An Eucritic Basalt with Cm - Sized

Introduction: We present the first mineralogical and oxygen isotope data for the new eucrite Northwest Africa (NWA) 5073 that has some unique features. This meteorite is a desert find with a total mass of 185 g and represents a non-brecciated unequili-brated eucrite with the coarsest texture ever found among samples of the HED suite. Results: NWA 5073 has a basaltic texture, mainly composed of zoned pyroxene and plagioclase laths (An 76-92 Ab 8-22 Or 0-3) up to 1.2 cm and 0.2 cm in length, respectively, with minor amounts of mesostasis. The latter consists of ilmenite, Fe-metal, chromite, phosphate (apatite), silica, and anorthite (~An 95). Euhedral to anhedral silica grains with sizes up to 0.8 mm were invariably found in the mesostasis, which probably represents the residual melt. Zr-bearing phases (zircon, baddeleyite, and zirconolite) were found in the mesostasis with diameters ranging from 1 to 25 µm [1]. Pyroxenes are unequilibrated with cores of about En 60 Fs 34 Wo 6 and rims of about En 39 Fs 51 Wo 10. Large pyroxene grains are crossed by veins of Fa-rich olivine (Fa 67-68), which are clearly restricted to large pyroxene crystals and always end abruptly at their boundaries, while adjacent minerals are free of them. Similar Fa-rich olivine veins were found in NWA 1000 [2]. NWA 5073 is weakly shocked (S2) [3,4]. Terrestrial weathering (W2-3; [5]) is indicated by the breakdown of about half of the metals and by the occurrence of calcite and Ba-and Sr-bearing sulfates. Based on oxygen isotope data (δ 17 O = 1.88 ‰; δ 18 O = 4.05 ‰; Δ 17 O (linearized [6]) =-0.239 ‰) NWA 5073 is a normal member of the HED suite. The Δ 17 O value for the sample is identical to the average HED value obtained by [7], whereas the δ 18 O is slightly higher compared to other eucrites analyzed by [7], but within the data range of [8]. Conclusions: This meteorite cooled rapidly as indicated by the presence of skeletal plagioclase, the unequilibrated nature of its pyroxenes and the occurrence of only thin (<1µm) exsolution lamellae in some pyroxenes. Based on grain sizes NWA 1000 resembles NWA 5073 [2]. However, NWA 1000 is severely shocked (S4), as documented by the transformation of half of the plagioclase into maskelynite [2]. Both samples are certainly not fall-paired, but may be launch-paired from the parent body. The occurrence of Fa-rich olivine …