^1,2Margrit A. Rindlisbacher,^2,3,4Michael K. Weisberg,^2,4Denton S. Ebel,^2,4Samuel P. Alpert
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13658]
¹Department of Geology, Mount Holyoke College, South Hadley, Massachusetts, 01075 USA
²Department of Earth and Planetary Sciences, American Museum of Natural History, New York, New York, 10024 USA
³Department of Physical Science, Kingsborough College CUNY, Brooklyn, New York, 11235 USA
⁴Department of Earth and Environmental Science, CUNY Graduate Center, New York, New York, 10016 USA
Published by arrangement with John Wiley & Sons

NWA 8785 is a remarkable, recently identified, unequilibrated enstatite chondrite. It was classified as an EL3 but contains highly unusual characteristics not observed in any other EL3, including a high abundance of FeO‐rich matrix and metal‐rich nodules that are texturally and mineralogically different from those in other EL3s. We characterized the mineral assemblages and compositions of metal‐rich nodules in a thin section of NWA 8785 and compared them to nodules in other EL3s to evaluate models for formation of metal‐rich nodules in EL3s. Of a total of 40 metal‐rich nodules, 10 were selected for detailed study. These metal‐rich nodules vary in their physical structure, texture, and mineral assemblages. Some contain the rare Al‐poor, alkali‐rich silicate mineral roedderite, a first discovery in an EL3, as well as the Cl‐bearing sulfide djerfisherite. The diversity of metal‐rich nodules in NWA 8785 suggests each nodule formed independently and supports their origin by primary processes prior to accretion. The high abundance of FeO‐rich matrix and the unique qualities of its metal‐rich nodules call into question classification of NWA 8785 as an EL3, but the Si content in its kamacite and Cr and Ti content in its troilite, and the presence of alabandite, support its classification as an EL3; thus, it is an EL3‐anomalous. Although alternative hypotheses exist, the presence of roedderite, as well as a magnetite‐rich matrix and sodalite, may provide the first evidence of extensive metasomatic alteration on the EL3 parent body.

^1,2Pranabendu Moitra,^2,3David G.Horvath,²Jeffrey C.Andrews-Hanna
Earth and Planetary Science Letters 567, 116986 Link to Article [https://doi.org/10.1016/j.epsl.2021.116986]
¹Department of Geosciences, University of Arizona, AZ, USA
²Lunar and Planetary Laboratory, University of Arizona, AZ, USA
³Planetary Science Institute, Tucson, AZ, USA
Copyright Elsevier

Volcanic activity on Mars has been dominantly effusive. The existence of a young (∼0.05-1 Ma) and well-preserved possible pyroclastic deposit along a segment of the Cerberus Fossae fissures, overlying the effusive lava flows making up the bulk of Elysium Planitia, provides the motivation and opportunity to explore the dynamics of explosive volcanic eruptions on Mars. Here we investigate the subsurface magmatic processes that may have led to magma fragmentation and the explosivity of the eruption forming the deposit. Using numerical models of magma ascent in a volcanic fissure, we show that the dissolved magmatic water with or without suspended crystals is capable of driving the inferred explosive magma fragmentation and the formation of the deposit. We also explore an alternative eruption scenario and show that an intruded dike explosively interacting with melted ground ice might also have generated the deposit. The close proximity of the proposed pyroclastic deposit (15-35 km) to the similarly aged Zunil impact crater suggests the possibility of an impact-triggered volcanic eruption scenario. Using scaling analysis, we find that the high seismic energy density associated with the impact may have been sufficient to trigger a volcanic eruption if a magma chamber was present in the subsurface. These findings have implications for the generation of similar explosive eruptions on Mars and other bodies, as well as the possibility of ongoing magmatic activity on Mars.