Large Meteorite Impacts and Planetary Evolution VI最新文献

{"title":"Systematic survey of K, Th, and U signatures in airborne radiometric data from Australian meteorite impact structures: Possible causes of circular features and implications","authors":"C. Niang, D. Baratoux, D. Diallo, P. Rochette, M. Jessell, W. Reimold, S. Bouley, O. Vanderhaeghe, G. Faye, Philippe Lambert","doi":"10.1130/2021.2550(15)","DOIUrl":"https://doi.org/10.1130/2021.2550(15)","url":null,"abstract":"\u0000 Airborne radiometric (gamma-ray) data provide estimates of the concentrations of potassium (K), thorium (Th), and uranium (U) in soil, regolith, and bedrock. Radiometric data constitute an important source of geochemical information, commonly used in mineral exploration and for geological mapping of Earth and other planets. Airborne radiometric data have rarely been applied to the exploration and analyses of impact structures, in contrast with other conventional geophysical tools (e.g., gravimetry, magnetism, and seismic reflection/refraction). This work represents the first systematic survey of the K, Th, and U radiometric signatures of Australian impact structures, based on the continent-wide airborne radiometric coverage of Australia. We first formulated several hypotheses regarding the possible causes of formation of circular radiometric patterns associated with impact structures. Then, the radiometric signatures of 17 exposed impact structures in Australia were documented. Our observations confirmed the supposition that impact structures are commonly associated with circular radiometric patterns. We then selected the five structures with the most prominent circular radiometric patterns (Gosses Bluff, Lawn Hill, Acraman, Spider, and Shoemaker), and we discuss the possible origin of these anomalies. Based on these five case studies, we argue that such patterns result from either crustal deformation induced by the impact event and/or from postimpact superficial processes controlled by the crater topography. This work also suggests that airborne radiometric data may be useful, in combination with other geophysical tools, in the search for new possible impact structures.","PeriodicalId":17949,"journal":{"name":"Large Meteorite Impacts and Planetary Evolution VI","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-06-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85670274","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Supplemental Material: 40Ar/39Ar age evidence for an impact-generated hydrothermal system in the Devonian Siljan crater, Sweden","authors":"M. Herrmann, C. Alwmark, Mitchell Storey","doi":"10.1130/2021.2550(26)","DOIUrl":"https://doi.org/10.1130/2021.2550(26)","url":null,"abstract":"Supplemental Material 1: Item S1 (additional information on ⁴⁰Ar/³⁹Ar age spectra of biotite), and Item S2 (additional information on ⁴⁰Ar/³⁹Ar age spectra of amphibole); and Supplemental Material 2: Tables S1–S4 (Ar isotopic ratios, apparent ages, J values, Ar isotopic abundances, and Ca/K and Cl/K ratios). <br>","PeriodicalId":17949,"journal":{"name":"Large Meteorite Impacts and Planetary Evolution VI","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-06-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81131740","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Australian impact cratering record: Updates and recent discoveries","authors":"Raiza R. Quintero, A. Cavosie, M. A. Cox, K. Miljković, A. Dugdale","doi":"10.1130/2021.2550(02)","DOIUrl":"https://doi.org/10.1130/2021.2550(02)","url":null,"abstract":"\u0000 There are currently 31 confirmed structures of impact origin in Australia. More than 49 additional structures have been proposed to have formed due to asteroid impact but await confirmation. Many discoveries have been made in Australia in the time since the last comprehensive review of the Australian impact cratering record was published in a peer-reviewed journal in 2005. These include further expanding the record of confirmed craters, and providing new insights into a variety of impact-related processes, such as shock deformation, phase transitions in accessory minerals, new impact age determinations, studies of oblique impacts, and more. This update is a review that focuses principally on summarizing discoveries made since 2005. Highlights since then include confirmation of five new Australian impact structures, identification of Earth’s oldest recognized impact structure, recognition of shock deformation in accessory minerals, discovery of the high-pressure phase reidite in Australia, determination of the links between impact craters and some ore deposits, and publication of the first generation of numerical hydrocode models for some Australian craters.","PeriodicalId":17949,"journal":{"name":"Large Meteorite Impacts and Planetary Evolution VI","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-06-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85528278","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Shock metamorphism in samples from the Shili impact structure (Kazakhstan) and discussion of its size and age","authors":"L. Ferrière, S. Rajpriye, P. Sapozhnikov, B. Baimagambetov","doi":"10.1130/2021.2550(05)","DOIUrl":"https://doi.org/10.1130/2021.2550(05)","url":null,"abstract":"\u0000 Four impact structures are known from the Republic of Kazakhstan, most of which have been poorly studied. This includes the Shili impact structure, an ~1.5-km-wide circular feature visible in satellite imagery. It is located in the western part of Kazakhstan, in the Aktobe Region, where the structure is centered at 49°10.5′N and 57°50′E. While the structure was first considered to be a salt diapir, its impact origin was confirmed in 1989 based on the findings of rare shocked quartz grains and a few poorly developed “shatter cones.” In this contribution, we report the results of a field campaign and a detailed petrographic investigation of 15 quartz sandstone samples. We confirm the presence of rare shocked quartz grains with planar fractures (PFs) and planar deformation features (PDFs). The characterization of shocked quartz allows us to not only confirm the impact origin of the structure, but also to estimate a shock pressure of at least 16 GPa (with a local peak-shock pressure of at least 20 GPa) for some of the rocks now outcropping at the surface. Signs of postimpact hydrothermal alteration include the decoration of many of the PDFs and the occurrence of fractures filled with secondary silica in a few samples. The name and some statistics commonly reported for this structure are also discussed. We suggest the structure be referred as “Shili,” after the name of a nearby river and also that of a phytonym. The minimum original diameter of the Shili impact crater is estimated at ~4–5 km based on a minimum central uplift diameter of 1 km. An early Eocene to Pliocene age for the formation of the Shili impact structure is inferred based on stratigraphy.","PeriodicalId":17949,"journal":{"name":"Large Meteorite Impacts and Planetary Evolution VI","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-06-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85773082","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Dedication of Large Meteorite Impacts and Planetary Evolution VI to Álvaro Penteado Crósta","authors":"W. Reimold, C. Koeberl","doi":"10.1130/2021.2550(001)","DOIUrl":"https://doi.org/10.1130/2021.2550(001)","url":null,"abstract":"\u0000 This paper does not have an abstract.\u0000 Originally, Álvaro Penteado Crósta (born on 7 August 1954) intended to be one of the volume editors of this GSA Special Paper. He was also looking forward to participating in the Large Meteorite Impacts and Planetary Evolution VI conference in October 2019, for which he had long served on the organizing committee. Unfortunately, a long and serious illness derailed both these plans. Therefore, we are instead honoring our dear friend and valued colleague, Álvaro Crósta, for his longstanding and successful impact cratering work, as the mainstay of impact cratering studies in Brazil and indeed in South America, by dedicating this Special Paper to him.\u0000 Álvaro Crósta has been a Full Professor (Professor Titular) of Geoscience in the fields of remote sensing, mineral exploration, and planetary geology at the Instituto de Geociências of the Universidade Estadual de Campinas (UNICAMP) in Brazil. He has had a highly distinguished academic career, culminating in his tenure (2012–2017) as vice-rector of his university. In 2017, Álvaro was inducted as a Full Member (Membro Titular) into the Academia Brasileira de Ciências...","PeriodicalId":17949,"journal":{"name":"Large Meteorite Impacts and Planetary Evolution VI","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-06-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84770968","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Genesis of the mafic granophyre of the Vredefort impact structure (South Africa): Implications of new geochemical and Se and Re-Os isotope data","authors":"W. Reimold, T. Schulz, S. König, C. Koeberl, N. Hauser, Dschamilja Wannek, R. Schmitt","doi":"10.1130/2021.2550(09)","DOIUrl":"https://doi.org/10.1130/2021.2550(09)","url":null,"abstract":"\u0000 This contribution is concerned with the debated origin of the impact melt rock in the central uplift of the world’s largest confirmed impact structure—Vredefort (South Africa). New major- and trace-element abundances, including those of selected highly siderophile elements (HSEs), Re-Os isotope data, as well as the first Se isotope and Se-Te elemental systematics are presented for the felsic and mafic varieties of Vredefort impact melt rock known as “Vredefort Granophyre.” In addition to the long-recognized “normal” (i.e., felsic, >66 wt% SiO2) granophyre variety, a more mafic (<66 wt% SiO2) impact melt variety from Vredefort has been discussed for several years. The hypothesis that the mafic granophyre was formed from felsic granophyre through admixture (assimilation) of a mafic country rock component that then was melted and assimilated into the superheated impact melt has been pursued here by analysis of the two granophyre varieties, of the Dominion Group lava (actually metalava), and of epidiorite mafic country rock types. Chemical compositions, including high-precision isotope dilution–derived concentrations of selected highly siderophile elements (Re, Os, Ir, Pt, Se, Te), and Re-Os and Se isotope data support this hypothesis. A first-order estimate, based on these data, suggests that some mafic granophyre may have resulted from a significant admixture (assimilation) of epidiorite to felsic granophyre. This is in accordance with the findings of an earlier investigation using conventional isotope (Sr-Nd-Pb) data. Moreover, these outcomes are in contrast to a two-stage emplacement model for Vredefort Granophyre, whereby a mafic phase of impact melt, derived by differentiation of a crater-filling impact melt sheet, would have been emplaced into earlier-deposited felsic granophyre. Instead, all chemical and isotopic evidence so far favors formation of mafic granophyre by local assimilation of mafic country rock—most likely epidiorite—by a single intrusive impact melt phase, which is represented by the regionally homogeneous felsic granophyre.","PeriodicalId":17949,"journal":{"name":"Large Meteorite Impacts and Planetary Evolution VI","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-06-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78093683","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Impact-induced hydrothermal dissolution in pyroxene: Petrographic and geochemical characterization of basalt-dominated polymict impact breccias from the Vargeão Dome, Brazil","authors":"Jennifer Epstein, L. Pittarello, A. Crósta, C. Koeberl","doi":"10.1130/2021.2550(24)","DOIUrl":"https://doi.org/10.1130/2021.2550(24)","url":null,"abstract":"\u0000 Constraints on impact-related hydrothermal alteration are important to enable the reconstruction of the possible processes affecting the surface of other terrestrial planets, such as Mars. Terrestrial impact structures excavated in basaltic targets provide the opportunity for analog studies. In Brazil, seven impact structures have been confirmed so far. Three of them, Vargeão Dome, Vista Alegre, and Cerro do Jarau, were formed in the same basaltic province belonging to the Paraná Basin, and they have several common characteristics. Oxidized basaltic breccias locally containing sandstone clasts occur in all these structures. In this work, selected samples of such breccias from the Vargeão Dome impact structure in southern Brazil were petrographically and geochemically investigated to further constrain the effects of the postimpact hydrothermal alteration. The breccia matrix shows typical oxidation effects induced by postimpact hydrothermal fluids, which highlight its heterogeneous nature, related to the impact event, and mixing components from different pre-impact stratigraphic formations. The detection of partially dissolved exsolution lamellae in pyroxene and of related alteration products constrains the effects of hydrothermal alteration in the basalts of the Vargeão Dome, which could serve as a terrestrial analog for planetary studies.","PeriodicalId":17949,"journal":{"name":"Large Meteorite Impacts and Planetary Evolution VI","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-06-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78223410","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Terrestrial and extraterrestrial chemical components of early Archean impact spherule layers from Fairview Gold Mine, northern Barberton greenstone belt, South Africa","authors":"G. J. Oliveira, W. Reimold, A. Crósta, N. Hauser, C. Koeberl, D. Mader, R. Schmitt, T. Mohr‐Westheide","doi":"10.1130/2021.2550(12)","DOIUrl":"https://doi.org/10.1130/2021.2550(12)","url":null,"abstract":"\u0000 Early Archean spherule layers, widely accepted to represent distal ejecta deposits from large-scale impact events onto the early Earth, have been described from several stratigraphic levels of the Barberton greenstone belt in South Africa. Recently, exploration drilling at the Fairview Gold Mine (25°43′53″S, 31°5′59″E) in the northern domain of the belt resulted in the discovery of a new set of spherule layer intersections. The Fairview spherule layers in drill cores BH5901, BH5907, BH5911, and BH5949 were intersected just a few meters apart, at about the same stratigraphic position within the transition from the Onverwacht Group to the Fig Tree Group. The Fairview spherule layers have petrographic and chemical similarities to at least three other well-known Barberton spherule layers (S2–S4), and multiple spherule layer bed intersections in drill cores BARB5 and CT3, all from about the same stratigraphic position. They are not uniform in composition, in particular with respect to abundances of highly siderophile elements. The highest concentrations of moderately (Cr, Co, Ni) and highly siderophile (Ir) elements are within the range of concentrations for chondrites and, thus, reinforce the impact hypothesis for the generation of the Fairview spherule layers. Iridium peak concentrations and Cr/Ir interelement ratios for spherule layer samples from drill cores BH5907, BH5911, and BH5949 suggest admixtures of 50%–60% chondritic material, whereas for the BH5901 spherule layer, only an admixture of 1% chondritic material is indicated. We discuss whether these four Fairview spherule layers represent the same impact event, and whether they can be correlated to any of the S2–S4, CT3, and BARB5 intersections.","PeriodicalId":17949,"journal":{"name":"Large Meteorite Impacts and Planetary Evolution VI","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-06-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75772263","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Shock effects in feldspars: An overview","authors":"A. Pickersgill, S. Jaret, L. Pittarello, F. Jörg, R. S. Harris","doi":"10.1130/2021.2550(23)","DOIUrl":"https://doi.org/10.1130/2021.2550(23)","url":null,"abstract":"\u0000 Feldspars are the dominant mineral in the crust of most terrestrial planetary bodies, including Earth, Earth’s moon, and Mars, as well as in asteroids, and thus in meteorites. These bodies have experienced large numbers of hypervelocity impact events, and so it is important to have a robust understanding of the effects of shock waves exerted on feldspars. However, due to their optical complexity and susceptibility to weathering, feldspars are underutilized as shock barometers and indicators of hypervelocity impact. Here, we provide an overview of the work done on shocked feldspars so far, in an effort to better frame the current strengths and weaknesses of different techniques, and to highlight some gaps in the literature.","PeriodicalId":17949,"journal":{"name":"Large Meteorite Impacts and Planetary Evolution VI","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-06-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79078455","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Micro–X-ray fluorescence (µXRF) analysis of proximal impactites: High-resolution element mapping, digital image analysis, and quantifications","authors":"P. Kaskes, T. Déhais, S. J. D. Graaff, S. Goderis, P. Claeys","doi":"10.1130/2021.2550(07)","DOIUrl":"https://doi.org/10.1130/2021.2550(07)","url":null,"abstract":"\u0000 Quantitative insights into the geochemistry and petrology of proximal impactites are fundamental to understand the complex processes that affected target lithologies during and after hypervelocity impact events. Traditional analytical techniques used to obtain major- and trace-element data sets focus predominantly on either destructive whole-rock analysis or laboratory-intensive phase-specific micro-analysis. Here, we present micro–X-ray fluorescence (µXRF) as a state-of-the-art, time-efficient, and nondestructive alternative for major- and trace-element analysis for both small and large samples (up to 20 cm wide) of proximal impactites. We applied µXRF element mapping on 44 samples from the Chicxulub, Popigai, and Ries impact structures, including impact breccias, impact melt rocks, and shocked target lithologies. The µXRF mapping required limited to no sample preparation and rapidly generated high-resolution major- and trace-element maps (~1 h for 8 cm2, with a spatial resolution of 25 µm). These chemical distribution maps can be used as qualitative multi-element maps, as semiquantitative single-element heat maps, and as a basis for a novel image analysis workflow quantifying the modal abundance, size, shape, and degree of sorting of segmented components. The standardless fundamental parameters method was used to quantify the µXRF maps, and the results were compared with bulk powder techniques. Concentrations of most major elements (Na2O–CaO) were found to be accurate within 10% for thick sections. Overall, we demonstrate that µXRF is more than only a screening tool for heterogeneous impactites, because it rapidly produces bulk and phase-specific geochemical data sets that are suitable for various applications within the earth sciences.","PeriodicalId":17949,"journal":{"name":"Large Meteorite Impacts and Planetary Evolution VI","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-06-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77870646","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}