Prepared for the National Aeronautics and Space Administration

Geologic Map of the Beta Regio Quadrangle (V–17), Venus

By Alexander Basilevsky

Pamphlet to accompany

Scientific Investigations Map 3023

2008

U.S. Department of the Interior

U.S. Geological Survey

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, altimetric, and radiometric mapping of the Venusian surface was done 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 meters. 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 degrees.

High resolution Doppler tracking of the spacecraft was 

done from September 1992 through October 1994 (mission 

cycles 4, 5, 6). Some 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 kilometers and an apoapsis near 8,000 kilometers. An 

additional 1,500 orbits were obtained following orbit-circularization in mid-1993. These data exist as a 75 degree by 75 

degree harmonic field.

Magellan Radar Data

Radar backscatter power is determined by the morphology of the surface at a broad range of scales; and the intrinsic 

reflectivity, or dielectric constant, of the material. Topography 

at scales of several meters and larger can produce quasi-specular echoes, with the strength of the return greatest when the 

local surface is perpendicular to the incident beam. This type of 

scattering is most important at very small angles of incidence, 

since 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, there also exists a rapid increase in reflectivity 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. As such, they can be used to 

augment studies of the surface and to discriminate between 

roughness and reflectivity effects. Observations of the nearnadir 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 rootmean-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

Physiography

The Beta Regio quadrangle (V–17) is in the northern 

hemisphere of Venus and extends from latitude 25° to 50° N. 

and from longitude 270° to 300° E. (figs. 1, 2). Its southern part 

covers a significant part of the prominent and generally domal 

topographic rise of Beta Regio and the northern area of the less 

prominent and generally flat topped rise of Hyndla Regio. Part 

of the lowland plains of Guinevere Planitia, most of which is 

below the 6,051 km datum, occupies the northern part of the 

quadrangle. Within the plains but close to the northeastern part 

of the Beta Regio rise there is a radiating system of radar-bright 

lineaments and grooves centered at Wohpe Tholus. The Beta 

Regio rise has two summits: Rhea Mons and Theia Mons, both 

of which reach altitudes more than 5 km above the datum. Rhea 

Mons is completely within the V–17 quadrangle. Only the 

northern part of Theia Mons is in the quadrangle. From north to 

south the Beta Regio rise is cut by the very prominent topographic trough of Devana Chasma, the deepest parts of which 

locally reach the altitude levels of the Guinevere Planitia. At the 

eastern and western flanks of Beta Regio rise, correspondingly, 

are the troughs of Aikhylu Chasma and Latona Chasma, which 

topographically are much less prominent than Devana Chasma. 

Close to Aikhylu Chasma there is a channel-like feature named 

Omutnitsa Vallis. The northern part of the Beta Regio rise is 

marked by the fracture belt of Agrona Linea.

Both within the upland and lowland parts of the quadrangle 

there are several isolated massifs of tesserae: Senectus, Lachesis, and Zirka in the eastern part of the quadrangle; Sudenitsa, 

in the west; and several unnamed massifs in the central part 

(fig. 1). As will be shown, only part of them are blocks of tes-
2

sera terrain, whereas others are composed of other geologic 

units although they somewhat resemble typical tessera terrain. 

Within the V–17 quadrangle there are also three topographically 

positive deformation belts: Dodona Dorsa, Iyele Dorsa, and 

Shishimora Dorsa. Four coronae are also present in the quadrangle; these are Rauni Corona, Urash Corona, Emegen Corona, 

and Blathnat Corona. In summary, the V–17 quadrangle is an 

interesting area for the analysis of the major geologic processes 

responsible for the observed morphology on the surface of 

Venus.

Previous Work

Beta Regio is one of a few regions of Venus that have been 

observed by Earth-based radar observations since 1964 (for 

example, Goldstein, 1965, 1967; Goldstein and Rumsey, 1972; 

Goldstein and others, 1978). Even at that time it was correctly 

concluded that its surface is rough but its geologic nature was 

unknown.

In 1975 the Venera 9 probe landed on the northeastern 

flank of Beta Regio rise (Keldysh, 1979; Moroz and Basilevsky, 

2003). The gamma spectrometer measurements showed that in 

its contents of K, U, and Th, the surface material at the landing site (31.01° N., 291.64° E.) is close to terrestrial basalts 

(Surkov and others, 1976; Surkov, 1997). The spacecraft landed 

on a steep (approximately 30°) slope covered with talus of 

decimeter-sized fragments of rocks (Florensky and others, 1977; 

Keldysh, 1979).

The Pioneer-Venus radar studies, started in 1978, showed 

Beta Regio quadrangle in global context. Together with later 

and more sophisticated Earth-based radar observations they 

showed that Beta Regio is an area of inter-related rifting and 

volcanism (Masursky and others, 1980; McGill and others, 

1981; Schaber, 1982; Campbell and others, 1984; Stofan and 

others, 1989). Devana Chasma was interpreted to be a part of 

global-wide system of rifts resembling terrestrial continental 

rifts (McGill and others, 1981; Schaber, 1982). Theia Mons, 

dominating the central part of Beta Regio rise, based on its 

topographic shape and radially extending flow-like radar-bright 

features, was interpreted as a large shield volcano (Masursky 

and others, 1980; Campbell and others, 1984; Stofan and others, 

1989). Rhea Mons, dominating the northern part of Beta Regio, 

based on its topography, the presence of flanking radar-bright 

deposits, and radar-dark oval feature at its summit, interpreted 

to be a caldera, was considered a volcano split by Devana 

Chasma rift (Masursky and others, 1980; Campbell and others, 

1984; Stofan and others, 1989).

The northern part of Beta Regio quadrangle was covered 

by the Venera 15/16 radar survey (Barsukov and others, 1984; 

Alexandrov and others, 1986; Kotelnikov and others, 1989) 

including SAR imaging with 1- to 2-km resolution. Photogeologic analysis of the images of the northern slope of Rhea Mons 

as well as the northern, northeastern, and northwestern flanks of 

the Beta Regio rise showed that the upper part of Rhea Mons is 

composed of the rough-surfaced unit resembling in its morphology tessera terrain, whereas within the lower standing Beta 

Regio flanks the smooth-surfaced unit dominates (Basilevsky, 

1988; Sukhanov and others, 1989). Thus it was concluded that 

the northern part of the Beta Regio rise was mainly the result of 

the tectonic doming, whereas volcanism played a secondary role 

smoothing the uplift flanks. The joint analysis of the Pioneer 

Venus radar reflectivity and roughness data and the Venera 

15/16 images permitted the prediction of the global distribution 

of tessera terrain (Kreslavskii and others, 1989; Bindschadler 

and others, 1990). According to this prediction, Rhea Mons and 

several other areas within the Beta Regio rise with high probability were considered tessera terrain.

Magellan observations provided the most complete highresolution data for Beta Regio, including 120–220 m/pixel SAR 

images (Saunders and others, 1992; Solomon and others, 1992; 

Senske and others, 1992). The global Venus tectonic overview 

by Solomon and others (1992) as well as a more regional study 

by Senske and others (1992) confirmed the early interpretation of Theia Mons as a large shield volcano superposed on the 

Devana Chasma rift and added the observation that this volcano 

was partly cut by later rifting faults. These researchers also 

found the rift in northern Beta Regio surrounded by tessera, 

and their discovery confirmed the prediction by Kreslavskii and 

others (1988) and Bindschadler and others (1990). Rhea Mons, 

the northern summit of Beta Regio, was interpreted as an area 

of tessera terrain with some smooth plains of possible volcanic 

origin (Solomon and others, 1992; Senske and others, 1992). 

The analysis also revealed the 37-km crater Balch cut by the 

north-trending rift faults and extended by rifting in an easterly 

direction by about 10 km. To the north of Beta Regio rise at the 

boundary with Guinevere Planitia, a zone of faults and grabens 

trending generally east was observed (Agrona Linea) and interpreted as cutting faults extending from Devana Chasma (Solomon and others, 1992).

The south half of the V–17 quadrangle has been covered 

by the study of Ivanov and Head (2001a) who, based on the 

analysis of the Magellan data, geologically mapped a global 

geotraverse at 30° N. latitude. This study, which covered 20 

contiguous Magellan C1-MIDRs, had mostly stratigraphic and 

partly structural emphasis and thus is closely related to the 

V–17 mapping project. The authors of that study tested and 

modified the regional and global stratigraphy of Venus worked 

out by Basilevsky and Head (1995a,b, 1998, 2000) and Basilevsky and others (1997) as a starting point and added new 

units. Within the southern part of the V–17 quadrangle, Ivanov 

and Head (2001a) identified and mapped eleven geologic units: 

nine stratigraphic material units and two structural units. The 

mapped stratigraphic units (from older to younger) are: (1) tessera terrain material (t), (2) material of densely fractured plains 

(pdf), (3) material of fractured and ridged plains (pfr), (4) material of shield plains (psh), (5) material of plains with wrinkle 

ridges (lower unit pwr1), (6) material of plains with wrinkle 

ridges (upper unit pwr2), (7 and 8) materials of lobate (pl) and 

smooth (ps) plains, and (9) undivided impact crater materials 

(cu), whose age could be correlative with any of the above eight 

units. The two structural units are represented by older fracture 

belts (fb) and younger rifted terrain (rt), considered correspondingly as areas of the older and younger rifting.

For the part of the V–17 quadrangle covered, their mapping 

showed the presence of several medium-sized (hundreds of kilo-
3

meters across) massifs of tessera. In between they mapped areas 

of the pdf, pfr, psh, and pwr units with an unusual dominance 

of psh over pwr. In agreement with the results of Solomon and 

others (1992) and Senske and others (1992), Rhea Mons was 

interpreted by Ivanov and Head (2001a) as an uplifted block of 

tessera cut by the Devana Chasma rift (rt) whereas Theia Mons 

was interpreted as a volcano made of the lobate plains material 

(pl). Their mapping also showed presence of the fracture belts 

(fb) along the northern part of Beta Regio rise (Agrona Linea). 

Contrary to the interpretation of Solomon and others (1992), 

these fracture belts were determined to be older than Devana 

Chasma structures. Ivanov and Head (2001a) noted that most 

the elevated areas within the Beta Regio were made up of a collection of older units predating plains with wrinkle ridges (pwr). 

From this finding, they concluded that Beta Regio was high 

standing before the emplacement of pwr plains.

In their study Ivanov and Head (2001a) identified a new 

type of terrain characterized by “a pattern of tectonic deformation that fits the formal definition of tessera (two sets of almost 

orthogonally cross-cutting structures). However this terrain is 

less deformed than typical tessera and some of the material of 

the unit appears to embay tessera massifs” (Ivanov and Head, 

2001a, p. 17,549). They found that this terrain was formed as 

a result of additional deformation of densely fractured plains 

(pdf) and fractured and ridges plains (pfr) and named it “tessera transitional terrain” (tt). They did not show tt as a separate 

unit on the map but briefly described its distribution within the 

geotraverse, including the covered part of the V–17 quadrangle, 

where it formed at the expense of pfr.

Basilevsky and Head (2002a) used the degree of degradation of crater-associated radar-dark haloes on Venus to estimate 

the age of the crater and neighboring units in fractions of T, 

the mean global surface age of Venus. The halo-degradation 

technique was applied to several regions of the planet including 

Beta Regio. For five craters within the Beta rise (Sanger, Olga, 

Raisa, Tako, and Balch) the degree of degradation of craterassociated dark haloes and the relations of these craters to the 

neighboring volcanic and tectonic units and features has been 

determined. It was found, in particular, that ejecta outflows of 

the crater Sanger, which sits on the eastern slope of the Beta 

Regio rise and has a clear dark halo (crater age is <0.5T), are 

cut by the faults branching from the Devana Chasma rift. This 

relation implies that the Devana rift was active at least 0.5T ago 

and may be even subsequent to that time (Basilevsky and Head, 

2002a).

Ernst and others (2003) mapped graben-fissure systems 

in a broad region, the central part of which is the V–17 area. In 

this region they identified 79 such systems and classified them 

into radiating (34), linear (26), and circumferential (19). A significant part of these systems lies within the V–17 quadrangle: 

9 radiating, 11 linear, and 5 circumferential. They found that 

many of the systems are (1) younger that t, pdf, and pfr units, 

(2) coeval with, and in many cases define, fracture belts, (3) 

partially flooded by pwr plains, and (4) older than pl–ps plains 

and young (rt) rifts. Ernst and others (2003) also found that 

many of the radiating systems have a central topographic uplift 

and extend well beyond it, and this relation implies that grabens 

and fissures are underlain by dikes.

Beta Regio belongs to the category of large Venusian topographic rises, which are called “volcanic rises” because they 

encompass large volcanoes. Pioneer Venus and then Magellan 

observations showed that Beta Regio is characterized by an 

extremely high amplitude anomaly in geoid and gravity (+110 

m, +150 mgal), a large ratio of geoid to topography, and apparent depth of compensation in the range of 225 to 400 km. These 

characteristics imply that the Beta Regio rise (like other volcanic rises) is a hotspot or the surface manifestation of mantle 

upwelling (see for example, Phillips and Malin, 1983; Phillips 

and others, 1991; Bindschadler and others, 1992a; Herrick and 

Phillips, 1992; Konopliv and Sjogren, 1994; Solomatov and 

Moresi, 1996; Smrekar and others, 1997; Hansen and others, 

1997; Konopliv and others, 1999).

Smrekar and others (1997) divided the Venusian hot spots 

into three types: (1) rift-dominated, (2) volcano-dominated, and 

(3) corona-dominated, and they classified Beta Regio as a riftdominated hot spot. Foster and Nimmo (1996) compared the rift 

system of Beta Regio to parts of the East African rift. According 

to these authors both rift systems have effective elastic thickness 

of approximately 30 km and maximum fault segment lengths 

of approximately 100 km. These rift systems differ, however, 

in the maximum width of their half graben: approximately 150 

km for Beta Regio and approximately 50 km for East Africa. 

The larger width of the Venusian rift suggests that the faults 

bounding it are stronger than faults of the East African rift. 

This strength may be due to the enhanced dryness of Venusian 

rocks that makes them mechanically very strong (Mackwell and 

others, 1995, 1998).

Leftwich and others (1999) made a spectral correlation 

analysis of observed free-air anomalies calculated for three 

large regions of Venus, including Beta Regio. The model for 

Beta Regio suggests a thickened (≥40 km) crust relative to 

the surrounding plains, and it suggests a thinner crust beneath 

the Devana Chasma rift zone. According to this analysis, Beta 

Regio may be thermodynamically supported by mantle upwelling or have a thickened crust that is not yet completely compensated. The authors conclude that Beta Regio rise may be 

volcanically active at present or perhaps volcanism ceased in 

geologically recent times.

Rathbun and others (1999) used Magellan altimetry, gravity, and SAR images to constrain some parameters important in 

the formation of the Beta Regio rise. Using altimetry data and a 

fault-dip angle derived from the split of crater Balch, they determined the extension in the rifts of this region and then estimated 

the hoop strain (from 0.1 to 2 percent) accommodated by the 

rifts from the extension in these rifts. Using two separate modeling techniques, they then compared the observed and modeled 

gravity and uplift for this area and concluded that a relatively 

low density contrast region now exists below Beta Regio and 

has caused the uplift and rifting.

The formation of Beta Regio rise due to uplift caused by 

a mantle plume was modeled by Vezolainen and others (2003, 

2004). In the first of these two works, a two-dimensional 

modeling was undertaken. The model predicts correct gravity 

and topography anomalies and fast uplift time for Beta Regio 

(approximately 500 m.y.), which agrees with the geologic 

constraints (Basilevsky and Head, 2002a; Basilevsky and others, 
4

2003). However, in this model the fast uplift requires very low 

viscosity of the lithosphere beneath Beta Regio rise that is difficult to reconcile with the experimental data on the rheology of 

dry rocks (Mackwell and others, 1995, 1998). If the upper crust 

is made realistically strong, the uplift time becomes about 1.2 

b.y., which is only marginally acceptable from both geologic 

and geodynamic points of view (Vezolainen and others, 2003). 

Either for some reason the lithosphere is indeed very weak there 

or the model needs to be modified.

Vezolainen and others (2004) explored using three-dimensional (3-D) modeling. This model satisfies constraints on gravity, topography, rheology, and the uplift rate substantially better 

than the two-dimensional model. The uplift time is reduced to 

an acceptable 800 m.y. The 3-D model gives the plume formation depth to be around 3,000 km, that is, approximately the 

mantle-core boundary. The model results depend only weakly 

on the initial lithosphere thickness so the thick present-day 

lithosphere (approximately 400 km) can be reconciled with a 

thin lithosphere at the time of global resurfacing (100–200 km) 

inferred from the melt generation rates and the flexural rigidity 

models (Vezolainen and others, 2004). Both models imply that 

the Beta Regio rise may still be growing.

Mapping Approach

The geologic mapping of the V–17 Beta Regio quadrangle used traditional methods of geologic unit definition and 

characterization for the Earth (for example, American Commission on Stratigraphic Nomenclature, 1961) and planets (for 

example, Wilhelms, 1990) appropriately modified for radar 

data (Tanaka, 1994). Unit definitions and mapped key relations 

are based on the full resolution Magellan synthetic aperture 

radar (SAR) data (mosaicked full-resolution basic image data 

records, C1-MIDR’s, F-MIDR’s, and F-Maps). These results 

have been transferred to the base map compiled at a scale of 1:5 

million. In addition to the SAR image data, digital versions of 

Magellan altimetry (including U.S. Geological Survey pseudostereo images), emissivity, Fresnel reflectivity, and roughness 

data (root mean square, rms, and slope) were used. During this 

project, a convenient source of the data the U.S. Geological 

Survey provides was also used (namely, http://pdsmaps.wr.usgs.

gov/PDS/public/explorer/html/fmappick.htm). The background 

for unit definition and characterization is described in Tanaka 

(1994), Basilevsky and Head (1995a, b; 2000), Basilevsky and 

others (1997), Hansen (2000), and Ivanov and Head (2001a).

Magellan Sar and Related Data

In this mapping project the images taken by the synthetic 

aperture radar (SAR) instrument (12.6 cm, S-band) flown on 

the Magellan spacecraft were used. They represent a record 

of the radar echo returned to the spacecraft antenna, which is 

influenced by surface composition, slope, and wavelength-scale 

surface roughness. Viewing and illumination geometry also 

influence the appearance of surface features in SAR images. 

For the V–17 quadrangle, only left-look Magellan images were 

acquired. Guidelines for geologic mapping using Magellan SAR 

images and their interpretation can be found in Elachi (1987), 

Saunders and others (1992), Ford and Pettengill (1992), Tyler 

and others (1992), and Tanaka (1994). In the area of the Beta 

Regio quadrangle, incidence angles are such that backscatter 

is dominated by variations in surface roughness at wavelength 

scales. Rough surfaces appear relatively bright, whereas smooth 

surfaces appear relatively dark. At the same time within the 

areas of approximately the same and not high surface roughness the surface slopes are easily seen. Variations also occur 

depending on the orientation of features relative to the incident 

radiation (illumination direction), with features normal to the 

illumination direction being more prominent than those oriented 

parallel to it. Full-resolution images have a pixel size of 75 m; 

C1-MIDR’s contain the SAR data displayed at approximately 

225 m/pixel. Altimetry data were of great importance in establishing geologic and stratigraphic relations between units too. 

Also essential in the analysis of the geology of the surface are 

data obtained by Magellan on the emissivity (passive thermal 

radiation), reflectivity (surface electrical properties), and rms 

slope (distribution of radar wavelength scale slopes). Aspects 

of these measurements were used in unit characterization and 

interpretation; background on the characteristics of these data 

and their interpretation can be found in Saunders and others 

(1992), Ford and Pettengill (1992), Tyler and others (1992), 

Tanaka (1994), and Campbell (1995).

General Geology

Two major geologic processes, volcanism and tectonism, 

have influenced the Beta Regio quadrangle to form most of 

the observed geologic features. Volcanism was found to be 

the dominant process of crustal formation on Venus (Head 

and others, 1992) and also in the formation of the observed 

geologic units in this map area. Tectonic activity has modified 

some of these materials (for example, Solomon and others, 

1992; Squyres and others, 1992) in a variety of modes of strain 

(extensional, contraction, and shear), and in places deformation 

is so extensive, as in the case of tessera terrain, that the deformational features become part of the definition of the material 

unit (see also Tanaka, 1994; Campbell and Campbell, 2002, 

Hansen and DeShon, 2002; Stofan and Guest, 2003; Ivanov 

and Head, 2004; Brian and others, 2005). Impact cratering also 

has locally influenced some areas in the quadrangle but has not 

been an influential process over the quadrangle as a whole (fig. 

1). Aeolian processes did operate within the V–17 quadrangle 

but their signatures here are insignificant (Greeley and others, 

1997). Steep slopes, especially in Devana Chasma rift and associated grabens and faults, created conditions for dowslope mass 

movement, including rock/debris avalanches (Malin, 1992). 

Atmosphere-surface interactions are apparently visible within 

the V–17 quadrangle in the form of areas of high reflectivity 

and low emissivity above approximately +4 km altitude (Klose 

and others, 1992).

Volcanic processes within the quadrangle formed four 

major types of the deposits. The first type is represented by 
5

the materials forming regional plains with relatively smooth 

primary surfaces (Head and others, 1992; Guest and others, 

1992; Basilevsky and others, 1997). They dominate within the 

Guinevere Planitia in the northern part of the quadrangle and in 

isolated areas in the southern part of it where they form the four 

members of the plains with wrinkle ridges (pwr1, pwr2, pwr3, 

pwru). The second type of deposit is material that forms fields 

of numerous small gentle-sloping shields (Aubele and Slyuta, 

1990; Head and others, 1992; Guest and others, 1992; Aubele, 

1994, 1995; Crumpler and others, 1997). These shields dominate in the eastern and southern parts of the V–17 quadrangle, 

especially within relatively low altitude parts of the Beta Regio 

rise, where they form the unit of shield plains (psh). The third 

type is represented by flows seen on the slopes of Theia Mons 

volcano (Head and others, 1992; Crumpler and others, 1997) 

that form the unit of lobate plains (pl). These flows are also 

observed in several other places of the quadrangle but with no 

association with prominent volcanic edifices. The fourth type 

consists of small fields of radar-dark, morphologically smooth 

material that locally form very gentle sloping shields with 

summit pits. These fields typically have narrow extensions that 

make them appear similar to amoeba and, in fact, were called 

“amoeboids” by Head and other (1992). These lavas form in the 

regional-scale unit of smooth plains (ps). In addition, materials 

that probably formed due to volcanic activity, but whose volcanic origin is partly or significantly masked by tectonic deformation, are present in many isolated areas of the quadrangle and 

form units of fractured and ridged plains (pfr), densely fractured 

plains (pdf) and possibly tessera (t) (Basilevsky and Head, 

1995a,b, 2000; Ivanov and Head, 2001a).

Tectonic processes within the V–17 quadrangle are manifested in several ways. The most prominent result is the Beta 

Regio rise, whose origin owing to tectonic domal uplift is now 

accepted (for example, Solomon and others, 1992; Senske and 

others, 1992; Hansen and others, 1997; Rathbun and others, 

1999; Vezolainen and others, 2004). The Devana Chasma, 

considered a rift zone (for example Masursky and others, 1980; 

McGill and others, 1981; Stofan and others, 1989; Solomon 

and others, 1992; Senske and others, 1992; Hansen and others, 

1997), is undoubtedly another product of tectonic activity in 

the quadrangle. The most heavily deformed parts of Devana 

Chasma and a few associated zones of smaller size have been 

mapped as tectonic unit r. The long east-trending belt of faults 

and fractures, including Agrona Linea and Shishimora Dorsa, 

is another product of tectonism in the area. These faults and 

fractures have been mapped as tectonic unit fb. In close association with Agrona Linea there are four coronae (Rauni, Urash, 

Emegen, and Blathnat) and four radiating systems of faults (so 

called “astra”). All of these features are of likely tectonic origin. 

Most of them (except the radiating system centered at Wohpe 

Tholus) have been shown on the geologic map as areas of unit 

fb. Tectonic deformation is responsible for the structure and 

morphology of one more tectonic unit: tessera transitional terrain (tt) that formed as a result of moderately dense faulting of 

units pfr and pdf.

Tectonic deformation significantly influenced the structure 

and morphology of two geologic units: tessera terrain (t) and 

densely fractured plains (pdf). Less intense tectonic deformation influenced fractured and ridged plains (unit pfr), shield 

plains (unit psh) and plains with wrinkle ridges (pwr). The 

youngest geologic units, namely lobate plains (pl) and smooth 

plains (ps), are only locally influenced by tectonic deformation.

Impact cratering within V–17 quadrangle resulted in 

the formation of 25 craters with diameters from 1.3 to 84 km 

(Schaber and others, 1998) and 3 splotches (fig. 1, table 1). 

Most of the craters are superposed on different geologic units 

of the area, and only a few of them are superposed by relatively 

young tectonic structures and volcanic lavas. The largest craters 

of the quadrangle show not only hummocky ejecta typical of 

Venusian impact craters but also ejecta outflows. Deposits of the 

fine fraction of the crater ejecta are seen around 21 of 25 craters 

of this area in the form of radar-dark haloes (fig. 3). The degree 

of preservation of crater-associated radar-dark haloes (Arvidson 

and others, 1992; Herrick and Phillips, 1994; Basilevsky and 

Head, 2002a; Basilevsky and others, 2003) and crater relations with neighboring geologic units and features were used 

to divide the craters of the V–17 quadrangle into three age 

categories.

Signatures of eolian processes are rather rare within the 

V–17 quadrangle. These processes require a debris source to 

produce deposits or friable material to be a subject of deflation 

(Greeley and others, 1997) so they often are in association with 

impact craters. Within the V–17 quadrangle the work of eolian 

processes can be inferred from the different degrees of preservation of the radar-dark crater-associated deposits (fig. 3) (see for 

example, Basilevsky and Head, 2002a; Basilevsky and others, 

2003) and can be seen in the form of local patches of radar-dark 

deposits not associated with craters but localized in windshadow locations (fig. 4).

In theV–17 quadrangle, features that formed owing to 

downslope mass wasting on rather steep slopes can be seen both 

on SAR images (in the form of groove-like features and talus 

fans in Devana Chasma rift) and on the Venera 9 TV panorama 

in the form of rock-fragment talus (both examples are shown in 

fig. 5).

Atmosphere-surface interaction within the V–17 quadrangle led to a significant increase in its reflectivity and decrease 

in emissivity above approximately +4 km altitude level probably 

owing to changes of mineral composition of the surface material 

(Klose and others, 1992).

Stratigraphy

Venus is a planet with a relatively small (approximately 

1,000) number of impact craters on its surface. This paucity of 

craters makes it possible to estimate a mean surface age of the 

planet and mean ages of a few globally distributed geologic 

units, but not the ages of units and features of rather small 

areas, which contain a small number of craters. The estimate of 

the mean surface age of the planet is approximately 750 m.y., 

but values between 300 m.y. and 1 b.y. are considered possible 

(McKinnon and others, 1997). This estimate is practically equal 

to the estimate of the global mean for the regional plains, which 

correspond to combination of units psh and pwr described 

herein (Basilevsky and Head, 2000). Within the V–17 quad-
6

rangle there are 25 impact craters (Schaber and others, 1998). 

With the total area of the quadrangle being approximately 6 x 

106 km2, their mean areal density is approximately 4 craters per 

106 km2, which is about two times greater than the global mean 

(approximately 2 craters per 106 km2). However this can not be 

a reliable indication of a relatively old mean surface age of the 

study region because a simple statistical test shows that for 95 

percent (2σ) confidence level, the density estimate for theV–17 

quadrangle lies within 2.5 to 6 craters per 106 km2 and for 99.7 

percent (3σ) confidence level it is 1.7 to 6.7 per 106 km2. So the 

difference between the mean age for the V–17 quadrangle and 

mean surface age for the planet is not reliable.

Crater areal densities on different geologic units within the 

V–17 quadrangle cannot be used for estimating their relative 

ages. Therefore, to establish the geologic history of the region, 

the analysis of crosscutting, embayment, and superposition 

relations among the units and structures as well as the degree 

of preservation of crater-associated radar-dark haloes were 

used. The crater-associated halo approach provided the possibility of assessing if a given crater formed within the first or 

the second halves of post-regional-plains time (Basilevsky and 

Head, 2002a; Basilevsky and others, 2003), and then, from the 

analysis of age relation between this crater and the surrounding 

units and structures, to assess the age of the surrounding units 

and structures.

In the study area eight geologic material units, two of 

which are divided into members, have been mapped. Seven 

units form the time sequence. One unit (impact crater materials) is usually mapped as extending throughout the entire time 

period (Campbell and Campbell, 2002; Hansen and De Shon, 

2002; Ivanov and Head, 2004), but this study resulted in the 

subdivision of the unit into three members of different ages. The 

requirement for units is distinct characteristics and age relations 

with other units adjacent to them both in space and time and 

this was the major criterion for unit identification. Typically the 

identified units and members maintain some specific morphology along the areas of their appearance, but morphologic similarity alone was not considered sufficient for unit identification. 

Age relations with other units and structures have always been 

used as a criterion. In the case of the crater materials unit, the 

degree of crater-associated dark-halo development and preservation was used to subdivide it into two subunits; one more 

subunit of crater materials has been identified on the basis of 

age relations with other neighboring geologic units.

Tectonic structure has been mapped independent of geologic units, but in some cases tectonic features are such a pervasive part of the morphology of the terrain that they become part 

of the definition of a unit at this scale. For example, the tessera 

unit (t) and densely fractured plains unit (pdf) are so saturated 

with faults that at the Magellan SAR resolution the undeformed 

materials of these units are practically invisible. However, the 

U.S. Geological Survey has accepted the mapping of these units 

as material units on Venus. See maps by Bender and others 

(2000) and Brian and others (2005) for examples.

In some cases structures have been used as one of the steps 

in the unit identification even if the density of structures was not 

very great. For example, the unit of plains with wrinkle ridges 

(pwr) is characterized by these ridges in practically all of its 

mapped localities. The undeformed material of the unit is easily 

seen and it is evident that wrinkle ridges are superposed on it. 

The association of these ridges with this material unit is so typical that their presence was used as a part of the unit definition. 

A situation similar to this is the unit of fractured and ridged 

plains (pfr); in most localities of this unit, broad ridges are 

observed and are morphologically very different from wrinkle 

ridges.

However, we emphasize that structures were used for unit 

identification only as only one of the steps. Other morphological 

characteristics and age relations with other units were the predominant step in determining unit identification. For example, 

in some places of the Devana Chasma rift zone, faults are very 

dense and criss-crossed so the resulting morphology is somewhat similar to that of tessera terrain. But these faults obviously 

cut the adjacent regional plains while tessera is embayed by 

them. So this rift terrain subarea is not confused with the older 

tessera unit and is thus not mapped as unit t. Sometimes the 

surface of fractured and ridged plains (pfr) is locally deformed 

by wrinkle ridges so as to look in this subarea to be part of unit 

pwr. However, examination of the stratigraphy shows that this 

wrinkle-ridged material is deformed also by the wide ridges 

typical for unit pfr and is embayed by the lower member of pwr

plains. These two observations allow this pfr plains subarea to 

be distinguished from pwr plains.

In some areas of the V–17 quadrangle there are structural 

zones in which it is possible to understand age relations with 

neighboring units, but because of the high density of the structures it is difficult, if not impossible, to judge what material is 

deformed within the zones. In these cases tectonic units were 

identified. Age of tectonic units is related to age of the deformation, not to age of deformed material. Their boundaries are typically gradual and thus outlined rather arbitrarily. Three tectonic 

units have been identified within the V–17 quadrangle and are 

described in the “Description of Map Units.”

This approach of unit identification strictly follows the 

guidelines on planetary geologic mapping (Wilhelms, 1990) and 

in particular on the geologic mapping of Venus (Tanaka, 1994) 

and is generally similar to the approach used by other mappers, 

although in relation of concrete units and structures, differences of opinion exist (see Bender and others 2000; DeShon 

and others, 2000; Ivanov and Head, 2001a,b; Rosenberg and 

McGill, 2001; Bridges and McGill, 2002; Campbell and Campbell, 2002; Hansen and DeShon, 2002; Brian and others, 2005). 

The stratigraphic units and structures and their relations are 

summarized in the “Description of Map Units.”

Tessera material (unit t, fig. 6). This unit is interpreted 

to be the stratigraphically oldest unit in the quadrangle. It is 

embayed by most of the other units within the map area. Tessera 

terrain is radar bright, consists of at least two sets of intersecting 

ridges and grooves, and is a result of tectonic deformation of 

some precursor terrain (Barsukov and others, 1986; Basilevsky 

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

1992; Solomon and others, 1992; Hansen and others, 1997). 

According to Ivanov (2001), in some rare localities (outside 

the V–17 quadrangle) it is possible to see that a precursor of 

tessera terrain is plains. Within V–17, as with other regions 

of Venus, ridges and grooves on the tessera surface show a 
7

spectrum of spacing from a few hundred meters to several 

kilometers with wider features consisting of clusters of smaller 

ones. Undeformed parts of tessera material are not present in 

the V–17 quadrangle. Tessera unit occupies approximately 5 

percent of the quadrangle (table 2), which is slightly smaller 

than the global abundance (8 percent) of this unit (Ivanov and 

Head, 1996). Within V–17, tessera unit forms two rather large 

blocks about 1,000 to 1,500 km long and 400 to 500 km wide. 

One block is about 1,500 km northwest of Rhea Mons, and the 

other is on the western flank of this mountain massif. Several 

blocks of a few hundred kilometers across and about 20 blocks 

of a few tens of kilometers across are also present in the V–17 

quadrangle. Within the study area there are four physiographic 

units called tessera (Lachesis, Zirka) or tesserae (Senectus, 

Sudenitsa), but only the northern part of Sudenitsa Tesserae is 

partly composed of tessera unit whereas others are composed of 

other units.

Densely fractured plains material (unit pdf, fig. 7). Next 

in the time sequence is densely fractured plains material, which 

is characterized by relatively flat surfaces on a regional scale 

and by swarms of parallel and subparallel lineaments (sometimes resolved as fractures). Typical spacing of these lineaments is less than 1 km. However, because the pdf terrain is 

often intimately intermixed with undeformed volcanic material (usually it is unit psh) the greater lineament spacing was 

observed in some places. Although the unmodified precursor 

terrain for the densely fractured plains material is not observed, 

the flatness suggests that it was plains and based on analogy 

with the younger and less deformed plains of Venus, it could 

be volcanic plains made of mafic lavas (Basilevsky and Head, 

2000). The pdf fractures are structural elements, but they are 

such a pervasive part of the morphology of this terrain that they 

become a key aspect of unit definition. Densely fractured plains 

are embayed by almost all younger material units, except the 

youngest units pl and ps, with which they are not observed in 

direct contact. In rare occurrences where pdf plains and tessera 

are in direct contact, the first one embays the second (fig. 8). 

Densely fractured plains occupy approximately 5 percent of 

the quadrangle (table 2), close or slightly greater than its 3 to 

5 percent global abundance estimated by Basilevsky and Head 

(2000). It predominantly occurs in the northeastern part of 

quadrangle composing Senectus and Lachesis Tesserae. Small 

patches of pdf plains also occur in other parts of V–17 quadrangle.

Fractured and ridged plains material (unit pfr, fig. 9). This 

unit, next in the time sequence, is composed of medium-bright 

material with a predominantly smooth surface. In this aspect, 

unit pfr is similar to the younger units pwr (member 2) and pl, 

which bear morphologic evidence that they are composed of 

mafic lavas. So one may suggest that unit pfr is also composed 

of mafic lavas. But contrary to units pwr and pl, the pfr unit is 

commonly deformed by broad (3- to 10-km wide) ridges tens of 

kilometers long that form so-called ridge belts. Unit pfr embays 

the older units t and pdf and is embayed by the younger units 

psh, pwr, and pl (figs. 9, 10). Unit pfr in slightly or moderate 

deformed state composes approximately 5 percent of the V–17 

quadrangle (table 2), similar to the 3 to 5 percent global abundance estimated by Basilevsky and Head (2000). It predominantly occurs in the south half of the V–17 quadrangle in the 

form of rather small, elongated zones separated from each other 

by the younger plains. In the north half of V–17 quadrangle, 

the pfr unit is also present but is significantly less abundant. 

Because it is deformed by faults and grabens, unit pfr makes up 

the predominant part of the tectonic unit tt.

Shield plains material (unit psh, figs. 6–11). Next after 

the fractured and ridged plains is the material of shield plains. 

It is typically of intermediate radar brightness and characterized by abundant, gently sloping shield-shaped features of a few 

kilometers in diameter, often with summit pits. Clusters of small 

shields were first recognized on the Venera 15/16 images (Barsukov and others, 1986; Aubele and Slyuta, 1990) and then with 

greater detail on Magellan SAR images (Head and others, 1992; 

Guest and others, 1992; Kreslavsky and Head, 1999). Their 

stratigraphic significance was recognized in observations in Vellamo Planitia (Aubele, 1994, 1995), which showed that many of 

the small shield fields represented a regional stratigraphic unit. 

Subsequently this unit has been recognized in many areas on the 

planet (Basilevsky and others, 1997; Ivanov and Head, 2001a; 

Basilevsky and Head, 1998, 2000), including this quadrangle. 

In association with shield clusters that give the unit a locally 

hilly texture are isolated outcrops in relatively smooth plains. 

The shields are interpreted to be of volcanic origin (Aubele and 

Slyuta, 1990; Guest and others, 1992; Head and others, 1992; 

Crumpler and Aubele, 2000) and are the likely sources of associated smooth areas. Embayment relations between shield plains 

and older units are shown in figures 6–10 and those between 

shield plains and younger units are shown in figures 12 and 

16. Although shield plains are typically embayed by the plains 

with wrinkle ridges and are wrinkle ridged, in some places of 

the quadrangle, separate shields and even shield clusters are 

superposed on wrinkle ridges (fig. 11). In the literature, such 

relatively young shield clusters are sometimes considered as 

member psh2 (for example, Basilevsky and Head, 2002b, fig. 

12). The psh unit is widely distributed mostly in the southwestern part of the quadrangle and is locally present in its other 

parts. Its total abundance within V–17 quadrangle is approximately 26 percent, which is significantly larger than the 10 to 15 

percent estimates of global occurrence of this unit (Basilevsky 

and Head, 2000).

Wrinkle ridged plains material (unit pwr, figs. 10, 11, 

12, 13, and 14). Next after unit psh is the material of wrinkleridged plains. This unit is composed of morphologically 

smooth, homogeneous plains material of intermediate-low to 

intermediate-high radar brightness complicated by narrow wrinkle ridges (a structural element). Within the V–17 quadrangle 

and in other areas of Venus, the wrinkle ridges are typically less 

than 1 km wide and tens of kilometers long. Locally, however, 

they may be smaller, whereas in other places they are larger. 

The unit is interpreted to be plains of volcanic origin deformed 

by wrinkle ridges (Head and others, 1992; Basilevsky and Head, 

1998, 2000). The volcanic (lava) origin of the pwr plains globally and within V–17 is supported by flow-like morphology of 

one of the members of this unit, although obvious edifices and 

other sources of these vast lava fields were not observed. Within 

the V–17 quadrangle is the landing site of the Venera 9 lander 

(31.01° N., 291.64° E.). Most of the landing ellipse is occupied 
8

by unit pwr so it is very probable that the geochemical analysis suggesting a basaltic composition for the surface material 

(Surkov, 1997) is characteristic of this unit (Basilevsky and 

Head, 1998, 2000).

Within V–17 quadrangle, unit pwr is subdivided into three 

members of different ages (pwr1, pwr2, and pwr3) and in some 

places where the correspondence of the pwr material to one 

of these members could not be determined, one more member 

(pwru = undivided) was mapped. Member 1 (pwr1) generally 

has a relatively low radar albedo (fig. 12). Within the field of 

member pwr1 at the northeastern flank of the Beta Regio rise 

there is Omutnitsa Vallis (fig. 13). It is a sinuous, flat-floored 

groove considered to be a lava channel elsewhere termed 

“canali” (Baker and others, 1992, 1997). Association of the 

largest canali of Venus, Baltis Vallis, with member pwr1 was 

described by Basilevsky and Head (1996). Member 2 (pwr2) 

generally has a relatively high radar albedo and lobate boundaries indicative of its superposition on pwr1 (fig. 12). Member 

3 (pwr3) has been observed only in one locality, northeast of 

Emegen Corona, where it intrudes into gaps and grabens within 

member 2 (fig. 14). Its material is relatively radar dark, significantly darker than the pwr2 material and noticeably darker than 

adjacent areas of member 1. In its dark surface, member pwr3

resembles unit ps, but it differs from unit ps in the presence 

of wrinkle ridges that form a network in common with wrinkle 

ridges of the adjacent areas of members pwr1 and pwr2. In several areas of V–17 it was difficult to classify the material of pwr

plains into the three members described. It occurred either when 

the pwr material was darkened to different degrees by haloes of 

adjacent impact craters or when isolated patches of pwr material 

were observed among the brighter and typically older units. In 

these cases it is mapped as member pwru (undivided).

Unit pwr occupies approximately 31 percent of the study 

area, which is significantly smaller than its global abundance 

(50–60 percent) estimated by Basilevsky and Head (2000). 

Abundances of the pwr members within V–17 are as follows: 

pwr1 approximately 11 percent, pwr2, approximately 11 percent, pwr3, approximately 0.2 percent, and pwru approximately 

9 percent. Plains of unit pwr dominate in the northeastern part 

of the V–17 quadrangle and form isolated fields among other 

units in the rest of the study area. Plains with wrinkle ridges and 

shield plains are often lumped together as “regional plains.”

Smooth plains material (unit ps, fig. 15). This is one of the 

two youngest non-crater material units. Smooth plains material 

is smooth and radar dark. It is observed in the form of fields of 

plains 10 to 60 km across, typically of planimetrically irregular 

outlines, and sometimes rather long tongues of the unit extend 

to adjacent units. As previously discussed, the ps fields have 

been called “amoeboids,” and described as specific lava flows 

(Head and others, 1992; Crumpler and Aubele, 2000). Pits 

about 1 km in diameter are sometimes seen within the ps fields 

and probably represent volcanic vents. Smooth plains material is 

usually superposed on unit psh, and in some cases on units pfr, 

pwr, and tectonic unit fb. Two fields of the ps unit are superposed by ejecta of impact craters Truth and Nalkowska. These 

craters are also superposed on units psh and pwr and have a 

faint radar-dark halo. This observation suggests that these two 

craters, and therefore these two fields of ps material, formed in 

the first part of the post-regional-plains time (Basilevsky and 

Head, 2002a; Basilevsky and others, 2003).

Within the V–17 quadrangle unit ps occupies only approximately 0.15 percent of the area. Basilevsky and Head (2000) 

did not estimate global abundance of unit ps. They estimated 

only the combined global abundance (10–15 percent) of units 

ps and pl (see below). In the V–17 quadrangle, unit ps forms 

about 20 fields. About half of them are concentrated in the area 

northeast of Emegen Corona.

Lobate plains material unit (unit pl, fig. 16). The second of 

the two youngest non-crater material units, lobate plains material, appears morphologically uniform at Magellan SAR resolution. It is mostly radar bright with darker subareas that together 

form a pattern of superposition of many individual flows. In 

generally high brightness and flow-like outlines of its fields, 

unit pl resembles the member pwr2. However the pwr2 fields 

are usually rather homogeneous in brightness while fields of pl

material typically are variegated with a pattern of flow superposition. In addition, the pwr2 fields are wrinkle-ridged whereas 

the pl fields are not. The prominent flow-like texture and 

association with obvious volcanic constructs (within V–17 it is 

Theia Mons) indicate that unit pl is composed of lavas (Head 

and others, 1992; Crumpler and Aubele, 2000). The Venera 14 

landing site, although outside V–17, was located within a field 

of pl units (Basilevsky and Head, 2000) and X-ray fluorescence 

analysis of the surface material at the site showed a composition close to tholeiitic basalt (Surkov, 1997). Unit pl embays 

and is superposed on all other non-crater material units except 

unit ps with which unit pl is not in contact. Within V–17, unit 

pl partly floods the 13-km impact crater Raisa and is superposed 

by the 11-km crater Tako. Both these craters have a faint halo 

so they are interpreted to have formed within the first half of 

post-regional-plains time (Basilevsky and Head, 2002a; Basilevsky and others, 2003). Unit pl is locally cut by some young 

fractures, mostly by those associated with the Devana Chasma 

rift. Unit pl occupies approximately 5 percent of the V–17 quadrangle. This is about half or smaller than the combined global 

abundance of units pl and ps estimated by Basilevsky and Head 

(2000) as 10 to 15 percent. Within V–17 most of unit pl is on 

the slopes of Theia Mons. A few fields of unit pl 100 to 200 

km across are in the northwestern and southeastern parts of the 

study area and several fields tens kilometers across are observed 

in other parts of the quadrangle. Among those in the other parts 

is a volcanic construct, Copacati Mons, about 80 km in diameter 

and 1 km high centered at 34.8° N., 276.8° E.

Impact crater material (units ci, ch, and cf, figs. 17, 18, 

and 19). Within the V–17 quadrangle there are 25 impact craters 

and three splotches (fig. 1, table 1; Schaber and others, 1992, 

1998). In most cases it was possible to map separately different 

facies of crater materials: intra-crater material (ci), hummocky 

ejecta (ch), and ejecta outflows (cf). In the cases when the crater 

was small (typically smaller than 6 km in diameter) or it was 

severely flooded by lavas (the 13-km crater Raisa) undivided 

crater materials (cu) were mapped. Based on age relations of 

the crater with regional (psh+pwr) plains and on the degree of 

crater-associated radar-dark halo (fig. 3), the craters were subdivided into three age facies: a lower one (c1)—pre-regionalplains craters; a middle one (c2)—post-regional-plains craters 
9

with faint or no halo; and an upper one (c3)—post-regionalplains craters with clear halo. According to Basilevsky and 

Head (2002a), craters with faint or no halo were formed within 

the first half of the post-regional-plains time period, while craters with clear haloes—in the second half of this period. Using 

these two approaches, several combinations were mapped: cu1, 

ch2, cf3, and so on.

Among the 25 craters of the V–17 quadrangle, one was 

classified as representing the lower unit c1 (crater Aigul, fig. 

17), twelve as the middle unit c2 (fig. 18), and twelve as the 

upper unit c3 (fig. 19). Splotches, which are radar-dark spots 

without visible craters inside (Schaber and others, 1992), are 

similar to the clear crater haloes in their darkness, so they 

were considered contemporaneous to facies c3. One crater, 

Aigul, which is embayed by psh material and classified as of 

c1 age, is deformed by the pdf-style fractures and by the faults 

branching from the fracture belt (fb). The floor of one crater, 

Deken, superposed on pwr plains and classified as of c2 age, is 

deformed by wrinkle ridge whose morphology and orientation 

are similar to those of wrinkle ridges of the adjacent pwr plains. 

Four craters (Zvereva, Sanger, Balch, and Olga) are cut by relatively young faults. The fault that cuts crater Zvereva is a part of 

the radiating system centered at Wohpe Tholus. The faults that 

cut craters Sanger, Balch, and Olga are structures of the Devana 

Chasma rift zone. Two of these craters (Zvereva and Sanger) 

have clear haloes that suggest the tectonic activity responsible 

for formation of the radiating system centered at Wohpe Tholus 

as well as Devana Chasma was ongoing in the second half of 

post-regional-plains time.

Structures

Tectonic Units

Tectonic units are introduced mostly when structures in the 

study area are spatially very dense and it is difficult or impossible to say what they are deforming. Their identification and 

mapping were recommended by Wilhelms (1990) and repeated 

by The Venus Geologic Mappers’ Handbook (Tanaka, 1994). 

Mapping tectonic units allows one not to hypothesize what 

material units are hidden by this heavy deformation and makes 

these areas more visible in the map. Three tectonic units have 

been mapped within the V–17 region: tessera transitional terrain 

(tt), fracture belts (fb), and rifted terrain (r).

Tessera transitional terrain (unit tt). In the south half of the 

V–17 quadrangle, extended areas of terrain are observed that 

resemble tessera in morphology. In a number of localities it is 

seen that this terrain is formed at the expense of fracturing of 

the material unit pfr and locally at the expense of the material 

unit pdf (fig. 20). Some of the fractures in this terrain resemble 

fractures and faults of tectonic unit r in their variable width (a 

few hundred meters to 3–4 km), whereas others with less variable width (a few hundred meters) resemble faults of tectonic 

unit fb. Contrary to units r and fb, this type of terrain forms 

equidimensional areas within which fractures are typically crisscrossed, rather than planimetric linear zones. In some cases, 

when this deformation affects the pfr ridges, the fractures are 

predominantly transverse to the ridge trends. The typical length 

of fractures is a few tens of kilometers. Areas with similar 

morphology have been identified by Ivanov and Head (2001a) 

as a tectonic unit known as tessera transitional terrain. Accordingly, we mapped these areas as tessera transitional terrain. The 

morphologic similarity of tt structures to those in the r and pdf

tectonic units implies that they are also of extensional origin. 

Structures of the tectonic unit tt are superposed on broad ridges 

that typically deform material unit pfr and they do not extend 

into the neighboring material units psh and pwr. As stated, the 

precursor terrain for unit tt seems to be the material units pfr

and pdf. However, because of the high density of deformation 

this conclusion is not completely firm. Tectonic unit tt occupies 

approximately 10 percent of the quadrangle area and composes 

the southern part of Sudenitsa Tesserae, Zirka Tessera, Hyndla 

Regio, and a significant part of Rhea Mons. When in contact 

with the unfractured unit pfr, tessera transitional terrain typically stands a few hundred meters above the adjacent pfr areas.

Fracture belts (unit fb). Within the quadrangle there are 

linear zones saturated with faults, which themselves are linear, 

or arcuate, or slightly anastomosing. These faults are typically 

tens of kilometers long and several hundred meters wide. Their 

trends are parallel or oblique to the trends of these zones so 

the faults are often mutually intersecting. These zones have 

been mapped as a tectonic unit of fracture belts (fig. 21). The 

fracture belts are considered in the literature as zones of extensional deformation close in origin to the zones of rifted terrain 

(Hansen and others, 1997; Banerdt and others, 1997; Basilevsky 

and Head, 2002b). Structures of the tectonic unit fb cut material 

units t, pdf, and pfr. They are embayed by units psh and pwr

but some of the fb faults cut units psh and pwr that distinguish 

them from the pdf faulting. Lavas of the pl and ps units, when 

in contact, embay fracture belts and in some cases the fb faults 

may be the source of small fields of pl lavas. Within the V–17 

quadrangle fracture belts occupy approximately 9 percent of 

the area, being concentrated within the 35 to 40° latitude zone 

forming Agrona Linea and Shishimora Dorsa. With the Agrona 

Linea are associated four coronae whose annulae are made of 

fb unit. Coronae Emegen and Blathnat are part of the Agrona 

Linea structure. Coronae Rauni and Urash are adjacent to 

northern periphery of Agrona Linea. In contrast with unit r, the 

V–17 fracture belts are not associated with topographic troughs. 

Those associated with the northern base of Beta Regio rise 

are at the +0.5 to +1.5 altitude range of the topographic slope. 

Those that make up Dodola Dorsa and Shishimora Dorsa stand 

a few hundreds meters above the adjacent regional psh+pwr

plains.

Rifted terrain (unit r). Long and short linear fractures and 

sometimes paired and facing scarps interpreted to be grabens 

are seen in practically all parts of the quadrangle. Their highest concentration is within and nearby Devana Chasma. The 

places saturated with fractures and grabens have been mapped 

as a tectonic unit rifted terrain (fig. 22). Rift faults are typically several tens of kilometers long, with the longest being 

100 to 150 km long. Fractures and grabens of rifted terrain 

are typically of variable width, and they range from about a 

hundred meters (limit of resolution) to several kilometers. A 
10

few grabens, including one that cuts the 40-km crater Balch (fig. 

3D), are as much as 15- to 20-km wide. Quite often the widths 

of individual faults are variable. The r fractures and grabens are 

planimetrically anastomosing and this, together with variability 

in their width, makes the morphology of this unit very distinctive and recognizable. The r faults deform all material units of 

the quadrangle including the youngest ps and pl units. Locally 

the r faults are flooded by pl lavas and this relation is especially 

typical on Theia Mons. The r faults are likely extensional in 

origin. Assuming that crater Balch, cut by grabens, was initially 

planimetrically circular, Solomon and others (1992) estimated 

that the easterly tectonic extension in this area was about 10 

km. The tectonic unit r occupies approximately 2.5 percent of 

the quadrangle area, mostly in the north-trending axial zone of 

Beta Regio rise, where it is associated with the Devana Chasma 

topographic trough, the deepest parts of which are at the +0.5 

km to –0.5 km altitude level.

Other Tectonic Features

Several types of tectonic features were observed and 

mapped within the quadrangle outside the tectonic units. Some 

of them are considered to be of extensional origin whereas 

others are contractional. A combination of contractional and 

extensional structures is typical for tessera-forming deformation. The matrix of tessera terrain in V–17 is ridge-and-groove 

ensembles, in which ridges and grooves abut each other with 

practically no horizontal surfaces between them (fig. 6). Ridgeto-ridge or groove-to-groove spacings in these ensembles vary 

from a few hundred meters to several kilometers with wider 

features often consisting of clusters of smaller ones. Locally 

the ridge-and-groove ensembles are cut by flat-bottom grooves 

with sharp edges and often with obviously late-plains material on their floors. Typically there are two dominant trends of 

the structures with 60 to 90° angles between them. Sometimes 

structures criss-cross each other. In other cases, tessera is a 

complicated mosaic of the 10- to 20-km-blocks within some 

part of which one trend dominates whereas in other blocks 

another trend dominates. Locally, structural trends within tessera are noticeably arcuate to almost ring-like (fig. 23). The 

densely packed ridge-and-groove matrix of tessera terrain probably formed as a result of compressive stresses whereas the 

flat-floored grooves are grabens (Basilevsky and others, 1986; 

Bindschadler and Head, 1991; Sukhanov, 1992; Bindschadler 

and others, 1992a,b; Solomon and others, 1992; Hansen and 

Willis, 1996; Ivanov and Head, 1996; Hansen and others, 

1997).

A specific variety of structures is characteristic of the 

material unit pdf (fig. 7). They are typically very linear, densely 

packed, and parallel to each other. In the northeastern part of 

the V–17 quadrangle, where the pdf unit occupies rather large 

areas, the unit is a mosaic of subareas. Within each subarea 

structures are parallel to each other, whereas in different subareas the orientation of the structures is different. The pdf faults 

are typically several tens of kilometers long and a few hundred 

meters to 1-km wide. Structures typical of the pdf unit are probably extensional faults, perhaps with involvement of shear.

Contractional structures within the V–17 are represented 

by ridges of two types. Ridges of the first type form ridge belts 

but locally single ridges are observed. These ridges usually 

deform material unit pfr (figs. 9, 10) and locally they deform 

material unit pdf. An example of when a ridge of this type 

deforms pdf material can be seen 200 km south of the crater 

Brooke (fig. 24). The ridges in these belts are the same as 

those observed and described in other areas of Venus (Frank 

and Head, 1990; Kryuchkov, 1990; Solomon and others, 1992; 

Hansen and others, 1997). Ridges are usually 3- to 5-km wide 

and sometimes as much as 10-km wide and a few tens of kilometers long. The ridge belts of V–17 quadrangle are significantly flooded by the material units psh, pwr, and pl and thus 

are observed as elongated islands from 100- to 200-km long and 

10- to 50-km wide. Within the ridge belts, ridges form clusters 

with 3- to 15-km ridge-to-ridge spacing whereas some rather 

extended areas of the pfr unit lack ridges.

The most abundant contractional structures within the 

V–17 quadrangle are wrinkle ridges that typically deform the 

material units pwr and psh and locally also observed in unit pfr. 

The wrinkle ridges are typically a few tens of kilometers long 

and several hundreds meters wide (figs. 4, 11–14). They usually 

form networks with ridge-to-ridge spacing varying from 3 to 5 

km (typical for member pwr3 and locally for psh) to 10 to 15 

km (typical for subunits pwr1 and pwr2). An origin of wrinkle 

ridges by compressive stress is commonly accepted by many 

researchers (Pleiscia, 1991; Watters, 1991; Solomon and others, 

1992; Banerdt and others, 1997, Bilotti and Suppe, 1997, 1999; 

Watters and Robinson, 1997). Wrinkle ridges are common on 

the plains of Venus and the orientation of their networks is 

indicative of the orientation of stresses that form them. The 

stress, in turn, may be indicative of the presence of topographic/

geoid swells at the time of wrinkle-ridge formation.

Young fractures and grabens cutting practically all material 

units of the study area are also seen without any direct association with Devana Chasma rift. These faults typically are long 

(tens to a few hundred kilometers), planimetrically linear or 

slightly arcuate, with their width being a few hundred meters 

to 1 km along the fault (fig. 18). These fractures are broadly 

contemporaneous with the structures of tectonic unit r.

Tectonic History

As a result of geologic mapping several thematic maps 

have been constructed (figs. 25–32) showing the presence and 

dominant trends of structures of different ages from tesseraforming deformation to young rift structures. These maps also 

show the material and tectonic units that host these structures. 

Also on these maps are shown the +0.5 km and +2.5 km altitude 

contour lines correspondingly outlining the position of the base 

and summit of the Beta Regio structural uplift. In cases where 

structures are numerous, the maps show only a representative 

part of them. Where structures are short, they were artificially 

made longer to emphasize their trends.

The major areas occupied by tessera unit and the major 

tessera-forming structures, are shown in figure 25. Except for 

a few small localities within the Guinevere Planitia, the largest 
11

of which is seen in the upper right, the tessera areas are concentrated within the Beta Regio uplift. Structural trends, which 

are mostly outlined by grabens that are part of tessera-forming 

structures, are rather variegated and show neither consistency 

within different tessera subareas nor with the planimetric geometry of the Beta Regio rise.

Major areas occupied by densely fractured plains unit (pdf) 

and the major pdf structures are shown in figure 26. Unlike the 

areal distribution of tessera unit, the pdf areas are concentrated 

within Guinevere Planitia and are rare within the Beta Regio 

rise. The pdf structural trends show a prevalence of northeastern 

orientations and the partial star-like pattern centered approximately at 41° N., 288° E. (fig. 26). No correlation is observed 

between the pdf structural trends and the planimetric geometry 

of the Beta Regio rise.

The major areas occupied by ridged and fractured plains 

unit (pfr), and the relatively broad ridges deforming it, are 

shown in figure 27. Clusters of these broad ridges form the 

ridge belts. The map shows that most pfr localities are within 

the Beta Regio rise and east of it within Hyndla Regio. With 

the exception of the ridges of Iyele Dorsa in northern V–17 

and their continuation to the south, which both trend north, the 

majority of ridge belts and single ridges show a slightly variable 

northwest orientation. No correlation of the ridge and ridge belt 

trends with the Beta Regio rise geometry was observed.

The major areas occupied by tessera transitional terrain (tt) 

and the fractures deforming them are shown in figure 28. The 

map shows that the tt localities are concentrated within the Beta 

Regio rise, Hyndla Regio, and Zirka Tessera, mostly in spatial 

association with areas occupied by the pfr unit. Major trends 

of the tt fractures are often transverse to the trends of the ridge 

belts, but some structures show different trends. No correlation of tt fracture trends and the Beta Regio rise geometry was 

observed.

The areas occupied by fracture belts (fb) and major trends 

of the fb structures are shown in figure 29. A significant part of 

the fb tectonic unit approximately follows the +0.5 km contour 

line. This contour roughly outlines the northern boundary of the 

Beta Regio topographic rise; this relation underscores the correlation of the fracture belts in this part of V–17 and the planimetric geometry of the Beta Regio rise. To the east, the fracture belt 

trend changes its orientation so that it becomes perpendicular 

to the base of the Beta Regio rise. Another cluster of fb structures approximately perpendicular to the base of Beta Regio is 

in the northwestern part of the quadrangle (Dodola Dorsa). The 

fb structures outline all four coronae of the quadrangle: Rauni, 

Urash, Emegen, and Blathnat. The fb structures are also part of 

the radiating structures centered at Wohpe Tholus.

The areas occupied by wrinkle-ridged regional plains (psh

+ pwr) and the major trends of wrinkle ridges are shown in 

figure 30. As noted, the psh unit crops out mostly within the 

Beta Regio rise, whereas the pwr unit is widespread outside 

Beta Regio. Orientation of trends of wrinkle ridges varies 

significantly within the quadrangle. North of Beta Regio the 

region within the Guinevera Planitia wrinkle-ridge trends show 

some parallelism with the orientation of the base of northern 

Beta Regio. But in other places they show no obvious relation 

with the planimetric geometry of the Beta Regio rise: along 

with orientations being parallel to the Beta Regio outlines, there 

are similar numbers of orientations normal and oblique to them. 

In this respect Beta Regio rise differs significantly from several 

large topographic rises (for example, Western Eistla) around 

which the wrinkle-ridge networks show an alignment parallel to 

the rise boundaries (Basilevsky, 1994; Bilotti and Suppe, 1999).

Areas occupied by the rifted terrain tectonic unit (r) and 

major post-regional-plains faults are shown in figure 31. Shown 

also are areas occupied by the post-regional-plains units ps

and pl. The map shows that unit r is in the northeast axial zone 

of the Beta Regio rise and that the faults feathering from unit 

r zone show northwestern and northeastern trends radiating 

to the north from Rhea and Theia Montes. This observation 

suggests that both rifting and the Beta Regio uplift are parts 

of the same process. In the northern part of the quadrangle a 

significant number of the young (post-regional-plains) faults 

radiate around Wohpe Tholus. Within the quadrangle there are 

also young faults that show no obvious association with either 

the Beta Regio uplift or with the radiating feature centered at 

Wohpe Tholus, but they are not abundant. In the areas where 

the young pl and ps lavas were observed, young faults are often 

present. This is especially typical for Theia Mons. However, 

young faults of Rhea Mons and most other areas show little if 

any association with young lavas.

Individual types of structures shown in figures 25 to 31 are 

combined in figure 32. This figure shows that the V–17 area is 

dominated by the Beta Regio uplift in the structural sense. It is 

very prominent in topography and is more than +5 km above the 

neighboring Guinevere Planitia. In its structural pattern the Beta 

Regio uplift is outlined by the Devana Chasma rift zone and by 

the fracture belts of Agrona Linea around its northern base.

Other structures of the area are significantly smaller than 

the Beta Regio uplift. Figure 32 shows several centers of radiating fractures, all mapped earlier by Ernst and others (2003). 

The most prominent are the following four, centered at 34.5° 

N., 293.5° E.; 39° N., 277° E.; 40° N., 279.5° E., 42° N., 287.5° 

E. The first three of these are part of the fracture belt. The 

fourth one, is centered at Wohpe Tholus, is composed of several 

generations of structures. Its northeast and southeast sectors 

have abundant faults associated with pdf. Its southwest sector 

is partly made of structures associated with fb. Young, postregional-plains structures radiate in almost all directions.

Swarms of ridge belts trending mostly northwest and going 

through the Beta Regio uplift with no alignment with it, as 

well as swarms of wrinkle ridges, are also shown in figure 33. 

The wrinkle ridges are mostly of variable orientations, except 

at the very northern part of V–17, where south-to-southwest 

trends dominate. Trends of tt, pdf, and t structures are present in 

relatively small windows, and they appear rather variable with 

almost no orientation heritage with time.

Geologic History

Eight material units, two of which are subdivided, and 

three tectonic units were identified and mapped. These material units and structural units r and fb are essentially the same 

as units identified and mapped by other researchers in other 
12

regions of Venus. Structural unit tt earlier identified by Ivanov 

and Head (2001a) was mapped here for the first time. Although 

other researchers often used unit names different from the V–17 

names, the inter-region (inter-quadrangle) unit correlations are 

not difficult (see summary of the unit inter-region correlations 

in Basilevsky and Head, 2000). A unique aspect of the V–17 

region is the presence within it of three different members of 

plains with wrinkle ridges (pwr1, pwr2, and pwr3). In most 

other regions of Venus there are only two members correlative 

to our pwr1 and pwr2 (see for example, Basilevsky and Head, 

2000). In some subareas, however, for the reasons described 

above, correspondence of the observed pwr material with either 

of these subunits could not be found, so the fourth subunit was 

introduced: undivided pwr material (pwru).

Among the impact crater materials (c), three subunits of 

different ages (c1, c2, and c3) have been distinguished. This 

was accomplished based on the degree of degradation of the 

crater-related radar-dark haloes (Basilevsky and Head, 2002a; 

Basilevsky and others, 2003) and using the analyses of age 

relations between craters and other units and structures. This 

approach provided the possibility to date semi-quantitatively 

several geologic events of the region. For example, the crater 

Deken (fig. 18) has a faint associated radar halo, which suggests it formed within the first half of the post-regional-plains 

time period. Southwest of the crater its ejecta outflow buries an 

adjacent graben and is also cut by another graben, both of which 

radiate from the stellate structure (astrum) centered at Wohpe 

Tholus. These relations suggest that at least part of these faults 

formed during this time interval. Another fault that is part of 

this structure cuts the crater Zvereva, which has an associated 

prominent dark halo. The observation that this fault cuts crater 

Zvereva implies that faulting forming this astrum continued into 

the second half of the post-regional-plains time. Deformation of 

the ejecta outflow of the crater Sanger (which has a prominent 

radar-dark halo) by faults branching from the Devana Chasma 

rift suggests that rifting activity occurred during the second part 

of post-regional-plains time.

The general time sequence of units mapped within V–17 is 

the same as in other regions of the planet, with tessera material (t) at the bottom of the stratigraphic column and materials of the lobate (pl) and smooth (ps) plains at the top. The 

abundance of some units and structures as well as the presence 

of the Beta Regio topographic rise are what make the V–17 

quadrangle different from many other regions of Venus. Within 

the V–17 quadrangle, the abundance of unit pwr (approximately 

31 percent) is about half the global abundance of this unit, 

whereas abundance of unit psh (approximately 26 percent) is 

about twice the global abundance (Basilevsky and Head, 2000). 

Within V–17, the tectonic unit tt, tessera transitional terrain 

(approximately 10 percent), is abundant, whereas in the regions 

mapped by Ivanov and Head (2001a) it is rather rare. Similarly, 

tectonic unit fb (approximately 9 percent) is characterized by 

an abundance 2 to 3 times greater than its global abundance 

(Basilevsky and Head, 2000). The presence of the Beta Regio 

structural uplift reflects the activity of a large mantle plume, 

which is responsible not only for the topographic rise but also 

for Theia Mons pl volcanism and the localization of the Devana 

Chasma rift as well as the Agrona Linea fracture belts.

Summarized in the following paragraphs are the results 

of the geologic analysis and mapping with emphasis on the 

geologic history. Tessera material (t), the oldest material unit 

of the area, is so heavily deformed by tectonism that its lithologic/petrologic nature can not be morphologically recognized. 

The morphology of tessera terrain within V–17, as elsewhere, 

implies intensive contractional and extensional deformation (see 

for example, Barsukov and others, 1986; Basilevsky and others, 

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

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

Gilmore and others, 1997). Structural trends of tessera-forming 

deformation are variegated, suggesting local rather than regional 

control of geometry of stresses responsible for deformation. The 

major areas where tessera terrain is observed are in the southern 

part of V–17, but smaller islands of tessera are also seen in the 

north among the younger units (fig. 25). These observations 

suggest that tessera material may be present everywhere in the 

quadrangle underlying the younger material units.

Next in time sequence is the material of densely fractures 

plains (pdf). If one removes the fracturing, the unit represents 

a plains-forming material. This was the basis on which Basilevsky and Head (1998, 2000) suggested that the pdf material 

was primarily mafic lavas. The fracturing in pdf is dense, probably extensional, and may also be characterized by local shear. 

Fracturing is subparallel within areas tens of kilometers across, 

and changes orientations within the largest outcrops that are 100 

to 300 km across. This observed change in orientation, as in the 

case of tessera-forming deformation, suggests local rather than 

regional control of geometry of stresses responsible for deformation. The structural pattern of the pdf unit is different from 

that of the t unit and this difference implies a significant change 

in deformation style. Major areas where the pdf unit is observed 

are concentrated in the northwestern part of the V–17 quadrangle. Smaller outliers of the unit are seen, however, in other areas 

of the quadrangle (fig. 26), so one may infer that the densely 

fractured plains material is rather widespread in the quadrangle 

underlying the younger material units.

The next-youngest unit, material of fractured and ridged 

plains (pfr), is typically deformed by broad contractional ridges 

that form ridge belts. This deformation is modest, so there is no 

doubt that the unit consists of a plains-forming material. Ignoring differences in deformation styles, the pfr and pwr materials 

appear very much the same, and this similarity was the basis for 

Basilevsky and Head (1998, 2000) to suggest that these units are 

basaltic lavas. Trends of ridges in pfr, although variable, show a 

certain consistency, suggesting regional rather than local control 

of geometry of stresses responsible for deformation. On the 

basis of these relationships, it appears that since the time of pdf

fracturing, the deformation style changed significantly: widespread but locally controlled extensional deformation changed 

into widespread but regionally controlled contractional deformation. The ridge belts of V–17 show no alignment with the 

planimetric geometry of the Beta Regio topographic rise. This 

observation implies that at the time of ridge formation the Beta 

Regio topographic rise either did not yet exist, or was not yet 

high enough to produce topographic stresses affecting the trends 

of ridge belts. The pfr unit is more abundant in the southern half 

of V–17, but its small islands are also seen among the younger 
13

plains in the north (fig. 27). It is inferred that the fractured and 

ridges plains material is rather widespread in the quadrangle, 

especially in its northern part, where it underlies the younger 

material units.

Following pfr ridging there were two deformational 

episodes: extensional fracturing that transformed large areas of 

the pfr unit into tessera transitional terrain (tt) and extensional 

fracturing that formed the fracture belts (fb). The first episode 

appears to be at least partly earlier than the second one. In 

rare cases where the tt unit is in contact with fb (in the eastern 

part of the quadrangle), fb faults cut the tt unit. The tt unit is 

embayed by psh+pwr regional plains. Although the fb unit is 

embayed by these plains, some fb unit faults cut into the plains. 

The tt structural pattern implies little or no predominant stress 

orientation (fig. 28), whereas the fb structures are organized in 

prominent linear belts locally complicated with concentric patterns. The concentric patterns outline the four coronae mapped 

within the V–17 quadrangle. A significant number of fb structures are in alignment with northern base of the Beta Regio rise 

(fig. 29). The tt structural pattern shows no alignment with the 

Beta Regio rise geometry.

Next in time was the emplacement of the shield plains unit 

(psh). The unit morphology suggests that it was formed when 

mafic lavas erupted from numerous spatially scattered edifices 

(Head and others, 1992). Compared to pfr-forming volcanism, 

which primarily produced morphologically smooth plains, the 

psh eruption style is quite different. Shield plains are typically 

wrinkle ridged but the wrinkle ridge network is usually a part of 

the pwr plains emplaced later. Within the V–17 quadrangle, the 

major areas of the psh unit are within the Beta Regio rise and 

are associated with fracture belts and densely fractured plains. 

The psh plains typically underlie the younger pwr, pl, and ps

units but it is not clear how widespread the unit is beneath them. 

The abundance of the psh unit within V–17 is about twice its 

global abundance. Ivanov and Head (2001a) interpreted this 

relationship to mean that the Beta Regio rise had reached sufficient elevation by the end of the time of emplacement of unit 

psh so lavas of unit pwr-flooded lows around the regional high, 

preferentially preserving the earlier psh unit. Alternatively, it 

may be at least partly due to more favorable thermal environment for the formation of the shield fields within the Beta Regio 

rise and fracture belts.

The younger member of the psh+pwr suite, plains with 

wrinkle ridges (pwr), consists of three members that form a 

stratigraphic sequence: pwr1, pwr2, and pwr3. Unit pwr1 is 

composed of the relatively dark primarily smooth material (fig. 

12), and it is considered part of the volcanic plains (see Head 

and others, 1992). Its volcanic nature is inferred on the basis 

of its smooth plains-like surface and embayment relations, 

although it has no visible eruption sources or flow-like features 

except the Omutnitsa Vallis channel (fig. 13), which belongs to 

category of features interpreted to be formed by lava flow and 

thermal erosion (Baker and others, 1992, 1997). The volcanic 

origin of the suite of pwr members is strengthened by the morphology of unit pwr2, which forms extensive relatively radar 

bright flows (fig. 12). Unit pwr3 consists of relatively radar dark 

material and, as with unit pwr1, does not show obvious morphologic evidence of volcanic sources and features. The abundance 

of the pwr1 and pwr2 members is about the same (approximately 10.5 percent), but keeping in mind that subunit pwr2 is 

almost certainly underlain by subunit pwr1, one can conclude 

that areas influenced by volcanic floods during emplacement of 

unit pwr2 became significantly smaller compared to emplacement of unit pwr1. The very small area of subunit pwr3 appears 

to continue this trend.

Unit pwr is deformed by wrinkle ridges whose networks 

form topography on the psh+pwr suite that is embayed and 

overlain by the younger units pl and ps. Wrinkle ridges were 

formed as a result of modest contractional deformation (Plescia, 1991; Watters, 1991; Solomon and others, 1992; Banerdt 

and others, 1997, Bilotti and Suppe, 1997, 1999; Watters and 

Robinson, 1997). Within the V–17 quadrangle they form a 

single network that deforms the psh unit and the pwr members 

with no evidence of different generations of ridges separated by 

the material (members) units. The orientation of wrinkle ridges 

within the V–17 quadrangle is generally not in alignment with 

the planimetric geometry of the Beta Regio rise. This observation implies that at the time of wrinkle ridging, the Beta Regio 

topographic rise either did not exist, or it was not high enough 

to produce topographic stress sufficient to influence the trends 

of ridge belts. The second option looks preferable because 

the fracture belts that formed earlier than the wrinkle ridges 

already show alignment with northern base of the Beta Regio 

rise.

Emplacement of the suite of smooth (ps) and lobate (pl) 

plains was next in time. The morphology of both of these 

material units suggests that they were formed from eruption 

of mafic lavas (see Head and others, 1992). In the case of the 

smooth plains these were eruptions of small volumes of very 

liquid lavas penetrating into narrow faults and gaps. This type of 

volcanism seems to be a continuation of the volcanic style typical of subunit pwr3. Eruptions of lavas that form lobate plains 

are mostly associated with the Theia Mons volcano. These were 

voluminous eruptions that formed rather extended fields of 

relatively radar-bright lavas. This partly resembles the volcanic 

style typical of subunit pwr2. A few fields of unit ps are superposed by the impact craters Truth and Nalkovska, which have 

faint radar-dark haloes. This characteristic implies that these 

lava fields were emplaced within the first half of post-regionalplains time. A similar age constraint is seen for the lobate plains 

lavas, superposed by the ejecta of the crater Tako, which has 

a faint associated halo. These observations, however, do not 

exclude the possibility that pl and ps volcanism continued into 

the second half of the post-regional-plains time.

Following the episode of contractional wrinkle ridging, and 

generally contemporaneous with the emplacement of units pl

and ps within the mapped area, there was a phase of extensional 

tectonism probably extending up to the present time. During this 

phase, the Devana Chasma rift zone and the linear extensional 

faults not directly related to the rift were formed. The Devana 

Chasma rift zone coincides with the north-trending axis of the 

Beta Regio rise, which suggests the rise and the rift formed 

as part of a single process. No observations suggest how soon 

the rifting started after the wrinkle ridging phase. Deformation 

of the ejecta outflow of the clear-halo crater Sanger by faults 

feathering from the Devana Chasma rift, however, suggests 
14

that the rift was active at least for some time within the second 

part of the post-regional-plains period. Results of geophysical 

modeling suggest that the Beta Regio uplift continues today (see 

Leftwich and others 1999; Vezolainen and others, 2003, 2004).

Within the V–17 quadrangle there are 25 impact craters. 

One of them, Aigul, formed prior to the emplacement of the 

shield plains and perhaps even earlier, before the dense fracturing of pdf material. The remaining 24 craters are superposed on 

the regional plains and the younger units. Based on the degree 

of preservation of crater-associated radar-dark haloes, one can 

conclude that twelve craters were formed within the first half 

of the post-regional-plains time, and that the remaining twelve 

craters were formed within the second half of this time period. 

Three splotches identified within the quadrangle appear as dark 

as the clear halo associated with the twelve younger craters and 

are probably of the same age.

In summary, with the exception of impact crater materials, 

the material units of this area are primarily composed of mafic 

lavas. For material of densely fractured plains, this statement 

is mostly a hypothesis, but for units pfr and pwr1 it is very 

probable and for all other units it is obvious. The style of the 

volcanism changed with time. It is not possible to say anything 

certain about the volcanism that formed material of the densely 

fractured plains, except that it was probably plains-forming. 

Judging from the similarities described of the pfr and pwr1

materials, one can conclude that the first was emplaced in 

vast plains-forming lava floods. This was followed by a phase 

of volcanism of very different style: fields of relatively small 

volcanic shields. Then, with some overlap, there was again a 

phase of vast lava floods. During emplacement of unit pwr2, the 

areal extent of the plains-forming floods shrank, and it became 

even more localized during emplacement of unit pwr3. The 

subsequent suite of lobate and smooth plains formed generally 

simultaneously with each other, but the styles of volcanism that 

formed them were different; often extensive lobate flows formed 

the lobate plains and very low shields formed small smooth 

fields, correspondingly.

By subdividing sequences of lavas into mappable units and 

unit suites as well as assessing their relationships to structures, 

the nature of deformational phases and their intensity can be 

assessed. The intensity of deformation obviously decreased with 

time, from very intensive tessera- and pdf-forming deformation 

to moderately intensive deformation that formed ridge belts and 

tt-faulting on unit pfr, and then the wrinkle ridge network on the 

suite of psh+pwr units plains. During the post-regional-plains 

time, there was a lack of globally distributed deformation. 

Deformational belts within the quadrangle can be traced subsequent to post-pfr time, first fracture belts and then the Devana 

Chasma rift zone with its branches. Rare but extensive linear 

faults formed during the post-regional-plains time, part of them 

as late as the activity associated with astrum centered at Wohpe 

Tholus.

The large-scale topography of the mapped area since the 

emplacement of the densely fractured plains probably consisted 

of two components: hilly plains in the north and relatively low 

uplands to the south. The signatures of development of the Beta 

Regio uplift in the southern part of the quadrangle are distinguishable since post-pfr time (fracture belts of the Beta north 

base), but significant growth of the Beta Regio rise occurred 

during the post-regional-plains time and perhaps it is ongoing.

Acknowledgements

Thanks are extended to Mikhail Ivanov and James Head 

for detailed discussion about regional and global units and relations. I particularly appreciate the helpful comments and discussions that occurred during the annual Venus Mappers meetings. 

The detailed map reviews by Kelly C. Bender and John E. Guest 

were very helpful. Financial support from the NASA Planetary 

Geology and Geophysics Program (Grant NAGW-5023 to JWH) 

is gratefully acknowledged.

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19

Figure 3. Examples of impact craters in the Beta Regio quadrangle: A, The crater Zvereva (D (diameter) = 

22.9 km, 45.36° N., 283.12° E.) with a clear radar-dark halo and a radar-bright hummocky ejecta; B, The 

crater Daphne (D = 15.5 km, 41.3° N., 280.4° E.) with a clear radar-dark halo and medium-bright ejecta 

outflows; C, The crater Wazata (D = 13.9 km, 33.6° N., 298.3° E.) with a faint halo; D, The crater Balch (D 

= 40 km, 29.9° N., 282.9° E.) with no halo. The crater Balch is cut by grabens of the Devana Chasma rift. 

Sizes of images are about 115 by 115 km for figure parts A, B, and D, and 70 by 70 km for figure part C.

A B

C D

0 20 KILOMETERS

0 20 KILOMETERS 0 20 KILOMETERS
20

0 20 KILOMETERS

Figure 4. Area of plains with wrinkle ridges on the northeastern flank of Beta Re gio topographic rise. This 

left-looking image, centered at 32° N., 295° E., shows a small volcanic shield (1) and wrinkle ridges (2), both 

illuminated from the left. Near a prominent wrinkle (marked 2) there is a radar-dark mantle with diffuse 

boundaries (marked 3). Accumulations of radar-dark material are also seen at the western base of several 

wrinkle ridges (marked 4). Size of image is about 70 by 70 km.

1

2

3

4

4

4
21

Figure 5. Signatures of downslope mass movement. Top: Part of Magellan F-Map image, centered at 30.4° 

N., 283.3° E., showing the western slope of the north-trending graben (white arrows mark upper edge of the 

slope) with downslope trending grooves in the upper part of the slope and accumulations of relatively bright 

material (talus?) in the lower part of it. Bottom: Part of the TV panorama taken by the Venera 9 lander.

Decimeter-sized rock fragments are on the steep slope dipping towards the image top. The T-shaped device 

in the lower right is 40 cm across.

0 20 KILOMETERS

N Magellan

Venera 9
22

pwr

psh psh

psh

t

t

0 20 KILOMETERS

Figure 6. Area of tessera terrain (t) embayed by shield plains (psh) and plains with wrinkle ridges (pwr). 

Image centered at 34.5° N., 275.5° E. Size of image is about 105 by 105 km.
23

psh

psh

pdf

pdf

pdf

pdf

0 20 KILOMETERS

Figure 7. Densely fractured plains (pdf) locally embayed by shield plains (psh). This image is centered at 

42.3° N., 291.5° E. and is part of Lachesis Tessera, which contrary to its name consists mostly of the unit pdf, 

not tessera terrain. Image centered at 42.4° N., 298.5° E. Size of image is about 75 by 75 km.

psh

psh

psh

psh

psh

psh

pdf

pdf

t

t

t

0 10 KILOMETERS

Figure 8. Densely fractured plains (pdf) that embay tessera terrain (t). Tessera is dominated by two transversal sets of structures whereas unit pdf is dominated by only one set; this distinction makes it possible to draw 

a boundary between them. Both pdf and t units are locally embayed by the shield plains (psh). Image 

centered at 44.2° N., 294.4° E. Size of image is about 55 by 55 km.
24

psh

t

t

psh

pwr

pfr

pfr

0 20 KILOMETERS

Figure 9. Fractured and ridged plains (pfr) embayed by shield plains (psh) and embaying tessera terrain (t). 

Tessera structures do not extend into unit pfr. Unit pfr is deformed by relatively broad (3–5 km) ridges. Image 

centered at 30.1° N., 272.4° E. Size of image is about 145 by 145 km.

pfr

pdf

pdf

psh

psh

psh psh

pwr

pwr

pwr

0 20 KILOMETERS

Figure 10. Fractured and ridged plains (pfr) embaying densely fractured plains (pdf). Both pfr and pdf units 

are embayed by pwr and psh materials. Image centered at 49.6° N., 294.2° E. Size of image is about 145 by 

145 km.
25

psh

pwr

0

Figure 11. Shield plains (psh) and pwr plains on the north-eastern flank of Beta Regio rise. The right figure 

shows an enlargement of part of the image with shields superposed on wrinkle ridges (labeled 1 and 2) and 

deformed by wrinkle ridges (labeled 3 and 4). Image centered at 32.8° N., 292.9° E.

2

1

4 3

20 KILOMETERS

pwr1

pwr1

pwr2

0 20 KILOMETERS

Figure 12. Member 1 (pwr1) and member 2 (pwr2) of plains with wrinkle ridges of Guinevere Planitia. 

Image centered at 48.1° N., 282.9° E. Size of image is about 75 by 75 km.
26

pwr

fb

0 20 KILOMETERS

Figure 13. The northeastern part of the 200-km-long Omutnitsa Vallis canali at the northeastern flank of 

Beta Regio rise. It is cut into pwr plains material. The plains and canali are both deformed by wrinkle ridges. 

White arrows show places of canali divergence, black arrows show where canali are deformed by wrinkle 

ridges. Image centered at 33.3° N., 292.5° E. Size of image is about 70 by 70 km.

pwr2 pwr2

pwr2

pwr2

pwr2

pwr2

pwr2

pwr2 pwr2

pwr2

pwr2

pwr2

pwr3

pdf

pdf

pdf

0 20 KILOMETERS

Figure 14. Member 3 of plains with wrinkle ridges (pwr3) among fields of pwr2 material. Image centered 

at 41.6° N., 294° E. Size of image is about 145 by 145 km.
27

psh

ps

ps

ps

ps

ps

fb

fb

0 20 KILOMETERS

Figure 15. Small fields of smooth plains (ps) among the shield plains (psh). Image centered at 40.3° N., 

285° E. Size of image is about 145 by 145 km.

psh

psh

psh

pwr

pl

0 20 KILOMETERS

Figure 16. Lobate plains material (pl) on the northwestern slope of Theia Mons. Pl lavas overlie and embay 

units psh and pwr. Image centered at 28.3° N., 280.2° E. Size of image is about 145 by 145 km.
28

psh

0 10 KILOMETERS

Figure 17. The crater Aigul, whose rim (marked by arrows) is deformed by northeast-trending fractures 

similar to those in unit pdf and the northwest-trending fractures similar to those in unit fb. Crater appears 

embayed and partly flooded by the psh material that relates it to unit c1 (see table 1 for explanation). Image 

centered at 38.2° N., 280.4° E. Size of image is about 35 by 35 km.

pdf

pdf

pdf

pdf

pdf

pwr

pwr

t

t

t

ci2

cf2

cf2

ch2

pwr

0 50 KILOMETERS

Figure 18. The crater Deken with its faint radar-dark halo (denoted by dotted areas) that relates it to unit c2

(see table 1). The northern part of the crater floor is deformed by wrinkle ridges, whose morphology and 

orientation are similar to those wrinkle ridges of the surrounding pwr plains. Dashed lines show the location 

of grabens. Southwest of the crater its ejecta outflow buries one of the graben and is cut by another graben. 

Image centered at 47.1° N., 288.4° E. Size of image is about 260 by 260 km.
29

pfr

psh

Hiromi

Letitia

Sanger

tt

t

h

ci3

cf3

cf3

ch3

0 50 KILOMETERS

Figure 19. The crater Sanger whose ejecta outflows are cut by faults (shown in white boxes) branching from 

the Devana Chasma rift zone. The faults are marked by black arrows in the inset figure. This crater has a 

prominent radar dark halo that classifies its materials as unit c3 (see table 1 for explanation of c1, c2, and c3). 

Materials of the crater Sanger are divided into three facies: intracrater materials (ci3), hummocky ejecta 

(ch3), and ejecta outflows (cf3). Although the potential halo of the crater Letitia is not seen on the 

background of ejecta and halo of Sanger, Letitia is classified as c3 because it is superposed on Sanger’s 

ejecta. The crater Hiromi is classified as c2 because it has no noticeable radar-dark halo. Image centered at 

33.8° N., 288.5° E. Size of image is about 300 by 300 km.
30

pwr

pdf

psh

psh

psh

psh

psh

psh

psh

psh

psh

pwr tt

tt

pfr

0 20 KILOMETERS

Figure 20. Tessera transitional terrain (tt) formed as a result of fracturing of the material units pfr (top) and 

pdf (bottom). All three units, tt, pfr and pdf, are embayed by pwr and psh plains. Images centered at 27° N., 

297.2° E. and 46.5° N., 294.5° E., correspondingly. Size of images is about 145 by 145 km.
31

pwr

fb

0 20 KILOMETERS

Figure 21. Fracture belt (fb) of Shishimora Dorsa in contact with pwr plains. The pwr plains embay most of 

the fb fractures but some fractures cut pwr material. Image centered at 38° N., 298.2° E. Size of image is 

about 145 by 145 km.

pwr

pwr pl

r

r

pwr

psh

psh

0 20 KILOMETERS

Figure 22. Part of the rifted terrain unit (r) on the northeastern slope of Theia Mons. Fractures and grabens 

of the r unit cut all material units (psh, pwr, and pl) of the area shown here. Image centered at 25.9° N., 

285.1° E. Size of image is about 75 by 75 km.
32

0 20 KILOMETERS

Figure 23. Tessera terrain with a local arcuate to ring-like structural pattern (arrows show two ring-like structures) on the southeastern flank of Rhea Mons. Image centered at 31.1° N., 285.3° E. Size of image is about 

110 by 110 km.

psh

pdf

0 20 KILOMETERS

Figure 24. A broad ridge (denoted by arrows) deforming material of the densely fractured plains (pdf). The 

ridge is very similar to those deforming unit pfr. The pdf unit in the left part of the image is deformed by 

grabens. Unit pdf and most of its structures are embayed by the material of unit psh. Image centered at 46.5° 

N., 296.7° E. Size of image is about 80 by 80 km.
33

Table 1. List of impact craters of the V–17 Beta Regio quadrangle, Venus. Coordinates and diameters (D)

are from Schaber and others (1998)

[WR, wrinkle ridges; F, young post-regional-plains fractures; halo types are: CH, clear radar-dark halo; FH, faint halo; NH, no halo; Obs, potential halo obscured 

by ejecta of other crater. fract., pdf-type fractures. Geologic ages of craters described in “Geologic History” section of pamphlet.]

No. Name

Latitude

(deg)

Longitude

(deg)

Diameter

(km) Superposed on Superposed by

Halo

type

Geol.

age

1 Esmeralda 48.44 296.6 22.9 pdf, psh, pwr nothing CH c3

2 Deken 47.13 288.48 48 t, pdf, pwr, F WR FH c2

3 Samantha 45.56 281.68 16.9 pwr, WR nothing FH c2

4 Zvereva 45.36 283.12 22.9 pwr F CH c3

5 Unnamed 43.8 290.5 1.4 pwr, WR, F nothing FH c3

6 Daphne 41.3 280.4 15.5 fb, psh nothing CH c3

7 Cholpon 40.03 290 6.3 pdf, pwr, F nothing CH c3

8 Unnamed 39.8 289.8 1.3 pdf nothing NH c3

9 Anya 39.5 297.8 18.1 pwr nothing CH c3

10 Lenore 38.69 292.2 15.5 pwr nothing CH c3

11 Sasha 38.34 277.79 4.6 psh nothing FH c2

12 Aigul 38.2 280.4 6 pdf? pdf fract.,

psh

NH c1

13 Lida 36.6 273.9 20.3 fb, psh nothing CH c3

14 Hiromi 35.21 287.3 6 pfr, psh F NH c2

15 Letitia 34.54 288.66 17.5 psh, Sanger CH nothing Obs c3

16 Sanger 33.77 288.56 83.6 t, psh, pwr r CH c3

17 Wazata 33.6 298.3 13.9 tt, pwr nothing FH c2

18 Balch 29.9 282.91 40 psh r NH c2

19 Truth 38.68 287.75 47.3 t, pdf, pwr,

WR, ps

nothing FH c2

20 Nalkowska 28.14 289.95 22.2 psh, pwr, ps nothing FH c2

21 Raisa 27.5 280.3 13.5 pwr? pl FH c2

22 Unnamed 27.3 277 3 psh nothing CH c3

23 Degu 27.3 289.8 5.5 psh, pwr nothing FH c2

24 Olga 26.1 283.8 15.5 pwr, r r CH? c2

25 Tako 25.11 285.27 10.7 psh, pl nothing? FH c2
34

Table 2. Percentage of unit 

areas in the V–17 quadrangle.

Unit Percent of area

t 5.11

pdf 4.67

pfr 5.15

psh 26.15

pwr1 10.58

pwr2 10.61

pwr3 0.19

pwru 9.36

all pwr units 30.74

pl 5.46

ps 0.15

cu 0.99

tt 10.34

fb 8.78

r 2.46

Total of units 100