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21.
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
22.
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
24.
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
28.
Based on 225 analyses of quartzites, siliceous granoblastites,calc silicate rocks, calcite and dolomite marbles, including120 analyses of pelites and semipelites, sedimentary trendsof chemical variation are identified in staurolite and sillimanitegrade rocks. The correlation of original clay mineral contentwith Ti, Fe, K, Rb, Y, Nb, Ca, Ni, Ga, Zn and probably Ba andMn is shown. A similar clay mineral (whose composition is calculated)was added to all the sediments except the quartz-rich sandstones,now quartzites. This pattern appears to be general for mostsediments, based on crustal averages. The form of the originaladdition of Sr in the sediments might be identified as eithercarbonate or feldspar by a Ca vs. Sr plot. The southern pelites in a 2–4 km peripheral zone to theConnemara orthogneisses and migmatites have been metasomatized.The crude order of elemental enrichment from the elements increasedthe most to those increased the least relative to the same stratigraphicalhorizons in the north is: Mn, Ba, Th, Cu, Ca, Sr, Y, Pb, Zn,Pr, Ge, Nd, La, Mg, S, Ce, Rb, Sm, Ti, Na, K and Ga while Si,Al, Cr, Ni, Co, Fe and P are unchanged or removed. The sourceof the material added is postulated to be the water-rich residualfraction of the migmatitic quartz diorite gneiss, the transportbeing by movement of a water-rich fluid out of the migmatites,the fixation being mainly in biotite and new, more calcic, plagioclaseporphyroblasts, there being a positive correlation between elementenrichment and ionic radius. 相似文献
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Major- and trace-element analyses, accompanied by modal analysesand mineralogical data, are given for thirty-three striped amphibolitesfrom Connemara. It is concluded that prior to metamorphism theserocks were intrusions, lavas or tuffs of sodic basalt composition. 相似文献
30.
The Chemical Distinction Between Ortho- and Para-amphibolites 总被引：1，自引：0，他引：1
Although ortho-amphibolites can often be distinguished chemicallyfrom para-amphi-bolites by their higher contents of Cr, Ni,and Ti, and lower Niggli k ratios, no criterion based on abundancelevels is generally applicable because many basic igneous rockshave low Cr, Ni, and Ti contents, and alkali metasomatism inmetamorphic terrains often disturbs the k ratio. Of much morevalue is the distinction between igneous and sedimentary trendsof variation. This requires enough analyses to establish a reliabletrend. Some critical plots are suggested, and the Karroo doleritesfrom South Africa and the Connemara striped amphi-bolites fromwestern Ireland are compared with amphibolites from Lang?y (N.Norway), Bakersville-Roan area (N. Carolina, U.S.A.), and NW.Queensland (Australia). The plots confirm the origin of theortho-amphibolites from these regions but some of the supposedpara-amphibolites may be ortho-amphibolites and more analysesare needed to define reliable trends of variation. 相似文献