2012

U.S. Department of the Interior

U.S. Geological Survey

Prepared for the National Aeronautics and Space Administration

Geologic Map of the Hecate Chasma Quadrangle (V–28), Venus

By Ellen R. Stofan, John E. Guest, and Antony W. Brian

Pamphlet to accompany

Scientific Investigations Map 3163

75°

50°

25°

75°

25°

–25°

0°

50°

0°

180° 210° 240° 270° 300° 330° 360°

–25°

–50° –50°

–75° –75°

V–1

V–29 V–30 V–28

V–40

V–62

V–41

V–27

V–26

V–15

V–14

V–16

V–39 V–42

V–18

V–51 V–54

V–17

V–52 V–53

V–60

V–6

V–5

V–19

V–50 V–55

V–31

V–38 V–43

V–7

V–59 V–61
This page intentionally left blank
i

Contents

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

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

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

Mapping Techniques ....................................................................................................................................2

General Geology ............................................................................................................................................2

Mappable Units ....................................................................................................................................2

Tessera Material .........................................................................................................................2

Plains Material ............................................................................................................................2

Volcanic Edifice and Flow Material .........................................................................................4

Corona Material ..........................................................................................................................5

Crater Material ............................................................................................................................7

Surficial Material .................................................................................................................................7

Structure ................................................................................................................................................7

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

References Cited ...........................................................................................................................................9

Tables

1. Coronae of V–28 .....................................................................................................................................12

2. Impact craters of V–28 ..........................................................................................................................12

Figures

1. Magellan topographic map of quadrangle V–28, extending from lat 0°–25° N., long

240°–270° E. (map sheet)

2. Magellan RMS slope roughness map of quadrangle V–28, extending from lat 0°–25° N., long 

240°–270° E. (map sheet)

3. Magellan emissivity map of quadrangle V–28, extending from lat 0°–25° N., long 240°–270° E. 

(map sheet)

4. Portion of Hinemoa edifice plains material (unit peH) illustrating high concentration of small 

edifices within the unit, and the closely spaced lineaments that deform the unit (map 

sheet)

5. Edifice field material (unit ef), characterized by small edifices surrounded by radar-dark flow 

deposits (map sheet)

6. The volcano Kono Mons is cut in half by Zverine Chasma; the dashed lines indicate the 

location of the Zverine trough rim (map sheet)
This page intentionally left blank
1

The Magellan Mission

The Magellan spacecraft orbited Venus from August 10, 

1990, until it plunged into the Venusian atmosphere on October 

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

the knowledge of the geological processes, surface properties, 

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

knowledge of the geophysics of Venus by analysis of Venusian 

gravity.

The Magellan spacecraft carried a 12.6-cm radar system to 

map the surface of Venus. The transmitter and receiver systems 

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

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

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

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

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

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

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

these full-resolution data compose the image base used in 

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

selected areas were collected for the vertical polarization sense. 

Incidence angles varied between about 20° and 45°.

High-resolution Doppler tracking of the spacecraft took 

place from September 1992 through October 1994 (mission 

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

gravity observations were obtained between September 1992 

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

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

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

Magellan Radar Data

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

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

scales of several meters and larger can produce quasi-specular 

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

surface is perpendicular to the incident beam. This type of 

scattering is most important at very small angles of incidence, 

because natural surfaces generally have few large tilted facets 

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

ridges or rift zones, where favorably tilted terrain can produce 

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

diffuse echoes from roughness at scales comparable to the radar 

wavelength are responsible for variations in the SAR return. In 

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

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

rapid increase in reflectivity exists at a certain critical elevation 

above which high-dielectric minerals or coatings are thought to 

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

all areas above that critical elevation.

The measurements of passive thermal emission from 

Venus, though of much lower spatial resolution than the SAR 

data, are more sensitive to changes in the dielectric constant 

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

studies of the surface and to discriminate between roughness 

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

the spacecraft, were modeled using the Hagfors expression 

for echoes from gently undulating surfaces to yield estimates 

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

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

have horizontal footprint sizes of about 10 km near periapsis 

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

reflectivity data provide a comparison to the emissivity maps, 

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

which contribute to the quasi-specular scattering component.

Introduction

The Hecate Chasma quadrangle (V–28) extends from lat 0° 

to 25° N. and from long 240° E. to 270° E. The quadrangle was 

mapped at 1:5,000,000 scale as part of the National Aeronautics 

and Space Administration (NASA) Planetary Geologic Mapping 

Program.

Hecate Chasma is an extensive rift system consisting of 

multiple branches (for example, Hamilton and Stofan, 1996) 

that lies in the lowland region of Hinemoa Planitia in the 

northern hemisphere of Venus. Here, we use the term “rift” 

and “chasma” (plural “chasmata”) to designate the trough and 

fracture zones that make up the Hecate system. Lineaments 

within the Hecate rift system that define Hecate, Zverine, and 

Hanwi Chasmata are mapped in red for emphasis. The system 

consists of several rifts and fracture belts, low-lying plains 

units, coronae and numerous small volcanic edifices including 

shields, domes and cones. The three branches of the Hecate rift 

system in this quadrangle are Hecate Chasma (centered at lat 

18.2° N., long 254.3° E.), Zverine Chasma (centered at lat 18.5° 

N., long 271° E.), and Hanwi Chasma (centered at lat 10.5° N., 

long 247° E.). The quadrangle also contains many intermediate to large volcanoes, including Polik-mana Mons and Nazit 

Mons. Eighteen coronae are located in the quadrangle (table 1), 

the largest of which is the 525 km across Taranga Corona, along 

with fourteen impact craters (table 2). Corona maximum widths 

are measured to the outer edge of the annulus (for example, 

Stofan and others, 1992). Lineaments that form the corona 

annulus are mapped in green for emphasis.

The overall topography of V–28 consists of plains located 

slightly below mean planetary radius (MPR, 6051.84, Ford 

and Pettengill, 1992) (fig. 1). The lowest regions are found in 

the rift trough (3.3 m below MPR), and the highest along the 

rift rim (4.3 km above MPR). The regions that are the roughest 

at Magellan radar wavelengths in the quadrangle occur along 

Hecate Chasma (root mean square [rms] slopes >10°), with 
2

most regions being relatively smooth (roughnesses comparable 

to the average Venus surface value of 2.84°, for example, Ford 

and Pettengill, 1992; Campbell and Campbell, 1992; Campbell, 

1995) (fig. 2). Emissivity values in the quadrangle are typical 

of most venusian plains regions, with a range in values for the 

quadrangle of 0.68–0.91 (fig. 3). The highest emissivity values 

in the quadrangle lie at the highest elevations in the quadrangle 

(corona rims and interiors).

Mapping Techniques

Standard planetary geologic mapping techniques (for 

example, Wilhelms, 1972, 1990) were used to construct a geologic map of the V–28 quadrangle. Magellan synthetic aperture 

radar (SAR) data were used for the map base; SAR backscatter in the Magellan data vary primarily as a function of surface 

roughness at the scale of the radar wavelength (12.6 cm), as 

well as the surface topography and intrinsic reflectivity. Magellan altimetry, RMS slope, reflectivity and emissivity data sets 

(figs. 1-3, Pettengill and others, 1992; Campbell, 1995) provide 

additional information on the properties of map units.

Synthetic parallax stereo images with a 10x vertical exaggeration and full-resolution Magellan image mosaics (F-Maps) 

produced by the U.S. Geological Survey (USGS) (both print and 

digital data) were used extensively to identify embayment relations and truncation of structures at contacts, the primary methods by which we determined relative ages of units. In particular, 

embayment relations could be clearly seen in the synthetic stereo 

data. Unit character and boundary locations not resolvable at 

C1-MIDR scale (225 m/pixel) were clearly seen at F-Map scale 

(75 m/pixel) (actual radar resolution is about 120 m). However, 

age relations determined with F-Maps are a function of the 

scale and nature of this radar data; age relations between units 

as well as their mechanism of formation are undoubtedly more 

complex (for example, Zimbelman, 2001). Apparently contradictory stratigraphic relations between major map units (that is, a 

unit appearing to be superposed by another unit in one place and 

superposed on the same unit in another location) were frequently 

found to be caused by the presence of additional subtle units 

only noticeable through digital manipulation of F-Map data.

For flow units tied to a particular source, subunits are 

numbered if stratigraphic relations between them could be 

determined (for example, fNa1–3); if not all units touched and 

therefore age relations are ambiguous, then subunits are lettered (for example, fPoa–c). F-Maps were also used to identify 

volcanic edifices, flow directions, and structures. Small volcanic 

edifices and structures are extremely numerous in this quadrangle, and thus are mapped in a representative fashion (Tanaka, 

1994), with approximately one in ten features shown, although 

less than that in the chasmata troughs due to the close spacing 

of features in those regions.

There are other difficulties in using radar data to construct 

a geologic map (for example, Ford and others, 1993; Hansen, 

2000). Geologic units will only be visible if they have backscatter characteristics distinctly different from the surrounding 

units, or if they can be defined by secondary structural relations 

(that is, embayment of secondary structures in unit 1 by unit 2). 

In plains regions or lava flow fields, younger and older units of 

similar backscatter may be mistakenly incorporated into a single 

unit. If the surface properties of a unit change laterally, potentially its radar signature can also change, and it may be mapped 

incorrectly as two or more units. In addition, structures tend to 

be more readily identified if they are oriented perpendicular to 

the radar look-direction (for example, Stofan and others, 1989). 

Thus, in Magellan data, N–S trending lineaments will tend to be 

well defined, but E–W trending structures are likely to be underrepresented or only weakly represented in the image data unless 

they have associated rough talus slopes. We did use secondary 

structures to help define units, in particular to aid in defining 

boundaries between plains and flow units, although secondary 

structures must be used with caution (for example, Hansen, 

2000).

General Geology

Six types of materials have been mapped in the V–28 

quadrangle: plains, volcanic edifice and flow, corona, tessera, 

crater, and surficial materials. All types of material units occur 

throughout the quadrangle, with the exception of tessera materials, which crop out only in the northwestern part of the mapped 

region. All materials are mapped as units, except for surficial 

material (shown by stippled pattern).

Mappable Units

Tessera Material

Three outcrops of materials with two or more dominant 

fracture and (or) ridge orientations were mapped as tessera 

material (unit t) (Hansen and Willis, 1996, 1998; Hansen, 

2006), following the convention for Venus (Tanaka, 1994), 

while units with a single or very dominant direction of fractures 

were mapped as unit pfH or unit peH. Tessera materials tend 

to be relatively radar-bright or rough at the Magellan radar 

wavelength (12.6 cm), and stand higher than the surrounding 

units (Barsukov and others, 1986). We interpret the tessera 

unit to represent locally older tectonically deformed regions, 

embayed by younger volcanic plains and flows. The outcrops in 

this region are too small to determine if the complex deformation was produced in a single event or multiple events, nor can 

we determine if all of the outcrops formed in the same event. 

Deformation at these fragments is similar to deformation in 

the interior of some coronae; some tessera fragments could be 

kipukas of corona materials, as suggested previously by Hansen 

and Willis (1996). The three outcrops of unit t lie to the north 

of Hecate Chasma and are embayed by unit pA, unit psH, unit 

pcH, unit phH, and unit fTb.

Plains Material

We identified nine plains material units in the Hecate 

Chasma quadrangle (from oldest to youngest): Hinemoa frac-
3

tured plains material (unit pfH), Hinemoa edifice plains material 

(unit peH), Hinemoa uniform plains material (unit puH), Hinemoa hummocky plains material (unit phH), Hinemoa mottled 

plains material (unit pmH), Hinemoa composite-flow plains 

material (unit pcH), Asteria plains material (unit pA), Hinemoa 

smooth plains material (unit psH), and Hinemoa lobate plains 

material (unit plH). Each of the plains units are composed of 

many small plains units of varying age, which are grouped into 

a mappable unit owing to their similarity in geomorphology 

and stratigraphic position relative to other plains units. Some 

of the plains units, including units pfH, peH, and plH, tend to 

crop out as isolated patches of materials. Plains units on Venus 

are interpreted to be volcanic in origin, owing to their similarity to volcanic plains on other planets (for example, Masursky 

and others, 1980; Barsukov and others, 1986), surface chemical 

compositions and images obtained by the Venera landers (for 

example, Surkov and others, 1984), and the lack of water on 

the planet for at least 2–3 billion years (Kasting and Pollack, 

1983) making a sedimentary origin unlikely. All of the plains 

units except unit psH and unit plH are cut by closely spaced 

(<10 km), sinuous lineaments that we interpret to be polygonal 

fractures (for example, Smrekar and others, 2002).

The Hinemoa fractured plains material (unit pfH) is the 

oldest local plains unit in the V–28 quadrangle. It is usually 

high standing, and typically occurs in small patches. We do not 

know if this unit represents a single time stratigraphic unit, or 

is an amalgam of different ages of kipukas of fractured plains. 

Unit peH, Hinemoa edifice plains material, is also typically 

high standing, and is younger than the outcrops of unit pfH

with which it is in contact (which does not include all outcrops 

of unit pfH). Unit peH has a high abundance of small edifices, 

wrinkle ridges and fractures (fig. 4). To determine the relative 

ages of small edifices within the unit, we looked for crosscutting 

relations with secondary structures and superposition relations, 

similar to the method of Ivanov and Head (2004) (their criteria 

1–3, 9, 10–12), and Addington (2001). However, Ivanov and 

Head (2004) relate ages of edifice fields to a unit ‘regional 

plains with wrinkle ridges’, which is not present in this quadrangle. Edifices within unit peH are both superposed on and cut 

by secondary structures. The small edifices deposits may have 

contributed to the formation of this plains unit, but the fact that 

they also superpose secondary structures indicates that their 

formation persisted after formation of the unit (fig. 4). If small 

edifices have mappable deposits, they were grouped into unit ef

(fig. 5, described below). In the neighboring V–40 quadrangle, 

unit peH corresponds to unit f2 (flow materials) (Chapman, 

1999). Unit peH is embayed by units phH, pmH, puH, and 

psH. Based on the lobate boundaries and abundant volcanic 

edifices within this unit, we interpret unit peH to be composed 

of multiple materials of volcanic origin, with the abundant small 

edifices within the unit forming over an unknown time span.

Hinemoa uniform plains material (unit puH) and Hinemoa hummocky plains material (unit phH) are two of the most 

widespread plains units in the V–28 quadrangle. Unit puH is 

relatively homogeneous, with few edifices or fractures, and is 

located primarily in the southeastern portion of the quadrangle. 

The Hinemoa hummocky plains material (unit phH) occurs 

primarily in the western portion of the quadrangle, and includes 

much of the Hecate rift system. Unit phH has a mottled texture, 

is cut by faults from the rifts, and has some flows and edifices. 

Unit puH is embayed by unit phH. Units puH and phH embay 

units peH and pfH. Corona and volcano flow materials superpose phH, which in turn is deformed by lineaments associated 

with Hecate Chasmata. These plains materials are interpreted to 

be volcanic in origin based on the identification of diffuse flow 

fronts within the units and their lobate boundaries.

Hinemoa mottled plains material, (unit pmH) located in 

the southern portion of the quadrangle, tends to be topographically higher than surrounding units. It has abundant small 

edifices and sub-unit-scale flow materials. It may be higher 

standing than surrounding plains units due to volcanic construction or uplift. Along the southern boundary of V–28, unit pmH

contacts correspond to units pd and pl (radar-dark and radarlight plains, respectively) mapped in V–40 quadrangle (Chapman, 1999). Unit pmH superposes units peH and puH, and is 

superposed by flow units associated with a corona and several 

volcanic features.

The Hinemoa composite-flow plains material (unit pcH) 

is located in the northwestern portion of the quadrangle, and 

is composed of multiple small-scale flow materials. Fractures 

associated with coronae and volcanoes cut the unit. Unit pcH

superposes units pfH, pA, and phH and is superposed by unit 

psH and several flow units originating from volcanoes.

Asteria plains material (unit pA), in the northern portion 

of the quadrangle, is cut by faults from Hecate and Zverine 

Chasmata. Unit pA is composed of smaller scale flow materials 

(<100 km across, with indistinct boundaries), and some small 

edifices. Unit pA embays units phH, peH, and pfH, but does 

not come into contact with unit puH. Unit pA is embayed by 

corona and flow materials.

The youngest plains units in the V–28 quadrangle are 

units psH and plH. The Hinemoa smooth plains material (unit 

psH) forms in patches typically hundreds of kilometers across, 

and has a sheet-like or homogeneous appearance. Unit plH

(Hinemoa lobate plains material) occurs in two small (<200 km 

across) patches in the north-central portion of the map, superposed on unit pA. The unit has small edifices, and superposes 

lineaments of Zverine Chasma. Outcrops of units psH and plH

tend to be small (<300 km across), and occur on opposite sides 

of V–28. Units psH and plH are interpreted to be volcanic in 

origin, owing to their typically lobate boundaries and association with edifices. The units are defined based on radar brightness and texture, and therefore outcrops of the same unit may or 

may not have formed at the same time. Unit plH superposes unit 

pA and is not in contact with any other units. Unit psH superposes units phH, pA, and pcH, and is superposed by Leyster 

and Nuriet impact craters, Hecate Chasma flows, and flows 

from a volcano and several coronae.

Plains units in the V–28 quadrangle are interpreted to be 

volcanic in origin (for example, Saunders and others, 1991; 

Head and others, 1992), as most units have lobate boundaries 

and abundant small edifices. Flows and groups of flows comprise each unit, but are not mapped as separate units as their 

boundaries can rarely be closed. Only the smooth and lobate 

plains units (units psH and plH) are sheet-like and homogeneous in appearance. All of the plains units are cut by linea-
4

ments, most of which we interpret to be extensional fractures 

based on their linearity. Few wrinkle ridges occur in V–28, 

being limited to units south of the Hecate rift system, and typically deforming unit peH.

Volcanic Edifice and Flow Material

The Hecate Chasma quadrangle contains a variety of mappable units associated with volcanic landforms including several 

large shield volcanoes (Nazit Mons, lat 22.5° N., long 240.1° 

E.; Polik-mana Mons, lat 24.8° N., long 264° E.; Kono Mons, 

lat 18° N., long 268° E.; and the western half of Xochiquetzal 

Mons, lat 3.5° N., long 270° E.), numerous intermediate volcanoes, abundant small volcanic edifices and a large flow field. 

Few of the units associated with these edifies are in contact 

with each other. The unusually high concentration of volcanic 

features in this quadrangle is consistent with it being located 

within the Beta-Atla-Themis zone, the highest concentration of 

volcanic features on Venus (Crumpler and others, 1997).

Volcanic complex material (unit vc) delineates material 

associated with fourteen unnamed volcanic centers. Unit vc

typically consists of a 5- to 50-km-diameter edifice (caldera or 

topographic high) surrounded by an apron of flow material that 

varies in extent from the edifice summit. Other occurrences of 

unit vc lack a distinct edifice. Unit vc overlies units phH, fPa2, 

pcH, ef, pmH, plH, pfH, peH, fSib, and pA, and is overlain by 

units fAl, fM, fArb, fNT1, psH, and fG. One volcanic center is 

cut by chasma fractures.

Shulzenko Patera material (unit fSh) is associated with a 

60-km-across depression surrounded by flow materials. Shulzhenko Patera material is overlain by Lama Tholus material 

(unit fL) and Aruru Corona materials (units fAra, b), but overlies 

Hinemoa uniform plains material (unit puH).

Edifice field material (unit ef) consists of clusters of small 

edifices with diameters of 5–20 km (for example, Guest and 

others, 1992). The unit is mapped due to its higher concentration of edifices than surrounding units, because it has mappable 

boundaries, and on the assumption that the edifices share a 

common source and (or) are stratigraphically related (fig. 5). 

We are limited in our ability to determine age relations between 

individual edifices within a field as the fields are generally 

lacking in secondary structures; the edifices formed over some 

unknown time period. Each field contains numerous small 

edifices, some only identifiable as pits. Unit ef is overlain by 

units fX, fSib, fAra, and vc and overlies units pfH, plH, pcH, 

and peH. It both overlies and is overlain by unit phH and unit 

pA, demonstrating that this unit is not representative of a single 

time-stratigraphic unit, but represents a morphologic grouping 

of units of differing ages.

Hecate Chasma flow material (unit fH) is mapped in four 

places along the Hecate system. The occurrences consist of 

digitate to sheet-like deposits located at the chasma topographic 

rim that are interpreted to have erupted from fissures associated 

with the chasma. Unit fH overlies units pA, psH, and phH and 

is overlain by units fPb and fGK1–2.

At Nazit Mons (350 km diameter), superposition relations determined from FMap and stereo data permit a sequence 

of flow units associated with the volcano to be mapped (Nazit 

Mons flow material members 1–3, units fNa1–3), although each 

of these Nazit flow units likely represent flow complexes rather 

than individual flows (that is, Stofan and others, 2001a). Flows 

associated with Nazit Mons (units fNa1–2) overlie corona flow 

unit fAc1, as well as plains units pcH, pfH, and phH.

The quadrangle contains a fluctus or flood lava deposit, 

Sobra Fluctus material (unit fSo). The unit lies just to the south 

of the southern branch of Hecate Chasma, and covers approximately 150,000 km2. The material emanated from either fractures associated with the chasma, or from a depression located 

within the unit at lat 5.1° N., long 248° E. The unit consists of 

lobate materials of intermediate brightness, with some darker 

flows along the southern margin. Unit fSo overlies unit phH, 

unit peH, and unit puH and is overlain by flows from Rind 

Corona. The flow deposit is cut by chasma-related fractures. 

Over 200 large flow fields have been identified elsewhere on 

Venus (for example, Roberts and others, 1992; Lancaster and 

others, 1995), and are interpreted to form from lithospheric 

extension accompanied by decompression melting of the mantle 

(Magee and Head, 2001), a likely mechanism for this flow 

deposit owing to its proximity to Hecate Chasma.

Tholi are small domical hills or mountains. Nipa and 

Iaso Tholi have a central vent surrounded by flows of varying 

backscatter, with diameters of 140 and 30 km, respectively. 

Nipa Tholus material (unit fNi) overlies units phH and fAE. 

Iaso Tholus has two mappable deposits: Iaso Tholus material 

members 1 and 2 (units fIa1 and fIa2). Unit fIa2 is superposed 

on unit fIa1, with the flow units superposed on units puH, peH, 

phH, and pmH.

Garbo Patera flow material (unit fG) is associated with a 

75-km-diameter, circular depression surrounded by concentric 

fractures interpreted as a caldera. The flow material extends for 

about 100 km. Unit fG overlies units vc, pmH, and phH, and is 

overlain by another unit vc, and units psH and fM.

Paoro Tholi material is divided into two members (units 

fPa1–2) that are associated with two overlapping shields with 

a diameter of 225 km. Observations of stereo images and full 

resolution radar images indicate that deposits from the eastern 

center (unit fPa2) overlie flows from the western center (unit 

fPa1). However, based on the complex nature of the boundary 

between the two centers, it is likely that they were active simultaneously. Unit fPa1 overlies units peH and fArb; unit fPa2

overlies units peH and puH and is overlain by unit vc.

Polik-mana Mons is a large volcano (600 km diameter) 

situated directly on Hecate Chasma. Associated with the edifice are three units: Polik-mana material members a–c (units 

fPoa–c). Age relations of flow units at Polik-mana Mons are 

difficult to determine, with the exception of unit fPoc, which 

overlies adjacent unit fPoa flows. The flow materials are largely 

superposed on the rift, but unit fPoa flows have been cut by rift 

fractures, suggesting that the volcano formed contemporaneously with the chasma. Flows from Polik-mana Mons overlie 

plains unit pA and unit fH.

Ixtab Mons is an 80-km-diameter topographic edifice with 

a summit caldera, located on the topographic rim of Hecate 

Chasma. Ixtab Mons material (unit fIx) overlies units phH, 

psH, and flows from Hecate Chasma, and is superposed and cut 

by chasma-parallel fractures. Lama Tholus (110 km diameter) 
5

has a central vent surrounded by radiating flow deposits. Lama 

Tholus flow material (unit fL) overlaps flows from Shulzhenko 

Patera (unit fSh) and plains units puH and peH. Flows from 

Lama Tholus are overlain by flows from Aruru Corona (unit 

fArb) and the crater Alina.

The volcano Xochiquetzal Mons (80 km diameter), is 

located outside the quadrangle at lat 3.5° N., long 270° E., but 

has flow units that extend into V–28. Xochiquetzal flow material (unit fX) superposes units puH, plH, ef, and pfH.

Alcyone Tholus is a 70-km diameter intermediate volcano 

with associated flow deposits that lies outside the quadrangle, 

at lat 2° S, long 256.5° E., in quadrangle V–40. Alcyone flow 

material (unit fAl) overlies unit pmH, and is overlain by Miti 

Corona material (unit fM). In the adjacent quadrangle V–40, 

Chapman (1999) mapped these two units as one unit, unit cp4 

(patera materials).

Wyrd Mons (150 km diameter) is a topographic edifice 

with a summit caldera, surrounded by radiating flows, located 

on the topographic rim of Hecate Chasma. Wyrd Mons material 

(unit fW) overlies flows from Taranga Corona (unit fTb), unit 

psH and unit phH, and is both superposed and cut by chasmaparallel fractures.

Serova Patera (60 km diameter) lies to the north of Hecate 

Chasma, and consists of a circular, rimmed caldera surrounded 

by a digitate flow apron. Serova Patera material (unit fSe) overlie flows from Taranga Corona (unit fTb), plains units puH and 

pcH, and the crater Johanna.

The volcano Kono Mons (350 km diameter) is cut by the 

trough of Zverine Chasma (fig. 6). Kono Mons flow material 

(unit fK) overlies unit pA and the crater Baranamtarra. Pajan 

Yan Tholus (80 km diameter) is an intermediate shield with 

central vent surrounded by radiating flow deposits. Pajan Yan 

Tholus material (unit fPY) overlies material from Ak-Ene 

Corona (unit fAE) and units puH and phH.

Some of the volcanic units described above are directly 

superposed on the chasmata, whereas most lie in the plains to 

the north and south of the chasma system. The plains units to 

the south of Hecate Chasma are characterized by an abundance 

of small edifices, particularly in units peH and pmH. Of the 

four large volcanoes in the quadrangle, two are superposed 

directly on the chasma, whereas two lie off the chasma. Formation of the chasma system and volcanism overlapped in time. 

Although it is clear that extension played a role in volcanism 

(for example, Magee and Head, 2001) for flow units along the 

rift such as Sobra Fluctus, the bulk of the volcanic units in this 

region lie to the south of the chasmata.

Corona Material

Eighteen coronae, ranging in maximum width from 125 

to 525 km, are located in the V–28 quadrangle (table 1), as 

well as flows from a nineteenth corona, Miti Corona, located 

outside the quadrangle. Of the eighteen coronae located within 

the quadrangle, ten have associated mappable deposits. Based 

on the classification scheme of Stofan and others (1992), eleven 

are classified as concentric coronae, three are concentric-double 

ring, one is a multiple corona, and three are asymmetric coronae. Most of the coronae (12 out of 18) are located along the 

chasma system, although only six lie directly on the fractures 

and troughs. Some of the coronae (for example, Taranga) have 

associated radial fractures that have been termed novae by 

other workers (Aittola and Raitala, 2005). Coronae topographic 

expression varies; some coronae such as Taranga and Aruru are 

large plateaus, and others, such as Prthivi Corona, are depressions. Few of the material units associated with coronae are in 

direct contact with other corona units, or with similar units (that 

is, all in contact with phH, for example), resulting in difficulty 

in determining how the formation of all of the coronae in this 

quadrangle fits into the overall history of V–28.

The coronae with no mappable deposits have concentric 

fractures that deform units fTb, phH, pA, peH, and pmH. 

These structures are located both along the chasmata and in the 

plains regions surrounding the chasmata. Three of the coronae 

with no mappable units lie along Hanwi Chasma, and all three 

are depressions or rimmed depressions. The feature at lat 0.7° 

N, long 254.8° E. does have structures that cut units peH and 

pmH, but is also partially overlain by flows within these units, 

suggesting that the formation of coronae and the chasma system 

has overlapped in time.

Taranga Corona is a rimmed plateau superposed on Hecate 

Chasma, with extensive flow deposits mapped as Taranga 

Corona material, members a and b (units fTa–b). It is the largest 

corona in the quadrangle, with a maximum width of 525 km. 

Unit fTb overlies tessera material (unit t) and units pfH, phH, 

pcH, and pA. Taranga Corona materials are overlain by GashanKi Corona material (unit fGK1), Prthivi Corona material, and 

units fW and fSe. It is also superposed by Johanna and Beecher 

impact craters. The most extensive unit of Taranga Corona material (unit fTb) may be composed of multiple materials, but much 

of the unit’s character is obscured by faults of Hecate Chasma. 

Similarly, the high plateau of the corona is also intensely 

deformed, and is mapped as a single unit, Taranga Corona material member a (unit fTa) as it has a distinct, mappable boundary 

with Taranga Corona material member b (unit fTb). In places 

unit fTa superposes unit fTb as it embays and superposes secondary structures that cut unit fTb, but along much of the boundary the age relation is uncertain. An apparent volcanic center 

with a small (~10 km across) summit depression interpreted as 

a caldera is located at lat 17° N, long 252.5° E. in the interior of 

Taranga. Although formation of the plateau-shaped topography 

of the corona postdated formation of Hecate Chasma, superposition of chasma fractures on corona-related flows indicate that 

formation of Hecate and Taranga overlapped in time.

Acrea Corona lies in the northwestern corner of the 

quadrangle and consists of a rimmed depression surrounded by 

multiple rings of concentric fractures. Its maximum width is 

500 km. An interior flow unit, Acrea Corona material, member 2 

(unit fAc2), lies in a central topographic low, and is surrounded 

by apparently older, heavily fractured flow unit, Acrea Corona 

material, member 1 (unit fAc1). Some of the fractures cutting 

unit fAc1 are regional fractures while others are related to the 

corona. Unit fAc1 overlies unit pcH and unit pA and is overlain 

by flows from Nazit Mons.

Tari Pennu Corona (200 km maximum width) lies along 

the southern margin of the V–28 quadrangle. It has a few, faint 

concentric fractures and a low, discontinuous topographic rim. 
6

Two flow units are mapped associated with the corona, Tari 

Pennu, material members 1 and 2 (units fTP1–2). Unit fTP2

superposes earlier corona flows (unit fTP1, mapped as corona 

materials in the adjacent quadrangle V–40 (Chapman, 1999)). 

Both corona material units superpose plains units puH and 

pmH.

Nei-Teukez Corona lies in the plains to the south of Hanwi 

Chasma and is a rimmed depression with a diameter of 125 km. 

Flow materials associated with Nei-Teukez Corona are split 

into two units, with a younger interior unit Nei-Teukez, material 

member 2 (unit fNT2) filling the central depression and an outer 

flow unit, Nei-Teukez, material member 1 (unit fNT1). Unit 

fNT1 is overlain by one of the flow units from Sinlaku Corona 

(unit fSib), a volcanic center and unit pmH. Unit fNT1 overlies 

units phH and peH.

Gashan-Ki Corona materials (units fGK1–2) are located 

just to the north of the southern arm of the Hecate rift, Hanwi 

Chasma. Gashan-Ki Corona has a somewhat irregular shape, 

with an outer rim and an irregular raised interior, and has a maximum width of 290 km. A later flow unit (unit fGK2) superposes 

unit fGK1 and is radial to it, and is interpreted to have originated from fractures of the corona. Gashan-Ki materials (units 

fGK1–2) overlie unit fTb, unit fH and unit phH, and are both cut 

by and superpose lineaments associated with Hecate Chasma.

Aruru Corona materials (units fAra–d), located in Hinemoa Planitia to the south of the Hecate and Zverine rifts, are 

extensive radiating sheet-like and digitate deposits associated 

with Aruru Corona. Aruru Corona is a rimmed plateau (450 by 

350 km), with folds on the southwestern margin. A small edifice 

with extensive flow material (unit fArc) is located in the interior 

of the corona. This interior unit is surrounded by extensive 

deposits, Aruru Corona material, member b (unit fArb). Two 

additional corona-associated units were mapped: unit fArd, 

which extends from a source on the flanks of Aruru, and unit 

fAra, a flow radial to the corona that predates fArb. Aruru material unit fAra overlies units puH and fSh, and is overlain by 

fArb. Unit fArb overlies unit fAra, plains units pfH, peH, phH, 

puH, and pmH, and volcanic units fSh and vc. Unit fArb is 

overlain by units psH, fArc, fArd, fL, and fPa1. Units fArc and 

fArd are not in contact with any units other than fArb, which 

they overlie. Studies of the gravity signature of Aruru indicate 

that the corona is not currently active (Kiefer and Peterson, 

2003).

Sinlaku Corona lies just to the south of the junction of the 

Hecate rift and Zverine Chasma. The corona is a 300 km across 

rimmed plateau, although unlike most rimmed coronae, the topographic rim has few associated fractures or ridges. Four units, 

Sinlaku Corona material, members a, b, c, and d (units fSia–d), 

are mapped associated with the corona. The outer deposits of 

Sinlaku Corona are sheet-like, whereas flows from the southern half of the coronae are digitate. Unit fSia is superposed by 

units fSib–d. Unit fSib is overlain by flows from an unnamed 

volcanic center and unit fSid. Sinlaku unit fSib superposes unit 

phH, psH, pmH, pA, and flows from Nei-Teukez Corona (unit 

fNT1). Unit fSic overlies unit fSia; unit fSid overlies unit fSib.

Ak-Ene Corona (maximum width 150 km) has a topographic rim and a flat interior, and lies in the plains south of 

Hanwi Chasma. Ak-Ene Corona material (unit fAE) overlies 

units phH and fTb and puH and is overlain by flows from Nipa 

and Pajan Yan Tholi. Ak-Ene was described as a relatively old 

corona by Aittola and Raitala (2005), but they did not recognize 

the flow deposits surrounding the corona.

The three youngest coronae in the quadrangle are Prthivi, 

Miti, and Rind Coronae. Prthivi Corona (diameter 300 km) is a 

rimmed depression that lies directly on Hanwi Chasma and to 

the east of Gashan-Ki Corona, deforming phH. Prthivi material 

(unit fPr) overlies unit fTb and unit phH. Flows from Prthivi 

are cut by lineaments associated with Hecate Chasma, but flow 

units from the corona superpose other sets of chasma-parallel 

fractures. Three more coronae that are depressions lie along 

Hanwi Chasma to the northeast of Prthivi Corona.

Miti Corona (180 km across) is a corona that lies to the 

south of the quadrangle, at lat 3.5° S, long 259.8° E. Miti 

Corona material (unit fM) superposes units puH, fG, fAl, and 

vc. Rind Corona is a rimmed depression (maximum width 150 

km across) located in the plains south of Hanwi Chasma. Rind 

Corona material (unit fR) superposes units phH and fSo.

In the V–28 quadrangle, six coronae lay directly on the 

chasmata and the other twelve are located near the chasmata 

(<1000 km away). This is similar to Parga Chasma, where 

coronae are found in a high concentration near the chasma but 

not necessarily superposed on it (Martin and others, 2007). 

For those coronae in contact with chasmata in V–28, we find 

evidence from faults and flows associated with Gashan-Ki and 

Prthivi Coronae (described above) that chasma formation and 

corona formation have overlapped in time. Taranga Corona is 

a notable exception, where the corona is superposed on Hecate 

Chasma, and thus formed after formation of Hecate (Hamilton 

and Stofan, 1996). Most, but not all, coronae have associated 

flow units that are younger than the plains in which they lie. 

Few units associated with volcanoes and coronae are in direct 

contact with one another, so very little relative age information 

of the timing of coronae in relation to volcano formation can be 

determined in this quadrangle. Where they are in direct contact, no specific sequence of formation can be determined. For 

example, flows from Serova Patera overlie flows from Taranga 

Corona, but flows from Paoro Tholi overlie flows from Aruru 

Corona. In turn, flows from Aruru Corona overlie Lama Tholus 

and Shulzhenko Patera. However, as it is only the outermost 

flow units that provide these age relations; all of these features 

may have been active concurrently. We interpret the overall 

spatial correlation of coronae and the chasma to indicate a 

related mechanism of formation, although coronae are forming over a broader region (500–1000 km) than Hecate Chasma 

itself (80–300 km), similar to Parga Chasma (Martin and others, 

2007).

The coronae in quadrangle V–28 have a great variation in 

topographic form, typical of most regions on Venus (Squyres 

and others, 1992a; Stofan and others, 1997; Stofan and others, 

2001b). However, it is interesting to note that Hanwi Chasma, 

to the south of Hecate Chasma, has coronae along it that are 

all depressions or rimmed depressions. This consistent pattern 

of corona topography (in this case depressions) along Hanwi 

Chasma was not identified on any of the fifteen branches of the 

Parga rift system (Martin and others, 2007), but may exist at 

other chasmata on Venus.
7

Coronae in this quadrangle also vary greatly in the apparent extent of associated volcanism. Associated volcanism 

includes interior (of the corona rim) and exterior (extending 

from the corona rim) flows and small to intermediate edifices 

located in the center of the corona. On the basis of morphology 

and similarity to flows associated with volcanic edifices, we 

interpret these flows to be volcanic in origin. Previous workers have determined that coronae in rift zones tend to have 

increased amounts of flow, interpreted to be the result of the 

intersection of upwelling with an extensional zone (Magee and 

Head, 1995). We find that coronae with high amounts of associated flows (Sinlaku, Aruru Coronae) are just as likely to lie off 

the rift as on (Taranga Corona), and many of the coronae along 

the rift have moderate to low associated flows (Prthivi Corona 

and several unnamed coronae). However, since we can only 

map areal extent and not true volumes of flows, our ability to 

define the actual amount of volcanism at an individual corona is 

limited.

Crater Material

There are fourteen impact craters located in the V–28 

quadrangle (unit c) (table 2). Two of the craters, Nuriet and 

Higgins, have very unusual morphology, with an indistinct, 

irregular crater and outflow-like deposits. Eleven have at least 

partial dark floors. The dark material could be either ponded 

impact melt or later flood lavas (Herrick and Sharpton, 2000), 

or fine debris (Izenberg and others, 1994).

All but three of the craters in V–28 are superposed on 

units phH or pA, which are also the two most areally extensive units in the quadrangle. The crater Pat is on unit pmH, the 

crater Leyster superposes units psH and puH, and crater Alina 

superposes unit fL. Nuriet crater is superposed on the boundary 

between four units (units phH, psH, fIx, and pcH), Ul’yana on 

unit pA and an edifice field (unit ef), Beecher superposes both 

unit phH and unit fTb, and the craters Gaze, Akeley, Yvette, and 

Higgins are on unit phH. Gaze is cut by Hecate faults, Beecher 

by Hanwi faults, and Wheatley and Baranamtarra are cut by 

faults from Zverine Chasma. Two craters are clearly superposed 

by other units. The crater Baranamtarra, located at lat 17° N., 

long 267° E., superposes unit pA but is covered by subsequent flows (unit fK) and cut by Zverine faults. Johanna crater 

superposes units phH, pcH, and fTb, and is partially covered by 

flows from Serova Patera (unit fSe).

Surficial Material

Radar-dark, diffuse materials are mapped as surficial material (lat 8.5° N., long 269° E. and lat 3.5° N., long 266.5° E.). 

These deposits are interpreted to be produced upon the break-up 

of an impactor in the atmosphere (Phillips and others, 1991). The 

resulting shock wave pulverizes the upper layers of the surface, 

producing a roughly circular region of impact debris (Phillips 

and others, 1991; Zahnle, 1992), or, the shock wave may smooth 

the surface (Ivanov and others, 1992). In both cases in this quadrangle, no crater is visible, just a diffuse, dark patch.

Structure

In quadrangle V–28, we have mapped structures associated 

with the chasmata, with coronae, and occurring in the plains. 

Structures are generally mapped as radar-bright lineaments, 

although some are mapped as wrinkle ridges on the basis of 

their sinuosity and similarity to wrinkle ridges on other planets 

(for example, Squyres and others, 1992b). All of the plains units 

except for plH and psH are cut by closely spaced (<10 km), 

intersecting lineaments that are at too small a scale to be represented on this 1:5,000,000-scale map (figs. 4, 5). We interpret 

these lineaments to be polygonal fractures, based on their similarity to polygonal fractures elsewhere on Venus (for example, 

Smrekar and others, 2002), but some also resemble wrinkle 

ridges. These sets of fractures also cut portions of volcanic unit 

fSo and some areas of unit vc.

Wrinkle Ridge. Wrinkle ridges are generally common on 

plains units on Venus (Squyres and others, 1992b; McGill, 

1993; Bilotti and Suppe, 1999), and are thought to record limited amounts of horizontal shortening (for example, Plescia and 

Golombek, 1986). Unlike most plains regions on Venus, plains 

units in Hinemoa Planitia generally lack wrinkle ridges. In the 

southeastern portion of the map, some NNE-trending wrinkle 

ridges cut units peH, fSo, and phH. In the southwestern portion 

of the map, a few E-trending and ENE-trending ridges cut units 

pmH, peH, puH, phH, and fG. Some of the closely spaced 

lineaments that we interpret as polygonal fractures (seen in figs. 

4 and 5) may be wrinkle ridges, as discussed above.

Fracture/Fault. Radar-bright lineaments interpreted to be 

faults and fractures cut most of the plains units in this quadrangle. In the units immediately surrounding the chasmata, 

fractures generally parallel the chasma trough. Two sets of 

fractures occur south of the chasma: a set that trends NNE and 

a set that trends NNW. The NNW-trending fractures cut all of 

the plains units in the southern portion of the map, while the 

NNE-trending set is embayed in unit peH and not visible in the 

other plains units. The age relation between fractures associated 

with Hecate Chasma and the NNE-trending set is not apparent, 

although both sets cut units fSo and phH. The three orientations 

of fracture sets indicate that different episodes of regional-scale 

tensional stress have affected this quadrangle at multiple times 

throughout its visible history. To the north of the chasmata, 

no regional sets of fractures occur. Most of these fractures are 

spatially related to local features such as volcanic centers or 

coronae.

Chasmata. Hecate Chasma extends for over 8000 km, from 

Atla Regio through Asteria Regio (Hamilton and Stofan, 1996). 

Hecate Chasma is a discontinuous trough and fracture system, 

with en echelon offset along its trend. Regions where the trough 

is topographically distinct in this quadrangle (for example, 

near Kono Mons versus southwest of Polik-mana Mons) tend 

to be characterized by more dense fracture spacing (Hamilton 

and Stofan, 1996), as at the sections of the chasma system in 

the V–28 quadrangle. The origin of chasma systems has been a 

subject of debate, with hypotheses ranging from extension and 

associated diapiric upwelling (Stofan and others, 1992; Hansen 

and Phillips, 1993) to subduction (Schubert and others, 1994; 

Schubert and Sandwell, 1995). We favor an extensional origin, 
8

on the basis of similarities of the chasmata to terrestrial rift 

systems.

Three branches of the Hecate system are contained in 

this quadrangle: Hecate Chasma, Hanwi Chasma, and Zverine 

Chasma. All three of these branches have troughs ranging from 

<500 m deep to over 2 km deep. The zone of fractures tends 

to extend beyond the trough. In places along each chasma, the 

fractures are closely spaced, and in other places the fractures 

are more widely spaced and tend to be slightly sinuous. Zverine Chasma appears to postdate the main Hecate Chasma, as it 

terminates abruptly against it, suggesting that Hecate acted as 

a structural barrier to Zverine. Hanwi Chasma does not have 

a clear age relation with the other two branches. Each chasma 

could have formed simultaneously, or may have formed at quite 

different times.

Geologic History

The geologic history of the V–28 quadrangle is dominated 

by formation of the chasmata, coronae, and volcanic edifices 

and flows. We can identify no regional-scale plains units; the 

numerous plains units appear to be local units. The plains units 

are interpreted to be volcanic in origin based on their lobate 

boundaries, the association with volcanic source vents (that 

is, edifices), and the generally accepted view that plains on 

Venus are volcanic in origin (for example, Head and others, 

1992). Identifying different plains units in the vicinity of the 

chasmata and across the chasmata is extremely difficult, owing 

to the close spacing of the fractures. Therefore, we do not feel 

overly confident of the age relation or continuity of plains units 

mapped in the immediate vicinity of the chasmata.

In addition, as described above, most units in the V–28 

map area are not in contact, leading us to formulate a correlation chart that is extremely horizontal, with most units having 

hachured tops and bottoms indicating uncertainty in the timing 

and extent of their formation. The horizontality of this chart 

should not be misconstrued to indicate that the units all formed 

simultaneously, rather, it reflects our inability to place the units 

with any confidence in a more specific stratigraphic sequence, 

with the exception of some of the events described below. 

Therefore, a number of geologic histories could be constructed 

for this quadrangle, most of which are not testable in the 

absence of age dating of surface rocks (for example, Stofan and 

others, 2005).

The earliest history of this quadrangle is preserved in 

a number of units (units peH, pfH, t) found to the north and 

south of Hecate Chasma. These units are all deformed to varying degrees; in general, they are more deformed than younger 

plains units. Their original character is not clear; unit peH is 

interpreted to be of volcanic origin, affected by later, possibly 

multiple episodes of tectonic and volcanic activity. The materials that make up the highly deformed units pfH and t are of 

unknown origin. The amount of time represented by these units, 

and whether they represent earlier episodes of rift formation 

and volcanism in this region, is not clear. A good example of the 

complexity of older plains units is unit peH, which embays a set 

of NNE-trending fractures, and is cut by Hecate Chasmata fractures and a NNW-trending set of fractures. The unit is overlain 

by younger edifices and coronae, and contains both embayed 

and superposed small edifices. This multi-staged history of unit 

peH took place over an unknown amount of time.

Later plains units of relatively limited areal extent (units 

phH, pcH, puH) were then formed by volcanic processes. 

These units are interpreted to be volcanic on the basis of their 

general morphology, numerous lobate patches that are either too 

small to be mappable units or do not have complete boundaries, 

and overall lobate boundaries. The only visible sources for these 

units are small edifices, although it is likely that many flows 

originated at fissures that have been covered by subsequent 

flows. Secondary structures on these units are primarily polygonal fractures and fractures associated with Hecate Chasmata, in 

particular, unit phH.

Volcanism and coronae formation occurred prior to, during 

and after formation of Hecate Chasmata. Evidence of this is 

seen at Kono Mons, which was split by the rift (portions of the 

edifice are located on the north and south rift flank) and yet 

continued to erupt as extension associated with the rift continued 

(that is, Kono flows are cut by rift-associated fractures) (fig. 6). 

In addition, crosscutting and superposition relations between 

chasma-associated fractures and flows of Polik-mana Mons 

indicate that formation of this volcano overlapped in time with 

the formation of Hecate Chasma. At Taranga Corona, the corona 

appears to largely postdate formation of Hecate Chasma, as it is 

largely superposed on the rift, but some Taranga flows are cut by 

chasma-associated fractures. We see no clear progression in the 

relative age of coronae and volcanoes along the rift. In addition, 

the volcanic edifices and coronae occur in a broad zone extending from several hundred kilometers north of the rift to over 500 

km south of the rift, not just directly on the rift. If the rift and 

coronae are a result of mantle upwelling, as has been interpreted 

by several previous workers (for example, Chapman and Zimbelman, 1998; Stofan and Smrekar, 2005), and coronae are favored 

to form in association with upwellings (for example, Johnson 

and Richards, 2003), then the underlying process of upwelling is occurring at a broader scale than the rift itself (Martin 

and others, 2007). Both this broader zone and the rift might be 

caused by extension of the lithosphere, but they have occurred at 

two different scales. Segmentation of the rift at Devana Chasma, 

to the east of the V–28 map area, has been interpreted to indicate 

that the system formed as two distinct rifts over two intersecting 

mantle plumes (Kiefer and Swafford, 2006); the multiple segments of Hecate do not have any simple geometric pattern that 

would indicate a similar mechanism of origin.

Volcanic features occur in a broad zone across the map. 

Edifice fields in the region appear to be relatively young based 

on superposition relations, and all of the plains units, particularly those to the south of the rift, tend to have high concentrations of small edifices. As described above, individual small 

edifices, both within edifice fields and within plains units, 

appear to have formed at different times, based on cross-cutting 

relations with local structures (fig. 4). The southern half of 

quadrangle V–28 has a high concentration of small and intermediate volcanoes, and lies within the Beta-Atla-Themis (BAT) 

region, the so-called BAT region, which was previously identi-
9

fied as having the highest regional concentration of volcanic 

features on Venus (Crumpler and others, 1997).

In this quadrangle, volcanic features are abundant along 

the chasmata and in the plains to the south. For example, 

Taranga Corona on Hecate Chasma has extensive flows, as do 

Sinlaku and Aruru Coronae which lie to the south of Hecate. 

A few flow materials units are directly associated with the 

chasma (unit fH and possibly unit fSo), but they are smaller in 

areal extent than volcanic units to the south of the chasma. The 

highest concentration of small edifices is to the south of Hecate 

Chasma; only a few edifices are located on the rift. If extension enhances volcanism in this region (for example, Magee 

and Head, 1995), then volcanic features should occur in higher 

abundance along the rift in comparison to the surrounding 

regions. However, a larger number of volcanic features occur 

south of the rift rather than along the rift. In this region, we 

interpret that upwelling and lithospheric extension have produced volcanism that occurred (and may be occurring) over a 

broad region that includes the rift, but also extends to the north 

(to a limited extent) and to the south.

On Venus, only about 17 percent of the total population of impact craters are either volcanically embayed and 

(or) deformed (Schaber and others, 1992). In this quadrangle, 

38 percent of craters are embayed or deformed (table 2). For 

example, in V–28, one crater is cut by faults from Hecate 

Chasma, one by Zverine Chasma faults, one by Hanwi Chasma 

faults, another is cut by Zverine faults and embayed by flows, 

and another (Johanna) is embayed by flows from Serova Patera. 

We have identified one more embayed and deformed crater than 

was listed in the Schaber and others (1998) database (Johanna). 

We also do not include in the embayed population the number 

of dark-floored craters (for example, Herrick and Sharpton, 

2000); therefore, we would argue that the 38 percent is likely 

to be an underestimate. Although detailed mapping is likely to 

raise the number of deformed and embayed craters on Venus, 

the V–28 region contains an anomalously high number of 

affected craters, a possible indication that this region has been 

more recently geologically active.

Two end-member models have been proposed for Venus: 

a directional model in which specific types of features formed 

globally at specific times (Basilevsky and Head, 1995, 1998; 

Head and Basilevsky, 1998; Ivanov and Head, 2001), and a nondirectional model in which types of geologic features form over 

the range of observable Venus history (Guest and Stofan, 1999; 

Stofan and others, 2005). An exception to the non-directional 

model is tessera; most workers agree that the majority of tessera plateaus (large-scale, high standing areas of tessera such 

as Alpha Regio to the southeast of the V–28 map area) seem to 

predate the plains that immediately surround them (for example, 

Ivanov and Head, 1996; Hansen and Willis, 1996). V–28 contains no tessera plateaus. The fragments of tessera-type terrain 

in the quadrangle are relatively older than the units with which 

they are in contact, but the fragments are small, and only in 

contact with units pA, pcH, phH, and fTb. Hypotheses for fragments of tessera range from an old, widespread unit that underlies much of the plains (for example, Ivanov and Head, 1996) 

to the tessera fragments forming at different times by different 

mechanisms (Hansen and Willis, 1996). The three outcrops of 

tessera in quadrangle V–28 are in close proximity (~100 km), 

suggesting that they once formed a larger unit that extended for 

over 400 km x 500 km. However, the origin of this unit and the 

age of it relative to the other “old” plains units (unit peH, unit 

pfH) in this quadrangle are not known.

Plains, volcano, and corona units in this quadrangle are 

more consistent with a non-directional model, with the important 

caveat that we are looking at a small portion of Venus representing an unknown amount of time. With respect to plains units, we 

see no evidence here for a widespread episode of resurfacing as 

described by the directional model; instead the patch-like, composite character of the V–28 plains units (including units peH, 

phH, pcH, and pA) support incremental resurfacing over time in 

this region (for example, Phillips and others, 1992), consistent 

with the non-directional model. Edifices (large and intermediate 

volcanoes, as well as small volcanoes) have formed throughout the history of the quadrangle, both pre- and post-dating rift 

formation (for example, fig. 6) and corona formation, again 

consistent with predictions of the non-directional rather than the 

directional model, which has specific episodes of small and large 

volcano formation (for example, Basilevsky and Head, 1995). 

Corona flows predate units pmH and psH, and formation of a 

corona has overlapped in time with the formation of units peH

and pmH. Again, the occurrence of corona units throughout the 

visible history of this quadrangle is inconsistent with the directional model, which confined corona formation to specific time 

periods (for example, Basilevsky and others, 1997). Multiple 

episodes of tensional stress have occurred, early in the history of 

the quadrangle (unit pfH) and at some later time with the formation of the multiple branches of Hecate and the NNW-trending 

fractures. However, while the formation of chasma, coronae, 

volcanoes, and plains units have overlapped in time, consistent with the non-directional model, we still have no ability to 

determine the duration of any of these events. While the overall 

surface of Venus has an average crater retention age of ~750 

m.y. (McKinnon and others, 1997), the inability to distinguish 

the Venus crater population from a random population prevents 

determination of ages of individual units (Campbell, 1999).

References Cited

Addington, E.A., 2001, A stratigraphic study of small volcano 

clusters on Venus: Icarus, v. 149, p. 16–36.

Aittola, M., and Raitala, J., 2005, Coronae and novae in the 

Hecate Chasma deformation area: Solar System Research, 

v. 39, p. 199–213.

Barsukov, V., and 29 authors, 1986, The geology and geomorphology of the Venus surface as revealed by the radar 

images obtained by Veneras 15 and 16: Journal of Geophysical Research, v. 91(B4), p. D378–D398.

Basilevsky, A.T., and Head, J.W., 1995, Global stratigraphy of 

Venus—Analysis of thirty-six test areas: Earth, Moon, and 

Planets, v. 43, p. 285–336.

Basilevsky, A.T., and Head, J.W., 1998, The geologic history 

of Venus—A stratigraphic view: Journal of Geophysical 

Research, v. 103, p. 8531–8544.
10

Basilevsky, A.T., Head, J.W., Schaber, G.G., and Strom, R.G., 

1997, The resurfacing history of Venus, in Bouger, S.W., 

Hunten, D.M., and Phillips, R.J., eds., Venus II—Geology, 

geophysics, atmosphere and solar environment: Tucson, 

The University of Arizona Press, p. 1047–1084.

Bilotti, F., and Suppe, J., 1999, The global distribution of 

wrinkle ridges on Venus: Icarus, v. 139, p. 137–157.

Campbell, B.A., 1995, Use and presentation of Magellan quantitative data in Venus mapping: U.S. Geological Survey 

Open-File Report 95–519, 27 p.

Campbell, B.A., 1999, Surface formation rates and impact 

crater densities on Venus: Journal of Geophysical 

Research, v. 104, p. 21,951–21,955.

Campbell, B.A., and Campbell, D.B., 1992, Analysis of volcanic surface morphology on Venus from comparisons 

of Arecibo, Magellan and Terrestrial airborne radar data: 

Journal of Geophysical Research, v. 97, p. 16,293–16,314.

Chapman, M.G., 1999, Geologic map of the Galindo Quadrangle (V–40), Venus: U.S. Geological Survey Geological 

Investigations Series I–2613, scale 1:5,000,000.

Chapman, M.G., and Zimbelman, J.R., 1998, Corona associations and their implications for Venus: Icarus, v. 132, p. 

344–361.

Crumpler, L.S., Aubele, J.C., Senske, D.A., Keddie, S.T., 

Magee, K.P., and Head, J.W., 1997, Volcanoes and centers 

of volcanism on Venus, in Bougher, S.W., Hunten, D.M., 

and Phillips, R.J., eds., Venus II—Geology, geophysics, 

atmosphere and solar environment: Tucson, The University 

of Arizona Press, p. 697–756.

Ford, J.P., and 7 others, 1993, Guide to Magellan Image 

Interpretation: Pasadena, Calif., National Aeronautics and 

Space Administration Jet Propulsion Laboratory Publication, 93-24, 287 p.

Ford, P.G., and Pettengill, G.H., 1992, Venus topography and 

kilometer-scale slopes: Journal of Geophysical Research, v. 

97, p. 13,103–13,114.

Guest, J.E., Bulmer, M.H., Aubele, J., Beratan, K., Greeley, R., 

Head, J.W., Michaels, G., Weitz, C., and Wiles, C., 1992, 

Small volcanic edifices and volcanism in the plains of 

Venus: Journal of Geophysical Research, v. 97, p. 15,949–

15,966.

Guest, J.E., and Stofan, E.R., 1999, A new view of the stratigraphic history of Venus: Icarus, v. 139, p. 55–66.

Hamilton, V.E., and Stofan, E.R., 1996, The geomorphology 

and evolution of Hecate Chasma, Venus: Icarus, v. 121, p. 

171–194.

Hansen, V.L., 2000, Geologic mapping of tectonic planets: 

Earth Planetary Science Letters, v. 176, p. 527–542.

Hansen, V.L., 2006, Geologic constraints on crustal plateau 

surface histories, Venus—The lava pond and bolide impact 

hypotheses: Journal of Geophysical Research, v. 111, 

(doi:10.1029/2006JE002714).

Hansen, V.L., and Phillips, R.J., 1993, Tectonics and volcanism 

of eastern Aphrodite Terra, Venus—No subduction, no 

spreading: Science, v. 260, p. 526–530.

Hansen, V.L., and Willis, J.J., 1996, Structural analysis of a 

sampling of tesserae—Implications for Venus geodynamics: Icarus, v. 123, p. 296–312.

Hansen, V.L., and Willis, J.J., 1998, Ribbon terrain formation, 

Southwestern Fortuna Tessera, Venus—Implications for 

lithosphere evolution: Icarus, v. 132, p. 321–343.

Head, J.W., and Basilevsky, A.T., 1998, Sequence of tectonic 

deformation in the history of Venus—Evidence from 

global stratigraphic relationships: Geology, v. 26, p. 35–38.

Head, J.W., Crumpler, L.S., Aubele, J.C., Guest, J.E., and 

Saunders, R.S., 1992, Venus volcanism—Classification of 

volcanic features and structures, associations, and global 

distribution from Magellan data: Journal of Geophysical 

Research, v. 97, p. 13,153–13,197.

Herrick, R.R., and Sharpton, V.L., 2000, Implications from stereo-derived topography of Venusian impact craters: Journal 

of Geophysical Research, v. 105, p. 20,245–20,262.

Ivanov, M.A., and Head, J.W., 1996, Tessera terrain on Venus—

A survey of the global distribution, characteristics, and 

relation to surrounding units from Magellan data: Journal 

of Geophysical Research, v. 101, p. 14,861–14,908.

Ivanov, M.A., and Head, J.W., 2001, Geology of Venus—Mapping of a global geotraverse at 30N: Journal of Geophysical Research, v. 106, p. 17,515–17,566.

Ivanov M.A., and Head, J.W., 2004, Stratigraphy of small shield 

volcanoes on Venus—Criteria for determining stratigraphic 

relationships and assessment of relative age and temporal abundance: Journal of Geophysical Research, v. 109, 

(doi:10.1029/2004JE002252).

Ivanov, B.A., Nemchinov, I.V., Svetsov, V.A., Provalov, A.A., 

Khazins, V.M., and Phillips, R.J., 1992, Impact cratering 

on Venus—Physical and mechanical models: Journal of 

Geophysical Research, v. 97, p. 16,167–16,182.

Izenberg, N., Arvidson, R.E., and Phillips, R.J., 1994, Impact 

crater degradation on venusian plains: Geophysical 

Research Letters, v. 21, p. 289–292.

Johnson, C.L., and Richards, M.A., 2003, A conceptual model 

for the relationship between coronae and large-scale mantle 

dynamics on Venus: Journal of Geophysical Research, v. 

108, (doi:10.1029/2002JE001962).

Kasting, J.F., and Pollack, J.B., 1983, Loss of water from Venus 

1. Hydrodynamic escape of hydrogen: Icarus, v. 53, p. 

479–508.

Kiefer, W.S., and Peterson, K., 2003, Mantle and crustal 

structure in Phoebe Regio and Devana Chasma, 

Venus: Geophysical Research Letters, v. 30, 

(doi:10.1029/2002GL015762).

Kiefer, W.S., and Swafford, L.C., 2006, Topographic analysis of 

Devana Chasma, Venus—implications for rift system segmentation and propagation: Journal of Structural Geology, 

v. 28, p. 2144–2155.

Lancaster, M.G., Guest, J.E., and Magee, K.P., 1995, Great lava 

flow fields on Venus: Icarus, v. 118, p. 69–86.

Magee, K.P., and Head, J.W., 1995, The role of rifting in the 

generation of melt—Implications for the origin and evolution of the Lada Terra-Lavinia Planitia region of Venus: 

Journal of Geophysical Research, v. 100, p. 1527–1552.

Magee, K.P., and Head, J.W., 2001, Large flow fields on 

Venus—Implications for plumes, rift associations and 

resurfacing: Geological Society of America Special Paper, 

v. 352, p. 81–101.
11

Martin, P., Stofan, E.R., Glaze, L.S., and Smrekar, S.E., 2007, 

Coronae of Parga Chasma, Venus: Journal of Geophysical 

Research, v. 112, (doi:10.1029/2006JE002758).

Masursky, H., Eliason, E., Ford, P.G., McGill, G.E., Pettengill, 

G.H., Schaber, G., and Schubert, G., 1980, Pioneer-Venus 

radar results—geology from images and altimetry: Journal 

of Geophysical Research, v. 85, p. 8232–8260.

McGill, G.E., 1993, Wrinkle ridges, stress domains, and kinematics of venusian plains: Geophysical Research Letters, v. 

20, p. 2407–2410.

McKinnon, W.B., Zahnle, K.J., Ivanov, B.A., and Melosh, H.J., 

1997, Cratering on Venus—Models and observations, in

Bougher, S.W., Hunten, D.M., and Phillips, R.J., eds., 

Venus II—Geology, geophysics, atmosphere and solar 

environment: Tucson, The University of Arizona Press, p. 

969–1014.

Pettengill, G.H., Ford, P.G., and Wilt, R., 1992, Venus surface 

radiothermal emission as observed by Magellan: Journal of 

Geophysical Research, v. 97, p. 13,091–13,102.

Phillips, R.J., Arvidson, R.E., Boyce, J.M., Campbell, D.B., 

Guest, J.E., Schaber, G.G., and Soderblom, L.A., 1991, 

Impact craters on Venus—Initial analysis from Magellan: 

Science, v. 252, p. 288–297.

Phillips, R.J., Raubertas, R.F., Arvidson, R.E., Sarkar, I.C., Herrick, R.R., Izenberg, N., and Grimm, R.E., 1992, Impact 

craters and Venus resurfacing history: Journal of Geophysical Research, v. 97, p. 15,923–15,948.

Plescia, J.B., and Golombeck, M.P., 1986, Origin of planetary 

wrinkle ridges based on study of terrestrial analogs: Geological Society of America Bulletin, v. 97, p. 1289–1299.

Roberts, K.M., Guest, J.E., Head, J.W., and Lancaster, M.G., 

1992, Mylitta Fluctus, Venus—Rift-related centralized volcanism and the emplacement of large-volume flow units: 

Journal of Geophysical Research, v. 97, p. 15,991–16,015.

Saunders, R.S., Arvidson, R., Head, J.W., Schaber, G., Solomon, S., and Stofan, E., 1991, Magellan—A first overview 

of Venus geology: Science, v. 252, p. 249–252.

Schaber, G.G., Kirk, R.L., and Strom, R.G., 1998, Data Base 

of impact craters on Venus based on analysis of Magellan 

radar images and altimetry data: U.S. Geological Survey 

Open-File Report 98–104.

Schaber, G.G., Strom, R.G., Moore, H.J., Soderblom, L.A., 

Kirk, R.L., Chadwick, D.J., Dawson, D.D., Gaddis, L.R., 

Boyce, J.M., and Russell, J., 1992, Geology and distribution of impact craters on Venus—What are they telling 

us?: Journal of Geophysical Research, v. 97, p. 13,257–

13,302.

Schubert, G., Moore, W.B., and Sandwell, D.T., 1994, Gravity 

over coronae and chasmata on Venus: Icarus, v. 112, p. 

130–146.

Schubert G., and Sandwell, D.T., 1995, A global survey of possible subduction sites on Venus: Icarus, v. 117, p. 173–196.

Smrekar, S.E., Moreels, P., Franklin, B.J., 2002, Characterization and origin of polygonal fractures on 

Venus: Journal of Geophysical Research, v. 107, (doi: 

10.1029/2001JE001808).

Squyres, S.W., Janes, D.M., Baer, G., Bindschadler, D.L., 

Schubert, G., Sharpton, V.L., Stofan, E.R., 1992a, The 

morphology and evolution of coronae on Venus: Journal of 

Geophysical Research, v. 97, p. 13,611–13,634.

Squyres, S.W., Jankowski, D.G., Simons, M., Solomon, S.C., 

Hager, B.H., and McGill, G.E., 1992b, Plains tectonism on 

Venus—The deformation belts of Lavinia Planitia: Journal 

of Geophysical Research, v. 97, p. 13,579–13,610.

Stofan, E.R., Brian, A.W., and Guest, J.E., 2005, Resurfacing 

styles and rates on Venus—Assessment of 18 venusian 

quadrangles: Icarus, v. 173, p. 312–321.

Stofan, E.R., Guest, J.E., and Copp, D.L., 2001a, Development 

of large volcanoes on Venus—Constraints from Sif, Gula 

and Kunapipi Montes: Icarus, v. 152, p. 75–95.

Stofan, E.R., Hamilton, V.E., Janes, D.M., and Smrekar, S.E., 

1997, Coronae on Venus— Morphology and origin, in

Bougher, S.W., Hunten, D.M., and Phillips, R.J., eds., 

Venus II—Geology, geophysics, atmosphere and solar 

environment: Tucson, The University of Arizona Press, p. 

931–965.

Stofan, E.R., Head, J.W., Campbell, D.B., Zisk, S.H., Bogomolov, A.F., Rzhiga, O.N., Basilevsky, A.T., and Armand, 

N., 1989, Geology of a Venus rift zone—Beta Regio and 

Devana Chasma: Geological Society of America Bulletin, 

v. 101, p. 143–156.

Stofan, E.R., Sharpton, V.L., Schubert, G., Baer, G., Bindschadler, D.L., Janes, D.M., and Squyres, S.W., 1992, 

Global distribution and characteristics of coronae and 

related features on Venus—Implications for the origin 

and relation to mantle processes: Journal of Geophysical 

Research. v. 97, p. 13,347–13,378.

Stofan, E.R., and Smrekar, S.E., 2005, Large topographic rises, 

coronae, large flow fields and large volcanoes on Venus—

Evidence for mantle plumes?, in Foulger, G.R., Natland, 

J.H., Presnall, D.C., and Anderson, D.L., eds., Plumes, 

plates and paradigms: Geological Society of America Special Volume 388, p. 841–861.

Stofan, E.R., Smrekar, S.E., Tapper, S.W., Guest, J.E., and Grindrod, P.M., 2001b, Preliminary analysis of an expanded 

corona database for Venus: Geophysical Research Letters, 

v. 28, p. 4267–4270.

Surkov, Yu. A., Barsukov, V.L., Moskalyeva, L.P., Kharyukova, 

V.P., and Kemurdzhian, A.L., 1984, New data on the composition, structure and properties of Venus rock obtained 

by Venera 13 and Venera 14: Journal of Geophysical 

Research, v. 89, p. B393–B402.

Tanaka, K.L., 1994, The Venus geologic mappers’ handbook: 

U.S. Geological Survey Open-File Report 94–438, 48 p.

Wilhelms, D.E., 1972, Geologic mapping of the Second Planet: 

U.S. Geological Survey Interagency Report, Astrogeology, 

v. 55, 36 p.

Wilhelms, D.E., 1990, Geologic mapping, in Greeley, R., and 

Batson, R.M., eds., Planetary mapping: New York, Cambridge University Press, 296 p.

Zahnle, K.J., 1992, Airburst origin of dark shadows on Venus: 

Journal of Geophysical Research, v. 97, p. 10,243–10,255.

Zimbelman, J.R., 2001, Image resolution and evaluation of 

genetic hypotheses for planetary landscapes: Geomorphology, v. 37, p. 179–199.
12

Table 1. Coronae of V–28.

Name Latitude (°N) Longitude (°E) Maximum Width (km) Type Topopgraphy

Tari Pennu 0 264.5 200 concentric rim only

unnamed 0.7 254.8 110 concentric-double ring raised, irregular

Rind 8 247.5 150 concentric rimmed depression

Aruru 9 262 450 asymmetric rimmed plateau

Ak-Ene 9.5 254.5 150 concentric-double ring rim only

unnamed 10 246 200 concentric-double ring rimmed depression

unnamed 10.5 251.5 300 concentric rimmed depression

Prthivi 11 248.5 300 concentric rimmed depression

Gashan-Ki 11.5 244 290 concentric raised, irregular

unnamed 13.5 253 200 concentric rimmed depression

unnamed 14 254.5 125 concentric depression

unnamed 14 256.5 180 concentric depression

Nei-Teukez 14 258.8 125 concentric rimmed depression

Taranga 16.5 251.5 525 asymmetric rimmed plateau

Sinlaku 17.5 260.5 300 concentric rimmed plateau

unnamed 19.5 265.5 150 concentric raised, irregular

unnamed 22.5 256.7 150 asymmetric raised, irregular

Acrea 24 243.5 500 multiple rimmed depression

Table 2. Impact craters of V–28.

Name Latitude

(°N)

Longitude

(°E)

Diameter

(km)

Description Superposed on: Superposed by:

Ulyana 24.3 253 13 bright floor with dark flow, central peak ef, pA

Nuriet 21 245.5 16 partial dark floor pcH, psH, phH, 

fIx

Johanna 19.5 247.3 15.9 bright floor fTb, phH, pcH fSe

Baranamtarra 17.9 267.8 25.6 dark floor, central peak pA fK, Zverine faults

Montez 17.9 266.5 18.2 dark floor, central peak pA

Gaze 17.9 240.1 32.9 bright floor phH Hecate faults

Wheatley 16.6 268 72.9 dark floor, inner ring pA Zverine faults

Beecher 13.1 253.5 42.8 bright floor with dark flow, central peak fTb, phH Hanwi faults

Akeley 8 244.5 22.7 central peak, partial dark floor phH

Yvette 7.4 249.6 10.4 dark floor phH

Higgins 7 242 33.3 multiple small craters, partial dark floor phH

Pat 2.9 262.6 11.1 bright floor with dark flow, central peak pmH

Leyster 1 260 45.1 dark floor, inner ring psH, puH