Sample records for biotite

  1. Sorption of Cs to biotite

    International Nuclear Information System (INIS)

    Full text of publication follows: Biotite is the dominant mineral that sorbs Cs in granitic bedrock. Experiments were performed on biotites separated from drill core material from Olkiluoto site. The biotites were characterised for grain size, surface area (BET), element composition (EDX micro-analyser) and mineral purity (XRD, point counting). Cation exchange capacities were determined using standard methods (AgTU, NH4Ac) and sorption capacities for Ca, Na and Cs using radioactive tracers. The sorption processes of Cs was studied in simple electrolyte solutions and groundwater simulants. Experiments with simple electrolyte solutions and groundwater simulants were performed to determine the mass balance of Cs sorption. Selectivity coefficients of sorption were calculated. The minerals were examined with SEM after the sorption experiments, and with XRD for possible changes in the lattice where applicable. Phreeqc is used for mechanistic modeling of batch experiments in groundwater simulants and for simulating of flow experiments. The data from batch experiments is verified for flow conditions in crushed mineral column experiments and the need for scaling of sorption data to fracture flow conditions is studied. Particle sizes of the biotites are 2/g. Mineral purity is > 90 %, the only major impurity is chlorite. Cation exchange capacities of the biotites are 0.013 meq/g to 0.018 meq/g. Cs sorption capacity in fresh groundwater simulant is equal to CEC, but in saline groundwaters the capacity is 1/3 of CEC. The major cation competing with Cs is K, but Na and Ca have to be taken account of when modeling the groundwater chemistry due to their high concentrations in the relevant groundwaters. (authors)

  2. A Report on a Biotite-Calcic Hornblende Geothermometer

    Institute of Scientific and Technical Information of China (English)

    吴春明; 潘裕生; 王凯怡; 张健


    This paper presents a biotite-calcic hornblende geothermometer which was empirically calibrated based on the garnet-biotite geothermometer and the garnet-plagioclase-hornblende-quartz geobarometer, in the ranges of 560 800°C (T) and 0.26?1.4 Gpa (P) using the data of metadolerite, amphibolite, metagabbro, and metapelite collected from the literature. Biotite was treated as symmetric Fe-Mg-AlVI-Ti quaternary solid solution, and calcic hornblende was simplified as symmetric Fe-Mg binary solid solution. The resulting thermometer may rebuild the input garnet-biotite temperatures well within an uncertainty of 50°C. Errors of 0.2 Gpa for input pressure, along with analytical errors of 5% for the relevant mineral compositions, may lead to a random error of 16°C for this thermometer, so that the thermometer is almost independent of pressure estimates. The thermometer may clearly discriminate different rocks of lower amphibolite, upper amphibolite and granulite facies on a high confidence level. It is assumed that there is a ferric iron content of 11.6% in biotite, and that the iron content in calcic hornblende may be calculated according to the method of Dale et al. (2000). This thermometer can be used for medium- to high-grade metabasites and metapelites.

  3. Microbial Lithotrophic Oxidation of Structural Fe(II) in Biotite

    Energy Technology Data Exchange (ETDEWEB)

    Shelobolina, Evgenya S.; Xu, Huifang; Konishi, Hiromi; Kukkadapu, Ravi K.; Wu, Tao; Blothe, Marco; Roden, Eric E.


    Microorganisms are known to participate in the weathering of primary phyllosilicate minerals through production of organic ligands and acids, and through uptake of products of weathering. Here we show that a lithotrophic Fe(II)-oxidizing, nitrate-reducing enrichment culture (Straub, 6 1996) can grow via oxidation of structural Fe(II) in biotite, a Fe(II)-rich trioctahedral mica found in granitic rocks. Oxidation of silt/clay sized biotite particles was detected by a decrease in extractable Fe(II) content and simultaneous nitrate reduction. Moessbauer spectroscopy confirmed structural Fe(II) oxidation. Approximately 107 cells were produced per {micro}mol Fe(II) oxidized, in agreement with previous estimates of the growth yield of lithoautotrophic circumneutral-pH Fe(II)-oxidizing bacteria. Microbial oxidation of structural Fe(II) resulted in biotite alterations similar to those found in nature, including decrease in unit cell b-dimension toward dioctahedral levels and iron and potassium release. The demonstration of microbial oxidation of structural Fe(II) suggests that microorganisms may be directly responsible for the initial step in the weathering of biotite in granitic aquifers and the plant rhizosphere.

  4. Effect of neutron and proton radiations on magnetization of biotite

    CERN Document Server

    Abdurakhimov, A U; Sharipov, S M; Yugaj, V P; Granovskij, A B; Radkovskaya, A A


    One analyzes curves of field dependence of magnetization of biotite measured in the initial state under 4.2 K temperature subsequent to irradiation of 14 MeV energy and 1.2 x 10 sup 1 sup 3 cm sup - sup 2 dose neutrons and by 3 MeV energy and 2.2 x 10 sup 1 sup 4 cm sup - sup 2 dose protons, as well as, subsequent to annealing under 1000 deg temperature during 15 min. Irradiation by neutrons and protons was determined to result in increase of magneto-ordered phase content in biotite and, thus, in increase of magnetization of specimen. It is accounted for by formation of oxides in melt radiation thermal peaks and by freezing of high-temperature phase states corresponding to magnetite or solid solution of magnetite and hematite there. Thermal treatment does not change content of magneto-ordered phase in specimens

  5. Frictional sliding of biotite gouge under hydrothermal conditions (United States)

    Lu, Z.; He, C.


    In order to understand the origin of compositionally-weak fault and the mechanical behavior of fault zone composed of biotite-rich rocks in general, this work investigated the frictional sliding behavior of biotite gouge under hydrothermal conditions by shearing 1-mm-thick biotite gouge layers sandwiched between saw-cut driver blocks, using a triaxial testing system with argon gas as confining medium. Experiments were conducted under effective normal stress of 200MPa, with pore pressure of 30MPa, temperatures from room temperature to 600°C, and shear displacement rate were stepped with our standard (0.0001-0.001mm/s) and slow velocity steps (0.00004-0.0002mm/s). The results show that the coefficient of friction of biotite is on the order of 0.29 in the low temperature range (25 to 100°C), and varies around 0.35 for temperatures over 200°C. The overall average of friction coefficient from room temperature up to 600°C is ca. 0.33, evidently weaker than framework minerals such as quartz and feldspar and also weaker than muscovite in the mica group. Within the sliding displacement up to 4mm in our experiments, velocity strengthening occurred at temperatures of 25-200°C, with steady-state rate dependence ranging from 0.001 to 0.006. Weak velocity weakening was found at 300°C, with steady-state rate dependence similar to neutral. At 400°C, the deformation behavior changed radically and very strong velocity strengthening occurred, with steady-state rate dependence ranging from 0.012 to 0.112. At 500 and 600°C, the experiments show strong velocity dependence in the early stage of sliding, but the sliding behavior gradually evolves to stick-slip as the shearing deformation proceeds, indicating strong velocity-weakening behavior. The strongest velocity dependence occurred at 400°C in the early stage of sliding, with stress exponent similar to that of power-law creep, but the confining pressure dependence of shear strength suggests that such a behavior is semi

  6. Argon diffusion from biotite at high temperature and pressure

    Institute of Scientific and Technical Information of China (English)

    陈道公; 贾命命; 李彬贤; 陆全明; 谢鸿森; 侯渭


    t The experiments of argon diffusion dynamics for biotite were carried out at 700 -1000℃ and 0.5 - 2,0 GPa and the diffusion coefficient and activation energy using different models have been calculated. The results indicate that the pressure does affect the argon diffusion and its effect is opposite to that of temperature. When p increases, the activation energy increases and diffusion coefficient decreases. The relation between pressure, closure temperature and cooling rate has been obtained. It is postulated that in low T and high p conditions, the argon diffusion from the environment to the system could occur and incur the appearance of the external argon in minerals.

  7. DTA Characters of Biotites of Different Genetic Types and Their Implications

    Institute of Scientific and Technical Information of China (English)



    A new method is proposed to determine the genetic types of granites.Based on detailed DTA measurements on biotite in granites from south China and the Sanjiang area,characteristic thermal properties are presented for biotites of different origins.Mechanisms are discussed for the differences in thermal behavior of biotite in terms of chemical composition,crystal structure,ordering and polytypism.These characteristic thermal parameters of biotite can be used to shed light on granie genesis with the advantages of rapidness ,simplicity and economy.

  8. Implications of micro-compositions of garnet and biotite from high-grade meta-pelites

    Institute of Scientific and Technical Information of China (English)


    Based on detailed studies on the compositional zoning of garnet and biotite in pelitic rocks from the Jingshan group of granulite facies in north Jiaodong, P-T pseudosections with isopleths of Fe/(Fe + Ms) in garnet and biotite were calculated in the KFMASH system for two representative rocks of sillimanite-garnet-cordierite-biotite gneiss (Vbi/Vs > 1 ) and sillimanite-garnet gneiss ( Vbi/Vg< 0.2) using the software THERMOCALC and the internally consistent thermodynamic dataset. With a comparison of the calculated Fe/(Fe + Mg) values in garnet and biotite in the peak P-T fields constrained by peak mineral assemblages with the measured ones,it is concluded that the coarse garnet crystals with diffusion zoning from high grade meta-pelites can preserve their peak compositions even when they have experienced a cooling event, and that biotite crystals surrounded by felsic minerals in biotite-rich rocks with Vbi/Vs> 1 can nearly preserve their peak compositions, and biotites in garnet-rich rocks with Vbi/Vg< 0.2 cannot preserve their peak compositions due to the influence of grain-boundary fluid.

  9. Biotite weathering in podzolic soil under conditions of a model field experiment (United States)

    Sokolova, T. A.; Tolpeshta, I. I.; Topunova, I. V.


    The biotite changes in the 1-5 μm fraction after its occurrence in the F, H, AE, and E horizons of a pale-podzolic soil for five years under conditions of a model field experiment were assessed by X-ray diffraction analysis. It was found that the main changes of the biotite in all the horizons included the degradational transformation of its crystal lattice to interstratified mica-vermiculite structures and vermiculite. The intensity of this process gradually decreased from the F horizon down the profile in parallel with the decrease in the amount of roots and the abundance and activity of microbiota. Chloritized structures were present among the products of the biotite weathering in the H, AE, and E horizons; the degree of chloritization gradually increased from the H horizon to the E horizon. The main identified products of the biotite weathering in the AE and E horizons formed during the 5 years of the model experiment were identified in the clay and fine-silt fractions from these horizons of the native pale-podzolic soils. Therefore, the vermiculite, soil chlorite, and mixed-layer illite-vermiculite minerals in the soils studied could be considered as products of the recent soil functioning. The obtained results and literature data showed that the weathering of biotite resulted in the formation of K- and Al-buffer systems.

  10. Rb-Sr ages of the biotite and muscovite of the Himalayas, eastern Nepal

    International Nuclear Information System (INIS)

    Rb-Sr ages of biotite from the southern flank of Mt. Everest, eastern Nepal, range from 14.1 to 1.3 m.y., the youngest biotite coexists with muscovite of 7.3 m.y. These different ages for different samples reflect the difference in cooling history related to the uplift of the Himalayas. The biotite ages decrease with increasing distance from the high mountain range, suggesting that the high range, i.e., the northern area, was uplifted earlier than the southern area. The relationship between the ages and altitutes of sampling sites indicates that the uplift rate of the northern area was 0.60 mm/yr. (author)

  11. Radiometric dating of brannerite and biotite minerals from Ladi-ka-bas, Sikar District, Rajasthan

    International Nuclear Information System (INIS)

    In this paper results of radiometric dating on brannerite and biotite minerals from Ladi-ka-bas area are reported. The area falls in the North Delhi Fold Belt of Rajasthan where occurrences of uranium mineralized rocks have been reported from a number of places. In Ladi-ka-bas area hydrothermal uranium mineralization is hosted within quartz-biotite schist, albitite, impure quartzite and carbonate rocks of the Mesoproterozoic Ajabgarh Group of Delhi Supergroup. The Branerite is the main uranium bearing phase in these mineralized rocks. The age data obtained in this study will be useful in understanding the uranium mineralization events in this very important region.

  12. Biotite dissolution and Cr(VI) reduction at elevated pH and ionic strength (United States)

    He, Y. Thomas; Bigham, Jerry M.; Traina, Samuel J.


    The effects of elevated pH, ionic strength, and temperature on sediments in the vadose zone are of primary importance in modeling contaminant transport and understanding the environmental impact of tank leakage at nuclear waste storage facilities like those of the Hanford site. This study was designed to investigate biotite dissolution under simulated high level waste (HLW) conditions and its impact on Cr(VI) reduction and immobilization. Biotite dissolution increased with NaOH concentrations in the range of 0.1 to 2 mol L -1. There was a corresponding release of K, Fe, Si, and Al to solution, with Si and Al showing a complex pattern due to the formation of secondary zeolite minerals. Dissolved Fe concentrations were an order of magnitude lower than the other elements, possibly due to the formation of green rust and Fe(OH) 2. The reduction of Cr(VI) to Cr(III) also increased with increased NaOH concentration. A homogeneous reduction of chromate by Fe(II) aq released through biotite dissolution was probably the primary pathway responsible for this reaction. Greater ionic strengths increased biotite dissolution and consequently increased Fe(II) aq release and Cr(VI) removal. The results indicated that HLW would cause phyllosilicate dissolution and the formation of secondary precipitates that would have a major impact on radionuclide and contaminant transport in the vadose zone at the Hanford site.

  13. Post-collisional adakitic biotite plagiogranites from Guangtoushan pluton (Mianxian, central China): Petrogenesis and tectonic implication

    Institute of Scientific and Technical Information of China (English)

    QIN Jiangfeng; LAI Shaocong; LI Yongfei


    The post-collisional Guangtoushan pluton intruded into the Mianlue suture, Central China. Geochemi-cally, the Guangtoushan biotite plagiogranites show many close compositional similarities to high-silica adakites from the supra-subduction zone setting, but tend to have a higher concentration of K2O (3.22%-3.84%). Chondrite-normalized rare earth element pattems are characterized by high ratios of (La/Yb)N, concave-upward shapes of the heavy rare earth element (HREE), and a lack of significant Eu anomalies. In conjunction with high abundances of Ba and Sr, as well as low abundances of Y and HREE, these pattems suggest a feldspar-poor, garnet±amohibole-rich fractionation mineral assemblage. Coupled with previous studies, we suggest that the Guangtoushan biotite plagiogranites were likely to be caused by subducting slab break-off during the late orogenic stage in the West Qinling orogenic belt.

  14. The effect of natural weathering on the chemical and isotopic compositions of biotites (United States)

    Clauer, Norbert; O'Neil, J.R.; Bonnot-Courtois, C.


    The effect of progressive natural weathering on the isotopic (Rb-Sr, K-Ar, ??D, ??18O) and chemical (REE, H2O+) compositions of biotite has been studied on a suite of migmatitic biotites from the Chad Republic. During the early stages of weathering the Rb-Sr system is strongly affected, the hydrogen and oxygen isotope compositions change markedly, the minerals are depleted in light REE, the water content increases by a factor of two, and the K-Ar system is relatively little disturbed. During intensive weathering the K-Ar system is more strongly disturbed than the Rb-Sr system. Most of the isotopic and chemical modifications take place under nonequilibrium conditions and occur before newly formed kaolinite and/or smectite can be detected. These observations suggest that 1. (a) "protominerals" may form within the biotite structure during the initial period of weathering, and 2. (b) only when chemical equilibrium is approached in the weathering profile are new minerals able to form. ?? 1982.

  15. Modeling and Measurement of 39Ar Recoil Loss From Biotite as a Function of Grain Dimensions (United States)

    Paine, J. H.; Nomade, S.; Renne, P. R.


    The call for age measurements with less than 1 per mil error puts a demand upon geochronologists to be aware of and quantify a number of problems which were previously negligible. One such factor is 39Ar recoil loss during sample irradiation, a phenomenon which is widely assumed to affect only unusually small crystals having exceptionally high surface/volume ratios. This phenomenon has important implications for thermochronologic studies seeking to exploit a range of closure temperatures arising from variable diffusion radii. Our study focuses on biotite, in which spatial isotope distributions cannot be reliably recovered by stepwise heating and which therefore lack recoil-diagnostic age spectrum behavior. Previous work by Renne et al. [Application of a deuteron-deuteron (D-D) neutron generator to 40Ar/39Ar geochronology, Applied Radiation and Isotopes, in press] used the SRIM code to calculate a ˜20% 39Ar recoil loss from the outermost 0.25 μ m of an infinite slab of phyllosillicate. This result is applied to measured grains of the biotite standard GA1550, a hypabyssal granite from the Mount Dromedary Complex, Australia. We measure the thickness and surface area of 166 grains and approximate the shape of each grain as a cylinder. Grain thickness ranges from 3 to 210 μ m, with an average grain radius of 350 μ m. We predict the amount of 39Ar recoil loss from each grain, finding an expected age error >0.1 % for grains thinner than 150 μ m, a >1% error for grain less than 10 μ m thick, and up to a 3% error for grains less than 3 μ m thick. These modeling results will be tested by analysis of the measured grains after irradiation in the Oregon State University TRIGA reactor. It is important to either account for 39Ar loss in thin biotite grains, or use sufficiently thick ones so that recoil loss is negligible. Our results indicate that only biotite grains thicker than 150 μ m should be used for neutron fluence monitoring in order to avoid bias greater than the

  16. Biofilm Formation and Adaptation by Pseudomonas fluorescens on both Biotite and Glass Coupons Under Varying Fe-Nutrient Availability (United States)

    Grant, M.; Helms, G. L.; Shi, Z.; Thomashow, L.; Keller, C. K.; Harsh, J. B.


    We isolated an efficient weathering strain of Pseudomonas fluorescens from the rhizosphere of a White Pine (Pinus strobus) seedling. We grew it in a drip-flow biofilm reactor using both Fe-abundant and Fe-deficient media on either a glass or biotite coupon. Our working hypothesis was that the bacterium would respond to Fe deficiency by enhancing biotite weathering through an increase in the relative amount of polysaccharides in the biofilm compared to the Fe-abundant treatment. Because Fe is necessary for biofilm development, we hypothesized that biomass production on the biotite surface would exceed that on a Fe-free glass slide only in the Fe-deficient medium. We quantified total biomass, specific number of viable cells (SNVC), and the concentrations of K, Mg, and Fe in the biofilm. High-resolution magic angle spinning proton nuclear magnetic resonance (HR-MAS 1H-NMR) spectroscopy was used to characterize the biofilm matrix in terms of relative biofilm constituent concentrations. Compared with biofilms grown on glass, biofilms grown on biotite had higher total biomass and SNVC irrespective of Fe supply, with a near doubling of both the biofilm biomass from 0.43 to 0.76 mg cm-2 and SNVC from 1.52 × 107 to 3.24 × 107 CFU cm-2 mg-1 when Fe was deficient, and an increase in biomass from 1.94 to 2.46 mg cm-2 and in SNVC from 8.39 × 107 to 1.96 × 108 CFU cm-2 mg-1 when Fe was sufficient. Similarly with Fe deficient, the cation concentrations in biofilms grown on biotite vs. glass increased 2.14 and 2.46 times for K and Mg, respectively, and 7.01 times for Fe. When Fe was sufficient, the concentrations of cations increased 1.24, 2.07, and 3.77 times for K, Mg, and Fe, respectively. Based on NMR spectra, no significant change in biofilm chemistry occurred between the glass and biotite systems whether Fe was deficient or not. However, we did observe an increase in the ratio of the integrated areas corresponding to the carbohydrate and protein NMR regions, increasing

  17. Scales of equilibrium and disequilibrium during cleavage formation in chlorite and biotite-grade phyllites, SE Vermont (United States)

    McWilliams, C.K.; Wintsch, R.P.; Kunk, M.J.


    Detailed electron microprobe analyses of phyllosilicates in crenulated phyllites from south-eastern Vermont show that grain-scale zoning is common, and sympathetic zoning in adjacent minerals is nearly universal. We interpret this to reflect a pressure-solution mechanism for cleavage development, where precipitation from a very small fluid reservoir fractionated that fluid. Multiple analyses along single muscovite, biotite and chlorite grains (30-200 ??m in length) show zoning patterns indicating Tschermakitic substitutions in muscovite and both Tschermakitic and di/trioctahedral substitutions in biotite and chlorite. Using cross-cutting relationships and mineral chemistry it is shown that these patterns persist in cleavages produced at metamorphic conditions of chlorite-grade, chlorite-grade overprinted by biotite-grade and biotite-grade. Zoning patterns are comparable in all three settings, requiring a similar cleavage-forming mechanism independent of metamorphic grade. Moreover, the use of 40Ar/ 39Ar geochronology demonstrates this is true regardless of age. Furthermore, samples with chlorite-grade cleavages overprinted by biotite porphyroblasts suggest the closure temperatures for the diffusion of Al, Si, Mg and Fe ions are greater than the temperature of the biotite isograd (>???400 ??C). Parallel and smoothly fanning tie lines produced by coexisting muscovite-chlorite, and muscovite-biotite pairs on compositional diagrams demonstrate effectively instantaneous chemical equilibrium and probably indicate simultaneous crystallization. These results do not support theories suggesting cleavages form in fluid-dominated systems. If crenulation cleavages formed in systems in which the chemical potentials of all major components are fixed by an external reservoir, then the compositions of individual grains defining these cleavages would be uniform. On the contrary, the fine-scale chemical zoning observed probably reflects a grain-scale process consistent with a

  18. Distinctive Reactivities at Biotite Edge and Basal Planes in the Presence of Organic Ligands: Implications for Organic-Rich Geologic CO2 Sequestration. (United States)

    Zhang, Lijie; Jun, Young-Shin


    To better understand how scCO2-saturated brine-mineral interactions can affect safe and efficient geologic CO2 sequestration (GCS), we studied the effects of organic ligands (acetate and oxalate) on biotite dissolution and surface morphological changes. The experimental conditions were chosen to be relevant to GCS sites (95 °C and 102 atm CO2). Quantitative analyses of dissolution differences between biotite edge and basal planes were made. Acetate slightly inhibited biotite dissolution and promoted secondary precipitation. The effect of acetate was mainly pH-induced aqueous acetate speciation and the subsequent surface adsorption. Under the experimental conditions, most of acetate exists as acetic acid and adsorbs to biotite surface Si and Al sites, thereby reducing their release. However, oxalate strongly enhanced biotite dissolution and induced faster and more significant surface morphology changes by forming bidentate mononuclear surface complexes. For the first time, we show that oxalate selectively attacks edge surface sites and enhances biotite dissolution. Thus, oxalate increases the relative reactivity ratio of biotite edge surfaces to basal surfaces, while acetate does not impact this relative reactivity. This study provides new information on reactivity differences at biotite edge and basal planes in the presence of organic ligands, which has implications for safe CO2 storage in organic-rich sites.

  19. Studying the interface between cyanobacteria and biotite mineral surfaces using FIB and TEM

    International Nuclear Information System (INIS)

    Recent analysis of the bioweathering of minerals has highlighted the challenges for investigating the interface between fungi or bacteria and the surface of the mineral that they live on. Transmission electron microscopy (TEM) with its ability to gather imaging information and collect elemental data at high spatial resolution is the ideal technique to analyse such interfaces. Further to this, a dual beam scanning electron and focused ion beam (FIB) microscope is an ideal instrument to prepare specimens for TEM because of its ability to simultaneously cut through hard and soft materials from specific sites of interest. There are however precautions that must be taken when analysing such mineral systems. The electron beam sensitive nature of most sheet silicate minerals means that consideration has to be made as to whether the structure and/or chemistry of the material is being altered during (S)TEM analysis. Here, results from a study of cyanobacteria grown on the surface of biotite are discussed. Particular reference is given to the methods used to determine an electron beam intensity threshold, below which STEM-EDX analysis could be performed without detrimental alteration to the mineral

  20. Hydrogen isotope investigation of amphibole and biotite phenocrysts in silicic magmas erupted at Lassen Volcanic Center, California (United States)

    Underwood, S.J.; Feeley, T.C.; Clynne, M.A.


    Hydrogen isotope ratio, water content and Fe3 +/Fe2 + in coexisting amphibole and biotite phenocrysts in volcanic rocks can provide insight into shallow pre- and syn-eruptive magmatic processes such as vesiculation, and lava drainback with mixing into less devolatilized magma that erupts later in a volcanic sequence. We studied four ~ 35 ka and younger eruption sequences (i.e. Kings Creek, Lassen Peak, Chaos Crags, and 1915) at the Lassen Volcanic Center (LVC), California, where intrusion of crystal-rich silicic magma mushes by mafic magmas is inferred from the varying abundances of mafic magmatic inclusions (MMIs) in the silicic volcanic rocks. Types and relative proportions of reacted and unreacted hydrous phenocryst populations are evaluated with accompanying chemical and H isotope changes. Biotite phenocrysts were more susceptible to rehydration in older vesicular glassy volcanic rocks than coexisting amphibole phenocrysts. Biotite and magnesiohornblende phenocrysts toward the core of the Lassen Peak dome are extensively dehydroxylated and reacted from prolonged exposure to high temperature, low pressure, and higher fO2 conditions from post-emplacement cooling. In silicic volcanic rocks not affected by alteration, biotite phenocrysts are often relatively more dehydroxylated than are magnesiohornblende phenocrysts of similar size; this is likely due to the ca 10 times larger overall bulk H diffusion coefficient in biotite. A simplified model of dehydrogenation in hydrous phenocrysts above reaction closure temperature suggests that eruption and quench of magma ascended to the surface in a few hours is too short a time for substantial H loss from amphibole. In contrast, slowly ascended magma can have extremely dehydrogenated and possibly dehydrated biotite, relatively less dehydrogenated magnesiohornblende and reaction rims on both phases. Eruptive products containing the highest proportions of mottled dehydrogenated crystals could indicate that within a few days

  1. Correlation between magnetic fabrics, strain and biotite microstructure with increasing mylonitisation in the pretectonic Wyangala Granite, Australia (United States)

    Lennox, P. G.; de Wall, H.; Durney, D. W.


    The Wyangala Granite is a foliated, porphyritic Silurian granite from the Palaeozoic Circum-Pacific type Eastern Lachlan Orogen (ELO) of Australia. It is a paramagnetic ilmenite-bearing, S/marginal I type two-mica- to mainly biotite-granite with different biotite contents and local chlorite alteration. Very highly strained quartz-epidote bands are present. In this contribution, anisotropy of magnetic susceptibility (AMS) is compared with independently measured intensity and 3D style of strain, biotite microstructure and degree of mylonitisation for low-strain granites with weak S-foliations, through medium-strain protomylonitic granites with moderate S- and C-foliations to a high-strain altered granite with a strong single foliation. The samples are further analysed for possible contributions from sample heterogeneity, magmatic flow and 'sub-magmatic' deformation. A good correlation, P‧AMS ~ 1.02 + 0.04 ln P‧(e)Qtz, is obtained between site-average degree of AMS (P‧AMS) in the granite and degree of finite-strain anisotropy (P‧(e)Qtz) from aspect ratios of quartz aggregates in S-foliations in hand specimen and outcrop (P‧AMS 1.03-1.14, P‧(e)Qtz 1.4-19). The magnetic fabric ellipsoids agree with a kinematic regime between neutral and pure oblate predicted by the March model. The observed quartz strains, however, exceed the AMS March strains and are near neutral, plano-linear character. The geological factors that may have contributed to these differences include intra- and inter-crystalline deformation of biotite and bimodality in S and C. Magmatic fabric is not clearly evident in either the AMS or the biotite data. New data for synkinematic oligoclase, low-titanium biotite and low-sodium K-feldspar show that conditions during deformation were approximately transitional greenschist-amphibolite facies: i.e., well below solidus. This agrees with published age data that put the granite emplacement in an extensional, back-arc setting in already deformed

  2. The failure of a slope cut into the weathering profile developed over a porphyritic biotite granite (United States)

    Raj, J. K.


    At about 1.00 a.m. on 24 September, 1981, at km 24.5 of the Kuala Lumpur-Karak highway, there occurred a failure of a 26 m high slope cut into the weathering profile developed over a porphyritic biotite granite. The failure, which is best classified a slump-flow, occurred some 5.7 years after the end of excavation and involved the downslope movement of about 2000 m 3 of weathered bedrock material (mainly gravelly silty sands) and a few coreboulders. Continued movement of failed material through minor slumping and gulleying led to eventual exposure of the failure surface which was mainly located along a relict fault plane striking parallel to, and dipping 48° towards, the highway. Failure occurred as a result of several converging factors; the triggering factor being ground vibrations set up at the time of passing of three large trucks. Conditions of instability, however, were already present in the slope materials through infiltration of rainwater that led to saturation and the loss of apparent or effective cohesion. Infiltration had been encouraged by clearing of vegetation at the top of the cut and the creation of a track along its western edge some 6 months prior to failure. Infiltration was also encouraged by rainfall patterns with the failure occurring after some 29 days with almost continuous daily rainfall; this wet period being preceded by an unusual 27 days of no rain. It is concluded that stability assessments of slope cuts in weathering profiles over granitic bedrock need to take into consideration not only shear strength parameters, but also local climatic and other environmental factors, including likely triggering factors.

  3. Formation and preservation of biotite-rich microdomains in high-temperature rocks from the Antananarivo Block, Madagascar (United States)

    Cenki-Tok, Bénédicte; Berger, Alfons; Gueydan, Frédéric


    Highly restitic rocks from the Antananarivo Block in northern Madagascar are investigated in this study in order to unravel processes of H2O-rich biotite formation in HT rocks. Polyphase metamorphism and melt migration occurred at 0.6 GPa and 850 °C. Biotite remains stable together with orthopyroxene and makes up to 45 vol% of the rock. In addition, three well-characterised and delimited microdomains having different textural, chemical and petrological characteristics are preserved. Thermodynamic models using the specific bulk compositions of the domains are in agreement with petrological observations. These rocks provide evidence that the lower crust may be strongly heterogeneous, locally associated to the formation of hydrous restites controlled by episodes of melt production and melt escape. This has significant consequences for understanding of the lower crust.

  4. Preservation of Sub-Microscopic Scale Structural Relics in Biotite: Implications for 40AR/39AR Geochronology (United States)

    Beltrando, M.; Di Vincenzo, G.; Ferraris, C.


    Relic crystals of magmatic biotite that undewent eclogite facies metamorphism were investigated by laser step-heating and laser in-situ 40Ar/39Ar techniques, in conjunction with SEM, EMP and TEM analyses, to elucidate the influence of recrystallization on K-Ar systematics. Samples were collected from meta-granitoids of the Gran Paradiso Massif (Western Alps), emplaced at upper crustal depths (P~0.25-0.35 GPa) in the Permian and metamorphosed at P>2.0 GPa and T~500-600°C in the Middle-Late Eocene. Two different samples, which underwent different degrees of Alpine re-equilibration, were examined. Sample JT1007 still preserves the original cm-sized magmatic quartz, k-feldspar and brown biotite (Bt 1), rarely rimmed by small green biotite crystals (Bt 2) related to Alpine metamorphism. Sample JT1008, instead, is characterized by a larger degree of Alpine re-equilibration, with static re-crystallization of the original magmatic quartz into aggregates of fine-grained polygonal crystals and common green biotite rims around brown Bt 1. Compositional profiling across Bt 1 in sample JT1007 reveals a progressive decrease in Ti content towards the crystal rims, which overlap with the composition of Bt 2. Compositional profiling across Bt 1 in sample JT1008, instead, reveals a homogeneous Ti content across the grain. This compositional pattern is mirrored by TEM investigation at the sub-micron scale, revealing a systematic zoning in Bt 1 from sample JT1007, with high-temperature magmatic politypes, surrounded by 1M politypes, still preserved in crystal cores. Crystal rims, instead, are characterized by 1M politypes only. Biotites from JT1008, instead, are homogeneous, solely consisting of 1M politypes. Infrared laser step-heating experiments on mineral separates from the two samples gave contrasting results: JT1008 yielded a flat spectrum, for more than 90% of the released 39ArK, with an error-weighted mean age of 36.5±0.3 Ma; JT1007 yielded a slightly saddle-shaped profile

  5. A Previously Unrecognized Example of the Shock-Induced Breakdown of Biotite to Garnet from the Steen River Impact Structure, Canada (United States)

    Walton, E. L.; Sharp, T. G.; Hu, J.; Tschauner, O.


    The novel shock-induced transformation of biotite to almandine garnet accompanied by fluid release and Fe-oxidation is reported from those grains adjacent to shock veins in crystalline basement rocks of the Steen River impact structure.

  6. Dietary germanium biotite supplementation enhances the induction of antibody responses to foot-and-mouth disease virus vaccine in pigs


    Lee, Jin-A; Jung, Bock-Gie; Jung, Myunghwan; Kim, Tae-Hoon; Yoo, Han Sang; Lee, Bong-Joo


    We evaluated the potential ability of germanium biotite (GB) to stimulate the production of antibodies specific for foot-and-mouth disease virus (FMDV). To this aim, we measured the total FMDV-specific antibody responses and IgM production after vaccination against FMD both experimentally and in the field. GB supplementation with FMDV vaccination stimulated the production of anti-FMDV antibodies, and effectively increased IFN-γ and TNF-α levels. These results suggest that GB may be a novel al...

  7. The 3D distribution of cordierite and biotite in hornfels from the Bugaboo contact aureole (British Columbia, Canada) (United States)

    Gaidies, Fred; Petley-Ragan, Arianne; Pattison, David


    The size, abundance, shape and spatial distribution of metamorphic minerals bears important information on the rates and mechanisms of fundamental processes that take place during metamorphic crystallization. X-ray computed tomography (XR-CT) has become the method of choice to study the three-dimensional (3D) disposition of minerals in rocks as it allows investigation of relatively large sample volumes at sufficiently high resolution required for statistically meaningful analyses, and as its non-destructive fashion permits further studies such as mineral chemical, isotopic or crystallographic analyses of select grains identified through XR-CT. We present results obtained through the quantification of the 3D disposition of cordierite and biotite crystals in a hornfels from the contact aureole of the Bugaboo Batholith (British Columbia, Canada) using XR-CT and global as well as scale-dependent pattern statistics (Petley-Ragan et al., 2016). The results demonstrate a random distribution of cordierite and biotite crystal sizes for all scales across the entire rock volume studied indicative of interface-controlled prograde metamorphic reaction kinetics. We show that the common approach to approximate the shape of crystals as spherical underestimates the influence of the Strauss hard-core process on rock texture which may be misinterpreted to reflect ordering of crystal sizes by inhibition of nucleation and growth commonly associated with diffusion-controlled reaction kinetics. According to our findings, Strauss hard-core ordering develops at length scales equal to and less than the average major axis of the crystal population. This is significantly larger than what is obtained if a spherical crystal geometry would be assumed, and increases with deviation from sphericity. For the cordierite and biotite populations investigated in this research, Strauss hard-core ordering developed at length scales of up to ˜2.2 and 1.25 mm, respectively, which is almost 1 mm longer than

  8. Equilibrium partitioning and subsequent re-distribution of halogens among apatite-biotite-amphibole assemblages from mantle-derived plutonic rocks: Complexities revealed (United States)

    Teiber, Holger; Scharrer, Manuel; Marks, Michael A. W.; Arzamastsev, Andrei A.; Wenzel, Thomas; Markl, Gregor


    The concentration of halogens in apatite, biotite and amphibole is investigated for a large variety of mantle-derived plutonic rocks (gabbros, diorites, monzonites, olivine- and pyroxene-bearing monzonitic to granitic rocks, syenites, carbonatites and a phoscorite). In all rocks studied, apatite occurs as an early magmatic phase, whereas biotite and amphibole may occur either as a late magmatic phase or as late-stage, potentially hydrothermal product replacing precursor olivine, pyroxene and Fe-Ti oxides (ilmenite and magnetite). Based on electron microprobe analyses for F and Cl and detailed textural observations, we test existing models of halogen partitioning between apatite and biotite. Bromine concentration data for apatite, biotite and amphibole are used to further refine our understanding of the geochemical similarities and differences between Cl and Br during magmatic and hydrothermal processes. Our data suggests that F and Cl contents in apatite, biotite and amphibole can indeed be useful monitors of the halogen systematics in magmas, but they may also be subject to post-magmatic changes to variable extents. The relatively small radius and compatible F cation seems to be less prone to post-magmatic alteration and is likely to best reflect the original magmatic halogen abundances - especially in apatite. However, the larger and probably more incompatible Cl anion, is more easily re-mobilized as reflected by strong redistribution of Cl in biotite and amphibole which have been clearly overprinted by hydrothermal fluids. In certain cases, the ability of halogens to re-distribute themselves after magmatic equilibrium partitioning (as emphasized by our data) suggests that observed partitioning (especially between apatite and biotite) may also be used as a very sensitive indicator for post-magmatic hydrothermal processes.

  9. Molybdenite Re-Os dating of biotite dehydration melting in the Rogaland high-temperature granulites, S Norway (United States)

    Bingen, Bernard; Stein, Holly


    The ability of the Re-Os system in molybdenite to record and preserve the age of granulite-facies metamorphism in polymetamorphic belts is tested using the Ørsdalen W-Mo district, Rogaland, S Norway. A low-pressure high-temperature granulite-facies domain, displaying osumilite and pigeonite isograds, is exposed around the 931±2 Ma Rogaland anorthosite complex. Available U-Pb monazite and zircon data show that a 0.93 Ga contact metamorphism overprints a 1.03-0.97 Ga regional Sveconorwegian metamorphism in the gneiss basement. Molybdenite and scheelite in the Ørsdalen district occur in orthopyroxene-bearing leucocratic veins parallel to the regional foliation. The veins are interpreted as migmatic leucosomes formed by fluid-absent incongruent melting of the biotite-rich host rock above ca. 800°C, producing a granulite-facies orthopyroxene±garnet residual assemblage. Molybdenite is interpreted as a product of the melting reaction, crystallized from trace amounts of Mo released from biotite in the host rock during partial melting. Four Re-Os analyses of molybdenite from three samples representing two mines yield an isochron age of 973±4 Ma. The isochroneity of the data indicates that the precipitation of molybdenite and the partial melting event are recorded on the district scale. The Re-Os system in molybdenite was not affected by subsequent 0.93 Ga contact metamorphism, corresponding to formation of garnet+quartz coronitic textures around molybdenite and other minerals in the deposits. The results indicate that granulite-facies conditions prevailed at 973±4 Ma, near the end of a protracted event of regional metamorphism (1.03-0.97 Ga). Biotite dehydration melting recorded in Ørsdalen took place at a pressure of ca. 5.5 kbar (orthopyroxene-garnet-plagioclase-quartz thermobarometry), possibly in association with regional decompression. The study shows that granulite-facies metamorphism (0.97 Ga) took place before intrusion of massif-type anorthosites in

  10. The catalytic effect of sodium and lithium ions on coupled sorption-reduction of chromate at the biotite edge-fluid interface (United States)

    Ilton, Eugene S.; Veblen, David R.; Moses, Carl O.; Raeburn, Stuart P.


    Large single crystals of biotite and near-endmember phlogopite were reacted with aqueous solutions bearing 20 μM Cr(VI) and different concentrations of NaCl, LiCl, RbCl, CsCl, NaClO 4, and Na 2SO 4. Solutions were maintained at 25 ± 0.5°C, 1 atm, and pH = 4.00 ± 0.02. Samples were extracted from the reaction chamber at 1, 3, 5, 10, and 20 h. The edges and basal planes of the reacted micas were analyzed by X-ray photoelectron spectroscopy (XPS) for major elements and Cr. XPS analyses of biotite show trivalent chromium on edge surfaces but no detectable chromium on the basal plane. XPS analyses of near-endmember phlogopites that were reacted in the same experiments as biotite showed no detectable Cr on either the basal plane or edge surfaces. Increasing Na and Li salt concentrations increased the rate of coupled sorption-reduction of chromate at the biotite edge-fluid interface, where the order of effectiveness was NaCl ˜ NaClO 4 > Na 2SO 4 > LiCl. In contrast, no Cr was detected on mica edges after reaction in RbCl and CsCl solutions. Comparison of equimolar NaCl and LiCl experiments indicate that the active agent is Na and Li, not ionic strength or the anion. Sulfate tends to block the reaction more so than chloride. We conclude that it is the substitution of hydrated cations for interlayer K in biotite that enhances the heterogeneous reduction of chromate at the biotite edge-fluid interface.

  11. Reviews in Garnet—Biotite Geothermometer:Its Versions,Inherent Problems of Accuracy and Precision,and Perspective for Further Research

    Institute of Scientific and Technical Information of China (English)

    吴春明; 潘裕生


    This paper briefly introduces twenty-one versions of garnet-biotite Fe-Mg exchange geothermometry,points out the sources of systematic errors inherent in geothermometry.The sources lie in that:(1) ideal Fe-Mg mixing in garnet and biotite is assumed;(2)non-ideal properties of bot garnet and biotite are not considered completely;(3) minor elements-Mn, Ca in garnet,and AlⅥ,Ti,Mn in biotite are almost neglected;(4)effects of pressure on equilibrium,although little,are almost not taken into consideration,and experiments were conducted at one fixed pressure;(5)the data used for egression analysis is too scarce in quantity;(6)internal consistency of the data used for empirical calibration is not fully guaranteed;(7) the authors take energy parameters W's(Margule's parametrs)independent of pressure and temperature,though the former are actually the functions of the latter items;and (8)the most important composition-activity relationship is not consistent with the mineral compositions used for calibration.Furthermore,it is believed that empirical calibrations cannot avoid the following problems;(1) effect of retrograde metamorphism;(2)inconsistent data set;(3)effect of pressure on temperature estimation;and (4)effect of Fe3+ calculation.Exact experimental work should be done in order to accurately calibrate the geotermometer in which the Margule's parameters should be treated as the functions of pressure,temperature,and mineral compositions.

  12. Fractional crystallization of high-K arc magmas: biotite- versus amphibole-dominated fractionation series in the Dariv Igneous Complex, Western Mongolia (United States)

    Bucholz, Claire E.; Jagoutz, Oliver; Schmidt, Max W.; Sambuu, Oyungerel


    Many studies have documented hydrous fractionation of calc-alkaline basalts producing tonalitic, granodioritic, and granitic melts, but the origin of more alkaline arc sequences dominated by high-K monzonitic suites has not been thoroughly investigated. This study presents results from a combined field, petrologic, and whole-rock geochemical study of a paleo-arc alkaline fractionation sequence from the Dariv Range of the Mongolian Altaids. The Dariv Igneous Complex of Western Mongolia is composed of a complete, moderately hydrous, alkaline fractionation sequence ranging from phlogopite-bearing ultramafic and mafic cumulates to quartz-monzonites to late-stage felsic (63-75 wt% SiO2) dikes. A volumetrically subordinate more hydrous, amphibole-dominated fractionation sequence is also present and comprises amphibole (±phlogopite) clinopyroxenites, gabbros, and diorites. We present 168 whole-rock analyses for the biotite- and amphibole-dominated series. First, we constrain the liquid line of descent (LLD) of a primitive, alkaline arc melt characterized by biotite as the dominant hydrous phase through a fractionation model that incorporates the stepwise subtraction of cumulates of a fixed composition. The modeled LLD reproduces the geochemical trends observed in the "liquid-like" intrusives of the biotite series (quartz-monzonites and felsic dikes) and follows the water-undersaturated albite-orthoclase cotectic (at 0.2-0.5 GPa). Second, as distinct biotite- and amphibole-dominated fractionation series are observed, we investigate the controls on high-temperature biotite versus amphibole crystallization from hydrous arc melts. Analysis of a compilation of hydrous experimental starting materials and high-Mg basalts saturated in biotite and/or amphibole suggests that the degree of K enrichment controls whether biotite will crystallize as an early high-T phase, whereas the degree of water saturation is the dominant control of amphibole crystallization. Therefore, if a melt

  13. Assessment of Blasting Performance Using Electronic Vis-à-Vis Shock Tube Detonators in Strong Garnet Biotite Sillimanite Gneiss Formations (United States)

    Sharma, Suresh Kumar; Rai, Piyush


    This paper presents a comparative investigation of the shock tube and electronic detonating systems practised in bench blasting. The blast trials were conducted on overburden rocks of Garnet Biotite Sillimanite Gneiss formations in one of the largest metalliferous mine of India. The study revealed that the choice of detonating system was crucial in deciding the fragment size and its distribution within the blasted muck-piles. The fragment size and its distribution affected the digging rate of excavators. Also, the shape of the blasted muck-pile was found to be related to the degree of fragmentation. From the present work, it may be inferred that in electronic detonation system, timely release of explosive energy resulted in better overall blasting performance. Hence, the precision in delay time must be considered in designing blast rounds in such overburden rock formations. State-of-art image analysis, GPS based muck-pile profile plotting techniques were rigorously used in the investigation. The study revealed that a mean fragment size (K50) value for shock tube detonated blasts (0.55-0.59 m) was higher than that of electronically detonated blasts (0.43-0.45 m). The digging rate of designated shovels (34 m3) with electronically detonated blasts was consistently more than 5000 t/h, which was almost 13 % higher in comparison to shock tube detonated blasts. Furthermore, favourable muck-pile shapes were witnessed in electronically detonated blasts from the observations made on the dozer performance.

  14. Decrease in water activity due to fluid absent partial melting monitored with water content in biotite in the Western Adamello contact aureole (Italy) (United States)

    Siron, Guillaume; Baumgartner, Lukas; Bouvier, Anne-Sophie; Vennemann, Torsten


    The fluorine and chlorine exchange on the hydroxyl site in micas is used to monitor changes in fluid composition (Munoz 1984). Most studies assume that the OH-site does not contain vaccancies, since the vast majority of studies use analytical techniques that does not allow to directly measure the OH- content of the mica. Nevertheless, studies have shown that significant amounts of O2- are present, and its concentration increases with temperature and titanium content. This feature was intrepreted as the consequence of a Ti-oxygen exchange in amphibolite and granulite facies rocks (Dyar et al. 1993, Cesare et al. 2008). Here, we present OH, F, Cl data for biotite from contact aureoles from biotite-schist to partially molten sillimanite-cordierite schists. OH-F-Cl content of biotites were analyzed using Secondary Ion Mass Spectrometry (SIMS), and major elements were analyzed by EMP. Samples were collected in the mid-crustal Western Adamello contact aureole (Italian Alps, Floess and Baumgartner, 2013). For that purpose we used biotite standards with water content constrained by Thermal Conversion Elemental Analyzer (TC/EA) see Bauer and Vennemann 2014, at a level of precision of 0.1-0.2 wt% (2SD). SIMS measurements typically have a precision of 0.1wt% (2SD), corresponding to the homogeneity of the internal standard at the SwissSIMS laboratory. OH- content decreases in samples with increasing peak temperature and Ti content (Ti range for biotites of 0.15-0.42 p.f.u for all samples). Nevertheless, within each individual sample, OH- is not a function of Ti. Ti variations are about 0.4 p.f.u., which is ten times the analytical uncertainty of the EMP analysis (0.004 p.f.u., 1SD). Water content is constant within analytical precision for each sample. The mean of OH- measurements is 3.41 p.f.u. in biotite and garnet grade samples, whereas those of samples in the partially molten zone have values of 3.27 p.f.u. We do not see any correlation with XMg or F and Cl. Hence, we

  15. Experimental study on dehy- dration melting of natural biotite-plagioclase gneiss from High Himalayas and implica- tions for Himalayan crust anatexis

    Institute of Scientific and Technical Information of China (English)


    Here we present the results of dehydration melting, melt morphology and fluid migration based on the dehydration melting experiments on natural biotite- plagioclase gneiss performed at the pressure of 1.0-1.4 GPa, and at the temperature of 770-1028℃. Experimental results demonstrate that: (ⅰ) most of melt tends to be distributed along mineral boundaries forming "melt film" even the amount of melt is less than 5 vol%; melt connectivity is con-trolled not only by melt topology but also by melt fraction; (ⅱ) dehydration melting involves a series of subprocesses including subsolidus dehydration reaction, fluid migration, vapor-present melting and vapor-absent melting; (ⅲ) ex-periments produce peraluminous granitic melt whose com-position is similar to that of High Himalayan leucogranites (HHLG) and the residual phase assemblage is Pl+Qz+Gat+Bio+Opx±Cpx+Ilm/Rut±Kfs and can be compa-rable with granulites observed in Himalayas. The experi-ments provide the evidence that biotite-plagioclase gneiss is one of source rocks of HHLG and dehydration melting is an important way to form HHLG and the granulites. Addition-ally, experimental results provide constraints on determining the P-T conditions of Himalayan crustal anatexis.

  16. Dating Magmatic Hornblende and Biotite and Hydrothermal Sericite by Laser Probe Technique:Constraints on Genesis of Wangershan Gold Deposit, Eastern Shandong Province,China

    Institute of Scientific and Technical Information of China (English)

    Li Jianwei; Vasconcelos P M; Zhou M F; Duzgoren-Aydin N S


    The Wangershan gold deposit and spatially related Shangzhuang granite, eastern Shandong Province, have been precisely dated by 40 Ar/39 Ar laser incremental heating technique. Magmatic hornblende and biotite, collected from the Shangzhuang granites, yielded well-defined and reproducible plateau ages at 128. 1-127.5 and 124.4-124. 1 Ma (2σ), measuring the cooling ages of the intrusion at ca. 500 ℃ and 300-350 ℃, respectively. Hydrothermal sericite extracted from auriferous vein gave high-quality plateau ages between (120. 6±0.3) Ma and (120. 0±0. 4) Ma (2σ). Given the similarity of the closure temperature for argon diffusion (300-350 ℃ ) in the sericite mineral to the homogenization temperature of primary fluid inclusions in the quartz from gold ores, and the intergrowth of sericite with native gold, present 40Ar/39 Ar sericite ages can be reliably interpreted in terms of the mineralization age for the Wangershan deposit. 40 Ar/39 Ar hornblende and biotite ages permit an estimate for the cooling rate of the Shangzhuang granite at about 50 ℃/Ma. There are abundant intermediate-mafic dikes in most gold camps of eastern Shandong, whose ages of formation have been previously constrained mainly at 121-119 Ma. The temporal association between the Shangzhuang granite, the Wangershan gold deposit, and the widespread dikes confirms that intrusive activity, gold mineralization, and dike emplacement in this region were broadly coeval, reflecting significant continental lithosphere thinning and resulting crustal extension of Early Cretaceous in eastern China.

  17. Tectono-thermal evolution of the Palaeoproterozoic Granites-Tanami Orogen, North Australian Craton: Implications from hornblende and biotite 40Ar/39Ar geochronology (United States)

    Li, Ben; Bagas, Leon; Jourdan, Fred


    The Palaeoproterozoic Granites-Tanami Orogen (GTO) hosts a number of gold deposits located in the southern margin of the North Australian Craton. The major stratigraphic succession is the Palaeoproterozoic Tanami Group which is subdivided into the Dead Bullock Formation and conformably overlying Killi Killi Formation. New geochemical data for the ca. 1864 Coora and Groundrush dolerite sills in the Dead Bullock Formation suggests that they have the same characteristics with the enriched back-arc basin basaltic rocks from the former Stubbins Formation, such as tholeiitic affinity, high TiO2 contents (0.94 to 1.24 wt.%) and low Mg# (41-45), slightly enriched LILE (Rb, Th, U, and K), weakly depleted HFSE (Nb, Ta), and relatively flat REE patterns. Their magma was generated by high degree decompressional melting (5-15%) of the asthenosphere source with an input of 3-4% subduction-related material. The petrological and geochemical similarities of igneous rocks provide new evidence for the assignment of the ca. 1864 Ma former Stubbins Formation and the Mount Charles Formations in the Dead Bullock Formation of the Tanami Group. These conclusions confirmed that the extensive Palaeoproterozoic Tanami Group was deposited in a back-arc basin environment. Hornblende and biotite 40Ar/39Ar geochronological study identified three major tectono-thermal events in the GTO since the deposition of the Dead Bullock Formation. The ca. 1840 Ma 40Ar/39Ar cooling age of metamorphic hornblende from the Coora and Groundrush dolerite sills in the Dead Bullock Formation provided precise age constraint for the first Palaeoproterozoic tectono-thermal event during the evolution of the Granites-Tanami back-arc basin. This age is highly consistent with the ca. 1850-1840 Ma subduction and peak metamorphism events in the North Australian Craton (NAC) associated with the Halls Creek Orogeny in the Halls Creek Orogen, and the Tennant Orogeny in the Tennant Creek Inlier. The 40Ar/39Ar age of 1753 ± 8 Ma

  18. 3D velocity distribution of P- and S-waves in a biotite gneiss, measured in oil as the pressure medium: Comparison with velocity measurements in a multi-anvil pressure apparatus and with texture-based calculated data (United States)

    Lokajíček, T.; Kern, H.; Svitek, T.; Ivankina, T.


    Ultrasonic measurements of the 3D velocity distribution of P- and S-waves were performed on a spherical sample of a biotite gneiss from the Outokumpu scientific drill hole. Measurements were done at room temperature and pressures up to 400 and 70 MPa, respectively, in a pressure vessel with oil as a pressure medium. A modified transducer/sample assembly and the installation of a new mechanical system allowed simultaneous measurements of P- and S-wave velocities in 132 independent directions of the sphere on a net in steps of 15°. Proper signals for P- and S-waves could be recorded by coating the sample surface with a high-viscosity shear wave gel and by temporal point contacting of the transmitter and receiver transducers with the sample surface during the measurements. The 3D seismic measurements revealed a strong foliation-related directional dependence (anisotropy) of P- and S-wave velocities, which is confirmed by measurements in a multi-anvil apparatus on a cube-shaped specimen of the same rock. Both experimental approaches show a marked pressure sensitivity of P- and S-wave velocities and velocity anisotropies. With increasing pressure, P- and S-wave velocities increase non-linearly due to progressive closure of micro-cracks. The reverse is true for velocity anisotropy. 3D velocity calculations based on neutron diffraction measurements of crystallographic preferred orientation (CPO) of major minerals show that the intrinsic bulk anisotropy is basically caused by the CPO of biotite constituting about 23 vol.% of the rock. Including the shape of biotite grains and oriented low-aspect ratio microcracks into the modelling increases bulk anisotropy. An important finding from this study is that the measurements on the sample sphere and on the sample cube displayed distinct differences, particularly in shear wave velocities. It is assumed that the differences are due to the different geometries of the samples and the configuration of the transducer-sample assembly

  19. 40Ar/39Ar age-spectrum data for hornblende, biotite, white mica, and K-feldspar samples from metamorphic rocks in the Great Smoky Mountains of North Carolina and Tennessee (United States)

    Kunk, Michael J.; McAleer, Ryan


    This report contains reduced 40Ar/39Ar data of hornblende, biotite, white mica and (or) sericite, and potassium-feldspar mineral separates and phyllite groundmass samples from metamorphic rocks of the Great Smoky Mountains in North Carolina and Tennessee. Included in this report are information on the location of the samples and a brief description of the samples. The data contained herein are not interpreted in a geological context, and care should be taken by users unfamiliar with argon isotopic data in the use of these results. No geological meaning is implied for any of the apparent ages presented below, and many of the individual apparent ages are not geologically meaningful. This report is primarily a detailed source document for subsequent publications that will integrate these data into a geological context. All the samples in this report were collected in and around the Great Smoky Mountain National Park in western North Carolina and eastern Tennessee.

  20. The Microarea Composition of Garnet and Biotite from the Ji‘an Group in Tonghua District and Its Significance as an Indicator of Metamorphic P—T—t Path

    Institute of Scientific and Technical Information of China (English)

    卢良兆; 靳是琴; 等


    The garnet(Grt)and biotite(Bt) from gneisses of the Ji'an Group are characterized by diffusion zoning at the rim,but equilibrium composition of metamorphic peak is usually remained in extensive interior area.Garnet with growth zoning is also found in the kyanite zone.In the light of microarea compositional variation of Grt and Bt,the temperature and pressure at the progressive,peak and post-peak metamorphic stages are determined by correctly using Grt Bt thermometer and GASP barometer.On this basis,a counterclockwise P-T-t path can be constructed,which reflects the closing process of an ensialic rift belt in this region during the Early Proterozoic.

  1. Archean high-Mg monzodiorite-syenite, epidote skarn, and biotite-sericite gold lodes in the Granny Smith-Wallaby district, Australia: U-Pb and Re-Os chronometry of two intrusion-related hydrothermal systems (United States)

    Mueller, Andreas G.; Hall, Gregory C.; Nemchin, Alexander A.; Stein, Holly J.; Creaser, Robert A.; Mason, Douglas R.


    The Granny Smith (37 t Au production) and Wallaby deposits (38 t out of a 180 t Au resource) are located northeast of Kalgoorlie, in 2.7 Ga greenstones of the Eastern Goldfields Province, the youngest orogenic belt of the Yilgarn craton, Western Australia. At Granny Smith, a zoned monzodiorite-granodiorite stock, dated by a concordant titanite-zircon U-Pb age of 2,665 ± 3 Ma, cuts across east-dipping thrust faults. The stock is fractured but not displaced and sets a minimum age for large-scale (1 km) thrust faulting (D2), regional folding (D1), and dynamothermal metamorphism in the mining district. The local gold-pyrite mineralization, controlled by fractured fault zones, is younger than 2,665 ± 3 Ma. In augite-hornblende monzodiorite, alteration progressed from a hematite-stained alkali feldspar-quartz-calcite assemblage and quartz-molybdenite-pyrite veins to a late reduced sericite-dolomite-albite assemblage. Gold-related monazite and xenotime define a U-Pb age of 2,660 ± 5 Ma, and molybdenite from veins a Re-Os isochron age of 2,661 ± 6 Ma, indicating that mineralization took place shortly after the emplacement of the main stock, perhaps coincident with the intrusion of late alkali granite dikes. At Wallaby, a NE-trending swarm of porphyry dikes comprising augite monzonite, monzodiorite, and minor kersantite intrudes folded and thrust-faulted molasse. The conglomerate and the dikes are overprinted by barren (1,600-m-long replacement pipe, which is intruded by a younger ring dike of syenite porphyry pervasively altered to muscovite + calcite + pyrite. Skarn and syenite are cut by pink biotite-calcite veins, containing magnetite + pyrite and subeconomic gold-silver mineralization (Au/Ag = 0.2). The veins are associated with red biotite-sericite-calcite-albite alteration in adjacent monzonite dikes. Structural relations and the concordant titanite U-Pb age of the skarn constrain intrusion-related mineralization to 2,662 ± 3 Ma. The main-stage gold-pyrite ore

  2. 黑龙江金厂矿区黑云母花岗岩成因及含矿性%Genesis and Ore-Bearing Potential for Biotite Granite in the Jinchang Au Deposit, Heilongjiang

    Institute of Scientific and Technical Information of China (English)

    张宏辉; 陈凯; 陈可忠; 占达积; 谭开远


    黑龙江省东宁县金厂金矿发现于20世纪60年代.20世纪90年代开始,武警黄金地质研究所和武警黄金第一总队在此开展找矿勘探工作并相应完成对其的科学研究工作.目前,该金矿已提交金资源量(333)超过 90 吨,是国内外罕见的以金为主的大型斑岩型金矿床.矿区主要岩性为花岗岩、花岗闪长岩、石英闪长岩等,可分为五期.通过研究印支晚期第三阶段黑云母花岗岩的演化、成岩成矿及含矿性,对找矿有指导作用.%The Jinchang Gold Deposit in Heilongjiang Province was discovered in the 1960's. The Geological Research Institute and First Corps of Gold Geological Party of CAPF have explored and researched since the 1990's. It has obtained gold reserves over 90 tons of gold (333). Au mineralization is related to the third stage biotite granite of the Late Indo-Chinese epoch.

  3. 陕西华阳川铀多金属矿床黑云母40Ar/39Ar年龄及其地质意义%40 Ar/39 Ar Geochronology of Biotite in Huayangchuan Uranium-Polymetallic Deposit in Shanxi Province and its Geological Significance

    Institute of Scientific and Technical Information of China (English)

    何升; 李子颖; 惠小朝; 郭建


    In this study , the forming age of Huayangchuan uranium‐polymetallic deposit was performed on the biotite using Ar Ar dating method.Biotite in carbonatite was dated with a plateau age of 132.58 ± 0.70 Ma ,an isochron age of 133.01 ± 0.74 Ma ,and biotite in biotite‐amphibole‐sulfide‐bearing peg‐matite was dated with a plateau age of 93.72 ± 2.38 Ma , an isochron age of 91.49 ± 1.97 Ma.Microprobe examination found that the biotite was formed prior to the betafite , and therefore the betafite was believed to be formed later than 93.72 ± 2.38 Ma ,which suggested there was a later Early Cretaceous magma hydrothermal U Nb Ti mineralization process in Xiaofuyu‐Huayangchuan‐Huan‐glongpu mineralization belte beside the discoved Triassic carbonatite vein‐type Mo Pb , there occured a Cretaceous porphyry Mo metalization process.%笔者采用Ar Ar测年技术,获得华阳川铀多金属矿床碳酸岩中黑云母40 Ar/39 Ar坪年龄132.58±0.70Ma ,等时线年龄133.01±0.74Ma ,含黑云母闪石硫化物伟晶岩中黑云母的40Ar/39Ar坪年龄93.72±2.38Ma ,等时线年龄91.49±1.97Ma。镜下特征显示,铌钛铀矿的形成晚于碳酸岩中的黑云母及含黑云母闪石硫化物伟晶岩中的黑云母。因此,铌钛铀矿的形成时间应晚于93.72±2.38Ma。这表明成矿带内除了已知存在三叠纪碳酸岩型Mo Pb矿和白垩纪斑岩型Mo矿的成矿过程之外,还存在早白垩世之后的岩浆热液型U Nb Ti成矿过程。

  4. SHRIMP U-Pb Dating of the Zircon from the Hercynian Biotite Monzonitic Granites in Urad Zhongqi,Inner Mongolia,and Its Geological Significance%内蒙古乌拉特中旗海西期黑云母二长花岗岩锆石SHRIMP U-Pb年龄及其地质意义

    Institute of Scientific and Technical Information of China (English)

    王挽琼; 刘正宏; 王兴安; 张超; 范志伟; 时溢; 朱凯


    对乌拉特中旗德尔斯地区黑云母二长花岗岩岩相学、锆石SHRIMP U-Pb年代学和岩石地球化学进行了研究,并讨论了岩石成因及研究区晚海西期构造演化.黑云母二长花岗岩发育两期:早期为中粗粒斑状黑云母二长花岗岩,晚期为中细粒黑云二长花岗岩.岩石中的锆石大部分具核-边结构:边部震荡环带发育,Th/U值为0.16~0.50,反映了岩浆成因;核部呈浑圆状,多数具岩浆环带,个别弱分带-无分带,Th/U值为0.06~0.44,表明核部大部分属岩浆型残留锆石,个别为变质型残留锆石.测年结果显示:边部锆石加权平均年龄为早、中二叠世((279±3)Ma、(266±3)Ma),代表黑云母二长花岗岩形成时代;核部残留锆石加权平均年龄为(1 972±63) Ma、(1 962±43) Ma,代表源岩的形成时代.岩石属于亚碱性系列,REE配分形式呈右倾型,LREE/HREE为5.86~22.81,明显亏损高场强元素Nb,富集大离子亲石元素Rb、Ba,显示活动大陆边缘火成岩的地球化学特征.黑云母二长花岗岩地球化学属性反映了早、中二叠世古亚洲洋向华北板块北缘的俯冲作用及古亚洲洋消亡的演化历史.%Petrography, SHRIMP U - Pb chronology of the zircon and geochemistry of the Hercynian biotite monzonitic granites in Deersi area of Urad Zhongqi are studied to constrain the genesis of the rock and regional tectonic evolution in the study area. The emplacement of the biotite monzonitic granite in this area can be divided into two periods, the earlier is medium-coarse prophyritic biotite monzonitic granite and the latter is medium-fine grain biotite monzonitic granite. Most of zircons from biotite monzonitic granites show core-mantle ring structure, fine-scale oscillatory zoning and Th/U ratios of 0. 16 - 0. 50, implying their magmatic origin. Whereas most of cores of rouded zircons have fine-scale oscillatory zoning and Th/U ratios of 0. 06 - 0. 44, which indicates their magmatic genesis and

  5. 大青山-乌拉山变质杂岩带大南沟地区含榴尖晶黑云钾长片麻岩成因及其形成的P-T条件%Petrogenesis and metamorphic P-T conditions of garnet-spinel-biotite-bearing paragneiss in Danangou area, Daqingshan-Wulashan metamorphic complex belt

    Institute of Scientific and Technical Information of China (English)

    蔡佳; 刘福来; 刘平华; 施建荣; 刘建辉


    大南沟贫硅的含榴尖晶黑云钾长片麻岩出露于华北克拉通西北部大青山-乌拉山变质杂岩带(孔兹岩带)中,主要以大小不等的透镜状和互层状产于石榴长英质粒状岩石和石榴堇青夕线黑云二长片麻岩中.本文通过岩相学、变质反应、成因矿物学、矿物化学以及相平衡模拟的综合研究,揭示合榴尖晶黑云钾长片麻岩的成因机制及其形成的P-T条件.研究表明,大南沟含榴尖晶黑云钾长片麻岩内尖晶石的Zn含量极低(XZn=Zn/(Fe2+Mg+ Zn)<0.006).含尖晶石的后成合晶微域反映峰后退变条件下局部的再平衡过程,其中石榴石分解形成的钾长石+尖晶石±斜长石后成合晶是由Grt+ Sil+ Melt→Kfs+Spl+ Pl反应形成的.而细粒尖晶石-刚玉-磁铁矿矿物组合及相应的退变结构是在晚期降温和氧化作用下,通过反应Splss+O2→Spl+ Mag+ Crn分解形成的.相平衡模拟结果表明含榴尖晶黑云钾长片麻岩峰期矿物组合为Bt+ Grt+ Spl+ Mag+ Sil+Kfs +P1+ Liq,稳定的温压条件在830~ 870℃和8.3~8.6kb,位于夕线石的稳定域.%Danangou garnet-spinel-biotite-bearing paragneiss occurs as interlayers or various lenses within garnet-bearing quartzofeldspathic rocks and garnet-cordierite-sillimanite-bearing paragneisses,Daqingshan-Wulashan metamorphic complex belt,North China Craton.The combined studies of petrography,metamorphic reaction,genetic mineralogy,and quantitative phase modeling provide insight into the origin of the garnet-spinel-biotite-bearing paragneiss.This typical silica-undersaturated metamorphic rock mainly consists of garnet,spinel,biotite,sillimanite,K-feldspar with secondary minerals of magnetite,apatite,quartz,etc.Thereinto,spinel has extremely low gahnite content with XZn ratio < 0.006 (XZn =Zn/(Fe2 + + Mg + Zn).Spinel-beating mineral assemblages within the same microdomain were formed at the late re-equilibration stage corresponding to the decompression or cooling

  6. Heat capacities and thermodynamic properties of annite (aluminous iron biotite) (United States)

    Hemingway, B.S.; Robie, R.A.


    The heat capacities have been measured between 7 and 650 K by quasi-adiabatic calorimetry and differential scanning calorimetry. At 298.15 K and 1 bar, the calorimetric entropy for our sample is 354.9??0.7 J/(mol.K). A minimum configurational entropy of 18.7 J/(mol.K) for full disorder of Al/Si in the tetrahedral sites should be added to the calorimetric entropy for third-law calculations. The heat capacity equation [Cp in units of J/mol.K)] Cp0 = 583.586 + 0.075246T - 3420.60T-0.5 - (4.4551 ?? 106)T-2 fits the experimental and estimated heat capacities for our sample (valid range 250 to 1000 K) with an average deviation of 0.37%. -from Authors

  7. Geochemistry, zircon U-Pb dating and Pb-Sr-Nd isotopic composition of the gneissic biotite granodiorite in Mainling County, Tibet%西藏米林县片麻状黑云花岗闪长岩地球化学特征、锆石U-Pb定年及Pb-Sr-Nd同位素组成

    Institute of Scientific and Technical Information of China (English)

    时超; 李荣社; 何世平; 王超; 辜平阳; 计文化; 查显锋; 张海迪


    The Himalayan orogenic belt, caused by the subduction and collision between Indian plate and Eurasian plate, is the youngest and largest currently active orogenic belt in the world. The LA-ICP-MS U-Pb zircon age of 515.5 ± 2.3 Ma from the gneissic biotite granodiorite that intruded into the Namche Barwa complex in eastern syntaxis of the Himalayan orogenic belt provides a geological record of Pan-African tectonic-mag-matic event in this area. The SiO2 content is 66.47% ~72.42%, the average of the A/CNK indexes is 1.03 (0.98 ~ 1.03), and all samples fall into the peraluminous region in the A/NK-A/CNK index diagram. The Rittmann index σ is between 1.53 and 3.08, belonging to the calc-alkaline series. Most of the samples fall into a high-K calc-alkaline series area in the SiQ ~ K2O diagram. The values of TiO2, MgO, FeOT , MnO and K2O show a good linear relationship with SiO2 content in the Harker diagrams. The chondrite-nomalized REE patterns indicate that the samples are enriched in LREE, (La/Yb)N values are 19.1~63.8, with slightly negative Eu anomalies (δEu = 0.62 ~0.79). Trace elements show the depletion of Ba, Nb, Ta, Sr and Z as well as the relative enrichment of Rb, Th and U. The negative e Nd(t) values(-8.67~-10.57) and Nd model ages (tdm= 1.84 ~ 3.42) of the gneissic biotite granodiorite of Tanya Township indicate that this rock had an old upper crust material source. Combined with the initial 87Sr/86Sr ratio features, the authors hold that the source rock of the gneissic biotite granodiorite of Tanya Township was granitic magma that partially melted in a high temperature environment. From the tectonic environment discrimination diagrams, it is inferred that metalumi-nous-weakly peraluminous gneissic biotite granodiorite of Tanya Township was formed in the post-collisional stage characterized by the conversion from a compressional environment to an extensional. Combined with the isotope age 513 Ma, the authors consider that the Pan-African collisional

  8. Biofilm adaptation to iron availability in the presence of biotite and consequences for chemical weathering (United States)

    Bacteria in nature often live within biofilms, exopolymeric matrices that provide a favorable environment that can differ markedly from their surroundings. Biofilms have been found growing on mineral surfaces and are expected to play a role in weathering those surfaces, but this role is not well und...

  9. Argon in hornblende, biotite and muscovite in geologic cooling - Ar-40/Ar-39-investigations

    International Nuclear Information System (INIS)

    The results of the Ar-40/Ar-39 studies are discussed under the aspect of whether the age data of the minerals indicate a cooling process. The author hopes that isotope dating of minerals with different closing temperatures will describe the temperature/time history of an area in the temperature range of 600 to 2000C. The findings are analyzed under three aspects: How much do they contribute to the initial methodological question, what do they contribute to the regional geology of the areas investigated, and in what respects do they extent the present knowledge of the geochronological analysis, i.e. its techniques and interpretation. (orig.)

  10. Study of granitic biotites by X-ray fluorescence analysis: determination of iron, manganese, titanium, calcium, potassium, silicon and aluminium

    International Nuclear Information System (INIS)

    A method for the quantitative determination of iron, manganese, titanium, calcium potassium, silicon, and aluminium, is reported, Sample preparation is carried out by the miniature flux technique, and rubidium is used as internal standard for silicon and aluminium. (Author) 5 refs

  11. 40Ar/39Ar Data for White Mica, Biotite, and K-Feldspar Samples from Low-Grade Metamorphic Rocks in the Westminster Terrane and Adjacent Rocks, Maryland (United States)

    Kunk, Michael J.; McAleer, Ryan


    This report contains reduced 40Ar/39Ar data of white mica and K-feldspar mineral separates and matrix of a whole rock phyllite, all from low-grade metamorphic rocks of the Westminster terrane and adjacent strata in central Maryland. This report presents these data in a preliminary form, but in more detail than can be accommodated in todays professional journals. Also included in this report is information on the location of the samples and a brief description of the samples. The data contained herein are not interpreted in a geological context, and care should be taken by readers unfamiliar with argon isotopic data in the use of these results; many of the individual apparent ages are not geologically meaningful. This report is primarily a detailed source document for subsequent publications that will integrate these data into a geological context.

  12. 磷霉素钙生物效价检定法的改进%Amelioration of bio-titer verification method for fosfomycin calcium

    Institute of Scientific and Technical Information of China (English)

    孔梅; 李慧芝; 吴连勇; 张荃



  13. Anomalous Seismic Velocity Drop in Iron and Biotite Rich Amphibolite to Granulite Facies Transitional Rocks from Deccan Volcanic Covered 1993 Killari Earthquake Region, Maharashtra (India): a Case Study (United States)

    Pandey, O. P.; Tripathi, Priyanka; Vedanti, Nimisha; Srinivasa Sarma, D.


    65 Ma Deccan Volcanic Province of western India forms one of the largest flood basaltic eruptions on the surface of the earth. The nature of the concealed crust below this earthquake prone region, which is marked by several low velocity zones at different depths has hardly been understood. These low velocity zones have been invariably interpreted as fluid-filled zones, genetically connected to earthquake nucleation. While carrying out detailed geological and petrophysical studies on the Late Archean basement cores, obtained from a 617 m deep KLR-1 borehole, drilled in the epicentral zone of 1993 Killari earthquake region of the southern Deccan Volcanic Province, we came across several instances where we observed remarkable drop in measured P-wave velocity in a number of high density cores. We provide detailed petrographic and geological data on 11 such anomalous samples which belong to mid-crustal amphibolite to granulite facies transitional rocks. They are associated with a mean P-wave velocity of 6.02 km/s (range 5.82-6.22 km/s) conforming to granitic upper crust, but in contrast have a high mean density of 2.91 g/cm3 (range 2.75-3.08 g/cm3), which characterise mid to lower crust. This velocity drop, which is as much as 15 % in some cores, is primarily attributed to FeOT enrichment (up to about 23 wt%) during the course of mantle-fluid driven retrogressive metasomatic reactions, caused by exhumation of deep-seated mafic rocks. Presence of Iron content (mainly magnetite), widely seen as opaques in thin sections of the rocks, seems to have resulted into sharp increase in density, as well as mean atomic weight. Our study indicates that the measured V p is inversely related to FeOT content as well as mean atomic weight of the rock.


    Institute of Scientific and Technical Information of China (English)

    宋书林; 姚杰; 王安平



  15. Evolution of the Santana do Araguaia (PA region based on geology and Pb-Pb zircon geochronology from granitoid rocks

    Directory of Open Access Journals (Sweden)

    Lívio Wagner Chaves Corrêa


    Full Text Available The region of Santana do Araguaia, focus of this study, is located in the southeast of Pará State, which, in its turn, lies in the southeastern Amazonian Craton. From the tectonic point of view, it is positioned in the Domain Santana do Araguaia, interpreted as an Archean terrain affected by the Transamazonic Cycle. A petrographic and geochronological study, supported by field data, was undertaken in granitoids of the region in order to unravel the evolution of this field. In modal terms, the studied rocks consist of biotite monzogranite, biotite metagranodiorite, hornblende-biotite granodiorite, hornblende-biotite metatonalite and enderbite. These rocks present themselves undeformed to moderately deformed, with some particularities: the biotite metagranodiorite presents foliation following an E-W trend; the hornblende-biotite metatonalite has a foliation following the NW-SE direction, usually with high to subvertical dives, the biotite monzogranite is isotropic, and lithologies hornblende-biotite granodiorite and enderbite show only a slight orientation of their crystals, mainly noticeable in thin section. These rock types were analyzed by evaporating Pb zircon method and the following ages were obtained: biotite metagranodiorite, 3066±3 Ma and 2829±13 Ma, hornblende-biotite metatonalite, 2852±2 Ma, biotite monzogranite, 2678 to 2342 Ma, hornblende-biotite granodiorite, 1990±7 Ma, and enderbite, 1988±4 Ma. The geochronological data indicate that the rocks crystallized both in the Archean and in the Paleoproterozoic; however, no evidence to prove the action of the Transamazonic Cycle was detected in the region.


    Institute of Scientific and Technical Information of China (English)

    WangRucheng; XuShijin; ShenWeizhou; XuKeqin


    The Suzhou granite is one of the farnous-Nb,Ta-bearing granites in China. Petrographic studies permitted to divide it into three intrusion stages;the first stage-medium-grained am-phibole-biotite granite,the second stage-medium-to-fine-grained biotite granite ,and the third

  17. 西伯利亚克拉通东南缘1.84Ga构造热事件——俄罗斯斯塔诺夫南带南缘混合岩化黑云斜长片麻岩锆石U-Pb年龄和Hf同位素记录%Recognition of the 1.84 Ga tectono-thermal event in the southeastern margin ofthe Siberian craton: record from zircon U-Pb dates and Hf isotopes of migmatitic biotite plagioclase gneiss from the southern edge of southern Stanov belt, Tydna,Far East, Russia

    Institute of Scientific and Technical Information of China (English)

    王彦斌; 童英; 王涛; Andrey Sorokin; 韩娟; 侯可军


    对俄罗斯远东腾达(Tydna)斯塔诺夫南带南缘混合岩化黑云斜长片麻岩中锆石进行了U-Pb年龄测定和Hf同位素测试,获得其锆石核部年龄主要为≥2.57、~2.39、~2.33和~2.20 Ga,锆石增生边年龄为1.84 Ga,可靠的最年轻碎屑锆石年龄为~2.20 Ga,表明其原岩沉积时代为古元古代,而不是以往认为的太古宙,混合岩化事件年龄为1.84 Ga.锆石核部εHf(t)值为2.7~ - 16.2,Hf同位素地壳模式年龄为3.7~2.8 Ga;锆石增生边的εHf(t)值为-7.5~-18.6,峰值为- 15,Hf同位素地壳模式年龄为3.6~2.9 Ga.锆石的εHf(t)值基本为负值说明这些岩石主要来自于地壳岩石的部分熔融;Hf同位素两阶段模式年龄的峰值在~3.4 Ga,表明它们可能主要来源于阿尔丹地盾下地壳物质的部分熔融.这些年龄资料将为西伯利亚克拉通东南缘地质构造演化提供重要的年代学制约.%These data indicate that the metamorphic rocks were formed in Paleoproterozoic instead of Archaean as conventionally thought. Hafnium analysis shows that the cores of zircons from migmatitic felsic gneiss have negative or positive as well as variable εHf(t) values ( - 16.2 to + 2.7) and Archean (3.7 to2.8 Ga) depleted-mantle model ages, the overgrowths of zircon have negative variable εHf (t) values ( - 18.6 to -7.5) and Archean (3.6 to 2.9 Ga) depleted-mantle model ages. The eHf(t) values of most zircon cores are negative, indicative of a recycled continental crust. The source region of these magmas might have been related to Archean material of the Aldan Craton, suggesting derivation from an isotopically heterogeneous old crust source. U-Pb in situ zircon dating shows a 1. 84 Ga overgrowth of zircons in migmatitic gneiss, implying Paleoproterozoic migmatization. The 1.84 Ga age of the migmatization event is correlated with the 1.9'-1.8 Ga high grade metamorphism recorded in other regions of the world such as North America craton, Greenland, Baltica, and North China Craton, and was probably related to the formation of the Columbia.

  18. Microstructural records of multiple retrograde local H2O supplement in the pelitic gneiss, Lützow-Holm Complex at Akarui Point, East Antarctica (United States)

    Nakamura, Aya; Kitamura, Masao; Kawakami, Tetsuo


    The alkali-feldspar and biotite in the sillimanite-biotite-garnet gneiss from East Antarctica preserves characteristic microstructural evidence of multi-stage H2O supplement during the retrograde metamorphism. The first microstructural evidence is the "zoned feldspar," in which the mesoperthitic zone, the anti-perthitic zone, and lamella-free plagioclase zone coexist within a single crystal. They are occasionally found next to biotite, and are always depleted in orthoclase (Or) component toward the biotite. The formation process of this microstructure could be explained by the diffusion that oversteps the solvus. The second microstructural evidence is the serrate boundary between alkali-feldspar and biotite. The projections of biotite are selectively developed next to Or lamellae of alkali-feldspar every 3-5 μm. These two microstructures would have formed as the biotite grew by consuming potash in alkali-feldspar when H2O-bearing fluid locally passed through the grain boundaries. The former microstructure was formed at 825-900 °C before lamella formation, and the latter microstructure was formed after the lamella formation. These microstructures are the indicators of fluid pathways formed under two different temperature conditions. The common coexistence of these microstructures implies that the fluid used similar pathways during the retrograde metamorphism.

  19. Magnetic petrology of the Água Azul and Água Limpa granodiorites, southern portion of the Carajás Domain – Pará

    Directory of Open Access Journals (Sweden)

    Eleilson Oliveira Gabriel


    Full Text Available The Água Azul and Água Limpa granodiorites (AAGrd and ALGrd, respectively outcrop in the extreme southern of the Carajás Domain as two elongated bodies following the EW regional trend and were previously included in the Xingu Complex. The ALGrd consists mainly of biotite-amphibole granodiorites and muscovite-biotite granodiorites, with subordinate amphibole-biotite tonalites; the AAGrd contains dominant epidote-amphibole-biotite granodiorites, epidote-amphibole-biotite tonalite and restricted (amphibole-epidote-biotite monzogranites. These rocks show geochemical signatures like of archaean sanukitoids. The magnetic susceptibility (MS values obtained in the ALGrd (average 17.54 × 10-4 SIv and AAGrd (average 4.19 × 10-4 SIv are relatively low. The main opaque minerals are magnetite and hematite, and ilmenite is lacking in these rocks. The ALGrd contains titanite associated with magnetite, while the AAGrd contains pyrite, chalcopyrite, and goethite. In the ALGrd, magnetite is more developed and large than in the AAGrd, justifying its highest values of MS. The oxidation of magnetite (martitization and the alteration of sulfides to goethite, occurred at low temperatures. The positive correlation between MS values and the modal content of opaque, amphibole, epidote + allanite and quartz + K-feldspar, as well as the negative correlation of MS with biotite and mafic observed in these units, reveal a trend of MS increasing in the direction: amphibole tonalites/amphibole granodiorites à biotite granodiorites/biotite monzogranites. The geochemical data confirm this fact, with a negative correlation between the MS values and Fe2O3T, FeO, and MgO, reflecting, for the two units, an upward trend in MS values parallel to magmatic differentiation. The geochemical and mineralogical affinities between these rocks and sanukitoids of the Rio Maria Domain suggest conditions of the oxygen fugacity between HM and FMQ buffers for the studied granitoids

  20. An experimental study on the behaviour of copper and other trace elements in magmatic systems


    Were, Patrick


    1. Distribution of trace elements between biotite and hydrous granitic melt. The synthetic system haplogranite-anorthite-biotite-H2O, doped with a suite of trace elements (V, Cr, Co, Ni, Cu, Zn, Rb, Cs, Sr, Ba, Mo, W, Nb, Ta, REE, Pb and Zr) was experimentally investigated over the temperature interval of 700-800°C at 200 MPa (H2O) to study the distribution of trace elements between biotite and coexisting hydrous melt. The starting materials were a series of volatile-free synthetic glasse...

  1. Experimental study of gold activation-transportation in the process of potash metasomatism-alteration ——North China platform gold deposit taken as an example

    Institute of Scientific and Technical Information of China (English)

    WANG; Yurong; HU; Shouxi


    Chemical reactions of plagioclase, biotite and their single minerals, as well as a mineral mixture of (plagioclase +biotite+quartz), with KCl and (KCl+KHCO3) solutions were carried out at 150400℃ and 5080 MPa. Experiments show that alkaline fluid promotes plagioclase’s changing into potash feldspar, while acid fluid helps plagioclase, potash feldspar and biotite alteration form chlorite and sericite. After chemical reaction the acidity-alkalinity of solutions often changes reversely. It was observed that gold dissolved from the tube wall and recrystallized on the surfaces of biotite and pyrite. Therefore the transportation and enrichment of gold are related to the elementary effect of the fluid-mineral interfaces. Fe3+-Fe2+, as an oxidition-reduction agent, and volatile components Cl? and CO2 play important roles in the reaction process.

  2. Experimental study of gold activation-transportation in the process of potash metasomatism-alteration——North China platform gold deposit taken as an example

    Institute of Scientific and Technical Information of China (English)


    Chemical reactions of plagioclase, biotite and their singleminerals, as well as a mineral mixture of (plagioclase +biotite+quartz), with KCl and (KCl+KHCO3) solutions were carried out at 150400℃ and 5080 MPa. Experiments show that alkaline fluid promotes plagioclase’s changing into potash feldspar, while acid fluid helps plagioclase, potash feldspar and biotite alteration form chlorite and sericite. After chemical reaction the acidity-alkalinity of solutions often changes reversely. It was observed that gold dissolved from the tube wall and recrystallized on the surfaces of biotite and pyrite. Therefore the transportation and enrichment of gold are related to the elementary effect of the fluid-mineral interfaces. Fe3+-Fe2+, as an oxidition-reduction agent, and volatile components Cl? and CO2 play important roles in the reaction process.

  3. Development of modal layering in granites: a case study from the Carna Pluton, Connemara, Ireland (United States)

    McKenzie, Kirsty; McCarthy, William; Hunt, Emma


    Modal layering in igneous rocks uniquely record dynamic processes operating in magma chambers and also host a large proportion of Earth's strategic mineral deposits. This research investigates the origin of biotite modal layering and primary pseudo-sedimentary structures in felsic magmas, by using a combination of Crystal Size Distribution (CSD) analysis and Electron Probe Microanalysis (EPMA) to determine the mechanisms responsible for the development of these structures in the Carna Pluton, Connemara, Ireland. The Carna Pluton is a composite granodiorite intrusion and is one of five plutons comprising the Galway Granite Complex (425 - 380 Ma). Prominent 30 cm thick modal layers are defined by sharp basal contacts to a biotite-rich (20%) granite, which grades upward over 10 cm into biotite-poor, alkali-feldspar megacrystic granite. The layering strikes parallel to, and dips 30-60° N toward the external pluton contact. Pseudo-sedimentary structures (cross-bedding, flame structures, slumping and crystal graded bedding) are observed within these layers. Petrographic observations indicate the layers contain euhedral biotite and fresh undeformed quartz and feldspar. Throughout the pluton, alkali-feldspar phenocrysts define a foliation that is sub-parallel to the strike of biotite modal layers. Together these observations indicate that the intrusion's concentric foliation, biotite layers and associated structures formed in the magmatic state and due to a complex interaction between magma flow and crystallisation processes. Biotite CSDs (>250 crystals per sample) were determined for nine samples across three biotite-rich layers in a single unit. Preliminary CSD results suggest biotite within basal contacts accumulated via fractional crystallisation within an upward-growing crystal pile, likely reflecting the yield strength of the magma as a limiting factor to gravitational settling of biotite. This is supported by the abrupt decrease in mean biotite crystal size across

  4. High grade metamorphism in the Bundelkhand massif and its implications on Mesoarchean crustal evolution in central India (United States)

    Singh, S. P.; Dwivedi, S. B.


    The Bundelkhand Gneissic Complex (BnGC) in the central part of the Bundelkhand massif preserves a supracrustal unit which includes pelitic (garnet-cordierite-sillimanite gneiss, garnet-sillimanite gneiss, biotite gneiss and garnet-biotite gneiss) and mafic (hornblende-biotite gneiss and garnetiferous amphibolite) rocks. Granulite facies metamorphism of the complex initiated with breaking down of biotite to produce garnet and cordierite in the pelitic gneisses. Geothermobarometric calculations indicate metamorphic conditions of 720°C/6.2 kbar, followed by a retrograde (687°C/4.9 kbar) to very late retrograde stages of metamorphism (579°C/4.4 kbar) which is supported by the formation of late cordierite around garnet. The P-T conditions and textural relations of the garnet-cordierite-bearing gneiss suggest a retrograde cooling path of metamorphism.

  5. High grade metamorphism in the Bundelkhand massif and its implications on Mesoarchean crustal evolution in central India

    Indian Academy of Sciences (India)

    S P Singh; S B Dwivedi


    The Bundelkhand Gneissic Complex (BnGC) in the central part of the Bundelkhand massif preserves a supracrustal unit which includes pelitic (garnet–cordierite–sillimanite gneiss, garnet–sillimanite gneiss, biotite gneiss and garnet–biotite gneiss) and mafic (hornblende–biotite gneiss and garnetiferous amphibolite) rocks. Granulite facies metamorphism of the complex initiated with breaking down of biotite to produce garnet and cordierite in the pelitic gneisses. Geothermobarometric calculations indicate metamorphic conditions of 720°C/6.2 kbar, followed by a retrograde (687°C/4.9 kbar) to very late retro-grade stages of metamorphism (579°C/4.4 kbar) which is supported by the formation of late cordierite around garnet. The P–T conditions and textural relations of the garnet–cordierite-bearing gneiss suggest a retrograde cooling path of metamorphism.

  6. Petrographic and geochemical comparisons between the lower crystalline basement-derived section and the granite megablock and amphibolite megablock of the Eyreville-B core, Chesapeake Bay impact structure (United States)

    Townsend, Gabrielle N.; Gibson, Roger L.; Horton, J. Wright; Reimold, Wolf Uwe; Schmitt, Ralf T.; Bartosova, Katerina


    The Eyreville B core from the Chesapeake Bay impact structure, Virginia, USA, contains a lower basement-derived section (1551.19 m to 1766.32 m deep) and two megablocks of dominantly (1) amphibolite (1376.38 m to 1389.35 m deep) and (2) granite (1095.74 m to 1371.11 m deep), which are separated by an impactite succession. Metasedimentary rocks (muscovite-quartz-plagioclase-biotite-graphite ± fibrolite ± garnet ± tourmaline ± pyrite ± rutile ± pyrrhotite mica schist, hornblende-plagioclase-epidote-biotite-K-feldspar-quartz-titanite-calcite amphibolite, and vesuvianite-plagioclase-quartz-epidote calc-silicate rock) are dominant in the upper part of the lower basement-derived section, and they are intruded by pegmatitic to coarse-grained granite (K-feldspar-plagioclase-quartz-muscovite ± biotite ± garnet) that increases in volume proportion downward. The granite megablock contains both gneissic and weakly or nonfoliated biotite granite varieties (K-feldspar-quartz-plagioclase-biotite ± muscovite ± pyrite), with small schist xenoliths consisting of biotite-plagioclase-quartz ± epidote ± amphibole. The lower basement-derived section and both megablocks exhibit similar middle- to upper-amphibolite-facies metamorphic grades that suggest they might represent parts of a single terrane. However, the mica schists in the lower basement-derived sequence and in the megablock xenoliths show differences in both mineralogy and whole-rock chemistry that suggest a more mafic source for the xenoliths. Similarly, the mineralogy of the amphibolite in the lower basement-derived section and its association with calc-silicate rock suggest a sedimentary protolith, whereas the bulk-rock and mineral chemistry of the megablock amphibolite indicate an igneous protolith. The lower basement-derived granite also shows bulk chemical and mineralogical differences from the megablock gneissic and biotite granites.

  7. The Pikes Peak batholith, Colorado front range, and a model for the origin of the gabbro-anorthosite-syenite-potassic granite suite (United States)

    Barker, F.; Wones, D.R.; Sharp, W.N.; Desborough, G.A.


    This study of the Pikes Peak batholith includes the mineralogy and petrology of quartz syenite at West Creek and of fayalite-bearing and fayalite-free biotite granite near Mount Rosa; major element chemistry of the batholith; comparisons with similar postorogenic, intracratonic, sodic to potassic intrusives; and genesis of the batholith. The batholith is elongate in plan, 50 by 100 km, composite, and generally subalkalic. It was emplaced at shallow depth 1,040 m. y. ago, sharply transects its walls and may have breached its roof. Biotite granite and biotite-hornblende granite are predominant; quartz syenite, fayalite granite and riebeckite granite are present in minor amounts. Fayalite-bearing and fayalite-free quartz syenite, fayalite-biotite granite and riebeckite granite show a well-defined sodic differentiation trend; the less sodic fayalite-free granites exhibit a broader compositional range and no sharp trends. Crystallization was largely at PH2O suite that includes gabbro or basalt, anorthosite, quartz syenite, fayalite granite, riebeckite granite, and biotite and/or hornblende granites is of worldwide occurrence. A model is proposed in which mantle-derived, convecting alkali olivine basaltic magma first reacts with K2O-poor lower crust of granulite facies to produce magma of quartz syenitic composition. The syenitic liquid in turn reacts with granodioritic to granitic intermediate crust of amphibolite facies to produce the predominant fayalite-free biotite and biotite-hornblende granites of the batholith. This reaction of magma and roof involves both partial melting and the reconstitution and precipitation of refractory phases, as Bowen proposed. Intermediate liquids include MgO-depleted and Na2O-enriched gabbro, which precipitated anorthosite, and alkali diorite. The heat source is the basaltic magma; the heat required for partial melting of the roof is supplied largely by heats of crystallization of phases that settle out of the liquid - mostly olivine

  8. Geochemistry and petrology of mafic enclaves of metasedimentary origin: case study from the Peninsular Ranges Batholith, California (United States)

    Liao, K.; Morton, D.; Lee, C.


    Dark clasts rich in amphibole or biotite, commonly referred to as "mafic enclaves", are frequently found in felsic plutons and are traditionally interpreted to represent fragments of mafic magmas, such as basalt, entrained by or intruded into felsic magma bodies. However, during emplacement, magmas often assimilate pre-existing wallrock, begging the question of whether some dark enclaves might have non-igneous protoliths. To investigate this process of forming dark enclaves in more detail, we examined the Cretaceous Domenigoni Valley pluton in the Peninsular Ranges Batholith in southern California. This pluton was emplaced into pre-existing metamorphic country rock, composed of Paleozoic to early Mesozoic calc-silicates, phyllites, and calcareous quartzites. Dark enclaves, in the form of amphibole- or biotite-bearing angular fragments, are abundant in the pluton. However, evidence for wallrock stoping is also seen in the extensive presence of wallrock xenoliths in varying extents of thermal and chemical equilibration with the host tonalite pluton. Enclaves with a clear calc-silicate protolith are represented by quartz-diopside-wollastonite-plagioclase rocks, whereas enclaves with clear pelitic protoliths are represented by biotite-quartz-alkali feldspar rocks. Several lines of evidence, however, suggest that the dark amphibole-rich and biotite-rich enclaves, although mafic in composition (high Mg and Fe), represent the fully equilibrated state of these assimilated wallrocks rather than fragments of basaltic magmas. First, many of the dark, biotite- and amphibole-bearing enclaves have SiO2 contents greater than 60 %, too high to represent typical mafic magmas. Second, although some biotite-rich enclaves have SiO2 contents dark amphibole-bearing enclaves have bulk Al and K lower than the host tonalite but similar to the quartz-diopside-wollastonite-plagioclase rocks thought to have a calc-silicate protolith. Fourth, composite enclaves exist wherein hornblende

  9. Origin and tectonic implications of the ∼200 Ma, collision-related Jerai pluton of the Western Granite Belt, Peninsular Malaysia (United States)

    Jamil, Azmiah; Ghani, Azman A.; Zaw, Khin; Osman, Syamir; Quek, Long Xiang


    Triassic granitoids (∼200-225 Ma) are widespread in the Western Belt of Peninsular Malaysia. The Main Range granite is the biggest batholith in the Western Belt composed of peraluminous to metaluminous granite and granodiorite and displays typical ilmenite-series characteristics. Jerai granitic pluton occurs at the northwestern part of the Main Range granite batholith. The Jerai granite can be divided into three facies: (i) biotite-muscovite granite; (ii) tourmaline granite; and (iii) pegmatite and aplopegmatite. Biotite-muscovite granite accounts for 90% of the Jerai pluton, and the rest is tourmaline granite. Geochemical data reveal that pegmatite and tourmaline granite are more differentiated than biotite-muscovite granite. Both pegmatite and tourmaline granite have a higher SiO2 content (70.95-83.94% versus 69.45-73.35%) and a more pronounced peraluminous character. The U-Pb zircon geochronology of the Jerai granite gave an age ranging from 204 ± 4.3 Ma, 205 ± 4 Ma and 205 ± 2 Ma for pegmatite biotite-muscovite granite and tourmaline granite, respectively. The biotite-muscovite Jerai granites are similar to S-type Main Range granite, but the tourmaline granite has a signature of late-stage hydrothermal fluid interaction such as tourmaline quartz pods, the accumulation of large pegmatitic K-feldspar, pronounced peraluminous character, higher SiO2 content. Age evidence of these two granitic facies suggest that they are from the same magma.

  10. The key role of mica during igneous concentration of tantalum (United States)

    Stepanov, Aleksandr; A. Mavrogenes, John; Meffre, Sebastien; Davidson, Paul


    Igneous rocks with high Ta concentrations share a number of similarities such as high Ta/Nb, low Ti, LREE and Zr concentrations and granitic compositions. These features can be traced through fractionated granitic series. Formation of Ta-rich melts begins with anatexis in the presence of residual biotite, followed by magmatic crystallization of biotite and muscovite. Crystallization of biotite and muscovite increases Ta/Nb and reduces the Ti content of the melt. Titanium-bearing oxides such as rutile and titanite are enriched in Ta and have the potential to deplete Ta at early stages of fractionation. However, mica crystallization suppresses their saturation and allows Ta to increase in the melt. Saturation with respect to Ta and Nb minerals occurs at the latest stages of magmatic crystallization, and columbite can originate from recrystallization of mica. We propose a model for prediction of intrusion fertility for Ta.

  11. An identification study of vermiculites and micas. Adsorption of metal ions in aqueous solution

    Energy Technology Data Exchange (ETDEWEB)

    Alexandre-Franco, Maria; Gomez-Serrano, Vicente [Extremadura Univ., Badajoz (Spain). Dept. doe Quimica Organica e Inorganica; Albarran-Liso, Angel [Extremadura Univ., Badajoz (Spain). Escuela de Ingenieros Agronomos


    This study deals with the identification of vermiculite in the presence of mica. Three natural silicates were first subjected to expansion by rapid heat treated at 400 C. Then, the starting silicates and their derived heat-treated products were analyzed by X-ray diffraction, FT-IR spectroscopy, N{sub 2} adsorption at - 196 C, and helium density measurement. The adsorption of cadmium, chromium, and lead was also carried out. Two of the silicates are composed of mainly biotite and the other of biotite and vermiculite. In general, the results of X-ray diffraction, FT-IR spectroscopy, and helium density measurements are well in agreement. The heat treatment at 400 C has little effect on the chemical composition, structure, and texture of the silicates. The development of microporosity is small in the silicates. Surprisingly, the adsorption capacity toward chromium and lead is larger for the biotite silicate than for the vermiculite containing silicate. (author)

  12. Mineral Chemistry and Pressure and Temperature Estimates of Metasedimentary Rocks of the Araxá Group in the Region of Morrinhos, South of Goiás State

    Directory of Open Access Journals (Sweden)

    Guillermo Rafael Beltran Navarro


    Full Text Available In the Morrinhos region, Goiás state, Brazil, the rocks of the Araxá Group have mineral assemblages related to themetamorphic peak which occurred in this region and is typical of the amphibolite facies (kyanite zone. These rocks areassociated with the initial stage of the main ductile deformation that occurred in this area. Thermobarometric calculations,including the associations, garnet + plagioclase + biotite + muscovite; garnet + plagioclase +biotite + muscovite + kyanite;garnet + plagioclase + biotite + muscovite + amphibole, with quartz in excess, indicate that the metamorphic peak occurredat temperatures of approximately 610ºC and pressures in the order of 10 kbar. The P-T path is probably clockwise and is inagreement with the tectonic conditions observed in collisional settings.

  13. Structural controls and evolution of gold-, silver-, and REE-bearing copper-cobalt ore deposits, Blackbird district, east-central Idaho: Epigenetic origins (United States)

    Lund, K.; Tysdal, R.G.; Evans, K.V.; Kunk, M.J.; Pillers, R.M.


    The Cu-Co ± Au (± Ag ± Ni ± REE) ore deposits of the Blackbird district, east-central Idaho, have previously been classified as Besshi-type VMS, sedex, and IOCG deposits within an intact stratigraphic section. New studies indicate that, across the district, mineralization was introduced into the country rocks as a series of structurally controlled vein and alteration systems. Quartz-rich and biotite-rich veins (and alteration zones) and minor albite and siderite veinlets maintain consistent order and sulfide mineral associations across the district. Both early and late quartz veins contain chalcopyrite and pyrite, whereas intermediate-stage tourmaline-biotite veins host the cobaltite. Barren early and late albite and late carbonate (generally siderite) form veins or are included in the quartz veins. REE minerals, principally monazite, allanite, and xenotime, are associated with both tourmaline-biotite and late quartz veins. The veins are in mineralized intervals along axial planar cleavage, intrafolial foliation, and shears.

  14. Geochemistry and Geochronology U-Pb SHRIMP of granites from Peixoto de Azevedo: Alta Floresta Gold Province; Geoquimica e geocronologia U-Pb (SHRIMP) de granitos da regiao de Peixoto de Azevedo: Provincia Aurifera Alta Floresta, MT

    Energy Technology Data Exchange (ETDEWEB)

    Silva, Fernanda Rodrigues da; Barros, Marcia Aparecida Sant' Ana; Pierosan, Ronaldo; Pinho, Francisco Edigio Cavalcante; Tavares, Carla; Rocha, Jhonattan, E-mail:, E-mail:, E-mail:, E-mail:, E-mail:, E-mail: [Universidade Federal de Mato Grosso (UFMT), Cuiaba, MT (Brazil). Inst. de Ciencias Exatas e da Terra; Rocha, Mara Luiza Barros Pita; Vasconcelos, Bruno Rodrigo; Dezula, Samantha Evelyn Max, E-mail:, E-mail:, E-mail: [Universidade de Brasilia (UNB), Brasilia, DF (Brazil). Programa de Pos-Graduacao em Geologia


    The analysis of petrographic, geochemical and geochronological data of granites in the Peixoto de Azevedo region, Mato Grosso, Brazil, in the eastern portion of the Alta Floresta Gold Province, led to the recognition of two granitic bodies bounded by regional major faults and shear zones. In the northwestern portion a body with featured as biotite granodiorite, coarse-grained, with porphyritic to inequigranular texture, metaluminous to peraluminous, high-K calc-alkaline and magnesium character. In the southeastern portion of the area, a biotite monzogranite coarse-grained, with equigranular to porphyritic texture, slightly peraluminous, high-K calc-alkaline and dominantly of ferrous character. U- Pb dating (SHRIMP) showed that the biotite monzogranite has an age of 1869 ± 10 Ma, similar to the Matupa Intrusive Suite, while the biotite granodiorite has an age of 1781 ± 10 Ma, that is the age expected to Peixoto Granite. Both units show patterns of rare earth elements with enrichment of light over heavy and negative Eu anomaly (La{sub N}/Yb{sub N} » 7.6 to 17.31 and ratios Eu/EU{sup ⁎} between 0.46 – 0.72 for biotite monzogranite and La{sub N}/Yb{sub N} » 7.13 to 29.09 with ratios Eu/Eu{sup ⁎} between 0.25 - 0.40 for the biotite granodiorite). Trace elements pattern for both present negative anomalies of Ba, P, Ti and Nb indicating an evolution from mineral fractionation and subduction related sources. In this paper, it is suggested that the monzogranite Matupa was developed in mature arc tectonic environment. For the Peixoto Granite, two hypotheses are suggested: (a) it was developed in younger magmatic arc environment associated with the Colider Magmatism or (b) it was generated in extensional tectonic environment during the Columbia Super continent break up. (author)

  15. Alpine orogenic evolution from subduction to collisional thermal overprint: The 40Ar/39Ar age constraints from the Valaisan Ocean, central Alps

    DEFF Research Database (Denmark)

    Wiederkehr, Michael; Sudo, Masafumi; Bousquet, Romain;


    in general. The timing of high-pressure metamorphism, subsequent retrogression and following Barrow-type overprint was studied by 40Ar/39Ar dating of biotite and several white mica generations that are well characterized in terms of mineral chemistry, texture and associated mineral assemblages. Four distinct...... age populations of white mica record peak pressure conditions (42–40 Ma) and several stages of subsequent retrograde metamorphic evolution (36–25 Ma). Biotite isotopic analyses yield consistent apparent ages that cluster around 18–16 Ma for the Barrow-type thermal overprint. The recorded isotopic data...

  16. U-Pb Zircon Dating of the Yeniutan Granitic Intrusion in the Western Sector of the North Qilian Mountains

    Institute of Scientific and Technical Information of China (English)


    Zircons from granodiorite and biotite granite in the Yeniutan granitic intrusion in the western North Qilian Mountains ylelded a weighted mean 206PH/apparent age of 460±3Ma, suggesting that the intrusion originated during the late stage of plate subuotion Its related Ta’ergou and Xiaoliugou deposits are two of the few large tungsten deposits formed in the plate subduction environment in the world. The U-Pb dating of the zircons from the biotite granite gave a discordant lower intercept age of 183±4 Ma, which implies that the Yanshanian event was probably superimposed on the North Qilian region.

  17. First direct radiometric dating of the Tortonian/Messinian boundary

    International Nuclear Information System (INIS)

    New volcanogenic layers found in the Northern Appennines of Romagna at the Tortonian/Messinian transition have been dated. The Globorotalia suterae FAD yielded a date of 7.72±0.15 Ma (K/Ar on biotites). The boundary taken as the Globorotalia conomiozea FAD is closely predated by 7.33 Ma (K/Ar on biotite and 39Ar/40Ar on plagioclase). An age of 7.26±0.10 Ma for the boundary is suggested. There are appropriate conditions for placing here the related Global Stratotype Section and Point

  18. An oxygen buffer for some peraluminous granites and metamorphic rocks. (United States)

    Zen, E.


    The mineral assemblage biotite-garnet-muscovite-magnetite-quartz and its sub-sets are common in many peraluminous granites, schists and gneisses. If the biotite and garnet are reasonably iron-rich, then the system is a useful buffer for fO2. Available thermochemical data indicate that, in T-fO2 space, the buffer curve is located between the hematite-magnetite curve and the quartz-magnetite-fayalite curve, in a region that previously had no buffer curve applicable to peraluminous rocks. -J.A.Z.

  19. Evaluation of geochronologic data from Granja Complex (CE, Brazil)

    International Nuclear Information System (INIS)

    This paper describes the geochronological data of Chaval Granitoid and the reinterpretation of the geological evolution of Granja Complex. The Chaval Granitoid, situated on the peak of Granja Complex, gave the Rb/Sr isochronic age of 507±27 Ma for initial ratio of 0,70557±0,00013. The Granja Complex area, characterized by a significant lithological alteration was dating with k/Ar in isolated minerals, giving 566±17 Ma for migmatite, (hornblend), 429±13 Ma for gneisses, (biotite), 627±19 Ma for granite (hornblende) and 512±15 Ma for granite (biotite). (C.G.C.)

  20. Las rocas básicas de Monte Castelo (La Coruña)

    NARCIS (Netherlands)

    Warnaars, F.W.


    A gabbroic complex is found 30 km to the North of Santiago de Compostela, Galicia. It turns out to be a multiple intrusion of different sills with a North-South trend. The borders of the sills are indicated by the occurrence of biotite and garnet, and sometimes xenoliths were found. Reaction-equatio

  1. Delineation of structures favourable to groundwater occurrence employing seismic refraction method — A case study from Tiruvuru, Krishna district, Andhra Pradesh

    Indian Academy of Sciences (India)

    N Sundararajan; Y Srinivas; M Narasimha Chary; G Nandakumar; A Hanmantha Chary


    The contacts associated with an outlier in biotite gneiss and sandstones near Tiruvuru, Krishna district, Andhra Pradesh which are generally favourable for groundwater occurrence were investigated employing refraction seismic method. Results were examined by correlating the signals with local geology, bore well data and other available information in order to improve the reliability of interpretation.

  2. A polyphase metamorphic evolution for the Xitieshan paragneiss of the north Qaidam UHP metamorphic belt, western China: In-situ EMP monazite- and U-Pb zircon SHRIMP dating

    NARCIS (Netherlands)

    Zhang, C.; Roermund, H.L.M. van; Zhang, L.; Spiers, C.


    In-situ electron microprobe (EMP) U–Th–Pbmonazite-, sensitive high-resolution ion microprobe (SHRIMP) zircon analyses, metamorphic phase equilibrium (Domino/Theriak)- and geothermobarometric calculations are performed on kyanite/sillimanite-bearing garnet biotite gneisses forming part of the dominan

  3. Data on the mineralogy and petrology of the dolomite-bearing northern contact zone of the Quérigut granite French Pyrenees

    NARCIS (Netherlands)

    Struwe, H.


    The northern part of the contact aureole of the biotite-granite of Quérigut contains limestones and dolomites, which have been metamorphosed over a distance of about 100 to 150 metres. Further, a wide innermost border zone of the igneous body is characterized by the development of some hornblende an

  4. 西藏南部花岗岩类中重结晶的黑云母与板块碰撞的关系

    Institute of Scientific and Technical Information of China (English)



    Recrystallized biotite occurs in granitoid rocks from some plutens in the Lhagoi Kangri and Kangdese belts in southern Xizang. These plutons are characterized by well-developed micro-fractures, orientational arrangement of dark minerals showing gneissose structures to varing extents. This is consistent with the fact that K-Ar ages of crystallized biotite (30--17 my) are much younger as compared with the host rooks. Recrystallized biotites are mostly recognized along the tectonic suture line between the Indian plate and the Eurasian continental plate, i.e., in the neighborhood of the Yarlung Zangbo River and its north bank as well as in the Lhagoi Kangri Ranges.The authors postulate that when drifting north-northeastward, the Indian sub-continental plate was conteracted by the Kangdese belt as a result of the subduction of the Indian plate underneath the Eurasian Continental plate, causing a dramatic increase instress on the southern side, i.e., near the tectanic suture line, of the rock belt followed by the rising of temperature which resulted in the recrystallization of biotite in some plutons.

  5. Differences of granitic weathering at the northern and southern feet of Dabie Mountains, Central China: Implication for tectonic and climatic environments

    Institute of Scientific and Technical Information of China (English)

    XU; Haijin(续海金); MA; Changqian(马昌前); LIU; Fan(刘凡); YANG; Kunguang(杨坤光)


    Two weathering profiles of Yanshanian granites on the southern and northern feet of the Dabie Mountains were investigated. The results showed that, on the southern foot of the Dabie Mountains, the weathering profile of the Sikongshan biotite monzonitic granite was eroded with remarkable loss of alkila, calcium and silicon, and richness of aluminium during hydrolysis process and in acidic mediums. Feldspar and biotite, major rock-forming minerals, were altered to illite→(vermiculite→1.4 nm transition minerals) →kaolinite→halloysite. However, on the northern foot of the Dabie Mountains, the Hepeng biotite orthogranite weathering profile was stable, without silicon depletion, but with remarkably enriched iron and noncrystalline during oxidizing process and in feebly acidic-neutral mediums. The major rock-forming minerals such as feldspar and biotite in the Hepeng weathering profile were weathered to smectites and halloysite→noncrystalline. The above results reveal that weathering differences of the granites between southern and northern feet of the Dabie Mountains may be related to climatic environments and tectonic movements. The southern foot, in hot and rainy environments, was uplifted by tectonics and was intensively leached. The soils in the southern slope were under acidic conditions. In contrast, the northern foot was slightly leached in hot and droughty environments, and the soils were under feebly acidic-neutral conditions.

  6. Geology and associated mineral occurrences of the Araxa Group, Mossamedes Region, Goias, Brazil

    International Nuclear Information System (INIS)

    In the region of Mossamedes, State of Goias, Brazil, the Precambrian metamorphic rocks of the Araxa group were mapped at the scale of 1:25,000, with emphasis on stratigraphic, structural, petrographic and economic aspects. These metamorphites represent a continous stratigraphic sequence which, from bottom to top can be subdivided into five informal lithostratigraphic units: 1) psamitic unit (quartzite, metaconglomerate); 2) psamitic-pelitic unit (quartzite, quartz schist, muscovite schist); 3) lower pelitic - volcanic unit (chlorite - biotite schist, fine grained blastoporphyritic gneiss, amphibolite and calc-schist); 4) upper pelitic - volcanic unit (garnet muscovite schist, biotite schist and gneiss, amphibolite, magnetite muscovite schist); 5) gneissic unit (epidote biotite gneiss, amphibolite). Three types of meta-intrusive rocks were found, besides basic dykes related to Mesozoic magmatism. Four phases of deformation affected the volcano-sedimentary sequence;D1, D2, D3 and D4, each of them developing distinct deformational features. Barrowian type metamorphism increases progressively from North to South from the biotite zone to the garnet zone (greenschist facies), reaching the staurolite-kyanite zone (amphibolite facies). The magmatism throughout the Group's evolution consists of mafic to felsic volcanic activity, mustly intermediary, as well as three intrusive events. Gold, copper and zinc minerals of economic interest occur within the studied area. The gold mineralizations are related to the pelitic-volcanic sequences. Copper occurs in several rocks from the pelitic-volcanic and gneissic sequences. (Author)

  7. Radioelemental, petrological and geochemical characterization of the Bundelkhand craton, central India: implication in the Archaean geodynamic evolution (United States)

    Ray, Labani; Nagaraju, P.; Singh, S. P.; Ravi, G.; Roy, Sukanta


    We have carried out radioelemental (232Th, 238U, 40K), petrological and geochemical analyses on granitoids and gneisses covering major rock formations of the Bundelkhand craton, central India. Our data reveal that above characteristics are distinct among granitoids (i.e. pink, biotite and grey granitoids) and gneisses (i.e. potassic and sodic types). Pink granitoid is K-feldspar-rich and meta-aluminous to per-aluminous in character. Biotite granitoid is meta-aluminous in character. Grey granitoid is rich in Na-feldspar and mafic minerals, granodiorite to diorite in composition and meta-aluminous in character. Among these granitoids, radioelements (Th, U, K) are highest in pink granitoid (45.0 ± 21.7 ppm, 7.2 ± 3.4 ppm, 4.2 ± 0.4 %), intermediate in biotite granitoid (44.5 ± 28.2 ppm, 5.4 ± 2.8 ppm, 3.4 ± 0.7 %) and lowest in grey granitoid (17.7 ± 4.3 ppm, 4.4 ± 0.6 ppm, 3.0 ± 0.4 %). Among gneisses, potassic-type gneisses have higher radioelements (11.8 ± 5.3 ppm, 3.1 ± 1.2 ppm, 2.0 ± 0.5 %) than the sodic-type gneisses (5.6 ± 2.8 ppm, 1.3 ± 0.5 ppm, 1.4 ± 0.7 %). Moreover, the pink granitoid and the biotite granitoid have higher Th/U (6 and 8, respectively) compared to the grey granitoid (Th/U: 4), implying enrichment of Th in pink and biotite granitoids relative to grey granitoid. K/U among pink, biotite and grey granitoids shows little variation (0.6 × 104, 0.6 × 104, 0.7 × 104, respectively), indicating relatively similar increase in K and U. Therefore, mineralogical and petrological data along with radioelemental ratios suggest that radioelemental variations in these lithounits are mainly related to abundances of the radioactive minerals that have formed by the fractionation of LILE from different magma sources. Based on present data, the craton can be divided into three distinct zones that can be correlated with its evolution in time and space. The central part, where gneisses are associated with metavolcanics of greenstone belt, is

  8. A geochemical investigation of selected areas in Greenville and Laurens counties, South Carolina--implications for mineral resources (United States)

    Jackson, John C.


    around the study areas have undergone sillimanite-muscovite-grade metamorphism (Nelson, 1988, p. 9). Nelson (1988, p. 13) reports that the Six Mile thrust sheet was metamorphosed about 344 Ma. The geology of these sheets as described in this study, including geologic contacts, rock descriptions, and unit names, generally follows that of Nelson and others (1987, 1989). Within the Paris Mountain study area, rocks of the Paris Mountain thrust sheet predominate (fig. 2) and consist of a biotite-muscovite-sillimanite schist (EZsp) that has extensive lenses of fine- to medium- grained biotite granite gneiss (Pzgp). Areas of biotite granite gneiss that occur in the southern part of the Paris Mountain study area contain extensive pegmatitic and leucogranitic phases. These pegmatitic zones consist mostly of coarse-grained microcline feldspar and quartz with minor amounts of muscovite, biotite, and garnet. Smaller pegmatite lenses (mineralogy, although some contain tourmaline crystals up to 5 cm in length. The Six Mile thrust sheet underlies the northern edge of the Paris Mountain study area, where it is composed of gneissic biotitic granites of the Caesars Head Granite (figs. 1 and 2). The northwestern part of the Simpsonville study area (figs. 1 and 3), within the Paris Mountain thrust sheet, is underlain by a biotite-muscovite-sillimanite schist (EZsp) that contains lenses of biotite granite gneiss (Pzgp). In the southeastern part of the Simpsonville study area, within the Laurens thrust sheet, biotite gneiss (EZgl), biotite granite gneiss (Pzgf), and minor amphibolite (EZal) are interlayered biotite (EZgl), granite gneiss (Dgg), and amphibolite (EZal) of the Laurens thrust sheet (fig. 4).

  9. Further support for a Cretaceous age for the feathered-dinosaur beds of Liaoning,China:New 40Ar/39Ar dating of the Yixian and Tuchengzi Formations

    Institute of Scientific and Technical Information of China (English)


    We report new 40Ar/39Ar dating results obtained from total fusion and incremental-heating analyses of sanidine and biotite from three tuffs found interbedded within the fossil-bearing deposits of Liaoning, northeast China. The first is a new sample of the Bed 6 Sihetun tuff from the Yixian Formation, previously dated by our team as middle Early Cretaceous, and recently considered by Lo et al., partially reset due to metamorphism from a nearby basaltic sill. The second is the Yixian Bed 9 tuff from Hengdaozi considered by Lo et al. to be unaffected by metamorphism and whose age, based on total fusion 40Ar/39Ar dating of biotite, argues for a Jurassic age for the Yixian Formation.The third tuff is a previously undated tuff from the upper part of the underlying Tuchengzi Formation. Single crystal total fusion 40Ar/39Ar analyses of the Sihetun sanidine showed homogeneous radiogenic Ar, Ca/K ratios, excellent reproducibility and gave a mean age of 125.0 ± 0.18 (1SD) ±0.04 (SE) Ma. Single sanidine crystal total fusion 40Ar/39Aranalyses of the Hengdaozi tuff gave a mean age of 125.0 +0.19 (1SD) ± 0.04 (SE) Ma, which is indistinguishable from the Sihetun tuff. The Tuchengzi Formation tuff gave a mean age of 139.4 ± 0.19 (1SD) ± 0.05 (SE) Ma. Detailed laser incremental-heating analyses of biotite from Sihetun, Hengdaozi, and Tuchengzi tuffs show disturbed Ar release patterns and evidence of trapped argon components. We conclude from these analyses that the total fusion dates on biotite by Lo et al. are erroneously old and isotopic dating of both biotite and sanidine from tuffs of the Yixian Formation point to a middle Early Cretaceous age. The upper part of the Tuchengzi Formation can be referred to the Early Cretaceous.``

  10. Petrography and geochemical study of Nezam-Abad area, Southwest of Shazand, Arak

    Directory of Open Access Journals (Sweden)

    Robabeh Jafari


    Full Text Available Nezam-Abad area is located in southwest of Shazand (Arak which is a part of Sanandaj-Sirjan zone. Major intrusive rocks of Nezam-Abad are quartz diorite and minor amount of granodiorite. Leucogranitic, pegmatite dykes and quartz-tourmaline veins were intruded the quartz diorite. Quartz diorites are mainly composed of plagioclase, hornblende, biotite, quartz and pyroxene as major minerals. Major minerals of leucogranite are microcline, orthoclase, albite, quartz, biotite and muscovite. Accessory minerals consist of apatite, zircon, sphene, epidote, allanite, tourmaline and opaque. The presence of hydrous minerals like hornblende and biotite in these rocks indicate that the corresponding magma initially contained >3 wt% H2O (wet magma. The occurrences of garnet and andalusite minerals suggest assimilation process. Primary textures in these rocks are granular, granophyre, and poikilitic. Secondary textures are perthite, myrmekite, sericitization, chloritization and kaolinitization. Later hydrothermal activities and tectonic strains are factors for presence of perthite texture in leucogranite. K amount for sericitization of feldspars come from the K-feldspars and chloritization of biotite. Transformation of biotite to muscovite indicates the act of K rich fluid in later stages. On the basis of chemical analysis on the intrusive rocks, it is shown that the magma was calc-alkaline, metaluminous-peraluminous and medium-K to high-K. Study of major elements in Harker diagrams indicates Al2O3, FeO, Fe2O3 and CaO decrease with increasing of SiO2 and K2O and Na2O increase indicating that fractional crystallization may have played an important role in the formation of granitoid rocks from Nezam-Abad.

  11. Primary uranium sources for sedimentary-hosted uranium deposits in NE China: insight from basement igneous rocks of the Erlian Basin (United States)

    Bonnetti, Christophe; Cuney, Michel; Bourlange, Sylvain; Deloule, Etienne; Poujol, Marc; Liu, Xiaodong; Peng, Yunbiao; Yang, Jianxing


    Carboniferous-Permian, Triassic and Jurassic igneous basement rocks around the Erlian Basin in northeast China have been investigated through detailed mineralogical, whole-rock geochemistry, geochronological data and Sm-Nd isotope studies. Carboniferous-Permian biotite granites and volcanic rocks belong to a calc-alkaline association and were emplaced during the Late Carboniferous-Early Permian (313 ± 1-286 ± 2 Ma). These rocks are characterised by positive ɛNd(t) (3.3-5.3) and fairly young T DM model ages (485-726 Ma), suggesting a dominant derivation from partial melting of earlier emplaced juvenile source rocks. Triassic biotite granites belong to a high-K calc-alkaline association and were emplaced during the Middle Triassic (243 ± 3-233 ± 2 Ma). Their negative ɛNd(t) (-2 to -0.1) and higher T DM model ages (703-893 Ma) suggest a contribution from Precambrian crust during the magma generation processes, leading to a strong enrichment in K and incompatible elements such as Th and U. Highly fractionated magmas crystallised in U-rich biotite (up to 21 ppm U) and two-mica granites. In biotite granite, the major U-bearing minerals are uranothorite and allanite. They are strongly metamict and the major part of their uranium (90 %) has been released from the mineral structure and was available for leaching. Mass balance calculations show that the Triassic biotite granites may have, at least, liberated ˜14,000 t U/km3 and thus correspond to a major primary uranium source for the U deposits hosted in the Erlian Basin.

  12. Retention of 137Cs and 90Sr by mineral sorbents surrounding vitrified nuclear waste

    International Nuclear Information System (INIS)

    In June 1960, twenty-five 14-cm diameter hemispheres of vitrified nuclear waste (glass blocks) were buried in a shallow sand aquifer in the lower Perch Lake Basin, Chalk River Nuclear Laboratories, Ontario, Canada. Almost all leaching of the glass blocks occurred during the first 18 months of emplacement, and consequently the burial experiment approximated a single-injection source of 137Cs and 90Sr. After about 11 years, most of the 90Sr that was released had been advected and dispersed from the site, whereas the bulk of the 137Cs had travelled no more than 0.3 m from the blocks. Three piezometers were installed and five cores of sediment were collected at the glass block site in 1978. Mineralogically pure segregates of sand grains were prepared by hand and characterized using binocular, petrographic and scanning electron microscopy, X-ray diffraction, and energy-dispersive X-ray spectroscopy. A technique also was developed to measure very low levels of 137Cs and 90Sr by counting small (10-100 mg) sediment samples directly with a thin window, flow proportional counter. Results show that sand-sized grains of altered biotite (biotite-vermiculite), biotite, muscovite, hornblende and serictized feldspar are able to retain 137Cs over a period of 18 years, and that grains of biotite-vermiculite, biotite and hematite-bearing feldspar (largely microline) can retain low levels of 90Sr over the same period of time. The amounts of 137Cs and 90Sr sorbed by the mineral grains ranged from undetectable levels to approximately 380 and 35 becquerels/gram sediment, respectively. This report contains the complete series of mineral segregates ranked on a weight basis according to the amounts of retained 137Cs and 90Sr. Ground-water quality data indicate that none of the retention is the result of the precipitation of strontium or cesium minerals

  13. Evidence of pre-Gondwana tectono-thermal event from the Bhilwara Supracrustal units of Rajasthan, north-west India (United States)

    Saha, Lopamudra; Sarkar, Saheli; Rakshit, Nibedita; Nasipuri, Pritam


    In the Indian subcontinent, two pre- Gondwana (pre- Pan African) orogenies are mostly recorded and well-studied from the Eastern Ghat Mobile Belt: (i) >1.1 Ga and (ii) ~950 Ma. During the ~950Ma orogeny, the pre-existing granulites have been re-melted under granulite facies conditions at ~8 kbar, 800-850ºC in the sillimanite stability field with formation of garnet-orthopyroxene in the restites. In this study we report garnet-sillimanite bearing and garnet-staurolite-kyanite bearing supracrustal rocks from the Bhilwara Supergroup in Rajasthan, N-W India. Peak assemblage in the garnet-sillimanite bearing metapelite is: garnet-sillimanite-biotite-plagioclase-quartz. Garnet porphyroblasts contain sillimanite-biotite bearing inclusion trails. Matrix foliations consist of biotite, sillimanite, quartz. Peak pressure-temperature calculated for garnet formation are ~7-8 kbar, 800ºC. Garnet is replaced along the margins by biotite during retrogression. Within garnet-staurolite-kyanite schist, peak assemblage is formed of garnet-staurolite-biotite-kyanite quartz, where garnet and staurolite occur as porphyroclasts and the matrix foliations are formed of kyanite-biotite-quartz. Mineral assemblages and compositions in the rock indicate peak pressure-temperature >8 kbar, 600ºC. The ages of the metamorphic events at sillimanite and kyanite facies are not well-constrained. However since the Bhilwara supracrustal units occur close to the Grenvillian orogenic belt at Sandmata Complex, the timing of the peak metamorphism can be constrained at ~1.0 Ga. Garnet-sillimanite-bearing assemblages noted in the Bhilwara Supracrustal Belt, has also been noted from the Grenvillian belts in the Eastern Ghat Mobile Belt. So the question that needs to be addressed is whether the Grenvillian orogenic belt recorded form the Sandmata Complex in Rajasthan and that of the Eastern Ghat Belt had been a continuous orogenic belt? Such possibilities can be addressed by establishing detailed structural

  14. Geología y petrología de los granitoides del sur de la Sierra de Comechingones, Córdoba, Argetina

    Directory of Open Access Journals (Sweden)

    Otamendi, J. E.


    Full Text Available The petrography and petrology characteristics of a group of granitoid bodies from the crystalline basement of Southern Comechingones Hills, is described here.In the metamorphic Complex biotitic gneisses, anphibolites, marbles and metabasic rocks were recognized. The main metamorphic episode in this area reached high-temperature within medium grade conditions.These granitoid are: biotitic granites, leucogranites and gneissic granites.The biotitic granites, with biotite, apatite sillimanite and garnet, are elongate bodies, concordant with the main penetrative schistosity. Have medium to small grain, with an important foliation, shown by the lineation of micaceous minerals.The muscovite, garnet, tourmaline, dumortierite and biotite leucogranites have tabular shape, and an extension more than one kilometre.The gneissic granites are plutons that intruded concordant to the regional structural trend. Biotite, sillimanite, monacite and apatite minerals are characteristic of these rocks. Radimetric ages obtained in nearby areas, show that granitoids may be of Lower Paleozoic age.Geology and petrology characteristics of granitoids suggest that they may have been produced by partial melt of crustal metasedimentary rocks.Se describe la petrografía y petrología de los granitoides aflorantes en el basamento cristalino del sur de la Sierra de Comechingones.Dentro del complejo metamórfico regional predominan gneises biotíticos, paranfibolitas, mármoles y metabasitas. El evento metamórfico principal alcanzó condiciones de alta temperatura dentro del grado medio.Entre los granitoides se reconocieron los siguientes tipos litológicos: granitos biotíticos, leucogranitos y granitos gnéisicos.Los granitos biotíticos con apatito, sillimanita y granate conforman cuerpos elongados, concordantes con la esquistosidad penetrativa principal. Son de grano fino a medio, con marcada foliación, dada por la alineación de elementos micáceos.Los leucogranitos, cuyos

  15. Kabbaldurga-type charnockitization: A local phenomenon in the granulite to amphibolite grade transition zone (United States)

    Raith, M.; Staehle, H. J.; Hoernes, S.


    In the deeply eroded Precambrian crust of South India and Sri Lanka, a series of spectacular exposures shows progressive development of coarse-grained charnockite through dehydration of amphibolite grade gneisses in different arrested stages. At Kabbaldurga, charnockitization of Archaean grey biotite-hornblende gneisses occurred about 2.5 Ga ago and evidently was induced by the influx of external carbonic fluids along a system of ductile shears and the foliation planes. The results of oxygen isotope thermometry and of geothermobarometry in adjacent areas indicate a P-T regime of 700 to 750 C and 5 to 7 kb. The decrease of water activity in the fluid infiltrated zones caused an almost complete breakdown of hornblende and biotite and the new growth of hypersthene. Detailed petrographic and geochemical studies revealed marked changes in mineralogy and chemistry from granodioritic to granitic which document the metasomatic nature of the process.

  16. 我国某地含褐钇钶矿碱性花岗岩的特征

    Institute of Scientific and Technical Information of China (English)



    The fergusonite alkaline granite referred to in this paper is a complex consisting of acmite-augite riebeckite granite, riebeckite granite and biotite riebeckite granite. Its principal rock-forming minerals include acmite-augite, riebeckite, quartz, perthite and biotite, with fergusonite, zircon, magnetite and galena as its accessary minerals. Astrophyllite and thorite are abundant in a late alkali granite dike. Petrochemically, it is rich in K, Na, Si, and such rare metals as Nb, Ta, Y, Yb, Zr and Hf, but depleted in Al and Ca. In comparison with that found in other types of granite, the fergusonite in the alkaline granite has higher ferromagnesian components, thorium, niobium, but lower rare earths and tantalum.

  17. New Rb-Sr mineral ages temporally link plume events with accretion at the margin of Gondwana (United States)

    Flowerdew, M.J.; Daly, J.S.; Riley, T.R.


    Five of six Rb-Sr muscovite mineral isochron ages from the Scotia Metamorphic Complex of the South Orkney Islands, West Antarctica, average 190 ± 4 Ma. The muscovite ages are interpreted to date foliation-formation and thus also accretion and subduction at the Gondwana margin. Coincident picrite and ferropicrite magmatism, indicative of melts from deep-seated depleted mantle, permits a causative link between accretion and the arrival of the Karoo – Ferrar – Chon Aike mantle plume in the Early Jurassic. Three biotite Rb-Sr mineral isochron ages are consistently younger and average 176 ± 5 Ma. The biotite ages may record post-metamorphic cooling or more likely retrogressive metamorphic effects during uplift.

  18. Bone Response to Four Dental Implants with Different Surface Topographies: A Histologic and Histometric Study in Minipigs. (United States)

    Kalemaj, Zamira; Scarano, Antonio; Valbonetti, Luca; Rapone, Biagio; Grassi, Felice Roberto


    This study evaluated four implant surfaces in a minipig model: (1) Kohno Straight dual-engineered surface (DES) (Sweden & Martina); (2) SLActive (Straumann); (3) SM Biotite-H coated with Brushite (DIO); and (4) UF hybrid sandblasted and acid etched (HAS) (DIO). The surfaces presented different topographic features on the macro-, micro-, and nanoscales. After 12 weeks in vivo, significant differences were observed in bone-to-implant contact. UF HAS, presenting moderate microroughness and high nanoroughness, showed some advantage compared to nanorough SM Biotite-H and SLActive. A more pronounced difference was observed between UF HAS and Kohno Straight DES, characterized by a nanosmooth surface. Newly formed bone was observed around all surfaces. PMID:27560680

  19. Molybdenum mineralization at Alpeiner Scharte, Tyrol (Austria): results of in-situ U Pb zircon and Re Os molybdenite dating (United States)

    Langthaler, K. J.; Raith, J. G.; Cornell, D. H.; Stein, H. J.; Melcher, F.


    Vein-type Mo mineralization at Alpeiner Scharte occurs in the Penninic units of the western Tauern Window in the Eastern Alps. Three types of previously undated metagranitoids (central gneisses) are distinguished and preserve intrusive contacts with pre-Alpine metamorphosed supracrustal rocks. The granitic protoliths represent fractionated late to post-orogenic, calc-alkaline, I-type magmas with minor S-type components. The Mo veins are restricted to a biotite and alkali feldspar-rich gneiss variety and occur in E W trending normally sub-vertical quartz veins with adjacent thin discontinuous garnet- and biotite-rich zones; the latter are interpreted as metamorphosed vein selvages. Prior to this work the age of the intrusive host rocks as well as the age of Mo mineralization were unknown.

  20. Low-temperature magnetic anisotropy in micas and chlorite

    DEFF Research Database (Denmark)

    Biedermann, Andrea R.; Bender Koch, Christian; Lorenz, Wolfram E A;


    of magnetic susceptibility. Because diamagnetic and paramagnetic susceptibility are both linearly dependent on field, separation of the anisotropic contributions requires understanding how the degree of anisotropy of the paramagnetic susceptibility changes as a function of temperature. Note that diamagnetic...... of approximately 6.3-8.7 for individual samples of muscovite, phlogopite and chlorite on cooling from RT to 77 K and between 11.2 and 12.4 for biotite. A decrease in temperature enhances the paramagnetic anisotropy in a mineral. Biotite exhibits a relatively stronger enhancement due to the onset of magnetic......Phyllosilicates, such as micas and chlorite, are common rock-forming minerals and often show preferred orientation in deformed rocks. In combination with single-crystal anisotropy, this leads to anisotropy of physical properties in the rock, such as magnetic susceptibility. In order to effectively...

  1. Uruguay geology contributions no. 7

    International Nuclear Information System (INIS)

    Arroyo Grande Formation (Lower Precambrian) are intruded by several granitoid bodies.The Marincho complex are represented by: a) a main unit integrated by hornblende diorites to monzoqranites, the main facies is a biotitic-hornblenditic granodiorite; b) An unconformable belt of porphyroblastics hornblendites and related granodiorites in complex relationships; c) A unit characterized by a two mica granite heterogranular to porphyritic wich cuts the previous sets; d) a little intrusion of gross leucogranite.The granodiorite of Arroyo Grande shows to be a apophysis to NW 01 Marincho Complex, being the most frecuent lacies a hornblende-biotite-granodiorite.The petrographic diagrams shows evolutive lines, suggesting different origins tor the main granodiorite, the Arroyo Grande granodiorite south granite and the hornbledites.

  2. Coupling limit equilibrium analyses and real-time monitoring to refine a landslide surveillance system in Calabria (southern Italy)


    G. G. R. Iovine; P. Lollino; S. L. Gariano; O. G. Terranova


    On 28 January 2009, a large debris slide was triggered by prolonged rainfalls at the southern suburbs of San Benedetto Ullano (Northern Calabria). The slope movement affected fractured and weathered migmatitic gneiss and biotitic schist, and included a pre-existing landslide. A detailed geomorphologic field survey, carried out during the whole phase of mobilization, allowed to recognize the evolution of the phenomenon. A set of datum points was located along the borders of the landslide and f...

  3. Petrology of the Lyngdal granodiorite (Southern Norway) and the role of fractional crystallization in the genesis of Proterozoic rapakivi-like granites.


    Bogaerts, Michel; Scaillet, Bruno; Liégeois, Jean-Paul; Vander Auwera, Jacqueline


    In south-western Norway, the Sveconorwegian orogenic thickening (1024–970 Ma) is followed by an important post-collisional magmatism (950–930 Ma), divided in two suites (Vander Auwera et al., 2003): the Anorthosite–Mangerite–Charnockite suite (AMC suite) and the Hornblende–Biotite Granitoids suite (HBG suite). The HBG suite displays a continuous trend from gabbronorites to granites. This paper presents the petrography and geochemistry (major and trace elements, Sr–Nd isotopes) of the Lyngdal ...

  4. Phosphate minerals of some granitic rocks associated quartz veins from northern and central Portugal


    Neiva, A.M.R.; Silva, M.M.V.G.; Antunes, I.M.H.R.; Ramos, J. M. F.


    Phosphate minerals are common in northern and central Portuguese granitic rocks. Childrenite, eosphorite and intermediate compositions in this solid-solution séries occur in muscovite granites at Paredes da Beira and Penamacor-Monsanto, muscovite-biotite granites at Penamacor-Monsanto and in aplite veins at Vidago. The composition of childrenite and eosphorite are similar in each of these localities. Germanite occurs in a muscovite granite at Segura.

  5. Impact de l’alteration sur le bilan chimique des diatexites du Massif de l’Edough (Annaba, NE Algérien)


    Hadj-Zobir, Soraya


    The studied section, located on the eastern part of the Edough massif (region of Annaba, Algeria), is characterized by a Mediterranean climate and the area is one of the most humid of Algeria (precipitation between 750 and 1200 mm/year). It consists of diatexites with homogeneous petrographic and metamorphic facies. The primary minerals are quartz, feldspar, oligoclase and biotite whereas weathering products are mostly represented by illite and montmorillonite. Although all samples comprise t...

  6. Intensive low-temperature tectono-hydrothermal overprint of peraluminous rare-metal granite: a case study from the Dlhá dolina valley (Gemericum, Slovakia

    Directory of Open Access Journals (Sweden)

    Breiter Karel


    Full Text Available A unique case of low-temperature metamorphic (hydrothermal overprint of peraluminous, highly evolved rare-metal S-type granite is described. The hidden Dlhá dolina granite pluton of Permian age (Western Carpathians, eastern Slovakia is composed of barren biotite granite, mineralized Li-mica granite and albitite. Based on whole-rock chemical data and evaluation of compositional variations of rock-forming and accessory minerals (Rb-P-enriched K-feldspar and albite; biotite, zinnwaldite and di-octahedral micas; Hf-(Sc-rich zircon, fluorapatite, topaz, schorlitic tourmaline, the following evolutionary scenario is proposed: (1 Intrusion of evolved peraluminous melt enriched in Li, B, P, F, Sn, Nb, Ta, and W took place followed by intrusion of a large body of biotite granites into Paleozoic metapelites and metarhyolite tuffs; (2 The highly evolved melt differentiated in situ forming tourmaline-bearing Li-biotite granite at the bottom, topaz-zinnwaldite granite in the middle, and quartz albitite to albitite at the top of the cupola. The main part of the Sn, Nb, and Ta crystallized from the melt as disseminated cassiterite and Nb-Ta oxide minerals within the albitite, while disseminated wolframite appears mainly within the topaz-zinnwaldite granite. The fluid separated from the last portion of crystallized magma caused small scale greisenization of the albitite; (3 Alpine (Cretaceous thrusting strongly tectonized and mylonitized the upper part of the pluton. Hydrothermal low-temperature fluids enriched in Ca, Mg, and CO2 unfiltered mechanically damaged granite. This fluid-driven overprint caused formation of carbonate veinlets, alteration and release of phosphorus from crystal lattice of feldspars and Li from micas, precipitating secondary Sr-enriched apatite and Mg-rich micas. Consequently, all bulk-rock and mineral markers were reset and now represent the P-T conditions of the Alpine overprint.

  7. The thermal history of the Lhasa Block, South Tibetan Plateau based on FTD and Ar-Ar dating

    CERN Document Server

    Yang, T F; Lo Chong Huah; Chung, S L; Tien, R L; Xu, R; Deng, W


    Twelve basement samples were collected from South Tibet Plateau for FTD and Ar-Ar analysis to demonstrate their uplifting history since Cenozoic era. The preliminary results from different minerals with different closure temperatures, including apatite and zircon for fission-track dating, and K-feldspar, biotite for Ar-Ar dating, show that at least four stages of thermal history can be recognized in the studied area.

  8. 40Ar/39Ar-Dating of deformation of transform-shear stage in evolution of the Early Caledonides in Western Sangilen (South-Eastern Tuva)

    International Nuclear Information System (INIS)

    Detail structural-metamorphic and isotopic investigations into borders of the Muguro-Chinchilig tectonic block are conducted. 40Ar/39Ar-isotope dating was conducted by the graduated warming-up with biotite for different zones. Carried studies demonstrate that in the boundary of 465 million years intensive shift disturbances entailing fragmentation of the Muguro-Chinchilig tectonic block and disturbances in entirety of its separate parts in borders of the Sangilen plateau (South-Eastern Tuva) were stated

  9. K/Ar chronologies of tephra units from the Middle Jurassic Sundance, and Late Early Cretaceous Mowry and Shell Creek Formations, Big Horn Basin, WY (United States)

    Jiang, H.; Meyer, E. E.; Johnson, G. D.


    The Middle Jurassic Sundance and Late Early Cretaceous Shell Creek and Mowry Formations of the Big Horn Basin, Wyoming, contain an extensive record of altered tephra. These tephra are likely related to contemporary volcanic activity in the Sierra Nevada and various Coast Range terranes to the west and provide valuable chronometric control on the sedimentary record within a portion of the Sevier-aged and later Cordilleran foreland basin. In addition, several of these altered tephra (bentonites) provide a valuable economic resource. Despite the prominence of these strata across the basin, few isotopic ages have been reported to date. Here we present new K/Ar ages on biotite phenocrysts from those tephra occurrences as a chronometric check on samples that contained zircons with significant Pb loss, that preclude more precise U/Pb age determinations. A bulk biotite sample extracted from an altered tuff in the Lower Sundance Formation gives an age of 167.5 × 5 Ma. This tuff occurs just above a dinosaur track-bearing peritidal sequence. Bulk biotite ages from the lower Shell Creek Formation give an age of 100.3 × 3 Ma and are statistically indistinguishable from biotite grains dated at 103.1 × 3 Ma extracted from the economically important 'Clay Spur' bentonite found at the top of the Mowry Shale. This work provides important new chronometric constraints on a portion of the Medial Jurassic to Late Early Cretaceous stratigraphy of the Big Horn Basin, Wyoming, and may be useful in understanding the regional tectonics that helped shape the development of the Sevier foreland basin and Western Interior Seaway.

  10. Petrography and geochemistry of the topaz-bearing granite stocks in Artjärvi and Sääskjärvi, western margin of the Wiborg rapakivi granite batholith

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    Sari Lukkari


    Full Text Available The Artjärvi and Sääskjärvi granite stocks at the western margin of the Wiborg rapakivi batholith are multiphase rapakivi granite intrusions in which the most evolved phase is topaz-bearing granite. The Artjärvi stock is composed of porphyritic and even-grained biotite granite and even-grained topaz granite, and the Sääskjärvi stock comprises even-grained biotite granite and porphyritic topazgranite. The granites are metaluminous to peraluminous A-type granites, showing within-plate (WPG geochemical characteristics. The topaz granites from the Artjärvi and Sääskjärvi stocks are petrographically and geochemically similar to other topaz-bearing rapakivi granites in Finland. The anomalous geochemistry of the topaz granite is essentially magmatic; postmagmatic reactions have only slightly modified its composition. Greisen veins, some of which are mineralized, are widely found associated with the Artjärvi and Sääskjärvi stocks.The most characteristic feature of the Artjärvi granite stock is a stockscheider at the roof contact of the topaz granite. The stockscheider is composed of schlieren layering and pegmatite layers parallel to the contact. The most probable mechanism for the formation of the schlieren layering is velocity-gradient sorting parallel to the flow, which led to accumulation of mafic minerals along the upper contact of the topaz granite. Cooling and contraction of the topaz granite formed fractures parallel to the roof contact and the residual pegmatite magmas were injected along the fractures forming pegmatite layers. Textures like graphic intergrowths, aplitic groundmass and fan-shaped alkali feldspar crystals associated with the Artjärvi porphyritic biotite granite and pegmatite indicatecrystallization from undercooled magma. Miarolitic cavities found in the porphyritic biotite granite and topaz granite indicate at least local volatile saturation.

  11. Magma mixing/mingling in the Eocene Horoz (Nigde) granitoids, Central southern Turkey: evidence from mafic microgranular enclaves (United States)

    Kocak, Kerim; Zedef, Veysel; Kansun, Gursel


    Mafic microgranular enclaves (MMEs) are widespread in the Horoz pluton with granodiorite and granite units. Rounded to elliptical MMEs have variable size (from a few centimetres up to metres) and are generally fine-grained with typical magmatic textures. The plagioclase compositions of the MMEs range from An18-An64 in the cores to An17-An29 in the rims, while that of the host rocks varies from An17 to An55 in the cores to An07 to An33 in the rims. The biotite is mostly eastonitic, and the calcic-amphibole is magnesio-hornblende and edenite. Oxygen fugacity estimates from both groups' biotites suggest that the Horoz magma possibly crystallised at fO2 conditions above the nickel-nickel oxide (NNO) buffer. The significance of magma mixing in their genesis is highlighted by various petrographic and mineralogical characteristics such as resorption surfaces in plagioclases and amphibole; quartz ocelli rimmed by biotite and amphibole; sieve and boxy cellular textures, and sharp zoning discontinuities in plagioclase. The importance of magma mixing is also evident in the amphiboles of the host rocks, which are slightly richer in Si, Fe3+ and Mg in comparison with the amphiboles of MMEs. However, the compositional similarity of the plagioclase and biotite phenocrysts from MMEs and their host rocks suggests that the MMEs were predominantly equilibrated with their hosts. Evidence from petrography and mineral chemistry suggests that the adakitic Horoz MMEs could be developed from a mantle-derived, water-rich magma (>3 mass%) affected by a mixing of felsic melt at P >2.3 kbar, T >730°C.

  12. The petrogenesis of the Early Permian Variscan granites of the Cornubian Batholith: Lower plate post-collisional peraluminous magmatism in the Rhenohercynian Zone of SW England (United States)

    Simons, B.; Shail, Robin K.; Andersen, Jens C. Ø.


    The Early Permian Cornubian Batholith was generated during an extensional regime following Variscan convergence within the Rhenohercynian Zone of SW England. Its component granites can be classified, using mineralogical, textural and geochemical criteria, into five main types, all of which are peraluminous (A/CNK > 1.1): G1 (two-mica), G2 (muscovite), G3 (biotite), G4 (tourmaline) and G5 (topaz). G1 granites formed through up to 20% muscovite and minor biotite dehydration melting of a metagreywacke source at moderate temperatures and pressures (731-806 °C, > 5 kbar). Younger G3 granites formed through higher temperature, lower pressure (768-847 °C, chemical data. Variations in the major elements, Ba, Sr and Rb indicate that G1 and G3 granites underwent 15%-30% fractionation of an assemblage dominated by plagioclase, alkali feldspar and biotite to form more evolved G2 and G4 granites, respectively. Decreasing whole-rock abundances of Zr, Th and REE support the fractionation of zircon, monazite, apatite and allanite. Subsolidus alteration in G2 and G4 granites is indicated by non-primary muscovite and tourmaline and modification of major and trace element trends for G3-G4 granites, particularly for P2O5 and Rb. Topaz (G5) granites show low Zr, REE and extreme enrichment in Rb (up to 1530 ppm) and Nb (79 ppm) that cannot be related in a straightforward manner to continued differentiation of the G1-G2 or G3-G4 series. Instead, they are considered to represent partial melting, mediated by granulite facies fluids, of a biotite-rich restite following extraction of G1 and/or G3 magmas; they do not exhibit the typical geochemical characteristics of intraplate A-type granites.

  13. Mikroskopische Studien ueber Gesteine aus den Molukken. 1. Gesteine von Ambon und den Uliassern. Mit einem französischen Résumé

    NARCIS (Netherlands)

    Schroeder van der Kolk, J.L.C.


    Dans le traité précédent j’ai décrit les types les plus caractéristiques parmi les échantillons de roche recueillis par M. MARTIN pendant ses voyages dans les Moluques. Ainsi il s’agit des Granites à biotite, des Péridotites, des Dacites, des Andésites à pyroxène, des Brèches volcaniques et aussi de

  14. Rare evidence for formation of garnet + corundum during isobaric cooling of ultrahigh temperature metapelites: New insights for retrograde P-T trajectory of the Highland Complex, Sri Lanka (United States)

    Dharmapriya, P. L.; Malaviarachchi, Sanjeeva P. K.; Galli, Andrea; Su, Ben-Xun; Subasinghe, N. D.; Dissanayake, C. B.


    We report the occurrence of coexisting garnet + corundum in spinel- and corundum-bearing, garnet-sillimanite-biotite-graphite gneiss (pelitic granulites) from the Highland Complex (HC), Sri Lanka. In the investigated pelitic granulites, two domains such as quartz-saturated and quartz-undersaturated are distinguishable. The quartz-saturated domains consist of porphyroblastic garnet, quartz, plagioclase, alkali-feldspar and biotite flakes rimming garnet. The quartz-undersaturated domains are constituted of two generations of garnet (Grt1 and Grt2), sillimanite, plagioclase, alkali-feldspar, corundum, spinel and biotite. Grt1 encloses rare Ti-rich biotite and numerous rutile needles and apatite rods. Grt2 contains rare sillimanite and/or spinel inclusions. Corundum occurs in mutual contact with Grt2, partially embedded at the rim or as an inclusions in Grt2. Thermobarometry on inclusion phases in Grt1 indicates that during the prograde history pelitic granulites attained a P of 10.5-11 kbar at T of ~ 850 °C. Textural observations coupled with both pseudosections calculated in the NCKFMASHTMnO system and Ti-in-Garnet geothermobarometry suggest that peak metamorphism occurred at ultrahigh temperature (UHT) conditions of 950-975 °C and pressures of 9-9.5 kbar. Peak T was followed by a period of isobaric cooling that formed corundum and Grt2 at approx. 930 °C along with exsolution of rutile needles and apatite rods in Grt1. Thermodynamic modelling confirms that corundum appears along an isobaric cooling path at about 920-930 °C and 9-9.5 kbar. Therefore, the investigated granulites provide a rare example of post-peak crystallization of garnet + corundum along a retrograde metamorphic trajectory under UHT conditions. Thus, isobaric cooling at the base of the crust could be regarded as an alternative process to form coexisting garnet + corundum.

  15. The petrogenesis of the Early Permian Variscan granites of the Cornubian Batholith: Lower plate post-collisional peraluminous magmatism in the Rhenohercynian Zone of SW England (United States)

    Simons, B.; Shail, Robin K.; Andersen, Jens C. Ø.


    The Early Permian Cornubian Batholith was generated during an extensional regime following Variscan convergence within the Rhenohercynian Zone of SW England. Its component granites can be classified, using mineralogical, textural and geochemical criteria, into five main types, all of which are peraluminous (A/CNK > 1.1): G1 (two-mica), G2 (muscovite), G3 (biotite), G4 (tourmaline) and G5 (topaz). G1 granites formed through up to 20% muscovite and minor biotite dehydration melting of a metagreywacke source at moderate temperatures and pressures (731-806 °C, > 5 kbar). Younger G3 granites formed through higher temperature, lower pressure (768-847 °C, data. Variations in the major elements, Ba, Sr and Rb indicate that G1 and G3 granites underwent 15%-30% fractionation of an assemblage dominated by plagioclase, alkali feldspar and biotite to form more evolved G2 and G4 granites, respectively. Decreasing whole-rock abundances of Zr, Th and REE support the fractionation of zircon, monazite, apatite and allanite. Subsolidus alteration in G2 and G4 granites is indicated by non-primary muscovite and tourmaline and modification of major and trace element trends for G3-G4 granites, particularly for P2O5 and Rb. Topaz (G5) granites show low Zr, REE and extreme enrichment in Rb (up to 1530 ppm) and Nb (79 ppm) that cannot be related in a straightforward manner to continued differentiation of the G1-G2 or G3-G4 series. Instead, they are considered to represent partial melting, mediated by granulite facies fluids, of a biotite-rich restite following extraction of G1 and/or G3 magmas; they do not exhibit the typical geochemical characteristics of intraplate A-type granites.


    Institute of Scientific and Technical Information of China (English)


    <正>20082178 Cheng Liangjuan(College of Re- sources and Environmental Sciences,Nanjing Agricultural University,Nanjing 210095, China);Li Fuchun Adsorption of Silicate Bacteria on Surface of Orthoclase and Biotite and Its Selectivity(Geological Journal of Chi- na Universities,ISSN1006—7493,CN32—1440/P,13 (4),2007,p.669—674,4 illus.,21 refs.,with English abstract) Key words:silicates,bacteria

  17. Composition and origin of aeolian and fluvial sands of Gavkhuni playa lake (southeast of Isfahan)


    H.R., Pakzad,; Van, M. A.; M., Pasandi,; Z., Aliniaie,


    Gavkhuni playa lake, located 130 km southeast of Isfahan, comprises of sand, mud and salt flats. This playa includes two environments as delta and playa lake. Sand dunes, 45 kilometers long, extend in the west of the playa. Rock fragments of andesite, dacite, tuff, granite, schist, gneiss, fossil bearing limestone, sandstone and also quartz and feldspar minerals form the alluvial and aeolian sediments. Heavy minerals including idocrase, tourmaline, biotite, wollastonite, magnetite, hematite, ...

  18. Metagabbro associated with the shear zone on Prins Karls Forland (Svalbard, Arctic) (United States)

    Maraszewska, Maria; Manecki, Maciej; Czerny, Jerzy; Schneider, David; Myhre, Per Inge; Faehnrich, Karol; Barnes, Christopher


    Prins Karls Forland (PKF) is a N-S elongated island situated west of Spitsbergen in the Svalbard archipelago, High Arctic. The northern part of the island is dominated by siliciclastic metasediments regionally metamorphosed to greenshist facies assemblages during one distinct stage of tectonism. Amphibolite facies garnet-mica schists, mica schists, quartzites and carbonate-silicate rocks exhibiting evidence of at least two distinct, strong deformation episodes (including mylonitization) locally outcrop on the east coast of PKF, termed the Pinkie Unit. A ~1 km wide shear zone containing ductile to brittle structures and distinct outcrops of greenstones (metagabbros and greenschists), associated with magnetite ore, separates these two contrasting tectonic units. Ten samples of greenstones were collected on the slopes of Lauratzonfjellet and Boureefjellet for petrologic and geochemical analyses. Despite intense localized shearing, the metagabbros are undeformed and preserve coarse crystalline, magmatic texture, which is locally poikilitic. The primary magmatic assemblage consists of brown hornblende, plagioclase, biotite and opaque minerals, with accessory apatite and titanite. No relicts of pyroxenes are preserved. Formation of secondary uralite, sericite and chlorite is observed. Metamorphic assemblage consists of actinolite pseudomorhs after hornblende, epidote, and second generation biotite. Blue amphibole is observed in one sample from Boureefjellet; greenschists from Boureefjellet also contain fibrous blue amphibole, as well as garnets, actinolite, epidote and biotite. Some rocks sampled on Boureefjellet are more strongly deformed and exhibit probably two stages of metamorphism: amphibolite facies metamorphism resulting in blue amphibole-garnet assemblage followed by greenschist facies metamorphism resulting in actinolite-epidote-biotite paragenesis. Parallel and overlapping patterns on chondrite-normalized REE diagrams and spider diagrams indicate that these

  19. Preliminary thermal expansion screening data for tuffs

    Energy Technology Data Exchange (ETDEWEB)

    Lappin, A.R.


    A major variable in evaluating the potential of silicic tuffs for use in geologic disposal of heat-producing nuclear wastes is thermal expansion. Results of ambient-pressure linear expansion measurements on a group of tuffs that vary treatly in porosity and mineralogy are presente here. Thermal expansion of devitrified welded tuffs is generally linear with increasing temperature and independent of both porosity and heating rate. Mineralogic factors affecting behavior of these tuffs are limited to the presence or absence of cristobalite and altered biotite. The presence of cristobalite results in markedly nonlinear expansion above 200{sup 0}C. If biotite in biotite-hearing rocks alters even slightly to expandable clays, the behavior of these tuffs near the boiling point of water can be dominated by contraction of the expandable phase. Expansion of both high- and low-porosity tuffs containing hydrated silicic glass and/or expandable clays is complex. The behavior of these rocks appears to be completely dominated by dehydration of hydrous phases and, hence, should be critically dependent on fluid pressure. Valid extrapolation of the ambient-pressure results presented here to depths of interest for construction of a nuclear-waste repository will depend on a good understanding of the interaction of dehydration rates and fluid pressures, and of the effects of both micro- and macrofractures on the response of tuff masss.

  20. Minerals from the Pohorje igneous massif

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    Nina Zupančič


    Full Text Available The mineralogical composition of Pohorje igneous rocks was determined by means of optical microscopy and X-ray poviwder diffraction. Quartz, plagioclases and K-feldspars are the major minerals in the granodiorite and its porphyritic varieties. Characteristic and accessory minerals are biotite, hornblende, apatite, orthite, epidote, zircon and opaque minerals. Muscovite, pyroxenes and garnets occur rarely. The major minerals in malchites are plagioclases and hornblende.Restitic crystals of plagioclases, apatite and zircon were present in magma from which the Pohorje igneous body solidified. Sulphides, apatite and zircon precipitated in the first stage of magma crystallisation. In the next stage orthite, epidote and sphene crystallized. Biotite crystals probably formed slightly beforehornblende. The precipitation continued with plagioclases, quartz of first generation, more acid plagioclases, biotite and quartz of second generation. The crystallisation sequence ended with K-feldspar that replaced other minerals.The primary minerals are somewhere autometamorphosed to chlorite, epidote, calcite, sphene, sericite, kaolinite and limonite. In some areas in the NW part of Pohorje igneous body the alteration was hydrothermal.

  1. The chemical, mechanical, and hydrological evolution of weathering granitoid (United States)

    Goodfellow, Bradley W.; Hilley, George E.; Webb, Samuel M.; Sklar, Leonard S.; Moon, Seulgi; Olson, Christopher A.


    Surprisingly few studies connect the chemical, mechanical, and hydrological evolution of rock as it weathers to saprolite and soil. We assess this coevolution in granodiorite from Monterey Peninsula, California, by measuring changes in bulk chemistry, mineralogy, volumetric strain, the oxidation state of Fe in biotite crystals, tensile strength, abrasion rate, connected porosity, and hydraulic conductivity in samples covering a range of weathering grades. We identify the oxidative dissolution of biotite as the key chemical reaction because of the volumetric expansion that accompanies formation of altered biotite and precipitation of ferrihydrite. We show how the associated accumulation of elastic strain produces an energy density that is sufficient to support rock fracturing over length scales equivalent to constituent crystals. The resulting intragranular and intergranular cracking profoundly reduces tensile strength and increases the abrasion rate, connected porosity, and hydraulic conductivity of the rock matrix. These changes increase the rate of plagioclase weathering, and ultimately the rock disintegrates into grus and clay. Major changes in rock properties can occur with only minor element leaching, and the threshold behavior of weathering that arises from the coevolution of chemical, hydrological, and mechanical properties may be difficult to capture using simplified weathering models that fail to incorporate these properties. Our results, which combine the mechanical and hydrological evolution of weathering rock with more common measurements of chemical changes, should help to more accurately model the effects of, and mechanical and hydrological feedbacks upon, chemical weathering of rock.

  2. Moessbauer and XRD Comparative Study of Host Rock and Iron Rich Mineral Samples from Paz del Rio Iron Ore Mineral Mine in Colombia

    Energy Technology Data Exchange (ETDEWEB)

    Fajardo, M.; Perez Alcazar, G. A. [Universidad del Valle, Departamento de Fisica (Colombia); Moreira, A. M.; Speziali, N. L. [Universidade Federal de Minas Gerais, Departamento de Fisica (Brazil)


    A comparative study between the host rock and the iron rich mineral samples from the Paz del Rio iron ore mineral mine in Colombia was performed using X-ray diffraction and Moessbauer spectroscopy. Diffraction results of the iron rich mineral sample show that goethite, hematite, quartz, kaolinite and siderite are the main phases, and that a small amount of illite is also present. By Moessbauer spectroscopy at room temperature (RT) the presence of all the above mentioned phases was detected except quartz as well as an additional presence of small amount of biotite. The goethite, which appears as four sextets with hyperfine fields of 33.5, 30.5, 27.5 and 18.5 T, respectively, is the majority phase. This result shows the different grades of formation of this oxyhydroxide. The Moessbauer spectrum of this sample at 80 K presents the same phases obtained at RT without any superparamagnetic effect. In this case the goethite appears as two sextets. Diffraction results of the host rock sample show a large amount of quartz and kaolinite and small amounts of illite and biotite, whereas by Moessbauer spectroscopy illite, kaolinite and biotite were detected.

  3. A study of small-scale foliation in lengths of core enclosing fault zones in borehole WD-3, Permit Area D, Lac du Bonnet Batholith

    Energy Technology Data Exchange (ETDEWEB)

    Ejeckam, R.B.


    Small-scale foliation measurements in lengths of core from borehole WD-3 of Permit Area D of the Lac du Bonnet Batholith have defined five major mean orientation sets. They strike NW, N and NE. The orientations (strike to the left of the dip direction/dip) of these sets are as follows: Set I - 028/74 deg; II - 001/66 deg; III - 100/58 deg; IV - 076/83 deg; and V - 210/40 deg. The small-scale foliations were defined by different mineral types such as biotite crystals, plagioclase, mineral banding and quartz lenses. Well-developed biotite foliation is commonly present whenever well-developed plagioclase foliation exists, but as the strength of development weakens, the preferred orientations of plagioclase foliation do not correspond to those of biotite. It is also noted that the foliations appear to strike in directions orthogonal to the fractures in the fracture zones in the same depth interval. No significant change in foliation orientation was observed in Zones I to IV. Set V, however, whose mean orientation is 210/40 deg, is absent from the Zone IV interval, ranging from 872 to 905 m. (auth)

  4. Two stages of isotopic exchanges experienced by the Ertaibei granite pluton, northern Xinjiang, China

    Institute of Scientific and Technical Information of China (English)



    18O/16O and D/H of coexisting feldspar, quartz, and biotite separates of twenty samples collected from the Ertaibei granite pluton, northern Xinjiang, China are determined. It is shown that the Ertaibei pluton experienced two stages of isotopic exchanges. The second stage of 18O/16O and D/H exchanges with meteoric water brought about a marked decrease in the δ18O values of feldspar and biotite from the second group of samples. The D/H of biotite exhibits a higher sensitivity to the meteoric water alteration than its 18O/16O. However, the first stage of 18O/16O exchange with the 18O-rich aqueous fluid derived from the dehydration within the deep crust caused the Δ18OQuariz-Feidspar reversal. It is inferred that the dehydration-melting may have been an important mechanism for anatexis. It is shown that the deep fluid encircled the Ertaibei pluton like an envelope which serves as an effective screen to the surface waters.

  5. Two stages of isotopic exchanges experienced by the Ertaibei granite pluton, northern Xinjiang, China

    Institute of Scientific and Technical Information of China (English)


    18O/16O and D/H of coexisting feldspar, quartz, and biotite separates of twenty samples collected from the Ertaibei granite pluton, northern Xinjiang, China are determined. It is shown that the Ertaibei pluton experienced two stages of isotopic exchanges. The second stage of 18O/16O and D/H exchanges with meteoric water brought about a marked decrease in the δ18O values of feldspar and biotite from the second group of samples. The D/H of biotite exhibits a higher sensitivity to the meteoric water alteration than its 18O/16O. However, the first stage of 18O/16O exchange with the 18O-rich aqueous fluid derived from the dehydration within the deep crust caused the δ18OQuartz-Feldspar reversal. It is inferred that the dehydration-melting may have been an important mechanism for anatexis. It is shown that the deep fluid encircled the Ertaibei pluton like an envelope which serves as an effective screen to the surface waters.

  6. Degradative crystal–chemical transformations of clay minerals under the influence of cyanobacterium-actinomycetal symbiotic associations

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    Ekaterina Ivanova


    Full Text Available Cyanobacteria and actinomycetes are essential components of soil microbial community and play an active role in ash elements leaching from minerals of the parent rock. Content and composition of clay minerals in soil determine the sorption properties of the soil horizons, water-holding capacity of the soil, stickiness, plasticity, etc. The transformative effect of cyanobacterial–actinomycetes associations on the structure of clay minerals – kaolinite, vermiculite, montmorillonite, biotite and muscovite – was observed, with the greatest structural lattice transformation revealed under the influence of association in comparison with monocultures of cyanobacterium and actinomycete. The range of the transformative effect depended both on the type of biota (component composition of association and on the crystal–chemical parameters of the mineral itself (trioctahedral mica – biotite, was more prone to microbial degradation than the dioctahedral – muscovite. The formation of the swelling phase – the product of biotite transformation into the mica–vermicullite mixed-layered formation was revealed as a result of association cultivation. Crystal chemical transformation of vermiculite was accompanied by the removal of potassium (К, magnesium (Mg and aluminum (Al from the crystal lattice. The study of such prokaryotic communities existed even in the early stages of the Earth's history helps to understand the causes and nature of the transformations undergone by the atmosphere, hydrosphere and lithosphere of the planet.contribution of treatments on structure induces and model parameters are discussed in the paper.

  7. Oxygen isotope, fluid inclusion, microprobe and petrographic studies of the preCambrian granites from the southern Wind River range and the Granite Mountains, central Wyoming, U.S.A.: Constraints on origin, hydrothermal alteration and uranium genesis (United States)

    Cheang, K. K.

    The Granite Mountain is comprised of the granite of Long Creek Mountain and the volumetrically dominant granite of Lankin Dome. Average delta 018 O values in per mil deg/00 of the granite of Long Creek Mountain is 8.2 + or - 0.3 deg/00 (N = 4) and average delta 018 8.5 + or - -0.5 deg/00 (N = 37), values of the two phases from the granite of Lankin Dome are: biotite granites = delta 018 8.5 + or 0.5 deg/00 (N = 37), leucocratic graphite = 8.4 + or - 0.3 deg/00 (N = 12). The average delta 018 values for Louis Lake Batholith are: hornblende-biotite granodiorite = 7.3 + or - 0.3 deg/00 (N = 13) and leucocratic biotite granite = 7.7 + or - 0.1 deg/00 (N = 6). It is concluded from the whole rock oxygen isotopic, mineralogical, chemical and strontium isotopic data that the unaltered granites in the Granite Mountains were probably derived from a uranium enriched source with some peraluminous metasedimentary component which favoured the preconcentration of uranium and thorium, whereas the Louis Lake Batholith was formed by partial melting of igneous source materials that are not strongly enriched in uranium.

  8. Cesium adsorption/desorption behavior of clay minerals considering actual contamination conditions in Fukushima. (United States)

    Mukai, Hiroki; Hirose, Atsushi; Motai, Satoko; Kikuchi, Ryosuke; Tanoi, Keitaro; Nakanishi, Tomoko M; Yaita, Tsuyoshi; Kogure, Toshihiro


    Cesium adsorption/desorption experiments for various clay minerals, considering actual contamination conditions in Fukushima, were conducted using the (137)Cs radioisotope and an autoradiography using imaging plates (IPs). A 50 μl solution containing 0.185 ~ 1.85 Bq of (137)Cs (10(-11) ~ 10(-9 )molL(-1) of (137)Cs) was dropped onto a substrate where various mineral particles were arranged. It was found that partially-vermiculitized biotite, which is termed "weathered biotite" (WB) in this study, from Fukushima sorbed (137)Cs far more than the other clay minerals (fresh biotite, illite, smectite, kaolinite, halloysite, allophane, imogolite) on the same substrate. When WB was absent on the substrate, the amount of (137)Cs sorbed to the other clay minerals was considerably increased, implying that selective sorption to WB caused depletion of radiocesium in the solution and less sorption to the coexisting minerals. Cs-sorption to WB continued for about one day, whereas that to ferruginous smectite was completed within one hour. The sorbed (137)Cs in WB was hardly leached with hydrochloric acid at pH 1, particularly in samples with a longer sorption time. The presence/absence of WB sorbing radiocesium is a key factor affecting the dynamics and fate of radiocesium in Fukushima.

  9. Petrology and mineral chemistry of peraluminous Marziyan granites, Sanandaj-Sirjan metamorphic belt (NW Iran

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    Darvishi Esmaiel


    Full Text Available The Marziyan granites are located in the north of Azna and crop out in the Sanandaj-Sirjan metamorphic belt. These rocks contain minerals such as quartz, K-feldspars, plagioclase, biotite, muscovite, garnet, tourmaline and minor sillimanite. The mineral chemistry of biotite indicates Fe-rich (siderophyllite, low TiO2, high Al2O3, and low MgO nature, suggesting considerable Al concentration in the source magma. These biotites crystallized from peraluminous S-type granite magma belonging to the ilmenite series. The white mica is rich in alumina and has muscovite composition. The peraluminous nature of these rocks is manifested by their remarkably high SiO2, Al2O3 and high molar A/CNK (> 1.1 ratio. The latter feature is reflected by the presence of garnet and muscovite. All field observations, petrography, mineral chemistry and petrology evidence indicate a peraluminous, S-type nature of the Marziyan granitic rocks that formed by partial melting of metapelite rocks in the mid to upper crust possibly under vapour-absent conditions. These rocks display geochemical characteristics that span the medium to high-K and calc-alkaline nature and profound chemical features typical of syn-collisional magmatism during collision of the Afro-Arabian continental plate and the Central Iranian microplate.

  10. Petrology and mineral chemistry of peraluminous Marziyan granites, Sanandaj-Sirjan metamorphic belt (NW Iran) (United States)

    Darvishi, Esmaiel; Khalili, Mahmoud; Beavers, Roy; Sayari, Mohammad


    The Marziyan granites are located in the north of Azna and crop out in the Sanandaj-Sirjan metamorphic belt. These rocks contain minerals such as quartz, K-feldspars, plagioclase, biotite, muscovite, garnet, tourmaline and minor sillimanite. The mineral chemistry of biotite indicates Fe-rich (siderophyllite), low TiO2, high Al2O3, and low MgO nature, suggesting considerable Al concentration in the source magma. These biotites crystallized from peraluminous S-type granite magma belonging to the ilmenite series. The white mica is rich in alumina and has muscovite composition. The peraluminous nature of these rocks is manifested by their remarkably high SiO2, Al2O3 and high molar A/CNK (> 1.1) ratio. The latter feature is reflected by the presence of garnet and muscovite. All field observations, petrography, mineral chemistry and petrology evidence indicate a peraluminous, S-type nature of the Marziyan granitic rocks that formed by partial melting of metapelite rocks in the mid to upper crust possibly under vapour-absent conditions. These rocks display geochemical characteristics that span the medium to high-K and calc-alkaline nature and profound chemical features typical of syn-collisional magmatism during collision of the Afro-Arabian continental plate and the Central Iranian microplate.

  11. Discovery of khondalite series from the western segment of Altyn Tagh and their petrological and geochronological studies

    Institute of Scientific and Technical Information of China (English)


    The khondalite series, which are characterized by aluminum-rich gneisses (schists) consisting of sillimanite-garnet-biotite-monzonite gneiss, garnet-biotite-monzonite gneiss, graphite-sillimanite-biotite schist, and garnet-amphibole two-pyroxene granulites occurring as lenses and layers within gneisses (schists), were discovered in Tula area of western segment of Altyn Tagh. The petrology and geochemistry indicate that the protoliths of aluminum-rich gneisses (schists) are aluminum-rich pelitic and pelitic arenaceous sedimentary rocks, the protoliths of basic granulites are continental tholeiitic basalts. Therefore, the khondalite series may be produced at continental margin. They had suffered granulitic facies metamorphism with peak temperatures of 700-850℃ and pressures of 0.8-1.2 GPa. The U-Pb and Pb-Pb isotopic dating of zircons provided the ages of 447-462 Ma representing the ages of peak granulitic metamorphism. The U-Pb dating of detrital zircons from aluminum-rich gneisses yielded older upper intercept ages which reflect the times of older materials derived from source rocks of the gneiss protoliths.

  12. Discovery of khondalite series from the western segment of Altyn Tagh and their petrological and geochronological studies

    Institute of Scientific and Technical Information of China (English)

    张建新[1; 张泽明[2; 许志琴[3; 杨经绥[4; 崔军文[5


    The khondalite series, which are characterized by aluminum-rich gneisses (schists) consisting of sillimanite-garnet-biotite-monzonite gneiss, garnet-biotite-monzonite gneiss, graphite-sillimanite-biotite schist, and garnet-amphibole two-pyroxene granulites occurring as lenses and layers within gneisses (schists), were discovered in Tula area of western segment of Altyn Tagh. The petrology and geochemistry indicate that the protoliths of aluminum-rich gneisses (schists) are aluminum-rich pelitic and pelitic arenaceous sedimentary rocks, the protoliths of basic granulites are continental tholeiitic basalts. Therefore, the khondalite series may be produced at continental margin. They had suffered granulitic facies metamorphism with peak temperatures of 700-850℃ and pressures of 0.8-1.2 GPa. The U-Pb and Pb-Pb isotopic dating of zircons provided the ages of 447-462 Ma representing the ages of peak granulitic metamorphism. The U-Pb dating of detrital zircons from aluminum-rich gneisses yielded older upper i

  13. Metamorphism of cordierite gneisses from Eastern Ghat Granulite Terrain, Andhra Pradesh, South India (United States)

    Murthy, D. S. N.; Charan, S. Nirmal


    Cordierite-bearing metapelites of the Eastern Ghat granulite terrain occur in close association of Khondalites, quartzites, calc-silicate rocks and charnockites. Rocks occurring between Bobbili in the north and Guntur in the south of Andhra Pradesh are studied. The association of the mineral and textural relationships suggest the following metamorphic reactions: Garnet + sillimanite + quartz = cordierite, hypersthene + sillimanite + quartz = cordierite, sillimanite + spinel = cordierite + corundum, and biotite + quartz + sillimanite = cordierite + K=feldspar. Generally the minerals are not chemically zoned except garnet-biotite showing zoning when they come in close contact with one another. The potential thermometers are provided by the Fe-Mg distribution of coexisting biotite-garnet and cordierite-garnet. Conflicting interpretation of the P/T dependence of these reactions involving cordierite are due to H2O in the cordierite. The presence of alkali feldspar-quartz assemblage which is common in these gneisses will be constrained from melting only if H2O activity is less than 0.5. The piezometric array inferred is convex towards the temperature array, indicating a rapid and isothermal crustal uplift probably aided by thrust tectonics.

  14. Petrology of metabasites in the south of Arousan, northeastern Isfahan province

    Directory of Open Access Journals (Sweden)

    Fereshteh Bayat


    Full Text Available Metagabbro, metadiabase and metabasalt of the Chah Palang and Me'raji mountains associated with Lower Paleozoic metamorphites are situated in the south of Arousan. Metabasites of these areas are relatively similar in terms of mineralogy and geochemical characteristics. Rock-forming minerals of the Me'raji metabasites are feldspar, amphibole, biotite, sphene, epidote, chlorite ± calcite. Metagabbro and metadiabase of the Chah Palang area are similar to the Me'raji metabasites in mineralogy and geochemistry. Volcanic rocks are overlain by metagabbros and consist of plagioclase, biotite, sphene, sanidine, chlorite, epidote and iron oxides. The rigid dykes, which are found in the volcanic units are associated with metagabbros and mineralogically are similar to the metavolcanics. Amphibolitic dykes are composed of amphibole, plagioclase and biotite with preferred orientation. Metabasites show limited range of differentiation. Me'raji metabasites are basalt and trachy-basalt in composition, whereas the Chah Palang ones present basalt and trachy-basalt composition. Similar to metabasites of the other parts of Iran, the studied basic rocks demonstrate alkaline to transitional chemical characteristic and are formed in an extensional environment by low-degree partial melting of a garnet-spinel peridotite. Metamorphic episodes have changed the studied rocks to amphibolite and greenschist, but the primitive igneous textures are preserved.

  15. Geology and uranium mineralisation around Ampulli Area, Papum-Pare District, Arunachal Pradesh, North-East India

    International Nuclear Information System (INIS)

    Uranium mineralisation associated with Middle Proterozoic Bomdila Group (Daling equivalent) metasediments have been located intermittently over a strike length of 310 m with 0.11 to 2.0 m thickness around Ampulli area of Papum-Pare district, Arunachal Pradesh. The metasediments trend NE-SW and dip 20°- 85° due either side. The grab and trench samples assayed 0.012 - 0.36% eU3O8, 0.006 - 0.19% U3O8 (beta/gamma), 0.009 - 0.235% U3O8 (Chem.) and less than 0.010% ThO2. The host rocks have been identified as tourmaline bearing biotite-quartz schist, garnet bearing muscovite-biotite-quartz schist and muscovite-biotite schist. Uraninite, brannerite and U-Ti complex are observed with uranocircite and meta-uranocircite, the secondary uranium minerals. Replacement of uraninite by molybdenite and pyrite suggested earlier oxide and later sulphide phase. Partial chemical analysis indicated aluminous nature of the host rock and their high K2O/Na2O (3.3-10.73) ratios are suggestive of predominance of potash feldspar over sodic and effects of potash metasomatism. Both syngenetic as well as epigenetic hydrothermal origin of uranium mineralisation has been suggested. (author)

  16. Charnockitic ortho gneisses and mafic granulite s of the Cerro Olivo complex, south-east Uruguay, Part 2: lithogeochemistry, mineral o chemistry and thermo barometry

    International Nuclear Information System (INIS)

    The Cerro Olivo complex in SE-Uruguay shows different kinds of orthogneisses containing biotite, amphibole and/or orthopyroxene-biotite (charnockitic gneisses). Minor occurrences of mafic granulites are associated. They include low and high pressure kinds. We present the lithogeochemistry and compared mineral chemistry analyses of both the charnockitic orthogneisses and the mafic rocks. Theres i a calc-alkaline geochemical affinity of the biotite-bearing and charnockitic gneisses, while the mafic rocks could derive from tholeitic gabbros. These results allow discrininatieg two kinds of mafic rocks: Low and hight MgO contents, both representing respectively garnet-bearing and garnet-free mafic granulites. The orthopyroxene in the Opx-Bt orthogneisses in FE-rich while MgO-rich mafic rocks show hypersthenes. The thermobarometric data of mafic granulites show temperatures higher than 850°C and two contrasting mineral assemblages, one formed by ∼ 1 Kbar and 770° - 800°C (pre-M). and the other by 5.5 Kbar and 680-700° (M). The mineral chemistry suggests the occurrence of contrasting protoliths to explain the stability of two different mineral associations

  17. Combined oxygen, hydrogen, /sup 40/Ar//sup 39/Ar isotopic evaluation of molybdenite mineralization, east Pioneer Mountains, Montana

    Energy Technology Data Exchange (ETDEWEB)

    Chesley, J.T.; Snee, L.W.; O' Neil, J.R.


    The Pear Lake molybdenite (moly) prospect is in the Eastern Pioneer Wilderness Area, 30 km south of the Cannivan Gulch moly deposit. It lies on a NW-SE trend with other prospects that are contemporaneous. Mineralized veins outcrop sporadically over a 4 square mile area, with a major concentration in the center of the study area. Previous studies have suggested potential moly-mineralization at depth. /sup 40/Ar//sup 39/Ar age-spectra on hornblend (hb) from the granodiorite host rock indicate emplacement at 75.0 +/- 1 Ma, with biotite closure at 69.0 +/- .3 Ma, in the vicinity of Pear Lake. Hydrothermal muscovites from the moly-bearing veins have ages of 68.0 +/- .5 Ma. partial resetting of biotite cooling dates in the vicinity of mineralization are observed, but biotites on the outer portion of the mineralizing system are undisturbed. These relations suggest that mineralization occurred after the host pluton had cooled to below 280/sup 0/C. Quartz-magnetite isotopic temperatures are 380 to 420/sup 0/C for moly-veins. These data suggest that magmatic hydrothermal fluids operated in the upper portion of this molysystem. These isotopic data, combined with geologic mapping, suggest that the Pear Lake moly prospect resulted from a weak, short-lived magmatic hydrothermal event at depth, and is unlikely to contain economic levels of molybdenum. The combined /sup 40/Ar//sup 39/Ar-stable isotope approach should prove useful in evaluating other hydrothermal systems.

  18. Cretaceous sedimentation and metamorphism of the western Alpine Schist protoliths associated with the Pounamu Ultramafic Belt, Westland, New Zealand

    International Nuclear Information System (INIS)

    The Pounamu Ultramafic Belt (PUB), part of the Alpine Schists, comprises a metamorphosed ophiolitic sequence overlain by a thin pelagic unit, a massive quartzofeldspathic biotite rock and quartzofeldspathic turbidites derived from a Torlesse/Otago Schist source. Constituent zircon populations from the biotite rock are euhedral/prismatic and are unabraded. One sample is near unimodal, with a U-Pb SHRIMP age of 106.6 ± 1.4 Ma (2σm), while the other has two peaks at 108.0 ± 1.6 Ma and 71.9 ± 1.8 Ma. The older age is interpreted to represent the age of igneous activity and sedimentation, while the younger peak is interpreted to represent the age of subsequent metamorphism. The whole-rock geochemistry of the biotite rock, its field distribution and zircon morphology are consistent with an origin by eruption of a dacitic air-fall tuff. The base of the Pounamu sequence divides predominantly psammitic Triassic metasediments to the east from intensely deformed, but regionally west-facing, Cretaceous metasediments to the west. These Cretaceous metasediments have undergone multiphase deformation and metamorphism by 72 Ma, a timing that contrasts markedly with previous interpretations for Jurassic amalgamation of the Haast Schists. (author)

  19. Middle cretaceous crustal anatexis associated to contractional deformation on Eden's shear zone

    International Nuclear Information System (INIS)

    The Puerto Eden's igneous and metamorphic complex (PEIMC) is composed by amphibolite facies schists, melanocratic and leucocratic diatexites (with biotite in schlieren structure), and orthomylonites intruded by schlieren bearing porphyritic biotite monzogranite, tabular garnet - tourmaline and white mica - garnet leucogranites, pegmatitic felsic dikes, andesitic dikes, and biotite hornblende granodiorites belonging to the South Patagonian Batholith (SPB). This locality represent the westernmost outcrop of the Eastern Andean Metamorphic Complex (EAMC), situated at 49o8min. 20.seg S - 74o 23min.20seg. W, on the eastern margin of the SPB. A common relationship exists in convergent orogenic belts between a shear zone system, high-grade metamorphic rocks, and granites, which suggests a feedback relationship between crustal anatexis and contractional deformation that helps granite extraction and focusses granite ascent (Solar et al, 1998). The aim of this study is to constraint the temporal relationship between the magmatic and deformational evolution in Puerto Eden, associated to one or more events of crustal anatexis recorded. This work is based on geochemistry and K-Ar radiometric age data set previously presented as part of first author's MSc thesis related to the petrogenesis of PEIMC (au)

  20. Rb-Sr and Sm-Nd study of granite-charnockite association in the Pudukkottai region and the link between metamorphism and magmatism in the Madurai Block (United States)

    Sekaran, M. Chandra; Bhutani, Rajneesh; Balakrishnan, S.


    Pudukkottai region in the northeastern part of the Madurai Block exposes the garnetiferous pink granite that intruded the biotite gneiss. Charnockite patches are associated with both the rock types. Rb-Sr biotite and Sm-Nd whole-rock isochron ages indicate a regional uplift and cooling at ˜550 Ma. The initial Nd isotope ratios (\\varepsilon _{ {Nd}}t=-20 to -22) and Nd depleted-mantle model ages (TDM = 2.25 to 2.79 Ga) indicate a common crustal source for the pink-granite and associated charnockite, while the biotite gneiss and the charnockite within it represent an older crustal source (\\varepsilon _{ {Nd}}t= -29 and TDM = > 3.2 Ga). The Rb-Sr whole-rock data and initial Sr-Nd isotope ratios also help demonstrate the partial but systematic equilibration of Sr isotope and Rb/Sr ratios during metamorphic mineral-reactions resulting in an `apparent whole-rock isochron'. The available geochronological results from the Madurai Block indicate four major periods of magmatism and metamorphism: Neoarchaean-Paleoproterozoic, Mesoproterozoic, mid-Neoproterozoic and late-Neoproterozoic. We suggest that the high-grade and ultrahigh-temperature metamorphism was preceded by magmatism which `prepared' the residual crust to sustain the high P- T conditions. There also appears to be cyclicity in the tectono-magmatic events and an evolutionary model for the Madurai Block should account for the cyclicity in the preserved records.

  1. Metamorphism of the Basement of the Qilian Fold Belt in the Minhe-Ledu Area, Qinghai Province, NW China

    Institute of Scientific and Technical Information of China (English)

    蔡金郎; 魏光华; 王庆树


    The basement of the central Qilian fold belt exposed along the Minhe-Ledu highway consists of psammiticschists, metabasitic rocks, and crystalline limestone. Migmatitic rocks occur sporadically among psammitic schist andmetabasitic rocks. The mineral assemblage of psammitic schist is muscovite + biotite + feldspar + quartz + tourmaline ±titanite ± sillimanite and that of metabasitic rocks is amphibole + plagioclase + biotite ± apatite ± magnetite ± pyroxene ±garnet ± quartz. The migmatitic rock consists of leucosome and restite of various volume proportions; the former consistsof muscovite + alkaline feldspar + quartz ± garnet ± plagioclase while the latter is either fragments of psammitic schist orthose of metabasitic rock. The crystalline limestone consists of calcite that has been partly replaced by olivine. The olivinewas subsequently altered to serpentine. Weak deformations as indicated by cleavages and fractures were imposed promi-nently on the psammitic schists, occasionally on metabasitic rocks, but not on migmatitic rocks. The basement experiencedmetamorphism up to temperature 606-778C and pressure 4.8-6.1 kbar (0.48-0.61 GPa), equivalent to amphibolite-granulite facies. The peak of the metamorphism is marked by a migmatization which occurred at several localities alongthe studied route 587-535 Ma ago. The basement also recorded a retrograde metamorphism of greenschist facies, duringwhich biotite, garnet, amphibole, and pyroxene were partly altered to chlorite.

  2. Volcanogenic Turonian and epiclastics of senonian in the Timok magmatic complex between Bor and the Tupižnica mountain, eastern Serbia

    Directory of Open Access Journals (Sweden)

    Đorđević Miodrag


    Full Text Available In the light of the findings presented in this paper, among the volcanic products of the Upper Cretaceous, referred to as "the first volcanic phase" (Drovenik, 1961, two lithostratigraphic units can be singled out within the Timok Magmatic Complex (TMC: - The lower one, consisting of volcanogenic, subaerial, dominantly hornblende andésite volcaniclastic, formed on land, and less abundant volcanic and sub-volcanic-hypoabyssal rocks. It is the main source of sulfide mine­ralization in Bor. It was formed before the Upper Turonian and consists of hornblende andésite and occasionally low biotite. Minor constituents are biotite-hornblende dacite and some andésite and dacite materials con­taining augite in addition to hornblende and biotite. - The upper one, from the Upper Turonian period when the volcanic activity of the region had ended, is marine deposited and epiclastic. Intercalated with Senonian marls, it is composed of land deposited Turonian volcanogenic material of all generations. Fresh material mostly consisting of hornblende andésite volcanoclastics prevails in it. Fresh epiclastics include ore mineral epiclasts. Epiclastics composed of epiclasts of hydro thermally altered rocks were observed which also include ore epiclasts. The ore epiclasts originate from copper ore. The boundary between the volcanogenic Turonian and the epiclastic deposits is a well-recognized unconformity. Table 1 in the text summarizes the main characteristics of the Turonian volcanogenic rocks, primarily those of volcaniclastics, as well as those of epiclastic deposits.

  3. The geology and geochemistry of the Lumwana Cu (± Co ± U) deposits, NW Zambia (United States)

    Bernau, Robin; Roberts, Stephen; Richards, Mike; Nisbet, Bruce; Boyce, Adrian; Nowecki, James


    The Lumwana Cu (± Co ± U) deposits of NW Zambia are large, tabular, disseminated ore bodies, hosted within the Mwombezhi Dome of the Lufilian Arc. The host rocks to the Lumwana deposits are two mineralogically similar but texturally distinct gneisses, a granitic to pegmatitic gneiss and a banded to augen gneiss which both comprise quartz-feldspar ± biotite ± muscovite ± haematite ± amphibole and intervening quartz-feldspar ± biotite schist. The sulphide ore horizons are typically developed within a biotite-muscovite-quartz-kyanite schist, although mineralization locally occurs within internal gneiss units. Contacts between the ore and host rocks are transitional and characterized by a loss of feldspar. Kinematic indicators, such as S-C fabrics and pressure shadows on porphyroblasts, suggest a top to the north shear sense. The sulphides are deformed by a strong shear fabric, enclosed within kyanite or concentrated into low strain zones and pressure shadows around kyanite porphyroblasts. This suggests that the copper mineralization was introduced either syn- or pre-peak metamorphism. In addition to Cu and Co, the ores are also characterized by enrichments in U, V, Ni, Ba and S and small, discrete zones of uranium mineralization, occur adjacent to the hanging wall and footwall of the copper ore bodies or in the immediate footwall to the copper mineralization. Unlike typical Copperbelt mineralization, unmineralized units show very low background copper values. Whole rock geochemical analyses of the interlayered schist and ore schist, compared to the gneiss, show depletions in Ca, Na and Sr and enrichments in Mg and K, consistent with replacement of feldspar by biotite. The mineral chemistry of muscovite, biotite and chlorite reflect changes in the bulk rock chemistry and show consistent increases in X Mg as the schists develop. δ34S for copper sulphides range from +2.3 ‰ to +18.5 ‰, with pyrite typically restricted to values between +3.9 ‰ and +6.2

  4. Unraveling eclogite-facies fluid-rock interaction using thermodynamic modelling and whole-rock experiments: the in-situ eclogitization of metapelites from Val Savenca (Sesia Zone, Western Alps) (United States)

    Jentsch, Marie; Tropper, Peter


    A common feature of HP and UHP terranes is the subduction of crustal rocks to great depths. Previous investigations have shown that this process is triggered by fluids present during an eclogite-facies metamorphic overprint. An examples is exposed in the metapelites at Val Savenca in the Sesia-Lanzo Zone, Italy where Alpine eclogite-facies metamorphism and fluid flow led to partial transformation of Variscan amphibolite-eclogite facies metapelites (garnet + biotite + sillimanite + K-feldspar + plagioclase + quartz) to zoisite ± jadeite + kyanite + phengite + quartz. This transformation took place under P-T conditions of 1.7 - 2.1 GPa at 600°C and low a(H2O) of 0.3-0.6. The replacement of plagioclase by jadeite + zoisite + kyanite + quartz takes place also along former fractures. Biotite is replaced by the assemblage phengite + omphacite ± kyanite adjacent to former plagioclase, otherwise by phengite + rutile/titanite. Garnet and clinopyroxene show variable compositions depending in which micro-domain (plagioclase or biotite) they grew. The extreme development of microdomains can best be studied by thermodynamic pseudosection modelling of individual microdomains using stoichiometric mixtures of protolith minerals from this domain and the program DOMINO (De Capitani & Petrakakis, 2010). The aim of these calculations was: 1.) to reproduce the observed mineral assemblage and 2.) to provide constraints on the amount of fluid present in the transformation. The results so far indicate that the amount of fluid was very low, otherwise paragonite would have formed instead of jadeite and reproduction of the observed mineral assemblage has only been partly successful so far since biotite is still stable in the calculations. In addition to understand the role of fluids in the mineralogical and textural transformation piston-cylinder experiments with a fresh, natural orthogneiss granulite from the Moldanubic Unit in upper Austria with the assemblage garnet + biotite + K

  5. Deformation partitioning and fabric development during shearing of felsic migmatites (Valpelline Series, NW Alps) (United States)

    Pariani, Federico; Menegon, Luca; Bistacchi, Andrea; Malaspina, Nadia


    The relationships between partial melting and deformation in the continental lower crust are critical for understanding lithosphere rheology and the processes leading to melt segregation. In metapelitic rocks in the lower portions of the crust partial melting typically occurs via dehydration of biotite and is generally characterized by a negative volume change when garnet is produced as a peritectic phase. As a result, segregation of biotite-derived melt by fracturing resulting from dilational strain is not common. Hence segregation of biotite-derived melts in the lower crust is likely to be controlled by active deformation via creation of structural anisotropies (fabric), which define migration pathways from the grain-size to the kilometre scale. This study investigates the relations between deformation mechanisms of minerals, fabric development and grain- and meso-scale deformation partitioning in felsic migmatites. The study area is located in the Valpelline Series of the Dent Blanche Nappe in the north-western Alps, which represents a slice of pre-Alpine lower crust dominated by metapelitic migmatites (i.e. 'kinzigites' in the Alpine literature). The migmatites are stromatic and show a leucosome-melanosome interlayering defining the dominant foliation (S2), which forms along a sinistral shear zone at least 1 km thick and laterally continuous for at least 8 km. Ti-in biotite geothermometry, mineral inclusions in garnet, and literature data indicate that S2 formed at P, T conditions of 800-820°C, 0.4-0.7 GPa, during dehydration melting of biotite. The melanosomes have about 80 vol% of garnet + biotite + sillimanite and are very poor in quartz and feldspars, indicating almost complete removal of melt. Garnet forms slightly elongated grains wrapped by biotite and sillimanite layers. Compositional maps of the elongated garnet do not show any zonation. EBSD analysis indicates that the elongated garnets are actually clusters of individual grains with no internal

  6. Formation of garnet + corundum during isobaric cooling at UHT conditions: an example from pelitic granulites of the Highland Complex, Sri Lanka (United States)

    Laksthitha Dharmapriya, Prasanna; Galli, Andrea; Prabath Malaviarachchi, Sanjeeva; Su, Ben-Xun


    Coexisting garnet and corundum have been reported from different rock types such as UHP rocks, aluminous eclogites, kimberlites and numerous granulites worldwide which experienced UHT conditions of 900-1050 °C at relatively high but not eclogitic pressures of 10-12 kbar. In pelitic granulites the assemblage garnet + corundum is usually interpreted to form at peak P during prograde heating along a clock-wise metamorphic path and subsequently breaks down during decompression to form sapphirine, cordierite-sapphirine-spinel or spinel-sillimanite bearing assemblages, depending on the PT-trajectory and bulk rock composition. In any cases, coexisting garnet + corundum are rarely preserved. Even less usual is the occurrence of garnet + corundum in pyroxene-free rocks. In this study, we report the occurrence of coexisting garnet + corundum within spinel- and corundum-bearing, orthopyroxene-free garnet-sillimanite-biotite-graphite gneisses from the Highland Complex (HC), Sri Lanka. In the investigated pelitic granulites, quartz-saturated domains and quartz-deficient domains are distinguishable. Quartz-saturated domains consist of quartz, plagioclase, alkali-feldspar, garnet-porphyroblasts and biotite flakes around garnet. Quartz-deficient domains are constituted of sillimanite, plagioclase, alkali-feldspar, corundum, spinel, biotite and two generations of garnet. Grt1 is coarse- to medium-grained (0.5-3 cm in diameter) and encloses rare Ti-rich biotite and numerous rutile needles and apatite rods. Grt2 is medium- to fine-grained (0.25-1 cm in diameter), contains rare sillimanite and/or spinel inclusions and is always associated with corundum. Corundum occurs in mutual contact with Grt2, partially embedded within rim area of Grt2 or as inclusions in Grt2. Rarely, tiny spinel inclusions can be observed in corundum. The chemistry of minerals preserved as inclusion in Grt1 indicates that pelitic granulites attained maximal P of 10.5-11 kbar at T around 850°C during their

  7. Mesoproterozoic suturing of Archean crustal blocks in western peninsular India: Implications for India-Madagascar correlations (United States)

    Ishwar-Kumar, C.; Santosh, M.; Wilde, S. A.; Tsunogae, T.; Itaya, T.; Windley, B. F.; Sajeev, K.


    The Kumta and Mercara suture zones welding together Archean crustal blocks in western peninsular India offer critical insights into Precambrian continental juxtapositions and the crustal evolution of eastern Gondwana. Here we present the results from an integrated study of the structure, geology, petrology, mineral chemistry, metamorphic P-T conditions, zircon U-Pb ages and Lu-Hf isotopes of metasedimentary rocks from the two sutures. The dominant rocks in the Kumta suture are greenschist- to amphibolite-facies quartz-phengite schist, garnet-biotite schist, chlorite schist, fuchsite schist and marble. The textural relations, mineral chemistry and thermodynamic modelling of garnet-biotite schist from the Kumta suture indicate peak metamorphic P-T conditions of ca. 11 kbar at 790 °C, with detrital SHRIMP U-Pb zircon ages ranging from 3420 to 2547 Ma, εHf (t) values from - 9.2 to 5.6, and TDMc model ages from 3747 to 2792 Ma. The K-Ar age of phengite from quartz-phengite schist is ca. 1326 Ma and that of biotite from garnet-biotite schist is ca. 1385 Ma, which are interpreted to broadly constrain the timing of metamorphism related to the suturing event. The Mercara suture contains amphibolite- to granulite-facies mylonitic quartzo-feldspathic gneiss, garnet-kyanite-sillimanite gneiss, garnet-biotite-kyanite-gedrite-cordierite gneiss, garnet-biotite-hornblende gneiss, calc-silicate granulite and metagabbro. The textural relations, mineral chemistry and thermodynamic modelling of garnet-biotite-kyanite-gedrite-cordierite gneiss from the Mercara suture indicate peak metamorphic P-T conditions of ca. 13 kbar at 825 °C, followed by isothermal decompression and cooling. For pelitic gneisses from the Mercara suture, LA-ICP-MS U-Pb zircon ages vary from 3249 to 3045 Ma, εHf (t) values range from - 18.9 to 4.2, and TDMc model ages vary from 4094 to 3314 Ma. The lower intercept age of detrital zircons in the pelitic gneisses from the Mercara suture ranges from 1464 to 1106

  8. Systematics of hydrothermal alteration at the volcanic-hosted Falun Zn-Pb-Cu-(Au-Ag) deposit - implications for ore genesis, structure and exploration in a 1.9 Ga ore district, Fennoscandian Shield, Sweden (United States)

    Kampmann, Tobias C.; Jansson, Nils J.; Stephens, Michael B.; Majka, Jarosław


    The Palaeoproterozoic, volcanic-hosted Falun Zn-Pb-Cu-(Au-Ag) sulphide deposit was mined for base and precious metals during several centuries, until its closure in 1992. The deposit is located in a 1.9 Ga ore district in the Bergslagen lithotectonic unit, Fennoscandian Shield, south-central Sweden. Both the ores and their host rock underwent polyphase ductile deformation, and metamorphism under amphibolite facies and later retrograde conditions at 1.9-1.8 Ga (Svecokarelian orogenic system). This study has the following aims: (i) Classify styles and intensities of alteration in the hydrothermally altered zone at Falun; (ii) identify precursor rocks to hydrothermally altered rocks and their spatial distribution at the deposit; (iii) evaluate the chemical changes resulting from hydrothermal alteration using mass change calculations; and (iv) assess the pre-metamorphic alteration assemblages accounting for the observed metamorphic mineral associations in the altered rocks at Falun. Results will have implications for both the ore-genetic and structural understanding of the deposit, as well as for local and regional exploration. Metamorphic mineral associations in the altered rocks include biotite-quartz-cordierite-(anthophyllite) and, more proximally, quartz-anthophyllite-(biotite-cordierite/almandine), biotite-cordierite-(anthophyllite) and biotite-almandine-(anthophyllite). The proximal hydrothermally altered zone corresponds to intense chlorite-style alteration. Subordinate dolomite or calcite marble, as well as calc-silicate (tremolite, diopside) rocks are also present at the deposit. Metavolcanic rocks around the deposit are unaltered, weakly sericitized or sodic-altered. Immobile-element (e.g. Zr, TiO2, Al2O3, REE) systematics of the silicate-rich samples at and around the deposit suggest that the precursors to the hydrothermally altered rocks at Falun were predominantly rhyolitic in composition, dacitic rocks being subordinate and mafic-intermediate rocks

  9. Mobility of gold during metamorphism of the Dalradian in Scotland (United States)

    Pitcairn, I. K.; Skelton, A. D. L.; Wohlgemuth-Ueberwasser, C. C.


    Mobility of Au and related metals during metamorphism has been suggested to be the source of metals enriched in orogenic Au deposits. This study investigates the mobility of Au, As, and Sb during metamorphism of the Dalradian metasedimentary rocks of Scotland. The metamorphic processes in the Dalradian of Scotland are extremely well studied, and the terrane is an ideal area to investigate mobility of these metals. Our results show that of the 25 major and trace elements analysed, only Au, As, Sb, S and volatile contents as shown by loss on ignition (LOI) values show systematic variation with the metamorphic grade of the samples. Average Au concentrations decrease from 1.1 ± 0.55 ppb and 0.72 ± 0.34 ppb in chlorite and biotite zone rocks down to 0.4 ± 0.22 ppb and 0.34 ± 0.13 ppb in kyanite and sillimanite zone rocks. Average As concentrations decrease from 4.8 ppm (range 0.5 to 17.8 ppm) and 1.96 ± 1.9 ppm in chlorite and biotite zone rocks down to 0.24 ± 0.15 ppm and 0.2 ± 0.12 ppm in kyanite and sillimanite zone rocks. Average Sb concentrations decrease from 0.18 ± 0.15 ppm and 0.11 ± 0.10 ppm in chlorite and biotite zone rocks down to 0.04 ± 0.02 ppm in both kyanite and sillimanite zone rocks. Sulphur and LOI concentrations also show significant decreases. Mass balance calculations indicate that compared to chlorite and biotite zone samples, sillimanite zone samples have an average mass loss of 62 ± 14%, 94 ± 4% and 74 ± 14% for Au, As, and Sb respectively. Every 1 km3 of chlorite-biotite zone mixed psammitic-pelitic protolith rock that is metamorphosed to sillimanite zone conditions would release 1.5 t Au, 8613 t As, 270 t Sb, and 1.02 Mt S. The mobility of these elements is strongly controlled by the paragenesis of sulphide minerals. Pyrite, sphalerite, galena and cobaltite (as well as gersdorffite) decrease in abundance with increasing metamorphic grade in the Dalradian metasedimentary rocks. A critical aspect of the sulphide paragenesis is the

  10. Redefinition and Significance of Metamorphism Xilinhot Group in Xilinhot Area, Inner Mongolia, China%内蒙古锡林浩特地区中元古代锡林浩特岩群的厘定及其意义

    Institute of Scientific and Technical Information of China (English)

    周文孝; 葛梦春


    Based on large scale geologic mapping and measuring section,the Xilin Col complex is divided into three parts:supracrustal rock,Late Proterozoic basic-uhrabasic rock and Early Paleozoic acid intrusive rocks.According to lithologic association and characteristics of deformation and metamorphism,biotite (garnet) plagioclase gneiss intercalated with several layers barred amphibolite,with thin layer magnetite quartzite on its top; medium-coarse biotite plagioclase gneiss and fine-grained felsic gneiss; lithologic association of migmatization banding biotite (hornblende) plagioclase gneiss and garnet monzonitic gneiss intercalated with barred amphibolite; sillimanite biotite plagioclase gneiss,barred biotite plagioclase gneiss,intercalated with garnet bearing biotite quartz schist.Comparison study on the different lithologic association,metamorphic characteristics and depositional environment of Baoyintu Group,Ailegemiao Formatio,Bainaimiao Group and others.This paper proposes to redefine these supercrustal rocks named "Xilinhot Group",which compose the Precambrian metamorphic basement of Xilin Col micro block.It's important to study the formation and development of Xilin Col micro block and the evolution of structural relationship between Siberia plate and North China plate.%通过大比例尺填图和剖面研究,将内蒙古锡林浩特地区的“锡林郭勒杂岩”解体分为3大部分:一套表壳岩、晚元古代基性-超基性侵入岩和早古生代酸性侵入岩.在此基础上根据变质岩的岩性组合和变形变质特点,可将其中的表壳岩化分为4个岩性段:黑云(石榴石)斜长片麻岩,间夹多层条纹状斜长角闪岩,在其顶部多见薄层含磁铁石英岩;中粗粒黑云斜长片麻岩和细粒长英质片麻岩;混合岩化条带状黑云(角闪)斜长片麻岩,含石榴石黑云二长片麻岩夹条纹状斜长角闪岩组合;夕线石黑云斜长片麻岩,条纹状黑云斜长片麻岩,间夹含石榴石黑云母

  11. Zircon LA-ICP MS U-Pb Age, Sr-Nd-Pb Isotopic Compositions and Geochemistry of the Triassic Post-collisional Wulong Adakitic Granodiorite in the South Qinling, Central China, and Its Petrogenesis

    Institute of Scientific and Technical Information of China (English)

    QIN Jiangfeng; LAI Shaocong; WANG Juan; LI Yongfei


    The Indosinian post-collisional Wulong pluton intruded into the Mesoproterozoic Fuping Group, South Qinling, central China. In the southern part of the pluton, some mafic enclaves have sharp or gradational contact relationships with the host biotite granodiorite. Geochemistry, zircon LA-ICP MS (laser ablation inductively-coupled plasma mass spectrometry) U-Pb chronology and Sr- Nd-Pb isotope geochemistry of the pluton are reported in this paper. The biotite granodiorite shows close compositional similarities to high-silica adakite. Its chondrite-normalized REE patterns are characterized by strong HREE depletion (Yb = 0.33-0.96 10-6 and Y = 4.77-11.19×10-6), enrichment of Ba (775-1386×10-6) and Sr (643-1115×10-6) and high Sr/Y (57.83-159.99) and Y/Yb (10.99-14.32) ratios, as well as insignificant Eu anomalies (δEu = 0.70-0.83), suggesting a feldspar-poor, garnet±amphibole-rich residual mineral assemblage. The mafic enclaves have higher MgO (4.15- 8.13%), Cr (14.79-371.31×10-6), Ni (20.00-224.24×10-6) and Nb/Ta (15.42-21.91) than the host granodiorite, implying that they are mantle-derived and might represent underplated mafic magma. Zircon LA-ICP MS dating of the granodiorite yields a 20.6Pb/238U weighted mean age of 208±2 Ma (MSWD=0.50, 1σ), which is the age of emplacement of the host biotite granodiorite. This age indicates that the Wulong pluton formed during the late-orogenic or post-collisional stage (≤242±21 Ma) of the South Qinling belt. The host biotite granodiorite displays 87Sr/86Sr = 0.7059-0.7062, Isr = 0.7044-0.7050,143Nd/144Nd = 0.51236-0.51238, εNd(t)=-2.26 to-2.66,2.6Pb/2.4pb=18.099-18.209,207Pb/2.4pb=15.873-15.979 and 2.8Pb/204pb=38.973-39.430. Those ratios are similar to those of the Mesoproterozoic Yaolinghe Group in the South Qinling. Furthermore, its Nd isotopic model age(~1.02 Ga) is consistent with the age (~1.1 Ga) of the Yaolinghe Group. Based on the integrated geological and geochemical studies, coupled with previous

  12. Petrogenesis of the Seleteguole granitoids from Jinhe county in Xinjiang (West China): Implications for the tectonic transformation of Northwest Tianshan (United States)

    Zhang, Wei; Leng, Cheng-Biao; Zhang, Xing-Chun; Su, Wen-Chao; Tang, Hong-Feng; Yan, Jia-Hui; Cao, Jing-Liang


    The Seleteguole Cu-Mo deposit in Jinghe County, Xinjiang is tectonically located on the northern margin of the Northwestern Tianshan. Three major intrusions including biotite granite, diorite porphyry and quartz diorite porphyry have been identified. The biotite granite, with a zircon U-Pb age of 307 ± 3 Ma, intruded carbonates and clastic rocks of the Middle Carboniferous Dongtujin Formation. The younger diorite porphyry and quartz diorite porphyry, with an identical zircon U-Pb age of 302 ± 3 Ma, locally intruded the biotite granite; where the granite in contact with the two porphyries were characterized by phyllic alteration. The mineralogical and geochemical characteristics indicate that all granitoids in Seleteguole belong to calc-alkaline I-type. These granitoids are enriched in LILE relative to HFSE with negative anomalies of Nb, P and Ti, typical of arc-related rocks. All three granitoids have positive zircon εHf(t) values, low Mg# ratios (34-39), and low Cr (geological and geochemical characteristics of the Late Carboniferous igneous rocks in the Northwestern Tianshan show that Late Carboniferous I-type granitoids, with juvenile Sr-Nd-(Hf) isotopic signatures, formed in a continent-marginal arc setting as a result of the subduction of Paleo-Junggar Ocean beneath the Yili Block. In combination with the compositions of the Early Permian granitoids in the region, we suggest that the tectonic setting of the Northwestern Tianshan transformed from a continental arc to an intracontinental extension setting at the Carboniferous-Permian boundary (ca. 300 Ma).

  13. Indicator minerals as guides to base metal sulphide mineralisation in Betul Belt, central India

    Indian Academy of Sciences (India)

    Biswajit Ghosh; M N Praveen


    Zn-bearing minerals that act as indicator minerals for base metal sulphide mineralization from the Proterozoic Betul Belt,central India with special emphasis on their genetic significance have been discussed.Sulphide mineralisation is hosted by the felsic volcanic rocks and has similarities with volcanic-hosted massive sulphide deposits in other parts of the world.Synvolcanic hydrothermal alteration is crudely zoned with an inner high Mg-Ca core and an outer wider envelop of Al-Fe rich mineral assemblage.Most of the prospects have strata bound,moderately to steeply dipping, multiple,sub-parallel sheet like ore bodies composed of disseminated and semi-massive to massive ores.Zn-bearing spinel,staurolite,biotite and ilmenite typically occur within the foot-wall altera- tion zones in close proximity to the sulphide mineralization.Zincian spinel is ubiquitous irrespective of the nature of alteration zone.Zincian staurolite is nearly absent in Mg-Ca alteration zones but commonly present in Al-Fe alteration zone along with zincian ilmenite.Zn-bearing biotite in intimate association with zincian spinel is generally found in Mg-Ca alteration zone and in the transition to Al-Fe alteration zone.Most of these indicator minerals can be considered as products of desulphidation of sphalerite during metamorphism.Mechanisms other than desulphidation like formation of gahnite by overstepping of the zinc saturation limit of biotite during retrogression to chlorite and formation of zincian staurolite at the expense of gahnite is also recorded.Field presence of these minerals has immense significance in exploration in Betul Belt as they occur in close spatial relationship with the sulphide rich zones and therefore act as direct vectors to ore.

  14. Contamination in mafic mineral-rich calc-alkaline granites: a geochemical and Sr-Nd isotope study of the Neoproterozoic Piedade Granite, SE Brazil

    Directory of Open Access Journals (Sweden)

    Leite Renato J.


    Full Text Available The Piedade Granite (~600 Ma was emplaced shortly after the main phase of granite magmatism in the Agudos Grandes batholith, Apiaí-Guaxupé Terrane, SE Brazil. Its main units are: mafic mineral-rich porphyritic granites forming the border (peraluminous muscovite-biotite granodiorite-monzogranite MBmg unit and core (metaluminous titanite-bearing biotite monzogranite BmgT unit and felsic pink inequigranular granite (Bmg unit between them. Bmg has high LaN/YbN (up to 100, Th/U (>10 and low Rb, Nb and Ta, and can be a crustal melt derived from deep-seated sources with residual garnet and biotite. The core BmgT unit derived from oxidized magmas with high Mg# (~45, Ba and Sr, fractionated REE patterns (LaN/YbN= 45, 87Sr/86Sr(t~ 0.710, epsilonNd(t ~ -12 to -14, interpreted as being high-K calc-alkaline magmas contaminated with metasedimentary rocks that had upper-crust signature (high U, Cs, Ta. The mafic-rich peraluminous granites show a more evolved isotope signature (87Sr/86Sr(t = 0.713-0.714; epsilonNd(t= -14 to -16, similar to Bmg, and Mg# and incompatible trace-element concentrations intermediate between Bmg and BmgT. A model is presented in whichMBmgis envisaged as the product of contamination between a mafic mineral-rich magma consanguineous with BmgT and pure crustal melts akin to Bmg.

  15. Petrology and radiogeology of the Stripa pluton

    Energy Technology Data Exchange (ETDEWEB)

    Wollenberg, H.; Flexser, S.; Andersson, L.


    Both the quartz monzonite and the metavolcanic leptite which it intruded are strongly fractured. Two stages of fracture filling are evident; an earlier stage encompassing quartz, sericite, feldspar, epidote, and chlorite, and a later stage dominated by carbonate minerals. The Stripa quartz monozite is chemically and mineralogically distinct from other plutons in the region. Muscovite is the predominant mica in the quartz monzonite; biotite has been altered to chlorite, hornblende is absent, and accessory minerals are scarce. In contrast, in other plutons in the Stripa region, biotite and hornblende are prominent mafic minerals and accessory minerals are abundant. The Stripa quartz monzonite is also considerably more radioactive than the the leptite and other plutons in the region. Uranium and thorium abundances are both approx. 30 ppM, considerably higher than in normal granitic rocks where the thorium-to-uranium ratio generally exceeds 2. Potassium-argon dating of muscovite from the Stripa quartz monzonite indicates that this rock may be older, at 1691 million years than granitic rock of the neighboring Gusselby and Kloten massifs, whose ages, based on K-Ar dating of biotite, are respectively 1604 and 1640 m.y. Heat flow and heat productivity considerations show that although Stripa quartz monzonite contains high abundances of radioelements, the pluton has little efect on the regional heat flow. If it occurs in a layered plutonic setting, it is not more than 1.5 km thick; otherwise it may comprise a stock, dike, or border phase that is relatively small compared with the large granitic plutons exposed in the region.

  16. 40Ar/ 39Ar and RbSr analyses from ductile shear zones from the Atacama Fault Zone, northern Chile: the age of deformation (United States)

    Scheuber, Ekkehard; Hammerschmidt, Konrad; Friedrichsen, Hans


    The influence of deformation on the K-Ar and the Rb-Sr isotope system is investigated. It is assumed that, due to the diffusion processes involved, deformation has a similar effect on isotopic equilibrium as has temperature. In order to examine the influence of deformation on the K-Ar and the Rb-Sr isotope systems two shear zones from the Atacama Fault Zone (AFZ), situated in the north Chilean Coastal Cordillera, have been investigated. The AFZ, which was active as a sinistral strike-slip fault during the Mesozoic, has two sets of shear zones, one formed under amphibolite (SZ1), one under greenschist facies conditions (SZ2), Rb-Sr and 40Ar/ 39Ar age determinations were conducted on samples from cross sections of each set. In SZ1 the hornblendes and bioties from a weakly deformed sample reveal cooling ages of 153-152 and 150 ± 1 Ma, respectively. Biotite from the center of the shear zone of SZ1 gave an isochron of 143.9 ± 0.3 Ma (MSWD = 0.04) which is interpreted as the age of deformation which produced resetting of the mineral system. In SZ2 hornblendes yielded 40Ar/ 39Ar plateau (cooling) ages of ˜ 138 Ma. Biotites from undeformed samples gave Rb-Sr and 40Ar/ 39Ar total degassing ages of 130 ± 1 Ma, whereas biotite from the mylonitic rocks yielded 126-125 Ma which dates the time of deformation. Sr isotope homogenization occurred in the mylonitic rocks, and is most likely a result of deformation. The formation of SZ1 can be correlated to the Araucanian (= Nevadan) phase. The deformation in SZ2 is related to the onset of uplift and cooling of the Coastal Cordilleran magmatic arc.

  17. Structural, petrological and geochronological analysis of the lithotypes from the Pien region (Parana State, Brazil) and adjacences

    International Nuclear Information System (INIS)

    The Pien area presents the major geotectonic domains separated by the Pien Shear Zone (PSZ). The northern one is the Rio Pien Granite-Mylonitic Suite composed by calc-alkaline granitoids of Neoproterozoic age. The southern domain is represented by the Amphibolite-Granulite where high grade metamorphism took place at the end of paleoproterozoic time. Considering the identified lithotypes, their geochemical affinity (particularly the Ti, Cr, Ni and REE content) and the geological context observed in the area, a geotectonical model of active continental margin related to subduction SSZ (Supra-Subduction Zone) is proposed. K-Ar on plagioclase from gabbronorites gave Neoproterozoic ages although Sm-Nd whole rock isochron yielded Paleoproterozoic ages. Based in geochemical data, it is proposed that the biotite gneiss and biotite-amphibole-gneiss which occur near the PSZ have a shoshonitic to high-K calc-alkaline features which are characteristic of active continental margins. K-Ar on biotite extracted from these rocks, gave Neoproterozoic ages. The available radiometric data for the Rio Pien mylonitic granitoids show that between 650-595 Ma the generation, deformation and cooling below the isotherm of 250 deg C occurred. On the other hand, the geochronological data for the Agudos do Sul Massif are in the 590-570 Ma interval showing its younger generation. The Sr87 / Sr86 initial ratios for both granitoids suggest more involvement of the continental crust in the origins of Agudos do Sul granitic Massif. The analyses of the entire set of the available data for the Pien area allows the suggestion of a geotectonic scenery related to the evolution of an active continental margin during the collages associated to the Brasiliano Cycle

  18. Structural, petrological and geochronological analysis of the lithotypes from the Pien region (Parana State, Brazil) and adjacences; Analise estrutural, petrologica e geocronologica dos litotipos da Regiao de Pien (PR) e adjacencias

    Energy Technology Data Exchange (ETDEWEB)

    Harara, Ossama Mohamed


    The Pien area presents the major geotectonic domains separated by the Pien Shear Zone (PSZ). The northern one is the Rio Pien Granite-Mylonitic Suite composed by calc-alkaline granitoids of Neoproterozoic age. The southern domain is represented by the Amphibolite-Granulite where high grade metamorphism took place at the end of paleoproterozoic time. Considering the identified lithotypes, their geochemical affinity (particularly the Ti, Cr, Ni and REE content) and the geological context observed in the area, a geotectonical model of active continental margin related to subduction SSZ (Supra-Subduction Zone) is proposed. K-Ar on plagioclase from gabbronorites gave Neoproterozoic ages although Sm-Nd whole rock isochron yielded Paleoproterozoic ages. Based in geochemical data, it is proposed that the biotite gneiss and biotite-amphibole-gneiss which occur near the PSZ have a shoshonitic to high-K calc-alkaline features which are characteristic of active continental margins. K-Ar on biotite extracted from these rocks, gave Neoproterozoic ages. The available radiometric data for the Rio Pien mylonitic granitoids show that between 650-595 Ma the generation, deformation and cooling below the isotherm of 250 deg C occurred. On the other hand, the geochronological data for the Agudos do Sul Massif are in the 590-570 Ma interval showing its younger generation. The Sr{sup 87} / Sr{sup 86} initial ratios for both granitoids suggest more involvement of the continental crust in the origins of Agudos do Sul granitic Massif. The analyses of the entire set of the available data for the Pien area allows the suggestion of a geotectonic scenery related to the evolution of an active continental margin during the collages associated to the Brasiliano Cycle 201 refs., 130 figs., 6 tabs., 2 maps

  19. Características petrográficas y geoquímicas de la Tonalita La Ovejería, borde oriental de la Sierra del Aconquija, Tafí del Valle, Tucumán: integración con la Granodiorita El Infiernillo

    Directory of Open Access Journals (Sweden)

    Castro, Antonio


    Full Text Available The La Ovejería Tonalite is a N-S elo ngated body that crops out on the eastern side of the Sierra del Aconquija, west of of Tafi del Valle, Tucumán Province, Argentina. It is located just south of thelarger, and probably genetically related, El Infiernillo Granodiorite. The studied pluton has a zoning determined by different grain sizes and mineralogies: the northern outcrops are medium-grained and composed of plagioclase, quartz scarce microcline, and biotite and pistacite (± tourmaline as major accessories; the southern part of the intrusive is fine grained and composed of plagioclase, quartz scarce microcline, and biotite and sphene as accessory minerals. Two meter thick granitic dikes cross-cut the tonalites. The tonalite is calc-alkaline and peraluminous, with an ASI between 1.10 and 1.48. It intrudes metamorphic basement rocks composed of low grade schists that are characterized by an increase in static metamorphism, by syntectonic intrusions and by the intensity of flow folds.The emplacement of the La Ovejería Tonalite probably occurred during the Lower Paleozoic and was structurally controlled by the Tafi Megafracture, like the other intrusive bodies of the area. The El Infiernillo intrusive is composed of a two-mica (± tourmaline equigranular granodiorite main facies and a biotite and epidote bearing (without primary muscovite tonalitic border facies. According to field relations and petrographic, geochemical and structural data, the La Ovejería Tonalite may correspond to the northern border facies of the El Infiernillo intrusive.

  20. Mechanisms and Processes Leading to Reverse Zoning in the Andong Granitoid Pluton, Andong Batholith, Korea

    Institute of Scientific and Technical Information of China (English)

    Sang Koo HWANG


    The Andong pluton consists of comagmatic granitoid rocks which constitute outstanding examples of reversely zoned granitoids. The pluton has three lithofacies: hornblende biotite tonalite, biotite granodiorite and porphyritic biotite granite. The zoned pattern forms by locating a tonalite core containing high-temperature mafic assemblages in central part,granodiorite rims in marginal part, and a porphyritic granite cap containing more felsic assemblages in topside of the pluton.Mineral abundances as well as bulk compositions of the granitoids indicate that the interior is enriched in mafic minerals and that it shows higher contents of oxides than the margin and topside. The compositional gradients change gradually with continuity between the lithofacies. The regular compositional variations within the pluton support the argument that the pluton behaved as an individual petrochemical system. Model abundances of the granitoids are in agreement with the bulk compositional gradients, suggesting that no significant interaction with country rocks occurred. Remobilization (resurgence) of deeper parts of the system into the more felsic magmas of the chamber explains the reverse zoning. Fractional crystallization was of importance and probably accounts for the selective removal of the settling phases. The Andong pluton is an example of reversely zoned plutons related by remobilization of more mafic but consanguineous magmas. Large-scale upwelling occurred in the pluton leading to the present arrangement of three lithofacies. It is conceivable that remnants of the reverse zoning become more difficult to discern as the plutonic rocks reach the latest stages of their evolution. In this case, the Andong pluton represents an earlier stage in the evolution of a felsic system that is usually represented by the final stages in normally zoned plutons.

  1. LA-ICP-MS U-Pb apatite dating of Lower Cretaceous rocks from teschenite-picrite association in the Silesian Unit (southern Poland

    Directory of Open Access Journals (Sweden)

    Szopa Krzysztof


    Full Text Available The main products of volcanic activity in the teschenite-picrite association (TPA are shallow, sub-volcanic intrusions, which predominate over extrusive volcanic rocks. They comprise a wide range of intrusive rocks which fall into two main groups: alkaline (teschenite, picrite, syenite, lamprophyre and subalkaline (dolerite. Previous 40Ar/39Ar and 40K/40Ar dating of these rocks in the Polish Outer Western Carpathians, performed on kaersutite, sub-silicic diopside, phlogopite/biotite as well as on whole rock samples has yielded Early Cretaceous ages. Fluorapatite crystals were dated by the U-Pb LA-ICP-MS method to obtain the age of selected magmatic rocks (teschenite, lamprophyre from the Cieszyn igneous province. Apatite-bearing samples from Boguszowice, Puńców and Lipowa yield U-Pb ages of 103± 20 Ma, 119.6 ± 3.2 Ma and 126.5 ± 8.8 Ma, respectively. The weighted average age for all three samples is 117.8 ± 7.3 Ma (MSWD = 2.7. The considerably smaller dispersion in the apatite ages compared to the published amphibole and biotite ages is probably caused by the U-Pb system in apatite being less susceptible to the effects of hydrothermal alternation than the 40Ar/39Ar or 40K/40Ar system in amphibole and/or biotite. Available data suggest that volcanic activity in the Silesian Basin took place from 128 to 103 Ma with the the main magmatic phase constrained to 128-120 Ma.

  2. On the genetic classification and tectonic implications of the Early Yanshanian granitoids in the Nanling Range, South China

    Institute of Scientific and Technical Information of China (English)

    LI XianHua; LI WuXian; LI Zheng-Xiang


    Early Yanshanian (Jurassic) granitoids are widespread in the Nanling Range of South China, and are associated with numerous non-ferrous and rare metal mineral deposits. These granitoids consist mainly of slightly peraluminous biotite monzogranites and K-feldspar granites that are closely associated in time and space with subordinate amphibole-bearing granites and muscovite- and garnet-bearing granites. In most previous studies, the biotite-bearing granites were classified as crustal transformation-type (corresponding to the S-type) granites which were interpreted to be derived from the regional Paleoproterozoic meta-sedimentary rocks. In this paper, we re-analyze the geochemical characteristics of a number of representative Early Yanshanian Nanling granitoids. There exists a clear negative correlation between SiO2 and P2O5 for the studied granitoids. The Early Yanshanian Nanling granitoid suites (including amphibole-bearing granodiorites→biotite monzogranites→K-feldspar granites→two-mica (muscovite) granites) are metaluminous to slightly peraluminous I-type or fractionated I-type granites. They were derived predominantly from Proterozoic igneous protoliths. The juvenile crust and/or newly mantle-derived materials might also have been involved in some of these granites. In addition, the I- and fractionated I-type granites are closely associated in time and space with minor amount of A-type felsic and mafic volcanic and intrusive rocks as well as alkaline rocks. All these rocks constitute a typical assemblage of anorogenic, intraplate magmatism, suggesting a dominant lithospheric extensional regime for the Nanling Range and neighboring region during the Early Yanshanian period.

  3. Occurrence of Tourmaline in Metasedimentary Rocks of the Isua Supracrustal Belt, Greenland: Implications for Ribose Stabilization in Hadean Marine Sediments (United States)

    Mishima, Shinpei; Ohtomo, Yoko; Kakegawa, Takeshi


    Abiotic formation of RNA was important for the emergence of terrestrial life, but the acknowledged difficulties of generating and stabilizing ribose have often raised questions regarding how the first RNA might have formed. Previous researchers have proposed that borate could have stabilized ribose; however, the availability of borate on the early Earth has been the subject of intense debate. In order to examine whether borate was available on the early Earth, this study examined metasedimentary rocks from the Isua Supracrustal Belt. Garnet, biotite, and quartz comprise the major constituents of the examined rocks. Field relationships and the chemical compositions of the examined rocks suggest sedimentary origin. The present study found that garnet crystals contain a number of inclusions of tourmaline (a type of borosilicate mineral). All tourmaline crystals are Fe-rich and categorized as schorl. Both garnet and tourmaline often contain graphite inclusions and this close association of tourmaline with garnet and graphite has not been recognized previously. Garnet-biotite and graphite geothermometers suggest that the tourmaline in garnet experienced peak metamorphic conditions (~500 °C and 5 kbar). The mineralogical characteristics of the tourmaline and the whole rock composition indicate that the tourmaline formed authigenically in the sediment during diagenesis and/or early metamorphism. Clay minerals in modern sediments have the capability to adsorb and concentrate borate, which could lead to boron enrichment during diagenesis, followed by tourmaline formation under metamorphic conditions. Clay minerals, deposited on the early Archean seafloor, were the precursors of the garnet and biotite in the examined samples. The studied tourmaline crystals were most likely formed in the same way as modern tourmaline in marine sediments. Therefore, boron enrichment by clays must have been possible even during the early Archean. Thus, similar enrichment could have been

  4. P-T-t-D paths of the North Himalayan metamorphic rocks: Implications for the Himalayan orogeny (United States)

    Ding, Huixia; Zhang, Zeming; Hu, Kaiming; Dong, Xin; Xiang, Hua; Mu, Hongchen


    Metamorphic P-T-t-D paths have been determined in the Yardoi gneiss dome of the eastern Himalaya that place new constraints on the genesis of the North Himalayan Gneiss Dome and tectonic evolution of the Himalayan orogen. Our study shows that the schists from the Yardoi dome underwent at least three stages of metamorphism and deformation. The first stage of prograde metamorphism is represented by the core of porphyroblastic garnet, showing distinct growth compositional zoning, and hosting mineral inclusions of biotite, muscovite, quartz and ilmenite; the curved inclusion trails define the first stage of deformation foliation (S1). The second stage of peak metamorphism is represented by the rim of porphyroblastic garnet and the aligned matrix minerals of biotite, muscovite, plagioclase, quartz, kyanite and staurolite, which define the main deformation foliation (S2). The third stage of retrograde metamorphism is characterized by occurrence of biotite, plagioclase, muscovite and sillimanite within the distributed shear bands, which define the late deformation foliation (S3). Phase equilibrium modeling reveals that Yardoi schists witnessed a peak metamorphism of upper amphibolite-facies under P-T conditions of 7-8 kbar and 615-665 °C, and records a clockwise P-T-t-D path with a prograde process of both temperature and pressure increase and subsequent retrogression of isothermal decompression. The zircon U-Pb dating indicates that the prograde process occurred during the Middle Eocene of 48-36 Ma and the retrograde metamorphism probably lasted to ca. 16 Ma. The present result shows that the formation of the Yardoi schists was related to the subduction and exhumation of Indian crust, the initial collision of Indian and Asian continents occurred at ca. 50 Ma, the northeastern margin of the Indian continent was shallowly underthrusted beneath the Asian continent, and distinct tectonic discontinuity is present in the Greater Himalayan Sequence.

  5. Timing and conditions of peak metamorphism and cooling across the Zimithang Thrust, Arunachal Pradesh, India (United States)

    Warren, Clare J.; Singh, Athokpam K.; Roberts, Nick M. W.; Regis, Daniele; Halton, Alison M.; Singh, Rajkumar B.


    The Zimithang Thrust juxtaposes two lithotectonic units of the Greater Himalayan Sequence in Arunachal Pradesh, NE India. Monazite U-Pb, muscovite 40Ar/39Ar and thermobarometric data from rocks in the hanging and footwall constrain the timing and conditions of their juxtaposition across the structure, and their subsequent cooling. Monazite grains in biotite-sillimanite gneiss in the hanging wall yield LA-ICP-MS U-Pb ages of 16 ± 0.2 to 12.7 ± 0.4 Ma. A schistose gneiss within the high strain zone yields overlapping-to-younger monazite ages of 14.9 ± 0.3 to 11.5 ± 0.3 Ma. Garnet-staurolite-mica schists in the immediate footwall yield older monazite ages of 27.3 ± 0.6 to 17.1 ± 0.2 Ma. Temperature estimates from Ti-in-biotite and garnet-biotite thermometry suggest similar peak temperatures were achieved in the hanging and footwalls (~ 525-650 °C). Elevated temperatures of ~ 700 °C appear to have been reached in the high strain zone itself and in the footwall further from the thrust. Single grain fusion 40Ar/39Ar muscovite data from samples either side of the thrust yield ages of ~ 7 Ma, suggesting that movement along the thrust juxtaposed the two units by the time the closure temperature of Ar diffusion in muscovite had been reached. These data confirm previous suggestions that major orogen-parallel out-of-sequence structures disrupt the Greater Himalayan Sequence at different times during Himalayan evolution, and highlight an eastwards-younging trend in 40Ar/39Ar muscovite cooling ages at equivalent structural levels along Himalayan strike.

  6. Variscan potassic dyke magmatism of durbachitic affinity at the southern end of the Bohemian Massif (Lower Austria) (United States)

    Zeitlhofer, Helga; Grasemann, Bernhard; Petrakakis, Konstantin


    Dykes in the Strudengau area (SW Moldanubian Zone, Austria) can be mineralogically divided into lamprophyres (spessartites and kersantites) and felsic dykes (granite porphyries, granitic dykes and pegmatoid dykes). Geochemical analyses of 11 lamprophyres and 7 felsic dykes show evidence of fractional crystallization. The lamprophyres are characterized by metaluminous compositions, intermediate SiO2 contents and high amounts of MgO and K2O; these rocks have high Ba (800-3000 ppm) and Sr (250-1000 ppm) contents as well as an enrichment of large-ion lithophile elements over high field strength elements, typical for enriched mantle sources with variable modifications due to fractionation and crustal contamination. This geochemical signature has been reported from durbachites (biotite- and K feldspar-rich mela-syenites particularly characteristic of the Variscan orogen in Central Europe). For most major elements, calculated fractionation trends from crystallization experiments of durbachites give an excellent match with the data from the Strudengau dykes. This suggests that the lamprophyres and felsic dykes were both products of fractional crystallization and subsequent magma mixing of durbachitic and leucogranitic melts. Rb-Sr geochronological data on biotite from five undeformed kersantites and a locally deformed granite porphyry gave cooling ages of c. 334-318 Ma, indicating synchronous intrusion of the dykes with the nearby outcropping Weinsberger granite (part of the South Bohemian Batholith, c. 330-310 Ma). Oriented matrix biotite separated from the locally deformed granite porphyry gave an Rb-Sr age of c. 318 Ma, interpreted as a deformation age during extensional tectonics. We propose a large-scale extensional regime at c. 320 Ma in the Strudengau area, accompanied by plutonism of fractionated magmas of syncollisional mantle-derived sources, mixed with crustal components. This geodynamic setting is comparable to other areas in the Variscan belt documenting an

  7. Age of Cu-Au mineralisation, Cloncurry district, eastern Mt Isa Inlier, Queensland, as determined by 40Ar/39Ar dating

    International Nuclear Information System (INIS)

    The 40Ar/39Ar dating of alteration biotite. muscovite and amphibole from a number of post-peak metamorphic Cu-Au deposits and alteration systems in the Cloncurry district. north Queensland has determined the timing of mineralisation and hydrothermal activity. Alteration biotite from the Ernest Henry Cu-Au, Starra Au-Cu, and Mt Elliott Cu-Au deposits, sericite associated with hematite breccias in the Wimberu Granite, muscovite from an albitite pipe that intrudes the Gilded Rose Breccia. And sericite from a granitoid near the Osborne Cu-Au deposit. yield ages which are broadly contemporaneous with the late ca 1510-1485 Ma phases of the Williams and Naraku Batholiths. Hornblende and biotite alteration, which pre-date Cu-Au mineralisation at Osborne. give a maximum age of ca 1540 Ma for the deposit. which is also a probable minimum age for peak metamorphism. Metamorphic minerals from the vicinity of Osborne yield dates which are significantly older (ca 1590-1570 Ma) than those from the hydrothermal phases. Dating by the K-Ar method of red. Hematitic K-feldspars which are regionally common in the Cloncurry district was not effective as the mineral yields ages up to 300 million years younger than coexisting alteration sericite. The 40Ar/39Ar age spectra obtained from most hydrothermal phases in the Eastern Fold Belt. Mt Isa Inlier commonly contain flat parts which comprise a large proportion of the released gas and are indicative of rapid cooling through the temperature of partial closure to Ar diffusion for the respective minerals. Copyright (1998) Blackwell Science Asia

  8. 40Ar/39Ar constraints on the timing and history of amphibolite facies gold mineralisation in the Southern Cross area, Western Australia

    International Nuclear Information System (INIS)

    The Southern Cross Greenstone Belt in Western Australia contains structurally controlled, hydrothermal gold deposits which are thought to have formed at or near the peak of amphibolite facies regional metamorphism during the Late Archaean. Although the geological features of deposits in the area are well documented. conflicting genetic models and ore-fluid sources have been used to explain the observed geological data. This paper presents new 40Ar/39Ar data which suggest that the thermal history of the Southern Cross area after the peak of regional metamorphism was more complex than has previously been suggested. After the main gold mineralisation event prior to ca 2620 Ma, the 40Ar/39Ar ages from amphiboles and biotites sampled from the alteration selvages of gold-bearing veins indicate that temperatures remained elevated in the region of 500 deg C for between 20 and 70 million years. These amphiboles and biotites from individual deposits yield ages that are in good agreement with one another to a high precision. implying increased cooling rates after the long period of elevated temperatures. Along the Southern Cross Greenstone Belt. however. amphibole-biotite pairs from the alteration selvages of gold-bearing quartz veins. while remaining in good agreement with one another, vary between deposits from ca 2560 Ma to ca 2440 Ma. Amphiboles from metabasalts that are associated with regional metamorphism and not hydrothermal alteration contain numerous exsolution lamellae that reduce the effective closure temperature of the amphiboles and yield geologically meaningless ages. These age relationships show that the thermal history of the area did not follow a simple cooling path and the area may have been tectonically active for a long period after the main gold mineralisation event before ca 2620 Ma. Such data may provide important constraints on subsequent genetic modelling of gold mineralisation and metamorphism. Copyright (1998) Blackwell Science Asia

  9. Petrology and radiogeology of the Stripa pluton

    International Nuclear Information System (INIS)

    Both the quartz monzonite and the metavolcanic leptite which it intruded are strongly fractured. Two stages of fracture filling are evident; an earlier stage encompassing quartz, sericite, feldspar, epidote, and chlorite, and a later stage dominated by carbonate minerals. The Stripa quartz monozite is chemically and mineralogically distinct from other plutons in the region. Muscovite is the predominant mica in the quartz monzonite; biotite has been altered to chlorite, hornblende is absent, and accessory minerals are scarce. In contrast, in other plutons in the Stripa region, biotite and hornblende are prominent mafic minerals and accessory minerals are abundant. The Stripa quartz monzonite is also considerably more radioactive than the the leptite and other plutons in the region. Uranium and thorium abundances are both approx. 30 ppM, considerably higher than in normal granitic rocks where the thorium-to-uranium ratio generally exceeds 2. Potassium-argon dating of muscovite from the Stripa quartz monzonite indicates that this rock may be older, at 1691 million years than granitic rock of the neighboring Gusselby and Kloten massifs, whose ages, based on K-Ar dating of biotite, are respectively 1604 and 1640 m.y. Heat flow and heat productivity considerations show that although Stripa quartz monzonite contains high abundances of radioelements, the pluton has little efect on the regional heat flow. If it occurs in a layered plutonic setting, it is not more than 1.5 km thick; otherwise it may comprise a stock, dike, or border phase that is relatively small compared with the large granitic plutons exposed in the region

  10. Ion-adsorption REEs in regolith of the Liberty Hill pluton, South Carolina, USA: An effect of hydrothermal alteration (United States)

    Bern, Carleton R.; Yesavage, Tiffany; Foley, Nora K.


    Ion-adsorbed rare earth element (REE) deposits supply the majority of world heavy REE production and substantial light REE production, but relatively little is known of their occurrence outside Southeast Asia. We examined the distribution and forms of REEs on a North American pluton located in the highly weathered and slowly eroding South Carolina Piedmont. The Hercynian Liberty Hill pluton experiences a modern climate that includes ~ 1500 mm annual rainfall and a mean annual temperature of 17 °C. The pluton is medium- to coarse-grained biotite-amphibole granite with minor biotite granite facies. REE-bearing phases are diverse and include monazite, zircon, titanite, allanite, apatite and bastnäsite. Weathered profiles were sampled up to 7 m-deep across the ~ 400 km2pluton. In one profile, ion-adsorbed REEs plus yttrium (REE + Y) ranged up to 581 mg/kg and accounted for up to 77% of total REE + Y in saprolite. In other profiles, ion-adsorbed REE + Y ranged 12–194 mg/kg and only accounted for 3–37% of totals. The profile most enriched in ion-adsorbed REEs was located along the mapped boundary of two granite facies and contained trioctahedral smectite in the saprolite, evidence suggestive of hydrothermal alteration of biotite at that location. Post-emplacement deuteric alteration can generate easily weathered REE phases, particularly fluorocarbonates. In the case of Liberty Hill, hydrothermal alteration may have converted less soluble to more soluble REE minerals. Additionally, regolith P content was inversely correlated with the fraction ion-adsorbed REEs, and weathering related secondary REE-phosphates were found in some regolith profiles. Both patterns illustrate how low P content aids in the accumulation of ion-adsorbed REEs. The localized occurrence at Liberty Hill sheds light on conditions and processes that generate ion-adsorbed REEs.

  11. The post-collisional volcanism of northern Tunisia: Petrology and evolution through time (United States)

    Halloul, Néji; Gourgaud, Alain


    The Neogene volcanism of Tunisia is bimodal, comprising both mafic lavas and rhyolites. The rhyolites occur as domes and related breccias, and as dykes in the Nefza area, associated with an albite granite. The rhyolites volcanics are 12.9-8.2 Ma. Mafic lavas occur in the Nefza and Mogods areas, as dykes and sills, and are younger than the felsic lavas at 8.4-5 Ma. The rhyolites exhibit phenocrysts of quartz, plagioclase (An 25-55), alkali feldspar (Or 63-91), biotite, Fe-Ti oxides and rare cordierite and tourmaline. A study of the cordierite shows it to be magmatic in character, in equilibrium with glass and other minerals, and with a large range of compositions (Fe * 34-64). Magmatic cordierite in rhyolites is exceptional and cordierite/liquid partition coefficients were determined for rare earth elements. According to mineralogical and geochemical data, including Sr isotopes, there are two groups of rhyolites. The first group is the cordierite bearing-rhyolites, which have Fe-rich biotite, and is related to localised crustal melting. The second group, which lack cordierite, but has Mg-rich biotite, is related to AFC processes. The mafic magma is represented by moderately Na-alkaline silica undersaturated hawaites and mugearites, with phenocrysts of olivine (Fo 69-85), plagioclase (An 49-67), clinopyroxene (augite) and ulvöspinel. Geochemical data suggest that they are transitional in nature, between calc-alkaline and alkaline magmas, as also found in Algeria and Morocco. These magmas evolved by fractional crystallization and crustal contamination. The magmatic change through time from calk-alkaline to transitional, as also found for Algeria and Morocco at the same point in time, is consistent with a slab breakoff process. The more recent mafic magmas are related to an extensional post-collisional environment.

  12. Precise revision of the garnet-muscovite geothermometer

    Institute of Scientific and Technical Information of China (English)

    WU; Chunming; (吴春明); ZHAO; Yingjun; (赵英俊)


    The garnet-muscovite geothermometer was refined through empirical calibration by using natural rocks metamorphosed under the physical conditions of 238—1306 MPa and 490—700℃. Input temperatures and pressures were determined through simultaneously applying the garnet-biotite geothermometer and the garnet-biotite-plagioclase-quartz barometer, assuming that all FeO in muscovite and garnet be ferrous. Garnet was treated as the asymmetric quaternary solid solution, and muscovite as the symmetric binary solid solution. Input muscovite compositions include Fe atoms between 0.03—0.19 and Mg atoms between 0.04—0.16 on the basis of 11 oxygen atoms, and input garnet compositions include spessartine fractions between 0.01—0.289, grossular fractions between 0.028—0.273, and the Fe/Mg ratio between 3.387-18.986. The resulting garnet-muscovite geothermometer reproduces temperatures within (50℃ compared with the garnet-biotite thermometer. Total random error of ±37℃ of the new thermometer may stem from the pressure uncertainty of ±200 MPa, and uncertainties of ±5% of Fe and Mg components in muscovite, and ±5% of Fe, Mg, Mn and Ca components in garnet, altogether. When there exist 10%, 20%, 30%, 40% and 50% Fe3+ in muscovite, respectively, the computed garnet-muscovite temperatures will be 1—6℃, 2—12℃, 3—16℃, 5—24℃ and 7—29℃, respectively, lower than those obtained when assuming that all FeO be ferrous. The new garnet-muscovite geothermometer can efficiently reflect temperature change of typical prograde sequences and contact aureole rocks, and may be applied to low- to high-grade and low- to high-pressure metamorphic rocks.

  13. Petrology of the anorogenic, oxidised Jamon and Musa granites, Amazonian Craton: implications for the genesis of Proterozoic A-type granites (United States)

    Dall'Agnol, Roberto; Rämö, O. Tapani; de Magalhães, Marilia Sacramento; Macambira, Moacir José Buenano


    The 1.88 Ga Jamon and Musa granites are magnetite-bearing anorogenic, A-type granites of Paleoproterozoic age. They intrude the Archaean rocks of the Rio Maria Granite-Greenstone Terrain in the eastern part of the Amazonian Craton in northern Brazil. A suite of biotite±amphibole monzogranite to syenogranite, with associated dacite porphyry (DP) and granite porphyry (GP) dykes, dominates in these subalkaline granites that vary from metaluminous to peraluminous and show high FeO/(FeO+MgO) and K 2O/Na 2O. In spite of their broad geochemical similarities, the Jamon and Musa granites show some significant differences in their REE patterns and in the behaviour of Y. The Jamon granites are related by fractional crystallisation of plagioclase, potassium feldspar, quartz, biotite, magnetite±amphibole±apatite±ilmenite. Geochemical modelling and Nd isotopic data indicate that the Archaean granodiorites, trondhjemites and tonalites of the Rio Maria region are not the source of the Jamon Granite and associated dyke magmas. Archaean quartz diorites, differentiated from the mantle at least 1000 m.y. before the emplacement of the granites, have a composition adequate to generate DP and the hornblende-biotite monzogranite magmas by different degrees of partial melting. A larger extent of amphibole fractionation during the evolution of the Musa pluton can explain some of the observed differences between it and the Jamon pluton. The studied granites crystallised at relatively high fO 2 and are anorogenic magnetite-series granites. In this aspect, as well as concerning geochemical characteristics, they display many affinities with the Proterozoic A-type granites of south-western United States. The Jamon and Musa granites differ from the anorthosite-mangerite-charnockite-rapakivi granite suites of north-eastern Canada and from the reduced rapakivi granites of the Fennoscandian Shield in several aspects, probably because of different magmatic sources.

  14. Rb–Sr and Sm–Nd study of granite–charnockite association in the Pudukkottai region and the link between metamorphism and magmatism in the Madurai Block

    Indian Academy of Sciences (India)

    M Chandra Sekaran; Rajneesh Bhutani; S Balakrishnan


    Pudukkottai region in the northeastern part of the Madurai Block exposes the garnetiferous pink granite that intruded the biotite gneiss. Charnockite patches are associated with both the rock types. Rb–Sr biotite and Sm–Nd whole-rock isochron ages indicate a regional uplift and cooling at ∼550 Ma. The initialNd isotope ratios (ε^t_{Nd} = −20 to −22) and Nd depleted-mantle model ages (T_{DM} = 2.25 to 2.79 Ga) indicate a common crustal source for the pink-granite and associated charnockite, while the biotite gneiss and the charnockite within it represent an older crustal source (ε^t_{Nd} = −29 and T_{DM} =>3.2 Ga). TheRb–Sr whole-rock data and initial Sr–Nd isotope ratios also help demonstrate the partial but systematic equilibration of Sr isotope and Rb/Sr ratios during metamorphic mineral-reactions resulting in an ‘apparent whole-rock isochron’. The available geochronological results from the Madurai Block indicate four major periods of magmatism and metamorphism: Neoarchaean–Paleoproterozoic, Mesoproterozoic, mid-Neoproterozoic and late-Neoproterozoic. We suggest that the high-grade and ultrahigh-temperature metamorphism was preceded by magmatism which ‘prepared’ the residual crust to sustain the high P–T conditions. There also appears to be cyclicity in the tectono-magmatic events and an evolutionary model for the Madurai Block should account for the cyclicity in the preserved records.

  15. "Gris Quintana": a Spanish granite from the Past into the Future. (United States)

    José Tejado, Juan; Mota, M. Isabel; Pereira, Dolores


    "Gris Quintana" is a medium-grained, biotite and amphibole granodiorite extracted in the Pluton of Quintana de la Serena (Extremadura, Spain). It is a constant light grey granite from the Hercynian geologic with excellent physicomechanical and physicochemical properties. The granodiorite is composed of plagioclase, biotite, quartz and alkali feldspar, with accessory allanite, titanite, apatite, zircon and ilmenite, mostly as inclusions within the biotite crystals. This commercial variety is extracted from many quarries in the late Hercynian plutons located in the Iberian Massif in Spain period (transition between Central Iberian and Ossa-Moren Zones), having large reserves of granite. Many of the quarries have their own transformation factory (high production zone), with which the sector is offered an endless variety of finishes and constructive rock typologies. A wide range of solutions to architects and designers are offered. Gris Quintana granite is one of the materials with highest technological benefits that are used in arquitecture. "Gris Quintana" granite has been used since ancient times, not only at a regional, but also at national and international level: paving, building (structural, exterior façadas, interior uses), urban decoration and funeral art. It can be found in monuments and more recently, in buildings of different styles and uses, that stand out in beauty and splendor, lasting in time. Some singular works in "Gris Quintana" granite all over the world: extension to the "Congreso de Diputados" (Parliament) in Madrid, "Puerta de San Vicente" in Madrid, Andalucia Parliament columns in Sevilla, New Senate Buiding in Madird, "Gran Vía" pavement in Madrid, "Teatro Real façade" in Madrid… "Gris Quintana" granite accomplishes all the requirements for its nomination as Global Heritage Stone Resource, for both its use in construction and for artistic purposes.

  16. Geology and pegmatites of part of the Fourmile area, Custer County, South Dakota (United States)

    Lang, Andrew J.; Redden, Jack Allison


    The Fourmile area, Custer County, S. Dak., is underlain by pre-Cambrian metamorphic rocks that surround the granitic core of the Black Hills. The main structure in the area is the upright limb of an overturned anticline that plunges about 30 ? S. 10 ? E. Three units of metamorphic rocks are described that have a total thickness of at least 7, 700 feet. The oldest of these units, a quartz-mica schist, is more than 6, 500 feet thick. The overlying unit, about 200 feet thick, is composed of thin beds of amphibolite and hornblende schist, lime-silicate rock, cordierite-biotite schist, microcline-biotite schist, and other types of rocks. The youngest unit, a quartz-mica-feldspar schist, is more than 1,000 feet thick. The presence of kyanite, staurolite, cordierite, and sillimanite in the rocks indicates that they have been subjected to high-grade metamorphism. About 420 pegmatites were mapped in the quartzmica-schist and the quartz-mica-feldspar schist. A few thin pegmatites in the third unit were not mapped. Most of these are concordant with the schistosity and relict (?) bedding of the enclosing metamorphic rocks. They are as much as 250 feet thick and range from 10 to 2, 600 feet in length. Nine peqmatites are zoned and classified as heterogeneous. The remainder are homogeneous and are poorly zoned. The major constituents are plaqioclase, quartz, perthite, and muscovite. The accessory minerals are tourmaline, apatite, garnet, and biotite. Beryl was observed in 15 peqmatites. The heterogeneous pegmatites contain commercial deposits of potash feldspar, mica (sheet and scrap), and beryl.

  17. Geological Characteristics of the Furong Tin Orefield, Hunan,40Ar-39Ar Dating of Tin Ores and Related Granite and Its Geodynamic Significance for Rock and Ore Formation

    Institute of Scientific and Technical Information of China (English)

    MAO Jingwen; LI Xiaofeng; CHEN Wen; LAN Xiaoming; WEI Shaoliu


    Furong, Hunan, is a large tin orefield discovered in China in recent years, which is mainly of the skarn-greisenchlorite type. On the basis of the geological characteristics of the orefield, 40Ar-39Ar dating was performed on muscovite from greisen-type tin ore and biotite from related amphibole-biotite granite, which yielded three sets of age data, i.e., a plateau age of 157.5±0.3 Ma and an i sochron age of 156.9±3 Ma for amphibole-biotite granite; a plateau age of 156.1 ±0.4Ma and an isochron age of 155.7±1.7 Ma for the Sanmen greisen-type tin ore; and a plateau age of 160.1±0.9 Ma and an isochron age of 157.5±1.5 Ma for the Taoxiwo greisen-type tin ore. The three sets of age data coincide well with each other They not only accurately reflect the timing of rock and ore formation but also indicate close relations between granite and tin deposits. In addition, the plateau ages of all three sets suggest that no subsequent thermal perturbation event occurred after the formation of granite and tin deposits. The Furong tin orefield is a component part of the southern Hunan large tungsten-tin polymetallic deposit concentration area and also a representative deposit formed in the time interval of 160-135 Ma in four peaks of Mesozoic tungsten-tin mineralization in the South China region. They might still correspond to the middle and late stages of the major geodynamic transition from a N-S- to an E-W-direction in eastern China.

  18. Isotopic evidence of Middle Proterozoic magmatism from Bombay High Field: Implications to crustal evolution of western offshore of India

    Indian Academy of Sciences (India)

    S S Rathore; A R Vijan; M P Singh; B N Prabhu; Anand Sahu


    Precambrian granitic basement rocks obtained from well BH-36 of Bombay High Field, western offshore of India has been studied both by Rb-Sr and K-Ar dating methods. Seven basement samples chosen from two cores have yielded whole rock Rb-Sr isochron age of 1446 ± 67Ma with an initial 87Sr/86Sr ratio of 0.7062 ± 0.0012. This age has been interpreted as the formation/emplacement time of the granite. Two biotite fractions of different grain size separated from a sample CC6B2T have yielded Rb-Sr mineral isochron age of 1385 ± 21 Ma. However, these fractions when studied by K-Ar dating method have yielded slightly higher but mutually consistent ages of 1458 ± 43Ma and 1465 ± 43Ma, respectively. Further, two biotites separated from additional samples CC5B9T and CC6B3B have yielded K-Ar ages of 1452 ± 42Ma and 1425 ± 40Ma with an overall mean age of 1438 ± 19Ma. This mean K-Ar age is indistinguishable from whole rock Rb-Sr isochron as well as mineral isochron age within experimental error. The similarity in the whole rock and biotite ages obtained by different isotopic methods suggests that no thermal disturbance has occurred in these rocks after their emplacement/formation around 1450Ma ago. The present study provides the evidence for the existence of an important Middle Proterozoic magmatic event around 1400-1450Ma on the western offshore of India which, hitherto, was thought to be mainly confined to the eastern Ghats, Satpura and Delhi fold belt of India. This finding may have an important bearing on the reconstruction of Proterozoic crustal evolution of western Indian shield.

  19. Occurrence of Tourmaline in Metasedimentary Rocks of the Isua Supracrustal Belt, Greenland: Implications for Ribose Stabilization in Hadean Marine Sediments. (United States)

    Mishima, Shinpei; Ohtomo, Yoko; Kakegawa, Takeshi


    Abiotic formation of RNA was important for the emergence of terrestrial life, but the acknowledged difficulties of generating and stabilizing ribose have often raised questions regarding how the first RNA might have formed. Previous researchers have proposed that borate could have stabilized ribose; however, the availability of borate on the early Earth has been the subject of intense debate. In order to examine whether borate was available on the early Earth, this study examined metasedimentary rocks from the Isua Supracrustal Belt. Garnet, biotite, and quartz comprise the major constituents of the examined rocks. Field relationships and the chemical compositions of the examined rocks suggest sedimentary origin. The present study found that garnet crystals contain a number of inclusions of tourmaline (a type of borosilicate mineral). All tourmaline crystals are Fe-rich and categorized as schorl. Both garnet and tourmaline often contain graphite inclusions and this close association of tourmaline with garnet and graphite has not been recognized previously. Garnet-biotite and graphite geothermometers suggest that the tourmaline in garnet experienced peak metamorphic conditions (~500 °C and 5 kbar). The mineralogical characteristics of the tourmaline and the whole rock composition indicate that the tourmaline formed authigenically in the sediment during diagenesis and/or early metamorphism. Clay minerals in modern sediments have the capability to adsorb and concentrate borate, which could lead to boron enrichment during diagenesis, followed by tourmaline formation under metamorphic conditions. Clay minerals, deposited on the early Archean seafloor, were the precursors of the garnet and biotite in the examined samples. The studied tourmaline crystals were most likely formed in the same way as modern tourmaline in marine sediments. Therefore, boron enrichment by clays must have been possible even during the early Archean. Thus, similar enrichment could have been

  20. Rb-Sr, K-Ar and fission track ages for granites from Penang Island, West Malaysia: an interpretation model for Rb-Sr whole-rock and for actual and experimental mica data (United States)

    Kwan, T. S.; Krähenbühl, R.; Jager, E.


    Penang Island represents the northwestern extension of the western magmatic belt of Peninsular Malaysia. Thirty-one samples of highly evolved biotite-and biotite-muscovite granites were used in an integrated study to unravel the complex magmatic, tectonic and cooling histories of these rocks. Highly distorted Rb-Sr whole-rock age patterns are evident. These are attributed to the partial post-magmatic Sr homogenization within the granite batholith which led to the rotation of isochrons towards younger ages and higher (87/86)Sr intercepts. The recognition of this mechanism allowed the establishment of a new Rb-Sr interpretation model. The intrusion ages of the granites can be extrapolated based on the evolutionary trend of the initial (87/86)Sr. Including the data of Bignell and Snelling, three episodes of granite emplacement at 307±8 Ma, 251±7 Ma and 211±2 Ma are suggested for Penang and the NW Main Range. The late-Triassic intrusive induced a hydrothermal conductive convection system which affected all the granites. It is considered to be responsible for the Rb-Sr whole-rock age distortion, the Rb-Sr and K-Ar biotite age resetting and the textural and mineralogical changes in the granites. The duration of the hydrothermal convections, deduced from the Rb-Sr whole rock ages, is about 6 Ma and 20 Ma in the northern and southern parts of Penang respectively. Fast regional cooling to 350±50°C within a time span of 1 3 Ma is recognized for the late-Triassic Feringgi intrusive from the mica ages, followed by a generally slow cooling rate of about 1°C/Ma. Fission track ages, in addition, indicate blockwise uplift along the N-S and NW-SE tending faults, thus resulting in the exposure of deeper crustal levels in southern and eastern Penang. A change in the tensional regime since Oligocene/Miocene, accompanied by a southwest tilting of the island, is indicated by the fission track apatite ages. Variable sometimes younger K-Ar, respectively Rb-Sr biotite ages mainly

  1. Mineral resource of the month: mica (United States)

    Hedrick, J.B.


    Humans have been using mica for millennia. Mica was first mined in India about 4,000 years ago, where it was used primarily in medicines, and some Hindu physicians still incorporate biotite mica into medicines today. Early civilizations also used mica for decorations, as windows and as surfaces on which to draw or paint. Maya temples were decorated with mica pigments, which were incorporated into the stucco to make it sparkle in the sun. In North America, ancient inhabitants adorned gravesites and burial mounds with animal figures made of mica.

  2. Ductility contrast induced by silicification in pelitic schist of the Ryoke metamorphic belt, Japan (United States)

    Mateen, Tayyaba; Yamamoto, Hiroshi; Rehman, Hafiz Ur; Terabayashi, Masaru


    Contrasting ductility is recognized in the rocks of Cretaceous Ryoke metamorphic belt in Iwakuni area, southwest Japan. Pelitic schist is ubiquitous in the region and differences in mineral assemblages mark increase in metamorphic grade. The area has been graded as chlorite-biotite zone in the north progressing into biotite- and muscovite-cordierite zones in the south. Pelitic schist near the boundary between the biotite- and muscovite-cordierite zones has undergone partial silicification to form whitish silicified schist layers which contain two types of quartz veins: those parallel to foliation in the host rock are called schistosity-concordant veins, and those inclined to host rock foliation, schistosity-discordant veins. In this study we examined the quartz structure in the silicified schist and in both types of veins to understand the ductility contrast induced by the silicification process. Crystallographic orientations of quartz in the veins and silicified schist rocks were studied using the Scanning Electron Microscopy (SEM) based Electron Back Scatter Diffraction (EBSD) technique. Quartz c-axis orientations in the silicified schist are nearly random, demonstrating an absence of post-silicification ductile deformation. Quartz grains in the schistosity-concordant veins have preferred c-axis orientations perpendicular to the schistosity indicating ductile shortening. In contrast, schistosity-discordant veins display distinct quartz c-axis fabric than that found in the schistosity-concordant veins. This is because the two types of host rocks exhibit a difference in ductility during deformation. The presence of deformed quartz veins in the undeformed silicified schist indicates transformation of the ductile pelitic schist into the brittle silicified schist at mid-crustal levels where these rocks originate, hence forming contrasting rock layers. Schistosity-concordant veins in the biotite-rich pelitic schist deformed with its host rock in a ductile manner while

  3. A desk study of surface diffusion and mass transport in clay

    International Nuclear Information System (INIS)

    Research into the properties of clays as barrier materials for nuclear waste disposal has led to the realization that they have important transport properties which are relatively insignificant in most other geological materials. Sorption has always been regarded as a purely retarding mechanism, but laboratory experiments over the past decade have indicated that surface diffusion of sorbed cations is a potentially significant transport mechanism in both compacted montmorillonite, and biotite gneiss. The present desk study about these issues was part of the CEC coordinated project Mirage-Second phase, research area Natural analogues

  4. Cooling age of the Birimian juvenile crust in West Africa. U-Pb, Rb-Sr and K-Ar data on the 2. 1 Ga granite-greenstone terrains from SW-Niger. Age de refroidissement de la croute juvenile birimienne d'Afrique de l'Ouest. Donnees U-Pb, Rb-Sr et K-Ar sur les formations a 2. 1 Ga du SW-Niger

    Energy Technology Data Exchange (ETDEWEB)

    Lama, C.; Dautel, D.; Zimmermann, J.L. (Centre National de la Recherche Scientifique (CNRS), 54 - Nancy (France). Centre de Recherches Petrographiques et Geochimiques); Barbey, P. (Nancy-1 Univ., 54 (France)); Cheilletz, A. (Centre National de la Recherche Scientifique (CNRS), 54 - Nancy (France). Centre de Recherches Petrographiques et Geochimiques Ecole Nationale Superieure de Geologie Appliquee et de Prospection Miniere, 54 - Nancy (France)); Pons, J. (Orleans Univ., 45 (France))


    A comparison between zircon U-Pb, whole-rock Rb-Sr and biotite-amphibole K-Ar data on Birimian granite-greenstone terrains from SW-Niger indicates that the youngest granitic plutons were emplaced at 2.115 [+-] 5 Ma and that both the plutons and the surrounding greenstones yield cooling ages around 2.118 Ma. The age similarity between the end of the plutonism and the cooling of plutons and surrounding greenstone further suggests rapid cooling at the end of the plutonic event and, thus, corroborates a model of greenstone metamorphism linked to the thermal effect of the plutons. (authors).

  5. Mineral resource of the month: vermiculite (United States)

    Tanner, Arnold O.


    Vermiculite comprises a group of hydrated, laminar magnesium-aluminum-iron silicate minerals resembling mica. They are secondary minerals, typically altered biotite, iron-rich phlogopite or other micas or clay-like minerals that are themselves sometimes alteration products of amphibole, chlorite, olivine and pyroxene. Vermiculite deposits are associated with volcanic ultramafic rocks rich in magnesium silicate minerals, and flakes of the mineral range in color from black to shades of brown and yellow. The crystal structure of vermiculite contains water molecules, a property that is critical to its processing for common uses.

  6. Susceptibility of Granite Rock to scCO2/Water at 200 degrees C and 250 degrees C

    Energy Technology Data Exchange (ETDEWEB)

    Sugama, T.; Gill, S., Ecker, L., Butcher, T., Warren, J.


    Granite rock comprising anorthoclase-type albite and quartz as its major phases and biotite mica as the minor one was exposed to supercritical carbon dioxide (scCO{sub 2})/water at 250 C and 13.78 MPa pressure for 104 hours. For comparison purpose, four other rocks, albite, hornblende, diorite, and quartz, also were exposed. During the exposure of granite, ionic carbonic acid, known as the wet carbonation reactant, preferentially reacted with anorthoclase-type albite and biotite, rather than with quartz. The susceptibility of biotite to wet carbonation was higher than that of anorthoclase-type albite. All the carbonation by-products of anorthoclase-type albite were amorphous phases including Na- and K-carbonates, a kaolinite clay-like compound, and silicon dioxide, while wet carbonation converted biotite into potassium aluminum silicate, siderite, and magnesite in crystalline phases and hydrogen fluoride (HF). Three of these reaction by-products, Na- and K-carbonates and HF, were highly soluble in water. Correspondingly, the carbonated top surface layer, about 1.27 mm thick as carbonation depth, developed porous microstructure with numerous large voids, some of which have a size of {>=} 10 {mu}m, reflecting the erosion of granite by the leaching of these water-soluble reaction by-products. Comparing with this carbonation depth, its depth of other minerals was considerable lower, particularly, for hornblende and diorite with 0.07 and 0.02 mm, while no carbonate compound was detected in quartz. The major factor governing these low carbonation depths in these rocks was the formation of water-insensitive scale-like carbonate by-products such as calcite (CaCO{sub 3}), siderite (FeCO{sub 3}), and magnesite (MgCO{sub 3}). Their formation within the superficial layer of these minerals served as protective barrier layer that inhibits and retards further carbonation of fresh underlying minerals, even if the exposure time was extended. Thus, the coverage by this barrier layer

  7. Paleoproterozoic migmatitic gneisses from the Tandilia belt (Argentina), Río de la Plata craton, record cooling at deep crustal levels (United States)

    Martínez, Juan Cruz; Massonne, Hans-Joachim; Dristas, Jorge Anastasio; Theye, Thomas; Graff, Ailín Ayelén


    We studied high-grade metamorphic rocks of the El Cristo hill area of the Tandilia belt. Mineral analyses and thermodynamic calculations were carried out for two adjacent rock samples: an amphibole-biotite gneiss and a garnet-biotite-bearing migmatite. Peritectic garnets in the migmatite show core compositions of pyr4.5(gro + andr)10spes6alm79.5 changing to pyr3.5(gro + andr)17spes6alm73.5 at their thin rims. Garnet compositions in the gneiss are pyr6.5(gro + andr)26spes12alm55.5 and pyr4.5(gro + andr)34spes12alm49.5 for core and rim, respectively. A P-T path was constructed by calculating pseudosections in the 11-component system Si-Ti-Al-Fe-Mn-Mg-Ca-Na-K-O-H and contouring them by isopleths for garnet components using the PERPLE_X software package. Supra-solidus crystallization of garnet cores in the migmatite began at 5.8 kbar and 660 °C. Garnet rims equilibrated at 7.0 kbar and 640 °C compatible with garnet cores in the amphibole-biotite gneiss (7.6 kbar and 660 °C). The further chemical development of garnet in this rock points to P-T conditions of 11.6 kbar and 620 °C and 12.2 kbar and 595 °C (outermost garnet rim). At this high-pressure stage Ca-amphibole was not stable. Most biotite formed during exhumation whereas the high-pressure accessory minerals, titanite and epidote, persisted. According to the obtained anti-clockwise P-T path the originally partly melted material was tectonically transported from ∼22 km (middle crust) to ∼40 km (lower crust) depths reaching a geothermal gradient as low as 15 °C km-1. This transport probably occurred along a major suture zone, which was active during the Paleoproterozoic (2.25-2.10 Ga), before a terminating collision of terranes near the SW boundary of the Rio de la Plata craton.

  8. Diffusion experiment of a radionuclide in granitic rock cores

    International Nuclear Information System (INIS)

    An effective diffusion coefficient of neptunium-237 which is one of hazardous long-lived radionuclide including high level radioactive waste was determined by using 40 mm diameter and 5 mm thick disks under an aerobic condition. An alpha autoradiography was performed for cross sections of a 20 mm thick granite disk to study the penetrated neptunium into granite. The effective diffusion coefficient of neptunium diffused through a water saturated granite was about 2.5 x 10-13 m2/sec. The autoradiograph of solid state track detectors clearly showed that biotite constituting granite has storage pores and keep diffusing species in it. (author)

  9. 华南某些不同时代花岗岩类岩石中铍地球化学特征的研究

    Institute of Scientific and Technical Information of China (English)



    Beryllium was determined from more than 40 granite bodies of different ages in southern China. Results show that it tends to increase with geologie age. The average beryllium contents for granites of various ages are (%): Hsuehfeng Period, 0.00016;Early Caledonian, 0.00034; Late Caledonian, 0.00035 ; Indosinian, 0.00055; Early Yenshanian, 0.00111; Late Yenshanian, 0.00032. The overall average content of beryllium of granite in this area is 0.00052%, 0.00047% and 0.00137% for biotite-granites and two-mica granites respectively. There seems to he a close relationship between Bemineralization and Yenshanian granites.

  10. Microstructures and Petrology of Melt Inclusions in the Anatectic Sequence of Jubrique (Betic Cordillera, S Spain): Implications for Crustal Anatexis (United States)

    Acosta-vigil, A.; Barich, A.; Garrido, C. J.; Cesare, B.; Tajčmanová, L.; Bartoli, O.


    We report a new occurrence of melt inclusions in polymetamorphic granulitic gneisses of the Jubrique unit, a complete though thinned crustal section located above the Ronda peridotite slab (Betic Cordillera, S Spain). The gneissic sequence is composed of mylonitic gneisses at the bottom and porphyroblastic gneisses on top. Mylonitic gneisses are strongly deformed rocks with abundant garnet and rare biotite. Except for the presence of melt inclusions, microstructures indicating the former presence of melt are rare or absent. Upwards in the sequence garnet decreases whereas biotite increases in proportion. Melt inclusions are present from cores to rims of garnets throughout the entire sequence. Most of the former melt inclusions are now totally crystallized and correspond to nanogranites, whereas some of them are partially made of glass or, more rarely, are totally glassy. They show negative crystal shapes and range in size from ≈5 to 200 micrometers, with a mean size of ≈30-40 micrometers. Daughter phases in nanogranites and partially crystallized melt inclusions include quartz, feldspars, biotite and muscovite; accidental minerals include kyanite, graphite, zircon, monazite, rutile and ilmenite; glass has a granitic composition. Melt inclusions are mostly similar throughout all the gneissic sequence. Some fluid inclusions, of possible primary origin, are spatially associated with melt inclusions, indicating that at some point during the suprasolidus history of these rocks granitic melt and fluid coexisted. Thermodynamic modeling and conventional thermobarometry of mylonitic gneisses provide peak conditions of ≈850 ºC and 12-14 kbar, corresponding to cores of large garnets with inclusions of kyanite and rutile. Post-peak conditions of ≈800-850 ºC and 5-6 kbar are represented by rim regions of large garnets with inclusions of sillimanite and ilmenite, cordierite-quartz-biotite coronas replacing garnet rims, and the matrix with oriented sillimanite. Previous

  11. Provenance of metasedimentary rocks of the Western Pernambuco-Alagoas Domain: Contribution to understand the crustal evolution of southern Borborema Province (United States)

    Cruz, Rodrigo Fabiano da; Pimentel, Márcio Martins; Accioly, Ana Cláudia de Aguiar


    The Borborema Province is a complex neoproterozoic orogen in northeastern Brazil, made of a mosaic of fault-bounded terrains and several metassedimentary sequences. In the present work, new zircon U-Pb provenance data for metasedimentary rocks in the Western Pernambuco-Alagoas Domain, southern part of the Province, are reported. Detrital zircon ages range from Archean to Neoproterozoic. Three samples of the Cabrobó Complex were investigated: (i) sillimanite-kyanite-garnet-biotite schist, which presented mostly Ediacaran and Cryogenian detrital zircon ages (youngest zircon at ca. 554 Ma) indicating erosion of neoproterozoic sources, (ii) garnet-biotite schist, which has a dominant Tonian/Stenian population, a less abundant Cryogenian (youngest zircon age at ca. 643 Ma) as well as Paleoproterozoic and Archean zircon grains, and (iii) tourmaline-muscovite quartzite, which contains detrital zircon varying in age between ca. 2.08 Ga and 1.57 Ga, and an abundant population close to the Meso/Paleoproterozoic boundary, possibly associated with the erosion of rocks formed during the Statherian taphrogenesis, known in the central part of the São Francisco Craton as well as in other areas of the Borborema Province. Two samples of the Riacho Seco Metasedimentary Complex were also investigated: (i) a biotite schist with a dominant population presenting ages mostly between 2.3 and 2.7 Ga (youngest zircon age at ca. 2023 Ma) and (ii) a magnetite-biotite-muscovite quartzite, having detrital zircon grains with ages ranging between ca. 1.9 and 2.7 Ga. The sedimentary rocks of the Riacho Seco Complex may have their origin related to the erosion of sources within the São Francisco Craton. The data for the Riacho Seco metasedimentary rocks, however, are not conclusive with respect to the depositional age of the original sedimentary rocks. The sequence might represent exposure of an old (Paleoproterozoic) sedimentary pile or, alternatively, it comprises a neoproterozoic passive

  12. A re-appraisal of the stratigraphy and volcanology of the Cerro Galán volcanic system, NW Argentina (United States)

    Folkes, Christopher B.; Wright, Heather M.; Cas, Ray A.F.; de Silva, Shanaka L.; Lesti, Chiara; Viramonte, Jose G.


    From detailed fieldwork and biotite 40Ar/39Ar dating correlated with paleomagnetic analyses of lithic clasts, we present a revision of the stratigraphy, areal extent and volume estimates of ignimbrites in the Cerro Galán volcanic complex. We find evidence for nine distinct outflow ignimbrites, including two newly identified ignimbrites in the Toconquis Group (the Pitas and Vega Ignimbrites). Toconquis Group Ignimbrites (~5.60–4.51 Ma biotite ages) have been discovered to the southwest and north of the caldera, increasing their spatial extents from previous estimates. Previously thought to be contemporaneous, we distinguish the Real Grande Ignimbrite (4.68 ± 0.07 Ma biotite age) from the Cueva Negra Ignimbrite (3.77 ± 0.08 Ma biotite age). The form and collapse processes of the Cerro Galán caldera are also reassessed. Based on re-interpretation of the margins of the caldera, we find evidence for a fault-bounded trapdoor collapse hinged along a regional N-S fault on the eastern side of the caldera and accommodated on a N-S fault on the western caldera margin. The collapsed area defines a roughly isosceles trapezoid shape elongated E-W and with maximum dimensions 27 × 16 km. The Cerro Galán Ignimbrite (CGI; 2.08 ± 0.02 Ma sanidine age) outflow sheet extends to 40 km in all directions from the inferred structural margins, with a maximum runout distance of ~80 km to the north of the caldera. New deposit volume estimates confirm an increase in eruptive volume through time, wherein the Toconquis Group Ignimbrites increase in volume from the ~10 km3 Lower Merihuaca Ignimbrite to a maximum of ~390 km3 (Dense Rock Equivalent; DRE) with the Real Grande Ignimbrite. The climactic CGI has a revised volume of ~630 km3 (DRE), approximately two thirds of the commonly quoted value.


    Institute of Scientific and Technical Information of China (English)


    <正>20111705 An Junbo(Team 603,Bureau of Nonferrous Metals Geological Exploration of Jilin Province,Hunchun 133300,China);Xu Renjie Geological Features and Ore Genesis of Baishilazi Scheelite Deposit in Yanbian Area(Jilin Geology,ISSN1001-2427,CN22-1099/P,29(3),2010,p.39-43,2 illus.,2 tables,7 refs.)Key words:tungsten ores,Jilin ProvinceThe Baishilazi scheelite deposit is located in contacting zone between the marble of the Late Palaeozoic Qinglongcun Group and the Hercynian biotite granite.The vein and lenticular major ore body is obviously controlled by NE-extending faults and con

  14. The rapakivi granite plutons of Bodom and Obbnäs, southern Finland: petrography and geochemistry

    Directory of Open Access Journals (Sweden)

    Kosunen, P.


    Full Text Available The Obbnäs and Bodom granite plutons of southernmost Finland show the typical petrographic and geochemical features of the Proterozoic rapakivi granites in Finland and elsewhere: they cut sharply across the 1900 Ma Svecofennian metamorphic bedrock and have the geochemical characteristics of subalkaline A-type granites. The Bodom pluton is composed of porphyritic granites (hornblende-, hornblende-biotite-, and biotite-bearing varieties and an even-grained granite that probably represent two separate intrusive phases. This lithologic variation does not occur in the Obbnäs pluton, which is almost entirely composed of porphyritic hornblende-biotite granite that gradually becomes more mafic to the southwest. Three types of hybrid granitoids resulting from magma mingling and mixing occur on the southwestern tip of the Obbnäs peninsula. The Bodom granites are syenogranites, whereas the composition of the Obbnäs granite varies from syeno- to monzogranite. The main silicates of both the Bodom and Obbnäs granites are quartz, microcline, plagioclase (An1541, biotite (siderophyllite, and generally also amphibole (ferropargasite or hastingsite. Plagioclase-mantled alkali feldspar megacrysts are absent or rare. The accessory minerals are fluorite, allanite, zircon, apatite, and iron-titanium oxides; the Obbnäs granite also contains titanite. The Bodom and Obbnäs granites are metaluminous to weakly peraluminous, with average A/CNK of 1.00 and 1.05, respectively, have high Fe/Mg (average FeOtot/[FeOtot+MgO] is 0.94 for the Bodom and 0.87 for the Obbnäs granites, and high Ga/Al (3.78 to 5.22 in Bodom and 2.46 to 4.18 in Obbnäs. The REE contents are high with LREE-enriched chondrite-normalized patterns and moderate (Obbnäs to relatively strong (Bodom negative Eu-anomalies. The Obbnäs granite is enriched in CaO, TiO2, MgO, and FeO, and depleted in SiO2 and K2O compared to the Bodom granites. Also, there are differences in the Ba, Rb, and Sr contents of

  15. Mineralogic investigation into occurrence of high uranium well waters in upstate South Carolina, USA

    Energy Technology Data Exchange (ETDEWEB)

    Warner, Richard, E-mail: [Department of Environmental Engineering and Earth Sciences, Clemson University, Clemson, SC 29634-0919 (United States); Meadows, Jason; Sojda, Scott; Price, Van; Temples, Tom [Department of Environmental Engineering and Earth Sciences, Clemson University, Clemson, SC 29634-0919 (United States); Arai, Yuji [Department of Entomology, Soils, and Plant Sciences, Clemson University, Clemson, SC 29634-0315 (United States); Fleisher, Chris [Department of Geology, University of Georgia, Athens, GA 30602-2501 (United States); Crawford, Bruce; Stone, Peter [Bureau of Water, South Carolina Department of Health and Environmental Control, Columbia, SC 29201 (United States)


    Research Highlights: > Oxidative dissolution of uraninite in biotite granite is primary source of uranium in high-U well waters near Simpsonville, SC. > Uranium is chiefly transported as mixed uranyl hydroxyl-carbonate complexes. > Local reduction has resulted in secondary precipitation of uranium along fractures as coffinite. > Dissolution of uraninite and precipitation of coffinite were geologically recent. - Abstract: High levels of U (up to 5570 {mu}g/L) have been discovered in well waters near Simpsonville, South Carolina, USA. In order to characterize the mineralogical source of the U and possible structural controls on its presence, a deep (214 m) well was cored adjacent to one of the enriched wells. The highest gamma-ray emissions in the recovered core occur in coarse biotite granite at a depth just below 52 m. A slickenlined fault plane at 48.6 m and narrow pegmatite layers at depths of 113, 203 and 207 m also yield high gamma-ray counts. Thin sections were made from the above materials and along several subvertical healed fractures. Uraninite and coffinite are the principal U-rich minerals in the core. Other U-bearing minerals include thorite and thorogummite, monazite, zircon and allanite. Primary uraninite occurs in the biotite granite and in pegmatite layers. Secondary coffinite is present as tiny (<5 {mu}m) crystals dispersed along fractures in the granite and pegmatites. Coffinite also occurs along the slickenlined fault plane, where it is associated with calcite and calcic zeolite and also replaces allanite. Coffinite lacks radiogenic Pb, hence is considerably younger than the uraninite. Dissolution of partially oxidized Ca-rich uraninite occurring in the surficial biotite granite (or secondary coffinite in fracture zones) is likely the main source for the current high levels of U in nearby area wells. The high-U well waters have a carbonate signature, consistent with pervasive calcite vein mineralization in the core. Aqueous speciation calculations

  16. New 40Ar/39Ar age constraints on the Late Palaeozoic tectonic evolution of the western Tianshan (Xinjiang, northwestern China), with emphasis on Permian fluid ingress


    De Jong, Koenraad; Wang, Bo; Faure, Michel; Shu, Liangshu S.; Cluzel, Dominique; Charvet, Jacques; Ruffet, Gilles; Yan CHEN


    Laser-probe dating of mylonite whole-rock samples from the North Tianshan—Main Tianshan fault zone that cross-cuts the North Tianshan domain's southern margin yielded 40Ar/39Ar spectra with 255–285 Ma ages. Biotite from an undeformed, Early Carboniferous granite, which cuts the steep mylonitic foliation in the Proterozoic basement of the Yili arcs's southern margin, gave a 263.4 ± 0.6 Ma plateau age (1σ). Pre-Carboniferous metasediments overlying this basement yielded plateau ages (1σ) of 253...

  17. Porphyry-Cu-Mo Stockwork Formation by Dynamic, Transient Hydrothermal Pulses: Mineralogic Insights From the Deposit at Butte, Montana (United States)

    Mercer, C. N.; Reed, M. H.


    The temperature profile in magmatic-hydrothermal systems directly affects the chemical behavior and pressure regime of hydrothermal fluids and the resulting diversity of mineralization. We combine textural observations of igneous and hydrothermal minerals using SEM-CL and -BSE images with three independent mineral thermobarometers to better understand the thermal profile at the porphyry-Cu-Mo deposit in Butte, Montana. We apply the two most recent (and controversial) forms of the Ti-in-quartz thermobarometer from Thomas et al. (2010) and Huang and Audétat (2011), the Zr-in-rutile thermobarometer of Tomkins et al. (2007), and the XMg-Ti-in-biotite thermometer of Henry et al. (2005) to estimate the formation temperatures of these magmatic and hydrothermal minerals. In a comparison of isobaric temperature distributions from Ti-in-quartz (Thomas et al., 2010) and Zr-in-rutile we find that the Thomas et al. calibration consistently yields temperatures that are 50 to 200°C lower than those from Zr-in-rutile. These quartz temperatures are unreasonably low for quartz phenocrysts and are considerably lower than previous estimates for vein quartz. Temperature estimates from the Zr-in-rutile and XMg-Ti-in-biotite thermobarometers agree well with each other and with previous temperature estimates. We conclude that application of the Ti-in-quartz thermobarometer of Thomas et al. is not appropriate for this natural system. Quartz temperatures calculated using the calibration of Huang and Audétat (2011) are closer to those from rutile and biotite. Application of the Ti-in-quartz thermobarometer of Huang and Audétat to hydrothermal samples yields maximum temperature estimates, however, and requires evaluation of trace element abundances (e.g., Ti, Al) and other crystal lattice impurities (e.g., fluid inclusions) in growth zones as a means to determine whether growth zones represent slow or fast-growing quartz. Using thermobarometry from rutile, biotite, and quartz (Huang and

  18. Zircon U-Pb geochronological framework of Qitianling granite batholith, middle part of Nanling Range, South China

    Institute of Scientific and Technical Information of China (English)


    The Qitianling granite batholith (QGB) is located in the southern Hunan Province, middle part of the Nanling Range, South China. Its total exposure area is about 520 km2. Based on our 25 single grain zircon U-Pb age data and 7 published data as well as the geological, petrological, and space distribution characteristics, we conclude that QGB is an Early Yanshanian (Jurassic) multi-staged composite pluton. Its formation process can be subdivided into three major stages. The first stage, emplaced at 163―160 Ma with a peak at about 161 Ma, is mainly composed of hornblende-biotite monzonitic granites and locally biotite granites, and distributed in the eastern, northern, and western peripheral parts of the pluton. The second stage, emplaced at 157―153 Ma with a peak at 157―156 Ma, is mainly composed of biotite granites and locally containing hornblende, and distributed in the middle and southeastern parts of the pluton. The third stage, emplaced at 150―146 Ma with a peak at about 149 Ma, is mainly composed of fine-grained (locally porphyritic) biotite granites, and distributed in the middle-southern part of the pluton. Each stage can be further disintegrated into several granite bodies. The first two intrusive stages comprise the major phase of QGB, and the third intrusive stage comprises the additional phase. Many second stage fine-grained granite bosses and dykes intruded into the first stage host granites with clear chilling margin-baking phenomena at their intrusive contacts. They were emplaced in the open fracture space of the earlier stage consolidated rocks. Their isotopic ages are mostly 2―6 Ma younger than their hosts. Conceivably, the time interval from magma emplacement, through cooling, crystallization, solidification, up to fracturing of the earlier stage granites cannot exceed 2―6 Ma. During the Middle-Late Jurassic in the Qitianling area and neighboring Nanling Range, the coeval granitic and basic-intermediate magmatic activities were widely

  19. Partial melting of subducted paleo-Pacific plate during the early Cretaceous: Constraint from adakitic rocks in the Shaxi porphyry Cu-Au deposit, Lower Yangtze River Belt (United States)

    Deng, Jianghong; Yang, Xiaoyong; Li, Shuang; Gu, Huangling; Mastoi, Abdul Shakoor; Sun, Weidong


    A large porphyry Cu-Au deposit associated with early Cretaceous intrusive rocks has been discovered and explored in the Shaxi area, Lower Yangtze River Belt (LYRB), eastern China. We studied two types of intrusive rocks in the Shaxi area: Cu-Au mineralization related diorites and quartz-diorites (adakitic rocks), and newly found high Sr/Y ratio biotite-gabbros. They were formed almost simultaneously with crystallization ages of ca. 130 to 129 Ma, younger than the early stage shoshonitic rocks (Longmenyuan, Zhuanqiao and Shuangmiao Fm.) in the Luzong volcanic basin, ~ 10 km south of the Shaxi area. These intrusive rocks show similar distribution patterns of trace elements (enriched in LILEs and depleted in HFSEs) and REEs (enriched in LREEs and depleted in HREEs, no Eu negative anomaly, flat HREE patterns). The diorites and quartz-diorites are adakitic rocks with calc-alkaline affinity, distinguished from other adakitic rocks in the LYRB which are high-K calc-alkaline series. The biotite-gabbros are not adakitic rocks, although they are characterized by high Sr/Y ratios. Shaxi adakitic rocks show positive zircon εHf(t) values, which may be attributed to the contribution of subducted oceanic crust, while the εHf(t) values of the biotite-gabbros are mostly negative, indicating the involvement of old crustal materials. Although Sr-Nd-Pb isotopes of Shaxi adakitic rocks are more depleted than those of other adakitic rocks in the LYRB, they are still slightly enriched, similar to continental arc adakites in the Andean Austral Volcanic Zone. The Shaxi adakitic rocks are characterized by high Sr contents and Sr/Y ratios, medium (La/Yb)N, MgO contents and Mg#, and low K2O/Na2O ratios, decoupling of Sr/Y and (La/Yb)N, low Th/U values, exhibiting characteristics of slab-derived adakitic rocks. They were not produced by fractional crystallization of basaltic magmas like adakitic rocks in Edong-Jiurui and Tongling but originally generated from partial melting of subducted

  20. Petrogenesis of syntectonic granites emplaced at the transition from thrusting to transcurrent tectonics in post-collisional setting: Whole-rock and Sr-Nd-Pb isotope geochemistry in the Neoproterozoic Quatro Ilhas and Mariscal Granites, Southern Brazil (United States)

    Florisbal, Luana Moreira; Bitencourt, Maria de Fátima; Janasi, Valdecir de Assis; Nardi, Lauro Valentim Stoll; Heaman, Larry M.


    The Neoproterozoic post-collisional period in southern Brazil (650-580 Ma) is characterized by substantial volumes of magma emplaced along the active shear zones that compose the Southern Brazilian Shear Belt. The early-phase syntectonic magmatism (630-610 Ma) is represented by the porphyritic, high-K, metaluminous to peraluminous Quatro Ilhas Granitoids and the younger heterogranular, slightly peraluminous Mariscal Granite. Quatro Ilhas Granitoids include three main petrographic varieties (muscovite-biotite granodiorite — mbg; biotite monzogranite — bmz; and leucogranite — lcg) that, although sharing some significant geochemical characteristics, are not strictly comagmatic, as shown by chemical and Sr-Nd-Pb isotope data. The most primitive muscovite-biotite granodiorite was produced by contamination of more mafic melts (possibly with some mantle component) with peraluminous crustal melts; the biotite monzogranite, although more felsic, has higher Ca, MgO, TiO2 and Ba, and lower K2O, FeOt, Sr and Rb contents, possibly reflecting some mixing with coeval mafic magmas of tholeiitic affinity; the leucogranite may be derived from pure crustal melts. The Mariscal Granite is formed by two main granite types which occur intimately associated in the same pluton, one with higher K (5-6.5 wt.% K2O) high Rb and lower CaO, Na2O, Ba and Zr as compared to the other (3-5 wt.% of K2O). The two Mariscal Granite varieties have compositional correspondence with fine-grained granites (fgg) that occur as tabular bodies which intruded the Quatro Ilhas Granoitoids before they were fully crystallized, and are inferred to correspond to the Mariscal Granite feeders, an interpretation that is reinforced by similar U-Pb zircon crystallization ages. The initial evolution of the post-collisional magmatism, marked by the emplacement of the Quatro Ilhas Granitoids varieties, activated sources that produced mantle and crustal magmas whose emplacement was controlled both by flat-lying and

  1. Sorption of cesium in intact rock

    Energy Technology Data Exchange (ETDEWEB)

    Puukko, E. [Univ. of Helsinki, Dept. of Chemistry (Finland)


    The mass distribution coefficient K{sub d} is used in performance assessment (PA) to describe sorption of a radionuclide on rock. The R{sub d} is determined using crushed rock which causes uncertainty in converting the R{sub d} values to K{sub d} values for intact rock. This work describes a method to determine the equilibrium of sorption on intact rock. The rock types of the planned Olkiluoto waste disposal site were T-series mica gneiss (T-MGN), T-series tonalite granodiorite granite gneiss (T-TGG), P-series tonalite granodiorite granite gneiss (P-TGG) and pegmatitic granite (PGR). These rocks contain different amount of biotite which is the main sorbing mineral. The sorption of cesium on intact rock slices was studied by applying an electrical field to speed up migration of cesium into the rock. Cesium is in the solution as a noncomplex cation Cs{sup +} and it is sorbed by ion exchange. The tracer used in the experiments was {sup 134}Cs. The experimental sorption on the intact rock is compared with values calculated using the in house cation exchange sorption model (HYRL model) in PHREEQC program. The observed sorption on T-MGN and T-TGG rocks was close to the calculated values. Two PGR samples were from a depth of 70 m and three samples were from a depth of 150 m. Cesium sorbed more than predicted on the two 70 m PGR samples. The sorption of Cs on the three 150 m PGR samples was small which was consistent with the calculations. The pegmatitic granite PGR has the smallest content of biotite of the four rock types. In the case of P-TGG rock the observed values of sorption were only half of the calculated values. Two kind of slices were cut from P-TGG drill core. The slices were against and to the direction of the foliation of the biotite rims. The sorption of cesium on P-TGG rock was same in both cases. The results indicated that there was no effect of the directions of the electric field and the foliation of biotite in the P-TGG rock. (orig.)

  2. K-Ar ages of the Jecheon granitic complex and related molybdenite deposits in South Korea

    International Nuclear Information System (INIS)

    K-Ar age determinations were carried out on the Jecheon mass and adjacent rocks occurring in the Ogcheon Zone of South Korea. Biotites separated from the Jecheon mass yield ages of 179, 169 and 159 Ma, confirming that the mass and the related molybdenum deposit were formed by the Daebo igneous activity. Muscovite from the Daehwa mine gives an age of 89 Ma and belongs to the Bulgugsa activity. Muscovite from pegmatite near the Dangdu mine, which intrudes into the Ogcheon Group, gives a Precambrian age of 1720 Ma. Thus the original rocks of the Ogcheon Group appear to have a middle Proterozoic age. (author)

  3. K-Ar ages of the Jecheon granitic complex and related molybdenite deposits in South Korea

    Energy Technology Data Exchange (ETDEWEB)

    Shibata, Ken; Uchiumi, Shigeru; Ishihara, Shunso (Geological Survey of Japan, Yatabe, Ibaraki (Japan)); Park, No-Young


    K-Ar age determinations were carried out on the Jecheon mass and adjacent rocks occurring in the Ogcheon Zone of South Korea. Biotites separated from the Jecheon mass yield ages of 179, 169 and 159 Ma, confirming that the mass and the related molybdenum deposit were formed by the Daebo igneous activity. Muscovite from the Daehwa mine gives an age of 89 Ma and belongs to the Bulgugsa activity. Muscovite from pegmatite near the Dangdu mine, which intrudes into the Ogcheon Group, gives a Precambrian age of 1720 Ma. Thus the original rocks of the Ogcheon Group appear to have a middle Proterozoic age.

  4. Mantle derivation of Archean amphibole-bearing granitoid and associated mafic rocks: evidence from the southern Superior Province, Canada (United States)

    Sutcliffe, Richard H.; Smith, Alan R.; Doherty, William; Barnett, Robert L.


    Amphibole-bearing, Late Archean (2.73 2.68 Ga) granitoids of the southern Superior Province are examined to constrain processes of crustal development. The investigated plutons, which range from tonalite and diorite to monzodiorite, monzonite, and syenite, share textural, mineralogical and geochemical attributes suggesting a common origin as juvenile magmas. Despite variation in modal mineralogy, the plutons are geochemically characterized by normative quartz, high Al2O3 (> 15 wt%), Na-rich fractionation trends (mol Na2O/K2O >2), low to moderate Rb (generallyenclaves and igneous layers and as intrusive units which exhibit textures indicative of contemporaneous mafic and felsic magmatism. Mafic mineral assemblages include: hornblende + biotite in tonalites; augite + biotite ± orthopyroxene ± pargasitic hornblende or hornblende+biotite in dioritic to monzodioritic rocks; and aegirine-augite ± silicic edenite ± biotite in syenite to alkali granite. Discrete plagioclase and microcline grains are present in most of the suites, however, some of the syenitic rocks are hypersolvus granitoids and contain only perthite. Mafic-ultramafic rocks have REE and Y contents indicative of their formation as amphibole-rich cumulates from the associated granitoids. Some cumulate rocks have skeletal amphibole with XMg(Mg/(Mg+ Fe2+)) indicative of crystallization from more primitive liquids than the host granitoids. Geochemical variation in the granitoid suites is compatible with fractionation of amphibole together with subordinate plagioclase and, in some cases, mixing of fractionated and primitive magmas. Mafic to ultramafic units with magnesium-rich cumulus phases and primitive granitoids (mol MgO/ (MgO+0.9 FeOTOTAL) from 0.60 to 0.70 and CT >150 ppm) are comagmatic with the evolved granitoids and indicate that the suites are mantle-derived. Isotopic studies of Archean monzodioritic rocks have shown LREE enrichment and initial 143Nd/144Nd ratios indicating derivation from mantle

  5. 湘南王仙岭花岗岩体的锆石U-Pb年代学、地球化学、锆石Hf同位素特征及其地质意义%Geochronology, geochemistry and zircon Hf isotopes of the Wangxianling granitic intrusion in South Hunan Province and its geological significance

    Institute of Scientific and Technical Information of China (English)

    郑佳浩; 郭春丽


    湘南王仙岭岩体由主体电气石黑云母花岗岩和侵入其内部的黑云母二长花岗岩组成,LA-MC-ICP MS锆石U-Pb 定年显示电气石黑云母花岗岩形成于印支期(235.0±1.3Ma),黑云母二长花岗岩形成于燕山期(155.9±1.0Ma),表明该岩体是两期岩浆活动的产物.这两期岩石均为高钾钙碱性系列,A/CNK值为1.07 ~1.66,属过铝-强过铝质花岗岩类.稀土元素显示LREE富集,HREE亏损,Eu负异常明显(0.01 ~0.38)的特征.早期电气石黑云母花岗岩和晚期黑云母二长花岗岩的εHf(t)值分别为-7.92~+4.61和-10.66~ -5.35;两阶段Hf模式年龄(tDM2)分别为1758 ~ 967Ma和1875 ~1538Ma.两期花岗岩均来自于古中元古代地壳物质重熔,其中早期电气石黑云母花岗岩在侵位上升过程中捕获了部分幔源老锆石,成岩过程中有少量地幔物质参与,且其源区具有高εHf(t)值的特点.综合前人研究成果,本文认为华南中生代印支期和燕山期均有钨锡矿化作用,印支期花岗质岩浆形成于碰撞挤压作用间隙伸展环境,而燕山期花岗质岩浆可能形成于大陆边缘弧后伸展环境.%The Wangxianling intrusion in South Hunan Province consists of two granitoids, the main tourmaline biotite granites and the biotite monzonite granites invading into the former. LA-MC-ICP MS zircon U-Pb dating shows that tourmaline biotite granites formed in Indosinian (235.0 ± 1.3Ma) while the biotite monzonite granites formed in Yanshanian (155.9 ± l.Oma), indicating that Wangxianling intrusion is the product of two-time magmatic activities. The compositions of these two period granites fall into the calc-alkaline category, with an A/CNK ratio of 1. 07 ~ 1. 66, which are peraluminous to strongly peraluminous granites. Their whole rock rare earth elements demonstrate total LREE enrichment and HREE deficit with significant negative Eu anomalies (0. 01 - 0. 38 ). The sm(t) values and two-staged Hf model ages of tourmaline

  6. Geology, petrography and geochronology of meridional and oriental regions from Morungaba complex, SP

    International Nuclear Information System (INIS)

    The Morungaba Granitoid Complex, covering about 330 km2, crops out as an elongate irregular Massif trending SW-NE, in the southeast part of the State of Sao Paulo, southeast Brazil. Major constituents are biotite granitoids with subordinate diorites. Over thirty facies types, each with distinctive structural-petrographic features, were recognized during detailed mapping of part of the Massif (about 200 km2), and mapped as groups of facies. Geochronological Rb/Sr data for several groups of associated facies are also presented. (author)

  7. Geology, petrology and geochronology of meridional and oriental regions of the Morungaba complex, SP

    International Nuclear Information System (INIS)

    This work studies the Morungaba Intensive Complex, in Southwestern of Sao Paulo State. Formed principally by granitoid rocks with biotite. 31 granitoid facies with structural was recognized. Petrographic own characteristics. The rocks from Morungaba Complex was joint in three magmatics groups, denominated: Roby Gray and Porphyritic. Petrographic and mineralogical composition studies of this three groups were done. Geochranological studies by Rb/Sr and K/sr methods made possible to establish the ages and evolution of this rocks. This Complex formation and evolution are associated with the dioritic rocks presence. This work also concluded that the Morungaba Intrusive Complex represent the pos-orogenic wents from Brazilian Cycle. (C.D.G.)

  8. Petrological studies of plutonic rocks of Ecuador

    International Nuclear Information System (INIS)

    The feldspars of many tonalitic plutonic rocks in the coastal regions and West Andean regions are zoned. This leads to the conclusion that they are relatively flat intrusions and to some extent transition rocks in the subvulcanite direction. This is in accordance with the genetic and chronological relationship between plutonites and the surrounding vulcanites of the Basic Igreous Complex (BIC). The composition of representative minerals, e.g. alkali feldspar, plagioclase feldspar, biotite, chlorite, and amphibole has been determined as well as the age of plutonite samples by the K/Ar dating method. (DG)

  9. Mineralogy and geochemistry of granitoids from Kinnaur region, Himachal Higher Himalaya, India: Implication on the nature of felsic magmatism in the collision tectonics

    Indian Academy of Sciences (India)

    Brajesh Singh; Santosh Kumar; Masao Ban; Kazuo Nakashima


    Felsic magmatism in the southern part of Himachal Higher Himalaya is constituted by Neoproterozoic granite gneiss (GGn), Early Palaeozoic granitoids (EPG) and Tertiary tourmaline-bearing leucogranite (TLg). Magnetic susceptibility values ($\\lt$3 ×10$^{−3}$ SI), molar Al$_2$O$^3$/(CaO+Na$_2$O+K$_2$O) ($\\geq$1.1), mineral assemblage (bt–ms–pl–kf–qtz ± tur ± ap), and the presence of normative corundum relate these granitoids to peraluminous S-type, ilmenite series (reduced type) granites formed in a syncollisional tectonic setting. Plagioclase from GGn (An$_{10}$–An$_{31}$) and EPG (An$_{15}$–An$_{33}$) represents oligoclase to andesine and TLg (An$_2$–An$_{15}$) represents albite to oligoclase, whereas compositional ranges of K-feldspar are more or less similar (Or$_{88}$ to Or$_{95}$ in GGn, Or$_{86}$ to Or$_{97}$ in EPG and Or$_{87}$ to Or$_{94}$ in TLg). Biotites in GGn (Mg/Mg+Fe$^t$ = 0.34–0.45), EPG (Mg/Mg+Fe$^t$ = 0.27–0.47), and TLg (Mg/Mg+Fe$^t$ = 0.25–0.30) are ferribiotites enriched in siderophyllite, which stabilised between FMQ and HM buffers and are characterised by dominant 3Fe$\\rightleftarrows$2Al, 3Mg$\\rightleftarrows$2Al substitutions typical of peraluminous (S-type), reducing felsic melts. Muscovite in GGn (Mg/Mg+Fe$^t$ = 0.58–0.66), EPG (Mg/Mg+Fe$^t$ = 0.31−0.59), and TLg (Mg/Mg+Fet = 0.29–0.42) represent celadonite and paragonite solid solutions, and the tourmaline fromEPG and TLg belongs to the schorl-elbaite series, which are characteristics of peraluminous, Li-poor, biotite-tourmaline granites. Geochemical features reveal that the GGn and EPG precursor melts were most likely derived from melting of biotite-rich metapelite and metagraywacke sources, whereas TLg melt appears to have formed from biotite-muscovite rich metapelite and metagraywacke sources. Major and trace elements modelling suggest that the GGn, EPG and TLg parental melts have experienced low degrees (∼13, ∼17 and ∼13%, respectively) of kf

  10. Partial melting of metavolcanics in amphibolite facies regional metamorphism

    Indian Academy of Sciences (India)

    Alan Bruce Thompson


    Metavolcanic rocks containing low-Ca amphiboles (gedrite, cummingtonite) and biotite can undergo substantial dehydration-melting. This is likely to be most prominent in Barrovian Facies Series (kyanite-sillimanite) and occurs at the same time as widespread metapelite dehydration- melting. In lower pressure facies series, metavolcanics will be represented by granulites rich in orthopyroxene when dehydration occurs at much lower temperatures than melting. In higher pressure facies series it is not well known whether metavolcanic rocks dehydrate or melt at temperatures lower or similar to that of metapelites.

  11. P-T path and timing of crustal thickening during amalgamation of East and West Gondwana: A case study from the Hafafit Metamorphic Complex, Eastern Desert of Egypt (United States)

    Abu El-Enen, Mahrous M.; Abu-Alam, Tamer S.; Whitehouse, Martin J.; Ali, Kamal A.; Okrusch, Martin


    The southeastern sector of the Hafafit Metamorphic Complex, southern Eastern Desert of Egypt comprises infrastructural orthogneisses of tonalite and syenogranite parentage, amphibolites, and a volcano-sedimentary association. These are overthrust by an obducted suprastructural ophiolite nappes via the Nugrus thrust. The protolith of the biotite-hornblende-gneisses was formed during island-arc accretion, while that of the garnet-biotite gneisses were formed in a within-plate regime, consistent with a transition to a post-collisional setting. The volcano-sedimentary association comprises interbedded and intercalated highly foliated metapelitic schists, metabasites, and leucocratic gneisses, deposited in a back-arc basin. The metapelites and the leucocratic gneisses originated from immature Fe-shales and arkoses derived from intermediate-mafic and acidic igneous rocks, respectively, via weak chemical weathering in a tectonically active island arc terrane. The intercalated amphibolites were derived from tholeiitic basalts generated in a back-arc setting. The volcano-sedimentary association was metamorphosed under upper-amphibolite facies conditions with pressures of 9-13 kbar and temperatures of 570-675 °C, as derived from conventional geothermobarometry and pseudosection calculation. A steep, tight clockwise P-T path is constrained and a geothermal gradient around 20 °C/km is estimated for the peak metamorphism. We assume that deformation and metamorphism are due to crustal thickening during the collision of East and West Gondwana, where peak metamorphism took place in the middle to lower crust at 33 km average crustal depth. This was followed by a subsequent quasi-isothermal decompression due to rapid exhumation during wrench tectonics. Sinistral transcurrent shearing with extensional denudation resulted in vertical ductile thinning that was accompanied by heat input from magmatism, as indicated by a higher geothermal gradient during retrograde metamorphism and

  12. The life cycle of iron Fe(III) oxide: impact of fungi and bacteria (United States)

    Bonneville, Steeve


    Iron oxides are ubiquitous reactive constituents of soils, sediments and aquifers. They exhibit vast surface areas which bind a large array of trace metals, nutrients and organic molecules hence controlling their mobility/reactivity in the subsurface. In this context, understanding the "life cycle" of iron oxide in soils is paramount to many biogeochemical processes. Soils environments are notorious for their extreme heterogeneity and variability of chemical, physical conditions and biological agents at play. Here, we present studies investigating the role of two biological agents driving iron oxide dynamics in soils, root-associated fungi (mycorrhiza) and bacteria. Mycorrhiza filaments (hypha) grow preferentially around, and on the surface of nutrient-rich minerals, making mineral-fungi contact zones, hot-spots of chemical alteration in soils. However, because of the microscopic nature of hyphae (only ~ 5 µm wide for up to 1 mm long) and their tendency to strongly adhere to mineral surface, in situ observations of this interfacial micro-environment are scarce. In a microcosm, ectomycorrhiza (Paxillus involutus) was grown symbiotically with a pine tree (Pinus sylvestris) in the presence of freshly-cleaved biotite under humid, yet undersaturated, conditions typical of soils. Using spatially-resolved ion milling technique (FIB), transmission electron microscopy and spectroscopy (TEM/STEM-EDS), synchrotron based X-ray microscopy (STXM), we were able to quantify the speciation of Fe at the biotite-hypha interface. The results shows that substantial oxidation of biotite structural-Fe(II) into Fe(III) subdomains occurs at the contact zone between mycorrhiza and biotite. Once formed, iron(III) oxides can reductively dissolve under suboxic conditions via several abiotic and microbial pathways. In particular, they serve as terminal electron acceptors for the oxidation of organic matter by iron reducing bacteria. We aimed here to understand the role of Fe(III) mineral

  13. Mineralogical study on volcanic ash of the eruption on September 27, 2014 at Ontake volcano, central Japan: correlation with porphyry copper systems (United States)

    Minami, Yusuke; Imura, Takumi; Hayashi, Shintaro; Ohba, Tsukasa


    The volcanic ash of the eruption on September 27, 2014 at Ontake volcano consists mostly of altered rock fragments. The ash contains partly altered volcanic rock fragments consisting of primary igneous minerals (plagioclase, orthopyroxene, titanomagnetite, and feldspars) and volcanic glass accompanied by alteration minerals to some extents, and contains no juvenile fragments. These features indicate that the eruption was a non-juvenile hydrothermal eruption that was derived from the hydrothermal system developed under the crater. The major minerals derived from hydrothermal alteration zones are silica mineral, kaolin-group mineral, smectite, pyrophyllite, muscovite, alunite, anhydrite, gypsum, pyrite, K-feldspar, albite, and rutile. Minor chlorite, biotite, and garnet are accompanied. Five types of alteration mineral associations are identified from observations on individual ash particles: silica-pyrite, silica-pyrite ± alunite ± kaolin, silica-pyrophyllite-pyrite, silica-muscovite ± chlorite, and silica-K-feldspar ± albite ± garnet ± biotite. The associations indicate development of advanced argillic, sericite, and potassic alteration zones under the crater. Occurrence of anhydrite veinlet and the set of alteration zones indicate hydrothermal alteration zones similar to late-stage porphyry copper systems. Comparing the mineral associations with the geologic model of the late-stage porphyry copper systems, the source depths of mineral associations are estimated to range from near surface to >2 km. The depths of advanced argillic alteration, sericite, and potassic zones are 0 to ~2, ~1.5 to ~2, and >2 km, respectively.

  14. Mineral Type and Solution Chemistry Affect the Structure and Composition of Actively Growing Bacterial Communities as Revealed by Bromodeoxyuridine Immunocapture and 16S rRNA Pyrosequencing. (United States)

    Kelly, L C; Colin, Y; Turpault, M-P; Uroz, S


    Understanding how minerals affect bacterial communities and their in situ activities in relation to environmental conditions are central issues in soil microbial ecology, as minerals represent essential reservoirs of inorganic nutrients for the biosphere. To determine the impact of mineral type and solution chemistry on soil bacterial communities, we compared the diversity, composition, and functional abilities of a soil bacterial community incubated in presence/absence of different mineral types (apatite, biotite, obsidian). Microcosms were prepared containing different liquid culture media devoid of particular essential nutrients, the nutrients provided only in the introduced minerals and therefore only available to the microbial community through mineral dissolution by biotic and/or abiotic processes. By combining functional screening of bacterial isolates and community analysis by bromodeoxyuridine DNA immunocapture and 16S rRNA gene pyrosequencing, we demonstrated that bacterial communities were mainly impacted by the solution chemistry at the taxonomic level and by the mineral type at the functional level. Metabolically active bacterial communities varied with solution chemistry and mineral type. Burkholderia were significantly enriched in the obsidian treatment compared to the biotite treatment and were the most effective isolates at solubilizing phosphorous or mobilizing iron, in all the treatments. A detailed analysis revealed that the 16S rRNA gene sequences of the OTUs or isolated strains assigned as Burkholderia in our study showed high homology with effective mineral-weathering bacteria previously recovered from the same experimental site. PMID:27138048

  15. Sorption processes of radiocesium in soil and bedrock

    Energy Technology Data Exchange (ETDEWEB)

    Lehto, Jukka [Helsinki Univ. (Finland). Lab. of Radiochemistry


    Three recent studies on cesium sorption in soil and bedrock are reviewed. {sup 137}Cs, originating from fallouts of nuclear weapons tests and the Chernobyl accident was found to decrease in an exponential manner in forest soil, and the highest fraction in soil profiles was found in the organic layer. Also, the mineral layer below the organic layer contained a large fraction of cesium inventory but at depths below 20 cm only a very small fraction was observed. In the bedrock of Olkiluoto, where the final repository for spent nuclear fuel from the Finnish nuclear power plants will be constructed, mica mineral biotite plays the most important role in cesium sorption. The selectivity of biotite decreases in the order Cs > K > Na > Ca and the overall selectivity coefficient for Cs/Ca exchange was approximately five and seven orders of magnitude higher than those for Cs/Na and Cs/K exchange reactions, respectively. Ion exchange isotherms for Cs/Na and Cs/K exchange were modelled by assuming three different ion exchange sites: frayed edge sites (FES), basal plane sites and intermediate sites. The selectivity coefficients derived for these sites were successfully used to predict cesium sorption in a mica gneiss rock. Sorption of cesium in mineral soil layers from the Olkiluoto overburden were studied using three different approaches: model batch experiments, an in-situ method and calculations. All three approaches gave the same trend but the distribution coefficient values varied in range of one order of magnitude.

  16. Phase equilibria of HP-UHP mica-schists in Jiangling,Eastern Dabieshan orogen

    Institute of Scientific and Technical Information of China (English)

    Hang Chu; Chunjing Wei; Shangguo Su


    The HP-UHP metamorphic terrane of Jiangling, eastern Dabieshan comprises extensively distributed granitic gneisses, mica-schists and numerous eclogite blocks. The mica-schists generally contain garnet, phengitic muscovite, biotite, plagioclase, quartz, rutile and a small amount of epidote and hornblende. Study on petrography and phases equilibria in the NCKMnFMASH system indicates that the present mineral assemblages in mica-schists are not in equilibrium. The earlier stage of mineral assemblage represented by garnet and phengite reflects a HP-UHP condition. The garnet compositions and the phengite Si contents give a PT condition of 580-00 ℃ at 2.6-2.8 GPa. The garnet zonation records an earlier progressive metamorphic process which may be associated with the appearance of glaucophane, jadeite and lawsonite. The later stage of mineral assemblage characterized by the presence of biotite and plagioclase reflects a PT condition of 620-635℃ at 0.9-1.1 GPa, belonging to the HP amphibolite facies. The main mineral assemblage in mica-schists from the Jiangling region has recorded a complete HP-UHP metamorphic process.

  17. Petrography and geochronology (U/Pb-Sm/Nd) the Passagem Granite, Pensamiento Granitoid Complex, Paragua Terrane, SW Amazon Craton, Mato Grosso, Brazil; Petrologia e geocronologia (U/Pb-Sm/Nd) do Granito Passagem, Complexo Granitoide Pensamiento, SW do Craton Amazonico (MT)

    Energy Technology Data Exchange (ETDEWEB)

    Jesus, Gisely Carmo de, E-mail: [Universidade Federal de Mato Grosso (ICET/UFMT), Cuiaba, MT (Brazil). Inst. de Ciencias Exatas e da Terra. Programa de Pos-Graduacao em Geociencias; Sousa, Maria Zelia Aguiar de, E-mail: [Universidade Federal de Mato Grosso(ICET/UFMT), Cuiaba, MT (Brazil). Inst. de Ciencias Exatas e da Terra. Dept. de Recursos Minerais; Ruiz, Amarildo Salina; Matos, Joao Batista de, E-mail:, E-mail: jmatos@cpd.ufmt.b [Universidade Federal de Mato Grosso (ICET/UFMT), Cuiaba, MT (Brazil). Inst. de Ciencias Exatas e da Terra. Dept. de Geologia Geral


    The Passagem granite includes stocks, plugs and dikes located in the Ricardo Franco hill - Vila Bela da Santissima Trindade region - state of Mato Grosso, central Brazil. The Passagem Granite is included in the Paragua terrane - SW Amazonian Craton. It consists of isotropic monzogranite, sienogranite and more rarely granodiorites with leucocratic dark gray to white color. These rocks range from hypidomorphic inequigranular to xenomorphic texture, fine to medium grained. Biotite is the only primary mafic present as essential phase and characterize an expanded slightly acid sequence formed by a sub-alkaline magmatism of high-potassium calc-alkaline, slightly peraluminous composition from arc magmatic tectonic environment during a post-collisional period. Mechanism of fractional crystallization of plagioclase, biotite, titanite, apatite and zircon associated with simultaneous crustal assimilation are suggested for the evolution of these rocks. The results support the hypothesis of a post-collisional magmatism in the Paragua terrane at 1284 +- 20 Ma corresponding to the crystallization age of the Passagem granite. This paper propose that Passagem Granite represents as an extension in Brazilian terrane of the Pensamiento Granitoid Complex. (author)

  18. Age and geological setting of uranium mineralization associated with the Main Donegal Granite, Ireland

    Energy Technology Data Exchange (ETDEWEB)

    O' Connor, P.J.; Long, C.B.; Basham, I.R; Swainbank, I.G.; Beddoe-Stephens, B.


    Both pegmatite-hosted and vein types of uranium mineralization are associated with the Main Donegal Granite, northwestern Ireland. A low-thorian uraninite is the main ore mineral in the mineralized biotite-pegmatites and its textural relations are consistent with late magmatic formation. The uraninite yields a /sup 207/Pb//sup 206/Pb age of 407 +- 4 m.y. concordant with the age of emplacement of the Main Donegal pluton, dated by whole-rock Rb-Sr methods at 407 +- 23 m.y. The uraninite is present not only in pegmatitic zones within the Main Donegal pluton but also with marginal microgranite sheets in the sheeted contact zone of the pluton. The main mineralogical control is biotite, but the distribution of U-bearing zones within the pluton suggests a dominant structural control and may be related to emplacement of the granite into an active late Caledonian transcurrent shear zone. Both the pegmatite-hosted uranium mineralization and that of vein type are closely associated geographically with the southwestern end of the pluton. The vein-type material consists of pitchblende formed under low-temperature hydrothermal conditions: a /sup 207/Pb//sup 206/Pb age of 295 +- 4 m.y. indicates a Hercynian episode of mineralization. The low-thorian uraninite is a potential source of labile uranium.

  19. The petrogenesis of sodic island arc magmas at Savo volcano, Solomon Islands (United States)

    Smith, D. J.; Petterson, M. G.; Saunders, A. D.; Millar, I. L.; Jenkin, G. R. T.; Toba, T.; Naden, J.; Cook, J. M.


    Savo, Solomon Islands, is a historically active volcano dominated by sodic, alkaline lavas, and pyroclastic rocks with up to 7.5 wt% Na2O, and high Sr, arc-like trace element chemistry. The suite is dominated by mugearites (plagioclase-clinopyroxene-magnetite ± amphibole ± olivine) and trachytes (plagioclase-amphibole-magnetite ± biotite). The presence of hydrous minerals (amphibole, biotite) indicates relatively wet magmas. In such melts, plagioclase is relatively unstable relative to iron oxides and ferromagnesian silicates; it is the latter minerals (particularly hornblende) that dominate cumulate nodules at Savo and drive the chemical differentiation of the suite, with a limited role for plagioclase. This is potentially occurring in a crustal “hot zone”, with major chemical differentiation occurring at depth. Batches of magma ascend periodically, where they are subject to decompression, water saturation and further cooling, resulting in closed-system crystallisation of plagioclase, and ultimately the production of sodic, crystal and feldspar-rich, high-Sr rocks. The sodic and hydrous nature of the parental magmas is interpreted to be the result of partial melting of metasomatised mantle, but radiogenic isotope data (Pb, Sr, Nd) cannot uniquely identify the source of the metasomatic agent.

  20. Cesium sorption and desorption behavior of clay minerals

    International Nuclear Information System (INIS)

    Cesium sorption and desorption of clay minerals (montmorillonite, beidellite, nontronite, weathered biotite, rectorite and illite) were investigated by consecutive sorption-desorption (CSD) experiments. In batch sorption experiment, two solutions with different Cs concentration 10-3 and 10-7 mol/L) were used. In batch desorption experiments, Cs sorbed samples in sorption experiments were treated 5 times with 1 mol/L ammonium acetate solution. In the case of CSD experiments using 10-3 mol/L Cs solution, the exchangeable cations (Na, Ca, and K) in the clay samples affected to the sorption ratio of Cs, and this effect depended on the type of clay mineral. The desorption ratios of untreated, Na-exchanged and Ca-exchanged weathered biotite ranged from 23 to 33%, while that of other samples was over 80%. In the case of CSD experiments using 10-7 mol/L Cs solution, the sorption ratio of montmorillonite was smaller than that of the other clay samples. In desorption experiments, more than 10-9 mol sorbed Cs remained in 1.0 g of the sample after 5 extraction times. These results indicate that all examined clay samples are able to strongly adsorb Cs with a capacity of more than 10-9 mol/g. (author)

  1. A model that helps explain Sr-isotope disequilibrium between feldspar phenocrysts and melt in large-volume silicic magma systems (United States)

    Duffield, Wendell A.; Ruiz, Joaquin


    Feldspar phenocrysts of silicic volcanic rocks are commonly in Sr-isotopic disequilibrium with groundmass. In some cases the feldspar is more radiogenic, and in others it is less radiogenic. Several explanations have been published previously, but none of these is able to accommodate both senses of disequilibrium. We present a model by which either more- or less-radiogenic feldspar (or even both within a single eruptive unit) can originate. The model requires a magma body open to interaction with biotite- and feldspar-bearing wall rock. Magma is incrementally contaminated as wall rock melts incongruently. Biotite preferentially melts first, followed by feldspar. Such melting behavior, which is supported by both field and experimental studies, first contaminates magma with a relatively radiogenic addition, followed by a less-radiogenic addition. Feldspar phenocrysts lag behind melt (groundmass of volcanic rock) in incorporating the influx of contaminant, thus resulting in Sr-isotopic disequilibrium between the crystals and melt. The sense of disequilibrium recorded in a volcanic rock depends on when eruption quenches the contamination process. This model is testable by isotopic fingerprinting of individual feldspar crystals. For a given set of geologic boundary conditions, specific core-to-rim Sr-isotopic profiles are expectable. Moreover, phenocrysts that nucleate at different times during the contamination process should record different and predictable parts of the history. Initial results of Sr-isotopic fingerprinting of sanidine phenocrysts from the Taylor Creek Rhyolite are consistent with the model. More tests of the model are desirable.

  2. Nitrogen in Ancient Mud: A Biosignature? (United States)

    Stüeken, Eva E.


    Nitrogen is an essential nutrient for all life on Earth and possibly elsewhere. Burial of nitrogen bound to organic matter constitutes the major flux of nitrogen into sediments today, which has led to the inference that nitrogen enrichments in sedimentary rocks may be a biosignature. However, abiotic processes such as lightning or volcanism can fix atmospheric N2 and contribute to sedimentary nitrogen burial in the absence of life. It is therefore uncertain whether observed nitrogen enrichments of up to 430 ppm in Paleoarchean metasedimentary biotite grains are indeed biogenic. This study seeks to address that problem with a numerical model. The NH4+ concentration of an abiotic ocean is modeled as a function of source fluxes, pH-dependent NH3 volatilization, and equilibrated adsorption of NH4+ onto clay particles. The results suggest that the observed nitrogen concentrations in Paleoarchean biotite can only be reconciled with purely abiotic processes if the ocean was more acidic (pH origin. While this does not necessitate a particular metabolism such as biological N2 fixation, the data provide evidence of nitrogen utilization back to 3.8 Gyr. Nitrogen abundances could thus provide useful information in extraterrestrial missions.

  3. Magnetic properties of sheet silicates

    International Nuclear Information System (INIS)

    Susceptibility, magnetisation and Moessbauer measurements are reported for a representative selection of 2:1 layer phyllosilicates. Eight samples from the mica, vermiculite and smectite groups include examples diluted in iron which are paramagnetic at all temperatures, as well as iron-rich silicates which order magnetically below 10 K. Anisotropic susceptibility of crystals of muscovite, biotite and vermiculite is quantitatively explained with a model where the Fe2+ ions lie in sites of effective trigonal symmetry, the trigonal axis lying normal to the sheets. The ferrous ground state is an orbital singlet. Ferric iron gives an isotropic contribution to the susceptibility. Fe2+-Fe2+ exchange interactions are ferromagnetic with Gapprox. equal to2 K, whereas Fe3+-Fe3+ coupling is antiferromagnetic in the purely ferric minerals. A positive paramagnetic Curie temperature for glauconite may be attributable to Fe2+ → Fe3+ charge transfer. Magnetic order was found to set in inhomogeneously for glauconite at 1-7 K. One biotite sample showed an antiferromagnetic transition at Tsub(N) = 7 K marked by a well-defined susceptibility maximum. Its magnetic structure, consisting of ferromagnetic sheets with moments in their planes coupled antiferromagnetically by other, weak interactions, resembles that found earlier for the 1:1 mineral greenalite. (orig.)

  4. 湘赣地洼型煤田中岩浆岩的岩石学及地球化学特征

    Institute of Scientific and Technical Information of China (English)

    童玉明; 邱明


    Commonly seen in Mesozoic coal fields of Diwa type in Hunan and Jiangxi are basic, intermediate and acidic intrusive and volcanic rocks. The sequence of magmatism is from acidic to basic. The rocks show a tendency to become younger in age from west to east. Biotite granite porphyry-quartz diorite porphyrite, diorite porphyrite-diabase, diabase-porphyrite and spilite are the main rock types. These rocks are geochemically eharacterized by an evolutionary sequence from acidic to basic and by the enrichment in alkaline elements (except for biotite granite porphyry which has undergone intense alteration). In the acidic rocks K2O> Na2O whereas in the basic rocks K2O < Na2O. All the rocks are rich in non-ferrous metals and rare dements. The majority of the magmatic rocks were emplaced during the most intensive pariod of Diwa development. The rocks generally run parallel with the strike of coal basins. They were emplaced mostly along the layers or cut across coal seams. The above data on tectono-magmatic activity in coal fields of Diwa type lend great support to Prof. Chert Guoda's proposal that the history of crustal evolution is divided into three major stages -- geosyncline, platform snd Diwa.

  5. Cesium adsorption/desorption behavior of clay minerals considering actual contamination conditions in Fukushima (United States)

    Mukai, Hiroki; Hirose, Atsushi; Motai, Satoko; Kikuchi, Ryosuke; Tanoi, Keitaro; Nakanishi, Tomoko M.; Yaita, Tsuyoshi; Kogure, Toshihiro


    Cesium adsorption/desorption experiments for various clay minerals, considering actual contamination conditions in Fukushima, were conducted using the 137Cs radioisotope and an autoradiography using imaging plates (IPs). A 50 μl solution containing 0.185 ~ 1.85 Bq of 137Cs (10-11 ~ 10-9 molL-1 of 137Cs) was dropped onto a substrate where various mineral particles were arranged. It was found that partially-vermiculitized biotite, which is termed “weathered biotite” (WB) in this study, from Fukushima sorbed 137Cs far more than the other clay minerals (fresh biotite, illite, smectite, kaolinite, halloysite, allophane, imogolite) on the same substrate. When WB was absent on the substrate, the amount of 137Cs sorbed to the other clay minerals was considerably increased, implying that selective sorption to WB caused depletion of radiocesium in the solution and less sorption to the coexisting minerals. Cs-sorption to WB continued for about one day, whereas that to ferruginous smectite was completed within one hour. The sorbed 137Cs in WB was hardly leached with hydrochloric acid at pH 1, particularly in samples with a longer sorption time. The presence/absence of WB sorbing radiocesium is a key factor affecting the dynamics and fate of radiocesium in Fukushima.

  6. Sorption processes of radiocesium in soil and bedrock

    International Nuclear Information System (INIS)

    Three recent studies on cesium sorption in soil and bedrock are reviewed. 137Cs, originating from fallouts of nuclear weapons tests and the Chernobyl accident was found to decrease in an exponential manner in forest soil, and the highest fraction in soil profiles was found in the organic layer. Also, the mineral layer below the organic layer contained a large fraction of cesium inventory but at depths below 20 cm only a very small fraction was observed. In the bedrock of Olkiluoto, where the final repository for spent nuclear fuel from the Finnish nuclear power plants will be constructed, mica mineral biotite plays the most important role in cesium sorption. The selectivity of biotite decreases in the order Cs > K > Na > Ca and the overall selectivity coefficient for Cs/Ca exchange was approximately five and seven orders of magnitude higher than those for Cs/Na and Cs/K exchange reactions, respectively. Ion exchange isotherms for Cs/Na and Cs/K exchange were modelled by assuming three different ion exchange sites: frayed edge sites (FES), basal plane sites and intermediate sites. The selectivity coefficients derived for these sites were successfully used to predict cesium sorption in a mica gneiss rock. Sorption of cesium in mineral soil layers from the Olkiluoto overburden were studied using three different approaches: model batch experiments, an in-situ method and calculations. All three approaches gave the same trend but the distribution coefficient values varied in range of one order of magnitude.

  7. Preliminary paragenetic interpretation of the Quaternary topaz rhyolite lava domes of the Blackfoot volcanic field, southeastern Idaho (United States)

    Lochridge, W. K., Jr.; McCurry, M. O.; Goldsby, R.


    The Quaternary topaz rhyolite lava domes of the bimodal, basalt-dominated Blackfoot volcanic field (BVF), SE Idaho occur in three clusters. We refer to these as the China Hat lava dome field (southernmost; ~ 57 ka), and the 1.4 to 1.5 Ma Sheep Island and White Mountain (northernmost) lava dome fields. The rhyolites and surrounding, more voluminous basalt lavas closely resemble coeval Quaternary rocks erupted to the north along the Eastern Snake River Plain segment of the Yellowstone-Snake River Plain volcanic track. However rhyolites in BVF are distinguished by having more evolved Sr- and Nd-isotopic ratios, as well as having phenocryst assemblages that includes hydrous phases (biotite and hornblende), thorite, and vapor-phase topaz. This study seeks to improve our understanding of the unique conditions of magma evolution that led to these differences. We focus on textural features of major and accessory phenocrysts as a basis for inferring paragenesis for rhyolites from the China Hat lava dome field. Preliminary work indicates that there are three sequentially formed populations of textures among magmatic phases: 1. population of anhedral quartz and plagioclase; 2. population of euhedral grains that includes quartz, sandine, plagioclase, biotite, hornblende, Fe-Ti oxides, zircon and apatite; 3. boxy cellular (skeletal?) sanidine and quartz. We speculate that the first population are resorbed antecrysts, the second formed prior to eruption as autocrysts (at or near equilibrium?), and the third formed soon before or during eruption.

  8. Relationship between the isotopic composition of strontium in newly formed continental clay minerals and their source material

    International Nuclear Information System (INIS)

    The 87Sr/86Sr ratios of recent montmorillonites and kaolinites newly formed in weathering profiles of western and central Africa and of Nosy Be and La Reunion islands near Madagascar are directly related to the composition and age of the parent rocks or minerals. They may, therefore, be used as a genetic tracer. The 87Sr/86Sr ratios are about 0.704 when these clays crystallise from recent basalts and they are higher than 0.715 when the parent rocks are of sialic composition and old in age. Kaolinites newly formed in situ from feldspars contain small amounts of Sr with abnormally high 87Sr/86Sr ratios: in this study they are higher than 1.094. When these minerals crystallize from biotites, their 87Sr/86Sr ratios are much lower and can be close to the value of the primary Sr trapped in the biotites during their crystallization. On the other hand, the 87Sr/86Sr of continental montmorillonites are less scattered: they range, in this study, between 0.704 and 0.722. These low values, as well as the high adsorption capacities of these minerals in the sedimentary environment, allow the assumption that they frequently have 87Sr/86Sr ratios close to that of marine Sr during sedimentation. Therefore, montmorillonites are able to form homogeneous authigenic minerals by synsedimentary alterations. (Auth.)

  9. Geochemical evidence for contribution of ore-forming materials from peraluminous granite basement-- Taking Fucheng pluton and No. 6722 uranium deposit in southern Jiangxi Province as examples

    Institute of Scientific and Technical Information of China (English)

    ZHANG; Bangtong(章邦桐); CHEN; Peirong(陈培荣); YANG; Dongsheng(杨东生); KONG; Xinggong(孔兴功)


    Using the induced fission-track method, mobile uranium leaching and lead isotope analysis, this work obtianed geochemical features of the peraluminous Fucheng granite basement and the host rock (shoshonite) of the No. 6722 uranium deposit in southern Jiangxi Province. (i) Uranium contents of the leucocratic rock-forming minerals (0.18 ?g/g for quartz, 0.36 ?g/g for feldspar) are lower than the uranium content of the whole rock (4.6 ?g/g). Biotite and some accessory mineral inclusions (zircon, monazite and uraninite) are the main uranium carriers of the Fucheng granite pluton. The fissure uranium in altered minerals (hydromica and chlorite) increased evidently. (ii) Leachable rate of mobile uranium in the biotite granite is 10.4%, while that in the altered granite increased to 31%. (iii) Caculation based on lead isotopes shows that during alteration the Fucheng granite lost uranium (?U = ?37% - ?65%), whereas the Caotaobei shoshonite gained uranium (?U = +37%- +58%). These features suggest that the ore-forming material of the No. 6722 uranium deposit was mainly derived from the altered peraluminous granite basement of Fucheng pluton.

  10. Geochronological evidence of Indosinian(high-pressure) metamorphic event and its tectonic significance in Taxkorgan area of the Western Kunlun Mountains,NW China

    Institute of Scientific and Technical Information of China (English)


    The CL images,LA-ICP-MS in situ trace elements analysis,and U-Pb dating for zircons indicate that the metamorphic ages of the sillimanite-garnet-biotite gneiss and the garnet-amphibole gneiss from eastern Taxkorgan of the Western Kunlun Mountains are 220±2 and 220±3 Ma respectively,and their protolith ages are younger than 253±2 and 480±8 Ma respectively.Two samples were collected at the same outcrops with HP mafic granulite and HP pelitic granulite.Mineral assemblage of the sillimanite-garnet-biotite gneiss(Grt+Sill+Per+Q) is consistent with that of HP pelitic granulite at early high amphibolite-granulite facies stage.Mineral assemblage of the garnet-amphibole gneiss(Grt+Amp+Pl+Q) is consistent with retro-metamorphic assemblage of HP mafic granulite at amphibolite facies stage.The dating results suggest that these HP granulites underwent peak metamorphism at 220±2 to 253±2 Ma.Thus,the Kangxiwar tectonic zone was probably formed by subduction and collision of the Paleo-Tethys Ocean during Indosinian.Protolith ages of the two samples,together with previously published U-Pb zircon dating age,suggest that the sillimanite-garnet schist-quartzite unit is a late Paleozoic unit,not a part of the Paleoproterozoic Bulunkuole Group.

  11. Oxygen isotope geochemistry of the Omeo Metamorphic complex, Victor: implications for metamorphic fluid flow, mineralisation and anatexis

    Energy Technology Data Exchange (ETDEWEB)

    Cartwright, I.; Harper, S. [Monash University, Clayton, VIC (Australia). Victorian Institute of Earth and Planetary Sciences


    Metamorphosed turbidites from the Omeo Metamorphic Complex show only minor changes in {delta}{sup 18}O values with increasing metamorphic grade from 13.4 {+-} 1.7 per mill in the chlorite and biotite zones to 12.3 {+-} 1.0 per mill in the sillimanite + K-feldspar zone. Rocks within 5 km of the S-type granite at Hume Dam have {delta}{sup 18}O values of 6.8-8.1 per mill that probably reflect interaction with heated meteoric-igneous fluids. Interaction with igneous fluids has also occurred close to other I- and S-type granites in this region. However, pervasive metamorphic fluid-rock interaction in this terrain did not occur, which limits the region`s potential for hydrothermal mineralisation. Anatexis at high grades was probably via dehydration-melting reactions that consumed muscovite and biotite, which is consistent with there being little fluid present during metamorphism. Small (kilometre scale or less) S-type granites in the sillimanite + K-feldspar zone have {delta}{sup 18}O values similar to those of the surrounding metasediments and probably formed by melting of those rocks. By contrast, larger (tens of kilometres scale) Ca-rich. peraluminous, S-type granites have lower {delta}{sup 18}O values than the surrounding metasediments, and may represent melts of underlying middle to lower crust . Copyright (1998) Blackwell Science Asia 31 refs., 1 tab., 3 figs.

  12. Long-lived high-temperature granulite-facies metamorphism in the Eastern Himalayan orogen, south Tibet (United States)

    Zhang, Zeming; Xiang, Hua; Dong, Xin; Ding, Huixia; He, Zhenyu


    The Namche Barwa Complex exposed in the Eastern Himalayan Syntaxis, south Tibet, underwent high-pressure (HP) and high-temperature (HT) granulite-facies metamorphism and associated anatexis. The HP pelitic granulites contain garnet, kyanite, sillimanite, cordierite, biotite, quartz, plagioclase, K-feldspar, spinel, ilmenite and graphite. These minerals show composite reaction texture and varying chemical compositions and form four successive mineral assemblages. Phase equilibrium modeling constrains the P-T conditions of 10-12 kbar and 550-700 °C for the prograde stage, 13-16 kbar and 840-880 °C for the peak-metamorphic stage, and 5-6 kbar and 830-870 °C for the late retrograde stage, indicating that the HP granulites recorded a clockwise P-T path involving the early heating burial and anatexis through dehydration melting of both muscovite and biotite, and the late isothermal decompression and gradual melt crystallization under HT granulite-facies conditions. The zircon U-Pb dating reveals that the HT granulite-facies metamorphism probably initiated at ca. 40 Ma, and lasted to ca. 8 Ma. Therefore, the present study provides robust evidence for a long-lived HT metamorphism and associated anatexis in the deeply buried Indian continent and important constraints on the leucogranite generation and tectonic evolution of the Himalayan orogen.

  13. Petrographical and geochemical characterization and deformation conditions of the San Cristobal pluton, Sierra de Velasco, La Rioja, Argentina; Caracterizacion petrografica y geoquimica y condiciones de deformacion del pluton San Cristobal, Sierra de Velasco, La Rioja, Argentina

    Energy Technology Data Exchange (ETDEWEB)

    Bellos, L.I.; Toselli, A.J.; Rossi, J.N.; Grosse, P.; Rosa, J.D. de la; Castro, A.


    The San Cristobal pluton is a 35 km2 granitic body that outcrops at the southestern tip of the Sierra de Velasco, located west of La Rioja city, Argentina. It is formed by monzogranites and syenogranites, together with scarce granodiorites, with medium to fine-grained, equigranular to slightly porphyritic textures. Their mineral assemblage consists of quartz + microcline + plagioclase + biotite {+-} muscovite + zircon + apatite + magnetite. The granite contains dioritic to tonalitic mafic enclaves. The central and eastern parts of the granite have been deformed by the NNW-SSE trending South Mylonitic shear zone formed by mylonitic rocks. The metamorphic host-rock is represented by scarce greenschist facies xenoliths and hornfels with the high T/P assemblage K-feldspar - cordierite - biotite {+-} sillimanite. The granites are calc-alkaline, weak- to moderately peraluminous, and formed as part of a continental magmatic arc developed along the active margin of western Gondwana during the Early Paleozoic. The depth of emplacement of the San Cristobal pluton is estimated at {approx}12 km. (Author).

  14. Incineration of ion-exchange resins in fluidized bed. Part of a coordinated programme on treatment of spent ion exchange resins

    International Nuclear Information System (INIS)

    Incineration of ion-exchange resins in a fluidized bed was studied on the pilot plant scale. The test programme performed consisted of the testing of various bed materials and finding the optimal conditions of incineration of spent resins. Granular resins were incinerated in an ethanol-water mixture. Incinernation converts the organic resin into inert oxide material, which can be solidified for instance with cement. The weight of the ash was 1...20% and the volume 2...30% of the original resins, which contained 15...25% moisture. When solidified with cement the volume of the ash-concrete is 4...22% of the concrete of equal compressive strength acquired by direct solidification. Water immersion and heat tests of solidified ash showed satisfactory results. The absorption of Cs and Co in various bed materials was studied by means of inactive tracer materials. Biotite and chamotte absorbed significantly, but this absorption does not drastically help on the off gas side. The sintering of the bed materials in the presence of sodium was studied. Corundum, chamotte and biotite have a safety limit of 5% sodium of the bed's weight at 8500C

  15. The Encantada Granite: registration of a peraluminous intrusion in the Rondonian Province - San Ignacio, in SW Amazonic Craton, Mato Grosso, Brazil

    Directory of Open Access Journals (Sweden)

    Brena Verginassi do Nascimento


    Full Text Available The Encantada Granite occurs on the extreme southwest of the state of Mato Grosso, SW of the Amazonian Craton, near the border of Brasil/Bolívia. It corresponds to an body oriented to NNW direction that intruded metasedimentary and metavolcanic rocks. It consists of leucogranites with monzo- to sienogranitic composition, marked by prominent schistosity. It is characterized by equigranular to porphyritic inequigranular texture, and composed of quartz, K-feldspar, plagioclase, muscovite and biotite with garnet, zircon, allanite and opaque minerals. Chlorite and epidote are the most common secondary minerals. The geochemical study allows the classification of the magmatism as having acid character, sub-alkaline, high-potassium-calc-alkaline to shoshonitic type. These rocks have alumina index saturation higher than 1, with normative corundum, and thus classified as peraluminous granite. Due to the reflection of the excess of aluminium, they have various aluminous phases, mainly muscovite, biotite and garnet; presents typical pattern of calc-alkaline rocks rich in potassium with enrichment of light ETRs over the heavy ones. The collected data allows to consider that the Encantada Granite rocks were generated from the partial melting of crustal rocks of pelitic composition.

  16. The role of phosphorus, magnesium and potassium availability in soil fungal exploration of mineral nutrient sources in Norway spruce forests. (United States)

    Rosenstock, Nicholas P; Berner, Christoffer; Smits, Mark M; Krám, Pavel; Wallander, Håkan


    We investigated fungal growth and community composition in buried meshbags, amended with apatite, biotite or hornblende, in Norway spruce (Picea abies) forests of varying nutrient status. Norway spruce needles and soil collected from forests overlying serpentinite had low levels of potassium and phosphorus, those from granite had low levels of magnesium, whereas those from amphibolite had comparably high levels of these nutrients. We assayed the fungal colonization of meshbags by measuring ergosterol content and fungal community with 454 sequencing of the internal transcribed spacer region. In addition, we measured fine root density. Fungal biomass was increased by apatite amendment across all plots and particularly on the K- and P-deficient serpentinite plots, whereas hornblende and biotite had no effect on fungal biomass on any plots. Fungal community (total fungal and ectomycorrhizal) composition was affected strongly by sampling location and soil depth, whereas mineral amendments had no effect on community composition. Fine root biomass was significantly correlated with fungal biomass. Ectomycorrhizal communities may respond to increased host-tree phosphorus demand by increased colonization of phosphorus-containing minerals, but this does not appear to translate to a shift in ectomycorrhizal community composition. This growth response to nutrient demand does not appear to exist for potassium or magnesium limitation. PMID:26996085

  17. Major magmatic events in Mt Meredith, Prince Charles Mountains: First evidence for early Palaeozoic syntectonic granites (United States)

    Gongurov, N.A.; Laiba, A.A.; Beliatsky, B.V.


    Precambrian rocks at Mt Meredith underwent granulite-facies metamorphism M1. Zircon isotope dating for two orthogneisses revealed the following age signatures: 1294±3 and 957±4Ma; 1105±5 and 887±2Ma. The oldest ages could reflect the time of orthogneiss protolith crystallization and the latest age determinations date Grenvillian metamorphism. The metamorphic rocks were intruded by two-mica and garnet-biotite granites. The granites and host rocks underwent amphibolite-facies metamorphism M2. Zircon isotope analysis of the two-mica granites showed age estimation within 550-510Ma and zircon dating of the garnet-biotite granites revealed the ages of 1107±5, 953±8, and 551±4Ma. As Pan-African age signatures were obtained from only the granite samples, it is possible to suggest that the granites were formed at the time of 510-550Ma and the zircons with greater age values were captured by granites from the host rocks.

  18. Early and Late Alkali Igneous Pulses and a High-3He Plume Origin for the Deccan Flood Basalts. (United States)

    Basu, A R; Renne, P R; Dasgupta, D K; Teichmann, F; Poreda, R J


    Several alkalic igneous complexes of nephelinite-carbonatite affinities occur in extensional zones around a region of high heat flow and positive gravity anomaly within the continental flood basalt (CFB) province of Deccan, India. Biotites from two of the complexes yield (40)Ar/(39)Ar dates of 68.53 +/- 0.16 and 68.57 +/- 0.08 million years. Biotite from a third complex, which intrudes the flood basalts, yields an (40)Ar/(39)Ar date of 64.96 +/- 0.1 1 million years. The complexes thus represent early and late magmatism with respect to the main pulse of CFB volcanism 65 million years ago. Rocks from the older complexes show a (3)He/(4)He ratio of 14.0 times the air ratio, an initial (87)Sr/(86)Sr ratio of 0.70483, and other geochemical characteristics similar to ocean island basalts; the later alkalic pulse shows isotopic evidence of crustal contamination. The data document 3.5 million years of incubation of a primitive, high-(3)He mantle plume before the rapid eruption of the Deccan CFB. PMID:17783739

  19. Occurrence of disseminated uraninite in Wheeler Basin, Grand County, Colorado

    International Nuclear Information System (INIS)

    Disseminated uraninite occurs in Wheeler Basin, Grand County, Colo., about 5 mi (8 km) southeast of Monarch Lake, in Precambrian metamorphic rocks consisting of migmatized gneiss and mixed gneiss and pegmatite. An intrusion of Precambrian Y Silver Plume Granite lies within 400 ft (122 m) of the occurrence. The disseminated uraninite is confined to parts of the host rock that are rich in biotite; highest grade found was 0.73 percent uranium. The disseminated uraninite occurs as cubes and grains, generally from 0.1 to 0.3 mm across. Unit cell edge of the uraninite, approximately 5.48 A, suggests its pegmatitic origin. The origin of the uraninite disseminations is attributed by us to remobilization and concentration of elements during metamorphism caused by the intrusion of Silver Plume Granite. Uranium and lead isotopic analyses by K. R. Ludwig of uraninite and monazite from biotite concentrations confirm an apparent age of 1,450 +- 20 m.y. for these minerals. This age is equivalent to that reported for the Silver Plume Granite. Although the Wheeler Basin occurrence is small in size, it has many similarities to the Roessing uranium deposit in South-West Africa

  20. Occurrence of disseminated uraninite in Wheeler Basin, Grand County, Colorado

    International Nuclear Information System (INIS)

    Disseminated uraninite occurs in Wheeler Basin. Grand County, Colo., about 5 mi (8 km) southeast of Monarch Lake, in Precambrian metamorphic rocks consisting of migmatized gneiss and pegmatite. An intrusion of Precambrian Y Silver Plume Granite lies within 400 ft (122 m) of the occurrence. The disseminated uraninite is confined to parts of the host rock that are rich in biotite; highest grade found was 0.73 percent uranium. The disseminated uraninite occurs as cubes and grains, generally from 0.1 to 0.3 mm across. Unit cell edge of the uraninite, approx. =5.48 A, suggests its pegmatitic origin. The origin of the uraninite disseminations is attributed by us to remobilization and concentration of elements during metamorphism caused by the intrusion of Silver Plume Granite. Uranium and lead isotopic analyses by K. R. Ludwig of uraninite and monazite from biotite concentrations confirm an apparent age of 1,450 +- 20 m.y. for these minerals. This age is equivalent to that reported for the Silver Plume Granite. Although the Wheeler Basin occurrence is small in size, it has many similarities to the Rossing uranium deposite in South-West Africa

  1. Formation of tectonic peperites from alkaline magmas intruded into wet sediments in the Beiya area, western Yunnan, China (United States)

    Xu, X.-W.; Cai, X.-P.; Zhong, J.-Y.; Song, B.-C.; Peters, S.G.


    Tertiary (3.78 Ma to 3.65 Ma) biotite-K-feldspar porphyritic bodies intrude Tertiary, poorly consolidated lacustrine sedimentary rocks in the Beiya mineral district in southwestern China. The intrusives are characterized by a microcrystalline and vitreous-cryptocrystalline groundmass, by replacement of some tabular K-feldspar phenocrysts with microcrystalline chlorite and calcite, and by Fe-rich rings surrounding biotite phenocrysts. Peculiar structures, such as contemporary contact faults and slickensides, ductile shear zones and flow folds, foliation and lineations, tension fractures, and banded and boudin peperites, are developed along the contact zones of the intrusives. These features are related to the forceful intrusion of the alkaline magmas into the wet Tertiary sediments. The partially consolidated magmas were deformed and flattened by continued forceful magma intrusion that produced boudinaged and banded peperites. These peperites characterized by containing oriented deformation fabrics are classified as tectonic peperites as a new type of peperite, and formation of these tectonic peperites was related to fracturing of magmas caused by forceful intrusion and shear deformation and to contemporary migration and injection of fluidized sediments along fractures that dismembered the porphyritic magma. Emplacement of the magma into the wet sediments in the Beiya area is interpreted to be related to a large pressure difference rather than to the buoyancy force. ?? 2007 Elsevier Ltd. All rights reserved.

  2. Sr isotope evolution during chemical weathering of granites -- impact of relative weathering rates of minerals

    Institute of Scientific and Technical Information of China (English)


    The Sr isotopic systematics in the weathering profiles of biotite granite and granite porphyry in southern Jiangxi Province were investigated. The results showed that during the chemical weathering of granites, remarked fractionation occurred between Rb and Sr. During the early stages of chemical weathering of granites, the released Sr/Si and Sr/Ca ratios are larger than those of the parent rocks, and the leaching rate of Sr is higher than those of Si, Ca, K, Rb, etc. Dynamic variations in relative weathering rates of the main Sr-contributing minerals led to fluctuation with time in 87Sr/86Sr ratios of inherent and released Sr in the weathering crust of granite. Successive weathering of biotite, plagioclase and K-feldspar made 87Sr/86Sr ratios in the weathering residues show such a fluctuation trend as to decrease first, increase, and then decrease again till they maintain stable. This work further indicates that when Sr isotopes are used to trace biogeochemical processes on both the catchment and global scales, one must seriously take account of the prefer-ential release of Sr from dissolving solid phase and the fluctuation of 87Sr/86Sr ratios caused by the variations of relative weathering rates of Sr-contributing minerals.

  3. The role of phosphorus, magnesium and potassium availability in soil fungal exploration of mineral nutrient sources in Norway spruce forests. (United States)

    Rosenstock, Nicholas P; Berner, Christoffer; Smits, Mark M; Krám, Pavel; Wallander, Håkan


    We investigated fungal growth and community composition in buried meshbags, amended with apatite, biotite or hornblende, in Norway spruce (Picea abies) forests of varying nutrient status. Norway spruce needles and soil collected from forests overlying serpentinite had low levels of potassium and phosphorus, those from granite had low levels of magnesium, whereas those from amphibolite had comparably high levels of these nutrients. We assayed the fungal colonization of meshbags by measuring ergosterol content and fungal community with 454 sequencing of the internal transcribed spacer region. In addition, we measured fine root density. Fungal biomass was increased by apatite amendment across all plots and particularly on the K- and P-deficient serpentinite plots, whereas hornblende and biotite had no effect on fungal biomass on any plots. Fungal community (total fungal and ectomycorrhizal) composition was affected strongly by sampling location and soil depth, whereas mineral amendments had no effect on community composition. Fine root biomass was significantly correlated with fungal biomass. Ectomycorrhizal communities may respond to increased host-tree phosphorus demand by increased colonization of phosphorus-containing minerals, but this does not appear to translate to a shift in ectomycorrhizal community composition. This growth response to nutrient demand does not appear to exist for potassium or magnesium limitation.

  4. Beneficiation of a low grade limestone sample

    Institute of Scientific and Technical Information of China (English)

    Rao Danda Srinivas; Vijayakumar Tadiparthi Venkata; Subba Rao Sripada; Bhaskar Raju Guntamadugu; Prabhakar Swarna


    Pilot scale column flotation studies were conducted on a low grade siliceous limestone ore.Silica content was reduced to less than 1% in the concentrate so that it became satisfactory for use in the paper or rubber industries.The limestone sample was crystalline and constituted primarily of calcite that contained quartz,feldspar,pyroxene,and biotite as gangue minerals.Quartz is the major silicate gangue whereas feldspar,pyroxene,and biotite exist in minor to trace quantities.Traces of pyrite were also observed within the sample.A reverse flotation process was adopted where the silicate gangue minerals were floated using two different commercial cationic collectors:Chem-750 F or Floatamine-D.The studies clearly suggest it is possible to produce a limestone concentrate assaying around 96-97% CaCO3 containing less than 1 % SiO2.The effect of feed flow rate,percent solids,froth depth,and wash water on the grade and recovery of the CaCO3 concentrate is discussed.

  5. The timing of tectonic transition from compression to extension in Dabieshan:Evidence from Mesozoic granites

    Institute of Scientific and Technical Information of China (English)

    MA Changqian; YANG Kunguang; MING Houli; LIN Guangchun


    With the methods of single grain zircon U-Pb and hornblende-biotite Ar-Ar dating, a U-Pb zircon age (135.4(2.7) Ma of Liujiawa high Sr/Y granite and 40Ar-39Ar plateau ages (139.0(1.0) Ma and (125.3(0.2) Ma of hornblende and biotite respectively of Fenliupu high Sr/Y granite in the Dabieshan high- and ultrahigh-pressure metamorphic belt are yielded. Following the emplacement of the high Sr/Y granites, extension-related mafic intrusions and late granitoids with negative Sr and Eu anomalies and isotopic ages of 105-130 Ma were emplaced. Geochemical comparison between the two types of granitoids shows that, from early to late, the alkalinities, the K2O contents and the Sr/Y ratios as well as FeO/(FeO+MgO) ratios of the rocks increase, while the abundance of Sr reduces, suggesting that as time goes on the depth of crustal melting decreases. Rheological stratification of the crust due to early Cretaceous partial melting of crustal rocks resulted in crustal extension and deep-buried rock exhumation. Therefore, the high Sr/Y granite that appeared at ~135 Ma is the product of the tectonic transition from early shortening to late overall extension.

  6. Petrography and geochronology (U/Pb-Sm/Nd) the Passagem Granite, Pensamiento Granitoid Complex, Paragua Terrane, SW Amazon Craton, Mato Grosso, Brazil

    International Nuclear Information System (INIS)

    The Passagem granite includes stocks, plugs and dikes located in the Ricardo Franco hill - Vila Bela da Santissima Trindade region - state of Mato Grosso, central Brazil. The Passagem Granite is included in the Paragua terrane - SW Amazonian Craton. It consists of isotropic monzogranite, sienogranite and more rarely granodiorites with leucocratic dark gray to white color. These rocks range from hypidomorphic inequigranular to xenomorphic texture, fine to medium grained. Biotite is the only primary mafic present as essential phase and characterize an expanded slightly acid sequence formed by a sub-alkaline magmatism of high-potassium calc-alkaline, slightly peraluminous composition from arc magmatic tectonic environment during a post-collisional period. Mechanism of fractional crystallization of plagioclase, biotite, titanite, apatite and zircon associated with simultaneous crustal assimilation are suggested for the evolution of these rocks. The results support the hypothesis of a post-collisional magmatism in the Paragua terrane at 1284 +- 20 Ma corresponding to the crystallization age of the Passagem granite. This paper propose that Passagem Granite represents as an extension in Brazilian terrane of the Pensamiento Granitoid Complex. (author)

  7. Evidences of a transamazonic cycle in Cabo Frio region, RJ, Brazil and its correlation with the craton of Angola, Africa

    International Nuclear Information System (INIS)

    The U-Pb dating in zircon based on air-abrasion method, whole rock Rb-Sr one, and K-Ar ones in biotite and amphibole of the samples collected from the Cabo Frio Region, Ribeira Orogenic Belt, have been carried out. The concordia diagram of the U-Pb dating indicates 2 different ages: 1981 ± 18 Ma for the upper intersect corresponding to the Transamazonic Cycle, and 488 ± 55 Ma for the lower one, Brazilian Cycle. The former is interpreted as age of zircon formation and the latter, as the time elapsed since epsodic lead loss. The whole rock Rb-Sr dating also shows Transamazonic age: 1799 ± 62 Ma, IR=0.706, and MSWD+0.570. The K-Ar age in amphibole is 571 ± 44 Ma and that in biotite is 474 ± 6 Ma. These data lead to the conclusion that the rocks of this region was formed in the Trasamazonic Cycle and remetamorphosed in the Brazilian Cycle. (author)

  8. 40Ar/39 Ar and paleomagnetic results from the Guapore shield: further implications for the nature of middle-late proterozoic mobile belts of Gondwana land

    International Nuclear Information System (INIS)

    Twenty sites in diverse rock units of the Serra dos Carajas region provide the first paleomagnetic poles from the Guapore shield of the Amazonian Craton. The most reliable results were obtained from the Pium Complex and the Carajas and Seringa granites. The ages of magnetization of these units are reasonably well constrained by isotopic data: 40 Ar/39 Ar data on a Pium hornblende indicate an Archean (>2.7 Ga) age for high grade metamorphism, but biotite and plagioclase from the same sample, plus biotite from another, all record a trans-Amazonian overprint. Thus the trans-Amazonian orogeny in this area produced temperatures between ca. 300 and 500 o C, apparently sufficient to re magnetize these rocks, and was followed by relatively rapid cooling uninterrupted by significant later regional metamorphism. Emplacement of the Carajas and Seringa granites, members of an extensive suite of anorogenic granitoids of the craton, is reasonably well constrained by previous studies at 1.70 to 1.83 Ga. A F and thermal demagnetization of specimens from three sites in the Pium complex and one in each of the granites reveals multicomponent behavior, but characteristic direction with moderately high coercivity and/or blocking temperature were isolated from all five sites. (author)

  9. First evidence for expressive neoproterozoic intraplated mafic rocks and magma mixing in post-collisional A-PA type granites, Southern Brazil: Geochemistry and U-Pb (zircon), Nd-Sr-18O(zircon) isotope investigations

    International Nuclear Information System (INIS)

    New and recent geological investigations around Pien-Tijucas suture zone, between Luis Alves and Curitiba Microplates (Basei et al.2000) led to mapping of Palermo, Agudos do Sul and Rio Negro A-PA type Granites with expressive expositions of alkaline felsic ans mafic rocks and, associated mafic and felsic hybrid rocks. The suture zone is formed by subduction arc-related Pien-Mandirituba deformed calc-alkaline I-type granite belt and serpentinized supra subduction zone (SSZ) obducted mantle rocks with intrusive Neoproterozoic (650-630 Ma) very high Cr and Ni tholeitic gabbros. The Pien-Mandirituba calc-alkaline I-type Granite Belt is constituted by three main granite suites. The older emplaced pre-collisional suite is constituted by deformed to highly deformed amphibole and biotite-rich, magmatic epidote-absent quartz-monzodiorites and granodiorites formed between 620 and 610 Ma. The second sincollisional granite suite is constituted by deformed and slightly deformed low content amphibole-biotite-magmatic epidote-bearing, quartz-monzodiorites, granodiorites and leucogranodiorites emplaced between 605 and 595 Ma. The third, also sincollisional, granite suite is deformed to highly deformed biotite ± amphibole monzogranites. The deformation age of the three non-cogenetic granite suites of this granite belt is between 605-595 Ma. The granite rocks of the Pien-Mandirituba Granite Belt are meta-aluminous to slightly peraluminous, high K calc-alkaline, generally with high Ba, high Sr and low Rb contents. Palermo, Agudos do Sul and Rio Negro Granites are components of the expressive Neoproterozoic volcanic and plutonic alkaline-peralkaline Serra do Mar Suite (Kaul 1997), emplaced in extensional post-collisional and anorogenic settings along the central portion and northern border of the Luis Alves Microplate and southern border of the Curitiba Microplate. Magma mixing evidence is rare ou absent in the other components of the Serra do Mar volcanic and plutonic suite. The

  10. Magmatic epidote, hornblende barometric estimates, and emplacement of the Conceicao das Creoulas pluton, Alto Pajeu Terrane, NE Brazil

    International Nuclear Information System (INIS)

    The Brasiliano-age magmatic epidote-bearing Conceicao das Creoulas batholith, in the Transversal Zone superterrane in northeastern Brazil, intruded migmatites and metagranitoids of the Riacho do Forno/Recanto Formations. This pluton is composed of porphyritic granodiorite and porphyritic monzogranite. Hornblendes in this pluton solidified between 6-7 Kbar in mafic enclaves and around 8 Kbar for porphyritic granodiorite as estimated by its Al contents. Temperatures for zircon saturation are in the 790-830 deg C range for the mafic enclaves and 800-850 deg C for the porphyritic granodiorite, whereas hornblende-plagioclase pairs yielded temperatures in the 670-690 de C range. In this pluton, epidote, undoubtedly of magmatic origin, with or without allanite cores, included in plagioclase, is rimmed by biotite or is partially resorpted by the magma. Sometimes, patches of hornblende and biotite are present inside epidote. Magmatic epidote compositions vary in the interval 20-25% mole of pistacite, and always exhibit Ti O2 < 0.20% by weight. This compositional range suggested crystallization along the NNO buffer. High initial ratio suggest a significant crustal component in the magma genesis. The magma probably was transported upward by diking and inflated outwards near or at its final site of emplacement, giving to the pluton a diapiric appearance. (author)

  11. Experiment on comprehensive utilization of low-grade phosphate ore%低品位含磷矿石的综合利用试验

    Institute of Scientific and Technical Information of China (English)

    孙晓华; 刘海宁


    The comprehensive recovery of apatite, diopside, biotite and iron ore in a low-grade phosphate ore was introduced.The experiments adopted low cost gravity-magnetic separation process flow and separated phosphate concentrate of 31% P2O5 from crude ore with 3.44% P2O5.At the same time, biotite of 31.06% and pyroxene of 51.14% were recovered, and iron concentrate with TFe 68.20% was attained.The technical and economic index was better.%介绍某低品位磷矿中磷灰石、透辉石、黑云母、铁矿石的综合回收情况,试验采用低成本的重选-磁选联合工艺流程,从P2O5品位为3.44%的原矿中选得P2O5为31%的磷精矿,同时回收了矿物量分别为31.06%和51.14%的黑云母和辉石产品,并得到含TFe为68.20%的铁精矿,取得较好的技术经济指标.

  12. Chronology and geochemistry of Mesozoic granitoids in the Bengbu area, central China: Constraints on the tectonic evolution of the eastern North China Craton (United States)

    Yang, De-Bin; Xu, Wen-Liang; Wang, Qing-Hai; Pei, Fu-Ping


    We performed zircon U-Pb dating and analyses of major and trace elements, and Sr-Nd-Pb isotopes for granitoids in the Bengbu area, central China, with the aim of constraining the magma sources and tectonic evolution of the eastern North China Craton (NCC). The analyzed zircons show typical fine-scale oscillatory zoning, indicating a magmatic origin. Zircon U-Pb dating reveals granitoids of two ages: Late Jurassic and Early Cretaceous ( 206Pb/ 238U ages of 160 Ma and 130-110 Ma, respectively). The Late Jurassic rocks (Jingshan intrusion) consist of biotite-syenogranite, whereas the Early Cretaceous rocks (Huaiguang, Xilushan, Nushan, and Caoshan intrusions) are granodiorite, syenogranite, and monzogranite. The Late Jurassic biotite-syenogranites and Early Cretaceous granitoids have the following common geochemical characteristics: SiO 2 = 70.35-74.56 wt.%, K 2O/Na 2O = 0.66-1.27 (mainly Nushan and Xilushan granitoids, suggests that the primary magmas were derived from partial melting of the Yangtze Craton (YC) basement. In contrast, the occurrence of Paleoproterozoic and Paleoarchean inherited zircons within the Huaiguang granitoids indicates that their primary magmas mainly originated from partial melting of the NCC basement. The occurrence of YC basement within the lower continental crust of the eastern NCC indicates that the YC was subducted to the northwest beneath the NCC, along the Tan-Lu fault zone, during the early Mesozoic.

  13. SHRIMP zircon U-Pb geochronology of early Mesozoic felsic igneous rocks from the southern Lancangjiang and its tectonic implications

    Institute of Scientific and Technical Information of China (English)

    PENG Touping; WANG Yuejun; FAN Weiming; LIU Dunyi; SHI Yuruo; MIAO Laicheng


    The SHRIMP zircon U-Pb geochronology of three typical samples, including two monzonitic granites from the Lincang batholith and a rhyolite from the Manghuai Formation are presented in the southern Lancangjiang, western Yunnan Province. The analyses of zircons for the biotite monzonitic granites from the northern (02DX-137) and southern (20JH-10) Lincang batholith show the single and tight clusters on the concordia, and yield the weighted mean 206pb/238U ages of 229.4 ± 3.0 Ma and 230.4 ± 3.6 Ma, respectively, representing the crystallized ages of these granites. The zircons for the rhyolitic sample (02DX-95) from the Manghuai Formation give a weighted mean 206Pb/238U age of 231.0 ± 5.0 Ma. These data suggest that the igneous rocks from the Lincang granitic batholith and Manghuai Formation have a similar crystallized age. In combination with other data, it is inferred that both were generated at a narrow age span (~230 Ma) and were originated from the postcollisional tectonic regime. An early Proterozoic 206Pb/238U apparent age of 1977±44 Ma is additionally obtained from one zircon from the biotite monzonitic granite (southern Lincang batholith), indicative of development of the early Proterozoic Yangtze basement in the region. These precisely geochronological data provide important constraints on better understanding the Paleozoic tectonic evolution of the Tethys, western Yunnan Province.

  14. Sand and clay mineralogy of sal forest soils of the Doon Siwalik Himalayas

    Indian Academy of Sciences (India)

    Mukesh; R K Manhas; A K Tripathi; A K Raina; M K Gupta; S K Kamboj


    The peteromineralogical characterization of the soil was carried out for the 12 soil profiles exposed in the Shorea robusta dominated forests of the Siwalik forest division, Dehradun. The quartz was observed as the dominating light mineral fraction (64–80%) in all the profiles studied. Biotite, hornblende, zircon, tourmaline, rutile and opaques comprising of iron minerals constituted the heavy mineral fraction (20%). The mineralogy of both the sand and clay fractions revealed a mixed mineralogy. The clay minerals in the order of their dominance were vermiculite, illite, kaolinite and mixed layer minerals. The presence of vermiculite and illite in appreciable quantities indicates that these were synthesized from the K-rich soil solution, as orthoclase and micas were present in significant quantities in the sand minerals. The mineral suites identified in the study shows that the geological, climatological and topographical factors of the region collectively played a dominant role in their formation and transformation. After critical appraisal of the results, it may be deduced that the mineralogical composition, physicochemical properties and total elemental analysis of the soils do not show any deficiency of the bases and other plant nutrients in general. The inherent fertility of the soil is good as indicated by the sand and clay mineralogy of the soil and the biotite and feldspar together with the mica is an important source of nutrients for the vegetation in the soils of the Doon valley.

  15. Garnet-sillimanite bearing gneisses from Darjeeling, eastern Himalaya: Textural relationship and P–T conditions

    Indian Academy of Sciences (India)

    Divya Prakash; Suparna Tewari


    The area around Darjeeling consists of medium grade metamorphic rocks and provides a classic example of inverted Himalayan metamorphism. The area under investigation shows upper amphibolite facies metamorphism (sillimanite-muscovite subfacies), rocks are intimately associated with the migmatites and granites. The presence of quartzite, calc-silicate rocks, graphitic schist and abundance of aluminous minerals like kyanite or sillimanite in these rocks indicate their metasedimentary character. Granetsillimanite bearing gneisses occupy most of the area of Darjeeling but not persistent throughout. Textural relationship suggests sequential growth of progressively higher-grade metamorphic minerals during D1 and D2 deformation. The relative XMg in the minerals varies in the order: biotite>staurolite>garnet, and the XMn decreases in the order: garnet>staurolite>biotite. The P–T evolution of these garnetsillimanite gneiss has been constrained through the use of conventional geothermobarometry, internally consistent TWEEQU programme and Perple_X software in the KFMASH model system, the combination of these three approaches demonstrates that the Darjeeling gneisses experienced peak pressure and temperature at 7.0 ± 0.3 kbar and 700 ± 30°C. The observation in this study has important bearing on the inverted metamorphism in the Himalayan metamorphic belt.

  16. Insights into the P–T evolution path of TsoMorari eclogites of the north-western Himalayas: Constraints on the geodynamic evolution of the region

    Indian Academy of Sciences (India)

    Preeti Singh; Ashima Saikia; Naresh Chandra Pant; Pramod Kumar Verma


    The present study is on the Ultra High Pressure Metamorphic rocks of the Tso Morari Crystalline Complex of the northwestern Himalayas. Five different mineral associations representative of five stages of P–T (pressure–temperature) evolution of these rocks have been established based on metamorphic textures and mineral chemistry. The pre-UHP metamorphic association 1 of Na-Ca-amphibole + epidote ± paragonite ± rutile ± magnetite with T–P of ∼500° C and 10 kbar. This is followed by UHP metamorphic regime marked by association 2 and association 3. Association 2 (Fe< Mg< Ca-garnet + omphacite + coesite + phengite + rutile ± ilmenite) marks the peak metamorphic conditions of atleast 33 kbar and ∼750° C. Association 3 (Fe< Mg< Ca-garnet + Na-Ca amphibole + phengite ± paragonite ± calcite ± ilmenite ± titanite) yields a P–T condition of ∼28 kbar and 700°C. The post-UHP metamorphic regime is defined by associations 4 and 5. Association 4 (Fe< Ca< Mg-garnet + Ca-amphibole + plagioclase (An05) + biotite + epidote ± phengite yields a P–T estimate of ∼14 kbar and 800°C) and association 5 (Chlorite + plagioclase (An0.5) + quartz + phengite + Ca- amphibole ± epidote ± biotite ± rutile ± titanite ± ilmenite) yields a P–T value of ∼7 kbar and 350°C.

  17. Brittleness and Packing Density Effects on Blast-hole Cuttings Yield of Selected Rocks

    Directory of Open Access Journals (Sweden)

    B. Adebayo


    Full Text Available This paper evaluates brittleness and packing density to analysis their effects on blast-hole cutting yield for three selected rocks in Nigeria. Brittleness test (S20 was carried out in accordance with Norwegian Soil and Rock Engineering and the Brittleness Index (BI for the selected rocks were estimated. The packing density determined from the photomicrograph of the rock samples. The grain size of 45 blast-holes drill cuttings collected from three selected while drilling of these rocks were determined using standard method of America Society for Testing and Materials (ASTM D 2487. The brittleness values are 50%, 44% and 42% for micro granite, porphyritic granite and medium biotite granite respectively. The result of BI varied from 10.32 – 11.59 and they are rated as moderately brittle rocks. The values of packing density varied from 92.20 – 94.55%, 91.00 -92.96% and 92.92 – 94.96% for all the rocks. The maximum weights of blast-hole particle size retained at 75 µm are 106.00g, 103.28 g and 99.76 g for medium biotite granite, micro granite and porhyritic granite respectively. Packing density values have correlation to some extent with (S20 values hence, this influence the yield of blast-hole cuttings as drilling progresses. The minimum weight of blast-hole cuttings particle size retained at 150 µm agrees with brittleness index classification for micro granite.

  18. 3D modelling and sheath folding at the Falun pyritic Zn-Pb-Cu-(Au-Ag) sulphide deposit and implications for exploration in a 1.9 Ga ore district, Fennoscandian Shield, Sweden (United States)

    Kampmann, Tobias C.; Stephens, Michael B.; Weihed, Pär


    Altered and mineralized rocks at the Falun pyritic Zn-Pb-Cu-(Au-Ag) sulphide deposit, situated in the Palaeoproterozoic Bergslagen ore district in the south-western part of the Fennoscandian Shield, have been metamorphosed at low-pressure, amphibolite-facies conditions and affected by ductile deformation. Using combined surface mapping of lithology and structure, drill core logging and microstructural work, the polyphase (D1 and D2) ductile deformation is demonstrated and a 3D model for the deposit created. Mineral associations include quartz, biotite, cordierite, anthophyllite, and minor almandine, andalusite and chlorite in silicate-rich altered rock, calcite or dolomite in marble and tremolite-actinolite or diopside-hedenbergite in skarn. The silicate minerals show varying growth patterns during the different phases of the tectonothermal evolution, with considerable static grain growth occurring between D1 and D2, and even after D2. F2 sheath folding along axes that plunge steeply to the SSE, parallel to a mineral stretching lineation and the dip direction of the S2 foliation, is suggested as a key deformation mechanism forming steeply plunging, cone- to rod-shaped mineralized bodies. This contrasts with a previous structural model invoking fold interference. A major shear zone with talc-chlorite-(quartz-biotite) mineral association separates the northern and southern structural domains at the deposit and bounds the polymetallic massive sulphides to the north.

  19. Science Letters: Discovery of ultrahigh-T spinel-garnet granulite with pure CO2 fluid inclusions from the Altay orogenic belt, NW China

    Institute of Scientific and Technical Information of China (English)

    厉子龙; 陈汉林; SANTOSHM.; 杨树锋


    We first report discovery of the spinel-garnet-orthopyroxene granulite with pure CO2 fluid inclusions from the Fuyun region of the late Paleozoic Altay orogenic belt in Central Asia, NW China. The rock is characterized by an assemblage of garnet, orthopyroxene, spinel, cordierite, biotite, plagioclase and quartz. Symplectites of orthopyroxene and spinel, and orthopyroxene and cordierite indicate decompression under UHT conditions. Mineral chemistry shows that the orthopyroxenes have high XMg and Al2O3 contents (up to 9.23 wt%). Biotites are enriched in TiO2 and XMg and are stable under granulite facies conditions. The garnet and quartz from the rock carry monophase fluid inclusions which show peak melting temperatures of around -56.7℃, indicating a pure CO2 species being presented during the ultrahigh-T metamorphism in the Altay orogenic belt. The inclusions homogenize into a liquid phase at temperatures around 15.3-23.8℃ translating into CO2 densities of the order of 0.86-0.88g/cm3. Based on preliminary mineral paragenesis, reaction textures and petrogenetic grid considerations, we infer that the rock was subjected to UHT conditions. The CO2-rich fluids were trapped during exhumation along a clockwise P-T path following isothermal decompression under UHT conditions.

  20. 某钽铌钨铍矿化花岗岩岩石化学特征

    Institute of Scientific and Technical Information of China (English)



    During the magmatie evolution from biotite granite through two-mlca granite to mineralized muscovite granite it has been noted that Na+, Mm2+, Si4+ increase while K+, Ca2+, Mg2+, Fe2+, Fe3+, Ti4+, and P5+ decrease systematically in this district. Oreforming metals occur in higher abundance in biotite granite which is thought to be the representative of primary magma, and have been enriched rapidly with magmatic evolution R+/R2+ Na+/K+, Rb/K, Mn/Fe and other petrochemical parameters increase whereas Ti4+/Si4+ decreases in a sympathetic way with the enrichment of niobium and tantalum, providing good indicators of the degree of differentiation and metasematism of the magma ,Within the mineralized granite, there is a same trend of variation upward whioh is found closely related to the enrichment of tantalum. Fluorine is strongly concentrated in wall rocks above blind mineralized granite, and the eontente of tantalum and niobium in wolframite from quartz veins genetically related to the granite increase towards buried mineralization. The latter two phenomena are suggested by the author as clues to buried ore bodies.

  1. Mineral chemistry and geochemistry of the Late Neoproterozoic Gabal Abu Diab granitoids, Central Eastern Dessert, Egypt: Implications for the origin of rare metal post-orogenic A-type granites (United States)

    Sami, Mabrouk; Ntaflos, Theodoros; Farahat, Esam S.; Ahmed, Awaad F.; Mohamed, Haroun A.


    The Neoproterozoic Gabal Abu Diab pluton is a part of the Arabian Nubian shield (ANS) continental crust and located in the Central Eastern Desert (CED) of Egypt. It constitutes multiphase granitic pluton intruded into granodiorite and metagabbro-diorite rocks with sharp and nonreactive contacts. Based on field observations, colors, structural variations and petrographic investigations, this granitic outcrop consists of an inner core of two-mica granite (TMG) followed outward by garnet bearing muscovite granite (GBMG) and albite granite (AG). Petrographical study indicated that medium to coarse-grained TMG is dominated by K-feldspar (Or88-98), quartz, plagioclase (albite, An0-7), muscovite and biotite with hypidiomorphic texture. With exception the appearance of garnet and the disappearance of biotite the GBMG resembles the TGM, while AG is leucocratic without any mafic mineral. The main accessories are zircon, Nb and Ta-bearing rutile, columbite, ilmenorutile, ilmenite, magnetite and apatite. This mineralogical similarity and the existence of columbite group minerals (CGM) in all granitoids, indicates a cogenetic relationship. Microprobe analyses reveal that, besides the CGM, rutile and ilmenite are the main repository phases for Nb-Ta-Ti. Columbite-(Mn) exists as individual subhedral crystals (up to 100μm in size) or intimate intergrowth with Nb-bearing rutile and/or ilmenite. The CGM are represented mostly by columbite-(Mn) with Ta/(Ta+Nb) and Mn/(Mn+Fe) ratio ranging from 0.02-0.08 and 0.4-0.9, respectively suggesting extreme degree of magmatic fractionation. Rutile contains significant amounts of Ta (up to 4 wt.% Ta2O5) and Nb (up to 22 wt.% Nb2O5). Biotites are phlogopite-annite in composition (Ann47-60Phlog40-53,on average) and are enriched with AlIV that characterize peraluminous granites. Garnets contain 60-69 mol.% spessartine and 28-36 mol.% almandine where, the ratio of spessartine and almandine together exceeds 95 mole percent, similar to garnet occur

  2. A complex magma reservoir system for a large volume intra- to extra-caldera ignimbrite: Mineralogical and chemical architecture of the VEI8, Permian Ora ignimbrite (Italy) (United States)

    Willcock, M. A. W.; Bargossi, G. M.; Weinberg, R. F.; Gasparotto, G.; Cas, R. A. F.; Giordano, G.; Marocchi, M.


    Intra-caldera settings record a wealth of information on caldera-forming processes, yet field study is rarely possible due to lack of access and exposure. The Permian Ora Formation, Italy, preserves > 1000 m of vertical section through its intra-caldera succession. This provides an excellent opportunity to detail its mineralogical and geochemical architecture and gain understanding of the eruption evolution and insight into the pre-eruptive magma system. Detailed juvenile clast phenocryst and matrix crystal fragment point count and image analysis data, coupled with bulk-rock chemistry and single mineral compositional data, show that the Ora ignimbrite succession is rhyolitic (72.5-77.7% SiO2), crystal-rich (~ 25-57%; average 43%) and has a constant main mineral population (volcanic quartz + sanidine + plagioclase + biotite). Although a seemingly homogeneous ignimbrite succession, important subtle but detectable lateral and vertical variations in modal mineralogy and bulk-rock major and trace elements are identified here. The Ora Formation is comprised of multiple lithofacies, dominated by four densely welded ignimbrite lithofacies. They are crystal-rich, typically lithic-poor (cake' stratigraphy. The intra-caldera succession is divided into two depo-centres: Southern and Northern, with proximal extra-caldera deposits preserved to the south and north of the system. The Southern and Northern intra-caldera ignimbrite successions are discriminated by variations in total biotite crystal abundance. Detailed mineralogical and chemical data records decreases across the caldera system from south to north in biotite phenocrysts in the groundmass of juvenile clasts (average 12-2%), matrix biotite (average 7.5-2%) and plagioclase crystal fragments (average 18-6%), and total crystal fragment abundance in the matrix (average 47-37%); a biotite compositional change to iron-rich (0.57-0.78 Fe); and bulk-rock element decreases in Fe2O3, MgO, P2O5, Ce, Hf, V, La and Zr, and

  3. Origin of peak and retrograde assemblages during Grenvillian orogeny from garnet-staurolite bearing mica schist of Bhilwara Supergroup, NW India: constraints from pseudosection modelling (United States)

    Prakash, Abhishek; Saha, Lopamudra; Sarkar, Saheli


    Fractionation of components due to formation of garnet porphyroblasts during prograde metamorphism, have been constrained from pseudosection analyses. Such fractionation process leads to changes in the effective bulk composition within the rock, which can be modelled with well-preserved growth zonation patterns in garnet porphyroblasts. On the contrary, textures and mineralogy in metamorphic rocks can be far more complex with different textural domains within a single rock preserving assemblages formed along different segments of the P-T paths or during different metamorphic events. Examples of such textures include pseudomorphs, reaction rims or coronae, symplectites formed by breakdown of both cores and rims of porphyroblasts. Apart from pressure and temperature, availability of fluids during metamorphic reactions plays important roles in defining mineral assemblages and textures. In this study we have constrained formation of garnet porphyroblasts and paragonite-albite-sillimanite-quartz-staurolite bearing domains within the mica schist from the Rajpura-Dariba sequence of the Bhilwara Supergroup in NW India. The mica schist is inter-layered with calc-silicates and quartzite and together the units form a NE-SW trending Grenvillian orogenic belt in southern part of Bhilwara Supergroup sequence. Within the mica schist, three distinct textural domains have been observed: (i) muscovite-biotite-quartz-feldspar bearing matrix foliation, (ii) garnet porphyroblasts within the matrix foliation, (iii) staurolite-paragonite-albite-staurolite-sillimanite-quartz bearing domains. Paragonite, albite and sillimanite occur exclusively in the pseudomorph domains. Garnet porphyroblasts show variation in compositions from cores (Spessartine0.14 Grossular0.10 Pyrope0.12 Almandine0.72) to rims (Spessartine0.09Grossular0.15Pyrope0.12Almandine0.75). The average XMg contents of staurolite and matrix biotite are 0.21 and 0.57 respectively. Pseudosections have been constructed from the

  4. 浙西南八都群泥质麻粒岩的变质演化与pT轨迹%The metamorphic evolution and pT path of pelitic granulite from the Badu Group in southwestern Zhejiang Province

    Institute of Scientific and Technical Information of China (English)

    赵磊; 周喜文


    浙西南古元古界八都群是目前华夏地块最古老的变质基底,以往研究认为其变质程度仅达角闪岩相.近来在对遂昌地区八都群富铝片麻岩的研究过程中,发现了具有“石榴石+夕线石+正/反条纹长石+黑云母”特征组合的泥质麻粒岩,表明该地体曾经历麻粒岩相变质改造.通过岩相学与矿物化学分析,确定该岩石经历了3个阶段的演化过程,即:早期进变质阶段(M1),形成“石榴石+黑云母+白云母+夕线石+斜长石+石英”的矿物组合;变质峰期阶段(M2-3),形成“石榴石+夕线石+三元长石+黑云母+石英”的矿物组合;峰期后降压冷却阶段(M4),形成“黑云母+白云母+新生斜长石+石英”的矿物组合.岩石中石榴石普遍发育与降温过程有关的扩散成分环带和与降压过程有关的斜长石后生合晶.通过石榴石-黑云母温度计和GASP压力计估算变质峰期的温压条件为800~850℃、0.6~0.7 GPa,峰期后退变质阶段的温压条件为560~590℃、0.25~0.33 GPa,具有顺时针样式的PT演化轨迹,反映一种陆壳碰撞增厚、后又拉伸减薄的动力学过程.%The Paleoproterozoic Badu Group in southwestern Zhejiang Province is the oldest metamorphic basement in the Cathaysia block, and its metamorphic grade was previously considered to be only of amphibolite facies. Recently, pelitic granulite with the typical mineral assemblage of garnet + sillimanite + perthite + antiperthite + biotite was discovered in the Al-rich gneiss of Suichang area. According to petrographic observation, micro-mineral composition and calculating results from garnet-biotite thermometer and GASP barometer, three stages of metamorphism were recognized in the pelitic granulite. The early prograde metamorphic stage (M1) was detected on the basis of inclusions of biotite, muscovite and sillimanite in garnet. The peak metamorphic stage (M2.3) is characterized by the presence of garnet, biotite

  5. 贺兰山北段贺兰山岩群富铝片麻岩碎屑锆石LA-ICP-MS U-Pb定年及区域对比%LA-ICP-MS U-Pb detrital zircon geochronology of alumina-rich gneiss of the Helanshan complex-group in the northern segment of Helanshan Mountains and regional comparison

    Institute of Scientific and Technical Information of China (English)

    校培喜; 由伟丰; 谢从瑞; 李平; 白生明


    贺兰山北段贺兰山岩群中发育一套富铝片麻岩,AlO含量较高,总体与粘土质岩石化学成分相似,显示孔兹岩系的特征,变质矿物组合主要为石榴子石、堇青石、硅线石、十字石、紫苏辉石等,变质级别迭角闪岩相一麻粒岩相.从宗别立岩组含石榴矽线黑云二长片麻岩中选取100粒各种类型的锆石进行了LA-ICP-MS U-Pb同位素测年.获得47个测年数据,锆石年龄多数介于1.80~2.15Ga之间,峰值为2.00~2.05Ga.碎屑锆石年龄频谱图与鄂尔多斯地块北缘的集宁岩群和乌拉山岩群十分相似,总体与吕粱构造运动的时限一致,为华北克拉通成熟陆壳演化阶段的产物.证明孔兹岩系形成于古元古代,之后长期处于稳定状态,很少受到构造热事件的干扰.%The Helanshan Group exposed in the northern segment of Helangshan mountains is high-grade metamorphosed rocks which are mainly composed of grey-biotite-sillimanite-cordierite-monzonitic-gneiss, sillimanite-garnet-biotite-plagioclase-gneiss,garnet-biotite-plagioclase-leptynite, sillimanite-garnet-monzonitic-leptite, sillimanite-biotite- plagioclase-leptynite, graphite-marble and hypersthene-plagioclase-gneiss. The gneiss of Helanshan Group belongs to khondalite series characterized by rich in Al2O3 and similar geochemistry to clay rocks, and its protolith rocks assemblages are alumina rich pelite and siltstone, which indicate that the gneiss is a suite of stable continental margin terrigenous clastic rock, the metamorphosed mineral assemblages of gneiss consist of garnet,cordierite, sillimanite, staurolite, hypersthene and so on. Forty-seven U-Pb data were obtained by LA-ICP-MS method for the detrital zircons of four garnet- sillimanite-biotite-monzonitic-gneiss from the Helanshan Group in this study. The majority ages of the grains from these four samples are clustered in the 1.80-2.15Ga, with characteristic age probability peaks at 2.00-2.05Ga. The detrital zircons ages

  6. C. 1.5 Ga metamorphism of the Lazdijai 13 volcano-sedimentary sequence in southern Lithuania: its origin and implications (United States)

    Siliauskas, Laurynas; Skridlaite, Grazina


    The concealed crystalline crust in the SW East European Craton consists of several domains finally accreted at 1.8-1.70 Ga (Bogdanova et al., 2014). However, some geological structures in the Lithuanian basement are still poorly reconstructed because of insufficient isotopic and geochemical data. Such is the Lazdijai 13 (Lz13) volcano-sedimentary sequence in southern Lithuania, preliminary dated at 1.83-1.80 Ga (U-Pb zircon age). The newly obtained monazite analyses (EPMA dating, Cameca SX-100 electron microprobe, Warsaw University) allowed dating of metamorphism of the Lz13 rocks. The 300 m thick Lz13 sequence is composed of deformed and metamorphosed volcanics, volcano-clastics and sediments, cross-cut by pegmatite and quartz veins. The upper part of the drilling (at c. 493 m) consists of exhalitic quartz chlorite cherts and metaandesitic rocks. They are underlain by medium-fine grained shists composed of quartz, biotite, garnet, cordierite, staurolite, minor plagioclase, K-feldspar, magnetite and monazite (felsic volcanics, 540 m) that were metamorphosed at 580° C and 6 kbar (garnet, biotite, cordierite geothermobarometry). Monazites are small, interstitial, fragmented and dissolved, some found as inclusions in magnetite. They yielded three ages: 1685±25 Ma, 1525±11Ma, and 1448±24 Ma. Another layer of a fine grained shist (quartz, biotite, garnet, K-feldspar, muscovite, 599 m) of sedimentary origin contains zircons and monazites arranged in thin, undulating lines. The monazites are small, interstitial, partly dissolved, in places overgrown by alanite aggregates. They yielded 1671±29 Ma and 1523±17 Ma ages. Below, at 757 m, a strongly deformed shist composed of quartz, biotite, K-feldspar, plagioclase, garnet and cordierite (former sediment) was metamorphosed at 498° C and 5.4 kbar (garnet, biotite, plagioclase and muscovite geothermobarometry). It contains very small, strongly dissolved and locally overgrown by alanite, monazite grains. Three of them were

  7. Low-rhenium molybdenite by metamorphism in northern Sweden: Recognition, genesis, and global implications (United States)

    Stein, Holly J.


    episodic melting of Archean-Paleoproterozoic supracrustal gneisses related to the Svecofennian orogeny. Petrographic traverses across the boundary between widespread, foliation-parallel units of aplitic to pegmatitic pink granite and hosting biotite gneiss directly capture the process of ore formation. Dehydration breakdown of zircon-rich biotite aligned with the foliation in the gneiss is accompanied by formation of new pristine, post-deformational biotite plus sulfides, oxides, hydrothermal zircon and fluorite, all associated with microcline-dominant leucosomes. This process has profound implication for the traditional leucogranite, intrusion-related genesis attributed to the broad classification of Mo-W-Sn-base and precious metal mineralization (e.g., South Mountain Batholith, Nova Scotia; Okiep, Namaqualand, South Africa; Mactung, Yukon; Pogo-Liese, Tintina, Alaska; Carajás and Goiás-Rio Tocantins, Brazil; New England Batholith, NSW, Australia; Bergslagen, Sweden; Nevoria, Western Australia; Alpeinerscharte, Austria; Erzgebirge, Germany; Sardinia-Corsica Batholith). In addition to biotite, metallogenic contributions (e.g., Mo, W, Sn, U, Bi, Cu, Pb, Zn, Fe, Ni, Co, Au, Ag, Te, As, Sb, REE) in various combinations may also be controlled by breakdown of amphibole. In effect, the trace element composition of dehydrating or recrystallizing components in a gneissic rock essentially defines the local and district metallogenic suite. In the absence of focusing structures (e.g., shear zones, sheeted vein development), this process will generally form small and disconnected subeconomic deposits with erratic and unpredictable grades. Low Re content in associated molybdenite is a key indicator for a subeconomic origin by local melting of biotite gneiss (Mo-W) or muscovite schist (Sn-W).

  8. Growth and Evolution of the Kerala Khondalite Belt, Southern India: Mineral and Whole rock Chemical Evidence for Intracrustal Melting and Magmatic Petrogenesis (United States)

    Gundlupet Rangasetty, R.; Chettootty, S.


    The Kerala Khondalite Belt (KKB) constitutes an important lower crustal segment in the southern Indian granulite terrain. Dominant rock types, except sillimanite bearing gneisses, are classified as sodic and potassic granitoids and a general supracrustal origin is ascribed to these rocks. We present here new results from our studies on mineral and whole rock major- and trace-element and REE systematic of major litho units of the belt. We address the petrogenesis, physical conditions during crystallization and tectonic setting of KKB rocks. Granitoids (gneiss and variants of charnockites) makeup more than 70% of exposed rock types in KKB. They are classified as sodic and potassic groups based on K2O/Na2O ratios. Mineral chemical analysis of granitoids, especially biotites from different groups document igneous parentage and as potential indicator of nature of the magma. Biotites from sodic group are Mg2+-rich (XMg:0.47-0.63), denote calc-alkaline host in contrast to those from potassic groups, which are Fe2+-types with much lower XMg (0.37-0.44) and suggest an alkaline host. Biotites in potassic group are poorer in A12O3 than sodic, indicating evolved nature of the magmatic protolith. Decrease in ΣAl with increasing Fe/(Fe+Mg) values of biotites indicate progressive oxidising condition during magma evolution. Compositional variation of biotite allow us to speculate that the host magmas of sodic charnockites as calc-alkaline, arc-type with features typical of Archaean TTGs and potassic groups as partial melts of meta-igneous lower crust with little mantle contribution. The sodic group has geochemical affinity to Archaean tonalities with low-K, calc-alkaline, metaluminous to peraluminous chemistry. Compositionally contrasting K-rich rocks are essentially of granitic composition. Most oxides in both the groups, with exceptions of K2O and Na2O, show negative correlation with SiO2. The sodic group is enriched in Sr and depleted in Rb and Th. They exhibit geochemical

  9. El plutón de Serrezuela: Evento magmático del Carbonífero en el sector norte de la sierra de Pocho, Córdoba, República Argentina The Serrezuela Pluton: Carboniferous magmatic event in the northerm sector of the Sierra de Pocho, Córdoba, Argentina

    Directory of Open Access Journals (Sweden)

    GM Gómez


    . El plutón de Serrezuela de edad carbonífera (321+7,4 Ma y 303+2MA, K/Ar, representa uno de los pulsos magmáticos graníticos mas jóvenes en este sector de las Sierras Pampeanas Orientales. Este cuerpo posiblemente registre el final del ciclo magmático generador de los vecinos batolito de Achala y plutón de La Playa bajo un régimen colisional.The Serrezuela granite is located at the Sierra de Serrezuela in the northern Sierra de Pocho, northwest Córdoba. It is a 16 km2 body, divided into two sectors by metamorphic outcrops. Structurally it is confined by several fractures related to major N-S regional lineaments. The Serrezuela pluton is composed of two main facies: biotite + muscovite monzogranite (BMM, and biotite tourmaline monzogranite (BTM. Both facies are calcalkaline peraluminous, with minor occurrences of a metaluminous biotite aplite. The BTM overlies the BMM facies with sharp contact, in a layer-like occurrence. The Serrezuela granitic stock is characterized by the presence of miarolitic cavities and widespread tourmalinization. A late quartz vein of considerable dimensions intrudes at the pluton boundary. Major element geochemistry shows some dispersion, whereas trace elements show a trend from biotite + muscovite monzogranite toward biotite tourmaline monzogranite. All rocks are strongly differentiated with the biotite + muscovite monzogranite being the least evolved and the most areally extended unit. A liquid fractionation mechanism is proposed for the differentiation and emplacement of the biotite tourmaline monzogranite. Changes in the foliation direction of the country rock, the presence of banded plagioclase and miarolitic cavities, suggests that the Serrezuela pluton had a forced emplacement into the country rocks at shallow crustal depth, along preexisting lineaments. Serrezuela pluton, is a Carboniferous K/Ar age granite (321± 7.4 Ma and 303± 2 Ma. It represents one of the youngest granitic magma pulses of this sector of the Eastern

  10. Crystallization conditions of porphyritic high-K calc-alkaline granitoids in the extreme northeastern Borborema Province, NE Brazil, and geodynamic implications (United States)

    Campos, Benedita Cleide Souza; Vilalva, Frederico Castro Jobim; Nascimento, Marcos Antônio Leite do; Galindo, Antônio Carlos


    An integrated textural and chemical study on amphibole, biotite, plagioclase, titanite, epidote, and magnetite was conducted in order to estimate crystallization conditions, along with possible geodynamic implications, for six Ediacaran porphyritic high-K calc-alkaline granite plutons (Monte das Gameleiras, Barcelona, Acari, Caraúbas, Tourão, and Catolé do Rocha) intrusive into Archean to Paleoproterozoic rocks of the São José do Campestre (SJCD) and Rio Piranhas-Seridó (RPSD) domains, northern Borborema Province. The studied rocks include mainly porphyritic leucocratic monzogranites, as well as quartz-monzonites and granodiorites. Textures are marked by K-feldspar megacrysts (5-15 cm long) in a fine-to medium-grained matrix composed of quartz, plagioclase, amphibole, biotite, as well as titanite, epidote, Fesbnd Ti oxides, allanite, apatite, and zircon as accessory minerals. Amphibole, biotite and titanite share similar compositional variations defined by increasing Al and Fe, and decreasing Mg contents from the plutons emplaced into the SJCP (Monte das Gameleiras and Barcelona) towards those in the RPSD (Acari, Caraúbas, Tourão, and Catolé do Rocha). Estimated intensive crystallization parameters reveal a weak westward range of increasing depth of emplacement, pressure and temperature in the study area. The SJCD plutons (to the east) crystallized at shallower crustal depths (14-21 km), under slightly lower pressure (3.8-5.5 kbar) and temperature (701-718 °C) intervals, and high to moderate oxygen fugacity conditions (+0.8 < ΔFQM < +2.0). On the other hand, the RPSD plutons (to the west) were emplaced at slightly deeper depths (18-23 km), under higher, yet variable pressures (4.8-6.2 kbar), temperatures (723-776 °C), and moderate to low oxygen fugacity conditions (-1.0 < ΔFQM < +1.8). These results reinforce the contrasts between the tectono-strutuctural domains of São José do Campestre and Rio Piranhas-Seridó in the northern Borborema Province.

  11. Petrology and radiogeology of the Stripa pluton

    Energy Technology Data Exchange (ETDEWEB)

    Wollenberg, Harold; Flexser, Steve; Andersson, Lennart


    To better define the character of the rock encompassing the thermomechanical and hydrological experiments at the Stripa mine in central Sweden, and to help determine the size of the Stripa pluton, detailed studies were conducted of the petrology and radiogeology of the quartz monzonite and adjacent rocks. Petrologic studies emphasized optical petrography, with supplementary X-ray diffraction, X-ray fluorescence and microprobe analyses. Radiogeologic investigations were based primarily on surface and underground gamma-ray spectrometric measurements of uranium, thorium and potassium, supplemented by laboratory gamma spectrometric analyses and fission-track radiographic determinations of the locations and abundance of uranium in the rock matrix. Both the quartz monzonite and the metavolcanic leptite which it intruded are strongly fractured. Two stages of fracture filling are evident; an earlier stage encompassing quartz, sericite, feldspar, epidote, and chlorite, and a later stage dominated by carbonate minerals. The Stripa quartz monzonite is chemically and mineralogically distinct from other plutons in the region. Muscovite is the predominant mica in the quartz monzonite; biotite has been altered to chlorite, hornblende is absent, and accessory minerals are scarce. In contrast, in other plutons in the Stripa region biotite and hornblende are prominent mafic minerals and accessory minerals are abundant. The Stripa quartz monzonite is also considerably more radioactive than the leptite and other plutons in the region. Uranium and thorium abundances are both- 30 ppm, considerably higher than in "normal" granitic rocks where the thorium-to-uranium ratio generally exceeds 2. Potassium-argon dating of muscovite from the Stripa quartz monzonite indicates that this rock may be older, at 1691 million years than granitic rock of the neighboring Gusselby and Kloten massifs, whose ages, based on K-Ar dating of biotite, are respectively 1604 and 1640 m.y. Heat flow and heat

  12. Garnet ships in a quartzite sea (United States)

    Rogowitz, Anna; Rice, A. Hugh N.; Grasemann, Bernhard; Huet, Benjamin


    During progressive deformation, a strong inclusion in a weaker matrix causes a stress concentration that may result in strain localization, seen in a matrix grain-size reduction. A superb example of this phenomena, but rather more complex, has been observed in north Norwegian Caledonides. A probably subvertical metadolerite dyke has been rotated to lie parallel to the penetrative regional low-angled foliation during the emplacement of the overlying nappe. The metadolerite, now only ~1.4 cm thick and lying between two quartzite layers has been retrogressed to a biotite schist with an assemblage of biotite, titanite, epidote group, garnet and quartz. Garnets are from 0.2 mm to 4 cm in size, subhedral and have two growth zones, with inclusions of predominantly titanite and rare amphibole. The country-rock metasedimentary schists contain staurolite, indicating mid-amphibolite-facies conditions (~550 °C and 6 kbar). During late deformation, some garnets were forced into the quartzite, resulting in the development of pronounced gouges (tectoglyphs), up to 70 mm long, 14 mm wide and 14 mm deep, deepening in the direction of movement. Quartz was pushed up at the sides of the gouges and forms a pronounced bow-wave at the front of the garnets. Where garnets are gouged into the quartzite, intense strain localization occurs. Both in front of and under the garnet, a up to 18 mm wide zone of quartz mylonite developed. The mylonitic foliation curves around the garnet, with a relatively sharp boundary to the adjacent quartzite that preserves an older random fabric. Deformation in the mylonite, which shows a strong crystallographic preferred orientation, seems to have occurred by (1) intense dislocation glide followed by (2) subgrain rotation resulting in an almost foam-like fabric. The grain size of the mylonite (at the quartzite-biotite schist interface) increases with increasing distance behind the present position of the garnets. This observation is consistent with an expected

  13. Geological characteristics of the Moshanhe iron deposit in Shandong%山东磨山河铁矿矿床地质特征

    Institute of Scientific and Technical Information of China (English)

    张朋朋; 张燕挥; 郭强


    The Moshanhe iron deposit belongs to a low grade sedimentary metamorphic iron deposit,and its ore-bearing host rock is mainly magnetic biotite schist.The iron ore bodies occur mainly in forms of bands,and lenticular shape.It is characterized with the small size of iron orebody,stable thickness and iron grade,and less harmful components.The main ore textures are granoblastic texture or hypidiomorphic granular texture and flake texture.The main ore mineral is magnetite.The industrial ore type belongs to weak magnetic type iron ore which could be processed.There is no clear boundary between the iron ore bodies and the bottom host rock of the biotite granulite or biotite schist,it needs the analysis results of the samples to determine the boundary.The ore body is an integrated component of Liuhang formation of Taishan Group,and has the same evolution history as Taishan Group.%磨山河铁矿床为磁铁黑云片岩型低品位磁铁矿床,成因属沉积变质型铁矿床.矿体以条带状、透镜状为主;规模较小,厚度、品位变化小,有害成分含量低.矿石主要呈鳞片花岗变晶结构或半自形晶粒结构,片状构造;主要矿石矿物为磁铁矿.矿石工业类型为弱磁性需选铁矿石.矿体与底板黑云变粒岩、黑云片岩界限模糊,需通过样品分析确定.矿体为新太古界泰山岩群柳杭组的组成部分,与泰山岩群的形成与演化过程一致.

  14. 广西DC矿田成矿作用和物质成分研究

    Institute of Scientific and Technical Information of China (English)

    章振根; 李锡林


    DC, a multi-metal ore field, is an important and well known producer of tin in China. Besides tin, also mined are zinc, lead, antimony, copper, arsenic, tungsten,mercury, silver and many other metals most of the deposits in this region occur in Devonian limestones and siliceous shales. The ore deposits in this field are predominated by cassiterite sulphide type. As to the origin of those deposits, they seem closely related to biotite granite. The oreforming material is mainly derived from magmatie rocks, and part of it may come from the host rocks. The appearance of horizontal zoning of ore deposits in this field is extremely distinct, with LXG biotite granite as the core. Found in the magmatie rocks is the molybdenum mineralization. From the biotite granite outwards there dlsplays such an occurring sequence as the following: copper (zinc) skarn ore deposits, seheelite ore deposits, wolframite ore deposits, eassiterite sulphide ore deposits, lead-zinc (antimony)ore deposits and mercury or arsenic ore deposits. In this region the mineralizingtemperature zoning is also distinguishable, basically in agreement with the horizontal zoning of ore deposits. In other words, the formation temaperature of ore deposits occurring around the granite is higher than that farther away from the granite. The following mineralization periods and stages can be divided: the first period,ineluding skarn sub-stage, eassiterite-quartz sub-stage, cassiterite-sulphide sub-stage,eassiterite-calcite sub-stage; the second period, including ferrosphalerite (galena)-franckeite sub-stage, jamesenite-boulangerite sub-stage; and the third period, including pyrite-calcite sub-stage. The characters of the material composition are as follows: ore minerals are characterized by great variety, perfect crystallinity, large grain-size and abundant sulfosalts. More than 90 species of minerals have been identified. What is more interesting is that lead and antimony in some of the cassitierite-sulfide deposits

  15. Molybdenite Re-Os, zircon U-Pb dating and Lu-Hf isotopic analysis of the Xiaerchulu Au deposit, Inner Mongolia Province, China (United States)

    Wang, Jia-xin; Nie, Feng-Jun; Zhang, Xue-ni; Jiang, Si-hong


    The Xiaerchulu Au deposit, located in the Southern Orogenic Belt (SOB) of Western Inner Mongolia (WIM), is hosted in an Early Permian (271-261 Ma) volcanic-plutonic sequence. Mineralization took place in silicified biotite granites or along the contact zone between the Neoproterozoic Baiyinbaolage Group and the biotite granite. In order to constrain the timing of the Xiaerchulu mineralization and discuss the petrogenesis of the hosting granites, molybdenite Re-Os, and zircon U-Pb and, Lu-Hf, and REE, geochemical, and Sr-Nd isotopic studies were completed in this study. We measured Re-Os isotopes of six molybdenite samples from the main ore body, which yielded a weighted average model age of 261.7 ± 1.5 Ma with a MSWD of 0.55, indicating that the time of mineralization was at ca. 262 Ma. High precision U-Pb dating for the studied granites yields Permian 206Pb/238U ages ranging from 271 to 269 Ma. These age data confirm that both the intrusion and related mineralization were initiated in Early Permian period. These granites are strongly peraluminous with A/CNK = 1.11-1.12, high SiO2-K2O contents, as well as containing biotite and muscovite, indicating a petrogenesis of typical S-type granites, the above consideration is also consistent with the result of discrimination diagrams. The Re contents of molybdenite, εNd(t), and zircon εHf(t), as well as the 176Hf/177Hf values of the granites, fall into the ranges from 1.153 to 2.740 μg/g, - 11.1 to - 9.3, - 8.8 to - 0.9, and 0.282358 to 0.282688, respectively. All of this evidence suggests that the metals were derived from a predominantly crustal source, the granites originated from crust in an extensional setting, and the rejuvenation of the continent may have play an important role during the ore-forming processes of the Early Permian epoch.

  16. Geochemical and isotopic evidence for the petrogenesis and emplacement tectonics of the Serra dos Órgãos batholith in the Ribeira belt, Rio de Janeiro, Brazil (United States)

    Machado, Rômulo; Philipp, Ruy Paulo; McReath, Ian; Peucat, Jean Jacques


    The Serra dos Órgãos batholith in the State of Rio de Janeiro (Brazil) is a NE-SW-trending elongated body that occupies ca. 5000 km2 in plan view. It is a foliated intrusion, especially at its borders and is crosscut by syn-magmatic shear zones, with foliations that are moderately-to steeply-dipping to the northwest and moderately-to shallow-dipping in the center and to the southeast, in a configuration of a large laccolith. It was emplaced between 560 and 570 Ma, during an extensional episode that was part of a series of events that comprise the Brasiliano Orogeny in SE Brazil, and which includes deformation, metamorphism and granite intrusion during the interval between 630 and 480 Ma. The two main rock types in the batholith are biotite-hornblende monzogranite, and biotite leucogranite, with subordinate tonalite, granodiorite, diorite, quartz diorite (enclaves), aplite and pegmatite. Harker-type diagrams help show two rock groups with similar trends of evolution: a dioritic and a granitic. The first one is tholeiitic, whereas the second is calc-alkaline, with medium-to high-K calc-alkaline affinity and metaluminous to slightly peraluminous character. In both groups strong decrease in Al2O3, MgO, FeOT and CaO relative to silica contents are observed, which is compatible with trends of fractional crystallization involving clinopyroxene and/or hornblende, plagioclase, opaque minerals, apatite, microcline and biotite. The Sr and Nd isotopic data suggest recycling of a Paleoproterozoic crust as an important petrological process to generate the batholith rocks. Geothermometry (amphibole composition) and geobarometry (saturation in zircon and apatite) indicate that most of the batholith solidified at mid to lower crustal levels at about 750 °C and between 5 and 5.5 kbar. We consider that Serra dos Órgãos crustal protoliths underwent melting caused by the interaction with hotter mafic magma at the base of the crust. These two magmas, with distinct initial

  17. Carbon, hydrogen, and oxygen isotope studies of the regional metamorphic complex at Naxos, Greece (United States)

    Rye, R.O.; Schuiling, R.D.; Rye, D.M.; Jansen, J.B.H.


    At Naxos, Greece, a migmatite dome is surrounded by schists and marbles of decreasing metamorphic grade. Sillimanite, kyanite, biotite, chlorite, and glaucophane zones are recognized at successively greater distances from the migmatite dome. Quartz-muscovite and quartz-biotite oxygen isotope and mineralogie temperatures range from 350 to 700??C. The metamorphic complex can be divided into multiple schist-rich (including migmatites) and marblerich zones. The ??18O values of silicate minerals in migmatite and schist units and quartz segregations in the schist-rich zones decrease with increase in metamorphic grades. The calculated ??18OH2O values of the metamorphic fluids in the schist-rich zones decrease from about 15??? in the lower grades to an average of about 8.5??? in the migmatite. The ??D values of OH-minerals (muscovite, biotite, chlorite, and glaucophane) in the schist-rich zones also decrease with increase in grade. The calculated ??DH2O values for the metamorphic fluid decrease from -5??? in the glaucophane zone to an average of about -70??? in the migmatite. The ??D values of water in fluid inclusions in quartz segregations in the higher grade rocks are consistent with this trend. The??18O values of silicate minerals and quartz segregations in marble-rich zones are usually very large and were controlled by exchange with the adjacent marbles. The ??D values of the OH minerals in some marble-rich zones may reflect the value of water contained in the rocks prior to metamorphism. Detailed data on 20 marble units show systematic variations of ??18O values which depend upon metamorphic grade. Below the 540??C isograd very steep ??18O gradients at the margins and large ??18O values in the interior of the marbles indicate that oxygen isotope exchange with the adjacent schist units was usually limited to the margins of the marbles with more exchange occurring in the stratigraphic bottom than in the top margins. Above the 540??C isograd lower ??18O values occur in

  18. Studies of microstructures of deformed charnockitic rocks in Telsiai deformation zone, Lithuania (United States)

    Vejelyte, Irma


    The Telsiai Deformation Zone (TDZ), a regional scale Precambrian deformation zone in the crystalline basement of Lithuania, transects the WLGD in the E-W direction and is approximately 15-20 km wide as mirrored by a belt of gravity and magnetic lows. As indicated by petrological and geophysical data the TDZ crosscuts a 1.82 Ga charnockitic pluton in a ductile manner. In turn, the TDZ appears to have been intruded by or accommodated a 1.46 Ga granitoid intrusion, defining at least its age in-between of these two magmatic events. The mesoanalyses and microanalyses of drillcores have been carried out on augen mylonite and ultramylonite, which were formed at upper amphibolite facies. The temperature during the deformation was 650-750 C° at pressure between 3.0 and 4.7 kbar. The deformed charnockites have a prominent foliation marked mainly by feldspar, biotite, quartz, orthopyroxene, garnet and ± clinopyroxene. Porphyroclasts of plagioclase are elongated and banded. They are partly recrystallized to fine-grained polygonal aggregates as a result of high temperature deformation. In places, plagioclase has been truncated by plagioclase-rich microshears. Quartz grains are in three manners: large old grains with deeply indented boundaries and undulate extinction; medium polygonal grains and ribbons grains. Large biotite grains are locally kinked, some of them have been partly neocrystallized to much smaller new grains of biotite parallel to the foliation. Garnet crystals are elongated and oriented to the foliation. Individual grains of them in the highest strain areas have been recrystallized to many small garnet grains. Large crystals of orthopyroxene are deformed and elongated, on their sheared rims tails of fine grained orthopyroxene and clinopyroxene have been formed. The subgrain rotation, grain-boundary migration recrystallization and recovery processes predominate in all minerals. Near residual plagioclase also are visible myrmekites. They formed along those sides

  19. Mineralogy and geochemistry of microgranular enclaves in Palaeoproterozoic Malanjkhand granitoids, central India: evidence of magma mixing, mingling, and chemical equilibration (United States)

    Kumar, Santosh; Rino, Vikoleno


    Palaeoproterozoic ( ca 2,480 Ma) felsic magmatism of Malanjkhand region of central Indian Precambrian shield, referred to as Malanjkhand granitoids (MG), contain xenoliths of country rocks and mesocratic to melanocratic, fine-grained porphyritic microgranular enclaves (ME). The shape of ME is spheroidal, ellipsoidal, discoidal, elongated, and lenticular, varying in size from a few centimeters to about 2 m across. The contact of ME with the host MG is commonly sharp, crenulate, and occasionally diffuse, which we attribute to the undercooling and disaggregation of ME globules within the cooler host MG. The ME as well as MG show hypidiomorphic texture with common mineral Hbl-Bt-Kfs-Pl-Qtz assemblage, but differ in modal proportions. The variation in minerals' composition, presence of apatite needles, elongated biotites, resorbed plagiclase, ocellar quartz, and other mafic-felsic xenocrysts strongly oppose the restite and cognate origins of ME. Compositions of plagioclases (An3-An29), amphiboles (Mg/Mg+Fe2+=0.55-0.69), and biotites (Mg/Mg+Fe2+=0.46-0.60) of ME are slightly distinct or similar to those of MG, which suggest partial to complete equilibration during mafic-felsic magma interactions. Al-in-amphibole estimates the MG pluton emplacement at ca 3.4 ± 0.5 kbar, and therefore, magma mixing and mingling must have occurred at or below this level. The FerightleftharpoonsMg substitution in biotites of ME and MG largely suggests subduction-related, calc-alkaline metaluminous (I-type) nature of felsic melts. Most major and trace elements against SiO2 produce near linear variation trends for ME and MG, probably generated by the mixing of mafic and felsic magmas in various proportions. Trace including rare earth elements patterns of ME-MG pairs, however, show partial to complete equilibration, most likely governed by different degrees of elemental diffusion. The available evidence supports the model of ME origin that coeval mafic (enclave) and felsic (MG) magmas produced

  20. Genetic Mechanism of Mineral Inclusions in Zircons from the Khondalite Series, Southeastern Inner Mongolia

    Institute of Scientific and Technical Information of China (English)


    The early Precambrian khondalite series is widely distributed in the Jining-Zhuozi-Fengzhen- Liangcheng area, southeastern Inner Mongolia. The khondalite series mainly consists of sillimanite garnet potash feldspar (or two-feldspar) gneiss and garnet biotite plagioclase gneiss. These gneissic rocks have commonly experienced granulite-facies metamorphism. In zircons separated from sillimanite garnet potash feldspar gneisses, many mineral inclusions, including Sil, Grt, Ky, Kfs, Qtz and Ap, have been identified by the Laser Raman spectroscopy. Generally, prograde metamorphic mineral inclusion assemblages such as Ky + Kfs + Qtz + Ap and Ky + Grt + Kfs + Qtz are preserved in the core of zircon, while peak granulite-facies metamorphic minerals including Sil + Grt + Kfs + Qtz and Sil + Grt + Kfs + Qtz + Ap are identified in the mantle and rim of the same zircon. However, in some zircons are only preserved the peak metamorphic minerals such as Sil + Grt + Kfs + Qtz and Sil + Grt + Kfs + Qtz + Ap from core to rim, and in others are inherited the primary cores with minor mineral inclusions of Kfs + Qtz, with peak metamorphic mineral inclusions around the inherited cores. These data indicate that the mineral assemblage evolution of sillimanite garnet potash feldspar gneisses in the study are did experience a polymorphic transformation of kyanite to sillimanite. In garnet biotite plagioclase gneisses, secondary electron microscopic images reveal that most zircons display distinct zoning textures, which comprise cores and rims, each with distinctive inclusion assemblages. The inherited mineral inclusions, mainly consisting of Kfs + Pl + Qtz, Kfs + Qtz and Kfs + Qtz + Ap, are preserved in the primary cores, while peak granulite-facies mineral asemblages, including Grt + Bt + Pl + Qtz + Ap, Grt + Bt + Pl + Qtz and Grt + Bt + Pl + Qtz + Rt, are identified on the rims. The occurrence of peak metamorphic mineral inclusions in zircons indicates that these gneissic rocks, including

  1. Strain localization in brittle-ductile shear zones: fluid abundant vs fluid limited conditions (an example from Wyangala area, Australia

    Directory of Open Access Journals (Sweden)

    L. Spruzeniece


    Full Text Available This study focuses on physiochemical processes occurring in a brittle-ductile shear zone at both fluid-present and fluid-limited conditions. In the studied shear zone (Wyangala, SE Australia, a coarse-grained two feldspar-quartz-biotite granite is transformed into a medium grained orthogneiss at the shear zone margins and a fine-grained quartz-muscovite phyllonite in the central parts. The orthogneiss displays cataclasis of feldspar and crystal-plastic deformation of quartz. Quartz accommodates most of the deformation and is extensively recrystallized showing distinct crystallographic preferred orientation (CPO. Feldspar-to-muscovite, biotite-to-muscovite and albitization reactions occur locally at porphyroclasts' fracture surfaces and margins. However, the bulk rock composition shows very little change in respect to the wall rock composition. In contrast, in the shear zone centre quartz occurs as large, weakly deformed porphyroclasts, in sizes similar to that in the wall rock, suggesting that it has undergone little deformation. Feldspars and biotite are almost completely reacted to muscovite, which is arranged in a fine-grained interconnected matrix. Muscovite-rich layers contain significant amounts of fine-grained intermixed quartz with random CPO. These domains are interpreted to have accommodated most of the strain. Bulk rock chemistry data shows a significant increase in SiO2 and depletion in NaO content compared to the wall rock composition. We suggest that the high and low strain fabrics represent markedly different scenarios and cannot be interpreted as a simple sequential development with respect to strain. We suggest that the fabrics and mineralogical changes in the shear zone centre have formed due to fluid influx probably along an initially brittle fracture. Here, hydration reactions dramatically changed the rheological properties of the rock. In the newly produced muscovite-quartz layers creep cavitation associated with grain

  2. Petrogenesis, geochronology, and tectonic significance of granitoids in the Tongshan intrusion, Anhui Province, Middle-Lower Yangtze River Valley, eastern China (United States)

    Zhang, Zhi-Yu; Du, Yang-Song; Teng, Chuan-Yao; Zhang, Jing; Pang, Zhen-Shan


    The Tongshan copper deposit in Anhui Province is a typical mid-sized skarn and porphyry type deposit in the Anqing-Guichi district along the Middle-Lower Yangtze River Valley, eastern China. The Tongshan intrusion is closely related to this mineralization. The intrusion mainly comprises rocks that are quartz diorite porphyry, quartz monzonite porphyry, and granodiorite porphyry. Plagioclase in these rocks is mostly andesine (An = 31.0-42.9), along with minor oligoclase. Biotite is magnesium-rich [Mg/(Mg + Fe) = 0.52-0.67] and aluminum-poor (Al2O3 = 12.32-14.09 wt.%), and can be classified as magnesio-biotite. Hornblende is TiO2-poor ( 0.60], and is magnesio-hornblende or edenite. The SHRIMP zircon U-Pb age of the quartz monzonite porphyry is 145.1 ± 1.2 Ma, which corresponds to the middle Yanshanian period. Whole-rock geochemical results show that the rocks are silica-rich (SiO2 = 60.23-66.23 wt.%) and alkali-rich (K2O + Na2O = 4.97-8.72 wt.%), and low in calcium (CaO = 2.61-5.66 wt.%). Trace element results show enrichments in large ion lithophile element (e.g., K, Rb, and Ba) and depletions in some high field strength elements (e.g., Nb, Ta, P, and Ti). The total rare earth element (REE) content of the rocks is low (ΣREE 10] and small positive Eu anomalies (average δEu = 1.16). These mineralogical, geochronological, and geochemical results show that the intrusion has a mixed crust-mantle source. The Tongshan intrusion was formed by multiple emplacements of crustally contaminated basaltic magma generated by varying degrees of partial melting of enriched lithospheric mantle and lower crust. Hornblende thermobarometry yielded magmatic crystallization temperatures of 652-788 °C and an average crystallization pressure of 1.4 kbar, which corresponds to a depth of approx. 4.7 km. Biotite thermobarometry yielded similar temperatures and lower pressures of 735-775 °C and 0.6 kbar (depth 2.1 km), respectively. The parental magma had a high oxygen fugacity and was

  3. Geochemistry of the Spor Mountain rhyolite, western Utah, as revealed by laser ablation ICP-MS, cathodoluminescence, and electron microprobe analysis (United States)

    Dailey, S. R.; Christiansen, E. H.; Dorais, M.; Fernandez, D. P.


    The Miocene topaz rhyolite at Spor Mountain in western Utah hosts one of the largest beryllium deposits in the world and was responsible for producing 85% of the beryllium mined worldwide in 2010 (Boland, 2012). The Spor Mountain rhyolite is composed primarily of Ca-poor plagioclase (An8), sodic sanidine (Or40), Fe-rich biotite (Fe/(Fe+Mg)>0.95; Al 1.2-1.4 apfu), and Ti-poor quartz, along with several trace-element rich accessory phases including zircon, monazite, thorite, columbite, and allanite. Cathodoluminescence (CL) studies of quartz show oscillatory zoning, with 80% of the examined crystals displaying euhedral edges and slightly darker rims. CL images were used to guide laser ablation (LA) ICP-MS analysis of quartz, along with analyses of plagioclase, sanidine, biotite, and glass. Ti concentrations in quartz are 20±6 ppm; there is no quantifiable variation of Ti from core to rim within the diameter of the laser spot (53 microns). Temperatures, calculated using Ti in quartz (at 2 kb, aTiO2=0.34), vary between 529±10 C (Thomas et al., 2011), 669±13 C (Huang and Audetat, 2012), and 691±13 C (Wark and Watson, 2006). Two feldspar thermometry yield temperatures of 686±33 C (Elkins and Grove, 1990) and 670±41 C (Benisek et al., 2010). Zr saturation temperatures (Watson and Harrison, 1983) average 711±28 C. Analysis of the glass reveal the Spor Mountain rhyolite is greatly enriched in rare elements (i.e. Li, Be, F, Ga, Rb, Nb, Mo, Sn, and Ta) compared to average continental crust (Rudnick and Gao, 2003). Be in the glass can have as much as 100 ppm, nearly 50 times the concentration in continental crust. REE partition coefficients for sanidine are 2 to 3 times higher in the Spor Mountain rhyolite when compared to other silicic magmas (Nash and Crecraft, 1985; Mahood and Hildreth, 1983), although plagioclase tends to have lower partition coefficients; biotite has lower partition coefficients for LREE and higher partition coefficients for HREE. The patterns of

  4. EMSP Project 70070: Reactivity of Primary Soil Minerals and Secondary Precipitates Beneath Leaking Hanford Waste Tanks - Final Report

    International Nuclear Information System (INIS)

    Since the late 1950s, leaks from 67 single-shell tanks at the Hanford Site have released about 1 million curies to the underlying sediments. The radioactive material was contained in water-based solutions generally characterized as having high pH values (basic solutions), high nitrate and nitrite concentrations, and high aluminum concentrations. The solutions were also hot, in some cases at or near boiling, as well as complex and highly variable in composition reflecting solutions obtained from multiple methods of reprocessing spent nuclear fuel. In order to understand the observed and probable distribution of radionuclides in the ground at Hanford, major reactions that likely occurred between the leaked fluids and the sediment minerals were investigated in laboratory experiments simulating environmental conditions. Reactions involving the dissolution of quartz and biotite and the simultaneous formation of new minerals were quantified at controlled pH values and temperature. Result s show that the dissolution of quartz and formation of new zeolite-like minerals could have altered the flow path of ground water and contaminant plumes and provided an uptake mechanism for positively-charged soluble radionuclides, such as cesium. The dissolution of biotite, a layered-iron-aluminum-silicate mineral, provided iron in a reduced form that could have reacted with negatively-charged soluble chromium, a toxic component of the wastes, to cause its reduction and precipitation as a new reduced-chromium mineral. The quantity of iron released in the experiments is sufficient to explain observations of reductions in dissolved chromium concentration in a plume beneath one Hanford tank. Fundamental data obtained in the project are the rates of the reactions at variable temperatures and pHs. Fundamental data were also obtained on aspects of the surface reactivity of clay or layered-silicate minerals, a small proportion of the total mass of the sediment minerals, but a large proportion

  5. Breakdown of Clays by Ectomycorrhizal Fungi Through Changes in Oxidation State of Iron (United States)

    Arocena, J. M.; Velde, B.


    Organisms are known to play a significant role in the transformation of clay minerals in soils. In our earlier work on canola, barley and alfalfa, we reported that Glomus, an arbuscular mycorrhizae, selectively transformed biotite into 2:1 expanding clays through the oxidation of Fe (II) in biotite to Fe(III). In this presentation, we will share similar results on clay transformations mediated by ectomycorrhizal fungi colonizing the roots of coniferous trees. Clay samples were isolated from rhizosphere soils of sub-alpine fir (Abies lasiocarpa (Hook.) Nutt.) in northern British Columbia (Canada). Chemical and mineralogical properties of these soils had been reported in our earlier paper. In this study, we subjected the clay samples to iron X-ray Absorption Near Edge Spectroscopy (Fe-XANES) at the Canadian Light Source synchrotron facility in Saskatoon (Canada). Our initial results showed relatively higher amounts of Fe (III) than Fe(II) in clays collected from rhizosphere of Piloderma (an ectomycorrhizal fungus) compared to soils influenced by non-Piloderma species and Control (non-rhizosphere soil). Coupled with the results of X-ray diffraction (XRD) analysis, there seems to be a positive relationship between the relative amounts of Fe(III) and the 2:1 expanding clays. This relationship is consistent with our results on agricultural plants in laboratory experiments on biotites where we suggested that oxidation of Fe(II) to Fe(III) results in the formation of 2:1 expanding clays. In a related data set on chlorite alteration we observed that after dithionite-citrate-bicarbonate (DCB) treatment, the d-spacing of a slight portion of chloritic expanding clays shifted to higher angles indicating decreased d-spacing towards micaceous clays. The reductive process initiated through the action of the DCB treatment seems to indicate the collapsed of expandable clays upon the reduction of Fe(III) to Fe(II). Initial results from the Fe-XANES and XRD analysis of DCB

  6. Metamorphic petrology of Olkiluoto

    Energy Technology Data Exchange (ETDEWEB)

    Tuisku, P.; Kaerki, A. (Kivitieto Oy, Oulu (Finland))


    The bedrock of Olkiluoto consists mostly of pelitic migmatites, and lesser amounts of biotite and hornblende gneisses, granite gneisses and granodiorite gneisses. The metapelites underwent partial dehydration melting through decomposition of biotite, sillimanite, plagioclase and quartz during the peak of regional metamorphism, producing the migmatites. Simple model systems were used to estimate the conditions of melting in metapelites and in quartzofeldspathic and granitic rocks. Pressure and temperature conditions of metamorphism in Olkiluoto have also been calculated by TWQ-thermobarometer and predicted from mineral assemblages of different rock types in the area. Regional metamorphism of Olkiluoto culminated with a voluminous migmatization of pelitic gneisses, in the temperature exceeding 660 deg C and relatively low pressure of about 3.5 - 4 kbar. The temperature may have risen up to approx 700 deg C producing granitic melt, which later crystallized to leucosomes. The mineral assemblages produced during the peak of regional metamorphism overprint the earlier S2 foliation. Granitic leucosomes associated with the culmination of the metamorphism were deformed by D3 deformation. Accordingly, the peak of metamorphism took place between D2 and D3 deformation phases. Muscovite-bearing shear bands of some granite pegmatites indicate that D3 deformation took place during subsequent cooling. Because granodiorite gneisses, having an age of about 1.86 Ga, are deformed by D2 deformation, the peak of regional metamorphism may be dated somewhere between 1.86 and 1.82 Ga, the latter being the minimum age of granite deformed by D3 deformation. The culmination of metamorphism is seen also in the mineral assemblages of more resistant rocks as biotite gneisses, hornblende gneisses and granodiorite gneisses. The cooling phase took place in low pressure, which is seen from some retrograde reaction products as andalusite, chlorite and muscovite replacing cordierite. Calculated

  7. Evolution of high-pressure mafic granulites and pelitic gneisses from NE Madagascar: Tectonic implications (United States)

    Ishwar-Kumar, C.; Sajeev, K.; Windley, B. F.; Kusky, T. M.; Feng, P.; Ratheesh-Kumar, R. T.; Huang, Y.; Zhang, Y.; Jiang, X.; Razakamanana, T.; Yagi, K.; Itaya, T.


    The occurrence of high-pressure mafic-ultramafic bodies within major shear zones is one of the indicators of paleo-subduction. In mafic granulites of the Andriamena complex (north-eastern Madagascar) we document unusual textures including garnet-clinopyroxene-quartz coronas that formed after the breakdown of orthopyroxene-plagioclase-ilmenite. Textural evidence and isochemical phase diagram calculations in the Na2O-CaO-K2O-FeO-MgO-Al2O3-SiO2-H2O-TiO2 system indicate a pressure-temperature (P-T) evolution from an isothermal (780 °C) pressure up to c. 24 kbar to decompression and cooling. Such a P-T trajectory is typically attained in a subduction zone setting where a gabbroic/ultramafic complex is subducted and later exhumed to the present crustal level during oceanic closure and final continental collision. The present results suggest that the presence of such deeply subducted rocks of the Andriamena complex is related to formation of the Betsimisaraka suture. LA-ICPMS U-Pb zircon dating of pelitic gneisses from the Betsimisaraka suture yields low Th/U ratios and protolith ages ranging from 2535 to 2625 Ma. A granitic gneiss from the Alaotra complex yields a zircon crystallization age of ca. 818 Ma and Th/U ratios vary from 1.08 to 2.09. K-Ar dating of muscovite and biotite from biotite-kyanite-sillimanite gneiss and garnet-biotite gneiss yields age of 486 ± 9 Ma and 459 ± 9 Ma respectively. We have estimated regional crustal thicknesses in NE Madagascar using a flexural inversion technique, which indicates the presence of an anomalously thick crust (c. 43 km) beneath the Antananarivo block. This result is consistent with the present concept that subduction beneath the Antananarivo block resulted in a more competent and thicker crust. The textural data, thermodynamic model, and geophysical evidence together provide a new insight to the subduction history, crustal thickening and evolution of the high-pressure Andriamena complex and its link to the terminal

  8. Petrology of upper Eocene-Oligocene plutonic rocks of Moalleman Damghan area (United States)

    Kohansal, Reza; Zolfaghari, Seddigheh; Hashem Emami, Mohammad


    The plutonic rocks of this area include cryptodoms, hypoabyssal plutonic bodies and dikes which intruded in to the late Lutetian- late Eocene rocks. The hypoabyssal plutonic rocks in Moalleman are classified in to two main groups: - Acidic rocks, including microgranite to microgranodiorite. - Intermediate rocks, including microquartzmonzodiorite to microquartzdiorite of hypoabyssal type. Presence of fine-grained mafic xenoliths with abundant biotite, amphibole and pyroxene in the intermediate rocks may be considered as an evidence of the role of mantle melting occurrence in the formation of these rocks. Occurrence of a felsitic texture, showing a high differentiation coefficient and existence of large quarts which are embayed, rounded and infiltered by material, and finally turmalinization in the acidic rocks due to Boron metasomatism suggest the role of crust in the formation of afore mentioned rocks as well. In some acidic rocks plagioclases show oscillatory zoning. This phenomenon along with the fact that biotite granites in these rocks crystallized before crystallization of quarts and after crystallization of alkali feldspar suggest that the crystallization of these rocks accomplished in the presence of 2 percent water, pertitic texture in some feldspars of the intermediate rocks this conclusion. Supports on the basis of the geochemical studies most of the hypoabyssal rocks of Moalleman area fall in subalkaline- calcoalkaline fields. Variation of immobile incompatible trace elements versus differentiation coefficient and the situation of samples in winkler diagram show the role of crustal- melting in the formation of acidic rocks. Trace element content of some rocks (e.g. Cu and Sm) with in this group show mantle specification, while some other rocks (e.g. Zr, Th, Hf) show crustal specification. The intermediate rocks of the study area therefore, indicate a hybridization of magmas from both the mantle and crust. Study of the temperature and water vapour

  9. Sources of granite magmatism in the Embu Terrane (Ribeira Belt, Brazil): Neoproterozoic crust recycling constrained by elemental and isotope (Sr-Nd-Pb) geochemistry (United States)

    Alves, Adriana; Janasi, Valdecir de Assis; Campos Neto, Mario da Costa


    Whole rock elemental and Sr-Nd isotope geochemistry and in situ K-feldspar Pb isotope geochemistry were used to identify the sources involved in the genesis of Neoproterozoic granites from the Embu Terrane, Ribeira Belt, SE Brazil. Granite magmatism spanned over 200 Ma (810-580 Ma), and is dominated by crust-derived relatively low-T (850-750 °C, zircon saturation) biotite granites to biotite-muscovite granites. Two Cryogenian plutons show the least negative εNdt (-8 to -10) and highest mg# (30-40) of the whole set. Their compositions are strongly contrasted, implying distinct sources for the peraluminous (ASI ∼ 1.2) ∼660 Ma Serra do Quebra-Cangalha batholith (metasedimentary rocks from relatively young upper crust with high Rb/Sr and low Th/U) and the metaluminous (ASI = 0.96-1.00) ∼ 630 Ma Santa Catarina Granite. Although not typical, the geochemical signature of these granites may reflect a continental margin arc environment, and they could be products of a prolonged period of oceanic plate consumption started at ∼810 Ma. The predominant Ediacaran (595-580 Ma) plutons have a spread of compositions from biotite granites with SiO2 as low as ∼65% (e.g., Itapeti, Mauá, Sabaúna and Lagoinha granites) to fractionated muscovite granites (Mogi das Cruzes, Santa Branca and Guacuri granites; up to ∼75% SiO2). εNdT are characteristically negative (-12 to -18), with corresponding Nd TDM indicating sources with Paleoproterozoic mean crustal ages (2.0-2.5 Ga). The Guacuri and Santa Branca muscovite granites have the more negative εNdt, highest 87Sr/86Srt (0.714-0.717) and lowest 208Pb/206Pb and 207Pb/206Pb, consistent with an old metasedimentary source with low time-integrated Rb/Sr. However, a positive Nd-Sr isotope correlation is suggested by data from the other granites, and would be consistent with mixing between an older source predominant in the Mauá granite and a younger, high Rb/Sr source that is more abundant in the Lagoinha granite sample. The

  10. The spatial variation of initial 87Sr/86Sr ratios in the Toki granite, Central Japan. Implications for the intrusion and cooling processes of a granitic pluton

    International Nuclear Information System (INIS)

    The spatial variation in initial 87Sr/ 86Sr ratios (SrI) in the Toki granite, Central Japan, shows heterogeneity ranging from 0.708942 to 0.710069, which provides information on the intrusion and cooling processes of plutons. The Toki granite has three mineralogy-based rock facies: muscovite-biotite granite (MBG), hornblende-biotite granite (HBG) and biotite granite (BG). Large SrI values were found to be distributed at the western margin (west MBG) and the lithologically central region (central BG), while small SrI values were found at the northeast margin (northeast MBG). Regions with high and low Sr concentrations were also found in the Toki granite. In the Sr-rich samples, SrI (0.708942-0.709789) increases with 100/Sr (0.7-1.5). This geochemical trend extends towards the country sedimentary rocks of the Mino Terrane, which can be interpreted to result from assimilation and fractional crystallization (AFC) between the original granitic magma and the Mino sedimentary rocks. The SrI values in the Sr-rich regions show a correlation with the Alumina Saturation Index (ASI). In particular, the west MBG, with large SrI values, is classified as a peraluminous granitoid with large ASI, suggesting that the western margin of the pluton was strongly affected by assimilation during the intrusion process. The Sr-poor samples are present both in the central BG, with large SrI values, and in the northeast MBG, with small SrI values. The Sr-poor samples have small ASI and large differentiation indices, indicating that the central BG and the northeast MBG were generated either by different AFC process with different amounts of contaminants or by the intrusion and fractionation of different source magma with different SrI values. Overall, the geochemical spatial variations found in the Toki granite can be explained by various degrees of assimilation and fractional crystallization in the magma chamber and/or multi-stage intrusions with different degrees of crystallization of plural

  11. Stable isotopic evidence for large-scale seawater infiltration in a regional metamorphic terrane; the Trois Seigneurs Massif, Pyrenees, France (United States)

    Wickham, Stephen M.; Taylor, Hugh P.


    Oxygen isotopic analyses of 95 metamorphic and igneous rocks and minerals from a Hercynian metamorphic sequence in the Trois Seigneurs Massif, Pyrenees, France, indicate that all lithologies at higher metamorphic grades than the “andalusite in” isograd have relatively homogeneous δ 18O values. The extent of homogenization is shown by the similarity of δ 18O values in metacarbonates, metapelites and granitic rocks (+11 to +13), and by the narrow range of oxygen isotopic composition shown by quartz from these lithologies. These values contrast with the δ 18O values of metapelites of lower metamorphic grade ( δ 18O about +15). Homogenization was caused by a pervasive influx of hydrous fluid. Mass-balance calculations imply that the fluid influx was so large that its source was probably high-level groundwaters or connate formation water. Hydrogen isotopic analyses of muscovite from various lithologies are uniform and exceptionally heavy at δD=-25 to -30, suggesting a seawater origin. Many lines of petrological evidence from the area independently suggest that metamorphism and anatexis of pelitic metasediment occurred at depths of 6 12 km in the presence of this water-rich fluid, the composition of which was externally buffered. Deep penetration of surface waters in such environments has been hitherto unrecognized, and may be a key factor in promoting major anatexis of the continental crust at shallow depth. Three types of granitoid are exposed in the area. The leucogranites and the biotite granite-quartz diorite are both mainly derived from fusion of local Paleozoic pelitic metasediment, because all these rocks have similar whole-rock δ 18O values (+11 to +13). The post-metamorphic biotite granodiorite has a distinctly different δ 18O (+9.5 to +10.0) and was probably derived from a deeper level in the crust. Rare mafic xenoliths within the deeper parts of the biotite granite-quartz diorite also have different δ 18O (+8.0 to +8.5) and possibly represent

  12. Petrogenesis of Garnet-bearing Rocks in the Grandfather Mountain Window, Blue Ridge Province, Western North Carolina (United States)

    Frushour, A. M.; Abbott, R. N.


    The Grandfather Mountain Window in western North Carolina exposes the lowest structural level in the Blue Ridge Province. Rocks in the window constitute a Late Proterozoic basement-cover sequence. The basement consists mainly of Blowing Rock Gneiss (sic, porphyroblastic schist) and Wilson Creek Gneiss, both overlain unconformably by the Grandfather Mountain Formation. All of these rocks have been pervasively overprinted by greenschist facies metamorphism. The typical greenschist mineral assemblage involves combinations of chlorite, muscovite, biotite, actinolite, epidote, calcite, quartz, albite and K-feldspar. Garnet discovered in basement rock calls into question the metamorphic grade. The average garnet (core-rim) is (Fe1.63-1.71Mn0.64-0.77Ca0.52-0.37Mg0.10-0.12)Al1.98-1.96Si3.06-3.04O12; the average biotite is (K0.96Na0.06Ca0.02)(Fe1.73Mg0.87Mn0.02Ti0.04Al0.23)(Si2.83Al1.17)O10(OH)2; the average muscovite is (K1.03Na0.02Ca0.02)(Al1.57Fe0.26Mg0.16Ti0.01)(Si3.31Al0.69)O10(OH)2. Thermometry involving Fe-Mn-Mg components in these minerals gives 766°C (+/- 91°C) at 13.6 kbars (+/- 1.4 kbar), respectively. There are at least four explanations for garnet in these rocks: (1) Garnet may have been stabilized in the greenschist facies by non-AFM components (esp. Mn), but the compositions are not unusual for metamorphic garnet, biotite and muscovite, and the calculated temperatures are too high for greenschist facies. (2) The garnet may be relict from earlier contact metamorphism, but the garnet is not spatially related to otherwise common metamorphosed (greenschist facies) mafic dikes. (3) The garnet is a product of heating during mylonitization. Finally, and most likely, (4) the garnet may be relict from an earlier episode of regional metamorphism. Samples of porphyroblastic schist and greenstone from the same outcrop give low temperature, greenschist facies conditions.

  13. Cl-rich hydrous mafic mineral assemblages in the Highiș massif, Apuseni Mountains, Romania (United States)

    Bonin, Bernard; Tatu, Mihai


    The Guadalupian (Mid-Permian) Highiș massif (Apuseni Mountains, Romania) displays a bimodal igneous suite of mafic (gabbro, diorite) and A-type felsic (alkali feldspar granite, albite granite, and hybrid granodiorite) rocks. Amphibole is widespread throughout the suite, and yields markedly high chlorine contents. Three groups are identified: Cl-rich potassic hastingsite (2.60-3.40 wt% Cl) within A-type felsic rocks and diorite, mildly Cl-rich pargasite to hornblende (0.80-1.90 wt% Cl) within gabbro, and low F-Cl hornblende within gabbro and hybrid granodiorite. Coexisting biotite is either Cl-rich within diorite, or F-Cl-poor to F-rich within A-type felsic rocks. Chlorine and fluorine are distributed in both mafic phases, according to the F-Fe and Cl-Mg avoidance rules. The low-Ti contents suggest subsolidus compositions. Cl-rich amphibole within diorite and A-type felsic rocks yields a restricted temperature range - from 575 °C down to 400 °C, whereas mildly Cl-rich amphibole within gabbro displays the highest range - from 675 to 360 °C. Temperatures recorded by Cl-rich biotite within diorite range from 590 to 410 °C. Biotite within A-type felsic rocks yields higher temperatures than amphibole: the highest values- from 640 to 540 °C - are recorded in low-F-Cl varieties, whereas the lowest values- from 535 to 500 °C - are displayed by F-rich varieties. All data point to halogen-rich hydrothermal fluids at upper greenschist facies conditions percolating through fractures and shear zones and pervasively permeating the whole Highiș massif, with F precipitating as interstitial fluorite and Cl incorporating into amphibole, during one, or possibly several, hydrothermal episodes that would have occurred during a ~ 150 My-long period of time extending from the Guadalupian (Mid-Permian) to the Albian (Mid-Cretaceous).

  14. The mineralogical characteristics of the hydrothermal types alteration from Nistru ore deposit, Baia Mare metallogenetic district

    Directory of Open Access Journals (Sweden)

    Floarea Damian


    Full Text Available The hydrothermal alteration types, which have affected intrusive and volcanic rocks from Nistru ore deposit, are related to fluids composition varied in their evolution within hydrothermal systems. The early stage of the hydrothermal activity has produced extensive propylitisation and potassic alteration (orthoclase, biotite, sericite associated with the central part of the quartz-micromonzodioritic porphyry stock. The late stage of the fluids differentiation is determined by the hydrogen-ion metasomatism (phyllic alteration, argillic alteration, characterized by a large vertical variation. The hydrogen-ion metasomatism is associated with the bor metasomatism, generated by acid solutions and at a high temperature. The vertical and lateral zoning character of the hydrothermal alterations is related to differences in rock composition and variation in physical-chemical conditions during the periods of subvolcanic intrusion and mineralization.

  15. 北京密云群变质作用的温度、压力研究

    Institute of Scientific and Technical Information of China (English)



    Metamorphic temperatures and pressures of the Archean Miyun Group have been determinad by using orthopyroxene-clinopyroxene garnet-clinopyroxene, garnet-biotite and δ18OQ2-δ18OMt geothermometers and by using the pure mineral components of clinopyroxanes, The results show that the temperature in the first stage of metamorphism of the Miyun Group is 820°±50℃ and the pressure is about 10kb, providing an indication of medium pressure granulite fades with a geothermal gradient of 22°--25℃/km. The corresponding burial depth is about 35 kin. The temperature prevailing during the second metamorphic stage is in the range 650°---700℃, indicating an intermediate fades between granulite and high amphibolite facies. Oxygen isotope data also show that the temperature of later superimposad regression metamorphism of high green schist fades in this region may be within the range of 470°-560℃,

  16. Contribution to the geochemical knowledge of the uranium-radium and thorium families in the southern Vosges. Applications of some results in the prospecting of uranium deposits

    International Nuclear Information System (INIS)

    This work's aim is to lead to a more accurate knowledge of the geochemistry of the Uranium-Radium and Thorium families in the Southern Vosges and to apply some of the results to the prospecting of uraniferous deposits: It has been showed: a bond between Calcium-Magnesium and Uranium-Thorium in the calco-alkaline granites. The host minerals of Uranium and Thorium are hornblende, biotite, titanite and epidote. a concentration of Uranium, at present time with secular disequilibrium in a thermal zone where the satellite mineralizations form an epithermal paragenesis. a disequilibrium of the Uranium-Radium family in the supergene minerals of the lead (phosphate and vanadate) showing the present circulations of Uranium. a bond between the radon grade of the spring waters and Uranium-Radium of the rocks. Such a relation allow to realize a prospecting method based on the determination of radioactive gases from the cold spring-waters of a common country. (author)

  17. geological mapping of the Onkalo open cut

    Energy Technology Data Exchange (ETDEWEB)

    Talikka, M. [Geological Survey of Finland, Espoo (Finland)


    Posiva Oy and Geological Survey of Finland carried out geological mapping of the ONKALO open cut in the latter half of the year 2004. The study area is located on the Olkiluoto Island in Eurajoki, SW Finland. The study included geological mapping, stereo-photography, and interpretation of 3D images. Fieldwork was carried out during the construction work. The main rock types are vein migmatite and grey gneiss with variation to granitic grey gneiss. The contacts of the rock types are gradual. The vein migmatite consists of fine- to medium-grained mica gneiss paleosome and granite or granite pegmatite neosome. The proportion of the neosome material varies between 15 and 35 percent and the neosome occurs as veins and bands up to ten centimetres in thickness. The granite I granite pegmatite is medium- to coarse-grained and not orientated. Main minerals in the mica gneiss are plagioclase, biotite, quartz, and in the granite / granite pegmatite potassium feldspar, plagioclase, and quartz. The grey gneiss is medium grained and fairly homogenous comprising mainly plagioclase, biotite, and quartz. The granitic grey gneiss contains also potassium feldspar crystals up to five cm in length. The rocks within the study area are generally well preserved. There is, however, a zone of strongly weathered rocks east of the ONKALO open cut. The main structural feature in the study area is S{sub 2} foliation, which is seen in the orientation of biotite grains. The degree of the foliation is weak to medium in the vein migmatite and weak to non-existence in the grey gneiss. The foliation (S{sub 2}) dips 20-70 deg to southeast with an average direction of 150/45 deg. The migmatisation took place during the second deformation phase and possibly proceeded along the lithologic layers. The neosome veins bend irregularly and folding is present in places. The fold axis of the small scale, isoclinal folds dip 50-70 deg to northeast. In fracture mapping a total of 231 fractures were measured

  18. Sur l'origine par altération du substratum schisteux de la minéralisation chlorurée des eaux d'une nappe côtière sous climat semi-aride (Chtouka-Massa, Maroc) (United States)

    Krimissa, Samira; Michelot, Jean-Luc; Bouchaou, Lhoussaine; Mudry, Jacques; Hsissou, Youssef


    The origin of chloride ions in groundwater from the Chtouka-Massa plain (Morocco) was studied by using chemical and isotopic analyses of water, and petrographic and chemical analyses of rocks. It appears that the schist formation, which forms the basement of the studied aquifer, is the main source of the high Cl - concentrations in groundwater. In these schists, chloride is, for a part, probably contained in biotites, and is released into groundwater through the weathering of these minerals. However, the exceptionally high chloride contents of these schists are difficult to explain if one does not assume that they also contain evaporitic-type minerals. To cite this article: S. Krimissa et al., C. R. Geoscience 336 (2004).

  19. The XPS study of physical and chemical forms of neptunium group on the surface of minerals

    Directory of Open Access Journals (Sweden)

    Teterin Anton Yu.


    Full Text Available The sorption behavior and the physical and chemical forms of neptunium on the surface of minerals of the two chlorate samples, biotite and kaolin, with different contents of Fe(II was studied. The liquid-liquid extraction and the X-ray photoelectron spectroscopy were employed to identify the valence forms of neptunium. On the basis of the obtained data the quantitative elemental composition of the surface of the studied minerals, as well as the ionic composition of the formed neptunium complexes was determined. It was shown that the Np(IV and Np(VI containing compounds did not form, while the complexes Np(VO+ -hydroxyl did form on the surface. The oxygen ions bonded with iron and oxygen belonging to water and/or of carboxyl were suggested to be present in the equatorial plane of the neptunyl group NpO+.

  20. Utilization of plastic detectors in autoradiographic studies of radioactive minerals from the Lagoa Real uranium Province, state of Bahia, Brazil

    International Nuclear Information System (INIS)

    A short account on an autoradiographic technique using plastic detectors, it's methodology, application and results is presented. With this technique the distribution of radioactive minerals in rocks can be studied in detail. As radioactive source for this study, samples mineralized in uraninite and/or pitchblende were used. The utilized detectors were the CR-39 (a polymer plate) and films of celulose nitrate: CA-80-15 and CN-85. The mineralization is associated to mafics (amphibole, pyroxene, biotite, garnet, etc.) and to plagioclase (albite or albite-oligoclase), occurring as small inclusions and also in microfractures, cleavages and grain boundaries, mainly among plagioclase crystals which occur close to or practically touching mafic minerals. (Author)

  1. The effects of retrograde reactions and of diffusion on 39Ar-40Ar ages of micas

    DEFF Research Database (Denmark)

    Allaz, Julien; Engi, Martin; Berger, Alfons;


    Effects of metamorphic reactions occurring during decompression were explored to understand their influence on 39Ar-40Ar ages of micas. Monometamorphic metasediments from the Lepontine Alps (Switzerland) were studied. Collected samples reached lower amphibolite facies during the Barrovian....... XRD-data indicated that some mineral separates prepared for Ar-Ar stepwise heating analysis were monomineralic, whereas others were composed of two white micas (muscovite with paragonite or margarite), or biotite and chlorite. In monomineralic samples 37Ar/39Ar and 38Ar/39Ar (proportional to Ca....../K and Cl/K ratios) did not change and the resulting ages can be interpreted unambiguously. In mineral separates containing two white micas, Ca/K and Cl/K ratios were variable, reflecting non-simultaneous laboratory degassing of the two heterochemical Ar-reservoirs. These ratios were used to identify each...

  2. A method for the concentration of fine-grained rutile (TiO2) from sediment and sedimentary rocks by chemical leaching (United States)

    Commeau, Judith A.; Valentine, Page C.


    Quaternary marine sediment in the Gulf of Maine basins contains 0.7 to 1.0 wt percent TiO2 (determined by X-ray fluorescence spectrometry). Most of this TiO2 exists in the form of silt-size rutile crystals that are visible by using the petrographic microscope with transmitted light (Valentine and Commeau, 1990). The identification of rutile was confirmed by using a scanning electron microscope (SEM) equipped with an energy-dispersive X-ray spectrometer (EDS) system. To quantify the amount of TiO2 in the sediment contributed by rutile and its polymorphs, anatase and brookite, it was necessary to eliminate as many of the other minerals as possible, especially titanium-bearing minerals such as ilmenite, ilmenomagnetite, biotite, hornblende, oyroxene, and sphene. We accomplished this by developing a method of chemical dissolution that removed the bulk of the raw material and left the TiO2 minerals intact.

  3. Geochemical, microtextural and petrological studies of the Samba prospect in the Zambian Copperbelt basement: a metamorphosed Palaeoproterozoic porphyry Cu deposit. (United States)

    Master, Sharad; Mirrander Ndhlovu, N.


    Ever since Wakefield (1978, IMM Trans., B87, 43-52) described a porphyry-type meta-morphosed Cu prospect, the ca 50 Mt, 0.5% Cu Samba deposit (12.717°S, 27.833°E), hosted by porphyry-associated quartz-sericite-biotite schists in northern Zambia, there has been controversy about its origin and significance. This is because it is situated in the basement to the world's largest stratabound sediment-hosted copper province, the Central African Copperbelt, which is hosted by rocks of the Neoproterozoic Katanga Supergroup. Mineralization in the pre-Katangan basement has long played a prominent role in ore genetic models, with some authors suggesting that basement Cu mineralization may have been recycled into the Katangan basin through erosion and redeposition, while others have suggested that the circulation of fluids through Cu-rich basement may have leached out the metals which are found concentrated in the Katangan orebodies. On the basis of ca 490-460 Ma Ar-Ar ages, Hitzman et al. (2012, Sillitoe Vol., SEG Spec. Publ., 16, 487-514) suggested that Samba represents late-stage impregnation of copper mineralization into the basement, and that it was one of the youngest copper deposits known in the Central African Copperbelt. If the Samba deposit really is that young, then it would have post-dated regional deformation and metamorphism (560-510 Ma), and it ought to be undeformed and unmetamorphosed. The Samba mineralization consists of chalcopyrite and bornite, occurring as disseminations, stringers and veinlets, found in a zone >1 km along strike, in steeply-dipping lenses up to 10m thick and >150m deep. Our new major and trace element XRF geochemical data (14 samples) show that the host rocks are mainly calc-alkaline metadacites. Cu is correlated with Ag (Cu/Ag ~10,000:1) with no Au or Mo. Our study focused on the microtextures and petrology of the Samba ores. We confirm that there is alteration of similar style to that accompanying classical porphyry Cu mineralization

  4. Kyanite-garnet gneisses of the Kåfjord Nappe - North Norwegian Caledonides: P-T conditions and monazite Th-U-Pb dating (United States)

    Ziemniak, Grzegorz; Kośmińska, Karolina; Majka, Jarosław; Janák, Marian; Manecki, Maciej


    The Kåfjord Nappe is the part of the Skibotn Nappe Complex traditionally ascribed to the Upper Allochthon of the North Norwegian Caledonides. Pressure-temperature (P-T) conditions and metamorphic age of the Kåfjord Nappe are not well constrained, geochronological data are limited to a single Rb-Sr age of c. 440 Ma (Dangla et al. 1978). Metamorphic evolution of kyanite-garnet gneisses of the Kåfjord Nappe is presented here. The kyanite-garnet gneisses are associated with a few meters thick amphibolite lenses. The gneisses mainly consist of quartz, plagioclase, biotite, muscovite, garnet, kyanite, and rutile. Retrograde minerals are represented by sillimanite and chlorite. Garnet occurs as two textural types. Garnet-I forms euhedral porphyroblasts with multiple small inclusions. Profiles through garnet-I show chemical zonation in all components. The composition varies from Alm64-68Prp11-16Grs13-18Sps2-8 in the core to Alm68-70Prp17-18Grs10-13Sps1-3 in the rim. Garnet-II is subhedral to anhedral, its core is inclusion-rich, whereas rim contains only single inclusions. Chemical composition of garnet-II is similar to that of the garnet-I rim. P-T conditions have been estimated using the garnet-biotite-muscovite-plagioclase (GBPM) geothermobarometer (Holdaway, 2001; Wu, 2014). Calculated peak P-T metamorphic conditions are 610-625 °C and 7.6-8.2 kbar corresponding to the amphibolite facies conditions. Phase equilibrium modelling in the NCKFMMnASH system yields peak metamorphic conditions of c. 620 °C at 8 kbar. Growth conditions of garnet-I core modelled in the NCKFMMnASH system are c. 570 °C at 9.7 kbar. Chemical Th-U-total Pb monazite dating has been performed. Preliminary dating results from the kyanite-garnet gneiss of the Kåfjord Nappe yield an array of dates from 468 Ma to 404 Ma. There is a correlation between an increase of yttrium content and decrease of monazite single dates. Compositional maps confirm an increase of yttrium towards the rim of the

  5. Sorption experiments at oxic and anoxic conditions

    International Nuclear Information System (INIS)

    Sorption of U, Pu, Np, Th and Tc at anoxic conditions were studied using radionuclides 233U, 236Pu, 237Np, 234Th and 99Tc. Samples were selected to represent common rocks and minerals in Finnish bedrock. The determinations of K-values and sorption percents in quartz plagioclase, potassium feldspar, honrnblende, biotite, mica gneiss, tonalite, granodiorite, porphyritic granite, granitic gneiss and rapakivi granite were performed by the autoradiographic method. The sorpion of these elements was studied under anoxic conditions using synthetic granitic ground water and synthetic bentonite water containing ferrous iron. For redox-sensitive U, Np and Pu experiments were made by spiking samples with water containing the radioactive isotope at one specified oxidation state

  6. Preservation of ancient impact ages on the R chondrite parent body: 40Ar/39Ar age of hornblende-bearing R chondrite LAP 04840 (United States)

    Righter, K.; Cosca, M. A.; Morgan, L. E.


    The hornblende- and biotite-bearing R chondrite LAP 04840 is a rare kind of meteorite possibly containing outer solar system water stored during metamorphism or postshock annealing deep within an asteroid. Because little is known regarding its age and origin, we determined 40Ar/39Ar ages on hornblende-rich separates of the meteorite, and obtained plateau ages of 4340(±40) to 4380(±30) Ma. These well-defined plateau ages, coupled with evidence for postshock annealing, indicate this meteorite records an ancient shock event and subsequent annealing. The age of 4340-4380 Ma (or 4.34-4.38 Ga) for this and other previously dated R chondrites is much older than most impact events recorded by ordinary chondrites and points to an ancient event or events that predated the late heavy bombardment that is recorded in so many meteorites and lunar samples.

  7. The Laramide Mesa formation and the Ojo de Agua caldera, southeast of the Cananea copper mining district, Sonora, Mexico (United States)

    Cox, Dennis P.; Miller, Robert J.; Woodbourne, Keith L.


    The Mesa Formation extends from Cananea, Mexico, southeast to the Sonora River and is the main host rock of Laramide porphyry copper deposits in the Cananea District and at the Alacran porphyry prospect to the east. The Mesa consists of two members-a lower andesite and an upper dacite. The lowest part of the dacite member is a crystal tuff about 100 m thick. This tuff is the outfall of a caldera centered near the village of Ojo de Agua, dated by 40Ar/39Ar at 65.8 Ma ?0.4. The Ojo de Agua Caldera is about 9 km in diameter and is filled by a light gray biotite dacite tuff with abundant flattened pumice fragments. The volume of the caldera is estimated to be 24 km3.

  8. Mineralized and Barren Tourmaline Breccia at Río Blanco-Los Bronces Copper Deposit, Central Chile (United States)

    Hohf, Michael; Seifert, Thomas; Ratschbacher, Lothar; Rabbia, Osvaldo; Krause, Joachim; Haser, Sabine; Cuadra, Patricio


    The Río Blanco-Los Bronces porphyry copper-molybdenum cluster (14.8-4.3 Ma) in central Chile is one of the largest mining districts of the world with more than 200 Mt of contained Cu; almost 30% of these resources are hosted by hydrothermal breccias. These breccia complexes are tourmaline-, biotite-, chlorite-, or iron oxide-cemented and are widespread in the Paleo-Eocene and Mio-Pliocene porphyry Cu-Mo belt of the central Andes. The ongoing research project aims to understand the time-space relationships between the different breccia bodies and the multiple porphyry intrusions. For this, two cross sections in the southern part of the deposit (Sur-Sur and La Americana areas) are studied. Most interesting from the economic/genetic point of view is the intermineral breccia (tourmaline- and biotite-cemented), which have high copper grades. It is under debate whether there is a vertical mineralogical zonation of the cement of the breccia body from tourmaline-rich at the top to biotite-dominated at the bottom, or there are two superimposed breccia formation events. Textural and mineralogical observations of benches- and tunnels-outcrops, drill cores, and polished-thin sections support the first hypothesis. Our work has been focused on tourmaline chemistry due to its high resistance to alteration and weathering, which allows this mineral to retain its original isotopic signature. Preliminary results of 127 microprobe measurements of tourmaline chemistry from the early mineralized breccia (BXT) and the late barren one (BXTTO) show that all the tourmalines belong to the alkali group and the composition ranges between the dravite-schorl end members. There is a pronounced negative correlation between Fe (ferric?) and Al, probably due to exchange at the Z octahedral position. The backscatter images of tourmaline show oscillatory and sector zonings, i.e., alternating light bands/zones (high CaO, FeO, Na2O) and darker ones (enriched in Al2O3 and MgO). There is no significant

  9. A desk study of surface diffusion and mass transport in clay

    International Nuclear Information System (INIS)

    The concept of a geological barrier to radionuclide migration from theoretical radioactive waste repositories has drawn attention to the physico-chemical properties of clays, which are traditionally regarded as retarding media. This report addresses the different mechanisms of transport of radionuclides through clay and in particular focuses on the surface diffusion movement of sorbed cations. The relative contributory importance of the different transport mechanisms is governed by the pore size distributions and interconnections within the clay fabric. Surface diffusion data in the literature have been from experiments using compacted montmorillonite and biotite gneiss. A possible programme of laboratory work is outlined, based on diffusion experiments, which describes the way of measuring the effect of surface diffusion more accurately in clays, mudstones and shales. (author)


    Directory of Open Access Journals (Sweden)

    Vladimir Majer


    Full Text Available Metharyolites of Vranica mountain are roks of emphasized porphyritic texture containing phenocrysts of quartz, K.feldspar and very rarely albite. The groundmass is microcrystallinic, characterized by finegrained phengite, biotite and area consisting of granophyric intergrowths of quartz and feldspar. Accessory minerals are ilmenite, rutila, apatite, zircon and chlorite. Metarhyolites are peraulminous rocks (PI=1.-4.1 having dominantly potassium character (K2O/Na2O=1,3-13,8. Incompatible elements are enriched relative to the normalizing chondrite composition, pointing to the crustal origin of metarhyolite magma. Although phengites typically occur in high pressure rocks, it seems that phengites of metarhyolites of Vranica mountain belong to the seldom group of phengites occurring in the low to medium pressure rocks (the paper is published in Croatian.

  11. Geochemical, petrological, geo dynamic and radiometric age dating investigation of Aqdarreh intrusion massive (north of Takab) northwest of Iran

    International Nuclear Information System (INIS)

    Aqdarreh intrusi body with an area of 30 km 2 is located in 34 km north of Takab, northwest of Iran. This batholith is situated in Central Iran, cutting Paleozoic rocks. Radiometric age of Aqdarreh batholith by K-Ar method is 48.38 m. a.,corresponding to Eocene magmatism. Aqdarreh intrusive body consists of tonalite, granodiorite, alkali feldspar granite and monzogranite in which the main mafic mineral is biotite. Further more, there is not any enclave in these rocks. Study of the investigated samples shows that Aqdarreh intrusive rocks have two different generations. Part of the collected samples belongs to I-type granite (calc-alkaline) and others represent the A-type granite (alkaline). It seems that this process is created by the contamination of alkaline magma by crustal materials. Geochemistry of the rare earth elements shows that the tectonic setting of the body is compatible with Post Orogenic Granitoids

  12. Chemical characteristics of zircon from A-type granites and comparison to zircon of S-type granites (United States)

    Breiter, Karel; Lamarão, Claudio Nery; Borges, Régis Munhoz Krás; Dall'Agnol, Roberto


    The trace element content in zircons from A-type granites and rhyolites was investigated by using back-scattered electron images and electron microprobe analyses. The studied Proterozoic (Wiborg batholith, Finland and Pará, Amazonas and Goiás states, Brazil) and Variscan (Krušné Hory/Erzgebirge, Czech Republic and Germany) plutons cover a wide range of rocks, from large rapakivi-textured geochemically primitive plutons to small intrusions of F-, Li-, Sn-, Nb-, Ta-, and U-enriched rare-metal granites. While zircon is one of the first crystallized minerals in less fractionated metaluminous and peraluminous granites, it is a late-crystallized phase in peralkaline granites and in evolved granites that may crystallize during the whole process of magma solidification. The early crystals are included in mica, quartz, and feldspar; the late grains are included in fluorite or cryolite or are interstitial. The zircon in hornblende-biotite and biotite granites from the non-mineralized plutons is poor in minor and trace elements; the zircon in moderately fractionated granite varieties is slightly enriched in Hf, Th, U, Y, and HREEs; whereas the zircon in highly fractionated ore-bearing granites may be strongly enriched in Hf (up to 10 wt.% HfO2), Th (up to 10 wt.% ThO2), U (up to 10 wt.% UO2), Y (up to 12 wt.% Y2O3), Sc (up to 3 wt.% Sc2O3), Nb (up to 5 wt.% Nb2O5), Ta (up to 1 wt.% Ta2O5), W (up to 3 wt.% WO3), F (up to 2.5 wt.% F), P (up to 11 wt.% P2O5), and As (up to 1 wt.% As2O5). Metamictized zircons may also be enriched in Bi, Ca, Fe, and Al. The increase in the Hf content coupled with the decrease in the Zr/Hf value in zircon is one of the most reliable indicators of granitic magma evolution. In the zircon of A-type granites, the Zr/Hf value decreases from 41-67 (porphyritic granite) to 16-19 (equigranular granite) in the Kymi stock, Finland, and from 49-52 (biotite granite) to 18-36 (leucogranite) in the Pedra Branca pluton, Brazil. In the in situ strongly

  13. Confirmation of pelitic granulite in the Altai orogen and its geological significance

    Institute of Scientific and Technical Information of China (English)

    WANG Wei; WEI ChunJing; WANG Tao; LOU YuXing; CHU Hang


    The existence of pelitic granulite in the Altai orogen was confirmed for the first time by detailed petro-graphic research and P-T pseudosection modeling. The pelitic granulite has the assemblage of garnet + cordierite + K-feldspar + biotite + sillimanite + plagioclase + quartz with some samples containing the paragenesis of cordierite + spinel. Peak conditions of the pelitic granulite determined from the P-T pseudosection involved P= 0.5-0.6 GPa, T= 780-800?*, belonging to medium-to low-pressure type. SHRIMP U-Pb dating of zircon presented a metamorphic age of 292.8 ± 2.3 Ma. The discovery of pelitic granulite reflects an extensional environment with high heat flow in the southern margin of the Altai orogen during the Early Permian, which provides an important petrological constraint on the evolution of the Altai orogen.

  14. Characterization of mineral phases of agricultural soil samples of Colombian coffee using Moessbauer spectroscopy and X-ray diffraction

    Energy Technology Data Exchange (ETDEWEB)

    Rodriguez, Humberto Bustos, E-mail:; Lozano, Dagoberto Oyola; Martinez, Yebrayl Antonio Rojas; Pinilla, Marlene Rivera [Universidad del Tolima, Grupo Ciencia de Materiales y Tecnologia en Plasma (Colombia); Alcazar, German Antonio Perez [Universidad del Valle, Grupo Metalurgia Fisica y Teoria de las Transiciones de Fase (Colombia)


    Soil chemical analysis, X-ray diffraction (XRD) and Moessbauer spectrometry (MS) of {sup 57}Fe were used to characterize mineral phases of samples taken from the productive layer (horizon A) of agricultural coffee soil from Tolima (Colombia). Chemical analysis shows the chemical and textural parameters of samples from two different regions of Tolima, i.e., Ibague and Santa Isabel. By XRD phases like illite (I), andesine (A) and quartz (Q) in both samples were identified. The quantity of these phases is different for the two samples. The MS spectra taken at room temperature were adjusted by using five doublets, three of them associated to Fe{sup + 3} type sites and the other two to Fe{sup + 2} type sites. According to their isomer shift and quadrupole splitting the presence of phases like illite (detected by DRX), nontronite and biotite (not detected by XRD) can be postulated.

  15. Characterization of mineral phases of agricultural soil samples of Colombian coffee using Mössbauer spectroscopy and X-ray diffraction (United States)

    Rodríguez, Humberto Bustos; Lozano, Dagoberto Oyola; Martínez, Yebrayl Antonio Rojas; Pinilla, Marlene Rivera; Alcázar, German Antonio Pérez


    Soil chemical analysis, X-ray diffraction (XRD) and Mössbauer spectrometry (MS) of 57Fe were used to characterize mineral phases of samples taken from the productive layer (horizon A) of agricultural coffee soil from Tolima (Colombia). Chemical analysis shows the chemical and textural parameters of samples from two different regions of Tolima, i.e., Ibagué and Santa Isabel. By XRD phases like illite (I), andesine (A) and quartz (Q) in both samples were identified. The quantity of these phases is different for the two samples. The MS spectra taken at room temperature were adjusted by using five doublets, three of them associated to Fe + 3 type sites and the other two to Fe + 2 type sites. According to their isomer shift and quadrupole splitting the presence of phases like illite (detected by DRX), nontronite and biotite (not detected by XRD) can be postulated.

  16. Tectonic model for the Late Paleozoic of southeastern New England

    Energy Technology Data Exchange (ETDEWEB)

    Wintsch, R.P.; Sutter, J.F.


    Hornblende and biotite /sup 40/Ar//sup 39/Ar age spectra from rocks in south-central Connecticut help define a Permian-Triassic cooling curve for the area. Together with petrologic and structural information, a time-temperature-pressure-strain path is established. Similar data for the Narragansett basin in Rhode Island and Massachusetts allow correlation of the late Paleozoic histories of the two areas. Together, these data suggest that in the late Paleozoic, south-central New England was part of a fold-thrust belt, and the Narragansett basin was a retroarc foreland basin. NW-SE compression during the final assembly of Pangaea resulted in SE directed thrusting, causing the development of clastic wedges in adjacent Rhode Island and Massachusetts in the Late Carboniferous-Early Permian. A clockwise rotation of this deformation from NW to NNE led to northward underthrusting and concomitant uplift of both eastern Connecticut and Rhode Island in the Permian and Triassic.

  17. U-Pb dating of zircon from the bed parallel anatectic granitic intrusion in the Baoban group in Hainan Island and the tectonic implication

    Institute of Scientific and Technical Information of China (English)

    DING Shijiang; HU Jianmin; SONG Biao; CHEN Mulun; XIE Shengzhou; FAN Yuan


    The petrological and geochemical features of the bed parallel granitic intrusion in the Pre-Cambrian Baoban group in Hainan Island attest to the anatexis origin of the granites. U-Pb dating analyses of zircons from the anatectic granite and the biotite two-feldspar gneiss in the Baoban group, using SHRIMP II in the Beijing Ion-probe Center, acquire 206Pb/238U ages of 368±3.5 Ma (of granite, 95% confidence level, MSDW=1.23) and 362.9±6.1 Ma (of gneiss, 95% confidence level, MSDW = 2.04) respectively. The two late Devonian ages indicate consistently a tectonic- thermal event experienced in Hainan Island, and are the first discovered record of the Devonian geological process in the district. This event possibly resulted from the deep thermal-dynamic process when the Gondwana continent began to break up in the Devonian period.

  18. Trachytic Rock and Associated Fenitization in the Bayan Obo Ore Deposit, Inner Mongolia, China: Evidence for Magmatic-Hydrothermal Mineralization Related to a Carbonatitic Complex

    Institute of Scientific and Technical Information of China (English)


    Trachytic rock and its altered rock-FONT-fenite-in the Bayan Obo ore district, Inner Mongolia, China, were referred to as slate or feldspar rock before, and identified by the authors for the first time (in 1992). In the paper the mineral assemblages, structures and textures and petrochemical compositions of the rocks, as well as the electron microprobe analysis of feldspars in the rocks are described. The Sm-Nd isochron age of the trachytic rock is 1096±56 Ma, with INd=0.51100±4 (2σ) and e Nd(t)= - 4.4±0.7. Alterations of the trachytic rock, including microclinization, riebeckitization, aegirinization and biotitization, and accompanied rare element and REE mineralizations are discussed. Based on the occurrence of the trachytic rock and associated fenitization it is deduced that the Bayan Obo Fe-Nb-REE ore deposit is genetically related to magmatic-hydrothermal activity of an alkali carbonatite complex.

  19. Geochemistry and SHRIMP Zircon U-Pb Age of Post-Collisional Granites in the Southwest Tianshan Orogenic Belt of China: Examples from the Heiyingshan and Laohutai Plutons

    Institute of Scientific and Technical Information of China (English)

    LONG Lingli; GAO Jun; WANG Jingbin; QIAN Qing; XIONG Xianming; WANG Yuwang; WANG Lijuan; GAO Liming


    The Heiyingshan granite and the Laohutai granite plutons exposed in the Southwest Tianshan resemble A-type granites geochemically. Analysis shows that the both are ferron calc-alkalic peraluminous or ferron aikali-calcic peraluminous with a relatively high concentration of SiO2 (>70%), high alkali contents (Na2O + K2O = 7.14%-8.56%; K2O>N2O; A/CNK = 0.99-1.20), and pronounced negative anomales in Eu, Ba, Sr, P and Ti. A SHRIMP zircon U-Pb age of 285±4 Ma was obtained for the Heiyingshan hornblende biotite granite intrusion. The geochemical and age dating data reported in this paper indicate that these granites were formed during the post-collisional crustal extension of the Southwest Tianshan orogenic belt, in agreement with the published data for the granites in the South Tianshan.

  20. A Palaeoproterozoic multi-stage hydrothermal alteration system at Nalunaq gold deposit, South Greenland

    DEFF Research Database (Denmark)

    Bell, Robin-Marie; Kolb, Jochen; Waight, Tod Earle;


    Nalunaq is an orogenic, high gold grade deposit situated on the Nanortalik Peninsula, South Greenland. Mineralisation is hosted in shear zone-controlled quartz veins, located in fine- and medium-grained amphibolite. The deposit was the site of Greenland’s only operating metalliferous mine until its...... closure in 2014, having produced 10.67 t of gold. This study uses a combination of field investigation, petrography and U/Pb zircon and titanite geochronology to define a multistage hydrothermal alteration system at Nalunaq. A clinopyroxene-plagioclase-garnet(-sulphide) alteration zone (CPGZ) developed in...... the Nanortalik Peninsula, close to regional peak metamorphism and prior to gold-quartz vein formation. The ca. 1783–1762-Ma gold-quartz veins are hosted in reactivated shear zones with a hydrothermal alteration halo of biotite...

  1. 斑岩铜(钼)矿成矿作用的地球化学特征

    Institute of Scientific and Technical Information of China (English)

    朱炳球; 徐外生


    Dealt with in this paper are some geochemical characteristics of mineralization of porphyry copper deposits, especially those observed in intrusive bodies, wa11 rocks, alteration zones, ores and individual pyrites. Productive intrusions have been correlated with barre nones from such aspects as major and trace elements, copper contents of biotite and pyrite,and distribution pattern of copper. In the mineralized rocks, trace elements show apparent zoning surrounding ore bodies; major and trace dements seem to show some reguIarity of variation in the process of alteration, and as a result each alteration zone displays its own peculiar element combination. Trace dements in ores can provide information on the genesis of ore deposits, thus of great help in distinguishing ore types while those in pyrites may be indicative of mineralization, provide dues for distinguishing orebearing from barren rocks,and reflect the degree of erosion of ore bodies.

  2. Isotopic chronology and geological events of Precambrian complex in Taihangshan region

    Institute of Scientific and Technical Information of China (English)

    刘树文; 梁海华; 赵国春; 华永刚; 简安华


    There are five major geological events in Precambrian complex, Taihangshan region determined by researching into geology and isotopic chronology of the complex. Basaltic magma erupted and quartz-dioritic to tonalitic magma intruded in earlier neo-Archaean, which formed horn-blende-plagiogneiss of Fuping gneiss complex and metamorphic mafic rock enclaves in TTG gneiss complex. Granulite fades metamorphism and emplacement of biotite-plagiogneiss occurred in late neo-Archaean. Extension and uplifting from the end of neo-Archaean to Paleoproterozoic era formed Chengnanzhuang large extensional deformation zones and metamorphic mafic veins emplaced into the deformation zones. Remobilization of Precambrian complex and tectonic uplifting in late Paleoproterozoic era formed Longquanguan ductile shear zone and emplacement of Nanying gneiss. Occurrence of regional granite pegmatite at the end of Paleoproterozoic era means the end of the Luliang movement.

  3. Isotopic chronology and geological events of Precambrian complex in Taihangshan region

    Institute of Scientific and Technical Information of China (English)


    There are five major geological events in Precambrian complex, Taihangshan region determined by researching into geology and isotopic chronology of the complex. Basaltic magma erupted and quartz-dioritic to tonalitic magma intruded in earlier neo-Archaean, which formed hornblende-plagiogneiss of Fuping gneiss complex and metamorphic mafic rock enclaves in TTG gneiss complex. Granulite facies metamorphism and emplacement of biotite-plagiogneiss occurred in late neo-Archaean. Extension and uplifting from the end of neo-Archaean to Paleoproterozoic era formed Chengnanzhuang large extensional deformation zones and metamorphic mafic veins emplaced into the deformation zones. Remobilization of Precambrian complex and tectonic uplifting in late Paleoproterozoic era formed Longquanguan ductile shear zone and emplacement of Nanying gneiss. Occurrence of regional granite pegmatite at the end of Paleoproterozoic era means the end of the Lliang movement.

  4. A Precambrian proximal ejecta blanket from Scotland (United States)

    Amor, Kenneth; Hesselbo, Stephen P.; Porcelli, Don; Thackrey, Scott; Parnell, John


    Ejecta blankets around impact craters are rarely preserved onEarth. Although impact craters are ubiquitous on solid bodiesthroughout the solar system, on Earth they are rapidly effaced,and few records exist of the processes that occur during emplacementof ejecta. The Stac Fada Member of the Precambrian Stoer Groupin Scotland has previously been described as volcanic in origin.However, shocked quartz and biotite provide evidence for high-pressureshock metamorphism, while chromium isotope values and elevatedabundances of platinum group metals and siderophile elementsindicate addition of meteoritic material. Thus, the unit isreinterpreted here as having an impact origin. The ejecta blanketreaches >20 m in thickness and contains abundant dark green,vesicular, devitrified glass fragments. Field observations suggestthat the deposit was emplaced as a single fluidized flow thatformed as a result of an impact into water-saturated sedimentarystrata. The continental geological setting and presence of groundwatermake this deposit an analogue for Martian fluidized ejecta blankets.

  5. Deep-seated geology of the granite intrusions at the Soultz EGS site based on data from 5 km-deep boreholes

    Energy Technology Data Exchange (ETDEWEB)

    Hooijkaas, Gerridina R. [Departments of Petrology and Isotope Geochemistry, Institute of Earth Sciences, Vrije Universiteit, De Boelelaan 1085, NL 1081 HV, Amsterdam (Netherlands); Genter, Albert; Dezayes, Chrystel [French Geological Survey, BRGM, 3 Avenue Claude Guillemin, BP6009, F-45060 Orleans Cedex 2 (France)


    The petrographic model for the deep-seated geology at the Soultz-sous-Forets Enhanced Geothermal System (EGS) site in the Rhine Graben, France, was revised on the basis of data from 5 km-deep wells. Several types of granite and sub-facies were characterized through thin-section analysis of drill cuttings. Various datalogs were studied to correlate them with petrography. The new geological model of the Soultz site is made up of a massive porphyritic granite that shows some paleo-weathering at its top, overlain by about 1400 m of Mesozoic and Tertiary sediments. Between 2700 and 3200 m depth, the same granite is highly fractured and hydrothermally altered. Below this zone, the granite is less fractured and is very rich in biotite and amphibole. Starting at 4700 m depth is a younger, fine-grained, two-mica and amphibole-rich granite that intrudes into the porphyritic granite. (author)

  6. Petrology, composition, and age of intrusive rocks associated with the Quartz Hill molybdenite deposit, southeastern Alaska. (United States)

    Hudson, T.; Smith, James G.; Elliott, R.L.


    A large porphyry molybdenum deposit (Quartz Hill deposit) was recently discovered in the heart of the Coast Range batholithic complex about 70 km E of Ketchikan, SE Alaska. Intrusive rocks associated with the mineral deposit form two composite epizonal to hypabyssal stocks and many dikes in country rocks. All observed metallization and alteration is within the Quartz Hill stock. Molybdenite forms fracture coatings and occurs in veins with quartz. Alteration is widespread and includes development of secondary quartz, pyrite, K-feldspar, biotite, white mica, chlorite, and zeolite. Field relations indicate that the stocks were emplaced after regional uplift and erosion of the Coast Range batholithic complex, and K-Ar data show that intrusion and alteration took place in late Oligocene time, about 27 to 30 Ma ago. Data from the Ketchikan quadrangle indicate that porphyry molybdenum metallization in the Coast Range batholithic complex is associated with regionally extensive but spotty, middle Tertiary or younger, felsic magmatism. -from Authors

  7. LA-ICP-MS zircon U-Pb dating,geochemistry of the Mishuling intrusion in western Qinling and their tectonic significance.%西秦岭糜署岭花岗岩体年代学、地球化学特征及其构造意义

    Institute of Scientific and Technical Information of China (English)

    李佐臣; 裴先治; 李瑞保; 裴磊; 胡波; 刘成军; 陈国超; 陈有炘


    An EW trending Indosinian granitoide belt distributes near the Mianlue Suture Zone in the southern margin of the Qinling Orogenic Belt.The Mishuling intrution is one of the Indosinian granitoids located in the western Qingling and north to the Mianlue Suture Zone.This article studies the LA-ICP-MS zircon U-Pb ages and geochemistry characteristics of the Mishuling biotite quartz monzonite and monzodiorite enclaves.The results show that the crystallization age of the Mishuling biotite quartz monzonite is 214.5 ±1.6Ma(MSWD =0.24).The A/CNK ratios of the Mishuling biotite quartz monzonite and monzodiorite enclaves range from 0.64 to 0.97,indicating that the granitoids are metaluminous rocks.The Σ REE of the granitoides are 197.3 × 10-6 ~ 246.6 × 10-6.The REE patterns show rightward incline and moderate negative Eu anomaly.The trace element geochemistry is characterized evidently by negative anomaly of Ta,Nb,P,Ti,Ba,Sr,etc.and positive anomaly of Rb,U,La,Zr,Hf,Nd,Y,etc.The host rock biotite quartz monzonite and enclaves monzodiorite are Ⅰ-type granitoids,which may originate from a single magma.The magma was formed by partial melting of basic rocks.The Mishuling intrusions are post-orogenic granitoids which were formed in a transitional tectonic setting from syn-(compressional setting) to post-collision (extensional setting).They were products formed by partial melting of thicken lower crust resulting from the collision between the North China plate and Yangtze plate.%秦岭造山带南缘勉略缝合带附近发育东西向展布的印支期花岗岩带,位于西秦岭地区勉略缝合带北侧的糜署岭岩体是该花岗岩带的一部分.本文对糜署岭岩体寄主岩及二长闪长质包体进行LA-ICP-MS锆石U-Pb定年和地球化学特征研究.结果表明,糜署岭岩体的结晶年龄为214.5±1.6Ma(MSWD =0.24).糜署岭岩体寄主岩和二长闪长质包体A/CNK在0.64~0.97之间,具有准铝质特征.稀土元素总量(ΣREE)为197.3×10-6

  8. Petrochemistry and petrology of I-type granitoids in an arc setting: the composite Torul pluton, Eastern Pontides, NE Turkey (United States)

    Kaygusuz, Abdullah; Siebel, Wolfgang; Şen, Cüneyt; Satir, Muharrem


    The Upper Cretaceous Torul pluton, located in the Eastern Pontides, is of sub-alkaline affinity and displays features typical of volcanic arc granitoids. It is a composite pluton consisting of granodiorite, biotite hornblende monzogranite, quartz monzodiorite, quartz monzonite and hornblende biotite monzogranite. The oldest syenogranite (77.9 ± 0.3 Ma) and the youngest quartz diorite form small stocks within the pluton. Samples from the granodiorites, biotite hornblende monzogranites, quartz monzodiorites, quartz monzonites and hornblende biotite monzogranites have SiO2 between 57 and 68 wt% and display high-K calc-alkaline, metaluminous to peraluminous characteristics. Chondrite-normalized REE patterns are fractionated (Lacn/Lucn = 6.0-14.2) with pronounced negative Eu anomalies (Eu/Eu* = 0.59-0.84). Initial ɛNd(i) values vary between -3.1 and -4.1, initial 87Sr/86Sr values between 0.7058 and 0.7072, and δ18O values between +4.4 and +7.3‰. The quartz diorites are characterized by relatively high Mg-number of 36-38, low contents of Na2O (2.3-2.5 wt%) and SiO2 (52-55 wt%) and medium-K calc-alkaline, metaluminous composition. Chondrite-normalized REE patterns are relatively flat [(La/Yb)cn = 2.8-3.3; (Tb/Yb)cn = 1.2] and show small negative Eu anomalies (Eu/Eu* = 0.74-0.76). Compared to the other rock types, radiogenic isotope signatures of the quartz diorites show higher 87Sr/86Sr (0.7075-0.7079) and lower ɛNd(i) (-4.5 to -5.3). The syenogranites have high SiO2 (70-74 wt%) and display high-K calc-alkaline, peraluminous characteristics. Their REE patterns are characterized by higher Lacn/Lucn (12.9) and Eu/Eu* (0.76-0.77) values compared to the quartz diorites. Isotopic signatures of these rocks [ɛNd(i) = -4.0 to -3.3; 87Sr/86Sr(i) = 0.7034-0.7060; δ18 O = + 4.9 to + 8.2] are largely similar to the other rock types but differ from that of the quartz diorites. Fractionation of plagioclase, hornblende, pyroxene and Fe-Ti oxides played an important role in the

  9. Evidence of heterogeneous crustal origin for the Pan-African Mbengwi granitoids and the associated mafic intrusions (northwestern Cameroon, central Africa) (United States)

    Mbassa, Benoît Joseph; Kamgang, Pierre; Grégoire, Michel; Njonfang, Emmanuel; Benoit, Mathieu; Itiga, Zénon; Duchene, Stéphanie; Bessong, Moïse; Nguet, Pauline Wonkwenmendam; Nfomou, Ntepe


    The Mbengwi plutonics consist of intermediate to felsic granitoids forming a continuous magmatic series from monzonite to granite and mafic intrusions. Their mineralogical composition consists of quartz, plagioclases, K-feldspars, biotite, muscovite, and amphibole. The accessory phase includes opaque minerals + titanite ± apatite ± zircon, while secondary minerals are pyrite, phengite, chlorite, epidote, and rarely calcite. These plutonics are assigned high-K calc-alkaline to shoshonitic series, metaluminous to weakly peraluminous and mostly belong to an I-type suite (A/CNK = 0.63-1.2). They are typically post-collisional, with a subduction signature probably being inherited from their protoliths emplaced during the subduction phase. The Sr and Nd isotopic data evidence that these plutonics result from melting of the lower continental crust with variable contribution of the oceanic crust. Their geochemical features are similar to those of western Cameroon granitoids related to the Pan-African D1 event in Cameroon.

  10. Preservation of ancient impact ages on the R chondrite parent body: 40Ar/39Ar age of hornblende-bearing R chondrite LAP 04840 (United States)

    Righter, K.; Cosca, M. A.; Morgan, L. E.


    The hornblende- and biotite-bearing R chondrite LAP 04840 is a rare kind of meteorite possibly containing outer solar system water stored during metamorphism or postshock annealing deep within an asteroid. Because little is known regarding its age and origin, we determined 40Ar/39Ar ages on hornblende-rich separates of the meteorite, and obtained plateau ages of 4340(±40) to 4380(±30) Ma. These well-defined plateau ages, coupled with evidence for postshock annealing, indicate this meteorite records an ancient shock event and subsequent annealing. The age of 4340-4380 Ma (or 4.34-4.38 Ga) for this and other previously dated R chondrites is much older than most impact events recorded by ordinary chondrites and points to an ancient event or events that predated the late heavy bombardment that is recorded in so many meteorites and lunar samples.

  11. Assessment of groundwater potential based on aquifer properties of hard rock terrain in the Chittar-Uppodai watershed, Tamil Nadu, India (United States)

    Kumar, T. Jeyavel Raja; Balasubramanian, A.; Kumar, R. S.; Dushiyanthan, C.; Thiruneelakandan, B.; Suresh, R.; Karthikeyan, K.; Davidraju, D.


    Aquifer performance was tested in 24 locations to assess the groundwater potential of the hard rock terrain in the Chittar-Uppodai watershed of the Tambaraparani River basin. Geologically, the area consists of biotite gneiss, charnockite, and quartzite. The aquifer characteristics, such as transmissivity ( T), the storage coefficient, specific capacity, optimum yield, and the recovery rate were calculated. The drawdown transmissivity was determined using Jacob's straight-line method, while the recovery transmissivity was determined by the Theis method. The drawdown transmissivity was low in the western areas, particularly at Kadayanallur, and was higher in the other areas. The recovery transmissivity was high in the western area, and, with the exception of Gangaikondan, was low at other locations. The assessment indicates that there is groundwater potential in the western part of the study area because of favorable results for recovery drawdown, aquifer thickness, and specific capacity.

  12. Tectono-metamorphic evolution of a hot orogen during Gondwanaland assembly: a case study from Palni hills metapelite granulite, south India (United States)

    Bhadra, S.; Nasipuri, P.


    This study deals with the tectono-metamorphic evolution of Sapphirine-cordierite-bearing metapelite granulite at Perumalmalai, south India, that occurs as enclave within deformed migmatitic enderbite gneiss of Kodaikanal massif, Madurai granulite block (MB), south India. Pre-peak mineral paragenesis is represented by an inclusion assemblage of sillimanite + plagioclase + Ti-rich biotite ±quartz in Al-rich orthopyroxene. Dehydration melting of biotite marked the onset of ultra-high temperature metamorphism (M1A, ~1000 °C, 10 Kbar). Early stage of retrograde metamorphism (M1B) is characterized by the development of type1-symplectite and corona textures. In type1-symplectite an innermost vermicular sapphirine (Spr - XMg: 0.90, Al/Si: 6.17) - cordierite (Crd) symplectite on sillimanite is followed by cordierite (XMg: 0.94) moat. A meso-perthitic layer laced the interface between cordierite moat and orthopyroxene porphyroblast, the latter showing prominent rim-ward decrease in Al2O3 (up to 3 wt%). The cordierite rim at the interface between sillimanite and orthopyroxene characterizes corona texture. Type1-symplectite and corona domains are circumnavigated by Ti-poor biotite (TiO2: ~3.2 wt%) showing shape preferred alignment, and set in a feldspar matrix showing wide compositional range. By implication, leucosome crystallization was possibly prolonged and enhanced by deformation. Type1-symplectite and corona textures were resulted from melt-solid interaction or silica-metasomatism during early stage of retrogression, Opx+Sil = Spr+Crd → Opx+Sil+melt = Crd. The retrograde metamorphism is constrained at 9 kbar and 950°C, implying an early stage of near-isothermal decompression. Late stage retrograde metamorphism (M2) is also characterized by symplectite textures, type2-symplectite, with innermost sapphirine-cordierite symplectite followed by cordierite corona. Sapphirine in type2-symplectite domain (XMg: 0.89; Al/Si: 5.92), which occurs as inclusion in Opx, is

  13. Grenvillian thermal event and remnant charnockite: Isotopic evidence from the Chilka Lake granulite-migmatite suite in the Eastern Ghats belt, India

    Indian Academy of Sciences (India)

    S Bhattacharya; M P Deomurari; W Teixeira


    Spectacular exposures of granulite-migmatite occur in the Chilka Lake area of the Eastern Ghats belt. The garnetiferous granite gneiss of peraluminous granitic composition, often contains restitic metapelite inclusions and is demonstrably a product of biotite-dehydration melting in pelitic rocks. On the other hand, older layers and bands of charnockitic rocks frequently occur as dismembered patches within the peraluminous granite, thus imparting a measled appearance of the granite exposures. The partial melting and emplacement of the peraluminous granite represent the Grenvillian thermal event, as evidenced by Rb-Sr whole rock and Pb-Pb zircon dating. On the other hand, minor patches of charnockite represent migmatized relict, as evidenced by some older zircons, in addition to those of Grenvillian age.

  14. Chronology and cooling history of the Tianmenshan pluton in South Jiangxi Province and their geological significance

    Institute of Scientific and Technical Information of China (English)

    ZENG Qingtao; MAO Jianren; HU Qing; ZHAO Xilin; YE Haimin


    Geochronological studies on the crust-derived Tianmenshan pluton were undertaken by SHRIMP zircon U-Pb dating and Ar-Ar dating of biotite, muscovite and K-feldspar, giving a petrogenetic age of 167 Ma. Owing to the closure systems in different minerals, the cooling history of the pluton can be determined with an age-temperature diagram. The late hydrothermal event has been recognized, which is related probably with mineralization. In terms of the comparative geochronological and petrologic records, it is concluded that there are some constrains on tectonic evolution and that the formation of the Tianmenshan pluton proceeded in a transition period from lndosinian post-orogeny extension to strong compressive tectonics. And the timing of the hydrothermal event matches the compressive climax of the Yanshanian orogeny. The temporal gap between granite emplacement and wolframite mineralization could last 10-20 Ma owing to the low cooling rate of the pluton.

  15. Investigation of silicate surface chemistry and reaction mechanisms associated with mass transport in geologic media

    International Nuclear Information System (INIS)

    The concentration and rate of transport of radionuclides through geologic media can be strongly influenced by the extent of sorption on aquifer surfaces. Over time intervals relevant to such transport processes, rock and mineral surfaces cannot be considered as inert, unreactive substrates but rather as groundwater/solidphase interfaces which are commonly in a state of natural or artificially induced disequilibrium. The goal of the present research is to define experimentally the type of water/rock interactions that will influence surface chemistry and hence sorption characteristics and capacities of natural aquifers. As wide a range of silicate minerals as possible was selected for study to represent rock-forming minerals in basalt, tuff, and granite. The minerals include K-feldspar, plagioclase feldspar, olivine, hornblende, biotite, and volcanic glass

  16. 40Ar/39Ar Dating of the Shaxi Porphyry Cu-Au Deposit in the Southern Tan-Lu Fault Zone, Anhui Province

    Institute of Scientific and Technical Information of China (English)

    YANG Xiaoyong; ZHENG Yongfei; XIAO Yilin; DU Jianguo; SUN Weidong


    Four samples of plagioclase and biotite from the Shaxi porphyry in the lower part of the Yangtze metallogenic belt were analyzed for age determination with the 40Ar/39Ar method. The results yield reproducible ages of 126 Ma to 135 Ma with a high level of confidence according to the agreement between isochron and plateau ages. The four Ar-Ar ages are relatively consistent within the analytical error. These ages are also consistent with, but more precise than, previous K-Ar and Rb-Sr ages and thus provide better constraints on the time of porphyry formation and associated Cu-Au mineralization along the middle to lower part of the Yangtze metallogenic belt. The ages of 126 to 135 Ma are interpreted to represent the intrusive time of the Shaxi porphyry, so that the Cu-Au mineralization should have occurred later due to the post-magmatic hydrothermal event.

  17. Age of Anzishan granulites in the Mianxian-Lueyang suture zone of Qingling orogen: With a discussion of the timing offinal assembly of Yangtze and North China craton blocks

    Institute of Scientific and Technical Information of China (English)


    Many granulite blocks have been recently discovered in the Anzishan area, Mianxian County, Shaanxi Province, in the central segment of the Mianxian-Lueyang suture zone. Sm-Nd isochron and 40Ar/39Ar ages of mineral samples of granulites from this area are reported in the note. The granulite mineral samples give a Sm-Nd isochron age of t=(206 ( 55) Ma (2(), with INd = 0.51302(7(2() and MSWD = 1.6, and a biotite 40Ar/39Ar plateau age of (199.7(1.7) Ma (2(). The formation and uplift of the granulites were related to subduction of the Yangtze block beneath the South Qinling microcontinent and their collision and the final amalgamation of the Yangtze and Sino-Korean craton blocks in the Indosinian, and their age is consistent with or close to those of the Dabie ultrahigh-pressure and high-pressure metamorphic rocks, so have great tectonic significance.

  18. A study of uranium series disequilibrium in core profiles and mineral separates from the samples of Lac du Bonnet granite from the URL site, Pinawa, Manitoba, Canada

    International Nuclear Information System (INIS)

    Uranium series disequilibrium measurements of actinide activities and activity ratios have been used to study the geochemical history of Lac du Bonnet granite, from the URL site, Pinawa, Canada. Measurements on core profiles between fractured surfaces and the parent rock show that the granite underwent high temperature events several million years ago, followed by more recent low temperature events within the last million years. The main locations for the rock/water interaction and exchange of actinides are the fracture surfaces. The results of similar measurements on separated mineral phases show that the 'soft' minerals such as biotite and feldspar are more vulnerable to weathering than the 'hard' accessory minerals such as zircon. (author)

  19. The biodegradation of layered silicates under the influence of cyanobacterial-actinomycetes associations (United States)

    Ivanova, Ekaterina


    The weathering of sheet silicates is well known to be related to local and global geochemical cycles. Content and composition of clay minerals in soil determine the sorption properties of the soil horizons, water-holding capacity of the soil, stickiness, plasticity, etc. Microorganisms have a diverse range of mechanisms of minerals' structure transformation (acid- and alkali formation, biosorption, complexing, etc). One of the methods is an ability of exopolysaccharide-formation, in particular the formation of mucus, common to many bacteria, including cyanobacteria. Mucous covers cyanobacteria are the specific econiches for other bacteria, including actinomycetes. The objective was to analyze the structural changes of clay minerals under the influence of the cyanobacterial-actinomycetes associative growth. The objects of the study were: 1) the experimental symbiotic association, consisting of free-living heterocyst-formative cyanobacterium Anabaena variabilis Kutz. ATCC 294132 and actinomycete Streptomyces cyaneofuscatus FR837630, 2) rock samples obtained from the Museum of the Soil Science Department of the Lomonosov Moscow State University: kaolinite, consisting of kaolin (96%) Al4 (OH) 8 [Si4O10]; mixed with hydromica, chlorite and quartz; vermiculite, consisting of vermiculite (Ca, Mg, ...)*(Mg, Fe)3(OH)2[(Si, Al)4O10]*4H2O and trioctahedral mica (biotite). The mineralogical compositions of the rocks were determined by the universal X-ray Diffractometer Carl Zeiss Yena. The operationg regime was kept constant (30 kv, 40 mA). The cultivation of the association of actinomycete S. cyanoefuscatus and cyanobacterium A. variabilis caused a reduction in the intensity of kaolinite and hydromica reflexes. However, since both (mica and kaolinite) components have a rigid structure, the significant structural transformation of the minerals was not revealed. Another pattern was observed in the experiment, where the rock sample of vermiculite was used as the mineral

  20. Intrusive rocks of the Holden and Lucerne quadrangles, Washington; the relation of depth zones, composition, textures, and emplacement of plutons (United States)

    Cater, Fred W.


    The core of the northern Cascade Range in Washington consists of Precambrian and upper Paleozoic metamorphic rocks cut by numerous plutons, ranging in age from early Triassic to Miocene. The older plutons have been eroded to catazonal depths, whereas subvolcanic rocks are exposed in the youngest plutons. The Holden and Lucerne quadrangles span a -sizeable and representative part of this core. The oldest of the formations mapped in these quadrangles is the Swakane Biotite Gneiss, which was shown on the quadrangle maps as Cretaceous and older in age. The Swakane has yielded a middle Paleozoic metamorphic age, and also contains evidence of zircon inherited from some parent material more than 1,650 m.y. old. In this report, the Swakane is assigned an early Paleozoic or older age. It consists mostly of biotite gneiss, but interlayered with it are scattered layers and lenses of hornblende schist and gneiss, clinozoisite-epidote gneiss, and quartzite. Thickness of the Swakane is many thousands of meters, and the base is not exposed. The biotite gneiss is probably derived from a pile of siliceous volcanic rocks containing scattered sedimentary beds and basalt flows. Overlying the Swakane is a thick sequence of eugeosynclinal upper Paleozoic rocks metamorphosed to amphibolite grade. The sequence includes quartzite and thin layers of marble, hornblende schist and gneiss, graphitic schist, and smaller amounts of schist and gneiss of widely varying compositions. The layers have been tightly and complexly folded, and, in places, probably had been thrust over the overlying Swakane prior to metamorphism. Youngest of the supracrustal rocks in the area are shale, arkosic sandstone, and conglomerate of the Paleocene Swauk Formation. These rocks are preserved in the Chiwaukum graben, a major structural element of the region. Of uncertain age, but possibly as old as any of the intrusive rocks in the area, are small masses of ultramafic rocks, now almost completely altered to

  1. Experimental constraints on the relative stabilities of the two systems monazite-(Ce) - allanite-(Ce) - fluorapatite and xenotime-(Y) - (Y,HREE)-rich epidote - (Y,HREE)-rich fluorapatite, in high Ca and Na-Ca environments under P-T conditions of 200-1000 MPa and 450-750 °C (United States)

    Budzyń, Bartosz; Harlov, Daniel E.; Kozub-Budzyń, Gabriela A.; Majka, Jarosław


    The relative stabilities of phases within the two systems monazite-(Ce) - fluorapatite - allanite-(Ce) and xenotime-(Y) - (Y,HREE)-rich fluorapatite - (Y,HREE)-rich epidote have been tested experimentally as a function of pressure and temperature in systems roughly replicating granitic to pelitic composition with high and moderate bulk CaO/Na2O ratios over a wide range of P-T conditions from 200 to 1000 MPa and 450 to 750 °C via four sets of experiments. These included (1) monazite-(Ce), labradorite, sanidine, biotite, muscovite, SiO2, CaF2, and 2 M Ca(OH)2; (2) monazite-(Ce), albite, sanidine, biotite, muscovite, SiO2, CaF2, Na2Si2O5, and H2O; (3) xenotime-(Y), labradorite, sanidine, biotite, muscovite, garnet, SiO2, CaF2, and 2 M Ca(OH)2; and (4) xenotime-(Y), albite, sanidine, biotite, muscovite, garnet, SiO2, CaF2, Na2Si2O5, and H2O. Monazite-(Ce) breakdown was documented in experimental sets (1) and (2). In experimental set (1), the Ca high activity (estimated bulk CaO/Na2O ratio of 13.3) promoted the formation of REE-rich epidote, allanite-(Ce), REE-rich fluorapatite, and fluorcalciobritholite at the expense of monazite-(Ce). In contrast, a bulk CaO/Na2O ratio of ~1.0 in runs in set (2) prevented the formation of REE-rich epidote and allanite-(Ce). The reacted monazite-(Ce) was partially replaced by REE-rich fluorapatite-fluorcalciobritholite in all runs, REE-rich steacyite in experiments at 450 °C, 200-1000 MPa, and 550 °C, 200-600 MPa, and minor cheralite in runs at 650-750 °C, 200-1000 MPa. The experimental results support previous natural observations and thermodynamic modeling of phase equilibria, which demonstrate that an increased CaO bulk content expands the stability field of allanite-(Ce) relative to monazite-(Ce) at higher temperatures indicating that the relative stabilities of monazite-(Ce) and allanite-(Ce) depend on the bulk CaO/Na2O ratio. The experiments also provide new insights into the re-equilibration of monazite-(Ce) via fluid

  2. Correlation of upper Llandovery–lower Wenlock bentonites in the När (Gotland, Sweden and Ventspils (Latvia drill cores: role of volcanic ash clouds and shelf sea currents in determining areal distribution of bentonite

    Directory of Open Access Journals (Sweden)

    Tarmo Kiipli


    Full Text Available Study of volcanic ash beds using biostratigraphy, sanidine composition and immobile elements within bentonites has manifested several well-established and some provisional correlations between Gotland and East Baltic sections. Energy dispersive X-ray fluorescence microanalysis of phenocrysts has revealed bentonites containing Mg-rich or Fe-rich biotite. Sanidine phenocrysts contain, in addition to a major Na and K component, often a few per cent of Ca and Ba. On the basis of new correlations the mapping of the distribution areas of bentonites has been extended from the East Baltic to Gotland. The bentonite distribution can be separated into two parts in North Latvia–South Estonia, indicating the existence of shelf sea currents in the Baltic Silurian Basin.

  3. Tephra records from abyssal sediments off western Sumatra in recent 135 ka:evidence from Core IR-GC1

    Institute of Scientific and Technical Information of China (English)

    QIU Zhongyan; HAN Xiqiu; JIN Xianglong; WANG Yejian; ZHU Jihao


    Three volcanic ash layers were identified in a deep-sea Core IR-GC1 from the north-eastern Indian Ocean, adjacent to western Indonesian arc. They were dominated by glass shards with minor mineral crystals, such as plagioclase, biotite, and hornblende. According to the morphology and major element compositions of the representative glass shards, combined with theδ18O-based age, it is suggested that ash Layer A is cor-related to the youngest Toba tuff (YTT), Layer B is supposed to be associated with a new eruption of Toba caldera in an age of 98 to 100 ka. Ash Layer C is different the geochemistry characteristics than those of Layer A and Layer B, suggesting that Layer C was not originated from Toba but registered another volcanic erup-tion event.

  4. Microstructures, deformation mechanisms and seismic properties of a Palaeoproterozoic shear zone: The Mertz shear zone, East-Antarctica (United States)

    Lamarque, Gaëlle; Bascou, Jérôme; Maurice, Claire; Cottin, Jean-Yves; Riel, Nicolas; Ménot, René-Pierre


    The Mertz shear zone (MSZ) is a lithospheric scale structure that recorded mid-crustal deformation during the 1.7 Ga orogeny. We performed a microstructural and crystallographic preferred orientation (CPO) study of samples from both mylonites and tectonic boudins that constitute relics of the Terre Adélie Craton (TAC). The deformation is highly accommodated in the MSZ by anastomosed shear bands, which become more scattered elsewhere in the TAC. Most of the MSZ amphibolite-facies mylonites display similar CPO, thermal conditions, intensity of deformation and dominant shear strain. Preserved granulite-facies boudins show both coaxial and non-coaxial strains related to the previous 2.45 Ga event. This former deformation is more penetrative and less localized and shows a deformation gradient, later affected by a major phase of recrystallization during retrogression at 2.42 Ga. Both MSZ samples and granulite-facies tectonic boudins present microstructures that reflect a variety of deformation mechanisms associated with the rock creep that induce contrasted CPO of minerals (quartz, feldspar, biotite, amphibole and orthopyroxene). In particular, we highlight the development of an "uncommon" CPO in orthopyroxene from weakly deformed samples characterized by (010)-planes oriented parallel to the foliation plane, [001]-axes parallel to the stretching lineation and clustering of [100]-axes near the Y structural direction. Lastly, we computed the seismic properties of the amphibolite and granulite facies rocks in the MSZ area in order to evaluate the contribution of the deformed intermediate and lower continental crust to the seismic anisotropy recorded above the MSZ. Our results reveal that (i) the low content of amphibole and biotite in the rock formations of the TAC, and (ii) the interactions between the CPO of the different mineralogical phases, generate a seismically isotropic crust. Thus, the seismic anisotropy recorded by the seismic stations of the TAC, including the

  5. Mineral deformation and subglacial processes on ice-bedrock interface of Hailuogou Glacier

    Institute of Scientific and Technical Information of China (English)

    LIU GengNian; CHEN YiXin; ZHANG Yue; FU HaiRong


    Hailuogou Glacier is located in a warm and humid maritime environment. It is large and moves very fast.The bottom of the glacier slides intensively and the temperature at the bottom approaches the pressure melting point. Therefore,there are abundant melting water and debris which act as effective "grinding tools"for glacial abrasion. Polarizing microscope is used to observe the mineral deformation characteristics on the ice-bedrock interface. It is found that feldspar,quartz,hornblende and biotite are exposed to deformation,fracture and chemical alteration to various extents. Bending deformation is common for biotite,due to their lattice characteristics,and the bending orientations are mostly the same as the glacier flow. Bending deformation also occurs in a few hornblendes. High-angle tension fracture and low-angle shear fracture are common for quartz and feldspar,some of them are totally crushed (mylonizations) due to their rigidity. Thus,all the abrasion,quarrying,subglacial water action and subglacial dissolution processes at the bottom of the glacier are verified at the micro-scale level.Mineral deformation and fracture are the basic subglacial erosion mechanisms. The abrasion thickness is 30-90 μm for each time and the average is 50 μm. Most of the debris are silt produced by glacial abrasion. The extent of mineral deformation and fracture decreases drastically downwards beneath the bedrock surface. The estimated erosion rate is about 2.2-11.4 mm/a,which is similar to that of other maritime alpine glaciers,smaller than that of large-scale piedmont glaciers In Alaska (10-30 mm/a),and larger than that of continental glaciers (0.1-1.0 mm/a). The type and size of a glacier are the main factors that influence its erosion rate.

  6. Increasing potassium (K release from K-containing minerals in the presence of insoluble phosphate by bacteria

    Directory of Open Access Journals (Sweden)

    Mohammad Reza Sarikhani


    Full Text Available Introduction: Phosphorus and potassium are major essential macronutrients for biological growth and development. Application of soil microorganisms is one approach to enhance crop growth. Some bacteria are efficient in releasing K and solubilizing P from mineral sources but their behavior was not studied more in presence together. Materials and methods: In this study the ability of seven bacterial strains, including Pseudomonas putida P13, P. putida Tabriz, P. fluorescens Tabriz, P. fluorescens Chao, Pantoea agglomerans P5, Azotobacter sp. and Bacillus megaterium JK3 to release mineral K from muscovite and biotite with application of insoluble (Ca3(PO42 or soluble (Na2HPO4 P-sources was investigated. Nutrient Broth was used to prepare an overnight culture of bacteria to inoculate in Aleksandrov medium, which was used to study the dissolution of silicate minerals. It should be mentioned that Aleksandrov medium was used to determine the amount of released P from tricalcium phosphate (TCP while muscovite was added to the medium as a sole source of potassium. Concentration of P was determined spectrophotometrically by ammonium-vanadate-molybdate method and K was determined by flame photometry. Results: The insoluble P-source led to a significantly increased released K into assay medium (66%, and the net release of K from the biotite was significantly enhanced. Among bacterial strains, the highest mean of released K was observed with P. putida P13 which released more K (27% than the control. The amounts of released K from micas in the presence of insoluble and soluble phosphate by P. putida P13 were 8.25 and 4.87 mg/g, respectively. Discussion and conclusion: Application of insoluble phosphate could increase K release from mica minerals. The enhanced releasing of mineral K might be attributed to the release of organic acids from the bacteria, a mechanism which plays a pivotal role in solubilizing phosphate from inorganic source of phosphate.

  7. Petrogenesis of Paleocene-Eocene porphyry deposit-related granitic rocks in the Yaguila-Sharang ore district, central Lhasa terrane, Tibet (United States)

    Zhao, Junxing; Li, Guangming; Evans, Noreen J.; Qin, Kezhang; Li, Jinxiang; Zhang, Xia'nan


    The Paleocene-Eocene ore deposits in the Gangdese Metallogenic Belt, Tibet, are thought to have been formed during the main period of India-Asia continental collision. This paper reports the whole-rock major element, trace element, and Sr-Nd-Hf isotopic compositions and zircon trace element contents of volcanic and intrusive rocks from the Paleocene Yaguila skarn Pb-Zn-Ag deposit and adjacent Eocene Sharang porphyry Mo deposit in the central Lhasa terrane, Tibet. Geochemical signatures and Nd-Hf isotopic compositions indicate that the Yaguila Cretaceous rhyolitic rocks were formed by the melting of ancient continental crust, whereas the Paleocene causative granite porphyry may have resulted from the interaction between mantle-derived and crustal-derived materials when continental collision was initiated. The dramatic increase of εNd(t) values between emplacement of the granite porphyry and later porphyritic biotite granite suggests a greater involvement of mantle materials during the crystallization of the barren biotite granite stock. The post-ore Miocene granodiorite porphyry has a similar geochemical signature to the Sharang Miocene dykes, suggesting they were both generated from melting of enriched lithospheric mantle. Nd-Hf mixing calculations indicate an increasing contribution of mantle materials in Paleocene to Eocene intrusions, consistent with the regional tectonic model of Neo-Tethyan oceanic slab roll-back and break-off. Zircons from both the Yaguila and Sharang ore-related porphyries have higher Ce anomalies than those from the barren granitoids, suggesting that Mo mineralization was closely related to highly oxidized and differentiated magma. The fertile intrusions in the Yaguila-Sharang district contain EuN/EuN∗ values from 0.3 to 0.6, higher than the non-mineralized intrusions. The processes of early crystallization of plagioclase and/or SO2-degassing from underlying magma can explain the observed negative Eu anomalies in zircon.

  8. Magmatic and tectonic evolution of the Ladakh Block from field studies (United States)

    Raz, U.; Honegger, K.


    The Ladakh Block is in an intermediate position between the Indian plate in the south and the Karakorum-Tibetan plate in the north. To the west it is separated from the Kohistan Arc by the Nanga Parbat Syntaxis, to the east it is cut off from the Lhasa Block by the Gartok-Nubra Fault. Present data, together with previously published results, show, that the Ladakh Block consists of an island arc in the south and a calc-alkaline batholith in the north with remnants of a continental crust. Migmatitic gneisses and metasedimentary sequences, such as quartzites and metapelites, interbedded with basaltic volcanics and overlain by thick platform carbonates were found as evidence of a continental crust. Remnants of megafossils ( Megalodon and Lithiotis) within the high-grade metamorphic marbles indicate a probable age of Late Triassic to Early Jurassic. These sediments were intruded by a faintly layered hornblende-gabbro, which preceded the calc-alkaline magmatic episode. Gabbro and gabbronorites are found as roof pendants and large inclusions within diorites and granodiorites. The major part of the batholith consists of granodiorite and biotite-granite plutons, ranging from Late Cretaceous to Tertiary. Associated with the intrusives are volcanic rocks with trachyandesite to alkalibasalt and basalt-andesite to rhyolite compositions. Garnet-bearing leucogranites succeeded the emplacement of the major plutons. The magmatic stage ended, finally, by intense fracturing and injections of NE-SW striking andesitic dykes. The southernmost unit of the Ladakh Block is formed by oceanic crust with serpentinized peridotite and hornblende-gabbro and is covered by volcanics of an island-arc type (Dras volcanics). These units are intruded by gabbronorite, as well as Middle and Upper Cretaceous granodiorite and coarse-grained biotite-granite. In a plate tectonic view the Ladakh Block represents a transitional sector between the pure island arc of Kohistan in the west and the Andean type

  9. Leucogranites of the Teton Range, Wyoming: A record of Archean collisional orogeny (United States)

    Frost, Carol D.; Swapp, Susan M.; Frost, B. Ronald; Finley-Blasi, Lee; Fitz-Gerald, D. Braden


    Leucogranitic rocks formed by crustal melting are a prominent feature of collisional orogens of all ages. This study describes leucogranitic gneisses associated with an Archean collisional orogeny preserved in the Teton Range of northwestern Wyoming, USA. These leucogneisses formed at 2.68 Ga, and initial Nd isotopic compositions suggest they are derived from relatively juvenile sources. Two distinct groups of leucogneisses, both trondhjemitic, are identified on the basis of field relations, petrology, and geochemistry. The Webb Canyon gneiss forms large, sheet-like bodies of hornblende biotite trondhjemite and granodiorite. This gneiss is silica-rich (SiO2 = 70-80%), strongly ferroan, comparatively low in alumina, and is characterized by high Zr and Y, low Sr, and high REE contents that define "seagull"-shaped REE patterns. The Bitch Creek gneiss forms small sills, dikes, and plutons of biotite trondhjemite. Silica, Zr, Y, and REE are lower and alumina and Sr are higher than in the Webb Canyon gneiss. These differences reflect different melting conditions: the Webb Canyon gneiss formed by dehydration melting in which amphibole and quartz breaks down, accounting for the low alumina, high FeO, high silica content and observed trace element characteristics. The Bitch Creek gneiss formed by H2O-excess melting in which plagioclase breaks down leaving an amphibole-rich restite, producing magmas higher in alumina and Sr and lower in FeO and HREE. Both melt mechanisms are expected in collisional environments: dehydration melting accompanies gravitational collapse and tectonic extension of dramatically thickened crust, and water-excess melting may occur when collision places a relatively cool, hydrous lower plate beneath a hotter upper plate. The Archean leucogranitic gneisses of the Teton Range are calcic trondhjemites and granodiorites whereas younger collisional leucogranites typically are true granites. The difference in leucogranite composition reflects the

  10. Cretaceous volcanic-intrusive magmatism in western Guangdong and its geological significance

    Institute of Scientific and Technical Information of China (English)

    GENG; Hongyan; XU; Xisheng; S.Y.O'Reilly; ZHAO; Ming; SUN; Tao


    Systematic zircon LA-ICPMS U-Pb dating reveals that Cretaceous volcanic-intrusive activities developed in western Guangdong. Representative volcanic rocks, i.e. Maanshan and Zhougongding rhyodacites, have zircon U-Pb isotopic ages of 100±1 Ma, and the intrusive ones including the Deqing monzonitic granite body and the Xinghua granodiorite body in the Shidong complex, as well as the Tiaocun granodiorite body in the Guangping complex yield ages of 99±2 Ma, ca.100 Ma, and 104±3 Ma respectively. The biotite-granites of the Shidong complex main body (461±35 Ma) and that of the Guangping complex (444±6 Ma) are Caledonian. In spite of the big time interval between Cretaceous volcanic-intrusive magmatisms and Caledonian intrusive ones, both of them are characterized by enrichment in Rb, Th, Ce, Zr, Hf, Sm, depletion in Ba, Nb, Ta, P, Ti, Eu, and weakly REE tetrad effect. Eu negative anomalies are: Cretaceous volcanic rocks (Eu/Eu*=0.74), Cretaceous intrusive rocks (Eu/Eu*=0.35-0.58), Caledonian biotite granites (Eu/Eu*=0.31-0.34). Studies of Sr-Nd isotope data show that all these igneous rocks have high initial 87Sr/86Sr ratios (0.7105-0.7518), and low εNd(t) values (-7.23--11.39) with their Nd two-stage model ages ranging from 1.6-2.0 Ga, which suggest that they all derived from the Proterozoic crustal basement of southeast China.The occurrence of Cretaceous volcanic-intrusive magmatisms in western Guangdong is related with the important lithospheric extension event in southeast China (including Nanling region) at ca. 100 Ma.The "volcanic line" defined by the large scale Mesozoic intermediate-acidic volcanic magmatisms in southeast China may further extend to the southwest margin of Nanling region.

  11. Structural and lithologic relationships in the Raleigh metamorphic belt near Lake Gaston, Virginia and North Carolina

    Energy Technology Data Exchange (ETDEWEB)

    Sacks, P.E.; Horton, J.W. Jr. (Geological Survey, Reston, VA (United States))


    Preliminary results of mapping along the NC-VA State line eastward from the Buggs Is. granite about 35 km to the Hollister fault zone yield new information about structural and lithologic relationships in the Raleigh metamorphic belt. The layered rocks are predominantly two-mica schist and sillimanite-mica schist interlayered with lesser amounts of muscovite-biotite-quartz-plagioclase paragneiss and hornblende-biotite gneiss. The overall rock assemblage here differs from those along strike near Goochland, VA, and near Raleigh, NC, and is reminiscent of an accretionary complex. Bodies of foliated to massive two-mica granite are abundant and commonly contain garnet. One body, the Wise pluton, contains a N--NW-striking, steeply dipping foliation, but the intrusive contact of the granite with the metamorphic rocks is discordant. The most prominent regional foliation, parallel to transposed compositional layering, is axial planar to relict, reclined, isoclinal outcrop-scale folds. This foliation is folded at both outcrop and map scale by open folds plunging NW and SW. Some foliated, two-mica granite sheets are warped by the open folds; other bodies of similar granite cut across these folds. Sillimanite needles are locally aligned with the hinges of some of the open folds, an indication that sillimanite-muscovite-grade metamorphism was associated with this folding event. The two-mica granites resemble other late Paleozoic granites in the region. If these granites prove to be late Paleozoic (Alleghanian), then the deformation and metamorphism that produced sillimanite along the hingelines also must be Alleghanian. Relatively younger, NW- and SE-plunging crenulations and chevron folds are associated with a crenulation cleavage that dips steeply NE or SW. Sillimanite needles are folded by these crenulations. Crenulation cleavage and related folds may have developed in response to transpression of these rocks between the dextral Lake Gordon and Hollister mylonite zones.

  12. Can the Metamorphic Basement of Northwestern Guatemala be Correlated with the Chuacús Complex? (United States)

    Cacao, N.; Martens, U.


    The Chuacús complex constitutes a northward concave metamorphic belt that stretches ca. 150 km south of the Cuilco-Chixoy-Polochic (CCP) fault system in central and central-eastern Guatemala. It represents the basement of the southern edge of the Maya block, being well exposed in the sierra de Chuacús and the sierra de Las Minas. It is composed of high-Al metapelites, amphibolites, quartzofeldspathic gneisses, and migmatites. In central Guatemala the Chuacús complex contains ubiquitous epidote-amphibolite mineral associations, and local relics of eclogite reveal a previous high-pressure metamorphic event. North of the CCP, in the Sierra de Los Cuchumatanes area of western Guatemala, metamorphic rocks have been considered the equivalent of the Chuacús complex and hence been given the name Western Chuacús group, These rocks, which were intruded by granitic rocks and later mylonitized, include chloritic schist and gneiss, biotite-garnet schist, migmatites, and amphibolites. No eclogitic relics have been found within metamorphic rocks in northwestern Guatemala. Petrographic analyses of garnet-biotite schist reveal abundant retrogression and the formation of abundant zeolite-bearing veins associated with intrusion. Although metamorphic conditions in the greenschist and amphibolite facies are similar to those in the sierra de Chuacús, the association with deformed intrusive granites is unique for western Guatemala. Hence a correlation with metasediments intruded by the Rabinal granite in the San Gabriel area of Baja Verapaz seems more feasible than a correlation with the Chuacús complex. This idea is supported by reintegration of the Cenozoic left-lateral displacement along the CCP, which would place the metamorphic basement of western Guatemala north of Baja Verapaz, adjacent to metasediments intruded by granites in the San Gabriel-Rabinal area.

  13. Dolomitic marbles and associated calc-silicates, Tandilia belt, Argentina: Geothermobarometry, metamorphic evolution, and P- T path (United States)

    Delpino, Sergio H.; Dristas, Jorge A.


    The metamorphic evolution of dolomitic marbles and associated calc-silicate rocks from Punta Tota (NE Tandilia belt, Buenos Aires province, Argentina) has been evaluated through petrographic, geothermobarometric, and fluid inclusion studies. Thin beds of dolomitic marble are intercalated in amphibolites and constitute the upper part of a stratified basement sequence, which starts at the base with garnet migmatites showing a great abundance of pegmatitic segregates, overlain by biotite-garnet gneisses. Peak metamorphic conditions are estimated at 750-800 °C and 5-6 kb, followed by near isobaric cooling to about 500-450 °C and 5.5-6.5 kb. Anhydrous progressive metamorphic assemblages in both marbles (Fo + Cal + Dol + Cpx + Spl) and adjacent calc-silicate rocks (Cpx + An + Cal + Qtz) strongly retrogressed to hydrous minerals (Tr, Tlc, Grs, Czo, Srp) with decreasing temperatures and increasing water activities. The intense rehydration of the rocks relates to the emplacement of volatile-rich pegmatitic bodies (Qtz + Pl + Kfs + Bt + Grt), which also resulted in the crystallization of clinochlore + phlogopite in the marble and biotite + muscovite in the adjacent calc-silicate rocks. Metamorphic reactions based on textural relations and evaluated on a suitable petrogenetic grid, combined with geothermobarometric results and fluid inclusion isochores, indicate a metamorphic evolution along a counterclockwise P- T path. Two probable geotectonic settings for the determined P- T trajectory are proposed: (1) thinning of the crust and overlying supracrustal basin in an ensialic intraplate tectonic setting and (2) development of a marginal back-arc basin, associated with an oceanic-continental convergent plate margin. In both models, the initial extensional regime is followed by a compressional stage, with overthickening of the basement and supracrustal rocks, during the climax of the Transamazonian cycle at approximately 1800 Ma ago. Continuous convergence and blockage of

  14. Comparison of inorganic ion exchange materials for removing cesium, strontium, and transuranic elements from K-basin water

    Energy Technology Data Exchange (ETDEWEB)

    Brown, G.N.; Bontha, J.R.; Carson, K.J.; Elovich, R.J.; DesChane, J.R.


    The work presented in this report was conducted by the Pacific Northwest National Laboratory (PNNL) under the Efficient Separations and Crosscutting Program (ESP), Office of Science and Technology, U.S. Department of Energy (DOE). The objective of this work was to investigate radionuclide uptake by several newly produced ion exchange materials under actual waste conditions, and to compare the performance of those materials with that of commercially available ion exchangers. The equilibrium uptake data presented in this report are useful for identifying potential materials that are capable of removing cesium and strontium from 105-KE Basin water. The data show the relative selectivities of the ion exchange materials under similar operating conditions. Additional flow studies are needed to predict material capacities and to develop complete ion exchange process flow sheets. The materials investigated in this study include commercially available ion exchangers such as IONSIV{reg_sign} IE-911 (manufactured by UOP), clinoptilolite (a naturally occurring zeolite), and materials produced on an experimental basis by AlliedSignal (biotites and nonatitanates), 3M (hexacyanoferrates), Selion Technologies, Inc. (hexacyanoferrates and titanates), and Texas A&M University (pharmacosiderites, biotites, and nonatitanates). In all, the performance of 14 ion exchange materials was evaluated at two solution-to-exchanger mass ratios (i.e., 10{sup 4} and 10{sup 5}) using actual 105-KE Basin water. Evaluation consisted of determining cesium and strontium batch distribution coefficients, loading, and decontamination factors. Actual 105-KE Basin water was obtained from a sample collected during the sludge dissolution work conducted by PNNL in FY 1996. This sample was taken from the bottom of the basin and contained significantly higher concentrations of the radioactive constituents than do samples taken from the top of the basin.

  15. Uranium in the Copper King Mine, Black Hawk No. 1 Claim, Larimer County, Colorado (United States)

    Granger, Harry Clifford; King, Robert Ugstad


    Radioactive rock was discovered on the dump of the Copper King mine, sec. 8, T. 10 N., R. 72 W., Larirrier County, Colo., in the summer of 1949. The mine had been prospected intermittently for copper and zinc since 1,916, but there is no record that ore was produced. The country rock is pre-Cambrian granite containing many schist inclusions and narrow pegmatite dikes. Pitchblende disseminated in chlorite and sulfides was deposited in an obscure vein system during an intermediate stage of mineralization. This stage was preceded by biotitic alteration of amphiboles and sulfide deposition. The latest stage of mineralization is represented-by the limonitic dense quartz vein followed during mining. The uranium-bearing vein is about 2-3 feet wide and the dense quartz vein is less than 6 inches wide. Both veins are bordered by 1-3 feet of biotite- and sulfide-bearing granite and arriphibole schist. The uranium content of 26 samples taken in the mine and on the dump ranges from 0.002 to 1.40 percent. These samples contained as much as 2.97 percent copper and 5.96 percent zinc. The general outlook for further prospecting near the Copper King shaft is not favorable, because much of the 'immediately surrounding area has been thoroughly investigated without finding abnormal radioactivity. The most favorable environment for concentration of uranium minerals appears to have been in or near schist inclusions in granite, and further exploration in nearby prospects may result in the discovery of other uranium-bearing deposits. In the Copper King mine, additional exploration would aid in determining the extent of the uranium-bearing material.

  16. Monzonitoid magmatism of the copper-porphyritic Lazurnoe deposit (South Primor'e): U-Pb and K-Ar geochronology and peculiarities of ore-bearing magma genesis by the data of isotopic-geochemical studies (United States)

    Sakhno, V. G.; Kovalenko, S. V.; Alenicheva, A. A.


    Magmatic rocks from the copper-porphyritic Lazurnoe deposit (Central Primor'e) have been studied. It has been found that rocks from the Lazurnyi massif are referred to gabbro-monzodiorites, monzodiorites, and monzo-granodiorites formed during two magmatic phases of different ages. The earlier phase is represented by gabbro-monzodiorites and diorites of the North Stock, and the later one, by gabbro-monzodiorites and monzo-grano-diorites of the South Stock. On the basis of isotopic dating by the U-Pb (SHRIMP) method for zircon and by the K-Ar method for hornblendes and biotites, the age of magmatic rocks is determined at 110 ± 4 for the earlier phase and at 103.5 ± 1.5 for the later one. Examination of the isotopic composition for Nd, Sr, Pb, Hf, δ18O, and REE spectra has shown that melts of the first phase are contaminated with crustal rocks and they are typical for a high degree of secondary alterations. Potassiumfeldspar, biotite, propylitic alterations, and sulfidization are manifested in these rocks. The rocks of the later stage of magmatism are characteristic for a primitive composition of isotopes and the absence of secondary alterations. They carry the features of adakite specifics that allows us to consider them derivatives of mantle generation under high fluid pressure. The intrusion of fluid-saturated melts of the second phase into the magmatic source of the first phase caused both an alteration pattern of rocks and copper-porphyritic mineralization. Isotopes of sulfur and oxygen allow us to consider the ore component to be of magmatic origin.

  17. Preliminary Geochemical and Petrologic Assessment of the Fanney Rhyolite and the Bloodgood Canyon and Apache Springs tuffs, Mogollon-Datil Volcanic Field, New Mexico (United States)

    Salings, E. E.; Rentz, S. P.; Michelfelder, G.; Sikes, E. R.


    Continental arc volcanoes represent a dramatic expression of a significant and fundamental phenomena in global tectonics: the subduction of an oceanic plate beneath a more buoyant continental plate. The subduction of an oceanic plate results in recycling of crustal material into the convecting mantle, partial melting, and primary basalt production. Moreover, during passage through thick continental crust, subduction zone magmas may substantially differentiate and melt crustal rocks giving rise to the great diversity of igneous lithologies characteristic of earth. These are important processes that must be understood in detail in order to interpret the long-term evolution of the earth and continental crust. Here we present variations in the isotopic and trace element composition of volcanic rocks from Bloodgood Canyon and Apache Springs tuffs, and the Fanney Rhyolite located in the western Mogollon-Datil Volcanic Field (MDVF). The project will address several questions. First, are the Bloodgood and Apache Springs tuffs and Fanney Rhyolite petrogenically related, and are these rhyolites expressions of a continental arc ignimbrite flare-up? Second, what petrogenic processes affected differentiation and where is the magma sourced? Finally, to what extent do these units represent a manifestation of the MDVF and the transition from arc magmatism to rifting? The Bloodgood Canyon is a crystal-rich rhyolite tuff containing quartz>k-feldspar>plagioclase>biotite, and pumice and lithic fragments. Rb ranges from 230-330ppm, Sr from 14-83ppm, and 87Sr/86Srm from 0.71619-0.72477.The Apache Springs Tuff is a rhyolite tuff containing quartz>k-feldspar>plagioclase>biotite, and lithics. Rb (228-233ppm) and 87Sr/86Srm (0.71025-0.71056) are restricted, while Sr (105-399ppm) is more variable in composition. The Fanney Creek is a massive rhyolite lava with flow banding and contains quartz phenocryst clusters and k-feldspars. Currently, no data exists for the Apache Springs Tuff.

  18. Paleoproterozoic, High-Metamorphic, Metasedimentary Units of Siberian Craton

    Institute of Scientific and Technical Information of China (English)



    Sensitive, high-resointion ion microprobe zircon U-Pb ages of Paleoproterozoic, high-grade,metasedimentary rocks from the south-western part of the Siberian Craton are reported. Early Precambrian, high-grade complexes, including garnet-biotite, hypersthene-biotite, and cordierite-bearing gneisses compose the Irkut terrane of the Sharyzhalgay Uplift. Protoliths of studied gneisses correspond to terrigenous sediments, ranging from greywacke to shale. The paragneiss model Nd ages of 2.4-3.1 Ga indicate Archean-to-Paleoproterozoic source provinces. Zircons from gneisses show core-rim textures in cathodoluminescence (CL) image. Round or irregular shaped cores indicate detrital origin. Structureless rims with low Th/U are metamorphic in origin. The three age groups of detrital cores are: ≥2.7, -2.3, and 1.95-2 Ga. The ages of metamorphic rims range from 1.86 to 1.85 Ga;therefore, the sediments were deposited between 1.95 and 1.86 Ga and derived from Archean and Paleoproterozoic source rocks. It should be noted that Paleoproterozoic metasedimentary rocks of the Irkut Block are not unique. High-grade metaterrigenons sediments, with model Nd ages ranging from 2.3 to 2.5 Ga, are widely distributed within the AIdan and Anabar Shields of the Siberian Craton. The same situation is observed in the North China Craton, where metasedimentary rocks contain detrital igneous zircon grains with ages ranging from 3 to 2.1 Ga (Wan et al., 2006). All of these sedimentary units were subjected to Late Paleoproterozoic metamorphism. In the Siberian Craton, the Paleoproterozoic sedimentary deposits are possibly marked passive margins of the Early Precambrian crustal blocks, and their high-grade metamorphism was related to the consolidation of the Siberian Craton.

  19. Hydrothermal alterations and O, H, C isotopic characterization of fluids and minerals in uraniferous massif of Saint Sylvestre (France). Extension to other French intragranitic uranium deposits

    International Nuclear Information System (INIS)

    Petrographical, mineralogical, geochemical and stable isotope (18O/16O, D/H, 13C/12C) studies have been performed on the leucogranitic massif of St Sylvestre (Limousin, Massif Central francais), particularly on the different hydrothermal alterations. The oxygen isotope geochemistry of granites confirms the unicity of the different facies and their sialic origin (delta18O whole rocks = +11.0 +- 0.5 per mill), with a major contribution of detritic sediments rich in organic matter and poor in carbonate (delta13C magm. CO2 = -10.6 per mill). Late lamprophyres have a deep-seated origin (delta18O = + 6 per mill). The pervasive chloritization of granitic biotites occurs during the convective circulation of a fluid of meteoric origin, at temperatures around 350-4500C. The chemical composition of chlorite which is buffered by that of biotite and the large 18O-shift of fluid towards high delta values indicate that water-rock ratio was not very high. Chloritization takes place in high permeability zones. In regions where porosity is generally low, fluids are ''canalised'' in localised micro-fissured zones. Very high water/rock ratios lead to the dissolution of quartz, and the formation of the ''feldspathic episyenite'' alteration facies. The isotopic features of this fluid (delta18O approximately - 8 per mill, deltaD approximately - 50 per mill) indicate an elevated altitude. An isotopically similar fluid is responsible for the later ''micaceous episyenite'' alteration facies, found in fractured zones. Mixing of this fluid with a sedimentary fluid (delta18O approximately + 10 per mill, deltaD approximately - 30 per mill, delta13C approximately - 18 per mill) yielded the conditions necessary for the deposit of primary economic ore. Such fluids, sedimentary or metamorphic in origin, have been recognized in most hercynian intragranitic U and Sn-W deposits

  20. Zr, Hf, U, Th and REE-Fertile Lower Proterozoic Potassic Granite from Parts of Andhra Pradesh, South India

    Institute of Scientific and Technical Information of China (English)

    Yamuna SINGH


    The medium- to coarse-grained and porphyritic granitoid of Dharmawaram, Karimnagar district, Andhra Pradesh, south India is a biotite-hornblende granite with notable contents of rare metal (Zr, Hf, Th) and rare earth (including Y) minerals like zircon, thorite, allanite, monazite and xenotime. Chemically, it is metaluminous (average A/C+N+K = 0.95)-type, potassic (ay. 5% K2O) granite, with dominantly sub-alkaline characters. It shows up to 8 times enrichment of rare metals (Zr, Hf, U, Th) and rare earths (including Y, Sc), with reference to their abundances in normal unevolved granite, and hence, fertile for some of these elements. Field, petrological, geochemical and isotopic data of potassic granite (PG) indicate involvement of silica-rich metasedimentary-basic crustal rocks (amphibole-quartzite,amphibolite, hornblende-biotite gneiss, etc.) in its genesis, at a depth range of 30 km. Further, chondrite-normalized REE patterns demonstrate that low-degree partial melting of source rocks is the major controlling factor in the genesis of PG.Mild negative Eu-anomaiy (av. Eu/Eu* = 0.48), plots of Ba-Rb-Sr in the field of anomalous granite and K/Rb ratios (av.239) in the range that is shown by normal unevolved granite together indicate less fractionated nature of the PG. Limited fractionation of metalumination-type, involving hornblende, led to occasional weak alumina saturation. Interestingly,geochemical and petrogenetic features of the studied PG broadly match with those potassic granites which are already known to host anomalously high enrichment of rare metals and rare earths in other parts of Andhra Pradesh and adjoining Kamataka.

  1. Geochemistry of Central Atlantic Magmatic Province (CAMP) sills from deep boreholes in the Amazonas and Solimões basins, Brazil (United States)

    Hatlen Heimdal, Thea; Svensen, Henrik H.; Pereira, Egberto; Planke, Sverre


    The Central Atlantic Magmatic Province (CAMP) is one of the most extensive Large Igneous Provinces (LIPs), and is associated with the breakup of Pangea and the subsequent opening of the central Atlantic Ocean. A large part of the province, including > 1 M km2 basins containing sill intrusions, is located in Brazil but has received limited attention due to the lack of outcrops. We have studied CAMP sills from seven deep boreholes (up to 3100 m deep) in the Amazonas and Solimões basins, northern Brazil. The boreholes contain up to ~ 482 m of sills (18 % of the stratigraphy), with a maximum individual sill thickness of 140 m. The sills were partly emplaced into thick Carboniferous evaporites. The main mineral phases of the sills include plagioclase and pyroxene, with accessory apatite, biotite, ilmenite and quartz. The majority of the sills are low-Ti dolerites (TiO2 < 2 wt.%), with the exception of four samples (with 2.2 - 3.3 wt.% TiO2). The low-Ti rocks range from basalt to basaltic andesite and plot in the tholeiitic field defined within the total alkali versus silica (TAS) classification. C1 chondrite normalized Rare Earth Element (REE) patterns for both Ti-groups show increasing LREE compared to HREE (La/Lu = 2.2 - 4.1) with no major anomalies, and attest to a relatively evolved nature (La = 17-65 ppm). Primitive mantle normalized patterns for low-Ti rocks show negative anomalies for Nb, Ta, P and Ti and positive for K, whereas the high-Ti rocks show generally opposite anomalies. Late stage patches in the dolerites contain apatite, quartz and Cl-bearing biotite, suggesting the presence of halogens that may partly derive from the host sedimentary rocks.

  2. SHRIMP U-Pb age and high temperature conditions of the collisional metamorphism in the Várzea do Capivarita Complex: Implications for the origin of Pelotas Batholith, Dom Feliciano Belt, southern Brazil (United States)

    Philipp, Ruy Paulo; Bom, Francisco Molina; Pimentel, Márcio Martins; Junges, Sérgio Luiz; Zvirtes, Gustavo


    The Várzea do Capivarita Complex is composed of pelitic gneisses with subordinate calc-silicate rock, marble and rare quartzite. It is part of the neoproterozoic Dom Feliciano Belt, in southern Brazil. The gneisses are associated to veins and tabular leucogranite bodies, which are the product of anatexis of the pelitic gneiss. The paragneisses of the Várzea do Capivarita Complex are tectonically juxtaposed to orthogneisses of the Arroio dos Ratos Complex. This complex is exposed as megaxenoliths in granites of the Encruzilhada do Sul Suite and as smaller fragments in the Quitéria and Cordilheira Granites, all part of the Pelotas Batholith. The metamorphic foliation is oriented to N30°W, with dips between 35 and 55° to the SW and mineral lineation is suborizontal with rake ranging from 15° to 30° and down dip to NW and SE, suggesting deformation associated with a transpressive system. Based on the paragenesis garnet-cordierite-sillimanite-biotite, metamorphism occurred at 720-820° C and pressure of 8-9 kbar, characterizing it as of intermediate pressure and high temperature series. Zircon grains of one sample of garnet-cordierite-sillimanite-biotite gneiss and one of peraluminous leucogranite was dated by the U-Pb SHRIMP method. The paragneiss metamorphic zircon yielded an age of 619 ± 4.3 Ma interpreted as an age of the main metamorphic event, whereas igneous zircon grains from the leucogranite indicates that magma crystallization took place at 620 ± 6.3 Ma. The main metamorphic foliation (S2) of the paragneiss and the leucogranite magmatic foliation (S0) are parallel to each other, indicating that they were formed during the same event. This suggests that anatexis of the paragneisses of the Várzea do Capivarite Complex generated the peraluminous leucogranites right after the climax of the collisional metamorphism.

  3. Permo-Triassic and Paleoproterozoic metamorphism related to continental collision in Yangpyeong, South Korea (United States)

    Oh, Chang Whan; Imayama, Takeshi; Lee, Seung Yeol; Yi, Sang-Bong; Yi, Keewook; Lee, Byung Choon


    Gneisses and migmatites exposed in the Yangpyeong area in the northern Gyeonggi Massif provide insight into the Paleoproterozoic and Triassic metamorphic events in South Korea. Garnet-biotite gneiss and sillimanite-garnet-biotite gneiss in the western part of the area reveal Paleoproterozoic metamorphism (1888-1871 Ma) at P-T conditions of 760-820 °C and 8-10 kbar and 710-750 °C and 5-7 kbar, respectively. These rocks were overprinted by low-P/T type metamorphism (590-650 °C, 3-4 kbar) during the Triassic (ca. 237 Ma). In contrast, a cordierite-rich migmatite near the post-collisional Triassic igneous complex in the eastern part of the area was strongly metamorphosed during the Triassic (ca. 235 Ma) at 750-790 °C and 7-8 kbar. The similar Triassic ages in the western and eastern areas suggest that low-P/T type metamorphism occurred as a second stage of regional metamorphism, which is characterized by the production of cordierite with an irregularly shaped garnet. The metamorphic grade of the Triassic metamorphism decreases spatially towards the west from granulite facies to amphibolite facies metamorphic conditions, and the Paleoproterozoic metamorphism is well preserved in the western part with low grade Triassic metamorphism. The new discovery of the Triassic metamorphic event in the Yangpyeong area, in addition to the previously reported Triassic post-collision igneous event, supports the idea that the continental collision belt between the North and South China blocks extends from the Hongseong area into the Odesan area through the Yangpyeong area in South Korea.

  4. Petrology and U/Pb geochronology of the Santa Maria Ipalapa region in the southeastern part of the Xolapa Complex, Mexico: Constrains of the metamorphic evolution of the Xolapa Terrane (United States)

    Gutiérrez Aguilar, F.; Victoria Morales, A.; Maldonado, R.


    The Xolapa Complex is a metamorphic-plutonic basement that forms a large belt with more than 600 km length and 50-100 km wide along the Pacific coast of southeastern Mexico. This Complex is constituted by a high grade sequence of meta-sedimentary and meta-igneous rocks, locally migmatisized, and which are intruded by strongly deformed plutonic rocks. Because of their representative characteristics, two samples were analyzed: 1) Para-schist: this rocks present a mineral assemblage composed of biotite, sillimanite, plagioclase, k-feldspar and garnet, and 2) Amphibolite: which are constituted by amphibole, plagioclase, biotite and garnet. The garnet porphydoblasts in the para-schist are subhedral, presents retrograde compositional zoning, with almandine and pyrope rich core (Alm74-75Sps7.-10.1Pyr12.1-12.5Grs3.8-3.9) and spessartine rich rim (Alm69-71Sps14-19Pyr7.9-9.6Grs3.6-3.7). The garnet in amphibolite, presents a prograde growth zoning with a slight increase in spessartine in the core (Alm59-60Grs24-25Pyr8.0-8.3Sps7.3-7.6), and low content of spessartine component toward the rim (Alm60-62Grs23-24Pyr8.8-9.6Sps5.4-5.5). In order to constrain the P-T evolution of the region, multiequilibria thermobarometry was applied to both samples, the para-schist unit presents P-T data from 706 (ºC) and 7.5 (kbar), in the other hand the garnet amphibolite unit shows P-T data from 734 (ºC) and 7 (kbar). This study provides new geochronological data (U/Pb in zircons) for the amphibolite facies metamorphism and for the migmatitic event in the region that contributes to the understanding of the tectonic evolution of southeastern Mexico.

  5. Origin, Age, and Geochemistry of the Tuff of Saguache Creek, Southwestern Colorado (United States)

    Turner, K. J.; Young, M. D.; Wendlandt, R. F.


    A crystal-poor, rhyolitic, ash-flow tuff in the Eastern San Juan Volcanic Field currently known as the tuff of Saguache Creek (TSC) was reinterpreted by Simon and Wendlandt (1999) as not being distal Sapinero Mesa Tuff. Currently there is no source caldera established for this tuff thereby leaving uncertainties in the volcanic history. Regional mapping of the TSC has subsequently been completed to constrain a possible source caldera. Petrographic studies, and EPMA and LA-ICPMS analyses of the mineral assemblage have been performed to characterize further the tuff, enable correlation of mapped TSC, and constrain petrogenetic models. Petrographic and chemical identification of the TSC builds on characteristics set forth by Simon (2000). These characteristics include abundant feldspar clusters, alkali feldspar mantled plagioclase, no modal quartz, Fe-Ti oxides (often with apatites and zircons), and sparse biotite and pyroxene. Pyroxenes show curiously high MnO (avg 2.70 wt%) and Mg# (avg 79.2) and might be xenocrystic. In comparison, biotites have much lower MnO (avg 0.82 wt%). Average sanidine (Or50) and plagioclase (Ab71) compositions fall within the documented range (Simon, 2000) and show little trace element substitution including Eu Conejos age volcanic deposits. Similarly, an andesitic topographic high just west of Trickle Mtn has TSC vitrophyre on the east-facing slope suggesting strong north-south channeling of the flow unit by paleo-topographic lows. Outcrop elevations also decrease from north to south supporting a possible source caldera to the north. This source could be explained by a distinct circular gravity low on the southeastern slope of the Continental Divide. The low is bordered to the north by a circular arrangement of peaks as well as debris breccias, andesitic flow breccias, and lahars.

  6. Petrography, geochemistry and geochronology of granite hosted rhyodacites associated with a disseminated pyrite mineralization (Arnolz, Southern Bohemian Massif, Austria) (United States)

    Göd, Richard; Kurzweil, Johannes; Klötzli, Urs


    The study focuses on a subvolcanic rhyodacite dyke intruding a fine grained biotite granite and paragneisses of the South Bohemian Massif, part of the Variscan Orogenic Belt in Central Europe. The subvertical dyke strikes NNE, displays a thickness of about 30 m and has been traced by boulder mapping for approximately 7 km. The rhyodacites have been affected by two hydrothermal fluids. An older one of oxidizing condition giving rise to a reddish to brownish type of rock (Type I) and a younger fluid of reducing condition causing a greenish variety (Type II). The hydrothermal alteration is associated with the formation of the clay minerals chlorite, sericite, kaolinite and smectite and a disseminated pyrite mineralization. Bulk chemistries of the rhyodacites emphasize the hydrothermal alterations to be isochemical with the exception of sulphur enriched up to a maximum of 0.6 wt%. Trace element composition of the rhyodacites points to a barren geochemical environment in terms of base and precious elements. Sulphur isotope investigations of pyrites from the rhyodacites and the hosting granites respectively yield d34S data ranging from +0.07 to -2.22 ‰, emphasizing a magmatic origin of the sulphur. Geochronological investigations yield in situ U/Pb zircon ages of 312 ± 4 Ma for the biotite granite and of 292 ± 4 Ma for the rhyodacitic dykes indicating a time gap of ≈ 20 Ma between these two intrusive events. A contemporaneous but geochemically specialized granitic intrusion associated with NW striking "felsitic" dykes occurs about 10 to 20 km to the NW of Arnolz. However, the rhyodacites around Arnolz differ significantly from these felsitic dykes in their geochemistry and alteration phenomena which points to a different magmatic source. This coincides with a change in the orientation of the dykes from a NW direction controlling the geochemically specialized intrusions in the NW to a dominating NNE direction mirrored by the studied rhyodacites at Arnolz.

  7. Timing and duration of hydrothermal activity at the Los Bronces porphyry cluster: an update (United States)

    Deckart, K.; Silva, W.; Spröhnle, C.; Vela, I.


    New geochronological data from the Los Bronces cluster of the Río Blanco-Los Bronces mega-porphyry Cu-Mo district establish a wide range of magmatism, hydrothermal alteration, and mineralization ages, both in terms of areal extent and time. The northern El Plomo and southernmost Los Piches exploration areas contain the oldest barren porphyritic intrusions with U-Pb ages of 10.8 ± 0.1 Ma and 13.4 ± 0.1 Ma, respectively. A hypabyssal barren intrusion adjacent northwesterly to the main pit area yields a slightly younger age of 10.2 ± 0.3 Ma (San Manuel sector, U-Pb), whereas in the Los Bronces (LB) open-pit area, the present day mineral extraction zone, porphyries range from 8.49 to 6.02 Ma (U-Pb). Hydrothermal biotite and sericite ages are up to 0.5 Ma younger but consistent with the cooling of the corresponding intrusion events of each area. Two quartz-molybdenite B-type veins from the LB open pit have Re-Os molybdenite ages of 5.65 ± 0.03 Ma and 5.35 ± 0.03 Ma consistent with published data for the contiguous Río Blanco cluster. The San Manuel exploration area within the Los Bronces cluster, located about 1.5-2 km southeast of the open-pit extraction zone, shows both the oldest hydrothermal biotite (7.70 ± 0.07 Ma; 40Ar/39Ar) and breccia cement molybdenite ages (8.36 ± 0.06 Ma; Re-Os) registered in the entire Río Blanco-Los Bronces district. These are also older than those reported from the El Teniente porphyry Cu(-Mo) deposit, suggesting that mineralization in the late Miocene to early Pliocene porphyry belt of Central Chile commenced 2 Ma before the previously accepted age of 6.3 Ma.

  8. Petrological and geochemical studies of ultramafic-mafic rocks from the North Puruliya Shear Zone (eastern India) (United States)

    Mandal, Aditi; Ray, Arijit


    Ultramafic and mafic rocks occur within a linear belt, trending nearly E-W along North Puruliya Shear Zone of the Chhotanagpur Gneissic Complex (CGC). These rocks are classified as gabbro, norite, gabbro-norite, dolerite, diorite, olivine-websterite and lherzolite. Mafic rocks (Group 1) often occur in association with ultramafic variants (Group 2) and sometimes in isolation. A genetic link has been established between these mafic and ultramafic rocks using disposition of ultramafic and mafic rocks in the outcrop, systematic variation in modal mineralogy, co-linearity of plots in biaxial chemical variation diagram. Chemical composition of biotite and clinopyroxene reveal calc-alkaline nature and arc signature in these mafic-ultramafic rocks and whole rock geochemical characters indicate similarity with arc magma in subduction zone setting. The high values of Mg no. (47-81) and Al 2 O 3 (5.5-17.9) of mafic rocks indicate primitive, aluminous nature of the parental melt and presence of amphibole and biotite indicate its hydrous nature. The parent mafic melt evolved through fractionation of olivine, spinel, clinopyroxene and plagioclase. The crystal cumulates gave rise to the ultramafic rocks and the associated mafic rocks formed from residual melt. Crustal contamination played an important role in magmatic evolution as evident from variation in abundance of Rb in different lithomembers. Mafic-ultramafic rocks of the present study have been compared with intra-cratonic layered complexes, mafic-ultramafic rocks of high grade terrain, Alaskan type ultramafic-mafic complex and ophiolites. It is observed that the ultramafic-mafic rocks of present study have similarity with Alaskan type complex.

  9. Age and origin of post collision Baltoro granites, south Karakoram, North Pakistan: Insights from in-situ U-Pb, Hf and oxygen isotopic record of zircons (United States)

    Mahar, Munazzam Ali; Mahéo, Gweltaz; Goodell, Philip C.; Pavlis, Terry L.


    Origin of post collision plutonism is critical to understand the tectonothermal evolution of the over thickened continental crust in collision zones. This has proven difficult to reconcile with the conventional whole rock geochemical and field based studies alone. We report in-situ study of zircon U-Pb, Hf and O isotopes from five samples of the Baltoro Plutonic Unit (BPU) in south Karakoram. The plutonic unit is the western part of the southern Asian margin of the India-Asia convergent zone. Baltoro granites and a biotite-rich enclave yielded similar and overlapping U-Pb ages ranging from 26 to 15 Ma. Hafnium isotopic composition (εHf (0)) is very heterogeneous ranging from - 17.1 to + 4.4 while the oxygen isotopic composition of the granites is homogeneous with mean δ18O ranging from 7.2 to 9.4‰. Based on U-Pb geochronology and Hf-O isotopic composition, the involvement of two main sources is suggested (1) Cretaceous calc-alkaline Karakoram crust and (2) Karakoram gneisses. Moreover, possible involvement of metasomatized Asian lithospheric mantle is supported by elevated oxygen composition of granites and identical Hf composition of biotite-rich enclave to the mantle derived Baltoro lamprophyre. However, direct contribution from juvenile pristine mantle is unlikely as no juvenile mantle type Hf and oxygen values were obtained. This also precludes the involvement of southward juvenile arc related component of Kohistan-Ladakh batholith. Our new U-Pb and Hf data are comparable to the Mesozoic Karakoram batholith, Miocene two-mica leucogranites in the Pangong Range and magmatism from the Lhasa terrane in south Tibet, suggesting a genetic link between the Karakoram and the rocks to the east. This magmatic event is best explained by lower crust partial melting promoted by both thermal equilibration following crustal thickening and heat advection by ultrapotassic magmas associated with the breakoff of the Indian continental margin.

  10. Contrasted crustal sources as defined by whole-rock and Sr-Nd-Pb isotope geochemistry of neoproterozoic early post-collisional granitic magmatism within the Southern Brazilian Shear Belt, Camboriú, Brazil (United States)

    Florisbal, Luana Moreira; de Assis Janasi, Valdecir; de Fátima Bitencourt, Maria; Stoll Nardi, Lauro Valentim; Heaman, Larry M.


    The early phase of post-collisional granitic magmatism in the Camboriú region, south Brazil, is represented by the porphyritic biotite ± hornblende Rio Pequeno Granite (RPG; 630-620 Ma) and the younger (˜610 Ma), equigranular, biotite ± muscovite Serra dos Macacos Granite (SMG). The two granite types share some geochemical characteristics, but the more felsic SMG constitutes a distinctive group not related to RPG by simple fractionation processes, as indicated by its lower FeOt, TiO2, K2O/Na2O and higher Zr Al2O3, Na2O, Ba and Sr when compared to RPG of similar SiO2 range. Sr-Nd-Pb isotopes require different sources. The SMG derives from old crustal sources, possibly related to the Paleoproterozoic protoliths of the Camboriú Complex, as indicated by strongly negative ɛNdt (-23 to -24) and unradiogenic Pb (e.g., 206Pb/204Pb = 16.0-16.3; 207Pb/204Pb = 15.3-15.4) and confirmed by previous LA-MC-ICPMS data showing dominant zircon inheritance of Archean to Paleoproterozoic age. In contrast, the RPG shows less negative ɛNdt (-12 to -15) and a distinctive zircon inheritance pattern with no traces of post-1.6 Ga sources. This is indicative of younger sources whose significance in the regional context is still unclear; some contribution of mantle-derived magmas is indicated by coeval mafic dykes and may account for some of the geochemical and isotopic characteristics of the least differentiated varieties of the RPG. The transcurrent tectonics seems to have played an essential role in the generation of mantle-derived magmas despite their emplacement within a low-strain zone. It may have facilitated their interaction with crustal melts which seem to be to a large extent the products of reworking of Paleoproterozoic orthogneisses from the Camboriú Complex.

  11. A study on the ground water flow and hydrogeochemical interaction in fractured rock masses

    International Nuclear Information System (INIS)

    A study site, the Precambrian gneiss complex in the vincinity of Chungyang has been investigated by geologic surface mapping, tunnel mapping and core drilling with chemical analysis and microscopic observation of rock samples and fracture filling materials. Four boreholes at depths between 50 and 200m were drilled. They are located in a potential fracture zone, which was selected based on the topographic characterisitcs and the fracture survey data. The hydraulic characteristics are described based on the results of constant pressure injection test and cross hole test. In the single hole test, the test sections varied between 1 and 5 m. The hydraulic conductivity of local fracture zones ranges from 1xlO-5 to lxlO-7 m/sec whereas that of the intact rock within the depth of 50 m is in the range of 7xlO-8 to 8xlO-9 m/sec. The field dispersivity values obtained from an injection phase range from 0.15 to 4.5 m at varying depths. The whole thickness dispersivity on the 18 m section obtained from a withdrawal phase is 0.4 m. The dispersion test in two well non-circulation mode was carried out along a single fracture set at depth between 11.5-14.5m. The longitudinal dispersivity obtained from the two well test is 8.14 m. The identified minerals of host rocks are quartz, K-feldspar,plagioclase, biotite, muscovite, sericite, chlorite, calcite, pyrite, zircon and opaque minerals. The primary minerals such as feldspar and biotite are highly altered into sericite and chlorite respectively. The fracture-filling materials from core samples identified by as calcite, kaolinite, smectite, chlorite, illitite, quartz, pyrite with fe- and Mn-oxides. (Author)

  12. Geochronology, geochemistry and tectonic implications of Late Triassic granites in the Mongolian Altai Mountains (United States)

    Dash, Batulzii; Boldbaatar, Enkhjargal; Zorigtkhuu, Oyun-Erdene; Yin, An


    Although the closure of the Paleo-Asian Ocean in western China and western Mongolia occurred in the Late Carboniferous and Early Permian, widespread intra-continental magmatism continued to occur across this region from the Late Permian to the end of the Triassic. In this study we document field relationships and geochemical characterization of a Late Triassic felsic intrusive complex in the western Mongolian Altai. The plutonic complex occurs as sills, dikes, and small stocks and its composition varies from biotite granite, two-mica granite, to leucogranite. Structurally, the plutonic complex occurs in the hanging wall of a segment of the regionally extensively (>1500 km long) Irtysh-Ertix-Bulgan thrust zone. As the plutonic bodies both cut and are deformed by the shear fabrics in this regional thrust shear zone, the duration of felsic magmatism and regional thrusting was temporally overlapping. This suggests that magmatism was coeval with crustal thickening. Major- and trace-element data and isotopic analysis of granitoid samples from our study area indicate that the felsic intrusions were derived from partial melting of meta-sediments, with the biotite and two-mica granite generated through vapor-absent melting and the leucogranite from flux melting. Although the Mongolian Altai intrusions were clearly originated from anatexis, coeval granite in the Chinese Altai directly west of our study area in the hanging wall of the Irtysh-Ertix-Bulgan thrust was derived in part from mantle melting. To reconcile these observations, we propose a Himalayan-style intracontinental-subduction model that predicts two geologic settings for the occurrence of felsic magmatism: (1) along the intracontinental thrust zone where granite was entirely generated by anatexis and (2) in the hanging wall of the intracontinental thrust where convective removal and/or continental subduction induced mantle melting.

  13. Post-collisional potassic granitoids from the southern and northwestern parts of the Late Neoproterozoic East African Orogen: a review (United States)

    Küster, Dirk; Harms, Ulrich


    Potassic metaluminous granitoids with enrichments of HFS elements constitute part of widespread post-collisional magmatism related to the Late Neoproterozoic Pan-African orogeny in northeastern Africa (Sudan, Ethiopia, Somalia) and Madagascar. The plutons were emplaced between 580 and 470 Ma and comprise both subsolvus and hypersolvus biotite-granite, biotite-hornblende-granite, quartz-monzonite and quartz-syenite. Pyroxene-bearing granitoids are subordinate. Basic dikes and enclaves of monzodioritic composition are locally associated with the granitoid plutons. Granitoids emplaced in pre-Neoproterozoic crust have Sr i-ratios between 0.7060 and 0.7236 and ɛNd( t) values between -15.8 and -5.6 while those emplaced in, or close to the contact with, juvenile Neoproterozoic crust have lower Sr i-ratios (0.7036-0.7075) and positive ɛNd( t) values (4.6). However, it is unlikely that the potassic granitoids represent products of crustal melting alone. The association with basic magmas derived from subduction-modified enriched mantle sources strongly suggests that the granitoids represent hybrid magmas produced by interaction and mixing of mantle and crust derived melts in the lower crust. The most intense period of this potassic granitoid magmatism occurred between 585 and 540 Ma, largely coeval with HT granulite facies metamorphism in Madagascar and with amphibolite facies retrogression in northeastern Africa (Somalia, Sudan). Granitoid magmatism and high-grade metamorphism are probably both related to post-collisional lithospheric thinning, magmatic underplating and crustal relaxation. However, the emplacement of potassic granites continued until about 470 Ma and implies several magmatic pulses associated with different phases of crustal uplift and cooling. The potassic metaluminous granites are temporally and spatially associated with post-collisional high-K calc-alkaline granites with which they share many petrographical, geochemical and isotopical similarities

  14. Alkali-calcic and alkaline post-orogenic (PO) granite magmatism: petrologic constraints and geodynamic settings (United States)

    Bonin, Bernard; Azzouni-Sekkal, Abla; Bussy, François; Ferrag, Sandrine


    The end of an orogenic Wilson cycle corresponds to amalgamation of terranes into a Pangaea and is marked by widespread magmatism dominated by granitoids. The post-collision event starts with magmatic processes still influenced by subducted crustal materials. The dominantly calc-alkaline suites show a shift from normal to high-K to very high-K associations. Source regions are composed of depleted and later enriched orogenic subcontinental lithospheric mantle, affected by dehydration melting and generating more and more K- and LILE-rich magmas. In the vicinity of intra-crustal magma chambers, anatexis by incongruent melting of hydrous minerals may generate peraluminous granitoids bearing mafic enclaves. The post-collision event ends with emplacement of bimodal post-orogenic (PO) suites along transcurrent fault zones. Two suites are defined, (i) the alkali-calcic monzonite-monzogranite-syenogranite-alkali feldspar granite association characterised by [biotite+plagioclase] fractionation and moderate [LILE+HFSE] enrichments and (ii) the alkaline monzonite-syenite-alkali feldspar granite association characterised by [amphibole+alkali feldspar] fractionation and displaying two evolutionary trends, one peralkaline with sodic mafic mineralogy and higher enrichments in HFSE than in LILE, and the other aluminous biotite-bearing marked by HFSE depletion relative to LILE due to accessory mineral precipitation. Alkali-calcic and alkaline suites differ essentially in the amounts of water present within intra-crustal magma chambers, promoting crystallisation of various mineral assemblages. The ultimate enriched and not depleted mantle source is identical for the two PO suites. The more primitive LILE and HFSE-rich source rapidly replaces the older orogenic mantle source during lithosphere delamination and becomes progressively the thermal boundary layer of the new lithosphere. Present rock compositions are a mixture of major mantle contribution and various crustal components

  15. The production of intermediate magmas through magma mixing and commingling: Evidence from the Hoover Dam Volcanics, Mohave County, Arizona and Clark County, Nevada

    Energy Technology Data Exchange (ETDEWEB)

    Mills, J.G. Jr. (Univ. of Nevada, Las Vegas, NV (United States). Dept. of Geoscience)


    The Hoover Dam Volcanic section ([approximately]14 Ma) is composed of the reversely-zoned dacitic tuff of Hoover Dam, Switchyard basaltic andesite, Sugarloaf dacite, Black Canyon dacite and Kingman Wash basaltic andesite (Mills, 1985). The origin of this suite is best explained by the commingling and mixing of end-member mafic and felsic magmas. These end-member magmas were most likely formed by partial melting of the mantle and subsequent advective heating and melting of the crust respectively. Textural evidence for these processes is observed in the Black Canyon dacite which contains enclaves of basaltic andesite, and, in the Paint Pots pluton which contains commingled basaltic andesite and monzonite. The Black Canyon dacite is a biotite (4%), homblende (1%) and plagioclase 10% phyric dacite flow which contains up to 5% enclaves of basaltic andesite. The enclaves contain 54 wt% SiO[sub 2], 7.22 ppm Tl, 65 ppm Rb, 1,274 ppm Sr and 1,810 ppm Ba. The gray to purplish-red enclaves have crenulate margins, are commonly vesiculated and contain phenocrysts of biotite (< 1%), hornblende ([much lt]1%), plagioclase (1%) and clinopyroxene( ) (2%). Chemically, the enclaves are distinct from the Switchyard and Kingman Wash basaltic andesites. The enclaves most likely represent a more primitive magma from which the Switchyard and Kingman Wash basaltic andesites were derived. These two units were subsequently chemically modified by mixing with crustal melt and/or crystal fractionation. The presence of a small, clinopyroxenite xenolith (clinopyroxene 90%, garnet 5%, plagioclase 4%) within one of the enclaves indicates an upper mantle source for the enclave magma.

  16. Genetic relationship of high-Mg dioritic pluton to iron mineralization: A case study from the Jinling skarn-type iron deposit in the North China Craton (United States)

    Jin, Ziliang; Zhang, Zhaochong; Hou, Tong; Santosh, M.; Han, Liu


    The Jinling complex is spatially and temporally associated with the Jinling skarn-type iron deposit. The complex is composed of biotite diorite, hornblende diorite, monzonite and quartz diorite. U-Pb dating of zircons from the biotite diorite and monzonite using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) yields ages of 126 ± 1.9 Ma and 128 ± 1.4 Ma, respectively. The unaltered rocks in the complex are characterized by variable contents of SiO2 (54.6-65.3 wt.%), MgO (2.7-9.2 wt.%), total FeO (3.5-8.8 wt.%), Na2O + K2O (5.2-8.9 wt.%), high Mg# values (73-88), Cr (103-452 ppm) and Ni (49-212 ppm) contents. The altered monzonite has lower MgO (2.1-3.7 wt.%), total FeO (1.2-2.6 wt.%) and higher Na2O + K2O (8.5-9.9 wt.%) contents. The initial (87Sr/86Sr)t ranges from 0.70450 to 0.70555 and εNd(t) shows a range of -3.0 to -8.0. The geochemical characteristics suggest that the primary magma witnessed the interaction between the partial melts of relatively oxidized delaminated ancient crust and mantle peridotite. Fractional crystallization and crustal contamination during the magmatic ascent and emplacement are also indicated. The Jinling skarn-type Fe deposit is of hydrothermal origin and the Fe enrichment can be ascribed to multiple factors. The delaminated ancient crustal source contributed to the high oxygen fugacity of the primary magma. Two-stage Fe-enrichment process involving fractional crystallization of the primary magma giving rise to high Cl and Fe contents in the magmatic hydrothermal fluid and later Fe-leaching process, accounts for the high-grade ore bodies.

  17. Zircon dating and mineralogy of the Mokong Pan-African magmatic epidote-bearing granite (North Cameroon) (United States)

    Tchameni, R.; Sun, F.; Dawaï, D.; Danra, G.; Tékoum, L.; Nomo Negue, E.; Vanderhaeghe, O.; Nzolang, C.; Dagwaï, Nguihdama


    We present the mineralogy and age of the magmatic epidote-bearing granite composing most of the Mokong pluton, in the Central Africa orogenic belt (North Cameroon). This pluton intrudes Neoproterozoic (~830 to 700 Ma) low- to high-grade schists and gneisses (Poli-Maroua group), and is crosscut or interleaved with bodies of biotite granite of various sizes. The pluton is weakly deformed in its interior, but solid-state deformation increases toward its margins marked by narrow mylonitic bands trending NNE-SSW. The magmatic epidote granitic rocks are classified as quartz monzodiorite, granodiorite, monzogranite, and syenogranite. They are medium- to coarse-grained and composed of K-feldspar + plagioclase + biotite + amphibole + epidote + magnetite + titanite + zircon + apatite. In these granites, the pistacite component [atomic Fe+3/(Fe3+ + Al)] in epidote ranges from 16 to 29 %. High oxygen fugacity (log ƒO2 - 14 to -11) and the preservation of epidote suggest that the magma was oxidized. Al-in hornblende barometry and hornblende-plagioclase thermometry indicate hornblende crystallization between 0.53 and 0.78 GPa at a temperature ranging from 633 to 779 °C. Zircon saturation thermometry gives temperature estimates ranging from 504 to 916 °C, the latter being obtained on samples containing inherited zircons. U/Pb geochronology by LA-ICP-MS on zircon grains characterized by magmatic zoning yields a concordia age of 668 ± 11 Ma (2σ). The Mokong granite is the only known occurrence magmatic epidote in Cameroon, and is an important milestone for the comparison of the Central Africa orogenic belt with the Brasiliano Fold Belt, where such granites are much more abundant.

  18. Geology, alteration, mineralization and geochemical study in Kalateh Taimour area, NE Iran

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    Zahra Alaminia


    Full Text Available The area is located 20 km northwest of Kashmar and about 4 km of Kalateh Taimour in Khorasan Razavi province. The study area is part of Tertiary volcanic-plutonic belt north of Daruneh fault and its situation in tectonic inliers between two important active faults, Doruneh and Taknar. Volcanic rocks are mainly intermediate to acid pyroclastic type. They formed during early Tertiary. The volcanic rocks of the Kalateh Taimour area are predominantly andesitic basalt, andesite, latite, trachyte, dacite and rhyodacite and are observed as lava, tuff, lapilli tuff and agglomerate. Field evidences and study show several subvolcanic bodies including quartz hornblende biotite monzodiorite porphyry, quartz biotite monzodiorite porphyry, quartz diorite porphyry and microdiorite which are intruded sometime in mid-Tertiary. In this belt, new methods of image processing were used for enhancing the alteration zones to help near infra red and short wavelength infrared and bands example band ratios and principle component method. Propylitic, sericitic and argillic are the main alteration types. Minor silicification is found in some areas. Alteration is extent but mineralization is limited. Mineralization is mainly controlled by fault system. Several mineralized faults are being discovered. Open space filling features are abundant. In the study area, disseminate and stock work mineralization are abundant. The amount of sulfide minerals is very small. Ancient mining is present in the area. Stream sediment geochemical study shows a very broad and high level of gold anomaly. Rock geochemical study show very high levels of Au, Ag, Cu, Pb, Zn and Au value is correlative to Cu, Pb, Zn and Ag values. Due to alteration modeling, non uniformity in mineralization and low abundance of sulfide mineralization suggest study in low sulphidation Au-Cu deposit.

  19. A Palaeoproterozoic multi-stage hydrothermal alteration system at Nalunaq gold deposit, South Greenland (United States)

    Bell, Robin-Marie; Kolb, Jochen; Waight, Tod Earle; Bagas, Leon; Thomsen, Tonny B.


    Nalunaq is an orogenic, high gold grade deposit situated on the Nanortalik Peninsula, South Greenland. Mineralisation is hosted in shear zone-controlled quartz veins, located in fine- and medium-grained amphibolite. The deposit was the site of Greenland's only operating metalliferous mine until its closure in 2014, having produced 10.67 t of gold. This study uses a combination of field investigation, petrography and U/Pb zircon and titanite geochronology to define a multi-stage hydrothermal alteration system at Nalunaq. A clinopyroxene-plagioclase-garnet(-sulphide) alteration zone (CPGZ) developed in the Nanortalik Peninsula, close to regional peak metamorphism and prior to gold-quartz vein formation. The ca. 1783-1762-Ma gold-quartz veins are hosted in reactivated shear zones with a hydrothermal alteration halo of biotite-arsenopyrite-sericite-actinolite-pyrrhotite(-chlorite-plagioclase-löllingite-tourmaline-titanite), which is best developed in areas of exceptionally high gold grades. Aplite dykes dated to ca. 1762 Ma cross-cut the gold-quartz veins, providing a minimum age for mineralisation. A hydrothermal calcite-titanite alteration assemblage is dated to ca. 1766 Ma; however, this alteration is highly isolated, and as a result, its field relationships are poorly constrained. The hydrothermal alteration and mineralisation is cut by several generations of ca. 1745-Ma biotite granodiorite accompanied by brittle deformation. A ca. 1745-Ma lower greenschist facies hydrothermal epidote-calcite-zoisite alteration assemblage with numerous accessory minerals forms halos surrounding the late-stage fractures. The contrasting hydrothermal alteration styles at Nalunaq indicate a complex history of exhumation from amphibolite facies conditions to lower greenschist facies conditions in an orogenic belt which resembles modern Phanerozoic orogens.

  20. Early Paleozoic Magmatism and Gold Mineralization in the Northern Altun, NW China

    Institute of Scientific and Technical Information of China (English)

    CHEN Xuanhua; WANG Xiaofeng; George GEHRELS; YANG Yi; QIN Hong; CHEN Zhengle; YANG Feng; CHEN Bailin; LI Xuezhi


    This paper discusses the relationships between granitic magmatism and gold mineralization and the exhumation history of the Dapinggou gold deposit in northern Altun, NW China based on the geochronological data,including zircon U-Pb ages, Rb-Sr isochron age and 40Ar-39Ar dating and MDD modeling data. The main granitic magmatism age in this area is attained from the ID TIMS U-Pb geochronology of zircons from the Kuoshibulak granite,the biggest granite in the northern Altun area, which gives a concordant age of 443±5 Ma in the Late Ordovician. Zircon ID TIMS U-Pb geochronology of the West Dapinggou biotite granite west of the Dapinggou gold deposit gives concordant ages around 485±10 Ma, representing the early stage of Ordovician magmatism. The Rb-Sr isochron age (487±21 Ma) of 6 quartz inclusion samples from quartz veins in this gold deposit is very close to that of the West Dapinggou granite. MDD modeling of step heating 40Ar- 39Ar data of K-feldspar from the same West Dapinggou biotite granite gives a rapid cooling history from 300℃ to 150℃ during 200-185 Ma. According to the age data and the geological setting of this area, we conclude that the Dapinggou gold deposit was formed at the early stage of the Early Paleozoic granitic magmatism in northern Altun, and exhumed in the Early Jurassic due to the normal faulting of the Lapeiquan detachment. The Early Paleozoic magmatism may provide heat source and produce geological fluids, which are very important for gold mineralization. Exhumation in the Mesozoic caused the uplift of the deposit towards the ground surface.

  1. The zinc stable isotope signature of waste rock drainage in Arctic Canada (United States)

    Matthies, Romy; Blowes, David


    Leachate emerging from a pilot-scale waste rock pile of the Diavik diamond mine, Northwest Territories, was monitored. The well-characterized waste rock consists of granite, pegmatitic granite and biotite schist with an average total sulfur and carbonate carbon concentration of 0.053 and 0.027 wt. %, respectively. During the field seasons of 2011 and 2012, the Zn stable isotope footprint was characterized alongside standard monitoring parameters. pH ranged between 4.3 and 6.8 and carbonate alkalinity was low or undetectable. Al and Fe concentrations averaged 6.78 mg L-1 and 175 µg L-1, respectively. The pH and metal mobility were governed by sulfide oxidation and sorption and co-precipitation onto iron and aluminium hydroxides. The main processes controlling zinc mobility in the range of 0.4 and 4.7 mg L-1 was the oxidative dissolution of sphalerite (ZnS) in the biotite schist and the attenuation of zinc onto secondary iron and aluminium hydroxides and desorption upon the pH declining below the pHpzc. The isotope ratios between -0.16 and +0.19 ‰ (δ66Zn, avg = +0.05 ‰, n = 43) are consistent with values reported from other sphalerite containing deposits. Zn isotope ratios and concentrations were largely uncorrelated suggesting that the processes affecting Zn mobility had little or no impact on the Zn isotope signature. Data indicate, that the Zn isotope ratios of the waste rock leachate may be used as a fingerprint to track anthropogenic, mine-derived Zn sources under varying environmental conditions.

  2. Fluoride abundance and controls in fresh groundwater in Quaternary deposits and bedrock fractures in an area with fluorine-rich granitoid rocks. (United States)

    Berger, Tobias; Mathurin, Frédéric A; Drake, Henrik; Åström, Mats E


    This study focuses on fluoride (F(-)) concentrations in groundwater in an area in northern Europe (Laxemar, southeast Sweden) where high F(-) concentrations have previously been found in surface waters such as streams and quarries. Fluoride concentrations were determined over time in groundwater in the Quaternary deposits ("regolith groundwater"), and with different sampling techniques from just beneath the ground surface to nearly -700m in the bedrock (fracture) groundwater. A number of potential controls of dissolved F(-) were studied, including geological variables, mineralogy, mineral chemistry and hydrology. In the regolith groundwater the F(-) concentrations (0.3-4.2mg/L) were relatively stable over time at each sampling site but varied widely among the sampling sites. In these groundwaters, the F(-) concentrations were uncorrelated with sample (filter) depth and the water table in meters above sea level (masl), with the thicknesses of the groundwater column and the regolith, and with the distribution of soil types at the sampling sites. Fluoride concentrations were, however, correlated with the anticipated spatial distribution of erosional material (till) derived from a F-rich circular granite intrusion. Abundant release of F(-) from such material is thus suggested, primarily via dissolution of fluorite and weathering of biotite. In the fresh fracture groundwater, the F(-) concentrations (1.2-7.4mg/L) were generally higher than in the regolith groundwater, and were uncorrelated with depth and with location relative to the granite intrusion. Two mechanisms explaining the overall high F(-) levels in the fracture groundwater were addressed. First, weathering/dissolution of fluorite, bastnäsite and apophyllite, which are secondary minerals formed in the fractures during past hydrothermal events, and biotite which is a primary mineral exposed on fracture walls. Second, long water-residence times, favoring water-rock interaction and build-up of high dissolved F

  3. Petrological and geochemical studies of ultramafic–mafic rocks from the North Puruliya Shear Zone (eastern India)

    Indian Academy of Sciences (India)

    Aditi Mandal; Arijit Ray


    Ultramafic and mafic rocks occur within a linear belt, trending nearly E–W along North Puruliya Shear Zone of the Chhotanagpur Gneissic Complex (CGC). These rocks are classified as gabbro, norite, gabbronorite, dolerite, diorite, olivine-websterite and lherzolite. Mafic rocks (Group 1) often occur in association with ultramafic variants (Group 2) and sometimes in isolation. A genetic link has been established between these mafic and ultramafic rocks using disposition of ultramafic and mafic rocks in the outcrop, systematic variation in modal mineralogy, co-linearity of plots in biaxial chemical variation diagram. Chemical composition of biotite and clinopyroxene reveal calc-alkaline nature and arc signature in these mafic–ultramafic rocks and whole rock geochemical characters indicate similarity with arc magma in subduction zone setting. The high values of Mg no. (47–81) and Al2O3 (5.5–17.9) of mafic rocks indicate primitive, aluminous nature of the parental melt and presence of amphibole and biotite indicate its hydrous nature. The parent mafic melt evolved through fractionation of olivine, spinel, clinopyroxene and plagioclase. The crystal cumulates gave rise to the ultramafic rocks and the associated mafic rocks formed from residual melt. Crustal contamination played an important role in magmatic evolution as evident from variation in abundance of Rb in different lithomembers. Mafic–ultramafic rocks of the present study have been compared with intra-cratonic layered complexes, mafic–ultramafic rocks of high grade terrain, Alaskan type ultramafic–mafic complex and ophiolites. It is observed that the ultramafic–mafic rocks of present study have similarity with Alaskan type complex.

  4. Petrogenesis and tectonic implications of the Yadong leucogranites, southern Himalaya (United States)

    Gou, Zhengbin; Zhang, Zeming; Dong, Xin; Xiang, Hua; Ding, Huixia; Tian, Zuolin; Lei, Hengcong


    The leucogranites in the Higher Himalayan Sequence (HHS) provide a probe to elucidate the crustal melting of continental collisional orogen. An integrated geochemical and geochronological study of the Yadong leucogranites, southern Himalaya, shows that these rocks have relatively high SiO2 contents of 69.77 to 75.32 wt.% and alumina saturation index (A/CNK) of 1.09-1.40, typical of peraluminous granites. They show moderately fractionated REE patterns with negative Eu anomalies, and are characterized by enriched LILE (Rb and Cs) and depleted HFSE (Zr, Hf, Nb and Ta). LA-ICP-MS U-Pb zircon dating of ten samples yields crystallization ages ranging from 21.0 to 11.7 Ma. The zircons have variable εHf(t) values of - 26.3 to - 3.5 and corresponding Hf two-stage model ages of 2.77-1.33 Ga. The present study reveals that the muscovite-biotite leucogranites (2ML) have higher TiO2, MgO, CaO, Sr, Ba and Zr contents, lower Rb/Sr ratios than the tourmaline-muscovite leucogranites (TML). Zircon and monazite saturation thermometry results show that the melt temperatures (681-784 °C) of the 2ML are 20-80 °C higher than those (663-705 °C) of the TML. Combining with previous results, we propose that the TML were derived from the muscovite-dehydration melting, whereas the 2ML dominantly resulted from the biotite-dehydration melting during the prograde metamorphism of the pelitic and felsic granulites of the HHS. Therefore, the Himalayan leucogranites were probably formed during the subduction of the Indian crust following the India and Asia collision.

  5. Petrogenesis of subvolcanic rocks from the Khunik prospecting area, south of Birjand, Iran: Geochemical, Sr-Nd isotopic and U-Pb zircon constraints (United States)

    Samiee, Somayeh; Karimpour, Mohammad Hassan; Ghaderi, Majid; Haidarian Shahri, Mohammad Reza; Klöetzli, Urs; Santos, José Francisco


    The Khunik prospecting area is located 106 km south of Birjand in eastern Iran, and is considered as an epithermal gold prospecting area. The mineralization is related to subvolcanic rocks. There are several outcrops of subvolcanic intrusions in the area which intruded into Paleocene-Eocene volcanic rocks (andesite, trachy-andesite and pyroclastic rocks). Petrographic studies indicate that subvolcanic rocks consist mainly of diorite, monzonite, quartz-monzonite, monzodiorite and quartz-monzodiorite. Mineralogically, these rocks contain plagioclase, K-feldspar, amphibole, pyroxene, biotite and quartz. Geochemically, they have features typical of high-K calk-alkaline to shoshonitic and are metaluminous, and also belong to magnetite granitoid series (I-type). Primitive mantle normalized trace element spider diagrams display enrichment in LILE, such as Rb, Ba, and Cs, compared to HFSE. Chondrite-normalized REE plots show moderately LREE enriched patterns (7.45 diagrams also show affinities with modern convergent margin magmas, suggesting that magmas of Khunik area formed in volcanic arc setting related to subduction of the oceanic crust under the Lut Block plate. The initial 87Sr/86Sr ratios (0.704196-0.704772) and εNdi values (+1.3 to +3.3) are compatible with an origin of the parental melts in a supra-subduction mantle wedge. Zircon U-Pb dating by LA-ICP-MS indicates the age of 38 ± 1 Ma (late Eocene) for subvolcanic units that are related to mineralization. A biotite granodiorite porphyry is the testimony of the youngest magmatic activity in the area, with an age of 31 ± 1 Ma (early Oligocene). The represented dates are interpreted as magmatic crystallization ages of subvolcanic intrusions.

  6. SHRIMP U-Pb zircon geochronology and its implications on the Xilin Gol Complex, Inner Mongolia, China

    Institute of Scientific and Technical Information of China (English)

    SHI Guanghai; LIU Dunyi; ZHANG Fuqin; JIAN Ping; MIAO Laicheng; SHI Yuruo; TAO Hua


    The Xilin Gol Complex, consisting of deformed and metamorphosed rocks, was exposed as a large geological unit within the Central Asian Orogenic Belt, but its forming and subsequent deformed and metamorphic time has been an issue of little consensus. Petrographic analyses and SHRIMP dating on biotite-plagioclase gneiss, one of the major rocks within the Xilin Gol Complex, in southeast Xilinhot City, Inner Mongolia, China, where the Xilin Gol Complex was identified and named, yield its lower limit age of 437 ( 3 Ma (2--) by its magmatic zircon SHRIMP U-Pb dating, and an upper limit age of 316 ( 3Ma (2--), which was constrained by SHRIMP dating of magmatic zircons from adjacent undeformed garnet-bearing granite which intruded the Complex. The Complex was thus determined to be formed and subsequently deformed/metamorphosed from the late Ordovician-early Silurian to the mid-Carboniferous. Consequently, it is not the Precambrian terrane as previously considered by most geologists. More or less, the major rock--biotite- plagioclase gneiss within the Complex is more likely to be Paleozoic fore-arc turbidite formation before metamorphism and intensive deformation, in which the detrital zircons gave sporadic Precambrian ages as old as up to 3.1 Ga. The source of the turbidite formation is multiple, which may be derived either from the North China Craton, or from the South- Mongolia Micro-continent, or probably came from a potential and undiscovered in situ terranes aged 600-800 Ma or even up to ca 3.1 Ga near the Complex.

  7. Tectono-metamorphic evolution of the Jomolhari massif: Variations in timing of syn-collisional metamorphism across western Bhutan (United States)

    Regis, Daniele; Warren, Clare J.; Young, David; Roberts, Nick M. W.


    Our current understanding of the rates and timescales of mountain-building processes is largely based on information recorded in U-bearing accessory minerals such as monazite, which is found in low abundance but which hosts the majority of the trace element budget. Monazite petrochronology was used to investigate the timing of crustal melting in migmatitic metasedimentary rocks from the Jomolhari massif (NW Bhutan). The samples were metamorphosed at upper amphibolite to granulite facies conditions (~ 0.85 GPa, ~ 800 °C), after an earlier High-Pressure stage (P > 1.4 GPa), and underwent partial melting through dehydration melting reactions involving muscovite and biotite. In order to link the timing of monazite growth/dissolution to the pressure-temperature (P-T) evolution of the samples, we identified 'chemical fingerprints' in major and accessory phases that were used to back-trace specific metamorphic reactions. Variations in Eu anomaly and Ti in garnet were linked to the growth and dissolution of major phases (e.g. growth of K-feldspar and dehydration melting of muscovite/biotite). Differences in M/HREE and Y from garnet core to rim were instead related to apatite breakdown and monazite-forming reactions. Chemically zoned monazite crystals reacted multiple times during the metamorphic evolution suggesting that the Jomolhari massif experienced a prolonged high-temperature metamorphic evolution from 36 Ma to 18 Ma, significantly different from the P-T-time path recorded in other portions of the Greater Himalayan Sequence (GHS) in Bhutan. Our data demonstrate unequivocally that the GHS in Bhutan consists of units that experienced independent high-grade histories and that were juxtaposed across different tectonic structures during exhumation. The GHS may have been exhumed in response to (pulsed) mid-crustal flow but cannot be considered a coherent block.

  8. New data on the paleocene section in Blateshnitsa Graben (Kraishte region, Western Bulgaria)

    International Nuclear Information System (INIS)

    Blateshnitsa Graben is superimposed upon a basement of allohtonous Palaeozoic anhimetamorphics and paraautohtonous Triassic and Jurassic sediments. According to the data from the Zemen borehole, the Graben is filled mainly by alluvial conglomerates and breccia conglomerates (in the lower part of the section) with rare interbeds, of sandstones, fine layered shales and three acid (to intermediate?) pyroclastic beds (in the upper part). K-Ar age of biotite crystalloclasts from the upper part (1.2 m) of the first pyroclastic bed was used to date the Blateshnitsa section. The data obtained (33.12 ± 1.50 Ma) indicate a Late Priabonian, Early Rupelian (or close to Priabonian - Rupelian boundary) age of the pyroclastic emission and accumulation. This first direct dating confirms the existing ideas on the age of Blateshnitsa Graben fill. The dated pyroclastics are transformed into zeolite rocks containing up to 35 % zeolite of heulandite type. They are formed at the expense of acid (to intermediate?) fine ash pumice fragments and glass shards, containing also a high amount (20-40 %) of crystalloclasts (mainly plagioclase and biotite, together with amphibole and quartz) and rare lithic fragments. The source of the pyroclastic component is under discussion. Redeposition of a loose fresh ash tephra by winds or current water is the most probable mechanism of its accumulation in fresh water Paleogene lake. It is supposed that the zeolitization took place in a hydrologically open system at shallow burial depths and in conditions, of humid and moderately warm climate. The Blateshnitsa zeolite rocks are a new find of such type of rocks for the territory of Bulgaria and the first Bulgarian occurrence formed in fresh water environment. Some problems on the Western Bulgaria Paleogene chrono- and lithostratigraphy are discussed. (Original)

  9. Provenance of the heavy metals in sand sediments of the Oman Sea (Sistan and Baluchestan district

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    Maryam Soleimani


    Full Text Available Introduction Mineral composition of source rock is one of the most important factors for concentration and distribution of heavy metals in sediments. Therefore, study on distribution of these elements and the related minerals in sediments provides information about natural origin of elements. Moreover, the interpretation of origin and distribution of sandy sediments is considerably enhanced by mineralogical and geochemical studies of these sediments. The main objective of this research is to evaluate distribution of Zn, Cu, Sr, Cd, Fe and Mn in sand sediments of the Oman Sea, their relationship with mineral composition of the sediments and also determining their provenance. Materials and Methods Sampling of surface sediments of the Oman Sea was performed in 16 sampling stations. Heavy minerals and rock fragments of the sediments in fine and coarse sand sizes respectively were qualitatively and quantitatively studied by polarizing microscope (Folk, 1974; Pettijohn et al., 1981; Tucker, 1988. Concentration of the heavy metals were also analyzed by AAS method (Mico et al., 2008. Result Mineralogical composition of the studied sediments contain quartz, feldspars and heavy minerals in their order of abundances. The rock fragments consist of sedimentary, igneous and metamorphic in their order of frequencies as well. The concentrations of the studied heavy metals (in ppm in the sediments are Cd (1.42, Cu (9.99, Zn (36.72, Sr (181.18, Mn (377.33 and Fe (20247.55 in their order of abundances. Distribution of the Zn concentration generally shows decreasing trend from west of the study area to the Guatr Bay. The concentrations of Zn and Cu show close relationship with the frequencies of biotite and muscovite. The Cu concentration also shows positive correlation with the Zn and Fe concentrations. Distribution of the Sr and Cd concentrations is similar to variation of the calcium carbonate content. The Cd and Sr concentrations also show positive correlation

  10. Ore genesis constraints on the Idaho Cobalt Belt from fluid inclusion gas, noble gas isotope, and ion ratio analyses (United States)

    Hofstra, Albert H.; Landis, Gary P.


    The Idaho cobalt belt is a 60-km-long alignment of deposits composed of cobaltite, Co pyrite, chalcopyrite, and gold with anomalous Nb, Y, Be, and rare-earth elements (REEs) in a quartz-biotite-tourmaline gangue hosted in Mesoproterozoic metasedimentary rocks of the Lemhi Group. It is the largest cobalt resource in the United States with historic production from the Blackbird Mine. All of the deposits were deformed and metamorphosed to upper greenschist-lower amphibolite grade in the Cretaceous. They occur near a 1377 Ma anorogenic bimodal plutonic complex. The enhanced solubility of Fe, Co, Cu, and Au as chloride complexes together with gangue biotite rich in Fe and Cl and gangue quartz containing hypersaline inclusions allows that hot saline fluids were involved. The isotopes of B in gangue tourmaline are suggestive of a marine source, whereas those of Pb in ore suggest a U ± Th-enriched source. The ore and gangue minerals in this belt may have trapped components in fluid inclusions that are distinct from those in post-ore minerals and metamorphic minerals. Such components can potentially be identified and distinguished by their relative abundances in contrasting samples. Therefore, we obtained samples of Co and Cu sulfides, gangue quartz, biotite, and tourmaline and post-ore quartz veins as well as Cretaceous metamorphic garnet and determined the gas, noble gas isotope, and ion ratios of fluid inclusion extracts by mass spectrometry and ion chromatography. The most abundant gases present in extracts from each sample type are biased toward the gas-rich population of inclusions trapped during maximum burial and metamorphism. All have CO2/CH4 and N2/Ar ratios of evolved crustal fluids, and many yield a range of H2-CH4-CO2-H2S equilibration temperatures consistent with the metamorphic grade. Cretaceous garnet and post-ore minerals have high RH and RS values suggestive of reduced sulfidic conditions. Most extracts have anomalous 4He produced by decay of U and Th and

  11. An interpretation of the metamorphic history of the Alpine Schist, northern Westland

    International Nuclear Information System (INIS)

    This thesis presents results of an investigation into the metamorphism of a section of the Alpine Schist in North Westland, between the Crooked River in the north and Griffin Creek in the south. The Alpine Schist is a narrow belt of dominantly quartzofeldspathic schist that has been rapidly extruded along the Alpine Fault. The schist is at its highest grade (garnet-oligoclase) immediately east of the Alpine Fault and grades to biotite zone facies at a distance of c. 3 km west of the fault in this study. Field mapping, optical microscopy, whole-rock analyses, mineral chemistry and zoning, geothermobarometry, stable isotopes and Sm-Nd age determinations for garnet growth zones have enabled a well constrained metamorphic history to be interpreted. As part of this an estimate for the timing and P-T conditions of the peak of Alpine Schist metamorphism in the study area has also been possible. Large polyphase garnet porphyroclasts sampled from mylonitised Alpine Schist at Macs Creek record up to five zones of garnet growth. Textures within these garnets indicate that at least some garnet growth predated the development of the alpine foliation and that garnet growth occurred at least sporadically through most of the Cenozoic, finishing with garnet rims overgrowing the developing mylonitic foliation. Garnet separates were prepared and sent to VIEPS Radiogenic Isotope Laboratory, La Trobe University, Melbourne, Australia for Sm-Nd garnet growth age determinations. For the core (zone 1), a two pint garnet-whole rock age of 98 ± 8.1 Ma indicates garnet growth in the mid-Cretaceous, during a time of widespread extension with scattered plutonism and volcanism in the New Zealand region, which predates the opening of the Tasman Sea by c. 20 Ma. A second Sm-Nd garnet growth age was obtained from zone 4, just inside the synmylonitic outermost rim (zone 5) and show that Alpine Schist garnet growth occurred in the Late Cenozoic. The broad age of 12 ± 37 M (MSWD = 0.89) for zone 4

  12. Unravelling the complex interaction between mantle and crustal magmas encoded in the lavas of San Vincenzo (Tuscany, Italy). Part I: Petrography and Thermobarometry (United States)

    Ridolfi, Filippo; Braga, Roberto; Cesare, Bernardo; Renzulli, Alberto; Perugini, Diego; Del Moro, Stefano


    The San Vincenzo Volcanic Complex was emplaced ~ 4.4 Ma. ago and consists of cordierite-bearing lavas which are the result of a complex interaction between mantle-derived and crustal anatectic magmas. The lavas are mostly characterized by porphyritic, glassy peraluminous rhyolites hosting variable contents of magmatic enclaves (clinopyroxene-bearing latites and amphibole-bearing clinopyroxene crystal mushes), sialic and ultramafic cognates (syenogranites, anorthosites, cordierite-biotite and pyroxenite inclusions), and crustal rocks (sillimanite-cordierite xenoliths, cordierite and biotite xenocrysts) of centimetric-to-millimetric size. Mineral chemistry shows large variations as well. Plagioclase and sanidine are represented respectively by An21-79Or1-13 and An≤ 1Or57-77. Cordierite has a Mg# of 51-78%, while garnet shows almandine compositions with low CaO (≤ 2 wt.%) and variable MnO contents (1-5 wt.%). Clinopyroxene indicates large ranges of Mg# (68-92%) and Al2O3 (0.5-6.3 wt.%), and relatively high CaO contents (up to 24 wt.%); orthopyroxene shows both ferroan enstatite (Mg# = 60-78%) and magnesian ferrosilite (Mg# = 39-44%) compositions; whereas amphibole shows only Mg-rich calcic compositions. On the basis of textural characteristics, as well as Ti and XMg variations, we have identified six different types of biotite associated with oxide minerals such as ilmenite and spinels of both aluminium (Al > 1 in Y site) and iron (Fe > 1 in Y site) subgroups. Compositional/textural relationships indicate crystallization at both equilibrium and disequilibrium conditions. Minerals with euhedral habits and homogeneous compositions usually occur in the same thin sections of partly-equilibrated crustal xenoliths (and xenocrysts) and zones of "active" mixing between mantle-derived and crustal magmas characterized by "needle-like" and skeletal microlites, and subhedral microphenocrysts of amphibole and biotite. These hybrid-mixed features, as well as the occurrence of

  13. Bedrock geology of the Mount Carmel and Southington quadrangles, Connecticut (United States)

    Fritts, Crawford Ellswroth


    New data concerning the geologic structure, stratigraphy, petrography, origin, and ages of bedrock formations in an area of approximately 111 square miles in south-central Connecticut were obtained in the course of detailed geologic mapping from 1957 to 1960. Mapping was done at a scale of 1:24,000 on topographic base maps having a 10-foot contour interval. Bedrock formations are classified in two principal categories. The first includes metasedimentary, meta-igneous, and igneous rocks of Precambrian to Devonian age, which crop out in the western parts of both quadrangles. The second includes sedimentary and igneous rocks of the Newark Group of Late Triassic age, which crop out in the eastern parts of the quadrangles. Diabase dikes, which are Late Triassic or younger in age, intruded rocks in both the western and eastern parts of the map area. Rocks in the western part of the area underwent progressive regional metamorphism in Middle to Late Devonian time. The arrangement of the chlorite, garnet, biotite, staurolite, and kyanite zones here is approximately the mirror-image of metamorphic zones in Dutchess County, New York. However, garnet appeared before biotite in politic rocks in the map area, because the ration MgO/FeO is low. Waterbury Gneiss and the intrusive Woodtick Gneiss are parts of a basement complex of Precambrian age, which forms the core of the Waterbury dome. This structure is near the southern end of a line of similar domes that lie along the crest of a geanticline east of the Green Mountain anticlinorium. The Waterbury Gneiss is believed to have been metamorphosed in Precambrian time as well as in Paleozoic time. The Woodtick Gneiss also may have been metamorphosed more than once. In Paleozoic time, sediments were deposited in geosynclines during two main cycles of sedimentation. The Straits, Southington Mountain, and Derby Hill Schists, which range in age from Cambrian to Ordovician, reflect a transition from relatively clean politic sediments to

  14. First evidence of the Ellesmerian metamorphism on Svalbard (United States)

    Kośmińska, Karolina; Majka, Jarosław; Manecki, Maciej; Schneider, David A.


    The Ellesmerian fold-and-thrust belt is exposed in the High Arctic from Ellesmere Island in the east, through North Greenland, to Svalbard in the west (e.g. Piepjohn et al., 2015). It developed during Late Devonian - Early Carboniferous, and overprinted older (mainly Caledonian) structures. It is thought that this fold-and-thrust belt was formed due to collision of the Pearya Terrane and Svalbard with the Franklinian Basin of Laurentia. Traditionally, the Ellesmerian fold-and-thrust belt comprises a passive continental margin affected by foreland deformation processes, but the exact larger scale tectonic context of this belt is disputable. It is partly because the Eocene Eurekan deformation superimposed significantly the Ellesmerian structures, thus making the reconstruction of the pre-Eurekan history very difficult. Here we present for the first time evidence for Ellesmerian metamorphism within the crystalline basement of Svalbard. These rocks are exposed in the Pinkie unit on Prins Karls Forland (W-Svalbard), which exhibits tectonic contacts with the overlying sequences. The Pinkie unit is mainly composed of strongly deformed lithologies such as laminated quartzites, siliciclastic rocks and garnet-bearing mica schists. Detrital zircon dating yielded ages as young as Neoproterozoic (0.95-1.05 Ga), thus the Pinkie unit is considered to be Neoproterozoic (Kośmińska et al., 2015a). The M1 assemblages and D1 structures are affected by D2 mylonitization (cf. Faehnrich et al., 2016, this meeting). Petrological characterization and Th-U-total Pb chemical monazite dating have been performed on the Pinkie metapelites. These rocks exhibit an apparent inverted Barrovian metamorphic sequence, within which three metamorphic zones have been distinguished: garnet+staurolite+muscovite+biotite, garnet+staurolite+kyanite+muscovite+biotite, garnet+kyanite+muscovite+biotite. The P-T estimates using the QuiG barometry coupled with thermodynamic modelling revealed that the

  15. The Magmatic and Genetic Evolution of Early Cretaceous Granitoids in Eastern Guangdong Province%粤东地区早白垩世花岗质岩浆作用及其成因演化

    Institute of Scientific and Technical Information of China (English)

    赵希林; 余明刚; 刘凯; 毛建仁; 叶海敏; 邢光福


    Granitoids in the Eastern Guangdong encompass three main rock types; the Dapu biotite-granites, the Dapu bitite-K-spar granites and the Jiexi bitite-K-spar granites. Zircon LA-ICP-MS U-Pb dating of the Dapu biotite-granites and the Jiexi bitite-K-spar granites indicates similar ages of emplacement of 136. 3 ?0. 6Ma and 134.9 ?.4Ma Respectively, which belongs to Early Cretaceous but not Late Jurassic; All of these three types of rocks are rich in Si, Al, medium in alkali content, but poor in Fe, Mg, Ca, Ti and P, belong to a high-K calc-alkaline series, as well as a weakly peraluminous granite series. The Dapu biotite-granites has8Eu mid-negative anomaly, slightly right-inclined REE distribution pattern, forming by the partial-melting of Proterozoic arenitic metasediments. The Dapu bitite-K-spar granites and the Jiexi bitite-K-spar granites have strongly 8Eu negative anomaly, seagull-like REE pattern. The Dapu bitite-K-spar granites and the Jiexi bitite-K-spar granites are coexist closely, forming in the same time, and shows continuous variation trend in geochemistry, have similar isotopic composition, may be formed by partial melting of Proterozoic pelitic metamorphic sedimentary rocks, are the results of different evolution stage of the same magma.%粤东地区出露有大埔黑云母花岗岩、大埔黑云母钾长花岗岩和揭西黑云母钾长花岗岩3种岩石类型,大埔黑云母花岗岩和揭西黑云母钾长花岗岩的LA-ICP-MS锆石U-Pb年龄分别为136.3±0.6Ma和134.9±0.4Ma,属于晚中生代早白垩世,而非前人认为的晚侏罗世;3种岩石在主量元素上总体具有富硅、铝,碱含量中等,贫铁、镁、钙、钛、磷的特征,属于高钾钙碱性的弱过铝质岩石;大埔黑云母花岗岩的δEu负异常中等,具略向右倾的轻稀土富集模式,可能是由时代相当于元古宙的富砂屑岩部分熔融形成的;大埔黑云母钾长花岗岩、揭西黑云母钾长花岗岩具有中等—强的δEu负异

  16. SR-Site: Oxygen ingress in the rock at Forsmark during a glacial cycle

    Energy Technology Data Exchange (ETDEWEB)

    Sidborn, Magnus (Kemakta Konsult AB (Sweden)); Sandstroem, Bjoern (WSP Sverige AB (Sweden)); Tullborg, Eva-Lena (Terralogica AB (Sweden)); Salas, Joaquin; Maia, Flavia; Delos, Anne; Molinero, Jorge (Amphos21 (Spain)); Hallbeck, Lotta; Pedersen, Karsten (Microbial Analytics Sweden AB (Sweden))


    matrix is the main source of reducing capacity. The ferrous iron occurs in different reduced minerals, of which biotite and chlorite are the most abundant. The release rate of ferrous iron from biotite is slower than for most of the ferrous minerals considered. Therefore, the ferrous iron is cautiously assumed to be comprised in biotite, as a model substance, and the release rate is calculated based on this assumption. Furthermore, the oxidation of ferrous iron by oxygen is assumed to occur in two consecutive steps; dissolution of ferrous iron from the mineral lattice into the pore solution followed by homogeneous oxidation of the dissolved ferrous ions. Direct oxidation of ferrous iron incorporated in the mineral lattice is hence also cautiously approximated by these two coupled processes. At early times, reduced minerals in the undisturbed rock matrix, which are directly exposed to the flowing water, are easily accessible from the flow paths in the fractures. In this situation, the extent of oxygen ingress along the flow path is determined by the relative rates of oxygen recharge and oxygen consuming reactions. Eventually, the reducing capacity of the rock close to the fracture becomes depleted and the remaining ferrous minerals can only be reached by diffusion in the rock matrix. With time, this diffusion resistance increases as the reducing capacity is depleted further into the rock matrix. The oxygen consuming reaction is then limited by the diffusion resistance. The extent of oxygen ingress is in this situation determined by the relative rates of oxygen recharge and diffusion into the rock matrix. Both of these situations are represented by two different models that are solved analytically in this report. The case of kinetically controlled oxygen consumption for early times is furthermore evaluated with the geochemical numerical codes PHREEQC and PHAST. Sensitivity analyses of important parameters such as the pH, availability of specific reactive mineral surfaces

  17. Fluorine-bearing grossular-rich garnet - an indicator for UHP - LT metamorphism of metagranitoids. (United States)

    Burchard, M.


    Melting experiments on biotite-phengite-gneiss at pressures of 1.5 to 4.5 GPa and temperatures of 675°C to 1000°C were performed to clarify the phase assemblages of S-type metagranitoids at high pressures. The starting material used was S-type granitic biotite-phengite-gneiss, which represents the country rock for the pyrope-quarztites from the Dora-Maira-Massif, Western Italy. These pyrope-quarztites contain the silicate ellenbergerite, which, together with the growth of pyrope, indicates P and T of more than 3 GPa and 700°C. Experimental evidence confirms that the presence of ellenbergerite indicates high water activities. For this reason all experiments were performed with a water fraction of 1.9 to 9.9 wt.%. The most important phases in the run products are melt, K-feldspar / K-felspar-hydrate, coesite / quartz, phengite, jadeite-rich clinopyroxene, almandine-grossular garnet, epidote, rutile and sphene. At pressures between 3.5 and 4.5 GPa and T of less than 675°C or 775°C, respectively, small, rare crystals of grossular garnets were observed. These grs-rich garnets form corona structures around the alm-grs garnets of the starting material. EMP-analysis shows that these garnets contain up to 1.2 wt.% F at 700°C, decreasing with temperature to 0.4 wt.% at 750°C. A garnet analysis from a run at 4 GPa and 700°C yields 69% grossular, 8% hydrogrossular, 6% fluorgrossular, 6% almandine, 2% spessartine and 3% andradite. The coexistence of such garnets with sphene and epidote in HP experiments shows that the high-pressure reaction sph + zoi -> grs + coe + H2O suggested by Chopin et al (1991) is not relevant at these conditions. From Chopin et al (1991) and Schertl at al (1991) it is known that there are extremely rare inclusions of grs-rich garnet in plagioclase and alm-grs garnet in the original rock, but these authors unfortunately did not analyze the F content. During a reinvestigation of the biotite-phengite gneiss grs inclusions in sph were found that

  18. New thermochronologic data reveals disturbed cooling histories near the intersection of Karakoram and Longmu Co faults, NW India (United States)

    Bohon, W.; Hodges, K.; Arrowsmith, R.; Van Soest, M. C.; Wartho, J.; Tripathy, A.


    from the Ladakh, Pangong, and Karakoram Ranges help constrain the timing and kinematics of the vertical component of slip along the KFS and the related exhumation of the blocks on either side of the fault. 40Ar/39Ar biotite ages cluster at 10 Ma within the Pangong Range. In the Karakoram Range, between the KFS (34°07'30" 78°12'10") and the inferred trace of the LCF (34°19'15" 78°18'10"), biotite ages are notably younger but inconsistent (7.5-9.2 Ma), indicative of younger exhumation of this part of the Karakoram. However, 40Ar/39Ar biotite ages from the Karakoram Range north of the LCF and farther NW in the Karakoram Range (beyond the NW terminus of the Pangong Range) are similar to those within the Pangong Range (~10 Ma). AHe and ZHe ages from the Karakoram Range directly north of the Pangong Range are consistently younger (ZHe 3.4-4.4; AHe 2.7-3.3 Ma) than the ages within the Pangong Range (ZHe 5.4-6.2; AHe 4.4-4.5 Ma), again implying differential exhumation of the part of the Karakoram Range between traces of the KFS and and LCF. Our work implies that the KFS and LCF are intimately linked, both influencing regional exhumation in northern Ladakh. Raterman, N.S., Cowgill, E., Lin, Ding, Variable structural style along the Karakoram fault explained using triple-junction analysis of intersecting faults, GEOSPHERE, Vol 3, Issue 2, p 71-85

  19. Isolation of a Siderophore-Producting Bacterial Strain and Mica-bacterial Interactions%一株产铁载体细菌的筛选及其与云母的相互作用

    Institute of Scientific and Technical Information of China (English)

    何琳燕; 张垠; 盛下放; 黄智


    Studies on the interactions between siderophore-producting bacteria and mica minerals will help us understand the mechanism of bio-weathering, the formation of soil, global cycle of several elements, and local environmental contamination. A siderophore(pyoverdins)-producting bacterial strain Z6 was isolated from rhizosphere soil of advantage wild plants sheep sorrel (Rumex acetosa L.) growing in Longshan potassium mine tailings in Nanjing, which was identified as Pseudomonas sp. By checking the individual morphology, colony characteristics, and 16S rDNA sequencing. Using the test cultures containing biotite or muscovite inoculated with Pseudomonas sp. Z6, we found that a strong increase in the amount of siderophore in the fiest 15 days and bacteria could influence silicon and iron mobilization from mica minerals consistently until 75 d of culture. The amounts of iron released from biotite in the presence of Z6 increased by 211 times and the silicon increased by a factor of 27.8, much higher than that in the negative control without minerals. SEM analysis revealed the formation of erosion and bacteria-mineral aggregates on the surface of mica. Cellular growth, siderophere production and pH change by Pseudomonas sp. Z6 cultivated in biotite were directly and quickly influenced, more significantly than that in muscovite experimental setup. The siderophore(pyoverdins)-producting bacterial strain Z6 might play an important role in the process of mica weathering. Production of bacterial siderophore may be related to the presence of different mica minerals.%产铁载体细菌与云母类矿物相互作用的研究有助于了解矿物生物风化和土壤形成的演化规律和机理.采用纯培养法自南京龙山废钾矿区酸模根际土壤分离筛选到一株高产荧光铁载体的细菌Z6,通过16S rDNA序列分析和生理生化反应将其鉴定为假单胞菌属(Pseudomonas sp.);通过室温静置培养试验研究Z6菌株与云母的相互作用结果

  20. Ages and sources of components of Zn-Pb, Cu, precious metal, and platinum group element deposits in the goodsprings district, clark county, Nevada (United States)

    Vikre, P.; Browne, Q.J.; Fleck, R.; Hofstra, A.; Wooden, J.


    ore breccias and relatively low S and Pb isotope values (??34S values vary from 0-??4%; 206Pb/204Pb replaced breccia clasts and margins of fissures in Paleozoic limestones and dolomites near porphyritic intrusions. Gold ?? silver deposits occur along contacts and within small-volume stocks and dikes of feldspar porphyry, one textural variety of porphyritic intrusions. Lead isotope compositions of copper ?? precious metal-PGE, gold ?? silver, and lead-dominant carbonate replacement deposits are similar to those of Mojave crust plutons, indicating derivation of Pb from 1.7 Ga crystalline basement or from Late Proterozoic siliciclastic sedimentary rocks derived from 1.7 Ga crystalline basement. Four texturally and modally distinctive porphyritic intrusions are exposed largely in the central part of the district: feldspar quartz porphyry, plagioclase quartz porphyry, feldspar biotite quartz porphyry, and feldspar porphyry. Intrusions consist of 64 to 70 percent SiO2 and variable K2O/Na2O (0.14-5.33) that reflect proportions of K-feldspar and albite phenocrysts and megacrysts as well as partial alteration to K-mica; quartz and biotite phenocrysts are present in several subtypes. Albite may have formed during emplacement of magma in brine-saturated basinal strata, whereas hydrothermal alteration of matrix, phenocrystic, and megacrystic feldspar and biotite to K-mica, pyrite, and other hydrothermal minerals occurred during and after intrusion emplacement. Small volumes of garnet-diopside-quartz and retrograde epidote-mica-amphibole skarn have replaced carbonate rocks adjacent to one intrusion subtype (feldspar-quartz porphyry), but alteration of carbonate rocks at intrusion contacts elsewhere is inconsp. Uranium-lead ages of igneous zircons vary inconsistently from ?? 180 to 230

  1. Gneiss wastes as secondary raw material for the ceramic industry: an example from the Verbano Cusio Ossola district (Piedmont, north-western Alps, Italy) (United States)

    Cavallo, Alessandro


    The Verbano Cusio Ossola province (VCO, Piedmont, north-western Italy) is one of the most important Italian quarrying districts, due to the peculiarity and variety of its exploited rock types, mainly orthogneisses such as Serizzo and Beola, and subordinately granites, marbles and other rocks. The most important and extensively exploited ornamental stone from the VCO province is surely the Serizzo, commercialized in four main varieties, and representing about 70% of all the stone production from the VCO area. The protholith of the Serizzo is a Permian granite - granodiorite metamorphosed during the alpine events, and the rock-forming minerals are mainly quartz, K-feldspar, plagioclase (andesine), biotite, with variable amounts of muscovite and epidote (allanite). The other important ornamental stone of the VCO province is the Beola, a series of heterogeneous materials (mainly orthogneisses) with marked (mylonitic) foliation and strong mineralogical lineation, occurring in the median Ossola Valley; its production (15% of the whole stones of the VCO) is subordinated with respect to that of Serizzo. The mineralogical composition of the Beola varieties is similar to Serizzo, consisting of quite homogeneous quartz, K-feldspar (orthoclase or microcline), plagioclase, biotite and muscovite. The main differences relate to the grain size, the rock fabric (generally mylonitic) and to the presence of accessory/secondary minerals. Recent regulatory developments and the growing environmental awareness, require an increasing reuse of wastes deriving from the extraction and processing of dimension stones (up to 50 % of the extracted gross volume). Granite wastes from the VCO (Baveno pink granite and Montorfano white granite), after specific industrial treatments (crushing, sieving, drying, magnetic separation of biotite and hornblende), are used successfully as quartz-feldspars mix in the ceramic industry, with very low FeOtot content. On the other hand, other quartzose

  2. Mineralogía y Geotermometría de los diques ácidos con grafito asociados a rocas ultramáficas de la Serranía de Ronda. Málaga

    Directory of Open Access Journals (Sweden)

    Galán, E.


    Full Text Available A geological, mineralogical and geothermometrical study of a group of acidic graphitebearing dikes from the Ronda ultramafic massif (Málaga province has been carried out. These dikes are hosted in serpentinized peridotites and they appear near the eastern and southern contacts of the massif. On the basis of their mineralogical features, two rock types have been distinguished, since they show or not hydrothermal alteration processes. Unaltered dikes present a mineral association composed by cordierite, garnet, quartz, biotite, graphite, Fe·Ti oxides, sulfides and minor amounts of plagioclase, sillimanite, hercynite and zircon. In the hydrothermally transformed dikes, this original mineral assemblage has been more or less erased, occuring "pinitization" of cordierite, chloritization of garnet and biotite, and ilmenite is transformed to "Ieucoxene". Graphite is a main mineral in both the unaltered and transformed dikes, ranging their abundance about 15%. The geothermometrical study has been done using the biotite-garnet pair and the value of graphite "c" parameter. The estimated temperatures are clase to 800º C, that are in good agreement with the given temperature for the emplacement of the ultramafic body. From all these data, formation of the dikes by anateetic partial melting of the sedimentary wall rocks (belonging to the Blanca Unit, in presence of a CO2- and CH4 rich fluid that migrated from the metamorphosed sediments towards low pressure fractures zones inside the peridotite massif, is proposed.Se ha realizado un estudio geológico, mineralógico y geotermométrico de un grupo de diques ácidos con grafito localizados en peridotitas serpentinizadas del macizo ultrabásico de Ronda (Málaga. Estos diques presentan distintos estados de alteración hidrotermal. En los diques inalterados, la paragénesis está compuesta por cordierita, granate, cuarzo, biotita, grafito, ilmenita, rutilo, sulfuros y pequeñas cantidades de plagioclasa

  3. Slow advance of the weathering front during deep, supply-limited saprolite formation in the tropical Highlands of Sri Lanka (United States)

    Hewawasam, Tilak; von Blanckenburg, Friedhelm; Bouchez, Julien; Dixon, Jean L.; Schuessler, Jan A.; Maekeler, Ricarda


    ; the remainder being contributed by dust, rain, and weathering of local marble bands. Spheroidal weathering is the key processes of converting the fresh bedrock into saprolite at the weathering front. The mineralogical composition of weathering rinds shows that the sequence of mineral decomposition is: pyroxene; plagioclase; biotite; K-feldspar. Observable biotite alteration does not appear to initiate spheroidal weathering within corestones; therefore, we infer that other processes than biotite oxidation, like pyroxene oxidation, clay formation from pyroxene and plagioclase decomposition, the development of secondary porosity by plagioclase dissolution, or even microbiologic processes at depth enable the coupling between slow advance of the weathering front and slow erosion at the surface. The comparison to tectonically more active tropical landscapes lets us conclude that the combination of hard rock with tightly interlocked mineral grains and slow erosion in the absence of tectonically-induced landscape rejuvenation lead to these exceptionally low weathering rates.

  4. Reconnaissance geology and geochronology of the Precambrian of the Granite Mountains, Wyoming (United States)

    Peterman, Zell E.; Hildreth, Robert A.


    The Precambrian of the western part of the Granite Mountains, Wyoming, contains a metamorphic complex of gneisses, schists, and amphibolites that were derived through amphibolite-grade metamorphism from a sedimentary-volcanic sequence perhaps similar to that exposed in the southeastern Wind River Mountains. Whole-rock Rb-Sr dating places the time of metamorphism at 2,860?80 million years. A high initial 87Sr/ 86 S r ratio of 0.7048 suggests that either the protoliths or the source terrane of the sedimentary component is several hundred million years older than the time of metamorphism. Following an interval of 300:t100 million years for which the geologic record is lacking or still undeciphered, the metamorphic complex was intruded by a batholith and satellite bodies of medium- to coarse-grained, generally massive biotite granite and related pegmatite and aplite. The main body of granite is dated at 2,550?60 million years by the Rb-Sr method. Limited data suggest that diabase dikes were emplaced and nephrite veins were formed only shortly after intrusion of the granite. Emplacement of the granite at about 2,550 million years ago appears to be related to a major period of regional granitic plutonism in the Precambrian of southern and western Wyoming. Granites, in the strict sense, that are dated between 2,450 and 2,600 million years occur in the Teton Range, the Sierra Madre, the Medicine Bow Mountains and the Laramie Range. This episode of granitic plutonism occured some 50 to 100 million years later than the major tonalitic to granitic plutonism in the Superior province of northern Minnesota and adjacent Ontario-the nearest exposed Precambrian W terrane that is analogous to the Wyoming province. Initial 87Sr / 86Sr ratios of some of the Wyoming granites are higher than expected if the rocks had been derived from juvenile magmas and it is likely that older crustal rocks were involved to some degree in the generation of these granites. Slightly to highly disturbed

  5. The region of the Piedra Berroqueña: A potencial Global Heritage Stone Province. (United States)

    Freire-Lista, David Martin; Fort, Rafael


    The Piedra Berroqueña region occupies an area of approximately 4000 km2 in the Sierra de Guadarrama, Spanish Central System, the centre of the Iberian Peninsula. This region has provided most of the building granites used in Madrid and surrounding provinces. Traditional methods of cutting and carving stone have been preserved and it is easy to locate historic quarries in its landscape in addition to mechanized quarries with large reserves of this dimension stone that is exported worldwide in the form of blocks or slabs with different finishes. The Piedra Berroqueña has been used as a building stone since before the Romans. Petrophysical and durability characteristics have allowed to endure monuments as representative as The Royal Monastery of San Lorenzo del Escorial (1563-1584), del Sol Gate (1857-1862), Royal Palace (1738-1764), Alcalá Gate (1770-1778) or Prado Museum (1785-1808) in Madrid, Spain. Also the Piedra Berroqueña is part of most residential buildings and streets of this city, as well as modern buildings around the world, such as airport terminals in Athens, Cork, the British consulate in Hong Kong and headquarters of banks in Jakarta, among others. Piedra Berroqueña province is presented in this abstract, which has many granite quarries with common characteristics such as their grey tones and the presence of darker enclaves "Gabarros or negrones". In the Piedra Berroqueña province four main types of granite can be distinguish: Peraluminous granites; with biotite and occasional cordierite, whose most representative historic quarries are in Alpedrete, Colmenar Viejo, El Boalo, El Berrocal and Collado Mediano. Biotite granites with occasional amphibole are present in historic quarries in El Berrueco, Lozoyuela-Navas-Sieteiglesias and Pelayo de la Presa, among others. Currently exploited in Valdemanco and La Cabrera and marketed under the commercial names of Aurora Blanco, Blanco Berrocal, Crema Champagne, Blanco Castilla, Crema Cabrera, Blanco Perla

  6. Geochemistry and Rb-sr geochronology of associated proterozoic peralkaline and subalkaline anorogenic granites from Labrador (United States)

    Collerson, Kenneth D.


    Anorogenic granites of middle to late Proterozoic age in the Davis Inlet — Flowers Bay area of Labrador are subdivided on the basis of petrology and geochemistry into three coeval suites. Two of these are high-temperature anhydrous hypersolvus granites: a peralkaline aegirine-sodic-calcic to sodic amphibole-bearing suite and a non-alkaline fayalite-pyroxene-bearing suite. The third is a group of non-alkaline subsolvus hornblende-biotite-bearing granites. Associated with the hypersolvus peralkaline suite is a group of genetically related syenites and quartz syenites. The granites cut ca. 3,000 Ma old Archaean gneisses as well as Elsonian layered basic intrusions of the Nain Complex. One of these, a crudely layered mass which ranges in composition from gabbro to diorite and monzonite, appears to be related to the syenites. The peralkaline granites and some of the syenites are extremely enriched in the high field-strength elements such as Y, Zr, Nd, as well as Rb, Ga and Zn, and have low abundances of Ba, Sr and most of the transition elements. In contrast, the non-alkaline hypersolvus and subsolvus granites do not show the same degree of enrichment. Concentration of the highly charged cations in the peralkaline suite is believed to be the result of halogen-rich fluid activity during fractionation of the magma. The sodic evolution trend in the peralkaline suite is reflected mineralogically by the development of aegirine and aegirine-hedenbergite solid solutions, and by a spectacular amphibole compositional range from katophorite through winchite, richterite, riebeckite to arfvedsonite and ferro eckermannite. Accessory phases which are ubiquitous in these rocks include aenigmatite, astrophyllite, fluorite, monazite and zircon. The non-alkaline hypersolvus granites typically contain iron-rich phases such as fayalite, eulite, ferrosilite-hedenbergite, and annite rich biotite. In the subsolvus granites, amphiboles range in composition from edenite through common

  7. Monazite and allanite U-Th-Pb vs mica 39Ar-40Ar ages in equilibrated metasediments: closure behavior and closure temperatures (United States)

    Allaz, J.; Engi, M.; Berger, A.; Janots, E.; Villa, I. M.


    muscovite, between 17.65±0.33 and 14.84±0.23 Ma for biotite, and similar ones for margarite and paragonite. Mica ages from disequilibrium samples are substantially younger if mica was involved in retrogression reactions (textural and petrological evidence). Compared to the monazite ages of 18-19 Ma from the same samples, Ar diffusive loss is minor for muscovite and low for biotite. Interpolating U-Pb and fission track ages, we conclude that muscovite and biotite K-Ar have TC of 490-540 and 430-480 °C in samples that record petrological equilibrium. In disequilibrium samples, the TC concept is meaningless: retrogression can occur anywhere in PT space. REFERENCES [1] Jäger E, Eclogae geol. Helv. 66, 11-21 (1973) [2] Dodson MH, Contrib. Min. Pet. 40, 259-274 (1973) [3] Köppel V, Grünenfelder M, Schweiz. Min. Geol. Mitt. 55, 129-132 (1975) [4] Janots E et al, Geology 37, 11-14 (2009)

  8. Magmatic-hydrothermal fluids and volatile metals in the Spirit Lake pluton and Margaret Cu-Mo porphyry system, SW Washington, USA (United States)

    Iveson, Alexander A.; Webster, James D.; Rowe, Michael C.; Neill, Owen K.


    The halogen-bearing minerals tourmaline, amphibole, and biotite formed during magmatic-hydrothermal processes associated with the late-stage cooling of the Spirit Lake granitoid pluton (Mt. St. Helens, WA) and with the younger sulphide-mineralised rocks of the Margaret Cu-Mo porphyry deposit located entirely within the pluton. Major- and trace-element discrimination suggests that one tourmaline population crystallised from fractionated late-stage melt pockets in granodiorite-monzogranitic dykes of the pluton. These coarse, euhedral, oscillatory, and complexly sector-zoned uvite tourmalines span a limited range in Mg/(Mg + Fe) [Mg#] space (0.4-0.7 apfu) and show the highest Ti, Ca, F, Nb, and Ta contents, and low X-site vacancies (0.6 apfu), lower Ca and F contents, and the highest Li, As, and HREE contents (>80 ppm Li, >1200 ppm As). This population appears to record direct, rapid crystallisation from magmatic ± meteoric fluid(s) bearing the signature of the breakdown of primary feldspars and pyroxenes, with fluid exsolution from fractionated melt patches likely triggered by the formation of the previous generation of tourmaline. Mineralised porphyry deposit tourmaline compositions from the stockwork span a much larger range in Mg# space (0.05-0.9 apfu) and are almost entirely Ca-free. X-sites of these schorl tourmalines are dominated by Na or vacancies, and the Y-sites are strongly Fe enriched. The highest Mn and Zn concentrations (>4000 and >1000 ppm, respectively) potentially reflect the composition of mineralising fluids during ore deposition. A number of boron isotopic analyses yield predominantly heavy boron, but δ11B values range from -5.2 to 6.2 ‰ and average 1.4 ‰. Whilst most plutonic tourmalines conform to reported a- and c-sector element partitioning models, those from the mineralised porphyry show large and variable sector fractionation differences, suggesting that external controls may also be important. Wider evidence for late-stage pervasive

  9. SHRIMP study of zircons from Early Archean rocks in the Minnesota River Valley: Implications for the tectonic history of the Superior Province (United States)

    Bickford, M.E.; Wooden, J.L.; Bauer, R.L.


    Interest in Paleoarchean to early Mesoarchean crust in North America has been sparked by the recent identification of ca. 3800-3500 Ma rocks on the northern margin of the Superior craton in the Assean Lake region of northern Manitoba and the Porpoise Cove terrane in northern Quebec. It has long been known that similarly ancient gneisses are exposed on the southern margin of the Superior craton in the Minnesota River Valley and in northern Michigan, but the ages of these rocks have been poorly constrained, because methods applied in the 1960s through late 1970s were inadequate to unravel the complexities of their thermotectonic history. Rocks exposed in the Minnesota River Valley include a complex of migmatitic granitic gneisses, schistose to gneissic amphibolite, metagabbro, and paragneisses. The best-known units are the Morton Gneiss and the Montevideo Gneiss. The complex of ancient gneisses is intruded by a major younger, weakly deformed granite body, the Sacred Heart granite. Regional geophysical anomalies that extend across the Minnesota River Valley have been interpreted as defining boundaries between distinct blocks containing the various gneissic units. New sensitive high-resolution ion microprobe (SHRIMP) U-Pb data from complex zircons yielded the following ages: Montevideo Gneiss near Montevideo, 3485 ?? 10 Ma, granodiorite intrusion, 3385 ?? 8 Ma; Montevideo Gneiss at Granite Falls, 3497 ?? 9 Ma, metamorphic event, 3300-3350 Ma, mafic intrusion, 3141 ?? 2 Ma, metamorphic overprint (rims), 2606 ?? 4 Ma; Morton Gneiss: 3524 ?? 9 Ma, granodiorite intrusion, 3370 ?? 8 Ma, metamorphic overprints (growth of rims), 3140 ?? 2 Ma and 2595 ?? 4 Ma; biotite-garnet paragneiss, 2619 ?? 20 Ma; and Sacred Heart granite, 2604 ?? 4 Ma. Zircons from a cordierite-bearing feldspar-biotite schist overlying the Morton Gneiss yielded well-defined age peaks at 3520, 3480, 3380, and 3140 Ma, showing detrital input from most of the older rock units; 2600 Ma rims on these zircons

  10. Timing and genesis of the adakitic and shoshonitic intrusions in the Laoniushan complex, southern margin of the North China Craton: Implications for post-collisional magmatism associated with the Qinling Orogen (United States)

    Ding, Li-Xue; Ma, Chang-Qian; Li, Jian-Wei; Robinson, Paul T.; Deng, Xiao-Dong; Zhang, Chao; Xu, Wang-Chun


    The NWW-striking Qinling Orogen formed in the Triassic by collision between the North China and Yangtze Cratons. Triassic granitoid intrusions, mostly middle- to high-K, calc-alkaline, are widespread in this orogen, but contemporaneous intrusions are rare in the southern margin of the North China Craton, an area commonly considered as the hinterland belt of the orogen. In this paper, we report zircon U-Pb ages, elemental geochemistry, and Sr-Nd-Hf isotope data for the Laoniushan granitoid complex that was emplaced in the southern margin of the North China Craton. Zircon U-Pb dating shows that the complex was emplaced in the late Triassic (228 ± 1 to 215 ± 4 Ma), indicating that it is part of the post-collisional magmatism in the Qinling Orogen. The complex consists of, from early to late, biotite monzogranite, quartz diorite, quartz monzonite, and hornblende monzonite, which span a wide compositional range, e.g., SiO 2 = 55.9-70.6 wt.%, K 2O + Na 2O = 6.6-10.2 wt.%, and Mg # of 24 to 54. The biotite monzogranite has high Al 2O 3 (15.5-17.4 wt.%), Sr (396-1398 ppm) and Ba (1284-3993 ppm) contents and relatively high La/Yb (mostly 14-30) and Sr/Y (mostly 40-97) ratios, but low Yb (mostly 1.3-1.6 ppm) and Y (mostly14-19 ppm) contents, features typical of adakitic rocks. The quartz monzonite, hornblende monzonite and quartz diorite have a shoshonitic affinity, with K 2O up to 5.58 wt.% and K 2O/Na 2O ratios averaging 1.4. The rocks are characterized by strong LREE/HREE fractionation in chondrite-normalized REE pattern, without obvious Eu anomalies, and show enrichment in large ion lithophile elements but depletion in high field strength elements (Nb, Ta, Ti). The biotite monzogranite (228 Ma) has initial 87Sr/ 86Sr ratios of 0.7061 to 0.7067, ɛNd(t) values of - 9.2 to - 12.6, and ɛ Hf(t) values of - 9.0 to - 15.1; whereas the shoshonitic granitoids (mainly 217-215 Ma) have similar initial 87Sr/ 86Sr ratios (0.7065 to 0.7075) but more radiogenic ɛNd(t) (- 12.4 to

  11. 青海西部祁漫塔格山卡尔却卡铜多金属矿床似斑状黑云二长花岗岩LA-ICP-MS锆石U-Pb年龄%Zircon LA-ICP-MS U-Pb age of monzogranites in the Kaerqueka copper-polymetallic deposit of Qimantag, western Qinghai Province

    Institute of Scientific and Technical Information of China (English)

    陈博; 栗亚芝; 张占玉; 耿建珍; 贾群子; 宋忠宝; 张晓飞; 陈向阳; 全守村; 张雨莲


    The Kaerqueka copper-polymetallic ore bodied in Qimantage region can mainly be found in monzonitic granite and skarn belts located in the contact zones between granodiorite, porphyritic biotitic monzogranite and Cambrian-Ordovician strata. Based on LA-ICP-MS U-Pb chronological study of zircons, the authors obtained the age (410.1Ma±2.6Ma) of biotitic monzogranite close to VE ore belt. Nevertheless, other researchers hold that the rock-forming and ore-forming processes took place in Indo-Chinese period based on the age of granodiorite (237Ma±2Ma) and the Re-Os model age (239Ma) of molybdenite. A comparison of the geochemi-cal characteristics between the two rock bodies has led the authors to reach the conclusion diat the mineralization was related not only to the Indo-Chinese intermediate-acid intrusive rocks but also to the late Caledonian acid intrusive rocks, and there existed a difference in magma origin between porphyritic biotitic monzogranite and granodiorite, suggesting that they were formed in different peri-ods of tectonic evolution. Ore deposits in Qiirantag region were formed in late Caledonian and in Indo-Chinese period. Although the outcrop of late Caledonian period is not so apparent as the one of Indo-Chinese period, due attention should be paid to the contribution of late Caledonian intiusives to mineralization.%祁漫塔格卡尔却卡铜多金属矿体主要产于花岗闪长岩、似斑状黑云母二长花岗岩体与寒武纪-奥陶纪滩间山群接触部位的矽卡岩带和二长花岗岩中.本次对矿区Ⅶ号带矽卡岩与矿体紧邻的似斑状黑云母二长花岗岩体进行LA-ICP-MS锆石U-Pb测年,获得年龄为410.1Ma±2.6Ma.结合前人获得的花岗闪长岩SHRIMP锆石U-Pb年龄(237 Ma±2Ma)和矿石矿物辉钼矿Re-Os模式年龄(239Ma),认为岩体成岩和成矿时代都发生在印支期,卡而却卡铜多金属矿成矿作用不仅与印支期中酸性侵入岩有关,也与加里东晚期酸性侵入

  12. 华南花岗岩两个成岩成矿系列的演化

    Institute of Scientific and Technical Information of China (English)



    Series Ⅰ(the Nanling Series)has a sequence of petrogenesis and mineralization:monzonitic granite or granodiorite→biotite granite→leucocratic granite→granoporphyry or quartz porphyry→intermediate-basic dikes;ree→Nb,Ta(Li,Rb,Cs),Be,Sn,W,Mo,Bi,As→Cu,Zn,Pb→Sb,Hg,U.Series Ⅱ(the Yangtze Series):pyroxene diorite(or gabbro)→diorite or quartz diorite→granodicrite (quartz monzonite)or monzonitic granite→granite→K-feldspar granite→granoporphyry or quartz porphyry(syenitic porphyry or quartz syenitic porphyry)→intermediate-bastic dikes;Fe→Cu(Au)→Mα(W)→Zn,Pb→Pb(Ag).There exists an evolutionary trend for each series.Obvious differences have been recognized between Series Ⅰand Ⅱ.As for Series Ⅱ,the bulk composition is close to that of andesite.Relatively high temperature of formation(980°-1,140℃),petrochemieal enrichment in Mg and Ca,the composition of biotite characterized by the high content of magnesium,assemblages of accessory minerals(magnetite-sphene-apatite or magnetite-ilmenite-REE-rich zircon), of biotite characterized by the high content of magnesium,assemblages of accessory minerals(magnetite-sphene-apatite or magnetite-ilmenite-REE-rich zircon),trace elements predominated by Cl and Sr with ∑ Ce>∑Y in the rocks and accessory minerals,relatively high δEn(0.74-0.99)without depleticn,δ18O10 times)characteristic of mantle derivation,very low 37Sr/86Sr(0.7036-0.7085)and the occurrence of intermediate-basic dikes(similar to basalts in composition)in the final evolutionary stage are sufficiently enough to show that Series Ⅱ has a.material souree in the lower crust or in the upper mantle.The fact that 37Sr/86Sr>0.7037 in most eases implies a partial coantamination by crystal materials.As for Series I,the bulk formation(600°-680℃),chemical composition noted for high SiO2,and K2O,complicated accessory mineralogy and assemblages(magnetite-ilmenite-zircon,or monazitexenotime-zircon),bioite with hih content of iron

  13. Interaction between Silicate-Dissolving Bacillus globisporus Q12 and Mica Minerals%硅酸盐矿物分解细菌Bacillus globisporus Q12与云母矿物相互作用的研究

    Institute of Scientific and Technical Information of China (English)

    黄智; 何琳燕; 黄静; 王琪; 盛下放


    The interactions between soil minerals and microorganisms are important ecological processes in soils. The interactions between the silicate-dissolving Bacillus globisporus Q12 isolated from weathered potassium-bearing minerals and micas (such as biotite and muscovite) were investigated through determinations of K,Si,FeN Al, cell growth and metabolism, and through analyses of transmission electron microscope (TEM)and scanning electron microscope (SEM), The results showed that different mica minerals have different effects on the cell growth and acid metabolism (such as organic acids)of Bacillus globisporus Q12,and that the strain showed better growth and metabolism on the biotite than on the muscovite. It was found that inoculation with the strain increased releasing of K, Si、Fe、Al from the micas minerals. SEM-EDX analyses showed that the strain Q12 could colonize the surfaces of the micas and accelerate the weathering of biotite and muscovite. The strain Q12 could also absorb cations and small grains,and such to form new minerals around the cells.%土壤矿物与微生物相互作用对土壤中一系列生态过程产生重要影响.本文通过对培养液进行K、Si、Fe、A1等元素分析,测定了菌株生长与代谢产物,结合扫描电镜和透射电镜的观察,研究了钾矿物表生硅酸盐矿物分解细菌Bacillus globisporus Q12菌株与云母矿物(黑云母和白云母)的相互作用规律.结果表明,不同的云母矿物对B.globisporus Q12菌株的生长与代谢有不同影响;与白云母相比,黑云母更适合B.globisporus Q12菌株的生长与酸性代谢产物(如有机酸等)的合成;供试菌株能促进黑云母和白云母矿物中K、Si、Fe、A1等元素的释放.扫描电镜、透射电镜观察与能谱分析发现,B.globisporusQ12菌株能在云母矿物表面定殖,加速云母矿物的风化;茵体自身也能吸附培养液中离子和矿物碎片而形成新的矿物.

  14. Bluish granites from Extremadura (Spain): a radiological evaluation. (United States)

    Pereira, Dolores; Neves, Luís.; Peinado, Mercedes; Pereira, Alcides; Rodríguez, Leticia; António Blanco, José


    We have found in the area of Trujillo (Extremadura, Spain) a variety of striking bluish granites, outcropping within the Plasenzuela pluton. They are all quarried under different names and are characterized by leucocratic minerals such as quartz, feldspar (both potassium and plagioclase), sometimes giving a fenocrystic texture and muscovite, with some biotite. As accessory phases, idiomorphic tourmaline is found. Recently a bluish phosphate distributed in the whole rock was detected, included within most mineral phases and fillings from stressed structures that are cutting the rock. We attribute the bluish color of the granites to this phosphate. Although biotite is almost always transformed to chlorite, the rock gives an excellent response to be polished. Physico-mechanical properties make this bluish granite a perfect option for most applications. Absorption coefficient is rather low and alteration by thermal changes has not been observed. A secondary facies with yellow colour also occurs, spatially close to the topographic surface, and probably represents an alteration product of the original granite. This facies is also commercialized as ornamental stone. A radiological survey was carried out in the field, using a gamma ray spectrometer. The radiological background is quite homogeneous in the pluton, without significant differences between gamma ray fluxes of both facies (altered and non altered). The average contents of U, Th and K2O determined in situ with the spectrometer are 7.4 ppm, 0.8 ppm and 3.67%, respectively (n=15). Using U as a Ra proxy, the I index of the EU technical document 112 can be determined, and results in a value of 0.64 for the referred composition. This implies that the rock can be used without any restrictions for building purposes. However, a marked difference was observed in radon exhalation tests carried out in laboratorial facilities. The dominant blue variety shows radon exhalation rates comprised between 0.02 and 0.04

  15. Geology and geochemistry of the Macheng Algoma-type banded iron-formation, North China Craton: Constraints on mineralization events and genesis of high-grade iron ores (United States)

    Wu, Huaying; Niu, Xianglong; Zhang, Lianchang; Pirajno, Franco; Luo, Huabao; Qin, Feng; Cui, Minli; Wang, Changle; Qi, Min


    The Macheng iron deposit is located in the eastern Hebei province of the North China Craton (NCC). It is hosted in Neoarchean metamorphic rocks of Baimiaozi formation in the Dantazi Group, consisting of biotite-leptynite, plagioclase-gneiss, plagioclase-amphibolite, migmatite, migmatitic granite and quartz schist. Geochemical analyses of the host biotite leptynite and plagioclase amphibolites show that their protoliths are both volcanics, inferred to be trachytic basalt and basaltic andesite, respectively. Based on the geochemical signature of the host rocks, together with geology of the iron deposit, it is inferred that the Macheng BIF is an Algoma-type iron exhalative formation, formed in an arc-related basin in the Neoarchean. Post-Archean Australian Shale (PAAS)-normalized rare earth elements (REEs) plus yttrium (Y) concentrations of different BIF ores with gneissic, striated and banded structure in the Macheng deposit, show similar patterns with depletions in light rare earth elements (LREEs) and middle rare earth elements (MREEs) relative to heavy rare earth elements (HREEs) and with apparently positive La, Y and Eu anomalies. Y/Ho ratios of the gneissic, striated and banded BIF ores vary from 37 to 56. These geochemical features of the BIF ores reveal their affinity with the sea water and the presence of a high-temperature hydrothermal component, indicating that both the seawater and high temperature hydrothermal fluids derived from alteration of oceanic basalts and komatiites may contribute to formation of the Macheng BIF. Geological, mineralogical and geochemical studies of the Macheng deposit recognized two kinds of high-grade iron ores. One is massive oxidized high-grade ore (Fe2O3T = 74.37-86.20 wt.%), mainly consisting of hematite with some magnetite, which shows geochemical characteristics of the gneissic, striated and banded BIF ores. The other type is magnetite high-grade ore, also massive and consisting of magnetite, with distinct characteristics

  16. Geochronology and geochemistry of the Triassic bimodal volcanic rocks and coeval A-type granites of the Olzit area, Middle Mongolia: Implications for the tectonic evolution of Mongol-Okhotsk Ocean (United States)

    Zhu, Mingshuai; Zhang, Fochin; Miao, Laicheng; Baatar, Munkhtsengel; Anaad, Chimedtseren; Yang, Shunhu; Li, Xingbo


    The Olzit volcanism in Middle Mongolia comprises a bimodal suite of basalts and peralkaline rhyolites adjacent to the Main Mongolia Lineament. The basalts are characterized by enrichment in LILE and LREE, and depletion in HFSE with typical Sr-Nd isotopic signatures (εNd(t) = -2.50 to -0.38 and (87Sr/86Sr)i = 0.7058-0.7063), indicating they were likely derived from partial melting of an enriched lithospheric mantle, modified by subducted slab-derived fluids. The rhyolites show a close affinity to A-type granites with enrichment in LILE and LREE, and depletion in Nb, Ta and Ti. They also show a significant negative Eu anomaly, and have εNd(t) values ranging from 0.50 to 1.38 and initial 87Sr/86Sr ratios ranging from 0.7022 to 0.7200, suggesting the rhyolites stem from partial melting of crustal rocks rather than fractional crystallization of the basaltic melt. The rhyolite porphyry yields a SHRIMP zircon U-Pb age of 207 ± 2 Ma (MSWD = 1.42), indicating the bimodal volcanic suite formed in the Late Triassic. The miarolitic per-alkaline granite and biotite-bearing granite, which are associated with the bimodal volcanic rocks, show typical A-type granitic geochemical affinity with εNd(t) = 0.89-0.91 and (87Sr/86Sr)i = 0.7021-0.7043, indicating they are likely generated by partial melting of crustal rocks similar to the rhyolitic end-member of bimodal suite. The miarolitic per-alkaline granite and biotite-bearing granite yielded SHRIMP zircon U-Pb ages of 209 ± 2 Ma (MSWD = 0.91) and 213 ± 3 Ma (MSWD = 1.65) respectively, which are nearly coeval with the age of the bimodal volcanic suites. In view of the new geochemical and chronological data in this study, we suggest the Olzit Late Triassic bimodal volcanic rocks together with the coeval A-type granites represent a back-arc basin extensional environment, which probably related to the roll-back of Mongol-Okhotsk oceanic plate during the southward subduction under the Central Mongolia microcontinent.

  17. Petrographic, geochemical and isotopic evidence of crustal assimilation processes in the Ponte Nova alkaline mafic-ultramafic massif, SE Brazil (United States)

    Azzone, Rogério Guitarrari; Montecinos Munoz, Patricio; Enrich, Gaston Eduardo Rojas; Alves, Adriana; Ruberti, Excelso; Gomes, Celsode Barros


    Crustal assimilation plus crystal fractionation processes of different basanite magma batches control the evolution of the Ponte Nova cretaceous alkaline mafic-ultramafic massif in SE Brazil. This massif is composed of several intrusions, the main ones with a cumulate character. Disequilibrium features in the early-crystallized phases (e.g., corrosion and sieve textures in cores of clinopyroxene crystals, spongy-cellular-textured plagioclase crystals, gulf corrosion texture in olivine crystals) and classical hybridization textures (e.g., blade biotite and acicular apatite crystals) provide strong evidence of open-system behavior. All samples are olivine- and nepheline-normative rocks with basic-ultrabasic and potassic characters and variable incompatible element enrichments. The wide ranges of whole-rock 87Sr/86Sri and 143Nd/144Ndi ratios (0.70432-0.70641 and 0.512216-0.512555, respectively) are indicative of crustal contribution from the Precambrian basement host rocks. Plagioclase and apatite 87Sr/86Sr ratios (0.70422-0.70927) obtained for the most primitive samples of each intrusion indicate disequilibrium conditions from early- to principal-crystallization stages. Isotope mixing-model curves between the least contaminated alkaline basic magma and heterogeneous local crustal components indicate that each intrusion of the massif is differentiated from the others by varied degrees of crustal contribution. The primary mechanisms of crustal contribution to the Ponte Nova massif involve the assimilation of host rock xenoliths during the development of the chamber environment and the assimilation of partial melts from the surrounding host rocks. Thermodynamic models using the melts algorithm indicate that parental alkaline basic magmas can be strongly affected by contamination processes subsequently to their initial stages of crystallization when there is sufficient energy to assimilate partial melts of crustal host rocks. The assimilation processes are considered to

  18. Fluid components in accessory minerals of Pan-African granitoids in the S(o)r Rondane Mountains, East Antarctica

    Institute of Scientific and Technical Information of China (English)

    LI Zi-long; CHEN Han-lin; YANG Shu-feng; TAINOSHO Yoshiaki; SHIRAISHI Kazuyuki; OWADA Masaaki


    Fluids (fluorine, chlorine, and OH) in accessory minerals (apatite, titanite and allanite) of Pan-African granitoids(Group-Ⅰ granitoids, Group-Ⅱ granitoids and Mefjell Plutonic Complex) from the Sor Rondane Mountains, East Antarctica were precisely measured by an electronic microprobe analyzer in this study. Apatites in the granites have commonly high fluorine contents. However, fluorine contents from the Group-Ⅰ, Group-Ⅱ granitoids and Mefjell Plutonic Complex (MPC) are of important variation, which F contents (3.21~7.20 wt%) in apatite from the Group-Ⅱ granitoids are much higher than those from the Group-Ⅰ granitoids (1.22~3.60 wt%) and the MPC (3.21~4.11 wt%). Titanite in the MPC has a low fluorine content (0.23~0.50 wt%), being less than those in the Group-Ⅰ granitoids (2.28 wt%) and Group-Ⅱ granitoids (1.85~2.78 wt%). Fluorine in allanite in the Group-Ⅱ granitoids seems to have much lower contents than those from the Group-Ⅰ granitoids and the MPC. Higher fluorine contents in the titanite from the Group-Ⅱ granitoids may be mainly controlled by late-magmatic fluid-rock interaction processes associated with melt, but may not be indicative of original magma contents based on its petrographic feature. Due to very lower chlorine contents from all of accessory minerals, the authors suggest that titanite and apatite with higher fluorine contents in the Group-Ⅱ granitoids have much lower H2O (OH) contents compared with those in the Group-Ⅰ granitoids according to the partition among (F, Cl, OH).Fluorine contents in whole-rock samples show a variation from the higher in the Group-Ⅰ granitoids to the lower in the Group-Ⅱ granitoids and the MPC, which are consistent with the changes of those from the biotite and hornblende as well as fluorite occurred in the Group-Ⅰ granitoids reported previously. Based on the above study of fluorine in accessory minerals and combined with the previous fluorine contents from biotites and

  19. Distinction between S-type and peraluminous I-type granites: Zircon versus whole-rock geochemistry (United States)

    Gao, Peng; Zheng, Yong-Fei; Zhao, Zi-Fu


    Biotite and two-mica granites are common in continental crust. Although they are generally peraluminous in lithochemistry, their petrogenesis has been controversial. Because they often show a negative correlation between P2O5 and SiO2 and a positive correlation between A/CNK and SiO2, they are commonly considered as the I-type granites of metaigneous origin. However, such lithochemical consideration is not certain in view of their other geochemical characteristics. To constrain the source nature of peraluminous granites, we performed a combined study of in situ U-Pb age, O isotope, and trace element for synmagmatic and relict zircons from Triassic biotite and two-mica granites in the Nanling Range, South China. Zircon U-Pb dating yields concordant ages of 230 ± 3 to 237 ± 3 Ma for synmagmatic zircons, and 335-2379 Ma for relict zircons with two clusters at ca. 440 Ma and ca. 800 Ma, respectively. Both the synmagmatic zircons and the ~ 440 Ma relict zircons are characterized by high δ18O values of 8.8-11.4‰ and 8.6-10.3‰, respectively. In contrast, the majority of the other relict zircons show relatively low δ18O values of 5.1-7.9‰. The high δ18O values for synmagmatic zircons indicate that the Triassic granites were originated from metasedimentary sources. The two age clusters for relict zircons overlap with two episodes of granitic magmatism, respectively, in the early Paleozoic and the middle Neoproterozoic in South China, suggesting their inheritance from the metasedimentary sources. Thus, these Triassic granites were derived from partial melting of metasedimentary rocks rather than metaigneous rocks; they belong to S-type granite although their lithochemical relationships are akin to common I-type granites. As such, the zircon in situ geochemical analyses have the capacity to unravel the source nature of controversial granites. Our data indicate that fractional crystallization of heterogeneous magmas is the possible mechanism for the decoupling

  20. Chronological and geochemical studies of granite and enclave in Baimashan pluton, Hunan, South China

    Institute of Scientific and Technical Information of China (English)

    CHEN; WeiFeng; CHEN; PeiRong; HUANG; HongYe; DING; Xing; SUN; Tao


    Zircon LA-ICP-MS U-Pb dating reveals that the Baimashan Pluton is composed mainly of late Indosinian (204.5±2.8 Ma-209.2±3.8 Ma) biotite granodiorites/monzonitic granites (LIGs) and early Yanshanian (176.7±1.7 Ma) two-micas monzonitic granites (EYGs),and the coeval (203.2±4.5 Ma-205.1±3.9 Ma) mafic microgranular enclaves (MMEs) are generally found in the former.In addition,the ages of cores within zircons from LIGs and MMEs ranging from 221.4±4.0 Ma to 226.5±4.1Ma provide evidence of multistage magma intrusion during Indosinian in the study area.Measured 3010±20.6 Ma of inherited zircon age suggests that there may be recycling Archaean curstal material in existence in this area.LIGs and EYGs share some similar geochemical features: subalkaline and peraluminous granites,enrichment of Th,U,K,Ta,Zr,Hf and LREE but depletion of Ba,Nb,P,Ti and Eu,low εNd(t) values but high (87Sr/86Sr)i ratios,and old T2DM (ca.1.9-2.0 Ga).The behaviors of incompatible elements and REE are mainly dominated by fractional crystallization of plagioclase,K-feldspar,ilmenite and apatite,but that of Sr isotope mainly controlled by EC-AFC.They are crust-sourced and derived from partial melting of paleo-Proterozoic metagreywackes and related to biotite dehydration melting.LIGs are formed in post-collisional tectonic setting as crustal local extension and thinning during late Indosinian.But EYGs may be evolved products of congeneric granitic magma with LIGs formed in late Indoinian,which were emplaced again when crust underwent extensive thinning and extension in post-orogenic tectonic setting during Yanshanian in SC after undergoing EC-AFC.MMEs should be cognate enclaves and derived from liquid immiscibility of host magma.

  1. Detection of Remarkably Low Isotopic Ratio of Iron in Anthropogenic Aerosols and Evaluation of its Contribution to the Surface Ocean (United States)

    Kurisu, M.; Iizuka, T.; Sakata, K.; Uematsu, M.; Takahashi, Y.


    It has been reported that phytoplankton growth in the High Nutrient-Low Chlorophyll (HNLC) regions is limited by dissolved iron (DFe) concentration (e.g., Martin and Fitzwater, 1988). Aerosol is known as one of the dominant sources of DFe to the ocean and classified into two origins such as anthropogenic and natural. A series of recent studies showed that Fe in anthropogenic aerosols is more soluble than that in natural aerosols (Takahashi et al., 2013) and has lower isotopic ratio (Mead et al., 2013). However, the difference between Fe isotopic ratio (δ56Fe: [(56Fe/54Fe)sample/(56Fe/54Fe)IRMM-14]-1) of two origins reported in Mead et al. (2013) is not so large compared with the standard deviation. Therefore, the aim of this study is to determine Fe species and δ56Fe in anthropogenic aerosols more accurately and to evaluate its contribution to the ocean surface. Iron species were determined by X-ray absorption fine structure (XAFS) analysis, while δ56Fe in size-fractionated aerosols were measured by MC-ICP-MS (NEPTUNE Plus) after chemical separation using anion exchange resin. Dominant Fe species in the samples were, ferrihydrite, hematite, and biotite. It was also revealed that coarse particles contained a larger amount of biotite and that fine particles contained a larger amount of hematite, which suggested that anthropogenic aerosols were emitted during combustion processes. In addition, results of Fe isotopic ratio analysis suggested that δ56Fe of coarse particles were around +0.25‰, whereas that of fine particles were -0.5 ˜ -2‰, which was lower than the δ56Fe in anthropogenic aerosol by Mead et al. (2013). The size-fractionated sampling made it possible to determine the δ56Fe in anthropogenic aerosol. Soluble component in fine particles extracted by simulated rain water also showed much lower δ56Fe (δ56Fe = -3.9±0.12‰), suggesting that anthropogenic Fe has much lower isotopic ratio. The remarkably low δ56Fe may be caused by the

  2. Rb-Sr isotopic composition of granites in the Western Krušné hory/Erzgebirge pluton, Central Europe: record of variations in source lithologies, mafic magma input and postmagmatic hydrothermal events (United States)

    Dolejš, David; Bendl, Jiří; Štemprok, Miroslav


    The late Variscan (327-318 Ma) Western Krušné hory/Erzgebirge pluton (Czech Republic and Germany) represents a multiply emplaced intrusive sequence ranging from low-F biotite monzogranites (with rare minor bodies of gabbrodiorites and granodiorites) to high-F topaz-zinnwaldite alkali-feldspar granites. This granite suite is characterized by progressively increasing concentrations of incompatible elements (Li, Rb, F), monotonous decrease in mafic components and compatible elements (FeOtot, MgO, TiO2, CaO, Sr) with increasing silica. Consequently, this leads to extreme variations in the Rb/Sr ratios (0.52 to 59), which impose highly variable 87Rb/86Sr and 87Sr/86Sr signatures. The low-F biotite monzogranites represent isotopically heterogeneous mixture with (87Sr/86Sr)323 = 0.707-0.709 between partial melts from the Saxothuringian metasediments and mantle-derived mafic precursors. The medium-F two-mica microgranites show variable (87Sr/86Sr)323 = 0.708-0.714, indicating involvement of multiple precursors and more mature crustal protoliths. The evolved high-F topaz-zinnwaldite alkali-feldspar granites were derived from a precursor with (87Sr/86Sr)320 = 0.707-0.708 at 324-317 Ma by differentiation, which produced the extreme Rb/Sr enrichment and variations. The Li/Rb ratios remain nearly constant (~0.5), thus insensitive to the degree of geochemical differentiation. In comparison to terrestrial variations, the high Li/Rb values indicate derivation of granitic magmas from predominantly sedimentary precursors, in accord with 7Li-6Li and 143Nd-144Nd isotope composition reported previously. The Rb-Sr element variations in each granite unit are sligthly different and indicate ascent and emplacement of separate magma batches, which do not form a single liquid line of descent. We consider the enrichment of granites in incompatible elements (Li, Rb, F) and compatible depletion of ferromagnesian components, CaO and Sr as a combined effect of multiple precursors, changes in

  3. Contribution to the geochemical knowledge of the uranium-radium and thorium families in the southern Vosges. Applications of some results in the prospecting of uranium deposits; Contribution a la connaissance geochimique des familles uranium-radium et du thorium dans les Vosges meridionales. Application de certains resultats en prospection des gisements d'uranium

    Energy Technology Data Exchange (ETDEWEB)

    Jurain, G. [Commissariat a l' Energie Atomique, Saclay (France). Centre d' Etudes Nucleaires


    This work's aim is to lead to a more accurate knowledge of the geochemistry of the Uranium-Radium and Thorium families in the Southern Vosges and to apply some of the results to the prospecting of uraniferous deposits: It has been showed: a bond between Calcium-Magnesium and Uranium-Thorium in the calco-alkaline granites. The host minerals of Uranium and Thorium are hornblende, biotite, titanite and epidote. a concentration of Uranium, at present time with secular disequilibrium in a thermal zone where the satellite mineralizations form an epithermal paragenesis. a disequilibrium of the Uranium-Radium family in the supergene minerals of the lead (phosphate and vanadate) showing the present circulations of Uranium. a bond between the radon grade of the spring waters and Uranium-Radium of the rocks. Such a relation allow to realize a prospecting method based on the determination of radioactive gases from the cold spring-waters of a common country. (author) [French] L'etude presentee ici a pour but de conduire a une connaissance plus precise de la geochimie des familles Uranium-Radium et Thorium dans les Vosges meridionales et d'appliquer certains resultats a la prospection des gites uraniferes. Il a ete mis en evidence: une liaison Calcium-Magnesium et Uranium-Thorium dans des granites calco-alcalins. Les mineraux hotes de l'Uranium et du Thorium sont: la hornblende, la biotite, le sphene, l'epidote. une concentration actuelle de l'Uranium en desequilibre seculaire dans une zone thermale ou les mineralisations satellites constituent une paragenese epithermale. un desequilibre de la famille Uranium-Radium dans des mineraux supergenes du plomb (phosphates et vanadates) prouvant les circulations actuelles de l'Uranium. une liaison entre la teneur en Radon des eaux de sources et celle en Uranium-Radium des roches. Une telle liaison permet de realiser une methode de prospection fondee sur le dosage du gaz radioactif des eaux de sources

  4. Mineralogy and radioactivity of pegmatites from South Wadi Khuda area, Eastern Desert, Egypt

    Institute of Scientific and Technical Information of China (English)

    Mohamed F.Raslan; Mohamed A.Ali; Mohamed G.El-Feky


    Radioactive minerals in pegmatites associated with granitic rocks are commonly encountered in the south of the Wadi Khuda area and found as dyke-like and small bodies. They are observed within garnet-muscovite granites near the contact with older granitoids. Field surveys indicated that the studied pegmatites vary in dimensions ranging from 2 to 10 m in width and from 10 to 500 m in length. They are composed mainly of intergrowth of milky quartz, reddish-pink K-feldspar and plagioclase together with small pockets of muscovite. Field radiometric measurements indicated that radioactivity in pegmatites is more than twice that of their enclosing country rocks. Radionuclide measurements revealed that the average contents of U and Th increase gradually from rocks of dioritic to granodioritic composition (1.5×10-6 U and 4.3×10-6 Th) and increase significantly in biotite granites (5.8×10-6 U and 15.2×10-6 Th) but drastically decrease in muscovite granites (2.2×10-6 U and 5.6×10-6 Th). The average contents of U and Th of anomalous pegmatites are 95.3×10-6 and 116.9×10-6, respectively, indicating their uraniferous nature. In the south of the Wadi Khuda area, pegmatites are low in average Th/U (1.4) and high in average U/K (35.6), which suggests that uranium concentrating processes did not affect the pegmatites, indicating poor source-rocks. Mineralogical investigations of the studied pegmatites revealed the presence of secondary uranium minerals (kasolite and autunite), in addition to zircon, thorite, apatite, garnet and biotite. Primary and secondary radioactive mineralizations indicated that the mineralization is not only magmatic, but also post-magmatic. Electron microprobe analyses showed distinct cryptic chemical zoning within thorite where UO2 decreases from core to rim. This feature in thorite is sporadic, suggesting non-uniform redistributions of UO2 within thorite during magmatic processes.

  5. Assessment of the oxygen consumption in the backfill. Geochemical modelling in a saturated backfill

    Energy Technology Data Exchange (ETDEWEB)

    Grandia, Fidel; Domenech, Cristina; Arcos, David; Duro, Lara [Enviros Spain S.L., Barcelona (Spain)


    The consumption of oxygen in the deep disposal is a major concern due to the ability of this element to corrode the canisters where high level nuclear wastes (HLNW) are disposed. The anoxic conditions initially present in a deep geologic environment are disturbed by the excavation of the repository facilities. After sealing the deposition holes and tunnels using clay-based materials, oxygen remains dissolved in porewater or as a gas phase in the unsaturated pores. The main mechanisms of oxygen depletion that can be considered in the backfill materials are: (1) diffusion into the surrounding rock and (2) kinetic reactions with accessory minerals and organic matter existing in the backfill. In this report, a set of numerical simulations are carried out in one and two dimensions in order to test the effect on the oxygen concentration in the pore water of all these mechanisms. The backfill considered is a 0/70 mixture of MX-80 bentonite and crushed material from the excavation itself. In addition to organic matter, the solid phases with reducing capacity in the backfill are Fe(II)-bearing minerals: pyrite (FeS{sub 2}) and siderite (FeCO) (as accessory minerals in the bentonite) and Fe-biotite (from the crushed granite). In the simulations, other chemical processes like cation exchange and surface complexation onto clay surfaces, and thermodynamic equilibrium with calcite, gypsum and quartz are considered. Initial composition of porewater is obtained by equilibrating the Forsmark groundwater with the backfill material. The 1D simulation consists of a number of cells with no reactive minerals or organic matter representing granite. The central cell, however, contains oxygen and reactive minerals resembling a backfill. Oxygen is allowed to move only by diffusion. The 2D model simulates the interaction with a backfill of a granitic groundwater flowing through a fracture. Like in the 1D model, the backfill contains oxygen and reactive solids. The results are very similar in

  6. Anisotropy of Pore Structure and Permeability in Granite: Preliminary Results (United States)

    Onishi, C. T.; Shimizu, I.; Mizoguchi, K.; Uehara, S.; Shimamoto, T.


    The permeability of rocks is sensitive to pore structures. In fault zones where brittle deformation dominates, connectivity of cracks is perhaps the most important factor to control the fluid permeability. The relationship between microstructure, porosity-pore structures and permeability were investigated, using drill core samples from the Toki Granite in Gifu Prefecture, Central Japan. Core samples taken from a borehole penetrating a fault strand of the Tsukiyoshi Fault at the depth of 700 m were used for analysis and measurements. The Toki Granite shows textural variations. For example, away from the fault zone, the granite is fresh, massive biotite granite. Toward the fault the granitic texture is largely destroyed, reflecting deformation due to fault movement, with extensive fracturing and development of calcite veins. The central part of the fault zone constitutes foliated ultra-cataclasites with a fine grained matrix. Microstructural observations indicate that fragmentation of crystals is the cause of grain size reduction in the fault zone and anisotropy in micro-crack development. The effective porosity of bulk samples measured by Helium pycnometer varies from 0.54% for unaltered fresh granite to over 5.4% for foliated cataclasite from the central part of the fault zone. The pore structures of the granite samples were visualized by the Laser Scanning Microscope (LSM). The samples were impregnated with low viscosity fluorescent resin under vacuum condition, and then observed by the LSM. Quasi 3-D images of pore structures were constructed from optical slices (confocal images) of thick sections. Micro-cracks in granites were successfully filled with the fluorescent resin. Micro-cracks were mainly observed at grain boundaries, and the intra and inter granular fractures. Permeability measurements were performed by a High Pressure Temperature (HPT) gas apparatus using the pore oscillation technique. Confining pressure was increased and then decreased in the range

  7. Influence of alkaline co-contaminants on technetium mobility in vadose zone sediments

    International Nuclear Information System (INIS)

    Pertechnetate was slowly reduced in a natural, untreated arid sediment under anaerobic conditions (0.02 nmol g−1 h−1), which could occur in low permeability zones in the field, most of which was quickly oxidized. A small portion of the surface Tc may be incorporated into slowly dissolving surface phases, so was not readily oxidized/remobilized into pore water. In contrast, pertechnetate reduction in an anaerobic sediment containing adsorbed ferrous iron as the reductant was rapid (15–600 nmol g−1 h−1), and nearly all (96–98%) was rapidly oxidized/remobilized (2.6–6.8 nmol g−1 h−1) within hours. Tc reduction in an anaerobic sediment containing 0.5–10 mM sulfide showed a relatively slow reduction rate (0.01–0.03 nmol g−1 h−1) that was similar to observations in the natural sediment. Pertechnetate infiltration into sediment with a highly alkaline water resulted in rapid reduction (0.07–0.2 nmol g−1 h−1) from ferrous iron released during biotite or magnetite dissolution. Oxidation of NaOH-treated sediments resulted in slow Tc oxidation (∼0.05 nmol g−1 h−1) of a small fraction of the surface Tc (13–23%). The Tc remaining on the surface was TcIV (by XANES), and autoradiography and elemental maps of Tc (by electron microprobe) showed Tc was present associated with specific minerals, rather than being evenly distributed on the surface. Dissolution of quartz, montmorillonite, muscovite, and kaolinite also occurred in the alkaline water, resulting in significant aqueous silica and aluminum. Over time, aluminosilicates, cancrinite, zeolite and sodalite were precipitating. These precipitates may be coating surface Tc(IV) phases, limiting reoxidation. - Highlights: • Pertechnetate was slowly reduced in natural arid sediment, and rapidly oxidized. • Sediment with added Fe2+ rapidly reduced pertechnetate, and was rapidly oxidized. • In 4 M NaOH, pertechnetate was rapidly reduced by Fe2+ from biotite dissolution. • In the Na

  8. Deciphering the brittle evolution of SW Norway through a combined structural, mineralogical and geochronological approach (United States)

    Scheiber, Thomas; Viola, Giulio; Fredin, Ola; Zwingmann, Horst; Wilkinson, Camilla Maya; Ganerød, Morgan


    SW Norway has experienced a complex brittle history after cessation of the Caledonian orogeny, and the recent discoveries of major hydrocarbon reserves in heavily fractured and weathered basement offshore SW Norway has triggered a renewed interest in understanding this complex tectonic evolution. In this contribution we present results from a multidisciplinary study combining lineament analysis, field work, paleo-stress inversion, mineralogical characterization and radiometric dating in the Bømlo area of SW Norway in order to develop a tectonic model for the brittle evolution of this important region. The study area mainly consists of the Rolvsnes granodiorite (U-Pb zircon age of ca. 466 Ma), which is devoid of penetrative ductile deformation features. The first identified brittle faults are muscovite-bearing top-to-the-NNW thrusts and E-W striking dextral strike-slip faults decorated with stretched biotite. These are mechanically compatible and are assigned to the same NNW-SSE transpressional regime. Ar-Ar muscovite and biotite dates of ca. 450 Ma (Late Ordovician) indicate fault activity in the course of a Taconian-equivalent orogenic event. During the subsequent Silurian Laurentia-Baltica collision variably oriented, lower-grade chlorite and epidote-coated faults formed in response to a ENE-WSW compressional stress regime. A large number of mainly N-S striking normal faults consist of variably thick fault gouge cores with illite, quartz, kaolinite, calcite and epidote mineralizations, accommodating mainly E-W extension. K-Ar dating of illites separated from representative fault gouges and zones of altered granodiorite constrain deformation ranging from the Permian to the Late Jurassic, indicating a long history of crustal extension where faults were repeatedly activated. In addition, a set of ca. SW-NE striking faults associated with alteration zones give Cretaceous dates, either representing a young phase of NW-SE extension or reactivation of previously formed

  9. Caledonian eclogite-facies metamorphism of early Proterozoic protoliths from the North-East Greenland Eclogite Province (United States)

    Brueckner, H.K.; Gilotti, J.A.; Nutman, A.P.


    High-pressure metamorphic assemblages occur in mafic, ultramafic and a few intermediate rocks in a gneiss complex that covers an area of approximately 400 ?? 100 km in the North-East Greenland Caledonides. Detailed petrologic and geochronologic studies were carried out on three samples in order to clarify the P-T-t evolution of this eclogite province. Geothermobarometry yields temperature estimates of 700-800 ??C and pressure estimates of at least 1.5 GPa from an ecologite senu stricto and a high as 2.35 GPa for a garnet websterite. The eclogite defines a garnet-clinopyroxene-amphibole-whole rock Sm-Nd isochron age of 405 ?? 24 Ma (MSWSD 0.9). Isofacial garnet websterites define garnet-clinopyroxene-orthopyroxene-amphibole-whole rock-(biotite) ages of 439 ?? 8 Ma (MSWD = 2.1) for a coarse=grained sample and 370 ?? 12 Ma (MSWD = 0.6) for a finer-grained variety. Overgrowths on zircons from the fine-grained pyroxenite and the eclogite give a pooled 206Pb/238U SHRIMP age of 377 ?? 7 Ma (n = 4). Significantly younger Rb-Sr biotite ages of 357 ?? 8, 330 ?? 6 and 326 ?? 6 agree withyoung Rb-Sr, K-Ar and 40Ar/39Ar mineral ages from the gneiss complex and indicate slow cooling of the eclogitic rocks. High-pressure metamorphism may have been at least 439 Ma old (Siluro-Ordovician) with cooling through amphibolite-facies conditions in the Devonian and continued crustal thinning and exhumation well into the Carboniferous. Sm-Nd whole rock model ages indicate the eclogite protoliths are Early Proterozoic in age, while 207Pb/206Pb SHRIMP ages of 1889 ?? 8 from an-hedral zircon cores probably reflect Proterozoic metasomatism. The samples have negative ??Nd values (-5 to -16) and elevated 87Sr/86Sr ratios (0.708-0.715), consistent with field evidence that the eclogite protoliths were an integral part of the continental crust long before Caledonian metamorphism. The presence of a large Caledonian eclogite terrane in Greenland requires modification of current tectonic models that

  10. Zircon U-Pb ages and Sr-Nd-Hf isotopes of the highly fractionated granite with tetrad REE patterns in the Shamai tungsten deposit in eastern Inner Mongolia, China: Implications for the timing of mineralization and ore genesis (United States)

    Jiang, Si-Hong; Bagas, Leon; Hu, Peng; Han, Ning; Chen, Chun-Liang; Liu, Yuan; Kang, Huan


    The Shamai tungsten deposit is located in the eastern part of the Central Asian Orogenic Belt (CAOB). Tungsten mineralization is closely related to the emplacement of fine- to medium-grained biotite monzogranite (G1) and porphyritic biotite monzogranite (G2) in the Shamai Granite. NW-trending joints and faults host orebodies in the Shamai Granite and Devonian hornfels. The mineralization is characterized by a basal veinlet zone progressing upwards to a thick vein zone followed by a mixed zone, a veinlet zone, and a thread vein zone at the top. The ore-related alteration typically consists of muscovite, greisen, and hornfels. In order to constrain the timing of the Shamai mineralization and discuss the ore genesis, muscovite Ar-Ar, molybdenite Re-Os, and zircon U-Pb geochronological, geochemical, and Sr-Nd-Hf isotopic studies were completed on the deposit. The U-Pb zircon dating yielded weighted mean ages of 153 ± 1 Ma for G1 and 146 ± 1 Ma for G2. Muscovite from a wolframite-bearing quartz vein yielded an Ar-Ar plateau age of 140 ± 1 Ma, whereas two molybdenite samples yielded identical Re-Os model ages of 137 ± 2 Ma. These two ages are younger than the two monzogranites, suggesting a prolonged magmatic-hydrothermal interaction during tungsten mineralization. Major and trace element geochemistry shows that both G1 and G2 are characterized by high SiO2 and K2O contents, high A/CNK values (1.08-1.40), a spectacular tetrad effect in their REE distribution patterns, and non-CHARAC (charge-and-radius-controlled) trace element behavior. This suggests that both G1 and G2 are highly differentiated peraluminous rocks with strong hydrothermal interaction. The Nd-Hf isotope data for the Shamai Granite (εNd(t) between - 1.9 and + 7.4, ɛHf(t) from 5.2 to 12.8) are largely compatible with the general scenario for much of the Phanerozoic granite emplaced in the CAOB. It is here suggested that the Shamai Granite originated from partial melting of a juvenile lower crust with

  11. Thermal and barometric constraints on the intrusive and unroofing history of the Black Mountains: Implications for timing, initial dip, and kinematics of detachment faulting in the Death Valley Region, California (United States)

    Holm, Daniel K.; Snow, J. Kent; Lux, Daniel R.


    Unroofing of the Black Mountains, Death Valley, California, has resulted in the exposure of 1.7 Ga crystalline basement, late Precambrian amphibolite facies metasedimentary rocks, and a Tertiary magmatic complex. The 40Ar/39Ar cooling ages, obtained from samples collected across the entire length of the range (>55 km), combined with geobarometric results from synextensional intrusions, provide time-depth constraints on the Miocene intrusive history and extensional unroofing of the Black Mountains. Data from the southeastern Black Mountains and adjacent Greenwater Range suggest unroofing from shallow depths between 9 and 10 Ma. To the northwest in the crystalline core of the range, biotite plateau ages from ˜13 to 6.8 Ma from rocks making up the Death Valley turtlebacks indicate a midcrustal residence (with temperatures >300°C) prior to extensional unroofing. Biotite 40Ar/39Ar ages from both Precambrian basement and Tertiary plutons reveal a diachronous cooling pattern of decreasing ages toward the northwest, subparallel to the regional extension direction. Diachronous cooling was accompanied by dike intrusion which also decreases in age toward the northwest. The cooling age pattern and geobarometric constraints in crystalline rocks of the Black Mountains suggest denudation of 10-15 km along a northwest directed detachment system, consistent with regional reconstructions of Tertiary extension and with unroofing of a northwest deepening crustal section. Mica cooling ages that deviate from the northwest younging trend are consistent with northwestward transport of rocks initially at shallower crustal levels onto deeper levels along splays of the detachment. The well-known Amargosa chaos and perhaps the Badwater turtleback are examples of this "splaying" process. Considering the current distance of the structurally deepest samples away from moderately to steeply east tilted Tertiary strata in the southeastern Black Mountains, these data indicate an average initial

  12. Argon behaviour in an inverted Barrovian sequence, Sikkim Himalaya: The consequences of temperature and timescale on 40Ar/39Ar mica geochronology (United States)

    Mottram, Catherine M.; Warren, Clare J.; Halton, Alison M.; Kelley, Simon P.; Harris, Nigel B. W.


    40Ar/39Ar dating of metamorphic rocks sometimes yields complicated datasets which are difficult to interpret in terms of timescales of the metamorphic cycle. Single-grain fusion and step-heating data were obtained for rocks sampled through a major thrust-sense shear zone (the Main Central Thrust) and the associated inverted metamorphic zone in the Sikkim region of the eastern Himalaya. This transect provides a natural laboratory to explore factors influencing apparent 40Ar/39Ar ages in similar lithologies at a variety of metamorphic pressure and temperature (P-T) conditions. The 40Ar/39Ar dataset records progressively younger apparent age populations and a decrease in within-sample dispersion with increasing temperature through the sequence. The white mica populations span ~ 2-9 Ma within each sample in the structurally lower levels (garnet grade) but only ~ 0-3 Ma at structurally higher levels (kyanite-sillimanite grade). Mean white mica single-grain fusion population ages vary from 16.2 ± 3.9 Ma (2σ) to 13.2 ± 1.3 Ma (2σ) from lowest to highest levels. White mica step-heating data from the same samples yields plateau ages from 14.27 ± 0.13 Ma to 12.96 ± 0.05 Ma. Biotite yield older apparent age populations with mean single-grain fusion dates varying from 74.7 ± 11.8 Ma (2σ) at the lowest structural levels to 18.6 ± 4.7 Ma (2σ) at the highest structural levels; the step-heating plateaux are commonly disturbed. Temperatures > 600 °C at pressures of 0.4-0.8 GPa sustained over > 5 Ma, appear to be required for white mica and biotite ages to be consistent with diffusive, open-system cooling. At lower temperatures, and/or over shorter metamorphic timescales, more 40Ar is retained than results from simple diffusion models suggest. Diffusion modelling of Ar in white mica from the highest structural levels suggests that the high-temperature rocks cooled at a rate of ~ 50-80 °C Ma- 1, consistent with rapid thrusting, extrusion and exhumation along the Main

  13. A large eruption convulsed in prehistoric times an extensive area of Catamarca, Southern Central Andes, NW Argentina (United States)

    Fernandez-Turiel, Jose-Luis; Ratto, Norma; Perez-Torrado, Francisco-Jose; Rodriguez-Gonzalez, Alejandro; Rejas, Marta; Lobo, Agustin


    Geomorphological, stratigraphical, mineralogical and chemical characteristics of many recent 30-160 cm ash deposits occurring at the Bolsón de Fiambalá in Catamarca, NW Argentina, allow their correlation. This lithostratigraphic unit is named Fiambalá Ash and it is uncovered or covered by colluvial deposits and present-day aeolian deposits, reworked products of the primary fall deposits. The grain size of these ash deposits is gritty rather than silty. They are nearly unique among regional ashes in containing hornblende phenocrysts. In addition, they are made up of glass (subangular blocky shards), feldspars, biotite, and quartz; magnetite, ilmenite, apatite and titanite are scarce. The glass is rhyolitic (˜75 to 79 % m/m SiO2; ˜3 to 4 % m/m Na2O; ˜3 to 5 % m/m K2O; 1 to 2 % m/m CaO; normalized to 100 %). On the other hand, in northern margins of Fiambalá basin, extensive remnants of fines-poor pumiceous debris flows and hyperconcentrated sandflow deposits as thick as 10 m are exposed on the walls of the river gorges, where the base is usually covered, e.g., Chuquisaca River. There is no significant unconformity or intercalation of other materials, thus suggesting rapid emplacement after a single eruptive event. A preliminary age of Fiambalá Ash based on archaeological studies bracket it between 1400-1270 and 1270-980 cal a BP (OxCal 4.2.4, SHCal13, 2 sigma). The geographical distribution, the geomorphological features observed in satellite images and the information on the main trends of the stratigraphy, the abundance of hornblende and biotite in the younger proximal ash fall deposits, ignimbrites and lava-domes of the Nevado Tres Cruces complex, favours this edifice as the strongest candidate to be the source of the Upper Holocene pyroclastic deposits found in the Fiambalá basin. The archaeological records seem to evidence the abrupt environmental and societal changes associated with this major eruption. Significant areas of Catamarca were likely

  14. Fractional crystallization of Si-undersaturated alkaline magmas leading to unmixing of carbonatites on Brava Island (Cape Verde) and a general model of carbonatite genesis in alkaline magma suites (United States)

    Weidendorfer, Daniel; Schmidt, Max W.; Mattsson, Hannes B.


    The carbonatites of Brava Island, Cape Verde hot spot, allow to investigate whether they represent small mantle melt fractions or form through extreme fractionation and/or liquid immiscibility from CO2-bearing silicate magmas. The intrusive carbonatites on Brava Island are part of a strongly silica-undersaturated pyroxenite, ijolite, nephelinite, nepheline syenite, combeite-foiditite, carbonatite series. The major and trace element composition of this suite is reproduced by a model fractionating olivine, clinopyroxene, perovskite, biotite, apatite, titanite, sodalite and FeTi oxides, all present as phenocrysts in the rocks corresponding to their fractionation interval. Fractionation of ~90 wt% crystals reproduces the observed geochemical trend from the least evolved ultramafic dikes (bulk X Mg = 0.64) to syenitic compositions. The modelled fractional crystallization leads to alkali enrichment, driving the melt into the carbonatite-silicate miscibility gap. An initial CO2 content of 4000 ppm is sufficient to saturate in CO2 at the point where the rock record suggests continuing unmixing carbonatites from nephelinites to nepheline syenites after 61 wt% fractionation. Such immiscibility is also manifested in carbonatite and silicate domains on a hand-specimen scale. Furthermore, almost identical primary clinopyroxene, biotite and carbonate compositions from carbonatites and nephelinites to nepheline syenites substantiate their conjugate character and our unmixing model. The modelled carbonatite compositions correspond to the natural ones except for their much higher alkali contents. The alkali-poor character of the carbonatites on Brava and elsewhere is likely a consequence of the release of alkali-rich CO2 + H2O fluids during final crystallization, which cause fenitization in adjacent rocks. We propose a general model for carbonatite generation during alkaline magmatism, where the fractionation of heavily Si-undersaturated, alkaline parent melts results in alkali and

  15. Geochemical and geochronologic analysis of the plutonic basement of the Tacaná Volcano Complex, Chiapas México. (United States)

    Paul William, L.


    The Tacana Volcano Complex (TVC) is located on the border between the State of Chiapas, southern Mexico, and Guatemala. This volcanic complex has been described as the last volcano in the northwest part of the Central American Volcanic Arc (CAVA). The region where the TVC was emplaced is influenced by the transpressional boundary formed by the shear movement between the North American and Caribbean Plates and the compressive stress by the subduction of the Cocos Plate under the North American Plate. The most recently study about TVC was by García-Palomo et al. (2004), who summarized the chronology of the TVC from basement formation to its recent activity and report that the active TVC lies on igneous basement rocks that were formed by two magmatic processes during the Mesozoic and Cenozoic. In this work, we present the results of detailed petrographic, geochemical and geochronologic analyses obtained from plutonic rocks in the basement of the TVC zone. The results show that t this basement (granites: SiO2 of 64.64 to 65.29 wt%, granodiorites: SiO2 of 60.18 wt%, and gabbros: SiO2 of 51.67 wt%) belongs to the suite of plutonic rocks of an orogenic environment. The granites are classified as both S-type peraluminosus granites derived form partial melting of continental crust, characterized by minerals such as quartz, k-feldspar, biotite, hornblende and some Fe-Ti oxides and I-type metaluminous granites derived from subduction processes with the main mineral phases being quartz, k-feldspar, hornblende, biotite and Fe-Ti oxides. The ages thus far obtained (K- Ma to 12.65 +/- 0.08 Ma) suggest that there were at least nine periods of magmatic activity that produced granitic and mafic magmas. Reference: Garcia-Palomo, A., Macias, J.L., Arce, J.L., Mora, J.C., Hughes, S., Saucedo, R., Espindola, J.M., Escobar, R., and Layer, P., (2004). GSA Special Paper 412, p 39-57.

  16. Geochemistry and petrogenesis of Mesoproterozoic A-type granitoids from the Danish island of Bornholm, southern Fennoscandia (United States)

    Johansson, Åke; Waight, Tod; Andersen, Tom; Simonsen, Siri L.


    Granitoids and gneisses from the Danish island of Bornholm have been investigated using whole rock geochemistry, Sr and Nd isotope geochemistry and Hf isotopes in zircon. Recent U-Pb dating shows that the rocks were formed during a short time interval at 1.45 to 1.46 Ga, penecontemporaneous with ongoing deformation. The strong similarity in geochemical signatures indicate that they all belong to a single igneous suite composed of alkali-calcic biotite-hornblende quartz monzonites to more evolved biotite granites, albeit with an apparent gap in SiO2 content at around 70 wt%, dividing the suite into an intermediate and a felsic part. These dominantly metaluminous rocks are strongly ferroan and potassic, and with highly elevated concentrations of many trace elements, traits that are typical for A-type granitoids. The presence of magnetite and titanite indicates relatively oxidized compositions, and Nb/Y ratios designate them to the A2 subtype. Initial whole rock εNd values range between + 1 and - 2 (with one outlier at + 4), and initial zircon εHf values between + 3 and - 4. These values may be explained by melting of relatively juvenile crust similar to that forming the Transscandinavian Igneous Belt alone, but the spread in Hf and Nd isotope compositions to values overlapping with the Svecofennian mantle at 1.45 Ga suggests involvement of a mantle-derived component. This indicates the magmatism was associated with juvenile crustal growth. There are no systematic differences in isotope or trace element characteristics between the orthogneisses and the less deformed granitoids, suggesting similar origins for both rock types, and no systematic changes in isotopic composition with SiO2 concentration. Trace element compositions indicate a within-plate setting, similar to other 1.45 Ga granites in southwest Fennoscandia, in spite of the close relation between magmatism and deformation on Bornholm. We therefore suggest intracratonic A-type magmatism within an active

  17. Evaluation of phase chemistry and petrochemical aspects of Samchampi–Samteran differentiated alkaline complex of Mikir Hills, northeastern India

    Indian Academy of Sciences (India)

    Abhishek Saha; Sohini Ganguly; Jyotisankar Ray; Nilanjan Chaterjee


    The Samchampi –Samteran alkaline complex occurs as a plug-like pluton within the Precambrian granite gneisses of Mikir Hills,Assam,northeastern India and it is genetically related to Sylhet Traps.The intrusive complex is marked by dominant development of syenite within which ijolite – melteigite suite of rocks is emplaced with an arcuate outcrop pattern.Inliers of alkali pyroxenite and alkali gabbro occur within this ijolite –melteigite suite of rocks.The pluton is also traversed by younger intrusives of nepheline syenite and carbonatite.Development of sporadic,lumpy magnetite ore bodies is also recorded within the pluton.Petrographic details of the constituent lithomembers of the pluton have been presented following standard nomenclatorial rules.Overall pyroxene compositions range from diopside to aegirine augite while alkali feldspars are typically orthoclase and plagioclase in syenite corresponds to oligoclase species.Phase chemistry of nepheline is suggestive of Na-rich alkaline character of the complex.Biotite compositions are typically restricted to a uniform compositional range and they belong to ‘biotite ’field in the relevant classification scheme.Garnets (developed in syenite and melteigite)typically tend to be Ti-rich andradite,which on a closer scan can be further designated as melanites.Opaque minerals mostly correspond to magnetite.Use of Lindsley ’s pyroxene thermometric method suggests an equilibration temperature from ∼450°–600°C for melteigite/alkali gabbro and ∼400° C for syenite.Critical assessment of other thermometric methods reveals a temperature of equilibration of ∼700°–1350°C for ijolite –melteigite suite of rocks in contrast to a relatively lower equilibration temperature of ∼600° C for syenite. Geobarometric data based on pyroxene chemistry yield an equilibration pressure of 5.32 –7.72 kb for ijolite,melteigite,alkali pyroxenite,alkali gabbro and nepheline syenite.The dominant syenite member of the

  18. Tectonic record, magmatic history and hydrothermal alteration in the Hercynian Guérande leucogranite, Armorican Massif, France (United States)

    Ballouard, C.; Boulvais, P.; Poujol, M.; Gapais, D.; Yamato, P.; Tartèse, R.; Cuney, M.


    The Guérande peraluminous leucogranite was emplaced at the end of the Carboniferous in the southern part of the Armorican Massif. At the scale of the intrusion, this granite displays structural heterogeneities with a weak deformation in the southwestern part, whereas the northwestern part is marked by the occurrence of S/C and mylonitic extensional fabrics. Quartz veins and pegmatite dykes orientations as well as lineations directions in the granite and its country rocks demonstrate both E-W and N-S stretching. Therefore, during its emplacement in an extensional tectonic regime, the syntectonic Guérande granite has probably experienced some partitioning of the deformation. The southwestern part is characterized by a muscovite-biotite assemblage, the presence of restites and migmatitic enclaves, and a low abundance of quartz veins compared to pegmatite dykes. In contrast, the northwestern part is characterized by a muscovite-tourmaline assemblage, evidence of albitization and gresenization and a larger amount of quartz veins. The southwestern part is thus interpreted as the feeding zone of the intrusion whereas the northwestern part corresponds to its apical zone. The granite samples display continuous compositional evolutions in the range of 69.8-75.3 wt.% SiO2. High initial 87Sr/86Sr ratios and low εNd(T) values suggest that the peraluminous Guérande granite (A/CNK > 1.1) was formed by partial melting of metasedimentary formations. Magmatic evolution was controlled primarily by fractional crystallization of K-feldspar, biotite and plagioclase (An20). The samples from the apical zone show evidence of secondary muscovitization. They are also characterized by a high content in incompatible elements such as Cs and Sn, as well as low Nb/Ta and K/Rb ratios. The apical zone of the Guérande granite underwent a pervasive hydrothermal alteration during or soon after its emplacement. U-Th-Pb dating on zircon and monazite revealed that the Guérande granite was emplaced

  19. Mid-Cretaceous oblique rifting of West Antarctica: Emplacement and rapid cooling of the Fosdick Mountains migmatite-cored gneiss dome (United States)

    McFadden, R. R.; Teyssier, C.; Siddoway, C. S.; Cosca, M. A.; Fanning, C. M.


    In Marie Byrd Land, West Antarctica, the Fosdick Mountains migmatite-cored gneiss dome was exhumed from mid- to lower middle crustal depths during the incipient stage of the West Antarctic Rift system in the mid-Cretaceous. Prior to and during exhumation, major crustal melting and deformation included transfer and emplacement of voluminous granitic material and numerous intrusions of mantle-derived diorite in dikes. A succession of melt- and magma-related structures formed at temperatures in excess of 665 ± 50 °C based on Ti-in-zircon thermometry. These record a transition from wrench to oblique extensional deformation that culminated in the development of the oblique South Fosdick Detachment zone. Solid-state fabrics within the detachment zone and overprinting brittle structures record translation of the detachment zone and dome to shallow levels. To determine the duration of exhumation and cooling, we sampled granite and gneisses at high spatial resolution for U-Pb zircon geochronology and 40Ar/39Ar hornblende and biotite thermochronology. U-Pb zircon crystallization ages for the youngest granites are 102 Ma. Three hornblende ages are 103 to 100 Ma and 12 biotite ages are 101 to 99 Ma. All overlap within uncertainty. The coincidence of zircon crystallization ages with 40Ar/39Ar cooling ages indicates cooling rates > 100 °C/m.y. that, when considered together with overprinting structures, indicates rapid exhumation of granite and migmatite from deep to shallow crustal levels within a transcurrent setting. Orientations of structures and age-constrained crosscutting relationships indicate counterclockwise rotation of stretching axes from oblique extension into nearly orthogonal extension with respect to the Marie Byrd Land margin. The rotation may be a result of localized extension arising from unroofing and arching of the Fosdick dome, extensional opening within a pull-apart zone, or changes in plate boundary configuration. The rapid tectonic and temperature

  20. Mineralogically triggered strain localization: inferences from ductile paired shear zones (Tauern Window, Eastern Alps) (United States)

    Duprat-Oualid, Sylvia; Grasemann, Bernhard; Huet, Benjamin; Yamato, Philippe; Habler, Gerlinde


    Lithosphere is mainly constituted by polyphase rocks whose mineralogical, structural and textural characteristics control the spatial distribution of strain, and so, its effective mechanical strength. Variations in local mineralogical compositions may lead to drastic changes in the local microstructures and texture leading, by mechanical feedback processes, to strain hardening or weakening. Understanding these small-scale relations between the petrological characteristics, the rheological properties and the development of progressive deformation is thus of fundamental importance for understanding the strength of rocks at large-scale, especially the mechanical behavior of plates boundaries. We acknowledge the importance of brittle precursors for the localization of strain in the viscous deforming part of the crust. In this study, we focus in centimeter-wide paired ductile shear zones shaped nearby along on both sides of ep-grt-qtz veins within a late Variscan metagranodiorite of the "Zentralgneis" in the Tauern Window (Berlinerhütte, Zillertal, Austria). The paired shear zones, underlined by biotite bands, localized at some centimeters away from the veins associated with a metasomatic domain, within the relatively undeformed host rock. According to their spatial orientations, they exhibit different intensities of shearing (from incipient linking of biotites to anastomosing ultra-mylonitic bands) and thus can be explored as successive strain domains of a shear zone developing in space and time. Here, we present a combination of high-resolution petro-chemical section across the paired shear zones with microstructural and textural measurements in order to constrain mineral reactions and deformation processes associated with the development of localized shear zones. Whole rock chemical analyzes combined with continuous mineralogical mapping revealed small chemical variations induced by fluid-rock interactions in the vicinity of the veins. Although macroscopically

  1. Sorption of Cs + to micaceous subsurface sediments from the Hanford site, USA (United States)

    Zachara, John M.; Smith, Steven C.; Liu, Chongxuan; McKinley, James P.; Serne, R. Jeffrey; Gassman, Paul L.


    The sorption of Cs + was investigated over a large concentration range (10 -9-10 -2 mol/L) on subsurface sediments from a United States nuclear materials site (Hanford) where high-level nuclear wastes (HLW) have been accidentally released to the vadose zone. The sediment sorbs large amounts of radiocesium, but expedited migration has been observed when HLW (a NaNO 3 brine) is the carrier. Cs + sorption was measured on homoionic sediments (Na +, K +, Ca 2+) with electrolyte concentrations ranging from 0.01 to 1.0 mol/L. In Na + electrolyte, concentrations were extended to near saturation with NaNO 3(s) (7.0 mol/L). The sediment contained nonexpansible (biotite, muscovite) and expansible (vermiculite, smectite) phyllosilicates. The sorption data were interpreted according to the frayed edge-planar site conceptual model. A four-parameter, two-site (high- and low-affinity) numeric ion exchange model was effective in describing the sorption data. The high-affinity sites were ascribed to wedge zones on the micas where particle edges have partially expanded due to the removal of interlayer cations during weathering, and the low-affinity ones to planar sites on the expansible clays. The electrolyte cations competed with Cs + for both high- and low-affinity sites according to the trend K + >> Na + ≥ Ca 2+. At high salt concentration, Cs + adsorption occurred only on high-affinity sites. Na + was an effective competitor for the high-affinity sites at high salt concentrations. In select experiments, silver-thiourea (AgTU) was used as a blocking agent to further isolate and characterize the high-affinity sites, but the method was found to be problematic. Mica particles were handpicked from the sediment, contacted with Cs +(aq), and analyzed by electron microprobe to identify phases and features important to Cs + sorption. The microprobe study implied that biotite was the primary contributor of high-affinity sites because of its weathered periphery. The poly-phase sediment

  2. Metamorphic history of LP/HT migmatites from the Bavarian Unit (Bohemian Massif) (United States)

    Sorger, Dominik; Hauzenberger, Christoph; Linner, Manfred; Iglseder, Christoph


    Granulite facies migmatites are commonly observed in the Bavarian Unit which were formed during a late Variscan (post 330 Ma) LP-HT overprint. This event is related to a delamination of mantle lithosphere and subsequent asthenospheric upwelling. Most of these rocks underwent high degrees of melting forming meta- and diatexites. Former work in the Sauwald area, Upper Austria, by Tropper et al. (2006) determined metamorphic conditions of 700-800°C and 0.4-0.5 Gpa. In this study samples were taken along the (1) Danube valley (west of Linz), from the (2) Lichtenberg area (north of Linz), the (3) Bad Leonfelden area (west of the Rodl Fault) and the (4) Sauwald area (south of the river Danube). Biotite and plagioclase bearing migmatite is very common and occurs all over the investigated area. These rocks are the product of intensive melting (anatexite) and formed at conditions of ~650-700°C and 0.25-0.45 Gpa. Scarce outcrops of garnet bearing Al-rich migmatitic metapelites occur along the Danube valley. The formation of the migmatitc texture with well-developed leucosomes (K-feldspar, plagioclase, quartz) and melanosomes (garnet, cordierite, sillimanite, spinel, ilmenite, ± biotite) indicate high temperature metamorphism. Most of the garnet grains show a homogenous iron-rich composition and form generally an almandine-pyrope (Xalm=0.78-0.80, Xprp=0.16-0.18) solid solution with minor contents of grossular and spessartine (Xgrs=0.028-0.032, Xsps=0.020-0.024). Large garnet porphyroblasts (up to 1cm in size) display a distinct chemical zoning, especially in grossular component. Elevated homogeneous grossular content in the core is followed discontinously by low grossular content at the rim indicating a two stage growth. Garnet core and rim also display different mineral inclusions. Thermobarometric calculations using garnet core compositions with inclusions and garnet rim compositions with matrix phases as well as pseudosection calculations allow the reconstruction of a P

  3. Petrochronological and structural arguments for upper plate thickening and relamination of the lower plate buoyant material in the Variscan Bohemian Massif (United States)

    Peřestý, Vít; Holder, Robert; Lexa, Ondrej; Racek, Martin; Jeřábek, Petr


    Recent tectonic models for the Variscan evolution of the Bohemian Massif emphasize the role of Rayleigh-Taylor instability for the 355-340 Ma evolution of the Moldanubian domain. This model is based on the presence of weak, low-density felsic material tectonically underplating a high-density mafic layer and its subsequent gravity-driven overturn. However, earlier phases of the Variscan orogeny concerning the emplacement of felsic low-density material to the base of the upper plate are so far poorly documented. We contribute to this problem by deciphering of polyphase early-Variscan (~375 Ma) deformation and metamorphism close to the main Variscan suture. Detailed structural, pseudosection and microstructural analyses combined with LASS monazite dating were carried out in metapelites along the western margin of the upper plate represented by the Teplá Crystalline Complex (TCC). This region is represented by a ~25 km wide deformation zone with E-W metamorphic gradients associated with two distinct early-Variscan events (~380-375 and ~375-370 Ma). The first compressional event produced a vertical NNE-SSW trending fabric and a continuous and prograde Barrovian metamorphic sequence ranging from biotite to kyanite zones at a field geotherm of 20 to 25 °C/km. Subsequently, a gently SE dipping normal shear-zone associated with retrogression develops along the base of the TCC. This sub-horizontal fabric shows normal metamorphic zonation ranging from sillimanite, biotite to chlorite zones and indicates vertical shortening related to unroofing of high pressure metabasites of the underlying Mariánské-Lázně Complex. The first metamorphic fabric is interpreted to result from early thickening of the upper plate during continental underthrusting of Saxothuringian continent (380 to 375 Ma) while the second deformation and metamorphism (~370 Ma) reflects vertical shortening produced by buoyant uplift of accreted Saxothuringian felsic crust. This event is the unique yet

  4. A natural field example indicating spinel + quartz as a non-diagnostic assemblage for ultrahigh temperature metamorphis from the Highland Complex, Sri Lanka (United States)

    Laksthitha Dharmapriya, Prasanna; Galli, Andrea; Prabath Malaviarachchi, Sanjeeva; Su, Ben-Xun; Deepal Subasinghe, Nalaka; Dissanayake, Chandrasekara; Nimalsiri, Thusitha; Zhu, Bin


    Though, co-existing spinel + quartz has been reported from a number of ultra-high-temperature (UHT) granulite terrains, experimental studies suggest that the stability of the assemblage could be shifted towards lower temperatures due to the incorporation into the spinel structure of Zn, Cr, Ti, Ni, V or Fe3+ at high oxidizing conditions. In this study, we report co-existing spinel + quartz within garnet-porphyroblasts in a non-UHT spinel- and cordierite-bearing garnet-sillimanite-biotite-graphite gneiss (khondalite) interbedded with orthopyroxene-garnet-biotite-bearing intermediate granulites from the Highland Complex (HC) in Sri Lanka. Zn-rich spinels were observed in four textural settings which probably formed during different stages along the PT trajectory followed by the khondalite: (a) spinel co-existing with tiny quartz (ZnO = 12.67-12.85 wt%), (b) spinel surrounded by sillimanite moats and in intergrowth with skeletal sillimanites (ZnO = 9.03-9.17 wt%), (c) symplectitic spinels at the margin of sillimanite (ZnO = 4.09-4.28 wt%), and (d) spinel co-existing with ilmenite or as isolated grains (ZnO = 7.61-7.97 wt% and Cr2O3 = 5.99-6.27 wt%). Textural settings (a) and (b) occur within garnet-porphyroblasts, while textures of (c) and (d) are present within cordierite moats after garnet in the rock matrix. Pseudosections calculated in the CNKFMASHTMnO system and conventional geothermobarometry suggest that the metamorphic peak conditions attained by the spinel + quartz bearing khondalites and associated intermediate granulites approached but not exceeded T of 900 °C at P of 7.5-8.5 kbar. After the peak of the metamorphism, the khondalite has undergone a stage of nearly-isobaric cooling down to T of 770 °C and P of 7.5 kbar, followed by a late stage of isothermal decompression down to P < 6.5 kbar and T of 770 °C. Hence, the stabilization of coexisting spinel + quartz to T < 900 °C could be due to the incorporation into spinel of large amount of Zn, which was

  5. Caracterización petrográfica y geoquímica y condiciones de deformación del plutón San Cristóbal, Sierra de Velasco (La Rioja, Argentina

    Directory of Open Access Journals (Sweden)

    Bellos, L. I.


    Full Text Available The San Cristóbal pluton is a 35 km2 granitic body that outcrops at the southestern tip of the Sierra de Velasco, located west of La Rioja city, Argentina. It is formed by monzogranites and syenogranites, together with scarce granodiorites, with medium to fine-grained, equigranular to slightly porphyritic textures. Their mineral assemblage consists of quartz + microcline + plagioclase + biotite ± muscovite + zircon + apatite + magnetite. The granite contains dioritic to tonalitic mafic enclaves. The central and eastern parts of the granite have been deformed by the NNW-SSE trending South Mylonitic shear zone formed by mylonitic rocks. The metamorphic host-rock is represented by scarce greenschist facies xenoliths and hornfels with the high T / P assemblage K-feldspar - cordierite - biotite ± sillimanite. The granites are calc-alkaline, weak- to moderately peraluminous, and formed as part of a continental magmatic arc developed along the active margin of western Gondwana during the Early Paleozoic. The depth of emplacement of the San Cristóbal pluton is estimated at ~12 km.

    El plutón San Cristóbal constituye un cuerpo granítico de 35 km2 que aflora en el extremo sudeste de la Sierra de Velasco, situada al oeste de la ciudad de La Rioja, Argentina. Está formado por monzogranitos y sienogranitos con escasas granodioritas, de texturas equigranulares de grano medio a fino a ligeramente porfíricas. La asociación mineral es cuarzo + microclino + plagioclasa + biotita ± moscovita + circón + apatito + magnetita. Contiene enclaves magmáticos máficos de composición diorítica a tonalítica. El granito fue afectado en su parte media y este por una zona de cizalla, formada por milonitas que integran la Faja Milonítica Sur, de rumbo NNO-SSE. La roca de caja se reconoce por xenolitos de esquistos y cuarcitas en facies esquistos verdes, y septos de corneanas con la paragénesis feldespato potásico cordierita

  6. P-T evolution of a spinel + quartz bearing khondalite from the Highland Complex, Sri Lanka: Implications for non-UHT metamorphism (United States)

    Dharmapriya, P. L.; Malaviarachchi, Sanjeewa P. K.; Galli, Andrea; Su, Ben-Xun; Subasinghe, N. D.; Dissanayake, C. B.; Nimalsiri, T. B.; Zhu, Bin


    Here, we report a natural field example for the coexistence of spinel + quartz as a non-UHT assemblage in spinel- and cordierite-bearing garnet-sillimanite-biotite-graphite gneiss (khondalite) interbedded with orthopyroxene-garnet-biotite bearing intermediate granulites from the Highland Complex (HC) in Sri Lanka. The khondalite contains Zn-rich spinel mainly in four textural assemblages namely: (a) spinel co-existing with tiny quartz (ZnO = 12.67-12.85 wt%), (b) spinel surrounded by sillimanite moates and in intergrowth with skeletal sillimanites (ZnO = 9.03-9.17 wt%), (c) symplectitic spinels at the margin of sillimanite (ZnO = 4.09-4.28 wt%) and (d) spinel co-existing with ilmenite or as isolated grains (ZnO = 7.61-7.97 wt% and Cr2O3 = 5.99-6.27 wt%). Assemblage (a) and (b) occur within garnet while assemblages of (c) and (d) are present within cordierite moates after garnet in the matrix. Pseudosections calculated in the NCKFMASHTMnO system and conventional geothermobarometry suggest that the metamorphic peak conditions attained by the spinel + quartz bearing khondalites and associated intermediate granulites did not exceed T of 900 °C and P of 7.5-8.5 kbar. Post-peak evolution was characterized by a stage of nearly-isobaric cooling down to T of 770 °C and P of 7.5 kbar, followed by a late stage of isothermal decompression down to P < 6.5 kbar and T of 770 °C. We propose that the incorporation of large amount of Zn into spinel from exotic, metasomatic fluids and possibly incorporation of Fe3+ into spinel under high oxidizing conditions may have shifted the stabilization of co-existing spinel + quartz to T < 900 °C. Hence, this study provides insights into the occurrence of spinel + quartz as a non- UHT assemblage suggesting that the coexistence of spinel + quartz should be treated with care and considered only as indicative, but not diagnostic of UHT metamorphism.

  7. Effect of partial melting on Vp and Vs in crustal enclaves from Mazarrón (SE Spain) (United States)

    Ferri, Fabio; Burlini, Luigi; Cesare, Bernardo


    The combination of compressional and shear wave velocity is an important tool in discriminating rock types and identifying residing melts within the continental crust. Here we report the laboratory measurements for Vp and Vs obtained in varying conditions up to those exceeding the beginning of melting (950 °C at 500 MPa confining pressure) on two residual garnet-biotite-sillimanite-cordierite-spinel metapelitic enclaves recovered from the Neogene dacites of Mazarrón (SE Spain). The enclaves preserve widespread interstitial rhyolitic glass as evidence of primary melt extraction. At 500 MPa, the experimental Vp ranges from 7.21 ÷ 7.46 km s- 1 at room temperature to 5.44 km/s at 950 °C. The mean Vs is 4.5 km/s at room temperature with shear-wave splitting of 0.25 ÷ 0.3 km/s, measured along three mutually orthogonal directions. When temperature increases, the Vs evidences a reversible slope change at about 650 °C, and the shear-wave splitting reduces to zero (isotropic material) at 850-950 °C, where the sample Vs is ~ 3.0 km/s. The Vp anisotropy is 7-10% up to 700 °C increasing to ~ 20% at 950 °C, while the Vs anisotropy continuously decreases with temperature from 5% to 7% at room temperature to zero at 950 °C. No mineral reactions are observed up to 650-700 °C; however, microstructure equilibrates due to the relaxation of the primary glass at the glass transition temperature. Between 850 °C and 950 °C, a new melting reaction is observed producing biotite + spinel + ilmenite + plagioclase + melt. At melting, the rock becomes isotropic for Vs, and Poisson's ratio increases to 0.30. Our seismic data show that the seismic signature of high grade metapelitic rocks is similar to that of mafic materials. The evolution of Vp and Vs at melting conditions is compatible with the geophysical data of the area, supporting the hypothesis of the current existence of anatectic melts at intermediate depths of the Alborán domain.

  8. Formation and emplacement of two contrasting late-Mesoproterozoic magma types in the central Namaqua Metamorphic Complex (South Africa, Namibia): Evidence from geochemistry and geochronology (United States)

    Bial, Julia; Büttner, Steffen H.; Frei, Dirk


    The Namaqua Metamorphic Complex is a Mesoproterozoic low-pressure, granulite facies belt along the southern and western margin of the Kaapvaal Craton. The NMC has formed between ~ 1.3 and 1.0 Ga and its central part consists essentially of different types of granitoids intercalated with metapelites and calc-silicate rocks. The granitoids can be subdivided into three major groups: (i) mesocratic granitoids, (ii) leucocratic granitoids and (iii) leucogranites. The high-K, ferroan mesocratic granitoids (54-75 wt% SiO2) have a variable composition ranging from granitic to tonalitic, and contain biotite and/or hornblende or orthopyroxene. They are strongly enriched in REE and LILE, indicating A-type chemical characteristics, and are depleted in Ba, Sr, Eu, Nb, Ta and Ti. The leucocratic granitoids and leucogranites (68-76 wt% SiO2) differ from the other group in having a granitic or slightly syenitic composition containing biotite and/or garnet/sillimanite. They have lower REE and MgO, FeOt, CaO, TiO2, MnO concentrations, but higher Na2O and K2O contents. Compositional variations in mesocratic granitoids indicate their formation by fractional crystallization of a mafic parental magma. Leucocratic granitoids and leucogranites lack such trends, which suggests melting of a felsic crustal source without subsequent further evolution of the generated magmas. The mineralogical and geochemical characteristics of the mesocratic granitoids are consistent magmatic differentiation of a mantle derived, hot (> 900 °C) parental magma. The leucocratic granitoids and leucogranites granites were formed from low-temperature magmas (< 730 °C), generated during fluid-present melting from metasedimentary sources. New U-Pb zircon ages reveal that both magma types were emplaced into the lower crust within a 30-40 million years interval between 1220-1180 Ma. In this time period the crust reached its thermal peak, which led to the formation of the leucocratic granitoids and leucogranites. A

  9. Mapping of groundwater potential zones in Salem Chalk Hills, Tamil Nadu, India, using remote sensing and GIS techniques. (United States)

    Thilagavathi, N; Subramani, T; Suresh, M; Karunanidhi, D


    This study proposes to introduce the remote sensing and geographic information system (GIS) techniques in mapping the groundwater potential zones. Remote sensing and GIS techniques have been used to map the groundwater potential zones in Salem Chalk Hills, Tamil Nadu, India. Charnockites and fissile hornblende biotite gneiss are the major rock types in this region. Dunites and peridodites are the ultramafic rocks which cut across the foliation planes of the gneisses and are highly weathered. It comprises magnesite and chromite deposits which are excavated by five mining companies by adopting bench mining. The thickness of weathered and fracture zone varies from 2.2 to 50 m in gneissic formation and 5.8 to 55 m in charnockite. At the contacts of gneiss and charnockite, the thickness ranges from 9.0 to 90.8 m favoring good groundwater potential. The mine lease area is underlined by fractured and sheared hornblende biotite gneiss where groundwater potential is good. Water catchment tanks in this area of 5 km radius are small to moderate in size and are only seasonal. They remain dry during summer seasons. As perennial water resources are remote, the domestic and agricultural activities in this region depend mainly upon the groundwater resources. The mines are located in gently slope area, and accumulation of water is not observed except in mine pits even during the monsoon period. Therefore, it is essential to map the groundwater potential zones for proper management of the aquifer system. Satellite imageries were also used to extract lineaments, hydrogeomorphic landforms, drainage patterns, and land use, which are the major controlling factors for the occurrence of groundwater. Various thematic layers pertaining to groundwater existence such as geology, geomorphology, land use/land cover, lineament, lineament density, drainage, drainage density, slope, and soil were generated using GIS tools. By integrating all the above thematic layers based on the ranks and

  10. Geology of the Ralston Buttes district, Jefferson County, Colorado: a preliminary report (United States)

    Sheridan, Douglas M.; Maxwell, Charles H.; Albee, Arden L.; Van Horn, Richard


    of the uranium deposits: (1) favorable structural environment and (2) favorable host rocks. The deposits in each of the two major areas are located where a northwesterly-trending Laramide fault system splits into a complex network of faults. Also, most of the deposits appear to be localized where the faults cut Precambrian rocks rich in hornblende, biotite, or garnet and biotite. The ore controls recognized in this relatively new uranium district may have wider application in areas of similar geology elsewhere in the Front Range.

  11. The geology, structure and mineralisation of the Oyu Tolgoi porphyry copper-gold-molybdenum deposits, Mongolia:A review

    Institute of Scientific and Technical Information of China (English)

    T.M. Mike Porter


    The Oyu Tolgoi cluster of seven porphyry Cu-Au-Mo deposits in southern Mongolia, define a narrow, linear, 12 km long, almost continuously mineralised trend, which contains in excess of 42 Mt of Cu and 1850 t of Au, and is among the largest high grade porphyry Cu-Au deposits in the world. These deposits lie within the Gurvansayhan island-arc terrane, a fault bounded segment of the broader Silurian to Carboniferous Kazakh-Mongol arc, located towards the southern margin of the Central Asian Orogenic Belt, a collage of magmatic arcs that were periodically active from the late Neoproterozoic to Permo-Triassic, extending from the Urals Mountains to the Pacific Ocean. Mineralisation at Oyu Tolgoi is associated with multiple, overlapping, intrusions of late Devonian (w372 to 370 Ma) quartz-monzodiorite intruding Devonian (or older) juvenile, probably intra-oceanic arc-related, basaltic lavas and lesser volcaniclastic rocks, unconformably overlain by late Devonian (w370 Ma) basaltic to dacitic pyroclastic and volcano sedimentary rocks. These quartz-monzodiorite intrusions range from early-mineral porphyritic dykes, to larger, linear, syn-, late- and post-mineral dykes and stocks. Ore was deposited within syn-mineral quartz-monzodiorites, but is dominantly hosted by augite basalts and to a lesser degree by overlying dacitic pyroclastic rocks. Following ore deposition, an allochthonous plate of older Devonian (or pre-Devonian) rocks was overthrust and a post-ore biotite granodiorite intruded at w365 Ma. Mineralisation is characterised by varying, telescoped stages of intrusion and alteration. Early A-type quartz veined dykes were followed by Cu-Au mineralisation associated with potassic alteration, mainly K-feldspar in quartz-monzodiorite and biotite-magnetite in basaltic hosts. Downward reflux of cooled, late-magmatic hydrothermal fluid resulted in intense quartz-sericite retrograde alteration in the upper parts of the main syn-mineral intrusions, and an equivalent chlorite

  12. Geologic Map of the Clark Peak Quadrangle, Jackson and Larimer Counties, Colorado (United States)

    Kellogg, Karl S.; Ruleman, Chester A.; Shroba, Ralph R.; Braddock, William A.


    The Clark Peak quadrangle encompasses the southern end of the Medicine Bow Mountains and the northernmost end of the Mummy Range. The Continental Divide traverses the map area and Highway 14 cross the Divide at Cameron Pass, in the southeastern corner of the map. Approximately the eastern half of the map, and a few areas to the west, are underlain by Early Proterozoic plutonic and metamorphic rocks. Most of these basement rocks are part of the ~1,715 Ma Rawah batholith, composed mostly of pinkish, massive to moderately foliated monzogranite and granodiorite intruded by numerous, large pegmatite- aplite bodies. The metamorphic rocks, many of which form large inclusions in the granitic rocks of the Rawah batholith, include biotite-hornblende gneiss, hornblende gneiss, amphibolite, and biotite schist. The crystalline basement rocks are thrust westward along the Medicine Bow thrust over a sequence of sedimentary rocks as old as the Upper Permian Satanka Shale. The Satanka Shale, Middle and Lower Triassic Chugwater group, and a thin sandstone tentatively correlated with the Lower Jurassic and Upper Triassic Jelm Formation are combined as one map unit. This undivided unit is overlain sequentially upward by the Upper Jurassic Sundance Formation, Upper Jurassic Morrison Formation, Lower Cretaceous Dakota Group, Upper and Lower Cretaceous Benton Group, Upper Cretaceous Niobrara Formation, and the Eocene and Paleocene Coalmont Formation. The Late Cretaceous to early Eocene Medicine Bow thrust is folded in places, and several back thrusts produced a complicated thrust pattern in the south part of the map. Early Oligocene magmatism produced rhyolite tuff, dacite and basalt flows, and intermediate dikes and small stocks. A 40Ar/39Ar date on sanidine from one rhyolite tuff is ~28.5 Ma; a similar whole-rock date on a trachybasalt is ~29.6 Ma. A very coarse, unsorted probably pre-Quaternary ridge-top diamicton crops out in the southern part of the quadrangle. Numerous glacial

  13. Slip transfer across fault discontinuities within granitic rock at the brittle-ductile transition (United States)

    Nevitt, J. M.; Pollard, D. D.; Warren, J. M.


    Fault mechanics are strongly influenced by discontinuities in fault geometry and constitutive differences between the brittle and ductile regions of the lithosphere. This project uses field observations, laboratory analysis and numerical modeling to investigate deformational processes within a contractional step at the brittle-ductile transition, and in particular, how slip is transferred between faults via ductile deformation across the step. The Bear Creek field area (central Sierra Nevada, CA) is comprised of late Cretaceous biotite-hornblende granodiorite and experienced a period of faulting at the brittle-ductile transition. Abundant echelon faults in Bear Creek, some of which were seismically active, provide many textbook examples of contractional steps, which are characterized by well-developed ductile fabrics. The occurrence of hydrothermal alteration halos and hydrothermal minerals in fracture fill documents the presence of water, which we suggest played a weakening role in the constitutive behavior of the granodiorite. Furthermore, the mechanism that accomplishes slip transfer in contractional steps appears to be related to water-enhanced ductile deformation. We focus our investigation on Outcrop SG10, which features a 10cm thick aplite dike that is offset 0.45m through a contractional step between two sub-parallel left-lateral faults. Within the step, the aplite undergoes dramatic thinning (stretch ~1/10) and the granodiorite is characterized by a well-developed mylonitic foliation, in which quartz and biotite plastically flow around larger grains of feldspars, hornblende and opaque minerals. Electron backscatter diffraction (EBSD) analysis gives a more quantitative depiction of the active micromechanics and reveals how slip is accommodated at the crystal scale throughout the step. We use Abaqus, a commercial finite element software, to test several constitutive laws that may account for the deformation observed both macro- and microscopically throughout

  14. Remobilisation features and structural control on ore grade distribution at the Konkola stratiform Cu-Co ore deposit, Zambia (United States)

    Torremans, K.; Gauquie, J.; Boyce, A. J.; Barrie, C. D.; Dewaele, S.; Sikazwe, O.; Muchez, Ph.


    The Konkola deposit is a high grade stratiform Cu-Co ore deposit in the Central African Copperbelt in Zambia. Economic mineralisation is confined to the Ore Shale formation, part of the Neoproterozoic metasedimentary rocks of the Katanga Supergroup. Petrographic study reveals that the copper-cobalt ore minerals are disseminated within the host rock, sometimes concentrated along bedding planes, often associated with dolomitic bands or clustered in cemented lenses and in layer-parallel and irregular veins. The hypogene sulphide mineralogy consists predominantly of chalcopyrite, bornite and chalcocite. Based upon relationships with metamorphic biotite, vein sulphides and most of the sulphides in cemented lenses were precipitated during or after biotite zone greenschist facies metamorphism. New δ34S values of sulphides from the Konkola deposit are presented. The sulphur isotope values range from -8.7‰ to +1.4‰ V-CDT for chalcopyrite from all mineralising phases and from -4.4‰ to +2.0‰ V-CDT for secondary chalcocite. Similarities in δ34S for sulphides from different vein generations, earlier sulphides and secondary chalcocite can be explained by (re)mobilisation of S from earlier formed sulphide phases, an interpretation strongly supported by the petrographic evidence. Deep supergene enrichment and leaching occurs up to a km in depth, predominantly in the form of secondary chalcocite, goethite and malachite and is often associated with zones of high permeability. Detailed distribution maps of total copper and total cobalt contents of the Ore Shale formation show a close relationship between structural features and higher copper and lower cobalt contents, relative to other areas of the mine. Structural features include the Kirilabombwe anticline and fault zones along the axial plane and two fault zones in the southern limb of the anticline. Cobalt and copper behave differently in relation to these structural features. These structures are interpreted to have

  15. Stabilization of garnet in metamorphosed altered turbidites near the St. Eugene lead-zinc deposit, southeastern British Columbia: Equilibrium and kinetic controls (United States)

    Pattison, David R. M.; Seitz, JennaLee D.


    The St. Eugene lead-zinc deposit, near Moyie, southeastern British Columbia, is a Mesoproterozoic vein deposit hosted by metaturbidites of the 1.5-1.4 Ga Belt-Purcell Supergroup. The regional metamorphic grade of the rocks is biotite zone, with the age of metamorphism being Mesoproterozoic (ca. 1.35 Ga). The vein system is enveloped by a metamorphosed alteration zone of increasing intensity as the vein is approached. Thin argillaceous tops of turbidite beds away from the vein are garnet-free, whereas those in the inner alteration zone are garnet-bearing. Compared to rocks away from the vein, those near the vein are enriched in Fe, Mn, Pb and Zn, with proportional reduction in other compositional parameters. Thermodynamic modeling of three rocks across the alteration gradient predicts increasing stabilization of garnet with increasing degree of alteration. Predicted and observed modes of garnet in the samples are in close agreement. In the most altered rock, the garnet-in line is displaced down-temperature by ~ 100 °C relative to the least altered rock. Approximately 2/3 of the garnet stabilization is accounted for by increase in Mn content and the rest by increase in Fe/(Fe + Mg). Kinetic factors played a role in the development of the mineral assemblages, including metastable persistence of zoisite, and disequilibrium (overstepped) initial growth of garnet. Estimates of peak pressure-temperature conditions from mineral assemblage constraints and from compositional isopleths are complicated by the kinetic effects but yield similar results: 490-510 °C and 3.6-4.0 kbar. The pressure-temperature estimates imply an average linear geothermal gradient of ~ 35 °C/km, broadly consistent with burial metamorphism in the Belt-Purcell extensional basin. However, the estimated pressure, equivalent to a depth of 13-15 km, is greater than the estimated ~ 8 km (~ 2.2 kbar) of stratigraphic overburden at the time of metamorphism. The results of this study support the idea that

  16. Re-Os Dating of the Pulang Porphyry Copper Deposit in Zhongdian, NW Yunnan, and Its Geological Significance

    Institute of Scientific and Technical Information of China (English)

    ZENG Pusheng; HOU Zengqian; WANG Haiping; QU Wenjun; MENG Yifeng; YANG Zhusen; LI Wenchang


    The Pulang porphyry copper deposit is located in the Zhongdian island arc belt, NW Yunnan, in the central part of the Sanjiang area, SW China, belonging to the southern segment of the Yidun island arc belt on the western margin of the Yangtze Platform. In the Yidun island arc, there occur well-known "Gacun-style" massive sulfide deposits in the northern segment and plenty of porphyry copper deposits in the southern segment, of which the Pulang porphyry copper deposit is one of the representatives. Like the Yulong porphyry copper deposit, this porphyry copper deposit is also one of the most important porphyry copper deposits in the eastern Qinghai-Tibet Plateau. But it is different from other porphyry copper deposits in the eastern Qinghai-Tibet Plateau (e.g. those in the Gangdise porphyry copper belt and Yulong porphyry copper belt) in that it formed in the Indosinian period, while others in the Himalayan period. Because of its particularity among the porphyry copper deposits of China, this porphyry copper deposit is of great significance for the study of the basic geology and the evaluation and prediction of mineral resources in the Zhongdian island arc belt.However, no accurate chronological data are available for determining the timing of mineralization of the porphyry copper deposit. By field observation in the study area and Re-Os dating of molybdenite and K-Ar dating of hydrothermal minerals and whole rock from the typical geological bodies, the timing of mineralization of the porphyry copper deposit has systematically been determined for the first time. The K-Ar age for the hydrothermal mineralization of biotite-quartz monzonitic porphyry that has undergone patassic silicate (biotite and K-feldspar) alteration ranges from 235.4±2.4 to 221.5±2.0 Ma and the Re-Os age for molybdenite in the quartz-molybdenite stage is ~213±3.8 Ma. These data are very close to each other, suggesting that the ore-forming processes of the Pulang porphyry copper deposit was

  17. Nature, origin and evolution of the granitoid-hosted early Proterozoic copper-molybdenum mineralization at Malanjkhand, Central India (United States)

    Sarkar, S. C.; Kabiraj, S.; Bhattacharya, S.; Pal, A. B.


    At Malanjkhand, Central India, lode-type copper (-molybdenum) mineralization occurs within calcalkaline tonalite-granodiorite plutonic rocks of early Proterozoic age. The bulk of the mineralization occurs in sheeted quartz-sulfide veins, and K-silicate alteration assemblages, defined by alkali feldspar (K-feldspar≫albite)+dusty hematite in feldspar±biotite±muscovite, are prominent within the ore zone and the adjacent host rock. Weak propylitic alteration, defined by albite+biotite+epidote/zoisite, surrounds the K-silicate alteration zone. The mineralized zone is approximately 2 km in strike length, has a maximum thickness of 200 m and dips 65° 75°, along which low-grade mineralization has been traced up to a depth of about 1 km. The ore reserve has been conservatively estimated to be 92 million tonnes with an average Cu-content of 1.30%. Supergene oxidation, accompanied by limited copper enrichment, is observed down to a depth of 100 m or more from the surface. Primary ores consist essentially of chalcopyrite an