+

+

+

c

cf

pl

ps

rp2

rp1

ppg

ppg

gb

gb

ppg

mb

psh

pr pdl

gb

mb

t

t

pdl pdl

pr

psh

ppg

rp1

rp1

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rp2

ps

rp2

pl

c

cf

gb

mb

rp1

rp1

mb

mb

t

t

pdl

pdl

pr

gb

pr

pr

t

rp1

rp2

rp1

gb

pdl

psh

psh

pdl

pdl

rp1

rp1

psh

t

rp2

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pl

pl

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c

rp1

rp1

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gb

psh

gb

pdl

c

ps

psh

psh

pdl

psh

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t

psh

gb

t

t

t

ps

gb

t

rp1

rp1

c

c

t

c

cf

cf

c

c

c

t

c

c

c

c

c

c

c

c

c

c

c

c

c

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cf

ps

psh

pdl

pl

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rp1

pl

ps

psh

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pl

ps

pl ps

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gb

pl

psh

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gb

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pdl

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psh

t

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mb

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pdl

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rp2

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pl

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rp1

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pl

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t

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mb

t

pdl

psh

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psh

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mb

pdl

rp1

rp1

ps

t

psh

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psh

t

psh

ps

gb

ps

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ps

mb

t

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gb

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rp1

ps

psh

rp2

t

mb

rp2

rp2

rp1

rp1

t

t

psh

psh

rp1

t

t

rp1

psh

rp2

rp2

rp2

mb

rp2

rp2

rp2

pdl

rp2

gb

rp2

rp2

psh

pr

rp1

pdl

rp2

rp2

rp1

gb

rp1

rp1

rp1

rp1

rp

psh 1

psh

psh

gb

psh

pdl

psh

rp1

rp1

rp1

rp1

gb

gb

pdl

rp1

rp1

t

rp1

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psh

psh

gb

rp1

gb

pdl

t

rp1

rp1

t

rp1

rp1 

rp1

gb

pr

pr

rp1

t

gb

t

t

ppg

rp1

pr

rp1

rp1

rp1

rp1

rp1

psh

psh

psh

psh

t

rp1

rp1

rp1

rp1

rp1

ppg

mb

ppg

rp1

gb

rp1

rp1

rp1

psh

psh

psh

pdl

psh

gb

psh

gb

gb

t

rp1

gb

rp1

rp1

rp1

psh

psh

psh

gb

pdl

psh

pdl

cf

pl

c

ps

rp1

ppg

pr

psh

rp2

pdl

mb

gb

t

Atropos Tessera

Moira Tessera

Clotho Tessera

Vesta Rupes

Djata Fluctus

Lunang Vallis

Neago Fluctūs

Beiwe Corona

Xilonen 

Corona

Ashnan

Corona

Auska Dorsum

Rangrid Fossae

Siddons

Patera

Sacajawea

Patera

Colette

Patera

Vires-Akka Chasma

S E D N A P L A N I T I A

L A K S H M I

P L A N U M

I S H T A R T E R R A

Akna

Montes

Danu Montes

Freyja Montes

Maxwell Montes

Omosi-Mama Corona

Ishtar Terra

Sedna

Beta

Regio

Eistla

Planitia

Atropos Tessera

Moira Tessera

Clotho Tessera

Ut Rupes

Vesta Rupes

Djata Fluctus

Lunang Vallis

Neago Fluctūs

Beiwe Corona

Xilonen 

Corona

Ashnan

Corona

Muta

Mons

Auska Dorsum

Rangrid Fossae

Siddons

Patera

Sacajawea

Patera

Colette

Patera

Vires-Akka Chasma

S E D N A P L A N I T I A

L A K S H M I

P L A N U M

I S H T A R

T E R R A

Akna

Montes

Danu Montes

Freyja Montes

Maxwell Montes

Omosi-Mama

Corona

Regio

Ut Rupes

Beiwe Corona

Xilonen 

Corona

Muta

Mons

Colette

Patera

Vires-Akka Chasma

Montes

Omosi-Mama

Corona

Ashnan

Corona

Cotton

Ivka

Sigrid

Tamara Berta

Osipenko

Wanda

Aftenia

Sévigné

Stefania

Lotta

Magda

Rita

Gražina

Unnamed

Corona

68° N., 348° E.

Unnamed

Crater

55.1° N., 350.6° E.

Lyudmila

Zlata

Magnani

Lind

Bahriyat

Volyana

Kartini

Akhmatova

Cotton

Ivka

Wanda

Rita

Magda

Lyudmila

Berta

Osipenko

Sévigné

Sigrid

Akhmatova

Tamara

Zlata

Gražina

Kartini

Stefania Lotta

Lind

Aftenia

Magnani

Bahriyat

Volyana

Muta

Mons

Ut Rupes

SCALE 1:4 711 886 (1 mm = 4.712 km) AT 25° LATITUDE

1:5 000 000 AT 34° and 73° LATITUDES

LAMBERT PROJECTION

50

60

75

70

65

55

500 400 300 200 100 0 100 200 300 400

Prepared for the

National Aeronautics and Space Administration

U.S. Department of the Interior

U.S. Geological Survey

Printed on recycled paper

Any use of trade, product, or firm names in this publication is for 

descriptive purposes only and does not imply endorsement by the U.S. 

Government

For sale by U.S. Geological Survey, Information Services, Box 25286, 

Federal Center, Denver, CO 80225, 1–888–ASK–USGS

Available at http://pubs.usgs.gov/sim/3116

Geologic Map of the Lakshmi Planum Quadrangle (V–7), Venus

By

Mikhail A. Ivanov1, 2 and James W. Head, III2

2010

1Vernadsky Institute of Geochemistry and Analytical Chemistry,

 Russian Academy of Sciences, Moscow, Russia

2Department of Geological Sciences, Brown University,

 Providence, RI

325°

330°

340°

345°

350°

355°

360°

330° 325°

335°

300°

305°

310°

315°

320°

75°

300°

50°

320°

315°

310°

305°

360°

355°

350°

345°

340°

335°

55°

60°

65°

70°

75°

70°

65°

60°

55°

50°

Prepared on behalf of the Planetary Geology and Geophysics Program, 

Solar System Exploration Division, Office of Space Science, National 

Aeronautics and Space Administration

Edited by Theresa Iki

Cartography by Darlene A. Ryan

Manuscript approved for publication February 26, 2010

Scientific Investigations Map 3116

Atlas of Venus: Lakshmi Planum Quadrangle (V–7)

Pamphlet accompanies map

500 KILOMETERS

MAJOR TECTONIC EVENT

?

?

Crater

Material

Tessera

Plains Material Material

SEQUENCE OF MAP UNITS

MATERIAL UNIT

TECTONIC

UNIT

Belt

Material

75°

50°

25°

75°

25°

–25°

0°

50°

0°

270° 300° 330° 0° 30° 60° 90°

–25°

–50° –50°

–75° –75°

V–1

V–20 V–21 V–31

V–43

V–62

V–32

V–30

V–29

V–18

V–17

V–19

V–7

V–42 V–33

V–9

V–54 V–45

V–8

V–55 V–44

V–2

V–61 V–56

V–6 V–3

V–60 V–57

V–10

V–53 V–46

V–22

V–41 V–34

QUADRANGLE LOCATION

Photomosaic showing location of map area. An outline of 

1:5,000,000-scale quadrangles is provided for reference.

300° 75°

310° 320° 330° 340° 350°

360°

70°

65°

60°

55°

50°

Figure 1. SAR image of Lakshmi Planum quadrangle (V–7), Venus, showing major physiographic 

features and locations of figures 4–23. See figure 3 for the location of impact craters. Lambert conformal 

projection.

Mountain belt

Groove belt

Tessera

Crater

Splotch

Corona

Tessera structures

300° 75°

310° 320° 330° 340° 350°

360°

70°

65°

60°

55°

50°

Figure 3. Map showing distribution of tesserae, main deformational belts, coronae, and impact craters and 

related deposits in the Lakshmi Planum quadrangle (V–7), Venus. Impact raters Osipenko and Berta, and 

Corona Xilonen are seen in the Venera-15/16 data only and are not included in the geographical map of the 

quadrangle V–7, which is based on the Magellan data. Lambert conformal projection.

300° 75°

310° 320° 330° 340° 350°

360°

70°

65°

60°

55°

50°

Figure 2. A. Topography of the Lakshmi Planum quadrangle (V–7), Venus. Contour interval is 1 km. B.

Position of the Lakshmi Planum quadrangle (V–7) relative to some major topographic features of Venus. 

Magellan topography data. Lambert azimuthal equal-area projection.

AREA OF MAP

Wrinkle ridges

Local grabens and sharp grooves

Ridge belts

Mountain belts

Plains extension

Tessera deformation

14

17b

10

6

8

5

16

4

18

9

12 17a

20

21

15

7,

19

23

11 22 13

DESCRIPTION OF MAP UNITS

[Map units are defined, characterized, and interpreted on the basis of radar 

backscatter; surface texture and morphology; associated features of apparent 

volcanic and tectonic origin; and roughness, reflectivity, emissivity, and 

topography. Although most map units are rock materials, some are defined on 

the basis of pervasive tectonic structure that obscures the underlying materials 

and becomes part of the characteristics of the surface morphology. Type 

localities are indicated for units previously defined (Basilevsky and Head, 

1995b), and reference localities are indicated for units in the map area]

MATERIAL UNIT

Crater Material

Undivided crater material—Impact craterform materials of 

various diameters including central peaks, floor, walls, rim, 

and ejecta but lacking dark paraboloid. Type locality: lat 

17.4° N., long 170.4° E. Reference locality: lat 55.6° N., long 

321.6° E. Interpretation: Impact crater and associated ejecta 

that has lost parabola of fines through erosion or formed 

without one

Crater flow material—Characterized by high radar backscatter; 

lobate margins common. Reference locality: lat 70.6° N., 

long 300.2° E. Interpretation: Outflows from inpact craters

Plains Material

Lobate plains material—Plains-forming material with internal 

elements arranged in parallel to sinuous to lobate radar bright 

and dark strips and patches; unit boundaries are typically 

lobate. Type locality: lat 5.5° N., long 196.0° E. Reference 

locality: lat 54.0° N., long 357.0° E. Interpretation: Complexes of lava flows deformed in places by subsequent extensional structures

Smooth plains material—Homogeneous plains material of 

uniform, generally low to intermediate backscatter. Type 

locality: lat 3.5° N., long 198.2° E. Reference locality: lat 

55.5° N., long 310.0° E. Interpretation: Volcanic plains material mostly unmodified by subsequent deformation; windblown material in places

Regional plains material—Homogeneous plains material of 

intermediate-dark to intermediate-bright radar backscatter 

complicated by narrow linear to anastomosing wrinkle ridges 

in parallel lines or intersecting networks. Type locality: lat 

8.0° N., long 177.0° E. Interpretation: Regional plains material of volcanic origin deformed by wrinkle ridges; sources of 

unit not obvious. Some small shield-shaped features appear 

to be kipukas of shield plains material

Upper unit—Plains-forming material with subdued pattern of 

internal elements arranged in parallel to sinuous to lobate 

radar bright and dark strips and patches; deformed by wrinkle 

ridges. Reference locality: lat 56.0° N., long 350.0° E. Interpretation: Lava flows subsequently deformed by wrinkle 

ridges

Lower unit—Plains material of generally low radar backscatter; commonly mottled locally. Modified by wrinkle ridges. 

Reference locality: lat 70.0° N., long 335.0° E. Interpretation: Vast lava plains subsequently deformed by wrinkle 

ridges

Pitted and grooved plains material—Plains material of intermediate radar backscatter characterized by numerous small and 

large pits and broad flat-floored grooves with scalloped 

edges; low shield-like features are seen in places. Reference 

locality: lat 61.5° N., long 340.0° E. Interpretation: Material 

of volcanic origin with abundant collapse features

Shield plains material—Plains material of intermediate radar 

backscatter characterized by abundant, small, shield-shaped 

features (a few as much as 10–20 km diameter) commonly 

with summit pits. Shield-shaped features occur in clusters, 

which give the locally hilly texture, and as isolated outcrops 

in relatively smooth plains; in places, deformed by wrinkle 

ridges. Reference locality: lat 56.0° N., long 315.0° E. Interpretation: Shield-shaped features are interpreted to be volcanic and are likely sources of adjacent plains material

Ridged plains material—Characterized by relatively smooth 

plains having generally densely spaced, sinuous ridges as 

much as 5–10 km wide and several tens of kilometers long. 

Type locality: lat 37.7° N., long 396.6° E. Reference locality: 

–1 1 3 5 7 9 KILOMETERS

Elevation, relative mean planetary radius

–1.5 0.5 2.5 4.5 6.5 8.5 KILOMETERS

Elevation, relative mean planetary radius

0 25 KILOMETERS 0 25 KILOMETERS 0 25 KILOMETERS

0 25 KILOMETERS 0 25 KILOMETERS 0 25 KILOMETERS

lat 56.5° S., long 340.5° E. Interpretation: Volcanic plains 

material deformed into ridgelike belts by compression

Densely lineated plains material—Flat plainslike material 

intensely lineated by closely spaced, narrow, parallel lineaments 10–20 km long and less than 1 km wide that form 

anastomosing patterns in places; radar bright due to dense 

fractures. Type locality: lat 48.5° N., long 15.0° E. Reference 

locality: lat 69.0° N., long 310.0° E. Interpretation: Volcanic 

plains material highly modified by fractures of probable 

extensional origin. Local changes in fracture density suggest 

some resurfacing during formation

Tessera Material

Tessera material—Radar bright and dominated by closely spaced 

ridges and grooves oriented in at least two directions, 

commonly orthogonally; terrain typically elevated. Embayed 

by plains materials. Type locality: lat 67.5° N., long 20.0° E. 

Reference locality: lat 58.5° N., long 310.0° E. Interpretation: Volcanic plains material very highly modified by 

fractures of probable extensional origin. Local changes in 

fracture density suggest some resurfacing during formation

TECTONIC UNIT

Belt Material

Groove belt material—Characterized by numerous short and 

long curvilinear subparallel lineaments that are typically 

wide enough to be resolved as fractures and grabens. Forms 

curvilinear belts several hundreds of kilometers long and 

100–150 km wide. Remnants of pre-existing plains can be 

seen at higher resolution but are not mappable at this scale. 

Distinguished from densely lineated plains material by type 

of fractures and belt-like form. Type locality: lat 55° N., long 

337° E. Interpretation: Various materials deformed into 

broad belts; fractures formed largely by extension

Mountain belt material—Characterized by densely packed 

ridges 5–15 km wide and several tens of kilometers long. 

Form elongated belts many hundreds of kilometers long and 

up to 200–250 km wide that surround the central portion of 

Lakshmi Planum and can reach 3–4 km above the surface of 

the planum and 9–10 km above the planetary datum. Type 

locality: lat 68° N., long 317° E. Interpretation: Various 

materials deformed into broad belts; ridges formed largely by 

compression

Contact

Ridge

Wrinkle ridge

Sharp groove

Flow front—Arrow indicates flow direction

Channel

Groove (in groove belts)

Steep-sided dome

Depression

Corona

Structures in tessera

Rim of impact crater (>10 km diameter)—Hachures point into 

crater

Central peak of impact crater

Rim and center of impact crater (<10 km diameter)

Dark parabola

0 25 KILOMETERS 0 25 KILOMETERS 0 25 KILOMETERS

0 25 KILOMETERS 0 25 KILOMETERS 0 25 KILOMETERS 0 25 KILOMETERS 0 25 KILOMETERS 0 50 KILOMETERS

A B

Figure 17. SAR image showing relations between mountain belts material (unit mb) and lower unit of 

regional plains material (unit rp1) within Lakshmi Planum. (A) Danu Montes at the southern edge of 

Lakshmi. Material of regional plains penetrates between ridges of the mountain belt (white arrows). 

Fragment of C1-MIDR.60N347;1; center of image approx. lat 56.5° N., long 318.0° E.; look direction, left; 

image size, approx. 115 x 115 km; north is up. (B) Freyja Montes at the northern edge of Lakshmi. The mountain belt unit and regional plains material are separated by a zone of low and broad ridges (black arrows) that 

appear to deform the surface of regional plains material. The deformed impact crater in the upper portion of 

the image is Gražina. Fragment of C1-MIDR.75N338;1; center of image approx. lat 72.5° N., long 338.5° E.; 

look direction, left; image size, approx. 230 x 230 km; north is up.

Figure 18. SAR image (A) showing relations (B) between tessera material (unit t) and densely lineated 

plains material (unit pdl). Tessera material displays more a complex pattern of deformation, whereas unit pdl

is deformed by sets of subparallel structures. The structural pattern of tessera material is abruptly terminated 

by the contact with densely lineated plains material (center and left side of image). Fragment of 

C1-MIDR.75N338;1; center of timage approx. lat 72.0° N., long 348.9° E.; look direction, left; image size, 

approx. 115 x 115 km; north is up.

Figure 19. SAR image (A) showing relations (B) between ridged plains material (unit pr) and a groove belt 

(unit gb). Structures of the belt oriented in E–W and N–S directions clearly cut broad ridges within ridged 

plains material. Younger plains materials (lower unit of regional plains, unit rp1, and upper unit of regional 

plains, unit rp2) are mildly tectonically deformed by wrinkle ridges and embay both ridged plains material 

and the groove belt. Fragment of C1-MIDR.60N347;1; center of image approx. lat 56.5° N., long 347.1° E.; 

look direction,left; image size, approx. 115 x 115 km; north is up.

Figure 20. SAR image (A) showing relations (B) between densely lineated plains material (unit pdl), groove 

belt (unit gb), and shield plains material (unit psh). Material of shield plains truncates structures of densely 

lineated plains material and grooves of a groove belt and sometimes penetrates into the belt (arrows). 

Fragment of C1-MIDR.60N319;1; center of image approx. lat 57.5° N., long 316.3° E.; look direction, left; 

image size, approx. 115 x 115 km; north is up.

Figure 21. SAR image (A) showing relations (B) between tessera material (unit t), densely lineated plains 

material (unit pdl), shield plains material (unit psh), and regional plains material (unit rp1). Both heavily 

tectonized units (t and pdl) are embayed by material of shield plains. The occurrence of shield plains material 

is within a slightly elevated area that is surrounded by regional plains material, which embays into shield 

plains material (arrow). Some small and dispersed shield-like features (crosses) are seen within regional 

plains material. Fragment of C1-MIDR.60N319;1; center of image approx. lat 56.5° N., long 318.0° E.; look 

direction, left; image size, approx. 115 x 115 km; north is up.

Figure 22. SAR image (A) showing relations (B) between the lower (unit rp1) and upper (unit rp2) units of 

regional plains material. The lower unit of regional plains material forms a homogeneous volcanic deposit 

(upper portion of the image) without visible internal structure. Distinctive flow-like features (curves contain 

arrows) of the upper unit of regional plains material appear to be superposed on the background of unit rp1. 

Wrinkle ridges (lines with open diamonds) deform both units. Fragment of C1-MIDR.60N347;1; center of 

image approx. lat 56.0° N., 352.5° E.; look direction, left; image size approx. 115 x 115 km; north is up.

Figure 23. SAR image (A) showing relations (B) between the upper unit of regional plains material and 

lobate plains material. The upper unit (unit rp2) is deformed by a network of wrinkle ridges (lines with open 

diamonds) that are mostly embayed and covered by lobate plains material (unit pl). Fragment of 

C1-MIDR.60N347;1; center of image approx. lat 53.5° N., long 339.2° E.; look direction, left; image size, 

approx. 115 x 115 km; north is up.

0 25 KILOMETERS

A B

0 25 KILOMETERS

A B

0 25 KILOMETERS

A B

0 25 KILOMETERS

A B

0 25 KILOMETERS

A B

0 25 KILOMETERS

A B

Figure 4. SAR image showing tessera material (unit t). Within 

tessera, several sets of tectonic structures (ridges and grooves) 

intersect to form a unique structural pattern. Fragment of 

C1-MIDR.75N338;1; center of the image, approx. lat 72.2° N., 

long 357.0° E. look direction, left; image size, area, approx. 115 

x 115 km; north is up.

Figure 5. Image showing densely lineated plains material (unit 

pdl). The surface of the unit is characterized by narrow parallel 

lineaments; some of them appear to be fractures. Fragment of 

C1-MIDR.60N291;1; center of image, approx. lat 59.1° N., 

long 301.5° E.; look direction, left; image size, approx. 115 x 

115 km; north is up.

Figure 6. Image showing densely lineated plains material (unit 

pdl) deformed by broad ridges (black arrows). Younger lava 

plains material partly fills valleys between the ridges (white 

arrows). The ridges complicate the surface of the unit pdl, 

which begin to resemble the structural pattern of tessera 

(Atropos Tessera area). Fragment of C1-MIDR.75N299;1; 

center of image, approx. lat 69.3° N., long 303.2° E.; look 

direction, left; image size, approx. 115 x 115 km; north is up.

Figure 7. Image showing ridged plains material (unit pr). The 

surface of the unit is typically deformed by broad (several km) 

ridges (arrows) that sometimes form short belt-like occurrences. Fragment of C1-MIDR.60N347;1; center of image, 

approx. lat 56.5° N., long 347.1° E.; look direction, left; image 

size, approx. 115 x 115 km; north is up.

Figure 8. SAR image showing shield plains material (unit 

psh). Numerous small (a few km across) shield-like features 

are seen on the surface of the unit. Sometimes, larger shields 

and cones with the summit caldera-like features (arrows) are 

seen within the occurrences of shield plains material. Fragment 

of C1-MIDR.60N319;1; center of image, approx. lat 64.3° N., 

long 306.0° E.; look direction, left; image size, approx. 115 x 

115 km; north is up.

Figure 9. SAR image showing pitted and grooved plains material (unit ppg). The morphologically smooth surface of this unit 

displays numerous rounded and elongated depressions that 

sometimes coalesce to form grooves with scalloped edges. The 

unit occurs exclusively at the southern edges of Lakshmi 

Planum. Fragment of C1-MIDR.60N347;1; center of image, 

approx. lat 61.7° N., long 339.8° E.; look direction, left; image 

size, approx. 115 x 115 km; north is up.

Figure 10. SAR image showing the lower unit of regional 

plains material (unit rp1). Networks of narrow and sinuous and 

apparently low wrinkle ridges deform the surface of this unit. 

The regional plains material is the most abundant unit in the 

map area and occurs both inside and outside Lakshmi Planum. 

Fragment of C1-MIDR.75N338;2; center of image, approx. lat 

69.8° N., long 327.7° E.; look direction, left; image size, 

approx. 115 x 115 km; north is up.

Figure 11. SAR image showing the upper unit of regional 

plains material (unit rp2). The surface of the unit is deformed 

by wrinkle ridges and is characterized by higher radar backscatter when compared to lower unit of regional plains material. 

Sometimes the unit shows lobate boundaries and flow-like 

features. In places, wrinkle ridges appear to be less abundant 

within the unit rp2 than within lower unit of regional plains 

material. Fragment of C1-MIDR.60N347;1; center of image, 

approx. lat 56.3° N., long 350.0° E.; look direction, left; image 

size, approx. 115 x 115 km; north is up.

Figure 12. SAR image showing smooth plains material (unit 

ps). This unit typically has low radar backscatter and displays 

dark featureless surface that is largely undeformed by tectonic 

structures. Fragment of C1-MIDR.60N347;1; center of image, 

approx. lat 59.5° N., long 332.5° E.; look direction, left; image 

size, approx. 115 x 115 km; north is up.

Figure 14. SAR image showing undivided crater material (unit 

c, black arrow) and crater outflow material (unit cf, white 

arrow). Crater Cotton (48 km in diameter), fragment of 

C1-MIDR.75N299;1; center of image approx. lat 70.6° N., long 

300.2° E.; look direction, left; image size, approx. 115 x 115 

km; north is up.

Figure 13. SAR image showing lobate plains material (unit 

pl). This unit is characterized by radar-bright flow-like features 

that usually are not deformed tectonically and embay tectonic 

structures within the other units. Boundaries of the unit 

typically have lobate shape. Fragment of C1-MIDR.60N347;1; 

center of image, appropx. lat 55.6° N., long 356.3° E.; look 

direction, left; image size, approx. 115 x 115 km; north is up.

Figure 15. SAR image showing groove belts (unit gb). Groove 

belts represent dense swarms of parallel lineaments, many of 

which are grabens and fractures. Fragment of C1-MIDR. 

60N347;1; center of image approx. lat 55.0° N., long 342.1° E.; 

look direction, left; image size, approx. 115 x 115 km; north is 

up.

Figure 16. SAR image showing mountain belt material (unit 

mb, Akna Montes). The unit occurs as swarms of broad 

(several km) parallel ridges that outline Lakshmi Planum from 

the south, west, north, and east. Fragment of C1-MIDR. 

75N299;1; center of image approx. lat 68.1° N., long 318.2° E.; 

look direction, left; image size, approx. 115 x 115 km: north is 

up.

A B

Descriptions of nomenclature used on map are listed at 

http://planetarynames.wr.usgs.gov/