Sample records for amphibole

  1. Fluorine end-member micas and amphiboles

    Energy Technology Data Exchange (ETDEWEB)

    Petersen, E.U.; Essene, E.J.; Peacor, D.R.; Valley, J.W.

    The near end-member minerals fluorphlogopite (XF = 0.96) and fluortremolite (XF = 0.82) have been found in Greenville marbles near Balmat, New York. These micas and amphiboles, like other fluorine-rich minerals reported in the literature, are extremely low in iron. The substitution of F for OH is partly responsible for stabilizing these minerals in the granulite facies marbles of the Adirondacks. Fluorine-rich amphiboles and micas are more common than generally recognized. A literature review shows that many amphiboles and micas have more than fifty percent of the interlayer site occupied by fluorine. This degree of solid solution qualifies these phases as independent minerals, but they are not currently recognized by the I.M.A. Identification of the mineralogically and petrologically important solid solution of fluorine for hydroxyl is currently obscured by use of names that imply hydroxyl end-members.

  2. Amphibole ceramics: conceptual development and preliminary experiments

    Energy Technology Data Exchange (ETDEWEB)

    Lauf, R.J.


    Certain natural silicate minerals, commonly called jade, are well known for their resistance to brittle fracture. One type of jade, nephrite, is a compacted form of the amphibole mineral series tremolite-actinolite. Nephrite is tough because the naturally acicular crystal habit of these amphibole minerals produces an interwoven fibrous microstructure that impedes crack propagation. Object of this work was to duplicate the fibrous microstructure of nephrite by pulverizing natural tremolite or actinolite and then compacting it by hot pressing to form a dense body. Two other materials were also investigated, namely, clinochrysotile (serpentine asbestos) and synthetic fluor-tremolite. For each material, the milling characteristics and densification were studied. The resulting microstructures were characterized, and fracture toughness was measured for a limited number of samples. The most ''fibrous'' microstructure was obtained by hot pressing clinochrysotile 15 min a 1000/sup 0/C. Actinolite, hot pressed 15 min at 1100/sup 0/C, had a critical fracture toughness K/sub IC/ = 4.5 MPa m/sup 1/2/, which compares favorably with the toughness of nephrite jade (K/sub IC/ = 3.6). Decomposition of tremolite and actinolite to more stable phases occurred to some degree during hot pressing. Results suggest that hot isostatic pressing at high water vapor pressure should yield a dense product without causing amphibole decomposition. 28 figs., 7 tabs.

  3. Comparative Toxicology of Libby Amphibole and Naturally Occurring Asbestos (United States)

    Summary sentence: Comparative toxicology of Libby amphibole (LA) and site-specific naturally occurring asbestos (NOA) provides new insights on physical properties influencing health effects and mechanisms of asbestos-induced inflammation, fibrosis, and tumorigenesis.Introduction/...

  4. Amphiboles of the Khibiny alkaline pluton, Kola Peninsula, Russia (United States)

    Konopleva, N. G.; Ivanyuk, G. Yu.; Pakhomovsky, Ya. A.; Yakovenchuk, V. N.; Men'shikov, Yu. P.; Korchak, Yu. A.


    The rocks of the Khibiny pluton contain 25 amphibole varieties, including edenite, fluoredenite, kaersutite, pargasite, ferropargasite, hastingsite, magnesiohastingsite, katophorite, ferrikatophorite, magnesiokatophorite, magnesioferrikatophorite, magnesioferrifluorkatophorite, ferrimagnesiotaramite, ferrorichterite, potassium ferrorichterite, richterite, potassium richterite, potassium fluorrichterite, arfvedsonite, potassium arfvedsonite, magnesioarfvedsonite, magnesioriebeckite, ferriferronyboite, ferrinyboite, and ferroeckermannite. The composition of rock-forming amphiboles changes symmetrically relative to the Central Ring of the pluton; i.e., amphiboles enriched in K, Ca, Mg, and Si are typical of foyaite near and within the Central Ring. The Fe and Mn contents in amphiboles increase in the direction from marginal part of the pluton to its center. Foyaite of the marginal zone contains ferroeckermannite, richterite, arfvedsonite, and ferrorichterite; edenite is typical of foyaite and hornfels of the Minor Arc. Between the Minor Arc and the Central Ring, foyaite contains ferroeckermannite, arfvedsonite, and richterite; amphiboles in rischorrite, foidolite and hornfels of the Central Ring are (potassium) arfvedsonite, (potassium) richterite, magnesiokatophorite, magnesioarfvedsonite, ferroeckermannite, and ferriferronyboite; amphiboles in foyaite within the Central Ring, in the central part of the pluton, are arfvedsonite, magnesioarfvedsonite, ferriferronyboite, katophorite, and richterite. It is suggested that such zoning formed due to the alteration of foyaite by a foidolite melt intruded into the Main (Central) Ring Fault.

  5. Preparation and characterization of "Libby Amphibole" toxicological testing material (United States)

    Lowers, Heather; Wilson, Stephen A.; Hoefen, Todd M.; Benzel, William M.; Meeker, Gregory P.


    The U.S. Environmental Protection Agency (USEPA) began work in Libby, Mont. in 1999 when an Emergency Response Team was sent to investigate local concern and media reports regarding asbestos-contaminated vermiculite. Since that time, the site has been granted Superfund status and site remediation to a safe level of asbestos has been ongoing. The amphibole asbestos from the Vermiculite Mountain vermiculite deposit near Libby, Mont. (Libby amphibole) is unusual in the sense that it is currently not classified as one of the regulated six asbestos minerals—chrysotile (a serpentine mineral) and the amphibole minerals amosite (asbestiform cummingtonite-grunerite), crocidolite (asbestiform riebeckite), asbestiform anthophyllite, asbestiform tremolite, and asbestiform actinolite. The amphiboles from the Vermiculite Mountain vermiculite deposit, primarily winchite and richterite, are related to tremolite and in the past have been referred to as sodium-rich tremolite or soda tremolite (Larsen, 1942; Boettcher, 1966; Wylie and Verkouteren, 2000; Gunter and others, 2003; Meeker and others, 2003). The public health issues in Libby, Mont. have brought to light many of the inconsistencies in the literature regarding fiber characteristics, nomenclature, and toxicology. To better understand the toxicological characteristics of the Libby amphibole, investigators require a sufficient quantity of material representing the range of fibrous amphiboles present in the vicinity of Vermiculite Mountain to use in toxicology studies. The material collected in 2000 (Meeker and others, 2003) has been exhausted and a second collection and preparation effort, funded by the USEPA, was conducted in 2007. Both the 2000 (LA2000) and 2007 (LA2007) materials were generated to support research needs identified by the USEPA and the National Toxicology Program, and new in-vivo and in-vitro toxicology studies are underway. This Open-File Report describes the process of preparation and summarizes the

  6. 77 FR 30528 - Notification of a Public Teleconference of the Science Advisory Board; Libby Amphibole Asbestos... (United States)


    ... AGENCY Notification of a Public Teleconference of the Science Advisory Board; Libby Amphibole Asbestos... teleconference of the SAB Libby Amphibole Asbestos Panel to discuss the Panel's revised draft review report of EPA's Toxicological Review of Libby Amphibole Asbestos (August 2011 Draft). DATES: The...

  7. The contamination of Lake Superior with amphibole gangue minerals. (United States)

    Langer, A M; Maggiore, C M; Nicholson, W J; Rohl, A N; Rubin, I B; Selikoff, I J


    Iron ore called taconite is mined in the Biwabik Iron Formation in the Eastern Mesabi region of the Mesabi Range, in eastern Minnesota. After mining, ore is shipped to Silver Bay, Minnnesota for processing and wet magnetic extraction. Tailings from the process are dumped, as a slurry, into a man-made containment delta constructed in Lake Superior. Submicroscopic amphibole fibers and/or cleavage fragments, a component of the gangue, apparently escape from the delta at Silver Bay, and enter Lake Superior. These particles contaiminate the potable water supplies of municipalities drawing directly from the lake. One of the gangue minerals is the amphibole grunerite, whose asbestiform variety is called amosite. Major emphasis of this study was directed at identification of submicroscopic particle pollutants, based on morphology, structure and chemical composition. Quantitative determination of fibrous amphibole phases, present in a range of water samples, was undertaken. Transmission electron microscopy, selected area electron diffraction, and an electron microprobe technique was used for identification and enumeration and this information was compared with data sets determined from standards. Grunerite fiber and/or acicular cleavage fragments, in some instances indistinguishable from asbestiform grunerite, are present in the tailings, lake water and drinking water of a number of municipalities, a result of contamination of the lake at the Silver Bay milling operation. This amphibole is found in drinking water in concentrations which range from 0.6 to 2.8 X 10(6) fiber/liter. The risk to health, associated with direct ingestion of grunerite fiber is unknown and is extrapolated from the asbestiform grunerite (amosite) data base. The biological activity of other fibrous amphiboles observed, unrelated to any asbestiform silicate variety, is presently unknown and warrants investigation. PMID:294208

  8. Parameterized Lattice Strain Models for REE Partitioning between Amphibole and Silicate Melt (United States)

    Shimizu, K.; Liang, Y.; Sun, C.; Jackson, C.; Saal, A. E.


    The distribution of REE between amphibole and silicate melt is important for understanding a variety of igneous processes involving amphibole. In general, amphibole-melt REE partition coefficients (DREE) depend on pressure (P), temperature (T), and compositions of amphibole and melt. A previous study parameterized the DREE in amphibole-melt solely as a function of melt composition [1]. Here, we use published REE partitioning data between amphibole and basaltic melt, the lattice strain model [2], and non-linear least squares regression method to parameterize key partitioning parameters in the lattice strain model (D0, r0, and E) as a function of P, T, and both amphibole and melt compositions. We focus on experimental data obtained by LA-ICP-MS and ion probe, and experiments close to equilibrium. Amphiboles and coexisting melts from the 38 experiments that we compiled span a wide range of compositions with the Mg# of amphibole and melt ranging from 36 to 100 and 15 to 99, respectively. Two models, which give nearly identical results, are explored in this study. In the first model, D0 is a function of T and amphibole composition: it negatively correlates with T and MgM1,2,3 content in amphibole, and positively correlates with TiM1,2,3 content in amphibole. In the second model, D0 is solely a function of the melt composition: it negatively correlates with the mole fraction of Ca in the melt. Interestingly, r0 and E are both constant and identical between the two models, suggesting D0 in the two models are equivalent. The latter allows us to develop a new thermometer for amphibole-melt equilibria. As an independent test, we compared model-derived temperatures with those reported in the phase equilibrium experiments. The predicted temperatures are within ±41°C on average of the reported temperatures, adding confidence to our parameterizations of D0. Our two parameterized lattice strain models can be used to model REE fractionation between amphibole and basaltic melts


    Inhalation toxicology studies are being conducted to inform the risk assessment ofLibby amphibole. The overall purpose of these studies is to compare the toxicity of inhaled Libby amphibole fibers to a positive control fiber sample (UICC amosite). A 2-week study was conducted to ...

  10. Systemic and Vascular Alterations in Rat models Exposed to Libby Amphibole (United States)

    Acute pulmonary injury and chronic diseases can impact systemic vasculature and extra pulmonary organ systems due to the hemodynamic properties of the pulmonary capillary network that allows mediators to release into the circulation. Exposure to Libby amphibole (LA) is associated...

  11. Pre-eruption Conditions and Magma Dynamics of Recent Amphibole-Bearing Etna Basalt (United States)

    Pompilio, M.; Rutherford, M. J.


    An intriguing aspect of the recent eruption of the Etna is the unexpected occurrence of amphibole crystals with breakdown rims in the early erupted magma. Amphibole was common in ancient (>15 Ka) intermediate to evolved Etnean products, but with the exception of rare relics reported in the hawaiite feeding the 122 BC Plinian eruption, amphibole has not been described in the recent volcanics. The presence of amphibole poses several questions about possible changes on the Etnean magma feeding system and the consequences upon eruptive style and hazard. Using analyses of the erupted material and hydrothermal experiments, we have attempted to constrain the physico-chemical conditions under which amphibole crystallizes in recent Etnean magmas. Experimental runs have been performed in a TZM apparatus between 950 and 1035° C of temperature and in the pressures range 50-200 Mpa using a natural sample of the amphibole-bearing lava as a starting material. This rock is a trachybasalt with a low abundance of phenocrysts of diopside (cpx), olivine (ol) (Fo83-75), plagioclase (pl) (An83-49), Mg-hastingsite-kaersutitic amphibole (amph) and Ti-Magnetite (mt) (Xusp=.37-46). 5-10 wt% of water was been added to each sample to assure the saturation at the pressures of interest. The { \\it f}O2 was controlled by a CH4-Ar pressurizing gas mixture set to maintain the charge under the NNO buffer. Experimental runs produced samples with a crystal content variable from 5 to 40%. Cpx and mt (Xusp=.03-31) are ubiquitous in all the investigated P-T range. At P=140 MPa pl (An57-90) is stable in addition to cpx and mt, but only at T 1024° C). Amphibole crystallizes at T75 Mpa. Experimental amphiboles range from pargasite to Mg-hastingsite with less frequent kaersutite crystals; they have a lower silica and an higher alumina content than those measured in natural samples. Experimental glasses in equilibrium with cpx, mt and ol plot along the liquid line of descent observed for natural historical

  12. Volatile (Li, B, F and Cl) mobility during amphibole breakdown in subduction zones (United States)

    Debret, Baptiste; Koga, Kenneth T.; Cattani, Fanny; Nicollet, Christian; Van den Bleeken, Greg; Schwartz, Stephane


    Amphiboles are ubiquitous minerals in the altered oceanic crust. During subduction, their breakdown is governed by continuous reactions up to eclogitic facies conditions. Amphiboles thus contribute to slab-derived fluid throughout prograde metamorphism and continuously record information about volatile exchanges occurring between the slab and the mantle wedge. However, the fate of volatile elements and especially halogens, such as F and Cl, in amphibole during subduction is poorly constrained. We studied metagabbros from three different localities in the Western Alps: the Chenaillet ophiolite, the Queyras Schistes Lustrés and the Monviso meta-ophiolitic complexes. These samples record different metamorphic conditions, from greenschist to eclogite facies, and have interacted with different lithologies (e.g. sedimentary rocks, serpentinites) from their formation at mid-oceanic ridge, up to their devolatilization during subduction. In the oceanic crust, the initial halogen budget is mostly stored in magmatic amphibole (F = 300-7000 ppm; Cl = 20-1200 ppm) or in amphibole corona (F = 100-7000 ppm; Cl = 80-2000 ppm) and titanite (F = 200-1500 ppm; Cl eclogite facies conditions, metagabbros display low halogens concentrations (< 20 ppm of F and < 100 ppm of Cl) relative to altered oceanic crust (F = 40-650 ppm; Cl = 40-1400 ppm) suggesting that these elements are continuously released by fluids during the first 30-80 km of subduction whatever the tectonic environment (e.g. slab, plate interface) and the considered fluid/rock interactions.

  13. Amphibole and hercynite spinel in Shergotty and Zagami Magmatic water, depth of crystallization, and metasomatism (United States)

    Treiman, A. H.


    Amphibole and spinel occur in the Shergotty and Zagami meteorites only in magmatic inclusions in pigeonite. The trapped magma is essentially identical to the parental magmas for Shergotty and Zagami. The amphibole is a kaersutite with minimal halogen content; by inference, it must have been hydrous. If so, the Shergotty and Zagami melts contained at least 0.2 wt pct H2O and were probably H2O-undersaturated. Pressures in excess of 1 kilobar seem necessary for the formation of amphibole. Spinel replaces magnetite in the inclusions, and olivine replaces magnetite elsewhere in the meteorites. To stabilize spinel, the melt in the inclusions must have become enriched in Al during fractionation, possibly because the small volume of the inclusions made nucleation of plagioclase unlikely. Pervasive replacement of magnetite through reduction reactions suggests that Shergotty and Zagami interacted with hydrogen-rich fluids during their cooling.

  14. Amphibole and hercynite spinel in Shergotty and Zagami Magmatic water, depth of crystallization, and metasomatism (United States)

    Treiman, A. H.


    Amphibole and spinel occur in the Shergotty and Zagami meteorites only in magmatic inclusions in pigeonite. The trapped magma is essentially identical to the parental magmas for Shergotty and Zagami. The amphibole is a kaersutite with minimal halogen content; by inference, it must have been hydrous. If so, the Shergotty and Zagami melts contained at least 0.2 wt pct H2O and were probably H2O-undersaturated. Pressures in excess of 1 kilobar seem necessary for the formation of amphibole. Spinel replaces magnetite in the inclusions, and olivine replaces magnetite elsewhere in the meteorites. To stabilize spinel, the melt in the inclusions must have become enriched in Al during fractionation, possibly because the small volume of the inclusions made nucleation of plagioclase unlikely. Pervasive replacement of magnetite through reduction reactions suggests that Shergotty and Zagami interacted with hydrogen-rich fluids during their cooling.

  15. A new calibration of seismic velocities, anisotropy, fabrics, and elastic moduli of amphibole-rich rocks (United States)

    Ji, Shaocheng; Shao, Tongbin; Michibayashi, Katsuyoshi; Long, Changxing; Wang, Qian; Kondo, Yosuke; Zhao, Weihua; Wang, Hongcai; Salisbury, Matthew H.


    large portion of the middle to lower crust beneath the continents and oceanic island arcs consists of amphibolites dominated by hornblende and plagioclase. We have measured P and S wave velocities (Vp and Vs) and anisotropy of 17 amphibole-rich rock samples containing 34-80 vol % amphibole at hydrostatic pressures (P) up to 650 MPa. Combined petrophysical and geochemical analyses provide a new calibration for mean density, average major element contents, mean Vp-P and Vs-P coefficients, intrinsic Vp and Vs anisotropy, Poisson's ratios, the logarithmic ratio Rs/p, and elastic moduli of amphibole-rich rocks. The Vp values decrease with increasing SiO2 and Na2O + K2O contents but increase with increasing MgO and CaO contents. The maximum (≤0.38-0.40 km/s) and minimum S wave birefringence values occur generally in the propagation direction parallel to Y and normal to foliation, respectively. Amphibole plays a critical role in the formation of seismic anisotropy, whereas the presence of plagioclase, quartz, pyroxene, and garnet diminishes the anisotropy induced by amphibole crystallographic preferred orientations (CPOs). The CPO variations cause different anisotropy patterns illustrated in the Flinn diagram of Vp(X)/Vp(Y)-Vp(Y)/Vp(Z) plots. The results make it possible to distinguish, in terms of seismic properties, the amphibolites from other categories of lithology such as granite-granodiorite, diorite, gabbro-diabase, felsic gneiss, mafic gneiss, eclogite, and peridotite within the Earth's crust. Hence, amphibole, aligned by dislocation creep, anisotropic growth, or rigid-body rotation, is the most important contributor to the seismic anisotropy of the deep crust beneath the continents and oceanic island arcs, which contains rather little phyllosilicates such as mica or chlorite.

  16. Amphibole Reaction Rims in Response to Decompression compared to Heating: An Experimental Approach (United States)

    Browne, B. L.; Gardner, J. E.; Larsen, J.


    Amphiboles are an important magmatic mineral phase common to a variety of volcanic settings, and are especially sensitive to variations in the water content and temperature of the surrounding induced during magmatic ascent or heating accompanying magma mixing events. As magma rises toward the surface hydrous amphiboles, stable at high water pressures, break down in response to degassing of the surrounding melt. Reaction rims also form around amphiboles that are destabilized when mixing with hotter, more primitive magmas occurs. In this study, we compare the thickness, composition, and rate of formation of amphibole reaction rims during a series of isothermal decompression and isobaric heating experiments using dacite and andesite magmas erupted from Redoubt volcano, Alaska in 1989-1990. The 1989-90 Redoubt dacite pumice consists of magnesio-hornblendes, plagioclase, othropyroxene, and Fe-Ti oxides in a high-silica rhyolite glass. In contrast, 1989-90 Redoubt andesite contains pargasitic amphiboles, orthopyroxene, clinopyroxene, plagioclase, and Fe-Ti oxides in a rhyodacite glass. Our results indicate that the reaction rims formed in response to decompression are distinguishable in thickness, grain size, and type of mineral formed in the rims from those formed in response to heating, regardless of the type of amphibole studied. First, decompression induced rims were thinner (5- 50 um) compared to those developing in response to heating (25- 200 um). Decompression induced rim growth rate ranges from 0.3 to 0.6 um/day compared to heating induced rim growth rate, which ranges from 0.4 to 1.6 um/day. Second, decompression rims were finer-grained (5-15 um diameter crystals) compared to heating reaction rims (5- 35 um diameter crystals). And third, decompression rims are predominantly composed of orthopyroxene and plagioclase, with lesser amounts of Fe-Ti oxides, whereas reaction rims that grew in response to heating experiments were composed almost entirely of

  17. Origin of amphibole-rich beach sands from Tila-Mati, Karwar, central-west coast of India

    Digital Repository Service at National Institute of Oceanography (India)

    Mislankar, P.G.; Iyer, S.D.

    size and sphericity are directly proportional while a decrease in sphericity results in an increase of amphiboles (60-80%). This is probably due to the elongated nature of the amphibole grains which are abraded in a low energy environment. The Tila...

  18. Early Onset of Atypical Proliferative Lesions in the Lungs of a Libby Amphibole (LA) Exposed Rat Model of Cardiovascular Disease-Associated Iron Overlo (United States)

    Rationale: Miners and residents of Libby, Montana have increased incidences of asbestos-related diseases associated with exposure to amphibole contaminated vermiculite. Amphiboles have been shown to bind endogenous iron and modulate fiber induced inflammatory response. We hypoth...

  19. Effects of Libby amphibole asbestos exposure on two rat models of rheumatoid arthritis (United States)

    Epidemiological data suggests that occupational exposure to the amphibole-containing vermiculite in Libby, MT was associated with increased risk for developing autoimmune diseases and had an odds ratio of 3.23 for developing rheumatoid arthritis (RA). Our goal was to determine wh...


    Exposure to Libby amphibole (LA) is associated with significant increases in asbestosis, lung cancer, and mesothelioma. To support biological potency assessment and dosimetry model development, a subchronic nose-only inhalation exposure study (6 hr/d, 5 d/wk, 13 wk) was conducted...

  1. Molecular engineering of a fluorescent bioprobe for sensitive and selective detection of amphibole asbestos.

    Directory of Open Access Journals (Sweden)

    Takenori Ishida

    Full Text Available Fluorescence microscopy-based affinity assay could enable highly sensitive and selective detection of airborne asbestos, an inorganic environmental pollutant that can cause mesothelioma and lung cancer. We have selected an Escherichia coli histone-like nucleoid structuring protein, H-NS, as a promising candidate for an amphibole asbestos bioprobe. H-NS has high affinity to amphibole asbestos, but also binds to an increasingly common asbestos substitute, wollastonite. To develop a highly specific Bioprobe for amphibole asbestos, we first identified a specific but low-affinity amosite-binding sequence by slicing H-NS into several fragments. Second, we constructed a streptavidin tetramer complex displaying four amosite-binding fragments, resulting in the 250-fold increase in the probe affinity as compared to the single fragment. The tetramer probe had sufficient affinity and specificity for detecting all the five types of asbestos in the amphibole group, and could be used to distinguish them from wollastonite. In order to clarify the binding mechanism and identify the amino acid residues contributing to the probe's affinity to amosite fibers, we constructed a number of shorter and substituted peptides. We found that the probable binding mechanism is electrostatic interaction, with positively charged side chains of lysine residues being primarily responsible for the probe's affinity to asbestos.

  2. The role of amphiboles in the metamorphic evolution of the UHP rocks: a case study from the Tso Morari Complex, northwest Himalayas (United States)

    Singh, Preeti; Pant, Naresch C.; Saikia, Ashima; Kundu, Amitava


    Amphiboles represent a crucial phase of the ultra-high-pressure (UHP) metamorphic rocks as their solid solution behavior reflects both bulk compositional and P- T changes. Three different types of amphibole have been reported from the UHP metamafic rocks of the Tso Morari Crystalline Complex, NW Himalayas: Na-rich (glaucophane); Na-Ca-rich (barroisite, taramite, winchite) and Ca-rich (tremolite, magnesio-hornblende, pargasite). The Na-amphibole is presented as a core of the zoned amphibole with Na-Ca-rich rim; Na-Ca-amphibole is presented as inclusion in garnets as well as in matrix, and Ca-amphibole is generally found in the matrix. The Na-Ca-amphibole is observed at two different stages of metamorphism. The first is pre-UHP, and the second is post-garnet-omphacite assemblage though with a significant difference in composition. The pressure-temperature estimations of the formation of these two sets of Na-Ca-amphiboles corroborate their textural associations. Ca-rich amphiboles are generally present in the matrix either as symplectite with plagioclase or as a pseudomorph after garnet along with other secondary minerals like chlorite and biotite. Two different types of zoning have been observed in the amphibole grains: (1) core is Na-rich followed by Na-Ca rim and (2) core of Na-Ca-amphibole is followed by Ca-rich rim. The pre-UHP (or the prograde P- T path) and post-UHP stages (or the retrograde P- T path) of Tso Morari eclogites are defined by characteristic amphibole compositions, viz. Na/Na-Ca-amphibole, Na-Ca-amphibole and Ca-amphibole and thus indicate their utility in inferring crustal evolution of this UHP terrain.

  3. Microchemistry of amphiboles near the roof of a mafic magma chamber: Insights into high level melt evolution (United States)

    Murphy, J. Brendan; Blais, Stephanie A.; Tubrett, Michael; McNeil, Daniel; Middleton, Matthew


    The Late Neoproterozoic Greendale Complex, located within the Avalon terrane of Nova Scotia, is a suite of appinitic rocks ranging from ultramafic to felsic in composition that were intruded during regional ensialic arc magmatism and crystallized at shallow crustal levels under conditions of high pH2O. Amphibole is the dominant mafic mineral in ultramafic to mafic rocks and displays the extraordinary variability in texture and modal abundance that is characteristic of appinite suites. These features allow sensitivity of amphibole composition (major, trace and REE) to the evolution of water-rich magma to be investigated. All amphiboles in mafic and ultramafic rocks are calcic, with (Ca + Na)B ≥ 1.34 and SiIV between 6.1 and 7.3. They predominantly range in composition from tschermakite to magnesiohornblende and display a dominance of edenite (Na,KA + AlIV = SiIV) substitution. Although each sample exhibits remarkably uniform Mg# over a wide range in Si of up to one formula unit, the mafic rock amphiboles are characterized by lower (0.5 to 0.7) Mg#, compared to the ultramafic rocks (0.7 and 0.9). REE profiles are bow-shaped, and are characterized by depletion in LREE (La/Sm ≈ 0.61), a slight depletion in HREE (Gd/Yb ≈ 1.55) as well as a negative Eu anomaly, which is attributed to co-precipitation of plagioclase. REE and trace element profiles of ultramafic amphiboles are divided into two groupings. Group A amphiboles occur in all specimens analyzed and their REE profiles are very similar to the whole-rock analyses of the mafic rocks and to those predicted from amphibole/melt partition coefficients. In contrast, Group B amphiboles display relative enrichment in light REEs (La/Sm ≈ 2.05), have lower ΣREE, and lack a negative Eu anomaly relative to Sm and Gd. Group B amphiboles are more enriched in Th and U and show a more pronounced depletion in Nb, Ti, Y and HREE. Group B amphiboles probably grew in a reaction relationship with olivine and pyroxene, and their

  4. Sumas Mountain chrysotile induces greater lung fibrosis in Fischer 344 rats than Libby amphibole, El Dorado tremolite, and Ontario ferroactinolite (United States)

    The physical properties of different types of asbestos may strongly affect health outcomes in exposed individuals. This study was designed to provide understanding of the comparative toxicity of naturally occurring asbestos (NOA) fibers including Libby amphibole (LA), Sumas Moun...

  5. Provenance of Tertiary volcanoclastic sediment in NW Thrace (Bulgaria): Evidence from detrital amphibole and pyroxene geochemistry (United States)

    Caracciolo, Luca; Orlando, Andrea; Marchev, Peter; Critelli, Salvatore; Manetti, Piero; Raycheva, Raya; Riley, David


    Detrital heavy mineral and bulk rock geochemistry and a review of sandstone petrographic data have been used to investigate the post-collisional effusive magmatism that followed the closure of the Vardar Ocean and the generation of volcanic sediments in a complex and compositionally variable volcanic region. Available petrographic data gives evidence of contributions from three key source areas corresponding to the three main tectonic units: the structurally lower Gneiss-Migmatite Complex (Byala Reka-Kechros and Kesebir-Kardamos domes) and the upper Variegated (Kimi) Complex, both fringed by the low-to-medium-grade Mesozoic rocks of the Circum-Rhodope Belt. Besides the deposition of siliciclastic material, volcanic contributions from both, intermediate and acid products represent an important source of sediment in the area. Despite dominant intermediate to acid volcanic products, volcanic lithic fragments in sandstones (microlithic, lathwork and brown vitric textures) indicate main inputs from intermediate and basic-intermediate products generating questions on the interpretation of volcanic detritus in reconstruction of provenance. Detrital amphibole and pyroxene chemistry is used to characterise the supply of volcanic material as well as the dispersal mechanisms and understand the role played by each of the volcanic centers present in the area in the infill of the north-western Thrace basin. Amphibole chemistry reveals high compositional heterogeneity according to both compositional variability of the numerous volcanic centres active at the time of deposition and presence of metamorphic amphibole. 4Al and AlT apfu values indicate that most of the amphiboles from the NERZ are not of volcanic origin and their presence can only be attributed to the numerous amphibolite facies metamorphic rocks abundantly documented in the area. Detrital amphibole compositions from the ZKVS indicate major contributions from the Iran Tepe and Zvedzel volcanoes. Analysed detrital

  6. Persistent effects of Libby amphibole and amosite asbestos following subchronic inhalation in rats


    Gavett, Stephen H; Parkinson, Carl U.; Willson, Gabrielle A.; Wood, Charles E.; Jarabek, Annie M.; Roberts, Kay C.; Kodavanti, Urmila P; Dodd, Darol E.


    Background Human exposure to Libby amphibole (LA) asbestos increases risk of lung cancer, mesothelioma, and non-malignant respiratory disease. This study evaluated potency and time-course effects of LA and positive control amosite (AM) asbestos fibers in male F344 rats following nose-only inhalation exposure. Methods Rats were exposed to air, LA (0.5, 3.5, or 25.0 mg/m3 targets), or AM (3.5 mg/m3 target) for 10 days and assessed for markers of lung inflammation, injury, and cell proliferation...

  7. The crystal structure and microtwinning of ferro-pedrizite, a new lithium amphibole (United States)

    Aksenov, S. M.; Rastsvetaeva, R. K.; Konovalenko, S. I.; Ananyev, S. A.; Chukanov, N. V.; Miroshkina, A. E.


    The structure of ferro-pedrizite—a new lithium mineral of the amphibole supergroup—has been studied by single-crystal X-ray diffraction. Fe2+ ions dominate over Mg in the chemical composition of this mineral. The parameters of the monoclinic unit cell are a = 9.3716(4) Å, b = 17.649(1) Å, c = 5.2800(6) Å, and β = 102.22(1)°. The experimental set of intensities contains a large number of significant reflections (~10%), which violate the Clattice. Consideration of pseudomerohedral twinning (matrix [1 0 0/00/-3/4 0]) allowed us to solve and refine the structure within the sp. gr. C2/ m to the final value R = 3.9% in the anisotropic approximation of atomic displacements using 4843 I > 2σ( I). The twin components are found to be 0.681(3)/0.319(3). Twinning has been revealed for the first time in amphiboles of the pedrizite family. The idealized formula of ferro-pedrizite ( Z = 2) is determined as NaLi2(Al2Li)[Si8O22](OH)2.

  8. Amphibole reaction rims as a record of pre-eruptive magmatic heating: An experimental approach (United States)

    De Angelis, S. H.; Larsen, J.; Coombs, M.; Dunn, A.; Hayden, L.


    Magmatic minerals record the pre-eruptive timescales of magma ascent and mixing in crustal reservoirs and conduits. Investigations of the mineral records of magmatic processes are fundamental to our understanding of what controls eruption style, as ascent rates and magma mixing processes are well known to control and/or trigger potentially hazardous explosive eruptions. Thus, amphibole reaction rims are often used to infer pre-eruptive magma dynamics, and in particular to estimate magma ascent rates. However, while several experimental studies have investigated amphibole destabilization during decompression, only two investigated thermal destabilization relevant to magma mixing processes. This study examines amphibole decomposition experimentally through isobaric heating of magnesio-hornblende phenocrysts within a natural high-silica andesite glass. The experiments first equilibrated for 24 h at 870 °C and 140 MPa at H2O-saturated conditions and ƒO2 ∼ Re-ReO prior to rapid heating to 880, 900, or 920 °C and hold times of 3-48 h. At 920 °C, rim thicknesses increased from 17 μm after 3 h, to 55 μm after 12 h, and became pseudomorphs after longer durations. At 900 °C, rim thicknesses increased from 7 μm after 3 h, to 80 μm after 24 h, to pseudomorphs after longer durations. At 880 °C, rim thicknesses increased from 7 μm after 3 h, to 18 μm after 36 h, to pseudomorphs after 48 h. Reaction rim microlites vary from 5-16 μm in size, with no systematic relationship between crystal size and the duration or magnitude of heating. Time-averaged rim microlite growth rates decrease steadily with increasing experimental duration (from 3.97 ×10-7 mms-1 to 3.1 to 3.5 ×10-8 mms-1). Time-averaged microlite nucleation rates also decrease with increasing experimental duration (from 1.2 ×103mm-3s-1 to 5.3 mm-3 s-1). There is no systematic relationship between time-averaged growth or nucleation rates and the magnitude of the heating step. Ortho- and clinopyroxene

  9. Amphibole reaction rim textures and mineralogy from the 2006 eruption of Augustine Volcano, Alaska: Nature vs. experiment (United States)

    Henton, S.; Larsen, J. F.; Coombs, M. L.


    Augustine Volcano forms a small island located in Alaska's Cook Inlet, approximately 180 miles southwest of Anchorage. The 2006 eruption began January 11, 2006, and evolved from an initial phase of explosive activity, through continuous and effusive phases, ending approximately mid-March 2006. We present data on the textural and mineralogical make-up of amphibole reaction rims from 2006 andesites from Augustine. Naturally formed reaction rims are compared to rims formed through decompression and heating experiments. Amphiboles make up less than 1 modal % of most samples. However, variations in composition and texture help to explain pre-and syn-eruptive magma histories. The Augustine 2006 amphiboles contain a mixture of rimmed and unrimmed grains. In order of decreasing abundance (by tally), the dominant phases in reaction rims are orthopyroxene, oxides, plagioclase, and clinopyroxene. Most amphibole reaction rims are between 1- 40 microns in thickness. Thicker rims (> 40 microns) were primarily erupted in the later effusive phase of the eruption. In general, the thickest reactions rims (> 60 microns average thickness) contain coarser individual reaction rim grains (with feret diameters of 15-50 microns). Reaction rims with average thickness of less than 60 microns tend to contain finer reaction rim grains (with feret diameters of 10 microns or less). Some reactions rims show a coarsening of rim grains across the rim, from the amphibole boundary to the glass boundary. Preliminary results show no systematic changes in the aspect ratios of reaction rim grains, either across the rim, or between the different rims. Some rims show a decrease in the An content of plagioclase across the rim, from the amphibole boundary to the glass boundary. Reaction rim textures and mineralogy are complex and suggest that multiple forcing factors (including heating and decompression) were responsible for their formation. This study will compare these natural reaction rims to those formed

  10. Amphibole perspective to unravel pre-eruptive processes and conditions in volcanic plumbing systems beneath intermediate arc volcanoes: A case study from Ciomadul volcano (SE Carpathians)

    NARCIS (Netherlands)

    Kiss, B.; Harangi, S.; Ntaflos, T.; Mason, P.R.D.; Pál-Molnár, E.


    Ciomadul is the youngest volcano in the Carpathian-Pannonian region produced crystal-rich high-K dacites that contain abundant amphibole phenocrysts. The amphiboles in the studied dacites are characterized by large variety of zoning patterns, textures, and a wide range of compositions (e.g., 6.4-15

  11. Surface chemistry and surface reactivity of fibrous amphiboles that are not regulated as asbestos

    Energy Technology Data Exchange (ETDEWEB)

    Fantauzzi, M.; Rossi, A. [Universita di Cagliari, ' ' Dipartimento di Scienze Chimiche e Geologiche' ' Centro Grandi Strumenti, Cagliari (Italy); INSTM unit, Monserrato, Cagliari (Italy); Pacella, A.; Gianfagna, A.; Andreozzi, G.B. [Sapienza Universita di Roma, Dipartimento di Scienze della Terra, Roma (Italy); Fournier, J. [Laboratoire de Reactivite de Surface, ' ' Le St Raphael' ' , UPMC Paris VI, UMR 7197, Ivry-sur-Seine, Paris (France)


    Three fibrous amphiboles that are not regulated as asbestos - two from Biancavilla (Sicily, Italy) and one from Libby (MT, USA) - were studied in order to establish relationships between surface chemistry and surface reactivity. The three fibrous samples, plus one prismatic fluoro-edenite from Biancavilla that was used for comparison, were investigated by X-ray photoelectron spectroscopy (XPS) in order to obtain their quantitative surface compositions and to determine the chemical environment of the Fe in each case. In particular, the Fe 2p{sub 3/2} peak was fitted and, for the first for these materials, the binding energies of Fe(II) oxide, Fe(III) oxide and Fe(III) oxyhydroxide were identified. Bulk chemistries and Fe oxidation states were obtained from previous studies for the samples from Biancavilla, and were investigated in the present work by electron microprobe (EMP) and {sup 57}Fe Moessbauer spectroscopy (MS) for the sample from Libby. Comparison between surface and bulk data revealed that the sample with the lowest bulk Fe oxidation state was the one most affected by surface oxidation, while the samples with bulk highly-oxidised Fe were showing very high signal of Fe (III) oxy-hydroxide probably due to weathering. The surface reactivities of the fibrous amphiboles were investigated by measuring the production of the [DMPO, HO] circle radical adduct using electron paramagnetic resonance (EPR) spectroscopy. Notably, significant chemical reactivity was observed; it was found to be comparable with - or, for the Libby sample, even higher than - that of fibrous tremolite (one of the six asbestos minerals). A positive linear correlation was observed when the production of HO circle radical was plotted versus the Fe(II) content on the fibre surface. Data on fibrous tremolite obtained from previous studies were added to substantiate the correlation. These results provide evidence that Fe(II) at the fibre surface controls the production of radicals at the fibre

  12. Iron topochemistry and surface reactivity of amphibole asbestos: relations with in vitro toxicity

    Energy Technology Data Exchange (ETDEWEB)

    Pacella, Alessandro; Andreozzi, Giovanni B. [Sapienza Universita di Roma, Dipartimento di Scienze della Terra, Rome (Italy); Fournier, Jeanine [UPMC Paris VI, UMR 7197, Laboratoire de Reactivite de Surface, Paris (France); Stievano, Lorenzo [UPMC Paris VI, UMR 7197, Laboratoire de Reactivite de Surface, Paris (France); Institut Charles Gerhardt-AIME, UMR CNRS 5253, Universite Montpellier 2, Montpellier (France); Giantomassi, Federica; Lucarini, Guendalina; Rippo, Maria Rita; Pugnaloni, Armanda [Universita' Politecnica delle Marche, Dipartimento di Scienze Cliniche e Molecolari, Torrette (Ancona) (Italy)


    Chemical reactivity of asbestos tremolite from Italy and USA localities and Union Internationale Contre le Cancer (UICC) crocidolite was studied in relation to Fe content, oxidation state, and structural coordination. Direct correlation between amount of Fe{sup 2+} at the exposed M(1) and M(2) sites of the amphibole structure and fiber chemical reactivity was established. The in vitro toxicity of the same samples was investigated on human alveolar A549 cell line. Relationship between crystal-chemical features and cell toxicity is not straightforward. UICC crocidolite has Fe content and chemical reactivity largely higher than that of tremolite samples, but all show comparable in vitro toxic potential. Results obtained evidenced that Fe topochemistry is not a primary factor for induced cell toxicity, though it accounts for asbestos chemical reactivity (and possibly genotoxicity). (orig.)

  13. An Evaluation of Potential Occupational Exposure to Asbestiform Amphiboles near a Former Vermiculite Mine

    Directory of Open Access Journals (Sweden)

    Julie F. Hart


    Full Text Available Amphibole asbestos (AA has been detected on the surface of tree bark in forests neighboring an abandoned vermiculite mine near Libby, Montana. In the present study, simulations were performed to assess potential AA exposure associated with United States Department of Agriculture Forest Service (FS occupational activities. Bark samples were collected prior, and personal breathing zone (PBZ and Tyvek clothing wipe samples were collected during and immediately after trials that simulated FS activities. Transmission electron microscopy (TEM analyses revealed AA bark concentrations up to 15 million structures per square centimeter (s/cm2. AA was detected in 25% of the PBZ TEM samples. AA was detected on wipe samples collected from all activities evaluated. This research demonstrates the potential for airborne exposure and transport of AA in the Kootenai National Forest. These findings are especially relevant to those that work in the area and to the general public who may conduct recreational activities.

  14. Cellular and inflammatory responses in bronchoalveolar lavage and lungs in rats after intratracheal instillation of Libby amphibole or amosite asbestos (United States)

    The high incidence of asbestos-related disease in residents of Libby, Montana, is associated with the mining of asbestos-contaminated vermiculite, but the etiology of disease related to Libby amphibole asbestos (LA) exposure is unclear. In this study, water elutriation was used t...

  15. In Vitro Dissolution of Libby Amphibole, Amosite Asbestos, and MMVF Using Acid and Synthetic Lung Fluid Media. (United States)

    Toxicity of inhaled fibers is dependent in part on biopersistence due to changes in size distribution after deposition and clearance in the respiratory tract. To model this in vivo behavior, respirable (PM2.5) Libby amphibole (LA) and amosite asbestos, and a reference material gl...

  16. Mantle amphibole control on arc and within-plate chemical signatures: Quaternary lavas from Kurdistan Province, Iran (United States)

    Kheirkhah, M.; Allen, M. B.; Neill, I.; Emami, M. H.; McLeod, C.


    New analyses of Quaternary lavas from Kurdistan Province in west Iran shed light on the nature of collision zone magmatism. The rocks are from the Turkish-Iranian plateau within the Arabia-Eurasia collision. Compositions are typically basanite, hawaiite and alkali basalt. Sr-Nd isotope values are close to BSE, which is similar to Quaternary alkali basalts of NW Iran, but distinct from a depleted source melting under Mount Ararat. The chemical signatures suggests variable melting of two distinct sources. One inferred source produced melts with La/Nb from~3.5 to~1.2, which we model as the result of depletion of amphibole during ≤1% melting in the garnet stability field. We infer phlogopite in the source of potassic lavas from Takab. Lithosphere delamination or slab break-off mechanisms for triggering melting are problematic, as the lithosphere is~150-200km thick. It is possible that the negative dT/dP section of the amphibole peridotite solidus was crossed as a result of lithospheric thickening in the collision zone. This explanation is conditional upon the mantle source being weakly hydrated and so only containing a small proportion of amphibole, which can be exhausted during small degrees of partial melting. Our model maybe viable for other magmatic areas within orogenic plateaux, e.g. northern Tibet. Depletion of mantle amphibole may also help explain larger scale transitions from arc to within-plate chemistry in orogens, such as the Palaeogene Arabia-Eurasia system.

  17. The Amphibole-Bearing Chondrite Meteorite LAP04840: Metamorphism and `Tectonics' in a Hydrous Asteroid (United States)

    Treiman, A. H.; McCanta, M. C.; Essene, E. J.


    LAP04840 is an R-chondrite found in Antarctica, and is unique among meteorites in containing abundant amphibole and biotite. Its chondrules (>500 μm diam) sit in a granoblastic matrix of grains ~20 μm across. Amphibole and biotite grains are anhedral to subhedral, to ~100 μm, and concentrated in chondrules. Commonly, they fit among the olivine and opx grains in regions that would (in anhydrous chondrules) have been occupied by cpx, mesostasis, or glass. Minerals are unzoned, and have constant compositions: olivine Fo62Fa38, Opx En60Wo01, plagioclase An07Ab90, magnesio-hornblende, (Ca1.52Na0.81K0.44) (Mg3.60Fe1.27Mn0.01Ti0.04Cr0.08) (Si6.95Al1.02Fe0.03) O22 (OH1.94?F0.05Cl0.01), sodian phlogopite (low Ti, F, Cl), magnetite (Mt63Chr28Sp05Usp04) and Fe-Ni sulfides. This assemblage is consistent with amphibolite facies equilibrium. Amph-plg thermometry (Holland &Blundy, 1994) gives 675°C, which is consistent with limits of ~600

  18. Prevention of disease caused by fluoro-edenite fibrous amphibole: the way forward

    Directory of Open Access Journals (Sweden)

    Caterina Bruno


    Full Text Available Few months after the publication of the monographic section of Annali dell'Istituto Superiore di Sanità second issue of 2014 "Health impact of fibres with fluoro-edenitic composition", the carcinogenicity of fluoro-edenite was assessed by the International Agency for Research on Cancer (IARC in the frame of Monograph 111. The IARC Working Group concluded that there is sufficient evidence in humans that exposure to fluoroedenite fibrous amphibole causes mesothelioma, and sufficient evidence of carcinogenicity in experimental animals. Fluoro-edenite was allocated to Group 1 (the agent is carcinogenic to humans. Now, in view of the recent IARC evaluation, preventive action in Biancavilla requires an upgrade. First of all, environmental monitoring has to be further implemented. All operations of house cleaning should be performed employing wet tools, in order to avoid dust-raising. It is very important that environmental and biological monitoring be related to epidemiological surveillance. The recently approved act of the Sicilian Government concerning a plan of health interventions in Biancavilla will favour cooperation between national, regional and local health institutions with the common goal of improving the quality and appropriateness of diagnostic and therapeutics procedures offered by the health services.

  19. Particle Size Characterization of Water-Elutriated Libby Amphibole 2000 and RTI International Amosite (United States)

    Lowers, Heather; Bern, Amy M.


    This report presents data on particle characterization analyzed by scanning electron microscopy on Libby amphibole collected by the U.S. Geological Survey in 2000 (LA2000) and amosite material collected by RTI International (RTI amosite). The particle characterization data were generated to support a portion of the Libby Action Plan. Prior to analysis, the raw LA2000 and RTI amosite materials were subjected to a preparation step. Each sample was water-elutriated by U.S. Environmental Protection Agency (USEPA) Office of Research and Development, Research Triangle Park using the methods generally described in another published report and then delivered to the U.S. Geological Survey, Denver Microbeam Laboratory for analysis. Data presented here represent analyses performed by the U.S. Geological Survey, Denver Microbeam Laboratory and USEPA National Enforcement Investigations Center. This report consists of two Excel spreadsheet files developed by USEPA, Region 8 Superfund Technical Assistance Unit and describe the particle size characterization of the LA2000 and RTI amosite, respectively. Multiple tabs and data entry cells exist in each spreadsheet and are defined herein.

  20. In vitro determinants of asbestos fiber toxicity: Effect on the relative toxicity of Libby Amphibole in pirmary human airway epithelial cells (United States)

    Background An abnormally high incidence of lung disease has been observed in the residents of Libby, Montana, which has been attributed to occupational and environmental exposure to fibrous amphiboles originating from a nearby contaminated vermiculite mine. The composition of L...

  1. Autoantibodies from mice exposed to Libby amphibole asbestos bind SSA/Ro52-enriched apoptotic blebs of murine macrophages

    International Nuclear Information System (INIS)

    Asbestos exposure is associated with increased autoimmune responses in humans. For example, in Libby, MT where significant asbestos exposure has occurred due to an asbestos-contaminated vermiculite mine near the community, residents have developed increased autoimmune responses compared to an unexposed population. However, the exact mechanism by which Libby amphibole asbestos generates autoimmune responses is unclear. A murine model of amphibole asbestos-induced autoimmunity was recently established, and one of the targets of the autoantibodies (AAs) was the SSA/Ro52 autoantigen. The purpose of this study was to determine whether the SSA/Ro52 autoantigen is exposed at the surface of cells as a result of asbestos exposure as a possible mechanism leading to antigenicity. Our results indicate that Libby asbestos induces apoptosis in murine macrophages as determined by phosphatidylserine exposure, cleavage of poly(ADP-ribose) polymerase and morphological changes such as nuclear condensation. Moreover, asbestos-induced apoptosis results in the formation of apoptotic cell surface blebs enriched in SSA/Ro52 as determined by confocal microscopy. Most importantly, apoptotic cell surface blebs are recognized by AAs from mice exposed to amphibole asbestos suggesting that these cell surface structures may be antigenic when presented in a pro-inflammatory context. This study supports the hypothesis that the induction of apoptosis plays a key role in environmentally induced autoimmunity through cell surface exposure of a known autoantigen

  2. A case control study of lung cancer and exposure to chrysotile and amphibole at a slovenian asbestos-cement plant. (United States)

    Dodic Fikfak, M; Kriebel, D; Quinn, M M; Eisen, E A; Wegman, D H


    A lung cancer case-control study was conducted in a Slovenian asbestos-cement factory for which unusually good records of asbestos exposures were available. The cohort consisted of all 6714 workers employed at the Salonit Anhovo factory after 31 December 1946 who worked there for at least one day between 1964 and 1994. Fifty-eight histologically confirmed cases of primary lung cancer and 290 controls were selected from the cohort. Working life exposure histories to amphibole and chrysotile forms of asbestos were estimated separately. Airborne asbestos concentrations were low. For example, the arithmetic mean exposure to all forms of asbestos in the highest exposure period (1947-1971) was 1.2 f/cm(3). Chrysotile asbestos made up about 90% of this exposure (mean 1.1 f/cm(3)), whereas amphibole accounted for 10% (0.1 f/cm(3)). Comparing those above and below the 90 percentile of cumulative exposure, the odds ratios for all asbestos, chrysotile and amphibole were 1.5, 1.6 and 2.0, respectively, but confidence intervals were wide. There are only a few asbestos-lung cancer studies with high-quality exposure data and exposures in this low range. Though imprecise, the findings are important to the ongoing debate about asbestos risks. PMID:17351264

  3. A review of scientific literature examining the mining history, geology, mineralogy, and amphibole asbestos health effects of the Rainy Creek igneous complex, Libby, Montana, USA. (United States)

    Bandli, Bryan R; Gunter, Mickey E


    This article reviews the past 90 yr of scientific research directed on multiple aspects of the unique geology and environmental health issues surrounding the vermiculite deposit found at Libby, MT. Hydrothermal alteration and extensive weathering of the ultramafic units resulted in the formation of a rich deposit of vermiculite that was mined for 67 yr and used in numerous consumer products in its expanded form. Later intrusions of alkaline units caused hydrothermal alteration of the pyroxenes, resulting in formation of amphiboles. Some of these amphiboles occur in the asbestiform habit and have been associated with pulmonary disease in former miners and mill workers. Identification of these amphibole asbestos minerals has received little attention in the past, but recent work shows that the majority of the amphibole mineral species present may not be any of the amphibole species currently regulated by government agencies. Epidemiological studies on former miners have, nevertheless, shown that the amphibole asbestos from the Rainy Creek igneous complex is harmful; also, a recent study by the Agency for Toxic Substances and Disease Registry shows that residents of Libby who had not been employed in the vermiculite mining or milling operations also appear to have developed asbestos-related pulmonary diseases at a higher rate than the general public elsewhere. Since November 1999, the U.S. Environmental Protection Agency has been involved in the cleanup of asbestos-contaminated sites in and around Libby associated with the mining and processing of vermiculite. PMID:16920668

  4. Libby amphibole-induced mesothelial cell autoantibodies promote collagen deposition in mice. (United States)

    Gilmer, John; Serve, Kinta; Davis, Chad; Anthony, Marti; Hanson, Robert; Harding, Tanner; Pfau, Jean C


    Libby amphibole (LA) causes a unique progressive lamellar pleural fibrosis (LPF) that is associated with pulmonary function decline. Pleural fibrosis among the LA-exposed population of Libby, MT, has been associated with the production of anti-mesothelial cell autoantibodies (MCAA), which induce collagen production from cultured human mesothelial cells. We hypothesized that the progressive nature of LPF could be at least partially attributed to an autoimmune process and sought to demonstrate that LA-induced MCAA trigger collagen deposition in vivo. C57BL/6 mice were exposed to LA for 7 mo, and serum was tested for MCAA by cell-based ELISA on primary mouse mesothelial cells. When treated in vitro with serum from mice exposed to LA, mesothelial cells upregulated collagen matrix production. This effect was lost when the serum was cleared of IgG using protein G beads, implicating IgG autoantibodies. Using the peritoneal cavity as a surrogate for the pleural cavity, groups of naïve (non-asbestos-exposed) mice were injected intraperitoneally with 1) control serum, 2) one dose of serum from LA-exposed mice (LA serum), 3) two doses of LA serum, or 4) two doses of LA serum cleared of IgG. After 1 mo, analysis of collagen in peritoneal walls using two-photon confocal microscopy (SHG analysis) and a hydroxyproline assay demonstrated significant increases in collagen by LA serum but not control or cleared serum. These data support the hypothesis that MCAA in LA-exposed mice induce fibrotic responses in vivo, demonstrating that an autoimmune component may be contributing to the progressive pleural fibrosis seen in LA-exposed patients. PMID:27106292

  5. Experimental Calibration of Amphibole Break Down Rates in Response to Decompression and Heating: Examples From the 1989-1990 eruptions of Redoubt Volcano, Alaska (United States)

    Browne, B. L.; Gardner, J. E.


    Amphiboles are an important mineral common to a variety of magmas, and are especially sensitive to subtle variations in the water content and temperature of the surrounding melt that induces disequilibria through changing pressure (via ascent) or heating (via magma mixing events). For example, as magma rises toward the surface, hydrous amphiboles, stable at high water pressures, react with their surrounding degassing melt to form anhydrous minerals. Also, when magmas of intermediate composition mix with more primitive magmas of higher temperature, hydrous amphiboles, stable at lower temperatures break down by reacting with the resulting hybrid melt. Only a handful of studies have been performed that directly address the stability of amphiboles as an indicator of the rate at which magmatic processes such as mixing and ascent occur. We examine the stability of amphibole through a series of decompression and heating experiments using dacitic and andesitic magma erupted from Redoubt volcano, Alaska in 1989-1990. Redoubt dacite contains magnesio-hornblende and orthopyroxene, whereas the andesite contains pargasitic amphiboles and clinopyroxene. Both contain plagioclase, magnetite, and ilmenite in rhyolitic glass. The stability limits of the hornblende and pargasite were first constrained by phase-equilibrium experiments. For the dacite, experiments indicate that the magma last equilibrated at approximately 840° C and 155 MPa. Isothermal decompression experiments were thus carried to examine the growth rate of reaction rims on the hornblendes in response to the degassing melt. All decompression experiments were initially held at 840° C and 150 MPa for approximately 5 days before decompression. These experiments show that during a 840° C constant rate decompression from 6 km to the surface, no reaction rims developed on amphibole in 2 or 3.5 days (10-20 cm/s), a 2-um rim developed in 5.5 days (1 cm/s), and a 9-um rim developed in 20 days (0.5 cm/s). The third series of

  6. Hydrogen isotope investigation of amphibole and glass in dacite magmas erupted in 1980-1986 and 2005 at Mount St. Helens, Washington (United States)

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


    In active, shallow, sub-volcanic magma conduits the extent of the dehydrogenation–oxidation reaction in amphibole phenocrysts is controlled by energetic processes that cause crystal lattice damage or conditions that increase hydrogen diffusivity in magmatic phases. Amphibole phenocrysts separated from dacitic volcanic rocks erupted from 1980 to 1986 and in 2005 at Mount St. Helens (MSH) were analyzed for δD, water content and Fe3+/Fe2+, and fragments of glassy groundmass were analyzed for δD and water content. Changes in amphibole δD values through time are evaluated within the context of carefully observed volcanic eruption behavior and published petrological and geochemical investigations. Driving forces for amphibole dehydrogenation include increase in magma oxygen fugacity, decrease in amphibole hydrogen fugacity, or both. The phenocryst amphibole (δD value c. –57‰ and 2 wt % H2O) in the white fallout pumice of the May 18, 1980 plinian eruptive phase is probably little modified during rapid magma ascent up an ∼7 km conduit. Younger volcanic rocks incorporate some shallowly degassed dacitic magma from earlier pulses, based on amphibole phenocryst populations that exhibit varying degrees of dehydrogenation. Pyroclastic rocks from explosive eruptions in June–October 1980 have elevated abundances of mottled amphibole phenocrysts (peaking in some pyroclastic rocks erupted on July 22, 1980), and extensive amphibole dehydrogenation is linked to crystal damage from vesiculation and pyroclastic fountain collapse that increased effective hydrogen diffusion in amphibole. Multiple amphibole δD populations in many 1980 pyroclastic rocks combined with their groundmass characteristics (e.g. mixed pumice textures) support models of shallow mixing prior to, or during, eruption as new, volatile-rich magma pulses blended with more oxidized, degassed magma. Amphibole dehydrogenation is quenched at the top surface of MSH dacite lava lobes, but the diversity in the

  7. Magnitude and symmetry of seismic anisotropy in mica- and amphibole-bearing metamorphic rocks and implications for tectonic interpretation of seismic data from the southeast Tibetan Plateau (United States)

    Ji, Shaocheng; Shao, Tongbin; Michibayashi, Katsuyoshi; Oya, Shoma; Satsukawa, Takako; Wang, Qian; Zhao, Weihua; Salisbury, Matthew H.


    We calibrated the magnitude and symmetry of seismic anisotropy for 132 mica- or amphibole-bearing metamorphic rocks to constrain their departures from transverse isotropy (TI) which is usually assumed in the interpretation of seismic data. The average bulk Vp anisotropy at 600 MPa for the chlorite schists, mica schists, phyllites, sillimanite-mica schists, and amphibole schists examined is 12.0%, 12.8%, 12.8%, 17.0%, and 12.9%, respectively. Most of the schists show Vp anisotropy in the foliation plane which averages 2.4% for phyllites, 3.3% for mica schists, 4.1% for chlorite schists, 6.8% for sillimanite-mica schists, and 5.2% for amphibole schists. This departure from TI is due to the presence of amphibole, sillimanite, and quartz. Amphibole and sillimanite develop strong crystallographic preferred orientations with the fast c axes parallel to the lineation, forming orthorhombic anisotropy with Vp(X) > Vp(Y) > Vp(Z). Effects of quartz are complicated, depending on its volume fraction and prevailing slip system. Most of the mica- or amphibole-bearing schists and mylonites are approximately transversely isotropic in terms of S wave velocities and splitting although their P wave properties may display orthorhombic symmetry. The results provide insight for the interpretation of seismic data from the southeast Tibetan Plateau. The N-S to NW-SE polarized crustal anisotropy in the Sibumasu and Indochina blocks is caused by subvertically foliated mica- and amphibole-bearing rocks deformed by predominantly compressional folding and subordinate strike-slip shear. These blocks have been rotated clockwise 70-90° around the east Himalayan Syntaxis, without finite eastward or southeastward extrusion, in responding to progressive indentation of India into Asia.

  8. Nonlinear Modelling of Orthopyroxene and Amphibole Mineral Modes in Orbicules from Fisher Lake CA (United States)

    Durant, D. G.; Fowler, A. D.


    Geochemical self-organization or spontaneous patterning, caused by positive feedback between reaction and transport, which creates amplification of any fluctuations in the system, can occur when a system is pushed into a far-from-equilibrium (FFE) state. The patterning is thus a construct of the system that allows the dissipation of those energies that pushed it into the FFE state and not a template forced onto the system by boundary conditions. The Fisher Lake CA orbicules contain plagioclase and orthopyroxene that show characteristics of FFE cooling; for instance, reverse-zoned radiating crystals organized in a highly complex pattern. The decimetre-scale orbicules are surrounded by a homogeneous mosaic of crystals characteristic of near-to-equilibrium (NTE) plutonic cooling environments. Thus the orbicular comb texture is interpreted as the response of a FFE magma toward achieving equilibrium. The innermost shell of an orbicule, containing the largest, most spectacular reverse-zoned branching orthopyroxene crystals, represents the largest step towards NTE. Rapid precipitation of minerals quickly decreased the free energy of the system such that an overshooting occurred, resulting in a chemical oscillation about the equilibrium value, which gradually decreased as the system approached NTE. Evidence of this mechanism is seen in the shell mineral modes of orthopyroxene and amphibole. Initially the oscillations are large and antithetical, i.e. as the amount of one mineral increases the other decreases and vice versa. The amplitudes of the oscillations gradually decrease flattening out to a more constant value or stable state; thus looking much like a damped pendulum. An empirical nonlinear model based on the modified Volterra-Lotka equations models these curves. The modelling demonstrates that pattern formation can occur without a periodic external forcing of the intensive variables of the magmatic system as the magma cools and solidifies. Smooth changes in these

  9. Crystallography of hornblende amphibole in LAP04840 R chondrite and implication for its metamorphic history

    International Nuclear Information System (INIS)

    LAP04840 is an unusual R chondrite that includes abundant hornblende amphibole. LAP04840 shows a texture of equilibrated chondrite composed of 59.3% olivine, 13.5% orthopyroxene, 13.3% hornblende, 6.2% plagio-clase, 6.0% Fe-Ni sulfide, and 1.7% accessory minerals. Hornblende replaces olivine and pyroxene in both chondrules and matrices, suggesting its secondary origin. All major phases in LAP04840 are homogeneous: olivine (Fa37), orthopyroxene (En70Wo1), and plagioclase (An8Or2). Hornblende is also nearly homogeneous, but the total sum by electron microprobe analysis is 96-98 wt%, suggesting the presence of Fe3+ and a hydroxyl group. Synchrotron Fe-XANES analysis gives a Fe3+/ΣFe ratio of ∼0.6 and micro-FT-IR analysis confirms the presence of a hydroxyl group. Thus, the structural formula is (Na0.40K0.04) (Ca1.46Mn0.02Fe0.062+Na0.46) (Al0.08Fe0.432+Fe0.753+Cr0.08Mg3.60) (Si7.02Al0.98)O22(OH)2. Single crystal X-ray diffraction of LAP04840 hornblende gives the following lattice constants: a=9.7957(9) A, b=18.0788(12) A, c=5.2949(5) A, β=104.747(3)deg. The relatively short distances of [M(1)-O=2.069 A], [M(2)-O=2.081 A], and [M(3)-O=2.058 A] suggest the feasible preference of small Fe3+ at these sites. The mineralogy and petrology of LAP04840 are consistent with its classification as an R6 chondrite. However, the presence of hornblende and biotite is quite unique among not only R chondrites but also asteroidal meteorites in general. The presence of these hydrous minerals suggests metamorphism under high pressure and an aqueous environment probably at depth in the parent body. A thermometer using hornblende and plagioclase equilibria gives T=670-690degC. Further, a barometer using Al content in hornblende gives P=∼0.1 GPa. Although these estimates bear some uncertainties, it is likely that the size of the R chondrite parent body was large enough to induce such metamorphism. (author)

  10. 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

  11. Trace-element composition and zoning in clinopyroxene- and amphibole-group minerals: Implications for element partitioning and evolution of carbonatites (United States)

    Reguir, Ekaterina P.; Chakhmouradian, Anton R.; Pisiak, Laura; Halden, Norman M.; Yang, Panseok; Xu, Cheng; Kynický, Jindřich; Couëslan, Chris G.


    The present work is a first comprehensive study of the trace-element composition and zoning in clinopyroxene- and amphibole-group minerals from carbonatites, incorporating samples from 14 localities worldwide (Afrikanda, Aley, Alnö, Blue River, Eden Lake, Huayangchuan, Murun, Oka, Ozernaya Varaka, Ozernyi, Paint Lake, Pinghe, Prairie Lake, Turiy Mys). The new electron-microprobe data presented here significantly extend the known compositional range of clinopyroxenes and amphiboles from carbonatites. These data confirm that calcic and sodic clinopyroxenes from carbonatites are not separated by a compositional gap, instead forming an arcuate trend from nearly pure diopside through intermediate aegirine-augite compositions confined to a limited range of CaFeSi 2O 6 contents (15-45 mol%) to aegirine with magnesio-ferrikatophorite, richterite, magnesioriebeckite, ferri-nyböite and (potassic-)magnesio-arfvedsonite. In comparison with the clinopyroxenes, the amphiboles contain similar levels of tetravalent high-field-strength elements (Ti, Zr and Hf) and compatible transition elements (Cr, Co and Ni), but are capable of incorporating much higher concentrations of Sc and incompatible elements (up to 500 ppm Sc, 43 ppm Rb, 1470 ppm Sr, 1230 ppm Ba, 80 ppm Pb, 1070 ppm REE, 140 ppm Y, and 180 ppm Nb). In some carbonatites, amphiboles contribute as much as 25% of the Zr + Hf, 15% of the Sr and 35% of the Rb + Ba whole-rock budget. Both clinopyroxenes and amphiboles may also host a significant share (~ 10%) of the bulk heavy-REE content. Our trace-element data show that the partitioning of REE between clinopyroxene (and, in some samples, amphibole) and the melt is clearly bimodal and requires a revision of the existing models assuming single-site REE partitioning. Clinopyroxenes and amphiboles from carbonatites exhibit a diversity of zoning patterns that cannot be explained exclusively on the basis of crystal chemistry and relative compatibility of different trace-element in

  12. Examination of Libby, Montana, Fill Material for Background Levels of Amphibole from the Rainy Creek Complex Using Scanning Electron Microscopy and X-Ray Microanalysis (United States)

    Adams, David T.; Langer, William H.; Hoefen, Todd M.; Van Gosen, Bradley S.; Meeker, Gregory P.


    Natural background levels of Libby-type amphibole in the sediment of the Libby valley in Montana have not, up to this point, been determined. The purpose of this report is to provide the preliminary findings of a study designed by both the U.S. Geological Survey and the U.S. Environmental Protection Agency and performed by the U.S. Geological Survey. The study worked to constrain the natural background levels of fibrous amphiboles potentially derived from the nearby Rainy Creek Complex. The material selected for this study was sampled from three localities, two of which are active open-pit sand and gravel mines. Seventy samples were collected in total and examined using a scanning electron microscope equipped with an energy dispersive x-ray spectrometer. All samples contained varying amounts of feldspars, ilmenite, magnetite, quartz, clay minerals, pyroxene minerals, and non-fibrous amphiboles such as tremolite, actinolite, and magnesiohornblende. Of the 70 samples collected, only three had detectable levels of fibrous amphiboles compatible with those found in the rainy creek complex. The maximum concentration, identified here, of the amphiboles potentially from the Rainy Creek Complex is 0.083 percent by weight.

  13. A Mössbauer and FTIR study of synthetic amphiboles along the magnesioriebeckite ferri-clinoholmquistite join (United States)

    della Ventura, Giancarlo; Redhammer, Günther J.; Iezzi, Gianluca; Hawthorne, Frank C.; Papin, Arnaud; Robert, Jean-Louis


    A series of amphiboles along the magnesioriebeckite—□Na2Mg3Fe3+ 2Si8O22(OH)2 ferri-clinoholmquistite—□Li2Mg3Fe3+ 2Si8O22(OH)2 - join, defined by the BLiB Na-1 exchange vector, were hydrothermally synthesized at 700°C, 0.4 GPa, NNO + 1 redox conditions. Powder XRD and SEM-EDAX showed a very high (> 90%) amphibole yield for all samples. X-ray patterns were indexed in the C2/m space group; refined cell-parameters show a linear decrease of a and β as a function of chemistry. IR spectra in the OH-stretching region show four main and rather sharp bands; these are assigned to Mg and Fe2+ at M(1,3), and indicate that the obtained amphiboles depart from the nominal octahedral composition (M1,3Mg3). The IR spectra also show that there is an increasing filling-up of the A-site for increasing Na in the system (increasing solid-solution toward, arfvedsonite). Mössbauer spectra show four well-defined quadrupole doublets which are assigned to Fe3+ at M2 and to Fe2+ at M1, M3 and M4, respectively. The Fe3+/Fe2+ content derived from fitted peak areas show variable Fe3+ concentration along the series. Mössbauer spectra also show a distinct alteration of 57Fe hyperfine parameters with changing Na Li at M4. The most evident variation is observed for the quadrupole splitting of Fe3+ at M2, which increases by ≈50% from ferri-clinoholmquistite to magnesio-riebeckite; this suggest that the M2 octahedron in ferri-clinoholmquistite is much closer to the ideal geometry than the M2 octahedron in magnesio-riebeckite. Mössbauer spectra show also a well-defined increase in the Fe2+ quadrupole splitting of the M1 and M3 octahedra, which is attributed to the Na Li distribution at the B-sites.

  14. 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

  15. The formation environment of potassic-chloro-hastingsite in the nakhlites MIL 03346 and pairs and NWA 5790: Insights from terrestrial chloro-amphibole (United States)

    Giesting, Paul A.; Filiberto, Justin


    Potassic-chloro-hastingsite has been found in melt inclusions in MIL 03346, its paired stones, and NWA 5790. It is some of the most chlorine-rich amphibole ever analyzed. In this article, we evaluate what crystal chemistry, terrestrial analogs, and experiments have shown about how chlorine-dominant amphibole (chloro-amphibole) forms and apply these insights to the nakhlites. Chloro-amphibole is rare, with about a dozen identified localities on Earth. It is always rich in potassium and iron and poor in titanium. In terrestrial settings, its presence has been interpreted to result from medium to high-grade alteration (>400 °C) of a protolith by an alkali and/or iron chloride-rich aqueous fluid. Ferrous chloride fluids exsolved from mafic magmas can cause such alteration, as can crustal fluids that have reacted with rock and lost H2O in preference to chloride, resulting in concentrated alkali chloride fluids. In the case of the nakhlites, an aqueous alkali-ferrous chloride fluid was exsolved from the parental melt as it crystallized. This aqueous chloride fluid itself likely unmixed into chloride-dominant and water-dominant fluids. Chloride-dominant fluid was trapped in some melt inclusions and reacted with the silicate contents of the inclusion to form potassic-chloro-hastingsite.

  16. 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.

  17. 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

  18. A Mössbauer and FTIR study of synthetic amphiboles along the magnesio-riebeckite - ferri-clinoholmquistite join (United States)

    della Ventura, G.; Redhammer, G.; Iezzi, G.; Papin, A.; Robert, J. L.


    Seven compositions along the magnesio-riebeckite - Na_2Mg_3Fe3+_2Si_8O22(OH)_2 - ferri-clinoholmquistite - Li_2Mg_3Fe3+_2Si_8O{22}(OH)_2 - solid-solution, defined by the ^BLi^BNa-1 exchange vector, were hydrothermally synthesized at 700^oC, 0.4 Gpa, NNO+1 redox conditions. Powder XRD and SEM-EDAX revealed a very high (>95%) amphibole yield for all samples. X-ray patterns were indexed in the C2/m space group; refined cell-parameters show a linear decrease of a and β as a function of chemistry. IR spectra in the OH-stretching region show four main and rather sharp bands, that are assigned to Mg and Fe2+ distributing at M(1,3), and suggest that the obtained amphiboles significantly depart from the nominal octahedral composition (M1,3Mg_3). The IR spectra also show that there is an increasing filling-up of the A-site for increasing Na in the system (solid-solution toward arfvedsonite). Mössbauer spectra shown four well-defined quadrupole doublets which can be assigned to Fe3+ at M(2) and to Fe2+ at M(1), M(3) and M(4), respectively. The Fe3+/Fe2+ content measured from fitted peak areas show variable ferric iron concentrations along the series. However, the most striking feature is a distinct alteration of 57Fe hyperfine parameters with changing Na-Li at M(4). The most evident variation is observed for the quadrupole splitting of Fe3+ at M(2), which increases by ≈ 50% from ferri-clinoholmquistite to magnesio-riebeckite. Since ferric iron quadrupole splitting is correlated with the distortion of the electronic and/or geometric environment around the Fe3+ probe nucleus, the recorded spectra suggest that the M(2) octahedron in ferri-clinoholmquistite is much closer to the ideal geometry than the M(2) octahedron in magnesio-riebeckite. A well-defined increase in the Fe2+ quadrupole splitting of the M(1) and M(3) sites is also observed with changing M(4) composition. Since M(1) and M(3) are not in direct contact with M(4), it is evident that factors other than the Na

  19. Li- and F-bearing alkali amphibole from granitic pegmatite at Hurricane Mountain, Carroll County, New Hampshire (United States)

    Foord, E.E.; Erd, Richard C.; Robie, S.B.; Lichte, F.E.; King, V.T.


    At Hurricane Mountain, Carroll County, New Hampshire, bodies of granitic pegmatite in riebeckite granite contain large (up to 10 cm long and 2 cm across) primary crystals of Li-bearing fluor-arfvedsonite in miarolitic cavities, grading to euhedral Li- and F-poor arfvedsonite. Fine-grained, fibrous, light blue-gray riebeckite occurs as a late-stage hydrothermal filling in the miarolitic cavities. The early, Li-rich, fluor-arfvedsonite has: a 9.836(5), b 17.997(7), c 5.316(4) A??, ?? 103.735(4)??, V 914.20(6) A??3; Z = 2, Dmeas. 3.34 g/cm3, Dcalc. 3.353 g/cm3; biaxial (-), 2Vmeas. 44(1)??, 2Vcalc. 46??; ?? 1.681(2), ?? 1.692(2), ?? 1.694(2), inclined dispersion, r > v; X ??? c -7??, Y = b, Z ??? a +7??; X dark blue, Y lavender gray, Z pale yellowish brown; X > Y > Z; X is opaque at 0.03 mm thickness. A structural formula, on the basis of 24 (O,OH,F) atoms is: (Na0.86K0.25)Na2(Fe2+2.54Fe3+1.485Mn0.10Zn 0.02Li0.49Ti0.07)(Si7.71Al 0.07)O22(F1.34OH0.63). Arfvedsonite within the miarolitic cavities contains less Li and F than that of the earlier generation, and the still later riebeckite contains only 0.09 wt.% Li2O and 0.3 wt.% F. The Fe3+:Fe2+ ratio of the early Li-bearing fluor-arfvedsonite and that of the euhedral arfvedsonite crystals within miarolitic cavities is 0.58. The late, fibrous, cavity-filling riebeckite has an Fe3+:Fe2+ ratio of 0.99. The total iron content of the three amphiboles increases with continued crystallization. These amphiboles are products of peralkaline pegmatites locally derived from peralkaline granite.

  20. Testing the Alpine provenance of heavy minerals in the Rhine: New results from single grain geochemical analyses of detrital garnets and amphiboles (United States)

    Hülscher, Julian; Bahlburg, Heinrich


    The Upper Rhine Graben (URG) is a major continental rift system in central Europe. At its flanks the metamorphic Black Forest and Vosges Mountains rise. Since the opening of the URG in the late Eocene a repeated input of alpine detritus is registered. From 2.9 Ma onward the Swiss Molasse Basin was drained into the URG. In sediments > 2.9 Ma in the URG the heavy mineral assemblage was dominated by zircon, rutile and tourmaline, upsection this changes to a dominance of garnet, epidote and green hornblende. This so-called "Alpine Spectrum" is recorded along the Rhine from the URG to the North Sea but maybe is not delivered exclusively from the Alps. Potential sources are also located along the URG, including Black Forest and Vosges. We test the question of whether the Alpine Spectrum is exclusively derived from the Alps and whether sources in Black Forest and Vosges need to be considered as well. Toward this end we have performed a single grain geochemical provenance analysis for garnets and amphiboles. We have sampled recent sediments from three rivers of the Swiss Molasse Basin, one river from the Vosges Mountains and three from the Black Forest to characterise the heavy mineral suites derived from these sources. This we combine with samples from the Rhine which represent the sink and which we obtained from drill cores near Freiburg and Pfungstadt. We added a sample from the Heidelberg Nord drill core to account for input from the Neckar. Main element geochemistry of ~330 amphiboles and ~850 garnets grains were analysed via electron microprobe. The results were used to perform a linear mixing model in order to quantify the influence of the different source areas. This is the first data set of this kind in the area. Garnets from the sources and the sinks are mostly dominated by almandine and show a varying content of pyrope, spessartine and grossular. The garnets from the Black Forest and the Vosges Mountains are enriched in pyrope and depleted in almandine, compared

  1. Does a Heavy Fe-Isotope Composition of Akilia Quartz-Amphibole-Pyroxene Rocks Necessitate a BIF Origin? (United States)

    Whitehouse, M J; Schoenberg, R; Fedo, C M; Kamber, B S


    The age and origin of the quartz-amphibole-pyroxene (qap) gneiss from the island of Akilia, southern West Greenland, have been the subject of intense debate since the light C-isotope composition of graphite inclusions in apatite was interpreted to indicate the presence of Earth's earliest biological activity. Although this claim for biogenic relicts has been vigorously challenged, the possibility that the rocks might represent some of Earth's earliest water-lain sediments and, hence, a suitable repository for life remains an open question. While some workers have suggested that the entire sequence represents an originally mafic-ultramafic igneous precursor subsequently modified by metasomatism, quartz injection, high-grade metamorphism, and extreme ductile deformation, others maintain that at least a small part of the sequence retains geochemical characteristics indicative of a chemical sedimentary origin. Fractionated Fe isotopes with δ(56)Fe values similar to those observed in Isua BIF have been reported from high-SiO2 units of qap and used to support a chemical sedimentary protolith for the qap unit. Here, we present new Fe isotope data from all lithologic variants in the qap gneiss on Akilia, including layers of undisputed ultramafic igneous origin. Since the latter require introduction of fractionated Fe into at least part of the qap unit, we argue that Fe isotopes must therefore be treated with considerable caution when used to infer BIF for part or all of the qap protolith. PMID:26496524

  2. Origin and implications of zoned amphiboles and other hydrous silicates during aqueous brine infiltration in the Bamble mega shearzone, S-Norway (United States)

    Sorensen, B. E.; Larsen, R. B.


    This study addresses the metasomatic alteration of ortho-amphibolites, in the Froland area in the Bamble sector, South Norway. Potassic alteration is associated with the introduction of biotite and the formation of conspicuous rims on the amphiboles. Significant color variation from deep blue green to light green in the rims encouraged a chemical study of their evolution. Dark blue-green rims are ferrotschermakite/ferropargasite. Rims gradually becomes richer in Mg and depleted in Fe, K, Na, Al and Cl and, finally, terminates with Cl poor actinolite (XMg ≈ 0.9). Simultaneously biotite experiences metasomatic alteration that is strongly correlated with the coexisting calcic amphibole rims. Fluid inclusions combined with phase diagram calculations documents that high salinity brines with near constant salinities of c. 30 wt% solvents, infiltrated and metasomatised the amphibolites throughout cooling and uplift from 630 to 280°C. The compositional changes reflect the complex interaction between brine fluids and hydrous minerals during cooling and uplift. Accordingly, the brine fluids fully control the composition of Fe-Mg silicates by metasomatosis. Models that argue that the biotite Fe/Mg ratio together with the P, T and the fluid compositin control the Cl content of (Munoz and Swenson 1981), can not explain the Froland amphiboles and biotites. This is because the silicate and whole rock chemistries are changed by interaction with the brine fluids. The compositional zoning reflects interaction with a fluid having constant halogen contents during gradually changing PT-conditions. In intensively altered areas the original amphibolite mineralogy is entirely replaced. Here we observe the large-scale metasomatic processes in a small scale version, for example following this pattern toward the centre of a vein: Amphibolite with small amount of biotite (host rock): Zone1: biotite-plagioclase zone (K-enrichment). Zone2: amphibole-plagioclase (K-depletion). Zone3

  3. A Carboniferous 40Ar/39Ar amphibole emplacement age for the Au-bearing Sams Creek alkali-feldspar granite dike, west Nelson, New Zealand

    International Nuclear Information System (INIS)

    A peralkaline alkali-feldspar granite dike associated with Au-sulfide mineralisation at Sams Creek has previously yielded inconsistent Triassic K-Ar ages, and has thwarted attempts at U-Pb zircon dating. We report here a disturbed 40Ar/39Ar step heating spectrum and both single and multi-grain laser fusion analyses of amphibole, from which we interpret an age of 319 ± 8 Ma (MSWD 0.05) for dike emplacement. Although the sample is a complex mix of arfvedsonite and late-stage riebeckite of possibly widely disparate ages, the age gradient is best explained by significant argon loss in a relatively low metamorphic grade setting from amphiboles, which are less retentive of radiogenic argon than most common amphiboles. The youngest step heating and laser ages of c.

  4. Geochemical characteristics of amphibole in the gabbroic rocks of the medial area of the Godzilla Megamullion, Parece Vela Basin, Philippine Sea (United States)

    Harigane, Y.; Morishita, T.; Snow, J. E.; Tamura, A.; Michibayashi, K.; Ohara, Y.; Arai, S.


    The oceanic core complexes (OCCs) are found on most slow spreading ridges proposed by Escartin et al. (2008), which has been suggested that OCC along a spreading axis represent the megamullion in morphological structure and the oceanic detachment fault in formation process by analogy of continental metamorphic core complex. The Godzilla Megamullion (GM), the largest OCC in the world, is located at the extinct Parece Vela Basin spreading ridge in the Philippine Sea (Ohara et al., 2001). Fault rocks are common on the surface of the GM, indicating the presence of a detachment fault exposed on the seafloor (Harigane et al., 2011). Harigane et al. (2008) reported that the hydrothermal metamorphism occurred retrogressively at the gabbroic rocks during the deformation related to the detachment fault. However, the origins of fluids and the fluid-rock interaction during deformation for the detachment fault are still unsolved. In this study, we present trace element geochemical analyses of amphibole and clinopyroxene of the gabbroic rocks sampled from the medial area of the GM using LA-ICP-MS at Kanazawa University and University of Houston. Most of the gabbroic rocks show a porphyroclastic texture that consist of plagioclase/clinopyroxene porphyroclasts and a fine-grained plagioclase/clinopyroxene/amphibole matrix. The amphibole compositions consist of pargasite and magnesio-hornblende (i.e. brown hornblende) with minor actinolite (i.e. green hornblende). These brown hornblendes have two distinct types in microstructure: bleb type and rim type. The bleb type occurs in the cores of clinopyroxene porphyroclasts and has no evidence of deformation. The rim type occurs as fine grains at the rim of clinopyroxene porphyroclasts. All green hornblende grains show no evidence of deformation and occur at the rim of brown hornblende and clinopyroxene grains. All chondrite-normalized REE patterns of clinopyroxene in the gabbroic rocks are characterized by flat heavy-REE and light

  5. 40Ar-39Ar and U-Pb ages of metadiorite from the East Kunlun Orogenic Belt: Evidence for Early-Paleozoic magmatic zone and excess argon in amphibole minerals

    Institute of Scientific and Technical Information of China (English)


    Single-grain zircon U-Pb and amphibole 40Ar-39Ar dating have beenconducted on a deformed and metamorphosed diorite in the East Kunlun Orogenic Belt, which intruded into the middle Proterozoic Kuhai Group exposed in the south of Xiangride region, Dulan County, NW Qinghai Province. The zircon gives a concordant U-Pb age of (446.5±9.1) Ma. The amphibole yields Ar plateau age of (488.0±1.2) Ma and an isochronal age of (488.9±5.6) Ma. Age results of both stepwise released Ar and conventional K-Ar analysis are remarkably higher than that of zircon U-Pb, suggesting that the amphibole contains excess argon and the amphibole plateau age cannot be taken as the timing of metamorphism or deformation. The zircon age is interpreted to be crystallization age of the diorite pluton, which suggests that an Early-Paleozoic magmatic zone indeed existed in the East Kunlun Orogenic Belt stretching along the region south to the Golmud, Normuhong and Xiangride.

  6. Adakite-like geochemical signature produced by amphibole-dominated fractionation of arc magmas: An example from the Late Cretaceous magmatism in Gangdese belt, south Tibet (United States)

    Xu, Wang-Chun; Zhang, Hong-Fei; Luo, Bi-ji; Guo, Liang; Yang, He


    Late Cretaceous (~ 106-76 Ma) adakite-like intrusive rocks in the middle-eastern Gangdese belt occur in an E-W trending belt paralleling the Indus-Yarlung suture, south Tibet. Their petrogenesis and geodynamic processes have been a subject of debate. We report here U-Pb zircon ages, geochemical and Sr-Nd-Hf isotopic data for adakite-like intrusive rocks as well as the normal arc rocks (gabbros and gabbroic diorites) in the middle Gangdese belt. LA-ICPMS U-Pb zircon analyses yielded an identical age of ~ 88 Ma for two adakite-like rocks, which are slightly younger than the gabbro and gabbroic diorite (ca. 94-90 Ma). Both the adakite-like rocks and the normal arc rocks have similar whole-rock Sr-Nd and zircon Hf isotope compositions, indicating that they have been derived from a common source. Similarly, the adakite-like and normal arc intrusive rocks in the eastern Gangdese belt also show similar Sr-Nd-Hf isotope compositions. In the middle-eastern Gangdese belt, the > 85 Ma Late Cretaceous intrusive rocks consist of a magma series from gabbro to granodiorite, including both normal arc rocks and adakite-like rocks. These rocks overlap in space and time that conform to a normal arc differentiation trend. In terms of major and trace elements, they also show a clear evolution from the normal arc magmatic into adakitic field. Thus, we suggest that these > 85 Ma Late Cretaceous intrusive rocks were ultimately derived from melting of the hydrated mantle wedge and the adakite-like rocks can be generated in normal arc magmas by amphibole-dominated fractionation. Taking into accounting for the spatial and temporal distribution of the Cretaceous magmatic rocks in the Lhasa terrane, we prefer a model of early Late Cretaceous rollback following Early Cretaceous low-angle oceanic slab subduction. At intermediate pressure and H2O-rich conditions, fractionation of amphibole changes the major and trace element compositions of arc magmas, and will efficiently drives basaltic

  7. Chemistry, mineralogy, and petrology of amphibole in Mount St. Helens 2004-2006 dacite: Chapter 32 in A volcano rekindled: the renewed eruption of Mount St. Helens, 2004-2006 (United States)

    Thornber, Carl R.; Pallister, John S.; Lowers, Heather; Rowe, Michael C.; Mandeville, Charles W.; Meeker, Gregory P.


    Textural, compositional, and mineralogical data are reported and interpreted for a large population of clinoamphibole phenocrysts in 22 samples from the seven successive dacite spines erupted at Mount St. Helens between October 2004 and January 2006. Despite the uniformity in bulk composition of magma erupted since 2004, there is striking textural and compositional diversity among amphibole phenocrysts and crystal fragments that have grown from, partly dissolved in, or been accidentally incorporated in the new dacite. This study demonstrates that magma erupted throughout the current dome-building episode is the end product of small-scale, thorough mixing of multiple generations of crystal-laden magma. The mixed amphibole population provides important clues to magma conditions within the dacite magma reservoir prior to ascent and, to some extent, the dynamics of mixing and ascent.

  8. Amphiboles of basic schists in the Sanbagawa metamorphic terrain of the Kodama-Nagatoro area, Kanto mountains. Kanto sanchi Kodamater dot Nagatoro chiiki no Sanbagawa enkisei hengan no kakusenseki

    Energy Technology Data Exchange (ETDEWEB)

    Hashimoto, M.; Funakoshi, R. (Hitachi Ltd., Tokyo (Japan))


    On the basis of mineral parageneses and the graphitizing degrees of pelitic and psammitic schists, the Sambagawa metamorphic terrain of the Kodama-Nagatoro area in Kanto mountains is divided into three zones, i.e. Zone l (chlorite zone), Zone 2 (garnet zone) and Zone 3 (biotite zone) in the order of lower temperature. Amphibole of basic schists is actinolite in Zone 1. The range of composition variance widens gradually with the increase in the temperature, ranging from actinolite to hornblend in Zone 2, and from actinolite to barroisite through actinolitic hornblend in Zone 3. The amount of Al in amphiboles increases gradually with the increase in temperature. The lowest value becomes higher with the widening of the range of variation towards higher side. The metamorphosis in this area is assumed to have taken place principally under increasing temperature with slight increase in pressure. 21 refs., 8 figs.

  9. The Late Cretaceous igneous rocks of Romania (Apuseni Mountains and Banat): the possible role of amphibole versus plagioclase deep fractionation in two different crustal terranes (United States)

    Vander Auwera, Jacqueline; Berza, Tudor; Gesels, Julie; Dupont, Alain


    We provide new whole-rock major and trace elements as well as 87Sr/86Sr and 143Nd/144Nd isotopic data of a suite of samples collected in the Late Cretaceous volcanic and plutonic bodies of the Apuseni Mts. (Romania) that belong to the Banatitic Magmatic and Metallogenic Belt, also called the Apuseni-Banat-Timok-Srednogorie belt. The samples define a medium- to high-K calc-alkaline differentiation trend that can be predicted by a three-step fractional crystallization process which probably took place in upper crustal magma chambers. Published experimental data indicate that the parent magma (Mg# = 0.47) of the Apuseni Mts. trend could have been produced by the lower crustal differentiation of a primary (in equilibrium with a mantle source) magma. The Late Cretaceous magmatic rocks of the Apuseni Mts. and Banat display overlapping major and trace element trends except that Sr is slightly lower and Ga is higher in the Apuseni Mts. parent magma. This difference can be accounted for by fractionating plagioclase-bearing (Apuseni Mts.) or amphibole-bearing (Banat) cumulates during the lower crustal differentiation of the primary magma to the composition of the parent magma of both trends. This, together with results obtained on the Late Cretaceous igneous rocks from the Timok area in Eastern Serbia, further suggests variation of the water content of the primary magma along and across the belt. The Apuseni Mts. versus the Banat samples display different isotopic compositions that likely resulted from the assimilation of two distinct crustal contaminants, in agreement with their emplacement in two separate mega-units of Alpine Europe.

  10. Water concentrations and hydrogen isotope compositions of alkaline basalt-hosted clinopyroxene megacrysts and amphibole clinopyroxenites: the role of structural hydroxyl groups and molecular water (United States)

    Kovács, István; Demény, Attila; Czuppon, György; Lécuyer, Christophe; Fourel, Francois; Xia, Qun-Ke; Liu, Jia; Pintér, Zsanett; Király, Edit; Török, Kálmán; Szabó, Ábel; Deloule, Etienne; Falus, György; Fancsik, Tamás; Zajacz, Zoltán; Sándorné Kovács, Judit; Udvardi, Beatrix


    The aim of this study was to determine both `water' contents (as OH- and H2O) and δD values of several clinopyroxene samples from alkaline basalts. These parameters were first obtained from five clinopyroxene samples using both the classical `off-line' vacuum extraction technique and the `on-line' high-temperature pyrolysis technique. Blanks measured with the `on-line' gas extraction techniques were low enough to prevent any contamination by atmospheric water vapour. The comparison of data has revealed that our `on-line' procedure is more effective for the extraction of `water' from clinopyroxenes and, consequently, this `on-line' technique was applied to ten additional clinopyroxene samples. Sample δD values cover a similar range from -95 to -45 ‰ (VSMOW) regardless of the studied locations, whereas the total `water' content varies from ~115 to ~2570 ppm. The structural hydroxyl content of clinopyroxene samples measured by micro-FTIR spectrometry varies from ~0 to 476 ppm expressed in molecular water equivalent. The total `water' concentrations determined by mass spectrometry differ considerably from structural hydroxyl contents constrained by micro-FTIR, thus indicating that considerable proportion of the `water' may be present in (nano)-inclusions. The structural hydroxyl concentration—apart from clinopyroxenes separated from amphibole clinopyroxenite xenoliths—correlates positively with the δD values of clinopyroxene megacrysts for each locality, indicating that structurally bond hydrogen in clinopyroxenes may have δD values higher than molecular water in inclusions. This implies that there may be a significant hydrogen isotope fractionation for structural hydroxyl during crystallization of clinopyroxene, while for molecular water there may be no or only negligible isotope fractionation.

  11. Comparing measured OH concentrations from olivine, orthopyroxene and clinopyroxene (NAMs) with aH2O estimated from amphibole equilibria in mantle xenoliths: a test of NAM OH retention (United States)

    Hunt, L. E.; Holyoke, C. W.; Lamb, W. M.; Popp, R. K.


    Determining values of H2O activity (aH2O) for mantle rocks will yield a better understanding of mantle processes that are controlled, in part, by the availability of H2O (e.g., melting and deformation). Values of mantle aH2O may, in some cases, be inferred from the OH contents of nominally anhydrous minerals (NAMs) contained in mantle xenoliths. However, mantle NAMs may suffer H2O loss during emplacement on the Earth's surface. H2O-buffering amphibole equilibria may also be used to determine values of mantle aH2O1. If NAMs reflect mantle H2O concentrations, then there should be a positive correlation between the OH contents of NAMs and values of aH2O estimated from amphibole equilibria. The chemistries of co-existing phases were characterized using the electron microprobe to estimate values of T and aH2O in nine amphibole-bearing xenoliths. We compared these values of aH2O with the OH concentrations (COH) of NAMs as measured using FTIR spectroscopy. In addition to amphibole, all samples contain olivine, two-pyroxenes, and spinel. Temperatures (T) estimated from the compositions of co-existing pyroxenes range from approximately 810 to 960oC. Minimum pressures (P), estimated based on the depth of the Moho at each location, are ≈10 - 12 kbar. Amphibole equilibria, in conjunction with these P-T estimates, yield low values of aH2O for all samples (≈ 0.02 - 0.14). The COH of olivine in all nine samples ranged from equilibria yield predicted olivine OH concentrations that range from 1 and 20 ppm wt. ppm, as determined using experimentally derived relations between aH2O and olivine COH 2,3. The COH in olivine, in combination with DOH opx/ol ≈ 6.7 4, yield orthopyroxene (opx) OH concentrations of equilibria, are generally consistent with the measured COH from all NAMs. Thus, low COH in NAMs from mantle xenoliths may reflect mantle conditions rather than H2O-loss during ascent, although some limited H2O-loss is possible. The conclusion that the OH content of NAMs

  12. Dehydration and partial melting of tremolitic amphibole coexisting with zoisite, quartz, anorthite, diopside, and water in the system H2O-CaO-MgO-Al2O3-SiO2 (United States)

    Quirion, Diane M.; Jenkins, David M.

    The greenschist to amphibolite transition as modeled by the reaction zoisite+tremolite + quartz= anorthite+diopside+water has been experimentally investigated in the chemical system H2O-CaO- MgO-Al2O3-SiO2 over the range of 0.4-0.8 GPa. This reaction is observed to lie within the stability fields of anorthite + water and of zoisite + quartz, in accord with phase equilibrium principles, and its position is in excellent agreement with the boundary calculated from current internally-consistent data bases. The small dP/dT slope of 0.00216 GPa/K (21.6 bars/K) observed for this reaction supports the pressure-dependency of this transition in this chemical system. Experimental reversals of the Al content in tremolitic amphibole coexisting with zoisite, diopside, quartz, and water were obtained at 600, 650, and 700°C and indicated Al total cations (atoms per formula unit, apfu) of only up to 0.5+/-0.08 at the highest temperature. Thermodynamic analysis of these and previous compositional reversal data for tremolitic amphibole indicated that, of the activity/composition relationships considered, a two-site-coupled cation substitution model yielded the best fit to the data and a S0 (1 bar, 298 K) of 575.4+/-1.6 J/K.mol for magnesio-hornblende. The calculated isopleths of constant Al content in the amphibole are relatively temperature sensitive with Al content increasing with increasing temperature and pressure. Finally, several experiments in the range of 1.0-1.3 GPa were conducted to define the onset of melting, and thus the upper-thermal limit, for this mineral assemblage, which must involve an invariant point located at approximately 1.05 GPa and 770°C.

  13. Geochemical Evidence from the Kohistan Complex for Differentiation of Garnet Granulitic lower Crust in Island Arcs by Dehydration Melting of Amphibole-bearing Plutonics: Implications for the Andesite Model of Continental Crustal Growth (United States)

    Garrido, C. J.; Bodinier, J.; Burg, J.; Zeilinger, G.; Hussain, S. S.; Dawood, H.; Gervilla, F.


    at depth > 30 km (ca 1.0 GPa,), together with the high geothermal regime now postulatedfor lower island arc crust, should cause dehydration melting of amphibole-bearing plutonic rocks generating dense garnet granulitic roots in island arcs. Dehydration melting of hornblende-bearing plutonics may hence be a common intracrustal chemical and physical differentiation process of island arcs-and a natural consequence of their maturation-leading to the addition of granitic partial melts to the middle-upper arc crust and formation of dense, unstable garnet granulite roots in the lower arc crust. Addition of LREE- and silica-rich melts produced by this process to the middle-upper island arc crust may drive its basaltic composition toward that of andesite affording a plausible solution to the arc paradox of formation of andesitic Continental-like Crust in island arc settings.

  14. 幔源角闪石巨晶中硫化物熔融包裹体研究%Melt Inclusions of Sulfide in Mantle-Driven Amphibole Megacrysts

    Institute of Scientific and Technical Information of China (English)

    李大鹏; 杜杨松; S.D.SCOTT; 秦新龙; A.F.A.MARQUES; R.N.S.SODHI


    用使得轻度演化的玄武岩浆释放大量硫,必然会在莫霍面附近形成大规模高浓度的硫富集区,这些组分在岩浆上侵作用、地壳减薄作用或者裂谷作用的影响下很容易再活化,进入区域岩浆-热液流体系统,最终参与形成区域大规模的硫化物矿床.%Sulphide deposits are of considerable economic importance but the origin of metals and sulphur in these deposits is commonly ambiguous and raises questions. Much attention has been focused on a primary mantle origin for sulphides after extensive research on sulphide melt inclusions (SMI) in mantle-derived xenoliths in basaltic and kimberlitic rocks. Most studies treated the evolution of magma and SMI separately by numerical simulations based on isotopic geochemistry or petrochemistry, few have attempted to use detailed chemical analysis and petrographic evidence for the origin of the sulphide, let alone describing how the SMI evolve in mantle-derived magmas. Using ToF-SIMS, we have analyzed the detailed element compositions, obtaining positive and negative ion maps of the SMI and surrounding host amphibole megacrysts Amp-M. SMI enclosed in mantle-derived Amp-M that represents melt trapped in the minerals provide important clues as to the behavior of immiscible sulphide liquids during the evolution of magmas and the formation of sulphide deposits. Temperature and pressure during formation of the Amp-M were estimated using the TiO2-Al2O3 geothermometer and geobarometer formula has two main interval distribution: The upper-mantle Amp-M: T: 850 ~ 900× (temperature), P: 0. 70 × 109 ~ 0. 82 × 109 Pa (pressure), corresponding to a depth of D: 23. 10~27. 06 km; and the lower-crust Amp-M: T: 900~ 950×, P; 1.09×109~l. 17×109Pa, D: 35.97—38.61 km. Observations and researches indicate that the upper-mantle Amp-M was formed from the crystallization of the upper-mantle alkaline basaltic magma, which resulted from previous partial melting of the upper mantle, and

  15. F-OH exchange equilibria between mica-amphibole mineral pairs (United States)

    Westrich, Henry R.


    Fluoride-hydroxyl exchange equilibria between phlogopite-pargasite and phlogopite-tremolite mineral pairs were experimentally determined at 1,173 K, 500 bars and 1,073 1,173 K, 500 bars respectively. The distribution of fluorine between phlogopite and pargasite was found to favor phlogopite slightly, Δ G {ex/.}(1,173 K)=-1.71 kJ anion-1, while in the case of phlogopite-tremolite, fluorine was preferentially incorporated in the mica, Δ G {ex/.}(1,073)=- 5.67 kJ anion-1 and Δ G {ex/.}(1,173K)=-5.84 kJ anion-1. These results have yielded new values of entropy and Gibbs energy of formation for fluortremolite, Δ S {f/∘}=-2,293.4±16.0JK-1 mol-1 and Δ G {f/∘}= -11,779.3±25.0 kJ mol-1, respectively. In addition, F-OH mineral exchange equilibria support a recent molten oxide calorimetric value for the Gibbs energy of fluorphlogopite, Δ G {f/∘}=-6,014.0±7.0 kJ mol-1, which is approximately 40 kJ mol-1 more exothermic than the tabulated value.

  16. Potential Mode of Action for Non-Cancer Effects following Exposure to Libby Amphibole Asbestos (United States)

    Evidence from different types of studies (in vitro assays, laboratory animal and occupational and epidemiological studies) and across multiple species point to fibrosis, autoimmunity and cardiovascular toxicity as possible non-cancer disease outcomes of interest after exposure to...


    The relative potency of LA compared to UICC amosite was assessed in a subacute inhalation study designed to set exposure levels for a future subchronic study. Male F344 rats (n=7/group) were exposed nose-only to air (control), 3 concentrations of LA, or I concentration of amosite...


    NRMRL hosted a meeting on July 17-18, 2003 entitled, "Analytical Method for Bulk Analysis of Vermiculite." The purpose of this effort was to produce an interim research method for use by U.S. EPA's Office of Research and Development (ORD) for the analysis of bulk vermiculite for...


    Background: Surface-available iron (Fe) is proposed to contribute to asbestos-induced toxicity through the production of reactive oxygen species.Objective: Our goal was to evaluate the hypothesis that rat models of cardiovascular disease with coexistent Fe overload would be incre...

  20. Pulmonary Toxicity and Modifications in Iron Homeostasis Following Libby Amphibole Asbestos Exposure in Rat Models of Cardiovascular Disease (United States)

    Rationale: Individuals suffering from cardiovascular disease (CVD) develop iron dysregulation which may influence pulmonary toxicity and injury upon exposure to asbestos. We hypothesized spontaneously hypertensive (SH) and spontaneously hypertensive heart failure (SHHF) rats woul...

  1. 76 FR 53125 - Draft Toxicological Review of Libby Amphibole Asbestos: In Support of the Summary Information on... (United States)


    ... indicate if you will need audio-visual aid (e.g., laptop and slide projector). In general, each... . To request accommodation of a disability, please contact Ms. Ross, preferably...

  2. 76 FR 30939 - Science Advisory Board Staff Office; Request for Nominations of Experts for SAB Libby Amphibole... (United States)


    ... and experience in the following areas related to asbestos, including: Mineralogy, industrial hygiene... scientific perspectives (which, among other factors, can be influenced by work history and affiliation),...

  3. Determining Satisfaction with Access and Financial Aspects of Care for Persons Exposed to Libby Amphibole Asbestos: Rural and National Environmental Policy Implications

    International Nuclear Information System (INIS)

    Libby, Montana is a Superfund site and epicenter of one of the worst environmental disasters in the USA history in terms of asbestos-related mortality and morbidity. Perceptions of access and financial aspects of care were explored among a national cohort of persons post asbestos exposure and prior to a 2009 Public Health Emergency Declaration. Our findings indicated the Libby cohort was significantly less satisfied with access and financial aspects of care as measured by two PSQ-III scales when compared to an adult, chronically ill patient sample. Participants with higher levels of respiratory morbidity and depression had significantly lower satisfaction scores

  4. Responses of Fischer Rats to Intratracheal Instillations of PM2.5 Samples of Libby Amphibole (LA), Sumas Mountain Chrysotile, EI Dorado Tremolite, and Ontario Actinolite. (United States)

    To support risk assessment efforts, a comparative intratracheal instillation (IT) study is being conducted to provide mechanistic understanding of the toxicity of different types of fibers encountered in EPA clean-up efforts. While other types of asbestos have been shown to cause...

  5. Persistent increases in inflammatory cytokines, Akt, and MAPK/ERK pathways after inhalation exposure of rats to Libby amphibole (LA) or amosite: comparison to effects after intratracheal exposure to LA or naturally occurring asbestos. (United States)

    Human exposure to LA and other mined or processed asbestos increases risk of lung inflammation, fibrosis, and cancer. Health risks from exposure to naturally occurring asbestos (NOA) are not as well-understood. Mechanisms of long-term toxicity were compared in male F344 rats expo...

  6. Petrology of an eclogite- and pyrigarnite-bearing polymetamorphic rock complex at Cabo Ortegal, NW Spain

    NARCIS (Netherlands)

    Vogel, D.E.


    At Cabo Ortegal, paragneisses are found in association with amphibolites, metagabbros, amphibolized eclogites, amphibolized (plagio) pyrigarnites, and serpentinized ultrabasic rocks. On the basis of petrographical and chemical evidence, their geological history was reconstructed as follows: Precambr

  7. Experimental Constraints on the Origin of the 1991 Pinatubo Dacite


    Prouteau, Gaëlle; Scaillet, Bruno


    Crystallization (dacite) and interaction (dacite–peridotite) experiments have been performed on the 1991 Pinatubo dacite (Luzon Island, Philippines) to constrain its petrogenesis. In the dacite–H2O system at 960 MPa, magnetite and either clinopyroxene (low H2O) or amphibole (high H2O) are the liquidus phases. No garnet is observed at this pressure. Dacite– peridotite interaction at 920 MPa produces massive orthopyroxene crystallization, in addition to amphibole ± phlogopite. Amphibole crystal...

  8. Different meanings for cummingtonite-hornblende association in plutonic rocks (Iberian Massif, Portugal)


    Solá, A. R.; Moita, P.; Santos, J. F.; Neiva, A.M.R.; Ribeiro, M. L.


    Cummingtonite-grunerite series is frequently related with metamorphism or volcanic environments but rarely described as belonging to a plutonic assemblage [1]. Recently, in Iberian Massif (Portugal), there have been several references [2,3,4,5] of this Fe-Mg amphibole intimately associated with Ca amphiboles (mainly hornblende) on plutonic rocks. Different textural relations between two amphibole types have been argued to for a primary (igneous) or subsolidus metamorphic origin for Fe-Mg amph...

  9. Origin of melt pockets in mantle xenoliths from southern Patagonia, Argentina (United States)

    Aliani, Paola; Ntaflos, Theodoros; Bjerg, Ernesto


    Peridotite mantle xenoliths collected north of Gobernador Gregores, Patagonia, affected by cryptic and modal metasomatism bear melt pockets of unusually large size. Melt pockets consist of second generation olivine (ol2), clinopyroxene (cpx2) and spinel (sp2) ± relict amphibole (amph) immersed in a yellowish vesicular glass matrix. Amphibole breakdown was responsible for melt pocket generation as suggested by textural evidence and proved by consistent mass-balance calculations: amph → cpx2 + ol2 + sp2 + melt. Composition of calculated amphibole in amphibole-free melt pockets is very similar to that measured in amphibole-bearing melt pockets from the same xenolith, i.e. amphibole was consumed in the melt pocket generation process. In melt pockets devoid of relict amphibole, mass-balance calculations show remarkable differences between the calculated amphibole and the measured amphibole compositions in melt pockets from the same xenolith. The participation of minor proportions of a consumed reactant phase could be a reasonable explanation. In some samples the calculated phase proportion of glass is in excess compared to modal estimations based on backscattered electron images, probably because a portion of the generated melt was able to migrate out of the melt pockets. Compositional inhomogeneity of cpx2 and variable Ti Kd in cpx2 vs. glass in the same melt pocket reflect fast nucleation and growth and disequilibrium crystallisation, respectively. This and the difference between forsterite content in calculated equilibrium olivine and second generation olivine, suggest that mineral equilibrium was inhibited by rapid quenching of melt pockets.

  10. Onshore heavy mineral placers of south Maharashtra, central west coast of India

    Digital Repository Service at National Institute of Oceanography (India)

    Gujar, A.R.; Ambre, N.V.; Mislankar, P.G.

    environment. Heavy mineral percentage ranges upto 98.37% (average 26.96%). Heavy mineral composition consists of opaques, pyroxenes, amphiboles, rutile, tourmaline, kyanite, zircon, staurolite, titanite, olivine garnet, epidote, sillimanite etc., the light...

  11. Acute Phase Response, Inflammation and Metabolic Syndrome Biomarkers of Libby Asbestos Exposure (United States)

    Background: Identification of biomarkers assists in the diagnosis of disease and the assessment of health risks from environmental exposures. Objective: We hypothesized that rats exposed to Libby amphibole (LA) would present with a unique serum proteomic profile which could help ...

  12. Acute Phase Response and Metabolic Syndrome Biomarkers of Libby Asbestos Exposure (United States)

    Identification of biomarkers assists in the disease diagnosis and environmental health risk assessment. Exposure to Libby amphibole (LA) has been associated with increased cardiovascular mortality. We hypothesized that rats exposed to LA would present a unique serum proteomic pro...

  13. Long-Term Toxicity of Naturally Occurring Asbestos in Male Fischer 344 Rats (United States)

    Naturally occurring asbestos (NOA) fibers are found in geologic deposits that may be disturbed by mining, earthworks, or natural processes, resulting in adverse health risks to exposed individuals. The toxicities of Libby amphibole and NOA samples including Sumas Mountain chrysot...

  14. Geochemical characteristics and the provenance of cretaceous basic dikes in Zhongdong area of Xiazhuang uranium ore field

    International Nuclear Information System (INIS)

    The NWW-extending Cretaceous amphibolic diabase dikes are developed in Xiazhuang uranium ore field, Northern Guangdong province. Geochemical characteristics and the provenance of Cretaceous amphibolic diabases from Xiazhuang area have been studied from the aspects of major and trace elemental geochemistry. It can be concluded that the amphibolic diabases formed at internal plate tectonic setting with less crustal rocks assimilation during their intrusion and evolution, which mostly represent the primary magma from the mantle. The rocks are enriched in LREE, LILE, incompatible elements (K, Rb, Ba, Th,Ta, Ce, et al), have no Nb, Ta, Zr and Hf anomalies and Eu depletion compared with that of OIB basalts. Trace elements ratios and discrimination diagrams indicate that the amphibolic diabases came from the enriched mantle (EMI and EMII) and related to activities of Cretaceous hotspots (mantle plume) in Xiazhuang district. (authors)

  15. The first data on paleomagnetism of Palaeoproterozoic rocks of the Serpovidny structure (the Kola region, northeastern Baltic Shield

    Directory of Open Access Journals (Sweden)

    Matyushkin A. V.


    Full Text Available The orientation of natural magnetization vector components in amphibolites and amphibole schists (magnetite up to 10 % coincides with that of the modern magnetic field vector. Different orientations have been discovered only in quartzitic gneiss (magnetite ≤ 2 % and regressively changed chlorite-amphibole schist. The palaeopole position determined for these rocks corresponds on the apparent pole wander path to ages of 1.95 Ga and ~1.80 Ga, respectively

  16. The first data on paleomagnetism of Palaeoproterozoic rocks of the Serpovidny structure (the Kola region, northeastern Baltic Shield)


    Matyushkin A. V.; Balagansky V. V.


    The orientation of natural magnetization vector components in amphibolites and amphibole schists (magnetite up to 10 %) coincides with that of the modern magnetic field vector. Different orientations have been discovered only in quartzitic gneiss (magnetite ≤ 2 %) and regressively changed chlorite-amphibole schist. The palaeopole position determined for these rocks corresponds on the apparent pole wander path to ages of 1.95 Ga and ~1.80 Ga, respectively

  17. First evidence of the mesozoic mafic-ultramafic magmatism in the Selenga-Stanovoy Terrane of the south-eastern rim of Siberian Craton

    International Nuclear Information System (INIS)

    For identifying the place of ultrabasite-basite magmatic complexes in the history of formation of the continental crust of the Selenga-Stanovoy Super Terrain the U-Pb geochronological studies of zircons from amphibolic gabbros of the Veselkinsky Massif are conducted. Bearing in mind the morphological specific features of zircons suggesting their magmatic origin, the obtained isotope age value (154±1 mln. years) corresponds to the age of crystallization of the melts, which are parent melts for amphibolic gabbros



    Lidia V. Solov’eva; Tatiana V. Kalashnikova; Sergei I. Kostrovitsky; Alexei V. Ivanov; Stanislav S. Matsuk; Ludmila F. Suvorova


    The area of studies covers the north-eastern part of the Siberian craton (the Birekte terrain), Russia. The influence of metasomatic and magmatic processes on the mantle lithosphere is studied based on results of analyses of phlogopite- and phlogopite-amphibole-containing deep-seated xenoliths from kimberlites of the Kuoika field. In the kimberlitic pipes, deep-seated xenoliths with mantle phlogopite- and phlogopite-amphibole mineralization are developed in two genetically different rock seri...

  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. Sulfate Saturated Hydrous Magmas Associated with Hydrothermal Gold Ores (United States)

    Chambefort, I.; Dilles, J. H.; Kent, A. J.


    Hydrothermal ore deposits associated with arc magmatism represent important sulfur anomalies. During degassing of magmatic systems the volatile may transport metals and sulfur and produce deposits. The ultimate origin of the magma-derived sulfur is still uncertain. The Yanacocha high-sulfidation epithermal Au deposit, Peru, is hosted by a Miocene volcanic succession (ca. 16 to 8 Ma). Magmatic rocks are highly oxidized >NNO+2 and show a range of composition from andesite to dacite. Two populations of amphibole occur in the Yanacocha dacitic ignimbrite deposits (~7 and 12 wt% Al2O3). Low Al amphiboles crystallized at ~ 1.5-2 kbar and 800°C (Plag-Hb thermobarometry) in equilibrium with plagioclase and pyroxene. High Al amphiboles only contain inclusions of anhydrite associated with apatite (up to 1.2 wt% SO3), and have a higher Cr2O3 content (up to 1000 ppm). We estimate these amphiboles form near the magma's liquidus at P(H2O)> 3kbar and 950 to 1000°C of a basaltic, basaltic andesite ascending magma. Low Al amphibole presents an REE pattern with negative anomalies in Sr, Ti and Eu, characteristic of plagioclase and titanite fractionation in the magma. High Al amphiboles are less enriched in REE and have no Sr, Ti, or Eu anomaly. Rare crystals of high Al amphibole display a low Al rim marked by higher REE contents compared to the core and a negative Eu anomaly. Magmatic sulfate occurrences have been discovered through the 8 m.y. volcanic sequence. Rounded anhydrite crystals are found included within clinopyroxene and both high and low Al amphibole. The rare high Al amphiboles (from the sample RC6) contain up to ~10 vol.%, ~5-80 micrometer-long anhydrite as irregularly shaped (amoeboid) blebs that do not show crystallographic forms and do not follow host cleavages. Extremely rare sulfide inclusions are found in plagioclase (Brennecka, 2006). The major and trace element contents of Yanacocha magmatic anhydrite have been analyzed by electron microprobe and LA

  1. Blueschist metamorphism and its tectonic implication of Late Paleozoic-Early Mesozoic metabasites in the mélange zones, central Inner Mongolia, China (United States)

    Zhang, Jinrui; Wei, Chunjing; Chu, Hang


    Blueschists in central Inner Mongolia are distributed as layers and blocks in mélanges including the southern zone in Ondor Sum area and the northern zone in Manghete and Naomuhunni areas. They have been attributed to the subduction of Early Paleozoic oceanic crust. Blueschists from Ondor Sum and Naomuhunni are characterized by occurrence of sodic amphibole coexisting with epidote, albite, chlorite, calcic amphibole (in Ondor Sum) and muscovite (in Naomuhunni). Blueschists in Manghete contain porphyroblastic albite with inclusions of garnet and epidote in a matrix dominated by calcic-sodic amphibole, epidote, chlorite, albite and muscovite. Phase equilibria modeling for three blueschist samples using pseudosection suggest that the AlM2 contents in sodic amphibole can be used as a good barometer in the limited assemblage involving sodic amphibole + actinolite + epidote + chlorite + albite + quartz under pressures 7-10 kbar. In the sodic amphibole-bearing assemblages, the NaM4 contents in sodic amphibole mainly decrease as temperature rises, being a potential thermometry. The calculated pseudosections constrain the P-T conditions of blueschists to be 3.2-4.2 kbar/355-415 °C in Ondor Sum, 8.2-9.0 kbar/455 °C-495 °C in Manghete and 6.6-8.1 kbar/420-470 °C in Naomuhunni. These P-T estimates indicate a rather high geothermal gradient of 18-25 °C/km for the blueschist metamorphism, being of intermediate P/T facies series. Available zircon U-Pb age data suggests that the protoliths of blueschists were formed later than Late Paleozoic-Early Mesozoic and metamorphosed soon afterwards. An alternative interpretation for the tectonic implication of blueschists in central Inner Mongolia is that they may be a new type attributed to closure of limited ocean basins and do not represent a tectonic regime occurred in conventional subduction setting.

  2. Origin of mafic and ultramafic cumulates from the Ditrău Alkaline Massif, Romania (United States)

    Pál-Molnár, Elemér; Batki, Anikó; Almási, Enikő; Kiss, Balázs; Upton, Brian G. J.; Markl, Gregor; Odling, Nicholas; Harangi, Szabolcs


    Mafic-ultramafic cumulates enclosed in gabbroic-dioritic rocks form part of the Mesozoic Ditrău Alkaline Massif in the Eastern Carpathians, Romania. The poikilitic olivine- and pyroxene-rich and nearly mono mineralic hornblendite rocks display typical cumulate textures with early crystallised olivine (Fo75-73), diopside and augite. In the early stages of their genesis the amphibole was intercumulus whilst in later stages it acquired cumulus status as the fractionating magma evolved. Using major and trace element compositions of minerals and whole-rock samples the origin of these cumulates is determined and the parental magma composition and depth of emplacement are calculated. Cumulus clinopyroxene has more primitive composition than intercumulus amphibole suggesting closed system fractionation for the evolution of poikilitic olivine- and pyroxene-rich cumulates. The evolution of the amphibole-rich mesocumulates is more clearly the result of closed system crystallisation dominated by the precipitation of clinopyroxene and amphibole cumulus crystals. Lamprophyre dykes of the Ditrău Alkaline Massif are proposed to reflect multiple basanitic parental magma batches from which the cumulus olivine and clinopyroxene crystallised. Relative to these dykes the calculated equilibrium melts for intercumulus amphibole in the cumulates was more primitive whilst that for the cumulus amphibole was more evolved. The calculated crystallisation temperature and pressure of ~ 1000-1050 °C and ~ 0.7 GPa, based on the composition of the amphiboles, indicate crystallisation at lower crustal depths. Rare earth element compositions are consistent with an intra-plate tectonic setting.

  3. Metasomatism in the oceanic lithosphere beneath La Palma, Canary Islands (United States)

    Janisch, Astrid; Ntaflos, Theodoros


    La Palma is the most active island within the Canary archipelago with historical eruption along the Cumbre Vieja Rift. Mantle peridotite xenoliths brought to the surface during the eruption 1677/78 at the site of San Antonio Volcano, close to Fuencaliente in the south of the island, gives us an excellent opportunity to study an old oceanic lithosphere. The collection of xenoliths comprises sp-harzburgites, sp-lherzolites, sp-dunites and pyroxenites but only the first three were used for this work. Metasomatic processes are evident in all samples. A common feature is a variable channelling of melt flow through the mantle xenoliths displayed in variations from pervasively metasomatized, through veined to dyke intruded peridotites. Orthopyroxene breakdown into olivine, clinopyroxene and glass is evidence for anhydrous melt percolation. Furthermore, fine-grained veins in various thicknesses consisting of olivine, pyroxene as well as amphibole with apatite and phlogopite reveal additional anhydrous and hydrous metasomatic processes, respectively. Peridotites mainly influenced by anhydrous metasomatism exhibit locally phlogopite and/or amphibole around spinel or in glass-veinlets. Pentlandite has been found in all veined samples. Amphiboles are mostly pargasites but kaersutites are also present in the amphibole-bearing veins. Two different types of amphibole veins have been recognized. The first type is an amphibole-apatite-glass-bearing amphibolite, forming a cross-cutting vein that propagates through the xenolith. The amphiboles in this vein are coarse-grained while the disseminated amphiboles are fine-grained. Clinopyroxene always occurs in association with amphibole and in textural equilibrium suggesting that both minerals have grown together. The glass is of tephritic/basanitic to trachy-basaltic composition. The second amphibole-vein contains phlogopite and traces of apatite. Textural evidence (cross-cutting olivine grains and the absence of hydrous minerals in the

  4. Experimental constraints on the P/T conditions of high silica andesite storage preceding the 2006 eruption of Augustine Volcano, Alaska (United States)

    Henton, S.; Larsen, J. F.; Traxler, N.


    We present new experimental results to constrain the P/T storage conditions of the high silica andesite (HSA) prior to the 2006 eruption of Augustine Volcano, Alaska. Augustine Volcano forms a small island located in Alaska’s Cook Inlet, approximately 180 miles southwest of Anchorage. The 2006 eruption began January 11, 2006, and evolved from an initial phase of explosive activity, through continuous and effusive phases, ending approximately mid-March 2006. Lithologies erupted indicate pervasive hybridization between high- (HSA; 62.2-63.3 wt. % SiO2) and low-silica andesite (LSA; 56.6-58.7 wt% SiO2). This study focuses on experiments using the HSA as starting material to constrain magma storage conditions, based on amphibole stability. Experiments were conducted between 100-160 MPa and 800-900 °C, utilzing H2O saturated conditions and fO2 of Re-ReO. Both lightly crushed and sintered HSA were used as starting powders, seeded respectively with 5 wt. % amphibole and a mix of 5 wt. % amphibole and 20 wt. % plagioclase. Experiments with sintered starting material tended toward a bimodal distribution of experimental phenocrysts and microlites, whilst experiments of the lightly crushed material are more phenocryst rich. Preliminary results indicate that amphibole is stable at conditions of 120-140 MPa and 820-840 °C. These pressures correspond with depths of approximately 4.6-5.4 km, which are consistent with prior magma storage models for Augustine 1986 and 2006 magmas, as well as amphiboles found in other arc andesites (e.g., Redoubt and Soufriere Hills volcanoes). Experimental amphiboles are magnesio-hornblendes, which is in keeping with the natural HSA amphiboles. Experimental and natural hornblendes are similar in composition, with the main difference being a small FeO enrichment (2-3 wt%) and MgO depletion (1-2wt%) in the experimental grains. Further work will provide a more complete assessment of amphibole stability and composition, and will be applied towards

  5. Crystallization conditions and petrogenesis of the lava dome from the ˜900 years BP eruption of Cerro Machín Volcano, Colombia (United States)

    Laeger, Kathrin; Halama, Ralf; Hansteen, Thor; Savov, Ivan P.; Murcia, Hugo F.; Cortés, Gloria P.; Garbe-Schönberg, Dieter


    The last known eruption at Cerro Machín Volcano (CMV) in the Central Cordillera of Colombia occurred ˜900 years BP and ended with the formation of a dacitic lava dome. The dome rocks contain both normally and reversely zoned plagioclase (An24-54), unzoned and reversely zoned amphiboles of dominantly tschermakite and pargasite/magnesio-hastingsite composition and olivine xenocrysts (Fo = 85-88) with amphibole/clinopyroxene overgrowth, all suggesting interaction with mafic magma at depth. Plagioclase additionally exhibits complex oscillatory zoning patterns reflecting repeated replenishment, fractionation and changes in intrinsic conditions in the magma reservoir. Unzoned amphiboles and cores of the reversely zoned amphiboles give identical crystallization conditions of 910 ± 30 °C and 360 ± 70 MPa, corresponding to a depth of about 13 ± 2 km, at moderately oxidized conditions (f = +0.5 ± 0.2 ΔNNO). The water content in the melt, calculated based on amphibole chemistry, is 7.1 ± 0.4 wt.%. Rims of the reversely zoned amphiboles are relatively enriched in MgO and yield higher crystallization temperatures (T = 970 ± 25 °C), slightly lower melt H2O contents (6.1 ± 0.7 wt.%) and overlapping pressures (410 ± 100 MPa). We suggest that these rims crystallized following an influx of mafic melt into a resident magma reservoir at mid-crustal depths, further supported by the occurrence of xenocrystic olivine. Crystallization of biotite, albite-rich plagioclase and quartz occurred at comparatively low temperatures (probably <800 °C) during early stages of ascent or storage at shallower levels. Based on amphibole mineral chemistry, the felsic resident melt had a rhyolitic composition (71 ± 2 wt.% SiO2), whereas the hybrid magma, from which the amphibole rims crystallized, was dacitic (64 ± 3 wt.% SiO2). The bulk rock chemistry of the CMV lava dome dacites is homogenous. They have elevated (La/Nb)N ratios of 3.8-4.5, typical for convergent margin magmas, and display

  6. Use of direct versus indirect preparation data for assessing risk associated with airborne exposures at asbestos-contaminated sites. (United States)

    Goldade, Mary Patricia; O'Brien, Wendy Pott


    At asbestos-contaminated sites, exposure assessment requires measurement of airborne asbestos concentrations; however, the choice of preparation steps employed in the analysis has been debated vigorously among members of the asbestos exposure and risk assessment communities for many years. This study finds that the choice of preparation technique used in estimating airborne amphibole asbestos exposures for risk assessment is generally not a significant source of uncertainty. Conventionally, the indirect preparation method has been less preferred by some because it is purported to result in false elevations in airborne asbestos concentrations, when compared to direct analysis of air filters. However, airborne asbestos sampling in non-occupational settings is challenging because non-asbestos particles can interfere with the asbestos measurements, sometimes necessitating analysis via indirect preparation. To evaluate whether exposure concentrations derived from direct versus indirect preparation techniques differed significantly, paired measurements of airborne Libby-type amphibole, prepared using both techniques, were compared. For the evaluation, 31 paired direct and indirect preparations originating from the same air filters were analyzed for Libby-type amphibole using transmission electron microscopy. On average, the total Libby-type amphibole airborne exposure concentration was 3.3 times higher for indirect preparation analysis than for its paired direct preparation analysis (standard deviation = 4.1), a difference which is not statistically significant (p = 0.12, two-tailed, Wilcoxon signed rank test). The results suggest that the magnitude of the difference may be larger for shorter particles. Overall, neither preparation technique (direct or indirect) preferentially generates more precise and unbiased data for airborne Libby-type amphibole concentration estimates. The indirect preparation method is reasonable for estimating Libby-type amphibole exposure and

  7. Scheelite distribution a long of amphibolitic belt from greenstone belt Barbacena, Minas Gerais, Brazil

    International Nuclear Information System (INIS)

    In the middle southern portion of the Minas Gerais state a 60 Km long and 12 Km wide tungsten belt was discovered, and related to the amphibolitic rocks of the Barbacena Greenstone. Tungsten, present as scheelite, is associated with amphibolites, amphibole schists and amphibole gneisses, with chemical characteristics indicating an igneous origin. Chemical analyses on pan concentrates by I.C.P. showed high values on lead, tin, yttrium, lanthanum, cerium and zirconium, and average values for zinc and copper. The scheelite mineralization is probably strata bound and has a possible submarine exhalative origin. (author)

  8. Equivocal carbonatite markers in the mantle xenoliths of the Patagonia backarc: the Gobernador Gregores case (Santa Cruz Province, Argentina) (United States)

    Rivalenti, Giorgio; Zanetti, Alberto; Mazzucchelli, Maurizio; Vannucci, Riccardo; Cingolani, Carlos A.

    Amphibole +/- phlogopite +/- apatite-bearing mantle xenoliths at Gobernador Gregores display modal, bulk-rock and phase geochemical characteristics held as indicators of carbonatitic metasomatism. However, part of these xenoliths has high TiO2/Al2O3 and those displaying the most pronounced carbonatitic geochemical markers modally trend towards harzburgite. Bulk-rock, clinopyroxene and amphibole show Zr, Hf and Ti negative anomalies, which increase at decreasing Na2O and high field strength elements (HFSE) concentrations. Steady variation trends between xenoliths which have and do not have carbonatitic characteristics suggest a control by reactive porous flow of only one agent, inferred to be initially a ne-normative hydrous basalt (because of the presence of wehrlites) evolving towards silica saturation. Variation trends exhibit cusps when amphibole appears in the mode. Appearance of amphibole may explain the Ti anomaly variations, but not those of Zr and Hf. Numerical modelling [Plate Model (Vernières et al. in J Geophys Res 102:24771-24784, 1997)] gives results consistent with the observed geochemical features by assuming the presence of loveringite. Modest HFSE anomalies in the infiltrating melt may be acquired during percolation in the garnet-facies.

  9. Experimental petrology of lunar material: the nature of mascons, seas, and the lunar interior. (United States)

    O'hara, M J; Biggar, G M; Richardson, S W


    One-atmosphere melting data show that Apollo 11 samples are near cotectic. Melting relations at pressures up to 35 kilobars show that clinopyroxenite or amphibole peridotite are possible lunar interiors. Mascons cannot be eclogite; they may be ilmenite accumulate. Hot lunar surface material will boil off alkalis. PMID:17781513

  10. 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.

  11. Early and Delayed Effects of Naturally Occurring Asbestos on Serum Biomarkers of Inflammation and Metabolism (United States)

    Studies recently showed that intratracheal (IT) instillation of Libby amphibole (LA) increases circulating acute-phase proteins (APP; a-2 macroglobulin, A2M; and a-1 acid glycoprotein, AGP) and inflammatory biomarkers (osteopontin and lipocalin) in rats. In this study, objectives...

  12. Trace elements in minerals from mafic and ultramafic cumulates of the central Sierra de Valle Fértil, Famatinian arc, Argentina (United States)

    Otamendi, Juan E.; Tiepolo, Massimo; Walker, Barry A.; Cristofolini, Eber A.; Tibaldi, Alina M.


    Trace element abundances in constituent minerals from mafic and ultramafic rocks of a deep arc crustal section are studied to observe their abundance and distribution. Five cumulate rocks were selected from a sequence that consists of pyroxene hornblende peridotite, olivine hornblende gabbronorite, pyroxene hornblende gabbronorite, hornblende gabbronorite, gabbro and anorthosite. Solid/liquid partition coefficients calculated with the equilibrium distribution model indicate that Cr, Ni, Co, Zn and V are highly compatible with an olivine-dominated mineral assemblage from the mafic and ultramafic cumulates. The compatibility of Ti and Sc would be dependent on the stability of clinopyroxene, amphibole and oxides in the magmatic system. With few exceptions, the other trace elements are incompatible with the minerals that form the cumulate. At most half the mass of Sr carried by a primitive arc magma could be stored in anorthite-rich plagioclase from the mafic cumulates. Magmatic amphibole fractionates Y, middle and heavy REE from other incompatible elements during crystal accumulation of mafic cumulates. In contrast, late magmatic to subsolidus amphibole has no effect on the differentiation of a primitive arc magma. In fact, the trace element variability of amphibole and clinopyroxene is easily related to different stages of magmatic evolution within the cumulate pile. The results presented here are helpful for modelling other cases of arc magma petrogenesis where the cumulate rocks with dominant mafic assemblages are not exposed.

  13. Investigation into the metamorphic Nappes of the Central Scandinavian Caledonides on the basis of Rb-Sr and K-Ar age determination

    International Nuclear Information System (INIS)

    This study concerns age determinations on several rock units of metamorphic nappes in the central Scandinavian Caledonides. Rb-Sr analyses on whole-rocks and minerals (biotite, muscovite/phengite, feldspars, garnet) were made as well as K-Ar determinations on biotite, muscovite/phengite, amphibole and feldspar. (Auth.)

  14. Magma storage and plumbing of adakite-type post-ophiolite intrusions in the Sabzevar ophiolitic zone, NE Iran

    Directory of Open Access Journals (Sweden)

    K. Jamshidi


    Full Text Available Subduction-related adakite-type intrusive rocks emplaced into the late Cretaceous-Paleocene Sabzevar ophiolite zone, NE Iran, range from Mg-andesite to rhyodacite in composition. Here we investigate the magma supply system to these subvolcanic intrusive rocks by applying thermobarometric mineral and mineral-melt equilibrium models, including amphibole thermobarometry, plagioclase-melt thermobarometry and clinopyroxene-melt barometry. Based on the results of these thermobarometric models, plagioclase crystallized dominantly at pressures of ~ 350 (468–130 MPa, while amphiboles record both low pressures (~ 300 MPa and very high pressures (> 700 MPa of crystallization. The latter is supported by the calculated pressures for clinopyroxene crystallization (550 to 730 MPa. The association of amphibole with clinopyroxene and no plagioclase in the most primitive samples (Mg-andesites is consistent with amphibole fractionation from very hydrous magmas at deep crustal levels of the plumbing system, which may have been a key process to intensify adakite-type affinities in this rock suite. Barometry, combined with frequent disequilibrium features, such as oscillatory-zoned and sieve-textured plagioclase crystals with An-rich overgrowths in more evolved samples, imply final magma differentiation occurred in an open upper crustal magma system that developed progressively stronger compositional modifications during high-level magma storage.

  15. Magma storage and plumbing of adakite-type post-ophiolite intrusions in the Sabzevar ophiolitic zone, northeast Iran (United States)

    Jamshidi, K.; Ghasemi, H.; Troll, V. R.; Sadeghian, M.; Dahren, B.


    Subduction-related adakite-type intrusive rocks emplaced into the late Cretaceous-Paleocene Sabzevar ophiolite zone, northeast Iran, range from Mg-andesite to rhyodacite in composition. Here we investigate the magma supply system to these subvolcanic intrusive rocks by applying thermobarometric mineral and mineral-melt equilibrium models, including amphibole thermobarometry, plagioclase-melt thermobarometry and clinopyroxene-melt barometry. Based on the results of these thermobarometric models, plagioclase crystallized dominantly at pressures of ~350 (130 to 468) MPa, while amphiboles record both low pressures (~300 MPa) and very high pressures (>700 MPa) of crystallization. The latter is supported by the calculated pressures for clinopyroxene crystallization (550 to 730 MPa). The association of amphibole with clinopyroxene and no plagioclase in the most primitive samples (Mg-andesites) is consistent with amphibole fractionation from very hydrous magmas at deep crustal levels of the plumbing system, which may have been a key process in intensifying adakite-type affinities in this rock suite. Barometry, combined with frequent disequilibrium features such as oscillatory-zoned and sieve-textured plagioclase crystals with An-rich overgrowths in more evolved samples, implies that final magma differentiation occurred in an open upper crustal magma system that developed progressively stronger compositional modifications during high-level magma storage.

  16. Magma storage and plumbing of adakite-type post-ophiolite intrusions in the Sabzevar ophiolitic zone, NE Iran (United States)

    Jamshidi, K.; Ghasemi, H.; Troll, V. R.; Sadeghian, M.; Dahren, B.


    Subduction-related adakite-type intrusive rocks emplaced into the late Cretaceous-Paleocene Sabzevar ophiolite zone, NE Iran, range from Mg-andesite to rhyodacite in composition. Here we investigate the magma supply system to these subvolcanic intrusive rocks by applying thermobarometric mineral and mineral-melt equilibrium models, including amphibole thermobarometry, plagioclase-melt thermobarometry and clinopyroxene-melt barometry. Based on the results of these thermobarometric models, plagioclase crystallized dominantly at pressures of ~ 350 (468-130) MPa, while amphiboles record both low pressures (~ 300 MPa) and very high pressures (> 700 MPa) of crystallization. The latter is supported by the calculated pressures for clinopyroxene crystallization (550 to 730 MPa). The association of amphibole with clinopyroxene and no plagioclase in the most primitive samples (Mg-andesites) is consistent with amphibole fractionation from very hydrous magmas at deep crustal levels of the plumbing system, which may have been a key process to intensify adakite-type affinities in this rock suite. Barometry, combined with frequent disequilibrium features, such as oscillatory-zoned and sieve-textured plagioclase crystals with An-rich overgrowths in more evolved samples, imply final magma differentiation occurred in an open upper crustal magma system that developed progressively stronger compositional modifications during high-level magma storage.

  17. Mesothelial Cell Autoantibodies Induce Collagen Deposition in vitro & Using a Case Study to Introduce Undergraduates to Bioinformatics (United States)

    Serve, Kinta M.


    Part I. Pleural fibrosis, a non-malignant, asbestos-related respiratory disease characterized by excessive collagen deposition, is progressive, debilitating, and potentially fatal. Disease severity may be influenced by the type of asbestos fiber inhaled, with Libby amphibole (LA) a seemingly more potent mediator of pleural fibrosis than chrysotile…

  18. Chemical petrology of polymetamorphic ultramafic rocks from Galicia, NW Spain

    NARCIS (Netherlands)

    Maaskant, P.


    The investigated polymetamorphic peridotites occur associated with metabasic rocks in several complexes of probably Precambrian age in the northern part of the Hesperian massif (Iberian peninsula). Spinel-clinopyroxene-, spinel-pargasite-, spinel-hornblende- and chlorite-amphibole-peridotites, wehrl

  19. Geochronologic study of polycyclic rocks from Sao Vicente complex in anticlinorium of Caico and Florania - RN, Brazil

    International Nuclear Information System (INIS)

    The characterization of geochronologic standard in a polycyclic area, verifying the interpretative potentials of Rubidium-Strontium and Potassium-Argon methods is the main objective of this paper. The determinations of K/Ar were made in amphiboles, moscovites and biotites. Petrology studies were also made for verifying the composition of several lithological types. (author)

  20. Origen de la escapolita en metapelitas y rocas anfibolicas de series del Cambrico Inferior del Occidente de Asturias (NW de España)

    NARCIS (Netherlands)

    Suárez, O.; Arias, E.


    Levels of layered green rocks, characterized by the presence of a fibrous green tremolitic-actinolitic amphibole and/or scapolite, cropping out in the core of the San Martin anticline in the base of Vegadeo limestone (Lower Cambrian) are studied. The origin of the scapolite, under the point of view

  1. The Cananeia Alkaline Body in the South Coast of São Paulo State: Mineral Chemistry

    Directory of Open Access Journals (Sweden)

    Celso de Barros Gomes


    Full Text Available The Cananeia alkaline occurrence of Late Cretaceous age (Ar-Ar, 83.6 Ma lies in the Ribeira Valley and it is representedby two small bodies: Morro de São João (1.8 km2 in Cananeia Island, and Morrete (0.4 km2, in the neighboringComprida Island. It is covered by Quaternary sediments and mostly constituted by intrusive rocks of syenitic composition,assembled into two principal groups: alkali feldspar syenites and quartz-alkali feldspar syenites. Microsyenites of variabletexture are subordinate. Regarding the mineralogy, the rocks are very rich in feldspars, mesoperthite being the most abundantphase, and plagioclase is only occasionally found as isolated crystals. Mafi c minerals consist dominantly of clinopyroxenesand amphiboles, both belonging to the calcic, calcic-sodic and sodic groups and showing signifi cant chemicalvariations, such as the increase in the Fe/Mg ratio and Na content, and the decrease in Ca, as a function of the degree ofevolution of the rocks. Textural relationships show that clinopyroxene reacts to form amphibole. Biotite is common, mainlyin association with amphibole and opaques. Biotite and opaques together are found at the borders of amphibole grainsor concentrated along their fractures and cleavage planes. Fayalitic olivine is rarely preserved. Most common accessoriesinclude opaques, mainly magnetite with exsolved ilmenite lamellae, apatite, titanite and zircon. Late to post-magmatic alterationprocesses can explain the replacement textures shown by the principal primary minerals and the exsolution structuresfound in feldspars and opaques.

  2. Gabbroic and Peridotitic Enclaves from the 2008 Kasatochi Eruption, Aleutian Islands, Alaska (United States)

    Kentner, A.; Nadin, E. S.; Izbekov, P. E.; Nye, C. J.; Neill, O. K.


    Kasatochi volcano of the Andreanof Islands in the western Aleutian Arc violently erupted over a two day period from August 7-8, 2008. The eruption involved multiple explosive events generating pyroclastic flows, which included abundant mafic and ultramafic enclaves that have since weathered out and accumulated in talus along the coast. These and other mafic enclaves sampled by modern island arc lavas provide insight into subduction magmatism because they emerge from a section of the subduction system that is less likely than shallower zones to be modified by magmatic processes such as mixing, assimilation, or fractionation. We present new whole rock, clinopyroxene, amphibole, plagioclase, and melt compositions from Kasatochi enclaves of the 2008 eruption. The highly crystalline (~40 vol. % phenocryst content), medium-K basaltic andesite host rock contains ~52-55 wt. % SiO2 and 0.6-0.9 wt. % K2O, and is composed of plagioclase, ortho- and clinopyroxene, amphibole, and Ti-magnetite in a microlite-rich groundmass. Upon eruption, this magma sampled two distinct enclave populations: gabbro and peridotite. The gabbro has abundant amphibole (mostly magnesio-hastingsite) and plagioclase with minor clinopyroxene, olivine, and magnetite, while the peridotite is composed of olivine with minor amounts of clinopyroxene and orthopyroxene. There is little textural variation amongst the peridotitic samples collected, but the gabbroic samples vary from layered to massive and cover a range in grain size from fine-grained to pegmatitic. The layered gabbros display centimeter-scale bands of alternating plagioclase- and amphibole-rich layers, with a strong preferential alignment of the amphibole grains. The coarser-grained samples are very friable, with ~10% pore space; disaggregation of these upon host-magma ascent likely formed the amphibole and plagioclase xenocrysts in the andesitic host. Based on the textural and compositional differences, we divide the enclaves into four groups

  3. Crystal reaming during the assembly, maturation, and waning of an eleven-million-year crustal magma cycle: thermobarometry of the Aucanquilcha Volcanic Cluster (United States)

    Walker, Barry A.; Klemetti, Erik W.; Grunder, Anita L.; Dilles, John H.; Tepley, Frank J.; Giles, Denise


    Phenocryst assemblages of lavas from the long-lived Aucanquilcha Volcanic Cluster (AVC) have been probed to assess pressure and temperature conditions of pre-eruptive arc magmas. Andesite to dacite lavas of the AVC erupted throughout an 11-million-year, arc magmatic cycle in the central Andes in northern Chile. Phases targeted for thermobarometry include amphibole, plagioclase, pyroxenes, and Fe-Ti oxides. Overall, crystallization is documented over 1-7.5 kbar (~25 km) of pressure and ~680-1,110 °C of temperature. Pressure estimates range from ~1 to 5 kbar for amphiboles and from ~3 to 7.5 kbar for pyroxenes. Pyroxene temperatures are tightly clustered from ~1,000-1,100 °C, Fe-Ti oxide temperatures range from ~750-1,000 °C, and amphibole temperatures range from ~780-1,050 °C. Although slightly higher, these temperatures correspond well with previously published zircon temperatures ranging from ~670-900 °C. Two different Fe-Ti oxide thermometers (Andersen and Lindsley 1985; Ghiorso and Evans 2008) are compared and agree well. We also compare amphibole and amphibole-plagioclase thermobarometers (Ridolfi et al. 2010; Holland and Blundy 1994; Anderson and Smith 1995), the solutions from which do not agree well. In samples where we employ multiple thermometers, pyroxene temperature estimates are always highest, zircon temperature estimates are lowest, and Fe-Ti oxide and amphibole temperature estimates fall in between. Maximum Fe-Ti oxide and zircon temperatures are observed during the middle stage of AVC activity (~5-3 Ma), a time associated with increased eruption rates. Amphibole temperatures during this time are relatively restricted (~850-1,000 °C). The crystal record presented here offers a time-transgressive view of an evolving, multi-tiered subvolcanic reservoir. Some crystals in AVC lavas are likely to be true phenocrysts, but the diversity of crystallization temperatures and pressures recorded by phases in individual AVC lavas suggests erupting magma

  4. Asbestos Lung Burden in Necroscopic Samples from the General Population of Milan, Italy. (United States)

    Casali, Michelangelo; Carugno, Michele; Cattaneo, Andrea; Consonni, Dario; Mensi, Carolina; Genovese, Umberto; Cavallo, Domenico Maria; Somigliana, Anna; Pesatori, Angela Cecilia


    The present study analysed the asbestos lung burden in necroscopic samples from 55 subjects free from asbestos-related diseases, collected between 2009 and 2011 in Milan, Italy. Multiple lung samples were analysed by light microscopy (asbestos bodies, AB) and EDXA-scanning electron microscopy (asbestos fibres and other inorganic fibres). Asbestos fibres were detected in 35 (63.6%) subjects, with a higher frequency for amphiboles than for chrysotile. Commercial (CA) and non-commercial amphiboles (NCA) were found in roughly similar frequencies. The estimated median value was 0.11 million fibres per gram of dry lung tissue (mf g(-1)) for all asbestos, 0.09 mf g(-1) for amphiboles. In 44 (80.0%) subjects no chrysotile fibres were detected. A negative relationship between asbestos mass-weighted fibre count and year of birth (and a corresponding positive increase with age) was observed for amphiboles [-4.15%, 95% confidence interval (CI) = -5.89 to -2.37], talc (-2.12%, 95% CI = -3.94 to -0.28), and Ti-rich fibres (-3.10%, 95% CI = -5.54 to -0.60), but not for chrysotile (-2.84%, 95% CI = -7.69 to 2.27). Residential district, birthplace, and smoking habit did not affect the lung burden of asbestos or inorganic fibres. Females showed higher burden only for amphiboles (0.12 versus 0.03 mf g(-1) in males, P = 0.07) and talc fibres (0.14 versus 0 mf g(-1) in males, P = 0.03). Chrysotile fibres were shorter and thinner than amphibole fibres and NCA fibres were thicker than CA ones. The AB prevalence was 16.4% (nine subjects) with concentrations ranging from 10 to 110 AB g(-1) dry, well below the 1000 AB g(-1) threshold for establishing occupational exposure. No AB were found in subjects younger than 30 years. Our study demonstrated detectable levels of asbestos fibres in a sample taken from the general population. The significant increase with age confirmed that amphibole fibres are the most representative of cumulative exposure. PMID:25878166

  5. Metasomatism in the lithospheric mantle beneath southern Patagonia, Argentina (United States)

    Kolosova-Satlberger, Olesya; Ntaflos, Theodoros; Bjerg, Ernesto


    Mantle xenoliths from Gobernador Gregores, southern Patagonia are spinel- lherzolites, harzburgites and wehrlites. Composite xenoliths consisting of websterites, olivine-websterites and spinel- lherzolites or harzburgites are present as well. The lithospheric mantle beneath Gobernador Gregores region was affected by multiple modal metasomatic events as can be inferred by the presence of amphibole, phlogopite and apatite. The existence of amphibole as inclusion in clinopyroxene suggests dehydration reaction of peridotites, which previously experienced modal metasomatism. This textural evidence records the earliest detectable metasomatic event. A second distinct modal metasomatic event consists of disseminated up to 6 mm in diameter coarse grained amphiboles (100*mg# =89.9) which show breakdown reactions and pseudomorphic replacement by glass and fine grained second generation of olivine, clinopyroxene and spinel. The intensity of the breakdown reaction is variable. In most cases amphibole occurs as a relict within these pseudomorphs. However, melt pockets of up to 10 mm in diameter are abundant, irregular in shape and having the same minerals such as in the pseudomorphs, indicate clearly amphibole breakdown because remnants of it were found enclosed by second generation clinopyroxene. Similar breakdown reactions experienced the phlogopite in the samples where is present. The Phlogopite (100*mg# =88.6) breakdown produces the same mineral phases as the amphibole. The second generation minerals formed after breakdown of amphibole and phlogopite show minor differences in their composition. However, the chemical composition of glass varies considerably. The glasses formed after breakdown of amphibole and phlogopite have trachyandesitic and tephriphonolitic composition, respectively. Some harzburgites and composite xenoliths reveal another metasomatic event: peridotite, enriched in orthopyroxene (mainly orthopyroxenite veinlets, rare websterite), suggests interaction with

  6. 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.

  7. Environmental concentrations of fibers with fluoro-edenitic composition and population exposure in Biancavilla (Sicily, Italy

    Directory of Open Access Journals (Sweden)

    Biagio Maria Bruni


    Full Text Available INTRODUCTION. The town of Biancavilla (Sicily was included in the National Priorities List of Contaminated Sites due to environmental dispersion of amphibole fibers owing to the extraction of materials from a local quarry. The present report summarizes results from several, hitherto unpublished, environmental surveys carried out in the area, as well as from published analyses of the chemistry and composition of fibers. METHODS. Data included here comprises environmental fiber concentrations by scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS analysis in soil, indoor and outdoor air, personal monitoring, as well as a chemical characterization of the fibers. The full chemical structure and spectroscopic characterization of fibers were obtained through a multi-analytical approach: SEM-EDS, X-ray powder diffraction (XRPD, as well as Mössbauer (MS and Fourier transform infrared (FT-IR spectroscopies. RESULTS. Data analyzed provided a spatial and temporal picture of fiber concentrations in Biancavilla, and a qualitative assessment of population exposure. Results suggest that until 2000, the population had been exposed to high levels of amphibole fibers. Mitigation measures adopted since 2001, gradually reduced exposure levels to about 0.10.4 ff/l. Previous studies on fibrous amphiboles from Biancavilla reported considerable chemical variability. Differences in composition, especially concerning the presence of Si, Ca, Fe, and Na, were found both within and between samples. Compared to the previously investigated prismatic fluoro-edenite, these fibrous fluorine amphiboles consistently showed higher average values of Si and Fe content, whereas Ca was significantly lower, which we consider a distinctive characteristic of the fluorine fibrous variety. CONCLUSIONS. The population of Biancavilla had been highly exposed to a suite of fibrous amphiboles for over 50 years. Dust mitigation measures have gradually reduced exposure, but

  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


    Directory of Open Access Journals (Sweden)

    Lidia V. Solov’eva


    Full Text Available The area of studies covers the north-eastern part of the Siberian craton (the Birekte terrain, Russia. The influence of metasomatic and magmatic processes on the mantle lithosphere is studied based on results of analyses of phlogopite- and phlogopite-amphibole-containing deep-seated xenoliths from kimberlites of the Kuoika field. In the kimberlitic pipes, deep-seated xenoliths with mantle phlogopite- and phlogopite-amphibole mineralization are developed in two genetically different rock series: magnesian (Mg pyroxenite-peridotite series (with magnesian composition of rocks and minerals and phlogopite-ilmenite (Phl-Ilm hyperbasite series (with ferrous types of rocks and minerals. This paper is focused on issues of petrography and mineralogy of the xenoliths and describes the evidence of metasomatic / magmatic genesis of phlogopite and amphibole. We report here the first data set of 40Ar/39Ar age determinations for phlogopite from the rocks of the magnesian pyroxenite-peridotite series and the ferrous Phl-Ilm hyperbasite series.The Mg series is represented by a continuous transition of rocks from Sp, Sp-Grt, Grt clinopyroxenite and ortopyroxenite to websterite and lherzolite. Many researchers consider it as a layered intrusion in the mantle [Ukhanov et al., 1988; Solov’eva et al., 1994]. The mantle metasomatic phlogopite and amphibole are revealed in all petrographic types of the rocks in this series and compose transverse veins and irregular patchs at grain boundaries of primary minerals. At contacts of xenolith and its host kimberlite, grains of phlogopite and amphibole are often cut off, which gives an evidence of the development of metasomatic phlogopite-amphibole mineralization in the rocks before its’ entraiment into the kimberlite. In the xenoliths with exsolution pyroxene megacrystalls, comprising parallel plates of clino- and orthopyroxene ± garnet ± spinel (former high-temperature pigeonite [Solov’eva et al., 1994], the

  10. Characteristics of ophiolite-related metamorphic rocks in the Beysehir ophiolitic mélange (Central Taurides, Turkey), deduced from whole rock and mineral chemistry (United States)

    Çelik, Ömer Faruk; Delaloye, Michel F.


    Small outcrops of the metamorphic rocks of the Beysehir ophiolite appear to the west of Gencek and to the south of Durak (South of Beysehir Lake) in the Central Tauride Belt in Turkey. Amphibolitic rocks in the ophiolitic mélange have an igneous origin. Protoliths of these rocks were probably alkali basalts, gabbros or some ultramafic cumulates, such as pyroxenite. The amphibolites of the Beysehir Ophiolite can be divided into four groups: (1) amphibole+garnet+plagioclase±epidote (as secondary minerals)±opaque such as ilmenite±accessory minerals such as sphene and apatite; (2) amphibole+pyroxene+plagioclase±epidote±accessory minerals such as sphene, apatite±chlorite, calcite (as secondary mineral); (3) amphibole±plagioclase±opaque±accessory minerals; (4) amphibole+plagioclase±epidote±biotite and muscovite±opaque±accessory minerals. These metamorphic rocks show mainly granoblastic, grano-nematoblastic, porphyroblastic and/or poikiloblastic textures. All amphiboles in the amphibolites are calcic and cluster in the range from magnesio-hastingsite, pargasite to actinolite. Amphibole compositions are characterized by SiO 2=(38.02-54.3%), Al 2O 3=(1.5-12.8), FeO=(10.03-14.67%), K 2O=(0.2-1.8%), MgO=(5.5-15.7), Mg*=(0.3-0.8). The amphibolites show an alkaline to subalkaline character. However, the primitive mantle normalized incompatible trace element diagram shows close similarity with the typical ocean island basalt (OIB) pattern. The Rock/Chondrite normalized REE diagram of the amphibolites also confirms their OIB signature. Tectonomagmatic discrimination diagrams based on the immobile trace elements suggest a mostly within-plate alkali basalt (WPB) environment. Beysehir ophiolitic mélange contains amphibolites from ophiolite-related metamorphic rocks, but the matrix of the Beysehir ophiolitic mélange is not metamorphosed. Blocks of metamorphic rocks and the ophiolitic rocks may have been incorporated into the ophiolitic mélange in an oceanic

  11. 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

  12. Gold-rich sulfide melt inclusions in xenocrysts from a mid-crustal magma chamber, Mt. Milligan porphyry deposit, British Columbia, Canada (United States)

    Hanley, J. J.; Guillong, M.


    Very coarse-grained amphibole xenocrysts (potassian magnesiohastingsite) hosted in an early monzonite stock at the Mt Milligan Cu-Au porphyry deposit, British Columbia, Canada contain coeval sulfide and silicate melt inclusions of primary origin. The sulfide melt inclusions have a bulk composition comparable to Cu-rich ISS. Late growth zones in the amphibole are devoid of sulfide inclusions and contain only low salinity, chalcopyrite-bearing fluid inclusions(average 7.4 wt% NaCleq.). Thermobarometry constrains the minimum conditions of sulfide entrapment (amphibole crystallization) to ˜8 kbar and ˜700°C. LA-ICPMS analyses of 22 sulfide melt inclusions show that it was highly enriched in Au (50± 20 ppm, 1σ), Ag (140± 70 ppm, 1σ) and Ni (5000 ± 3000 ppm, 1σ). Ratios of Cu/Au (7500± 2500, 1σ) and Au/Ag (0.45± 0.24, 1σ) are identical to metal ratios in porphyry- stage veins, demonstrating that these metals were not fractionated from one another during suspected volatile exsolution, fluid-melt partitioning, and subsequent transport and precipitation of ore metals. The extremely Au- rich composition of the sulfide melt may reflect fractional crystallization of the sulfide liquid prior to entrapment in the amphibole. Both the xenocrysts and rare, high Mg, alkali basalt xenoliths hosted in the intrusions are depleted in Cr, Co, Ni and Cu, reflecting the sequestering of the base metals into a sulfide liquid in a mid- crustal magma chamber where amphibole and Cr-spinel were cumulus phases. The results of this study show that a Cu-Au-rich sulfide melt coexisted with a amphibole-saturated alkalic basaltic liquid in mid-crustal magma chamber prior to the emplacement of the main intrusions and associated porphyry stage mineralization at Mt. Milligan. This sulfide melt appears to have destabilized with the appearance (exsolution) of a single-phase low salinity aqueous fluid. Identification and analysis of ore metals in sulfide melt inclusions in relatively common

  13. Retrograde metasomatic effects on phase assemblages in an interlayered blueschist-greenschist sequence (Coastal Cordillera, Chile) (United States)

    Halama, Ralf; Konrad-Schmolke, Matthias


    Interlayered blueschists and greenschists of the Coastal Cordillera (Chile) are part of a Late Palaeozoic accretionary complex. They represent metavolcanic rocks with oceanic affinities based on predominantly OIB-type REE patterns and immobile trace element ratios. Both rock types have similar mineralogies, albeit with different mineral modal abundances. Amphibole is the major mafic mineral and varies compositionally from glaucophane to actinolite. The presence of glaucophane relicts as cores in zoned amphiboles in both blueschists and greenschists is evidence for a pervasive high-pressure metamorphic stage, indicating that tectonic juxtaposition is an unlikely explanation for the cm-dm scale interlayering. During exhumation, a retrograde greenschist-facies overprint stabilized chlorite + albite + winchitic/actinolitic amphibole + phengitic white mica ± epidote ± K-feldspar at 0.4 ± 0.1 GPa. Geochemical variability can be partly ascribed to primary magmatic and partly to secondary metasomatic processes that occurred under greenschist-facies conditions. Isocon diagrams of several adjacent blueschist-greenschist pairs with similar protolith geochemistry were used to evaluate metasomatic changes due to retrograde fluid-rock interaction. The most important geochemical changes are depletion of Si and Na and addition of water in the greenschists compared to the blueschists. Transition metals and LILE are mobilized to varying degrees. The unsystematic deviations from magmatic fractionation trends suggest open system conditions and influx of an external fluid. Pseudosection and water isopleth calculations show that the rocks were dehydrating during most of their exhumation history and remained at water-saturated conditions. The mineralogical changes, in particular breakdown of blue amphibole and replacement by chlorite, albite and calcic/sodic-calcic amphibole, are the prime cause for the distinct coloring. Pseudo-binary phase diagrams were used as a means to link bulk

  14. Retrograde metamorphism of the eclogite in North Qaidam, western China:Constraints by joint 40Ar/39Ar in vacuo crushing and stepped heating

    Institute of Scientific and Technical Information of China (English)

    Rongguo Hu; Jan Wijbrans; Fraukje Brouwer; Linghao Zhao; Min Wang; Huaning Qiu


    Two amphiboles and a syn-metamorphic quartz vein from the Yuka terrane, North Qaidam, western China, have been analyzed by joint 40Ar/39Ar crushing in vacuo and stepwise heating techniques. The crushing in vacuo results provide information to directly constrain the timing of fluid activity and the age of amphibolite-facies retrogression. The stepwise heating results could further be used to decipher the thermal history of the UHP rocks. Amphiboles from amphibolites and quartz vein within garnet-amphibolite lens analyzed by in vacuo crushing yield similarly shaped age spectra and exhibit rela-tively flat age plateaus for the last several steps. The characteristics of gas release patterns and geochronological data testify to the presence of significant excess 40Ar within the fluid inclusions. The age plateaux with weighted mean ages (WMA) ranges from 488 to 476 Ma for amphiboles and 403 Ma for quartz (2s). These data points constitute amphibole WMA yielding excellent isochrons with isochron ages of 469 and 463 Ma with initial 40Ar/36Ar ratios of 520 and 334, respectively. The isochron ages are interpreted to represent initial amphibolite-facies retrogression. The data points constituting the quartz age plateaux give an isochron age of 405 Ma with initial 40Ar/36Ar ratio of 295, recording a significant aqueous fluid flow episode during the early Devonian. Age spectra obtained by stepwise heating of amphibole residues remaining after crushing experiments are characterized by younger and relatively complex age spectra, which are probably influenced by the combined effects of resetting argon and/or mineral inclusions. Nevertheless, we note that the spectra shapes have features in common: excluding the last two steps, minimum apparent ages are found at temperatures of around 500 ?C, corresponding to 319 and 249 Ma, perhaps representing the time of isotopic resetting or resulting from release gas from mineral inclusions of, e.g., biotite or feldspar. Maximum apparent ages

  15. Argon Isotopic and Experimental Petrologic Evidence for Phenocrysts Versus Xenocrysts in the Youngest Toba Tuff (United States)

    Layer, P. W.; Gardner, J. E.; Rutherford, M. J.


    One of the largest known eruptions is that of the 74 ka Youngest Toba Tuff (YTT), which vented more than 2800 cubic km of magma from the Toba Caldera in Sumatra, Indonesia. The YTT was preceded by the 501 ka Middle Toba Tuff, and it has been proposed that the hiatus between them represents the time needed to develop a large magma body (Chesner, 1998). A controversial aspect of the YTT is that the aluminum content of the amphiboles in the magma indicates growth at pressures of ca. 300 MPa, whereas water contents in glass inclusions suggest much lower pressures, implying that the magma was greatly water undersaturated before eruption (Chesner, 1998). To develop a fuller understanding of the YTT magma's petrogenesis, we investigated the experimental phase equilibria of the magma and measured the argon isotopic signatures of sanidine, biotite, amphibole, and plagioclase. We find that biotite, plagioclase, and quartz are stable under almost all pressure-temperature conditions investigated, with sanidine crystallizing at low temperatures. Amphibole does not crystallize at temperatures and pressures recorded by the natural mineral assemblage and we can find no conditions under which amphibole is stable. Biotite and sanidine 40Ar/39Ar isochron ages are concordant at about 77 ka, similar to previous age determinations. Amphiboles and some plagioclases show significantly older ages, some as great as 1.5 Ma. Our results suggest that the YTT magma contained pheoncrysts of biotite, plagioclase, quartz, and sanidine, and resided at nearly water saturated pressures of 100 - 150 MPa. All amphiboles and some plagioclases were xenocrysts and were entrained throughout the entire 2800 cubic km of magma. Diffusion loss modeling of the xenocrysts indicates that these phases could not have resided in the magma chamber since the Middle Toba eruption, and that some were incorporated into the YTT magma perhaps only a few years prior to eruption. This study indicates that combining

  16. Radium equivalent and annual effective dose from geological samples from Pedra - Pernambuco - Brazil

    International Nuclear Information System (INIS)

    The natural radioactivity of an uranium-anomalous area utilized for agricultural activities in Pedra, Brazil, was monitored. For this, samples from the granite and calcium-silicate amphibole rocks underlying this area and also from samples of the soil derived from these rocks were collected and analyzed by high-resolution gamma spectrometry. The equivalent radium (Raeq) was used as a reference for estimating the rate of the effective equivalent dose. The average, minimum and maximum values for the samples were of 319.2 Bq kg-1 (91.1-758.5 Bq kg-1) for soil; 327.5 Bq kg-1 (36.3-1624.0 Bq kg-1) for granitic rocks and 70,124.5 Bq kg-1 (16,979.6-147,159.0 Bq kg-1) for the calcium-silicate amphibole rocks. An estimation of the external exposition was carried out based on the calculation of the parameters obtained.

  17. Petrology and In Situ Trace Element Chemistry of a Suite of R Chondrites (United States)

    Mittlefehldt, D. W.; Peng, Z. X.; Torrano, Z. A.


    Rumuruti (R) chondrites are characterized by low chondrule/matrix modal ratios, high oxidation state, small mean chondrule size, abundant sulfides and low metal contents, and are of petrologic types 3 to 6 [1, 2]. LAP 04840 (R5, [3]) and MIL 11207 (R6), contain the high-T hydrous phases amphibole and mica [3, 4]; not all equilibrated R chondrites contain these [2]. R chondrites thus can provide evidence on whether there are compositional effects caused by high-T, high-fluid metamorphism of nebular materials. We are investigating a suite of R chondrites of diverse petrologic grades to further understand the nature of the metamorphic processes that engendered them [5]. We report on our petrological studies, plus preliminary in situ analyses of trace elements in amphibole-bearing R chondrites.

  18. 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)

  19. Metasomatic silicate chemistry at the Bayan Obo Fe REE Nb deposit, Inner Mongolia, China: Contrasting chemistry and evolution of fenitising and mineralising fluids (United States)

    Smith, M. P.


    Fenite aureoles around carbonatite dykes, and alteration associated with Fe-REE-Nb ore bodies at Bayan Obo, Inner Mongolia, China, show alkali silicate assemblages containing aegirine-augite, (magnesio-)riebeckite, (magnesio-)arfvedsonite, and phlogopite, accompanied by varying amounts of apatite, albite and quartz. In both fenites and orebodies simple thermodynamic constraints indicate mineral parageneses are consistent with rock buffered cooling accompanied by the infiltration of a range of externally buffered hydrothermal fluids. Statistical analysis of amphibole chemistry indicates that even in apparently texturally well constrained paragenetic stages wide variations in chemistry occur in both the ore bodies and fenites. Much of this variation is attributable to the Mg and F content of amphibole, and is therefore interpreted as a result of variation in externally controlled variables ( P, T, initial fluid composition) rather than internally controlled variables such as protolith composition. Similarities in chemistry exist between fenite and some ore body amphiboles. Thermodynamic analysis of the composition of biotite and apatite allows constraints to be placed on the F-content of hydrothermal fluids, and indicates relatively consistent compositions in fenites and orebodies (log aHF/ aH 2O = - 3.8 to - 3.6 at 300 °C and 1 kbar). Amphibole and biotite associated with niobate mineralization are both enriched in fluorine relative to the rest of the paragenesis, and biotite compositions indicate significantly higher HF activities in the hydrothermal fluid (log aHF/ aH 2O = - 2.6 at 300 °C and 1 kbar). The data presented here reinforce previous interpretations of the complex, multistage nature of mineralisation at Bayan Obo, but are still consistent with a direct involvement of carbonatite derived fluids during ore genesis.

  20. The emplacement of peridotites and associated oceanic rocks from the Lizard Complex, southwest England.


    Cook, C.A.; Holdsworth, R. E.; Styles, M.T.


    Upper mantle peridotites and associated oceanic rocks from the Lizard Complex, southwest England, preserve evidence for a multistage geological history. Steeply dipping pre-emplacement fabrics record high-temperature (900-1100 degreesC) shearing and exhumation of the mantle peridotites apparently formed during localized NE-SW rifting in a pull-apart basin setting (c. 400-390 Ma). Associated oceanic rocks (Landewednack amphibolites) preserve a pre-emplacement prograde brown amphibole-bearing m...

  1. Zoning and contamination rate of magnesium and heavy metals of iron, zinc and copper in the north and northwest aquifer of Khoy (Zourabad) based on GIS and determining the contaminated source


    Fariborz Khodadadi; Abdolnaser Fazlnia; Hossein Pirkharrati


    Introduction Heavy metals are the most toxic pollutants in aquatic ecosystems. This contamination can result from the release of heavy metal elements during alteration and weathering of ultramafic and mafic rocks (ophiolite zones). Among the important metals and pollutants in the ophiolite; chromium, cobalt, nickel, iron, magnesium, manganese, zinc and copper could be noted. Basically, a mass of serpentine consists of serpentine, amphibole, talc, chlorite, magnetite, and the remainder of o...

  2. Comparative hazards of chrysotile asbestos and its substitutes: A European perspective.


    Harrison, P T; Levy, L S; Patrick, G.; Pigott, G H; Smith, L. L.


    Although the use of amphibole asbestos (crocidolite and amosite) has been banned in most European countries because of its known effects on the lung and pleura, chrysotile asbestos remains in use in a number of widely used products, notably asbestos cement and friction linings in vehicle brakes and clutches. A ban on chrysotile throughout the European Union for these remaining applications is currently under consideration, but this requires confidence in the safety of substitute materials. Th...

  3. Mineral fibres, fibrosis, and asbestos bodies in lung tissue from deceased asbestos cement workers.


    Albin, M; L. Johansson; Pooley, F D; Jakobsson, K; Attewell, R; Mitha, R


    Lung tissue from 76 deceased asbestos cement workers (seven with mesothelioma) exposed to chrysotile asbestos and small amounts of amphiboles, has been studied by transmission electron microscopy, together with lung tissue from 96 controls. The exposed workers with mesothelioma had a significantly higher total content of asbestos fibre in the lungs than those without mesothelioma, who in turn, had higher concentrations than the controls (medians 189, 50, and 29 x 10(6) fibres/g (f/g]. Chrysot...

  4. Asbestos bodies in bronchoalveolar lavage fluids of brake lining and asbestos cement workers.


    Dumortier, P; De Vuyst, P; Strauss, P.; Yernault, J C


    Asbestos body (AB) concentrations in bronchoalveolar lavage samples of 15 brake lining (BL) workers exposed only to chrysotile have been determined and compared with those from 44 asbestos cement (AC) workers extensively exposed to amphiboles. The mean AB concentrations (263 +/- 802 and 842 +/- 2086 AB/ml respectively) for those groups did not differ significantly but were much higher than those found in control groups. Analytical electron microscopy of asbestos body cores showed that in the ...

  5. Geochemical aspects of some Japanese lavas. (United States)

    Philpotts, J. A.; Martin, W.; Schnetzler, C. C.


    K, Rb, Sr, Ba and rare-earth concentrations in some Japanese lavas have been determined by mass-spectrometric stable-isotope dilution. The samples fall into three rare-earth groups corresponding to tholeiitic, high alumina and alkali basalts. Japanese tholeiites have trace element characteristics similar to those of oceanic ridge tholeiites except for distinctly higher relative concentrations of Ba. Japanese lavas may result from various degrees of partial fusion of amphibole eclogite.

  6. On the age of granulites in the Western Belomorian Belt and of the thrust formation

    International Nuclear Information System (INIS)

    To solve the problems relating to genesis of the Western Belomorian Belt the U-Pb dating method was employed for determining the age of zircons sampled from the rocks making up the belt. Estimated age (2727±32 mln. years) of orthopyroxenic diorites and tonalites crystallization from magma and their subsequent transformations under simultaneously occurring metamorphism of granulite fraction was obtained. Metamorphism of amphibolic facies correlates with thrust formation, its age 2707±1 mln. years

  7. Pleural macrophage recruitment and activation in asbestos-induced pleural injury.


    Choe, N; Tanaka, S.; Xia, W; Hemenway, D R; Roggli, V L; Kagan, E


    The pathogenesis of asbestos-induced pleural fibrosis is poorly understood. Moreover, there has been a long-standing controversy regarding the relative potential of different commercial types of asbestos to cause pleural disease. We postulated that inhaled asbestos fibers translocate to the pleural space where they stimulate the recruitment and activation of pleural macrophages. To test this hypothesis, and to determine whether there are differences between inhaled amphibole and serpentine as...

  8. Tumors that mimic asbestos-related mesothelioma: time to consider a genetics-based tumor registry?


    Kerger, Brent D.; James, Robert C.; Galbraith, David A.


    The diagnosis of mesothelioma is not always straightforward, despite known immunohistochemical markers and other diagnostic techniques. One reason for the difficulty is that extrapleural tumors resembling mesothelioma may have several possible etiologies, especially in cases with no meaningful history of amphibole asbestos exposure. When the diagnosis of mesothelioma is based on histologic features alone, primary mesotheliomas may resemble various primary or metastatic cancers that have direc...

  9. The origin and age of the metamorphic sole from the Rogozna Mts., Western Vardar Belt: New evidence for the one-ocean model for the Balkan ophiolites (United States)

    Borojević Šoštarić, S.; Palinkaš, A. L.; Neubauer, F.; Cvetković, V.; Bernroider, M.; Genser, J.


    This study brings new geochronological and petrochemical data from the metamorphic sole beneath the Rogozna Mts., Western Vardar ophiolite belt. The Rogozna metamorphic sole is located at the base of a serpentinite nappe and consists of amphibolites and talc-chlorite schists. The Rogozna amphibolites are medium- to fine-grained rocks with nematoblastic texture and pronounced foliation. They consist of green amphibole (~ 70 vol.%) with variable silica contents (6.4 to 7.8 Si apfu), as well as Mg# (molMg/[Mg + Fetot]; 0.53 to 0.77) and variably albitized plagioclase (~ 30 vol.%; Ab24-Ab98). Amphibolites are overprinted by a retrograde assemblage containing actinolite, epidote, clinoclore, sericite, chlorite, and magnetite. The amphibolites formed due to metamorphism of two basaltic suites: subalkaline/tholeiitic and alkaline. Subalkaline/tholeiitic amphibolites possess low Zr, Nb, Y, Th, Hf, TiO2, and P2O5 values and a LREE-depleted pattern, typical for the N-MORB (normal mid ocean ridge basalt) to BAB (back-arc basalt) origin. Alkaline amphibolites show elevated concentrations of Zr, Nb, Y, Th, Hf, TiO2, and P2O5 with a LREE-enriched pattern typically displayed by OIB (ocean island basalt). Amphibolites were crystallized during intra-oceanic thrusting at temperatures between 685 °C and 765 °C and at a depth of 12-17 km. 40Ar/39Ar cooling ages of amphibole, ranging from 165 to 170 Ma, slightly postdate the sole formation. Talc-chlorite schists are related to retrograde greenschist-facies metamorphism. They consist of Fe-rich talc and Cr-rich chlorite (peninite-diabantite) pseudomorphs after amphibole and MORB-type Cr-Al spinel, surrounded by Al- and Mg-poor ferrit chromite. The occurrence of ferrit chromite is related to earlier, amphibolite facies metamorphism. Chlorite pseudomorphs after amphibole were formed at 300-410 °C.

  10. The ophiolite massif of Kahnuj (western Makran, Southern Iran): new geological and geochronological data

    International Nuclear Information System (INIS)

    The ophiolite massif of Kahnuj (600 km2) consists, from bottom to top, of layered gabbros, isotropic gabbros and ouralite gabbros, agmatites of dioritic to plagio-granitic composition, a sheeted dyke complex and lastly a basaltic pillow lava unit. Amphiboles from gabbros were dated (40K-40Ar ages) between 156 and 139 Ma and the agmatites are nearly contemporaneous. Potassic granitic veins dated at 93-88 Ma are related to the development of the Ganj arc complex. (authors)

  11. Sinkinematic ultramafic-mafic magmatism in the Red River shear zone

    International Nuclear Information System (INIS)

    To investigate into manifestations the mantle ultramafic-mafic magnetism synchronous with displacement motions in the Red River zone one carried out Ar-Ar-dating of the bulk samples of the amphibolic gabbros, pyroxenites and peridotites from various areas of the mentioned zone. One determined three phases of formation of the ultramafic-mafic association of the Red River zone that corresponded to the age equal to 49-42, 35 and 25 million years

  12. Caracterización del plutón granodiorífico de Los Pedroches en su sector noroccidental (Comarca de La Serena, Badajoz)


    AIonso Olazabal, A.; Carracedo Sánchez, Manuel; Larrea Bilbao, F. J.; A. Aranguren


    This paper is a brief description of the Hercynian calc-alkaline granodioritic pluton of the Los Pedroches batholith at its NW branch (La Serena, Badajoz). This study is located in the National Topographic Map N.T.M. number 805 of Castuera, and it takes into account only the plutonic rocks. Three main lithotypes have been recognized through field, petrological and geochemical studies: biotiticgranodiorite±amphibole, piroxenic granodiorite and Las Cabezas granite. Whole chemistry defines a pot...

  13. Generation of tonalitic and dioritic magmas by coupled partial melting of gabbroic and metasedimentary rocks within the deep crust of the famatinian magmatic Arc, Argentina


    Juan E. Otamendi; Mihai N. Ducea; Alina M Tibaldi; Bergantz, Geoerge W.; Rosa Díaz, Jesús de la; Graciela I Vujovich


    The source regions of dioritic and tonalitic magmas have been identified in a deep crustal section of the Famatinian arc (Sierras Pampeanas of western Argentina). The source zones of intermediate igneous rocks are located at the transition between a gabbro-dominated mafic unit and a tonalite-dominated intermediate unit. In the upper levels of the mafic unit mafic magmas intruded into metasedimentary wall-rocks, crystallized mainly as amphibole gabbronorite and caused the partial melting of th...

  14. Petrology and geochemistray of Imam-Zadeh Hashem mafic and ultramafic bodies, southern Guilan province


    Mojgan Salavati; Reza Fahim Guilani


    Mafic and ultramafic plutonic igneous bodies, with small and big outcrops, between Shemshak rock units (Jurassic) are observed in east of Imam Zadeh Hashem, in southern Guilan province. Ultramafic cumulates consist of clinopyroxenite, and plagiofer clinopyroxenite, olivine clinopyroxenite, and mafic rocks, based on mineralogy consist of gabbros, olivine gabbros, biotite gabbros and amphibole gabbros. According to geochemical data, studied rocks have tholeiitic nature and in the tectonic setti...

  15. Retroperitoneal and pleural fibrosis in an insulator working in power plants


    Uibu, Toomas; Jäntti, Matti; Järvenpää, Ritva; Oksa, Panu; Tossavainen, Antti; Vanhala, Esa; Roto, Pekka


    We describe a case history of a former insulator who developed concomitant retroperitoneal and pleural fibrosis. In his work, the patient had been exposed on a daily basis to asbestos dust while demolishing and installing pipeline insulations. The heavy asbestos exposure was confirmed by a high level of asbestos content in his autopsy lung sample. We propose that both retroperitoneal fibrosis and diffuse pleural thickening were induced in our patient by an abundant amount of amphibole asbesto...

  16. Thermal structure of low-grade accreted Lower Cretaceous distal turbidites, the Central Pontides, Turkey: insights for tectonic thickening of an accretionary wedge




    Abstract: Albian-Turonian subduction-accretionary complexes are exposed widely in the Central Pontides. A major portion of the accretionary complexes is made up of a metaflysch sequence consisting of slate/phyllite and metasandstone intercalation with blocks of marble, Na-amphibole bearing metabasite, and serpentinite. The metaflysch sequence represents distal parts of a large Lower Cretaceous submarine turbidite fan deposited on the Laurasian active continental margin that was subsequently a...

  17. Naturally Occurring Asbestos in the Southern Nevada Region: Potential for Human Exposure (United States)

    Buck, B. J.; Metcalf, R. V.; Berry, D.; McLaurin, B.; Kent, D.; Januch, J.; Goossens, D.


    Naturally occurring fibrous actinolite, winchite, magnesioriebeckite, richterite, magnesiohornblende, and erionite have been found in rock, soil, and dust in southern Nevada and northwestern Arizona. The areas containing naturally occurring asbestos (NOA) include urban areas (e.g. Boulder City) and rural areas where people routinely enjoy outdoor activities including horseback riding, running, hiking, bicycling, and off-road-vehicle (ORV) recreation. A recent study showing mesothelioma in young people and women suggests some form of environmental exposure. Rock, soil, dust and clothing were analyzed using scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS); additional rock samples were analyzed using wavelength dispersive electron probe microanalysis (EPMA); additional soil samples were analyzed using PLM (polarizing light microscopy) and TEM (transmission electron microscopy) using the Fluidized Bed Asbestos Segregator preparation method. Winds have transported and mixed the Ca-amphiboles, which are primarily from Nevada, with the Na-amphiboles that are primarily from northwestern Arizona. Erionite, which has not previously been reported in this area, was a common soil component found in 5 of 6 samples. The erionite source has not yet been determined. Winds have transported the amphibole and erionite particles into the Nellis Dunes Recreation Area - an ORV recreation area located 35 km north of Boulder City that otherwise would not be geologically predicted to contain fibrous amphiboles. In Boulder City, wind directions are primarily bimodal N-NE and S-SW with the strongest winds in the spring coming from the S-SW. The arid climate in this part of the Mojave Desert greatly increases the potential for wind erosion and human exposures. These results suggest that the entire Las Vegas Basin has, at times, received these particles through wind transport. Because the most likely human exposure pathway is through inhalation of dust, the Las Vegas

  18. Magma storage and plumbing of adakite-type post-ophiolite intrusions in the Sabzevar ophiolitic zone, northeast Iran


    Jamshidi, K.; H. Ghasemi; Troll, V. R.; M. Sadeghian; B. Dahren


    Subduction-related adakite-type intrusive rocks emplaced into the late Cretaceous–Paleocene Sabzevar ophiolite zone, northeast Iran, range from Mg-andesite to rhyodacite in composition. Here we investigate the magma supply system to these subvolcanic intrusive rocks by applying thermobarometric mineral and mineral–melt equilibrium models, including amphibole thermobarometry, plagioclase–melt thermobarometry and clinopyroxene–melt barometry. Based on the results of these ther...

  19. Magma storage and plumbing of adakite-type post-ophiolite intrusions in the Sabzevar ophiolitic zone, NE Iran


    Jamshidi, K.; H. Ghasemi; Troll, V. R.; M. Sadeghian; B. Dahren


    Subduction-related adakite-type intrusive rocks emplaced into the late Cretaceous-Paleocene Sabzevar ophiolite zone, NE Iran, range from Mg-andesite to rhyodacite in composition. Here we investigate the magma supply system to these subvolcanic intrusive rocks by applying thermobarometric mineral and mineral-melt equilibrium models, including amphibole thermobarometry, plagioclase-melt thermobarometry and clinopyroxene-melt barometry. Based on the results of ...

  20. Application of the Moessbauer effect in the investigation of mineral raw materials

    International Nuclear Information System (INIS)

    The application is described of a method for an improved resolution of complex experimental Moessbauer spectra. The method is based on the application of the speedy Fourier transformation. The efficiency is illustrated by the measured spectra and by the improved spectra obtained from them. The application of the Moessbauer effect is discussed in research on minerals of the isomorphous series enstatite-hypersthene and on amphiboles. (author)

  1. Metabolism of various carbon sources by Azospirillum brasilense.


    Westby, C A; Cutshall, D S; Vigil, G V


    Azospirillum brasilense Sp7 and two mutants were examined for 19 carbon metabolism enzymes. The results indicate that this nitrogen fixer uses the Entner-Doudoroff pathway for gluconate dissimilation, lacks a catabolic but has an anabolic Embden-Meyerhof-Parnas hexosephosphate pathway, has amphibolic triosephosphate enzymes, lacks a hexose monophosphate shunt, and has lactate dehydrogenase, malate dehydrogenase, and glycerokinase. The mutants are severely deficient in phosphoglycerate and pyr...

  2. 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.

  3. Anomalously high δD values in the mantle (United States)

    Xia, Qun-Ke; Deloule, Etienne; Wu, Yuan-Bao; Chen, Dao-Gong; Cheng, Hao


    Hydrogen isotopic compositions of four amphibole grains from three lherzolite xenoliths hosted in Cenozoic basanites of Nushan, eastern China have been analyzed by ion microprobe. δD values of all analyzed points range from -94 to +46‰. Large heterogeneities of D/H ratios within single grains have been observed with variations of δD up to 80‰ on the scale of less than 400 μm. Neither correlation between δD values and water contents of the analyzed points nor regular variation between δD values and positions of analyzed points within the same grain can be found, implying that the scatter of δD values could not result from a late shallow process such as hydrogen loss or hydrothermal alterations and should be considered as inherited from the source at depth. Chemical compositions of Nushan amphiboles are very homogeneous, excluding the possibility that the scatter of δD values could arise from variable fractionation factors between a single fluid source and minerals. Therefore, metasomatic fluids responsible for the formation of Nushan amphiboles should have variable and unusually high hydrogen isotopic compositions. We suggest that this variation in the metasomatic fluids could be related to melt degassing in the mantle source.

  4. Erionite induces production of autoantibodies and IL-17 in C57BL/6 mice

    International Nuclear Information System (INIS)

    Background: Erionite has similar chemical and physical properties to amphibole asbestos, which induces autoantibodies in mice. Current exposures are occurring in North Dakota due to the use of erionite-contaminated gravel. While erionite is known to cause mesothelioma and other diseases associated with asbestos, there is little known about its effects on the immune system. Objectives: We performed this study to determine whether erionite evokes autoimmune reactions in mice. Methods: Bone marrow derived macrophages (BMDM) were used to measure toxicity induced by erionite. Cytokine production by BMDM and splenocytes of C57BL/6 mice was examined by bead arrays and ELISA following exposure to erionite, amphiboles and chrysotile. Wild type C57BL/6 mice were exposed to saline, erionite, amphibole asbestos (Libby 6-Mix) or chrysotile through intratracheal instillations at equal mass (60 μg/mouse). Seven months after exposure, sera were examined for anti-nuclear antibodies (ANA) and IL-17. Immunohistochemistry was used to detect immune complex deposition in the kidneys. Results: Erionite and tremolite caused increased cytokine production belonging to the TH17 profile including IL-17, IL-6, TGF-β, and TNF-α. The frequency of ANA was increased in mice treated with erionite or amphibole compared to saline-treated mice. IL-17 and TNF-α were elevated in the sera of mice treated with erionite. The frequency of immune complex deposition in the kidneys increased from 33% in saline-treated mice to 90% with erionite. Conclusions: These data demonstrate that both erionite and amphibole asbestos induce autoimmune responses in mice, suggesting a potential for adverse effects in exposed communities. - Highlights: • Erionite, a fibrous mineral, is a current public health concern in the western USA. • Erionite exposure induces antinuclear autoantibodies in exposed mice. • Erionite induces a clear Th17 cytokine response in vitro and in vivo. • These responses were distinct from

  5. Hydrothermal alteration products of gabbros help accommodate exhumation-related deformation in mantle-derived ultramafics exposed at the Mid-Atlantic Ridge (United States)

    Picazo, S.; Cannat, M.; Escartin, J.; Gibert, B.; Delacour, A.; Silantyev, S.


    Outcrops of deeply-derived ultramafic rocks and gabbros are widespread along slow spreading ridges but the rheology and dynamics of the exhumation faults and of their uplifted footwalls are still poorly known. Previous studies of samples collected within meters of exposed exhumation fault surfaces in the Atlantic have shown that a gabbroic component was added to the primarily ultramafic material in the fault zone, allowing for the growth of abundant amphibole, chlorite and talc. The nature of this component (altered magmatic intrusions or metasomatic hydrothermal fluids) could not, however, be ascertained in the pervasively sheared fault material. In this abstract we report on a set of 474 samples collected at the Mid-Atlantic Ridge (MAR) during the Serpentine cruise (2007; RV Pourquoi Pas? PI Y. Fouquet) next to the ultramafic-hosted Ashadze (13°N) and Logatchev (14°45'N) vent fields. Most of these 474 samples are weakly to moderately deformed and are interpreted as representing the upper few hundred meters below their respective exhumation fault zone, rather than the fault zone itself. The large number of samples, and their overall moderate degree of deformation gives us a chance to propose a semi-statistical study of plastic, brittle-plastic and brittle deformation in ultramafic rocks next to a MAR exhumation system, in relation with the magmatic and hydrothermal history. Our primary finding is that significant brittle-plastic deformation systematically involves amphibole±chlorite±talc-bearing ultramafic lithologies. Serpentine is commonly present in these deformed assemblages, but we did not find serpentine-only shear zones. Amphibole (in successive generations ranging from hornblende to tremolite) and chlorite occur in veins, many of which also contain zircon and some relict plagioclase, indicating a magmatic origin. Relicts of primary peridotite minerals in the most amphibole-rich samples indicate that magmatic injection followed on an episode of

  6. Noble gas transport during devolatilization of oceanic crust (United States)

    Jackson, C.; Smye, A.; Shuster, D. L.; Parman, S. W.; Kelley, S. P.; Hesse, M. A.; Cooper, R. F.


    Here we examine the role of slab dehydration in determining the elemental pattern of recycled noble gases. As a first step, we apply newly reported measurements of He-Ne-Ar (light noble gases) solubility and diffusivity in amphibole to parameterize a 1D diffusive-reaction transport model that simulates noble gas behavior during fluid loss from down-going oceanic crust. Recent experiments demonstrate that noble gases are highly soluble in ring-structured minerals, such as amphibole and other common hydrothermal products in slabs [1]. These results suggest that ring-structured minerals have the potential to strongly influence the budget of noble gases input into subduction zones and the elemental fractionations associated with volatile loss from slabs New measurements of He-Ne-Ar solubility in a suite of amphiboles have been completed utilizing the methodology described in [1]. These new measurements confirm that all light noble gases are highly soluble in amphibole, and that noble gas solubility correlates with the availability of unoccupied ring sites. New experimental measurements of He and Ne diffusivity have also been completed using a step-degassing approach at the Berkeley Geochronology Center. These measurements suggest that vacant ring sites in amphibole act to slow noble gas diffusion. We combine the newly acquired He and Ne diffusivity measurements with literature values for Ar diffusivity [2] to parameterize the diffusive-reaction transport model. Application of these data to the diffusive-reaction transport model yields several new insights. The relative mobility of Ne compared to Ar allows for efficient extraction of Ne from "hot" slabs by shallow depths (supercritical fluids, causing noble gases to partition back into minerals from any fluids retained in slabs at depth. The efficiency of noble gas extraction is particularly sensitive to the thermal regime and porosity of the slab (i.e. cold slabs with low porosity have the potential to recycle

  7. 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).

  8. Experimentally determined distribution of fluorine and chlorine upon hydrous slab melting, and implications for F-Cl cycling through subduction zones (United States)

    Van den Bleeken, Greg; Koga, Kenneth T.


    Fluorine and chlorine are volatile elements known to be enriched in primitive arc magmas, and variations of F/Cl ratios can carry information about slab devolatilization processes. Recent experiments on the fractionations of these elements suggest that aqueous fluid has limited capacity to enrich the magma source region in F. Hence, it is difficult to explain observations of primitive arc magmas particularly rich in F. To complement previous experimental studies, we examined the fractionation of fluorine and chlorine during hydrous partial melting of subducting slab. Element-doped phase equilibria experiments were carried out in a complex chemical system at conditions equivalent to potential slab melting temperatures (750-1000 °C) across the amphibolite to eclogite facies transition (1.3-3 GPa). Partition coefficients of F and Cl between hydrous silicic melts and minerals were determined by electron microprobe and/or ion probe. Fluorine is compatible in amphibole (DFamp/glass = 1.18-1.85), and incompatible in garnet (0.034-0.140), clinopyroxene (0.059-0.505), and allanite (0.205-0.504). Hence, amphibole is an important F host, and can retain significant quantities of F in the solid residue of partial melting. On the contrary, Cl is incompatible, with DClmineral/glass generally decreasing from amphibole (0.079-0.625; one outlier at 1.87) to allanite (0.163), clinopyroxene (0.066-0.158), and garnet (0.031-0.153; outlier at 0.492). As a result, Cl is easily mobilized during partial melting. Fluorine and chlorine release during slab melting have been quantified by applying our partition coefficients to a non-modal batch melting model. The model shows that amphibole plays a key role in F/Cl fractionation during partial melting, while F/Cl is close to that of source for the melting of amphibole free eclogite. Moreover, the results from a flux-melting model employing several source compositions are compared to F and Cl abundances in primitive arc magmas. The observed

  9. Erionite induces production of autoantibodies and IL-17 in C57BL/6 mice

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    Zebedeo, Christian Nash; Davis, Chad [Department of Biological Sciences, Idaho State University, Pocatello, ID (United States); Peña, Cecelia [Northwest Nazarene University, Nampa, ID (United States); Ng, Kok Wei [Department of Biological Sciences, Idaho State University, Pocatello, ID (United States); Pfau, Jean C., E-mail: [Department of Biological Sciences, Idaho State University, Pocatello, ID (United States)


    Background: Erionite has similar chemical and physical properties to amphibole asbestos, which induces autoantibodies in mice. Current exposures are occurring in North Dakota due to the use of erionite-contaminated gravel. While erionite is known to cause mesothelioma and other diseases associated with asbestos, there is little known about its effects on the immune system. Objectives: We performed this study to determine whether erionite evokes autoimmune reactions in mice. Methods: Bone marrow derived macrophages (BMDM) were used to measure toxicity induced by erionite. Cytokine production by BMDM and splenocytes of C57BL/6 mice was examined by bead arrays and ELISA following exposure to erionite, amphiboles and chrysotile. Wild type C57BL/6 mice were exposed to saline, erionite, amphibole asbestos (Libby 6-Mix) or chrysotile through intratracheal instillations at equal mass (60 μg/mouse). Seven months after exposure, sera were examined for anti-nuclear antibodies (ANA) and IL-17. Immunohistochemistry was used to detect immune complex deposition in the kidneys. Results: Erionite and tremolite caused increased cytokine production belonging to the T{sub H}17 profile including IL-17, IL-6, TGF-β, and TNF-α. The frequency of ANA was increased in mice treated with erionite or amphibole compared to saline-treated mice. IL-17 and TNF-α were elevated in the sera of mice treated with erionite. The frequency of immune complex deposition in the kidneys increased from 33% in saline-treated mice to 90% with erionite. Conclusions: These data demonstrate that both erionite and amphibole asbestos induce autoimmune responses in mice, suggesting a potential for adverse effects in exposed communities. - Highlights: • Erionite, a fibrous mineral, is a current public health concern in the western USA. • Erionite exposure induces antinuclear autoantibodies in exposed mice. • Erionite induces a clear Th17 cytokine response in vitro and in vivo. • These responses were

  10. Heavy mineral assemblages of the Storegga tsunami deposit (United States)

    Cascalho, J.; Costa, P.; Dawson, S.; Milne, F.; Rocha, A.


    This study applies heavy mineral analysis to the Storegga tsunami deposit across a range of locations (Whale Firth, Maggie's Kettle Loch and Scatsta Voe) in Shetland (Scotland). The usefulness of this proxy is tested in the identification and characterization of these palaeotsunami units. Furthermore, provenance relationships are established based on the mineralogical content of tsunami deposits and their potential source. Finally, the capability of identifying different phases of tsunami inundation in an 8200 years old tsunami deposit is attempted. Our results show that, overall, tsunamigenic samples presented a clear dominance of garnets and amphiboles. While Whale Firth presented a more balanced distribution between these two mineral groups, in Maggie's Kettle Loch and Scatsta Voe the tsunamigenic samples are dominated by amphiboles (> 90% of transparent heavy minerals). Focusing on the two dominant heavy minerals (garnets and amphiboles) and their vertical variation, one could observe that garnets mimic the heavy mineral concentration variability - higher values at the base and decreasing values to the top. This effect of concentration of the heaviest of the heavy minerals assemblage presents similarities with the formation of beach placer deposits. In fact, based on the heavy mineral vertical variation of the tsunami deposits in Maggie's Kettle Loch, Scatsta Voe and Whale Firth it is possible to conclude that hornblende (most likely amphibole of the assemblage) has the lowest concentration factor indicating that its transport process is more efficient and consequently most of its particles eventually may have moved offshore in the backwash phase of the tsunami. Furthermore, the more platy shape of amphiboles also favours a slower deposition. The opposite can be observed for garnets, which require more energy to be transported (i.e. they are more difficult to entrain by the tsunami waves) and tend to be more easily preserved in the formation of a tsunamigenic

  11. High-K andesite petrogenesis and crustal evolution: Evidence from mafic and ultramafic xenoliths, Egmont Volcano (Mt. Taranaki) and comparisons with Ruapehu Volcano, North Island, New Zealand (United States)

    Price, Richard C.; Smith, Ian E. M.; Stewart, Robert B.; Gamble, John A.; Gruender, Kerstin; Maas, Roland


    This study uses the geochemistry and petrology of xenoliths to constrain the evolutionary pathways of host magmas at two adjacent andesitic volcanoes in New Zealand's North Island. Egmont (Mt. Taranaki) is located on the west coast of the North Island and Ruapehu lies 140 km to the east at the southern end of the Taupo Volcanic Zone, the principal locus of subduction-related magmatism in New Zealand. Xenoliths are common in the eruptives of both volcanoes but the xenoliths suites are petrographically and geochemically different. Ruapehu xenoliths are predominantly pyroxene-plagioclase granulites derived from Mesozoic meta-greywacke basement and the underlying oceanic crust. The xenolith population of Egmont Volcano is more complex. It includes sedimentary, metamorphic and plutonic rocks from the underlying basement but is dominated by coarse grained, mafic and ultramafic igneous rocks. Gabbroic xenoliths (Group 1) are composed of plagioclase, clinopyroxene and amphibole whereas ultramafic xenoliths are dominated by amphibole (Group 2) or pyroxene (Group 3) or, in very rare cases, olivine (Group 4). In Group 1 xenoliths plagioclase and clinopyroxene and in some cases amphibole show cumulate textures. Amphibole also occurs as intercumulate poikilitic crystals or as blebs or laminae replacing pyroxene. Some Group 2 xenoliths have cumulate textures but near monomineralic amphibole xenoliths are coarse grained with bladed or comb textures. Pyroxene in Group 3 xenoliths has a polygonal granoblastic texture that is commonly overprinted by veining and amphibole replacement. Group 1 and most Group 2 xenoliths have major, trace element and Sr, Nd and Pb isotope compositions indicating affinity with the host volcanic rocks. Geochemical variation can be modelled by assimilation fractional crystallisation (AFC) and fractional crystallisation (FC) of basaltic parents assuming an assimilant with the composition of average crystalline basement and Group 1 xenoliths have

  12. NOA at the Calaveras Dam Replacement Project (CDRP) - Challenges and Solutions (United States)

    Erskine, B.


    The San Francisco Public Utilities Commission is one year into construction of the Calaveras Dam Replacement Project (CDRP), a new earthen dam east of Sunol designed to withstand an M 7.1 earthquake on the nearby active Calaveras fault. The zoned earthen dam will be constructed primarily of on-site materials, many of which contain NOA. The upstream shell will be composed of Franciscan complex blueschist which contains crocidolite. This material will be blasted and processed at an on-site quarry. The impermeable core of the dam will be constructed of clay-rich alluvium that contains asbestos derived from Franciscan rocks. This material will be excavated from the south end of the reservoir and transported several miles to the dam. Currently, approximately 3 million yards of Franciscan complex material is being excavated and disposed of within permitted on-site engineered landfills. NOA-bearing rocks that include serpentinite, greenschist, blueschist, and eclogite contain variable amounts and assemblages of chrysotile, actinolite, crocidolite, tremolite, and winchite-class amphiboles. All of these are detected in air samples collected within a sophisticated air monitoring array and analyzed by TEM. The CDRP represents the largest construction project involving NOA in the country. As such, applying regulations that were designed for building materials and routine construction sites, and controlling airborne emissions on such a massive scale, is a major challenge requiring innovative solutions. Because construction occurs simultaneously at distinct and distant parts of the site, and the rugged topography of the site induces complex meteorological conditions, it is sometimes difficult to ascertain the driving activity and location of a source that caused a trigger level exceedance at a perimeter monitoring station. One helpful tool is forensic correlation of source material and air test data using speciation of amphiboles. At the CDRP, we are developing the ability to

  13. Dynamic evolution in a Cretaceous high-P/T subduction channel evidenced by the juxtaposition of amphibolite blocks with different P-T paths: an example from the Kamuikotan belt, northern Japan (United States)

    Okamoto, A.; Takeshita, T.


    A subduction channel developed at the boundary between a subducting oceanic plate and an overlying plate could be geologically defined as the place, where accretionary sediments were dragged down to great depth with an oceanic plate to suffer a high-P/T type metamorphism, and transformed to high-P/T metamorphic rocks (e.g. blueschist and eclogite). In the study area, while typical high-P/T metamorphic rocks (blueschist), which originated from Cretaceous accretionary sediments, amphibolites and metacherts also occur as tectonic blocks in mélange surrounded by either serpentinite or pelitic matrix, which originally suffered intermediate-P/T type metamorphism, but later the same high-P/T type metamorphism as the sediments did. In this research, we have analyzed mineral assemblages in these amphibolites and metacherts, and conducted micro-chemical analyses of compositional zoning in amphibole and garnet from these rocks with an EPMA. As a result, compositional zoning in some constituent amphibole can be divided into 3 types. Type I is a dominant type, where actinolite is overgrown by glaucophane, indicating pressure increase. Type II, which has been found in only one sample, is defined as the compositional zoning in amphibole consisting of magnesiohornblende, actinolite and glaucophane from core to rim. The compositional zoning shows a change of the temperature gradient from low-P/T (or intermediate-P/T) type to high-P/T type, which could reflect a cooling of the subduction channel with time from the onset of subduction to a steady state. Type III is characterized by the compositional zoning in amphibole from tschermakite to glaucophane-magnesioriebeckite. This also shows a cooling of the subduction channel with time. In this sample, garnet also shows a compositional zoning from a Mn-rich and Ca-poor inner core to a Mn-poor and Ca-rich outer core, which is surrounded by a Mn-rich rim, showing a compositional discontinuity across the core-rim boundary. The

  14. Late Neoproterozoic Nuqara Dokhan Volcanics, Central Eastern Desert, Egypt: Geochemistery and petrogenesis (United States)

    Hassan, Tharwat; Asran, Asran; Amron, Taha; Natflos, Theo


    The Nuqara volcanic is one of the northernmost outcrops of the Arabian-Nubian Shield Dokhan volcanics. The origin and tectonic setting of the late Neoproterozoic Dokhan volcanics (ca. 610-560 Ma) in the Egyptian Eastern Desert is highly debated. The debate concerns the tectonic setting where they formed during transition between convergent to extensional regime or after the East- and the West-Gondwana collision (~600Ma). In order to solve this problem, lavas from Nuqara area were studied geologically and geochemically. Nuqara Dokhan volcanics comprises two main rock suites: (a) an intermediate volcanic suite, consisting of basaltic andesite, andesite and their associated pyroclastics rocks; and (b) a felsic volcanic suite composed of dacite, rhyolite and ignimbrites. The two suites display well-defined major and trace element trends and continuum in composition with wide ranges in SiO2 (52-75.73%), CaO (9.19-0.22%), MgO (5.29-0.05%), Sr (1367-7.4 ppm), Zr (688.5-172.7 ppm), Cr (207-0.4 ppm), and Ni (94.3-0.2 ppm). The Nuqara Dokhan volcanics are characterized by strong enrichment in LILE relative to HFSE and affiliated to the calc-alkaline subducted - related magmatism. Geochemical Modeling displays that the evolution of these rocks was governed by fractional crystallization of plagioclase, amphiboles, pyroxene, magnetite and apatite in the intermediate varieties and plagioclase, amphibole, magnetite, apatite and zircon in the felsic varieties. The obtained mineral chemistry of these volcanics reveals: (a) Plagioclase range in composition from An55 to An40 in basaltic andesite and from An39 to An24 in andesite. (b) Alkali feldspars have sanidine composition. (c) Clinopyroxenes have augite composition. The low Al2O3 contents (1.94-5.588 wt %) indicate that clinopyroxene crystallized at low - pressure conditions. (d) Amphiboles have magnesio- hornblende composition.

  15. 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.

  16. Mineral chemistry of paleoproterozoic volcano-plutonism from the São Félix do Xingu (PA region, Amazonian Craton

    Directory of Open Access Journals (Sweden)

    Raquel Souza da Cruz


    Full Text Available The Sobreiro and Santa Rosa formations are result of large paleoproterozoic volcanic activities in the São Félix do Xingu (PA region, SE of Amazonian Craton. The Sobreiro Formation is composed of andesitic lava flow facies, with subordinate dacite and rhyodacite, and autoclastic volcaniclastic facies characterized by tuff, lapilli-tuff, and massive polymictic breccia. These rocks exhibit clinopyroxene, amphibole, and plagioclase phenocrysts in a microlytic or trachytic groundmass. The clinopyroxene is augite with subordinate diopside, and reveals chemical variations typical of minerals generated by arc-related magmatism. The amphibole is magnesiohastingsite, has oscillatory oxidizing conditions, and reveals breakdown rim textures linked to degassing during magma ascent. The Santa Rosa Formation has polyphase evolution controlled by large NE-SW crustal fissures, materialized by rhyolitic and dacitic lava flow facies. Volcaniclastic facies of ignimbrites, lapilli-tuffs, felsic crystal tuffs, and massive polymict breccias represents an explosive cycle in this unit. Metric dikes and stocks of granitic porphyries and equigranular granitoids complete this suite. K-feldspar, plagioclase, and quartz phenocrysts surrounded by quartz and K-feldspar integrowth occur in these rocks. Electron microprobe pressure and temperature estimates in clinopyroxene phenocrysts reveal formation depth between 58 and 17.5 km (17.5 – 4.5 kbar at temperatures between 1,249 and 1,082 ºC; and between 28 and 15 km (7.8 – 4.1 kbar for amphibole grains of the Sobreiro Formation, suggesting polybaric evolution. A model with generation of hydrated basaltic magma from partial melting of mantle wedge and accumulation in a hot zone of the lower crust, from which the andesitic and dacitic magmas are formed by the assimilation of continental crust and following fractional crystallization is proposed.

  17. P- T conditions of crystallization and origin of plagioclase-mantled alkali feldspar megacrysts in the Mesozoic granitoids in the Qinling orogen (China) (United States)

    Wang, Xiaoxia; Wang, Tao; Haapala, Ilmari; Mao, Jingwen


    The Qinling orogen between the North China and South China cratons was intruded at 211-217 Ma by calc-alkaline quartz monzonitic to monzogranitic plutons characterized by I- to A-type geochemistry and in many places contain plagioclase-mantled alkali feldspar megacrysts (rapakivi texture sensu lato). The felsic rocks contain mafic to intermediate magmatic enclaves suggestive of mingling and mixing of mafic and felsic magmas. The P- T conditions of crystallization have been determined for early mineral assemblages (inner parts of alkali feldspar megacrysts and their plagioclase, quartz, amphibole and biotite inclusions) and late assemblages (matrix minerals) of the rapakivi-textured granitoids. Al contents in amphibole from the early and late mineral assemblages yield pressures of 1.2-3.0 and 0.7-3.0 kbar, respectively, and indicate only minor pressure change between the crystallization of the early and late assemblages. Amphibole-plagioclase thermometry gives temperatures mainly of the order of 900 to 1000 °C for both the early and late assemblages indicating nearly isothermal conditions. Feldspar thermometers yield lower temperatures. Relative abundances of minerals and their chemical compositions indicate that the late mineral assemblages tend to be richer in MgO, Na 2O and CaO than the early assemblages. Rapakivi texture is interpreted in this case mainly as a result of compositional changes related to the hybridization between granitic and more mafic magmas. Small release of pressure during crystallization of the magmas may have contributed to the origin of the mantled alkali feldspar megacrysts.

  18. Halogen (F, Cl, Br, I) behaviour in subducting slabs: A study of lawsonite blueschists in western Turkey (United States)

    Pagé, Lilianne; Hattori, Keiko; de Hoog, Jan C. M.; Okay, Aral I.


    We examined the F, Cl, Br and I abundance of minimally retrogressed lawsonite blueschists from the Tavsanli Zone in northwest Turkey to evaluate the behaviour of halogens in subduction zones, and to determine the role coexisting high pressure minerals may play in transporting the halogens to the Earth's mantle. The blueschists contain sodic amphibole and lawsonite, with variable amounts of phengite and chlorite, and minor apatite. A positive correlation between Cl, Br and I contents in bulk rocks suggests their overall coherent behaviour in subduction zones, although high ratios of I/Cl and Br/Cl compared to altered oceanic crust indicate that Cl is preferentially lost relative to Br and I before or during blueschist metamorphism. Iodine and F are enriched relative to altered oceanic crust, suggesting incorporation from marine sediments. In situ analyses of minerals in thin sections reveal F preferentially concentrates in apatite (avg. 3.13 wt%), over phengite (482 ppm), lawsonite (avg. 413 ppm) and Na-amphibole (257 ppm). Chlorine also preferentially resides in apatite (138 ppm), followed by equal partitioning between phengite (59 ppm) and Na-amphibole (56 ppm), and lower concentrations in lawsonite (27 ppm). Upon apatite decomposition at a depth of ∼200 km, F may redistribute into lawsonite and phengite in slabs, whilst Cl is likely expelled to the overlying mantle wedge. Given the stability of lawsonite and phengite to a depth of 280-300 km in cold subduction zones, they may transport F beyond subarc depths, contributing to the high F in magmas derived from the deep mantle.

  19. 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

  20. Age, protoliths and tectonic implications of the Toudaoqiao blueschist, Inner Mongolia, China (United States)

    Miao, Laicheng; Zhang, Fochin; Jiao, Shujuan


    The Toudaoqiao blueschist is located in the northern Great Xing'an Range of China, part of the eastern Central Asian Orogenic Belt, and was discovered in the 1980s, but the age of its formation and metamorphism and the nature of its protolith, have long remained uncertain. Thin-section examination and microprobe analyses show that the Toudaoqiao blueschist has a mineral assemblage of sodic amphibole + chlorite + epidote + albite + phengite ± apatite ± quartz. Electron microprobe analyses attest that sodic amphibole is magnesioriebeckite in composition. The blueschist-facies metamorphism occurred under metamorphic P-T conditions of ∼7 kbar and 450-480 °C, estimated from pseudosection as well as the compositions of the Na-amphibole and phengite. The protolith of the blueschist is mainly composed of alkali basalt, with a minor amount of tholeiitic basalt. The alkali basalt shows similarities in chemical composition to oceanic island basalt (OIB), suggesting derivation from an OIB-like asthenospheric mantle source in a within-plate setting. The tholeiitic basalt has geochemical features transitional between mid-ocean ridge basalt and island arc tholeiite, which implies an origin from a depleted mantle source that would have been selectively metasomatized in a supra-subduction setting. Sensitive high resolution ion microprobe (SHRIMP) zircon dating confirms that the protolith of the Toudaoqiao blueschist formed at 516 ± 11 Ma, in the middle Cambrian, and experienced blueschist facies metamorphism during the Silurian at ca. 436 Ma. The juxtaposition of the two distinct rock types and the association of the blueschist with mélange suggest that the origin of the Toudaoqiao blueschist belt involve collision-accretionary processes. Based on these new results and regional data, we propose that the Toudaoqiao blueschist belt represents the suture zone between the Erguna and Xing'an terranes and that suturing took place during the Early Silurian period. The southwestern

  1. Production of carbonatite-source regions in depleted upper mantle: metasomatism by alkaline magmas

    Energy Technology Data Exchange (ETDEWEB)

    Meen, J.K.


    The peridotite-H/sub 2/O-CO/sub 2/ solidus displays a cusp at approximately 22 kbar (corresponding to the intersection of the amphibole-out curve and the solidus). Low-temperature alkaline melts formed near the solidus at P>22 kbar will recross the solidus along the line of the cusp and, at lower pressures, react with wall-rocks. Depleted periodotite of the upper mantle may thus be enriched in low-melting components. Experimental studies on a join between carbonated alkaline rock and harzburgite at P=20 kbar demonstrate that carbonate is a supersolidus phase, except at high ratios of H/sub 2/O to CO/sub 2/, and that amphibole forms at temperatures very close to that of the solidus. Interaction of carbonated alkaline magma and harzburgite produces, with decreasing temperature, clinopyroxene, carbonate, and hornblende. Thus, two different kinds of carbonated 1herzolite source region may be formed. In the first case, a carbonated 1herzolite is formed in equilibrium with a residual magma. This 1herzolite will be enriched in Sr over Rb and in Nd over Sm, but not in U over Pb. Total consumption of the magma will produce a carbonate-amphibole-1herzolite and this will also be enriched in U over Pb. These two source regions will develop, with time, similar Sr-Nd isotopic characteristics (low /sup 87/Sr//sup 86/Sr and low /sup 143/Nd//sup 144/Nd), but will have very different Pb-isotopic ratios. The effects of minor minerals on the partitioning of trace elements may, however, by important, and these will also be discussed.

  2. Vein Formation and Element Mobility During Serpentinization of Peridotites: Mineralogy and Thermodynamic Modeling (United States)

    Schwarzenbach, E. M.; Caddick, M. J.; Beard, J. S.


    Serpentinization is a common mineralogical process that occurs in ultramafic rocks when water interacts with the primary minerals olivine and pyroxene to form a rock dominated by serpentine. Temperature of hydration and the primary mineralogy of the peridotite strongly influence the alteration products. We studied peridotites with low to extremely low degrees of serpentinization from two settings, the Santa Elena ophiolite in Costa Rica and the Gakkel Ridge, to test how temperature and primary mineralogy control reactions, reaction sequences, and subsequent vein textures during peridotite hydration. Serpentinization of a harzburgite from Costa Rica occurred at around 250°C, resulting in olivine-hosted veins that are a mixture of brucite and serpentine - with a bulk composition approximately equivalent to hydrated host olivine - and later stage veins that also contain magnetite. Serpentinite that formed by hydration of orthopyroxene is accompanied by talc, with a bulk composition (serp + tlc) that is depleted in silica relative to the orthopyroxene host. In contrast, veins in orthopyroxene in an almost un-serpentinized peridotite (degree of serpentinization ~ 5 %) from the ultra-slow spreading Gakkel Ridge have an average composition very similar to the host orthopyroxene, whilst veins in olivine suggest slight enrichment in silica compared to the host olivine. Replacement of orthopyroxene here results in the formation of serpentine, talc and amphibole. The presence of amphibole in orthopyroxene and the higher degree of orthopyroxene replacement compared to olivine suggests that serpentinization occurred at higher temperatures than in the Santa Elena peridotites, resulting in the mobilization of more silica through the system. Thermodynamic models of the hydration of olivine and orthopyroxene agree with the mineralogical observations and show that hydration of olivine first results in the simple formation of serpentine and brucite. Increasing water-rock ratios then

  3. Quartz exsolution topotaxy in clinopyroxene from the UHP eclogite of Weihai, China (United States)

    Xu, Haijun; Zhang, Junfeng; Zong, Keqing; Liu, Liang


    Abundant oriented silica precipitates of α-quartz (4.0 ± 1.0 vol.%), in part coexisting with calcic amphiboles (precipitates have topotactic relationships with their host clinopyroxenes. Three types of crystallographic topotactic relationship have been identified between quartz and host clinopyroxene: (1) 52% quartz precipitates share the same orientation for the c-axes with [0001]qz//[001]cpx; (2) 34% quartz precipitates share the same orientation for the a-axes with [11 2 bar0]qz//[001]cpx; and (3) 11% quartz precipitates share the same orientation for the s-planes with (11 2 bar1)qz//(100)cpx. Other quartz axes and planes disperse in large or small girdles around the shared axes or planes. Many quartz rods/needles are elongated parallel to the [001]cpx with the long axes of quartz being either [0001]qz or [11 2 bar0]qz. Amphibole precipitates have also a strong crystallographic relationship with host clinopyroxene, i.e., (100)amp//(100)cpx, [010]amp//[010]cpx, and [001]amp//[001]cpx. These results provide quantitative microstructural evidence supporting an exsolution origin for oriented quartz needles/rods in clinopyroxene and demonstrate that the exsolution of quartz from clinopyroxene occurred within the stability field of α-quartz rather than coesite. The oriented precipitates of α-quartz, in part coexisting with calcic amphiboles, in host clinopyroxene are probably promoted by supercritical fluid or partial melting during the early exhumation of eclogites. Our results suggest that oriented quartz precipitates in clinopyroxene cannot be used as an indisputable UHP-indicator.

  4. Acute phase response, inflammation and metabolic syndrome biomarkers of Libby asbestos exposure

    International Nuclear Information System (INIS)

    Identification of biomarkers assists in the diagnosis of disease and the assessment of health risks from environmental exposures. We hypothesized that rats exposed to Libby amphibole (LA) would present with a unique serum proteomic profile which could help elucidate epidemiologically-relevant biomarkers. In four experiments spanning varied protocols and temporality, healthy (Wistar Kyoto, WKY; and F344) and cardiovascular compromised (CVD) rat models (spontaneously hypertensive, SH; and SH heart failure, SHHF) were intratracheally instilled with saline (control) or LA. Serum biomarkers of cancer, inflammation, metabolic syndrome (MetS), and the acute phase response (APR) were analyzed. All rat strains exhibited acute increases in α-2-macroglobulin, and α1-acid glycoprotein. Among markers of inflammation, lipocalin-2 was induced in WKY, SH and SHHF and osteopontin only in WKY after LA exposure. While rat strain- and age-related changes were apparent in MetS biomarkers, no LA effects were evident. The cancer marker mesothelin was increased only slightly at 1 month in WKY in one of the studies. Quantitative Intact Proteomic profiling of WKY serum at 1 day or 4 weeks after 4 weekly LA instillations indicated no oxidative protein modifications, however APR proteins were significantly increased. Those included serine protease inhibitor, apolipoprotein E, α-2-HS-glycoprotein, t-kininogen 1 and 2, ceruloplasmin, vitamin D binding protein, serum amyloid P, and more 1 day after last LA exposure. All changes were reversible after a short recovery regardless of the acute or long-term exposures. Thus, LA exposure induces an APR and systemic inflammatory biomarkers that could have implications in systemic and pulmonary disease in individuals exposed to LA. -- Highlights: ► Biomarkers of asbestos exposure are required for disease diagnosis. ► Libby amphibole exposure is associated with increased human mortality. ► Libby amphibole increases circulating proteins involved

  5. Petrologic characteristics of the 1982 and pre-1982 eruptive products of El Chichon volcano, Chiapas, Mexico. (United States)

    McGee, J.J.; Tilling, R.I.; Duffield, W.A.


    Studies on a suite of rocks from this volcano indicate that the juvenile materials of the 1982 and pre-1982 eruptions of the volcano have essentially the same mineralogy and chemistry. Data suggest that chemical composition changed little over the 0.3 m.y. sample period. Modally, plagioclase is the dominant phenocryst, followed by amphibole, clinopyroxene and minor phases including anhydrite. Plagioclase phenocrysts show complex zoning: the anorthite-rich zones are probably the result of changing volatile P on the magma and may reflect the changes in the volcano's magma reservoir in response to repetitive, explosive eruptive activity.-R.E.S.

  6. Radiometric dating of Mesozoic basic eruptive rocks of the Krizna nappe in the NW part of the Low Tatra

    International Nuclear Information System (INIS)

    The Mesozoic of the Central West Carpathians is generally poor in occurrences of volcanics. The Krizna nappe is one of the units where basic effusive rocks-basalts accompanied by volcanoclastics are present in the Cretaceous. Basalts with olivine, augite and amphibole of analogous character from vein bodies are found in the Middle and/or Upper Triassic carbonates of the same unit. Radiometric ages of 106 to 116x106 y. for vein bodies in the Middle and/or Upper Triassic are identical with the geological position of the effusive bodies in the Lower Cretaceous. All occurrences are products of the Lower Cretaceous volcanism. (author)

  7. Radiometric dating of metamorphites of amphibolite facies from the Rudnany deposit, Spissko-Gemerske Rudohorie Mts

    International Nuclear Information System (INIS)

    Eruptive rocks from granodiorites to ultrabasic and rocks of amphibolite facies from the siderite deposit of Rudnany are discussed. They reach the Carboniferous, are characterized by intensive hydrothermal and metasomatic alterations. The genesis and mutual relations have so far been little cleared. The metamorphism into amphibolite facies is uncommon in the epimetamorphosed Spissko-gemerske rudohorie Mts. Its age ranging has been questionable. By the argon method the ages of 324, 320 and 281 mil. y were proved at amphiboles from amphibolites. These results disprove the views on the Alpine age of metamorphism and are an evidence of its Variscan age. (author)

  8. Geochemistry and petrogenesis of the Gallego Volcanic Field, Solomon Islands, SW Pacific and geotectonic implications (United States)

    Petterson, M. G.; Haldane, M. I.; Smith, D. J.; Billy, D.; Jordan, N. J.


    The Upper Miocene to present day Gallego Volcanic Field (GVF) is located in northwest Guadalcanal, Solomon Islands, SW Pacific, and potentially includes the offshore Savo volcano. The GVF is a multi-centred complex covering an area of ~ 800 km 2 on Guadalcanal and a further ~ 30 km 2 on the island of Savo, north of west Guadalcanal. GVF volcanism is characterised by effusive eruptions of lava, intrusion of sub-volcanic plutons, as well as pyroclastic flow and fall deposits dominated by block and ash flow deposits. Geochemical analysis of a representative suite of samples from the GVF demonstrates that the GVF comprise largely a 'main suite' of basalts to andesites and minor trachyandesites. The predominant mineralogy of the GVF comprises plagioclase, amphibole, clinopyroxene and magnetite-ilmenite. Associated with the 'main suite' are cognate nodules composed of hornblendite, gabbros, and clinopyroxenite. Interpretation of major and trace element geochemistry and petrographic studies suggests that fractionation was dominated by early clinopyroxene, and later amphibole + clinopyroxene + minor plagioclase. Geochemical features such as the incompatibility of Sr suggest that plagioclase largely crystallised en-masse late in the fractionation sequence. The presence of amphibole and late fractionation of plagioclase is suggestive of derivation from initially water-rich magmas. The region is characterised by strong geographically-related geochemical variations as evidenced by the Woodlark (and Manus) basins: basalts become more arc-like within the ocean basins with decreasing distance to the subducting trench. The GVF-Savo volcanoes are spatially and geochemically affected by deep N-S fractures that show some evidence of sympathetic geochemical variations with distance from the trench (e.g. Sr/Y ratios). Comparison with a range of international data for Th/Nb vs Pb/Nb and Dy/Yb vs SiO 2 indicate that: amphibole was indeed a strong controlling phase on magmatic evolution

  9. Petrology of the Mesoarchean Rio Maria suite and the discrimination of sanukitoid series (United States)

    Oliveira, Marcelo Augusto de; Dall'Agnol, Roberto; Almeida, José de Arimatéia Costa de


    The rocks of 2.87 Ga Rio Maria sanukitoid suite of the eastern Amazonian craton include granodiorites, intermediate rocks, layered rocks and mafic enclaves. Their REE patterns and the behavior of Rb, Ba, Sr, and Y allowed the distinction of a granodioritic (granodiorite and intermediate rocks) and a monzonitic (mafic enclaves) sanukitoid series. Petrogenetic modeling indicated that the granodiorites and intermediate rocks are not related by fractional crystallization. The internal evolution of the intermediate rocks were leaded by fractionation of amphibole + biotite ± apatite, whereas the granodiorites evolved by fractionation of plagioclase + amphibole ± biotite. The layered rocks were probably derived from the granodiorite magma by an accumulation of 50% of amphibole (dark layer) and of 30% of amphibole ± plagioclase (gray layer). The petrogenesis of the Rio Maria suite required melting of a modified mantle extensively metasomatized by addition of about 30% TTG-like melt to generate the granodiorite (11% of melt) and intermediate magmas (14% of melt), and ~ 20% TTG-like melt in the case of mafic enclave magma (9% of melt). Modeling and geochemical data, particularly the behavior of Sr and Y, suggest that mafic enclave and granodiorite magmas were originated at different depths and should have mingled during their ascent and final emplacement. The modal and geochemical differences observed between the granodioritic and monzonitic sanukitoid series of Rio Maria are apparently a general feature of the Archean sanukitoids. This indicates the existence of at least two distinct sanukitoid series and suggests that the nature of the sanukitoid series is strongly dependent of the pressure of magma generation. Our results indicate that the sanukitoid magmas were originated in a two stage process. The envisaged model admits an active subduction tectonic setting in the Rio Maria terrane in between 2.98 and 2.92 Ga when the TTG magmas responsible by the mantle

  10. Metamorphism of basic and pelitic rocks at Sulitjelma, Norway (United States)

    Boyle, Alan P.


    The Sulitjelma area of the Scandinavian Caledonides consists of a variety of metasedimantary units with small basic intrusions, and a large ophiolitic complex of predominantly basic composition. All units underwent prograde greenschist facies to amphibolite facies regional metamorphism during the Scandinavian phase of the Caledonian orogeny. The resultant mineral assemblages and relationships are consistent with the presence of a miscibility gap in the actinolite-hornblende series under greenschist facies conditions; a garnet forming reaction in pelites involving the consumption of carbonate in order to produe the observed grossular content; some conflict between low-baric and medium-baric pressure estimates from equilibria involving Ca amphibole bearing assemblages in metabasites.

  11. Acute phase response, inflammation and metabolic syndrome biomarkers of Libby asbestos exposure

    Energy Technology Data Exchange (ETDEWEB)

    Shannahan, Jonathan H. [Curriculum in Toxicology, University of North Carolina at Chapel Hill School of Medicine, Chapel Hill, NC 27599 (United States); Alzate, Oscar [Systems Proteomics Center, University of North Carolina at Chapel Hill School of Medicine, Chapel Hill, NC 27599 (United States); Winnik, Witold M.; Andrews, Debora [Proteomics Core, Research Core Unit, National Health and Environmental Effects Research Laboratory, Office of Research and Development, U.S. Environmental Protection Agency, Research Triangle Park, NC 27711 (United States); Schladweiler, Mette C. [Cardiopulmonary and Immunotoxicology Branch, Environmental Public Health Division, National Health and Environmental Effects Research Laboratory, Office of Research and Development, U.S. Environmental Protection Agency, Research Triangle Park, NC 27711 (United States); Ghio, Andrew J. [Clinical Research Branch, Environmental Public Health Division, National Health and Environmental Effects Research Laboratory, Office of Research and Development, U.S. Environmental Protection Agency, Chapel Hill, NC 27599 (United States); Gavett, Stephen H. [Cardiopulmonary and Immunotoxicology Branch, Environmental Public Health Division, National Health and Environmental Effects Research Laboratory, Office of Research and Development, U.S. Environmental Protection Agency, Research Triangle Park, NC 27711 (United States); Kodavanti, Urmila P., E-mail: [Cardiopulmonary and Immunotoxicology Branch, Environmental Public Health Division, National Health and Environmental Effects Research Laboratory, Office of Research and Development, U.S. Environmental Protection Agency, Research Triangle Park, NC 27711 (United States)


    Identification of biomarkers assists in the diagnosis of disease and the assessment of health risks from environmental exposures. We hypothesized that rats exposed to Libby amphibole (LA) would present with a unique serum proteomic profile which could help elucidate epidemiologically-relevant biomarkers. In four experiments spanning varied protocols and temporality, healthy (Wistar Kyoto, WKY; and F344) and cardiovascular compromised (CVD) rat models (spontaneously hypertensive, SH; and SH heart failure, SHHF) were intratracheally instilled with saline (control) or LA. Serum biomarkers of cancer, inflammation, metabolic syndrome (MetS), and the acute phase response (APR) were analyzed. All rat strains exhibited acute increases in α-2-macroglobulin, and α1-acid glycoprotein. Among markers of inflammation, lipocalin-2 was induced in WKY, SH and SHHF and osteopontin only in WKY after LA exposure. While rat strain- and age-related changes were apparent in MetS biomarkers, no LA effects were evident. The cancer marker mesothelin was increased only slightly at 1 month in WKY in one of the studies. Quantitative Intact Proteomic profiling of WKY serum at 1 day or 4 weeks after 4 weekly LA instillations indicated no oxidative protein modifications, however APR proteins were significantly increased. Those included serine protease inhibitor, apolipoprotein E, α-2-HS-glycoprotein, t-kininogen 1 and 2, ceruloplasmin, vitamin D binding protein, serum amyloid P, and more 1 day after last LA exposure. All changes were reversible after a short recovery regardless of the acute or long-term exposures. Thus, LA exposure induces an APR and systemic inflammatory biomarkers that could have implications in systemic and pulmonary disease in individuals exposed to LA. -- Highlights: ► Biomarkers of asbestos exposure are required for disease diagnosis. ► Libby amphibole exposure is associated with increased human mortality. ► Libby amphibole increases circulating proteins involved

  12. 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.

  13. Syntectonic emplacement of the Middle Jurassic Concon Mafic Dike Swarm, Coastal Range, central Chile (33 degrees S)


    C. Creixell; M.A. Parada; Roperch, Pierrick; D. Morata; Arriagada, C; Arce, C.P. de


    The Concon Mafic Dike Swarm (CMDS) consists of basaltic to andesitic dikes emplaced into deformed Late Palcozoic granitoids during the development of the Jurassic arc of central Chile. The dikes are divided into an early group of thick dikes (512 in) and a late group of thin dikes (0.5-3 m). Two new amphibole Ar-40/Ar-39 dates obtained from undeformed and deformed dikes, constrain the age of emplacement and deformation of the CMDS between 163 and 157 Ma. Based on radiometric ages, field obser...

  14. Erosion patterns in the Changjiang (Yangtze River) catchment revealed by bulk-sample versus single-mineral provenance budgets (United States)

    Vezzoli, Giovanni; Garzanti, Eduardo; Limonta, Mara; Andò, Sergio; Yang, Shouye


    The Changjiang, the fourth longest river on Earth and the largest in Eurasia, has a complex sediment-routing system presently interrupted by the Three Gorges Dam, the world's largest hydroelectric engineering project. To study sediment-generation processes in the huge catchment and compare the different erosion patterns obtained by different methodological approaches, high-resolution petrographic and heavy-mineral analyses were performed on sands from the trunk river and its major tributaries. The frequency distributions of diverse groups of detrital amphiboles were also investigated. Rigorous statistical methods were used to define end-members, evaluate mineralogical variability, assess similarities among samples, and eventually calculate the relative contributions from each major tributary to the trunk river by forward end-member modelling of integrated compositional data. The litho-quartzose sand with few heavy minerals generated in Tibetan headwaters evolves downstream to feldspatho-litho-quartzose with medium-rank metamorphic rock fragments and moderately rich amphibole-epidote suites. Sand across the Sichuan basin and as far as the Three Gorges Dam is enriched in mafic volcanic, clinopyroxene, and carbonate grains eroded from Permian basalts and Paleozoic strata of the South China Block. The final (Yangtze) tract is characterized by litho-feldspatho-quartzose sand with moderately poor, amphibole-dominated suites with epidote, clinopyroxene, and garnet. The orogenic compositional signature acquired in the upper part of the basin is thus carried all the way to the Chinese passive margin, as observed also for the Yellow River in the north. Even after long-distance transport across wide continental areas, detrital modes thus reveal the tectonic character of the source rather than the geodynamic environment of the sink. Quantitative provenance analysis indicates that left-bank tributaries draining the Longmen and Qinlin mountains supply most of the sand reaching

  15. First data on Sm-Nd systematization of Khanka Massif metamorphic rocks, Primor'e

    International Nuclear Information System (INIS)

    The age of the metamorphic rocks of the Khanka massif, Primor'e, is determined through the method of the Sm-Nd isotopic dating. The results of the isotopic studies on the amphibolites of the Nakhimov suite of the Khanka massif indicated that the rocks of this suite are not older than 1.7 billion years. The obtained age corresponds to the time of the amphibolite protolith formation, the source whereof is the moderately depleted mantle. The isotopic age of the amphibole and plagioclase mineral fractions constitutes 733 ± 25 mln years, which reflects the time of the Nakhimov suite rocks metamorphism

  16. Micro-PIXE analysis of silicate reference standards (United States)

    Czamanske, G.K.; Sisson, T.W.; Campbell, J.L.; Teesdale, W.J.


    The accuracy and precision of the University of Guelph proton microprobe have been evaluated through trace-element analysis of well-characterized silicate glasses and minerals, including BHVO-1 glass, Kakanui augite and hornblende, and ten other natural samples of volcanic glass, amphibole, pyroxene, and garnet. Using the 2.39 wt% Mo in a NIST steel as the standard, excellent precision and agreement between reported and analyzed abundances were obtained for Fe, Ni, Cu, Zn, Ga, Rb, Sr, Y, Zr, and Nb. -from Authors

  17. Dating blueschist metamorphism: a combined 40Ar/39Ar and electron microprobe approach

    International Nuclear Information System (INIS)

    40Ar/39Ar and electron microprobe examination of blueschist samples from the Iceberg Lake schist, southern Alaska suggest that phengite inclusions are the source of 40Ar in crossite. Because such fine-grained inclusions may be susceptible to argon loss, caution should be exercised in interpreting K-Ar ages from this phase, and possibly other low-K amphiboles from blueschist suites. The estimated blocking temperature for phengite in the matrix (3140 to 4500C), however, is close to the estimated peak metamorphic temperatures (3250 +- 500C), suggesting that phengite 40Ar/39Ar plateau dates may coincide closely with the time of blueschist metamorphism. (author)

  18. Partial melting of lower crust at 10-15 kbar: constraints on adakite and TTG formation (United States)

    Qian, Qing; Hermann, Jörg


    The pressure-temperature ( P- T) conditions for producing adakite/tonalite-trondhjemite-granodiorite (TTG) magmas from lower crust compositions are still open to debate. We have carried out partial melting experiments of mafic lower crust in the piston-cylinder apparatus at 10-15 kbar and 800-1,050 °C to investigate the major and trace elements of melts and residual minerals and further constrain the P- T range appropriate for adakite/TTG formation. The experimental residues include the following: amphibolite (plagioclase + amphibole ± garnet) at 10-15 kbar and 800 °C, garnet granulite (plagioclase + amphibole + garnet + clinopyroxene + orthopyroxene) at 12.5 kbar and 900 °C, two-pyroxene granulite (plagioclase + clinopyroxene + orthopyroxene ± amphibole) at 10 kbar and 900 °C and 10-12.5 kbar and 1,000 °C, garnet pyroxenite (garnet + clinopyroxene ± amphibole) at 13.5-15 kbar and 900-1,000 °C, and pyroxenite (clinopyroxene + orthopyroxene) at 15 kbar and 1,050 °C. The partial melts change from granodiorite to tonalite with increasing melt proportions. Sr enrichment occurs in partial melts in equilibrium with 20 wt%, respectively. Major elements and trace element patterns of partial melts produced by 10-40 wt% melting of lower crust composition at 10-12.5 kbar and 800-900 °C and 15 kbar and 800 °C closely resemble adakite/TTG rocks. TiO2 contents of the 1,000-1,050 °C melts are higher than that of pristine adakite/TTG. In comparison with natural adakite/TTG, partial melts produced at 10-12.5 kbar and 1,000 °C and 15 kbar and 1,050 °C have elevated HREE, whereas partial melts at 13.5-15 kbar and 900-1,000 °C in equilibrium with >20 wt% garnet have depressed Yb and elevated La/Yb and Gd/Yb. It is suggested that the most appropriate P- T conditions for producing adakite/TTG from mafic lower crust are 800-950 °C and 10-12.5 kbar (corresponding to a depth of 30-40 km), whereas a depth of >45-50 km is unfavorable. Consequently, an overthickened crust and

  19. The ophiolite massif of Kahnuj (western Makran, Southern Iran): new geological and geochronological data; Le massif ophiolitique de Kahnuj (Makran occidental, Iran meridional): nouvelles donnees geologiques et geochronologiques

    Energy Technology Data Exchange (ETDEWEB)

    Kananian, A. [University of Tarbiat Modarress, Geological Dept., Faculty of Science, Teheran (Iran, Islamic Republic of); Juteau, Th.; Bellon, H. [Universite de Bretagne Occidentale, IUEM, 29 - Brest (France); Darvishzadeh, A. [University of Teheran, Geological Dept., Faculty of Science, Teheran (Iran, Islamic Republic of); Sabzehi, M. [Geological Survey of Iran, Teheran (Iran, Islamic Republic of); Whitechurch, H. [Universite Louis Pasteur, EOST, Institut de Physique du Globe, 67 - Strasbourg (France); Ricou, L.E. [Institut de Physique du Globe, 75 - Paris (France)


    The ophiolite massif of Kahnuj (600 km{sup 2}) consists, from bottom to top, of layered gabbros, isotropic gabbros and ouralite gabbros, agmatites of dioritic to plagio-granitic composition, a sheeted dyke complex and lastly a basaltic pillow lava unit. Amphiboles from gabbros were dated ({sup 40}K-{sup 40}Ar ages) between 156 and 139 Ma and the agmatites are nearly contemporaneous. Potassic granitic veins dated at 93-88 Ma are related to the development of the Ganj arc complex. (authors)

  20. The evolution of young silicic lavas at Medicine Lake Volcano, California: Implications for the origin of compositional gaps in calc-alkaline series lavas (United States)

    Grove, T.L.; Donnelly-Nolan, J. M.


    At Medicine Lake Volcano, California, the compositional gap between andesite (57-62 wt.% SiO2) and rhyolite (73-74 wt.% SiO2) has been generated by fractional crystallization. Assimilation of silicic crust has also occurred along with fractionation. Two varieties of inclusions found in Holocene rhyolite flows, hornblende gabbros and aphyric andesites, provide information on the crystallization path followed by lavas parental to the rhyolite. The hornblende gabbros are magmatic cumulate residues and their mineral assemblages are preserved evidence of the phases that crystallized from an andesitic precursor lava to generate the rhyolite lavas. The andesitic inclusions represent samples of a parental andesite and record the early part of the differentiation history. Olivine, plagioclase and augite crystallization begins the differentiation history, followed by the disappearance of olivine and augite through reaction with the liquid to form orthopyroxene and amphibole. Further crystallization of the assemblage plagioclase, amphibole, orthopyroxene, magnetite, and apatite from a high-SiO2 andesite leads to rhyolite. This final crystallization process occurs on a cotectic that is nearly horizontal in temperature-composition space. Since a large amount of crystallization occurs over a limited temperature interval, a compositional gap develops between rhyolite and high SiO2 andesite. Liquidus surfaces with shallow slopes in temperature-composition space are characteristic of several late-stage crystallization assemblages in the andesite to rhyolite compositional range. Experimentally produced plagioclase+ amphibole+orthopyroxene+magnetite and plagioclase+ augite+low-Ca pyroxene+magnetite cotectics have liquidus slopes that are nearly flat. At other calc-alkaline volcanic centers crystallization processes involving large compositional changes over small temperature intervals may also be important in the development of bimodal volcanism (i.e. the existence of a composition

  1. 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)

  2. Application of X-ray luminescence separation to preliminary enrichment of lean scheelite-containing ores

    International Nuclear Information System (INIS)

    Investigations of preliminary enrichment of lean ores of amphibole hornfels by the method of X-ray luminescence separation was conducted. Pile and enriched products with different WO3 content were obtained from these ores; WO3 content in pile products was 2-2.5 times lower as compared to factory tailing products. WO3 content in separator concentrate corresponds in all cases to the requirements for the ore designated for flotation enrichment. Carbonate modulus decreases 2.5-4 times in separation concentrate, simplifying the conditions of flotation

  3. Geochemistry and metamorphic evolution of a Ti-metagabbro in the Asnawa Group of the Shalair terrain (Sanandaj-Sirjan Zone), Kurdistan region, Iraq. (United States)

    Yara, Irfan; Schulz, Bernhard; Tichomirowa, Marion; Mohammad, Yousif; Matschullat, Jörg


    Geochemistry and metamorphic evolution of a Ti-metagabbro in the Asnawa Group of the Shalair terrain (Sanandaj-Sirjan Zone), Kurdistan region, Iraq. We present geochemical data, mineral chemistry, petrography, and theP-T conditions of a Ti-metagabbro from the Asnawa Group in the Shalair Terrain (Sanandaj-Sirjan Zone).Geochemical data indicate that this Ti-metagabbro has tholeiitic characteristics with low-K contents. Factor analyses of the elements indicate fractionation of common mineral phases such as clinopyroxene, hornblende, plagioclase, Ti-bearing phases (rutile, ilmenite, titanite), and apatite. The normal mid-oceanic ridge basalt (N-MORB)-normalized incompatible trace element diagram shows close similarity with typical N-MORB pattern. Tectonomagmatic discrimination diagrams suggest a dominating MORB environment. The rock/chondrite-normalized REE diagram of the amphibolites also shows their N-MORB-type signature, with relative enrichment in LREE. The rock derived from mixed primitive and depleted mantel. The formation and preservation of the various metamorphic mineral assemblages and their mineral chemical characteristicsare strongly affected by the original magmatic whole-rock composition. This can be demonstrated by different microdomains, which contain different amphiboles and plagioclases. The metamorphic history can be subdivided into the stages M1-M2-M3. The first stage of metamorphism was recorded by crystallisation of actinolite replacing clinopyroxene and igneous amphibole (M1 stage, 410< T < 490°C; 1.8 < P <2.2 kbar). Increase of temperature resulted in the formation of hornblende pseudomorphism and hornblende and sphene coronae growing on previous amphibole or clinopyroxene and ilmenite, respectively (M2 stage, 540 < T <580°C; 4.5 < P < 5.5 kbar). The third stage (M3 stage, 730 < T °C < 780°C; 6.5 < P < 7.5 kbar) led to the formation of a ferro-tschermakite corona, around the M2 amphibole, and rutile that developed on the sphene and ilmenite

  4. Geochronological stages of magmatism of Sorsk copper-molybdenum-porphyry are district, Kuznetsk Alatau (K-Ar, Ar-Ar and Rb-Sr methods)

    International Nuclear Information System (INIS)

    Studies on biotite, amphibole and feldspar rocks were conducted through K-Ar, 39Ar-40Ar and Rb-Sr methods for evaluation of geochronological stages of magmatism development of the Sorsk copper-molybdenum-porphyry ore district. It is shown that general duration of magmatism development at the Sorsk district exceeds 100 mln years with intervals between individual magmatic pulses about 30 mln years. Dating by magmatites, related to ore-bearing porphyry complex and ore-metasotamic formations, is within the interval of 380-400 mln years. 13 refs.; 2 figs

  5. Early paleozoic granitoid magmatism and metamorphism in Derbina microcontinent of East Sayan: new isotopic-geochronological data

    International Nuclear Information System (INIS)

    The results of of complex U-Pb, Ar-Ar and Sm-Nd geochronological and isotopic-geochemical studies of granitoids from the Derbina microcontinent located in the central part of the East Sayan are presented. The results of U-Pb dating of magmatic zircon (498 ± 5 mln. years) agree well with data of Ar-Ar dating for amphibole (507 ± 7 mln. years). The totality of the isotopic-geochronological data suggests repeated manifestations of the Early Paleozoic metamorphism and collision granite formation within the Derbina microcontinent

  6. Mineral chemical and petrographic occurrences os iron of the south east of Uruguay (Nico Pere z terrane)

    International Nuclear Information System (INIS)

    Two iron-formation deposits from S E Uruguay were petrographic ally and mineralogically investigated (including microprobe mineral chemistry). The deposit from Piedra de Gigante (ANCAP) quarry is related to tectonic slivers of a platform succession in ortho gneiss of ca. 1750 Ma. Data of detrital zircon in this platform succession point to Meso- to Neo proterozoic age.The iron deposit of Piedra del Gigante (ANCAP) quarry belongs to a succession of mica schists, quartz-muscovite schists, marbles and basic rocks. Magnetite rich layers alternate with banded rocks rich in hematite, carbonate and amphibole. Carbonate is dolomite (Mg0.7Ca1.08Mn0.05Fe0.11(CO3)2) and the amphibole is a pale green tremolite (Na0,18Ca1,68Mn0,07Mg4,16Fe+++0,2Fe++0,55Al0,03(Si7,86Al0,13)O22(OH)2). This iron deposit shows strong deformation associated with martitization of magnetite and formation of specularite rich layers where relicts of magnetite (partly martitized) are occasionally observed. Available data are not conclusive about the genesis. The low iron-content of the amphibole together with dolomite in the mineral association cast doubts on a BIF-type origin, but low contents of Al2O3, V2O3, MnO and ZnO in magnetite do not indicate an igneous origin. High oxygen fugacity during martitization in medium-T metamorphic conditions could have determined that iron rich amphiboles were not formed as is normally expected in iron-formations. In the outcrop of Cerro la Higuerita (Grupo Arroyo del Soldado; Ediacaran) a succession of metapelites (bottom), iron rich pelites and iron formations (top) is observed. The metapelites contain evidences of volcanic contribution (phenochrysts of quartz and alkali feldspar as well as shards in the matrix) suggesting a volcanic source for the iron. This iron-formation contains magnetite pheno blasts (partly martitized) and fine disseminated laths of hematite in the matrix, together with grunerite (Na0,04Ca0,17 Mn0,02Mg1,36Fe5,35Al0,07(Si7,97Al0,03)O22(OH)2

  7. Petrogenesis of the Kösedağ Pluton, Suşehri-NE Sivas, East-Central Pontides, Turkey




    The Kösedağ syenite crops out as a shallow-seated pluton within the Eocene volcano-sedimentary rocks and is unconformably overlain by Lower Miocene limestones in the Suşehri-NE Sivas region, east-central Pontides. It consists of syenites and quartz syenites with a phaneritic, porphyritic texture characterized by K-feldspar megacrysts set in a coarse- to medium-grained groundmass comprising K-feldspar, plagioclase, clinopyroxene, amphibole, biotite and quartz. Major element geochemistry data r...

  8. Asbestos quantification in track ballast, a complex analytical problem (United States)

    Cavallo, Alessandro


    Track ballast forms the trackbeb upon which railroad ties are laid. It is used to bear the load from the railroad ties, to facilitate water drainage, and also to keep down vegetation. It is typically made of angular crushed stone, with a grain size between 30 and 60 mm, with good mechanical properties (high compressive strength, freeze - thaw resistance, resistance to fragmentation). The most common rock types are represented by basalts, porphyries, orthogneisses, some carbonatic rocks and "green stones" (serpentinites, prasinites, amphibolites, metagabbros). Especially "green stones" may contain traces, and sometimes appreciable amounts of asbestiform minerals (chrysotile and/or fibrous amphiboles, generally tremolite - actinolite). In Italy, the chrysotile asbestos mine in Balangero (Turin) produced over 5 Mt railroad ballast (crushed serpentinites), which was used for the railways in northern and central Italy, from 1930 up to 1990. In addition to Balangero, several other serpentinite and prasinite quarries (e.g. Emilia Romagna) provided the railways ballast up to the year 2000. The legal threshold for asbestos content in track ballast is established in 1000 ppm: if the value is below this threshold, the material can be reused, otherwise it must be disposed of as hazardous waste, with very high costs. The quantitative asbestos determination in rocks is a very complex analytical issue: although techniques like TEM-SAED and micro-Raman are very effective in the identification of asbestos minerals, a quantitative determination on bulk materials is almost impossible or really expensive and time consuming. Another problem is represented by the discrimination of asbestiform minerals (e.g. chrysotile, asbestiform amphiboles) from the common acicular - pseudo-fibrous varieties (lamellar serpentine minerals, prismatic/acicular amphiboles). In this work, more than 200 samples from the main Italian rail yards were characterized by a combined use of XRD and a special SEM

  9. Asbestos content of lung tissue in patients with malignant peritoneal mesothelioma: A study of 42 cases. (United States)

    de Ridder, Gustaaf G; Kraynie, Alyssa; Pavlisko, Elizabeth N; Oury, Tim D; Roggli, Victor L


    Lung tissue from 42 peritoneal mesothelioma cases was analyzed by light microscopy and scanning electron microscopy/energy dispersive spectrometry. There were 34 men and 8 women with a mean age of 61 ± 10 years. Also, 17% of cases had histologically confirmed asbestosis, and 26% had only parietal pleural plaques. The asbestos body count exceeded our normal range in 22 of 42 cases (52%). Cases with asbestos-related pulmonary disease had higher fiber burdens than those without. The vast majority of fibers were commercial amphiboles (amosite with lesser amounts of crocidolite). These findings concur with previously published epidemiological observations. PMID:27281118

  10. Shape of pinch and swell structures as a viscosity indicator: Application to lower crustal polyphase rocks (United States)

    Gardner, Robyn L.; Piazolo, Sandra; Daczko, Nathan R.


    Pinch and swell structures occur where a more competent layer in a weaker matrix is subjected to layer-parallel extension. In this contribution, we use numerical models to explore the use of pinch and swell structure shape symmetry and asymmetry as a determinant of relative viscosity between layers. Maximum asymmetry is attained when the matrix viscosity on one side is subtly weaker than the competent layer, while the other side is significantly weaker. Our numerical results are directly applied to asymmetrically developed pinch and swell structures in exposed lower continental crust. Here, shape geometries observed in a shear zone comprised of plagioclase-dominated, garnet-dominated and mixed amphibole-plagioclase-dominated bands, reveals that the plagioclase-dominated band is the most competent band and is marginally stronger (2×) and significantly stronger (10-40×) than the fine grained garnet-dominated and mixed amphibole-plagioclase-dominated band, respectively. Based on the experimentally determined viscosity of a plagioclase-dominated material and quantitative microstructural analysis, the viscosity range of the natural rock bands is 2.8 × 1015 to 1.1 × 1017 Pa s. Consequently, the assumption that the experimentally-derived plagioclase flow law is an appropriate proxy for the middle to lower continental crust may lead to a viscosity over-estimation by up to forty times.

  11. The zeta potential of mineral fibres. (United States)

    Pollastri, Simone; Gualtieri, Alessandro F; Gualtieri, Magdalena Lassinantti; Hanuskova, Miriam; Cavallo, Alessandro; Gaudino, Giovanni


    For the first time, the zeta (ξ) potential of pathogenic mineral fibres (chrysotiles, amphiboles and erionite) was systematically investigated to shed light on the relationship between surface reactivity and fibre pathogenicity. A general model explaining the zeta potential of chrysotile, amphiboles and erionite has been postulated. In double distilled water, chrysotiles showed positive values while crocidolite and erionite showed negative values. In contact with organic solutions, all fibres exhibited negative values of zeta potential. The decrease of the surface potential is deemed to be a defensive chemical response of the macrophage cells to minimize hemolytic damage. Negatively charged surfaces favour the binding of collagen and redox activated Fe-rich proteins, to form the so-called asbestos bodies and prompt the formation of HO via the reaction with peroxide (H2O2+e(-)→HO+HO(-)). An additional mechanism accounting for higher carcinogenicity is possibly related to the Ca(2+) sequestration by the fibres with surface negative potential, impairing the mitochondrial apoptotic pathway. It was also found that with a negative zeta potential, the attractive forces prevailed over repulsions and favoured processes such as agglomeration responsible of a tumorigenic chronic inflammation. PMID:24929786

  12. Occult exposure to asbestos in steel workers revealed by bronchoalveolar lavage

    Energy Technology Data Exchange (ETDEWEB)

    Corhay, J.-L.; Delavignette, J.-P.; Bury, T.; Saint-Remy, P.; Radermecker, M.-F. (CHU, Liege (Belgium))

    To investigate the asbestos burden in a steelplant environment, we counted asbestos bodies (ABs) in the bronchoalveolar lavage fluid (BALF) of 65 steel workers who had retired during the previous 5 y. They had worked for at least 15 y in the same area of the plant (coke oven or blast furnace) as maintenance or production workers. On the basis of occupational anamnesis, 28 had occasional past professional exposure to asbestos; the remaining 37 workers denied any contact with asbestos. A total of 54 white-collar workers who had no occupational exposure to asbestos were included in the study as controls. An increased prevalence and concentration of ABs was found in the BALF of steel workers. Electron microscopy and EDAX analysis of AB from steel workers revealed that the core fibers were mainly amphiboles. More ABs were found in the BALF of maintenance workers than in production workers. However, the BALF from steel workers who denied any contact with asbestos revealed an increased AB burden v. controls. This demonstrates that steel workers may be subject to an occult exposure to amphiboles in the steelplant environment.

  13. The Distribution, Character, and Rhenium Content of Molybdenite in the Aitik Cu-Au-Ag-(Mo Deposit and Its Southern Extension in the Northern Norrbotten Ore District, Northern Sweden

    Directory of Open Access Journals (Sweden)

    Christina Wanhainen


    Full Text Available Molybdenite in the Aitik deposit and its southern extension was studied through mineralogical/chemical analysis and laboratory flotation tests. It is demonstrated that molybdenite varies considerably in grain size, ranging from coarse (>20 μm to very fine (<2 μm and occurs predominantly as single grains in the groundmass of the rocks, as grain aggregates, and intergrown with chalcopyrite and pyrite. The dominating molybdenite-bearing rocks are the mica schists, the quartz-monzodiorite, and the Salmijärvi biotite-amphibole gneiss, the latter containing mostly medium-coarsegrained molybdenite. Later geological features, such as garnet-magnetite-anhydrite-K feldspar alteration and pegmatite dikes appear to be responsible for a significant part of the distribution pattern of molybdenite. Molybdenite grains contain up to 1587 ppm Re, with an average of 211 ± 10 ppm in Aitik molybdenite and 452 ± 33 ppm in Salmijärvi molybdenite. The higher Re concentrations are found in molybdenite associated with sericite- and quartz-amphibole-magnetite altered rocks, whereas low Re values occur in rocks in which potassic alteration is prominent. Molybdenite recovery is influenced by the mineralogy of the host rock and the alteration grade; hence both of these factors will have an impact on potential recoveries. The recovery of molybdenite was lower from flotation feeds with significant amounts of Mg-bearing clay-micas.

  14. Trace element abundances in megacrysts and their host basalts: constraints on partition coefficients and megacryst genesis

    International Nuclear Information System (INIS)

    In an effort to obtain information about mineral/melt trace element partitioning during the high pressure petrogenesis of basic rocks, we determined rare earth and other trace element abundances in megacrysts of clinopyroxene, orthopyroxene, amphibole, mica, anorthoclase, apatite and zircon, and in their host basalts. In general, the ranges of mineral/melt partition coefficients established from experimental partitioning studies and phenocryst/matrix measurements overlap with the ranges of megacryst/host abundance ratios. Our data for Hf, Sc, Ta and Th partitioning represent some of the only estimates available. Consideration of phase equilibria, major element partitioning and isotopic ratios indicate that most of the pyroxene and amphibole megacrysts may have been in equilibrium with their host magmas at high pressures. In contrast, it is unlikely that mica, anorthoclase, apatite and zircon megacrysts formed in equilibrium with their host basalts; instead, we conclude that they were precipitated from more evolved magmas and have been mixed into their present host magmas. Consequently, the trace element abundance ratios for megacryst/host should not be interpreted as partition coefficients, but only as guides for understanding trace element partitioning during high pressure petrogenesis. (author)

  15. Petrografía y geoquímica preliminar de los basaltos cretácicos de la sierra de Las Quijadas y cerrillada de Las Cabras, provincia de San Luis, Argentina

    Directory of Open Access Journals (Sweden)

    Martínez Amancay N.


    Full Text Available Preliminary petrography and geochemistry of the Cretacic basalts of the Sierra de Las Quijadasand Cerrillada de Las Cabras, San Luis province, Argentina. We present preliminary results of the petrologyand geochemistry of Cretaceous basalts exposed in the anticlines of the sierra of Las Quijadas and cerrillada ofLas Cabras. In the mountainous western of San Luis crop out at least two depositional sequences which togetherexceed the 1500 m thick and consists mainly of clastic sedimentary sequences typical continental red beds belongingto the Giant Group and Lagarcito Formation. Within this group, recognizes two types of basalt events, representedby lava flows and dykes. The lava flows were described in the northeastern sector of the anticline, in a landscapeof gentle hills. The dykes were found on the western flank of the anticline, northern sector of that mountain.Basalt lava flows have porphyritic texture with phenocrystals show idiomorphic olivine with clinopyroxene,amphibole and plagioclase, while the basaltic dykes show olivine in porphyritic texture embedded in a plagioclasepaste without orientation, amphibole and apatite needles. The basalts of the cerrillada de Las Cabras presented asa volcanic breccia associated with basaltic bombs. They have phenocrystals of olivine and clinopyroxene in pastewith plagioclase oriented. The basalts are classified as alkali basalts and related to intraplate basalts. When analyzingrare earth elements chondrite normalized according to Nakamura’s design are observed with a steep negative slopefor the heavy rare earth elements, a design that is similar to that found in alkaline basalts from the Sierra Chica deCórdoba.

  16. Calcio-carbonatite melts and metasomatism in the mantle beneath Mt. Vulture (Southern Italy) (United States)

    Rosatelli, Gianluigi; Wall, Frances; Stoppa, Francesco


    At Mt. Vulture volcano (Basilicata, Italy) calcite globules (5-150 μm) are hosted by silicate glass pools or veins cross-cutting amphibole-bearing, or more common spinel-bearing mantle xenoliths and xenocrysts. The carbonate globules are rounded or elongated and are composed of a mosaic of 2-20 μm crystals, with varying optical orientation. These features are consistent with formation from a quenched calciocarbonatite melt. Where in contact with carbonate amphibole has reacted to form fassaitic pyroxene. Some of these globules contain liquid/gaseous CO 2 bubbles and sulphide inclusions, and are pierced by quench microphenocrysts of silicate phases. The carbonate composition varies from calcite to Mg-calcite (3.8-5.0 wt.% MgO) both within the carbonate globules and from globule to globule. Trace element contents of the carbonate, determined by LAICPMS, are similar to those of carbonatites worldwide including ΣREE up to 123 ppm. The Sr-Nd isotope ratios of the xenolith carbonate are similar to the extrusive carbonatite and silicate rocks of Mt. Vulture testifying to derivation from the same mantle source. Formation of immiscibile silicate-carbonatite liquids within mantle xenoliths occurred via disequilibrium immiscibility during their exhumation.

  17. 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.

  18. 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.

  19. Well log responses in metamorphic rocks near Maribor

    Directory of Open Access Journals (Sweden)


    Full Text Available In the Stražun forest at Pobrežje near Maribor, (Eastern Slovenia six boreholes have been drilled from 860 to 1600m deep. The paper describes geological conditions in mentioned boreholes, as well as in wider surroundings of Maribor with stress on metamorphic rocks. Based on pétrographie analysis of the rocks cuttings and well logs the upper phyllitic part ant the lower Pohorje series of themetamorphic complex could be separated. The first one includes phyllites with phyllitic quartzites and silicate marmorized limestones. The Pohorje series is represented by two-mica gneiss and schist, mainly with inclusions of amphibolite and eclogite, and subordinately retrograde chlorite-amphibole schist. The welllog responses for particular lithological sequences of metamorphic complex have been distinguished on the basis of conventional electrologs and gamma ray measurements.The problem of lithological interpretation of well logs in these rocks is described. Two fields of well log responses are distinguishable, as separated by the degree of natural radioactivity. Apart from veined quartzite, all rocks fromthe phyllitic part of the metamorphic complex are highly radioactive. In the Pohorje series gneiss, schist and diaphtorite-phyllonite are highly radioactive, while amphibolite, eclogite and retrograde chlorite-amphibole schist have low radioactivity.Finally, typical well log responses in lithological sequences of the discussed metamorphic rocks are presented.

  20. Geochemistry and evolution of MORB-type eclogites from the Muenchberg Massif, southern Germany

    International Nuclear Information System (INIS)

    In the Muenchberg Massif in the Variscan foldbelt of southern Germany two varieties of eclogite are known which are intercalated with amphibolite-facies meta-igneous and meta-sedimentary rocks: a dark kyanite-free and a lighter colored kyanite-bearing type. Kyanite-free eclogites, which are discussed here, have a major and trace element composition which suggests derivation from ocean-floor basalts with melt to cumulate compositions. Internal Sm-Nd isochroms (clinopyroxene-amphibole-garnet) and one Rb-Sr isochron (clinopyroxene-amphibole-mica) yield eclogitization ages in the range of 380 to 395 Ma. Thus, the age of eclogitization is only marginally higher (Nd of 8.7 ± 0.6 and is likely to record the age of igneous formation of the eclogite protoliths. Sr isotopic compositions back-calculated to that time are anomalously high and variable if compared to Nd isotopes. This can be explained by alteration with an aqueous or fluid phase with high 87Sr/86Sr, most likely seawater, either during igneous formation in an oceanic rift environment or subduction-related eclogitization. In addition, some eclogites show a marked enrichment of incompatible, immobile elements and plot far below the whole-rock Sm-Nd isochron. These features are ascribed to the presence of an evolved crustal component, probably acquired during extrusion of the basaltic protoliths by mixing with country-rock gneisses. (orig.)

  1. Impaired mitochondrial metabolism and protein synthesis in streptozotocin diabetic rat hepatocytes

    International Nuclear Information System (INIS)

    Isolated hepatocytes prepared from control, streptozotocin diabetic rats were incubated at 30 degrees C in Krebs-Henseleit bicarbonate buffer, pH 7.4, containing 0.5 mM concentration of each of the 20 natural amino acids. Effect of insulin on the oxidation of 2,3-14C and 1,4-14C succinate (suc) carbons and their incorporation into hepatocyte protein, lipid and various metabolic intermediates was studied. Mitochondrial oxidation of suc carbons and their incorporation into protein and lipid was significantly lower in diabetic and insulin treated diabetic rats. Diabetic rats failed to exhibit any significant insulin effect on the oxidation of either 2,3 or 1,4-14C suc carbons. Amphibolic channeling of 2,3-14C suc carbons into amino acids was significantly reduced in hepatocytes of diabetic rats, however, more of these carbons were diverted into the gluconeogenesis pathway. Diabetes caused a far greater decrease in the oxidation of 2,3-14C suc carbons as compared to 1,4-14C suc. Based on an earlier report that insulin stimulates only the intramitochondrial Krebs cycle reactions, the authors conclude that the diminished level of anabolic activities in the diabetic rat hepatocytes is due to the subsequent reduction in amphibolic channeling of metabolic intermediates

  2. Geology of the Biwabik Iron Formation and Duluth Complex. (United States)

    Jirsa, Mark A; Miller, James D; Morey, G B


    The Biwabik Iron Formation is a approximately 1.9 billion year-old sequence of iron-rich sedimentary rocks that was metamorphosed at its eastern-most extent by approximately 1.1 billion year-old intrusions of the Duluth Complex. The metamorphic recrystallization of iron-formation locally produced iron-rich amphiboles and other fibrous iron-silicate minerals. The presence of these minerals in iron-formation along the eastern part of what is known as the Mesabi Iron Range, and their potential liberation by iron mining has raised environmental health concerns. We describe here the geologic setting and mineralogic composition of the Biwabik Iron Formation in and adjacent to the contact metamorphic aureole of the Duluth Complex. The effects of metamorphism are most pronounced within a few kilometers of the contact, and decrease progressively away from it. The contact aureole has been divided into four metamorphic zones-each characterized by the composition and crystal structure of the metamorphic minerals it contains. The recrystallization of iron-formation to iron-rich amphibole minerals (grunerite and cummingtonite) and iron-pyroxene minerals (hedenbergite and ferrohypersthene) is best developed in zones that are most proximal to the Duluth Complex contact. PMID:17997209

  3. 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)

  4. Geology of the hills in the region of the City of Santiago de Chile: New isotopic constraints

    International Nuclear Information System (INIS)

    Geological, geochronological and geochemical data demonstrate that the area where the city of Santiago de Chile is established used to be a huge volcanic field. At present, it is possible to distinguish in the area at least three volcanic cycles, which are geographically superimposed and deeply eroded. The first is Oligocene in age, the second Lower to Middle Miocene and the third is Middle to Upper Miocene. The Oligocene cycle is represented by volcanic and volcanoclastic rocks of the Provincia-San Ramon-Abanico and Conchali belts, and welded tuffs of the San Cristobal and Renca hills. The Lower to Middle Miocene cycle consists of subvolcanic rocks, mostly of basaltic to basaltic-andesite composition, characterized by the presence of clino- and orthopyroxene. The Middle to Upper Miocene cycle is composed predominantly of amphibole-bearing subvolcanic rocks of dacitic composition. The latter are found at the Manquehue hill, which limits the northern part of the city, and the hills at the Rinconada de Conchali. In this communication, we present new Sr-, Nd- and Pb- isotope data obtained from two subvolcanic samples of basaltic composition collected from the San Cristobal hill and at the Santa Lucia hill (Lower to Middle Miocene) and one amphibole-bearing subvolcanic sample of dacitic composition from the Manquehue hill (Middle to Upper Miocene) (au)

  5. Petrochemistry and tectonic significance of Lower Cretaceous Barros Arana Formation basalts, southernmost Chilean Andes (United States)

    Stern, C. R.; Mohseni, P. P.; Fuenzalida, P. R.

    The Lower Cretaceous Barros Arana Formation (Albian, hornblende KAr age of 104 Ma), in the Magallanes region of Chile, consists of a sequence of spilitized clinopyroxene- and amphibole-bearing mafic dikes and lavas, and volcaniclastic breccias, occurring within the sedimentary infill of the Rocas Verdes marginal basin and its eastward extension onto the Cretaceous continental platform. Although the original alkali and alkaline earth element concentrations of the basaltic lavas and dikes have been altered by spilitization, the presence of relict pargasitic amphibole phenocrysts, the absence of orthopyroxene, and high LREE contents and LREE/HREE ratios imply mildly alkaline affinities for these basalts. Their low TiO 2 and HFSE (Zr, Nb, Ta, and Hf) contents and high LREE/HFSE ratios suggest affinities with convergent plate boundary arc magmas. The Barros Arana basalts are interpreted as mafic members of the mildly alkaline shoshonitic rock suite of subduction-related arcs. They may have formed as subduction geometry began to undergo the changes (flattening) that ultimately led to the initiation of the closure, deformation, and uplift of the Rocas Verdes basin by the late or post-Albian. The low initial 87Sr/ 86Sr (0.7031) and high initial 143Nd/ 144Nd (0.51277) of the basalts indicate that a generally extensional tectonic regime east of the main calc-alkaline arc allowed eruption of these mafic shoshonites without interaction with continental crust (in contrast to the contemporaneous plutons of the Patagonian batholith).

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

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    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.

  7. Geochemistry and petrogenesis of post-collisional ultrapotassic syenites and granites from southernmost Brazil: the Piquiri Syenite Massif. (United States)

    Nardi, Lauro V S; Plá-Cid, Jorge; Bitencourt, Maria de Fátima; Stabel, Larissa Z


    The Piquiri Syenite Massif, southernmost Brazil, is part of the post-collisional magmatism related to the Neoproterozoic Brasiliano-Pan-African Orogenic Cycle. The massif is about 12 km in diameter and is composed of syenites, granites, monzonitic rocks and lamprophyres. Diopside-phlogopite, diopside-biotite-augite-calcic-amphibole, are the main ferro-magnesian paragenesis in the syenitic rocks. Syenitic and granitic rocks are co-magmatic and related to an ultrapotassic, silica-saturated magmatism. Their trace element patterns indicate a probable mantle source modified by previous, subduction-related metasomatism. The ultrapotassic granites of this massif were produced by fractional crystallization of syenitic magmas, and may be considered as a particular group of hypersolvus and subsolvus A-type granites. Based upon textural, structural and geochemical data most of the syenitic rocks, particularly the fine-grained types, are considered as crystallized liquids, in spite of the abundance of cumulatic layers, schlieren, and compositional banding. Most of the studied samples are metaluminous, with K2O/Na2O ratios higher than 2. The ultrapotassic syenitic and lamprophyric rocks in the Piquiri massif are interpreted to have been produced from enriched mantle sources, OIB-type, like most of the post-collisional shoshonitic, sodic alkaline and high-K tholeiitic magmatism in southernmost Brazil. The source of the ultrapotassic and lamprophyric magmas is probably the same veined mantle, with abundant phlogopite + apatite + amphibole that reflects a previous subduction-related metasomatism. PMID:18506262

  8. The Araxá Group in the South-Southwest Region of the Goiás State

    Directory of Open Access Journals (Sweden)

    Guillermo Rafael Beltran Navarro


    Full Text Available In the S – SW region of Goiás State, Brazil, the Araxá Group is constituted of a metasedimentary sequence containing schistoseand gneissic (garnet-biotite-quartz schists, feldspatic garnet-biotite-quartz schists, garnet-biotite-quartz paragneisses,with muscovite and locally amphibole, epidote, kyanite and staurolite. This sequence presents intercalations of metaultramaficrocks (serpentinite, actinolite schist, talc schist, chlorite schist, metamafic ones (amphibolite, amphibole schistcontaining or not garnet, garnet amphibolite and associated granitic bodies. Chemically, the Araxá Group metasedimentspresent peraluminous composition, showing enrichment in LILE, when compared with HFSE and REE, and displayingnegative anomalies of Nb, Ta, Sr, P and Ti. Their chemical composition is that of greywake and the chemical characteristicsof the sediments are generated in magmatic arcs. Isotopic data for Sm/Nd – model ages (TDM between 1,04 – 1,51 and1,76 – 2,26 Ga – and U/Pb (predominance of zircon with ages < 900 Ma suggest that these metasediments have Neoproterozoicrocks as the source rocks. Chemical and isotopic characteristics of the studied metasediments suggest that theirsource are rocks originated in magmatic arcs and that they were deposited in a fore arc basin developed in the margins ofNeoproterozoic island arcs.

  9. Polycyclic orogeny in Central Ogcheon metamorphic belt, Korea: evidence from 40Ar/39Ar hornblende ages

    International Nuclear Information System (INIS)

    Full text: The Ogcheon fold-thrust belt is one of the key Phanerozoic belts for delineating the regional correlation in East Asia including mainland China and Japan. This NE-trending belt consists of the Ogcheon metamorphic belt (OMB) in the southwest and the Taebaeksan sedimentary zone in the northeast. The OMB comprises Late (?) Proterozoic to Paleozoic metasedimentary and metavolcanic sequences intruded by Mesozoic granitoids. The age of initial intracontinental rifting is constrained to be earlier than 756 Ma by the U-Pb zircon age of a felsic metavolcanic rock (Lee et al., 1998, Precamb. Res. 89, 47-57). Polyphase tectonism in the OMB is characterised by the Middle Paleozoic Ogcheon orogeny responsible for the ductile stacking of thrust nappes and the Triassic Songrim orogeny occurring at shallower depths under the brittle-ductile transitional regime (Cluzel et al., 1990, Tectonophysics, 183, 41-56). Peak metamorphic conditions of the former are in the range of 5-8 kbar and 520-590 deg C, whereas those of the latter are 1-3 kbar and 350-500 deg C (Min and Cho, 1998, Lithos, 43, 31-51). Major ambiguity in the polycyclic model of the OMB results from the lack of isotopic age data. In order to determine the age of peak metamorphism, we analysed hornblende crystals of quartzose amphibole schists in central OMB, using the 40Ar/39Ar dating technique. Mineral assemblages of amphibole schists are represented by calcic amphiboles + plagioclase + epidote ± garnet + quartz + titanite + Fe-Ti oxide (magnetite or ilmenite). Amphibole separates commonly display discordant age spectra. Nevertheless, amphiboles of five analysed samples yield 40Ar/39Ar intercept dates ranging from 432±4 Ma to 499±10 Ma. Three of them yield plateau dates of 440-492 Ma, defined by more than three contiguous steps accounting for >50% of the total 39ArK released. Two of these plateau dates (465±4 Ma and 492±4 Ma) are from hornblende fractions of different grain size in a garnet

  10. L-tectonites and deep mantle wedge deformations in the Limo ultramafic massif (Cabo Ortegal Complex, NW Spain) (United States)

    Puelles, Pablo; Ábalos, Benito; Gil Ibarguchi, José Ignacio; Mendia, Miren; José Santos Zalguegui, Francisco


    The Cabo Ortegal Complex is one of the Allochthonous Complexes of northwest Iberia. The complexes are variable subducted continental and oceanic lithosphere fragments obducted onto the Gondwana edge during the Variscan orogeny. They comprise a Lower Allochthon, a sandwiched ophiolitic complex, and an Upper Allochthon made of rock units metamorphosed under high-pressure conditions and amalgamated in an oblique subduction/collision orogenic channel. The structurally uppermost high-pressure sheet consists of arc-root lithospheric mantle peridotites that rest on high-pressure granulite facies rocks, eclogites and gneisses with eclogite boudins. The ultramafic rocks outcrop in three major massifs (Limo, Herbeira and Uzal from N to S) and in a number of much smaller klippen structures. They are serpentinized amphibole-bearing harzburgite, chromian spinel- and PGE-bearing dunite, and garnet-bearing massive pyroxenite. The Limo ultramafic massif has been considered so far as a fairly massive harzburgitic massif without a clear internal arrangement or fabric. However, new field data and microstructural observations show that harzburgites are L-tectonites and that this fabric is recognizable at various scales (from aerial photos to the outcrop and microscopic scales). The structures described form a hm-thick ultramafic tectonite stack which resembles the structural relationships already known in the easternmost sector of the neighbour Herbeira massif. Subhorizontal mineral and stretching lineations are defined by spinel and orthopyroxene and trend N010°-030°E. Extremely elongated sheath-like folds bear axes parallel to the lineation and show axial ratios >15, tubular and isoclinal structures in XZ sections and eye- and anvil-structures in structural sections perpendicular to the lineation. Sigmoidal shapes of peridotite foliation trajectories in XZ sections indicate a top-to-the-NNE tectonic displacement of hanging wall blocks (according to present-day geographic

  11. Eclogite in West Papua (Wandamen Peninsula), petrological and geochemical characterization : geodynamical implications (United States)

    de Sigoyer, Julia; Pubellier, Manuel; Bailly, Vivien; Ringenbach, Jean-Claude


    The Lengguru accretionary wedge (West Papua) is located in a very active geodynamical context. It results from the oblique convergence between the Pacific plate and the Australian plate. All the wedge has been build between 11 and 2 Ma (Bailly et al., 09). Exceptional boulders of fresh eclogites were discovered in the internal part of the Lengguru wedge, in the so called Wandamen peninsula. The Wandamen peninsula displays an increasing metamorphic gradient from West to East. This metamorphic peninsula may also be regarded as the continuation of the inner part of the Central range of Papua New Guinea farther east. The eclogites area embedded in metasediments that present similarities with Mesozoic and Cenozoic sediments of the Australian margin in the continuation of Lengguru wedge. According to geochemical analysis of major and traces elements on the two freshest eclogites, their protolith has a Fe-Ti gabbroic composition. The CIPW norm of these rocks suggest a protolith, with 32% of pyroxenes, 47% of anorthite, less than 3% of olivine, with 7% of ilmenite and 7% of magnetite. Major elements show a tholeiitic characters. Traces elements suggest a T MORB signature with a high content of TiO2. The eclogites are medium to coarse grained. The metamorphic paragenesis consists of clinopyroxenes, garnets, amphiboles, rutiles, quartz and accessory minerals like apatites. Clinopyroxenes with omphacitic composition (XJd: 0.3-0.4) are poecilitic, rare textures of retrogression (symplectites) are observed. Symplectites are composed by diopside or Na-Ca-Fe pyroxene XJd (0.18) and albite, locally calcic amphiboles can replace the clinopyroxene. Garnet of several millimeters (3-4 mm) result from the aggregation of smaller euhedral crystals (500-700 µm). Some of them display atoll microstructure and exhibit a core filled by omphacite, slightly green amphibole, or by quartz. They contain minute inclusions of omphacite, amphibole, apatite, quartz. Many rutiles exsolutions are

  12. 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

  13. 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.

  14. Unraveling an antique subduction process from metamorphic basement around Medellín city, Central Cordillera of Colombian Andes (United States)

    Bustamante, Andres; Juliani, Caetano


    In the surroundings of Caldas and El Retiro cities (Colombia) metamorphic rocks derived from basic and pelitic protoliths comprise the Caldas amphibole schist and the Ancón schist respectively. Subordinated metamorphosed granite bodies (La Miel gneiss) are associated to these units, and The El Retiro amphibolites, migmatites and granulites crops out eastwards of these units, separated by shear zones. The Caldas amphibole schist and the Ancón schist protoliths could have been formed in a distal marine reduced environment and amalgamated to the South American continent in an apparent Triassic subduction event. The El Retiro rocks are akin to a continental basement and possible include impure metasediments of continental margin, whose metamorphism originated granulite facies rocks and migmatites as a result of the anatexis of quartz-feldspathic rocks. The metamorphism was accompanied by intense deformation, which has juxtaposed both migmatites and granulite blocks. Afterward, heat and fluid circulation associated with the emplacement of minor igneous intrusions resulted in intense fluid-rock interaction, variations in the grain size of the minerals and, especially, intense retrograde metamorphic re-equilibrium. Thermobarometric estimations for the Caldas amphibole schist indicate metamorphism in the Barrovian amphibolite facies. The metamorphic path is counter-clockwise, but retrograde evolution could not be precisely defined. The pressures of the metamorphism in these rocks range from 6.3 to 13.5 kbar, with narrow temperature ranging from 550 to 630 °C. For the Ancón schist metapelites the P- T path is also counter-clockwise, with a temperature increase evidenced by the occurrence of sillimanite and the cooling by later kyanite. The progressive metamorphism event occurred at pressures of 7.6-7.2 kbar and temperatures of 645-635 °C for one sample and temperature between 500 and 600 °C under constant pressure of 6 kbar. The temperature estimated for these rocks

  15. Origin of high Sr/Y magmas from the northern Taihang Mountains: Implications for Mesozoic porphyry copper mineralization in the North China Craton (United States)

    Gao, Yongfeng; Santosh, M.; Wei, Ruihua; Ma, Guoxi; Chen, Zhikuan; Wu, Jinluan


    A number of porphyry Cu deposits have been described from east China which occur in association with Mesozoic high Sr/Y rocks within the continental interior rather than in an arc setting. However, the origin of these high Sr/Y rocks remains controversial. In this study we report precise zircon U-Pb age, as well as major-trace element and Sr-Nd-Pb isotope compositions from the Mujicun Cu mineralized porphyries in the northern Taihang orogen of eastern North China Craton (NCC). LA-ICP-MS zircon U-Pb dating yields an emplacement age of 143 ± 2 Ma, identical to the molybdenite Re-Os isochron ages of 142.5 ± 1.4 Ma for this intrusion. Like most of the Mesozoic adakitic rocks from the eastern NCC, the ore-bearing porphyries and associated volcanic lavas from northern Taihang orogen are rich in large ion lithophile elements and light REE, and have highly differentiated REE patterns. The porphyries and associated volcanic lavas have Sr-Nd-Pb isotopic compositions showing EM1-like isotopic signatures. Such geochemical and isotopic features confirm that the parental magma for these rocks originated from melting of an enriched sub-continental lithospheric mantle source. In comparison to the associated lavas, the ore-bearing porphyries have pronounced low FeO3T, TiO2 and P2O5 contents, and middle-heavy REE (and Y) and Zr concentrations, indicating fractional crystallization of amphibole with the observed accessory mineral assemblage such as Fe-Ti oxides, titanite, zircon and apatite. On the other hand, most of the porphyries exhibit relatively high Al2O3, Ba and Sr concentrations and pronounced positive Eu anomalies, excluding significant plagioclase fractionation due to suppression of the high water content in the magmas. The presence of the contemporary amphibole cumulates regionally exposed in the study area strongly support significant amphibole fractionation during the formation of the Mujicun porphyries. Thus, fractionation of a water-saturated magma is proposed as a

  16. Strain localization and fluid infiltration during subduction initiation: the record from sheared mafic amphibolites at the base of the New Caledonian ophiolite (United States)

    Soret, Mathieu; Agard, Philippe; Dubacq, Benoît; Vitale-Brovarone, Alberto; Monié, Patrick; Chauvet, Alain; Whitechurch, Hubert


    Most of our knowledge on subduction inception and obduction processes comes from metamorphic soles structurally associated with peridotite tectonites at the base of many ophiolites, and from early-obduction, rarely deformed, magmatic dikes emplaced at different level of the mantle sequence. These dikes record a partial refertilization of obducted ophiolites through subduction-derived fluids. However, these dikes are rarely deformed and/or metamorphosed. Here, we study the base of the New Caledonian ophiolite, using a combination of structural field studies and petrological-geochemical-geochronological analysis, with the aim of linking deformation and metasomatism through fluid infiltration and recrystallization. We report the existence of strongly sheared mafic amphibolites within the base of the New Caledonian obducted ophiolite, ~ 50-100 m above the basal thrust contact and peridotites), highly boudinaged and amphibolitized at high temperatures (750-800 °C), providing evidence that strain localized at the base of the ophiolite. Mafic protoliths of these amphibolites consisted of plagioclase and orthopyroxene (± olivine and calcic amphibole in places). We show that deformation is intimately associated to at least three major stages of fluid infiltration on mafic intrusions. The first stage of deformation and metasomatism coincides with amphibolitization and controlled the later channelization of fluids. The formation of calcic amphiboles records the percolation of Ca and Al-rich aqueous fluids. Amphibole-plagioclase geothermobarometry indicates high temperature and low pressure conditions (i.e. 750-800 °C; 3-5 kbar). Thermochronological data from hornblende (40Ar/39Ar) suggest that this deformation episode occurred at ~ 55 Ma, coinciding with E-dipping subduction initiation and incipient obduction. The main metasomatic stage is evidenced by a phlogopite-rich matrix wrapping peridotite and amphibolite boudins. The formation of phlogopite records the percolation

  17. Geochronology and geochemistry of leucosomes in the North Dabie Terrane, East China: implication for post-UHPM crustal melting during exhumation (United States)

    Wang, Shui-Jiong; Li, Shu-Guang; Chen, Li-Juan; He, Yong-Sheng; An, Shi-Chao; Shen, Ji


    Migmatites are widespread in the North Dabie ultrahigh-pressure metamorphic terrane (NDT) of Dabie orogen, East China. Idiomorphic and poikilitic amphibole grains in both leucosome and melanosome contain inclusions of plagioclase, quartz and biotite, suggesting formation of leucosome by fluid-present melting of biotite + plagioclase + quartz-bearing protoliths at P = 5-7 kbar, T = 700-800 °C. Precise SIMS zircon U-Pb dating indicates that migmatization of Dabie orogen initiated at ~140 Ma and lasted for ~10 Ma, coeval with the formation of low-Mg# adakitic intrusions in Dabie orogen. Based on mineralogical, petrographic and geochemical data, leucosomes in NDT can be subdivided into three groups. (1) High La/Yb(N)-Medium Sr/Y group (Group I), whose high Dy/Yb(N) but medium Sr/Y ratios are caused by amphibole and plagioclase residual during partial melting of dioritic to granodioritic gneisses. (2) Low La/Yb(N)-Low Sr/Y group (Group II), whose flat HREE patterns are produced by entrainment of peritectic amphiboles into melts derived from partial melting of dioritic gneiss. (3) High La/Yb(N)-High Sr/Y and Eu# group (Group III), whose extremely high Sr and Eu but low other REE concentrations are caused by accumulation of plagioclase and quartz. Although Group I and III fall in the adakitic fields on La/Yb(N)-Yb(N) and Sr/Y-Y diagrams, they are chemically distinct from contemporary high-pressure adakitic intrusions in Dabie orogen in a series of geochemical indexes, for example, lower Dy/Yb(N) and/or Sr/Y ratios at given La/Yb(N) ratio, lower Sr/CaO ratios, lower Rb concentration but higher K/Rb ratios. Therefore, leucosomes are produced by anatexis of the exhumed ultrahigh-pressure metamorphic rocks at middle crustal level, instead of partial melting of thickened lower crust with garnet-rich and plagioclase-poor residual. The coeval occurrence of migmatites and high-pressure adakitic intrusions in Dabie orogen indicates large-scale partial melting of middle to

  18. Hydration of the lithospheric mantle by the descending plate in a continent-continent collisional setting and its geodynamic consequences (United States)

    Massonne, Hans-Joachim


    At the beginning of continent-continent collision the descending plate dehydrates. The influence of this dehydration on the adjacent lithospheric mantle was studied. For this reason, pressure (P), temperature (T) and T-H2O pseudosections were calculated for an average mantle composition using the computer software PERPLE_X. These pseudosections were contoured by isopleths, for instance, for volumes of amphibole, chlorite, and serpentine. In addition, P-T pseudosections were considered for four psammopelitic rocks, common in the upper portion of the continental crust, in order to quantify the release of H2O in these rocks during prograde metamorphism. At pressures around 1 GPa, a maximum of slightly more than 10 vol.% chlorite, almost 20 vol.% amphibole, and some talc but no serpentine forms when only 1.8 wt.% H2O is added to the dry ultrabasite at temperatures of 600 °C. For example, hydrous phases amount to about 35 vol.% serpentine and 10 vol.% each of chlorite and amphibole at 1 GPa, 550 °C, and 5 wt.% H2O. The modelled psammopelitic rocks can release 0.8-2.5 wt.% H2O between 450 and 650 °C at 0.8-1.4 GPa. On the basis of the above calculations, different collisional scenarios are discussed highlighting the role of hydrated lithospheric mantle. In this context a minimum hydration potential of the front region of the descending continental plate is considered, which amounts to 4.6 × 1016 kg releasable H2O for a 1000 km wide collisional zone, due to a thick sedimentary pile at the continental margin. Further suggestions are that (1) the lower crustal plate in a continent-continent collisional setting penetrates the lithospheric mantle, which is hydrated during the advancement of this plate, (2) the maximum depths of the subduction of upper continental crust is below 70 km and (3) hydrated mantle above the descending crustal plate is thrust onto this continental crust.

  19. Interpreting Assemblages with Titanite (Sphene): It Does not have to be Greek to You. (United States)

    Xirouchakis, Dimitrios M.; Lindsley, Donald H.; McKay, Gordon A. (Technical Monitor)


    + Orthopyroxene + Augite + Ilmenite + Magnetite. Decreasing temperature and pressure conditions appear to favor titanite crystallization, thus, it is not unsurprising that titanite is frequently observed in slowly cooled rocks, albeit, in association with amphibole. We argue that the titanite + amphibole association is likely favored by high water activity, regardless of oxygen fugacity. Because water activity increases during crystallization of a pluton, the association titanite + amphibole, and consequently titanite, is likely to be more common in plutonic rocks than in volcanic rocks.

  20. Lifetime of an ocean island volcano feeder zone: constraints from U-Pb dating on coexisting zircon and baddeleyite, and 40/39Ar age determinations, Fuerteventura, Canary Islands (United States)

    Allibon, James; Ovtcharova, Maria; Bussy, Francois; Cosca, Michael; Schaltegger, Urs; Bussien, Denise; Lewin, Eric


    High-precision isotope dilution - thermal ionization mass spectrometry (ID-TIMS) U-Pb zircon and baddeleyite ages from the PX1 vertically layered mafic intrusion Fuerteventura, Canary Islands, indicate initiation of magma crystallization at 22.10 ± 0.07 Ma. The magmatic activity lasted a minimum of 0.52 Ma. 40Ar/39Ar amphibole dating yielded ages from 21.9 ± 0.6 to 21.8 ± 0.3, identical within errors to the U-Pb ages, despite the expected 1% theoretical bias between 40Ar/39Ar and U-Pb dates. This overlap could result from (i) rapid cooling of the intrusion (i.e., less than the 0.3 to 0.6 Ma 40Ar/39Ar age uncertainties) from closure temperatures (Tc) of zircon (699-988 °C) to amphibole (500-600 °C); (ii) lead loss affecting the youngest zircons; or (iii) excess argon shifting the plateau ages towards older values. The combination of the 40Ar/39Ar and U/Pb datasets implies that the maximum amount of time PX1 intrusion took to cool below amphibole Tc is 0.8 Ma, suggesting PX1 lifetime of 520,000 to 800,000 Ma. Age disparities among coexisting baddeleyite and zircon (22.10 ± 0.07/0.08/0.15 Ma and 21.58 ± 0.15/0.16/0.31 Ma) in a gabbro sample from the pluton margin suggest complex genetic relationships between phases. Baddeleyite is found preserved in plagioclase cores and crystallized early from low silica activity magma. Zircon crystallized later in a higher silica activity environment and is found in secondary scapolite and is found close to calcite veins, in secondary scapolite that recrystallised from plagioclase. close to calcite veins. Oxygen isotope δ18O values of altered plagioclase are high (+7.7), indicating interaction with fluids derived from host-rock carbonatites. The coexistence of baddeleyite and zircon is ascribed to interaction of the PX1 gabbro with CO2-rich carbonatite-derived fluids released during contact metamorphism.

  1. El Ventorrillo, a paleostructure of Popocatépetl volcano: insights from geochronology and geochemistry (United States)

    Sosa-Ceballos, G.; Macías, J. L.; García-Tenorio, F.; Layer, P.; Schaaf, P.; Solís-Pichardo, G.; Arce, J. L.


    Volcán Popocatépetl (México) was constructed over the remains of a volcanic paleostructure. Based on fieldwork, 40Ar/39Ar dating, U-Pb dating, and geochemistry, we have determined the age, chemistry, and location of this paleostructure and named it El Ventorrillo. Most remnants of El Ventorrillo are covered by deposits from subsequent activity of Popocatépetl, except for the El Abanico scarp and the Barranca de Nexpayantla, where the stratigraphy of El Ventorrillo eruptive products can be investigated. Inception of volcanism at El Ventorrillo occurred at 331 ± 10 ka with emission of the Nexpayantla andesitic lavas, and continued with extrusion of the Yoloxochitl (267 ± 31 ka) and microwave (227 ± 6 ka) domes. Intrusion of dikes occurred at 298 ± 94 and 230 ± 3 ka. Activity at El Ventorrillo continued with the emission of lavas that built the El Abanico scarp (193 ± 29 to 96 ± 8 ka) and continued until the Tutti Frutti eruption destroyed the cone 14.1 kyr ago. El Ventorrillo magmas produced rocks divided into two mineralogical groups. The first group contains biotite-amphibole-rich rocks and the second group consists of biotite-amphibole-free lavas. The rocks that contain biotite and amphibole are older than 198 ± 13 ka, whereas the rocks with no hydrous phases are younger than 227 ± 6 ka and contain skarn and granodiorite xenoliths. We interpret the change to an anhydrous mineral assemblage and the occurrence of skarn and granodiorite xenoliths as evidence for the formation of a new, shallower reservoir. A granodiorite xenolith was chosen for 40Ar/39Ar dating and U-Pb zircon analyses. The U-Pb method yielded an age of 540 ± 110 ka and the 40Ar/39Ar an age of 109 ± 24 ka. These ages are interpreted to indicate granodiorite crystallization (540 ± 110 ka), which metamorphosed the calcareous basement beneath Popocatépetl into skarn and an influx of magma (109 ± 24 ka) that reheated the granodiorite. Major and trace elements, Sr, Nd, and Pb isotopic

  2. Rehydration Metamorphism of the Iratsu Eclogite Mass in the Sambagawa Belt, Japan (United States)

    Kuwatani, T.; Toriumi, M.


    The Iratsu eclogite mass in the Sambagawa metamorphic belt, central Shikoku, Japan, underwent pervasive rehydration metamorphism so that most of all retrogressed to amphibolite. The Iratsu eclogite mass is originated from gabbro and basalt, and is interpreted as a relic of a fossil subducted slab. Gradual stages of rehydration retrogression from eclogite to low-grade greenschist are preserved by disequilibrium textures of incomplete reactions. Hence, the Iratsu eclogite mass provide an exceptional opportunity to study the process of rehydration reactions and exhumation of a subducted oceanic crust. The petrological investigations showed that the retrogressed eclogites can be classified into two types by reaction textures during rehydration stage: One is the perfectly equilibrated type, which is a rock almost perfectly retrogressed into well-foliated epidote-amphibolite consists of amphibole + epidote + chlorite + plagioclase + quartz +/- garnet, mainly sampled from the rim of the Iratsu body. The other is the locally equilibrated type, which is a rock partially retrogressed rock often preserved garnet and omphacite and weakly foliated sampled from the central part of the Iratsu body. Garnet grains are rimmed by amphibole (pargasite) + epidote layers, whereas omphacite grains broke into symplectites of amphibole (hornblende) + plagioclase. Such clear distinction of the mineral assemblages and mineral compositions between two parts around the dissolving minerals demonstrates that the system was not equilibrated as a whole but locally equilibrated in each part around the dissolving minerals. Partial pseudomorphs, which are frequently observed in rocks of the locally equilibrated type, are the most reliable evidence of a reaction, since the replaced mineral and the solid products can be directly observed. In this study, we developed the new methodology based on a simple mass-balance relation, by improving Gresens 1967 and Godard & Mabit 1998. Our method can easily

  3. Analysis of micro-particles in TRISTAN vacuum chambers

    International Nuclear Information System (INIS)

    Micro-particles in the beam chamber of a TRISTAN vacuum system were investigated from the point of view of suppressing micro-particles trapped in the accumulation ring. Micro-particles coming from ion pumps (IP) and distributed ion pumps (DIP), aluminium alloy particles produced during treatment of aluminium alloy chambers for welding, micro-particles from the environment, i.e.soil (granite rocks or amphiboles), particles of concrete and painting materials were identified. A molten iron particle found in a chamber suggests interaction between the particle and bunched electron beam. Most of the particles coming from outside the chambers can be avoided by using high class clean rooms. The particles from the ion pumps can be reduced using different pumps which do not emit particles. The particles produced during assembly of, for example, DIP must be suppressed by accepting different assembling from the traditional ones. (author)

  4. Distributional Feature of Detrital Minerais in the Superficial Sediment of South Yellow Sea

    Institute of Scientific and Technical Information of China (English)

    王红霞; 林振宏; 郭玉贵


    The composition of detrital minerals with grades of 0.063 - 0.25 mm in the superficial sediment of South Yellow Sea is mainly studied in the paper. The research result shows that the minerals can be divided into more than fifty sorts. The light minerals are mainly feldspar, quartz, mica, etc. The heavy minerals are mainly composed of amphibole, epidote, mica, autogeny pyrite, magnetite, hematite, garnet,zircon and so on, which mainly distribute in the sediments of silty clay and lutaceous silt. According to the content and distribution of the main minerals, the research area isdivided into five miteral combination provinces. The assembled types of minerals in every province have close relationship with its hydrodynamic conditions and sedimentary environment. And the sorts of detrital minerals also show that the detrital substances in the sedimentary areas mainly originate from the drainage areas of rivers,bedrock weathering, and transformed sediment, etc.

  5. Mineral chemistry and magnetic petrology of the Archean Planalto Suite, Carajás Province - Amazonian Craton: Implications for the evolution of ferroan Archean granites (United States)

    Cunha, Ingrid Roberta Viana da; Dall'Agnol, Roberto; Feio, Gilmara Regina Lima


    The Planalto Suite is located in the Canaã dos Carajás subdomain of the Carajás Province in the southeastern part of the Amazonian Craton. The suite is of Neoarchean age (∼2.73 Ga), ferroan character, and A-type affinity. Magnetic petrology studies allowed for the distinction of two groups: (1) ilmenite granites showing low magnetic susceptibility (MS) values between 0.6247×10-3 and 0.0102 × 10-3 SI and (2) magnetite-ilmenite-bearing granites with comparatively higher but still moderate MS values between 15.700×10-3 and 0.8036 × 10-3 SI. Textural evidence indicates that amphibole, ilmenite, titanite, and, in the rocks of Group 2, magnetite also formed during magmatic crystallization. However, compositional zoning suggests that titanite was partially re-equilibrated by subsolidus processes. The amphibole varies from potassian-hastingsite to chloro-potassian-hastingsite and shows Fe/(Fe + Mg) > 0.8. Biotite also shows high Fe/(Fe + Mg) ratios and is classified as annite. Plagioclase porphyroclasts are oligoclase (An25-10), and the grains of the recrystallized matrix show a similar composition or are albitic (An9-2). The dominant Group 1 granites of the Planalto Suite were formed under reduced conditions below the FMQ buffer. The Group 2 granites crystallized under more oxidizing conditions on or slightly above the FMQ buffer. Pressures of 900-700 MPa for the origin and of 500-300 MPa for the emplacement were estimated for the Planalto magmas. Geothermometers suggest initial crystallization temperatures between 900 °C and 830 °C, and the water content in the magma is estimated to be higher than 4 wt%. The Neoarchean Planalto Suite and the Estrela Granite of the Carajás Province reveal strong mineralogical analogies, and their amphibole and biotite compositions have high total Al contents. The latter characteristic is also observed in the same minerals of the Neoarchean Matok Pluton of the Limpopo Belt but not in those of the Proterozoic rapakivi A

  6. Petrology of plagiogranite from Sjenica, Dinaridic Ophiolite Belt (southwestern Serbia) (United States)

    Milovanović, Dragan; Srećković-Batoćanin, Danica; Savić, Marija; Popovic, Dana


    The Sjenica plagiogranite occurs in the southern part of the Dinaridic Ophiolite Belt, 5 km northwest of Sjenica. The main minerals are albite with strongly altered biotite (replaced with chlorite), with occasional amphibole (magnesio hornblende to tschermakite) and quartz. An enclave of fine-grained granitic rocks with garnet grains was noted too. Secondary minerals are calcite and chlorite (daphnite). Major, trace and REE geochemistry coupled with field observations support a model by which the Sjenica plagiogranite could be formed by fractional crystallization of mantle origin mafic magma in a supra-subduction zone setting. Occurrences of calcite and chlorite nests in the Sjenica plagiogranites revealed that these rocks underwent hydrothermal alteration due to intensive sea water circulation in a sub-sea-floor environment.

  7. Asbestos in drinking water

    International Nuclear Information System (INIS)

    Measurements and analysis of more than 100 samples of tap-water, originated from different countries of the Federal Republik of Germany, have been performed by means of the standardized TEM-procedure (ISO). The results have shown that the drinking water is contaminated with fine fibers, with chrysotile and amphibole asbestos. The majority of investigated samples contained less than 106 fibers/liter, and the fibers were thin and shorter than 5 μm. Nevertheless, in some tap-water samples the asbestos fiber concentrations were higher than 106 fibers/liter and/or the content of long fibers (longer than 5 μm) was relatively high. It is recommended tapwater with asbestos fiber concentrations over 106 fibers/liter and/or with greater content of long fibers should not be used for cooking or drinking unless filtered. (orig.)

  8. Mineral characterization of soil type ranker formed on serpentines occurring in southern Belgrade environs Bubanj Potok

    Directory of Open Access Journals (Sweden)

    Cekić Božidar Đ.


    Full Text Available The paper addresses the issue of health risk associated with the presence of chrysotile in the soil type ranker formed on massive serpentines occurring in the area of Bubanj Potok, a settlement located in the southern Belgrade environs, Serbia. Characterization of the ranker soil was conducted by scanning electron microscopy, X-ray diffraction, micro-Raman spectroscopy and transmission 57Fe Mössbauer spectroscopy. Scanning electron microscopy figures showed regular shaped smectite (montmorillonite particles, aggregates of chlorite, and elongated sheets of serpentines minerals antigorite. X-ray diffraction analysis confirmed the presence of detrital mineral quartz polymorph as well as minor amounts of other mineral species. Micro-Raman spectroscopy identified the presence of dominant minerals, such as montmorillonite, kaolinite, muscovite, gypsum, calcite, albite, amphiboles (hornblende/kaersutite and orthoclase. Important polymorph silica modifications of quartz, olivine (forsterite, pyroxene (enstatite/ferrosilite, diopside/hedenbergite, and serpentine (antigorite/lizardite/chrysotile were identified.

  9. Dose dependence and thermal stability of the thermoluminescence emission in inorganic dust from mint and camomile (United States)

    Gómez-Ros, J. M.; Furetta, C.; Cruz-Zaragoza, E.; Lis, M.; Torres, A.; Monsivais, G.


    The inorganic phase extracted from mint and camomile samples obtained from commercial products in Mexico was selected according to different grain sizes and exposed to 60Co gamma radiation at different doses in the range 0.5-12 kGy. Thermoluminescence (TL) glow curves show a single broad peak, centred around 175 °C for prompt readouts. X-ray diffraction analysis indicates the inorganic dust is mainly composed by quartz, Na,K-feldspars and amphiboles, which use to be characterized by TL emissions associated to continuous distribution of trapping centres. The high fading of the TL signal during the first days of storage at room temperature can be related to the shallowest part of the distribution while the deepest traps originate the asymptotic behaviour for longer storage times. The TL intensity also increases significatively with the grain size, being linear with the absorbed dose at least up to 10 kGy.

  10. Heterogeneity of exposure and attribution of mesothelioma: Trends and strategies in two American counties

    International Nuclear Information System (INIS)

    As mesothelioma risk has begun to decline in the United States, two trends are gaining relative importance. 'Legacy' exposures causing this disease are most important in locales having past asbestos industry, shipyards, and/or local distribution of asbestos amphibole-containing material as a result. 'Future' exposures are of particular concern in relation to so-called 'naturally occurring asbestos' (NOA) areas which include unequivocally asbestiform amphibole. In this paper, Jefferson Parish, Louisiana is used as an example of the first trend, and El Dorado County, California as an example of the second. Available tumor registry, epidemiology, historical and mineralogical data, and lung-retained fibre content are used as indicators of disease and exposure. Jefferson Parish, LA was chosen as the prototype of 'legacy' exposures on the basis of historical evidence of asbestos plants with known mesotheliomas in the workforce, known shipyards in the same area, EPA records of distribution of crocidolite-containing scrap to and remediation of over 1400 properties, NIOSH published data on mesothelioma by county, and exposure data including lung-retained fibre analyses in victims, where available. El Dorado, CA was chosen as the prototype of NOA amphibole exposures on the basis of tumor registry data, activity-based EPA sampling data in one area, and lung-retained fibre analyses in area pets, and future risk assessment based on tremolite-specific modelling in Libby, Montana and elsewhere. As expected, the legacy exposure area was high in mesothelioma incidence and mortality. Lung-retained fibre content confirms crocidolite exposures in exposed plant-workers and those exposed to crocidolite-containing scrap, and amosite in shipyard workers. In contrast, to date, cancer registry data in the NOA-amphibole ('future') county does not show a clear increase in incidence or mortality, but grouped county data from the area show a shift in higher incidence rates to the NOA areas and

  11. K/Ar ages from basal gneiss region

    International Nuclear Information System (INIS)

    K/Ar and 40Ar/39Ar geochronology of minerals from the Stadlandet region, Norway, is complicated by the presence of excess 40Ar in many samples. There is a correlation between excess 40Ar concentration and textural occurrence of samples. Amphiboles and micas closely accociated with eclogite pods are likely to contain significant concentrations of excess 40Ar, while samples from the country rocks are not. K/Ar and 40Ar/39Ar ages for hornblende from the country rocks suggest that post-metamorphic cooling through 5000C occured about 410 Ma ago, shortly after eclogite formation. Biotites containing no excess 40Ar cooled through 3000C about 370 Ma ago. A post-metamorphic cooling rate of about 50C/Ma can be inferred

  12. Shoshonitic intrusion magmatism in Pajeu-Paraiba belt: the Bom Jardim complex

    International Nuclear Information System (INIS)

    The Bom Jardim complex is a multi phase intrusion emplaced within the basement of the Pajeu-Paraiba belt, in the Borborema province, N.E., Brazil, during the Pan African (Brasiliano) orogeny, 600 Ma ago. The Bom Jardim complex is primarily composed of monzonites and syenites with subordinated granites. The major and trace elements geochemistry has established a shoshonitic affinity for the monzonite-syenite assemblages, whereas the granites are clearly of a high-K calc-alkaline character. The main geochemical trends determined for the complex are the result of fractionation of mainly amphibole, biotite, alkali feldspar ±clinopyroxene within the developing magmas. The enrichment in transition metal elements, LILE and high LILE/HSFE ratios, coupled with an initial Sr sup(87)/Sr sup(86) ratio of 0.70709 is consistent with a subduction related magma source. (author)

  13. 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)

  14. Are the Vinjamur rocks carbonatites or meta-limestones?

    International Nuclear Information System (INIS)

    New whole-rock rare earth element (REE) data for the metacarbonate rocks inter bedded with schists at Vinjamur in the Nellore schist belt of Andhra Pradesh, show low total REE contents (σ9-128 ppm) that are inconsistent with an igneous carbonatitic origin but which correspond more closely with a sedimentary limestone origin. The REE data of these rocks however, do not give absolute discrimination between marbles of meta-limestone and metacarbonatite origin. Micro-probe analytical data give better discrimination, and the chemical compositions of the calcite, micas, amphibole, plagioclase, apatite, monazite and staurolite in the Vinjamur marbles give strong and consistent evidence of a metamorphosed sedimentary rather than an igneous origin. (author). 35 refs., 7 figs., 9 tabs

  15. Moessbauer study of natural iron-oxide complexes

    International Nuclear Information System (INIS)

    Typical Fe-oxide complex assemblage in rock samples taken from Lake Victoria Goldfield in Tanzania was studied using Moessbauer spectroscopy between room temperature and 4.2 K. The room temperature Moessbauer spectrum of a typical rock sample from the region is a mixture of two-line patterns and a six-line pattern. At 200 K the two-line pattern starts to develop into a rather asymmetric, broad width six-line pattern which at 4.2 K has hyperfine field, B82, of about 50 T, δ = -0.20 mm/s and δ= 0.24 mm/s. The analysis of the 57Fe-Moessbauer spectra shows that the rock sample is composed of hexagonal pyrrhotite, amphibole silicate and α-FeOOH. Details of the characterisation of the phases of the Fe-oxide complex, α-FeOOH is the basis of the report

  16. Dating blueschist metamorphism: a combined /sup 40/Ar//sup 39/Ar and electron microprobe approach

    Energy Technology Data Exchange (ETDEWEB)

    Sisson, V.B.; Onstott, T.C.


    /sup 40/Ar//sup 39/Ar and electron microprobe examination of blueschist samples from the Iceberg Lake schist, southern Alaska suggest that phengite inclusions are the source of /sup 40/Ar in crossite. Because such fine-grained inclusions may be susceptible to argon loss, caution should be exercised in interpreting K-Ar ages from this phase, and possibly other low-K amphiboles from blueschist suites. The estimated blocking temperature for phengite in the matrix (314/sup 0/ to 450/sup 0/C), however, is close to the estimated peak metamorphic temperatures (325/sup 0/ +- 50/sup 0/C), suggesting that phengite /sup 40/Ar//sup 39/Ar plateau dates may coincide closely with the time of blueschist metamorphism.

  17. Short fiber tremolite free chrysotile mesothelioma cohort revealed. (United States)

    Egilman, David; Bird, Tess


    In 1995, Dell and Teta published a cohort mortality study of asbestos molding compound workers at a Union Carbide Corporation (UCC) plastics manufacturing plant in Bound Brook, New Jersey. They reported that the factory workers were exposed to "asbestos (mostly chrysotile)," implying that the asbestos used at the Bound Brook plant occasionally contained amphiboles. However, UCC statements and testimony from recent litigation indicate that the Bound Brook plant exclusively used short fiber chrysotile asbestos. These recent documents also point to lower exposures than those reported by Dell and Teta. This chrysotile-only cohort should be included in analyses of chrysotile potency. Am. J. Ind. Med. 59:196-199, 2016. © 2016 Wiley Periodicals, Inc. PMID:26725926

  18. A New Type of Kelyphite Produced by Isochemical Breakdown of Garnet, Discovered from the Czech Moldanubian Zone (United States)

    Obata, M.; Ozawa, K.; Naemura, K.; Ueda, T.


    Kelyphite is a fine-grained, mineral intergrowth developed around garnet in many mafic and ultramafic rocks of high-pressure origin. Typical mineral assemblage of kelyphites developed in garnet peridotites is Opx+Cpx+spinel ±amphibole, which has been interpreted to be a reaction product between garnet and olivine (Kushiro and Yoder, 1966), which is referred to as kelyphite I. In general, these kelyphites are not isochemical to mother garnet but a significant gain of Mg and loss of Al occur with respect to original garnets (e.g. Obata, 2011). We found, probably for the first time in the world, a new type of kelyphite (named kelyphite II) that appears to have been formed by an isochemical breakdown of garnet inside kelyphite I in a garnet peridotite from the Czech Moldanubian Zone. The garnet peridotite had once equilibrated at 2.3-3.5 GPa, 850-1030°C and were partially re-equilibrated in the spinel-lherzolites facies as it ascended and was incorporated into a thickened lower continental crust (Naemura et al., 2009). The temperature of the kelyphite I formation has been estimated to be 730-770°C by applying two-pyroxene geothermometer. The kelyphite II is much finer-grained and darker-colored than kelyphite I and shows a very straight lamellar structure consisting of Opx, spinel and plagioclase (anorthite), in which spinel occur exclusively within the Opx lamella (less than 1 micron thickness). Furthermore, the kelyphite II is typically separated from adjacent garnet by a thin hydrous zone (10 to 20 micron width) that consists of amphibole and spinel-like fine lamella (named kelyphite III), the bulk of which contains more Ca and Na (and therefore less Mg and Fe) than the garnet. The transitional boundary between the kelyphite I and kelyphite II areas (typically of hundreds of microns width) may be divided into several mineral zones of distinct mineral assemblages that all contain Ca-amphibole (pargasitic hornblende). Microprobe analyses revieled that Opx in

  19. Poly-view Analysis on Endogenous Innovation and Corporation's Selection of Innovation Patterns

    Institute of Scientific and Technical Information of China (English)

    TIAN Hai-feng; LI Kai


    Today, there are still some amphibolous understanding on the concepts of endogenous innovation and its three patterns in academia field. Grasping the intension and extension of these concepts will contribute to direct the innovation undertakers engaging innovation and the governments establishing innovation system. In order to achieve such aims, we firstly introduced the concept of endogenous innovation and its three patterns. Secondly, this paper established a concept model to describe the typical route of a technology's forming. Based on this model, we went deep into analysis on original innovation, integrative innovation, and re-innovation after digesting the introduced technology from different views. Through these analyses, we also discussed which kind of innovation is suitable for different corporations. In the last part of this paper, we summarized our main conclusions and gave some suggestions to the corporations and governments.

  20. [Asbestos import in Italy: the transit through Livorno harbour from 1957 to 1995]. (United States)

    Nemo, Alessandro; Boccuzzi, Maria Teresa; Silvestri, Stefano


    This work aims to describe quantities, type of packaging and geographical area of origin of the asbestos fibres unloaded in Livorno harbour between 1957 and 1995. Historical data, available for this period, were collected from Il Messaggero Marittimo, a periodical journal dealing with Livorno harbour activities. Collaboration between the local Health and Safety Unit (ASL 6) and the Institute for Study and Prevention of Cancer (ISPO), both Regional Institutions of the National Health Service, made it possible to carry out this work. The computation of the collected data for the whole period allows the description of the quantities, year by year and the assessment of the percentage imported through Livorno on the total tonnage imported in Italy during the same period. The detection of the geographical areas of origin allowed to estimate the quantities subdivided by type of fibre (serpentine/amphiboles). These results will help the historical assessment of occupational asbestos exposure of the Livorno dockers. PMID:19585878

  1. Anorogenic peralkalic granites and associated volcanics from Northwestern part of Indian Peninsular Shield

    International Nuclear Information System (INIS)

    The cauldron associated Siwana peralkalic granites and associated silic volcanic rocks of Malani igneous suite are classified as anorogenic and are emplaced in a within plate setting at high crustal levels. These rocks are characterized by relatively high alkali contents, low Ca O and high Fe O(t)/Mg O ratios. The major element chemistry is reflected in the mineralogy by the occurrence of alkali-rich amphiboles and pyroxenes. Trace element abundance, particularly elevated concentration of high-field strength cations are distinctive. A possible petrogenetic model of low degree of crustal partial melting under anhydrous conditions of an enriched (in LILE and HFSE) lower crust is proposed. The result of preliminary isotopic studies on these rocks are conflicting and provide a scope for further studies. (author)

  2. Heterogeneity of exposure and attribution of mesothelioma: Trends and strategies in two American counties

    Energy Technology Data Exchange (ETDEWEB)

    Case, B W [Department of Pathology and School of Environment, McGill University, Montreal, Quebec (Canada); Abraham, J L, E-mail: [Department of Pathology, SUNY Upstate Medical University, Syracuse, NY 13210 (United States)


    As mesothelioma risk has begun to decline in the United States, two trends are gaining relative importance. 'Legacy' exposures causing this disease are most important in locales having past asbestos industry, shipyards, and/or local distribution of asbestos amphibole-containing material as a result. 'Future' exposures are of particular concern in relation to so-called 'naturally occurring asbestos' (NOA) areas which include unequivocally asbestiform amphibole. In this paper, Jefferson Parish, Louisiana is used as an example of the first trend, and El Dorado County, California as an example of the second. Available tumor registry, epidemiology, historical and mineralogical data, and lung-retained fibre content are used as indicators of disease and exposure. Jefferson Parish, LA was chosen as the prototype of 'legacy' exposures on the basis of historical evidence of asbestos plants with known mesotheliomas in the workforce, known shipyards in the same area, EPA records of distribution of crocidolite-containing scrap to and remediation of over 1400 properties, NIOSH published data on mesothelioma by county, and exposure data including lung-retained fibre analyses in victims, where available. El Dorado, CA was chosen as the prototype of NOA amphibole exposures on the basis of tumor registry data, activity-based EPA sampling data in one area, and lung-retained fibre analyses in area pets, and future risk assessment based on tremolite-specific modelling in Libby, Montana and elsewhere. As expected, the legacy exposure area was high in mesothelioma incidence and mortality. Lung-retained fibre content confirms crocidolite exposures in exposed plant-workers and those exposed to crocidolite-containing scrap, and amosite in shipyard workers. In contrast, to date, cancer registry data in the NOA-amphibole ('future') county does not show a clear increase in incidence or mortality, but grouped county data from the area show a

  3. 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.

  4. Potassic/ultrapotassic magmatism pos a tardi-orogenic (associated to subduction) in the western of Bahia: batolite monzo-syenitic from Guanambi-Urandi and the syenites from Correntina, Brazil

    International Nuclear Information System (INIS)

    The western portion of Bahia State is characterized by polimetamorfic rocks (granulites and gneissic-migmatitics) intruded by great volume of undeformated monzonitic and syenitic rocks. Tectonically, this region is interpreted as an Early Proterozoic mobile belt. Clynopiroxene-syenitic rocks are more conspicuous in the western side of the Sao Francisco river (Correntina Syenites), while amphibole-mica monzonitic and syenitic rocks (Guanambi-Urandi Batholith) occur southeastward. The Guanambi-Urandi, a 6000 km2 batholith, shows a slight sigmoidal shape whereas the Correntina Syenites outcrop along the valleys where the Phanerozoic cover difficults the mapping. The existing geochronological data reveal a contemporaneity between these set of rocks, about 2 Ga. Our geochemical data point to potassic plutonism, with high Ba, Sr, REE and moderate Ti, Zr, Nb and Y. The above characteristics suggest an orogenic environment, probably linked a subduction zone. (author)

  5. Thermal modeling of pluton emplacement and associated contact metamorphism:Parashi stock emplacement in the Serranía de Jarara (Alta Guajira, Colombia

    Directory of Open Access Journals (Sweden)

    Zuluaga C. Carlos A.


    Full Text Available

    In the northernmost portion of the Serrania de Jarara (Alta Guajira, Colombia, low - medium grade metamorphic rocks from the Etpana Metamorphic Suite were thermally affected by emplacement of a small calc-alkaline intrusion (Parashi Stock. Detailed petrographic analysis in collected rock samples across the NE and NW plutonic contacts show occurrences of textural and mineralogical changes in the country rock fabric that evidence contact metamorphism overprinting regional metamorphism of the Etpana Suite. These changes include growth of andalusite (chiastolite, calcic clinopyroxeneand amphibole porphyroblast crosscutting Sn+1 metamorphicfoliation. Hornblende-plagioclase barometry (ca. 3.1 kbar and cooling models for the stock show maximum time temperature evolution in the country rock at the interpreted depth of intrusion (ca. 11 km and help to evaluate the behavior of the country rock with the changing local geotherm.

  6. 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.

  7. Petrography and geochemistry of metamafic rocks intercalated in gneisses from Goiás Magmatic Arc, region of Indiara (GO

    Directory of Open Access Journals (Sweden)

    Guillermo Rafael Beltran Navarro


    Full Text Available In Indiara region (GO, dozens of metamafic rocks lenses of various dimensions (metric to kilometric occur, intercalated in gneisses of the Goiás Magmatic Arc and oriented according to the direction of the main foliation (Sn. These lenses consist of amphibolite (amphibole schists and amphibolites, have chemical compositions of sub-alkaline basalts to andesitic basalts and sub-alkaline tholeiitic affinity. The distribution of major and trace elements, as well as rare earth elements (REE, suggests that these rocks are derived from a source with similar geochemical signature. The analyzed rocks are enriched in large ion litophile elements (Cs, Rb, Ba, K, Th and U in relation to elements of high field strength (Nb, Ta, Zr, Hf and Y and in relation to REE, Sr, P and Ti, showing weak to medium negative anomalies of Nb, Ta and P and suggesting that these rocks were generated in a magmatic arc environment.

  8. The mafic dyke swarm of Uaua (Brazil): geological and petrographical aspects

    International Nuclear Information System (INIS)

    The Uaua mafic dike swarm stands out as one of the most extensive swarms in the Sao Francisco craton. These dikes crop out around the town of Uaua (State of Bahia) and to the east near the Rio Capim greenstone belt. The dikes intrude the Archean basement which is composed of medium-to high-grade gneisses and migmatites. Table 1 shows the geochronological results for basement rocks, which have yielded ages between 2,730-3,016 m.y. (Tb-Sr,whole rock isochron) indicating a Late Archean evolution for these rocks. On the other hand, available 40 Ar-39 Ar (biotite) and K-Ar (amphibole) determinations for basement rocks yield Early Proterozoic ages, the result of overprinting of the Transamazonico orogenic cycle. (author)

  9. Heterogeneity of exposure and attribution of mesothelioma: Trends and strategies in two American counties (United States)

    Case, B. W.; Abraham, J. L.


    As mesothelioma risk has begun to decline in the United States, two trends are gaining relative importance. "Legacy" exposures causing this disease are most important in locales having past asbestos industry, shipyards, and/or local distribution of asbestos amphibole-containing material as a result. "Future" exposures are of particular concern in relation to so-called "naturally occurring asbestos" (NOA) areas which include unequivocally asbestiform amphibole. In this paper, Jefferson Parish, Louisiana is used as an example of the first trend, and El Dorado County, California as an example of the second. Available tumor registry, epidemiology, historical and mineralogical data, and lung-retained fibre content are used as indicators of disease and exposure. Jefferson Parish, LA was chosen as the prototype of "legacy" exposures on the basis of historical evidence of asbestos plants with known mesotheliomas in the workforce, known shipyards in the same area, EPA records of distribution of crocidolite-containing scrap to and remediation of over 1400 properties, NIOSH published data on mesothelioma by county, and exposure data including lung-retained fibre analyses in victims, where available. El Dorado, CA was chosen as the prototype of NOA amphibole exposures on the basis of tumor registry data, activity-based EPA sampling data in one area, and lung-retained fibre analyses in area pets, and future risk assessment based on tremolite-specific modelling in Libby, Montana and elsewhere. As expected, the legacy exposure area was high in mesothelioma incidence and mortality. Lung-retained fibre content confirms crocidolite exposures in exposed plant-workers and those exposed to crocidolite-containing scrap, and amosite in shipyard workers. In contrast, to date, cancer registry data in the NOA-amphibole ("future") county does not show a clear increase in incidence or mortality, but grouped county data from the area show a shift in higher incidence rates to the NOA areas and

  10. 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

  11. 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.

  12. Re-evaluation of Non-regulatory Asbestos Group Minerals for Regulatory Agencies (United States)

    Dogan, M.; Dogan, A.


    There are established rules and regulations for some asbestos group minerals - amphibole group minerals of actinolite, amosite, anthophyllite, crocidolite, tremolite; and serpentine group minerals of chrysotile- called "regulatory". There are also "non-regulatory" naturally occurring asbestos (NOA) group minerals as constituent of rocks and soil, including richterite, winchite, fluoro-edenite, balangeroite, carlosturanite, gageite, arfvedsonite, and magnesio-arfvedsonite. Strong evidences for carcinogenicity of these NOA minerals in later cohorts of cancer patients demonstrated the risks associated with these minerals. In addition, although the chrysotile asbestos regulated by some organizations such as WHO, World Trade Organization, United Nations, US EPA, International Labour Organization, and EU Countries; however, controversies still continue surrounding the use of chrysotile. Determinations of polymineralic fibrous veins, mixed particles, amphibole cleavage fragments, and genetic predisposition are also important issues (i.e. Dogan et al., 2006).Therefore, accurate characterizations of chemical composition, morphology, structure, and defects are necessary in order to find out mechanism(s) of carcinogenicity of all asbestos group minerals. Calculation methods of chemical composition are still under debate because of assumption of no vacancies at any sites and intergrowth of minerals. Substitution(s) may cause deviations from the ideal chemical formula and wide variations in chemical compositions. Detail morphological and chemical quantification of individual asbestos group minerals in micro- and nano-scale may help to evaluate its true carcinogenetic mechanism(s), and consequently prevention and possibly treatment of related diseases. we propose that nonregulatory asbestos minerals and the chrysotile should be re-evaluated. The amount of fibers inhaled, in terms of weight percent and number, need also be re-evaluated by mineralogists. Finally, Regulatory

  13. Tracing slab dehydration using neon and argon isotope systematics in high pressure minerals (United States)

    Smye, A.; Jackson, C.; Parman, S. W.; Kelley, S. P.


    Mounting evidence suggests that noble gases are transported from Earth's surface reservoirs back into the mantle during subduction of oceanic lithosphere [e.g. 1]. Recent experiments [2] show that noble gases are relatively soluble in ring-structured minerals, such as amphibole, highlighting the potential for hydrated oceanic crust to control the input flux of noble gases into subduction zones. However, it is unclear whether the return flux of noble gases is controlled by mineral solubility alone or whether diffusive loss during subduction is important. Here, we address this issue by combining the solubility data with recently acquired He and Ne [3], and previously published Ar [4], diffusivity measurements in amphibole to parameterize a diffusion-solubility model, simulating noble gas fractionation during subduction. The model predicts that the light noble gases, He and Ne, are efficiently extracted from hot slabs at depths shallower than 50 km, whereas Ar and, by implication, Kr and Xe are retained in the slab past sub-arc depths. Conversely, cold slabs with low porosity volume fractions have the potential to recycle Ne. Our modelling shows that the Ne/Ar elemental ratio of slab minerals is strongly influenced by thermal regime and grain boundary porosity. We test these predictions against a new laser fusion dataset of Ne and Ar isotopic measurements in high-pressure minerals from a suite of exhumed high-pressure rocks that have experienced varying degrees of subduction and dehydration. Refs: [1] Holland, G. and Ballentine, C. (2006). Nature 441, 186-191. [2] Jackson et al. (2013). Nat.Geosci. 6, 562-565. [3] Jackson et al. submitted. [4] Harrison, T.M. (1981). CMP 78, 324-331.

  14. 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

  15. Bimodal tholeiitic-dacitic magmatism and the Early Precambrian crust (United States)

    Barker, F.; Peterman, Z.E.


    Interlayered plagioclase-quartz gneisses and amphibolites from 2.7 to more than 3.6 b.y. old form much of the basement underlying Precambrian greenstone belts of the world; they are especially well-developed and preserved in the Transvaal and Rhodesian cratons. We postulate that these basement rocks are largely a metamorphosed, volcanic, bimodal suite of tholeiite and high-silica low-potash dacite-compositionally similar to the 1.8-b.y.-old Twilight Gneiss - and partly intrusive equivalents injected into the lower parts of such volcanic piles. We speculate that magmatism in the Early Precambrian involved higher heat flow and more hydrous conditions than in the Phanerozoic. Specifically, we suggest that the early degassing of the Earth produced a basaltic crust and pyrolitic upper mantle that contained much amphibole, serpentine, and other hydrous minerals. Dehydration of the lower parts of a downgoing slab of such hydrous crust and upper mantle would release sufficient water to prohibit formation of andesitic liquid in the upper part of the slab. Instead, a dacitic liquid and a residuum of amphibole and other silica-poor phases would form, according to Green and Ringwood's experimental results. Higher temperatures farther down the slab would cause total melting of basalt and generation of the tholeiitic member of the suite. This type of magma generation and volcanism persisted until the early hydrous lithosphere was consumed. An implication of this hypothesis is that about half the present volume of the oceans formed before about 2.6 b.y. ago. ?? 1974.

  16. 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.

  17. K-Ar geochronology of mafic dyke swarms from the meridional part of Sao Francisco craton and implications on tectonic context

    International Nuclear Information System (INIS)

    The southern region of the Sao Francisco Craton is made up of gneissic-granitoid terranes (mainly of amphibolite facies) associated with supracrustals, which can be separed into two crustal provinces, the oldest formed during the Archean (3-2-2.6 Ga.), and the youngest in the Early Proterozoic (2.4-2.0 Ga.). Mafic dyke swarms inject the basement complexes in the area west of Belo Horizonte city, but not the Late proterozoic Bambui sedimentary cover. These dykes show NNW, NW, WNW, NNE and ENE trends and are of anorogenic character. Most dykes are tholeiitic in composition. Metamorphic recrystallization at greenschist to amphibolite facies as well as minor hidrothermal and/or deuteric transformations are characteristics in the majority of the these dykes. About sixty K/Ar determinations have been performed on plagioclases, amphiboles and whole rocks. They are interpretated combining the use of K/Ar diagrams and histogram, and according to the crustal evolution proposed for the craton. The available radiometric data suggest that the main period of mafic intrusions took place in the Early proterozoic as supported by the apparent ages on amphiboles. However, the beginning of the Middle Proterozoic (1.7-1.5 Ga.) probably corresponds to a period of tensional tectonics as well. On the other hand, most ages obtained on plagioclases and whole rocks, can be associated with Late Proterozoic processes of argon gain or loss. The results are tectonicaly associated with crustal rifting of the continental mass. This two radiometric groupings are characteristic for the evolution of the Early proterozoic crustal provine and of the Mid-Proterozoic intracratonic Espinhaco System respectively. The youngest Late Proterozoic apparent ages associated with the reflections of the contemporaneous evolution of the Braziliano marginal mobile belt which is also suggested by the partial resetting of the K/Ar ages of basement rocks within the eastern part of the Sao Francisco Craton. (author)

  18. LA-ICP-MS zircon U-Pb dating and phenocryst EPMA of dikes, Guocheng, Jiaodong Peninsula: Implications for North China Craton lithosphere evolution

    Institute of Scientific and Technical Information of China (English)


    Widespread dike swarm, including diorite-, monzonite-porphyry and lamprophyre, intruded in the al- tered breccia gold deposits along basin marginal faults, Guocheng, Jiaodong Peninsula. Petrography exhibits biotite enclaves in amphibole phenocrysts and the presence of acicular apatites in these dikes. Electron probe microanalyses (EPMA) show that the amphibole and clinopyroxene phenocryst’s mantle in diorite porphyry and lamprophyre respectively has sharply higher MgO (Mg#) and Cr2O3 contents in contrast to their cores. The plagioclase phenocryst in monzonite porphyry has reverse zoning. These results indicate that the magma mixing between mantle-derived mafic and crust-derived felsic magmas occurred in the original process of the dikes. Zircon cathodoluminescence (CL) images show well-developed magmatic oscillatory zones and the acquired LA-ICP-MS zircon U-Pb weighted mean 206Pb/238U ages are 114±2 Ma (MSDW=1.5) for monzonite porphyry (GS1) and 116±1 Ma (MSDW=0.8) for diorite porphyry (GS2), respectively. Earlier magmatic events in the northwest Jiaodong Peninsula represented by some inherited or captured zircons also occur in these dikes. Magmatic zircons from GS1 and GS2 display consistent chondrite-normalized REE patterns and Nb/Ta values, implying that they may share a similar or same source. HREE enrichment and obvious negative Eu anomalies of these zircons preclude garnet presented in their source. Our results, combined with preciously pub- lished data, indicate that dike intrusion and gold mineralization among quartz vein, altered tectonite and altered breccia gold deposits are broadly contemporaneous throughout the Jiaodong Peninsula. These also imply that the intensive crust-mantle interaction and asthenospheric underplating had oc- curred in the Early Cretaceous in the Peninsula, together with foundering of lower crust in the early Mesozoic, representing the different stages of lithosphere thinning in the North China Craton (NNC).

  19. LA-ICP-MS zircon U-Pb dating and phenocryst of dikes, Guocheng, Jiaodong Peninsula: Implications for North China Craton lithosphere evolution

    Institute of Scientific and Technical Information of China (English)

    TAN Jun; WEI JunHao; GUO LingLi; ZHANG KeQing; YAO ChunLiang; LU JianPei; LI HongMei


    Widespread dike swarm, including diorite-, monzonite-porphyry and lamprophyre, intruded in the altered breccia gold deposits along basin marginal faults, Guocheng, Jiaodong Peninsula. Petrography exhibits biotite enclaves in amphibole phenocrysts and the presence of acicular apatites in these dikes.Electron probe microanalyses (EPMA) show that the amphibole and clinopyroxene phenocryst's mantle in diorite porphyry and lamprophyre respectively has sharply higher MgO (Mg#) and Cr203 contents in contrast to their cores. The plagioclase phenocryst in monzonite porphyry has reverse zoning. These results indicate that the magma mixing between mantle-derived mafic and crust-derived felsic magmas occurred in the original process of the dikes. Zircon cathodoluminescence (CL) images show well-developed magmatic oscillatory zones and the acquired LA-ICP-MS zircon U-Pb weighted mean 206pb/238U ages are 114±2 Ma (MSDW=1.5) for monzonite porphyry (GS1) and 116±1 Ma (MSDW=0.8) for diorite porphyry (GS2), respectively. Earlier magmatic events in the northwest Jiaodong Peninsula represented by some inherited or captured zircons also occur in these dikes. Magmatic zircons from GSl and GS2 display consistent chondrite-normalized REE patterns and Nb/Ta values, implying that they may share a similar or same source. HREE enrichment and obvious negative Eu anomalies of these zircons preclude garnet presented in their source. Our results, combined with preciously published data, indicate that dike intrusion and gold mineralization among quartz vein, altered tectonite and altered breccia gold deposits are broadly contemporaneous throughout the Jiaodong Peninsula.These also imply that the intensive crust-mantle interaction and asthenospheric underplating had occurred in the Early Cretaceous in the Peninsula, together with foundering of lower crust in the early Mesozoic, representing the different stages of lithosphere thinning in the North China Craton (NNC).

  20. Microwave irradiation of asbestos containing materials

    International Nuclear Information System (INIS)

    Full text: Dangerous wastes, i.e. fly ashes, nuclear waste, asbestos containing materials, can be regarded as multi-component materials having a wide range of compositions, and usually it is the presence of only some of these components that makes all the mixture a product to be disposed of. Thus, a process allowing selective treatment of the 'unwanted' portion of the waste, and to do this volumetrically, could represent an enormous advantage in terms of time and money, especially as far as materials presenting low thermal conductivity are concerned. This is the case of asbestos containing materials, which are mixtures of gypsum, cement, and minor polymeric components, whose inertitazion requires long heat treatments at temperature higher than the decomposition temperature of amphiboles, the dangerous mineral fibre in commercial items. Shorter heating time under 2.45 GHz irradiation, have suggested that the selectivity of microwave radiation for OH groups contained in the crystalline amphibole can be exploited to inertize asbestos containing materials. The experiments were performed either on small samples in closed multimode cavity or on large pieces under an open applicator. In both cases, depending on the output power and on sample positioning and lining, it was possible to lead the samples to complete inertisation, or, prolonging the thermal treatment, to vitrification. The treated samples are constituted mainly of enstatite, an harmless magnesium silicate, which could then be inserted as secondary raw materials in the body composition of many ceramic materials, like tiles and bricks. The open applicator with a remote control panel allowed the treatment of portion of contamined soil, such as, for example, the ground surrounding asbestos mining and treatment installations. The maximum installed power, 18 kW, is higher than that used in closed cavities, and inevitably the same happens regarding power losses. Improvements of applicator design for power

  1. UHP kyanite eclogite associated with garnet peridotite and diamond-bearing granulite, northern Bohemian Massif (United States)

    Kotková, Jana; Janák, Marian


    Kyanite eclogites enclosed in garnet peridotites may provide important information on P-T evolution of orogenic peridotites in deep subduction and collision zones. Kyanite eclogite interlayered with garnet peridotite occurs in the borehole T-7, in the Saxothuringian basement of the northern part of the Bohemian Massif. This orogenic peridotite of mantle origin is associated with felsic granulites, which contain diamond as a consequence of deep subduction of the continental crust. Here, we report on the metamorphic evolution of kyanite eclogite, which shows a well-preserved peak-pressure mineral assemblage of garnet, omphacite, kyanite and phengite. Conventional geothermobarometry, average PT method and thermodynamic modelling constrain the metamorphic conditions of this assemblage up to 3.5-4.5 GPa at 900-1050 °C. Two compositional types of garnet, i.e., Mg-rich and Ca-rich, have been recognised. Thermodynamic modelling shows that the composition of Ca-rich garnet with XCa (0.35-0.37) in the core corresponds to stability of garnet at 3.5-4.5 GPa. Amphibole and zoisite are preserved as inclusions in garnet cores, and they are stable below 2.5 GPa, indicating that garnet grew at the expense of these phases at increasing P-T conditions during the prograde evolution of the rock. A post-peak metamorphism decompression and cooling are recorded by decrease of Ca-Eskola end-member in omphacite, drop in XMg and XGrs at garnet rim and a very restricted formation of pargasitic amphibole in the matrix. The absence of symplectites after omphacite in the investigated eclogite may be due to a very low content of quartz and possibly also fluid in the rock. Our study suggests that kyanite-bearing eclogite underwent UHP metamorphism as a consequence of subduction, together with interlayered garnet peridotite. Both rocks were incorporated into the subducted continental crust (diamond-bearing granulites) during the Variscan orogeny.

  2. Phase transition in the subducted oceanic lithosphere and generation of the subduction zone magma

    Institute of Scientific and Technical Information of China (English)

    WEI ChunJing; ZHANG YingHui


    Two metamorphic processes, I.e. Subsolidus dehydration and partial melting occurring in MORB, metasediments and peridotite of subducted oceanic lithosphere are discussed on the basis of available experimental work and phase equilibrium modeling. Phase diagrams of hydrous MORB show that in most cold subduction P-T (pressure-temperature) regimes a large portion of water in the basic layer has released below the onset of blueschist facies (< 20 km), and at a depth (60-70 km) of transition from lawsonite blueschist to lawsonite eclogite facies through glaucophane dehydration; only a smaller portion of water will escape from the slab through dehydration of lawsonite and chloritoid in the depth range suitable for arc magma formation; and a very small portion of water stored in lawsonite and phengite will fade into the deeper mantle. The role of amphibole for arc magma formation is still arguable. In cold subduction P-T regimes, the dehydration of chlorite and talc in Al-poor metasediments,and chloritoid and carpholite in Al-rich metapelites at a depth around 80-100 km will make some contributions to the formation of arc magma. Comparatively, dehydration of serpentine in hydrated peridotite occurs at depths of 120-180 km, playing an important role in the arc magmatism. Subduction of oceanic crust along warm P-T regimes will cross the solidi at a depth over 80 km, resulting in partial melting under fluid-saturated and fluid-absent conditions in the metasediments involving biotite and phengite, and in the basic rocks involving epidote and amphibole. The melt compositions of the basic crust are adakitic at pressures < 3.0 Gpa, but become peraluminous granitic at higher pressures.

  3. Zircon U-Pb age, Lu-Hf isotope, mineral chemistry and geochemistry of Sundamalai peralkaline pluton from the Salem Block, southern India: Implications for Cryogenian adakite-like magmatism in an aborted-rift (United States)

    Renjith, M. L.; Santosh, M.; Li, Tang; Satyanarayanan, M.; Korakoppa, M. M.; Tsunogae, T.; Subba Rao, D. V.; Kesav Krishna, A.; Nirmal Charan, S.


    The Sundamalai peralkaline pluton is one among the Cryogenian alkaline plutons occurring in the Dharmapuri Rift Zone (DRZ) of the Salem Block in the Southern Granulite Terrane (SGT) of India. Here we present zircon U-Pb age and Lu-Hf isotopic composition, mineral chemistry and geochemistry of the pluton to explore the petrogenesis and geodynamic implications. Systematic modal variation of orthoclase, Na-plagioclase, Ca-amphibole (ferro-edenite and hastingsite) and quartz developed quartz-monzonite and granite litho units in the Sundamalai pluton. Thermometry based on amphibole-plagioclase pair suggests that the pluton was emplaced and solidified at around 4.6 kbar pressure with crystallization of the major phases between 748 and 661 °C. Estimated saturation temperature of zircon (712-698 °C) is also well within this range. However, apatite saturation occurred at higher temperatures between 835 and 870 °C, in contrast with monazite saturation (718-613 °C) that continued up to the late stage of crystallization. Estimated oxygen fugacity values (log fO2: -14 to -17) indicate high oxidation state for the magma that stabilized titanite and magnetite. The magmatic zircons from Sundamalai pluton yielded a weighted mean 206Pb/238U age of 832.6 ± 3.2 Ma. Geochemically, the Sundamalai rocks are high-K to shoshonitic, persodic (Na2O/K2O ratio > 1), silica-saturated (SiO2:65-72 wt.%), and peralkaline in composition (aluminum saturation index, ASI aborted rifting along the DRZ generating the magma that crystallized the Sundamalai rocks. Age of this pluton is comparable with that of the other Cryogenian felsic alkaline plutons from Salem Block suggesting extensive rift-related magmatism at this time in the SGT.

  4. Evolution of the Mesozoic Granites in the Xiong'ershan-Waifangshan Region, Western Henan Province, China, and Its Tectonic Implications

    Institute of Scientific and Technical Information of China (English)

    HAN Yigui; ZHANG Shihong; Franco PIRAJNO; ZHANG Yuanhou


    Based on the new data of isotopic ages and geochemical analyses, three types of Mesozoic granites have been identified for the Xiong'ershan-Waifangshan region in western Henan Province: high-Ba-Sr I-type granite emplaced in the early stage (~160 Ma), I-type granite in the middle stage (~130 Ma) and anorogenic A-type granite in the late stage (~115 Ma).Geochemical characteristics of the high-Ba-Sr I-type granite suggest that it may have been generated from the thickened lower crust by partial melting with primary residues of amphibole and garnet. Gradual increase of negative Eu anomaly and Sr content variations reflect progressive shallowing of the source regions of these granites from the early to late stage. New 40Ar/39Ar plateau ages of the early-stage Wuzhangshan granite (156.0±1.1 Ma, amphibole) and middle-stage Heyu granite (131.8±0.7 Ma, biotite) are indistinguishable from their SHRIMP U-Pb ages previous published, indicating a rapid uplift and erosion in this region. The representative anorogenic A-type granite, Taishanmiao pluton, was emplaced at ~115 Ma. The evolution of the granites in this region reveals a tectonic regime change from post-collisional to anorogenic between ~160 Ma and ~115 Ma. The genesis of the early- and middle-stage I-type granites could be linked to delamination of subducted lithosphere of the Qinling orogenic belt, while the late-stage A-type granites represent the onset of extension and the end of orogenic process. In fact, along the Qinling -Dabie-Sulu belt, the Mesozoic granitoids in western Henan, Dabieshan and Jiaodong regions are comparable on the basis of these temporal evolutionary stages and their initial 87Sr/86Sr ratios,which may suggest a similar geodynamic process related to the collision between the North China and Yangtze cratons.

  5. Metamorphism and metasomatic alteration of an eclogite block in the Franciscan Complex near Mt. Hamilton, Diablo Range, California

    Energy Technology Data Exchange (ETDEWEB)

    Herrington, K.L.; Cloos, M.


    Petrographic, microprobe and whole rock analysis of a rounded, 10 m eclogite that is typical of the rare high-grade blocks found in the Franciscan mud-matrix melange terranes show the block also underwent high-pressure/lower-temperature hydration and metasomatic alteration. Fe-Mg partitioning between garnet and omphacite and experimental phase relations indicate initial recrystallization at 5007 kb. Hydration of the block is evident because towards the margins omphacite is replaced by brown calcic-amphibole + white mica and by blue sodic-amphibolte + white mica. During hydration and rind formation, the block lost SiO/sub 2/, CaO, and Na/sub 2/O and gained K/sub 2/O. Parts of the rind are replaced by tremolite + chlorite. Cavities lined with radiating, euhedral sodic-amphibole + aragonite and pseudomorphic textural relationships show the block was not penetratively deformed after recrystallization. The tectonic history of the eclogite block can be explained as follows: The eclogite is a fragment of the top of the descending plate that was imbricated with hot ultramafics at the base of the overriding plate to form a metamorphic aureole at 20+ km-depth during the initial stages of Franciscan subduction. The overriding plate and imbricated aureole cooled with continued convergence. The blueschist assemblage and rind formed as waters migrated upwards into the aureole from underlying subducting or accreted sediments. Aragonite and the lack of alterations characteristic of greenschist-facies conditions indicates either synsubduction or very rapid post-subduction uplift.

  6. Asbestos-related diseases of the lungs and pleura: uses, trends and management over the last century. (United States)

    Becklake, M R; Bagatin, E; Neder, J A


    Asbestos is a descriptive term for a group of naturally occurring minerals known to mankind since ancient times. The main types of asbestos (chrysotile, and the amphiboles crocidolite and amosite) differ in chemical structure, biopersistence in human tissue and toxicity. Commercial exploitation, with little thought for environmental controls, increased over the twentieth century, particularly after World War II, to accommodate globalisation and the demands of the world's burgeoning cities. As its ill-health effects, both non-malignant (fibrosis of the lungs or asbestosis; pleural effusion, plaques and thickening) and malignant (mesothelioma, lung and other cancers), became evident, public pressure rose to control its use. The last decades of the last century saw decreases in exposure and rates of asbestosis in industrialised and in some less-industrialised countries, where pleural plaques and malignant mesothelioma are currently the most frequent manifestations of asbestos exposure. Longer follow-up of asbestos-exposed cohorts in mining and manufacturing has also strengthened the evidence of a fibre gradient in toxicity, with chrysotile exhibiting lower toxicity than the amphiboles, and amosite lower toxicity than crocidolite. The last decades of the twentieth century saw stabilisation and/or declines in mesothelioma rates in several industrialised countries. In less-industrialised countries, data on disease are sparse, exposure generally high and rates may peak in the future. Management of asbestos-related disease in the workplace requires collaboration between workers and unions (responsible for monitoring workplace dust levels, to which they must have access) and companies (responsible for engineering controls), reinforced by appropriate government regulations and by community support. PMID:17394680

  7. Geology and Chemical Characterization of the Ultrapotassic Peralkaline Magmatism of the Manaíra-Princesa Isabel Dike Swarm, Borborema Provine

    Directory of Open Access Journals (Sweden)

    Maria Helena Bezerra Maia de Hollanda


    Full Text Available The Manaíra-Princesa Isabel dike swarm forms one of the most expressive examples of Neoproterozoic (c. 600 Maperalkaline magmatism in the Borborema Province (NE Brazil. It consists of about a hundred NE-trending bodies intrusivein older, Neoproterozoic porphyritic granites (Princesa Isabel and Tavares plutons, and orthogneisses and low-grademetasediments of the Eo-neoproterozoic Riacho Gravatá complex. The dike swarm includes mostly silica-saturated syenites,with potassic to ultrapotassic, peralkaline affinity, containing microcline and sodic amphibole ± pyroxene as the mainmineral assemblage. Amphibole is dominantly Mg-riebeckite (Manaíra, Princesa Isabel and Tavares sub-swarms, whereaspyroxene is mainly aegirine-augite (Manaíra and Tavares sub-swarms. A minor set of dikes from this swarm is slightlymetaluminous with Mg-biotite as the major mafic phase. Geochemical and isotopic signatures indicate strong enrichmentin incompatible elements (Rb, Ba, K, Th, U, in association with a negative Nb anomaly, and strongly radiogenic 87Sr/86Srand 143Nd/144Nd (= negative εNd values initial ratios. These features suggest a common source, which was probably an enriched lithospheric mantle reservoir, chemically modifi ed by an ancient subduction component inferred to be Paleoproterozoic fromTDM model ages. Conversely, Pb isotopic ratios lower than average crustal values indicate the influence of a non-radiogenic componentinteracting with the enriched mantle source. A SHRIMP U-Pb age of c. 600 Ma obtained for the Manaíra-Princesa Isabel dike swarmdefi nes an important crustal exhumation period which was relatively synchronous with intensive tectonomagmatic activity related tothe Brasiliano orogeny, which occurred in distinct structural domains within the Transverse Zone of the Borborema Province.

  8. A comparison of heavy mineral assemblage between the loess and the Red Clay sequences on the Chinese Loess Plateau (United States)

    Peng, Wenbin; Wang, Zhao; Song, Yougui; Pfaff, Katharina; Luo, Zeng; Nie, Junsheng; Chen, Wenhan


    QEMSCAN-based (Quantitative Evaluation of Minerals by Scanning Electron Microscopy) heavy mineral analysis has recently been demonstrated an efficient way to allow a rapid extraction of provenance information from sediments. However, one key issue to correctly obtain a provenance signal using this technique is to clearly separate effects of diagenetic alteration on heavy minerals in sediments, especially in fine-grained loess. Here we compare heavy mineral assemblages of bottom Quaternary loess (L33) and upper Pliocene Red Clay of three sites on the Chinese Loess Plateau (CLP). Two sites (Chaona and Luochuan) with similar modern climate conditions show similar heavy mineral assemblages but contain much less of the unstable heavy mineral amphibole than the drier Xifeng site. This result provides strong evidence supporting that climate-caused diagenesis is an important factor controlling heavy mineral assemblages of fine-grained loess. However, heavy mineral assemblages are similar for loess and paleosol layers deposited after 0.5 Ma on the Chinese Loess Plateau regardless of climate differences, suggesting that time is also a factor controlling heavy mineral assemblages of loess and Red Clay. Our high resolution sampling of the upper Miocene-Pliocene Chaona Red Clay sequence reveals similar heavy mineral compositions with a minor amphibole content, different from the drier Xifeng site results of the same age. This result indicates that the monsoonal climate pattern might have been maintained since the late Miocene. Furthermore, it indicates that the heavy mineral method is promising in tracing provenance for sites northwest of the Xifeng site on the Loess Plateau.

  9. Mineral fibres and health

    International Nuclear Information System (INIS)

    The use of inorganic fibrous materials is a comparatively new phenomenon and was uncommon before the Industrial Revolution. Humans evolved in a comparatively fibre-free environment and consequently never fully developed the defence mechanisms needed to deal with the consequences of inhaling fibres. However, the urban environment now has an airborne fibre concentration of around 1 f.l-1, which is a tenfold increase on the natural background. Any sample of ambient air collected indoors or outdoors will probably contain some mineral fibres, but there is little evidence that these pose any risk to human health. They come from asbestos used in brakes, glass and mineral wools used as insulation and fire proofing of buildings, gypsum from plaster and a variety of types from many sources. Few of these have the potential to do any harm. Asbestos is the only fibre of note but urban levels are insignificant compared to occupational exposures. When the health of cohorts occupationally exposed to the several types of asbestos is studied the problem can be put into perspective. Studies of workers in the chrysotile industry exposed to much higher dust levels than in a factory today show no excess lung cancer or mesothelioma. By comparison those living near crocidolite mines, let alone working in them, may develop asbestos-related disease. As always, dose is the critical factor. Chrysotile is cleared from the lungs very efficiently, only the amphiboles are well retained. The only real health problem comes from the earlier use of asbestos products that may now be old, friable and damaged and made from amphibole or mixed fibre. If though, these are still in good condition, they do not pose a health problem. Asbestos-related diseases are very rare in those not occupationally exposed. Where they exist exposure has nearly always been to crocidolite. (author)

  10. The Age and Geodynamic Evolution of the Metamorphic sole rocks from Izmir-Ankara-Erzıncan suture zone (Northern-Turkey) (United States)

    Melih Çörtük, Rahmi; Faruk Çelik, Ömer; Özkan, Mutlu; Sherlock, Sarah C.; Marzoli, Andrea; Altıntaş, İsmail Emir; Topuz, Gültekin


    The İzmir-Ankara-Erzincan suture zone in northern Turkey is one of the major tectonic zones separating the Pontides to the North from the Anatolide-Tauride block and Kı rşehir Massif to the South. The accretionary complex of the İzmir-Ankara-Erzincan suture zone, near Artova, is composed mainly of peridotites with varying degree serpentinization, metamorphic rocks, basalt, sandstones, pelagic and neritic limestones. The metamorphic rocks are represented by amphibolite, garnet micaschit, calc-schist and marble. The metamorphic rocks were interpreted as the metamorphic sole rocks. Because; (i) They are tectonically located beneath the serpentinized peridotites. (ii) Foliation planes of both the amphibolites and mantle tectonites are parallel to each other. (iii) The metamorphic rocks are crosscut by non-metamorphic dolerite dikes which exhibite Nb and Ta depletion relative to Th enrichment on the N-MORB normalized multi-element spider diagram. The dolerite dikes display flat REE patterns (LaN/YbN=0.85-1.24). These geochemical signatures of the dolerite dikes are indicative of subduction component during their occurrences. Geochemical observations of the amphibolites suggest E-MORB- and OIB-like signatures (LaN/SmN= 1.39-3.14) and their protoliths are represented by basalt and alkali basaltic rocks. Amphiboles from the amphibolites are represented by calcic amphiboles (magnesio-hornblende, tchermakite and tremolite) and they yielded 40Ar-39Ar ages between 157.8 ± 3.6 Ma and 139 ± 11 Ma. These cooling ages were interpreted to be the intra-oceanic subduction/thrusting time of the İzmir-Ankara-Erzincan oceanic domain. This study was funded by TÜBİTAK (Project no: 112Y123).

  11. 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.

  12. Characterization of the sub-continental lithospheric mantle beneath the Cameroon volcanic line inferred from alkaline basalt hosted peridotite xenoliths from Barombi Mbo and Nyos Lakes (United States)

    Pintér, Zsanett; Patkó, Levente; Tene Djoukam, Joëlle Flore; Kovács, István; Tchouankoue, Jean Pierre; Falus, György; Konc, Zoltán; Tommasi, Andréa; Barou, Fabrice; Mihály, Judith; Németh, Csaba; Jeffries, Teresa


    We carried out detailed petrographic, major and trace element geochemical, microstructural and FTIR analyses on eight characteristic ultramafic xenoliths from Nyos and Barombi Mbo Lakes in the continental sector of the Cameroon Volcanic Line (CVL). The studied xenoliths are spinel lherzolites showing lithologies similar to the other xenoliths reported previously along the CVL. They have protogranular and porphyroclastic textures. One of the Barombi xenolith contains amphibole, which had not been previously reported in this locality. Amphibole is common in the Nyos xenoliths suite. Peridotite xenoliths from both localities show some chemical heterogeneity, but Barombi xenoliths generally are less depleted in basaltic elements with respect to Nyos xenoliths. Trace element compositions of Nyos spinel lherzolites show a moderately depleted initial (premetasomatic) composition and variable enrichment in REE. Evidence for both modal and cryptic metasomatism is present in Nyos xenoliths. Rare earth element patterns of clinopyroxene suggest that interaction between mafic melts and the upper mantle occurred beneath the Nyos locality. Barombi Mbo xenoliths, on the other hand, record a small degree of partial melting. The Barombi Mbo xenoliths have weak, dominantly orthorhombic olivine crystal preferred orientations, whereas Nyos ones have strong axial-[010] patterns, which may have formed in response to transpression. Nominally anhydrous mantle minerals (NAMs) of the Barombi Mbo xenoliths show generally higher bulk concentrations of 'water' (70-127 ppm) than Nyos xenoliths (32-81 ppm). The Barombi Mbo xenoliths could originate from a juvenile segment of the lithospheric mantle, which had been originally part of the asthenosphere. It became a part of the lithosphere in response to thermal relaxation following the extension, forming a weakly deformed lower lithospheric mantle region along the CVL. The Nyos xenoliths, however, represent a shallow lithospheric mantle bearing

  13. Group II Xenoliths from Lunar Crater Volcanic Field, Central Nevada: Evidence for a Kinked Geotherm (United States)

    Roden, M.; Mosely, J.; Norris, J.


    Group II xenoliths associated with the 140 Ka Easy Chair Crater, Lunar Crater volcanic field, NV, consist of amphibole rich-inclusions including amphibolites, pyroxenites, and gabbros. Abundant minerals in these inclusions are kaersutite, aluminous (7.3-9.7 wt% Al2O3), calcic clinopyroxene, primarily diopside, and olivine (Mg# 69-73) with accessory spinel, sulfide and apatite. Although most apatites are fluor-hydroxyapatite solid solutions, one xenolith contains Cl- and OH-rich apatite suggesting that Cl may have been an important constituent in the parent magma(s) . The xenoliths show abundant evidence for equilibration at relatively low temperatures including amphibole and orthopyroxene exsolution in clinopyroxene, and granules of magnetite in hercynite hosts. If latter texture is due to exsolution, then this particular Group II xenolith equilibrated at temperatures near or below 500oC or at a depth of about 15 km along a conductive geotherm. It may be that all the Group II xenoliths equilibrated at low temperatures given the abundant exsolution textures although Fe-Mg exchange relations suggest equilibration at temperatures in excess of 800oC. Low equilibration temperatures are in conflict with the unusually high equilibration temperatures, >1200oC (Smith, 2000) displayed by Group I xenoliths from this same volcanic field. Taken at face value, the geothermometric results indicate unusually high temperatures in the upper mantle, normal temperatures in the crust and the possibility of a kinked geotherm in the region. Curiously the LCVF lies in an area of "normal" heat flow, south of the Battle Mountain area of high heat flow but the number of heat flow measurements in the Lunar Crater area is very low (Humphreys et al., 2003; Sass, 2005). References: Humphreys et al., 2003, Int. Geol. Rev. 45: 575; Sass et al., 2005,; Smith, 2000, JGR 105: 16769.

  14. Ocorrência de rochas da fácies granulito no Cinturão Mineiro, Minas Gerais, Brasil Occurrence of granulite-facies rocks in the Mineiro Belt, Minas Gerais, Brazil

    Directory of Open Access Journals (Sweden)

    Newton Souza Gomes


    Full Text Available Na região de Lagoa Dourada, inserida no Cinturão Mineiro, ocorrem granitóides paleoproterozóicos, que intrudem seqüências supracrustais arqueanas do greenstone belt Rio das Velhas. Os granitóides são cortados por rochas máficas anfibolitizadas, que portam xenólitos de granulitos. Trata-se de granulitos máficos caracterizados pela textura granoblástica e pela paragênese ortopiroxênio-clinopiroxênio-anfibólio-plagioclásio. Como fases secundárias, registram-se actinolita, cummingtonita, carbonato, epídoto, granada e quartzo. Determinações geotermométricas baseadas nos pares minerais ortopiroxênio-clinopiroxênio e anfibólio-plagioclásio produziram valores de temperatura entre 700 e 853ºC. As fases secundárias são produtos de um processo metamórfi co posterior.Paleoproterozoic granitoids intruding the Archean greenstone belt of Rio das Velhas are found in the region of Lagoa Dourada, which belongs to the Mineiro Belt. The granitoids are cut by amphibolitized mafi c rocks which contain xenoliths of granulite facies rocks. The rocks are mafi c granulites, characterized by their granoblastic texture and by parageneses orthopyroxene-clinopyroxene-amphibole-plagioclase. As secondary minerals, actinolite, carbonate, epidote, cummingtonite, garnet and quartz can be found. Geothermometric determinations based on the mineral pairs orthopyroxene-clinopyroxene and amphibole-plagioclase yielded temperature values between 700ºC and 853ºC. The secondary mineral phases are interpreted as a result of a younger metamorphic event.

  15. The Lagoa Real subalkaline granitic complex (south Bahia, Brazil): a source for uranium mineralizations associated with Na-Ca metasomatism

    International Nuclear Information System (INIS)

    In the central zone of the Sao Francisco Craton (South Bahia), the lower Proterozoic Lagoa Real granites and orthogneisses overthrust to the West the younger Urandi and Espinhaco metamorphic series, probably a late Brazilian event. This thrust is related to the regional metamorphism (amphibolite facies) of the Lagoa Real granites and induces a reverse HP metamorphism in the over thrusted series. Undeformed granites (sao Timoeto type) present two feldspars, perthitic orthoclase largely predominant over plagioclase (oligoclase ≥ albite), blue quartz, Fe-rich amphibole and biotite ± clinopyroxene assemblages, ilmenite ≥ magnetite, zircon, apatite, allanite and Nb ± Ti-REE oxides and silicates. The crystallization of the granites begins at high temperature and under low fO2 and PH2O conditions. Fractional crystallization of pyroxene and plagioclase leads to silica enrichment during magmatic differentiation. Increasing fO2 and PH2O are observed during this evolution. Orthogneisses show strongly recrystallized paragenesis: equal abundance of non-perthitic microcline and plagioclase (oligoclase ≤ albite), quartz, more Al-rich amphibole and biotite, magnetite, sphene, zircon, allanite, Nb ± Ti-REE oxides and silicates, and ± apatite. HT Na and Ca metasomatism occurs 330 Ma later than granite emplacement and is synchronous with important uranium mineralizations. Major elements and trace-elements geochemistry of the granites and orthogneisses indicate subalkaline to alkaline typology. Incompatible behaviour of Th, REE, Y, Zr, Nb, and F points out a convergence with alkaline magmatism. CI, F, Th, Y, REE, NB enrichments and Ba, Sr depletions are also related to a late magmatic stage. U-Th-rich and metamict accessory minerals of the granites represent a favorabl source for the Lagoa Real uranium ore-deposits

  16. Anatexis at the roof of an oceanic magma chamber at IODP Site 1256 (equatorial Pacific): an experimental study (United States)

    Erdmann, Martin; Fischer, Lennart A.; France, Lydéric; Zhang, Chao; Godard, Marguerite; Koepke, Jürgen


    Replenished axial melt lenses at fast-spreading mid-oceanic ridges may move upward and intrude into the overlying hydrothermally altered sheeted dikes, resulting in high-grade contact metamorphism with the potential to trigger anatexis in the roof rocks. Assumed products of this process are anatectic melts of felsic composition and granoblastic, two-pyroxene hornfels, representing the residue after partial melting. Integrated Ocean Drilling Program Expeditions 309, 312, and 335 at Site 1256 (eastern equatorial Pacific) sampled such a fossilized oceanic magma chamber. In this study, we simulated magma chamber roof rock anatectic processes by performing partial melting experiments using six different protoliths from the Site 1256 sheeted dike complex, spanning a lithological range from poorly to strongly altered basalts to partially or fully recrystallized granoblastic hornfels. Results show that extensively altered starting material lacking primary magmatic minerals cannot reproduce the chemistry of natural felsic rocks recovered in ridge environments, especially elements sensitive to hydrothermal alteration (e.g., K, Cl). Natural geochemical trends are reproduced through partial melting of moderately altered basalts from the lower sheeted dikes. Two-pyroxene hornfels, the assumed residue, were reproduced only at low melting degrees (<20 vol%). The overall amphibole absence in the experiments confirms the natural observation that amphibole is not produced during peak metamorphism. Comparing experimental products with the natural equivalents reveals that water activity ( aH2O) was significantly reduced during anatectic processes, mainly based on lower melt aluminum oxide and lower plagioclase anorthite content at lower aH2O. High silica melt at the expected temperature (1000-1050 °C; peak thermal overprint of two-pyroxene hornfels) could only be reproduced in the experimental series performed at aH2O = 0.1.

  17. Study on the distributions of Cd, Co, Sr, Zn, Ag, Cu, Pb, Mn and Ni in the eolian sands of the Gavkuni playa (southeast of Isfahan

    Directory of Open Access Journals (Sweden)

    Hamidreza Pakzad


    of heavy metals was determined by Atomic adsorption Spectroscopy (AAS after preparation of the samples. Discussion of Results & Conclusion The eolian sands located at west of the playa includes sand dunes and sand flats. About 85% of the eolian sands are in fine sand size range. These sediments are composed of igneous, sedimentary and metamorphic rock fragments and also quartz, feldspar and different heavy minerals. The igneous and metamorphic rock fragments decrease in the eolian sands from north to south of the playa and conversely sedimentary rock fragments increase in the sediments. The silicate heavy minerals of the sediments are zircon, amphibole, pyroxene, epidote, clinozoisite, spinel, idocrase, wollastonite, teremolite-actinolite and apatite in their order of abundances. The non-silicate heavy minerals include hematite, limonite, magnetite, pyrite and sphalerite. The metamorphic rocks outcropping in north of the study area (Feshark Skarn are the origin of spinel, idocrase, wollastonite and tremolite-actinolite. The volcanic rocks occurring in north and northeast of the basin are the provenance of zircon, amphibole, pyroxene, epidote, clinozoisite, magnetite and apatite. Cd exists in the carbonates hosting sulfides of Zn, Pb, Cd and Ag complex occurring in the drainage basin of the Gavkhuni playa. This element is more concentrated in the samples containing basic igneous rock fragments and minerals such as plagioclase, biotite and amphibole. Sr shows positive significant correlation with the calcium carbonate content and its concentration is higher in the samples containing more carbonate grains. Cd and Sr also show high significant positive correlation and their concentration increase with increase in the amount of sedimentary (carbonate rock fragments. The Co concentration decreases in the eolian sands from north to south of the playa. The amount of this element increases in the fine-grained samples containing more heavy minerals particularly hematite

  18. Zircon U-Pb geochronology and geochemical characteristics of neutral-acidic intrusions of Wuligou in South Qilian Mountains:their implications on forming gold deposit%党河南山乌里沟中酸性岩体锆石 U-Pb 年龄、地球化学特征及与金矿成矿关系

    Institute of Scientific and Technical Information of China (English)

    张翔; 张莉莉; 汪禄波; 刘博; 戴霜; 金治鹏; 蒙珍; 杨怀玉


    通过对南祁连山党河南山东段乌里沟金矿区中酸性侵入岩锆石 U-Pb 年龄测定及岩石地球化学分析,探讨了岩体形成的构造环境及其与金矿成矿的关系。矿区角闪石闪长岩体侵位年龄为457±6.3 Ma,岩石中各组分的质量分数:SiO2为48.98%~59.16%,Al2 O3为14.51%~16.77%,K2 O+Na2 O 为8.24%~9.47%,属准铝质、碱性-过碱性岩系列;DI 为58~79,属 I 型花岗岩类;岩石 Cr 和 Mg#值较低,Na2 O 和 K2 O 含量接近,表明源岩含有较多的壳源成分;稀土总量中等,轻稀土富集,具弱 Eu 负异常;相对富集大离子亲石元素 Rb、Ba、Th、K、U,亏损 Nb、Ta、P、Ti。矿区二长花岗岩属碱性岩系列,比角闪石闪长岩稀土总量低、更加亏损 Nb、Ta 等,与角闪石闪长岩属同一岩浆源,分异程度比角闪石闪长岩高。两种岩石均具岛弧岩浆岩特征,是中晚奥陶世南祁连俯冲到较浅部位熔融形成。岩体金含量高,目前探明的矿体产于岩体内部及接触带,围岩蚀变强烈,显示岩体为金矿成矿提供物质来源和成矿热液。%This paper reports the zircon U-Pb dating and the lithogeochemistry of the small-scale neutral-acidic intrusions in the Wuligou gold deposit in the east of Danghenanshan,South Qilian Mt., and interprets their tectonic settings and the linkage to gold mineralization.Our data show that the emplacement age of the amphibole diorite is 457 ±6.3 Ma.The mass fraction of SiO2 is 48.98% ~59.16%,that of A1 2 O3 is 14.51%~16.77%,that of (K2 O+Na2 O)is 8.24%~9.47% and that of DI is 58 ~ 79,indicating that the amphibole diorite belongs to the ultra-alkaline to alkaline,sub-aluminous rock series and I-type granitoid rocks.The amphibole diorite is poor in Cr and has low value of Mg# ,suggesting that its source rock has many crust materials.The total REE is moderate and LREE is rich,with slightly negative Eu

  19. 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

  20. Tectonic history of the central Sanandaj-Sirjan zone, Iran: Potentially Permian to Mesozoic polymetamorphism and implications for tectonics of the Sanandaj-Sirjan zone (United States)

    Shakerardakani, Farzaneh; Neubauer, Franz; Genser, Johann; Masoudi, Fariborz; Mehrabi, Behzad; Monfaredi, Behzad; Friedl, Gertrude


    The determination of metamorphic conditions and of its age is critical to the understanding of the mountain belt formation as metamorphism is an expression of subduction or plate collision. In this study, we report the metamorphic evolution, preliminary Ar-Ar mineral ages and structures from two amphibolite-grade metamorphic units of the Dorud-Azna region in the central part of Sanandaj-Sirjan metamorphic zone and discuss the tectonic implications. The Sanandaj-Sirjan metamorphic zone is nearly parallel to the Main Zagros Reverse Fault and is located above the Neotethyan ophiolitic suture. Structural studies and our previous U-Pb zircon dating work demonstrated that the area comprise three metamorphosed tectonic units, which are from footwall to hangingwall: (1) The Triassic June complex is metamorphosed within greenschist facies conditions, overlain by (2) the amphibolite-grade metamorphic Panafrican Galeh-Doz orthogneiss, which is intruded by some mafic dykes, and (3) the Amphibolite-Metagabbro unit with Carboniferous metagabbro bodies. To the East, the Darijune gabbro intruded within the Permian Kuh-e-June Marble and the mentioned two other metamorphic units. The granitic Galeh-Doz orthogneiss displays two different P-T conditions. The best average estimates for the magmatic mineral assemblage (plagioclase core + amphibole core + K-feldspar + quartz) range between 675 and 710 °C and 3.7 and 4.2 kbar, whilst the temperature of 530 and 625 °C and pressure of 0.7 to 2.8 kbar is consistent with the first metamorphic mineral assemblage. Ar-Ar amphibole ages from the Galeh-Doz orthogneiss give plateau-like steps between 260 and 270 Ma. We interpret this age as the cooling age after an amphibolite facies-grade metamorphism. An amphibole from relatively well preserved dyke within the Galeh-Doz orthogneiss gives staircase pattern with an age of 261 ± 3 Ma in the first step considered similarly as a metamorphic overprint in metamorphic rocks, whereas plateau-like steps

  1. Multistage metasomatism in ultrahigh-pressure mafic rocks from the North Dabie Complex (China) (United States)

    Malaspina, Nadia; Hermann, Jörg; Scambelluri, Marco; Compagnoni, Roberto


    Release of metamorphic fluids within the slab and/or from the slab to the mantle wedge in subduction environments can produce important metasomatic effects. Ultrahigh-pressure (UHP) metasomatised rocks represent ideal materials to study the element exchange at pressures corresponding to sub-arc depths in subduction zones. We present a petrologic and geochemical study of eclogites (s.l.) from the Dabie Mountains (China). The investigated samples were collected in the North Dabie Complex, where eclogite-facies rocks are significantly overprinted by granulite-facies metamorphism and partial melting. The studied eclogites are included in meta-lherzolitic bodies, which are in turn hosted by leucocratic gneisses. The textural relations among the various rock-forming minerals enabled us to identify several re-crystallisation stages. The peak (UHP) paragenesis consists of garnet, clinopyroxene and rutile. UHP garnet and clinopyroxene display oriented inclusions of polycrystalline rods of rutile + ilmenite and of albite, K-Ba-feldspar and quartz, respectively. Garnet and clinopyroxene are both rimmed by an inclusion free zone that formed after the peak, still at high-pressure conditions. Such optical zoning does not correspond to a difference in major element concentrations between garnet core and rim. This observation provides evidence that the major element composition of garnet was reset during exhumation, thus preventing thermobarometric determination of peak metamorphic conditions. Further decompression is documented by the formation of limited ilmenite + amphibole and granulite-facies coronas consisting of clinopyroxene, orthopyroxene, plagioclase and amphibole around garnet. In order to investigate the stability of observed mineral parageneses, a series of reconnaissance piston cylinder synthesis experiments were carried out in an identical bulk composition. The experimental study indicates that the peak metamorphic paragenesis is stable at P˜3.5 GPa and T ≥ 750

  2. CO 2 fluid and silicate glass as monitors of alkali basalt/peridotite interaction in the mantle wedge beneath Gobernador Gregores, Southern Patagonia (United States)

    Scambelluri, M.; Vannucci, R.; De Stefano, A.; Preite-Martinez, M.; Rivalenti, G.


    A suite of mantle-wedge amphibole + phlogopite-bearing spinel peridotite xenoliths in Plio-Pleistocene alkali basalts from Southern Patagonia (Gobernador Gregores, Santa Cruz Province, Argentina) contains carbonic fluid inclusions, glass and carbonate in several textural domains. Here we present a microstructural and fluid inclusion study showing that fluid (corresponding to pure CO 2) and glass post-date the hydrous mantle assemblage and formed soon before and/or during xenolith entrainement in the host alkali basalt. The high densities preserved by a number of CO 2 inclusions indicate that fluid infiltration took place at mantle depths. The low densities pertaining to the majority of analyzed fluid inclusions derive from inclusion re-equilibration during xenolith ascent. Glass occurs in reaction haloes around clinopyroxene, amphibole and phlogopite, where it hosts microlites of new pyroxene, olivine and locally carbonate. Glass veins cut the mantle minerals and locally contain primary carbonate. Glasses vary widely in composition depending on the textural domains and attain Si- and alkali-rich compositions (SiO 2 = 47.0-68.3 wt.%; Na 2O + K 2O = 5.8-12.2 wt.%). Incompatible trace element patterns of glasses in anhydrous xenoliths are closely similar to those of the host alkali basalts, whereas the compositions of interstitial and vein glasses in the hydrous xenoliths indicate that a compositional control has been exerted by the local mineral assemblage (mainly amphibole). The δ18O values of carbonate from the glass pockets and veins in the xenoliths, as well as of carbonate globules and amygdales in the host basalts are in the range 19.62 to 21.04‰. Corresponding δ13C values are - 9.25 to - 10.12‰ and - 7.59 to - 9.32‰, respectively. These values are very different from those of primary carbonatites and the δ18O values clearly exceed those expected for minerals and glasses from mantle assemblages. The similarity of isotopic ratios of carbonates from both

  3. 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

  4. New constraints on the textural and geochemical evolution of the upper mantle beneath the Styrian basin (United States)

    Aradi, Laszlo; Hidas, Károly; Zanetti, Alberto; János Kovács, István; Patkó, Levente; Szabó, Csaba


    Plio-Pleistocene alkali basaltic volcanism sampled sporadically the upper mantle beneath the Carpathian-Pannonian Region (CPR, e.g. [1]). Lavas and pyroclasts often contain mantle derived xenoliths, and the majority of them have been extensively studied [1], except the westernmost Styrian Basin Volcanic Field (SBVF, Eastern Austria and Slovenia). In the SBVF only a few volcanic centers have been studied in details (e.g. Kapfenstein & Tobaj). Based on these studies, the upper mantle beneath the SBVF is consists of dominantly high temperature, texturally and geochemically homogeneous protogranular spinel lherzolite. New major and trace element data from rock-forming minerals of ultramafic xenoliths, coupled with texture and deformation analysis from 12 volcanic outcrops across the SBVF, suggest that the lithospheric roots of the region are more heterogeneous than described previously. The studied xenoliths are predominantly lherzolite, amphibole is a common phase that replaces pyroxenes and spinels and proves modal metasomatism. Phlogopite coupled with apatite is also present in amphibole-rich samples. The texture of the xenoliths is usually coarse-grained and annealed with low abundance of subgrain boundaries in both olivine and pyroxenes. Olivine crystal preferred orientation (CPO) varies between the three most abundant one: [010]-fiber, orthogonal and [100]-fiber symmetry [2]. The CPO of pyroxenes is usually coherent with coeval deformation with olivine, however the CPO of amphibole is suggesting postkinematic epitaxial overgrowth on the precursor pyroxenes. According to equilibrium temperatures, the studied xenolith suite samples a broader temperature range (850-1100 °C) than the literature data, corresponding to mantle depths between 30 and 60 km, which indicates that the xenolith suite only represents the shallower part of the recent 100 km thick lithospheric mantle beneath the SBVF. The equilibrium temperatures show correlation with the varying CPO symmetries

  5. Adakitic volcanism in the eastern Aleutian arc: Petrology and geochemistry of Hayes volcano, Cook Inlet, Alaska (United States)

    McHugh, K.; Hart, W. K.; Coombs, M. L.


    Located in south-central Alaska, 135 km northwest of Anchorage, Hayes volcano is responsible for the most widespread tephra fall deposit in the regional Holocene record (~3,500 BP). Hayes is bounded to the west by the Cook Inlet volcanoes (CIV; Mt. Spurr, Redoubt, Iliamna, and Augustine) and separated from the nearest volcanism to the east, Mount Drum of the Wrangell Volcanic Field (WVF), by a 400 km-wide volcanic gap. We report initial results of the first systematic geochemical and petrologic study of Hayes volcano. Hayes eruptive products are calc-alkaline dacites and rhyolites that have anomalous characteristics within the region. Major and trace element analyses reveal that the Hayes rhyolites are more silicic (~74 wt. % SiO2) than compositions observed in other CIV, and its dacitic products possess the distinctive geochemical signatures of adakitic magmas. Key aspects of the Hayes dacite geochemistry include: 16.03 - 17.54 wt. % Al2O3, 0.97 - 2.25 wt. % MgO, Sr/Y = 60 - 78, Yb = 0.9 - 1.2 ppm, Ba/La = 31 - 79. Such signatures are consistent with melting of a metamorphosed basaltic source that leaves behind a residue of garnet ± amphibole ± pyroxene via processes such as melting of a subducting oceanic slab or underplated mafic lower crust, rather than flux melting of the mantle wedge by dehydration of the down-going slab. Additionally, Hayes tephras display a distinctive mineralogy of biotite with amphibole in greater abundance than pyroxene, a characteristic not observed at other CIV. Furthermore, Hayes rhyolites and dacites exhibit little isotopic heterogeneity (87Sr/86Sr = 0.70384 - 0.70395, 206Pb/204Pb = 18.866 - 18.889) suggesting these lavas originate from the same source. Hayes volcano is approximately situated above the western margin of the subducting Yakutat terrane and where the dip of the Pacific slab beneath Cook Inlet shallows northward. Due to its position along the margin of the subducting Yakutat terrane, it is plausible that Hayes magmas

  6. Sphene-centered ocellar texture as a petrological tool to unveil the mechanism facilitating magma mixing (United States)

    Gogoi, Bibhuti; Saikia, Ashima; Ahmad, Mansoor


    The sphene-centered ocellar texture is a unique magma mixing feature characterized by leucocratic ocelli of sphene enclosed in a biotite/hornblende-rich matrix (Hibbard, 1991). The ocelli usually consist of plagioclase, K-feldspar and quartz with sphene crystals at its centre. Although geochemical and isotopic data provide concrete evidence for the interaction between two compositionally distinct magmas, the exact processes by which mixing takes place is yet uncertain. So, textural analysis can be used to decipher the behaviour of two disparate magmas during mixing. Presented work is being carried out on the sphene ocelli, occurring in hybrid rocks of the Nimchak Granite Pluton (NGP), to understand its formation while two compositionally different magmas come in contact and try to equilibrate. The NGP is ca. 1 km2in extent which has been extensively intruded by number of mafic dykes exhibiting well preserved magma mixing and mingling structures and textures in the Bathani Volcano-Sedimentary Sequence (BVSS) located on the northern fringe of the Proterozoic Chotanagpur Granite Gneiss Complex (CGGC) of eastern Indian Shield. From petrographic and mineral chemical studies we infer that when basaltic magma intruded the crystallizing granite magma chamber, initially the two compositionally different magmas existed as separate entities. The first interaction that took place between the two phases is diffusion of heat from the relatively hotter mafic magma to the colder felsic one followed by diffusion of elemental components like K and incompatible elements from the felsic to the mafic domain. Once thermal equilibrium was attained between the mafic and felsic melts, the rheological contrasts between the two phases were greatly reduced. This allowed the felsic magma to back-vein into the mafic magma. The influx of back-veined felsic melt into the mafic system disrupted the equilibrium conditions in the mafic domain wherein minerals like amphibole, plagioclase and biotite

  7. Granite formation and the continental crust: an experimental and field perspective on the key role of deep crustal fractionation (United States)

    Müntener, Othmar; Ulmer, Peter; Nandedkar, Rohit; Hürlimann, Niklaus


    A major question in Earth Sciences is how continental crust forms and how it is modified over geological timescales. Statistical geochemistry advocates for a secular evolution of granitoids from the Archean to the present. Several processes are constantly modifying the continental crust yet the initial formation of silicic crust is generally related to two hypotheses. One is melting of mafic or pelitic crust while the alternative is fractionation from primary mantle derived melts, but both processes may occur simultaneously. Volatiles and heat play a key role in determining the respective solidi of lower crustal rocks, with the important difference that volatiles available for partial melting processes are restricted to structural bound volatiles in hydrous phases, while crystallization produces a much larger variability of potential magmatic water contents. Here we present an experimental perspective on both melting and crystallization processes in the lower crust, with an emphasis on experimentally derived liquid lines of descent by fractional and equilibrium crystallization at middle to lower crustal levels for hydrous, calc-alkaline magmas. These results indicate that fractionation can explain some features of plutonic-volcanic systems that are commonly ascribed to partial melting. Experimental data at pressures of 0.7 to 1.5 GPa, simulating thin and thick lower continental crustal settings are compiled. The temperature ranged from near-liquidus conditions at 1300 - 1150 °C to near-solidus conditions at 700 °C. We investigate the mutual phase relations of the principal phases olivine, cpx, opx, garnet, amphibole, plagioclase and Fe-Ti-oxides. Crystallization experiments and field data demonstrate that liquids at 0.7 to 1.0 GPa evolve from metaluminous to slightly peraluminous, corundum normative compositions. We use new trace element partitioning data to model the trace element evolution of siliceous magmas. These data relax the necessity of generating large

  8. An Experimental Perspective on Lower Crustal Processing of (Arc) Magmas (Invited) (United States)

    Muntener, O.; Ulmer, P.


    A major question in Earth Sciences is how continental crust forms and how it is modified over geological timescales. While there are a multitude of processes that constantly modify the continental crust (recycling), the initial formation of silicic crust is generally related to two hypotheses. One is melting of mafic or pelitic crust while the alternative is fractionation from primary mantle derived melts. These processes may occur simultaneously since the lower crust is energetically the most favorable place for modification processes of crustal rocks. Volatiles and heat play a key role in determining the respective solidi of lower crustal rocks, with the important difference that volatiles available for partial melting processes are restricted to structural bound volatiles in hydrous phases, while crystallization produces a much larger variability of potential magmatic water contents. Here we present an experimental perspective on both melting and crystallization processes in the lower crust, with an emphasis on experimentally derived liquid lines of descent by fractional and equilibrium crystallization at middle to lower crustal levels for hydrous, calc-alkaline magmas. These results indicate that fractionation can explain some features of plutonic-volcanic systems that are commonly ascribed to partial melting. Experimental simulation of fractional crystallization is particularly suited to understand the major controls on phase relations and compositions of magmas in the lower crust. Experimental data at pressures of 0.4 to 1.5 GPa, simulating thin and thick lower continental crustal settings are compiled and will be presented. The temperature ranged from near-liquidus conditions at 1300 - 1150 °C to near-solidus conditions at 700 °C. We investigate the mutual phase relations of the principal phases olivine, cpx, opx, garnet, amphibole, plagioclase and Fe-Ti-oxides. Crystallization experiments at lower crustal conditions demonstrate that liquids at 0.7 to 1

  9. Geochemical Evolution of Baru Volcano and the Origin of the Adakite Signal (United States)

    Hidalgo, P. J.; Rooney, T. O.


    Subduction zones constitute environments where the exchange of mantle and crustal material is possible. This exchange plays a central role in the evolution of the continental crust and the Earth's mantle and may be probed by examining the geochemical properties of arc magmas. At Baru volcano, volcanic products range from "typical" calc-alkaline arc magmas that swiftly transition to adakitic compositions. This compositional transition may have significant implications for the thermal state of subduction zones. Specifically, are adakites the result of slab melting resulting from increased heat within the mantle wedge/subducting slab, or could volatile fluxing of the mantle be responsible for adakite genesis? At Baru volcano, we have used a robust geochronological and geochemical dataset to examine processes that are responsible for generation of magmas from the Miocene to present. For primitive rocks that span Miocene to Quaternary, we have used Arc-Basalt Simulator II to model water contents and degrees of melting. Our data show a distinct drop in modeled water content (3.5%-6% vs. 2%-5%) and degree of melting (20%-23% vs 10%-15%) between the Miocene period of typical arc volcanism and the Quaternary adakitic volcanism. Despite the lower modeled water contents for magmas during the Quaternary adakitic phase, these water values are significantly enriched over those recorded in melts generated by slab melting processes (adakites in the Panama arc may be produced by fractional crystallization of amphibole and garnet. The water content of arc magmas is a critical control in the composition of the fractionating assemblage. At moderate pressures (~12 Kb), elevated magmatic water contents promote amphibole stability and fractionation path that yields normal island arc magmas. However, with decreasing magma water contents garnet may become stable at the expense of amphibole, yielding an adakitic magmatic signature. Our data reveal that in arcs with moderate crustal

  10. Geology and Geochemistry of the Early Proterozoic Kortejärvi and Laivajoki Carbonatites, Central Fennoscandian Shield, Finland

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    Nykänen, J.


    Full Text Available This paper provides for the first time extensive petrological, mineralogical and geochemical data on the early Proterozoic Kortejärvi and Laivajoki carbonatites, northern Finland, which form metamorphosed and highly strained bodies 2 and 4 km long within a Svecokarelian shear zone in central Fennoscandian Shield. They are not exposed, but have been penetrated by a couple of deep drill holes. In terms of modal mineralogy, both intrusions contain calcite carbonatite and dolomite-calcite carbonatite as their main rock types, but Kortejärvi also contains dolomite carbonatite and calcite-dolomite carbonatite, some glimmerite and olivine-magnetite rock and Laivajärvi tremolite-calcite carbonatite, tremolite-dolomite carbonatite, serpentine-talc-dolomite rock and glimmerite. The main country rock is an amphibolite which is not fenitized. No alkaline rocks have been detected in these intrusions. Calcite is most common mineral in both occurrences. Other carbonate minerals include dolomite with minor ankerite and occassional siderite. In addition to low-Ti phlogopite, tetraferriphlogopite is also encountered. Fresh olivine is rare, and its alteration products include titaniferous clinohumite. The amphiboles are mainly calcic amphiboles, including actinolite, tremolite and edenite. The only sodic-calcic amphibole is accessory richterite. Other essential minerals are Ti-poor magnetite with ilmenite exsolutions, fluorapatite (3.95-4.89 wt. % F, monazite, and allanite-(Ce. Geochemically, the Kortejärvi rocks are mostly magnesiocarbonatites, whereas those of Laivajärvi, due to their higher magnetite content, are ferrocarbonatites. Of the trace elements, Nb is much lower (8-30 ppm in proper carbonatites than the average for carbonatites and U and Th (<0.9 ppm and<2.4 pm, respectively lower than average. Sr is typical, but not high (1830-3480 ppm, and Ba is rather low (27-348 ppm. The REEs are hosted by allanite and monazite and their concentrations in the

  11. Geología y petrología del cuerpo Máfico-Ultramáfico Las Juntas, Sierra de Valle Fértil, Provincia de San Juan Geology and petrology of mafic-ultramafic body from Las Juntas, Valle Fértil, San Juan

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    Baliani Ignacio


    cumulates, and massive plagioclaserich cumulates. The cumulate gabbroic section largely consists of olivine gabbronorites interalyered with amphibole pyroxene gabbronorites and amphibole-bearing plagioclaserich gabbros (anorthosites. The cumulate ultramafic banks are largely composed of peridotites and dunites that contain varying proportions of pyroxenes, chromerich spinels, amphibole and small proportion of plagioclase. The cogenetic relation between mafic and ultramafic rocks is inferred from the Mg-Fe silicates compositions among all these rocks. The Fe-Mg exchange coefficient olivine-liquid and clinopyroxene-liquid reflect that this magma had Mg/Mg + Fe+² ratio of around 0.6; so that the magma had Mg/Mg + Fe+² ratio lower than that of a peridotiticmantle-derived primary magma. By implication, the main conclusion of this study is that primitive primary magmas originated at the lithospheric mantle - lower crust boundary zone ascended to feed chambers emplaced at upper levels within the lower crust (20 - 25 Km. This petrologic process is typical and characteristic of subduction-related magmatism, which in this case was related to the Famatinian arc.

  12. Mineral chemistry, crystallization conditions and geodynamic implications of the Oligo-Miocene granitoids in the Biga Peninsula, Northwest Turkey (United States)

    Aysal, Namık


    Widespread plutonic rocks in NW Turkey occur within the southward-younging and overlapping magmatic belts across the Aegean region. Post-collisional magmatism is represented by a series of granitoidic intrusions and volcanic successions. K-Ar and U-Pb LA-ICP-MS zircon dating of the Kazdağ and Yenice plutons yielded ages between 20.5 ± 0.5 Ma and 27.89 ± 0.17 Ma (Late Oligocene-Early Miocene). The granitoid samples are high-K calc-alkaline and metaluminous to slightly peraluminous. The 87Sr/86Sr values for the granitoids, enclaves and leucocratic rocks range between 0.705168 and 0.708357. The initial 143Nd/144Nd ratios calculated for the crystallization ages of ca. 23-27 Ma are between 0.512425 and 0.512614, and the εNd values vary from -3.5 to 0.2. The Nd TDM model ages range between 0.73 and 1.13 Ga. These samples are enriched in LILEs and LREE and depleted in HFSEs with negative Eu anomalies, indicating that the melts were derived from an enriched lithospheric mantle modified by subducted slab-derived melts. Energy constrained-assimilation and fractional crystallization (EC-AFC) modelling indicates that fractional crystallization and crustal assimilation modified the parent magma's composition during its residence in the upper crust. The mineral chemistry of amphiboles, pyroxenes, biotites and feldspars is used to constrain the pressure (P), temperature (T), oxygen fugacity (logƒO2) and water contents (H2Omelt) during the crystallization of the magmas in the studied granitoids. The clinopyroxene temperatures are in the range of 823-910 ± 45 °C. The amphibole temperatures for the studied plutonic rocks are in the range of 707-926 °C (mean = 798 ± 45 °C), and the crystallization depths are estimated to be in the interval of 1.02-10.2 km. The NW Anatolian plutonic rocks can be considered to have been equilibrated at the oxygen fugacities of calcic amphiboles (logƒO2) between -8.99 and -13.96 bars (mean = -12.11 bar) and H2Omelt contents between 1.63% and

  13. Rochas metaultramáficas de Lamim, sul do Quadrilátero Ferrífero, MG: contribuição ao conhecimento do protólito da pedra-sabão

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    Hanna Jordt-Evangelista


    Full Text Available A região de Lamim, sudeste do Quadrilátero Ferrífero (QF, é constituída de gnaisses e rochas metamáficas e metaultramáficas, estas do Grupo Nova Lima, base do greenstone belt Rio das Velhas. As principais rochas metaultramáficas são pedra-sabão, amplamente explotada no QF, e serpentinito. A região distingue-se por rochas com olivina preservada, interpretadas como o protólito magmático das metaultramáficas. São olivina-anfibólio fels com textura semelhante a cumulus, com inclusão de vários grãos de olivina em anfibólio de porte maior. O teor relativamente alto de ferro da olivina (Fo75Fa25 indica a sua origem magmática. Há dois tipos de anfibólio, cristais centimétricos de tremolita, envolvendo vários grãos de olivina, interpretados como pseudomorfoses, substituindo o piroxênio intercumulus original, e antofilita acicular. Os teores de serpentina, clorita, dolomita e talco variam. A composição química e as texturas sugerem que o provável protólito das rochas metaultramáficas são komatiitos peridotíticos plutônicos e não komatiitos vulcânicos encontrados em outras regiões do QF. O peridotito foi variavelmente metamorfizado em condições de fácies xisto verde alto a anfibolito baixo durante a infiltração de fluidos aquosos que acompanharam o processo metamórfico-metassomático.The region of Lamim, in the southeastern portion of the Quadrilátero Ferrífero (QF, is composed of gnaisses, metamafic and metaultramafic rocks. The last ones belong to the Nova Lima group, base of the Archean Rio das Velhas greenstone belt. The main metaultramafic rocks are soapstone, largely exploited in the QF, and sepentinite. Rocks preserving olivine, interpreted as the magmatic protolith of the metaultramafic rocks, distinguish the region of Lamim. These rocks are olivine-amphibole fels with cumulus-like textures characterized by the inclusion of several grains of olivine within larger amphibole crystals. The relatively high

  14. 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

  15. Petrology of mafic and ultramafic layered rocks from the Jaboncillo Valley, Sierra de Valle Fértil, Argentina: Implications for the evolution of magmas in the lower crust of the Famatinian arc (United States)

    Otamendi, J. E.; Cristofolini, E.; Tibaldi, A. M.; Quevedo, F. I.; Baliani, I.


    This work presents the field setting, petrography, mineralogy and geochemistry of a gabbroic and peridotitic layered body that is lens-shaped and surrounded by gabbronorites, diorites, and metasedimentary migmatites. This body exposed at Jaboncillo Valley is one among several examples of mafic and ultramafic layered sequences in the Sierras Valle Fértil and La Huerta, which formed as part of the lower crust of the Ordovician Famatinian magmatic arc in central-western Argentina. The layered sequence grew at deep crustal levels (20-25 km) within a mafic lower crust. The base of the layered body was detached during the tectonic uplift of the Famatinian lower crust, whereas the roof of the layered body is exposed in the eastern zone. In the inferred roof, olivine-bearing rocks vanish, cumulate textures are less frequent, and the igneous sequence becomes dominated by massive or thinly banded gabbronorites. Mainly based on the petrographic relationships, the inferred order of crystallization in the gabbroic and peridotitic layered sequence is: (1) Cr-Al-spinel + olivine, (2) Cr-Al-spinel + olivine + clinopyroxene + magnetite, (3) Cr-Al-spinel + olivine + plagioclase + magnetite ± orthopyroxene, and (4) Al-spinel + orthopyroxene + amphibole. A strong linear negative correlation between olivine and plagioclase modal proportions combined with field, petrographic and geochemical observations are used to demonstrate that the physical separation of olivine and plagioclase results in rock diversity at scales of a few centimeters to tens of meters. However, the composition of olivine (Fo ˜ 0.81) and plagioclase (An > 94%) remains similar throughout the layered sequence. Spinels are restricted to olivine-bearing assemblages, and display chemical trends characteristic of spinels found in arc-related cumulates. Gabbroic and peridotitic layered rocks have trace element concentrations reflecting cumulates of early crystallizing minerals. The trace element patterns still retain the

  16. Quantitative analysis of material transfer during the ascent of garnet-amphibolite mass in the Sambagawa metamorphic belt, Japan (United States)

    Uno, M.; Toriumi, M.


    During regional metamorphism at convergent plate boundaries, fluids are thought to be prevailing and assisting the metamorphic reactions. These fluids may also play important roles in deformation of the crust, generation of earthquakes and formation of arc magma through dehydration of subducting slabs. Aanalysis of fluid and mass transfer in the regional metamorphic rocks may, therefore, provide unique and rather direct information on the fluid processes at convergent boudaries. In the analysis of mass transfer in the regional metamorphic belt, time-integrated mass transfer (Auge, 1994a,b) and time-integrated fluid flux (Ferry, 1992; Penniston-Dorland&Ferry, 2008) had been successfully estimated, assuming an initial composition. Although these analyses may evaluate the overall material transfer, they may not resolve the variation of flux in a P-T-time domain, which is also critical to test the assumption regarding the initial composition. Here we present a new method for analyzing mass transfer based on mineral reactions, which does not require an assumption on the initial composition. Firstly, it is based on time-differentiated mass balance equation for each element at coordinate z (axis perpendicular to schistosity and banding); [dm(z,t) = Σ X(z,t)dM(z,t)+Σ M(z,t)dX(z,t) ;;(Eq.1).] The composition of each mineral (X), and its difference along time (dX), mode of each mineral (M) were input into Eq.1 from analysis of natural sample. Amount of growth of minerals (dM) were only measurable for two zoned minerals, garnet and amphibole. Secondly, the mass divergence regarding each element (dm) were assumed to be spatially continuous and be a function of z; [dm(z,t) = a_0(t)/2 + a_1(t) cos(ω z) + a_2(t) cos(ω z) + ldots ;(Eq.2).] Using Eq.1 and Eq.2, dM(z) was expressed as a function of (a0, a1, a2…); [dM(z,t) = g_z(a_0, a_1, a_2…, t)] Finally, parameters (a0, a1, a2…) were optimized by dMgrt(z,t) and dMamp(z,t), which were the moles of growth measured from

  17. The chromite deposits associated with ophiolite complexes, Southeastern Desert, Egypt: Petrological and geochemical characteristics and mineralization

    Institute of Scientific and Technical Information of China (English)

    Gehad M.Saleh


    The podiform chromitites occur in a well-preserved mantle sequence consisting of lherzolite-harzburgite with abundant lenses of olivine dunite. The podiform chromitite deposits are common as small and irregularly shaped masses in the Southeastern Desert (SED) of Egypt. The podiform chromitites exhibit a wide range of compositions from high Cr to high Al varieties. The Cr of chrome spinel ranges from 0.67 to 0.88 in olivine-dunite, quite similar to that of the high-Cr chromitite, whereas it is around 0.62 in lherzolite-harzburgite. Primary hydrous mineral inclusions, amphibole and phlogopite, in chrome spinel have been reported for the first time from the Pan-African Proterozoic podiform chromitites. On the other hand, petrographic and geochemical evidence suggests that podiform chromitites in the SED of Egypt were formed as a result of crystallization of mafic melts, probably of boninitic composition, the boninitic parental magmas were probably produced by a second stage of melting above a subduction zone. Three types of chromite ores can be distinguished within the SED of Egypt: (a) sulphide-poor podiform ores; (b) brecciated ores; and (c) sulphide-rich ores. Two textural types of inclusions in chromite are distinguished: (1) primary silicate inclusions generally have high Mg-number (>96), Cr and Ni, and are dominated by pargasitic amphibole, forsterite, diopside, enstatite and Na-phlogopite. A diversity of primary and secondary platinum group minerals (PGM) is described from the chromitites, including alloys, sulphides, sulpharsenides and arsenides of Ru, Os, Ir, Rh, Ni, Cu, Fe and Co; (2) in addition to primary PGM and hydrous silicates, the fluids are of low to moderate salinity, sodium-dominated aqueous solutions with complex gas contents. Variable amounts of water, hydrogen, hydrocarbons, carbon dioxides and nitrogen have been determined in inclusion-rich samples. The chondrite-normalized PGE patterns of lherzolite-harzburgite and olivine-dunite have

  18. Co-magmatic andesite enclaves in the Late Eocene andesites from Recsk, North Hungary: Implication for the magma chamber processes. (United States)

    Czuppon, Gy.; Harangi, Sz.


    The eastrenmost occurrences of the Late Eocene-Oligocene Periadriatic magmatism can be found around Recsk, at the northeast Mátra Mts., Northern Hungary. This Late Eocene (37 Ma) igneous body was displaced several hundreds km away from their original position along the Balaton-Darnó line during the Early Miocene when the North Pannonian block escaped from the compressive Alpine regime. It is built up by andesite lava and subvolcanic bodies associating with porphyry copper deposits. The andesites contain numerous igneous enclaves, homogeneously distributed in the lava body. Based on the mineral assemblage, the igneosu inclusions are subdivided in two groups: 1. Type enclave contains hornblende, plagioclase, biotite, whereas 2. Type enclave consists also orthopyroxene. They show various textures from hypidiomorphic granular to pylotaxitic ones. The host andesite contains the same mineral assemblage, but with less mafic minerals. Composition of the mineral phases in the andesite and the inclusions overlaps each other. Plagioclases show various zoning patterns (normal, reverz and oscillatory) and a relatively large range in anorthite content from 40 to 85 mol%. The amphiboles are tschermakites and magnesio-hornblendes, having relatively high mg-number (0.69-0.91). They often show oscillatory zoning, too. The bulk rock compositions of the andesites and the igneous inclusions are induistinguishable from one another. They are medium-K calc-alkaline andesites with trace element characters typical of subduction-related volcanic rocks (high LILE/HFSE ratios, enrichment of LILE). Therefore, the igneous inclusions are cogenetic with the host andesites. The textural features and composition of the mineral phases indicate disequilibrium crystallization in the magma chamber and repeated replenishment of mafic magma batches. We propose that the igneous inclusions could be derived from the crystal-rich mush zone of the andesitic magma chamber. Intrusion of fresh magma could

  19. Petrology and SHRIMP U-Pb dating of Xitieshan eclogite, North Qaidam UHP metamorphic belt, NW China (United States)

    Zhang, Cong; Zhang, Lifei; Roermund, Herman Van; Song, Shuguang; Zhang, Guibin


    Normal bimineralic and phengite-bearing eclogites have been recognized within mafic boudins (or lenses) enclosed in granitic and pelitic gneisses in the Xitieshan terrane, NW China. Bimineralic eclogite contains the primary M1 mineral assemblage Grt + Omp + Rt + Qtz+/-Zrn. Inclusions in M1 omphacite may be coesite pseudomorphs. Phengite eclogite consists of the M1 mineral assemblage Grt + Omp + Phn + Qtz + Rt+/-Zrn. Most eclogites are retrogressed to various degrees and contain hornblende, diopside and plagioclase, which commonly form symplectitic and/or kelyphitic intergrowths. The peak M1 P-T conditions of the Xitieshan eclogite are calculated to be P = 2.71-3.17 GPa and T = 751-791 °C, consistent with the presence of coesite pseudomorphs in omphacite. In addition, we have identified two stages of retrograde metamorphism; an early isothermal decompression stage (M2) followed by a later stage (M3) that developed under decreasing temperatures and pressures. During M2 internally-derived fluids played an important role, whereas during M3 and below externally-derived fluids dominated. The composition of garnet in M1changed little during M2 isothermal decompression (ITD), although pyrope contents in garnet locally decrease from core to rim where the grains have amphibole and pargasite + plagioclase coronas. Also the jadeite content (56%) of M1 omphacite decreased in the presence of active fluids during retrograde metamorphism. M1 phengite is replaced by the M2 assemblage Ms + Bt accompanied by K-feldspar + quartz. Amphibole compositions changed from magnesio-katophorite in M2 to pargasite in M3. Zircon U-Pb SHRIMP dating shows that the bimineralic eclogite has a magmatic protolith age of 877 ± 8 Ma and a metamorphic age of 439 ± 8 to 461 ± 4 Ma. We conclude that the Xitieshan metabasic rocks formed in the late Proterozoic and were subsequently subducted to depths of about 100 km, where they were metamorphosed to UHP eclogite during the late Ordovician (440-460 Ma

  20. Mineralogy and petrogenesis of a Ba-Ti-Zr-rich peralkaline dyke from Šebkovice (Czech Republic): Recognition of the most lamproitic Variscan intrusion (United States)

    Krmíček, Lukáš; Cempírek, Jan; Havlín, Aleš; Přichystal, Antonín; Houzar, Stanislav; Krmíčková, Michaela; Gadas, Petr


    A peralkaline, ultrapotassic dyke found at Šebkovice (Třebíč district, western Moravia) is a mineralogically extreme member of a dyke swarm occurring along the south-eastern border of the Moldanubian Region of the Bohemian Massif. The dyke shows a simple zoning, with a very fine-grained marginal zone grading into a medium-grained central zone. It has a primary mineral assemblage of microcline and potassic amphiboles, with accessory apatite and altered phlogopite. The microcline exhibits an unusual red luminescence colour and pronounced substitution of Fe3+ for Al, with measured contents of Fe2O3 up to 8.5 wt.% (0.31 apfu Fe3+). Amphiboles have very high K (up to 0.99 apfu) and Si contents; their compositions follow an alkaline fractionation trend from potassic-richterite to potassic-magnesio-arfvedsonite, characterized by an increase of Na/K and a decrease of Ca, Mg, Fe2+ and Ti via heterovalent substitutions [B]Ca + [C](Mg,Fe2+) → [B]Na + [C]Fe3+ and Ti + Mg → 2Fe3+. The most evolved apatite is significantly enriched in SrO (up to 9.7 wt.%; 0.49 apfu Sr). The core of the dyke and late veinlets contain unique late- to post-magmatic Ba-Ti-Zr-bearing mineral assemblages of baotite, henrymeyerite, titanite, rutile, benitoite and bazirite. Anhedral baotite fills interstices distributed inhomogeneously in the dyke centre; it is locally replaced by a Ba-bearing titanite + henrymeyerite + rutile + quartz assemblage. Henrymeyerite (the second record in a lamproite) shows variable Fe/Ti ratios and represents a solid solution of the hepta- and hexatitanate components. Euhedral crystals of benitoite and bazirite are enclosed in the late-stage quartz-titanite-apatite veinlets in the fine-grained margin of the intrusion. In terms of a mineralogical-genetic classification, the Šebkovice dyke can be considered as a new high-silica (~ 57 wt.% SiO2) variety of lamproite (variety Šebkovice), and represents a unique expression of post-collisional potassic magmatism on the

  1. Petrology and geochemistry of ca. 2100-1000 a.B.P. magmas of Augustine volcano, Alaska, based on analysis of prehistoric pumiceous tephra (United States)

    Tappen, Christine M.; Webster, James D.; Mandeville, Charles W.; Roderick, David


    Geochemical and textural features of whole-rock samples, phenocrysts, matrix glasses, and silicate melt inclusions from five prehistoric pumiceous tephra units of Augustine volcano, Alaska, were investigated to interpret processes of magma storage and evolution. The bulk-rock compositions of the tephra (designated G, erupted ca. 2100 a.B.P.; I ca. 1700 a.B.P.; H ca. 1400 a.B.P.; and C1 and C2 ca. 1000 a.B.P.) are silicic andesite; they contain rhyolitic matrix glasses and silicate melt inclusions with 74-79 wt.% SiO 2. The rocks are comprised of microlite-bearing matrix glass and phenocrysts of plagioclase, orthopyroxene, clinopyroxene, magnesio-hornblende, titanomagnetite, and ilmenite ± Al-rich amphibole with minor to trace apatite and rare sulfides and quartz. The felsic melt inclusions in plagioclase, pyroxenes, and amphibole are variably enriched in volatile components and contain 1.6-8.0 wt.% H 2O, 2100-5400 ppm Cl, < 40-1330 ppm CO 2, and 30-390 ppm S. Constraints from Fe-Ti oxides imply that magma evolution occurred at 796 ± 6 °C to 896 ± 8 °C and log ƒ O2 of NNO + 2.2 to + 2.6. This is consistent with conditions recorded for 1976, 1986, and 2006 eruptive materials and implies that magmatic and eruptive processes have varied little during the past 2100 years. Prehistoric Augustine magmas represented by these silicic andesites evolved via fractional crystallization, magma mingling and mixing, and/or chemical contamination due to magma-volcanic rock interaction. The occurrence of fractional crystallization is supported by the abundance of normally zoned phenocrysts, the presence of felsic matrix glass and melt inclusions within andesitic rock samples, trace-element data, and by geochemical modeling. The modeling constrains the influence of crystal fractionation on melt differentiation and is consistent with the evolution of the melt phase from felsic andesite to rhyodacite compositions. Magma mixing, mingling, and/or contamination by magma-volcanic rock

  2. Talc indices from Boumnyebel (Central Cameroon), physico-chemical characteristics and geochemistry (United States)

    Nkoumbou, C.; Njopwouo, D.; Villiéras, F.; Njoya, A.; Yonta Ngouné, C.; Ngo Ndjock, L.; Tchoua, F. M.; Yvon, J.


    Two talc schist occurrences were discovered in the Boumnyebel area, embedded in the Pan-African mica schist, at the junction between Archean, Eburnean and Neoproterozoic formations in Cameroon. They have been analysed by different techniques such as chemical analyses, XRD, DRIFTS, DTA and TG. The talc schist of the northern deposit contains talc (up to 95 wt%) with chlorite, goethite and lepidocrocite as minor minerals. The talc schist of the southern deposit has up to 88% of talc and is speckled with dark green phenoblasts of amphiboles (coexisting prismatic tremolite and magnesio-riebeckite). Due to its high talc content, the amphibole-free talc schist is economically attractive. Chemical analyses show that most of the rocks consist of SiO 2, MgO and Fe 2O 3, except the sample from the southern deposit that displays some amounts of Al 2O 3 and CaO. Among trace elements, Ni, Co and Cr are as high as in serpentinized peridotites, and suggest a protolith of ultrabasic nature. Chromium concentration in tremolite reaches 6178 ppm; most of the trace elements (Cd, Cr, Dy, Er, Eu, Ga, Gd, Ho, Lu, Nd, Pr, Sm, Sn, Sr, Tb, Tm, Y, Yb, Zr) are compatible with a tremolite lattice. The regional metamorphism yielded garnet micaschist nappes and thus belongs to the upper greenschist facies. Based on the high talc contents of the rocks and occasional coexisting tremolite and magnesio-riebeckite, the origin of the talc deposits is assigned to a hydrothermal alteration of ultramafic rocks. During the hydrothermal event, the fluid composition changed from silica-rich to lime-rich, but very few trace element contents were affected. Thus the low Rb, Sr, Th, Nb, K, Ta, Y, Zr, Hf, MREE and HREE and high Ni, Cr, Co contents of the rocks point to depleted peridotites (harzburgite-lherzolite) and pyroxenite as protoliths. The hydrothermal alteration is expressed in the positive cerium anomaly accompanied by little LREE enrichment of talc-rich rocks and hornblendite. The studied talc schist

  3. Geochemistry of the iliniza volcanic complex, ecuador: adakitic suites petrogenesis in the ecuadorian forearc (United States)

    Hidalgo, S.; Monzier, M.; Martin, H.; Eissen, J. P.; Cotten, J.


    The presence of volcanic rocks with an adakitic imprint or even true adakites in the Ecuadorian volcanic arc is known since the late 90s. Adakitic magmas are generated by the partial melting of the subducting oceanic crust, a process that may happen in a special geodynamic context, like a flat subduction or when the subducting lithosphere is young, both being possible in Ecuador. In order to constrain the adakitic magma´s role in the Ecuadorian arc evolution, a geochemical study of the Iliniza Volcanic Complex (IVC) was undertaken, including 58 whole rock analysis, 236 electron microprobe data and 16 LA-ICP-MS analysis. This poorly known volcanic complex is located 60 km south-south-west of Quito in the Western Cordillera of Ecuador. It is comprised of twin peaks (North Iliniza and South Iliniza) and at least three satellite domes (Huayrapungu, Pilongo and Tishigcuchi). This volcanic complex, made up of medium-K andesites and dacites, presents three different geochemical series with a varying adakitic imprint that requires different individual evolutions. The older Iliniza series shows a simple evolution with fractional crystallization of amphibole, plagioclase, clinopyroxene, magnetite and apatite from a parental magma, the product of the mixing of 36% adakitic and 64% calc-alkaline magma. The intermediate Pilongo series magma is the product of a moderate to high degree (26%) of partial melting of the subducting oceanic crust, that arrived to the surface with little or no interaction with the mantle wedge and no crustal contamination. The more recent Tishigcuchi series shows three stages of evolution that includes (1) metasomatism of the mantle wedge peridotite by slab melts, (2) partial melting of this enriched source and (3) minor degree fractional crystallization of amphibole. The relative ages of the edifices do not show a geochemical evolution from a calc-alkaline magma to an adakitic one, as it is observed for several volcanoes of the Ecuadorian arc. The

  4. Petrology and geochemistry of eclogites from the Kechros Metamorphic Complex in eastern Rhodope (NE Greece) (United States)

    Mposkos, Evripides; Baziotis, Ioannis; Asimow, Paul


    The Rhodope Metamorphic Province (RMP) is one of the major tectonic units in northern Greece. It consists of different tectonometamorphic complexes involved in the Alpine collisional history between the Eurasian and African plates. In eastern Rhodope a Jurassic UHP metamorphism is documented in the uppermost Kimi Complex by the presence of microdiamond inclusions in garnets from pelitic gneisses (Mposkos and Kostopoulos 2001). Partially or completely amphibolitized eclogites are common recording P-T conditions >1.8 GPa and 7500C for the eclogitic stage and 1.5 GPa and 8200C for an early stage of exhumation (Bauer et al. 2007). In the underlying Kechros Complex lenses of kyanite eclogites in orthogneisses with Permian ages of their gabbroic protoliths and of common eclogites within metapelites associated with serpentinized peridotites occur. The mineral assemblage of the kyanite eclogites is Grt+Omp(Jd35-55)+Ky+sodic-Tr+Hbl+Zo/Czo+Phg+Qtz+Rt. Garnet shows growth zoning with core composition Grs0.19Prp0.15Alm0.63Sps0.03 and rim composition Grs0.20Prp0.27Alm0.52Sps0.01. Matrix omphacite is in textural equilibrium with kyanite, but commonly it is replaced by Ca-amphibole. A decrease in jadeite component from the core to the rim indicates a re-equilibration tendency during exhumation. Temperatures of 550-6000C and minimum pressure of 1.5 GPa are obtained with Grt-Cpx geothermometry and the jadeite component (Jd55) in omphacite. However, the coexistence of matrix omphacite with kyanite constrains the minimum pressure to 2.1 GPa assuming H2O activity equal to unity. In the common eclogites the HP mineral assemblage is Grt+Omp+Czo+Gln+Ca-Amph. Glaucophane is present only as inclusions in garnet. In retrogressed samples Ca-amphibole replaces garnet and omphacite. It shows compositional zoning with increasing Al2O3 content from 5.0 wt% in the core up to 20.0 wt% in the rim. In the eclogites subjected to extensive retrogression, margarite associated with zoisite and albite


    Directory of Open Access Journals (Sweden)

    Castellanos O.M


    (Zone II,
    plagioclase + amphibole garnet epidote (Zone III, amphibole + diopside + garnet + plagioclase (Zone IV, plagioclase + diopside scapolite (Zone V, epidote calcite (Zone VI, and calcite dolomite (Zone VII.

  6. The eruptive chronology of the Ampato-Sabancaya volcanic complex (Southern Peru) (United States)

    Samaniego, Pablo; Rivera, Marco; Mariño, Jersy; Guillou, Hervé; Liorzou, Céline; Zerathe, Swann; Delgado, Rosmery; Valderrama, Patricio; Scao, Vincent


    We have reconstructed the eruptive chronology of the Ampato-Sabancaya volcanic complex (Southern Peru) on the basis of extensive fieldwork, and a large dataset of geochronological (40K-40Ar, 14C and 3He) and geochemical (major and trace element) data. This volcanic complex is composed of two successive edifices that have experienced discontinuous volcanic activity from Middle Pleistocene to Holocene times. The Ampato compound volcano consists of a basal edifice constructed over at least two cone-building stages dated at 450-400 ka and 230-200 ka. After a period of quiescence, the Ampato Upper edifice was constructed firstly during an effusive stage (80-70 ka), and then by the formation of three successive peaks: the Northern, Southern (40-20 ka) and Central cones (20-10 ka). The Southern peak, which is the biggest, experienced large explosive phases, resulting in deposits such as the Corinta plinian fallout. During the Holocene, eruptive activity migrated to the NE and constructed the mostly effusive Sabancaya edifice. This cone comprised many andesitic and dacitic blocky lava flows and a young terminal cone, mostly composed of pyroclastic material. Most samples from the Ampato-Sabancaya define a broad high-K magmatic trend composed of andesites and dacites with a mineral assemblage of plagioclase, amphibole, biotite, ortho- and clino-pyroxene, and Fe-Ti oxides. A secondary trend also exists, corresponding to rare dacitic explosive eruptions (i.e. Corinta fallout and flow deposits). Both magmatic trends are derived by fractional crystallisation involving an amphibole-rich cumulate with variable amounts of upper crustal assimilation. A marked change in the overall eruptive rate has been identified between Ampato (~ 0.1 km3/ka) and Sabancaya (0.6-1.7 km3/ka). This abrupt change demonstrates that eruptive rates have not been homogeneous throughout the volcano's history. Based on tephrochronologic studies, the Late Holocene Sabancaya activity is characterised by strong

  7. Evidencias de metasomatismo en el manto sublitosférico de Patagonia Evidences of metasomatism in the sublitospheric mantle of Patagonia

    Directory of Open Access Journals (Sweden)

    P.A. Aliani


    Full Text Available Los xenolitos ultramáficos recolectados en la Estancia Poklepovic, provincia de Santa Cruz, comprenden lherzolitas, harzburgitas y wehrlitas y se encuentran alojados en lavas alcalinas y conos cineríticos. La mayoría de los xenolitos contienen vidrio en venillas y/o bolsillos de fundido y la gran mayoría comprende además anfíbol, mica o ambas. El metasomatismo crítptico se manifiesta por el enriquecimento en tierras raras livianas en los análisis de roca total en muestras sin fases minerales hidratadas, bolsillos de fundido, ni venillas con vidrio. El metasomatismo modal es evidente en muestras con fases minerales hidratadas, bolsillos de fundido o venillas con vidrio y se refleja en la química de roca total, que muestra concentraciones elevadas de los elementos incompatibles. Las relaciones texturales permiten considerar al menos dos eventos metasomáticos claramente diferenciables. El primero produce la cristalización de anfíbol y mica y el otro es responsable del desarrollo de los bolsillos de fundido. La presencia de venillas con vidrio (± carbonato en muestras en las que no se han identificado bolsillos de fundido sugiere que las mismas podrían ser el resultado de un evento metasomático distinto. Las evidencias texturales indican que al menos parte del carbonato presente en estos xenolitos precipitó a partir de aguas meteóricas ricas en carbonato.Ultramafic xenoliths from Estancia Poklepovic, Santa Cruz province, comprise lherzolites, harzburgites and wehrlites, hosted by alkaline lavas and cinder cones. Most of the samples carry glass veins and/or melt pockets and most of them also bear amphibol, mica or both. Criptic metasomatism is demonstrated by enrichment of light rare earth elements in bulk rock analyses of samples devoid of hydrous phases, melt pockets and glass veins. Modal metasomatism is evident in samples carrying hydrous phases, melt pockets and glass veins, which led to high contents of incompatible elements in

  8. Mica-dominated seismic properties of mid-crust beneath west Yunnan (China) and geodynamic implications (United States)

    Shao, Tongbin; Ji, Shaocheng; Oya, Shoma; Michibayashi, Katsuyoshi; Wang, Qian


    Measurements of crystallographic preferred orientations (CPO) and calculations of P- and S-wave velocities (Vp and Vs) and anisotropy were conducted on three quartz-mica schists and one felsic mylonite, which are representative of typical metamorphic rocks deformed in the middle crust beneath the southeastern Tibetan plateau. Results show that the schists have Vp anisotropy (AVp) ranging from 16.4% to 25.5% and maximum Vs anisotropy [AVs(max)] between 21.6% and 37.8%. The mylonite has lower AVp and AVs(max) but slightly higher foliation anisotropy, which are 13.2%, 18.5%, and 3.07%, respectively, due to the lower content and CPO strength of mica. With increasing mica content, the deformed rocks tend to form transverse isotropy (TI) with fast velocities in the foliation plane and slow velocities normal to the foliation. However, the presence of prismatic minerals (e.g., amphibole and sillimanite) forces the overall symmetry to deviate from TI. An increase in feldspar content reduces the bulk anisotropy caused by mica or quartz because the fast-axis of feldspar aligns parallel to the slow-axis of mica and/or quartz. The effect of quartz on seismic properties of mica-bearing rocks is complex, depending on its content and prevailing slip system. The greatest shear-wave splitting and fastest Vp both occur for propagation directions within the foliation plane, consistent with the fast Pms (S-wave converted from P-wave at the Moho) polarization directions in the west Yunnan where mica/amphibole-bearing rocks have developed pervasive subvertical foliation and subhorizontal lineation. The fast Pms directions are perpendicular to the approximately E-W orienting fast SKS (S-wave traversing the core as P-wave) directions, indicating a decoupling at the Moho interface between the crust and mantle beneath the region. The seismic data are inconsistent with the model of crustal channel flow as the latter should produce a subhorizontal foliation where vertically incident shear

  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. Apatite as an indicator of fluid salinity: An experimental study of chlorine and fluorine partitioning in subducted sediments (United States)

    Li, Huijuan; Hermann, Joerg


    In order to constrain the salinity of subduction zone fluids, piston-cylinder experiments have been conducted to investigate the partitioning behaviour of Cl and F in subducted sediments. These experiments were performed at H2O-undersaturated conditions with a synthetic pelite starting composition containing 800 ppm Cl, over a pressure and temperature range of 2.5-4.5 GPa and 630-900 °C. Repetitive experiments were conducted with 1900 ppm Cl + 1000 ppm F, and 2100 ppm Cl. Apatite represents the most Cl-abundant mineral phase, with Cl concentration varying in the range 0.1-2.82 wt%. Affinity for Cl decreases over the following sequence: aqueous fluid > apatite ⩾ melt > other hydrous minerals (phengite, biotite and amphibole). It was found that addition of F to the Cl-bearing starting composition significantly lowers the Cl partition coefficients between apatite and melt (DClAp-melt) and apatite and aqueous fluid (DClAp-aq). Cl-OH exchange coefficients between apatite and melt (KdCl-OHAp-melt) and apatite and aqueous fluid (KdCl-OHAp-aq) were subsequently calculated. KdCl-OHAp-melt was found to vary from 1 to 58, showing an increase with temperature and a decrease with pressure and displaying a regular decrease with increasing H2O content in melt. Mole fractions of Cl and OH in melt were calculated based on an ideal mixing model for H2O, OH, O, Cl and F. The Cl contents of other hydrous minerals (phengite, biotite and amphibole) fall between 200 and 800 ppm, with resultant Cl partition coefficients from 0.02 to 0.49, appearing independent of the bulk Cl and F content. Preliminary data from this study show that the partitioning behaviour of F is strongly in favour of apatite relative to melt and phengite, with DFAp-melt = 15-51. Apatites from representative eclogite facies metasediments were examined and found to have low Cl contents close to ∼100 ppm. Calculations using our experimentally determined KdCl-OHAp-aq of 0.004 at 2.5 GPa, 630 °C indicate a low

  11. Geochemical and Sr-Nd-Pb isotopic evidence for ancient lower continental crust beneath the Xi Ujimqin area of NE China (United States)

    Gao, Xiaofeng; Guo, Feng; Xiao, Peixi; Kang, Lei; Xi, Rengang


    The Central Asian Orogenic Belt (CAOB) is the largest Phanerozoic accretionary orogen on Earth. The role that Precambrian continental microblocks played in its formation, however, remains a highly controversial topic. New zircon U-Pb age data and whole-rock geochemical and Sr-Nd-Pb isotopic studies on Permian (253-251 Ma) andesites from the Xi Ujimqin area provide the first evidence for the existence of a continental lower mafic crust in the eastern segment of the CAOB. These Permian lavas generally have chemical compositions similar to experimental melts of garnet pyroxenites. Based on Sr-Nd-Pb isotopic compositional differences, they can be further subdivided into two groups. Group 1 has moderately radiogenic Sr (87Sr/86Sr(i) = 0.7060-0.7062) and nonradiogenic Nd (εNd(t) = - 9.0-8.3) and Pb (e.g., 206Pb/204Pb = 17.18-17.23) isotopic compositions similar to the ancient lower mafic crust beneath the North China Craton (NCC). Compared with Group 1, Group 2 has less radiogenic Sr (87Sr/86Sr(i) = 0.7051-0.7055), and more radiogenic Nd (εNd(t) = - 0.2-+1.4) and Pb (e.g., 206Pb/204Pb = 18.04-18.20) isotopic compositions as observed in the Phanerozoic granitoids and felsic lavas of the CAOB. The combined geochemical and isotopic data indicate that Group 1 was derived from ancient lower mafic crust of the NCC affinity, with a residual assemblage of pyroxene + plagioclase + amphibole. The source for Group 2 was a mixture of ancient lower mafic crust and a juvenile crustal component, and melting left a residue of orthopyroxene + clinopyroxene + plagioclase + garnet + amphibole. Generation of these two types of late Permian andesites favors a model whereby breakoff of a subducted slab and subsequent lithospheric extension triggered extensive asthenospheric upwelling and melting of the continental mafic lower crust of the eastern CAOB. The discovery of ancient lower continental crust of the NCC affinity in the CAOB implies that the NCC experienced continental breakup during

  12. Reaction rim growth on olivine in silicic melts: Implications for magma mixing (United States)

    Coombs, M.L.; Gardner, J.E.


    Finely crystalline amphibole or pyroxene rims that form during reaction between silicic host melt and cognate olivine xenocrysts, newly introduced during magma mixing events, can provide information about the timing between mixing and volcanic eruptions. We investigated rim growth experimentally by placing forsteritic olivine in rhyolitic and rhyodacitic melts for times between 25 and 622 h at 50 and 150 MPa, H2O-saturated, at the Ni-NiO buffer. Rims of orthopyroxene microlites formed from high-silica rhyolite and rhyodacite melts at 885??C and 50 MPa, and in the rhyolite at 150 MPa and 885??C. Rims of amphibole with lesser orthopyroxene formed in the rhyolite at 150 MPa and 800??C and in the rhyodacite at 150 MPa and 885??C. Irregular, convolute olivine edges and mass balance between olivine, melt, and rim phases show that olivine partly dissolved at all conditions. Iron-rich zones at the exteriors of olivines, which increased in width parabolically with time, show that Fe-Mg interdiffusion occurring in olivines was not outpaced by olivine dissolution. Linear increases of the square of rim widths with time suggest that diffusion within the melt is the rate-controlling process for olivine dissolution and rim growth. Rims grew one-half to one order-of-magnitude faster when melt water contents were doubled, unless conditions were far above the liquidus. Rim growth rate in rhyolite increases from 0.055 ?? 0.01 ??m2/h at 885 ??C and 50 MPa to 0.64 ?? 0.13 ??m2/h at 800 ??C and 150 MPa. Melt composition has a lesser effect on rim growth rates, with growth rate increasing as melt SiO2 content decreases. Pyroxene rims on olivines in andesite erupted from Arenal volcano (Costa Rica) grew at a rate of 3.0 ?? 0.2 ??m2/h over an eleven-year period. This rate is faster than those of the experiments due to lower melt viscosity and higher temperatures, and suggests that a magma mixing event preceded the start of the eruption by days.

  13. Mineral and whole-rock geochemistry of the Topuk Granitoid (Bursa, Western Anatolia, Turkey) (United States)

    Orhan, Ayşe; Demirbilek, Mehmet; Mutlu, Halim


    The Eocene aged Topuk Granitoid exposing in the Tavşanlı Zone at south of the Izmir-Ankara Suture Zone is one of the granitoids which were formed as a result of collision of the Anatolide-Tauride block with the Sakarya continent in the late Cretaceous. Nearly east-west extending, elliptical shaped Topuk Granitoid was intruded into the Paleozoic and Mesozoic metamorphites and upper Cretaceous ophiolitic rocks. The intrusion is in granodiorite composition and contains spherical/ellipsoidal mafic microgranular enclaves (MME) with composition of monzodiorite to monzogabbro. The granitoid which contains xenoliths is frequently cut by porphyritic granodiorite, granite aplite and quartz dikes at the margins. Topuk Granitoid is represented by an I-type pluton with medium to high K calc-alkaline affinity and metaluminous melt composition. Ocean ridge granite (ORG) normalized element distributions show that the granitoid, dikes and MME's have similar patterns. A significant enrichment of LIL (Rb, Ba, K, Th and Sr) elements and relatively depletion of HFS (Ta, Nb, Ce, Hf, Y, Zr and Ti) elements are indicative of formation from hybrid magma in a subduction environment. In tectonic discrimination diagrams (Ta -Yb and Rb-Y+Nb), samples of the Topuk Granitoid are plotted into the volcanic arc granite (VAG) field which is characteristic for the post collision granites. The results of mineral chemistry show that plagioclases are in oligoclase-andesine (An20-49) composition, amphiboles are of magnesio-hornblende and biotites are of Fe-Mg-biotite composition. In the Al2O3-FeO-MgO diagram biotite minerals are accompanied by amphibole and other ferromagnesian minerals and represent biotites of calc-alkaline orogenic zones. Calculations based on the hornblende-barometer indicate that the calc-alkaline magma was crystallized under pressure of 2-6 kbars (mean=4 kbars) and at depth of 7-20 km (mean=12 km). The whole-rock and mineral chemistry data show that the Topuk Granitoid was formed

  14. Violent Explosive Eruptions in the Ararat Valley, Armenia and Associated Volcanic Hazards (United States)

    Meliksetian, Khachatur; Savov, Ivan; Connor, Charles; Gevorgyan, Hripsime; Connor, Laura; Navasardyan, Gevorg; Manucharyan, Davit; Jrbashyan, Ruben; Ghukasyan, Yura


    The Anatolian-Armenian-Iranian volcanically active orogenic plateau is located in the collision zone between the Arabian and Eurasian plates. The majority of regional geodynamic and petrologic models of collision-related magmatism use the model proposed by Keskin (2003), where volcanism is driven by Neo-Tethyan slab break-off, however an updated model by Neill et al. (2015) and Skolbeltsyn et al.(2014) comprise break-off of two slabs. One of the significant (and understudied) features of the regionally extensive collision zone volcanism is the diversity of eruption styles and also the presence of large number of highly explosive (Plinian) eruptions with VEI≥5 during the Middle-Upper Pleistocene. Geological records of the Ararat depression include several generations of thick low aspect ratio Quaternary ignimbrites erupted from Aragats volcano, as well as up to 3 m thick ash and pumice fall deposit from the Holocene-historically active Ararat volcano. The Ararat tephra fall deposit is studied at 12 newly discovered outcrops covering an area ˜1000 km2. It is noteworthy, that the Ararat tephra deposits are loose and unwelded and observed only in cross-sections in small depressions or in areas where they were rapidly covered by younger, colluvium deposits, presumably of Holocene age. Therefore, the spatial extent of the explosive deposits of Ararat is much bigger but not well preserved due to rapid erosion. Whole rock elemental, isotope (Sr, Nd) and mineral chemistry data demonstrate significant difference in the magma sources of the large Aragats and Ararat stratovolcanoes. Lavas and pyroclastic products of Aragats are high K calc-alkaline, and nearly always deprived from H2O rich phases such as amphibole. In contrasts lavas and pyroclastic products from Ararat are medium K calc-alkaline and volatile-rich (>4.6 wt% H2O and amphibole bearing) magmas. Here we shall attempt to reveal possible geochemical triggers of explosive eruptions in these volcanoes and assess

  15. Some not so obvious reasons to teach optical mineralogy (United States)

    Gunter, M. E.


    Hands-on, interactive, critical thinking, interdisciplinary, spiral learning, and 3-D visualization are familiar words in pedagogy, while Becke lines, dispersion staining, grain mounts, sign of elongation, extinction angle, and optical indicatrix are words seldom used in today's geosciences curriculum. However, the teaching of these seemingly rather historical optical methods, and proper training in the use of the polarized (not petrographic) light microscope (PLM), will by themselves lead to improved learning of our students. And this, if for no other reason, might warrant the inclusion of a semester-long optical mineralogy course. However, another $70 billion per year concern in the U.S. also warrants inclusion of optical mineralogy in a geosciences curriculum. That dollar amount (which would be approximately 10% of annual petroleum sales in the U.S.) centers around the cost spent (wasted?) on asbestos litigation in the U.S. Unfortunately, because we no longer teach PLM skills in the geosciences curriculum, many of the microscopists, regulators, and "expert" witnesses involved in the asbestos issue have little or no formal training in mineralogy or optical mineralogy. This, in turn, often leads to formulation of regulations that make little sense (e.g., that quartz, the most abundant mineral species in the earth's crust is now listed as a human carcinogen) and unsolved mineralogical issues (e.g., OSHA deregulated high-aspect ratio amphibole cleavage fragments in 1994 but did not propose a method to distinguish them from amphibole fibers). The current asbestos issues often deal with tremolite contamination in chrysotile or talc. There are simple PLM methods that we could teach whereby thousands of particles could be screened in minutes to find these possible contaminates, whereas electron beam or X-ray diffraction methods require orders of magnitude more time and cost - and this is only one of many examples. Finally, one might also argue that since minerals

  16. Obduction of Tethyan-type ophiolites-A case-study from the Thetford-Mines ophiolitic Complex, Quebec Appalachians, Canada (United States)

    Tremblay, Alain; Ruffet, Gilles; Bédard, Jean H.


    Oceanic plagiogranites and peridotite-hosted granites (PHG) of the Thetford-Mines ophiolite (TMO) yield mean U-Pb zircon ages of 479.2 ± 1.6 Ma and 469.5 ± 2.8 Ma, and are interpreted to be the products of fractionation of basaltic magma and melting of the Laurentian margin, respectively. The existing 40Ar/39Ar age for the ophiolitic metamorphic sole of the TMO is a hornblende isochron age of 477 ± 5 Ma for amphibolite facies rocks. Sites previously sampled for U-Pb and 39Ar-40Ar analyses were resampled for more accurate 39Ar-40Ar dating, in order to better constrain the thermo-tectonic evolution of the ophiolite and underlying Laurentian margin rocks on which they were overthrust, and quantify the time required for obduction of Tethyan-type ophiolites in the Canadian Appalachians. Amphiboles from TMO gabbro and plagiogranite yield 39Ar-40Ar plateau ages of 477-475 Ma. In contrast, muscovites from PHG yield cooling ages of 466-465 Ma, and show evidence for thermal resetting at ca. 460 Ma for both a granitic mylonite and a crosscutting pegmatite facies. The amphibolitic metamorphic sole yields 39Ar-40Ar ages of ca. 471 Ma in amphibole, and high-temperature ages of ca. 466 Ma in muscovite, with evidence for recrystallization to ages as young as 457 Ma. Muscovites from the sub-ophiolitic Laurentian metasedimentary basement, and micaschist clasts in supraophiolitic debris flows of the TMO, yield similar pseudo-plateau and high-temperature ages of ca. 463-464 Ma. The U-Pb and 39Ar-40Ar data suggest that the obduction of peri-Laurentian oceanic crust lasted approximately 5 to 10 m.y. Since both facies formed approximately m.y. after the ophiolitic crust, this supports models whereby the still-hot ophiolitic mantle provided the heat needed to generate the PHG and the metamorphic sole between ca. 475 and 470 Ma. Muscovite ages of PHG record cooling below ca. 450-500 °C by ca. 465 Ma, but 39Ar-40Ar ages from both a mylonitized PHG facies and micaschist clasts suggest

  17. Early Cretaceous gabbroic rocks from the Taihang Mountains: Implications for a paleosubduction-related lithospheric mantle beneath the central North China Craton (United States)

    Wang, Yuejun; Fan, Weiming; Zhang, Hongfu; Peng, Touping


    SHRIMP zircon U-Pb ages and geochemical and Sr-Nd-Pb isotopic data are presented for the gabbroic intrusive from the southern Taihang Mountains to characterize the nature of the Mesozoic lithospheric mantle beneath the central North China Craton (NCC). The gabbroic rocks emplaced at 125 Ma and are composed of plagioclase (40-50%), amphibole (20-30%), clinopyroxene (10-15%), olivine (5-10%) and biotite (5-7%). Olivines have high MgO (Fo = 78-85) and NiO content. Clinopyroxenes are high in MgO and CaO with the dominant ones having the formula of En 42-46Wo 41-50Fs 8-13. Plagioclases are dominantly andesine-labradorite (An = 46-78%) and have normal zonation from bytownite in the core to andesine in the rim. Amphiboles are mainly magnesio and actinolitic hornblende, distinct from those in the Precambrian high-pressure granulites of the NCC. These gabbroic rocks are characterized by high MgO (9.0-11.04%) and SiO 2 (52.66-55.52%), and low Al 2O 3, FeOt and TiO 2, and could be classified as high-mg basaltic andesites. They are enriched in LILEs and LREEs, depleted in HFSEs and HREEs, and exhibit ( 87Sr/ 86Sr) i = 0.70492-0.70539, ɛNd( t) = - 12.47-15.07, ( 206Pb/ 204Pb) i = 16.63-17.10, Δ8/4 = 70.1-107.2 and Δ7/4 = - 2.1 to - 9.4, i.e., an EMI-like isotopic signatures. Such geochemical features indicate that these early Cretaceous gabbroic rocks were originated from a refractory pyroxenitic veined-plus-peridotite source previously modified by an SiO 2-rich melt that may have been derived from Paleoproterozoic subducted crustal materials. Late Mesozoic lithospheric extension might have induced the melting of the metasomatised lithospheric mantle in response to the upwelling of the asthenosphere to generate these gabbroic rocks in the southern Taihang Mountains.

  18. Mineralogical and geochemical constraints on contribution of magma mixing and fractional crystallization to high-Mg adakite-like diorites in eastern Dabie orogen, East China (United States)

    Zhang, Chao; Ma, Changqian; Holtz, Francois; Koepke, Jürgen; Wolff, Paul Eric; Berndt, Jasper


    The Liujiawa pluton which is located near the eastern boundary of the Dabie orogen is composed of multiple lithologic units including mainly gabbronorites, diorites, granodiorites and hornblende gabbros. Gabbronorites and hornblende gabbros occur as enclaves in dioritic hosts which show gradual contact with granodiorites. Zircon U-Pb dating indicates that gabbronorites and diorites formed coevally at ~ 128 Ma, but they have distinct zircon Hf isotopes with εHf(t) of - 26 to - 23 (gabbronorite) and of - 32 to - 27 (diorite) respectively. Petrographic observations and rock-forming mineral compositions clearly show mixing between mafic and felsic magma end-members, which might have formed the homogeneous whole-rock Sr-Nd isotopes with εNd(t) of - 17 to - 25 and initial 87Sr/86Sr of 0.707 to 0.709. As revealed by zircon Hf isotopes, F concentrations in amphibole and biotite and thermodynamic modeling of crystallization, the gabbronorites represent enriched lithospheric mantle-derived magmas which evolved by fractional crystallization of orthopyroxene, clinopyroxene, magnetite and/or amphibole, whereas the granodiorites may be derived from the Dabie Archean basement. Mineralogical and geochemical data as well as major and trace element modeling show that the origin of diorites, previously interpreted as high-Mg adakites, can be explained by magma mixing between the crust-derived granodioritic magmas and the differentiation products of mantle-derived gabbronoritic magmas. As a result, the high-Mg adakite-like geochemistry of the diorites is a consequence of magma differentiation at a crustal depth, involving fractional crystallization and magma mixing, rather than an intrinsic feature of primitive melts. The mantle upwelling in the adjacent central Middle-Lower Yangtze River metallogenic (MLYR) belt during Late Jurassic-Early Cretaceous belt might have acted as a precursor and triggered the partial melting of lithospheric mantle beneath the eastern Dabie orogen and the

  19. Characterization of jade and silicates of the jade family for application in radiation dosimetry; Caracterizacao do jade e dos silicatos da familia do jade para aplicacao em dosimetria das radiacoes

    Energy Technology Data Exchange (ETDEWEB)

    Melo, Adeilson Pessoa de


    The main dosimetric properties of jade and of Brazilian silicates of the jade family were studied for application in radiation dosimetry of high doses. Jade is a common denomination of two different silicates: jadeite, Na Al(Si{sub 2}O{sub 6}), and nephrite, Ca{sub 2}(Mg, Fe){sub 5}(Si{sub 4}O{sub 11}){sub 2} (OH){sub 2}, that belong to the subclasses of the pyroxenes and amphiboles respectively. The jade samples studied in this work were from: Austria, New Zealand, United States and Brazil. The Brazilian silicates of the jade family studied in this work were the amphiboles: tremolite,Ca{sub 2}Mg{sub 5}(Si{sub 4}O{sub 11}){sub 2}(OH){sub 2} e actinolite, Ca{sub 2}Fe{sub 5}(Si{sub 4}O{sub 11}){sub 2}(OH){sub 2}; and the pyroxenes: rhodonite, MnSiO{sub 3} and diopside, Ca Mg(Si{sub 2}O{sub 6}). The mineralogical and chemical composition of these materials were obtained using the neutron activation analysis and X-ray diffraction techniques. The main dosimetric properties (emission curves, calibration curves, reproducibility, lower detection limits, angular and energy dependence, etc) were studied using the thermoluminescent (T L), thermally stimulated exo-emission (TSEE) and electronic paramagnetic resonance (EPR) techniques. The jade-Teflon and the silicate-Teflon samples present two T L peaks around 115 deg C (peak 1) and 210 deg C (peak 2). The calibration curves of the studied materials present a linear behaviour between 0.5 Gy and 1 kGy. The TSEE emission peak occurs at 240 deg C for all samples, and the calibration curves present a sub linear behaviour between 100 Gy and 20 kGy. In the case of the EPR technique, only jade USA has a potential application for radiation dosimetry. A static computational simulation of the most probable intrinsic and extrinsic defects in rhodonite was also realized. Among the basic defects, the Schottky defects of rhodonite are the most probable to occur and, among the extrinsic defects, the divalent and trivalent dopants present the

  20. Characterization of jade and silicates of the jade family for application in radiation dosimetry

    International Nuclear Information System (INIS)

    The main dosimetric properties of jade and of Brazilian silicates of the jade family were studied for application in radiation dosimetry of high doses. Jade is a common denomination of two different silicates: jadeite, Na Al(Si2O6), and nephrite, Ca2(Mg, Fe)5(Si4O11)2 (OH)2, that belong to the subclasses of the pyroxenes and amphiboles respectively. The jade samples studied in this work were from: Austria, New Zealand, United States and Brazil. The Brazilian silicates of the jade family studied in this work were the amphiboles: tremolite,Ca2Mg5(Si4O11)2(OH)2 e actinolite, Ca2Fe5(Si4O11)2(OH)2; and the pyroxenes: rhodonite, MnSiO3 and diopside, Ca Mg(Si2O6). The mineralogical and chemical composition of these materials were obtained using the neutron activation analysis and X-ray diffraction techniques. The main dosimetric properties (emission curves, calibration curves, reproducibility, lower detection limits, angular and energy dependence, etc) were studied using the thermoluminescent (T L), thermally stimulated exo-emission (TSEE) and electronic paramagnetic resonance (EPR) techniques. The jade-Teflon and the silicate-Teflon samples present two T L peaks around 115 deg C (peak 1) and 210 deg C (peak 2). The calibration curves of the studied materials present a linear behaviour between 0.5 Gy and 1 kGy. The TSEE emission peak occurs at 240 deg C for all samples, and the calibration curves present a sub linear behaviour between 100 Gy and 20 kGy. In the case of the EPR technique, only jade USA has a potential application for radiation dosimetry. A static computational simulation of the most probable intrinsic and extrinsic defects in rhodonite was also realized. Among the basic defects, the Schottky defects of rhodonite are the most probable to occur and, among the extrinsic defects, the divalent and trivalent dopants present the best possibility of inclusion in rhodonite. (author)

  1. The Gifford Creek Ferrocarbonatite Complex, Gascoyne Province, Western Australia: Associated fenitic alteration and a putative link with the ~ 1075 Ma Warakurna LIP (United States)

    Pirajno, Franco; González-Álvarez, Ignacio; Chen, Wei; Kyser, Kurt T.; Simonetti, Antonio; Leduc, Evelyne; leGras, Monica


    The Gifford Creek Ferrocarbonatite Complex (GFC), located in the Neoarchean-Palaeoproterozoic Gascoyne Province, Western Australia, comprises sills, dykes, and veins of ferrocarbonatite intruding the Pimbyana Granite and Yangibana Granite of the Durlacher Supersuite and metasedimentary rocks of the Pooranoo Metamorphics. The ferrocarbonatites are associated with complex and irregularly distributed zones of fenitic alteration. These ferrocarbonatites and fenites are also associated with a swarm of ironstone veins, containing magnetite, hematite and goethite. The GFC and associated fenite outcrops are distributed within a ~ 700 km2 area, north of the Lyons River Fault. Ferrocarbonatite sills and dykes are predominant in a northwest-trending belt, along the southern margin of the complex; whereas ferrocarbonatite veins tend to be distributed in a series of sub-parallel west-northwest-trending linear belts, generally associated with the Fe oxide veins with sinuous trends. These veins have margins of Fe-rich carbonates associated with zones of alteration that have a fenitic character. The fenitic haloes are characterised by the presence of Na-K-feldspars and/or Na-amphiboles and magnetite. In some cases monomineralic feldspar zones (orthoclasite) are present. Fenitic alteration is spatially associated with the carbonatites, but it can also form discrete veins and veinlets in basement granitic rocks (Pimbyana and Yangibana Granites). Petrographic, XRD and SEM analyses show that the ferrocarbonatites are dominantly composed of ankerite-dolomite, magnetite, arfvedsonite-riebeckite, and lesser calcite. Alkali amphibole has compositions ranging from potassian magnesio-arfvedsonite to magnesio-riebeckite. Sills and dykes north of the Lyons River, are characterised by a carbonate-rich matrix, containing > 50 vol.% ankerite-dolomite, with accessory quantities of apatite, barite, monazite, and phlogopite. In-situ U-Pb age determination of apatite grains by LA-ICP-MS on a sample

  2. Geochemical modeling and Nd-Sr data links nephelinite-phonolite successions and xenoliths of Trindade Island (South Atlantic Ocean, Brazil) (United States)

    Bongiolo, E. M.; Pires, G. L. C.; Geraldes, M. C.; Santos, A. C.; Neumann, R.


    The Trindade Island corresponds to the eastern end of the submarine E-W Vitória-Trindade Chain as part of the Trindade plume track on the South American plate. It is a suitable site for petrogenetic investigations, since a series of unusual rock compositions crops out within nephelinite-phonolite successions and scarce xenoliths. Software-based geochemical modeling and Nd-Sr analyses, coupled with field work, petrography and literature data were used to evaluate and model the petrogenetic processes that led to the formation of variable rock compositions. Results show the formation of: (1) nephelinites at 1490 °C and 3 GPa, from 0.1 to 7% of partial melting of an enriched garnet-lherzolitic source or from 1 to 5% partial melting of TiO2-rich garnet-phogopite lherzolite (up to 2.5 wt.% of CO2). Nephelinites represent low viscosity (18 Pa s), high-temperature (1170 °C) and high-density (2.79 g/cm3) lavas; (2) pyroxenite, jacupirangite and melteigite cumulates at 900 °C and 0.5 GPa, after 46%, 49% and 56% fractional crystallization of nephelinites, and leaving phonotephrites as residual liquids; (3) monchiquites, from fractional melting of enriched, CO2-bearing garnet-amphibole-phlogopite peridotites or from hydrated nephelinite magmas. They may evolved to sannaite via fractional crystallization or may generate phonolites through extraction of pyroxene and amphibole cumulates at 1080 to 970 °C and 1.2 to 0.9 GPa; (4) sannaites may represent 'hydrous' phonotephrites, and can evolve to phonolites and phonolitic foidites via fractional crystallization; and (5) bebedourite cumulates at 850 °C and 0.38 to 0.4 GPa, from phonotephritic or sannaitic magmas after 20% and 26% of fractional crystallization, leaving phonolites and phonolite-foidites as residual liquids. Phonolites and phonolitic foidites, the most evolved rocks of the nephelinite-phonolite association, represent higher-viscosity (1.1 × 106 Pa s), lower-temperature (950 °C), and lower-density (2.48 g/cm3

  3. Metasomatic modification of oceanic crust during early stages of subduction recorded in Mariana blueschist (United States)

    Zack, Thomas; Savov, Ivan P.; Pabst, Sonja; Schmitt, Axel K.


    Serpentine mud volcanoes from the Mariana forearc bear unique witness of metasomatic processes in an active subduction zone in the form of centimeter-size blueschist-facies xenoliths. Charcateristic metamorphic assemblages point to conditions of ca 400°C and a formation depth of 27 km. Bulk rock compositions of amphibole-talc schists and chlorite-rich schists lie on a mixing line, extending from typical MORB towards SiO2-enriched mantle. Such mixing trends are remarkably similar to findings from the amphibolite-facies assemblages of the Catalina schist, although they equilibrated at much lower temperatures (Pabst et al. 2012). These observations demonstrate that the material experienced severe metasomatic changes at the slab-mantle interface in the shallow forearc. Further supporting evidence derives from δ11B measurements: phengite, amphibole and chlorite within the clasts have boron isotope values of -6±4‰, significantly lighter than oceanic crust, requiring isotopic fractionation by fluids carrying an isotopically heavy B component (Pabst et al. 2012). Although most current models assume that the Mariana blueschists record conditions of the ongoing subduction process, our recent findings indicate otherwise. Large (>100 µm) rutiles with high U (ca 20 ppm) found in one blueschist clast were dated by HR-SIMS at UCLA employing recently established U/Pb dating techniques (Schmitt & Zack 2012). Rutile concordia ages were tightly constrained at 48.1±2.9 Ma and are reproduced by concordia ages of low Th/U zircons at 47.5±1.5 Ma in the same sample. As those ages are interpreted to be formation ages of metasomatically modified blueschists and are only a few million years older than subduction initiation (at ca 50-52 Ma), we draw the following conclusions: (1) fast cooling of the downgoing oceanic crust must occur right after subduction initiation; (2) effective metasomatic and mechanical mixing processes (subduction channels?) must be established early in

  4. Miocene to Quaternary volcanism in NW Iran Azerbaijan: new geochemical and geochronological data (United States)

    Lechmann, Anna; Burg, Jean-Pierre; Faridi, Mohammad


    The Mesozoic to Present geology of Iran has been shaped by the northward subduction of the Neo-Tethys Ocean during convergence and subsequent collision between Arabia and Eurasia, leading to the generation of magmatic arcs and seeding the conditions for the formation of the Turkish-Iranian Plateau. Over this Plateau, Miocene to Quaternary magmatic rocks cover vast areas. Processes, such as lithospheric delamination or slab break-off, which led to this widespread magmatism are still debated. We present major and trace element analyses together with LA-ICP-MS U-Pb zircon ages of domes and lavas from NW Iran Azerbaijan, with the goal to shed light on the generation and evolution of these recent magmatic rocks and compare them with previously published information. We focused on morphologically prominent domes scattered over the region. The sampled domes, dominantly dacitic to rhyolitic in composition, and the lavas, showing a wide range from basaltic to dacitic and few alkaline compositions, have tholeiitic to calc-alkaline and shoshonitic chemical features. REE patterns are steep and flatten towards the HREE. Plots of primitive mantle normalized trace elements systematically show a negative Nb-Ta anomaly indicating a subduction-modified component in the mantle source and/or crustal contamination. U-Pb zircon ages on one lava, two tuffs and 12 dacitic domes yield two distinct age distributions: (1) middle Miocene (ca. 10-12 Ma) and (2) latest Miocene - late Pleistocene (ca. 2-5.5 Ma). Ascribing these two age clusters to trace element compositions reveals that REE patterns became more depleted from middle Miocene to late Pleistocene. On a plot of Rb/Sr vs Ba/Rb the samples follow a low Rb/Sr trend typical for an amphibole-bearing mantle source. First Sr-Nd isotope results lie within or near the mantle array, making crustal contamination enigmatic. Coeval lavas in neighbouring regions (e.g. Ararat) show similar major/trace element and Sr-Nd isotopic compositions and the

  5. Dynamics of mineral crystallization at inclusion-garnet interface from precipitated slab-derived fluid phase: first in-situ synchrotron x-ray measurements (United States)

    Malaspina, Nadia; Alvaro, Matteo; Campione, Marcello; Nestola, Fabrizio


    Remnants of the fluid phase at ultrahigh pressure (UHP) in subduction environments may be preserved as primary multiphase inclusions in UHP minerals. These inclusions are frequently hosted by minerals stable at mantle depths, such as garnet, and show the same textural features as fluid inclusions. The mineral infillings of the solid multiphase inclusions are generally assumed to have crystallized by precipitation from the solute load of dense supercritical fluids equilibrating with the host rock. Notwithstanding the validity of this assumption, the mode of crystallization of daughter minerals during precipitation within the inclusion and/or the mechanism of interaction between the fluid at supercritical conditions and the host mineral are still poorly understood from a crystallographic point of view. A case study is represented by garnet orthopyroxenites from the Maowu Ultramafic Complex (China) deriving from harzburgite precursors metasomatised at ~ 4 GPa, 750 °C by a silica- and incompatible trace element-rich fluid phase. This metasomatism produced poikilitic orthopyroxene and inclusion-rich garnet porphyroblasts. Solid multiphase primary inclusions in garnet display a size within a few tens of micrometers and negative crystal shapes. Infilling minerals (spinel: 10-20 vol.%; amphibole, chlorite, talc, mica: 80- 90 vol.%) occur with constant volume ratios and derive from trapped solute-rich aqueous fluids. To constrain the possible mode of precipitation of daughter minerals, we performed for the first time a single-crystal X-ray diffraction experiment by means of Synchrotron Radiation at DLS-Diamond Light Source. In combination with electron probe microanalyses, this measurement allowed the unique identification of each mineral phase and their reciprocal orientations. We demonstrated the epitaxial relationship between spinel and garnet and between some hydrous minerals. Epitaxy drives a first-stage nucleation of spinel under near-to-equilibrium conditions

  6. Orogenic plateau magmatism of the Arabia-Eurasia collision zone (United States)

    Allen, M. B.; Neill, I.; Kheirkhah, M.; van Hunen, J.; Davidson, J. P.; Meliksetian, Kh.; Emami, M. H.


    generally applicable as melt triggers. Enigmatic lavas are erupted over the thick lithosphere of Kurdistan Province, Iran. These alkali basalts and basanites have the chemical characteristics of small degree (<1%) melts in the garnet stability field. Most possess supra-subduction zone chemistry (La/Nb = 1-3), but this signature is highly variable. Similar La/Nb variability occurs in the basic lavas of Damavand volcano in the Alborz Mountains of northern Iran. Modelling suggests the depletion of residual amphibole during the progression of partial melting can explain the observed La/Nb range. This melting may occur as the result of lithospheric thickening. At depths of ~90 km, amphibole-bearing peridotite crosses an experimentally-determined "backbend" in its solidus. Melting can continue while the source remains hydrated. Such "compression" melting may apply to parts of other orogenic plateaux, including Tibet.

  7. Gem-bearing basaltic volcanism, Barrington, New South Wales: Cenozoic evolution, based on basalt K-Ar ages and zircon fission track and U-Pb isotope dating

    International Nuclear Information System (INIS)

    Based on basalt K-Ar and zircon fission track dating, Barrington shield volcano was active for 55 million years. Activity in the northeast, at 59 Ma, preceded more substantial activity between 55 and 51 Ma and more limited activity on western and southern flanks after 45 Ma. Eruptions brought up megacrystic gemstones (ruby, sapphire and zircon) throughout the volcanism, particularly during quieter eruptive periods. Zircon fission track dating (thermal reset ages) indicates gem-bearing eruptions at 57, 43, 38, 28 and 4-5 Ma, while U-Pb isotope SHRIMP dating suggests two main periods of zircon crystallisation between 60 and 50 Ma and 46-45 Ma. Zircons show growth and sector twinning typical of magmatic crystallisation and include low-U, moderate-U and high-U types. The 46 Ma high-U zircons exhibit trace and rare-earth element patterns that approach those of zircon inclusions in sapphires and may mark a sapphire formation time at Barrington. Two Barrington basaltic episodes include primary lavas with trace-element signatures suggesting amphibole/apatite-enriched lithospheric mantle sources. Other basalts less-enriched in Th, Sr, P and light rare-earth elements have trace-element ratios that overlap those of HIMU-related South Tasman basalts. Zircon and sapphire formation is attributed to crystallisation from minor felsic melts derived by incipient melting of amphibole-enriched mantle during lesser thermal activity. Ruby from Barrington volcano is a metamorphic type, and a metamorphic/metasomatic origin associated with basement ultramafic bodies is favoured. Migratory plate/plume paths constructed through Barrington basaltic episodes intersect approximately 80% of dated Palaeogene basaltic activity (65-30 Ma) along the Tasman margin (27-37 deg S) supporting a migratory plume-linked origin. Neogene Barrington activity dwindled to sporadic gem-bearing eruptions, the last possibly marking a minor plume trace. The present subdued thermal profile in northeastern New South

  8. Quartz And Zircon as markers of the magmatic-hydrothermal evolution of the Antônio Vicente Granite, Velho Guilherme Intrusive Suite, Carajás Province

    Directory of Open Access Journals (Sweden)

    Claudio Nery Lamarão


    Full Text Available the Antônio Vicente Granite, Carajás Province, by scanning electron microscope-cathodoluminescence (SEM-CL images. In the lessevolved rocks, containing amphibole and biotite, well developed anhedral to subhedral, luminescent and intensely fractured crystalsdominate, named Qz1. Hydrothermal fluids that percolated the granite modified the magmatic quartz (Qz1 into Qz2 and Qz3 throughprocesses of alteration, dissolution and recrystallization, with these changes much more evident in the intensely altered syenograniterocks. Qz4 constitute medium-to-coarse grained crystals, usually luminescent and comparatively little fractured. Its occurrence is restrictedto strongly hydrotermalized syenogranite rocks and bodies of greisens, suggesting the beginning of the greisenization process.In the greisens, medium-to-coarse grained euhedral, concentrically zoned quartz crystals dominate, with typical features of hydrothermalorigin (Qz5. Fine crystals of zoned cassiterite (≤ 100 μm are common and fill cavities in the types Qz4 and Qz5. Zircon crystalsdominantly anhedral, corroded, with the highest contents of Hf and the lower Zr/Hf ratios belong to more evolved and hydrothermallyaltered rocks and to associated greisens, both carriers of Sn mineralization. This fact suggests that the geochemical signature of zircon,especially Zr/Hf ratio, can be used for the preliminary assessment of metallogenic potential of tin granites.

  9. Magma genesis of the pre-extensional early miocene silicic pyroclastic rocks of the Pannonian Basin (United States)

    Olah, I.; Harangi, Sz.


    The Neogene evolution of the Pannonian Basin was accompanied with various volcanic activities started with explosive eruptions of silicic magmas followed by formation of calc-alkaline and alkaline volcanic rocks and subordinate potassic-ultrapotassic volcanic products. The Miocene silicic ignimbrites and pyroclastic fall deposits cover a large region in the Pannonian Basin and therefore have a great stratigraphic significance. In addition, they have strong geodynamic implications because they were formed just before and coeval with the extensional formation of the Pannonian Basin. Traditionally, they are divided into three horizons; however, our new geochemical and volcanologic data do not prove the existence of these three separate units. In this paper, we are focusing on the oldest, pre-extensional silicic pyroclastic rocks. Based on the detailed investigation of the main mineral phases (e.g., plagioclases, amphibole, biotite) and the accessory minerals, especially zircons, we suggest a complex magmagenesis including mixing of mantle derived and crustal derived melts. Detailed zircon morphology studies involving the method of Pupin and CL image analysis proved that it could be used to correlate the scattered localities. In addition, these data showed systematic change in the magmagenesis of the different occurrences. Early Miocene silicic ignimbrites from the southern part of the Pannonian Basin contain greater mantle component, whereas those from the northern regions could involve more crustal component. In addition, zoning patterns and mineral chemical data of the pehnocrysts suggest non-equilibrium crystallization process in an open system magma chamber.

  10. First Direct Detection of Clay Minerals on Mars (United States)

    Singer, R. B.; Owensby, P. D.; Clark, R. N.


    Magnesian clays or clay-type minerals were conclusively detected in the martian regolith. Near-IR spectral observations of Mars using the Mauna Kea 2.2-m telescope show weak but definite absorption bands near microns. The absorption band positions and widths match those produced by combined OH stretch and Mg-OH lattice modes and are diagnostic of minerals with structural OH such as clays and amphiboles. Likely candidate minerals include serpentine, talc, hectorite, and sponite. There is no spectral evidence for aluminous hydroxylated minerals. No distinct band occurs at 2.55 microns, as would be expected if carbonates were responsible for the 2.35 micron absorption. High-albedo regions such as Elysium and Utopia have the strongest bands near 2.35 microns, as would be expected for heavily weathered soils. Low-albedo regions such as Iapygia show weaker but distinct bands, consistent with moderate coatings, streaks, and splotches of bright weathered material. In all areas observed, the 2.35-micron absorption is at least three times weaker than would be expected if well-crystallized clay minerals made up the bulk of bright soils on Mars.

  11. The Pan-African evolution of NW Angola and peri-atlantic correlations (United States)

    Monié, P.; Bosch, D.; Bruguier, O.; Vauchez, A.; N'sungani, P.; Rolland, Y.


    At the end of Neoproterozoic times, assembly of the Gondwana supercontinent resulted in the closure of several oceanic domains and accretion of large cratons. Various tectono-metamorphic belts developed at the margins of these cratons during the Panafrican orogeny. During this work, we conducted a study combining petro-structural and geochronological investigations on the West Congolian belt (NW Angola) resulting from the collision between the Congo and Sao Francisco cratons. U-Pb zircon/monazite and Ar-Ar amphibole/biotite ages from high-grade metamorphic rocks, migmatites and metagranites indicate that this area underwent two main deformation events at c. 540 and 490 Ma, which were followed by tectonically assisted exhumation during eastward thrusting of the hinterland domain onto the foreland domain. High grade conditions in the West Congo Belt are 20 to 40 Ma younger than in the Ribeira-Araçuai belt of Brazil, its South-American counterpart, or in the westernmost Kaoko belt of Namibia, its African correlative. In the present state of knowledge, a more appropriate counterpart to the West Congo Belt may be restricted to the Cabo Frio Terrane in the eastern Ribeira belt, which yields a broadly similar evolution.

  12. Oxygen isotopes in coexisting garnets, clinopyroxenes and phlogopites of Roberts Victor eclogites: implications for petrogenesis and mantle metasomatism (United States)

    Ongley, Jennifer S.; Basu, Asish R.; Kurtis Kyser, T.


    δ 18O values of coexisting garnet, clinopyroxene and phlogopite for twelve compositionally and texturally diverse Roberts Victor eclogite xenoliths range from +3.8 to +7.1, +4.0 to +7.4 and +5.9 to +7.4, respectively. Differences between theδ 18O values of coexisting garnets and clinopyroxenes are normally zero; however, there is some variation in theδ 18O values of different fractions of the same mineral in four samples which suggests the presence of isotopic zonation and inhomogeneity, possibly resulting from the introduction of a secondary fluid which metasomatized the eclogites and resulted in the formation of phlogopite, amphibole and celsian. Theδ 18O value of the metasomatic fluid is generally buffered by the isotopic composition of the primary garnet and clinopyroxene, as indicated by a correlation between the isotopic composition of phlogopite and the primary pyroxene and garnet. The large range inδ 18O values of the eclogites and the similarity in the isotopic composition of coexisting pyroxene and garnet support the interpretation that the Roberts Victor eclogites represent metamorphosed, altered basalts. The eclogites were subjected to infiltration metasomatism in the mantle prior to their incorporation in the kimberlite, and the source of this fluid was probably unrelated to the eclogite.

  13. Important role of magma mixing in generating the Mesozoic monzodioritic-granodioritic intrusions related to Cu mineralization, Tongling, East China: Evidence from petrological and in situ Sr-Hf isotopic data (United States)

    Chen, C. J.; Chen, B.; Li, Z.; Wang, Z. Q.


    The Mesozoic ore-bearing high-Mg monzodioritic-granodioritic rocks in the Tongling mining district (East China) have been described as having adakitic affinities, and their origin has been attributed to partial melting of delaminated eclogite at depth in the mantle, followed by interaction of the resultant granitic magma with mantle peridotite. Here we present petrological data and in situ Sr isotopic data for zoned plagioclase that are inconsistent with the eclogite-derived model and instead propose a model that involves magma mixing of siliceous crustal melts and basaltic magma that was derived from metasomatized mantle in a back-arc extensional regime. The principal geochemical signatures of these Mesozoic rocks include a high-K calc-alkaline affinity, high values of Mg#, high Sr-Ba abundances, high Sr/Y and La/Yb ratios, εNd(t) = - 13.1 to - 9.0, and ISr = 0.70707-0.70824. The magma mixing model is supported by (1) the common existence of mafic microgranular enclaves (MMEs) and the disequilibrium textures of plagioclase and amphibole, (2) the 87Sr/86Sr ratios of embayed high-Ca cores of plagioclase that are distinctly lower than in the euhedral low-Ca overgrowth rims, (3) the negative correlations between whole-rock Nd and Sr isotopic ratios, and (4) the significant differences in the values of εHf(t) (- 9.5 to - 26) within different zircons from the same intrusion.

  14. Pervasive, tholeiitic refertilisation and heterogeneous metasomatism in Northern Victoria Land lithospheric mantle (Antarctica) (United States)

    Pelorosso, Beatrice; Bonadiman, Costanza; Coltorti, Massimo; Faccini, Barbara; Melchiorre, Massimiliano; Ntaflos, Theodoros; Gregoire, Michel


    The petrology of peridotite xenoliths in the Cenozoic volcanics from Greene Point (Northern Victoria Land, Antarctica) provides new constraints on the characterisation of the lithospheric mantle beneath the West Antarctic Rift. Based on mineral major and trace element models, this mantle domain is proposed to represent a residuum after 10% and 20% partial melting. Moreover, melting models and isotopic results for Sr and Nd systematics highlight the substantial contribution of tholeiitic melts percolating through peridotites. Close correlation with trace element contents in clinopyroxene phenocrysts from Ferrar and Karoo tholeiites allows us to ascribe this refertilisation event to the Jurassic. This asthenospheric melt was also able to transfer a garnet signature to the Northern Victoria Land mantle segment. The rare presence of glass and secondary phases indicate that Greene Point xenoliths were heterogeneously affected by alkaline metasomatism, probably related to the West Antarctic Rift System opening; this has also been widely observed in other Northern Victoria Land localities (i.e., Baker Rocks). Temperature and fO2 were calculated (950 °C; Δlog fO2 (QFM), - 1.70 to - 0.39) at a fixed pressure of 15 kbar, confirming the tendency of the anhydrous Greene Point xenolith population to have higher equilibration temperatures and comparable redox conditions, compared to the nearby amphibole-bearing peridotites from Baker Rocks.

  15. Extreme Mantle Heterogeneity beneath the Jingpohu Area, Northeastern China-Geochemical Evidence of Holocene Basaltic Rock

    Institute of Scientific and Technical Information of China (English)


    Holocene basaltic rocks of the Jingpohu area are located in the "Crater Forest" and Hamatang districts to the northwest of the Jingpohu Lake. Although there is only a distance of 15 km between the two districts, their petrological characteristics are very different: alkaline olivine basalt without any megacrysts in the former, and leucite tephrite with Ti-amphibole, phlogopite and anorthoclasite megacrysts in the latter. On the basis of their geochemical characteristics, the two types of basaltic rocks should belong to weakly sodian alkaline basalts. But leucite tephrite is characterized by higher Al2O3, Na2O and K2O, higher enrichment in light rare earth elements (LREE) and large ion lithophile elements (LILE), lower MgO and CaO, compatible elements and moderately compatible elements and lower Mg# values and Na/K ratios in comparison with alkaline olivine basalt. However, the two types of basaltic rocks have similar Sr, Nd, Pb isotopic compositions, which suggests that the mantle beneath the Jingpohu area was homogeneous before undergoing some geological processes about 3490 years ago. As the activity of the mantle plume led to different degrees of metasomatism, extreme mantle source heterogeneities occurred beneath the Jingpohu area. In comparison with alkaline olivine basalt, the leucite tephrite was derived from the more enriched mantle source region and resulted from strong metasomatism.

  16. Estudos de Orville Derby sobre os depósitos manganesíferos do Brasil: Edição comemorativa dos 150 anos de nascimento do cientista

    Directory of Open Access Journals (Sweden)

    Fernando Roberto Mendes Pires


    Full Text Available Em comemoração ao 150º aniversário de nascimento de Derby, breve comentário de seus trabalhos é apresentado. De 173 trabalhos científicos, Derby publicou 7 artigos sobre depósitos de manganês no período 1898-1908. Em dois desses artigos, Derby definiu o protominério de manganês "queluzito", consistindo de granada espessartita, anfibolio, e rodocrosita e tefroita, posteriormente identificados por Hussak. Nesse trabalho tentamos comparar as descrições de Derby do protominério com nossos estudos termodinâmicos aplicados às condições de equilíbrio controladas pelos potenciais químicos de SiO2 e CO2 no protominério.In commemoration of the 150th anniversary of Derby's birthday a brief review of his work has been presented. From 173 scientific works, Derby published 7 papers on the Manganese deposits in the period 1898-1908. In two of these papers, Derby defined the manganese protore "queluzite", consisting of spessartite garnet, amphibole and rhodochrosite and tephroite, later recognized by Hussak. In this work we tried to compare the Derby's descriptions with our thermodynamic studies applied to the equilibrium conditions, controlled by the chemicals potentials of SiO2 and CO2 in the protore.

  17. Pyroxene zonation trends in mafic nepheline syenite and ijolite, Diamond Jo quarry, Magnet Cove igneous alkalic complex, Arkansas

    Energy Technology Data Exchange (ETDEWEB)

    Flohr, M.J.K.; Ross, M.


    Compositions of pyroxenes from mafic nepheline syenite and ijolite from Magnet Cove (NS and IJ) define zoning trends that reflect changing conditions in the crystallizing magmas and are used to contrast Magnet Cove with other alkalic complexes. The Na-Mg-Fe/sup 2 +/+Mn plot is used to compare NS and IJ pyroxenes with pyroxenes from nepheline syenites from S. Qoroq Centre, Greenland, and the Coldwell Complex intrusions, Ontario. Trends from the three areas are similar, but differences exists. Zoning in individual NS grains is greater than ranges for individual intrusions from S. Qoroq. Also, NS pyroxenes with compositions more magnesisan than Mg/sub 50/Nag are more Al-rich than S. Qoroq and Coldwell pyroxenes, indicating crystallization from a more undersaturated magma. These NS pyroxenes also contain 2-3 times more Ti and Fe/sup 3 +/. Despite different concentrations of Al, Ti, and Fe/sup 3 +/, the general crystallization trends shown by all elements considered are similar in NS and S. Qoroq pyroxenes. Sparse biotite and the absence of amphibole in NS indicate an H/sub 2/O-poor parent magma compared with those of the Coldwell and S. Qoroq nepheline syenites, which contain these phases. Mg-rich biotites and pyroxenes in IJ indicate that it formed from a less evolved liquid than NS.

  18. New investigations in southwestern Guinea: consequences for the Rokelide belt (West Africa) (United States)

    Villeneuve, Michel; Bellon, Hervé; Corsini, Michel; Le Metour, Joël; Chatelee, Sébastien


    The southern Guinean terranes belong to the "Rokelide belt" that is located in the southwestern part of the West African craton (Senegal to Liberia). Field investigations and K-Ar and 40Ar-39Ar radiometric analysis performed on samples collected from southern Guinea provide a new interpretation for metamorphic terranes not yet dated. A K-Ar whole-rock age of a gneiss and 40Ar-39Ar plateau ages of amphiboles separated from a mylonitic gneiss of the Ouankifondi formation and a gneiss from the Kissi-Kissi formation yield several Pan-African metamorphic ages at circa 650, 560, and 530 Ma, respectively. Field investigations show that these formations are unconformably capped by the Kolente group. The previous structural framework and the geodynamic evolution of the Rokelide belt based on the coeval evolution of the Ouankifondi and Kissi-Kissi formations and the Kolente group are reassessed. The Rokelide belt is linked to the Bassaride belt. Correlations with adjacent Sierra Leonean terranes and with northern Guinea and Senegal are considered.

  19. Environmental cancer risks (United States)

    Bell, Peter M.

    In a long-awaited report (‘Assessment of Technologies for Determining Cancer Risks From the Environment’), the U.S. Office of Technology Assessment (OTA) has evaluated the role of environmental factors in cancer diseases. Environment is interpreted broadly as encompassing anything that interacts with humans, including the natural environment, food, radiation, the workplace, etc. Geologic factors range from geographic location to radiation and specific minerals. The report, however, is based on an inadequate data base in most instances, and its major recommendations are related to the establishment of a national cancer registry to record cancer statistics, as is done for many other diseases. Presently, hard statistics are lacking in the establishment of some association between the cause-effect relationship of most environmental factors and most carcinogens. Of particular interest, but unfortunately based on unreliable data, are the effects of mineral substances such as ‘asbestos.’ USGS mineralogist Malcolm Ross will review asbestos and its effects on human health in the forthcoming Mineralogical Society of America's Short Course on the Amphiboles (Reviews in Mineralogy, 9, in press, 1981).

  20. Late-orogenic, post-orogenic, and anorogenic granites: Distinction by major-element and trace-element chemistry and possible origins

    Energy Technology Data Exchange (ETDEWEB)

    Rogers, J.J.W.; Greenberg, J.K. (Univ. of North Carolina, Chapel Hill (USA))


    Granites classified into four categories based solely on tectonics of occurrence and associated rock types also have compositional characteristics that are consistent within groups and different among groups. Orogenically related granites include late-orogenic varieties (LO) associated with calc-alkaline batholiths, and post-orogenic varieties (PO), which occur in broad zones of isolated diapiric plutons in recently deformed orogenic belts. Inclined REE patterns, moderate Sr contents, and K{sub 2}O-SiO{sub 2} relationships show that late-orogenic granites formed by fractionation of plagioclase, clinopyroxene, and amphibole from calcalkaline magmas. Flatter REE patterns and K{sub 2}O contents near 5%, plus the absence of associated magmatic rocks, indicate that the post-orogenic granites developed by partial melting of subduction-produced mafic/intermediate magmatic rocks. Both the late- and post-orogenic granites can be part of material newly added to continental crust as a result of orogeny. Anorogenic granites in anorthosite/rapakivi complexes (AR) or alkaline ring complexes (RC) have LIL contents too high to have been equilibrated with a mafic mineral assemblage. These anorogenic rocks probably formed by partial melting of preexisting sialic crust and do not represent new crustal increment.

  1. Early Permian supra-subduction assemblage of the South Island terrane, Percy Isles, New England Fold Belt, Queensland

    International Nuclear Information System (INIS)

    Ultramafic-intermediate rocks exposed on the South Island of the Percy Isles have been previously grouped into the ophiolitic Marlborough terrane of the northern New England Fold Belt. However, petrological, geochemical and geochronological data all suggest a different origin for the South Island rocks and a new terrane, the South Island terrane, is proposed. The South Island terrane rocks differ from ultramafic-mafic rocks of the Marlborough terrane not only in lithological association, but also in geochemical features and age. These data demonstrate that the South Island terrane is genetically unrelated to the Marlborough terrane but developed in a supra-subduction zone environment probably associated with an Early Permian oceanic arc. There is, however, a correlation between the South Island terrane rocks and intrusive units of the Marlborough ophiolite. This indicates that the two terranes were in relative proximity to one another during Early Permian times. A K/Ar age of 277 ± 7 Ma on a cumulative amphibole-rich diorite from the South Island terrane suggests possible affinities with the Gympie and Berserker terranes of the northern New England Fold Belt. Copyright (1999) Geological Society of Australia

  2. Strain and texture measurements on geological samples using neutron diffraction at IBR-2, Joint Institute for Nuclear Research, Dubna (Russia) (United States)

    Frischbutter, A.; Janssen, Ch.; Scheffzük, Ch.; Walther, K.; Ullemeyer, K.; Behrmann, J. H.; Nikitin, A. N.; Ivankina, T. I.; Kern, H.; Leiss, B.


    Information on texture and residual stress in geological samples is very important for the calculation of physical properties connected with the evaluation of the geomechanical behavior of parts of the earths’s crust in connection with processes from human activities (mining, tunnelling) and natural processes of deformation (seismicity, earthquakes). Texture and stress are not independent of each other and in the general case should be analyzed together. Complications arise because geological samples are generally composed of several phases (minerals) whose elastic constants may be significantly different. Nevertheless, modern neutron diffractometers such as SKAT and EPSILON-MDS at the fast pulsed reactor IBR-2 at the FLNP of the JINR make it possible to obtain the needed diffraction patterns. This was shown especially for texture measurements on samples with quartz as the main component as well as for mica, feldspar, amphibole, and several other minerals. In order to extend strain measurements beyond samples composed of quartz, dolomite, and/or anhydrite to such frequently occurring minerals as feldspars and mica it would be necessary on the one hand to use Rietveld refinement with corrections due to texture and anisotropic peak broadening. With an increase in the number of mineral phases suitable for these diffractometers, it is in general necessary to improve the experimental conditions for SKAT and EPSILON-MDS, especially to significantly raise the flux of incident neutrons on the sample.

  3. Compositions of magmas and carbonate silicate liquid immiscibility in the Vulture alkaline igneous complex, Italy (United States)

    Solovova, I. P.; Girnis, A. V.; Kogarko, L. N.; Kononkova, N. N.; Stoppa, F.; Rosatelli, G.


    This paper presents a study of melt and fluid inclusions in minerals of an olivine-leucite phonolitic nephelinite bomb from the Monticchio Lake Formation, Vulture. The rock contains 50 vol.% clinopyroxene, 12% leucite, 10% alkali feldspars, 8% hauyne/sodalite, 7.5% nepheline, 4.5% apatite, 3.2% olivine, 2% opaques, 2.6% plagioclase, and < 1% amphibole. We distinguished three generations of clinopyroxene differing in composition and morphology. All the phenocrysts bear primary and secondary melt and fluid inclusions, which recorded successive stages of melt evolution. The most primitive melts were found in the most magnesian olivine and the earliest clinopyroxene phenocrysts. The melts are near primary mantle liquids and are rich in Ca, Mg and incompatible and volatile elements. Thermometric experiments with the melt inclusions suggested that melt crystallization began at temperatures of about 1200 °C. Because of the partial leakage of all primary fluid inclusions, the pressure of crystallization is constrained only to minimum of 3.5 kbar. Combined silicate-carbonate melt inclusions were found in apatite phenocrysts. They are indicative of carbonate-silicate liquid immiscibility, which occurred during magma evolution. Large hydrous secondary melt inclusions were found in olivine and clinopyroxene. The inclusions in the phenocrysts recorded an open-system magma evolution during its rise towards the surface including crystallization, degassing, oxidation, and liquid immiscibility processes.

  4. Petrography and zircon U-Pb isotopic study of the Bayanwulashan Complex: Constrains on the Paleoproterozoic evolution of the Alxa Block, westernmost North China Craton (United States)

    Wu, Sujuan; Hu, Jianmin; Ren, Minghua; Gong, Wangbin; Liu, Yang; Yan, Jiyuan


    The Bayanwulashan Metamorphic Complex (BMC) exposes along the eastern margin of the Alxa Block, the westernmost part of the North China Craton (NCC). BMC is principally composed of metamorphic rocks with amphibole plagiogneiss, biotite plagioclase gneiss and granitic gneiss. Our research has been focused on the petrography and zircon U-Pb geochronology of the BMC to better understand the evolution of the Alxa Block and its relationship with the NCC. Evidences from field geology, petrography, and mineral chemistry indicate that two distinct metamorphic assemblages, the amphibolite and greenschist facies, had overprinted the preexisting granitic gneiss and suggest that the BMC experienced retrograde metamorphic episodes. The LA-ICP-MS zircon U-Pb ages reveal that the primary magmatic activities of BMC were at ca. 2.30-2.24 Ga and the two metamorphic events were at ca. 1.95-1.91 Ga and ca. 1.88-1.85 Ga respectively. These ages indicate that BMC initially intruded during Paleoproterozoic, not as previously suggested at Archean period. The Early Paleoproterozoic metamorphic records and the magmatic thermochronological data in BMC exhibit different evolution paths between the Alxa Block and the NCC. The Alxa Block was most likely an independent Early Paleoproterozoic terrain. Following different amalgamation processes, The Alxa Block combined with Western Block at ca. 1.95 Ga and then united with NCC at ca. 1.85 Ga.

  5. Alochtónne jemnozrnné sedimenty a ich vztah ku genéze Liskovskej jaskyne (Chočské podhorie, severné Slovensko

    Directory of Open Access Journals (Sweden)

    Katarína Bónová


    Full Text Available A combination of sedimentological and mineralogical methods with emphasis on heavy mineral assemblage research applied to allochthonous sediments in the Liskovská Cave located in the western part of the Liptovská Basin (in the tectonic horst composed of Triassic limestones at foothills of the Chocské vrchy Mts. were used for the identification their provenance and sedimentary history. Allochthonous fine-grained mud was studied in three profiles (LI-1 to LI-3. The sediments originated from the suspension in slow water flow to stagnant water (slackwater facies. This material could be later redeposited during the younger flooding event and small-scale slumps and gravity flows (mudflows have been locally generated on steeper cave floors. Based on mineralogical study the cave sediments are composed of quartz, muscovite, calcite, chlorite, K-feldspar, plagioclase and dolomite. A heavy mineral assemblage is formed by garnet, zircon, apatite, monazite, tourmaline, staurolite, amphibole, rutile, titanite, epidote, sillimanite, allanite, andalusite, pyroxene and xenotime. Opaque minerals are represented by ilmenite, pyrite, magnetite, Cr-spinel, hematite, Cu-sulfides and Feoxyhydroxides. Their mineralogical character indicates the heterogenous source material which was transported by the Váh River. The results are significant for a more accurate reconstruction of origin and development of the cave, mainly its sedimentary phases in Middle and Late Pleistocene related to floods from the adjacent river bed.

  6. Exsolution lamellae and optic orientation of clinoamphiboles. (United States)

    Jaffe, H W; Robinson, P; Klein, C


    Exsolution lamellae are abundant in coexisting hornblende and cummingtonite, and in hornblende coexisting with anthophyllite in Ordovician volcanics metamorphosed in the kyanite and sillimanite zones in central Massachusetts and adjacent New Hampshire. The lamellae have the same orientation relative to the internal structure as the (100) and (001) exsolution lamellae in clinopyroxenes, but are indexed (100) and (ī01) with the C2/m space group commonly chosen for amphiboles. Specimens from the kyanite zone contain very thin (100) and (ī01) lamellae. In the sillimanite zone, both (100) and (ī01) lamellae are thicker and more abundant in iron-rich specimens than they are in magnesian specimens, as might be expected by analogy with pyroxenes from layered mafic intrusions. The (ī01 lamellae allow correct determination of the relations between the optic vibration directions and the crystallographic axes for two alternatively selected space group C2/m and I2/m. This evidence shows that there has been much confusion concerning these relations. PMID:17784317

  7. 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.

  8. Gemstones and geosciences in space and time. Digital maps to the "Chessboard classification scheme of mineral deposits" (United States)

    Dill, Harald G.; Weber, Berthold


    The gemstones, covering the spectrum from jeweler's to showcase quality, have been presented in a tripartite subdivision, by country, geology and geomorphology realized in 99 digital maps with more than 2600 mineralized sites. The various maps were designed based on the "Chessboard classification scheme of mineral deposits" proposed by Dill (2010a, 2010b) to reveal the interrelations between gemstone deposits and mineral deposits of other commodities and direct our thoughts to potential new target areas for exploration. A number of 33 categories were used for these digital maps: chromium, nickel, titanium, iron, manganese, copper, tin-tungsten, beryllium, lithium, zinc, calcium, boron, fluorine, strontium, phosphorus, zirconium, silica, feldspar, feldspathoids, zeolite, amphibole (tiger's eye), olivine, pyroxenoid, garnet, epidote, sillimanite-andalusite, corundum-spinel - diaspore, diamond, vermiculite-pagodite, prehnite, sepiolite, jet, and amber. Besides the political base map (gems by country) the mineral deposit is drawn on a geological map, illustrating the main lithologies, stratigraphic units and tectonic structure to unravel the evolution of primary gemstone deposits in time and space. The geomorphological map is to show the control of climate and subaerial and submarine hydrography on the deposition of secondary gemstone deposits. The digital maps are designed so as to be plotted as a paper version of different scale and to upgrade them for an interactive use and link them to gemological databases.

  9. 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

  10. Exploration for xenotime placers and their source rocks in Balrampur-Bhandaria area, Surguja district, Madhya Pradesh and Garhwa districts, Bihar, India

    International Nuclear Information System (INIS)

    Exploration taken up in Balrampur-Bhandaria area constituting the western part of Chhotanagar Granite Gneiss Complex, has brought to light, potential xenotime placers along several streams in Kanhar river basin. Fluvial bed-form placer bodies of side bars, island bars and braid bars with xenotime concentrates analysing up to 4.83% Y2O3 are found over a stretch of 1-5 km along these streams. Monazite is found along with xenotime and ilmenite garnet, magnetite, zircon, tourmaline, epidote and amphibole are the associated heavy minerals. Geologically, the area represents a heterogeneous provenance, predominantly comprising Precambrian metasedimentary, granitic and Gondwana Supergroup of rocks. Studies on heavy minerals separated from various granitic rocks and their residual soils revealed that grey and pink granites and the associated pegmatites with concentrates analyzing up to 4.49% Y2O3, constitute the main source rocks for the xenotime placers. Streams draining metasedimentary rocks are devoid of xenotime while, those drawing Gondwana rocks are rich in monazite. Xenotime rich placers are confined to 2nd and 3rd order streams, due to the restricted aerial extent of the source rocks in the area. Compared to the placers of Mahan river basin and Siri river in Ib river basin the placers identified in Kanhar river basin are richer in xenotime, with sizeable reserves (already established) and hence attain importance for future exploitation. (author)

  11. Laser-induced breakdown spectroscopy analysis of asbestos

    International Nuclear Information System (INIS)

    Laser-induced breakdown spectroscopy was applied to test the possibility of detecting and identifying asbestos in different samples in view of the perspective at field operation without sample preparation which is peculiar to this technique. Several like-resin materials were first investigated by laser-induced breakdown spectroscopy, in order to find an asbestos container assuring safe laboratory operation during the material characterization aimed to identify indicators suitable for a quick identification on field. Successively, spectra of asbestos samples of both in serpentine and amphibole forms were measured and the variability in elemental composition was calculated from the emission spectra. Ratios of intensities of characteristic elements were tested as indicators for asbestos recognition. Laser-induced breakdown spectroscopy results were compared with those obtained by analyzing the same asbestos samples with a scanning electron microscopy equipped with an energy dispersive X-ray spectroscopy, a good correlation was found for Mg/Si and Fe/Si, thus showing the capability of laser-induced breakdown spectroscopy as a diagnostic tool for this category of materials. In particular, it was demonstrated that the method based on two indicators derived from laser-induced breakdown spectroscopy intensity ratios allows to discriminate between asbestos and cements in single shot measurements suitable to field operation

  12. Biological effects: asbestos-cement manufacturing. (United States)

    Weill, H


    Fourteen cohorts of asbestos-cement workers have been studied. These studies have demonstrated exposure-response relationships for lung cancer, mesothelioma and asbestosis. For lung cancer, relatively consistent results have been observed, with risk two-fold or less in 13 of the 14 cohorts. Among New Orleans workers, excess risk was restricted to those with X-ray evidence of asbestosis. Workers employed at least 21 years but without X-ray abnormalities, experienced no elevated risk, while those with small opacities (1/0 or higher) had substantially elevated risk (SMR > 400). Exposures in these two groups had been similar. These results suggest that asbestosis may be a necessary precursor for asbestos-induced lung cancer; if so, then the no-threshold model for lung cancer risk is inappropriate since there is general agreement that very low exposures will not result in radiologically detectable lung fibrosis. Further data on this potential link are needed. As in other industries, mesothelioma risk was strongly related to amphibole exposure, especially to crocidolite in asbestos-cement pipe manufacture. A cluster of cases has recently been reported in a family amosite-cement business. Among New Orleans workers, risk of asbestosis was related to cumulative exposure but there was little evidence of risk below 30 f ml-1-years. Progression of asbestosis in these workers was slow, related to past cumulative exposure and not related to lung function decline. Asbestosis risk is therefore not likely to develop in workers under current controlled exposure conditions. PMID:7978975

  13. Estimating NOA Health Risks from Selected Construction Activities at the Calaveras Dam Replacement Project (CDRP) (United States)

    Hernandez, D. W.


    The CDRP is a major construction project involving up to 400 workers using heavy earth moving equipment, blasting, drilling, rock crushing, and other techniques designed to move 7 million yards of earth. Much of this material is composed of serpentinite, blueschist, and other rocks that contain chrysotile, crocidolite, actinolite, tremolite, and Libby-class amphiboles. To date, over 1,000 personal, work area, and emission inventory related samples have been collected and analyzed by NIOSH 7400, NIOSH 7402, and CARB-AHERA methodology. Data indicate that various CDRP construction activities have the potential to generate significant mineral fibers and structures that could represent elevated on site and off site health risks. This presentation will review the Contractors air monitoring program for this major project, followed by a discussion of predictive methods to evaluate potential onsite and offsite risks. Ultimately, the data are used for planning control strategies designed to achieve a Project Action Level of 0.01 f/cc (one tenth the Cal/OSHA PEL) and risk-based offsite target levels.

  14. Application of jade samples for high-doses using the EPR technique

    International Nuclear Information System (INIS)

    Full text: The dosimeter characteristics of jade samples were studied for application in dosimetry. Jade is the common denomination of two silicates: jadeite, and actinolite, which belong respectively to the subclasses of pyroxenes and amphiboles. Green materials were acquired as jade with origin in New Zealand, Austria and USA. The dosimetric properties of these materials were already studied using the thermoluminescence technique, showing their potential use for high dose dosimetry. At the Metrology Laboratory of IPEN, Sao Paulo, glasses, sand and Brazilian natural stones have been studied in relation to their dosimetric properties for high-doses using different techniques. In the present work jade samples were studied using the electronic paramagnetic resonance (EPR) technique to investigate the potential applications in gamma radiation dosimetry. The EPR spectra of different jade samples were obtained after irradiation with different absorbed doses of 50 Gy up to 10 kGy. The jade samples present one g-factor at 2.010 that grows with the absorbed dose; it can be attributed to an electron center. The EPR spectra obtained of the USA jade samples and their main dosimetric properties as reproducibility, calibration curves and energy dependence were investigated. There is no evidence in the literature about jade applications in radiation dosimetry using the EPR technique; only crystallographic aspects of synthetic samples were compared to natural ones

  15. 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 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.

  16. Sheep lymph-nodes as a biological indicator of environmental exposure to fluoro-edenite. (United States)

    Ledda, Caterina; Loreto, Carla; Pomara, Cristoforo; Rapisarda, Giuseppe; Fiore, Maria; Ferrante, Margherita; Bracci, Massimo; Santarelli, Lory; Fenga, Concettina; Rapisarda, Venerando


    A significantly increased incidence of pleural mesothelioma in Biancavilla (Sicily, Italy) has been attributed to exposure to fluoro-edenite (FE), a fibrous amphibole extracted from a local stone quarry. The lymph-nodes draining the pulmonary lobes of sheep grazing around the town were examined, to gain insights into fibre diffusion. The pasture areas of six sheep flocks lying about 3km from Biancavilla were located using the global positioning system. The cranial tracheobronchial and one middle mediastinal lymph-node as well as four lung tissue samples were collected from 10 animals from each flock and from 10 control sheep for light and scanning electron microscopy (SEM) examination. The lymph-nodes from exposed sheep were enlarged and exhibited signs of anthracosis. Histologically, especially at the paracortical level, they showed lymph-follicle hyperplasia with large reactive cores and several macrophages (coniophages) containing grey-brownish particulate interspersed with elements with a fibril structure, forming aggregates of varying dimensions (coniophage nodules). Similar findings were detected in some peribronchiolar areas of the lung parenchyma. SEM examination showed that FE fibres measured 8-41µm in length and 0.4-1.39µm in diameter in both lymph-nodes and lung tissue. Monitoring of FE fibres in sheep lymph-nodes using appropriate techniques can help set up environmental pollution surveillance. PMID:26855127

  17. Geochemical study of volcanic and associated granitic rocks from Endau Rompin, Johor, Peninsular Malaysia

    Indian Academy of Sciences (India)

    Azman A Ghani; Ismail Yusoff; Meor Hakif Amir Hassan; Rosli Ramli


    Geochemical studies and modelling show that both volcanic and granitic magmas from the western part of the Johor National Park, Endau Rompin are different and probably have different sources. The geochemical plot suggests that both dacite/rhyolite and andesite probably have a common origin as in many of the geochemical plots, these two groups form a similar trend. Volcanic rocks have a transitional geochemical character between tholeiite and calc alkaline on a Y versus Zr plot. (La/Yb)N versus La and TiO2 versus Zr modelling show that the crystallization of both granitic and volcanic magmas are controlled by a different set of minerals. The rare earth elements (REE) patterns of some of the granite and volcanic samples have pronounced negative Eu anomaly indicating plagioclase fractionation. The difference between both profiles is that the granite samples show a concave shape profile which is consistent with liquids produced by partial melting of quartz feldspathic rocks containing amphibole among the residual phase. Both magmas were generated at a different time during the subduction of Sibumasu beneath the Indochina blocks.

  18. Mineralogical and chemical character- istics of newer Dolerite Dyke around Keonjhar, Orissa: Implication for hydrothermal activity in subduction zone setting

    Indian Academy of Sciences (India)

    Piyali Sengupta; Arijit Ray; Sayantani Pramanik


    The newer dolerite dykes around Keonjhar within the Singbhum Granite occur in NE–SW, NW–SE and NNE–SSW trends. The mafic dykes of the present study exhibit several mineralogical changes like clouding of plagioclase feldspars, bastitisation of orthopyroxene, and development of fibrous amphibole (tremolite–actinolite) from clinopyroxene, which are all considered products of hydrothermal alterations. This alteration involves addition and subtraction of certain elements. Graphical analyses with alteration index and elemental abundances show that elements like Rb, Ba, Th, La and K have been added during the alteration process, whereas elements like Sc, Cr, Co, Ni, Si, Al, Fe, Mg and Ca have been removed. It is observed that in spite of such chemical alteration, correlation between major and trace elements, characteristic of petrogenetic process, is still preserved. This might reflect systematic alteration (addition or subtraction) of elements without disturbing the original element to element correlation. It has also been established by earlier workers that the evolution of newer dolerite had occurred in an arc-back arc setting which may also be true for newer dolerites of the present study. This is evident from plots of pyroxene composition and whole rock composition of newer dolerite samples in different tectonic discrimination diagrams using immobile elements. The newer dolerite dykes of the Keonjhar area may thus be considered to represent an example of hydrothermal activity on mafic rocks in an arc setting.

  19. Pan-African granulites of central Dronning Maud Land and Mozambique: A comparison within the East-African-Antarctic orogen (United States)

    Engvik, A.K.; Elevevold, S.; Jacobs, J.; Tveten, E.; de Azevedo, S.; Njange, F.


    Granulite-facies metamorphism is extensively reported in Late Neoproterozoic/Early Palaeozoic time during formation of the East-African-Antarctic orogen (EAAO). Metamorphic data acquired from the Pan-African orogen of central Dronning Maud Land (cDML) are compared with data from northern Mozambique. The metamorphic rocks of cDML are characterised by Opx±Grt-bearing gneisses and Sil+Kfs-bearing metapelites which indicate medium-P granulite-facies metamorphism. Peak conditions, which are estimated to 800-900ºC at pressures up to 1.0 GPa, were followed by near-isothermal decompression during late Pan-African extension and exhumation. Granulite-facies lithologies are widespread in northern Mozambique, and Grt+Cpx-bearing assemblages show that high-P granulite-facies conditions with PT reaching 1.55 GPa and 900ºC were reached during the Pan-African orogeny. Garnet is replaced by symplectites of Pl+Opx+Mag indicating isothermal decompression, and the subsequent formation of Pl+amphibole-coronas suggests cooling into amphibolite facies. It is concluded that high-T metamorphism was pervasive in EAAO in Late Neoproterozoic/Early Paleozoic time, strongly overprinting evidences of earlier metamorphic assemblages.

  20. Petrographic and geochemical characteristics of metabasaltes of nappe Bork between Kobeliarovo and Vysna Slana

    International Nuclear Information System (INIS)

    A short overview of the results of petrological and geochemical research of metabasaltes of several lithostratigraphic units of nappe Bork in NW part Spis-Gemer-Rudohorie Mountain is shown. This area is from a geological point of view typical by high-pressure-low temperature (HP/LT) metamorphism, represented by facies of blue shale with index mineral sodium amphibole - glaucophan. Rocks rich in glaucophan - glaucophanites are mostly formed at the expense of effusive basalt. It can be seen thanks to preserved relics intersertal or ofitic structure, but also the test results in the classification diagrams. Using a variety of discrimination diagrams we proved, that in pre-metamorphic form of HP/LT metamorphism is probably the result of tightening in subduction zone and for Hacava formation also the result of rapid exhumation. Metabasaltes of Kobeliarovo and Steinberg formations were exhumed more slowly, and consequently in their metamorphic evolution a retrograde metamorphosis into the green slate facies took place. Subduction and exhumation were associated with closing of Meliata Ocean in the Upper Jurassic (150-160 Ma). (authors)

  1. 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

  2. Geochemical provenance of soils in Kerman urban areas, Iran: Implications for the influx of aeolian dust (United States)

    Dehbandi, Reza; Aftabi, Alijan


    The investigation of the interaction of aeolian dust with residual soils has not been fully explored in the Kerman urban areas, Iran. To assess the geochemical influence of aeolian dust on the residual soils of the Kerman urban areas of Iran, 27 samples were studied petrogeochemically. The arid-semi-arid climate of the area together with the southwest-northeast prevailing wind, have deposited aeolian sands over the residual soils. Residual soils reflect similar mineral compositions to that of the underlying bedrock and include mostly calcite and quartz. However, the minor occurrences of pyroxene, amphibole, olivine, plagioclase and volcanic clasts in urban soils and aeolian dust are attributed to volcanogenic inputs transported by aeolian dust. Urban soils and aeolian dust show different geochemical signatures from the local carbonate rocks. All samples contain trace element concentrations that are higher than the carbonate bedrock. Discrimination diagrams indicate that immobile trace elements have geochemical affinity to the detrital ferromagnesian dust inputs and are different from the local carbonate bedrock. Based on the elemental bivariate and ternary diagrams, the soils and aeolian dust are derived from the interaction of carbonate and volcanic rocks. This highlights that the urban soils in the Kerman urban areas have been formed by interactions of the aeolian dust with the primitive residual soils.

  3. Floatability of Fe-bearing silicates in the presence of starch: Adsorption and spectroscopic studies

    International Nuclear Information System (INIS)

    Natural polysaccharides such as starch, dextrin, cellulose and their derivatives are promising non-toxic and biodegradable organic flocculants and flotation depressants. This paper presents the investigation of mechanism of adsorption of corn starch on quartz and Fe-bearing amphibole, i.e. pargasite. The direct measurement of starch adsorption on the mineral surfaces shows no difference between quartz and pargasite. However, the starch adsorption on the magnetite is more important. FT-IR spectroscopy studies reports different adsorption mechanism of starch on quartz and pargasite surface. The key changes observed in starch absorption on quartz are the major shifts in C-0 stretching frequencies presumed existence of a hydrogen bond between starch and quartz surface. The similar changes were observed in this region of IR-band for pargasite. The appearance and disappearance of the bands in the region 960-920 cm−1 corresponds probably to formation of a new chemical bond between starch O-H groups and metal atoms on pargasite surface with formation of a surface complex. This result confirms that adsorption of the starch on the pargasite surface is droved by two mechanism. Hence, existence of strong chemical bond between starch and pargasite surface explains decrease of its floatability compared to quartz in process of iron ore flotation and forces to search new conditioning reagent modes.

  4. Geophysical modeling and structure of Ushuaia Pluton, Fuegian Andes, Argentina (United States)

    Peroni, Javier Ignacio; Tassone, Alejandro Alberto; Menichetti, Marco; Cerredo, María Elena


    Within the area of Ushuaia Bay (Tierra del Fuego, southernmost South America) the deformed Lower Cretaceous sedimentary rocks of Yahgán Formation host the Ushuaia Pluton. The intrusive body is oval in map view; it is compositionally varied with rocks ranging from the ultrabasic to the mesosiliceous realm. The emplacement time is constrained within the Albian-Cenomanian span by new amphibole K/Ar data. Meso- and microstructures of Ushuaia Pluton and its host indicate a synkinematic emplacement with a dominant extensional component. A set of transcurrent and normal faults related to the sinistral strike-slip Beagle Channel Fault System affects the pluton and its host. On the basis of aeromagnetic data combined with field information, a new model is presented for the Ushuaia Pluton. Modeling results fit well with a laccolithic body with an estimated volume of around 111 km 3. The model pluton cross-section displays a central zone with an average thickness of 2000 m which progressively thins toward the margins (˜ 500 m) and a southern root which reaches 5000 m deep. The combined structural and geophysical model supports a transtensive scenario for the Ushuaia Pluton emplacement at Early-Late Cretaceous boundary.

  5. Flowage differentiation in an andesitic dyke of the Motru Dyke Swarm (Southern Carpathians, Romania) inferred from AMS, CSD and geochemistry (United States)

    Nkono, Collin; Féménias, Olivier; Diot, Hervé; Berza, Tudor; Demaiffe, Daniel


    Two dykes of different thickness (5.5 m for TJ31 and 23 m for TJ34) from the late Pan-African calc-alkaline Motru Dyke Swarm (S. Carpathians, Romania) have been studied by electron microprobe (mineral chemistry), crystal size distribution (CSD), anisotropy of magnetic susceptibility (AMS) and whole-rock geochemistry. All the physical and chemical variations observed across the dyke's width point to concordant results and show that the variations of both modal abundance and size of the amphibole and biotite microphenocrysts inside the dykes (deduced from the classical CSD measurements) are the result of a mechanical segregation of suspended crystals during magmatic transport. Despite a pene-contemporaneous regional tectonic, the flow-induced differentiation in the thicker dyke is characterized by the concentration of pre-existing Ti-rich pargasite-tschermakite, clinopyroxene and plagioclase crystals in the core of the dyke and of the extracted differentiated liquid near the walls. This mechanical differentiation induces a chemical differentiation with a basaltic andesite composition for the core of the dyke whereas the margins are andesitic. Thus the chilled margins appear as a slightly more evolved liquid with a Newtonian behaviour when compared to the average composition of the dyke. The localization of the liquid on both sides of the dyke has certainly facilitated the ascent of the central part of the dyke that behaved as a Binghamian mush.

  6. Geochemistry of Two Types of Basalts in the Emeishan Basaltic Province: Evidence for Mantle Plume-Lithosphere Interaction

    Institute of Scientific and Technical Information of China (English)

    张招崇; 王福生


    Based on the temporal-spatial distribution and geochemical characteristics, the Emeishan basalts can be divided into two types: high-P2O-TiO2 basalt (HPT) and low-P2O5-TiO2 basalt (LPT), which differ distinctly in geochemistry: the LPTs are characterized by relatively high abundances of MgO, total FeO and P2O5 and compatible elements (Cr, Ni, Sc), and relatively low contents of moderately compatible elements (V, Y, Yb, Co), LREE and other incompatible elements compared with the HPT. On the diagrams of trace element ratios, they are plotted on an approximately linear mixing line between depleted and enriched mantle sources, suggesting that these two types of basalts resulted from interactions of varying degrees between mantle plume and lithospheric mantle containing such volatile-rich minerals as amphibole and apatite. The source region of the LPT involves a smaller proportion of lithospheric components, while that of the HTP has a larger proportion of lithospheric components. Trachyte is generated by partial melting of the basic igneous rocks at the base of the lower continental crust. Both the two types of magmas underwent certain crystal fractionation and contamination of the lower crust at high-level magma chambers and en route to the surface.

  7. Petrology and geochemistry of dolerite dykes of Dharmapuri and Salem districts of Tamil Nadu

    International Nuclear Information System (INIS)

    Dolerite dyke sets occur distributed in the Dharmapuri and Salem districts of northern Tamil nadu. These dykes have been emplaced in the older basement composed of granulite and gneissic rocks and cut across the later formed lineament controlled alkaline complexes. They are composed of medium to coarse calcic plagioclase and clinopyroxene with biotite, amphibole, uralite, olivine, orthopyroxene, and anhedral quartz as accessories. Based on geochemical characters, the olivine bearing dykes are classed as Type I and the quartz bearing dykes as Type II. The Type I dykes resemble basalt and the Type II dykes, basaltic andesite. They display LILE> HFSE in terms of abundance. The REE values indicate enrichment of LREE relative to MREE and HREE and an E-MORB or Plume MORB signature. The geochemistry of the sampled dykes suggests derivation from a mantle plume. This plume was emplaced into the garnet lherzolite layer and subsequently into the shallower spinel lherzolite layer in the mantle. Polybaric melting of lherzolite protoliths with varying proportions of garnet and spinel occurred with subsequent fractionation to produce a source melts with E-MORB characteristics. Emplacement of these dykes was aided by crustal extension and associated fracturing to develop a dyke swarm. (author)

  8. Limits of solution of trace elements in minerals according to Henry's law: review of experimental data

    International Nuclear Information System (INIS)

    Results of a survey of experimental data on trace element partitioning between crystals and coexisting liquid and between crystals and coexisting aqueous fluid are reported. These studies involve combinations of elements such as Cs, Rb, K, Na, Li, Ba, Sr, Ni, and Sm dissolved in minerals such as feldspars, micas, feldspathoids, garnets, pyroxenes, amphibole, and olivine. It is shown that the concentration ranges of these elements in minerals with solution behaviour according to Henry's Law appear to extend to less than 1 wt.% and often to less than 100 ppm of the element in the crystalline phase. The available data indicate that the concentration ranges of solution in minerals according to Henry's Law can be positively correlated with the difference of ionic radii between trace element and the host element for which the tracer is assumed to substitute. Furthermore, studies involving crystals and coexisting aqueous fluid have been used to determine whether Henry's Law or Raoult's Law adequately describes the solution. Based on the assumption that the aqueous fluid solution can be considered ideal, models have been proposed stating that if the difference between the ionic radii of the tracer and the host element in the crystalline phase is less than about 10% (relative to the host element), the solution is ideal (Raoult's Law). With larger differences between the ionic radii, there is an excess free energy of mixing, although Henry's Law is still obeyed in the concentration ranges where crystal-fluid partition coefficients are independent of element concentration. (author)

  9. The Pangidi Anorthosite Complex, Eastern Ghats Granulite Belt, India: Mesoproterozoic Sm-Nd isochron age and evidence for significant crustal contamination

    International Nuclear Information System (INIS)

    The Pangidi Anorthosite Complex (PAC) is a small, magmatically layered body emplaced into high-grade supracrustal rocks and metamorphosed together with the host rocks in the southern sector of the Eastern Ghats Granulite Belt, South India. It is dominated by coarse-grained anorthosite and leuconorite, minor leuco-gabbronorite and ultramafics with chromitites. The anorthositic rocks contain plagioclase (An55-70) + orthopyroxene (En50-60) + augite + amphibole + ilmenite + magnetite with accessory olivine, biotite, apatite and rarely coronal garnet related to metamorphic reconstitution. Despite a less calcic plagioclase composition in the anorthosites, the major and trace element distributions are akin to comparable litho types (at similar SiO2 wt %) of the Kondapalli layered anorthosite complex in close proximity. However, the PAC shows distinct effects of metamorphism and significant modal volume of secondary hydrous mineral phases unlike the latter. A five point whole-rock Sm-Nd isochron gives 1739 ± 220 million years (Ma) (2δ) age for the complex, which constraints the younger limit to its intrusion and probably metamorphism under amphibolite to granulite facies conditions. The PAC is characterized by strikingly low εNd(at1750 Ma) of -14.4± 3.7, indicating the importance of crustal contamination in its genesis possibly involving significantly older (Late Archaean) crustal components. (author)

  10. Araxa Group in the type-area: A fragment of Neoproterozoic oceanic crust in the Brasilia Fold Belt; Grupo Araxa em sua area tipo: um fragmento de crosta oceanica Neoproterozoica na faixa de dobramentos Brasilia

    Energy Technology Data Exchange (ETDEWEB)

    Seer, Hildor Jose [Centro Federal de Educacao Tecnologica de Araxa, (CEFET), MG (Brazil); Brod, Jose Affonso; Fuck, Reinhardt Adolfo; Pimentel, Marcio Martins; Boaventura, Geraldo Resende; Dardenne, Marcel Auguste [Brasilia Univ., DF (Brazil). Inst. de Geociencias


    This study reviews the geological characteristics and puts forward a new evolution model for the Araxa Group in its type-area, the southern segment of the Neo proterozoic Brasilia Belt, Minas Gerais, Brazil. The Araxa Group is confined within a thrust sheet belonging to a syn formal regional fold, the Araxa Syn form, overlying two other thrust sheets made of the Ibia and Canastra Groups. The Araxa Group is described as a tectono stratigraphic terrane in the sense of Howell (1993). It comprises an igneous mafic sequence, with fine and coarse grained amphibolites, associated with pelitic meta sedimentary rocks, and subordinate psanmites. All rocks were metamorphosed to amphibolite facies at ca. 630 Ma ago and were intruded by collisional granites. The amphibolites represent original basaltic and gabbroic rocks, with minor ultramafic (serpentinite/ amphibole-talc schist). The basalts are similar to high Fe O tholeiites, with REE signatures that resemble E-MORB and {epsilon}{sub Nd(T)} =+ 1.1. The meta sedimentary rocks are interpreted as the result of a marine deep-water sedimentation. They have Sm-Nd model ages of 1,9 Ga, and {epsilon}{sub Nd(T)} = -10.21. The amphibolites and metasediments could represent a fragment of back-arc oceanic crust. The data presented here differ significantly from the original definition of Barbosa et al. (1970) who describe the Araxa Group as a pelitic/psanmitic sequence and the collisional granites as a basement complex. (author)

  11. Geology of the Spruce Pine District, Avery, Mitchell, and Yancy Counties, North Carolina (United States)

    Brobst, Donald Albert


    The Spruce Pine pegmatite district, a northeastward-trending belt 25 miles long and 10 miles wide, lies in parts of Avery, Mitchell, and Yancey Counties in the Blue Ridge Province of western North Carolina. The most abundant rocks in the district are interlayered mica and amphibole gneisses and schists, all of which are believed to be of Precambrian age. These rocks are cut by small bodies of dunite and associated rocks of Precambrian (?) age, large bodies of alaskite and associated pegmatite of early Paleozoic age, and basaltic and diabasic dikes and sills of Triassic (?) age. The rocks of the district have been weathered to saprolite that is locally 50 feet thick. The major structure in the area is a southwestward-plunging asymmetrical synclinorium that has its steeper limb on the northwest side. Feldspar, muscovite as sheet and scrap (ground) mica, and kaolin from the alaskite and associated pegmatite account for over 90 percent of the total mineral production of the district. Amounts of other pegmatite minerals, including quartz, beryl, columbite-tantalite, rare-earth and uranium minerals are an extremely small part of the mineral resources. Actual or potential products from other rocks are olivine, vermiculite, asbestos, talc, chromium and nickel, soapstone, mica schist, garnet, kyanite, dolomite marble, and construction materials.

  12. Reinterpretation of Mesozoic ophiolite arc, and blueschist terranes in southwestern Baja California

    Energy Technology Data Exchange (ETDEWEB)

    Sedlock, R.L. (San Jose State Univ., CA (United States). Geology Dept.)


    The nature and significance of disrupted Mesozoic oceanic rocks on Isla Santa Margarita and Isla Magdalena, western Baja California Sur, have been reinterpreted on the basis of detailed mapping and petrologic studies. Three structural units are recognized. (1) The upper plate consists of ophiolitic, arc, and forearc basin rocks. Ophiolitic rocks, including metamorphosed ultramafic rocks, gabbro, dikes, volcanic rocks, and chert, underwent strong contractional deformation and penetrative greenschist-facies metamorphism. Arc rocks, including gabbro, a dike and sill complex, compositionally diverse volcanic rocks, lahars, and volcaniclastic strata, lack a penetrative fabric and are weakly metamorphosed. Forearc basin rocks consist of unmetamorphosed conglomerated and rhythmically bedded siliciclastic turbidites. (2) The lower plate is a subduction complex consisting of weakly to moderately foliated and metamorphosed pillow and massive lavas, breccia, and tuff( ), interbedded red and green siliceous argillite, and rare radiolarian ribbon chert and limestone. Blueschist-facies metamorphism is indicated by lawsonite, aragonite, sodic amphibole, and sodic clino-pyroxene. (3) Serpentine-matrix melange crops out in shallowly dipping fault zones between the upper and lower plates. The structural and petrologic characteristics of the Mesozoic units, the geometry of contacts between them, and the age of extension are similar to those in the Isla Cedros-Vizcalno Peninsula region, 400 km to the northwest. The author infers that syn-subduction extension was a regional event that affected much of the western Baja forearc during the Late Cretaceous and Paleogene.

  13. Petrography, mineralogy and geochemistry of Cretaceous sediment samples from western Khorat Plateau, Thailand, and considerations on their provenance (United States)

    Saminpanya, Seriwat; Duangkrayom, Jaroon; Jintasakul, Pratueng; Hanta, Rattanaphorn


    At Mo Hin Khao on the western flank of Khorat Plateau, Thailand, the Phra Wihan Formation reveals litharenite and sublitharenite with some subarkose and arkose. A cuesta in the eroded sedimentary sequence exhibits spectacular rock pillars of considerable geotourist potential. The rock sequence is high in silica (SiO2 67-98 wt%) and contains quartz, mica, magnetite, chert fragments and accessory minerals such as zircon and tourmaline and amphibole species. These accessory minerals suggest felsic rocks, such as granite, granodiorite and pegmatite, were sources for the sandstones. Geochemical analyses of the sedimentary sequence suggest that source rocks may lie in the passive continental margin, before sediment transport and deposition in the Khorat Basin by rivers flowing across a large flood plain. Many depositional sequences/episodes formed thick beds of cross bedded clastic rocks. A high average maturity index (>5) indicates sedimentary reworking/recycling. Chemical Index of Alteration (CIA) values range from 47 to 98, suggesting variable chemical weathering within the source area rocks, largely representing moderate to high degrees of weathering. The average CIA value of these sediments (78) suggests that relatively extreme alteration factors were involved.

  14. Stratigraphy, petrology, and geochemistry of the Spurr Volcanic Complex, eastern Aleutian Arc, Alaska. [(Appendix for geothermal fluid chemistry)

    Energy Technology Data Exchange (ETDEWEB)

    Nye, C.J.


    The Spurr Volcanic Complex (SVC) is a calcalkaline, medium-K, sequence of andesites erupted over the last quarter of a million years by the easternmost currently active volcanic center in the Aleutian Arc. The ancestral Mt. Spurr was built mostly of andesites of uniform composition (58 to 60% SiO/sub 2/), although andesite production was episodically interrupted by the introduction of new batches of more mafic magma. Near the end of the Pleistocene the ancestral Mt. Spurr underwent Bezyianny-type avalanche caldera formation, resulting in the production of a volcanic debris avalanche with overlying ashflows. Immediately afterward, a large dome (the present Mt. Spurr) was emplaced in the caldera. Both the ashflows and dome are made of acid andesite more silicic than any analyzed lavas from the ancestral Mt. Spurr (60 to 63% SiO/sub 2/), yet contain olivine and amphibole xenocrysts derived from more mafic magma. The mafic magma (53 to 57% SiO/sub 2/) erupted during and after dome emplacement, forming proto-Crater Peak and Crater Peak. Hybrid pyroclastic flows and lavas were also produced. Proto-Crater Peak underwent glacial dissection prior to the formation of Crater Peak in approximately the same location. Appendices II through VIII contain a summary of mineral compositions; Appendix I contains geochemical data. Appendix IX by R.J. Motyka and C.J. Nye describes the chemistry of geothermal fluids. 78 refs., 16 figs., 3 tabs.

  15. Investigation of Chinese archaic jade by PIXE and {mu}Raman spectrometry

    Energy Technology Data Exchange (ETDEWEB)

    Chen, T.H. [UMR 171 du CNRS, Centre de Recherche et de Restauration des Musees de France, Palais du Louvre, Porte des Lions, 14 Quai Francois Mitterrand, 75001, Paris (France); Ecole Doctorale MMRMM, Universite de Versailles - St Quentin en Yvelines, 45 Avenue des Etats Unis, 78035, Versailles Cedex (France); Calligaro, T.; Pages-Camagna, S.; Menu, M. [UMR 171 du CNRS, Centre de Recherche et de Restauration des Musees de France, Palais du Louvre, Porte des Lions, 14 Quai Francois Mitterrand, 75001, Paris (France)


    External-beam particle-induced X-ray emission (PIXE) and {mu}Raman spectrometry were used for elemental and structural studies of Chinese archaic nephrite jades of the Guimet Asian Museum in Paris in a non-destructive way. Nephrite is a variety of tremolite-actinolite of the amphibole group, with variable iron and magnesium contents. In the present work, in addition to identification of materials, the cation distribution in nephrite was investigated. Cation order-disorder is related to thermodynamic properties of minerals, and hence associated with geological conditions of the mineral formation. Besides, it plays an important role in the mechanism of coloration. So far, little work has been done on the cation distribution in nephrite. We thus initiated this research expecting to answer open questions concerning art and archaeological issues such as jade provenance and colour. The OH stretching vibration band of nephrite, depending on the electronegativity of the bonded cations, presents a fine structure. The study of this fine structure, together with the total cation content obtained by PIXE, allows estimation of the cation distribution in nephrite. In this study, six jade artefacts, dated from the Neolithic period to the Han dynasty (about 3000 BC to 220 AD), with diverse colours including white, yellow-green, green, dark green and black, were analysed. The data obtained permits establishing a geological database for determination of nephrite provenance and explaining the correlation between colour and cation distribution. (orig.)

  16. Towards a Model for Albitite-Type Uranium

    Directory of Open Access Journals (Sweden)

    Andy Wilde


    Full Text Available Albitite-type uranium deposits are widely distributed, usually of low grade (<1% U3O8, but are often large and collectively contain over 1 million tonnes of U3O8. Uranium is hosted in a wide range of metamorphic lithologies, whose only common characteristic is that they have been extensively mylonitised. Ore minerals are disseminated and rarely in megascopic veins, within and adjacent to albitised mylonites. Grain size is uniformly fine, generally less than 50 microns. Scanning electron microscopy reveals that spatial association between uranium and various Ti-bearing phases is common. Gangue minerals include albite, carbonates (calcite and dolomite, and sodic pyroxene and amphibole. The ore rarely contains economic metals apart from uranium, phosphorous at Itataia being an exception. There is widespread evidence of hydrothermal zirconium mobility and hydrothermal zircon and other Zr phases are frequent and in some cases abundant gangue minerals. Positive correlations are noted between uranium and various high field strength elements. The group remains poorly described and understood, but a link to iron-oxide copper-gold (IOCG deposits and/or carbonatite and/or alkaline magmatism is plausible.

  17. Pyrite-pyrrhotite intergrowths in calcite marble from Bistriški Vintgar, Slovenia (United States)

    Zavašnik, J.


    Roman marble quarry in Bistrica gorge in southern Pohorje Mt. (north-eastern Slovenia) is situated in a 20 m thick lens of layered marble, at the contact zone between granodiorite and metamorphites. Grey and yellowish non-homogenous calcite marble is heavily included by mica, quartz, feldspars, zoisite, pyrite and amphiboles. In the present research, we have studied numerous pyrite (FeS2) crystals associated with yellowish-bronze non-stoichiometric pyrrhotite (Fe1-xS), not previously reported from this locality. SEM investigation revealed unusual sequence of crystallisation: primary skeletal pyrrhotite matrix is sparsely overgrown by well-crystalline pyrite, both being overgrown by smaller, well-developed hexagonal pyrrhotite crystals of the second generation. With TEM we identify the pyrrhotite as 5T-Fe1-xS phase, where x is about 0.1 and is equivalent to Fe9S10. The pyrite-pyrrhotite coexistence allows us a construction of fO2-pH diagram of stability fields, which reflects geochemical conditions at the time of marble re-crystallisation.

  18. X-Ray Diffraction (XRD and X-Ray Fluorescence (XRF Analysis of Proto-historic Votive Tablets from Chawas Cave, Hulu Kelantan, Malaysia

    Directory of Open Access Journals (Sweden)

    Zuliskandar Ramli


    Full Text Available This research was conducted to determine the origin of votive tablets found in prehistoric and proto-historic site of Chawas Cave in Hulu Kelantan. The votive tablets found in Chawas Cave showed several Buddhist images which are associated with the Srivijaya Kingdom which existed from 7th century AD until 12th century AD. To determine if the votive tablets were produced by communities that lived in Hulu Kelantan, hence the study of the chemical composition of the votive tablets should be carried out. Two techniques were employed in this research, namely the X-Ray Diffraction (XRD and X-Ray Fluorescence (XRF techniques. The techniques will determine the mineral content as well as the major and trace element content of the votive tablets. Analysis showed that all the votive tablet samples have mineral known as clinochlore. Clinochlore is one of the chlorites, namely a group of phyllosilicate minerals. Chlorite is commonly found in igneous rocks as an alteration product of mafic minerals such as pyroxene, amphibole and biotite. The votive tablets were found in a cave which consisted of limestone cave formation and it showed that the votive tablets were not produced by the local community of Hulu Kelantan. Major elements also showed that the chemical composition of the votive tablets is not similar to the composition of clay samples taken from several rivers in Hulu Kelantan.

  19. A geochemical study of metasomised peridotite and MARID nodules from the Kimberley pipes, South Africa

    International Nuclear Information System (INIS)

    A study has been made of a large collection of metasomatised peridotite, and MARID (Mica-Amphibole-Rutile-Ilmenite-Diopside) xenoliths from the Kimberley pipes, with the aim of obtaining an understanding of enrichment processes operating in the sub-continental lithospheric mantle. Petrographic and chemical evidence presented here suggest that metasomatism increases progressively in the sequence GP-GPP-PP-PKP. Pressures and temperatures of equilibration of the peridotites in this study, suggest that metasomatism increases in intensity upwards in the sub-continental lithospheric mantle (SCLM). Sr isotope data suggest that the metasomatism is young, but in addition much older enrichments have been recorded by Nd isotopes. A mineralogic expression of the ancient enrichments cannot be clearly identified, but is best represented by enriched Nd-isotopic compositions of non-metasomatic garnet. Rare phlogopites with low 143Nd/144Nd ratios are interpreted as the product of complex mixing between the young metasomatic fluids and old enriched SCLM. Data obtained in this study show that MARID mineral compositions are Fe and Ti rich compared to most peridotites, and are much poorer in Cr, Al, Mg and Ni. New and published MARID mineral Nd and Sr isotopic measurements range from slightly depleted to highly enriched compositions. MARID mineral compositions tend to overlap with those of the PKP group, and the two groups share several other charateristics

  20. An investigation of trace and isotope light elements in mineral phases from well RN-17 (Reykjanes Peninsula, SW Iceland)

    International Nuclear Information System (INIS)

    The light lithophile (Li, Be and B) and halogen (F, Cl) elements are powerful tracers of fluid transfer due to their mobility during high temperature hydrothermal processes and metamorphic devolatilisation. Moreover, although a great deal of studies have been carried out on these elements in whole rock and minerals of altered rocks from divergent and convergent plate margins, an inventory for mineral phases from the altered Icelandic oceanic crust is still incomplete. In the present paper we report the results of in situ EPMA and SIMS investigations on variously altered magmatic (plagioclase and clinopyroxene) and hydrothermal phases (amphibole and epidote) from selected cuttings drilled at different depths (400 - 3000 m) of the well RN-17, Reykjanes geothermal system (SW Iceland). Our study has benefited from the use of high-magnification SEM investigations; from ICP-MS on Li, P-TIMS determinations of boron isotope composition (δ11B) and ID analyses of B contents on the whole rock. Particularly, SIMS data on epidote have shown that alteration beneath Reykjanes has been more efficient in the shallow and intermediate cuttings, while whole rock data on boron isotope composition have revealed that the alteration has been caused firstly by δ11B-poor fluids and successively by δ11B-rich seawater-hydrothermal fluids.

  1. The chemical environment of iron in mineral fibres. A combined X-ray absorption and Mössbauer spectroscopic study. (United States)

    Pollastri, Simone; D'Acapito, Francesco; Trapananti, Angela; Colantoni, Ivan; Andreozzi, Giovanni B; Gualtieri, Alessandro F


    Although asbestos represents today one of the most harmful contaminant on Earth, in 72% of the countries worldwide only amphiboles are banned while controlled use of chrysotile is allowed. Uncertainty on the potential toxicity of chrysotile is due to the fact that the mechanisms by which mineral fibres induces cyto- and geno-toxic damage are still unclear. We have recently started a long term project aimed at the systematic investigation of the crystal-chemistry, bio-interaction and toxicity of the mineral fibres. This work presents a systematic structural investigation of iron in asbestos and erionite (considered the most relevant mineral fibres of social and/or economic-industrial importance) using synchrotron X-ray absorption and Mössbauer spectroscopy. In all investigated mineral fibres, iron in the bulk structure is found in octahedral sites and can be made available at the surface via fibre dissolution. We postulate that the amount of hydroxyl radicals released by the fibers depends, among other factors, upon their dissolution rate; in relation to this, a ranking of ability of asbestos fibres to generate hydroxyl radicals, resulting from available surface iron, is advanced: amosite > crocidolite ≈ chrysotile > anthophyllite > tremolite. Erionite, with a fairly high toxicity potential, contains only octahedrally coordinated Fe(3+). Although it needs further experimental evidence, such available surface iron may be present as oxide nanoparticles coating and can be a direct cause of generation of hydroxyl radicals when such coating dissolves. PMID:26073382

  2. Intermediate-depth earthquake generation: what hydrous minerals can tell us (United States)

    Deseta, N.; Ashwal, L.; Andersen, T. B.


    .8 to 14 wt %) but the gabbro is not (H2O content from 0 to 2.6 wt%). The hydrous nature of the PST is due to the preferential melting of hydrous minerals (chlorite and serpentine - peridotite, glaucophane, epidote, Mg-hornblende - gabbro) in the host rock, rather than later hydration associated with exhumation (greenschist facies metamorphism and later alteration). However, in the case of the gabbro, the melt can be hydrous, but is not always. Anhydrous, glassy PST is formed in association with hydrous PST in the gabbro host rock. The gabbroic PST nucleate at the boundary between a coarse-grained pegmatoidal gabbro and a fine-grained gabbro, whereas the exclusively hydrous peridotite-hosted PST only nucleate along pre-existing hydrated fractures. These facts are significant when considering the mechanism of formation of the pseudotachylyte; which is commonly thought to be associated with the preferential melting of hydrous minerals. An anhydrous melt in proximity to other hydrous melts formed contemporaneously must have formed by the same mechanism; one which can exploit more than just one rheological characteristic in the rock vis. hydrous mineralogy AND grain size changes. Furthermore the presence of anhydrous PST suggests that little or no fluid ingress occurred prior to or during PST generation. Hydrous crystallisation products in the gabbro such as glaucophane and edenite indicate that whole-sale melting of the wallrock amphiboles (glaucophane, edenite, actinolite) took place to produce a melt with dissolved H2O, out of which such blue amphiboles were able to crystallise. It is important to note that in order for amphiboles to crystallise out of a melt, H2O is required but necessarily to an under-saturated degree. i.e. it cannot be 'free' water occurring as a separate phase in the melt (Carmen and Gilbert, 1983 and Koons, 1982). It is unlikely therefore that the water in the gabbro-derived fusion melt was the result of solid-state dehydration of the wallrock

  3. Uraniferous albitites from the Lagoa Real Uranium Province, state of Bahia, Brazil

    International Nuclear Information System (INIS)

    The Uranium Province of Lagoa Real is located in the region of Caetite, throughout the south-central portion of the state of Bahia. The basic chronostratigraphic units are the metamorphic rocks - granitic rocks and gneisses of the Archean basement - and cataclastic metasomatic rocks - albitites and quartzo-feldspathic lithologies of the lower Proterozoic. The albitites, host rocks for the uranium mineralization, occur regionally as numerous lenticular and discontinuos bodies arranged submeridionally according to two main alignments forming an arc, and are therefore called linear albities in allusion to similar features in Kasachstan, Russia, where they were first given this designation. The name albitite was employed to designate the metasomatites in which albitite dominates over the other minerals. The uranium mineralization consists of uraninite and pitchblende and is confined to the ore zones of those albitites containing aegirine, alkali-amphiboles, andradite, biotite and carbonates Furthermore, it displays lithologic-structural control, the morphology being controlled by the location of shear zones. This mineralization usually takes the shape of ore shoots which pitch in the direction and dip of the lineation. The authors describe the various types of albitites (mineralized or unmineralized) and their structural and petrographic characteristics, mode of occurence, geometry, metasomatic alterations, chemistry, uranium mineralization, as well as their genetic aspects. (Author)

  4. Quaternary evolution of the rivers of northeast Hainan Island, China: Tracking the history of avulsion from mineralogy and geochemistry of river and delta sands (United States)

    Pe-Piper, Georgia; Piper, David J. W.; Wang, Ying; Zhang, Yongzhan; Trottier, Corwin; Ge, Chendong; Yin, Yong


    The mineralogy and geochemistry of sands were investigated in the Nandu and Wanquan rivers, Hainan Island, China, to determine the history of avulsion in the lower reaches of the Nandu River. The study also provided the opportunity to assess the utility of geochemical analysis of sands as a provenance tool. Much of the heavy mineral fraction in the rivers consists of subangular Fe-Ti oxide and Fe-(hydr)oxide minerals, and less stable minerals such as amphibole, epidote, and andalusite, whereas rounded resistant ilmenite, rutile, tourmaline and zircon predominate on the deltaic coast. Mineral assemblage and chemical composition of individual samples are related to specific source areas and river tributaries. The results demonstrate northwestwards flow of the Nandu River during the mid-Holocene and earlier avulsion of the river to the northeast coast, probably during a Late Pleistocene marine highstand. Minor basement tilting, producing little relief, was sufficient to divert the lower reaches of rivers, and this effect was enhanced where basalt flows dammed former river courses. Bulk sample REE geochemistry is largely controlled by the relative abundance of monazite, allanite, titanite, zircon and epidote, derived principally from granites. Detrital geochemistry alone shows too much variability to interpret provenance. However, a smaller number of heavy mineral analyses provide an understanding of the mineralogical origins of geochemical variation, thus enabling interpretations of provenance.

  5. Garnet peridotites from Pohorje: Petrography, geothermobarometry and metamorphic evolution

    Directory of Open Access Journals (Sweden)

    Mirijam Vrabec


    Full Text Available Ultrahigh-pressure (UHP metamorphism has been recorded in Eo-Alpine garnet peridotites from the PohorjeMts., Slovenia, belonging to the Eastern Alps. The garnet peridotite bodies are found within serpentinized metaultrabasitesin the SE edge of Pohorje and are closely associated with UHP kyanite eclogites. These rocks belongto the Lower Central Austroalpine basement unit of the Eastern Alps, exposed in the proximity of the Periadriaticfault system.Garnet peridotites show signs of a complex four-stage metamorphic history. The protolith stage is represented bya low-P high-T assemblage of olivine + Al-rich orthopyroxene + Al-rich clinopyroxene + Cr-spinel. Due to metamorphism,primary clinopyroxene shows exsolutions of garnet, orthopyroxene, amphibole, Cr-spinel and ilmenite. TheUHP metamorphic stage is defined by the assemblage garnet + olivine + Al-poor orthopyroxene + clinopyroxene +Cr-spinel. Subsequent decompression and final retrogression stage resulted in formation of kelyphitic rims aroundgarnet and crystallization of tremolite, chlorite, serpentine and talc.Pressure and temperature estimates indicate that garnet peridotites reached the peak of metamorphism at 4 GPaand 900 °C, that is well within the UHP stability field. Garnet peridotites in the Pohorje Mountains experiencedUHP metamorphism during the Cretaceous orogeny and thus record the highest-pressure conditions of all Eo-Alpinemetamorphism in the Alps.

  6. Eclogites of the Dabie Region: Retrograde Metamorphism and Fluid Evolution

    Institute of Scientific and Technical Information of China (English)

    顾连兴; 杜建国; 翟建平; 赵成浩; 范建国; 张文兰


    Based upon fluid effects, retrograde metamorphism of eclogites in the Dabie region can be divided into the fluid-poor, fluid-bearing and fluid-rich stages. The fluid-poor stage is marked by polymorphic inversion, recrystallization and exsolution of solid solutions, and is thought to represent eclogite-facies retrograde environments. The fluid-bearing stage is likely to have occurred at the late stage of ecologite-facies diaphthorosis and is represented by kyanite porphyroblasts, rutile, and sodic pyroxene in association with high-pressure hydrous minerals such as phengite and zoisite (clinozoisite) without significant amount of hydrous minerals such as amphibole, epidote and biotite. The fluid-rich stage might have commenced concomitantly with lower amphibolite-facies diaphthoresis and persisted all the way towards the near-surface environment. The product of this stage is characterized by plentiful hydrous and volatile-bearing phases.The dissemination-type rutile mineralizations in eclogites might have formed by preferential shearing-induced pressure solution of gangue minerals at the fluid-bearing stage. The accompanying vein rutile was precipitated from fluids of this stage after local transport and concentration, and may hence represent proximal mobilization of titanium from the eclogite. Therefore, rutile veins can be used as an exploration indicator for dissemination-type rutile deposits.

  7. Coexistence and mixing of magmas in the late precambrian Itaporanga batholith, State of Paraiba, Northeastern Brazil

    International Nuclear Information System (INIS)

    The Precambrian Cachoeirinha-Salgueiro Fold Belt (CSF) located in the western portion of the states of Pernambuco and Paraiba is intruded, in its northern portion, by several coarsely porphyritic potassic calc-alkalic batholiths. These batholiths were syntectonically emplaced in relation to the Brasiliano cycle (=Pan-African) and are commonly associated with potassium diorites suggesting coexistence and mixing between felsic and mafic magmas. In the Itaporanga batholith three petrographic domains were mapped. A hybrid zone characterized by intense mechanical mixing of granite to granodiorite and potassium diorite magmas is located towards the border of the batholith. A commingling zone where felsic porphyritic granite to granodiorite and potassium diorite rocks are individualized at outcrop scale is located towards the center of the batholith. Finally a felsic porphyritic facies occur in the hybrid zone. Similarity among chemical analyses of amphiboles from potassium dioritic enclaves of the Itaporanga batholith and from the potassium diorite stock east of it suggest a common source for both magmas. This hypothesis is corroborated by similar REE patterns for potassium dioritic enclaves of the Itaporanga batholith and for the potassium diorite stock. The batholith shows a well developed foliation which dips towards its core suggesting that the present level of exposure represents the root zone of a diapir, where intense interaction between felsic and mafic magmas took place. (author)

  8. Evaluation of the odd-even effect in limits of detection for electron microprobe analysis of natural minerals

    International Nuclear Information System (INIS)

    Limit of detection (LOD), being a fundamental quality parameter for analytical techniques, has been recently investigated and a systematic behavior has been observed for most odd-even element pairs for many techniques. However, to the best of our knowledge very few LOD data are available in published literature for electron microprobe analysis; these consist of three papers, two being on rare-earth elements and the third covering a large number of elements of atomic number between 21 and 92. These data confirm the systematic behavior of LODs for many odd-even pairs. To initiate to full this gap, we determined LODs for several major rock-forming chemical elements from Na to Fe with atomic numbers between 11 and 26, during the microprobe analysis of common minerals (olivine, plagioclase, pyroxene, amphibole, quartz, and opaques) in volcanic rocks. The odd-even effect of nuclear stability seems to be present in LOD data for most odd-even pairs investigated. Nevertheless, the experimental strategy concerning the reference materials, calibration procedure, and blank measurements, should be substantially modified to better evaluate the systematic behavior of LOD values in microprobe analysis.

  9. Preliminary study of geotectonic evolution of the southern region of Sao Francisco (MG, Brazil) craton: an interpretation based on Rb-Sr, K-Ar, Pb-Pb and fission track data

    International Nuclear Information System (INIS)

    The results obtained from isotopic dating techniques (Rb-Sr, K-Ar, Pb-Pb and fission tracks) applied to samples from the southern region of Sao Francisco craton (Mg, Brazil) are discussed. Rb-Sr and Pb-Pb ages, in total rock, allowed the determination of crust enlargement, with eventual modifications of the pre-existing crust, during the Late Archean period (3000 to 2600 million years) and the Inferior Proterozoic period (2400 to 2100 m.y.). Three main cooling periods of time were determined by K-Ar dating of mica, amphiboles and total rock at the craton border: 2200 to 1700 m.y., 1300 to 1100 m.y. and 900 to 400 m.y. related, respectively, to superposition of three cycles: Transamazonico, Uruacuano and Brasiliano. Cooling below 1100C, detected by the fission track method applied to apatites, pointed out an age of 850 m.y. at the internal parts and 550 m.y. at the craton periphery, thus showing a progressive action of Brazilian marginal movable zones in the studied region. The application of these two techniques together enabled the evaluation of the rocks cooling shape. Cooling of these samples was complex between 2700 and 2200 m.y. and slow from 2000 m.y. onwards. The integrated treatment of data from the various dating techniques is of great importance to know the geotectonic evolution of ancient polycyclic sites. (C.L.B.)

  10. Thermochemistry of minerals stable near the earth's surface

    International Nuclear Information System (INIS)

    The present proposal continues the evolution, of changing emphasis from silicate melts to glass and toward crystalline minerals stable in the shallow crustal environment, particularly amphiholes, micas, and related hydrous phases adding zeolites and carbonates to our areas of interest. This is made possible both by recent advances in our high-temperature calorimetric techniques and by an interest in extending our ideas about the systematics of ionic substitutions to more complex structures. The proposal presents the following: (a) a listing of papers, theses, and abstracts in the past 3 years supported by the present grant, (b) a summary of work on glasses containing highly charged cations and on some related crystalline phases, with proposed new directions, (c) a discussion of advances in calorimetric methods and what new possibilities they open, (d) completed and planned work on amphiboles, micas, and clays, (e) completed and proposed work on amorpous low temperature materials, (f) proposed work on zeolites, and (g) proposed work on carbonates and (h) a discussion of the energy relevance of the above projects. This is followed by the required forms, budget pages, and CV. 34 refs., 5 figs., 1 tab

  11. Mineralogical study of the hornblende gabbro in Zetang ophiolite, southern Tibet, and its genetic implications%西藏泽当蛇绿岩中角闪辉长岩矿物学特征及其成因启示

    Institute of Scientific and Technical Information of China (English)

    陈艳虹; 杨经绥; 张岚; 熊发挥; 来盛民


    西藏泽当蛇绿岩位于雅鲁藏布江缝合带东段,由地幔橄榄岩、辉长岩、玄武岩等组成,地幔橄榄岩中发育有少量辉石岩、辉长岩、异剥钙榴岩、斜长花岗岩和角闪辉长岩。本文研究的角闪辉长岩侵入于泽当地幔橄榄岩的辉石岩中,主要由角闪石、葡萄石+绿纤石和少量Fe-Ti氧化物组成。岩石中角闪石呈自形,伟晶结构,褐色,均一的干涉色,与交代成因的角闪石相比具有较高的Al2O3(7.0%~11.0%)、TiO2(1.0%~2.5%)和Na2O (1.0%~1.9%)含量,指示其为岩浆成因;Fe-Ti氧化物以磁铁矿为主(TiO2=1.2%~13.2%;Fe2O3=40.6%~61.4%;FeO=31.1%~43.6%),与钛铁矿(TiO2=36.2%~50.8%;Fe2O3=2.5%~24.6%;FeO=33.0%~43.7%)经常呈矿物对共生或出溶钛铁矿,磁铁矿—钛铁矿计算矿物平衡氧逸度(-logfo2)为12.4~22.8,约为NNO+1,比正常MORB氧化程度高,指示岩浆结晶时具有较高的水逸度。其锆石εHf(t)值为11.0~19.8,显示亏损地幔源区特征。岩石地球化学分析显示其具有高的Al2O3(20.4%~22.4%)、TiO2(1.0%~1.5%),低的MgO(4.1%~5.5%)含量类似高铝玄武岩的特征。泽当角闪辉长岩可能由亏损地幔部分熔融形成的含水岩浆经过演化(分离结晶作用等)形成的低镁高铝类似高铝玄武岩的岩浆结晶形成。然而样品严重亏损轻稀土(LREE),与常见于岛弧区的高铝玄武岩不同,可能为蛇纹石化的洋壳或地幔橄榄岩在俯冲早期脱水使得地幔楔发生部分熔融导致。对泽当蛇绿岩中侵入岩及地幔橄榄岩进行更详细的调查研究将对揭示泽当蛇绿岩的形成环境构造背景提供更多的线索。%Zetang ophiolite is mainly composed of peridotite, gabbro and basalt. Hornblende gabbro, which was intruded into the peridotite, comprises amphibole, prehnite+pumpellyite and minor Fe-Ti oxides. The amphibole in hornblende gabbro is brown euhedral with homogeneous interference color and has higher

  12. Toxicología del asbesto Toxicology of asbest

    Directory of Open Access Journals (Sweden)

    G. Luis


    Full Text Available El asbesto o amianto está constituido por un grupo de minerales metamórficos fibrosos ampliamente extendidos en el mundo. Las principales variedades de asbesto son las serpentinas y los anfíboles. El asbesto llega al organismo al inhalar sus fibras y partículas. La exposición a este material puede ocasionar diferentes enfermedades irreversibles como asbestosis, mesotelioma maligno, placas pleurales y cáncer de pulmón. Todas ellas presentan un período de latencia largo. En 1978 el asbesto fue declarada sustancia cancerígena siendo totalmente prohibido su uso en España en el año 2002.Asbest is a group of fibrous metamorphic minerals widespread in the world. The principal varieties of asbestos are serpentines and amphiboles. Asbest reaches human when the fiber an particles are inhaled. The exposure can cause irreversible diseases, like asbestosis, malignant mesothelioma, pleural plaques and lung cancer. All of them have a long latency period. In 1978, asbest was considered a carcinogenic substance and was totally forbidden in Spain during 2002.

  13. A risk assessment for exposure to grunerite asbestos (amosite) in an iron ore mine. (United States)

    Nolan, R P; Langer, A M; Wilson, R


    The potential for health risks to humans exposed to the asbestos minerals continues to be a public health concern. Although the production and use of the commercial amphibole asbestos minerals-grunerite (amosite) and riebeckite (crocidolite)-have been almost completely eliminated from world commerce, special opportunities for potentially significant exposures remain. Commercially viable deposits of grunerite asbestos are very rare, but it can occur as a gangue mineral in a limited part of a mine otherwise thought asbestos-free. This report describes such a situation, in which a very localized seam of grunerite asbestos was identified in an iron ore mine. The geological occurrence of the seam in the ore body is described, as well as the mineralogical character of the grunerite asbestos. The most relevant epidemiological studies of workers exposed to grunerite asbestos are used to gauge the hazards associated with the inhalation of this fibrous mineral. Both analytical transmission electron microscopy and phase-contrast optical microscopy were used to quantify the fibers present in the air during mining in the area with outcroppings of grunerite asbestos. Analytical transmission electron microscopy and continuous-scan x-ray diffraction were used to determine the type of asbestos fiber present. Knowing the level of the miner's exposures, we carried out a risk assessment by using a model developed for the Environmental Protection Agency. PMID:10097051

  14. Pulmonary asbestos body counts and electron probe analysis of asbestos body cores in patients with mesothelioma: a study of 25 cases

    International Nuclear Information System (INIS)

    Malignant mesotheliomas of the pleura and peritoneum are well-recognized risks of asbestos exposure. We determined the asbestos body content of the lungs from 24 cases of malignant mesothelioma (19 pleural, five peritoneal) and compared such to the content of lungs from 50 consecutive adult autopsies and four cases of overt asbestosis using a Clorox-digestion concentration technique. The cores of 90 asbestos bodies were examined by energy dispersive x-ray analysis and compared with similar data from 120 standard asbestos fibers and 20 fiberglass fibers. The malignant mesothelioma patients had asbestos body counts intermediate between those of the general population and those of patients with asbestosis, although some of the mesothelioma cases overlapped with the general population. These latter cases often lacked an identifiable occupational exposure to asbestos. EDXA studies demonstrated an amphibole core in 88 of the 90 asbestos bodies (amosite or crocidolite in 80 of 88, anthophyllite or tremolite in eight of 88), and chrysotile in two instances

  15. Incidence of pleural mesothelioma in a community exposed to fibres with fluoro-edenitic composition in Biancavilla (Sicily, Italy

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    Caterina Bruno


    Full Text Available INTRODUCTION. Amphibolic fibres with fluoro-edenitic composition characterize Biancavilla soil, including the major quarry from which building materials have been extensively extracted. These fibres induce mesothelioma in experimental animals and their in vitro biological action is similar to that of crocidolite. MATERIALS AND METHODS. Malignant mesothelioma case series and incidence were examined to evaluate the disease burden on Biancavilla inhabitants. RESULTS. The incidence of pleural mesothelioma in Biancavilla is steadily higher than in the Sicilian Region, risk estimates are more elevated in women than in men, the most affected age class is constituted by subjects aged less than 50. DISCUSSION AND CONCLUSIONS. Environmental exposure to fibres with fluoro-edenitic composition appears to be causally related to the elevated mesothelioma occurrence in Biancavilla. In this frame, environmental clean-up is the main goal to be pursued in public health terms. A contribution of scientific research to public health decision making with respect to priority setting for environmental clean-up can derive from some further selected epidemiological investigations.

  16. The low-grade Canal de las Montañas Shear Zone and its role in the tectonic emplacement of the Sarmiento Ophiolitic Complex and Late Cretaceous Patagonian Andes orogeny, Chile (United States)

    Calderón, M.; Fosdick, J. C.; Warren, C.; Massonne, H.-J.; Fanning, C. M.; Cury, L. Fadel; Schwanethal, J.; Fonseca, P. E.; Galaz, G.; Gaytán, D.; Hervé, F.


    The Canal de las Montañas Shear Zone (CMSZ), southern Patagonian Andes (51-52°S), is a low-grade mylonite belt generated from felsic ignimbritic, pelitic and basaltic protoliths of the Late Jurassic-Early Cretaceous Rocas Verdes basin. The different types of rock fabrics across the CMSZ are thought to be associated with relatively intermediate and high strain conditions, characterized by the development of a narrow western belt of S-Ć-type mylonites and phyllonites interpreted as the metamorphic sole thrust of the Sarmiento Ophiolitic Complex. Highly strained rocks of the CMSZ display a reverse, continent-ward tectonic transport, with a minor dextral component of shearing. Transitional pumpellyite-actinolite and upper greenschist facies metamorphic conditions at ca. 5-6 kbar and 230-260 °C indicate that the primary shearing event occurred in a subduction zone setting. In-situ 40Ar/39Ar laserprobe chronology yielded ages of ca. 85 Ma on syntectonic phengite which are interpreted as representing cooling synchronous with mica crystallization during the main compressive deformational event. The 78-81 Ma U-Pb zircon crystallization ages of cross-cutting plutonic and hypabyssal rocks and 40Ar/39Ar amphibole age of ca.79 Ma from lamprophyric dikes within the fold-thrust belt constrain an upper age limit of the ophiolite tectonic emplacement deformation.

  17. Chemical Weathering of New Pyroclastic Deposits from Mt. Merapi (Java), Indonesia

    Energy Technology Data Exchange (ETDEWEB)

    Fiantis, Dian; Nelson, Malik; Van Ranst, Eric; Shamshudin, Josup; Qafoku, Nikolla


    Java Island, Indonesia with abundant amount of pyroclastic deposits is located in the very active and dynamic Pacific Ring of Fires. Studying the geochemical weathering indices of these pyroclastic deposits is important to get a clear picture about weathering profiles on deposits resulting from the eruption of Mt. Merapi. Immediately after the first phase of the eruption (March to June 2006), moist and leached pyroclastic deposits were collected. These pyroclastic deposits were found to be composed of volcanic glass, plagioclase feldspar in various proportions, orthopyroxene, clinopyroxene, olivine, amphibole, and titanomagnetite. Total elemental composition of the bulk samples (including trace elements and heavy metals) were determined by wet chemical methods and X-ray fluorescence (XRF) analyses. Weathering of the pyroclastic deposits was studied using various weathering indices. The Ruxton ratio, weathering index of Parker, Vought resudual index and chemical index of weathering of moist pyroclastic are lower than the leached sample but the alteration indices (chemical and plagioclase) are slightly higher in the moist compared to the leached pyroclastic deposits.

  18. The evolution of Neoproterozoic magmatism in Southernmost Brazil: shoshonitic, high-K tholeiitic and silica-saturated, sodic alkaline volcanism in post-collisional basins

    Directory of Open Access Journals (Sweden)

    Sommer Carlos A.


    Full Text Available The Neoproterozoic shoshonitic and mildly alkaline bimodal volcanism of Southernmost Brazil is represented by rock assemblages associated to sedimentary successions, deposited in strike-slip basins formed at the post-collisional stages of the Brasilian/Pan-African orogenic cycle. The best-preserved volcano sedimentary associations occur in the Camaquã and Campo Alegre Basins, respectively in the Sul-riograndense and Catarinense Shields and are outside the main shear belts or overlying the unaffected basement areas. These basins are characterized by alternation of volcanic cycles and siliciclastic sedimentation developed dominantly on a continental setting under subaerial conditions. This volcanism and the coeval plutonism evolved from high-K tholeiitic and calc-alkaline to shoshonitic and ended with a silica-saturated sodic alkaline magmatism, and its evolution were developed during at least 60 Ma. The compositional variation and evolution of post-collisional magmatism in southern Brazil are interpreted as the result mainly of melting of a heterogeneous mantle source, which includes garnet-phlogopite-bearing peridotites, veined-peridotites with abundant hydrated phases, such as amphibole, apatite and phlogopite, and eventually with the addition of an asthenospheric component. The subduction-related metasomatic character of post-collisional magmatism mantle sources in southern Brazil is put in evidence by Nb-negative anomalies and isotope features typical of EM1 sources.

  19. Dynamics of mineral crystallization from precipitated slab-derived fluid phase: first in situ synchrotron X-ray measurements (United States)

    Malaspina, Nadia; Alvaro, Matteo; Campione, Marcello; Wilhelm, Heribert; Nestola, Fabrizio


    Remnants of the fluid phase at ultrahigh pressure (UHP) in subduction environments may be preserved as primary multiphase inclusions in UHP minerals. The mode of crystallization of daughter minerals during precipitation within the inclusion and/or the mechanism of interaction between the fluid at supercritical conditions and the host mineral are still poorly understood from a crystallographic point of view. A case study is represented by garnet-orthopyroxenites from the Maowu Ultramafic Complex (China) deriving from harzburgite precursors metasomatized at ~4 GPa, 750 °C by a silica- and incompatible trace element-rich fluid phase. This metasomatism produced poikilitic orthopyroxene and inclusion-rich garnet porphyroblasts. Solid multiphase primary inclusions in garnet display a size within a few tens of micrometres and negative crystal shapes. Infilling minerals (spinel: 10-20 vol%; amphibole, chlorite, talc, mica: 80-90 vol%) occur with constant volume proportions and derive from trapped solute-rich aqueous fluids. To constrain the possible mode of precipitation of daughter minerals, we performed for the first time a single-crystal X-ray diffraction experiment by synchrotron radiation at Diamond Light Source. In combination with electron probe microanalyses, this measurement allowed the unique identification of each mineral phase and reciprocal orientations. We demonstrated the epitaxial relationship between spinel and garnet and between some hydrous minerals. Such information is discussed in relation to the physico-chemical aspects of nucleation and growth, shedding light on the mode of mineral crystallization from a fluid phase trapped at supercritical conditions.

  20. The evolution of Neoproterozoic magmatism in Southernmost Brazil: shoshonitic, high-K tholeiitic and silica-saturated, sodic alkaline volcanism in post-collisional basins. (United States)

    Sommer, Carlos A; Lima, Evandro F; Nardi, Lauro V S; Liz, Joaquim D; Waichel, Breno L


    The Neoproterozoic shoshonitic and mildly alkaline bimodal volcanism of Southernmost Brazil is represented by rock assemblages associated to sedimentary successions, deposited in strike-slip basins formed at the post-collisional stages of the Brasilian/Pan-African orogenic cycle. The best-preserved volcano sedimentary associations occur in the Camaquã and Campo Alegre Basins, respectively in the Sul-riograndense and Catarinense Shields and are outside the main shear belts or overlying the unaffected basement areas. These basins are characterized by alternation of volcanic cycles and siliciclastic sedimentation developed dominantly on a continental setting under subaerial conditions. This volcanism and the coeval plutonism evolved from high-K tholeiitic and calc-alkaline to shoshonitic and ended with a silica-saturated sodic alkaline magmatism, and its evolution were developed during at least 60 Ma. The compositional variation and evolution of post-collisional magmatism in southern Brazil are interpreted as the result mainly of melting of a heterogeneous mantle source, which includes garnet-phlogopite-bearing peridotites, veined-peridotites with abundant hydrated phases, such as amphibole, apatite and phlogopite, and eventually with the addition of an asthenospheric component. The subduction-related metasomatic character of post-collisional magmatism mantle sources in southern Brazil is put in evidence by Nb-negative anomalies and isotope features typical of EM1 sources. PMID:16936944

  1. Petrogenesis and geochemical characterisation of ultramafic cumulate rocks from Hawes Head, Fiordland, New Zealand

    International Nuclear Information System (INIS)

    Early Cretaceous parts of the western Median Batholith (Western Fiordland Orthogneiss) represent the exposed root of a magmatic arc of dioritic to monzodioritic composition (SiO2 = 51-55 wt%; Na2O/K2O = 3.7-8.8 in this study). We characterise for the first time the field relationships, petrography, mineralogy and geochemistry of ultramafic and mafic cumulates at Hawes Head, the largest exposure of ultramafic rocks in western Fiordland. We distinguish three related rock types at Hawes Head: hornblende peridotite (MgO = 21-35 wt%); hornblendite (MgO = 15-16 wt%); and pyroxenite (MgO = 21 wt%). Petrogenetic relationships between the ultramafic rocks and the surrounding Misty Pluton of the Western Fiordland Orthogneiss are demonstrated by: (i) mutually cross-cutting relationships; (ii) similar mafic phases (e.g. pyroxene and amphibole) with elevated Mg-numbers (e.g. olivine Mg/(Mg+Fe) = 0.77-0.82); (iii) fractionation trends in mineral geochemistry; and (iv) shared depleted heavy rare earth element patterns. In addition, the application of solid/liquid partition coefficients indicates that olivine in the ultramafic rocks at Hawes Head crystallised from a magma with Mg/(Mg+Fe) = 0.54-0.57. The olivine grains therefore represent a plausible early crystallising phase of the adjacent Western Fiordland Orthogneiss (Mg/(Mg+Fe) = 0.51-0.55). (author). 42 refs., 5 figs., 1 tab.

  2. Sm/Nd isotopic data for the Santana do Ipanema high-K mega dykes as evidence for Brasiliano decompression melting at the Pernambuco-Alagoas (PE-AL) Massif, Borborema province

    International Nuclear Information System (INIS)

    This work deals with the Sm-Nd signatures of some mega dykes located close to the Northern limit of the batholith in the Santana do Ipanema plutonic complex (SIC), which comprises 6 intrusive suites. Their composition ranges from syenites to quartz syenites. They are mesocratic to leucocratic, usually equigranular but sometimes porphyritic. Their accessory mineralogy is comprised of sphene, opaque, amphibole, ± pyroxene, apatite, zircon, biotite, allanite and epidote. The main minerals are microcline, plagioclase and quartz. The SIC rocks are metaluminous and intermediate to acid, with Si O2 ranging from 55,6 wt% to 66.4 wt% and Ba ranging from 3889 ppm to 10253 pp,. The K2 O/Na2 O ratio ranges widely as well, from 0,59 to 2.07, making these rocks a quite heterogeneous suite. The diagram shows two patterns, one with troughs at Nb, Zr and Ti, while the other one shows troughs at Nb, Hf and Eu. The Zr data available show a wide range, from 133 ppm to 314 ppm, suggesting this suite was the result of different degrees of partial melting of a same enriched LIL protolith. Five isotope Sm-Nd data has been obtained for these rocks, yielding epsilon Nd (0.60 Ga) values which ranges from -9.3 to -3.6, and Tdm which ranges from 2.34 Ga to 1.26 Ga. The isotope data agree with the heterogeneous character showed by the trace elements

  3. Condiciones físicas de formación de gabros ymigmatitas derivadas de rocas máficas en el centro de la Sierra de ValleFértil, San Juan Physical conditions for the formation ofgabbros and migmatites derived from mafic rocks in the center of Sierra deValle Fértil, San Juan

    Directory of Open Access Journals (Sweden)

    AlinaM. Tibaldi


    resultadosexperimentales se demuestra que la transición desde rocas ígneas máficas amigmatitas máficas ocurrió por enfriamiento isobárico, y que el emplazamientocontinuo de magmas debió ser la fuente de calor que mantuvo la secuencia enfacies de granulitas sin dejar que el enfriamiento fuera rápido. Se interpretala geología del centro de la sierra de Valle Fértil como un ejemplo del núcleoplutónico-metamórfico del arco magmático Famatiniano donde el gradientemetamórfico anormalmente alto refleja que un volumen importante de magmasmáficos alcanzaban, y dominaban, en paleo-profundidades de entre 16 y 20kilómetros.A sequence of plutonicmafic rocks inter-stratified with both mafic- and metasedimentary-derivedmigmatites is found along the San Juan valley in the center of the Sierra deValle Fértil. This natural example shows the transition from igneous tometamorphic petrologic processes which occurred during the crystallization ofmafic magmas and the subsequent partial melting of crystallized gabbroic rocks.This work studies the mineralogical changes associate to this petrologictransition. Thermobarometric estimates based on amphibole-plagioclase indicatethat the mafic magmas crystallized at around 1100ºC and 5 ± 0.5 kbar. Theconditions under which gabbroic rocks were partially melted are estimated usingtwo pyroxenes thermometry and amphibole-plagioclase thermobarometry. Similarphysical conditions in the range between 740 and 840ºC and 5 to 6.5 kbar arerecovery from mineral assemblages in the mesosomes and leucosomes of maficmigmatites. The main mineral compositional changes that accompanied the partialprocess of the gabbroic rocks are: 1 depletion of aluminium content and Mg#ratio in pyroxenes; 2 depletion of anorthite mole fraction of theplagioclases; and 3 depletion of the Mg# ratio in amphiboles. These mineralcompositional variations are consistent with those found by experimentallymelting mafic protoliths. Experimental results showed that the temperature forpromoting

  4. Concentration of 238U and 232Th among constituent minerals of two igneous plutonic rocks exhibiting elevated natural radioactivity levels

    International Nuclear Information System (INIS)

    The concentrations of 238U and 232Th of the constituent minerals in two plutonic rock samples, from N. Greece, exhibiting elevated levels of bulk rock natural radioactivity were determined by using LA-ICP-MS. The available data of whole rock 238U and 232Th concentrations were also used. The minerals were separated using a combination of heavy liquids of various densities, shaking table and magnetic separation techniques. The great variation in the concentrations of 238U and 232Th is probably indicative of the different distribution of U and Th within the same rock, as well as to secondary post-magmatic processes that were responsible for the redistribution of U and Th. An estimation of the contribution of each mineral constituent to the natural radioactivity levels of the bulk rock is attempted. Thorite and zircon contribute the most to the whole rock 238U and 232Th content, while the contribution of apatite is moderate. The contribution of the rest of the minerals examined (fluorite, quartz, plagioclase, K-feldspar, amphibole, pyroxene, magnetite and biotite) is not important. (author)

  5. Morb - n. petrology and geochemistry of the metagabbro of Rio Olivares NNW Sector of Manizales (Caldas)

    International Nuclear Information System (INIS)

    The Rio Olivares metagabbro is a body of igneous intrusive rocks that outcrops along the Rio Olivares at NNW of the Manizales city (Department of Caldas, Colombia). This igneous body is defined by series of centimetro metric-sized faulted slivers within the western sector of Quebradagrande complex. Petrographic analyses show rocks with cumulus and isotropic gabbroic textures. The primary minerals are: calcium plagioclase and clinopyroxene, secondary minerals are: Amphibole, chlorite, epidote, plagioclase and less quartz, carbonate and occasionally opaque minerals. According to geochemical distribution of major elements, those rocks were generated from fractional crystallization of unique magma showing a typical tendency of tholeiitic series. Taking into account the behavior of trace elements in geotectonic discrimination diagrams; they were generated in an ocean floor setting and their sources coming from an n-morb segment in the upper mantle. REE patterns normalized with respect to chondrite, show relatively homogeneous patterns, flats and enriched up to 10 times compared to the typical n-morb. These rocks are part of the oceanic basement of the early cretaceous Quebradagrande complex, and they are affected by my ionitization and ocean floor metamorphism.

  6. Petrology and geochemistray of Imam-Zadeh Hashem mafic and ultramafic bodies, southern Guilan province

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    Mojgan Salavati


    Full Text Available Mafic and ultramafic plutonic igneous bodies, with small and big outcrops, between Shemshak rock units (Jurassic are observed in east of Imam Zadeh Hashem, in southern Guilan province. Ultramafic cumulates consist of clinopyroxenite, and plagiofer clinopyroxenite, olivine clinopyroxenite, and mafic rocks, based on mineralogy consist of gabbros, olivine gabbros, biotite gabbros and amphibole gabbros. According to geochemical data, studied rocks have tholeiitic nature and in the tectonic setting diagrams, display arc characteristic. The chondrite normalized REE patterns show low enrichment in LREEs relative to HREEs. The negative Nb and Ti anomalies in primitive mantle and MORB-normalized multi-element diagrams of the rocks are characteristic of island arc magmas. Also, enrichment in LILE and depletion of HFSE may indicate a subduction-related tectonic setting. According to geological and geochemical evidence, Imam-Zadeh Hashem ultramafic and sub-alkaline gabbro rocks can be as a part of the Southern Caspian Sea Ophiolite sequence (SCO that formed in a suprasubduction tectonic system.

  7. A proton microprobe study of metasomatism in the upper mantle

    International Nuclear Information System (INIS)

    The lithospheric upper mantle is that part which is mechanically coupled to the overlying crust and isolated from the underlying asthenospheric mantle. Alkalic basaltic magmas derived from partial melting of the asthenosphere frequently carry accidental inclusions (spinel peridotite xenoliths) of the lithospheric mantle to the surface and a suite of such xenoliths from western Victoria is being used to study the composition of the upper mantle and the processes which cause modifications to its geochemistry. In order to study this process, incompatible element concentrations in clinopyroxenes, amphiboles and phlogopites have been determined using proton and electron microprobes. As the probe can analyse a spot only 20 microns in diameter, it was possible to look for zoning in trace element concentrations within and between individual grains. Such zoning helps to determine what the concentrations were prior to and after metasomatism, and constrain the timing of the event. It is also a rapid, non destructive technique which requires only minimal amounts of sample and preparation. The results show that clinopyroxens from Mt. Porndon have much higher Sr and sometimes higher Zr than expected for primitive mantle compositions, indicating they have been enriched in these elements. 4 refs., 2 figs

  8. Mineralogical Study of a Biologically-Based Treatment System That Removes Arsenic, Zinc and Copper from Landfill Leachate

    Directory of Open Access Journals (Sweden)

    Maryam Khoshnoodi


    Full Text Available Mineralogical characterization by X-ray diffraction (XRD and a high throughput automated quantitative evaluation of minerals by scanning electron microscopy (QEMSCAN was conducted on samples from a sulphate-reducing biochemical reactor (BCR treating high concentrations of metals (As, Zn, Cu in smelter waste landfill seepage. The samples were also subjected to energy dispersive X-ray (EDX analysis of specific particles. The bulk analysis results revealed that the samples consisted mainly of silicate and carbonate minerals. More detailed phase analysis indicated four different classes: zinc-arsenic sulphosalts/sulphates, zinc-arsenic oxides, zinc phosphates and zinc-lead sulphosalts/sulphates. This suggests that sulphates and sulphides are the predominant types of Zn and As minerals formed in the BCR. Sphalerite (ZnS was a common mineral observed in many of the samples. In addition, X-ray point analysis showed evidence of As and Zn coating around feldspar and amphibole particles. The presence of arsenic-zinc-iron, with or without cadmium particles, indicated arsenopyrite minerals. Copper-iron-sulphide particles suggested chalcopyrite (CuFeS2 and tennantite (Cu,Fe12As4S13. Microbial communities found in each sample were correlated with metal content to describe taxonomic groups associated with high-metal samples. The research results highlight mineral grains that were present or formed at the site that might be the predominant forms of immobilized arsenic, zinc and copper.

  9. Current status of uranium exploration in Sri Lanka

    International Nuclear Information System (INIS)

    Apart from the few occurrences of Gondwana (Jurassic), Miocene and later sediments, most of Sri Lanka consists of Precambrian rocks of Archaean age. These rocks underwent metamorphism under amphibolite and granulite facies conditions about 200 Ma ago. Nine anomalous areas for uranium mineralization were identified after a preliminary geochemical survey of the whole island, except for the northwestern Miocene belt. Consistent low contents of uranium in stream sediment samples suggested that solution or hydromorphic dispersion of uranium is not a prominent mechanism and that most of the uranium dispersion is rather mechanical in nature in most of the country. Six of the above areas lie either within or close to the boundary between the Highland Series and the Vijayan Complex. The latter mainly consists of granitic gneisses, hornblende biotite gneisses, granitoids and migmatites formed under amphibolite facies conditions. Denser sampling (one sample per 1 km2) in Phase II of the programme in two areas, namely Maha Cya and Mala Oya, indicated that further exploration work would be worthwhile. A number of samples from these areas had uranium values greater than 500 ppm. Further, the composition of the amphiboles and pyroxenes from rocks of the Maha Cya area are comparable to those in rocks from known areas of uranium mineralization such as the Mary Kathleen uranium deposit in Australia. (author). 6 refs, 6 figs

  10. Advanced mineral and lithological mapping using high spectral resolution TIR data from the active CO2 remote sensing system; CO2 laser wo mochiita kosupekutoru bunkaino netsusekigai remote sensing data no ganseki kobutsu shikibetsu eno oyo

    Energy Technology Data Exchange (ETDEWEB)

    Okada, K. [Sumitomo Metal Mining Co. Ltd., Osaka (Japan); Hato, M. [Earth Remote Sensing Data Analysis Center, Tokyo (Japan); Cudahy, T.; Tapley, I.


    A study was conducted on rock/mineral mapping technology for the metal ore deposit survey using MIRACO2LAS, an active type thermal infrared ray remote sensing system which was developed by CSIRO of Australia and is now the highest in spectral resolution in the world, and TIMS of NASA which is a passive type system. The area for the survey is the area of Olary/Broken Hill and Mt. Fitton of Australia. A good correlation is seen between the ground reflectance measured by MIRACO2LAS and the value measured by the chamber CO2 laser of rocks sampled at the above-mentioned area. In case that the width of spectral characteristics is below 300nm, the inspection ability by MIRACO2LAS`s high spectral resolution is more determined in mineral mapping as compared with TIMS which is large in band width. Minerals mapped using MIRACO2LAS are quartz, talc, amphibole, hornblende, garnet, supessartine, dolomite, magnesite, etc. 4 refs., 3 figs.

  11. The Fontaine Pluton : an early Ross Orogeny calc-alkaline gabbro from southern Victoria Land, Antarctica

    International Nuclear Information System (INIS)

    The Fontaine Pluton is a previously undescribed mafic intrusion outcropping at Fontaine Bluff on the south side of the Carlyon Glacier in southern Victoria Land, Antarctica. It is the southern-most member of a laterally extensive mafic suite emplaced at mid-crustal depths during the initial stages of the Ross Orogeny. The pluton comprises recrystallised hornblende-biotite gabbro, which in places shows well-defined centimetre to metre scale primary igneous layering. Recrystallised ultramafic enclaves composed of amphibole-chlorite-talc are inferred to be remnants of a chemically and mineralogically distinct cumulate fraction. The intrusion has a 87Sr/86Sr(i) ratio of 0.70679 and a 143Nd/144Nd(i) ratio of 0.51187 (εNd(i) = -1.2). This, coupled with other geochemical data, implies that the Fontaine Pluton was formed by c. 15% partial melting of a depleted mantle source that was subsequently contaminated by continental crust. Preliminary U-Pb geochronology on zircon suggests an emplacement age for the pluton of 546 ± 10 Ma. These new data indicate that Ross Orogeny magmatism in this area of southern Victoria Land was initiated in the late Neoproterozoic along a subducting plate margin. (author). 55 refs., 10 figs., 3 tabs

  12. Multiple sources of magmatism: granitoids from southeast kohistan, nw himalayas Pakistan

    International Nuclear Information System (INIS)

    The Kohistan island arc terrane in the northwestern Himalayas of N. Pakistan is sandwiched between the Indian and Karakoram plates. The base of the arc is occupied by a major stratiform ultramafic-gabbroic complex (the Sapat-Babusar complex). which overrides the crust of the Indian plate along the Indus suture (i. e., the Main Mantle Thrust; MMT). It was intruded into the base of a thick pile of metavolcanics (the Kamila belt), which comprise a tectonic collage of MORB-type tholeiitic basalts, island-arc tholeiites and calc-alkaline andesites. The Chilas complex, comprising ultramafic and gabbronorite rocks, is also intrusive into the Kamila belt. It is emplaced onto the top rather than the base of the Kamila belt. A sizeable proportion of granitoid rocks are present in the south-eastern part of Kohistan. Which intruded the Kamila amphibolites. These are predominantly dioritic in composition but include gabbros, granodiorites, granites and trondhjemites. The granitoids occur in two types: (I) large sheet-like lenticular masses, and (2) minor intrusives in the form of veins sills or dykes. Three large sheets like bodies are mapped. All these bodies are composite, comprising gabbros, diorite/tonalite. granodiorite and granite. The minor intrusions of granitic and trondhjemitic composition are abundantly present in the form of veins, sills and dykes and are characterized by variation in distribution. Strong shearing transformed the rocks into blastomylonite gneisses. The mineral assemblage consists of quartz, plagioclase, Amphibole, epidote, chlorite, biotite, muscovite, sphene, magnetite and apatite. (author)

  13. Laser-induced breakdown spectroscopy analysis of minerals: Carbonates and silicates

    International Nuclear Information System (INIS)

    Laser-induced breakdown spectroscopy (LIBS) provides an alternative chemical analytical technique that obviates the issues of sample preparation and sample destruction common to most laboratory-based analytical methods. This contribution explores the capability of LIBS analysis to identify carbonate and silicate minerals rapidly and accurately. Fifty-two mineral samples (18 carbonates, 9 pyroxenes and pyroxenoids, 6 amphiboles, 8 phyllosilicates, and 11 feldspars) were analyzed by LIBS. Two composite broadband spectra (averages of 10 shots each) were calculated for each sample to produce two databases each containing the composite LIBS spectra for the same 52 mineral samples. By using correlation coefficients resulting from the regression of the intensities of pairs of LIBS spectra, all 52 minerals were correctly identified in the database. If the LIBS spectra of each sample were compared to a database containing the other 51 minerals, 65% were identified as a mineral of similar composition from the same mineral family. The remaining minerals were misidentified for two reasons: 1) the mineral had high concentrations of an element not present in the database; and 2) the mineral was identified as a mineral with similar elemental composition from a different family. For instance, the Ca-Mg carbonate dolomite was misidentified as the Ca-Mg silicate diopside. This pilot study suggests that LIBS has promise in mineral identification and in situ analysis of minerals that record geological processes

  14. 40Ar/39Ar dating and geochemistry of tholeiitic magmatism related to the early opening of the Central Atlantic rift

    International Nuclear Information System (INIS)

    Tholeiitic effusive and intrusive magnetism from Iberia, Morocco, Algeria and Mali, realted to the early opening of the Central Atlantic rift, was dated by the 40Ar/39Ar step-heating method. Four plateau ags, rangin from 203.7±2.7 to 197.1±1.8 Ma, were obtained on plagioclase from dykes from theTaoudenni area (Mali) and two lava flows from Morocco. The Messejana dyke (Iberia), which previously yielded discrepant conventional K-Ar dates, did not furnish any 40Ar/39Ar plateau dates. However, there is a clear inverse relationship between apparent age and K/Ca atio for gas fractions from a plagioclase separate (proportional to the alteration degree) which, combined with dates obtained on amphibole, biotite and pyroxene, allows us to determine an age of around 200 Ma for this body. These data, and those obtained on the Foum Zguid (Morocco) and the Ksi Ksou (Algeria) dykes, give evidence of a brief magmatic event (between 206 and 195 Ma ago) which affected a large area ca. 2500 km long. Trace-element modelling shows that most of these formations originated from a homogeneous, enriched, source material. Such a brief magmatic episode related to the opening of a continental rift is in agreement with findings in other magmatic provinces (e.g. the Deccan traps and the Red Sea rift, precisely dated by the 40Ar/39Ar method as well). (orig.)

  15. Rare-earth element modelling of Archean meta-igneous and igneous rocks, Lake Despair area, northwestern Ontario

    International Nuclear Information System (INIS)

    Archean felsic to intermediate meta-igneous rocks from the Lake Despair area, northwestern Ontario, have highly-fractionated REE patterns (Lasub(N)/Lusub(N) 10-100). They are rich in LREEs (ca. 40-100 x chondrites) and poor in HREEs (ca, 1-7 x chondrites). Simple models for the REEs suggest eclogite-quartz eclogite parents for these rocks. The Footprint Gneiss, the major rock type of the Rainy Lake Batholith, was formed by limited melting (ca. 10%) of a quartz eclogite under hydrous conditions. The putative parent may have been transformed basalt derived from primitive, LREE-rich Archean mantle. The mafic metavolcanic rocks have a REE chemistry similar to modern island-arc or mid-ocean ridge tholeiites. Felsic metavolcanic rocks, and granodiorite from the Northwest Bay complex, have REE abundances compatible with an origin by partial melting (ca. 10%), under hydrous conditions, of quartz eclogite of tholeiitic REE chemistry. The Jackfish Lake plutonic complex, which is composed mostly of diorite, has REE abundances that are best described by 10% melting of eclogite (with tholeiitic-REE chemistry) under hydrous conditions. A small portion of the diorite magma was subsequently fractionated, largely by the early crystallization of amphibole, and formed more leucocratic rock types (e.g. leucodiorite and granodiorite). The REE data were obtained by neutron activation analysis. (Auth.)

  16. The calc-alkaline and adakitic volcanism of the Sabzevar structural zone (NE Iran): Implications for the Eocene magmatic flare-up in Central Iran (United States)

    Moghadam, Hadi Shafaii; Rossetti, Federico; Lucci, Federico; Chiaradia, Massimo; Gerdes, Axel; Martinez, Margarita Lopez; Ghorbani, Ghasem; Nasrabady, Mohsen


    A major magmatic flare-up is documented along the Bitlis-Zagros suture zone in Eocene-Oligocene times. The Cenozoic magmatism of intraplate Central Iran is an integrant part of this tectono-magmatic scenario. The Cenozoic magmatism of the Sabzevar structural zone consists of mostly intermediate to felsic intrusions and volcanic products. These igneous rocks have calc-alkaline and adakitic geochemical signatures, with nearly coincident zircon U-Pb and mica Ar-Ar ages of ca. 45 Ma. Adakitic rocks have quite low HREE and high Sr/Y ratio, but share most of their geochemical features with the calc-alkaline rocks. The Sabzevar volcanic rocks have similar initial Sr, Nd and Pb isotope ratios, showing their cogenetic nature. Nd model ages cluster tightly around ~ 0.2-0.3 Ga. The geochemistry of the Sabzevar volcanic rocks, along with their isotopic signatures, might strangle that an upper mantle source, metasomatized by slab-derived melts was involved in generating the Sabzevar calc-alkaline rocks. A bulk rock trace element modeling suggests that amphibole-plagioclase-titanite-dominated replenishment-fractional crystallization (RFC) is further responsible for the formation of the middle Eocene Sabzevar adakitic rocks. Extensional tectonics accompanied by lithospheric delamination, possibly assisted by slab break-off and melting at depth was responsible for the Eocene formation of the Sabzevar magmatic rocks and, more in general, for the magmatic "flare-up" in Iran.

  17. Reworked old crust-derived shoshonitic magma: The Guarany pluton, Northeastern Brazil (United States)

    Ferreira, Valderez P.; Sial, Alcides N.; Pimentel, Marcio M.; Armstrong, Richard; Guimarães, Ignez P.; da Silva Filho, Adejardo F.; de Lima, Mariucha Maria C.; da Silva, Thyego R.


    The 572 Ma Guarany stock consists of magmatic epidote-bearing hornblende monzodiorite to biotite granite that intruded Paleoproterozoic orthogneisses about 10 km inland from the coast in northeastern Brazil. Co-magmatic diorite enclaves and dikes are abundant throughout the pluton. The monzodiorite-granite pluton and diorite enclaves are shoshonitic and display continuous trends in variation diagrams. They display chemical and isotopic characteristics of crustal melts, such as enrichment in incompatible elements, high back-calculated initial 87Sr/86Sr ratios (avg. 0.71253), negative εNd (0.57Ga) values (avg. - 14.58), as well as high and variable (+ 9.1 to + 11.1‰VSMOW) δ18O (zircon) values. Correlations between O-isotope and whole-rock silica contents, as well as initial 87Sr/86Sr ratios with 1/Sr concentrations, suggest hybridization of a lower continental crustal melt with more felsic crustal rocks, concomitant with fractional crystallization. Amphibole chemistry and whole rock Zr, TiO2 and P2O5 contents suggest magma solidification at a pressure ~ 7 kbar and near liquidus temperature ~ 900 °C. The parental magma was likely formed by partial melting of old (tDM = 2.0 Ga) amphibolitic lower continental crustal rocks, in a post-collisional setting, probably triggered by underplating of mantle-derived mafic magma during the period of relaxation after collision.

  18. Mineral Chemistry and Geochemistry of Volcanic Rocks in The North of Pasinler (Erzurum

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    Oktay KILIÇ


    Full Text Available In the north of Pasinler (Erzurum, Upper Miocene-Pliocene volcanic rocks crop out. These volcanites are composed of basaltic andesite, andesite, dacite, rhyolite lavas and rhyolitic pyroclastics. The rocks show porphyritic, microlitic porphyritic, hyalo-microlitic porphyritic, vitrophyric, glomeroporphyritic, pilotaxitic and hyalopilitic textures. The investigated volcanites contain plagioclase (An29-80, olivine (Fo65-82, clinopyroxene (augite, orthopyroxene (enstatite, amphibole (Mg#: 0.57-0.71, biotite (phlogopite: 0.44-0.47, annite: 0.33-0.37, sanidine, quartz and opaque mineral (titano-magnetite and ilmenite. The volcanic rocks are calc-alkaline in character and have medium to high-K contents. Major oxide and trace element variations point out open-system magmatic differentiation in the evolution of rocks. Geochemical data indicate an important role of fractionation of phenocryst phases in the rocks during differentiation process. However, it is considered that assimilation±magma mixing might have accompanied to the process. High LILE (K, Rb, Ba, Th and relatively low HFSE (Nb, Ta, Hf, Zr contents of the rocks indicate that these rocks derived from parental magmas carrying subduction signature.

  19. Comparative hazards of chrysotile asbestos and its substitutes: A European perspective. (United States)

    Harrison, P T; Levy, L S; Patrick, G; Pigott, G H; Smith, L L


    Although the use of amphibole asbestos (crocidolite and amosite) has been banned in most European countries because of its known effects on the lung and pleura, chrysotile asbestos remains in use in a number of widely used products, notably asbestos cement and friction linings in vehicle brakes and clutches. A ban on chrysotile throughout the European Union for these remaining applications is currently under consideration, but this requires confidence in the safety of substitute materials. The main substitutes for the residual uses of chrysotile are p-aramid, polyvinyl alcohol (PVA), and cellulose fibers, and it is these materials that are evaluated here. Because it critically affects both exposure concentrations and deposition in the lung, diameter is a key determinant of the intrinsic hazard of a fiber; the propensity of a material to release fibers into the air is also important. It is generally accepted that to be pathogenic to the lung or pleura, fibers must be long, thin, and durable; fiber chemistry may also be significant. These basic principles are used in a pragmatic way to form a judgement on the relative safety of the substitute materials, taking into account what is known about their hazardous properties and also the potential for uncontrolled exposures during a lifetime of use (including disposal). We conclude that chrysotile asbestos is intrinsically more hazardous than p-aramid, PVA, or cellulose fibers and that its continued use in asbestos-cement products and friction materials is not justifiable in the face of available technically adequate substitutes. PMID:10417355

  20. Araxa Group in the type-area: A fragment of Neoproterozoic oceanic crust in the Brasilia Fold Belt

    International Nuclear Information System (INIS)

    This study reviews the geological characteristics and puts forward a new evolution model for the Araxa Group in its type-area, the southern segment of the Neo proterozoic Brasilia Belt, Minas Gerais, Brazil. The Araxa Group is confined within a thrust sheet belonging to a syn formal regional fold, the Araxa Syn form, overlying two other thrust sheets made of the Ibia and Canastra Groups. The Araxa Group is described as a tectono stratigraphic terrane in the sense of Howell (1993). It comprises an igneous mafic sequence, with fine and coarse grained amphibolites, associated with pelitic meta sedimentary rocks, and subordinate psanmites. All rocks were metamorphosed to amphibolite facies at ca. 630 Ma ago and were intruded by collisional granites. The amphibolites represent original basaltic and gabbroic rocks, with minor ultramafic (serpentinite/ amphibole-talc schist). The basalts are similar to high Fe O tholeiites, with REE signatures that resemble E-MORB and εNd(T) =+ 1.1. The meta sedimentary rocks are interpreted as the result of a marine deep-water sedimentation. They have Sm-Nd model ages of 1,9 Ga, and εNd(T) = -10.21. The amphibolites and metasediments could represent a fragment of back-arc oceanic crust. The data presented here differ significantly from the original definition of Barbosa et al. (1970) who describe the Araxa Group as a pelitic/psanmitic sequence and the collisional granites as a basement complex. (author)

  1. A Neoproterozoic age for the chromitite and gabbro of the Tapo ultramafic Massif, Eastern Cordillera, Central Peru and its tectonic implications (United States)

    Tassinari, Colombo C. G.; Castroviejo, Ricardo; Rodrigues, Jose F.; Acosta, Jorge; Pereira, Eurico


    The ultramafic-mafic rocks of the Tapo Complex are exposed in the Eastern Cordillera of the Central Peruvian Andes. This complex is composed of serpentinised peridotites and metabasites with some podiform chromitite lenses and chromite disseminations and overlies the sandstones, conglomerates, and tuffs of the Carboniferous Ambo Group. The metagabbros and amphibolites show a tholeiitic affiliation and a flat REE spider diagram, with a slight LREE depletion and a positive Eu anomaly suggesting magmatic accumulation of plagioclase, in an ocean ridge or ocean island environment. Sm-Nd isotopic analyses were performed on chromite as well as on whole rock from the gabbro. All samples yielded an Sm-Nd isochrone age of 718 ± 47 Ma with an initial 143Nd/ 144Nd of 0.51213 ± 0.00005. The ɛNd (718 Ma) values calculated for both chromite and gabbro are in close agreement, around 8.0, implying that they were formed at the same time from the same mantelic magma source. Furthermore a K-Ar age on amphibole of 448 ± 26 Ma was obtained, interpreted as the cooling age of a younger orogenic event. These rocks represent slices of oceanic crust (from a dismembered ophiolitic complex), metamorphosed and later overthrust on upper Palaeozoic continental formations.

  2. Zeolite rocks from the paleogene lacustrine volcano-sedimentary deposits in Gorna Glogovitsa Graben (Kraishte region, Western Bulgaria)

    International Nuclear Information System (INIS)

    Analcime-clinoptilolite and clinoptilolite-analcime zeolite rocks established in the Paleogene deposits of Gorna Glogovitza Graben are the forth Tertiary zeolite rocks deposit in Western Bulgaria. Terrigenous and abiogenic (calcareous) lacustrine sedimentation in the Graben has been influenced of process(es) of acid ash pyroclastics deposition. Pyroclastic material constitutes of glass-shards, pumice fragments (with plagioclase, biotite, amphibole and scarce sanidine microphenocrysts), crystalloclasts and cognate phenorhyolitic-penorhyodacitic fragments. Glassy components have been completely transformed according to the following reactions' sequence: volcanic glass →clinoptilolite → analcime → K-feldspar. Such an authigenic silicate association formed in lacustrine environment is interpreted as characteristic of high salinity (about 50000 ppm) and high pH value (nearly 9.5) of the basin/pore wa-ter. The environments in which Gorna Glogovitza Graben and other Bulgarian and Serbian Tertiary analcime rocks were formed can be hardly compared. A suggestion about a similar environment of analcime formation in Gorna Glogovitza Graben and Slanci basin (near Belgrade, Serbia) can be made based on the very close cell parameters of the analcime (respectively a0 = 13.70980 A, cell volume = 2576.87 A3 and a0 13.699-13.707 A, cell volume - 2571-2575 A3)

  3. Revisiting Emplacement Depths of the Fine Gold Intrusive Suite, West-Central Sierra Nevada (United States)

    Head, D.; Lackey, J.


    The Fine Gold Intrusive Suite (FGIS) is a large intrusive complex in the west central portion of the Sierra Nevada Batholith. Portions of the Sierra Nevada Batholith have been well studied for plutonic pressure and crystallization histories (e.g., Ague and Brimhall, 1988, GSAB), whereas the regional depth of emplacement of the FGIS is not well characterized, and in previous work pressure estimates were not corrected for crystallization temperatures. An accurate sense of barometric gradient in the FGIS is important to evaluate the roles of pre-batholithic structural breaks in controlling magma emplacement levels, and also to reconstruct erosional levels within the Sierra Nevada as a whole. In this study, samples from the FGIS, all from the Bass Lake Tonalite, were petrographically characterized to identify those samples that contain mineral assemblage and crystallization textures appropriate for application of the Aluminum-in-Hornblende barometer of Hammarstrom and Zen (1986) re-calibrated by Anderson and Smith (1995). Analysis of these samples and use of the barometer results in both pressure and temperature of crystallization. FGIS amphiboles are typical magnesio-hornblende on average: K0.2Na0.1Ca1.8[Mg2.4(Al,Fe3+)(0.2-0.6)]Si6.7Ti0.1Al1.3O22(OH)2. Plagioclase compositional ranges are Ab(54-69)An(30-45)Or(0-1). Bass Lake Tonalite data of Ague and Brimhall (1988) were re-calculated for typical plagioclase composition in the Bass Lake Tonalite (Ab62An37Or1), yielding slightly higher crystallization pressures (3.3 to 5.8 kbar) than the original range (2.4 to 4.5 kbar). New FGIS crystallization pressures of 2.6 to 3.5 kbar match the recalculated data well, thus providing larger coverage for estimates of emplacement depth. Apparent temperatures from adjacent amphibole and plagioclase rims were found to be 691 to 767°C. When all barometric data are considered together, and uncertainties of the calibration are factored in, we find that FGIS crystallization pressures

  4. Interpreting Al-in Hornblende and Hbl-Plag thermobarometry results from the Tuolumne batholith and magmatic lobes in conjunction with single mineral element distribution electron microprobe maps (United States)

    Memeti, V.; Krause, J.; Anderson, J. L.; Paterson, S. R.


    Several recent thermobarometry studies have been conducted on the 95-85 Ma Tuolumne batholith, Sierra Nevada, CA, since Ague & Brimhall (1988) first reported ~2.5-3 kbar pressures and an emplacement depth of ~ 10 km from these sphene bearing granodioritic rocks. Average pressure estimates from more recent reports using the simultaneous solution of the plagioclase-amphibole thermometer by Holland & Blundy (1994), and the temperature corrected Al-in-hornblende barometer by Anderson & Smith (1995) are around 2 kbar, but vary in detail from 2 to 3 kbar. Further complications are revealed on temperature-pressure plots since some results fall below the granite and tonalite solidi and are thus subsolidus in nature. Many recent studies also indicate that single minerals in volcanic and plutonic rocks preserve complex magmatic growth histories, and in one sample or thin section can show heterogeneous mineral chemistries and multiple mineral populations, likely due to recycling and mixing processes occurring in large magma chambers. This implies that the pairing of minerals for thermobarometry calculations and thus the usage of these methods is complicated and requires the prior evaluation of the geochemistry of the individual minerals used for the analyses. We have done pressure and temperature estimates using the thermometer by Holland & Blundy (1994) and the Al-in-hornblende barometer by Anderson & Smith (1995) in conjunction with X-ray electron microprobe element distribution maps of the amphiboles and plagioclase grains used for the thermobarometry. With this approach, we attempt to better control the process of analyses pairing for the calculations since we establish a better awareness of the nature of individual mineral chemistry heterogeneities and the presence of multiple mineral populations. We selected a number of granodiorite samples from the peripheral magmatic lobes of the batholith, which have been determined to represent less complex and shorter lived, local

  5. Geochemistry of sapphirine-apatite-calcite-bearing gabbroic dykes from the Finero Phlogopite Peridotite (Ivrea-Verbano Zone): evidence for multistage interaction with the ambient peridotite (United States)

    Tommaso, Giovanardi; Alberto, Zanetti; Maurizio, Mazzucchelli; Tomoaki, Morishita; Antonio, Langone


    The Finero Phlogopite-Peridotite (FPP) is a mantle unit outcropping in the northernmost tip of the Ivrea-Verbano Zone (IVZ, Southern Alps). It shows a virtually complete recrystallization due to pervasive to channelled melt migration. The pervasive metasomatism formed a main lithologic association constituted by phlogopite harzburgites associated to phlogopite pyroxenites (mainly olivine-websterites, websterites and orthopyroxenites). These lithologies are also rich in amphibole and do not show significant chemical gradients among them (Zanetti et al., 1999). The channelled migration stages formed dunite bodies, which sometimes contain stratiform chromitites and, more rarely, pyroxenite layers similar to those associated to phlogopite harzburgite. The FPP also shows a discrete number of other, subordinate rock-types, which are characterised by the presence of apatite usually associated to carbonates (i.e. calcite or dolomite) and exhibit marked modal and chemical gradients with respect to the host phlogopite harzburgite. Examples of these lithologies are apatite-dolomite-bearing wehrlites and harzburgites (e.g. Zanetti et al. 1999; Morishita et al., 2008), apatite-calcite zircon-syenites and hornblendites. Ar-Ar amphibole analysis and U-Pb zircon and apatite data return Triassic ages for these rocks, which have been considered to document the time of melt/fluid injection. Notwithstanding the apparent mineralogical and chemical differences with the main lithologic sequences, apatite-carbonates-bearing rocks have been frequently interpreted as cogenetic to phlogopite harzburgites. To debate the petrogenesis of these rocks, a detailed field, petrological and geochemical investigation has been carried out on a swarm of apatite-calcite-bearing gabbroic veins that randomly cut the main lithologic association. Preliminary investigation evidenced as these veins show complex metasomatic haloes and a symmetric internal layering, characterised by crystallisation of magmatic

  6. Análisis e interpretación de los materiales volcánicos del Cerro de los Frailes (Cabo de Gata. Almería

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    Fernández Soler, J. M.


    Full Text Available The formation of Los Frailes volcano had two stages, which produced amphibole andesites (Frailes-I and two-pyroxene andesites (Frailes-II respectively, Iying on the extension of the dacites and andesites of the southernmost Cabo de Gata volcanoes (Revancha-Sabinal. The FRAILES-I stage is discontinuous, and has mainly produced domes and autoclastic breccias, in addition to an intermediate level of pumice-and-ash flow; this unit has some intercalated sedimentary levels. To the NE it is covered by a formation of sedimentary and hydroclastic rocks. The Frailes-II stage is continuous, and has formed some lava flows, the two summit domes, and sorne pyroclastic rocks of scarcely explosive origin. Other volcanic features are some domes and dikes of biotite-amphibole dacites, which affect to the Frailes-I-group; these are the southern continuation of the dacitic volcanic group of Rodalquilar-Rellana-Garbanzal. The generally accepted idea of a succesion in Cabo de Gata of cycles which started very explosively and ended with subvolcanic extrussions (domes does not seem to be very realistic at least in the building of Los Frailes. A review of geochronological data, and the field disposition of the described materials does not discard the hypothesis that the pyroxene andesites of FrailesI-I might have been formed simultaneously or even than later the ignimbritic dacites of the Rodalquilar group.La formación del volcán de Los Frailes se produjo en dos ciclos, de composiciones andesítica anfibólica (Frailes-I y andesitica de dos piroxenos (Frailes-II, apoyadas sobre la prolongación hacia el este de las andesitas y dacitas del extremo sur de Cabo de Gata (edificio de Revancha-Sabinal-Cabo de Gata. El ciclo Frailes-I es discontínuo y ha formado domos y brechas autoclásticas principalmente, mas un nivel intermedio de colada piroclástica pumítica; este ciclo contiene niveles sedimentarios intercalados. Al NE es cubierto por una formación de rocas

  7. Eclogite Facies Relicts and Decompression Assemblages; Evidence for the Exhumation of a Large Coherent Metabasite Block From > 40 km Depth; Central Metamorphic Terrane, Eastern Klamath Mountains, Northern California (United States)

    Barrow, W. M.; Fairhurst, R. J.; Metcalf, R. V.


    Recent exhumation models for eclogite terranes have focused on the exhumation of sialic rocks. Exhumed high pressure terranes are typically > 85% - 90% sialic material with only minor amounts of mafic and ultramafic rock. Most known metabasitic eclogites are blocks in mélange rather than large coherent bodies. The Central Metamorphic terrane (CMt) is a large (~300 km3) coherent, fault-bounded package of metabasites thought to represent a remnant of a downing plate subducted in an intra-oceanic convergent margin. Thermochronology indicates that the CMt was metamorphosed and later accreted to the base of the Trinity ophiolite along the Trinity fault during Early Permian extension (Hbl and Musc 40Ar/39Ar ages of 275 Ma - 294 Ma). Previous work suggested that the peak metamorphic temperatures and pressures were ~650°C and 0.4 to 0.8 GPa (Peacock and Norris, 1989) which is consistent with the amphibolite facies mineral assemblage. Trace element data confirm the NMORB-like composition of CMt metabasite protoliths. Newly discovered relict textures, however, suggest that CMt amphibolites record much deeper subduction burial with subsequent decompression exhumation. A decompression sequence consisting of rutile cores within ilmenite crystals mantled by titanite is observed in CMt amphibolite samples. Zr-in-rutile thermometry (Watson et al., 2006) combined with experimental data for rutile stability in metabasites (Ernst and Lui, 1998) suggests that relict rutile crystals preserve early P-T conditions of ~600°C and > 1.3 GPa consistent with eclogite facies metamorphism. Transition from eclogite facies is further supported by ilmenite-plagioclase-amphibole symplectites suggesting replacement of garnet (Bhowmik and Roy, 2003) during decompression. Amphibole compositions vary significantly and reflect lower grade (low Na, Al, Ti actinolite) overprint of earlier amphibolite facies compositions (high Na, Al, Ti magnesio- hornblende). Application of the Al-Ti hornblende

  8. A glimpse into Augustine volcano's pre-glacial past: Insight from a massive rhyolite deposit (United States)

    Nadeau, P. A.; Webster, J. D.; Mandeville, C. W.; Goldoff, B. A.; Shimizu, N.; Monteleone, B. D.


    Augustine is a very high threat island volcano located on the west side of Cook Inlet, Alaska, and is the most historically active volcano in the region. As a result, Augustine has been almost wholly resurfaced by deposits from the last ~2000 years BP and little is known about older activity. Erosive pyroclastic flows associated with the 2006 eruption of Augustine created new exposures within the drainage of Augustine Creek, to the southwest of the summit. Among the newly exposed deposits is a >30 m-thick coarse pumice fall unit, which underlies ~8 m of glacial till. The lower 6 m of the deposit contain lithics 1-2 cm in diameter, while the upper 25 m of the fall are lithic-poor but contain pumice blocks up to 2 m in diameter. The majority of the unit is white pumice, with ~10% volume percent denser gray banded pumices. Yellowed, slightly weathered pumices are found at the base of the section. A similar deposit was also found on the north side of the island and may represent the same eruptive unit. Samples from the newly-discovered unit include slightly rounded and weathered pumice from the base of the unit (yellow pumice), a large fragment from near the deposit top (white pumice), and gray, banded pumice (flow-banded pumice), also from near the top of the unit. Plagioclase, orthopyroxene, amphibole, quartz, Fe-Ti oxides, and minor apatite comprise the phenocryst assemblage. Amphiboles in the white and flow-banded pumices are split into two distinct populations: a low-Al, high-Mg cummingtonite population and a high-Al population that ranges from magnesio-hornblende to ferri-tschermakite. Yellow pumices contain only cummingtonite. Analyses of melt inclusions in each of the main phenocryst phases indicate mostly rhyolitic melt compositions with water, carbon dioxide, and sulfur contents comparable to, and chlorine contents slightly lower than, more recent (<2000 year-BP) Augustine melt inclusions. A single olivine and a single clinopyroxene, both from the white

  9. Hydrothermal Alteration in Submarine Basaltic Rocks from the Reykjanes Geothermal Field, Iceland. (Invited) (United States)

    Zierenberg, R. A.; Schiffman, P.; Fowler, A. P.; Marks, N.; Fridleifsson, G.; Elders, W. A.


    The Iceland Deep Drilling Project (IDDP) is preparing to drill to 4-5 km in the Reykjanes Geothermal Field to sample geothermal fluids at supercritical temperature and pressure for power generation. The Reykjanes geothermal field is the on-land extension of the Reykjanes Ridge spreading center. The upper 1-2 kilometers drilled at Reykjanes are submarine basalts and basaltic sediments, hyalloclastites, and breccias, with an increasing proportion of basaltic intrusive rocks below 2 km depth. Geothermal fluids are evolved seawater with a composition similar to mid-ocean ridge hydrothermal systems. Zn- and Cu-rich sulfide scale, locally enriched in Au and Ag, are deposited in production pipes. The sulfide deposits are compositionally and isotopically similar to seafloor massive sulfides. In anticipation of deeper drilling, we have investigated the mineralogy and geochemistry of drill cuttings from a 3 km deep well (RN-17). The depth zoning of alteration minerals is similar to that described from other Icelandic geothermal fields, and is comparable to observed seafloor metamorphic gradients in ODP drill holes and ophiolites. Chlorite-epidote alteration occurs at depths >400 m and passes downhole through epidote-actinolite alteration and into amphibole facies (hornblende-calcic plagioclase) alteration below 2.5 km. Local zones of high temperature (>800°C), granoblastic-textured, pyroxene hornfels, are interpreted to form by contact metamorphism during dike/sill emplacement. Similar granoblasically altered basalts were recovered from the base of the sheeted dikes in IODP Hole 1256D. Downhole compositional variations of drill cuttings, collected every 50 m, suggest that rocks below ~ 2 km are little altered. Whole-rock oxygen isotope profiles are consistent with low water/rock ratios, but suggest that early stages of hydrothermal alteration included meteoric water-derived fluids. Strontium isotope profiles indicate more extensive exchange with seawater-derived fluids

  10. Consistent magmatic and magnetic anisotropy data in La Gloria Pluton, central Chile: Implications for the magma flow record in a shallow pluton (United States)

    Payacan, I.; Gutierrez, F. J.; Bachmann, O.; Parada, M.


    The magmatic origin of the anisotropy of magnetic susceptibility (AMS) is examined in comparison with magmatic anisotropy data in a small, shallow, silicic magma reservoir in the upper crust. La Gloria Pluton (LGP) is a 10 Ma granodiorite/quartz monzonite of about 250 km3 located in the southern Andes, central Chile. LGP represents a particularly simple case of a silicic intrusion which was assembled in a few pulses and cooled over a short time interval. Hornblende, biotite and minor magnetite are ubiquitous mafic phases. The AMS tensor indicates that magnetic fabric has an oblate shape (i.e. magnetic foliation is higher than magnetic lineation). Lineations are weak (values up to 1.05), have a N-NW trend with a nearly horizontal dip and represent axisymmetric convection parallel to the main pluton elongation. Foliations are more pronounced (values up to 1.14), having NW trends and dips that vary gradually from vertical at the walls, to horizontal at the center and near the roof of the chamber. We interpret this to represent shear localization near the magma locking point along solidification fronts. Magmatic anisotropy data were obtained by measuring mineral length, width and orientation in the three main planes of the AMS tensor. We define the planes Pmax, Pint, and Pmin as orthogonal to the maximum, intermediate, and minimum axes of the AMS tensor, respectively. Mineral data were collected for plagioclase and amphibole + bitotite independently. For each site, the Bingham distribution with 95% of confidence is used to determine the mean mineral orientation and their angle difference with the AMS axes. Preliminary results indicate that mean crystal orientations are well defined for Pmax and Pint for all analyzed minerals, but Pmin is only well constrained for amphibole + bitotite and poorly constrained for plagioclase. Angle differences generally decrease with magnetic anisotropy but are independent of the size and aspect ratio of the crystals. Mean values of

  11. Mineralogía y termo-barometría de los Complejos máficos Sol de Mayo y Suya Taco, Norte de las Sierras de Comechingones, Córdoba Mineralogy and thermo-barometry of the Sol de Mayo and Suya Taco mafic complexes from northern Sierra de Comechingones, Córdoba

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    Alina M. Tibaldi


    the latter method may be not applicable to rocks crystallized from Fe-rich magmas. Amphibole-plagioclase thermometry estimates, which use typical core compositions, yield equilibrium temperature in the range of 750-850ºC. Whereas using rim compositions, Amph-pl thermometry estimates significantly give lower temperatures (< 600ºC, suggesting that amphiboles mostly crystallized at post-magmatic stages. Orthopyroxene-biotite Fe-Mg exchange thermometry shows that these minerals tend to equilibrate within two distinct thermal ranges (430-650ºC and 740-1030ºC. This indicates that biotites might have crystallized at both late-magmatic and post-magmatic stages. Barometric estimates have some variability in function of the type of calibration used, however they show a systematic pattern in which the equilibrium pressure determined in the Suya Taco complex are lower (5.5 ± 1 kbar than those obtained in the Sol de Mayo complex (8 ± 1 kbar. Overall, this result is consistent with barometry already performed in granulitic xenoliths. The P-T conditions deduced from igneous rocks indicate that the hosting regional metasedimentary sequence were experiencing amphibolite-facies temperatures and residing at middle crustal levels.

  12. 柴达木地块北缘南北沟岩体地球化学特征及成矿前景%Geochemical Characteristics of Nanbeigou Intrusion in the Northern Margin of Qaidam Massif and Its Prospecting Potential

    Institute of Scientific and Technical Information of China (English)

    姜常义; 王子玺; 杜玮; 王梦玺


    Nanbeigou intrusion is located in the northern margin of Qaidam massif,and the outcrop area is 4.5 km2 .The intrusion is emplaced into amphibole plagiogneiss from Paleoproterozoic Dakendaban Group and amphibolite from Mesoproterozoic.It consists of pale gabbro,gabbro,melagabbro. They extend mainly gradual transition,and part shows intrusive contact.Rock alteration is strong,most of pyroxenes alter to amphibole,and part shows biotitization and chloritization;plagioclase shows saussuritization at different levels.Chemical composition of major element belongs to tholeiitic series.The rocks relatively enrich in large ion lithophile element (LILE), deplete in high field strength element (HFSE),and obviously deplete in Nb and Ta.The primary magma of intrusion is high Mg tholeiitic (mass fraction of MgO is 1 1��1%),and is developed by the middle-upper crustal assimilation contamination in a certain extent during the magma evolution.The intrusion,which forms in ancient island arc environment,is the product of Qaidam massif subduction to Qilian massif in Early Paleozoic. According to the degree of magmatic differentiation,characteristics of primary magma and assimilation contamination,it is comprehensively concluded that Nanbeigou intrusion has good metallogenetic potentiality of Cu-Ni sulfide deposit.%南北沟岩体位于柴达木地块北缘,出露面积4.5 km2.岩石主要类型有淡色辉长岩、辉长岩、暗色辉长岩,各岩石类型之间多为过渡关系,局部呈侵入接触.主量元素化学组成属拉斑玄武岩系列.岩石相对富集大离子亲石元素,亏损高场强元素,明显亏损 Nb、Ta.岩体原生岩浆属于高镁拉斑玄武岩(Mg O质量分数为11.1%),在岩浆演化过程中遭受了一定程度中—上地壳物质的同化混染作用.岩体形成于古岛弧环境,是早古生代柴达木地块向祁连地块俯冲过程的产物.从岩浆分异程度、原生岩浆性质、同化混染等方面综合评

  13. Augustine Volcano's late Pleistocene rhyolite eruption and its modern-day residuum (United States)

    Coombs, M. L.; Vazquez, J. A.


    The pre-Holocene eruptive history of Augustine Volcano, the most active volcano in the populated Cook Inlet region of Alaska, is poorly known due to the effects of glaciation and voluminous products of Holocene eruptions that cover the majority of this island volcano. Among its oldest known deposits, thought to be latest Pleistocene in age, are a basalt-rhyolite hyaloclastite, which is interbedded with an overlying pumiceous rhyolite tephra fall, that crop out on the south side of the island (Waitt and Beget, 2009). Dense and pumiceous rhyolite clasts from the deposits are compositionally similar (71-74 wt. % SiO2; Larsen et al., 2010) and contain phenocrysts of plagioclase, quartz, amphibole, and Fe-Ti oxides. These basalt-rhyolite deposits are the most compositionally extreme products of the volcano; Holocene eruptions, including historical eruptions in 1976, 1986, and 2006, produced andesites and dacites. In 2006, one such eruption produced gabbro inclusions (54.4-60.2 wt% SiO2) that consist of plagioclase, amphibole, pyroxenes, Fe-Ti oxides, and small amounts of interstitial glass, suggesting a cumulate origin. Both the Pleistocene-age rhyolite and the 2006 gabbro inclusions fall along a whole-rock compositional trend depleted in incompatible elements relative to mid-Holocene-present andesites and dacites. To investigate differentiation and the timing of rhyolite magma generation at Augustine, we have determined high-spatial resolution 238U-230Th ages of zircon crystallization for the rhyolite as well as for the gabbros and high-silica andesites erupted in 2006. Sensitive high-resolution ion microprobe (SHRIMP-RG) analyses of indium-mounted, unpolished zircon rims from the rhyolite yield a single 238U-230Th isochron age of ca. 27 ka, which we interpret to reflect the final interval of crystallization immediately prior to eruption. Sectioned core ages for rhyolite zircon, however, fall into two populations: one at ca. 27 ka, and a second, smaller population that

  14. 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

  15. Static and fault-related alteration in the lower ocean crust, IODP Expedition 345, Hess Deep (United States)

    McCaig, Andrew; Faak, Kathrin; Marks, Naomi; Nozaka, Toshio; Python, Marie; Wintsch, Robert; Harigane, Yumiko; Titarenko, Sofya


    IODP Expedition 345 drilled the first holes in the lower plutonic crust at a fast-spreading ridge, recovering primitive layered gabbros (Gillis et al 2014). Alteration can be subdivided into two series: 1) a largely static pseudomorphic alteration affecting predominantly olivine. This began in the amphibolite facies with minor secondary cinopyroxene and hornblendic amphibole replacing primary pyroxene, and sporadically developed corona textures with tremolite and chlorite replacing olivine and plagioclase respectively, but was predominantly in the greenschist and sub-greenschist facies with talc, serpentine, clay minerals,oxides andsulphides replacing olivine, and prehnite and locally other calcsilicates replacing plagioclase, commonly in micro-vein networks. Albitic plagioclase is sporadically developed, and locally zeolite and carbonate. 2) An overprinting metasomatic alteration under sub-greenschist or perhaps lowermost greenschist conditions(zeolite. This alteration is spatially related to cataclastic fault zones and macroscopic veins. Comminuted plagioclase in cataclasites is commonly completely replaced by prehnite, while chlorite may completely pseudomorph olivine, locally with textures suggesting replacement of previous secondary minerals such as talc and serpentine. Chlorite also ubiquitously occurs as patches replacing plagioclase along grain boundaries, locally associated with carbonate and amphibole needles. Metamorphosed dykes show chilled margins within the cataclasites, and are affected by cataclastic deformation. Faults, dykes and overprinting alteration are all inferred to be related to the westward propagation of Cocos-Nazca spreading that formed Hess Deep. Samples of different alteration and cataclastic domains were cut out of this section chips for isotopic analysis. 87Sr/86Sr ratios of cataclasites and dyke rocks are in the range 0.7037 - 0.7048, indicating alteration by seawater at moderate integrated fluxes. The highest values were in

  16. Petrochemistry of igneous rocks of the California-Vetas mining district, Santander, Colombia: Implications for northern Andean tectonics and porphyry Cu (-Mo, Au) metallogeny (United States)

    Bissig, Thomas; Mantilla Figueroa, Luis Carlos; Hart, Craig J. R.


    /204Pb and 208Pb/204Pb ratios. The geochemical signature suggests that late Miocene granodiorite porphyries represent oxidized and water-rich melts. However, in contrast to many other porphyry districts in the Andes, they do not have low Y (< 15 ppm) or depleted HREE, which together with the high Sr, Al and Na content indicates that neither plagioclase nor garnet were important residual phases in the MASH zone at the base of the crust. The trough shaped MREE suggest that amphibole was present in the source. The 87Sr/86Sr values of the Miocene rocks are consistent with a mantle derived melt which interacted with the radiogenic continental crust. The magmatism occurred above the shallow subducting Caribbean slab attributed to subduction of part of the Caribbean plateau (a.k.a. proto-Caribbean oceanic complex). It may be related to slab break-off and incursion of hot asthenospheric mantle, but dehydration of the Caribbean slab probably provided additional volatiles which made amphibole a major residual phase and provided water for the hydrous porphyry related magmas.

  17. Contribution to chlorine cycle: a Cl stable isotope approach on Mantle-Ocean exchanges (United States)

    Bonifacie, M.; Jendrzejewski, N.; Pineau, F.; Agrinier, P.


    The stable isotope composition of chlorine (37Cl/35Cl) can be used to trace its geochemical cycle and is a powerfull tool to constrain the origin of high chlorine contents found for some fresh MORB glasses. Despite the fact that chlorine is a volatile element of primary importance, its cycle and isotopic fractionation factors during exchange processes between Earth's reservoirs or phases are poorly known. Furthermore, the scarcity of data for solid samples (rocks or minerals) reflects the analytical difficulty to extract chlorine from silicate structure. The classical methods of pyrohydrolysis followed by isotope-ratio mass spectrometric measurements on CH_3Cl gas have been optimised. Our technique represents the most quantitative and precise method of chlorine extraction for δ37Cl determination on solids published to date. Mean extraction yields are 100 ± 3%, δ37Cl values on duplicate extractions show reproducibility better than 0.2 ppm and the blanks represent less than 5% of the sample size. To characterise chlorine behaviour during the oceanic crust alteration, we have analysed fresh MORB glasses (from SWIR and EPR), altered basalts from leg 504B site (EPR), serpentinized peridotites (from SWIR and MAR) and an altered gabbro from the Hess Deep site (EPR). All samples (n=9) are depleted in 37Cl (δ37Cl from -1.4 to 0 ppm) relative to seawater (δ37Cl =0 ppm); Cl concentrations are between 200 and 2200 ppm. Our results on fresh MORBs: δ37Cl = -1.4 ppm and -0.6 ppm are in the lower range already published (-3 to +11 ppm, e.g. Magenheim et al., 95; Stewart, 2000). However, our δ37Cl range of altered samples: δ37Cl = -1.3 to -0.2 ppm (basalts, serpentinised peridotites and gabbro) is outside the range observed by Magenheim et al., 95 (+0.4 to +7.5 ppm in amphibole-rich rocks and smectite veins) despite the fact that in both study amphibole-rich rocks from the same site (i.e. leg 504B) have been analysed. On this site, our δ37Cl results are very homogeneous

  18. Change of the Surface Soil in the Ohno River Drainage and its Impact on the Detrital Composition of the Sediments in the Beppu Bay, the Southwestern Japan, during the Holocene (United States)

    Irino, T.; Yamamoto, M.; Ikehara, K.; Kuwae, M.; Takemura, K.


    Detrtal fraction contained in marine sediments can be generally used as climate proxies because variations in provenance and mineralogy could be affected by the precipitation distribution and weathering intensity. Change in the surface soil composition could be observed if a well-preserved depositional soil sequence was found. In order to detect the change in provenances and interpret the terrestrial environment using detrital proxies in the marine sediments, it is necessary to know the variability or range of the mineral composition of a particular provenance during the targeted time periods. The Ohno River is located in the northeast Kyushu Island, the southwestern Japan, which has the head water region at the Mt. Kuju and Mt. Aso, flows eastward combining some tributaries from the south, and then flows northward to the Beppu Bay. Surface geology of the drainage area is roughly divided into two as andosol in the northeast and brown forest soil in the south. Such contrasting detrital provenances could provide a variety of grain composition to the marine sediments deposited in the Beppu Bay. The No. 5 boring core was drilled at a landfill site on the mouth of the Ono River. The core continuously recovers 97 m length and consists of Holocene marine sediments which could be a good record of the terrestrial environment of hinterland (the Ohno River Basin). We also found a soil sequence on the foot of the Mt. Kuju at 850 m altitude, which covers the similar time interval as the No.5. The soil sequence consists of brown loam overlain by the alternation of tephra and andosol. We tried to compare the variations in mineral compositions both for this soil sequence and the No.5 core since about 8,000 yrs age. The No. 5 core mainly consists of smectite, illite, chlorite (or kaolinite), amphiboles, quartz, feldspars, and amorphous materials with minor calcite. Amorphous material is supposed to mainly consists biogenic opal. Amorphous material is higher during 7000 to 3500 yrs

  19. Evidence for Archean inheritance in the pre-Panafrican crust of Central Cameroon: Insight from zircon internal structure and LA-MC-ICP-MS Usbnd Pb ages (United States)

    Ganwa, Alembert Alexandre; Klötzli, Urs Stephan; Hauzenberger, Christoph


    The main geological feature of Central Cameroon is the wide spread occurrence of granitoids emplaced in close association with transcurrent regional shear zones. The basement of this vast domain is a Paleoproterozoic ortho-and para-derivative formation, which has been intensely reworked, together with subsequent intrusions and sediments, during the Panafrican orogenesis in the Neoproterozoic. As consequence, the area underwent pervasive metamorphism and intense deformation. This makes it difficult to distinguish between Panafrican metasediments or syntectonic plutonites and their respective basement. Our study presents zircon features (CL-BSE-SE) and in-situ U-Th-Pb LA-MC-ICP-MS geochronology of a meta-sedimentary pyroxene-amphibole-bearing gneiss of the Méiganga area in Central Cameroon. Based on the Internal structures of the zircon four characteristic zonation patterns can be deciphered: 1) cores with magmatic oscillatory zonation 2) zircons with oscillatory or sector zonation, 3) zircons with sector zoning or blurred zoning, and 4) narrow bright un-zoned rims. These groups suggest that the rock experienced a number of geological events. Considering this zircon characteristic, the U-Th-Pb data allow to distinguish four ages: 2116 ± 57 Ma, consistent with ages from the Paleoproterozoic West Central African Belt; 2551 ± 33 Ma which marks a late Neoarchean magmatic event; 2721 ± 27 Ma related to a Neoarchean magmatic even in Central Cameroon, similar to one found in the Congo Craton. A zircon core gives ages around 2925 Ma which provides some evidence of the presence of the Mesoarchean basement prior to the Neoarchean magmatism. A weighted average of lower intercepts ages gives a value of 821 ± 50 Ma, representing the age of later metamorphism event. The various characteristic group and related ages reflect not only the complexity of the history of the pyroxene amphibole gneiss, but also show that the meta-sediment has at least three zircon

  20. Melt evolution beneath a rifted craton edge: 40Ar/39Ar geochronology and Sr-Nd-Hf-Pb isotope systematics of primitive alkaline basalts and lamprophyres from the SW Baltic Shield (United States)

    Tappe, Sebastian; Smart, Katie A.; Stracke, Andreas; Romer, Rolf L.; Prelević, Dejan; van den Bogaard, Paul


    A new high-precision 40Ar/39Ar anorthoclase feldspar age of 176.7 ± 0.5 Ma (2-sigma) reveals that small-volume alkaline basaltic magmatism occurred at the rifted SW margin of the Baltic Shield in Scania (southern Sweden), at a time of global plate reorganization associated with the inception of Pangea supercontinent break-up. Our combined elemental and Sr-Nd-Hf-Pb isotope dataset for representative basanite and nephelinite samples (>8 wt.% MgO) from 16 subvolcanic necks of the 30 by 40 km large Jurassic volcanic field suggests magma derivation from a moderately depleted mantle source (87Sr/86Sri = 0.7034-0.7048; εNdi = +4.4 to +5.2; εHfi = +4.7 to +8.1; 206Pb/204Pbi = 18.8-19.5). The mafic alkaline melts segregated from mixed peridotite-pyroxenite mantle with a potential temperature of ∼1400 °C at 2.7-4.2 GPa (∼90-120 km depths), which places ultimate melt generation within the convecting upper mantle, provided that the lithosphere-asthenosphere boundary beneath the southern Baltic Shield margin was at ⩽100 km depth during Mesozoic-Cenozoic rifting. Isotopic shifts and incompatible element enrichment relative to Depleted Mantle reflect involvement of at least 20% recycled oceanic lithosphere component (i.e., pyroxenite) with some minor continent-derived sediment during partial melting of well-stirred convecting upper mantle peridotite. Although pargasitic amphibole-rich metasomatized lithospheric mantle is excluded as the main source of the Jurassic magmas from Scania, hydrous ultramafic veins (i.e., hornblendite) may have caused subtle modifications to the compositions of passing sublithospheric melts. For example, modeling suggests that the more radiogenic Hf (εHfi = +6.3 to +8.1) and Pb (206Pb/204Pbi = 18.9-19.5) isotopic compositions of the more sodic and H2O-rich nephelinites, compared with relatively homogenous basanites (εHfi = +4.7 to +6.1; 206Pb/204Pbi = 18.8-18.9), originate from minor interactions between rising asthenospheric melts and

  1. Zircon U-Pb age, Lu-Hf isotope, mineral chemistry and geochemistry of Sundamalai peralkaline pluton from the Salem Block, southern India: Implications for Cryogenian adakite-like magmatism in an aborted-rift (United States)

    Renjith, M. L.; Santosh, M.; Li, Tang; Satyanarayanan, M.; Korakoppa, M. M.; Tsunogae, T.; Subba Rao, D. V.; Kesav Krishna, A.; Nirmal Charan, S.


    The Sundamalai peralkaline pluton is one among the Cryogenian alkaline plutons occurring in the Dharmapuri Rift Zone (DRZ) of the Salem Block in the Southern Granulite Terrane (SGT) of India. Here we present zircon U-Pb age and Lu-Hf isotopic composition, mineral chemistry and geochemistry of the pluton to explore the petrogenesis and geodynamic implications. Systematic modal variation of orthoclase, Na-plagioclase, Ca-amphibole (ferro-edenite and hastingsite) and quartz developed quartz-monzonite and granite litho units in the Sundamalai pluton. Thermometry based on amphibole-plagioclase pair suggests that the pluton was emplaced and solidified at around 4.6 kbar pressure with crystallization of the major phases between 748 and 661 °C. Estimated saturation temperature of zircon (712-698 °C) is also well within this range. However, apatite saturation occurred at higher temperatures between 835 and 870 °C, in contrast with monazite saturation (718-613 °C) that continued up to the late stage of crystallization. Estimated oxygen fugacity values (log fO2: -14 to -17) indicate high oxidation state for the magma that stabilized titanite and magnetite. The magmatic zircons from Sundamalai pluton yielded a weighted mean 206Pb/238U age of 832.6 ± 3.2 Ma. Geochemically, the Sundamalai rocks are high-K to shoshonitic, persodic (Na2O/K2O ratio > 1), silica-saturated (SiO2:65-72 wt.%), and peralkaline in composition (aluminum saturation index, ASI AI < 0). The initial magma was mildly metaluminous which evolved to strongly peralkaline as result of fractional crystallization (plagioclase effect) controlled differentiation between quartz-monzonite and granite. Both rock types have high content of Na2O (5.1-6.3 wt.%), Ba (350-2589 ppm) and Sr (264-1036 ppm); low content of Y (8.7-17 ppm) and Yb (0.96-1.69 ppm); elevated ratios of La/Yb (11-46) and Sr/Y (46-69) and are depleted in Ti, with a positive Sr anomaly suggesting an adakite-like composition and garnet controlled

  2. Geochemical radioactive investigation of beach sands and stream sediments, using heavy minerals, trace elements and radon measurements, (Qerdaha sheet of the Syrian coast)

    International Nuclear Information System (INIS)

    Reconnaissance geochemical radiometric survey of stream sediments resulting from the weathering of outcropped rocks in and around the study area was performed. This survey included heavy mineral sampling, trace and radioelements and radon measurements to evaluate the radioactivity of the source rocks and to understand the nature and distribution of the heavy minerals and trace elements in the study area. Several techniques were used to achieve these objectives. The results of heavy mineral geochemical survey show that the abundant minerals are iron oxides (magnetite, hematite, goehtite and limonite) pyroxene and olivine; less abundant minerals are apatite, ilmenite, garnet, barite, siderite and gloconite, while rare minerals are zircon and rutile. Amphibole is reported as an abundant mineral in sand dunes and is less abundant in samples located in the northern part of the study area. The amphibole seems to be derived from the ophiolitic complex north of the study area. Grain size analysis of heavy minerals revealed that the concentration of economic minerals such as zircon rutile and ilmenite increases with the decrease of the grain size. The microscopic study showed fragments and fossils of foraminifere mostly impregnated with heavy metals such as iron and manganese resulting from diagenetic metasomatism and replacement processes of. Fish teeth (< 2 mm) and oolite of iron were also noticed in most of the samples. The morphology of heavy mineral grains shows that most of the grains are angular to subangular suggesting that they were transported for short distance from their source rocks. Normally, phosphate pellets, gloconite and iron ooids are not considered since their original morphological features show clear roundness that attributed to their sedimentological origin, not to transportation factor. The source rock of most of the heavy mineral assemblage is the basalt. Apatite and gloconite are derived from the phosphorite and phosphatized limestone encountered

  3. A Dynamic study of Mantle processes applying In-situ Methods to Compound Xenoliths: implications for small to intermediate scale heterogeneity (United States)

    Baziotis, Ioannis; Asimow, Paul; Koroneos, Antonios; Ntaflos, Theodoros; Poli, Giampero


    spinel lherzolite (Irving 1980). The Dish Hill volcanic field contains lherzolite xenoliths with amphibole-rich veins previously interpreted by Wilshire et al. (1980) in terms of reaction of a H2O- and Fe-rich fluid with the lherzolite host producing notable losses of Mg and Al. The Cima volcanic field, located in the southern Basin and Range province, provides samples with contacts among such diverse lithologies as Cr-diopside spinel peridotite, websterite, gabbro, clinopyroxenite and wehrlite (Wilshire et al. 1991). The San Quintin example contains large websterite veins crosscutting lherzolite matrix. Chino Valley xenoliths show cumulate textures with alternating orthopyroxene- and clinopyroxene-rich layers. We discuss and assign the observed reaction textures and mechanisms between the different minerals (e.g. olivine, clinopyroxene, orthopyroxene), layers (e.g. clinopyroxenite and lherzolite) and the consequent compositional changes across/among the minerals and the lithologic contacts. Thus, we characterize the possible genetic origin scenarios for the observed contacts between adjacent lithologies of the composite xenoliths. Those examples, most likely to represent original subsolidus contacts that underwent partial melting together, will have the most direct relevance as benchmarks for application of future kinetic models of melt extraction from heterogeneous mantle lithologies. References Irving, A.J. (1980). Petrology and Geochemistry of Composite Ultramafic Xenoliths in Alkalic Basalts and Implications for Magmatic Processes within the Mantle. American Journal of Science, 280, 389-426. Wilshire, H.G., et al. (1980). Amphibole-Rich Veins in Lherzolite Xenoliths, Dish Hill and Deadman Lake, California. American Journal of Science, 280, 576-593. Wilshire, H.G., et al. (1991). Petrology of Lower Crustal and Upper Mantle Xenoliths from the Cima Volcanic Field, California. Journal of Petrology, 32(1), 169-200.

  4. Petrology of pyroxenitic vein in spinel-plagioclas lherzolites from Zabargad island, Red Sea, Egypt (United States)

    Gjerazi, Ingrid; Ntaflos, Theodoros


    The island of Zabargad (St. John's island), located off the coast of Egypt contains three peridotite bodies, which comprise of Spinel- and Plagioclase-Lherzolithes. The studied rock is a composite peridotite consisting of a pyroxenitic vein with coarse grained augites of approx. 3 cm, originating from the Main Peridotite Hill (MPH) in Zabargad. Information on the nature and formation of this peridotite from Zabargad was obtained through the mineralogical and petrographic analysis, using a polarizing light microscope and electron microprobe, of five thin sections originating from the aforementioned peridotite. Furthermore, the chemical heterogeneities and the modal changes of the peridotite through its interaction with intrusive pyroxenitic veins were studied in order to create a better understanding of the origin of the rock and of the geology of the island. Results have shown, that the mineralogical composition of this peridotite comprises of: olivine, clinopyroxene, orthopyroxene, plagioclase, amphibole and spinel. In the host rock, the Fo (forsterite) content of olivine varies from approx. 88% to 89% and in the vein it remains well within the boundaries of 89%. Compared to primary xenoliths originating from the fertile, undepleted mantle with an Mg-number (100*Mg#), which ranges from 89.2% to 89.9%, the similarities with the olivines can clearly be seen. The vein clinopyroxenes can be divided into three distinct groups. The first groupconsists of coarse-grained, primary augites. The second group corresponds fine-grained clinopyroxenes found closer to the matrix. These clinopyroxenes have been formed due to the recrystallization of the primary augites from the emplacement of the dike. The third group consists of fine-grained clinopyroxenes located in the transition zone between vein and matrix. The spinels are Cr-rich with 100*cr# ranging from 6 to 22. In the spinel cr# versus olivine mg# diagram, the spinels plot whithin the Olivine-Spinel Mantle Array (OSMA

  5. Petrogenesis of Tertiary continental intra-plate lavas between Siebengebirge and Westerwald, Germany: Constraints from trace element systematics and Nd, Sr and Pb isotopes (United States)

    Schubert, S.; Jung, S.; Pfänder, J. A.; Hauff, F.; Garbe-Schönberg, D.


    New 39Ar/40Ar ages and major- and trace-element and radiogenic isotope data are presented for basanites and alkali basalts from the transition area between the Westerwald and Siebengebirge volcanic fields (Germany) that belongs to the Central European Volcanic Province (CEVP). The 39Ar/40Ar ages indicate ages of c. 24 and c. 5 Ma which are fully compatible with previous K/Ar ages indicating that the evolution of this volcanic field belongs to the Westerwald area (28-22 Ma and 5 Ma) rather than to the Siebengebirge area (26-23 Ma). Based on the occurrence of > 30 isolated volcanic plugs with a simple igneous history, this volcanic field can be viewed as a monogenetic volcanic field. Compositions of some basanites are primitive, whereas others and the alkali basalts show decreasing Cr and Ni contents and CaO/Al2O3 ratios. However, increasing TiO2, Al2O3 and incompatible elements (Sr, Zr, Y, Hf, Ta) concentrations with decreasing MgO indicating fractionation of mainly olivine with minor amounts of clinopyroxene and spinel can be noticed. Rare earth element systematics suggest that most of the alkaline rocks are generated by different degrees of melting (5%-10%) of a garnet-bearing peridotite containing some residual amphibole. Negative anomalies of Rb and K in primitive mantle-normalized diagrams and a lack of Ba/Rb fractionation suggest that amphibole was the major OH-bearing mineral phase in the mantle. The alkaline rocks have a restricted range in 87Sr/86Sr and 143Nd/144Nd ratios ranging from 0.7033 to 0.7044 and from 0.51275 to 0.51285, respectively. Lead isotope compositions (206Pb/204Pb: 19.21-19.65; 207Pb/204Pb: 15.62-15.67; 208Pb/204Pb: 39.10-39.46) of the alkaline rocks are within the range of most OIB in which the higher values approach the composition of the European Asthenospheric Reservoir (EAR). The correlation between Sr and Nd isotopes and trace element constraints (Ce/Pb; Nb/U) indicates that for some samples interaction with crustal rocks during

  6. Petrography, sulfide mineral chemistry, and sulfur isotope evidence for a hydrothermal imprint on Musina copper deposits, Limpopo Province, South Africa: Evidence for a breccia pipe origin? (United States)

    Chaumba, Jeff B.; Mundalamo, Humbulani R.; Ogola, Jason S.; Cox, J. A.; Fleisher, C. J.


    The Musina copper deposits are located in the Central Zone of the Limpopo orogenic belt in Limpopo Province, South Africa. We carried out a petrographic, sulfide composition, and δ34S study on samples from Artonvilla and Campbell copper deposits and a country rock granitic gneiss to Artonvilla Mine to place some constrains on the origin of these deposits. The assemblages at both Artonvilla and Campbell Mines of brecciated quartz, potassium feldspar, muscovite, chlorite, calcite, and amphibole are consistent with sericitic alteration. Quartz, amphibole, feldspars, and micas often display angular textures which are consistent with breccias. Sulfur concentrations in pyrite from Artonvilla Mine plot in a narrow range, from 50.2 wt. % to 55.7 wt. %. With the exception of a positive correlation between Fe and Cu, no well defined correlations are shown by data from the Musina copper deposits. The occurrence of sulfides both as inclusions in, or as interstitial phases in silicates, suggests that hydrothermal alteration that affected these deposits most likely helped concentrate the mineralization at the Musina copper deposits. Sulfur concentrations in chalcopyrite samples investigated vary widely whereas the copper concentrations in chalcopyrite are not unusually higher compared to those from chalcopyrite from other tectonic settings, probably indicating that either the Cu in the Musina copper deposits occurs in native form, and/or that it is hosted by other phases. This observation lends support to the Cu having been concentrated during a later hydrothermal event. One sample from Artonvilla Mine (AtCal01) yielded pyrite δ34S values of 3.1and 3.6‰ and chalcopyrite from the same sample yielded a value of 3.9‰. A country rock granitic gneiss to Artonvilla Mine yielded a δ34Spyrite value of 8.2‰. For Campbell Mine samples, one quartz vein sample has a δ34Spyrite value of 0.5‰ whereas chalcopyrite samples drilled from different areas within the same sample

  7. Metasomatized granulites of the Mozambique belt: consequences for lithospheric U, Th, REE fertilisation and metallogenesis in the ancient Gondwanaland supercontinent

    International Nuclear Information System (INIS)

    The 1,0 Ga old Lurio belt extends for ca. 1 000 km from Nsanje (S Malawi) through NE Mozambique to the Indian ocean. Lower crustal levels are locally exposed along its southern tectonic front. In this article mineralogical and geochemical data for an andesinite-mafic-ultramafic suite from Nsanje were reported.The results indicate that this complex terrane equilibrated first at P ∼ 13 kbr and T ∼ 9000C and subsequently cooled under an eclogite-garnet granulite georem. During a later event (P ∼ 7-10 kbar, T ∼ 650 - 8000C) distinctive metasomatic mica, amphibole, scapolite, apatite, diopsidic pyroxene (MASAD)-bearing assemblages and pegmatoids were formed by CO2, Cl, H2O, S and F rich fluids with higher REE, U, Th and Zr concentrations than the high-grade precursors. MASAD and older high-pressure granulite parageneses underwent subsequent dehydratation and reequilibration under medium-pressure granulite facies conditions perhaps during the Lurio orogenic event. MASAD-like assemblages are relatively common within the late Proterozoic medium- and high-pressure granulite terranes of Central Gondwana, especially in the newly defined Lurio-Zambezi Eclogite Province. The data provide indicate that the metasomatizing, MASAD-forming fluids had crypto-carbonatitic affinities and were introduced into the crust from the upper mantle during protorifting episodes between ca. 1,1 and 0,5 Ga ago. The MASAD assemblages may therefore represent the crustal equivalent of the metasomatic and MARID suites discovered in mantle xenoliths

  8. Neoproterozoic alkaline magmatism in Ilha do Cardoso, southeastern coast of Sao Paulo State, Brazil

    International Nuclear Information System (INIS)

    This work focuses on the geology and geochronology of rocks cropping out on Cardoso Island, on the southeastern coast of Sao Paulo State, close to the boundary with Parana State. The island, with an area of about 151 km2 is a protected area administered by the Forest Institute of the Secretariat for the Environment of the State of Sao Paulo. It is mountainous, with a peak at 814 m, and is covered by dense Atlantic Forest vegetation. The island is made up mainly of an igneous complex with light grey leucocratic, inequigranular, medium to coarse-grained syenites. The Tres Irmaos Syenite (STI), composed of pyroxene, hornblende, and perthitic to mesoperthitic microcline, predominates has magmatic flow structures, and it cut by the pinkish grey, leucocratic medium-grained Cambriu alkali-feldspar granites (GC). Geochemical analysis of STI and GC demonstrate their metaluminous alkaline nature and late orogenic to anorogenic character. The bodies formed between 620 and 570 Ma according to U-Pb dating of zircons and cooled between 597 and 531 Ma (K-Ar in amphiboles). Whole rock Sm-Nd analyses yield Meso- and Paleoproterozoic TDM ages (1,500 - 2,200 Ma). A belt of low-grade metasedimentary rocks occurs in the northern part of the island. Quartz schist, quartz-mica schist and mica-quartz schist, often-containing andalusite and cordierite, predominate. Geochemical and geochronological data suggest that the sources of the metasediments were continental arc andesites of whose protoliths separated from the mantle between 1,800 and 2,200 Ma during the Paleoproterozoic. These metasediments probably continue on the continent in the Taquari region and extend southwards in narrow strips between the granitoids of the Paranagua Domain. (author)

  9. Structural analysis and magmatism characterization of the Major Gercino shear zone, Santa Catarina State, Brazil; Analise estrutural e caracterizacao do magmatismo da zona de cisalhamento Major Gercino, SC

    Energy Technology Data Exchange (ETDEWEB)

    Passarelli, Claudia Regina


    This work describes the geometric and kinematic characteristics of the Major Gercino Shear Zone (MGSZ) in the Canelinha-Garcia area. This shear zone is one of the major lineaments that affect all southern Brazilian precambrian terrains. In Santa Catarina State, it separates, along its whole extension, the supracrustal rocks of the Brusque belt (northern part) from the Granitoid belt (southern). This zone is characterized by a regional NE trend and a dextral sense of movement where ductile-brittle structures predominate. The MGSZ is composed of two mylonitic belts separated by granitoid rocks probably associate