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Abstract The preferred model for the extension of brittle crust involves the rotation of planar fault blocks. We show that in general the distortion at the ends of the blocks does not affect the measurement of extension. The horizontal displacement on a normal fault, the heave, is observed with little distortion on a seismic reflection time-section. It can be used to estimate the amount of extension. We demonstrate that the sum of the heaves is not equal to the actual elongation if the blocks have rotated. However, the error in the extension factor, β, introduced by equating elongation with the sum of the heaves is small. It increases with the amount of rotation from 0 for no rotation to 13% for the maximum observed angle of rotation of 30o . We compare this value with the practical error introduced by uncertainties in seismic velocities when the elongation is measured from a depth-converted seismic section. This latter error is significantly smaller being approximately 5% for an error in velocity of 20% when the rotation angle is less than 30o . 相似文献
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International collaborations between private companies, national research laboratories, and universities in the field of GIS have opened up new ways of exchanging knowledge and experiences between different countries. However, when a collaboration involves the actual design and implementation of an operational GIS, rather than simply theoretical or applied research, or the development of specific applications, many problems can arise, sometimes leading either to the partial success or to the complete failure of a project. Some of these problems are frequently encountered in all kinds of international collaborations: problems arising from different cultural mentalities, difficulties establishing a single common leadership, difficulties with communication and information exchange, and so on. Problems relating to the specific nature of GIS are also present, for example the absence of digital geographic data format standards, the absence of metadata standards, the omission of GIS or IS design methods, etc. This paper focuses on a joint Sino-Belgian project for the design and implementation of an urban geographical information system (UGIS) integrating remote sensing techniques in Hangzhou city, China and examines the general, specific, and international aspects of the problems encountered in an international collaboration. 相似文献
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The control of cathodoluminescence in dolomite by iron and manganese 总被引：10，自引：0，他引：10
BERNARD J. PIERSON 《Sedimentology》1981,28(5):601-610
Variations in the cathodoluminescent properties of carbonates are usually attributed to differing proportions of manganese (Mn2+) as the most important activator, and iron (Fe2+) as the main inhibitor of luminescence. Interactions between manganese and iron concentrations and the luminescent properties of dolomite are demonstrated by petrographic and chemical analyses of 86 samples of dolomite representing a range of depositional environments and ages (Cambrian to Cretaceous) and a wide geographical distribution (North America and Europe). Iron and manganese are positively correlated in the dolomites, with the former showing a greater range of variation. Very small amounts of manganese are sufficient to activate the luminescence and as little as 100 ppm Mn2+ is present in highly luminescing samples. The intensity of luminescence is not proportional to the manganese concentration. Iron begins to quench luminescence as its concentration reaches 10,000 ppm. Above that level, luminescence is rapidly lost and total extinction occurs among samples containing more than 15,000 ppm Fe2+, regardless of the manganese concentration. 相似文献
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CORDIER CAROLE; CLEMENT JEAN-PHILIPPE; CAROFF MARTIAL; HEMOND CHRISTOPHE; BLAIS SYLVAIN; COTTEN JOSEPH; BOLLINGER CLAIRE; LAUNEAU PATRICK; GUILLE GERARD 《Journal of Petrology》2005,46(11):2281-2312
This study is based on a set of coarse-grained igneous rockscollected from two zoned plutons located in the central partof Tahiti Nui and Raiatea. The Ahititera pluton (central depressionof Tahiti Nui) comprises a great diversity of rocks, rangingfrom ultrabasic to felsic in composition. It shows a concentriczonation with nepheline-free rocks in its periphery and nepheline-bearingrocks in its central part. The Faaroa pluton (central depressionof Raiatea) is entirely mafic and includes only gabbros andtheralites. The two plutons have variable Nd–Sr isotopicsignatures, especially the Ahititera rocks, which are subdividedinto three groups based on their mineralogy, geochemistry andisotope composition. The isotopic variability probably reflectslocal heterogeneities in the Society mantle plume. Petrographicand isotopic data have been used to define two magmatic suitesin Ahititera, identifiable from their degree of Si undersaturation.The evolution of the mildly Si-undersaturated suite is controlledby simple fractional crystallization, whereas the strongly Si-undersaturatedsuite requires additional H2O influx. The third isotopic groupincludes only theralites. The rare earth element (REE) compositionsof the mafic rocks from both plutons do not correlate with theirisotopic signature. The REE patterns of the most Si-undersaturatedrocks are systematically characterized by steeper slopes. Suchfeatures are also observed in lavas from seamounts located withinthe present-day hotspot area. It appears that REE concentrationsin Society lavas and intrusives are probably mainly governedby variable degrees of partial melting of a garnet-free mantlesource and are independent of their isotopic signature. KEY WORDS: cumulates; fractional crystallization; partial melting; French Polynesia; plutonic rocks; Society Islands; Tahiti; Raiatea 相似文献
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Fabric characteristics of subaerial slope deposits 总被引：1，自引：0，他引：1
The clast fabrics of certain types of terrestrial slope deposits are reviewed and compared, including the deposits of rockfalls, solifluction, debris flows, dry grain flows, frost-coated clast flows and run-off. The analysis is based on modern deposits in active environments. The study shows that fabric characteristics allow discrimination between ‘collective’and individual movement of rock particles. The individual particle movement generally results in a random clast orientation, whereas the processes of ‘collective’movement typically create distinct preferred orientations. The highest fabric strengths together with low values of spherical variance are found in solifluction deposits. A survey of Pleistocene slope deposits indicates, however, that clast fabric has to be used with caution in the identification of past slope dynamics, because significant post-depositional changes may occur during ageing and burial of deposits. The diagnostic significance of fabric characteristics may also be low due to the overlap of the statistical values that typify different processes. 相似文献
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EISSEN JEAN-PHILIPPE; JUTEAU THIERRY; JORON JEAN-LOUIS; DUPRE BERNARD; HUMLER ERIC; AL'MUKHAMEDOV ALEXANDER 《Journal of Petrology》1989,30(4):791-839
Detailed studies by submersible were carried out in the axialzone of the Red Sea Rift near 18?N during the Soviet Red Seaexpedition of the Oceanological Institute of the Academy ofSciences (December 1979–March 1980). The initial bathymetric,magnetic and seismic surveys established the general organizationof the symmetric tectonic steps (1–3) descending towardsthe axial rift. The 4–5 km wide inner floor of the riftwas explored during 21 dives. It is occupied by 100–300m high, young pillowed volcanoes, isolated or grouped to formelongated hills, frequently cut by open fissures except in thezone of most recent extrusion. The 42 samples collected are typical plagioclase ? olivine ?clinopyroxene ? spinel, more or less porphyritic mid-ocean ridgebasalts whose compositions were mainly controlled by polybaricfractionation of plagioclase, olivine and minor clinopyroxene.They have been separated into porphyritic and sub-aphyric groupsusing modes and mineralogical criteria. Mineral-liquid equilibria,crystal zonation, and modal proportions indicate some magmamixing but probably only of closely related magma batches withineach described group, as can occur inside a single magma chamber.Crystal accumulation is believed to have played a significantrole in only a few porphyritic samples. Three sub-groups (from less to more evolved; (a) FeO*/MgO<1?22;(b) 1?16<FeO*/MgO < 1?48; and (c)FeO*/MgO>1?49) weredistinguished on the basis of glass and whole-rock major elementchemistry. Glass compositions follow the multisaturated cotectic-likecurve for MORB-type basalts and show a general evolution verycomparable to what is observed on the Mid-Atlantic Ridge near36?N, but arc less diverse than in the FAMOUS area. 87Sr/86Sr,143Nd/144Nd, and 206Pb/204Pb data for 4 samples show strongsimilarities to those from the Mid-Atlantic and East PacificRidges, and indicate no continental contamination despite thefact that they have been produced during recent continentalbreak-up and ocean opening. 206Pb/204Pb values, Th/Ta vs. Th/Tbcorrelations, and rare earth element patterns allow recognitionof three different groups of samples, indicating that the RedSea Rift near 18?N is fed by a heterogeneous mantle source.The chondrite-normalized LREE. 相似文献
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地面核磁共振找水仪及其在水文地质调查工作中的应用研究 总被引：6，自引：0，他引：6
本文概要介绍了地面核磁共振找水方法的原理和世界上最新的直接探查地下水的仪器设备--地面核磁感应系统的特点,并以实例说明了NMR找水方法的应用效果,提出了关于提高NUMIS系统抗干扰能力、完善解释方法、研制系列仪器等方面的建议. 相似文献
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An amphibole-bearing gneiss from the Seward Peninsula, Alaska,underwent local dehydration to two-pyroxene gneiss. Dehydrationwas driven isothermally and isobarically, close to the metamorphicmaximum, by a small amount of CO2-rich fluid evolved from anunderlying impure marble layer. Stable isotope evidence indicatesthat the CO2 diffused 85 cm into the gneiss through a stationarypore fluid that was seldom fully connected. This created a gradientin H2O activity from 0.20 to 0.24 within the two-pyroxene alterationzone. Whole-rock analyses and mineral mass balances suggestthat, apart from loss of H2O, the change proceeded isochemically,a conclusion that differs from some of the more recent detailedchemical studies of outcrop-scale charnockitic alteration. Hornblendereacted out according to the reaction Hbl+1.86 Qtz=1.26 Cpx+1.36Opx+0.96 An65+0.29 Kfs+0.23 Ilm+H2O. Biotite was largely conserved.Clinopyroxene, orthopyroxene, and new-formed plagioclase occurin relatively fine-grained granular aggregates. New-formed K-feldsparoccurs as replacement antiperthite. It is argued that the reactiondid not involve the production of anatectic melt. We suggestthat CO2-induced dehydration in its simplest form is isochemical.We further suggest that the sequence of disappearance of biotiteand hornblende in prograde granulite terranes may be indicativeof the process of simple dehydration (at low aH2O) or vapor-absentdehydration melting (at higher T and aH2O). Our observationsmay be helpful in interpreting cases where the evidence forintroduced CO2 is more ambiguous. 相似文献