Analysis of cylindrical cavity expansion in a strain weakening material     

J. P. Carter  S. K. Yeung 《Computers and Geotechnics》1985,1(3):161-180

A numerical technique is suggested that allows a prediction of the behaviour of a single phase, strain softening material during the expansion of a long cylindrical cavity. The method provides the entire pressure-expansion relationship, including the identification of the limit pressure at large deformations.The numerical solutions, obtained using the finite element technique and allowing for finite deformations, show very good agreement with closed form answers that are available for a restricted class of material models. Results are also presented for the more general, dilatant (or collapsing), strain softening materials for which closed form solutions do not exist. The importance of the rate of dilation and rate of softening in determining the behaviour during cavity expansion is illustrated.  相似文献   

The Motunau fault revisited     

R.M. Carter  L. Carter 《Tectonophysics》1985,115(1-2)

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Pollen analysis of a late pliocene and early pleistocene section from the Gubik Formation of Arctic Alaska     

Robert E. Nelson  L. David Carter 《Quaternary Research》1985,24(3):295-306

A 14-m-thick section of marine and nonmarine sediments of the Gubik Formation of northern Alaska, exposed in bluffs near Ocean Point on the Colville River, has been studied by means of pollen analysis. Pollen from the marine sediments, of probable late Pliocene age, records a boreal forest of spruce and birch with minor amounts of alder in the adjacent terrestrial vegetation. Pine and perhaps true fir were probably at or near their northern limit here, but hemlocks and hardwoods were absent. The suggested environment for the Arctic Slope during the time represented by the marine sediments is similar to that of present-day Anchorage. Pollen floras from the overlying fluvial strata, of early or middle Pleistocene age, record predominantly herbaceous taxa indicating tundra conditions probably more severe than those of the present day. These deposits were most likely contemporaneous with glacial conditions in the Brooks Range to the south. Pollen of woody taxa (spruce, alder, birch, heaths) is rare through most of the section, although birch and alder percentages similar to those found in modern river sediments indicate an interstadial or interglacial warming in midsection. Inland climates during glacial episodes may have been similar to those of the present Arctic coast.  相似文献   

A camera using a 1040×1040 array     

I. S. Glass  D. B. Carter  K. Sekiguchi  Y. Nakada 《Experimental Astronomy》1994,3(1-4):125-126

A JHKK survey camera based on a 1040×1040 PtSi Charge Sweep Device has been constructed in a joint programme of the University of Tokyo, the National Astronomical Observatory of Japan and the South African Astronomical Observatory. We describe its design, construction and initial testing.  相似文献   

Factors controlling the lengths of channel-fed lava flows     

Harry Pinkerton  Lionel Wilson 《Bulletin of Volcanology》1994,56(2):108-120

Factors which control lava flow length are still not fully understood. The assumption that flow length as mainly influenced by viscosity was contested by Walker (1973) who proposed that the length of a lava flow was dependent on the mean effusion rate, and by Malin (1980) who concluded that flow length was dependent on erupted volume. Our reanalysis of Malin's data shows that, if short duration and tube-fed flows are eliminated, Malin's Hawaiian flow data are consistent with Walker's assertion. However, the length of a flow can vary, for a given effusion rate, by a factor of 7, and by up to 10 for a given volume. Factors other than effusion rate and volume are therefore clearly important in controlling the lengths of lava flows. We establish the relative importance of the other factors by performing a multivariate analysis of data for recent Hawaiian lava flows. In addition to generating empirical equations relating flow length to other variables, we have developed a non-isothermal Bingham flow model. This computes the channel and levee width of a flow and hence permits the advance rates of flows and their maximum cooling-limited lengths for different gradients and effusion rates to be calculated. Changing rheological properties are taken into account using the ratio of yield strength to viscosity; available field measurements show that this varies systematically from the vent to the front of a lava flow. The model gives reasonable agreement with data from the 1983–1986 Pu'u Oo eruptions and the 1984 eruption of Mauna Loa. The method has also been applied to andesitic and rhyolitic lava flows. It predicts that, while the more silicic lava flows advance at generally slower rates than basaltic flows, their maximum flow lengths, for a given effusion rate, will be greater than for basaltic lava flows.  相似文献   

The Homestead kimberlite, central Montana, USA: mineralogy, xenocrysts, and upper-mantle xenoliths     

B. Carter Hearn Jr.   《Lithos》2004,77(1-4):473-491

The Homestead kimberlite was emplaced in lower Cretaceous marine shale and siltstone in the Grassrange area of central Montana. The Grassrange area includes aillikite, alnoite, carbonatite, kimberlite, and monchiquite and is situated within the Archean Wyoming craton. The kimberlite contains 25–30 modal% olivine as xenocrysts and phenocrysts in a matrix of phlogopite, monticellite, diopside, serpentine, chlorite, hydrous Ca–Al–Na silicates, perovskite, and spinel. The rock is kimberlite based on mineralogy, the presence of atoll-textured groundmass spinels, and kimberlitic core-rim zoning of groundmass spinels and groundmass phlogopites.

Garnet xenocrysts are mainly Cr-pyropes, of which 2–12% are G10 compositions, crustal almandines are rare and eclogitic garnets are absent. Spinel xenocrysts have MgO and Cr₂O₃ contents ranging into the diamond inclusion field. Mg-ilmenite xenocrysts contain 7–11 wt.% MgO and 0.8–1.9 wt.% Cr₂O₃, with (Fe⁺³/Fe^tot) from 0.17–0.31. Olivine is the only obvious megacryst mineral present. One microdiamond was recovered from caustic fusion of a 45-kg sample.

Upper-mantle xenoliths up to 70 cm size are abundant and are some of the largest known garnet peridotite xenoliths in North America. The xenolith suite is dominated by dunites, and harzburgites containing garnet and/or spinel. Granulites are rare and eclogites are absent. Among 153 xenoliths, 7% are lherzolites, 61% are harzburgites, 31% are dunites, and 1% are orthopyroxenites. Three of 30 peridotite xenoliths that were analysed are low-Ca garnet–spinel harzburgites containing G10 garnets. Xenolith textures are mainly coarse granular, and only 5% are porphyroclastic.

Xenolith modal mineralogy and mineral compositions indicate ancient major-element depletion as observed in other Wyoming craton xenolith assemblages, followed by younger enrichment events evidenced by tectonized or undeformed veins of orthopyroxenite, clinopyroxenite, websterite, and the presence of phlogopite-bearing veins and disseminated phlogopite. Phlogopite-bearing veins may represent kimberlite-related addition and/or earlier K-metasomatism.

Xenolith thermobarometry using published two-pyroxene and Al-in-opx methods suggest that garnet–spinel peridotites are derived from 1180 to 1390 °C and 3.6 to 4.7 GPa, close to the diamond–graphite boundary and above a 38 mW/m² shield geotherm. Low-Ca garnet–spinel harzburgites with G10 garnets fall in about the same T and P range. Most spinel peridotites with assumed 2.0 GPa pressure are in the same T range, possibly indicating heating of the shallow mantle. Four of 79 Cr diopside xenocrysts have P–T estimates in the diamond stability field using published single-pyroxene P–T calculation methods.  相似文献   

Local erosion rates versus active tectonics: cosmic ray exposure modelling in Provence (south-east France)     

Lionel Siame  Olivier Bellier  Rgis Braucher  Michel Sbrier  Marc Cushing  Didier Bourls  Bruno Hamelin  Emmanuel Baroux  Beatrice de Voogd  Grant Raisbeck  Franoise Yiou 《Earth and Planetary Science Letters》2004,220(3-4):345-364

Over the past decade, in situ-produced cosmogenic nuclides have revolutionised the study of landscape evolution. In particular, numerous studies have demonstrated that, in active tectonic settings, cosmic ray exposure dating of deformed or displaced geomorphic features makes it possible to quantify long-term deformation rates. In western European countries, erosion due to climatically driven processes and human activities is probably the factor that most limits the accuracy of exposure ages and landscape modification rates. In this study, we present the results of a depth-profiling technique applied to alluvial terraces located along the Rhône and the Moyenne Durance rivers. The expected decrease with depth of the measured ¹⁰Be concentrations has been modelled using a χ² inversion method in order to constrain the exposure history of the alluvial sediments. The results suggest that: (1) over the Quaternary, the local surface erosion rates including both regional uplift and climatically driven processes acting on landforms are on the order of 30 m/Myr in southeastern France, and (2) providing a fairly good bracketing of the exposure age, the modelled abandonment age of alluvial terraces affected by the Moyenne Durance Fault allows estimating incision rates, comparing the alluvial terrace elevations with topographic river profiles, and a minimum vertical slip rate value of roughly 0.02 mm/yr for the southern segment of the Moyenne Durance Fault.  相似文献   

Adsorption of amino acid-containing organic matter by calcite and quartz     

Paul W. Carter 《Geochimica et cosmochimica acta》1978,42(8):1239-1242

Adsorption experiments using fulvic acid with calcite and quartz demonstrate that carbonate surfaces are able to selectively adsorb aspartic acid-rich organic matter. Quartz does not have this ability, instead exhibiting a preference for the aspartic acid-poor fraction. The relative abundance of aspartic acid in the fraction adsorbed onto calcite is highly dependent on the ratio of fulvic acid to calcite. At high ratios, fulvic acid is adsorbed with a relative abundance of aspartic acid that is more than twice that in the original fulvic acid. With decreasing ratios, there is a concomitant decrease in the relative abundance of aspartic acid in the adsorbed fraction. Selective adsorption may be the most likely mechanism by which aspartic acid-rich organic matter is included in non-biogenic car- bonates such as ooids. This process may be a factor influencing the distribution of amino acids within ooids, their rate of growth, and may ultimately be a factor in limiting their size.  相似文献   

Concepts,Conceptualization, and Conceptions in Geography     

Rod Lane  Jennifer Carter  Theresa Bourke 《The Journal of geography》2019,118(1):11-20

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Testing the genetic relationship between fluid alteration and brecciation in CM chondrites     

Maximilien J. Verdier‐Paoletti  Yves Marrocchi  Lionel G. Vacher  Jrme Gattacceca  Andrey Gurenko  Corinne Sonzogni  Matthieu Gounelle 《Meteoritics & planetary science》2019,54(8):1692-1709

Boriskino is a poorly studied CM chondrite with numerous millimeter‐ to centimeter‐scale clasts exhibiting sharp boundaries. Clast textures and mineralogies attest to diverse geological histories with various degrees of aqueous alteration. We conducted a petrographic, chemical, and isotopic study on each clast type of the breccia to investigate if there exists a genetic link between brecciation and aqueous alteration, and to determine the controlling parameter of the extent of alteration. Boriskino is dominated by CM2 clasts for which no specific petrographic type could be assigned based on the chemical compositions and modal abundances of constituents. One clast stands out and is identified as a CM1 lithology, owing to its lack of anhydrous silicates and its overall abundance of dolomite‐like carbonates and acicular iron sulfides. We observe that alteration phases near clast boundaries exhibit foliation features, suggesting that brecciation postdated aqueous alteration. We measured the O‐isotopic composition of Ca‐carbonates and dolomite‐like carbonates to determine their precipitation temperatures following the methodology of Verdier‐Paoletti et al. (2017). Both types of carbonates yield similar ranges of precipitation temperatures independent of clast lithology, ranging from ?13.9 ± 22.4 (2σ) to 166.5 ± 47.3 °C, precluding that temperature alone accounts for the differences between the CM1 and CM2 lithologies. Instead, we suggest that initial water/rock ratios of 0.75 and 0.61 for the CM1 and CM2 clasts, respectively, might control the extent of aqueous alteration. Based on these estimates, we suggest that Boriskino clasts originated from a single parent body with heterogeneous distribution of water either due to local differences in the material permeability or in the initial content of ice available. These conditions would have produced microenvironments with differing geochemical conditions thus leading to a range of degrees of aqueous alteration.  相似文献