**GEOLOGIC MAP**

**OF THE**

**VICTORIA (H-2)**

**QUADRANGLE**

**OF MERCURY**

By

George E. McGill and Elbert A. King

1983

Prepared for the

National Aeronautics and Space Administration

by

U.S. Department of the Interior, U.S. Geological Survey

(Published in hardcopy as USGS Miscellaneous Investigations Series Map
I--1409, as part of the Atlas of Mercury, 1:5,000,000 Geologic Series.
Hardcopy is available for sale from U.S. Geological Survey, Information
Services, Box 25286, Federal Center, Denver, CO 80225)

Please direct questions or comments about the digital version to:

Richard Kozak

U.S. Geological Survey

2255 N. Gemini Drive

Flagstaff, AZ 86001

e-mail: rkozak@flagmail.wr.usgs.gov

> **DESCRIPTION OF MAP UNITS**
>
> **PLAINS MATERIALS**

ps SMOOTH PLAINS MATERIAL---Forms mostly small areas of plains that
appear smooth at available image resolution. Albedo similar to or higher
than that of intermediate plains unit. Superposed craters all smaller
than 20 km in diameter and of low density. Characteristically occupies
floors of craters, including large c4 craters. Reference area: lat 36°
N., long 29°. *Interpretation:* A mixture of ejecta from small craters
and material mass wasted from walls of large craters. May include some
volcanic materials

psi INTERMEDIATE PLAINS MATERIAL---Forms smooth to moderately rough
plains characterized by many bright patches and streaks on a background
generally slightly darker than intercrater plains material. Commonly
associated with elongate symmetric and asymmetric ridges and rounded
scarps, all of which appear younger. superposed craters are of moderate
density, are of c2 age or younger, and are mostly less than 50 km in
diameter. Also superposed are secondary craters from several c4 and
fresh c3 craters 100 to 150 km in diameter. Reference area: lat 30° N.,
long 25°. *Interpretation:* Probably basaltic lava flows, but no
unequivocal supporting evidence has been found in the Victoria
quadrangle

pc CRATERED PLAINS MATERIAL---Forms moderately rough to rough surfaces
very similar to intercrater plains material. Unit defined to correlate
with similar unit in Kuiper quadrangle (De Hon and others, 1981) to the
south; elsewhere on Victoria quadrangle cratered plains material is
included in intercrater plains material. Reference area: lat 22° N.,
long 42°. *Interpretation:* Volcanic rock, clastic blanket generated by
secondary impact events, or both

pi INTERCRATER PLAINS MATERIAL---Forms moderately rough to very rough
surfaces with an albedo generally slightly higher than that of the
intermediate plains unit. Contacts with intermediate plains and cratered
plains units locally gradational. Density of superposed craters high.
Reference area: lat 27° N., long 40°. *Interpretation:* Undivided rim
and ejecta materials of overlapping, very old craters and basins.
Probably also includes material similar to that forming intermediate
plains unit.

> **CRATER AND BASIN MATERIALS**
>
> Subscripts refer to degradation sequence from cl (most degraded) to c5
> (least degraded). Degree of degradation is inferred to represent
> relative age (cl oldest to c5 youngest) of craters of closely similar
> diameters (see McCauley and others, 1981, for discussion of this age
> sequence). Craters less than about 20 km in diameter are not mapped.
> *Interpretation:* Impact craters. A very few irregular, small craters
> may be endogenic

c5 CRATER MATERIAL---Undivided floor, rim, wall, and ejecta material of
craters with complete and well-defined rims, central peaks, textured
ejecta blankets, and high-albedo halos and rays. All are \<50 km in
diameter. Density of superposed craters low

cp5 CENTRAL PEAK MATERIAL---Single or multiple rugged peaks near center
of crater

cf5 FLOOR MATERIAL---Rough material on crater floor

cr5 RADIAL EJECTA MATERIAL---Grooved and ridged material extending
outward from raised rim as lineated apron with many secondary craters

c4 CRATER MATERIAL---Undivided rim, wall, and ejecta material of craters
with complete and well-defined rims, central peaks, and textured ejecta
blankets. Density of superposed craters low, but higher than on smooth
plains material. Unit includes floor material for most craters less than
35 km in diameter

cp4 CENTRAL PEAK MATERIAL---Same as cp5 except occurs within c4 craters

cf4 FLOOR MATERIAL---Same as cf5 except occurs within c4 craters

cr4 RADIAL EJECTA MATERIAL---Radially textured annulus around unit c4;
includes secondary craters that are sufficiently well preserved to be
clearly visible around most of the periphery of larger craters

cs4 SECONDARY CHAIN MATERIAL---Aligned crater chains related to c4
craters

c3 CRATER MATERIAL---undivided rim, wall, and ejecta material of craters
with complete and well-defined rims. Most have central peaks. Density of
superposed craters low to moderate. Unit includes floor material for
most craters less than 35 km in diameter

cp3 CENTRAL PEAK MATERIAL---Same as cp5 except occurs within c3 craters

cf3 FLOOR MATERIAL---Same as cf5 except occurs within c3 craters

cr3 RADIAL EJECTA MATERIAL---Around largest craters, includes moderately
well preserved textured ejecta blankets and incompletely preserved
fields of secondary craters

c2 CRATER MATERIAL---Undivided floor, rim, wall, and ejecta material of
craters with complete but subdued rims. Only largest craters have
remnants of textured ejecta blankets. Secondary craters not
recognizable. Density of superposed craters moderate

cp CENTRAL PEAK MATERIAL---Same as cp5 except seen in very few c2
craters

c1 CRATER MATERIAL---Undivided material of craters with subdued and
incomplete rims and no recognizable central peaks, ejecta blankets, or
secondary craters. Density of superposed craters moderate to high

csu CRATER CHAIN MATERIAL, UNDIVIDED--- Crater chains not associated
with any visible crater

> Contact
>
> Scarp---Line marks top; hachures point downslope
>
> Crest of elongate ridge
>
> Crater rim crest
>
> Crater rim---Greatly subdued or buried
>
> Area of bright crater-ray material---Interpreted as ejecta from
> relatively recent impacts

**INTRODUCTION**

Most of the Victoria quadrangle lies within an area that appears bright
on telescopic images of the planet, the bright-albedo feature Aurora,
which approximately coincides with the east half of the quadrangle
(Davies and others, 1978, fig. 11). As is common with most of the imaged
portions of Mercury, the Victoria quadrangle is dominated by basins and
large craters, with plains materials occupying the areas between them.

Almost all the pictures acquired by Mariner 10 that were used for
mapping were obtained during the first encounter: those covering the
southeast half of the quadrangle are incoming close-encounter images,
and those covering the north-west corner are outgoing close-encounter
images. At the time the pictures were obtained, the terminator was at
about long 7° to 8°, within the eastern part of the quadrangle. A large
gap in coverage between the incoming and outgoing images appears as a
northeast-trending diagonal blank strip on the base map. A small part of
this gap was filled in the southwestern part of the quadrangle by very
poor second-encounter images.

No images provide a vertical view; in fact, the smallest angle between
the planetary surface normal and the camera axis is about 50°. The high
obliquity of the images, the wide range in sun-elevation angles, and the
complete transection of the quadrangle by the gap in coverage greatly
hamper geologic mapping. Only in about 15 percent of the quadrangle,
near the southeast corner, do data permit separation of units with the
confidence possible in other quadrangles on Mercury.

**STRATIGRAPHY**

Three widespread units are recognized within the Victoria quadrangle.
These are, from oldest to youngest, intercrater plains material,
intermediate plains material, and smooth plains material. In addition,
central peak, floor, rim, and ejecta materials related to the numerous
craters and basins larger than about 20 km in diameter are mapped. The
simplicity of the stratigraphic scheme is at least in part due to
deficiencies in the data base; the history of plains formation almost
certainly is more complex than our threefold division indicates, but we
were not able to define consistent criteria of albedo, texture, and
cratering for more than three plains units because of the highly
variable quality of available pictures.

PLAINS MATERIALS

**Intercrater Plains Material**

About half of the intercrater area consists of material characterized by
a very high density of small, mostly degraded craters, and an irregular
to rough surface. Superposition relations suggest that this unit is
about the same age as, or older than, all mappable craters and basins.
The origin of intercrater plains material is enigmatic; some may be
primitive crust, as implied by Trask and Guest (1975), but more likely
it is of mixed origin, dominated by breccias formed by
now-unrecognizable ancient craters. Some of the more plainslike areas
included within this unit may well have an origin similar to that of
intermediate plains material.

**Cratered Plains Material**

Within the 5° overlap area with the Kuiper quadrangle to the south, an
area has been mapped that displays moderately rough to rough terrain and
a high

density of mostly degraded craters. This unit is very similar to
intercrater plains material, and cannot be distinguished from it
anywhere else in the Victoria quadrangle. Most of the cratered plains
material is probably volcanic in origin, but some of it may consist of
impact breccias.

**Intermediate Plains Material**

Smooth to moderately irregular plains occupy most of the area between
large craters not underlain by intercrater plains material. These plains
superficially resemble the plains of the lunar maria; they generally
have a relatively low albedo (Hapke and others, 1975) and are
characterized by numerous elongate ridges. Like the lunar maria, the two
younger mercurian plains units have been ascribed to volcanic activity
(Trask and Guest, 1975; Strom and others, 1975; Trask and Strom, 1976),
although this interpretation has been questioned (Wilhelms, 1976). A
volcanic origin seems most probable, but no compelling evidence exists
in the Victoria quadrangle to support this opinion.

The elongate ridges, though clearly associated with intermediate plains
material, are not restricted to it. Locally, ridges extend into
intercrater plains material adjacent to intermediate plains material,
and large young (c4 and c3) craters superposed on the intermediate
plains material commonly are transected by these ridges .

**Smooth Plains Material**

Partly filling most craters is plains material that is smoother and less
densely cratered than intermediate plains material. Because most areas
underlain by this unit are enclosed within craters, contacts between
smooth plains and older plains units are rare. Smooth plains material
thus is defined almost entirely by texture and apparent crater density.
Few superposition data directly support the inferred age sequence, but
the relative youth of the smooth plains unit is indicated by its
presence on the floors of craters that are superposed on intermediate
plains material. The smooth plains unit probably includes materials of a
wide range in age, but the exposed areas are too small to test this
possibility quantitatively. Although a volcanic origin cannot be ruled
out for all or part of the smooth plains material, it is more probably a
mixture of ejecta from very small craters and colluvium mass wasted from
crater walls.

**STRUCTURE**

The ridges associated with the intermediate plains unit are best
interpreted as tectonic in origin because they extend into adjacent
exposures of intercrater plains material and, more significantly,
because they transect ejecta, rims, and floors of craters. The ridges
range in length from about 50 km to many hundreds of kilometers, are
sinuous to lobate in plan, and generally trend about north-south. Most
are asymmetric, with one slope steeper than the other, and at places
they can be more logically referred to as rounded scarps. Commonly, an
individual ridge changes along trend from symmetric ridge to asymmetric
ridge to rounded scarp. Strom and others (1975) interpreted most of
these features to be surface expressions of thrust faults, and we can
find no evidence within the Victoria quadrangle not already considered
in their discussion.

Because of their globally systematic orientations, these ridges and
scarps have been associated with stresses developed by tidal despinning
of

Mercury (Melosh, 1977). However, most trend approximately north-south
and thus do not fit the pattern expected in the midlatitude belt, unless
stresses from overall contraction were superposed on the stresses due to
despinning (Melosh, 1977, figs. 3 and 5).

**GEOLOGIC HISTORY**

The oldest material and features in the Victoria quadrangle are the
intercrater plains material and areally associated, severely degraded
basins. No craters are clearly older than intercrater plains material,
and the relative ages of the cl basins are ambiguous. Numerous large
craters are superposed on intercrater plains material; by analogy with
lunar and martian history (Hartmann, 1966, 1973; Neukum and others,
1975), these craters most likely date from more than about 4 b.y. ago.

The available evidence suggests a relatively long history of plains
formation. Some of the material included in the intercrater plains unit
appears to have been plainslike before the intense cratering
characteristic of the unit. In addition, the younger plains units
exhibit densities of superposed craters ranging from moderate to very
sparse. The intermediate plains material is older than the freshest (c4
and some c3) large craters (100-150 km in diameter) but younger than all
basins, and younger than all large craters that are more than moderately
degraded (some c3, and all c2 and c1). Thus, the material mapped as the
intermediate plains unit overlaps in time of origin the tail end of the
primordial bombardment.

The stresses responsible for the elongate ridges and scarps must have
occurred after the end of the primordial bombardment and after
emplacement of the intermediate plains unit. Where smooth plains
material abuts ridges and scarps, the evidence is mostly ambiguous
because we cannot tell if ridge formation involved smooth plains
material or if the ridges are upwarped intermediate plains material with
smooth plains material ponded against them. On the floors of some
craters, such as Gluck, scarps apparently offset material mapped as
smooth plains, but the exposures are so small that this interpretation
could easily be challenged. Ridges appear to be both older and younger
than medium-size craters (30--60 km in diameter) on the intermediate
plains unit, but intersections of ridges with craters in this size range
are too rare to constrain the time of ridge formation. Thus, ridge
formation obviously occurred after emplacement of the intermediate
plains unit, but how long after remains uncertain in this quadrangle.

Smooth plains material is apparently younger than all large craters, and
hence is the youngest material in the quadrangle with the exception of
the local material related to some very small craters (\<20 km in
diameter).

**CRATER DISTRIBUTIONS**

Figures 1 to 3 are plots of cumulative diameter versus frequency of
craters on the three plains units. Figures 1 and 2 include craters ≥3 km
in diameter on the large areas of intercrater and intermediate plains
units in the southeastern portion of the quadrangle. The two counting
areas together are approximately bounded by lats 20° and 32° and longs
15° and 42° and are separated by an irregular but approximately
east-west-trending contact; the intercrater plains material lies to the
south and the intermediate plains material to the north. Figure 3
includes craters ≥1.2 km in diameter on smooth plains material that
covers the floors of six large craters.

Because of the varied and generally poor quality of the imagery,
detailed cratering history cannot be inferred from these plots. However,
three

observations seem valid: (1) the density of large craters is distinctly
higher for intercrater than for intermediate plains material; (2) for
the intercrater and intermediate plains material, curves for craters
with diameters between 3 and 15 km nearly coincide (the abundant, mostly
degraded small craters characteristic of intercrater plains material but
not characteristic of intermediate plains material are less than 3 km in
diameter); and (3) craters of all sizes on the smooth plains unit are
much less abundant than on the other units, although the smooth-plains
plot is unreliable in detail because of the small total number of
craters counted and the need to combine counts from isolated exposures.

A serious sampling problem exists for counting craters on the
intermediate plains unit, because those in the diameter range of 50 to
150 km commonly occur in clusters, and it is very difficult to determine
which craters of a cluster are younger than the surrounding plains unit
and which are older. The area counted for figure 2 does not include any
of these clusters. Immediately to the north, however, intermediate
plains material surrounds three clusters of large craters, including
Holbein, the c4 crater \~100 km in diameter centered at lat 36° N., long
29°. This large crater clearly is younger than the surrounding
intermediate plains material, and superposition relations suggest that
two or three of the 50- to 60-km-diameter craters east of it also may be
younger. The ages of other craters in the clusters, relative to the age
of intermediate plains, are ambiguous. A second count of intermediate
plains material was made that included the area of clusters of large
craters, and that was based on the extreme assumption that
[all]{.underline} these large craters are younger than intermediate
plains material. The resulting plot (not shown) differs from figure 2 at
the large-crater end, as would be expected, but it still shows a lower
density of large craters than does the plot of craters from intercrater
plains material. Because not all the large craters occurring in
scattered clusters are likely to be younger than intermediate plains
material, the true plot cumulative diameter versus frequency should not
differ much from that shown in figure 2.

**REFERENCES**

Davies, M. E., Dwornik, S. E., Gault, D. E., and Strom, R. G., 1978,
Atlas of Mercury: National Aeronautics and Space Administration, Special
Publication SP-423, 128 p.

De Hon, R. A., Scott, D. H., and Underwood, J. R., Jr., 1981, Geologic
map of the Kuiper quadrangle of Mercury: U.S. Geological Survey
Miscellaneous Investigations Series Map I-1233, scale 1:5,000,000.

Hapke, B. W., Danielson, G. E., Jr., Klaasen, K. P., and Wilson, Lionel,
1975, Photometric observations of Mercury from Mariner 10, 1975: Journal
of Geophysical Research, v. 80, no. 17, p. 2431--2443.

Hartmann, W. K., 1966, Early lunar cratering: Icarus, v. 5, no. 4, p.
406--418.

\_\_\_\_\_1973, Martian cratering, 4, Mariner 9 initial analysis of
cratering chronology: Journal of Geophysical Research, v. 78, no. 20, p.
4096--4116.

McCauley, J. F., Guest, J. E., Schaber, G. G., Trask, N. J., and
Greeley, Ronald, 1981, Stratigraphy of the Caloris Basin, Mercury:
Icarus, v.47, no.2, p.184--202.

Melosh, H. J., 1977, Global tectonics of a despun planet: Icarus, v. 31,
no. 2, p. 221--243.

Neukum, Gerhard, Konig, Beate, Fechtig, H., and Storzer, D., 1975,
Cratering in the Earth-Moon system: Consequences for age determination
by crater counting: Lunar Science Conference, 6th Proceedings, p.
2597--2620.

Strom, R. G., Trask, N. J., and Guest, J. E., 1975, Tectonism and
volcanism on Mercury: Journal of Geophysical Research, v. 80, no. 17, p.
2478--2507.

Trask, N. J., and Guest, J. E., 1975, Preliminary geologic terrain map
of Mercury: Journal of Geophysical Research, v. 80, no. 17, p.
2461--2477.

Trask, N. J., and Strom R. G., 1976, Additional evidence of mercurian
volcanism: Icarus, v. 28, no. 4, p. 559--563.

Wilhelms, D. E., 1976, Mercurian volcanism questioned: Icarus, v. 28,
no. 4, p. 551--558.

**NOTES ON BASE**

This map sheet is one of a series covering that part of the surface of
Mercury that was illuminated during the Mariner 10 encounters (Davies
and Batson, 1975). The source of map data was the Mariner 10 television
experiment (Murray, 1975).

ADOPTED FIGURE

The map projections are based on a sphere with a radius of 2439 km.

PROJECTION

The Lambert conformal conic projection is used for this sheet, with a
scale of 1:4,623,000 at lat 22.5°. Latitudes are based on the assumption
that the spin axis of Mercury is perpendicular to the plane of the
orbit. Longitudes are positive westward in accordance with the usage of
the International Astronomical Union (IAU, 1971). Meridians are numbered
so that a reference crater named Hun Kal (lat 0.6°S) is centered on long
20° (Murray and others, 1974; Davies and Batson, 1975).

CONTROL

Planimetric control is provided by photogrammetric triangulation using
Mariner 10 pictures (Davies and Batson, 1975). Discrepancies between
images in the base mosaic and computed control point positions appear to
be less than 2 km, except for the area in the northwest corner of the
quadrangle. Pictures of this area are so foreshortened that accurate map
transformations were not possible. Since the base mosaic was controlled
by a later iteration of the control net, large discrepancies exist
between this sheet and the Kuiper (H-6) sheet to the south. These
discrepancies were not adjusted, so that features in the zone of overlap
on this sheet appear at different latitudes and longitudes than they do
on the Kuiper quadrangle.

MAPPING TECHNIQUES

Mapping techniques are similar to those described by Batson (1973a,
1973b). A mosaic was made with pictures that had been digitally
transformed to the Lambert conformal conic projection. Shaded relief was
copied from the mosaics and portrayed with uniform illumination with the
sun to the west. Many Mariner 10 pictures besides those in the base
mosaic were examined to improve the portrayal. The shading is not
generalized and may be interpreted with nearly photographic reliability
(Inge, 1972; Inge and Bridges, 1976).

Shaded relief analysis and representation were made by Susan L. Davis.

NOMENCLATURE

All names on this sheet are approved by the International Astronomical
Union (IAU, 1977).

H-2 Abbreviation for Mercury (Hermes) sheet number 2.

H 5M 45/45 G: Abbreviation for Mercury (Hermes) 1:5,000,000 series;
center of sheet, 45° N lat, 45° long; geologic map, G.

REFERENCES

Batson, R. M., l973a, Cartographic products from the Mariner 9 mission:
Journal Geophysical Research, v. 78, no. 20, p. 4424--4435.

\_\_\_\_\_\_1973b, Television cartography: U.S. Geological Survey
open-file report, Astrogeology 58, 35 p.

Davies, M. E., and Batson, R. M., 1975, Surface coordinates and
cartography of Mercury: Journal Geophysical Research, v. 80, no. 17, p.
2417--2430.

Inge, J. L., 1972, Principles of lunar illustration: Aeronautics Chart
and Information Center Reference Publications RP-72-1, 60 p.

Inge, J. L., and Bridges, P. M., 1976, Applied photointerpretation for
airbrush cartography: Photogrammetric Engineering and Remote Sensing, v.
42, no. 6, p. 749--760.

International Astronomical Union, 1971, Commission 16: Physical study of
planets and satellites, *in* 14th General Assembly, Brighton, 1970,
Proceedings: International Astronomical Union Transactions, v. 14B, p.
105--108.

\_\_\_\_\_\_\_977, Working Group for Planetary System Nomenclature, *in*
16th General Assembly, Grenoble, 1976, Proceedings: International
Astronomical Union Transactions, v. 16b, p. 321--325, 330--332,
351--355.

Murray, B. C., 1975, The Mariner 10 pictures of Mercury---an overview:
Journal Geophysical Research, v. 80, no. 17, p. 2342--2344.

Murray, B. C., Belton, M. J. S., Danielson, G. E., Davies, M. E., Gault,
D. E., Hapke, Bruce, O'Leary, Brian, Strom, R. G., Soumi, Verner, and
Trask, Newell, 1974, Mercury's surface: Preliminary description and
interpretation from Mariner 10 pictures: Science, v. 185, no. 4146, p.
169--179.