic data, rms slope, microwave 

emissivity, and corrected reflectivity data (figs. 2–5) provided 

insight into various physical properties of the surface. However, because the resolution of these datasets is relatively low 

(compared to the SAR base map) and the information conveyed 

therein is commonly influenced by surficial materials (rather 

than the regional geologic units), we used these data sets to help 

support more regional observations based on radar backscatter. 

We include basic radar statistics of the physical properties for 

each geologic unit (table 4). Derivations for radar backscatter 

(as outlined by Campbell, 1995) were not used to delineate the 

boundaries or contact relations of geologic units and are not 

included in table 4.

The discrete geologic units of the Metis Mons region 

were initially identified using photographic prints of ten fullresolution (75 m/pixel) Magellan SAR mosaics (F-MAPs) at 

1:1,500,000 scale produced by the U.S. Geological Survey. 

Geologic contacts were hand-drawn on mylar overlays and 

then scanned, reprojected, vectorized, and merged within a 

geographic information system (GIS). All structure and surface 

features were digitally streamed into a dedicated GIS project 

using the digital Magellan backscatter base map. The spatial and 

interpretational accuracy of all scanned linework was iteratively 

quality checked and refined to produce an internally consistent 

1:5,000,000-scale geologic map. The combined use of handand digital-mapping techniques resulted in increased spatial 

detail and accuracy of geologic information, as well as unit 

statistics (table 4) and area calculations (table 5). For clarity, all 

digitized unit outcrops that were <150 km2 were individually 

analyzed and merged with adjacent units.

The remote, radar-based identification and interpretation 

of geologic materials, structures, and temporal relations for 

the production of a geologic map require a careful approach to 

avoid overinterpretation and maintain objectivity (for example, 

Wilhelms, 1972, 1990; Tanaka, 1994; Hansen, 2000). We 

delineated geologic units by coupling variation in the intensity 

of radar backscatter intensity with crosscutting relations among 

geologic units and surface features. However, some outcrops 

have insufficiently distinct stratigraphic, geomorphic, radarbackscatter, and (in some cases) tectonic character to merit a 

clear unit assignment. In these cases, we represent the unit and 

its boundary using the best lines of geologic and stratigraphic 

reasoning observed and appropriately convey the uncertainty in 

both the unit descriptions and map text.

Though radar data permit effective mapping of surface 

morphologies and structures (Daily and others, 1978; Ford and 

others, 1989, 1993; Sabins, 1997), geologic unit boundaries 

are often difficult to trace in comparison with those expressed 

by remote data sets typically available for rock surfaces on 

Earth and Mars. This is due to a limited radar-based perspective for Venus (with few look directions) versus a perspective 

gained through a greater diversity of data sets used in the remote 

geologic mapping of Earth and Mars (for example, visible and 

multi-spectral images, topography), which add greater perspective and thus greater confidence in differentiating rock material 

types, ages, and other fundamental characteristics and associations. In addition, even with distinctive features (for example, 

topographic promontories that are embayed by lava flows), there 

are wide-ranging confidence levels regarding where the position 

of the contact should be placed for parts of the outcrop margins. 

A particular challenge in radar-based geologic mapping is in the 

level of confidence attributed to identifying discrete volcanic 

flow units that are likely to consist of a range of surface roughnesses, which appear as grades of radar backscatter. Although 

stratigraphic clues such as structures may be helpful in delineating major stages in the emplacement of volcanic flows, they may 

be scattered and provide considerable local uncertainty in contact 
3

placement. Because of these uncertainties, we use two different 

contact types. A certain contact is used where the unit margin is 

clearly demarcated. An approximate contact is used where the 

unit margin is unknown, gradational, or otherwise complex; in 

these instances, the contact may be drawn based on inferences 

made from the type and trend of local tectonic structures.

We attempted to determine ages of map units based on 

their emplacement relative to adjacent units (see table 5 and 

Correlation of Map Units). Thus, we avoid to the extent possible 

defining map units and basing unit ages on secondary structures 

that tend to obscure the origin and material age of the units (see 

Hansen, 2000). We recognize that the termination of tectonic 

structures and surface features likely represents either the actual 

extent of surface deformation or the margin of an onlapping unit 

where the structures are buried (Hansen, 2000). However, we 

are not able to wholly disregard the occurrence and continuity 

of tectonic structures and other surface features when defining 

geologic units and interpreting the geologic history. Some of the 

geologic units that we identify herein are delineated by the density and relative ages of structures that deform them. In some 

cases, burial by a younger unit is evidenced where multiple sets 

of structures disappear along a common boundary.

We have identified a total of 27 geologic units in the Metis 

Mons map region based on morphologic characteristics, geologic 

associations, and stratigraphic relations. These units can be subdivided into five major material groups: mons material, plains 

material, corona material, tessera material, and crater material. 

Because of the uncertainty in relative age among widely spaced 

outcrops of each unit, the upper and lower extents of the unit 

boxes are jagged in the Correlation of Map Units to depict those 

uncertainties. According to the format generally followed in 

planetary geologic maps (Tanaka, 1994), we arrange our groups 

and units in the Correlation of Map Units from youngest to 

oldest (left to right) and show crater materials at the far right.

Although many of the V–6 map units and structures are 

similar to those mapped in other Venus 1:5,000,000-scale quadrangles, we find that stratigraphic relations shown in table 5 are 

complex and only locally applicable. We therefore do not infer 

that our geologic reconstruction has relative-age significance 

and correlations with similar-appearing units and structures 

on regional to global scales as proposed by some (Grosfils and 

Head, 1994; Basilevsky and Head, 1995, 2000a; Ivanov and 

Head, 2001), and we acknowledge that more complex regional 

and global histories are possible (Guest and Stofan, 1999). The 

stratigraphy and locations of geologic contacts mapped in V–6 

agree in some respects with those of the adjoining Pandrosos 

Dorsa (V–5) quadrangle (Rosenberg and McGill, 2001). This is 

most evident with tessera material, except where the V–5 map 

indicates “densely lineated terrain”. Our map differs moderately in the delineation and subdivision of plains materials due 

primarily to a differing approach to identifying map units.

Stratigraphy

In the following sections, we describe the map units generally from oldest to youngest and by unit groupings.

Tessera Material

Tessera material (unit t) is the oldest unit in the region, as 

documented elsewhere on Venus (Basilevsky and Head, 1995, 

2000a; Tanaka and others, 1997; Ivanov and Head, 2001). However, tessera material outcrops are likely to consist of mixtures 

of materials and structures of varying ages and origins (Ivanov 

and Head, 1996; Gilmore and others, 1997, 1998; Hansen 

and others, 1997, 2000), including those resulting from large 

impacts into ancient, thin lithosphere (Hansen, 2006; Hansen 

and Young, 2007). Virilis and Atropos Tesserae occur in the 

southwestern and northeastern parts of the quadrangle, respectively, and are composed almost entirely of tessera material. 

Smaller and more discontinuous outcrops of tessera material 

occur in western Kawelu Planitia and eastern Libuše Planitia. 

Tessera material is defined by a high-backscatter surface and a 

minimum of two intersecting sets of tectonic structures, including lineaments and wrinkle ridges (Hansen and Willis, 1996, 

1998). Tessera material within the map region commonly occurs 

as plateaus that are tens to hundreds of kilometers wide and 

that extend as much as 1 km above the surrounding plains (fig. 

2). Structurally controlled depressions commonly appear to be 

occupied by plains-type materials of comparatively low backscatter (for example, lat 65.96° N., long –118.76° E.). The density and complex pattern of structures that characterizes tessera 

material within the map region imply that the unit resulted from 

multiple stages of deformation that obscure features associated 

with its primary emplacement. Tessera material is likely to form 

the basal geologic unit upon which all other geologic materials 

have been emplaced. Due to the structural complexity of tessera 

material and its defining nature to that unit, symbols depicted 

within the boundaries of the unit are intended to convey only 

the local type and trend of tectonic structures.

Corona Material

Following (and perhaps concurrent with) tessera formation, 

concentrated magmatic activity produced ten coronae (table 1) 

in the map region, partly made up of ten intensely or moderately deformed corona units: Otau Corona material (unit cO), 

Demeter Corona material (unit cD), Coatlicue Corona material 

(unit cC), older and younger Feronia Corona material (units cF1

and cF2, respectively), Rananeida Corona material (unit cR), 

Bau Corona material (unit cBu), Bachue Corona material (unit 

cBa), and older and younger Azham Corona (units cA1 and 

cA2, respectively). Coronae materials were mapped individually 

because they have spatially and geologically distinctive tectonic 

and magmatic histories (see Stofan and Head, 1990; Stofan and 

others 1992, 1997). Coronae materials generally make up the 

interiors and annuli of the coronae and adjacent plains made up 

of flows radiating outward from the annuli. In some cases, the 

coronae materials merge with plains units along approximate 

contacts. For the unnamed corona at lat 61° N., long 245° E., we 

identify part of its annulus as a topographic warp and part as unit 

p2. It also has an interior depression that connects with a broad 

trough that extends northwest. However, we do not map a corona 

unit, because it appears largely indistinct with unit p3 materials.
4

Timing relations among the coronae are largely uncertain. Only Feronia and Azham Coronae show distinct evidence 

for two stages of corona-related deformation; each corona is 

defined by two units of distinctly contrasting backscatter and 

structural characteristics. Feronia Corona contains material near 

its center that generally has low backscatter and few mappable 

lineaments relative to surrounding material. This material is 

mapped as younger Feronia Corona material (unit cF2) and is 

interpreted to represent relatively less deformed, late-stage lava 

flows sourced from within Feronia Corona. Similarly, Azham 

Corona contains materials near its center and along its southern 

margin that generally have moderate backscatter and contrasting structural lineaments relative to its northern margin. This 

material is mapped as younger Azham Corona material (unit 

cA2) and is interpreted to represent late-stage tectonism during 

corona growth.

Throughout the quadrangle, corona materials display high 

variability in their degrees of modificational states, generally 

ranging from Feronia Corona that displays a distinct, radarbright annulus to Demeter Corona that displays an annulus 

subdued by inundation of lava plains, as indicated by the older 

parts that crop out through the plains. We identify a tectonic 

annulus 139 x 255 km across within Mokosha Mons as a 

corona-like feature made up of deformed plains units. The 

annulus rises as much as 300 m above the interior and may be 

the result of corona-like sagging due to loss of dynamic support 

(Herrick and others, 2005). Co-evolution of volcanic shield 

growth and corona-like activity is indicated by their temporal 

overlap, which has been documented for Atai Mons on Venus 

(Grindrod and others, 2006).

Plains Material

Plains materials (plains units p1, p2, p3, and p4) are 

interpreted to be lava plains and are divided according to four 

inferred stages of plains emplacement. The older units show 

significantly more deformation, as evidenced by their high 

backscatter and density of mappable structures, and have 

generally lost much of their planar character. The oldest of the 

plains materials, unit p1, displays complex structure, including 

numerous wrinkle ridges and lineaments that are partly aligned 

with regional ridge and fracture belts and topographic warps. 

Unit p1 is gradational and perhaps coeval with some older 

coronae materials, as well as some outcrops of tessera material, 

as evidenced by its high backscatter and structural complexity. For example, unit p1 occurs as scattered, highly deformed 

outcrops west and south of Senectus Tessera in the southeastern 

part of the map. Unit p2, however, appears to overlie unit p1, 

infills low areas of Virilis Tessera, and is both similar in age to 

and younger than various adjacent corona material units (table 

5). Material that has backscatter and structural characteristics of 

unit p2 is in contact with unit t in Senectus Tessera. Structural 

features within unit p2 likely record tectonic events associated 

with most of the same local and regional magmatic centers of 

activity that contributed to the deformation of unit p1, but of 

generally lesser intensity and (or) longevity. Elongated patches 

of both units p1 and p2 have been deformed into ridge and fracture belts that are as much as 400 km long and several to tens of 

kilometers wide.

Subsequent to the emplacement and deformation of the 

older plains materials (units p1 and p2), widespread effusive 

volcanism erupted lavas that buried much of the older plains in 

the map region, resulting in unit p3. This unit generally postdates units p1 and p2 and corona materials (see table 5) and is 

interpreted to have resulted from plains volcanism. However, 

the chief differentiating characteristics are significantly less 

associated wrinkle ridges and structural lineaments, which we 

interpret as having resulted from comparatively diminished tectonic activity. Sources for the eruption may be corona margins 

and (or) ancestral mons edifices located along ridge and fracture 

belts. Utrenitsa Vallis forms a system of sinuous, narrow (<1 to 

3 km wide), singular or multiple channel forms within unit p3

that extend hundreds of kilometers from near Montessori crater 

southward onto Guinevere Planitia and across topographic 

plains of very low relief, including between discontinuous 

ridge-forming outcrops of unit p1. Locally, the channel system 

splays into braided reaches of multiple narrow channels, such 

as where it crosses the west terminus of Charykh-Keyok Dorsa. 

Overall, the channel fits the canali-type classification of Komatsu and others (1993); various modes of canali origin involving 

constructional and erosional processes and perhaps exotic lava 

compositions have been proposed (see Baker and others, 1997).

Emplacement of voluminous flood lavas from local sources 

such as fissures and central vents, which generally postdate the 

emplacement of unit p3, resulted in small to moderately extensive outcrops in the low-lying regional plains, adjacent to some 

of the coronae and shield volcanoes, and within the floors of 

some of the larger impact craters. These materials mostly have 

variable backscatter, local structures, and small shields and are 

mapped as unit p4. In places, unit p4 is marked by narrow linear 

to anastomosing or intersecting networks of lineaments, narrow 

linear to anastomosing wrinkle ridges in parallel lines or intersecting networks, and volcanic edifices generally less than 5 

km in diameter. Part of a large outcrop of unit p4 east and south 

of Montessori crater may consist of microdunes superposed 

on units p3 and p4 (see next section and fig. 6). In addition, an 

outcrop of unit p4 north of Atira Mons appears to be a landslide 

deposit originating from an east-facing amphitheater within an 

adjacent, steep-sided dome (mapped as unit pd). An unnamed 

channel-form feature occurs in unit p4 north-northwest of Atira 

Mons. The channel form is 80 km long, trends east-west, and is 

<2 km wide for most of its length. The channel form is defined 

by a set of moderate backscatter surfaces that parallel a lowbackscatter interior, suggesting a levee-bounded flow. Crosscutting relations with wrinkle ridges indicate that the channel-form 

feature predates and postdates local contractional ridge formation.

Plains dome material (unit pd) consists of five gently sloping to steep-sided edifices that protrude through or are emplaced 

onto adjacent plains and flow materials. The unit has an apparent stratigraphic position that correlates with the emplacement 

of units p3 and p4. The domes include circular, pancake-shaped 

features to irregular hills with scalloped margins that likely 

resulted from flank collapse (Guest and others, 1992). The 

domes may represent relatively viscous volcanism (McKenzie 
5

and others, 1992) or growth of a lava dome beneath a solidified 

basaltic lava crust (Stofan and others, 2000).

Mons Material

Mons materials are predominantly defined by overlapping 

lobate margins and digitate terminations that are interpreted 

to be spatially and stratigraphically complex suites of lava 

flows sourced from multiple locations, including mons summit 

calderas and fractures. Volcanic eruptions that were generally 

centered along the axes and (or) intersections of major ridge and 

fracture belts and topographic warps resulted in the emplacement of complexly overlapping flows associated with the construction of large shield volcanoes known as Atira, Mokosha, 

Metis, and Bagbartu Montes (see table 2 for their dimensions). 

Their shield-forming lavas are grouped as mons materials. Each 

edifice consists of an older and younger unit that is separated 

by a time-transgressive contact. This inference is based on the 

occurrence of low-backscatter material generally located within 

the center of the mons edifices. Crosscutting relations between 

mons materials and surrounding plains show that the younger 

mons materials correlate with the youngest plains materials. 

These units generally abut and surround subtle topographic rises 

and ridge belts composed of older plains material (units p1 and 

p2), as well as adjacent corona materials.

Older Atira Mons material (unit mA1) forms the bulk 

of the Atira Mons shield and includes flank flows that bury 

adjacent plains units p3 and p4, as well as linear and irregularly 

shaped outcrops of units p2 and p1. Well-defined lobes of unit 

mA1 are apparent on the north and south flanks of Atira Mons 

and possibly reflect some of the later stages of volcanic eruption 

during the emplacement of the unit. The marginal flows abut 

and flow around topographic warps and collections of wrinkle 

ridges. The shallow summit caldera (~110 km in diameter) is 

higher on the west side and is filled with younger Atira Mons 

material (unit mA2) that contains wrinkle ridges and several 

volcanic edifices of varying diameter. The summit caldera is 

broadly defined by a topographic warp. Compared to other 

mons features in the quadrangle, Atira Mons is the most symmetrical and has no distinct lineaments and few small volcanic 

edifices that might have served as source regions for the lavas of 

unit mA1; such features might be buried. In addition, the flanks 

of Atira Mons are deformed by wrinkle ridges that generally 

parallel the orientation of those that occur in the surrounding, low-lying plains. This suggests that the latest growth of 

Atira Mons predates the contractional tectonism that deformed 

regional mons and plains materials.

Older Mokosha Mons material (unit mMo1) consists of 

radiating flank and plains flows sourced from fractures and 

volcanic vent edifices within and peripheral to Mokosha Mons. 

Unit mMo1 extends from the Mokosha Mons edifice to the 

northwest, where it abuts and flows around ridge and fracture 

belts comprised of unit p1. Marginal flows extend across unit 

p3 to the north, west, and south and unit p4 to the east. The 

orientation of lobe margins mapped within unit mMo1 implicates two possible regional vents for the unit. The main vent 

is likely the Mokosha Mons summit caldera, which is defined 

by a corona-like, deformed annulus ridge (made up of units p1

and p2). This annulus contains younger Mokosha Mons material (unit mMo2), which is marked by multiple, small volcanic 

edifices. A secondary vent, also comprised of multiple volcanic 

edifices and fractures, is located on a moderate topographic rise 

to the northwest of the main Mokosha edifice (fig. 2). A younger 

mons material unit is not identifiable within or proximal to the 

secondary vent area.

Metis Mons forms the broadest and tallest volcano in the 

map region (table 2). Older Metis Mons material (unit mMe1) 

generally lacks clear flow fronts and is exposed as patchy outcrops at the upper flanks and near the summit region of Metis 

Mons. Unit mMe1 has moderate backscatter, likely due to the 

presence of lineaments. Though unit mMe1 is interpreted to 

form the bulk of the shield, it is largely buried by the younger 

Metis Mons material (unit mMe2), which consists of welldefined lobate flows with variable backscatter surfaces. The 

flows that compose unit mMe2 radiate from Ilbis Fossae and 

extend in all directions, where they abut high-standing materials or terminate as digitate lobes in the plains. To the north, 

unit mMe2 abuts and flows around the older and more heavily deformed Bachue Corona material (unit cBa). To the west, 

south, and east, unit mMe2 abuts and flows around ridge-forming outcrops of units p1 and p2 and extends onto and buries 

low-standing occurrences of units p3 and p4. Unit mMe2 is 

dissected by Ilbis Fossae, a major northwest-southeast-trending 

set of fractures. Numerous small volcanic shields along this axis 

likely formed in conjunction with the emplacement of the surrounding flow units.

Bagbartu Mons forms a major topographic high between 

Feronia and Coatlicue Coronae. Older Bagbartu Mons material 

(unit mB1) is characterized by overlapping high- and low-backscatter lobes that are generally oriented radial to both a system 

of fractures on Feronia’s southern rim and a summit caldera at 

the center of Bagbartu Mons. The unit extends to the east and 

west from the summit caldera for almost 600 km in each direction. Unit mB1 abuts and flows around older plains and corona 

materials on the north and south flank. Backscatter markedly 

decreases at the base of the edifice where the unit extends across 

unit p4 and is deformed by wrinkle ridges. Additionally, unit 

mB1 appears to embay the west and north margins of Indira 

crater. Younger Bagbartu Mons material (unit mB2) forms a 

field of relatively low backscatter plains within the summit 

caldera of Bagbartu Mons. Therein, the unit contains multiple 

small volcanic edifices and several structural lineaments, where 

it perhaps reflects late-stage growth of Bagbartu Mons. Summit 

lineaments may represent newly formed structures or the reactivation of ancient structures possibly predating the volcano’s 

development and associated with a structure belt that may have 

linked Feronia and Coatlicue Coronae. Tectonism may have 

been related to the formation of the Bagbartu Mons summit 

caldera through evacuation of an underlying magma chamber.

In addition, we have mapped undifferentiated mons material (unit mu) in several locations throughout the quadrangle 

where the material consists of lobate margins but is not strictly 

associated with any major mons-forming edifice. The largest 

outcrop of this material defines the extent of a small unnamed 

mons located south of Bagbartu Mons and east of Coatlicue 
6

Corona (lat 61.7° N., long 280.3° E.). This outcrop, which is 

on an east-west-trending topographic rise, has multiple small 

volcanic edifices and well-defined flow lobes that extend to the 

north onto unit p4 and either abuts or grades into older Bagbartu 

Mons material (unit mB1). To the south, unit mu extends over 

and perhaps grades with unit p4, where it is deformed by a few 

fractures. Other isolated outcrops of unit mu include (1) northerly flows within unit p4 north of (and perhaps sourced from) 

radial fractures of Feronia Corona, (2) westerly flows within 

unit p3 west of Azham Corona, (3) northerly flows within unit 

p4 north of Atira Mons, and (4) westerly flows within unit p3

southeast of Otau Corona.

On Venus, large volcanoes may develop over sustained 

sites of mantle upwelling, facilitated by the absence of plate 

tectonics (McGovern and Solomon, 1998). According to McGill 

(1998, 2000), some shield volcanoes may evolve into coronae 

due to thinning of the lithosphere. In the V–6 quadrangle, we 

observe that Mokosha Mons includes coronae-like, extensional tectonic structures encircling the volcano’s summit and 

embayed by shield lavas. Also, Metis Mons buries the southern 

part of the highly deformed structural ring of Bachue Corona; 

local fracturing of Ilbis Fossae indicates some minor, late-stage, 

corona-related deformation of the shield. Magmatic activity 

appears to have resulted in concentrated deformation, including 

possible reactivation of the pre-existing structural fabric at all 

four shield volcanoes, similar to the summit region of Bagbartu 

Mons. Thus large shields in the map region chiefly postdate the 

development of underlying and adjacent coronae. However, we 

recognize that key temporal relations between earlier development of the coronae and shields may be completely obscured.

Impact Crater Material

Among the youngest materials within the map region is 

crater material (unit c). The larger craters all appear to overlie surrounding units, except for Katya and Tolgonay craters 

that may be embayed by plains units p3 and p4, respectively. 

Crosscutting of crater materials by structures is generally difficult to determine using the Magellan radar backscatter data; 

four craters have ejecta that appear fractured, and two of those 

seem to have fractured rims. Crater material possesses distinctive hummocky textures, some of the highest backscatter of 

any map units in the map area, complex rims, and low- and 

high-backscatter haloes (see table 3 and next section) owing, 

in part, to cratering operating within the tremendously thick 

atmosphere (nearly 100 times that of Earth) and extreme surface 

temperatures of Venus (~750 K) (Campbell and others, 1992; 

Herrick and others, 1997; McKinnon and others, 1997). We 

recognize a possible deformed crater at lat 55.6° N., long 243.5° 

E. mapped as tessera material, which consists of radar-bright 

ridges and a subtle, central depression; however, it could also 

be a deformed volcanic vent. Some crater floors have high 

backscatter and appear to be relatively pristine, but others have 

low backscatter and may be flooded by younger lavas or impact 

melt and (or) are blanketed by aeolian deposits. Though the 

latter contain morphologies and backscatters most similar to 

unit p4, stratigraphic associations that clearly differentiate unit 

p4 from unit p3 on the floors of craters are lacking. As a result, 

these localized plains-unit designations should be treated with 

appropriate uncertainty. Twelve craters <15 km in diameter 

were not mapped as unit outcrops but rather designated with 

map symbols. Craters >15 km in diameter, which typically 

occur as segmented and (or) embedded circular scarps, are identified with crater rim symbols. Though the west-facing, inner 

rim walls mostly appear steeper than other wall sections, this 

observation may result from the east-looking Magellan SAR 

observations for the map region. Altogether, 22 impact craters 

have been identified in V–6 (table 3).

Crater flow material (unit cf) commonly emanates from 

impact craters and displays mostly high-backscatter, coarse 

texture, and lobate margins. Crater flows have a range of morphologic expressions, generally grade into crater rim and ejecta 

materials, and are interpreted to be chiefly composed of ejected 

impact melt.

Tectonic Structures

Magellan-based oblique radar illumination produces 

strong signal returns and peaks that highlight relative topographic highs (ridge and fracture belts, wrinkle ridges, and flow 

margins) and lows (channel forms, depressions), depending on 

shape, size (vs. radar resolution), roughness, and orientation 

with respect to radar illumination direction and wavelength 

(Tanaka and others, 2010). Structural features of inferred tectonic origin mapped in V–6 include wrinkle ridges, lineaments 

(generally interpreted as narrow graben or fractures), ridge and 

fracture belts (generally >15 km wide), and major topographic 

warps. Because these features are much too dense to map 

completely at 1:5,000,000, only representative structures are 

mapped to portray their general spatial distributions and orientations. Areas of very high backscatter mostly reflect high structural density, which obscures the original backscatter character 

of many map surfaces (for example, tessera outcrops).

Wrinkle ridges form sinuous ridges mostly <1 km wide and 

tens to hundreds of kilometers in length. Individually, these features have low relief, though collectively they can form major 

physiographic and topographic features. Most are organized 

into sets that are evenly spaced a few tens of kilometers apart 

and are most clearly recognized on dark plains and coronae 

units. The more prominent ridge sets follow subparallel, gently 

curving trends; less prominent wrinkle ridges commonly are 

oriented orthogonally to the trend of prominent wrinkle ridges 

to form a localized reticulate pattern. Wrinkle ridges on Venus 

generally represent modest, distributed crustal shortening (<5%) 

in the brittle upper crust (Banerdt and others, 1997).

Lineaments are several to tens of kilometers long and 

generally 1 to 2 km wide and have radar-bright margins and 

darker floors, some of which may be flooded by younger lavas. 

However, most lineaments are too narrow to resolve their relief, 

but they are commonly aligned with wider ones that form linear 

troughs. Thus, we generally interpret these features to be narrow 

graben or fractures (Banerdt and others, 1997). In V–6, lineaments can form dense, anastomosing swarms (for example, 
7

Minerva Fossae), sometimes accompanied by interspersed 

wrinkle ridges (for example, Lampedo Linea). Lineaments are 

common tectonic structures in tessera material (unit t) and in 

regions of more highly deformed coronae, plains, and mons 

materials. Lineaments are likely to result from shallow crustal 

extension and may radiate from major volcanic and tectonic 

features, which may be underlain by igneous dikes in cases 

(Grosfils and Head, 1994).

Ridge and fracture belts are linear to dense arcuate collections of ridges and fractures that are generally >15 km wide, 

100 to 500 km long, and hundreds to more than a thousand 

meters high. They generally occur in swarms where a concentration of contractional strain has accumulated due to compressive stresses oriented normal to their origins, perhaps driven by 

stresses within the mantle (Banerdt and others, 1997, and references therein). Subsequent extension, perhaps as the result of 

magmatic-driven activity and (or) overthickening of the underlying crust, results in the formation of fractures. In most cases, 

ridge and fracture belts in V–6 form moderate topographic 

warps in older plains units, as well as in certain corona rims. In 

places, they are densely deformed by fractures, smaller wrinkle 

ridges, and lineaments, many of which are likely not detectable 

due to the high backscatter of these regions. Herein, we map the 

major trends and axes of these features.

Topographic warps are broad features that have variable width, length, and height. These are discriminated from 

ridge and fracture belts due to the fact that they are not always 

expressed by dense collections of ridges and fractures. Often, 

topographic warps can trend both parallel and perpendicular to 

wrinkle ridges and lineaments and define the annuli of some 

regional coronae (for example, Azham, Coatlicue, and Rananeida Coronae). Topographic warps characteristically define the 

ellipsoidal annulus of Demeter Corona within plains unit p3, as 

well as in the summit depressions of regional mons features.

Surficial Features

The map units and structure in the Metis Mons quadrangle 

show modest correlations with Magellan backscatter, altimetry, 

rms slope, emissivity, and reflectivity (figs. 1–5; table 4). Commonly, differences in radar backscatter are sufficiently distinct 

among adjacent map units and their structures to help delineate 

unit boundaries. The brightest units in radar backscatter have 

the coarsest texture at radar wavelength (12.6 cm) and (or) steep 

facets that produce mirror-like reflections of the radar signal. 

These include the densely fractured tessera material, plains unit 

p1, and earlier coronae materials. Also, the mons flow units 

show relatively bright individual flow surfaces, notably for 

parts of the younger Bagbartu flow material. The bright flows 

may result from the rugged texture of aa lava (Plaut, 1991). 

Similarly, crater materials have high backscatter that likely 

represents rugged textures of coarse, rubbly ejecta and perhaps 

aa-like impact melt flows. On the other hand, older plains and 

flow units generally show less distinctive radar backscatter 

signatures probably owing to weathering and burial by aeolian 

fines that mute the surface textures. In places, relatively bright, 

diffuse splotches detected on plains appear to be wind streaks 

that may include dunes.

Emissivity, reflectivity, and rms-slope data, however, show 

substantially lower resolution than the Magellan SAR that was 

primarily used as the base map for geological mapping. In many 

instances, these data are likely to relate to surface properties 

rather than to bedrock geology. Emissivity and reflectivity data 

for Venus have spatial resolutions of ~30–70 km and mainly 

correspond to the small-scale surface roughness and density 

of surface material (Pettengill and others, 1992); however, the 

dynamic ranges of these data in V–6 are too low to discriminate 

much geologically (table 4). The rms slope relates to meterscale roughness and thus correlates with the original roughness character of materials, subsequent deformation, and (or) 

smoothing or roughening due to weathering or surficial deposition. The rms-slope mapping of the planet was completed at 5 

km/pixel resolution (Ford and Pettengill, 1992).

Radar properties of surfaces associated with Montessori 

and Cotton craters show some striking associated patterns that 

indicate surficial materials. First, the craters are surrounded by 

diffuse, low-backscatter, low-emissivity parabolic haloes best 

observed on smooth plains. The haloes extend more than 1,000 

km west of the craters and darken about half of the quadrangle 

from the northeast to the southwest corners (fig. 1). More than 

50 such parabolic haloes associated with larger impact craters across Venus reportedly mark the redistribution of ejecta 

fines by a westward wind flow (Campbell and others, 1992). 

Hayashi crater also is surrounded by dark plains that may be 

halo material associated with this crater and (or) the extended 

halo of Montessori. Smaller haloes are associated with Indira, 

Golubkina, and Olya craters; these may have produced lesser 

amounts of fines and (or) the fines have been weathered and (or) 

dispersed.

Montessori crater shows some particularly interesting radar 

features. In the backscatter data, a 48-km-diameter circular 

dark splotch occurs 70 km east of the center of Montessori. The 

splotch has a small, 1.6-km-diameter crater centered within it 

and appears to form a small topographic high (fig. 2); thus, it 

likely represents a circular volcanic shield with a summit vent 

crater. Montessori is surrounded by an inner, low-backscatter 

parabolic halo that in turn is partly surrounded by a splotchy 

intermediate-backscatter, parabolic halo that is 100–200 km 

wide and is mapped as plains unit p5. Also, some striped, lowand high-backscatter streaks trend east-west within ~150 km of 

the crater; no obvious deflections of the streaks around topographic features are observed. The rms-slope data show that, 

near the crater, the low-backscatter halo has low meter-scale 

roughness, whereas the bright halo has high roughness. The 

low-rms-slope inner parabola forms a tail as much as 300 km 

wide that extends perhaps more than 1,300 km west, crossing 

some moderate topographic slopes and overprinting the otherwise moderately high rms northern slope of Mokosha Mons, as 

well as some local structures; it also appears to be restricted in 

extent from the north by some densely lineated plains and the 

Rananeida Corona annulus.

We interpret that the splotchy intermediate-backscatter 

halo may consist of microdunes that produce a rough surface at 

meter scales in the rms slope data and have sides that face west 
8

near the incidence angle of the radar beam (~27–30°). Because 

only left-looking backscatter data are available for this area, 

supportive information on the origin of these features, such 

as a reduced backscatter return using right-look data, is not 

available. In comparison, proposed microdunes in the southern 

hemisphere on Venus that are based on contrasting backscatter 

patches between left- and right-looking data, occur in association with three parabolic crater haloes (Weitz and others, 

1994; Greeley and others, 1997). Those authors estimated that 

microdunes detected by such means have wavelengths on the 

order of 10 to 30 cm based in part on laboratory simulations. 

The low-rms-slope, low-backscatter, inner parabola extending 

west of Montessori may consist of a sufficient thickness of fines 

to significantly lower the decimeter- and meter-scale roughness 

and, hence, lower the backscatter and rms slope of the surface. 

Similar, west-trending, low-rms-slope, inner parabolas surrounded by high-rms-slope outer parabolas coalesce and extend 

west of the closely spaced craters Guan Daosheng and Eudocia 

(both in the Barrymore quadrangle, V–59; see Ford and Pettengill, 1992, fig. 1), which also have proposed microdunes (Weitz 

and others, 1994). The demarcation between the inner and outer 

parabolas may represent both impact-induced activity (including both winds and material emplacement) and prevailing winds 

and consequent winnowing of sand-size particles to form the 

outer parabolas. Because the outer halo does not cover the dark 

shield, the shield either postdates the dune material or it created 

an obstacle to dune migration.

Geologic History

The history of geologic events in the Metis Mons quadrangle (V–6) is recorded by the distribution and ages of the mapped 

material and tectonic units and their modificational features, 

which include extensional and contractional structures. We 

unravel their relative ages based on standard crosscutting, overlap, and embayment relations (Wilhelms, 1972, 1990; Tanaka, 

1994; Hansen, 2000). Though radar data permit effective mapping of surfaces and structures (Ford and others, 1989, 1993; 

Sabins, 1997; Tanaka and others, 2010), several factors could 

influence the radar signature, including radar shadow, foreshortening, and layover (for example, Ford and others, 1993), and 

thus radar interpretation needs to be separated from geologic 

interpretation to the extent possible (for example, Hansen and 

others, 1999, 2000). In addition, we recognize that timing 

relations among and within geologic units and sets of tectonic 

structures are likely complex. For lava units, individual flows 

may span a time range that is poorly constrained by mapping 

relations, especially for sequences of stacked flows (for example, Guest and Stofan, 1999). Similarly, unique and identifiable 

structures can laterally transition into multiple tectonic fabrics 

that collectively display single or multiple morphologies and 

orientations developed over multiple stages of activity related 

to episodic magmatism at coronae and large volcanoes; some of 

these may involve other pre-existing structure belts (Bleamaster 

and Hansen, 2005). Given such geologic complexities and the 

inability for the mapping to provide full time constraints on the 

formation of geologic units and structures, we provide a generalized reconstruction of the geologic history of the Metis Mons 

quadrangle.

Geologic mapping indicates overlapping stages of major 

geologic activity (each of indefinite duration) for the Metis 

Mons (V–6) quadrangle of Venus (see Correlation of Map 

units). These stages can be characterized by the following 

dominant materials, from oldest to youngest: (1) tessera material; (2) materials of coronae and corona-like features and older 

plains units; (3) younger plains material and steep-sided domes; 

and (4) mons materials making up the large volcanic shields, 

isolated patches of flows, and crater and crater flow materials. 

Given the uncertainties and complexities previously mentioned, 

these stages represent peak and (or) waning periods in the 

cumulative production of the dominant exposed materials and 

features specified for each stage; rates of activity are uncertain. 

Each of the stages following the formation of tessera material 

resulted in a significant preserved record of areal resurfacing. Tectonically, some parts of coronae and various structural 

belts may have been active for most of the recorded geologic 

record of the Metis Mons map region, though activity waned 

or became more localized over time. Impact craters generally 

appear to be undeformed or modestly deformed, indicating that 

much of the deformation in the quadrangle occurred in a relatively short period of time and (or) deformation and volcanic 

resurfacing was effective at destroying older craters. The following discussion summarizes the geologic activity for each of 

these stages, which are named for their predominant features.

Tessera stage

This evolutionary stage of units within the V–6 quadrangle 

chiefly includes the formation of tessera materials, though 

older corona and plains materials might temporally overlap. 

The oldest materials in the V–6 quadrangle consist of isolated 

patches of relatively high standing tessera material surrounded 

by various plains materials; in places, tessera material is transitional with older coronae and plains materials deformed by similar complex structure but may also include other ancient crustal 

materials. Tessera material records the earliest and perhaps 

the largest degree of structural deformation in the map region; 

various models have been proposed to account for the crustal 

deformation that it records (for example, Basilevsky and others, 

1986; Bindschadler and Head, 1991; Solomon and others, 

1992; Hansen and Willis, 1996, 1998; Ivanov and Head, 1996; 

Gilmore and others, 1997, 1998; Hansen and others, 2000). 

The complex structural history of tessera material in the Metis 

Mons region is difficult to unravel and may include regional and 

global strain and deformation from now-unrecognizable local 

centers of magmatic activity, including coronae and structure 

belts or perhaps large impacts (Hansen, 2006).

Corona stage

This evolutionary stage of units within the V–6 quadrangle 

chiefly includes the formation of corona materials, as well as 

older plains materials (units p1 and p2). Coronae in the V–6 
9

quadrangle display tectonic, volcanic, and topographic signatures that indicate complex evolutionary histories (table 1). The 

most highly deformed, generally older parts of the coronae are 

defined by structural complexities. These include prominent, 

high-radar backscatter, structurally complex ridge belts that commonly define the coronae annuli, as well as high-standing coronae interiors that have dominantly radial or intersecting patterns 

of grabens and lineaments and minor formation of wrinkle ridges 

at the interior margins. Coronae are interpreted to have formed 

contemporaneously with local to regional outcrops of plains 

units p1 and p2, perhaps as the result of magma plumes and convection cells blistering the surface of the map region. Plains units 

p1 and p2 collectively form structural belts in places and considerable overlap with tessera material development is possible, as 

evidenced by lateral gradations and because only plains unit p2

of all corona stage units clearly postdates tessera material. Coronae development included dense radial and concentric fracturing 

and faulting, ridge development, and volcanism, resulting in 

complexly deformed lava sequences (in some cases, very similar 

in appearance to some of the tessera outcrops). The structures 

marking most outcrops of corona stage materials are more than 

an order of magnitude denser than the structures that deform 

younger plains materials. Broader structural interactions occur 

among coronae, especially where individual coronae are linked 

by major ridge and fracture belts. A major coronae belt trending ~N. 70° W. extends for >1,700 km across the center of the 

quadrangle and links structures that dominate Coatlicue, Rananeida, and Azham Coronae, as well as Lampedo Linea. Demeter 

Corona and others display annuli subdued by the inundation of 

lavas, which is indicated by the older parts of the corona that 

crop out through the relatively young plains materials. The ridge 

and fracture belts may also mark reactivated, pre-existing zones 

of lithospheric weakness, perhaps related to a phase of tectonism 

prior to a proposed global volcanic resurfacing event (Strom 

and others, 1994). Coronae and ridge and fracture belts may 

have been active for most of the recorded geological history of 

the Metis Mons map region, though activity apparently waned 

and became more localized during the plains and mons stages. 

Coronae are interpreted to have formed mostly via plume-driven 

tectonism, resulting in multiple concentric ridges and both radial 

and concentric lineaments within coronae and the adjacent plains 

materials (see Stofan and others, 1992, for details on formational 

models of coronae).

Plains stage

This evolutionary stage of units within the V–6 quadrangle 

chiefly includes the widespread emplacement and deformation of plains unit p3, the most extensive geologic unit within 

the quadrangle (see table 5). During this stage, unit p3 partly 

buried and (or) embayed older, generally more highly deformed 

materials and structures including tessera material and inactive 

or less active coronae and structure belts. Locally intense extensional and contractional deformation, including ridge and fracture belt growth, diminished, except for localized reactivation 

of faults within structural belts due to global to local stresses 

related to the relaxation of crustal materials and (or) the resurgence of corona activity. Instead, plains-stage tectonic deformation was dominated by distributed contraction and extension in 

the brittle upper crust that formed systems of wrinkle ridges and 

fractures. Lineaments generally parallel the northwest-southeast 

or northeast-southwest trends of regional structural belts. 

Wrinkle ridges generally trend concentric or radial to nearby 

coronae or appear to be influenced by other structure systems. 

The distributions and orientations of these features indicate that 

coronae-related and other local to regional stresses continued, 

and some of these structures likely resulted from reactivation 

and upward propagation of buried structures.

Mons stage

This evolutionary stage of units within the V–6 quadrangle 

chiefly includes the voluminous fissure-fed eruptions and major 

central volcanism related to the four large shield volcanoes—

Atira, Mokosha, Metis, and Bagbartu Montes—as well as plains 

unit p4. Geologic mapping indicates more than one episode 

of volcanism for some of the large shields. Some investigators 

have noted that collectively the broad shield volcanoes have 

among the lowest crater densities of any features on Venus 

(Namiki and Solomon, 1994; Price and Suppe, 1994; Basilevsky 

and Head, 2000b), but the timing of initial shield volcanism 

is uncertain. In addition, the growth of the four large shield 

volcanoes in the quadrangle led to local deformation within 

these features, including some rift-like faulting through Metis 

Mons to form Ilbis Fossae and perhaps relatively pronounced 

wrinkle-ridge development in places on the plains units surrounding Atira, Mokosha, and Metis Montes. Local corona and 

corona-like deformation during this stage formed an elongate 

structural annulus in Mokosha Mons, the caldera-like, partly 

enclosed depression at the summit of Atira Mons, the ridged 

annulus of Demeter Corona, and the complex radiating lineaments in northern Bagbartu Mons. Other lineaments associated 

with young lavas of plains unit p4 reflect local extension related 

to fissure volcanism. Many impact craters postdate the emplacement of other materials formed during this stage according to 

superposition of their ejecta, including the more diffuse radar 

dark and bright haloes surrounding some of them (see table 3). 

These haloes appear to be made up of fines that are susceptible 

to redistribution by aeolian activity (for example, fig. 6).

Summary

In summary, the overall geologic sequence in the V–6 

quadrangle represents a lowlands style of resurfacing and tectonism that demonstrates broad magmatic and tectonic evolution 

recorded in tessera and plains materials, as well as local evolution of coronae and large shield volcanoes. However, extensive 

uncertainties, exceptions, and complexities exist in determining precisely the relative ages of materials and features in the 

quadrangle. Some of the more notable uncertainties include 

(1) duration of plains volcanism (for example, catastrophic vs. 

gradual resurfacing) and how it may have evolved in style (for 

example, such as the dominance of shield vs. fissure vent types), 
10

and (2) relative ages among spatially disconnected features 

ranging from small volcanic edifices, impact craters, and local 

structure systems to more extensive coronae structures and 

large shield volcanoes. Thus, the general stages in evolution 

described in this quadrangle show similar trends locally, but the 

mapping does not constrain the synchronicity among these local 

sets of features and the evolutionary stages they display. Given 

the available constraints, the geologic evolution of V–6 may 

be consistent with either (1) models involving discrete stages 

of global tectonic and volcanic activity (Basilevsky and others, 

1997; Basilevsky and Head, 2000a,b; Ivanov and Head, 2001) 

combined with stages of regional, coronae development (Stofan 

and Head, 1990) or (2) scenarios of significantly more nondirectional, time-transgressive, activity (Guest and Stofan, 1999; 

Hansen, 2000; Hansen and Young, 2007).

Acknowledgments

We are grateful to the many Venus geologic mappers that 

have presented useful results and views, including comments 

on this mapping effort, at the annual Planetary Geologic Mapper’s meetings, Lunar and Planetary Science Conferences, and 

other professional meetings; many of their methods and insights 

have been incorporated into this map. We especially thank 

Trent Hare, Bonnie Redding, and Donna Galuszka of the U.S. 

Geological Survey for assistance with the digital scanning, editing, and conversion of hand-drawn linework into a Geographic 

Information Systems-ready format and with image processing 

of gridded Magellan data sets.

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13

Table 2. Location and description of large volcanoes of the Metis Mons 

quadrangle (V–6), Venus.

Volcano Lat

(° N.)

Long

(° E.)

Width

(km)

Elevation

range (m)

Height (m)

Atira Mons 52.2 267.6 600 276–1,498 1,222

Bagbartu Mons 65.5 279.0 300–750 275–1,612 1,337

Metis Mons 70.9 251.8 750–800 286–2,827 2,541

Mokosha Mons 57.5 255.0 500 312–2,2931 1,981

Unnamed mons 61.7 280.3 260–174 223–1,612 1,389

1Includes corona-like annulus at summit.

Table 1. Location and description of coronae and corona-like features of the Metis Mons quadrangle (V–6), Venus.

[---, no data]

Feature Lat

(° N.)

Long

(° E.)

Trend Size

range1

(km)

Elevation

range2 (m)

Height

(m)

Interior moat

or depression

depth (m)

Exterior

moat

depth (m) 

Moat

width3

(km) 

Azham Corona 66.4 252.9 N. 51° W. 194–352 261–1,391 1,130 302 418 30–40

Bachue Corona 73.3 261.4 N. 79° E. 408–614 286–3,298 3,012 --- --- ---

Bau Corona 52.8 259.3 N. 89° W. 322–529 239–1,671 1,432 311 --- 60

Coatlicue Corona 63.4 273.9 N. 79° W. 270–380 299–1,474 1,175 --- --- ---

Demeter Corona 53.9 294.8 N. 69° E. 406–816 –126–731 8,57 --- 641 40–130

Feronia Corona 68.0 281.7 N. 80° W. 533–704 262–1,243 9,81 --- --- ---

Mokosha Mons 57.7 255.0 N. 11° E. 139–255 1164–2,293 1,129 <300 --- ---

Otau Corona 67.8 298.7 N. 64° W. 119–177 287–1,345 1,058 --- --- ---

Rananeida Corona 62.6 263.5 N. 59° W. 431–469 255–1,161 906 576 --- 80

Unnamed corona 61.1 245.0 N. 75° E. 80–150 –33–724 757 <500 --- ---

1Size defined by outer margin of topographic annulus, locally defined by bounding ridge belts where topography is subtle.

2Values of surrounding plains elevation and highest feature elevation relative to mean planetary radius (MPR).

3Moats discontinuous except for those of Demeter Corona.
14

Table 3. Location and description of impact craters (21) of the Metis Mons quadrangle (V–6), Venus.

Crater

name

Latitude

(deg N.)

Longitude

(deg E.)

Diameter

(km)

Comments

Cotton 70.8 300.2 48.1 Only west edge in map area; bright floor (off map); 

extensive dark parabolic halo

Duncan 68.1 291.7 40.3 Small flow extends 40 km west; smooth, dark floor

Golubkina 60.3 286.5 28.4 Part of floor smooth, dark; small, irregular, dark 

halo

Hayashi 53.8 243.9 41.0 Moderately bright flows extend north and east <90 

km; relaxed rim, smooth, dark floor

Hull 59.4 263.6 47.3 Flows extend west and southeast <110 km; smooth, 

dark floor

Indira 64.1 289.8 16.6 Very bright flows extend 35 km south; rough floor; 

small, irregular, dark halo

Johnson 51.8 254.6 24.5 Ejecta possibly fractured; smooth, dark floor

Julie 50.9 242.6 13.2 Relaxed rim; rough floor

Katya 52.8 285.7 10.5 Partly embayed on southwest flank by plains unit 3 

(p3); rough floor

Margit 60.1 273.1 14.0 Possibly south-trending impact; rough floor; possible ejecta patch 50 km south (see fig. 6)

Montessori 59.4 280.0 42.4 Small flow extends 30 km west; smooth, bright 

floor; extensive dark parabolic halo; bright halo 

forms swath east and south of crater; distinctive 

low rms slope; diffuse low emissivity plains west 

of crater

Natalia 67.1 272.9 10.8 Dark flows extend west (mapped as plains unit p4); 

rough floor

Obukhova 70.7 289.7 46.0 Ejecta and rim fractured on west side; channels cut 

southwestern and northeastern ejecta; smooth, 

dark floor

Olya 51.4 291.8 13.4 Irregular dark halo may be flows (not mapped)

Outi 61.7 267.7 10.4 Possibly fractured, including possible flows (not 

mapped)

Tolgonay 68.8 271.1 4.6 Possibly partly embayed ejecta; fractured rim, 

ejecta; dark floor

unnamed 51.2 251.8 1.4 Bright ejecta

unnamed 66.8 297.2 2.8 Small crater south of Otau Corona; bright, speckled 

ejecta

unamed “a” 52.5 298.8 3.0 Western crater of pair south of Demeter Corona; 

bright ejecta rays

unnamed “b” 52.5 298.9 3.2 Eastern crater of pair south of Demeter Corona; 

bright ejecta rays

Zdravka 65.1 299.0 12.5 Flows extend <50 km southwest and northeast
15

Table 4. Elevation, emissivity, reflectivity, and rms-slope data of map units in the Metis Mons 

quadrangle (V–6), Venus.

Unit

label

Elevation (m)

[mean (min, max)]

RMS slope1 (°)

[mean (min, max)]

Emissivity

[mean (min, max)]

Reflectivity

[mean (min, max)]

mB2 724 (389, 1,225) 3.0 (1.4, 6.7) 0.869 (0.866, 0.874) 0.16 (0.11, 0.28)

mMe2 1271 (–197, 2,899) 3.4 (0.6, 9.0) 0.870 (0.857, 0.896) 0.11 (0.03, 0.26)

mMo2 1821 (1533, 2,186) 3.2 (1.4, 4.6) 0.860 (0.851, 0.876) 0.13 (0.07, 0.20)

mA2 958 (530, 1,508) 2.8 (1.5, 5.4) 0.863 (0.854, 0.876) 0.13 (0.09, 0.17)

mu 430 (–19, 1,626) 3.5 (1.1, 9.1) 0.866 (0.845, 0.896) 0.13 (0.06, 0.27)

mB1 592 (–219, 1,697) 2.7 (0.7, 8.0) 0.869 (0.844, 0.895) 0.12 (0.05, 0.26)

mMe1 1932 (1194, 2,406) 5.1 (1.0, 9.1) 0.872 (0.864. 0.878) 0.13 (0.08, 0.25)

mMo1 809 (235, 2,370) 2.8 (0.6, 6.9) 0.863 (0.842, 0.901) 0.13 (0.07, 0.22)

mA1 433 (–44, 1,392) 3.1 (0.6, 7.6) 0.860 (0.834, 0.915) 0.13 (0.07, 0.18)

pd 404 (–42, 1,753) 3.1 (1.3, 5.9) 0.858 (0.845, 0.886) 0.13 (0.08, 0.19)

p4 330 (–575, 1,582) 2.5 (0.5, 9.9) 0.862 (0.828, 0.927) 0.13 (0.05, 0.34)

p3 171 (–1322, 2,482) 2.6 (0.5, 10.0) 0.870 (0.838, 0.926) 0.11 (0.04, 0.31)

p2 472 (–1340, 2,582) 3.3 (0.6, 9.9) 0.872 (0.834, 0.916) 0.11 (0.04, 0.33)

p1 299 (–875, 2,354) 3.4 (0.6, 10.1) 0.877 (0.840, 0.910) 0.10 (0.04, 0.33)

cA2 463 (–204, 1,087) 4.5 (1.2, 9.0) 0.888 (0.875, 0.899) 0.10 (0.06, 0.23)

cF2 823 (142, 1,160) 3.7 (2.1, 7.7) 0.889 (0.885, 0.899) 0.080 (0.05, 0.16)

cBa 849 (–316, 3,641) 4.2 (0.6, 8.4) 0.874 (0.861, 0.885) 0.08 (0.02, 0.22)

cBu 724 (129, 1,314) 3.3 (1.0, 7.1) 0.897 (0.872, 0.915) 0.09 (0.06, 0.14)

cR 269 (–375, 829) 3.6 (0.7, 10.2) 0.882 (0.860, 0.913) 0.09 (0.05, 0.20)

cC 790 (–141, 1,682) 4.7 (0.6, 10.3) 0.884 (0.859, 0.900) 0.12 (0.05, 0.32)

cD –47 (–339, 573) 2.7 (1.2, 5.9) 0.885 (0.875, 0.896) 0.107 (0.070, 0.135)

cO 881 (440, 1,368) 4.5 (1.8, 9.6) 0.878 (0.863, 0.883) 0.116 (0.070, 0.240)

cA1 789 (–40, 1,396) 4.6 (2.2, 9.0) 0.883 (0.878, 0.890) 0.108 (0.060, 0.235)

cF1 677 (–935, 1,275) 4.4 (1.2, 8.9) 0.887 (0.860, 0.900) 0.088 (0.040, 0.180)

t 809 (–700, 2,880) 3.9 (0.8, 10.2) 0.881 (0.845, 0.920) 0.093 (0.045, 0.255)

c 427 (–969, 2,053) 2.4 (0.5, 6.8) 0.865 (0.834, 0.903) 0.116 (0.070, 0.190)

cf 366 (–175, 1,193) 2.4 (0.8, 6.5) 0.874 (0.844, 0.915) 0.112 (0.070, 0.175)

1Values were extracted for each geologic unit from gridded, interpolated datasets (3.2 km/pixel resolution).
16

Table 5. Description of geologic map units of the Metis Mons quadrangle (V–6), Venus, including relative-age 

relations with adjoining map units.

[<, younger than; ~, relative in age with; >, older than]

Unit

label

Unit

name

Area

(103 km2)

Relative age relations

Mons Materials

mB2 Younger Bagbartu Mons material 9 < mB1; ~ mB1

mMe2 Younger Metis Mons material 492 < mMe1, p1, p2, p3, p4, cBa, cA2; ~ p4, mMe1

mMo2 Younger Mokosha Mons material 20 < p1, p2, p3, mA1; ~ pd; > pd

mA2 Younger Atira Mons material 9 < mA1; ~ mA1

mu Mons material, undivided 57 < p1, p2, p3, p4, cC; ~ mB1, p4; > p4

mB1 Older Bagbartu Mons material 279 < cF1, cC, p2, p3, p4; ~ p4, mu; > mu, c, cf

mMe1 Older Metis Mons material 14 > mMe2

mMo1 Older Mokosha Mons material 276 < p1, p2, p3; ~ mMo2, p4; > mMo2, pd, p4

mA1 Older Atira Mons material 208 < p1, p2, p3; ~ mA2, p4; > mA2, p4

Plains Materials

pd Plains dome material 6 < mMo1, mMo2, p1, p3, p4; ~ mMo2, p3

p4 Plains unit 4 1.409 < mA1, p1, p2, p3, cBa, cBu, cR, cF1, cO, t; ~ mMe2, mu, 

mB1, mA1, c, cf; > mMe2, mB1, mu, pd, c, cf

p3 Plains unit 3 2.993 < p1, p2, cA1, cA2, cBa, cBu, cR, cF1, cC, cD, cO, t; ~ pd, 

c, cf; > mB2, mMe2, mMo1, mA1, pd, p4, mu, c, cf

p2 Plains unit 2 869 < p1; mMe1, cA1, cBa, cR, cF1, cC, t; ~ cR, cA2, cC, cD, 

cO; > mB1, mMe2, mMo1, mMo2, mA1, mu, p3, p4

p1 Plains unit 1 383 < t; ~ cC, cR, cF1, t; > mMe2, mMo1, mMo2, mA1, p2, p3, 

p4, c, cf

Corona Materials

cA2 Younger Azham Corona material 33 < cA1; ~ p2; > p3, p4, mMe2

cF2 Younger Feronia Corona material 10 < cF1

cBa Bachue Corona material 55 > p2, p3, p4, mMe2

cBu Bau Corona material 18 > p3, p4

cR Rananeida Corona material 34 ~ p1, p2; > p2, p3, p4

cC Coatlicue Corona material 52 ~ p1, p2; > p2, p3, p4, mB1, mu

cD Demeter Corona material 8 ~ cD; > p3, p4

cO Otau Corona material 12 ~ p2; > p3, p4

cA1 Older Azham Corona material 12 > p2, p3

cF1 Older Feronia Corona material 136 ~ p1; > mB1, mu, p2, p3, p4, cF2

Tessera Material

t Tessera material 33 ~ p1; > p1, p2, p3, p4

Crater Materials

c Crater material 40 < mB1, p1, p3, p4; ~ p3, p4

cf Crater flow material 21 < mB1, p1, p3, p4; ~ p3, p4