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1.
Ijolite-carbonatite complexes are ubiquitously surrounded of an aureole of metasomatically altered rocks. The process of alteration is termed fenitization and is generally caused by peralkaline fluids emanating from cooling alkaline, i.e. ijolite and carbonatite magmas. Ijolites and carbonatites normally occur together and attempts to determine the source of the fenitizing fluids may therefore lead to controversial, if not erroneous, conclusions.
Mineralogical and chemical data of fenites from Oldoinyo Lengai (Tanzania), Fen (Norway), and Alnö (Sweden) are reviewed in the present paper in order to reveal the main factors controlling the fenitization around ijolite and carbonatite. Despite the overall alkaline nature of the process, variables such as XCO2 of the fluid, activity gradients of SiO2, Al2O3 and CaO, FeO/MgO ratio, f O2 and temperature gradients may differ, producing distinctive patterns of fenitization around the two magmatic sources. The ijolitic-type fluid has low XCO2, high activities of alkalies, SiO2 and Al2O3, and low activity of CaO. The f O2 evolves along the hm-mt buffer conditions and the temperature falls gradually with distance from the magmatic source. The carbonatitic-type fluid has high XCO2, high activities of alkalies and CaO, and low activities of SiO2 and Al2O3. Temperatures and f O2 are initially high, but decrease sharply with distance from the source. Moreover, the CO2-rich fluid may complex and transport the REE.  相似文献   
2.
The Rosia Poieni deposit is the largest porphyry copper deposit in the Apuseni Mountains, Romania. Hydrothermal alteration and mineralization are related to the Middle Miocene emplacement of a subvolcanic body, the Fundoaia microdiorite. Zonation of the alteration associated with the porphyry copper deposit is recognized from the deep and central part of the porphyritic intrusion towards shallower and outer portions. Four alteration types have been distinguished: potassic, phyllic, advanced argillic, and propylitic. Potassic alteration affects mainly the Fundoaia subvolcanic body. The andesitic host rocks are altered only in the immediate contact zone with the Fundoaia intrusion. Mg-biotite and K-feldspar are the main alteration minerals of the potassic assemblage, accompanied by ubiquitous quartz; chlorite, and anhydrite are also present. Magnetite, pyrite, chalcopyrite and minor bornite, are associated with this alteration. Phyllic alteration has overprinted the margin of the potassic zone, and formed peripheral to it. It is characterized by the replacement of almost all early minerals by abundant quartz, phengite, illite, variable amounts of illite-smectite mixed-layer minerals, minor smectite, and kaolinite. Pyrite is abundant and represents the main sulfide in this alteration zone. Advanced argillic alteration affects the upper part of the volcanic structure. The mineral assemblage comprises alunite, kaolinite, dickite, pyrophyllite, diaspore, aluminium-phosphate-sulphate minerals (woodhouseite-svanbergite series), zunyite, minamyite, pyrite, and enargite (luzonite). Alunite forms well-developed crystals. Veins with enargite (luzonite) and pyrite in a gangue of quartz, pyrophyllite and diaspore, are present within and around the subvolcanic intrusion. This alteration type is partially controlled by fractures. A zonal distribution of alteration minerals is observed from the centre of fractures outwards with: (1) vuggy quartz; (2) quartz + alunite; (3) quartz + kaolinite ± alunite and, in the deeper part of the argillic zone, quartz + pyrophyllite + diaspore; (4) illite + illite-smectite mixed-layer minerals ± kaolinite ± alunite, and e) chlorite + albite + epidote. Propylitic alteration is present distal to all other alteration types and consists of chlorite, epidote, albite, and carbonates. Mineral parageneses, mineral stability fields, and alteration mineral geothermometers indicate that the different alteration assemblages are the result of changes in both fluid composition and temperature of the system. The alteration minerals reflect cooling of the hydrothermal system from >400 °C (biotite), to 300–200 °C (chlorite and illite in veinlets) and to lower temperatures of kaolinite, illite-smectite mixed layers, and smectite crystallization. Hydrothermal alteration started with an extensive potassic zone in the central part of the system that passed laterally to the propylitic zone. It was followed by phyllic overprint of the early-altered rocks. Nearly barren advanced argillic alteration subsequently superimposed the upper levels of the porphyry copper alteration zones. The close spatial association between porphyry mineralization and advanced argillic alteration suggests that they are genetically part of the same magmatic-hydrothermal system that includes a porphyry intrusion at depth and an epithermal environment of the advanced argillic type near the surface.Editorial handling: B. Lehmann  相似文献   
3.
High-pressure (HP) metamorphic rocks, including garnet peridotite, eclogite, HP granulite, and HP amphibolite, are important constituents of several tectonostratigraphic units in the pre-Alpine nappe stack of the Getic–Supragetic (GS) basement in the South Carpathians. A Variscan age for HP metamorphism is firmly established by Sm–Nd mineral–whole-rock isochrons for garnet amphibolite, 358±10 Ma, two samples of eclogite, 341±8 and 344±7 Ma, and garnet peridotite, 316±4 Ma.

A prograde history for many HP metamorphic rocks is documented by the presence of lower pressure mineral inclusions and compositional zoning in garnet. Application of commonly accepted thermobarometers to eclogite (grt+cpx±ky±phn±pg±zo) yields a range in “peak” pressures and temperatures of 10.8–22.3 kbar and 545–745 °C, depending on tectonostratigraphic unit and locality. Zoisite equilibria indicate that activity of H2O in some samples was substantially reduced, ca. 0.1–0.4. HP granulite (grt+cpx+hb+pl) and HP amphibolite (grt+hbl+pl) may have formed by retrogression of eclogites during high-temperature decompression. Two types of garnet peridotite have been recognized, one forming from spinel peridotite at ca. 1150–1300 °C, 25.8–29.0 kbar, and another from plagioclase peridotite at 560 °C, 16.1 kbar.

The Variscan evolution of the pre-Mesozoic basement in the South Carpathians is similar to that in other segments of the European Variscides, including widespread HP metamorphism, in which PTt characteristics are specific to individual tectonostratigraphic units, the presence of diverse types of garnet peridotite, diachronous subduction and accretion, nappe assembly in pre-Westphalian time due to collision of Laurussia, Gondwana, and amalgamated terranes, and finally, rapid exhumation, cooling, and deposition of eroded debris in Westphalian to Permian sedimentary basins.  相似文献   

4.
 Two karst areas within Permian and Triassic carbonate rocks of the Codru Moma Mountains in the northwestern part of Romania yield thermal waters. Major karst springs occur where groundwater flow is intercepted by hydraulic barriers, which also results in the movement of water from deeper levels. At Moneasa, thermal groundwater rises along faults and fractures associated with a thrust, and at Vascau Town, water rises along faults marginal to the Beius Basin. Geochemistry suggests that the thermal component of the Moneasa groundwaters is derived from dolomites and that at least a proportion of the Vascau thermal waters originates from deeply buried Permian sandstones. Received, August 1999 / Revised, March 2000 / Accepted, March 2000  相似文献   
5.
The main terrains involved in the Cretaceous–Tertiary tectonism in the South Carpathians segment of the European Alpine orogen are the Getic–Supragetic and Danubian continental crust fragments separated by the Severin oceanic crust-floored basin. During the Early–Middle Cretaceous times the Danubian microplate acted initially as a foreland unit strongly involved in the South Carpathians nappe stacking. Multistage folding/thrusting events, uplift/erosion and extensional stages and the development of associated sedimentary basins characterize the South Carpathians during Cretaceous to Tertiary convergence and collision events. The main Cretaceous tectogenetic events responsible for contraction and crustal thickening processes in the South Carpathians are Mid-Cretaceous (“Austrian phase”) and Latest Cretaceous (“Laramide” or “Getic phase”) in age. The architecture of the South Carpathians suggests polyphase tectonic evolution and mountain building and includes from top to bottom: the Getic–Supragetic basement/cover nappes, the Severin and Arjana cover nappes, and Danubian basement/cover nappes, all tectonically overriding the Moesian Platform. The Severin nappe complex (including Obarsia and Severin nappes) with Late Jurassic–Early Cretaceous ophiolites and turbidites is squeezed between the Danubian and Getic–Supragetic basement nappes as a result of successive thrusting of dismembered units during the inferred Mid- to Late Cretaceous subduction/collision followed by tectonic inversion processes.

Early Cretaceous thick-skinned tectonics was replaced by thin-skinned tectonics in Late Cretaceous. Thus, the former Middle Cretaceous “Austrian” nappe stack and its Albian–Lower Senonian cover got incorporated in the intra-Senonian “Laramide/Getic” stacking of the Getic–Supragetic/Severin/Arjana nappes onto the Danubian nappe duplex. The two contraction events are separated by an extensional tectonic phase in the upper plate recorded by the intrusion of the “Banatitic” magmas (84–73 Ma). The overthrusting of the entire South Carpathian Cretaceous nappe stack onto the fold/thrust foredeep units and to the Moesian Platform took place in the Late Miocene (intra-Sarmatian) times and was followed by extensional events and sedimentary basin formation.  相似文献   

6.
The AuPbZn low-sulfidation epithermal ore deposits of Troita, Trestia, and Magura (Apuseni Mountains, Romania) are spatially related to the Bolcana Cu-porphyry. In an attempt to demonstrate the connection between these mineralizations, a geometric study was made based on structural measurements and GOCAD© geomodeller 3D representation of deposits. This study indicates that a specific spatial distribution of the different Au and PbZn veins of the epithermal deposits occurs around the Cu-porphyry, which cannot result from telescoped systems. To cite this article: O. Cardon et al., C. R. Geoscience 337 (2005).  相似文献   
7.
The association between heat waves and the urban heat island effect can increase the impact on environment and society inducing biophysical hazards. Heat stress and their associated public health problems are among the most frequent. This paper explores the heat waves impact on surface urban heat island and on the local economy loss during three heat periods in Cluj-Napoca city in the summer of 2015. The heat wave events were identified based on daily maximum temperature, and they were divided into three classes considering the intensity threshold: moderate heat waves (daily maximum temperature exceeding the 90th percentile), severe heat waves (daily maximum temperature over the 95th percentile), and extremely severe heat waves (daily maximum temperature exceeding the 98th percentile). The minimum length of an event was of minimum three consecutive days. The surface urban heat island was detected based on land surface temperature derived from Landsat 8 thermal infrared data, while the economic impact was estimated based on data on work force structure and work productivity in Cluj-Napoca derived from the data released by Eurostat, National Bank of Romania, and National Institute of Statistics. The results indicate that the intensity and spatial extension of surface urban heat island could be governed by the magnitude of the heat wave event, but due to the low number of satellite images available, we should consider this information only as preliminary results. Thermal infrared remote sensing has proven to be a very efficient method to study surface urban heat island, due to the fact that the synoptic conditions associated with heat wave events usually favor cloud free image. The resolution of the OLI_TIRS sensor provided good results for a mid-extension city, but the low revisiting time is still a drawback. The potential economic loss was calculated for the working days during heat waves and the estimated loss reached more than 2.5 mil. EUR for each heat wave day at city scale, cumulating more than 38 mil. EUR for the three cases considered.  相似文献   
8.
The Bolcana ore deposit (Metaliferi Mountains, western Romania) is a porphyry ore deposit with associated epithermal veins. On the basis of different parageneses, four alteration types were distinguished: potassic, phyllic, argillic and propylitic. The mineralogical and geochemical data and estimated crystallisation temperatures of alteration minerals indicate an evolution of the system from an early period of porphyry type mineralisation (Cu+Au) to a late period of low-sulphidation epithermal mineralisation (Au+base metal). To cite this article: V. Milu et al., C. R. Geoscience 335 (2003).  相似文献   
9.
Summary Metamorphic rocks in the pre-Alpine basement of the Getic-Supragetic units (Median Dacides of the Carpathian belt) are spatially related to different lithotectonic units, some of which contain high-pressure relicts reflecting an early stage of oceanic and continental subduction, locally synchronous with mylonitic shear zones. Kyaniteamphibole ± quartz-bearing eclogites preserve a complete metamorphic clockwise loop; the estimated peak conditions within the outer part of the Cumpana unit were at least 20 kb at 780–860 °C. Pre-eclogite-stage magmatic phases occur in some units with true equilibrated eclogites. Clinopyroxene-plagioclase inclusions in garnet of a garnet-clinopyroxene assemblage within a metagabbro indicate a temperature around 760–790 °C at a maximum pressure of about 19 kb. The units finally evolved together during stages of exhumation under metamorphic conditions ranging from the Barrovian-type (minimum age of 330 Ma) to the high-temperature/low-pressure type. The absolute age of the high-pressure stage and the eclogite protoliths is unknown. In comparison with other collision belts, it is likely that the gneiss units of the Median Dacides underwent a complete cycle of underthrusting and exhumation similar to other segments of the European Variscides, and that the formation of the eclogite occurred during the early stages of subduction.
Résumé Les roches métamorphiques du socle pré-alpin des domaines Gétiques et Supragétiques (Dacides médianes de la chaîne des Carpathes) appartiennent à des unités lithotectoniques différentes dont certaines contiennent des reliques de métamorphisme haute pression reflétant un stade précoce de subduction continentale et océanique, localement synchrone de zones de cisaillement mylonitiques. Des éclogites é disthène-amphibole ± quartz permettent de reconstituer un trajet PT horaire complet. Les conditions paroxysmales sont estimées au sein de l'unité de Cumpana é plus de 20 kb pour 780–860 °C. Des phases magmatiques pré-éclogitiques coexistent avec des phases de haute pression dans les éclogites de certaines unités et des inclusions de clinopyroxene-plagioclase dans les grenats d'un métagabbro indiquent une température de 760–790 °C pour une pression maximale de 19 kb. L'ensemble des unités évolue finalement durant les stades d'exhumation sous les mêmes conditions de métamorphisme barrovien (âge minimum de 330 Ma) puis de haute température-basse pression. L'âge du stade de haute pression et des protholithes reste inconnu. En comparaison avec d'autres chaînes de collision, il est vraisemblable que les Dacides médianes ont subi un cycle d'enfouissement et d'exhumation similaire é celui décrit dans d'autres segments de la chaîne varisque européenne, la formation des éclogites étant attribuée aux premiers stades de la subduction.


With 9 Figures  相似文献   
10.
The Precambrian migmatitic gneisses at Alnö have been altered to fenite by fluids emanating from alkaline and carbonatitic magmas intruded during early to middle Cambrian times. Fenitization, related to carbonatitic sources, was promoted by peralkaline, carbonate-rich fluids, in which the main chemical components and REE were mobile. Composition-volume relationships of progressively fenitized protolith suggest mainly isovolumetric equilibration, but a modest decrease of volume (6%) did occur in the highest grade of the process. The fenitizing fluids introduced essentially CaO, CO2, Na2O, and K2O while removing SiO2 and Al2O3. Different trends of fenitization, defined as sodic, potassic and intermediate, show differing REE distribution and abundance patterns. The sodic carbonate-rich fluid introduced all the REE, but the La/Lu ratio was high. The extreme REE enrichments of high-grade fenites are associated with the widespread formation of calcite, apatite and possibly titanite. The potassic carbonaterich fluid introduced essentially light REE, but produced also the redistribution of heavy REE in the high-grade fenites. REE distribution patterns of intermediate fenites suggest the re-equilibration of fenite with a highly oxidizing alkaline fluorine-rich fluid, possibly in a later post-magmatic episode.  相似文献   
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