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New Locations of Fe-Mg-Spinel-Bearing Lithologies on the Moon As Revealed by Chandrayaan-1 Moon Mineralogy Mapper (M3) Observations

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New Locations of Fe-Mg-Spinel-Bearing Lithologies on the Moon As Revealed by Chandrayaan-1 Moon Mineralogy Mapper (M3) Observations 45th Lunar and Planetary Science Conference (2014) 1829.pdf NEW LOCATIONS OF FE-MG-SPINEL-BEARING LITHOLOGIES ON THE MOON AS REVEALED BY CHANDRAYAAN-1 MOON MINERALOGY MAPPER (M3) OBSERVATIONS. Mamta Chauhan, Sa- tadru Bhattacharya and Prakash Chauhan, Space Applications Centre (ISRO), Ahmedabad - 380 015, India (sa- [email protected]). Introduction: One of the major contributions of exposures occur within the anorthositic terrain (blue Chandrayaan-1 mission is the discovery of spinel- colour, Figure 2). At Montes Teneriffe we have ob- bearing lithologies on the Moon [1]. Spinel is found served a prominent 2000-nm absorption without any mostly in two geological settings – 1) along the basin detectable 1000-nm feature diagnostic of Mg-spinel rings/crater rims of large impact basins/craters and 2) and the same has also been found at Mons Pico along- in the central peaks of complex craters with or without side crystalline plagioclase. To the west of crater Pla- mafic silicates and have so far been reported from to, spinel-trocolite-rich exposure is found along the both the near and the far side [1-10] of the Moon. inner flank of a crater as shown in Figure 3c. Crater Apart from pink-spinel anorthosites, spinel has also Moretus is a complex crater in the South Pole Atkin been found in association with noritic, dunitic and region, lying south of crater Short. The central peak of troctolitic lithologies. However, the petrogenesis of this crater shows exposures of Fe-Mg spinels. These these spinel-bearing lithologies is not yet completely Fe-Mg-spinels occur along the flank of the central understood. It is therefore important to document the peak of the crater in close association with crystalline global distribution of these newly discovered rocks in plagioclase and orthopyroxene-bearing lithologies. order to understand the extent of these lithological Discussions: The geological setting of most of the entities and also to constrain the bulk composition of reported Fe-Mg-spinel is similar, being either asso- the lunar mantle and lower crust. Here we report the ciated with the feldspathic terrain at the margin of detection of new spinel-bearing exposures at three basins/crater rims or exposed on the central peaks. different locations on the Moon as shown in Figure 1 The semicircular relief feature and the central protrud- based on Chandrayaan-1 Moon Mineralogy Mapper ing ridge of crater Letronne represents the remnant (M3) data [11]. highlands. The spinel exposures at crater Letronne are located at the southern edge of the crater rim and at the central peak. Previous study using Clementine data revealed the presence of iron anomaly in its topo- graphic highs, suggesting excavation of pre-existing mafics prior to impact induced flooding of the basin by basalts [12]. Mons Pico and Montes Teneriffe are isolated series of ridges lying in the northern part of Mare Imbrium basin near Sinus Iridium. Their geo- logical setting also suggest them to be remnants of highlands later affected by basaltic flooding. The cra- ter Moretus is a complex crater with impact originated central peak and spinel-bearing exposures are located at its peak. Association of Mg-spinel in anorthositic setting represent Pink spinel anorthosites and with an in- crease in the mafic content, the composition moves towards spinel-norite/spinel-troctolite, and thus be- Figure 1. Location of new spinel-bearing lithologies longs to Mg-suite of rocks, which are differentiated on the Moon. products formed by crust-mantle interactions and em- Observations: At crater Letronne, pure Mg-spinel- bedded in the deep crust in the form of layered intru- rich surface exposures have been detected at the sions [1,13,14,15]. The Mg-spinels exposures on the southern edge along the rim of the crater and at its crustal highland rims and on the central peaks of the central peak (Figure 2). The reflectance spectra of the crater thus represent the sample of deeply-embedded detected Mg-spinels are displayed in Figure 2b show- layered plutons, excavated either by an earlier basin ing a characteristic 2000-nm absorption feature that forming event or impacts. lack a 1000-nm mafic feature. The detected Mg-spinel 45th Lunar and Planetary Science Conference (2014) 1829.pdf Conclusion: The study of the occurrences and dis- tribution of these newly discovered mafic components of upper mantle/lower crustal affinity has significant petrological implications, which will help in better understanding the lunar crustal stratigraphy and will provide better constraints on the bulk composition of the lunar mantle. Apart from the above mentioned locations, we have also reported the presence of Fe- Mg-spinel at Sinus Iridium along its rims and terraces (Abstract in this LPSC-2014). References: [1] Pieters C. M. et al. (2011) JGR, 116, E00G08. [2] Lal D. et al. (2011) LPS XXXXII,Abstract #1339. [3] Dhingra D. et al. (2011) GRL, 38, L11201. [4] Kaur P. et al. (2012) LPS XXXXIII,Abstract #1434. [5] Bhattacharaya S. et al. (2012) Curr. Sci., 103(1), 21-23. [6] Kaur P. et al. (2013a) LPS XXXXIV, Abstract #1348. [7] Kaur P. et al. (2013b) LPS XXXXIV, Abstract #1547. [8] Sun Y. et al. (2013) LPS XXXXIV, Abstract# 1393. [9] Ya- mamoto S. et al. (2013) LPS XXXXIV, Abstract #1768. [10] Bhattacharaya S. et al. (2013) Curr. Sci., 105(5), 685-691. [11] Pieters C. M. et al. (2009) Curr. Sci., Figure 4. FCC (R=930nm, G=1249 nm, B=2018nm) 96(4), 500-505. [12] Antenenko I. and Osinski G. showing the central peak of crater Moretus in the (2009) AGU, P31B-04. [13] Taylor L. A. (2009) LPS South-Pole Atkin basin of the Moon. 4a. Close up XXXXI, Abstract # 2785. [14] Prissel T. C. et al view of the central peak showing locations of Pink (2013) LPS XXXXIV, Abstract #3066. [15] Pieters C. spinel anorthosite and norite rich exposure (4c-4e). M. (2013) LPS XXXXIV, Abstract #2545. Figure 2. IBD-Albedo FCC image of crater Letronne showing the locations of spinel-rich exposures (red arrows) with or without Low-Ca pyroxene component. 2a. Corresponding spectra of Mg-spinels rich expo- sures. Figure 3. IBD-Albedo FCC of, Mons-Pico, Montes Teneriffe and adjoining areas of crater Plato showing locations of Mg-spinel (red arrow, in case of Montes Teneriffe – white arrow), crystalline plagioclase (yel- low arrow) and spinel-troctolite (red arrows). Corres- ponding spectra are presented in Figures 3a, 3b and 3c as indicated by blue arrows. .
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