Northwest Africa (NWA) 6704 is a unique achondrite characterized by a near-chondritic major element composition with a remarkably intact igneous texture. To investigate the origin of this unique achondrite, we have conducted a combined petrologic, chemical, and 187 Re-187 Os, O, and Ti isotopic study. The meteorite consists of orthopyroxene megacrysts (En 55-57 Wo 3-4 Fs 40-42 ; Fe/Mn = 1.4) up to 1.7 cm in length with finer interstices of olivine (Fa 50-53 ; Fe/Mn = 1.1-2.1), chromite (Cr# ~ 0.94), awaruite, sulfides, plagioclase (Ab 92 An 5 Or 3 ) and merrillite. The results of morphology, lattice orientation analysis, and mineral chemistry indicate that orthopyroxene megacrysts were originally hollow dendrites that most likely crystallized under high supersaturation and super-cooling conditions (1-10 2 °C/h), whereas the other phases crystallized

Here we describe a new analytical technique for the high-precision measurement of 182 W/ 184 W and 183 W/ 184 W using negative thermal ionization mass spectrometry (N-TIMS). We improve on the recently reported method of Trinquier et al. (2016), which described using Faraday cup collectors coupled with amplifiers utilizing 10 13 Ω resistors to continuously monitor the 18 O/ 16 O of WO 3 − and make per-integration oxide corrections. In our study, we report and utilize a newly measured oxygen mass fractionation line, as well as average 17 O/ 16 O and 18 O/ 16 O, which allow for more accurate per-integration oxide interference corrections. We also report a Faraday cup and amplifier configuration that allows 18 O/ 16 O to be continuously monitored for WO 3 − and ReO 3 − , both of which are ionized during analyses of W using Re ribbon. The long-term external precision of 182 W/ 184 W is 5.7 ppm and 3.7 ppm (2SD) when mass bias corrected using 186 W/ 184 W and 186 W/ 183 W, respectively. For 183 W/ 184 W mass bias is corrected using 186 W/ 184 W, yielding a longterm external precision of 6.6 ppm. An observed, correlated variation in 182 W/ 184 W and 183 W/ 184 W, when mass bias corrected using 186 W/ 184 W, is most likely the result of Faraday cup degradation over months-long intervals.

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