NASA Technical Reports Server (NTRS) 19940028724: Martian deltas: Morphology and distribution

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by  NASA Technical Reports Server (NTRS)

LPI TechnicaI Report 93-06. Part I 45
Coexisting pigeonite and augite are also found in ~12categories ses within and below the ISM field, as seen in Fig. I. This analysis
of lunar mare basalts and well-developed skeletal pigeonite mantled supports the possibility of komatiite-type lava on the Syrtis Major
by augite isfound inApollo 15and Apollo 12pigeonite basalts [6]. plateau because these coexisting pyroxenes are indicative of magne-
All 12of these basalt groups are magnesium rich, ranging inweight sian komatiite-type lava.
percent MgO from 7.03% to 19.97%, and averaging 10.7% [6]. Like An important caveat to the analysis presented here and to that of
komatiites, the coexisting pyroxenes in the Apollo 12 pigeonite [I]isthat Syrtis Major plateau is composed of alarge sand sheet and
basalts are thought to form by rapid metastable crystallization of a dune field, with varying degrees of variable fine-grained dust coat-
supercooled liquid [7]. Regardless of the specific mechanism that ings [1]. The question arises whether the materials observed repre-
forms skeletal textures and coexisting pigeonite and augite, these sent locally derived or transported materials. Additionally, iflocal or
features are characteristic of highly magnesian lavas like komatiites. distal in origin, certain phases inthe Syrtis Major material may have
Discussion: Using ISM data, Mustard etal. [I] estimated the been preferentially concentrated byeolian activity orchemical weath-
composition of Syrtis Major pyroxenes. According to Mustard etal., ering. The relatively low spatial resolution of ISM (24 km) makes
the pyroxene compositions represented by their ISM analysis falls in these questions difficult to answer.
an area of"unusual" composition on the pyroxene quadrilateral, and Athermal emission spectrometer (TES) with aspectral resolution
therefore the data may represent an average composition of augite of 5-10 cm-l, from 5 to 60 pm, and aspatial resohition of 3km (e.g.
and pigeonite as intimate exsolution lamella. Telescopic reflectance the Mars Observer Thermal Emission Spectrometer [I0]), would
measurements of several dark regions on Mars are indicative of- easily reveal the presence and nature of komatiitic lavas on Syrtis
coexisting pyroxenes, which correlates with the modal mineralogy of Major as indicated by the evidence discussed. In addition, TES-type
Shergotite meteorites, which may have originated from Mars [8]. data could be used to study weathering products and to trace sedi-
Comparison with Shergotite meteorites and terrestrial komatiites ment transport paths in an attempt to distinguish primary igneous
suggests that exsolution lamella are not required by the results of[ 1]. materials from reworked sediments. Finally, aTES would reveal if
If the ISM data represent an average of two pyroxene compositions, Syrtis Major lava composition evolves from peridotitic to basaltic
then discrete pyroxenes may be implied. Furthermore, ifcoexisting compositions over time as seen in terrestrial komatiites [3].
pyroxenes were detected by the ISM on Syrtis Major, then they may References: [I] Mustard J. F. et al., (1993) JGR, 98, 3387-
have formed by amechanism like that previously described for the 3400. [2] Takahashi E. (1991) JGR, 95, 15941-15954. [3] Amdt
crystallization ofpyroxenes inmafic komatiite and Apollo 12pigeo- N.T. et al. (1977) J. Pet., 18, 319-369. [4] Cameron W.E. and
nite basalts. Nisbet E. G. (1982) In Komatiites (Arndt N. T. and Nisbet E G.,
Figure 1shows a pyroxene quadrilateral with the Syrtis Major eds.), George Allen and Unwin, Boston, 29-50. [5] Campbell I. H.
ISM pyroxene field of [11 superposed over the compositions of and Arndt N. T. (1982) Geol. Mag., 119, 605-610. [6] BVSP,
pyroxenes found in a pyroxenitic komatiite flow, the Shergotile Basaltic Volcanism Study Project (1981) Pergamon, New York,
meteorite, and an Apollo 12 pigeonite basalt. The majority of 1286 pp. [7] Klein C. et al. (1971) Proc. LSC 2,d, 265-284.
pyroxenitic komatiite pyroxene analyses do not fall within the ISM [8] Straub D. W. etal. (1991 )JGR, 96, 18819-18830.19] McGetchin
field because their source liquid contained relatively little Fe com- T. R. and Smyth J. R. (1978) Icarus, 34, 512-536. [10]Christensen
pared to potential martian lavas [e.g., 3,9]. Many individual pyrox- 772'(" 33230
P. R.et al. (1992) JGR, 97, 7719- ___N94-
erie analyses from the Shergotite and the Apollo 12pigeonite basalt
do fall within the ISM field. More importantly, the averaged compo-
sition of coexisting pyroxenes in the plotted samples will also fall
within theISM field. These samples perform better than the komatiite MARTIAN DELTAS: MORPHOLOGY AND DISTRIBU-[ 1 f
because the higher Fe content in these rocks allows greater substi- TION. J.W.RiceJr) andD.H.Scott-',lDepartmentofGeography,
tution of Fe in the pyroxene structure as Mg is consumed initially. Arizona State University, Tempe AZ 85283, USA, -_Astrogeology
A crystallization trend is defined that places these pyroxene analy- Branch, U.S. Geological Survey, 2255 N. Gemini Drive, Flagstaff
AZ 86001, USA.
The identification ofdeltas on Mars has been an enigma over the
(Ca)
years for planetary geologists. However, recent detailed mapping
D_. I lid (I :500,000 scale) has revealed numerous examples of martian del-
tas. We will document and describe the location and morphology of
these deltas.
Deltas are alluvial regions composed of sediment deposited in
relatively still water (lakes, bays, seas) atriver mouths. Deposition on
o .. , .... %, deltas occurs when river velocity is reduced upon entering standing
___.a_m. ._._...................... ::: :\ bodies of water. Factors that contribute to delta morphology are river
(Ng} (Fe] regime, coastal processes, structural stability, and climate [I].
En 50 i'm The largest delta systems on Mars are located near the mouths
of Maja, Maumee, Vedra, Ma'adim, Kasei, and Brazos Valles.
Fig. 1. Pyroxene compositions fromSyrtis MajorISMand analogs. ISMfield There are also several smaller-scale deltas emplaced near channel
(rhomboid) from [1]:pyroxenitic komatiite data (squares) provided byD. P. mouths situated in lsmenius Lacus, Memnonia, and Arabia.
Reyes. [sampleDPY-10,unpublisheddata, Reyes. 1993]:andApollo 12pigeonite Delta morphology will be used to reconstruct type, quantity, and
basalt (circles) andShergotite meteorite (stars) data from [6]. sediment load size transported by the debouching channel systems
46
Resu#s from the MSA77 Program
[2,3]. For example, arcuate deltas are deposited by bed load or heated at 120°C for ~1 day after sitting in weak acetic acid for 1+
mixed load systems that bring large quantities of coarse material to days. Bas was simply heated. Runs were performed at warm (25°C)
the coastline as opposed to the elongate (birdfoot) deltas composed and cold (-25°C) temperatures, about 1 bar CO-, pressure, and
of large quantities of fine sediment deposited by acombination of specific surface areas of-I m'-/g (-I pm particles). Experiments
suspended load and mixed load rivers. Methods initially developed included "vapor" (H20 premixed with CO._, for ~1-10 monolayer
for terrestrial systems will be used to gain information on the coverage), "damp" (H20 pipetted onto powder before soaking in),
relationships between martian delta morphology, river regime, and and "wet" (ma, o ~ m_mple) runs.
coastal processes. BET specific surface areas were determined for Di Iand Bas, and
References: [1] Morgan J. P. (1970) SEPM, 15, 31-47. quantitative results are given for experiments using these starting
[2] Axelsson V. (1967) Geogr. Ann., 49, 2-127. [3] Galloway W. E. compositions (Table 2). Pressure drops (Ap) for DiIand Bas show
(1975) Houston Geol. Soc., 87-98. N94-33231 -apid short-term (~1day) CO, uptake and considerably slower Iong-
:rm AP (Figs. 1and 2). We know the changes are not due to H20
dsorption since there is always sufficient water to maintain
P,,ap(H20). However, we assume the short-term signal reflects CO 2
CARBONATE FORMJ_TION ON MARS: LATEST EXPER- adsorption (consistent with previous measurements [7,12] and con-
r,
IMENTS. S.K. Stephens I,D. J. Stevenson 1,G. R. Rossman t,and firmed by desorptlon experiments). Curves for Di2, Ol I, and OI 2
L. F. Keyser 2,tDivision of Geological and Planetary Sciences, 170- are qualitatively similar to those for Dil, whereas Qtz and Plag
25, California Institute of Technology, Pasadena CA 91125, USA, show near-zero short-term AP and very slow long-term signal--
2Earth and Space Sciences Division, 183-901, Jet Propulsion indistinguishable from a leak (<10 tt mol/m:/s).
Laboratory, California Institute ofTechnology, Pasadena CA 91109, Discussion: Thermodynamic calculations [131 suggest that
USA. reactions should form carbonates from diopside and olivine, and
possibly plagioclase, atmartian Pand T.PD results can be classified
Introduction: Laboratory simulations of martian CO 2storage into three groups: diopsides and olivines, quartz and plagioclase,
address a fundamental question about martian climate history: and basalt. Bas takes up more CO 2than monominerallic, crystalline
Could carbonate formation have reduced CO: pressure from ahypo- diopside, and olivine, despite the fact that it is probably >50%
thetical >1 bar to the present 7 mbar in <3-4 b.y.? We address this feldspar and quartz (i.e., relatively unreactive), suggesting arole for
problem with experiments and analysis [1,2]designed to verify and glass (vs. crystalline mineral).
improve previous [3,4] kinetic measurements, reaction mechanisms, No long-term AP was expected for Qtz (no cations), although
and product characterizations. Our theoretical modeling [5,6] has adsorption was anticipated, while with Plag we expected apossible
sought to improve existing models of martian CO2history [7-I0], long-term signal, and again the absence of an adsorption effect was
which generally assume anearly CO 2greenhouse atmosphere (ques- puzzling. One explanation involves the progressive polymerization
tioned by Kasting [Ill). of silicate tetrahedra: olivine (isolated tetrahedra) and pyroxene
Experimental Results: Asensitive manometer monitored the (chains) vs. feldspar and quartz (three-dimensional frameworks).
pressure drop (laD) of CO2due to uptake by powdered silicate for The structure of olivine and diopside may make iteasier for cations
periods of 3 to 100+ days. Initially we focused on monomineralic, to physically adsorb (and/or chemically bond with) anions.
crystalline samples, but more recently we ran basaltic glass (see Also puzzling is the result of an X-ray photoelectron spectros-
Table I). Grinding was done in atungsten-carbide shattcrbox. Di I copy (XPS) analysis performed on Di2 exposed to similar P(CO 2)
was not treated further, and all other monomineralic samples were and H20 vapor conditions as the PD experiment with Dil (vapor)
TABLE I. Mineralsandrocksusedforexperimental samples.
Sample Approximate Composition Sample Description Locale
Diopside I CaMgSi20s Bulk. broken crystals, DogLake. Quebec
[DiI] -5% impurities
Diopside 2 CaMgSi._O,, Green.euhedral crystals. Rajastan, India
[Di2] <2%impurities
Olivine 1 Mg_Fe,,SiO_ Bulk,broken crystals. Gabbs, Nevada
[OI1] [Forsterite 98%] -5% impurities
Olivine 2 Mg,_Fe.j:SiO, Translucent green pebbles (crystals). SanCarlos, Arizona
[OI2] <2% impurities
Quartz SiO2 Clear, euhedral crystal. Mr.Ida,Arkansas
[Qtz] <1%impurities
Plagioclase Ab__An.7 Clear,euhedral crystal Ponderosa Mine.Oregon
[Plag] [Ab- NaAISi._Os, <1%impurities
An - CaAl:Si__Os]
Basalt Tholeiite -98 wl%black glass, -..0.3wt% dissolved H20 Kilauea, Hawaii
[Bas] [50wt%, SiO2.13%AI20._. -I wt% crystals, 1991lava flow,
12%FeO. 9%MgO. 11%CaO] quenched inair