133 results found
Raducan SD, Davison TM, Luther R, et al., 2019, The role of asteroid strength, porosity and internal friction in impact momentum transfer, ICARUS, Vol: 329, Pages: 282-295, ISSN: 0019-1035
McMullan S, Daly L, Collins GS, et al., 2019, THE UK FIREBALL NETWORK: STAGE TWO OF THE GLOBAL FIREBALL OBSERVATORY., 82nd Annual Meeting of the Meteoritical-Society (MetSoc), Publisher: WILEY, ISSN: 1086-9379
McMullan S, Collins GS, 2019, Uncertainty quantification in continuous fragmentation airburst models, ICARUS, Vol: 327, Pages: 19-35, ISSN: 0019-1035
Rae ASP, Collins G, Morgan J, Impact-induced porosity and micro-fracturing at the Chicxulub impact structure, Journal of Geophysical Research: Planets, ISSN: 2169-9097
Porosity and its distribution in impact craters has an important effect on the petrophysical properties of impactites: seismic wave-speeds and reflectivity, rock permeability, strength, and density. These properties are important for the identification of potential craters and the understanding of the process and consequences of cratering. The Chicxulub impact structure, recently drilled by the joint International Ocean Discovery Program and International Continental scientific Drilling Program Expedition 364, provides a unique opportunity to compare direct observations of impactites with geophysical observations and models. Here, we combine small scale petrographic and petrophysical measurements with larger scale geophysical measurements and numerical simulations of the Chicxulub impact structure. Our aim is to assess the cause of unusually high porosities within the Chicxulub peak ring and the capability of numerical impact simulations to predict the gravity signature and the distribution and texture of porosity within craters. We show that high porosities within the Chicxulub peak ring are primarily caused by shock-induced micro-fracturing. These fractures have preferred orientations, which can be predicted by considering the orientations of principal stresses during shock, and subsequent deformation during peak-ring formation. Our results demonstrate that numerical impact simulations, implementing the Dynamic Collapse Model of peak-ring formation, can accurately predict the distribution and orientation of impact-induced micro-fractures in large craters which plays an important role in the geophysical signature of impact structures.
Lyons RJ, Bowling TJ, Ciesla FJ, et al., 2019, The effects of impacts on the cooling rates of iron meteorites, Meteoritics and Planetary Science, Vol: 54, Pages: 1604-1618, ISSN: 1086-9379
© The Meteoritical Society, 2019. Iron meteorites provide a record of the thermal evolution of their parent bodies, with cooling rates inferred from the structures observed in the Widmanstätten pattern. Traditional planetesimal thermal models suggest that meteorite samples derived from the same iron core would have identical cooling rates, possibly providing constraints on the sizes and structures of their parent bodies. However, some meteorite groups exhibit a range of cooling rates or point to uncomfortably small parent bodies whose survival is difficult to reconcile with dynamical models. Together, these suggest that some meteorites are indicating a more complicated origin. To date, thermal models have largely ignored the effects that impacts would have on the thermal evolution of the iron meteorite parent bodies. Here we report numerical simulations investigating the effects that impacts at different times have on cooling rates of cores of differentiated planetesimals. We find that impacts that occur when the core is near or above its solidus, but the mantle has largely crystallized can expose iron near the surface of the body, leading to rapid and nonuniform cooling. The time period when a planetesimal can be affected in this way can range between 20 and 70 Myr after formation for a typical 100 km radius planetesimal. Collisions during this time would have been common, and thus played an important role in shaping the properties of iron meteorites.
Timms NE, Pearce MA, Erickson TM, et al., 2019, New shock microstructures in titanite (CaTiSiO5) from the peak ring of the Chicxulub impact structure, Mexico, CONTRIBUTIONS TO MINERALOGY AND PETROLOGY, Vol: 174, ISSN: 0010-7999
Derrick JG, Rutherford ME, Chapman DJ, et al., 2019, Investigating shock processes in bimodal powder compaction through modelling and experiment at the mesoscale, INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES, Vol: 163, Pages: 211-219, ISSN: 0020-7683
Bellucci JJ, Nemchin AA, Grange M, et al., 2019, Terrestrial-like zircon in a clast from an Apollo 14 breccia, Earth and Planetary Science Letters, Vol: 510, Pages: 173-185, ISSN: 0012-821X
© 2019 Elsevier B.V. A felsite clast in lunar breccia Apollo sample 14321, which has been interpreted as Imbrium ejecta, has petrographic and chemical features that are consistent with formation conditions commonly assigned to both lunar and terrestrial environments. A simple model of Imbrium impact ejecta presented here indicates a pre-impact depth of 30–70 km, i.e. near the base of the lunar crust. Results from Secondary Ion Mass Spectrometry trace element analyses indicate that zircon grains recovered from this clast have positive Ce/Ce ⁎ anomalies corresponding to an oxygen fugacity +2 to +4 log units higher than that of the lunar mantle, with crystallization temperatures of 771±88 to 810 ± 37 °C (2σ) that are unusually low for lunar magmas. Additionally, Ti-in-quartz and zircon calculations indicate a pressure of crystallization of 6.9±1.2 kbar, corresponding to a depth of crystallization of 167±27 km on the Moon, contradicting ejecta modelling results. Such low-T, high-fO 2 , and high-P have not been observed for any other lunar clasts, are not known to exist on the Moon, and are broadly similar to those found in terrestrial magmas. The terrestrial-like redox conditions inferred for the parental magma of these zircon grains and other accessory minerals in the felsite contrasts with the presence of Fe-metal, bulk clast geochemistry, and the Pb isotope composition of K-feldspar grains within the clast, all of which are consistent with a lunar origin. The dichotomy between redox conditions and the depth of origin inferred from the zircon compositions compared to the ejecta modelling necessitates a multi-stage petrogenesis. Two, currently unresolvable hypotheses for the origin and history of the clast are allowed by these data. The first postulates that the relatively oxidizing conditions were developed in a lunar magma, possibly by fractional crystallization and enrichment of incompatible elements in a fluid-rich
Urrutia-Fucugauchi J, Pérez-Cruz L, Morgan J, et al., 2019, Peering inside the peak ring of the Chicxulub Impact Crater—its nature and formation mechanism, Geology Today, Vol: 35, Pages: 68-72, ISSN: 0266-6979
© 2019 John Wiley & Sons Ltd, The Geologists' Association & The Geological Society of London The IODP-ICDP Expedition 364 drilled into the Chicxulub crater, peering inside its well-preserved peak ring. The borehole penetrated a sequence of post-impact carbonates and a unit of suevites and clast-poor impact melt rock at the top of the peak ring. Beneath this sequence, basement rocks cut by pre-impact and impact dykes, with breccias and melt, were encountered at shallow depths. The basement rocks are fractured, shocked and uplifted, consistent with dynamic collapse, uplift and long-distance transport of weakened material during collapse of the transient cavity and final crater formation.
Hopkins RT, Osinski GR, Collins GS, 2019, Formation of Complex Craters in Layered Targets With Material Anisotropy, JOURNAL OF GEOPHYSICAL RESEARCH-PLANETS, Vol: 124, Pages: 349-373, ISSN: 2169-9097
Rae ASP, Collins GS, Poelchau M, et al., 2019, Stress-Strain Evolution During Peak-Ring Formation: A Case Study of the Chicxulub Impact Structure, JOURNAL OF GEOPHYSICAL RESEARCH-PLANETS, Vol: 124, Pages: 396-417, ISSN: 2169-9097
Rutherford ME, Derrick JG, Chapman DJ, et al., 2019, Insights into local shockwave behavior and thermodynamics in granular materials from tomography-initialized mesoscale simulations, JOURNAL OF APPLIED PHYSICS, Vol: 125, ISSN: 0021-8979
Daubar I, Lognonné P, Teanby NA, et al., 2018, Impact-seismic investigations of the InSight mission, Space Science Reviews, Vol: 214, ISSN: 0038-6308
Impact investigations will be an important aspect of the InSight mission. One of the scientific goals of the mission is a measurement of the current impact rate at Mars. Impacts will additionally inform the major goal of investigating the interior structure of Mars. In this paper, we review the current state of knowledge about seismic signals from impacts on the Earth, Moon, and laboratory experiments. We describe the generalized physical models that can be used to explain these signals. A discussion of the appropriate source time function for impacts is presented, along with spectral characteristics including the cutoff frequency and its dependence on impact momentum. Estimates of the seismic efficiency (ratio between seismic and impact energies) vary widely. Our preferred value for the seismic efficiency at Mars is 5 × 10 − 4, which we recommend using until we can measure it during the InSight mission, when seismic moments are not used directly. Effects of the material properties at the impact point and at the seismometer location are considered. We also discuss the processes by which airbursts and acoustic waves emanate from bolides, and the feasibility of detecting such signals. We then consider the case of impacts on Mars. A review is given of the current knowledge of present-day cratering on Mars: the current impact rate, characteristics of those impactors such as velocity and directions, and the morphologies of the craters those impactors create. Several methods of scaling crater size to impact energy are presented. The Martian atmosphere, although thin, will cause fragmentation of impactors, with implications for the resulting seismic signals. We also benchmark several different seismic modeling codes to be used in analysis of impact detections, and those codes are used to explore the seismic amplitude of impact-induced signals as a function of distance from the impact site. We predict a measurement of the current impact flux will be possibl
Johnson BC, Andrews-Hanna JC, Collins GS, et al., 2018, Controls on the Formation of Lunar Multiring Basins, JOURNAL OF GEOPHYSICAL RESEARCH-PLANETS, Vol: 123, Pages: 3035-3050, ISSN: 2169-9097
Riller U, Poelchau MH, Rae ASP, et al., 2018, Rock fluidization during peak-ring formation of large impact structures, NATURE, Vol: 562, Pages: 511-+, ISSN: 0028-0836
Luther R, Zhu M-H, Collins G, et al., 2018, Effect of target properties and impact velocity on ejection dynamics and ejecta deposition, METEORITICS & PLANETARY SCIENCE, Vol: 53, Pages: 1705-1732, ISSN: 1086-9379
Collins GS, Rae ASP, Morgan JV, et al., 2018, THE FORMATION OF PEAK RINGS IN LARGE IMPACT CRATERS, 81st Annual Meeting of the Meteoritical-Society, Publisher: WILEY, Pages: 6215-6215, ISSN: 1086-9379
Derrick JG, LaJeunesse JW, Davison TM, et al., 2018, Mesoscale simulations of shock compaction of a granular ceramic: effects of mesostructure and mixed-cell strength treatment, MODELLING AND SIMULATION IN MATERIALS SCIENCE AND ENGINEERING, Vol: 26, ISSN: 0965-0393
Brooker LM, Balme MR, Conway SJ, et al., 2018, Clastic polygonal networks around Lyot crater, Mars: Possible formation mechanisms from morphometric analysis, Icarus, Vol: 302, Pages: 386-406, ISSN: 0019-1035
© 2017 The Authors Polygonal networks of patterned ground are a common feature in cold-climate environments. They can form through the thermal contraction of ice-cemented sediment (i.e. formed from fractures), or the freezing and thawing of ground ice (i.e. formed by patterns of clasts, or ground deformation). The characteristics of these landforms provide information about environmental conditions. Analogous polygonal forms have been observed on Mars leading to inferences about environmental conditions. We have identified clastic polygonal features located around Lyot crater, Mars (50°N, 30°E). These polygons are unusually large (>100 m diameter) compared to terrestrial clastic polygons, and contain very large clasts, some of which are up to 15 metres in diameter. The polygons are distributed in a wide arc around the eastern side of Lyot crater, at a consistent distance from the crater rim. Using high-resolution imaging data, we digitised these features to extract morphological information. These data are compared to existing terrestrial and Martian polygon data to look for similarities and differences and to inform hypotheses concerning possible formation mechanisms. Our results show the clastic polygons do not have any morphometric features that indicate they are similar to terrestrial sorted, clastic polygons formed by freeze-thaw processes. They are too large, do not show the expected variation in form with slope, and have clasts that do not scale in size with polygon diameter. However, the clastic networks are similar in network morphology to thermal contraction cracks, and there is a potential direct Martian analogue in a sub-type of thermal contraction polygons located in Utopia Planitia. Based upon our observations, we reject the hypothesis that polygons located around Lyot formed as freeze-thaw polygons and instead an alternative mechanism is put forward: they result from the infilling of earlier thermal contraction cracks by wind-blown mat
Derrick JG, Rutherford ME, Davison TM, et al., 2018, Interrogating Heterogeneous Compaction of Analogue Materials at the Mesoscale Through Numerical Modeling and Experiments, 20th Biennial Conference of the Topical-Group of the American-Physical-Society (APS) on Shock Compression of Condensed Matter (SCCM), Publisher: AMER INST PHYSICS, ISSN: 0094-243X
Holm-Alwmark S, Rae ASP, Ferriere L, et al., 2017, Combining shock barometry with numerical modeling: Insights into complex crater formation-The example of the Siljan impact structure (Sweden), METEORITICS & PLANETARY SCIENCE, Vol: 52, Pages: 2521-2549, ISSN: 1086-9379
Muxworthy AR, Bland PA, Davison TM, et al., 2017, Evidence for an impact-induced magnetic fabric in Allende, and exogenous alternatives to the core dynamo theory for Allende magnetization, METEORITICS & PLANETARY SCIENCE, Vol: 52, Pages: 2132-2146, ISSN: 1086-9379
Kring DA, Claeys P, Gulick SPS, et al., 2017, Chicxulub and the Exploration of Large Peak-Ring Impact Craters through Scientific Drilling, GSA Today, Vol: 27, Pages: 4-8, ISSN: 1052-5173
The Chicxulub crater is the only well-preserved peak-ring crater on Earth and linked, famously, to the K-T or K-Pg mass extinction event. For the first time, geologists have drilled into the peak ring of that crater in the International Ocean Discovery Program and International Continental Scientific Drilling Program (IODP-ICDP) Expedition 364. The Chicxulub impact event, the environmental calamity it produced, and the paleobiological consequences are among the most captivating topics being discussed in the geologic community. Here we focus attention on the geological processes that shaped the ~200-km-wide impact crater responsible for that discussion and the expedition’s first year results.
Melosh HJ, Bland PA, Collins GS, et al., 2017, A SPECULATIVE "FIEFDOM" MODEL FOR CHONDRITE ORIGINS., 80th Annual Meeting of the Meteoritical-Society, Publisher: WILEY, Pages: A232-A232, ISSN: 1086-9379
Collins GS, Lynch E, McAdam R, et al., 2017, A numerical assessment of simple airblast models of impact airbursts, METEORITICS & PLANETARY SCIENCE, Vol: 52, Pages: 1542-1560, ISSN: 1086-9379
Watters WA, Hundal CB, Radford A, et al., 2017, Dependence of secondary crater characteristics on downrange distance: High-resolution morphometry and simulations, JOURNAL OF GEOPHYSICAL RESEARCH-PLANETS, Vol: 122, Pages: 1773-1800, ISSN: 2169-9097
Rae ASP, Collins GS, Grieve RAF, et al., 2017, Complex crater formation: Insights from combining observations of shock pressure distribution with numerical models at the West Clearwater Lake impact structure, METEORITICS & PLANETARY SCIENCE, Vol: 52, Pages: 1330-1350, ISSN: 1086-9379
Forman LV, Bland PA, Timms NE, et al., 2017, Defining the mechanism for compaction of the CV chondrite parent body, GEOLOGY, Vol: 45, Pages: 559-562, ISSN: 0091-7613
Rutherford ME, Chapman DJ, Derrick JG, et al., 2017, Probing the early stages of shock-induced chondritic meteorite formation at the mesoscale, SCIENTIFIC REPORTS, Vol: 7, ISSN: 2045-2322
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