The thermal and radiation exposure history of lunar meteorites     

Paul H. BENOIT  Derek W. G. SEARS  Steven J. K. SYMES 《Meteoritics & planetary science》1996,31(6):869-875

Abstract— We have measured the natural and induced thermoluminescence (TL) of seven lunar meteorites in order to examine their crystallization, irradiation, and recent thermal histories. Lunar meteorites have induced TL properties similar to Apollo samples of the same provenance (highland or mare), indicating similar crystallization and metamorphic histories. MacAlpine Hills 88104/5 has experienced the greatest degree of impact/regolith processing among the highland-dominated meteorites. The basaltic breccia QUE 94281 is dominated by mare component but may also contain a significant highland component. For the mare-dominated meteorites, EET 87521 may have a significant highland impact-melt component, while Asuka 881757 and Y-793169 have been heavily shocked. The thermal history of Y-793169 included slow cooling, either during impact processing or during its initial crystallization. Our natural TL data indicate that most lunar meteorites have apparently been irradiated in space a few thousand years, with most <15,000 a. Elephant Moraine 87521 has the lowest irradiation exposure time, being <1,000 a. Either the natural TL of ALHA81005, Asuka 881757 and Y-82192 was only partially reset by lunar ejection or these meteorites were in small perihelia orbits (≤0.7 AU).  相似文献   

Sketch-based Identification of Bench and Terrace Slope Breaks in the Laramie Basin, Wyoming     

Steven D Prager  J Michael Daniels  Scott Kelley 《Transactions in GIS》2007,11(5):703-719

This study presents a semi‐automated approach to support the identification of fluvial landform slope breaks in the Laramie Basin, southeastern Wyoming. The landforms in question form the edges of terraces and benches and tend to be subtle and varied depending on where they appear in the landscape. Because of this variation combined with DEM error, conventional raster filtering methods were unable to readily identify the benches with any consistency. In an effort to automate the collection of benches, a two stage, sketch‐based algorithm was designed to detect bench edges on a semi‐automated basis and was integrated into a commercial GIS environment for testing and execution. The approach of tailoring an algorithm to detect a particular feature proved viable and, in fact, more consistent in many cases than heads‐up digitizing. However, feature complexity appears to be a significant driver in the accuracy of the algorithmic approach with the unlikely finding that more complex features are more accurately identified than less complex features. This research demonstrates that user cognition, DEM resolution, algorithm functionality and landform characteristics are thus all important and interrelated factors requiring consideration when implementing approaches to topographic feature identification.  相似文献   

Continuous measurement of the depth of water table (inundation) in wetlands with fluctuating surfaces     

Nigel Roulet  Steven Hardill  Neil Comer 《水文研究》1991,5(4):399-403

Assessment of the water table in compressible and/or floating peatland mats requires a remote sensor that can measure simultaneously the elevation of the peat surface and the water level. A simple device, comprising two potentiometers, a float and ‘bog shoe’ was used to measure the water level and peat surface witin 0-3 mm. The water table (depth of water level relative to the peat surface) was then calculated.  相似文献   

On the observability of radiation forces acting on near-Earth asteroids     

David Vokrouhlický  Steven R. Chesley  Andrea Milani 《Celestial Mechanics and Dynamical Astronomy》2001,81(1-2):149-165

We consider the perturbations on near-earth asteroid orbits due to various forces stemming from solar radiation. We find that the existence of precise radar astrometric observations at multiple apparitions, spanning periods on the order of 10 years, allows the detection of such forces on bodies as large as kilometer across. Indeed, the perturbations are so substantial that certain of the forces can be essential to fit an orbit to the observations. In particular, we show that the recoil force of thermal radiation from the asteroid, known as the Yarkovsky effect, is the most important of these unmodeled perturbations. We also show that the effect of reflected light can be important if even moderate albedo variations are present, while moderate changes in oblateness appear to have a far smaller effect. An unexpected result is that the Poynting–Robertson effect, typically only considered for submillimeter dust particles, could be observable on smaller asteroids with high eccentricity, such as 1566 Icarus. Finally, we also study the possibility of improving the orbit uncertainty through well-timed optical observations which might help in better detection of these nongravitational perturbations.  相似文献   

Spectral evidence for zeolite in the dust on Mars     

Steven W. Ruff 《Icarus》2004,168(1):131-143

Spectral features observed in Mars Global Surveyor Thermal Emission Spectrometer data (∼1670-220 cm⁻¹) of martian surface dust provide clues to its mineralogy. An emissivity peak at ∼1630 cm⁻¹ is consistent with the presence of an H₂O-bearing mineral. This spectral feature can be mapped globally and shows a distribution related to the classical bright regions on Mars that are known to be dust covered. An important spectral feature at ∼830 cm⁻¹ present in a newly derived average spectrum of surface dust likely is a transparency feature arising from the fine particulate nature of the dust. Its shape and location are consistent with plagioclase feldspars and also zeolites, which essentially are the hydrous form of feldspar. The generally favored visible/near-infrared spectral analog for martian dust, JSC Mars-1 altered tephra, does not display the ∼830 cm⁻¹ feature. Zeolites commonly form from the interaction of low temperature aqueous fluids and volcanic glass in a variety of geologic settings. The combination of spectral features that are consistent with zeolites and the likelihood that Mars has (or had) geologic conditions necessary to produce them makes a strong case for recognizing zeolite minerals as likely components of the martian regolith.  相似文献   

Genesis of the mafic impact melt rock in the northwest sector of the Vredefort Dome,South Africa     

Wolf Uwe Reimold  Natalia Hauser  Alisson Lopes Oliveira  Ana Rita Pereira Maciel  Steven Goderis  Lidia Pittarello  Wencke Wegner  Mario Fischer-Goedde  Christian Koeberl  Vinciane Debaille  Carolinna Silva Maia de Souza 《Meteoritics & planetary science》2023,58(7):907-944

Genesis and emplacement of Vredefort Granophyre, the impact melt rock exposed on the Vredefort Dome, the erosional remnant of the central uplift of the Vredefort impact structure, South Africa, have long been debated. This debate was recently reinvigorated by the discovery that besides the previously known felsic variety of >66 wt% SiO₂, a second, somewhat more mafic phase of <66 wt% SiO₂ occurs along a Granophyre dike on farms Kopjeskraal and Eldorado in the northwest sector of the dome. Two hypotheses have been put forward to explain the genesis and emplacement of this second phase: (1) successive injections of impact melt into extensional fractures opened in the course of central uplift formation/crater modification, with melts of distinct compositions derived from a differentiating impact melt body in the crater, and (2) generation of the more mafic phase as a product of admixture/assimilation of a mafic country rock component, either the so-called epidiorite of possible Ventersdorp Supergroup affiliation or the Dominion Group meta-lava (DGL), to Felsic Granophyre. In the latter model, contamination with mafic country rock would have occurred during downward intrusion and stoping into and below the crater floor. The so-called Mafic Granophyre has previously only ever been sampled on a single site (Farm Kopjeskraal). In this study, samples of Granophyre occurring along the southerly extension of this dike on farm Rensburgdrif, and from a second dike on the Rietkuil property further southwest were investigated by field work, and petrographic, geochemical, and isotopic analysis. The mafic phase indeed occurs in the interior of the dike at Rensburgdrif, and also on Rietkuil. New geochemical and Sr-Nd isotope data support the hypothesis that the Mafic Granophyre composition represents a mixture between Felsic Granophyre and a mafic country rock. A 20% admixture of epidiorite or DGL to Felsic Granophyre provides an excellent match for the chemical composition of the Mafic Granophyre. The Sr-Nd isotope data indicate that this admixture likely involved the epidiorite component rather than DGL. Together with earlier Sr-Nd-Os-Se isotopic data, and other geochemical data, these results further support formation of the Mafic Granophyre by local assimilation/admixture of epidiorite to Felsic Granophyre.  相似文献   

Fluid mobilization of rare earth elements,Th, and U during the terrestrial alteration of H chondrites     

Ryoga Maeda  Steven Goderis  Akira Yamaguchi  Thibaut Van Acker  Frank Vanhaecke  Vinciane Debaille  Phillippe Claeys 《Meteoritics & planetary science》2023,58(7):1018-1038

The chemical effects of terrestrial alteration, with a particular focus on lithophile trace elements, were studied for a set of H chondrites displaying various degrees of weathering from fresh falls to altered finds collected from hot deserts. According to their trace element distributions, a considerable fraction of rare earth elements (REEs), Th, and U resides within cracks observed in weathered meteorite specimens. These cracks appear to accumulate unbound REEs locally accompanied by Th and U relative to the major element abundances, especially P and Si. The deposition of Ce is observed in cracks in the case of most of the weathered samples. Trace element maps visually confirm the accumulation of these elements in such cracks, as previously inferred based on chemical leaching experiments. Because the positive Ce anomalies and unbound REE depositions in cracks occur in all weathered samples studied here while none of such features are observed in less altered samples including falls (except for altered fall sample Nuevo Mercurio), these features are interpreted to have been caused by terrestrial weathering following chemical leaching. However, the overall effects on the bulk chemical composition remain limited as the data for all Antarctic meteorites studied in this work (except for heavily weathered sample A 09516, H6) are in good agreement with published data for unaltered meteorites.  相似文献   

Exploring spatial relationships between stream channel features,water depths and flow velocities during flash floods using HEC-GeoRAS and Geographic Information Systems     

Leal  Miguel  Reis  Eusébio  Santos  Pedro Pinto 《地理学报(英文版)》2022,32(4):757-782

Journal of Geographical Sciences - Water depths and flow velocities decisively influence the damage caused by flash floods. Geographic Information System (GIS) is a powerful and useful tool,...  相似文献   

How societal expectations,new digital tools,and the COVID crisis are driving a step-change in human centric remediation     

John Horst  Carly Foster  Steven Perry  Ajani Stewart  Megan Klar  Beto Altamirano  Prasoon Sinha 《Ground Water Monitoring & Remediation》2021,41(3):13-21

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The Kwakshua Watersheds Observatory,central coast of British Columbia,Canada     

Ian J. W. Giesbrecht  William C. Floyd  Suzanne E. Tank  Ken P. Lertzman  Brian P. V. Hunt  Maartje C. Korver  Allison A. Oliver  Ray Brunsting  Paul Sanborn  Santiago G. Gonzalez Arriola  Gordon W. Frazer  Kyra A. St. Pierre  Shawn Hateley  James McPhail  Colby Owen  Stewart Butler  Bryn Fedje  Emma Myers  Lucy Quayle  Emily Haughton  Isabelle Desmarais  Rob White  David J. Levy-Booth  Colleen T. E. Kellogg  Jennifer M. Jackson  William W. Mohn  Steven J. Hallam  Justin Del Bel Belluz 《水文研究》2021,35(6):e14198

The Kwakshua Watersheds Observatory (KWO) is an integrative watersheds observatory on the coastal margin of a rain-dominated bog-forest landscape in British Columbia (BC), Canada. Established in 2013, the goal of the KWO is to understand and model the flux of terrestrial materials from land to sea – the origins, pathways, processes and ecosystem consequences – in the context of long-term environmental change. The KWO consists of seven gauged watersheds and a network of observation sites spanning from land to sea and along drainage gradients within catchments. Time-series datasets include year-round measurements of weather, soil hydrology, streamflow, aquatic biogeochemistry, microbial ecology and nearshore oceanographic conditions. Sensor measurements are recorded every 5 min and water samples are collected approximately monthly. Additional observations are made during high-flow conditions. We used remote sensing to map watershed terrain, drainage networks, soils and terrestrial ecosystems. The watersheds range in size from 3.2 to 12.8 km², with varying catchment characteristics that influence hydrological and biogeochemical responses. Despite local variation, the overall study area is a global hotspot for yields of dissolved organic carbon, dissolved organic nitrogen and dissolved iron at the coastal margin. This observatory helps fill an important gap in the global network of observatories, in terms of spatial location (central coast of BC), climate (temperate oceanic), hydrology (very high runoff, pluvial regime), geology (igneous intrusive, glacially scoured), vegetation (bog rainforest) and soils (large stores of organic carbon).  相似文献