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1.
Luminescence decay time data are presented for 17 samples of synthetic calcite and a natural calcite between room temperature and approximately 15 K. The majority of the samples have Mn concentration in the range 0.0001–0.01 atoms per formula unit (apfu). Their spectra are consistent with a single exponential decay. It was necessary to use a “stretched” exponential to obtain adequate fits to the spectra of two samples having Mn concentrations of 0.036 and 0.091 apfu. The decay time at room temperature ranges from approximately 40–57 ms. At low temperature the corresponding range is 51–120 ms, indicating that thermal quenching of the decay time takes place. The decay time is dependent on the concentration of Mn, reaching a maximum (at both room- and low-temperature) in the range 0.001–0.003 apfu. The composition dependence is greater at low temperature. The results are discussed in terms of the Mott-Seitz and multiphonon mechanisms of thermal quenching. It is concluded that the latter provides a better fit to the data and is more consistent with models of the luminescence process in calcite:Mn.  相似文献   

2.
 The aim of this paper was to study the weathering mechanism of marbles and granites exposed to the marine environment at the Delos archaeological site. Alterations, as granular disintegration, contour scaling and alveolus formations, can be observed either at the base of blocks and columns, or at the median-high zones of monuments. A white marble, which originated from Naxos Island, had a weak porosity (0.2%). Its porous network was organized into two subnetworks of rectilinear and sinuous cracks, which limited capillary transfer to ∼10 cm. The granite, which originated from Delos Island, had a relatively high porosity (2.15%), and had a well-connected system of cracks and microporous zones of weathered minerals. This homogeneous network allowed good capillary transfer for long distances (1–2 m). For the marble, as for the granite, evaporation occurred mainly at depth in the stone, and encouraged its deterioration. This damage depends on the dissolution and crystallization of salts, which occur in cycles. First, by the capillary transfer of water and salt from the ground, when the stones are located near the sea. This processes can explain the deterioration of the marble and the granite bases, and the decay of granite on all its surfaces. Second, by fixation of water vapor by sea salt deposited on the stone by wind. This phenomenon can explain the degradations observed on the median-high parts of monuments in marble and granite, even though, for the granite, the first mechanism was more active.  相似文献   

3.
According to Madeley’s (2003) comparative framework of state–church relations in Europe, Poland is part of the historic Northeast-Southeast multi-confessional culture belt. The aim of this paper is to analyse the historic relationships between the Polish state and church in relation to this framework with special attention to the post-Second World War period and to the consequences for the Polish religious landscape. In contrast to the multi-confessionality of the historic Polish polities, after the Second World War Poland became a mono-confessional, Roman-Catholic country. Territorial changes, the resettlement of people and the annihilation of the Jewish population by the Nazis were responsible for this religious homogenisation. Consequently, the relationship between state and church was almost completely confined to the relationship with the Roman-Catholic Church. During the 45 years of communist dominance, that church became the largest public organisation independent of the state authorities and played the most important role in the struggle against the ‘atheisation’ of Polish society as a consequence of the strong support for the church by the majority of people. The post–1989 period is characterised by a liberalisation towards non-Catholic religious communities and – after an initial reluctance – a positive attitude of the Polish Roman-Catholic Church (strongly supported by the Polish Pope John Paul II) towards the Polish membership of the European Union.
Elżbieta Bilska-WodeckaEmail:
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4.
This paper presents a combination of seismic imaging, geomorphologic, and tectonic data and an interpretation of the M = 5.1 1980 Arudy earthquake sequence putting in relation the seismicity, the inherited faults, and the geomorphologic (Würm and postwürm) markers in this region of the Pyrenees. Since the anticlockwise rotation of the regional compression axis in Oligocene time, western Pyrenees are under a dextral regime and the resulting motion is accommodated along major inherited E–W dextral strike-slip faults. The Arudy aftershocks sequence is controlled by antecedent horsetail splay faults built at the boundary between two shallow Mesozoic crustal blocks most probably due to their differing rheology. This boundary has played the role of a seismic barrier stopping the E–W slip motion. The Arudy earthquake has reactivated the eastern segment of the main E–W strike-slip fault, while the post-seismic aftershocks correspond to local relaxation processes in normal tectonic behavior.  相似文献   

5.
Summary The Cu–Fe–Au–Mo (W) deposits in southeastern Hubei are an important component of the Middle–Lower Yangtze River metallogenic belt. Molybdenite from the Fengshandong Cu- (Mo), Ruanjiawan W–Cu- (Mo), Qianjiawan Cu–Au, Tongshankou Cu–Mo and Tonglüshan Cu- (Fe) deposits yielded Re–Os ages of 144.0 ± 2.1 Ma, 143.6 ± 1.7 Ma, 137.7 ± 1.7 Ma, 142.3 ± 1.8–143.7 ± 1.8 Ma and 137.8 ± 1.7–138.1 ± 1.8 Ma, respectively. Phlogopite from the Tieshan Fe- (Cu) deposit yielded an Ar–Ar age of 140.9 ± 1.2 Ma. These data and other published isotopic ages (Re–Os molybdenite and Ar–Ar mica ages) for the Cu–Fe–Au–Mo (W) deposits in the Middle–Lower Yangtze River metallogenic belt show that Cu–Fe–Au–Mo (W) mineralisation in the Tongling, Anqing, Jiurui and Edong ore districts developed in a narrow time span between 135.5 and 144.9 Ma, reflecting an important regional metallogenic event. An integrated study of available petrological and geochronological data, together with relationships to magmatism and the regional geodynamic framework, indicate that the Cu–Fe–Au–Mo (W) mineralisation in the Middle–Lower Yangtze River belt occurred during a regime of lithospheric extension. This extension is probably related to Late Mesozoic processes of lower crustal delamination and lithospheric thinning in East China.  相似文献   

6.
The development of the post-socialist city has already been characterised by substantial restructuring processes. Particular emphasis should be drawn to the take-off of the tertiary sector and the comprehensive blight phenomena in the previously industrial areas. The urban housing sector has witnessed increasing housing affordability problems, a marginalisation of communal housing stock, an increase of segregation and an intensification of the decay in the old housing stock. In all East Central European states the spatial development processes of industry and services within the cities basically show clear parallels to the pattern of urban development in continental Europe. In Hungary housing policy, tenure structure and the level of segregation already show relatively closer similarities to the neoliberal, Anglo–American pattern of development. The other ECE states show closer similarities to the corporatist welfare states of continental Europe. As far as medium-term urban development in East Central Europe is concerned, it is to be assumed that – regardless of the specific path of further development – overall solutions shall not be found for the fundamental problems which are the legacy of the socialist era – the decay of old housing stock, large scale derelict industrial areas and the extent and deficiencies of high-rise housing estates. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

7.
Calcite was synthesized by four methods, and the luminescence decay-time was measured for nine samples before and after heating hydrothermally in the temperature range 200–400°C. Decay-time data were collected between room temperature and approximately 15 K. The decay time at room temperature is approximately 50 ms, with little difference between a given calcite before and after hydrothermal treatment. The decay time at 15 K is always greater than at room temperature as the effect of thermal quenching diminishes. Differences in decay time before and after heating are more apparent at low temperature owing to this reduction in thermal quenching. The decay time decreased significantly in two samples, and an increase in decay time was observed in the remaining seven samples following heating. Among the latter group, the change in decay time was insignificant in three samples. The results are compared with previous data in which it was shown that the effect of heating is to increase the intensity of luminescence.  相似文献   

8.
The first findings of Au and Ag tellurides (sylvanite and petzite) in sulfide-quartz ore of the Shirokinsky ore and placer cluster located in the Sette-Daban Horst-Anticlinorium are described. These minerals were found for the first time at the gold deposits of East Yakutia. The chemical compositions (wt %) of sylvanite (23.65–24.61 Au, 12.7–13.13 Ag, 59.3–59.97 Te, 96.26–97.97 in total) and petzite (23.17–25.24 Au, 42.27–44.40 Ag, 31.26–33.37 Te, 98.19–102.55 in total) are reported. Galena as a host mineral is associated with native gold, electrum, hessite, and stützite. The finding of Au-Ag and Ag tellurides provides evidence for the development of Au-telluride mineralization in the Sette-Daban Horst-Anticlinorium.  相似文献   

9.
In the context of a research and development program on waste disposal, an experimental site (Tournemire tunnel, Aveyron, France) was selected by the French Institute for Nuclear Protection and Safety (IPSN) in order to undertake studies on potential fluid flow at different scales of space and time within a 250-m-thick argillaceous formation. The argillite has a low natural water content (~3–5%) and very low radii access porosity. Diffusion (tritiated water) coefficients (1×10–12 to 2×10–11 m2/s) and hydraulic conductivities derived from different types of laboratory tests (10–14 to 10–13 m/s) are characteristics of a very low-permeable rock. In situ hydraulic tests (including long-term hydraulic-head measurements) were used to obtain values for hydraulic head and hydraulic conductivity at a scale of 1–10 m (10–13 to 10–11 m/s). Despite uncertainties on these data (due to a scale factor, presence of fissures, and possible artefacts due to hydro-chemo-mechanical coupling), it is expected that fluid flow is essentially governed by diffusion processes. Identification of possible natural flows at larger scales of time and space was investigated using natural isotopic tracers from interstitial fluids. Modelling, based on the deuterium profile along the clay formation and assuming pure diffusion processes, provides estimations of possible flow times. However, lack of knowledge concerning the past geological evolution of the site and the possible role of a fracture network do not permit reduction of uncertainties on these estimations at this stage. Electronic Publication  相似文献   

10.
Summary ?To enhance the ability to distinguish tholeiitic from alkalic magma parentages by mineral compositions, I determined trace-element abundances in plagioclase separated from xenolithic gabbros of Mauna Kea volcano. These gabbros have origins in tholeiitic and alkalic magmas of the Hamakua postshield stage of Mauna Kea volcanism. Chondrite-normalized rare-earth element (REE) patterns for plagioclase show that highly calcic plagioclase, ≥ An78, from alkalic magma has greater light-REE/heavy-REE (LREE/HREE) ratios than less calcic plagioclase, An64–75, from tholeiitic magma (ratios, 22–33 vs < 20), suggesting that higher LREE/HREE ratios are inherent to plagioclase of alkalic magmas. However, with compositional evolution (i.e., to lower An), plagioclase REE patterns are of limited use for distinguishing tholeiitic from alkalic parentage because LREE/HREE ratios within each group increase and overlap in the range of ∼ 20–90. Sr, Ba, Hf, and Ta can also discern parentages as their abundances in plagioclase largely reflect abundances inherent to their parental magmas. The best expressions for identifying parentage use Sr abundances (Sr vs An; vs Ce/Yb; vs Sr/Ce), although Hf, Ba, and Ta abundances vs An and vs Ce/Yb are also useful – the distinctions due to tholeiitic plagioclase having relatively low Sr (∼ 500–1000 ppm), Ba (< 100 ppm), Hf (< 0.10 ppm), and Ta (< 0.05 ppm). These relationships help to distinguish between the effects of differentiation on trace-element abundances in plagioclase and their abundances owed to intrinsic concentrations in their magmas. They create compositional fields for tholeiitic and alkalic parentages that remain graphically separated even though differentiation may have enriched the plagioclase in incompatible elements.
Zusammenfassung ?Plagioklas aus tholeitischen und alkalischen Magmen von Hawaii: Unterscheidung aufgrund von REE, Sr, Ba, Hf und Ta Um die M?glichkeit der Unterscheidung tholeitischer von alkalischer Magmaherkunft durch Mineralzusammensetzungen zu verbessern, habe ich die Spurenelementverteilung in Plagioklasen, die von xenolithischen Gabbros des Mauna Kea Vulkans abgetrennt wurden, untersucht, Diese Gabbros entstammen tholeitischen und alkalischen Magmen des Hamakua “Post-Schild” Stadiums des Mauna Kea Vulkanismus. Chondritisch normalisierte Seltene Erd (SEE) Verteilungs-Muster für Plagioklase zeigen, dass stark kalzische Plagioklase, > An78, aus alkalischen Magmen h?here leichte SEE/schwere SEE (LSEE/HSEE) Verh?ltnisse zeigen, als weniger kalzische Plagioklase, An64–75 aus tholeitischem Magma (Verh?ltniszahlen 22–33 gegenüber < 20). Dies weist darauf hin, dass h?here LSEE/HSEE-Verh?ltnisse typisch für Plagioklase aus alkalischen Magmen sind. Im Zuge der Evolution der Zusammensetzungen (d.h. zu niedrigeren An-Werten hin), sind die SEE Verteilungsmuster von Plagioklasen weniger hilfreich um tholeitische von alkalischer Herkunft zu unterscheiden. Dies ist deshalb so, weil die Verh?ltniszahlen innerhalb jeder Gruppe zunehmen und im Bereich von 20–90 überlappen. Sr, Ba, Hf und Ta k?nnen auch dazu dienen, um die Herkunft der Plagioklase zu definieren, da ihre H?ufigkeit gro?teils auf H?ufigkeiten, die für die Ursprungsmagmen typisch sind, zurückgehen. Die besten Herkunft-Parameter sind die Sr H?ufigkeiten (Sr vs An; vs Ce/Yb; vs Sr/Ce), obwohl die H?ufigkeit von Hf, Ba und Ta gegen An und gegen Ce/Yb auch nützlich sind. Diese Unterscheidungen gehen darauf zurück, dass tholeitische Plagioklase relativ niedrige Sr (∼ 500–1000 ppm), Ba (< 500 ppm) Hf (< 0.10 ppm) und Ta (< 0.5 ppm) führen. Diese Beziehungen erleichtern die Unterscheidung zwischen den Auswirkungen der Differenzierung auf die Spurenelement-Verteilungsmuster in Plagioklasen und auf ihre H?ufigkeiten, die auf die intrisischen Konzentrationen in den Ursprungsmagmen zurückgehen. Sie definieren charakteristische Felder für tholeitische und für alkalische Herkunft, die graphisch separiert bleiben, auch wenn die Gehalte der Plagioklase an inkompatiblen Elementen durch Differenzierung zugenommen haben mag.

Received July 22, 1999;revised version accepted December 7, 1999  相似文献   

11.
A simplest equation within the framework of the Mie-Grüneisen–Einstein approach is considered. Pressure estimation values are presented that are derived by conventional arithmetic and algebraic calculations as a function of temperature and volume. The equation under consideration complies with the Mie-Grüneisen–Debye model at high temperature. Different versions of an equation of state (EoS) of MgO proposed by Speziale et al. (J Geophys Res 106B:515–528, 2001) as a pressure standard at high temperatures are subject to analyses. In the literature, at least four versions of Speziale et al. EoS of MgO are discussed; the discrepancy between them reaching a few GPa at T > 2,000 K and P > 100 GPa. Our analyses of these equations suggest that the volume dependence of the Debye temperature is accepted arbitrarily and does not agree with the definition of the Grüneisen parameter, γ = −(∂lnΘ/∂lnV) T . Pressure as a function of temperature and volume in the Mie-Grüneisen–Einstein approach or the Gao pressure calculator can be used to estimate true pressure at compression x = V/V 0 < 1 with the Speziale et al. EoS of MgO.  相似文献   

12.
We use a lattice vibrational technique to derive thermophysical and thermochemical properties of the pure elements aluminum and iron in pressure–temperature space. This semi-empirical technique is based on either the Mie–Grüneisen–Debye (MGD) approach or an extension of Kieffer’s model to incorporate details of the phonon spectrum. It includes treatment of intrinsic anharmonicity, electronic effects based on the free electron gas model, and magnetic effects based on the Calphad approach. We show that Keane’s equation of state for the static lattice is better suitable to represent thermodynamic data for aluminum from 1 bar to pressures in the multi-megabar region relative to Vinet’s universal and the Birch–Murnaghan equation of state. It appears that the MGD and Mie–Grüneisen–Kieffer approach produce similar results, but that the last one better represents heat capacity below room temperature. For iron we show that the high temperature behavior of thermal expansivity can be explained within the Calphad approach by a pressure-dependent Curie temperature with a slope between –1 and 0 K/GPa.  相似文献   

13.
Summary The Precambrian rocks in western Ethiopia consist of high- and low-grade terranes intruded by granitoids with a wide compositional spectrum. The formation ages of these granitoid rocks are, so far, poorly understood. Single-grain zircon Pb/Pb evaporation and conventional U/Pb dating conducted on four granitoids places time constraints on their emplacement and tectonothermal events. Three granitoid magmatic events were identified at 815 Ma, 700–730 Ma, and 620–625 Ma, which were marked by emplacement of the calc-alkaline Ujjukka granite and granodiorite, the anatectic Suqii-Wagga two-mica granite and the Guttin K-feldspar megacrystic granite, and the anorogenic Ganjii monzogranite, respectively. We interpret the 815 Ma age to mark a major magmatic episode in this part of Africa. A tectonothermal event at ∼ 630 Ma preceded the emplacement of the within-plate granitoids at 620–625 Ma. The decrease of ages from the calc-alkaline to anorogenic granitoids suggests a shift of magmatic styles and tectonic setting of the granitoids over a period of 200 million years. The Suqii-Wagga and Guttin granites, representing the granitoid population in the migmatitic terrane, formed as part of the successive evolution of the granitoid magmatism in the region. The presence of xenocrystic zircons of Mesoproterozoic ages in both granitoid populations emplaced into the low-grade volcanosedimentary sequence and the high-grade, often migmatitic, gneisses suggest contribution of pre-Pan-African crust to the origin and evolution of the granitoids. Conventional U/Pb studies of zircons from the Guttin K-feldspar megacrystic granite and the Ganjii monzogranite yielded upper intercept ages of ∼ 3 Ga and ∼ 2 Ga, respectively, possibly indicating the presence of reworked Archean-Proterozoic crustal material.
Zusammenfassung U/Pb und Pb/Pb Zirkonalter granitoider Gesteine aus dem Gebiet von Wallagga: Hinweise zur magmatischen und tektonischen Entwicklung pr?kambrischer Gesteine in A¨thiopien Das Pr?kambrium im westlichen ?thiopien besteht aus hoch- und niedrigmetamorphen Basement Serien, die von Granitoiden unterschiedlichster Zusammensetzung intrudiert werden. Die Bildungsalter dieser Magmatite sind bisher nur ungenügend bekannt gewesen. Neue Pb/Pb-Evaporations- und konventionelle U/Pb-Datierungen an Einzelzirkonen von vier verschiedenen Plutoniten erlauben nun Rückschlüsse auf deren Intrusionsalter und die damit verbundene tektonische Entwicklung der Region. Drei zeitlich getrennte magmatische Ereignisse lassen sich unterscheiden: Intrusion der kalk-alkalischen Ujjukka Granite um 815 Ma; Bildung der anatektischen Zweiglimmer Granite der Suqii-Wagga Suite um 700–730 Ma; Intrusion der grob porphyrischen K-Feldspat Granite von Guttin und der anorogenen Ganjii Monzogranite um 620–625 Ma. Das 815 Ma Ereignis wird als wichtige magmatische Phase in diesem Teil von Afrika interpretiert. Ein thermisches Ereignis um 630 Ma geht der Platzname von “within-plate” Granitoiden um 620–625 Ma voraus. Die beobachtete Altersabnahme von den kalk-alkalischen zu den anorogenen Granitoiden spricht für eine pr?gnante ?nderung des tektonischen Regimes über einen Zeitraum von ca. 200 Ma. Die Suquii-Wagga und Guttin Granite sind in das hochgradige, migmatische Basement intrudiert. Dies mag für eine sukzessive tektonische Entwicklung dieser Abfolgen sprechen. Ererbte, mesoproterozoische Zirkone deuten auf die Aufarbeitung pr?-panafrikanischer Gesteine hin. Obere Einstichpunkte von den U/Pb Analysen im Altersbereich von ca. 3 Ga in den Guttin Graniten und von ca. 2 Ga in den Ganjii Monzograniten sprechen ebenfalls für die Inkorporation von proterozoischen bis archaischen Krustenkomponenten.

Received June 7, 2000; accepted October 29, 2000  相似文献   

14.
This study examines rainfall thresholds for erosion and sediment yield in the upper Yangtze River basin. Sediment reduction effects of soil conservation measures depend on the magnitudes of rainstorm. When the latter is less than a critical threshold, sediment reduction effects of soil conservation measures are positive; when this magnitude is exceeded, the effect is negative. An analysis based on data from the Jialingjiang River shows that the sediment reduction by soil conservation measures increased with annual precipitation to a peak, and then decreased to a negative value. The annual precipitation at the peak and zero values of sediment reduction are 970 and 1,180 mm, respectively, which can be regarded as two thresholds. Annual precipitation at the zero-value of sediment reduction has a return period of 25 years. In general, the design standard of soil conservation works in China is related with rainstorms with return periods of 10–20 years. When the magnitude of rainstorm exceeds this, the soil conservation works may be partly or totally destroyed by rainstorms, and the previously trapped sediment may be released, resulting in a sharp increase in sediment yield. It was also found in the lower Jinshajiang River that when annual precipitation exceeds 1,050 mm or high-flow season precipitation exceeds 850 mm, the annual sediment yield increased sharply. These can also be regarded as key rainfall thresholds for erosion and sediment yields. When precipitation is less than the two thresholds, dominant erosion types are sheet, rill and gully erosions. When precipitation crosses the two thresholds, debris flows may occur more frequently. As a result, the previously stored loose sediment is released and sediment yield increases sharply.  相似文献   

15.
 Two test cases from Israel are presented herein employing the decay rate of radon along the flow path to assess groundwater flow velocities. Groundwater flow reaching the fault zone emerges in several places along the rift fault zone as thermal springs because of deep water confinement. The high water temperature of the surface is indicative of high vertical flow velocities, which maintains the original high temperatures. Knowing the Rn content at a source point and at a given down-gradient, and assuming no Rn addition from the water itself or along the flow path, one can calculate the flow velocity based on the Rn half-life time. The decay of Rn in western Galilee was found to be ∼570–150 pCi/l, and in the Dead Sea area from 5000–2000 pCi/l along a respective flow path of 1000 and 200 m, Based on the above, the calculated flow velocities were compared with those obtained from pumping tests in the study area. The method is applicable, because of the short Rn half-life, to cases of high Rn contents, short distances and high flow velocities. Received: 18 January 2000 · Accepted: 21 March 2000  相似文献   

16.
Summary ?Part of the Mesoproterozoic (1.6 Ga) Gawler Range Volcanics in South Australia is composed of mingled feldspar- quartz- phyric dacite, rhyodacite and rhyolite lavas. Field relationships suggest that dacite erupted first, locally grading into rhyodacite, followed by mingled dacite and rhyolite or rhyodacite and rhyolite, and finally in some areas rhyolite, and imply that the three lithofacies co-existed in a compositionally stratified magma chamber. Data on the bulk rock, groundmass and melt inclusion compositions suggest that post-eruption alteration has had very little effect on the original rock compositions. Melt inclusions in quartz from rhyolite and rhyodacite-dacite, respectively, belong to two compositional populations. Inclusions in the rhyolitic quartz have less evolved compositions with lower SiO2 (72–76.4 wt %) and higher Al2O3 (13.2–15.6 wt%) and Na2O (2.5–4.2 wt%) abundances. In contrast, melt inclusions in quartz from the rhyodacite-dacite are more “evolved” (i.e., 75.5–78.3 wt% SiO2, 11.2–12.7 wt% Al2O3 and 1.7–2.2 wt% Na2O). The two melt populations define a single compositional trend towards groundmass compositions, which are essentially similar in all three lithofaci es (77.8–80.5 wt% SiO2, 9.9–11.1  wt% Al2O3 and 2.2–2.4 wt% Na2O). This trend is consistent with the derivation of the groundmass melt from a single precursor melt of rhyolitic composition by means of crystallisation of dominant plagioclase, K-feldspar and minor quartz. Plagioclase-enriched dacite-rhyodacite magma comprises a mixture of the residual melt and plagioclase phenocryst s that accumulated in the upper part of the magma chamber and erupted first. Similar residual melt containing quartz and K-feldspar phenocrysts was present deeper in the magma chamber and erupted later to form quartz-, K-feldspar-phyric rhyolite.
Zusammenfassung ?Die Bildung von Si-reichem Dacit aus rhyolitischer Schmelze: Evidenz aus Schmelzeinschlüssen in Laven der 1.6 Ga Gawler Range Volcanics, Südaustralien Ein Teil der mesoproterozoischen (1.6 Ga) Gawler Range Volcanics in Südaustralien setzt sich aus “mingled” Feldspat- Quarz-phyrischen dacitischen, rhyodacitischen und rhyolithischen Laven zusammen. Gel?ndebefunde legen nahe, da? die Dacite, die lokal in Rhyodacite übergehen, zuerst eruptierten, gefolgt vom “mingled” Dacit und Rhyolith oder Rhyodacit und Rhyolith. Schlie?lich bildeten sich in einigen Gebieten Rhyolithe. Diese Beobachtungen lassen die Schlu?folgerung zu, da? die drei Lithofazies in einer geschichteten Magmenkammer koexistierten. Die Daten der Gesamtgesteins-, Grundmasse- und Schmelzeinschlu?- Zusammensetzungen zeigen, da? Alterationsvorg?nge nach der Eruption einen sehr minimalen Effekt auf die ursprüngliche Gesteinszusammensetzung hatten. Die Schmelzeinschl üsse in den Rhyolithen und Rhyodaciten geh?ren zwei unterschiedlich en Populationen an. Die Schmelzeinschlüsse in Quarz der Rhyolithe sind weniger deutlich “entwickelt” mit niedrigeren SiO2 (72–76.4 Gew.%) und h?heren Al2O3 (13.2–15.6 Gew.%) und Na2O-(2.5–4. 2 Gew.%) Gehalten. Im Unterschied dazu sind die Einschlüss e in Quarz aus Rhyodacit-Dacit st?rker “entwickelt” (i.e., 75.5–78.3 Gew.% SiO2, 11.2–12.7 G ew.% Al2O3 und 1.7–2.2 Gew.% Na2O). Die beiden Populationen von Schmelzeinschlüssen definieren einen einzigen Entwicklungstrend hin zur Zusammensetzung der Grundmasse, die in allen drei Lithofazies ?hnlich ist (77.8–80.5 Gew.% SiO2, 9.9–11.1 Gew.% Al2O3 und 2.2–2.4 Gew.% Na2O). Dieser Trend ist mit der Herkunft der Grundmasse-bildenden Schmelze aus einer einzigen Ausgangsschmelze rhyolithischer Zusammensetzung infolge der Kristallisation von haupts?chlich Plagioklas, Alkalifeldspat und untergeordnet Quarz konsistent. Dacit-Rhyodacitmagmen, die an Plagioklas angereichert sind, stellen eine Mischung der Residualschmelze mit Plagioklas- Ph?nokristallen, die sich in den oberen Teilen der Magmenkammer akkumuli ert haben, dar; sie eruptierten zuerst. ?hnliche residuale Schmelzen mit Quarz und Akalifeldspat-Ph?nokristallen waren auf die tieferen Teilen der Magmenkammer beschr?nkt; sie eruptierten sp?ter und bildeten die Quarz- und Akalifeldspat-phyrischen Rhyolithe.

Received April 1, 1999;/revised version accepted July 27, 1999  相似文献   

17.
The Erdenetuin-Obo porphyry Cu-Mo deposit was formed at the final stage of development of magmatic activity occasionally manifested in the Late Permian-Early Triassic in the period of at least 40 Ma. Early plutonic (host) and late ore-bearing porphyry intrusive complexes were formed in that period. The plutonic complex is multiphase, while the porphyry complex is polyrhythmical and multiphase within rhythms. The obtained data on the U-Pb isotopic composition (SHRIMP II) of zircons from unaltered rocks of the ore field are discussed: gabbro, diorite, and granodiorite of the plutonic complex and granodiorite-porphyry I and II of the first and second rhythms of the ore-bearing complex, respectively. Zircons of different age levels and genotypes were identified in the course of performed investigations. Gabbro are dominated by postmagmatic (superimposed) zircons with the datings of 239–225 Ma. The age of xenogenic zircon brought out from the basement rocks is estimated at 1146 ± 11 Ma. Zircons occur as magmatic and postmagmatic (superimposed) minerals dated 252–247, 244–233 Ma in diorite and 244–242, 239–224 Ma in granodiorite. The ages of postmagmatic zircons from diorite are partially overlapped by datings of magmatic zircons from granodiorite and granodiorite-porphyry. In the porphyry complex, the datings of magmatic zircons are 240–234 and 222–220 Ma in granodiorite-porphyries I and II, respectively. There are also inherited zircons with datings coinciding with those of magmatic zircons from precursor intrusive rocks. Datings of such zircons are 249–241 and 257–231 Ma for granodiorite-porphyries I and II, respectively. As a whole, zircon datings in all studied igneous rocks forming a virtually uninterrupted range in the period of 257–220 Ma allow us to suggest the relation of the ore magmatic system to the long-living constantly active deep source occasionally delivering melt to the upper levels.  相似文献   

18.
Deposition of quartz–molybdenite–pyrite–topaz–muscovite–fluorite and subsequent hübnerite and sulfide–fluorite–rhodochrosite mineralization at the Sweet Home Mine occurred coeval with the final stage of magmatic activity and ore formation at the nearby world-class Climax molybdenum deposit about 26 to 25 m.y. ago. The mineralization occurred at depths of about 3,000 m and is related to at least two major fluid systems: (1) one dominated by magmatic fluids, and (2) another dominated by meteoric water. The sulfur isotopic composition of pyrite, strontium isotopes and REY distribution in fluorite suggest that the early-stage quartz–molybdenite–pyrite–topaz–muscovite–fluorite mineral assemblage was deposited from magmatic fluids under a fluctuating pressure regime at temperatures of about 400°C as indicated by CO2-bearing, moderately saline (7.5–12.5 wt.% NaCl equiv.) fluid inclusions. LA-ICPMS analyses of fluid inclusions in quartz demonstrate that fluids from the Sweet Home Mine are enriched in incompatible elements but have considerably lower metal contents than those reported from porphyry–Cu–Au–Mo or Climax-type deposits. The ore-forming fluid exsolved from a highly differentiated magma possibly related to the deep-seated Alma Batholith or distal porphyry stock(s). Sulfide mineralization, marking the periphery of Climax-type porphyry systems, with fluorite and rhodochrosite as gangue minerals was deposited under a hydrostatic pressure regime from low-salinity ± CO2-bearing fluids with low metal content at temperatures below 400°C. The sulfide mineralization is characterized by mostly negative δ34S values for sphalerite, galena, chalcopyrite, and tetrahedrite, highly variable δ18O values for rhodochrosite, and low REE contents in fluorite. The Pb isotopic composition of galena as well as the highly variable 87Sr/86Sr ratios of fluorite, rhodochrosite, and apatite indicates that at least part of the Pb and Sr originated from a much more radiogenic source than Climax-type granites. It is suggested that the sulfide mineralization at the Sweet Home Mine formed from magmatic fluids that mixed with variable amounts of externally derived fluids. The migration of the latter fluids, that were major components during late-stage mineralization at the Sweet Home Mine, was probably driven by a buried magmatic intrusion.  相似文献   

19.
Recent studies of Chesapeake Bay hypoxia suggest higher susceptibility to hypoxia in years after the 1980s. We used two simple mechanistic models and Bayesian estimation of their parameters and prediction uncertainty to explore the nature of this regime shift. Model estimates show increasing nutrient conversion efficiency since the 1980s, with lower DO concentrations and large hypoxic volumes as a result. In earlier work, we suggested a 35% reduction from the average 1980–1990 total nitrogen load would restore the Bay to hypoxic volumes of the 1950s–1970s. With Bayesian inference, our model indicates that, if the physical and biogeochemical processes prior to the 1980s resume, the 35% reduction would result in hypoxic volume averaging 2.7 km3 in a typical year, below the average hypoxic volume of 1950s–1970s. However, if the post-1980 processes persist the 35% reduction would result in much higher hypoxic volume averaging 6.0 km3. Load reductions recommended in the 2003 agreement will likely meet dissolved oxygen attainment goals if the Bay functions as it did prior to the 1980s; however, it may not reach those goals if current processes prevail.  相似文献   

20.
Summary Exceptionally Cr-rich metabasalts related to a komatiite-dominant volcanic sequence occur in the Archaean Kuhmo greenstone belt, eastern Finland. These basalts contain more chromium (1300–4500 ppm) than any other terrestrial basalts analysed so far, and also have high nickel concentrations (200–1700 ppm). In stratigraphy, these Cr-rich basalts occur above the komatiite and komatiitic basalt units forming the uppermost units of the komatiite sequence. Extremely reducing conditions during magma generation or fractional crystallization are suggested as a reason for these exceptional compositions. Low oxygen fugacity has prevented crystallization of chromite and decreased the olivine/liquid partition coefficient for nickel in olivine fractionation, thus causing the enrichment of Cr and Ni in the residual melt.
Zusammenfassung Au?ergew?hnlich Cr-reiche Basalte in der komatiitischen vulkanischen Assoziation des Archaischen Kuhmo-Grünsteingürtels in Ostfinnland Im archaischen Kuhmo-Grünsteingürtel in Ostfinnland treten au?ergew?hnlich Cr-reiche Metabasalte auf, die mit einer komatiitdominanten vulkanischen Sequenz verbunden sind. Diese Basalte enthalten mehr Chrom (1300–4500 ppm) als alle anderen terrestrischen Basalte, die bislang analysiert worden sind, und sie weisen zudem auch hohe Nickelkonzentrationen auf (200–1700 ppm). In der Stratigraphie treten die Cr-reichen Basalte über dem Komatiit und den komatiitischen Basalteinheiten auf und bilden die obersten Einheiten der Komatiitsequenz. Extrem reduzierende Bedingungen w?hrend der Magmabildung oder fraktionierte Kristallisation werden als eine Ursache für diese au?ergew?hnlichen Zusammensetzungen vorgeschlagen. Die niedrige Sauerstoff-Fugazit?t hat die Kristallisation des Chromits gehemmt, den Verteilungskoeffizienten Olivin/Schmelze für Nickel bei der Olivinfraktionierung herabgesetzt und dadurch die Anreicherung von Cr und Ni in der Restschmelze verursacht.

Received November 24, 1997; revised version accepted July 22, 1999  相似文献   

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