Large Meteorite Impacts and Planetary Evolution VI最新文献

{"title":"Supplemental Material: Mars Crater Database: A participative project for the classification of the morphological characteristics of large Martian craters","authors":"A. Lagain, S. Bouley, D. Baratoux, C. Marmo, F. Costard, O. Delaa, A. Pio Rossi, M. Minin, G. Benedix, M. Ciocco, B. Bedos, A. Guimpier, E. Dehouck, D. Loizeau, A. Bouquety, J. Zhao, A. Vialatte, M. Cormau, E. Le Conte des Floris, F. Schmidt, P. Thollot, J. Champion, M. Martinot, J. Gargani, P. Beck, J. Boisson, N. Paulien, A. Séjourné, K. Pasquon, N. Christoff, I. Belgacem, F. Landais, B. Rousseau, L. Dupeyrat, Maximilien Franco, F. Andrieu, B. Cecconi, S. Erard, B. Jabaud, V. Malarewicz, G. Beggiato, G. Janez, L. Elbaz, C. Ourliac, M. Catheline, M. Fries, A. Karamoko, J. Rodier, R. Sarian, A. Gillet, S. Girard, M. Pottier, S. Strauss, C. Chanon, P. Lavaud, A. Boutaric, M. Savourat, E. Garret, E. Leroy, M. Parquet, L. Parquet, M.-A. Delagoutte, O. Gamblin","doi":"10.1130/2021.2550(29)","DOIUrl":"https://doi.org/10.1130/2021.2550(29)","url":null,"abstract":"Completed version of Mars Crater Database created in this study","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":"81945811","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":"Extreme plastic deformation and subsequent Pb loss in shocked xenotime from the Vredefort Dome, South Africa","authors":"A. Cavosie, C. Kirkland, S. Reddy, N. Timms, C. Talavera, Maya R. Pincus","doi":"10.1130/2021.2550(20)","DOIUrl":"https://doi.org/10.1130/2021.2550(20)","url":null,"abstract":"\u0000 Accessory mineral U-Pb geochronometers are crucial tools for constraining the timing of deformation in a wide range of geological settings. Despite the growing recognition that intragrain age variations within deformed minerals can spatially correlate to zones of microstructural damage, the causal mechanisms of Pb loss are not always evident. Here, we report the first U-Pb data for shock-deformed xenotime, from a detrital grain collected at the Vredefort impact structure in South Africa. Orientation mapping revealed multiple shock features, including pervasive planar deformation bands (PDBs) that accommodate up to 40° of lattice misorientation by <100>{010} slip, and also an ~50-µm-wide intragrain shear zone that contains {112} deformation twin lamellae in two orientations. Twenty-nine in situ secondary ion mass spectrometry (SIMS) U-Pb analyses from all microstructural domains yielded a well-defined discordia with upper-intercept age of 2953 ± 15 Ma (mean square of weighted deviates [MSWD] = 0.57, n = 29, 2σ), consistent with derivation from Kaapvaal craton bedrock. However, the 1754 ± 150 Ma lower concordia intercept age falls between the 2020 Ma Vredefort impact and ca. 1100 Ma Kibaran orogenesis and is not well explained by multiple Pb-loss episodes. The pattern and degree of Pb loss (discordance) correlate with increased [U] but do not correlate to microstructure (twin, PDB) or to crystallinity (band contrast) at the scale of SIMS analysis. Numerical modeling of the Pb-loss history using a concordia-discordia-comparison (CDC) test indicated that the lower concordia age is instead best explained by an alteration episode at ca. 1750 Ma, rather than a multiple Pb-loss history. In this example, the U-Pb system in deformed xenotime does not record a clear signature of impact age resetting; rather, the implied high dislocation density recorded by planar deformation bands and the presence of deformation twins facilitated subsequent Pb loss during a younger event that affected the Witwatersrand basin. Microstructural characterization of xenotime targeted for geochronology provides a new tool for recognizing evidence of deformation and can provide insight into complex age data from highly strained grains, and, as is the case in this study, elucidate previously unrecognized alteration events.","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":"79886170","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":"Anisotropy of magnetic susceptibility (AMS) of impact melt breccia and target rocks from the Dhala impact structure, India","authors":"A. Singh, J. K. Pati, S. Patil, W. Reimold, Arun Kumar Rao, O. P. Pandey","doi":"10.1130/2021.2550(14)","DOIUrl":"https://doi.org/10.1130/2021.2550(14)","url":null,"abstract":"\u0000 The ~11-km-wide, Paleoproterozoic Dhala impact structure in north-central India comprises voluminous exposures of impact melt breccia. These outcrops are discontinuously spread over a length of ~6 km in a semicircular pattern along the northern, inner limit of the monomict breccia ring around the central elevated area. This study of the magnetic fabrics of impact breccias and target rocks from the Dhala impact structure identified a weak preferred magnetic orientation for pre-impact crystalline target rocks. The pre- and synimpact rocks from Dhala have magnetite and ilmenite as common magnetic phases. The distributions of magnetic vectors are random for most impact melt breccia samples, but some do indicate a preferred orientation. Our anisotropy of magnetic susceptibility (AMS) data demonstrate that the shape of susceptibility ellipsoids for the target rocks varies from prolate to oblate, and most impact melt breccia samples display both shapes, with a slight bias toward the oblate geometry. The average value for the corrected degree of anisotropy of impact melt rock (P′ = 1.009) is lower than that for the target rocks (P′ = 1.091). The present study also shows that both impact melt breccia and target rock samples of the Dhala structure have undergone minor postimpact alteration, and have similar compositions in terms of magnetic phases and high viscosity. Fine-grained iron oxide or hydroxide is the main alteration phase in impact melt rocks. Impact melt rocks gave a narrow range of mean magnetic susceptibility (Km) and P′ values, in contrast to the target rock samples, which gave Km = 0.05–12.9 × 10−3 standard international units (SI) and P′ = 1.036–1.283. This suggests similar viscosity of the source magma, and limited difference in the degrees of recorded deformation. Between Pagra and Maniar villages, the Km value of impact melt breccias gradually decreases in a clockwise direction, with a maximum value observed near Pagra (Km = 1.67 × 10−3 SI). The poor grouping of magnetic fabrics for most impact melt rock samples implies local turbulence in rapidly cooled impact melt at the front of the melt flow immediately after the impact. The mean K1 for most impact melt samples suggests subhorizontal (<5°) flow in various directions. The average value of Km for the target rocks (4.41 × 10−3 SI) is much higher compared to the value for melt breccias (1.09 × 10−3 SI). The results of this study suggest that the melt breccias were likely part of a sheet-like body of sizeable extent. Our magnetic fabric data are also supported by earlier core drilling information from ~70 locations, with coring depths reaching to −500 m. Our extensive field observations combined with available widespread subsurface data imply that the impact melt sheet could have covered as much as 12 km2 in the Dhala structure, with an estimated minimum melt volume of ~2.4 km3.","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":"86897400","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":"Tabun Khara Obo impact crater, Mongolia: Geophysics, geology, petrography, and geochemistry","authors":"T. Amgaa, D. Mader, W. Reimold, C. Koeberl","doi":"10.1130/2021.2550(04)","DOIUrl":"https://doi.org/10.1130/2021.2550(04)","url":null,"abstract":"\u0000 Tabun Khara Obo is the only currently known impact crater in Mongolia. The crater is centered at 44°07′50″N and 109°39′20″E in southeastern Mongolia. Tabun Khara Obo is a 1.3-km-diameter, simple bowl-shaped structure that is well visible in topography and clearly visible on remote-sensing images. The crater is located on a flat, elevated plateau composed of Carboniferous arc-related volcanic and volcanosedimentary rocks metamorphosed to upper amphibolite to greenschist facies (volcaniclastic sandstones, metagraywacke, quartz-feldspar–mica schist, and other schistose sedimentary rocks). Some geophysical data exist for the Tabun Khara Obo structure. The gravity data correlate well with topography. The −2.5–3 mGal anomaly is similar to that of other, similarly sized impact craters. A weak magnetic low over the crater area may be attributed to impact disruption of the regional trend.\u0000 The Tabun Khara Obo crater is slightly oval in shape and is elongated perpendicular to the regional lithological and foliation trend in a northeasterly direction. This may be a result of crater modification, when rocks of the crater rim preferentially slumped along fracture planes parallel to the regional structural trend. Radial and tangential faults and fractures occur abundantly along the periphery of the crater. Breccias occur along the crater periphery as well, mostly in the E-NE parts of the structure. Monomict breccias form narrow (<1 m) lenses, and polymict breccias cover the outer flank of the eastern crater rim. While geophysical and morphological data are consistent with expectations for an impact crater, no diagnostic evidence for shock metamorphism, such as planar deformation features or shatter cones, was demonstrated by earlier authors. As it is commonly difficult to find convincing impact evidence at small craters, we carried out further geological and geophysical work in 2005–2007 and drilling in 2007–2008.\u0000 Surface mapping and sampling did not reveal structural, mineralogical, or geochemical evidence for an impact origin. In 2008, we drilled into the center of the crater to a maximum depth of 206 m, with 135 m of core recovery. From the top, the core consists of 3 m of eolian sand, 137 m of lake deposits (mud, evaporites), 34 m of lake deposits (gypsum with carbonate and mud), 11 m of polymict breccia (with greenschist and gneiss clasts), and 19 m of monomict breccia (brecciated quartz-feldspar–mica schist). The breccias start at 174 m depth as polymict breccias with angular clasts of different lithologies and gradually change downward to breccias constituting the dominant lithology, until finally grading into monomict breccia. At the bottom of the borehole, we noted strongly brecciated quartz-feldspar schist. The breccia cement also changes over this interval from gypsum and carbonate cement to fine-grained clastic matrix. Some quartz grains from breccia samples from 192, 194.2, 196.4, 199.3, 201.6, and 204 m depth showed planar deformation features","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":"85017868","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":"Comparison of stress orientation indicators in Chicxulub’s peak ring: Kinked biotites, basal PDFs, and feather features","authors":"M. Ebert, M. Poelchau, T. Kenkmann, S. Gulick, B. Hall, J. Lofi, N. McCall, A. Rae","doi":"10.1130/2021.2550(21)","DOIUrl":"https://doi.org/10.1130/2021.2550(21)","url":null,"abstract":"\u0000 During hypervelocity impacts, target rocks are subjected to shock wave compression with high pressures and differential stresses. These differential stresses cause microscopic shear-induced deformation, which can be observed in the form of kinking, twinning, fracturing, and shear faulting in a range of minerals. The orientation of these shear-induced deformation features can be used to constrain the maximum shortening axis. Under the assumption of pure shear deformation, the maximum shortening axis is parallel to the maximum principal axis of stress, σ1, which gives the propagation direction of the shock wave that passed through a rock sample. In this study, shocked granitoids cored from the uppermost peak ring of the Chicxulub crater (International Ocean Discovery Program [IODP]/International Continental Drilling Project [ICDP] Expedition 364) were examined for structures formed by shearing. Orientations of kink planes in biotite and basal planar deformation features (PDFs) in quartz were measured with a U-stage and compared to a previous study of feather feature orientations in quartz from the same samples. In all three cases, the orientations of the shortening axis derived from these measurements were in good agreement with each other, indicating that the shear deformation features all formed in an environment with similar orientations of the maximum principal axis of stress. These structures formed by shearing are useful tools that can aid in understanding the deformational effects of the shock wave, as well as constraining shock wave propagation and postshock deformation during the cratering process.","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":"79855600","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":"Dynamics of collapse of an impact central uplift: Evidence from folds and faults in the collar of the Vredefort Dome, South Africa","authors":"Shalene Manzi, R. Gibson, A. Tshibubudze","doi":"10.1130/2021.2550(27)","DOIUrl":"https://doi.org/10.1130/2021.2550(27)","url":null,"abstract":"\u0000 Structural analysis of overturned metasedimentary strata of the lower Witwatersrand Supergroup in the inner collar of the Vredefort Dome reveals the presence of tangential folds and faults associated with the 2.02 Ga impact. The folds are distinct from previously identified subradially oriented, vertical to plunging-inclined, gentle folds that are interpreted as the products of convergent flow (constriction) during the initial stages of central uplift formation. The tangential folds comprise disharmonic, open, asymmetric, horizontal to plunging-inclined anticline-syncline pairs with centripetally dipping axial planes and right-way-up intermediate limbs. They display centripetal-down vergence (anticline radially outward of the syncline) that is consistent with steep inward-directed shear of the overturned strata. We attribute this kinematic pattern to subvertical collapse of the Vredefort central uplift during the latter stages of crater modification. The folds are cut by pseudotachylite-bearing steep to vertical tangential faults that display center-down slip of <10 m up to ~150 m. Both the tangential folds and the faults suggest that the large-scale overturning of strata related to outward collapse of the Vredefort central uplift was accompanied by a component of inward-directed collapse via layer-parallel shearing and folding, followed by faulting. Subradially oriented faults with conjugate strike separations of 1–2 km in the NNE collar of the dome suggest penecontemporaneous tangential extension of the inner collar rocks. This evidence indicates that second-order structures in the metasedimentary collar of the Vredefort Dome preserve a complex, multistage record of evolving strain associated with both initial convergent and upward flow (constriction) related to central uplift rise and later divergent and downward flow (flattening) linked to its collapse, and that centripetally directed collapse features may be important components of the structural inventory of very large central uplifts.","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":"89909958","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":"Petrographic and chemical studies of the Cretaceous-Paleogene boundary sequence at El Guayal, Tabasco, Mexico: Implications for ejecta plume evolution from the Chicxulub impact crater","authors":"T. Salge","doi":"10.1130/2021.2550(08)","DOIUrl":"https://doi.org/10.1130/2021.2550(08)","url":null,"abstract":"\u0000 A combined petrographic and chemical study of ejecta particles from the Cretaceous-Paleogene boundary sequence of El Guayal, Tabasco, Mexico (520 km SW of Chicxulub crater), was carried out to assess their formation conditions and genetic relation during the impact process. The reaction of silicate ejecta particles with hot volatiles during atmospheric transport may have induced alteration processes, e.g., silicification and cementation, observed in the ejecta deposits. The various microstructures of calcite ejecta particles are interpreted to reflect different thermal histories at postshock conditions. Spherulitic calcite particles may represent carbonate melts that were quenched during ejection. A recrystallized microstructure may indicate short, intense thermal stress. Various aggregates document particle-particle interactions and intermixing of components from lower silicate and upper sedimentary target lithologies. Aggregates of recrystallized calcite with silicate melt indicate the consolidation of a hot suevitic component with sediments at ≳750 °C. Accretionary lapilli formed in a turbulent, steam-condensing environment at ~100 °C by aggregation of solid, ash-sized particles. Concentric zones with smaller grain sizes of accreted particles indicate a recurring exchange with a hotter environment.\u0000 Our results suggest that during partial ejecta plume collapse, hot silicate compo nents were mixed with the fine fraction of local surface-derived sediments, the latter of which were displaced by the preceding ejecta curtain. These processes sustained a hot, gas-driven, lateral basal transport that was accompanied by a turbulent plume at a higher level. The exothermic back-reaction of CaO from decomposed carbonates and sulfates with CO2 to form CaCO3 may have been responsible for a prolonged release of thermal energy at a late stage of plume evolution.","PeriodicalId":17949,"journal":{"name":"Large Meteorite Impacts and Planetary Evolution VI","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-06-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85859286","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":"U-Pb geochronology of apatite crystallized within a terrestrial impact melt sheet: Manicouagan as a geochronometer test site","authors":"M. McGregor, C. McFarlane, J. Spray","doi":"10.1130/2021.2550(22)","DOIUrl":"https://doi.org/10.1130/2021.2550(22)","url":null,"abstract":"\u0000 The Manicouagan impact event has been the subject of multiple age determinations over the past ~50 yr, providing an ideal test site for evaluating the viability of different geochronometers. This study highlights the suitability of Manicouagan’s essentially pristine impact melt body as a medium for providing insight into the U-Pb isotope systematics of geochronometers in the absence of shock-related overprinting. We performed in situ laser-ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) U-Pb geochronology on apatite and zircon, both of which crystallized as primary phases. This study is the first application of U-Pb geochronology to apatite crystallized within a terrestrial impact melt sheet. U-Pb analyses were obtained from 200 melt-grown apatite grains (n = 222 spots), with a data subset providing a lower-intercept age of 212.5 ± 8.0 Ma. For melt-grown zircon, a total of 30 analyses from 28 grains were obtained, with a subset of the data yielding a lower-intercept age of ± 1.6 Ma. The lower precision (±8.0 Ma; ±3%) obtained from apatite is a consequence of low U and a high and variable common-Pb composition. This resulted from localized Pb*/PbC heterogeneity within the impact melt sheet that was incorporated into the apatite crystal structure during crystallization (where Pb*/PbC is the ratio of radiogenic Pb to common Pb). While considered a limitation to the precision obtainable from melt-grown apatite, its ability to record local-scale isotopic variations highlights an advantage of U-Pb studies on melt-grown apatite. The best-estimate ages from zircon and apatite overlap within error and correlate with previously determined ages for the Manicouagan impact event. An average formation age from the new determinations, combined with previous age constraints, yields a weighted mean age of 214.96 ± 0.30 Ma for the Manicouagan impact structure.","PeriodicalId":17949,"journal":{"name":"Large Meteorite Impacts and Planetary Evolution VI","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-06-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76774716","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: Shock-twinned zircon in ejecta from the 45-m-diameter Kamil crater in southern Egypt","authors":"A. Cavosie, L. Folco","doi":"10.1130/2021.2550(17)","DOIUrl":"https://doi.org/10.1130/2021.2550(17)","url":null,"abstract":"Table S1: Electron backscatter diffraction (EBSD) analysis conditions","PeriodicalId":17949,"journal":{"name":"Large Meteorite Impacts and Planetary Evolution VI","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-05-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86057571","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 deformation microstructures in xenotime from the Spider impact structure, Western Australia","authors":"M. A. Cox, A. Cavosie, M. Poelchau, T. Kenkmann, P. Bland, K. Miljković","doi":"10.1130/2021.2550(19)","DOIUrl":"https://doi.org/10.1130/2021.2550(19)","url":null,"abstract":"The rare earth element–bearing phosphate xenotime (YPO4) is isostructural with zircon, and therefore it has been predicted that xenotime forms similar shock deformation microstructures. However, systematic characterization of the range of micro structures that form in xenotime has not been conducted previously. Here, we report a study of 25 xenotime grains from 10 shatter cones in silicified sandstone from the Spider impact structure in Western Australia. We used electron backscatter diffrac tion (EBSD) in order to characterize deformation and microstructures within xenotime. The studied grains preserve multiple sets of planar fractures, lamellar {112} deformation twins, high-angle planar deformation bands (PDBs), partially recrystallized domains, and pre-impact polycrystalline grains. Pressure estimates from micro structures in coexisting minerals (quartz and zircon) allow some broad empirical constraints on formation conditions of ~10–20 GPa to be placed on the observed microstructures in xenotime; at present, more precise formation conditions are unavailable due to the absence of experimental constraints. Results from this study indicate that the most promising microstructures in xenotime for recording shock deformation are lamellar {112} twins, polycrystalline grains, and high-angle PDBs. The {112} deformation twins in xenotime are likely to be a diagnostic shock indicator, but they may require a different stress regime than that of {112} twinning in zircon. Likewise, polycrystalline grains are suggestive of impact-induced thermal recrystallization; however, in contrast to zircon, the impact-generated polycrystalline xenotime grains here appear to have formed in the solid state, and, in some cases, they may be difficult to distinguish from diagenetic xenotime with broadly similar textures.","PeriodicalId":17949,"journal":{"name":"Large Meteorite Impacts and Planetary Evolution VI","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85722202","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}