Terrestrial Impact Research Articles

Geology and mineralogy of the Auki Crater, Tyrrhena Terra, Mars: A possible post impact-induced hydrothermal system

A variety of hydrothermal environments have been documented in terrestrial impact structures. Due to both past water interactions and meteoritic bombardment on the surface of Mars, several authors have predicted various scenarios that include the formation of hydrothermal systems. Geological and mineralogical evidence of past hydrothermal activity have only recently been found on Mars. Here, we present a geological and mineralogical study of the Auki Crater using the spectral and visible imagery data acquired by the CRISM (Compact Reconnaissance Imaging Spectrometer for Mars), CTX (Context Camera) and HiRISE (High Resolution Imaging Science Experiment) instruments on board the NASA MRO mission.The Auki Crater is a complex crater that is ∼38km in diameter located in Tyrrhena Terra (96.8°E and 15.7°S) and shows a correlation between its mineralogy and morphology. The presence of minerals, such as smectite, silica, zeolite, serpentine, carbonate and chlorite, associated with morphological structures, such as mounds, polygonal terrains, fractures and veins, suggests that the Auki Crater may have hosted a post impact-induced hydrothermal system. Although the distribution of hydrated minerals in and around the central uplift and the stratigraphic relationships of some morphological units could also be explained by the excavation and exhumation of carbonate-rich bedrock units as a consequence of crater formation, we favor the hypothesis of impact-induced hydrothermal circulation within fractures and subsequent mineral deposition. The hydrothermal system could have been active for a relatively long period of time after the impact, thus producing a potential transient habitable environment.

Differentiated impact melt sheets may be a potential source of Hadean detrital zircon: COMMENT

Kenny et al.’s (2016) ion microprobe zircon crystallization temperature data for the Sudbury impact crater adds to the existing database (Wielicki et al., 2012) for terrestrial impact melts. They note that zircons from the granophyre layer had not previously been analyzed by ion microprobe commensurate with its volumetric importance (20%–45%; Lightfoot et al., 1997) potentially biasing its comparator value when evaluating possible sources for the Hadean Jack Hills zircon population. However, the authors neglected to quantify the degree to which their data set further constrains this issue. Using data from their GSA Data Repository item 2016143, we tested the hypothesis that variants of the impact zircon record (as determined solely from ion microprobe data; Wielicki et al., 2012; Kenny et al., 2016) represent the same probability distribution (i.e., the null hypothesis) as the Hadean population (Harrison and Schmitt, 2007) through a Kolmogorov-Smirnov test (R Core Team, 2013). We reject the null hypothesis for both the case that the Kenny et al. data alone represent the Hadean population (p = 2 × 10), and that for all reported impact zircons (p < 2 × 10; Wielicki et al., 2012; Kenny et al., 2016). In fact, the hypothesis that the granophyre data alone are equivalent to the Hadean population can be rejected (p = 4 × 10). Taken at face value, these results appear to support the conclusion of Wielicki et al. (2012) that the Hadean Jack Hills zircon temperature distribution was not derived in any significant way from impact-derived zircons. However, Kenny et al. raise the prospect of a selection process preferentially destroying high-temperature Hadean zircons and thus biasing the detrital record to lower temperatures. In fact, nature does tend to bias the detrital zircon record, but that mechanism operates in exactly the opposite sense. Late crystallizing, thus low-temperature, granitoid zircons are known to contain elevated U and Th concentrations which lead to metamictization (Claiborne et al., 2010) and thus their likely removal from the detrital record, resulting in preferential preservation of higher-temperature zircons (Harrison and Schmitt, 2007). Thus, without the benefit of some as yet unknown selection mechanism, the probability of extracting the Hadean Ti-in-zircon temperature distribution from the data reported by Kenny et al., or any published data set of impactproduced zircons, remains vanishingly small.

Frictional melting processes and the generation of shock veins in terrestrial impact structures: Evidence from the Steen River impact structure, Alberta, Canada

Shock-produced melt within crystalline basement rocks of the Steen River impact structure (SRIS) are observed as thin (1–510μm wide), interlocking networks of dark veins which cut across and displace host rock minerals. Solid-state phase transformations, such as ferro-pargasite to an almandine–andradite–majorite garnet and amorphization of quartz and feldspar, are observed in zones adjacent to comparatively wider (50–500μm) sections of the shock veins. Shock pressure estimates based on the coupled substitution of Na+, Ti4+ and Si4+ for divalent cations, Al3+ and Cr3+ in garnet (14–19GPa) and the pressure required for plagioclase (Ab62–83) amorphization at elevated temperature (14–20GPa) are not appreciably different from those recorded by deformation effects observed in non-veined regions of the bulk rock (14–20GPa). This spatial distribution is the result of an elevated temperature gradient experienced by host rock minerals in contact with larger volumes of impact-generated melt and large deviatoric stresses experienced by minerals along vein margins.Micrometer-size equant crystals of almandine–pyrope–majorite garnet define the shock vein matrix, consistent with rapid quench (100–200ms) at 7.5–10GPa. Crystallization of the vein occurred during a 0.1–0.15s shock pressure pulse. Majoritic garnet, formed during shock compression by solid state transformation of pargasite along shock vein margins, is observed in TEM bright field images as nanometer-size gouge particles produced at strain rates in the supersonic field (106–108). These crystals are embedded in vesiculated glass, and this texture is interpreted as continued movement and heating along slip planes during pressure release. The deformation of high-pressure minerals formed during shock compression may be the first evidence of oscillatory slip in natural shock veins, which accounts for the production of friction melt via shear when little or no appreciable displacement is observed. Our observations of the mineralogy, chemistry and microtextures of shock veins within crystalline rocks of the SRIS allow us to propose a model for shock vein formation by shear-induced friction melting during shock compression.

Condensate glasses from the Zhamanshin crater. I. Irghizites

The presence of condensate glass was established for the first time in natural terrestrial impact glasses. Its existence was previously predicted on the basis of shock evaporation experiments. Condensate glass was found in the irghizites of the Zhamanshin crater. Its characteristic features were described, including a combination of high silica content with the presence of nanoscale crystalline nuclei and typical globular morphology under TEM.

A GAIA Revised Oort Cloud Encounter with Gliese 710

The encounter between Gliese 710 and the solar system is re-examined in light of the newly published parallax and proper motion measurements within the GAIA data 1 release. The up-dated astrometric parameters are found to be significantly different from those implicated by the earlier Hipparcos Catalog and the revised encounter will see GL 710 pass some 5 times closer to the Sun than previously indicated. The closest encounter distance is now found to be 0.064  0.020 pc at a time 1.36  0.12 million years from the present. There is now a 100% certainty that GL 710 will pass through the outer boundary of the Oort cloud, and it will possibly pass as close as 5200 AU to the Sun, indicating the potential for non-negligible gravitational perturbations of those cometary nuclei located close to the inner boundary of the Oort cloud. The revised encounter conditions indicate that a relatively strong cometary shower is likely within the inner solar system, although how this will modify the terrestrial impact probability remains unclear. We find that GL 710 might be expected to capture and accrete several thousands of cometary nuclei as it moves through the Oort cloud, and such impacts can be expected to drive anomalous flare activity. We additionally find that GL 710 will quite likely trigger sublimation-driven outgassing from cometary nuclei situated within a few astronomical units of its path across the Oort cloud.

Uranium–lead zircon systematics in the Sudbury impact crater-fill: implications for target lithologies and crater evolution

The Sudbury impact structure is one of only a few terrestrial impact craters capable of providing insight into large impact processes. However, despite more than a century of study, no consensus exists regarding its depths of excavation and melting. This study presents 3920 U–Pb zircon dates for target lithologies and the crater-fill as well as new Pb-isotope data for target lithologies in an attempt to further constrain these depths and understand the behaviour of zircon in large impacts. Only 1.5% of the crater-fill zircons have dates within uncertainty of the 1.85 Ga impact event, with most seeming to preserve their pre-impact U–Pb systematics. The preponderance of undisturbed zircon in the crater-fill suggests that this mineral is an effective means of tracing target lithologies in impact basins. A significant fraction of crater-fill zircon was dated between 2.50 and 2.61 Ga, which is negligible amongst known target lithologies, and therefore identifies previously unrecognized target rocks. The Pb-isotope systematics are compatible with the proposal that the 2.6 Ga rock represents typical mid- to lower-crustal basement and could have been an important contributor to the melt-sheet. The combined data argue against a shallow melting scenario. With regard to Hadean terrestrial zircon, the lesson from Sudbury is that zircon can be recycled through multiple large impact events and still preserve the age of the original crust. Supplementary materials: Sample information, trace element and Pb-isotope data for granitoid and gneiss feldspar, Pb modelling parameters, U–Pb zircon data, concordia diagrams and airborne radiometric images are available at http://www.geolsoc.org.uk/SUP18881 .

The Stac Fada impact ejecta deposit and the Lairg Gravity Low: evidence for a buried Precambrian impact crater in Scotland?

The Stac Fada Member, an impact ejecta deposit within the Mesoproterozoic Stoer Group, is represented today by just a narrow outcrop, truncated by faulting and erosion, extending for 50km north-south along the coast of north-west Scotland. It appears to represent a non-erosive Single Layer Ejecta deposit rather than the erosively emplaced Double Layer Ejecta deposits characteristic of terrestrial impact craters and it is unique in preserving spallation debris, ejected very early in the impact process, beneath the ejecta blanket. Various sedimentary structures associated with the Stac Fada Member, from ejecta intrusions along bedding planes immediately beneath it, to erosional troughs eroded into its top, consistently indicate emplacement from the east. No surface manifestation of an impact crater has been identified but there is a remarkable correspondence between its location, as inferred from these directional data, and the position of the Lairg Gravity Low, an ∼40km diameter geophysical anomaly centred more than 50km east of the closest point on the Stoer Group outcrop. Proximal-distal facies changes along the outcrop of the ejecta deposit are consistent with this inferred relationship between the ejecta deposit and the gravity low. Post-impact drainage reconfiguration suggests a regional isostatic doming in response to excavation of the crater that also appears to be centred on the Lairg Gravity Low. Comparison with gravity data from impact craters elsewhere suggests that the Lairg Gravity Low represents a complex crater at least 40km in diameter that now lies buried beneath the Moine Thrust complex.

The Canadian space agency planetary analogue materials suite

The Canadian Space Agency (CSA) recently commissioned the development of a suite of over fifty well-characterized planetary analogue materials. These materials are terrestrial rocks and minerals that are similar to those known or suspected to occur on the lunar or martian surfaces. These include: Mars analogue sedimentary, hydrothermal, igneous and low-temperature alteration rock suites; lunar analogue basaltic and anorthositic rock suites; and a generic impactite rock suite from a variety of terrestrial impact structures. Representative thin sections of the materials have been characterized by optical microscopy and electron probe microanalysis (EPMA). Reflectance spectra have been collected in the ultraviolet, visible, near-infrared and mid-infrared, covering 0.2–25μm. Thermal infrared emission spectra were collected from 5 to 50μm. Raman spectra with 532nm excitation, and laser-induced fluorescence spectra with 405nm excitation were also measured. Bulk chemical analysis was carried out using X-ray fluorescence, with Fe valence determined by wet chemistry. Chemical and mineralogical data were collected using a field-portable Terra XRD–XRF instrument similar to CheMin on the MSL Curiosity rover. Laser-induced breakdown spectroscopy (LIBS) data similar to those measured by ChemCam on MSL were collected for powdered samples, cut slab surfaces, and as depth profiles into weathered surfaces where present. Three-dimensional laser camera images of rock textures were collected for selected samples.The CSA intends to make available sample powders (<45μm and 45–1000μm grain sizes), thin sections, and bulk rock samples, and all analytical data collected in the initial characterisation study to the broader planetary science community.Aiming to complement existing planetary analogue rock and mineral libraries, the CSA suite represents a new resource for planetary scientists and engineers. We envision many potential applications for these materials in the definition, development and testing of new analytical instruments for use in planetary missions, as well as possible calibration and ground-truthing of remote sensing data sets. These materials may also be useful as reference materials for cross-calibration between different instruments and laboratories. Comparison of the analytical data for selected samples is useful for highlighting the relative strengths, weaknesses and synergies of different analytical techniques.

Condensate constituent in impact glasses of the Zhamanshin crater

The presence of condensate glass, which had been forecasted exclusively based on experiments on shock evaporation, was first discovered in natural terrestrial impact glasses. The condensate glass was found in irghizites and zhamanshinites of the Zhamanshin crater. The glass characteristics, a combination of a high silica content and the occurrence of nanosize crystalline nuclei, as well as the typical globular morphology, were determined by means of transmission electron microscopy.

Precambrian reidite discovered in shocked zircon from the Stac Fada impactite, Scotland

Terrestrial impact events have had a profound influence on Earth’s geological, geochemical, and biological evolution. However, the record of Precambrian impacts is poorly constrained due to the dynamic nature of plate tectonics, erosion, and deposition of younger rocks that may destroy or cover the evidence. Here we report the first Precambrian occurrence of the rare mineral reidite (ZrSiO4) within grains of shocked zircon in the ca. 1.18 Ga Stac Fada Member (Stoer Group), northwestern Scotland. The reidite, preserved as <2-µm-wide lamellae, is unambiguous evidence of shock pressures in excess of ∼30 GPa and confirms the impact origin for the Stac Fada deposit. The reidite lamellae are locally deformed, and sites of deformation record its decomposition to baddeleyite (ZrO2) and amorphous silica, the first natural example of this transformation. The findings demonstrate that reidite and baddeleyite may form and be transported in high-energy ejecta without physical or chemical breakdown and are stable during sedimentary diagenesis and low-grade metamorphism. Thus, reidite may be preserved over time scales exceeding 1 b.y., establishing the use of reidite within detrital shocked zircon from Precambrian strata as a viable and valuable means of recognizing and characterizing ancient terrestrial impact events.

Measures proposed for planetary defence: Obstacles in existing international law and implications for space arms control

Whereas the Earth is showered by extraterrestrial matters on a constant basis, most of them cannot survive the very high heat produced in their entry into the atmosphere to make a terrestrial impact. Impacts that are capable of inflicting terrestrial casualties and damages are even rarer. However, their consequences can be high, and even so nowadays with the change of human settlement patterns on the Earth. With the development of space science and technology, human beings are now capable of predicting possible impacts with some accuracy, and even minimizing the chance of actual collision. For the later purpose, many proposals have been put forward, which either employ weapons readily found on the Earth, or envisage newly developed technologies that could nevertheless be used for military purposes. This short note applies existent international law to these measures, and attempts to shed some light on their implications for ongoing discussions of space arms control.

Prospecting for possible impact structures in Morocco

The current terrestrial impact crater record includes 188 accepted structures (http://www.passc.net/EarthImpactDatabase and Ferrière et al., 2015). This number continues to increase slowly but quite regularly. The heterogeneous distribution of impact structures is strongly influenced by the knowledge about impact cratering of exploration geologists, who have to be familiar with the possible field evidence for impact structures – and ultimately with the recognition criteria accepted for confirmation of new impact structures. For remote and poorly explored areas, satellite imagery is a powerful tool to identify circular structures that, at all scales, could be considered possible candidates for impact structures. Here, we present the results of a first systematic survey of circular structures over the Moroccan surface area (a total of 710,850 km2) using the imagery available through the Google-Earth software. Structures whose origins could not be elucidated from available geological data were then visited to determine their origin (impact or non-impact). Thirteen sites with one or more circular structures were investigated but none of them could be associated with an impact event. Instead, our results illustrate the diversity of geological processes that can produce circular structures, including magmatic and tectonic processes, bioconstruction, and even anthropogenic activity. It also demonstrates that circular structures are very common in surface imagery of the Earth but are generally not associated with impact events. This result questions whether this simple approach for the search of impact structures should be extended to other parts of the world. It also emphasizes that remote sensing imagery should not be used in isolation of other data.

Lessons from the Chelyabinsk event

AbstractRecent investigations on small asteroids, initiated by the Chelyabinsk event, are reviewed. New estimates of the terrestrial impact rate, importance of Sun-grazing conditions in the evolution of near-Earth objects, and problems associated with dangerous objects approaching the Earth from the Sun direction are discussed.

Melting and cataclastic features in shatter cones in basalt from the Vista Alegre impact structure, Brazil

AbstractShatter cones are one of the most widely recognized pieces of evidence for meteorite impact events on Earth, but the process responsible for their formation is still debated. Evidence of melting on shatter cone surfaces has been rarely reported in the literature from terrestrial impact craters but has been recently observed in impact experiments. Although several models for shatter cones formation have been proposed, so far, no one can explain all the observed features. Shatter cones' from the Vista Alegre impact structure, Brazil, formed in fine‐grained basalt of the Jurassic‐Cretaceous Serra Geral Formation (Paraná large igneous province). A continuous quenched melt film, consisting of a crystalline phase, mica, and amorphous material, decorates the striated surface. Ultracataclasites, containing subrounded pyroxene clasts in an ultrafine‐grained matrix, occur subparallel to the striated surface. Several techniques were applied to characterize the crystalline phase in the melt, including Raman spectroscopy and transmission electron microscopy. Results are not consistent with any known mineral, but they do suggest a possible rare or new type of clinopyroxene. This peculiar evidence of melting and cataclasis in relation with shatter cone surfaces is interpreted as the result of tensile fracturing at the tip of a fast propagating shock‐induced rupture, which led to the formation of shatter cones at the tail of the shock front, likely during the early stage of the impact events.

EScience and Informatics for international science programs

Both eScience and Informatics, their conceptual approaches, methods, and extant technical solutions, are still relatively new approaches in many science fields. Collectively, they intend to facilitate the electronic conduct of science (eScience) and the application of foundational principles drawn from experience in a number of fields of Informatics (e.g., helioinformatics, geoinformatics, and climateinformatics). The Climate and Weather of the Sun-Earth System II (CAWSES II) eScience and Informatics effort had the goal of promoting an international virtual institute and several virtual observatories in order to advance system-level science investigations aligned with the four CAWSES II Task Groups. This contribution elaborates on the key elements of eScience and Informatics applicable to CAWSES II as a virtual organization in the context of the current science-data landscape. We examine what was adopted for CAWSES II and highlight the successes and challenges of the effort. Based on the lessons learned from this effort and other international communities, we present opportunities going forward that are relevant to both smaller collaborations and successor large-scale programs (such as the Variability of the Sun and Its Terrestrial Impact (VarSITI)) that are being recognized more as networks of science facilitated by a variety of modern information technologies.

Meteorite traces on a shatter cone surface from the Agoudal impact site, Morocco

AbstractThe recently discovered Agoudal impact site in Morocco is a small, eroded impact structure with well-developed shatter cones. A scanning electron microscopic study of a shatter cone surface has revealed the presence of schreibersite – a phosphide very rare on Earth but common in iron meteorites – and Fe–Ni oxides. This is the first reported evidence for primary meteoritic matter adherent to shatter cones and suggests that the Agoudal crater was formed by the impact of an iron meteorite, probably the Agoudal IIAB iron. Shatter cones from other terrestrial impact structures might also hold valuable information about the nature of the impacting projectiles.

Disc dark matter in the Galaxy and potential cycles of extraterrestrial impacts, mass extinctions and geological events

A cycle in the range of 26–30Myr has been reported in mass extinctions, and terrestrial impact cratering may exhibit a similar cycle of 31 ± 5Myr. These cycles have been attributed to the Sun’s vertical oscillations through the Galactic disc, estimated to take from ∼30 to 42Myr between Galactic plane crossings. Near the Galactic mid-plane, the Solar system’s Oort Cloud comets could be perturbed by Galactic tidal forces, and possibly a thin dark matter (DM) disc, whichmightproduceperiodiccometshowersandextinctionsontheEarth.PassageoftheEarth through especially dense clumps of DM, composed of Weakly Interacting Massive Particles (WIMPs) in the Galactic plane, could also lead to heating in the core of the planet through capture and subsequent annihilation of DM particles. This new source of periodic heating in the Earth’s interior might explain a similar ∼30Myr periodicity observed in terrestrial geologic activity, which may also be involved in extinctions. These results suggest that cycles of geological and biological evolution on the Earth may be partly controlled by the rhythms of Galactic dynamics.

Rotational Pixel Swapping Method for Detection of Circular Features in Binary Images

We propose a new automatic method called the rotational pixel swapping (RPSW) method to detect circular features in binary images of remote sensing images. The method is based on a multiplication operation between the original image and the rotated images. We show that the RPSW selectively enhances rotational symmetric patterns and weakens nonrotational symmetric patterns, including noise components, without any noise reduction processes. The method can detect not only simple circles but also more complex circular features such as incomplete ring structures or several concentric rings. Furthermore, we demonstrate that the RPSW provides the stable detection of circular features such as terrestrial impact structures, which are irregular imperfect circular shapes, in binary images based on Earth-observation satellite images. The RPSW would provide a potential method of future surveys or statistical studies using huge data sets of multiband or hyperspectral images obtained by Earth-observation satellites.

Organic Geochemistry and Paleoenvironments of Deposition of the Middle Jurassic Sediments from the Tabas Basin, Central Iran

In an attempt to reconstruct the paleoenvironments of deposition for the Middle Jurassic Baghamshah formation, samples collected from six outcrop sections along the Shotori swell were subjected to detailed geochemical analyses. Bulk geochemical and biological marker data indicate a logical trend of the variation of organic input, salinity, and oxicity within Baghamshah paleoenvironments across the studied area. An increase in terrestrial character from southern end towards the central parts of the Shotori swell parallels with a uniform increase in the oxicity and a decrease in the salinity. The northernmost sections are characterized by less terrestrial impact, reduced oxicity, and elevated salinity compared to the central and southern sections. These variations are interpreted in the framework of past geometric configuration and a hypothetical paleogeomorphologic model is tentatively proposed for the Middle Jurassic of the area. According to these results, the depositional setting of the studied formation decreased in depth from Section-1 towards Section-4, suggesting that the proximity of the latter section to the Yazd Block may have had a strong control over the observed geochemical variations. The terrestrial organic input and the oxicity of the environment are conspicuously low for northern sections and their salinity shows a sharp increase compared to other sections. We hypothesize that a fault plan exists across the northern and southern Shotori Mountains that had played an active role in creating the current geochemical variations.

Impacts of Tourism on the Coastal Environment of South China Sea: Terrestrial Perspective

At recent times, Asia and the Pacific have been rated very high as major tourism destinations. This transdisciplinary (nature and social science concepts) study reveals that tourism activities generate pressure on forest ecosystems and coastal biodiversity. Dongguan forest (site) park attracted impact on terrestrial ecosystem with impact base respondent (9 000), while Shenzhen (18 000), Guangzhou (18 000) and Zhuhai (12 000) districts showed much higher values on general impact. A coastal activity survey and impact base of visitor response model evaluation was used. A general impact and causative platform were identified as driving fundamental (direct/indirect) factors in the region. Subjective and observed broad impacts were presented however; trampling had a major terrestrial impact on both ecosystems. Further investigation is needed to evaluate the economic impact of tourism in the region using industrial, urban and tourism potential factors after the 2008 Olympic Games in China. Strategies for appropriate action and government regulations are recommended concepts of terrestrial and coastal conservation planning and land use.