An Investigation on the Morphological and Mineralogical Characteristics of Posidonius Floor Fractured Lunar Impact Crater Using Lunar Remote Sensing Data

Lunar floor-fractured craters (FFCs) are a distinguished type of crater found on the surface of the Moon with radial, concentric, and/or polygonal fractures. In the present study, we selected the Posidonius FCC to explore the mineralogy, morphology and tectonic characteristics using remote sensing datasets. The Posidonius crater is vested with a wide moat of lava separating the crater rim inner wall terraces from the fractured central floor. Lunar Reconnaissance Orbiter’s (LRO) images and Digital Elevation Model (DEM) data were used to map the tectonics and morphology of the present study. The Moon Mineralogy Mapper (M3) data of Chandrayaan-1 were used to investigate the mineralogy of the region through specified techniques such as integrated band depth, band composite and spectral characterization. The detailed mineralogical analysis indicates the noritic-rich materials in one massif among four central peak rings and confirm intrusion (mafic pluton). Spectral analysis from the fresh crater of the Posidonius moat mare unit indicates clinopyroxene pigeonite in nature. Integrated studies of the mineralogy, morphology and tectonics revealed that the study region belongs to the Class-III category of FFCs. The lithospheric loading by adjacent volcanic load (Serenitatis basin) generates a stress state and distribution of the fracture system.

Assessing the shock state of the lunar highlands: Implications for the petrogenesis and chronology of crustal anorthosites

Our understanding of the formation and evolution of the primary lunar crust is based on geochemical systematics from the lunar ferroan anorthosite (FAN) suite. Recently, much effort has been made to understand this suite's petrologic history to constrain the timing of crystallisation and to interpret FAN chemical diversity. We investigate the shock histories of lunar anorthosites by combining Optical Microscope (OM) 'cold' cathodoluminescence (CL)-imaging and Fourier Transform Infrared (FTIR) spectroscopy analyses. In the first combined study of its kind, this study demonstrates that over ~4.5 Ga of impact processing, plagioclase is on average weakly shocked (<15 GPa) and examples of high shock states (>30 GPa; maskelynite) are uncommon. To investigate how plagioclase trace-element systematics are affected by moderate to weak shock (~5 to 30 GPa) we couple REE+Y abundances with FTIR analyses for FAN clasts from lunar meteorite Northwest Africa (NWA) 2995. We observe weak correlations between plagioclase shock state and some REE+Y systematics (e.g., La/Y and Sm/Nd ratios). This observation could prove significant to our understanding of how crystallisation ages are evaluated (e.g., plagioclase-whole rock Sm-Nd isochrons) and for what trace-elements can be used to differentiate between lunar lithologies and assess magma source compositional differences.

Impact structures in Africa: A review

More than 50 years of space and planetary exploration and concomitant studies of terrestrial impact structures have demonstrated that impact cratering has been a fundamental process - an essential part of planetary evolution - ever since the beginning of accretion and has played a major role in planetary evolution throughout the solar system and beyond. This not only pertains to the development of the planets but to evolution of life as well. The terrestrial impact record represents only a small fraction of the bombardment history that Earth experienced throughout its evolution. While remote sensing investigations of planetary surfaces provide essential information about surface evolution and surface processes, they do not provide the information required for understanding the ultra-high strain rate, high-pressure, and high-temperature impact process. Thus, hands-on investigations of rocks from terrestrial impact craters, shock experimentation for pressure and temperature calibration of impact-related deformation of rocks and minerals, as well as parameter studies pertaining to the physics and chemistry of cratering and ejecta formation and emplacement, and laboratory studies of impact-generated lithologies are mandatory tools. These, together with numerical modeling analysis of impact physics, form the backbone of impact cratering studies. Here, we review the current status of knowledge about impact cratering - and provide a detailed account of the African impact record, which has been expanded vastly since a first overview was published in 1994. No less than 19 confirmed impact structures, and one shatter cone occurrence without related impact crater are now known from Africa. In addition, a number of impact glass, tektite and spherule layer occurrences are known. The 49 sites with proposed, but not yet confirmed, possible impact structures contain at least a considerable number of structures that, from available information, hold the promise to be able to expand the African impact record drastically - provided the political conditions for safe ground-truthing will become available. The fact that 28 structures have also been shown to date NOT to be of impact origin further underpins the strong interest in impact in Africa. We hope that this review stimulates the education of students about impact cratering and the fundamental importance of this process for Earth - both for its biological and geological evolution. This work may provide a reference volume for those workers who would like to search for impact craters and their ejecta in Africa.

Lonar lake, India: an impact crater in basalt

Discovery of shock-metamorphosed material establishes the impact origin of Lonar Crater. Coarse breccia with shatter coning and microbreccia with moderately shocked fragments containing maskelynite were found in drill holes through the crater floor. Trenches on the rim yield strongly shocked fragments in which plagioclase has melted and vesiculated, and bombs and spherules of homogeneous rock melt. As the only known terrestrial impact crater in basalt, Lonar Crater provides unique opportunities for comparison with lunar craters. In particular, microbreccias and glass spherules from Lonar Crater have close analogs among the Apollo specimens.

Economic natural resource deposits at terrestrial impact structures

Economic deposits associated with terrestrial impact structures range from world-class to relatively localized occurrences. The more significant deposits are introduced under the classification: progenetic, syngenetic or epigenetic, with respect to the impact event. However, there is increasing evidence that post-impact hydrothermal systems at large impact structures have remobilized some progenetic deposits, such as some of the Witwatersrand gold deposits at the Vredefort impact structure. Impact-related hydrothermal activity may also have had a significant role in the formation of ores at such syngenetic ‘magmatic’ deposits as the Cu-Ni-platinum-group elements ores associated with the Sudbury impact structure. Although Vredefort and Sudbury contain world-class mineral deposits, in economic terms hydrocarbon production dominates natural resource deposits found at impact structures. The total value of impact-related resources in North America is estimated at US$18 billion per year. Many impact structures remain to be discovered and, as targets for resource exploration, their relatively invariant, but scale-dependent properties, may provide an aid to exploration strategies.

Fission-Track Dating of Haughton Astrobleme and Included Biota, Devon Island, Canada

Haughton Astrobleme is a major extraterrestrial impact structure located on Devon Island in the Canadian Arctic Archipelago, Northwest Territories. Apatite grains separated from shocked Precambrian gneiss contained in a polymict breccia from the center of the astrobleme yielded a fission-track date of 22.4 million +/- 1.4 million years before the present or early Miocene (Aquitanian). This provides a date for the impact event and an upper limit on the age of crater-filling lake sediments and a flora and vertebrate fauna occurring in them. A geologically precise date for these fossils provides an important biostratigraphic reference point for interpreting the biotic evolution of the Arctic.