Meteorite Impact Research Articles

An Insight to the Sedimentological Developments of Quaternary Detritus Ring Fluvial Network, Altun Kupri Paleolake, NE IRAQ

During the Quaternary, an active basin in the shape of open lake originated along the Lesser Zab river at Altun Kupri area. The radial complex of fluvial deposit morphologically initiated by the coarse detritus material, that were transported by the Lesser Zab river and other surrounded valleys in a shape of delta towards the proximal part of coastal plain and the fine sediment to the distal part of it. The coarse one prograde along the fine gradually resulting in the accumulation of about 60 m thickness of continuous Pleistocene fluvial succession mostly of coarse grained sediments with minor sand, silt and clay intervals and some tongues and bands of calcareous mud. The bulk of basin fill is made of two depositional systems, the western and southwestern side was filled up by progradation delta systems, but the northern side was gradually filled up by fluvial sediment of Lesser Zab channel. The water impounded in this lake because of Awanah anticline as a ridge in front of the lake which is open with output channel that crosses the shallow gorge and the gorge became deeper and deeper gradually till the water drooped from the lake. There are several possibilities that this ring shape depression of Altun Kupri paleolake generated, first: the depression at Altun Kupri is formed as a result of dissolving lenses of Anhydrite and gypsum of the Fat’ha Formation beneath the northern limb of Awanah Anticline after the collapse of the cavity roof. second: the presence of ring shape cliffs of about 50m thick and depression is bounded by 8km in diameter of cross bedded conglomerates and sandstone and the third: the depression of Altun Kupri paleolake can be developed by meteoritic impact, with several sedimentological and structural evidence such as a delta distributary fan, and there was a hanging terrace at a high level along the gorge

Late Ediacaran organic microfossils from Finland

AbstractHere we present a detailed accounting of organic microfossils from late Ediacaran sediments of Finland, from the island of Hailuoto (northwest Finnish coast), and the Saarijärvi meteorite impact structure (~170 km northeast of Hailuoto, mainland Finland). Fossils were recovered from fine-grained thermally immature mudstones and siltstones and are preserved in exquisite detail. The majority of recovered forms are sourced from filamentous prokaryotic and protistan-grade organisms forming interwoven microbial mats. Flattened Nostoc-ball-like masses of bundled Siphonophycus filaments are abundant, alongside Rugosoopsis and Palaeolyngbya of probable cyanobacterial origin. Acritarchs include Chuaria, Leiosphaeridia, Symplassosphaeridium and Synsphaeridium. Significantly, rare spine-shaped sclerites of bilaterian origin were recovered, providing new evidence for a nascent bilaterian fauna in the terminal Ediacaran. These findings offer a direct body-fossil insight into Ediacaran mat-forming microbial communities, and demonstrate that alongside trace fossils, detection of a bilaterian fauna prior to the Cambrian might also be sought among the emerging record of small carbonaceous fossils (SCFs).

Origin of β-cristobalite in Libyan Desert Glass: The hottest naturally occurring silica polymorph?

Abstract Identifying and determining the origin of β-cristobalite, a high-temperature silica polymorph, in natural samples is challenging as it is rarely, if ever, preserved due to polymorphic transformation to α-cristobalite at low temperature. Formation mechanisms for β-cristobalite in high-silica rocks are difficult to discern, as superheating, supercooling, bulk composition, and trace element abundance all influence whether cristobalite crystallizes from melt or by devitrification. Here we report a study of α-cristobalite in Libyan Desert Glass (LDG), a nearly pure silica natural glass of impact origin found in western Egypt, using electron microprobe analysis (EMPA), laser ablation inductively coupled mass spectrometry (LA-ICP-MS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD). The studied grains are mostly 250 μm in diameter and consist of ~150 μm wide cores surrounded by ~50 μm wide dendritic rims. Compositional layering in LDG continues across cristobalite grains and mostly corresponds to variations in Al content. However, layering is disrupted in cores of cristobalite grains, where Al distribution records oscillatory growth zoning, whereas in rims the high Al occurs along grain boundaries. Cristobalite cores thus nucleated within layered LDG at conditions that allowed mobility of Al into crystallographically controlled growth zones, whereas rims grew when Al was less mobile. Analysis of 37 elements indicates little evidence of preferential partitioning; both LDG and cristobalite are variably depleted relative to the upper continental crust, and abundance variations correlate to layering in LDG. Orientation analysis of {112} twin systematics in cristobalite by EBSD confirms that cores were formerly single β-cristobalite crystals. Combined with published experimental data, these results provide evidence for high-temperature (>1350 °C) magmatic crystallization of oscillatory zoned β-cristobalite in LDG. Dendritic rims suggest growth across the glass transition by devitrification, driven by undercooling, with transformation to α-cristobalite at low temperature. This result represents the highest formation temperature estimate for naturally occurring cristobalite, which is attributed to the near pure silica composition of LDG and anomalously high temperatures generated during melting by meteorite impact processes.

Iron-rich microstructure records of high temperature multi-component silicate melt behavior in nuclear fallout

Above-ground nuclear explosions that interact with the surface of the earth entrain materials from the surrounding environment, influencing the resulting physical and chemical evolution of the fireball, which can affect the final chemical phase and mobility of hazardous radionuclides that are dispersed in the environment as fallout particles. The interaction of iron with a nuclear explosion is of specific interest due to the potential for iron to act as a redox buffer and because of the likelihood of significant masses of metals to be present in urban environments. We investigated fallout from a historic surface interacting nuclear explosion conducted on a steel tower and report the discovery of widespread and diverse iron-rich micro-structures preserved within the samples, including crystalline dendrites and micron-scale iron-rich spheres with liquid immiscibility textures. We assert these micro-structures reflect local redox conditions and cooling rates and can inform interpretation of high temperature events, enabling new insights into fireball condensation physics and chemistry when metals from the local environment (i.e. structural steel) are vaporized or entrained. These observations also significantly expand the availability of silicate immiscibility datasets applicable to rapidly quenched systems such as meteorite impact melt glass.

Dynamics of recent landslides (

Landslides are common features found on steep slopes on Mars and the role of water in their formation is an open question. Our study focuses on three young martian landslides whose mechanism of formation is unknown and knowing their formation mechanism could give us key information on recent martian climate and/or tectonics. They are less than 5 ​km long, and formed during the Late Amazonian Epoch, with an age <20 ​Ma when Mars is thought to have had a hyperarid climate. To better understand the dynamics and formation mechanism of these landslides, we combine two approaches: geomorphic comparison between martian and terrestrial landslides using remote sensing data from the High Resolution Imaging Science Experiment (HiRISE) and the Colour and Stereo Surface Imaging System (CaSSIS), and numerical modelling using a dry granular flow dynamical model. Our geomorphic analysis revealed two contrasting morphologies suggesting differing dynamics and formation mechanisms. Two of the three martian landslides resemble terrestrial rockslides, while the third is more akin to terrestrial mudslides. The numerical modelling, although not fully conclusive, broadly supports our interpretations from the morphological observations. We suggest that the two landslides resembling terrestrial rockslides could have been triggered by shaking by meteorite impact or marsquakes in the absence of water. On the contrary, we suggest liquid water (originating from ground-ice melted by geothermal heat flux) may have been involved in the initiation of the landslide resembling a terrestrial mudslide. Our results show the value of using morphological comparison between martian and terrestrial landslides combined with numerical modelling to inform the hypotheses of landslide-formation on Mars where in situ analysis is not usually possible.

Crustal Velocity Variations and Constraints on Material Properties in the Charlevoix Seismic Zone, Eastern Canada

AbstractCrustal velocity variation within impact‐related seismic zones is commonly attributed to factors such as the presence of dense fracture networks, fluid pressure change, and compositional variations. In this study, we combine seismic tomography, rock physics analysis, and gravity anomaly modeling to quantitatively investigate the mechanisms that influence crustal velocity heterogeneities in the Charlevoix Seismic Zone (CSZ), the most active seismic zone in eastern Canada. Earthquakes in the CSZ align in two broad NE‐SW trending clusters, possibly due to the reactivation of St. Lawrence paleorift faults. Within the meteorite impact structure, earthquakes are diffusely distributed, and ubiquitous lower velocity volumes have been attributed to crustal damage from tectonic inheritance exacerbated by the meteorite impact. The Bouguer gravity anomaly contrast across the St. Lawrence River is due to density disparities between the Grenville Province on the north shore and the Appalachians on the south shore. We find a higher velocity region northeast of the impact structure that does not exhibit an observable gravity anomaly, which suggests the co‐existence of rock types of comparable densities but different elastic moduli (e.g., anorthosite and charnockite). Outside the impact structure, compositional variations control velocity changes, whereas inside the impact structure, velocity variations can be explained by porosity enhancement of up to 10% by low (0.1) aspect‐ratio cracks. Our results suggest that intense fracturing and compositional alteration, rather than pore pressure change, have the primary control on seismic velocity variations, and consequently, earthquake processes in the CSZ.

Yilan crater, China: Evidence for an origin by meteorite impact

AbstractThe Yilan crater is 1.85 km in diameter and is located in the northeast of China's Heilongjiang Province. The crater is exposed in the Early Jurassic granite of the regional Paleozoic–Mesozoic granite complexes. The southern third of the crater rim is missing, but other rim sections are well preserved, with a maximum elevation above the present crater floor of 150 m. A drillcore from the center of the structure shows that the crater fill consists of 110 m thick lacustrine sediments underlain by a 319 m thick brecciated granite unit mainly composed of unconsolidated granite clasts and fragments. Melt products derived from the target granite, which include melted (and recrystallized) granite clasts, vesicular glass, and teardrop‐shaped glass, were found in the brecciated granite unit at 218–237 m depth. Petrographic investigations of unmelted granite clasts in the brecciated granite unit from this depth interval show the presence of multiple sets of planar deformation features (PDFs) in quartz. Orientation measurements for 79 PDF sets in 38 quartz grains with a U‐stage indicate the dominance of the ω{103} and π{102} orientations with a relative frequency of 39% and 18%, respectively. Only 7.6% of the observed PDFs remain unindexed. The observations of PDFs with the appropriate orientations are clear evidence of shock metamorphism and thus of an impact origin of the Yilan structure. Crystallite aggregates of coesite embedded in silica glass were found in the impact‐melted granite clasts. The carbon‐14 dates of possibly impact‐produced charcoal and lacustrine sediments from the crater fill suggest a young age for the impact event of 0.0493 ± 0.0032 Ma.

Constraints on the origins of iron silicide spherules in ultrahigh‐temperature distal impact ejecta

AbstractTerrestrially occurring iron silicide spherules, described in the geological literature for 160 years as cosmogenic and approved as “extraterrestrial” minerals by IMA CNMMN in 1984, so far have escaped any serious examination by meteoriticists. Our isotopic and REE data, obtained for silicide spherules for the first time, disagree with the meteoritic origin of gupeiite (Fe3Si) and xifengite (Fe5Si3) spherules from two continents. Despite departures from terrestrial norms (87Rb/86Sr—0.0174; 87Sr/86Sr—0.700181; 3He/4He—7.57 × 10−6; 40Ar/36Ar—325.9), the compositions of 143Nd/144Nd (0.512034) and 147Sm/144Nd (0.06357), as well as REE abundances, clarify provenance from upper crust sediments for samples with U/Pb age of 121–314 ka from the Ala‐Tau range in the Urals. However, the morphology of flanged button shapes, ring waves, and eccentro‐radiating ridges reliably constrains the origin of silicide spherules to distal meteoritic impact ejecta. Arc jet ablation experiments have previously demonstrated that similar morphologies, observed on australite tektites, reflect aerodynamic ablation rates corresponding to flight velocities well into orbital range. These features are generally accepted as conclusive evidence for hypervelocity atmospheric entry from space. Internal structure, consistent with accretion through the coalescence of 3–5 µm droplets, and composition, closely corresponding to 1893–1154 K span of C‐type condensation sequences, indicate a high probability of processing through recondensation of ejecta vapor.

Assessing the statistical uniqueness of the Younger Dryas: a robust multivariate analysis

Abstract. During the last glacial period (ca. 120–11 kyr BP), dramatic temperature swings, known as Dansgaard–Oeschger (D–O) events, are clearly manifest in high-resolution oxygen isotope records from the Greenland Ice Sheet. Although variability in the Atlantic Meridional Overturning Circulation (AMOC) is often invoked, a unified explanation for what caused these “sawtooth-shaped” climate patterns has yet to be accepted. Of particular interest is the most recent D–O-shaped climate pattern that occurred from ∼ 14 600 to 11 500 years ago – the Bølling–Allerød (BA) warm interstadial and the subsequent Younger Dryas (YD) cold stadial. Unlike earlier D–O stadials, the YD is frequently considered a unique event, potentially resulting from a rerouting and/or flood of glacial meltwater into the North Atlantic or a meteorite impact. Yet, these mechanisms are less frequently considered as the cause of the earlier stadials. Using a robust multivariate outlier detection scheme – a novel approach for traditional paleoclimate research – we show that the pattern of climate change during the BA/YD is not statistically different from the other D–O events in the Greenland record and that it should not necessarily be considered unique when investigating the drivers of abrupt climate change. In so doing, our results present a novel statistical framework for paleoclimatic data analysis.

In-situ U-Pb dating of Ries Crater lacustrine carbonates (Miocene, South-West Germany): Implications for continental carbonate chronostratigraphy

The Nördlinger Ries Crater lacustrine basin (South-West Germany), formed by a meteorite impact in the Miocene (Langhian; ∼14.9 Ma), offers a well-established geological framework to understand the strengths and limitations of U-Pb LA-ICPMS (in situ Laser Ablation-Inductively Coupled Plasma Mass Spectrometry) geochronology as chronostratigraphic tool for lacustrine (and more broadly continental) carbonates. The post-impact deposits include siliciclastic basinal facies at the lake centre and carbonate facies at the lake margins, coevally deposited in a time window of >1.2 and <2 Ma. Depositional and diagenetic carbonate phases (micrites and calcite cements) were investigated from three marginal carbonate facies (Hainsfarth bioherm, Adlersberg bioherm and Wallerstein mound). Petrography combined with C and O stable isotope analyses indicate that most depositional and early diagenetic carbonates preserved pristine geochemical compositions and thus the U-Pb system should reflect the timing of original precipitation. In total, 22 U-Pb ages were obtained on 10 different carbonate phases from five samples. The reproducibility and accuracy of the U-Pb (LA-ICPMS) method were estimated to be down to 1.5% based on repeated analyses of a secondary standard (speleothem calcite ASH-15d) and propagated to the obtained ages. Micrites from the Hainsfarth, Adlersberg and Wallerstein facies yielded ages of 13.90 ± 0.25, 14.14 ± 0.20 and 14.33 ± 0.27 Ma, respectively, which overlap within uncertainties, and are consistent with the weighted average age of 14.30 ± 0.20 Ma obtained from all the preserved depositional and early diagenetic phases. Data indicate that sedimentation started shortly after the impact and persisted for >1.2 and <2 Ma, in agreement with previous constraints from literature, therefore validating the accuracy of the applied method. Later calcite cements were dated at 13.2 ± 1.1 (nw=2), 10.2 ± 2.7 and 9.51 ± 0.77 Ma, implying multiple post-depositional fluid events. This study demonstrates the great potential of the U-Pb method for chronostratigraphy in continental systems, where correlations between time-equivalent lateral facies are often out of reach. In Miocene deposits the method yields a time resolution within the 3rd order depositional sequences (0.5–5 Ma).

Scientific Basis and Geophysical Consequences of Geomagnetic Reversals and Excursions: A Fundamental Statement

Convection in Earth’s georeactor sub-shell is responsible for generating the geomagnetic field and for maintaining the critical balances necessary for stable sub-core nuclear fission. External factors capable of disrupting sub-shell convection are trauma at Earth’s surface, for example by meteorite impact, and electrical energy transfer via Faraday’s electromagnetic induction into the georeactor by changes in the solar wind or in the magnetospheric ring current. Reduced sub-shell convection not only leads to decreased geomagnetic field intensity, but to increased uranium settling out into the sub-core where it undergoes uncontrolled nuclear fission until sub-shell convection is reestablished. Periods of uncontrolled georeactor nuclear fission are responsible for causing geophysical phenomena at Earth’s surface that are associated with geomagnetic reversals and excursions. Anticipated consequences of sub-shell convection collapse include increases in volcanic activity, increases in the number and intensity of earthquakes, warming of the oceans, and diminishment of atmospheric convection resulting in global warming at the surface. The most worrisome potentiality is triggering the eruption of the Yellowstone super-volcano. Changes in solar wind flux, too small to cause geomagnetic field collapse, however, may cause increases in earthquakes and volcanic eruptions. The understanding described here potentially provides a basis for the development of earthquake and volcanic eruption prediction methodologies.

A Review on Chemical and Ecological Status of Lonar Lake

Meteoric impact crater Lonar Lake is located in Buldhana district of Maharashtra always remained as point of attraction among the researchers of different fields since many decades as it has rich chemical and biological diversity in it. Physicochemical qualities of water samples were analysed by many researchers and revealed that, the water is alkaline with high pH and categorised by high concentration of Alkalinity, Sulphate, sodium, Total dissolved solids, Magnesium, Chloride and Dissolved Oxygen. Due to this, interesting microbial complexity have been developed across the Lake. From this review, it is found that alkalinity has been decreased by nearly 19 percent, salinity nearby 7 percent and therefore its pH is seen to drop up to 6.2. This decreases is mainly due to process of sedimentation of salt at the bottom of the Lake. This has affected the living of Micro-organism. Many researches have been carried to study the nature of Lonar Lake from different fields. Therefore, an attempt is made to assemble important aspects of Lonar Lake from various fields. Conservation of Lonar Lake with proper management is necessary as it has uniqueness and beauty in itself.

The Environment at Lake El’gygytgyn Area (Northeastern Russian Arctic) Prior to and After the Meteorite Impact at 3.58 Ma

Upper Pliocene sediments from a number of fluvial outcrops in central Chukotka, northeastern Russian Arctic, along the Enmyvaam, Mechekrynnetveem, and Chanuvenvaam Rivers, have been newly studied for pollen, non-pollen-palynomorphs and, for the first time for Pliocene sediments in Eurasia, charcoals. The sediments have survived the El’gygytgyn meteorite impact event at ∼3.58 Ma. The stratigraphy of the studied outcrops suggests that the lowermost sediments were accumulated shortly before the impact event, between ∼3.60 and 3.58 Ma. At that time, coniferous forests with spruces, pines, firs, birches, larches, and alders dominated in the area. Some relatively thermophilic broad-leaved taxa (Corylus, Carpinus, Ulmus, and Myrica) might also have grown in local forests. Summer temperatures were at least 10°C warmer than today. Charcoal concentrations and composition suggest the presence of high intensity fires. Periods of rather wet climate and soil conditions are marked by common shrubby and boggy habitats with ericaceous plants and Sphagnum, and are associated with less, and probably low-intensity surface fires with less charcoal. The impact event caused widespread fires reflected by up to 4 times higher charcoal concentrations in the sediments. The sediments found above the so-called “chaotic horizon” (sediments accumulated synchronously or very shortly after the impact event) contain late Pliocene pollen assemblages comparable to those in Lake El’gygytgyn, reflecting that pine-spruce forests with some firs, birches, larches, and alder dominated in the study area. Some thermophilic taxa might also still have grown in the area. However, the age control for the sediments above the so-called chaotic horizon is poor. The uppermost sediments from the studied sections can be attributed with certainty to the Late Pleistocene and Holocene according to their stratigraphic positions and pollen assemblages. The combined pollen and charcoal analysis allowed correlating hardly datable fluvial sediments and points to varying fire regimes in warmer-than-present climates, when forest extended further north compared to today.

Ocean resurge-induced impact melt dynamics on the peak-ring of the Chicxulub impact structure, Mexico

Core from Hole M0077 from IODP/ICDP Expedition 364 provides unprecedented evidence for the physical processes in effect during the interaction of impact melt with rock-debris-laden seawater, following a large meteorite impact into waters of the Yucatán shelf. Evidence for this interaction is based on petrographic, microstructural and chemical examination of the 46.37-m-thick impact melt rock sequence, which overlies shocked granitoid target rock of the peak ring of the Chicxulub impact structure. The melt rock sequence consists of two visually distinct phases, one is black and the other is green in colour. The black phase is aphanitic and trachyandesitic in composition and similar to melt rock from other sites within the impact structure. The green phase consists chiefly of clay minerals and sparitic calcite, which likely formed from a solidified water–rock debris mixture under hydrothermal conditions. We suggest that the layering and internal structure of the melt rock sequence resulted from a single process, i.e., violent contact of initially superheated silicate impact melt with the ocean resurge-induced water–rock mixture overriding the impact melt. Differences in density, temperature, viscosity, and velocity of this mixture and impact melt triggered Kelvin–Helmholtz and Rayleigh–Taylor instabilities at their phase boundary. As a consequence, shearing at the boundary perturbed and, thus, mingled both immiscible phases, and was accompanied by phreatomagmatic processes. These processes led to the brecciation at the top of the impact melt rock sequence. Quenching of this breccia by the seawater prevented reworking of the solidified breccia layers upon subsequent deposition of suevite. Solid-state deformation, notably in the uppermost brecciated impact melt rock layers, attests to long-term gravitational settling of the peak ring.

Diagnostic Simulations of the Lunar Sodium Tail and Bright Spot

AbstractNumerical simulations of the lunar sodium tail and its bright sodium spot are presented. As an attempt to do reverse engineering to understand the lunar sodium exosphere, we simulated velocity distributions of the sodium tail and its bright spot that emerges in the night sky around new Moon phases. In this work, three physical sodium sources (i.e., photon‐stimulated desorption [PSD], solar‐wind ion sputtering [SIS], meteor impact vaporization [MIV]), the dust anisotropy effect reported by Lunar Atmosphere and Dust Environment Explorer (LADEE), three gravitational sources (i.e., the Moon, the Earth, and the Sun), and variable solar radiation pressure effects are considered. We simulated velocity distributions of the lunar bright spot considering different source contribution ratios and their temperatures in order to find the best initial parameters which can account for the important observed recessional velocity of 12.4 km/s by Mierkiewicz et al. (2006, https://doi.org/10.1029/2006GL027650). We found that the upper limits of Maxwellian temperatures of 1,800 K for the PSD and 2,500 K for the MIV and that the best contribution ratio of the three major sodium sources (i.e., PSD: SIS: MIV) is found at the case of 2: 1: 3 (i.e., MIV dominant). Based on the previous brightness observations of the bright spot, the total production rate of the lunar sodium is estimated to usually vary between 0.4 and 1.3 × 1022/s. We introduce an interesting event in the lunar sodium tail, the Sodium Ring phenomena, which can occur transiently during the total solar eclipse due to the umbra and penumbra effects of the Earth.

Multi-collector 40Ar/39Ar dating of microtektites from Transantarctic Mountains (Antarctica): A definitive link with the Australasian tektite/microtektite strewn field

Microtektites represent high-velocity/distal meteorite impact ejecta. Demonstrating that microtektites found at several locations throughout East-Antarctica consist of a homogeneous class of geological objects belonging to the Australasian tektite/microtektite strewn field is fundamental to define the actual extent of the largest and youngest known tektite field on Earth produced by an asteroidal impact ∼0.8 Ma ago. This study presents new 40Ar/39Ar analyses performed by multi-collector noble gas mass spectrometry on individual microtektites from two key locations in the Transantarctic Mountains: Miller Butte, in northern Victoria Land, and Mount Raymond, over 1,000 km further south, in the Grosvenor Mountains. Results indicate that particles are heavily contaminated by at least one extraneous Ar component, which is not correlated with size nor with bulk chemical composition, and precludes a straightforward interpretation of 40Ar/39Ar data. Analysis of data from step-heating and total fusion analyses in three-isotope correlation diagrams yielded indistinguishable isochron ages from the two locations, with a combined isochron average of 800 ± 89 ka (95% confidence level). These age results improve by more than one order of magnitude previously published 40Ar/39Ar age determinations and improve by ∼4 times a previous fission track date, thus providing conclusive evidence that microtektites found throughout the Transantarctic Mountains of Antarctica belong to a single source – the Australasian field. This study strengthens the southward extension of the Australasian field (∼4,000 km southward with respect to Australasian microtektites recovered at lower latitudes from deep sea sediments), thus implying a launch distance of nearly 12,000 km from the putative impact location in Indochina. From a broad perspective, results also reveal a contrasting behavior between microtektites from the Transantarctic Mountains, highly contaminated by extraneous Ar, and Australasian macroscopic tektites, weakly or negligibly contaminated. Although future dedicated experimental work, aimed at the definition of physical homogeneity of microtektites at the submicroscale and at the understanding of the true intra-particle spatial distribution of Ar isotopes are necessary, we speculatively hypothesize that the contrasting behavior between tektites and microtektites may reflect displacement in different environments.

Stirred not shaken; critical evaluation of a proposed Archean meteorite impact in West Greenland

Large meteorite impacts have a profound effect on the Earth's geosphere, atmosphere, hydrosphere and biosphere. It is widely accepted that the early Earth was subject to intense bombardment from 4.5 to 3.8 Ga, yet evidence for subsequent bolide impacts during the Archean Eon (4.0 to 2.5 Ga) is sparse. However, understanding the timing and magnitude of these early events is important, as they may have triggered significant change points to global geochemical cycles. The Maniitsoq region of southern West Greenland has been proposed to record a ∼3.0 Ga meteorite impact, which, if confirmed, would be the oldest and only known impact structure to have survived from the Archean. Such an ancient structure would provide the first insight into the style, setting, and possible environmental effects of impact bombardment continuing into the late Archean. Here, using field mapping, geochronology, isotope geochemistry, and electron backscatter diffraction mapping of 5,587 zircon grains from the Maniitsoq region (rock and fluvial sediment samples), we test the hypothesis that the Maniitsoq structure represents Earth's earliest known impact structure. Our comprehensive survey shows that previously proposed impact-related geological features, ranging from microscopic structures at the mineral scale to macroscopic structures at the terrane scale, as well as the age and geochemistry of the rocks in the Maniitsoq region, can be explained through endogenic (non-impact) processes. Despite the higher impact flux, intact craters from the Archean Eon remain elusive on Earth.

Potential mineral resources in the planets and preliminary discussion on planetary resource geology

了解并利用行星矿产资源、可持续永久开发太空成为行星科学与深空探测的一项重要研究任务。而行星矿产资源的开发利用，需要运用行星科学与地质学特别是矿床学的基础理论，利用行星观测、探测及开发技术方法，研究行星矿产资源形成演化规律，查明行星矿产资源的类型、特征、储量和分布规律；进行行星矿产资源的地质调查、岩石-矿石成分、结构与性能、元素赋存状态、开发利用条件评价与预测，为行星矿产资源开发与太空的可持续永久开发建设提供基础理论与关键技术方法。因此，行星矿产资源学是研究行星矿产资源的品种、类型与分布规律、行星矿产资源成因演化与比较行星成矿学、行星矿产资源勘查评价技术与开采利用工程学的交叉学科。笔者从行星资源地质学的视角，从地球与月球的层圈结构、演化历史、岩石组成与表生环境，研判月球可能产出的矿产资源类型。认为与月海玄武岩、月幔（柱）和陨石撞击成因的层状岩体与镁铁-超镁铁质小岩体有关的铬铁矿-铜镍钴硫化物-铂族元素-钒钛磁铁矿-金刚石矿产，KREEP岩以及月幔柱熔融上覆岩石圈所产生碱性岩相伴的铌-钽-铍-铀等稀有-稀土矿产，具有形成条件与产出可能，从而拓展可能的矿产类型、品种，从更宽广的视角研究月球矿产并规划月球基地建设资源供给。火星上由于水（以及可能存在的板块构造）的存在，除岩浆矿床之外，火星可能具备发育与化学风化沉积、次生富集作用以及变质作用有关矿产的形成条件，具有形成金属与非金属资源的禀赋，可与地球矿产相媲美。未来行星资源地质学应加强地质学、行星化学、行星地质学、行星物理学、矿业工程、冶金工程和材料学的交叉融合及理论应用，发展行星地质勘探方法与智能机器人工程技术，发展高/低温、高/低压、高辐照、低/微重力环境条件下样品采集、加工、多尺度测试分析理论与方法，培养行星资源地质资源与开发工程学科人才。;How to understand and utilize planetary mineral resources and make a sustainable and permanent development of space has become a new frontier research direction of planetary science. The exploration and development of planetary mineral resources require the understanding of the types, characteristics, reserves and distribution and evaluating development and utilization conditions of planetary mineral resources, by using the basic theories of planetary science and geology, especially economic geology, combined with planetary observation and exploration techniques. Therefore, Planetary Resource Geology (PRG) is an interdisciplinary subject, contains the study of the variety, type and distribution law of planetary mineral resources, genetic evolution and comparison of planetary mineral resources, planetary metallogeny, exploration and evaluation technology and mining and utilization engineering of PRG. From the perspective of PRG, we try to predict the possible types of mineral resources in Lunar from the similarity of Earth and Lunar in the lithosphere structure, the rock composition and the supergene environment. There should be the chromite, Cu-Ni-Co sulfide, PGE (platinum group element), V-Ti magnetite minerals related to the layered rock mass and mafic-ultramafic small rock mass of the origin of the lunar mantle (even mantle plume) and meteorite impact, the REE and Nb-Ta hosted by KREEP rocks, thus will hopefully expand the possible types and commodities and provide a broader resource perspective for the construction of the lunar bases. Due to existence of water and possible plate tectonics, Mars can host a variety of metallic and non-metallic mineral deposits related to magmatism, sedimentation, metamorphism, chemical weathering and secondary enrichment which has a lot in common with the Earth. In the future, the discipline of PRG should strengthen the cross-integration and theoretical application of geology, metallurgical engineering, materials science, planetary chemistry, planetary geology and planetary physics, develop planetary geological exploration technology, including intelligent robot engineering, sample collection, multi-scale test and analysis under extreme high/low temperature, high irradiation and low microgravity environment, and cultivate talents of planetary resources, geological resources development engineering.

From Destruction to Creation: Understanding Meteorite Impact Craters

From Destruction to Creation: Understanding Meteorite Impact Craters

Meteorite crater re-interpreted as iceberg pit in west-central Sweden

ABSTRACT This study shows the occurrence of numerous iceberg imprints on the bottom of former ice-dammed lakes in Härjedalen, west-central Sweden. Discussion of the genesis of the so-called “impact crater” known as the Tor structure at Torbygget, which is located in this area, motivated an examination of the area using high-resolution digital elevation models. Previous investigations have suggested that this crater was created by a meteorite impact about 2000 years ago, forming a semi-round depression. The results of our investigation clearly indicate that the feature was formed by a grounding iceberg, scouring the bed of an ice-dammed lake during deglaciation about 11 000-10 000 cal. BP. Geomorphic evidence of an ice-dammed lake (multiple and abundant well-developed shorelines) are consistent with earlier mapping efforts in the area. Furthermore, an abundance of geomorphological traces of iceberg activity is found within the paleo-ice-dammed lake basins. Based on this we suggest that the depression at Torbygget is not an impact crater but formed by a grounded iceberg.