Anand, M.

Liu, Y.

Taylor, L. A.

Thaisen, K. G.

Zhang, A.

English

Open Research Online (The Open University)

Open Research OnlineThe Open University’s repository of research publicationsand other research outputsMineralogy and petrology of a lunar highland brecciameteorite, MIL 07006Conference or Workshop ItemHow to cite:Liu, Y.; Zhang, A.; Thaisen, K. G.; Anand, M. and Taylor, L. A. (2009). Mineralogy and petrology of a lunarhighland breccia meteorite, MIL 07006. In: 40th Lunar and Planetary Science Conference, 23-27 Mar 2009, Houston.For guidance on citations see FAQs.c© [not recorded]Version: [not recorded]Link(s) to article on publisher’s website:http://www.lpi.usra.edu/meetings/lpsc2009/pdf/2105.pdfCopyright and Moral Rights for the articles on this site are retained by the individual authors and/or other copyrightowners. For more information on Open Research Online’s data policy on reuse of materials please consult the policiespage.oro.open.ac.ukMINERALOGY AND PETROGRAPHY OF A LUNAR HIGHLAND BRECCIA METEORITE, MIL 07006.  Y. Liu1, A. Zhang1,2, K.G. Thaisen1, M. Anand3, and L.A. Taylor1.  1Planetary Geosciences Institute, Dept. of Earth & Planetary Sciences, Univ. of Tennessee, Knoxville, TN 37996. (yangl@utk.edu);  2 Purple Mountain Observa-tory, Nanjing, 21008, China; 3 Earth and Environmental Sciences, Open Univ., Milton Keynes UK.  Introduction: Lunar breccias provide a lithic buf-fet of delicious clasts revealing tidbits of lunar petro-logic data.  A small lunar breccia meteorite, Miller Range (MIL) 07006 (~1.4 g) was recently found on the Miller Range Ice Field in Antarctica [1].  This meteor-ite was tentatively characterized as a basaltic breccia [1].  However, upon detailed examination of mineral chemistry, we found that another chip (MIL 07006, 9) is a feldspathic regolith breccia, which is consistent with the classification based on the bulk-rock compo-sition [2].  Mineral chemistry indicates the majority of lithic/mineral clasts a highland origin, some with pos-sible basaltic affinity.   Figure 1.  Photo mosaic of MIL 07006, 9.  A, B, and D indi-cate some lithic clasts. All three contain silica (white ar-rows) while clasts A and B also contain ilmenite. Clasts A shows compositional zonation in pyroxene. Clast D is a gab-bro clast. Petrography: MIL 07006, 9 consists of angular lithic and mineral clasts welded in a dark matrix.  The matrix consists of glassy material with abundant vesi-cles, which are typical for lunar regolith.  Most clasts contain extensive fractures.  Most lithic clasts, 0.5–2 mm in size, are feldspathic (breccia, ferroan anortho-site, impact-melt glass).  Two small clasts (50–100 μm) are suspected to be basaltic (A and B in Fig. 1) based on its texture, zoned pyroxene, and presence of silica and ilmenite.  However, the small size of the clast and similar mineral chemistry to highland rocks make the definition ambiguous (Figs. 2 and 3).  Clast D is a gabbro.  This sample also contains a highly ve-sicular fusion crust (0.12–0.30 mm thick), covering ~40 % of the outer surface of this meteorite. Mineral fragments mainly include large plagioclase grains (~1 mm) and small pyroxene and olivine grains (<0.5 mm).  Pyroxene fragments typically contain ex-solution lamellae.  Thickness of these lamellae varies from 0.5 to 2.5 μm.  Olivine fragments are generally unzoned.  Ilmenite commonly occurs as individual chips (≤10 μm), and also as minute grains (<1 μm) associated with silica or impact-formed glass.  Chromian ulvöspinel, Ti-chromites and a Al-rich spinel are <50 μm in size.  Troilite grains also occur as monomineralic fragments.  Micron to sub-micron FeNi grains occur in the matrix and in impact-melt clasts.  Several FeNi metal grains occur as anhedral grains of  Figure 2. Compositions of pyroxene and olivine in MIL 07006, 9.  Figure 3.  Compositional ranges of plagioclase and mafic minerals in some  lithic clasts  from MIL 07006, 9. Fields are from [3].2105.pdf40th Lunar and Planetary Science Conference (2009) Figure 5.  Composition of fusion crust.  Bulk rock data are from [2].<30 μm in size.  Phosphates were not found in lithic clasts in this section. Mineral Chemistry: Electron microprobe (EMP) analyses, with a Cameca SX100, were performed for major- and minor-element chemistry of minerals and glasses.  Feldspar: Anorthosite and gabbro clasts, as well as large monomineralic fragments, contain crystalline plagioclase.  Maskelynite grains occur as small mineral fragments in the matrix.  Plagioclase grains in anortho-sites, gabbros, and fragments show inter- and intra-granular homogeneity with An97±1, and with FeO con-tent similar to highland plagioclase (<0.25 wt%, [4]).  Plagioclase in clast A ranges from An93 to An96 and those in clast B is relatively uniform with lower An (An91) . Pyroxene: Compositions of pyroxenes in anortho-site and gabbro clasts range from pigeonite to augite with Mg# from 50 to 69 (Fig. 2).  Pyroxenes in clasts A and B show compositional variations (Fig. 2).  Py-roxene and plagioclase in clast A lie approximately in FAN field whereas those in clast B lie in Mg-suite field (Fig. 3).  Pyroxene fragments show a wider range of composition from orthopyroxene (En79Wo3, Mg# = 82) to Fe-rich augite (En28Wo21, Mg# = 35).  Fe and Mn concentrations in pyroxenes are distributed in the area between the Earth and the Moon lines (Fig. 2), similar to other feldspathic lunar breccias (e.g., Dho 025 and Dho 081 [5]), supporting the lunar origin for this meteorite. Olivine: Olivine in two gabbro clasts (Fo61 and Fo51) occurs as anhedral interstitial grains among pla-gioclase (An96).  Olivine inclusions in plagioclase have relatively higher Mg# (Fo77).  Olivine fragments show a compositional range from Fo82 to Fo39 (Fig. 2).  Fe-Mn values in MIL 07006 olivines are consistent with a lunar origin.  Figure 4.  Compositions of spinels and metal in MIL 07006.  Fields in the Co-Ni plot are from [6]. Oxides: Ilmenite grains large enough for EMP analyses contain MgO of 0.75-1.85 wt%.  Composi-tions of spinel minerals show a wide variation from Ti-chromite to ulvöspinel (Fig. 4), with variable Mg# of 2.3-8.5. The  Al-rich spinel grain (Mg# = 44) associ-ated with Fo70 olivine contains ~33 wt% Al2O3, typical for highland rocks [6,7].    Metal: Metal grains large enough to be analyzed by EMP contain <0.1 wt% Si and <0.4 wt% P.  The con-tents of Co and Ni in these FeNi grains show a limited range of variation and plot inside the meteoritic range (Fig. 4), similar to Apollo 14 and 16 breccias and me-teoritic [6].  A few FeNi grains are associated with akaganeite (β-FeOOH) grains that could have formed by terrestrial oxyhydration of lawrencite (FeCl2).  Lawrencite is indigenous in Apollo 16 highland rocks [8].  Fusion crust: Composition of the fusion crust is heterogeneous (Fig. 5) and depends to some extent on the substrate mineralogy [9]. The average composition of 93 analyses on fusion crust (26 wt% Al2O3 and 5.9 wt% FeO) are similar to the bulk rock data (~27 wt% Al2O3 and 5.6 wt% FeO) by [2] (Fig. 5).  Other phases:  Silica-rich glass is found throughout the section as individual fragments or associated with ilmenite and Fe-rich pyroxene (En27Wo33, Mg# = 40).  Silica-rich glass generally contains SiO2 >93 wt% with <2 wt% Al2O3 and <0.03 wt% K2O.  The silica-rich glass associated with Fe-rich pyroxene contains 0.34 wt% K2O.   Discussion:  Mineral and bulk-rock chemistry and petrology suggest MIL 07006, 9 is a feldspathic re-golith breccia.  Bulk-rock chemistry of MIL 07006 is similar to feldspathic regolith breccias: ALHA 81005, DaG 262, DaG 400, Dho 025, NEA 001 and Yamato 791197 [2].  The scarcity of basaltic clasts in MIL 07006 is similar to DaG 262/400 and Dho 025 litholo-gies [4].  The high abundance of FAN clasts and the scarcity of basaltic clast in MIL 07006, indicate that the source area on the Moon is the highland terrain.   References: [1] Ant. Met. News Lett. (2008) 31(2). [2] Korotev R. (2008) http://meteorites.wustl.edu/.  [3] Lucey P. et al. (2006) Rev. Mineral., 60, 83-219. [4] Taylor L.A. et al. (2009) this volume. [5] Cahill J. T. et al.. (2004) Meteoritics & Planet. Sci., 39, 503–530. [6] Papike J. et al. (1991) Lunar sourcebook,121-182. [7] Haggerty S. (1978) Mare Crisium: The View from Luna 24. GCA Supp. 9, 523-535. [8] Taylor L. et al. (1973) LPSC, 4, 829-839. [9] Thaisen K.G. and Taylor L.A. (2009) Meteoritics & Planet. Sci. (in revision).  2105.pdf40th Lunar and Planetary Science Conference (2009)

Mineralogy and petrology of a lunar highland breccia meteorite, MIL 07006

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Mineralogy and petrology of a lunar highland breccia meteorite, MIL 07006

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