44th Lunar and Planetary Science Conference (2013) 1225.pdf

Composition Analysis of the Marius Hills Volcanic Complex using Diviner Lunar Radiometer Experiment and Moon Mineralogy Mapper. K. M. Lehman1,2 , G. Y. Kramer2, R. G. Mayne1,3, W. S. Kiefer2, 1School of Geology, Energy, and the Environment, Texas Christian University, Fort Worth, TX ([email protected]), 2Lunar and Planetary Institute, Houston, TX. 3Monnig Meteorite Gallery, Fort Worth, TX.

Introduction: the material [9, 10]. It is also important to note that a low CF value has a high correlation to high visual al- The Marius Hills Volcanic Complex, located in bedo, and that space weathering causes the CF value to Central Oceanus Procellarum at 13.3 N, 306.8 E , has move to longer wavelengths [10, 11]. All this makes an undoubtedly complicated volcanic history. Over 250 domes and complex surrounding volcanic geo- the CF value very helpful in understanding the geology morphologies suggest multiple volcanic episodes[1]. In of an area. This value is complementary to M3 spectra, allowing for more felsic materials to be observed and light of this, many have investigated potential compo- for a deeper understanding of the entire compositional sitional differences using both Clementine and Chan- mixture as comparison between spectra compositions dryann-1’s Moon Mineralogy Mapper (M3 ) and have and Diviner compositions occur. identified the area as a high titanium basalt with glass features surrounding cones associated with pyroclastic Methodology: [2,3,4]. Beyond subtle variation in FeO percent, TiO2 Three different data sets were used to analyze percent and olivine content, the complex has been this region: Clementine, M3 spectral data, and the deemed compositionally homogenous [2,3,5]. Recent Gridded Level 3 Diviner Christiansen Feature map. geophysical research has shown a large gravity anoma- ly under the Marius Hills complex that can be best We initially used RGB (Band-Ratio Color Com- explained by a large magma chamber, large enough to posite) [12], TiO2 [13], FeO [14] spectral image maps allow for significant magma evolution [6]. This new from the 5 channel UV VIS imager on the Clementine evidence made it important to analyze possible compo- spacecraft. We also used M3 data to create spectral sitional differences using data sets that have not been parameter maps, that were designed to highlight re- used before. gions that are rich in particular materials such as oli- vine and high calcium pyroxene. The M3 maps were Our study makes use of two complementary spec- overlaid on to the Clementine data to differentiate tral datasets. M3 is an imaging reflectance spectrometer chemically different areas. These areas were then ana- that can detect 85 channels between 460 to 3000 nm, lyzed using the M3 spectral profiles to see if there and has a spatial resolution of 140 meter per pixel [7]. were actual notable changes in the spectra. We particu- M3 can determine mineralogy in reflectance spectra larly focused on looking for possible spectral differ- through diagnostic absorptions at specific wavelengths, ences between the Marius Hills volcanic domes and which result from electronic transitions between an the lava plains between the domes. Based on the geo- iron atom and its surrounding oxygens in a crystal logic regions mapped out using these parameters we structure [8]. The specific wavelengths at which these extracted representative M3 spectra for more detailed absorptions occur are dictated by the composition and spectral analysis. crystal structure of a specific mineral. M3 is particular- ly effective at detecting pyroxene and olivine, but can We also looked for possible differences in the lo- only detect plagioclase when it is verypure. Previous cation of Christiansen absorption frequency using Di- analysis of the near infrared spectrum of the Marius viner radiometer results[9, 10]. Areas that displayed Hills used a preliminary calibration of M3 spectroscopy differences were then compared with their M3 spectral [5], whereas our analysis uses the final calibration of counterparts to see if there was a correlation between the M3 dataset. the two data sets. Finally, Lunar Reconnaissance Or- The Lunar Reconnaissance Orbiter’s (LRO) Di- biter Camera (LROC) and WAC GLD 100 stereo to- viner Lunar Radiometer Experiment has a spatial reso- pography model were used to try to understand the lution of 950 m/pixel [10]. Diviner produces thermal geomorphology of the areas that appeared chemically emissivity data, and can provide compositional infor- different. mation from 3 wavelengths centered around 8 microns M3 Analysis: that are used to characterize the Christiansen Feature (CF) [9, 10]. Each CF value is indicative of a certain The analysis of the Marius Hills complex us- silicate mineral composition, with higher values being ing the most recent M3 calibration bears similar results a more mafic material and lower values being felsic [9, to previous studies. The complex appears relatively 10]. This feature is not affected by vitrification and the homogenous spectrally, with variations only seen in value can be assumed to be based on linear mixing of the absorption band depths and the reddening (ma- 44th Lunar and Planetary Science Conference (2013) 1225.pdf

recent M3 calibration. muted pyroxene absorptions and a brightening of the

Plagioclase rich areas spectra. 0.2 Pyroxene rich areas Discussion 0.15 The new Diviner data shows what M3 could 0.1 not alone, plagioclase rich regions in the Marius Hills complex. Mineral components that combine to form 0.05 reflectance spectra do not mix linearly at modal abun- dances as low as 10 percent strongly absorbing dark 0 minerals, such as olivine, pyroxene, ilmenite, can Apparent Reflectance 0.5 1.5 2.5 3.5 overwhelm and obscure a plagioclase spectrum [10]. Wavelength (micron) Bright craters and bright areas surrounding domes in

the NAC images which are associated with low CF Plagioclase rich areas values are assumed to be the plagioclase-rich areas. 1.30 Pyroxene rich areas These bright, plagioclase rich areas, are often sur- 1.20 rounded by very low albedo which may be more il- 1.10 menite rich materials. 1.00 0.90 Reflectance 0.80 Figure 2: This map, which has a WAC image overlaid by a

Continuum Removed 0.70 color relief map based on WAC GLD 100 topography as its 0.5 1.0 1.5 2.0 2.5 3.0 3.5 base, displays the plagioclase rich domes. The 8 major domes Wavelength (micron) that are observed as plagioclase rich by the Diviner Lunar

Radiometer Experiment are outlined in heavy black. FigureFigure 1: These 1: These graph graph displays displays the the difference difference betweenbetween the the PlagioclasePlagioclase rich rich areas areas (purple) (purple) andand thethe surrounding surrounding non plnonplagia- o- gioclase rich areas (blue). Top: Raw spectra Bottom: Continu- clase-umrich Removed areas (blue).spectra. Top:Removing Raw the spectra continuum Bottom: slope from Continuum the Removedtop spectra spectra. em phasizesRemoving the relativethe continuum strength of slope the 1 from and 2 the top mciron absorbtions for pyroxene. As can be seen, the Plagio- Discussion: spectraclase em richphasizes areas are the brighter relative with strength muted absorptions. of the 1 and 2 micron absor ptions for pyroxene. As can be seen, the Plagioclase-rich Figure 2: This map,The which new has aD WACivin imageer data overlaid reveals by a col theor presence of areas areDiviner brighter Analysis with muted absorptions. relief map based on WAC GLD 100 topography as its base, Previous studies have used Diviner data to displays theplagi plagioclaseoclase rich- richdomes. regions The 8 major within domes thatthe are Ma rius Hills. This map more silica rich areas on the moon, but none of observed as plagioclase rich by the Diviner Lunar Radiometer Experimentconclusion are outlined in heavywas black.not possible using M3 data, because turity)these of the have spectra. focused As on theseen Marius in Figure Hills Complex 1, the spectra [9, display10]. classic Although pyroxene the area had absorptions, an average CF primarily value of 8.3 that of strong absorptions from even small abundances of py- microns suggesting a pyroxene rich substance, there Remoteroxene sensingand olivine observations overwhelm show that the the weak near-infrared clinopyroxene,are areas across with the its complex 1 and that 2 micronhave CF absorvalues prantionsg- Marius Hills basalts are relatively high in Ti [17]. ing 7.9- 8.2 microns suggesting a more plagioclase rich Based on absorptionthis, we use ofApollo plagioclase 17 high titanium [ 16]. Brightbasalt craters and shiftedarea. to longerThese plagiwavelengthsoclase regions [15]. are Previous associated studies with 70215 as an analog for the crystallization of the Marius had describedmany craters, an rilles, olivine possible rich vo flowlcanic within vents and the with co m8 plexHills basalts.bright Petrographic areas surrounding observations domes and exper in thei- NAC images large domes. The largest of these lower CF value mental crystallizationwhich are studiesassocia showted thatwith the low major CF mi valuesn- are assumed [5], butdomes we isdid made not upsee of this 65 divinervariation pixels using covering the mostap- erals in 70215 began crystallizing in the following or- recentproximately M3 calibr 62a tion.km2. For each roughly km sized pixel, der: olivine,to be ilmenite, the plagioclase and then pyroxene-rich areas. and plagi Theseo- bright, plagio- the CF value, and thus the composition, can be as- clase appearedclase rich nearl yareas, simultaneously are often near surrounded 1150 °C by very low al- Divinersumed Analysis: to be based on linear mixing of the constituent [16]. With further cooling, olivine reacts with the re- minerals. For example, a CF value of An94-96 plagio- sidual liquidbedo to producewhich mayadditional be more clinopyroxene. ilmenite R riche- materials. clase is 7.9 microns. Therefore these km-sized areas cent gravityConcl mappingusion revealed: the presence of a large Previouswith CF b estudiestween 7.9 have and 8.2used microns Diviner contain data either to map a gravity anomaly beneath the Marius Hills that may be more plagioclasesilica rich- rich areas bas alton for the the moon, whole regionbut none or contain of th ese due to the presence of a solidified magma chamber [6] concentrated regions of exposed plagioclase surround- and which wouldBy provide examining a location the for Marius magmatic Hills evo- complex using cal- have edfocused by more on mafic the minerals Marius [10 Hills]. Complex [9, 10]. lution to ibrated occur by M3 separation data and of crystals Diviner and CF residual value map, three im- Although theThese area areashad an when average compared CF tovalue Clementine of 8.3 mi-liquid. If portant the separation concl u ofsions crystals were and made. magma First, oc- the M3 spectra RGB and TiO2 parameters are shown to be surrounded curred near 1150 °C, the residual magma would be cronsby suggesting higher Ti materials. a pyroxene When rich spectrally substance, analyzed there us- are enriched in plagioclase and depleted in olivine and 3 showed that the complex was relatively compositional- areas ingacross M data,the complex these plagioclase that have rich CF areas va l displayedues ranging ilmenite relatively homogenous, to the starting supporting composition. earlierMoreover, observations. Se- 7.98.2 microns suggesting a more plagioclase rich ar- cond, the olivine-rich basalts previously observed [5] ea. These plagioclase regions are associated with many in the complex were not seen in the more recent M3 craters, rilles, possible volcanic vents and with 8 large calibration nor the Diviner data. Finally, Diviner data domes. The largest of these lower CF value domes is made plagioclase rich areas observable, which might made up of 65 diviner pixels covering approximately be suggestive of magma evolution of the large magma 62 km2. For each roughly km sized pixel, the CF val- chamber observed geophysically. ue, and thus the composition, can be assumed to be based on linear mixing of the constituent minerals. For example, a CF value of An94-96 plagioclase is 7.9 References: [1]J.L. Whitford-Stark and J.W. Head (1977) Proc. Lun. microns. Therefore these km-sized areas with CF be- Plan. Sci. Conf. 8, 2705-2724 [2] C.M. Weitz and J.W. Head (1999) JGR:104, 18933-18956 [3] D. J. Heather, S. K. Dunkin, L. Wilson tween 7.9 and 8.2 microns contain either a plagioclase (2003) JGR:108, 2002JE001938. [4] Prettyman et al.(2005) rich basalt for the whole region or contain concentrated JGR:111, 2005JE002656 [5] S. Besse et. al. (2011) JGR: 116, regions of exposed plagioclase surrounded by more 2010JE003725. [6] W. S. Kiefer. JGR 2012JE004111 [7] C.M. Pie- mafic minerals [10]. ters et al. (2009) Curr. Sci. 96(4), 500-505. [8] R. G. Burns (1993) Camb. Univ. Press, 551 [9] T. D. Glotch et al.(2010) Sci. 329, 1510 These areas when compared to Clementine RGB [10] B. T. Greenhagen et al.(2010) Sci. 329, 1507 [11] P. J. Lucey et and TiO2 parameters are shown to be surrounded by al. (2010) Proc. Lun. Plan. Sci. Conf. 41, 1600 [12]A. S. McEwen (1994) Sci. 266, 1858-162 [13] P. G. Lucey et al. (2000) JGR 105, higher Ti materials. When spectrally analyzed using 20297-20305 [14] B. B. Wilcox et al (2005) JGR:110, M3 data, these plagioclase rich areas displayed muted 2005JE002512 [15] R. L. Klima et al. (2011) Met. Plan. Sci. 46, pyroxene absorptions and a brightening of the spectra. 37939 [16] C. M. Pieters (1983) JGR 88, 9534-9544