Day: March 13, 2017

Petrographic and geochemical evidence for multiphase formation of carbonates in the Martian orthopyroxenite Allan Hills 84001

Posted by

0

1Carles E. Moyano-Cambero, 1Josep M. Trigo-Rodríguez, 2M. Isabel Benito, 3Jacinto Alonso-Azcárate, 4Martin R. Lee, 5Narcís Mestres, 6,7Marina Martínez-Jiménez, 1Francisco J. Martín-Torres, 8Jordi FraxedasMeteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12851]
1Institute of Space Sciences (IEEC-CSIC), Campus UAB, Cerdanyola del Vallès, Barcelona, Spain
2Departamento de Estratigrafía-IGEO, Facultad de Ciencias Geológicas, Universidad Complutense de Madrid-CSIC, Madrid, Spain
3Fac. de Ciencias Ambientales y Bioquímica, Universidad de Castilla-La Mancha, Toledo, Spain
4School of Geographical and Earth Sciences, University of Glasgow, Glasgow, G12 800, UK
5Institut de Ciència de Materials de Barcelona (ICMAB-CSIC), Campus UAB, Bellaterra, Barcelona, Spain
6Instituto Andaluz de Ciencias de la Tierra (CSIC-UGR), Armilla, Granada, Spain
7Division of Space Technology, Department of Computer Science, Electrical and Space Engineering, Luleå University of Technology, Kiruna, Sweden
8Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and the Barcelona Institute of Science and Technology, Campus UAB, Bellaterra, Barcelona, Spain
Published by arrangement with John Wiley & Sons

Martian meteorites can provide valuable information about past environmental conditions on Mars. Allan Hills 84001 formed more than 4 Gyr ago, and owing to its age and long exposure to the Martian environment, and this meteorite has features that may record early processes. These features include a highly fractured texture, gases trapped during one or more impact events or during formation of the rock, and spherical Fe-Mg-Ca carbonates. In this study, we have concentrated on providing new insights into the context of these carbonates using a range of techniques to explore whether they record multiple precipitation and shock events. The petrographic features and compositional properties of these carbonates indicate that at least two pulses of Mg- and Fe-rich solutions saturated the rock. Those two generations of carbonates can be distinguished by a very sharp change in compositions, from being rich in Mg and poor in Fe and Mn, to being poor in Mg and rich in Fe and Mn. Between these two generations of carbonate is evidence for fracturing and local corrosion.

A gamma-ray spectroscopy survey of Omani meteorites

Posted by

0

1Patrick Weber, 2Beda A. Hofmann, 3Tamer Tolba, 3Jean-Luc Vuilleumier
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12847]
1Hôpital Neuchâtelois, Service de Radiothérapie, La Chaux-de-Fonds, Switzerland
2Naturhistorisches Museum der Burgergemeinde Bern, Bern, CH-3005, Switzerland
3Albert Einstein Center for Fundamental Physics, LHEP, University of Bern, Bern, Switzerland
Published by arrangement with John Wiley & Sons

/enhanced/static/common/js/patches/ie.js?version=1.13.3
<!–

The gamma-ray activities of 33 meteorite samples (30 ordinary chondrites, 1 Mars meteorite, 1 iron, 1 howardite) collected during Omani-Swiss meteorite search campaigns 2001–2008 were nondestructively measured using an ultralow background gamma-ray detector. The results provide several types of information: Potassium and thorium concentrations were found to range within typical values for the meteorite types. Similar mean 26Al activities in groups of ordinary chondrites with (1) weathering degrees W0-1 and low 14C terrestrial age and (2) weathering degree W3-4 and high 14C terrestrial age are mostly consistent with activities observed in recent falls. The older group shows no significant depletion in 26Al. Among the least weathered samples, one meteorite (SaU 424) was found to contain detectable 22Na identifying it as a recent fall close to the year 2000. Based on an estimate of the surface area searched, the corresponding fall rate is ~120 events/106 km2*a, consistent with other estimations. Twelve samples from the large JaH 091 strewn field (total mass ~4.5 t) show significant variations of 26Al activities, including the highest values measured, consistent with a meteoroid radius of ~115 cm. Activities of 238U daughter elements demonstrate terrestrial contamination with 226Ra and possible loss of 222Rn. Recent contamination with small amounts of 137Cs is ubiquitous. We conclude that gamma-ray spectroscopy of a selection of meteorites with low degrees of weathering is particularly useful to detect recent falls among meteorites collected in hot deserts.