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TEMPERATURE CONSTRAINT OF THE MISTASTIN LAKE IMPACT STRUCTURE IMPACT MELT ROCKS

Impact melt is a product of hypervelocity cratering events formed by the instantaneous melting of near-surface target rocks. The temperatures of impact melt upon formation are believed to be superheated, vastly exceeding the liquidus temperature of igneous rocks formed via endogenic processes. However, quantitative understanding of the formation and duration of superheated temperatures remains incomplete. To date, only one datum on the hottest post-shock temperature (>2370 °C) has been derived by Timms et al. (2017) [1]. These authors studied the microstructures and crystallographic orientations preserved within a rim of vermicular ZrO2 of a zircon grain entrained within impact glass at the Mistastin Lake impact structure, Canada. Diagnostic crystallographic orientation indicated the presence of cubic zirconia, requiring a minimum temperature for the impact melt of >2370°C from the dissociation of zircon to cubic zirconia and liquid SiO2. With only one temperature datum, it cannot be stated whether the temperature of the impact melt sheet was homogenous across the entire structure or if the thermal history of the melt varied with spatial distribution. In this study, we present a preliminary investigation of 70 zircon grains, 22 of which exhibit rims of vermicular ZrO2 dissociation textures, similar to those studied by Timms et al. (2017). To acquire a more accurate temperature profile representative of impact melt, zircon crystals were collected from different types of impact melt bearing units, including additional samples of the impact glass studied by Timms et al. (2017). Of the 22 zircon grains with dissociation textures, at least 4 grains in the impact glass show diagnostic evidence of pre-existing cubic zirconia, and 1 grain from a glass-bearing breccia exhibits granular zircon textures, possible evidence of a transition from high-P to high-T conditions. These results show the heterogeneous post-shock temperature distribution of superheated impact melt within the Mistastin impact structure. [1] Timms, N.E., Erickson, T.M., Zanetti, M.R., Pearce, M.A., Cayron, C., Cavosie, A.J., Reddy, S.M., Wittmann, A. and Carpenter, P.K., 2017. Cubic zirconia in> 2370° C impact melt records Earth's hottest crust. Earth and Planetary Science Letters, 477, pp.52-58.

rock↗
DOE OSTI2020

Balancing Water Sustainability and Productivity Objectives in Microalgae Cultivation: Siting Open Ponds by Considering Seasonal Water-Stress Impact Using AWARE-US

Microalgae have great potential as an energy crop. Scaling-up algal biofuel production in the United States (US) should be done with careful attention to water stress. This study evaluates the regional and seasonal water-stress impact of potential algae-pond deployments in the US. Three site-selection strategies focusing on biomass yield, water-use efficiency (WUE), and water-stress impact, respectively, are applied and compared to meet a US algae biomass production target of 30 million metric tons/yr ash-free dry weight, which converts to 20.8 billion L renewable diesel, via hydrothermal liquefaction. Ranking algae ponds based on biomass yield leads to freshwater consumption of 2.66 km3/yr, resulting in the highest water-stress impact (39.1 US equivalent km3). Under the WUE scenario, water consumption is reduced by 81%, but biomass yield is reduced by 12%. In contrast, adding a water-stress constraint to the biomass-yield ranking reduces water consumption by 50% and water-stress impact by 97%, with a small yield reduction (1.7%). Results show that pond location has a significant effect on water stress and that water stress is not proportional to water consumption or yield. Furthermore, capturing seasonal water patterns is critical for planning because sites in water-abundant regions can have short-term but significant water-stress impacts.

algae, Biofuel, water scarcity footprint, hydrothe↗
DOE OSTI2017

Audience Based View of Publication Impact

With increasing pressure to demonstrate a return on investment, scienti c user facilities and government funded research projects must strive to demonstrate positive impact of their research on oth- ers. Historically, citation counts and journal impact factor have been widely used as a single quantitative measure of impact. However, with the expansion of various modes of communication, citation counts no longer hold as much merit as a single measure of impact. This work seeks to expand on citation counts by considering the audience to which a publication draws attention. Based on commu- nication mode, there are various audiences that may be "impacted" but those audiences are not fully captured by citation count. Conse- quently, we propose that impact measures for publications should be oriented around the audience with quanti able measures based on the various communication modes.

Patton, Robert↗
NASA NTRS1993

Long-term microparticle flux variability indicated by comparison of Interplanetary Dust Experiment (IDE) timed impacts for LDEF's first year in orbit with impact data for the entire 5.77-year orbital lifetime

The electronic sensors of the Interplanetary Dust Experiment (IDE) recorded precise impact times and approximate directions for submicron to approximately 100 micron size particles on all six primary sides of the spacecraft for the first 346 days of the LDEF orbital mission. Previously-reported analyses of the timed impact data have established their spatio-temporal features, including the demonstration that a preponderance of the particles in this regime are orbital debris and that a large fraction of the debris particles are encountered in megameter-size clouds. Short-term fluxes within such clouds can rise several orders of magnitude above the long-term average. These unexpectedly large short-term variations in debris flux raise the question of how representative an indication of the multi-year average flux is given by the nearly one year of timed data. One of the goals of the IDE was to conduct an optical survey of impact sites on detectors that remained active during the entire LDEF mission, to obtain full-mission fluxes. We present here the comparisons and contrasts among the new IDE optical survey impact data, the IDE first-year timed impact data, and impact data from other LDEF micrometeoroid and debris experiments. The following observations are reported: (1) the 5.77 year long-term integrated microparticle impact fluxes recorded by IDE detectors matched the integrated impact fluxes measured by other LDEF investigators for the same period; (2) IDE integrated microparticle impact fluxes varied by factors from 0.5 to 8.3 for LDEF days 1-346, 347-2106 and 1-2106 (5.77 years) on rows 3 (trailing edge, or West), 6 (South side), 12 (North side), and the Earth and Space ends; and (3) IDE integrated microparticle impact fluxes varied less than 3 percent for LDEF days 1-346, 347-2106 and 1-2106 (5.77 years) on row 9 (leading edge, or East). These results give further evidence of the accuracy and internal consistency of the recorded IDE impact data. This leads to the further conclusion that the utility of long-term ratios for impacts on various sides of a stabilized satellite in low Earth orbit (LEO) is extremely limited. These observations and their consequences highlight the need for continuous, real time monitoring of the dynamic microparticle environment in LEO.

Simon, Charles G.↗
NASA NTRS2020

Constraining the Temperature of Impact Melt from the Mistastin Lake Impact Structure Using Zircon Crystal Structures

Impact melt is a product of hyper-velocity impact events formed by the instantaneous melting of near-surface target rocks. Constraining the temperature of impact melt is vital to understanding its prograde heating and cooling history, which can have implications for inferring the environment of early Earth ~4.0 billion years ago when microbial life potentially arose. To date, only one datum on the initial impact melt temperature has been derived by Timms et al. These authors studied zirconia microstructures and crystallographic orientations that revealed the former presence of cubic zirconia, found in a black impact glass at the Mistastin Lake impact structure, Canada. The presence of cubic zirconia indicates a minimum temperature for the impact melt of >2370°C from the dissociation temperature of zircon to cubic zirconia and liquid SiO2. With only one temperature datum, it is still difficult to constrain the entire temperature range experienced during the impact melting process; from its instantaneous formation to thermal equilibrium with the “cold” clasts collected along the crater floor and walls. In addition, obtaining a temperature value from only one type of impactite limits the inferred temperature range, because each impactite experiences a different cooling history. In this study, we present a preliminary investigation of 61 zircon crystals, 14 of which are similar to those studied by Timms et al., from the Mistastin Lake impact structure. To acquire a more accurate temperature profile representative of impact melt, zircon crystals were collected from different types of impactites containing impact melt, including additional samples of the black impact glass studied by Timms et al.

Tolometti, G. D.↗
DOE OSTI2018

Impacts of Glutaraldehyde on Microbial Community Structure and Degradation Potential in Streams Impacted by Hydraulic Fracturing

The environmental impacts of hydraulic fracturing, particularly those of surface spills in aquatic ecosystems, are not fully understood. The goals of this study were to (1) understand the effect of previous exposure to hydraulic fracturing fluids on aquatic microbial community structure and (2) examine the impacts exposure has on biodegradation potential of the biocide glutaraldehyde. Microcosms were constructed from hydraulic fracturing-impacted and nonhydraulic fracturing-impacted streamwater within the Marcellus shale region in Pennsylvania. Microcosms were amended with glutaraldehyde and incubated aerobically for 56 days. Microbial community adaptation to glutaraldehyde was monitored using 16S rRNA gene amplicon sequencing and quantification by qPCR. Abiotic and biotic glutaraldehyde degradation was measured using ultra-performance liquid chromatography--high resolution mass spectrometry and total organic carbon. It was found that nonhydraulic fracturing-impacted microcosms biodegraded glutaraldehyde faster than the hydraulic fracturing-impacted microcosms, showing a decrease in degradation potential after exposure to hydraulic fracturing activity. Hydraulic fracturing-impacted microcosms showed higher richness after glutaraldehyde exposure compared to unimpacted streams, indicating an increased tolerance to glutaraldehyde in hydraulic fracturing impacted streams. Beta diversity and differential abundance analysis of sequence count data showed different bacterial enrichment for hydraulic fracturing-impacted and nonhydraulic fracturing-impacted microcosms after glutaraldehyde addition. These findings demonstrated a lasting effect on microbial community structure and glutaraldehyde degradation potential in streams impacted by hydraulic fracturing operations.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2020

Impacts of Climate Change on Energy Systems in Global and Regional Scenarios

A growing number of studies report the impact of climate change on the supply, demand, transport, and cost of energy. However, there is lack of comprehensive overview and understanding of climate change impacts on energy across technologies and scales. Here, we conduct a systematic assessment of results from 186 papers on potential impacts of climate change on energy. Results show that increased cooling demand and decreased heating demand is anticipated globally. Similarly, increases in bio-energy and hydro power and a possible decrease in thermal electricity supply is projected. Overall changes in heating and cooling demand, increased thermal cooling, and reduced hydropower supply in Europe, India and Latin America are projected 35 at the regional scale. Furthermore, our review revealed that studies use a wide range of inconsistent methods and data sources. To move forward, the study proposes a consistent multi-model assessment framework for a comprehensive understanding of climate impacts on energy.

Yalew, Seleshi G.↗
NASA NTRS1992

The use of impact force as a scale parameter for the impact response of composite laminates

The building block approach is currently used to design composite structures. With this approach, the data from coupon tests is scaled up to determine the design of a structure. Current standard impact tests and methods of relating test data to other structures are not generally understood and are often used improperly. A methodology is outlined for using impact force as a scale parameter for delamination damage for impacts of simple plates. Dynamic analyses were used to define ranges of plate parameters and impact parameters where quasi-static analyses are valid. These ranges include most low velocity impacts where the mass of the impacter is large and the size of the specimen is small. For large mass impacts of moderately thick (0.35 to 0.70 cm) laminates, the maximum extent of delamination damage increased with increasing impact force and decreasing specimen thickness. For large mass impact tests at a given kinetic energy, impact force and hence delamination size depends on specimen size, specimen thickness, boundary conditions, and indenter size and shape. If damage is reported in terms of impact force instead of kinetic energy, large mass test results can be applied directly to other plates of the same size.

Jackson, Wade C.↗
NASA NTRS1992

The use of impact force as a scale parameter for the impact response of composite laminates

The building block approach is currently used to design composite structures. With this approach, the data from coupon tests are scaled up to determine the design of a structure. Current standard impact tests and methods of relating test data to other structures are not generally understood and are often used improperly. A methodology is outlined for using impact force as a scale parameter for delamination damage for impacts of simple plates. Dynamic analyses were used to define ranges of plate parameters and impact parameters where quasi-static analyses are valid. These ranges include most low-velocity impacts where the mass of the impacter is large, and the size of the specimen is small. For large-mass impacts of moderately thick (0.35-0.70 cm) laminates, the maximum extent of delamination damage increased with increasing impact force and decreasing specimen thickness. For large-mass impact tests at a given kinetic energy, impact force and hence delamination size depends on specimen size, specimen thickness, boundary conditions, and indenter size and shape. If damage is reported in terms of impact force instead of kinetic energy, large-mass test results can be applied directly to other plates of the same thickness.

Jackson, Wade C.↗
NASA NTRS2009

Pulling Marbles from a Bag: Deducing the Regional Impact History of the SPA Basin from Impact Melt Rocks

The South Pole-Aitken (SPA) basin is an important target for absolute age-dating. Vertical and lateral impact mixing ensures that regolith within SPA will contain rock fragments from SPA itself, local impact craters, and faraway giant basins. About 20% of the regolith at any given site is foreign [1, 2], but much of this material will be cold ejecta, not impact melt. We calculated the fraction of contributed impact melt using scaling laws to estimate the amount and provenance of impact melt, demonstrating that SPA melt is the dominant impact melt rock (>70%) likely to be present. We also constructed a statistical model to illustrate how many randomly-selected impact-melt fragments would need to be dated, and with what accuracy, to confidently reproduce the impact history of a site. A detailed impact history becomes recognizable after a few hundred to a thousand randomly-selected marbles, however, it will be useful to have more information (e.g. compositional, mineralogical, remote sensing) to group fragments. These exercises show that SPA melt has a high probability of being present in a scoop sample and that dating of a few hundred to a thousand impact-melt fragments will yield the impact history of the SPA basin.

Cohen, Barbara A.↗
DOE OSTI2017

Climate impacts on hydropower and consequences for global electricity supply investment needs

Recent progress in global scale hydrological and dam modeling has allowed for the study of climate change impacts on global hydropower production. Here we explore the possible consequences of these impacts for the electricity supply sector. Regional hydropower projections are developed for two emissions scenarios by forcing a coupled global hydrological and dam model with downscaled, bias-corrected climate realizations derived from sixteen general circulation models. Consequent impacts on power sector composition and associated emissions and investment costs are explored using the Global Change Assessment Model (GCAM). Changes in hydropower generation resulting from climate change can shift power demands onto and away from carbon intensive technologies, resulting in significant impacts on power sector CO2 emissions for certain world regions—primarily those located in Latin America, as well as Canada and parts of Europe. Reduced impacts of climate change on hydropower production under a low emissions scenario coincide with increased costs of marginal power generating capacity—meaning impacts on power sector investment costs are similar for high and low emissions scenarios. Individual countries where impacts on investment costs imply significant risks or opportunities are identified.

Turner, Sean W. D. (ORCID:0000000344009800)↗
DOE OSTI2023

Hydropower Potential at Non-Powered Dams: A Multi-Criteria Decision Analysis Tool based on Grid, Community, Industry, and Environmental Impacts

Non-powered dams (NPDs) are dams that do not include hydraulic turbine (hydropower) equipment. Currently, there are more than 80,000 such dams in the United States, which provide a variety of non-energy benefits, including flood control, water supply, navigation, and recreation. Approximately 500 of these NPDs are identified as having the potential to add hydropower generation (totaling up to a capacity of more than 8200 MW). A large share of investment costs and environmental impacts of dam construction have already been incurred at these NPDs. Hence, adding power to the existing dam structure is hypothesized to be achieved at a lower cost, with less risk, and a shorter timeframe than the development required for new dam construction. The abundance of NPDs, the associated environmental favorability, and cost advantages, combined with the reliability, predictability, and dispatchability of hydropower, make NPDs a strong candidate in the nation’s renewable energy portfolio. To assess the NPD to hydropower conversion potential, in this study, we developed a GIS-based multi-criterial decision analysis tool, which allows users to rank these NPDs based on the grid, community, industry, and environmental impacts (i.e., GCIE impacts). This web-based interactive tool (developed using open-source Python and JavaScript) lets the user choose from a wide range of features to define each of the GCIE impact scores through a user-friendly graphical user interface. These features are related to dam operation, hydropower generation opportunity, power market economy, social vulnerability and risk, proximity to critical infrastructure and energy generating facilities, environmental concerns (air, water, and critical habitat), and exposure to natural hazards. The overall priority score of NPDs is calculated based on user-defined weights for each of the GCIE impact scores. Besides ranking NPDs, the tool can also be used to estimate the energy-storage feasibility (battery, hydrogen, and pump-storage hydropower) at each of the potential sites.

13 HYDRO ENERGY↗
NASA NTRS1994

Coincidence in Time of the Imbrium Basin Impact and Apollo 15 KREEP Volcanic Flows: The Case for Impact-Induced Melting

On the Earth there is no firm evidence that impacts can induce volcanic activity. However, the Moon does provide a very likely example of volcanism induced by an immense impact: the Imbrium basin-forming event was immediately succeeded by a crustal partial melting event that released basalt flows characterized by K, rare-earth elements (REE), P, and other trace elements (KREEP) over a wide area creating the Apennine Bench Formation. Impact total melting is inconsistent with the chemistry and petrography of these Apollo 15 KREEP basalts, which are quite unlike the impact melts recognized at Taurus-Littrow as the products of the Serenitatis impact. The Imbrium impact and the KREEP volcanic events are indistinguishable in radiometric age, and thus the volcanism occurred less than about 20 Ma later than the impact (less than about 0.5% of lunar history). The sample record indicates that such KREEP volcanism had not occurred in the region prior to that time, and demonstrates that it never occurred again. Such coincidence in time implies a genetic relationship between the two events, and impact-induced partial melting or release appears to be the only feasible process. Nonetheless, the characteristics of the Apollo 15 KREEP basalts suggest large-degree crustal melting that is not easy to reconcile with the inability of lunar pressure release alone to induce partial melting unless the source was already almost at its melting point. The earliest history of the surface of the Earth, at a time of greater internal heat production and basin-forming impacts, could have been greatly influenced by impact-induced melting.

Ryder, Graham↗
DOE OSTI2018

Mining project's economic impact on local communities, as a social determinant of health: A documentary analysis of environmental impact statements

Australian mining developments cause indirect economic impacts on nearby communities leading to poor health and wellbeing of local residents. Economic instability is a recognised social determinant of health (SDoH); however, SDoHs are rarely considered adequately in Environmental Impact Assessments (EIAs). This research aimed to determine the extent economic impacts as a SDoH are considered in three Environmental Impact Statements (EISs) of mining projects in the New South Wales, Australia. We adopted an exploratory case study design following Yin (2012). Three cases in New South Wales, Australia, were purposively sampled as being of concern to the local community who had sought legal advice about the content of the EIS (although not necessarily for health reasons). Two were open cut mines: Watermark located in the Liverpool Plains and Warkworth Continuation in the Hunter Valley Region. The third is a comparative case – the underground Mandalong Southern Extension located in Lake Macquarie. We adapted a health-focused EIA coding framework to investigate how economic indicators as SDoH were explicitly mentioned in EISs and applied this to the three cases. Economic indicators as SDoH were rarely considered. There was a greater focus on population characteristics rather than the potential economic impacts of the mining projects on the communities. Causal association of economic determinants and health outcomes were insufficiently reported compared to best practice, and health data were not used to inform assessments. Despite two EISs – Warkworth Continuation and Watermark – associating some economic indicators to health outcomes, impacts were not adequately discussed when compared to the known literature on economic impacts of mines. Our findings show that the three EISs were inadequately utilised to determine economic impacts of mining projects on the health and wellbeing of local communities. The evidence base linking economic impacts of mines to health is underdeveloped, which compromises assessing the quality of economic coverage in EISs. EIA scoping should enable sufficient inclusion of broader determinants of health using appropriate methodology, and the economic-focused content of EISs should be subject to rigorous peer-review process to fully inform government approvals for projects. Our methods lend themselves to research in other contexts to investigate the quality of EIAs.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS2017

Experimental Hypervelocity Dust Impact in Olivine: FIB/TEM Characterization of Micron-Scale Craters with Comparison to Natural and Laser-Simulated Small-Scale Impact Effects

The space weathering of regoliths on airless bodies and the formation of their exospheres is driven to a large extent by hypervelocity impacts from the high relative flux of micron to sub-micron meteoroids that comprise approximately 90 percent of the solar system meteoroid population. Laboratory hypervelocity impact experiments are crucial for quantifying how these small impact events drive space weathering through target shock, melting and vaporization. Simulating these small scale impacts experimentally is challenging because the natural impactors are both very small and many have velocities above the approximately 8 kilometers-per-second limit attainable by conventional chemical/light gas accelerator technology. Electrostatic "dust" accelerators, such as the one recently developed at the Colorado Center for Lunar Dust and Atmospheric Studies (CCLDAS), allow the experimental velocity regime to be extended up to tens of kilometers-per-second. Even at these velocities the region of latent target damage created by each impact, in the form of microcraters or pits, is still only about 0.1 to 10 micrometers in size. Both field-emission analytical scanning electron microscopy (FE-SEM) and advanced field-emission scanning transmission electron microscopy (FE-STEM) are uniquely suited for characterizing the individual dust impact sites in these experiments. In this study, we have used both techniques, along with focused ion beam (FIB) sample preparation, to characterize the micrometer to nanometer scale effects created by accelerated dust impacts into olivine single crystals. To our knowledge this work presents the first TEM-scale characterization of dust impacts into a key solar system silicate mineral using the CCLDAS facility. Our overarching goal for this work is to establish a basis to compare with our previous results on natural dust-impacted lunar olivine and laser-irradiated olivine.

Christoffersen, R.↗
DOE OSTI2018

Concussion, microvascular injury, and early tauopathy in young athletes after impact head injury and an impact concussion mouse model

The mechanisms underpinning concussion, traumatic brain injury, and chronic traumatic encephalopathy, and the relationships between these disorders, are poorly understood. We examined post-mortem brains from teenage athletes in the acute-subacute period after mild closed-head impact injury and found astrocytosis, myelinated axonopathy, microvascular injury, perivascular neuroinflammation, and phosphorylated tau protein pathology. To investigate causal mechanisms, we developed a mouse model of lateral closed-head impact injury that uses momentum transfer to induce traumatic head acceleration. Unanaesthetized mice subjected to unilateral impact exhibited abrupt onset, transient course, and rapid resolution of a concussion-like syndrome characterized by altered arousal, contralateral hemiparesis, truncal ataxia, locomotor and balance impairments, and neurobehavioural deficits. Experimental impact injury was associated with axonopathy, blood–brain barrier disruption, astrocytosis, microgliosis (with activation of triggering receptor expressed on myeloid cells, TREM2), monocyte infiltration, and phosphorylated tauopathy in cerebral cortex ipsilateral and subjacent to impact. Phosphorylated tauopathy was detected in ipsilateral axons by 24 h, bilateral axons and soma by 2 weeks, and distant cortex bilaterally at 5.5 months post-injury. Impact pathologies co-localized with serum albumin extravasation in the brain that was diagnostically detectable in living mice by dynamic contrast-enhanced MRI. These pathologies were also accompanied by early, persistent, and bilateral impairment in axonal conduction velocity in the hippocampus and defective long-term potentiation of synaptic neurotransmission in the medial prefrontal cortex, brain regions distant from acute brain injury. Surprisingly, acute neurobehavioural deficits at the time of injury did not correlate with blood–brain barrier disruption, microgliosis, neuroinflammation, phosphorylated tauopathy, or electrophysiological dysfunction. Furthermore, concussion-like deficits were observed after impact injury, but not after blast exposure under experimental conditions matched for head kinematics. Computational modelling showed that impact injury generated focal point loading on the head and seven-fold greater peak shear stress in the brain compared to blast exposure. Moreover, intracerebral shear stress peaked before onset of gross head motion. By comparison, blast induced distributed force loading on the head and diffuse, lower magnitude shear stress in the brain. We conclude that force loading mechanics at the time of injury shape acute neurobehavioural responses, structural brain damage, and neuropathological sequelae triggered by neurotrauma. These results indicate that closed-head impact injuries, independent of concussive signs, can induce traumatic brain injury as well as early pathologies and functional sequelae associated with chronic traumatic encephalopathy. These results also shed light on the origins of concussion and relationship to traumatic brain injury and its aftermath.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS1992

Basaltic impact melts in the Apollo collections: How many impacts and which events are recorded?

Many of the rocks in the Apollo collections from the lunar highlands are impact melt breccias of basaltic bulk composition. They are known by a variety of names including low-K Fra Mauro basalt, VHA basalt, and basaltic impact melts. These rocks have been studied to understand the compositional nature of the lunar crust, to decipher the processes of large body impact, and to comprehend the record of impact bombardment of the Moon. Study of terrestrial craters has led to a model for impact melt generation whereby target lithologies are totally melted during impact. The impact melt makes up a few percent of the total volume of crater material; superheated silicate liquids of the impact melt have extremely low viscosities and mix intimately. This mixing thoroughly homogenizes the melt chemically during the excavation of the crater. Colder, unmelted debris is overridden by the melt sheet as the crater cavity grows. Incorporation of these cold clasts rapidly chills the melt, with zones of greater and lesser amounts of clasts being primarily responsible for modestly differing thermal regimes. The net effect of this process is the production of a suite of rocks that have extreme chemical homogeneity, but wide petrographic diversity. Strict application of this model to the petrogenesis of basaltic impact melts from the Moon has some fairly significant consequences for how we interpret early lunar history. The consequences are briefly discussed.

Spudis, Paul D.↗
NASA NTRS1993

Post-impact alteration of the Manson impact structure

Core materials from the Manson impact site (Manson, Iowa) are examined in order to evaluate post-impact alteration processes. Diagenetic interpretation of post-impact events is based on petrologic, mineralogic, and geochemical investigation of core materials including the following: target strata, disturbed and disrupted strata, ejecta, breccias, microbreccias, and impact melt. The diagenetic study utilizes research cores obtained by the continental scientific drilling project (CSDP) at the Manson structure, as well as core and cuttings of related materials. Samples include impactites (breccias, microbreccias, and melt material), crater fill material (sedimentary clast breccias), disturbed and disrupted target rocks, and reference target material (Amoco Eisheid No. 1 materials). The study of multiple cores will permit development of a regional picture of post-impact thermal history. The specific objectives are as follows: (1) provide a detailed description of authigenic and alteration mineralogy from diverse lithologies encountered in research drill cores at the Manson impact structure, and (2) identify and relate significant post-impact mineral alteration to post-impact thermal regime (extent and duration). Results will provide mineralogical and geochemical constraints on models for post-impact processes including the following: infilling of the crater depression; cooling and hydrothermal alteration of melt rocks; and subsequent long-term, low-temperature alteration of target rocks, breccias, and melt rocks. Preliminary petrologic and x-ray diffraction examination of fracture linings and void fillings from research core M1 indicate the presence of quartz, chlorite, mixed-layer clays, gypsum/anhydrite, calcite, and minor pyrite.

Crossey, L. J.↗