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Author: Michael Raymond Zanetti Publisher: ISBN: Category : Cratering Languages : en Pages : 0
Book Description
The formation of an impact crater ejecta blanket can be viewed as a form of organized chaos. Material that is ejected from a crater is heavily brecciated, but falls back to the surface along ballistic trajectories, generally preserving an inverted sense of the original stratigraphy. As the ejecta re-impacts the area surrounding the crater it forms a thick blanket of ejected material and reworked target surface that gradually thins away from the crater rim. Within the crater, crater modification processes, such as wall terrace formation and impact melt drainage, transform the crater in expectable ways. The approach adopted in this research is to use what is known about impact cratering and ejecta emplacement processes to geologically map craters on the Moon using remote-sensing data, determine the timing of individual impacts on the Moon, and investigate terrestrial impact melt glass. Research has been divided into three parts: 1) a detailed geomorphologic and geologic map of the lunar crater Aristarchus; 2) detailed crater size-frequency distribution measurements on the ejecta blankets of the lunar craters Aristarchus and Tycho; and 3) characterization of zircon decomposition in impact melt glass from the Mistastin Lake impact structure, Labrador, Canada. Mapping the geomorphology and geology of Aristarchus has shown that there are differences in the distribution of morphologic and compositional units related to pre-existing topography. I use the basic principles of inverted stratigraphy and remote-sensing data to investigate the geology of the subsurface material excavated by the crater and determine that Aristarchus likely excavated a buried pluton, or hypabyssal intrusive body, related to the large, possibly bi-modal, Cobra Head volcanic complex on the southern Aristarchus Plateau. Measuring crater size-frequency distributions on the ejecta blankets of Aristarchus and Tycho were done to determine the timing of these impacts; however, my measurements revealed that there is a significant difference in crater density, irrespective of crater diameter, between impact melt and ejecta blanket units. I show that the difference in crater density between these units can most likely be explained by a mechanism of self-secondary cratering, where late-arriving fragments of ejecta crater the surface of the ejecta blanket after it forms, but prior to the arrival of impact melt flows. These measurements call into question the long-held notion that ejecta blankets represent completely resurfaced units through ballistic sedimentation, free of impact craters immediately after formation, and these measurements suggest that cratering flux over the last billion years of the Solar System may be considerably lower. Lastly, I use field observations and a number of state-of-the-art laboratory analyses of a sample of impact melt glass from the Mistastin Lake impact structure to study the decomposition of zircon grains and the provenance of the impact melt. From my measurements, I show that zircon grains from a mangerite target rock were entrained in a superheated melt of very low viscosity and quenched, preserving high temperature mineral phases, and revealing how zircon grains undergo decomposition in a natural sample.
Author: Michael Raymond Zanetti Publisher: ISBN: Category : Cratering Languages : en Pages : 0
Book Description
The formation of an impact crater ejecta blanket can be viewed as a form of organized chaos. Material that is ejected from a crater is heavily brecciated, but falls back to the surface along ballistic trajectories, generally preserving an inverted sense of the original stratigraphy. As the ejecta re-impacts the area surrounding the crater it forms a thick blanket of ejected material and reworked target surface that gradually thins away from the crater rim. Within the crater, crater modification processes, such as wall terrace formation and impact melt drainage, transform the crater in expectable ways. The approach adopted in this research is to use what is known about impact cratering and ejecta emplacement processes to geologically map craters on the Moon using remote-sensing data, determine the timing of individual impacts on the Moon, and investigate terrestrial impact melt glass. Research has been divided into three parts: 1) a detailed geomorphologic and geologic map of the lunar crater Aristarchus; 2) detailed crater size-frequency distribution measurements on the ejecta blankets of the lunar craters Aristarchus and Tycho; and 3) characterization of zircon decomposition in impact melt glass from the Mistastin Lake impact structure, Labrador, Canada. Mapping the geomorphology and geology of Aristarchus has shown that there are differences in the distribution of morphologic and compositional units related to pre-existing topography. I use the basic principles of inverted stratigraphy and remote-sensing data to investigate the geology of the subsurface material excavated by the crater and determine that Aristarchus likely excavated a buried pluton, or hypabyssal intrusive body, related to the large, possibly bi-modal, Cobra Head volcanic complex on the southern Aristarchus Plateau. Measuring crater size-frequency distributions on the ejecta blankets of Aristarchus and Tycho were done to determine the timing of these impacts; however, my measurements revealed that there is a significant difference in crater density, irrespective of crater diameter, between impact melt and ejecta blanket units. I show that the difference in crater density between these units can most likely be explained by a mechanism of self-secondary cratering, where late-arriving fragments of ejecta crater the surface of the ejecta blanket after it forms, but prior to the arrival of impact melt flows. These measurements call into question the long-held notion that ejecta blankets represent completely resurfaced units through ballistic sedimentation, free of impact craters immediately after formation, and these measurements suggest that cratering flux over the last billion years of the Solar System may be considerably lower. Lastly, I use field observations and a number of state-of-the-art laboratory analyses of a sample of impact melt glass from the Mistastin Lake impact structure to study the decomposition of zircon grains and the provenance of the impact melt. From my measurements, I show that zircon grains from a mangerite target rock were entrained in a superheated melt of very low viscosity and quenched, preserving high temperature mineral phases, and revealing how zircon grains undergo decomposition in a natural sample.
Author: G. R. Osinski Publisher: John Wiley & Sons ISBN: 1118447328 Category : Science Languages : en Pages : 362
Book Description
Impact cratering is arguably the most ubiquitous geological process in the Solar System. It has played an important role in Earth’s history, shaping the geological landscape, affecting the evolution of life, and generating economic resources. However, it was only in the latter half of the 20th century that the importance of impact cratering as a geological process was recognized and only during the past couple of decades that the study of meteorite impact structures has moved into the mainstream. This book seeks to fill a critical gap in the literature by providing an overview text covering broad aspects of the impact cratering process and aimed at graduate students, professionals and researchers alike. It introduces readers to the threat and nature of impactors, the impact cratering process, the products, and the effects – both destructive and beneficial. A series of chapters on the various techniques used to study impact craters provide a foundation for anyone studying impact craters for the first time.
Author: National Aeronautics and Space Adm Nasa Publisher: ISBN: 9781724119995 Category : Languages : en Pages : 28
Book Description
The combined use of impact crater morphology and mechanics provides important information on the physical conditions of both planetary atmospheres and planetary and asteroid surfaces present during crater formation, while an understanding of the rate of crater production on the surface of asteroids provides information of their surface and spin rate evolution. The research performed with support from this project improves our understanding of (1) the mechanics of impact cratering in order to gain insights on the evolution of these physical surface conditions on planets with atmospheres and asteroids, and (2) how impact flux across an asteroid surface may vary due to anisotropic distribution of impactors in the solar system. As part of this project, we have undertaken three studies. In the first study, we investigate atmospheric effects on the morphology of ejecta excavated during a cratering event in order to determine the atmospheric and target conditions from observed crater morphologies. In the second study, we use the physical and morphological consequences of oblique impacts on an asteroid to understand how the asteroid Mathilde (recently imaged by the Near Earth Asteroid Rendezvous - NEAR- spacecraft) could have survived the formation of five giant craters. In a third study, we use a Monte Carlo method to calculate the impact flux on an asteroid given a distribution of impactors on elliptical orbits. In the following section, we present the result obtained from all three studies. Appleby, John F. and Barnouin-Jha, Oliver S. and Cheng, Andrew F. Unspecified Center ...
Author: Rogelio Daniel Acevedo Publisher: Springer ISBN: 3319130935 Category : Science Languages : en Pages : 108
Book Description
A complete and updated catalogue of impact craters and structures in South America from 2014 is presented here. Approximately eighty proven, suspected and disproven structures have been identified by several sources in this continent. All the impact sites of this large continent have been exhaustively reviewed: the proved ones, the possible ones and some very doubtful. Many sites remain without a clear geological "in situ" confirmation and some of them could be even rejected. Argentina and Brazil are leading the list containing almost everything detected. In Bolivia, Chile, Colombia, Guyana, Paraguay, Perú, Uruguay and Venezuela only a few were observed. Only Ecuador is waiting for new discoveries. So far, the largest well stated impact site is still the Araguainha structure in Brazil with its 40 kilometers in diameter. However, two possible impact structures are larger than Araguainha: Malvinas, (with 250 kilometers in diameter) and Vichada in Colombia, (50 kilometers). This study also reports the existence of some Tertiary-Quaternary glassy impactite layers: the "escorias" and "tierras cocidas" of the pampas in Argentina.
Author: Billy P. Glass Publisher: Springer Science & Business Media ISBN: 3540882626 Category : Science Languages : en Pages : 723
Book Description
Impact cratering is an important geological process on all solid planetary bodies, and, in the case of Earth, may have had major climatic and biological effects. Most terrestrial impact craters have been erased or modified beyond recognition. However, major impacts throw ejecta over large areas of the Earth's surface. Recognition of these impact ejecta layers can help fill in the gaps in the terrestrial cratering record and at the same time provide direct correlation between major impacts and other geological events, such as climatic changes and mass extinctions. This book provides the first summary of known distal impact ejecta layers
Author: Fred J. Calef Publisher: ISBN: Category : Cratering Languages : en Pages : 508
Book Description
"Impact cratering is one of the principal geologic processes operating throughout the solar system. On Mars, small rayed impact craters (SRC) form continuously and randomly on the surface. Ejecta retention, the timespan and ability of excavated ejecta to remain in place around a crater rim, records a lineage of recent surface processes. However, the timescales under which small rayed craters are produced and their origin, whether terrestrial or cosmic, plays an important role in further investigating surface processes and possible recent climate variations. By examining thousands of randomly chosen panchromatic images from the Mars Orbiter Camera Narrow Angle (MOCNA) camera, a population of 630 SRC was catalogued across three equatorial and two polar regions on Mars. The survey of MOCNA images also revealed intriguing Enigmatic Linear Features (ELFs) in the northern hemisphere of Mars, which a short side study revealed to be a unique form of dust-devil track. From statistically examining several physical parameters, dust deposition and periglacial erosion were found to be the major factors affecting ejecta retention for the SRC. SRC morphology revealed ejecta retention sequences that followed four stages of ejecta retention from the initial impact to eventual erasure from the surface. By reconstructing the current cratering rate from estimates of atmospheric filtering, it was possible to calculate the ejecta retention age across Mars. In general, SRC ejecta are retained on the surface for
Author: H. J. Melosh Publisher: Oxford University Press, USA ISBN: Category : Science Languages : en Pages : 264
Book Description
This major study of crater morphology examines the physics of impact cratering, the geologic processes associated with it, and its role in planetary evolution. Melosh outlines landmark events in the history of impact cratering and places modern developments in historical perspective. Since important impact structures exist on our planet as well as on bodies in the solar system, this valuable contribution will serve as a vital reference in the diverse fields of geology, paleontology and planetary science.
Author: Bhairavi Shankar Publisher: ISBN: Category : Languages : en Pages : 388
Book Description
Hyperve locity collisions of asteroids onto planetary bodies have catastrophic effects on the target rocks through the process of shock metamorphism. The resulting features, impact craters, are circular depressions with a sharp rim surrounded by an ejecta blanket of variably shocked rocks. With increasing impact energy, the inner crater cavity can preserve complex morphologies including terraced walls, central uplifts, and melted rocks. The lack of erosion due to the absence of water or an atmosphere makes the Moon the perfect target to study impact crater processes, in particular the distribution of highly shocked materials within impact craters of different sizes. This study focuses on the characterization and distribution of highly shocked impact melt deposits using multispectral satellite datasets around three complex craters on the farside of the Moon. The study sites have varying morphologies of central uplifts on the crater floor: 1) the 81 km Olcott crater has a cluster of peak hills; 2) Kovalevskaya crater i s a 113 km diameter complex crater with a central peak; and 3) Schrödinger basin has a central peak ring. Models propose that the collapse of crater walls and central uplifts during the final stages of crater formation determine where much of the melt rich rocks are eventually emplaced. The results of th is study indicate that for increasing crater sizes, the volume of melt - rich rocks generated also increases - at rates greater than model estimates. Impact melt deposits are emplaced beyond the crater rims at each of the sites and preserve a range of morphologies, including melt veneers, melt sheet, and ponded deposits. The regional and local topography, together with crater modification processes greatly affect where the impact melts are finally emplaced. The compositional analyses of the farside crust, using multispectral reflectance spectroscopy in the UV-VIS-NIR range, indicates that there is increasing evidence of highly mafic compositions (i.e., rocks rich in high-Ca pyroxene, olivine, spinel) intercalate d with in the original crustal highlands (rocks rich in plagioclase feldspar, and low-Ca pyroxenes) on the lunar farside, proving that the lunar farside is a far more geologically complicated terrain than originally assumed.
Author: Tyler Michael Powell Publisher: ISBN: Category : Languages : en Pages : 0
Book Description
Impact craters dominate the landscapes of many planetary bodies. Among their most striking characteristics are their rays: radial streaks formed by high velocity ejecta launched to great distances. This dissertation investigates the influence of distal ejecta on planetary surfaces by studying two classes of features: secondary impact craters and lunar cold spots. Secondary impact craters form when rock fragments ejected from a primary crater re-impact the surface at high velocity. Individual primary craters have been shown to produce upwards of 10^6-10^9 secondary craters which form nearly instantaneously in geologic time. This has led many to question whether crater chronology models can be applied effectively. In chapter 2, we develop a model for the global accumulation of secondary craters with time for Mars, accounting for the spatial clustering of secondaries. We show that the number of km-scale secondaries produced on Mars may exceed primaries after only a few 100 Ma. However, most secondaries are clustered around their parent primaries, and regions far from large primaries have significantly fewer secondaries than the global average. The crossover diameter between primary and secondary crater production on a typical surface is estimated to exceed 1 km after ~1-2 Ga, though subsequent crater erasure has significantly influenced the number of secondaries visible today. In chapter 3, we produce updated global maps of nighttime temperature for the Moon using data from the Diviner Lunar Radiometer Experiment on the Lunar Reconnaissance Orbiter (LRO). We implement several improvements, including a correction for errors in instrument pointing, which result in a substantial increase in effective resolution. In addition, we develop a model which mostly removes the effect of topography on nighttime temperature by accounting for scattering and emission from the surrounding terrain. These improvements allow smaller and fainter thermal features to be identified than was previously possible. Lunar cold spots are extensive ray-like regions of reduced nighttime temperature surrounding young impact craters on the Moon. In chapter 4, we show that South Ray crater at the Apollo 16 landing site has a faint cold spot. Its temperature anomaly and ~2 Ma age are consistent with the fading rate of other large cold spots. Additionally, we show that the mean depth of astronaut footprints is greater at the Apollo 16 landing site than the other Apollo sites. This suggests that cold spots are caused by a decompaction of the upper regolith, consistent with estimates derived from thermal modeling. In chapter 5, we present the thermophysical properties of a global survey of cold spots and several new cold spots formed during the LRO mission lifetime. We show that the temperature anomaly of new cold spots scales with crater diameter, forming an upper envelope to the properties of pre-existing cold spots. This indicates a greater depth of regolith modification by larger cold spots. Using thermal modeling, we present bounds on the depth of regolith modification for new cold spots and estimate how this scales with crater size.
Author: Michael Raymond Zanetti
Author: Michael Raymond Zanetti
Author: G. R. Osinski
Author: National Aeronautics and Space Adm Nasa
Author: Rogelio Daniel Acevedo
Author: Billy P. Glass
Author: Fred J. Calef
Author: H. J. Melosh
Author: Nicholas Martin Short
Author: Bhairavi Shankar
Author: Tyler Michael Powell