¹R. Keerthana, ¹R. Annadurai, ²K.N. Kusuma
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2025.116871]
¹Department of Civil Engineering, Faculty of Engineering and Technology, SRM Institute of Science and Technology, Kattankulathur 603 203, Tamil Nadu, India
²Department of Earth Sciences, Pondicherry University, Puducherry 605 014, India
Copyright Elsevier

This study investigates the morphology, mineralogy, and chronology of the Briggs crater (37 km diameter), situated west of the Oceanus Procellarum, employing high-resolution data from recent lunar missions. Lunar Reconnaissance Orbiter (LRO) images, Terrain Mapping Camera (TMC) Ortho images, and Digital Elevation Models (DEMs) from both the Chandrayaan-2 and Kaguya were employed to study the morphology of the crater. The morphological investigation identified distinct features in Briggs Crater, including a well-preserved crater rim, terraced walls, a convex floor indicative of subsurface uplift, an uplifted central peak, mounds, and prominent NE-SW and N-S trending concentric and radial fractures. Additionally, a fresh impact crater and localized slumping along the crater walls suggest ongoing surface modifications. Briggs Crater exhibits characteristics of a Class-2 Floor-Fractured Crater (FFC), including an uplifted floor and prominent concentric fractures, consistent with previously established classifications. The presence of radial and concentric fractures on the Briggs Crater floor suggests a combination of brittle and ductile deformation. Variations in fracture dimensions indicate differential stress distribution during floor uplift, likely influenced by subsurface magmatic intrusion or impact-induced processes. Integrated Band Depth (IBD) and Mineral indices-based color composite images were generated using M³ datasets to better understand mineralogy. These images enable the extraction of spectral signatures for mineralogical investigation and highlight the diversity of lithological composition. Spectral absorption analysis, IBD mapping, and mineral indices collectively confirm that the central peak exposes fresh High-Calcium Pyroxene (HCP) from deeper crustal levels, while the floor, rim, wall, and ejecta show weaker, mixed, and weathered pyroxene signatures. Integrating morphology and mineralogy with Crater Size-Frequency Distributions (CSFD)-based chronology, it has been suggested that Briggs Crater formed during the late Imbrian period (3.6 Ga). The N-S trending concentric fractures on the Briggs crater floor likely represent tectonic or magmatic activity that occurred between ~310 Ma and ~ 270 Ma during the Eratosthenian period, significantly after the initial crater formation.

¹Peter Mc Ardle,¹Rhian H. Jones,²Patricia L. Clay,¹Romain Tartèse,¹Ray Burgess,²Brian O’Driscoll,³Eric W.G. Hellebrand,¹Jonathan Fellowes,⁴Arthur Goodwin,¹Lewis Hughes
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.70065]
¹Department of Earth and Environmental Sciences, The University of Manchester, Manchester, UK
²Department of Earth and Environmental Sciences, University of Ottawa, Ottawa, Ontario, Canada
³Department of Earth Sciences, Utrecht University, Utrecht, Netherlands
⁴Ordnance Survey, Southampton, UK
Published by arrangement with John Wiley & Sons

Enstatite chondrites (ECs) formed on at least two parent bodies, EH and EL. After the accretion of the EC parent bodies, EC material was subjected to varying degrees of parent body thermal metamorphism (measured by petrologic types 3–6), due to heat released by radioactive isotope decay. Current schemes to determine the petrologic type of the ECs are qualitative and ambiguous, and many studies have included known or misclassified shock-melted ECs, which altogether have led to inconsistent classifications. In this study, we attempt to distinguish shock-melted ECs from other ECs so that we can assess the effects of thermal metamorphism alone. We identified a suite of geochemical parameters that allow us to classify rapidly cooled, quenched shock-melt ECs, including high-Fe (Mg,Mn,Fe)S monosulfide, high-Cr troilite, and high-Ni kamacite. We then screened out shock-melted samples. This then allowed us to establish a quantitative scheme to determine the petrologic type of an EC. This classification scheme is based on the petrography and geochemistry of glass, silicate minerals, sulfides, and metal. Specifically, for EH chondrites (which are similar but distinct from the EL group), among other parameters, the size and abundance of feldspar progressively increase from EH3 to EH6 (<13 μm, <8.5% modal% to >13 μm, 11.5 modal%), while the FeO content of enstatite changes from types 3–4 to types 5–6 (<0.45 wt% to >0.45 wt%). Additionally, we build on the work of others to propose a scheme that subdivides the EH3. Using the average Cr2O3 content of olivine, we divide the EH3 and EH4 chondrites into EH3Low (mean Cr2O3 > 0.25 wt%) and EH3High-EH4 subtypes (Cr2O3 < 0.25 wt%).