¹Geoffrey H. Howarth, ²Arya Udry
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12799]
¹Department of Geological Sciences, University of Cape Town, Rondebosch, South Africa
²Department of Geoscience, University of Nevada, Las Vegas, Las Vegas, Nevada, USA
Published by arrangement with John Wiley & Sons

Olivine-phyric shergottites represent primitive basaltic to picritic rocks, spanning a large range of Mg# and olivine abundances. As primitive olivine-bearing magmas are commonly representative of their mantle source on Earth, understanding the petrology and evolution of olivine-phyric shergottites is critical in our understanding of Martian mantle compositions. We present data for the olivine-phyric shergottite Northwest Africa (NWA) 10170 to constrain the petrology with specific implications for magma plumbing-system dynamics. The calculated oxygen fugacity and bulk-rock REE concentrations (based on modal abundance) are consistent with a geochemically intermediate classification for NWA 10170, and overall similarity with NWA 6234. In addition, we present trace element data using laser ablation ICP-MS for coarse-grained olivine cores, and compare these data with terrestrial and Martian data sets. The olivines in NWA 10170 contain cores with compositions of Fo77 that evolve to rims with composition of Fo58, and are characterized by cores with low Ni contents (400–600 ppm). Nickel is compatible in olivine and such low Ni content for olivine cores in NWA 10170 suggests either early-stage fractionation and loss of olivine from the magma in a staging chamber at depth, or that Martian magmas have lower Ni than terrestrial magmas. We suggest that both are true in this case. Therefore, the magma does not represent a primary mantle melt, but rather has undergone 10–15% fractionation in a staging chamber prior to extrusion/intrusion at the surface of Mars. This further implies that careful evaluation of not only the Mg# but also the trace element concentrations of olivine needs to be conducted to evaluate pristine mantle melts versus those that have fractionated olivine (±pyroxene and oxide minerals) in staging chambers.

^1,2R. Liu,^1,3L. Hu,¹M. Humayun
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12803]
¹National High Magnetic Field Laboratory and Department of Earth, Ocean and Atmospheric Science, Florida State University, Tallahassee, Florida, USA
²Department of Geosciences, Texas Tech University, Lubbock, Texas, USA
³Department of Geology and Geophysics, University of Utah, Salt Lake City, Utah, USA
Published by arrangement with John Wiley & Sons

Rhenium is an important element with which to test hypotheses of isotope variation. Historically, it has been difficult to precisely correct the instrumental mass bias in thermal ionization mass spectrometry. We used W as an internal standard to correct mass bias on the MC-ICP-MS, and obtained the first precise δ187Re values (~±0.02‰, 2SE) for iron meteorites and chondritic metal. Relative to metal from H chondrites, IVB irons are systematically higher in δ187Re by ~0.14 ‰. δ187Re for other irons are similar to H chondritic metal, although some individual samples show significant isotope fractionation. Since 185Re has a high neutron capture cross section, the effect of galactic cosmic-ray (GCR) irradiation on δ187Re was examined using correlations with Pt isotopes. The pre-GCR irradiation δ187Re for IVB irons is lower, but the difference in δ187Re between IVB irons and other meteoritic metal remains. Nuclear volume-dependent fractionation for Re is about the right magnitude near the melting point of iron, but because of the refractory and compatible character of Re, a compelling explanation in terms of mass-dependent fractionation is elusive. The magnitude of a nucleosynthetic s-process deficit for Re estimated from Mo and Ru isotopes is essentially unresolvable. Since thermal processing reduced nucleosynthetic effects in Pd, it is conceivable that Re isotopic variations larger than those in Mo and Ru may be present in IVBs since Re is more refractory than Mo and Ru. Thus, the Re isotopic difference between IVBs and other irons or chondritic metal remains unexplained.

^1,2,3Kathleen E. Vander Kaaden, ^1,3Francis M. McCubbin, ⁴Larry R. Nittler, ⁵Patrick N. Peplowski, ⁴Shoshana Z. Weider, ⁴Elizabeth A. Frank,⁶Timothy J. McCoy
Icarus (in Press) Link to Article [http://dx.doi.org/10.1016/j.icarus.2016.11.041]
¹Institute of Meteoritics, Department of Earth & Planetary Sciences, University of New Mexico, Albuquerque, NM 87131, USA.
²Lunar and Planetary Institute, 3600 Bay Area Boulevard, Houston, TX 77058, USA
³NASA Johnson Space Center, Mailcode XI2, 2101 NASA Parkway, Houston, TX 77058, USA.
⁴Department of Terrestrial Magnetism, Carnegie Institution of Washington, DC 20015, USA.
⁵The Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723, USA.
⁶Department of Mineral Sciences, National Museum of Natural History, 10th and Constitution Aves. NW, Smithsonian Institution, Washington, DC 20560, USA.
Copyright Elsevier

Orbital data from the MESSENGER mission to Mercury have facilitated a new view of the planet’s structure, chemical makeup, and diverse surface, and have confirmed Mercury’s status as a geochemical endmember among the terrestrial planets. In this work, the most recent results from MESSENGER’s X-Ray Spectrometer, Gamma-Ray Spectrometer, and Neutron Spectrometer have been used to identify nine distinct geochemical regions on Mercury. Using a variation on the classical CIPW normative mineralogy calculation, elemental composition data is used to constrain the potential mineralogy of Mercury’s surface; the calculated silicate mineralogy is dominated by plagioclase, pyroxene (both orthopyroxene and clinopyroxene), and olivine, with lesser amounts of quartz. Petrologically, the rocks on the surface of Mercury are highly diverse and vary from komatiitic to boninitic. The high abundance of alkalis on Mercury’s surface results in several of the nine regions being classified as alkali-rich komatiites and/or boninites. In addition, Mercury’s surface terranes span a wide range of SiO2 values that encompass crustal compositions that are more silica-rich than geochemical terranes on the Moon, Mars, and Vesta, but the range is similar to that of Earth. Although the composition of Mercury’s surface appears to be chemically evolved, the high SiO2 content is a primitive feature and a direct result of the planet’s low oxygen fugacity.

^1,2M.J. Genge, ³J. Larsen, ⁴M. Van Ginneken,^1,2M.D. Suttle
Geology (in Press) Link to Article [doi: 10.1130/G38352.1]
¹Department of Earth Sciences and Engineering, Imperial College London, Exhibition Road, London SW7 2AZ, UK
²Department of Earth Science, Natural History Museum, Cromwell Road, London SW7 2BT, UK
³Project Stardust, Oslo, Norway
⁴Département des Géosciences, Université Libre de Bruxelles, Avenue FD. Roosevelt, 2 B-1050 Bruxelles, Belgium

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¹Rainer Bartoschewitz et al. (>10)*
Chemie der Erde – Geochemistry (in Press) Link to Article [http://dx.doi.org/10.1016/j.chemer.2016.10.004]
¹Bartoschewitz Meteorite Laboratory, Weiland 37, D-38518 Gifhorn, Germany
*Find the extensive, full author and affiliation list on the publishers website
Copyright Elsevier

On April 23rd 2013 at 2:07 a.m., a 1.3 kg meteorite fell in the Braunschweig suburb Melverode (52° 13′ 32.19″ N. 10° 31′ 11.60″ E). Its estimated velocity was 250 km/h and it formed an impact pit in the concrete fall site with a diameter of 7 cm and a depth of 3 cm. Radial dust striae are present around the impact pit. As a result of the impact, the meteorite disintegrated into several hundred fragments with masses up to 214 g. The meteorite is a typical L6 chondrite, moderately shocked (S4) – but with a remarkably high porosity (up to 20 vol%). The meteorite was ejected from its parent body as an object with a radius of about 10–15 cm (15–50 kg). The U,Th-He gas retention age of ∼550 Ma overlaps with the main impact event on the L-chondrite parent body ∼470 Ma ago that is recorded by many shocked L chondrites. The preferred cosmic-ray exposure age derived from production of radionuclides and noble gas isotopes is (6.0 ± 1.3) Ma.

¹Richard C. Greenwood, ²Thomas H. Burbine, ¹Martin F. Miller, ¹Ian. A. Franchi
Chemie der Erde – Geochemistry (in Press) Link to Article [http://dx.doi.org/10.1016/j.chemer.2016.09.005]
¹Planetary and Space Sciences, School of Physical Sciences, The Open University, Walton Hall, Milton Keynes MK7 6AA, United Kingdom
²Astronomy Department, Mount Holyoke College, South Hadley, MA 01075, USA
Copyright Elsevier

A number of distinct methodologies are available for determining the oxygen isotope composition of minerals and rocks, these include laser-assisted fluorination, secondary ion mass spectrometry (SIMS) and UV laser ablation. In this review we focus on laser-assisted fluorination, which currently achieves the highest levels of precision available for oxygen isotope analysis. In particular, we examine how results using this method have furthered our understanding of early-formed differentiated meteorites. Due to its rapid reaction times and low blank levels, laser-assisted fluorination has now largely superseded the conventional externally-heated Ni “bomb” technique for bulk analysis. Unlike UV laser ablation and SIMS analysis, laser-assisted fluorination is not capable of focused spot analysis. While laser fluorination is now a mature technology, further analytical improvements are possible via refinements to the construction of sample chambers, clean-up lines and the use of ultra-high resolution mass spectrometers.

High-precision oxygen isotope analysis has proved to be a particularly powerful technique for investigating the formation and evolution of early-formed differentiated asteroids and has provided unique insights into the interrelationships between various groups of achondrites. A clear example of this is seen in samples that lie close to the terrestrial fractionation line (TFL). Based on the data from conventional oxygen isotope analysis, it was suggested that the main-group pallasites, the howardite eucrite diogenite suite (HEDs) and mesosiderites could all be derived from a single common parent body. However, high precision analysis demonstrates that main-group pallasites have a Δ17O composition that is fully resolvable from that of the HEDs and mesosiderites, indicating the involvement of at least two parent bodies. The range of Δ17O values exhibited by an achondrite group provides a useful means of assessing the extent to which their parent body underwent melting and isotopic homogenization. Oxygen isotope analysis can also highlight relationships between ungrouped achondrites and the more well-populated groups. A clear example of this is the proposed link between the evolved GRA 06128/9 meteorites and the brachinites.

The evidence from oxygen isotopes, in conjunction with that from other techniques, indicates that we have samples from approximately 110 asteroidal parent bodies (∼60 irons, ∼35 achondrites and stony-iron, and  ∼15 chondrites) in our global meteorite collection. However, compared to the likely size of the original protoplanetary asteroid population, this is an extremely low value. In addition, almost all of the differentiated samples (achondrites, stony-iron and irons) are derived from parent bodies that were highly disrupted early in their evolution.

High-precision oxygen isotope analysis of achondrites provides some important insights into the origin of mass-independent variation in the early Solar System. In particular, the evidence from various primitive achondrite groups indicates that both the slope 1 (Y&R) and CCAM lines are of primordial significance. Δ17O differences between water ice and silicate-rich solids were probably the initial source of the slope 1 anomaly. These phases most likely acquired their isotopic composition as a result of UV photo-dissociation of CO that took place either in the early solar nebula or precursor giant molecular cloud. Such small-scale isotopic heterogeneities were propagated into larger-sized bodies, such as asteroids and planets, as a result of early Solar System processes, including dehydration, aqueous alteration, melting and collisional interactions.

There is increasing evidence that chondritic parent bodies accreted relatively late compared to achondritic asteroids. This may account for the fact that apart from a few notable exceptions’ such as the aubrite-enstatite chondrite association, known chondrite groups could not have been the parents to the main achondrite groups.

^1,2,3Stefan T.M. Peters, ^1,2Carsten Münker, ^1,2Markus Pfeifer, ^1,2Bo-Magnus Elfers, ^1,2Peter Sprung
Earth and Planetary Science Letters (in Press) Link to Article [http://dx.doi.org/10.1016/j.epsl.2016.11.009]
¹Institut für Geologie und Mineralogie, Universität zu Köln, Zülpicherstr. 49b, 50674 Cologne, Germany
²Steinmann-Institut, Poppelsdorfer Schloss, 53115 Bonn, Germany
³Geowissenschaftliches Zentrum der Georg-August-Universität Göttingen, Department of Isotope Geology, Goldschmidtstrasse 1, 37077 Göttingen, Germany
Copyright Elsevier

Some nuclides that were produced in supernovae are heterogeneously distributed between different meteoritic materials. In some cases these heterogeneities have been interpreted as the result of interaction between ejecta from a nearby supernova and the nascent solar system. Particularly in the case of the oldest objects that formed in the solar system – Ca–Al rich inclusions (CAIs) – this view is confirm the hypothesis that a nearby supernova event facilitated or even triggered solar system formation. We present Hf isotope data for bulk meteorites, terrestrial materials and CAIs, for the first time including the low-abundance isotope 174Hf (∼0.16%). This rare isotope was likely produced during explosive O/Ne shell burning in massive stars (i.e., the classical “p-process”), and therefore its abundance potentially provides a sensitive tracer for putative heterogeneities within the solar system that were introduced by supernova ejecta. For CAIs and one LL chondrite, also complementary W isotope data are reported for the same sample cuts. Once corrected for small neutron capture effects, different chondrite groups, eucrites, a silicate inclusion of a IAB iron meteorite, and terrestrial materials display homogeneous Hf isotope compositions including 174Hf. Hafnium-174 was thus uniformly distributed in the inner solar system when planetesimals formed at the

¹A. A. Garde, ²Martin B. Klausen
Journal of the Geological Society 173, 954-965 Link to Article [doi: 10.1144/jgs2015-147]
¹Geological Survey of Denmark and Greenland, Øster Voldgade 10, 1350 Copenhagen K, Denmark
²Department of Earth Sciences, Stellenbosch University, Private Bag X1, Matieland 7602, South Africa

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¹Grethe Hystad, ²Robert T. Downs, ³Robert M. Hazen, ²Joshua J. Golden
Mathematical Geosciences (in Press) Link to Article [doi:10.1007/s11004-016-9661-y]
¹Mathematics, Statistics, and Computer SciencePurdue University Northwest Hammond USA
²Department of Geosciences University of Arizona Tucson USA
³Geophysical Laboratory Carnegie Institution for Science Washington USA

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¹Rudra Chatterjee, ¹John C. Lassiter
Chemical Geology 442, 11-22 Link to Article [http://dx.doi.org/10.1016/j.chemgeo.2016.08.033]
¹Department of Geological Sciences, Jackson School of Geosciences, The University of Texas at Austin, 1 University Station C1160, Austin, TX -78712-0254, United States

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