Publications

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2012
Paniello, RC, Day JMD, Moynier F.  2012.  Zinc isotopic evidence for the origin of the Moon. Nature. 490:376-U104.   10.1038/nature11507   AbstractWebsite

Volatile elements have a fundamental role in the evolution of planets. But how budgets of volatiles were set in planets, and the nature and extent of volatile-depletion of planetary bodies during the earliest stages of Solar System formation remain poorly understood(1,2). The Moon is considered to be volatile-depleted and so it has been predicted that volatile loss should have fractionated stable isotopes of moderately volatile elements(3). One such element, zinc, exhibits strong isotopic fractionation during volatilization in planetary rocks(4,5), but is hardly fractionated during terrestrial igneous processes(6), making it a powerful tracer of the volatile histories of planets. Here we present high-precision zinc isotopic and abundance data which show that lunar magmatic rocks are enriched in the heavy isotopes of zinc and have lower zinc concentrations than terrestrial or Martian igneous rocks. Conversely, Earth and Mars have broadly chondritic zinc isotopic compositions. We show that these variations represent large-scale evaporation of zinc, most probably in the aftermath of the Moon-forming event, rather than small-scale evaporation processes during volcanism. Our results therefore represent evidence for volatile depletion of the Moon through evaporation, and are consistent with a giant impact origin for the Earth and Moon.

2009
Liu, Y, Floss C, Day JMD, Hill E, Taylor LA.  2009.  Petrogenesis of lunar mare basalt meteorite Miller Range 05035. Meteoritics & Planetary Science. 44:261-284. AbstractWebsite

Miller Range (MIL) 05035 is a low-Ti mare basalt that consists predominantly of pyroxene (62.3 vol%) and plagioclase (26.4 vol%). Pyroxenes are strongly shocked and complexly zoned from augite (Wo(33)) and pigeonite (Wo(17)) cores with Mg# = 50-54 to hedenbergite rims. Coexisting pyroxene core compositions reflect crystallization temperatures of 1000 to 1100 degrees C. Plagioclase has been completely converted to maskelynite with signs of recrystallization. Maskelynite is relatively uniform in composition (An(94)Ab(6)-An(91)Ab(9)), except at contacts with late-stage mesostasis areas (elevated K contents, An(82)Ab(15)Or(3)). Symplectites (intergrowth of Fe-augite, fayalite, and silica) of different textures and bulk compositions in MIL 05035 suggest formation by decomposition of Ferro-pyroxene during shock-induced heating, which is Supported by the total maskelynitization of plagioclase, melt pockets, and the presence of a relict pyroxferroite grain. Petrography and mineral chemistry imply that crystallization of MIL 05035 Occurred in the sequence of Fe-poor pyroxenes (Mg# = 50-54), followed by plagioclase and Fe-rich pyroxenes (Mg# = 20-50), and finally hedenbergite, Fe-Ti oxides, and minor late-stage phases. Petrography, bulk chemistry, mineral compositions, and the age of MIL 05035 Suggest it is possibly Source crater-paired with Asuka (A-) 881757 and Yamato (Y-) 793169, and may also be launch-paired with Meteorite Hills (MET) 01210. MIL 05035 represents an old (similar to 3.8-3.9 Ga), incompatible element-depleted low-Ti basalt that was not sampled during the Apollo or Luna missions. The light-REE depleted nature and lack of Eu anomalies For this meteorite are consistent with an origin distant from the Procellarum KREEP Terrane, and genesis from an early Cumulate mantle-source region generated by extensive differentiation of the Moon.

2006
Day, JMD, Taylor LA, Floss C, McSween HY.  2006.  Petrology and chemistry of MIL 03346 and its significance in understanding the petrogenesis of nakhlites on Mars. Meteoritics & Planetary Science. 41:581-606. AbstractWebsite

Antarctic meteorite Miller Range (MIL) 03346 is a nakhlite composed of 79% clinopyroxene, similar to 1% olivine, and 20% vitrophyric intercumulus material. We have performed a petrological and geochemical study of MIL 03346, demonstrating a petrogenetic history similar to previously discovered naklilites. Quantitative textural study of MIL 03346 indicates long (> 1 x 10(1) yr) residence times for the Cumulus augite, whereas the skeletal Fe-Ti oxide, fayalite, and sulfide in the vitrophyric intercumulus matrix suggest rapid cooling, probably as a lava flow. From the relatively high forsterite contents of olivine (up to Fo(43)) compared with other nakhlites and compositions of augite cores (Wo(38-42)En(35-40)Fs(22-28)) and their hedenbergite rims, we suggest that MIL 03346 is part of the same or a similar Martian Cumulate-rich lava flow as other nakhlites. However, MIL 03346 has experienced less equilibration and faster cooling than other nakhlites discovered to date. Calculated trace element concentrations based upon modal abundances of MIL 03346 and its constituent minerals are identical to whole rock trace element abundances. Parental melts for augite have REE patterns that are approximately parallel with whole rock and intercumulus melt using experimentally defined partition coefficients. This parallelism reflects closed-system crystallization for MIL 03346, where the only significant petrogenetic process between formation of augite and eruption and emplacement of the nakhlite flow has been fractional crystallization. A model for the petrogenesis of MIL 03346 and the naklilites (Nakhla, Governador Valadares, Lafayette, Yamato-000593, Northwest Africa (NWA) 817, NWA 998) Would include: 1) partial melting and ascent of melt generated from a long-term LREE depleted mantle Source, 2) crystallization of cumulus augite (+/- olivine, +/- magnetite) in a shallow-level Martian magma chamber, 3) eruption of the crystal-laden naklilite magma onto the surface of Mars, 4) cooling, crystal settling, overgrowth, and partial equilibration to different extents within the flow, 5) secondary alteration through hydrothermal processes, possibly immediately succeeding or during emplacement of the flow. This model might apply to single-or multiple-flow models for the nakhlites. Ultimately, MIL 03346 and the other nakhlites preserve a record of magmatic processes in volcanic rocks oil Mars with analogous petrogenetic histories to pyroxene-rich terrestrial lava flows and to komatiites.