Magma genesis at Gale Crater: Evidence for Pervasive Mantle Metasomatism

Science.gov (United States)

Filiberto, J.

2017-12-01

Basaltic rocks have been analyzed at Gale Crater with a larger range in bulk chemistry than at any other landing site [1]. Therefore, the rocks may have experienced significantly different formation conditions than those experienced by magmas at Gusev Crater or Meridiani Planum. Specifically, the rocks at Gale Crater have higher potassium than other Martian rocks, with a potential analog of the Nakhlite parental magma, and are consistent with forming from a metasomatized mantle source [2-4]. Mantle metasomatism would not only affect the bulk chemistry but mantle melting conditions, as metasomatism fluxes fluids into the source region. Here I will combine differences in bulk chemistry between Martian basalts to calculate formation conditions in the interior and investigate if the rocks at Gale Crater experienced magma genesis conditions consistent with metasomatism - lower temperatures and pressures of formation. To calculate average formation conditions, I rely on experimental results, where available, and silica-activity and Mg-exchange thermometry calculations for all other compositions following [5, 6]. The results show that there is a direct correlation between the calculated mantle potential temperature and the K/Ti ratio of Gale Crater rocks. This is consistent with fluid fluxed metasomatism introducing fluids to the system, which depressed the melting temperature and fluxed K but not Ti to the system. Therefore, all basalts at Gale Crater are consistent with forming from a metasomatized mantle source, which affected not only the chemistry of the basalts but also the formation conditions. References: [1] Cousin A. et al. (2017) Icarus. 288: 265-283. [2] Treiman A.H. et al. (2016) Journal of Geophysical Research: Planets. 121: 75-106. [3] Treiman A.H. and Medard E. (2016) Geological Society of America Abstracts with Programs. 48: doi: 10.1130/abs/2016AM-285851. [4] Schmidt M.E. et al. (2016) Geological Society of America Abstracts with Programs. 48: doi: 10

Meteor Crater (Barringer Meteorite Crater), Arizona: Summary of Impact Conditions

Science.gov (United States)

Roddy, D. J.; Shoemaker, E. M.

1995-09-01

Meteor Crater in northern Arizona represents the most abundant type of impact feature in our Solar System, i.e., the simple bowl-shaped crater. Excellent exposures and preservation of this large crater and its ejecta blanket have made it a critical data set in both terrestrial and planetary cratering research. Recognition of the value of the crater was initiated in the early 1900's by Daniel Moreau Barringer, whose 27 years of exploration championed its impact origin [1]. In 1960, Shoemaker presented information that conclusively demonstrated that Meteor Crater was formed by hypervelocity impact [2]. This led the U.S. Geological Survey to use the crater extensively in the 1960-70's as a prime training site for the Apollo astronauts. Today, Meteor Crater continues to serve as an important research site for the international science community, as well as an educational site for over 300,000 visitors per year. Since the late 1950's, studies of this crater have presented an increasingly clearer view of this impact and its effects and have provided an improved view of impact cratering in general. To expand on this data set, we are preparing an upgraded summary on the Meteor Crater event following the format in [3], including information and interpretations on: 1) Inferred origin and age of the impacting body, 2) Inferred ablation and deceleration history in Earth's atmosphere, 3) Estimated speed, trajectory, angle of impact, and bow shock conditions, 4) Estimated coherence, density, size, and mass of impacting body, 5) Composition of impacting body (Canyon Diablo meteorite), 6) Estimated kinetic energy coupled to target rocks and atmosphere, 7) Terrain conditions at time of impact and age of impact, 8) Estimated impact dynamics, such as pressures in air, meteorite, and rocks, 9) Inferred and estimated material partitioning into vapor, melt, and fragments, 10) Crater and near-field ejecta parameters, 11) Rock unit distributions in ejecta blanket, 12) Estimated far

Modeling of nuclear waste disposal by rock melting

International Nuclear Information System (INIS)

Heuze, F.E.

1982-04-01

Today, the favored option for disposal of high-level nuclear wastes is their burial in mined caverns. As an alternative, the concept of deep disposal by rock melting (DRM) also has received some attention. DRM entails the injection of waste, in a cavity or borehole, 2 to 3 kilometers down in the earth crust. Granitic rocks are the prime candidate medium. The high thermal loading initially will melt the rock surrounding the waste. Following resolidification, a rock/waste matrix is formed, which should provide isolation for many years. The complex thermal, mechanical, and hydraulic aspects of DRM can be studied best by means of numerical models. The models must accommodate the coupling of the physical processes involved, and the temperature dependency of the granite properties, some of which are subject to abrupt discontinuities, during α-β phase transition and melting. This paper outlines a strategy for such complex modeling

Ponds, Flows, and Ejecta of Impact Cratering and Volcanism: A Remote Sensing Perspective of a Dynamic Moon

Science.gov (United States)

Stopar, Julie D.

Both volcanism and impact cratering produce ejecta and associated deposits incorporating a molten rock component. While the heat sources are different (exogenous vs. endogenous), the end results are landforms with similar morphologies including ponds and flows of impact melt and lava around the central crater. Ejecta from both impact and volcanic craters can also include a high percentage of melted rock. Using Lunar Reconnaissance Orbiter Camera Narrow Angle Camera (LROC NAC) images, crucial details of these landforms are finally revealed, suggesting a much more dynamic Moon than is generally appreciated. Impact melt ponds and flows at craters as small as several hundred meters in diameter provide empirical evidence of abundant melting during the impact cratering process (much more than was previously thought), and this melt is mobile on the lunar surface for a significant time before solidifying. Enhanced melt deposit occurrences in the lunar highlands (compared to the mare) suggest that porosity, target composition, and pre-existing topography influence melt production and distribution. Comparatively deep impact craters formed in young melt deposits connote a relatively rapid evolution of materials on the lunar surface. On the other end of the spectrum, volcanic eruptions have produced the vast, plains-style mare basalts. However, little was previously known about the details of small-area eruptions and proximal volcanic deposits due to a lack of resolution. High-resolution images reveal key insights into small volcanic cones (0.5-3 km in diameter) that resemble terrestrial cinder cones. The cones comprise inter-layered materials, spatter deposits, and lava flow breaches. The widespread occurrence of the cones in most nearside mare suggests that basaltic eruptions occur from multiple sources in each basin and/or that rootless eruptions are relatively common. Morphologies of small-area volcanic deposits indicate diversity in eruption behavior of lunar basaltic

The potassic sedimentary rocks in Gale Crater, Mars, as seen by ChemCam Onboard Curiosity

Science.gov (United States)

Le Deit, Laetitia; Mangold, Nicolas; Forni, Olivier; Cousin, Agnes; Lasue, Jeremie; Schröder, Susanne; Wiens, Roger C.; Sumner, Dawn Y.; Fabre, Cecile; Stack, Katherine M.; Anderson, Ryan; Blaney, Diana L.; Clegg, Samuel M.; Dromart, Gilles; Fisk, Martin; Gasnault, Olivier; Grotzinger, John P.; Gupta, Sanjeev; Lanza, Nina; Le Mouélic, Stephane; Maurice, Sylvestre; McLennan, Scott M.; Meslin, Pierre-Yves; Nachon, Marion; Newsom, Horton E.; Payre, Valerie; Rapin, William; Rice, Melissa; Sautter, Violaine; Treiman, Alan H.

2016-01-01

The Mars Science Laboratory rover Curiosity encountered potassium-rich clastic sedimentary rocks at two sites in Gale Crater, the waypoints Cooperstown and Kimberley. These rocks include several distinct meters thick sedimentary outcrops ranging from fine sandstone to conglomerate, interpreted to record an ancient fluvial or fluvio-deltaic depositional system. From ChemCam Laser-Induced Breakdown Spectroscopy (LIBS) chemical analyses, this suite of sedimentary rocks has an overall mean K2O abundance that is more than 5 times higher than that of the average Martian crust. The combined analysis of ChemCam data with stratigraphic and geographic locations reveals that the mean K2O abundance increases upward through the stratigraphic section. Chemical analyses across each unit can be represented as mixtures of several distinct chemical components, i.e., mineral phases, including K-bearing minerals, mafic silicates, Fe-oxides, and Fe-hydroxide/oxyhydroxides. Possible K-bearing minerals include alkali feldspar (including anorthoclase and sanidine) and K-bearing phyllosilicate such as illite. Mixtures of different source rocks, including a potassium-rich rock located on the rim and walls of Gale Crater, are the likely origin of observed chemical variations within each unit. Physical sorting may have also played a role in the enrichment in K in the Kimberley formation. The occurrence of these potassic sedimentary rocks provides additional evidence for the chemical diversity of the crust exposed at Gale Crater.

Shock pressure estimation in basement rocks of the Chicxulub impact crater using cathodoluminescence spectroscopy of quartz

Science.gov (United States)

Tomioka, N.; Tani, R.; Kayama, M.; Chang, Y.; Nishido, H.; Kaushik, D.; Rae, A.; Ferrière, L.; Gulick, S. P. S.; Morgan, J. V.

2017-12-01

The Chicxulub impact structure, located in the northern Yucatan Peninsula, Mexico, was drilled by the joint IODP-ICDP Expedition 364 in April-May 2016. This expedition is the first attempt to obtain materials from the topographic peak ring within the crater previously identified by seismic imaging. A continuous core was successfully recovered from the peak ring at depths between 505.7 and 1334.7 mbsf. Uplifted, fractured, and shocked granitic basement rocks forming the peak ring were found below, in the impact breccia and impact melt rock unit (747.0-1334.7 mbsf; Morgan et al. 2016). In order to constrain impact crater formation, we investigated shock pressure distribution in the peak-ring basement rocks. Thin sections of the granitic rocks were prepared at intervals of 60 m. All the samples contains shocked minerals, with quartz grains frequently showing planar deformation features (PDFs). We determined shock pressures based on the cathodoluminescence (CL) spectroscopy of quartz. The strong advantage of the CL method is its applicability to shock pressure estimation for individual grains for both quartz and diaplectic SiO2 glass with high-spatial resolution ( 1 μm) (Chang et al. 2016). CL spectra of quartz shows a blue emission band caused by shock-induced defect centers, where its intensity increases with shock pressure. A total of 108 quartz grains in ten thin sections were analyzed using a scanning electron microscope with a CL spectrometer attached (an acceleration voltage of 15 kV and a beam current of 2 nA were used). Natural quartz single crystals, which were experimentally shocked at 0-30 GPa, were used for pressure calibration. CL spectra of all the quartz grains in the basement rocks showed broad blue emission band at the wavelength range of 300-500 nm and estimated shock pressures were in the range of 15-20 GPa. The result is consistent with values obtained from PDFs analysis in quartz using the universal stage (Ferrière et al. 2017; Rae et al. 2017

El'gygytgyn impact crater, Chukotka, Arctic Russia: Impact cratering aspects of the 2009 ICDP drilling project

Science.gov (United States)

Koeberl, Christian; Pittarello, Lidia; Reimold, Wolf Uwe; Raschke, Ulli; Brigham-Grette, Julie; Melles, Martin; Minyuk, Pavel; Spray, John

2013-01-01

The El'gygytgyn impact structure in Chukutka, Arctic Russia, is the only impact crater currently known on Earth that was formed in mostly acid volcanic rocks (mainly of rhyolitic, with some andesitic and dacitic, compositions). In addition, because of its depth, it has provided an excellent sediment trap that records paleoclimatic information for the 3.6 Myr since its formation. For these two main reasons, because of the importance for impact and paleoclimate research, El'gygytgyn was the subject of an International Continental Scientific Drilling Program (ICDP) drilling project in 2009. During this project, which, due to its logistical and financial challenges, took almost a decade to come to fruition, a total of 642.3 m of drill core was recovered at two sites, from four holes. The obtained material included sedimentary and impactite rocks. In terms of impactites, which were recovered from 316.08 to 517.30 m depth below lake bottom (mblb), three main parts of that core segment were identified: from 316 to 390 mblb polymict lithic impact breccia, mostly suevite, with volcanic and impact melt clasts that locally contain shocked minerals, in a fine-grained clastic matrix; from 385 to 423 mblb, a brecciated sequence of volcanic rocks including both felsic and mafic (basalt) members; and from 423 to 517 mblb, a greenish rhyodacitic ignimbrite (mostly monomict breccia). The uppermost impactite (316–328 mblb) contains lacustrine sediment mixed with impact-affected components. Over the whole length of the impactite core, the abundance of shock features decreases rapidly from the top to the bottom of the studied core section. The distinction between original volcanic melt fragments and those that formed later as the result of the impact event posed major problems in the study of these rocks. The sequence that contains fairly unambiguous evidence of impact melt (which is not very abundant anyway, usually less than a few volume%) is only about 75 m thick. The reason for

Mineralogy of Rocks and Sediments at Gale Crater, Mars

Science.gov (United States)

Achilles, Cherie; Downs, Robert; Blake, David; Vaniman, David; Ming, Doug; Rampe, Elizabeth; Morris, Dick; Morrison, Shaunna; Treiman, Allan; Chipera, Steve; Yen, Albert; Bristow, Thomas; Craig, Patricia; Hazen, Robert; Crisp, Joy; Grotzinger, John; Des Marias, David; Farmer, Jack; Sarrazin, Philippe; Morookian, John Michael

2017-04-01

The Mars Science Laboratory rover, Curiosity, is providing in situ mineralogical, geochemical, and sedimentological assessments of rocks and soils in Gale crater. Since landing in 2012, Curiosity has traveled over 15 km, providing analyses of mudstones and sandstones to build a stratigraphic history of the region. The CheMin X-ray diffraction (XRD) instrument is the first instrument on Mars to provide quantitative mineralogical analyses of drilled powders and scooped sediment based on X-ray crystallography. CheMin identifies and determines mineral abundances and unit-cell parameters of major crystalline phases, and identifies minor phases at abundances >1 wt%. In conjunction with elemental analyses, CheMin-derived crystal chemistry allows for the first calculations of crystalline and amorphous material compositions. These mineralogy, crystal chemistry, and amorphous chemistry datasets are playing central roles in the characterization of Gale crater paleoenvironments. CheMin has analyzed 17 rock and sediment samples. In the first phase of the mission, Curiosity explored the sedimentary units of Aeolis Palus (Bradbury group), including two mudstones from Yellowknife Bay. CheMin analyses of the Yellowknife Bay mudstones identified clay minerals among an overall basaltic mineral assemblage. These mineralogical results, along with imaging and geochemical analyses, were used to characterize an ancient lacustrine setting that is thought to have once been a habitable environment. Following the investigations of the Bradbury group, Curiosity arrived at the lower reaches of Aeolis Mons, commonly called Mt. Sharp. A strategic sample campaign was initiated, drilling bedrock at X-ray amorphous phases. Adjacent to fractures, light-toned, halo-like zones are thought to result from significant aqueous alteration of the primary sandstone and show decreased abundances of feldspar and pyroxene, and an increase in the amorphous component, specifically high-silica phases. The Murray

The Mechanics of Peak-Ring Impact Crater Formation from the IODP-ICDP Expedition 364

Science.gov (United States)

Melosh, H.; Collins, G. S.; Morgan, J. V.; Gulick, S. P. S.

2017-12-01

deformation state described by the process of "acoustic" fluidization initiated by strong elastic vibrations accompanying the opening and collapse of the crater. The shattered core, cut by both melt rock and clastic dikes, is consistent with the block model of acoustic fluidization supporting its application to crater collapse both on the Earth and on other planets.

Textures of the soils and rocks at Gusev crater from Spirit's Microscopic Imager

DEFF Research Database (Denmark)

Herkenhoff, K.E.; Squyres, S.W.; Arvidson, R.

2004-01-01

The Microscopic Imager on the Spirit rover analyzed the textures of the soil and rocks at Gusev crater on Mars at a resolution of 100 micrometers. Weakly bound agglomerates of dust are present in the soil near the Columbia Memorial Station. Some of the brushed or abraded rock surfaces show igneous...... textures and evidence for alteration rinds, coatings, and veins consistent with secondary mineralization. The rock textures are consistent with a volcanic origin and subsequent alteration and/or weathering by impact events, wind, and possibly water....

Hailar crater - A possible impact structure in Inner Mongolia, China

Science.gov (United States)

Xiao, Zhiyong; Chen, Zhaoxu; Pu, Jiang; Xiao, Xiao; Wang, Yichen; Huang, Jun

2018-04-01

Hailar crater, a probable impact structure, is a circular depression about 300 m diameter in Inner Mongolia, northeast China. With broad elevated rims, the present rim-to-floor depth is 8-20 m. Regional geological background and geomorphological comparison suggest that this feature is likely not formed by surface processes such as salt diapir, karst, aeolian, glacial, or volcanic activity. Its unique occurrence in this region and well-preserved morphology are most consistent with it being a Cenozoic impact crater. Two field expeditions in 2016 and 2017 investigated the origin of this structure, recognizing that (1) no additional craters were identified around Hailar crater in the centimeter-scale digital topography models that were constructed using a drone imaging system and stereo photogrammetry; (2) no bedrock exposures are visible within or adjacent to the crater because of thick regolith coverage, and only small pieces of angular unconsolidated rocks are present on the crater wall and the gently-sloped crater rim, suggesting recent energetic formation of the crater; (3) most samples collected from the crater have identical lithology and petrographic characteristics with the background terrain, but some crater samples contain more abundant clasts and silicate hydrothermal veins, indicating that rocks from depths have been exposed by the crater; (4) no shock metamorphic features were found in the samples after thin section examinations; and (5) a systematic sample survey and iron detector scan within and outside of the crater found no iron-rich meteorites larger than 2 cm in size in a depth of 30 cm. Although no conclusive evidence for an impact origin is found yet, Hailar crater was most likely formed by an impact based on its unique occurrence and comparative geomorphologic study. We suggest that drilling in the crater center is required to verify the impact origin, where hypothesized melt-bearing impactites may be encountered.

Calculation of craters resulting from impact rupture of rock mass using pulse hydrodynamic problem formulation

Science.gov (United States)

Gorodilov, LV; Rasputina, TB

2018-03-01

A liquid–solid hydrodynamic model is used to determine shapes and sizes of craters generated by impact rupture of rocks. Near the impact location, rock is modeled by an ideal incompressible liquid, in the distance—by an absolute solid. The calculated data are compared with the experimental results obtained under impact treatment of marble by a wedge-shaped tool.

Stability of nuclear crater slopes in rock

International Nuclear Information System (INIS)

Fleming, Robert W.; Frandsen, Alton D.; LaFrenz, Robert L.

1970-01-01

The United States Army Engineer Nuclear Cratering Group was established in 1962 to participate with the Atomic Energy Commission in a joint research and development program to develop nuclear engineering and construction technology. A major part of this research effort has been devoted to studies of the engineering properties of craters. The program to date has included field investigations of crater properties in various media over a broad range of chemical and nuclear explosive yields, studies of man-made and natural slopes, and studies directed toward the development of analytical and empirical methods of crater stability analysis. From this background, a general understanding has been developed of the effects of a cratering explosion on the surrounding medium and of physical nature of the various crater zones which are produced. The stability of nuclear crater slopes has been a subject of prime interest in the feasibility study being conducted for an Atlantic-Pacific sea-level canal. Based on experimental evidence assembled to date, nuclear crater slopes in dry dock and dry alluvium have an initially stable configuration. There have been five nuclear craters produced to date with yields of 0.4 kt or more on which observations are based and the initial configurations of these craters have remained stable for over seven years. The medium, yield, crater dimensions, and date of event for these craters are summarized. It is interesting to note that the Sedan Crater has been subjected to strong seismic motions from nearby detonations without adverse effects

Stability of nuclear crater slopes in rock

Energy Technology Data Exchange (ETDEWEB)

Fleming, Robert W; Frandsen, Alton D; LaFrenz, Robert L [U.S. Army Engineer Nuclear Cratering Group, Lawrence Radiation Laboratory, Livermore, CA (United States)

1970-05-15

The United States Army Engineer Nuclear Cratering Group was established in 1962 to participate with the Atomic Energy Commission in a joint research and development program to develop nuclear engineering and construction technology. A major part of this research effort has been devoted to studies of the engineering properties of craters. The program to date has included field investigations of crater properties in various media over a broad range of chemical and nuclear explosive yields, studies of man-made and natural slopes, and studies directed toward the development of analytical and empirical methods of crater stability analysis. From this background, a general understanding has been developed of the effects of a cratering explosion on the surrounding medium and of physical nature of the various crater zones which are produced. The stability of nuclear crater slopes has been a subject of prime interest in the feasibility study being conducted for an Atlantic-Pacific sea-level canal. Based on experimental evidence assembled to date, nuclear crater slopes in dry dock and dry alluvium have an initially stable configuration. There have been five nuclear craters produced to date with yields of 0.4 kt or more on which observations are based and the initial configurations of these craters have remained stable for over seven years. The medium, yield, crater dimensions, and date of event for these craters are summarized. It is interesting to note that the Sedan Crater has been subjected to strong seismic motions from nearby detonations without adverse effects.

Geotechnical modeling of high-level nuclear waste disposal by rock melting

International Nuclear Information System (INIS)

Heuze, F.E.

1981-12-01

A new strategy has been developed for the geotechnical modeling of nuclear waste disposal by rock melting (DRM). Three seeparate tasks were performed to reach this objective: a review of the four scenarios which have been proposed for DRM, to date; an evaluation of computer-based numerical models which could be used to analyze the mechanical, thermal, and hydraulic processes involved in DRM; and a critical review of rock mass properties which are relevant to the design and safety of waste disposal by rock melting. It is concluded that several geotechnical aspects of DRM can be studied realistically with current state-of-the-art model capabilities and knowledge of material properties. The next step in the feasibility study of DRM should be a best-estimate calculation of the four cavity-melt and canister-burial concepts. These new analyses will indicate the most critical areas for subsequent research

Study of melt produced bodies observed at Henbury crater region

International Nuclear Information System (INIS)

Hopper, V.D.; Sewell, D.K.B.; Aitken, D.K.

1989-01-01

Spherical and non spherical bodies derived from target rock and meteorite components have been found in samples of soil in the Henbury crater region. From a study of the composition of these bodies, the compositions of the meteorite and the target rock, it has been possible to separate the bodies into three groups showing differing degrees of volatilization of various oxides. The composition of a number of the soil samples were measured using X-ray fluorescence. A selected number were then examined by a scanning electron microscope fitted with an energy dispersive X-ray analyzer. Where Ni was definitely identified, it was examined by an electron microprobe X-ray analyzer. A major finding was the depletion of SiO 2 in the production of both Group 1 and Group 3 bodies. Group 3 bodies are not volatilized to the same extent as Group 1. With no reference to the target rock , the general order of volatility appears to be Na 2 O>MgO>K 2 O>TiO 2 , SiO 2 and Al 2 O 3 , the significant change being the place of SiO2. 13 refs., 7 figs., 5 tabs

VNIR Multispectral Observations of Rocks at Spirit of St. Louis Crater and Marathon Valley on Th Rim of Endeavour Crater Made by the Opportunity Rover Pancam

Science.gov (United States)

Farrand, W. H.; Johnson, J. R.; Bell, J. F., III; Mittlefehldt, D.W.

2016-01-01

The Mars Exploration Rover Opportunity has been exploring the western rim of the 22 km diameter Endeavour crater since August, 2011. Recently, Opportunity has reached a break in the Endeavour rim that the rover team has named Mara-thon Valley. This is the site where orbital observations from the MRO CRISM imaging spectrometer indicated the presence of iron smectites. On the outer western portion of Marathon Valley, Opportunity explored the crater-form feature dubbed Spirit of St. Louis (SoSL) crater. This presentation describes the 430 to 1009 nm (VNIR) reflectance, measured by the rover's Pancam, of rock units present both at Spirit of St. Louis and within Marathon Valley.

Deformation mechanisms and melt nano-structures in experimentally deformed olivine-orthopyroxene rocks with low melt fractions

NARCIS (Netherlands)

Kloe, P.A. de

2001-01-01

The major part of the Earth’s upper mantle is thought to be solid, with some regions in the mantle where the rocks contain a small melt fraction These partially molten rocks are associated with important geological processes such as magma production beneath mid-oceanic ridges and may also play an

Igneous rocks formed by hypervelocity impact

Science.gov (United States)

Osinski, Gordon R.; Grieve, Richard A. F.; Bleacher, Jacob E.; Neish, Catherine D.; Pilles, Eric A.; Tornabene, Livio L.

2018-03-01

Igneous rocks are the primary building blocks of planetary crusts. Most igneous rocks originate via decompression melting and/or wet melting of protolith lithologies within planetary interiors and their classification and compositional, petrographic, and textural characteristics, are well-studied. As our exploration of the Solar System continues, so too does the inventory of intrusive and extrusive igneous rocks, settings, and processes. The results of planetary exploration have also clearly demonstrated that impact cratering is a ubiquitous geological process that has affected, and will continue to affect, all planetary objects with a solid surface, whether that be rock or ice. It is now recognized that the production of igneous rocks is a fundamental outcome of hypervelocity impact. The goal of this review is to provide an up-to-date synthesis of our knowledge and understanding of igneous rocks formed by hypervelocity impact. Following a brief overview of the basics of the impact process, we describe how and why melts are generated during impact events and how impact melting differs from endogenic igneous processes. While the process may differ, we show that the products of hypervelocity impact can share close similarities with volcanic and shallow intrusive igneous rocks of endogenic origin. Such impact melt rocks, as they are termed, can display lobate margins and cooling cracks, columnar joints and at the hand specimen and microscopic scale, such rocks can display mineral textures that are typical of volcanic rocks, such as quench crystallites, ophitic, porphyritic, as well as features such as vesicles, flow textures, and so on. Historically, these similarities led to the misidentification of some igneous rocks now known to be impact melt rocks as being of endogenic origin. This raises the question as to how to distinguish between an impact versus an endogenic origin for igneous-like rocks on other planetary bodies where fieldwork and sample analysis may not

Cubic zirconia in >2370 °C impact melt records Earth's hottest crust

Science.gov (United States)

Timms, Nicholas E.; Erickson, Timmons M.; Zanetti, Michael R.; Pearce, Mark A.; Cayron, Cyril; Cavosie, Aaron J.; Reddy, Steven M.; Wittmann, Axel; Carpenter, Paul K.

2017-11-01

Bolide impacts influence primordial evolution of planetary bodies because they can cause instantaneous melting and vaporization of both crust and impactors. Temperatures reached by impact-generated silicate melts are unknown because meteorite impacts are ephemeral, and established mineral and rock thermometers have limited temperature ranges. Consequently, impact melt temperatures in global bombardment models of the early Earth and Moon are poorly constrained, and may not accurately predict the survival, stabilization, geochemical evolution and cooling of early crustal materials. Here we show geological evidence for the transformation of zircon to cubic zirconia plus silica in impact melt from the 28 km diameter Mistastin Lake crater, Canada, which requires super-heating in excess of 2370 °C. This new temperature determination is the highest recorded from any crustal rock. Our phase heritage approach extends the thermometry range for impact melts by several hundred degrees, more closely bridging the gap between nature and theory. Profusion of >2370 °C superheated impact melt during high intensity bombardment of Hadean Earth likely facilitated consumption of early-formed crustal rocks and minerals, widespread volatilization of various species, including hydrates, and formation of dry, rigid, refractory crust.

Determination of the heavy rare earth radionuclides in melted rock

International Nuclear Information System (INIS)

Li Yinming; Wang Yalong; Zhang Quanshi

1995-01-01

There are some heavy rare earth radionuclides in the melted rocks, such as 160 Tb, 168,170 Tm, 88,91 Y, 174,177 Lu, 169 Yb, etc.. Because their contents are very low in the melted rocks and the light rare earth fission products are interfered with their determination, it is very complicated to measure them quantitatively. So a new method has been studied in which P507 resin is used to separate and purify the rare earths. Radioactive sources are prepared by the pieces of filter paper for determining chemical yield with X-fluorescence analysis, and radioactive activity is determined with the γ-spectra analysis. It is proved that this method has satisfied the demands of experiments

Rock Magnetic Study of IODP/ICDP Expedition 364 Site M0077A Drill Cores: Post-Impact Sediments, Impact Breccias, Melt, Granitic Basement and Dikes

Science.gov (United States)

Fucugauchi, J. U.; Perez-Cruz, L. L.; Rebolledo-Vieyra, M.; Tikoo, S.; Zylberman, W.; Lofi, J.

2017-12-01

Drilling at Site M0077 sampled post-impact sediments overlying a peak ring consisting of impact breccias, melt rock and granitoids. Here we focus on characterizing the peak ring using magnetic properties, which vary widely and depend on mineralogy, depositional and emplacement conditions and secondary alterations. Rock magnetic properties are integrated with Multi-Sensor Core Logger (MSCL) data, vertical seismic profile, physical properties, petrographic and chemical analyses and geophysical models. We measure low-field magnetic susceptibility at low- and high-frequencies, intensity and direction of natural remanent magnetization (NRM) and laboratory-induced isothermal (IRM) and anhysteretic (ARM) magnetizations, alternating-field demagnetization of NRM, IRM and NRM, susceptibility variation with temperature, anisotropy of magnetic susceptibility, hysteresis and IRM back-field demagnetization. Post-impact carbonates show low susceptibilities and NRM intensities, variable frequency-dependent susceptibilities and multivectorial remanences residing in low and high coercivity minerals. Hysteresis loops show low coercivity saturation magnetizations and variable paramagnetic mineral contents. Impact breccias (suevites) and melt rock show higher susceptibilities, low frequency-dependent susceptibilities, high NRM, ARM and IRM intensities and moderate ARM intensity/susceptibility ratios. Magnetic signal is dominated by fine-grained magnetite and titanomagnetites with PSD domain states. Melt rocks at the base of impactite section show the highest susceptibilities and remanence intensities. Basement section is characterized by low susceptibilities in the granites and higher values in the dikes, with NRM and ARM intensities increasing towards the base. The high susceptibilities and remanence intensities correlate with high seismic velocities, density and decreased porosity and electrical resistivity. Fracturing and alteration account for the reduced seismic velocities

Differential melt scaling for oblique impacts on terrestrial planets

Science.gov (United States)

Abramov, Oleg; Wong, Stephanie M. Wong; Kring, David A. Kring

2012-01-01

Analytical estimates of melt volumes produced by a given projectile and contained in a given impact crater are derived as a function of impact velocity, impact angle, planetary gravity, target and projectile densities, and specific internal energy of melting. Applications to impact events and impact craters on the Earth, Moon, and Mars are demonstrated and discussed. The most probable oblique impact (45°) produces ∼1.6 times less melt volume than a vertical impact, and ∼1.6 and 3.7 times more melt volume than impacts with 30° and 15° trajectories, respectively. The melt volume for a particular crater diameter increases with planetary gravity, so a crater on Earth should have more melt than similar-size craters on Mars and the Moon. The melt volume for a particular projectile diameter does not depend on gravity, but has a strong dependence on impact velocity, so the melt generated by a given projectile on the Moon is significantly larger than on Mars. Higher surface temperatures and geothermal gradients increase melt production, as do lower energies of melting. Collectively, the results imply thinner central melt sheets and a smaller proportion of melt particles in impact breccias on the Moon and Mars than on Earth. These effects are illustrated in a comparison of the Chicxulub crater on Earth, linked to the Cretaceous–Tertiary mass extinction, Gusev crater on Mars, where the Mars Exploration Rover Spirit landed, and Tsiolkovsky crater on the Moon. The results are comparable to those obtained from field and spacecraft observations, other analytical expressions, and hydrocode simulations.

In-situ rock melting applied to lunar base construction and for exploration drilling and coring on the moon

International Nuclear Information System (INIS)

Rowley, J.C.; Neudecker, J.W.

1984-01-01

An excavation technology based upon melting of rock and soil has been extensively developed at the prototype hardware and conceptual design levels for terrestrial conditions. Laboratory and field tests of rock-melting penetration have conclusively indicated that this excavation method is insensitive to rock, soil types, and conditions. Especially significant is the ability to form in-place glass linings or casings on the walls of boreholes, tunnels, and shafts. These factors indicate the unique potential for in situ construction of primary lunar base facilities. Drilling and coring equipment for resource exploration on the moon can also be devised that are largely automated and remotely operated. It is also very likely that lunar melt-glasses will have changed mechanical properties when formed in anhydrous and hard vacuum conditions. Rock melting experiments and prototype hardware designs for lunar rock-melting excavation applications are suggested

Iron-Manganese Redox Reactions in Endeavour Crater Rim Apron Rocks

Science.gov (United States)

Ming, D. W.; Mittlefehldt, D. W.; Gellert, R.; Peretyazhko, T.; Clark, B. C.; Morris, R. V.; Yen, A. S.; Arvidson, R. E.; Crumpler, L. S.; Farrand, W. H.;

An experimental investigation of the effect of impact generated micro-deformations in Moenkopi and Coconino Sandstone from Meteor Crater, Arizona on subsequent weathering

Science.gov (United States)

Verma, A.; Bourke, M. C.; Osinski, G.; Viles, H. A.; Blanco, J. D. R.

2017-12-01

Impact cratering is an important geological process that affects all planetary bodies in our solar system. As rock breakdown plays an important role in the evolution of landforms and sediments, it is important to assess the role of inheritance in the subsequent breakdown of impacted rocks.The shock pressure of several gigapascals generated during the impact can exceed the effective strength of target lithology by three to four orders of magnitude and is responsible for melting, vaporisation, shock metamorphism, fracturing and fragmentation of rocks. Environmental conditions and heterogeneities in rock properties exert an important control in rock breakdown. Similar to other subaerial rocks, impacted rocks are affected by a range of rock breakdown processes. In order to better understand the role of inheritance of the impact on rock breakdown, a rock breakdown experiment was conducted in a simulated environmental cabinet under conditions similar to the arid conditions found at the Meteor Crater site. We sampled Moenkopi and Coconino Sandstone from the Meteor Crater impact site in Arizona. For comparison, samples were also collected at control sites close by that have similar rock formations but did not undergo impact. Several established techniques (X-ray CT, SEM, Equotip, SfM) were used to characterise the rock samples before the environmental cabinet experiments. Our laboratory analysis (XRD, SEM, optical microscopy, X-ray CT) on impacted rock samples from Meteor Crater, show that rock porosity and permeability changes due to compaction and fracturing during impact. There were no high-pressure polymorphs of quartz or glass detected in XRD analysis. We ran the experiments on a total of 28 petrophysically characterised 5x5x5 cm sample blocks of Coconino and Moenkopi Sandstone (24 impacted rocks and 4 non-impacted). The results will be presented at the AGU Fall meeting 2017.

Nevada Test Site craters used for astronaut training

Science.gov (United States)

Moore, H. J.

1977-01-01

Craters produced by chemical and nuclear explosives at the Nevada Test Site were used to train astronauts before their lunar missions. The craters have characteristics suitable for reconnaissance-type field investigations. The Schooner test produced a crater about 300 m across and excavated more than 72 m of stratigraphic section deposited in a fairly regular fashion so that systematic observations yield systematic results. Other features common on the moon, such as secondary craters and glass-coated rocks, are present at Schooner crater. Smaller explosive tests on Buckboard Mesa excavated rocks from three horizontal alteration zones within basalt flows so that the original sequence of the zones could be determined. One crater illustrated the characteristics of craters formed across vertical boundaries between rock units. Although the exercises at the Nevada Test Site were only a small part of the training of the astronauts, voice transcripts of Apollo missions 14, 16, and 17 show that the exercises contributed to astronaut performance on the moon.

Weathering Profiles in Phosphorus-Rich Rocks at Gusev Crater, Mars, Suggest Dissolution of Phosphate Minerals into Potentially Habitable Near-Neutral Waters.

Science.gov (United States)

Adcock, Christopher T; Hausrath, Elisabeth M

2015-12-01

Abundant evidence indicates that significant surface and near-surface liquid water has existed on Mars in the past. Evaluating the potential for habitable environments on Mars requires an understanding of the chemical and physical conditions that prevailed in such aqueous environments. Among the geological features that may hold evidence of past environmental conditions on Mars are weathering profiles, such as those in the phosphorus-rich Wishstone-class rocks in Gusev Crater. The weathering profiles in these rocks indicate that a Ca-phosphate mineral has been lost during past aqueous interactions. The high phosphorus content of these rocks and potential release of phosphorus during aqueous interactions also make them of astrobiological interest, as phosphorus is among the elements required for all known life. In this work, we used Mars mission data, laboratory-derived kinetic and thermodynamic data, and data from terrestrial analogues, including phosphorus-rich basalts from Idaho, to model a conceptualized Wishstone-class rock using the reactive transport code CrunchFlow. Modeling results most consistent with the weathering profiles in Wishstone-class rocks suggest a combination of chemical and physical erosion and past aqueous interactions with near-neutral waters. The modeling results also indicate that multiple Ca-phosphate minerals are likely in Wishstone-class rocks, consistent with observations of martian meteorites. These findings suggest that Gusev Crater experienced a near-neutral phosphate-bearing aqueous environment that may have been conducive to life on Mars in the past. Mars-Gusev Crater-Wishstone-Reactive transport modeling-CrunchFlow-Aqueous interactions-Neutral pH-Habitability.

Viscosity characteristics of selected volcanic rock melts

Science.gov (United States)

Hobiger, Manuel; Sonder, Ingo; Büttner, Ralf; Zimanowski, Bernd

2011-02-01

A basic experimental study of the behavior of magma rheology was carried out on remelted volcanic rocks using wide gap viscometry. The complex composition of magmatic melts leads to complicated rheologic behavior which cannot be described with one simple model. Therefore, measurement procedures which are able to quantify non-Newtonian behavior have to be employed. Furthermore, the experimental apparatus must be able to deal with inhomogeneities of magmatic melts. We measured the viscosity of a set of materials representing a broad range of volcanic processes. For the lower viscous melts (low-silica compositions), non-Newtonian behavior is observed, whereas the high-silica melts show Newtonian behavior in the measured temperature and shear rate range (T = 1423 K - 1623 K, γ˙ = 10 - 2 s - 1 - 20 s - 1 ). The non-Newtonian materials show power-law behavior. The measured viscosities η and power-law indexes m lie in the intervals 8 Pa s ≤ η ≤ 210 3 Pa s, 0.71 ≤ m ≤ 1.0 (Grímsvötn basalt), 0.9 Pa s ≤ η ≤ 350 Pa s, 0.61 ≤ m ≤ 0.93 (Hohenstoffeln olivine-melilitite), and 8 Pa s ≤ η ≤ 1.510 4 Pa s, 0.55 ≤ m ≤ 1.0 (Sommata basalt). Measured viscosities of the Newtonian high-silica melts lie in the range 10 4 Pa s ≤ η ≤ 310 5 Pa s.

Oceanic mantle rocks reveal evidence for an ancient, 1.2-1.3 Ga global melting event

Science.gov (United States)

Dijkstra, A. H.; Sergeev, D.; McTaminey, L.; Dale, C. W.; Meisel, T. C.

2011-12-01

It is now increasingly being recognized that many oceanic peridotites are refertilized harzburgites, and that the refertilization often masks an extremely refractory character of the original mantle rock 'protolith'. Oceanic peridotites are, when the effects of melt refertilization are undone, often too refractory to be simple mantle melting residues after the extraction of mid-ocean ridge basalts at a spreading center. Rhenium-osmium isotope analysis is a powerful method to look through the effects of refertilization and to obtain constraints on the age of the melting that produced the refractory mantle protolith. Rhenium-depletion model ages of such anomalously refractory oceanic mantle rocks - found as abyssal peridotites or as mantle xenoliths on ocean islands - are typically >1 Ga, i.e., much older than the ridge system at which they were emplaced. In my contribution I will show results from two case studies of refertilized anciently depleted mantle rocks (Macquarie Island 'abyssal' peridotites and Lanzarote mantle xenoliths). Interestingly, very refractory oceanic mantle rocks from sites all around the world show recurring evidence for a Mesoproterozoic (~1.2-1.3 Ga) melting event [1]. Therefore, oceanic mantle rocks seem to preserve evidence for ancient melting events of global significance. Alternatively, such mantle rocks may be samples of rafts of ancient continental lithospheric mantle. Laser-ablation osmium isotope 'dating' of large populations of individual osmium-bearing alloys from mantle rocks is the key to better constrain the nature and significance of these ancient depletion events. Osmium-bearing alloys form when mantle rocks are melted to high-degrees. We have now extracted over >250 detrital osmium alloys from placer gold occurrences in the river Rhine. These alloys are derived from outcrops of ophiolitic mantle rocks in the Alps, which include blocks of mantle rocks emplaced within the Tethys Ocean, and ultramafic lenses of unknown

Determination of chemical composition of soils and rocks at the MER landing sites Gusev crater and Meridiani Planum using the APXS

Science.gov (United States)

Brueckner, J.

2004-05-01

The new Alpha Particle X-Ray Spectrometer (APXS) is a small, light-weight instrument to obtain x-ray spectra from Martian surface samples. The sensor head contains a high-resolution x-ray detector that is surrounded by a circle of radioactive Cm-244 sources. Alpha and x-ray radiation emitted by the sources is used to induce x-ray excitation in the sample. Elements from sodium to zinc (increasing by atomic weight) are detected and their concentrations determined. The APXS is mounted on each Instrument Deployment Device (IDD) of the two Mars Exploration Rovers (MER) Spirit and Opportunity. Rover Spirit landed in the large Gusev crater that seems to have been altered by water activities in the past based on evidence of orbital images. Rover Opportunity landed in a very small crater of the Meridiani Planum, where the mineral hematite that points to water-related processes is expected to be found. Inside the little crater, a light-colored outcrop is exposed that shows widespread fine layering. The first APXS high-resolution x-ray spectrum of a Gusev soil indicated many similarities to the composition of the Mars Pathfinder (MPF) and Viking soils. However, differences are also noticeable: Low-Z elements are somewhat higher compared to MPF soils, while high-Z elements are depleted, notably Ti. Potassium in the soils reflects the K concentration of the local rocks at the different landing sites pointing toward a local contribution to the soil's composition. The Rock Abrasion Tool was used to grind the first rock on Mars at Gusev: Adirondack's undisturbed and ground surface was measured by the APXS. The composition of its fresh surface is different from the MPF soilfree rock, noticeably in Mg and Al, and clearly exhibits a basaltic nature related to the composition of basaltic shergottites. The first rock at the Meridiani crater outcrop (dubbed Robert-E) exhibited a very high sulfur concentration, more than a factor of 15 compared to rock Adirondack, indicating it is

The Microstructure of Lunar Micrometeorite Impact Craters

Science.gov (United States)

Noble, S. K.; Keller, L. P.; Christoffersen, R.; Rahman, Z.

2016-01-01

The peak of the mass flux of impactors striking the lunar surface is made up of objects approximately 200 micrometers in diameter that erode rocks, comminute regolith grains, and produce agglutinates. The effects of these micro-scale impacts are still not fully understood. Much effort has focused on evaluating the physical and optical effects of micrometeorite impacts on lunar and meteoritic material using pulsed lasers to simulate the energy deposited into a substrate in a typical hypervelocity impact. Here we characterize the physical and chemical changes that accompany natural micrometeorite impacts into lunar rocks with long surface exposure to the space environment (12075 and 76015). Transmission electron microscope (TEM) observations were obtained from cross-sections of approximately 10-20 micrometers diameter craters that revealed important micro-structural details of micrometeorite impact processes, including the creation of npFe (sup 0) in the melt, and extensive deformation around the impact site.

Crystallisation condition of the Quaternary basanites of volcanic centre Black Rock, monogenetic field Lunar Crater

Science.gov (United States)

Turova, Mariia; Plechov, Pavel; Scherbakov, Vasily; Larin, Nikolay

2017-04-01

The Lunar Crater volcanic field is located in a tension zone Basin and Range Province (USA). This tension is connected with dives oceanic plate under the continental plate [1]. Lunar Crater consists of flows basalt, basanite, trachybasalt has a different age [2]. In this work we investigate the youngest rock - basanite. The basanite is highly crystalline consisting of about megacrysts (3-10 cm) 30-60 wt% phenocrysts ( 800-1500 µm) and microphenocrysts (100-800 µm) and 40-60% microlites (Mathematical, Physical and Engineering Sciences. - 1981. - T. 300. - №. 1454. - C. 407-434. 2. Wood, X., and Keinle, Y., 1990, Volcanoes of North America: Cambridge,United Kingdom, Cambridge University Press, 354 p. 3. Nimis P. Clinopyroxene geobarometry of magmatic rocks. Part 2. Structural geobarometers for basic to acid, tholeiitic and mildly alkaline magmatic systems //Contributions to Mineralogy and Petrology. - 1999. - T. 135. - №. 1. - C. 62-74. 4. Ballhaus C., Berry R. F., Green D. H. High pressure experimental calibration of the olivine-orthopyroxene-spinel oxygen geobarometer: implications for the oxidation state of the upper mantle //Contributions to Mineralogy and Petrology. - 1991. - T. 107. - №. 1. - C. 27-40.

Fluids in crustal deformation: Fluid flow, fluid-rock interactions, rheology, melting and resources

Science.gov (United States)

Lacombe, Olivier; Rolland, Yann

2016-11-01

Fluids exert a first-order control on the structural, petrological and rheological evolution of the continental crust. Fluids interact with rocks from the earliest stages of sedimentation and diagenesis in basins until these rocks are deformed and/or buried and metamorphosed in orogens, then possibly exhumed. Fluid-rock interactions lead to the evolution of rock physical properties and rock strength. Fractures and faults are preferred pathways for fluids, and in turn physical and chemical interactions between fluid flow and tectonic structures, such as fault zones, strongly influence the mechanical behaviour of the crust at different space and time scales. Fluid (over)pressure is associated with a variety of geological phenomena, such as seismic cycle in various P-T conditions, hydrofracturing (including formation of sub-horizontal, bedding-parallel veins), fault (re)activation or gravitational sliding of rocks, among others. Fluid (over)pressure is a governing factor for the evolution of permeability and porosity of rocks and controls the generation, maturation and migration of economic fluids like hydrocarbons or ore forming hydrothermal fluids, and is therefore a key parameter in reservoir studies and basin modeling. Fluids may also help the crust partially melt, and in turn the resulting melt may dramatically change the rheology of the crust.

Shock melting and vaporization of lunar rocks and minerals.

Science.gov (United States)

Ahrens, T. J.; O'Keefe, J. D.

1972-01-01

The entropy associated with the thermodynamic states produced by hypervelocity meteoroid impacts at various velocities are calculated for a series of lunar rocks and minerals and compared with the entropy values required for melting and vaporization. Taking into account shock-induced phase changes in the silicates, we calculate that iron meteorites impacting at speeds varying from 4 to 6 km/sec will produce shock melting in quartz, plagioclase, olivine, and pyroxene. Although calculated with less certainty, impact speeds required for incipient vaporization vary from 7 to 11 km/sec for the range of minerals going from quartz to periclase for aluminum (silicate-like) projectiles. The impact velocities, which are required to induce melting in a soil, are calculated to be in the range of 3 to 4 km/sec, provided thermal equilibrium is achieved in the shock state.

APXS of First Rocks Encountered by Curiosity in Gale Crater: Geochemical Diversity and Volatile Element (K and ZN) Enrichment

Science.gov (United States)

Schmidt, M. E.; King, P. L.; Gellert, R.; Elliott, B.; Thompson, L.; Berger, J.; Bridges, J.; Campbell, J. L; Grotzinger, J.; Hurowitz, J.;

Giordano Bruno crater on the Moon: Detection and Mapping of Hydration Features of Endogenic and/or Exogenic Nature

Science.gov (United States)

Saran Bhiravarasu, Sriram; Bhattacharya, Satadru; Chauhan, Prakash

2017-10-01

We analyze high resolution spectral and spatial data from the recent lunar missions and report the presence of strong hydration features within the inner flank, hummocky floor, ejecta and impact melt deposits of crater Giordano Bruno. Hydroxyl-bearing lithologies at Giordano Bruno are characterized primarily by a prominent absorption feature near 2800 nm, the band minima of which goes beyond 3000 nm. The hydration features are found to be associated with low-Ca pyroxene-bearing noritic lithologies along the inner crater flanks, whereas similar features are also seen within the hummocky crater floor in association with shocked plagioclase-bearing anorthositic lithology. Interestingly, the ejecta blanket is characterized by sharp, narrow features centered near 2800 nm similar to the features previously reported from Compton-Belkovich volcanic complex and central peak of crater Theophilus. The low-Ca pyroxene-bearing rock exposures within the crater inner flanks are characterized by both presence and absence of the hydration features. Enhanced hydration is also seen within the ejecta blanket covering the nearby Harkhebi K and J craters. We also analyze the impact melts and ejecta using radar images at regions interior and exterior to the Giordano Bruno crater rim.Anomalous behaviors of hydration feature associated with low-Ca pyroxene-rich exposures, its nature and occurrences within the impact melt sheets inside the crater along with the ejecta blankets could possibly indicate endogenic and/or exogenic nature of the observed hydration feature. Initial results indicate the presence of strongest hydration feature in the partially shadowed pole-facing slopes (with low-Ca pyroxene-bearing exposures) and its complete absence in the equator-facing sun-lit slopes. This hints at a possible exogenic origin, whereas the same feature occurring (with same mineral) under both sun-lit and shadowed conditions suggest it to be of magmatic origin. We propose that the heterogeneous

'Escher' Rock

Science.gov (United States)

2004-01-01

[figure removed for brevity, see original site] Chemical Changes in 'Endurance' Rocks [figure removed for brevity, see original site] Figure 1 This false-color image taken by NASA's Mars Exploration Rover Opportunity shows a rock dubbed 'Escher' on the southwestern slopes of 'Endurance Crater.' Scientists believe the rock's fractures, which divide the surface into polygons, may have been formed by one of several processes. They may have been caused by the impact that created Endurance Crater, or they might have arisen when water leftover from the rock's formation dried up. A third possibility is that much later, after the rock was formed, and after the crater was created, the rock became wet once again, then dried up and developed cracks. Opportunity has spent the last 14 sols investigating Escher, specifically the target dubbed 'Kirchner,' and other similar rocks with its scientific instruments. This image was taken on sol 208 (Aug. 24, 2004) by the rover's panoramic camera, using the 750-, 530- and 430-nanometer filters. The graph above shows that rocks located deeper into 'Endurance Crater' are chemically altered to a greater degree than rocks located higher up. This chemical alteration is believed to result from exposure to water. Specifically, the graph compares ratios of chemicals between the deep rock dubbed 'Escher,' and the more shallow rock called 'Virginia,' before (red and blue lines) and after (green line) the Mars Exploration Rover Opportunity drilled into the rocks. As the red and blue lines indicate, Escher's levels of chlorine relative to Virginia's went up, and sulfur down, before the rover dug a hole into the rocks. This implies that the surface of Escher has been chemically altered to a greater extent than the surface of Virginia. Scientists are still investigating the role water played in influencing this trend. These data were taken by the rover's alpha particle X-ray spectrometer.

PYROXENITE VEINS WITHIN SSZ PERIDOTITES – EVIDENCE OF MELT-ROCK INTERACTION (EGIINGOL MASSIF), MAJOR AND TRACE ELEMENT COMPOSITION OF MINERALS

OpenAIRE

A. A. Karimov; M A. Gornova; V. A. Belyaev

2017-01-01

Evidence of melt-rock reaction between suprasubduction zone (SSZ) peridotites and island arc boninititc and tholeiitic melts are identified. This process is the cause of replacive dunites and pyroxenite veins forming, which are represent the ways of island-arc melts migration. The peridotite-melt interaction is confirmed by compositional features of rocks and minerals. Influence of boninitic melt in peridotites of South Sandwich island arc leads to increasing of TiO2 and Cr-number (Cr#) in sp...

Rock Melt Borehole Sealing System, Final Technical Report for SBIR Phase I Grant No. DE-SC0011888

Energy Technology Data Exchange (ETDEWEB)

Osnes, John D. [RE/SPEC Inc., Argonne, IL (United States); Vining, Cody A. [RE/SPEC Inc., Argonne, IL (United States); Nopola, Jay R. [RE/SPEC Inc., Argonne, IL (United States); Roggenthen, William M. [South Dakota School of Mines & Technology, Rapid City, SD (United States)

2015-03-19

Purpose of Research Deep borehole disposal is one option that has received attention in recent years as a possible strategy for long-term disposal of the tens of thousands of tons of spent nuclear fuel. The feasibility of the deep borehole option relies upon designing and constructing an effective seal within the borehole to ensure that the waste package does not communicate with the shallow subsurface biosphere through the borehole itself. Some of the uncertainty associated with the long-term suitability of the deep borehole option is related to (1) the degradation of traditional sealing materials over time and (2) the inability of traditional sealing methods to adequately seal a Disturbed Rock Zone surrounding the borehole. One possible system to address these concerns consists of encapsulating the waste in a melt generated from either the waste itself or a plug above the waste. This current project expanded on previous work to further advance the deep borehole disposal concept. Research Objectives & Findings The overarching objective of the study was to evaluate the feasibility of constructing a downhole heater that is capable of meeting the technical and logistical requirements to melt rock. This ultimate objective was accomplished by two primary approaches. The first approach was to define the heater requirements and conceptually design a system that is capable of melting rock. The second approach was to determine the feasibility of conducting an in situ, field-scale melting experiment to validate the suitability of the rock melt seal concept. The evaluation and conceptual design of the heater system resulted in the following primary findings: • Borehole wall temperatures capable of producing a partial melt are achievable under most expected thermal conductivities with a 12-kilowatt heater. • Commercially available components have been identified that meet the requirements of the heater system, including resistive elements that are capable of providing the

Hard rock excavation at the CSM/OCRD test site using crater theory and current United States controlled smooth wall blasting practices, June 1982

International Nuclear Information System (INIS)

Sperry, P.E.; Chitombo, G.P.; Hustrulid, W.A.

1984-08-01

This report is the fourth in a series describing experiments conducted by the Colorado School of Mines for the Office of Crystalline Repository Development (OCRD) to determine the extent of blast damage in rock surrounding an underground opening. The report describes the application of tunnel design procedures based upon crater theory and current United States controlled smooth wall blasting practices for the excavation of the CSM/OCRD test room in the Colorado School of Mines, Experimental Mine (Edgar Mine) in Idaho Springs, Colorado. Ten blast rounds were used to excavate the test room. The first seven rounds were designed with Swedish Techniques, and described in the third report in this series, and the design of rounds eight through ten used crater theory. Crater theory is described in this document along with its application to the CSM/OCRD Room excavation. Calculation for spacing, burden, number and type of holes, explosives placement, and overall powder factor are discussed. A series of single charge cratering test shots, designed to evaluate some of the input data for the blast designs, are discussed. The input data include: Strain Energy Factor E, a dimensionless factor which varies according to the explosive and rock type; Critical Depth, N, the charge depth at which the explosive begins to fracture rock at the free face; Optimum Depth Ratio Δ 0 , which is a ratio between Optimum Charge Depth, d 0 , and Critical Charge Depth, d/sub c/; and charge Weight, W. A non-linear least squared regression method to best fit the general bell-shape curve of the crater results is discussed. Both scaled weight and scaled volume criteria are reported in the analysis of results. 10 references, 17 figures, 16 tables

Fluid-Evaporation Records Preserved in Meridiani Rocks

Science.gov (United States)

Rao, M. N.; Nyquist, Laurence E.; Sutton, S. R.

2009-01-01

We have shown earlier that the high SO3/Cl ratios found in secondary mineral assemblages in shergottite GRIM glasses (Gas-Rich Impact-Melt) likely resulted from interactions of regolith materials with sulfate-rich (and Cl-poor) solutions. The low SO3/Cl ratios determined in secondary salts in nakhalite fracture-fillings presumably formed by rock interactions with chloride-rich (and SO4-poor) solutions near Mars surface. The SO3 and Cl abundances determined by APXS in abraded rocks (RAT) from Endurance, Fram and Eagle craters indicate that these salt assemblages likely formed by evaporative concentration of brine fluids at Meridiani. The SO3/Cl ratios in the abraded rocks are examined here, instead of their absolute abundances, because the abundance ratios might provide better guide-lines for tracking the evolution of evaporating fluids at Meridiani. The SO3/Cl ratios in these samples, in turn, might provide clues for the mobile element ratios of the altering fluids that infiltrated into the Meridiani rocks.

Monturaqui meteorite impact crater, Chile: A field test of the utility of satellite-based mapping of ejecta at small craters

Science.gov (United States)

Rathbun, K.; Ukstins, I.; Drop, S.

2017-12-01

Monturaqui Crater is a small ( 350 m diameter), simple meteorite impact crater located in the Atacama Desert of northern Chile that was emplaced in Ordovician granite overlain by discontinuous Pliocene ignimbrite. Ejecta deposits are granite and ignimbrite, with lesser amounts of dark impact melt and rare tektites and iron shale. The impact restructured existing drainage systems in the area that have subsequently eroded through the ejecta. Satellite-based mapping and modeling, including a synthesis of photographic satellite imagery and ASTER thermal infrared imagery in ArcGIS, were used to construct a basic geological interpretation of the site with special emphasis on understanding ejecta distribution patterns. This was combined with field-based mapping to construct a high-resolution geologic map of the crater and its ejecta blanket and field check the satellite-based geologic interpretation. The satellite- and modeling-based interpretation suggests a well-preserved crater with an intact, heterogeneous ejecta blanket that has been subjected to moderate erosion. In contrast, field mapping shows that the crater has a heavily-eroded rim and ejecta blanket, and the ejecta is more heterogeneous than previously thought. In addition, the erosion rate at Monturaqui is much higher than erosion rates reported elsewhere in the Atacama Desert. The bulk compositions of the target rocks at Monturaqui are similar and the ejecta deposits are highly heterogeneous, so distinguishing between them with remote sensing is less effective than with direct field observations. In particular, the resolution of available imagery for the site is too low to resolve critical details that are readily apparent in the field on the scale of 10s of cm, and which significantly alter the geologic interpretation. The limiting factors for effective remote interpretation at Monturaqui are its target composition and crater size relative to the resolution of the remote sensing methods employed. This

Compositions of Bedrock Containing Craters on Mars as Viewed by TES, THEMIS, and CRISM

Science.gov (United States)

Edwards, C. S.; Rogers, D.; Bandfield, J. L.; Christensen, P. R.

2009-12-01

An investigation of Martian high thermal inertia crater surfaces has been made using derived THEMIS thermal inertia data. High thermal inertia surfaces or interpreted bedrock are defined as any pixel in a THEMIS image with a thermal inertia over 1200 J K-1m-2s-1/2 and may refer to in situ rock exposures or rock-dominated surfaces. While three different surface morphologies (valley and crater walls, crater floors, and plains surface) were originally identified [Edwards et al., in press], the focus of this study is to better characterize the compositional, thermophysical, and geological characteristics of the crater floors surface. These surfaces may be related to impact-associated volcanism that often occurs in conjunction with large energetic impacts. These craters are commonly modified, lack a central peak, have shallow sloped walls, and little to no visible ejecta, indicating the relatively old ages of these impacts. They are generally large, ranging in size from 18.5 to 179km in diameter, with an average of ~52km [Edwards et al., in press]. Boulders are also observed in high-resolution imagery (e.g. HiRISE) along with fine scale randomly oriented cracks and fractures. TES spectra for ~60 of the 92 originally identified sites have been examined in detail and can be broken down into two distinctive spectral groups, olivine bearing (~80%, with >10% olivine and often >20%) and non-olivine bearing craters (~20%, with inertia crater floors. In this case, magma is likely derived from decompression melting of the mantle due to the removal of overlying material. This magma reaches the surface through fractures and cracks in the basement rock likely caused by the impact event. This is consistent with the observed compositions, as material derived directly from the Martian mantle is expected to be significantly more mafic than the surrounding country rock. These sites are likely locations where the some of the most primitive material on Mars is observed and can be used to

Response of rocks to large stresses

International Nuclear Information System (INIS)

Schock, R.N.

1976-01-01

To predict the dimensions and characteristics of impact- and explosion-induced craters, one must know the equation of state of the rocks in which the crater is formed. Recent experimental data shed light upon inelastic processes that influence the stress/strain behavior of rocks. We examine these data with a view to developing models that could be used in predicting cratering phenomena. New data is presented on the volume behavior of two dissimilar rocks subjected to tensile stresses

Blocky craters: implications about the lunar megaregolith

International Nuclear Information System (INIS)

Thompson, T.W.; Roberts, W.J.; Hartmann, W.K.; Shorthill, R.W.; Zisk, S.H.

1979-01-01

Radar, infrared, and photogeologic properties of lunar craters have been studied to determine whether there is a systematic difference in blocky craters between the maria and terrae and whether this difference may be due to a deep megaregolith of pulverized material forming the terra surface, as opposed to a layer of semi-coherent basalt flows forming the mare surface. Some 1310 craters from about 4 to 100 km diameter have been catalogued as radar and/or infrared anomalies. In addition, a study of Apollo Orbital Photography confirmed that the radar and infrared anomalies are correlated with blocky rubble around the crater. Analysis of the radar and infrared data indicated systematic terra-mare differences. Fresh terra craters smaller than 12 km were less likely to be infrared and radar anomalies than comparable mare craters: but terra and mare craters larger than 12 km had similar infrared and radar signatures. Also, there are many terra craters which are radar bright but not infrared anomalies. The authors interpretation of these data is that while the maria are rock layers (basaltic flow units) where craters eject boulder fields, the terrae are covered by relatively pulverized megaregolith at least 2 km deep, where craters eject less rocky rubble. Blocky rubble, either in the form of actual rocks or partly consolidated blocks, contributes to the radar and infrared signatures of the crater. However, aging by impacts rapidly destroys these effects, possibly through burial by secondary debris or by disintegration of the blocks themselves, especially in terra regions. (Auth.)

PYROXENITE VEINS WITHIN SSZ PERIDOTITES – EVIDENCE OF MELT-ROCK INTERACTION (EGIINGOL MASSIF, MAJOR AND TRACE ELEMENT COMPOSITION OF MINERALS

Directory of Open Access Journals (Sweden)

A. A. Karimov

2017-01-01

Full Text Available Evidence of melt-rock reaction between suprasubduction zone (SSZ peridotites and island arc boninititc and tholeiitic melts are identified. This process is the cause of replacive dunites and pyroxenite veins forming, which are represent the ways of island-arc melts migration. The peridotite-melt interaction is confirmed by compositional features of rocks and minerals. Influence of boninitic melt in peridotites of South Sandwich island arc leads to increasing of TiO2 and Cr-number (Cr# in spinels [Pearce et al., 2000] e.g. REE patterns of clinopyroxene from Voykar are equilibrium to boninitic melts [Belousov et al., 2009]. We show that pyroxenites are formed sequential, orthopyroxenites are originated firstly, websterites – after, and the main forming process is interaction of SSZ peridotites with percolating boninite-like melts.

Cogenetic Rock Fragments from a Lunar Soil: Evidence of a Ferroan Noritic-Anorthosite Pluton on the Moon

Science.gov (United States)

Jolliff, B. L.; Haskin, L. A.

1995-01-01

The impact that produced North Ray Crater, Apollo 16 landing site, exhumed rocks that include relatively mafic members of the lunar ferroan anorthositic suite. Bulk and mineral compositions indicate that a majority of 2-4 mm lithic fragments from sample 67513, including impact breccias and monomict igneous rocks, are related to a common noritic-anorthosite precursor. Compositions and geochemical trends of these lithic fragments and of related samples collected along the rim of North Ray Crater suggest that these rocks derived from a single igneous body. This body developed as an orthocumulate from a mixture of cumulus plagioclase and mafic intercumulus melt, after the plagioclase had separated from any cogenetic mafic minerals and had become concentrated into a crystal mush (approximately 70 wt% plagioclase, 30 wt% intercumulus melt). We present a model for the crystallization of the igneous system wherein "system" is defined as cumulus plagioclase and intercumulus melt. The initial accumulation of plagioclase is analogous to the formation of thick anorthosites of the terrestrial Stillwater Complex; however, a second stage of formation is indicated, involving migration of the cumulus-plagioclase-intercumulus-melt system to a higher crustal level, analogous to the emplacement of terrestrial massif anorthosites. Compositional variations of the lithic fragments from sample 67513 are consistent with dominantly equilibrium crystallization of intercumulus melt. The highly calcic nature of orthocumulus pyroxene and plagioclase suggests some reaction between the intercumulus melt and cumulus plagioclase, perhaps facilitated by some recrystallization of cumulus plagioclase. Bulk compositions and mineral assemblages of individual rock fragments also require that most of the mafic minerals fortned in close contact with cumulus plagioclase, not as separate layers. The distribution of compositions (and by inference, modes) has a narrow peak at anorthosite and a broader, larger

Mid-IR Reflectance (DRIFT) Spectral Variations in Basaltic Mineralogy with Direction of Impact at Lonar Crater, India

Science.gov (United States)

Basavaiah, N.; Chavan, R. S.; Arif, M.

2012-12-01

Identification of spectral changes with the direction of impact has important implications for understanding the impact cratering phenomenon occurring on both terrestrial and extraterrestrial planets and also for geology of the crater. Fortuitously, Lonar Impact Crater (India) is the only well-preserved terrestrial simple crater excavated on Deccan basalts and serves as an excellent analogue to craters on Mars and Moon. An ~570 ka old Lonar crater was suggested to be formed by an oblique impact of a chondritic impactor that struck the pre-impact target from the east into a sequence of six basaltic Deccan flows and created a 1.88 km diameter crater with two layers of ejecta blanket. Here we report preliminary laboratory studies of spectral results on fine-grained rock powers (IR (4000-400 cm-1) Diffuse Reflectance Infrared Fourier Transform (DRIFT) spectroscopy. The basalts were collected from two profiles in the east and south sections of the crater wall and the upper most crater rim, which later subdivided into sector-wise samples to carry out a systematic study of spectral properties of Lonar basalts, together with impact related samples of breccias and impact melts. For the first time, data of the shock metamorphism of Lonar basalt is examined using DRIFT spectroscopy. Infrared spectra of rock powders of relatively unshocked and shocked basalts are obtained to document the mineralogical variations and the distribution of primary (e.g. Plagioclase Feldspar, Pyroxene), and secondary Phyllosilicate minerals (e.g. Illite, Smectite, Montmorillonite, Saponite, Serpentine) with direction of impact. The spectral data between pre-impact unshocked and post-impact shocked basalts are interpreted to reflect the effect of shock pressure and alteration that rock have undergone. On western crater rim sector, typical silicate spectral features in 900-1200 cm-1 which attributed to Si-O stretching, are observed to change slightly in the width and shift in position as a result of

A Tale of 3 Craters

Science.gov (United States)

2004-01-01

11 November 2004 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image captures some of the complexity of the martian upper crust. Mars does not simply have an impact-cratered surface, it's upper crust is a cratered volume. Over time, older craters on Mars have been eroded, filled, buried, and in some cases exhumed and re-exposed at the martian surface. The crust of Mars is layered to depths of 10 or more kilometers, and mixed in with the layered bedrock are a variety of ancient craters with diameters ranging from a few tens of meters (a few tens of yards) to several hundred kilometers (more than one or two hundred miles). The picture shown here captures some of the essence of the layered, cratered volume of the upper crust of Mars in a very simple form. The image shows three distinct circular features. The smallest, in the lower right quarter of the image, is a meteor crater surrounded by a mound of material. This small crater formed within a layer of bedrock that once covered the entire scene, but today is found only in this small remnant adjacent to the crater. The intermediate-sized crater, west (left) of the small one, formed either in the next layer down--that is, below the layer in which the small crater formed--or it formed in some layers that are now removed, but was big enough to penetrate deeply into the rock that is near the surface today. The largest circular feature in the image, in the upper right quarter of the image, is still largely buried. It formed in layers of rock that are below the present surface. Erosion has brought traces of its rim back to the surface of Mars. This picture is located near 50.0oS, 77.8oW, and covers an area approximately 3 km (1.9 mi) across. Sunlight illuminates this October 2004 image from the upper left.

Evolved Rocks in Ocean Islands Formed by Melting of Metasomatized Mantle

Science.gov (United States)

Ashwal, L. D.; Torsvik, T. H.; Horvath, P.; Harris, C.; Webb, S. J.; Werner, S. C.; Corfu, F.

2015-12-01

Evolved rocks like trachyte occur as minor components of many plume-related basaltic ocean islands (e.g. Hawaii, Gran Canaria, Azores, Réunion), and are typically interpreted as products of extreme fractional crystallization from broadly basaltic magmas. Trachytes from Mauritius (Indian Ocean) suggest otherwise. Here, 6.8 Ma nepheline-bearing trachytes (SiO2 ~63%, Na2O + K2O ~12%) are enriched in all incompatible elements except Ba, Sr and Eu, which show prominent negative anomalies. Initial eNd values cluster at 4.03 ± 0.15 (n = 13), near the lower end of the range for Mauritian basalts (eNd = 3.70 - 5.75), but initial Sr is highly variable (ISr = 0.70408 - 0.71034) suggesting secondary deuteric alteration. Fractional crystallization models starting with a basaltic parent fail, because when plagioclase joins olivine in the crystallizing assemblage, residual liquids become depleted in Al2O3, produce no nepheline, and do not approach trachytic compositions. Mauritian basalts and trachytes do not fall near the ends of known miscibility gaps, eliminating liquid immiscibility processes. Partial melting of extant gabbroic bodies, either from the oceanic crust or from Réunion plume-related magmas should yield quartz-saturated melts different from the critically undersaturated Mauritian trachytes. A remaining possibility is that the trachytes represent direct, small-degree partial melts of fertile, perhaps metasomatized mantle. This is supported by the presence of trachytic glasses in many mantle xenoliths, and experimental results show that low-degree trachytic melts can be produced from mantle peridotites even under anhydrous conditions. If some feldspar is left behind as a residual phase, this would account for the negative Ba, Sr and Eu anomalies observed in Mauritian trachytes. Two trachyte samples that are less depleted in these elements contain xenocrysts of anorthoclase, Al-rich cpx and Cl-rich kaersutite that are out of equilibrium with host trachyte magmas

Distribution of siderophile and other trace elements in melt rock at the Chicxulub impact structure

Science.gov (United States)

Schuraytz, B. C.; Lindstrom, D. J.; Martinez, R. R.; Sharpton, V. L.; Marin, L. E.

1994-01-01

Recent isotopic and mineralogical studies have demonstrated a temporal and chemical link between the Chicxulub multiring impact basin and ejecta at the Cretaceous-Tertiary boundary. A fundamental problem yet to be resolved, however, is identification of the projectile responsible for this cataclysmic event. Drill core samples of impact melt rock from the Chichxulub structure contain Ir and Os abundances and Re-Os isotopic ratios indicating the presence of up to approx. 3 percent meteoritic material. We have used a technique involving microdrilling and high sensitivity instrumental neutron activation analysis (INAA) in conjunction with electron microprobe analysis to characterize further the distribution of siderophile and other trace elements among phases within the C1-N10 melt rock.

Characterization and petrologic interpretation of olivine-rich basalts at Gusev Crater, Mars

Science.gov (United States)

McSween, H.Y.; Wyatt, M.B.; Gellert, Ralf; Bell, J.F.; Morris, R.V.; Herkenhoff, K. E.; Crumpler, L.S.; Milam, K.A.; Stockstill, K.R.; Tornabene, L.L.; Arvidson, R. E.; Bartlett, P.; Blaney, D.; Cabrol, N.A.; Christensen, P.R.; Clark, B. C.; Crisp, J.A.; Des Marais, D.J.; Economou, T.; Farmer, J.D.; Farrand, W.; Ghosh, A.; Golombek, M.; Gorevan, S.; Greeley, R.; Hamilton, V.E.; Johnson, J. R.; Joliff, B.L.; Klingelhofer, G.; Knudson, A.T.; McLennan, S.; Ming, D.; Moersch, J.E.; Rieder, R.; Ruff, S.W.; Schrorder, C.; de Souza, P.A.; Squyres, S. W.; Wanke, H.; Wang, A.; Yen, A.; Zipfel, J.

2006-01-01

Rocks on the floor of Gusev crater are basalts of uniform composition and mineralogy. Olivine, the only mineral to have been identified or inferred from data by all instruments on the Spirit rover, is especially abundant in these rocks. These picritic basalts are similar in many respects to certain Martian meteorites (olivine-phyric shergottites). The olivine megacrysts in both have intermediate compositions, with modal abundances ranging up to 20-30%. Associated minerals in both include low-calcium and high-calcium pyroxenes, plagioclase of intermediate composition, iron-titanium-chromium oxides, and phosphate. These rocks also share minor element trends, reflected in their nickel-magnesium and chromium-magnesium ratios. Gusev basalts and shergottites appear to have formed from primitive magmas produced by melting an undepleted mantle at depth and erupted without significant fractionation. However, apparent differences between Gusev rocks and shergottites in their ages, plagioclase abundances, and volatile contents preclude direct correlation. Orbital determinations of global olivine distribution and compositions by thermal emission spectroscopy suggest that olivine-rich rocks may be widespread. Because weathering under acidic conditions preferentially attacks olivine and disguises such rocks beneath alteration rinds, picritic basalts formed from primitive magmas may even be a common component of the Martian crust formed during ancient and recent times. Copyright 2006 by the American Geophysical Union.

Consequences of Melt-Preferred Orientation for Magmatic Segregation in Deforming Mantle Rock

Science.gov (United States)

Katz, R. F.; Taylor-West, J.; Allwright, J.; Takei, Y.; Qi, C.; Kohlstedt, D. L.

2014-12-01

In partially molten regions of the mantle, deviatoric stresses cause large-scale deformation and mantle flow. The same stresses also lead to preferential wetting of coherently oriented grain boundaries [DK97, T10]. This alignment is called melt-preferred orientation (MPO). Because of the contrast between the physical properties of melt and solid grains, MPO has the potential to introduce anisotropy into the mechanical and transport properties of the liquid/solid aggregate. Here we consider the possible consequences for (and of) anisotropic viscosity and permeability of the partially molten aggregate. The consequences are evaluated in the context of laboratory experiments on partially molten rocks. The controlled experiments involve deformation of an initially uniform mixture of solid olivine and liquid basalt [KZK10]. The resultant patterns of melt segregation include two robust features: (i) melt segregation into bands with high melt fraction oriented at a low angle to the shear plane; and (ii) melt segregation associated with an imposed gradient in shear stress, in experiments where this is present. Although there are other reproducible features of experiments, these are the most robust and provide a challenge to models. A theoretical model for the effect of MPO on mantle viscosity under diffusion creep is available [TH09] and makes predictions that are consistent with laboratory experiments [TK13,KT13,QKKT14,AK14]. We review the mechanics of this model and the predictions for flow in torsional and pipe Poiseuille flow, showing a quantitative comparison with experimental results. Furthermore, it is logical to expect MPO to lead to anisotropy of permeability, and we present a general model of tensorial permeability. We demonstrate the consequences of this anisotropy for simple shear deformation of a partially molten rock. REFERENCES: DK97 = Daines & Kohlstedt (1997), JGR, 10.1029/97JB00393. T10 = Takei (2010), JGR, 10.1029/2009JB006568. KZK10 = King, Zimmerman

Scaling of cratering experiments: an analytical and heuristic approach to the phenomenology

International Nuclear Information System (INIS)

Killian, B.G.; Germain, L.S.

1977-01-01

The phenomenology of cratering can be thought of as consisting of two phases. The first phase, where the effects of gravity are negligible, consists of the energy source dynamically imparting its energy to the surroundings, rock and air. As illustrated in this paper, the first phase can be scaled if: radiation effects are negligible, experiments are conducted in the same rock material, time and distance use the same scaling factor, and distances scale as the cube root of the energy. The second phase of cratering consists of the rock, with its already developed velocity field, being thrown out. It is governed by the ballistics equation, and gravity is of primary importance. This second phase of cratering is examined heuristically by examples of the ballistics equation which illustrate the basic phenomena in crater formation. When gravity becomes significant, in addition to the conditions for scaling imposed in the first phase, distances must scale inversely as the ratio of gravities. A qualitative relationship for crater radius is derived and compared with calculations and experimental data over a wide range of energy sources and gravities

Diversity of Rock Compositions at Gale Crater Observed by ChemCam and APXS on Curiosity, and Comparison to Meteorite and Orbital Observations

Science.gov (United States)

Wiens, R. C.; Maurice, S.; Grotzinger, J. P.; Gellert, R.; Mangold, N.; Sautter, V.; Ollila, A.; Dyar, M. D.; Le Mouelic, S.; Ehlmann, B. L.; Clegg, S. M.; Lanza, N.; Cousin, A.; Forni, O.; Gasnault, O.; Lasue, J.; Blaney, D. L.; Newsom, H. E.; Herkenhoff, K. E.; Anderson, R. B.; D'Uston, L.; Bridges, N. T.; Fabre, C.; Meslin, P.; Johnson, J.; Vaniman, D.; Bridges, J.; Dromart, G.; Schmidt, M. E.; Team, M.

2013-12-01

Gale crater was selected as the Curiosity landing site because of the apparent sedimentary spectral signatures seen from orbit. Sedimentary materials on Mars have to this point showed very little expression of major element mobility, so compositions of precursor igneous minerals play a strong role in the compositions of sediments. In addition, pebbles and float rocks on Bradbury Rise (sols 0-50, > 324) appear to be mostly igneous in origin, and are assumed to have been carried down from the crater rim. Overall in the first year on Mars ChemCam obtained >75,000 LIBS spectra on > 2,000 observation points, supported by > 1,000 RMI images, and APXS obtained a significant number of observations. These show surprisingly variable compositions. The mean ChemCam compositions for Bradbury Rise dust-free rocks and pebbles (62 locations) give SiO2 = 56%, FeOT = 16% and show high alkalis consistent with Jake Matijevic (sol ~47) APXS Na2O ~6.6 wt%. ChemCam observations on the conglomerate Link (sol 27) gave Rb > 150 ppm and Sr > 1500 ppm. These compositions imply the presence of abundant alkali feldspars in the material infilling the lower parts of Gale crater. They are generally consistent with the more feldspar-rich SNC meteorites but show a radical departure from larger scale orbital observations, e.g., GRS, raising the question of how widespread these compositions are outside of Gale crater. Sedimentary materials at Yellowknife Bay encompassing the Sheepbed (sols 125-300) and Shaler (sols 121, 311-324) units, potentially including Point Lake (sols 301-310) and Rocknest (sols 57-97), appear to have incorporated varying amounts of igneous source materials. Seven rocks investigated at Rocknest show significant additions of Fe, with mean FeOT = 25% (154 locations), suggesting that FeO was a cementing agent. ChemCam observations at Shaler show varying amounts of alkali feldspar (i.e., related to Bradbury Rise), Fe-rich material (Rocknest-like), and potassium-rich material

Characterizing the nature of melt-rock reaction in peridotites from the Santa Elena Ophiolite, NW Costa Rica

Science.gov (United States)

Carr, D.; Loocke, M. P.; Snow, J. E.; Gazel, E.

2017-12-01

The Santa Elena Ophiolite (SEO), located on the northwestern coast of Costa Rica, consists primarily of preserved oceanic mantle and crustal rocks thrust above an accretionary complex. The SEO is predominantly characterized by mantle peridotites (i.e., primarily spinel lherzolite with minor amounts of harzburgite and dunite) cut and intruded by minor pegmatitic gabbros, layered gabbros, plagiogranites, and doleritic and basaltic dykes. Previous studies have concluded that the complex formed in a suprasubduction zone (SSZ) setting based on the geochemical nature of the layered gabbros and plagiogranites (i.e., depleted LREE and HFSE and enriched LILE and Pb), as well, as the peridotites (i.e., low-TiO2, Zr, and V, and high MgO, Cr, and Ni)(Denyer and Gazel, 2009). Eighteen ultramafic samples collected during the winter 2010/2011 field season (SECR11) exhibit abundant evidence for melt-rock reaction (e.g., disseminated plagioclase and plagioclase-spinel, clinopyroxene-spinel, and plagioclase-clinopyroxene symplectites) and provide a unique opportunity to characterize the textural and chemical nature of melt-rock reaction in the SEO. We present the results of a petrologic investigation (i.e., petrography and electron probe microanalysis) of 28 thin sections (19 spinel lherzolites, of which 14 are plagioclase-bearing, 4 pyroxenite veins, and 5 harzburgites) derived from the SECR11 sample set. The results of this investigation have the potential to better our understanding of the nature of melt generation and migration and melt-rock interaction in the SEO mantle section and shed further light on the complex petrogenetic history of the SEO. Denyer, P., Gazel, E., 2009, Journal of South American Earth Sciences, 28:429-442.

Mineral Fractionation during Sediment Comminution and Transport in Fluvio-Deltaic and Lacustrine Rocks of the Bradbury Group, Gale Crater, Mars

Science.gov (United States)

Siebach, K. L.; Baker, M. B.; Grotzinger, J. P.; McLennan, S. M.; Gellert, R.; Thompson, L. M.; Hurowitz, J.

2017-12-01

Mineral distribution patterns in sediments of the Bradbury group in Gale crater, interpreted from observations by the Mars Science Laboratory rover Curiosity, show the importance of transport mechanics in source-to-sink processes on Mars. The Bradbury group is comprised of basalt-derived mudstones to conglomerates exposed along the modern floor of Gale crater and analyzed along a 9-km traverse of the Curiosity rover. Over 110 bulk chemistry analyses of the rocks were acquired, along with two XRD mineralogical analyses of the mudstone. These rocks are uniquely suited for analysis of source-to-sink processes because they exhibit a wide range of compositions, but (based on multiple chemical weathering proxies) they appear to have experienced negligible cation-loss during weathering and erosion. Chemical variations between analyses correlate with sediment grain sizes, with coarser-grained rocks enriched in plagioclase components SiO2, Al2O3, and Na2O, and finer-grained rocks enriched in components of mafic minerals, consistent with grain-size sorting of mineral fractions during sediment transport. Further geochemical and mineralogical modeling supports the importance of mineral fractionation: even though the limited XRD data suggests that some fraction (if not all) of the rocks contain clays and an amorphous component, models show that 90% of the compositions measured are consistent with sorting of primary igneous minerals from a plagioclase-phyric subalkaline basalt (i.e., no corrections for cation-loss are required). The distribution of K2O, modeled as a potassium feldspar component, is an exception to the major-element trends because it does not correlate with grain size, but has an elevation-dependent signal likely correlated with the introduction of a second source material. However, the dominant compositional trends within the Bradbury group sedimentary rocks are correlated with grain size and consistent with mineral fractionation of minimally

Unusual Physical Properties of the Chicxulub Crater Peak Ring: Results from IODP/ICDP Expedition 364

Science.gov (United States)

Christeson, G. L.; Gebhardt, C.; Gulick, S. P. S.; Le Ber, E.; Lofi, J.; Morgan, J. V.; Nixon, C.; Rae, A.; Schmitt, D. R.

2017-12-01

IODP/ICDP Expedition 364 Hole M0077A drilled into the peak ring of the Chicxulub impact crater, recovering core between 505.7 and 1334.7 m below the seafloor (mbsf). Physical property measurements include wireline logging data, a vertical seismic profile (VSP), Multi-Sensor Core Logger (MSCL) measurements, and discrete sample measurements. The Hole M0077A peak ring rocks have unusual physical properties. Across the boundary between post-impact sediment and crater breccia we measure a sharp decrease in velocities and densities, and an increase in porosity. Mean crater breccia values are 3000-3300 m/s, 2.14-2.15 g/cm3, and 31% for velocity, density, and porosity, respectively. This zone is also associated with a low-frequency reflector package on MCS profiles and a low-velocity layer in FWI images, both confirmed from the VSP dataset. The thin (24 m) crater melt unit has mean velocity measurements of 3800-4150 m/s, density measurements of 2.32-2.34 g/cm3, and porosity measurements of 20%; density and porosity values are intermediate between the overlying impact breccia and underlying granitic basement, while the velocity values are similar to those for the underlying basement. The Hole M0077A crater melt unit velocities and densities are considerably less than values of 5800 m/s and 2.68 g/cm3 measured at an onshore well located in the annular trough. The uplifted granitic peak ring materials have mean values of 4100-4200 m/s, 2.39-2.44 g/cm3, and 11% for compressional wave velocity, density, and porosity, respectively; these values differ significantly from typical granite which has higher velocities (5400-6000 m/s) and densities (2.62-2.67 g/cm3), and lower porosities (<1%). All Hole M0077A peak-ring velocity, density, and porosity measurements indicate considerable fracturing, and are consistent with numerical models for peak-ring formation.

Ar-Ar dating techniques for terrestrial meteorite impacts

Science.gov (United States)

Kelley, S. P.

2003-04-01

The ages of the largest (>100 km) known impacts on Earth are now well characterised. However the ages of many intermediate sized craters (20-100 km) are still poorly known, often the only constraints are stratigraphic - the difference between the target rock age and the age of crater filling sediments. The largest impacts result in significant melt bodies which cool to form igneous rocks and can be dated using conventional radiometric techniques. Smaller impacts give rise to thin bands of melted rock or melt clasts intimately mixed with country rock clasts in breccia deposits, and present much more of a challenge to dating. The Ar-Ar dating technique can address a wide variety of complex and heterogeneous samples associated with meteorite impacts and obtain reasonable ages. Ar-Ar results will be presented from a series of terrestrial meteorite impact craters including Boltysh (65.17±0.64 Ma, Strangways (646±42 Ma), and St Martin (220±32 Ma) and a Late Triassic spherule bed, possibly representing distal deposits from Manicouagan (214±1 Ma) crater. Samples from the Boltysh and Strangways craters demonstrate the importance of rapid cooling upon the retention of old ages in glassy impact rocks. A Late Triassic spherule bed in SW England is cemented by both carbonate and K-feldspar cements allowing Ar-Ar dating of fine grained cement to place a mimimum age upon the age of the associated impact. An age of 214.7±2.5 Ma places the deposit with errors of the age of the Manicouagan impact, raising the possibility that it may represent a distal deposit (the deposit lay around 2000 km away from the site of the Manicouagan crater during the Late Triassic). Finally the limits of the technique will be demonstrated using an attempt to date melt rocks from the St Martin Crater in Canada.

Summary of results of cratering experiments

International Nuclear Information System (INIS)

Toman, J.

1969-01-01

The use of nuclear excavation as a construction technique for producing harbors, canals, highway cuts, and other large excavations requires a high assurance that the yield and depth of burst selected for the explosive will produce the desired configuration within an acceptable degree of tolerance. Nuclear excavation technology advanced significantly during 1968 as a result of the successful execution of Projects Cabriolet, Buggy, and Schooner. Until these experiments were conducted, the only nuclear data available for designing large excavations were derived from Sedan (100 kt in alluvium), Danny Boy (0.42 kt in basalt), and Sulky (0.090 kt in basalt). Applicable experience has now been extended to include two additional rock types: tuff and porphyritic trachyte, non-homogeneous formations with severe geologic layering, and a nuclear row in hard rock. The continued development of cratering calculations using in situ geophysical measurements and high-pressure test data have provided a means for predicting the cratering characteristics of untested materials. Chemical explosive cratering experiments conducted in the pre-Gondola series during the past several years have been directed toward determining the behavior of weak, wet clay shales. This material is important to nuclear excavation because of potential long-term stability problems which may affect the cratered slopes. (author)

Summary of results of cratering experiments

Energy Technology Data Exchange (ETDEWEB)

Toman, J [Lawrence Radiation Laboratory, Livermore, CA (United States)

1969-07-01

The use of nuclear excavation as a construction technique for producing harbors, canals, highway cuts, and other large excavations requires a high assurance that the yield and depth of burst selected for the explosive will produce the desired configuration within an acceptable degree of tolerance. Nuclear excavation technology advanced significantly during 1968 as a result of the successful execution of Projects Cabriolet, Buggy, and Schooner. Until these experiments were conducted, the only nuclear data available for designing large excavations were derived from Sedan (100 kt in alluvium), Danny Boy (0.42 kt in basalt), and Sulky (0.090 kt in basalt). Applicable experience has now been extended to include two additional rock types: tuff and porphyritic trachyte, non-homogeneous formations with severe geologic layering, and a nuclear row in hard rock. The continued development of cratering calculations using in situ geophysical measurements and high-pressure test data have provided a means for predicting the cratering characteristics of untested materials. Chemical explosive cratering experiments conducted in the pre-Gondola series during the past several years have been directed toward determining the behavior of weak, wet clay shales. This material is important to nuclear excavation because of potential long-term stability problems which may affect the cratered slopes. (author)

New insight into lunar impact melt mobility from the LRO camera

Science.gov (United States)

Bray, Veronica J.; Tornabene, Livio L.; Keszthelyi, Laszlo P.; McEwen, Alfred S.; Hawke, B. Ray; Giguere, Thomas A.; Kattenhorn, Simon A.; Garry, William B.; Rizk, Bashar; Caudill, C.M.; Gaddis, Lisa R.; van der Bogert, Carolyn H.

2010-01-01

The Lunar Reconnaissance Orbiter Camera (LROC) is systematically imaging impact melt deposits in and around lunar craters at meter and sub-meter scales. These images reveal that lunar impact melts, although morphologically similar to terrestrial lava flows of similar size, exhibit distinctive features (e.g., erosional channels). Although generated in a single rapid event, the post-impact mobility and morphology of lunar impact melts is surprisingly complex. We present evidence for multi-stage influx of impact melt into flow lobes and crater floor ponds. Our volume and cooling time estimates for the post-emplacement melt movements noted in LROC images suggest that new flows can emerge from melt ponds an extended time period after the impact event.

Origin of discrepancies between crater size-frequency distributions of coeval lunar geologic units via target property contrasts

Science.gov (United States)

van der Bogert, C. H.; Hiesinger, H.; Dundas, C. M.; Krüger, T.; McEwen, A. S.; Zanetti, M.; Robinson, M. S.

2017-12-01

Recent work on dating Copernican-aged craters, using Lunar Reconnaissance Orbiter (LRO) Camera data, re-encountered a curious discrepancy in crater size-frequency distribution (CSFD) measurements that was observed, but not understood, during the Apollo era. For example, at Tycho, Copernicus, and Aristarchus craters, CSFDs of impact melt deposits give significantly younger relative and absolute model ages (AMAs) than impact ejecta blankets, although these two units formed during one impact event, and would ideally yield coeval ages at the resolution of the CSFD technique. We investigated the effects of contrasting target properties on CSFDs and their resultant relative and absolute model ages for coeval lunar impact melt and ejecta units. We counted craters with diameters through the transition from strength- to gravity-scaling on two large impact melt deposits at Tycho and King craters, and we used pi-group scaling calculations to model the effects of differing target properties on final crater diameters for five different theoretical lunar targets. The new CSFD for the large King Crater melt pond bridges the gap between the discrepant CSFDs within a single geologic unit. Thus, the observed trends in the impact melt CSFDs support the occurrence of target property effects, rather than self-secondary and/or field secondary contamination. The CSFDs generated from the pi-group scaling calculations show that targets with higher density and effective strength yield smaller crater diameters than weaker targets, such that the relative ages of the former are lower relative to the latter. Consequently, coeval impact melt and ejecta units will have discrepant apparent ages. Target property differences also affect the resulting slope of the CSFD, with stronger targets exhibiting shallower slopes, so that the final crater diameters may differ more greatly at smaller diameters. Besides their application to age dating, the CSFDs may provide additional information about the

Crater Mound Formation by Wind Erosion on Mars

Science.gov (United States)

Steele, L. J.; Kite, E. S.; Michaels, T. I.

2018-01-01

Most of Mars' ancient sedimentary rocks by volume are in wind-eroded sedimentary mounds within impact craters and canyons, but the connections between mound form and wind erosion are unclear. We perform mesoscale simulations of different crater and mound morphologies to understand the formation of sedimentary mounds. As crater depth increases, slope winds produce increased erosion near the base of the crater wall, forming mounds. Peak erosion rates occur when the crater depth is ˜2 km. Mound evolution depends on the size of the host crater. In smaller craters mounds preferentially erode at the top, becoming more squat, while in larger craters mounds become steeper sided. This agrees with observations where smaller craters tend to have proportionally shorter mounds and larger craters have mounds encircled by moats. If a large-scale sedimentary layer blankets a crater, then as the layer recedes across the crater it will erode more toward the edges of the crater, resulting in a crescent-shaped moat. When a 160 km diameter mound-hosting crater is subject to a prevailing wind, the surface wind stress is stronger on the leeward side than on the windward side. This results in the center of the mound appearing to "march upwind" over time and forming a "bat-wing" shape, as is observed for Mount Sharp in Gale crater.

Permeability and 3-D melt geometry in shear-induced high melt fraction conduits

Science.gov (United States)

Zhu, W.; Cordonnier, B.; Qi, C.; Kohlstedt, D. L.

2017-12-01

Observations of dunite channels in ophiolites and uranium-series disequilibria in mid-ocean ridge basalt suggest that melt transport in the upper mantle beneath mid-ocean ridges is strongly channelized. Formation of high melt fraction conduits could result from mechanical shear, pyroxene dissolution, and lithological partitioning. Deformation experiments (e.g. Holtzman et al., 2003) demonstrate that shear stress causes initially homogeneously distributed melt to segregate into an array of melt-rich bands, flanked by melt-depleted regions. At the same average melt fraction, the permeability of high melt fraction conduits could be orders of magnitude higher than that of their homogenous counterparts. However, it is difficult to determine the permeability of melt-rich bands. Using X-ray synchrotron microtomography, we obtained high-resolution images of 3-dimensional (3-D) melt distribution in a partially molten rock containing shear-induced high melt fraction conduits. Sample CQ0705, an olivine-alkali basalt aggregate with a nominal melt fraction of 4%, was deformed in torsion at a temperature of 1473 K and a confining pressure of 300 MPa to a shear strain of 13.3. A sub-volume of CQ0705 encompassing 3-4 melt-rich bands was imaged. Microtomography data were reduced to binary form so that solid olivine is distinguishable from basalt glass. At a spatial resolution of 160 nm, the 3-D images reveal the shape and connectedness of melt pockets in the melt-rich bands. Thin melt channels formed at grain edges are connected at large melt nodes at grain corners. Initial data analysis shows a clear preferred orientation of melt pockets alignment subparallel to the melt-rich band. We use the experimentally determined geometrical parameters of melt topology to create a digital rock with identical 3-D microstructures. Stokes flow simulations are conducted on the digital rock to obtain the permeability tensor. Using this digital rock physics approach, we determine how deformation

Reverse polarity magnetized melt rocks from the Chicxulub impact structure, Yucatan Peninsula, Mexico

Science.gov (United States)

Urrutia-Fucugauchi, Jaime; Marin, Luis E.; Sharpton, Virgil L.; Quezada, Juan Manuel

1993-03-01

Further paleomagnetic data for core samples of melt rock recovered in the Petroleos Mexicanos (PEMEX) exploratory wells within the Chicxulub structure, northern Yucatan peninsula, Mexico are reported. A previous report by Sharpton showed that the rocks studied contain high iridium levels and shocked breccia clasts, and an Ar-40/Ar-39 age of 65.2 plus or minus 0.4 Ma. The geomagnetic polarity determined for two samples is reverse (R) and was correlated with chron 29R that includes the K/T boundary. Our present analysis is based on two samples from each of three clasts of the melt rock from PEMEX well Y6-N17 (1295 to 1299 m b.s.l.). This study concentrates on the vectorial nature and stability of the remanence (NRM), the magnetic mineralogy and remanence carriers (i.e., the reliability and origin of the record), and on the implications (correlation with expected paleolatitude and polarity). The relative orientation of the drill core samples with respect to the horizontal is known. Samples were stable under alternating field (AF) and thermal treatments, and after removal of a small component they exhibited single-vectorial behavior. The characteristic remanence inclinations show small dispersion and a mean value (-43 deg) in close agreement with the expected inclination and paleolatitude (derived from the North American apparent polar wander path). Isothermal remenence (IRM) acquisition experiments, Lowrie-Fuller tests, coercivity and unblocking temperature spectra of NRM and saturation IRM, susceptibility and Q-coefficient analyses, and the single-component nature indicate a dominant mineralogy of iron-rich titanomagnetites with single or pseduo-single domain states. The stable characteristic magnetization may be interpreted as a result of shock heating of the rock at the time of formation of the inpact structure and its polarity, age, and paleolatitude are consistent with a time about the K/T boundary.

Impact-generated Hydrothermal Activity at the Chicxulub Crater

Science.gov (United States)

Kring, D. A.; Zurcher, L.; Abramov, O.

2007-05-01

Borehole samples recovered from PEMEX exploration boreholes and an ICDP scientific borehole indicate the Chicxulub impact event generated hydrothermal alteration throughout a large volume of the Maya Block beneath the crater floor and extending across the bulk of the ~180 km diameter crater. The first indications of hydrothermal alteration were observed in the crater discovery samples from the Yucatan-6 borehole and manifest itself in the form of anhydrite and quartz veins. Continuous core from the Yaxcopoil-1 borehole reveal a more complex and temporally extensive alteration sequence: following a brief period at high temperatures, impact- melt-bearing polymict breccias and a thin, underlying unit of impact melt were subjected to metasomatism, producing alkali feldspar, sphene, apatite, and magnetite. As the system continued to cool, smectite-series phyllosilicates appeared. A saline solution was involved. Stable isotopes suggest the fluid was dominated by a basinal brine created mostly from existing groundwater of the Yucatan Peninsula, although contributions from down-welling water also occurred in some parts of the system. Numerical modeling of the hydrothermal system suggests circulation occurred for 1.5 to 2.3 Myr, depending on the permeability of the system. Our understanding of the hydrothermal system, however, is still crude. Additional core recovery projects, particularly into the central melt sheet, are needed to better evaluate the extent and duration of hydrothermal alteration.

Creation of High Resolution Terrain Models of Barringer Meteorite Crater (Meteor Crater) Using Photogrammetry and Terrestrial Laser Scanning Methods

Science.gov (United States)

Brown, Richard B.; Navard, Andrew R.; Holland, Donald E.; McKellip, Rodney D.; Brannon, David P.

2010-01-01

Barringer Meteorite Crater or Meteor Crater, AZ, has been a site of high interest for lunar and Mars analog crater and terrain studies since the early days of the Apollo-Saturn program. It continues to be a site of exceptional interest to lunar, Mars, and other planetary crater and impact analog studies because of its relatively young age (est. 50 thousand years) and well-preserved structure. High resolution (2 meter to 1 decimeter) digital terrain models of Meteor Crater in whole or in part were created at NASA Stennis Space Center to support several lunar surface analog modeling activities using photogrammetric and ground based laser scanning techniques. The dataset created by this activity provides new and highly accurate 3D models of the inside slope of the crater as well as the downslope rock distribution of the western ejecta field. The data are presented to the science community for possible use in furthering studies of Meteor Crater and impact craters in general as well as its current near term lunar exploration use in providing a beneficial test model for lunar surface analog modeling and surface operation studies.

Proceedings of the Geophysical Laboratory/Lawrence Radiation Laboratory Cratering Symposium

Energy Technology Data Exchange (ETDEWEB)

Nordyke, Milo D. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

1961-10-01

The geological papers in this morning's session will deal descriptively with surficial features and end products of impact craters caused by meteorite falls. Such items as breccia, structural deformation, normal and inverse stratigraphy, glass (fused rock), and coesite will frequently be mentioned. Meteor and explosion crater data are presented.

High Resolution Digital Elevation Models of Pristine Explosion Craters

Science.gov (United States)

Farr, T. G.; Krabill, W.; Garvin, J. B.

2004-01-01

In order to effectively capture a realistic terrain applicable to studies of cratering processes and landing hazards on Mars, we have obtained high resolution digital elevation models of several pristine explosion craters at the Nevada Test Site. We used the Airborne Terrain Mapper (ATM), operated by NASA's Wallops Flight Facility to obtain DEMs with 1 m spacing and 10 cm vertical errors of 4 main craters and many other craters and collapse pits. The main craters that were mapped are Sedan, Scooter, Schooner, and Danny Boy. The 370 m diameter Sedan crater, located on Yucca Flat, is the largest and freshest explosion crater on Earth that was formed under conditions similar to hypervelocity impact cratering. As such, it is effectively pristine, having been formed in 1962 as a result of a controlled detonation of a 100 kiloton thermonuclear device, buried at the appropriate equivalent depth of burst required to make a simple crater. Sedan was formed in alluvium of mixed lithology and subsequently studied using a variety of field-based methods. Nearby secondary craters were also formed at the time and were also mapped by ATM. Adjacent to Sedan and also in alluvium is Scooter, about 90 m in diameter and formed by a high-explosive event. Schooner (240 m) and Danny Boy (80 m) craters were also important targets for ATM as they were excavated in hard basalt and therefore have much rougher ejecta. This will allow study of ejecta patterns in hard rock as well as engineering tests of crater and rock avoidance and rover trafficability. In addition to the high resolution DEMs, crater geometric characteristics, RMS roughness maps, and other higher-order derived data products will be generated using these data. These will provide constraints for models of landing hazards on Mars and for rover trafficability. Other planned studies will include ejecta size-frequency distribution at the resolution of the DEM and at finer resolution through air photography and field measurements

Basalt-trachybasalt samples in Gale Crater, Mars

International Nuclear Information System (INIS)

Edwards, Peter H.; Anderson, Ryan B.; Dyar, Darby

2017-01-01

The ChemCam instrument on the Mars Science Laboratory (MSL) rover, Curiosity, observed numerous igneous float rocks and conglomerate clasts, reported previously. A new statistical analysis of single-laser-shot spectra of igneous targets observed by ChemCam shows a strong peak at ~55 wt% SiO 2 and 6 wt% total alkalis, with a minor secondary maximum at 47–51 wt% SiO 2 and lower alkali content. The centers of these distributions, together with the rock textures, indicate that many of the ChemCam igneous targets are trachybasalts, Mg# = 27 but with a secondary concentration of basaltic material, with a focus of compositions around Mg# = 54. We suggest that all of these igneous rocks resulted from low-pressure, olivine-dominated fractionation of Adirondack (MER) class-type basalt compositions. This magmatism has subalkaline, tholeiitic affinities. The similarity of the basalt endmember to much of the Gale sediment compositions in the first 1000 sols of the MSL mission suggests that this type of Fe-rich, relatively low-Mg#, olivine tholeiite is the dominant constituent of the Gale catchment that is the source material for the fine-grained sediments in Gale. The similarity to many Gusev igneous compositions suggests that it is a major constituent of ancient Martian magmas, and distinct from the shergottite parental melts thought to be associated with Tharsis and the Northern Lowlands. Finally, the Gale Crater catchment sampled a mixture of this tholeiitic basalt along with alkaline igneous material, together giving some analogies to terrestrial intraplate magmatic provinces.

Soft Rock Yields Clues to Mars' Past

Science.gov (United States)

2004-01-01

[figure removed for brevity, see original site] Figure 1 This image taken by the Mars Exploration Rover Spirit shows the rock outcrop dubbed 'Clovis.' The rock was discovered to be softer than other rocks studied so far at Gusev Crater after the rover easily ground a hole into it with its rock abrasion tool. Spirit's solar panels can be seen in the foreground. This image was taken by the rover's navigation camera on sol 205 (July 31, 2004). Elemental Trio Found in 'Clovis' Figure 1 above shows that the interior of the rock dubbed 'Clovis' contains higher concentrations of sulfur, bromine and chlorine than basaltic, or volcanic, rocks studied so far at Gusev Crater. The data were taken by the Mars Exploration Rover Spirit's alpha particle X-ray spectrometer after the rover dug into Clovis with its rock abrasion tool. The findings might indicate that this rock was chemically altered, and that fluids once flowed through the rock depositing these elements.

Terrestrial Analogs for Surface Properties Associated with Impact Cratering on the Moon - Self-secondary Impact Features at Kings Bowl, Idaho

Science.gov (United States)

Matiella Novak, M. A.; Zanetti, M.; Neish, C.; Kukko, A.; Fan, K.; Heldmann, J.; Hughes, S. S.

2017-12-01

The Kings Bowl (KB) eruptive fissure and lava field, located in the southern end of Craters of the Moon National Monument, Idaho, is an ideal location for planetary analogue field studies of surface properties related to volcanic and impact processes. Here we look at possible impact features present in the KB lava field near the main vent that resulted in squeeze-ups of molten lava from beneath a semi-solid lava lake crust. These may have been caused by the ejection of blocks during the phreatic eruption that formed the Kings Bowl pit, and their subsequent impact into a partially solidified lava pond. We compare and contrast these features with analogous self-secondary impact features, such as irregular, rimless secondary craters ("splash craters") observed in lunar impact melt deposits, to better understand how self-secondary impacts determine the surface properties of volcanic and impact crater terrains. We do this by analyzing field measurements of these features, as well as high-resolution DEM data collected through the Kinematic LiDAR System (KLS), both of which give us feature dimensions and distributions. We then compare these data with self-secondary impact features on the Moon and related surface roughness constrained through Lunar Reconnaissance Orbiter observations (Mini-RF and LROC NACs). Possible self-secondary impact features can be found in association with many lunar impact craters. These are formed when ballistic ejecta from the crater falls onto the ejecta blanket and melt surrounding the newly formed crater. Self-secondary impact features involving impact melt deposits are particularly useful to study because the visibly smooth melt texture serves to highlight the impact points in spacecraft imagery. The unusual morphology of some of these features imply that they formed when the melt had not yet completely solidified, strongly suggesting a source of impactors from the primary crater itself. We will also discuss ongoing efforts to integrate field

Morphometry and Morphology of Fresh Craters on Titan

Science.gov (United States)

Kirk, R. L.; Wood, C. A.; Neish, C.; Lucas, A.; Hayes, A. G.; Cassini Radar Team

2011-12-01

-bright ejecta to a distance of 15-20 km (0.3-0.5 diameters) beyond the rim. Compared to the ejecta blankets of Ksa and Sinlap, this deposit has been encroached upon only slightly by dunes and thus appears more nearly symmetrical. We initially interpreted the ejecta as having a thickness of several hundred meters (which would be unique on Titan) based on apparent shading at the northern edge, but close inspection shows this to be an optical illusion caused by a thin band of dark plains showing between the edge of the ejecta and nearby bright flow fields that encircle about 3/4 of the circumference. Although these flows may predate the impact crater, they bear a striking resemblance to melt flows associated with crater ejecta on Venus (Asimow and Wood, 1992, JGR 97, 13643; Chadwick and Schubert, 1993, JGR 98, 20891), reinforcing the intriguing possibility of low viscosity impact melt formation on Titan, as Soderblom et al. (2010, JGR 208, 905) argue occurred at Selk crater.

Tectonic and volcanic implications of a cratered seamount off Nicobar Island, Andaman Sea

Digital Repository Service at National Institute of Oceanography (India)

KameshRaju, K.A.; Ray, D.; Mudholkar, A.V.; Murty, G.P.S.; Gahalaut, V.K.; Samudrala, K.; Paropkari, A.L.; Ramachandran, R.; SuryaPrakash, L.

seamount with well-developed crater at the summit was discovered near to the center of the Nicobar swarm. Rock samples collected by TV-guided grab from the seamount crater are dacite, rhyolite and andesite type with a veneer of ferromanganese oxide coating...

Widespread melt/rock interaction and seismic properties of the lithosphere above mantle plumes: Evidence from mantle xenoliths from French Polynesia

Science.gov (United States)

Tommasi, A.; Godard, M.; Coromina, G.; Dautria, J. M.; Barczus, H.

2003-04-01

In addition to thermal erosion, plume/lithosphere interaction may induce significant changes in the lithosphere chemical composition. To constrain the extent of this process in an oceanic environment and its consequences on the lithosphere seismic properties, we studied the relationship between petrological processes and microstructure in mantle xenoliths from the Austral-Cook, Society and Marquesas islands. Olivine forsterite contents in our sp-peridotites vary continuously from Fo91 to Fo83, the lowest Fo being observed in dunites and wehrlites. Yet, their high Ni content (up to 2500 ppm) precludes a cumulate origin. These rocks are rather interpreted as resulting from melt/rock reactions involving olivine precipitation and pyroxene dissolution, the dunites indicating high melt-rock ratios. Moreover, wehrlites display poikiloblastic diopside enclosing corroded olivines. Late crystallization of clinopyroxene, also observed in lherzolites, may result from a near-solidus melt-freezing reaction occurring at the boundary of a partial melting domain developed at the expenses of lithospheric mantle. These data suggest that the lithosphere above a mantle plume undergoes a complex sequence of magmatic processes that significantly change its composition. Yet, crystal preferred orientations and thus seismic anisotropy are little affected by these processes. Lherzolites and harzburgites, independent from composition, show high-temperature porphyroclastic microstructures and strong olivine CPO. Although dunites and wehrlites display annealing microstructures to which is associated a progressive dispersion of the olivine CPO, very weak CPO are limited to a few dunites and wehrlites, suggesting that CPO destruction is restricted to domains of intense magma-rock interaction due to localized flow or accumulation of magmas. Conversely, the compositional changes result in lower seismic velocities for P- and S-waves. Relative to normal mantle, seismic anomalies may attain -2.5 (2

Acoustic fluidization and the scale dependence of impact crater morphology

Science.gov (United States)

Melosh, H. J.; Gaffney, E. S.

1983-01-01

A phenomenological Bingham plastic model has previously been shown to provide an adequate description of the collapse of impact craters. This paper demonstrates that the Bingham parameters may be derived from a model in which acoustic energy generated during excavation fluidizes the rock debris surrounding the crater. Experimental support for the theoretical flow law is presented. Although the Bingham yield stress cannot be computed without detailed knowledge of the initial acoustic field, the Bingham viscosity is derived from a simple argument which shows that it increases as the 3/2 power of crater diameter, consistent with observation. Crater collapse may occur in material with internal dissipation Q as low as 100, comparable to laboratory observations of dissipation in granular materials. Crater collapse thus does not require that the acoustic field be regenerated during flow.

Crater lake and post-eruption hydrothermal activity, El Chichón Volcano, Mexico

Science.gov (United States)

Casadevall, Thomas J.; De la Cruz-Reyna, Servando; Rose, William I.; Bagley, Susan; Finnegan, David L.; Zoller, William H.

1984-01-01

Explosive eruptions of Volcán El Chichón in Chiapas, Mexico on March 28 and April 3–4, 1982 removed 0.2 km3 of rock to form a 1-km-wide 300-m-deep summit crater. By late April 1982 a lake had begun to form on the crater floor, and by November 1982 it attained a maximum surface area of 1.4 × 105 m2 and a volume of 5 × 106 m3. Accumulation of 4–5 m of rainfall between July and October 1982 largely formed the lake. In January 1983, temperatures of fumaroles on the crater floor and lower crater walls ranged from 98 to 115°C; by October 1983 the maximum temperature of fumarole emissions was 99°C. In January 1983 fumarole gas emissions were greater than 99 vol. % H2O with traces of CO2, SO2, and H2S. The water of the lake was a hot (T = 52–58°C), acidic (pH = 0.5), dilute solution (34,046 mg L−1 dissolved solids; Cl/S = 20.5). Sediment from the lake contains the same silicate minerals as the rocks of the 1982 pyroclastic deposits, together with less than 1% of elemental sulfur. The composition and temperature of the lake water is attributed to: (1) solution of fumarole emissions; (2) reaction of lake water with hot rocks beneath the lake level; (3) sediments washed into the lake from the crater walls; (4) hydrothermal fluids leaching sediments and formational waters in sedimentary rocks of the basement; (5) evaporation; and (6) precipitation.

Goat paddock cryptoexplosion crater, Western Australia

Science.gov (United States)

Harms, J.E.; Milton, D.J.; Ferguson, J.; Gilbert, D.J.; Harris, W.K.; Goleby, B.

1980-01-01

Goat Paddock, a crater slightly over 5 km in diameter (18??20??? S, 126??40???E), lies at the north edge of the King Leopold Range/Mueller Range junction in the Kimberley district, Western Australia (Fig. 1). It was noted as a geological anomaly in 1964 during regional mapping by the Bureau of Mineral Resources, Geology and Geophysics and the Geological Survey of Western Australia. The possibility of its being a meteorite impact crater has been discussed1, although this suggestion was subsequently ignored2. Two holes were drilled by a mining corporation in 1972 to test whether kimberlite underlay the structure. Here we report the findings of five days of reconnaissance in August 1979 which established that Goat Paddock is a cryptoexplosion crater containing shocked rocks and an unusually well exposed set of structural features. ?? 1980 Nature Publishing Group.

The Geology of the Marcia Quadrangle of Asteroid Vesta: Assessing the Effects of Large, Young Craters

Science.gov (United States)

Williams, David A.; Denevi, Brett W.; Mittlefehldt, David W.; Mest, Scott C.; Schenk, Paul M.; Yingst, R. Aileen; Buczowski, Debra L.; Scully, Jennifer E. C.; Garry, W. Brent; McCord, Thomas B.;

Melting in super-earths.

Science.gov (United States)

Stixrude, Lars

2014-04-28

We examine the possible extent of melting in rock-iron super-earths, focusing on those in the habitable zone. We consider the energetics of accretion and core formation, the timescale of cooling and its dependence on viscosity and partial melting, thermal regulation via the temperature dependence of viscosity, and the melting curves of rock and iron components at the ultra-high pressures characteristic of super-earths. We find that the efficiency of kinetic energy deposition during accretion increases with planetary mass; considering the likely role of giant impacts and core formation, we find that super-earths probably complete their accretionary phase in an entirely molten state. Considerations of thermal regulation lead us to propose model temperature profiles of super-earths that are controlled by silicate melting. We estimate melting curves of iron and rock components up to the extreme pressures characteristic of super-earth interiors based on existing experimental and ab initio results and scaling laws. We construct super-earth thermal models by solving the equations of mass conservation and hydrostatic equilibrium, together with equations of state of rock and iron components. We set the potential temperature at the core-mantle boundary and at the surface to the local silicate melting temperature. We find that ancient (∼4 Gyr) super-earths may be partially molten at the top and bottom of their mantles, and that mantle convection is sufficiently vigorous to sustain dynamo action over the whole range of super-earth masses.

Rock Formation and Cosmic Radiation Exposure Ages in Gale Crater Mudstones from the Mars Science Laboratory

Science.gov (United States)

Mahaffy, Paul; Farley, Ken; Malespin, Charles; Gellert, Ralph; Grotzinger, John

2014-05-01

The quadrupole mass spectrometer (QMS) in the Sample Analysis at Mars (SAM) suite of the Mars Science Laboratory (MSL) has been utilized to secure abundances of 3He, 21Ne, 36Ar, and 40Ar thermally evolved from the mudstone in the stratified Yellowknife Bay formation in Gale Crater. As reported by Farley et al. [1] these measurements of cosmogenic and radiogenic noble gases together with Cl and K abundances measured by MSL's alpha particle X-ray spectrometer enable a K-Ar rock formation age of 4.21+0.35 Ga to be established as well as a surface exposure age to cosmic radiation of 78+30 Ma. Understanding surface exposures to cosmic radiation is relevant to the MSL search for organic compounds since even the limited set of studies carried out, to date, indicate that even 10's to 100's of millions of years of near surface (1-3 meter) exposure may transform a significant fraction of the organic compounds exposed to this radiation [2,3,4]. Transformation of potential biosignatures and even loss of molecular structural information in compounds that could point to exogenous or endogenous sources suggests a new paradigm in the search for near surface organics that incorporates a search for the most recently exposed outcrops through erosional processes. The K-Ar rock formation age determination shows promise for more precise in situ measurements that may help calibrate the martian cratering record that currently relies on extrapolation from the lunar record with its ground truth chronology with returned samples. We will discuss the protocol for the in situ noble gas measurements secured with SAM and ongoing studies to optimize these measurements using the SAM testbed. References: [1] Farley, K.A.M Science Magazine, 342, (2013). [2] G. Kminek et al., Earth Planet Sc Lett 245, 1 (2006). [3] Dartnell, L.R., Biogeosciences 4, 545 (2007). [4] Pavlov, A. A., et al. Geophys Res Lett 39, 13202 (2012).

Ancient aqueous environments at Endeavour crater, Mars

Science.gov (United States)

Arvidson, R. E.; Squyres, S. W.; Bell, J.F.; Catalano, J.G.; Clark, B. C.; Crumpler, L.S.; de Souza, P.A.; Fairén, A.G.; Farrand, W. H.; Fox, V.K.; Gellert, Ralf; Ghosh, A.; Golombeck, M.P.; Grotzinger, J.P.; Guinness, E.A.; Herkenhoff, Kenneth E.; Jolliff, B.L.; Knoll, A.H.; Li, R.; McLennan, S.M.; Ming, D. W.; Mittlefehldt, D. W.; Moore, Johnnie N.; Morris, R.V.; Murchie, S.L.; Parker, T.J.; Paulsen, G.; Rice, J.W.; Ruff, S.W.; Smith, M.D.; Wolff, M.J.

2014-01-01

Opportunity has investigated in detail rocks on the rim of the Noachian age Endeavour crater, where orbital spectral reflectance signatures indicate the presence of Fe+3-rich smectites. The signatures are associated with fine-grained, layered rocks containing spherules of diagenetic or impact origin. The layered rocks are overlain by breccias, and both units are cut by calcium sulfate veins precipitated from fluids that circulated after the Endeavour impact. Compositional data for fractures in the layered rocks suggest formation of Al-rich smectites by aqueous leaching. Evidence is thus preserved for water-rock interactions before and after the impact, with aqueous environments of slightly acidic to circum-neutral pH that would have been more favorable for prebiotic chemistry and microorganisms than those recorded by younger sulfate-rich rocks at Meridiani Planum.

What Really Happened to Earth's Older Craters?

Science.gov (United States)

Bottke, William; Mazrouei, Sara; Ghent, Rebecca; Parker, Alex

2017-10-01

Most assume the Earth’s crater record is heavily biased, with erosion/tectonics destroying older craters. This matches expectations, but is it actually true? To test this idea, we compared Earth’s crater record, where nearly all D ≥ 20 km craters are pick out from older craters with eroded fragments. Moreover, an inverse relationship between rock abundance (RA) and crater age exists. Using measured RA values, we computed ages for 111 rocky craters with D ≥ 10 km that formed between 80°N and 80°S over the last 1 Gyr.We found several surprising results. First, the production rate of D ≥ 10 km lunar craters increased by a factor of 2.2 [-0.9, +4.4; 95% confidence limits] over the past 250 Myr compared to the previous 750 Myr. Thus, the NEO population is higher now than it has been for the last billion years. Second, the size and age distributions of lunar and terrestrial craters for D ≥ 20 km over the last 650 Myr have similar shapes. This implies that crater erasure must be limited on stable terrestrial terrains; in an average sense, for a given region, the Earth either keeps all or loses all of its D ≥ 20 craters at the same rate, independent of size. It also implies the observed deficit of large terrestrial craters between 250-650 Myr is not preservation bias but rather reflects a distinctly lower impact flux. We predict 355 ± 86 D ≥ 20 km craters formed on Earth over the last 650 Myr. Only 38 ± 6 are known, so the ratio, 10.7 ± 3.1%, is a measure of the Earth’s surface that is reasonably stable to large crater formation over 650 Myr. If erosion had dominated, the age distribution of terrestrial craters would be strongly skewed toward younger ages, which is not observed. We predict Chicxulub-type impacts were rare over the last Gyr, with the event 66 Ma a probable byproduct of the current high terrestrial impact flux.

Deposition, exhumation, and paleoclimate of an ancient lake deposit, Gale crater, Mars

OpenAIRE

Grotzinger, JP; Gupta, S; Malin, MC; Rubin, DM; Schieber, J; Siebach, K; Sumner, DY; Stack, KM; Vasavada, AR; Arvidson, RE; Calef, F; Edgar, L; Fischer, WF; Grant, JA; Griffes, J

2015-01-01

The landforms of northern Gale crater on Mars expose thick sequences of sedimentary rocks. Based on images obtained by the Curiosity rover, we interpret these outcrops as evidence for past fluvial, deltaic, and lacustrine environments. Degradation of the crater wall and rim probably supplied these sediments, which advanced inward from the wall, infilling both the crater and an internal lake basin to a thickness of at least 75 meters. This intracrater lake system probably existed intermittentl...

Computer simulations of large asteroid impacts into oceanic and continental sites--preliminary results on atmospheric, cratering and ejecta dynamics

Science.gov (United States)

Roddy, D.J.; Schuster, S.H.; Rosenblatt, M.; Grant, L.B.; Hassig, P.J.; Kreyenhagen, K.N.

1987-01-01

40 km at ???30 s and began to decay at velocities of 500 m/s to develop large-tsunami conditions. After ???30 s, strong gravitational rebound drove both craters toward broad flat-floored shapes. At 120 s, transient crater diameters were ???80 km (continental) and ???105 km (oceanic) and transient depths were ???27 km; crater floors consisting of melted and fragmented hot rock were rebounding rapidly upward. By 60 s, the continental crater had ejected ???2 ?? 1014 t, about twice the mass ejected from the oceanic crater. By 120 s, ???70,000 km3 (continental) and ???90,000 km3 (oceanic) target material were excavated (no mantle) and massive ejecta blankets were formed around the craters. We estimate that in excess of ???70% of the ejecta would finally lie within ???3 crater diameters of the impact, and the remaining ejecta (???1013 t), including the vaporized asteroid, would be ejected into the atmosphere to altitudes as high as the ionosphere. Effects of secondary volcanism and return of the ocean over hot oceanic crater floor could also be expected to contribute substantial material to the atmosphere. ?? 1987.

Influence of plasma pressure gradient on melt layer macroscopic erosion of metal targets in disruption simulation experiments

Energy Technology Data Exchange (ETDEWEB)

Tereshin, V.I.; Garkusha, I.E. E-mail: garkusha@ipp.kharkov.ua; Bandura, A.N.; Byrka, O.V.; Chebotarev, V.V.; Makhlaj, V.A.; Solyakov, D.G.; Wuerz, H

2003-03-01

Melt layer erosion of metal targets under pulsed high heat loads is discussed. Tungsten, copper, aluminum, and titanium targets were exposed to perpendicular and inclined plasma impact in the quasi-steady-state plasma accelerator QSPA Kh-50. Melt layer motion results in erosion crater formation with rather large mountains of the resolidified material at the crater edge. It is shown that macroscopic motion of the melt layer and surface cracking are the main factors responsible for tungsten erosion.

Influence of plasma pressure gradient on melt layer macroscopic erosion of metal targets in disruption simulation experiments

International Nuclear Information System (INIS)

Tereshin, V.I.; Garkusha, I.E.; Bandura, A.N.; Byrka, O.V.; Chebotarev, V.V.; Makhlaj, V.A.; Solyakov, D.G.; Wuerz, H.

2003-01-01

Melt layer erosion of metal targets under pulsed high heat loads is discussed. Tungsten, copper, aluminum, and titanium targets were exposed to perpendicular and inclined plasma impact in the quasi-steady-state plasma accelerator QSPA Kh-50. Melt layer motion results in erosion crater formation with rather large mountains of the resolidified material at the crater edge. It is shown that macroscopic motion of the melt layer and surface cracking are the main factors responsible for tungsten erosion

Morphology and chemistry of projectile residue in small experimental impact craters

Science.gov (United States)

Horz, F.; Fechtig, H.; Janicke, J.; Schneider, E.

1983-01-01

Small-scale impact craters (5-7 mm in diameter) were produced with a light gas gun in high purity Au and Cu targets using soda lime glass (SL) and man-made basalt glass (BG) as projectiles. Maximum impact velocity was 6.4 km/s resulting in peak pressures of approximately 120-150 GPa. Copious amounts of projectile melts are preserved as thin glass liners draping the entire crater cavity; some of this liner may be lost by spallation, however. SEM investigations reveal complex surface textures including multistage flow phenomena and distinct temporal deposition sequences of small droplets. Inasmuch as some of the melts were generated at peak pressures greater than 120 GPa, these glasses represent the most severely shocked silicates recovered from laboratory experiments to date. Major element analyses reveal partial loss of alkalis; Na2O loss of 10-15 percent is observed, while K2O loss may be as high as 30-50 percent. Although the observed volatile loss in these projectile melts is significant, it still remains uncertain whether target melts produced on planetary surfaces are severely fractionated by selective volatilization processes.

Three dimensional characterization of laser ablation craters using high resolution X-ray computed tomography

Science.gov (United States)

Galmed, A. H.; du Plessis, A.; le Roux, S. G.; Hartnick, E.; Von Bergmann, H.; Maaza, M.

2018-01-01

Laboratory X-ray computed tomography is an emerging technology for the 3D characterization and dimensional analysis of many types of materials. In this work we demonstrate the usefulness of this characterization method for the full three dimensional analysis of laser ablation craters, in the context of a laser induced breakdown spectroscopy setup. Laser induced breakdown spectroscopy relies on laser ablation for sampling the material of interest. We demonstrate here qualitatively (in images) and quantitatively (in terms of crater cone angles, depths, diameters and volume) laser ablation crater analysis in 3D for metal (aluminum) and rock (false gold ore). We show the effect of a Gaussian beam profile on the resulting crater geometry, as well as the first visual evidence of undercutting in the rock sample, most likely due to ejection of relatively large grains. The method holds promise for optimization of laser ablation setups especially for laser induced breakdown spectroscopy.

Deposition, exhumation, and paleoclimate of an ancient lake deposit, Gale crater, Mars

Science.gov (United States)

Grotzinger, J. P.; Gupta, S.; Malin, M. C.; Rubin, D. M.; Schieber, J.; Siebach, K.; Sumner, D. Y.; Stack, K. M.; Vasavada, A. R.; Arvidson, R. E.; Calef, F.; Edgar, L.; Fischer, W. F.; Grant, J. A.; Griffes, J.; Kah, L. C.; Lamb, M. P.; Lewis, K. W.; Mangold, N.; Minitti, M. E.; Palucis, M.; Rice, M.; Williams, R. M. E.; Yingst, R. A.; Blake, D.; Blaney, D.; Conrad, P.; Crisp, J.; Dietrich, W. E.; Dromart, G.; Edgett, K. S.; Ewing, R. C.; Gellert, R.; Hurowitz, J. A.; Kocurek, G.; Mahaffy, P.; McBride, M. J.; McLennan, S. M.; Mischna, M.; Ming, D.; Milliken, R.; Newsom, H.; Oehler, D.; Parker, T. J.; Vaniman, D.; Wiens, R. C.; Wilson, S. A.

2015-10-01

The landforms of northern Gale crater on Mars expose thick sequences of sedimentary rocks. Based on images obtained by the Curiosity rover, we interpret these outcrops as evidence for past fluvial, deltaic, and lacustrine environments. Degradation of the crater wall and rim probably supplied these sediments, which advanced inward from the wall, infilling both the crater and an internal lake basin to a thickness of at least 75 meters. This intracrater lake system probably existed intermittently for thousands to millions of years, implying a relatively wet climate that supplied moisture to the crater rim and transported sediment via streams into the lake basin. The deposits in Gale crater were then exhumed, probably by wind-driven erosion, creating Aeolis Mons (Mount Sharp).

Geology of McLaughlin Crater, Mars: A Unique Lacustrine Setting with Implications for Astrobiology

Science.gov (United States)

Michalski, J. R.; Niles, P. B.; Rogers, A. D.; Johnson, S. S.; Ashley, J. W.; Golombek, M. P.

2016-01-01

McLaughlin crater is a 92-kmdiameter Martian impact crater that contained an ancient carbonate- and clay mineral-bearing lake in the Late Noachian. Detailed analysis of the geology within this crater reveals a complex history with important implications for astrobiology [1]. The basin contains evidence for, among other deposits, hydrothermally altered rocks, delta deposits, deep water (>400 m) sediments, and potentially turbidites. The geology of this basin stands in stark contrast to that of some ancient basins that contain evidence for transient aqueous processes and airfall sediments (e.g. Gale Crater [2-3]).

The geology and mechanics of formation of the Fort Rock Dome, Yavapai County, Arizona

Science.gov (United States)

Fuis, Gary S.

1996-01-01

The Fort Rock Dome, a craterlike structure in northern Arizona, is the erosional product of a circular domal uplift associated with a Precambrian shear zone exposed within the crater and with Tertiary volcanism. A section of Precambrian to Quaternary rocks is described, and two Tertiary units, the Crater Pasture Formation and the Fort Rock Creek Rhyodacite, are named. A mathematical model of the doming process is developed that is consistent with the history of the Fort Rock Dome.

Melt inclusions: Chapter 6

Science.gov (United States)

,; Lowenstern, J. B.

2014-01-01

Melt inclusions are small droplets of silicate melt that are trapped in minerals during their growth in a magma. Once formed, they commonly retain much of their initial composition (with some exceptions) unless they are re-opened at some later stage. Melt inclusions thus offer several key advantages over whole rock samples: (i) they record pristine concentrations of volatiles and metals that are usually lost during magma solidification and degassing, (ii) they are snapshots in time whereas whole rocks are the time-integrated end products, thus allowing a more detailed, time-resolved view into magmatic processes (iii) they are largely unaffected by subsolidus alteration. Due to these characteristics, melt inclusions are an ideal tool to study the evolution of mineralized magma systems. This chapter first discusses general aspects of melt inclusions formation and methods for their investigation, before reviewing studies performed on mineralized magma systems.

Petrogenesis of basaltic volcanic rocks from the Pribilof Islands, Alaska, by melting of metasomatically enriched depleted lithosphere, crystallization differentiation, and magma mixing

Science.gov (United States)

Chang, J.M.; Feeley, T.C.; Deraps, M.R.

2009-01-01

The Pribilof Islands, Alaska, are located in the Bering Sea in a continental intraplate setting. In this study we examine the petrology and geochemistry of volcanic rocks from St. Paul (0??54-0??003 Ma) and St. George (2??8-1??4 Ma) Islands, the two largest Pribilof Islands. Rocks from St. George can be divided into three groups: group 1 is a high-MgO, low-SiO. 2 suite composed primarily of basanites; group 2 is a high-MgO, high-SiO 2 suite consisting predominantly of alkali basalts; group 3 is an intermediate- to low-MgO suite that includes plagioclase-phyric subalkali basalts and hawaiites. Major and trace element geochemistry suggests that groups 1 and 2 formed by small-degree partial melting of amphibole-bearing to amphibole-free garnet peridotite. Group 1 rocks were the earliest melts produced from the most hydrous parts of the mantle, as they show the strongest geochemical signature of amphibole in their source. The suite of rocks from St. Paul ranges from 14??4 to 4??2 wt % MgO at relatively constant SiO 2 contents (43??1-47??3 wt %). The most primitive St. Paul rocks are modeled as mixtures between magmas with compositions similar to groups 1 and 2 from St. George Island, which subsequently fractionated olivine, clinopyroxene, and spinel to form more evolved rocks. Plagioclase-phyric group 3 rocks from St. George are modeled as mixtures between an evolved melt similar to the evolved magmas on St. Paul and a fractionated group 2 end-member from St. George. Mantle potential temperatures estimated for primitive basanites and alkali basalts are ???1400??C and are similar to those of mid-ocean ridge basalts (MORB). Similarly, 87Sr/. 86Sr and 143Nd/. 144Nd values for all rocks are MORB-like, in the range of 0??702704-0??703035 and 0??513026-0??513109, respectively. 208Pb/. 204Pb vs 206Pb/. 204Pb values lie near the MORB end-member but show a linear trend towards HIMU (high time-integrated 238U/. 204Pb). Despite isotopic similarities to MORB, many of the major and

On the crypto-explosive crater and its relation with gold mineralization in larma Au-U deposit

International Nuclear Information System (INIS)

Chen Guohua; Jing Hongxiang; Huang Shutao

1998-01-01

A new type of gold mineralization-controlling structure-hydrothermal crypto-explosive crater was identified at the Larma gold-uranium deposit in the border regions between Gansu and Sichuan provinces, western China. The hydrothermal crypto-explosive crater is ellipse-shaped at the surface, while funnel-like in profile. A silica-cap composed of hydrothermal siliceous breccia is distributed at the top of the crater, while hydrothermal crypto-explosive breccia are in the centre. The configuration of the crater is roughly consistent with the distribution of gold ore bodies. The formation mechanism of the crater is: first, a silica cap composed of hydrothermal siliceous metasomatic rock was formed at the contact area between the siliceous rock and the slate, and blocked the movement of hydrothermal fluid and resulted in the appearance of over-pressed geothermal environment. Then, at 49.5 Ma, the rejuvenation of the EW-striking faults in larma area resulted in the breaking of the brittle silica cap, followed by the crypto-explosion of hydrothermal fluid. In Larma gold-uranium deposit, the hydrothermal crypto-explosion gave rise to the precipitation of gold from the hydrothermal fluid, while the crypto-explosive crater provided the space for gold mineralization

Underwater research methods for study of nuclear bomb craters, Enewetak, Marshall Islands

Science.gov (United States)

Shinn, E.A.; Halley, R.B.; Kindinger, J.L.; Hudson, J.H.; Slate, R.A.

1990-01-01

Three craters, created by the explosion of nuclear fusion devices, were mapped, sampled, core drilled and excavated with airlifts at Enewetak Atoll in the Marshall Islands by using scuba and a research submersible. The craters studied were Mike, Oak, and Koa. Tests took place near sea level at the transition between lithified reef flat and unlithified lagoonal sediments, where water depth ranged from 1 to 4 m. Craters produced by the blasts ranged from 30 to 60 m in depth. The purpose of our study was to determine crater diameter and depth immediately after detonation. Observations of submerged roadways and testing structures and upturned crater rims similar to those characteristic of meteor impacts indicate that the initial, or transient, craters were smaller than their present size. At some later time, while the area was too radioactive for direct examination, the sides of the craters slumped owing to dewatering of under lying pulverized rock. Core drilling of crater margins with a diver-operated hydraulic coring device provided additional data. On the seaward margin of the atoll, opposite Mike, a large portion of the atoll rim approximately the size of a city block had slumped into the deep ocean, leaving a clean vertical rock section more than 400m high. An abundance of aggressive grey reef sharks displaying classic territorial behavior prevented use of scuba at the Mike slump site. The two-person submersible R.V. Delta provided protection and allowed observations down to 300 m. During the 6-week period of study, we made more than 300 scuba and 275 submersible dives. Mapping was with side scan sonar and continuous video sweeps supplemented by tape-recorded verbal descriptions made from within the submersible. A mini-ranger navigation system linked to the submersible allowed plotting of bottom features, depth and sediment type with spatial accuracy to within 2 m.

Steady as a rock: Biogeomorphic influence of nurse rocks and slope processes on kūpaoa (Dubautia menziesii) shrubs in Haleakalā Crater (Maui, Hawai'i)

Science.gov (United States)

Pérez, Francisco L.

2017-10-01

This study examines biogeomorphic interactions between nurse rocks, slope processes, and 300 kūpaoa (Dubautia menziesii) shrubs in Haleakalā Crater (Maui, Hawai'i). Research objectives were to: assess the association of kūpaoa with substrates upslope and downslope of plants, and proximity to the closest rock uphill; contrast shrub/substrate relationships with site frequency of sediment types; measure surface soil shear-strength and compressibility on 50 paired locations near boulders; and investigate the aggregation characteristics and spatial patterns of kūpaoa in relation to rock and substrate variation. Data analyzed came from three 100-plant surveys at 3 sites: a plant census at 2720-2975 m altitude, and wandering-quarter transects (WQTs) across two areas (2610-2710 m); ground sediment cover was estimated along four phototransects on these sites. Data for the three 100-plant surveys included substrate type-outcrops, blocks, cobbles, pebbles, exposed soil, organic litter-upslope from each plant, and distance to the largest rock upslope. The two surveys examined along WQTs included substrate type found downslope from kūpaoa, plant height, plant diameters across and along the slope, and distance between successively censused plants. Most plants grew downslope of nurse rocks; > 74% were adjacent to blocks or outcrops, and > 17% near cobbles. Plants showed avoidance for finer substrates; only 5.3% and 2.7% grew on/near bare soils and pebbles, respectively. About 92% of kūpaoa were ≤ 10 cm downslope of rocks; > 89% grew ≤ 2 cm away, and 83% in direct contact with a rock. Some seedlings also grew on pukiawe (Leptecophylla tameiameiae) nurse plants. Several stable rock microsites protected plants from disturbance by slope processes causing debris shift. Site sediments were significantly finer than substrates near plants; shrubs grew preferentially adjacent to boulders > 20 cm wide, which were more common near plants than across sites. Soils downslope of 50

Deposition, exhumation, and paleoclimate of an ancient lake deposit, Gale crater, Mars.

Science.gov (United States)

Grotzinger, J P; Gupta, S; Malin, M C; Rubin, D M; Schieber, J; Siebach, K; Sumner, D Y; Stack, K M; Vasavada, A R; Arvidson, R E; Calef, F; Edgar, L; Fischer, W F; Grant, J A; Griffes, J; Kah, L C; Lamb, M P; Lewis, K W; Mangold, N; Minitti, M E; Palucis, M; Rice, M; Williams, R M E; Yingst, R A; Blake, D; Blaney, D; Conrad, P; Crisp, J; Dietrich, W E; Dromart, G; Edgett, K S; Ewing, R C; Gellert, R; Hurowitz, J A; Kocurek, G; Mahaffy, P; McBride, M J; McLennan, S M; Mischna, M; Ming, D; Milliken, R; Newsom, H; Oehler, D; Parker, T J; Vaniman, D; Wiens, R C; Wilson, S A

2015-10-09

The landforms of northern Gale crater on Mars expose thick sequences of sedimentary rocks. Based on images obtained by the Curiosity rover, we interpret these outcrops as evidence for past fluvial, deltaic, and lacustrine environments. Degradation of the crater wall and rim probably supplied these sediments, which advanced inward from the wall, infilling both the crater and an internal lake basin to a thickness of at least 75 meters. This intracrater lake system probably existed intermittently for thousands to millions of years, implying a relatively wet climate that supplied moisture to the crater rim and transported sediment via streams into the lake basin. The deposits in Gale crater were then exhumed, probably by wind-driven erosion, creating Aeolis Mons (Mount Sharp). Copyright © 2015, American Association for the Advancement of Science.

Aqueous processes at Gusev crater inferred from physical properties of rocks and soils along the Spirit traverse

Science.gov (United States)

Cabrol, N.A.; Farmer, J.D.; Grin, E.A.; Ritcher, L.; Soderblom, L.; Li, R.; Herkenhoff, K.; Landis, G.A.; Arvidson, R. E.

2006-01-01

Gusev crater was selected as the landing site for Spirit on the basis of morphological evidence of long-lasting water activity, including possibly fluvial and lacustrine episodes. From the Columbia Memorial Station to the Columbia Hills, Spirit's traverse provides a journey back in time, from relatively recent volcanic plains showing little evidence for aqueous processes up to the older hills, where rock and soil composition are drastically different. For the first 156 sols, the only evidence of water action was weathering rinds, vein fillings, and soil crust cementation by salts. The trenches of Sols 112-145 marked the first significant findings of increased concentrations of sulfur and magnesium varying in parallel, suggesting that they be paired as magnesium-sulfate. Spirit's arrival at West Spur coincided with a shift in rock and soil composition with observations hinting at substantial amounts of water in Gusev's past. We used the Microscopic Imager data up to Sol 431 to analyze rock and soil properties and infer plausible types and magnitude of aqueous processes through time. We show the role played early by topography and structure. The morphology, texture, and deep alteration shown by the rocks in West Spur and the Columbia Hills Formation (CHF) suggest conditions that are not met in present-day Mars and required a wetter environment, which could have included transport of sulfur, chlorine, and bromine in water, vapor in volcanic gases, hydrothermal circulation, or saturation in a briny fluid containing the same elements. Changing conditions that might have affected flow circulation are suggested by different textural and morphological characteristics between the rocks in the CHF and those of the plains, with higher porosity proxy, higher void ratio, and higher water storage potential in the CHF. Soils were used to assess aqueous processes and water pathways in the top layers of modern soils. We conclude that infiltration might have become more difficult

Two mechanisms of crater formation in ultraviolet-pulsed-laser irradiated SiO2 thin films with artificial defects

International Nuclear Information System (INIS)

Papernov, S.; Schmid, A.W.

2005-01-01

Atomic force microscopy was employed to investigate the morphology of ultraviolet nanosecond-pulsed-laser damage in SiO 2 thin films. Gold nanoparticles, 18.5-nm diameter, embedded in the film were used as calibrated absorbing defects. Damage-crater diameter, depth, and cross-sectional profiles were measured as a function of laser fluence and the lodging depth of gold nanoparticles. The results indicate that, at laser fluences close to the crater-formation threshold and for lodging depths of a few particle diameters, the dominating regime of the material removal is melting and evaporation. The morphology of craters initiated by deep absorbing defects, with a lodging depth larger than ∼10 particle diameters, clearly points to a two-stage material-removal mechanism. The process starts with the material melting within the narrow channel volume and, upon temperature and pressure buildup, film fracture takes place. Crater-diameter variation with lodging depth and laser fluence is compared with theoretical predictions

Scientific Drilling of Impact Craters - Well Logging and Core Analyses Using Magnetic Methods (Invited)

Science.gov (United States)

Fucugauchi, J. U.; Perez-Cruz, L. L.; Velasco-Villarreal, M.

2013-12-01

Drilling projects of impact structures provide data on the structure and stratigraphy of target, impact and post-impact lithologies, providing insight on the impact dynamics and cratering. Studies have successfully included magnetic well logging and analyses in core and cuttings, directed to characterize the subsurface stratigraphy and structure at depth. There are 170-180 impact craters documented in the terrestrial record, which is a small proportion compared to expectations derived from what is observed on the Moon, Mars and other bodies of the solar system. Knowledge of the internal 3-D deep structure of craters, critical for understanding impacts and crater formation, can best be studied by geophysics and drilling. On Earth, few craters have yet been investigated by drilling. Craters have been drilled as part of industry surveys and/or academic projects, including notably Chicxulub, Sudbury, Ries, Vredefort, Manson and many other craters. As part of the Continental ICDP program, drilling projects have been conducted on the Chicxulub, Bosumtwi, Chesapeake, Ries and El gygytgyn craters. Inclusion of continuous core recovery expanded the range of paleomagnetic and rock magnetic applications, with direct core laboratory measurements, which are part of the tools available in the ocean and continental drilling programs. Drilling studies are here briefly reviewed, with emphasis on the Chicxulub crater formed by an asteroid impact 66 Ma ago at the Cretaceous/Paleogene boundary. Chicxulub crater has no surface expression, covered by a kilometer of Cenozoic sediments, thus making drilling an essential tool. As part of our studies we have drilled eleven wells with continuous core recovery. Magnetic susceptibility logging, magnetostratigraphic, rock magnetic and fabric studies have been carried out and results used for lateral correlation, dating, formation evaluation, azimuthal core orientation and physical property contrasts. Contributions of magnetic studies on impact

Cratering on Small Bodies: Lessons from Eros

Science.gov (United States)

Chapman, C. R.

2003-01-01

Cratering and regolith processes on small bodies happen continuously as interplanetary debris rains down on asteroids, comets, and planetary satellites. Butthey are very poorly observed and not well understood. On the one hand, we have laboratory experimentation at small scales and we have examination of large impact craters (e.g. Meteor Crater on Earth and imaging of abundant craters on terrestrial planets and outer planet moons). Understanding cratering on bodies of intermediate scales, tens of meters to hundreds of km in size, involves either extrapolation from our understanding of cratering phenomena at very different scales or reliance on very preliminary, incomplete examination of the observational data we now have for a few small bodies. I review the latter information here. It has been generally understood that the role of gravity is greatly diminished for smaller bodies, so a lot of cratering phenomena studied for larger bodies is less applicable. But it would be a mistake to imagine that laboratory experiments on gravitationless rocks (usually at 1 g) are directly applicable, except perhaps to those monolithic Near Earth Asteroids (NEAs) some tens of meters in size that spin very rapidly and can be assumed to be "large bare rocks" with "negative gravity". Whereas it had once been assumed that asteroids smaller than some tens of km diameter would retain little regolith, it is increasingly apparent that regolith and megoregolith processes extend down to bodies only hundreds of meters in size, perhaps smaller. Yet these processes are very different from those that pertain to the Moon, which is our chief prototype of regolith processes. The NEAR Shoemaker spacecraft's studies of Eros provide the best evidence to date about small-body cratering processes, as well as a warning that our theoretical understanding requires anchoring by direct observations. Eros: "Ponds", Paucity of Small Craters, and Other Mysteries. Although Eros is currently largely detached

Impact cratering on porous targets in the strength regime

Science.gov (United States)

Nakamura, Akiko M.

2017-12-01

Cratering on small bodies is crucial for the collision cascade and also contributes to the ejection of dust particles into interplanetary space. A crater cavity forms against the mechanical strength of the surface, gravitational acceleration, or both. The formation of moderately sized craters that are sufficiently larger than the thickness of the regolith on small bodies, in which mechanical strength plays the dominant role rather than gravitational acceleration, is in the strength regime. The formation of microcraters on blocks on the surface is also within the strength regime. On the other hand, the formation of a crater of a size comparable to the thickness of the regolith is affected by both gravitational acceleration and cohesion between regolith particles. In this short review, we compile data from the literature pertaining to impact cratering experiments on porous targets, and summarize the ratio of spall diameter to pit diameter, the depth, diameter, and volume of the crater cavity, and the ratio of depth to diameter. Among targets with various porosities studied in the laboratory to date, based on conventional scaling laws (Holsapple and Schmidt, J. Geophys. Res., 87, 1849-1870, 1982) the cratering efficiency obtained for porous sedimentary rocks (Suzuki et al., J. Geophys. Res. 117, E08012, 2012) is intermediate. A comparison with microcraters formed on a glass target with impact velocities up to 14 km s-1 indicates a different dependence of cratering efficiency and depth-to-diameter ratio on impact velocity.

Two stage melt-rock interaction in the lower oceanic crust of the Parece Vela basin (Philippine sea), evidence from the primitive troctolites from the Godzilla Megamullion

Science.gov (United States)

Sanfilippo, A.; Dick, H. J.; Ohara, Y.

2011-12-01

Godzilla Megamullion is a giant oceanic core complex exposed in an extinct slow- to intermediate-spreading segment of the Parece Vela Basin (Philippine sea) [1; 2]. It exposes lower crust and mantle rocks on the sea-floor, offering a unique opportunity to unravel the architecture and the composition of the lower oceanic lithosphere of an extinct back arc basin. Here we present data on primitive troctolites and associated olivine-gabbros from the breakaway area of the Godzilla Megamullion. On the basis of the olivine/plagioclase volume ratio, the troctolites are subdivided into Ol-troctolites (Ol/Pl >1) and Pl-troctolites (Ol/Plthe olivine and a melt crystallizing plagioclase and clinopyroxene. We interpret these rocks as reaction products of a dunite matrix with transient basaltic melts [e.g. 3; 4]. Pl-troctolites have euhedral plagioclase and poikilitic olivine and clinopyroxene. Irregular shapes and inverse zoning of the plagioclase chadacrysts within the olivine indicate disequilibrium between existing plagioclase and an olivine-clinopyroxene saturated melt. The occurrence of plagioclase chadacrysts within clinopyroxene ranging from irregular to euhedral in shape suggests crystallization of new lower-Na plagioclase with the clinopyroxene. Olivine oikocrysts in the Pl-troctolites have low-NiO olivine in equilibrium with a high-MgO melt. The Pl-troctolites, then, may be the product of reaction between a plagioclase cumulate and a basaltic melt produced by mixing the high-MgO melt residual to the formation of the Ol-troctolites with new magma. The effect of melt-rock reaction in the Pl- and Ol- troctolites explains the sharp decrease in plagioclase An with respect to Mg# in clinopyroxene and olivine. Furthermore, the melt is shifted towards lower Na, which is consistent with the low Na8 values of the associated MORB glasses (2.4-2.7 wt %). Our results, then, show that melt-rock interaction was a process active in the lower oceanic crust of the Parece Vela basin and

Geology of drill hole USW VH-2, and structure of Crater Flat, southwestern Nevada

International Nuclear Information System (INIS)

Carr, W.J.; Parrish, L.D.

1985-01-01

A 1219 meter (4000 ft) drill hole in Crater Flat shows the absence of buried Pliocene or Quaternary volcanic rocks, and penetrates a section of Timber Mountain, Paintbrush, and the upper part of the Crater Flat Tuffs, similar to that exposed adjacent to Crater Flat. A prominent negative aeromagnetic anomaly between the drill hole and Bare Mountain is attributed to a westward thickening section of a reversely magnetized Miocene basalt. The relatively shallow depth of this basalt in the west-central part of Crater Flat indicates that no large amount of tectonic movement has occurred in approximately the last 10 m.y. Massive brecciated wedges of Paleozoic rocks are penetrated in two stratigraphic intervals in the drill hole; the older one, between the Tiva Canyon Member of the Paintbrush Tuff and the Rainier Mesa Member of the Timber Mountain Tuff, correlates with the time of maximum faulting east of Crater Flat in the Yucca Mountain area. The younger slide masses are correlated with a large slide block of probable late Miocene age exposed along the southwestern rim of Crater Flat. The structural pattern and style buried beneath central and western Crater Flat is deduced to be similar to that exposed at Yucca Mountain, but less developed. The major fault system controlling the steep east face of Bare Mountain, though probably still active, is believed to have developed mainly as a result of caldera collapse between 13 and 14 m.y. ago. Relations between faulting and four episodes of basalt eruption in the Crater Flat area strongly suggest contemporaneity of the two processes. 17 refs., 2 figs., 3 tabs

Layers of 'Cabo Frio' in 'Victoria Crater'

Science.gov (United States)

2006-01-01

This view of 'Victoria crater' is looking southeast from 'Duck Bay' towards the dramatic promontory called 'Cabo Frio.' The small crater in the right foreground, informally known as 'Sputnik,' is about 20 meters (about 65 feet) away from the rover, the tip of the spectacular, layered, Cabo Frio promontory itself is about 200 meters (about 650 feet) away from the rover, and the exposed rock layers are about 15 meters (about 50 feet) tall. This is an approximately true color rendering of images taken by the panoramic camera (Pancam) on NASA's Mars Exploration Rover Opportunity during the rover's 952nd sol, or Martian day, (Sept. 28, 2006) using the camera's 750-nanometer, 530-nanometer and 430-nanometer filters.

Imaging the Chicxulub central crater zone from large scale seismic acoustic wave propagation and gravity modeling

Science.gov (United States)

Fucugauchi, J. U.; Ortiz-Aleman, C.; Martin, R.

2017-12-01

Large complex craters are characterized by central uplifts that represent large-scale differential movement of deep basement from the transient cavity. Here we investigate the central sector of the large multiring Chicxulub crater, which has been surveyed by an array of marine, aerial and land-borne geophysical methods. Despite high contrasts in physical properties,contrasting results for the central uplift have been obtained, with seismic reflection surveys showing lack of resolution in the central zone. We develop an integrated seismic and gravity model for the main structural elements, imaging the central basement uplift and melt and breccia units. The 3-D velocity model built from interpolation of seismic data is validated using perfectly matched layer seismic acoustic wave propagation modeling, optimized at grazing incidence using shift in the frequency domain. Modeling shows significant lack of illumination in the central sector, masking presence of the central uplift. Seismic energy remains trapped in an upper low velocity zone corresponding to the sedimentary infill, melt/breccias and surrounding faulted blocks. After conversion of seismic velocities into a volume of density values, we use massive parallel forward gravity modeling to constrain the size and shape of the central uplift that lies at 4.5 km depth, providing a high-resolution image of crater structure.The Bouguer anomaly and gravity response of modeled units show asymmetries, corresponding to the crater structure and distribution of post-impact carbonates, breccias, melt and target sediments

Mineralogy of a mudstone at Yellowknife Bay, Gale crater, Mars

NARCIS (Netherlands)

Vaniman, D.T.; Bish, D.L.; Ming, D.W.; Bristow, T.F.; Morris, R.V.; Blake, D.F.; Chipera, S.J.; Morrison, S.M.; Treiman, A.H.; Rampe, E.B.; Rice, M.; Achilles, C.N.; Grotzinger, J.P.; McLennan, S.M.; Williams, J.; Bell III, J.F.; Newsom, H.E.; Downs, R.T.; Maurice, S.; Sarrazin, P.; Yen, A.S.; Morookian, J.M.; Farmer, J.D.; Stack, K.; Milliken, R.E.; Ehlmann, B.L.; Sumner, D.Y.; Berger, G.; Crisp, J.A.; Hurowitz, J.A.; Anderson, R.; Des Marais, D.J.; Stolper, E.M.; Edgett, K.S.; Gupta, S.; Spanovich, N.; MSL Science Team, the|info:eu-repo/dai/nl/292012217

2014-01-01

Sedimentary rocks at Yellowknife Bay (Gale crater) on Mars include mudstone sampled by the Curiosity rover. The samples, John Klein and Cumberland, contain detrital basaltic minerals, calcium sulfates, iron oxide or hydroxides, iron sulfides, amorphous material, and trioctahedral smectites. The John

Widespread melt/rock interaction and seismic properties of the lithosphere above mantle plumes: A petrological and microstructural study of mantle xenoliths from French Polynesia

Science.gov (United States)

Tommasi, A.; Godard, M.

2002-12-01

In addition to thermal erosion, plume/lithosphere interaction may induce significant changes in the lithosphere chemical composition. To constrain the extent of this process in an oceanic environment and its consequences on the lithosphere seismic properties, we studied the relationship between petrological processes and microstructure in mantle xenoliths from the Austral-Cook, Society and Marquesas islands. Olivine forsterite contents in our sp-peridotites vary continuously from Fo91 to Fo83, the lowest Fo being observed in dunites and wehrlites. Yet, their high Ni content (up to 2500 ppm) precludes a cumulate origin. These rocks are rather interpreted as resulting from melt/rock reactions involving olivine precipitation and pyroxene dissolution, the dunites indicating high melt-rock ratios. Moreover, wehrlites display poikiloblastic diopside enclosing corroded olivines. Late crystallization of clinopyroxene, also observed in lherzolites, may result from a near-solidus melt-freezing reaction occurring at the boundary of a partial melting domain developed at the expenses of lithospheric mantle. These data suggest that the lithosphere above a mantle plume undergoes a complex sequence of magmatic processes that significantly change its composition. Yet, crystal preferred orientations and thus seismic anisotropy are little affected by these processes. Lherzolites and harzburgites, independent from composition, show high-temperature porphyroclastic microstructures and strong olivine CPO. Although dunites and wehrlites display annealing microstructures to which is associated a progressive dispersion of the olivine CPO, very weak CPO are limited to a few dunites and wehrlites, suggesting that CPO destruction is restricted to domains of intense magma-rock interaction due to localized flow or accumulation of magmas. Conversely, the compositional changes result in lower seismic velocities for P- and S-waves. Relative to normal mantle, seismic anomalies may attain -2

Organic molecules in the Sheepbed Mudstone, Gale Crater, Mars

NARCIS (Netherlands)

Freissinet, C.; Glavin, D. P.; Mahaffy, P. R.; Miller, K. E.; Eigenbrode, J. L.; Summons, R. E.; Brunner, A. E.; Buch, A.; Szopa, C.; Archer, P. D.; Franz, H. B.; Atreya, S. K.; Brinckerhoff, W. B.; Cabane, M.; Coll, P.; Conrad, P. G.; Des Marais, D. J.; Dworkin, J. P.; Fairén, A. G.; François, P.; Grotzinger, J. P.; Kashyap, S.; ten Kate, I. L.; Leshin, L. A.; Malespin, C. A.; Martin, M. G.; Martin-Torres, F. J.; Mcadam, A. C.; Ming, D. W.; Navarro-González, R.; Pavlov, A. A.; Prats, B. D.; Squyres, S. W.; Steele, A.; Stern, J. C.; Sumner, D. Y.; Sutter, B.; Zorzano, M. P.

The Sample Analysis at Mars (SAM) instrument on board the Mars Science Laboratory Curiosity rover is designed to conduct inorganic and organic chemical analyses of the atmosphere and the surface regolith and rocks to help evaluate the past and present habitability potential of Mars at Gale Crater.

Zhamanshin and Aouelloul - Craters produced by impact of tektite-like glasses?

Science.gov (United States)

O'Keefe, John A.

1987-01-01

It is shown that the enhanced abundance of siderophile elements and chromium in tektite-like glasses from the two impact craters of Zhamanshin and Aouelloul cannot be explained as a result of contamination of the country rock by meteorites nor, probably, comets. The pattern is, however, like that found in certain Australasian tektites, and in Ivory Coast tektites. It is concluded, in agreement with earlier suggestions by Campbell-Smith and Hey, that these craters were formed by the impact of large masses of tektite-like glass, of which the glasses which were studied are fragments. It follows that it is necessary, in considering an impact crater, to bear in mind that the projectile may have been a glass.

Joint M3 and Diviner Analysis of the Mineralogy, Glass Composition, and Country Rock Content of Pyroclastic Deposits in Oppenheimer Crater

Science.gov (United States)

Bennett, Kristen A.; Horgan, Briony H. N.; Greenhagen, Benjamin T.; Allen, Carlton C.; Paige, David A.; Bell, James F., III

2013-01-01

Here we present our analysis of the near- and mid-infrared spectral properties of pyroclastic deposits within the floor fractured Oppenheimer Crater that are hypothesized to be Vulcanian in origin. These are the first results of our global study of lunar pyroclastic deposits aimed at constraining the range of eruption processes on the Moon. In the near-infrared, we have employed a new method of spectral analysis developed in Horgan et al. (2013) of the 1 ?m iron absorption band in Chandrayaan-1 Moon Mineralogy Mapper (M3) spectra. By analyzing both the position and shape of the 1 ?m band we can detect and map the distribution of minerals, glasses, and mixtures of these phases in pyroclastic deposits. We are also using mid-infrared spectra from the Lunar Reconnaissance Orbiter Diviner Lunar Radiometer Experiment to develop 200 m/pixel Christiansen Feature (CF) maps, which correlate with silica abundance. One of the benefits of using CF maps for analysis of pyroclastic deposits is that they can be used to detect silicic country rock that may have been emplaced by Vulcanian-style eruptions, and are sensitive to iron abundance in glasses, neither of which is possible in the near-infrared. M3 analysis reveals that the primary spectral endmembers are low-calcium pyroxene and iron-bearing glass, with only minor high-calcium pyroxene, and no detectable olivine. The large deposit in the south shows higher and more extensive glass concentrations than the surrounding deposits. We interpret the M3 spectra of the pyroclastic deposits as indicating a mixture of low-calcium pyroxene country rock and juvenile glass, and no significant olivine. Analysis of Diviner CF maps of the Oppenheimer crater floor indicates an average CF value of 8.16, consistent with a mixture of primarily plagioclase and some pyroxene. The average CF values of the pyroclastic deposits range from 8.31 in the SW to 8.24 in the SE. Since CF values within the deposits are as high as 8.49, the lower average CF

Wind-blown sandstones cemented by sulfate and clay minerals in Gale Crater, Mars

OpenAIRE

Milliken, R. E.; Ewing, Ryan C.; Fischer, W. W.; Hurowitz, J.

2014-01-01

Gale Crater contains Mount Sharp, a ~5km thick stratigraphic record of Mars’ early environmental history. The strata comprising Mount Sharp are believed to be sedimentary in origin, but the specific depositional environments recorded by the rocks remain speculative. We present orbital evidence for the occurrence of eolian sandstones within Gale Crater and the lower reaches of Mount Sharp, including preservation of wind-blown sand dune topography in sedimentary strata—a phenomenon ...

Layers of 'Cabo Frio' in 'Victoria Crater' (Stereo)

Science.gov (United States)

2006-01-01

This view of 'Victoria crater' is looking southeast from 'Duck Bay' towards the dramatic promontory called 'Cabo Frio.' The small crater in the right foreground, informally known as 'Sputnik,' is about 20 meters (about 65 feet) away from the rover, the tip of the spectacular, layered, Cabo Frio promontory itself is about 200 meters (about 650 feet) away from the rover, and the exposed rock layers are about 15 meters (about 50 feet) tall. This is a red-blue stereo anaglyph generated from images taken by the panoramic camera (Pancam) on NASA's Mars Exploration Rover Opportunity during the rover's 952nd sol, or Martian day, (Sept. 28, 2006) using the camera's 430-nanometer filters.

Protracted fluid-induced melting during Barrovian metamorphism in the Central Alps

DEFF Research Database (Denmark)

Rubatto, Daniela; Hermann, Jörg; Berger, Alfons

2009-01-01

that repeated melting events occurred within a single Barrovian metamorphic cycle at roughly constant temperature; that in the country rocks zircon formation was limited to the initial stages of melting, whereas further melting concentrated in the segregated leucosomes; that melting occurred at different times......The timing and dynamics of fluid-induced melting in the typical Barrovian sequence of the Central Alps has been investigated using zircon chronology and trace element composition. Multiple zircon domains in leucosomes and country rocks yield U-Pb ages spanning from ~32 to 22 Ma. The zircon formed...... in samples a few meters apart because of the local rock composition and localized influx of the fluids; and that leucosomes were repeatedly melted when fluids became available. The geochronological data force a revision of the temperature-time path of the migmatite belt in the Central Alps. Protracted...

Mechanical Aqueous Alteration Dominates Textures of Gale Crater Rocks: Mars Hand Lens Imager (MAHLI) Results

Science.gov (United States)

Aileen Yingst, R.; Minitti, Michelle; Edgett, Kenneth; McBride, Marie; Stack, Kathryn

2015-04-01

lusters, set in gray, fine sand; and dark gray, well-cemented, and fine grained, with rare pebble-sized clasts. The latter also exhibits pores or vugs that may have resulted from removal of these larger coasts. Pebbly sandstones: This texture is characterized by a poorly-cemented, poorly sorted matrix of coarse sand to granules with a variety of colors and lusters. Whereas two endmembers in this class (Bardin Bluffs and Altar Mountain) have a similar fine-grained matrix, they exhibit different populations and proportions of granules to cm-sized pebbles. Bardin Bluffs displays a fining upwards texture and grain-to-grain contact; the stratigraphically lower Altar Mountain does not. Massive and Vuggy rocks: These two classes are gray and fine-grained. Many of these rocks occur in a sedimentary context, suggesting that differences in grain characteristics and relationships stem from variations in cementation and/or weathering history. In general, most rock textures indicate fluvial or possibly lacustrine sediments; MAHLI has not unambiguously identified eolian or igneous rock textures, although some pebble-sized clasts may have an igneous provenance and some might derive from impact melt.

The Chicxulub crater - impact metamorphism of sulfate and carbonate lithologies

Science.gov (United States)

Deutsch, A.; Langenhorst, F.; Hornemann, U.; Ivanov, B. A.

2003-04-01

It is discussed whether in the aftermath of the Chicxulub event, impact-released CO_2 and SO_x have changed the Earth's climate, acting also as lethal thread for life. Undoubtedly, vaporization of carbonates and sulfates, which are major target lithologies at the Chicxulub impact site, occurred in the footprint of the projectile. What happened to these lithologies outside this very restricted zone was so far unconstrained. Petrologic observations on PEMEX and UNAM as well as on the CSDP cores allow to set up a general classification for shock-related pro-grade effects on sulfate and carbonate sedimentary rocks. Shock effects in lithic breccias are restricted to brecciation and formation of twins in calcite. Suevites mostly lack melted carbonate clasts; annealing effects in anhydrite fragments are absent. The underlying melt breccias contain anhydrite fragments still displaying a sedimentary texture, and limestone clasts, whose texture reflect crystallization from melt. Impact melt breccias from deeper levels frequently contain partially resorbed anhydrite clasts and a melt matrix with the Ca-rich mineral assemblage quartz + plagioclase + clinopyroxene; this mineral assemblage provides evidence for partial dissociation of CaSO_4. Large clasts of anhydrite consist of equant crystals with 120^o triple junctions, a feature indicative for re-crystallization in the solid state. Tagamites (impact melt rocks) are virtually free of clasts from sedimentary lithologies. These rocks have an extremely high formation temperature, which caused total dissociation of CaSO_4 and CaCO_3. Finally, up to 100 μm wide veins of anhydrite + calcite + quartz cut the matrix of all lithologies except the tagamites. They probably represent "degassing vents". The given scheme is in qualitative accordance with data of shock recovery and annealing experiments as well as with modeling results. In addition, it substantiates that annealing plays a fundamental role in the impact metamorphism of

Mafic Materials in Scott Crater? A Test for Lunar Reconnaissance Orbiter

Science.gov (United States)

Cooper, Bonnie L.

2007-01-01

Clementine 750 nm and multispectral ratio data, along with Lunar Orbiter and radar data, were used to study the crater Scott in the lunar south polar region. The multispectral data provide evidence for mafic materials, impact melts, anorthositic materials, and a small pyroclastic deposit. High-resolution radar data and Lunar Orbiter photography for this area show differences in color and surface texture that correspond with the locations of the hypothesized mafic and anorthositic areas on the crater floor. This region provides a test case for the upcoming Lunar Reconnaissance Orbiter. Verification of the existence of a mafic deposit at this location is relevant to future lunar resource utilization planning.

Population characteristics of submicrometer-sized craters on regolith particles from asteroid Itokawa

Science.gov (United States)

Matsumoto, Toru; Hasegawa, S.; Nakao, S.; Sakai, M.; Yurimoto, H.

2018-03-01

We investigated impact crater structures on regolith particles from asteroid Itokawa using scanning electron microscopy. We observed the surfaces of 51 Itokawa particles, ranging from 15 μm to 240 μm in size. Craters with average diameters ranging from 10 nm to 2.8 μm were identified on 13 Itokawa particles larger than 80 μm. We examined the abundance, spatial distribution, and morphology of approximately 900 craters on six Itokawa particles. Craters with sizes in excess of 200 nm are widely dispersed, with spatial densities from 2.6 μm2 to 4.5 μm2; a fraction of the craters was locally concentrated with a density of 0.1 μm2. The fractal dimension of the cumulative crater diameters ranges from 1.3 to 2.3. Craters of several tens of nanometers in diameter exhibit pit and surrounding rim structures. Craters of more than 100 nm in diameter commonly have melted residue at their bottom. These morphologies are similar to those of submicrometer-sized craters on lunar regolith. We estimated the impactor flux on Itokawa regolith-forming craters, assuming that the craters were accumulated during direct exposure to the space environment for 102 to 104 yr. The range of impactor flux onto Itokawa particles is estimated to be at least one order of magnitude higher than the interplanetary dust flux and comparable to the secondary impact flux on the Moon. This indicates that secondary ejecta impacts are probably the dominant cratering process in the submicrometer range on Itokawa regolith particles, as well as on the lunar surface. We demonstrate that secondary submicrometer craters can be produced anywhere in centimeter- to meter-sized depressions on Itokawa's surface through primary interplanetary dust impacts. If the surface unevenness on centimeter to meter scales is a significant factor determining the abundance of submicrometer secondary cratering, the secondary impact flux could be independent of the overall shapes or sizes of celestial bodies, and the secondary

Boring and Sealing Rock with Directed Energy Millimeter-Waves

Science.gov (United States)

Woskov, P.; Einstein, H. H.; Oglesby, K.

2015-12-01

Millimeter-wave directed energy is being investigated to penetrate into deep crystalline basement rock formations to lower well costs and to melt rocks, metals, and other additives to seal wells for applications that include nuclear waste storage and geothermal energy. Laboratory tests have established that intense millimeter-wave (MMW) beams > 1 kW/cm2 can melt and/ or vaporize hard crystalline rocks. In principle this will make it possible to create open boreholes and a method to seal them with a glass/ceramic liner and plug formed from the original rock or with other materials. A 10 kW, 28 GHz commercial (CPI) gyrotron system with a launched beam diameter of about 32 mm was used to heat basalt, granite, limestone, and sandstone specimens to temperatures over 2500 °C to create melts and holes. A calibrated 137 GHz radiometer view, collinear with the heating beam, monitored real time peak rock temperature. A water load surrounding the rock test specimen primarily monitored unabsorbed power at 28 GHz. Power balance analysis of the laboratory observations shows that the temperature rise is limited by radiative heat loss, which would be expected to be trapped in a borehole. The analysis also indicates that the emissivity (absorption efficiency) in the radiated infrared range is lower than the emissivity at 28 GHz, giving the MMW frequency range an important advantage for rock melting. Strength tests on one granite type indicated that heating the rock initially weakens it, but with exposure to higher temperatures the resolidified black glassy product regains strength. Basalt was the easiest to melt and penetrate, if a melt leak path was provided, because of its low viscosity. Full beam holes up to about 50 mm diameter (diffraction increased beam size) were achieved through 30 mm thick basalt and granite specimens. Laboratory experiments to form a seal in an existing hole have also been carried out by melting rock and a simulated steel casing.

Constraints on mechanisms for the growth of gully alcoves in Gasa crater, Mars, from two-dimensional stability assessments of rock slopes

Science.gov (United States)

Okubo, C.H.; Tornabene, L.L.; Lanza, N.L.

2011-01-01

The value of slope stability analyses for gaining insight into the geologic conditions that would facilitate the growth of gully alcoves on Mars is demonstrated in Gasa crater. Two-dimensional limit equilibrium methods are used in conjunction with high-resolution topography derived from stereo High Resolution Imaging Science Experiment (HiRISE) imagery. These analyses reveal three conditions that may produce observed alcove morphologies through slope failure: (1) a ca >10m thick surface layer that is either saturated with H2O ground ice or contains no groundwater/ice at all, above a zone of melting H2O ice or groundwater and under dynamic loading (i.e., seismicity), (2) a 1-10m thick surface layer that is saturated with either melting H2O ice or groundwater and under dynamic loading, or (3) a >100m thick surface layer that is saturated with either melting H2O ice or groundwater and under static loading. This finding of three plausible scenarios for slope failure demonstrates how the triggering mechanisms and characteristics of future alcove growth would be affected by prevailing environmental conditions. HiRISE images also reveal normal faults and other fractures tangential to the crowns of some gully alcoves that are interpreted to be the result of slope instability, which may facilitate future slope movement. Stability analyses show that the most failure-prone slopes in this area are found in alcoves that are adjacent to crown fractures. Accordingly, crown fractures appear to be a useful indicator of those alcoves that should be monitored for future landslide activity. ?? 2010.

Layers of 'Cabo Frio' in 'Victoria Crater' (False Color)

Science.gov (United States)

2006-01-01

This view of 'Victoria crater' is looking southeast from 'Duck Bay' towards the dramatic promontory called 'Cabo Frio.' The small crater in the right foreground, informally known as 'Sputnik,' is about 20 meters (about 65 feet) away from the rover, the tip of the spectacular, layered, Cabo Frio promontory itself is about 200 meters (about 650 feet) away from the rover, and the exposed rock layers are about 15 meters (about 50 feet) tall. This is an enhanced false color rendering of images taken by the panoramic camera (Pancam) on NASA's Mars Exploration Rover Opportunity during the rover's 952nd sol, or Martian day, (Sept. 28, 2006) using the camera's 750-nanometer, 530-nanometer and 430-nanometer filters.

High concentrations of manganese and sulfur in deposits on Murray Ridge, Endeavour Crater, Mars

Science.gov (United States)

Arvidson, Raymond E.; Squyres, Steven W.; Morris, Richard V.; Knoll, Andrew H.; Gellert, Ralf; Clark, Benton C.; Catalano, Jeffrey G.; Jolliff, Bradley L.; McLennan, Scott M.; Herkenhoff, Kenneth E.; VanBommel, Scott; Mittelfehldt, David W.; Grotzinger, John P.; Guinness, Edward A.; Johnson, Jeffrey R.; Bell, James F.; Farrand, William H.; Stein, Nathan; Fox, Valerie K.; Golombek, Matthew P.; Hinkle, Margaret A. G.; Calvin, Wendy M.; de Souza, Paulo A.

2016-01-01

Mars Reconnaissance Orbiter HiRISE images and Opportunity rover observations of the ~22 km wide Noachian age Endeavour Crater on Mars show that the rim and surrounding terrains were densely fractured during the impact crater-forming event. Fractures have also propagated upward into the overlying Burns formation sandstones. Opportunity’s observations show that the western crater rim segment, called Murray Ridge, is composed of impact breccias with basaltic compositions, as well as occasional fracture-filling calcium sulfate veins. Cook Haven, a gentle depression on Murray Ridge, and the site where Opportunity spent its sixth winter, exposes highly fractured, recessive outcrops that have relatively high concentrations of S and Cl, consistent with modest aqueous alteration. Opportunity’s rover wheels serendipitously excavated and overturned several small rocks from a Cook Haven fracture zone. Extensive measurement campaigns were conducted on two of them: Pinnacle Island and Stuart Island. These rocks have the highest concentrations of Mn and S measured to date by Opportunity and occur as a relatively bright sulfate-rich coating on basaltic rock, capped by a thin deposit of one or more dark Mn oxide phases intermixed with sulfate minerals. We infer from these unique Pinnacle Island and Stuart Island rock measurements that subsurface precipitation of sulfate-dominated coatings was followed by an interval of partial dissolution and reaction with one or more strong oxidants (e.g., O2) to produce the Mn oxide mineral(s) intermixed with sulfate-rich salt coatings. In contrast to arid regions on Earth, where Mn oxides are widely incorporated into coatings on surface rocks, our results demonstrate that on Mars the most likely place to deposit and preserve Mn oxides was in fracture zones where migrating fluids intersected surface oxidants, forming precipitates shielded from subsequent physical erosion.

Melt layer macroscopic erosion of tungsten and other metals under plasma heat loads simulating ITER off-normal events

International Nuclear Information System (INIS)

Garkusha, I.E.; Bandura, A.N.; Byrka, O.V.; Kulik, N.V.; Landman, I.; Wuerz, H.

2002-01-01

This paper is focused on experimental analysis of metal layer erosion and droplet splashing of tungsten and other metals under heat loads typical for ITER FEAT off-normal events,such as disruptions and VDE's. Plasma pressure gradient action on melt layer results in erosion crater formation with mountains of displaced material at the crater edge. It is shown that macroscopic motion of melt layer and surface cracking are the main factors responsible for tungsten damage. Weight loss measurements of all exposed materials demonstrate inessential contribution of evaporation process to metals erosion

IODP-ICDP Expedition 364: Drilling the Chicxulub impact crater to understand planetary evolution and mass extinction

Science.gov (United States)

Gulick, S. P. S.; Morgan, J. V.

2017-12-01

The most recent of Earth's five largest mass extinction events occurred 66 Ma, coeval with the impact of a 12 km asteroid, striking at 60 degrees into what is today the Yucatán Peninsula, México, producing the 200 km-wide Chicxulub crater. This impact, by some estimations, drove the extinction of 75% of life on Earth at the genus level. The mass extinction event marks the boundary between the Cretaceous and Paleogene. Proposed kill mechanisms include thermal effects caused by the reentry of fast ejecta into Earth's atmosphere, dust and sulfate aerosols reducing Earth's solar insolation, ocean acidification, and metal toxicity due to the chemical make-up of the impactor. The magnitude and duration of these processes is still debated, and further evaluation of the proposed kill mechanisms requires an understanding of the mechanics of the Chicxulub impact as well as the resulting global environmental perturbations. In April and May 2016, the International Ocean Discovery Program, with co-funding from the International Continental Scientific Drilling Program, successfully cored into the Chicxulub impact crater with nearly 100% recovery. These cores include the first-ever samples of the transition from an intact peak ring through post-impact sediments. A peak ring is a discontinuous ring of mountains observed within the central basin of all large impact craters on rocky planets. Newly drilled cores include the uplifted target rocks, melt-rich impactites, hydrothermal deposits, a possible settling layer, and the resumption of carbonate sedimentation. The discovery that Chicxulub's peak ring consists of largely granitic crust uplifted by 10 km calibrates impact models and allows for observation of impact processes. At the top of the peak ring, the K-Pg boundary deposit includes a impactite sequence 130 m thick deposited by processes that range from minutes to likely years post-impact. This sequence is then overprinted by hydrothermal processes that lasted at least 100s

Two Martian Winters at Gusev Crater and Meridiani Planum: New Results From the MER Mossbauer Spectrometers

Science.gov (United States)

Klingelhoefer, Goestar; Morris, Richard V.; Schroeder, Christian; Rodionov, Daniel S.; Yen, Albert S.; Ming, Douglas W.; Cohen, Barbara A.; Fleischer, Iris; Mittlefehldt, David W.; McCoy, Tim;

Opportunity Mars Rover mission: Overview and selected results from Purgatory ripple to traverses to Endeavour crater

Science.gov (United States)

Arvidson, R. E.; Ashley, James W.; Bell, J.F.; Chojnacki, M.; Cohen, J.; Economou, T.E.; Farrand, W. H.; Fergason, R.; Fleischer, I.; Geissler, P.; Gellert, Ralf; Golombek, M.P.; Grotzinger, J.P.; Guinness, E.A.; Haberle, R.M.; Herkenhoff, K. E.; Herman, J.A.; Iagnemma, K.D.; Jolliff, B.L.; Johnson, J. R.; Klingelhofer, G.; Knoll, A.H.; Knudson, A.T.; Li, R.; McLennan, S.M.; Mittlefehldt, D. W.; Morris, R.V.; Parker, T.J.; Rice, M.S.; Schroder, C.; Soderblom, L.A.; Squyres, S. W.; Sullivan, R.J.; Wolff, M.J.

2011-01-01

Opportunity has been traversing the Meridiani plains since 25 January 2004 (sol 1), acquiring numerous observations of the atmosphere, soils, and rocks. This paper provides an overview of key discoveries between sols 511 and 2300, complementing earlier papers covering results from the initial phases of the mission. Key new results include (1) atmospheric argon measurements that demonstrate the importance of atmospheric transport to and from the winter carbon dioxide polar ice caps; (2) observations showing that aeolian ripples covering the plains were generated by easterly winds during an epoch with enhanced Hadley cell circulation; (3) the discovery and characterization of cobbles and boulders that include iron and stony-iron meteorites and Martian impact ejecta; (4) measurements of wall rock strata within Erebus and Victoria craters that provide compelling evidence of formation by aeolian sand deposition, with local reworking within ephemeral lakes; (5) determination that the stratigraphy exposed in the walls of Victoria and Endurance craters show an enrichment of chlorine and depletion of magnesium and sulfur with increasing depth. This result implies that regional-scale aqueous alteration took place before formation of these craters. Most recently, Opportunity has been traversing toward the ancient Endeavour crater. Orbital data show that clay minerals are exposed on its rim. Hydrated sulfate minerals are exposed in plains rocks adjacent to the rim, unlike the surfaces of plains outcrops observed thus far by Opportunity. With continued mechanical health, Opportunity will reach terrains on and around Endeavour's rim that will be markedly different from anything examined to date. Copyright 2011 by the American Geophysical Union.

Nuclear waste management by in-situ melting

International Nuclear Information System (INIS)

Angelo, J.A. Jr.

1976-01-01

A systematic assessment of the in-situ melting concept as an ultimate waste disposal option shows that the placement of solidifed, high-level radioactive wastes in an in-situ melting cavity with a crushed rock backfill not only eliminates the major deficiencies inherent in other in-situ melting schemes, but also satisfies reasonable criteria for ultimate disposal. In-situ melting reduces the waste isolation time requirements to several hundred years. Calculated spent fuel and processing waste afterheat values assess the role of actinide and cladding material nuclides in creating the total afterheat and provide quantitative variation with time for these values for contamporary and advanced-design fission reactors. The dominant roles of 134 Cs in thermal spectrum reactor afterheats during the first decade of cooling of the actinide nuclides in all typical waste after-heats following a century or two of cooling are identified. The spatial and temporal behavior of a spherically symmetric waste repository experiencing in-situ melting in an equal density, homogeneous medium for silicate rock and salt is controlled primarily by the overall volumetric thermal source strength, the time-dependent characteristics of the high-level wastes, and the thermophysical properties of the surrounding rock environment. Calculations were verified by experimental data. The hazard index for typical high-level wastes is dominated by the fission product nuclides for the first three centuries of decay. It is then controlled by the actinides, especially americium, which dominates for 10,000 years. With in-situ melting, the hazard index for the re-solidifed rock/waste matrix deepunderground falls below the hazard index of naturally occurring uranium ore bodies within a few hundred years, whether or not the more hazardous actinide nuclides are selectively removed from the wastes prior to storage

Zircon (Hf, O isotopes) as melt indicator: Melt infiltration and abundant new zircon growth within melt rich layers of granulite-facies lenses versus solid-state recrystallization in hosting amphibolite-facies gneisses (central Erzgebirge, Bohemian Massif)

Science.gov (United States)

Tichomirowa, Marion; Whitehouse, Martin; Gerdes, Axel; Schulz, Bernhard

2018-03-01

In the central Erzgebirge within the Bohemian Massif, lenses of high pressure and ultrahigh pressure felsic granulites occur within meta-sedimentary and meta-igneous amphibolite-facies felsic rocks. In the felsic granulite, melt rich parts and restite form alternating layers, and were identified by petrology and bulk rock geochemistry. Mineral assemblages representing the peak P-T conditions were best preserved in melanocratic restite layers. In contrast, in the melt rich leucocratic layers, garnet and related HP minerals as kyanite are almost completely resorbed. Both layers display differences in accessory minerals: melanosomes have frequent and large monazite and Fe-Ti-minerals but lack xenotime and apatite; leucosomes have abundant apatite and xenotime while monazite is rare. Here we present a detailed petrographic study of zircon grains (abundance, size, morphology, inclusions) in granulite-facies and amphibolite-facies felsic gneisses, along with their oxygen and hafnium isotope compositions. Our data complement earlier Usbnd Pb ages and trace element data (REE, Y, Hf, U) on zircons from the same rocks (Tichomirowa et al., 2005). Our results show that the degree of melting determines the behaviour of zircon in different layers of the granulites and associated amphibolite-facies rocks. In restite layers of the granulite lenses, small, inherited, and resorbed zircon grains are preserved and new zircon formation is very limited. In contrast, new zircons abundantly grew in the melt rich leucocratic layers. In these layers, the new zircons (Usbnd Pb age, trace elements, Hf, O isotopes) best preserve the information on peak metamorphic conditions due to intense corrosion of other metamorphic minerals. The new zircons often contain inherited cores. Compared to cores, the new zircons and rims show similar or slightly lower Hf isotope values, slightly higher Hf model ages, and decreased oxygen isotope ratios. The isotope compositions (Hf, O) of new zircons indicate

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

Science.gov (United States)

Cohen, Barbara A.; Coker, Robert F.

2010-01-01

The South Pole Aitken (SPA) basin is the stratigraphically oldest identifiable lunar basin and is therefore one of the most important targets for absolute age-dating to help understand whether ancient lunar bombardment history smoothly declined or was punctuated by a cataclysm. A feasible near-term approach to this problem is to robotically collect a sample from near the center of the basin, where vertical and lateral mixing provided by post-basin impacts ensures that such a sample will be composed of small rock fragments from SPA itself, from local impact craters, and from faraway giant basins. The range of ages, intermediate spikes in the age distribution, and the oldest ages are all part of the definition of the absolute age and impact history recorded within the SPA basin.

Multivariate analyses of crater parameters and the classification of craters

Science.gov (United States)

Siegal, B. S.; Griffiths, J. C.

1974-01-01

Multivariate analyses were performed on certain linear dimensions of six genetic types of craters. A total of 320 craters, consisting of laboratory fluidization craters, craters formed by chemical and nuclear explosives, terrestrial maars and other volcanic craters, and terrestrial meteorite impact craters, authenticated and probable, were analyzed in the first data set in terms of their mean rim crest diameter, mean interior relief, rim height, and mean exterior rim width. The second data set contained an additional 91 terrestrial craters of which 19 were of experimental percussive impact and 28 of volcanic collapse origin, and which was analyzed in terms of mean rim crest diameter, mean interior relief, and rim height. Principal component analyses were performed on the six genetic types of craters. Ninety per cent of the variation in the variables can be accounted for by two components. Ninety-nine per cent of the variation in the craters formed by chemical and nuclear explosives is explained by the first component alone.

CUMULATE ROCKS ASSOCIATED WITH CARBONATE ASSIMILATION, HORTAVÆR COMPLEX, NORTH-CENTRAL NORWAY

Science.gov (United States)

Barnes, C. G.; Prestvik, T.; Li, Y.

2009-12-01

The Hortavær igneous complex intruded high-grade metamorphic rocks of the Caledonian Helgeland Nappe Complex at ca. 466 Ma. The complex is an unusual mafic-silicic layered intrusion (MASLI) because the principal felsic rock type is syenite and because the syenite formed in situ rather than by deep-seated partial melting of crustal rocks. Magma differentiation in the complex was by assimilation, primarily of calc-silicate rocks and melts with contributions from marble and semi-pelites, plus fractional crystallization. The effect of assimilation of calcite-rich rocks was to enhance stability of fassaitic clinopyroxene at the expense of olivine, which resulted in alkali-rich residual melts and lowering of silica activity. This combination of MASLI-style emplacement and carbonate assimilation produced three types of cumulate rocks: (1) Syenitic cumulates formed by liquid-crystal separation. As sheets of mafic magma were loaded on crystal-rich syenitic magma, residual liquid was expelled, penetrating the overlying mafic sheets in flame structures, and leaving a cumulate syenite. (2) Reaction cumulates. Carbonate assimilation, illustrated by a simple assimilation reaction: olivine + calcite + melt = clinopyroxene + CO2 resulted in cpx-rich cumulates such as clinopyroxenite, gabbro, and mela-monzodiorite, many of which contain igneous calcite. (3) Magmatic skarns. Calc-silicate host rocks underwent partial melting during assimilation, yielding a Ca-rich melt as the principal assimilated material and permitting extensive reaction with surrounding magma to form Kspar + cpx + garnet-rich ‘cumulate’ rocks. Cumulate types (2) and (3) do not reflect traditional views of cumulate rocks but instead result from a series of melt-present discontinuous (peritectic) reactions and partial melting of calc-silicate xenoliths. In the Hortavær complex, such cumulates are evident because of the distinctive peritectic cumulate assemblages. It is unclear whether assimilation of �

Arrested diatreme development: Standing Rocks East, Hopi Buttes, Navajo Nation, USA

Science.gov (United States)

Lefebvre, Nathalie S.; White, James D. L.; Kjarsgaard, Bruce A.

2016-01-01

Maar-diatreme volcanoes, defined by their relatively large pyroclastic debris-filled subsurface structures and craters that cut into the pre-eruptive land surface, are typically found in small-volume mafic to ultramafic monogenetic volcanic fields. Diatremes are associated with strong explosions throughout most of their development, focused along feeder dikes and generally attributed to magma-water interaction, or high magmatic volatiles. Detailed mapping of the magnificently exposed Standing Rocks East (SRE) diatreme shows evidence of additional eruptive complexity, and offers new insights into how the plumbing and vent structures of small-volume volcanoes evolve during an eruption. SRE is part of a larger, basanitic volcanic complex that includes several diatremes formed along a series of irregular, offset NW-SE trending dikes exposed 300 m below the pre-eruptive land surface. Its similarly oriented elliptical-shaped diatreme structure comprises predominantly country rock lithic-rich breccia of coarse inhomogeneously mixed wall-rock blocks sourced from above and below the current surface, plus sparse juvenile material. Domains of pyroclastic deposits crosscut the country rock breccia deposits, and the best exposed is the NW massif rising 35 m above the current erosional surface. It represents a cross-section of an evolving crater floor, and comprises matrix-rich lapilli tuff and spatter deposits cut by irregularly distributed dikes, some with very complex textures. The most significant deposit, in terms of volume, is an unbedded lapilli tuff that is poorly sorted and has a well-mixed population of wall-rock and juvenile clast varieties, thus resembling deposits typical of diatremes. It is overlain by and locally intercalated with spatter deposits, and this irregular contact demarcates the base of what was during eruption an uneven, evolving crater floor. The generally massive, variably welded spatter deposits constitute mostly lapilli-sized juvenile clasts with

Water in the oceanic lithosphere: Salt Lake Crater xenoliths, Oahu, Hawaii

Science.gov (United States)

Peslier, A. H.; Bizimis, M.

2010-12-01

Water can be present in nominally anhydrous minerals of peridotites in the form of hydrogen bonded to structural oxygen. Such water in the oceanic upper mantle could have a significant effect on its physical and chemical properties. However, the water content of the MORB source has been inferred indirectly from the compositions of basalts. Direct determinations on abyssal peridotites are scarce because they have been heavily hydrothermally altered. Here we present the first water analyses of minerals from spinel peridotite xenoliths of Salt Lake Crater, Oahu, Hawaii, which are exceptionally fresh. These peridotites are thought to represent fragments of the Pacific oceanic lithosphere that was refertilized by alkalic Hawaiian melts. A few have unradiogenic Os and radiogenic Hf isotopes and may be fragments of an ancient ( 2 Ga) depleted and recycled lithosphere. Water contents in olivine (Ol), orthopyroxene (Opx), and clinopyroxene (Cpx) were determined by FTIR spectrometry. Preliminary H_{2}O contents show ranges of 8-10 ppm for Ol, 151-277 ppm for Opx, and 337-603 ppm for Cpx. Reconstructed bulk rock H_{2}O contents range from 88-131 ppm overlapping estimates for the MORB source. Water contents between Ol minerals of the same xenolith are heterogeneous and individual OH infrared bands vary within a mineral with lower 3230 cm^{-1} and higher 3650-3400 cm^{-1} band heights from core to edge. This observation suggests disturbance of the hydrogen in Ol likely occurring during xenolith entrainment to the surface. Pyroxene water contents are higher than most water contents in pyroxenes from continental peridotite xenoliths and higher than those of abyssal peridotites. Cpx water contents decrease with increasing degree of depletion (e.g. increasing Fo in Ol and Cr# in spinel) consistent with an incompatible behavior of water. However Cpx water contents also show a positive correlation with LREE/HREE ratios and LREE concentrations consistent with refertilization. Opx

Water in the Oceanic Lithosphere: Salt Lake Crater Xenoliths, Oahu, Hawaii

Science.gov (United States)

Peslier, Anne H.; Bizimis, Michael

2010-01-01

Water can be present in nominally anhydrous minerals of peridotites in the form of hydrogen bonded to structural oxygen. Such water in the oceanic upper mantle could have a significant effect on its physical and chemical properties. However, the water content of the MORB source has been inferred indirectly from the compositions of basalts. Direct determinations on abyssal peridotites are scarce because they have been heavily hydrothermally altered. Here we present the first water analyses of minerals from spinel peridotite xenoliths of Salt Lake Crater, Oahu, Hawaii, which are exceptionally fresh. These peridotites are thought to represent fragments of the Pacific oceanic lithosphere that was refertilized by alkalic Hawaiian melts. A few have unradiogenic Os and radiogenic Hf isotopes and may be fragments of an ancient (2 Ga) depleted and recycled lithosphere. Water contents in olivine (Ol), orthopyroxene (Opx), and clinopyroxene (Cpx) were determined by FTIR spectrometry. Preliminary H_{2}O contents show ranges of 8-10 ppm for Ol, 151-277 ppm for Opx, and 337-603 ppm for Cpx. Reconstructed bulk rock H_{2}O contents range from 88-131 ppm overlapping estimates for the MORB source. Water contents between Ol minerals of the same xenolith are heterogeneous and individual OH infrared bands vary within a mineral with lower 3230 cm^{-1} and higher 3650-3400 cm^{-1} band heights from core to edge. This observation suggests disturbance of the hydrogen in Ol likely occurring during xenolith entrainment to the surface. Pyroxene water contents are higher than most water contents in pyroxenes from continental peridotite xenoliths and higher than those of abyssal peridotites. Cpx water contents decrease with increasing degree of depletion (e.g. increasing Fo in Ol and Cr# in spinel) consistent with an incompatible behavior of water. However Cpx water contents also show a positive correlation with LREE/HREE ratios and LREE concentrations consistent with refertilization. Opx water

Alkali trace elements in Gale crater, Mars, with ChemCam: Calibration update and geological implications

Science.gov (United States)

Payré, V.; Fabre, C.; Cousin, A.; Sautter, V.; Wiens, R. C.; Forni, O.; Gasnault, O.; Mangold, N.; Meslin, P.-Y.; Lasue, J.; Ollila, A.; Rapin, W.; Maurice, S.; Nachon, M.; Le Deit, L.; Lanza, N.; Clegg, S.

2017-03-01

The Chemistry Camera (ChemCam) instrument onboard Curiosity can detect minor and trace elements such as lithium, strontium, rubidium, and barium. Their abundances can provide some insights about Mars' magmatic history and sedimentary processes. We focus on developing new quantitative models for these elements by using a new laboratory database (more than 400 samples) that displays diverse compositions that are more relevant for Gale crater than the previous ChemCam database. These models are based on univariate calibration curves. For each element, the best model is selected depending on the results obtained by using the ChemCam calibration targets onboard Curiosity. New quantifications of Li, Sr, Rb, and Ba in Gale samples have been obtained for the first 1000 Martian days. Comparing these data in alkaline and magnesian rocks with the felsic and mafic clasts from the Martian meteorite NWA7533—from approximately the same geologic period—we observe a similar behavior: Sr, Rb, and Ba are more concentrated in soluble- and incompatible-element-rich mineral phases (Si, Al, and alkali-rich). Correlations between these trace elements and potassium in materials analyzed by ChemCam reveal a strong affinity with K-bearing phases such as feldspars, K-phyllosilicates, and potentially micas in igneous and sedimentary rocks. However, lithium is found in comparable abundances in alkali-rich and magnesium-rich Gale rocks. This very soluble element can be associated with both alkali and Mg-Fe phases such as pyroxene and feldspar. These observations of Li, Sr, Rb, and Ba mineralogical associations highlight their substitution with potassium and their incompatibility in magmatic melts.

Uniaxial Compressive Strengths of Rocks Drilled at Gale Crater, Mars

Science.gov (United States)

Peters, G. H.; Carey, E. M.; Anderson, R. C.; Abbey, W. J.; Kinnett, R.; Watkins, J. A.; Schemel, M.; Lashore, M. O.; Chasek, M. D.; Green, W.; Beegle, L. W.; Vasavada, A. R.

2018-01-01

Measuring the physical properties of geological materials is important for understanding geologic history. Yet there has never been an instrument with the purpose of measuring mechanical properties of rocks sent to another planet. The Mars Science Laboratory (MSL) rover employs the Powder Acquisition Drill System (PADS), which provides direct mechanical interaction with Martian outcrops. While the objective of the drill system is not to make scientific measurements, the drill's performance is directly influenced by the mechanical properties of the rocks it drills into. We have developed a methodology that uses the drill to indicate the uniaxial compressive strengths of rocks through comparison with performance of an identically assembled drill system in terrestrial samples of comparable sedimentary class. During this investigation, we utilize engineering data collected on Mars to calculate the percussive energy needed to maintain a prescribed rate of penetration and correlate that to rock strength.

Degraded Crater Rim

Science.gov (United States)

2002-01-01

(Released 3 May 2002) The Science The eastern rim of this unnamed crater in Southern Arabia Terra is very degraded (beaten up). This indicates that this crater is very ancient and has been subjected to erosion and subsequent bombardment from other impactors such as asteroids and comets. One of these later (younger) craters is seen in the upper right of this image superimposed upon the older crater rim material. Note that this smaller younger crater rim is sharper and more intact than the older crater rim. This region is also mantled with a blanket of dust. This dust mantle causes the underlying topography to take on a more subdued appearance. The Story When you think of Arabia, you probably think of hot deserts and a lot of profitable oil reserves. On Mars, however, Southern Arabia Terra is a cold place of cratered terrain. This almost frothy-looking image is the badly battered edge of an ancient crater, which has suffered both erosion and bombardment from asteroids, comets, or other impacting bodies over the long course of its existence. A blanket of dust has also settled over the region, which gives the otherwise rugged landscape a soft and more subdued appearance. The small, round crater (upper left) seems almost gemlike in its setting against the larger crater ring. But this companionship is no easy romance. Whatever formed the small crater clearly whammed into the larger crater rim at some point, obliterating part of its edge. You can tell the small crater was formed after the first and more devastating impact, because it is laid over the other larger crater. How much younger is the small one? Well, its rim is also much sharper and more intact, which gives a sense that it is probably far more youthful than the very degraded, ancient crater.

High Sr/Y rocks are not all adakites!

Science.gov (United States)

Moyen, Jean-François

2010-05-01

The name of "adakite" is used to describe a far too large group of rocks, whose sole common feature is high Sr/Y and La/Yb ratios. Defining adakites only by this criterion is misleading, as the definition of this group of rocks does include many other criteria, including major elements. In itself, high (or commonly moderate!) Sr/Y ratios can be achieved via different processes: melting of a high Sr/Y (and La/Yb) source; deep melting, with abundant residual garnet; fractional crystallization or AFC; or interactions of felsic melts with the mantle, causing selective enrichment in LREE and Sr over HREE. A database of the compositions of "adakitic" rocks - including "high silica" and "low silica" adakites, "continental" adakites and Archaean adakites—was assembled. Geochemical modeling of the potential processes is used to interpret it, and reveals that (1) the genesis of high-silica adakites requires high pressure evolution (be it by melting or fractionation), in equilibrium with large amounts of garnet; (2) low-silica adakites are explained by garnet-present melting of an adakite-metasomatized mantle, i.e at depths greater than 2.5 GPa; (3) "Continental" adakites is a term encompassing a huge range of rocks, with a corresponding diversity of petrogenetic processes, and most of them are different from both low- and high- silica adakites; in fact in many cases it is a complete misnomer and the rocks studied are high-K calc-alkaline granitoids or even S-type granites; (4) Archaean adakites show a bimodal composition range, with some very high Sr/Y examples (similar to part of the TTG suite) reflecting deep melting (> 2.0 GPa) of a basaltic source with a relatively high Sr/Y, while lower Sr/Y rocks formed by shallower (1.0 GPa) melting of similar sources. Comparison with the Archaean TTG suite highlights the heterogeneity of the TTGs, whose composition spreads the whole combined range of HSA and Archaean adakites, pointing to a diversity of sources and processes

Stratigraphic architecture of bedrock reference section, Victoria Crater, Meridiani Planum, Mars

Science.gov (United States)

Edgar, Lauren A.; Grotzinger, John P.; Hayes, Alex G.; Rubin, David M.; Squyres, Steve W.; Bell, James F.; Herkenhoff, Ken E.

2012-01-01

The Mars Exploration Rover Opportunity has investigated bedrock outcrops exposed in several craters at Meridiani Planum, Mars, in an effort to better understand the role of surface processes in its geologic history. Opportunity has recently completed its observations of Victoria crater, which is 750 m in diameter and exposes cliffs up to ~15 m high. The plains surrounding Victoria crater are ~10 m higher in elevation than those surrounding the previously explored Endurance crater, indicating that the Victoria crater exposes a stratigraphically higher section than does the Endurance crater; however, Victoria strata overlap in elevation with the rocks exposed at the Erebus crater. Victoria crater has a well-developed geomorphic pattern of promontories and embayments that define the crater wall and that reveal thick bedsets (3–7m) of large-scale cross-bedding, interpreted as fossil eolian dunes. Opportunity was able to drive into the crater at Duck Bay, located on the western margin of Victoria crater. Data from the Microscopic Imager and Panoramic Camera reveal details about the structures, textures, and depositional and diagenetic events that influenced the Victoria bedrock. A lithostratigraphic subdivision of bedrock units was enabled by the presence of a light-toned band that lines much of the upper rim of the crater. In ascending order, three stratigraphic units are named Lyell, Smith, and Steno; Smith is the light-toned band. In the Reference Section exposed along the ingress path at Duck Bay, Smith is interpreted to represent a zone of diagenetic recrystallization; however, its upper contact also coincides with a primary erosional surface. Elsewhere in the crater the diagenetic band crosscuts the physical stratigraphy. Correlation with strata present at nearby promontory Cape Verde indicates that there is an erosional surface at the base of the cliff face that corresponds to the erosional contact below Steno. The erosional contact at the base of Cape Verde

Petrogenesis of siliceous high-Mg series rocks as exemplified by the Early Paleoproterozoic mafic volcanic rocks of the Eastern Baltic Shield: enriched mantle versus crustal contamination

Science.gov (United States)

Bogina, Maria; Zlobin, Valeriy; Sharkov, Evgenii; Chistyakov, Alexeii

2015-04-01

The Early Paleoproterozoic stage in the Earth's evolution was marked by the initiation of global rift systems, the tectonic nature of which was determined by plume geodynamics. These processes caused the voluminous emplacement of mantle melts with the formation of dike swarms, mafic-ultramafic layered intrusions, and volcanic rocks. All these rocks are usually considered as derivatives of SHMS (siliceous high-magnesian series). Within the Eastern Baltic Shield, the SHMS volcanic rocks are localized in the domains with different crustal history: in the Vodlozero block of the Karelian craton with the oldest (Middle Archean) crust, in the Central Block of the same craton with the Neoarchean crust, and in the Kola Craton with a heterogeneous crust. At the same time, these rocks are characterized by sufficiently close geochemical characteristics: high REE fractionation ((La/Yb)N = 4.9-11.7, (La/Sm)N=2.3-3.6, (Gd/Yb)N =1.66-2.74)), LILE enrichment, negative Nb anomaly, low to moderate Ti content, and sufficiently narrow variations in Nd isotope composition from -2.0 to -0.4 epsilon units. The tectonomagmatic interpretation of these rocks was ambiguous, because such characteristics may be produced by both crustal contamination of depleted mantle melts, and by generation from a mantle source metasomatized during previous subduction event. Similar REE patterns and overlapping Nd isotope compositions indicate that the studied basaltic rocks were formed from similar sources. If crustal contamination en route to the surface would play a significant role in the formation of the studied basalts, then almost equal amounts of contaminant of similar composition are required to produce the mafic rocks with similar geochemical signatures and close Nd isotopic compositions, which is hardly possible for the rocks spaced far apart in a heterogeneous crust. This conclusion is consistent with analysis of some relations between incompatible elements and their ratios. In particular, the

D/H in Water Evolved from Martian Rocks in Gale Crater

Science.gov (United States)

Mahaffy, P. R.; Franz, H. B.; Atreya, S. K.; Webster, C. R.

2017-12-01

The Sample Analysis at Mars (SAM) instrument suite with its Quadrupole Mass Spectrometer (QMS) and Tunable Laser Spectrometer (TSL) measures isotopes such as δ34S in SO2 [1], δ37Cl in HCl [2], δ15N in N2 or NO [3], δ13C in CH4 [4], δ13C and δ18O in CO2 [5-6], δD in H2O [7], and a variety of noble gas isotopes [8-9]. Fractionation of isotopes of H, C, O, N, Ar, and Xe indicates a substantial loss of atmosphere to space. For xenon this may have occurred early in the history of Mars by hydrodynamic escape [10] or spread over time for C, O, N, and Ar [11]. Nevertheless, the detailed history of atmospheric loss and the predictions of the climate when the Gale crater was a lake are still not well constrained. Isotopes from light elements that are presently measured in the atmosphere but that were also locked into minerals in rocks more than 3 billion years ago are of particular interest as they may provide additional constraints on the history of atmospheric loss. These include 15N/14N presently measured in atmospheric N2 [3] but also in nitrogen released from ancient nitrates as NO [12] and D/H in atmospheric water [13] and in water or hydroxyl locked into minerals and released in the SAM evolved gas analysis (EGA) experiments [7]. D/H in water can be measured by both the TSL and the QMS. Typically the D/H decreases over the course of the EGA temperature ramp, since gas that has exchanged with the current atmosphere is released at lower temperatures. Less easily exchanged gas reflecting the D/H ratio in the water of formation of a mineral, such as that from the dehydroxylation of a phylosillicate, is released at higher temperatures. We will examine some of the D/H measurements made on drilled and powdered rocks and the trends in the variation of the D/H ratio with release temperature. We will compare these ratios with the D/H in atmospheric water and discuss possible consequences for loss of D/H over time. References: [1] Franz et al., in press. [2] Farley et al

Chicxulub Impact Crater and Yucatan Carbonate Platform - Stratigraphy and Petrography of PEMEX Borehole Cores

Science.gov (United States)

Gutierrez-Cirlos, A. G.; Perez-Drago, G.; Perez-Cruz, L.; Urrutia-Fucugauchi, J.

2008-12-01

Chicxulub impact crater is the best preserved of the three large multi-ring structures documented in the terrestrial record. Chicxulub, formed 65 Ma ago, is associated with the Cretaceous/Tertiary (K/T) boundary layer and the impact related to the organism extinctions and events marking the boundary. The crater is buried under Tertiary sediments in the Yucatan carbonate platform in the southern Gulf of Mexico. The structure was initially recognized from gravity and magnetic anomalies in the PEMEX exploration surveys of the northwestern Yucatan peninsula. The exploration program included eight deep boreholes completed from 1952 through the 1970s. The investigations showing Chicxulub as a large complex impact crater formed at the K/T boundary have relayed on the PEMEX decades-long exploration program. However, despite frequent use of PEMEX information and core samples, significant parts of the database and cores remain to be evaluated, analyzed and incorporated with results from recent efforts. Access to PEMEX Core Repository has permitted to study the cores and collect new samples from some of the boreholes. We analyzed cores from Yucatan-6, Chicxulub-1, Sacapuc-1, Ticul-1, Yucatan-1 and Yucatan-4 boreholes to make new detailed stratigraphic correlations and petrographic characterization, using information from PEMEX database and the recent studies. In C-1 cores, breccias show 4-8 cm clasts of fine grained altered melt dispersed in a medium to coarse grained matrix composed of pyroxene and feldspar with little macroscopic alteration. Clasts contain 0.2 to 0.1 cm fragments of silicate material (basement) that show variable degrees of digestion. Melt samples from C-1 N10 comes from interval 1,393-1,394 m, and show a fine-to-medium grained coherent microcrystalline groundmass. Melt and breccias in Y-6 extend from about 1,100 m to more than 1,400 m. Sequence is well sorted, with an apparent gradation in both the lithic and melt clasts. In this presentation we report on

Network topology of olivine-basalt partial melts

Science.gov (United States)

Skemer, Philip; Chaney, Molly M.; Emmerich, Adrienne L.; Miller, Kevin J.; Zhu, Wen-lu

2017-07-01

The microstructural relationship between melt and solid grains in partially molten rocks influences many physical properties, including permeability, rheology, electrical conductivity and seismic wave speeds. In this study, the connectivity of melt networks in the olivine-basalt system is explored using a systematic survey of 3-D X-ray microtomographic data. Experimentally synthesized samples with 2 and 5 vol.% melt are analysed as a series of melt tubules intersecting at nodes. Each node is characterized by a coordination number (CN), which is the number of melt tubules that intersect at that location. Statistically representative volumes are described by coordination number distributions (CND). Polyhedral grains can be packed in many configurations yielding different CNDs, however widely accepted theory predicts that systems with small dihedral angles, such as olivine-basalt, should exhibit a predominant CN of four. In this study, melt objects are identified with CN = 2-8, however more than 50 per cent are CN = 4, providing experimental verification of this theoretical prediction. A conceptual model that considers the role of heterogeneity in local grain size and melt fraction is proposed to explain the formation of nodes with CN ≠ 4. Correctly identifying the melt network topology is essential to understanding the relationship between permeability and porosity, and hence the transport properties of partial molten mantle rocks.

Constraining lithospheric removal and asthenospheric input to melts in Central Asia: A geochemical study of Triassic to Cretaceous magmatic rocks in the Gobi Altai (Mongolia)

Science.gov (United States)

Sheldrick, Thomas C.; Barry, Tiffany L.; Van Hinsbergen, Douwe J. J.; Kempton, Pamela D.

2018-01-01

Throughout northeast China, eastern and southern Mongolia, and eastern Russia there is widespread Mesozoic intracontinental magmatism. Extensive studies on the Chinese magmatic rocks have suggested lithospheric mantle removal was a driver of the magmatism. The timing, distribution and potential diachroneity of such lithospheric mantle removal remains poorly constrained. Here, we examine successions of Mesozoic lavas and shallow intrusive volcanic plugs from the Gobi Altai in southern Mongolia that appear to be unrelated to regional, relatively small-scale deformation; at the time of magmatism, the area was 200 km from any active margin, or, after its Late Jurassic-Early Cretaceous closure, from the suture of the Mongol-Okhotsk Ocean. 40Ar/39Ar radiometric age data place magmatic events in the Gobi Altai between 220 to 99.2 Ma. This succession overlaps Chinese successions and therefore provides an opportunity to constrain whether Mesozoic lithosphere removal may provide an explanation for the magmatism here too, and if so, when. We show that Triassic to Lower Cretaceous lavas in the Gobi Altai (from Dulaan Bogd, Noyon Uul, Bulgantiin Uul, Jaran Bogd and Tsagaan Tsav) are all light rare-earth element (LREE) and large-ion lithophile element (LILE)-enriched, with negative Nb and Ta anomalies (Nb/La and Ta/La ≤ 1). Geochemical data suggest that these lavas formed by low degrees of partial melting of a metasomatised lithospheric mantle that may have been modified by melts derived from recycled rutile-bearing eclogite. A gradual reduction in the involvement of garnet in the source of these lavas points towards a shallowing of the depth of melting after 125 Ma. By contrast, geochemical and isotope data from the youngest magmatic rocks in the area - 107-99 Ma old volcanic plugs from Tsost Magmatic Field - have OIB-like trace element patterns and are interpreted to have formed by low degrees of partial melting of a garnet-bearing lherzolite mantle source. These rocks did

Ground penetrating radar geologic field studies of the ejecta of Barringer Meteorite Crater, Arizona, as a planetary analog

Science.gov (United States)

Russell, Patrick S.; Grant, John A.; Williams, Kevin K.; Carter, Lynn M.; Brent Garry, W.; Daubar, Ingrid J.

2013-09-01

penetrating radar (GPR) has been a useful geophysical tool in investigating a variety of shallow subsurface geological environments on Earth. Here we investigate the capabilities of GPR to provide useful geologic information in one of the most common geologic settings of planetary surfaces, impact crater ejecta. Three types of ejecta are surveyed with GPR at two wavelengths (400 MHz, 200 MHz) at Meteor Crater, Arizona, with the goal of capturing the GPR signature of the subsurface rock population. In order to "ground truth" the GPR characterization, subsurface rocks are visually counted and measured in preexisting subsurface exposures immediately adjacent to and below the GPR transect. The rock size-frequency distribution from 10 to 50 cm based on visual counts is well described by both power law and exponential functions, the former slightly better, reflecting the control of fragmentation processes during the impact-ejection event. GPR counts are found to overestimate the number of subsurface rocks in the upper meter (by a factor of 2-3x) and underestimate in the second meter of depth (0.6-1.0x), results attributable to the highly scattering nature of blocky ejecta. Overturned ejecta that is fractured yet in which fragments are minimally displaced from their complement fragments produces fewer GPR returns than well-mixed ejecta. The use of two wavelengths and division of results into multiple depth zones provides multiple aspects by which to characterize the ejecta block population. Remote GPR measurement of subsurface ejecta in future planetary situations with no subsurface exposure can be used to characterize those rock populations relative to that of Meteor Crater.

Effects of surface shape on the geometry and surface topography of the melt pool in low-power density laser melting

KAUST Repository

Kim, Youngdeuk

2011-04-15

The quantitative correlations between workpiece volume and melt pool geometry, as well as the flow and thermal features of the melt pool are established. Thermocapillary convections in melt pool with a deformable free surface are investigated with respect to surface shape and laser intensity. When the contact angle between the tangent to the top surface and the vertical wall at the hot center is acute, the free surface flattens, compared with that of the initial free surface. Otherwise, the free surface forms a bowl-like shape with a deep crater and a low peripheral rim when the contact angle at the hot center is obtuse. Increasing the workpiece volume at a fixed laser intensity and a negative radial height gradient cause linear decreases in the geometric size and magnitude of flow and temperature of the melt pool. Conversely, linear increases are observed with a positive radial height gradient. © 2011 American Institute of Chemical Engineers (AIChE).

The Context of Carbonates in Gusev and Jezero Craters

Science.gov (United States)

Ruff, S. W.; Hamilton, V. E.

2017-12-01

Gusev and Jezero are Noachian-aged craters with evidence of a lake in early Mars history. Both are among three remaining candidates for the Mars 2020 rover mission, which is intended to collect and cache rock samples for possible future return to Earth. Gusev was explored by the Spirit rover from 2004 to 2010, revealing outcrops dubbed Comanche composed of olivine-rich volcanic tephra that hosts up to 30% Mg-Fe carbonate, clear evidence for the role of near-neutral pH fluids [1]. Jezero also displays evidence for olivine- and carbonate-bearing materials, likely Mg-carbonate based on orbital spectral observations [2]. In both craters, the carbonates occur in materials that are among the oldest stratigraphic units in each, perhaps an indication of more clement climatic conditions on early Mars compared to those that prevailed for most of its history. We are undertaking investigations of various rover-based and orbital measurements of the carbonates in Gusev to better understand their geologic context and origin. In doing so, the results shed light on carbonate occurrences in Jezero. The Comanche outcrops are contained in the Columbia Hills, which represent a kipuka or island of eroded older terrain fully encircled by lava flows, here with a crater retention age of 3.65 Ga (Fig. 1). In situ and orbital observations [3] demonstrate that carbonate-bearing outcrops extend beyond those visited by Spirit. The distinctive morphology and thermal inertia signature of these outcrops and their unaltered host rocks are recognizable in other kipukas on the floor of Gusev [4]. Carbonate also occurs in kipukas in Jezero (Fig. 2), but larger occurrences extend beyond the crater rim and in isolated places among the delta fan deposits [2]. The presence of carbonates outside of the crater suggests an origin unrelated to a former lake, unlike the Comanche carbonates, which may have arisen through evaporation of dilute brines from an ephemeral lake in Gusev [4]. In both cases, the clear

Cratering Studies in Thin Plastic Films

Science.gov (United States)

Shu, A. J.; Bugiel, S.; Gruen, E.; Hillier, J.; Horanyi, M.; Munsat, T. L.; Srama, R.

2013-12-01

Thin plastic films, such as Polyvinylidene Fluoride (PVDF), have been used as protective coatings or dust detectors on a number of missions including the Dust Counter and Mass Analyzer (DUCMA) instrument on Vega 1 and 2, the High Rate Detector (HRD) on the Cassini Mission, and the Student Dust Counter (SDC) on New Horizons. These types of detectors can be used on the lunar surface or in lunar orbit to detect dust grain size distributions and velocities. Due to their low power requirements and light weight, large surface area detectors can be built for observing low dust fluxes. The SDC dust detector is made up of a permanently polarized layer of PVDF coated on both sides with a thin layer (≈ 1000 Å) of aluminum nickel. The operation principle is that a micrometeorite impact removes a portion of the metal surface layer exposing the permanently polarized PVDF underneath. This causes a local potential near the crater changing the surface charge of the metal layer. The dimensions and shape of the crater determine the strength of the potential and thus the signal generated by the PVDF. The theoretical basis for signal interpretation uses a crater diameter scaling law which was not intended for use with PVDF. In this work, a crater size scaling law has been experimentally determined, and further simulation work is being done to enhance our understanding of the mechanisms of crater formation. LS-Dyna, a smoothed particle hydrodynamics (SPH) code from the Livermore Software Technology Corp. was chosen to simulate micrometeorite impacts. SPH is known to be well suited to the large deformities found in hypervelocity impacts. It is capable of incorporating key physics phenomena, including fracture, heat transfer, melting, etc. Furthermore, unlike Eulerian methods, SPH is gridless allowing large deformities without the inclusion of unphysical erosion algorithms. Material properties are accounted for using the Grüneisen Equation of State. The results of the SPH model can

Leakage of active crater lake brine through the north flank at Rincon de la Vieja volcano, northwest Costa Rica, and implications for crater collapse

Science.gov (United States)

Kempter, K.A.; Rowe, G.L.

2000-01-01

The Active Crater at Rincon de la Vieja volcano, Costa Rica, reaches an elevation of 1750 m and contains a warm, hyper-acidic crater lake that probably formed soon after the eruption of the Rio Blanco tephra deposit approximately 3500 years before present. The Active Crater is buttressed by volcanic ridges and older craters on all sides except the north, which dips steeply toward the Caribbean coastal plains. Acidic, above-ambient-temperature streams are found along the Active Crater's north flank at elevations between 800 and 1000 m. A geochemical survey of thermal and non-thermal waters at Rincon de la Vieja was done in 1989 to determine whether hyper-acidic fluids are leaking from the Active Crater through the north flank, affecting the composition of north-flank streams. Results of the water-chemistry survey reveal that three distinct thermal waters are found on the flanks of Rincon de la Vieja volcano: acid chloride-sulfate (ACS), acid sulfate (AS), and neutral chloride (NC) waters. The most extreme ACS water was collected from the crater lake that fills the Active Crater. Chemical analyses of the lake water reveal a hyper-acidic (pH ~ 0) chloride-sulfate brine with elevated concentrations of calcium, magnesium, aluminum, iron, manganese, copper, zinc, fluorine, and boron. The composition of the brine reflects the combined effects of magmatic degassing from a shallow magma body beneath the Active Crater, dissolution of andesitic volcanic rock, and evaporative concentration of dissolved constituents at above-ambient temperatures. Similar cation and anion enrichments are found in the above-ambient-temperature streams draining the north flank of the Active Crater. The pH of north-flank thermal waters range from 3.6 to 4.1 and chloride:sulfate ratios (1.2-1.4) that are a factor of two greater than that of the lake brine (0.60). The waters have an ACS composition that is quite different from the AS and NC thermal waters that occur along the southern flank of Rincon

Silicate melt metasomatism in the lithospheric mantle beneath SW Poland

Science.gov (United States)

Puziewicz, Jacek; Matusiak-Małek, Magdalena; Ntaflos, Theodoros; Grégoire, Michel; Kukuła, Anna

2014-05-01

The xenoliths of peridotites representing the subcontinental lithospheric mantle (SCLM) beneath SW Poland and adjacent parts of Germany occur in the Cenozoic alkaline volcanic rocks. Our study is based on detailed characterization of xenoliths occurring in 7 locations (Steinberg in Upper Lusatia, Księginki, Pilchowice, Krzeniów, Wilcza Góra, Winna Góra and Lutynia in Lower Silesia). One of the two major lithologies occurring in the xenoliths, which we call the "B" lithology, comprises peridotites (typically harzburgites) with olivine containing from 90.5 to 84.0 mole % of forsterite. The harzburgites contain no clinopyroxene or are poor in that mineral (eg. in Krzeniów the group "B" harzburgites contain pfu in ortho-, and pfu in clinopyroxene). The exception are xenoliths from Księginki, which contain pyroxenes characterised by negative correlation between mg# and Al. The REE patterns of both ortho- and clinopyroxene in the group "B" peridotites suggest equilibration with silicate melt. The rocks of "B" lithology were formed due to alkaline silicate melt percolation in the depleted peridotitic protolith. The basaltic melts formed at high pressure are usually undersaturated in both ortho- and clinopyroxene at lower pressures (Kelemen et al. 1992). Because of cooling and dissolution of ortho- and clinopyroxene the melts change their composition and become saturated in one or both of those phases. Experimental results (e.g. Tursack & Liang 2012 and references therein) show that the same refers to alkaline basaltic silicate melts and that its reactive percolation in the peridotitic host leads to decrease of Mg/(Mg+Fe) ratios of olivine and pyroxenes. Thus, the variation of relative volumes of olivine and orthopyroxene as well as the decrease of mg# of rock-forming silicates is well explained by reactive melt percolation in the peridotitic protolith consisting of high mg# olivine and pyroxenes (in the area studied by us that protolith was characterised by olivine

Fluid outflows from Venus impact craters - Analysis from Magellan data

Science.gov (United States)

Asimow, Paul D.; Wood, John A.

1992-01-01

Many impact craters on Venus have unusual outflow features originating in or under the continuous ejecta blankets and continuing downhill into the surrounding terrain. These features clearly resulted from flow of low-viscosity fluids, but the identity of those fluids is not clear. In particular, it should not be assumed a priori that the fluid is an impact melt. A number of candidate processes by which impact events might generate the observed features are considered, and predictions are made concerning the rheological character of flows produce by each mechanism. A sample of outflows was analyzed using Magellan images and a model of unconstrained Bingham plastic flow on inclined planes, leading to estimates of viscosity and yield strength for the flow materials. It is argued that at least two different mechanisms have produced outflows on Venus: an erosive, channel-forming process and a depositional process. The erosive fluid is probably an impact melt, but the depositional fluid may consist of fluidized solid debris, vaporized material, and/or melt.

Alkali trace elements in Gale crater, Mars, with ChemCam: Calibration update and geological implications

International Nuclear Information System (INIS)

Payre, Valerie; Fabre, Cecile; Cousin, Agnes; Sautter, Violaine; Wiens, Roger Craig

2017-01-01

The Chemistry Camera (ChemCam) instrument onboard Curiosity can detect minor and trace elements such as lithium, strontium, rubidium, and barium. Their abundances can provide some insights about Mars' magmatic history and sedimentary processes. We focus on developing new quantitative models for these elements by using a new laboratory database (more than 400 samples) that displays diverse compositions that are more relevant for Gale crater than the previous ChemCam database. These models are based on univariate calibration curves. For each element, the best model is selected depending on the results obtained by using the ChemCam calibration targets onboard Curiosity. New quantifications of Li, Sr, Rb, and Ba in Gale samples have been obtained for the first 1000 Martian days. Comparing these data in alkaline and magnesian rocks with the felsic and mafic clasts from the Martian meteorite NWA7533—from approximately the same geologic period—we observe a similar behavior: Sr, Rb, and Ba are more concentrated in soluble- and incompatible-element-rich mineral phases (Si, Al, and alkali-rich). Correlations between these trace elements and potassium in materials analyzed by ChemCam reveal a strong affinity with K-bearing phases such as feldspars, K-phyllosilicates, and potentially micas in igneous and sedimentary rocks. However, lithium is found in comparable abundances in alkali-rich and magnesium-rich Gale rocks. This very soluble element can be associated with both alkali and Mg-Fe phases such as pyroxene and feldspar. Here, these observations of Li, Sr, Rb, and Ba mineralogical associations highlight their substitution with potassium and their incompatibility in magmatic melts.

Dome craters on Ganymede

International Nuclear Information System (INIS)

Moore, J.M.; Malin, M.C.

1987-01-01

Voyager observations reveal impact craters on Ganymede that are characterized by the presence of broad, high albedo, topographic domes situated within a central pit. Fifty-seven craters with central domes were identified in images covering approx. 50% of the surface. Owing to limitations in resolution, and viewing and illumination angles, the features identified are most likely a subset of dome craters. The sample appears to be sufficiently large to infer statistically meaningful trends. Dome craters appear to fall into two distinct populations on plots of the ratio of dome diameter to crater rim diameter, large-dome craters and small-dome craters. The two classes are morphologically distinct from one another. In general, large dome craters show little relief and their constituent landforms appear subdued with respect to fresh craters. The physical attributes of small-dome craters are more sharply defined, a characteristic they share with young impact craters of comparable size observed elsewhere in the solar system. Both types of dome craters exhibit central pits in which the dome is located. As it is difficult to produce domes by impact and/or erosional processes, an endogenic origin for the domes is reasonably inferred. Several hypotheses for their origin are proposed. These hypotheses are briefly reviewed

The central uplift of Ritchey crater, Mars

Science.gov (United States)

Ding, Ning; Bray, Veronica J.; McEwen, Alfred S.; Mattson, Sarah S.; Okubo, Chris H.; Chojnacki, Matthew; Tornabene, Livio L.

2015-01-01

Ritchey crater is a ∼79 km diameter complex crater near the boundary between Hesperian ridged plains and Noachian highland terrain on Mars (28.8°S, 309.0°E) that formed after the Noachian. High Resolution Imaging Science Experiment (HiRISE) images of the central peak reveal fractured massive bedrock and megabreccia with large clasts. Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) spectral analysis reveals low calcium pyroxene (LCP), olivine (OL), hydrated silicates (phyllosilicates) and a possible identification of plagioclase bedrock. We mapped the Ritchey crater central uplift into ten units, with 4 main groups from oldest and originally deepest to youngest: (1) megabreccia with large clasts rich in LCP and OL, and with alteration to phyllosilicates; (2) massive bedrock with bright and dark regions rich in LCP or OL, respectively; (3) LCP and OL-rich impactites draped over the central uplift; and (4) aeolian deposits. We interpret the primitive martian crust as igneous rocks rich in LCP, OL, and probably plagioclase, as previously observed in eastern Valles Marineris. We do not observe high-calcium pyroxene (HCP) rich bedrock as seen in Argyre or western Valles Marineris. The association of phyllosilicates with deep megabreccia could be from impact-induced alteration, either as a result of the Richey impact, or alteration of pre-existing impactites from Argyre basin and other large impacts that preceded the Ritchey impact, or both.

The central uplift of Ritchey crater, Mars

Science.gov (United States)

Ding, Ning; Bray, Veronica J.; McEwen, Alfred S.; Mattson, Sarah S.; Okubo, Chris H.; Chojnacki, Matthew; Tornabene, Livio L.

2015-05-01

Ritchey crater is a ∼79 km diameter complex crater near the boundary between Hesperian ridged plains and Noachian highland terrain on Mars (28.8°S, 309.0°E) that formed after the Noachian. High Resolution Imaging Science Experiment (HiRISE) images of the central peak reveal fractured massive bedrock and megabreccia with large clasts. Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) spectral analysis reveals low calcium pyroxene (LCP), olivine (OL), hydrated silicates (phyllosilicates) and a possible identification of plagioclase bedrock. We mapped the Ritchey crater central uplift into ten units, with 4 main groups from oldest and originally deepest to youngest: (1) megabreccia with large clasts rich in LCP and OL, and with alteration to phyllosilicates; (2) massive bedrock with bright and dark regions rich in LCP or OL, respectively; (3) LCP and OL-rich impactites draped over the central uplift; and (4) aeolian deposits. We interpret the primitive martian crust as igneous rocks rich in LCP, OL, and probably plagioclase, as previously observed in eastern Valles Marineris. We do not observe high-calcium pyroxene (HCP) rich bedrock as seen in Argyre or western Valles Marineris. The association of phyllosilicates with deep megabreccia could be from impact-induced alteration, either as a result of the Richey impact, or alteration of pre-existing impactites from Argyre basin and other large impacts that preceded the Ritchey impact, or both.

Ceres' intriguing Occator crater and its faculae: formation and evolution

Science.gov (United States)

Buczkowski, D.; Scully, J. E. C.; Bowling, T.; Bu, C.; Castillo, J. C.; Jaumann, R.; Longobardo, A.; Nathues, A.; Neesemann, A.; Palomba, E.; Platz, T.; Quick, L. C.; Raponi, A.; Raymond, C. A.; Ruesch, O.; Russell, C. T.; Schenk, P.; Stein, N.

2017-12-01

Since March 2015, the Dawn spacecraft has orbited and explored Ceres, which is a dwarf planet and the largest object in the asteroid belt (radius 470 km). One of the most intriguing features on Ceres' surface is Occator crater, a 92-km-diameter impact crater that contains distinctive bright spots, called faculae, within its floor (Nathues et al., 2015; Russell et al., 2016; Schenk et al., 2017). Occator crater has been dated to 20-30 million years old (Nathues et al., 2017; Neesemann et al., 2017). The single scattering albedo of Occator's faculae is 0.67-0.80, which is greater than Ceres' average single scattering albedo of 0.09-0.11 (Li et al., 2016). The central facula is named Cerealia Facula, and is located in a 9 km wide and 700 m deep pit. There are also multiple additional faculae in the eastern crater floor, which are named the Vinalia Faculae. The faculae are mostly composed of sodium carbonate, are distinct from Ceres' average surface composition and are proposed to be the solid residues of crystallized brines (De Sanctis et al., 2016). The presence of such bright, apparently fresh, material on the surface of a dwarf planet that is billions of years old is intriguing, and indicates that active processes involving brines occurred within the geologically recent past. The Dawn Science Team has investigated whether the processes that formed the crater and the faculae are entirely endogenic, entirely exogenic or a combination of both. For example, the extensive lobate materials within the crater floor have been proposed to be impact melt, mass wasting deposits or cryolava flows (e.g. Buczkowski et al., 2017; Jaumann et al., 2017; Nathues et al., 2017; Schenk et al., 2017). Each possibility has the potential to provide fascinating insights into Ceres' evolution, including the potential for liquids within Ceres' interior today. The team's in-depth investigation of Occator crater will be presented in an upcoming special issue of the journal Icarus. This special

Mineralogy of an active eolian sediment from the Namib dune, Gale crater, Mars

Science.gov (United States)

Achilles, C. N.; Downs, R. T.; Ming, D. W.; Rampe, E. B.; Morris, R. V.; Treiman, A. H.; Morrison, S. M.; Blake, D. F.; Vaniman, D. T.; Ewing, R. C.; Chipera, S. J.; Yen, A. S.; Bristow, T. F.; Ehlmann, B. L.; Gellert, R.; Hazen, R. M.; Fendrich, K. V.; Craig, P. I.; Grotzinger, J. P.; Des Marais, D. J.; Farmer, J. D.; Sarrazin, P. C.; Morookian, J. M.

2017-11-01

The Mars Science Laboratory rover, Curiosity, is using a comprehensive scientific payload to explore rocks and soils in Gale crater, Mars. Recent investigations of the Bagnold Dune Field provided the first in situ assessment of an active dune on Mars. The Chemistry and Mineralogy (CheMin) X-ray diffraction instrument on Curiosity performed quantitative mineralogical analyses of the history of the dune material and offers an important opportunity for ground truth of orbital observations. CheMin's analysis of the mineralogy and phase chemistry of modern and ancient Gale crater dune fields, together with other measurements by Curiosity's science payload, provides new insights into present and past eolian processes on Mars.

Apollo 17 'melt sheet': chemistry, age and Rb/Sr systematics

Energy Technology Data Exchange (ETDEWEB)

Winzer, S R [Martin Marietta Labs., Baltimore, Md. (USA); Nava, D F; Schuhmann, S; Philpotts, J A [National Aeronautics and Space Administration, Greenbelt, Md. (USA). Goddard Space Flight Center; Schuhmann, P J; Lum, R K.L.; Lindstrom, M M; Lindstrom, D J [Maryland Univ., College Park (USA)

1977-01-01

Major, minor and trace element compositions, age data and Rb/Sr systematics of Apollo 17 boulders have been compiled, and additional analyses performed on a norite breccia clast (77215) included in the Apollo 17, Station 7 boulder. The Apollo 17 boulders are found to be identical or nearly so in major, minor and trace element composition, suggesting that they all originated as an impact melt analogous to melt sheets found in larger terrestrial craters. The matrix dates (/sup 40/Ar//sup 39/Ar) and Rb/Sr systematics available suggest that this impact melt formed by a single impact about 4 b.y. ago. This impact excavated, shocked, brecciated and melted norites, norite cumulates and possibly anorthositic gabbros and dunites about 4.4 b.y. old. The impact was likely a major one, possibly the Serenitatis basin-forming event.

Wind-blown sandstones cemented by sulfate and clay minerals in Gale Crater, Mars

Science.gov (United States)

Milliken, R. E.; Ewing, R. C.; Fischer, W. W.; Hurowitz, J.

2014-02-01

Gale Crater contains Mount Sharp, a ~5 km thick stratigraphic record of Mars' early environmental history. The strata comprising Mount Sharp are believed to be sedimentary in origin, but the specific depositional environments recorded by the rocks remain speculative. We present orbital evidence for the occurrence of eolian sandstones within Gale Crater and the lower reaches of Mount Sharp, including preservation of wind-blown sand dune topography in sedimentary strata—a phenomenon that is rare on Earth and typically associated with stabilization, rapid sedimentation, transgression, and submergence of the land surface. The preserved bedforms in Gale are associated with clay minerals and elsewhere accompanied by typical dune cross stratification marked by bounding surfaces whose lateral equivalents contain sulfate salts. These observations extend the range of possible habitable environments that may be recorded within Gale Crater and provide hypotheses that can be tested in situ by the Curiosity rover payload.

Initial results from the Mini-TES experiment in Gusev Crater from the Spirit Rover

Science.gov (United States)

Christensen, P. R.; Ruff, S. W.; Fergason, R. L.; Knudson, A. T.; Anwar, S.; Arvidson, R. E.; Bandfield, J. L.; Blaney, D. L.; Budney, C.; Calvin, W. M.;

Ancient Martian aeolian processes and palaeomorphology reconstructed from the Stimson formation on the lower slope of Aeolis Mons, Gale crater, Mars

OpenAIRE

Banham, Steven G.; Gupta, Sanjeev; Rubin, David M.; Watkins, Jessica A.; Sumner, Dawn Y.; Edgett, Kenneth S.; Grotzinger, John P.; Lewis, Kevin W.; Edgar, Lauren A.; Stack-Morgan, Kathryn M.; Barnes, Robert; Bell, James F., III; Day, Mackenzie D.; Ewing, Ryan C.; Lapotre, Mathieu G. A.

2018-01-01

Reconstruction of the palaeoenvironmental context of Martian sedimentary rocks is central to studies of ancient Martian habitability and regional palaeoclimate history. This paper reports the analysis of a distinct aeolian deposit preserved in Gale crater, Mars, and evaluates its palaeomorphology, the processes responsible for its deposition, and its implications for Gale crater geological history and regional palaeoclimate. Whilst exploring the sedimentary succession cropping out on the nort...

Deep Drilling Into the Chicxulub Impact Crater: Pemex Oil Exploration Boreholes Revisited

Science.gov (United States)

Fucugauchi, J. U.; Perez-Cruz, L.

2007-05-01

The Chicxulub structure was recognized in the 1940´s from gravity anomalies in oil exploration surveys by Pemex. Geophysical anomalies occur over the carbonate platform in NW Yucatan, where density and magnetic susceptibility contrasts with the carbonates suggested a buried igneous complex or basement uplift. The exploration program developed afterwards included several boreholes, starting with the Chicxulub-1 in 1952 and eventually comprising eight deep boreholes completed through the 1970s. The investigations showing Chicxulub as a large impact crater formed at the K/T boundary have relayed on the Pemex decades-long exploration program. Despite frequent reference to Pemex information, original data have not been openly available for detailed evaluation and incorporation with results from recent efforts. Logging data and core samples remain to be analyzed, reevaluated and integrated in the context of recent marine, aerial and terrestrial geophysical surveys and the drilling/coring projects of UNAM and ICDP. In this presentation we discuss the paleontological data, stratigraphic columns and geophysical logs for the Chicxulub-1 (1582m), Sacapuc-1 (1530m), Yucatan-6 (1631m) and Ticul-1 (3575m) boreholes. These boreholes remain the deepest ones drilled in Chicxulub and the only ones providing samples of the melt-rich breccias and melt sheet. Other boreholes include the Y1 (3221m), Y2 (3474m), Y4 (2398m) and Y5A (3003m), which give information on pre-impact stratigraphy and crystalline basement. We concentrate on log and microfossil data, stratigraphic columns, lateral correlation, integration with UNAM and ICDP borehole data, and analyses of sections of melt, impact breccias and basal Paleocene carbonates. Current plans for deep drilling in Chicxulub crater focus in the peak ring zone and central sector, with proposed marine and on-land boreholes to the IODP and ICDP programs. Future ICDP borehole will be located close to Chicxulub-1 and Sacapuc-1, which intersected

Volatile diffusion in silicate melts and its effects on melt inclusions

Directory of Open Access Journals (Sweden)

P. Scarlato

2005-06-01

Full Text Available A compendium of diffusion measurements and their Arrhenius equations for water, carbon dioxide, sulfur, fluorine, and chlorine in silicate melts similar in composition to natural igneous rocks is presented. Water diffusion in silicic melts is well studied and understood, however little data exists for melts of intermediate to basic compositions. The data demonstrate that both the water concentration and the anhydrous melt composition affect the diffusion coefficient of water. Carbon dioxide diffusion appears only weakly dependent, at most, on the volatilefree melt composition and no effect of carbon dioxide concentration has been observed, although few experiments have been performed. Based upon one study, the addition of water to rhyolitic melts increases carbon dioxide diffusion by orders of magnitude to values similar to that of 6 wt% water. Sulfur diffusion in intermediate to silicic melts depends upon the anhydrous melt composition and the water concentration. In water-bearing silicic melts sulfur diffuses 2 to 3 orders of magnitude slower than water. Chlorine diffusion is affected by both water concentration and anhydrous melt composition; its values are typically between those of water and sulfur. Information on fluorine diffusion is rare, but the volatile-free melt composition exerts a strong control on its diffusion. At the present time the diffusion of water, carbon dioxide, sulfur and chlorine can be estimated in silicic melts at magmatic temperatures. The diffusion of water and carbon dioxide in basic to intermediate melts is only known at a limited set of temperatures and compositions. The diffusion data for rhyolitic melts at 800°C together with a standard model for the enrichment of incompatible elements in front of growing crystals demonstrate that rapid crystal growth, greater than 10-10 ms-1, can significantly increase the volatile concentrations at the crystal-melt interface and that any of that melt trapped

Volatile and organic compositions of sedimentary rocks in Yellowknife Bay, Gale Crater, Mars

NARCIS (Netherlands)

Ming, D.W.; Archer Jr., P.D.; Glavin, D.P.; Eigenbrode, J.L.; Franz, H.B.; Sutter, B.; Brunner, A.E.; Stern, J.C.; Freissinet, C.; McAdam, A.C.; Mahaffy, P.R.; Cabane, M.; Coll, P.; Campbell, J.L.; Atreya, S.K.; Niles, P.B.; Bell III, J.F.; Bish, D.L.; Brinckerhoff, W.B.; Buch, A.; Conrad, P.G.; Des Marais, D.J.; Ehlmann, B.L.; Fairén, A.G.; Farley, K.; Flesch, G.J.; Francois, P.; Gellert, R.; Grant, J.A.; Grotzinger, J.P.; Gupta, S.; Herkenhoff, K.E.; Hurowitz, J.A.; Leshin, L.A.; Lewis, K.W.; McLennan, S.M.; Miller, K.E.; Moersch, J.; Morris, R.V.; Navarro-González, R.; Pavlov, A.A.; Perrett, G.M.; Pradler, I.; Squyres, S.W.; Summons, R.E.; Steele, A.; Stolper, E.M.; Sumner, D.Y.; Szopa, C.; Teinturier, S.; Trainer, M.G.; Treiman, A.H.; Vaniman, D.T.; Vasavada, A.R.; Webster, C.R.; Wray, J.J.; Yingst, R.A.; MSL Science Team, the|info:eu-repo/dai/nl/292012217

2014-01-01

H2O, CO2, SO2, O2, H2, H2S, HCl, chlorinated hydrocarbons, NO, and other trace gases were evolved during pyrolysis of two mudstone samples acquired by the Curiosity rover at Yellowknife Bay within Gale crater, Mars. H2O/OH-bearing phases included 2:1 phyllosilicate(s), bassanite, akaganeite, and

Redox stratification of an ancient lake in Gale crater, Mars.

Science.gov (United States)

Hurowitz, J A; Grotzinger, J P; Fischer, W W; McLennan, S M; Milliken, R E; Stein, N; Vasavada, A R; Blake, D F; Dehouck, E; Eigenbrode, J L; Fairén, A G; Frydenvang, J; Gellert, R; Grant, J A; Gupta, S; Herkenhoff, K E; Ming, D W; Rampe, E B; Schmidt, M E; Siebach, K L; Stack-Morgan, K; Sumner, D Y; Wiens, R C

2017-06-02

In 2012, NASA's Curiosity rover landed on Mars to assess its potential as a habitat for past life and investigate the paleoclimate record preserved by sedimentary rocks inside the ~150-kilometer-diameter Gale impact crater. Geological reconstructions from Curiosity rover data have revealed an ancient, habitable lake environment fed by rivers draining into the crater. We synthesize geochemical and mineralogical data from lake-bed mudstones collected during the first 1300 martian solar days of rover operations in Gale. We present evidence for lake redox stratification, established by depth-dependent variations in atmospheric oxidant and dissolved-solute concentrations. Paleoclimate proxy data indicate that a transition from colder to warmer climate conditions is preserved in the stratigraphy. Finally, a late phase of geochemical modification by saline fluids is recognized. Copyright © 2017, American Association for the Advancement of Science.

Mineralogy of an Active Eolian Sediment from the Namib Dune, Gale Crater, Mars

OpenAIRE

Achilles, C. N.; Downs, R. T.; Ming, D. W.; Rampe, E. B.; Morris, R. V.; Treiman, A. H.; Morrison, S. M.; Blake, D. F.; Vaniman, D. T.; Ewing, R. C.; Chipera, S. J.; Yen, A. S.; Bristow, T. F.; Ehlmann, B. L.; Gellert, R.

2017-01-01

The Mars Science Laboratory rover, Curiosity, is using a comprehensive scientific payload to explore rocks and soils in Gale crater, Mars. Recent investigations of the Bagnold Dune Field provided the first in situ assessment of an active dune on Mars. The Chemistry and Mineralogy (CheMin) X-ray diffraction instrument on Curiosity performed quantitative mineralogical analyses of the

The Apollo 17 'melt sheet': chemistry, age and Rb/Sr systematics

International Nuclear Information System (INIS)

Winzer, S.R.; Nava, D.F.; Schuhmann, S.; Philpotts, J.A.

1977-01-01

Major, minor and trace element compositions, age data and Rb/Sr systematics of Apollo 17 boulders have been compiled, and additional analyses performed on a norite breccia clast (77215) included in the Apollo 17, Station 7 boulder. The Apollo 17 boulders are found to be identical or nearly so in major, minor and trace element composition, suggesting that they all originated as an impact melt analogous to melt sheets found in larger terrestrial craters. The matrix dates ( 40 Ar/ 39 Ar) and Rb/Sr systematics available suggest that this impact melt formed by a single impact about 4 b.y. ago. This impact excavated, shocked, brecciated and melted norites, norite cumulates and possibly anorthositic gabbros and dunites about 4.4 b.y. old. The impact was likely a major one, possibly the Serenitatis basin-forming event. (Auth.)

Modelling of crater formation on anode surface by high-current vacuum arcs

Science.gov (United States)

Tian, Yunbo; Wang, Zhenxing; Jiang, Yanjun; Ma, Hui; Liu, Zhiyuan; Geng, Yingsan; Wang, Jianhua; Nordlund, Kai; Djurabekova, Flyura

2016-11-01

Anode melting and crater formation significantly affect interruption of high-current vacuum arcs. The primary objective of this paper is to theoretically investigate the mechanism of anode surface crater formation, caused by the combined effect of surface heating during the vacuum arc and pressure exerted on the molten surface by ions and electrons from the arc plasma. A model of fluid flow and heat transfer in the arc anode is developed and combined with a magnetohydrodynamics model of the vacuum arc plasma. Crater formation is observed in simulation for a peak arcing current higher than 15 kA on 40 mm diam. Cu electrodes spaced 10 mm apart. The flow of liquid metal starts after 4 or 5 ms of arcing, and the maximum velocities are 0.95 m/s and 1.39 m/s for 20 kA and 25 kA arcs, respectively. This flow redistributes thermal energy, and the maximum temperature of the anode surface does not remain in the center. Moreover, the condition for the liquid droplet formation on the anode surfaces is developed. The solidification process after current zero is also analyzed. The solidification time has been found to be more than 3 ms after 25 kA arcing. The long solidification time and sharp features on crater rims induce Taylor cone formation.

Characterization of frictional melting processes in subduction zone faults by trace element and isotope analyses

Science.gov (United States)

Ishikawa, T.; Ujiie, K.

2017-12-01

Pseudotachylytes found in exhumed accretionary complexes, which are considered to be formed originally at seismogenic depths, are of great importance for elucidating frictional melting and concomitant dynamic weakening of the fault during earthquake in subduction zones. However, fluid-rich environment of the subduction zone faults tends to cause extensive alteration of the pseudotachylyte glass matrix in later stages, and thus it has been controversial that pseudotachylytes are rarely formed or rarely preserved. Chemical analysis of the fault rocks, especially on fluid-immobile trace elements and isotopes, can be a useful means to identify and quantify the frictional melting occurred in subduction zone faults. In this paper, we report major and trace element and Sr isotope compositions for pseudotachylyte-bearing dark veins and surrounding host rocks from the Mugi area of the Shimanto accretionary complex (Ujiie et al., J. Struct. Geol. 2007). Samples were collected from a rock chip along the microstructure using a micro-drilling technique, and then analyzed by ICP-MS and TIMS. Major element compositions of the dark veins showed a clear shift from the host rock composition toward the illite composition. The dark veins, either unaltered or completely altered, were also characterized by extreme enrichment in some of the trace elements such as Ti, Zr, Nb and Th. These results are consistent with disequilibrium melting of the fault zone. Model calculations revealed that the compositions of the dark veins can be produced by total melting of clay-rich matrix in the source rock, leaving plagioclase and quartz grains almost unmolten. The calculations also showed that the dark veins are far more enriched in melt component than that expected from the source rock compositions, suggesting migration and concentration of frictional melt during the earthquake faulting. Furthermore, Sr isotope data of the dark veins implied the occurrence of frictional melting in multiple stages

Distal Ejecta from Lunar Impacts: Extensive Regions of Rocky Deposits

Science.gov (United States)

Bandfield, Joshua L.; Cahill, Joshua T. S.; Carter, Lynn M.; Neish, Catherine D.; Patterson, G. Wesley; Williams, Jean-Pierre; Paige, David A.

2016-01-01

Lunar Reconnaissance Orbiter (LRO) Diviner Radiometer, Mini-RF, and LRO Camera data were used to identify and characterize rocky lunar deposits that appear well separated from any potential source crater. Two regions are described: 1) A approximate 18,000 sq km area with elevated rock abundance and extensive melt ponds and veneers near the antipode of Tycho crater (167.5 deg E, 42.5 deg N). This region has been identified previously, using radar and aging data. 2) A much larger and more diffuse region, covering approximately 730,000 sq km, centered near 310 deg E, 35 deg S, containing elevated rock abundance and numerous granular flow deposits on crater walls. The rock distributions in both regions favor certain slope azimuths over others, indicating a directional component to the formation of these deposits. The spatial distribution of rocks is consistent with the arrival of ejecta from the west and northwest at low angles (approximately 10-30 deg) above the horizon in both regions. The derived age and slope orientations of the deposits indicate that the deposits likely originated as ejecta from the Tycho impact event. Despite their similar origin, the deposits in the two regions show significant differences in the datasets. The Tycho crater antipode deposit covers a smaller area, but the deposits are pervasive and appear to be dominated by impact melts. By contrast, the nearside deposits cover a much larger area and numerous granular flows were triggered. However, the features in this region are less prominent with no evidence for the presence of impact melts. The two regions appear to be surface expressions of a distant impact event that can modify surfaces across wide regions, resulting in a variety of surface morphologies. The Tycho impact event may only be the most recent manifestation of these processes, which likely have played a role in the development of the regolith throughout lunar history

Evidence of the impacting body of the Ries crater - the discovery of Fe-Cr-Ni veinlets below the crater bottom

Science.gov (United States)

El, Goresy A.; Chao, E.C.T.

1976-01-01

Fe-Cr-Ni particles and veinlets have been discovered in the top 15 m of the compressed zone with abundant shatter cones below the bottom of the Ries crater. The metallic particles are less than a few microns across. They occur in various minerals along healed intergranular and locally in intragranular microfractures in quartz diorite, amphibolite and chloritized granite of the basement crystalline rocks. The particles consist of major Fe, Cr, and Ni with minor Si and Ca. Origin due to contamination is absolutely ruled out. We believe that these Fe-Cr-Ni particles are probably condensed from the vaporized impacting body which produced the Ries crater. These particles were injected with high velocity into microfractures near the top of the compressed zone, implanted in and across various minerals before these microfractures were resealed. The presence of Si and Ca as well as the fact that the Cr content is nearly twice that of Ni, led us to conclude that the Ries impacting body is very likely not an iron meteorite but a stony meteorite. ?? 1976.

Centrifuge impact cratering experiment 5

Science.gov (United States)

1984-01-01

Transient crates motions, cratering flow fields, crates dynamics, determining impact conditions from total crater welt, centrifuge quarter-space cratering, and impact cratering mechanics research is documented.

Craters on comets

Science.gov (United States)

Vincent, J.; Oklay, N.; Marchi, S.; Höfner, S.; Sierks, H.

2014-07-01

This paper reviews the observations of crater-like features on cometary nuclei. ''Pits'' have been observed on almost all cometary nuclei but their origin is not fully understood [1,2,3,4]. It is currently assumed that they are created mainly by the cometary activity with a pocket of volatiles erupting under a dust crust, leaving a hole behind. There are, however, other features which cannot be explained in this way and are interpreted alternatively as remnants of impact craters. This work focusses on the second type of pit features: impact craters. We present an in-depth review of what has been observed previously and conclude that two main types of crater morphologies can be observed: ''pit-halo'' and ''sharp pit''. We extend this review by a series of analysis of impact craters on cometary nuclei through different approaches [5]: (1) Probability of impact: We discuss the chances that a Jupiter Family Comet like 9P/Tempel 1 or the target of Rosetta 67P/Churyumov-Gerasimenko can experience an impact, taking into account the most recent work on the size distribution of small objects in the asteroid Main Belt [6]. (2) Crater morphology from scaling laws: We present the status of scaling laws for impact craters on cometary nuclei [7] and discuss their strengths and limitations when modeling what happens when a rocky projectile hits a very porous material. (3) Numerical experiments: We extend the work on scaling laws by a series of hydrocode impact simulations, using the iSALE shock physics code [8,9,10] for varying surface porosity and impactor velocity (see Figure). (4) Surface processes and evolution: We discuss finally the fate of the projectile and the effects of the impact-induced surface compaction on the activity of the nucleus. To summarize, we find that comets do undergo impacts although the rapid evolution of the surface erases most of the features and make craters difficult to detect. In the case of a collision between a rocky body and a highly porous

Experimental impact crater morphology

Science.gov (United States)

Dufresne, A.; Poelchau, M. H.; Hoerth, T.; Schaefer, F.; Thoma, K.; Deutsch, A.; Kenkmann, T.

2012-04-01

The research group MEMIN (Multidisciplinary Experimental and Impact Modelling Research Network) is conducting impact experiments into porous sandstones, examining, among other parameters, the influence of target pore-space saturation with water, and projectile velocity, density and mass, on the cratering process. The high-velocity (2.5-7.8 km/s) impact experiments were carried out at the two-stage light-gas gun facilities of the Fraunhofer Institute EMI (Germany) using steel, iron meteorite (Campo del Cielo IAB), and aluminium projectiles with Seeberg Sandstone as targets. The primary objectives of this study within MEMIN are to provide detailed morphometric data of the experimental craters, and to identify trends and characteristics specific to a given impact parameter. Generally, all craters, regardless of impact conditions, have an inner depression within a highly fragile, white-coloured centre, an outer spallation (i.e. tensile failure) zone, and areas of arrested spallation (i.e. spall fragments that were not completely dislodged from the target) at the crater rim. Within this general morphological framework, distinct trends and differences in crater dimensions and morphological characteristics are identified. With increasing impact velocity, the volume of craters in dry targets increases by a factor of ~4 when doubling velocity. At identical impact conditions (steel projectiles, ~5km/s), craters in dry and wet sandstone targets differ significantly in that "wet" craters are up to 76% larger in volume, have depth-diameter ratios generally below 0.19 (whereas dry craters are almost consistently above this value) at significantly larger diameters, and their spallation zone morphologies show very different characteristics. In dry craters, the spall zone surfaces dip evenly at 10-20° towards the crater centre. In wet craters, on the other hand, they consist of slightly convex slopes of 10-35° adjacent to the inner depression, and of sub-horizontal tensile

Experimental test of the viscous anisotropy hypothesis for partially molten rocks.

Science.gov (United States)

Qi, Chao; Kohlstedt, David L; Katz, Richard F; Takei, Yasuko

2015-10-13

Chemical differentiation of rocky planets occurs by melt segregation away from the region of melting. The mechanics of this process, however, are complex and incompletely understood. In partially molten rocks undergoing shear deformation, melt pockets between grains align coherently in the stress field; it has been hypothesized that this anisotropy in microstructure creates an anisotropy in the viscosity of the aggregate. With the inclusion of anisotropic viscosity, continuum, two-phase-flow models reproduce the emergence and angle of melt-enriched bands that form in laboratory experiments. In the same theoretical context, these models also predict sample-scale melt migration due to a gradient in shear stress. Under torsional deformation, melt is expected to segregate radially inward. Here we present torsional deformation experiments on partially molten rocks that test this prediction. Microstructural analyses of the distribution of melt and solid reveal a radial gradient in melt fraction, with more melt toward the center of the cylinder. The extent of this radial melt segregation grows with progressive strain, consistent with theory. The agreement between theoretical prediction and experimental observation provides a validation of this theory.

Geochemical, isotopic, and petrographic investigations of rocks from the Bosumtwi impact

International Nuclear Information System (INIS)

Losiak, A.

2013-01-01

The Bosumtwi structure is a 1.07 milion year old, well-preserved, 10.5 km wide complex impact crater. It is associated with one of only four tektite strewn fields known on Earth and it is the source of the Ivory Coast tektites. It was drilled in 2004 by the International Continental Scientific Drilling Program (ICDP), and since then it has been the object of intensive research on various aspects of impact cratering process. This thesis is a continuation of those studies. Chapter 3 of this thesis presents a full and detailed characterization of the three granitoid intrusions and one mafic dike located in the vicinity of the Bosumtwi crater in terms of petrology, major and trace element geochemistry, geochronology, as well as isotopic composition. This allows us to characterize magmatic evolution of the West African Craton in this area and better understand the geological framework and target rocks of the impact. This study shows that the similar composition (strongly peraluminous muscovite granites and granodiorites) and age (between 2092±6 Ma and 2098±6 Ma) of granitic intrusions in the proximity of the Bosumtwi crater suggest that they are co-genetic. The granitoids were probably formed as a result of anatexis of TTGs (or rocks derived from them) at relatively low pressure and temperature. We propose that the intrusions from the Bosumtwi area are genetically related to the Banso granite occurring to the east of the crater and can be classified as basin-type, late-stage granitoids. Also a mafic dike located to the NE of the Bosumtwi crater seems to be genetically related to those felsic intrusions. Based on those findings a revised version of the geological map of the Bosumtwi crater area is proposed. Chapter 4 presents results of the investigation of the spatial relations between a statistically significant number of shocked quartz grains (278) showing PDFs (409) developed within a given area of a single thin section (⁓35 mm 2 ) from the Bosumtwi impact crater

Melt compositions and processes in the kimberlite provience of southern West Greenland

DEFF Research Database (Denmark)

Pilbeam, Llewellyn; Nielsen, Troels; Waight, Tod Earle

2011-01-01

] whilst the silica content and H2O/CO2 ratio of the bulk rocks increases towards Sisimuit [2, 3]. A common carbonatite rich end-member is implicated [2]. This is in contrast to the prevailing dogma of a continuum from carbonatite though aillikite to kimberlite with increasing melting degree [4......]. The authors have demonstrated that a process of DFC (digestion fractional crystallisation) whereby the cognate olivine crystallisation is coupled to entrained xenocrystic orthopyroxene assimilation is a key process during the formation of the Majugaa occurrence of the Manitsoq region [5]. Mass balance...... considerations are here applied to the Majuagaa bulk rock in term of the DFC mechanism obtaining an estimate of parental melt and magma composition for the Majuagaa kimberlite. We use bulk rock major and trace element geochemistry together with mineral chemistry to investigate the range of melt compositions...

Chesapeake Bay impact structure: A blast from the past

Science.gov (United States)

Powars, David S.; Edwards, Lucy E.; Gohn, Gregory S.; Horton, J. Wright

2015-10-28

About 35 million years ago, a 2-mile-wide meteorite smashed into Earth in what is now the lower Chesapeake Bay in Virginia. The oceanic impact vaporized, melted, fractured, and displaced rocks and sediments and sent billions of tons of water, sediments, and rocks into the air. Glassy particles of solidified melt rock rained down as far away as Texas and the Caribbean. Large tsunamis affected most of the North Atlantic basin. The resulting impact structure is more than 53 miles wide and has a 23-mile-wide, filled central crater surrounded by collapsed sediments. Now buried by hundreds of feet of younger sediments, the Chesapeake Bay impact structure is among the 20 largest known impact structures on Earth.

Evidence for rapid topographic evolution and crater degradation on Mercury from simple crater morphometry

Science.gov (United States)

Fassett, Caleb I.; Crowley, Malinda C.; Leight, Clarissa; Dyar, M. Darby; Minton, David A.; Hirabayashi, Masatoshi; Thomson, Bradley J.; Watters, Wesley A.

2017-06-01

Examining the topography of impact craters and their evolution with time is useful for assessing how fast planetary surfaces evolve. Here, new measurements of depth/diameter (d/D) ratios for 204 craters of 2.5 to 5 km in diameter superposed on Mercury's smooth plains are reported. The median d/D is 0.13, much lower than expected for newly formed simple craters ( 0.21). In comparison, lunar craters that postdate the maria are much less modified, and the median crater in the same size range has a d/D ratio that is nearly indistinguishable from the fresh value. This difference in crater degradation is remarkable given that Mercury's smooth plains and the lunar maria likely have ages that are comparable, if not identical. Applying a topographic diffusion model, these results imply that crater degradation is faster by a factor of approximately two on Mercury than on the Moon, suggesting more rapid landform evolution on Mercury at all scales.Plain Language SummaryMercury and the Moon are both airless bodies that have experienced numerous impact events over billions of years. These impacts form craters in a geologic instant. The question examined in this manuscript is how fast these craters erode after their formation. To simplify the problem, we examined craters of a particular size (2.5 to 5 km in diameter) on a particular geologic terrain type (volcanic smooth plains) on both the Moon and Mercury. We then measured the topography of hundreds of craters on both bodies that met these criteria. Our results suggest that craters on Mercury become shallower much more quickly than craters on the Moon. We estimate that Mercury's topography erodes at a rate at least a factor of two faster than the Moon's.

Elemental Geochemistry of Sedimentary Rocks at Yellowknife Bay, Gale Crater, Mars

Science.gov (United States)

McLennan, S. M.; Anderson, R. B.; Bell, J. F.; Bridges, J. C.; Calef, F.; Campbell, J. L.; Clark, B. C.; Clegg, S.; Conrad, P.; Cousin, A.; Des Marais, D. J.; Dromart, G.; Dyar, M. D.; Edgar, L. A.; Ehlmann, B. L.; Fabre, C.; Forni, O.; Gasnault, O.; Gellert, R.; Gordon, S.; Grant, J. A.; Grotzinger, J. P.; Gupta, S.; Herkenhoff, K. E.; Hurowitz, J. A.; King, P. L.; Le Mouélic, S.; Leshin, L. A.; Léveillé, R.; Lewis, K. W.; Mangold, N.; Maurice, S.; Ming, D. W.; Morris, R. V.; Nachon, M.; Newsom, H. E.; Ollila, A. M.; Perrett, G. M.; Rice, M. S.; Schmidt, M. E.; Schwenzer, S. P.; Stack, K.; Stolper, E. M.; Sumner, D. Y.; Treiman, A. H.; VanBommel, S.; Vaniman, D. T.; Vasavada, A.; Wiens, R. C.; Yingst, R. A.; Kemppinen, Osku; Bridges, Nathan; Johnson, Jeffrey R.; Minitti, Michelle; Cremers, David; Farmer, Jack; Godber, Austin; Wadhwa, Meenakshi; Wellington, Danika; McEwan, Ian; Newman, Claire; Richardson, Mark; Charpentier, Antoine; Peret, Laurent; Blank, Jennifer; Weigle, Gerald; Li, Shuai; Milliken, Ralph; Robertson, Kevin; Sun, Vivian; Baker, Michael; Edwards, Christopher; Farley, Kenneth; Griffes, Jennifer; Miller, Hayden; Newcombe, Megan; Pilorget, Cedric; Siebach, Kirsten; Brunet, Claude; Hipkin, Victoria; Marchand, Geneviève; Sánchez, Pablo Sobrón; Favot, Laurent; Cody, George; Steele, Andrew; Flückiger, Lorenzo; Lees, David; Nefian, Ara; Martin, Mildred; Gailhanou, Marc; Westall, Frances; Israël, Guy; Agard, Christophe; Baroukh, Julien; Donny, Christophe; Gaboriaud, Alain; Guillemot, Philippe; Lafaille, Vivian; Lorigny, Eric; Paillet, Alexis; Pérez, René; Saccoccio, Muriel; Yana, Charles; Armiens-Aparicio, Carlos; Rodríguez, Javier Caride; Blázquez, Isaías Carrasco; Gómez, Felipe Gómez; Gómez-Elvira, Javier; Hettrich, Sebastian; Malvitte, Alain Lepinette; Jiménez, Mercedes Marín; Martínez-Frías, Jesús; Martín-Soler, Javier; Martín-Torres, F. Javier; Jurado, Antonio Molina; Mora-Sotomayor, Luis; Caro, Guillermo Muñoz; López, Sara Navarro; Peinado-González, Verónica; Pla-García, Jorge; Manfredi, José Antonio Rodriguez; Romeral-Planelló, Julio José; Fuentes, Sara Alejandra Sans; Martinez, Eduardo Sebastian; Redondo, Josefina Torres; Urqui-O'Callaghan, Roser; Mier, María-Paz Zorzano; Chipera, Steve; Lacour, Jean-Luc; Mauchien, Patrick; Sirven, Jean-Baptiste; Manning, Heidi; Fairén, Alberto; Hayes, Alexander; Joseph, Jonathan; Squyres, Steven; Sullivan, Robert; Thomas, Peter; Dupont, Audrey; Lundberg, Angela; Melikechi, Noureddine; Mezzacappa, Alissa; DeMarines, Julia; Grinspoon, David; Reitz, Günther; Prats, Benito; Atlaskin, Evgeny; Genzer, Maria; Harri, Ari-Matti; Haukka, Harri; Kahanpää, Henrik; Kauhanen, Janne; Kemppinen, Osku; Paton, Mark; Polkko, Jouni; Schmidt, Walter; Siili, Tero; Wray, James; Wilhelm, Mary Beth; Poitrasson, Franck; Patel, Kiran; Gorevan, Stephen; Indyk, Stephen; Paulsen, Gale; Bish, David; Schieber, Juergen; Gondet, Brigitte; Langevin, Yves; Geffroy, Claude; Baratoux, David; Berger, Gilles; Cros, Alain; d'Uston, Claude; Lasue, Jérémie; Lee, Qiu-Mei; Meslin, Pierre-Yves; Pallier, Etienne; Parot, Yann; Pinet, Patrick; Schröder, Susanne; Toplis, Mike; Lewin, Éric; Brunner, Will; Heydari, Ezat; Achilles, Cherie; Oehler, Dorothy; Sutter, Brad; Cabane, Michel; Coscia, David; Israël, Guy; Szopa, Cyril; Robert, François; Sautter, Violaine; Buch, Arnaud; Stalport, Fabien; Coll, Patrice; François, Pascaline; Raulin, François; Teinturier, Samuel; Cameron, James; DeLapp, Dorothea; Dingler, Robert; Jackson, Ryan Steele; Johnstone, Stephen; Lanza, Nina; Little, Cynthia; Nelson, Tony; Williams, Richard B.; Jones, Andrea; Kirkland, Laurel; Baker, Burt; Cantor, Bruce; Caplinger, Michael; Davis, Scott; Duston, Brian; Edgett, Kenneth; Fay, Donald; Hardgrove, Craig; Harker, David; Herrera, Paul; Jensen, Elsa; Kennedy, Megan R.; Krezoski, Gillian; Krysak, Daniel; Lipkaman, Leslie; Malin, Michael; McCartney, Elaina; McNair, Sean; Nixon, Brian; Posiolova, Liliya; Ravine, Michael; Salamon, Andrew; Saper, Lee; Stoiber, Kevin; Supulver, Kimberley; Van Beek, Jason; Van Beek, Tessa; Zimdar, Robert; French, Katherine Louise; Iagnemma, Karl; Miller, Kristen; Summons, Roger; Goesmann, Fred; Goetz, Walter; Hviid, Stubbe; Johnson, Micah; Lefavor, Matthew; Lyness, Eric; Breves, Elly; Fassett, Caleb; Blake, David F.; Bristow, Thomas; Edwards, Laurence; Haberle, Robert; Hoehler, Tori; Hollingsworth, Jeff; Kahre, Melinda; Keely, Leslie; McKay, Christopher; Wilhelm, Mary Beth; Bleacher, Lora; Brinckerhoff, William; Choi, David; Dworkin, Jason P.; Eigenbrode, Jennifer; Floyd, Melissa; Freissinet, Caroline; Garvin, James; Glavin, Daniel; Harpold, Daniel; Jones, Andrea; Mahaffy, Paul; Martin, David K.; McAdam, Amy; Pavlov, Alexander; Raaen, Eric; Smith, Michael D.; Stern, Jennifer; Tan, Florence; Trainer, Melissa; Meyer, Michael; Posner, Arik; Voytek, Mary; Anderson, Robert C.; Aubrey, Andrew; Beegle, Luther W.; Behar, Alberto; Blaney, Diana; Brinza, David; Christensen, Lance; Crisp, Joy A.; DeFlores, Lauren; Ehlmann, Bethany; Feldman, Jason; Feldman, Sabrina; Flesch, Gregory; Jun, Insoo; Keymeulen, Didier; Maki, Justin; Mischna, Michael; Morookian, John Michael; Parker, Timothy; Pavri, Betina; Schoppers, Marcel; Sengstacken, Aaron; Simmonds, John J.; Spanovich, Nicole; Juarez, Manuel de la Torre; Webster, Christopher R.; Yen, Albert; Archer, Paul Douglas; Cucinotta, Francis; Jones, John H.; Niles, Paul; Rampe, Elizabeth; Nolan, Thomas; Fisk, Martin; Radziemski, Leon; Barraclough, Bruce; Bender, Steve; Berman, Daniel; Dobrea, Eldar Noe; Tokar, Robert; Williams, Rebecca M. E.; Cleghorn, Timothy; Huntress, Wesley; Manhès, Gérard; Hudgins, Judy; Olson, Timothy; Stewart, Noel; Sarrazin, Philippe; Vicenzi, Edward; Wilson, Sharon A.; Bullock, Mark; Ehresmann, Bent; Hamilton, Victoria; Hassler, Donald; Peterson, Joseph; Rafkin, Scot; Zeitlin, Cary; Fedosov, Fedor; Golovin, Dmitry; Karpushkina, Natalya; Kozyrev, Alexander; Litvak, Maxim; Malakhov, Alexey; Mitrofanov, Igor; Mokrousov, Maxim; Nikiforov, Sergey; Prokhorov, Vasily; Sanin, Anton; Tretyakov, Vladislav; Varenikov, Alexey; Vostrukhin, Andrey; Kuzmin, Ruslan; Wolff, Michael; Botta, Oliver; Drake, Darrell; Bean, Keri; Lemmon, Mark; Lee, Ella Mae; Sucharski, Robert; Hernández, Miguel Ángel de Pablo; Ávalos, Juan José Blanco; Ramos, Miguel; Kim, Myung-Hee; Malespin, Charles; Plante, Ianik; Muller, Jan-Peter; Navarro-González, Rafael; Ewing, Ryan; Boynton, William; Downs, Robert; Fitzgibbon, Mike; Harshman, Karl; Morrison, Shaunna; Dietrich, William; Kortmann, Onno; Palucis, Marisa; Williams, Amy; Lugmair, Günter; Wilson, Michael A.; Rubin, David; Jakosky, Bruce; Balic-Zunic, Tonci; Frydenvang, Jens; Jensen, Jaqueline Kløvgaard; Kinch, Kjartan; Koefoed, Asmus; Madsen, Morten Bo; Stipp, Susan Louise Svane; Boyd, Nick; Pradler, Irina; Jacob, Samantha; Owen, Tobias; Rowland, Scott; Atlaskin, Evgeny; Savijärvi, Hannu; Boehm, Eckart; Böttcher, Stephan; Burmeister, Sönke; Guo, Jingnan; Köhler, Jan; García, César Martín; Mueller-Mellin, Reinhold; Wimmer-Schweingruber, Robert; McConnochie, Timothy; Benna, Mehdi; Franz, Heather; Bower, Hannah; Brunner, Anna; Blau, Hannah; Boucher, Thomas; Carmosino, Marco; Atreya, Sushil; Elliott, Harvey; Halleaux, Douglas; Rennó, Nilton; Wong, Michael; Pepin, Robert; Elliott, Beverley; Spray, John; Thompson, Lucy; Williams, Joshua; Vasconcelos, Paulo; Bentz, Jennifer; Nealson, Kenneth; Popa, Radu; Kah, Linda C.; Moersch, Jeffrey; Tate, Christopher; Day, Mackenzie; Kocurek, Gary; Hallet, Bernard; Sletten, Ronald; Francis, Raymond; McCullough, Emily; Cloutis, Ed; ten Kate, Inge Loes; Kuzmin, Ruslan; Arvidson, Raymond; Fraeman, Abigail; Scholes, Daniel; Slavney, Susan; Stein, Thomas; Ward, Jennifer; Berger, Jeffrey; Moores, John E.

2014-01-01

Sedimentary rocks examined by the Curiosity rover at Yellowknife Bay, Mars, were derived from sources that evolved from an approximately average martian crustal composition to one influenced by alkaline basalts. No evidence of chemical weathering is preserved, indicating arid, possibly cold, paleoclimates and rapid erosion and deposition. The absence of predicted geochemical variations indicates that magnetite and phyllosilicates formed by diagenesis under low-temperature, circumneutral pH, rock-dominated aqueous conditions. Analyses of diagenetic features (including concretions, raised ridges, and fractures) at high spatial resolution indicate that they are composed of iron- and halogen-rich components, magnesium-iron-chlorine-rich components, and hydrated calcium sulfates, respectively. Composition of a cross-cutting dike-like feature is consistent with sedimentary intrusion. The geochemistry of these sedimentary rocks provides further evidence for diverse depositional and diagenetic sedimentary environments during the early history of Mars.

Elemental geochemistry of sedimentary rocks at Yellowknife Bay, Gale crater, Mars.

Science.gov (United States)

McLennan, S M; Anderson, R B; Bell, J F; Bridges, J C; Calef, F; Campbell, J L; Clark, B C; Clegg, S; Conrad, P; Cousin, A; Des Marais, D J; Dromart, G; Dyar, M D; Edgar, L A; Ehlmann, B L; Fabre, C; Forni, O; Gasnault, O; Gellert, R; Gordon, S; Grant, J A; Grotzinger, J P; Gupta, S; Herkenhoff, K E; Hurowitz, J A; King, P L; Le Mouélic, S; Leshin, L A; Léveillé, R; Lewis, K W; Mangold, N; Maurice, S; Ming, D W; Morris, R V; Nachon, M; Newsom, H E; Ollila, A M; Perrett, G M; Rice, M S; Schmidt, M E; Schwenzer, S P; Stack, K; Stolper, E M; Sumner, D Y; Treiman, A H; VanBommel, S; Vaniman, D T; Vasavada, A; Wiens, R C; Yingst, R A

2014-01-24

Sedimentary rocks examined by the Curiosity rover at Yellowknife Bay, Mars, were derived from sources that evolved from an approximately average martian crustal composition to one influenced by alkaline basalts. No evidence of chemical weathering is preserved, indicating arid, possibly cold, paleoclimates and rapid erosion and deposition. The absence of predicted geochemical variations indicates that magnetite and phyllosilicates formed by diagenesis under low-temperature, circumneutral pH, rock-dominated aqueous conditions. Analyses of diagenetic features (including concretions, raised ridges, and fractures) at high spatial resolution indicate that they are composed of iron- and halogen-rich components, magnesium-iron-chlorine-rich components, and hydrated calcium sulfates, respectively. Composition of a cross-cutting dike-like feature is consistent with sedimentary intrusion. The geochemistry of these sedimentary rocks provides further evidence for diverse depositional and diagenetic sedimentary environments during the early history of Mars.

Martian Low-Aspect-Ratio Layered Ejecta (LARLE) craters: Distribution, characteristics, and relationship to pedestal craters

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Barlow, Nadine G.; Boyce, Joseph M.; Cornwall, Carin

2014-09-01

Low-Aspect-Ratio Layered Ejecta (LARLE) craters are a unique landform found on Mars. LARLE craters are characterized by a crater and normal layered ejecta pattern surrounded by an extensive but thin outer deposit which terminates in a sinuous, almost flame-like morphology. We have conducted a survey to identify all LARLE craters ⩾1-km-diameter within the ±75° latitude zone and to determine their morphologic and morphometric characteristics. The survey reveals 140 LARLE craters, with the majority (91%) located poleward of 40°S and 35°N and all occurring within thick mantles of fine-grained deposits which are likely ice-rich. LARLE craters range in diameter from the cut-off limit of 1 km up to 12.2 km, with 83% being smaller than 5 km. The radius of the outer LARLE deposit displays a linear trend with the crater radius and is greatest at higher polar latitudes. The LARLE deposit ranges in length between 2.56 and 14.81 crater radii in average extent, with maximum length extending up to 21.4 crater radii. The LARLE layer is very sinuous, with lobateness values ranging between 1.45 and 4.35. LARLE craters display a number of characteristics in common with pedestal craters and we propose that pedestal craters are eroded versions of LARLE craters. The distribution and characteristics of the LARLE craters lead us to propose that impact excavation into ice-rich fine-grained deposits produces a dusty base surge cloud (like those produced by explosion craters) that deposits dust and ice particles to create the LARLE layers. Salts emplaced by upward migration of water through the LARLE deposit produce a surficial duricrust layer which protects the deposit from immediate removal by eolian processes.

Melt rock components in KREEPy breccia 15205: Petrography and mineral chemistry of KREEP basalts and quartz-normative mare basalts

Science.gov (United States)

Shervais, John W.; Vetter, Scott K.

1993-05-01

Many current models for the origin of lunar highland rocks feature as an essential component the assimilation of KREEPy material by primitive magmas parental to the Mg-rich suite and alkali suite plutonic rocks. Similar models have also been proposed for the origin of various mare basalt suites. However, any model which considers assimilation of KREEP an important petrologic process must sooner-or-later deal with the question: what is KREEP? Because pristine KREEP basalts are rare, and most known samples are small (e.g., 15382/15386), the geochemical variability of KREEP basalts is poorly known. Other KREEP compositions which are commonly used in these models include the hypothetical 'high-K KREEP' component of Warren and Wasson, which is derived from Apollo 14 soil data, and the 'superKREEP' quartz-monzodiorite 15405. Lunar breccia 15205 is a polymict regolith breccia that consists of approximately 20% KREEP basalt clasts and 20% quartz-normative basalt clasts in a KREEP-rich matrix. Bulk rock mixing calculations show that this sample comprises about 84% KREEP. The clasts range up to 1 cm in size, but most are considerably smaller. The primary aim is to characterize pristine KREEP basalts petrographically, to establish the range in chemical compositions of KREEP basalts, and to test models that were proposed for their origin. In addition, we may be able to extend the compositional range recognized in the quartz-normative basalt suite and cast some light on its origin as well. Preliminary whole rock geochemical data on the KREEP basalts are presented in a companion paper by M.M. Lindstrom and co-workers. Concentration is on petrography and mineral chemistry of these clasts, and the implications these data have for the origin of the different melt rock suites.

Rust and schreibersite in Apollo 16 highland rocks - Manifestations of volatile-element mobility

Science.gov (United States)

Hunter, R. H.; Taylor, L. A.

Rust is a manifestation of halogen and volatile-metal mobility in the lunar environment. Schreibersite is stable as the primary phosphorus-bearing phase in the highland rocks, a consequence of the inherently low oxygen fugacity within impact-generated melts. Apatite and whitlockite are subordinate in these rocks. The partitioning of P into phosphide in impact-generated melts, and the failure of phosphate to crystallize, effects a decoupling of the halogens and phosphorus. Of the Apollo 16 rocks, 63% contain rust, 70% contain schreibersite, and 52% contain both phases, thereby establishing the pervasiveness of volatile-elements throughout the highland rocks. The major portion of these volatile-bearing phases occur in impact melt-rocks or in breccia matrices. Rhabdites of schreibersite in some of the FeNi grains indicate that there is a meteoritic contribution to the phosphorus in these rocks. Cl/P2O5 ratios in lunar highland rocks are a function of secondary effects, with any apparent Cl-P correlations being coincidential. The present observations preclude the validity of models based on such elemental ratios in these rocks. The presence of rust in the clast laden matrices of pristine rocks indicates fugitive element localization. Pristine clasts may have been contaminated. The basis for a pristine volatile chemistry is questioned.

Pseudotachylitic breccia from the Dhala impact structure, north-central India: Texture, mineralogy and geochemical characterization

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Pati, J. K.; Reimold, W. U.; Greshake, A.; Schmitt, R. T.; Koeberl, C.; Pati, P.; Prakash, K.

2015-05-01

Pseudotachylitic breccia (PTB) occurs in a drill core from the crater floor of the 11 km diameter, Proterozoic Dhala impact structure, India. PTBs were intersected in late Archean granitoids between 348.15 m and 502.55 m depth in the MCB-10 drill core from the center of the Dhala structure. The breccias comprise both cataclastic-matrix as well as melt breccias. The presence of microlites and vesicles in the groundmass and a widely observed flow fabric in the PTB support the presence of melt in the groundmass of some samples. Clasts in PTB are derived from the Archean granitoid basement. PTB matrix, the matrix of impact melt breccia also occurring between 256.50 m and 502.55 m depth, and the target granitoids vary in terms of silica, total alkali, magnesium and iron oxide contents. Chondrite-normalized REE patterns of PTB and target granitoids are similar, but the elemental abundances in the PTB are lower. The restricted size of PTB as veins and pods of up to 2.5 cm width, their occurrence at varied depths over a core length of 150 m, the clast population, and the chemical relationships between PTB and their host rocks all suggest the derivation of these breccias locally from the fractured basement granitoids involving in-situ melting. We favor that this took place due to rapid decompression during the collapse and modification stage of impact cratering, with, locally, additional energy input from frictional heating. Locally, amphibolite and dioritic mylonite occur in the host granitoids and their admixture could have contributed to the comparatively more mafic composition of PTB. Alteration of these crater floor rocks could have involved preferential reduction of silica and alkali element abundances, possibly due to impact-induced hydrothermal activity at crater floor level. This process, too, could have resulted in more mafic compositions.

Drainage systems of Lonar Crater, India: Contributions to Lonar Lake hydrology and crater degradation

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Komatsu, Goro; Senthil Kumar, P.; Goto, Kazuhisa; Sekine, Yasuhito; Giri, Chaitanya; Matsui, Takafumi

2014-05-01

Lonar, a 1.8-km-diameter impact crater in India, is a rare example of terrestrial impact craters formed in basaltic bedrock. The estimated age of the crater ranges widely from less than 12 ka to over 600 ka, but the crater preserves a relatively pristine morphology. We conducted a study of various drainage systems of Lonar Crater. The crater floor hosts a shallow 5-m-deep lake, which fluctuates seasonally. Our investigation reveals that the lake level is influenced by surface runoff that is active during the monsoon and groundwater input effective during both the rainy and the dry seasons. The groundwater discharge is observed as springs on the inner rim walls corresponding to weathered vesicular basalt and/or proximal ejecta, which are underlain by thick massive basalt layers. This observation indicates that groundwater movement is lithologically controlled: it passes preferentially through permeable vesicular basalt or proximal ejecta but is hindered in less permeable massive basalt. It is hypothesized that groundwater is also structurally controlled by dipping of basalt layers, interconnectivity of the permeable lithologic units through fractures, and preferential pathways such as fractures within the permeable lithologic units. Investigation on hydrological processes at Lonar Crater and its lake could provide useful insights into purported paleo-crater lakes presumably formed in the basaltic crust of Mars. The Lonar Crater interior shows signs of degradation in the forms of gullies and debris flows, and the Dhar valley incising in the rim leading to form a fan delta. The ejecta surface is characterized by the presence of channels, originating from the rim area and extending radially away from the crater center. The channels probably resulted from surface runoff, and its erosion contributes to the removal of the ejecta. Lonar Crater is a valuable analog site for studying degradation processes with potential application to impact craters occurring on

Petrogenesis of basalt-trachyte lavas from Olmoti Crater, Tanzania

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Mollel, Godwin F.; Swisher, Carl C., III; McHenry, Lindsay J.; Feigenson, Mark D.; Carr, Michael J.

2009-08-01

Olmoti Crater is part of the Plio-Pleistocene Ngorongoro Volcanic Highland (NVH) in northern Tanzania to the south of Gregory Rift. The Gregory Rift is part of the eastern branch of the East African Rift System (EARS) that stretches some 4000 km from the Read Sea and Gulf of Aden in the north to the Zambezi River in Mozambique. Here, we (1) characterize the chemistry and mineral compositions of lavas from Olmoti Crater, (2) determine the age and duration of Olmoti volcanic activity through 40Ar/ 39Ar dating of Olmoti Crater wall lavas and (3) determine the genesis of Olmoti lavas and the relationship to other NVH and EARS volcanics and (4) their correlation with volcanics in the Olduvai and Laetoli stratigraphic sequences. Olmoti lavas collected from the lower part of the exposed crater wall section (OLS) range from basalt to trachyandesite whereas the upper part of the section (OUS) is trachytic. Petrography and major and trace element data reflect a very low degree partial melt origin for the Olmoti lavas, presumably of peridotite, followed by extensive fractionation. The 87Sr/ 86Sr data overlap whereas Nd and Pb isotope data are distinct between OLS and OUS samples. Interpretation of the isotope data suggests mixing of enriched mantle (EM I) with high-μ-like reservoirs, consistent with the model of Bell and Blenkinsop [Bell, K., Blenkinsop, J., 1987. Nd and Sr isotopic compositions of East African carbonatites: implications for mantle heterogeneity. Geology 5, 99-102] for East African carbonatite lavas. The isotope ratios are within the range of values defined by Oceanic Island Basalt (OIB) globally and moderate normalized Tb/Yb ratios (2.3-1.6) in these lavas suggest melting in the lithospheric mantle consistent with other studies in the region. 40Ar/ 39Ar incremental-heating analyses of matrix and anorthoclase separates from Olmoti OLS and OUS lavas indicate that volcanic activity was short in duration, lasting ˜200 kyr from 2.01 ± 0.03 Ma to 1.80 ± 0

Nature of the Yucatan Block Basement as Derived From Study of Granitic Clasts in the Impact Breccias of Chicxulub Crater

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Vera-Sanchez, P.; Rebolledo-Vieyra, M.; Perez-Cruz, L.; Urrutia-Fucugauchi, J.

2008-05-01

The tectonic and petrologic nature of the basement of the Yucatan Block is studied from analyses of basement clasts present in the impact suevitic breccias of Chicxulub crater. The impact breccias have been sampled as part of the drilling projects conducted in the Yucatan peninsula by Petroleos Mexicanos, the National University of Mexico and the Chicxulub Scientific Drilling Project. Samples analyzed come mainly from the Yaxcopoil-1, Tekax, and Santa Elena boreholes, and partly from Pemex boreholes. In this study we concentrate on clasts of the granites, granodiorites and quartzmonzonites in the impact breccias. We report major and trace element geochemical and petrological data, which are compared with data from the granitic and volcanic rocks from the Maya Mountains in Belize and from the Swannee terrane in Florida. Basement granitic clasts analyzed present intermediate to acidic sub-alkaline compositions. Plots of major oxides (e.g., Al2O3, Fe2O3, TiO2 and CaO) and trace elements (e.g., Th, Y, Hf, Nb and Zr) versus silica allow separation of samples into two major groups, which can be compared to units in the Maya Mountains and in Florida basement. The impact suevitic breccia samples have been affected by alteration likely related to the hydrothermal processes associated with the crater melt sheet. Cloritization, seritization and fenitization alterations are recognized, due to the long term hydrothermalism. Krogh et al. (1993) reported U-Pb dates on zircons from the suevitic breccias, which gave dates of 545 +/- 5 Ma and 418 +/- 6 Ma, which were interpreted in terms of the deep granitic metamorphic Yucatan basement. The younger date correlates with the age for the Osceola Granite and the St. Lucie metamorphic complex of the Swannee terrane in the Florida peninsula. The intrusive rocks in the Yucatan basement may be related to approx. 418 Ma ago collisional event in the Late Silurian.

Oxygen and hydrogen isotope studies of plutonic granitic rocks

International Nuclear Information System (INIS)

Taylor, H.P. Jr.

1978-01-01

The primary deltaD values of the biotites and hornblendes in granitic batholiths are remarkably constant at about -50 to -85, identical to the values in regional metamorphic rocks, marine sediments and greenstones, and most weathering products in temperate climates. Therefore the primary water in these igneous rocks is probably not 'juvenile', but is ultimately derived by dehydration and/or partial melting of the lower crust or subducted lithosphere. Most granitic rocks have delta 18 O = +7.0 to +10.0, probably indicating significant involvment of high- 18 O metasedimentary or altered volcanic rocks in the melting process; such an origin is demanded for many other granodiorites and tonalites that have delta 18 O = +10 to +13. Gigantic meteoric-hydrothermal convective circulation systems were established in the epizonal portions of all batholiths, locally producing very low delta 18 O values (particularly in feldspars) during subsolidus exchange. Some granitic plutons in such environments also were emplaced as low- 18 O magmas probably formed by melting or assimilation of hydrothermally altered roof rocks. However, the water/rock ratios were typically low enough that over wide areas the only evidence for meteoric water exchange in the batholiths is given by low D/H ratios (deltaK as low as -180); for example, because of latitudinal isotopic variations in meteoric waters, as one moves north through the Cordilleran batholiths of western North America an increasingly higher proportion of the granitic rocks have deltaD values lower than -120. The lowering of deltaD values commonly corelates with re-setting of K-Ar ages. (Auth.)

Mercury's Densely Cratered Surface

Science.gov (United States)

1974-01-01

Mariner 10 took this picture (FDS 27465) of the densely cratered surface of Mercury when the spacecraft was 18,200 kilometers (8085 miles) from the planet on March 29. The dark line across top of picture is a 'dropout' of a few TV lines of data. At lower left, a portion of a 61 kilometer (38 mile) crater shows a flow front extending across the crater floor and filling more than half of the crater. The smaller, fresh crater at center is about 25 kilometers (15 miles) in diameter. Craters as small as one kilometer (about one-half mile) across are visible in the picture.The Mariner 10 mission, managed by the Jet Propulsion Laboratory for NASA's Office of Space Science, explored Venus in February 1974 on the way to three encounters with Mercury-in March and September 1974 and in March 1975. The spacecraft took more than 7,000 photos of Mercury, Venus, the Earth and the Moon.Image Credit: NASA/JPL/Northwestern University

Rapakivi texture formation via disequilibrium melting in a contact partial melt zone, Antarctica

Science.gov (United States)

Currier, R. M.

2017-12-01

akin to rapakivi granites observed globally in Proterozoic systems. In essence, the melt zone is an embryonic rapakivi granite; not yet fully developed and displaying clear ties to its parental rock.

Buried Craters of Utopia

Science.gov (United States)

2003-01-01

MGS MOC Release No. MOC2-365, 19 May 2003Beneath the northern plains of Mars are numerous buried meteor impact craters. One of the most heavily-cratered areas, although buried, occurs in Utopia Planitia, as shown in this Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image. The history of Mars is complex; impact craters provide a tool by which to understand some of that history. In this case, a very ancient, cratered surface was thinly-buried by younger material that is not cratered at all. This area is near 48.1oN, 228.2oW; less than 180 km (112 mi) west of the Viking 2 lander site. Sunlight illuminates the scene from the lower left.

Phase behavior and reactive transport of partial melt in heterogeneous mantle model

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Jordan, J.; Hesse, M. A.

2013-12-01

The reactive transport of partial melt is the key process that leads to the chemical and physical differentiation of terrestrial planets and smaller celestial bodies. The essential role of the lithological heterogeneities during partial melting of the mantle is increasingly recognized. How far can enriched melts propagate while interacting with the ambient mantle? Can the melt flow emanating from a fertile heterogeneity be localized through a reactive infiltration feedback in a model without exogenous factors or contrived initial conditions? A full understanding of the role of heterogeneities requires reactive melt transport models that account for the phase behavior of major elements. Previous work on reactive transport in the mantle focuses on trace element partitioning; we present the first nonlinear chromatographic analysis of reactive melt transport in systems with binary solid solution. Our analysis shows that reactive melt transport in systems with binary solid solution leads to the formation of two separate reaction fronts: a slow melting/freezing front along which enthalpy change is dominant and a fast dissolution/precipitation front along which compositional changes are dominated by an ion-exchange process over enthalpy change. An intermediate state forms between these two fronts with a bulk-rock composition and enthalpy that are not necessarily bounded by the bulk-rock composition and enthalpy of either the enriched heterogeneity or the depleted ambient mantle. The formation of this intermediate state makes it difficult to anticipate the porosity changes and hence the stability of reaction fronts. Therefore, we develop a graphical representation for the solution that allows identification of the intermediate state by inspection, for all possible bulk-rock compositions and enthalpies of the heterogeneity and the ambient mantle. We apply the analysis to the partial melting of an enriched heterogeneity. This leads to the formation of moving precipitation

A 2D double-porosity model for melting and melt migration beneath mid-oceanic ridges

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Liu, B.; Liang, Y.; Parmentier, E.

2017-12-01

Several lines of evidence suggest that the melting and melt extraction region of the MORB mantle is heterogeneous consisting of an interconnected network of high permeability dunite channels in a low porosity harzburgite or lherzolite matrix. In principle, one can include channel formation into the tectonic-scale geodynamic models by solving conservation equations for a chemically reactive and viscously deformable porous medium. Such an approach eventually runs into computational limitations such as resolving fractal-like channels that have a spectrum of width. To better understand first order features of melting and melt-rock interaction beneath MOR, we have formulated a 2D double porosity model in which we treat the triangular melting region as two overlapping continua occupied by the low-porosity matrix and interconnected high-porosity channels. We use melt productivity derived from a thermodynamic model and melt suction rate to close our problem. We use a high-order accurate numerical method to solve the conservation equations in 2D for porosity, solid and melt velocities and concentrations of chemical tracers in the melting region. We carry out numerical simulations to systematically study effects of matrix-to-channel melt suction and spatially distributed channels on the distributions of porosity and trace element and isotopic ratios in the melting region. For near fractional melting with 10 vol% channel in the melting region, the flow field of the matrix melt follows closely to that of the solid because the small porosity (exchange between the melt and the solid. The smearing effect can be approximated by dispersion coefficient. For slowly diffusing trace elements (e.g., LREE and HFSE), the melt migration induced dispersion can be as effective as thermal diffusion. Therefore, sub-kilometer scale heterogeneities of Nd and Hf isotopes are significantly damped or homogenized in the melting region.

Geochemical evidence for waning magmatism and polycyclic volcanism at Crater Flat, Nevada

International Nuclear Information System (INIS)

Perry, F.V.; Crowe, B.M.

1992-01-01

This paper reports that petrologic and geochemical studies of basaltic rocks in the Yucca Mountain region are currently focused on understanding the evolution of volcanism in the Crater Flat volcanic field and the mechanisms of polycyclic volcanic field and the mechanisms of polycyclic volcanism at the Lathrop Wells volcanic center, the youngest center in the Crater Flat volcanic field. Geochemical and petrologic data indicate that the magma chambers which supplied the volcanic centers at Crater Flat became situated at greater crustal depths as the field evolved. Deep magma chambers may be related to a waning magma flux that was unable to sustain upper crustal magma conduits and chambers. Geochemical data from the Lathrop Wells volcanic center indicate that eruptive units identified from field and geomorphic relationships are geochemically distinct. The geochemical variations cannot be explained by fractional crystallization of a single magma batch, indicating that several magma batches were involved in the formation of the Lathrop Wells center. Considering the low magma flux in the Yucca Mountain region in the Quaternary, the probability of several magma batches erupting essentially simultaneously at Lathrop Wells is considered remote

Shock compression behavior of bi-material powder composites with disparate melting temperatures

International Nuclear Information System (INIS)

Sullivan, Kyle T.; Swift, Damian; Barham, Matthew; Stölken, James; Kuntz, Joshua; Kumar, Mukul

2014-01-01

Laser driven experiments were used to investigate the shock compression behavior of powder processed Bismuth/Tungsten (Bi/W) composite samples. The constituents provide different functionality to the composite behavior as Bi could be shock melted at the pressures attained in this work, while the W could not. Samples were prepared by uniaxial pressing, and the relative density was measured as a function of particle size, applied pressure, and composition for both hot and cold pressing conditions. This resulted in sample densities between 73% and 99% of the theoretical maximum density, and also noticeable differences in microstructure in the hot and cold pressed samples. The compression waves were generated with a 1.3 × 1.3 mm square spot directly onto the surface of the sample, using irradiances between 10 12 and 10 13  W/cm 2 , which resulted in calculated peak pressures between 50 and 150 GPa within a few micrometers. Sample recovery and post-mortem analysis revealed the formation of a crater on the laser drive surface, and the depth of this crater corresponded to the depth to which the Bi had been melted. The melt depth was found to be primarily a function of residual porosity and composition, and ranged from 167 to 528 μm. In general, a higher porosity led to a larger melt depth. Direct numerical simulations were performed, and indicated that the observed increase in melt depth for low-porosity samples could be largely attributed to increased heating associated with work done for pore collapse. However, the relative scaling was sensitive to composition, with low volume fraction Bi samples exhibiting a much stronger dependence on porosity than high Bi content samples. Select samples were repeated using an Al foil ablator, but there were no noticeable differences ensuring that the observed melting was indeed pressure-driven and was not a result of direct laser heating. The resultant microstructures and damage near the spall surface were also investigated

Grinding into Soft, Powdery Rock

Science.gov (United States)

2004-01-01

This hole in a rock dubbed 'Clovis' is the deepest hole drilled so far in any rock on Mars. NASA's Mars Exploration Rover Spirit captured this view with its microscopic imager on martian sol 217 (Aug. 12, 2004) after drilling 8.9 millimeters (0.35 inch) into the rock with its rock abrasion tool. The view is a mosaic of four frames taken by the microscopic imager. The hole is 4.5 centimeters (1.8 inches) in diameter. Clovis is key to a developing story about environmental change on Mars, not only because it is among the softest rocks encountered so far in Gusev Crater, but also because it contains mineral alterations that extend relatively deep beneath its surface. In fact, as evidenced by its fairly crumbly texture, it is possibly the most highly altered volcanic rock ever studied on Mars. Scientific analysis shows that the rock contains higher levels of the elements sulfur, chlorine, and bromine than are normally encountered in basaltic rocks, such as a rock dubbed 'Humphrey' that Spirit encountered two months after arriving on Mars. Humphrey showed elevated levels of sulfur, chlorine, and bromine only in the outermost 2 millimeters (less than 0.1 inch) of its surface. Clovis shows elevated levels of the same elements along with the associated softness of the rock within a borehole that is 4 times as deep. Scientists hope to compare Clovis to other, less-altered rocks in the vicinity to assess what sort of water-based processes altered the rock. Hypotheses include transport of sulfur, chlorine, and bromine in water vapor in volcanic gases; hydrothermal circulation (flow of volcanically heated water through rock); or saturation in a briny soup containing the same elements. In this image, very fine-grained material from the rock has clumped together by electrostatic attraction and fallen into the borehole. NASA/JPL/Cornell/USGS

Size-Frequency Distribution of Small Lunar Craters: Widening with Degradation and Crater Lifetime

Science.gov (United States)

Ivanov, B. A.

2018-01-01

The review and new measurements are presented for depth/diameter ratio and slope angle evolution during small ( D model. The uncertainty of crater retention age due to crater degradational widening is estimated. The collected and analyzed data are discussed to be used in the future updating of mechanical models for lunar crater aging.

Interaction of the lithospheric mantle and crustal melts for the generation of the Horoz pluton (Niğde, Turkey: whole-rock geochemical and Sr–Nd–Pb isotopic evidence

Directory of Open Access Journals (Sweden)

Kerim Kocak

2016-08-01

Full Text Available The Horoz pluton includes granitic and granodioritic rocks, with widespread mafic microgranular enclaves (MMEs. Petrochemically, the rocks of the pluton show calc-alkaline to shoshonitic and metaluminous to slightly peraluminous composition. The rocks also exhibit an enrichment in large ion lithophile elements, e.g. Rb, K, and depletions of high field strength elements such as Y, Lu, and Mg#, Ni, with a slightly concave-upward rare earth element pattern. Both granitic and granodioritic rocks exhibit geochemical characteristics of tonalite, trondhjemite and granodiorite assemblages, possibly developed by the partial melting of a thickened lower crust. The granitoids have high concentrations of Na2O (2.6–4.5 wt%, Sr (347–599 ppm, intermediate-high (La/YbN (8.2–18.1, mostly >11 , Al2O3 (13.2–16.9 wt%, average 15.3 wt%, low MgO (0.2–1.4 wt%, average 0.84 wt% and Co (0.7–10.3 ppm. The MMEs include higher Na2O (4.5–5.5 wt%, Sr (389–1149 ppm, Al2O3 (16.9–19.2 wt%, average 17.8 wt%, MgO (1.4–4.4 wt%, average 2.75 wt% and Co (6.2–18.7 ppm contents in comparison with that of their hosts. There is a lack of negative Eu anomalies, except a few samples. Both host rocks and MMEs have a low initial 87Sr/86Sr ratio (respectively 0.7046–0.7051 and 0.7047–0.7058, low eNd value (–1.8 to –0.2 and –0.6 to 0.7 at 50 Ma and highly radiogenic 208Pb/204Pb ratios (39.43–39.47 and 39.39–39.54. Whole-rock chemistry and isotopic data suggest that parent magmas of both MMEs and their hosts have derived from melts of the mixing between the lithospheric mantle and crustal end members, than fractional crystallization processes in crustal levels.

Tin in granitic melts: The role of melting temperature and protolith composition

Science.gov (United States)

Wolf, Mathias; Romer, Rolf L.; Franz, Leander; López-Moro, Francisco Javier

2018-06-01

Granite bound tin mineralization typically is seen as the result of extreme magmatic fractionation and late exsolution of magmatic fluids. Mineralization, however, also could be obtained at considerably less fractionation if initial melts already had enhanced Sn contents. We present chemical data and results from phase diagram modeling that illustrate the dominant roles of protolith composition, melting conditions, and melt extraction/evolution for the distribution of Sn between melt and restite and, thus, the Sn content of melts. We compare the element partitioning between leucosome and restite of low-temperature and high-temperature migmatites. During low-temperature melting, trace elements partition preferentially into the restite with the possible exception of Sr, Cd, Bi, and Pb, that may be enriched in the melt. In high-temperature melts, Ga, Y, Cd, Sn, REE, Pb, Bi, and U partition preferentially into the melt whereas Sc, V, Cr, Co, Ni, Mo, and Ba stay in the restite. This contrasting behavior is attributed to the stability of trace element sequestering minerals during melt generation. In particular muscovite, biotite, titanite, and rutile act as host phases for Sn and, therefore prevent Sn enrichment in the melt as long as they are stable phases in the restite. As protolith composition controls both the mineral assemblage and modal contents of the various minerals, protolith composition eventually also controls the fertility of a rock during anatexis, restite mineralogy, and partitioning behavior of trace metals. If a particular trace element is sequestered in a phase that is stable during partial melting, the resulting melt is depleted in this element whereas the restite becomes enriched. Melt generation at high temperature may release Sn when Sn-hosts become unstable. If melt has not been lost before the breakdown of Sn-hosts, Sn contents in the melt will increase but never will be high. In contrast, if melt has been lost before the decomposition of Sn

Classification Scheme for Diverse Sedimentary and Igneous Rocks Encountered by MSL in Gale Crater

Science.gov (United States)

Schmidt, M. E.; Mangold, N.; Fisk, M.; Forni, O.; McLennan, S.; Ming, D. W.; Sumner, D.; Sautter, V.; Williams, A. J.; Gellert, R.

2015-01-01

The Curiosity Rover landed in a lithologically and geochemically diverse region of Mars. We present a recommended rock classification framework based on terrestrial schemes, and adapted for the imaging and analytical capabilities of MSL as well as for rock types distinctive to Mars (e.g., high Fe sediments). After interpreting rock origin from textures, i.e., sedimentary (clastic, bedded), igneous (porphyritic, glassy), or unknown, the overall classification procedure (Fig 1) involves: (1) the characterization of rock type according to grain size and texture; (2) the assignment of geochemical modifiers according to Figs 3 and 4; and if applicable, in depth study of (3) mineralogy and (4) geologic/stratigraphic context. Sedimentary rock types are assigned by measuring grains in the best available resolution image (Table 1) and classifying according to the coarsest resolvable grains as conglomerate/breccia, (coarse, medium, or fine) sandstone, silt-stone, or mudstone. If grains are not resolvable in MAHLI images, grains in the rock are assumed to be silt sized or smaller than surface dust particles. Rocks with low color contrast contrast between grains (e.g., Dismal Lakes, sol 304) are classified according to minimum size of apparent grains from surface roughness or shadows outlining apparent grains. Igneous rocks are described as intrusive or extrusive depending on crystal size and fabric. Igneous textures may be described as granular, porphyritic, phaneritic, aphyric, or glassy depending on crystal size. Further descriptors may include terms such as vesicular or cumulate textures.

Modeling the Rock Glacier Cycle

Science.gov (United States)

Anderson, R. S.; Anderson, L. S.

2016-12-01

Rock glaciers are common in many mountain ranges in which the ELA lies above the peaks. They represent some of the most identifiable components of today's cryosphere in these settings. Their oversteepened snouts pose often-overlooked hazards to travel in alpine terrain. Rock glaciers are supported by avalanches and by rockfall from steep headwalls. The winter's avalanche cone must be sufficiently thick not to melt entirely in the summer. The spatial distribution of rock glaciers reflects this dependence on avalanche sources; they are most common on lee sides of ridges where wind-blown snow augments the avalanche source. In the absence of rockfall, this would support a short, cirque glacier. Depending on the relationship between rockfall and avalanche patterns, "talus-derived" and "glacier-derived" rock glaciers are possible. Talus-derived: If the spatial distribution of rock delivery is similar to the avalanche pattern, the rock-ice mixture will travel an englacial path that is downward through the short accumulation zone before turning upward in the ablation zone. Advected debris is then delivered to the base of a growing surface debris layer that reduces the ice melt rate. The physics is identical to the debris-covered glacier case. Glacier-derived: If on the other hand rockfall from the headwall rolls beyond the avalanche cone, it is added directly to the ablation zone of the glacier. The avalanche accumulation zone then supports a pure ice core to the rock glacier. We have developed numerical models designed to capture the full range of glacier to debris-covered glacier to rock glacier behavior. The hundreds of meter lengths, tens of meters thicknesses, and meter per year speeds of rock glaciers are well described by the models. The model can capture both "talus-derived" and "glacier-derived" rock glaciers. We explore the dependence of glacier behavior on climate histories. As climate warms, a pure ice debris-covered glacier can transform to a much shorter rock

A model for the dynamics of crater-centered intrusion: Application to lunar floor-fractured craters

Science.gov (United States)

Thorey, Clément; Michaut, Chloé

2014-01-01

Lunar floor-fractured craters are a class of craters modified by post-impact mechanisms. They are defined by distinctive shallow floors that are convex or plate-like, sometimes with a wide floor moat bordering the wall region. Radial, concentric, and polygonal floor fractures suggest an endogenous process of modification. Two mechanisms have been proposed to account for such deformations: viscous relaxation and spreading of a magma intrusion at depth below the crater. To test the second assumption and bring more constraints on the intrusion process, we develop a model for the dynamics of magma spreading below an elastic overlying layer with a crater-like topography. As predicted in earlier more qualitative studies, the increase in lithostatic pressure at the crater wall zone prevents the intrusion from spreading laterally, leading to the thickening of the intrusion. Additionally, our model shows that the final crater floor appearance after the uplift, which can be convex or flat, with or without a circular moat bordering the wall zone, depends on the elastic thickness of the layer overlying the intrusion and on the crater size. Our model provides a simple formula to derive the elastic thickness of the overlying layer hence a minimum estimate for the intrusion depth. Finally, our model suggests that crust redistribution by cratering must have controlled magma ascent below most of these craters.

Elasticity of water-saturated rocks as a function of temperature and pressure.

Science.gov (United States)

Takeuchi, S.; Simmons, G.

1973-01-01

Compressional and shear wave velocities of water-saturated rocks were measured as a function of both pressure and temperature near the melting point of ice to confining pressure of 2 kb. The pore pressure was kept at about 1 bar before the water froze. The presence of a liquid phase (rather than ice) in microcracks of about 0.3% porosity affected the compressional wave velocity by about 5% and the shear wave velocity by about 10%. The calculated effective bulk modulus of the rocks changes rapidly over a narrow range of temperature near the melting point of ice, but the effective shear modulus changes gradually over a wider range of temperature. This phenomenon, termed elastic anomaly, is attributed to the existence of liquid on the boundary between rock and ice due to local stresses and anomalous melting of ice under pressure.

Three dimensional rock microstructures: insights from FIB-SEM tomography

Science.gov (United States)

Drury, Martyn; Pennock, Gill; de Winter, Matthijs

2016-04-01

Most studies of rock microstructures investigate two-dimensional sections or thin slices of three dimensional grain structures. With advances of X-ray and electron tomography methods the 3-D microstructure can be(relatively) routinely investigated on scales from a few microns to cm. 3D studies are needed to investigate the connectivity of microstructures and to test the assumptions we use to calculate 3D properties from 2D sections. We have used FIB-SEM tomography to study the topology of melts in synthetic olivine rocks, 3D crystal growth microstructures, pore networks and subgrain structures. The technique uses a focused ion beam to make serial sections with a spacing of tens to hundreds of nanometers. Each section is then imaged or mapped using the electron beam. The 3D geometry of grains and subgrains can be investigated using orientation contrast or EBSD mapping. FIB-SEM tomography of rocks and minerals can be limited by charging of the uncoated surfaces exposed by the ion beam. The newest generation of FIB-SEMs have much improved low voltage imaging capability allowing high resolution charge free imaging. Low kV FIB-SEM tomography is now widely used to study the connectivity of pore networks. In-situ fluids can also be studied using cryo-FIB-SEM on frozen samples, although special freezing techniques are needed to avoid artifacts produced by ice crystallization. FIB-SEM tomography is complementary, in terms of spatial resolution and sampled volume, to TEM tomography and X-ray tomography, and the combination of these methods can cover a wide range of scales. Our studies on melt topology in synthetic olivine rocks with a high melt content show that many grain boundaries are wetted by nanometre scale melt layers that are too thin to resolve by X-ray tomography. A variety of melt layer geometries occur consistent with several mechanisms of melt layer formation. The nature of melt geometries along triple line junctions and quadruple points can be resolved

Crater in Utopia

Science.gov (United States)

2004-01-01

23 March 2004 Craters of the martian northern plains tend to be somewhat shallow because material has filled them in. Their ejecta blankets, too, are often covered by younger materials. This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows an example--a crater in Utopia Planitia near 43.7oN, 227.3oW. Erosion has roughened some of the surfaces of the material that filled the crater and covered its ejecta deposit. The picture covers an area about 3 km (1.9 mi) across. Sunlight illuminates the scene from the lower left.

Composition and structure of the shallow subsurface of Ceres revealed by crater morphology

Science.gov (United States)

Bland, Michael T.; Carol A. Raymond,; Schenk, Paul M.; Roger R. Fu,; Thomas Kneisl,; Hendrick Pasckert, Jan; Hiesinger, Harald; Frank Preusker,; Ryan S. Park,; Simone Marchi,; Scott King,; Castillo-Rogez, Julie C.; Christopher T. Russell,

2016-01-01

Before NASA’s Dawn mission, the dwarf planet Ceres was widely believed to contain a substantial ice-rich layer below its rocky surface. The existence of such a layer has significant implications for Ceres’s formation, evolution, and astrobiological potential. Ceres is warmer than icy worlds in the outer Solar System and, if its shallow subsurface is ice-rich, large impact craters are expected to be erased by viscous flow on short geologic timescales. Here we use digital terrain models derived from Dawn Framing Camera images to show that most of Ceres’s largest craters are several kilometres deep, and are therefore inconsistent with the existence of an ice-rich subsurface. We further show from numerical simulations that the absence of viscous relaxation over billion-year timescales implies a subsurface viscosity that is at least one thousand times greater than that of pure water ice. We conclude that Ceres’s shallow subsurface is no more than 30% to 40% ice by volume, with a mixture of rock, salts and/or clathrates accounting for the other 60% to 70%. However, several anomalously shallow craters are consistent with limited viscous relaxation and may indicate spatial variations in subsurface ice content.

Magnetic Properties of Three Impact Structures in Canada

Science.gov (United States)

Scott, R. G.; Pilkington, M.; Tanczyk, E. I.; Grieve, R. A. F.

1995-09-01

Magnetic anomaly lows associated with the West Hawk Lake (Manitoba), Deep Bay (Saskatchewan) and Clearwater Lakes (Quebec) impact structures, are variable in lateral extent and intensity, a characteristic shared with most impact structures [1]. Drill core from the centres of these structures provides a unique opportunity to ground truth the causes of the reduction in magnetic field intensity in impact structures. Magnetic susceptibility and remanent magnetization levels have been found to be well below regional levels in melt rocks, impact breccias, fractured/shocked basement rocks in the central uplifts, and post-impact sediments. Deep Bay, formed in Pre-Cambrian paragneisses, is a complex crater with a submerged central uplift. It has been extensively infilled with non-magnetic black shales of Cretaceous age [2]. An airborne magnetic low of about 100 nT is associated with the Deep Bay structure. Below the shales and along the rim of the structure are highly brecciated country rocks with variable amounts of very fine rock flour. Susceptibility and remanent magnetization are both weak due to extensive alteration in the brecciated rocks. Alteration of the brecciated rocks, and the effect of several hundred meters of non-magnetic sedimentary infill, both contribute to the magnetic low. West Hawk Lake, a simple crater, was excavated in metavolcanic and metasedimentary rocks of the Superior Province [3], and has a ground magnetic low of about 250 nT. As with Deep Bay, West Hawk Lake has been infilled with dominantly non-magnetic sediments. Brecciation and alteration are extensive, with breccia derived from greenschist-facies meta-andesite displaying slightly higher susceptibilities and remanent magnetizations than breccia derived from the more felsic metasediments. Brecciation has effectively randomized magnetization vectors, and subsequent alteration resulted in the destruction of magnetic phases. These two factors contribute to the magnetic low over this structure

Two-dimensional computer simulation of hypervelocity impact cratering: some preliminary results for Meteor Crater, Arizona

Energy Technology Data Exchange (ETDEWEB)

Bryan, J.B.; Burton, D.E.; Cunningham, M.E.; Lettis, L.A. Jr.

1978-06-01

A computational approach used for subsurface explosion cratering was extended to hypervelocity impact cratering. Meteor (Barringer) Crater, Arizona, was selected for the first computer simulation because it is one of the most thoroughly studied craters. It is also an excellent example of a simple, bowl-shaped crater and is one of the youngest terrestrial impact craters. Initial conditions for this calculation included a meteorite impact velocity of 15 km/s, meteorite mass of 1.67 x 10/sup 8/ kg, with a corresponding kinetic energy of 1.88 x 10/sup 16/ J (4.5 megatons). A two-dimensional Eulerian finite difference code called SOIL was used for this simulation of a cylindrical iron projectile impacting at normal incidence into a limestone target. For this initial calculation, a Tillotson equation-of-state description for iron and limestone was used with no shear strength. Results obtained for this preliminary calculation of the formation of Meteor Crater are in good agreement with field measurements. A color movie based on this calculation was produced using computer-generated graphics. 19 figures, 5 tables, 63 references.

Two-dimensional computer simulation of hypervelocity impact cratering: some preliminary results for Meteor Crater, Arizona

International Nuclear Information System (INIS)

Bryan, J.B.; Burton, D.E.; Cunningham, M.E.; Lettis, L.A. Jr.

1978-06-01

A computational approach used for subsurface explosion cratering was extended to hypervelocity impact cratering. Meteor (Barringer) Crater, Arizona, was selected for the first computer simulation because it is one of the most thoroughly studied craters. It is also an excellent example of a simple, bowl-shaped crater and is one of the youngest terrestrial impact craters. Initial conditions for this calculation included a meteorite impact velocity of 15 km/s, meteorite mass of 1.67 x 10 8 kg, with a corresponding kinetic energy of 1.88 x 10 16 J (4.5 megatons). A two-dimensional Eulerian finite difference code called SOIL was used for this simulation of a cylindrical iron projectile impacting at normal incidence into a limestone target. For this initial calculation, a Tillotson equation-of-state description for iron and limestone was used with no shear strength. Results obtained for this preliminary calculation of the formation of Meteor Crater are in good agreement with field measurements. A color movie based on this calculation was produced using computer-generated graphics. 19 figures, 5 tables, 63 references

Archaean ultra-depleted komatiites formed by hydrous melting of cratonic mantle.

Science.gov (United States)

Wilson, A H; Shirey, S B; Carlson, R W

2003-06-19

Komatiites are ultramafic volcanic rocks containing more than 18 per cent MgO (ref. 1) that erupted mainly in the Archaean era (more than 2.5 gigayears ago). Although such compositions occur in later periods of Earth history (for example, the Cretaceous komatiites of Gorgona Island), the more recent examples tend to have lower MgO content than their Archaean equivalents. Komatiites are also characterized by their low incompatible-element content, which is most consistent with their generation by high degrees of partial melting (30-50 per cent). Current models for komatiite genesis include the melting of rock at great depth in plumes of hot, diapirically rising mantle or the melting of relatively shallow mantle rocks at less extreme, but still high, temperatures caused by fluxing with water. Here we report a suite of ultramafic lava flows from the Commondale greenstone belt, in the southern part of the Kaapvaal Craton, which represents a previously unrecognized type of komatiite with exceptionally high forsterite content of its igneous olivines, low TiO(2)/Al(2)O(3) ratio, high silica content, extreme depletion in rare-earth elements and low Re/Os ratio. We suggest a model for their formation in which a garnet-enriched residue left by earlier cratonic volcanism was melted by hydration from a subducting slab.

Formation of Intermediate Plutonic Rocks by Magma Mixing: the Shoshonite Suite of Timna, Southern Israel.

Science.gov (United States)

Fox, S.; Katzir, Y.

2017-12-01

In magmatic series considered to form by crystal fractionation intermediate rocks are usually much less abundant than expected. Yet, intermediate plutonic rocks, predominantly monzodiorites, are very abundant in the Neoproterozoic Timna igneous complex, S. Israel. A previously unnoticed plutonic shoshonitic suite was recently defined and mapped in Timna (Litvinovsky et al., 2015). It mostly comprises intermediate rocks in a seemingly 'continuous' trend from monzodiorite through monzonite to quartz syenite. Macroscale textures including gradational boundaries of mafic and felsic rocks and MME suggest that magma mixing is central in forming intermediate rocks in Timna. Our petrographic, microtextural and mineral chemistry study delineates the mode of incipient mixing, ultimate mingling and crystal equilibration in hybrid melts. An EMP study of plagioclase from rocks across the suite provides a quantitative evaluation of textures indicative of magma mixing/mingling, including recurrent/patchy zoning, Ca spike, boxy/sponge cellular texture and anti-Rapakivi texture. Each texture has an affinity to a particular mixing region. A modal count of these textures leads to a kinetic mixing model involving multi temporal and spatial scales necessary to form the hybrid intermediate rocks. A `shell'-like model for varying degrees of mixing is developed with the more intensive mixing at the core and more abundant felsic and mafic end-members towards the outer layer. REE patterns in zircon shows that it originated from both mafic and felsic parent melts. Whole rock Fe vs Sr plot suggests a two-stage mixing between the monzogabbro and quartz-syenite producing first mesocratic syenite, and subsequent mixing with a fractionating monzogabbro resulting in monzonitic compositions. A fractionating monzogabbro intruded into a syenitic melt sequentially. While slowly cooling, the monzogabbro heated the immediate syenitic melt, lowering the viscosity and rheological obstruction to overturn

Lunar floor-fractured craters: Modes of dike and sill emplacement and implications of gas production and intrusion cooling on surface morphology and structure

Science.gov (United States)

Wilson, Lionel; Head, James W.

2018-05-01

Lunar floor-fractured craters (FFCs) represent the surface manifestation of a class of shallow crustal intrusions in which magma-filled cracks (dikes) rising to the surface from great depth encounter contrasts in host rock lithology (breccia lens, rigid solidified melt sheet) and intrude laterally to form a sill, laccolith or bysmalith, thereby uplifting and deforming the crater floor. Recent developments in the knowledge of lunar crustal thickness and density structure have enabled important revisions to models of the generation, ascent and eruption of magma, and new knowledge about the presence and behavior of magmatic volatiles has provided additional perspectives on shallow intrusion processes in FFCs. We use these new data to assess the processes that occur during dike and sill emplacement with particular emphasis on tracking the fate and migration of volatiles and their relation to candidate venting processes. FFCs result when dikes are capable of intruding close to the surface, but fail to erupt because of the substructure of their host impact craters, and instead intrude laterally after encountering a boundary where an increase in ductility (base of breccia lens) or rigidity (base of solidified melt sheet) occurs. Magma in dikes approaching the lunar surface experiences increasingly lower overburden pressures: this enhances CO gas formation and brings the magma into the realm of the low pressure release of H2O and sulfur compounds, both factors adding volatiles to those already collected in the rising low-pressure part of the dike tip. High magma rise velocity is driven by the positive buoyancy of the magma in the part of the dike remaining in the mantle. The dike tip overshoots the interface and the consequent excess pressure at the interface drives the horizontal flow of magma to form the intrusion and raise the crater floor. If sill intrusion were controlled by the physical properties at the base of the melt sheet, dikes would be required to approach to

Melt migration modeling in partially molten upper mantle

Science.gov (United States)

Ghods, Abdolreza

The objective of this thesis is to investigate the importance of melt migration in shaping major characteristics of geological features associated with the partial melting of the upper mantle, such as sea-floor spreading, continental flood basalts and rifting. The partial melting produces permeable partially molten rocks and a buoyant low viscosity melt. Melt migrates through the partially molten rocks, and transfers mass and heat. Due to its much faster velocity and appreciable buoyancy, melt migration has the potential to modify dynamics of the upwelling partially molten plumes. I develop a 2-D, two-phase flow model and apply it to investigate effects of melt migration on the dynamics and melt generation of upwelling mantle plumes and focusing of melt migration beneath mid-ocean ridges. Melt migration changes distribution of the melt-retention buoyancy force and therefore affects the dynamics of the upwelling plume. This is investigated by modeling a plume with a constant initial melt of 10% where no further melting is considered. Melt migration polarizes melt-retention buoyancy force into high and low melt fraction regions at the top and bottom portions of the plume and therefore results in formation of a more slender and faster upwelling plume. Allowing the plume to melt as it ascends through the upper mantle also produces a slender and faster plume. It is shown that melt produced by decompressional melting of the plume migrates to the upper horizons of the plume, increases the upwelling velocity and thus, the volume of melt generated by the plume. Melt migration produces a plume which lacks the mushroom shape observed for the plume models without melt migration. Melt migration forms a high melt fraction layer beneath the sloping base of the impermeable oceanic lithosphere. Using realistic conditions of melting, freezing and melt extraction, I examine whether the high melt fraction layer is able to focus melt from a wide partial melting zone to a narrow region

A high-precision 40Ar/39Ar age for the Nördlinger Ries impact crater, Germany, and implications for the accurate dating of terrestrial impact events

Science.gov (United States)

Schmieder, Martin; Kennedy, Trudi; Jourdan, Fred; Buchner, Elmar; Reimold, Wolf Uwe

2018-01-01

40Ar/39Ar dating of specimens of moldavite, the formation of which is linked to the Ries impact in southern Germany, with a latest-generation ARGUS VI multi-collector mass spectrometer yielded three fully concordant plateau ages with a weighted mean age of 14.808 ± 0.021 Ma (± 0.038 Ma including all external uncertainties; 2σ; MSWD = 0.40, P = 0.67). This new best-estimate age for the Nördlinger Ries is in general agreement with previous 40Ar/39Ar results for moldavites, but constitutes a significantly improved precision with respect to the formation age of the distal Ries-produced tektites. Separates of impact glass from proximal Ries ejecta (suevite glass from three different surface outcrops) and partially melted feldspar particles from impact melt rock of the SUBO 18 Enkingen drill core failed to produce meaningful ages. These glasses show evidence for excess 40Ar introduction, which may have been incurred during interaction with hydrothermal fluids. Only partially reset 40Ar/39Ar ages could be determined for the feldspathic melt separates from the Enkingen core. The new 40Ar/39Ar results for the Ries impact structure constrain the duration of crater cooling, during the prevailing hydrothermal activity, to locally at least ∼60 kyr. With respect to the dating of terrestrial impact events, this paper briefly discusses a number of potential issues and effects that may be the cause for seemingly precise, but on a kyr-scale inaccurate, impact ages.

Landscape evolution on Mars - A model of aeolian denudation in Gale Crater

Science.gov (United States)

Day, M. D.; Kocurek, G.; Grotzinger, J. P.

2015-12-01

Aeolian erosion has been the dominant geomorphic agent to shape the surface of Mars for the past ~3.5 billion years. Although individual geomorphic features evidencing aeolian activity are well understood (e.g., yardangs, dune fields, and wind streaks), landscapes formed by aeolian erosion remain poorly characterized. Intra-crater sedimentary mounds are hypothesized to have formed by wind deflation of craters once filled with flat-lying strata, and, therefore, should be surrounded by landscapes formed by aeolian erosion. Here we present a landscape evolution model that provides both an initial characterization of aeolian landscapes, and a mechanism for large-scale excavation. Wind excavation of Gale Crater to form the 5 km high Mount Sharp would require removal of 6.4 x 104 km3 of sediment. Imagery in Gale Crater from satellites and the Mars Science Laboratory rover Curiosity shows a surface characterized by first-cycle aeolian erosion of bedrock. The overall landscape is interpreted to represent stages in a cycle of aeolian deflation and excavation, enhanced by physical weathering (e.g., thermal fracturing, cratering). Initial wind erosion of bedrock is enhanced along fractures, producing retreating scarps. Underlying less resistant layers then erode faster than the armoring cap rock, increasing relief in scarps to form retreating mesas. As scarp retreat continues, boulders from the armoring cap unit break away and cover the hillslopes of less resistant material below the scarps. Eventually all material from the capping unit is eroded away and a boulder-capped hill remains. Winnowing of fine material flattens hillslope topography, leaving behind a desert pavement. Over long enough time, this pavement is breached and the cycle begins anew. This cycle of landscape denudation by the wind is similar to that of water, but lacks characteristic subaqueous features such as dendritic drainage networks.

Apparatus for sealing access holes to cavities within the earth with rock glass

International Nuclear Information System (INIS)

Holman, R.R.

1979-01-01

Apparatus is disclosed for establishing a solid, very low permeable rock glass plug to seal access holes through rock to underground storage vaults. The apparatus is designed to supply a filler material having a constituency substantially matching that of the rock formation surrounding the access port to the vault, through a central feeder tube under pressure to the vault. Means are provided for heating the filler material and surrounding rock formation at the point where the filler material exits the feeder tube, to a temperature sufficient to melt both the rock formation and the filler material. The remaining portion of the feeder tube is cooled to preserve the surrounding rock formaion spaced from the feeder orifice. The melt at the extremity of the feeder tube is forced through the orifice to a region below the tool by the force of the pressure feed. As the melt is forced below the tool, the tool is retracted until the access hole is completely sealed. A second embodiment is provided to seal enlarged openings which further includes a cooled core follower that enables the deposit to be fused in layers closing in the circumference of the hole until a final pass fuses the central core

Snow-avalanche impact craters in southern Norway: Their morphology and dynamics compared with small terrestrial meteorite craters

Science.gov (United States)

Matthews, John A.; Owen, Geraint; McEwen, Lindsey J.; Shakesby, Richard A.; Hill, Jennifer L.; Vater, Amber E.; Ratcliffe, Anna C.

2017-11-01

This regional inventory and study of a globally uncommon landform type reveals similarities in form and process between craters produced by snow-avalanche and meteorite impacts. Fifty-two snow-avalanche impact craters (mean diameter 85 m, range 10-185 m) were investigated through field research, aerial photographic interpretation and analysis of topographic maps. The craters are sited on valley bottoms or lake margins at the foot of steep avalanche paths (α = 28-59°), generally with an easterly aspect, where the slope of the final 200 m of the avalanche path (β) typically exceeds 15°. Crater diameter correlates with the area of the avalanche start zone, which points to snow-avalanche volume as the main control on crater size. Proximal erosional scars ('blast zones') up to 40 m high indicate up-range ejection of material from the crater, assisted by air-launch of the avalanches and impulse waves generated by their impact into water-filled craters. Formation of distal mounds up to 12 m high of variable shape is favoured by more dispersed down-range deposition of ejecta. Key to the development of snow-avalanche impact craters is the repeated occurrence of topographically-focused snow avalanches that impact with a steep angle on unconsolidated sediment. Secondary craters or pits, a few metres in diameter, are attributed to the impact of individual boulders or smaller bodies of snow ejected from the main avalanche. The process of crater formation by low-density, low-velocity, large-volume snow flows occurring as multiple events is broadly comparable with cratering by single-event, high-density, high-velocity, small-volume projectiles such as small meteorites. Simple comparative modelling of snow-avalanche events associated with a crater of average size (diameter 85 m) indicates that the kinetic energy of a single snow-avalanche impact event is two orders of magnitude less than that of a single meteorite-impact event capable of producing a crater of similar size

Rock-welding materials for deep borehole nuclear waste disposal.

Energy Technology Data Exchange (ETDEWEB)

Yang, Pin [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Wang, Yifeng [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Rodriguez, Mark A. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Brady, Patrick Vane [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Swift, Peter N. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

2015-11-01

The concept of deep borehole nuclear waste disposal has recently been proposed. Effective sealing of a borehole after waste emplacement is generally required. In a high temperature disposal mode, the sealing function will be fulfilled by melting the ambient granitic rock with waste decay heat or an external heating source, creating a melt that will encapsulate waste containers or plug a portion of the borehole above a stack of the containers. However, there are certain drawbacks associated with natural materials, such as high melting temperatures, slow crystallization kinetics, the resulting sealing materials generally being porous with low mechanical strength, insufficient adhesion to waste container surface, and lack of flexibility for engineering controls. Here we show that natural granitic materials can be purposefully engineered through chemical modifications to enhance the sealing capability of the materials for deep borehole disposal. This work systematically explores the effect of chemical modification and crystallinity (amorphous vs. crystalline) on the melting and crystallization processes of a granitic rock system. A number of engineered granitic materials have been obtained that have decreased melting points, enhanced viscous densification, and accelerated recrystallization rates without compromising the mechanical integrity of the materials.

Iron Abundances in Lunar Impact Basin Melt Sheets From Orbital Magnetic Field Data

Science.gov (United States)

Oliveira, Joana S.; Wieczorek, Mark A.; Kletetschka, Gunther

2017-12-01

Magnetic field data acquired from orbit shows that the Moon possesses many magnetic anomalies. Though most of these are not associated with known geologic structures, some are found within large impact basins within the interior peak ring. The primary magnetic carrier in lunar rocks is metallic iron, but indigenous lunar rocks are metal poor and cannot account easily for the observed field strengths. The projectiles that formed the largest impact basins must have contained a significant quantity of metallic iron, and a portion of this iron would have been retained on the Moon's surface within the impact melt sheet. Here we use orbital magnetic field data to invert for the magnetization within large impact basins using the assumption that the crust is unidirectionally magnetized. We develop a technique based on laboratory thermoremanent magnetization acquisition to quantify the relationship between the strength of the magnetic field at the time the rock cooled and the abundance of metal in the rock. If we assume that the magnetized portion of the impact melt sheet is 1 km thick, we find average abundances of metallic iron ranging from 0.11% to 0.45 wt %, with an uncertainty of a factor of about 3. This abundance is consistent with the metallic iron abundances in sampled lunar impact melts and the abundance of projectile contamination in terrestrial impact melts. These results help constrain the composition of the projectile, the impact process, and the time evolution of the lunar dynamo.

Crater Degradation on Mercury: A Global Perspective

Science.gov (United States)

Kinczyk, M. J.; Byrne, P. K.; Prockter, L. M.; Susorney, H. C. M.; Chapman, C. R.; Barnouin, O. S.

2017-12-01

On geologic timescales, initially fresh craters are subjected to many weathering mechanisms. Whereas water and wind are, or were, effective erosive mechanisms such as on Earth and Mars, micrometeorite bombardment and modification due to subsequent impacts are the dominant processes that degrade craters and crater rays on airless bodies like the Moon and Mercury. Classifying craters based on their state of degradation can help determine the relative ages of landforms proximal to, and crosscut by, these craters. However, this method is most effective when used together with statistical analysis of crater distributions. Pre-MESSENGER degradation classification schemes lacked sufficient detail to be consistently applied to craters of various sizes and morphological types—despite evidence suggesting that the ejecta deposits of large basins persist much longer than those of smaller craters, for instance—yet broad assumptions have been made regarding the correlation of crater class to the planet's time-stratigraphic sequence. Moreover, previous efforts to categorize craters by degradation state have either been restricted to regional study sites or applied only to a subset of crater age or size. As a result, numerous interpretations of crater degradation state persist for Mercury, challenging a complete understanding of this process on the innermost planet. We report on the first global survey of crater degradation on Mercury. By modifying an established 5-class scheme, we have systematically applied a rigorous set of criteria to all craters ≥40 km in diameter on the planet. These criteria include the state and morphology of crater deposits separately (e.g., rim, floor, wall, ejecta) and degradation classes were assigned as the collection of these individual attributes. This approach yields a consistent classification of craters of different sizes. Our results provide the first comprehensive assessment of how craters of various states of degradation are distributed

Using nuclear magnetic resonance and transient electromagnetics to characterise water distribution beneath an ice covered volcanic crater: the case of Sherman Crater Mt. Baker Washington.

Science.gov (United States)

Irons, Trevor P.; Martin, Kathryn; Finn, Carol A.; Bloss, Benjamin; Horton, Robert J.

2014-01-01

Surface and laboratory Nuclear Magnetic Resonance (NMR) measurements combined with transient electromagnetic (TEM) data are powerful tools for subsurface water detection. Surface NMR (sNMR) and TEM soundings, laboratory NMR, complex resistivity, and X-Ray Diffraction (XRD) analysis were all conducted to characterise the distribution of water within Sherman Crater on Mt. Baker, WA. Clay rich rocks, particularly if water saturated, can weaken volcanoes, thereby increasing the potential for catastrophic sector collapses that can lead to far-travelled, destructive debris flows. Detecting the presence and volume of shallow groundwater is critical for evaluating these landslide hazards. The TEM data identified a low resistivity layer (conditions which would allow for sNMR detection of the clay layer are investigated. Using current instrumentation the combined analysis of the TEM and sNMR data allow for valuable characterisation of the groundwater system in the crater. The sNMR is able to reduce the uncertainty of the TEM in regards to the presence of a bulk water layer, a valuable piece of information in hazard assessment.

Petrologic and geochemical characterization of the Bullfrog Member of the Crater Flat Tuff: outcrop samples used in waste package experiments

International Nuclear Information System (INIS)

Knauss, K.G.

1983-09-01

In support of the Waste Package Task within the Nevada Nuclear Waste Storage Investigation (NNWSI), experiments on hydrothermal rock/water interaction, corrosion, thermomechanics, and geochemical modeling calculations are being conducted. All of these activities require characterization of the initial bulk composition, mineralogy, and individual phase geochemistry of the potential repository host rock. This report summarizes the characterization done on samples of the Bullfrog Member of the Crater Flat Tuff (Tcfb) used for Waste Package experimental programs. 11 references, 17 figures, 3 tables

Two-dimensional computer simulation of hypervelocity impact cratering: some preliminary results for Meteor Crater, Arizona

International Nuclear Information System (INIS)

Bryan, J.B.; Burton, D.E.; Cunningham, M.E.; Lettis, L.A. Jr.

1978-04-01

A computational approach used for subsurface explosion cratering has been extended to hypervelocity impact cratering. Meteor (Barringer) Crater, Arizona, was selected for our first computer simulation because it was the most thoroughly studied. It is also an excellent example of a simple, bowl-shaped crater and is one of the youngest terrestrial impact craters. Shoemaker estimates that the impact occurred about 20,000 to 30,000 years ago [Roddy (1977)]. Initial conditions for this calculation included a meteorite impact velocity of 15 km/s. meteorite mass of 1.57E + 08 kg, with a corresponding kinetic energy of 1.88E + 16 J (4.5 megatons). A two-dimensional Eulerian finite difference code called SOIL was used for this simulation of a cylindrical iron projectile impacting at normal incidence into a limestone target. For this initial calculation a Tillotson equation-of-state description for iron and limestone was used with no shear strength. A color movie based on this calculation was produced using computer-generated graphics. Results obtained for this preliminary calculation of the formation of Meteor Crater, Arizona, are in good agreement with Meteor Crater Measurements

Electrochemistry of lunar rocks

Science.gov (United States)

Lindstrom, D. J.; Haskin, L. A.

1979-01-01

Electrolysis of silicate melts has been shown to be an effective means of producing metals from common silicate materials. No fluxing agents need be added to the melts. From solution in melts of diopside (CaMgSi2O6) composition, the elements Si, Ti, Ni, and Fe have been reduced to their metallic states. Platinum is a satisfactory anode material, but other cathode materials are needed. Electrolysis of compositional analogs of lunar rocks initially produces iron metal at the cathode and oxygen gas at the anode. Utilizing mainly heat and electricity which are readily available from sunlight, direct electrolysis is capable of producing useful metals from common feedstocks without the need for expendable chemicals. This simple process and the products obtained from it deserve further study for use in materials processing in space.

X-ray Diffraction Results from Mars Science Laboratory: Mineralogy of Rocknest at Gale Crater

Science.gov (United States)

Bish, D. L.; Blake, D. F.; Vaniman, D. T.; Chipera, S. J.; Morris, R. V.; Ming, D. W.; Treiman, A. H.; Sarrazin, P.; Morrison, S. M.; Downs, R. T.; Achilles, C. N.; Yen, A. S.; Bristow, T. F.; Crisp, J. A.; Morookian, J. M.; Farmer, J. D.; Rampe, E. B.; Stolper, E. M.; Spanovich, N.; Achilles, Cherie; Agard, Christophe; Verdasca, José Alexandre Alves; Anderson, Robert; Anderson, Ryan; Archer, Doug; Armiens-Aparicio, Carlos; Arvidson, Ray; Atlaskin, Evgeny; Atreya, Sushil; Aubrey, Andrew; Baker, Burt; Baker, Michael; Balic-Zunic, Tonci; Baratoux, David; Baroukh, Julien; Barraclough, Bruce; Bean, Keri; Beegle, Luther; Behar, Alberto; Bell, James; Bender, Steve; Benna, Mehdi; Bentz, Jennifer; Berger, Gilles; Berger, Jeff; Berman, Daniel; Bish, David; Blake, David F.; Avalos, Juan J. Blanco; Blaney, Diana; Blank, Jen; Blau, Hannah; Bleacher, Lora; Boehm, Eckart; Botta, Oliver; Böttcher, Stephan; Boucher, Thomas; Bower, Hannah; Boyd, Nick; Boynton, Bill; Breves, Elly; Bridges, John; Bridges, Nathan; Brinckerhoff, William; Brinza, David; Bristow, Thomas; Brunet, Claude; Brunner, Anna; Brunner, Will; Buch, Arnaud; Bullock, Mark; Burmeister, Sönke; Cabane, Michel; Calef, Fred; Cameron, James; Campbell, John "Iain"; Cantor, Bruce; Caplinger, Michael; Rodríguez, Javier Caride; Carmosino, Marco; Blázquez, Isaías Carrasco; Charpentier, Antoine; Chipera, Steve; Choi, David; Clark, Benton; Clegg, Sam; Cleghorn, Timothy; Cloutis, Ed; Cody, George; Coll, Patrice; Conrad, Pamela; Coscia, David; Cousin, Agnès; Cremers, David; Crisp, Joy; Cros, Alain; Cucinotta, Frank; d'Uston, Claude; Davis, Scott; Day, Mackenzie "Kenzie"; Juarez, Manuel de la Torre; DeFlores, Lauren; DeLapp, Dorothea; DeMarines, Julia; DesMarais, David; Dietrich, William; Dingler, Robert; Donny, Christophe; Downs, Bob; Drake, Darrell; Dromart, Gilles; Dupont, Audrey; Duston, Brian; Dworkin, Jason; Dyar, M. Darby; Edgar, Lauren; Edgett, Kenneth; Edwards, Christopher; Edwards, Laurence; Ehlmann, Bethany; Ehresmann, Bent; Eigenbrode, Jen; Elliott, Beverley; Elliott, Harvey; Ewing, Ryan; Fabre, Cécile; Fairén, Alberto; Farley, Ken; Farmer, Jack; Fassett, Caleb; Favot, Laurent; Fay, Donald; Fedosov, Fedor; Feldman, Jason; Feldman, Sabrina; Fisk, Marty; Fitzgibbon, Mike; Flesch, Greg; Floyd, Melissa; Flückiger, Lorenzo; Forni, Olivier; Fraeman, Abby; Francis, Raymond; François, Pascaline; Franz, Heather; Freissinet, Caroline; French, Katherine Louise; Frydenvang, Jens; Gaboriaud, Alain; Gailhanou, Marc; Garvin, James; Gasnault, Olivier; Geffroy, Claude; Gellert, Ralf; Genzer, Maria; Glavin, Daniel; Godber, Austin; Goesmann, Fred; Goetz, Walter; Golovin, Dmitry; Gómez, Felipe Gómez; Gómez-Elvira, Javier; Gondet, Brigitte; Gordon, Suzanne; Gorevan, Stephen; Grant, John; Griffes, Jennifer; Grinspoon, David; Grotzinger, John; Guillemot, Philippe; Guo, Jingnan; Gupta, Sanjeev; Guzewich, Scott; Haberle, Robert; Halleaux, Douglas; Hallet, Bernard; Hamilton, Vicky; Hardgrove, Craig; Harker, David; Harpold, Daniel; Harri, Ari-Matti; Harshman, Karl; Hassler, Donald; Haukka, Harri; Hayes, Alex; Herkenhoff, Ken; Herrera, Paul; Hettrich, Sebastian; Heydari, Ezat; Hipkin, Victoria; Hoehler, Tori; Hollingsworth, Jeff; Hudgins, Judy; Huntress, Wesley; Hurowitz, Joel; Hviid, Stubbe; Iagnemma, Karl; Indyk, Steve; Israël, Guy; Jackson, Ryan; Jacob, Samantha; Jakosky, Bruce; Jensen, Elsa; Jensen, Jaqueline Kløvgaard; Johnson, Jeffrey; Johnson, Micah; Johnstone, Steve; Jones, Andrea; Jones, John; Joseph, Jonathan; Jun, Insoo; Kah, Linda; Kahanpää, Henrik; Kahre, Melinda; Karpushkina, Natalya; Kasprzak, Wayne; Kauhanen, Janne; Keely, Leslie; Kemppinen, Osku; Keymeulen, Didier; Kim, Myung-Hee; Kinch, Kjartan; King, Penny; Kirkland, Laurel; Kocurek, Gary; Koefoed, Asmus; Köhler, Jan; Kortmann, Onno; Kozyrev, Alexander; Krezoski, Jill; Krysak, Daniel; Kuzmin, Ruslan; Lacour, Jean Luc; Lafaille, Vivian; Langevin, Yves; Lanza, Nina; Lasue, Jeremie; Le Mouélic, Stéphane; Lee, Ella Mae; Lee, Qiu-Mei; Lees, David; Lefavor, Matthew; Lemmon, Mark; Malvitte, Alain Lepinette; Leshin, Laurie; Léveillé, Richard; Lewin-Carpintier, Éric; Lewis, Kevin; Li, Shuai; Lipkaman, Leslie; Little, Cynthia; Litvak, Maxim; Lorigny, Eric; Lugmair, Guenter; Lundberg, Angela; Lyness, Eric; Madsen, Morten; Mahaffy, Paul; Maki, Justin; Malakhov, Alexey; Malespin, Charles; Malin, Michael; Mangold, Nicolas; Manhes, Gérard; Manning, Heidi; Marchand, Geneviève; Jiménez, Mercedes Marín; García, César Martín; Martin, Dave; Martin, Mildred; Martínez-Frías, Jesús; Martín-Soler, Javier; Martín-Torres, F. Javier; Mauchien, Patrick; Maurice, Sylvestre; McAdam, Amy; McCartney, Elaina; McConnochie, Timothy; McCullough, Emily; McEwan, Ian; McKay, Christopher; McLennan, Scott; McNair, Sean; Melikechi, Noureddine; Meslin, Pierre-Yves; Meyer, Michael; Mezzacappa, Alissa; Miller, Hayden; Miller, Kristen; Milliken, Ralph; Ming, Douglas; Minitti, Michelle; Mischna, Michael; Mitrofanov, Igor; Moersch, Jeff; Mokrousov, Maxim; Jurado, Antonio Molina; Moores, John; Mora-Sotomayor, Luis; Morookian, John Michael; Morris, Richard; Morrison, Shaunna; Mueller-Mellin, Reinhold; Muller, Jan-Peter; Caro, Guillermo Muñoz; Nachon, Marion; López, Sara Navarro; Navarro-González, Rafael; Nealson, Kenneth; Nefian, Ara; Nelson, Tony; Newcombe, Megan; Newman, Claire; Newsom, Horton; Nikiforov, Sergey; Niles, Paul; Nixon, Brian; Dobrea, Eldar Noe; Nolan, Thomas; Oehler, Dorothy; Ollila, Ann; Olson, Timothy; Owen, Tobias; Hernández, Miguel Ángel de Pablo; Paillet, Alexis; Pallier, Etienne; Palucis, Marisa; Parker, Timothy; Parot, Yann; Patel, Kiran; Paton, Mark; Paulsen, Gale; Pavlov, Alex; Pavri, Betina; Peinado-González, Verónica; Pepin, Robert; Peret, Laurent; Perez, Rene; Perrett, Glynis; Peterson, Joe; Pilorget, Cedric; Pinet, Patrick; Pla-García, Jorge; Plante, Ianik; Poitrasson, Franck; Polkko, Jouni; Popa, Radu; Posiolova, Liliya; Posner, Arik; Pradler, Irina; Prats, Benito; Prokhorov, Vasily; Purdy, Sharon Wilson; Raaen, Eric; Radziemski, Leon; Rafkin, Scot; Ramos, Miguel; Rampe, Elizabeth; Raulin, François; Ravine, Michael; Reitz, Günther; Rennó, Nilton; Rice, Melissa; Richardson, Mark; Robert, François; Robertson, Kevin; Manfredi, José Antonio Rodriguez; Romeral-Planelló, Julio J.; Rowland, Scott; Rubin, David; Saccoccio, Muriel; Salamon, Andrew; Sandoval, Jennifer; Sanin, Anton; Fuentes, Sara Alejandra Sans; Saper, Lee; Sarrazin, Philippe; Sautter, Violaine; Savijärvi, Hannu; Schieber, Juergen; Schmidt, Mariek; Schmidt, Walter; Scholes, Daniel "Dan"; Schoppers, Marcel; Schröder, Susanne; Schwenzer, Susanne; Martinez, Eduardo Sebastian; Sengstacken, Aaron; Shterts, Ruslan; Siebach, Kirsten; Siili, Tero; Simmonds, Jeff; Sirven, Jean-Baptiste; Slavney, Susie; Sletten, Ronald; Smith, Michael; Sánchez, Pablo Sobrón; Spanovich, Nicole; Spray, John; Squyres, Steven; Stack, Katie; Stalport, Fabien; Steele, Andrew; Stein, Thomas; Stern, Jennifer; Stewart, Noel; Stipp, Susan Louise Svane; Stoiber, Kevin; Stolper, Ed; Sucharski, Bob; Sullivan, Rob; Summons, Roger; Sumner, Dawn; Sun, Vivian; Supulver, Kimberley; Sutter, Brad; Szopa, Cyril; Tan, Florence; Tate, Christopher; Teinturier, Samuel; ten Kate, Inge; Thomas, Peter; Thompson, Lucy; Tokar, Robert; Toplis, Mike; Redondo, Josefina Torres; Trainer, Melissa; Treiman, Allan; Tretyakov, Vladislav; Urqui-O'Callaghan, Roser; Van Beek, Jason; Van Beek, Tessa; VanBommel, Scott; Vaniman, David; Varenikov, Alexey; Vasavada, Ashwin; Vasconcelos, Paulo; Vicenzi, Edward; Vostrukhin, Andrey; Voytek, Mary; Wadhwa, Meenakshi; Ward, Jennifer; Webster, Chris; Weigle, Eddie; Wellington, Danika; Westall, Frances; Wiens, Roger Craig; Wilhelm, Mary Beth; Williams, Amy; Williams, Joshua; Williams, Rebecca; Williams, Richard B. "Mouser"; Wilson, Mike; Wimmer-Schweingruber, Robert; Wolff, Mike; Wong, Mike; Wray, James; Wu, Megan; Yana, Charles; Yen, Albert; Yingst, Aileen; Zeitlin, Cary; Zimdar, Robert; Mier, María-Paz Zorzano

2013-09-01

The Mars Science Laboratory rover Curiosity scooped samples of soil from the Rocknest aeolian bedform in Gale crater. Analysis of the soil with the Chemistry and Mineralogy (CheMin) x-ray diffraction (XRD) instrument revealed plagioclase (~An57), forsteritic olivine (~Fo62), augite, and pigeonite, with minor K-feldspar, magnetite, quartz, anhydrite, hematite, and ilmenite. The minor phases are present at, or near, detection limits. The soil also contains 27 ± 14 weight percent x-ray amorphous material, likely containing multiple Fe3+- and volatile-bearing phases, including possibly a substance resembling hisingerite. The crystalline component is similar to the normative mineralogy of certain basaltic rocks from Gusev crater on Mars and of martian basaltic meteorites. The amorphous component is similar to that found on Earth in places such as soils on the Mauna Kea volcano, Hawaii.

Alumina+Silica+/-Germanium Alteration in Smectite-Bearing Marathon Valley, Endeavour Crater Rim, Mars

Science.gov (United States)

Mittlefehldt, D. W.; Gellert, R.; Van Bommel, S.; Arvidson, R. E.; Clark, B. C.; Ming, D. W.; Schroeder, C.; Yen, A. S.; Fox, V. K.; Farrand, W. H.;

Dynamics of upper mantle rocks decompression melting above hot spots under continental plates

Science.gov (United States)

Perepechko, Yury; Sorokin, Konstantin; Sharapov, Victor

2014-05-01

Numeric 2D simulation of the decompression melting above the hot spots (HS) was accomplished under the following conditions: initial temperature within crust mantle section was postulated; thickness of the metasomatized lithospheric mantle is determined by the mantle rheology and position of upper asthenosphere boundary; upper and lower boundaries were postulated to be not permeable and the condition for adhesion and the distribution of temperature (1400-2050°C); lateral boundaries imitated infinity of layer. Sizes and distribution of lateral points, their symmetry, and maximum temperature varied between the thermodynamic condition for existences of perovskite - majorite transition and its excess above transition temperature. Problem was solved numerically a cell-vertex finite volume method for thermo hydrodynamic problems. For increasing convergence of iterative process the method of lower relaxation with different value of relaxation parameter for each equation was used. The method of through calculation was used for the increase in the computing rate for the two-layered upper mantle - lithosphere system. Calculated region was selected as 700 x (2100-4900) km. The time step for the study of the asthenosphere dynamics composed 0.15-0.65 Ma. The following factors controlling the sizes and melting degree of the convective upper mantle, are shown: a) the initial temperature distribution along the section of upper mantleb) sizes and the symmetry of HS, c) temperature excess within the HS above the temperature on the upper and lower mantle border TB=1500-2000oC with 5-15% deviation but not exceed 2350oC. It is found, that appearance of decompression melting with HS presence initiate primitive mantle melting at TB > of 1600oC. Initial upper mantle heating influence on asthenolens dimensions with a constant HS size is controlled mainly by decompression melting degree. Thus, with lateral sizes of HS = 400 km the decompression melting appears at TB > 1600oC and HS

Complex explosive volcanic activity on the Moon within Oppenheimer crater, Icarus

Science.gov (United States)

Bennett, Kristen A; Horgan, Briony H N; Gaddis, Lisa R.; Greenhagen, Benjamin T; Allen, Carlton C.; Hayne, Paul O; Bell, James F III; Paige, David A.

2016-01-01

Oppenheimer Crater is a floor-fractured crater located within the South Pole-Aitken basin on the Moon, and exhibits more than a dozen localized pyroclastic deposits associated with the fractures. Localized pyroclastic volcanism on the Moon is thought to form as a result of intermittently explosive Vulcanian eruptions under low effusion rates, in contrast to the higher-effusion rate, Hawaiian-style fire fountaining inferred to form larger regional deposits. We use Lunar Reconnaissance Orbiter Camera images and Diviner Radiometer mid-infrared data, Chandrayaan-1 orbiter Moon Mineralogy Mapper near-infrared spectra, and Clementine orbiter Ultraviolet/Visible camera images to test the hypothesis that the pyroclastic deposits in Oppenheimer crater were emplaced via Vulcanian activity by constraining their composition and mineralogy. Mineralogically, we find that the deposits are variable mixtures of orthopyroxene and minor clinopyroxene sourced from the crater floor, juvenile clinopyroxene, and juvenile iron-rich glass, and that the mineralogy of the pyroclastics varies both across the Oppenheimer deposits as a whole and within individual deposits. We observe similar variability in the inferred iron content of pyroclastic glasses, and note in particular that the northwest deposit, associated with Oppenheimer U crater, contains the most iron-rich volcanic glass thus far identified on the Moon, which could be a useful future resource. We propose that this variability in mineralogy indicates variability in eruption style, and that it cannot be explained by a simple Vulcanian eruption. A Vulcanian eruption should cause significant country rock to be incorporated into the pyroclastic deposit; however, large areas within many of the deposits exhibit spectra consistent with high abundances of juvenile phases and very little floor material. Thus, we propose that at least the most recent portion of these deposits must have erupted via a Strombolian or more continuous fire

Surface Hydrological Processes of Rock Glaciated Basins in the San Juan Mountains, Colorado

Science.gov (United States)

Mateo, E. I.

2017-12-01

Glaciers in the western United States have been examined in terms of their summer meltwater contributions to regional hydrological systems. In the San Juan Mountains of Colorado where glaciers do not and cannot exist due to a rising zero-degree isotherm, rock glaciers take the place of valley glaciers during the summer runoff period. Most of the rock glaciers in Colorado are located on a northerly slope aspect, however, there are multiple in the southwest region of the state that occur on different aspects. This study asked how slope aspect and rising air temperatures influenced the hydrological processes of streams below rock glaciers in the San Juan Mountains during the 2016 summer season. This project focused on three basins, Yankee Boy basin, Blue Lakes basin, and Mill Creek basin, which are adjacent to each other and share a common peak, Gilpin Peak. Findings of this one-season study showed that air temperature significantly influenced stream discharge below each rock glacier. Discharge and air temperature patterns indicate a possible air temperature threshold during late summer when rock glacier melt increased at a greater rate. The results also suggest that slope aspect of rock glacier basins influences stream discharge, but temperature and precipitation are likely larger components of the melt regimes. The continuation of data collection during the 2017 summer season has allowed for more detailed analysis of the relationship between air temperature and rock glacier melt. This continual expansion of the original dataset is crucial for understanding the hydrological processes of surface runoff below rock glaciers.

How old is Autolycus crater?

Science.gov (United States)

Hiesinger, Harald; Pasckert, Jan Henrik; van der Bogert, Carolyn H.; Robinson, Mark S.

2016-04-01

Accurately determining the lunar cratering chronology is prerequisite for deriving absolute model ages (AMAs) across the lunar surface and throughout the Solar System [e.g., 1]. However, the lunar chronology is only constrained by a few data points over the last 1 Ga and there are no calibration data available between 1 and 3 Ga and beyond 3.9 Ga [2]. Rays from Autolycus and Aristillus cross the Apollo 15 landing site and presumably transported material to this location [3]. [4] proposed that at the Apollo 15 landing site about 32% of any exotic material would come from Autolycus crater and 25% would come from Aristillus crater. [5,6] proposed that the 39Ar-40Ar age of 2.1 Ga derived from three petrologically distinct, shocked Apollo 15 KREEP basalt samples, date Autolycus crater. Grier et al. [7] reported that the optical maturity (OMAT) characteristics of these craters are indistinguishable from the background values despite the fact that both craters exhibit rays that were used to infer relatively young, i.e., Copernican ages [8,9]. Thus, both OMAT characteristics and radiometric ages of 2.1 Ga and 1.29 Ga for Autolycus and Aristillus, respectively, suggest that these two craters are not Copernican in age. [10] interpreted newer U-Pb ages of 1.4 and 1.9 Ga from sample 15405 as the formation ages of Aristillus and Autolycus. If Autolycus is indeed the source of the dated exotic material collected at the Apollo 15 landing site, than performing crater size frequency distribution (CSFD) measurements for Autolycus offers the possibility to add a new calibration point to the lunar chronology, particularly in an age range that was previously unconstrained. We used calibrated and map-projected LRO NAC images to perform CSFD measurements within ArcGIS, using CraterTools [11]. CSFDs were then plotted with CraterStats [12], using the production and chronology functions of [13]. We determined ages of 3.72 and 3.85 Ga for the interior (Ai1) and ejecta area Ae3, which we

Experimental simulation of impact cratering on icy satellites

Science.gov (United States)

Greeley, R.; Fink, J. H.; Gault, D. E.; Guest, J. E.

1982-01-01

Cratering processes on icy satellites were simulated in a series of 102 laboratory impact experiments involving a wide range of target materials. For impacts into homogeneous clay slurries with impact energies ranging from five million to ten billion ergs, target yield strengths ranged from 100 to 38 Pa, and apparent viscosities ranged from 8 to 200 Pa s. Bowl-shaped craters, flat-floored craters, central peak craters with high or little relief, and craters with no relief were observed. Crater diameters increased steadily as energies were raised. A similar sequence was seen for experiment in which impact energy was held constant but target viscosity and strength progressively decreases. The experiments suggest that the physical properties of the target media relative to the gravitationally induced stresses determined the final crater morphology. Crater palimpsests could form by prompt collapse of large central peak craters formed in low target strength materials. Ages estimated from crater size-frequency distributions that include these large craters may give values that are too high.

Sliding rocks on Racetrack Playa, Death Valley National Park: first observation of rocks in motion.

Directory of Open Access Journals (Sweden)

Richard D Norris

Full Text Available The engraved trails of rocks on the nearly flat, dry mud surface of Racetrack Playa, Death Valley National Park, have excited speculation about the movement mechanism since the 1940s. Rock movement has been variously attributed to high winds, liquid water, ice, or ice flotation, but has not been previously observed in action. We recorded the first direct scientific observation of rock movements using GPS-instrumented rocks and photography, in conjunction with a weather station and time-lapse cameras. The largest observed rock movement involved > 60 rocks on December 20, 2013 and some instrumented rocks moved up to 224 m between December 2013 and January 2014 in multiple move events. In contrast with previous hypotheses of powerful winds or thick ice floating rocks off the playa surface, the process of rock movement that we have observed occurs when the thin, 3 to 6 mm, "windowpane" ice sheet covering the playa pool begins to melt in late morning sun and breaks up under light winds of -4-5 m/s. Floating ice panels 10 s of meters in size push multiple rocks at low speeds of 2-5 m/min. along trajectories determined by the direction and velocity of the wind as well as that of the water flowing under the ice.

The size distributions of fragments ejected at a given velocity from impact craters

Science.gov (United States)

O'Keefe, John D.; Ahrens, Thomas J.

1987-01-01

The mass distribution of fragments that are ejected at a given velocity for impact craters is modeled to allow extrapolation of laboratory, field, and numerical results to large scale planetary events. The model is semi-empirical in nature and is derived from: (1) numerical calculations of cratering and the resultant mass versus ejection velocity, (2) observed ejecta blanket particle size distributions, (3) an empirical relationship between maximum ejecta fragment size and crater diameter, (4) measurements and theory of maximum ejecta size versus ejecta velocity, and (5) an assumption on the functional form for the distribution of fragments ejected at a given velocity. This model implies that for planetary impacts into competent rock, the distribution of fragments ejected at a given velocity is broad, e.g., 68 percent of the mass of the ejecta at a given velocity contains fragments having a mass less than 0.1 times a mass of the largest fragment moving at that velocity. The broad distribution suggests that in impact processes, additional comminution of ejecta occurs after the upward initial shock has passed in the process of the ejecta velocity vector rotating from an initially downward orientation. This additional comminution produces the broader size distribution in impact ejecta as compared to that obtained in simple brittle failure experiments.

Elemental geochemistry of sedimentary rocks at Yellowknife Bay, Gale crater, Mars

NARCIS (Netherlands)

McLennan, S.M.; Anderson, R.B.; Bell III, J.F.; Bridges, J.C.; Calef III, F.; Campbell, J.L.; Clark, B.C.; Clegg, S.; Conrad, P.; Cousin, A.; Des Marais, D.J.; Dromart, G.; Dyar, M.D.; Edgar, L.A.; Ehlmann, B.L.; Fabre, C.; Forni, O.; Gasnault, O.; Gellert, R.; Gordon, S.; Grant, J.A.; Grotzinger, J.P.; Gupta, S.; Herkenhoff, K.E.; Hurowitz, J.A.; King, P.L.; Mouélic, S.L.; Leshin, L.A.; Léveillé, R.; Lewis, K.W.; Mangold, N.; Maurice, S.; Ming, D.W.; Morris, R.V.; Nachon, M.; Newsom, H.E.; Ollila, A.M.; Perrett, G.M.; Rice, M.S.; Schmidt, M.E.; Schwenzer, S.P.; Stack, K.; Stolper, E.M.; Sumner, D.Y.; Treiman, A.H.; VanBommel, S.; Vaniman, D.T.; Vasavada, A.; Wiens, R.C.; Yingst, R.A.; ten Kate, Inge Loes|info:eu-repo/dai/nl/292012217

2014-01-01

Sedimentary rocks examined by the Curiosity rover at Yellowknife Bay, Mars, were derived from sources that evolved from an approximately average martian crustal composition to one influenced by alkaline basalts. No evidence of chemical weathering is preserved, indicating arid, possibly cold,

Lunar Bouguer gravity anomalies - Imbrian age craters

Science.gov (United States)

Dvorak, J.; Phillips, R. J.

1978-01-01

The Bouguer gravity of mass anomalies associated with four Imbrian age craters, analyzed in the present paper, are found to differ considerably from the values of the mass anomalies associated with some young lunar craters. Of the Imbrian age craters, only Piccolomini exhibits a negative gravity anomaly (i.e., a low density region) which is characteristic of the young craters studied. The Bouguer gravity anomalies are zero for each of the remaining Imbrian age craters. Since, Piccolomini is younger, or at least less modified, than the other Imbrian age craters, it is suggested that the processes responsible for the post-impact modification of the Imbrian age craters may also be responsible for removing the negative mass anomalies initially associated with these features.

SMALL CRATERS AND THEIR DIAGNOSTIC POTENTIAL

Directory of Open Access Journals (Sweden)

R. Bugiolacchi

2017-07-01

Full Text Available I analysed and compared the size-frequency distributions of craters in the Apollo 17 landing region, comprising of six mare terrains with varying morphologies and cratering characteristics, along with three other regions allegedly affected by the same secondary event (Tycho secondary surge. I propose that for the smaller crater sizes (in this work 9–30 m, a] an exponential curve of power −0.18D can approximate Nkm−2 crater densities in a regime of equilibrium, while b] a power function D−3 closely describes the factorised representation of craters by size (1 m. The saturation level within the Central Area suggests that c] either the modelled rates of crater erosion on the Moon should be revised, or that the Tycho event occurred much earlier in time than the current estimate. We propose that d] the size-frequency distribution of small secondary craters may bear the signature (in terms of size-frequency distribution of debris/surge of the source impact and that this observation should be tested further.

LU60645GT and MA132843GT Catalogues of Lunar and Martian Impact Craters Developed Using a Crater Shape-based Interpolation Crater Detection Algorithm for Topography Data

Science.gov (United States)

Salamuniccar, Goran; Loncaric, Sven; Mazarico, Erwan Matias

2012-01-01

For Mars, 57,633 craters from the manually assembled catalogues and 72,668 additional craters identified using several crater detection algorithms (CDAs) have been merged into the MA130301GT catalogue. By contrast, for the Moon the most complete previous catalogue contains only 14,923 craters. Two recent missions provided higher-quality digital elevation maps (DEMs): SELENE (in 1/16° resolution) and Lunar Reconnaissance Orbiter (we used up to 1/512°). This was the main motivation for work on the new Crater Shape-based interpolation module, which improves previous CDA as follows: (1) it decreases the number of false-detections for the required number of true detections; (2) it improves detection capabilities for very small craters; and (3) it provides more accurate automated measurements of craters' properties. The results are: (1) LU60645GT, which is currently the most complete (up to D>=8 km) catalogue of Lunar craters; and (2) MA132843GT catalogue of Martian craters complete up to D>=2 km, which is the extension of the previous MA130301GT catalogue. As previously achieved for Mars, LU60645GT provides all properties that were provided by the previous Lunar catalogues, plus: (1) correlation between morphological descriptors from used catalogues; (2) correlation between manually assigned attributes and automated measurements; (3) average errors and their standard deviations for manually and automatically assigned attributes such as position coordinates, diameter, depth/diameter ratio, etc; and (4) a review of positional accuracy of used datasets. Additionally, surface dating could potentially be improved with the exhaustiveness of this new catalogue. The accompanying results are: (1) the possibility of comparing a large number of Lunar and Martian craters, of e.g. depth/diameter ratio and 2D profiles; (2) utilisation of a method for re-projection of datasets and catalogues, which is very useful for craters that are very close to poles; and (3) the extension of the

Fluvial to Lacustrine Facies Transitions in Gale Crater, Mars

Science.gov (United States)

Sumner, Dawn Y.; Williams, Rebecca M. E.; Schieber, Juergen; Palucis, Marisa C.; Oehler, Dorothy Z.; Mangold, Nicolas; Kah, Linda C.; Gupta, Sanjeev; Grotzinger, John P.; Grant, John A., III;

Transformations to granular zircon revealed: Twinning, reidite, and ZrO2 in shocked zircon from Meteor Crater (Arizona, USA)

Science.gov (United States)

Cavosie, Aaron; Timms, Nicholas E.; Erickson, Timmons M.; Hagerty, Justin J.; Hörz, Friedrich

2016-01-01

Granular zircon in impact environments has long been recognized but remains poorly understood due to lack of experimental data to identify mechanisms involved in its genesis. Meteor Crater in Arizona (United States) contains abundant evidence of shock metamorphism, including shocked quartz, the high pressure polymorphs coesite and stishovite, diaplectic SiO2 glass, and lechatelierite (fused SiO2). Here we report the presence of granular zircon, a new shocked mineral discovery at Meteor Crater, that preserve critical orientation evidence of specific transformations that occurred during its formation at extreme impact conditions. The zircon grains occur as aggregates of sub-µm neoblasts in highly shocked Coconino Formation Sandstone (CFS) comprised of lechatelierite. Electron backscatter diffraction shows that each grain consists of multiple domains, some with boundaries disoriented by 65°, a known {112} shock-twin orientation. Other domains have crystallographic c-axes in alignment with {110} of neighboring domains, consistent with the former presence of the high pressure ZrSiO4 polymorph reidite. Additionally, nearly all zircon preserve ZrO2 + SiO2, providing evidence of partial dissociation. The genesis of CFS granular zircon started with detrital zircon that experienced shock-twinning and reidite formation from 20 to 30 GPa, ultimately yielding a phase that retained crystallographic memory; this phase subsequently recrystallized to systematically oriented zircon neoblasts, and in some areas partially dissociated to ZrO2. The lechatelierite matrix, experimentally constrained to form at >2000 °C, provided an ultra high-temperature environment for zircon dissociation (~1670 °C) and neoblast formation. The capacity of granular zircon to preserve a cumulative P-T record has not been recognized previously, and provides a new method for retrieving histories of impact-related mineral transformations in the crust at conditions far beyond which most rocks melt.

Do Hf isotopes in magmatic zircons represent those of their host rocks?

Science.gov (United States)

Wang, Di; Wang, Xiao-Lei; Cai, Yue; Goldstein, Steven L.; Yang, Tao

2018-04-01

Lu-Hf isotopic system in zircon is a powerful and widely used geochemical tracer in studying petrogenesis of magmatic rocks and crustal evolution, assuming that zircon Hf isotopes can represent initial Hf isotopes of their parental whole rock. However, this assumption may not always be valid. Disequilibrium partial melting of continental crust would preferentially melt out non-zircon minerals with high time-integrated Lu/Hf ratios and generate partial melts with Hf isotope compositions that are more radiogenic than those of its magma source. Dissolution experiments (with hotplate, bomb and sintering procedures) of zircon-bearing samples demonstrate this disequilibrium effect where partial dissolution yielded variable and more radiogenic Hf isotope compositions than fully dissolved samples. A case study from the Neoproterozoic Jiuling batholith in southern China shows that about half of the investigated samples show decoupled Hf isotopes between zircons and the bulk rocks. This decoupling could reflect complex and prolonged magmatic processes, such as crustal assimilation, magma mixing, and disequilibrium melting, which are consistent with the wide temperature spectrum from ∼630 °C to ∼900 °C by Ti-in-zircon thermometer. We suggest that magmatic zircons may only record the Hf isotopic composition of their surrounding melt during crystallization and it is uncertain whether their Hf isotopic compositions can represent the primary Hf isotopic compositions of the bulk magmas. In this regard, using zircon Hf isotopic compositions to trace crustal evolution may be biased since most of these could be originally from disequilibrium partial melts.

White Rock

Science.gov (United States)

2002-01-01

(Released 19 April 2002) The Science 'White Rock' is the unofficial name for this unusual landform which was first observed during the Mariner 9 mission in the early 1970's. As later analysis of additional data sets would show, White Rock is neither white nor dense rock. Its apparent brightness arises from the fact that the material surrounding it is so dark. Images from the Mars Global Surveyor MOC camera revealed dark sand dunes surrounding White Rock and on the floor of the troughs within it. Some of these dunes are just apparent in the THEMIS image. Although there was speculation that the material composing White Rock could be salts from an ancient dry lakebed, spectral data from the MGS TES instrument did not support this claim. Instead, the White Rock deposit may be the erosional remnant of a previously more continuous occurrence of air fall sediments, either volcanic ash or windblown dust. The THEMIS image offers new evidence for the idea that the original deposit covered a larger area. Approximately 10 kilometers to the southeast of the main deposit are some tiny knobs of similarly bright material preserved on the floor of a small crater. Given that the eolian erosion of the main White Rock deposit has produced isolated knobs at its edges, it is reasonable to suspect that the more distant outliers are the remnants of a once continuous deposit that stretched at least to this location. The fact that so little remains of the larger deposit suggests that the material is very easily eroded and simply blows away. The Story Fingers of hard, white rock seem to jut out like icy daggers across a moody Martian surface, but appearances can be deceiving. These bright, jagged features are neither white, nor icy, nor even hard and rocky! So what are they, and why are they so different from the surrounding terrain? Scientists know that you can't always trust what your eyes see alone. You have to use other kinds of science instruments to measure things that our eyes can

Mantle melting and melt refertilization beneath the Southwest Indian Ridge: Mineral composition of abyssal peridotites

Science.gov (United States)

Chen, Ling; Zhu, Jihao; Chu, Fengyou; Dong, Yan-hui; Liu, Jiqiang; Li, Zhenggang; Zhu, Zhimin; Tang, Limei

2017-04-01

As one of the slowest spreading ridges of the global ocean ridge system, the Southwest Indian Ridge (SWIR) is characterized by discontinued magmatism. The 53°E segment between the Gallieni fracture zone (FZ) (52°20'E) and the Gazelle FZ (53°30'E) is a typical amagmatic segment (crustal thickness 1cm) Opx, and Mg-rich mineral compositions akin to harzburgite xenoliths that sample old continental lithospheric mantle (Kelemen et al., 1998). Melt refertilization model shows that Group 2 peridotites were affected by an enriched low-degree partial melt from the garnet stability field. These results indicate that depleted mantle which experiences ancient melting event are more sensitive to melt refertilization, thus may reduce the melt flux, leading to extremely thin crust at 53°E segment. This research was granted by the National Basic Research Programme of China (973 programme) (grant No. 2013CB429705) and the Fundamental Research Funds of Second Institute of Oceanography, State Oceanic Administration (JG1603, SZ1507). References: Johnson K T M, Dick H J B, Shimizu N. Melting in the oceanic upper mantle: An ion microprobe study of diopsides in abyssal peridotites[J]. Journal of Geophysical Research, 1990, 95(B3):2661-2678. Kelemen P B, Hart S R, Bernstein S. Silica enrichment in the continental upper mantle via melt/rock reaction[J]. Earth & Planetary Science Letters, 1998, 164(1-2):387-406. Zhou H, Dick H J. Thin crust as evidence for depleted mantle supporting the Marion Rise.[J]. Nature, 2013, 494(7436):195-200.

Pseudotachylitic breccia in mafic and felsic rocks

Science.gov (United States)

Kovaleva, Elizaveta; Huber, Matthew S.

2017-04-01

Impact-produced pseudotachylitic breccia (PTB) is abundant in the core of the Vredefort impact structure and was found in many pre-impact lithologies (e.g., Reimold and Colliston, 1994; Gibson et al., 1997). The mechanisms involved in the process of forming this rock remain highly debated, and various authors have discussed many possible models. We investigate PTB from two different rock types: meta-granite and meta-gabbro and test how lithology controls the development of PTB. We also report on clast transport between different lithologies. In the core of the Vredefort impact structure, meta-granite and meta-gabbro are observed in contact with each other, with an extensive set of PTB veins cutting through both lithologies. Microstructural analyses of the PTB veins in thin sections reveals differences between PTBs in meta-granite and meta-gabbro. In granitic samples, PTB often develops along contacts of material with different physical properties, such as a contact with a migmatite or pegmatite vein. Nucleation sites of PTB have features consistent with ductile deformation and shearing, such as sigmoudal-shaped clasts and dragged edges of the veins. Preferential melting of mafic and hydrous minerals takes place (e.g., Reimold and Colliston, 1994; Gibson et al., 2002). Refractory phases remain in the melt as clasts and form reaction rims. In contrast, PTB in meta-gabbro develop in zones with brittle deformation, and do not exploit existing physical contacts. Cataclastic zones develop along the faults and progressively produce ultracataclasites and melt. Thus, PTB veins in meta-gabbro contain fewer clasts. Clasts usually represent multi-phase fragments of host rock and not specific phases. Such fragments often originate from the material trapped between two parallel or horse-tail faults. The lithological control on the development of PTB does not imply that PTB develops independently in different lithologies. We have observed granitic clasts within PTB veins in meta

Machine cataloging of impact craters on Mars

Science.gov (United States)

Stepinski, Tomasz F.; Mendenhall, Michael P.; Bue, Brian D.

2009-09-01

This study presents an automated system for cataloging impact craters using the MOLA 128 pixels/degree digital elevation model of Mars. Craters are detected by a two-step algorithm that first identifies round and symmetric topographic depressions as crater candidates and then selects craters using a machine-learning technique. The system is robust with respect to surface types; craters are identified with similar accuracy from all different types of martian surfaces without adjusting input parameters. By using a large training set in its final selection step, the system produces virtually no false detections. Finally, the system provides a seamless integration of crater detection with its characterization. Of particular interest is the ability of our algorithm to calculate crater depths. The system is described and its application is demonstrated on eight large sites representing all major types of martian surfaces. An evaluation of its performance and prospects for its utilization for global surveys are given by means of detailed comparison of obtained results to the manually-derived Catalog of Large Martian Impact Craters. We use the results from the test sites to construct local depth-diameter relationships based on a large number of craters. In general, obtained relationships are in agreement with what was inferred on the basis of manual measurements. However, we have found that, in Terra Cimmeria, the depth/diameter ratio has an abrupt decrease at ˜38°S regardless of crater size. If shallowing of craters is attributed to presence of sub-surface ice, a sudden change in its spatial distribution is suggested by our findings.

Areally Extensive Surface Bedrock Exposures on Mars: Many Are Clastic Rocks, Not Lavas

Science.gov (United States)

Rogers, A. Deanne; Warner, Nicholas H.; Golombek, Matthew P.; Head, James W.; Cowart, Justin C.

2018-02-01

Areally extensive exposures of intact olivine/pyroxene-enriched rock, as well as feldspar-enriched rock, are found in isolated locations throughout the Martian highlands. The petrogenetic origin(s) of these rock units are not well understood, but some previous studies favored an effusive volcanic origin partly on the basis of distinctive composition and relatively high thermal inertia. Here we show that the regolith development, crater retention, and morphological characteristics for many of these "bedrock plains" are not consistent with competent lavas and reinterpret the high thermal inertia orbital signatures to represent friable materials that are more easily kept free of comminution products through eolian activity. Candidate origins include pyroclastic rocks, impact-generated materials, or detrital sedimentary rocks. Olivine/pyroxene enrichments in bedrock plains relative to surrounding materials could have potentially formed through deflation and preferential removal of plagioclase.

Nuclear cratering on a digital computer

International Nuclear Information System (INIS)

Terhune, R.W.; Stubbs, T.F.; Cherry, J.T.

1970-01-01

Computer programs based on the artificial viscosity method are applied to developing an understanding of the physics of cratering, with emphasis on cratering by nuclear explosives. Two established codes, SOC (spherical symmetry) and TENSOR (cylindrical symmetry), are used to illustrate the effects of variations in the material properties of various media on the cratering processes, namely shock, spall, and gas acceleration. Water content is found to be the most important material property, followed by strength, porosity, and compressibility. Crater profile calculations are presented for Pre-Gondola Charley (20-ton nitromethane detonation in shale) and Sedan (100-kt nuclear detonation in alluvium). Calculations also are presented for three 1-Mt yields in saturated Divide basalt and 1-Mt yield in dry Buckboard basalt, to show crater geometry as a function of the burial depth for large explosive yields. The calculations show, for megaton-level yields, that gas acceleration is the dominate mechanism in determining crater size and depends in turn on the water content in the medium. (author)

Nuclear cratering on a digital computer

Energy Technology Data Exchange (ETDEWEB)

Terhune, R W; Stubbs, T F; Cherry, J T [Lawrence Radiation Laboratory, University of California, Livermore, CA (United States)

1970-05-01

Computer programs based on the artificial viscosity method are applied to developing an understanding of the physics of cratering, with emphasis on cratering by nuclear explosives. Two established codes, SOC (spherical symmetry) and TENSOR (cylindrical symmetry), are used to illustrate the effects of variations in the material properties of various media on the cratering processes, namely shock, spall, and gas acceleration. Water content is found to be the most important material property, followed by strength, porosity, and compressibility. Crater profile calculations are presented for Pre-Gondola Charley (20-ton nitromethane detonation in shale) and Sedan (100-kt nuclear detonation in alluvium). Calculations also are presented for three 1-Mt yields in saturated Divide basalt and 1-Mt yield in dry Buckboard basalt, to show crater geometry as a function of the burial depth for large explosive yields. The calculations show, for megaton-level yields, that gas acceleration is the dominate mechanism in determining crater size and depends in turn on the water content in the medium. (author)

Pyroclastic Deposits in the Floor-fractured Crater Alphonsus

Science.gov (United States)

Allen, Carlton C.; Donaldson-Hanna, Kerri L.; Pieters, Carle M.; Moriarty, Daniel P.; Greenhagen, Benjamin T.; Bennett, Kristen A.; Kramer, Georgiana Y.; Paige, David A.

2013-01-01

samples, but within the range of analyzed pyroclastic glasses. The NAC images of the pyroclastic vents highlight their bright wall materials. The M3 spectra of the southeastern vent indicate that this bright material is noritic, likely crater floor material exposed by explosive eruption. These observations address the hypothesis that Nubium lavas intruded the fracture network beneath Alphonsus, leading to localized vulcanian-style eruptions. This model implies that the eruption products should be dominated by crystalline basalt fragments similar in elemental composition and mineralogy to mare lavas. The bright noritic material exposed in the vent walls is consistent with explosive eruptions. The estimated FeO abundances for the pyroclastic deposits are too low to be consistent with FeO abundances measured in mare basalts, but are within the range of pyroclastic glass samples. The visible- to near-infrared (VIS-NIR) spectra of the pyroclastic deposits and Nubium soils are significantly different, suggesting that the pyroclastics are unrelated to the mare basalts. The pyroclastic spectra are consistent with Fe-bearing glass plus small amounts of noritic wall rock. Similar glassy materials dominate regional pyroclastic deposits, suggesting a deep source for the pyroclastics observed in Alphonsus.

Frictional melt generated by the 2008 Mw 7.9 Wenchuan earthquake and its faulting mechanisms

Science.gov (United States)

Wang, H.; Li, H.; Si, J.; Sun, Z.; Zhang, L.; He, X.

2017-12-01

Fault-related pseudotachylytes are considered as fossil earthquakes, conveying significant information that provide improved insight into fault behaviors and their mechanical properties. The WFSD project was carried out right after the 2008 Wenchuan earthquake, detailed research was conducted in the drilling cores. 2 mm rigid black layer with fresh slickenlines was observed at 732.6 m in WFSD-1 cores drilled at the southern Yingxiu-Beichuan fault (YBF). Evidence of optical microscopy, FESEM and FIB-TEM show it's frictional melt (pseudotachylyte). In the northern part of YBF, 4 mm fresh melt was found at 1084 m with similar structures in WFSD-4S cores. The melts contain numerous microcracks. Considering that (1) the highly unstable property of the frictional melt (easily be altered or devitrified) under geological conditions; (2) the unfilled microcracks; (3) fresh slickenlines and (4) recent large earthquake in this area, we believe that 2-4 mm melt was produced by the 2008 Wenchuan earthquake. This is the first report of fresh pseudotachylyte with slickenlines in natural fault that generated by modern earthquake. Geochemical analyses show that fault rocks at 732.6 m are enriched in CaO, Fe2O3, FeO, H2O+ and LOI, whereas depleted in SiO2. XRF results show that Ca and Fe are enriched obviously in the 2.5 cm fine-grained fault rocks and Ba enriched in the slip surface. The melt has a higher magnetic susceptibility value, which may due to neoformed magnetite and metallic iron formed in fault frictional melt. Frictional melt visible in both southern and northern part of YBF reveals that frictional melt lubrication played a major role in the Wenchuan earthquake. Instead of vesicles and microlites, numerous randomly oriented microcracks in the melt, exhibiting a quenching texture. The quenching texture suggests the frictional melt was generated under rapid heat-dissipation condition, implying vigorous fluid circulation during the earthquake. We surmise that during

Chemistry and texture of the rocks at Rocknest, Gale Crater: Evidence for sedimentary origin and diagenetic alteration

Science.gov (United States)

Blaney, Diana L.; Wiens, R.C.; Maurice, S.; Clegg, S.M.; Anderson, Ryan; Kah, L.C.; Le Mouélic, S.; Ollila, A.; Bridges, N.; Tokar, R.; Berger, G.; Bridges, J.C.; Cousin, A.; Clark, B.; Dyar, M.D.; King, P.L.; Lanza, N.; Mangold, N.; Meslin, P.-Y.; Newsom, H.; Schroder, S.; Rowland, S.; Johnson, J.; Edgar, L.; Gasnault, O.; Forni, O.; Schmidt, M.; Goetz, W.; Stack, K.; Sumner, D.; Fisk, M.; Madsen, M.B.

2014-01-01

A suite of eight rocks analyzed by the Curiosity Rover while it was stopped at the Rocknest sand ripple shows the greatest chemical divergence of any potentially sedimentary rocks analyzed in the early part of the mission. Relative to average Martian soil and to the stratigraphically lower units encountered as part of the Yellowknife Bay formation, these rocks are significantly depleted in MgO, with a mean of 1.3 wt %, and high in Fe, averaging over 20 wt % FeOT, with values between 15 and 26 wt % FeOT. The variable iron and low magnesium and rock texture make it unlikely that these are igneous rocks. Rock surface textures range from rough to smooth, can be pitted or grooved, and show various degrees of wind erosion. Some rocks display poorly defined layering while others seem to show possible fractures. Narrow vertical voids are present in Rocknest 3, one of the rocks showing the strongest layering. Rocks in the vicinity of Rocknest may have undergone some diagenesis similar to other rocks in the Yellowknife Bay Formation as indicated by the presence of soluble calcium phases. The most reasonable scenario is that fine-grained sediments, potentially a mixture of feldspar-rich rocks from Bradbury Rise and normal Martian soil, were lithified together by an iron-rich cement.

Quantifying Cyclic Thermal Stresses Due to Solar Exposure in Rock Fragments in Gale Crater, Mars

Science.gov (United States)

Hallet, B.; Mackenzie-Helnwein, P.; Sletten, R. S.

2017-12-01

Curiosity and earlier rovers on Mars have revealed in detail rocky landscapes with decaying outcrops, rubble, stone-littered regolith, and bedrock exposures that reflect the weathering processes operating on rock exposed to Mars' cold and hyperarid environment. Evidence from diverse sources points to the importance of thermal stresses driven by cyclic solar exposure in contributing to the mechanical weathering of exposed rock and generation of regolith in various settings on Earth [1,2,3], and even more so on extraterrestrial bodies where large, rapid cyclic temperature variations are frequent (e.g. Mars [4], as well as comets [5], asteroids [6] and other airless bodies [7]). To study these thermal stresses, we use a 3d finite element (FE) model constrained by ground-based surface temperature measurements from Curiosity's Environmental Monitoring Station (REMS). The numerical model couples radiation and conduction with elastic response to determine the temperature and stress fields in individual rocks on the surface of Mars based on rock size and thermo-mechanical properties. We provide specific quantitative results for boulder-size basalt rocks resting on the ground using a realistic thermal forcing that closely matches the REMS temperature observations, and related thermal inertia data. Moreover, we introduce analytical studies showing that these numerical results can readily be generalized. They are quite universal, informing us about thermal stresses due to cyclic solar exposure in general, for rock fragments of different sizes, lithologies, and fracture- thermal- and mechanical-properties. Using Earth-analogue studies to gain insight, we also consider how the shapes, fractures, and surface details of rock fragments imaged by Curiosity likely reflect the importance of rock breakdown due to thermal stresses relative to wind-driven rock erosion and other surface processes on Mars. References:[1] McFadden L et al. (2005) Geol. Soc.Am. Bull. 117(1-2): 161-173 [2

Polygons on Crater Floor

Science.gov (United States)

2003-01-01

MGS MOC Release No. MOC2-357, 11 May 2003This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) picture shows a pattern of polygons on the floor of a northern plains impact crater. These landforms are common on crater floors at high latitudes on Mars. Similar polygons occur in the arctic and antarctic regions of Earth, where they indicate the presence and freeze-thaw cycling of ground ice. Whether the polygons on Mars also indicate water ice in the ground is uncertain. The image is located in a crater at 64.8oN, 292.7oW. Sunlight illuminates the scene from the lower left.

Preliminary Results from Initial Investigations of Ceres' Cratering Record from Dawn Imaging Data

Science.gov (United States)

Schmedemann, Nico; Michael, Gregory; Ivanov, Boris A.; Kneissl, Thomas; Neesemann, Adrian; Hiesinger, Harald; Jaumann, Ralf; Raymond, Carol A.; Russell, Christopher T.

2015-04-01

The highly successful Dawn mission [1] finished data collection at Vesta in 2012 and is now on its way to the dwarf planet Ceres. According to the current Ceres approach timeline of the Dawn mission, the ground resolution of the Dawn FC camera [2] will be about 10 times better than Hubble data [3] at the time of the presentation of this work. This may allow for identification of craters about 15 km in diameter. Initial mapping of sample areas may provide enough information of the cratering record in order to compare it with the theoretical Ceres crater production function we present at the 46th LPSC conference (March 16-20, 2015, The Woodlands, Texas) [4]. Our preliminary crater production function for Ceres is derived from the assumption of an icy crust just below a thin surface layer of dust [5], and a projectile population that is very similar to the one that impacted the Moon [6]. In order to scale the lunar cratering record to Ceres we use the Ivanov scaling laws [7], which allow for crater scaling based on parameters that can be derived from observations. The lunar-like approach gave reasonable good results for the crater production function on the asteroids Vesta, Ida, Lutetia and Gaspra [8]. Since the lunar surface is of basaltic composition, the correct scaling between the different materials is challenging. One crucial parameter is the transition diameter from simple to complex craters. Based on the simple to complex transition diameter on Iapetus, an icy satellite of Saturn, we expect this transition at about 12 km crater size at Ceres. This value may be slightly different due to the different temperatures at Ceres and Iapetus. If the simple to complex transition is observed at much larger diameters, the reason could be a substantial fraction of rock in the shallow subsurface of Ceres. In an ice-rich surface material high relaxation rates may also be expected that could change the shape of the crater production function. A thorough geological mapping

Yucatan Subsurface Stratigraphy from Geophysical Data, Well Logs and Core Analyses in the Chicxulub Impact Crater and Implications for Target Heterogeneities

Science.gov (United States)

Canales, I.; Fucugauchi, J. U.; Perez-Cruz, L. L.; Camargo, A. Z.; Perez-Cruz, G.

2011-12-01

Asymmetries in the geophysical signature of Chicxulub crater are being evaluated to investigate on effects of impact angle and trajectory and pre-existing target structural controls for final crater form. Early studies interpreted asymmetries in the gravity anomaly in the offshore sector to propose oblique either northwest- and northeast-directed trajectories. An oblique impact was correlated to the global ejecta distribution and enhanced environmental disturbance. In contrast, recent studies using marine seismic data and computer modeling have shown that crater asymmetries correlate with pre-existing undulations of the Cretaceous continental shelf, suggesting a structural control of target heterogeneities. Documentation of Yucatan subsurface stratigraphy has been limited by lack of outcrops of pre-Paleogene rocks. The extensive cover of platform carbonate rocks has not been affected by faulting or deformation and with no rivers cutting the carbonates, information comes mainly from the drilling programs and geophysical surveys. Here we revisit the subsurface stratigraphy in the crater area from the well log data and cores retrieved in the drilling projects and marine seismic reflection profiles. Other source of information being exploited comes from the impact breccias, which contain a sampling of disrupted target sequences, including crystalline basement and Mesozoic sediments. We analyze gravity and seismic data from the various exploration surveys, including multiple Pemex profiles in the platform and the Chicxulub experiments. Analyses of well log data and seismic profiles identify contacts for Lower Cretaceous, Cretaceous/Jurassic and K/Pg boundaries. Results show that the Cretaceous continental shelf was shallower on the south and southwest than on the east, with emerged areas in Quintana Roo and Belize. Mesozoic and upper Paleozoic sediments show variable thickness, possibly reflecting the crystalline basement regional structure. Paleozoic and Precambrian

Floor-Fractured Craters through Machine Learning Methods

Science.gov (United States)

Thorey, C.

2015-12-01

Floor-fractured craters are impact craters that have undergone post impact deformations. They are characterized by shallow floors with a plate-like or convex appearance, wide floor moats, and radial, concentric, and polygonal floor-fractures. While the origin of these deformations has long been debated, it is now generally accepted that they are the result of the emplacement of shallow magmatic intrusions below their floor. These craters thus constitute an efficient tool to probe the importance of intrusive magmatism from the lunar surface. The most recent catalog of lunar-floor fractured craters references about 200 of them, mainly located around the lunar maria Herein, we will discuss the possibility of using machine learning algorithms to try to detect new floor-fractured craters on the Moon among the 60000 craters referenced in the most recent catalogs. In particular, we will use the gravity field provided by the Gravity Recovery and Interior Laboratory (GRAIL) mission, and the topographic dataset obtained from the Lunar Orbiter Laser Altimeter (LOLA) instrument to design a set of representative features for each crater. We will then discuss the possibility to design a binary supervised classifier, based on these features, to discriminate between the presence or absence of crater-centered intrusion below a specific crater. First predictions from different classifier in terms of their accuracy and uncertainty will be presented.

Geology of Lofn Crater, Callisto

Science.gov (United States)

Greeley, Ronald; Heiner, Sarah; Klemaszewski, James E.

2001-01-01

Lofn crater is a 180-km-diameter impact structure in the southern cratered plains of Callisto and is among the youngest features seen on the surface. The Lofn area was imaged by the Galileo spacecraft at regional-scale resolutions (875 m/pixel), which enable the general geology to be investigated. The morphology of Lofn crater suggests that (1) it is a class of impact structure intermediate between complex craters and palimpsests or (2) it formed by the impact of a projectile which fragmented before reaching the surface, resulting in a shallow crater (even for Callisto). The asymmetric pattern of the rim and ejecta deposits suggests that the impactor entered at a low angle from the northwest. The albedo and other characteristics of the ejecta deposits from Lofn also provide insight into the properties of the icy lithosphere and subsurface configuration at the time of impact. The "target" for the Lofn impact is inferred to have included layered materials associated with the Adlinda multiring structure northwest of Loh and ejecta deposits from the Heimdall crater area to the southeast. The Lofn impact might have penetrated through these materials into a viscous substrate of ductile ice or possibly liquid water. This interpretation is consistent with models of the current interior of Callisto based on geophysical information obtained from the Galileo spacecraft.

Rainfall as primary driver of discharge and solute export from rock glaciers: The Col d'Olen Rock Glacier in the NW Italian Alps.

Science.gov (United States)

Colombo, Nicola; Gruber, Stephan; Martin, Maria; Malandrino, Mery; Magnani, Andrea; Godone, Danilo; Freppaz, Michele; Fratianni, Simona; Salerno, Franco

2018-10-15

Three hypotheses exist to explain how meteorological variables drive the amount and concentration of solute-enriched water from rock glaciers: (1) Warm periods cause increased subsurface ice melt, which releases solutes; (2) rain periods and the melt of long-lasting snow enhance dilution of rock-glacier outflows; and (3) percolation of rain through rock glaciers facilitates the export of solutes, causing an opposite effect as that described in hypothesis (2). This lack of detailed understanding likely exists because suitable studies of meteorological variables, hydrologic processes and chemical characteristics of water bodies downstream from rock glaciers are unavailable. In this study, a rock-glacier pond in the North-Western Italian Alps was studied on a weekly basis for the ice-free seasons 2014 and 2015 by observing the meteorological variables (air temperature, snowmelt, rainfall) assumed to drive the export of solute-enriched waters from the rock glacier and the hydrochemical response of the pond (water temperature as a proxy of rock-glacier discharge, stable water isotopes, major ions and selected trace elements). An intra-seasonal pattern of increasing solute export associated with higher rock-glacier discharge was found. Specifically, rainfall, after the winter snowpack depletion and prolonged periods of atmospheric temperature above 0 °C, was found to be the primary driver of solute export from the rock glacier during the ice-free season. This occurs likely through the flushing of isotopically- and geochemically-enriched icemelt, causing concomitant increases in the rock-glacier discharge and the solute export (SO 4 2- , Mg 2+ , Ca 2+ , Ni, Mn, Co). Moreover, flushing of microbially-active sediments can cause increases in NO 3 - export. Copyright © 2018 Elsevier B.V. All rights reserved.

Characteristics of ejecta and alluvial deposits at Meteor Crater, Arizona and Odessa Craters, Texas: Results from ground penetrating radar

Science.gov (United States)

Grant, J. A.; Schultz, P. H.

1991-01-01

Previous ground penetrating radar (GRP) studies around 50,000 year old Meteor Crater revealed the potential for rapid, inexpensive, and non-destructive sub-surface investigations for deep reflectors (generally greater than 10 m). New GRP results are summarized focusing the shallow sub-surfaces (1-2 m) around Meteor Crater and the main crater at Odessa. The following subject areas are covered: (1) the thickness, distribution, and nature of the contact between surrounding alluvial deposits and distal ejecta; and (2) stratigraphic relationships between both the ejecta and alluvium derived from both pre and post crater drainages. These results support previous conclusions indicating limited vertical lowering (less than 1 m) of the distal ejecta at Meteor Crater and allow initial assessment of the gradational state if the Odessa craters.

Geochemical characterization of Parana Basin volcanic rocks: petrogenetic implications

International Nuclear Information System (INIS)

Marques, L.S.

1988-01-01

A detailed study of the geochemical characteristics of Parana Basin volcanic rocks is presented. The results are based on the analyses of major and trace elements of 158 samples. Ninety three of these volcanic samples belong to 8 flow sequences from Rio Grande do Sul and Santa Catarina States. The remaining sixty five samples are distributed over the entire basin. In order to study the influence of crustal contamination processes in changing chemical characteristics of the volcanic rocks, 47 samples representative of the crystalline basement of the southern and southeastern Parana Basin were also analysed. Several petrogenetic models were tested to explain the compocional variability of the volcanic rocks, in particular those of southern region. The results obtained sugest an assimilation-fractional crystallization process as viable to explain the differences of both the chemical characteristics and Sr isotope initial ratios observed in basic and intermediate rocks. A model involving melting processes of basic material, trapped at the base of the crust, with composition similar to low and high TiO 2 basalts appears to be a possibility to originate the Palmas and Chapeco acid melts, respectively. The study of ''uncontaminated'' or poorly contaminated low TiO 2 basic rocks from the southern, central and northern regions shows the existence of significant differences in the geochemical charactetistics according to their geographical occurrence. A similar geochemical diversity is also observed in high TiO 2 basalts and Chapeco volcanics. Differences in incompatible element ratios between low and high TiO 2 ''uncontaminated'' or poorly contaminated basalts suggest that they could have been produced by different degrees of melting in a garnet peridotite source. Geochemical and isotopic (Sr and Nd) data also support the view that basalts from northern and southern regions of Parana Basin originated from mantle source with different composition. (author) [pt

Three-dimensional geophysical mapping of shallow water saturated altered rocks at Mount Baker, Washington: Implications for slope stability

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Finn, Carol A.; Deszcz-Pan, Maryla; Ball, Jessica L.; Bloss, Benjamin J.; Minsley, Burke J.

2018-05-01

Water-saturated hydrothermal alteration reduces the strength of volcanic edifices, increasing the potential for catastrophic sector collapses that can lead to far traveled and destructive debris flows. Intense hydrothermal alteration significantly lowers the resistivity and magnetization of volcanic rock and therefore hydrothermally altered rocks can be identified with helicopter electromagnetic and magnetic measurements. Geophysical models constrained by rock properties and geologic mapping show that intensely altered rock is restricted to two small (500 m diameter), >150 m thick regions around Sherman Crater and Dorr Fumarole Field at Mount Baker, Washington. This distribution of alteration contrasts with much thicker and widespread alteration encompassing the summits of Mounts Adams and Rainier prior to the 5600 year old Osceola collapse, which is most likely due to extreme erosion and the limited duration of summit magmatism at Mount Baker. In addition, the models suggest that the upper 300 m of rock contains water which could help to lubricate potential debris flows. Slope stability modeling incorporating the geophysically modeled distribution of alteration and water indicates that the most likely and largest ( 0.1 km3) collapses are from the east side of Sherman Crater. Alteration at Dorr Fumarole Field raises the collapse hazard there, but not significantly because of its lower slope angles. Geochemistry and analogs from other volcanoes suggest a model for the edifice hydrothermal system.

Three-dimensional geophysical mapping of shallow water saturated altered rocks at Mount Baker, Washington: Implications for slope stability

Science.gov (United States)

Finn, Carol A.; Deszcz-Pan, Maria; Ball, Jessica L.; Bloss, Benjamin J.; Minsley, Burke J.

2018-01-01

Water-saturated hydrothermal alteration reduces the strength of volcanic edifices, increasing the potential for catastrophic sector collapses that can lead to far traveled and destructive debris flows. Intense hydrothermal alteration significantly lowers the resistivity and magnetization of volcanic rock and therefore hydrothermally altered rocks can be identified with helicopter electromagnetic and magnetic measurements. Geophysical models constrained by rock properties and geologic mapping show that intensely altered rock is restricted to two small (500 m diameter), >150 m thick regions around Sherman Crater and Dorr Fumarole Field at Mount Baker, Washington. This distribution of alteration contrasts with much thicker and widespread alteration encompassing the summits of Mounts Adams and Rainier prior to the 5600 year old Osceola collapse, which is most likely due to extreme erosion and the limited duration of summit magmatism at Mount Baker. In addition, the models suggest that the upper ~300 m of rock contains water which could help to lubricate potential debris flows. Slope stability modeling incorporating the geophysically modeled distribution of alteration and water indicates that the most likely and largest (~0.1 km3) collapses are from the east side of Sherman Crater. Alteration at Dorr Fumarole Field raises the collapse hazard there, but not significantly because of its lower slope angles. Geochemistry and analogs from other volcanoes suggest a model for the edifice hydrothermal system.

Process parameters, orientation, and functional properties of melt-processed bulk Y-Ba-Cu-O superconductors

International Nuclear Information System (INIS)

Zakharchenko, I.V.; Terryll, K.M.; Rao, K.V.; Balachandran, U.

1995-03-01

This study compared the microstructure, texturing, and functional properties (critical currents) of YBa 2 Cu 3 O 7-x -based bulk pellets that were prepared by the quench-melt-growth-process (QMGP), melt-textured growth (MTG), and conventional solid-state reaction (SSR) approaches. Using two X-ray diffraction (XRD) methods, θ-2θ, and rocking curves, the authors found that the individual grains of two melt-processed pellets exhibited remarkable preferred orientational alignment (best rocking curve width = 3.2 degree). However, the direction of the preferred orientation among the grains was random. Among the three types of bulk materials studied, the QMGP sample was found to have the best J c values, ∼ 4,500 A/cm 2 at 77 K in a field of 2 kG, as determined from SQUID magnetic data

Equilibrium chemical transformations in NaPO3 + NaCl melts

International Nuclear Information System (INIS)

Kovarskaya, E.N.; Rodionov, Yu.I.

1988-01-01

Because of the problems of the burial of solidified radioactive wastes into different geological rock formations, in particular into massives of rock-salt, the state of molten polyphosphate-chloride mixtures (taking into account the chemical character of the interaction of their components) for a prolonged period of time. The equilibrium products of the reaction in the NaPO 3 -NaCl system were studied in melts in air in the composition range of 30-70 mole % NaCl. It was shown that with increase in the NaCl content in the mixtures, the polyphosphate gradually depolymerizes to sodium tri-, di-, and monophosphates, and the composition of the equilibrium melts is dependent only on the ratio between the components in the initial molten mixtures. The time until the equilibrium is attained is shorter, the higher is the experimental temperature

Low-velocity impact cratering experiments in granular slopes

Science.gov (United States)

Hayashi, Kosuke; Sumita, Ikuro

2017-07-01

Low-velocity impact cratering experiments are conducted in sloped granular targets to study the effect of the slope angle θ on the crater shape and its scales. We use two types of granular matter, sand and glass beads, former of which has a larger friction coefficient μs = tanθr , where θr is the angle of repose. Experiments show that as θ increases, the crater becomes shallower and elongated in the direction of the slope. Furthermore the crater floor steepens in the upslope side and a thick rim forms in the downslope side, thus forming an asymmetric profile. High-speed images show that these features are results of ejecta being dispersed farther towards the downslope side and the subsequent avalanche which buries much of the crater floor. Such asymmetric ejecta dispersal can be explained by combining the Z-model and a ballistic model. Using the topographic maps of the craters, we classify crater shape regimes I-III, which transition with increasing θ : a full-rim crater (I), a broken-rim crater (II), and a depression (III). The critical θ for the regime transitions are larger for sand compared to glass beads, but collapse to close values when we use a normalized slope θ^ = tanθ / tanθr . Similarly we derive θ^-dependences of the scaled crater depth, length, width and their ratios which collapse the results for different targets and impact energies. We compare the crater profiles formed in our experiments with deep craters on asteroid Vesta and find that some of the scaled profiles nearly overlap and many have similar depth / length ratios. This suggests that these Vestan craters may also have formed in the gravity regime and that the formation process can be approximated by a granular flow with a similar effective friction coefficient.

Juvenile helium in ancient rocks: II. U-He,K-Ar, Sm-Nd, and Rb-Sr systematics in the Monche Pluton. 3He/4He ratios frozen in uranium-free ultramafic rocks

International Nuclear Information System (INIS)

Tolstikhin, I.N.; Dokuchaeva, V.S.; Kamensky, I.L.; Amelin, Yu.V.

1992-01-01

The important geodynamic parameter, the 3 He/ 4 He ratio in rocks and fluids of the continental crust, is generally decreasing from the mantle values (≅ 10 -5 ) to the radiogenic ratio (≅ 10 -8 ) on the time scale of about 1 Ga or less. However, the ratios, observed in some ancient rocks and minerals, are much higher than the radiogenic value due to a preferential retention of trapped He, when compared with radiogenic helium and/or a low U/ 3 He ratio in a sample. The distribution of He, Ar, Nd, and Sr isotopes, K, Rb, Sm, and U in ultrabasic rocks, in rock-forming minerals, in ores from the 2.49 Ga Monche Pluton, and in basic rocks of the Main Range (the Kola Peninsula) enables one to distinguish sources of the rocks and trapped fluids and outline some peculiarities of petrogenetic and fluid processes. The initial values of var-epsilon Nd (T) = -0.9 ± 0.5 , 87 Sr/ 86 Sr(T) = 0.7021 ± 0.0002, for the 2.49 Ga Monche Pluton are rather similar to these for other layered intrusions of the Baltic Shield. They differ considerably from the model values for the depleted 2.5 Ga old mantle. The observed and rather different sources of 3 He and 4 He as well as the considerable constancy of their ratio in different minerals, separated from both the ultramafic rocks and gabbros, implies: (1) an intensive process of mixing between mantle and crustal components: a melt convection in the chamber may have occurred; (2) the two types of rocks could originate by crystallization differentiation of one and the same melt. Practically all 3 He and 4 He are concentrated in secondary amphiboles; hence the fluid which stimulated the metamorphic process was probably released from the ultramafite-bearing melt

Origin of Fe-rich lherzolites and wehrlites from Tok, SE Siberia by reactive melt percolation in refractory mantle peridotites

Science.gov (United States)

Ionov, Dmitri A.; Chanefo, Ingrid; Bodinier, Jean-Louis

2005-10-01

Lherzolite-wehrlite (LW) series xenoliths from the quaternary Tok volcanic field in the southeastern Siberian craton are distinguished from the more common lherzolite-harzburgite (LH) series by (a) low Mg numbers (0.84-0.89) at high modal olivine (66-84%) and (b) widespread replacement of orthopyroxene (0-12%) and spinel by clinopyroxene (7-22%). The LW series peridotites are typically enriched in Ca, Fe, Mn and Ti, and depleted in Si, Ni and Cr relative to refractory LH series rocks (Mg number ≥0.89), which are metasomatised partial melting residues. Numerical modelling of Fe-Mg solid/liquid exchange during melt percolation demonstrates that LW series rocks can form by reaction of host refractory peridotites with evolved (Mg numbers 0.6-0.7), silica-undersaturated silicate melts at high melt/rock ratios, which replace orthopyroxene with clinopyroxene and decrease Mg numbers. This process is most likely related to underplating and fractionation of basaltic magma in the shallow mantle, which also produced olivine-clinopyroxene cumulates found among the Tok xenoliths.

Paleo-environmental Setting of the Murray Formation of Aeolis Mons, Gale Crater, Mars, as Explored by the Curiosity Rover

Science.gov (United States)

Lewis, K. W.; Fedo, C.; Grotzinger, J. P.; Gupta, S.; Stein, N.; Rivera-Hernandez, F.; Watkins, J. A.; Banham, S.; Edgett, K. S.; Minitti, M. E.; Schieber, J.; Edgar, L. A.; Siebach, K. L.; Stack, K.; Newsom, H. E.; House, C. H.; Sumner, D. Y.; Vasavada, A. R.

2017-12-01

Since landing, the Mars Science Laboratory Curiosity rover climbed 300 meters in elevation from the floor of north Gale crater up the lower northwest flank of Aeolis Mons ("Mount Sharp"). Nearly 200 meters of this ascent was accomplished in the 1.5 years alone, as the rover was driven up-section through the sedimentary rocks of the informally designated "Murray" formation. This unit comprises a large fraction of the lower strata of Mt. Sharp along the rover traverse. Our exploration of the Murray formation reveals a diverse suite of fine-grained facies. Grain sizes range from finer grains than can be resolved by the MAHLI imager (particles bearing Vera Rubin Ridge, continues to reveal the complex and long-lived depositional history of the Gale crater basin.

Moon - 'Ghost' craters formed during Mare filling.

Science.gov (United States)

Cruikshank, D. P.; Hartmann, W. K.; Wood, C. A.

1973-01-01

This paper discusses formation of 'pathological' cases of crater morphology due to interaction of craters with molten lavas. Terrestrial observations of such a process are discussed. In lunar maria, a number of small impact craters (D less than 10 km) may have been covered by thin layers of fluid lavas, or formed in molten lava. Some specific lunar examples are discussed, including unusual shallow rings resembling experimental craters deformed by isostatic filling.

Exploration of microbial diversity and community structure of Lonar Lake: the only hypersaline meteorite crater lake within basalt rock

Directory of Open Access Journals (Sweden)

Dhiraj ePaul

2016-01-01

Full Text Available Lonar Lake is a hypersaline and hyperalkaline soda lake and the only meteorite impact crater in the world created in the basalt rocks. Although culture-dependent studies have been reported, the comprehensive understanding of microbial community composition and structure of Lonar Lake remain obscure. In the present study, microbial community structure associated with Lonar Lake sediment and water samples was investigated using high throughput sequencing. Microbial diversity analysis revealed the existence of diverse, yet near consistent community composition. The predominance of bacterial phyla Proteobacteria (30% followed by Actinobacteria (24%, Firmicutes (11% and Cyanobacteria (5% was observed. Bacterial phylum Bacteroidetes (1.12%, BD1-5 (0.5%, Nitrospirae (0.41% and Verrucomicrobia (0.28% were detected as relatively minor populations in Lonar Lake ecosystem. Within Proteobacteria, Gammaproteobacteria represented the most abundant population (21-47% among all the sediments and as a minor population in water samples. Bacterial members Proteobacteria and Firmicutes were present significantly higher (p≥0.05 in sediment samples, whereas members of Actinobacteria, Candidate_division_TM7 and Cyanobacteria (p≥0.05 were significantly abundant in water samples. It was noted that compared to other hypersaline soda lakes, Lonar Lake samples formed one distinct cluster, suggesting a different microbial community composition and structure. The present study reports for the first time the different composition of indigenous microbial communities between the sediment and water samples of Lonar Lake. Having better insight of community structure of this Lake ecosystem could be useful in understanding the microbial role in the geochemical cycle for future functional exploration of the unique hypersaline Lonar Lake.

UNAM Scientific Drilling Program of Chicxulub Impact Structure-Evidence for a 300 kilometer crater diameter

Science.gov (United States)

Urrutia-Fucugauchi, J.; Marin, L.; Trejo-Garcia, A.

As part of the UNAM drilling program at the Chicxulub structure, two 700 m deep continuously cored boreholes were completed between April and July, 1995. The Peto UNAM-6 and Tekax UNAM-7 drilling sites are ˜150 km and 125 km, respectively, SSE of Chicxulub Puerto, near the crater's center. Core samples from both sites show a sequence of post-crater carbonates on top of a thick impact breccia pile covering the disturbed Mesozoic platform rocks. At UNAM-7, two impact breccia units were encountered: (1) an upper breccia, mean magnetic susceptibility is high (˜55 × 10-6 SI units), indicating a large component of silicate basement has been incorporated into this breccia, and (2) an evaporite-rich, low susceptibility impact breccia similar in character to the evaporite-rich breccias observed at the PEMEX drill sites further out. The upper breccia was encountered at ˜226 m below the surface and is ˜125 m thick; the lower breccia is immediately subjacent and is >240 m thick. This two-breccia sequence is typical of the suevite-Bunte breccia sequence found within other well preserved impact craters. The suevitic upper unit is not present at UNAM-6. Instead, a >240 m thick evaporite-rich breccia unit, similar to the lower breccia at UNAM-7, was encountered at a depth of ˜280 m. The absence of an upper breccia equivalent at UNAM-6 suggests some portion of the breccia sequence has been removed by erosion. This is consistent with interpretations that place the high-standing crater rim at 130-150 km from the center. Consequently, the stratigraphic observations and magnetic susceptibiity records on the upper and lower breccias (depth and thickness) support a ˜300 km diameter crater model.

Investigations of Ceres's Craters with Straightened Rim

Science.gov (United States)

Frigeri, A.; De Sanctis, M. C.; Ammannito, E.; Raponi, A.; Formisano, M.; Ciarniello, M.; Magni, G.; Combe, J. P.; Marchi, S.; Raymond, C. A.; Schwartz, S. J.

2017-12-01

Dwarf planet Ceres hosts some geological features that are unique in the solar system because its composition, rich in aqueously-altered silicates, is usually found on full-size planets, whereas its mean radius is smaller than most natural satellites in the solar system. For example, the local high-albedo, carbonate-rich areas or faculaeare specific to Ceres; also, the absence of big impact crater structures is key to understand the overall mechanical behaviour of the Cerean crust. After the first findings of water ice occurring in the shadowed areas of craters on Ceres by the NASA/Dawn mission (1, 2), we analyzed the morphology of craters looking for features similar to the ones where the water ice composition has been detected analyzing the data from the VIR spectrometer (3). These craters fall outside of the family of polygonal craters which are mainly related to regional or global scale tectonics (4). We analyzed the morphology on the base of the global mosaic, the digital terrain model derived by using the stereo photogrammetry method and the single data frames of the Framing Camera. Our investigation started from crater Juling, which is characterized by a portion of the rim which forms a straight segment instead of a portion of a circle. This linear crater wall is also steep enough that it forms a cliff that is in the shadowed area in all images acquired by Dawn. Very smooth and bright deposits lay at the foot of this crater-wall cliff. Then, we identified several other craters, relatively fresh, with radius of 2 to 10 kilometers, showing one or two sectors of the crater-rim being truncated by a mass-wasting process, probably a rockfall. Our first analysis show that in the selected craters, the truncated sectors are always in the north-eastern sector of the rim for the craters in the southern hemisphere. Conversely, the craters on the northern hemisphere exhibit a truncated rim in their south-eastern sector. Although a more detailed analysis is mandatory

A Hydrous Seismogenic Fault Rock Indicating A Coupled Lubrication Mechanism

Science.gov (United States)

Okamoto, S.; Kimura, G.; Takizawa, S.; Yamaguchi, H.

2005-12-01

In the seismogenic subduction zone, the predominant mechanisms have been considered to be fluid induced weakening mechanisms without frictional melting because the subduction zone is fundamentally quite hydrous under low temperature conditions. However, recently geological evidence of frictional melting has been increasingly reported from several ancient accretionary prisms uplifted from seismogenic depths of subduction zones (Ikesawa et al., 2003; Austrheim and Andersen, 2004; Rowe et al., 2004; Kitamura et al., 2005) but relationship between conflicting mechanisms; e.g. thermal pressurization of fluid and frictional melting is still unclear. We found a new exposure of pseudotachylyte from a fossilized out-of-sequence thrust (OOST) , Nobeoka thrust in the accretionary complex, Kyushu, southwest Japan. Hanging-wall and foot-wall are experienced heating up to maximum temperature of about 320/deg and about 250/deg, respectively. Hanging-wall rocks of the thrust are composed of shales and sandstones deformed plastically. Foot-wall rocks are composed of shale matrix melange with sandstone and basaltic blocks deformed in a brittle fashion (Kondo et al, 2005). The psudotachylyte was found from one of the subsidiary faults in the hanging wall at about 10 m above the fault core of the Nobeoka thrust. The fault is about 1mm in width, and planer rupture surface. The fault maintains only one-time slip event because several slip surfaces and overlapped slip textures are not identified. The fault shows three deformation stages: The first is plastic deformation of phyllitic host rocks; the second is asymmetric cracking formed especially in the foot-wall of the fault. The cracks are filled by implosion breccia hosted by fine carbonate minerals; the third is frictional melting producing pseudotachylyte. Implosion breccia with cracking suggests that thermal pressurization of fluid and hydro-fracturing proceeded frictional melting.

Partial reactive crystallization of variable CO2-bearing siliceous MORB-eclogite-derived melt in fertile peridotite and genesis of alkalic basalts with signatures of crustal recycling

Science.gov (United States)

Mallik, A.; Dasgupta, R.

2013-12-01

The presence of heterogeneity in the form of recycled altered oceanic crust (MORB-eclogite) has been proposed in the source of HIMU ocean island basalts (OIBs) [1]. Partial melts of recycled oceanic crust, however, are siliceous and Mg-poor and thus do not resemble the major element compositions of alkalic OIBs that are silica-poor and Mg-rich. In an upwelling heterogenous mantle, MORB-eclogite undergoes melting deeper than volatile-free peridotite, hence, andesitic partial melt derived from eclogite will react with subsolidus peridotite. We have examined the effect of such a melt-rock reaction under volatile-free conditions at 1375 °C, 3 GPa by varying the melt-rock ratio from 8 to 50 wt.% [2]. We concluded that the reacted melts reproduce certain major element characteristics of oceanic basanites, but not nephelinites. Also, the melt-rock reaction produces olivine and garnet-bearing websteritic residue. Because presence of CO2 has been invoked in the source of many HIMU ocean islands, the effect of CO2 on such a melt-rock reaction needs to be evaluated. Accordingly, we performed reaction experiments on mixtures of 25% and 33% CO2-bearing andesitic partial melt and peridotite at 1375 °C, 3 GPa by varying the dissolved CO2 content of the reacting melts from 1 to 5 wt.% (bulk CO2 from 0.25 to 1.6 wt.%) [3, this study]. Owing to melt-rock reaction, with increasing CO2 in the bulk mixture, (a) modes of olivine and cpx decrease while melt, opx and garnet increase, (b) reacted melts evolve to greater degree of Si-undersaturation (from andesite through basanite to nephelinite), (c) enhanced crystallization of garnet take place with higher CO2 in the melt, reducing alumina content of the reacted melts, and (d) CaO and MgO content of the reacted melts increase, without affecting FeO* and Na2O contents (indicating greater propensity of Ca2+ and Mg2+ over Fe2+ and Na+ to enter silicate melt as carbonate). For a given melt-MgO, the CO2-bearing reacted melts are a better

Asteroid families from cratering: Detection and models

Science.gov (United States)

Milani, A.; Cellino, A.; Knežević, Z.; Novaković, B.; Spoto, F.; Paolicchi, P.

2014-07-01

A new asteroid families classification, more efficient in the inclusion of smaller family members, shows how relevant the cratering impacts are on large asteroids. These do not disrupt the target, but just form families with the ejecta from large craters. Of the 12 largest asteroids, 8 have cratering families: number (2), (4), (5), (10), (87), (15), (3), and (31). At least another 7 cratering families can be identified. Of the cratering families identified so far, 7 have >1000 members. This imposes a remarkable change from the focus on fragmentation families of previous classifications. Such a large dataset of asteroids believed to be crater ejecta opens a new challenge: to model the crater and family forming event(s) generating them. The first problem is to identify which cratering families, found by the similarity of proper elements, can be formed at once, with a single collision. We have identified as a likely outcome of multiple collisions the families of (4), (10), (15), and (20). Of the ejecta generated by cratering, only a fraction reaches the escape velocity from the surviving parent body. The distribution of velocities at infinity, giving to the resulting family an initial position and shape in the proper elements space, is highly asymmetric with respect to the parent body. This shape is deformed by the Yarkovsky effect and by the interaction with resonances. All the largest asteroids have been subjected to large cratering events, thus the lack of a family needs to be interpreted. The most interesting case is (1) Ceres, which is not the parent body of the nearby family of (93). Two possible interpretations of the low family forming efficiency are based on either the composition of Ceres with a significant fraction of ice, protected by a thin crust, or with the larger escape velocity of ~500 m/s.

The Global Contribution of Secondary Craters on the Icy Satellites

Science.gov (United States)

Hoogenboom, T.; Johnson, K. E.; Schenk, P.

2014-12-01

At present, surface ages of bodies in the Outer Solar System are determined only from crater size-frequency distributions (a method dependent on an understanding of the projectile populations responsible for impact craters in these planetary systems). To derive accurate ages using impact craters, the impactor population must be understood. Impact craters in the Outer Solar System can be primary, secondary or sesquinary. The contribution of secondary craters to the overall population has recently become a "topic of interest." Our objective is to better understand the contribution of dispersed secondary craters to the small crater populations, and ultimately that of small comets to the projectile flux on icy satellites in general. We measure the diameters of obvious secondary craters (determined by e.g. irregular crater shape, small size, clustering) formed by all primary craters on Ganymede for which we have sufficiently high resolution data to map secondary craters. Primary craters mapped range from approximately 40 km to 210 km. Image resolution ranges from 45 to 440 m/pixel. Bright terrain on Ganymede is our primary focus. These resurfaced terrains have relatively low crater densities and serve as a basis for characterizing secondary populations as a function of primary size on an icy body for the first time. Although focusing on Ganymede, we also investigate secondary crater size, frequency, distribution, and formation, as well as secondary crater chain formation on icy satellites throughout the Saturnian and Jovian systems principally Rhea. We compare our results to similar studies of secondary cratering on the Moon and Mercury. Using Galileo and Voyager data, we have identified approximately 3,400 secondary craters on Ganymede. In some cases, we measured crater density as a function of distance from a primary crater. Because of the limitations of the Galileo data, it is necessary to extrapolate from small data sets to the global population of secondary craters

Impact cratering experiments in Bingham materials and the morphology of craters on Mars and Ganymede

Science.gov (United States)

Fink, J. H.; Greeley, R.; Gault, D. E.

1982-01-01

Results from a series of laboratory impacts into clay slurry targets are compared with photographs of impact craters on Mars and Ganymede. The interior and ejecta lobe morphology of rampart-type craters, as well as the progression of crater forms seen with increasing diameter on both Mars and Ganymede, are equalitatively explained by a model for impact into Bingham materials. For increasing impact energies and constant target rheology, laboratory craters exhibit a morphologic progression from bowl-shaped forms that are typical of dry planetary surfaces to craters with ejecta flow lobes and decreasing interior relief, characteristic of more volatile-rich planets. A similar sequence is seen for uniform impact energy in slurries of decreasing yield strength. The planetary progressions are explained by assuming that volatile-rich or icy planetary surfaces behave locally in the same way as Bingham materials and produce ejecta slurries with yield strenghs and viscosities comparable to terrestrial debris flows. Hypothetical impact into Mars and Ganymede are compared, and it is concluded that less ejecta would be produced on Ganymede owing to its lower gravitational acceleration, surface temperature, and density of surface materials.

Technical problems and future cratering experiments

Energy Technology Data Exchange (ETDEWEB)

Knox, J B [Lawrence Radiation Laboratory, Livermore, CA (United States)

1969-07-01

This paper reviews some of the key technical problems that remain to be solved in nuclear cratering technology. These include: (1) developing a broader understanding of the effects that material properties and water content of the earth materials around the shot have on cratering behavior, (2) extending the experimental investigation of retarc formation to include intermediate yields and various materials, and (3) improving our ability to predict the escape of radioactive material to the atmosphere to form the cloud source responsible for fallout. The formation processes of ejecta craters, retarcs, and subsidence craters are described in the light of our present understanding, and the major gaps in our understanding are indicated. Methods of calculating crater and retarc formation are discussed, with particular reference to the input information needed. Methods for calculating fallout are presented, and their shortcomings are discussed. A preliminary analysis of the safety factors associated with the presently proposed nuclear excavation concepts is presented. (author)

Technical problems and future cratering experiments

International Nuclear Information System (INIS)

Knox, J.B.

1969-01-01

This paper reviews some of the key technical problems that remain to be solved in nuclear cratering technology. These include: (1) developing a broader understanding of the effects that material properties and water content of the earth materials around the shot have on cratering behavior, (2) extending the experimental investigation of retarc formation to include intermediate yields and various materials, and (3) improving our ability to predict the escape of radioactive material to the atmosphere to form the cloud source responsible for fallout. The formation processes of ejecta craters, retarcs, and subsidence craters are described in the light of our present understanding, and the major gaps in our understanding are indicated. Methods of calculating crater and retarc formation are discussed, with particular reference to the input information needed. Methods for calculating fallout are presented, and their shortcomings are discussed. A preliminary analysis of the safety factors associated with the presently proposed nuclear excavation concepts is presented. (author)

Analytical results, geology, and sample locality map of mercury-sulfur-gypsum mineralization at Crater, Inyo County, California

Science.gov (United States)

Erickson, M.S.; Marsh, S.P.; Roemer, T.A.

1984-01-01

The Crater mercury-su l fur-gypsum ~ineral ized area is located in east-central California along the crest of the Last Chance Range, west of the north end of Death Valley (fig. 1). The area is in the northwest quarter of the Last Chance Range 15-minute quadrangle and occupies the area between 117 39 and 117 45 longitude and 37 10 and 37 15 latitudP.. The area studied lies between 5000 ( 1525 m) and 6000 ( 1830 m) feet above sea level. Relief isgenerally moderate but can be extreme in some places, as at Hanging Rock Canyon (plate 1). The climate is arid, and there are no active streams in the area. The range fronts east and west of the area are precipitous and incised by many steep canyons, whereas the range crest has relatively low relief. The old abandoned town and mine site of Crater 1 ie in this area of low relief. Access to the Crater area is by paved and dirt roads from Big Pine to the west or from the north end of the Death Valley National Monument to the southeast.

Cratering statistics on asteroids: Methods and perspectives

Science.gov (United States)

Chapman, C.

2014-07-01

Crater size-frequency distributions (SFDs) on the surfaces of solid-surfaced bodies in the solar system have provided valuable insights about planetary surface processes and about impactor populations since the first spacecraft images were obtained in the 1960s. They can be used to determine relative age differences between surficial units, to obtain absolute model ages if the impactor flux and scaling laws are understood, to assess various endogenic planetary or asteroidal processes that degrade craters or resurface units, as well as assess changes in impactor populations across the solar system and/or with time. The first asteroid SFDs were measured from Galileo images of Gaspra and Ida (cf., Chapman 2002). Despite the superficial simplicity of these studies, they are fraught with many difficulties, including confusion by secondary and/or endogenic cratering and poorly understood aspects of varying target properties (including regoliths, ejecta blankets, and nearly-zero-g rubble piles), widely varying attributes of impactors, and a host of methodological problems including recognizability of degraded craters, which is affected by illumination angle and by the ''personal equations'' of analysts. Indeed, controlled studies (Robbins et al. 2014) demonstrate crater-density differences of a factor of two or more between experienced crater counters. These inherent difficulties have been especially apparent in divergent results for Vesta from different members of the Dawn Science Team (cf. Russell et al. 2013). Indeed, they have been exacerbated by misuse of a widely available tool (Craterstats: hrscview.fu- berlin.de/craterstats.html), which incorrectly computes error bars for proper interpretation of cumulative SFDs, resulting in derived model ages specified to three significant figures and interpretations of statistically insignificant kinks. They are further exacerbated, and for other small-body crater SFDs analyzed by the Berlin group, by stubbornly adopting

Constraints on the Parental Melts of Enriched Shergottites from Image Analysis and High Pressure Experiments

Science.gov (United States)

Collinet, M.; Medard, E.; Devouard, B.; Peslier, A.

2012-01-01

Martian basalts can be classified in at least two geochemically different families: enriched and depleted shergottites. Enriched shergottites are characterized by higher incompatible element concentrations and initial Sr-87/Sr-86 and lower initial Nd-143/Nd-144 and Hf-176/Hf-177 than depleted shergottites [e.g. 1, 2]. It is now generally admitted that shergottites result from the melting of at least two distinct mantle reservoirs [e.g. 2, 3]. Some of the olivine-phyric shergottites (either depleted or enriched), the most magnesian Martian basalts, could represent primitive melts, which are of considerable interest to constrain mantle sources. Two depleted olivine-phyric shergottites, Yamato (Y) 980459 and Northwest Africa (NWA) 5789, are in equilibrium with their most magnesian olivine (Fig. 1) and their bulk rock compositions are inferred to represent primitive melts [4, 5]. Larkman Nunatak (LAR) 06319 [3, 6, 7] and NWA 1068 [8], the most magnesian enriched basalts, have bulk Mg# that are too high to be in equilibrium with their olivine megacryst cores. Parental melt compositions have been estimated by subtracting the most magnesian olivine from the bulk rock composition, assuming that olivine megacrysts have partially accumulated [3, 9]. However, because this technique does not account for the actual petrography of these meteorites, we used image analysis to study these rocks history, reconstruct their parent magma and understand the nature of olivine megacrysts.

Usability of small impact craters on small surface areas in crater count dating: Analysing examples from the Harmakhis Vallis outflow channel, Mars

Science.gov (United States)

Kukkonen, S.; Kostama, V.-P.

2018-05-01

The availability of very high-resolution images has made it possible to extend crater size-frequency distribution studies to small, deca/hectometer-scale craters. This has enabled the dating of small and young surface units, as well as recent, short-time and small-scale geologic processes that have occurred on the units. Usually, however, the higher the spatial resolution of space images is, the smaller area is covered by the images. Thus the use of single, very high-resolution images in crater count age determination may be debatable if the images do not cover the studied region entirely. Here we compare the crater count results for the floor of the Harmakhis Vallis outflow channel obtained from the images of the ConTeXt camera (CTX) and High Resolution Imaging Science Experiment (HiRISE) aboard the Mars Reconnaissance Orbiter (MRO). The CTX images enable crater counts for entire units on the Harmakhis Vallis main valley, whereas the coverage of the higher-resolution HiRISE images is limited and thus the images can only be used to date small parts of the units. Our case study shows that the crater count data based on small impact craters and small surface areas mainly correspond with the crater count data based on larger craters and more extensive counting areas on the same unit. If differences between the results were founded, they could usually be explained by the regional geology. Usually, these differences appeared when at least one cratering model age is missing from either of the crater datasets. On the other hand, we found only a few cases in which the cratering model ages were completely different. We conclude that the crater counts using small impact craters on small counting areas provide useful information about the geological processes which have modified the surface. However, it is important to remember that all the crater counts results obtained from a specific counting area always primarily represent the results from the counting area-not the whole

The Carancas meteorite impact crater, Peru: Geologic surveying and modeling of crater formation and atmospheric passage

Science.gov (United States)

Kenkmann, T.; Artemieva, N. A.; Wünnemann, K.; Poelchau, M. H.; Elbeshausen, D.; Núñez Del Prado, H.

2009-08-01

The recent Carancas meteorite impact event caused a worldwide sensation. An H4-5 chondrite struck the Earth south of Lake Titicaca in Peru on September 15, 2007, and formed a crater 14.2 m across. It is the smallest, youngest, and one of two eye-witnessed impact crater events on Earth. The impact violated the hitherto existing view that stony meteorites below a size of 100 m undergo major disruption and deceleration during their passage through the atmosphere and are not capable of producing craters. Fragmentation occurs if the strength of the meteoroid is less than the aerodynamic stresses that occur in flight. The small fragments that result from a breakup rain down at terminal velocity and are not capable of producing impact craters. The Carancas cratering event, however, demonstrates that meter-sized stony meteoroids indeed can survive the atmospheric passage under specific circumstances. We present results of a detailed geologic survey of the crater and its ejecta. To constrain the possible range of impact parameters we carried out numerical models of crater formation with the iSALE hydrocode in two and three dimensions. Depending on the strength properties of the target, the impact energies range between approximately 100-1000 MJ (0.024- 0.24 t TNT). By modeling the atmospheric traverse we demonstrate that low cosmic velocities (12- 14 kms-1) and shallow entry angles (<20°) are prerequisites to keep aerodynamic stresses low (<10 MPa) and thus to prevent fragmentation of stony meteoroids with standard strength properties. This scenario results in a strong meteoroid deceleration, a deflection of the trajectory to a steeper impact angle (40-60°), and an impact velocity of 350-600 ms-1, which is insufficient to produce a shock wave and significant shock effects in target minerals. Aerodynamic and crater modeling are consistent with field data and our microscopic inspection. However, these data are in conflict with trajectories inferred from the analysis of

Preliminary Geological Map of the Peace Vallis Fan Integrated with In Situ Mosaics From the Curiosity Rover, Gale Crater, Mars

Science.gov (United States)

Sumner, D. Y.; Palucis, M.; Dietrich, B.; Calef, F.; Stack, K. M.; Ehlmann, B.; Bridges, J.; Dromart, J.; Eigenbrode, J.; Farmer, J.;

Exploring the KT source crater: Progress and future prospects

Science.gov (United States)

Sharpton, Virgil L.

It has been 15 years since an iridium-enriched clay layer at the Cretaceous-Tertiary (KT) boundary was discovered, providing the first hard evidence linking the most recent mass extinction event to a comet or asteroid strike [Alvarez et al., 1980]. Now it is widely accepted that the site of this collision is on the Yucatan platform, centered near Progreso, Mexico. The 200-300-km-wide crater lies buried beneath 300-1000 m of limestone laid down in the intervening 65 million years, and few clues of its presence remain at the surface, save an arcuate arrangement of water-filled sinkholes centered approximately on the structure (Figure 1). Yet prominent circular anomalies in gravity and magnetic anomaly maps gained the interest of Petroleos Mexicanos (Pemex), and in the early 1950s they began an exploration campaign that included deep drilling to recover samples of the subsurface rocks. The buried feature became known as the Chicxulub structure. Pemex drilling continued throughout the early 1970s and by that time, three wells near the center had recovered silicate rocks with igneous textures, initially mistaken for volcanic rocks. Other wells, located between 130 km and 210 km from ground zero recovered breccia deposits hundreds of meters thick that showed evidence of catastropic or explosive conditions. By 1980, Antonio Camargo, a geophysicist at Pemex, felt the evidence pointed to impact, although a volcanic origin for the Chicxulub structure could not be ruled out.

Gale Crater - Why are We There and What do We Hope to Learn?

Science.gov (United States)

Allen, Carlton C.

2012-01-01

The Mars Science Laboratory Rover Curiosity is commencing a two-year investigation of Gale crater and Mt. Sharp, the craters prominent central mound. Gale is a 155 km, late Noachian/early Hesperian impact crater located near the dichotomy boundary separating the southern highlands from the northern plains. The central mound is composed of layered sedimentary rock, with upper and lower mound units separated by a prominent erosional unconformity. The lower mound is of particular interest, as it contains secondary minerals indicative of a striking shift from water-rich to water-poor conditions on early Mars. A key unknown in the history of Gale is the relationship between the sedimentary units in the mound and sedimentary sequences in the surrounding region. We employed orbital remote sensing data to determine if areas within a 1,000 km radius of Gale match the characteristics of sedimentary units in Mt. Sharp. Regions of interest were defined based on: the mound s inferred age, altitude range, and THEMIS nighttime brightness (a proxy for thermal inertia). Using orbital CTX, MOC and HiRISE images we examined all areas within our regions of interest for analogous geomorphic units in the same altitude ranges as the corresponding units in Mt. Sharp. The results are consistent with the hypothesis that sedimentary units in both the upper and lower sections of the Gale mound are related to nearby regional units located along the dichotomy boundary. This relationship supports an inferred geologic history that includes several episodes of widespread sedimentary deposition and erosion in the martian mid-latitudes. In this model Mt. Sharp is the remnant of regional sedimentary deposits that partially or completely filled the crater, became lithified, and were subsequently deeply eroded. Key questions that will be addressed by Curiosity include the compositions of the sediments, the modes of deposition, the mechanisms of lithification, and the nature of the erosion.

Mineralogy, petrology and whole-rock chemistry data compilation for selected samples of Yucca Mountain tuffs

International Nuclear Information System (INIS)

Connolly, J.R.

1991-12-01

Petrologic, bulk chemical, and mineralogic data are presented for 49 samples of tuffaceous rocks from core holes USW G-1 and UE-25a number-sign 1 at Yucca Mountain, Nevada. Included, in descending stratigraphic order, are 11 samples from the Topopah Spring Member of the Paintbrush Tuff, 12 samples from the Tuffaceous Beds of Calico Hills, 3 samples from the Prow Pass Member of the Crater Flat Tuff, 20 samples from the Bullfrog Member of the Crater Flat Tuff and 3 samples from the Tram Member of the Crater Flat Tuff. The suite of samples contains a wide variety of petrologic types, including zeolitized, glassy, and devitrified tuffs. Data vary considerably between groups of samples, and include thin section descriptions (some with modal analyses for which uncertainties are estimated), electron microprobe analyses of mineral phases and matrix, mineral identifications by X-ray diffraction, and major element analyses with uncertainty estimates

Fresh Impact Crater and Rays in Tharsis

Science.gov (United States)

2002-01-01

The Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) Extended Mission has included dozens of opportunities to point the spacecraft directly at features of interest so that pictures of things not seen during the earlier Mapping Mission can be obtained. The example shown here is a small meteorite impact crater in northern Tharsis near 17.2oN, 113.8oW. Viking Orbiter images from the late 1970's showed at this location what appeared to be a dark patch with dark rays emanating from a brighter center. The MOC team surmised that the dark rays may be indicating the location of afresh crater formed by impact sometime in the past few centuries (since dark ray are quickly covered by dust falling out of the martian atmosphere). All through MOC's Mapping Mission in 1999 and 2000, attempts were made to image the crater as predictions indicated that the spacecraft would pass over the site, but the crater was never seen. Finally, in June 2001, Extended Mission operations allowed the MOC team to point the spacecraft (and hence the camera, which is fixed to the spacecraft)directly at the center of the dark rays, where we expected to find the crater.The picture on the left (above, A) is a mosaic of three MOC high resolution images and one much lower-resolution Viking image. From left to right, the images used in the mosaic are: Viking 1 516A55, MOC E05-01904, MOCM21-00272, and MOC M08-03697. Image E05-01904 is the one taken in June 2001 by pointing the spacecraft. It captured the impact crater responsible for the rays. A close-up of the crater, which is only 130 meters (427 ft)across, is shown on the right (above, B). This crater is only one-tenth the size of the famous Meteor Crater in northern Arizona.The June 2001 MOC image reveals many surprises about this feature. For one, the crater is not located at the center of the bright area from which the dark rays radiate. The rays point to the center of this bright area, not the crater. Further, the dark material ejected from the

Excess europium content in Precambrian sedimentary rocks and continental evolution

Science.gov (United States)

Jakes, P.; Taylor, S. R.

1974-01-01

It is proposed that the europium excess in Precambrian sedimentary rocks, relative to those of younger age, is derived from volcanic rocks of ancient island arcs, which were the source materials for the sediments. Precambrian sedimentary rocks and present-day volcanic rocks of island arcs have similar REE patterns, total REE abundances, and excess Eu, relative to the North American shale composite. The present upper crustal REE pattern, as exemplified by that of sediments, is depleted in Eu, relative to chondrites. This depletion is considered to be a consequence of development of a granodioritic upper crust by partial melting in the lower crust, which selectively retains europium.

Contribution of early impact events to metal-silicate separation, thermal annealing, and volatile redistribution: Evidence in the Pułtusk H chondrite

Science.gov (United States)

Krzesińska, Agata M.

2017-11-01

Three-dimensional X-ray tomographic reconstructions and petrologic studies reveal voluminous accumulations of metal in Pułtusk H chondrite. At the contact of these accumulations, the chondritic rock is enriched in troilite. The rock contains plagioclase-rich bands, with textures suggesting crystallization from melt. Unusually large phosphates are associated with the plagioclase and consist of assemblages of merrillite, and fluorapatite and chlorapatite. The metal accumulations were formed by impact melting, rapid segregation of metal-sulfide melt and the incorporation of this melt into the fractured crater basement. The impact most likely occurred in the early evolution of the H chondrite parent body, when post-impact heat overlapped with radiogenic heat. This enabled slow cooling and separation of the metallic melt into metal-rich and sulfide-rich fractions. This led to recrystallization of chondritic rock in contact with the metal accumulations and the crystallization of shock melts. Phosphorus was liberated from the metal and subsumed by the silicate shock melt, owing to oxidative conditions upon slow cooling. The melt was also a host for volatiles. Upon further cooling, phosphorus reacted with silicates leading to the formation of merrillite, while volatiles partitioned into the residual halogen-rich, dry fluid. In the late stages, the fluid altered merrillite to patchy Cl/F-apatite. The above sequence of alterations demonstrates that impact during the early evolution of chondritic parent bodies might have contributed to local metal segregation and silicate melting. In addition, postshock conditions supported secondary processes: compositional/textural equilibration, redistribution of volatiles, and fluid alterations.

Determining long-term regional erosion rates using impact craters

Science.gov (United States)

Hergarten, Stefan; Kenkmann, Thomas

2015-04-01

More than 300,000 impact craters have been found on Mars, while the surface of Moon's highlands is even saturated with craters. In contrast, only 184 impact craters have been confirmed on Earth so far with only 125 of them exposed at the surface. The spatial distribution of these impact craters is highly inhomogeneous. Beside the large variation in the age of the crust, consumption of craters by erosion and burial by sediments are the main actors being responsible for the quite small and inhomogeneous crater record. In this study we present a novel approach to infer long-term average erosion rates at regional scales from the terrestrial crater inventory. The basic idea behind this approach is a dynamic equilibrium between the production of new craters and their consumption by erosion. It is assumed that each crater remains detectable until the total erosion after the impact exceeds a characteristic depth depending on the crater's diameter. Combining this model with the terrestrial crater production rate, i.e., the number of craters per unit area and time as a function of their diameter, allows for a prediction of the expected number of craters in a given region as a function of the erosion rate. Using the real crater inventory, this relationship can be inverted to determine the regional long-term erosion rate and its statistical uncertainty. A limitation by the finite age of the crust can also be taken into account. Applying the method to the Colorado Plateau and the Deccan Traps, both being regions with a distinct geological history, yields erosion rates in excellent agreement with those obtained by other, more laborious methods. However, these rates are formally exposed to large statistical uncertainties due to the small number of impact craters. As higher crater densities are related to lower erosion rates, smaller statistical errors can be expected when large regions in old parts of the crust are considered. Very low long-term erosion rates of less than 4

Investigation of Secondary Craters in the Saturnian System

Science.gov (United States)

Hoogenboom, T.; Schenk, P.; White, O. L.

2012-03-01

To derive accurate ages using impact craters, the impact source must be determined. We investigate secondary crater size, frequency, distribution, formation, and crater chain formation on icy satellites throughout the Jupiter and Saturn systems.

Age Distribution of Lunar Impact-Melt Rocks in Apollo Drive-Tube 68001/2

Science.gov (United States)

Curran, N. M.; Bower, D. M.; Frasl, B.; Cohen, B. A.

2018-01-01

Apollo 16 double-drive tube 68001 /68002 provides impact and volcanic materials along a depth of approximately 60 cm in five compositional distinct units. 68001 /2 offers the potential to study distinct populations of impact melts with depth to understand how 'gardening' affects these samples. We will use unbiased major-element chemistry, mineralogy, and age to understand the impact history of Apollo 16 landing site. The study demonstrates the techniques that landed missions require to identify lithologies of interest (e.g., impact melts).

Trace element partitioning in rock forming minerals of co-genetic, subduction-related alkaline and tholeiitic mafic rocks in the Ural Mountains, Russia

Science.gov (United States)

Krause, J.; Brügmann, G. E.; Pushkarev, E. V.

2009-04-01

The partitioning of trace elements between rock forming minerals in igneous rocks is largely controlled by physical and chemical parameters e.g. temperature, pressure and chemical composition of the minerals and the coexisting melt. In the present study partition coefficients for REE between hornblende, orthopyroxene, feldspars, apatite and clinopyroxene in a suite of co-genetic alkaline and tholeiitic mafic rocks from the Ural Mountains (Russia) were calculated. The results give insights to the influence of the chemical composition of the parental melt on the partitioning behaviour of the REE. Nepheline-bearing, alkaline melanogabbros (tilaites) are assumed to represent the most fractionated products of the melt that formed the ultramafic cumulates in zoned mafic-ultramafic complexes in the Ural Mountains. Co-genetic with the latter is a suite of olivine gabbros, gabbronorites and hornblende gabbros formed from a tholeiitic parental melt. Negative anomalies for the HFSE along with low Nb and Ta contents and a positive Sr anomaly indicate a subduction related origin of all parental melts. The nepheline gabbros consist predominantly of coarse-grained clinopyroxene phenocrysts in a matrix of fine grained clinopyroxene, olivine, plagioclase, K-feldspar and nepheline with accessory apatite. The tholeiitic gabbros have equigranular to porphyric textures with phenocrysts of olivine, pyroxene and hornblende in a plagioclase rich matrix with olivine hornblende, pyroxene and accessory apatite. Element concentrations of adjacent matrix grains and rims of phenochrysts were measured with LA-ICPMS. The distribution of REE between hornblende and clinopyroxene in the tholeiitic rocks is similar for most of the elements (DHbl•Cpx(La-Tm) = 2.7-2.8, decreasing to 2.6 and 2.4 for Yb and Lu, respectively). These values are about two times higher than published data (e.g. Ionov et al. 1997). Partition coefficients for orthopyroxene/clinopyroxene systematically decrease from the HREE

Volatile and Organic Compositions of Sedimentary Rocks in Yellowknife Bay, Gale Crater, Mars

Science.gov (United States)

Ming, D. W.; Archer, P. D.; Glavin, D. P.; Eigenbrode, J. L.; Franz, H. B.; Sutter, B.; Brunner, A. E.; Stern, J. C.; Freissinet, C.; McAdam, A. C.; Mahaffy, P. R.; Cabane, M.; Coll, P.; Campbell, J. L.; Atreya, S. K.; Niles, P. B.; Bell, J. F.; Bish, D. L.; Brinckerhoff, W. B.; Buch, A.; Conrad, P. G.; Des Marais, D. J.; Ehlmann, B. L.; Fairén, A. G.; Farley, K.; Flesch, G. J.; Francois, P.; Gellert, R.; Grant, J. A.; Grotzinger, J. P.; Gupta, S.; Herkenhoff, K. E.; Hurowitz, J. A.; Leshin, L. A.; Lewis, K. W.; McLennan, S. M.; Miller, K. E.; Moersch, J.; Morris, R. V.; Navarro-González, R.; Pavlov, A. A.; Perrett, G. M.; Pradler, I.; Squyres, S. W.; Summons, R. E.; Steele, A.; Stolper, E. M.; Sumner, D. Y.; Szopa, C.; Teinturier, S.; Trainer, M. G.; Treiman, A. H.; Vaniman, D. T.; Vasavada, A. R.; Webster, C. R.; Wray, J. J.; Yingst, R. A.; Kemppinen, Osku; Bridges, Nathan; Johnson, Jeffrey R.; Minitti, Michelle; Cremers, David; Edgar, Lauren; Farmer, Jack; Godber, Austin; Wadhwa, Meenakshi; Wellington, Danika; McEwan, Ian; Newman, Claire; Richardson, Mark; Charpentier, Antoine; Peret, Laurent; King, Penelope; Blank, Jennifer; Weigle, Gerald; Schmidt, Mariek; Li, Shuai; Milliken, Ralph; Robertson, Kevin; Sun, Vivian; Baker, Michael; Edwards, Christopher; Ehlmann, Bethany; Griffes, Jennifer; Newcombe, Megan; Pilorget, Cedric; Rice, Melissa; Siebach, Kirsten; Stack, Katie; Brunet, Claude; Hipkin, Victoria; Léveillé, Richard; Marchand, Geneviève; Sánchez, Pablo Sobrón; Favot, Laurent; Cody, George; Flückiger, Lorenzo; Lees, David; Nefian, Ara; Martin, Mildred; Gailhanou, Marc; Westall, Frances; Israël, Guy; Agard, Christophe; Baroukh, Julien; Donny, Christophe; Gaboriaud, Alain; Guillemot, Philippe; Lafaille, Vivian; Lorigny, Eric; Paillet, Alexis; Pérez, René; Saccoccio, Muriel; Yana, Charles; Armiens-Aparicio, Carlos; Rodríguez, Javier Caride; Blázquez, Isaías Carrasco; Gómez, Felipe Gómez; Gómez-Elvira, Javier; Hettrich, Sebastian; Malvitte, Alain Lepinette; Jiménez, Mercedes Marín; Martínez-Frías, Jesús; Martín-Soler, Javier; Martín-Torres, F. Javier; Jurado, Antonio Molina; Mora-Sotomayor, Luis; Caro, Guillermo Muñoz; López, Sara Navarro; Peinado-González, Verónica; Pla-García, Jorge; Manfredi, José Antonio Rodriguez; Romeral-Planelló, Julio José; Fuentes, Sara Alejandra Sans; Martinez, Eduardo Sebastian; Redondo, Josefina Torres; Urqui-O'Callaghan, Roser; Mier, María-Paz Zorzano; Chipera, Steve; Lacour, Jean-Luc; Mauchien, Patrick; Sirven, Jean-Baptiste; Manning, Heidi; Hayes, Alexander; Joseph, Jonathan; Sullivan, Robert; Thomas, Peter; Dupont, Audrey; Lundberg, Angela; Melikechi, Noureddine; Mezzacappa, Alissa; DeMarines, Julia; Grinspoon, David; Reitz, Günther; Prats, Benito; Atlaskin, Evgeny; Genzer, Maria; Harri, Ari-Matti; Haukka, Harri; Kahanpää, Henrik; Kauhanen, Janne; Kemppinen, Osku; Paton, Mark; Polkko, Jouni; Schmidt, Walter; Siili, Tero; Fabre, Cécile; Wilhelm, Mary Beth; Poitrasson, Franck; Patel, Kiran; Gorevan, Stephen; Indyk, Stephen; Paulsen, Gale; Schieber, Juergen; Gondet, Brigitte; Langevin, Yves; Geffroy, Claude; Baratoux, David; Berger, Gilles; Cros, Alain; d'Uston, Claude; Forni, Olivier; Gasnault, Olivier; Lasue, Jérémie; Lee, Qiu-Mei; Maurice, Sylvestre; Meslin, Pierre-Yves; Pallier, Etienne; Parot, Yann; Pinet, Patrick; Schröder, Susanne; Toplis, Mike; Lewin, Éric; Brunner, Will; Heydari, Ezat; Achilles, Cherie; Oehler, Dorothy; Coscia, David; Israël, Guy; Dromart, Gilles; Robert, François; Sautter, Violaine; Le Mouélic, Stéphane; Mangold, Nicolas; Nachon, Marion; Stalport, Fabien; Raulin, François; Cameron, James; Clegg, Sam; Cousin, Agnès; DeLapp, Dorothea; Dingler, Robert; Jackson, Ryan Steele; Johnstone, Stephen; Lanza, Nina; Little, Cynthia; Nelson, Tony; Wiens, Roger C.; Williams, Richard B.; Jones, Andrea; Kirkland, Laurel; Baker, Burt; Cantor, Bruce; Caplinger, Michael; Davis, Scott; Duston, Brian; Edgett, Kenneth; Fay, Donald; Hardgrove, Craig; Harker, David; Herrera, Paul; Jensen, Elsa; Kennedy, Megan R.; Krezoski, Gillian; Krysak, Daniel; Lipkaman, Leslie; Malin, Michael; McCartney, Elaina; McNair, Sean; Nixon, Brian; Posiolova, Liliya; Ravine, Michael; Salamon, Andrew; Saper, Lee; Stoiber, Kevin; Supulver, Kimberley; Van Beek, Jason; Van Beek, Tessa; Zimdar, Robert; French, Katherine Louise; Iagnemma, Karl; Miller, Kristen; Goesmann, Fred; Goetz, Walter; Hviid, Stubbe; Johnson, Micah; Lefavor, Matthew; Lyness, Eric; Breves, Elly; Dyar, M. Darby; Fassett, Caleb; Blake, David F.; Bristow, Thomas; Edwards, Laurence; Haberle, Robert; Hoehler, Tori; Hollingsworth, Jeff; Kahre, Melinda; Keely, Leslie; McKay, Christopher; Wilhelm, Mary Beth; Bleacher, Lora; Choi, David; Dworkin, Jason P.; Floyd, Melissa; Garvin, James; Harpold, Daniel; Jones, Andrea; Martin, David K.; Raaen, Eric; Smith, Michael D.; Tan, Florence; Meyer, Michael; Posner, Arik; Voytek, Mary; Anderson, Robert C.; Aubrey, Andrew; Beegle, Luther W.; Behar, Alberto; Blaney, Diana; Brinza, David; Calef, Fred; Christensen, Lance; Crisp, Joy A.; DeFlores, Lauren; Feldman, Jason; Feldman, Sabrina; Jun, Insoo; Keymeulen, Didier; Maki, Justin; Mischna, Michael; Morookian, John Michael; Parker, Timothy; Pavri, Betina; Schoppers, Marcel; Sengstacken, Aaron; Simmonds, John J.; Spanovich, Nicole; Juarez, Manuel de la Torre; Yen, Albert; Cucinotta, Francis; Jones, John H.; Rampe, Elizabeth; Nolan, Thomas; Fisk, Martin; Radziemski, Leon; Barraclough, Bruce; Bender, Steve; Berman, Daniel; Dobrea, Eldar Noe; Tokar, Robert; Williams, Rebecca M. E.; Cleghorn, Timothy; Huntress, Wesley; Manhès, Gérard; Hudgins, Judy; Olson, Timothy; Stewart, Noel; Sarrazin, Philippe; Vicenzi, Edward; Wilson, Sharon A.; Bullock, Mark; Ehresmann, Bent; Hamilton, Victoria; Hassler, Donald; Peterson, Joseph; Rafkin, Scot; Zeitlin, Cary; Fedosov, Fedor; Golovin, Dmitry; Karpushkina, Natalya; Kozyrev, Alexander; Litvak, Maxim; Malakhov, Alexey; Mitrofanov, Igor; Mokrousov, Maxim; Nikiforov, Sergey; Prokhorov, Vasily; Sanin, Anton; Tretyakov, Vladislav; Varenikov, Alexey; Vostrukhin, Andrey; Kuzmin, Ruslan; Clark, Benton; Wolff, Michael; Botta, Oliver; Drake, Darrell; Bean, Keri; Lemmon, Mark; Schwenzer, Susanne P.; Anderson, Ryan B.; Lee, Ella Mae; Sucharski, Robert; Hernández, Miguel Ángel de Pablo; Ávalos, Juan José Blanco; Ramos, Miguel; Kim, Myung-Hee; Malespin, Charles; Plante, Ianik; Muller, Jan-Peter; Ewing, Ryan; Boynton, William; Downs, Robert; Fitzgibbon, Mike; Harshman, Karl; Morrison, Shaunna; Dietrich, William; Kortmann, Onno; Palucis, Marisa; Williams, Amy; Lugmair, Günter; Wilson, Michael A.; Rubin, David; Jakosky, Bruce; Balic-Zunic, Tonci; Frydenvang, Jens; Jensen, Jaqueline Kløvgaard; Kinch, Kjartan; Koefoed, Asmus; Madsen, Morten Bo; Stipp, Susan Louise Svane; Boyd, Nick; VanBommel, Scott; Jacob, Samantha; Owen, Tobias; Rowland, Scott; Atlaskin, Evgeny; Savijärvi, Hannu; Boehm, Eckart; Böttcher, Stephan; Burmeister, Sönke; Guo, Jingnan; Köhler, Jan; García, César Martín; Mueller-Mellin, Reinhold; Wimmer-Schweingruber, Robert; Bridges, John C.; McConnochie, Timothy; Benna, Mehdi; Bower, Hannah; Blau, Hannah; Boucher, Thomas; Carmosino, Marco; Elliott, Harvey; Halleaux, Douglas; Rennó, Nilton; Wong, Michael; Pepin, Robert; Elliott, Beverley; Spray, John; Thompson, Lucy; Gordon, Suzanne; Newsom, Horton; Ollila, Ann; Williams, Joshua; Vasconcelos, Paulo; Bentz, Jennifer; Nealson, Kenneth; Popa, Radu; Kah, Linda C.; Tate, Christopher; Day, Mackenzie; Kocurek, Gary; Hallet, Bernard; Sletten, Ronald; Francis, Raymond; McCullough, Emily; Cloutis, Ed; ten Kate, Inge Loes; Kuzmin, Ruslan; Arvidson, Raymond; Fraeman, Abigail; Scholes, Daniel; Slavney, Susan; Stein, Thomas; Ward, Jennifer; Berger, Jeffrey; Moores, John E.

2014-01-01

H2O, CO2, SO2, O2, H2, H2S, HCl, chlorinated hydrocarbons, NO, and other trace gases were evolved during pyrolysis of two mudstone samples acquired by the Curiosity rover at Yellowknife Bay within Gale crater, Mars. H2O/OH-bearing phases included 2:1 phyllosilicate(s), bassanite, akaganeite, and amorphous materials. Thermal decomposition of carbonates and combustion of organic materials are candidate sources for the CO2. Concurrent evolution of O2 and chlorinated hydrocarbons suggests the presence of oxychlorine phase(s). Sulfides are likely sources for sulfur-bearing species. Higher abundances of chlorinated hydrocarbons in the mudstone compared with Rocknest windblown materials previously analyzed by Curiosity suggest that indigenous martian or meteoritic organic carbon sources may be preserved in the mudstone; however, the carbon source for the chlorinated hydrocarbons is not definitively of martian origin.

Volatile and organic compositions of sedimentary rocks in Yellowknife Bay, Gale crater, Mars

Science.gov (United States)

Ming, D. W.; Archer, P.D.; Glavin, D.P.; Eigenbrode, J.L.; Franz, H.B.; Sutter, B.; Brunner, A.E.; Stern, J.C.; Freissinet, C.; McAdam, A.C.; Mahaffy, P.R.; Cabane, M.; Coll, P.; Campbell, J.L.; Atreya, S.K.; Niles, P.B.; Bell, J.F.; Bish, D.L.; Brinckerhoff, W.B.; Buch, A.; Conrad, P.G.; Des Marais, D.J.; Ehlmann, B.L.; Fairén, A.G.; Farley, K.; Flesch, G.J.; Francois, P.; Gellert, Ralf; Grant, J. A.; Grotzinger, J.P.; Gupta, S.; Herkenhoff, K. E.; Hurowitz, J.A.; Leshin, L.A.; Lewis, K.W.; McLennan, S.M.; Miller, Karl E.; Moersch, J.; Morris, R.V.; Navarro- González, R.; Pavlov, A.A.; Perrett, G.M.; Pradler, I.; Squyres, S. W.; Summons, Roger E.; Steele, A.; Stolper, E.M.; Sumner, D.Y.; Szopa, C.; Teinturier, S.; Trainer, M.G.; Treiman, A.H.; Vaniman, D.T.; Vasavada, A.R.; Webster, C.R.; Wray, J.J.; Yingst, R.A.

2014-01-01

H2O, CO2, SO2, O2, H2, H2S, HCl, chlorinated hydrocarbons, NO, and other trace gases were evolved during pyrolysis of two mudstone samples acquired by the Curiosity rover at Yellowknife Bay within Gale crater, Mars. H2O/OH-bearing phases included 2:1 phyllosilicate(s), bassanite, akaganeite, and amorphous materials. Thermal decomposition of carbonates and combustion of organic materials are candidate sources for the CO2. Concurrent evolution of O2 and chlorinated hydrocarbons suggests the presence of oxychlorine phase(s). Sulfides are likely sources for sulfur-bearing species. Higher abundances of chlorinated hydrocarbons in the mudstone compared with Rocknest windblown materials previously analyzed by Curiosity suggest that indigenous martian or meteoritic organic carbon sources may be preserved in the mudstone; however, the carbon source for the chlorinated hydrocarbons is not definitively of martian origin.

Volatile and organic compositions of sedimentary rocks in Yellowknife Bay, Gale crater, Mars.

Science.gov (United States)

Ming, D W; Archer, P D; Glavin, D P; Eigenbrode, J L; Franz, H B; Sutter, B; Brunner, A E; Stern, J C; Freissinet, C; McAdam, A C; Mahaffy, P R; Cabane, M; Coll, P; Campbell, J L; Atreya, S K; Niles, P B; Bell, J F; Bish, D L; Brinckerhoff, W B; Buch, A; Conrad, P G; Des Marais, D J; Ehlmann, B L; Fairén, A G; Farley, K; Flesch, G J; Francois, P; Gellert, R; Grant, J A; Grotzinger, J P; Gupta, S; Herkenhoff, K E; Hurowitz, J A; Leshin, L A; Lewis, K W; McLennan, S M; Miller, K E; Moersch, J; Morris, R V; Navarro-González, R; Pavlov, A A; Perrett, G M; Pradler, I; Squyres, S W; Summons, R E; Steele, A; Stolper, E M; Sumner, D Y; Szopa, C; Teinturier, S; Trainer, M G; Treiman, A H; Vaniman, D T; Vasavada, A R; Webster, C R; Wray, J J; Yingst, R A

2014-01-24

H2O, CO2, SO2, O2, H2, H2S, HCl, chlorinated hydrocarbons, NO, and other trace gases were evolved during pyrolysis of two mudstone samples acquired by the Curiosity rover at Yellowknife Bay within Gale crater, Mars. H2O/OH-bearing phases included 2:1 phyllosilicate(s), bassanite, akaganeite, and amorphous materials. Thermal decomposition of carbonates and combustion of organic materials are candidate sources for the CO2. Concurrent evolution of O2 and chlorinated hydrocarbons suggests the presence of oxychlorine phase(s). Sulfides are likely sources for sulfur-bearing species. Higher abundances of chlorinated hydrocarbons in the mudstone compared with Rocknest windblown materials previously analyzed by Curiosity suggest that indigenous martian or meteoritic organic carbon sources may be preserved in the mudstone; however, the carbon source for the chlorinated hydrocarbons is not definitively of martian origin.

Asthenospheric percolation of alkaline melts beneath the St. Paul region (Central Atlantic Ocean)

Science.gov (United States)

Brunelli, Daniele; Seyler, Monique

2010-01-01

Two peridotite suites collected by submersible in the equatorial Atlantic Ocean (Hekinian et al., 2000) were studied for textures, modes, and in situ major and trace element compositions in pyroxenes. Dive SP12 runs along the immersed flank of the St. Peter and Paul Rocks islets where amphibole-bearing, ultramafic mylonites enriched in alkalies and incompatible elements are exposed (Roden et al., 1984), whereas dive SP03 sampled a small intra-transform spreading centre situated about 370 km east of the St. Peter and Paul Rocks. Both suites are characterized by undeformed, coarse-grained granular textures typical of abyssal peridotites, derived from residual mantle after ˜ 15% melting of a DMM source, starting in the garnet stability field. Trace element modelling, textures and lack of mineral zoning indicate that the residual peridotites were percolated, reacted and refertilized by ˜ 2.6% partially aggregated melts in the uppermost level of the melting region. This relatively large amount of refertilization is in agreement with the cold and thick lithosphere inferred by previous studies. Freezing of trapped melts occurred as the peridotite entered the conductive layer, resulting in late-stage crystallization of olivine, clinopyroxene, spinel, ± plagioclase. Chondrite-normalized REE patterns in clinopyroxenes from SP03 indicate that they last equilibrated with (ultra-) depleted partial melts. In contrast, REE concentrations in clinopyroxenes from SP12 display U and S shaped LREE-enriched patterns and the calculated compositions of the impregnating melts span the compositional range of the regional basalts, which vary from normal MORB to alkali basalt sometimes modified by chromatographic fractionation with no, or very limited, mineral reaction. Thus the mylonitic band forming the St. Peter and St. Paul Rocks ridge is not a fragment of subcontinental lithospheric mantle left behind during the opening of the Central Atlantic, nor the source of the alkaline basalts

Engineering geology model of the Crater Lake outlet, Mt. Ruapehu, New Zealand, to inform rim breakout hazard

Science.gov (United States)

Cook, Stefan C. W.; Kennedy, Ben M.; Villeneuve, Marlène C.

2018-01-01

Mt. Ruapehu, in the central North Island of New Zealand, hosts a hot acidic Crater Lake over the active volcanic vent with a surface elevation of c. 2530 m.a.s.l. Volcanic activity and other montane processes have previously resulted in catastrophic releases of some or all of the c. 10 Mm3 of water retained in the lake, creating serious hazards downstream. A major lahar in March 2007 exposed a 10 m high face representative of the rock units impounding the lake, providing an opportunity to conduct both field and laboratory analysis to characterise the rock mass conditions at the outlet to assess the stability of the outlet area. This paper presents an engineering geology model of Crater Lake outlet. Our model shows three andesitic geological units at the outlet, each with different geological histories and physical and mechanical properties, which impact its stability. Geotechnical methods used to characterise the outlet include laboratory testing of the strength, stiffness, porosity and unit weight, and field-based rock mass characterisation using the geological strength index (GSI) and rock mass rating (RMR). Field observations, geomorphology mapping, historic and contemporary photographs, and laboratory results are combined to create cross sections that provide key information for establishing the engineering geology model. The units are recognised in what is informally termed the Crater Lake Formation: i) The upper surface layer is a c. 2 m thick sub-horizontal dark grey lava unit (Armoured Lava Ledge) with sub-horizontal cooling joints spaced at 0.2 m to 2.0 m intervals. The intact rock has a porosity range of 15-27%, density range of 1723-2101 kg/m3, GSI range of 45-75, and unconfined compressive strength (UCS) range of 19-48 MPa. ii) Below this, and outcropping down the majority of the outlet waterfall is a poorly sorted breccia unit composed of block and matrix material (Lava Breccia). The blocks range from 0.1 m to 0.8 m in diameter with an average porosity

Geochemical evidence for the melting of subducting oceanic lithosphere at plate edges

Science.gov (United States)

Yogodzinski, G. M.; Lees, J. M.; Churikova, T. G.; Dorendorf, F.; Wöerner, G.; Volynets, O. N.

2001-01-01

Most island-arc magmatism appears to result from the lowering of the melting point of peridotite within the wedge of mantle above subducting slabs owing to the introduction of fluids from the dehydration of subducting oceanic crust. Volcanic rocks interpreted to contain a component of melt (not just a fluid) from the subducting slab itself are uncommon, but possible examples have been recognized in the Aleutian islands, Baja California, Patagonia and elsewhere. The geochemically distinctive rocks from these areas, termed `adakites', are often associated with subducting plates that are young and warm, and therefore thought to be more prone to melting. But the subducting lithosphere in some adakite locations (such as the Aleutian islands) appears to be too old and hence too cold to melt. This implies either that our interpretation of adakite geochemistry is incorrect, or that our understanding of the tectonic context of adakites is incomplete. Here we present geochemical data from the Kamchatka peninsula and the Aleutian islands that reaffirms the slab-melt interpretation of adakites, but in the tectonic context of the exposure to mantle flow around the edge of a torn subducting plate. We conclude that adakites are likely to form whenever the edge of a subducting plate is warmed or ablated by mantle flow. The use of adakites as tracers for such plate geometry may improve our understanding of magma genesis and thermal structure in a variety of subduction-zone environments.

Geohydrology of rocks penetrated by test well USW H-6, Yucca Mountain, Nye County, Nevada

International Nuclear Information System (INIS)

Craig, R.W.; Reed, R.L.

1991-01-01

Test well USW H-6 is one of several wells drilled in the Yucca Mountain area near the southwestern part of the Nevada Test Site for investigations related to isolation of high-level nuclear waste. This well was drilled to a depth of 1,220 meters. Rocks penetrated are predominantly ash-flow tuffs of Tertiary age, with the principal exception of dacitic(?) lave penetrated at a depth from 877 to 1,126 meters. The composite static water level was about 526 meters below the land surface; the hydraulic head increased slightly with depth. Most permeability in the saturated zone is in two fractured intervals in Crater Flat Tuff. Based on well-test data using the transitional part of a dual-porosity solution, an interval of about 15 meters in the middle part of the Bullfrog Member of the Crater Flat Tuff has a calculated transmissivity of about 140 meters squared per day, and an interval of about 11 meters in the middle part of the Tram Member of the Crater Flat Tuff has a calculated transmissivity of about 75 meters squared per day. The upper part of the Bullfrog Member has a transmissivity of about 20 meters squared per day. The maximum likely transmissivity of any rocks penetrated by the test well is about 480 meters squared per day, based on a recharge-boundary model. The remainder of the open hole had no detectable production. Matrix hydraulic conductivity ranges from less than 5 x 10 -5 to 1 x 10 -3 meter per day. Ground water is a sodium bicarbonate type that is typical of water from tuffaceous rock of southern Nevada. The apparent age of the water is about 14,6000 years. 29 refs., 26 figs., 5 tabs

Cratering Equations for Zinc Orthotitanate Coated Aluminum

Science.gov (United States)

Hyde, James; Christiansen, Eric; Liou, Jer-Chyi; Ryan, Shannon

2009-01-01

The final STS-125 servicing mission (SM4) to the Hubble Space Telescope (HST) in May of 2009 saw the return of the 2nd Wide Field Planetary Camera (WFPC2) aboard the shuttle Discovery. This hardware had been in service on HST since it was installed during the SM1 mission in December of 1993 yielding one of the longest low Earth orbit exposure times (15.4 years) of any returned space hardware. The WFPC2 is equipped with a 0.8 x 2.2 m radiator for thermal control of the camera electronics (Figure 1). The space facing surface of the 4.1 mm thick aluminum radiator is coated with Z93 zinc orthotitanate thermal control paint with a nominal thickness of 0.1 0.2 mm. Post flight inspections of the radiator panel revealed hundreds of micrometeoroid/orbital debris (MMOD) impact craters ranging in size from less than 300 to nearly 1000 microns in diameter. The Z93 paint exhibited large spall areas around the larger impact sites (Figure 2) and the craters observed in the 6061-T651 aluminum had a different shape than those observed in uncoated aluminum. Typical hypervelocity impact craters in aluminum have raised lips around the impact site. The craters in the HST radiator panel had suppressed crater lips, and in some cases multiple craters were present instead of a single individual crater. Humes and Kinard observed similar behavior after the WFPC1 post flight inspection and assumed the Z93 coating was acting like a bumper in a Whipple shield. Similar paint behavior (spall) was also observed by Bland2 during post flight inspection of the International Space Station (ISS) S-Band Antenna Structural Assembly (SASA) in 2008. The SASA, with similar Z93 coated aluminum, was inspected after nearly 4 years of exposure on the ISS. The multi-crater phenomena could be a function of the density, composition, or impact obliquity angle of the impacting particle. For instance, a micrometeoroid particle consisting of loosely bound grains of material could be responsible for creating the

High-pressure anatectic paragneisses from the Namche Barwa, Eastern Himalayan Syntaxis: Textural evidence for partial melting, phase equilibria modeling and tectonic implications

Science.gov (United States)

Guilmette, C.; Indares, A.; Hébert, R.

2011-05-01

Rare kyanite-bearing anatectic paragneisses are found as boudins within sillimanite-bearing paragneisses of the core of the Namche Barwa Antiform, Tibet. In the present study, we document an occurrence from the NW side of the Yarlung Zangbo River. These rocks mainly consist of the assemblage garnet + K-feldspar + kyanite ± biotite + quartz + rutile ± plagioclase with kyanite locally pseudomorphed by sillimanite. The documented textures are consistent with the rocks having undergone biotite-dehydration melting in the kyanite stability field, under high-P granulite facies conditions, and having experienced melt extraction. However textures related to melt crystallization are ubiquitous both in polymineralic inclusions in garnet and in the matrix, suggesting that a melt fraction had remained in these rocks. Phase equilibria modelling was undertaken in the NCKFMASTHO system with THERMOCALC. P-T pseudosections built with the bulk compositions of one aluminous and one sub-aluminous paragneiss samples predict a biotite-kyanite-garnet-quartz-plagioclase-K-feldspar-liquid-rutile ± ilmenite field, in which biotite-dehydration melting occurs, located in the P-T range of ~ 800-875 °C and ~ 10-17 kbar. In addition, the topologies of these pseudosections are consistent with substantial melt loss during prograde metamorphism. A second set of P-T pseudosections with melt-reintegrated model bulk compositions were thus constructed to evaluate the effect of melt loss. The integration of textural information, precise mineral modes, mineral chemistry, and phase equilibria modelling allowed to constrain a P-T path where the rocks are buried to lower crustal depths at peak P-T conditions higher than 14 kbar and 825 °C, possibly in the order of 15-16 kbar and 850 °C, followed by decompression and cooling to P-T conditions of around 9 kbar and 810 °C, under which the remaining melt was solidified. The implications for granite production at the NBA and for Himalayan tectonic models

Pancam Peek into 'Victoria Crater' (Stereo)

Science.gov (United States)

2006-01-01

[figure removed for brevity, see original site] Left-eye view of a stereo pair for PIA08776 [figure removed for brevity, see original site] Right-eye view of a stereo pair for PIA08776 A drive of about 60 meters (about 200 feet) on the 943rd Martian day, or sol, of Opportunity's exploration of Mars' Meridiani Planum region (Sept. 18, 2006) brought the NASA rover to within about 50 meters (about 160 feet) of the rim of 'Victoria Crater.' This crater has been the mission's long-term destination for the past 21 Earth months. Opportunity reached a location from which the cameras on top of the rover's mast could begin to see into the interior of Victoria. This stereo anaglyph was made from frames taken on sol 943 by the panoramic camera (Pancam) to offer a three-dimensional view when seen through red-blue glasses. It shows the upper portion of interior crater walls facing toward Opportunity from up to about 850 meters (half a mile) away. The amount of vertical relief visible at the top of the interior walls from this angle is about 15 meters (about 50 feet). The exposures were taken through a Pancam filter selecting wavelengths centered on 750 nanometers. Victoria Crater is about five times wider than 'Endurance Crater,' which Opportunity spent six months examining in 2004, and about 40 times wider than 'Eagle Crater,' where Opportunity first landed. The great lure of Victoria is the expectation that a thick stack of geological layers will be exposed in the crater walls, potentially several times the thickness that was previously studied at Endurance and therefore, potentially preserving several times the historical record.

High-level radioactive waste isolation by incorporation in silicate rock

International Nuclear Information System (INIS)

Schwartz, L.L.; Cohen, J.J.; Lewis, A.E.; Braun, R.L.

1978-01-01

A number of technical possibilities for isolating high-level radioactive materials have been theoretically investigated at various times and places. Isolating such wastes deep underground to ensure long term removal from the biosphere is one such possibility. The present concept involves as a first step creating the necessary void space at considerable depth, say 2 to 5 km, in a very-low-permeability silicate medium such as shale. Waste in dry, calcined or vitrified form is then lowered into the void space, and the access hole or shaft sealed. Energy released by the radioactive decay raises the temperature to a point where the surrounding rock begins to melt. The waste is then dissolved in it. The extent of this melt region grows until the heat generated is balanced by conduction away from the molten zone. Resolidification then begins, and ends when the radioactive decay has progressed to the point that the temperature falls below the melting point of the rock-waste solution. Calculations are presented showing the growth and resolidification process. A nuclear explosion is one way of creating the void space. (author)

Origins of two types of serpentinites from the Qinling orogenic belt, central China and associated fluid/melt-rock interactions

Science.gov (United States)

Wu, Kai; Ding, Xing; Ling, Ming-Xing; Sun, Wei-dong; Zhang, Li-Peng; Hu, Yong-Bin; Huang, Rui-Fang

2018-03-01

(e.g., high Al2O3 content and Al2O3/SiO2) and conjoint enrichment in light rare earth elements and high field strength elements, however, suggest melt-rock interactions before serpentinization. Combined with their geochemical affinity to "subducted serpentinites", we conclude that their protoliths (refractory mantle wedge peridotite) experienced melt-rock interactions and then were incorporated into the subduction channel before serpentinization. Studies on these two types of serpentinites indicate that serpentinites from the orogenic belt are most likely characterized by multi-source, multi-stage and multi-genesis, further providing important constraints on subduction channel processes.

Electron microprobe analyses of selected samples from deep rock disposal experiment No. 1

International Nuclear Information System (INIS)

Hlava, P.F.; Chambers, W.F.

1976-04-01

Deep Rock Disposal Experiment No. 1 was designed to provide information about the interaction between a molten, glass-based, nuclear waste simulant and rock material. Selected samples from this experiment were examined by optical microscopy and electron probe microanalysis. Analysis of the homogenized material in the convection cell that was created in the central portion of the melt region shows that an amount of rock equal to about one-half of the original amount of waste simulant was incorporated in the melt during the experiment. Stagnant melt at the sides of the cell formed a glass with large compositional gradients. A white band separated the convected and stagnant materials. The color of the band is attributed to light scattering by small crystallites formed during cooling. Four types of crystallites grew from the melt: two oxides, a Mg--Fe borate, and a silicate. Spinel (MgO, Cr 2 O 3 , FeO (Fe 2 O 3 ), and NiO) was the most common crystallite in the glass. The spinel crystallites found within the convection cell displayed skeletal morphology and oscillatory zoning which indicates growth at varying temperatures as they were carried along by convection. A single cluster of nonskeletal (Fe,Cr) 2 O 3 crystallites was found at the bottom of the melt zone where convection did not occur. Mg--Fe borate crystallites grew in clusters in the central portion of the convection cell after convection ceased. A silicate similar to Fe-rich diopside (CaMgSi 2 O 6 ) with unusual amounts of Ce 2 O 3 and other heavy metal oxides formed as larger crystallites in the stagnant melt at the side of the convection cell and as many very small crystallites in the white band

A schematic model of crater modification by gravity

Science.gov (United States)

Melosh, H. J.

1982-01-01

The morphology of craters found on planets and moons of the solar system is examined and a development model which can account for the observed crater characteristics is discussed. The prompt collapse of craters to form flat floors, terraced walls, and central peak structures is considered to be the result of an approximate Bingham plastic rheology of the material surrounding the crater. This rheology is induced dynamically by the strong incoherent acoustic 'noise' accompanying excavation of the crater. Central pits, peak rings, and other multiple symmetric-profile rings originate by oscillation of this fluid. Large craters with transient depths comparable to the lithosphere thickness are subject to collapse by fragmentation of the lithosphere as well as fluidization. The considered concepts are developed mathematically. A model emerges which appears capable of explaining most of the qualitative features of large impact structures.

Dissolution Rates of Allophane, FE-Containing Allophane, and Hisingerite and Implications for Gale Crater, Mars

Science.gov (United States)

Ralston, S. J.; Hausrath, E. M.; Tschauner, O.; Rampe, E. B.; Christoffersen, R.

2018-01-01

Investigations with the CheMin Xray Diffractometer (XRD) onboard the Curiosity rover in Gale Crater demonstrate that all rock and soil samples measured to date contain approximately 15-70 weight percentage X-ray amorphous materials. The diffuse scattering hump from the X-ray amorphous materials in CheMin XRD patterns can be fit with a combination of allophane, ferrihydrite, and rhyolitic and basaltic glass. Because of the iron-rich nature of Mars' surface, Fe-rich poorly-crystalline phases, such as hisingerite, may be present in addition to allophane.

Microbial Preservation in Sulfates in the Haughton Impact Structure Suggests Target in Search for Life on Mars

Science.gov (United States)

Parnell, J.; Osinski, G. R.; Lee, P.; Cockell, C. S.

2005-01-01

Microbes in Haughton Crater Sulfates: Impact craters are of high interest in planetary exploration because they are viewed as possible sites for evidence of life [1]. Hydrothermal systems in craters are particularly regarded as sites where primitive life could evolve. Evidence from the Miocene Haughton impact structure shows that crater hydrothermal deposits may also be a preferred site for subsequent colonization and hence possible extant life: Hydrothermal sulfates at Haughton are colonized by viable cyanobacteria [2]. The Haughton impact structure, Devon Island, Canadian High Arctic, is a 24 km-diameter crater of mid-Tertiary age. The structure preserves an exceptional record of impact-induced hydrothermal activity, including sulfide, and sulfate mineralization [3]. The target rocks excavated at the site included massive gypsum-bearing carbonate rocks of Ordovician age. Impact-remobilized sulfates occur as metre-scale masses of intergrown crystals of the clear form of gypsum selenite in veins and cavity fillings within the crater s impact melt breccia deposits [4]. The selenite is part of the hydrothermal assemblage as it was precipitated by cooling hot waters that were circulating as a result of the impact. Remobilization of the sulfate continues to the present day, such that it occurs in soil crusts (Fig. 1) including sandy beds with a gypsum cement. The sulfate-cemented beds make an interesting comparison with the sulfate-bearing sandy beds encountered by the Opportunity MER [5]. The selenite crystals are up to 0.3 m in width, of high purity, and transparent. They locally exhibit frayed margins where cleavage surfaces have separated. This exfoliation may be a response to freeze-thaw weathering. The selenite contains traces of rock detritus, newly precipitated gypsum, and microbial colonies. The rock detritus consists of sediment particles which penetrated the opened cleavages by up to 2cm from the crystal margins. Some of the detritus is cemented into place

Crater topography on Titan: Implications for landscape evolution

Science.gov (United States)

Neish, C.; Kirk, R.; Lorenz, R.; Bray, V.; Schenk, P.; Stiles, B.; Turtle, E.; Cassini Radar Team

2012-04-01

Unique among the icy satellites, Titan’s surface shows evidence for extensive modification by fluvial and aeolian erosion, which act to change the topography of its surface over time. Quantifying the extent of this landscape evolution is difficult, since the original, ‘non-eroded’ surface topography is generally unknown. However, fresh craters on icy satellites have a well-known shape and morphology, which has been determined from extensive studies on the airless worlds of the outer solar system (Schenk et al., 2004). By comparing the topography of craters on Titan to similarly sized, pristine analogues on airless bodies, we can obtain one of the few direct measures of the amount of erosion that has occurred on Titan. Cassini RADAR has imaged >30% of the surface of Titan, and more than 60 potential craters have been identified in this data set (Wood et al., 2010; Neish and Lorenz, 2012). Topographic information for these craters can be obtained from a technique known as ‘SARTopo’, which estimates surface heights by comparing the calibration of overlapping synthetic aperture radar (SAR) beams (Stiles et al., 2009). We present topography data for several craters on Titan, and compare the data to similarly sized craters on Ganymede, for which topography has been extracted from stereo-derived digital elevation models (Bray et al., 2012). We find that the depths of craters on Titan are generally within the range of depths observed on Ganymede, but several hundreds of meters shallower than the average (Fig. 1). A statistical comparison between the two data sets suggests that it is extremely unlikely that Titan’s craters were selected from the depth distribution of fresh craters on Ganymede, and that is it much more probable that the relative depths of Titan are uniformly distributed between ‘fresh’ and ‘completely infilled’. This is consistent with an infilling process that varies linearly with time, such as aeolian infilling. Figure 1: Depth of

Eruptive history and geochronology of Mount Mazama and the Crater Lake region, Oregon

Science.gov (United States)

Bacon, Charles R.; Lanphere, Marvin A.

2006-01-01

Geologic mapping, K-Ar, and 40Ar/39Ar age determinations, supplemented by paleomagnetic measurements and geochemical data, are used to quantify the Quaternary volcanic history of the Crater Lake region in order to define processes and conditions that led to voluminous explosive eruptions. The Cascade arc volcano known as Mount Mazama collapsed during its climactic eruption of ∼50 km3 of mainly rhyodacitic magma ∼7700 yr ago to form Crater Lake caldera. The Mazama edifice was constructed on a Pleistocene silicic lava field, amidst monogenetic and shield volcanoes ranging from basalt to andesite similar to parental magmas for Mount Mazama. Between 420 ka and 35 ka, Mazama produced medium-K andesite and dacite in 2:1 proportion. The edifice was built in many episodes; some of the more voluminous occurred approximately coeval with volcanic pulses in the surrounding region, and some were possibly related to deglaciation following marine oxygen isotope stages (MIS) 12, 10, 8, 6, 5.2, and 2. Magmas as evolved as dacite erupted many times, commonly associated with or following voluminous andesite effusion. Establishment of the climactic magma chamber was under way when the first preclimactic rhyodacites vented ca. 27 ka. The silicic melt volume then grew incrementally at an average rate of 2.5 km3 k.y.−1 for nearly 20 k.y. The climactic eruption exhausted the rhyodacitic magma and brought up crystal-rich andesitic magma, mafic cumulate mush, and wall-rock granodiorite. Postcaldera volcanism produced 4 km3 of andesite during the first 200–500 yr after collapse, followed at ca. 4800 yr B.P. by 0.07 km3 of rhyodacite. The average eruption rate for all Mazama products was ∼0.4 km3 k.y.−1, but major edifice construction episodes had rates of ∼0.8 km3 k.y.−1. The long-term eruption rate for regional monogenetic and shield volcanoes was d∼0.07 km3 k.y.−1, but only ∼0.02 km3 k.y.−1 when the two major shields are excluded. Plutonic xenoliths and evidence for

Composition and origin of rhyolite melt intersected by drilling in the Krafla geothermal field, Iceland

Science.gov (United States)

Zierenberg, R.A.; Schiffman, P.; Barfod, G.H.; Lesher, C.E.; Marks, N.E.; Lowenstern, Jacob B.; Mortensen, A.K.; Pope, E.C.; Bird, D.K.; Reed, M.H.; Friðleifsson, G.O.; Elders, W.A.

2013-01-01

The Iceland Deep Drilling Project Well 1 was designed as a 4- to 5-km-deep exploration well with the goal of intercepting supercritical hydrothermal fluids in the Krafla geothermal field, Iceland. The well unexpectedly drilled into a high-silica (76.5 % SiO2) rhyolite melt at approximately 2.1 km. Some of the melt vesiculated while extruding into the drill hole, but most of the recovered cuttings are quenched sparsely phyric, vesicle-poor glass. The phenocryst assemblage is comprised of titanomagnetite, plagioclase, augite, and pigeonite. Compositional zoning in plagioclase and exsolution lamellae in augite and pigeonite record changing crystallization conditions as the melt migrated to its present depth of emplacement. The in situ temperature of the melt is estimated to be between 850 and 920 °C based on two-pyroxene geothermometry and modeling of the crystallization sequence. Volatile content of the glass indicated partial degassing at an in situ pressure that is above hydrostatic (~16 MPa) and below lithostatic (~55 MPa). The major element and minor element composition of the melt are consistent with an origin by partial melting of hydrothermally altered basaltic crust at depth, similar to rhyolite erupted within the Krafla Caldera. Chondrite-normalized REE concentrations show strong light REE enrichment and relative flat patterns with negative Eu anomaly. Strontium isotope values (0.70328) are consistent with mantle-derived melt, but oxygen and hydrogen isotope values are depleted (3.1 and −118 ‰, respectively) relative to mantle values. The hydrogen isotope values overlap those of hydrothermal epidote from rocks altered by the meteoric-water-recharged Krafla geothermal system. The rhyolite melt was emplaced into and has reacted with a felsic intrusive suite that has nearly identical composition. The felsite is composed of quartz, alkali feldspar, plagioclase, titanomagnetite, and augite. Emplacement of the rhyolite magma has resulted in partial melting of

Mechanical and geometric controls on the structural evolution of pit crater and caldera subsidence

Science.gov (United States)

Holohan, E. P.; SchöPfer, M. P. J.; Walsh, J. J.

2011-07-01

Pit craters and calderas are volcanic depressions produced by subsidence of a magma reservoir roof. To identify how geometric and mechanical factors may influence the structural evolution of this subsidence, we used two-dimensional distinct element method numerical models. The reservoir host rock was represented as an assemblage of bonded circular particles that interact according to elastic-frictional laws. Varying particle and bond properties produced a range of bulk material properties characteristic of natural rock masses. Fracturing results when bonds break, once their shear or tensile strength is exceeded. The magma reservoir was represented as a region of nonbonded low-friction particles. Withdrawal of magma was simulated by incrementally reducing the area of the reservoir particles. Resultant gravity-driven failure and subsidence of the reservoir roof were explicitly replicated. Interaction of the roof's strength, Young's modulus, thickness/diameter ratio (T/D), and the reservoir's shape yields a variety of model structures and subsidence styles. In conceptual terms, four end-member subsidence styles developed: (1) "central sagging" favored by low strength and low T/D; (2) "central snapping" favored by high strength, low T/D, and a sill-like reservoir shape; (3) "single central block" favored by low to intermediate strength, high Young's modulus, and intermediate T/D; and (4) "multiple central blocks" favored by high strength, low Young's modulus, and high T/D. Most model realizations incorporated some combination of each style, however. The models provide a geomechanical framework for understanding natural pit crater or caldera structures, as at Nindiri (Nicaragua), Fernandina (Galapagos), Dolomieu (La Reunion), and Miyakejima (Japan).

Detection of lunar floor-fractured craters using machine learning methods

Science.gov (United States)

Thorey, C.

2015-10-01

About 200 Floor Fractured Craters (FFCs) have been identified by Schultz (1976) on the Moon, mainly around the lunar maria. These craters are a class of impact craters that are distinguished by having radi-ally and concentric floor-fractured networks and ab-normally shallow floors. In some cases, the uplift of the crater floor can be as large as 50% of the initial crater depth. These impact craters are interpreted to have undergone endogenous deformations after their formation.

Computer modeling of the Cabriolet Event

International Nuclear Information System (INIS)

Kamegai, M.

1979-01-01

Computer modeling techniques are described for calculating the results of underground nuclear explosions at depths shallow enough to produce cratering. The techniques are applied to the Cabriolet Event, a well-documented nuclear excavation experiment, and the calculations give good agreement with the experimental results. It is concluded that, given data obtainable by outside observers, these modeling techniques are capable of verifying the yield and depth of underground nuclear cratering explosions, and that they could thus be useful in monitoring another country's compliance with treaty agreements on nuclear testing limitations. Several important facts emerge from the study: (1) seismic energy is produced by only a fraction of the nuclear yield, a fraction depending strongly on the depth of shot and the mechanical properties of the surrounding rock; (2) temperature of the vented gas can be predicted accurately only if good equations of state are available for the rock in the detonation zone; and (3) temperature of the vented gas is strongly dependent on the cooling effect, before venting, of mixing with melted rock in the expanding cavity and, to a lesser extent, on the cooling effect of water in the rock

Simple Impact Crater Shapes From Shadows - The Sequel

Science.gov (United States)

Chappelow, J. E.

2008-12-01

At the last LPSC meeting I presented the outline of a method for determining simple impact crater shapes from shadows. In theory the shadow cast within a simple crater provides enough information to derive its cross-sectional shape from shadow measurements, at least to the maximum depth to which the shadow extends. Under certain simple assumptions, this can be done analytically. If the crater is conic-section - shaped, then it can be shown that the down-sun bound of any shadow cast within it is elliptical, with one axis along the direction of illumination and the other (perpendicular to it) of semi-length D/2 (where D is diameter). The properties of this shadow-ellipse can be related to the parameters of the crater shape conic-section, thus measurements of the shadow-ellipse yield not only crater depth and diameter but also the approximate crater shape, in terms of conic sections. The method also does not depend upon the shadow crossing near the crater center, which avoids a pitfall of older shadow measurement methods. The technique is also amenable to computer implementation, which has already been largely completed. Once computerized, crater measurements can be made rapidly and repeatably. The program reads in an image, its resolution, and the solar elevation and azimuth. The user then defines the crater rim by 'clicking' on three points, and the shadow ellipse by clicking on two more. The program calculates and outputs the diameter, the depth, and parameters describing the crater's approximating conic-section. It is highly applicable to situations where only single-image photography is available, for example MESSENGER flybys of Mercury. At the meeting I will present the finished math for this method and give some examples of its use.

Experimental petrology and origin of rocks from the Descartes Highlands

Science.gov (United States)

Walker, D.; Longhi, J.; Grove, T. L.; Stolper, E.; Hays, J. F.

1973-01-01

Petrographic studies of Apollo 16 samples indicate that rocks 62295 and 68415 are crystallization products of highly aluminous melts. 60025 is a shocked, crushed and partially annealed plagioclase cumulate. 60315 is a recrystallized noritic breccia of disputed origin. 60335 is a feldspathic basalt filled with xenoliths and xenocrysts of anorthosite, breccia, and anorthite. The Fe/(Fe+Mg) of plagioclase appears to be a relative crystallization index. Low pressure melting experiments with controlled Po2 indicate that the igneous samples crystallized at oxygen fugacities well below the Fe/FeO buffer. Crystallization experiments at various pressures suggest that the 62295 and 68415 compositions were produced by partial or complete melting of lunar crustal materials, and not by partial melting of the deep lunar interior.

Shallow and deep fresh impact craters in Hesperia Planum, Mars

Science.gov (United States)

Mouginis-Mark, Peter J.; Hayashi, Joan N.

1993-01-01

The depths of 109 impact craters about 2-16 km in diameter, located on the ridged plains materials of Hesperia Planum, Mars, have been measured from their shadow lengths using digital Viking Orbiter images (orbit numbers 417S-419S) and the PICS computer software. On the basis of their pristine morphology (very fresh lobate ejecta blankets, well preserved rim crests, and lack of superposed impact craters), 57 of these craters have been selected for detailed analysis of their spatial distribution and geometry. We find that south of 30 deg S, craters less than 6.0 km in diameter are markedly shallower than similar-sized craters equatorward of this latitude. No comparable relationship is observed for morphologically fresh craters greater than 6.0 km diameter. We also find that two populations exist for older craters less than 6.0 km diameter. When craters that lack ejecta blankets are grouped on the basis of depth/diameter ratio, the deeper craters also typically lie equatorward of 30 S. We interpret the spatial variation in crater depth/diameter ratios as most likely due to a poleward increase in volatiles within the top 400 m of the surface at the times these craters were formed.

Cumulates, Dykes and Pressure Solution in the Ice-Salt Mantle of Europa: Geological Consequences of Pressure Dependent Liquid Compositions and Volume Changes During Ice-Salt Melting Reactions.

Science.gov (United States)

Day, S.; Asphaug, E.; Bruesch, L.

2002-12-01

Water-salt analogue experiments used to investigate cumulate processes in silicate magmas, along with observations of sea ice and ice shelf behaviour, indicate that crystal-melt separation in water-salt systems is a rapid and efficient process even on scales of millimetres and minutes. Squeezing-out of residual melts by matrix compaction is also predicted to be rapid on geological timescales. We predict that the ice-salt mantle of Europa is likely to be strongly stratified, with a layered structure predictable from density and phase relationships between ice polymorphs, aqueous saline solutions and crystalline salts such as hydrated magnesium sulphates (determined experimentally by, inter alia, Hogenboom et al). A surface layer of water ice flotation cumulate will be separated from denser salt cumulates by a cotectic horizon. This cotectic horizon will be both the site of subsequent lowest-temperature melting and a level of neutral buoyancy for the saline melts produced. Initial melting will be in a narrow depth range owing to increasing melting temperature with decreasing pressure: the phase relations argue against direct melt-though to the surface unless vesiculation occurs. Overpressuring of dense melts due to volume expansion on cotectic melting is predicted to lead to lateral dyke emplacement and extension above the dyke tips. Once the liquid leaves the cotectic, melting of water ice will involve negative volume change. Impact-generated melts will drain downwards through the fractured zones beneath crater floors. A feature in the complex crater Mannan'an, with elliptical ring fractures around a conical depression with a central pit, bears a close resemblance to Icelandic glacier collapse cauldrons produced by subglacial eruptions. Other structures resembling Icelandic cauldrons occur along Europan banded structures, while resurgence of ice rubble within collapse structures may produce certain types of chaos region. More general contraction of the ice mantle

Coesite from Wabar crater, near Al Hadida, Arabia

Science.gov (United States)

Chao, E.C.T.; Fahey, J.J.; Littler, J.

1961-01-01

The third natural occurrence of coesite, the high pressure polymorph of silica, is found at the Wabar meteorite crater, Arabia. The Wabar crater is about 300 feet in diameter and about 40 feet deep. It is the smallest of three craters where coesite has been found.

The effect of pressurized magma chamber growth on melt migration and pre-caldera vent locations through time at Mount Mazama, Crater Lake, Oregon

Science.gov (United States)

Karlstrom, Leif; Wright, Heather M.; Bacon, Charles R.

2015-01-01

The pattern of eruptions at long-lived volcanic centers provides a window into the co-evolution of crustal magma transport, tectonic stresses, and unsteady magma generation at depth. Mount Mazama in the Oregon Cascades has seen variable activity over the last 400 ky, including the 50 km3 climactic eruption at ca. 7.7 ka that produced Crater Lake caldera. The physical mechanisms responsible for the assembly of silicic magma reservoirs that are the precursors to caldera-forming eruptions are poorly understood. Here we argue that the spatial and temporal distribution of geographically clustered volcanic vents near Mazama reflects the development of a centralized magma chamber that fed the climactic eruption. Time-averaged eruption rates at Mount Mazama imply an order of magnitude increase in deep magma influx prior to the caldera-forming event, suggesting that unsteady mantle melting triggered a chamber growth episode that culminated in caldera formation. We model magma chamber–dike interactions over ∼50 ky preceding the climactic eruption to fit the observed distribution of surface eruptive vents in space and time, as well as petrologically estimated deep influx rates. Best fitting models predict an expanding zone of dike capture caused by a growing, oblate spheroidal magma chamber with 10–30 MPa of overpressure. This growing zone of chamber influence causes closest approaching regional mafic vent locations as well as more compositionally evolved Mazama eruptions to migrate away from the climactic eruptive center, returning as observed to the center after the chamber drains during the caldera-forming eruption.

Optimizing laser crater enhanced Raman scattering spectroscopy

Science.gov (United States)

Lednev, V. N.; Sdvizhenskii, P. A.; Grishin, M. Ya.; Fedorov, A. N.; Khokhlova, O. V.; Oshurko, V. B.; Pershin, S. M.

2018-05-01

The laser crater enhanced Raman scattering (LCERS) spectroscopy technique has been systematically studied for chosen sampling strategy and influence of powder material properties on spectra intensity enhancement. The same nanosecond pulsed solid state Nd:YAG laser (532 nm, 10 ns, 0.1-1.5 mJ/pulse) was used for laser crater production and Raman scattering experiments for L-aspartic acid powder. Increased sampling area inside crater cavity is the key factor for Raman signal improvement for the LCERS technique, thus Raman signal enhancement was studied as a function of numerous experimental parameters including lens-to-sample distance, wavelength (532 and 1064 nm) and laser pulse energy utilized for crater production. Combining laser pulses of 1064 and 532 nm wavelengths for crater ablation was shown to be an effective way for additional LCERS signal improvement. Powder material properties (particle size distribution, powder compactness) were demonstrated to affect LCERS measurements with better results achieved for smaller particles and lower compactness.

Primary magmas and mantle sources of Emeishan basalts constrained from major element, trace element and Pb isotope compositions of olivine-hosted melt inclusions

Science.gov (United States)

Ren, Zhong-Yuan; Wu, Ya-Dong; Zhang, Le; Nichols, Alexander R. L.; Hong, Lu-Bing; Zhang, Yin-Hui; Zhang, Yan; Liu, Jian-Qiang; Xu, Yi-Gang

2017-07-01

Olivine-hosted melt inclusions within lava retain important information regarding the lava's primary magma compositions and mantle sources. Thus, they can be used to infer the nature of the mantle sources of large igneous provinces, which is still not well known and of the subject of debate. We have analysed the chemical compositions and Pb isotopic ratios of olivine-hosted melt inclusions in the Dali picrites, Emeishan Large Igneous Province (LIP), SW China. These are the first in-situ Pb isotope data measured for melt inclusions found in the Emeishan picrites and allow new constraints to be placed on the source lithology of the Emeishan LIP. The melt inclusions show chemical compositional variations, spanning low-, intermediate- and high-Ti compositions, while their host whole rocks are restricted to the intermediate-Ti compositions. Together with the relatively constant Pb isotope ratios of the melt inclusions, the compositional variations suggest that the low-, intermediate- and high-Ti melts were derived from compositionally similar sources. The geochemical characteristics of melt inclusions, their host olivines, and whole-rocks from the Emeishan LIP indicate that Ca, Al, Mn, Yb, and Lu behave compatibly, and Ti, Rb, Sr, Zr, and Nb behave incompatibly during partial melting, requiring a pyroxenite source for the Emeishin LIP. The wide range of Ti contents in the melt inclusions and whole-rocks of the Emeishan basalts reflects different degrees of partial melting in the pyroxenite source at different depths in the melting column. The Pb isotope compositions of the melt inclusions and the OIB-like trace element compositions of the Emeishan basalts imply that mixing of a recycled ancient oceanic crust (EM1-like) component with a peridotite component from the lower mantle (FOZO-like component) could have underwent solid-state reaction, producing a secondary pyroxenite source that was subsequently partially melted to form the basalts. This new model of pyroxenite

3D structure of the Gusev Crater region

NARCIS (Netherlands)

van Kan - Parker, M.; Zegers, T.E.; kneissl, T.; Ivanov, B.; Neukum, G.; Foing, B.

2010-01-01

Gusev Crater lies within the Aeolis Quadrangle of Mars at the boundary between the northern lowlands and southern highlands. The ancient valley Ma'adim Vallis dissects the highlands south of Gusev Crater and is thought to have fed the crater with sediments.High Resolution Stereo Camera data and

Crater ejecta scaling laws: fundamental forms based on dimensional analysis

International Nuclear Information System (INIS)

Housen, K.R.; Schmidt, R.M.; Holsapple, K.A.

1983-01-01

A model of crater ejecta is constructed using dimensional analysis and a recently developed theory of energy and momentum coupling in cratering events. General relations are derived that provide a rationale for scaling laboratory measurements of ejecta to larger events. Specific expressions are presented for ejection velocities and ejecta blanket profiles in two limiting regimes of crater formation: the so-called gravity and strength regimes. In the gravity regime, ejectra velocities at geometrically similar launch points within craters vary as the square root of the product of crater radius and gravity. This relation implies geometric similarity of ejecta blankets. That is, the thickness of an ejecta blanket as a function of distance from the crater center is the same for all sizes of craters if the thickness and range are expressed in terms of crater radii. In the strength regime, ejecta velocities are independent of crater size. Consequently, ejecta blankets are not geometrically similar in this regime. For points away from the crater rim the expressions for ejecta velocities and thickness take the form of power laws. The exponents in these power laws are functions of an exponent, α, that appears in crater radius scaling relations. Thus experimental studies of the dependence of crater radius on impact conditions determine scaling relations for ejecta. Predicted ejection velocities and ejecta-blanket profiles, based on measured values of α, are compared to existing measurements of velocities and debris profiles

The Mars Science Laboratory Mission: Early Results from Gale Crater Landing Site

Science.gov (United States)

Flatow, I.; Grotzinger, J. P.; Blake, D.; Crisp, J. A.; Edgett, K. S.; Gellert, R.; Gomez-Elvira, J.; Hassler, D. M.; Mahaffy, P. R.; Malin, M. C.; Meyer, M. A.; Mitrofanov, I.; Vasavada, A. R.; Wiens, R. C.

2012-12-01

The Mars Science Laboratory rover, Curiosity, landed at Gale Crater on August 5th (PDT) and initiated an investigation of modern and ancient environments. The 155-km diameter Gale Crater was chosen as Curiosity's field site based on several attributes: the interior Mount Sharp preserves a succession of flat-lying strata extending almost 5 km above the elevation of the landing site; the lower few hundred meters of the mound show a progression with relative age from clay-bearing to sulfate-bearing strata, separated by an unconformity from overlying likely anhydrous strata; the landing ellipse is characterized by a mixture of alluvial fan and high thermal inertia/high albedo stratified deposits; and a number of stratigraphically/geomorphically distinct fluvial features. Gale's regional context and strong evidence for a progression through multiple potentially habitable environments, represented by a stratigraphic record of extraordinary extent, ensure preservation of a rich record of the environmental history of early Mars. Curiosity has an expected lifetime of at least one Mars year (~23 months), and drive capability of at least 20 km. The MSL science payload was specifically assembled to assess habitability and includes a gas chromatograph-mass spectrometer and gas analyzer that will search for organic carbon in rocks, regolith fines, and the atmosphere (SAM); an x-ray diffractometer that will determine mineralogical diversity (CheMin); focusable cameras that can image landscapes and rock/regolith textures in natural color (MAHLI, Mastcam); an alpha-particle x-ray spectrometer for in situ determination of rock and soil chemistry (APXS); a laser-induced breakdown spectrometer to remotely sense the chemical composition of rocks and minerals (ChemCam); an active/passive neutron spectrometer designed to search for water in rocks/regolith (DAN); a weather station to measure modern-day environmental variables (REMS); and a sensor designed for continuous monitoring of

Electron microscope observations of impact crater debris amongst contaminating particulates on materials surfaces exposed in space in low-Earth orbit

Science.gov (United States)

Murr, L. E.; Rivas, J. M.; Quinones, S.; Niou, C.-S.; Advani, A. H.; Marquez, B.

1993-01-01

Debris particles extracted from a small sampling region on the leading edge of the Long Duration Exposure Facility (LDEF) spacecraft have been examined by analytical transmission electron microscopy and the elemental frequency observed by energy-dispersive X-ray spectrometry and compared with upper atmosphere (Earth) particle elemental frequency and the average elemental compositions of interplanetary dust particles. A much broader elemental distribution was observed for the exposed spacecraft surface debris milieu. Numerous metal microfragment analyses, particularly aluminum and stainless steel, were compared with scanning electron microscope observations-of impact crater features, and the corresponding elemental spectra on selected LDEF aluminium tray clamps and stainless steel bolts. The compositions and melt features for these impact craters and ejecta have been shown to be consistent with microcrystalline debris fragments in the case of aluminum, and these observations suggest an ever changing debris milieu on exposed surfaces for space craft and space system materials.

Effects of Friction and Plastic Deformation in Shock-Comminuted Damaged Rocks on Impact Heating

Science.gov (United States)

Kurosawa, Kosuke; Genda, Hidenori

2018-01-01

Hypervelocity impacts cause significant heating of planetary bodies. Such events are recorded by a reset of 40Ar-36Ar ages and/or impact melts. Here we investigate the influence of friction and plastic deformation in shock-generated comminuted rocks on the degree of impact heating using the iSALE shock-physics code. We demonstrate that conversion from kinetic to internal energy in the targets with strength occurs during pressure release, and additional heating becomes significant for low-velocity impacts (projectile mass to temperatures for the onset of Ar loss and melting from 8 and 10 km s-1, respectively, for strengthless rocks to 2 and 6 km s-1 for typical rocks. Our results suggest that the impact conditions required to produce the unique features caused by impact heating span a much wider range than previously thought.

Usage of energy- dispersial analysis in studying rocks melts

Directory of Open Access Journals (Sweden)

Kudelas Dušan

2001-09-01

Full Text Available EDS analysis of constituent minerals of nefelitic basanite from locality Konrádovce – lava stream of ceric basalt formation of upper Phocene-Pleistocene age was carried out using the electron microscope JEOL JSM-840 and the energy-dispersive microanalyser KEVEX DELTA+ with MIRROR QUANTEX+ software.Based on the results of EDS microanalysis, the primary rock can be, from the petrographic point of view, described as nefelitic basanite. The following substances were determined in the primer matter and porfiric phenocrysts:- isometric grainsof pyroxene-augite (point A1,- grainsof nepheline-kalsite (point A2,- cryptocrystallic glassy matter (point A3,- grainsof olivine (point A4,- microlite of basic plagioclase (point A5.The energy-dispersive analysis is fast and full spectrum is taken at the same time. In common, a required time is less than one minute. Results of the measurement donot depend significantly on the topography of sample and it is also possible to analyze a rough surface which makes easier the preparation of samples. A very important aspect of the mentioned method is the precision of obtained results in order to identify the chemical composition of analyzed point which, in a subsequent step, allows to determine the type of mineral. EDS is a convenient and powerful supplement of microscopic studies which are, sometime, unable to distinguish exactly the complete composition of the analyzed rocks.

Mineralogy of a Mudstone at Yellowknife Bay, Gale Crater, Mars

Science.gov (United States)

Vaniman, D. T.; Bish, D. L.; Ming, D. W.; Bristow, T. F.; Morris, R. V.; Blake, D. F.; Chipera, S. J.; Morrison, S. M.; Treiman, A. H.; Rampe, E. B.; Rice, M.; Achilles, C. N.; Grotzinger, J. P.; McLennan, S. M.; Williams, J.; Bell, J. F.; Newsom, H. E.; Downs, R. T.; Maurice, S.; Sarrazin, P.; Yen, A. S.; Morookian, J. M.; Farmer, J. D.; Stack, K.; Milliken, R. E.; Ehlmann, B. L.; Sumner, D. Y.; Berger, G.; Crisp, J. A.; Hurowitz, J. A.; Anderson, R.; Des Marais, D. J.; Stolper, E. M.; Edgett, K. S.; Gupta, S.; Spanovich, N.; Agard, Christophe; Alves Verdasca, José Alexandre; Anderson, Ryan; Archer, Doug; Armiens-Aparicio, Carlos; Arvidson, Ray; Atlaskin, Evgeny; Atreya, Sushil; Aubrey, Andrew; Baker, Burt; Baker, Michael; Balic-Zunic, Tonci; Baratoux, David; Baroukh, Julien; Barraclough, Bruce; Bean, Keri; Beegle, Luther; Behar, Alberto; Bender, Steve; Benna, Mehdi; Bentz, Jennifer; Berger, Jeff; Berman, Daniel; Blanco Avalos, Juan J.; Blaney, Diana; Blank, Jen; Blau, Hannah; Bleacher, Lora; Boehm, Eckart; Botta, Oliver; Böttcher, Stephan; Boucher, Thomas; Bower, Hannah; Boyd, Nick; Boynton, Bill; Breves, Elly; Bridges, John; Bridges, Nathan; Brinckerhoff, William; Brinza, David; Brunet, Claude; Brunner, Anna; Brunner, Will; Buch, Arnaud; Bullock, Mark; Burmeister, Sönke; Cabane, Michel; Calef, Fred; Cameron, James; Campbell, John “Iain”; Cantor, Bruce; Caplinger, Michael; Caride Rodríguez, Javier; Carmosino, Marco; Carrasco Blázquez, Isaías; Charpentier, Antoine; Choi, David; Clark, Benton; Clegg, Sam; Cleghorn, Timothy; Cloutis, Ed; Cody, George; Coll, Patrice; Conrad, Pamela; Coscia, David; Cousin, Agnès; Cremers, David; Cros, Alain; Cucinotta, Frank; d'Uston, Claude; Davis, Scott; Day, Mackenzie “Kenzie”; de la Torre Juarez, Manuel; DeFlores, Lauren; DeLapp, Dorothea; DeMarines, Julia; Dietrich, William; Dingler, Robert; Donny, Christophe; Drake, Darrell; Dromart, Gilles; Dupont, Audrey; Duston, Brian; Dworkin, Jason; Dyar, M. Darby; Edgar, Lauren; Edwards, Christopher; Edwards, Laurence; Ehresmann, Bent; Eigenbrode, Jen; Elliott, Beverley; Elliott, Harvey; Ewing, Ryan; Fabre, Cécile; Fairén, Alberto; Farley, Ken; Fassett, Caleb; Favot, Laurent; Fay, Donald; Fedosov, Fedor; Feldman, Jason; Feldman, Sabrina; Fisk, Marty; Fitzgibbon, Mike; Flesch, Greg; Floyd, Melissa; Flückiger, Lorenzo; Forni, Olivier; Fraeman, Abby; Francis, Raymond; François, Pascaline; Franz, Heather; Freissinet, Caroline; French, Katherine Louise; Frydenvang, Jens; Gaboriaud, Alain; Gailhanou, Marc; Garvin, James; Gasnault, Olivier; Geffroy, Claude; Gellert, Ralf; Genzer, Maria; Glavin, Daniel; Godber, Austin; Goesmann, Fred; Goetz, Walter; Golovin, Dmitry; Gómez Gómez, Felipe; Gómez-Elvira, Javier; Gondet, Brigitte; Gordon, Suzanne; Gorevan, Stephen; Grant, John; Griffes, Jennifer; Grinspoon, David; Guillemot, Philippe; Guo, Jingnan; Guzewich, Scott; Haberle, Robert; Halleaux, Douglas; Hallet, Bernard; Hamilton, Vicky; Hardgrove, Craig; Harker, David; Harpold, Daniel; Harri, Ari-Matti; Harshman, Karl; Hassler, Donald; Haukka, Harri; Hayes, Alex; Herkenhoff, Ken; Herrera, Paul; Hettrich, Sebastian; Heydari, Ezat; Hipkin, Victoria; Hoehler, Tori; Hollingsworth, Jeff; Hudgins, Judy; Huntress, Wesley; Hviid, Stubbe; Iagnemma, Karl; Indyk, Steve; Israël, Guy; Jackson, Ryan; Jacob, Samantha; Jakosky, Bruce; Jensen, Elsa; Jensen, Jaqueline Kløvgaard; Johnson, Jeffrey; Johnson, Micah; Johnstone, Steve; Jones, Andrea; Jones, John; Joseph, Jonathan; Jun, Insoo; Kah, Linda; Kahanpää, Henrik; Kahre, Melinda; Karpushkina, Natalya; Kasprzak, Wayne; Kauhanen, Janne; Keely, Leslie; Kemppinen, Osku; Keymeulen, Didier; Kim, Myung-Hee; Kinch, Kjartan; King, Penny; Kirkland, Laurel; Kocurek, Gary; Koefoed, Asmus; Köhler, Jan; Kortmann, Onno; Kozyrev, Alexander; Krezoski, Jill; Krysak, Daniel; Kuzmin, Ruslan; Lacour, Jean Luc; Lafaille, Vivian; Langevin, Yves; Lanza, Nina; Lasue, Jeremie; Le Mouélic, Stéphane; Lee, Ella Mae; Lee, Qiu-Mei; Lees, David; Lefavor, Matthew; Lemmon, Mark; Malvitte, Alain Lepinette; Leshin, Laurie; Léveillé, Richard; Lewin-Carpintier, Éric; Lewis, Kevin; Li, Shuai; Lipkaman, Leslie; Little, Cynthia; Litvak, Maxim; Lorigny, Eric; Lugmair, Guenter; Lundberg, Angela; Lyness, Eric; Madsen, Morten; Mahaffy, Paul; Maki, Justin; Malakhov, Alexey; Malespin, Charles; Malin, Michael; Mangold, Nicolas; Manhes, Gérard; Manning, Heidi; Marchand, Geneviève; Marín Jiménez, Mercedes; Martín García, César; Martin, Dave; Martin, Mildred; Martínez-Frías, Jesús; Martín-Soler, Javier; Martín-Torres, F. Javier; Mauchien, Patrick; McAdam, Amy; McCartney, Elaina; McConnochie, Timothy; McCullough, Emily; McEwan, Ian; McKay, Christopher; McNair, Sean; Melikechi, Noureddine; Meslin, Pierre-Yves; Meyer, Michael; Mezzacappa, Alissa; Miller, Hayden; Miller, Kristen; Minitti, Michelle; Mischna, Michael; Mitrofanov, Igor; Moersch, Jeff; Mokrousov, Maxim; Molina Jurado, Antonio; Moores, John; Mora-Sotomayor, Luis; Mueller-Mellin, Reinhold; Muller, Jan-Peter; Muñoz Caro, Guillermo; Nachon, Marion; Navarro López, Sara; Navarro-González, Rafael; Nealson, Kenneth; Nefian, Ara; Nelson, Tony; Newcombe, Megan; Newman, Claire; Nikiforov, Sergey; Niles, Paul; Nixon, Brian; Noe Dobrea, Eldar; Nolan, Thomas; Oehler, Dorothy; Ollila, Ann; Olson, Timothy; Owen, Tobias; de Pablo Hernández, Miguel Ángel; Paillet, Alexis; Pallier, Etienne; Palucis, Marisa; Parker, Timothy; Parot, Yann; Patel, Kiran; Paton, Mark; Paulsen, Gale; Pavlov, Alex; Pavri, Betina; Peinado-González, Verónica; Pepin, Robert; Peret, Laurent; Perez, Rene; Perrett, Glynis; Peterson, Joe; Pilorget, Cedric; Pinet, Patrick; Pla-García, Jorge; Plante, Ianik; Poitrasson, Franck; Polkko, Jouni; Popa, Radu; Posiolova, Liliya; Posner, Arik; Pradler, Irina; Prats, Benito; Prokhorov, Vasily; Purdy, Sharon Wilson; Raaen, Eric; Radziemski, Leon; Rafkin, Scot; Ramos, Miguel; Raulin, François; Ravine, Michael; Reitz, Günther; Rennó, Nilton; Richardson, Mark; Robert, François; Robertson, Kevin; Rodriguez Manfredi, José Antonio; Romeral-Planelló, Julio J.; Rowland, Scott; Rubin, David; Saccoccio, Muriel; Salamon, Andrew; Sandoval, Jennifer; Sanin, Anton; Sans Fuentes, Sara Alejandra; Saper, Lee; Sautter, Violaine; Savijärvi, Hannu; Schieber, Juergen; Schmidt, Mariek; Schmidt, Walter; Scholes, Daniel “Dan”; Schoppers, Marcel; Schröder, Susanne; Schwenzer, Susanne; Sebastian Martinez, Eduardo; Sengstacken, Aaron; Shterts, Ruslan; Siebach, Kirsten; Siili, Tero; Simmonds, Jeff; Sirven, Jean-Baptiste; Slavney, Susie; Sletten, Ronald; Smith, Michael; Sobrón Sánchez, Pablo; Spray, John; Squyres, Steven; Stalport, Fabien; Steele, Andrew; Stein, Thomas; Stern, Jennifer; Stewart, Noel; Stipp, Susan Louise Svane; Stoiber, Kevin; Sucharski, Bob; Sullivan, Rob; Summons, Roger; Sun, Vivian; Supulver, Kimberley; Sutter, Brad; Szopa, Cyril; Tan, Florence; Tate, Christopher; Teinturier, Samuel; ten Kate, Inge; Thomas, Peter; Thompson, Lucy; Tokar, Robert; Toplis, Mike; Torres Redondo, Josefina; Trainer, Melissa; Tretyakov, Vladislav; Urqui-O'Callaghan, Roser; Van Beek, Jason; Van Beek, Tessa; VanBommel, Scott; Varenikov, Alexey; Vasavada, Ashwin; Vasconcelos, Paulo; Vicenzi, Edward; Vostrukhin, Andrey; Voytek, Mary; Wadhwa, Meenakshi; Ward, Jennifer; Webster, Chris; Weigle, Eddie; Wellington, Danika; Westall, Frances; Wiens, Roger Craig; Wilhelm, Mary Beth; Williams, Amy; Williams, Rebecca; Williams, Richard B. “Mouser”; Wilson, Mike; Wimmer-Schweingruber, Robert; Wolff, Mike; Wong, Mike; Wray, James; Wu, Megan; Yana, Charles; Yingst, Aileen; Zeitlin, Cary; Zimdar, Robert; Zorzano Mier, María-Paz

2014-01-01

Sedimentary rocks at Yellowknife Bay (Gale crater) on Mars include mudstone sampled by the Curiosity rover. The samples, John Klein and Cumberland, contain detrital basaltic minerals, calcium sulfates, iron oxide or hydroxides, iron sulfides, amorphous material, and trioctahedral smectites. The John Klein smectite has basal spacing of ~10 angstroms, indicating little interlayer hydration. The Cumberland smectite has basal spacing at both ~13.2 and ~10 angstroms. The larger spacing suggests a partially chloritized interlayer or interlayer magnesium or calcium facilitating H2O retention. Basaltic minerals in the mudstone are similar to those in nearby eolian deposits. However, the mudstone has far less Fe-forsterite, possibly lost with formation of smectite plus magnetite. Late Noachian/Early Hesperian or younger age indicates that clay mineral formation on Mars extended beyond Noachian time.

Mineralogy of a mudstone at Yellowknife Bay, Gale crater, Mars.

Science.gov (United States)

Vaniman, D T; Bish, D L; Ming, D W; Bristow, T F; Morris, R V; Blake, D F; Chipera, S J; Morrison, S M; Treiman, A H; Rampe, E B; Rice, M; Achilles, C N; Grotzinger, J P; McLennan, S M; Williams, J; Bell, J F; Newsom, H E; Downs, R T; Maurice, S; Sarrazin, P; Yen, A S; Morookian, J M; Farmer, J D; Stack, K; Milliken, R E; Ehlmann, B L; Sumner, D Y; Berger, G; Crisp, J A; Hurowitz, J A; Anderson, R; Des Marais, D J; Stolper, E M; Edgett, K S; Gupta, S; Spanovich, N

2014-01-24

Sedimentary rocks at Yellowknife Bay (Gale crater) on Mars include mudstone sampled by the Curiosity rover. The samples, John Klein and Cumberland, contain detrital basaltic minerals, calcium sulfates, iron oxide or hydroxides, iron sulfides, amorphous material, and trioctahedral smectites. The John Klein smectite has basal spacing of ~10 angstroms, indicating little interlayer hydration. The Cumberland smectite has basal spacing at both ~13.2 and ~10 angstroms. The larger spacing suggests a partially chloritized interlayer or interlayer magnesium or calcium facilitating H2O retention. Basaltic minerals in the mudstone are similar to those in nearby eolian deposits. However, the mudstone has far less Fe-forsterite, possibly lost with formation of smectite plus magnetite. Late Noachian/Early Hesperian or younger age indicates that clay mineral formation on Mars extended beyond Noachian time.

Crater Topography on Titan: Implications for Landscape Evolution

Science.gov (United States)

Neish, Catherine D.; Kirk, R.L.; Lorenz, R. D.; Bray, V. J.; Schenk, P.; Stiles, B. W.; Turtle, E.; Mitchell, K.; Hayes, A.

2013-01-01

We present a comprehensive review of available crater topography measurements for Saturn's moon Titan. In general, the depths of Titan's craters are within the range of depths observed for similarly sized fresh craters on Ganymede, but several hundreds of meters shallower than Ganymede's average depth vs. diameter trend. Depth-to-diameter ratios are between 0.0012 +/- 0.0003 (for the largest crater studied, Menrva, D approximately 425 km) and 0.017 +/- 0.004 (for the smallest crater studied, Ksa, D approximately 39 km). When we evaluate the Anderson-Darling goodness-of-fit parameter, we find that there is less than a 10% probability that Titan's craters have a current depth distribution that is consistent with the depth distribution of fresh craters on Ganymede. There is, however, a much higher probability that the relative depths are uniformly distributed between 0 (fresh) and 1 (completely infilled). This distribution is consistent with an infilling process that is relatively constant with time, such as aeolian deposition. Assuming that Ganymede represents a close 'airless' analogue to Titan, the difference in depths represents the first quantitative measure of the amount of modification that has shaped Titan's surface, the only body in the outer Solar System with extensive surface-atmosphere exchange.

Geologic map of Tooting crater, Amazonis Planitia region of Mars

Science.gov (United States)

Mouginis-Mark, Peter J.

2015-01-01

Tooting crater has a diameter of 27.2 km, and formed on virtually flat lava flows within Amazonis Planitia ~1,300 km west of the summit of Olympus Mons volcano, where there appear to have been no other major topographic features prior to the impact. The crater formed in an area ~185 x 135 km that is at an elevation between −3,870 m and −3,874 m relative to the Mars Orbiter Laser Altimeter (MOLA) Mars datum. This fortuitous situation (for example, a bland, horizontal target) allows the geometry of the crater and the thickness of the ejecta blanket to be accurately determined by subtracting the appropriate elevation of the surrounding landscape (−3,872 m) from the individual MOLA measurements across the crater. Thus, for the first time, it is possible to determine the radial decrease of ejecta thickness as a function of distance away from the rim crest. On the basis of the four discrete ejecta layers surrounding the crater cavity, Tooting crater is classified as a Multiple-Layered Ejecta (MLE) crater. By virtue of the asymmetric distribution of secondary craters and the greater thickness of ejecta to the northeast, Morris and others (2010) proposed that Tooting crater formed by an oblique impact from the southwest. The maximum range of blocks that produced identifiable secondary craters is ~500 km (~36.0 crater radii) from the northeast rim crest. In contrast, secondary craters are only identifiable ~215 km (15.8 radii) to the southeast and 225 km (16.5 radii) to the west.

Pb isotopes during crustal melting and magma mingling - A cautionary tale from the Miki Fjord macrodike, central east Greenland

DEFF Research Database (Denmark)

Waight, Tod Earle; Lesher, Charles

2010-01-01

Pb isotopic data are presented for hybrid rocks formed by mingling between mantle-derived tholeiitic magma of the Eocene Miki Fjord macrodike (East Greenland) and melt derived from the adjacent Precambrian basement. Bulk mixing and AFC processes between end-members readily identified in the field...... grain boundaries during disequilibrium melting of the host rock by the mafic magma. The crustal melt involved in magma interactions was therefore heterogeneous with respect to Pb isotopes on a metre-scale. These results illustrate the difficulties inherent in interpreting isotopic variations...... in contaminated mafic magmas even when the end-members are well constrained by field relations. We show that the Pb isotopic composition of the crustal contaminants and contamination trajectories for the Miki Fjord hybrid magmatic lithologies are markedly different from regional basement gneisses and contaminated...

OCENER, a one-dimensional computer code for the numerical simulation of the mechanical effects of peaceful underground nuclear explosions in rocks

International Nuclear Information System (INIS)

Gupta, S.C.; Sikka, S.K.; Chidambaram, R.

1979-01-01

An account is given of a one-dimensional spherical symmetric computer code for the numerical simulation of the effects of peaceful underground nuclear explosions in rocks (OCENER). In the code, the nature of the stress field and response of the medium to this field are modelled numerically by finite difference form of the laws of continuum mechanics and the constitutive relations of the rock medium in which the detonation occurs. It enables to approximate well the cavity growth and fracturing of the surrounding rock for contained explosions and the events upto the time the spherical symmetry is valid for cratering-type explosions. (auth.)

Optimizing laser crater enhanced Raman spectroscopy.

Science.gov (United States)

Lednev, V N; Sdvizhenskii, P A; Grishin, M Ya; Filichkina, V A; Shchegolikhin, A N; Pershin, S M

2018-03-20

Raman signal enhancement by laser crater production was systematically studied for 785 nm continuous wave laser pumping. Laser craters were produced in L-aspartic acid powder by a nanosecond pulsed solid state neodymium-doped yttrium aluminum garnet laser (532 nm, 8 ns, 1 mJ/pulse), while Raman spectra were then acquired by using a commercial spectrometer with 785 nm laser beam pumping. The Raman signal enhancement effect was studied in terms of the number of ablating pulses used, the lens-to-sample distance, and the crater-center-laser-spot offset. The influence of the experiment parameters on Raman signal enhancement was studied for different powder materials. Maximum Raman signal enhancement reached 11 fold for loose powders but decreased twice for pressed tablets. Raman signal enhancement was demonstrated for several diverse powder materials like gypsum or ammonium nitrate with better results achieved for the samples tending to give narrow and deep craters upon the laser ablation stage. Alternative ways of cavity production (steel needle tapping and hole drilling) were compared with the laser cratering technique in terms of Raman signal enhancement. Drilling was found to give the poorest enhancement of the Raman signal, while both laser ablation and steel needle tapping provided comparable results. Here, we have demonstrated for the first time, to the best of our knowledge, that a Raman signal can be enhanced 10 fold with the aid of simple cavity production by steel needle tapping in rough highly reflective materials. Though laser crater enhancement Raman spectroscopy requires an additional pulsed laser, this technique is more appropriate for automatization compared to the needle tapping approach.

Crystal-Chemical Analysis Martian Minerals in Gale Crater

Science.gov (United States)

Morrison, S. M.; Downs, R. T.; Blake, D. F.; Bish, D. L.; Ming, D. W.; Morris, R. V.; Yen, A. S.; Chipera, S. J.; Treiman, A. H.; Vaniman, D. T.;

The central uplift of Elorza Crater: Insights into its geology and possible relationships to the Valles Marineris and Tharsis regions

Science.gov (United States)

Hopkins, R. T.; Tornabene, L. L.; Osinski, G. R.

2017-03-01

The majority of hydrated silicate occurrences on Mars are associated with impact craters (Ehlmann et al., 2011; Carter et al., 2013). Three formation mechanisms have been suggested to account for this correlation: (1) aqueous alteration occurred pre-impact, and was subsequently exposed via the impact (pre-impact; Bibring et al., 2006; Ehlmann et al., 2011), (2) heat generated from the impact facilitated the formation of a hydrothermal system, leading to alteration products (syn-impact; e.g. Marzo et al., 2010; Osinski et al., 2013), and/or (3) altered materials were deposited after crater formation, or formed within the crater well after the impact had taken place (post-impact). In this study, we analyze the central uplift of Elorza Crater, a ∼40 km diameter impact crater located ∼300 km north of Valles Marineris. To determine whether hydrated minerals found within the uplift were generated pre-, syn-, or post-impact, we used a data synthesis approach, utilizing High Resolution Imaging Science Experiment (HiRISE), Compact Reconnaissance Imaging Spectrometer for Mars (CRISM), Context Camera (CTX), and Thermal Emission Imaging System (THEMIS) imagery. Opaline silica is observed in two locations on the southwestern side of the uplift and is interpreted to have been pre-existing or formed via hydrothermal alteration due to stratigraphic relationships with the overlying impact melt unit. Both Fe/Mg smectite and low-calcium pyroxene (LCP) are found throughout the uplift. Bedrock exposures on the northern wall of Coprates Chasma containing Fe/Mg smectite and LCP suggest an uplifted origin for these units. In all cases, although a pre-existing origin is probable, it is difficult to rule out the possibility of an impact-generated hydrothermal origin. Using the observed stratigraphy exposed in Coprates Chasma and bedrock exposures analyzed in nearby craters, we were able to constrain the pre-impact stratigraphy around Elorza. The near-subsurface consists of Hesperian

100 New Impact Crater Sites Found on Mars

Science.gov (United States)

Kennedy, M. R.; Malin, M. C.

2009-12-01

Recent observations constrain the formation of 100 new impact sites on Mars over the past decade; 19 of these were found using the Mars Global Surveyor Mars Orbiter Camera (MOC), and the other 81 have been identified since 2006 using the Mars Reconnaissance Orbiter Context Camera (CTX). Every 6 meter/pixel CTX image is examined upon receipt and, where they overlap images of 0.3-240 m/pixel scale acquired by the same or other Mars-orbiting spacecraft, we look for features that may have changed. New impact sites are initially identified by the presence of a new dark spot or cluster of dark spots in a CTX image. Such spots may be new impact craters, or result from the effect of impact blasts on the dusty surface. In some (generally rare) cases, the crater is sufficiently large to be resolved in the CTX image. In most cases, however, the crater(s) cannot be seen. These are tentatively designated as “candidate” new impact sites, and the CTX team then creates an opportunity for the MRO spacecraft to point its cameras off-nadir and requests that the High Resolution Imaging Science Experiment (HiRISE) team obtain an image of ~0.3 m/pixel to confirm whether a crater or crater cluster is present. It is clear even from cursory examination that the CTX observations are areographically biased to dusty, higher albedo areas on Mars. All but 3 of the 100 new impact sites occur on surfaces with Lambert albedo values in excess of 23.5%. Our initial study of MOC images greatly benefited from the initial global observations made in one month in 1999, creating a baseline date from which we could start counting new craters. The global coverage by MRO Mars Color Imager is more than a factor of 4 poorer in resolution than the MOC Wide Angle camera and does not offer the opportunity for global analysis. Instead, we must rely on partial global coverage and global coverage that has taken years to accumulate; thus we can only treat impact rates statistically. We subdivide the total data

Dynamics of crater formations in immersed granular materials

Science.gov (United States)

Varas, G.; Vidal, V.; Géminard, J.

2009-12-01

Craters are part of the widespread phenomena observed in nature. Among the main applications to natural phenomena, aside from meteorite impact craters, are the formation and growth of volcanic edifices, by successive ejecta emplacement and/or erosion. The time evolution and dynamics play a crucial role here, as the competition between volcanic-jet mass-flux (degassing and ejecta) and crater-size evolution may control directly the eruptive regime. Crater morphology in dry granular material has been extensively studied, both experimentally and theoretically. Most of these studies investigate the final, steady crater shape resulting from the collision of solid bodies with the material surface and scaling laws are derived. In immersed granular material, craters generated by an underwater vortex ring, or underwater impact craters generated by landslide, have been reported. In a previous experimental study, Gostiaux et al. [Gran. Matt., 2002] have investigated the dynamics of air flowing through an immersed granular layer. They reported that, depending on the flow rate, the system exhibits two qualitatively different regimes: At small flow rate, the bubbling regime during which bubbles escape the granular layer independently one from another; At large flow rate, the open-channel regime which corresponds to the formation of a channel crossing the whole thickness of the granular bed through which air escapes almost continuously. At intermediate flow rate, a spontaneous alternation between these two regimes is observed. Here, we report the dynamics of crater formations at the free surface of an immersed granular bed, locally crossed by an ascending gas flow. We reproduce the experimental conditions of Gostiaux et al. (2002) in two dimensions: In a vertical Hele-Shaw cell, the crater consists of two sand piles which develop around the location of the gas emission. We observe that the typical size of the crater increases logarithmically with time, independently of the gas

Uranium-thorium disequilibria and partitioning on melting of garnet peridotite

International Nuclear Information System (INIS)

Beattie, P.

1993-01-01

The abundances of isotopes in the 238 U decay series can be used as both tracers and chronometers of magmatic processes. In the subsolidus asthenosphere, the activity of each daughter isotope (defined as the product of its concentration and decay constant, and denoted by parentheses) is assumed to be equal to that of its parent. By contrast, ( 230 Th/ 238 U) is greater than unity in most recent mid-ocean-ridge and ocean-island basalts, implying that thorium is more incompatible (that is, it is partitioned into the melt phase more strongly) than uranium. Melting of spinel peridotite cannot produce the ( 230 Th) excesses, because measured partition coefficients for pyroxenes and olivine demonstrate that uranium is more incompatible than thorium for this rock. Here I report garnet-melt partitioning data which show that for this mineral-melt pair thorium does behave more incompatibility than uranium, thus supporting the suggestion that mid-ocean-ridge basalts (MORB) are produced by melting initiated at depths where garnet is stable. Using these data, I show that the observed ( 230 Th/ 238 U) ratios of MORB and most ocean-island basalts can be explained by slow, near-fractional melting initiated in the garnet stability field. (author)

Surface age of venus: use of the terrestrial cratering record

International Nuclear Information System (INIS)

Schaber, G.G.; Shoemaker, E.M.; Kozak, R.C.

1987-01-01

The average crater age of Venus' northern hemisphere may be less than 250 m.y. assuming equivalence between the recent terrestrial cratering rate and that on Venus for craters ≥ 20 km in diameter. For craters larger than this threshold size, below which crater production is significantly affected by the Venusian atmosphere, there are fairly strong observational grounds for concluding that such an equivalence in cratering rates on Venus and Earth may exist. However, given the uncertainties in the role of both active and inactive comet nuclei in the cratering history of Earth, we conclude that the age of the observed surface in the northern hemisphere of Venus could be as great as the 450-m.y. mean age of the Earth's crust. The observed surface of Venus might be even older, but no evidence from the crater observations supports an age as great as 1 b.y. If the age of the observed Venusian surface were 1 b.y., it probably should bear the impact scars of a half dozen or more large comet nuclei that penetrated the atmosphere and formed craters well over 100 km in diameter. Venera 15/16 mapped only about 25% of Venus; the remaining 75% may tell us a completely different story

Impact spacecraft imagery and comparative morphology of craters

International Nuclear Information System (INIS)

Moutsoulas, M.; Piteri, S.

1979-01-01

The use of hard-landing 'simple' missions for wide-scale planetary exploration is considered. As an example of their imagery potentialities, Ranger VII data are used for the study of the morphological characteristics of 16 Mare Cognitum craters. The morphological patterns of lunar craters, expressed in terms of the Depth/Diameter ratios appear to be in most cases independent of the crater location or size. (Auth.)

Geomorphology of crater and basin deposits - Emplacement of the Fra Mauro formation

Science.gov (United States)

Morrison, R. H.; Oberbeck, V. R.

1975-01-01

Characteristics of continuous deposits near lunar craters larger than about 1 km wide are considered, and it is concluded that (1) concentric dunes, radial ridges, and braided lineations result from deposition of the collision products of ejecta from adjacent pairs of similarly oriented secondary-crater chains and are, therefore, concentrations of secondary-crater ejecta; (2) intracrater ridges are produced within preexisting craters surrounding a fresh primary crater by ricocheting and focusing of secondary-crater ejecta from the preexisting craters' walls; and (3) secondary cratering has produced many of the structures of the continuous deposits of relatively small lunar craters and is the dominant process for emplacement of most of the radial facies of the continuous deposits of large lunar craters and basins. The percentages of Imbrium ejecta in deposits and the nature of Imbrium sculpturing are investigated.

Sub-surface structures and collapse mechanisms of summit pit craters

Science.gov (United States)

Roche, O.; van Wyk de Vries, B.; Druitt, T. H.

2001-01-01

Summit pit craters are found in many types of volcanoes and are generally thought to be the product of collapse into an underpressured reservoir caused by magma withdrawal. We investigate the mechanisms and structures associated with summit pit crater formation by scaled analogue experiments and make comparisons with natural examples. Models use a sand plaster mixture as analogue rock over a cylinder of silicone simulating an underpressured magma reservoir. Experiments are carried out using different roof aspect ratios (roof thickness/roof width) of 0.2-2. They reveal two basic collapse mechanisms, dependant on the roof aspect ratio. One occurs at low aspect ratios (≤1), as illustrated by aspect ratios of 0.2 and 1. Outward dipping reverse faults initiated at the silicone margins propagates through the entire roof thickness and cause subsidence of a coherent block. Collapse along the reverse faults is accommodated by marginal flexure of the block and tension fractures at the surface (aspect ratio of 0.2) or by the creation of inward dipping normal faults delimiting a terrace (aspect ratio of 1). At an aspect ratio of 1, overhanging pit walls are the surface expressions of the reverse faults. Experiments at high aspect ratio (>1.2) reveal a second mechanism. In this case, collapse occurs by stopping, which propagates upwards by a complex pattern of both reverse faults and tension fractures. The initial underground collapse is restricted to a zone above the reservoir and creates a cavity with a stable roof above it. An intermediate mechanism occurs at aspect ratios of 1.1-1.2. In this case, stopping leads to the formation of a cavity with a thin and unstable roof, which collapses suddenly. The newly formed depression then exhibits overhanging walls. Surface morphology and structure of natural examples, such as the summit pit craters at Masaya Volcano, Nicaragua, have many of the features created in the models, indicating that the internal structural geometry of

The Rock that Hit New York

Energy Technology Data Exchange (ETDEWEB)

Meade, Roger Allen [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Keksis, August Lawrence [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

2016-10-03

On January 12, 1975, a rock seemed to fall from the sky over New York State’s Schoharie County hitting the tractor of a local farmer, who was “preparing his fields for spring planting.” As the farmer later described the event to a reporter from the UFO INVESTIGATOR, the object glanced off the tractor, fell to the ground, and melted its way through a patch of ice that was two and one half inches thick. The farmer, Leonard Tillapaugh, called the county sheriff, Harvey Stoddard, who recovered the rock, noting that it “was still warm.” Why and how a sample of the rock came to Los Alamos is not known. However, it captivated a wide Laboratory audience, was subjected to rigorous testing and evaluation. Los Alamos used the scientific method in the manner promoted by Hynek. Did Los Alamos solve the mystery of the rock’s origin? Not definitively. Although the exact origin could not be determined, it was shown conclusively that the rock was not from outer space. With that said, the saga of Rock that hit New York came to an end. Nothing more was said or written about it. The principals involved have long since passed from the scene. The NICAP ceased operations in 1980. And, the rock, itself, has disappeared.

A concept of row crater enhancement

International Nuclear Information System (INIS)

Redpath, B.B.

1970-01-01

Linear craters formed by the simultaneous detonation of a row of buried explosives will probably have a wider application than single charges in the explosive excavation of engineering structures. Most cratering experience to date has been with single charges, and an analytical procedure for the design of a row of charges to excavate a crater with a specified configuration has been lacking. There are no digital computer codes having direct application to a row of charges as there are for single charges. This paper derives a simple relationship which can be used to design row charges with some assurance of achieving the desired result and with considerable flexibility in the choice of explosive yield of the individual charges

Cutting Craters

Science.gov (United States)

2003-01-01

[figure removed for brevity, see original site] Released 12 November 2003The rims of two old and degraded impact craters are intersected by a graben in this THEMIS image taken near Mangala Fossa. Yardangs and low-albedo wind streaks are observed at the top of the image as well as interesting small grooves on the crater floor. The origin of these enigmatic grooves may be the result of mud or lava and volatile interactions. Variable surface textures observed in the bottom crater floor are the result of different aged lava flows.Image information: VIS instrument. Latitude -15.2, Longitude 219.2 East (140.8 West). 19 meter/pixel resolution.Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time. NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

Crater populations in the early history of Mercury

International Nuclear Information System (INIS)

Guest, J.E.; Gault, D.E.

1976-01-01

Crater populations on two major geologic units of Mercury have been classified into three morphologic types which characterize their state of degradation. The results indicate that one or more processes either prior to or contemporary with the formation of the 1300 km diameter Caloris Planitia reduced the population of fresh craters smaller than 70--80 km diameter and totally erased the population of fresh craters smaller than 20--30 km

Survival Times of Meter-Sized Rock Boulders on the Surface of Airless Bodies

Science.gov (United States)

Basilevsky, A. T.; Head, J. W.; Horz, F.; Ramsley, K.

2015-01-01

This study considers the survival times of meter-sized rock boulders on the surfaces of several airless bodies. As the starting point, we employ estimates of the survival times of such boulders on the surface of the Moon by[1], then discuss the role of destruction due to day-night temperature cycling, consider the meteorite bombardment environment on the considered bodies in terms of projectile flux and velocities and finally estimate the survival times. Survival times of meter-sized rocks on lunar surface: The survival times of hand specimen-sized rocks exposed to the lunar surface environment were estimated based on experiments modeling the destruction of rocks by meteorite impacts, combined with measurements of the lunar surface meteorite flux, (e.g.,[2]). For estimations of the survival times of meter-sized lunar boulders, [1] suggested a different approach based on analysis of the spatial density of boulders on the rims of small lunar craters of known absolute age. It was found that for a few million years, only a small fraction of the boulders ejected by cratering process are destroyed, for several tens of million years approx.50% are destroyed, and for 200-300 Ma, 90 to 99% are destroyed. Following [2] and other works, [1] considered that the rocks are mostly destroyed by meteorite impacts. Destruction of rocks by thermal-stress. However, high diurnal temperature variations on the surface of the Moon and other airless bodies imply that thermal stresses may also be a cause of surface rock destruction. Delbo et al. [3] interpreted the observed presence of fine debris on the surface of small asteroids as due to thermal surface cycling. They stated that because of the very low gravity on the surface of these bodies, ejecta from meteorite impacts should leave the body, so formation there of fine debris has to be due to thermal cycling. Based on experiments on heating-cooling of cm-scale pieces of ordinary and carbonaceous chondrites and theoretical modeling of

The role and conditions of second-stage mantle melting in the generation of low-Ti tholeiites and boninites: the case of the Manihiki Plateau and the Troodos ophiolite

Science.gov (United States)

Golowin, Roman; Portnyagin, Maxim; Hoernle, Kaj; Sobolev, Alexander; Kuzmin, Dimitry; Werner, Reinhard

2017-12-01

High-Mg, low-Ti volcanic rocks from the Manihiki Plateau in the Western Pacific share many geochemical characteristics with subduction-related boninites such as high-Ca boninites from the Troodos ophiolite on Cyprus, which are believed to originate by hydrous re-melting of previously depleted mantle. In this paper we compare the Manihiki rocks and Troodos boninites using a new dataset on the major and trace element composition of whole rocks and glasses from these locations, and new high-precision, electron microprobe analyses of olivine and Cr-spinel in these rocks. Our results show that both low-Ti Manihiki rocks and Troodos boninites could originate by re-melting of a previously depleted lherzolite mantle source (20-25% of total melting with 8-10% melting during the first stage), as indicated by strong depletion of magmas in more to less incompatible elements (Sm/Yb Y 0.5). In comparison with Troodos boninites, the low-Ti Manihiki magmas had distinctively lower H2O contents ( 2 wt% in boninites), 100 °C higher liquidus temperatures at a given olivine Fo-number, lower fO2 (ΔQFM + 0.2) and originated from deeper and hotter mantle (1.4-1.7 GPa, 1440 °C vs. 0.8-1.0 GPa, 1300 °C for Troodos boninites). The data provide new evidence that re-melting of residual upper mantle is not only restricted to subduction zones, where it occurs under hydrous conditions, but can also take place due to interaction of previously depleted upper mantle with mantle plumes from the deep and hotter Earth interior.

Summit crater lake observations, and the location, chemistry, and pH of water samples near Mount Chiginagak volcano, Alaska: 2004-2012

Science.gov (United States)

Schaefer, Janet R.; Scott, William E.; Evans, William C.; Wang, Bronwen; McGimsey, Robert G.

2013-01-01

Mount Chiginagak is a hydrothermally active volcano on the Alaska Peninsula, approximately 170 km south–southwest of King Salmon, Alaska (fig. 1). This small stratovolcano, approximately 8 km in diameter, has erupted through Tertiary to Permian sedimentary and igneous rocks (Detterman and others, 1987). The highest peak is at an elevation of 2,135 m, and the upper ~1,000 m of the volcano are covered with snow and ice. Holocene activity consists of debris avalanches, lahars, and lava flows. Pleistocene pyroclastic flows and block-and-ash flows, interlayered with andesitic lava flows, dominate the edifice rocks on the northern and western flanks. Historical reports of activity are limited and generally describe “steaming” and “smoking” (Coats, 1950; Powers, 1958). Proximal tephra collected during recent fieldwork suggests there may have been limited Holocene explosive activity that resulted in localized ash fall. A cluster of fumaroles on the north flank, at an elevation of ~1,750 m, commonly referred to as the “north flank fumarole” have been emitting gas throughout historical time (location shown in fig. 2). The only other thermal feature at the volcano is the Mother Goose hot springs located at the base of the edifice on the northwestern flank in upper Volcano Creek, at an elevation of ~160 m (fig. 2, near sites H1, H3, and H4). Sometime between November 2004 and May 2005, a ~400-m-wide, 100-m-deep lake developed in the snow- and ice-filled summit crater of the volcano (Schaefer and others, 2008). In early May 2005, an estimated 3 million cubic meters (3×106 m3) of sulfurous, clay-rich debris and acidic water exited the crater through tunnels at the base of a glacier that breaches the south crater rim. More than 27 km downstream, these acidic flood waters reached approximately 1.3 m above normal water levels and inundated a fertile, salmon-spawning drainage, acidifying the entire water column of Mother Goose Lake from its surface waters to its

Partial melting of UHP calc-gneiss from the Dabie Mountains

Science.gov (United States)

Liu, Penglei; Wu, Yao; Liu, Qiang; Zhang, Junfeng; Zhang, Li; Jin, Zhenmin

2014-04-01

Exhumation melting has been proposed for the ultra-high pressure (UHP) metamorphic rocks in the Dabie Mountains based on melting experiments. We document here the first petrological and mineralogical evidence demonstrating that the UHP calc-gneisses from the Ganjialing area in the Dabie Mountains experienced partial melting during early exhumation. The assemblage of garnet, phengite (Si = 3.65 pfu), coesite, rutile and carbonate preserved in the calc-gneisses indicates a peak metamorphic condition of 692-757 °C and 4.0-4.8 GPa. Partial melting is indicated by several lines of evidence: the melting textures of phengite, the feldspar-dominated films, bands, branches, blebs and veins, the euhedral K-feldspars, the intergrowth film of plagioclase and K-feldspar, the plagioclase + biotite intergrowth after garnet and the epidote poikiloblasts. Polyphase inclusions in garnet are characterized with wedge-like offshoots and serrate outlines whereas those in epidote display negative crystal shapes, which can be best interpreted by entrapment of former melts. We propose a wet melting reaction of Phn + Q ± Na-Cpx + H2O = Bt + Pl + Grt + felsic melts, which likely took place at ca.650-800 °C and ca.1.0-2.0 GPa, to interpret the melting event in the calc-gneisses. Chemical exchanges between garnet and melts produced new garnet domains with higher almandine, spessartine, MREE, HREE and Y but lower grossular, pyrope, P, Sc, Ti, V and Zr contents. Zr-in-rutile thermometer reveals a low temperature of 620-643 °C at 5 GPa, indicating a later reset for Zr in rutile. Healed fractures are suggested to be responsible for the formation of some polyphase inclusions in garnet.

Cratering record in the inner solar system: Implications for earth

International Nuclear Information System (INIS)

Barlow, N.G.

1988-01-01

Internal and external processes have reworked the Earth's surface throughout its history. In particular, the effect of meteorite impacts on the early history of the earth is lost due to fluvial, aeolian, volcanic and plate tectonic action. The cratering record on other inner solar system bodies often provides the only clue to the relative cratering rates and intensities that the earth has experienced throughout its history. Of the five major bodies within the inner solar system, Mercury, Mars, and the Moon retain scars of an early episode of high impact rates. The heavily cratered regions on Mercury, Mars, and the Moon show crater size-frequency distribution curves similar in shape and crater density, whereas the lightly cratered plains on the Moon and Mars show distribution curves which, although similar to each other, are statistically different in shape and density from the more heavily cratered units. The similarities among crater size-frequency distribution curves for the Moon, Mercury, and Mars suggest that the entire inner solar system was subjected to the two populations of impacting objects but Earth and Venus have lost their record of heavy bombardment impactors. Thus, based on the cratering record on the Moon, Mercury, and Mars, it can be inferred that the Earth experienced a period of high crater rates and basin formation prior to about 3.8 BY ago. Recent studies have linked mass extinctions to large terrestrial impacts, so life forms were unable to establish themselves until impact rates decreased substantially and terrestrial conditions became more benign. The possible periodicity of mass extinctions has led to the theory of fluctuating impact rates due to comet showers in the post heavy bombardment period. The active erosional environment on the Earth complicates attempts to verify these showers by erasing geological evidence of older impact craters

The effects of buoyancy on shear-induced melt bands in a compacting porous medium

Science.gov (United States)

Butler, S. L.

2009-03-01

It has recently been shown [Holtzman, B., Groebner, N., Zimmerman, M., Ginsberg, S., Kohlstedt, D., 2003. Stress-driven melt segregation in partially molten rocks. Geochem. Geophys. Geosyst. 4, Art. No. 8607; Holtzman, B.K., Kohlstedt, D.L., 2007. Stress-driven melt segregation and strain partitioning in partially molten rocks: effects of stress and strain. J. Petrol. 48, 2379-2406] that when partially molten rock is subjected to simple shear, bands of high and low porosity are formed at a particular angle to the direction of instantaneous maximum extension. These have been modeled numerically and it has been speculated that high porosity bands may form an interconnected network with a bulk, effective permeability that is enhanced in a direction parallel to the bands. As a result, the bands may act to focus mantle melt towards the axis of mid-ocean ridges [Katz, R.F., Spiegelman, M., Holtzman, B., 2006. The dynamics of melt and shear localization in partially molten aggregates. Nature 442, 676-679]. In this contribution, we examine the combined effects of buoyancy and matrix shear on a deforming porous layer. The linear theory of Spiegelman [Spiegelman, M., 1993. Flow in deformable porous media. Part 1. Simple analysis. J. Fluid Mech. 247, 17-38; Spiegelman, M., 2003. Linear analysis of melt band formation by simple shear. Geochem. Geophys. Geosyst. 4, doi:10.1029/2002GC000499, Article 8615] and Katz et al. [Katz, R.F., Spiegelman, M., Holtzman, B., 2006. The dynamics of melt and shear localization in partially molten aggregates. Nature 442, 676-679] is generalized to include both the effects of buoyancy and matrix shear on a deformable porous layer with strain-rate dependent rheology. The predictions of linear theory are compared with the early time evolution of our 2D numerical model and they are found to be in excellent agreement. For conditions similar to the upper mantle, buoyancy forces can be similar to or much greater than matrix shear-induced forces. The

Topography of the Martian Impact Crater Tooting

Science.gov (United States)

Mouginis-Mark, P. J.; Garbeil, H.; Boyce, J. M.

2009-01-01

Tooting crater is approx.29 km in diameter, is located at 23.4degN, 207.5degE, and is classified as a multi-layered ejecta crater [1]. Our mapping last year identified several challenges that can now be addressed with HiRISE and CTX images, but specifically the third dimension of units. To address the distribution of ponded sediments, lobate flows, and volatile-bearing units within the crater cavity, we have focused this year on creating digital elevation models (DEMs) for the crater and ejecta blanket from stereo CTX and HiRISE images. These DEMs have a spatial resolution of approx.50 m for CTX data, and 2 m for HiRISE data. Each DEM is referenced to all of the available individual MOLA data points within an image, which number approx.5,000 and 800 respectively for the two data types

A global catalogue of Ceres impact craters ≥ 1 km and preliminary analysis

Science.gov (United States)

Gou, Sheng; Yue, Zongyu; Di, Kaichang; Liu, Zhaoqin

2018-03-01

The orbital data products of Ceres, including global LAMO image mosaic and global HAMO DTM with a resolution of 35 m/pixel and 135 m/pixel respectively, are utilized in this research to create a global catalogue of impact craters with diameter ≥ 1 km, and their morphometric parameters are calculated. Statistics shows: (1) There are 29,219 craters in the catalogue, and the craters have a various morphologies, e.g., polygonal crater, floor fractured crater, complex crater with central peak, etc.; (2) The identifiable smallest crater size is extended to 1 km and the crater numbers have been updated when compared with the crater catalogue (D ≥ 20 km) released by the Dawn Science Team; (3) The d/D ratios for fresh simple craters, obviously degraded simple crater and polygonal simple crater are 0.11 ± 0.04, 0.05 ± 0.04 and 0.14 ± 0.02 respectively. (4) The d/D ratios for non-polygonal complex crater and polygonal complex crater are 0.08 ± 0.04 and 0.09 ± 0.03. The global crater catalogue created in this work can be further applied to many other scientific researches, such as comparing d/D with other bodies, inferring subsurface properties, determining surface age, and estimating average erosion rate.

Frictional processes during flank motion at Mount Etna (Italy): experimental characterisation of slip on similar and dissimilar volcanic and sedimentary rocks.

Science.gov (United States)

Rozanski, Wojciech; Lavallee, Yan; Kendrick, Jackie; Castagna, Angela; Mitchell, Thomas; Heap, Michael; Vinciguerra, Sergio; Hirose, Takehiro; Dingwell, Donald

2015-04-01

The edifice of Mount Etna (Italy) is structurally unstable, exhibiting a near continuous ESE seaward sliding along a set of faults due to interplay between regional tectonics, gravity instability and magma intrusion. Continuous seismic and ground deformation monitoring reveals the resulting large-scale flank motion at variable rates. The mechanisms controlling this faulting kinetic remains, however, poorly constrained. Examination of the fault zones reveals a range of rock types along the different fault segments: fresh and altered basalt, clay and limestone. As lithological contrasts can jeopardise the structural stability of an edifice, we experimentally investigate the frictional properties of these rocks using low- to high-velocity-rotary shear tests on similar and dissimilar rocks to better understand episodes of slow flank motion as well as rapid and catastrophic sector collapse events. The first set of experiments was performed at velocities up to 1.2 m/s and at normal stresses of 1.5 MPa, commensurate with depths of the contacts seen in the Etna edifice. Friction experiments on clay gouge shows the strong rate-weakening dependence of slip in this material as well as the release of carbon dioxide. Friction experiments on solid rocks show a wider range of mechanical behaviour. At high velocity (>0.6 m/s) volcanic rocks tend to melt whereas the clay and limestone do not; rather they decarbonate, which prevents the rock from achieving the temperature required for melting. Experiments on dissimilar rocks clearly show that composition of host rocks affects the composition and viscosity of the resultant frictional melt, which can have a dramatic effect on shear stress leading to fault weakening or strengthening depending on the combination of host rock samples. A series of low- to moderate-slip velocity experiments is now being conducted to complement our dataset and provide a more complete rock friction model applicable to Mount Etna.

An experimental study of pressure shadows in partially molten rocks

Science.gov (United States)

Qi, Chao; Zhao, Yong-Hong; Kohlstedt, David L.

2013-11-01

As a two-phase, solid-melt material flows around rigid particles, melt-depleted and melt-enriched regions (i.e., pressure shadows) develop due to the coupled fluxes of melt and solid driven by pressure gradients around the particles. To study this compaction-decompaction process, samples composed of fine-grained San Carlos olivine plus mid-ocean ridge basalt containing dispersed sub-millimeter-sized, single crystal beads of olivine were deformed in torsion at a temperature of 1473 K and a confining pressure of 300 MPa. Indicated by melt distribution maps obtained from reflected-light optical and backscattered electron microscopy, melt-enriched and melt-depleted regions around the beads became observable at a local shear strain of γ≈1 in samples with an initially homogeneously distributed melt fraction of ϕ≈0.05. The melt-enriched regions (ϕbarhigh≈0.06 to 0.10) and the melt-depleted regions (ϕbarlow≈0.02 to 0.04), extending as far as one radius of the bead, were symmetrically distributed around the bead. The flow field of the olivine matrix determined from crystallographic preferred orientations agrees with theoretical predictions based on two-phase flow analysis. These experiments are the first to produce pressure shadows in partially molten rocks. One implication of this study is that it will be possible to constrain the ratio of bulk to shear viscosity, which is inferred from the distribution of melt using a combination of experimental observations and numerical simulations.

Seismogenic frictional melting in the magmatic column as the driving force of stick-slip motion

Science.gov (United States)

Kendrick, J. E.; Lavallee, Y.; Hirose, T.; Di Toro, G.; Hornby, A.; De Angelis, S.; Henton De Angelis, S.; Ferk, A.; Hess, K.; Leonhardt, R.; Dingwell, D. B.

2013-12-01

Lava dome eruptions subjected to high extrusion rates commonly evolve from endogenous to exogenous growth and limits to their structural stability hold catastrophic potential as explosive eruption triggers. In the conduit strain localisation in magma, accompanied by seismogenic failure, marks the onset of brittle magma ascent dynamics. The rock record of exogenous dome structures preserves vestiges of cataclastic processes and of thermal anomalies, key to unravelling subsurface processes. A combined structural, thermal and magnetic investigation of shear bands from Mount St. Helens (MSH) and Soufrière Hills volcano (SHV) reveal evidence of faulting and frictional melting within the magmatic column. High velocity rotary shear (HVR) experiments demonstrate the propensity for melting of andesitic and dacitic material (from SHV and MSH respectively) at upper conduit stress conditions. Such melting events may be linked to the step-wise extrusion of magma accompanied by repetitive long-period (LP) seismicity. Using a source duration calculated from the waveforms at seismic stations around SHV, and slip distance per drumbeat calculated from extrusion rate, frictional melting of SHV andesite in a high velocity rotary shear apparatus can be achieved at small slip distances (HVR experiments which mimic rapid velocity fluctuations in stick-slip behavior demonstrate velocity-weakening behavior of melt, with a tendency for unstable slip. We postulate that pseudotachylyte generation could be the underlying cause of stick-slip motion and associated seismic 'drumbeats', which are so commonly observed at dome-building volcanoes, allowing for a fixed spatial locus and the occurrence of 'families' of similar seismic events. We conclude that, given the ease with which melting is achieved in volcanic rocks, and considering the high ambient temperatures in volcanic conduits, frictional melting is a highly probable consequence of viscous magma ascent.

A chemical and thermodynamic model of oil generation in hydrocarbon source rocks

Science.gov (United States)

Helgeson, Harold C.; Richard, Laurent; McKenzie, William F.; Norton, Denis L.; Schmitt, Alexandra

2009-02-01

Thermodynamic calculations and Gibbs free energy minimization computer experiments strongly support the hypothesis that kerogen maturation and oil generation are inevitable consequences of oxidation/reduction disproportionation reactions caused by prograde metamorphism of hydrocarbon source rocks with increasing depth of burial.These experiments indicate that oxygen and hydrogen are conserved in the process.Accordingly, if water is stable and present in the source rock at temperatures ≳25 but ≲100 °C along a typical US Gulf Coast geotherm, immature (reduced) kerogen with a given atomic hydrogen to carbon ratio (H/C) melts incongruently with increasing temperature and depth of burial to produce a metastable equilibrium phase assemblage consisting of naphthenic/biomarker-rich crude oil, a type-II/III kerogen with an atomic hydrogen/carbon ratio (H/C) of ˜1, and water. Hence, this incongruent melting process promotes diagenetic reaction of detritus in the source rock to form authigenic mineral assemblages.However, in the water-absent region of the system CHO (which is extensive), any water initially present or subsequently entering the source rock is consumed by reaction with the most mature kerogen with the lowest H/C it encounters to form CO 2 gas and a new kerogen with higher H/C and O/C, both of which are in metastable equilibrium with one another.This hydrolytic disproportionation process progressively increases both the concentration of the solute in the aqueous phase, and the oil generation potential of the source rock; i.e., the new kerogen can then produce more crude oil.Petroleum is generated with increasing temperature and depth of burial of hydrocarbon source rocks in which water is not stable in the system CHO by a series of irreversible disproportionation reactions in which kerogens with higher (H/C)s melt incongruently to produce metastable equilibrium assemblages consisting of crude oil, CO 2 gas, and a more mature (oxidized) kerogen with a lower

Migmatites and migmatite-like rocks of Olkiluoto

International Nuclear Information System (INIS)

Kaerki, A.

2015-02-01

Bedrock of the Olkiluoto Island in the western end of the Palaeoproterozoic Svecofennian Accretionary Arc Complex, SW Finland is composed of high-grade metamorphic pelites, arenites and intermediate, arc type metavolcanic rocks intruded by granodioritic to tonalitic plutonic rocks. Regional metamorphism culminated with voluminous migmatization in the temperature of 660 - 700 deg C and relatively low pressure of about 3.5 - 4 kbar. The end result of polyphase metamorphism and deformation is a metamorphic rock succession composed of diverse migmatite rocks, metatexites and diatexites. Metatexites are migmatites in which several, discrete components can be detected, and in which the paleosome with some pre-partial-melting textures is identifiable. Diatexites are more advanced migmatites in which the pre-migmatization structures are often totally destroyed and the rock is dominated by different neosome components meaning leucosome, melanosome or mesosome. Based on the migmatite structures the metatexites of Olkiluoto have been classified into six subgroups. Dike-structured metatexites are composed of well preserved paleosome intruded by one single set of narrow, subparallel leucosome dikes which cover ca. 5 - 10 % of the whole rock volume. Net-structure is composed of a network of narrow leucosome dikes which show a reticulated structure in a plane section and cover less than 30 % of the whole rock volume. Breccia-structure is composed of angular or rounded paleosome blocks surrounded by moderate amount of leucosome. Patch-structure is composed of irregular leucosome patches which intruded the well preserved paleosome and compose typically 20 - 70 % of the rock volume. Layer-structure is characterized by more or less regular leucosome dikes sub-parallel to the foliation of the well preserved paleosome. Vein-structured metatexites and also diatexites include a set of pipe-like, longish leucosome veins most probably generated by synchronous melting and deformation

Migmatites and migmatite-like rocks of Olkiluoto

Energy Technology Data Exchange (ETDEWEB)

Kaerki, A. [Kivitieto Oy, Oulu (Finland)

2015-02-15

Bedrock of the Olkiluoto Island in the western end of the Palaeoproterozoic Svecofennian Accretionary Arc Complex, SW Finland is composed of high-grade metamorphic pelites, arenites and intermediate, arc type metavolcanic rocks intruded by granodioritic to tonalitic plutonic rocks. Regional metamorphism culminated with voluminous migmatization in the temperature of 660 - 700 deg C and relatively low pressure of about 3.5 - 4 kbar. The end result of polyphase metamorphism and deformation is a metamorphic rock succession composed of diverse migmatite rocks, metatexites and diatexites. Metatexites are migmatites in which several, discrete components can be detected, and in which the paleosome with some pre-partial-melting textures is identifiable. Diatexites are more advanced migmatites in which the pre-migmatization structures are often totally destroyed and the rock is dominated by different neosome components meaning leucosome, melanosome or mesosome. Based on the migmatite structures the metatexites of Olkiluoto have been classified into six subgroups. Dike-structured metatexites are composed of well preserved paleosome intruded by one single set of narrow, subparallel leucosome dikes which cover ca. 5 - 10 % of the whole rock volume. Net-structure is composed of a network of narrow leucosome dikes which show a reticulated structure in a plane section and cover less than 30 % of the whole rock volume. Breccia-structure is composed of angular or rounded paleosome blocks surrounded by moderate amount of leucosome. Patch-structure is composed of irregular leucosome patches which intruded the well preserved paleosome and compose typically 20 - 70 % of the rock volume. Layer-structure is characterized by more or less regular leucosome dikes sub-parallel to the foliation of the well preserved paleosome. Vein-structured metatexites and also diatexites include a set of pipe-like, longish leucosome veins most probably generated by synchronous melting and deformation

Sedimentary processes of the Bagnold Dunes: Implications for the eolian rock record of Mars

OpenAIRE

Ewing, R. C.; Lapotre, M. G. A.; Lewis, K. W.; Day, M.; Stein, N.; Rubin, D. M.; Sullivan, R.; Banham, S.; Lamb, M. P.; Bridges, N. T.; Gupta, S.; Fischer, W. W.

2017-01-01

The Mars Science Laboratory rover Curiosity visited two active wind-blown sand dunes within Gale crater, Mars, which provided the first ground-based opportunity to compare Martian and terrestrial eolian dune sedimentary processes and study a modern analog for the Martian eolian rock record. Orbital and rover images of these dunes reveal terrestrial-like and uniquely Martian processes. The presence of grainfall, grainflow, and impact ripples resembled terrestrial dunes. Impact ripples were pre...

Sedimentary processes of the Bagnold Dunes: Implications for the eolian rock record of Mars

OpenAIRE

Ewing, R. C.; Lapotre, M. G. A.; Lewis, K. W.; Day, M.; Stein, N.; Rubin, D. M.; Sullivan, R.; Banham, S.; Lamb, M. P.; Bridges, N. T.; Gupta, S.; Fischer, W. W.

2017-01-01

Abstract The Mars Science Laboratory rover Curiosity visited two active wind‐blown sand dunes within Gale crater, Mars, which provided the first ground‐based opportunity to compare Martian and terrestrial eolian dune sedimentary processes and study a modern analog for the Martian eolian rock record. Orbital and rover images of these dunes reveal terrestrial‐like and uniquely Martian processes. The presence of grainfall, grainflow, and impact ripples resembled terrestrial dunes. Impact ripples...

Petrography and petrology of Quaternary volcanic rocks from Ghezel Ghaleh, northwest Qorveh

Directory of Open Access Journals (Sweden)

Alireza Bajelan

2014-10-01

Full Text Available Introduction In the east and northeast of Sanandaj in the Qorveh-Bijar-Takab axis, there are series of basaltic composition volcanoes with Quaternary age. The study area is part of the Sanandaj-Sirjan zone and is located between 47°52' and 47°57' E longitudes and 35°26 and '35°30' N latitudes. Due to the location of the volcanic cone on Pliocene clastic sediments and Quaternary travertine, the age of these volcanoes is considered to be Quaternary. The cones mostly consist of low scoria, ash, volcanic bombs, lapilli deposits and basaltic lava (Moein Vaziri and Aminsobhani, 1985. Petrological and geochemical studies have been carried out to evaluate Quaternary magmatism in the area and to determine the nature of the lithological characteristics, such as the evaluation of source rocks and magma type, degree of partial melting and the tectonic setting of Ghezel Ghaleh rocks (Moein Vaziri, 1997. Simplified geological map of the study area is characterized by ER-Mapper software. Materials and methods In the course of field studies in the region, 40 samples were taken, 30 thin sections were prepared and polished. XRD analyses were performed on some whole rock samples. All major, minor and trace elements were assessed by ICP-MS at Lab Weft Laboratory in Australia. Results Based on the classification of structural zones, the area is located in the Sanandaj-Sirjan zone, hundred kilometers away from the main Zagros thrust along the NW-SE direction. After early Cimmerian orogeny, andesitic volcanic activity took place (Moein Vaziri and Aminsobhani, 1985. A major secondary mineral in these rocks is iddingsite, formed by hydration and oxidation of the olivine (Shelley, 1993. According to SiO2 against Na2O + K2O (TAS diagram (Irvine and Baragar , 1971 and cationic R1 and R2 diagram (De La Roche et el., 1980, volcanic rocks of the area indicate alkaline series. Discussion To obtain more information on the tectonic setting of these rocks, the Zr/Y-Zr diagram

Combined stable isotope trajectories for water-rock interaction

International Nuclear Information System (INIS)

Blattner, P.; Department of Scientific and Industrial Research, Lower Hutt

1981-01-01

The 'mixed' model of water-rock interaction (1980 Workshop) is explained in detail. Based on the magnitude of the oxygen isotope shifts of their recharge water, different geothermal systems can be placed in an evolutionary series, from incipient (large shift of water) to mature (small shift of water). Isotopes of different chemical elements may be combined, to yield a stringent test of whether or not a given change in rock composition may be ascribed to interaction with water (L-shaped trajectories). For the acidic eruptives of the Taupo Volcanic Zone, available strontium and oxygen isotope data practically rule out an origin by partial melting of greywacke basement

Tungsten melt layer erosion due to J x B force under conditions relevant to ITER ELMs

Energy Technology Data Exchange (ETDEWEB)

Garkusha, I.E. [Institute of Plasma Physics of the NSC KIPT, Akademicheskaya 1, 61108 Kharkov (Ukraine)]. E-mail: garkusha@ipp.kharkov.ua; Bazylev, B.N. [Forschungszentrum Karlsruhe, IHM, 76021 Karlsruhe (Germany); Bandura, A.N. [Institute of Plasma Physics of the NSC KIPT, Akademicheskaya 1, 61108 Kharkov (Ukraine); Byrka, O.V. [Institute of Plasma Physics of the NSC KIPT, Akademicheskaya 1, 61108 Kharkov (Ukraine); Chebotarev, V.V. [Institute of Plasma Physics of the NSC KIPT, Akademicheskaya 1, 61108 Kharkov (Ukraine); Landman, I.S. [Forschungszentrum Karlsruhe, IHM, 76021 Karlsruhe (Germany); Kulik, N.V. [Institute of Plasma Physics of the NSC KIPT, Akademicheskaya 1, 61108 Kharkov (Ukraine); Makhlaj, V.A. [Institute of Plasma Physics of the NSC KIPT, Akademicheskaya 1, 61108 Kharkov (Ukraine); Petrov, Yu.V. [Institute of Plasma Physics of the NSC KIPT, Akademicheskaya 1, 61108 Kharkov (Ukraine); Solyakov, D.G. [Institute of Plasma Physics of the NSC KIPT, Akademicheskaya 1, 61108 Kharkov (Ukraine); Tereshin, V.I. [Institute of Plasma Physics of the NSC KIPT, Akademicheskaya 1, 61108 Kharkov (Ukraine)

2007-06-15

The behavior of tungsten under repetitive hydrogen plasma impacts causing surface melting in conditions of an applied J x B force of up to 20 MN/m{sup 3} is studied with the plasma accelerator QSPA Kh-50. Tungsten samples of EU trademark have been exposed to up to 100 pulses simulating ITER ELMs of the energy load 0.7 MJ/m{sup 2} and the duration 0.25 ms. An electric current J flows across the magnetic field B of 1.4 T, and the resulting J x B force produces a displacement of the melt with formation of an erosion crater and an inclination of the surface profile along the force. Surface morphology and the damage by surface cracks are discussed. Comparisons of experimental results with numerical simulations of the code MEMOS-1.5D are presented.

Stratigraphy of the Caloris Basin, Mercury: Implications for Volcanic History and Basin Impact Melt

Science.gov (United States)

Ernst, Carolyn M.; Denevi, Brett W.; Barnouin, Olivier S.; Klimczak, Christian; Chabot, Nancy L.; Head, James W.; Murchie, Scott L.; Neumann, Gregory A.; Prockter, Louis M.; Robinson, Mark S.;

Features of the distribution of uranium in igneous rocks - uranium deposits associated with igneous rocks

International Nuclear Information System (INIS)

Soerensen, H.

1977-01-01