JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 104, NO. E8, PAGES 18,933-18,956,AUGUST 25, 1999
Spectral properties of the Marius Hills volcanic complex
and implications for the formation of lunar domes and
cones
Catherine M. Weitz • and James W. Head III
Brown University,Providence,
Departmentof GeologicalSciences, RhodeIsland
Abstract. We haveusedmultispectral datafrom the Clementine UV-visible camerato studythe
of to
volcanicfeatures the MariusHills complexandtheircomparison otherlunardomesand
cones.Thereare several mareunitsidentifiedin thecomplex, eachwith a uniqueTi content, as
by in
indicated their415/750 nm value. The domes MariusHills are spectrally identicalto the
mare plainsof the complex,supporting similar compositions.In contrast, most of the volcanic
of
cones thecomplexarelowerin reflectance, bluerin color,andhaveweakermafic absorptions
thanthemareanddomes.The spectral of can
characteristics thecones bestbe explained fine- by
in
grainedcrystallization the spatter the
that compose cones. Other lunarcones,suchasMons
Esam in northernTranquillitatis,have spectral properties similarto thoseat Marius Hills. The
and dark
Rima Parrycones theirassociated mantledeposit appearredder with a strongermafic
absorption than the Marius Hills cones. The conesIsis and Osirisin southern Mare Serenitatis,
of
thedomes RumkerHills, andseveral in
domes northern are
Mare Tranquillitatis spectrally
similarto adjacent mare units. The Mairan andGruithuisen domesin northernOceanus
Procellarum havea feldspathic signature of
characteristic highland materialalthough they areredder
andbrighter thanadjacenthighland to
soils. They appear represent highland materialthat
resembles domes rather than actual mare domes, like those at Marius and Rumker Hills. The
of can by in
diversity lunarvolcanicfeatures bestbe explained differences accumulation ratesand
coolingof ejectedclasts from variouseruptionstyles. Mare domes may haveformedat lower
effusion smallshields
rates,therebyallowinglava to construct 200 km depths and the resulting phaseangles. Thereforewe usedonly these lower-phaseangle
eruptions werelikely at high effusionrates. Cones at Rima orbits to producethe mosaics and color ratio images. When
as by of
ParryV wereinterpreted having formed degassing a spectrawere taken from other areasof the Moon, we listed the
near-surface dike [Head and Wilson, 1993], indicating that phase angle, and for the spectral ratios, we applied this
undercertain circumstances, was possible to produceonly
it 30
wavelengthcorrectionto a standard ø phase angle [McEwen,
cones and no associated mare on the Moon. 1996]. All spectra were taken using 4x4 pixel boxes, and
Studies of lunar domes and cones have been restricted to to from largeerrorsandpoor data
thosethat appeared suffer
LunarOrbiter(LO) and Apollo photographic quality were rejected. Several individual Clementine frames
high-resolution
of
imagesbecause the small size of these features. Galileo were mosaicked togetherboth alongand across orbits to cover
spectraldataof the Marius Hills region indicatedcomplex the Marius Hills region and the other lunar domesand cones.
variations in volcanic activity, including variability in the Because each Marius Hill's mosaic combines orbits taken at
composition the basaltsand pyroclasticdeposits[Sunshine
of differentphaseangles, there are subtle color variations that
et al., 1994]. The resolutionof the Galileo data was only 1.5- can be seen across the mosaics because of variations in the
2 km, making it difficult to studythe spectralpropertiesof the photometriccorrectionas a function of wavelength. In
smaller domesand cones. Only now do we have Clementine contrast,all color differencesseenalong eachorbit are more
multispectral data with resolutions below 200 m to resolve indicativeof compositional variations ratherthan calibration
these featuresand show their spectralcharacteristics. In this errors. The color ratio imagesare simply a way to show
paper, we have usedClementine UV-visible (UVVIS) data to relative compositional differences between the various
examine the various volcanic features of the Marius Hills geologic units. Quantitative differencesare identified in the
region. We have also studiedvolcanic domesand conesfrom spectrafor these units.
other regions of the Moon for comparison, including (1) the Color ratio images were producedand used to assist in
cones Isis and Osiris in southeastern Mare Serenitatis; (2) identifyingvariousgeologicunits. Eachcolor ratio consists
Rima Parry V conesin Fra Mauro crater; (3) the cones Mons of (1) 750/415 nm ratio in the red channel;(2) 750/950 nm in
Esam and domes Grace and Diana in northern Tranquillitatis; the green channel; and (3)415/750 nm in the blue channel.
(4) the domes of Rumker Hills in northern Oceanus of
The 415/750 value,or UV/VIS slope,is a measure both the
Procellarum; and (5) Mairan and Gruithuisen domes in color andthe maturitylevel for lunarsoils. An important
northeasternOceanusProcellarum. Our goal was to use the characteristic of lunar soils is their maturation over time due to
spectralpropertiesof the lunar cones and domesin order to weathering.
space causes strength the 1000
Maturation the of
determineif they were spectrally distinct from the mare and nm absorptionand the overall reflectanceto decreasewhile the
whether these differences could be used to learn more about the continuumslope (i.e., 750/415 ratio) increases[Pieterset al.,
volcanic activity that emplacedthe features. Fischer
1993a; andPieters,1994]. Space produces
weathering
18,936 ANDHEAD:
WEITZ HILLS
MARIUS COMPLEX
VOLCANIC
this optical alteration by the development of a regolith color for a mare unit implies a relatively low TiO2 content
containing
"':'.... ' *4
..•:..::' :::'::>...._•:::: ...., :•** ::::;
...,.. .... ....... ..... '?: .':
e:.'.
ß .................... '::.:
;•,.:.:;:;, :.:K':"';;
......
::;:,;;•;;:.; .... a::a'":'
.:.:F•::.
Figure •. High-resolutionLO V-216 photo illustratingseveraltypes of cone morphologies. A horseshoe-shaped
cone to the south (•lack-white •ow) has been breachedto the southwest, •d it has visible layering along the
in
fl•ks. A l•ger coneto the right (white •ow) hasbeenbreached both the north •d southwhere a channel can be
seenemergingfrom eachdirection. The cone in the north (black •ow) has • i:egula shape, •d it too has been
breached. Locationshownin Figure 2 and North is at the top.
Plate lb shows the location of 121 domes and 46 cones in the LO of of
resolution V images portions the Marius Hills region
region. Topographic data showthat the low domesare 25 km show that many of the cones have a horseshoeappearance
in diameterand 50-200 m high, while the steeperdomesare 2- (Figure6). Morphologically, these conesare very similar to
15 km in diameterand 200-500 m in height [Whitford-Stark terrestrial cinder cones, such as those in Hawaii and the Snake
and Head, 1977]. Figure 5 shows a high-resolution LO V River Plain. The horseshoe appearanceindicates that the
image of several domes. The large dome at the top (black cones were breached on one side where lava flowed out. Cones
arrow) has a flatter, smoother surfacebelow and two rougher, on
are located both on the mare and superimposed domes.
steeperdomes superimposed. Otherdomes showa similar two- Figure 6 showsthreeconeslocatedto the west on the plateau.
part sequence with a smooth, broad dome beneath rougher, The largestcone (white arrow) is situatedon a dome, and it has
steeper domes. In the Clementine data, the domes are been breached both to the north and south, where a channel can
spectrally indistinguishable from the surrounding mare. be seenemergingfrom eachbreach. A smaller cone located to
Domes are visible in both the red and blue mare units shown inthe south(black-white arrow) has a horseshoeappearance and
Plate lb. Many of the domes have sharp, truncated boundaries possible layering inside the cone. The third cone (black
with the adjacentmare plains, indicating that the domeshave arrow) has a very irregular shape and also shows breaching
been embayedby younger mare and therefore represent a where a channelcan be seenemergingto the north.
relatively older stageof volcanismin the region. The volcanic cones are readily visible as black spots in
The volcanic conesin the complex are <3 km in diameter Plate l a, and they are located in both the red and blue mare
and<300 m in height[Whitford-Stark Head, 1977]. High- unitsof Plate lb. There are numerous
and dark spots in the color
18,942 WEITZ AND HEAD: MARIUS HILLS VOLCANIC COMPLEX
0.72
ß Blue Mare
¸ Red Mare
O Intermediate Mare
ß Dark Spots
i
0.70
[] Red Spots
0.68 -
0.66 -
.
¸ o
0.64 -
_
~
¸ []
0.62 -
¸ []
0.60
0.93 0.94 0.95 0.96 0.97 0.98 0.99 1.00
750/900 nm
Figure7. Ratio for
values thevolcanic
features Marius
of (DS),which
Hills. Thedarkspots to
correspondvolcanic
cones, colorandweakest
havethebluest maficabsorption. contrast, redspots
In the several
(RS) thatsurround cones
a and
have veryredcolor strong compared themare darkspots.
maficabsorptions to and
ratio images that have not been identified as conesby previous penetrated the
through mareto the centralpeak of Mariusand
investigators, perhaps becausea significant amount of the a
exposed mixtureof mareandfeldspathic highlandmaterial.
cone has been destroyed. Although there may be other cones can
Smalldark spots be seenalong the wall of Marius, one in
in the complex,in Plate lb we show only the conesidentified and
the southwest anotherin the northwest (Figure8). Both
by previous investigatorson the basis of LO photos. In a few and
havelow reflectances spectra with flatter slopesbetween
by
cases,the dark spotsare surrounded red circles in the color to
the 415 and750 nm channelscompared the maresoils. A
ratio images. In the LO images, the dark spots correspond to plausible explanation for these dark spots is that they
the interior of the cones, while the red circles represent the representlocalized dark mantle deposits producedfrom
cone flanks. Figure 7 showsa plot of 415/750 versus750/900 vulcanian eruptions,similarto dark spots seenon the floor of
nm for some of the volcanic cones and mare units. The dark the craterAlphonsus [Head and Wilson, 1979; Coombset al.,
spotsassociated with the volcanic coneshave the bluest color 1990].
and weakest mafic band of all the units, while the red spots Several large depressionsare visible in the Marius Hills
have the strongest mafic absorption and a 415/750 ratio region and are shownin Plate lb (cross-hatched areas). The
similar to the reddestmare units. An interpretation of the depressions to
located thenorthof Mariuscrater haveupraised
in
volcanic cones spectrais discussed section 4.6 when they rims andoval shapes. They are also alignedalong wrinkle
are comparedto other lunar cones. in
ridges themareandarepartially in
visible Plate 1A by their
3.3 Other Features
bright greencolor along the walls. We suggest that these
featuresformedduringlava migration and drainageor from
Marius craterhas a bright blue color along its walls where magma withdrawlat depthwhichcaused at
collapse the surface.
freshmare hasbeen exposed(Plate lb). The crateris 40 km in of
Onefinal feature interestin the regionis a streakin the
diameterand, using crater excavation estimates for this size south blue is
thatappears in Platela. The streak a portionof
crater [Melosh, 1989; Cintala and Grieve, 1994], the crater the Reiner Gamma Formation located to the south. It has been
shouldhave excavateddown to 4-6 km depth. Thereforethe as ray
proposed a crater from Cavalerius its
although unusual
mare must be at least several kilometers thick in this area since shapeandmagneticpropertiessuggest other possibilities,
the ejecta is spectrally characteristic of the basalt units. including gas
recent emissions [McCauley, 1967]. Telescopic
Becausethe crater has been embayedby younger mare, its multispectral imagesof Reiner Gammaby Bell and Hawke
stratigraphyindicates that a significant amount of volcanism a
[1981]showed deep0.95 gm pyroxene and
absorption no red
occurred both before and after crater formation. At the center continuum of
characteristic maturesoils. From spectral
of Marius is a small crater (-2 km diameter) that appears mixing models,Bell andHawke [1981] suggested that the
to
relatively blue in Plate l a compared other craters, which brightareas by of
weredominated majoramounts very fresh
appeargreen. Spectrafor the crater walls indicate a weak mafic mare basaltfragments of
with minoramounts freshhighland
absorption to
but a high reflectancecomparable the other fresh rocks. A studyof the FormationusingClementinedatashowed
craters. Therefore we suggest that the crater may have to
a high soil iron content(14%) compared the surrounding
WEITZ AND HEAD: MARIUS HILLS VOLCANIC COMPLEX 18,943
750 of
Figure 8, Clementine nm mosaic Marius (40 showdarkspots
crater km diameter).Thetwo whitearrows
localizeddark mantledeposits.
alongthe craterwalls that may represent
of
mareandthepresence extremely immature maresoils [Pinet imagesto determinethe heights and slopes of Isis and Osiris.
et al., 1997]. Our Clementine resultsindicate a high albedo, Figure 10 showsprofiles acrosseach of the cones. Osiris has a
low 750/415 ratio, and a moderate750/950 value comparedto to
symmetricalshapeperpendicular the rille, while along the
the adjacentplains units. Reiner Gammadoesnot have the rille it is higher to the south. It has a height of 90 m and a
samestrong mafic absorptionband as fresh impact craters, width of 2.5 km on the basisof the E-W transect,with a slope
which is why it appearsblue in Plate l a rather than green. of 7.0ø. For comparison, the cones of Marius Hills have
we
Therefore agreewith the previouswork by Bell andHawke heights <300 m and widths <3 km [Whitford-Stark and Head,
[1981] and Pinet et al. [1997] that this portion of the Reiner 1977]. Slopesfor terrestrialconescan be up to 33ø because of
GammaFormation can best be explainedas a mixture of fresh the angle of repose for cinders, but the greater dispersalof
mare andhighlanddebris. clastson the Moon favors lower slopes [McGetchin and Head,
1973; Wilson and Head, 1981]. Isis has a more asymmetric
shapethan Osiris, both along and perpendicularto the rille.
4. Other Lunar Volcanic Cones
Apollo 17 photographs show that the northwestern rim is
We have also studied cones and domes from five other breached, and a channel can be seenemerging from the cone.
locations on the Moon (Figure 1) to assist in our Isis is about 70 m high and 2 km in diameteron the basis of
interpretationof the Marius Hills spectra:(1) the cones Isis thetransect to
perpendidulartherille (SW-NE),with a slopeof
and Osiris in southeastern Mare Serenitatis; (2) cones 7.1ø. The other cones along the rille are too small to be
associatedwith the rille Rima Parry V in Fra Mauro crater; (3) resolved in the topography.
the cones of Mons Esam and the domes Grace and Diana in In the Clementine data, the cones are only a few pixels
across because of their small size and resolution of the data.
.(4)
northernTranquillitatis; the domesof RumkerHills in
northwestern Oceanus Procellarum; and (5) Mairan and The conesarejust visible in the 750 nm imagesbecause their
Gruithuisen domes in northern Oceanus Procellarum. flanks are slightly higher in reflectance than the adjacent
mare. Spectrally, the cones appear to be similar to the
4.1 Isis and Osiris adjacentmare, unlike the cones at Marius Hills, which have
lower reflectancesand weaker mafic absorptions than the
IsisandOsirisare the largestof five conesalignedalong a neighboringmare soils.
linear rille in southeasternMare Serenitatis (Figure 9) [Scott,
to of
1973]. The rille is recognizable the south the cones,but, 4.2 Rima Parry V Cones
beginningwith Osirisandextending northto Isis, it becomes
lessvisible in the Apollo 17 photographs.Isis and Osiris are The 50 km long linear rille Rima Parry V is located in
locatedat the edgeof the basin, so it is possible that other Fra
southern Mauro crater (Figure 11). Justoffset from the rille
cones once existed farther inside the basin but became is a row of volcanic cones to the west (black arrow) and two
completelyburiedas the basin filled up with youngermare. cones to the east [Wilhelms, 1987; Head and Wilson, 1993].
We haveused topographicmaps derived fromApollo 17 stereo Head and Wilson [1993] suggested that the cones were
18,944 WE1TZAND HEAD:MARIUS HILLS VOLCANICCOMPLEX
N
•
Isis
•
Small
Cone •"."
A
Osiris
2 krn
(AS and map Isis in Mare
Figure 9. Apollo17 image 17-2317) sketch of thecones andOsiris southeastern
Serenitatis.Isis is to the north,Osirisis to the south,andsmallerconesarein between. All the conesarealigned
along extensiona graben
linearly the of visible thesouth.
to Also are of profiles
shown thelocations topographic
in
presented Figure 10.
composed spatterand produced
of from strombolianeruptions north. The cone appearsin morphology to be broaderand
from a near-surface dike. On the basis of the horizontal flatter, though,than thoseto the north. An unusualdepression
extensionof the graben, the top of the dike is estimatedto be to the westof the rille (small white arrow) is morphologically
at 650 m depthwith a width of about150 m [Headand Wilson, by
similarto pit cratersproduced magmawithdrawlat depth.
1993]. Spectra of the cones and other geologic units are In the color ratio image (Plate 2a), the cones are
shownin Figure 12. Using representative for
spectra highland indistinguishable from the surrounding terrain. Freshimpact
rocks taken by Tompkins and Pieters [1999, Figure 7], we craters appear blue and green, indicating the presence of
to
interpretthe H2 spectrum representanorthositeexposedby the
highlandmaterial. Surrounding Rima Parry V cones is a
a fresh crateron the southernrim of the crater Parry (Plate 2a). of
darkveneer debristhat is visible in the 750 nm image and
H1 showsa larger crateron the rim of Parry-Bonpland(Plate theLO photograph. The debrishas the samespectrum the as
2a) that couldrepresent mixtureof gabbroand anorthosite.A
a cones. The Alphonsus dark mantle deposits (Figure 1) are
fresh crater on the smooth plains (Plate 2a, FC) has a shape thought to form from vulcanian eruptions when a caprock in
similar to H1 but much lower reflectance, suggestingthat it is the conduit gas
caused buildupuntil enoughoverpressurization
more mature. The smoothplainsthat coverthe region have an permittedan eruption that emplaceda localized dark mantle
anorthositic signature although it is relatively low in deposit[Head and Wilson, 1979; Hawke et al., 1989; Coombs
reflectance, suggesting that it is composedof mature soils et al., 1990]. There are no volcanic cones associated with the
from an impact melt origin. A fresh highland signature is Alphonsus deposits;instead,they have centralpits aligned on
observedonly where there has been masswasting or exposure linear rilles. Therefore, while the Alphonsus eruptions
by youngercraters. Comparedto the smoothplains,the cones emplaced only a dark mantle deposit from vulcanianactivity,
have a lower reflectance,a slightly larger 415/750 value, and a the Rima Parry eruptions appear to be strombolian style
similar 750/950 value. There is no indicationin the spectraof activity that produced both dark mantle depositsand spatter
any mare plains in the area that may have been erupted in cones. A further discussionof the types of eruptions is
association with the formation of the cones. discussed in section 5.
In addition to the cones identified on the floor of Fra Mauro
crater,thereis a large coneon the floor of the crater Bonpland,
4.3 Cones and Domes in Northern Tranquillitatis
about 10 km offset to the eastof the Rima Parry V rille (Figure
11, large white arrow). LO V images show an unusual feature There are numerous mare domes located in northeastern
here, but it has not yet been documented volcanic. In the
as Tranquillitatisbasin. Most of the domes are found within the
Clementine data, the cone has the spectral shape and low high-Ti mare,but a few are alsoin the older low-Ti mare farther
reflectance characteristic of the Rima Parry V cones to the there exists topographic
north [Staidet al., 1996]. Because
WEITZ AND HEAD: MARIUS HILLS VOLCANIC COMPLF_,X 18,945
tq UJ
Z
<:
(w) j. H91=JH (w) .I.H913H
o
o
(m) 1H913H
(m) .I.H•I•IH
18,946 WEITZ AND HEAD: MARIUS HILLS VOLCANIC COMPLEX
11. 16 photo
Figure Apollo P-5425 ofRima Parry rilleand
V volcanic (black The
associated cones arrow). bright
highlands tothe of craters Mauro and
correspond rims the Fra (top) Bonpland(bottom). large
The white shows
arrow
cone
another on Earth. farther the
craters seen
located to south. small
The white arrow an
indicatesunusual that pit
depression resembles
data derived from Apollo 15 photography for the more 160 m highand8 km across, with a slopeof 2.0ø. Its central
northern domes, we have focused. on them. These domes pit is 1 km wideand80 m deep. Dianais shorter than Grace,
includeGrace,Diana, and an unnamed dome (Figure 13). In butit hasa muchdeeper pit.
central It is 45 m high and5 km
additionto the domes, Mons Esam representsoverlapping deepcentralpit
wide,with a slopeof 2.6ø. Its unusually
cones aligned linearly, similar to the Rima Parry V cones. to
compared its smallheight be to
could attributed embayment
Topographic profiles for the domesGrace and Diana and the of the coneby other mare(perhaps from Grace),thereby
conesof Mons Esamare shown in Figure 14. Graceis about its but
reducing height. MonsEsamis only 4 km across over
ratio and of
Plate2. Color images 750nmframes lunar
domes cones
and studied thispaper.The
in ratios
the in in
represent 750/415 red,750/950 green, 415/750 blue. (Plate Thecones
and in 2a) with
associated therille
Parry are
Rima by
V shown blue arrows. cones associated mantle
The and dark have in
deposits a lowalbedo the750
In color image, blue
nmmosaic. the ratio fresh while red orange
the represents highlands, the and show
colors more
highland Nomare can identified. H2,and represent locations in Figure
mature soils. units be H1, FC spectra shown
The Grace Diana and unnamed (U)along thecones
12.(Plate2b) domes (G), (D), an dome with Esam are
Mons (ME)
by in
shown an-ows the750nmimage.Mons Esam a much
has albedo thedomes, characteristic at
lower than a seen
Hills 2c) in
Marius aswell. (Plate Outlined yellow the750nmimage thelocations 11domes,
on are of while the
Rumker is in
Hills boundary shown white. Thedomes red
havethe same colorasthe mareon the RumkerHills.
the Hills
SurroundingRumker areother mareunits higher contents. 2d)Twoof thethree
with Ti (Plate domes
Mairan
are in 750 image yellow
shown the nm by arrows. domes a red
The similar theadjacent
have color to highlands.
2e) Gruithuisen areshown these
(Plate All three domes in images. domes
The appear redder the
slightly than
highlands thecolorratioimage.
surrounding in
WEITZ AND HEAD: MARIUS HILLS VOLCANIC COMPLEX 18,947
A B
N. Tranquillitatis
Rima Parry
H1
2O km 20 km
c D
Mairan Domes
Rumker Hills
III
30 km
E Gruithuisen Domes
20 km
20 km
18,948 WEITZ AND HEAD: MARIUS HILLS VOLCANIC COMPLEX
i , , , I , , , , I , , , • I • • • • I .... I , , , , I
4000 Cones • Highlands
--•- -Volcanic I[
• Plains ---I•--Highlands
-Smooth 2
Crater
- -&-- Fresh
3500
3000
2500 mmffff
.... m
.• m.m
m
• 2ooo .•' .---- . .•... -•- - -
ffmmfmmm
ffmmff mmm
. .
-
• • ...... •--••
lOOO
500 ' ' ' ' I ' ' ' ' I ' ' ' ' I ' • ' ' I ' ' ' ' I ' ' ' ' I
r00 500 600 700 800 900 1000
Wavelen•,h
Figure 12. Spectrafor Rima Parry V conesand other geologicunits. The cones have a low reflectance and a weak
mafic absorption that may be due to volcanic glasses or glassy spatter. The other spectra are characteristicof
anorthositic commonlyfound in highland rocks [Tompkinsand Pieters, 1999].
breccia and noritic signatures
ø, it to
260 m high, with a slopeof 11.0 making comparable The high-Ti mare has a lower reflectancethan the low-Ti mare.
the conesof Marius Hills and Isis and Osiris. Central pits are Another unnameddome located farther to the west (Plate 2b, U)
although
visiblealongthe structure, they aretoo smalland in the low-Ti mare has a large pit crater. Grace is spectrally
shallowto be resolvedin the topographydata. similar to this unnameddome except that it has a slightly
The color ratio image(Plate2b) showsa red, low-Ti mare stronger mafic absorption. Diana has a spectrum that is
anda blue,high-Timare. Spectra in 15
shown Figure reveal in
intermediate reflectance and shape betweenthe high-Ti mare
that Mons Esam is similar to the high-Ti mare but with a and the unnamed dome. Thereforeit appears that Graceand the
slightlyflatterUV/VIS slope(i.e., higher415/750 value). unnameddome eruptedas part of the low-Ti mare eruptions
in
Mons Esamhas the lowestreflectance the image, similar to followed by emplacementof younger high-Ti mare and the
of
the low reflectance the Rima ParryV andMariusHills cones. Mons Esam cones. Diana appearsto representan intermediate-
Figure 13. Apollo 17 frame M-305 showing the domes Grace (black arrow) and Diana (black-white arrow) in
northernMare Tranquillitatis. The conesof Mons Esam are to the northeastand anotherunnameddome (Mute arrow)
is to the west.
WEITZ AND HEAD: MARIUS HILLS VOLCANIC COMPLEX 18,949
DIANA
GRACE 6400
6500 6500
6300 6300
6400
6200
4 6 8 0 2
Distance (km) Distance (km)
MONS ESAM
6600 660O
650O 65O0
6400
63OO
0 2 4 6 8 9
Distance (km)
Figure 14. Topographic for
profiles Grace, Diana,andMonsEsam (LunarTopophotomap61A2S1). Graceand
are with central
Diana relativelylow features shieldvolcanoes.Thecones Mons
pits, very similarto Icelandic of
are and
Esam steeper rougher, of and
whichis moretypical spatter rampart on
cones Earth.
Ti unit or a spectral mixture of the low-Ti and high-Ti mare mare to the east. The orange unit located to the southwestis
units. spectrally similar to the mare on the Hills but has a weaker
UV/VIS slope. Because the domesare spectrally identical to
4.4 Domes of the Rumker Hills the mare on the Hills, it supports Whirford-Starkand Head's
[1977] interpretation that the domes were producedby low
on
Over 30 domesmay be concentrated the 80 km diameter
effusion rates, perhaps at the terminal stages of the eruptions
Rumker Hills in northern Oceanus Procellamm [Smith, 1974].
that emplacedthe mare on the Hills. We do not believe that
Plate 2c shows the Clementine color ratio image with the 1 1
the domesrepresentstratovolcanoes, as suggested Smith by
largestdomesoutlinedon the 750 nm mosaic. Smith [1974]
[1974], because on Earth stratovolcanoes form above
dividedthe domesinto three types, each related to a different
subductionzones by multiple eruptions of lava flows and
eruptionperiod. All the domesappearrelatively flat compared
pyroclastic deposits and we see no evidenceof this at Rumker
to those of Marius Hills, with a smooth, circular appearance Hills. The blue craters seen in the north of Rumker Hills have
and somewith possiblesummitpit craters [Whitford-Stark and
a spectrum of
(Figure 16, Crater Wall) characteristic highland
Head, 1977]. In the color ratio image, Rumker Hills has a
material. We propose that the highland material was either
brightred color. To the west are youngerred mare, and to the
east are blue mare units. Several of the northern craters on the
carriedin by secondarycratersor exposedbeneath the low-Ti
mare in the north.
Hills have a blue color, indicating the presence of either
highlandmaterialsor low-Ti mare. 4.5 Mairan and Gruithuisen Domes
Spectra for the various geologic units in the image are
shownin Figure 16. One of the domesis spectrallyidentical The Mairan and Gruithuisen domes are distinguished by
to the mare on the Rumker Hills, suggesting that it was their red color in the infrared, their high topography,and their
produced from the same eruption that emplacedthe low-Ti morphological similarity to volcanic domes [Head and
mare. The purplemareunit in Plate2c just west of the Rumker McCord, 1978]. Their morphology and texture have been
Hills has the lowest reflectance, even lower than the high-Ti interpretedto be due to more silicic compositionscomparedto
18,950 WEITZ AND HEAD: MARIUS HILLS VOLCANIC COMPLEX
, , , , I , , , , I [ , ] , I , , J , I , , , , I , , , , I
1200
11oo
/
/
/
/
/
lOOO /
/
/
/
/
/
900 /
/
/
/
800
/
/
;. Grace
'-I
ß "Diana
7OO
-- ß -Mons Esam
- -&- - Low-Ti Mare
ß - v- - High-Ti Mare
• Unamed Dome
6OO
500 .... i , , ,,, • , , , ' I ' ' ' ' I ' ' ' ' I ' ''' ' I
400 500 600 700 800 900 1000
Wavelength (nm)
e of and
Figur 15. ThespectrumGrace anunnamed aresimilar
dome Grace a slightlystronger
except has mafic
Both similar the
absorption. are to low-Ti but
mare withlower
reflectances. isintermediate
Diana the
between high-
andlow-Tiunits.Mons is to
Esam similar thehigh-Ti
mare slightly
although in
lower reflectance.
mare domes [Head.and McCord, 1978]. Head amt McCord all threeGruithuisendomes.TheMairandomes as
appear a red
[1978] observed that their strong ultraviolet absorption color, similar to the adjacenthighlands. The Gruithuisen
distinguishedthem from the highlands and could indicate a domes red to
also appear compared the bluish-redhighland
lower content of iron or titanium. Plate 2d shows the color soils.
ratio image and 750 nm frame for two of the Mairan domes, Figures17 and 18 show the spectrafor the variousdomes
while Plate 2e illustrates the color ratio and 750 nm mosaic for andgeologic all
units. The domes have spectra characteristic
1800
1600
1400
1200
IOO0
800 --- -- Rumker Hills
ß - •- - Dome
-'-I' - Intermedlate-Ti Mare
6OO •-- High-Ti Mare
--O-- Low-Ti Mare
-
ß z3- - Crater Wall
4OO
400 500 600 700 800 900 1000
Wavelength(nm)
of Hills surrounding units.The
Figure 16. Spectra theRumker and mare are indistinguishable
domes spectrally
the on Rumker The
from mare the mare
Hills. other units in their
vary UV/VIS and absoftions all
slopes mafic but
flatter
have UV/VISslopes
compared Rumker The
tothe Wall refers blue
Hills. Crater spectra tothe secondary craters
the of matehal.
in thenorththatindicate presence highland
WEITZ AND HEAD: MARIUS HILLS VOLCANIC COMPLEX 18,951
, , , , I , , , , I , , , , I , , , , I , , , , I , , , , I
2500
-- -- Mare
' ' O' ' Highlands
• -Mairan 1
Dome ,,•.-
2000
•-- Mairan2
--,--
Dome
Mairan Dome 3 ß,
,/,' '
/'
ß ,/ •'•',0' '
1500
/ ,•.'.."
1000
500 ' ' ' ' I ' ' ' ' I ' ' ' ' I ' ' ' ' [ ' ' ' ' I ' ' ' ' I
400 500 600 700 800 900 1000
Wavelength (nm)
and
Figure 17. The threeMairan domeshave higher reflectances steeperUV/VIS slopesthan the highland soils,
of
but their shapeis characteristic highland-likefeldspathicmaterialrather than mare.
material,which is also seenin the highland compared the surrounding
of feldspathic to highlands, their overall spectral
rocks. The highest albedo and lowest 415/750 value is
character more similar to highland material than to mare.
to on
corresponds freshimpactcraters the domes (Figure18, can
Their brighter appearance be explainedby steeperslopes
Highland Crater), as noted previously in telescopicdata causingmore masswasting and exposure of fresher surfaces.
[Chevrelet al., 1995]. Thesefreshcratersappeardarkblue on Their lower 415/750 ratios are more consistent with a mature
the ¾ domein Plate 2e, and their spectraresemblethat of soil, however. In summary,the Mairan and Gruithuisendomes
anorthosite[Tompkinsand Pieters, 1999]. Although the representnonmare material with an unusually high UV/VIS
domesdo have smaller415/750 values and higher albedos slope,perhaps due to lower titanium contents. However, it is
, , , , I , , , , I , , , , I , , , , I , , , , I , , , , I
I 3
3000 '7 Dome I
I'' ,x-- Dome 1(y) I
I '--I' -Highland Crater I
...,.l"
I •" Highlands I
2500 I -'0'" Mare I
2000 ,/ ./' .- ....
.....zx zx'''"x
j
./ / .ß
...... :_:.2:.._+._.--*
limaIll
1500
_.
I"' ./'
/ .--":5'""....'---
..-'..'.•'"
..-_'.5-: _........
.., :5,,.-' • •..o- .......
1000 ø'-;'"" -•' '
500 .... • ....
400 500 600 700 800 900 1000
Wavelength (nm)
Figure 18. The threeGruithuisendomes and UV/VIS slopes
alsohavehigherreflectances steeper than the highland
soils. The Highland was on
Craterspectrum takenfroma freshcrater the8 dome.
18,952 AND MARIUS VOLCANIC
WE1TZ HEAD: HILLS COMPLEX
clear that these domes could not be formed by the same On the basisof the spectralpropertieslisted in Table 1, the
eruption
styles emplaced othermare
that the domes studied domes of the Rumker Hills have the lowest 415/750 ratio and
in
thispaper.
Previousstudies HeadandMcCord
by [1978],Head therefore are the reddestfeature studiedin this paper, even
et al. [1978], and Malin [1974] show that the featuresare redderthan the Mairan and Gruithuisenhighland domes. The
morphologically spectrally
and fromthe highlands, AristarchusPlateauDMD is also very red and has a 750/950
distinct
suggesting they cannotsimplybe remnant
that highland value similar to the Rumker Hills. However, the red color of
Plateaumay be due to the high Ti content the
islandsbut also requirean explanationfor their spectral the Aristarchus of
Chevrel al. [1999] outlineevidence there volcanic glasses[Bell et al., 1976], while the red color of the
signature. et that
may be adjacent non-mareregions associated with this Rumker domes indicates a very low Ti content in the mare
volcanic style as well. [Pieters, 1978]. Additionally, the 750/950 nm value for the
Rumker Hills reflects the strength of the high-Ca pyroxene
absorptionin the mare, while the ratio indicates the presence
4.6 Spectral Comparison of Lunar Cones and in
of a glassband absorption the Aristarchus Plateau DMD. In
Domes
termsof reflectance,the Rumker Hills have the highest values
to
In order spectrally all
compare the conesanddomes in comparedto all the other mafic featuresstudied. The dome
this study,we have listedrepresentative ratiosand Grace in northern Tranquillitatis has a similar color and
spectral
reflectancevalues for these features(Table 1). All the ratio reflectance to the low-Ti domes in Marius Hills, as well as a
to
valueshave been corrected 30ø phaseangle to remove any mafic signaturecharacteristic mare soils. A low-Ti domeof
of
differences by
caused phase anglevariations [McEwen, 1996], Marius Hills has a 415/750 value similar to the high-Ti mare
and only those spectrathat did not show an erroneous of Serenitatis (22øN, 29øE), illustrating that the lowest
inflection at 950 nm are listed. We show the 750/950 values titanium mare units at Marius Hills are actually relatively high
rather than the 750/900 ratio because this is the more standard in titanium comparedto other lunar mare. An intermediate
ratio usedby the lunar sciencecommunity,and we want to color domeat Marius Hills has a slightly stronger mafic band
our
compare values those to by In to
taken others. addition the than both the low- and high-Ti domes. Except for the low-Ti
domesand cones studiedin this paper, we also show the dome, the domes at Marius Hills have lower reflectances than
spectralratiosof the TaurusLittrowandAristarchus Plateau other lunar domes and both Mare Serenitatis mare units.
darkmantle deposits(DMDs). The Taurus LittrowDMD refers The Rima Parry V cones are spectrally identical to their
to theregionaldeposit at edge
located thesoutheastern of Mare surrounding dark mantle deposit. Telescopic near-infrared
Serenitatis.Samples fromtheApollo 17 site, located reflectance
returned spectraof 25 localized dark mantle depositstaken
at theeastern of
edge theTaurus that
LittrowDMD, indicate the by Hawke et al. [1989] indicate three compositional groups,
deposit containssubmillimeter blackbeads
crystalline mixed depending upon their 1.0 gm absorption. ClementineUVVIS
of
with lesseramounts orangeglasses[Heiken et al., 1974; spectraconfirm the three co•npositional et
groups [Gaddis al.,
to
Pieterset al., 1974]. The black beadsare compositionally 1997]. After applyingan offset for comparison Clementine
to
equivalent the orange glasses wereproduced the spectra
and from by
obtained Gaddiset al. [1999], we find that the Rima
sameeruption,but the presence olivine and ilmenite Parry spectrafall betweengroups1 and2, with the 950/750
of
crystals reflects slower cooling rates [Arndt and von value matching that of group 2 (fragmentedbasaltic material)
Engelhardt, 1987]. Whereas Taurus
the Littrow DMD i s and the 415/750 ratio similar to that of group 1 (mixture of
spectrally by beads[Pieterset al., highlands and glassy juvenile material with smaller amounts
dominated crystallized
1973; Adamset al., 1974; Gaddis al., 1985; Hawkeet al., of basalt material). The Rima Parry cones and dark mantle
et
1990], Aristarchus Plateau dominated volcanicglasses have a 715/950 value similar to the Aristarchus Plateau DMD
is by
[Zisk et al., 1977; Luceyet al., 1986; McEwen al., 1994; but slightly bluer in color. One possibility is that the cones
et
Weitz et al., 1998]. and dark mantle are composedof glassy material, with the
Spectral
Table 1. Representative Ratiosand Reflectances
Feature 415/750* 750/950* %Reflectance at 750 nm
Marius Hills black cones 0.67 0.92 7.7
Mons Esam 0.66 0.91 8.6
MariusHills high-Ti dome 0.66 0.95 8.1
Osiris 0.66 0.94 9.0
Marius Hills intermediate dome 0.65 0.97 9.2
Taurus Littrow DMD 0.65 0.89 7.9
Mare Serenitatis
high-Ti 0.63 0.94 10.0
Marius Hills low-Ti dome 0.63 0.96 9.8
Diana 0.63 0.91 9.4
Grace 0.62 0.93 10.0
Marius Hills red cones 0.60 1.00 9.1
Mare Serenitatis low-Ti 0.60 0.94 10.3
Rima Parry 0.59 0.96 11.9
Gruithuisen dome 0.59 0.92 21.1
Mairan dome 0.58 0.92 21.7
Aristarchus Plateau DMD 0.54 0.96 10.5
Rurnker Hills 0.53 0.94 12.6
DMD, dark mantledeposit.
have normalized 30 phase
* Ratios been to ø angle.
WErlZ AND HE•: MARIUS HILLS VOLCANIC COMPLEX 18,953
difference color between glasses Aristarchus
in the at Plateau mafic and glass absorptionsaround1000 nm, assumingthat
and those at Rima Parry resulting from distinct titanium the cone flanks are a mixture of lava and glass-richspatter.
contents[Bell et al., 1976]. However,this hypothesiscannot
be determinedwith certainty becausethe spectra represent 5. Formation of Lunar Volcanic Features
whereas studies Bell et al. [1976] were
maturesurfaces, the by
forpure,freshvolcanic
glasses. theRimaParryglasses
If were In a manner similar to basaltic eruptions on Earth [Wilson
partially crystallized, they would plot closer to the Taurus and Head, 1981; Head and Wilson, 1989], a variety of volcanic
Littrow 750/950 value. Since they do not, we believe they features can form on the Moon, depending upon the
of
have a higherproportion glasses.The conesthemselves are accumulation of
rate and temperature the clasts. The highest
likely to be composed of glassy spatter to develop the fluxes, accumulationrates, and clast temperatures will tend to
constructs. A further examination of how they formed is form sinuous and
rilles. The high temperatures turbulentnature
discussed section 5. Rima Parry cones have the highest
in of the flows causethermal erosion of the underlying substrate
reflectances all the cones, although they are lower than the
of to form the rilles and their source depressions[Carr, 1973;
Rumker Hills domes. The cone Osiris has spectral ratios Hulme, 1973; Head and Wilson, 1980; Wilson and Head,
consistent with mare soils. 1980]. Clementine data show that the rilles expose fresh mare
To account the spectra the dark spots in Marius Hills
for of along their walls, consistent with layering visible in Apollo
of
that correspond cones (Table 1, Marius Hills black cones) 15 photographs Hadley rille [Howard et al., 1972]. As clast
to
requires material that will darken the soil and remove any temperatures
a and accumulation lava ponds and
rates decrease,
mafic signature, similar to the effect that agglutinatesproduce lava flows will result. Actual preserved do
pyroclasts not form
in lunar soils. On Earth, the flanks of basaltic volcanic cones until the clasts reach sufficiently low temperatures that they
are composed scoria, including spatter and cinder, and we can cool rapidly.
of
assume that the lunar cones are formed of similar scoria in Basaltic cones are common constructs on Earth. The cones
order to build up a cone. Basaltic spatter sometimes has a form around a vent and result from Hawaiian or strombolian
microcrystalline structure(microlites) becauseof a cooling style eruptions that commonly produceassociatedlava flows
rate that allowed nucleation of crystals but inhibited their [Wilson and Head, 1981; Head and Wilson, 1989]. Cinder
growth [Cas and Wright, 1988]. Glasses alsounstable
are over cones often have slopes related to the angle of repose for
time and can devitrify to form microlites,a commonprocess in cinder,and they have large cratersrelative to their basal width
obsidians on Earth [Lofgren, 1971] and thought to have [Wood, 1979]. Basaltic spatter cones form above dikes when
occurred the Apollo 17 orange glasses [Weitz et al., 1996].
in large clasts land hot but accumulate slowly so there is
Assuming that lunar spatterhas similar microlites, they would sufficient time to cool before the next clast lands.
have been crushedto fine-grained sizes during regolith On the Moon, lunar domes are thought to form from
formation and could act as a darkening agent to explain the relatively low eruption rates and low gas contents, both of
spectra for the dark spots. The cones of Mons Esam in which would tendto cause buildupof lava arounda vent. Lower
northern Tranquillitatis basin are similar to the cones of lava temperaturesleading to increased viscosity may also
Marius Hills, and their spectral signaturesindicate that they favor dome formation, rather than extensive mare flows.
too may have microlites to decrease reflectanceand mafic
the Domes can form from strombolianor Hawaiian eruptionswhen
absorption, as well as producea bluer color. Becausethe hot magma clasts are not accumulatingrapidly and there is
Marius Hills and Mons Esam cones have stronger mafic adequate time for the claststo cool and increasetheir viscosity
absorptions than the TaurusLittrow DMD, we suggest that before the next one is deposited. On Earth, low effusion rates
they developedfewer ilmenite crystals to allow a stronger formed the low shield Mauna Ulu in Hawaii [Swanson et al.,
mafic signatureto be identified. 1979], and lunar domes, like those of Rumker Hills and
The annularred spots(Table 1, Marius Hills red cones) that Northern Tranquillitatis, may have also resulted from low
correspond the cone flanks and surround
to some of the dark effusionrates,particularlyin the terminal phasesof eruptions
spots have a very strong mafic absorption and similar that emplacedthe mare.
415/750 nm ratios to the other mare units. They do not have The Marius Hills representa distinct type of domesowing
spectralratios that match any of the three groupsof localized to their somewhatsteeperslopesand roughersurfaces. If mare
dark mantle deposits[Gaddiset al., 1999]. Strombolian and lavas erupted over jagged highlands, then the rough
Hawaiian eruptions produce some fine ash and achneliths topography associatedwith the Marius Hills domes could be
(small glassyfragments, suchas Pele tears) that are glass-richexplained by thin mare overlying a rougher substrate.
andcan be carried farther away from the vents than the larger However, no underlying highlands are visible or exposed by
spatter. If submillimeter glass beads were producedduring impact craters,implying that the dome morphologyis a result
cone formation, then we should be able to identify these of the magmasthat composethem. Their morphology must
glasses looking for a glass absorptionsimilar to that seen
by thereforeresultfrom higher-viscosity magmas, shorter flows,
in dark mantle deposits composedof volcanic glass beads, or lower effusion rates. There are several processesthat can
suchas the Aristarchus Plateau. The Marius Hills red spots areincrease magma viscosity, including an increase in silica
bluer andhave a much stronger glassband absorption than the content, lower magma temperatures, and higher crystal
Aristarchus Plateau volcanic glasses. Bell et al. [1976] contents[Head et al., 1978]. It is unlikely that lunar magmas
determined that the color of volcanic glassesis a function of were able to differentiate to produce more evolved
their Ti and Fe contents. Therefore, assuming similar Fe compositions [Rutherford et al., 1974]. Lower eruption
contents, the redder color of Aristarchus Plateau volcanic temperaturesand higher crystal contents are expected in
glasses may reflect a higher Ti contentcompared the glasses magmas
to eruptedin the terminal stage of an eruption when the
on the coneflanks. The stronger mafic bandin the red spotsi s mass flux has decreased. Therefore we interpret the Marius
difficult to explain but may result from a combination of the Hills domes to represent the result of cooler, more viscous
18,954 WEITZ AND HEAD: MARIUS HILLS VOLCANIC COMPLEX
magmas eruptedduring the later phases of eruptions; these enoughto form only spatter. The morphologicaldifferences
domessubsequentlybecameembayedby younger, more fluid between Isis andOsirismay reflectthe locationalong the dike
mare lavas. wherethey formed,with Isis forming at one end whereclasts
Volcanic cones on Earth can be producedby Hawaiian, to
stayedhotterin an optically denseplume compared a lower
strombolian, and vulcanian style eruptions. Formation of in
optical density plume at Osiris. The differences plume
volcanic cones on the Moon requireshigh cooling rates that optical densitycouldbe from either a lower gas content or a
allow clasts to land cool enough to form spatter and cinder higher volume flux at Isis.
rather than lava. Cones must be composedof clasts that are
Mons Esam also has no visible dark mantle depositand
larger than submillimeter;otherwise,the clasts will be widely the of
more closelymatches spectralcharacteristics the Marius
dispersedto form dark mantle deposits [Wilson and Head, Hills volcanic cones,even thoughits morphologyis similar
1981]. Completely and partially weldedspatter will produce to the Rima Parry cones. The low reflectanceand weak mafic
volcanic cones, as will cinders. For terrestrial cones, spatter
of
signature the Mons Esamconesimplies a similar cooling
and cinder are both producedfrom the same fragmentation historyto the clasts namely,
that form the MariusHills cones;
processat the vent, but the larger size of spatter allows it to clasts to
thatformedspatter developa coneandsomecooling
cool more slowly and form irregular shapes, while cinder is in the clasts to form microlites. The lack of associated dark
smaller scoria that is deposited as a solid. Lunar volcanic mantle deposits at both Mons Esam and Marius Hills cones
cones most likely formed either at the end of eruptions when that in large
indicates gasbubbles the magmaweresufficiently
of
eruptionrateswere lower or by degassing near-surface dikes to form only largerclasts duringfragmentation. The conesat
[Headand Wilson, 1993]. Many lunar cones, like those in Rima Parry V, Isis, Osiris, and Mons Esam are aligned
Marius Hills and Isis, have associated small lava flows,
linearly, but no alignment is recognizablefor the cones in
indicating that some clasts landed hot and could coalesceto Marius Hills. This observation suggeststhat the cones at
form flows.
the
Marius Hills represent terminal stagesof earliereruptions
Wood [1979] found that average terrestrial cinder cones dueto decreasing massfluxes. Nearthe endof the eruptions,
were produced from magma chambers at depths of -3 km, the magma risespeed mayhave decreased sufficientlyto allow
whereaslarger cones couldhave sourcedepths at the base of gas bubbles to coalesce into larger bubbles, which would
the crust (-40 km). He suggestedthat the smaller volume for subsequently to
burstat the surface producespatteror cinder.
lunar conesimplies either lower effusion rates from shallower is of
This styleof eruption characteristic strombolian activity
magma chambersor high eruption rates from brief eruptions on Earth.
[Wood,1979]. In termsof volume, Osiris is 0.13 km3, the the
The MariusHills complexillustrates varietyof volcanic
larger in
cones Marius Hills are0.5-0.8 km3, andcinder cones features can form on the Moon. The high concentration
that of
in Arizonaare0.2-0.4 km3 [HeadandWilson, 1979]. On the sinuous
rilles, domes,and conessuggests somethingunusual
basis of morphometricrelations, Wood [1979] proposedthat aboutthisregioncompared the rest of the Moon [Whitford-
to
Isis and Osiris representedcinder cones, while three cones in Starkand Head, 1977]. Crustalthicknesscalculated Zuber
by
the Marius Hills region were equivalent to terrestrial shield no
et al. [1994] showed unusuallythin crust here that would
volcanoes. However, Head and Wilson [1991] outlines
at to on
favor eruptions this location compared elsewhere the
evidencethat shallow magma reservoirsshouldbe very rare on Moon. One possibility to accountfor the presenceof these
the Moon because of the density trap at the base of the is
volcanic features an anomalous crust,and perhapsmantle,
anorthositic crust. This densitytrap preventedabundantdikes has
beneaththe region. Recently, LunarProspector measured
from stalling in one location in the shallow crust, which is high concentrations of Th in OceanusProcellamm and Mare
on
requiredto form shieldvolcanoes Earth. The smallersize of et
Imbrium [Lawrence al., 1999]. This region, termedthe
lunar volcanoesimplies that there were fewer eruptions or one Lunar Hot Spot,is believed to have formed before the Imbrium
long eruption that could build up a small shield. Lower impact [Korotev, 1999]. Marius Hills is located toward the
effusion rates would have prevented lavas from traveling far center of the Procellarum basin, and its centralized location
from the vent, which would favor dome formation.
may have resultedin the unusualvolcanism seen here. There
In the case of Isis, Osiris, Mons Esam, and Rima Parry V, are several different compositions for the mare units in the
the cones most likely formed along a rille by degassingof a are
complex,indicatingthat severalmagmasources required,
near-surface dike [Head and Wilson, 1996]. At a certain depth Ti we
eachwith a different content. In summary, proposethat
below the surface, the dike will causeenough extension to the Marius Hills Complex formed by numerous dikes
produce a graben. If the dike is shallow enough, then to and
propagating the surface eruptinglavasthat produced
of
degassing the dike can occurand pyroclastic cones will be extensive mare units at high mass effusion rates. At the
produced. Head and Wilson [1993] have calculatedthat the terminal stagesof these eruptions, the mass flux decreased,
dike at Rima Parry V had a width of-150 m andwas locatedat a
resulting in the formation of the domesby increased
depthof-650 m. Rima Parry V has an associated dark mantle
in and
crystallization the magmas decreasing temperatures,and
deposit that is spectrally similar to DMDs composed of by
the cones explosive activityfromhighervolatile contents
volcanic glasses. Therefore, at Rima Parry, the erupted in the latter stages the eruptions.
of
submillimeter clasts formed a thin blanket of debris, which
becamethe DMD, while the larger clastsresultedin spatterthat 6. Conclusions
built up the cones. Isis and Osiris may not have similar dark
mantle deposits because(1)they have been embayed by properties the lunar domes and conescan be
The spectral of
youngermare that wouldhave coveredthem up or (2) little or summarized as follows:
no fine-grained in
clastswereproduced the eruptions. Isis is mareunitsin the Marius Hills complex
1. Thereare several
to
breached the northindicating an
that it produced associated andthe widerangeof titanium contentsin theseunits argues
lava flow whereclastswere hot enoughafter landing to for multiple eruptionsfrom severaldistinct source regions at
coalesceand form lava, while at Osiris, all clasts landedcold depth. The domes Marius Hills are spectrally
at to
identical the
WEITZ AND HEAD: MARIUS HILLS VOLCANIC COMPLEX 18,955
adjacent mare and occur in both the high- and low-Ti mare Bell, P.M., H. K. Mao, and R. A. Weeks, Optical spectraand electron
units. The cones are spectrally distinct from the mare and paramagnetic of
resonance lunarand synthetic A
glasses: studyof the
effectsof controlled atmosphere, and temperature,Proc.
composition,
domeswith lower reflectances,weaker mafic absorptions, and Lunar Sci. Conf., 7th, 2543-2559, 1976.
bluer colors. The spectral properties of the cones are Carr, M. H., The role of lava erosion in the formation of lunar rilles and
consistent with spatter that has some fine-grained martian channels, Icarus, 22, 1-23, 1973.
crystallization. 528
Cas,R. A. F., andJ. V. Wright, VolcanicSuccessions, pp., Chapman
and Hall, London, UK, 1988.
2. The cones Isis and Osiris are spectrally similar to the
Charette, M.P., T. B. McCord, C. M. Pieters, and J. B. Adams,
adjacentmare units. Applicationof remote spectralreflectance measurements lunarto
3. The Rima Parry V cones may represent glassy spatter geologyclassification of
and determination titaniumcontentof lunar
whereastheir associated dark mantledepositmay be composed soils,J. Geophys. Res., 79, 1605-1613, 1974.
of volcanic glassessimilar to those found at the Aristarchus Chevrel, S. D., P. C. Pinet, J. W. Head, and F. Bellagh, UV-VIS-NIR
in
spectralclassification the Gruithuisendomes region (abstract),
Plateau,but with higher titanium contents. Lunar Planet. Sci., XXVI, 241-242, 1995.
4. The Mons Esam cones of northern Mare Tranquillitatis Chevrel,S. D., P. C. Pinet,andJ. W. Head, GruithuisenDomes region:A
were erupted concurrently with the high-Ti mare at this candidate for an extended non-mare volcanism unit on the Moon, J.
location and are spectrally similar to those at Marius Hills. Geophys. Res., in press,1999.
Cintala,M. J., andR. A. F. Grieve, The effects of differential scalingof
The domesof northern Mare Tranquillitatis, including Grace
on
impactmelt and crater dimensions lunar and terrestrialcraters:
and an unnameddome, are spectrallysimilar to the low-Ti mare Some brief examples, in Large Meteorite Impacts and Planetary
in the region. The dome Diana has an intermediate color Evolution,edited by B. O. Dressier, R. A. F. Grieve, and V. L.
betweenthe high- and low-Ti mare units. Sharpton, Geol. Soc.Am. Spec.Pap. 293, 51-59, 1994.
5. The domesof RumkerHills are spectrallyidenticalto the Coombs,C. R., B. R. Hawke, P. G. Lucey,P. D. Owensby,and S. H. Zisk,
The Alphonsus Region:A geologicremote-sensing perspective,Proc.
very low-Ti mare that is also on the Rumker Hills. Lunar Planet. Sci. Conf., 20th, 161-174, 1990.
6. The Mairan and Gruithuisen domes are spectrally similar Dunkin, S. K., and D. J. Heather,The MariusHills Volcanic Complex:A
to the adjacenthighland soils except that they are redderand stratigraphicstudy.In Lunar and Planetary Science XXX, Abstract
have higherreflectances.They are not mare domesbut instead #1180, Lunarand Planetary Institute,Houston(CD-ROM), 1999.
Fischer,E. M., and C. M. Pieters, Remote determination of exposure
have a highland-likesignature.
degree and iron concentration of lunar soils using VIS-NIR
The formation of the volcanic constructs studied in this
spectroscopic methods, Icarus,111,475-488, 1994.
paper is interpretedas follows: of
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