¹Thomas Kenkmann,¹Gerwin Wulf,^1,2Amar Agarwal
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.1345]
¹Institute of Earth and Environmental Sciences—Geology, Albert‐Ludwigs‐Universität Freiburg, Albertstrasse 23‐B, 79104 Freiburg im Breisgau, Germany
²Department of Earth Sciences, Indian Institute of Technology‐Kanpur, Kanpur‐208016, India
Published by arrangement with John Wiley & Sons

The Ramgarh structure is a morphological landmark in southeastern Rajasthan, India. Its 200 m high and 3.5–4 km wide annular collar has provoked many hypotheses regarding its origin, including impact. Here, we document planar deformation features, planar fractures, and feather features in quartz grains of the central part of the Ramgarh structure, which confirm its impact origin. The annular collar does not mark the crater rim but represents the outer part of a central uplift of an approximately 10 km diameter complex impact structure. The apparent crater rim is exposed as a low‐angle normal fault and can be traced as lineaments in remote sensing imagery. The central uplift shows a stratigraphic uplift of ~1000 m and is rectangular in shape. It is dissected by numerous faults that are co‐genetic with the formation of the central uplift. The central uplift has a bilateral symmetry along an SW‐NE axis, where a large strike‐slip fault documents a strong horizontal shear component. This direction corresponds to the assumed impact trajectory from the SW toward the NE. The uprange sector is characterized by concentric reverse faults, whereas radial faults dominate downrange. Sandstones of the central uplift are infiltrated by Fe‐oxides and suggest an impact‐induced hydrothermal mineralization overprint. The impact may have occurred into a shallow water environment as indicated by soft‐sediment deformation features, observed near the apparent crater rim, and the deposition of a diamictite layer above them. Gastropods embedded in the diamictite have Middle Jurassic age and may indicate the time of the impact.

^1,2M. Kimura,^3,4N. Sugiura,^1,5A. Yamaguchi,³K. Ichimura
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13474]
¹National Institute of Polar Research, Tokyo, 190‐8518 Japan
²Ibaraki University, Mito, 310‐8512 Japan
³University of Tokyo, Tokyo, 113‐0033 Japan
⁴Planetary Exploration Research Center, Chiba Institute of Technology, Chiba, 275‐0016 Japan
⁵Department of Polar Science, School of Multidisciplinary Science, SOKENDAI, The Graduate University for Advanced Studies, Tokyo, 190‐8518 Japan
Published by arrangement with John Wiley & Sons

All mesosiderites previously reported were subjected to thermal metamorphism and/or partial melting on the parent body. Therefore, their primordial features have been mostly lost. Here, we report detailed petrological and mineralogical features on a mesosiderite, Northwest Africa (NWA) 1878. This meteorite comprises silicate lithology and aggregates of small spheroidal Fe‐Ni metal grains. Silicate lithology typically shows igneous texture without recrystallization features, and mainly consists of low‐Ca pyroxene and plagioclase. Pyroxenes often show normal zoning. Exsolution lamella of augite is rarely noticed and very thin in width, compared with other mesosiderites. A few magnesian olivine grains are encountered without typical corona texture around them. They are not equilibrated with pyroxene on a large scale. Plagioclase shows a wide compositional range. These results show that NWA 1878 hardly experienced thermal metamorphism, distinguished from mesosiderites of subgroups 1–4. Therefore, we propose that this is classified as subgroup 0 mesosiderite. Nevertheless, NWA 1878 was locally subjected to secondary reactions, such as weak reduction of pyroxene and Fe‐Mg diffusion between olivine and pyroxene, on the parent body.