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1.
This paper records, for the first time, the mineralization of gold (0.98–2.76 ppm) and uranium (133–640 ppm) in marbles from the Arabian-Nubian Shield of the Eastern Desert of Egypt. These auriferous and uraniferous marbles are hosted by sheared and altered ophiolitic serpentinized ultramafic rocks of Gebel El-Rukham (ER), Wadi Daghbag (DG), and Wadi Al Barramiyah (BM). They occur as massive or banded in pod-like or bedded shapes. The ER and BM-mineralized marbles are impure calcitic, whereas the DG marble is impure calcitic to impure dolomitic. Their protolith are pure limestones and dolomitic limestones with probable argillaceous components (BM marble), and their metamorphism (Pan-African) was retrograde. Peaks of metamorphism were at granulite-amphibolite facies for the ER and BM marbles, forming diopside (Al2O3?=?0.17–1.07 wt.%) at 600–900°C and augite (Al2O3?=?2.45–9.40 wt.%) at 825–975°C, and at the amphibolite facies for DG marble, recrystallising the carbonate minerals and forming tremolite. The lowest temperatures of metamorphism were at the upper subgreenschist facies as chlorite (ER and BM marbles) and kaolinite (DG marble) were formed. Metamorphic fluids were, most probably, essentially binary H2O–CO2 mixtures with low NaCl and HF concentrations. Gold in the studied mineralized marbles occurs as native nuggets (10–35 μm) having globule, rod, crescent, and streak shapes, in pores, vugs, and fissures. The source of gold in all marbles is mostly the country ultramafic rocks. Timing of gold mineralization relative to the marblization and metamorphism of the country source ultramafic rocks was both syn- and post-metamorphic. Concerning the ER and DG marbles, it was syn-metamorphic, where Au liberation and transportation were mostly by the metamorphic fluids. The composition and temperature of these fluids were most probably inappropriate for formation of the sulfide complexes of gold. The gold mineralization of BM marble, on the other hand, was mostly post-metamorphic. The mineralising fluid was of surficial origin under oxidizing conditions. The encountered uranium minerals are of secondary origin such as autunite, uranophane, and carnotite. These minerals occur as fine oval aggregates and irregular grains (10–50 μm) usually filling fissures and vugs. The uranium mineralization can be classified as surficial of ages <1.5 Ma. It is proposed that the U was transported from its source (might be flesite and trachyte dikes for the ER and DG marbles and granite rocks for BM marble) to the marble rocks by surface and/or underground water related to the pluvial periods in Egypt. In BM marble, U and Au have mutual mineralizing fluid but different paragenesis.  相似文献   

2.
The sulfation of four types of calcitic and dolomitic lime mortars exposed to SO2 in the presence of particulate matter from diesel vehicle exhaust emissions has been investigated. The binders mineralogy and mortars texture are the main factors influencing the formation of deleterious sulfate salts. The type of binder also influences the pore size distribution and the total porosity of the mortars: for equal aggregate (quartz or dolomite), dolomitic lime mortars have smaller pores and higher porosity than calcitic ones. During the first 24 h exposure to SO2, calcitic lime mortars undergo a higher weight increase than dolomitic ones due to rapid formation of gypsum on their surface. However, at the end of the sulfation test (10 days), dolomitic mortars show a higher weight increase due to massive formation of epsomite and gypsum, which is facilitated by their higher porosity and the high reactivity of Mg phases in the porous and partially carbonated binder. Control samples (not covered with diesel particulate matter) also develop calcium and magnesium sulfates upon long term exposure to SO2. This is due to the presence of uncarbonated Ca and Mg hydroxides that promote SO2 fixation as sulfates. However, the amount and size of sulfate crystals are significantly smaller than those observed on samples covered with diesel particulate matter. These results show that diesel particulate matter enhances the sulfation of lime mortars and demonstrate that sulfation of dolomitic lime is an important mechanism for the in situ formation of highly soluble and deleterious hydrated magnesium sulfates (epsomite and hexahydrite). The use of dolomitic limes in the conservation of monuments exposed to air pollution in urban environments may therefore pose a significant risk.  相似文献   

3.
Microstructure‐based finite-element analysis with a microcracking algorithm was used to simulate an actual degradation phenomenon of marble structures, i.e., microcracking. Both microcrack initiation and crack propagation were characterized, as were their dependence on lattice preferred orientation (LPO), grain shape preferred orientation (SPO), grain size, marble composition (calcite and dolomite) and grain‐boundary fracture toughness. Two LPOs were analyzed: a random orientation distribution function and an orientation distribution function with strong directional crystalline texture generated from a March–Dollase distribution. Three SPOs were considered: equiaxed grains; elongated grains and a mixture of equiaxed and elongated grains. Three different grain sizes were considered: fine grains of order 200 μm (only calcitic marble); medium size grains of order 1 mm (calcitic and dolomitic marbles); and large grains of order 2 mm (only dolomitic marble). The fracture surface energy for the grain boundaries, γig, was chosen to be 20 and 40 % of the fracture surface energy of a grain, γxtal, so that both intergranular and transgranular fracture were possible. Studies were performed on these idealized marble microstructures to elucidate the range of microcracking responses. Simulations were performed for both heating and cooling by 50 °C in steps of 1 °C. Microcracking results were correlated with the thermoelastic responses, which are indicators related to degradation. The results indicate that certain combinations of LPO, SPO, grain size, grain‐boundary fracture toughness and marble composition have a significant influence on the thermal-elastic response of marble. Microstructure with the smallest grain size and the highest degree of SPO and LPO had less of a tendency to microcrack. Additionally, with increasing SPO and LPO microcracking becomes more spatially anisotropic. A significant observation for all microstructures was an asymmetry in microcracking upon heating and cooling: more microcracking was observed upon cooling than upon heating. Given an identical microstructure and crystallographic texture, calcite showed larger thermal stresses than dolomite, had an earlier onset of microcracking upon heating and cooling, and a greater microcracked area at a given temperature differential. Thermal expansion coefficients with and without microcracking were also determined.  相似文献   

4.
《Applied Geochemistry》1999,14(3):283-299
The chemical characteristics, 3H contents and radioactivity of groundwaters from the Sierras Blanca and Mijas (Southern Spain) have been studied in relation to the chemical composition and radioactivity of the aquifer host rocks, and the residence time of the water. The Sierras Blanca and Mijas are made up of calcitic and dolomitic marbles of Triassic age. The groundwaters that drain the calcitic marbles (which outcrop principally in the western Sierra Blanca) have less mineralization, which descreases quickly with recharge (as does the 3H content), and the gross alpha and beta activities are below detection limit. This is due to the short residence time of water inside the aquifers which are conduit flow systems. The waters of the dolomitic marbles (eastern Sierra Blanca and Sierra Mijas) have higher and less variable mineralization and contain greater concentrations of Mg2+, SiO2 and SO2−4 (ions normally associated with slow flows). The 3H contents are more uniform with time (indicating an older age) and there is detectable natural radioactivity, because the waters have a longer residence time in the aquifers, which are diffuse flow systems.  相似文献   

5.
《Ore Geology Reviews》2003,22(1-2):17-39
Many talc deposits occur in the Hwanggangri Mineralized Zone (HMZ) in dolomitic marbles of the Cambro-Ordovician Samtaesan Formation within 1 km of the contact with the Cretaceous Muamsa Granite. Talc commonly forms fine-grained, fibrous aggregates, or pseudomorphs after tremolite; abundant tremolite is included as impurities in the talc ore. Talc generally was derived from tremolite in calc-silicate rock within the dolomitic marble. Calc-silicate rock, consisting mainly of tremolite and diopside, was generated from silicic metasomatism during the prograde stage, which promoted decarbonation reactions until dolomite was exhausted locally. Hydrothermal alteration of calc-silicate rock to talc is marked by the addition of Mg and Si, and the leaching of Ca; Cr, Co, and Ni were relatively immobile during the retrograde stage. Contact metamorphism related to the granite intrusion generated the successive appearance of tremolite, diopside, and forsterite, or wollastonite-bearing assemblages in the marble, depending on the bulk rock composition. The XCO2 content of the metamorphic fluids rose initially above XCO2=0.6, and decreased steadily toward a water-rich composition with increasing temperature above 600 °C in the calcitic marble, while buffered reaction of the dolomitic marble occurred at higher XCO2 conditions above 600 °C. Talc mineralization developed under metastable conditions with infiltration of large amounts of igneous fluids along a fault-shattered zone during the retrograde stage and is characterized by the loss of Ca2+ with the addition of Mg2+. Oxygen and carbon isotopic variations of carbonate and calc-silicate minerals are in agreement with theoretical relationships determined for decarbonation products of contact metamorphism. Talc formation temperatures obtained from oxygen isotope fractionation, T–XCO2 relationships, and activity diagrams range from 380 to 400 °C.  相似文献   

6.
The Salumber-Ghatol belt in Rajasthan, India, situated along southern margin of the Aravalli Craton, hosts a cluster of Cu-Au deposits in calcitic and dolomitic marbles that belong to Debari Group of the Paleo-mesoproterozoic Aravalli Supergroup. The Fe-Mn rich dolomitic marble of the Delwara Formation hosts Cu-Au-Fe-oxide mineralization at Ghagri and associated distal K-Fe-Mg rich altered rocks (cryptocrystalline microcline + magnesioriebeckite + magnetite + phlogopite) and proximal feldspathised carbonate rocks (medium grained albite + microcline + dolomite + magnetite). The calcitic marble of Mukandpura Formation hosts Dugocha Cu-Au deposit with development of distal graphitetourmaline-bearing albitites and proximal albite-microcline-magnetite rocks. Calcite and dolomite carbonates of Bhukia region with development of albite-actinolite-bearing alteration assemblages host the largest of the Cu-Au deposits in this belt. The second generation folds and associated ductile-brittle shear zones of the multiply deformed events constitute conduits for the mineralizing fluids at all locations in this belt.  相似文献   

7.
Metacarbonates of the Moldanubian Zone (Bohemian Massif, Czech Republic) were studied to obtain qualitative and quantitative mineralogical-petrographic as well as stable isotopic data for the purpose of stone provenance studies, potentially applicable in material research studies of cultural heritage artefacts. Twenty-six samples from twelve different historical quarries, as well as two samples from historical artefacts, were analysed by both mineralogical-petrographic and geochemical methods including: polarizing microscopy, cathodoluminescence, scanning electron microscopy with microanalysis, petrographic image analysis, powder X-ray diffraction, and isotope ratio mass spectrometry. The petrographic characteristics allowed for the discrimination of groups of (1) calcitic marbles, (2) dolomitic marbles, and (3) carbonate–silicate rocks. These groups exhibit characteristic features such as (1) the presence/abundance of major rock-forming minerals, (2) grain geometric characteristics (specifically, mean carbonate grain size and index of grain size homogeneity), and (3) the presence of specific accessory phases. The content of non-carbonate minerals, some rock fabric parameters, as well as the carbon and oxygen isotope data exhibited significant variability, even within a single quarry in the case of some impure marbles and carbonate–silicate rocks. Although the carbon and oxygen isotopic ranges displayed overlaps among the quarries studied, the isotopic signatures throughout the Moldanubian Zone allowed for discrimination of a group of white calcitic marbles with high carbon and oxygen depletion, as well as white dolomite–calcitic marble with higher carbon isotope values when compared with other marble resources of the Bohemian Massif. A combination of the isotopic signature with detailed mineralogical-petrographic characteristics seems to provide sufficient information for discrimination of the Moldanubian marbles from one another. The provenance of the Vrchotovy Janovice artefact is very probably from the Rabí quarry, among the Moldanubian marbles. The provenance of the artefact from the Prague Klementinum was not definitively assigned; however, the Nehodiv quarry was considered its probable source locality.  相似文献   

8.
The paper addresses the composition and genesis of endogenous borates from hypabyssal skarn deposits of Japan (Honshu Island) that were formed after dolomitic, rhodochrosite, and calcareous marbles in the contact aureoles of magmatic intrusions of diverse felsicity (from granites to diorite-monzonites). Metasomatic bodies formed at the prograde stage of the mineral formation are characterized by clearly expressed zoning of primitive type. Borates occur in the calciphyres at the Neichi, Kaso, and Rito mines, and are developed in calcitic marbles at the Fuka mine. Depending on initial composition of carbonate rocks, borates are represented by suanite, kotoite, jimboite, and takedaite in the outer zones of spinel-forsterite and galaxite-jacobsite-tephroite calciphyres or calcitic marbles, respectively. It was shown that early borates are subjected to hydration that is expressed in variable deficit of boron. At the next stages of hydrothermal mineral formation, they are replaced by pertsevite, wiserite, sibirskite, and other borates.  相似文献   

9.
Vast marble deposits occur in a cover sequence of the Menderes Massif, SW Turkey. Four major marble deposits are recognized in Mu?la province based on the stratigraphic levels. These are Permo-Carboniferous aged black marbles (1), Triassic aged marbles (2), Upper Cretaceous aged marbles (3), and Paleocene aged pelagic marbles (4). This study deals with Triassic aged marbles of the southern part of the Menderes Massif. The Triassic marbles from SW Turkey consist of two big marble horizons in the Çayboyu (ÇM) and Kestanecik (KM) regions. The characteristic samples are collected from different stratigraphic levels in marble deposits in the ÇM and KM horizons. Mineralogical and major, trace, and rare earth element (REE) analyses of marble, limestone, and schist were conducted on these samples to reveal their petrographical and geochemical characteristics. The ÇM horizon is represented by calcitic marble layers. Nickel, cobalt, manganese, and iron elements filled in fractures, fissures, and intergranular spaces of calcite crystals and these elements give the pinky colour to the marble from the ÇM horizon. KM marbles were deformed, metamorphosed, and recrystallized under greenschist facies P–T conditions. As a result of the metasomatic reaction of magnesium and manganese rich fluids with marbles, dolomite, and manganese, minerals such as rhodochrosite and pyrolusite have crystallized along vein walls and layers in the KM horizon. Dolomitization was determined in KM marbles, whereas ÇM marbles show the character of limestone. MgO, MnO, Fe2O3, Ni, and Zn contents of marbles from the KM horizon are higher than those of ÇM marbles due to metasomatic reactions. The Sr content in white coloured marbles ranges between 11.20 ppm and 112.20 ppm and this concentration reaches up to 272.70 ppm due to metasomatic reactions and fluid intake. The REE content of Triassic marbles is independent of the abundance of carbonate and the REE enrichment observed due to syn-metamorphic fluid flow. The significant negative Eu anomaly in REE patterns indicates that the protoliths of Triassic marbles are carbonate rocks of sedimentary origin.  相似文献   

10.
Abstract In the Twin Lakes area, central Sierra Nevada, California, most contact metamorphosed marbles contain calcite + dolomite + forsterite ± diopside ± phlogopite ± tremolite, and most calc-silicate hornfelses contain calcite + diopside + wollastonite + quartz ± anorthite ± K-feldspar ± grossular ± titanite. Mineral-fluid equilibria involving calcite + dolomite + tremolite + diopside + forsterite in two marble samples and wollastonite + anorthite + quartz + grossular in three hornfels samples record P± 3 kbar and T± 630° C. Various isobaric univariant assemblages record CO2-H2O fluid compositions of χCO2= 0.61–0.74 in the marbles and χCO2= 0.11 in the hornfelses. Assuming a siliceous dolomitic limestone protolith consisting of dolomite + quartz ° Calcite ± K-feldspar ± muscovite ± rutile, all plausible prograde reaction pathways were deduced for marble and hornfels on isobaric T-XCO2 diagrams in the model system K2O-CaO-MgO-Al2O3-SiO2-H2O-CO2. Progress of the prograde reactions was estimated from measured modes and mass-balance calculations. Time-integrated fluxes of reactive fluid which infiltrated samples were computed for a temperature gradient of 150 °C/km along the fluid flow path, calculated fluid compositions, and estimated reaction progress using the mass-continuity equation. Marbles and hornfelses record values in the range 0.1–3.6 × 104 cm3/cm2 and 4.8–12.9 × 104 cm3/cm2, respectively. For an estimated duration of metamorphism of 105 years, average in situ metamorphic rock permeabilities, calculated from Darcy's Law, are 0.1–8 × 10?6 D in the marbles and 10–27 × 10?6 D in the hornfelses. Reactive metamorphic fluids flowed up-temperature, and were preferentially channellized in hornfelses relative to the marbles. These results appear to give a general characterization of hydrothermal activity during contact metamorphism of small pendants and screens (dimensions ± 1 km or less) associated with emplacement of the Sierra Nevada batholith.  相似文献   

11.
Eclogite facies carbonate rocks have been discovered associated with the granulite–eclogite transitional rocks within Bergen Arc system, Caledonian Orogen of western Norway. The local occurrences of marbles and calc‐silicates are found subparallel to the mafic eclogite facies shear zones on Holsnøy Island. Marbles contain the assemblage calcite (Ca0.99Sr0.01CO3), calcian strontianite (Ca0.18?0.44Sr0.53?0.84CO3), clinopyroxene (Jd7?32), epidote/allanite (Ps0?33), titanite, garnet (Alm52?56Grs28?33Pyp11?16), barite (Ba0.90?0.99Sr0.01?0.10SO4), celestine (Sr0.67?0.98Ba0.01?0.23Ca0.01?0.11SO4), and one apparently homogeneous grain of intermediate composition (Ba0.49Ca0.01Sr0.50SO4). Adjacent eclogites have clinopyroxene with similar jadeite contents (Jd14?34) and similar garnet (Alm51?60Grs26?36Pyp8?14) compositions. The marbles have high contents of Sr (9500–11000 p.p.m) and Y (115–130 p.p.m). However, low concentrations of some key trace elements (110–160 p.p.m. Ba and <5 p.p.m. Nb) appear to indicate that the marble is not a metamorphosed carbonatite. The 87Sr/86Sr ratios range from 0.7051 to 0.7059. Field and petrological relationships suggest that metasomatic reactions and fluids played a significant role in producing and/or modifying the marbles. The breakdown of scapolite in the granulite into carbonates and sulphates during eclogite facies metamorphism may have contributed to the metasomatic formation of the marbles along shear zones. Fluids involved during subduction are an important catalyst for metamorphism and are recognized to have played a critical role in the localized transformation from granulite to eclogite in the Holsnøy Island area. Thermobarometry indicates 640–690 °C and 18–20 kbar for adjacent eclogites and temperatures of 580–650 °C for the calc‐silicates. The marble assemblages are consistent with fluid that is dominantly comprised of H2O (XCO2 < 0.03) under high‐pressure conditions. Phase equilibria of the marbles constrain the fO2 of the fluids and imply oxidizing conditions of the deep crustal fluids. At present the source of the fluids remains unresolved. The results provide additional insights into the variable and evolving nature of fluids related to subduction and high‐pressure metamorphism.  相似文献   

12.
Marble decay induced by thermal strains: simulations and experiments   总被引：1，自引：1，他引：0  
Thermoelastic behavior of different marble types was analyzed using computational modeling and experimental measurements. Eight marble samples with different composition, grain size, grain boundary geometry, and texture were investigated. Calcitic and dolomitic marbles were considered. The average grain size varies from 75 μm to 1.75 mm; grain boundary geometry differs from nearly equigranular straight grain boundaries to inequigranular-interlobate grain boundaries. Four typical marble texture types were observed by EBSD measurements: weak texture; strong texture; girdle texture and high-temperature texture. These crystallographic orientations were used in conjunction with microstructure-based finite element analysis to compute the thermoelastic responses of marble upon heating. Microstructural response maps highlight regions and conditions in the marble fabric that are susceptible to degradation phenomena. This behavior was compared to the measured thermal expansion behavior, which shows increasing residual strains upon repetitive heating–cooling cycles. The thermal expansion behavior as a function of temperature changes can be classified into four categories: (a) isotropic thermal expansion with small or no residual strain; (b) anisotropic thermal expansion with small or no residual strain; (c) isotropic thermal expansion with a residual strain; and (d) anisotropic thermal expansion with residual strain. Thermal expansion coefficients were calculated for both simulated and experimental data and also modeled from the texture using the MTEX software. Fabric parameters control the amount and directional dependence of the thermal expansion. Marbles with strong texture show higher directional dependence of the thermal expansion coefficients and have smaller microstructural values of the maximum principal stress and strain energy density, the main precursors of microcracking throughout the marble fabric. In contrast, marbles with weak texture show isotropic thermal expansion behavior, have a higher propensity to microcracking, and exhibit higher values of maximum principal stress and strain energy density. Good agreement between the experimental and computational results is observed, demonstrating that microstructure-based finite-element simulations are an excellent tool for elucidating influences of rock fabric on thermoelastic behavior.  相似文献   

13.
The low-grade base metal sulphide Cu–Zn–Pb and Fe mineralization of Qandil Series develop in shear zones that occur in formations of the north-western part of the Zagros Orogen. This sulphide mineralization occurs either as quartz vein type or disseminated type associated with metamorphic rocks (marbles and phyllites). This study aims to characterize these sulphide-rich ores by means of their mineralogical and geochemical features, including also the features of the corresponded host formations and those of marbles (calcitic and dolomitic) and phyllites. Petrographical data indicate the presence of Cu, Zn, Pb and Fe sulphides in hydrothermal quartz (±calcite) veins of different generations. Geochemical data of surface samples indicate enrichment of Cu and Fe in shear zones with low concentrations in Zn and Pb. The REE data indicate that the genesis of these sulphide ores took place in a hydrothermal system and was generally attributed to high temperature (> 250 °C).The mineralization seems to be fault-controlled, which is favoured by the significant tectonic deformation of the area.  相似文献   

14.
Acid precipitation leaves fingerprints upon marble surfaces. Preserved in weathering crusts on dated monuments, these fingerprints serve as guides to identify levels of acidity of a region. We collected scrapings from protected surfaces of tombstones made of Georgia marble whose dates of installation could be determined with reasonable certainty. These scrapings were allowed to equilibrate in 100 ml of deionized water, and the solutions were analyzed for, among other species, sulfates and nitrates. In Louisville, it was found that sulfate is present on tombstones that had been installed as late as 1985. However, to the east, 25 miles away, 1967 is the date of the latest monument with sulfate. An acidity map was produced showing time contours, in other words, the time needed to produce discernible quantities of sulfate. This map reveals that the effect of SO2 on marble diminishes rapidly with increased distance away from the western Louisville industrial area. The use of marble monuments to monitor changes in the acid deposition patterns is suggested.  相似文献   

15.
High-temperature, intermediate-pressure calc-silicate marbles occur in the granulite-facies terrain of the La Huerta Range in the Province of San Juan, NW-Argentina, in three bulk-compositional varieties: Type (1) dolomite-absent scapolite-wollastonite-grandite-clinopyroxene-quartz—calcite marbles; Type (2) diopside-forsterite-spinel-corundum—calcite marbles with dolomite exolution lamellae in calcite; Type (3) serpentinized forsterite-spinel-dolomite marbles. An isobaric cooling path from peak-metamorphic conditions of 860°C to 750°C at 6.5 kbar is inferred from scapolite-wollastonite-grandite reaction textures in Type (1) and is consistent with cooling after an advective heat input from related gabbroic and tonalitic intrusive bodies. Stable carbon and oxygen isotope geochemistry was used to decipher the fluid/rock evolution of the three marble types. An interpreted four-stage temperature-time-fluid flow path comprises: (1) infiltration of pre-peak-metamorphic fluids, depleted in δ18O, that caused a shift of primary sedimentary δ18O ratios to lower values (19.6–20.0); (2) syn-metamorphic fluid liberation from Type (1) marbles with evidence for processes close to batch devolatilization that caused a weak coupled 13C and 18O depletion during prograde metamorphism. A different devolatilization behaviour, close to Rayleigh fractionation, texturally associated with fold settings indicates that granulite-facies fluid flow was focused rather than pervasive; (3) H2O-absent conditions were dominant when coronal grandite formed during incipient high-temperature isobaric cooling at the expense of scapolite and wollastonite in the Type (1) marbles; (4) intense post-peak- hydration of Type (2) and Type (3) marbles is the last recognizable metasomatic event. In combination, the three marble types record fluid infiltration both before and after the metamorphic peak.  相似文献   

16.
Present study reviews the tectono-stratigraphic status of Babarmal pink marble from the Aravalli Supergroup through mapping and petrographic study of marble as well as associated lithologies. The pink marble is predominantly calcitic and characteristically different from dolomitic carbonate rocks of the Jhamarkotra Formation, the Lower Aravalli Group. The marble is devoid of organic matter and phosphate content unlike the Jhamarkotra dolomite. The pink marble is underlain by quartz-pebble rich conglomerate. This assemblage represents a rare lithological association which has not been reported so far from the Aravalli Supergroup.  相似文献   

17.
Three calcitic marble types often used as cladding material and different in lattice preferred orientation (texture), grain shape preferred orientation, grain size distribution and grain interlocking are investigated to study the combined effect of thermal cycles (day-night) and moisture on the decay of marble, particularly on the bowing phenomenon. Repetitive heating-cooling under dry conditions leads to considerable inelastic residual strain only in the first thermal cycle. The residual strain continuously increases again if water is present, whereby the moisture content after a thermal cycle has a certain impact on the decay rate. The water-enhanced thermal dilatation strongly correlates with the deterioration rate obtained from the laboratory bow test. All applied approaches reveal that the texture in combination with the grain shape preferred orientation control the intensity and anisotropy of marble deterioration, thus, the cutting direction of facade panels has to be considered in terms of durability. On-site analysis from building facades confirm the laboratory results such as the bowing tendency of different marbles, directional dependence, relevance of moisture content during cyclical heating and the loss of strength due to environmental impact.Special Issue: Stone decay hazards  相似文献   

18.
 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   

19.
The skarn complex of Traversella was formed at the expense of various rock types (calcic hornfels, gneiss, dolomitic marble) occurring in the contact aureole of the dioritic intrusion of Traversella (30±5 Ma). Application of phase equilibria has fixed the temperature of the primary stage of skarn formation between 550° C to 625° C. Similar applications indicate a larger range of temperature (525° C to 300° C) for the secondary stage. The different types of skarn (primary stage) are enriched in REE relative to the corresponding precursor rock (T.R.=126 ppm (protolith) to 228 ppm (inner zone) for the skarn on gneisses; T.R.=14 ppm to 71 ppm for the skarn on calcic hornfelses; T.R.=12 ppm to 200 ppm for the skarn on dolomitic marbles), but all the inner zones of these different types of skarn show a similar REE distribution with a slight LREE fractionation and no Eu anomaly. It is inferred that the primary metasomatic fluid has a parallel REE pattern. The oxygen isotope composition of water in equilibrium with the early stage of skarn at T=600° C ranges from 8.3 per mil to 8.9 per mil. At the beginning of the first hydroxylation stage (secondary stage), the fluid σ 18O remains in the range observed in the primary stage but within it, there is a sharp decrease from 8.0 per mil to 5.0 per mil. During the sulphidation stage, the fluid σ 18O decreases more gradually from 5.0 per mil to 3.0 per mil. The I Sr of the early skarn silicates ranges from the values observed in the dolomitic marbles (0.70874 to 0.70971) to the I Sr of the intrusion (0.70947 to 0.71064). During the secondary stage, there is a progressive increase of the minerals I Sr up to 0.71372. The REE pattern of the primary metasomatic fluid does not put any precise constraint on the primary fluid source. On the other hand, both stable and radiogenic isotopes suggest that the early high-temperature metasomatic fluid was isotopically equilibrated with the dioritic intrusion. This implies that this early fluid is either exsolved from the crystallizing intrusion or a metamorphic water previously equilibrated with the intrusion. During the secondary stage, the replacement of the early anhydrous phases by hydrated parageneses is accompanied by the mixing with meteoric fluid as indicated by stable (σ 18O) and radiogenic (87Sr/86Sr) isotopes.  相似文献   

20.
Representative diamond-bearing gneisses and dolomitic marble, eclogite and Ti-clinohumite-bearing garnet peridotite from Unit I at Kumdy Kol and whiteschist from Unit II at Kulet, eastern Kokchetav Massif, northern Kazakhstan, were studied. Diamond-bearing gneisses contain variable assemblages, including Grt+Bt+Qtz±Pl±Kfs±Zo±Chl±Tur±Cal and minor Ap, Rt and Zrn; abundant inclusions of diamond, graphite+chlorite (or calcite), phengite, clinopyroxene, K-feldspar, biotite, rutile, titanite, calcite and zircon occur in garnet. Diamond-bearing dolomitic marbles consist of Dol+Di±Grt+Phl; inclusions of diamond, dolomite±graphite, biotite, and clinopyroxene were identified in garnet. Whiteschists carry the assemblage Ky+Tlc+Grt+Rt; garnet shows compositional zoning, and contains abundant inclusions of talc, kyanite and rutile with minor phlogopite, chlorite, margarite and zoisite. Inclusions and zoning patterns of garnet delineate the prograde P–T path. Inclusions of quartz pseudomorphs after coesite were identified in garnet from both eclogite and gneiss. Other ultrahigh-pressure (UHP) indicators include Na-bearing garnet (up to 0.14 wt% Na2O) with omphacitic Cpx in eclogite, occurrence of high-K diopside (up to 1.56 wt% K2O) and phlogopite in diamond-bearing dolomitic marble, and Cr-bearing kyanite in whiteschist. These UHP rocks exhibit at least three stages of metamorphic recrystallization. The Fe-Mg partitioning between clinopyroxene and garnet yields a peak temperature of 800–1000 °C at P >40 kbar for diamond-bearing rocks, and about 740–780 °C at >28–35 kbar for eclogite, whiteschist and Ti-bearing garnet peridotite. The formation of symplectitic plagioclase+amphibole after clinopyroxene, and replacement of garnet by biotite, amphibole, or plagioclase mark retrograde amphibolite facies recrystallization at 650–680 °C and pressure less than about 10 kbar. The exsolution of calcite from dolomite, and development of matrix chlorite and actinolite imply an even lower grade greenschist facies overprint at c. 420 °C and 2–3 kbar. A clockwise P–T path suggests that supracrustal sediments together with basaltic and ultramafic lenses apparently were subjected to UHP subduction-zone metamorphism within the diamond stability field. Tectonic mixing may have occurred prior to UHP metamorphism at mantle depths. During subsequent exhumation and juxtaposition of many other tectonic units, intense deformation chaotically mixed and mylonitized these lithotectonic assemblages.  相似文献   

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