^1,2Berengere Mougel,^1,3Frederic Moynier,^4,5Christian Koeberl,⁶Daniel Wielandt,⁶Martin Bizzarro
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13312]
¹Institut de Physique du Globe de Paris, Université Sorbonne Paris Cité, CNRS UMR7154, 1 rue Jussieu, 75238 Paris Cedex 05, France
²Centro de Geociencias, Universidad Nacional Autónoma de México, Blvd. Juriquilla No 3001, Querétaro, 76230 Mexico
³Institut Universitaire de France, 1 rue Descartes, 75231 Paris Cedex 05, France
⁴Department of Lithospheric Research, University of Vienna, Althanstrasse 14, 1090 Vienna, Austria
⁵Natural History Museum, Burgring 7, 1010 Vienna, Austria
⁶Centre for Star and Planet Formation, Natural History Museum of Denmark, University of Copenhagen, Øster Voldgade 5‐7 DK‐1350, Copenhagen, Denmark
Published by arrangement with John Wiley & Sons

The existence of mass‐independent chromium isotope variability of nucleosynthetic origin in meteorites and their components provides a means to investigate potential genetic relationship between meteorites and planetary bodies. Moreover, chromium abundances are depleted in most surficial terrestrial rocks relative to chondrites such that Cr isotopes are a powerful tool to detect the contribution of various types of extra‐terrestrial material in terrestrial impactites. This approach can thus be used to constrain the nature of the bolide resulting in breccia and melt rocks in terrestrial impact structures. Here, we report the Cr isotope composition of impact rocks from the ~0.57 Ma Lonar crater (India), which is the best‐preserved impact structure excavated in basaltic target rocks. Results confirm the presence of a chondritic component in several bulk rock samples of up to 3%. The impactor that created the Lonar crater had a composition that was most likely similar to that of carbonaceous chondrites, possibly a CM‐type chondrite.

¹H. Nekvasil,²N.J. DiFrancesco,¹A.D. Rogers,³A.E. Coraor,⁴P.L. King
Journal of Geophysical Research, Planets (in Press) Link to Article [https://doi.org/10.1029/2018JE005911]
¹Stony Brook University, Department of Geosciences, Stony Brook, NY, USA
²SUNY Oswego, Department of Atmospheric and Geological Sciences, Oswego, NY, USA
³Institute for Molecular Engineering, The University of Chicago, Chicago, IL, USA
⁴Research School of Earth Sciences, The Australian National University, Canberra, ACT, Australia
Published by arrangement with John Wiley & Sons

Martian magmas were likely enriched in S and Cl with respect to H₂O. Exsolution of a vapor phase from these magmas and ascent of the gas bubbles through the magma plumbing system would have given rise to shallow magmas that were gas‐charged. Release and cooling of this gas from lava flows during eruption may have resulted in the addition of a significant amount of vapor‐deposited phases to the fines of the surface. Experiments were conducted to simulate degassing of gas‐charged lava flows and shallow intrusions in order to determine the nature of vapor‐deposited phases that may form through this process. The results indicate that magmatic gas may have contributed a large amount of Fe, S, and Cl to the martian surface through the deposition of iron oxides (magnetite, maghemite, hematite), chlorides (molysite, halite, sylvite), sulfur and sulfides (pyrrhotite, pyrite). Primary magmatic vapor‐deposited minerals may react during cooling to form a variety of secondary products, including iron oxychloride (FeOCl), akaganéite (Fe³⁺O (OH,Cl)), and jarosite (KFe³⁺₃(OH)₆(SO₄)₂). Vapor‐deposition does not transport significant amounts of Ca, Al, or Mg from the magma and hence, this process does not directly deposit Ca‐ or Mg‐sulfates.

¹D.P. Quinn,²B.L. Ehlmann
Journal of Geophysical Research, Planets (in Press) Link to Article [https://doi.org/10.1029/2018JE005706]
¹Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California, USA
²Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA
Published by arrangement with John Wiley & Sons

Ancient stratigraphy on Isidis Basin’s western margin records the history of water on early Mars. Noachian units are overlain by layered, basaltic‐composition sedimentary rocks that are enriched in polyhydrated sulfates and capped by more resistant units. The layered sulfates –uniquely exposed at northeast Syrtis Major – comprise a sedimentary sequence up to 600‐m thick that has undergone a multi‐stage history of deposition, alteration, and erosion. Siliciclastic sediments enriched in polyhydrated sulfates are bedded at m‐scale and were deposited on slopes up to 10°, embaying and thinning against pre‐existing Noachian highlands around the Isidis basin rim. The layered sulfates were modified by volume‐loss fracturing during diagenesis. Resultant fractures hosted channelized flow and jarosite mineral precipitation to form resistant ridges upon erosion. The structural form of the layered sulfates is consistent with packages of sediment fallen from either atmospheric or aqueous suspension; coupling with substantial diagenetic volume‐loss may favor deepwater basin sedimentation. After formation, the layered sulfates were capped by a “smooth capping unit” and then eroded to form paleovalleys. Hesperian Syrtis Major lavas were channelized by this paleotopography, capping it in some places and filling it in others. Later fluvial features and phyllosilicate‐bearing lacustrine deposits, sharing a regional base level of ~‐2300m, were superimposed on the sulfate‐lava stratigraphy. The layered sulfates suggest surface bodies of water and active groundwater upwelling during the Noachian–Hesperian transition. The northeast Syrtis Major stratigraphy records at least four distinct phases of surface and subsurface aqueous activity spanning from late Noachian to early Amazonian time.