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1.
Continuous measurements of aerosol size distributions in the mid-point diameter range 20.5–500 nm were made from October 2005 to March 2006 at Pune (18°32′N, 73°51′E), India using Scanning Mobility Particle Sizer (SMPS). Volatilities of atmospheric aerosols were also measured at 40°, 125°, 175°, 300° and 350°C temperatures with Thermodenuder–SMPS coupled system to determine aerosol volatile fractions. Aerosols in nucleated, CCN and accumulated modes are characterized from the measured percentage of particles volatized at 40°, 125°, 175°, 300° and 350°C temperatures. Averaged monthly aerosol concentration is at its maximum in November and gradually decreases to its minimum at the end of March. The diurnal variations of aerosol concentrations gradually decrease in the night and in early morning hours (0400–0800 hr). However, concentration attains minimum in its variations in the noon (1400–1600 hr) due to higher ventilation factor (product of mixing height and wind speed). The half an hour averaged diurnal variation of aerosol number concentration shows about 5 to 10-fold increase despite the ventilation factor at higher side before 1200 hr. This sudden increase in aerosol concentrations is linked with prevailing conditions for nucleation bursts. The measurement of volatile fraction of ambient aerosols reveals that there are large number of highly volatile particles in the Aitken mode in the morning hours and these volatile fractions of aerosols at temperatures <150°C are of ammonium chloride and ammonium sulfate, acetic and formic acids.  相似文献   

2.
Samples of enstatite and forsterite were crystallized in the presence of a hydrous fluid at 15 kbar and 1100 °C. Water contents in quenched samples were measured by 1H MAS NMR and by FTIR. If the samples were prepared in the same way, similar water concentrations were obtained by both methods. There is no evidence that one or the other method would severely over or underestimate water contents in nominally anhydrous minerals. However, measured water contents vary by orders of magnitude depending on sample preparation. The lowest water contents are measured by polarized FTIR spectroscopy on clear, inclusion-free single crystals. These water contents probably reflect the real point defect solubility in the crystals. Polycrystalline material shows much higher total water concentrations, presumably due to hydrous species on grain boundaries, growth defects, and in submicroscopic fluid inclusions. Grinding the sample in air further increases water concentration. This effect is even more pronounced if the sample is ground in water and subsequently dried at 150 °C. Polarized FTIR measurements on clear single crystals of enstatite saturated at 15 kbar and 1100 °C give 199 ± 25 ppm by weight of water. The spectra show sharp and strongly polarized bands. These bands are also present in spectra measured through turbid, polycrystalline aggregates of enstatite. However, in these spectra, they are superimposed on much broader, nearly isotropic bands resulting from hydrous species in grain boundaries, growth defects, and submicroscopic fluid or melt inclusions. Total water contents for these polycrystalline aggregates are between 2000 and 4000 ppm. Water contents measured by FTIR on enstatite powders are 5300 ppm after grinding in air and 12 600 ppm after grinding under water und subsequent drying at 150 °C. Received: 25 June 1999 / Revised, accepted: 4 October 1999  相似文献   

3.
The Pueblo Viejo deposit (production to 1996: 166 t Au, 760 t Ag) is located in the Dominican Republic on the Caribbean island of Hispaniola and ranks as one of the largest high-sulfidation/acid-sulfate epithermal deposits (reserves in 2007: 635 t Au, 3,648 t Ag). One of the advanced argillic ore bodies is cut by an inter-mineral andesite porphyry dike, which is altered to a retrograde chlorite–illite assemblage but overprinted by late-stage quartz–pyrite–sphalerite veins and associated low-grade Au, Ag, Zn, Cd, Hg, In, As, Se, and Te mineralization. The precise TIMS U–Pb age (109.6 ± 0.6 Ma) of the youngest zircon population in this dike confirms that the deposit is part of the Early Cretaceous Los Ranchos intra-oceanic island arc. Intrusion-related gold–sulfide mineralization took place during late andesite–dacite volcanism within a thick pile (>200 m) of carbonaceous sand- and siltstones deposited in a restricted marine basin. The high-level deposit was shielded from erosion after burial under a late Albian (109–100 Ma) ophiolite complex (8 km thick), which was in turn covered by the volcano-sedimentary successions (>4 km) of a Late Cretaceous–Early Tertiary calc-akaline magmatic arc. Estimates of stratigraphic thickness and published alunite, illite, and feldspar K-Ar ages and closure temperatures (alunite 270 ± 20°C, illite 260 ± 30°C, K-feldspar 150°C) indicate a burial depth of about 12 km at 80 Ma. During peak burial metamorphism (300°C and 300 MPa), the alteration assemblage kaolinite + quartz in the deposit dehydrated to pyrophyllite. Temperature–time relations imply that the Los Ranchos terrane then cooled at a rate of 3–4°C/Ma during slow uplift and erosion.  相似文献   

4.
The author’s database, which presently includes data from more than 18500 publications on fluid and melt inclusions in minerals and is continuing to be appended, was used to generalize results on physicochemical parameters of the formation of hydrothermal deposits and occurrences of tin and tungsten. The database includes data on 320 tin and tin-tungsten deposits and occurrences and 253 tungsten and tungstentin deposits around the world. For most typical minerals of these deposits (quartz, cassiterite, tungsten, scheelite, topaz, beryl, tourmaline, fluorite, and calcite), histograms of homogenization temperatures of fluid inclusions were plotted. Most of 463 determinations made for cassiterite are in the range of 300–500°C with maximum at 300–400°C, while those for wolframite and scheelite (453 determinations) fall in the range of 200–400°C with maximum at 200–300°C. Representative material on pressures of hydrothermal fluids included 330 determinations for tin and 430 determinations for tungsten objects. It was found that premineral, ore, and postmineral stages spanned a wide pressure range from 70–110 bar to 6000–6400 bar. High pressures of the premineral stages at these deposits are caused by their genetic relation with felsic magmatism. Around 50% of pressure determinations lie in the range of 500–1500 bar. The wide variations in total salinity and temperatures (from 0.1 to 80 wt % NaCl equiv and 20–800°C) were obtained for mineral-forming fluids at the tin (1800 determinations) and tungsten (2070 determinations) objects. Most of all determinations define a salinity less than 10 wt % NaCl equiv. (∼60%) and temperature range of 200–400°C (∼70%). The average composition of volatile components of fluids determined by different methods is reported. Data on gas composition of the fluids determined by Raman spectroscopy are examined. Based on 180 determinations, the fluids from tin objects have the following composition (in mol %): 41.2 CO2, 39.5 CH4, 19.15 N2, and 0.15 H2S. The volatile components of tungsten deposits (190 determinations) are represented by 56.1 CO2, 30.7 CH4, 13.2 N2, and 0.01 H2S. Thus, the inclusions of tungsten deposits are characterized by higher CO2 content and lower (but sufficiently high) contents of CH4 and N2. The concentrations of tin and tungsten in magmatic melts and mineral-forming fluids were estimated from analysis of individual inclusions. The geometric mean Sn contents are 87 ppm (+ 610 ppm/−76 ppm) in the melts (569 determinations) and 132 ppm (+ 630 ppm/−109 ppm) in the fluids (253 determinations). The geometric mean W values are 6.8 ppm (+ 81/−6.2 ppm) in the magmatic melts (430 determinations) and 30 ppm (+ 144 ppm/−25 ppm) in the mineral-forming fluids (391 determinations).  相似文献   

5.
The Lianhuashan tungsten deposit occurs in the volcanic terrain in the coastal area of Southeast China,where rhyolite,quartz porphyry and granite consitute a complee magmatic series.The orebodies are located in the endo-and exo-contacts between the quartz porphyry and the metasandstone of the Xiaoping coal measues.Hongenization temperatures of melt inclusions in zircon and quartz are 1100℃and 1050℃ for rhyolite,1000℃ and 860℃for quartz porphyry,and 950-1000℃and 820℃ for granite,respectively,demonstrating that the rockforming temperatures dropped successively from the eruptive to the intrusive rocks and that the homogenization temperatures of melt inclusions in zircon are 50-180℃higher than those in quartz.Homogenization temperatures of gas-liquid inclusions in quartz are 230-520℃（mostly 230-270℃）for quartz porphyry,200-450℃（mostly 200-360℃）for ore-bearing quartz veins,150-210℃for granite 170-200℃ for the vein quartz in it.Quartz from the quartz porphyry and from the ore-earing quartz veins show similar characteristics in inclusion type and homogenization temperature,indicating that intergranular solutions must have been formed upon cooling of magma and that ore-forming solutions for the tungstem mineralization were evolved mainly from ore-bearing intergranular solutions in the quartz porphyry.  相似文献   

6.
Geotechnical properties of municipal sewage sludge   总被引：3，自引：0，他引：3  
The geotechnical properties of municipal sewage sludge, in particular those pertinent to the handling and landfilling of the material, are presented. Index, drying, compaction, shear strength and consolidation tests were conducted on the material at different states of biodegradation. The organic content and specific gravity of solids were found to be inversely related, with typical organic contents of 50–70% and specific gravity of solids values of 1.55–1.80. The density of the compacted material was low in comparison with mineral soils. Standard Proctor compaction yielded a maximum dry density of 0.56 tonne/m3 at 85% water content. Laboratory vane-shear and triaxial compression tests indicated that, below about 180% water content, the shear strength of the sludge material increased exponentially with reducing water content. Consolidated-undrained triaxial compression tests on the pasteurised sludge material indicated an effective angle of shearing resistance of 32° for the moderately degraded material and 37° for the strongly degraded material. Biogas was produced at rates of up to 0.33 L/day/kg slurry due to ongoing biodegradation and the resulting pore pressure response must be taken into account in any stress analysis. Consolidation tests using the hydraulic consolidation cell, oedometer and triaxial apparatus indicated that the sludge material was highly compressible although practically impermeable, for example the coefficient of permeability for the moderately degraded slurry was of the order of 10−9m/s. However, creep deformation was significant with typical coefficient of secondary compression values of 0.02–0.08 for the compacted material. A more free-draining material was produced at higher states of biodegradation.  相似文献   

7.
Laboratory driven ionic thermal exchange of alkali feldspars from K to Na produces samples which are strongly luminescent in the ultraviolet region near 320 nm. The sites providing this luminescence are suggested as being correlated with the motion of Na atoms along interface-interphases of the material (i.e. with Na-O bond fracture). The thermoluminescence peaks show multi-order kinetics. Thermal preheatings of low albite sensitize the feldspar lattice with respect to thermoluminescence generated by exposure to UV irradiation and heating produces a strong blue luminescence spread over the range 350 nm to 500 nm band in feldspars. The upper temperature for thermoluminescence in feldspars is ∼300 °C, which is also the point where ionic conductivity of albite (010) begins, but the 300 °C region is also the starting point of a large second glow peak in adularia. Whilst it seems appropriate to link the Na motion to the 350–500 nm emission, it is unclear whether these changes are the result of the large anisotropic thermal vibration of Na atoms or the massive Na jumps that occur when the lattice reaches 300 °C. A speculative model is considered in which the UV TL emissions of natural minerals are linked to different interface-interphases (grain boundaries, exsolution limits, twinning planes, antiphase domains). Increased interface coherency energies are related to the kinetic order and the spectral position of luminescence emission peaks. Received: 3 December 1998 / Revised, accepted: 17 April 1999  相似文献   

8.
Zonal and sectorial monazite-(Ce) crystals from ceramic granite pegmatites of the Adui pluton are enriched in Ce and La, whereas monazite from the miarolitic gemstone pegmatites at the western contact of the pluton are enriched in Nd, Sm, Gd, and Y. This difference is caused by earlier crystallization of ceramic pegmatites and higher temperatures of their formation (650–600°C for ceramic pegmatites and 550–300°C for miarolitic pegmatites). Monazites from ceramic and miarolitic pegmatites of the Adui pluton differ in La and Nd contents, but their compositional trend in La-Nd coordinates is similar to the variation in monazite composition from the early to late granite pegmatites in the Ilmeny Mountains. It is suggested that decrease in temperature is a factor controlling REE contents in monazite. Heterovalent P ↔ Si and REE ↔ Th, Ca isomorphism in the consecutive zones of growth pyramids in monazite is both unidirectional and wave-like. Monazite from granite pegmatites of the Adui pluton and Ilmeny Mountains crystallized mainly under slightly alkaline conditions.  相似文献   

9.
Located adjacent to the Banded Gneissic Complex, Rampura–Agucha is the only sulfide ore deposit discovered to date within the Precambrian basement gneisses of Rajasthan. The massive Zn–(Pb) sulfide orebody occurs within graphite–biotite–sillimanite schist along with garnet–biotite–sillimanite gneiss, calc–silicate gneisses, amphibolites, and garnet-bearing leucosomes. Plagioclase–hornblende thermometry in amphibolites yielded a peak metamorphic temperature of 720–780°C, whereas temperatures obtained from Fe–Mg exchange between garnet and biotite (580–610°C) in the pelites correspond to postpeak resetting. Thermodynamic considerations of pertinent silicate equilibria, coupled with sphalerite geobarometry, furnished part of a clockwise P–T–t path with peak P–T of ∼6.2 kbar and 780°C, attained during granulite grade metamorphism of the major Zn-rich stratiform sedimentary exhalative deposits orebody and its host rocks. Arsenopyrite composition in the metamorphosed ore yielded a temperature [and log f(S 2)] range of 352°C (−8.2) to 490°C (−4.64), thus indicating its retrograde nature. Contrary to earlier research on the retrogressed nature of graphite, Raman spectroscopic studies on graphite in the metamorphosed ore reveal variable degree of preservation of prograde graphite crystals (490 ± 43°C with a maximum at 593°C). The main orebody is mineralogically simple (sphalerite, pyrite, pyrrhotite, arsenopyrite, galena), deformed and metamorphosed while the Pb–Ag-rich sulfosalt-bearing veins and pods that are irregularly distributed within the hanging wall calc–silicate gneisses show no evidence of deformation and metamorphism. The sulfosalt minerals identified include freibergite, boulangerite, pyrargyrite, stephanite, diaphorite, Mn–jamesonite, Cu-free meneghinite, and semseyite; the last three are reported from Agucha for the first time. Stability relations of Cu-free meneghinite and semseyite in the Pb–Ag-rich ores constrain temperatures at >550°C and <300°C, respectively. Features such as (1) low galena–sphalerite interfacial angles, (2) presence of multiphase sulfide–sulfosalt inclusions, (3) microcracks filled with galena (±pyrargyrite) without any hydrothermal alteration, and (4) high contents of Zn, Ag (and Sb) in galena, indicate partial melting in the PbS–Fe0.96S–ZnS–(1% Ag2S ± CuFeS2) system, which was critical for metamorphic remobilization of the Rampura–Agucha deposit.  相似文献   

10.
A temperature–time path was constructed for high-temperature low-pressure (HT–LP) migmatites of the Bayerische Wald, internal zone of the Variscan belt, Germany. The migmatites are characterised by prograde biotite dehydration melting, peak metamorphic conditions of approximately 850 °C and 0.5–0.7 GPa and retrograde melt crystallisation at 800 °C. The time-calibration of the pressure–temperature path is based on U–Pb dating of single zircon and monazite grains and titanite separates, on 40Ar/39Ar ages obtained by incremental heating experiments on hornblende separates, single grains of biotite and K-feldspar, and on 40Ar/39Ar spot fusion ages of biotite determined in situ from sample sections. Additionally, crude estimates of the duration of peak metamorphism were derived from garnet zoning patterns, suggesting that peak temperatures of 850 °C cannot have prevailed much longer than 2.5 Ma. The temperature–time paths obtained for two areas approximately 30 km apart do not differ from each other considerably. U–Pb zircon ages reflect crystallisation from melt at 850–800 °C at 323 Ma (southeastern area) and 326 Ma (northwestern area). The U–Pb ages of monazite mainly coincide with those from zircon but are complicated by variable degrees of inheritance. The preservation of inherited monazite and the presence of excess 206Pb resulting from the incorporation of excess 230Th in monazite formed during HT–LP metamorphism suggest that monazite ages in the migmatites of the Bayerische Wald reflect crystallisation from melt at 850–800 °C and persistence of older grains at these temperatures during a comparatively short thermal peak. The U–Pb ages of titanite (321 Ma) and 40Ar/39Ar ages of hornblende (322–316 Ma) and biotite (313–309 Ma) reflect cooling through the respective closure temperatures of approximately 700, 570–500 and 345–310 °C published in the literature. Most of the feldspars' ages (305–296 Ma) probably record cooling below 150–300 °C, while two grains most likely have higher closure temperatures. The temperature–time paths are characterised by a short thermal peak, by moderate average cooling rates and by a decrease in cooling rates from 100 °C/my at temperatures between 850–800 and 700 °C to 11–16 °C/my at temperatures down to 345–310 °C. Further cooling to feldspar closure for Ar was probably even slower. The lack of decompressional features, the moderate average cooling rates and the decline of cooling rates with time are not easily reconciled with a model of asthenospheric heating, rapid uplift and extension due to lithospheric delamination as proposed elsewhere. Instead, the high peak temperatures at comparatively shallow crustal levels along with the short thermal peak require external advective heating by hot mafic or ultramafic material. Received: 7 July 1999 / Accepted: 28 October 1999  相似文献   

11.
 Melting relations on the enstatite−diopside (En, Mg2Si2O6−Di, CaMgSi2O6) join, including the compositions of crystalline phases and melts coexisting along the solidi, were experimentally determined in the pressure range 70–224 kbar with a split-sphere anvil apparatus (USSA-2000). Melting is peritectic in enstatite-rich compositions at 70–124 kbar (1840–2100° C) and eutectic at higher pressures, while the diopside-rich clinopyroxene melts azeotropically at 70–165 kbar and up to 300° C lower temperatures than the eutectic. Orthopyroxene is replaced with enstatite-rich clinopyroxene at 120 kbar and 2090°C. First garnet with 17 mol% Di forms on the solidus at 158 kbar and 2100° C. Two garnets coexist on the solidus at 165–183 kbar and 2100° C, garnet coexists with CaSiO3 perovskite at 183–224 kbar (2100–2230° C) and two coexisting perovskites are stable at higher pressures. The melting curve of diopside was determined at 80–170 kbar; the slope becomes negative at 140 kbar and 2155° C. At 170 kbar and 2100° C, diopside with 96% Di breaks down to garnet with 89% Di and CaSiO3 perovskite. The new data were used to calculate an improved temperature-pressure phase diagram for the CMAS system, which can be useful for estimating the mineralogy of the Earth's upper mantle. Received: 15 October 1994 / Accepted: 15 October 1995  相似文献   

12.
A detailed seismicity map of the Central Indian Ridge for the period 1912–1993 is presented, and the earthquakes pertaining to four major transforms offsetting the ridge are utilized to study the moment release pattern. The scalar moment release for the period 1912–1993, and the summed moment rate tensors for both short period (1977–1993) and long period (1912–1993) bring out a unified picture of moment release pattern. The fraction of seismic slip calculated based on depths of 100°C and 400°C limiting temperatures suggests that the Marie-Celeste transform requires a slip almost to a depth of 400°C isotherm to account for the observed moment, and the Argo transform requires depth of faulting much above the 400°C isotherm. A very small fraction of slip is accounted seismically for Vema (53%) and 12° 12′S (23%) even to depths of 100°C isotherm, suggesting a very low order of moment release along these transforms. The horizontal plate velocities and the corresponding strain rates obtained from moment tensor summation of long period data (82 years) give rise to (V y y ; V y x mm. yr−1) of 6.0 and 6.1 along Marie-Celeste, 1.3 and 0.50 along Argo, 0.06 and 0.06 along 12° 12′S, 1.6 and 0.25 along Vema transforms. The corresponding strain rates (ε y y ;ε y x × 10−15 S−1) are 12.7 and 6.8 along MarieCeleste, 6.9 and 1.4 along Argo, 0.27 and 0.14 along 12° 12′S, 7.3 and 0.58 along Vema transforms. These results suggest that the strain rates were highest and almost all predicted motion is taken up seismically along the Marie-Celeste transform. The strain rates are lower along Argo transform and the observed moment release require shallower depth of faulting in order to slip to be accounted seismically. The Vema and 12° 12′S transforms are characterized by low strain rates and less than 15 per cent of motion is accommodated seismically within the seismogenic layer. It is proposed that the deficiency of moment release along the Vema and 12° 12′S multiple transform system may be due to most of the plate motion occurring aseismically.  相似文献   

13.
The pre-Mesozoic, mainly Variscan metamorphic basement of the Col de Bérard area (Aiguilles Rouges Massif, External domain) consists of paragneisses and micaschists together with various orthogneisses and metabasites. Monazite in metapelites was analysed by the electron microprobe (EMPA-CHIME) age dating method. The monazites in garnet micaschists are dominantly of Variscan age (330–300 Ma). Garnet in these rocks displays well developed growth zonations in Fe–Mg–Ca–Mn and crystallized at maximal temperatures of 670°C/7 kbar to the west and 600°C/7–8 kbar to the east. In consequence the monazite is interpreted to date a slightly pressure-dominated Variscan amphibolite-facies evolution. In mylonitic garnet gneisses, large metamorphic monazite grains of Ordovician–Silurian (~440 Ma) age but also small monazite grains of Variscan (~300 Ma) age were discovered. Garnets in the mylonitic garnet gneisses display high-temperature homogenized Mg-rich profiles in their cores and crystallized near to ~800°C/6 kbar. The Ordovician–Silurian-age monazites can be assigned to a pre-Variscan high-temperature event recorded by the homogenised garnets. These monazite age data confirm Ordovician–Silurian and Devonian–Carboniferous metamorphic cycles which were already reported from other Alpine domains and further regions in the internal Variscides.  相似文献   

14.
Summary In the Kutná Hora Complex, the Běstvina Formation, which is similar to Gf?hl granulite, contains eclogite that has escaped widespread retrograde recrystallization. The eclogite assemblage, garnet + omphacite + quartz + rutile ± plagioclase, yields an estimate for peak metamorphic conditions of 18–20 kbar and 835–935 °C, which is comparable to that determined from felsic granulite, 14–20 kbar and 900–1000 °C. Garnet in eclogite exhibits both prograde and retrograde compositional zoning, from which constraints on thermal history of the Gf?hl terrane can be derived by diffusion modelling. At 900 °C, a garnet grain of 800–1000 μm radius would homogenize in 7.5–11.7 million years, but the existence of compositional gradients on a length scale of 100–200 μm suggests that the duration of peak metamorphism may have been limited to ∼500,000 years. Diffusion modelling of retrograde zoning in garnet yields a cooling rate of 150–100 °C/m.y. for a radius of 800–1000 μm and initial temperature of 900 °C. The relatively brief duration of high-pressure/high-temperature metamorphism and rapid cooling and exhumation of the Gf?hl terrane may be a consequence of lithospheric delamination during Early Carboniferous collision of Bohemia (Teplá-Barrandia) and Moldanubia (Franke, 2000).  相似文献   

15.
To estimate the behavior of Au, Pd, REE, and Y in magmatic and postmagmatic processes, a series of experimental studies on the solubility of noble metals and REE in magma, magmatic fluid, and hydrothermal solutions has been performed in wide temperature and pressure ranges (300–400°C, 860–1350°C; 1–14 kbar). The coefficients of Au and Pd partitioning (D F/L) between fluid and tholeiitic melt have been determined. Depending on P, T, and the composition of the system, they vary from 1 to 11 for Au and 0.02 to 1 for Pd. The phase solubility technique was used to determine Au and Pd solubility in hydrothermal fluid. The effects of temperature, composition, and fluid acidity on Au and Pd solubility have been estimated. The high solubility of these metals in aqueous chloride solutions has been established for both Au (28–803 mg/kg at T = 300°C, 305–1123 mg/kg at T = 350°C, and 330–1400 mg/kg at T = 400°C) and Pd (40–126 mg/kg at T = 300°C, 62–152 mg/kg at T = 350°C, and 20–210 mg/kg at T = 400°C). The coefficients of REE and Y partitioning (D F/L) between fluid and tholeiitic or alkaline melts have been determined. They vary from 0.00n to 2 depending on P, T, and fluid composition. The experimental data on Au and Pd solubility in solutions and magmatic fluids and the wide variation of REE D F/L between fluid and melt show that magmatic and hydrothermal fluids are efficient agents of Au, Pd, and REE transfer and fractionation. The obtained experimental data were used for elucidating sources of fluids and their role in the genesis of Au-Pd-REE occurrences in the Subpolar Urals.  相似文献   

16.
Electron microprobe analyses of small chlorite grains (10–20 μm width) in diagenetically altered rocks from three deep wells and a series of outcrop samples ranging in maximum age from 4 to 1300 Ma show an increasingly smaller range in grain-to-grain composition as a function of the average age of the specimens in a series. The scatter of composition in a sample in each series changes little with depth despite present day, or estimated maximum temperature differences of 70° C to 100° C from top to bottom. Comparison of these chlorite compositions with those published for geothermal and metamorphic rocks formed under conditions of 300–450° C indicates that the homogeneity of chlorite composition is a function of both the temperature of equilibration and its duration. Apparently total homogenization of Fe/(Fe+Mg), Al/(Al+Mg+Fe) content will occur after 1010 years at low temperatures. Simple calculations indicate that a slow process such as solid state diffusion could be responsible for the eventual homogenization of mineral grain composition to reach chemical equilibrium after phase equilibrium has been reached.  相似文献   

17.
This paper discusses the structural features required to stimulate a strong thermoluminescence (TL) glow peak near 300°C in clear natural quartz. For that reason, fresh TL data taken from several specimens prepared from five single crystals with known impurity content are shown. The TL emission was measured with a test dose of 10 mGy of γ-rays in the readout intervals 50–160 and 160–320°C. The readings were carried out prior and after the administration of a pre-dose of 175 kGy of γ-rays followed by heat-treatments at 400°C. For each single specimen, the OH content and the population of inclusions were evaluated by infrared spectroscopy and optical microscopy, respectively. The darkening induced by high γ dose was evaluated by optical spectroscopy. It was observed that the absorption at 475 nm and TL responses decrease with increase of the OH. It was shown that both smoky darkening and TL signals were better explained in terms of Li/Al and Li/OH content ratios rather than the absolute values of aluminum and alkali concentrations. The sensitization with high γ dose and heating is essential to create and stabilize a class of defects sites with Li+ ions dislodged from [AlO4/Li]0 and Li-dependent OH centers. It is suggested that the defect sites formed with Li+ act as electron traps during test dose irradiation, whereas electron-hole recombination occurs essentially at [AlO4]0 centers during the TL output near 300°C.  相似文献   

18.
Pressure–temperature conditions of tourmaline breakdown in a metapelite were determined by high-pressure experiments at 700–900°C and 4–6 GPa. These experiments produced an eclogite–facies assemblage of garnet, clinopyroxene, phengite, coesite, kyanite and rare rutile. The modal proportions of tourmaline clearly decreased between 4.5 and 5 GPa at 700°C, between 4 and 4.5 GPa at 800°C, and between 800 and 850°C at 4 GPa, with tourmaline that survived the higher temperature conditions appearing corroded and thus metastable. Decreases in the modal abundance of tourmaline are accompanied by decreasing modal abundance of coesite, and increasing that of clinopyroxene, garnet and kyanite; the boron content of phengite increases significantly. These changes suggest that, with increasing pressure and temperature, tourmaline reacts with coesite to produce clinopyroxene, garnet, kyanite, and boron-bearing phengite and fluid. Our results suggest that: (1) tourmaline breakdown occurs at lower pressures and temperatures in SiO2-saturated systems than in SiO2-undersaturated systems. (2) In even cold subduction zones, subducting sediments should release boron-rich fluids by tourmaline breakdown before reaching depths of 150 km, and (3) even after tourmaline breakdown, a significant amount of boron partitioned into phengite could be stored in deeply subducted sediments.  相似文献   

19.
Application of multiple chronometers (including U–Pb and 40Ar/39Ar geochronology and zircon and apatite (U–Th)/He thermochronology) to porphyry intrusions at the Bajo de la Alumbrera porphyry copper–gold deposit, Argentina, reveals a complex history of reheating that spans millions of years. Previous U–Pb geochronology, combined with our new 40Ar/39Ar data, shows that the multiple porphyritic intrusions at Bajo de la Alumbrera were emplaced during two episodes, the first at about 8.0 Ma (P2 and associated porphyries) and the second about a million years later (Early and Late P3 porphyries). Complex overprinting alteration events have obscured the earliest hydrothermal history of the deposit. By contrast, 40Ar/39Ar data reveal the close temporal relationship of ore-bearing potassic alteration assemblages (7.12 ± 0.13 Ma; biotite) to the emplacement of the P3 intrusions. Consistent with low closure temperatures, younger ages have been determined for associated hydrothermal alkali feldspar (6.82 ± 0.05 Ma and 6.64 ± 0.09 Ma). The temperature-sensitive Ar data also record an unexpected prolonged cooling history (to below 200°C) extending to 5.9 Ma. Our data suggest that the Bajo de la Alumbrera system underwent protracted cooling, after the collapse of the main hydrothermal system, or that one or more low-temperature (~100–200°C) reheating events occurred after emplacement of the porphyritic intrusions at Bajo de la Alumbrera. These have been constrained in part by our new 40Ar/39Ar data (including multidomain diffusion modeling) and (U–Th)/He ages. Single-grain (U–Th)/He ages (n = 5) for phenocrystic zircon from P2 and P3 intrusive phases bracket these thermal events to between 6.9 (youngest crystallization of intrusion) and 5.1 Ma. Multidomain modeling of alkali feldspar data (from both igneous and hydrothermal crystals) is consistent with the deposit cooling rapidly from magmatic temperatures to below about 300°C, with a more protracted history down to 150°C. We conclude that the late-stage low-temperature (150 to 200°C) thermal anomaly localized at Bajo de la Alumbrera resulted from radiation of heat and/or fluids sourced from deeper-seated magma bodies, emplaced beneath the deposit. To produce the observed thermal longevity of the porphyry system, magma bodies underlying the Bajo de la Alumbrera deposit must have been repeatedly replenished by new magma batches. Without replenishment, crystallization of the source magma will occur, and heat release will stop, leading to rapid cooling (in less than ten thousand years). The influx of deep-seated magma may have caused the development of late low-temperature hydrothermal alteration assemblages at Bajo de la Alumbrera, at the same time that mineralization formed at Agua Rica, some 25 km away. All available chronologic data for the Bajo de la Alumbrera deposit suggest that the hydrothermal system was active episodically over at least a three-million and possibly up to a four-million-year period. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   

20.
The Homestake gold deposit, located in the Black Hills, South Dakota, USA, is one of the largest known hydrothermal gold deposits globally, with total mining production exceeding 40 Moz Au. Rhenium–osmium geochronology of ore-associated arsenopyrite and pyrrhotite was performed in an effort to delineate the timing of gold mineralization in relation to known tectonothermal events in the northern Black Hills. Arsenopyrite yields a rhenium–osmium (Re–Os) age of 1,736 ± 8 Ma (mean squared weighted deviation = 1.6), consistent with existing age constraints for gold mineralization, whereas Re–Os pyrrhotite data are highly scattered and do not yield a meaningful mineralization age. This is taken to indicate that the Re–Os arsenopyrite chronometer is robust to at least 400°C, whereas the Re–Os pyrrhotite chronometer is likely disturbed by temperatures of 300–350°C. The Re–Os arsenopyrite age and initial Os ratio (0.28 ± 0.15) are interpreted to indicate that gold was introduced at ca. 1,730 Ma, coincident with the onset of exhumation of crustal blocks and, possibly, the earliest intrusive phases of Harney Peak granite magmatism. New in situ U–Pb monazite analyses from an aplite dike in the east-central Black Hills indicate that granite magmatism was a protracted event, persisting until at least ca. 1,690 Ma.  相似文献   

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