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**th Annual Meteoritical Society Meeting (****) **49.pdf

NEW LUNAR METEORITE NORTHWEST AFRICA 773: DUAL ORIGIN BY CUMULATE

CRYSTALLIZATION AND IMPACT BRECCIATION. T.J. Fagan1, K. Keil1, G.J. Taylor1, T.L. Hicks1, M.

Killgore2, T.E. Bunch3, J.H. Wittke4, O. Eugster5, S. Lorenzetti5, D.W. Mittlefehldt6, R.N. Clayton7 and T. Mayeda7.

1

Hawai i Institute of Geophysics and Planetology, University of Hawai i at Manoa, Honolulu HI 96822, USA (fa-

abpcjy@r.postjobfree.com) 2Southwest Meteorite Lab, P.O. Box 95, Payson, AZ 85547, USA, 3Space Science Division,

NASA Ames Research Center, Moffett Field, CA 94035, USA, 4Department of Geology, Northern Arizona Univer-

sity, Flagstaff, AZ 86011, USA, 5Physikalisches Institut, Universit t Bern, CH-3012 Bern, Switzerland, 6SN2,

NASA/Johnson Space Center, Houston TX 77258, USA, 7Enrico Fermi Institute, University of Chicago, Chicago,

IL 60637, USA.

Introduction: Northwest Africa 773 was recov- Oxygen isotopes: Two fragments broken from

ered from Dchira, Western Sahara in fall, 2000 [1]. It NWA 773 yield whole-rock oxygen isotopic composi-

tions of 18O = +4.99, 17O = +2.50 for the cumulate;

consists of two lithologies: a green olivine-rich cu-

and 18O = +4.93, 17O = +2.60 for the breccia. These

mulate, and a black impact breccia. In this abstract, we

describe this meteorite and our efforts to ascertain its compositions are lower than previously analyzed lunar

parent body. meteorites [3], but are on the terrestrial fractionation

Mineralogy and Petrology: Approximately one- line and within the field of whole-rock values of

half of the meteorite consists of cumulate olivine gab- Apollo samples [4].

bronorite. The other half consists of heterolithic im- Noble gases: Analyses of three grain size fractions

pact breccia with a regolith component. Partial yield solar gas concentrations and isotopic ratios simi-

maskelynitization of feldspar indicates shock stage S2. lar to lunar meteorite QUE 94281, a regolith breccia

[5]. The ratio of solar 4He/20Ne of ~ 9 is typical for

Terrestrial weathering has caused some fracturing, but

pre-terrestrial minerals in the meteorite appear fresh. gas-rich lunar meteorites, and much lower than values

Cumulate olivine gabbronorite. The cumulate for non-lunar meteorites.

lithology consists primarily of olivine (Fo69), pi- Conclusions: NWA 773 formed by a combination

geonite (Wo11En65), augite (Wo36En49), plagioclase of cumulate crystallization of olivine gabbronorite and

(An89Or02) and K,Ba-feldspar (hyalophane, brecciation of multiple lithologies, including a regolith

An03Or93Cs04). Olivine is the most abundant phase (51 component. Mineralogy, Mn/Fe ratios, a KREEP-like

vol followed by pigeonite (22%), augite (10%), trace element pattern with a deep Eu anomaly, oxygen

plagioclase (14%), alkali feldspar (1.5%). Chromite, isotopic composition, and noble gas concentrations

ilmenite, troilite, Fe,Ni-metal, and phosphate(s) are indicate a lunar origin for NWA 773.

also present. Olivine occurs in a network of coarse, References: [1] Grossman J. N. (2001) Meteorit.

equant to prismatic, subhedral crystals. The pyroxenes Bull., 85, in press. [2] Papike J. J. (1998) in Revs.

generally occur as anhedral crystals between olivine Mineral. 36, 7.1-7.11. [3] Clayton R. N. and Mayeda

grains. Feldspars are interstitial to the mafic silicates. T. K. (1996) GCA 60, 1999. [4] Clayton R. N. and

Ratios of Fe/Mn in olivine (99, by weight), pigeonite Mayeda T. K. (1975) Proc. Lunar Sci Conf. 6, 1761.

(53), and augite (46) are similar to lunar values [2]. [5] Polnau E. and Eugster O. (1998) MAPS 33, 313.

A small (14.5 mg) sample of the cumulate lithology

shows that it is enriched in light rare earth elements

(REE) by ~ 40X CI and heavy REE by ~ 20X CI. The

REE pattern exhibits a well-defined negative Eu

anomaly.

Impact breccia. The breccia is composed of

lithic and mineral fragments in a fine, granular matrix.

Lithic fragments include pieces of the cumulate rock, a

variety of basalts, FeO-rich symplectites, and unusual

clasts characterized by fayalite, silica, plagioclase, and

hyalophane. Mineral fragments include fayalite, silica

glass, and hedenbergitic (Wo36En05) pyroxene. Rego-

lith agglutinates have also been identified in the brec-

cia. The breccia is somewhat more enriched in REE

(light REE ~ 60X CI) than the cumulate, but exhibits a

similar pattern of light REE enrichment and deep Eu

anomaly.

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