Caporali, S.

Franchi, I. A.

Greenwood, R. C.

Moggi-Cecchi, V.

Pratesi, G.

English

Open Research Online (OU)

Open Research OnlineThe Open University’s repository of research publicationsand other research outputsNorthwest Africa 10639 and 10640: Two newmonomict eucrites from SaharaConference or Workshop ItemHow to cite:Moggi-Cecchi, V.; Pratesi, G.; Caporali, S.; Franchi, I. A. and Greenwood, R. C. (2016). Northwest Africa10639 and 10640: Two new monomict eucrites from Sahara. In: 79th Annual Meeting of the Meteoritical Society,7-12 Aug 2016, Berlin, Germany.For guidance on citations see FAQs.c© [not recorded]Version: Version of RecordCopyright 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.ukNORTHWEST AFRICA 10639 AND 10640: TWO NEW MONOMICT EUCRITES FROM SAHARA. V. Moggi-Cecchi1, G.Pratesi1,2, S.Caporali3, I.A.Franchi4, R.C.Greenwood4, 1Museo di Storia Naturale, Università degli Studi di Firenze, Via G. La Pira 4, I-50121, Firenze, Italy, 2Dipartimento di Scienze della Terra, Università de-gli Studi di Firenze, Via G. La Pira 4, I-50121, Firenze, Italy, e-mail: vanni.moggicecchi@unifi.it, 3Dipartimento di Chimica, Università degli Studi di Firenze, Via della Lastruccia 3, 50019, Sesto Fiorentino (FI), Italy, 4Planetary and Space Sciences Research Institute, Open University, Walton Hall, Milton Keynes, GB-MK7 6AA United Kingdom.  Introduction: These two meteorites were purchased in 2015 at the Erfoud Market by Hichame Mimaghador, from a Moroccan dealer. The main masses, weighing 232 and 41.9 g, respectively, are both partially covered by a black fusion crust. The sawn surface of both samples shows a brecciated texture with white clasts set in a fine grained matrix. Both meteorites have been approved by the Nomenclature Committee of the Meteoritical Society with the names NWA 10639 and 10640, respectively [1]. Hichame Mimaghador owns both the main masses. The type specimens, weighing 36.2 and 8.4g, respectively, and two thin sections are on deposit at the Museo di Storia Naturale dell’Università di Firenze (sample N° RI-3233 and RI-3234). Instruments and methods: Optical microscopy was undertaken at the laboratories of the Dipartimento di Sci-enze della Terra, Università di Firenze, Italy, using an Axioplan-2 polarizing optical microscope equipped with Axi-ocam-HR camera. SEM-SE images have been performed at the Dipartimento di Chimica, Università degli Studi di Firenze laboratories by means of a Hitachi SEM. EMPA-WDS analyses have been performed at the Firenze labora-tories of the IGG – CNR (National Council of Research) with a Jeol Microbeam microprobe. Oxygen isotope analy-sis was undertaken at the Open University. Experimental results: Both meteorites were investigated by means of optical microscopy, SEM, EMPA and Micro-Raman techniques. A thin section of each sample was analyzed. Both thin sections displays a monomict brec-ciated texture consisting of basaltic eucrite clasts and related crystalline debris set in a finer-grained homogeneous matrix consisting of the same phases (mean grain size 20 μm). Eucritic clasts are mainly characterized by clinopy-roxene, with minor anorthitic plagioclase and orthopyroxene displaying very fine (1-2 μm width for NWA 10639 and 2-3 μm for NWA 10640) pigeonite exsolution lamellae. Minor phases include ilmenite, troilite, chromite, and, for NWA 10639, Fe-Ni metal. NWA 10639 displays a low weathering and a medium shock stage. NWA 10640 dis-plays moderate degree of weathering and a medium shock stage. EMPA analyses of selected grains were performed in order to determine the general minerochemical features of the matrix and of single crystals for classification purposes. Both samples display a calcic plagioclase (An90.1Or0.9, for NWA 10639 and An88.0Or0.9 for NWA 10640), low-Ca pyroxene (Fs55.2En42.4Wo2.4, Fe/Mn=37.6, and  Fs56.1En43.6Wo2.3, Fe/Mn=36.5, respectively), augite (Fs29.7En30.6Wo39.7, Fe/Mn=32.8, and Fs39.2En28.0Wo32.9, Fe/Mn=35.4, respectively), pigeonite exsolution lamellae in low-Ca pyroxene (Fs57.7En33.8Wo8.5, Fe/Mn = 33.7 and (Fs59.4En29.9Wo10.7, Fe/Mn = 34.2, respectively). Oxygen isotope analyses performed on both samples provided the following results: δ17O = 1.87 ‰, δ18O = 4.01 ‰, Δ17O = -0.21 ‰ for NWA 10639 and δ17O = 1.82 ‰, δ18O = 3.89 ‰, Δ17O = -0.21 ‰ for NWA 10640. Discussion and conclusions:  The textural and minerochemical data are distinctive and point to a classification as monomict eucrite [1,2]. Ox-ygen isotope data confirm this hypothesis [3]. References: [1] Bouvier, A. et al. (2016) MAPS, in press; [2] Grady M. et al. (2014), Atlas of Meteorites, 1st ed., CUP, Cambridge, pp.350; [3] Scott, E.R.D. et al. (2009), GCA, 73, 5835-5853.   6431.pdf79th Annual Meeting of the Meteoritical Society (2016)

Northwest Africa 10639 and 10640: Two new monomict eucrites from Sahara

Moggi Cecchi, Vanni

Pratesi, Giovanni

Caporali, Stefano

Florence Research

Open Research OnlineThe Open University’s repository of research publicationsand other research outputsNorthwest Africa 10639 and 10640: Two newmonomict eucrites from SaharaConference ItemHow to cite:Moggi-Cecchi, V.; Pratesi, G.; Caporali, S.; Franchi, I. A. and Greenwood, R. C. (2016). NorthwestAfrica 10639 and 10640: Two new monomict eucrites from Sahara. In: 79th Annual Meeting of theMeteoritical Society, 7-12 August 2016, Berlin, Germany.For guidance on citations see FAQs.c© [not recorded]Version: Version of RecordCopyright and Moral Rights for the articles on this site are retained by the individual authors and/or othercopyright owners. For more information on Open Research Online’s data policy on reuse of materials pleaseconsult the policies page.oro.open.ac.ukNORTHWEST AFRICA 10639 AND 10640: TWO NEW MONOMICT EUCRITES FROM SAHARA. V. Moggi-Cecchi1, G.Pratesi1,2, S.Caporali3, I.A.Franchi4, R.C.Greenwood4, 1Museo di Storia Naturale, Università degli Studi di Firenze, Via G. La Pira 4, I-50121, Firenze, Italy, 2Dipartimento di Scienze della Terra, Università de-gli Studi di Firenze, Via G. La Pira 4, I-50121, Firenze, Italy, e-mail: vanni.moggicecchi@unifi.it, 3Dipartimento di Chimica, Università degli Studi di Firenze, Via della Lastruccia 3, 50019, Sesto Fiorentino (FI), Italy, 4Planetary and Space Sciences Research Institute, Open University, Walton Hall, Milton Keynes, GB-MK7 6AA United Kingdom.  Introduction: These two meteorites were purchased in 2015 at the Erfoud Market by Hichame Mimaghador, from a Moroccan dealer. The main masses, weighing 232 and 41.9 g, respectively, are both partially covered by a black fusion crust. The sawn surface of both samples shows a brecciated texture with white clasts set in a fine grained matrix. Both meteorites have been approved by the Nomenclature Committee of the Meteoritical Society with the names NWA 10639 and 10640, respectively [1]. Hichame Mimaghador owns both the main masses. The type specimens, weighing 36.2 and 8.4g, respectively, and two thin sections are on deposit at the Museo di Storia Naturale dell’Università di Firenze (sample N° RI-3233 and RI-3234). Instruments and methods: Optical microscopy was undertaken at the laboratories of the Dipartimento di Sci-enze della Terra, Università di Firenze, Italy, using an Axioplan-2 polarizing optical microscope equipped with Axi-ocam-HR camera. SEM-SE images have been performed at the Dipartimento di Chimica, Università degli Studi di Firenze laboratories by means of a Hitachi SEM. EMPA-WDS analyses have been performed at the Firenze labora-tories of the IGG – CNR (National Council of Research) with a Jeol Microbeam microprobe. Oxygen isotope analy-sis was undertaken at the Open University. Experimental results: Both meteorites were investigated by means of optical microscopy, SEM, EMPA and Micro-Raman techniques. A thin section of each sample was analyzed. Both thin sections displays a monomict brec-ciated texture consisting of basaltic eucrite clasts and related crystalline debris set in a finer-grained homogeneous matrix consisting of the same phases (mean grain size 20 μm). Eucritic clasts are mainly characterized by clinopy-roxene, with minor anorthitic plagioclase and orthopyroxene displaying very fine (1-2 μm width for NWA 10639 and 2-3 μm for NWA 10640) pigeonite exsolution lamellae. Minor phases include ilmenite, troilite, chromite, and, for NWA 10639, Fe-Ni metal. NWA 10639 displays a low weathering and a medium shock stage. NWA 10640 dis-plays moderate degree of weathering and a medium shock stage. EMPA analyses of selected grains were performed in order to determine the general minerochemical features of the matrix and of single crystals for classification purposes. Both samples display a calcic plagioclase (An90.1Or0.9, for NWA 10639 and An88.0Or0.9 for NWA 10640), low-Ca pyroxene (Fs55.2En42.4Wo2.4, Fe/Mn=37.6, and  Fs56.1En43.6Wo2.3, Fe/Mn=36.5, respectively), augite (Fs29.7En30.6Wo39.7, Fe/Mn=32.8, and Fs39.2En28.0Wo32.9, Fe/Mn=35.4, respectively), pigeonite exsolution lamellae in low-Ca pyroxene (Fs57.7En33.8Wo8.5, Fe/Mn = 33.7 and (Fs59.4En29.9Wo10.7, Fe/Mn = 34.2, respectively). Oxygen isotope analyses performed on both samples provided the following results: δ17O = 1.87 ‰, δ18O = 4.01 ‰, Δ17O = -0.21 ‰ for NWA 10639 and δ17O = 1.82 ‰, δ18O = 3.89 ‰, Δ17O = -0.21 ‰ for NWA 10640. Discussion and conclusions:  The textural and minerochemical data are distinctive and point to a classification as monomict eucrite [1,2]. Ox-ygen isotope data confirm this hypothesis [3]. References: [1] Bouvier, A. et al. (2016) MAPS, in press; [2] Grady M. et al. (2014), Atlas of Meteorites, 1st ed., CUP, Cambridge, pp.350; [3] Scott, E.R.D. et al. (2009), GCA, 73, 5835-5853.   6431.pdf79th Annual Meeting of the Meteoritical Society (2016)

NORTHWEST AFRICA 10639 AND 10640: TWO NEW MONOMICT EUCRITES FROM SAHARA.

Northwest Africa 10639 and 10640: Two new monomict eucrites from Sahara

Abstract

Similar works

Full text

Available Versions

Open Research Online (OU)

Florence Research