¹Addi Bischoff, ¹Marian Horstmann, ²Jean-Alix Barrat,
³Marc Chaussidon, ⁴Andreas Pack, ^4,5Daniel Herwartz, ¹Dustin Ward, ¹Christian Vollmer, ⁶Stephan Decker

¹Institut für Planetologie and Institut für Mineralogie, Westfälische Wilhelms-Universität Münster, 48149 Münster, Germany
²Institut Universitaire Européen de la Mer, Université de Bretagne Occidentale, 29280 Plouzané, France
³Institut de Physique du Globe, 75235 Paris, France
⁴Geowissenschaftliches Zentrum, Universität Göttingen, 37077 Göttingen, Germany
⁵Institut für Geologie und Mineralogie, Universität zu Köln, 50674 Köln, Germany
⁶Meteorite Museum, 55430 Oberwesel, Germany

Volcanism is a substantial process during crustal growth on planetary bodies and well documented to have occurred in the early Solar System from the recognition of numerous basaltic meteorites. Considering the ureilite parent body (UPB), the compositions of magmas that formed a potential UPB crust and were complementary to the ultramafic ureilite mantle rocks are poorly constrained. Among the Almahata Sitta meteorites, a unique trachyandesite lava (with an oxygen isotope composition identical to that of common ureilites) documents the presence of volatile- and SiO2-rich magmas on the UPB. The magma was extracted at low degrees of disequilibrium partial melting of the UPB mantle. This trachyandesite extends the range of known ancient volcanic, crust-forming rocks and documents that volcanic rocks, similar in composition to trachyandesites on Earth, also formed on small planetary bodies ∼4.56 billion years ago. It also extends the volcanic activity on the UPB by ∼1 million years (Ma) and thus constrains the time of disruption of the body to later than 6.5 Ma after the formation of Ca–Al-rich inclusions.

Reference
Bischoff A, Horstmann M, Barrat J-A, Chaussidon M, Pack A, Herwartz D, Ward D, Vollmer C, Decker S (2014) Trachyandesitic volcanism in the early Solar System. Proceedings of the National Academy of Sciences 111, 35, 12689–12692
Link to Article [doi: 10.1073/pnas.1404799111]

¹François S. Paquay, ¹Greg Ravizza, ²Rodolfo Coccioni
¹Dept. of Geology and Geophysics, University of Hawaii at Manoa, 1680 East West Road POST 712 Honolulu, HI 96822 USA
²Dipartimento di Scienze della Terra, della Vita e dell’Ambiente dell’Universita, Campus Scientifico, Località Crocicchia, 61209 Urbino,

A reconstruction of seawater 187Os/188Os ratios during the late Eocene (∼36-34 Ma), based upon bulk sediment analyses from the sub-Antarctic Southern Atlantic Ocean (Ocean Drilling Program (ODP) Site 1090), Eastern Equatorial Pacific Ocean (ODP Sites 1218 and 1219) and the uplifted (land-based) Tethyan section (Massignano, Italy), confirms that the previously reported abrupt shift to lower 187Os/188Os is a unique global feature of the marine Os isotope record that occurs in magnetochron C16n.1n. This feature is interpreted to represent the change in seawater 187Os/188Os caused by the Popigai impact event. Higher in the Massignano section, two other iridium anomalies previously proposed to represent additional impact events do not show a comparable excursion to low 187Os/188Os, suggesting that these horizons do not record multiple large impacts. Comparison of records from three different ocean basins indicates that seawater 187Os/188Os begins to decline in advance of the Popigai impact event. At Massignano this decline coincides with a previously reported episode of elevated 3He flux, suggesting that increased influx of interplanetary dust particles (IDPs) contributed to the pre-impact shift in 187Os/188Os and not to the longer-term latest Eocene 187Os/188Os decline that occurred ∼1 million year after the Popigai impact event.

Reference
Paquay FS, Ravizza G, Coccioni R (2014) The influence of extraterrestrial material on the late Eocene marine Os isotope record. Geochimica et Cosmoschimica Acta (in Press)
Link to Article [DOI: 10.1016/j.gca.2014.08.024]

Copyright Elsevier