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Article re: NWA 6704 meteorite
No full textHeadline: "Rocks from Space Picture of the Day: Northwest Africa 6704…a 'most intriguing' New Ungrouped Achondrite
Information about the NWA 6704 meteorite
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Mineralogical Criteria for the Parent Asteroid of the “Carbonaceous” Achondrite NWA 6704
No full textThe unique achondrite meteorite Northwest Africa (NWA) 6704 and its paired samples are fragments of an unknown parent asteroid that experienced large-scale igneous melting early in our solar system's history. The geochemistry and mineralogy of NWA 6704 show that its parent asteroid has affinities with carbonaceous chondrites and that the precursor materials were relatively oxidized. While large-scale melting has affected the meteorite, there is no evidence for equilibration with a metallic melt. NWA 6704 paired meteorites therefore provide insights into the evolution of planetesimals and bodies that accreted from source materials, possibly in the ice-rich outer solar system. Currently, we lack an understanding of the distribution of potential parent asteroids of the NWA 6704 meteorites. We have undertaken a detailed multiwavelength (0.35-25 mu m) spectroscopic and geochemical investigation of NWA 6704 to provide constraints on the potential parent asteroids of these enigmatic meteorites. In comparison with asteroid spectra, NWA 6704 is similar to the S(VI) subtypes of the S-asteroid complex. By using the Bus-DeMeo Taxonomic Classifier, we determine that NWA 6704 has affinities toward V-type (Vesta type) asteroids. We have determined that the parent asteroid of NWA 6704 would be a V-type asteroid that is not dynamically linked to Vesta and also fall in the S(VI) subtype of the Band I center versus Band area ratio diagram. A search in the literature for potential parent bodies yielded one asteroid, (34698) 2001 OD22, as a possible candidate.This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]
Carbonaceous achondrites Northwest Africa 6704/6693: Milestones for early Solar System chronology and genealogy
No full textNorthwest Africa (NWA) 6704/6693 are medium- to coarse-grained achondrites with unique petrologic and geochemical traits that are distinct from the currently established meteorite groups. Here, we report on the extinct 26Al-26Mg and 53Mn-53Cr systems to establish fine-scale chronology of its formation and Cr and Ti isotopic anomalies to constrain the composition of the source reservoir of NWA 6704/6693. Excesses in the neutron-rich 54Cr and 50Ti isotopes, due to nucleosynthetic anomalies, separate NWA 6704/6693 from the vast majority of established achondrites and instead resemble the excesses seen among the carbonaceous chondrites; specifically, the CR-type chondrites. The excesses in these isotopes indicate a common feeding zone during accretion in the protoplanetary disk between the source of NWA 6704/6693 and that of the carbonaceous chondrites. The 26Al-26Mg data for pyroxene and plagioclase from NWA 6704 yield a (26Al/27Al)0 = (3.15 ± 0.38)×10−7 (MSWD = 0.49) and an initial δ26Mg∗ = −0.004 ± 0.005 at the time of isotopic closure. This initial (26Al/27Al)0 translates to an absolute age of 4563.14 ± 0.38 Ma, relative to the D’Orbigny angrite. However, given the potential heterogeneity of 26Al, the D’Orbigny angrite might not be a good age anchor for the purpose of calculating 26Al-26Mg ages. The 26Al-26Mg age relative to another carbonaceous achondrite, NWA 2976, is 4562.66 ± 0.60 Ma. The 53Mn-53Cr systematics of NWA 6704/6693 indicate a (53Mn/55Mn)0 of (2.59 ± 0.34) × 10−6 (MSWD = 1.2) with an evolved initial ε53Cr of +0.14 ± 0.03. The (53Mn/55Mn)0 yields an 53Mn-53Cr age of 4562.17 ± 0.76 Ma relative to the D’Orbigny angrite. Concordant ages determined using the short-lived 26Al-26Mg and 53Mn-53Cr systems and extant 207Pb-206Pb system (4562.60 ± 0.30 Ma for NWA 6704/6693; Amelin et al., 2019) indicate rapid cooling and nearly contemporaneous closing of multiple isotope systems. The ancient crystallization ages and positive 54Cr and 50Ti anomalies of NWA 6704/6693 indicate widespread melting and differentiation processes occurring in both non-carbonaceous (NC) and carbonaceous chondrite (CC) regions of the protoplanetary disk. Additionally, we report the Cr and Ti isotopic composition for a petrologic range of CR-type materials (CR2, CR6, and achondrites). The additional Cr and Ti isotopic data for these CR-type materials indicates a range in isotopic composition not previously observed based on CR2 chondrites alone
[Louisville, New Albany & Corydon R. R., Engine Drawing Card, Sketch No. 6704]
No full textThis engine drawing card was created for Louisville, New Albany, & Corydon Railroad, Class 8-26C. Section J-8-C. Sketch 6704. Copy Spec. C5535, C8499
^40Ar-^39Ar and Noble Gas Systematics of the Ungrouped Achondrite Northwest Africa 6704
No full textNWA 6704 petrology, noble gas and Ar-Ar data suggest this achondrite experienced at least two thermal events after crystallization: 4.52±0.01 and ?2.20±0.33 Ga
California Poll: 6704 -- September 8-14, 1967
No full textThe Field Poll, established in 1945 as The California Poll by Mervin Field, has operated continuously as an independent, non-partisan, media-sponsored public opinion news service. Each year the Field Polls cover a wide range of political and social topics examining California public opinion. Continuing measures are made of voter support for leading political figures vying for major state and federal offices, job ratings of important political figures and reactions to significant political events. Voter awareness, understanding and predispositions of major campaign issues and salient statewide ballot propositions are also tracked over time. For poll 6704 N=1023
^40Ar-^39Ar and Noble Gas Systematics of the Ungrouped Achondrite Northwest Africa 6704
No full textNWA 6704 petrology, noble gas and Ar-Ar data suggest this achondrite experienced at least two thermal events after crystallization: 4.52±0.01 and ?2.20±0.33 Ga
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