Sample records for amphibole

  1. Equilibrium coexistence of three amphiboles (United States)

    Robinson, P.; Jaffe, H.W.; Klein, C.; Ross, M.


    Electron probe and wet chemical analyses of amphibole pairs from the sillimanite zone of central Massachusetts and adjacent New Hampshire indicated that for a particular metamorphic grade there should be a restricted composition range in which three amphiboles can coexist stably. An unequivocal example of such an equilibrium three amphibole rock has been found in the sillimanite-orthoclase zone. It contains a colorless primitive clinoamphibole, space group P21/m, optically and chemically like cummingtonite with blue-green hornblende exsolution lamellae on (100) and (-101) of the host; blue-green hornblende, space group C2/m, with primitive cummingtonite exsolution lamellae on (100) and (-101) of the host; and pale pinkish tan anthophyllite, space group Pnma, that is free of visible exsolution lamellae but is a submicroscopic intergrowth of two orthorhombic amphiboles. Mutual contacts and coarse, oriented intergrowths of two and three host amphiboles indicate the three grew as an equilibrium assemblage prior to exsolution. Electron probe analyses at mutual three-amphibole contacts showed little variation in the composition of each amphibole. Analyses believed to represent most closely the primary amphibole compositions gave atomic proportions on the basis of 23 oxygens per formula unit as follows: for primitive cummingtonite (Na0.02Ca0.21- Mn0.06Fe2+2.28Mg4.12Al0.28) (Al0.17Si7.83), for hornblende (Na0.35Ca1.56Mn0.02Fe1.71Mg2.85Al0.92) (Al1.37Si6.63), and for anthophyllite (Na0.10Ca0.06Mn0.06Fe2.25Mg4.11Al0.47) (Al0.47Si7.53). The reflections violating C-symmetry, on X-ray single crystal photographs of the primitive cummingtonite, are weak and diffuse, and suggest a partial inversion from a C-centered to a primitive clinoamphibole. Single crystal photographs of the anthophyllite show split reflections indicating it is an intergrowth of about 80% anthophyllite and about 20% gedrite which differ in their b crystallographic dimensions. Split reflections are

  2. 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/...

  3. 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 public...

  4. The composition and morphology of amphiboles from the Rainy Creek complex, near Libby, Montana (United States)

    Meeker, G.P.; Bern, A.M.; Brownfield, I.K.; Lowers, H.A.; Sutley, S.J.; Hoefen, T.M.; Vance, J.S.


    Thirty samples of amphibole-rich rock from the largest mined vermiculite deposit in the world in the Rainy Creek alkaline-ultramafic complex near Libby, Montana, were collected and analyzed. The amphibole-rich rock is the suspected cause of an abnormally high number of asbestos-related diseases reported in the residents of Libby, and in former mine and mill workers. The amphibole-rich samples were analyzed to determine composition and morphology of both fibrous and non-fibrous amphiboles. Sampling was carried out across the accessible portions of the deposit to obtain as complete a representation of the distribution of amphibole types as possible. The range of amphibole compositions, determined from electron probe microanalysis and X-ray diffraction analysis, indicates the presence of winchite, richterite, tremolite, and magnesioriebeckite. The amphiboles from Vermiculite Mountain show nearly complete solid solution between these end-member compositions. Magnesio-arfvedsonite and edenite may also be present in low abundance. An evaluation of the textural characteristics of the amphiboles shows the material to include a complete range of morphologies from prismatic crystals to asbestiform fibers. The morphology of the majority of the material is intermediate between these two varieties. All of the amphiboles, with the possible exception of magnesioriebeckite, can occur in fibrous or asbestiform habit. The Vermiculite Mountain amphiboles, even when originally present as massive material, can produce abundant, extremely fine fibers by gentle abrasion or crushing.

  5. Universal single grain amphibole thermobarometer for mantle rocks - preliminary calibration. (United States)

    Ashchepkov, Igor


    Calibration of S-Al- K-Na-Ca distribution in the structure of the mantle amphiboles (Cr- hornblende, pargasite, kaersutite) using experimental data (Niida, Green, 1999; Wallace Green, 1991, Conceicao, Green, 2004; Medard et al, 2006; Safonov, Butvina, 2013; 2016; Pirard, Hermann, 2015 etc) allows to obtain an equation for pressure estimates in 0.5 - 4.5 GPa interval. Regression calculated pressures with experimental values (R 0.82) and precision 5 kbar allow to use barometer for a wide range of mantle rocks from peridotite to pyroxenites and megacrystals. For the higher pressures (Cr- pargasite richterite) calibration is carried by the cross- correlations with the estimates calculated for the natural associations obtained using clino- and orthopyroxene. IT was used KD =Si/(8-Al-2.2*Ti)*(Na+K))/Ca for the following equation: P(GPa)=0.0035*(4+K/(Na+K))*2*Mg)/Fe+3.75*(K+Na)/Ca))*KD*ToK**0.75/ (1+3.32*Fe)-ln(1273/ToK*5*(8*Mg-Al*2 +3*Ti+8*Cr+3*K)/10 Th advantage of this barometer comparing with the previous (Ridolfi, Renzulli, 2012) is that is working with all mantle amphibole types. For the calculations of the PT parameters of the natural xenocrysts it was used monomineral version of Gar-Amph termometer (Ravna et al., 2000) in combination with the received barometer. Contents of Ca- Mg and Fe in associated garnets were calculated usinf the regressions obtained from natural and experimental associations. Aplication of the mantle amphibole thermobarometry for the reconstruction of sections of the cratonic mantle lithosphere of Yakutia show that amphibloles are distributed in various parts of mantle sections in deifferent mantle terranes of Yakutia. The most abundant amphoboles from Alakite region are distributed within all mantle section. In the SCLM beneat Yubileyaya pipe thehalf of them belong to the spinel garnet facie refering to the upper pyroxenitic suit and Cr- hornblende - mica viens. The second group reffer to the eclogite pyroxenite layer in the middle part of

  6. Interpreting magnetic fabrics in amphibole-bearing rocks (United States)

    Biedermann, Andrea R.; Kunze, Karsten; Hirt, Ann M.


    If amphibole is a major constituent in a rock, its magnetic fabric can be largely controlled by the crystallographic preferred orientation of amphibole. This study describes the (para)magnetic anisotropy in two amphibolites, both containing ca. 70% hornblende with rather strong crystallographic preferred orientation. Both amphibolites display a significant and well-defined anisotropy of magnetic susceptibility, with the minimum susceptibility approximately normal to foliation. However, in one amphibolite, the maximum susceptibility is parallel to the lineation, whereas in the other it is not. This seemingly inconsistent observation can be explained by the intrinsic susceptibility anisotropy of single crystals of hornblende, and their texture in the rocks. Numerical models show how the principal susceptibility axes relate to macroscopic foliation and lineation for point and fiber textures. This study underlines the potential of using magnetic anisotropy to obtain information about mineral fabrics in mafic rocks. At the same time, it highlights the necessity for taking into account single crystal properties of the mineral(s) responsible for the anisotropy and their crystallographic preferred orientation when interpreting magnetic fabrics.

  7. Thermally-induced amphibole reaction rim development: EBSD insights into microlite orientation (United States)

    De Angelis, Sarah; Lavallée, Yan; Larsen, Jessica; Mariani, Elisabetta


    Amphibole is an important mineral present in many calc-alkaline volcanic deposits. A hydrous phase, volcanic amphibole is only stable at pressures greater than 100 MPa (approx. 4 km), temperature less than ~860-870 oC, and in melts containing at least 4 wt % H2O. When removed from their thermal and barometric stability field, amphiboles decompose to form aggregate rims of anhydrous minerals. The thickness, texture, and mineralogy of these rims are thought to be reflective of the process driving amphibole disequilibrium (e.g. heating, decompression, etc). However, significant overlap in rim thicknesses and microlite textures means that distinguishing between processes it not simple. This study employed backscatter diffraction (EBSD) to examine both experimental heating-indced amphibole reaction rims and natural amphibole reaction rim from Augustine Volcano. We collected crystal orientation maps of amphibole reaction rims to investigate if different types of disequilibrium produce different patterns of microlite orientation. We identified two types of reaction rim: Type 1- reaction rim microlites are generally oriented at random and share little or no systematic relationship with the crystallographic orientation of the host amphibole, and; Type 2- reaction rim microlites exhibit a topotactic relationship with the host amphibole (they share the same crystallographic orientation). Experimentally produced heating reaction rims are without exception Type 2. However the natural reaction rims are evenly distributed between Types 1 and 2. Further experimental data on decompression induced reaction rim formation is needed to investigate if Type 1 reaction rims resemble the breakdown of amphibole due to decompression. If so, reaction rim microlite orientation could provide a clear method for distinguishing between heating and decompression processes in amphibole bearing magmas.

  8. Voluminous arc dacites as amphibole reaction-boundary liquids (United States)

    Blatter, Dawnika L.; Sisson, Thomas W.; Hankins, W. Ben


    dacite-granodiorite-tonalite compositions. Higher-K dacites than the Yn would also saturate with biotite, further limiting their compositional diversity. Theoretical evaluation of the energetics of peritectic melting of pargasitic amphiboles indicates that melting and crystallization of amphibole occur abruptly, proximal to amphibole's high-temperature stability limit, which causes the system to dwell thermally under the conditions that produce dacitic compositions. This process may account for the compositional homogeneity of dacites, granodiorites, and tonalites in arc settings, but their relative mobility compared to rhyolitic/granitic liquids likely accounts for their greater abundance.

  9. Optical Spectra and Color Nature of Lithium Amphiboles

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    S.I. Konovalenko


    Full Text Available Optical absorption spectra of two lithium amphiboles of the pedrisite group from rare-metal peg-matites of the Sangilen rare-metal province in the southeastern part of Tyva have been studied. One of them – a limit magnesian fluoro-sodium pedrisite of yellow-green color – was taken from the rocks hosting pegmatites, and another one – fluoro-sodium ferro-pedrisite of violet-blue color – was taken from pegmatites as such. It has been demonstrated that the color of the yellow-green mineral is associated with absorption bands of Cr3+ ions in the octahedral coordination. Absorption bands of Cr3+ ions in the spectrum of fluoro-sodium pedrisite are formed by a transmission window in the yellow-green region of the spectrum. Therefore, the color of this sample is yellow-green. The color of violet-blue pedrisite is de-fined by intensive absorption bands of charge transfer Fe2+ → Fe3+ 550, 680 nm. Very strong absorption bands of 550 and 680 nm are formed by a transmission window in the violet-blue region of the spectrum. Thus, the color of ferro-pedrisite is violet-blue.

  10. Magma reservoir conditions beneath Tsurumi volcano, SW Japan: Evidence from amphibole thermobarometry and seismicity (United States)

    Nagasaki, Shiho; Ishibashi, Hidemi; Suwa, Yukiko; Yasuda, Atsushi; Hokanishi, Natsumi; Ohkura, Takahiro; Takemura, Keiji


    Calcic amphibole phenocrysts in the Tsurumidake summit (TS) lava, which was produced during the most recent eruption at Tsurumi Volcano (SW Japan) at around 7.5-10.5 ka, have been analyzed to determine the pre-eruptive conditions, such as temperature (T), pressure (P), oxygen fugacity (fO2), SiO2 content (SiO2melt), and FeO*/MgO ratio (FeO*/MgOmelt), of coexisting silicate melts in the magma reservoir beneath the volcano. Although most of the amphibole phenocrysts have been completely decomposed to a fine-grained opaque symplectite, 6% of the grains remain intact. The degree of amphibole breakdown (DAB), defined as the ratio of the area of symplectite to the area of symplectite plus relict amphibole in each phenocryst, varies from 20% to 100%. Compositional zoning was not observed in the amphibole grains, however, two distinct groups of amphibole phenocrysts have been identified based on their chemical compositions: group-I amphiboles, which are relatively Si-poor, and [6]Al-rich, and have a relatively high Mg# [100Mg/(Mg + Fe2 +)]; and group-II amphiboles, which are Si-rich, and [6]Al-poor, and have a relatively low Mg#. Empirical equations for geothermobarometry, oxygen barometry and chemometry that exclusively rely on the amphibole composition were applied to estimate the T-P-fO2-SiO2melt-FeO*/MgOmelt conditions of the silicate melts with which the amphibole crystals equilibrated. The results show that group-I and group-II amphiboles equilibrated with andesitic melts (group-I melts) and dacitic-rhyolitic melts (group-II melts), respectively. The T-P-fO2 conditions of group-I melts were estimated as 374-483 MPa ( 13.9-17.9 km depth), 950 °C, and NNO + 1.3, respectively, and those of group-II melts were 93-242 MPa ( 3.4-9.0 km depth), 824-913 °C, and NNO + 0.6-1.7, respectively. The estimated T-P-fO2-SiO2melt-FeO*/MgOmelt conditions were almost constant for group-I melts, whereas the T, ΔNNO, and FeO*/MgOmelt values of group-II melts decreased with increasing

  11. Amphibole Thermometry and a Comparison of Results from Plutonic and Volcanic Systems (United States)

    Sherman, T. M.; Putirka, K. D.; De Los Reyes, A. M. A.; Ratschbacher, B. C.


    Recent work (Ridolfi and Renzulli 2014) shows that amphiboles can be used to infer magmatic temperatures, even without knowledge of co-existing liquids. Here, we apply this approach, using new calibrations, to investigate felsic-mafic magma interactions, in a volcanic (Lassen Volcanic Center, a Cascade volcano) and plutonic (the Jurassic Guadalupe Igneous Complex) system. Preliminary data suggest that volcanic processes, as might be expected, preserve higher temperatures than plutonic materials (on average, volcanic amphiboles recorded 907±57.3°C while plutonic amphiboles recorded 764±59.7°C). We also find that the average T of a given mineral grain decreases with increased mineral size such that those crystallized below 800°C sometimes reach sizes beyond ~1mm, while those near 900°C appear truncated to ~0.3mm. It is not clear if T is the only control on amphibole crystal growth; however, our results would imply that larger grains not only require more time to grow but require continued undercooling. Significant cooling or heating is also recorded in many volcanically- and plutonically-grown grains, which may reflect transitioning between magmas of different T and composition. Core-to-rim cooling trends (with a common T of drop of 80oC) likely represent mafic-to-felsic magma transitions, whereas core-to-rim heating of similar magnitudes indicate a felsic-mafic transition. Some grains, though, exhibit a constant T (in the range 700-900°C) from core to rim, which perhaps indicates some shielding from magma mixing processes. Amphiboles might thus provide a reliable record of the intensity of magma mingling and mixing experienced by any particular enclave. Interestingly, volcanically-derived amphiboles appear to mostly record cooling towards the rims, while their plutonic counterparts tend to experience heating. It would thus appear that at Lassen, amphiboles are unaffected by later mafic magma recharge, but at the GIC, the plutonic amphiboles are more likely to

  12. 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...

  13. 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...

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

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    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.


    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...

  16. How deep, how hot: comparing pressure and temperature estimates from amphibole and rhyolite-MELTS thermobarometry (United States)

    Pamukcu, A. S.; Gualda, G. A.


    Accurately constraining the pressure and temperature of magma residence is problematic, but it is key to understanding the structure and evolution of magmatic systems. Various thermometers exist (Fe-Ti oxides, Ti-in-zircon, Zr-in-sphene, etc.), but there are fewer barometers that can be applied to volcanic rocks. Most barometers capitalize on amphibole, a relatively common mineral whose composition is sensitive to pressure and temperature changes. Glass composition is a function of pressure for magmas saturated in quartz and feldspar, and a new thermobarometer based on rhyolite-MELTS simulations using glass (matrix glass and crystal-hosted glass inclusions) compositions has been recently proposed. We compare results from amphibole and matrix glass thermobarometry. We focus on outflow high-silica rhyolite pumice from the Peach Spring Tuff (CA-NV-AZ, USA), which are characterized by sanidine+plagioclase×quartz+amphibole+sphene in a high-silica rhyolite glass matrix. Compositional variations in amphibole are slight and described by edenite and Ti-Tschermak substitution, with little Al-Tschermak substitution, suggesting small changes in temperature but not in pressure. Plagioclase compositions are also nearly homogeneous. Thus, we expect thermobarometry results to cluster around a single pressure and temperature, making these samples excellent candidates for comparing thermobarometers. Amphibole×plagioclase thermobarometry reveals: - Amphibole-plagioclase: results vary widely depending on the calibration (e.g. 150-420 MPa, 520-730 °C); combined Anderson & Smith (1995) barometer with Holland & Blundy (1990) thermometer is most consistent, suggesting crystallization at 230 MPa, 680 °C. - Amphibole-only: calibrations give significantly different results (75-115 MPa, 770-960 °C [Ridolfi et al. 2010]; 400-950 MPa, 800-950°C [Ridolfi & Renzulli 2012]). Results suggest the recent re-calibration is particularly unreliable for these rocks, and the earlier calibration is

  17. Amphibole trace elements as indicators of magmatic processes at Mount St. Helens (United States)

    Hampel, T. R.; Rowe, M. C.; Kent, A.; Thornber, C. R.


    Amphibole has the capability of incorporating a wide variety of trace elements resulting from a range of magmatic processes. Prior studies have used trace elements such as Li and Cu in amphibole to investigate volatile mobility associated with magma ascent regarding the 2004-2008 eruption of Mount St. Helens (Rowe et al. 2008). In order to investigate magmatic processes associated with the 2004-2008 eruption of Mount St. Helens we have measured a range of fluid-mobile trace elements in conjunction with major element compositions of amphibole phenocrysts in dacite lava. Major elements and volatiles (Cl, F) were measured by electron microprobe analysis at Washington State University and trace elements (Li, Sc, Co, Cu, Zn, Sr, Y, Zr, Mo, Ag, Sn, Sb, Te, Ba, Ce, W, and Pb) were analyzed by laser ablation (LA)-ICP-MS at Oregon State University. Amphibole crystallization temperatures were calculated after Ridolfi et al. (2010). Core to rim transects were measured by electron microprobe to evaluate volatile concentrations and temperature profiles across individual phenocrysts. Core temperatures from 17 days and 226 days post eruption are consistently hotter than the rim temperatures 997 to 881 degrees C, respectively. Amphiboles from the end of the eruption (811 days post eruption) appear to be more complex, with phenocrysts having both increasing and decreasing temperatures toward the rims. The overall calculated temperature range of the amphiboles at the end of the eruption is 1022 to 919 degrees C. There is much diversity in the concentrations of Li and Cu within the phenocrysts in both the samples and throughout the eruption. Concentrations steadily increase in the beginning of the eruption then drop dramatically toward the middle, slowly increase toward the end eruption. Overall concentrations of Sr, Sb, Co, Sn, Mo, Ba, Ce, Sc, and Y do not change over the course of the eruption but do vary sample to sample. Preliminary data for Zn, Sb, Ag, and W suggest the

  18. The role of amphibole in Merapi arc magma petrogenesis: insights from petrology and geochemistry of lava hosted xenoliths and xenocrysts (United States)

    Chadwick, J. P.; Troll, V. R.; Schulz, B.; Dallai, L.; Freda, C.; Schwarzkopf, L. M.; Annersten, H.; Skogby, H.


    Recently, increasing attention has been paid to the role of amphibole in the differentiation of arc magmas. The geochemical composition of these magmas suggests that deep to mid crustal fractionation of amphibole has occurred. However, this phase is typically an infrequent modal phenocryst phase in subduction zone eruptive deposits(1). Nevertheless, erupted material only represents a portion of the magmatism produced in subduction zone settings, with many opportunities for melts to stall on route to the surface. This discrepancy between whole rock geochemistry and petrological interpretation of arc magmas has lead many scientists to postulate that, at mid to deep crustal levels, there may be significant volumes of amphibole bearing lithologies. Amphibole instability at shallow levels can also contribute to its scarcity in eruptive deposits. This argument is strengthened by field and petrological evidence, including the widespread occurrence of amphibole-rich intrusive rocks in exhumed orogenicbelts formed during subduction zone activity, e.g. the Adamello batholith (2),as well as the presence of amphibole-rich xenoliths and xenocrysts preserved in arc lavas worldwide, e.g. in Indonesia, Antilles, and Central America. Thus, amphibole appears to play an integral role in subduction zone magmatism and identifying and constraining this role is central to understanding arc magma petrogenisis. Amphibole-rich melts or bodies in the deep to mid crust could be a significant hydrous reservoir for intra-crustal melts and fluids (1). In this preliminary study, we have carried out petrological and geochemical analyses of recent basaltic andesite and amphibole bearing crystalline igneous inclusions and xenocrysts from Merapi volcano in Java, Indonesia. The basaltic andesite geochemistry is consistent with amphibole fractionation and the crystalline inclusions are cogenetic to the Merapi magmatic system. These inclusions are likely to represent fractionation residues reflecting

  19. Pre-eruptive magmatic conditions at Augustine Volcano, Alaska, 2006: Evidence from amphibole geochemistry and textures (United States)

    De Angelis, Sarah; Larsen, Jessica D; Coombs, Michelle L.


    Variations in the geochemistry and texture of amphibole phenocrysts erupted from Augustine Volcano in 2006 provide new insights into pre- and syn-eruptive magma storage and mixing. Amphiboles are rare but present in all magma compositions (low- to high-silica andesites) from the 3 month long eruption. Unzoned magnesiohornblende in the high- and low-silica andesites exhibit limited compositional variability, relatively high SiO2 (up to 49·7 wt %), and relatively low Al2O3 (temperature-dependent substitutions. Both high- and low-silica andesites represent remnant magmas that were stored in the shallow crust at 4–8 km depth, remaining distinct owing to a complex subsurface plumbing system. Intermediate-silica andesites and quenched mafic inclusions represent pre-eruptive hybrids of resident high- and low-silica andesite magmas and an intruding basalt. Amphiboles in explosive phase high-silica andesites are largely euhedral and unreacted, consistent with the high magma flux rates from depth during this phase (up to 13 800 m3 s–1). Phenocrysts from the other lithologies have reaction rims that range from 1 to >1000 μm in thickness. Reaction rim microlite sizes correlate with reaction rim thicknesses. Reaction rims 80 μm thick contain microlites 10–100 μm in length. Differentiating between heating- and decompression-induced amphibole reaction rim formation is problematic because of a lack of experimental constraints. We attempt a new approach to assessing reaction rim formation, based on a kinetic theory of crystal nucleation and growth, in which the differences in reaction rim textures represent different degrees of amphibole disequilibrium. Large crystals and low number densities suggest relatively lower levels of disequilibrium resulting in growth-dominated crystallization. Smaller crystals and larger number densities are indicative of higher nucleation rates and a high driving force.

  20. Using Pyroxene and Amphibole Compositions to Determine Protolith of Banded Quartz- Amphibole-Pyroxene Rocks on Akilia, Southwest Greenland: a Lithology Suitable for Hosting Earth's Oldest Life? (United States)

    Hage, M. M.; Usui, T.; Fedo, C. M.; Whitehouse, M. J.


    At ˜ 3.8 Ga in age, Earth's oldest known supracrustal rocks are exposed in SW Greenland and are comprised dominantly of mafic igneous rocks with less common sedimentary units, included banded iron formation (BIF). The great antiquity of the supracrustal rocks and repeated claims for a fossil record makes Greenland one of the prime astrobiological destinations on Earth, however, many primary characteristics of these rocks have been overprinted during multiple high-grade metamorphic events, which results in complex field relationships (e.g., Myers and Crowley, 2000; Whitehouse and Fedo, 2003). One example of this concerns an ˜ 5 m thick lithology dominated by bands of quartz, amphibole, pyroxene interpreted by some as BIF (Mojzsis et al., 1996; Nutman et al., 1997; Dauphas et al., 2004) on Akilia, SW Greenland. Correct identification of these rocks is of the utmost importance because they are reported to contain grains of apatite with 13C- depleted graphite inclusions that have been claimed as evidence for the oldest (> 3800 Mya) life on Earth (Mojzsis et al., 1996; Nutman et al., 1997; McKeegan et al., 2007). We analyzed mafic mineral compositions by electron microprobe from samples collected from a detailed measured section and from sample 92-197, the rock originally claimed to host Earth's oldest chemofossil. Ultramafic rocks from outside the quartz-amphibole-pyroxene (QAP) lithology are dominated by enstatite, anthophyllite, and hornblende and possess bulk trace-element signatures indicative of an igneous origin. Sample AK 38, a band of mixed pyroxene and amphibole that occurs within the QAP unit also has a bulk trace- element composition consistent with an ultramafic protolith, but contains Fe-rich clinopyroxene (Mg# = ˜ 50). AK 38 amphiboles are dominated by actinolite, although a few analyses of anthophyllite point towards an original Mg-rich protolith. Other QAP samples contain Fe-rich clino- and orthopyroxenes, actinolite and hornblende. Magnetite is

  1. 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.

  2. Amphibole incongruent melting under Lithospheric Mantle conditions in spinel peridotites from Balaton area, Hungary (United States)

    Ntaflos, Theodoros; Abart, Rainer; Bizimis, Michel


    Pliocene alkali basalts from the western Pannonian Basin carry mantle xenoliths comprising hydrous and anhydrous spinel peridotites. We studied coarse and fine grained fertile to depleted spinel lherzolites, spinel harzubrgites and dunites from Szentbékálla, Balaton, in detail, using XRF, EPMA and LA-ICP-MS and MC-ICP-MS techniques. Pliocene alkali basalts containing mantle xenoliths with three major types of textures are widespread in the studied area: fine-grained primary and secondary equigranular, coarse-grained protogranular and transitional between equigranular and protogranular textures. Melt pockets, are common in the studied xenoliths. The shape of several melt pockets resembles euhedral amphibole. Other samples have thin films of intergranular glass attributed to the host basalt infiltration. Calculations have shown that such xenoliths experienced an up to 2.4% host basalt infiltration. The bulk rock Al2O3 and CaO concentrations vary from 0.75 to 4.1 and from 0.9 to 3.6 wt% respectively, and represent residues after variable degrees of partial melting. Using bulk rock major element abundances, the estimated degree of partial melting ranges from 4 to 20%.. The Primitive Mantle normalized clinopyroxene trace element abundances reveal a complicated evolution of the Lithospheric mantle underneath Balaton, which range from partial melting to modal and cryptic metasomatism. Subduction-related melt/fluids and/or infiltration of percolating undersaturated melts could be account for the metasomatic processes. The radiogenic isotopes of Sr, Nd and Hf in clinopyroxene suggest that this metasomatism was a relatively recent event. Textural evidence suggests that the calcite filling up the vesicles in the melt pockets and in veinlets cross-cutting the constituent minerals is of epigenetic nature and not due to carbonatite metasomatism. Mass balance calculations have shown that the bulk composition of the melt pockets is identical to small amphibole relics found as

  3. The amphiboles of the REE-rich A-type peralkaline Strange Lake pluton - fingerprints of magma evolution (United States)

    Siegel, Karin; Williams-Jones, Anthony E.; van Hinsberg, Vincent J.


    Major and trace element compositions of amphibole in igneous environments commonly reflect evolving magma compositions. In this study, we use the amphibole-group minerals from the Strange Lake, REE-enriched peralkaline granitic pluton to gain insights into the evolution of the magma. This 1240 Ma old pluton consists of two main intrusive facies, an early hypersolvus granite, which occurs as separate northern and southern intrusions, and a more evolved transsolvus granite. In the hypersolvus granite the amphibole is a late interstitial phase, whereas in the transsolvus granite, it is present as phenocrysts. The amphibole compositions vary from calcic-sodic (ferro-ferri-katophorite) in the southern hypersolvus granite to sodic (arfvedsonite, ferro-ferri-leakeite) in the other, more evolved granitic units. High Na, Si, Li, and low Al and Ca concentrations in the amphibole phenocrysts of the transsolvus granite indicate formation from a more evolved magma compared to the hypersolvus granite, despite the fact that these crystals formed early. We interpret the increasing Fe3+/Fe2+ ratios in the amphibole of the hypersolvus granite to reflect crystal chemical effects (Na/Ca-ratio) and increasingly oxidizing conditions in the magma, whereas in the phenocrysts of the transsolvus granite, the increasing ratio was the product of increasing proportions of F- and OH- in the melt. The amphiboles of all the granite units have elevated Nb, Zr, Hf and REE concentrations compared to the bulk rock, suggesting that these elements are compatible in amphibole. By contrast the much lower Ti concentration was due to saturation of the magma in sodium-titanosilicates. The amphibole REE concentrations vary greatly among the granite units. Amphibole of the southern and northern hypersolvus granite contains 0.16 and 0.07 wt.% ∑ REE + Y, on average, respectively, and in the transsolvus granite, the average ∑ REE content is only 0.01 wt.%, despite the more evolved nature of its host

  4. Different slip systems controlling crystallographic preferred orientation and intracrystalline deformation of amphibole in mylonites from the Neyriz mantle diapir, Iran (United States)

    Elyaszadeh, Ramin; Prior, David J.; Sarkarinejad, Khalil; Mansouri, Hadiseh


    A deformed layered gabbro and a mylonitic gabbro sample from the marginal shear zone of the Neyriz mantle diapir in Iran were analyzed using electron backscatter diffraction (EBSD). Both samples have the common amphibole crystallographic preferred orientation (CPO) in which (100) lies perpendicular to foliation and parallel to lineation. Amphibole grains in the layered gabbro sample have little internal deformation, whereas in the mylonitic gabbro sample the amphibole grains are strongly distorted and contain low angle grain boundaries. There is a subtle change in CPO as a function of grain size in the mylonitic gabbro. Coarse grains (porphyroclasts) have a (100) CPO oriented with the main foliation reference frame whilst fine grains have a (100) CPO oriented with the C‧ shear bands. Detailed analysis of porphyroclast distortions and subgrain boundary trace analysis suggests that hard slip systems, most particularly (110) control intracrystalline deformation. Schmid factor analysis suggest that these slip systems are not involved in foliation formation but are linked kinematically to C‧ shear bands. It is unlikely that the slip systems that control intracrystalline deformation are important in CPO formation. We interpret that subgrain rotation recrystallization lead to grain size reduction and the elongate recrystallized grains were rotated towards the C‧ shear bands by grain boundary sliding. This rigid body rotation, possibly in combination with easy slip on (100) are considered the main cause of CPO formation. Amphibole zonation patterns in the layered gabbro sample suggest that oriented growth of amphibole may have contributed to CPO.

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

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


    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  to 3.1 to ). Time-averaged microlite nucleation rates also decrease with increasing experimental duration (from  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 together constitute 57–90

  6. 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

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

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    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.

  8. 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.

  9. Amphibole and felsic veins from the gabbroic oceanic core complex of Atlantis Bank (Southwest Indian Ridge, IODP Hole U1473A): when the fluids meets the melts (United States)

    Sanfilippo, A.; Tribuzio, R.; Antonicelli, M.; Zanetti, A.


    We present a petrological/geochemical investigation of brown amphibole and felsic veins drilled during IODP 360 expedition at Atlantis Bank, a gabbroic oceanic core complex from Southwest Indian Ridge. The main purpose of this study is to unravel the role of seawater and magmatic components in the origin of these veins. Brown amphibole veins were collected at 90-170 mbsf. These veins typically include minor modal amounts of plagioclase and are associated with alteration halos made up of brown amphibole and whitish milky plagioclase in host gabbros. Two sets of late magmatic felsic veins, which mostly consist of plagioclase and minor brown amphibole, were selected. Amphibole-plagioclase geothermometry (Holland and Blundy, 1994) documents that crystallization of brown amphibole and felsic veins occurred in the 850-700 °C interval. In the brown amphibole veins, amphibole and plagioclase have relatively low concentrations of incompatible trace elements and significant Cl (0.2-0.3 wt%). The development of these veins at near surface levels is therefore attributed to seawater-derived fluids migrating downward through cracks developing in the exhuming gabbro. To explain the high temperature estimates for the development of these shallow veins, however, the seawater-derived fluids must have interacted not only with the gabbros, but also with a high temperature magmatic component. This petrogenetic hypothesis is consistent with oxygen and hydrogen isotopic compositions of amphiboles from shallow veins in adjacent Hole 735B gabbros (Alt and Bach, 2006). Trace element compositions of amphibole and plagioclase from the felsic veins show formation by silicate melts rich in incompatible elements. In addition, Cl concentrations in amphibole from the felsic veins are low, thereby indicating that the melts feeding these veins had low or no seawater component. We cautiously propose that: (i) the felsic veins were generated by SiO2-rich melts residual after crystallization of Fe

  10. 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

  11. Elasticity of Pargasite Amphibole: A Hydrous Phase at Mid Lithospheric Discontinuity (United States)

    Peng, Y.; Mookherjee, M.


    Mid Lithospheric Discontinuity (MLD) is characterized by a low shear wave velocity ( 3 to 10 %). In cratons, the depth of MLD varies between 80 and 100 km. The reduction of the shear wave velocity at MLD is similar to what is observed in the lithosphere-asthenosphere boundary (LAB). Such low velocity at MLD could be caused by partial melting, temperature induced grain boundary sliding, changes in the elastic anisotropy, and/or metasomatism which may lead to the formation of hydrous phases including mica and amphibole. Thus, it is clear that in order to assess the role of metasomatism at MLD, we need better constraints on the elasticity of hydrous phases. However, such elasticity data are scarce. In this study, we explore elasticity of pargasite amphibole [NaCa2(Mg4Al)(Si6Al2)O22(OH)2] using density functional theory (DFT) with local density approximation (LDA) and generalized gradient approximation (GGA). We find that the pressure-volume results can be adequately described by a finite strain equation with the bulk modulus, K0 being 102 and 85 GPa for LDA and GGA respectively. We also determined the full elastic constant tensor (Cij) using the finite difference method. The bulk modulus, K0 determined from the full elastic constant tensor is 104 GPa for LDA and 87 GPa for GGA. The shear modulus, G0 determined from the full elastic constant tensor is 64 GPa for LDA and 58 GPa for GGA. The bulk and shear moduli predicted with LDA are 5 and 1 % stiffer than the recent results [1]. In contrast, the bulk and shear moduli predicted with GGA are 12 and 10 % softer compared to the recent results [1]. The full elastic constant tensor for pargasite shows significant anisotropy. For instance, LDA predicts compressional (AVP) and shear (AVS) wave anisotropy of 22 and 20 % respectively. At higher pressure, elastic moduli stiffen. However, temperature is likely to have an opposite effect on the elasticity and this remains largely unknown for pargasite. Compared to the major mantle

  12. 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.

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

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    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.

  14. Exposure to Sumas Mountain chrysotile induces similar gene expression changes as Libby Amphibole but has greater effect on long-term pathology and lung function (United States)

    This study was designed to provide understanding of the toxicity of naturally occurring asbestos (NOA) including Libby amphibole (LA), Sumas Mountain chrysotile (SM), El Dorado Hills tremolite (ED) and Ontario ferroactinolite cleavage fragments (ON). Rat-respirable fractions (aer...

  15. 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...

  16. Direct observation of reactant-product interfaces formed in natural weathering of exsolved, defective amphibole to smectite: Evidence for episodic, isovolumetric reactions involving structural inheritance (United States)

    Banfield, Jillian F.; Barker, William W.


    High-resolution transmission electron microscopy (HRTEM) and energy-dispersive X-ray microanalysis (EDS) were employed to characterize grain boundary structures in naturally weathered amphibole. Our observations provide insights into the submicroscopic mineralogic controls on transport of solutions to and from reaction sites. Finely exsolved amphibole (anthophyllite/gedrite) in outcropping, slightly weathered gedrite gneiss transforms isovolumetrically to smectite. Stacking faults and exsolution lamellar boundaries focus weathering reactions, whereas chain width defects decrease the susceptibility of the surrounding amphibole to alteration. Relatively Al-poor anthophyllite lamellae alter slightly more readily than those of Al-rich gedrite. Large quantites of Mg, Fe, Si, and Al are removed from reaction sites. However, smectite compositions directly reflect limited redistribution of elements incorporated into clay products. Topotactic relationships between products and reactants and interface structures suggest that smectite formation requires only partial depolymerization of amphibole structural units. Up to one-third of the amphibole I-beams may be directly inherited by smectite. Grain boundary structures within smectite mimic current amphibole-smectite interfaces and may represent previous reaction fronts. Such interfaces may be the result of episodic reaction, possibly attributable to the balance between rates of consumption of water by reactions and resupply by dewatering of larger fractures (which are themselves episodically supplied by rainfall). In this coherent, slightly weathered rock, transport of solution to and from reaction sites is restricted to diffusion along semi-coherent, subnanometer-wide grain boundaries and smectite interlayers. This contrasts with weathering grains within a soil, more deeply weathered rock, or laboratory mineral dissolution experiments, where a much larger volume of solution is in contact with weathering surfaces. We suggest

  17. Magmatic-hydrothermal fluid evolution of the Dalli porphyry Cu-Au deposit; using Amphibole and Plagioclas mineral chemistry

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    Houshang Pourkaseb


    Full Text Available Introduction The formation of porphyry copper deposits is attributed to the shallow emplacement, and subsequent cooling of the hydrothermal system of porphyritic intrusive rocks (Titley and Bean, 1981. These deposits have usually been developed along the chain of subduction-related volcanic and calc-alkalin batholiths (Sillitoe, 2010. Nevertheless, it is now confirmed that porphyry copper systems can also form in collisional and post collisional settings (Zarasvandi et al., 2015b. Detailed studies on the geochemical features of ore-hosting porphyry Cu-Mo-Au intrusions indicate that they are generally adakitic, water and sulfur- riched, and oxidized (Wang et al., 2014. For example, high oxygen fugacity of magma has decisive role in transmission of copper and gold to the porphyry systems as revealed in (Wang et al., 2014. In this regard, the present work deals with the mineral chemistry of amphibole and plagioclase in the Dalli porphyry Cu-Au deposit. The data is used to achieve the physical and chemical conditions of magma and its impact on mineralization. Moreover, the results of previous studies on the hydrothermal system of the Dalli deposit such as Raman laser spectroscopy and fluid inclusion studies are included for determination of the evolution from magmatic to hydrothermal conditions. Materials and methods In order to correctly characterize the physical and chemical conditions affecting the trend of mineralization, 20 least altered and fractured samples of diorite and quartz-diorite intrusions were chosen from boreholes. Subsequently, 20 thin-polished sections were prepared in the Shahid Chamran University of Ahvaz. Finally, mineral chemistry of amphibole and plagioclase were determined using electron micro probe analyses (EMPA in the central lab of the Leoben University. Results Amphibole that is one of the the main rock-forming minerals can form in a wide variety of igneous and metamorphic rocks. Accordingly, amphibole chemistry can be

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

    International Nuclear Information System (INIS)

    Ota, Kouhei; Mikouchi, Takashi; Sugiyama, Kazumasa


    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 (Fa 37 ), orthopyroxene (En 70 Wo 1 ), and plagioclase (An 8 Or 2 ). Hornblende is also nearly homogeneous, but the total sum by electron microprobe analysis is 96-98 wt%, suggesting the presence of Fe 3+ and a hydroxyl group. Synchrotron Fe-XANES analysis gives a Fe 3+ /ΣFe ratio of ∼0.6 and micro-FT-IR analysis confirms the presence of a hydroxyl group. Thus, the structural formula is (Na 0.40 K 0 . 04 ) (Ca 1.46 Mn 0.02 Fe 0.06 2+ Na 0.46 ) (Al 0.08 Fe 0.43 2+ Fe 0.75 3+ Cr 0.08 Mg 3.60 ) (Si 7.02 Al 0.98 )O 22 (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 Fe 3+ 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)

  19. 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

  20. 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.

  1. In situ major and trace element analysis of amphiboles in quartz monzodiorite porphyry from the Tonglvshan Cu-Fe (Au) deposit, Hubei Province, China: insights into magma evolution and related mineralization (United States)

    Duan, Deng-Fei; Jiang, Shao-Yong


    The Tonglvshan deposit is the largest Cu-Fe (Au) skarn deposit in the Edong district, which is located in the westernmost part of the Middle and Lower Yangtze River metallogenic belt, China. In this study, we performed a detailed in situ analysis of major and trace elements in amphiboles from the ore-related Tonglvshan quartz monzodiorite porphyry using electron microprobe (EMPA) analysis and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Two distinct populations of amphiboles, which can be distinguished by their aluminum content, are found in the quartz monzodiorite porphyry. The low-aluminum (Low-Al) amphiboles are subhedral or anhedral and formed at 46.3-73.5 MPa and 713-763 °C. In contrast, the high-aluminum (High-Al) amphiboles are euhedral and formed at 88-165 MPa and 778-854 °C. Some euhedral amphiboles are partially or completely replaced by Low-Al amphibole. The compositions of parental melts in equilibrium with the High-Al amphibole ( Melt 1) and Low-Al amphibole ( Melt 2) were computed by applying solid/liquid partition coefficients. This modeling shows that magma in equilibrium with High-Al amphibole ( Melt 1) underwent 40% fractional crystallization of amphibole, plagioclase and apatite at a depth of 5 km to evolve to magma in equilibrium with Low-Al amphibole ( Melt 2). Copper enrichment occurred in the magma after undergoing fractional crystallization. The magma had a high oxygen fugacity, increasing from NNO + 1 ( Melt 1) through NNO + 2 to HM ( Melt 2), which could have prevented the loss of Cu (and possibly Au) to sulfide minerals during crystallization. Finally, the evolved magma intruded to shallower depths, where it presumably exsolved aqueous ore-forming fluids. Therefore, the large Cu-Fe-Au reserves of the Tonglvshan deposit can likely be attributed to a combination of controlling factors, including high oxygen fugacity, fractional crystallization, fluid exsolution, and a shallow emplacement depth.

  2. Amphibole stability using new thermobarometric formulations on calc-alkaline magmas of Volcán Doña Inés, Chile (United States)

    Hines, R. A.; Walker, J. A.


    Location and delineation of subvolcanic magma chambers have heavily relied on geophysical, particularly seismic, data. However, new and improved thermobarometric formulations can yield equally important constraints on the depths and conditions of magmatic storage and movement. The objective of this study was to utilize the single phase thermobarometric algorithms of Ridolfi et al. (2010) to determine the conditions of amphibole stability in the volcanic system beneath Volcán Doña Inés, a large stratovolcano from the Mid-Late Miocene magmatic arc in the Central Volcanic Zone of the Andes, Chile. According to Moulds (1989), Doña Inés had three main eruptive vents: the main central vent; a second vent low on its flanks, called Loma Doña Inés; and a sister cone, called Gemelas. The barometric, thermometric, hygrometric, and oxygen fugacity formulations of Ridolfi et al. (2010) are based on the total aluminum (AlT) content, the silicon index (Si*), the octahedral aluminum index ([6]Al*), and the magnesium index (Mg*) of the amphibole grains, respectively. For this study, 120 amphiboles from 20 andesite-dacite samples from Doña Inés were analyzed approximately 30 times per grain with an electron microprobe. Amphibole compositions range from tschermakitic pargasite, to magnesiohornblende, to magnesiohastingsite, with the central vent crystals exhibiting the widest variability. Preliminary results from the thermobarometer indicate that amphibole crystallization beneath the central vent occurred between 213-928 ± 102 MPa and 872-1016 ± 22 *C, with magmatic water contents of approximately 5.2-9.9 ± 1.5 wt%. Conditions of formation of amphibole at Loma Doña Inés were between 230-405 ± 37 MPa and 901-980 ± 22 *C, with approximately 5.4-6.2 ± 0.9 wt% magmatic H2O and were similar at the sister cone Gemelas: 259-309 ± 34 MPa, 902-952 ± 22 *C, and 5.1-6.2 ± 0.9 wt% magmatic H2O. Temperatures obtained from amphibole stability agree well with the previous from

  3. 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

  4. 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.

  5. Characterization of Libby, MT amphibole (LA) elongated particles for toxicology studies: Field Collection, sample preparation, dose characterization, and particle counting methods using SEM/EDS (United States)

    Since 1999, the US EPA and USGS have been studying the chemistry, mineralogy, and morphology of the amphiboles from the Rainy Creek Complex of Libby, MT (LA), following an increased incidence of lung and pleural diseases. LA material collected in 2000 (LA2000) was described in M...

  6. New Insights into Trace Element Partitioning in Amphibole from Multiple Regression Analysis, with Application to the Magma Plumbing System of Mt. Lamington (Papua New Guinea) (United States)

    Zhang, J.; Humphreys, M.; Cooper, G.; Davidson, J.; Macpherson, C.


    We present a new multiple regression (MR) analysis of published amphibole-melt trace element partitioning data, with the aim of retrieving robust relationships between amphibole crystal-chemical compositions and trace element partition coefficients (D). We examined experimental data for calcic amphiboles of kaersutite, pargasite, tschermakite (Tsch), magnesiohornblende (MgHbl) and magnesiohastingsite (MgHst) compositions crystallized from basanitic-rhyolitic melts (n = 150). The MR analysis demonstrates the varying significance of amphibole major element components assigned to different crystallographic sites (T, M1-3, M4, A) as independent variables in controlling D, and it allows us to retrieve statistically significant relationships for REE, Y, Rb, Sr, Pb, Ti, Zr, Nb (n > 25, R2 > 0.6, p-value Ridolfi & Renzulli 2012) with lower Rb and Sr and higher Pb, relative to a hot, andesitic-dacitic melt (950-1,000±50 ºC; 60-70±5 wt % SiO2) where MgHst are crystallized. REE and Nb contents are similar in both types of melts despite higher REE and Nb in MgHbl-Tsch. Therefore, the REE compositional disparity between MgHst and MgHbl-Tsch is driven by the difference in the DREE, rather than the melt REE concentrations.

  7. Amphibole as an archivist of magmatic crystallization conditions: problems, potential, and implications for inferring magma storage prior to the paroxysmal 2010 eruption of Mount Merapi, Indonesia (United States)

    Erdmann, Saskia; Martel, Caroline; Pichavant, Michel; Kushnir, Alexandra


    Amphibole is widely employed to calculate crystallization temperature and pressure, although its potential as a geobarometer has always been debated. Recently, Ridolfi et al. (Contrib Mineral Petrol 160:45-66, 2010) and Ridolfi and Renzulli (Contrib Mineral Petrol 163:877-895, 2012) have presented calibrations for calculating temperature, pressure, fO2, melt H2O, and melt major and minor oxide composition from amphibole with a large compositional range. Using their calibrations, we have (i) calculated crystallization conditions for amphibole from eleven published experimental studies to examine the problems and the potential of the new calibrations; and (ii) calculated crystallization conditions for amphibole from basaltic-andesitic pyroclasts erupted during the paroxysmal 2010 eruption of Mount Merapi in Java, Indonesia, to infer pre-eruptive conditions. Our comparison of experimental and calculated values shows that calculated crystallization temperatures are reasonable estimates. Calculated fO2 and melt SiO2 content yields potentially useful estimates at moderately reduced to moderately oxidized conditions and intermediate to felsic melt compositions. However, calculated crystallization pressure and melt H2O content are untenable estimates that largely reflect compositional variation in the crystallizing magmas and crystallization temperature and not the calculated parameters. Amphibole from Merapi's pyroclasts yields calculated conditions of ~200-800 MPa, ~900-1,050 °C, ~NNO + 0.3-NNO + 1.1, ~3.7-7.2 wt% melt H2O, and ~58-71 wt% melt SiO2. We interpret the variations in calculated temperature, fO2, and melt SiO2 content as reasonable estimates, but conclude that the large calculated pressure variation for amphibole from Merapi and many other arc volcanoes is evidence for thorough mixing of mafic to felsic magmas and not necessarily evidence for crystallization over a large depth range. In contrast, bimodal pressure estimates obtained for other arc magmas

  8. Petrological constraints on the high-Mg basalts from Capo Marargiu (Sardinia, Italy): Evidence of cryptic amphibole fractionation in polybaric environments (United States)

    Tecchiato, Vanni; Gaeta, Mario; Mollo, Silvio; Scarlato, Piergiorgio; Bachmann, Olivier; Perinelli, Cristina


    This study deals with the textural and compositional characteristics of the calc-alkaline stratigraphic sequence from Capo Marargiu Volcanic District (CMVD; Sardinia island, Italy). The area is dominated by basaltic to intermediate hypabyssal (dikes and sills) and volcanic rocks (lava flows and pyroclastic deposits) emplaced during the Oligo-Miocene orogenic magmatism of Sardinia. Interestingly, a basaltic andesitic dome hosts dark-grey, crystal-rich enclaves containing up 50% of millimetre- to centimetre-sized clinopyroxene and amphibole crystals. This mineral assemblage is in equilibrium with a high-Mg basalt recognised as the parental magma of the entire stratigraphic succession at CMVD. Analogously, centimetre-sized clots of medium- and coarse-grained amphibole + plagioclase crystals are entrapped in andesitic dikes that ultimately intrude the stratigraphic sequence. Amphibole-plagioclase cosaturation occurs at equilibrium with a differentiated basaltic andesite. Major and trace element modelling indicates that the evolutionary path of magma is controlled by a two-step process driven by early olivine + clinopyroxene and late amphibole + plagioclase fractionation. In this context, enclaves represent parts of a cumulate horizon segregated at the early stage of differentiation of the precursory high-Mg basalt. This is denoted by i) resorption effects and sharp transitions between Mg-rich and Mg-poor clinopyroxenes, indicative of pervasive dissolution phenomena followed by crystal re-equilibration and overgrowth, and ii) reaction minerals found in amphibole coronas formed at the interface with more differentiated melts infiltrating within the cumulate horizon, and carrying the crystal-rich material with them upon eruption. Coherently, the mineral chemistry and phase relations of enclaves indicate crystallisation in a high-temperature, high-pressure environment under water-rich conditions. On the other hand, the upward migration and subsequent fractionation of the

  9. Amphibole genesis in Harrow Peaks mantle xenoliths and its role in the petrological evolution of Northern Victoria Land subcontinental lithospheric mantle (United States)

    Pelorosso, Beatrice; Bonadiman, Costanza; Coltorti, Massimo; Gentili, Silvia


    A petrological study of hydrous and anhydrous mantle xenoliths from Harrow Peaks, Northern Victoria Land (Antarctica) has been carried out, aiming at mapping the evolution of this lithospheric mantle domain and to better constrain the formation of the hydrous phases, in particular amphibole. Samples vary in composition from lherzolite to harzburgite with textural evidences of matrix/melt interaction (secondary minerals and spongy textures). Olivine and orthopyroxene are mainly present as large primary grains, whereas clinopyroxene can also occur as resorbed grains or newly formed small crystals, often associated to glassy patches. Spinel is present as small anhedral crystals or larger dendritic grains. Amphiboles occur both as disseminated and in veins; the latter frequently associated with secondary clinopyroxenes and spinels. Considering fusible element content in orthopyroxene (i.e. Al2O3 2.50 wt.%), Harrow Peaks lithosphere domain reflects a relatively residual character. On the other hand, the presence of "convex upward" clinopyroxene -REE pattern, as already observed in clinopyroxene from mantle xenoliths of the nearby Greene Point (Pelorosso et al., 2016), together with their LREE enriched content (LaN from 9 to 30), suggest that Harrow Peaks lithospheric mantle was variably affected by enrichment processes, i.e. refertilisation and metasomatism. Amphiboles from Harrow Peaks can be classified as kaersutite, magnesio-hastingsite, and ferri-kaersutite with pretty high TiO2 contents (2.74 wt% 5.30 wt%, Gentili et al., 2015); they present variably enriched trace element patterns (LaN from 12 to 56, LaN/YbN from 1 to 5). Compared with the nearby amphibole-bearing xenolith area of Baker Rocks (Coltorti et al., 2004; Bonadiman et al., 2014), Harrow Peaks amphiboles, present a lower enrichment in TiO2 and LREE that may be related to an incipient stage of peridotite/melt interaction. This fact may also justify the different geochemical features of amphiboles, that in

  10. 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.

  11. Experimental and natural partitioning behaviour of trace-elements between hydrous evolved melts, amphibole, plagioclase, and clinopyroxene at shallow crustal conditions (United States)

    Iveson, A. A.; Webster, J. D.; Rowe, M. C.; Neill, O. K.


    New experimental data for crystal-melt partitioning behaviour of a suite of trace-elements are presented. Hydrous rhyo-dacitic starting glasses from Mt. Usu, Japan, were doped with Li, Sc, Cr, Mn, Ni, Cu, Zn, Ga, Rb, Sr, Y, Nb, Mo, Ba, W, and Pb. Aqueous solutions were added such that the volatile phase(s) coexisting with amphibole, plagioclase, and clinopyroxene at run conditions buffered the S, F, and Cl contents of the melts. Internally-heated pressure vessel experiments were conducted at 750-850 °C, 1.0-4.0 Kbar, and ƒO2 ≈ NNO-NNO+2 log units. Major- and minor-element concentrations in the phenocrysts and glasses were analysed by EPMA, and trace-element contents by SIMS and/or LA-ICP-MS. The long run durations, homogeneous glasses, and minimal compositional zonation of crystals suggest that near-equilibrium conditions were achieved. Results of multiple phenocryst and glass analyses show that Nernst-type crystal-melt partition coefficients for these elements range from strongly incompatible e.g. Dmineral/melt ≈ 0 for Nb into plagioclase, to moderately incompatible e.g. Dmineral/melt ≈ 0.75 for Ga into amphibole, to strongly compatible e.g. Dmineral/melt > 50 for Ni into amphibole and clinopyroxene. Furthermore, unlike other elements investigated, partitioning of Li between phenocrysts and melt is similar for all three phases, with average DLicpx/melt ≈ 0.26 > DLiplag/melt ≈ 0.24 > DLiamph/melt ≈ 0.19. Relative to major-element composition of crystalline phases, the temperature, pressure, and ƒO2 conditions do not appear to strongly affect this behaviour. The incorporation of F and Cl into amphiboles is also consistent with the Fe-F and Mg-Cl crystallographic avoidance principles. Importantly, across two orders of magnitude in concentration, partitioning behaviours of all analysed trace-elements appear to obey Henry's Law. The experimental data are integrated with new amphibole, plagioclase, and pyroxene analyses from eruptive products of Augustine

  12. Mafic microgranular enclaves (MMEs) in amphibole-bearing granites of the Bintang batholith, Main Range granite province: Evidence for a meta-igneous basement in Western Peninsular Malaysia (United States)

    Quek, Long Xiang; Ghani, Azman A.; Chung, Sun-Lin; Li, Shan; Lai, Yu-Ming; Saidin, Mokhtar; Amir Hassan, Meor H.; Muhammad Ali, Muhammad Afiq; Badruldin, Muhammad Hafifi; Abu Bakar, Ahmad Farid


    Mafic microgranular enclaves (MMEs) with varying sizes are a common occurrence in porphyritic amphibole-bearing granite of the Bintang batholith, which is part of the Main Range granite province. The MMEs of the amphibole-bearing granite are significant as they are related to the I-type granitoids within the Main Range granite province. Petrographic observations indicate the MMEs are mantled with coarse mafic crystals on the rim and contain similar minerals to the host (biotite + plagioclase + K-feldspar + pyroxene + amphibole), but in different proportions. Geochemical analyses indicate the MMEs are shoshonitic with mg# comparable to the granite host. Substantial similarities exist between the MMEs and granite with regards to the normalized rare earth element patterns and trace elements variation diagrams. The MMEs and granite are not completely coeval as the MME zircon U-Pb age (224.3 ± 1.2 Ma) is slightly older than its granite host zircon U-Pb age (216.2 ± 1.0 Ma). The age difference is also observed from the unusual 500 m-long Tiak MME and another amphibole-bearing granite sample from the south of the pluton, which yield 221.8 ± 1.1 Ma and 217.4 ± 1.0 Ma respectively. The oldest inherited zircons found in the MME and granite are 2.0 Ga and 1.3 Ga respectively, while the oldest xenocrystic zircons found in the MME and granite are 2.5 Ga and 1.5 Ga respectively. Identical negative εHf(t) values from zircon U-Pb and Lu-Hf analysis for a MME-granite pair indicates the rocks were generated from a similar, ancient source in the basement. Combining the results, we suggest that incongruent melting of an ancient protolith played an important part in the evolution of the MMEs and granite and the MMEs characteristics are best explained as restite. The zircon Hf model age (two-stage) and the I-type peritectic and restitic mineral assemblages in the MMEs further describe the protolith as Early Proterozoic-Late Archean (≈2.5 Ga) meta-igneous rock. This shows the

  13. 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

  14. Persistence of fertile and hydrous lithospheric mantle beneath the northwestern Ethiopian plateau: Evidence from modal, trace element and Sr-Nd-Hf isotopic compositions of amphibole-bearing mantle xenoliths (United States)

    Alemayehu, Melesse; Zhang, Hong-Fu; Aulbach, Sonja


    We present new trace element compositions of amphiboles, Sr-Nd-Hf isotope compositions of clinopyroxenes and mineral modes for spinel peridotite xenoliths that were entrained in a Miocene alkali basalt (Gundeweyn, northwestern Ethiopian plateau), in order to understand the geochemical evolution and variation occurring within the continental lithospheric mantle (CLM) in close proximity to the East African Rift system, and its dynamic implications. With the exception of a single amphibole-bearing sample that is depleted in LREE (La/YbN = 0.45 × Cl), amphiboles in lherzolites and in one harzburgite show variable degrees of LREE enrichment (La/YbN = 2.5-12.1 × Cl) with flat HREE (Dy/YbN = 1.5-2.1 × Cl). Lherzolitic clinoyroxenes have 87Sr/86Sr (0.70227 to 0.70357), 143Nd/144Nd (0.51285 to 0.51346), and 176Hf/177Hf (0.28297 to 0.28360) ranging between depleted lithosphere and enriched mantle. LREE-enriched clinopyroxenes generally have more enriched isotope compositions than depleted ones. While lherzolites with isotope compositions similar to those of the Afar plume result from the most recent metasomatic overprint, isotope compositions more depleted than present-day MORB can be explained by an older melt extraction and/or isotopic rehomogenisation event, possibly related to the Pan-African orogeny. Several generations of amphibole are recognized in accord with this multi-stage evolution. Texturally unequilibrated amphibole occurring within the peridotite matrix and in melt pockets attest to continued hydration and refertilization of the lithospheric mantle subsequent to Oligocene flood basalt magmatism, during which an earlier-emplaced inventory of amphibole was likely largely consumed. However, a single harzburgite contains amphibole with the highest Mg# and lowest TiO2 content, which is interpreted as sampling a volumetrically subordinate mantle region beneath the Ethiopian plateau that was not tapped during flood basalt magmatism. Strikingly, both trace

  15. Fabric and elastic properties of antigorite, mica and amphibole-rich rocks and implications for the tectonic interpretation of seismic anisotropy (United States)

    Shao, Tongbin

    C. Comparisons of laboratory velocities measured at high pressure with CPO data measured using EBSD techniques demonstrate that seismic anisotropy in high temperature serpentinites, which is essentially controlled by the antigorite c-axis fabric, is independent on the operating slip system but strongly dependent on the regime and magnitude of finite strain experienced by the rock. Extrapolation of experimental data with both pressure and temperature suggests that Vp anisotropy decreases but shear-wave splitting (DeltaVs) and V p/Vs increase with increasing pressure in either cold or hot subduction zones. For a cold, steeply subducting slab, antigorite is most likely deformed by nearly coaxial flattening or trench-parallel movement, forming trench-parallel seismic anisotropy. For a hot, shallowly subducting slab, however, antigorite is most likely deformed by simple shear or transpression. Trench-normal seismic anisotropy can be observed when the subducting dip angle is smaller than 30°. The geophysical characteristics of the Tibetan Plateau, such as strong heterogeneity in V p, Vs and attenuation, shear-wave splitting and electric conductivity, may be explained by the presence of strongly deformed serpentinites in lithospheric shear zones reactivated along former suture zones between amalgamated blocks, hydrated zones of subducting lithospheric mantle, and the crust-mantle boundary if the temperature is below 700 °C in the region of interest. Chapter 3 provides a detailed calibration on the magnitude and symmetry of seismic anisotropy for 132 schists to constrain their departures from transverse isotropy (TI) that is usually assumed in the interpretation of seismic data. The average bulk Vp anisotropy at 600 MPa for 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

  16. Fluor-ferro-leakeite, NaNa2(FC2+2Fe3+2Li)Si8O22F2, a new alkali amphibole from the Canada Pinabete pluton, Questa, New Mexico, U.S.A. (United States)

    Hawthorne, F.C.; Oberti, R.; Ungaretti, L.; Ottolini, L.; Grice, Joel D.; Czamanske, G.K.


    Fluor-ferro-leakeite is a new amphibole species from the Canada Pinabete pluton, Questa, New Mexico, U.S.A.; it occurs in association with quartz, alkali feldspar, acmite, ilmenite, and zircon. It forms as anhedral bluish black crystals elongated along c and up to 1 mm long. It is brittle, H = 6, Dmeas = 3.37 g/cm3, Dcalc = 3.34 g/cm3. In plane-polarized light, it is strongly pleochroic, X = very dark indigo blue, Y = gray blue, Z = yellow green; X ??? c = 10?? (in ??obtuse), Y = b, Z ??? a = 4?? (in ?? obtuse), with absorption X > Y > Z. Fluor-ferro-leakeite is biaxial positive, ?? = 1.675(2), ??= 1.683(2), ?? = 1.694(1); 2V = 87(2)??; dispersion is not visible because of the strong absorption. Fluor-ferro-leakeite is monoclinic, space group C2/m, a = 9.792(1), b = 17.938(1), c = 5.3133(4) A??, ??= 103.87(7)??, V = 906.0(1) A??3, Z = 2. The ten strongest X-ray diffraction lines in the powder pattern are [d(I,hkl)]: 2.710(100,151), 2.536(92,202), 3.404(57,131), 4.481(54,040), 8.426(45,110), 2.985(38,241), 2.585(38,061), 3.122(29,310), 2.165(26,261), and 1.586(25,403). Analysis by a combination of electron microprobe, ion microprobe, and crystal-structure refinement (Hawthorne et al. 1993) gives SiO2 51.12, Al2O3 1.13, TiO2 0.68, Fe2O3 16.73, FeO 8.87, MgO 2.02, MnO 4.51, ZnO 0.57, CaO 0.15, Na2O 9.22, K2O 1.19, Li2O 0.99, F 2.87, H2Ocalc 0.60, sum 99.44 wt%. The formula unit, calculated on the basis of 23 O atoms, is (K0.23Na0.76)(Na1.97Ca0.03)(Mg 0.46Fe2+1.4Mn2+0.59Zn0.07Fe3+1.93-Ti 0.08Al0.02Li0.61])(Si7.81Al 0.19)O22(F1.39OH0.61). A previous crystal-structure refinement (Hawthorne et al. 1993) shows Li to be completely ordered at the M3 site. Fluor-ferro-leakeite, ideally NaNa2(Fe2+2Fe3+2Li)Si8O22F2, is related to leakeite, NaNa2(Mg2Fe3+3Li)Si 8O22(OH)2, by the substitutions Fe2+ ??? Mg and F ??? OH.

  17. Amphibolic role of the Krebs cycle in the insulin-stimulated protein synthesis

    International Nuclear Information System (INIS)

    Mohan, C.; Memon, R.A.; Bessman, S.P.


    It has been a generally held view that insulin does not significantly affect the incorporation of amino acids into liver protein. This interpretation was based on data obtained from studies using the branched chain amino acids, which are poorly metabolized by the hepatic tissue. The effect of insulin on 14CO2 formation and protein incorporation of several 1-14C-labeled or U-14C-labeled amino acids was studied in isolated rat hepatocytes and diaphragm pieces. It was shown that insulin enhanced 14CO2 formation and protein incorporation primarily of those carbons of amino acids which are metabolized through the mitochondrial Krebs cycle. Using aminooxyacetic acid (0.5 mM), a potent inhibitor of the transamination reaction, it was shown that there exists an insulin-sensitive pool of glutamate which is preferentially utilized for protein synthesis in the presence of insulin. The insulin effect on protein incorporation of 14C-labeled glutamate generated in the Krebs cycle was abolished in the presence of aminooxyacetic acid. The authors interpret these results to signify that mitochondrial transamination of alpha-ketoglutarate to glutamate is essential for insulin stimulation of 14C incorporation into hepatocyte protein


    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...

  19. 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..., beginning at 1 p.m. and ending at 5 p.m., Eastern Daylight Time, or when the last presentation has been completed. If you would like to make a presentation at the listening session, you should register by...

  20. 76 FR 30939 - Science Advisory Board Staff Office; Request for Nominations of Experts for SAB Libby Amphibole... (United States)


    ... (DFO), SAB Staff Office, by telephone/voice mail at (202) 564-2049, or via e-mail at [email protected], air sampling and detection methods, exposure assessment, occupational medicine, pulmonary medicine... biographical sketch of the nominee indicating current position, educational background, research activities...

  1. Stable isotopes and amphibole chemistry on hydrothermally altered granitoids in the North Chilean Precordillera: a limited role for meteoric water?

    NARCIS (Netherlands)

    Agemar, T.; Wörner, G.; Heumann, A.


    Whole rock and mineral stable isotope and microprobe analyses are presented from granitoids of the North Chilean Precordillera. The Cretaceous to Tertiary plutonic rocks contain important ore deposits and frequently display compositional and textural evidence of hydrothermal alteration even in

  2. Measurement of Libby Amphibole (LA) Elongated Particle Dissolution Rates and Alteration of Size/Shape Distributions in Support of Human Dosimetry Model Development and Relative Potency Determinations (United States)

    To maximize the value of toxicological data in development of human health risk assessment models of inhaled elongated mineral particles, improvements in human dosimetry modeling are needed. In order to extend the dosimetry model of deposited fibers (Asgharian et aI., Johnson 201...

  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)

    Winters, Ch.A.; Kuntz, S.W.; Hill, W.; Weinert, C.; Rowse, K.


    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. 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...

  5. 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:

  6. Probing crustal thickness evolution and geodynamic processes in the past from magma records : An integrated approach

    NARCIS (Netherlands)

    Ganne, J.; Schellart, W. P.; Rosenbaum, G.; Feng, X.; De Andrade, V.


    A new and simple integrated approach is proposed for qualitatively unravelling the crustal thickness of fossil magmatic systems based on the chemical and thermal records in amphibole-bearing magmatic rocks. Statistical analyses applied to a large multidimensional amphibole database show that Ti-rich

  7. Petrology, geochemistry of hornblende gabbro and associated ...

    Indian Academy of Sciences (India)

    Representative amphibole composition of intrusives of Paharpur. Black-filled squares represent the amphibole compositions. as secondary grains as evident from their irregu- lar, rim-like occurrences and large; anhedral char- acter. Secondary hornblendes are thought to have formed due to alteration of pyroxenes and pla-.

  8. Petrological and geochemical characteristics of Paleoproterozoic ...

    Indian Academy of Sciences (India)

    grained carbonatites show hypidiomorphic texture and mostly composed of calcite with appreciable amount of silicate miner- als like clinopyroxene, phlogopite and olivine (often pseudomorphed by calcite, amphibole and chlorite). It is difficult ...

  9. 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,


    African Journals Online (AJOL)

    Si, and Ti/AL implied high pressure/temperature crystallization conditions under bimodal or tholeiitic-alkaline transition magmatism in an island arc environment. Key words: Pyroxenite Ultramafic amphibole Island arcs. [Global Jnl Geol. Sci.

  11. 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

  12. 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

  13. 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.

  14. Crystal fractionation processes at Baru volcano from the deep to shallow crust (United States)

    Hidalgo, Paulo J.; Rooney, Tyrone O.


    Linking shallow and deep crustal processes at volcanic arcs is an important component in evaluating the growth and evolution of the continental crust. Commonly, deep crustal processes and the nature of subarc lithosphere are studied long after the volcanism has ceased in obducted arc terranes. In active arcs, studies of deep crustal processes focus on cumulates derived from middle-lower crustal levels. Although uncommon in the erupted magmas, these cumulates are required by crustal differentiation models of arc magmatism. Quaternary magmas at Baru volcano in Panama contain ubiquitous amphibole-bearing cumulates that provide an opportunity to probe the magma plumbing system of an active arc volcano. We have determined that these cumulates are related to their host magmas by crystal fractionation processes. Pressure and temperature estimates for amphiboles within these cumulates and the host rock are consistent with sampling of mush/magma zones from throughout the arc crust. These mush zones would be localized in deep hot crustal zones where magmatic differentiation of water-saturated arc magmas takes place by crystallization of amphibole-rich cumulates. The identification of middle-lower crustal cumulates is not exclusive to Baru volcano; similar cumulates are common throughout the Panamanian arc and are consistent with a widespread amphibole-rich layer present within the arc crust of Panama. Our results highlight the importance of amphibole fractionation in the differentiation sequence of island arcs effectively driving the residual magma to the average andesitic composition of the continental crust.


    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


    Directory of Open Access Journals (Sweden)

    Vesnica Garašić


    Full Text Available Mineral relationships and their chemistry were studied in some basic magmatic rocks of Banija ophiolite complex. On the basis of mineral and structural characteristics three kind of rocks are distinguished: metadiabase I (being characterized by secondary amphibole, metadiabase II (being characterized by secondary albite and spilite. Detailed chemistry of all mineral phases, specially of zoned clinopyroxenes and zoned amphiboles is given. The black opaque phases consist of different Fe-Ti-Mn oxides (ilmenite, Mn-ilmenite, magnetite, Ti-magnetite, ferropseudobrookite being often at the rims replaced by Al- and Fe-rich titanite. All rocks are hydrothermally metamorphosed whereby amphibole replaced partly or completely clinopyroxene and plagioclase was altered in albite, prehnite, pumpellyite and/or sericite. Secondary chlorite occurs too. The whole rock chemistry of each studied rock corresponds to tholeiitic basalts.

  17. Petrology of blueschist facies metamorphic rocks of the Meliata Unit

    Directory of Open Access Journals (Sweden)

    Faryad Shah Wali


    Full Text Available Meliata blueschists originated from basalts, limestones, pelites, psammitic and amphibolite facies basement rocks. Compositionally, the metabasalts have a geochemical signature mostly indicative of a transitional arc-MORB origin, but some mafic rocks having affinity with within plate basalts also present. The mafic blueschists consist of blue amphibole, epidote and albite, rarely also garnet, Na-pyroxene and chloritoid. Apart from phengite and quartz the metapelites and metapsammites contain one or more of the minerals: chloritoid, paragonite, glaucophane, albite, chlorite, occasionally also Na-pyroxene and garnet. Amphibolite facies rocks contain relic garnet, plagioclase and hornblende, the latter two replaced by albite and blue amphibole, respectively. The zoning patterns of blue amphibole, garnet and chloritoid suggest their formation during prograde stage of metamorphism. P-T conditions of meta-morphism are estimated to be about 350-460 oC and 10-12 kbar.

  18. Geochemistry and tectonic setting of the Golabad granitoid complex (SW Nain, Iran) (United States)

    Mansouri Esfahani, Mahin; Khalili, Mahmoud; Alaminia, Zahra


    The Oligo-Miocene Golabad granitoid complex intrusive into the Eocene volcanic rocks occurs in the Urumieh-Dokhtar Magmatic Arc (UDMA) in Iran. According to microscopic and chemical studies, the granitoid complex consists of three different rock types: 1) plutonic rocks comprising diorite, quartz diorite, granodiorite and granite; 2) volcanic rocks composed of basalt, andesite basalt, ± pyroxene bearing andesite and rhyolite, and 3) pyroclastic rocks. The main mineral constituents of these rocks are mostly plagioclase (oligoclase and andesine), quartz, K-feldspar, amphibole (magnesio-hornblende and actinolite-hornblende) and Mg-biotite. In addition, apatite, titanite, zircon, and opaque minerals are common accessory minerals. The studied enclaves are classified as mafic micro-granular enclaves (MME) with monzodiorite compositions. Geochemically, the rocks in this study represent medium to high-K calc-alkaline series, metaluminous and I-type nature. Plotting, the chemical composition of plagioclase on the An-Ab-Or ternary diagram, the temperature of crystallization is estimated to range from 700 to 900 °C at a pressure of 4.5 Kbar. High TiO2 values of biotites from the Golabad granitoid complex suggest magmatic origin and the crystallization temperature is estimated to range from 700 to 750 °C. The amphiboles according to their chemical analysis, are classified as igneous amphiboles generated in high oxygen fugacity conditions. The chemical data of the amphiboles and biotites pointed out to the I- type nature of the Golabad granitoid complex emplaced in an active continental margin subduction setting. The amphibole crystallization pressure was estimated by Al in amphibole varies from 1.09 to 2.28 Kbar. Using the calculated pressure the depth of the formation of the Golabad granitoid complex estimated from 4 to 9 Km.

  19. 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 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 several

  20. 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

  1. Magma Plumbing System of Baru Volcano From Deep to Shallow Crust (United States)

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


    Linking shallow and deep crustal processes at volcanic arcs has been an important component in evaluating the growth and evolution of the continental crust. Commonly, deep crustal processes and the nature of sub-arc lithosphere are studied long after the volcanism has ceased in locations such as obducted arc terranes. In active arcs, studies of deep crustal processes focus on rare cumulates or restites derived from lower crustal levels. Although uncommon in the erupted magmas, these cumulates are required by crustal differentiation models of arc magmatism. Quaternary magmas at Baru volcano in Panama contain ubiquitous amphibole bearing cumulates that provide an opportunity to probe the magma plumbing system of an active arc volcano. These cumulates are present in andesitic-dacitic lavas and pyroclastic flows of adakitic character and are not related to their host magmas by crystal fractionation processes. Two cumulate groups can be readily identified. The first group typically consists of 2-5 cm nodules of large amphiboles (3-6 mm) with minor (Baru volcano. The first cumulate group may be derived from deep hot zones were magmatic differentiation of water-saturated arc magmas takes place by crystallization of amphibole-rich cumulates. The second group is consistent with derivation from shallow levels where crystallization was triggered by rapid decompression. We propose that the contrasting cumulate origin may be explained by the host adakitic magma first eroding and disaggregating an amphibole rich crystal accumulation zone in the lower-mid crust (e.g. amphibole sponge; Davidson et al., 2007, Geology, p787-790). Later, this mixture of adakitic-magma + cumulates ascended rapidly to shallower depths and entrained a shallow level cumulate pile (second cumulate group). The identification of lower-mid crustal amphibole-rich cumulates is not exclusive to Baru volcano, such cumulates have been also identified in other regions of the Panamanian arc (e.g. Quaternary

  2. On the application of probability representations for estimation of the argon method resolution

    International Nuclear Information System (INIS)

    Kol'tsova, T.V.


    By considering the dating of amphiboles and biotites by the argon method, it is shown that there is a possibility to use the common F and t criteria for revealing any meaning difference in their ages. The dependence of the alternative inference of possible variations of the active parameters is considered, and a graphical procedure for selecting the optimum number of determinations for a given accuracy of analysis is suggested. The meaning difference in the age of amphiboles and biotites from the Northern Ladoga Lake region permits interesting conclusions to be made on the paleothermal history of the investigated rocks

  3. Sedimentary carbonate-hosted giant Bayan Obo REE-Fe-Nb ore deposit of Inner Mongolia, China; a cornerstone example for giant polymetallic ore deposits of hydrothermal origin (United States)

    Chao, E.C.T.; Back, J.M.; Minkin, J.A.; Tatsumoto, M.; Junwen, Wang; Conrad, J.E.; McKee, E.H.; Zonglin, Hou; Qingrun, Meng; Shengguang, Huang


    Detailed, integrative field and laboratory studies of the textures, structures, chemical characteristics, and isotopically determined ages and signatures of mineralization of the Bayan Obo deposit provided evidence for the origin and characteristics favorable for its formation and parameters necessary for defining giant polymetallic deposits of hydrothermal origin. Bayan Obo is an epigenetic, metasomatic, hydrothermal rare earth element (REE)-Fe-Nb ore deposit that is hosted in the metasedimentary H8 dolostone marble of the Middle Proterozoic Bayan Obo Group. The metasedimentary sequence was deposited on the northern continental slope of the North China craton. The mine area is about 100 km south of the suture marking Caledonian subduction of the Mongolian oceanic plate from the north beneath the North China craton. The mineralogy of the deposit is very complex, consisting of more than 120 different minerals, some of which are epigenetic minerals introduced by hydrothermal solutions, and some of which are primary and secondary metamorphic minerals. The major REE minerals are monazite and bastnaesite, whereas magnetite and hematite are the dominant Fe-ore minerals, and columbite is the most abundant Nb mineral. Dolomite, alkali amphibole, fluorite, barite, aegirine augite, apatite, phlogopite, albite, and microcline are the most widespread gangue minerals. Three general types of ores occur at Bayan Obo: disseminated, banded, and massive ores. Broad zoning of these ore types occurs in the Main and East Orebodies. Disseminated ores are in the outermost zone, banded ores are in the intermediate zone, and massive ores are in the cores of the orebodies. On the basis of field relations, host rocks, textures, structures, and mineral assemblages, many varieties of these three types of ores have been recognized and mapped. Isotopic dating of monazite, bastnaesite, aeschynite, and metamorphic and metasomatic alkali amphiboles associated with the deposit provides constraints

  4. Thermal Properties of Soils (United States)


    plagio - clase feldspar and pyroxene. The tine fraction may Surface area and its effects contain the clay "sheet" minerals (i.e. kaolinite. illite...Pyroxene, Kaoliniwe Unified By By Ortho. Plagio . amphibole, Basic clay min. Hematite Soil Soil soil petrogr. X.ray clase clase and Igneous and clay and no

  5. 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)

    Reymer, A.P.S.


    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.)

  6. Structural petrology of the garnet-peridotite of Alpe Arami (Ticino, Switzerland)

    NARCIS (Netherlands)

    Möckel, J.R.


    The decomposition of pyrope-rich garnet into spinel-amphibole symplektite and the alteration of the latter into chlorite indicate the presence of three successive mineral parageneses in the peridotite of Alpe Arami: a garnet-peridotite, a spinelamphibole-peridotite, and a chlorite-peridotite

  7. Petrology, isotopic and fluid inclusion studies of eclogites from Sujiahe, NW Dabie Shan (China), July 1 2002

    NARCIS (Netherlands)

    Fu, B.; Zheng, Y.-F.; Touret, J.L.R.


    In addition to the Triassic Hong'an low-T-high-P eclogite and the Xinxian coesite-bearing kyanite-glaucophane eclogite, Silurian coesite-free amphibole eclogites occur in the Sujiahe region, NW Dabie Shan of central China. A comprehensive study of petrology, Nd-Sr, O-H isotopes and fluid inclusions

  8. Journal of Earth System Science | Indian Academy of Sciences

    Indian Academy of Sciences (India)

    Classical field method, conic sections method and Ramsay's fold classification method were applied to (i) have the general orientation of folds, (ii) analyze the fold shapes and (iii) classify the geometry of the folded bands. Fold axes in banded amphibole gneiss plunge moderately (<15◦) towards the NNE or SSW.


    African Journals Online (AJOL)

    The kigom granites in central Nigeria are alkali amphibole bearing and peralkaline in nature. They are hypersolvus in character and contain mesoperthite in which the albite (Or1-2) and microcline are present in approximately equal proportions. The albite is fully ordered while K-rich feldspar is dominantly microcline.

  10. Partial melting of metavolcanics in amphibolite facies regional ...

    Indian Academy of Sciences (India)

    R. Narasimhan (Krishtel eMaging) 1461 1996 Oct 15 13:05:22

    Petrol. 12 25–62. Holdaway M J 1971 Stability of andalusite and the alu- minum silicate phase diagram; Am. J. Sci.; 271, 97–131. Hollocher K 1985 Geochemistry of metamorphosed vol- canic rocks in the Middle Ordovician Partridge Forma- tion, and amphibole dehydration reactions in the high-grade metamorphic zones of ...

  11. contact metamorphism in the supracrustal rocks of the sukumaland ...

    African Journals Online (AJOL)


    intrusion in metabasites at Mawemeru area produced heat that baked the respective country rocks through ... felsic pyroclastic and lava flows and .... grains in the matrix have the chemical composition of ferrotschermakite similar to rims of the coarse laths. M4 site in these amphiboles has intermediate values of Na ranging ...

  12. Mineralogical and chemical characteristics of newer dolerite dyke ...

    Indian Academy of Sciences (India)

    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.

  13. Anphibole, an undesirable presence in cosmetic talc

    International Nuclear Information System (INIS)

    Amaral, M.A.M.


    A semi-quantitative X-ray diffractometric study, compared to CaO analysis, for the evaluation of the percentage of amphibole present in cosmetic talcs is presented. Scanning electron images show these needle-like minerals togheter with talc; these minerals can cause from simple allergies to serious health problems to the human being. (Author) [pt

  14. Journal of Earth System Science | Indian Academy of Sciences

    Indian Academy of Sciences (India)

    Calc-silicate rocks of the Kajalbas area of Delhi Fold Belt, Rajasthan, are characterised by foliation parallel alternate bands of amphibolerich and clinopyroxene–plagioclase feldspar-rich layers of varying thicknesses (mm to decimetre thick). Textural relation suggests that the amphibole grains formed from clinopyroxene ...

  15. Insights into the P–T evolution path of Tso Morari eclogites of the ...

    Indian Academy of Sciences (India)

    The pre-UHP metamorphic association 1 of Na-Ca-amphibole + epidote ± paragonite ± rutile ... 1. Introduction. Reported occurrence of coesite, the high pressure polymorph of quartz as inclusions in the garnets of eclogitic rocks from Norway and the Alps region in the early .... with near horizontal axial plane. The third gen-.

  16. crustal shear zone

    Indian Academy of Sciences (India)

    area of Delhi Fold Belt, Rajasthan, are characterised by foliation parallel alternate bands of amphibole- ... Kajalbas, the present study area (lat: 25. ◦. 38 ... (b). Stereographic plot showing the π girdle of calc-silicate foliation (n = 56) contoured at intervals of 3%, 6%, 12% and 24%. (in increasing shades of grey; max 27.78%).

  17. Analyse sédimentologique et paléoenvironnements des sédiments ...

    African Journals Online (AJOL)

    More trendlines particle size parameters are growing straight. Director of straight regression coefficient is close to one (1). Thus there is a good correlation between the characteristic parameters. The mineralogical contains both heavy minerals such as amphibole (actinolite, hornblende), tourmaline, diopside and epidote ...

  18. Journal Article: Localized Pleural Thickening: Smoking and Exposure to Libby Vermiculite (United States)

    There is limited research on the combined effects of smoking and asbestos exposure on risk of localized pleural thickening (LPT). This analysis uses data from the Marysville cohort of workers occupationally exposed to Libby amphibole asbestos (LAA). Workers were interviewed to ...

  19. Hydrological indications of aeolian salts in mid-latitude deserts of ...

    Indian Academy of Sciences (India)

    A great difference in salt composition between aeolian and lacustrinesediments suggests that the inorganic salt is a latent geoproxy in revealing local hydrological variationsand climate change in the desert areas. But the environmental indications could be amphibolous for thesedimentary sequences with dual/multiple ...

  20. Magmatism and Eurekan deformation in the High Arctic Large Igneous Province: 40Ar–39Ar age of Kap Washington Group volcanics, North Greenland

    DEFF Research Database (Denmark)

    Tegner, Christian; Storey, Michael; Holm, Paul Martin


    of alkaline volcanics from Kap Kane, part of the Kap Washington Group volcanics at the northern tip of Greenland, provides an emplacement age of 71.2±0.5 Ma obtained from amphibole in lapilli tuffs, and a thermal resetting age of 49–47 Ma obtained in feldspar and whole-rocks from trachyte flows. Patch...

  1. Journal of Earth System Science | Indian Academy of Sciences

    Indian Academy of Sciences (India)

    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, ...

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

    International Nuclear Information System (INIS)

    Pessoa, D.A.R.


    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)

  3. 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…

  4. 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

  5. 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

  6. Post-collisional magmatism in the Late Miocene Rodna-Bârgău district (East Carpathians, Romania): Geochemical constraints and petrogenetic models (United States)

    Fedele, Lorenzo; Seghedi, Ioan; Chung, Sun-Lin; Laiena, Fabio; Lin, Te-Hsien; Morra, Vincenzo; Lustrino, Michele


    Post-collisional magmatism in the Late Miocene Rodna-Bârgău subvolcanic district (East Carpathians) gave rise to a wide variety of rock compositions, allowing recognition of four groups of calcalkaline rocks with distinctive petrography, mineral chemistry, whole-rock geochemistry and Sr-Nd-Hf isotope features. New U-Pb zircon datings, together with literature data, indicate that the emplacement of the four rock groups was basically contemporaneous in the 11.5-8 Ma time span. The low potassium group (LKG) includes the most abundant lithotypes of the area, ranging from basaltic andesite to dacite, characterized by K-poor tschermakitic amphibole, weak enrichment in LILE and LREE, relatively low 87Sr/86Sr, coupled with relatively high 143Nd/144Nd and 176Hf/177Hf. The high potassium group (HKG) includes amphibole-bearing microgabbro, amphibole andesite and amphibole- and biotite dacite, with K-richer magnesio-hastingsite to hastingsite amphibole, more marked enrichments in incompatible elements, higher 87Sr/86Sr and lower 143Nd/144Nd and 176Hf/177Hf. These two main rock groups seem to have originated from similar juxtaposed mantle sources, with the HKG possibly related to slightly more enriched domains (with higher H2O reflected by the higher modal amphibole) with respect to LKG (with higher plagioclase/amphibole ratios). The evolution of the two rock series involved also open-system processes, taking place mainly in the upper crust for the HKG, in the lower crust for LKG magmas. In addition, limited occurrences of generally younger strongly evolved peraluminous rhyolites and microgranites (Acid group) and sialic-dominated "leucocratic" andesites and dacites (LAD group) were also recognized to the opposite outermost areas of the district. These two latter rock groups were generated by the melting of a basic metamorphic crustal source (respectively in hydrous and anhydrous conditions), favored by the heat released by mantle melts from the adjoining central area. The

  7. 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. © The Author 2015. Published by Oxford

  8. 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

  9. Mafic and ultramafic enclaves in Ustica Island lavas: Inferences on composition of lower crust and deep magmatic processes (United States)

    Alletti, M.; Pompilio, M.; Rotolo, S. G.


    Ustica Island, southern Tyrrhenian Sea, is constituted of Quaternary alkaline volcanics. A variety of enclaves representative of deep to supra-crustal settings were recently found in a hawaiitic lava flow. Enclaves consist of: (i) Ultramafic meta-cumulates, i.e. clinopyroxenites and wherlites characterized by variably deformed porphyroclastic to granoblastic textures. (ii) Mafic cumulates, i.e. gabbros (± amphibole) and troctolites, the first often characterized by frequent amphibole breakdown coronas (olivine + Ti-augite + plagioclase + magnetite + ilmenite + rhönite) in response to an H 2O decrease during the ascent, while the troctolites interpreted as meta-cumulates. (iii) Microsyenites, consist of anorthoclase and Fe-clinopyroxene organized in a granular sub-ipidiomorphic texture. Amphibole is absent in Ustica lavas and is found only in some old, now exposed, sub-intrusive volcanic bodies. This evidence suggests a late appearance of amphibole on the liquidus, at a high crystal content that inhibits further ascent of the magma. The importance of the amphibole as a medium pressure liquidus phase in Ustica mafic magmas is in the bearings on the geochemistry of lavas e.g. in buffering Na and Ti abundances, in trace elements partitioning, etc. Density measurements pointed out higher values for clinopyroxenites (3160 to 3300 kg/m 3) than for gabbros (ca. 2900 kg/m 3). Given the density contrast between enclaves and host lavas (2790 kg/m 3) and assuming appropriate rheological models, we calculated a minimum ascent rate of 0.01 m/s, corresponding to an ascent time in the range of 5-29 days for a depth of entrapment of 25 km.

  10. 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.

  11. A mineral and cumulate perspective to magma differentiation at Nisyros volcano, Aegean arc (United States)

    Klaver, Martijn; Matveev, Sergei; Berndt, Jasper; Lissenberg, C. Johan; Vroon, Pieter Z.


    Lavas and pyroclastic products of Nisyros volcano (Aegean arc, Greece) host a wide variety of phenocryst and cumulate assemblages that offer a unique window into the earliest stages of magma differentiation. This study presents a detailed petrographic study of lavas, enclaves and cumulates spanning the entire volcanic history of Nisyros to elucidate at which levels in the crust magmas stall and differentiate. We present a new division for the volcanic products into two suites based on field occurrence and petrographic features: a low-porphyricity andesite and a high-porphyricity (rhyo)dacite (HPRD) suite. Cumulate fragments are exclusively found in the HPRD suite and are predominantly derived from upper crustal reservoirs where they crystallised under hydrous conditions from melts that underwent prior differentiation. Rarer cumulate fragments range from (amphibole-)wehrlites to plagioclase-hornblendites and these appear to be derived from the lower crust (0.5-0.8 GPa). The suppressed stability of plagioclase and early saturation of amphibole in these cumulates are indicative of high-pressure crystallisation from primitive hydrous melts (≥ 3 wt% H2O). Clinopyroxene in these cumulates has Al2O3 contents up to 9 wt% due to the absence of crystallising plagioclase, and is subsequently consumed in a peritectic reaction to form primitive, Al-rich amphibole (Mg# > 73, 12-15 wt% Al2O3). The composition of these peritectic amphiboles is distinct from trace element-enriched interstitial amphibole in shallower cumulates. Phenocryst compositions and assemblages in both suites differ markedly from the cumulates. Phenocrysts, therefore, reflect shallow crystallisation and do not record magma differentiation in the deep arc crust.

  12. Diffusion controlled corona growth in mafic dykes from Southern Granulite Terrain, India and their petrological implications (United States)

    Banerjee, Ayoti; Banerjee, Meenakshi; Dutta, Upama; Sengupta, Pulak; Bhui, Uttam K.; Rajagopal, Anand; Mukhopadhyay, Dhruba


    Diffusion controlled corona growth in mafic dykes from Southern Granulite Terrain, India and their petrological implications Metamorphosed garnetiferous mafic dykes from Southern Granulite Terrain (SGT) are found intruding the high grade Archaean-Palaeoproterozoic felsic orthogneiss and their retrogressed equivalent. They contain phenocrysts of clinopyroxene (Cpx) and plagioclase (Pl) that preserve ophitic, subophitic and intergranular textures. The clinopyroxene contains closely spaced cleavage-parallel exsolution lamellae of orthopyroxene (Opx) and tiny rods of Fe-Ti oxides. Orthopyroxene is also found around clinopyroxene as granular exsolution. Large grains of Fe-Ti oxides occur within the interstitial space. Garnet (Grt) and quartz (Qtz) form at the contact of plagioclase and clinopyroxene. The product minerals are found as symplectite and/or corona rimming the reactants. In the corona, quartz always occurs near clinopyroxene whereas garnet forms close to the plagioclase. The proportions of garnet and quartz in symplectite are fairly constant and range from 75:25 to 70:30 (vol %). Similar coronitic texture is exhibited by amphibole (Amp) and quartz. Thin amphibole+quartz corona forms between plagioclase and clinopyroxene where amphibole occurs near plagioclase and quartz near clinopyroxene, though the rock is dominated by garnet over amphibole in the corona. Corona of garnet/amphibole is also found on Fe-Ti oxides at the contact of plagioclase and the products show TiO2 enrichement when they occur near Fe-Ti oxides. Formation of hydrous amphibole from anhydrous minerals necessitates the system to be open to H2O. Additionally, balanced chemical reactions for Pl+Cpx=Grt+Qtz and Pl+Cpx=Amp+Qtz require Fe+2 incorporation to explain the observed volume proportion of the product minerals. Formation of garnet/amphibole near plagioclase and quartz near clinopyroxene indicate restricted mobility of Al and Si within the reaction domain. Preferential enrichment of TiO2

  13. Metamorphic evolution of metadolerites from the Frido Unit ophiolites (Southern Apennine-Italy) (United States)

    Cristi Sansone, Maria T.; Prosser, Giacomo; Rizzo, Giovanna; Tartarotti, Paola


    The Southern Apennines chain is a fold-and-thrust belt resulting from the convergence of the African and European plates and simultaneous roll-back of SE-directed Ionian subduction (Upper Oligocene-Quaternary). Ophiolites in the Southern Apennines are related to northwest subduction of the oceanic lithosphere pertaining to the Ligurian sector of the Jurassic western Tethys. The ophiolitic sequences are enclosed within remnants of the Liguride accretionary wedge now incorporated in the Southern Apennine chain and they crop out in the north-eastern slope of the Pollino Ridge (Calabria-Lucania border zone). Mafic and ultramafic rocks, with garnet-bearing felses, amphibolites, gneiss and granitoides occur as tectonic slices within a matrix mainly composed of calcschists and phyllites. Metadolerites occur as dikes cutting through serpentinized peridotites. Metadolerites have different kinds of texture reflecting various degree of crystallinity and strain: porphyritic or aphyric, intersertal/intergranular, blastophitic, cataclastic to mylonitic. In all metadolerites primary plagioclase and clinopyroxene can be observed. The metamorphic mineral assemblage consists of brown amphibole, green amphibole, chlorite, blue amphibole, pumpellyite, prehnite, quartz, epidote, white mica, lawsonite and plagioclase (Pl2 and Pl3). Accessory phases are opaque minerals, Fe-hydroxides and zircon. Metadolerites are cross- cut by veins filled with pumpellyite, chlorite, prehnite, tremolite, plagioclase, white, mica, quartz, lawsonite, epidote and zircon. The veins are straight, a few millimetres in thickness and occur isolated or in closely spaced sets. The vein morphology ranges from planar to sinuous and irregular. On the basis of metamorphic mineral phases three different types of metadolerite can be distinguished: i) rocks with a high content of prehnite crystals in cataclastic-mylonitic bands, exhibiting an intersertal or a blastophitic texture or a mylonitic fabric and in some cases a

  14. Mantle xenoliths from Szentbékálla, Balaton: Geochemical and petrological constraints on the evolution of the lithospheric mantle underneath Pannonian Basin, Hungary (United States)

    Ntaflos, Theo; Bizimis, Michael; Abart, Rainer


    Pliocene alkali basalts from the Bakony-Balaton Highland Volcanic Field (BBHVF) in the western Pannonian Basin carry mantle xenoliths comprising hydrous and anhydrous spinel peridotites. The studied mantle xenoliths from Szentbékálla, near Lake Balaton, Hungary, are fine- and coarse-grained fertile to depleted spinel lherzolites, spinel harzburgites and dunites, with protogranular, porphyroclastic, and secondary protogranular and mosaic equigranular textures. Melt pockets, with shapes resembling amphibole, are common in a number of samples, whereas other samples have thin films of intergranular glass. Bulk-rock major element abundances show that the mantle lithosphere beneath this area experienced variable degrees (up to 20%) of partial melting. The clinopyroxene trace elements systematics retain a record of melt depletion and metasomatic processes attributed to subduction-related melt/fluids or to the infiltration of percolating undersaturated melts in the Pannonian lithospheric mantle. The radiogenic isotopes of Sr, Nd and Hf in clinopyroxene suggest that this metasomatism was a relatively recent event. Textural evidence suggests that the calcite filling up the vesicles in the melt pockets and in veinlets cross-cutting the constituent minerals is of epigenetic nature and not due to carbonatite metasomatism. The non-metasomatized primitive mantle normalized clinopyroxene REE abundances mimic those, but at higher values, of their bulk-rock REE patterns. Bulk-rock and clinopyroxene REE with upward and downward LREE respectively, indicate up to 2.4% host basalt infiltration. The calculated bulk composition of the melt pockets is identical to small amphibole relics found as inclusions in second generation clinopyroxene within the melt pockets, suggesting incongruent melting of amphibole, without the need for additional metasomatic melt/fluids to initiate the amphibole breakdown. The heat for the temperature increase necessary for amphibole breakdown was derived from

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

    Directory of Open Access Journals (Sweden)

    Rongguo Hu


    Full Text Available 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 relatively 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 (2σ. 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

  16. Mechanical behaviour of the Oman metamorphic sole: rheology of amphibolites at lower crustal conditions during subduction initiation (United States)

    Soret, Mathieu; Agard, Philippe; Ildefonse, Benoît; Dubacq, Benoît; Prigent, Cécile; Yamato, Philippe


    Amphibolites are commonly found in the middle to lower continental crust and along oceanic transform faults and detachments. Amphibolites are also the main component of metamorphic soles beneath highly strained peridotites at the base of large-scale ophiolites as exemplified in Oman. Metamorphic soles are crustal slivers stripped from the slab during early subduction and underplated below the upper plate (future ophiolite) mantle when the subduction interface is still young and warm (i.e. during the first million years -My- of intra-oceanic subduction). Understanding the rheological behaviour of amphibolitic rocks is therefore of major interest to model and quantify deformation and strain localisation in varied geodynamical environments. This contribution focuses on the deformation mechanisms of amphibole through a microstructural and petrological study of garnet-bearing and garnet-free clinopyroxene-bearing amphibolites, using EBSD analysis. The first aim is to test the influence of progres- sive changes in PT conditions during deformation and of the appearance/disappearance of anhydrous minerals (plagioclase, clinopyroxene and garnet) on the mechanical behaviour of mafic amphibolites. The second aim is to track deformation mechanisms during early subduction, through the study of these metamorphosed oceanic rocks, commonly 10-100 m thick, which range from high- to low-grade away from the contact with the peridotites (i.e. from 800 ± 100˚C - 0.9 ± 0.2 GPa to 500 ± 100˚C - 0.5 ± 0.1 GPa) and are essentially mafic at the top). Our study points out the existence of two major steps of deformation in the high-temperature amphibolite slices of the metamorphic soles during the early subdduction dynamics. These two steps witness important mechanical coupling and progressive strain localization at plate interface under cooling and hydrated conditions after subduction initiation. During the accretion of the first slice of metamorphic sole at 850 ± 50˚C (the garnet

  17. 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

  18. Following the Amphibolite to Greenschist Metamorphic Path through the Structural Parameters of Spinels from Amsaga (Mauritania

    Directory of Open Access Journals (Sweden)

    Davide Lenaz


    Full Text Available We investigated the crystal and structural behavior of several Cr-bearing spinels from the Archean chromitites of Amsaga (Mauritania. The chemical and structural data testified a retrograde metamorphism from amphibolite to greenschist facies, witnessed by relative changes in the amount of all the major oxides (Cr, Al, Mg, Fe2+, Fe3+, the relative proportion of Fe3+/Fetot as well as the structural parameters, including the cell edge and the oxygen coordinate. The general agreement between electron microprobe and Mössbauer data indicates that the analyzed spinels are stoichiometric. The structural data revealed that the oxygen positional parameter of amphibole-bearing samples is the highest observed among Cr-bearing spinels with similar Cr# and Mg#. Consequently, it is suggested that a structural study of detrital Cr-spinels could be important in discriminating an amphibole-chromitite source from an ophiolite source.

  19. Asbestos Workshop: Sampling, Analysis, and Risk Assessment (United States)


    coatings Vinyl/asbestos floor tile Automatic transmission components Clutch facings Disc brake pads Drum brake linings Brake blocks Commercial and...A naturally-occurring pliant and fibrous mineral with heat-resistant properties • Serpentine Class: joint compound,‘popcorn’ceilings, brake pads...values for amphiboles and chrysotile; separate IUR values based on smoking status and gender EMDQ March 2012 14 Asbestos Risk Calculation EMDQ March

  20. Etude Petrographique et Geochimique du Complexe Annulaire de ...

    African Journals Online (AJOL)

    Geochemical point view, this fenitization is marked by a decrease of the Si2O, Al2O3 and an enrichment in Na2O, Fe2O3, MgO, P2O5, Ce, La, Nb. The carbonatites of the principal body and dykes are characterized by the abundance of the carbonates (calcite and dolomite) and the apatite presence, amphibole, magnétite, ...

  1. Magmatic storage conditions, decompression rate, and incipient caldera collapse of the 1902 eruption of Santa Maria Volcano, Guatemala (United States)

    Andrews, Benjamin J.


    Phase equilibria experiments and analysis of natural pumice and phenocryst compositions indicate the 1902 Santa Maria dacite was stored at ~ 140-170 MPa and 840-850 °C prior to eruption. H2O-saturated, cold-seal experiments conducted in vessels with an intrinsic log fO2 of NNO + 1 ± 0.5 show that the natural phase assemblage (melt + plagioclase + amphibole + orthopyroxene + Fe-Ti oxides + apatite) is stable from approximately 115-140 MPa at temperatures below ~ 825 °C, to ~ 840-860 °C at 150 MPa, to > 850 and Ridolfi et al., 2010) applied to experimental samples suggest two populations of amphiboles, phenocrysts grown during the experiments and inherited xenocrysts, but the pressure-temperature conditions returned by the geothermobarometer are routinely > 50 MPa and > 50 °C greater than experimental run conditions; precise estimates of magmatic conditions based solely upon amphibole composition are likely inaccurate. The experimental results and analysis of natural crystals suggest that although the natural amphiboles likely record a broad range of magmatic conditions, only the lower bounds of that range reflect pre-eruptive storage conditions. Comparison of Santa Maria microlite abundances with decompression experiments examining other silicic systems from the literature suggests that the 1902 dacite decompressed at the rate of ~ 0.005 to 0.01 MPa/s during the eruption. Applying the decompression rate with the previously described eruption rate of approximately 2-3 × 108 kg/s (Williams and Self, 1983; Carey and Sparks, 1986) to the conduit model CONFLOW reveals that the eruption conduit was dike-like with an along-strike length > 1 km. Despite depositing ~ 20 km3 of dacite tephra (equivalent to ~ 8.5 km3 magma), the 1902 eruption did not form an obvious caldera. This work suggests that collapse of the dike-like conduit terminated the eruption, preventing full caldera collapse.

  2. X-Ray And Electron Microprobe Analysis Of Some Plagioclases From The Jabal Abu Safiyah Intrusion


    Al Mohandis, Ahmed A. [احمد عبد القادر المهندس


    The Jabal Abu Safiyah is a layered intrusion, which was emplaced within volcanosedimentary rocks. It extends in an arc for about 15 km and displays clear layering. The lower zone plagioclases were studied by electron microprobe and X-ray diffraction techniques to investigate their chemistry and structural state. Cumulus plagioclase forms the dominant phase in all thin sections studied, except in the amphibolized clinopyroxenite. Cumulus plagioclases from the lower zone of the Jabal Abu Saf...

  3. Hydrothermal Spinel, Corundum and Diaspore in Gabbroic Rocks from the Hess Deep Rift, IODP Site U1415 (United States)

    Nozaka, T.; Meyer, R.; Wintsch, R. P.


    Hydrothermal alteration of oceanic lower crust has significant implications on geophysical properties of oceanic plates and global-scale geochemical cycles. A first order observation on the hydrothermal alteration at fast-spreading ridges is provided by the gabbroic rocks recovered from the Integrated Ocean Drilling Program (IODP) Site U1415 at the Hess Deep Rift near the East Pacific Rise. Shipboard observations of these rocks have revealed an alteration sequence formed under temperature conditions ranging from amphibolite to zeolite facies with mineral assemblages including amphibole, secondary clinopyroxene, chlorite, talc, serpentine, prehnite, zeolite and clay minerals (Gillis et al., 2014). Amphibolite-facies alteration is illustrated by the tremolite-chlorite corona textures between primary olivine and plagioclase in primitive olivine gabbro or troctolite lithologies (Nozaka and Fryer, 2011). The abundance of these alteration mineral assemblages within some sampled intervals suggests localized high-temperature fluid flow near the spreading axis. Our post-cruise studies prove that some of the coronitic amphiboles, particularly those of incipient-stage corona have hornblendic compositions, suggesting a somewhat higher-temperature formation condition than tremolite. We report here another set of alteration products from Site U1415: that is, Al-spinel, corundum and diaspore. They occur in intensely altered parts of the drilled troctolites. The Al-spinel is associated with An-rich plagioclase and pargasitic amphibole that points to even higher temperature conditions than the amphibole-chlorite corona formation. The Al-spinel is partly replaced by corundum, and the corundum, in turn, is pseudomorphically replaced by diaspore. From modes of occurrence and chemical compositions of minerals, and thermodynamic calculations of the stability conditions for these mineral assemblages, we conclude that the highly aluminous phases were formed by localized fluid flow at

  4. 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.

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

    International Nuclear Information System (INIS)

    Kananian, A.; Juteau, Th.; Bellon, H.; Darvishzadeh, A.; Sabzehi, M.; Whitechurch, H.; Ricou, L.E.


    The ophiolite massif of Kahnuj (600 km 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 ( 40 K- 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)

  6. Early Cretaceous Surtseyan volcanoes of the Baño Nuevo Volcanic Complex (Aysén Basin, Eastern Central Patagonian Cordillera, Chile)




    Tens of Surtseyan tuff cones are exposed in the Río Coichel valley, between Ñireguao and Estancia Baño Nuevo (Southern Chilean Andes). The Early Cretaceous products of the submarine eruptions rest on, or are interbedded with, shallow marine sandstones of the Hauterivian-early Aptian Apeleg Formation. The Early Cretaceous rocks typically contain large amphibole phenocrysts, clinopyroxene and plagioclase, and have compositions that range from relatively primitive basalts to andesites. The basal...

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

    International Nuclear Information System (INIS)

    Benada, J.


    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)

  8. Constraining the thermal and tectonic evolution of a greenschist facies shear zone on Syros, Greece by using stable isotopes and mineral chemistry. (United States)

    Cisneros, M.; Barnes, J.; Behr, W. M.


    Retrograde metamorphic rocks are key to understanding the exhumation history of high-pressure/low-temperature terranes. The Cycladic Blueschist Unit of Syros, Greece experienced peak metamorphic conditions of 15 kbar and 500 °C at 50 Ma and was subsequently exhumed to the shallow-crust ( 1-3 km) by 15 Ma; however, the processes associated with exhumation from mantle depths to the mid-crust remain poorly understood. We present structural, microstructural, and geochemical analyses of greenschist facies metamafic rocks exposed on Lotos beach in Syros that help to constrain the early exhumation history of these rocks. The outcrop preserves two main fabrics: 1) an early transposition foliation (Ss) defined by tight, isoclinal folds with shallow hingelines, and 2) upright open folds with a steep axial-planar cleavage (Sc). Ss is associated with viscous deformation and alignment of both amphibole and epidote into the foliation plane, whereas Sc is associated with semi-brittle deformation, amphibole overgrowths, and boudinage in elongate epidote (ep). Amphiboles display a progressive evolution from Na-to-Ca-rich end-members and exhibit continuous crystallization throughout Ss and Sc, as evidenced by new amphibole growth and overgrowths oriented parallel to foliation. Cal-qtz precipitates in ep boudin necks and chl + cal pseudomorphs after actinolite represent the last stage of lower greenschist facies metamorphism. These results indicate that foliation-forming deformation initiated prior-to or during blueschist facies and continued through lowermost greenschist facies. Oxygen isotope thermometry indicates that qtz-cal pairs equilibrated at 187 °C. Carbon and oxygen isotope values of fluids in equilibrium with qtz-cal pairs (δ18O and δ13C ≈ 0 ‰) indicate a seawater-derived fluid source. Preliminary results suggest this shear zone experienced cooling during decompression, followed by interaction with fluids transferred along a low-angle detachment.

  9. African Journal of Science and Technology (AJST) L'OR, LE ...

    African Journals Online (AJOL)


    minéraux lourds du profil étudié sont le zircon, les oxydes de fer, l'ilménite, le rutile, la tourmaline. La staurotide, l'anatase sont sous forme de traces. Ces minéraux lourds ont été décrits dans l'environnement géologique proche. (Baras, 1992; Wédraogo et Napon, 1987) dans des granites à biotite et amphibole, des gneiss à ...

  10. 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

  11. Mineral chemistry indicates the petrogenesis of rhyolite from the southwestern Okinawa Trough (United States)

    Chen, Zuxing; Zeng, Zhigang; Wang, Xiaoyuan; Zhang, Yuxiang; Yin, Xuebo; Chen, Shuai; Ma, Yao; Li, Xiaohui; Qi, Hanyan


    To reveal the petrogenesis of rhyolite from the southwestern Okinawa Trough, the mineral chemistry of plagioclase, orthopyroxene, amphibole, quartz and Fe-Ti oxide phenocrysts were analyzed using an electron microprobe, and in suit Sr and Ba contents of plagioclase analysed by LA-ICPMS were chosen for fingerprinting plagioclases of different provenances. Results indicate an overall homogeneous composition for each of the mineral phases except for plagioclase phenocrysts which have a wide range of composition (An=39 88). Plagioclase crystals characterized by An contents of >70 are not in equilibrium with their whole-rock compositions, and coarse-sieved plagioclase phenocryst interiors record high An contents (>70) and Sr/Ba ratios (>7), which are similar to the those of plagioclase crystals in basalt. Therefore, these crystals must have been introduced to the rhyolitic magma from a more mafic source. Equilibrium temperatures estimated using orthopyroxene-liquid, iron-titanium oxide, titanium-in-quartz and amphibole geothermometers show consistent values ranging from 792 to 869°C. The equilibrium pressure calculated using amphibole compositions is close to 121 MPa which corresponds to an approximate depth of 4 km. The fO2 conditions estimated from Fe-Ti oxides and amphiboles plot slightly above the NNO buffer, which indicates that the rock formed under more oxidized conditions. Our results suggests that petrogenesis of the rhyolite due to basaltic magma ascend with the high An and Sr/Ba plaigoclases from deep magma chamber into the shallow chamber where the fractional crystallization and crustal assimilation happened. It also indicates that a two-layer magma chamber structure may occur under the southwestern Okinawa Trough.

  12. Evaluation of asbestos exposures during firewood-harvesting simulations in Libby, MT, USA--preliminary data. (United States)

    Hart, Julie F; Ward, Tony J; Spear, Terry M; Crispen, Kelly; Zolnikov, Tara R


    Research was conducted in order to assess potential exposure to asbestos while harvesting firewood from amphibole-contaminated trees near Libby, MT, USA. Three firewood-harvesting simulations took place in the summer and fall of 2006 in the Kootenai Forest inside the US Environmental Protection Agency (EPA) restricted zone surrounding the former W.R. Grace vermiculite mine. Another simulation was conducted near Missoula, MT, USA, which served as the control. The work practices following each simulation were consistent throughout each trial. Personal breathing zone (PBZ) asbestos concentrations were measured by phase contrast microscopy (PCM) and transmission electron microscopy (TEM). Surface wipe samples of personal protective clothing were measured by TEM. The mean (n = 12) PBZ PCM sample time-weighted average (TWA) concentration was 0.29 fibers per milliliter, standard deviation (SD = 0.54). A substantial portion (more than five fibers per sample) of non-asbestos fibers (cellulose) was reported on all PBZ samples (excluding field blanks) when analyzed by TEM. The mean (n = 12) PBZ TEM sample TWA concentration for amphibole fibers 5-microm long was 0.07 fibers per milliliter (SD = 0.08). Substantial amphibole fiber concentrations were revealed on Tyvek clothing wipe samples. The mean concentration (n = 12) was 29 826 fibers per square centimeter (SD = 37 555), with 91% (27 192 fibers per square centimeter) comprised fibers firewood-harvesting activities in asbestos-contaminated areas and that the potential for exposure exists during such activities.

  13. High-Pressure Polymorphism in Orthoamphiboles (United States)

    Finkelstein, G. J.; Zhang, D.; Shelton, H.; Dera, P.


    Amphiboles are double-chain silicate minerals that are the structurally hydrated counterpart to single-chain, anhydrous pyroxenes. They may play an important role in the earth as a carrier for volatiles in subduction zones, as well as a generator for seismic anisotropy in the upper mantle. Recent work has described previously unrecognized high-pressure polymorphism at low temperatures in a variety of pyroxene minerals, which may be relevant for the structure and dynamics of thick, cold, subducted slabs. However, high-pressure polymorphism in amphiboles above a few GPa in pressure has not been well explored, and if similar polymorphism to pyroxenes exists in this mineral family, it may affect the extent and depth of volatile transport in amphiboles, as well as their rheological properties. At low temperatures and high pressures, orthopyroxenes undergo crystal structure transitions at lower pressures than clinopyroxenes (10-30 GPa vs. > 50 GPa), so for this study we have investigated polymorphism in the anthophyllite-gedrite (Al-free and Al rich) orthoamphibole solid solution series. Using neon gas-loaded diamond anvil cells, we compressed both phases to a maximum pressure of 31 GPa, and observed transitions to new monoclinic structures in both endmembers. In this presentation, we will discuss the details of these transitions and implications for the earth's interior.

  14. Geology, petrography and geochemistry of the A-type granites from the Morro Redondo Complex (PR-SC, southern Brazil, Graciosa Province

    Directory of Open Access Journals (Sweden)



    Full Text Available The Morro Redondo Complex is one of the most important occurrences of the Graciosa A-type Province, southern Brazil. It consists of the Papanduva and Quiriri granitic plutons and a contemporaneous bimodal volcanic association. The Papanduva Pluton includes massive and deformed peralkaline alkali-feldspar granites with Na-Ca and Na-amphiboles and clinopyroxenes. The deformed types are the most evolved rocks in the province and carry rare ‘agpaitic’ minerals, some being described for the first time in granites from Brazil. The larger Quiriri Pluton comprises massive, slightly peraluminous, biotite syeno- and monzogranites with rare Ca-amphibole. Biotite compositions are relatively homogeneous, whereas sodic amphiboles and clinopyroxenes show increasing Na and Fe3+ evolving paths. The Morro Redondo granites are ferroan, with high SiO2, alkalis and HFSE contents; the peralkaline types registering the highest fe#. LILE and HFSE abundances increase with the agpaitic index and the most evolved are HHP granites, with radiogenic heat production up to 5.7 µWm–3. Geothermobarometric estimates indicate emplacement under low pressures (∼100 MPa, at temperatures up to 850-800 °C, and relatively reduced (QFM and oxidized (+1 REPLACE_LT ΔQFM REPLACE_LT +3 environments for the Papanduva and Quiriri Plutons, respectively. In both cases, melts evolved to relatively high oxidation states upon crystallization progress.

  15. Combined Lu-Hf and Sm-Nd geochronology of the Mariánské Lázně Complex: New constraints on the timing of eclogite- and granulite-facies metamorphism (United States)

    Collett, Stephen; Štípská, Pavla; Schulmann, Karel; Peřestý, Vít; Soldner, Jeremie; Anczkiewicz, Robert; Lexa, Ondrej; Kylander-Clark, Andrew


    Lu-Hf and Sm-Nd garnet-whole rock geochronology combined with petrographic observations, minero-chemical variations, thermodynamic modelling and structural data was used to constrain the P-T-t-d evolution of eclogites from the Mariánské Lázně Complex (Bohemian Massif). Boudins of mostly isotropic eclogite with relict steep eclogite-facies fabric are affected by steep migmatitic foliation, which is followed on a regional scale by the development of almost pervasive, predominantly SE-dipping, extensional foliation. The structural succession shows continuous transition from eclogite to garnetiferous migmatitic amphibolite and to amphibolite migmatite. A least retrogressed sample of eclogite shows clusters of fine-grained inclusion-poor garnet, omphacite relicts surrounded by a fine-grained clinopyroxene-plagioclase symplectite with minor amphibole, biotite-plagioclase intergrowths after white mica, kyanite with plagioclase-spinel coronas and accessory rutile. Rare potassic white mica occurs as inclusions in omphacite. A more retrogressed eclogite, with no omphacite or kyanite relicts, contains inclusion-poor garnet surrounded by amphibole-plagioclase corona in a matrix dominated by plagioclase-amphibole symplectite with minor clinopyroxene. In places, the symplectite is overgrown by coarse-grained amphibole. Peak P-T conditions, inferred from combined conventional thermobarometry and phase-equilibria modelling and based on inclusions of white mica (up to 3.33 Si p.f.u.), matrix omphacite (Jd33-36) and garnet core (Alm33-38Prp38-42Grs22-25Sps1) compositions are 25 kbar at 650-750 °C. A HT overprint occurred at 14-18 kbar and >800 °C based on coexisting clinopyroxene (Jd18-24), plagioclase (An18-35), and amphibole (Na(B) textures, calculated P-T conditions, and distinct Lu-Hf and Sm-Nd ages, provide a complete P-T-t-D path characterised by rapid ( 15 Ma) transition from HP subduction, crustal thickening to extensional HT shearing. This unconventional exhumation

  16. 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

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

    International Nuclear Information System (INIS)

    Zebedeo, Christian Nash; Davis, Chad; Peña, Cecelia; Ng, Kok Wei; Pfau, Jean C.


    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 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 distinct

  18. Lithium-bearing fluor-arfvedsonite from Hurricane Mountain, New Hampshire: A crystal-chemical study (United States)

    Hawthorne, F.C.; Oberti, R.; Ottolini, L.; Foord, E.E.


    The structures of two crystals of Li-bearing fluor-arfvedsonite (1) (K0.32Na0.68)Na2(Li0.48Fe 2+2.83Mn2+0.10Zn 0.06Fe3+1.46Ti0.07) (Si7.88Al0.12)O22[Fu1.15(OH) 0.85] and (2) (K0.25Na0.75)Na2(Li0.48Fe 2+2.84Mn2+0.11Zn 0.05Fe3+1.45Ti0.07)(Si 7.89Al0.11)O22[F1.35(OH) 0.65] from a granitic pegmatite, Hurricane Mountain, New Hampshire, have been refined to R indices of 1.5(1.6)% based on 1380(1387) reflections measured with MoK?? X-radiation. The unit cell parameters are (1) a 9.838(4), b 17.991(6), c 5.315(2) A??, 103.78(3)??, V 913.7 A??3 and (2) a 9.832(3), b 17.990(7), c 5.316(3) A??, ?? 103.79(3)??, V 913.2 A??3. Site-scattering refinement shows Li to be completely ordered at the M(3) site in these crystals. The amphibole composition is intermediate between fluor-arfvedsonite and fluor-ferro-leakeite with a small component (???10%) of fluor-ferro-ferri-nybo??ite. These amphibole crystals project into miarolitic cavities in a pegmatitic phase of a riebeckite granite. The early-crystallizing amphibole is close to fluor-ferro-leakeite in composition, but becomes progressively depleted in Li and F as crystals project out into miarolitic cavities; the final amphibole to crystallize is a fibrous Li-poor riebeckite. Li plays a significant role in late-stage fractionation involving the crystallization of alkali amphibole in peralkaline granitic environments.

  19. Neoproterozoic Rosetta Gabbro from northernmost Arabian-Nubian Shield, south Jordan: Geochemistry and petrogenesis (United States)

    Jarrar, Ghaleb H.; Stern, Robert J.; Theye, Thomas; Yaseen, Najel; Pease, Victoria; Miller, Nathan; Ibrahim, Khalil M.; Passchier, Cees W.; Whitehouse, Martin


    An Ediacaran mafic intrusion of south Jordan is a distinctive appinitic igneous rock with a possibly unique texture, characterized by spherical clots up to 40 mm in diameter composed of amphibole cores from which plagioclase euhedra radiate; we call it the Rosetta Gabbro. It is exposed as a small (ca. 750 m2) outcrop in the Neoproterozoic basement of south Jordan. A second outcrop of otherwise similar gabbro is located about 400 m to the north of the Rosetta Gabbro, but it lacks the distinctive texture. The Rosetta Gabbro could represent a magma pipe. It intrudes the Aqaba Complex ( 600 Ma) granitoids and metasediments of the Janub Metamorphic Complex (633-617 Ma). The gabbro is an Ol- to QZ tholeiite with the following chemical characteristics: SiO2 = 46.2-47.8 wt.%; Al2O3 = 16.4-17.7 wt.%, TiO2 = 1.70-2.82 wt.%, Na2O = 1.27-2.83 wt.%. K2O = 0.82-1.63 wt.%; Mg# 58-63; Σ REE = 70-117 ppm; La/Yb 6 to 8; and Eu/Eu* = 1.05-1.2. The investigated gabbro has the geochemical features of a continental flood tholeiitic basalt emplaced in a within-plate tectonic setting. Two varieties of amphiboles are found: 1) large, 3-5 mm, brown ferri-titanian-tschermakite (K0.09Na0.28)(Na0.20Ca1.80)(Mn0.04Fe3 +1.1Mg2.34Fe2 +0.90Ti0.29Al0.22)(Al1.85Si6.15)O22(OH)1.95 of the calcic amphibole group which is riddled with opaques; and 2) acicular yellowish-light green ferrian-magnesiohornblende (K0.04Na0.153)(Ca1.755Na0.245) (Fe3 +0.66Mn0.01Fe2 +1.01Mg3.03Ti0.06Al0.22)(Al1.03Si6.97)O22(OH)1.95. Scattered flakes of phlogopite also occur. Tabular radiating plagioclase (An64-79) are complexly twinned, with broad lamellae that show no zoning. Laser-ablation ICP-MS analyses of amphibole and plagioclase reveal considerable variation in trace element abundance, in spite of more subtle major element variations except for TiO2 in amphibole. The REE in the amphibole shows an order of magnitude variation with a concave-downward pattern and a positive Eu anomaly Eu/Eu* = 0.6-2, though far less

  20. The evaluation of physico-chemical parameters of the Nasrand Plutonic complex by using mineral composition

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    Fatemeh Sarjoughian


    Full Text Available Introduction Mineral composition is sensitive to variations in the composition of the magma and can be used to characterize the physical conditions of crystallization such as temperature, pressure, oxygen fugacity and water content. The studies have demonstrated that geobarometery by amphibole provides a tool for determining the depth of crystallization and knowledge of the depth of crystallization of hornblende through to solidification of calc-alkaline plutons (Anderson and Smith, 1995. The composition of pyroxene can be used as crystallization pressure and temperature indicators of pyroxene too. Anlytical methods The mineral compositions of the Nasrand intrusion were determined by electron microprobe, with special emphasis on the amphibole, feldspar, and pyroxene at the Naruto University, Japan, the EPMA (Jeol- JXA-8800R was used at operating conditions of 15 kV, 20 nA acceleration voltage and 20s counting time. Results The Nasrand intrusion (33°13'–33°15' N, 52°33'–52°34'E with an outcrop area of about 40 km2 is situated in the Urumieh–Dokhtar magmatic belt, SE of Ardestan. It is composed of granite and granodiorite and various dikes of diorite and gabbro which are intruded in it. It is intruded into Eocene volcanic rocks, including andesite, rhyolite, and dacite. The petrographical studies indicate that the granitic and granodioritic rocks contain major minerals such as quartz, K-feldspar, plagioclase, and amphibole, which are in an approximate equilibrium state. The gabbroic-dioritic dikes usually show microgranular porphyric texture. They mainly consist of plagioclase, amphibole, and pyroxene. The plagioclase shows variable composition from albite to oligoclase in the granitoid rocks and from oligoclase to bytownite in dioritic and gabbroic dikes (Deer et al., 1991. The amphiboles are calcic and their composition varies from hornblende to actinolite, whereas the composition of the basic dikes is inclined to hastingsite (Leake et

  1. Deformation of the Songshugou ophiolite in the Qinling orogen (United States)

    Sun, Shengsi; Dong, Yunpeng


    The Qinling orogen, middle part of the China Central Orogenic Belt, is well documented that was constructed by multiple convergences and subsequent collisions between the North China and South China Blocks mainly based on geochemistry and geochronology of ophiolites, magmatic rocks as well as sedimentary reconstruction. However, this model is lack of constraints from deformation of subduction/collision. The Songshugou ophiolite outcropped to the north of the Shangdan suture zone represents fragments of oceanic crust and upper mantle. Previous works have revealed that the ophiolite was formed at an ocean ridge and then emplaced in the northern Qinling belt. Hence, deformation of the ophiolite would provide constraints for the rifting and subduction processes. The ophiolite consists chiefly of metamorphosed mafic and ultramafic rocks. The ultramafic rocks contain coarse dunite, dunitic mylonite and harzburgite, with minor diopsidite veins. The mafic rocks are mainly amphibolite, garnet amphibolite and amphibole schist, which are considered to be eclogite facies and retrograde metamorphosed oceanic crust. Amphibole grains in the mafic rocks exhibit a strong shape-preferred orientation parallel to the foliation, which is also parallel to the lithologic contacts between mafic and ultramafic rocks. Electron backscattered diffraction (EBSD) analyses show strong olivine crystallographic preferred orientations (CPO) in dunite including A-, B-, and C-types formed by (010)[100], (010)[001] and (100)[001] dislocation slip systems, respectively. A-type CPO suggests high temperature plastic deformation in the upper mantle. In comparison, B-type may be restricted to regions with significantly high water content and high differential stress, and C-type may also be formed in wet condition with lower differential stress. Additionally, the dunite evolved into amphibolite facies metamorphism with mineral assemblages of olivine + talc + anthophyllite. Assuming a pressure of 1.5 GPa

  2. Adakite Induced Metasomatism of the Mantle Wedge: a Systematic Experimental Study at 1.6 GPa (United States)

    Rapp, R. P.; Laporte, D.; Martin, H.


    In order to better understand the origin and nature of the slab-derived agent in subduction zones, and how the arc geochemical signature is imparted to the mantle wedge, it is necessary to have specific geochemical parameters to differentiate between fluids and partial melts generated by dehydration of the crustal component (MORB) of the downgoing oceanic lithosphere. ``Adakite'' magmatism in subduction zones is generally attributed to partial melting of basaltic oceanic crust during prograde metamorphism and dehydration of the subducting slab. In this study, we focus on adakites or ``slab melts'' as the agent of metasomatism of the overlying mantle wedge, armed beforehand with relatively comprehensive major- and trace-element constraints on the geochemical nature of these melts from our previous work. We have conducted a series of melt-rock reaction experiments in the piston-cylinder apparatus at 1.6 GPa and temperatures of 1000-1250°C in which we systematically vary the proportion of adakite melt relative to mantle peridotite. Our starting materials consist of mechanical mixtures of an adakite glass containing ~8 wt% H2O (pre-hydrated in an internally-heated pressure vessel at 900°C and 2.5 kbar for 3-4 hours), and a natural depleted peridotite powder made from a xenolith from the Kamchatkan sub-arc mantle. Experiments were conducted in thick-walled, pressure-welded gold capsules at temperatures below 1100°C, and in Ag-Pd capsules at higher temeperatures; the adakite melt:peridotite rock ratio has been varied from 2:1 to 1:4, with the mixtures allowed to equilibrate over the course of 5-10 days, depending on run temperature. Our results indicate that the reaction between adakite melt and peridotite is dominated by the consumption of olivine and crystallization of orthopyroxene and amphibole, and takes the general form: melts1 (pristine adakite) + olivine 0 melt2 (hybridized adakite) + orthopyroxene + amphibole. The chemical characteristics of metasomatic

  3. Petrographic and petrogenetic studies of adakitic magmatism of Gavdel (Shivar Dagh in Garehdagh-South Arminian Zone (Northwest of Iran (Irankuh Pb-Zn deposit, Southwest of Isfahan

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    Ahmad Jahangiri


    Full Text Available Gavdel intrusive body, situated in NW Iran and NE of Uromieh-Dokhtar zone, is a part of Garehdagh, South-Arminian Zone (Arasbaran. The major outcrops of intrusive include of granodiorite, monzonite accompanied with granodioritic dyke. The studied samples display granular texture with essential minerals of, plagioclase, K-feldspar, amphibole ± quartz ± clinopyroxene. Geochemically, the studied rocks characterized by SiO2 in the range of (59.1-67.8%, Al2O3 (14.09-18.3%, high Sr (507.18-1150 ppm content , high ratios of Sr/Y (32.93-83.54, La/Yb and low Y (12.05-16.13 contents, which can indicate the adakitic characters of studied rocks. These features of Gavdel intrusive display geochemical similarity with high SiO2 adakites (HAS that comprise enriched LREE, LILE and depleted HFS elements such as Ta, Nb, and Ti. The fractionated REE pattern and low HREE and Y amount can be related to the occurrence of garnet or amphibole in residual source of adakitic magmas. High content of Sr and depletion of Ta, Nb and Ti can be ascribed either to the absence of plagioclase and the presence of Fe-Ti oxides in melt residue or fractionation of titanomagnetite and amphibole minerals with respect to petrograhic indications. Subducted slab breaking off followed by its partial melting and the overlying sediments accompanied by crustal assimilation through magma rising generated the magma in the studied area and the NW of Iran.

  4. Peridotites and mafic igneous rocks at the foot of the Galicia Margin: an oceanic or continental lithosphere? A discussion

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    Korprobst, J.; Chazot, G.


    An ultramafic/mafic complex is exposed on the sea floor at the foot of the Galicia Margin (Spain and Portugal). It comprises various types of peridotites and pyroxenites, as well as amphibole-diorites, gabbros, dolerites and basalts. For chronological and structural reasons (gabbros were emplaced within peridotites before the continental break-up) this unit cannot be assigned to the Atlantic oceanic crust. The compilation of all available petrological and geochemical data suggests that peridotites are derived from the sub-continental lithospheric mantle, deeply transformed during Cretaceous rifting. Thus, websterite dykes extracted from the depleted MORB mantle reservoir (DMM), were emplaced early within the lithospheric harzburgites; subsequent boudinage and tectonic dispersion of these dykes in the peridotites, during deformation stages at the beginning of rifting, resulted in the formation of fertile but isotopically depleted lherzolites. Sterile but isotopically enriched websterites, would represent melting residues in the peridotites, after significant partial melting and melt extraction related to the thermal erosion of the lithosphere. The latter melts are probably the source of brown amphibole metasomatic crystallization in some peridotites, as well as of the emplacement of amphibole-diorite dykes. Melts directly extracted from the asthenosphere were emplaced as gabbro within the sub-continental mantle. Mixing these DMM melts together with the enriched melts extracted from the lithosphere, provided the intermediate isotopic melt-compositions - in between the DMM and Oceanic Islands Basalts reservoir - observed for the dolerites and basalts, none of which are characterized by a genuine N-MORB signature. An enriched lithospheric mantle, present prior to rifting of the Galicia margin, is in good agreement with data from the Messejana dyke (Portugal) and more generally, with those of all continental tholeiites of the Central Atlantic Magmatic Province (CAMP

  5. 40Ar/ 39Ar mineral age constraints for the tectonothermal evolution of the Sambagawa metamorphic belt, central Shikoku, Japan: a Cretaceous accretionary prism (United States)

    Takasu, A.; Dallmeyer, R. D.


    The Sambagawa metamorphic belt exposed in central Shikoku, Japan, is tectonostratigraphically represented by the Oboke and structurally overlying Besshi nappe complexes. Oboke units consist of metamorphic rocks largely derived from clastic protoliths (sandstone and conglomerate) whereas Besshi units are dominated by rocks with oceanic protolith affinities (shale, chert, and greenstone). Whole-rock schist samples from low-grade Oboke units record intermediate temperature. {40Ar }/{39Ar } plateau ages of 70-77 Ma, which are interpreted to closely date attainment of maximum metamorphic conditions. Whole-rock schist samples from Besshi units (chlorite zone) record plateau ages of 85-94 Ma suggesting an earlier metamorphic climax within this structural level. Amphibole within the albite-biotite zone in Besshi records {36Ar }/{40Ar } vs. {39Ar }/{40Ar } plateau isotope correlation ages of 84-87 Ma, which are interpreted as dating the post-metamorphic cooling through temperatures required for intracrystalline retention of argon. A slightly older isotope correlation age (94 Ma) is recorded by amphibole from the higher grade oligioclase-biotite zone. Contrasts in amphibole cooling ages are interpreted as reflecting thrust-related metamorphic inversion and resultant earlier cooling of higher grade structural units. Muscovite from all structural levels of the Besshi nappe complex records {40Ar }/{39Ar } plateau ages of 76-89 Ma. These are interpreted to date post-metamorphic cooling through appropriate closure temperatures following structural assembly of the Besshi nappe complex. Protoliths of the Besshi units originated at approx. 130 Ma and attained maximum metamorphic conditions during entrainment in an accretionary complex at approx. 90-100 Ma. Higher grade sequences developed at deeper levels along the hanging wall of the accretionary complex. During subsequent structural uplift to shallower crustal levels the Besshi nappe complex was tectonically emplaced over Oboke

  6. Pre-eruptive conditions of dacitic magma erupted during the 21.7 ka Plinian event at Nevado de Toluca volcano, Central Mexico (United States)

    Arce, J. L.; Gardner, J. E.; Macías, J. L.


    The Nevado de Toluca volcano in Central Mexico has been active over the last ca. 42 ka, during which tens of km3 of pyroclastic material were erupted and two important Plinian-type eruptions occurred at ca. 21.7 ka (Lower Toluca Pumice: LTP) and ca. 10.5 ka (Upper Toluca Pumice: UTP). Samples from both the LTP and UTP contain plagioclase, amphibole, iron-titanium oxides, and minor anhedral biotite, set in a vesicular, rhyolitic, glassy matrix. In addition, UTP dacites contain orthopyroxene. Analysis of melt inclusions in plagioclase phenocrysts yields H2O contents of 2-3.5 wt.% for LTP and 1.3-3.6 wt.% for UTP samples. Ilmenite-ulvospinel geothermometry yields an average temperature of ~ 868 °C for the LTP magma (hotter than the UTP magma, ~ 842 °C; Arce et al., 2006), whereas amphibole-plagioclase geothermometry yields a temperature of 825-859 °C for the LTP magma. Water-saturated experiments using LTP dacite suggest that: (i) amphibole is stable above 100 MPa and below 900 °C; (ii) plagioclase crystallizes below 250-100 MPa at temperatures of 850-900 °C; and (iii) pyroxene is stable only below pressures of 200-100 MPa and temperatures of 825-900 °C. Comparison of natural and experimental data suggests that the LTP dacitic magma was stored at 150-200 MPa (5.8-7.7 km below the volcano summit). No differences in pressure found between 21.7 ka and 10.5 ka suggest that these two magmas were stored at similar depths. Orthopyroxene produced in lower temperature LTP experiments is compositionally different to those found in UTP natural samples, suggesting that they originated in two different magma batches. Whole-rock chemistry, petrographic features, and mineral compositions suggest that magma mixing was responsible for the generation of the dacitic Plinian LTP eruption.

  7. Direct evidence of hydration into mantle during shearing below a trasform fault: Prince Edward transform fault, Southwest Indian Ridge (United States)

    Michibayashi, K.; Kakihata, Y.; Dick, H. J.


    Southwest Indian Ridge (SWIR) is located to the southwest of Rodriguez Triple Junction, where three Indian ocean ridges meet (Zhou & Dick, 2013, Nature). SWIR is one of the slowest spreading ocean ridges in the world. In this study, we studied microstructural development of 21 peridotite samples obtained from Prince Edward transform fault of SWIR by PROTEA5 cruise in 1983. The peridotites consist dominantly of olivine, orthopyroxene and clinopyroxene with minor amounts of amphibole and plagioclase as well as secondary minerals such as serpentine and magnetite. The peridotites were classified into four groups based on their microstructures: 3 ultramylonites mostly consisting of extremely fine crystals (3-5µm), 13 heterogeneous tectonites consisting of coarse-grained crystals and fine-grained matrix, 1 cataclasite and 4 intensely serpentinized peridotites. Olivine Mg# is 0.90-0.91 and spinel Cr# is 0.1-0.35. Amphibole crystals have chemical compositions of tremolite and magnesio-hornblende and they were intensely deformed within the ultramylonites and the heterogeneous tectonites, indicating that they have occurred before or during intense shearing in mantle. Moreover, extremely fine grain sizes of olivine and microboudin textures in both pyroxene and spinel crystals suggest that these peridotites have been sheared under high stress conditions. Furthermore, olivine crystal-fabrics within the amphibole bearing peridotites have B and E types that could be developed under hydrous conditions, whereas olivine fabrics within the other peridotites have A and D types that could be developed under anhydrous conditions (Karato et al., 2008, Annu. Rev. Earth Planet. Sci.). Consequently, the petrophysical characteristics of peridotites in this study indicate that the uppermost mantle below the Prince Edward transform fault has been locally but intensely hydrated during shearing due to transform movement.

  8. 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.

  9. Crustal xenoliths from Calbuco Volcano, Andean Southern Volcanic Zone: implications for crustal composition and magma-crust interaction (United States)

    Hickey-Vargas, Rosemary; Abdollahi, Mohammad J.; Parada, Miguel A.; López-Escobar, Leopoldo; Frey, Fred A.


    Crustal xenoliths in the 1961 andesite flow of Calbuco Volcano, in the southern Southern Volcanic Zone (SSVZ) of the Andes, consist predominantly of pyroxene granulites and hornblende gabbronorites. The granulites contain plagioclase+pyroxene+magnetite±amphibole, and have pronounced granoblastic textures. Small amounts of relict amphibole surrounded by pyroxene-plagioclase-magnetite-glass symplectites are found in some specimens. These and similar textures in the gabbronorites are interpreted as evidence of dehydration melting. Mineral and bulk rock geochemical data indicate that the granulites are derived from an incompatible trace element depleted basaltic protolith that underwent two stages of metamorphism: a moderate pressure, high temperature stage accompanied by melting and melt extraction from some samples, followed by thermal metamorphism after entrainment in the Calbuco andesite lavas. High ɛNd T values (+4.0 to +8.6), Nd-isotope model ages of 1.7 2.0 Ga, and trace element characteristics like chondrite normalized La/YbCalbuco. Crystallization pressures for the gabbros based on total Al contents in amphibole are 6 8 kbar. These pressures point to middle to lower crustal storage of the Calbuco magma. Neither granulite nor gabbro xenoliths have the appropriate geochemical characteristics to be contaminants of Calbuco andesites, although an ancient sedimentary contaminant is indicated by the lava compositions. The presence of oceanic metabasaltic xenoliths, together with the sedimentary isotopic imprint, suggests that the lower crust beneath the volcano is analogous to the coastal metamorphic belt, which is an accretionary complex of intercalated basalts and sediments that formed along the Paleozoic Gondwanan margin. If this is the case, the geochemical composition of the lower and middle crust beneath the SSVZ is significantly different from that of most recent SSVZ volcanic rocks.

  10. Geology, mineralogy and magma evolution of Gunung Slamet Volcano, Java, Indonesia (United States)

    Vukadinovic, Danilo; Sutawidjaja, Igan

    Gunung Slamet, Central Java, is a large stratovolcano within the Sunda magmatic arc of Indonesia. The volcanic edifice includes products of two large overlapping Quaternary stratocones. Basaltic andesites and andesites, with rare basalts, dominate the western region of the complex, known as Slamet Tua (old); and basalts and basaltic andesites compose the eastern cone, called Slamet Muda (young). On the basis of stratigraphy, trace-element content, {Zr}/{Nb}, {Zr}/{K} and {87Sr}/{86Sr} ratios, Slamet lavas can be broadly categorized as relating to high abundance magma (HAM) and low abundance magma (LAM) types. The Tua and Lebaksiu sequences generally comprise the LAM group, and are older, more salic and have higher {87Sr}/{86Sr} ratios than those of HAM. LAM andesites contain some amphibole, but HAM andesites do not. Models involving randomized magma replenishment, tapping and fractionation (RTF) were developed to explain the geochemical features of both LAM and HAM rock groups. The salic lavas of the LAM suite can be generated if fractionation was dominant relative to replenishment and tapping in LAM magma chambers. Conversely, magma chambers with a high proportion of replenishment and tapping relative to fractionation can produce dominantly mafic lavas, such as those of the HAM suite. Concave-upward heavy-rare-earth element (HREE) patterns for LAM andesites are probably due to significant amphibole fractionation; HAM andesites display flat HREE patterns and do not require amphibole fractionation from parental basalts. The high TiO 2 contents of HAM basalts and basaltic andesites (relative to those of "average" arc rocks) are due to either suppressed crystallization—or minor accumulation—of Ti-magnetite, in conjunction with RTF processes.

  11. 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 (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.

  12. 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)

  13. Origine de la minéralisation des eaux des aquifères discontinus ...

    African Journals Online (AJOL)

    ... représentés dans ces eaux. Les principaux ions à l'origine de la minéralisation des eaux sont issus de l'altération des roches, de l'hydrolyse des minéraux silicatés tels que l'anorthite dans les plagioclases et de la décomposition des minéraux ferro-magnésiens comme la biotite et l'amphibole présentes dans les roches.

  14. 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.

  15. 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

  16. Contrasting estimates on the depth of magma storage zones in volcanic systems from mineral barometry and phase equilibrium experiments: a case study from Mount Merapi, Indonesia (United States)

    Erdmann, Saskia; Martel, Caroline


    Mount Merapi, located in central Java, erupts on average every 5-10 years by discharging block-and-ash flows that pose local, but spatially restricted hazards. In 2010, however, the volcano erupted with a force that has been unprecedented in over 100 years. Its proximity to the metropolis of Yogyakarta with a population of >4 million makes short- and long-term eruption forecasting a task of vital importance. Critical to the appraisal of the volcano's hazard potential are tight constraints on its upper-crustal magma plumbing system and particularly on the location of its pre-eruptive reservoir. Previous petrological studies have estimated on the basis of amphibole and clinopyroxene barometry that the main magma storage zone below Merapi is located at depths of >10-15 km, while geophysical surveys have inferred significant magma storage zones at depths of ~5.5-9 km. We have carried out phase equilibrium experiments on basaltic andesite erupted in 2010, which indicate that the main pre-eruptive reservoir is located at a depth of ~7-8 km (~200 MPa). Our results thus corroborate the findings of earlier geophysical surveys and highlight the extreme uncertainty of mineral-based pressure estimates for volcanic magma systems. We point out that the commonly employed amphibole barometric calibrations of Ridolfi et al. (2010) and Ridolfi & Renzulli (2012) calculate low crystallization pressure for amphibole crystallized from felsic melt and high crystallization pressure for amphibole crystallized from mafic melt, and that the calculated pressure is thus largely unrelated to true values. Commonly employed clinopyroxene barometers (e.g., those of Nimis 1999; Putirka 2008) are also of limited use for estimating the location of crustal magma reservoirs, because the methods have large standard errors and are extremely temperature-sensitive. As a result, the calculated crystallization pressures inevitably indicate crystallization over a large range of depths, often from deep- to

  17. 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

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

    International Nuclear Information System (INIS)

    Zhaboev, M.N.; Semochkin, G.A.; Blinov, Yu.I.; Dzhambaev, F.M.; Novikov, V.V.; Tereshchenko, S.V.


    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 WO 3 content were obtained from these ores; WO 3 content in pile products was 2-2.5 times lower as compared to factory tailing products. WO 3 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

  19. Fluorine and chlorine in mantle minerals and the halogen budget of the Earth's mantle (United States)

    Urann, B. M.; Le Roux, V.; Hammond, K.; Marschall, H. R.; Lee, C.-T. A.; Monteleone, B. D.


    The fluorine (F) and chlorine (Cl) contents of arc magmas have been used to track the composition of subducted components, and the F and Cl contents of MORB have been used to estimate the halogen content of depleted MORB mantle (DMM). Yet, the F and Cl budget of the Earth's upper mantle and their distribution in peridotite minerals remain to be constrained. Here, we developed a method to measure low concentrations of halogens (≥0.4 µg/g F and ≥0.3 µg/g Cl) in minerals by secondary ion mass spectroscopy. We present a comprehensive study of F and Cl in co-existing natural olivine, orthopyroxene, clinopyroxene, and amphibole in seventeen samples from different tectonic settings. We support the hypothesis that F in olivine is controlled by melt polymerization, and that F in pyroxene is controlled by their Na and Al contents, with some effect of melt polymerization. We infer that Cl compatibility ranks as follows: amphibole > clinopyroxene > olivine orthopyroxene, while F compatibility ranks as follows: amphibole > clinopyroxene > orthopyroxene ≥ olivine, depending on the tectonic context. In addition, we show that F, Cl, Be and B are correlated in pyroxenes and amphibole. F and Cl variations suggest that interaction with slab melts and fluids can significantly alter the halogen content of mantle minerals. In particular, F in oceanic peridotites is mostly hosted in pyroxenes, and proportionally increases in olivine in subduction-related peridotites. The mantle wedge is likely enriched in F compared to un-metasomatized mantle, while Cl is always low (<1 µg/g) in all tectonic settings studied here. The bulk anhydrous peridotite mantle contains 1.4-31 µg/g F and 0.14-0.38 µg/g Cl. The bulk F content of oceanic-like peridotites (2.1-9.4 µg/g) is lower than DMM estimates, consistent with F-rich eclogite in the source of MORB. Furthermore, the bulk Cl budget of all anhydrous peridotites studied here is lower than previous DMM estimates. Our results indicate that

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

    Tanner, Arnold O.


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

  1. Petrological studies of plutonic rocks of Ecuador

    International Nuclear Information System (INIS)

    Aly, S.


    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) [de

  2. A review of experimental studies of crystal/liquid trace element partitioning (United States)

    Irving, A. J.


    Experimental techniques for examining trace-element behavior are reviewed. Applications of these techniques are described for a variety of partition coefficients including: olivine/liquid, subcalcic pyroxene/liquid, calcic pyroxene/liquid, amphibole/liquid, plagioclase/liquid, alkali feldspar/liquid, garnet/liquid, apatite/liquid and whitlockite/liquid, ilmenite/liquid, armalcolite/liquid and pseudobrookite/liquid, magnetite/liquid and spinel/liquid, perovskite/liquid, and melilite/liquid partition coefficients. Partition coefficients between immiscible liquids are discussed and suggestions for further work are noted. A detailed bibliography is included.

  3. 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

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

    International Nuclear Information System (INIS)

    Memon, R.A.; Bessman, S.P.; Mohan, C.


    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- 14 C and 1,4- 14 C 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- 14 C suc carbons. Amphibolic channeling of 2,3- 14 C 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- 14 C suc carbons as compared to 1,4- 14 C 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

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

    International Nuclear Information System (INIS)

    Vergara, M; Lopez-Escobar, I; Palma, J.L; Hickey-Vargas, R


    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)

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

    Directory of Open Access Journals (Sweden)

    Fereshteh Bayat


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

  7. Garnet-Amphibolites Mineralogy and thermobarometry in Aliabad-Damagh (south of Hamedan, Sanandaj-Sirjan Zone

    Directory of Open Access Journals (Sweden)

    Ali Akbar Baharifar


    Full Text Available The garnet-amphibolites in Aliabad-Damagh area, occurs as layers and are enveloped by staurolite-schist. They composed predominantly of garnet, hornblende, feldspar (± muscovite and quartz with titanite, epidote, ilmenite and graphite as accessory minerals. The euhedral garnet porphyroblasts mainly composed of almandine and grossular components, with normal compositional zoning. The hornblende crystals as prophyroblast or in the matrix, are magnesio- and ferro-hornblende (amphibole core to tchermakitic-hornbelende (amphibole rim in composition. Muscovites, if present, with minor phengite and paragonite components, are foliated forming minerals. Feldspars vary from pure K-feldspar to sanidine composition in the vicinity of hornblendes and oligoclase in matrix. Epidotes as pure clinozoisite to epidote, form small crystals inside hornblende or in the matrix. Using different thermobarometry methods, T and P estimated as 600-620 (± 25 °C and 5-6 (± 1 kbar, respectively. Calculated P-T-t path, considering core and rim composition of hornblendes, is in accordance with low-pressure (at the beginning of metamorphism to medium-pressure type (at the end. Considering P-T-t path, metamorphism could occur during Neo-Tethys subduction and collision process in the Mesozoic time

  8. Magma storage constrains by compositional zoning of plagioclase from dacites of the caldera forming eruptions of Vetrovoy Isthmus and Lvinaya Past’ Bay (Iturup Island, Kurile Islands) (United States)

    Maksimovich, I. A.; Smirnov, S. Z.; Kotov, A. A.; Timina, T. Yu; Shevko, A. V.


    The Vetrovoy Isthmus and the Lvinaya Past’ Bay on the Iturup island (Kuril island arc) are the results of large Plinian eruptions of compositionally similar dacitic magmas. This study is devoted to a comparative analysis of the storage and crystallization conditions for magma reservoirs, which were a source of large-scale explosive eruptions. The plagioclase is most informative mineral in studying of the melt evolution. The studied plagioclases possess a complex zoning patterns, which are not typical for silicic rocks in island-arc systems. It was shown that increase of Ca in the plagioclase up to unusually high An95 is related to increase of H2O pressure in both volcanic magma chambers. The study revealed that minerals of the Vetrovoy Isthmus and Lvinaya Past’ crystallized from compositionally similar melts. Despite the compositional similarity of the melts, the phenocryst assemblage of the Lvinaya Past’ differs from the Vetrovoy Isthmus by the presence of the amphibole, which indicates that the pressure in the magmatic chamber exceeded 1-2 kbar at a 4-6 wt. % of H2O in the melt. The rocks of the Vetrovoy Isthmus do not contain amphibole phenocrysts, but melt and fluid inclusions assemblages in plagioclase demonstrate that the magma degassed in the course of evolution. This is an indication that the pressure did not exceed significantly 1-2 kbar.

  9. Uranium mineralization at Lagoa Real, BA, Brazil: the role of fluids in its genesis

    Energy Technology Data Exchange (ETDEWEB)

    Prates, Sonia Pinto; Neves, Jose Marques Correia; Fuzikawa, Kazuo, E-mail: pratess@cdtn.b [Centro de Desenvolvimento da Tecnologia Nuclear (CDTN/CNEN-MG), Belo Horizonte, MG (Brazil)


    The Lagoa Real uranium province is situated in the central-south of Bahia state . Brazil and it is presently by far the most important and best known uranium occurrence in Brazil. Nowadays 34 anomalies are known in a 30 Km long and 5 km wide area. An open pit mine was open in Cachoeira Mine, in the north portion of the area, and it is the only uranium mine in operation in Brazil and even in South America as well. The uranium mineralization in the Lagoa Real uranium province occurs in metamorphic rocks named albitites, due to their albite content (over 70%). Uraninite is the main uranium mineral, followed by pechblende, uranophane, torbernite and other uranyl minerals. Uraninite occurs as tiny round and irregular crystals (20 a 30 mum) included or associated to mafic minerals, mainly pyroxene and garnet, and also to amphibole and biotite and sometimes to albite. Some secondary minerals such as, for instance, uranophane, torbernite and tyuyamunite are also found. The main albitites minerals from the Cachoeira mine (plagioclase, garnet, biotite, pyroxene, amphibole and titanite) were studied by means of Infrared Spectroscopy Techniques. Good results were obtained from small quantities of material (around 2 mg) and allowed the minerals identification, and also to know their composition (from the peak position) and to detect the presence of water molecules, which indicates an aqueous phase during the uranium formation, probably rich in Fluorine. (author)

  10. 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.

  11. Petrography and Geochemistry (Trace, Ree and Pge of Pedda Cherlo Palle Gabbro-Diorite Pluton, Prakasam Igneous Province, Andhra Pradesh, India

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    Subramanyam K.S.V.


    Full Text Available Prakasam Igneous Province (PIP is an important geological domain in the Eastern Dharwar Craton (EDC, found in the junction zone between the EDC and Eastern Ghat Mobile Belt (EGMB. The Pedda Cherlo Palle (PCP gabbros are massive, leucocratic-mesocractic, and show cumulus textures with minerals plagioclase, cpx, and amphiboles. Compositionally, plagioclase is a labradorite-bytownite, cpx is diopside to augite, olivines are hyalosiderites and amphiboles are magnesiohornblendes. PCP gabbros have normal SiO2, high Al2O3, moderate to high TiO2, Na2O and medium Fe2O3, so, classified as subalkaline tholeiitic gabbros. Fractionated rare earth element (REE patterns, high abundance of large ion lithofile elements (LILE and transitional metals coupled with light REE (LREE relative enrichment over heavy REE (HREE and Nb are characteristics of partial melting of depleted mantle and melts that have undergone fractional crystalisation. These partial melts are enriched in LREE and LILE, due to the addition of slab derived sediment and fluids. PCP gabbros contain low abundance (5.1 to 24.6 ng/g of platinum group elements (PGE, and show an increase in the order Ir>Os>Pt>Ru»Pd>Rh. We propose that the subduction related intraoceanic island arc might have accreted to the southeastern margin of India to the east of Cuddapah basin in a collisional regime that took place during Ur to Rodinia amalgamations.

  12. Sources of Fe in eolian and soil detritus at Yucca Mountain, Nevada, USA

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    Vaniman, D.; Chipera, S.; Bish, D.


    Eolian deposits and adjacent soil horizons at Exile Hill near Yucca Mountain, Nevada, provide a desert environment where the origins of exotic eolian materials can be discerned. Petrographic, chemical, X-ray diffraction, and electron microprobe data allow an assessment of Fe mineral sources. Fe-rich minerals in local rhyolitic tuff bedrock consist of distinctive biotite and amphibole phenocrysts and groundmass Mn-hematites. Although the local tuffs contain only 1% FeO, detrital components of eolian and soil deposits have {approximately}3% FeO. Exotic minerals from distant sources provide most of the excess Fe in the surficial deposits. The exotic Fe sources are principally smectite, low-Mn hematite, low-F biotite, and high-Fe amphibole not found in local tuffs. Iron contents and the exotic Fe fraction increase with decreasing grain size, such that the clay fractions have {approximately}5--6% FeO, almost all of which is in exotic smectites. The distant origin of these smectites is evident in their high Fe content and distinct Sc/FeO enrichment trends, which differ from the strong local Sc/FeO control defined by coarser soil detritus. Approximate crustal average lanthanide composition in soil and eolian smectites rule out any significant contribution of local smectite derived from tuff alteration. The eolian and soil smectites instead inherit their high Fe content from eolian biotite.

  13. Sources of Fe in eolian and soil detritus at Yucca Mountain, Nevada, USA

    International Nuclear Information System (INIS)

    Vaniman, D.; Chipera, S.; Bish, D.


    Eolian deposits and adjacent soil horizons at Exile Hill near Yucca Mountain, Nevada, provide a desert environment where the origins of exotic eolian materials can be discerned. Petrographic, chemical, X-ray diffraction, and electron microprobe data allow an assessment of Fe mineral sources. Fe-rich minerals in local rhyolitic tuff bedrock consist of distinctive biotite and amphibole phenocrysts and groundmass Mn-hematites. Although the local tuffs contain only 1% FeO, detrital components of eolian and soil deposits have ∼3% FeO. Exotic minerals from distant sources provide most of the excess Fe in the surficial deposits. The exotic Fe sources are principally smectite, low-Mn hematite, low-F biotite, and high-Fe amphibole not found in local tuffs. Iron contents and the exotic Fe fraction increase with decreasing grain size, such that the clay fractions have ∼5--6% FeO, almost all of which is in exotic smectites. The distant origin of these smectites is evident in their high Fe content and distinct Sc/FeO enrichment trends, which differ from the strong local Sc/FeO control defined by coarser soil detritus. Approximate crustal average lanthanide composition in soil and eolian smectites rule out any significant contribution of local smectite derived from tuff alteration. The eolian and soil smectites instead inherit their high Fe content from eolian biotite

  14. Studies of thermal and radiation effects on water-rock systems related to envisaged isolation of high level radioactive wastes in crystalline formations of the Ukrainian shield (Ukraine)

    International Nuclear Information System (INIS)

    Litovchenko, A.; Kalinichenko, E.; Ivanitsky, V.; Bagmut, M.; Plastinina, M.; Zlobenko, B.


    In this work there are presented the general data on the study of thermal and radiation effects in minerals separated from rocks of the Ukrainian shield. These minerals (quartz, feldspar, amphiboles, apatite, biotite, kaolinite, etc.), exposed by doses 10 4 , 10 6 , 10 8 Gy by Co 60 source, were studied by a complex of physical methods. Special attention was given to the study of radiation defects formation (electron-hole paramagnetic centres, OH- groups destruction, changes in a charge state of ions) in a mineral structure. The mentioned radiation defects were used in the extrapolation method. The connection between structural peculiarities of minerals (containing uranium and thorium) and processes of their metamyctization are considered. It is demonstrated that the minerals, which have large channels or interlayer spaces in their structure, as a rule, are not metamyct. Using the spectroscopic methods of the extrapolation it is shown that the crystalline massifs, which do not have detectable amounts of hydroxyl containing minerals (biotite, amphibole, etc.) and ions Fe 2- , are perspective for long-lived radioactive wastes (RAW) dumping. As it follows from obtained results, the rocks, containing minerals with OH- groups and gas-liquid inclusions, should be considered as the 'mineral-water' system. (author)

  15. 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.

  16. Polychronous (Early Cretaceous to Palaeogene) emplacement of the Mundwara alkaline complex, Rajasthan, India: 40Ar/39Ar geochronology, petrochemistry and geodynamics (United States)

    Pande, Kanchan; Cucciniello, Ciro; Sheth, Hetu; Vijayan, Anjali; Sharma, Kamal Kant; Purohit, Ritesh; Jagadeesan, K. C.; Shinde, Sapna


    The Mundwara alkaline plutonic complex (Rajasthan, north-western India) is considered a part of the Late Cretaceous-Palaeogene Deccan Traps flood basalt province, based on geochronological data (mainly 40Ar/39Ar, on whole rocks, biotite and hornblende). We have studied the petrology and mineral chemistry of some Mundwara mafic rocks containing mica and amphibole. Geothermobarometry indicates emplacement of the complex at middle to upper crustal levels. We have obtained new 40Ar/39Ar ages of 80-84 Ma on biotite separates from mafic rocks and 102-110 Ma on whole-rock nepheline syenites. There is no evidence for excess 40Ar. The combined results show that some of the constituent intrusions of the Mundwara complex are of Deccan age, but others are older and unrelated to the Deccan Traps. The Mundwara alkaline complex is thus polychronous and similar to many alkaline complexes around the world that show recurrent magmatism, sometimes over hundreds of millions of years. The primary biotite and amphibole in Mundwara mafic rocks indicate hydrous parental magmas, derived from hydrated mantle peridotite at relatively low temperatures, thus ruling out a mantle plume. This hydration and metasomatism of the Rajasthan lithospheric mantle may have occurred during Jurassic subduction under Gondwanaland, or Precambrian subduction events. Low-degree decompression melting of this old, enriched lithospheric mantle, due to periodic diffuse lithospheric extension, gradually built the Mundwara complex from the Early Cretaceous to Palaeogene time.

  17. Determining magmatic series and oxygen fugacity of volcanic rocks in the east of Kamu, north of Isfahan, based on biotite chemistry

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    Mohammad Sayari


    Full Text Available Volcanic rocks of interest are situated in the middle part of the Urumieh-Dokhtar Magmatic Arc (UDMA. They are parts of a vast magmatic province located in the north of Bitlis-Zagros suture zone. Having a prevailing porphyritic texture, these rocks include phenocrysts of plagioclase, amphibole and biotite in a matrix composed of feldspar, quartz, opaque, glass and microlite and mineralogically show composition of dacite to andesite. Minerals are mostly fresh. Effects of alteration are limited to weak chloritization and saussuritization in some amphiboles and rim of plagioclases, respectively. All of the analyzed biotites in the Miocene-Pliocene volcanic rocks in the east of Kamu are of Mg-biotite. According to a widespread classification of micas to 6 general end-members, biotites of interest are averagely composed of 55.45% phlogopite, 15.90% talc, 12.72% Ti-phlogopite, 11.44% eastonite, 3.71% ferri-eastonite and 0.78% muscovite. Chemical composition of biotites indicates a calk-alkaline magmatic series for the magma from which biotites are crystallized. Estimation of the oxygen fugacity of magma, based on chemical composition and Fe3+ content of biotite, shows that the oxygen fugacity was limited to FMQ buffer in quality and was about 10-15 bar in quantity. This value accords the oxygen fugacity for intermediate-acidic volcanic rocks.

  18. The geological processes time scale of the Ingozersky block TTG complex (Kola Peninsula) (United States)

    Nitkina, Elena


    Ingozersky block located in the Tersky Terrane of the Kola Peninsula is composed of Archean gneisses and granitoids [1; 5; 8]. The Archaean basement complexes on the regional geological maps have called tonalite-trondemit-gneisses (TTG) complexes [6]. In the previous studies [1; 3; 4; 5; 7] within Ingozersky block the following types of rocks were established: biotite, biotite-amphibole, amphibole-biotite gneisses, granites, granodiorites and pegmatites [2]. In the rocks of the complex following corresponding sequence of endogenous processes observed (based on [5]): stage 1 - the biotitic gneisses formation; 2 - the introduction of dikes of basic rocks; 3 phase - deformation and foliation; 4 stage - implementation bodies of granite and migmatization; 5 stage - implementation of large pegmatite bodies; stage 6 - the formation of differently pegmatite and granite veins of low power, with and without garnet; stage 7 - quartz veins. Previous U-Pb isotopic dating of the samples was done for biotite gneisses, amphibole-biotite gneisses and biotite-amphibole gneisses. Thus, some Sm-Nd TDM ages are 3613 Ma - biotite gnesses, 2596 Ma - amphibole-biotite gnesses and 3493 Ma biotite-amphibole gneisses.. U-Pb ages of the metamorphism processes in the TTG complex are obtained: 2697±9 Ma - for the biotite gneiss, 2725±2 and 2667±7 Ma - for the amphibole-biotite gneisses, and 2727±5 Ma for the biotite-amphibole gneisses. The age defined for the biotite gneisses by using single zircon dating to be about 3149±46 Ma corresponds to the time of the gneisses protolith formation. The purpose of these studies is the age establishing of granite and pegmatite bodies emplacement and finding a geological processes time scale of the Ingozerskom block. Preliminary U-Pb isotopic dating of zircon and other accessory minerals were held for granites - 2615±8 Ma, migmatites - 2549±30 Ma and veined granites - 1644±7 Ma. As a result of the isotope U-Pb dating of the different Ingozerskogo TTG

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

    Jirsa, M.A.; Miller, J.D.; Morey, G.B.


    The Biwabik Iron Formation is a ???1.9 billion year-old sequence of iron-rich sedimentary rocks that was metamorphosed at its eastern-most extent by ???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. ?? 2007 Elsevier Inc. All rights reserved.

  20. 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)

    Zimbres, E.; Kawashita, K.; Van Schmus, W.R.


    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)

  1. Pleural mesothelioma and lung cancer risks in relation to occupational history and asbestos lung burden (United States)

    Gilham, Clare; Rake, Christine; Burdett, Garry; Nicholson, Andrew G; Davison, Leslie; Franchini, Angelo; Carpenter, James; Hodgson, John; Darnton, Andrew; Peto, Julian


    Background We have conducted a population-based study of pleural mesothelioma patients with occupational histories and measured asbestos lung burdens in occupationally exposed workers and in the general population. The relationship between lung burden and risk, particularly at environmental exposure levels, will enable future mesothelioma rates in people born after 1965 who never installed asbestos to be predicted from their asbestos lung burdens. Methods Following personal interview asbestos fibres longer than 5 µm were counted by transmission electron microscopy in lung samples obtained from 133 patients with mesothelioma and 262 patients with lung cancer. ORs for mesothelioma were converted to lifetime risks. Results Lifetime mesothelioma risk is approximately 0.02% per 1000 amphibole fibres per gram of dry lung tissue over a more than 100-fold range, from 1 to 4 in the most heavily exposed building workers to less than 1 in 500 in most of the population. The asbestos fibres counted were amosite (75%), crocidolite (18%), other amphiboles (5%) and chrysotile (2%). Conclusions The approximate linearity of the dose–response together with lung burden measurements in younger people will provide reasonably reliable predictions of future mesothelioma rates in those born since 1965 whose risks cannot yet be seen in national rates. Burdens in those born more recently will indicate the continuing occupational and environmental hazards under current asbestos control regulations. Our results confirm the major contribution of amosite to UK mesothelioma incidence and the substantial contribution of non-occupational exposure, particularly in women. PMID:26715106

  2. Well log responses in metamorphic rocks near Maribor

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    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.

  3. Water contents of clinopyroxenes from sub-arc mantle peridotites (United States)

    Turner, Michael; Turner, Simon; Blatter, Dawnika; Maury, Rene; Perfit, Michael; Yogodzinski, Gene


    One poorly constrained reservoir of the Earth's water budget is that of clinopyroxene in metasomatised, mantle peridotites. This study presents reconnaissance Sensitive High-Resolution, Ion Microprobe–Stable Isotope (SHRIMP–SI) determinations of the H2O contents of (dominantly) clinopyroxenes in rare mantle xenoliths from four different subduction zones, i.e. Mexico, Kamchatka, Philippines, and New Britain (Tabar-Feni island chain) as well as one intra-plate setting (western Victoria). All of the sub-arc xenoliths have been metasomatised and carry strong arc trace element signatures. Average measured H2O contents of the pyroxenes range from 70 ppm to 510 ppm whereas calculated bulk H2O contents range from 88 ppm to 3 737 ppm if the variable presence of amphibole is taken into account. In contrast, the intra-plate, continental mantle xenolith from western Victoria has higher water contents (3 447 ppm) but was metasomatised by alkali and/or carbonatitic melts and does not carry a subduction-related signature. Material similar to the sub-arc peridotites can either be accreted to the base of the lithosphere or potentially be transported by convection deeper into the mantle where it will lose water due to amphibole breakdown.

  4. Mesothelioma and other lung disease in taconite miners; the uncertain role of non-asbestiform EMP. (United States)

    Mandel, Jeffrey H; Odo, Nnaemeka U


    The purpose of this paper was to assess the role of non-asbestiform amphibole EMPs in the etiology of mesotheliomas and other lung disease in taconite (iron ore) miners. Increased mesothelioma rates have been described in Minnesota taconite workers since the late 1990s. Currently, over 100 cases have been reported by the Minnesota Department of Health within the complete cohort of miners in Minnesota. Geologic sampling has indicated that only the eastern part of the iron range contains non-asbestiform amphibole elongate mineral particles (EMPs), in close proximity to the ore. This type of EMP has been less studied and also exists in talc and gold mining. A series of investigations into the state's taconite industry have been recently completed. Results from a cohort mortality study indicated an SMR of 2.77 (95% CI = 1.87-3.96) for mesothelioma. In a case-control study, the odds ratio for mesothelioma for high vs. low EMP exposure was 2.25 (5% CI = 1.13-4.5) but EMPs in this study were counted by phase contrast microscopy. Odds ratios were not elevated in mines located in the eastern part of the Mesabi iron range. The overall findings suggest that mesothelioma in taconite miners is related to EMP exposure. Because of the way EMPs were counted, results from these studies cannot allow a firm conclusion about the association between EMP exposure and the reported excess mesothelioma. Copyright © 2018 Elsevier Inc. All rights reserved.

  5. New insights into the origin of the bimodal volcanism in the middle Okinawa Trough: not a basalt-rhyolite differentiation process (United States)

    Zhang, Yuxiang; Zeng, Zhigang; Chen, Shuai; Wang, Xiaoyuan; Yin, Xuebo


    In the middle Okinawa Trough (MOT), rhyolites have been typically considered as products of crystallization differentiation of basaltic magma as a feature of bimodal volcanism. However, the evidence is insufficient. This paper compared chemical trends of volcanic rocks from the MOT with fractional crystallization simulation models and experimental results and utilized trace element modeling combined with Rayleigh fractionation calculations to re-examine fractional crystallization processes in generating rhyolites. Both qualitative and quantitative studies indicate that andesites, rather than rhyolites, originate by fractional crystallization from basalts in the MOT. Furthermore, we established two batch-melting models for the MOT rhyolites and proposed that type 1 rhyolites are produced by remelting of andesites with amphiboles in the residue, while type 2 rhyolites are derived from remelting of andesites without residual amphiboles. It is difficult to produce melts with a SiO2 content ranging from 62% to 68% either by magmatic differentiation from basalts or by remelting of andesites, and this difficulty might help account for the compositional gap (Daly gap) for bimodal volcanism in the Okinawa Trough.

  6. Evidence from Volatiles and Trace Elements for Continental Mantle in the Source of Gakkel Ridge MORB (United States)

    Michael, P. J.; Langmuir, C.; Goldstein, S. L.; Graham, D. W.; Ionov, D. A.; Matzen, A. K.


    Along Gakkel ridge, the Western Volcanic Zone [WVZ: 8° W 3°E] has several elongate robust volcanic highs with no offsets. A Sparsely Magmatic Zone [SMZ: 3°E -29°E] extends from a sharp boundary at 3°E where the axis abruptly becomes 1000 m deeper and only peridotites are exposed on the axial valley floor for 120 km, and there is sparse volcanism for 250km. The Eastern Volcanic Zone [EVZ: 29°E -85°E] has localized volcanic centers separated by lengthy sections of tectonized seafloor [1]. A remarkable transition in the composition of the Arctic mantle coincides closely with the bathymetric boundary at 3°E. All MORB from the WVZ are enriched in Ba and H2O at a given level of mantle enrichment (i.e., at constant La/Sm) compared to MORB globally and from the EVZ. H2O/Ce and Ba/Nb remain high to the southwest along the WVZ, through Knipovich and Jan Mayen Ridges and possibly south of Iceland [2], suggesting a large, regional anomaly. WVZ and EVZ lavas have distinct isotopic compositions, with the WVZ displaying a "DUPAL-like" signature that is absent in the EVZ [3]. H2O/Ce and Ba/Nb decline to Pacific-like values to the east, but the transition for trace element and volatile ratios is not as sharp as for isotopic ratios: H2O/Ce, Ba/La and Ba/Nb remain somewhat elevated to 25°E along Gakkel Ridge. The WVZ's distinctive composition may arise from incorporation of subcontinental lithospheric mantle (SCLM) [3] that was stranded during recent continental breakup in this region [4]. Phlogopite and amphibole that were residual after small extents of melting to make alkali basalts could account for elevated Ba [3]. We show here that this hypothesis is viable by examining ratios of H2O, K2O, Ba, Rb, REE, Cl and F in basalts from Gakkel Ridge and comparing them with amphibole and phlogopite from mantle xenoliths from Spitsbergen [5]. High H2O/K2O ratios in WVZ basalts indicate that amphibole is present in the WVZ source: up to 0.7% modal at 8°W, diminishing to the east

  7. Magma storage conditions of historic Plinian eruptions of Volcán de Colima, México (United States)

    Macias, J.; Arce, J.; Sosa, G.; Gardner, J. E.; Saucedo, R.


    Volcán de Colima has a historical record with major explosive eruptions occurring every ~100 years (1606, 1690, 1818, and 1913) followed by intra-Plinian effusive activity. The 1818 and 1913 Plinian eruptions erupted andesitic magmas (Pl > Opx > Cpx >> Hbl + Fe-Ti oxides + Ap and rare resorbed Ol) with homogeneous bulk compositions (1913; 58.3 × 0.5 wt.% SiO2, 1818; 58.9 × 0.2 wt.% SiO2; Saucedo et al., 2010). Instead, intra-Plinian magmas are devoid of hornblende and have compositions of 59-61 wt. % in silica (Savov et al., 2008). Pre-eruptive temperatures of oxide Fe-Ti pairs in 1818 and 1913 products yielded temperatures of 830×20°C colder than intra-Plinian magmas usually >970°C (Luhr et al., 2002) depending on the mineral phase analyzed. Amphibole in 1818 and 1913 products consists of two populations: a) large xenocrysts, with plag-px-Fe-Ti oxide rims with equilibrium pressures and temperatures of 380 MPa and 950 °C (Ridolfi et al., 2010), and b) microphenocryst with equilibrium pressures and temperatures of 190-280 MPa and 870-910 °C, respectively. Some phenocrysts in the 1818 magma have a high pressure core overgrowth by a low pressure rim. In order to understand the storage conditions of Colima explosive magmas we carried out a set of hydrothermal experiments with a 1818 pumice sample. Experiments were water oversaturated and close to the oxygen fugacity of the NNO buffer. Experiments show that amphibole is stable at pressures greater than 75 MPa at 850°C, and greater than 100 MPa at 925°C. For the same range of temperature, plagioclase is stable at pressures below ~210 MPa and 100 MPa, respectively. Experimental plagioclase and experimental glass were analyzed and compared to those from the natural sample, yielding an approximate storage pressure of 210 MPa. This pressure is confirmed by the chemical equilibrium of microphenocrystic amphibole of the natural sample. Given the nearly equivalent composition of the most recent Plinain magmas is

  8. Interplay between deformation, fluid release and migration across a nascent subduction interface: evidence from Oman-UAE and implications for warm subduction zones (United States)

    Agard, Philippe; Prigent, Cécile; Soret, Mathieu; Guillot, Stéphane; Dubacq, Benoît


    Frozen-in subduction plate interfaces preserving the first 1-2 My of the subduction history are found beneath ophiolites. These contacts are a key target to study the inception of mantle wedge metasomatism and the mechanical coupling between the upper plate and the top part of the sinking slab shortly after subduction initiation. Combining structural field and EBSD data, detailed petrology, thermodynamic modelling and geochemistry on both sides, i.e. the base of the mantle wedge (Oman-UAE basal peridotites) and the underlying accreted crustal fragments from the subducting slab (metamorphic soles), this study documents the continuous evolution of the plate contact from 1 GPa 900-750°C to 0.6 GPa 750-600°C, with emphasis on strain localization and feedbacks between deformation and fluid migration. In the mantle wedge, the (de)formation of proto-ultramylonitic peridotites is coeval with mantle metasomatism by focused hydrous fluid migration. Peridotite metasomatism results in the precipitation of new minerals (clinopyroxene, amphibole and spinel ± olivine and orthopyroxene) and their enrichment in FMEs (particularly B, Li and Cs, with concentrations up to 40 times that of the PM). Boron concentrations and isotopes (δ11B of metasomatized peridotites up to +25‰) suggest that these fluids with a "subduction signature" are probably sourced from the dehydrating amphibolitic metamorphic sole. Concomitantly, deformation in the lower plate results in the stepwise formation, detachment and accretion to the mylonitic s.l. mantle of successive slices of HT metabasalts from the downgoing slab, equilibrated at amphibolite/granulite conditions (900-750°C). Two major stages may be outlined: - between 900 and 750°C, the garnet-clinopyroxene-amphibole bearing sinking crust (with melting < 6 vol%) gets juxtaposed and mechanically coupled to the mantle, leading to the transfer of subduction fluids and metasomatism (possibly into the arc zone ultimately). Deformation is

  9. Geochemistry of Giuncana eclogite, North Sardinia (Italy) and comparison with coeval Sardinian eclogites (United States)

    Franceschelli, Marcello; Cruciani, Gabriele; Langone, Antonio; Scodina, Massimo; Puxeddu, Mariano


    The Giuncana eclogites are massive to poorly foliated, medium-to fine-grained rocks. The eclogites are embedded within Grt + St + Ky-bearing micaschist and paragneisses. Based on microstructural relationships and mineral assemblages, four stages of mineralogical re-equilibration have been distinguished in the Giuncana retrogressed eclogites. The stage I is characterized by the occurrence of omphacite enclosed in garnet porphyroblasts along with rutile, epidote, quartz, pargasitic amphibole and plagioclase. The stage II is defined by the breakdown of omphacite and formation of two types of symplectitic microstructures: (i) amphibole + quartz symplectite, and (ii) clinopyroxene + plagioclase ± amphibole symplectite. The stage III is documented by the widespread formation of amphibole as zoned porphyroblasts in the matrix, or as corona-type microstructure around garnet. The stage IV is characterized by the growth of actinolite at the rim of matrix amphibole, and by the growth of albite, chlorite, and epidote in the matrix. LA-ICP-MS U-Pb zircon data on retrogressed eclogites sampled in the Giuncana locality from the Sardinian Medium Grade Metamorphic Complex yielded a weighted average age of 454 ± 6 Ma, in agreement with U-Pb zircon ages of 453-460 Ma obtained on eclogites from the High Grade Metamorphic Complex. The Giuncana eclogites are very similar to the other well known Sardinian eclogites. Taken as a whole the Ordovician eclogites from N Sardinia mostly plot in the fields of back-arc basins and continental flood basalts and near the boundary between basaltic andesites and subalkaline basalts. All the Sardinian eclogites show positive anomalies of K, Rb, Ba, U and Pb and negative anomalies of Nb, La, Ce and Sr. Th is depleted in the Giuncana eclogites and enriched in the Punta de li Tulchi and Punta Tittinosu eclogites. All these data reveal a clear crustal contamination of the Sardinian Ordovician mantle. Downgrading LREE and flat HREE patterns typical of N

  10. Magma-mixing in the genesis of Hercynian calc-alkaline granitoids: an integrated petrographic and geochemical study of the Sázava intrusion, Central Bohemian Pluton, Czech Republic (United States)

    Janoušek, Vojtěch; Braithwaite, Colin J. R.; Bowes, D. R.; Gerdes, Axel


    The Devonian-early Carboniferous (354.1±3.5 Ma: conventional zircon U-Pb age) Sázava intrusion (biotite-amphibole quartz diorite, tonalite and granodiorite) of the Central Bohemian Pluton (CBP) associated with bodies of (olivine, pyroxene-) amphibole gabbro, gabbrodiorite, (quartz) diorite and rare hornblendite, gives an opportunity for a comparative study of a rather shallow, calc-alkaline magma-mixing zone at two levels, separated by a vertical difference of approximately 1 km. The deeper section (Příbram) displays the direct evidence for the existence of a long-lived, periodically tapped and replenished, floored magma chamber (MASLI). The contacts between the subhorizontal sheet-like basic bodies and the surrounding, commonly cumulus-rich, Sázava granitoid, are arcuate, and cut by a series of veins and ascending pipes. Shallow-dipping swarms of strongly elongated and flow-aligned mafic microgranular enclaves (MME), concordant with the contacts of the basic bodies, are commonplace. The higher level (Teletín) section shows relatively independent basic intrusions, some of them distinctly hybrid in character and mainly of quartz dioritic composition, surrounded by relatively homogeneous, nearly cumulus-free Sázava tonalite rich in texturally variable MME. Larger quartz microdiorite bodies and the MME, both interpreted as hybrids, contain varying proportions of highly heterogeneous plagioclase megacrysts with complex zoning, particularly well shown by cathodoluminescence (CL). Most often the megacrysts have cores of labradorite-anorthite, partly resorbed and overgrown by andesine rims but some are strongly brecciated and fragments have been annealed by rim growth. Also characteristic are long prisms of apatite, oikocrysts of quartz and K-feldspar and zoned amphibole. The latter has brown pargasite and magnesiohastingsite cores, resorbed and overgrown by magnesiohornblende, compositionally similar to the amphibole in the Sázava tonalite. The brown cores are

  11. 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

  12. Emplacement processes of tuffaceous sandstones at IODP Site C0011B, Nankai Trough, derived from modal analysis (United States)

    Schindlbeck, J. C.; Kutterolf, S.; Freundt, A.


    Tuffaceous sandstones are characterized by their high amount (25 to 75%) of pyroclasts in their modal composition. During IODP Expedition 322 three interbeds of tuffaceous sandstones have been found within a moderately lithified and bioturbated silty claystone sequence in the late Miocene (>7.07 to ~9.0 Ma) upper part of the middle Shikoku Basin facies. Of the three sandstones, units 1 and 2 are single beds whereas unit 3 is composed of three beds. Modal analyses of 29 sandstone thin sections reveal systematic vertical changes within each bed. Generally low-density pyroclasts are enriched at the top (50-60 vol%) of each sandstone bed whereas dense lithic components (25-30 vol%) and minerals (25-30 vol%) are enriched at the bottom. The vertically varying abundance of various types of lithic fragments (sedimentary, volcanoclastic and metamorphic) suggests that these have also been segregated according to their respective densities. The highest amount of fine-grained matrix glass is found in the middle of each bed. Pumice and lithic fragments in the middle and upper parts of the sandstone beds carry ash coatings. For sandstone package 3, in contrast to 1 and 2, core pictures and thin section analyses indicate a subdivision in three units showing the same significant variations in top to bottom enrichment. This suggests three sedimentation events following each other in short time intervals. Glass and mineral chemistry of each sandstone bed show no significant vertical variations. Specifically the matrix glass-shard major element compositions are identical to the pumice clast composition in each tuffaceous sandstone bed. The compositions of amphibole and pyroxene crystals differ only slightly between the sandstone packages. Application of the Ridolfi et al. (2009) thermobarometric calculations to amphiboles of sandstone packages 1 and 2 suggests that each of these was derived from a volcanic system comprising both a deep and a shallow magma reservoir. Thickness and

  13. Petrology and Geochemistry of an Upper Crustal Mafic Complex- Hidden Lakes, Sierra Nevada Batholith, California (United States)

    Lewis, M.; Bucholz, C. E.; Jagoutz, O. E.; Eddy, M. P.


    Magmatic differentiation in arc settings is likely a polybaric process, with crystallization of primitive basalts occurring primarily in the lower crust and more evolved melts in the upper crust. The general lack of mafic-ultramafic cumulates in the silicic paleo-arc upper crust supports this model. However, the Sierra Nevada Batholith preserves numerous mafic intrusions up to 25 km2, suggesting that significant volumes of mafic magma may differentiate at shallow crustal levels. Previous studies on several such intrusions report ages contemporaneous with Cretaceous batholith emplacement (Coleman et al., 1995), but only a few have investigated their chemistry and relationship to arc magmatism (Frost, 1987; Frost & Mahood, 1987; Sisson et al., 1996). We present field observations, petrography, mineral chemistry, and bulk rock compositional data for the Hidden Lakes Mafic Complex (HLMC), located in the Central Sierra Nevada Batholith. Preliminary CA-ID-TIMS U-Pb zircon ages constrain crystallization between 90 and 95 Ma, slightly older than the surrounding Cretaceous felsic plutons (89-90 Ma) and younger than adjacent Jurassic granodiorites (172 Ma). This 2.2 km2 complex consists of biotite+amphibole gabbros through qtz-monzonites, in gradational contact, and contains local pods of biotite- and amphibole-bearing olivine-orthopyroxenites and gabbronorites. Mineral compositions and field relations suggest that these lithologies were derived from a common crystallization sequence. The most primitive olivine-pyroxenite contains olivine and orthopyroxene in equilibrium with a melt with Mg# 54. Subsequent crystallization over a temperature range of 1025 to 700°C produced more evolved lithologies up to qtz-monzonites. Al-in-hornblende calculations for HLMC qtz-monzonites indicate a crystallization depth of 9-10 km, well into the upper crust. The early crystallization of amphibole requires a parental basalt with >6 wt% H2O, which may have enabled it to ascend into the upper

  14. Tectonic origin and deformation process of the Mayer Kangri medium-high pressure metamorphic dome in Central Qiangtang of Tibet (United States)

    Wang, Y.; Liang, X.


    The metamorphic characteristics, deformation process, geochronology of the medium-high pressure metamorphic rocks in blueschist bearing Central Qiangtang Metamorphic belt (CQMB) of Tibet were less well constrained. It is, however, commonly assumed that these rock slices in the margin also contain important implications on the evolution of the entire metamorphic belt. The well-exposed Mayer Kangri medium-high pressure metamorphic dome in north flank of the CQMB provides an unique opportunity to investigate the outer part of the CQMB, which could facilitate the study on the subduction-exhumation-post orogenic scenarios of the Triassic accretionary orogeny in Central Qiangtang. Field structural analyses indicate the Mayer Kangri metamorphic dome are bounded by low-angle normal faults (LANF) within the hanging wall of low-green schist facies mélange. It majorly consists of epidote-amphibolites, quartz-phengite schist, epidote-albite schist. The outcrop and micro structural observations of footwall metamorphic rocks show an open anticline with multiple foliation replacement, which largely differentiate themselves from the dextral strike-slip shearing of the hanging wall. Well-zoned amphiboles were found within the epidote-amphibolite after micro-structural observations and electron probe microanalyses (EPMA), which indicate that the amphibole zonation demonstrates a Hastingsite core, a Ferro-actinolite mantle and a Ferro-winchite rim in most cases. The mean temperature and pressure estimates of the zoned amphibolites change from 544 °, 0.98Gpa in the core, to 426°, 0.34Gpa in the mantle, and to ca.364° and 0.70 GPa in the rim. The detailed analyses on the stepwise-heating Ar-Ar results of the zoned amphiboles provide good constrains on the episodic deformation process of the CQMB. For Hast-cores, we obtained near plateau ages of 242.4-241.2 Ma, indicating the onset of the oceanic subduction is earlier than the Anisian stage of Middle Triassic. The subsequent

  15. Garnet - two pyroxene rock from the Gridino complex, Russia: a record of the early metasomatic stage (United States)

    Morgunova, Alena A.; Perchuk, Alexei L.


    The Gridino complex is one of the oldest high pressure complexes on the Earth. The most spectacular exposures occur in islands and in a 10-50 m wide belt along the shore of the White Sea in the Gridino area. The exotic blocks show wide range of compositions. In addition to predominating amphibolites and eclogites, there are also peridotites, zoisitites and sapphirine-bearing rocks. The peridotites are represented by garnet - two pyroxene rocks and orthopyroxenites. It this paper we present an intriguing results of the petrological study of the garnet- two pyroxene rock. The garnet- two pyroxene rock considered occurs as elliptical body 4×6 m in size within amphibole-biotite gneiss in the island Visokii. The rock consists of mosaic of coarse-grained primary garnet, clinopyroxene and orthopyroxene. Accessories are represented by magnetite, ilmenite, pyrite and zircon. Garnet contains inclusions of clinopyroxene, Mg-calcite and chlorite. The chlorite inclusions always intergrow with dendritic mineral enriched in REE (mainly Ce) situated on the wall of vacuole which shows the tendency of negative crystal shape. Similar chlorite inclusions are hosted by clino- and orthopyroxenes. The chlorite is of diabantite composition. The inclusions are often surrounded by the two systems of cracks - radial and concentric, which is really exotic phenomenon for crystalline rock. The primary minerals experienced different degree of the retrograde alteration expressed as amphibolization and/or growth of the orthopyroxene-amphibole-garnet symplectites. The retrogression is patchy in the central part of garnet- two pyroxene body, but intensifies towards the rims where primary minerals are absent. Mineral thermobarometry reveals HP rock equilibration at 670-750 оС and 14-20 kbar followed by subisothermal decompression down to 640-740 оС and 6-14 kbar. Specific composition of the chlorite and its association with REE phase in all rock-forming minerals suggests that anhydrous HP

  16. 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.

  17. Inclusions in Minerals: the Importance of Host Mineral Composition, Pressure and Temperature for Potential Inclusion Alteration (United States)

    Marquardt, K.; Markl, G.


    Inclusions in minerals are used to decipher details of the host mineral/rock history. They frequently originate from the time of mineral formation; be it diamond, garnet or `common' feldspar. Thus protected they survive changing pressure and temperature for different durations compared to their non-enclosed counterparts. Inclusions may (partially) equilibrate at a later point in history, and thus provide complementary information on past processes and alteration pathways less commonly discussed. The study investigates partially altered pyroxene inclusions in feldspars indicative of high-p-T fluid transport during granulite facies metamorphism in charnockites from the Lofoten Islands in Northern Norway. The protoliths formed about 1750 Ma ago, at about 800 - 900°C and 4 kbar. During crustal thickening, they reached high-pressure granulite-facies conditions of about 8-11 kbar at 700°C (1). While this event caused large magmatic pyroxenes to react with an infiltrating fluid to form corona textures of amphibole; pyroxenes inside feldspars behaved very differently. Pyroxenes enclosed in orthoclase-rich feldspar were partially hydrated to amphiboles. Contrastingly, feldspar with lower orthoclase content protected the magmatic pyroxenes efficiently. Transport and transformation mechanisms recorded in these µm to nm textures were studied by EMPA and TEM. Focused Ion Beam (FIB) prepared TEM-foils revealed that pyroxenes, when spatially connected to albite exsolution lamellae, show dissolution features. Based on composition, nanostructures and the known p-T-history, we propose the following succession of events. Ternary feldspar containing small magmatic pyroxenes began to exsolve between about 800 and 700°C. The exsolution changed from coherent to incoherent and a fluid infiltrated the feldspar accompanied by a formation of nanotunnels. Gradually the tunnels grew larger so that finally whole film perthites acted as pathways. When the fluid had access to pyroxene

  18. Hydrated Spinel Websterite Xenoliths From Moses Rock Diatreme, Navajo Volcanic Field: Metasomatism in the Mantle Wedge of the Colorado Plateau Above the De-watering Farallon Plate (United States)

    Schulze, D. J.; Chow, R.; Helmstaedt, H. H.


    Expansion and density decrease in ultramafic rocks in the mantle wedge above the subducted and dewatering Farallon Plate in the Cenozoic may have been the driving force behind uplift of the Colorado Plateau. Here we document the effects of such hydration on spinel websterites that resulted in rocks dominated by pargasitic amphibole, Mg-chlorite and Cr-magnetite/chromite. Xenoliths of spinel websterite from the Moses Rock diatreme in the Navajo Volcanic Field on the Colorado Plateau have granoblastic to mosaic porphyroclastic texture. Porphyroclasts (up to 2 cm across) of lamellar intergrowths of clinopyroxene and orthopyroxene are set in a granular matrix of sub-equal amounts of the two pyroxenes. Both pyroxenes are magnesian and aluminous, with Mg/(Mg+Fe) in the range 0.89 to 0.93 and Al2O3 contents of approximately 4.0 to 9.5 wt%. Many samples contain aluminous spinel with Al/(Al+Cr) = 0.82 to 0.94. The effects of hydration on these samples exist as partial to complete replacement of the pyroxenes by amphibole (tremolite/edenite/pargasite/magnesio-hornblende), pseudomorphing original pyroxene textures, and replacement of primary spinel by Cr-rich magnetite or chromite with Al/(Al+Cr) = 0.07 to 0.35 intergrown with, and surrounded by, clinochlore. Unusual minerals associated with replacement of primary spinel include one example with corundum + zoisite, one with secondary garnet (molar Ca:Mg:Fe = 20:40:40) and two samples with aluminous talc (5 to 7 wt% Al2O3). By analogy with Alpine peridotites and mantle xenolith suites from basalt occurrences, the spinel websterites probably existed as veins and lenses in spinel peridotite of the shallow upper mantle beneath the Colorado Plateau prior to hydration. De-watering of the subducted Farallon Plate in Cenozoic time was likely the source of water-rich fluids that caused the hydration at fairly shallow depths (within amphibole stability), as suggested for hydration of spinel peridotite xenoliths from the Buell Park and

  19. Geochemistry of the Topuk Pluton associated with the Kozbudaklar W-skarn deposit (Western Anatolia, Turkey): Implication for crystallization conditions (United States)

    Orhan, Ayşe; Demirbilek, Mehmet; Mutlu, Halim


    The Kozbudaklar scheelite-bearing skarn deposit in the Tavşanlı Zone, western Turkey, occurs at the contact between Eocene Topuk pluton and Triassic İnönü marble of calcic character. The Topuk pluton is medium-coarse grained, granodiorite in composition and has a hypidiomorphic equigranular texture. The host rock contains mafic microgranular enclaves (MME) of monzodiorite-monzogabbro composition and is interrupted by porphyritic granodiorite and granite-aplite vein rocks. The pluton is calk-alkaline, metaluminous and composed of I-type melt character. δ18O and δD compositions of silicate minerals from granodioritic host rock are 5.9-10.6‰ and -77.0 to -71.4‰ and conformable with the range of unaltered I-type granites. Trace element contents indicate that pluton is crystallized from mantle-derived magma interacted with continental crust in a volcanic arc or subduction related setting. Major and trace element concentrations of Topuk pluton are quite consistent with geochemical patterns of Cu-skarn granitoids. Results of mineral chemistry analysis of the pluton yield that plagioclases are of oligoclase-andesine, amphiboles are of magnesio-hornblende and biotites are of ferro-magnesian composition. Amphiboles and biotites of granodioritic host rock are represented by calc-alkaline, I-type melt composition evolved in a subduction environment. Based on the results of plagioclase-Al in hornblende and amphibole chemistry data from the pluton, two different stages are proposed for the magma crystallization. The first stage was developed in a relatively deeper environment (>15 km) under high pressure (>4 kbar) and low log ƒO2 (>-17.6) conditions which reflect fractional crystallization and magma-mixing depth of basaltic magma and these conditions are not correlated with scheelite mineralization. The second crystallization stage of magma which proceeded at shallow depths (-12.9 to -11.0) values are accompanied by high H2O contents (5.39-6.88 wt.%). High water

  20. Geochemical characterization of mid-distal Nisyros tephra on Datça peninsula (southwestern Anatolia) (United States)

    Gençalioğlu-Kuşcu, Gonca; Uslular, Göksu


    We present new distal records of tephra deposits that overly the Kos ignimbrite in seven locations of Datça peninsula. Tephra in one of these locations were previously associated with Nisyros Kyra sub-unit based only on the field characteristics. We use different proxies such as field observations, petrography, mineral, glass, and whole-rock chemistry in order to characterize and correlate the previously and recently identified pumice fall deposits on Datça. The total thickness of the fall deposit reaches to 3.5 m. The size of the pumice clasts is generally within the range of lapilli, and they have vitrophyric texture consisting mainly of plagioclase (andesine to labradorite) with scarce clinopyroxene (diopside to augite), olivine (Fo48-50), amphibole (magnesio-hastingsite), and biotite crystals. Amphibole is a ubiquitous phenocryst in all Datça tephra units and used as a criterion for the correlation. Glass major element analyses by EMPA reveal two different groups with andesitic and dacitic compositions. Difference in silica content (up to ca. 4 wt%) detected in the same specimen also designates the heterogeneity in pumice glass. This heterogeneity in glass composition is also supported by the frequent occurrence of banded pumice clasts in Datça tephra. Whole-rock composition of the pumice is mainly andesitic with calc-alkaline affinity. Multi-element patterns on primitive-mantle normalized diagram display typical arc-magmatism signature (i.e. depletion in Nb, Ta, Ti, and P). In order to check and eliminate the potential alternatives, we compared the distal deposits on Datça not only with Kyra, but also with other Nisyros tephra units. Yet, Kyra is the only unit that has comparable depositional characteristics, calcic amphibole crystals, andesitic-dacitic glass and whole-rock chemistry, and distal tephra deposits on neighboring islands (Tilos and Chalki). Therefore, we associate Datça tephra deposits with some proximal Kyra subunits of intermediate

  1. Geochronology, geochemical and Sr-Nd-Hf-Pb isotopic compositions of the granitoids in the Yemaquan orefield, East Kunlun orogenic belt, northern Qinghai-Tibet Plateau: Implications for magmatic fractional crystallization and sub-solidus hydrothermal alteration (United States)

    Yin, Shuo; Ma, Changqian; Xu, Jiannan


    A general consensus has emerged that high field strength elements (HFSE) can mobile to some extent in a hydrothermal fluid. However, there are hot debates on whether sub-solidus hydrothermal alteration can lower the Nb/Ta ratio in evolved melts. In this study, we present petrography, geochronology and geochemistry of the barren and mineralized rocks in the Yemaquan skarn iron deposit, northern Qinghai-Tibet Plateau, to probe magmatic-hydrothermal transition. The barren rocks consist of diorites, granodiorites, granites and syenogranites, whereas the porphyritic granodiorites are associated with mineralization for an excellent consistency between the magmatic zircon U-Pb age (225 ± 2 Ma) and the hydrothermal phlogopite 40Ar-39Ar age (225 ± 1.5 Ma). The Sr-Nd-Hf-Pb isotopic data demonstrate that the Yemaquan granitoids are originated from a relatively homogenous enriched mantle with different degrees of crust contamination (assimilation fractional crystallization, AFC). Trace elements signatures indicate that the porphyritic granodiorites related to mineralization display amphibole crystallization for high water contents, whereas the barren granites have gone through biotite crystallization due to potassium enrichment by continuous upper crust contamination, both of which are responsible for their Nb/Ta ratios, respectively. Modeling results suggest that a basaltic melt with Nb/Ta ratio of 15.3 can reach a minimum Nb/Ta ratio of 12 in the producing granodioritic melt by amphibole fractional crystallization based on partition coefficients of Nb and Ta between amphibole and melts from previous experiments. This may explain the average Nb/Ta ratio (13.7) of the barren granodiorites, while it cannot account for the average Nb/Ta ratio (8.4) of the mineralized porphyritic granodiorites, and it is even lower than that of the granites (10.3) with biotite fractional crystallization. Exsolution of a magmatic-hydrothermal fluid is inevitable when a water saturated magma

  2. 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.

  3. Variation in Volatile and Ore Metal Abundances Along the New Zealand Volcanic Arc as Recorded by Minerals and Melt Inclusions (United States)

    Rowe, M. C.; Iveson, A. A.; Norling, B.; Chambefort, I. S.; Webster, J. D.


    Volatile and ore metals within magmas record a wide variety of magmatic processes in the Earth's shallow upper crust. These elements have previously been linked to volatile degassing or exsolution and such processes as eruption triggering and the formation of magmatic ore deposits. However, it is unknown why different volcanoes, or different eruptions of the same volcano, record such wide-ranging geochemical behaviour. More fundamental questions related to the source of these metals also remain unanswered, such as what role (if any) does subduction play in controlling metal fluctuations. In an effort to ascertain the sources of volatile and ore metal variation in intermediate-silicic magmas, this study attempts to take a more comprehensive look at the causes of volatile and ore metal variation in arc magmas as a function of composition and location within a single arc system. This study focuses on the New Zealand arc system, stretching from Mt Taranaki to White Island, examining volatile and trace metals (including Li, Cu, As, Mo, Sb, Sn, W, and Tl) from varying phenocryst phases and melt inclusions. Melt inclusion compositions range from basaltic (51 wt% SiO2) to high-Si rhyolite (81 wt% SiO2), however are predominantly andesitic to dacitic. Sulfur and Cl melt compositions are also highly variable, with concentrations from below detection limit up to ~2000 ppm S and 5300 ppm Cl. Trace metal abundances were determined for all major phenocryst phases, including plagioclase, clinopyroxene, orthopyroxene, and amphibole and biotite where available. Comparing trace metal abundances of phenocrysts and inclusions to both glass and crystal major element/volatile compositions allows for a systematic comparison of volcanoes along the arc. Lithium and Cu are the only two trace metals above detection limit in all analysed phases, however, Cu variations are highly variable compared to other ore metals. New experimental crystallisation runs with hydrous dacite also allow us to

  4. Long-term controls on continental-scale bedrock river terrace deposition from integrated clast and heavy mineral assemblage analysis: An example from the lower Orange River, Namibia (United States)

    Nakashole, Albertina N.; Hodgson, David M.; Chapman, Robert J.; Morgan, Dan J.; Jacob, Roger J.


    Establishing relationships between the long-term landscape evolution of drainage basins and the fill of sedimentary basins benefits from analysis of bedrock river terrace deposits. These fragmented detrital archives help to constrain changes in river system character and provenance during sediment transfer from continents (source) to oceans (sink). Thick diamondiferous gravel terrace deposits along the lower Orange River, southern Namibia, provide a rare opportunity to investigate controls on the incision history of a continental-scale bedrock river. Clast assemblage and heavy mineral data from seven localities permit detailed characterisation of the lower Orange River gravel terrace deposits. Two distinct fining-upward gravel terrace deposits are recognised, primarily based on mapped stratigraphic relationships (cross-cutting relationships) and strath and terrace top elevations, and secondarily on the proportion of exotic clasts, referred to as Proto Orange River deposits and Meso Orange River deposits. The older early to middle Miocene Proto Orange River gravels are thick (up to 50 m) and characterised by a dominance of Karoo Supergroup shale and sandstone clasts, whereas the younger Plio-Pleistocene Meso Orange River gravels (6-23 m thick) are characterised by more banded iron formation clasts. Mapping of the downstepping terraces indicates that the Proto gravels were deposited by a higher sinuosity river, and are strongly discordant to the modern Orange River course, whereas the Meso deposits were deposited by a lower sinuosity river. The heavy minerals present in both units comprise magnetite, garnet, amphibole, epidote and ilmenite, with rare titanite and zircon grains. The concentration of amphibole-epidote in the heavy minerals fraction increases from the Proto to the Meso deposits. The decrease in incision depths, recorded by deposit thicknesses above strath terraces, and the differences in clast character (size and roundness) and type between the two

  5. Isotopic and trace element compositions of upper mantle and lower crustal xenoliths, Cima volcanic field, California: Implications for evolution of the subcontinental lithospheric mantle (United States)

    Mukasa, S.B.; Wilshire, H.G.


    Ultramafic and mafic xenoliths from the Cima volcanic field, southern California, provide evidence of episodic modification of the upper mantle and underplating of the crust beneath a portion of the southern Basin and Range province. The upper mantle xenoliths include spinel peridotite and anhydrous and hydrous pyroxenite, some cut by igneous-textured pyroxenite-gabbro veins and dikes and some by veins of amphibole ?? plagioclase. Igneous-textured pyroxenites and gabbros like the dike rocks also occur abundantly as isolated xenoliths inferred to represent underplated crust. Mineral and whole rock trace element compositions among and within the different groups of xenoliths are highly variable, reflecting multiple processes that include magma-mantle wall rock reactions, episodic intrusion and it filtration of basaltic melts of varied sources into the mantle wall rock, and fractionation. Nd, Sr, and Pb isotopic compositions mostly of clinopyroxene and plagioclase mineral separates show distinct differences between mantle xenoliths (??Nd = -5.7 to +3.4; 87Sr/86Sr = 0.7051 - 0.7073; 206Pb/204Pb = 19.045 - 19.195) and the igneous-textured xenoliths (??Nd = +7.7 to +11.7; 87Sr/86Sr = 0.7027 - 0.7036 with one carbonate-affected outlier at 0.7054; and 206Pb/204Pb = 18.751 - 19.068), so that they cannot be related. The igneous-textured pyroxenites and gabbros are similar in their isotopic compositions to the host basaltic rocks, which have ??Nd of+5.1 to +9.3; 87Sr/86Sr of 0.7028 - 0.7050, and 206Pb/204Pb of 18.685 - 21.050. The igneous-textured pyroxenites and gabbros are therefore inferred to be related to the host rocks as earlier cogenetic intrusions in the mantle and in the lower crust. Two samples of peridotite, one modally metasomatized by amphibole and the other by plagioclase, have isotopic compositions intermediate between the igneous-textured xenoliths and the mantle rock, suggesting mixing, but also derivation of the metasomatizing magmas from two separate and

  6. Controls on long-term low explosivity at andesitic arc volcanoes: Insights from Mount Hood, Oregon (United States)

    Koleszar, Alison M.; Kent, Adam J. R.; Wallace, Paul J.; Scott, William E.


    The factors that control the explosivity of silicic volcanoes are critical for hazard assessment, but are often poorly constrained for specific volcanic systems. Mount Hood, Oregon, is a somewhat atypical arc volcano in that it is characterized by a lack of large explosive eruptions over the entire lifetime of the current edifice (~ 500,000 years). Erupted Mount Hood lavas are also compositionally homogeneous, with ~ 95% having SiO2 contents between 58 and 66 wt.%. The last three eruptive periods in particular have produced compositionally homogeneous andesite-dacite lava domes and flows. In this paper we report major element and volatile (H2O, CO2, Cl, S, F) contents of melt inclusions and selected phenocrysts from these three most recent eruptive phases, and use these and other data to consider possible origins for the low explosivity of Mount Hood. Measured volatile concentrations of melt inclusions in plagioclase, pyroxene, and amphibole from pumice indicate that the volatile contents of Mount Hood magmas are comparable to those in more explosive silicic arc volcanoes, including Mount St. Helens, Mount Mazama, and others, suggesting that the lack of explosive activity is unlikely to result solely from low intrinsic volatile concentrations or from substantial degassing prior to magma ascent and eruption. We instead argue that an important control over explosivity is the increased temperature and decreased magma viscosity that results from mafic recharge and magma mixing prior to eruption, similar to a model recently proposed by Ruprecht and Bachmann (2010). Erupted Mount Hood magmas show extensive evidence for mixing between magmas of broadly basaltic and dacitic-rhyolitic compositions, and mineral zoning studies show that mixing occurred immediately prior to eruption. Amphibole chemistry and thermobarometry also reveal the presence of multiple amphibole populations and indicate that the mixed andesites and dacites are at least 100 °C hotter than the high-SiO2

  7. New insights into the origin of the felsic volcanic rocks in the middle Okinawa Trough (United States)

    Zhang, Y.; Zeng, Z.


    The Okinawa Trough (OT) is a nascent back arc basin developing in the eastern margin of the Eurasian Plate. The middle segment of the OT (MOT) is featured by bimodal volcanism with dominant basalts and rhyolites and scarce intermediate volcanic rocks. The MOT rhyolites are divided into two types: type 1 rhyolites have lower heavy rare earth element (HREE) contents while type 2 rhyolites feature higher HREE contents and have slightly more enriched Sr-Nd isotopic ratios than type 1 rhyolites. The MOT rhyolites share similar Sr-Nd isotopic compositions with the MOT basalts and thus they have been typically considered as products of crystallization differentiation of basaltic magma. However, the evidence is insufficient. This paper compared chemical trends of volcanic rocks from the MOT with fractional crystallization simulation models and experimental results and utilized trace element modeling (e.g., Th vs. Rb, Rb/Nd vs. Rb, Rb vs. Rb/V, 1/V vs. Rb/V) combined with quantitative calculations to re-examine the magmatic processes in generating the rhyolites. The trace element discriminant models show that the andesites indicate a fractional crystallization trend, type 1 rhyolites present a partial melting trend, and type 2 rhyolites define a mixing trend. Further, by establishing Rayleigh fractionation and batch melting models, we found that the andesites originated by fractional crystallization of basaltic magma while the rhyolites were the products of remelting of andesites. Type 2 rhyolites have higher Dy/Yb and Nb/Ta ratios than type 1 rhyolites, implying that the former might be influenced by a greater contribution of amphibole. Quantitative models suggest that type 1 rhyolites could have formed via the remelting of andesites when amphiboles remain in the source, whereas type 2 rhyolites could have formed without residual amphiboles. Quasi-linear correlations between some major oxides, trace element ratios and Sr-Nd isotopic ratios for type 2 rhyolites suggest that

  8. Thorianite from the Hogatza Placer, Alaska

    International Nuclear Information System (INIS)

    Staatz, M.H.


    The thorianite in the Hogatza placer was derived from a gneissic monzonite that forms a border facies of the otherwise rather massive granodiorite of the Zane Hills pluton. The border facies is 5 to 10 times as radioactive as the main igneous mass. The uranium content of 11 samples of the gneissic monzonite ranged from 11 to 129 ppM (parts per million) and averaged 47 ppM. The thorium content of these samples ranged from 46 to 268 ppM and averaged 128 ppM. Concentrates of the heavy minerals from these rocks vary somewhat, but amphibole, pyroxene, magnetite, zircon, and sphene are abundant in most. Allanite and biotite occur in many samples, and thorianite, garnet, pyrite, molybdenite, muscovite, goethite, betafite, and thorite occur sparsely in some samples. The thorianite occurs as small cubes similar to those found in the Hogatza placer

  9. Mineralogical indicators of intrachamber magma degassing and oxidation in Shiveluch (Kamchatka) (United States)

    Salova, T.; Simakin, A.


    Processes of the intrachamber magma degassing precede degassing in the conduit on the final stages of eruption and may be of no less importance. Appearance of the free fluid phase at the depth can be responsible for intrachamber elements transport, pressure buildup and local magma oxidation. We interpret phenocrysts zonality in Shiveluch andesites in terms of such degassing based on our experimental data. High magnesium andesite of Shiveluch volcano (Kamchatka) was studied at PH2O=2 kbar. Bulk hydrous glass was prepared in the series of operations including hydrothermal reducing of the initially melted oxidized rock powder under hydrothermal conditions and remelting. The Fe2+/Fe3+ ratio in the final hydrous glass was estimated with Mossbauer spectroscopy. It corresponds to fO2 = NNO - NNO+2 in the andesite melt at the experimental PT parameters. Short experiments yield crystals grown from the melt with Fe2+/Fe3+ ratio close to the initial value. Liquidus temperature of amphibole was found to be 970oC. The analysis of composition of amphiboles grown at T=950oC demonstrates that the sum Fe3+ +Ti (in M1+M2) is inversely correlated with alumina content in the octahedral coordination: Al_VI= 0.601-0.330(Fe3+ + Ti). The Al_VI content rises with melt reduction (Simakin et al., 2009). Liquidus temperatures of plagioclase have been found at PH2O=1 kbar (1000оС) and 2 kbar (960оС). They are in excellent correspondence with values predicted with model by Putirka (2005): 1006оС and 956оС correspondingly. While using this model we analyse composition of plagioclase at the variation of the water content in the wide range (1-6 wt.%) while changing melt temperature to keep plagioclase on the liquidus. It appears that dependence of the anorthite content in plagioclase on the water content has minimum. It means that degassing coupled with magma heating may result in both direct and inverse zonality in plagioclase. The examples of zonality pattern of magmatic minerals that

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

    International Nuclear Information System (INIS)

    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

  11. 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

  12. 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.

  13. U-Pb geochronology by La-CIP-MS and petrography of Sao Carlos massif - stanniferous province of Rondonia

    International Nuclear Information System (INIS)

    Debowski, Beatriz P.; Geraldes, Mauro Cesar; Nogueira, Camila; Almeida, Bruna Saar de


    U-Pb dating by ICP-MS-LA were performed in four samples of the Massif Sao Carlos massif, representative of the younger Granites of Rondonia belonging to the stanniferous province of the same State. Dated samples are granites of pink in colour and coarse-grained to porphyry with main mineralogy consisting of feldspar pertitic to mesopertitic, quartz, plagioclase in lower proportion, biotite and amphibole in some cases. Ages obtained were 986 ± 14 Ma, 974 ± 10 Ma, ± 8 Ma 992.7 and 996 ± 8 Ma and represent the age of crystallization of the Massif. Such ages are concordant with others reported on the bibliography ratifying the inclusion of the massif in the younger Granites of Rondonia, which are directly associated with the most significant mineralization of cassiterite in the State

  14. Chemistry and mineralogy of garnet pyroxenites from Sabah, Malaysia (United States)

    Morgan, B.A.


    Garnet pyroxenites and corundum-garnet amphibolites from the Dent peninsula of eastern Sabah (North Borneo) occur as blocks in a slump breccia deposit of late Miocene age. The earliest formed minerals include pyrope-almandine garnet, tschermakitic augite, pargasite, and rutile. Cumulate textures are present in two of the six specimens studied. The earlier fabric has been extensively brecciated and partly replaced by plagioclase, ilmenite, and a fibrous amphibole. The bulk composition and mineralogy of these rocks are similar to those of garnet pyroxenite lenses within ultramafic rocks. Estimated temperature and pressure for the origin of the Sabah garnet pyroxenites is 850??150?? C and 19??4 kbar. ?? 1974 Springer-Verlag.

  15. U-Pb geochronology by La-CIP-MS and petrography of Sao Carlos massif - stanniferous province of Rondonia; Geocronologia U-Pb por La-ICP-MS e petrografia do macico Sao Carlos - Provincia Estanifera de Rondonia

    Energy Technology Data Exchange (ETDEWEB)

    Debowski, Beatriz P.; Geraldes, Mauro Cesar; Nogueira, Camila; Almeida, Bruna Saar de [Universidade do Estado do Rio de Janeiro, (UERJ), RJ (Brazil)


    U-Pb dating by ICP-MS-LA were performed in four samples of the Massif Sao Carlos massif, representative of the younger Granites of Rondonia belonging to the stanniferous province of the same State. Dated samples are granites of pink in colour and coarse-grained to porphyry with main mineralogy consisting of feldspar pertitic to mesopertitic, quartz, plagioclase in lower proportion, biotite and amphibole in some cases. Ages obtained were 986 ± 14 Ma, 974 ± 10 Ma, ± 8 Ma 992.7 and 996 ± 8 Ma and represent the age of crystallization of the Massif. Such ages are concordant with others reported on the bibliography ratifying the inclusion of the massif in the younger Granites of Rondonia, which are directly associated with the most significant mineralization of cassiterite in the State.

  16. Analysis of suspended solids by single-particle scattering. [for Lake Superior pollution monitoring (United States)

    Diehl, S. R.; Smith, D. T.; Sydor, M.


    Light scattering by individual particulates is used in a multiple-detector system to categorize the composition of suspended solids in terms of broad particulate categories. The scattering signatures of red clay and taconite tailings, the two primary particulate contaminants in western Lake Superior, along with two types of asbestiform fibers, amphibole and chrysolite, were studied in detail. A method was developed to predict the concentration of asbestiform fibers in filtration plant samples for which electron microscope analysis was done concurrently. Fiber levels as low as 50,000 fibers/liter were optically detectable. The method has application in optical categorization of samples for remote sensing purposes and offers a fast, inexpensive means for analyzing water samples from filtration plants for specific particulate contaminants.

  17. Krebs cycle rewired for macrophage and dendritic cell effector functions. (United States)

    Ryan, Dylan Gerard; O'Neill, Luke A J


    The Krebs cycle is an amphibolic pathway operating in the mitochondrial matrix of all eukaryotic organisms. In response to proinflammatory stimuli, macrophages and dendritic cells undergo profound metabolic remodelling to support the biosynthetic and bioenergetic requirements of the cell. Recently, it has been discovered that this metabolic shift also involves the rewiring of the Krebs cycle to regulate cellular metabolic flux and the accumulation of Krebs cycle intermediates, notably, citrate, succinate and fumarate. Interestingly, a new role for Krebs cycle intermediates as signalling molecules and immunomodulators that dictate the inflammatory response has begun to emerge. This review will discuss the latest developments in Krebs cycle rewiring and immune cell effector functions, with a particular focus on the regulation of cytokine production. © 2017 Federation of European Biochemical Societies.

  18. Interplay between water infiltration, metamorphic reactions and strain localization during subduction of gabbro from the basement rocks of the Lofoten anorthosite complex (United States)

    Nasipuri, P.; Stunitz, H.; Menegon, L.; Berger, A.


    Eclogitization of lower crustal rocks occurs during subduction processes. During the prograde segment of subduction cycle and subsequent exhumation, ranges of mineral assemblages are produced under different P-T conditions. In this contribution, we describe the role of water and formation of syn-kinematic mineral assemblages in the ductile shear zone within leucogabbro and in the retrograde equivalent (characterized by alternate bands of mafic and felsic layers) that are separated by a distance of 100-150 meter. In the undeformed gabbro, Plagioclase (Pl0), olivine (Ol0) and orthopyroxene (Opx0) form the igneous texture. The onset of metamorphism (M1, 700 0C, 1GPa) during subduction processes is indicated by growth of metamorphic Opx1 and Grt1 corona around Pl0 and Ol0. Cm- wide alternating bands of a mixture of Pl-amphibole (Amph) ± Spl and GrtI(M1) - Opx -Omph - Grt II (M2A, 650-750 0C, > 1.8 GPa) phase mixtures characterize shear zones. Omph overgrow deformed Opx grains (D1). Clinopyroxene (Cpx) -Pl symplectite (M2B, 600-650 0C, 1 GPa) occur at the outer rim the Omph. Breakdown of Grt I/IIto Amph ± Pl (An rich) ± Spl with increased water activity form during M3 metamorphism. In the retrograde eclogite, the mafic layer is composed of Cpx, sodic Pl and Qtz (grain size 50 μm). Coarse-grained calcic Pl (grain size 50-75 μm) forms the felsic layer. Grt porphyrolcast (eq. Grt I/II) with inclusions of Pl and Qtz occur within the mafic layer. A thin layer of amphibole and clinozoisite layer overgrows at the contact between the mafic and felsic layer (6000C, 0.6-0.8 GPa). In the ductile shear zone, crystallographic data of recrystallized Opx0 (grain size 20-30 μm) and the relict Opx0, chemical similarity and the grain size reduction indicate that Opx deformed by at the onset of subduction. The deformed Opx grains show sinistral sense of shear. Although, the fine-grained Pl is expected to show random CPO characteristics of diffusion creep, the strong CPO of Pl is

  19. 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.

  20. Mineral chemical compositions of late Cretaceous volcanic rocks in the Giresun area, NE Turkey: Implications for the crystallization conditions (United States)

    Oǧuz, Simge; Aydin, Faruk; Uysal, İbrahim; Şen, Cüneyt


    This contribution contains phenocryst assemblages and mineral chemical data of late Cretaceous volcanic (LCV) rocks from the south of Görele and Tirebolu areas (Giresun, NE Turkey) in order to investigate their crystallization conditions. The LCV rocks in the study area occur in two different periods (Coniasiyen-Early Santonian and Early-Middle Campanian), which generally consist of alternation of mafic-intermediate (basaltic to andesitic) and felsic rock series (dacitic and rhyolitic) within each period. The basaltic and andesitic rocks in both periods generally exhibit porphyritic to hyalo-microlitic porphyritic texture, and contain phenocrysts of plagioclase and pyroxene, whereas the dacitic and rhyolitic rocks of the volcanic sequence usually show a vitrophyric texture with predominant plagioclase, K-feldspar, quartz and lesser amphibole-biotite phenocrysts. Zoned plagioclase crystals of the mafic and felsic rocks in different volcanic periods are basically different in composition. The compositions of plagioclase in the first-stage mafic rocks range from An52 to An78 whereas those of plagioclase from the first-stage felsic rocks have lower An content varying from An38 to An50. Rim to core profile for the zoned plagioclase of the first-stage mafic rocks show quite abrupt and notable compositional variations whereas that of the first-stage felsic rocks show slight compositional variation, although some of the grains may display reverse zoning. On the other hand, although no zoned plagioclase phenocryst observed in the second-stage mafic rocks, the compositions of microlitic plagioclase show wide range of compositional variation (An45-80). The compositions of zoned plagioclase in the second-stage felsic rocks are more calcic (An65-81) than those of the first-stage felsic rocks, and their rim to core profile display considerable oscillatory zoning. The compositions of pyroxenes in the first- and second-stage mafic-intermediate rocks vary over a wide range from

  1. [Talc pneumoconiosis among soapstone handicraft workers in a rural area of Ouro Preto, Minas Gerais, Brazil]. (United States)

    Bezerra, Olívia Maria de Paula Alves; Dias, Elizabeth Costa; Galvão, Márcio Antônio Moreira; Carneiro, Ana Paula Scalia


    Talc pneumoconiosis in Brazil has received little research attention to date. The disease was investigated in Mata dos Palmitos, a district of Ouro Preto, Minas Gerais State, among soapstone handicraft workers. The district has some 180 inhabitants, of whom 108 are engaged in handicrafts production, while 15 alternate handicrafts production with work in the soapstone quarries. A clinical and occupational investigation was conducted, along with a respiratory symptoms standardized questionnaire, chest x-ray (ILO standard), and spirometry. Clinical data showed a low prevalence of respiratory complaints. Dyspnea was the most frequent symptom. Chronic bronchitis was identified in 12 adult workers. Chest x-rays showed evidence of small lung opacities in 5 workers, and in 11 there was suspicion of the same opacities. One worker showed a plaque-shaped pleural thickening. Seven workers showed abnormal spirometry. The soapstone dust composition showed breathable asbestos fibers from the amphibole group (tremolite-actinolite). The results suggest talc asbestosis occurrence among soapstone handicraft workers.

  2. Mineralogy and geochemistry of Eocene Helete formation , Adiyaman, Turkey (United States)

    Choi, J.; Lee, I.; Yildirim, E.


    Helete formation is located at Adiyaman, Turkey which is in the Alpine-Himalayan orogeny belt. Helete formation is represented by andesitic, basaltic and gabbroic rocks cut by localized felsic intrusions and overlain by open-marine Nummulitic carbonate sediments. Electron microprobe analyses were conducted for 15 rocks samples of Helete formation. These rock samples are named as basalt, andesite, gabbro, diorite, dacite, and granite. Basalt and andesite samples are composed of clinopyroxene(augite), plagioclase(Ab98-96), carbonate, and hyaline. Gabbro samples have wide range of plagioclase composition from anorthite to albite(Ab92-16), and other minerals like clinopyroxene(augite) and amphibole(hornblende and actinolite). Diabase samples consist of epidote group minerals and sphene with plagioclase(Ab80), pyroxene and hornblende. Dacite samples are composed of dolomite and quartz. Granite samples are composed of quartz, chlorite, and plagioclase which range from albite to oligoclase in composition (Ab98-89).

  3. Geochemistry and petrology of Late Cretaceous subvolcanic rocks (Macka-Trabzon) in the north of the eastern Black Sea region, NE-Turkey (United States)

    Aydin, Faruk


    In this study, geochronological, geochemical and isotopical data for the early Campanian subvolcanic rocks (Macka-Trabzon) in the north of the eastern Blacksea region, northeastern Turkey, have initially been presented with the aim of determining its magma source and geodynamic evolution. The subvolcanic rocks cutting the subduction-related Late Cretaceous volcano-sedimantary rocks in the region are characterized by several sills and dykes with columnar structures and they consist of amphibole-rich quartz-diorite and quartz-tonalite porphyries, with some dioritic mafic microgranular enclaves. The host rocks have a microgranular porphyritic texture, and they contain 15-25% phenocryst of plagioclase and amphibole and have a matrix that is composed primarily of fine-grained quartz, orthoclase, and plagioclase. Accessory apatite, zircon and Fe-Ti oxides are present in all of the rocks. Secondary minerals such as epidote, calcite, sericite and clays are sometimes observed in the matrix or as hydothermal alteration products of some amphibole and plagioclase phenocrysts. When compared to the host rocks, the magmatic enclaves without quartz are fine-grained, and they contain higher ferromagnesian phases and lower feldspar minerals. Ar-Ar geochronology studies on the amphibole separates reveal that the porphyries have a crystallization ages of 81±0.5 Ma. All samples show a high-K calc-alkaline differentiation trend and I-type features with metaluminous character. The rocks and magmatic enclaves are characterized by enrichment of LILE and depletion of HFSE with negative Nb, Ti, Zr and P anomalies. The chondrite-normalized REE patterns are not fractionated [(La/Yb)N = 9-11] and do not display Eu anomalies (Eu/Eu* = 0.7-0.9). The porphyritic rocks and their enclaves are almost isotopically similar. Sr-Nd isotopic data for all of the samples display initial Sr = 0.7085-0.7087, epsilon Nd (81 Ma) = -6.0 to -6.9, with TDM = 1.38-1.63 Ga. The lead isotopic ratios are (206Pb/204Pb

  4. Economic potential of the heavy minerals of the beaches between Baruva and Bavanapadu, Andhra Pradesh

    International Nuclear Information System (INIS)

    Rajasekhara Reddy, D.; Prasad, V.S.S.; Malathi, V.; Reddy, K.S.N.; Varma, D.D.


    The economic potentiality of the heavy minerals in the beaches between Baruva and Bavanapadu extending for about 45 km was examined. In the sub-surface sediments, the heavy minerals were studied at an interval of 1 m up to a maximum depth of 5.8m. In general the concentration of heavy minerals is high in dunes followed by backshore and foreshore regions. Heavy mineral content increases from surface to sub-surface in dunes, decreases in foreshore and does not vary much in backshore. The heavy minerals include mainly ilmenite, garnet, sillimanite and ortho-pyroxenes with minor amounts of amphiboles, zircon, monazite, rutile etc. Majority of the heavies such as ilmenite, monazite, zircon etc. are concentrated in finer fractions while some of the heavies like garnet and sillimanite are concentrated in coarser fractions. The inferred reserves estimated for the area indicate its economical potential. (author)

  5. Petrology and geochemistry of igneous inclusions in recent Merapi deposits

    DEFF Research Database (Denmark)

    Chadwick, J.P.; Troll, V.R.; Waight, Tod Earle


    basalt to andesite compositions. Results for mineral geobarometry on the inclusions suggest a crystallisation history for the plutonic inclusions and the recent and historic Merapi magmas that spans the full depth of the crust, indicating a multi-chamber magma system with high amounts of semi......Recent basaltic-andesite lavas from Merapi volcano contain abundant and varied igneous inclusions suggesting a complex sub-volcanic magmatic system for Merapi volcano. In order to better understand the processes occurring beneath Merapi, we have studied this suite of inclusions by petrography......, geochemistry and geobarometric calculations. The inclusions may be classified into four main suites: (1) highly crystalline basaltic-andesite inclusions, (2) co-magmatic enclaves, (3) plutonic crystalline inclusions and (4) amphibole megacrysts. Highly crystalline basaltic-andesite inclusions and co...

  6. 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)

    Brandao, P.M.C.


    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) [pt

  7. 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

  8. The mesothelioma in Europe; Le mesotheliome en Europe

    Energy Technology Data Exchange (ETDEWEB)

    Bignon, J. [Paris-12 Univ., 94 - Creteil (France)


    Though the primitive malignant tumors of the pleura have been identified in the years 1890, it is only in 1960 that Wagner and his team have published a study of 33 cases of mesothelioma in South Africa, attributed to crocidolite exposure for mines workers and their family. This publication went five years after the demonstration by Richard Doll in Great Britain of epidemiology relations between lungs cancer and professional exposure to asbestos dusts. Later, the research were on the type of asbestos fibers at the origin of the mesothelioma. The power of the chrysotile to induce this tumor among human beings was the object of controversy. but it is clear that the exposure to three kinds of amphibole asbestos (crocidolite, tremolite and anthophyllite) is responsible of the most important incidence of this cancer, even after low concentrations exposures. (N.C.)

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

    International Nuclear Information System (INIS)

    Guimaraes, I.P. de; Silva Filho, A.F. da


    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)

  10. Dynamic Metasomatism: Stable Isotopes, Fluid Evolution, and Deformation of Albitite and Scapolite Metagabbro (Bamble Lithotectonic Domain, South Norway

    Directory of Open Access Journals (Sweden)

    Ane K. Engvik


    Full Text Available New stable isotopic data from mineral separates of albite, scapolite, amphibole, quartz, and calcite of metasomatic rocks (Bamble lithotectonic domain give increased knowledge on fluid type, source, and evolution during metamorphism. Albite from a variety of albitites gives δ18OSMOW values of 5.1–11.1‰, while quartz from clinopyroxene-bearing albitite gives 11.5–11.6‰. δ18OSMOW values for calcite samples varies between 3.4 and 12.4‰ and shows more consistent δ13C values of −4.6 to -6.0‰. Amphibole from scapolite metagabbro yields a δ18OSMOW value of 4.3 to 6.7‰ and δDSMOW value of −84 to −50‰, while the scapolite gives δ18OSMOW values in the range of 7.4 to 10.6‰. These results support the interpretation that the original magmatic rocks were metasomatised by seawater solutions with a possible involvement from magmatic fluids. Scapolitisation and albitisation led to contrasting chemical evolution with respect to elements like P, Ti, V, Fe, and halogens. The halogens deposited as Cl-scapolite were dissolved by albitisation fluid and reused as a ligand for metal transport. Many of the metal deposits in the Bamble lithotectonic domain, including Fe-ores, rutile, and apatite deposits formed during metasomatism. Brittle to ductile deformation concurrent with metasomatic infiltration illustrates the dynamics and importance of metasomatic processes during crustal evolution.

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

    International Nuclear Information System (INIS)

    Maruejol, P.; Cuney, M.; Poty, B.; Neto, A.M.


    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 fO 2 and P H2O conditions. Fractional crystallization of pyroxene and plagioclase leads to silica enrichment during magmatic differentiation. Increasing fO 2 and P H2O 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 [pt

  12. 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)

    Teixeira, W.; Kawashita, K.; Pecchio, M.; Tame, N.R.


    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) [pt

  13. 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).

  14. Origin and age of the Eisenkappel gabbro to granite suite (Carinthia, SE Austrian Alps). (United States)

    Miller, C; Thöni, M; Goessler, W; Tessadri, R


    The northern part of the Karawanken plutonic belt is a gabbro-granite complex located just north of the Periadriatic lineament near the Slovenian-Austrian border. Petrographic and geochemical studies of the Eisenkappel intrusive complex indicate that this multiphase plutonic suite developed by a combination of crystal accumulation, fractional crystallization and assimilation processes, magma mixing and mingling. The mafic rocks are alkaline and have within-plate geochemical characteristics, indicating anorogenic magmatism in an extensional setting and derivation from an enriched mantle source. The mafic melts triggered partial melting of the crust and the formation of granite. The granitic rocks are alkalic, metaluminous and have the high Fe/Fe + Mg characteristics of within-plate plutons. Temperature and pressure conditions, derived from amphibole-plagioclase and different amphibole thermobarometers, suggest that the analysed Eisenkappel gabbros crystallized at around 1000 ± 20 °C and 380-470 MPa, whereas the granitic rock crystallized at T ≤ 800 ± 20 °C and ≤ 350 MPa. Mineral-whole rock Sm-Nd analyses of two cumulate gabbros yielded 249 ± 8.4 Ma and 250 ± 26 Ma (εNd: + 3.6), garnet-whole rock Sm-Nd analyses of two silicic samples yielded well-constrained ages of 238.4 ± 1.9 Ma and 242.1 ± 2.1 Ma (εNd: - 2.6).

  15. Geochemical Relationships between Volcanic and Plutonic Upper to Mid Crustal Exposures of the Rosario Segment, Alisitos Arc (Baja California, Mexico): An Outstanding Field Analog to the Izu-Bonin-Mariana Arc (United States)

    Morris, R.; DeBari, S. M.; Busby, C. J.; Medynski, S.


    Exposed paleo-arcs, such as the Rosario segment of the Cretaceous Alisitos Arc in Baja California, Mexico, provide an opportunity to explore the evolution of arc crust through time. Remarkable 3-D exposures of the Rosario segment record crustal generation processes in the volcanic rocks and underlying plutonic rocks. In this study, we explore the physical and geochemical connection between the plutonic and volcanic sections of the extensional Alisitos Arc, and elucidate differentiation processes responsible for generating them. These results provide an outstanding analog for extensional active arc systems, such as the Izu-Bonin-Mariana (IBM) Arc. Upper crustal volcanic rocks have a coherent stratigraphy that is 3-5 km thick and ranges in composition from basalt to dacite. The most felsic compositions (70.9% SiO2) are from a welded ignimbrite unit. The most mafic compositions (51.5% SiO2, 3.2% MgO) are found in basaltic sill-like units. Phenocrysts in the volcanic units include plagioclase +/- amphibole and clinopyroxene. The transition to deeper plutonic rocks is clearly an intrusive boundary, where plutonic units intrude the volcanic units. Plutonic rocks are dominantly a quartz diorite main phase with a more mafic, gabbroic margin. A transitional zone is observed along the contact between the plutonic and volcanic rocks, where volcanics have coarsely recrystallized textures. Mineral assemblages in the plutonic units include plagioclase +/- quartz, biotite, amphibole, clinopyroxene and orthopyroxene. Most, but not all, samples are low K. REE patterns are relatively flat with limited enrichment. Normalization diagrams show LILE enrichment and HFSE depletion, where trends are similar to average IBM values. We interpret plutonic and volcanic units to have similar geochemical relationships, where liquid lines of descent show the evolution of least to most evolved magma types. We provide a model for the formation and magmatic evolution of the Alisitos Arc.

  16. Mayer Kangri metamorphic complexes in Central Qiangtang (Tibet, western China): implications for the Triassic-early Jurassic tectonics associated with the Paleo-Tethys Ocean (United States)

    Wang, Yixuan; Liang, Xiao; Wang, Genhou; Yuan, Guoli; Bons, Paul D.


    The Mesozoic orogeny in Central Qiangtang Metamorphic Belt, northern Tibet, provides important insights into the geological evolution of the Paleo-Tethys Ocean. However, the Triassic-early Jurassic tectonics, particularly those associated with the continental collisionstage, remains poorly constrained. Here we present results from geological mapping, structural analysis, P-T data, and Ar-Ar geochronology of the Mayer Kangri metamorphic complex. Our data reveal an E-W-trending, 2 km wide dome-like structure associated with four successive tectonic events during the Middle Triassic and Early Jurassic. Field observations indicate that amphibolite and phengite schist complexes in this complex are separated from the overlying lower greenschist mélange by normal faulting with an evident dextral shearing component. Open antiform-like S2 foliation of the footwall phengite schist truncates the approximately north-dipping structures of the overlying mélange. Microtextures and mineral chemistry of amphibole reveal three stages of growth: Geothermobarometric estimates yield temperatures and pressures of 524 °C and 0.88 GPa for pargasite cores, 386 °C and 0.34 GPa for actinolite mantles, and 404 °C and 0.76 GPa for winchite rims. Peak blueschist metamorphism in the phengite schist occurred at 0.7-1.1 GPa and 400 °C. Our Ar-Ar dating of amphibole reveals rim-ward decreasing in age bands, including 242.4-241.2 Ma, ≥202.6-196.8, and 192.9-189.8 Ma. The results provide evidence for four distinct phases of Mesozoic tectonic evolution in Central Qiangtang: (1) northward oceanic subduction beneath North Qiangtang ( 244-220 Ma); (2) syn-collisional slab-break off (223-202 Ma); (3) early collisional extension driven by buoyant extrusion flow from depth ( 202.6-197 Ma); and (4) post-collision contraction and reburial (195.6-188.7 Ma).

  17. Noble Gases Trace Earth's Subducted Water Flux (United States)

    Smye, A.; Jackson, C.; Konrad-Schmolke, M.; Parman, S. W.; Ballentine, C. J.


    Volatile elements are transported from Earth's surface reservoirs back into the mantle during subduction of oceanic lithosphere [e.g. 1]. Here, we investigate the degree to which the fate of slab-bound noble gases and water are linked through the subduction process. Both water and noble gases are soluble in ring-structured minerals, such as amphibole, that are common constituents of subducted oceanic lithosphere. Heating and burial during subduction liberates noble gases and water from minerals through a combination of diffusion and dissolution. Combining a kinetic model, parameterized for noble gas fractionation in amphibole [2], with thermodynamic phase equilibria calculations, we quantify the effect of subduction dehydration on the elemental composition of slab-bound noble gases. Results show that post-arc slab water and noble gas fluxes are highly correlated. Hot subduction zones, which likely dominate over geologic history, efficiently remove noble gases and water from the down-going slab; furthermore, kinetic fractionation of noble gases is predicted to occur beneath the forearc. Conversely, hydrated portions of slab mantle in cold subduction zones transport noble gases and water to depths exceeding 200 km. Preservation of seawater-like abundances of Ar, Kr and Xe in the convecting mantle [1] implies that recycling of noble gases and water occurred during cold subduction and that the subduction efficiency of these volatile elements has increased over geological time, driven by secular cooling of the mantle. [1] Holland, G. and Ballentine, C. (2006). Nature 441, 186-191. [2] Jackson et al. (2013). Nat.Geosci. 6, 562-565.

  18. 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

  19. Mineral chemistry as a tool for understanding the petrogenesis of Cryogenian (arc-related)-Ediacaran (post-collisional) gabbros in the western Arabian Shield of Saudi Arabia (United States)

    Surour, Adel A.; Ahmed, Ahmed H.; Harbi, Hesham M.


    Metagabbros and gabbros in the Ablah-Shuwas belt (western Saudi Arabia) represent part of significant mafic magmatism in the Neoproterozoic Arabian Shield. The metagabbros are Cryogenian, occasionally stratified and bear calcic amphiboles (hornblende, magnesio-hornblende and actinolite) typical of calc-alkaline complexes. These amphiboles suggest low pressure ( 1-3 kbar), high f_{{{{O}}2 }} and crystallization temperature up to 727 °C, whereas it is 247-275 °C in the case of retrograde chlorite. Rutile and titanite in metagabbros are Fe-rich and replace Mn-bearing ilmenite precursors at high f_{{{{O}}2 }}. On the other hand, younger gabbros are fresh, layered and comprised of olivine gabbro and olivine-hornblende gabbro with an uppermost layer of anorthositic gabbro. The fresh gabbros are biotite-bearing. They are characterized by secondary magnetite-orthopyroxene symplectitic intergrowth at the outer peripheries of olivine. The symplectite forms by deuteric alteration from residual pore fluids moving along olivine grain boundaries in the sub-solidus state. In fresh gabbros, ortho- and clinopyroxenes indicate crystallization at 1300-900 and 800-600 °C, respectively. Geochemically, the Cryogenian metagabbros ( 850-780 Ma) are tholeiitic to calc-alkaline in composition and interpreted as arc-related. Younger, fresh gabbros are calc-alkaline and post-collisional ( 620-590 Ma, i.e., Ediacaran), forming during the late stages of arc amalgamation in the southern Arabian Shield. The calc-alkaline metagabbros are related to a lithospheric mantle source previously modified by subduction. Younger, fresh gabbros were probably produced by partial melting of an enriched mantle source (e.g., garnet lherzolite).

  20. Formation of atoll garnets in the UHP eclogites of the Tso Morari Complex, Ladakh, Himalaya (United States)

    Jonnalagadda, Mallika K.; Karmalkar, Nitin R.; Duraiswami, Raymond A.; Harshe, Shivani; Gain, Sarah; Griffin, William L.


    The eclogites of the Tso Morari Complex, Ladakh, NW Himalayas preserve both garnets with spectacular atoll textures, as well as whole porphyroblastic garnets. Whole garnets are euhedral, idiomorphic and enclose inclusions of amphibole, phengite and zoisite within the cores, and omphacite and quartz/coesite towards the rims. Detailed electron microprobe analyses and back-scattered electron images show well-preserved prograde zoning in the whole garnets with an increase in Mg and decrease in Ca and Mn contents from the core to the rim. The atoll garnets commonly consist of euhedral ring over island/peninsular core containing inclusions of phengite, omphacite and rarely amphibole between the core and ring. Compositional profiles across the studied atoll grains show elemental variations with higher concentrations of Ca and Mn with low Mg at the peninsula/island cores; contrary to this low Ca, Mn and high Mg is observed at the outer rings. Temperature estimates yield higher values at the Mg-rich atoll garnet outer rings compared to the atoll cores. Atoll garnet formation was favoured by infiltration of fluid formed due to breakdown of hydrous phases, and/or the release of structurally bounded OH from nominally anhydrous minerals at the onset of exhumation. Infiltration of fluids along pre-existing fracture pathways and along mineral inclusion boundaries triggered breakdown of the original garnet cores and released elements which were subsequently incorporated into the newly-grown garnet rings. This breakdown of garnet cores and inward re-growth at the outer ring produced the atoll structure. Calibrated geo-thermobarometers and mineral equilibria reflect that the Tso Morari eclogites attain peak pressures prior to peak temperatures representing a clockwise path of evolution.

  1. 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.

  2. Mineral fibres and health

    International Nuclear Information System (INIS)

    Hoskins, J.A.


    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)

  3. Host-rock controlled epigenetic, hydrothermal metasomatic origin of the Bayan Obo REEFe-Nb ore deposit, Inner Mongolia, P.R.C. (United States)

    Chao, E.C.T.; Back, J.M.; Minkin, J.A.; Yinchen, R.


    Bayan Obo, a complex rare earth element (REE)FeNb ore deposit, located in Inner Mongolia, P.R.C. is the world's largest known REE deposit. The deposit is chiefly in a marble unit (H8), but extends into an overlying unit of black shale, slate and schist unit (H9), both of which are in the upper part of the Middle Proterozoic Bayan Obo Group. Based on sedimentary structures, the presence of detrital quartz and algal fossil remains, and the 16-km long geographic extent, the H8 marble is a sedimentary deposit, and not a carbonatite of magmatic origin, as proposed by some previous investigators. The unit was weakly regionally metamorphosed (most probably the lower part of the green schist facies) into marble and quartzite prior to mineralization. Tectonically, the deposit is located on the northern flank of the Sino-Korean craton. Many hypotheses have been proposed for the origin of the Bayan Obo deposit; the studies reported here support an epigenetic, hydrothermal, metasomatic origin. Such an origin is supported by field and laboratory textural evidence; 232Th/208Pb internal isochron mineral ages of selected monazite and bastnaesite samples; 40Ar/39Ar incremental heating minimum mineral ages of selected alkali amphiboles; chemical compositions of different generations of both REE ore minerals and alkali amphiboles; and evidence of host-rock influence on the various types of Bayan Obo ores. The internal isochron ages of the REE minerals indicate Caledonian ages for various episodes of REE and Fe mineralization. No evidence was found to indicate a genetic relation between the extensive biotite granitic rocks of Hercynian age in the mine region and the Bayan Obo are deposit, as suggested by previous workers. ?? 1992.

  4. Geology, zircon geochronology, and petrogenesis of Sabalan volcano (northwestern Iran) (United States)

    Ghalamghash, J.; Mousavi, S. Z.; Hassanzadeh, J.; Schmitt, A. K.


    Sabalan Volcano (NW Iran) is an isolated voluminous (4821 m elevation; > 800 km2) composite volcano that is located within the Arabia-Eurasia collision zone. Its edifice was assembled by recurrent eruptions of trachyandesite and dacite magma falling into a relatively restricted compositional range (56-67% SiO2) with high-K calc-alkaline and adakitic trace element (Sr/Y) signatures. Previous K-Ar dating suggested protracted eruptive activity between 5.6 and 1.4 Ma, and a two stage evolution which resulted in the construction of the Paleo- and Neo-Sabalan edifices, respectively. The presence of a topographic moat surrounding Neo-Sabalan and volcanic breccias with locally intense hydrothermal alteration are indicative of intermittent caldera collapse of the central part of Paleo-Sabalan. Volcanic debris-flow and debris-avalanche deposits indicate earlier episodes of volcanic edifice collapse during the Paleo-Sabalan stage. In the Neo-Sabalan stage, three dacitic domes extruded to form the summits of Sabalan (Soltan, Heram, and Kasra). Ignimbrites and minor pumice fall-out deposits are exposed in strongly dissected drainages that in part have breached the caldera depression. Lavas and pyroclastic rocks are varyingly porphyritic with Paleo-Sabalan rocks being trachyandesites carrying abundant phenocrysts (plagioclase + amphibole + pyroxene + biotite). The Neo-Sabalan rocks are slightly more evolved and include dacitic compositions with phenocrysts of plagioclase + amphibole ± alkali-feldspar ± quartz. All Sabalan rock types share a common accessory assemblage (oxides + apatite + zircon). High spatial resolution and sensitivity U-Pb geochronology using Secondary Ionization Mass Spectrometry yielded two clusters of zircon ages which range from 4.5 to 1.3 Ma and 545 to 149 ka, respectively (all ages are averages of multiple determinations per sample). U-Th zircon geochronology for selected Neo-Sabalan rocks agrees with the U-Pb ages, with the youngest zircon rims dating

  5. Resetting of Neoarchaean hornblendes from the Murmansk Terrane (Kola Peninsula, Russia) revealed by a combined 40Ar/39Ar and Rb-Sr analysis (United States)

    de Jong, K.; Timmerman, M. J.; Cliff, R. A.; Wijbrans, J. R.; Daly, J. S.; Balagansky, V. V.


    We present isotope data from amphiboles from the 2.6--2.8 Ga Murmansk Terrane in the northern foreland of the 1.9 Ga Lapland-Kola Orogen of northern Fennoscandia. Most amphiboles are zoned with tschermakitic cores that progressively change to actinolite in 5--10 μm wide areas in rims, defect zones or adjacent to biotite. Biotite chiefly occurs along cleavages, fractures and grain boundaries of amphibole, showing that its hydration and fluid ingress are confined to lattice imperfections. Furnace step heating of hornblende separate MT-11 gave spectra with increasing apparent ages and Ca/K ratios (a proxy for 37ArCa/39Ar_K). Hornblende is intergrown with biotite that also occurs in the matrix. Yet, laser step heating of single hornblende grain MT-11 yielded flat spectra with Neoarchaean apparent ages and constant Ca/K ratios. This suggests that the hornblende grain that was drilled from a thin section and which was not affected by biotite growth retained its Neoarchaean age. In contrast, the hornblende separate with intergrown biotite from this sample has a partially reset Neoarchaean isotope system. Hornblende MT-27 has Neoarchaean apparent ages and lacks low Ca/K ratios in both single grain and mineral separate spectra; it is not affected by biotite growth and this mineral is also absent from the matrix. Age spectra of other hornblende separates have increasing apparent ages to 2.56--2.65 Ga during final 39Ar release; their Ca/K ratio spectra similarly increase. Low Ca/K ratios for gas release below 950^oC imply degassing of included biotite. Apparent ages of the first heating increments may be as young as 1.8 Ga, comparable to the K-Ar and 40Ar/39Ar ages of the youngest biotites. Hornblende-plagioclase pairs from aliquots used for 40Ar/39Ar furnace step heating yielded sharply discordant Rb-Sr ages. MT-11 yielded an 1881 ± 23 Ma Rb-Sr age that compares well with the K-Ar and 40Ar/39Ar ages of biotite in the sample. In contrast, hornblende of sample MT-27 has a

  6. A New Occurrence of Alkaline Magmatism on the Kola Peninsula: An Agpaitic Dyke in the Kandalaksha Region. (United States)

    Akimenko, Mariya; Kogarko, Lia; Sorokhtina, Natalia; Kononkova, Natalia; Mamontov, Vladimir


    A new occurrence of alkaline dyke magmatism was discovered in 2010 during the geological works performed by the Murmansk Geological Prospecting Expedition in the "Mokhnatye Roga" area located 55 km to the southeast of the Kovdor massif (67°15' N, 31°30' E). The "Mokhnatye Roga" area is located in the Ensk segment of the northwestern part of the Belomorian mobile belt. We performed a complete petrological and geochemical description of the sections in Holes 19 and 24, which reveal one of the largest dykes in the area. The dyke, with a length of ≈4 km and a width of ≈160 m, has an eastern orientation with steep dipping (60°-90°) to the north. The thickness of Quaternary deposits ranges from 0.8 to 4.0 m; alkaline rocks occur in the range of 4.0-93.9 m being followed by host amphibole-biotite gneiss with interbeds of plagioamphibolite (AR2 mt) along the section. Among the major minerals of the dyke are the minerals of the lamprophyllite group (20-25 vol %), aegirine-augite (10-15 vol %), enigmatite (10-15 vol %), nepheline (10-15 vol %), orthoclase (15-20 vol %), alkaline amphibole (5-10 vol %), and astrophyllite (up to 5 vol %). The minor minerals are represented by shcherbakovite, sodalite, natrolite, barite, Mn carbonate, ilmenite, rutile, sphalerite, and goethite. The texture of the rock is porphyric: the groundmass is composed of finegranular nepheline and orthoclase, which are observed as individual large euhedral crystals as well. In addition, large phenocrysts are represented by the minerals of the lamprophyllite, enigmatite, pyroxene, and alkaline amphibole groups. Based on the generally accepted classifications [1], the studied agpaitic rock may be related to nepheline syenite; according to the mineral and chemical compositions, it is close to syenite of the Niva massif [2] located 35 km to the northeast from the "Mokhnatye Roga" area. Agpaitic syenite of the "Mokhnatye Roga" area is extremely enriched in dispersed and rare lithophile elements. The

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

    Directory of Open Access Journals (Sweden)

    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

  8. Petrogenesis of basaltic volcanic rocks from the Pribilof Islands, Alaska, by melting of metasomatically enriched depleted lithosphere, crystallization differentiation, and magma mixing (United States)

    Chang, J.M.; Feeley, T.C.; Deraps, M.R.


    The Pribilof Islands, Alaska, are located in the Bering Sea in a continental intraplate setting. In this study we examine the petrology and geochemistry of volcanic rocks from St. Paul (0??54-0??003 Ma) and St. George (2??8-1??4 Ma) Islands, the two largest Pribilof Islands. Rocks from St. George can be divided into three groups: group 1 is a high-MgO, low-SiO. 2 suite composed primarily of basanites; group 2 is a high-MgO, high-SiO 2 suite consisting predominantly of alkali basalts; group 3 is an intermediate- to low-MgO suite that includes plagioclase-phyric subalkali basalts and hawaiites. Major and trace element geochemistry suggests that groups 1 and 2 formed by small-degree partial melting of amphibole-bearing to amphibole-free garnet peridotite. Group 1 rocks were the earliest melts produced from the most hydrous parts of the mantle, as they show the strongest geochemical signature of amphibole in their source. The suite of rocks from St. Paul ranges from 14??4 to 4??2 wt % MgO at relatively constant SiO 2 contents (43??1-47??3 wt %). The most primitive St. Paul rocks are modeled as mixtures between magmas with compositions similar to groups 1 and 2 from St. George Island, which subsequently fractionated olivine, clinopyroxene, and spinel to form more evolved rocks. Plagioclase-phyric group 3 rocks from St. George are modeled as mixtures between an evolved melt similar to the evolved magmas on St. Paul and a fractionated group 2 end-member from St. George. Mantle potential temperatures estimated for primitive basanites and alkali basalts are ???1400??C and are similar to those of mid-ocean ridge basalts (MORB). Similarly, 87Sr/. 86Sr and 143Nd/. 144Nd values for all rocks are MORB-like, in the range of 0??702704-0??703035 and 0??513026-0??513109, respectively. 208Pb/. 204Pb vs 206Pb/. 204Pb values lie near the MORB end-member but show a linear trend towards HIMU (high time-integrated 238U/. 204Pb). Despite isotopic similarities to MORB, many of the major and

  9. 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 (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

  10. Origin of the Ciomadul Dacite, Carpathian-Pannonian Region, Eastern-Central Europe: Rejuvenation of a Pre-Existing Crystal Mush (United States)

    Kiss, B.; Harangi, S.; Molnar, K.; Jankovics, E. M.; Lukacs, R.; Ntaflos, T.


    Dacitic composite volcanoes and calderas worldwide have many common specific characters. Notably, their activities are fairly unpredictable since the repose time between the active phases could be rather long, i.e. even several tens or hundreds ka. This nature might be related to the origin of such magmas. Petrological observations indicate that relatively old, cool, highly crystalline magma body (i.e., a crystal mush) could be present beneath the seemingly inactive dacitic volcanoes before reawakening. Reactivation of such locked magma chambers could occur due to the upwelling and intrusion of mafic magma and recent calculations suggest that this process takes place rather fast. Understanding the nature and time-scale of such remobilization events is crucial to explain the reason of the change in volcanic behaviour from dormant to active phase (i.e., the reawakening of the volcano). In this study, we show the role and the character of a pre-existing near-solidus granodioritic crystal mush to generate the eruptible dacitic magma in the Ciomadul volcano. The Ciomadul dacite is a crystal-rich rock with ubiquitous plagioclases and amphiboles. They form viscous lava domes and pumices generated by sub-plinian explosive eruptions. Combined, mineral-scale textural and geochemical investigations indicate a complex origin of these minerals, formed partly in a low temperature dioritic-granodioritic crystal mush body, partly in higher temperature hybrid magma. In addition, biotite, titanite, apatite, allanite, zircon, K-feldspar and quartz occur in various amounts and are interpreted also as antecrysts derived from the remobilized mushy body. High-Mg olivines and clinopyroxenes represent basaltic magma intruded into the mush. The nature of the crystal mush was closely investigated through the detailed analysis of the crystal clots found often in the Ciomadul dacites. Their texture resembles plutonic rocks, but they contain interstitial vesiculated glasses. The glass could

  11. 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

  12. Early Cretaceous Na-rich granitoids and their enclaves in the Tengchong Block, SW China: Magmatism in relation to subduction of the Bangong-Nujiang Tethys ocean (United States)

    Zhu, Ren-Zhi; Lai, Shao-Cong; Santosh, M.; Qin, Jiang-Feng; Zhao, Shao-Wei


    The Na-rich intermediate-to-felsic granitic rocks provide insights into the generation of magmas in subduction zones. This paper presents zircon LA-ICP-MS U-Pb ages as well as whole-rock geochemical, mineral chemical, and in situ zircon Hf isotopic data on Na-rich granitic rocks from the Tengchong Block, SW China. The granodiorites and associated mafic magmatic enclaves (MMEs) from the Menglian batholith yield zircon U-Pb ages of 116.1 ± 0.8 to 117.8 ± 0.6 Ma and 117.7 ± 0.7 Ma, respectively. Both host granodiorites and enclaves show calc-alkaline and sodium-rich nature, enrichment in large-ion lithophile elements (LILEs), and variable depletion in zircon Hf isotopic compositions. Euhedral amphiboles in both granodiorites and associated enclaves are magnesian-hornblende with high Mg and Ca and contain euhedral plagioclase inclusions of labradorite to andesine (An36-57) composition. The granodiorite was most likely derived through the mixing of partial melts derived from juvenile basaltic lower crust and a minor evolved component of ancient crustal sources. The quartz monzodiorite-granodiorites and associated MMEs from the Xiaotang-Mangdong batholith yield zircon U-Pb ages of 120.3 ± 1.3 to 122.6 ± 0.8 Ma and 120.7 ± 1.5 Ma. These rocks are also sodium-rich and show calc-alkaline trend with negative zircon Hf isotopic compositions (- 5.55 to + 0.58). The MMEs in the host intrusions are monzogabbro with variable and depleted zircon Hf isotopic compositions. The amphiboles in the both host intrusions and the enclaves show Al-rich ferro-tschermakite composition. We infer that the quartz monzodiorite-granodiorites were derived from magmas generated by the melting of ancient basaltic rocks in the lower arc crust induced by the underplating of mantle-derived mafic magmas. The formation of the different types of Na-rich granitic rocks is correlated to the subduction of Bangong-Nujiang Tethyan ocean. A comparison with magmatism in the northern magmatic belt suggests

  13. The redox budget of crust-derived fluid phases at the slab-mantle interface (United States)

    Malaspina, N.; Langenhorst, F.; Tumiati, S.; Campione, M.; Frezzotti, M. L.; Poli, S.


    The redox processes taking place in the portion of the mantle on top of the subducting slab are poorly investigated and the redox potential of crust-derived fluid phases is still poorly constrained. A case study of supra-subduction mantle affected by metasomatism from crust-derived fluid phases is represented by garnet orthopyroxenites from the Maowu Ultramafic Complex (China) deriving from harzburgite precursors metasomatised at ∼4 GPa, 750-800 °C by a silica- and incompatible trace element-rich fluid phase. This metasomatism produced poikilitic orthopyroxene and inclusion-rich garnet porphyroblasts. Solid multiphase primary micro-inclusions in garnet display negative crystal shapes and infilling minerals (spinel, ±orthopyroxene, amphiboles, chlorite, ±talc, ±mica) occur with constant modal proportions, indicating that they derive from trapped solute-rich aqueous fluids. FT-IR hyper spectral imaging analyses and Raman spectroscopy, together with X-ray microtomography performed on single inclusions indicate that liquid water is still preserved at least in some inclusions (±spinel). To investigate the redox budget of these fluid phases, we measured for the first time the Fe3+ concentration of the micron-sized precipitates of the multiphase inclusions using EELS on a TEM. Results indicate that spinel contains up to 12% of Fe3+ with respect to the total iron, amphibole about 30%, while the ratio in inclusion phases such as chlorite and phlogopite may reach 70%. The Fe3+ fraction of the host garnet is equal to that measured in spinel as also confirmed by Flank Method EPMA measurements. Forward modelling fO2 calculations indicate that the garnet orthopyroxenites record ΔFMQ = -1.8 ÷ -1.5, therefore resulting apparently more reduced with respect to metasomatised supra-subduction garnet-peridotites. On the other hand, oxygen mass balance, performed both on the Maowu hybrid orthopyroxenite and on metasomatised supra-subduction garnet peridotites, indicate that the

  14. Tracing the HIMU component within Pan-African lithosphere beneath northeast Africa: Evidence from Late Cretaceous Natash alkaline volcanics, Egypt (United States)

    Abu El-Rus, M. A.; Chazot, G.; Vannucci, R.; Paquette, J.-L.


    A large late Cretaceous ( 90 Ma) volcanic field (the Natash volcanic province) crops out in southeast Egypt at the northwestern boundary of the Arabian-Nubian shield. The lavas are mainly of alkaline affinity and exhibit a continuous compositional range from alkali olivine basalt (AOB) to trachyte and rhyolite. All basaltic lavas in the province record various extents of fractional crystallization of olivine, clinopyroxene, plagioclase and spinel. The basaltic lavas show variations in Sr-Nd-Pb-Hf isotopic ratios [(87Sr/86Sr)i = 0.7030-0.70286; (143Nd/144Nd)i = 0.512653-0.512761; (206Pb/204Pb)i = 19.28-19.94; (177Hf-176Hf)i = 0.28274-0.28285], that correlate markedly with the major and trace element ratios and abundances. Assimilation of crustal material cannot explain these correlations, and we invoke instead melting of a multicomponent mantle source. We infer the existence of High-μ (HIMU), Enriched mantle type-I (EM-I) and Depleted mantle (DM) domains in the melting source, with a predominant contribution from the HIMU-type. We suggests further that the basaltic lavas originate from low degrees of partial melting (F < 5%) at moderate potential temperatures (TP) 1391-1425 °C and pressures of 2.0-2.6 GPa. The melting pressure estimations imply that melting entirely occurred within lithospheric mantle, most likely in the presence of residual amphibole as presence negative K-anomalies in the primitive mantle-normalized patterns of the fractionation-corrected melts. The presence of amphibole within the lithosphere is a strong evidence that the lithospheric mantle underwent metasomatic enrichment prior to melting in Late Cretaceous. This metasomatic event affected on the Pb isotopic compositions of the Natash volcanics by adding Th and U to the melting source. Time-integrated calculations to remove the decoupling between 206Pb and 207Pb isotopes that most probably resulted from the metasomatic event indicate a tentative link between the metasomatism occurring in the

  15. Lesser Antillean Arc Initiation and Migration as a Proxy of Slab Dynamics: Geothermochronology, Thermobarometry and Structure of Saint Martin Granodiorites (United States)

    Noury, M.; Münch, P.; Philippon, M. M.; Bernet, M.; Bruguier, O.; Balvay, M.


    In subduction zones, volcanic arc initiation, cessation, migration and associated upper plate deformation -i.e faulting and vertical motions- reflect large-scale slab dynamics. At the northeastern edge of the Caribbean plate, the Greater Caribbean subduction zone waned out during the Mid Eocene, following the subduction of the Bahamas bank. This arc cessation was contemporaneous with (i) a plate boundary re-organization (evolving from subduction to transform), (ii) upper plate deformation and (iii) arc initiation in the Lesser Antilles. As part of the GAARANTI project that aims at unraveling the relationships between the evolution of terrestrial Caribbean biodiversity and vertical motions resulting from the Lesser Antilles subduction zone dynamic, we study the Saint Martin granodiorites, one of the two Oligocene plutons outcropping in the Lesser Antillean forearc. We investigate the birth and evolution of the Lesser Antillean arc and its thermo-mechanical impact on the Caribbean upper plate. In order to characterize the P,T,t path of the pluton we performed several thermochronological analyses covering a wide range of temperature (U-Pb on zircon -Tc 850°C, Ar/Ar on amphibole -Tc 550°C- and biotite -Tc 325°C-, zircon and apatite fission-tracks -Tc 250 and 110°C, respectively as well as U-Th/He on apatite -Tc 60°C) coupled with in-situ thermobarometry analyses (Al in hornblendes) and structural data. Geochronology and thermobarometry reveal that the granodiorites emplaced at ca. 28 Ma, at a depth of 5 km. Based on the age difference between amphibole and biotite Ar/Ar ages, we show that the northern pluton cooled faster than the southern one. Preliminary thermochronological results show a fast cooling between 29 and 25 Ma and then a continuous and slow cooling since 25 Ma and inverse modeling points to a 10 Ma cooling event. Our investigations give insights on the thermo-mechanical evolution of the arc-forearc region of the Lesser Antilles subduction zone

  16. (United States)

    Barbieri, Pietro Gino; Somigliana, Anna Benedetta; Lombardi, Sandra; Festa, Roberto; Girelli, Roberto; Sarnico, Michela


    The occurrence of malignant mesothelioma is almost always causally associated to asbestos exposure but, considering women occurrences, this association is often difficult to demonstrate and consequently the asbestos exposure is defined as 'unknown'. To describe the working activity and to give occupational asbestos exposure probability estimation related to an uncommon and poorly investigated productive sector: doll manufacture. From the Province of Brescia Mesothelioma Registry, established in 1993 on population-based criteria, we have extracted the certified mesothelioma diagnosis cases, related to patients who were employed for some time in doll manufacture. Among the 757 total cases of malignant mesothelioma registered and studied up to 2016, we found 3 cases of pleural epithelial mesothelioma histologically diagnosed in young women who had worked in two doll manufacturing companies and whose asbestos exposure had been initially defined as 'unknown', because an environmental, family or extra-professional asbestos exposure was considered unlikely. However, the judicial autopsy performed on one of the 3 women had allowed examining lung tissue samples with Scanning Electron Microscopy. This technique showed a concentration of amphiboles fibers of about 12,000,000 per gram of dry lung tissue, with a consequent re-classification of asbestos exposure from 'unknown' to 'occupational certified'. Mesotheliomas in women with no apparent occupational asbestos exposure are normally referred to life or family environmental exposure. Moreover, it is known that occupational asbestos exposure in women is difficult to recognize. Previously, only one publication had reported two cases of mesothelioma in cloth doll manufacture. The occurrence of two mesothelioma cases in the same company out of the three here presented was suggesting an occupational exposure. The finding of a high amphibole fibers lung concentration confirmed the previous hypothesis, despite the impossibility to

  17. Explosive to Effusive Transition in Intermediate Volcanism: An Analysis of Changing Magma System Conditions in Dominica (United States)

    Bersson, J.; Waters, L. E.; Frey, H. M.; Nicolaysen, K. P.; Manon, M. R. F.


    The oscillation between explosive and effusive intermediate (59-62 wt% SiO2) volcanism in the Roseau Valley on Dominica, an island in the Lesser Antilles Arc, provides an opportunity to investigate temporal changes in the magmatic system. Here, we test the relationship between the Roseau ignimbrites (1-65 ka) and the Micotrin dome ( 1.1 ka) which are proposed to originate from the same magmatic system, with a detailed petrologic analysis of phenocrysts to determine commonalities or changes in pre-eruptive conditions (i.e., intensive variables). The ignimbrites are saturated in five phenocrysts (plagioclase + orthopyroxene + clinopyroxene + ilmenite + magnetite ± amphibole ± quartz), and the lava dome contains the same assemblage, but with notable differences: amphiboles are entirely reacted, and quartz occurs in greater abundance. Plagioclase in the ignimbrites ranges in composition from An46-93, and those in the dome range from An46-85. Two Fe-Ti oxide geo-thermometry reveal pre-eruptive temperatures from 730-820°C for three different ignimbrite units, whereas the pre-eruptive temperature for the dome is slightly hotter (850±23°C). Values of fO2 (relative to NNO) derived from Fe-Ti oxide oxygen-barometry range from +0.3 to +1.32 ΔNNO for the ignimbrites, which overlap with those from the dome (+0.5 to +0.9 ΔNNO). Pre-eruptive temperatures, plagioclase compositions, whole rock and glass compositions are incorporated into a plagioclase-liquid hygrometer to determine pre-eruptive melt H2O contents for each sample. H2O contents for ignimbrites range from 7.1-9.3 wt%, and those from the lava dome range from 6.7-7.1 wt%. Application of a H2O solubility model shows that water contents for the Roseau magmas correspond to pressures of 3-5 kbar. The most notable difference between the explosive and effusive magmas is that the lava dome has a higher pre-eruptive temperature than the ignimbrites. However, the results collectively suggest that more recent volcanism in

  18. Temporal Evolution of Volcanic and Plutonic Magmas Related to Porphyry Copper Ores Based on Zircon Geochemistry (United States)

    Dilles, J. H.; Lee, R. G.; Wooden, J. L.; Koleszar, A. M.


    Porphyry Cu (Mo-Au) and epithermal Au-Ag ores are globally associated with shallow hydrous, strongly oxidized, and sulfur-rich arc intrusions. In many localities, long-lived magmatism includes evolution from early andesitic volcanic (v) and plutonic (p) rocks to later dacitic or rhyolitic compositions dominated by plutons. We compare zircon compositions from three igneous suites with different time spans: Yerington, USA (1 m.y., p>v), El Salvador, Chile (4 m.y., p>v), and Yanacocha, Peru (6 m.y., v>p). At Yerington granite dikes and ores formed in one event, at ES in 2 to 3 events spanning 3 m.y., and at Yanacocha in 6 events spanning 5 m.y. At both ES and Yanacocha, high-Al amphiboles likely crystallized at high temperature in the mid-crust and attest to deep magmas that periodically recharged the shallow chambers. At Yanacocha, these amphiboles contain anhydrite inclusions that require magmas were sulfur-rich and strongly oxidized (~NNO+2). The Ti-in-zircon geothermometer provides estimates of 920º to 620º C for zircon crystallization, and records both core to rim cooling and locally high temperature rim overgrowths. Ore-related silicic porphyries yield near-solidus crystallization temperatures of 750-650°C consistent with low zircon saturation temperatures. The latter zircons have large positive Ce/Ce* and small negative Eu/Eu*≥0.4 anomalies attesting to strongly oxidized conditions (Ballard et al., 2001), which we propose result from crystallization and SO2 loss to the magmatic-hydrothermal ore fluid (Dilles et al., 2015). The Hf, REE, Y, U, and Th contents of zircons are diverse in the magma suites, and Th/U vs Yb/Gd plots suggest a dominant role of crystal fractionation with lesser roles for both crustal contamination and mixing with high temperature deep-sourced mafic magma. Ce/Sm vs Yb/Gd plots suggest that magma REE contents at contamination are most evident in pre-ore magmas, whereas ore-forming intrusions at low temperatures are dominated by crystal


    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.

  20. 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

  1. Chemical Analysis of Reaction Rims on Olivine Crystals in Natural Samples of Black Dacite Using Energy-Dispersive X-Ray Spectroscopy, Lassen Peak, CA. (United States)

    Graham, N. A.


    Lassen Volcanic Center is the southernmost volcanic region in the Cascade volcanic arc formed by the Cascadia Subduction Zone. Lassen Peak last erupted in 1915 in an arc related event producing a black dacite material containing xenocrystic olivine grains with apparent orthopyroxene reaction rims. The reaction rims on these olivine grains are believed to have formed by reactions that ensued from a mixing/mingling event that occurred prior to eruption between the admixed mafic andesitic magma and a silicic dacite host material. Natural samples of the 1915 black dacite from Lassen Peak, CA were prepared into 15 polished thin sections and carbon coated for analysis using a FEI Quanta 250 Scanning Electron Microscope (SEM) to identify and measure mineral textures and disequilibrium reaction rims. Observed mineralogical textures related to magma mixing include biotite and amphibole grains with apparent dehydration/breakdown rims, pyroxene-rimmed quartz grains, high concentration of microlites in glass matrix, and pyroxene/amphibole reaction rims on olivine grains. Olivine dissolution is evidenced as increased iron concentration toward convolute edges of olivine grains as observed by Backscatter Electron (BSE) imagery and elemental mapping using NSS spectral imaging software. In an attempt to quantify the area of reaction rim growth on olivine grains within these samples, high-resolution BSE images of 30 different olivine grains were collected along with Energy-Dispersive X-Ray Spectroscopy (EDS) of different phases. Olivine cores and rims were extracted from BSE images using Photoshop and saved as separate image files. ImageJ software was used to calculate the area (μm2) of the core and rim of these grains. Average pyroxene reaction rim width for 30 grains was determined to be 11.68+/-1.65 μm. Rim widths of all 30 grains were averaged together to produce an overall average rim width for the Lassen Peak black dacite. By quantifying the reaction rims on olivine grains

  2. 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

  3. Synkinematic emplacement of the magmatic epidote bearing Major Isidoro tonalite-granite batholith: Relicts of an Ediacaran continental arc in the Pernambuco-Alagoas domain, Borborema Province, NE Brazil (United States)

    Silva, Thyego R. da; Ferreira, Valderez P.; Lima, Mariucha M. Correia de; Sial, Alcides N.; Silva, José Mauricio R. da


    The Neoproterozoic Major Isidoro batholith (˜100 km2), composed of metaluminous to slightly peraluminous magmatic epidote-bearing tonalite to granite, is part of the Águas Belas-Canindé composite batholith, which intruded the Pernambuco-Alagoas Domain of the Borborema Province, northeastern Brazil. These rocks contain biotite, amphibole, titanite and epidote that often shows an allanite core as key mafic mineral phases. K-diorite mafic enclaves are abundant in this pluton as well as are amphibole-rich clots. The plutonic rocks are medium-to high-K calc-alkaline, with SiO2 varying from 59.1 to 71.6%, Fe# from 0.6 to 0.9 and total alkalis from 6.1 to 8.5%. Chondrite-normalized REE patterns are moderately fractionated, show (La/Lu)N ratios from 13.6 to 31.8 and discrete negative Eu anomalies (0.48-0.85). Incompatible-element spidergrams exhibit negative Nb-Ta and Ti anomalies. This batholith was emplaced around 627 Ma (U-Pb SHRIMP zircon age) coevally with an amphibolite-facies metamorphic event in the region. It shows Nd-model age varying from 1.1 to 1.4 Ga, average ɛNd(627Ma) of -1.60 and back-calculated (627 Ma) initial 87Sr/86Sr ratios from 0.7069 to 0.7086. Inherited zircon cores that yielded 206Pb/238U ages from 800 to 1000 Ma are likely derived from rocks formed during the Cariris Velhos (1.1-0.9 Ga) orogenic event. These isotopic data coupled with calculated δ18O(w.r.) value of +8.75‰ VSMOW indicate an I-type source and suggest a reworked lower continental crust as source rock. A granodioritic orthogneiss next to the Major Isidoro pluton, emplaced along the Jacaré dos Homens transpressional shear zone, yielded a U-Pb SHRIMP zircon age of 642 Ma, recording early tectonic movements along this shear zone that separates the Pernambuco-Alagoas Domain to the north, from the Sergipano Domain to the south. The emplacement of the Major Isidoro pluton was synkinematic, coeval with the development of a regional flat-lying foliation, probably during the peak of

  4. The abundance and hydrogen isotopic composition of water in SNC meteorites (United States)

    Leshin, Laurie Ann


    The water in the current martian atmosphere contains approximately 5 times more deuterium (D) than water on Earth (corresponding to a delta-D value of approximately +4000) resulting from preferential loss of hydrogen relative to deuterium from the martian atmosphere. This thesis places constraints on the D/H of other martian water reservoirs by measuring the D/H of water in hydrous phases within the SNC meteorites, thought to be samples of martian igneous rocks. Results from vacuum extractions of volatiles from bulk SNC samples by stepwise heating show the water yields to decrease and delta-D values to increase to well above terrestrial values with increasing temperature indicative of mixing between terrestrial water (contamination) released at low temperatures and martian water released at high temperatures. The high temperature delta-D values reach approximately +2000 for Shergotty, the most D-enriched sample. However, even the highest delta-D values measured may represent lower limits on the true values due to partial exchange with lighter terrestrial water D/H and water contents of individual amphibole, biotite and apatite grains in several SNC meteorites were measured using an ion microprobe. The amphiboles contain an order of magnitude less water than previously assumed, suggesting that SNC parent magmas may have been less hydrous than previously proposed. The delta-D values of the phases range from approximately +500 to +4300. The variability and D-enriched nature of these values imply that the primary igneous phases have not retained a martian magmatic water signature. Rather, the high and variable D/H of the water in these phases, like that released at high temperatures from bulk SNC samples, is concluded to result from the interaction of the samples with D-enriched martian crustal fluids after crystallization, probably in an environment similar to terrestrial magmatic hydrothermal systems. The data presented in this thesis represent the first direct

  5. Seeing through the magnetite: Reassessing Eoarchean atmosphere composition from Isua (Greenland ≥3.7 Ga banded iron formations

    Directory of Open Access Journals (Sweden)

    Allen P. Nutman


    Full Text Available Estimates of early atmosphere compositions from metamorphosed banded iron formations (BIFs including the well-studied ≥3.7 BIFs of the Isua supracrustal belt (Greenland are dependent on knowledge of primary versus secondary Fe-mineralogical assemblages. Using new observations from locally well preserved domains, we interpret that a previously assumed primary redox indicator mineral, magnetite, is secondary after sedimentary Fe-clays (probably greenalite ± carbonates. Within ∼3.7 Ga Isua BIF, pre-tectonic nodules of quartz + Fe-rich amphibole ± calcite reside in a fine-grained (≤100 μm quartz + magnetite matrix. We interpret the Isua nodule amphibole as the metamorphosed equivalent of primary Fe-rich clays, armoured from diagenetic oxidative reactions by early silica concretion. Additionally, in another low strain lacunae, ∼3.76 Ga BIF layering is not solid magnetite but instead fine-grained magnetite + quartz aggregates. These magnetite + quartz aggregates are interpreted as the metamorphosed equivalent of Fe-clay-rich layers that were oxidised during diagenesis, because they were not armoured by early silicification. In almost all Isua BIF exposures, this evidence has been destroyed by strong ductile deformation. The Fe-clays likely formed by abiotic reactions between aqueous Fe2+ and silica. These clays along with silica ± carbonate were deposited below an oceanic Fe-chemocline as the sedimentary precursors of BIF. Breakdown of the clays on the sea floor may have been by anaerobic oxidation of Fe2+, a mechanism compatible with iron isotopic data previously published on these rocks. The new determinations of the primary redox-sensitive Fe-mineralogy of BIF significantly revise estimates of early Earth atmospheric oxygen and CO2 content, with formation of protolith Fe-rich clays and carbonates compatible with an anoxic Eoarchean atmosphere with much higher CO2 levels than previously estimated for Isua and in the

  6. Coexistence of alkaline-carbonatite complexes and high-MgO CFB in the Paranà-Etendeka province: Insights on plume-lithosphere interactions in the Gondwana realm (United States)

    Natali, Claudio; Beccaluva, Luigi; Bianchini, Gianluca; Siena, Franca


    A careful review of petrological and geochemical data on the Paranà-Etendeka igneous province is reported, with particular attention being devoted to the relationships between high-MgO CFB (tholeiitic basalts-picrites) and nearly coeval alkaline-carbonatite complexes linked to the same extensional tectonics on a regional scale. At 135-130 Ma, the tectonomagmatic activity was focused in Etendeka, the centre of the restored province, and characterised by an exclusive occurrence of the hottest and deepest high-MgO CFB (potential temperature Tp up to 1590 °C and pressure up to 5 GPa) possessing the same Sr-Nd-Pb isotopic composition of the "Gough" geochemical component, a marker of the initial Tristan plume activity. Etendeka high-MgO CFB thus represent the most genuine proxies of sublithospheric melts generated at the plume axis and are relatively unaffected by lithospheric contamination. Nearly coeval (133-128 Ma) alkaline‑carbonatite complexes cluster around the extensional structures of the Ponta Grossa Arch (e.g., Jacupiranga and Juquia in Brazil) and the Damara Belt (e.g., Erongo, Okurusu, Okenyenya and Paresis in Namibia), both of which intersect the early track of the south Atlantic opening. Compared to high-MgO CFB, alkaline magmas display distinctive isotopic signatures and an incompatible element distribution consistent with their generation from lithospheric mantle sources, which were variably metasomatised (veined?) by amphibole and phlogopite. Metasomes of alkaline mantle sources have a HIMU affinity and are dominated by amphibole in Namibia, whereas they display EM1 tendency and a more relevant role of phlogopite in Brazil, which implies important lithospheric differences at a regional scale. The tectonomagmatic features of Paranà-Etendeka -also shared by other Gondwana LIPs, such as Deccan and Karoo- can be reconciled by a generalized model where a hot plume impinging on a relatively thick lithosphere caused, in the axial zone, the contemporaneous

  7. Long term storage of explosively erupted magma at Nevado de Toluca volcano, Mexico (United States)

    Arce, J. L.; Gardner, J.; Macias, J. L.


    Dacitic magmas production is common in subduction-related volcanoes, occurring in those with a long period of activity as a result of the magmatic evolution. However, in this evolution many factors (i.e. crystal fractionation, assimilation, magma mixing) can interact to produce dacites. Nevado de Toluca volcano (4,680 masl; 19°09'N; 99°45'W) Central Mexico has recorded a long period of time producing dacites explosively, at least during 42 ka of activity, involving several km3 of magma, with two important Plinian-type eruptions occurred at ~21.7 ka (Lower Toluca Pumice) and ~10.5 ka (Upper Toluca Pumice). Questions like, what was the mechanism responsible to produce voluminous dacitic magma and how the volatiles and pressure changed in the Nevado de Toluca system, remain without answers. Dacites from the Lower Toluca Pumice (LTP) contain plagioclase, amphibole, iron-titanium oxides, and minor resorbed biotite, set in a glassy-vesicular matrix and the Upper Toluca Pumice (UTP) dacites contain the same mineral phases plus orthopyroxene. Ilmenite- ulvospinel geothermometry yielded a temperature of ~860°C for the LTP dacite, a little hotter than the UTP (~ 840°C). Based on hydrothermal experiments data, amphibole is stable above 100 MPa under 900°C, while plagioclase crystallizes up to 250-100 MPa at temperatures of 850-900°C. Pyroxene occurs only at pressures of 200-100 MPa with its respective temperatures of 825-900°C. Water contents in the LTP magma (2-3.5 wt %) are similar to that calculated for the UTP magma (1.3-3.6 wt %). So, there are only small changes in temperature and pressure from ~21.7 ka to 10.5 ka. It is noteworthy that orthopyroxene is absent in the LTP, however reaction-rimmed biotite (probably xenocrystic) is commonly observed in all dacites. Hence, almost all dacitic magmas seem to be stored at relatively similar pressures, water contents, and temperatures. All of these data could suggest repetitive basic magma injections producing the

  8. Platinum-Group Minerals and Other Accessory Phases in Chromite Deposits of the Alapaevsk Ophiolite, Central Urals, Russia

    Directory of Open Access Journals (Sweden)

    Federica Zaccarini


    Full Text Available An electron microprobe study has been carried out on platinum-group minerals, accessory phases, and chromite in several chromite deposits of the Alapaevsk ophiolite (Central Urals, Russia namely the Bakanov Kluch, Kurmanovskoe, Lesnoe, 3-d Podyony Rudnik, Bol’shaya Kruglyshka, and Krest deposits. These deposits occur in partially to totally serpentinized peridotites. The microprobe data shows that the chromite composition varies from Cr-rich to Al-rich. Tiny platinum-group minerals (PGM, 1–10 µm in size, have been found in the chromitites. The most abundant PGM is laurite, accompanied by minor cuproiridsite and alloys in the system Os–Ir–Ru. A small grain (about 20 μm was found in the interstitial serpentine of the Bakanov Kluch chromitite, and its calculated stoichiometry corresponds to (Ni,Fe5P. Olivine, occurring in the silicate matrix or included in fresh chromite, has a mantle-compatible composition in terms of major and minor elements. Several inclusions of amphibole, Na-rich phlogopite, and clinopyroxene have been identified. The bimodal Cr–Al composition of chromite probably corresponds to a vertical distribution in the ophiolite sequence, implying formation of Cr-rich chromitites in the deep mantle, and Al-rich chromitites close to the Moho-transition zone, in a supra-subduction setting. The presence of abundant hydrous silicate inclusions, such as amphibole and phlogopite, suggests that the Alapaevsk chromitites crystallized as a result of the interaction between a melt enriched in fluids and peridotites. Laurite and cuproiridsite are considered to be magmatic in origin, i.e., entrapped as solid phases during the crystallization of chromite at high temperatures. The sulfur fugacity was relatively high to allow the precipitation of Ir-bearing sulfides, but below the Os–OsS2 buffer. The alloys in the system Os–Ir–Ru are classified as secondary PGM, i.e., formed at low temperature during the serpentinization process. The

  9. Chemical composition of the continental crust: Insights from a quantitative interpretation of the Vp/Vs ratio (United States)

    Guerri, M.; Youssof, M.; Fullea, J.


    The processes driving continental crust formation are not yet fully understood. One of the fundamental keys necessary to investigate the enigma is represented by crustal composition. The Vp/Vs ratio from seismic receiver functions or tomography studies is a powerful tool to constrain the crustal composition. However, to date only qualitative relationships between Vp/Vs and composition have been proposed. We present a quantitative interpretation of the Vp/Vs in terms of major oxide components, based on thermo-elastic constrained modelling of rock phase equilibria and physical properties. The geophysical-petrological approach is implemented in the new release of the software package LitMod, which now allows for integrated and self-consistent modeling of the entire lithosphere (crust + lithospheric mantle) and upper mantle. Forward modelling of the Vp/Vs, based on petrology and thermodynamics, reveals that, as expected, mafic compositions have higher Vp/Vs than felsic ones. However, in high temperature settings (surface heat flow > 75 mW/m2), the quartz alpha / quartz beta transition strongly increases Vp, leaving Vs almost unaltered, leading to SiO2-rich compositions displaying Vp/Vs values higher than those associated with mafic compositions. Additionally, we highlight the importance of H2O, the presence of which stabilizes amphibole (in place of pyroxene), characterized by a relatively low Vp/Vs. If H2O is present, mafic compositions show Vp/Vs ratios that are comparable to those produced by anhydrous SiO2-rich compositions. The destabilization of amphibole (in favour of pyroxene) generates a sharp seismic discontinuity, potentially detectable by, for example, seismic refraction and receiver function investigations. We invert the Vp/Vs ratio for composition and hydrous state of the crust in the Southern African cratons. Our results show that the Kaapvaal craton, Archean in age, has an intermediate (SiO2 60 wt%) composition. The finding has implications on our

  10. Exposure of UK industrial plumbers to asbestos, Part I: Monitoring of exposure using personal passive samplers. (United States)

    Burdett, Garry; Bard, Delphine


    Epidemiological data suggest that there has been and may continue to be a significant risk to maintenance workers, who through their work may disturb asbestos-containing materials (ACM). The sampling and assessment of maintenance workers' exposure is a particular problem because they may not know that they are working with ACM. A strategy to monitor their true exposure has been developed and applied to one group of workers. The asbestos exposure of industrial plumbers was measured using personal passive samplers developed at the Health and Safety Laboratory (HSL). The light-weight samplers, which collect particles by electrostatic attraction, are simple to use and do not require prior knowledge that asbestos is to be disturbed as does conventional sampling. The samplers were issued by post and analysed, after return, using transmission electron microscopy (TEM). The strategy was found to be a reasonably efficient and cost-effective way to obtain data on maintenance worker's exposure to asbestos. The results of the TEM analysis of the passive samplers showed that the percentage of workers exposed to >5 microm long asbestos fibres was 62% in Round 1 and 58% in Round 2. For phase contrast microscopy equivalent (PCME) asbestos fibres, the values were 46 and 29%, respectively. The three samples with the highest numbers of fibres were followed up and were associated with plumbers working in areas which had supposedly been stripped of asbestos just prior to their starting work, suggesting that poor removal, clean-up and clearance practice presents a significant part of the risk to plumbers. Although flow rates will vary with conditions and time, an approximate average sampling rate from previous comparisons was used to calculate the concentration. This gave an average exposure to regulated PCME fibres of 0.009 f ml-1 for amphibole asbestos and 0.049 f ml-1 for chrysotile. The calculate risk based on the PCME fibre types collected and their estimated concentrations, showed

  11. Lithospheric origin for Neogene-Quaternary Middle Atlas lavas (Morocco): Clues from trace elements and Sr-Nd-Pb-Hf isotopes (United States)

    Bosch, Delphine; Maury, René C.; El Azzouzi, M'hammed; Bollinger, Claire; Bellon, Hervé; Verdoux, Patrick


    This study presents new geochemical data on 26 mafic lavas from the Middle Atlas and Central Morocco volcanic provinces, including Miocene nephelinites and Pliocene-Quaternary (3.9-0.6 Ma) nephelinites, basanites, alkali and subalkaline basalts. Most of them represent near-primary magmas, although some alkali basalts were derived from the minor fractionation of olivine and diopside phenocrysts. These evolved samples and the subalkaline basalt display higher 207Pb/204Pb and Zr/Nb ratios and lower εNd consistent with their contamination by lower crustal granulites during an open fractionation process. The progressive enrichment in incompatible elements observed from alkali basalts to nephelinites suggests their derivation from decreasing partial melting degrees of an enriched mantle source located at the garnet-spinel transition zone. The strong negative spikes observed for K in multielement patterns indicate that this source contained a residual pargasitic amphibole. We propose that partial melting occurred at around 2 GPa, i.e. near the lithosphere-asthenosphere boundary beneath the Middle Atlas (60-80 km). The trace element and isotopic Sr-Nd-Pb-Hf signature of the uncontaminated lavas displays a geochemical flavour intermediate between those of high μ (HIMU), “C”, and enriched mantle components. It is very similar to that of abundant metasomatic amphibole- and clinopyroxene-rich lithospheric peridotites and pyroxenites carried by Middle Atlas lavas, which likely represent an analog of the source of these lavas. It is therefore not necessary to postulate the contribution of a “fresh” asthenospheric mantle to their genesis. We propose that they resulted from the partial melting of the base of a veined lithospheric mantle metasomatised during the late Cretaceous by alkaline melts from the Central Atlantic plume, the ancestor of the Canary plume. Melting was probably triggered by the flux of a hot mantle within a regional SW-NE sub-lithospheric channel, in

  12. 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(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 cataclasites overprinted by prehnite. δ18O values range from +1 to + 6 per mil, indicating alteration at temperatures generally >200 °C. Preliminary modelling using Comsol Multiphysics suggests that the temperatures of the overprinting alteration

  13. Rehydration reactions and microstructure development in lower crustal granulites from the Bergen Arcs, Norway (United States)

    Erickson, Timmons; Reddy, Steven; Clark, Chris; Hand, Martin; Bhowany, Kamini; Prent, Alex


    An investigation of the feedbacks generated between lower crust-derived fluids and deformation microstructures formed within retrogressed granulites from the Bergen Arcs on the west coast of Norway will be presented. We hope to assess the role of deformation microstructures in assisting fluid infiltration into nominally impermeable lower crustal rocks, the role of fluids in driving mineral reactions and thus weakening the rock strength, and the interplay between these mechanisms. Granulite wall-rock adjacent to an amphibolite facies shear zone near Isdal, Norway has been sectioned, texturally mapped using electron backscatter diffraction (EBSD) and chemically mapped using energy dispersive x-ray spectrometry (EDS). The granuilte protolith is made up of a Precambrian anorthosite - gabbro assemblage of plagioclase and coronas of garnet around clinopyroxene. Local alteration of the granulite to eclogite and amphibolite occurred during the Caledonian orogen and has been attributed to the infiltration of fluids during the high strain event (Mukai et al., 2014). In thin section a thin ( 75 µm) rim of pargasite amphibole can be seen between the garnet and plagioclase, while the rim of amphibole is thicker (600 µm) when between the clinopyroxene and plagioclase. Plagioclase is coarse grained (mms in diameter) and displays prominent growth twins within the undeformed regions of the granulite. However, within a sheared domain of the granulite the grain size has been significantly reduced (max diameter = 74 µm) as has the growth twinning. The plagioclase from the sheared domain also displays a crystallographic preferred orientation (CPO) which does not appear to be inherited from the 'parent' grains. Within the strained domain there is also an increase in the reaction of garnet to pargasite, which also displays a strong CPO. These textural relationships offer the opportunity to study the active mechanisms during hydration of the lower crust and evaluate the relationships

  14. Amphibolite to granulite progressive metamorphism in the Niquelândia Complex, Central Brazil: regional tectonic implications (United States)

    Filho, C. F. Ferreira; De Moraes, R.; Fawcett, J. J.; Naldrett, A. J.


    The Niquelândia Complex is a major Proterozoic mafic and ultramafic layered intrusion in central Brazil. Ductile deformation and associated metamorphic recrystallization are widespread along ductile shear zones. Bands of alumina and silica-rich rocks (less than few meters thick) occur in the central parts of these ductile shear zones. Metamorphic grade, ranging from amphibolite to granulite facies, increases progressively downward in the layered intrusion stratigraphy. The three mapped metamorphic zones: amphibolite zone, amphibolite-granulite transition zone and granulite zone, are parallel to the intrusion stratigraphy. Metabasites show progressive changes in mineral assemblages, texture, and Ca-amphibole composition in a traverse covering the three metamorphic zones. With increasing metamorphic grade, amphibolites (hbl+pl ± cpx ± grt ± ep) give way to hornblende granulites (hbl+pl+cpx+opx) and anhydrous mafic granulites (pl+cpx+opx). The Ti, A1 IV and Na+K content of amphiboles increase progressively with metamorphic grade. Quartz-rich rocks have kyanite as the Al 2SiO 5 polymorph in the amphibolite zone, whereas sillimanite occurs in the granulite zone. Geothermobarometry and mineral stability data indicate P-T conditions of peak metamorphism at about 700 °C and 6-8 kbars in the amphibolite zone and temperatures higher than 800 °C in the granulite zone. In quartz-rich rocks of the granulite zone, retrogressive processes are indicated by reaction coronas of sil+grt between peak metamorphic assemblages of hc+qtz and replacement of sillimanite by kyanite. These reactions have an appreciable temperature dependence and together they indicate a retrogressive path characterized by an initial period of nearly isobaric cooling. Previously reported U-Pb zircon dating demonstrates the coeval nature of the amphibolite and granulite facies metamorphism and supports the notion that the entire terrain represents a single continuous crustal section. The metamorphic age

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

    International Nuclear Information System (INIS)

    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 2 O 6 ), and nephrite, Ca 2 (Mg, Fe) 5 (Si 4 O 11 ) 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,Ca 2 Mg 5 (Si 4 O 11 ) 2 (OH) 2 e actinolite, Ca 2 Fe 5 (Si 4 O 11 ) 2 (OH) 2 ; and the pyroxenes: rhodonite, MnSiO 3 and diopside, Ca Mg(Si 2 O 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 best possibility of inclusion in rhodonite. (author)

  16. 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

  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. 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

  19. 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

  20. 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

  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. 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

  3. Vesiculation processes during the 1997 Vulcanian explosions of Soufrière Hills Volcano, Montserrat (United States)

    Giachetti, Thomas; Druitt, Timothy H.; Burgisser, Alain; Arbaret, Laurent


    Soufrière Hills Volcano had two periods of repetitive Vulcanian activity in 1997, during which 88 explosions occurred. Each explosion discharged the contents of the upper 0.5-2 km of the conduit, two thirds as pyroclastic flows and the rest as fallout from 3-15 km high buoyant plumes: frothy pumices from a deep, gas-rich zone, lava and breadcrust bombs from a degassed lava plug, and dense pumices from a transition zone. Vesicles constitute 1-66 vol% of breadcrust bombs and 24-79% of pumices, all those larger than a few tens of µm being interconnected. Small vesicles (bombs formed from originally non-vesicular magma. Most large vesicles (> few hundreds of µm) in pumices are interpreted as pre-dating explosion, implying pre-explosive conduit porosities up to 55%. About 15% of large vesicles in pumices, and all those in breadcrust bombs, are angular voids formed by syn-explosive fracturing of amphibole phenocrysts. An intermediate-sized vesicle population formed by coalescence of the small syn-explosive bubbles. Nucleation took place heterogeneously on titanomagnetite, number densities of which greatly exceed those of vesicles, and bubble growth took place mainly by decompression. Growth took place under disequilibrium conditions largely by decompression-driven expansion; diffusive outgassing of melt was limited by the short timescale of the explosions, accounting for the high water contents preserved in matrix glasses. Development of vesicle textures was controlled by the time interval between decompression and onset of clast-surface cooling. Plug fragments entered the air quickly after fragmentation (~10 s), so interiors continued to vesiculate once the rinds had quenched. A larger time interval for deep-derived pumices (~50 s) allowed complete vesiculation prior to quench, accounting for the textural similarity between flow and fall pumices, despite different thermal histories after leaving the vent. This also allowed syn-explosive coalescence to proceed further

  4. Bubble nucleation, growth and coalescence during the 1997 Vulcanian explosions of Soufrière Hills Volcano, Montserrat (United States)

    Giachetti, T.; Druitt, T. H.; Burgisser, A.; Arbaret, L.; Galven, C.


    Soufrière Hills Volcano had two periods of repetitive Vulcanian activity in 1997. Each explosion discharged the contents of the upper 0.5-2 km of the conduit as pyroclastic flows and fallout: frothy pumices from a deep, gas-rich zone, lava and breadcrust bombs from a degassed lava plug, and dense pumices from a transition zone. Vesicles constitute 1-66 vol.% of breadcrust bombs and 24-79% of pumices, all those larger than a few tens of µm being interconnected. Small vesicles (bombs formed from originally non-vesicular magma. Most large vesicles (> few hundreds of µm) in pumices are interpreted as pre-dating explosion, implying pre-explosive conduit porosities up to 55%. About a sixth of large vesicles in pumices, and all those in breadcrust bombs, are angular voids formed by syn-explosive fracturing of amphibole phenocrysts. An intermediate-sized vesicle population formed by coalescence of the small syn-explosive bubbles. Bubble nucleation took place heterogeneously on titanomagnetite, number densities of which greatly exceed those of vesicles, and growth took place mainly by decompression. Development of pyroclast vesicle textures was controlled by the time interval between the onset of explosion-decompression and surface quench in contact with air. Lava-plug fragments entered the air quickly after fragmentation (˜ 10 s), so the interiors continued to vesiculate once the rinds had quenched, forming breadcrust bombs. Deeper, gas-rich magma took longer (˜ 50 s) to reach the surface, and vesiculation of resulting pumice clasts was essentially complete prior to surface quench. This accounts for the absence of breadcrusting on pumice clasts, and for the textural similarity between pyroclastic flow and fallout pumices, despite different thermal histories after leaving the vent. It also allowed syn-explosive coalescence to proceed further in the pumices than in the breadcrust bombs. Uniaxial boudinage of amphibole phenocrysts in pumices implies significant syn

  5. 40Ar/39Ar constraints on the activity of the Temsamane extensional detachment (eastern Rif, Morocco) (United States)

    Jabaloy Sánchez, A.; Booth-Rea, G.; Azdimousa, A.; Asebriy, L.; Vázquez-Vílchez, M.; Martínez-Martínez, J. M.; Gabites, J.


    The subducted North Maghrebian passive margin was exhumed by an upper crustal brittle-ductile extensional detachment and brittle low-angle normal faults in a continental subduction transform setting. The Temsamane detachment in the eastern Rif is defined by a ductile shear zone approximately 100 m thick with a low-angle ramp geometry that cuts down into the Temsamane fold-nappe stack. The shear zone shows southwestward kinematics and separates epizone metapelites of the Temsamane units below from the epizone to diagenetic rocks of the Tanger-Ketama-Aknoul units above. To the east, the detachment becomes brittle, branching into a listric-fan that cuts through 10-6 Ma sediments and volcanoclastics in the Tres Forcas cape. New 40Ar/39Ar radiometric ages on amphiboles and micas from the footwall of the Temsamane detachment indicate that the metamorphic peak was reached in the footwall (Temsamane units) at ca. 21 Ma, producing the amphibolite epidote facies in the Ras Afrou Unit. The cooling of the footwall rocks below the 325 °C occurred between the 16 and 13 Ma, while apatite fission track ages indicate that the cooling below the 120 °C occurred at ca. 11 Ma. The 40Ar/39Ar radiometric ages on amphiboles and micas of the metamorphic klippes over the Temsamene units (Ait-Amrâne massif) indicates that the Jurassic marbles of the Tanger-Ketama Unit reached their metamorphic peak at ca. 80 Ma, in agreement with previously published K/Ar ages in micas. The rocks of the Tanger-Ketama Unit cooled below the 120 °C between 17.0 ± 2.4 Ma and 13.9 ± 1.8 Ma. We interpret the increase of cooling rates of the footwall rocks between 15-13 Ma and 11 Ma as due to the activity of the Temsamane detachment fault. Thus, both the North Maghrebian and the South Iberian subducted passive margins were exhumed in the Betic and Rif branches of the Gibraltar arc by SW-directed brittle-ductile detachments during the Late Miocene in an oblique collisional setting.

  6. Protracted Storage and Lower Crust Differentiation at Baru Volcano, Panama (United States)

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


    Baru volcano is located inboard of the subducting Cocos and Coiba ridges in the Western Panamanian arc, providing an opportunity to explore the role of ridge subduction in arc volcanism. The extraordinary exposure of Miocene to present stratigraphy revealed on the flanks of Baru volcano, allows for the study of the temporal chemical variation of erupted magmas. Detailed chemical and geochronological analyses of Baru volcano indicate two periods of volcanism with substantial chemical dissimilarities. The first period of volcanism (~13 ma-9 ma) is characterized by typical island arc calcalkaline volcanism similar to other sections of the Central American Volcanic Arc. The second period of volcanism (~0.15 ma - present) is characterized by heterogeneous major (i.e. SiO2 48-64%, MgO 1.5-14.5%, 4-15% CaO, etc) and trace element contents, that display adakitic-like features such as steep REE patterns, pronounced depletions in the HREE, low Y, high Sr, and high Sr/Y. This adakite-like volcanism is responsible for most of the volume of this 3474 m high edifice. We interpret that the transition from normal arc volcanism to adakite-like volcanism is associated with an increased depth of magmatic fractionation and protracted storage in the Panamanian lithosphere. Parental water rich basalts stored at deep crustal levels would allow for garnet to be a stable crystallizing phase resulting in the adakite-like signature, while protracted storage could allow for extensive amphibole crystallization. Our interpretations are supported by the observation that amphibole is the sole mafic phase present in the adakite-like Panamanian magmas, while is absent in the older calcalkaline volcanism. Increased depth of magmatic differentiation and storage could be explained as a byproduct of oceanic ridge-trench interaction. The arrival of the Cocos and Coiba ridges to the Middle America Trench likely caused significant perturbations of the Panamanian lithosphere such as: enhanced plate

  7. Lamprophyres from the Harohalli dyke swarm in the Halaguru and Mysore areas, Southern India: Implications for backarc basin magmatism (United States)

    Lanjewar, Shubhangi; Randive, Kirtikumar


    The Bangalore and Harohalli dyke swarms occur in the eastern part of the Dharwar craton. The older Bangalore dyke swarm is made up of dolerites, trending east-west, and the younger contains alkaline dykes that trend approximately north-south. The lamprophyres of the Harohalli dyke swarm occur in the Halaguru and Mysore industrial areas where they are exposed as fresh porphyritic - panidiomorphic dykes, containing crustal xenoliths, and showing chilled contacts with the country rock charnokites. They are chiefly composed of amphiboles which form well-developed phenocrysts. Clinopyroxenes are present in some of the dykes. Compositional zoning is observed in clinopyroxenes and amphiboles; their zoning patterns indicate that the magma experienced cryptic variations and that fractional crystallization was a dominant process in the evolution of the Harohalli Lamprophyres (HRL). The HRL are calc-alkaline with shoshonitic affinity and exhibit a K2O/Na2O ratio of ∼1. They show primitive (MORB-like) trace-element characters. LILE and LREE both show marginally enriched patterns; whereas HFSE and HREE show strongly depleted patterns. In the regional geologic sense, HRL dykes are characterised by two major influences; namely, (i) primary source region characteristics, which are geochemically more primitive, roughly falling within fields of primitive - MORB and enriched- MORB and (ii) the continental lithosphere. The data points for the HRL distinctly show their proximity to N-MORB and scatter towards the continental crust. Moreover, features like xenolith assimilation might influence the trace-element characteristics of the HRL dykes. Such magmas with mixed characters can be formed in a backarc basin environment. Geochemical proxies such as Ba/Nb vs Nb/Yb, Ba/Th vs Th/Nb, and the water content of magmas; which have been effectively used for discriminating backarc basin magmas worldwide, also indicate that the HRL magmas were generated in a backarc environment with inputs from

  8. Timing of exhumation of the Ereendavaa metamorphic core complex (north-eastern Mongolia) - U-Pb and 40Ar/39Ar constraints (United States)

    Daoudene, Yannick; Ruffet, Gilles; Cocherie, Alain; Ledru, Patrick; Gapais, Denis


    The occurrence of numerous NE-SW trending rift basins that locally bound metamorphic core complexes in Transbaikalia, northern Mongolia and north-eastern China indicates that the eastern domain of the Central Asian Orogenic Belt was affected by a large-scale NW-SE extensional tectonic event during late Jurassic to early Cretaceous times. Available geochronological information about the formation of metamorphic core complexes in the region define partly synchronous periods in Transbaikalia (134-121 Ma) and North China (136-110 Ma) suggesting dome exhumation during the early Cretaceous. In north-eastern Mongolia, the Ereendavaa Range, lined by the Onon Shear Zone, was recently interpreted as one of these metamorphic core complexes, of late Jurassic to early Cretaceous age, on the basis of U-Pb zircons data from two synkinematic pegmatite dykes. However, this wide time range remains to be discussed. The present work constrains the tectono-thermal evolution of the range by providing new MC-ICP-MS U-Pb zircons ages from pegmatite dykes and metamorphic igneous rocks, and mica and amphibole 40Ar/39Ar laser step-heating ages from metamorphic and magmatic rocks that crop out within the range. The results show that (1) the Ereendavaa range was the locus of a widespread magmatic activity prior to its exhumation from late Jurassic times, (2) cooling of the range began at least at 137.9 ± 0.3 Ma as revealed by a 40Ar/39Ar plateau ages obtained from an hornblende sampled within the range core, and (3) exhumation along the Onon Shear Zone occurred from 130.3 ± 1.9 Ma down to 124.8 ± 0.3 Ma, as shown by ages of most of micas and amphiboles from the Shear zone. These more accurate ages are consistent with metamorphic core complex ages from adjacent areas. Furthermore, they argue for an extensional dynamic paroxysm at the scale of eastern Asia during a narrow time range in the early Cretaceous between ca. 130 Ma and ca. 120 Ma.

  9. Mafic enclaves in dacitic domes and their relation with La Poruña scoria cone, Central Andes, northern Chile (United States)

    González-Maurel, O. P.; Gallmeyer, G.; Godoy, B.; Menzies, A.; le Roux, P. J.; Harris, C.


    Chao Dacite, Chillahuita, Cerro Pabellón, Chanka, Chac-Inca, and Cerro La Torta (or Tocorpuri) are dacitic domes of late Pleistocene age (30 to 140 ka; Renzulli et al., 2006; Tierney et al., 2016) located in Northern Chilean Central Andean province (NCCA; 17°20'S - 27°40'S). While, La Poruña is a 180 m high basaltic-andesite scoria cone erupted ca. 100 ka (Wörner et al., 2000). This scoria cone is also located at the NCCA, 26 km to the SW of Chanka and 45 km to the NW of Chao Dacite. The dacitic domes are generally porphyritic and highly crystalline lavas (30 - 50 vol % phenocrysts, plagioclase > biotite > amphibole > quartz ≥ accessory), with hyalopilitic or intersertal groundmass. These domes contain mafic enclaves, mostly andesite in composition, with plagioclase > amphibole > biotite ≥ clinopyroxene ≥ olivine ≥ accessory phenocryst (10 - 20 vol %) in a lightly oxidized groundmass with intersertal or intergranular textures. In contrast, La Poruña rocks are mostly aphanitic (75 - 85 vol % groundmass) and highly vesicular, with plagioclase > olivine ≥ clinopyroxene ≥ orthopyroxene phenocrysts in an intersertal or hyalopilitic groundmass. Although petrographically different, the composition (57 wt % SiO2; 580 ppm Sr, 87Sr/86Sr = 0.7066) of mafic enclaves from Cerro Pabellón dome are similar to the lava flows and pyroclastic blocks of La Poruña scoria cone (55 - 59 wt % SiO2; 560 - 610 ppm Sr; 0.7062 - 0.7066 87Sr/86Sr). Based on this data and the eruption ages of these volcanic structures, we suggest that the mafic enclaves and La Poruña magmas are co-genetic. Thus, we propose that the genesis of these mafic enclaves is associated with the origin of less evolved parental magmas erupted in the NCCA, such as those from La Poruña. In this case, the mafic enclaves would represent batches of less evolved magmas that ascended from deeper sources and probably contributed in the eruption of the dacitic domes. Renzulli et al., 2006. In XI Congreso Geol

  10. Non-occupational exposure to asbestos and risk of pleural mesothelioma: review and meta-analysis. (United States)

    Marsh, Gary M; Riordan, Alexander S; Keeton, Kara A; Benson, Stacey M


    To conduct an updated literature review and meta-analysis of studies of pleural malignant mesothelioma (PMM) risk among persons exposed to asbestos non-occupationally (household and neighbourhood). We performed a literature search for articles available in the National Center for Biotechnology Information's PubMed database published between 1967 and 2016. Meta-analyses were conducted to calculate pooled PMM risk estimates, stratifying for household or neighbourhood exposure to asbestos and/or predominant asbestos fibre type (chrysotile, amphibole or mixed). Eighteen studies in 12 countries comprising 665 cases met the meta-analysis inclusion criteria. We identified 13 estimates of PMM risk from neighbourhood exposures, 10 from household and one from mixed exposure, and combined the estimates using random-effects models. The overall meta-relative risk (meta-RR) was 5.9 (95% CI 4.4 to 8.7). The meta-RRs for household and neighbourhood exposures were 5.4 (95% CI 2.6 to 11.2) and 6.9 (95% CI 4.2 to 11.4), respectively. We observed trends in risk in relation to fibre type for both household and neighbourhood studies. For chrysotile, mixed and amphibole fibres, respectively, meta-RRs for neighbourhood studies were 3.8 (95% CI 0.4 to 38.4), 8.4 (95% CI 4.7 to 14.9) and 21.1 (95% CI 5.3 to 84.5) and meta-RRs for household studies were 4.0 (95% CI 0.8 to 18.8), 5.3 (95% CI 1.9 to 15.0) and 21.1 (95% CI 2.8 to 156.0). PMM risks from non-occupational asbestos exposure are consistent with the fibre-type potency response observed in occupational settings. By relating our findings to knowledge of exposure-response relationships in occupational settings, we can better evaluate PMM risks in communities with ambient asbestos exposures from industrial or other sources. © Article author(s) (or their employer(s) unless otherwise stated in the text of the article) 2017. All rights reserved. No commercial use is permitted unless otherwise expressly granted.

  11. Domes and Flows: Do Temporal Trends in Dacitic Magma Chemistry and Rheological Behavior at Santiaguito, Guatemala, Reflect Magma Chamber or Conduit Processes? (United States)

    Avard, G.; Whittington, A.; Rose, W.; Matias, O.; Cornejo, J.


    Santiaguito is a dacitic dome complex growing in the crater left by the 1902 plinian eruption of the stratovolcano Santa Maria, in Guatemala. The domes began growing in 1922 and are still active, with frequent small ash and steam eruptions, and semi-continous extrusion of crystal-rich dacitic lava both as spines on the domes (endogenous growth) and slow-moving block-lava "stealth" flows (exogenous growth). All four vents have produced both domes and flows, and at times multiple vents have been active. Between 1999 and 2004, one flow reached a length of 4 km. New flows emerged from the same vent in 2004 and 2005-2006 (ongoing). Flow morphology is controlled by rheology, which in turn depends on lava composition, crystal content, and volatile content. Samples of flows erupted from 1987 to the present share many features, including a phenocryst population dominated by complexly zoned plagioclase, a micro-crystalline plagioclase-rich rhyolitic groundmass, and a complete absence of hydrous phases. Small amphibole crystals with thick oxide rims are found only in samples more than 30 years old. Bulk-rock chemical analyses confirm a decrease in magma SiO2 content, from 63.5 - 66 wt.% before 1980, to 61 - 63 wt.% today. It has been suggested that this decreasing SiO2 content reflects the tapping of deeper and hotter magma; the lack of amphibole indicates that it must also be drier. From these preliminary results, we infer that magma chemistry is probably dictated by long time-scale changes in the magma chamber, while eruptive style is probably controlled by phenocryst content, matrix volatile content and microlite growth, which owe more to ascent dynamics and conduit processes than the parental magma. The lack of a direct correlation between bulk magma chemistry and extrusive style may also apply to other dacitic volcanoes such as Mount Saint Helens, suggesting that they also have the potential to produce kilometer-long flows if changes occur to the conduit system.

  12. High-pressure granulite-facies metamorphism in central Dronning Maud Land (East Antarctica): Implications for Gondwana assembly (United States)

    Palmeri, Rosaria; Godard, Gaston; Di Vincenzo, Gianfranco; Sandroni, Sonia; Talarico, Franco M.


    Central Dronning Maud Land (DML; East Antarctica) is located in a key region of the Gondwana supercontinent. The Conradgebirge area (central DML) consists of orthogneisses, derived from both volcanic and plutonic protoliths, and minor metasedimentary rocks, intruded by Cambrian syn- to post-metamorphic plutons and dykes. Mafic-ultramafic boudins in the metavolcanic and metaplutonic gneisses from Conradgebirge consist of amphibolites and high-grade garnet-bearing pyroxene- and amphibole-rich granofels. They occur either as discontinuous levels or as pods boudinaged within highly-strained and strongly-migmatized gneisses. Bulk-rock major and trace-element compositions, together with geochemical discriminant diagrams (e.g., Th/Yb versus Ta/Yb and V versus Ti), suggest derivation from enriched mantle source for the mafic rocks boudinaged in metaplutonic gneisses, whereas a calc-alkaline signature is common for the mafic boudins in metavolcanic rocks. The microstructural study and P-T modelling of an ultramafic metagabbroic rock reveal a prograde metamorphic evolution from amphibolite-facies (ca. 0.5 GPa; 500 °C) up to high-P granulite-facies conditions (ca. 1.5-1.7 GPa; 960-970 °C). Partial melting is testified by "nanogranitoid" inclusions enclosed in garnet. An almost isothermal decompression down to ca. 0.4 GPa and 750-850 °C produced well-developed An + Opx-bearing symplectites around garnet. A final isobaric cooling at nearly 0.4 GPa is testified by Grt coronas around high-T symplectites. The above reconstruction traces a clockwise loading-heating P-T evolution with a peak metamorphism at high-P granulite-facies conditions suggesting crustal thickening at nearly 570 Ma, followed by a tectonically assisted rapid exhumation, and then, by an isobaric cooling. 40Ar-39Ar dating of amphibole and biotite at 505-480 Ma testify mineral re-equilibration at upper crustal level (T < 650 °C) during the isobaric cooling. This tectono-metamorphic scenario seems

  13. Diffusion in coronas around clinopyroxene: modelling with local equilibrium and steady state, and a non-steady-state modification to account for zoned actinolite-hornblende (United States)

    Ashworth, J. R.; Birdi, J. J.; Emmett, T. F.


    Retrograde coronas of Caledonian age, between clinopyroxene and plagioclase in the Jotun Nappe Complex, Norway, illustrate the effects of diffusion kinetics on mineral distributions among layers and on the compositions of hornblende-actinolite. One corona type comprises a symplectite of epidote + quartz adjacent to plagioclase, and a less well-organized intergrowth of amphibole + quartz replacing clinopyroxene. The observed mineral proportions imply an open-system reaction, but the similarity of Al/Si ratios in reactant plagioclase and product symplectite indicates approximate conservation of Al2O3 and SiO2. The largest inferred open-system flux is a loss of CaO, mostly derived from consumption of clinopyroxene. The approximate layer structure, Pl|Ep + Qtz|Hbl + Qtz|Act±Hbl + Qtz|Cpx, is modelled using the theory of steady-state diffusion-controlled growth with local equilibrium. To obtain a solution, it is necessary to use a reactant plagioclase composition which takes into account aluminous (epidote) inclusions. The results indicate that, in terms of Onsager diffusion coefficients L ii , Ca is more mobile than AL ( L CaCa/ L AlAl≳3.) (where ≳ means greater than or approximately equal to). This behaviour of Ca is comparable with that of Mg in previously studied coronas around olivine. Si is non-diffusing in the present modelling, because of silica saturation. Oxidation of some Fe2+ to Fe3+ occurs within the corona. Mg diffuses towards its source (clinopyroxene) to maintain local equilibrium. Other coronas consist of two layers, hornblende adjacent to plagioclase and zoned amphibole + quartz adjacent to clinopyroxene. In the zoned layer, actinolitic hornblende forms relict patches, separated from quartz blebs by more aluminous hornblende. A preliminary steady-state, local-equilibrium model of grain-boundary diffusion explains the formation of low-Al and high-Al layers as due to Al immobility. Zoning and replacement are qualitatively explained in terms of

  14. Polymagmatic Activity at a Monogenetic Volcanic Centre: Defining the Evolution of a Plumbing System (United States)

    Brenna, M.; Cronin, S. J.; Smith, I. E.; Sohn, Y.; Nemeth, K.


    Detailed stratigraphic samples of the Udo Tuff Cone and lava shield offshore of Jeju Island, South Korea provide insight into the evolutionary processes that affected the composition of the basaltic magma batches that fed the eruption. These are compared and contrasted with the model proposed by Smith et al. (2008, Contributions to Mineralogy and Petrology 155, 511-527) for the magmatic evolution of the Crater Hill monogenetic centre in the Auckland Volcanic Field. The eruption started in both cases with the most evolved alkalic magma, having lowest concentrations of MgO and highest of incompatible trace elements. The erupted magma became more primitive as the eruptions proceeded. However, at Crater Hill the eruption terminated with extrusion of the most primitive magma, whereas at Udo the last magma to erupt had shifted back to an intermediate composition. At Crater Hill, the chemical compositions show a single uninterrupted spectrum, but at Udo the eruption sequence can be subdivided into lower and upper tuff stages separated by a small MgO gap from c. 8.0 to c. 9.0 wt%. Furthermore, at Udo, a second tholeiitic magma batch forming the lava shield erupted shortly after the alkalic tuff cone, with no evidence of weathering or reworked material at their contact. Fractionation processes for the Udo tuff can be modelled similarly to those of Crater Hill. A primary magma generated in garnet peridotite at c. 2.5 to 3 GPa underwent mainly clinopyroxene ± spinel fractionation at c. 1.5 GPa. Slightly enriched LREEs in the Udo magma (compared to the Crater Hill) suggest that crystal fractionation possibly occurred in the presence of residual amphibole in the upper mantle. The tholeiitic magma at Udo was generated in a chemically different source with residual garnet at c. 1.5 to 2.5 GPa and evolved through olivine fractionation at a shallower level compared to the alkalic magma and without residual amphibole. The Crater Hill model can be adapted to Udo by assuming the two

  15. Chemistry and mineralogy of some Plio-Pleistocene tuffs from the Shungura Formation, southwest Ethiopia (United States)

    Martz, A. M.; Brown, F. H.


    The Shungura Formation of southwestern Ethiopia has yielded many tens of thousands of vertebrate fossils including hominids and microvertebrates, and in addition has also yielded fossil wood, pollen, and invertebrates. Widespread tuffs have made subdivision and detailed mapping of the formation possible, have provided material for potassium-argon dating, and have allowed direct lithostratigraphic correlation with the Koobi Fora Formation in northern Kenya. The basis for correlation between the two formations is the distinctive chemistry of the tuffs, but systematic chemical variation within some tuffs invalidates some statistical correlation techniques. Here chemical analysis of glass separates and minerals from tuffs of the Shungura and Usno Formations are presented which may allow further ties to be established when data become available on other tuffs of the Koobi Fora Formation. The tuffs consist primarily of glass, but also contain phenocrysts of anorthoclase, hedenbergitic pyroxene, sodic amphibole, ilmenite, titanomagnetite, chevkinite, quartz, zircon, and rarely orthopyroxene and plagioclase. The glasses show evidence of alkali loss during hydration, and are not now peralkaline, although it is likely that they were initially. The source volcanoes were most likely situated within the Ethiopian rift valley, or on its margins.

  16. Mantle wedge infiltrated with saline fluids from dehydration and decarbonation of subducting slab. (United States)

    Kawamoto, Tatsuhiko; Yoshikawa, Masako; Kumagai, Yoshitaka; Mirabueno, Ma Hannah T; Okuno, Mitsuru; Kobayashi, Tetsuo


    Slab-derived fluids play an important role in heat and material transfer in subduction zones. Dehydration and decarbonation reactions of minerals in the subducting slab have been investigated using phase equilibria and modeling of fluid flow. Nevertheless, direct observations of the fluid chemistry and pressure-temperature conditions of fluids are few. This report describes CO2-bearing saline fluid inclusions in spinel-harzburgite xenoliths collected from the 1991 Pinatubo pumice deposits. The fluid inclusions are filled with saline solutions with 5.1 ± 1.0% (wt) NaCl-equivalent magnesite crystals, CO2-bearing vapor bubbles, and a talc and/or chrysotile layer on the walls. The xenoliths contain tremolite amphibole, which is stable in temperatures lower than 830 °C at the uppermost mantle. The Pinatubo volcano is located at the volcanic front of the Luzon arc associated with subduction of warm oceanic plate. The present observation suggests hydration of forearc mantle and the uppermost mantle by slab-derived CO2-bearing saline fluids. Dehydration and decarbonation take place, and seawater-like saline fluids migrate from the subducting slab to the mantle wedge. The presence of saline fluids is important because they can dissolve more metals than pure H2O and affect the chemical evolution of the mantle wedge.

  17. The dolerite dyke swarm of Mongo, Guéra Massif (Chad, Central Africa): Geological setting, petrography and geochemistry (United States)

    Nkouandou, Oumarou Faarouk; Bardintzeff, Jacques-Marie; Mahamat, Oumar; Fagny Mefire, Aminatou; Ganwa, Alembert Alexandre


    Dolerite dykes are widespread in the Mongo area within the granitic Guéra Massif (Chad, Central Africa). Dykes are several hundred metres to several kilometres long, a metre to decametre thick, and vertical, crosscutting the Pan-African granitic basement rocks. They are controlled by major Pan-African NNE-SSW, NE-SW and ENE-WSW faults. Rocks constituting the dykes exhibit typical doleritic textures (i.e. intergranular, ophitic or subophitic). They are mainly composed of phenocrysts, microcrysts and microlites of clinopyroxene, amphibole, plagioclase, alkali feldspar and Fe-Ti oxides. Mongo dolerites are classified into two groups: Group 1 of basalt and trachybasalt and Group 2 of basaltic trachyandesite, which follow a trend with continental tholeiite affinities, and are differentiated through fractional crystallization. Trace element enrichment and REE contents show the high melting degree at shallow depths of enriched sub-continental lithospheric mantle, whose composition is intermediate between OIB and MORB, contaminated by small amounts of sediment during older subduction. Mongo dolerites are interpreted as imprints of either the final stage of stabilization of ancient continental crust, or the initiation of tectonic activity related to Pan-African mobile belts.

  18. Evaluation of public and worker exposure due to naturally occurring asbestos in gravel discovered during a road construction project. (United States)

    Perkins, Robert A; Hargesheimer, John; Vaara, Leah


    During a repair and reconstruction project of an unpaved highway in a remote region of Alaska, workers discovered, after construction had commenced, that the materials used from a local material site contained asbestos (variously described as tremolite or actinolite). The regional geology indicated the presence of ultramafic rock, which often contains asbestos. Evaluation of asbestos exposure to workers, their equipment, and living quarters was required, as was the possible future exposure of workers and the general public to asbestos already used in the roadway construction. In addition, a decision was needed on whether to use materials from the contaminated site in the future. Of the almost 700 breathing zone air monitoring samples taken of the workers, 3% of the samples indicated exposures at or near 0.1 f/cc by the National Institute for Occupational Safety and Health (NIOSH) 7400 phase contrast microscopy (PCM) procedure. Thirty-six of the PCM samples underwent transmission electron microscopy (TEM) analysis by the NIOSH 7402 procedure, which indicated that about 40% of the fibers were asbestos. After classifying samples by tasks performed by workers, analysis indicated that workers, such as road grader operators who ground or spread materials, had the highest exposures. Also, monitoring results indicated motorist exposure to be much less than 0.1 f/cc. The design phase of any proposed construction project in regions that contain ultramafic rock must consider the possibility of amphibole contamination of roadway materials, and budget for exploration and asbestos analysis of likely materials sites.

  19. Equilibration conditions of eclogite lenses from Isla Margarita, Venezuela: Implications for the tectonic evolution of the metasedimentary Juan Griego Group (United States)

    Bocchio, R.; De Capitani, L.; Liborio, G.; Maresch, W. V.; Mottana, A.


    The constituent primary and secondary minerals in a suite of fifteen samples of eclogite, amphibole-eclogite and garnet-amphibolite, scattered as boudins and pods in metapelitic schists and gneisses on Isla Margarita, Venezuela, have been analysed by electron microprobe to augment existing bulk-rock chemical data. The large sample population available allows spurious effects of stoichiometric Fe 3+ calculation procedures and bulk-rock influence to be recognised and eliminated. All samples belong to one population with a relatively homogeneous character. The equilibration temperatures are derived from {Fe 2+}/{Mg} fractionation between garnet and clinopyroxene and range from 525-650 °C. Jadeite contents of clinopyroxene and the persistence of minor stable albite constrain pressures to between 13 and 19 kbar. Combined with new evidence for high-pressure metamorphism in the enclosing metapelites and with existing data on an eclogitic metabasic unit exposed in north-eastern Isla Margarita (La Rinconada Group), these data show convincingly that the Margarita crustal block is and has been a relatively coherent unit ever since the entire complex suffered high-pressure metamorphism in Late Mesozoic times.

  20. Mineral alteration of two different bed rocks and soil derived from them in Lahijan

    International Nuclear Information System (INIS)

    Pourmasoumi Parashkooh, M.; Ramezanpour, H.


    Microscopical studies were carried out, in addition to physico-chemical and mineralogical analysis, in order to evaluate the effect of parent material and weathering on soil genesis in forest regions of Lahijan. Two representative soil pedons in mountain landform developed on granite and andesitic basalt located about 8 km southeast of Lahijan were selected and sampling were taken from each horizon by Kubiena boxes or clod. Mineral and their weathering were studied by a polarized microscope under plain and cross light and comparison was made with total elemental analysis by X-ray fluorescence and X-ray analysis (XRD). All evidences showed that there is a close structural relationship between the host mineral and the weathering products. Microscopic observation of soils and weathered rock derived from granite showed evidence of the alteration of feldspars to sericite and chlorite under hydrothermal condition and clay minerals under soil condition. In soils and weathered rock derived from andesitic basalt, alteration of plagioclase (labradorite) and olivine to chlorite and clay minerals as well as pyroxene to amphibole were dominant process. Moreover, higher depth of soil under andesitic basalt with comparison to granite was the morphological evidence of intense weathering effects of humid condition in the study area for different minerals.

  1. 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.

  2. Water in Pyroxene and Olivine from Martian Meteorites (United States)

    Peslier, A. H.


    Water in the interior of terrestrial planets can be dissolved in fluids or melts and hydrous phases, but can also be locked as protons attached to structural oxygen in lattice defects in nominally anhydrous minerals (NAM) like olivine, pyroxene, or feldspar [1-3]. Although these minerals contain only tens to hundreds of ppm H2O, this water can amount to at least one ocean in mass when added at planetary scales because of the modal dominance of NAM in the mantle and crust [4]. Moreover these trace amounts of water can have drastic effects on melting temperature, rheology, electrical and heat conductivity, and seismic wave attenuation [5]. There is presently a debate on how much water is present in the martian mantle. Secondary ionization mass spectrometry (SIMS) studies of NAM [6], amphiboles and glass in melt inclusions [7-10], and apatites [11, 12] from Martian meteorites report finding as much water as in the same phases from Earth's igneous rocks. Most martian hydrous minerals, however, generally have the relevant sites filled with Cl and F instead of H [13, 14], and experiments using Cl [15] in parent melts can reproduce Martian basalt compositions as well as those with water [16]. We are in the process of analyzing Martian meteorite minerals by Fourier transform infrared spectrometry (FTIR) in order to constrain the role of water in this planet s formation and magmatic evolution

  3. 14C age of the ash found in the peat bed of upland dog, Nakagawa-Gun, Hokkaido

    International Nuclear Information System (INIS)

    Igarashi, Yaeko; Kondo, Tsutomu; Fujiwara, Koichiro.


    The determination of the 14 C age of volcanic ash forming thin layer, which was found in a peat bed, was carried out. The samples were collected from the peat bed which distributes on the flat top of upland about 450m above sea level. The moor spread in the experimental plantation of the agricultural department of Hokkaido University. The thin layer of volcanic ash was found 20 cm deep in the peat bed and with about 1-3 cm thickness. The determination of 14 C age was made on the peat directly beneath the volcanic ash layer, along with the mineralogical studies. The obtained 14 C age was 480 480 +- 100 Y.B.P. (A.D. 1470), and this is presumed to be the age of eruption of the volcanic ash. The color of the ash was greenish yellow or orange in wet state, and grayish white in dry state. The volcanic ash was fine grained pumiceous, and round or nearly round grains predominate. By macroscopic observation, the grains were found to be composed of fibrous volcanic glass. The volcanic ash was well sorted, and the central grain size was 0.11 mm. Heavy liquid method was applied for the determination of heavy minerals. The weight percentage of heavy minerals was 1.59, and the characteristic of this ash was the entire absence of amphibole. Further investigation is necessary for clarifying the distribution of volcanic ash and the source of eruption. (Ishimitsu, A.)

  4. Petrology of Ortsog-Uul peridotite-gabbro massif in Western Mongolia (United States)

    Shapovalova, M.; Tolstykh, N.; Shelepaev, R.; Cherdantseva, M.


    The Ortsog-Uul mafic-ultramafic massif of Western Mongolia is located in a tectonic block with overturned bedding. The massif hosts two intrusions: a rhythmically-layered peridotite-gabbro association (Intrusion 1) and massive Bt-bearing amphibole-olivine gabbro (Intrusion 2). Intrusions 1 and 2 have different petrology features. Early Intrusion 1 (278±2.5Ma) is characterized by lower concentrations of alkalis, titanium and phosphorus than late Intrusion 2 (272±2Ma). The chondrite-normalized REE and primitive mantle-normalized rare elements patterns of Ortsog-Uul intrusions have similar curves of elements distribution. However, Intrusion 2 is characterized higher contents of REE and rare elements. High concentrations of incompatible elements are indicative of strong fractionation process. It has been suggested that Intrusions 1 and 2 derived from compositionally different parental melts. Model calculations (COMAGMAT-3.57) show that parental melts of two intrusions were close to high-Mg picrobasaltic magmas. The concentration of MgO in melt is 16.21 (Intrusion 1) and 16.17 (Intrusion 2). Isotopic data of Ortsog-Uul magmatic rocks exhibit different values of εNd (positive and negative) for Intrusion 1 and 2, respectively.

  5. Hydrous melts weaken the mantle, crystallization of pargasite and phlogopite does not: Insights from a petrostructural study of the Finero peridotites, southern Alps (United States)

    Tommasi, Andréa; Langone, Antonio; Padrón-Navarta, José Alberto; Zanetti, Alberto; Vauchez, Alain


    This study reports petrostructural observations in the pargasite and phlogopite-bearing Finero peridotite massif (Italian Western Alps), which suggest that the pervasive foliation in this massif was formed by deformation concomitant with percolation of hydrous Si-rich melts: (1) diffuse contacts, but systematic parallelism between the pyroxenitic layers and the foliation of the peridotite (2) strong shape and crystal preferred orientations (SPO and CPO), but subhedral or interstitial shapes and weak intracrystalline deformation of the hydrous phases, (3) CPO, but interstitial shapes of the pyroxenes, (4) very coarse olivine grain sizes, which are correlated to the olivine abundance, and (5) elongated shapes, but weak intracrystalline deformation, and extremely weak and highly variable CPO of olivine. The pervasive deformation of the Finero peridotite occurred therefore under conditions that allowed coexistence of H2O-CO2-bearing melts, pargasite, and spinel, that is, temperatures of 980-1080 °C and pressures peridotites' strength leads to onset of strain localization. The latter is not correlated to the local abundance in pargasite or phlogopite, implying that crystallization of amphiboles or phlogopite, even at concentrations of 25 vol.%, does not produce rheological weakening in the upper mantle.

  6. [Asbestos exposure assessment in the first case of intrasplenic mesothelioma]. (United States)

    Miscetti, Giorgio; Bodo, Patrizia; Lumare, A; Abbritti, E P; Garofani, Patrizia; Burani, V


    In 2013 the International Journal of Surgical Pathology published a case report of intrasplenic malignant mesothelioma (MM) in a 48-year-old man: it was the first report in literature describing a case of primitive intra-splenic MM, described without  a history of asbestos exposure. To verify the possible past exposure to asbestos, ignored by the patient himself, by studying in depth his environmental and occupational history. Information about the occupational and non-occupational history of the subject was collected by Experts of the Operational Unit of Occupational Health and Safety Control (UOC PSAL) of the Local Health Unit Umbria 1 - Perugia, using the Italian National Mesothelioma Register (ReNaM) questionnaire and guide lines; an inspection was  carried out at the past canning industry where the patient worked in the period 1982-1990 and material was taken to be analysed by MOCF and SEM. Samples showed the presence of asbestos  fibres belonging to the amphibole class (amosite and crocidolite) and to the serpentine class (chrysotile). The survey described the past occupational exposure to asbestos in a canning industry, where  the subject worked in the period 1982-1990,  unknown to the patient himself. The authors strongly confirm the  usefulness of standardized methods, such as the ReNaM Questionnaire, and the importance of technical expertise of the investigator to find and analyse the suspect materials and to demonstrate  possible past occupational exposure to asbestos.

  7. Strata-bound copper-iron sulfide mineralization in a Proterozoic front arc setting at Boksputs, Northwest Cape, South Africa — a possible Besshi-type deposit (United States)

    Geringer, G. J.; Pretorius, J. J.; Cilliers, F. H.


    A low-grade, copper-iron sulfide deposit is present at Boksputs in the Northwest Cape, South Africa. It occurs in the Proterozoic amphibolite belt, the Areachap Group, along the eastern margin of the Namaqua mobile belt. The mineralization, which is dominated by pyrite, chalcocopyrite, sphalerite, and magnetite, occurs as disseminated ore and thin layers of massive-type ore in the lower massive amphibiolite and associated amphibole gneisses of the Kraalkop antiform and synform. Chemically, the host-rock amphibolite resembles low-K arc tholeiite and calc-alkaline volcanics, whereas the upper amphibolite is calc-alkaline. The sulfide mineralization and the host-rock composition is explained in terms of modern plate tectonic principles. It is concluded that the Boksputs mineralization is a syngenetic, strata-bound, copper-iron deposit which to some extend resembles Besshi-type deposits. It is associated with low-K arc tholeiite which is tectonically related to a front arc environment or a rifted arc system along the eastern margin of the Namaqua mobile belt.

  8. 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.

  9. Geology of the Riacho do Pontal iron oxide copper-gold (IOCG prospect, Bahia, Brazil: hydrothermal alteration approached via hierarchical cluster analysis

    Directory of Open Access Journals (Sweden)

    Sérgio Roberto Bacelar Huhn

    Full Text Available The Riacho do Pontal prospect is situated on the border between the Borborema Province and the São Francisco Craton, in Bahia state. It comprises rocks polydeformed during the Neoproterozoic. The prospect area includes migmatites and gneissic rocks intruded by several sin- to post-tectonic granites. Structural analysis indicates a strong relationship between the development of ductile to brittle-ductile shear zones and associated hydrothermalism. The main tracts of high-strain rate are represented by the Riacho do Pontal (north and Macururé (south shear zones. Several copper occurrences have been mapped within the Riacho do Pontal prospect along secondary shear zones. In these areas, the gneissic rocks were affected by intense hydrothermal alteration. Hierarchical cluster analysis permitted the identification of the main hydrothermal mineral associations present in these rocks, which resulted from potassic (biotite and sodic-calcic (amphibole-albite alteration, in addition to silicification and iron alteration (hematite. These hydrothermal alteration types are similar to those typically found in iron oxide copper-gold deposits developed at intermediate crustal levels. Hematite-quartz-albite-chalcopyrite-pyrite hydrothermal breccias host the highest-grade copper ore (chalcopyrite-pyrite-chalcocite zones. The spatial relationship between copper deposits and shear zones improves the metallogenic potential for copper of the Borborema Province and has important implications for mineral exploration in the region.

  10. Geometallurgy of ironsand from the Waikato North Head deposit, New Zealand (United States)

    Mauk, Jeffrey L.; Cocker, Helen A; Rogers, Harold; Ogiliev, Jamie; Padya, Alex B


    The Waikato North Head deposit produces a magnetic mineral concentrate from Quaternary sands that formed in a coastal setting in the North Island of New Zealand. Detailed examination of the magnetic mineral fraction of the different stratigraphic horizons mined at Waikato North Head shows that the youngest units yield concentrates with significant concentrations of gangue minerals that are included as composite grains, inclusions in titanomagnetite, and as gangue grains with titanomagnetite inclusions. The most abundant gangue minerals in the magnetic fractions of all mined units are pyroxene and amphibole; feldspar, quartz, and biotite are less abundant. The magnetic minerals, which are predominantly titanomagnetite, are used as feed for the Iron Plant in New Zealand Steel’s Glenbrook Steel Mill. From time to time, excessive accretion formation impacts the operation of the rotary reduction kilns of the Iron Plant. Olivine group minerals are the most common silicate phase in these accretions, and we hypothesise that the silicon and magnesium in these minerals are derived from the gangue minerals that are included in the magnetic mineral concentrate from the ironsands. Although various remediation processes are possible, the simplest and most cost effective would appear to be ensuring adequate blending of material from different stratigraphic units, particularly when the youngest strata are being mined in the deposit.

  11. An Overview on the Possibility of Scandium and REE Occurrence in Sulawesi, Indonesia

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    Adi Maulana


    Full Text Available DOI:10.17014/ijog.3.2.139-147The development in modern-high technology application is growing rapidly, resulting in the constant supply of critical metal and rare earth elements (REE. Currently, resources of these elements are restricted and new source of these elements need to be discovered accordingly. Scandium (Sc as one of critical metals is an important metal for electrolyte of solid oxide fuel cells and other advance technology. In addition, REE are the important elements in the use of permanent magnets and rechargeable batteries. This manuscript reports an overview on the possibility of scandium and rare earth element occurrences in Sulawesi. Sc is concentrated in limonite layers in Soroako ultramafic rocks as a result of Fe3+ site substitution of mafic minerals (pyroxene, amphibole, etc. during a laterization process. REE are enriched in association with clay minerals in B horizon from heavily weathered granitic rocks in Palu and Masamba, suggesting the possibility of ion-adsorption style mineralization. The lateritic soil of the ultramafic rocks and the weathered crusts of the granitic rocks in Sulawesi could be the potential sources of scandium and rare earth elements, respectively.

  12. Geochemistry and paleotectonomagmatic setting of metabasites protolith from Asalem metamorphic complex (northwest Rasht

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    Mohsen Nasrabady


    Full Text Available Asalem metamorphic complex consists mostly of metabasite, metapelite and serpentinite. Metabasites display metamorphic features of greenschist and blueschist facies. Greenschist facies rocks that found as both foliated and massive types contain mineralogical assemblage of actinolite, chlorite, albite and epidote. Blueschists contain mineralogical assemblage of sodic amphibole, epidote and phengite. Whole rock analyses of the metabasites indicate basaltic to andesitic composition with mainly calcalkaline nature of their protolith. According to the discrimination diagrams of tectonomagmatic setting, the protolith of investigated metabasites has been islands arc and somewhat mid ocean ridge. The patterns of rare earth elements and spider diagrams of the Asalem metabasites resemble to the basic and intermediate magmatism of islands arc or suprasubduction setting as well. Greenschists and blueschists facies rocks of the Asalem metamorphic complex have been probably equivalent to islands arc or young and hot oceanic crust of suprasubduction zone setting. This portion of oceanic basin unlike the subducted even and thick oceanic lithosphere of Paleotethys during accretion in the shallower levels of accretionary prisms, have underwent metamorphic conditions of blueschist and greenschist facies and finally gave rise to the formation of the metabasites of the Asalem metamorphic complex.

  13. Mineral growth in melt conduits as a mechanism for igneous layering in shallow arc plutons: mineral chemistry of Fisher Lake orbicules and comb layers (Sierra Nevada, USA) (United States)

    McCarthy, Anders; Müntener, Othmar


    Different processes have been proposed to explain the variety of igneous layering in plutonic rocks. To constrain the mechanisms of emplacement and crystallization of ascending magma batches in shallow plutons, we have studied comb layers and orbicules from the Fisher Lake Pluton, Northern Sierra Nevada. Through a detailed study of the mineralogy and bulk chemistry of 70 individual layers, we show that comb layers and orbicule rims show no evidence of forming through a self-organizing, oscillatory crystallization process, but represent crystallization fronts resulting from in situ crystallization and extraction of evolved melt fractions during decompression-driven crystallization, forming a plagioclase-dominated cres-cumulate at the mm- to m-scale. We propose that the crystal content of the melt and the dynamics of the magmatic system control the mechanisms responsible for vertical igneous layering in shallow reservoirs. As comb layers crystallize on wall rocks, the higher thermal gradients will increase the diversity of comb layering, expressed by inefficient melt extraction, thereby forming amphibole comb layers and trapped apatite + quartz saturated evolved melt fractions. High-An plagioclase (An90-An97.5) is a widespread phase in Fisher lake comb layers and orbicule rims. We show that a combination of cooling rate, latent heat of crystallization and pressure variations may account for high-An plagioclase in shallow melt extraction zones.

  14. Patherns in the rare earth elements of the Serra do Carambei granite (Parana) and the others associated ignous rocks

    International Nuclear Information System (INIS)

    Pinto-Coelho, C.V.; Marini, O.J.


    The rare earth elements (REE) distribution patters in igneous rocks of the Serra do Carambei Granite area (Parana) were a very important tool to elucidate the genetic processes and the cogenetic relationships between these rocks. The porphyroid facies of the Cunhaporanga Granitoid Complex has a REE distribution pattern characterized by decreasing concentrations in direction to the heavy rare earth elements (HREE) and the smooth Eu negative anomalie, compatible with amphibole fractionation during the magma ascent and the incipient plagioclase fractionation. The REE pattern of the Serra do Carambei Granite is characterized by the strong Eu negative anomalie, by the light rare earth element (LREE) depletion and by the HREE increase. This shape of the REE patterns is frequently observed in Sn-W granites, according to French authors. However in the igneous rocks of the Serra do Carambei Granite area this is not true. ''Rhyolite'' dytes intrusives in the Serra do Carambei Granite exhibit REE pattern similar to the wall rock, indicating then the same genetic processes. The Castro Group rhyolites have REE patterns with decreasing concentrations in direction to the HREE and smooth Eu negative anomalie. The REE distribution patterns is against the consanguinity between the ''rhyolites'' intruded in the Serra do Carambei Granite and the rhyolites of the Castro Group and also between these rhyolites and the above mentioned Granite. (author) [pt

  15. The Sao Jose do Rio Pardo mangeritic-granitic suite, south eastern Brazil

    International Nuclear Information System (INIS)

    Campos Neto, M.C.; Figueiredo, M.C.H.; Janasi, V.A.; Basei, M.A.S.; Fryer, B.J.


    In the Sao Jose do Rio Pardo region, Sao Paulo and Minas Gerais States, occur some intrusive, folded tabular bodies of mangerites associated with hornblende granitoids. The country rocks correspond to a complex association of gneisses and migmatites, locally with granulite facies assemblages. Both the magnerites and hornblende granitoids present a tectonic foliation with mineral flattening and stretching. Petrographically the mangeritic rocks are mainly dark green quartz mangerites with mesoperthite, plagioclase, quartz, hypersthene, clinopyroxene and variable amounts of hornblende, with zircon as conspicuous acessory. The pink hornblende granitoids are mainly granite s.s. exhibiting higher quartz and amphibole contents and lacking pyroxenes. Hololeucocratic alkali feldspar granites are locally associated to the hornblende granites. The textures of the mangerites and granites almost always show an important metamorphic overprinting, with relictic mesoperthite and pyroxene crystal into a granoblastic matrix. The magneritic-granitic suite is characterized by relatively high Fe/(Fe + Mg), K and HFS elements and low Ca contents, being comparable to typical anorogenic magneritic-granitic suites from Svcandinavia and North America. The Rb/Sr data indicate a Late Proterozoic metamorphic isotopic rehomogenization (930 Ma, Ro = 0.706). Geological evidence suggest that the intrusive age could be Middle Proterozoic, wich is reinforced by another Rb-Sr value of about 1300 Ma. (author) [pt

  16. Petrogenesis of Mount Rainier andesite: magma flux and geologic controls on the contrasting differentiation styles at stratovolcanoes of the southern Washington Cascades (United States)

    Sisson, Thomas W.; Salters, V.J.M.; Larson, P.B.


    Quaternary Mount Rainier (Washington, USA) of the Cascades magmatic arc consists of porphyritic calc-alkaline andesites and subordinate dacites, with common evidence for mingling and mixing with less evolved magmas encompassing andesites, basaltic andesites, and rarely, basalts. Basaltic andesites and amphibole andesites (spessartites) that erupted from vents at the north foot of the volcano represent some of Mount Rainier's immediate parents and overlap in composition with regional basalts and basaltic andesites. Geochemical (major and trace elements) and isotopic (Sr, Nd, Pb, O) compositions of Mount Rainier andesites and dacites are consistent with modest assimilation (typically ≤20 wt%) of evolved sediment or sediment partial melt. Sandstones and shales of the Eocene Puget Group, derived from the continental interior, are exposed in regional anticlines flanking the volcano, and probably underlie it in the middle to lower crust, accounting for their assimilation. Mesozoic and Cenozoic igneous basement rocks are unsuitable as assimilants due to their high 143Nd/144Nd, diverse206Pb/204Pb, and generally high δ18O.

  17. Neogene magmatism and its possible causal relationship with hydrocarbon generation in SW Colombia (United States)

    Vásquez, Mónica; Altenberger, Uwe; Romer, Rolf L.


    The Cretaceous oil-bearing source and reservoir sedimentary succession in the Putumayo Basin, SW Colombia, was intruded by gabbroic dykes and sills. The petrological and geochemical character of the magmatic rocks shows calc-alkaline tendency, pointing to a subduction-related magmatic event. K/Ar dating of amphibole indicates a Late Miocene to Pliocene age (6.1 ± 0.7 Ma) for the igneous episode in the basin. Therefore, we assume the intrusions to be part of the Andean magmatism of the Northern Volcanic Zone (NVZ). The age of the intrusions has significant tectonic and economic implications because it coincides with two regional events: (1) the late Miocene/Pliocene Andean orogenic uplift of most of the sub-Andean regions in Peru, Ecuador and Colombia and (2) a pulse of hydrocarbon generation and expulsion that has reached the gas window. High La/Yb, K/Nb and La/Nb ratios, and the obtained Sr-Nd-Pb isotopic compositions suggest the involvement of subducted sediments and/or the assimilation of oceanic crust of the subducting slab. We discuss the possibility that magma chamber(s) west of the basin, below the Cordillera, did increase the heat flow in the basin causing generation and expulsion of hydrocarbons and CO2.

  18. 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.

  19. Coexistence and mixing of magmas in the late precambrian Itaporanga batholith, State of Paraiba, Northeastern Brazil

    International Nuclear Information System (INIS)

    Mariano, G.; Sial, A.N.


    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)

  20. Syn-collisional felsic magmatism and continental crust growth: A case study from the North Qilian Orogenic Belt at the northern margin of the Tibetan Plateau (United States)

    Chen, Shuo; Niu, Yaoling; Xue, Qiqi


    The abundant syn-collisional granitoids produced and preserved at the northern Tibetan Plateau margin provide a prime case for studying the felsic magmatism as well as continental crust growth in response to continental collision. Here we present the results from a systematic study of the syn-collisional granitoids and their mafic magmatic enclaves (MMEs) in the Laohushan (LHS) and Machangshan (MCS) plutons from the North Qilian Orogenic Belt (NQOB). Two types of MMEs from the LHS pluton exhibit identical crystallization age ( 430 Ma) and bulk-rock isotopic compositions to their host granitoids, indicating their genetic link. The phase equilibrium constraints and pressure estimates for amphiboles from the LHS pluton together with the whole rock data suggest that the two types of MMEs represent two evolution products of the same hydrous andesitic magmas. In combination with the data on NQOB syn-collisional granitoids elsewhere, we suggest that the syn-collisional granitoids in the NQOB are material evidence of melting of ocean crust and sediment. The remarkable compositional similarity between the LHS granitoids and the model bulk continental crust in terms of major elements, trace elements, and some key element ratios indicates that the syn-collisional magmatism in the NQOB contributes to net continental crust growth, and that the way of continental crust growth in the Phanerozoic through syn-collisional felsic magmatism (production and preservation) is a straightforward process without the need of petrologically and physically complex processes.

  1. X-Ray Fingerprinting Techniques for Recognizing A Hydrological Role in the Formation of Minerals on the Surface of Mars (United States)

    Metzger, Ellen P.; John, R.


    Previous work has demonstrated the ability of a miniaturized XRD-XRF instrument to perform in-situ analyses without sample preparation or acquisition. Deployment of this instrument on a Martian rover will allow a large number of rapid qualitative analyses, which will maximize the diversity of samples studied and selected for possible return. As a first step in designing a decision tree for recognizing minerals in complex mixtures, d spacings were plotted against intensity for several mineral groups comprising rock and soil types inferred for the surface of Mars (weathered basalt, playa and hydrothermal deposits, clay-rich soils). In all groups, d spacings cluster in a range from about 1-4 angstroms, which can under certain circumstances obscure patterns for individual phases. However, within the silicate family, minerals containing either bound OH- or molecules of H20 (clays, micas, amphiboles, zeolites) are characterized by a shift of peaks to higher d spacings. Large d spacings (greater than about 7 angstroms) thus act as a first-order filter for distinguishing hydrous from anhydrous silicates. The ability to quickly verify the presence of silicates that have interacted with water has important implications for using mineral chemistry and structure to help decipher the hydrologic and atmospheric history of Mars. This represents a beginning for developing more sophisticated methods of pattern recognition. These will combine XRD and XRF analyses with optical data to rapidly7 discern environmentally diagnostic assemblages without the necessity of identifying every peak individual mineral phase.

  2. Petrogenetic processes, crystallization conditions and nature of the Lower-Oligocene calc-alkaline spessartitic lamprophyres from Kal-e-kafi area (East of Anarak, Isfahan province

    Directory of Open Access Journals (Sweden)

    Gholam Hossain Nazari


    Full Text Available Introduction Lamprophyres are mesocratic to melanocratic igneous rocks, usually hypabyssal, with a panidiomorphic texture and abundant mafic phenocrysts of dark mica or amphibole (or both with or without pyroxene, with or without olivine, set in a matrix of the same minerals, and with alkali-feldspar restricted to the groundmass (Woolley et al., 1996. Lamprophyres are frequently associated with orogenic settings and a mantle modified by dehydration of subducted slab (Gibson et al., 1995. Small outcrops of lamprophyres with Paleozoic to Oligocene age are reported from the central parts of Iran (Torabi 2009 and 2010. The primary magmas of these lamprophyres were derived from decompression melting of the mantle induced by a tensional regime of continental crust (Torabi, 2010. Bayat and Torabi (2011 called the western part of the CEIM (Central-East Iranian Microcontinent (Anarak to Bayazeh a “Paleozoic lamprophyric province” and suggested that the lamprophyre magmas were formed by subduction of Paleo-Tethys oceanic crust from the Early to late Paleozoic which resulted in the mantle metasomatism and enrichment. Lamprophyric dykes and stocks of the Kal-e-kafi area (Central Iran, Northern part of Yazd Block cross-cut the Eocene volcanic rocks and other older rock units such as Cretaceous limestone. These lamprophyres are mainly composed of hornblende (magnesio-hastingsite, clinopyroxene (diopside and plagioclase (labradorite to bytownite as phenocryst, in a matrix of fine to medium grained of the same minerals and orthoclase, apatite, magnetite, chlorite and epidote. In this paper that is a report on the first study on the calc-alkaline lamprophyres of Central Iran, the petrography and mineral chemistry of calc-alkaline lamprophyric dykes of the Kal-e-kafi area are discussed. Materials and methods Chemical composition of minerals were conducted at Kanazawa University (Kanazawa, Japan using the wavelength-dispersive electron probe microanalyzer

  3. Study on the uranium mineralization genesis of the Cachoeira, Lagoa Real, Bahia, mine, as auxiliary in the discovery and comprehension of mineral beds; Estudo da genese da mineralizacao uranifica da mina da Cachoeira, Lagoa Real, BA, como auxilio na descoberta e compreensao de jazidas minerais

    Energy Technology Data Exchange (ETDEWEB)

    Oliveira, Lucilia Aparecida Ramos de; Rios, Francisco Javier; Chaves, Alexandre de Oliveira; Pereira, Ana Rosa Passos [Centro de Desenvolvimento da Tecnologia Nuclear (CDTN/CNEN-MG), Belo Horizonte, MG (Brazil)]. E-mail:


    The acknowledgement of the geological history of a ore reserve allows to infer relative to a large area with possibility to contain the large mineral content or even give the localization of new anomalies or mineral reserve. The study of ore reserve genesis is of great importance for the stages to obtain the mineral, from the prospection until the mineral mining. Fluid inclusions (FI) are fluid quantities which are imprison in the minerals during the formation process or some process where deformation occurs. The study of fluid inclusions, together with the petrographic mapping of the blades associated to the uranium para genesis of Lagoa Real, Brazil, are been used for a better comprehension of the uranium orogenesis. The main analysis techniques used in this context were the petrography and microthermometry. With the petrographic analysis fluid inclusions were observed and mapped in various minerals present in rocks associated to uranium mineralization, such as amphiboles, pyroxenes and grenades. The micro thermometric studies were only performed in the pyroxenes and the grenades due to the fluid inclusions types found in these minerals, and also the supposed relationships that those minerals have with uranium mineralization at that region. (author)

  4. The Cauaburi magmatic arc: Litho-stratigraphic review and evolution of the Imeri Domain, Rio Negro Province, Amazonian Craton (United States)

    Carneiro, Marcia C. R.; Nascimento, Rielva S. C.; Almeida, Marcelo E.; Salazar, Carlos A.; Trindade, Ivaldo Rodrigues da; Rodrigues, Vanisse de Oliveira; Passos, Marcel S.


    A lithostratigraphic review of the Cauaburi Complex was carried out by means of field, tectono-metamorphic and geochemical data, which were the basis for the sub-division of the Cauaburi Complex orthogneisses into the Santa Izabel do Rio Negro, Cumati and São Jorge facies. These rocks crop out between São Gabriel da Cachoeira and Santa Izabel do Rio Negro, Amazonas, Brazil. The gneisses of the Santa Izabel do Rio Negro and Cumati facies are metaluminous and of calc-alkaline affinity; in turn, the rocks of the São Jorge facies are peraluminous and of alkaline affinity. They vary from (amphibole)-biotite granodiorites/monzogranites (Cumati and Santa Izabel do Rio Negro facies) to spessartite-bearing biotite monzogranites (São Jorge facies). The Cauaburi Complex geochemical signature is compatible with that of granites generated in collisional settings (magmatic arc?) and its evolution is related to three distinct tectono-metamorphic events: D1, causing foliation S1, which developed during the Cauaburi Complex syn-tectonic emplacement in the Cauaburi Orogeny; D2/M2, causing foliation S2, which was generated under amphibolite facies conditions (717.9 °C and 5.84 kbars), and the emplacement of I- and S-type granite during the Içana Orogen, and low-temperature D3, associated with the K'Mudku Event, which caused foliation S3 and reworking via transcurrent shear zones under greenschist facies conditions.

  5. Uranium mineralization at Lagoa Real, BA-Brazil: some contributions to understand its genesis

    Energy Technology Data Exchange (ETDEWEB)

    Prates, Sonia Pinto; Neves, Jose Marques Correia; Fuzikawa, Kazuo [Centro de Desenvolvimento da Tecnologia Nuclear (CDTN/CNEN-MG), Belo Horizonte, MG (Brazil)], E-mail:


    The Lagoa Real uranium province is situated in the central-south of Bahia state - Brazil. It was found in 1977 by Empresas Nucleares Brasileiras - NUCLEBRAS and nowadays 34 anomalies are known in a 30 Km length and 5 km wide area. An open pit mine was open in Cachoeira Mine, in the north portion of the area. The uranium mineralization in the Lagoa Real uranium province occurs in metamorphic rocks named albitites, due to their albite content (over 70%). The albitites are enclosed in the gneisses and granites of the Lagoa Real Complex. Uraninite is the main uranium mineral, followed by pechblende, uranophane, torbernite and other uranyl minerals. Uraninite occurs as tiny round and irregular crystals (20 a 30 {mu}m) included or associated to mafic minerals, mainly pyroxene and garnet, and also to amphibole and biotite and sometimes to albite. X-Ray Diffraction, Infra-Red Spectroscopy and thermal analysis preliminary data (structures, crystalline degree, water loss temperature, thermochemical events) obtained from these minerals provide information which enables the understanding of metallogenesis of the uranium mineralization. (author)

  6. 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.

  7. Sr, Nd and Pb isotope and geochemical data from the Quaternary Nevado de Toluca volcano, a source of recent adakitic magmatism, and the Tenango Volcanic Field, Mexico (United States)

    Martínez-Serrano, Raymundo G.; Schaaf, Peter; Solís-Pichardo, Gabriela; Hernández-Bernal, Ma. del Sol; Hernández-Treviño, Teodoro; Julio Morales-Contreras, Juan; Macías, José Luis


    Volcanic activity at Nevado de Toluca (NT) volcano began 2.6 Ma ago with the emission of andesitic lavas, but over the past 40 ka, eruptions have produced mainly lava flows and pyroclastic deposits of predominantly orthopyroxene-hornblende dacitic composition. In the nearby Tenango Volcanic Field (TVF) pyroclastic products and lava flows ranging in composition from basaltic andesite to andesite were erupted at most of 40 monogenetic volcanic centers and were coeval with the last stages of NT. All volcanic rocks in the study area are characterized by a calc-alkaline affinity that is consistent with a subduction setting. Relatively high concentrations of Sr (>460 ppm) coupled with low Y (45 km) that underlies the volcanoes of the study area, the geochemical and isotopic patterns of these rocks indicate low interaction with this crust. NT volcano was constructed at the intersection of three fault systems, and it seems that the Plio-Quaternary E-W system played an important role in the ascent and storage of magmas during the recent volcanic activity in the two regions. Chemical and textural features of orthopyroxene, amphibole and Fe-Ti oxides from NT suggest that crystallization of magmas occurred at polybaric conditions, confirming the rapid upwelling of magmas.

  8. Garnet peridotites from Pohorje: Petrography, geothermobarometry and metamorphic evolution

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    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.

  9. Determination of P-T and tectonic setting of Ghaleh Yaghmesh plutonic complex (west of Yazd province by using of mineral chemistry

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    Bahareh Fazeli


    Full Text Available The Ghaleh Yaghmesh plutonic massif is located the westernmost part of Yazd province and in the central part of the Urumieh – Dokhtar magmatic arc (UDMA. This massif with quartzdiorite, tonalite and granodiorite composition is Oligocene in age and intruded the volcanic and pyroclastic rocks including rhyolite, rhyodacite, and andesitic, as well as rhyodacitic and rhyolitic tuff belonging to the Eocene. Tonalite and granodiorite contain mafic microgranular enclaves with quartzdiorite composition. According to mineral chemistry, the plagioclases are oligoclase to labradorite in composition. The amphiboles have high magnesian and are calcic nature (magnesio-hornblende. The biotites from the tonalites are enriched in magnesian. Compositionally, clinopyroxene display augite and augite–diopside in quartz-diorite and enclaves respectively. Thermometery of the clinopyroxene and hornblende– plagioclase show 1100-1125°C and 730-900°C respectively. The pressure of the studied rocks, on the base of chemical data of magnesio-hornblende, ranges from 1.5 to 1.75 kbar, which is equal to the depth of about 5.5-6.5 km. The overall field, petrography and mineral chemistry data support the I-type calc-alkaline nature of the studied granitoid, which formed during high oxygen fugacity and volcanic arc, and subduction is suggested for its formation environment.

  10. Geochronologic synthesis of the Piedra Alta Terrane, Uruguay

    International Nuclear Information System (INIS)

    Preciozzi, F.; Peel, E.


    In the Pre cordillera of Córdoba there are sixteen bands of ductile deformation, which allows tectonic significance assign them to four groups. One of them, which belongs to Deformation Gaza Tunnels, consists of post metamorphic strips uprooting of Orogen Pampeano Cambrian reverse nature, produced by convergent general shear (transpressional), related to collisional stages terrain Posthumous Pampa against Gondwana margin, and famatinian subduction. New radiometric data obtained by the K / Ar method amphiboles and micas allow better narrow activity tectonics of the strip, which would have nucleated after the M2 metamorphic peak (ca. 534 Ma), uprooted the Orogen Cambrian and Ordovician exhumándolo up early (onset of subduction Famatinian), when located the Charquina (474 ​​Ma) granodiorite. The period of tectonic activity FDLT (ca. 64 Ma), coincide with the approach of land Cuyania the Gondwana margin, prior to placement and final collision in the Middle to Late Ordovician. At the same time, in the field Pampeano they would be producing con tractional stages end collision with terrain Pampa the western margin of Gondwana. Subsequently, the FDLT would have cooled to the middle Silurian, when the Sierras de Cordoba and San Luis They continued their exhumation through isotherm muscovite. After cooling this generalized, deformation occurs and Devonian magmatism that penetrativamente affected the Pre cordillera eastern

  11. Evaluation of the odd-even effect in limits of detection for electron microprobe analysis of natural minerals

    Energy Technology Data Exchange (ETDEWEB)

    Verma, Surendra P., E-mail: [Departamento de Sistemas Energeticos, Centro de Investigacion en Energia, Universidad Nacional Autonoma de Mexico, Priv. Xochicalco s/no., Col Centro, A.P. 34, Temixco, Mor. 62580 (Mexico); Pandarinath, Kailasa [Departamento de Sistemas Energeticos, Centro de Investigacion en Energia, Universidad Nacional Autonoma de Mexico, Priv. Xochicalco s/no., Col Centro, A.P. 34, Temixco, Mor. 62580 (Mexico); Velasco-Tapia, Fernando [Facultad de Ciencias de la Tierra, Universidad Autonoma de Nuevo Leon, Carretera Linares-Cerro Prieto km. 8, Linares, N.L. 67700 (Mexico); Rodriguez-Rios, Rodolfo [Facultad de Ingenieria e Instituto de Geologia, Universidad Autonoma de San Luis Potosi, Av. Dr. Manuel Nava No. 8, Zona Universitaria, San Luis Potosi, S.L.P. 78240 (Mexico)


    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.

  12. Petrogenesis, detrital zircon SHRIMP U-Pb geochronology, and tectonic implications of the Upper Paleoproterozoic Seosan iron formation, western Gyeonggi Massif, Korea (United States)

    Kim, Chang Seong; Jang, Yirang; Samuel, Vinod O.; Kwon, Sanghoon; Park, Jung-Woo; Yi, Keewook; Choi, Seon-Gyu


    This study involves investigations on the Upper Paleoproterozoic iron formation (viz., Seosan iron formation) from the Seosan Group, Gyeonggi Massif of the southwestern Korean Peninsula. It occurs as thin banded layers within meta-arkosic sandstone, formed by alternating processes of chemical (hydrothermal) and detrital depositions under a shallow marine environment. It mainly consists of alternating layers of iron oxides, mostly hematite, and quartz. Minor amounts of magnetite surrounded by muscovite, clinopyroxene and amphibole indicate hydrothermal alteration since its formation. Meta-arkosic sandstone is composed of recrystallized or porphyroclastic quartz and microcline, with small amounts of hematite and pyrite clusters. The Seosan iron formation has high contents of total Fe2O3 and SiO2 with positive Eu anomalies similar to those of other Precambrian banded iron formations, and its formation is clearly related to hydrothermal alteration since its deposition. Detrital zircon SHRIMP U-Pb geochronology data from a meta-arkosic sandstone (SN-1) and an iron formation (SN-2) show mainly two age groups of ca. 2.5 Ga and ca. 1.9-1.75 Ga. This together with intrusion age of the granite gneiss (ca. 1.70-1.65 Ga) clearly indicate that the iron formations were deposited during the Upper Paleoproterozoic. The dominant Paleoproterozoic detrital zircon bimodal age peaks preserved in the Seosan iron formation compare well with those from the South China Craton sedimentary basins, reflecting global tectonic events related to the Columbia supercontinent in East Asia.

  13. Proterozoic metamorphism and uplift history of the north-central Laramie Mountains, Wyoming, USA (United States)

    Patel, S.C.; Frost, B.R.; Chamberlain, K.R.; Snyder, G.L.


    The Laramie Mountains of south-eastern Wyoming contain two metamorphic domains that are separated by the 1.76 Ga. Laramie Peak shear zone (LPSZ). South of the LPSZ lies the Palmer Canyon block, where apatite U-Pb ages are c. 1745 Ma and the rocks have undergone Proterozoic kyanite-grade Barrovian metamorphism. In contrast, in the Laramie Peak block, north of the shear zone, the U-Pb apatite ages are 2.4-2.1 Ga, the granitic rocks are unmetamorphosed and supracrustal rocks record only low-T amphibolite facies metamorphism that is Archean in age. Peak mineral assemblages in the Palmer Canyon block include (a) quartz-biotite-plagioclase-garnet-staurolite-kyanite in the pelitic schists; (b) quartz-biotite-plagioclase-low-Ca amphiboles-kyanite in Mg-Al-rich schists, and locally (c) hornblende-plagioclase-garnet in amphibolites. All rock types show abundant textural evidence of decompression and retrograde re-equilibration. Notable among the texturally late minerals are cordierite and sapphirine, which occur in coronas around kyanite in Mg-Al-rich schists. Thermobarometry from texturally early and late assemblages for samples from different areas within the Palmer Canyon block define decompression from > 7 kbar to textures. The Proterozoic tectonic history of the central Laramie Range is similar to exhumation that accompanied late-orogenic oblique convergence in many Phanerozoic orogenic belts.

  14. Retrograde corona texture in pre-Himalayan metamorphic mafic xenoliths, Sutlej valley, NW Himalaya: Implication on rare occurrence of high-grade rocks in the Himalaya (United States)

    Thakur, S. S.


    The present study documents extensive retrogression in mafic xenoliths embedded in the Kinnaur Kailash Granite (∼500 Ma), Sutlej valley, NW Himalaya. Most of the mafic xenoliths are hornblende-rich and are characterized by numerous retrograde corona textures such as garnet coronae around clinopyroxene and plagioclase, titanite coronae around ilmenite, and hornblende coronae around clinopyroxene. This implies that the mafic xenoliths had undergone granulite-facies metamorphism in the early stage of metamorphic evolution, and have been extensively retrograded at a later stage to the present day amphibole-rich mafic xenoliths. The retrogression path traced by these mafic xenoliths can be constrained through P-T estimates using hbl-grt and hbl-pl geothermometry, hbl-grt-pl geobarometry, and Thermocalc3.21 calculations. The estimated results suggest temperatures in the range of 536-662 °C and pressures in the range of 4.5-6.7 kbar for the formation of the corona textures. P-T calculation of garnet forming reaction rim around clinopyroxene further shows that retrogression had started at ∼650 °C and ∼7.3 kbar. These observations suggest that retrogression played a major role in the obliteration of most of the high-grade pre-Himalayan xenoliths from the Himalaya.

  15. Reaction-Enhanced Permeability in Gabbroic Crust, IODP Site 1309, mid Atlantic Ridge (United States)

    McCaig, A. M.; Condliffe, E.; Frost, B. R.; Jamtveit, B.


    Thermal cracking is normally assumed to be the main mechanism of permeability generation in the oceanic crust. Here we present microstructural evidence that metamorphic reactions played a significant role in creating porosity and permeability in gabbroic rocks beneath a detachment fault at 30° N in the Atlantic ocean. At least two mechanisms for permeability generation have been identified: 1) In basaltic intrusions, euhedral zoning in amphibole replacing clinopyroxene suggests a dissolution/precipitation mechanism similar to textures observed in epidosites from the Troodos ophiolite. The basaltic sills lack macroscopic fractures and alteration patterns suggest a fingering instability allowed fluid to enter the rock. 2) Volume increase reactions in olivine gabbros and troctolites. These generated radial crack networks filled with secondary minerals where olivine was surrounded by other phases, and are seen both in serpentinization reactions and in reaction between olivine and plagioclase forming tremolite-chlorite coronas. Discrete-element modelling shows how isolated olivines can be linked by propagating networks of cracks allowing fluid to access initially impermeable crust. Assuming that most fluid flow occurs along major fractures, reaction permeability provides an effective mechanism for fluid to access intervening unaltered rock, and may be important for scavenging ore-forming components from the crust. The most permeable part of the system is likely to be at the reaction front before precipitating minerals occlude the porosity, and this may promote front-parallel fluid flow.

  16. Redetermination of katayamalite, KLi3Ca7Ti2(SiO312(OH2

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    Marcelo B. Andrade


    Full Text Available The crystal structure of katayamalite, ideally KLi3Ca7Ti2(SiO312(OH2 (potassium trilithium heptacalcium dititanium dodecasilicate dihydroxide, was previously reported in triclinic symmetry (C-1, with isotropic displacement parameters for all atoms and without the H-atom position [Kato & Murakami (1985. Mineral. J. 12, 206–217]. The present study redetermines the katayamalite structure with monoclinic symmetry (space group C2/c based on single-crystal X-ray diffraction data from a sample from the type locality, Iwagi Island, Ehime Prefecture, Japan, with anisotropic displacement parameters for all non-H atoms, and with the H atoms located by difference Fourier analysis. The structure of katayamalite contains a set of six-membered silicate rings interconnected by sheets of Ca atoms on one side and by an ordered mixture of Li, Ti and K atoms on the other side, forming layers which are stacked normal to (001. From the eight different metal sites, three are located on special positions, viz. one K and one Li atom on twofold rotation axes and one Ca atom on an inversion center. The Raman spectrum of kataymalite shows a band at 3678 cm−1, similar to that observed for hydroxyl-amphiboles, indicating no or very weak hydrogen bonding.

  17. Chemical and boron isotopic composition of tourmaline from the Mariinsky emerald deposit, Central Urals, Russia (United States)

    Baksheev, Ivan A.; Trumbull, Robert B.; Popov, Mikhail P.; Erokhin, Yuri V.; Kudryavtseva, Olesya E.; Yapaskurt, Vasily O.; Khiller, Vera V.; Vovna, Galina M.; Kiselev, Vladimir I.


    Tourmaline is abundant at the Mariinsky schist-hosted emerald deposit in the Central Urals, Russia, both in emerald-bearing phlogopite veins (type 1) and later, emerald-free pockets, lenses, and veinlets cutting the phlogopite veins (type 2). The Ca content in tourmaline is influenced by the host rocks (ultramafic and mafic rocks), associated minerals, and minerals crystallized before tourmaline (amphibole, fluorite, margarite). The Na concentration in tourmaline depends on the presence or absence of paragonite, and the association with micas also strongly influences the contents of Li, Zn, Ni, and Co in tourmaline. Type 1 tourmalines associated with phlogopite are relatively depleted in these elements, whereas type 2 tourmalines associated with margarite or paragonite are enriched. Some differences in isomorphic substitutions along with the trace element composition (Zn, V, Sr, Co, REE) may have value in exploration of emerald-bearing and emerald-free veins in schist-hosted emerald deposits. The δ11B values in tourmaline of all types fall in a narrow total range from -11.3 to -8.4‰. These values, combined with a mineralization temperature of 420-360 °C, yield an estimated δ11B fluid composition of -7.4 to -6.8‰ suggesting a mixed source of boron, likely dominated from the granitic rocks surrounding the emerald belt. The narrow range of B-isotope compositions in tourmaline from throughout the Mariinsky deposit suggests a well-mixed hydrothermal system.

  18. Investigation of Chinese archaic jade by PIXE and μRaman spectrometry

    International Nuclear Information System (INIS)

    Chen, T.H.; Calligaro, T.; Pages-Camagna, S.; Menu, M.


    External-beam particle-induced X-ray emission (PIXE) and μRaman 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.)

  19. 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.)

  20. Investigation of Chinese archaic jade by PIXE and μRaman spectrometry (United States)

    Chen, T.-H.; Calligaro, T.; Pagès-Camagna, S.; Menu, M.

    External-beam particle-induced X-ray emission (PIXE) and μRaman 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.

  1. Laser-induced breakdown spectroscopy analysis of minerals: Carbonates and silicates

    International Nuclear Information System (INIS)

    McMillan, Nancy J.; Harmon, Russell S.; De Lucia, Frank C.; Miziolek, Andrzej M.


    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

  2. Angiogenesis correlates with macrophage and mast cell infiltration in lung tissue of animals exposed to fluoro-edenite fibers. (United States)

    Musumeci, Giuseppe; Loreto, Carla; Giunta, Salvatore; Rapisarda, Venerando; Szychlinska, Marta Anna; Imbesi, Rosa; Castorina, Alessandro; Annese, Tiziana; Castorina, Sergio; Castrogiovanni, Paola; Ribatti, Domenico


    Angiogenesis plays a crucial role in progression of pleural malignant mesothelioma. A significantly increased incidence of pleural mesothelioma has been attributed to exposure to fluoro-edenite, a fibrous amphibole extracted from a local stone quarry. In this study, we have investigated the expression of CD68-positive macrophages, tryptase-positive mast cells and CD31 positive areas, as expression of microvascular density, in lung tissue of sheeps exposed to fluoro-edenite fibers vs controls, by immunohistochemical, morphometric and Western blot analysis. The result have evidenced a significant increase in the expression of CD68-positive macrophages, tryptase-positive mast cells as well as a significant increase in microvascular density evaluated as CD31 positive areas in lung tissue of of sheeps exposed to fluoro-edenite fibers vs controls. These data confirmed the important role played by tumor microenvironment components, including macrophages and mast cells, in favour of angiogenesis in pleural mesothelioma induced by fluoro-edenite exposure. Copyright © 2016 Elsevier Inc. All rights reserved.

  3. Multiple sources of magmatism: granitoids from southeast kohistan, nw himalayas Pakistan

    International Nuclear Information System (INIS)

    Sayab, M.; Qazi, M.S.


    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)

  4. Some antarctic lacustrine sediments from northern Victoria Land investigation by Moessbauer spectroscopy, INNA and XRD

    International Nuclear Information System (INIS)

    Stievano, L.; Bertelle, M.; Leotta, G.; Calogero, S.; Constantinescu, S.; Oddone, M.


    Fifteen lacustrine sediments, sampled during the 1994-1995 Austral summer in Northern Victoria Land (Antarctica), were characterised by 57 Fe Moessbauer spectroscopy, instrumental neutron activation analysis and X-ray diffraction. These sediments are related to the intrusive rocks from Granite Harbour, to the metamorphic rocks of the Complex of Wilson Terrane and the volcanic rocks from Mc Murdo. The samples contain quartz, alkaline feldspars, plagioclases, amphiboles, biotite, chlorite and muscovite except for the sediments of volcanic origin that contain alkaline feldspars, plagioclases and pyroxenes. The paramagnetic components of the Moessbauer spectra were assigned mainly to the iron sides in biotites except for those displayed from the sediments of volcanic origin assigned mainly to pyroxenes. Moessbauer spectra at room temperature do not display magnetic ordering except for those of the sediments of volcanic origin containing bulk magnetite, hematite and goethite. Moessbauer spectra collected at the liquid helium temperature always exhibit magnetic ordering. This spectral difference has been attributed to the different dimensions of the iron oxide particles in the sediments. The scarce weathering involves a partial transformation of magnetite in hematite and goethite in the sediment of volcanic origin. In the remaining sediments a partial hydrolysis of biotite together with a partial oxidation of iron (II) retained in silicates is present. (authors)

  5. Composition And Characteristic Of The Surficial Sediments In The Southern Corniche Of Jeddah, Red Sea Coast

    Directory of Open Access Journals (Sweden)

    Talha A Al-Dubai


    Full Text Available This work discusses the composition and characteristic of the surficial sediments in the southern corniche of Jeddah, Saudi Red Sea coast, in an attempt to infer the surficial distribution pattern of minerals and provenance of sediments. Twenty-six superficial sediments samples were collected from backreef and forereef areas and were analyzed for grain size, CaCO3 content, and mineralogy. The textural of grain size range from gravel to mud fraction. The mud-dominated substrates (<63 µm occur generally in the back-reef area near the shoreline (sheltered area and in the lagoon. Gravel rich-sediments are mostly found in forereef regions. The highest content of aragonite and Mg-calcite occur in the forereef area, probably because to suitability the forereef region for chemical and biochemical precipitation of these minerals. High Mg-calcite and Dolomite are low in both the regions. The pyrite occurs in lagoon; this indicates the reductive conditions in this part. However, on the contrary the percentage of carbonate minerals were low in the backreef-flat area, which could be attributed to the supply of non-carbonate terrigenous materials. The terrigenous material contains quartz, k-feldspar, plagioclase and amphibole minerals and are dominant in backreef-flat area with averages of 12.7%, 7.13%, 2.93% and 0.65%, respectively. Their abundance could be attributed to the supply of terrigenous materials by Aeolian deposits and intermittent Wadis.

  6. Petrology and geochemistry of REE-rich Mafé banded iron formations (Bafia group, Cameroon) (United States)

    Nkoumbou, Charles; Gentry, Fuh Calistus; Tchakounte Numbem, Jacqueline; Belle Ekwe Lobé, Yolande Vanessa; Nwagoum Keyamfé, Christin Steve


    Archaean-Paleoproterozoic foliated amphibole-gneisses and migmatites interstratified with amphibolites, pyroxeno-amphibolites and REE-rich banded-iron formations outcrop at Mafé, Ndikinimeki area. The foliation is nearly vertical due to tight folds. Flat-lying quartz-rich mica schists and quartzites, likely of Pan-African age, partly cover the formations. Among the Mafé BIFs, the oxide BIF facies shows white layers of quartz and black layers of magnetite and accessory hematite, whereas the silicate BIF facies is made up of thin discontinuous quartz layers alternating with larger garnet (almandine-spessartine) + chamosite + ilmenite ± Fe-talc layers. REE-rich oxide BIFs compositions are close to the East Pacific Rise (EPR) hydrothermal deposit; silicate BIFs plot midway between EPR and the associated amphibolite, accounting for a contamination by volcanic materials, in addition to the hydrothermal influence during their oceanic deposition. The association of an oceanic setting with alkaline and tholeiitic magmatism is typical of the Algoma-type BIF deposit. The REE-rich BIFs indices recorded at Mafé are interpreted as resulting from an Archaean-Paleoproterozoic mineralization.

  7. 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.

  8. Chemical and boron isotopic composition of tourmaline from the Mariinsky emerald deposit, Central Urals, Russia (United States)

    Baksheev, Ivan A.; Trumbull, Robert B.; Popov, Mikhail P.; Erokhin, Yuri V.; Kudryavtseva, Olesya E.; Yapaskurt, Vasily O.; Khiller, Vera V.; Vovna, Galina M.; Kiselev, Vladimir I.


    Tourmaline is abundant at the Mariinsky schist-hosted emerald deposit in the Central Urals, Russia, both in emerald-bearing phlogopite veins (type 1) and later, emerald-free pockets, lenses, and veinlets cutting the phlogopite veins (type 2). The Ca content in tourmaline is influenced by the host rocks (ultramafic and mafic rocks), associated minerals, and minerals crystallized before tourmaline (amphibole, fluorite, margarite). The Na concentration in tourmaline depends on the presence or absence of paragonite, and the association with micas also strongly influences the contents of Li, Zn, Ni, and Co in tourmaline. Type 1 tourmalines associated with phlogopite are relatively depleted in these elements, whereas type 2 tourmalines associated with margarite or paragonite are enriched. Some differences in isomorphic substitutions along with the trace element composition (Zn, V, Sr, Co, REE) may have value in exploration of emerald-bearing and emerald-free veins in schist-hosted emerald deposits. The δ11B values in tourmaline of all types fall in a narrow total range from -11.3 to -8.4‰. These values, combined with a mineralization temperature of 420-360 °C, yield an estimated δ11B fluid composition of -7.4 to -6.8‰ suggesting a mixed source of boron, likely dominated from the granitic rocks surrounding the emerald belt. The narrow range of B-isotope compositions in tourmaline from throughout the Mariinsky deposit suggests a well-mixed hydrothermal system.

  9. Calymmian magmatism in the basement of the Jauru Terrain (Rondonian - San Ignacio Province), Amazon Craton: U-Pb and Sm-Nd geochemistry and geochronology

    Energy Technology Data Exchange (ETDEWEB)

    Fachetti, Frankie James Serrano; Costa, Ana Claudia Dantas da; Silva, Carlos Humberto da, E-mail:, E-mail:, E-mail: [Universidade Federal de Mato Grosso (UFMT), Cuiaba, MT (Brazil). Instituto de Ciencias Exatas e da Terra


    The Taquarussu Orthogneiss and the Guadalupe Granodiorite, part of the Rondonian-San Ignacio Province basement, southwest of the Amazonian Craton, correspond to oriented bodies with a NW trend. The rocks show granodiorite composition with minor occurrences of coarse grained monzogranites consisting essentially of plagioclase, quartz, microcline, orthoclase and biotite. The accessory minerals are amphibole, titanite, garnet, apatite, epidote, zircon and opaque. The geochemical data indicate that the rocks are classified as granodiorites and monzogranites, with an intermediate to acid magmatism, sub-alkaline character, from the calc-alkaline to the high-K calc-alkaline series, with alumina ratios ranging from metaluminous to lightly peraluminous. The rocks were classified as generated in volcanic islands arc environment and the U-Pb data (SHRIMP zircon) show a concord age 1575 ± 6 Ma. The Sm-Nd model age (T{sub DM}) is 1.63 Ga with εNd (t = 1.57 Ga) ranging from -1.52 to +0.78. These data indicate that these rocks are probably a juvenile crust with a possible contamination of crustal rocks. (author)

  10. Intraplate mantle oxidation by volatile-rich silicic magmas

    Energy Technology Data Exchange (ETDEWEB)

    Martin, Audrey M.; Médard, Etienne; Righter, Kevin; Lanzirotti, Antonio


    The upper subcontinental lithospheric mantle below the French Massif Central is more oxidized than the average continental lithosphere, although the origin of this anomaly remains unknown. Using iron oxidation analysis in clinopyroxene, oxybarometry, and melt inclusions in mantle xenoliths, we show that widespread infiltration of volatile (HCSO)-rich silicic melts played a major role in this oxidation. We propose the first comprehensive model of magmatism and mantle oxidation at an intraplate setting. Two oxidizing events occurred: (1) a 365–286 Ma old magmatic episode that produced alkaline vaugnerites, potassic lamprophyres, and K-rich calc-alkaline granitoids, related to the N–S Rhenohercynian subduction, and (2) < 30 Ma old magmatism related to W–E extension, producing carbonatites and hydrous potassic trachytes. These melts were capable of locally increasing the subcontinental lithospheric mantle fO2 to FMQ + 2.4. Both events originate from the melting of a metasomatized lithosphere containing carbonate + phlogopite ± amphibole. The persistence of this volatile-rich lithospheric source implies the potential for new episodes of volatile-rich magmatism. Similarities with worldwide magmatism also show that the importance of volatiles and the oxidation of the mantle in intraplate regions is underestimated.

  11. Uraniferous albitites from the Lagoa Real Uranium Province, state of Bahia, Brazil

    International Nuclear Information System (INIS)

    Brito, W. de; Raposo, C.; Matos, E.C. de


    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) [pt

  12. Geochemical and petrological study of the anphibolites from Cassia Region, MG

    International Nuclear Information System (INIS)

    Correia, C.T.; Girardi, V.A.V.


    The orthoamphibolites of the Cassia Region, Minas Gerais State, belong to two different groups distinguished by their TiO 2 contents (average contents 2.67% respectively). (La, Nb, V, Zr, Ce, and Zn). The titanium-poor group is slightly enriched in SiO 2 . The remarkable differences in incompatible element ratios between ATi and BTi(e.g., 4-,5 and 11-fold for Ce/Y, Zr/Nb and Y/La, respectively) indicate that the parent basaltic rocks of both groups were not derived either by fractional crystallizatin or by partial melting from a homogeneous source. It is suggested that the parent basilitic rocks of ATi and BTi were related to chemically hetrogeneous mantles materials. The clear discrimination of both groups in the Ti-Zr-Y diagram is attributed to geochemical characteristics of their genesis and does not necessarily indicate different environments. Metamorphic grade in the Cassia region increases from SSW to NNE. In the amphibolites, progresssive metamorphism is indicated by increase in the anorthite content of plagioclase; by changes of colour and composition of the amphiboles, which vary from tschermakitic hornblendes (green) to edenitic hornblendes (brownish-green to brown); and by increase in the pyrope content of garnet. The temperatures obtained through geothermometry of the amplhibolities vary from 650 0 C to slightly greater than 725 0 C. Minimum pressures are estimated around 6.5Kb [pt

  13. Alteration history studies in the Exploratory Studies Facility, Yucca Mountain, Nevada, USA

    International Nuclear Information System (INIS)

    Levy, S.S.; Chipera, S.J.; Norman, D.I.


    By mid-1995, the Exploratory Studies Facility (ESF) extended about 1. 1 km from Exile Hill westward toward Yucca Mountain, mostly within densely welded, devitrfied Tiva Canyon Tuff. Secondary mineral occurrences in this unit include breccia cements of mordenite, a fibrous zeolite, and vapor-phase deposits of silica, alkali feldspar, apatite, hollandite, amphibole, and zircon. Calcite is also a common secondary mineral in faults and fractures. Studies of water and gas contents in fluid inclusions in calcites from a fault in nonwelded tuff and a fracture in densely welded tuff suggest mineral deposition under transient locally saturated conditions. Calcite in the nonwelded tuff incorporated air from the unsaturated tuff adjacent to the fault. A highly altered interval within pre-Pah Canyon tuffs just above the top of the Topopah Spring Tuff may be a fossil fumarole or other hydrothermal feature associated with cooling pyroclastic deposits, overprinted by later zeolitic alteration. The observed quartz, cristobalite, opal-CT, and fluorite have been widely identified as products of syngenetic devitrification and vapor-phase alteration in and above the Topopah Spring Tuff. Smectite, also an abundant secondary mineral at the ESF site, has been observed elsewhere at this stratigraphic level. Zeolitic alteration of nonwelded tuffs above the Topopah Spring Tuff, as seen in the ESF, has also been noted in drill core and outcrop at northeastern Yucca Mountain. The hydrologic and geochemical conditions that favored zeolitization only in certain areas of this stratigraphic interval have yet to be determined

  14. Floatability of Fe-bearing silicates in the presence of starch: Adsorption and spectroscopic studies (United States)

    Severov, V. V.; Filippova, I. V.; Filippov, L. O.


    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.

  15. Mineralogical textural and compositional data on the alteration of basaltic glass from Kilauea, Hawaii to 300 degrees C: Insights to the corrosion of a borosilicate glass waste-form

    International Nuclear Information System (INIS)

    Smith, D.K.


    Mineralogical, textural and compositional data accompanying greenschist facies metamorphism (to 300 degrees C) of basalts of the East Rift Zone (ERZ), Kilauea, Hawaii may be evaluated relative to published and experimental results for the surface corrosion of borosilicate glass. The ERZ alteration sequence is dominated by intermittent palagonite, interlayered smectite-chlorite, chlorite, and actinolite-epidote-anhydrite. Alteration is best developed in fractures and vesicles where surface reaction layers root on the glass matrix forming rinds in excess of 100 microns thick. Fractures control fluid circulation and the alteration sequence. Proximal to the glass surface, palagonite, Fe-Ti oxides and clays replace fresh glass as the surface reaction layer migrates inwards; away from the surface, amphibole, anhydrite, quartz and calcite crystallize from hydrothermal fluids in contact with the glass. The texture and composition of basaltic glass surfaces are similar to those of a SRL-165 glass leached statically for sixty days at 150 degrees C. While the ERZ reservoir is a complex open system, conservative comparisons between the alteration of ERZ and synthetic borosilicate glass are warranted. 31 refs., 2 figs

  16. 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

  17. 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.

  18. 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)

  19. The occurrence of ferropyrosmalite in the mineralized breccias from Igarape Bahia (North region, Brazil) Au-Cu ({+-} ETR-U) deposit, Carajas mineral Province; Ocorrencia de ferropirosmalita nas brechas mineralizadas do deposito de Au-Cu-({+-} ETR-U) de Igarape Bahia, Provincia mineral de Carajas

    Energy Technology Data Exchange (ETDEWEB)

    Tazava, Edison; Gomes, Newton Souza [Ouro Preto Univ., MG (Brazil). Escola de Minas. Dept. de Geologia]. E-mail:; Oliveira, Claudinei Gouveia de [Brasilia Univ., DF (Brazil). Inst. de Geociencias]. E-mail:


    In the last years, several works report the presence of pyrosmalite mineral series [(Fe, Mn){sub 8} Si{sub 6} O{sub 15} (OH, Cl){sub 10}] commonly associated with volcanic exhalative massive sulphide or Fe-Mn metamorphosed deposits. In this paper, we present the inedit occurrence of ferropyrosmalite in the Au-Cu ({+-} REE-U) of Igarape Bahia deposit, located in the Au-Cu district of the Carajas Mineral Province. We consider the Igarape Bahia mineralization as being related to the genesis of iron-oxide class deposit, like the Olympic Dam type. Ferropyrosmalite occurs in two different contexts: associated with carbonate veins; associated with heterolithic breccias, composed by BIF and mafic metavolcanic fragments immersed in a magnetic, chalcopyrite, bornite, pyrite, carbonates (calcite to siderite), uranium and REE minerals, and gold, - rich matrix. The growth of ferropyrosmalite is probably due to the substitution of iron rich minerals (chloride, magnetite and siderite), controlled by magmatic fluid influx rich in chlorine. The permeability of breccias and the discontinuity of veins favour fluid percolation. The mode of occurrence of ferropyrosmalite and its relation with amphibole (ferro-hornblende-actinolite) indicate metasomatic growth of the former under temperatures in the transition of greenschist/amphibolite facies. The ferropyrosmalite of the Igarape Bahia deposit represents an uncommon type of occurrence linked to hydrothermal/magmatic conditions. (author)

  20. 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.

  1. 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)

    Roggli, V.L.; McGavran, M.H.; Subach, J.; Sybers, H.D.; Greenberg, S.D.


    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

  2. Incidence of pleural mesothelioma in a community exposed to fibres with fluoro-edenitic composition in Biancavilla (Sicily, Italy

    Directory of Open Access Journals (Sweden)

    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.

  3. 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

  4. Petrological insights on the effusive-explosive transitions of the Nisyros-Yali Volcanic Center, South Aegean Sea (United States)

    Popa, Razvan-Gabriel; Bachmann, Olivier; Ellis, Ben; Degruyter, Wim; Kyriakopoulos, Konstantinos


    Volcanoes erupting silicic, volatile-rich magmas can exhibit both effusive and explosive eruptions, even during closely spaced eruptive episodes. Understanding the effusive-explosive transition is fundamental in order to assess the hazards involved. Magma properties strongly influence the processes during magma ascent that determine the eruptive style. Here, we investigate the link between changing conditions in the magma reservoir and the eruptive style. The Quaternary Nisyros-Yali volcanic center, from the South Aegean Sea, provides an excellent natural laboratory to study this process. Over the last 60-100 kyrs, it produced a series of dacitic to rhyolitic eruptions that emplaced alternating effusive and explosive deposits (with explosive eruptions likely shortly following effusive ones). For this study, nine fresh and well-preserved units (five effusive and four explosive) were sampled and analyzed for whole-rock, groundmass glass and mineral compositions, in order to draw insights into the magma chamber processes and thermodynamic conditions that preceded both types of eruptions. Silicic magmas in Nisyros-Yali record a complex, open-system evolution, dominated by fractionation in mushy reservoirs at mid to upper crustal depths, frequently recharged by warmer input from below. Storage temperatures recorded by the amphibole-plagioclase thermometer span a wide range, and they are always cooler than the pre-eruptive temperatures yielded by Fe-Ti oxide thermometry for the same unit, whether it is effusive or explosive. However, magmas feeding effusive eruptions typically reached cooler conditions (expressed by the presence of low-Al, low-Ti amphiboles) than in the explosive cases. The difference between the pre-eruptive and the lowest storing temperatures in the Nisyros series are in the order of 10-30°C for explosive units, while the difference is of about 40-110°C for the effusive units. The Yali series does not perfectly fit this pattern, where explosive units

  5. Sequence of construction of Ciomadul (Csomád) dacitic lava domes, East Carpathians, by unspiked K-Ar Cassignol-Gillot technique in comparison with other radiometric methods (United States)

    Dibacto, Stéphane; Lahitte, Pierre; Karátson, Dávid; Veres, Daniel; Gertisser, Ralf


    eruptive ages. We separated and dated different phases containing potassium, i.e. feldspar, amphibole, biotite, plagioclase microlite, and groundmass. Ages obtained on feldspar, amphibole, biotite are systematically older than those obtained on the groundmass illustrating that these phenocrysts were formed before (or well before) the eruption, and brought up by the magma during the eruption. On the other hand, plagioclase microlite displays a complex range of ages, from the age of groundmass to the age of plagioclase phenocrysts. Finally the influence of the groundmass size fraction used (ideally, from 63 to 250 micrometres) was also tested. The applied methodology allows us to propose an appropriate procedure to separate the adequate material in order to obtain the K-Ar age of the eruption, i.e. the groundmass, in which there is no risk of presence of older, inherited phenocrysts.

  6. Geochemistry of tephra from Bed I, Olduvai Gorge, Tanzania: Stratigraphic correlations and implications for magmatic evolution (United States)

    McHenry, L.


    At least 10 predominantly trachytic and rhyolitic tuffs are preserved interbedded in volcaniclastic sediments of Plio-Pleistocene Bed I, Olduvai Gorge, Tanzania. Physical correlation of the tuffs is complicated by faulting and variation in preservation and lithofacies. Differences in the degree and type of tephra alteration (clay, zeolitic, none) and preservation of glass shards within the various depositional environments (saline-alkaline lake, lake margin, wetlands, alluvial fan) make correlation by conventional glass chemistry methods impossible. However, variations in overall mineralogy and chemical compositions of co-magmatic phenocrysts (feldspar, augite, titanomagnetite, amphibole) have proven useful to uniquely characterize the tuffs for correlation purposes. Samples of 10 major tuffs in the Olduvai Bed I sequence were collected from various depostional and preservational environments situated up to 15 km apart. Thin sections and mineral separates (10-60 grains of each type of phenocryst/ sample, 2-3 samples/ tuff) were analyzed by electron microprobe for major and minor elements. The lower Bed I tuffs are rhyolitic and easily distinguished from the upper tuffs by the presence of quartz and high-Fe augite. Feldspar composition has been previously found to separate all of the upper tuffs (1B-1F) except the two trachyandesitic tuffs (1D and the "unnamed" tuff between 1E and 1F). Mn and Ti concentrations in the titanomagnetites separate the upper tuffs (MnO%: 1B=1.5-2, 1C=1.3-1.6, 1D=1.1-1.4, 1E=1.5-1.7, unnamed= 0.9-1.2, 1F=1.6-2; TiO2%: 1B, 1E=23-26, 1C=18-22, 1D=25-27, unnamed=20-21, 1F= 12-20). Tuffs 1B, unnamed, and 1F contain abundant amphibole, 1D contains none. Mn and Fe concentrations in the augites also separate the tuffs (MnO%: 1B=1.2-1.5, 1C=0.9-1.2, 1D=0.6-0.9, 1E=0.9-1.1, unnamed=0.5-0.7, 1F=variable; FeO%: 1B=19-21, 1C=15-19, 1D=12-16, 1E=13-16, unnamed=11-14, 1F=variable). Results of these findings provide new widespread markers in the Olduvai

  7. Raman counting of heavy minerals in turbidites: Indus Fan, IODP Expedition 355 (United States)

    Andò, Sergio


    Raman spectroscopy is an innovative tool with tremendous potential. Thorny long-standing problems that cannot be solved confidently with a polarizing microscope alone, such as the determination of opaque heavy minerals or of detrital grains as small as a few microns, can finally be addressed. Heavy-mineral species commonly found in sediments convey specific information on the genesis of their source rocks and are therefore crucial in provenance diagnoses and palaeotectonic reconstructions. A high-resolution mineralogical study of Indus Fan turbiditic sediments cored during IODP Expedition 355 (Arabian Sea Monsoon) in the Laxmi Basin was carried out to investigate and quantify the different compositional signatures of sand and silt fractions. Silt and sand in turbidite deposits recovered at IODP Sites U1456 and U1457 were chosen as the best natural archive for this source-to-sink study. An integrated mineralogical dataset was obtained by coupling traditional and innovative single-grain heavy-mineral analyses. Reliable quantitative results even in the medium to fine silt classes, which represent the dominant sediment sizes encountered in the recovered cores, were obtained by point-counting of single grains under the microscope assisted by Micro-Raman spectroscopy. Preliminary data from the studied turbidites document rich and diverse heavy-mineral assemblages in both sand and silty-sand fractions. Multiple varietal studies of amphibole, epidote and garnet varieties, representing the dominant heavy-mineral trial in orogenic detritus derived from collided ranges such as the Himalaya, were performed to highlight the wide unexplored potential of Raman spectroscopy when applied to provenance studies. Discriminating within the isomorphous series of garnets is possible, and diverse pyralspite and ugrandite garnets are distinguished by the position of characteristic peaks found at high frequencies and caused by Si-O stretching modes (873-880 cm-1 in ugrandites, 907-926 cm-1

  8. Do the eclogites of the Variscan Malpica-Tuy shear zone in NW Spain point to continental subduction? (United States)

    Li, Botao; Massonne, Hans-Joachim


    High-pressure (HP: P > 10 kbar) rocks such as eclogite typically occur in suture zones of collided continental plates in Phanerozoic times. In case of an extended area at the surface of a denuded orogen with HP and even ultrahigh pressure (UHP) metamorphic rocks, they are often interpreted as the result of continental subduction. We have tested this idea for the HP-UHP area of the Malpica-Tuy zone of the Variscan orogen, which was formed by the collision of Gondwana and Laurussia. For the test, we have initially studied an eclogite and its surrounding gneiss of this zone in detail. The eclogite contains the assemblage garnet, omphacite, amphibole, rutile, ilmenite, clinozoisite/epidote, quartz, and phengite with Si-contents as high as 3.45 per formula unit (pfu) in inner portions and 3.27-3.35 pfu in rims. Garnet exhibits chemical zonation with Gro25Alm55Pyr15Spe5, Gro29Alm57Pyr13Spe1, and Gro23Alm56Pyr20Spe1 as inner core, mantle, and outermost rim compositions, respectively. The gneiss is a former medium-grained granite now composed of quartz, plagioclase, K-feldspar, biotite, phengite, garnet, clinozoisite/epidote, titanite, apatite and ilmenite. Phengite shows Si contents between 3.40 (core) and 3.00 (rim) pfu. Garnet is chemically zoned with Gro69.6Alm27Pyr0.4Spe3, Gro65.5Alm32.5Pyr0.5Spe1.5, Gro65.7Alm31.7Pyr0.6Spe2, and Gro56.6Alm41.6Pyr1.2Spe0.6 as core, mantle, rim and outermost rim compositions, respectively. P-T pseudosections were calculated with the PERPLEX computer program in the system Na2O-K2O-CaO-FeO-O2-MnO-MgO-Al2O3-SiO2-TiO2-H2O for the bulk-rock compositions of the studied eclogite and gneiss. These pseudosections were contoured by isopleths of various parameters such as molar fractions of garnet components. Based on this contouring a P-T path was derived that starts at HP conditions for both lithologies. Garnet began to form at 22 kbar and 565°C in the eclogite. Subsequently, the temperatures increased to 585°C and the pressure decreased to

  9. The crustal magma storage system of Volcán Quizapu, Chile, and the effects of magma mixing on magma diversity (United States)

    Bergantz, George W.; Cooper, Kari M.; Hildreth, Edward; Ruprecht, Phillipp


    Crystal zoning as well as temperature and pressure estimates from phenocryst phase equilibria are used to constrain the architecture of the intermediate-sized magmatic system (some tens of km3) of Volcán Quizapu, Chile, and to document the textural and compositional effects of magma mixing. In contrast to most arc magma systems, where multiple episodes of open-system behavior obscure the evidence of major magma chamber events (e.g. melt extraction, magma mixing), the Quizapu magma system shows limited petrographic complexity in two large historical eruptions (1846–1847 and 1932) that have contrasting eruptive styles. Quizapu magmas and peripheral mafic magmas exhibit a simple binary mixing relationship. At the mafic end, basaltic andesite to andesite recharge magmas complement the record from peripheral cones and show the same limited range of compositions. The silicic end-member composition is almost identical in both eruptions of Quizapu. The effusive 1846–1847 eruption records significant mixing between the mafic and silicic end-members, resulting in hybridized andesites and mingled dacites. These two compositionally simple eruptions at Volcán Quizapu present a rare opportunity to isolate particular aspects of magma evolution—formation of homogeneous dacite magma and late-stage magma mixing—from other magma chamber processes. Crystal zoning, trace element compositions, and crystal-size distributions provide evidence for spatial separation of the mafic and silicic magmas. Dacite-derived plagioclase phenocrysts (i.e. An25–40) show a narrow range in composition and limited zonation, suggesting growth from a compositionally restricted melt. Dacite-derived amphibole phenocrysts show similar restricted compositions and furthermore constrain, together with more mafic amphibole phenocrysts, the architecture of the magmatic system at Volcán Quizapu to be compositionally and thermally zoned, in which an andesitic mush is overlain by a homogeneous dacitic

  10. Hybridization in the subvolcanic Jaala-Iitti complex and its petrogenetic relation to rapakivi granites and associated mafic rocks of southeastern Finland

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    Salonsaari, P.T.


    Full Text Available The 1630 Ma Jaala-Iitti complex is an example of bimodal rapakivi granite magmatism in which the interaction of granite and diabase magmas have led locally to hybridization. The dyke-like complex is situated at the northwestern margin of the Wiborg rapakivi batholith in southeastern Finland, cutting both the Proterozoic Svecofennian metamorphic crust and the Wiborg batholith. The complex consists mainly of non-hybridized compositionally homogeneous granites, i.e., hornblende granite and hornblende-quartz-feldspar porphyry which represent the felsic end-member (ca. 68 wt% SiO2 of the complex. The mafic end-member (ca. 51 wt% SiO2 is present as globules of disaggregated Fe-rich tholeiitic magma forming magmatic mafic enclaves (MMEs and composite MMEs. Commonly MMEs and large (up to 2 metres in diameter pillow-like MMEs show magma mixing and mingling characteristics. Hybrid rocks in the complex are monzogranitic and are characterized by (a quartz grains and quartz aggregates (partially melted xenoliths mantled by amphibole rims (ocellar texture with occasional augite, (b alkali feldspar megacrysts mantled by a micrographic plagioclase-quartz intergrowth, and (c alkali feldspar megacrysts mantled by a plagioclase shell with occasional amphibole inclusions. These textures are also found in hybrid MMEs and especially in pillow-like MMEs. Alkali feldspar and quartz megacrysts in hybrid rocks are derived from partially crystallized felsic magma and from disaggregated rapakivi granite and granitoid xenoliths whereas in the MMEs the xenocrysts are solely derived from partially crystallized felsic magma. Disaggregation of the mafic magma to form MMEs and equilibration with the host have produced micro-enclaves and recrystallized borders of MMEs. Disaggregation of the mafic magma has also produced needle-like apatite crystals incorporated from the mafic magma into the hybrid magma; acicular apatite is typical in MMEs and pillow-like MMEs and is indicative

  11. Origin of Mafic Microgranular Enclaves (MMEs and Their Host Rocks of the Cretaceous Xiaojiang-Liangnong Granitic Complexes in the Southeast Coast Magmatic Belt, S China

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    Pei-Shan Hsieh


    Full Text Available Cretaceous Late Yanshanian (LY magmatism produced large amounts of I-type granitoids in the Southeast Coast Mag matic Belt (SCMB. I-type granitoids from Xiaojiang-Liangnong complexes (N Zhejiang in the northern part of this belt are characterized by containing abundant mafic microgranular enclaves (MMEs. On the basis of petrography and mineralogy, two types of MMEs are recognized. One (Type 1, enclosed in the granodiorite, is composed of amphibole, high-Ti tabularbiotite, plagioclase, K-feld spar, and quartz. Us ing the Al-in-am phibole geobarometer, a shallow origin (4 - 8 km of am phiboles is suggested. The other (Type 2, enclosed in al kali feld spargranite, is amphibole-free and composed of low-Ti acicular biotite, plagioclase, K-feld spar, and quartz. Geo chemistry of major and traceel ements seems to re flect two different evolving trends for these host granitoids. The Sr-Nd isotopic features indicate that all the studied samples vary in a narrow range of Isr (0.7078 to 0.7082 and eNd(T (-5.6 to -8.3, except the Type 2 enclaves and hosts that show slightly morede pleted compositions (Isr = 0.7073 to 0.7075 and eNd(T = -5.0 to -6.0. U-Pb zir con ages obtained are 109.6 ¡_ 0.9 Ma for the granodiorite and 113.5 ¡_ 1.1 Ma for the alkalifeld spargran ite, with 103.2 ¡_ 0.9 Ma for the Type 2 MMEs. In her ited ages of 117.0 ¡_ 2.0 Ma and 119.8 ¡_ 1.1 Ma seem to presentin the former two samples. Similarities of mineral chemistry and isotopic composition among the MMEs-host pairs as well as the youn ger age of MMEs suggest that MMEs of Xiaojiang-Liangnong complexes most likely represent mixing/mingling products formed as a consequence of the in tru sion of ba saltic magma into the host granitoids un der dif fer ent cool ing con di tions. Judg ing from the pres ence of in her ited zir con ages, the com po si tion gap be tween high-Ti and low-Ti bi o tite in granodiorite and al kali feld spar gran ite, and lower zirconsaturation temperatures for

  12. From Mush to Eruption in 1000 Years: Rapid Assembly of the Super-Sized Oruanui Magma Body (United States)

    Allan, A. S.; Morgan, D. J.; Wilson, C. J.; Millet, M.


    The mush model is useful in explaining how large volumes of evolved silicic melt can be generated in and extracted from a crystal-rich source to form crystal-poor rhyolite magma bodies at shallow crustal levels. It is unclear, however, how processes of melt extraction and/or formation of the melt-dominant magma body might be reflected in the crystal record, and what physical and temporal constraints can be applied. Textural observations and in situ geochemical fingerprints in crystals from pumices of the ~25.4 ka Oruanui eruption (Taupo, New Zealand), offer new perspectives on the processes, physical conditions and timing of the melt extraction and accumulation. Almost all orthopyroxene (opx) and plagioclase (plag) cores have textures showing a period of disequilibrium (partial dissolution and/or resorption) followed by stable conditions (infilling of raddled cores; euhedral rim overgrowths). Trace element contents in amphibole (amph), which was stable and actively crystallizing in all but the most evolved parcels of Oruanui magma, complement textural evidence showing that Mn and Zn liberated by opx dissolution were preferentially sequestered in amph. Concentrations of these opx-loving elements show a prominent inflection when plotted against indices of melt evolution (e.g. Eu/Eu* in amph) marking a return to opx stability and subsequent crystallization. Plagioclase, the most abundant crystal phase, records a more complex history with significant inheritance, but textural and chemical evidence suggests that at least some of Oruanui plag crystals experienced the same departure from and return to stability as the opx. Amphibole trace element data are linked to in situ estimates of P-T-fO2 and melt H2O determined via the Ridolfi et al. (2010: Contrib Mineral Petrol 160, 45) thermobarometer. Textural and geochemical evidence combined with P-T-H2O model values indicate that three major Oruanui crystal phases (opx, amph, plag) record a significant decompression event

  13. Petrological and geochemical studies of mantle xenoliths from La Palma, Canary Islands (United States)

    Janisch, Astrid; Ntaflos, Theodoros


    La Palma is the second youngest island, after El Hierro, of the Canary archipelago. The archipelago consists of seven large islands, forming an east-west-trending island chain, and several seamounts. All together they form a volcanic belt of around 800 km length and 450 km width, which presumably comprises roughly the Canary hotspot. The islands are located off the western coast of Morocco, Africa. The distance ranges from 100 km to 500 km. Concurrently with the distance, subaerial volcanism age progresses from the oldest lava in the east to the youngest in the west of the archipelago. Presently, La Palma is in the shield building stage of growth (alongside with El Hierro and Tenerife) and is furthermore the fastest growing island of the Canary archipelago. Historical volcanic eruptions are restricted on the younger islands, La Palma and El Hierro, with the last eruption at the south end of La Palma in 1971. Mantle xenoliths described in this work were collected at the slopes of San Antonio Volcano, Fuencaliente, brought to the surface during the 1677/1678 eruption. The mantle xenolith collection comprises sp-lherzolites, sp-harzburgites and pyroxenites. The texture can be distinguished between coarse-grained matrix and fine-grained veins in various thicknesses, mostly with olivine and pyroxene but also with amphibole, phlogopite as well as apatite. Mineral analyses reveal the existence of primary and secondary ol, cpx and opx. Primary ol has Fo contents of 89.2 to 91.7 and NiO ranging from 0.3 to 0.45 wt.%, whereas secondary ol show Fo values of 78.4 to 91.9 but with NiO below 0.3 wt.%. Primary cpx are predominantly Cr-Diopsides with En48.7-51.9-Wo43.5-44.3-Fs4.1-4.9 and Mg# of 91.5 to 92.4. Secondary cpx, primarily Ti-Augit, display En36.7-44.4-Wo47.7-49.6-Fs6.7-13.0 and Mg# of 75.3 to 90.8. Primary opx compositions are in range of En89.3-90.6-Wo1.3-1.5-Fs8.1-9.3 with Mg# between 90.7 and 92.0. Secondary opx exhibit En88.7-89.2-Wo1.7-1.9-Fs9.1-9.5 and Mg# of 90

  14. Gneisses of Brazil's cultural heritage buildings and its most frequent degradations (United States)

    Gilberto Costa, Antônio


    Macroscopic descriptions of cultural heritage buildings constructed using gneisses in the cities of Rio de Janeiro, Belo Horizonte and Ouro Preto, Brazil, allowed to identify alterations and degradations, in part conditioned by the mineralogical composition and the structures present in these stone materials. It is important to emphasize that: - some changes still begin in the environments where these materials were formed, experiencing an intensification from the processes of extraction, processing and application; - modifications occurring after the applications are understood herein as degradations. The studied gneisses present banding consisting of parts with different thicknesses and mineralogical contents. Due to these differentiated contents, clear bands were identified and constituted essentially by felsic minerals, such as feldspars and quartz, as well as dark bands formed by mafic minerals represented by: biotite, garnets, amphiboles, such as hornblende or pyroxene (hyperstene). In addition to these minerals, low contents of oxides and sulphides were found. Also under the influence of this distribution of minerals, planar structures or foliations, more or less developed, that can be very penetrative have been identified, mainly when these rocks were submitted to the performance of milonitization processes. From the set of changes and degradations observed stand out those related to the decomposition of minerals that make up these materials. In these cases, feldspars and other silicates, such as micas, amphiboles and pyroxenes, were decomposed due to the hydrolysis and products were generated which compromised the resistance of these stone materials, leading to their consequent disintegration. On the other hand, the presence of expansive clays in these products, caused volume increases which also contributed to the expansion of the weathered surface layer (blistering). This process may result detachments in the form of scales to cavities in cases of

  15. Reconstruction of P-T-t metamorphic conditions from symplectites: insights from Pouso Alegre mafic rocks (Brasília Belt, Brazil) (United States)

    Tedeschi, Mahyra; Lanari, Pierre; Rubatto, Daniela; Hermann, Jörg; Pedrosa-Soares, Antônio Carlos; Dussin, Ivo; Aurélio Pinheiro, Marco; Bouvier, Anne-Sophie; Baumgartner, Lukas


    Reconstructing the metamorphic history of polycyclic tectono-metamorphic mafic rocks that preserve potential relicts of high-pressure metamorphism is challenging because such rocks are commonly retrogressed and rare in supercrustal sequences. However, pressure-temperature-time (P-T-t) information is required to obtain the paleo-geothermal gradients and thus to define those units as markers for suture zones. The mafic rocks from Pouso Alegre in the Meridional Brasília Orogen (SW-Brazil) outcrop as rare lenses within Sil-Grt gneisses, Amp-Grt orthogneisses and Bt granites. They are heavily weathered. They have previously been defined as "retro-eclogites", based on the characteristic symplectite texture and some mineralogical observations. They have been intepreted to mark the suture zone between the Paranapanema and São Francisco cratons, although no quantitative estimates of the pressure is available to support this conclusion. In this study we investigated in detail these samples to refine their P-T-t history. As commonly observed in retrogressed eclogites, the studied mafic rock shows symplectite and corona textures overprinting the former paragenesis of Garnet (Grt) - Clinopyroxene (Cpx) 1 - Amphibole (Amp) 1 - Rutile (Rt). Phase equilibrium modelling shows that this assemblage is stable at 690°C and 13.5 kbar, in line with Zr-in-rutile thermometry (720 ±30° C). Local compositions of the symplectite domains were used to retrieve the jadeite content of Cpx1. This low-Jd cpx is in line with the predictions of the model and confirms a maximum pressure of 14 kbar. The symplectite formed from the reaction Cpx1+Qz+H2O→Cpx2+Amp+Pl+Qz taking place at conditions of 600-750°C and <7 kbar. Zircon and monazite U-Th-Pb geochronology was performed for the mafic and surrounding rocks. Zircon core dates from the mafic rock spread along concordia from ca. 1.7 to 1.0 Ga with a cluster at 1520±17 Ma, which is interpreted as the protolith crystallization age. Zircon rim

  16. Cretaceous high-pressure metamorphic belts of the Central Pontides (northern Turkey): pre-collisional Pacific-type accretionary continental growth of Laurasian Margin (United States)

    Aygul, Mesut; Okay, Aral I.; Oberhaensli, Roland; Sudo, Masafumi


    Cretaceous blueschist-facies metamorphic rocks crop out widely in the central part of the Pontides, an east-west trending mountain belt in northern Turkey. They comprise an accretionary wedge along to the southern Laurasian active continental margin and predate the opening of Black Sea basin. From North to South, the wedge consists of a low grade metaflysch unit with marble, Na-amphibole-bearing metabasite and serpentinite blocks. An extensional shear zone separates the accreted distal terrigenous sediments from HP/LT micaschists and metabasites of oceanic origin, known as Domuzdaǧ Complex. The shear zone reaches up to one km in thickness and consists of tectonic slices of serpentinite, metabasite, marble, phyllite and micaschist with top to the NW sense of shear. The Domuzdaǧ Complex predominantly consists of carbonaceous micaschist and metabasite with serpentinite, and minor metachert, marble and metagabbro. Metabasites consist mainly of epidote-blueschists sometimes with garnet. Fresh lawsonite-blueschists are found as blocks within the shear zone. Peak metamorphic assemblages in the micaschists are chloritoid-glaucophane and garnet-chloritoid-glaucophane-lawsonite in addition to phengite, paragonite, quartz, chlorite and rutile (P: 17 ± 1 Kbar, T: 390-450 °C). To the south, lithologies change slightly, with metabasite and thick, pale marble with few metachert and metapelitic horizons. The degree of metamorphism also changes. The metabasites range from high-pressure upper-greenschist facies with growth of sodic-amphibole to lower greenschist without any HP index mineral, suggesting a general decrease in pressure toward south within the prism. While Domuzdaǧ Complex represents deep-seated underplated oceanic sediments and basalts, the carbonate-rich southern parts can be interpreted as seamounts integrated into the accretionary prism. Ar/Ar dating on phengite separates both from terrigenous and oceanic metasediments give consistent plateau ages of 100 ± 2

  17. Monitoring environmental risk in fibrous minerals in New Caledonia: a comparison between different analytical methods. (United States)

    Petriglieri, Jasmine Rita; Laporte-Magoni, Christine; Salvioli-Mariani, Emma; Gunkel-Grillon, Peggy; Tribaudino, Mario; Mantovani, Luciana; Bersani, Danilo; Lottici, Pier Paolo; Tomatis, Maura


    The New Caledonia is covered by ultrabasic units for more than a third of its surface, and it is one of the largest world producers of nickel ore. Mining activity, focused on extraction from lateritic ore deposits formed by the alteration of ultramafic rocks, must deal with the natural occurrence of asbestos and fibrous minerals. Almost all outcrops of geological units in open mines contain serpentine and amphibole, also as asbestos varieties (Lahondère, 2007). Owing to humid tropical to sub-tropical conditions, weathering processes and supergene mineralization are one of the main responsible for fibrogenesis of asbestos minerals. The presence of fibrous minerals in mining and storage sites requires attention due to public health problems and for the safety of the operators. In this context, the evaluation of risk and health hazard to prevent the effects due to exposition is closely linked to the formation, alteration and release of fibers into the environment. It has been demonstrated that different fibrous minerals have different toxicity (Fubini & Otero-Arean, 1999; Fubini & Fenoglio, 2007). An analytical strategy to discriminate and characterize, with certainty, the different varieties of the asbestiform phases is required to the establishment of an environmental monitoring system. We have therefore analyzed by different methods a set of about fifty asbestos sampled for mapping environmental risk in fibrous minerals in New Caledonia. The samples contain serpentines (chrysotile, antigorite) and amphibole (tremolite), all fibrous and have been sorted by their different degree of alteration. Data obtained with the more traditional mineralogical and petrological analytical techniques - such as optical microscopy, X-ray diffraction, secondary electron microscopy (SEM-EDS), and transmission electron microscopy - have been completed by the employment of more specialized tools as phase contrast microscopy (PCM), Raman spectroscopy, and thermal analysis (DTA). Moreover

  18. Detachment Fault Initiation and Control by Partially Molten Zones in the Lower Ocean Crust (United States)

    Dick, H. J.; Natland, J. H.; MacLeod, C. J.; Robinson, P. T.


    beneath the rift valley, and as a consequence numerous inliers of the dike gabbro transition are found exposed across the gabbro massif. Olivine gabbros that underwent localized deformation and shearing were strongly affected both by crystallization of abundant oxides and new more sodic plagioclase and iron-rich pyroxene, and by local re-equilibration of existing calcic plagioclase and pyroxene with the invading iron-titanium rich melt. This was likely accompanied by dissolution of existing olivine and crystallization of secondary igneous clinopyroxene. Brown amphibole after clinopyroxene and plagioclase also formed, with some amphibole rimming relict olivine. The latter processes makes it hard to differentiate between ferrogabbros that crystallized directly from a melt, and those produced by hybridization of pre-existing olivine gabbro by migrating melts in the shear zone. Dredge samples collected at numerous localities at oceanic transforms along the SW Indian, American-Antarctic, and Mid-Atlantic Ridge with similar fabrics show that the relationship between oxide gabbros and deformation is widely associated with the exposure of plutonic rocks at oceanic core complexes. Atlantis Bank therefore provides the general case for the formation of the numerous large gabbro massifs exposed on the ocean floor at all slow and ultraslow spreading ridges.

  19. 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

  20. 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

  1. 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

  2. Computation of thermodynamic equilibrium in systems under stress (United States)

    Vrijmoed, Johannes C.; Podladchikov, Yuri Y.


    Metamorphic reactions may be partly controlled by the local stress distribution as suggested by observations of phase assemblages around garnet inclusions related to an amphibolite shear zone in granulite of the Bergen Arcs in Norway. A particular example presented in fig. 14 of Mukai et al. [1] is discussed here. A garnet crystal embedded in a plagioclase matrix is replaced on the left side by a high pressure intergrowth of kyanite and quartz and on the right side by chlorite-amphibole. This texture apparently represents disequilibrium. In this case, the minerals adapt to the low pressure ambient conditions only where fluids were present. Alternatively, here we compute that this particular low pressure and high pressure assemblage around a stressed rigid inclusion such as garnet can coexist in equilibrium. To do the computations we developed the Thermolab software package. The core of the software package consists of Matlab functions that generate Gibbs energy of minerals and melts from the Holland and Powell database [2] and aqueous species from the SUPCRT92 database [3]. Most up to date solid solutions are included in a general formulation. The user provides a Matlab script to do the desired calculations using the core functions. Gibbs energy of all minerals, solutions and species are benchmarked versus THERMOCALC, PerpleX [4] and SUPCRT92 and are reproduced within round off computer error. Multi-component phase diagrams have been calculated using Gibbs minimization to benchmark with THERMOCALC and Perple_X. The Matlab script to compute equilibrium in a stressed system needs only two modifications of the standard phase diagram script. Firstly, Gibbs energy of phases considered in the calculation is generated for multiple values of thermodynamic pressure. Secondly, for the Gibbs minimization the proportion of the system at each particular thermodynamic pressure needs to be constrained. The user decides which part of the stress tensor is input as thermodynamic

  3. 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

  4. Structure, petrology and U-Pb zircon age of Mesoproterozoic nepheline syenites from the Rengali Province, eastern India: Implications for their petrogenesis and geodynamic evolution (United States)

    Sheikh, Janisar M.; Champati, Anil K.; Patel, Suresh C.; Prabhakar, Naraga; Gerdes, Axel


    Three Mesoproterozoic nepheline syenite intrusions, namely Chhatabar, Lodhajhari and Baradangua intrusions, have been concordantly emplaced within a polydeformed and amphibolite facies metamorphosed sedimentary sequence (quartzites and mica schists) in the Rengali Province, eastern India. The metasedimentary sequence and the nepheline syenite intrusions both record three phases of folding (F1, F2 and F3). The penetrative fabric in quartzites is a schistosity (S1SS), while that in mica schists is a crenulation cleavage (S2SS), which has transposed to S1SS. The nepheline syenite intrusions exhibit magmatic to solid state deformation structures and microstructures. Magmatic layering in the rocks is commonly transposed by a prominent schistosity (S1NN). Fold geometries and deformation fabrics of the metasedimentary sequence and the nepheline syenites indicate that the latter were emplaced syntectonically during F1 folding of the metasedimentary sequence. The dominant rock type in the intrusions is nepheline syenite, while nepheline monzosyenite and nepheline monzodiorite occur in subordinate amounts in the form of centimeter to metre scale layers. Essential felsic minerals in the rocks are microcline (Or88-92Ab8-12) and nepheline, while sodic plagioclase (Ab88-96An4-12Or0.3-1.4) is additionally present in nepheline monzosyenite and nepheline monzodiorite. End member compositions of nephelines (Ne77-80Ks17-20Qtz1.6-3.6An0.5-2.6) fall below the 500oC isotherm in the nepheline-kalsilite-quartz projection from anorthite which indicates low temperature re-equilibration of the mineral after magmatic crystallization. Common mafic minerals in the rocks include biotite and amphibole, the latter being taramite in nepheline syenite, and hastingsite in nepheline monzosyenite and nepheline monzodiorite. Melt-present deformation microstructures which indicate syntectonic emplacement of the intrusions include late magmatic grains of nearly pure albite (Ab98-99An0.8-1.5Or0.2-0.6) and

  5. 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.

  6. Evolution of the northern Albertine Rift reflected in the provenance of synrift sediments (Nkondo-Kaiso area, Uganda) (United States)

    Schneider, Sandra; Hornung, Jens; Hinderer, Matthias


    Rift sediments are important archives for the evolution of the East African Rift System. We present a source-to-sink study of the Nkondo-Kaiso area in the northern Albertine Rift from a ∼200 m thick late Miocene to early Pleistocene sediment succession. The multi-proxy provenance analysis includes framework petrography, heavy mineral studies and single grain studies of garnet and rutile. Mineral textures and provenance signatures indicate two major stages. Sediment of Stage 1 (late Miocene - late Pliocene; ∼6.5-2.6 Ma) is less mature with quartz contents of 58-81%, K-feldspar of 9-15%, plagioclase of 4-15%, and rock fragments of 1-9%. Heavy mineral spectra are dominated by epidote and amphibole with minor abundances of zircon, sillimanite and garnet. Garnet is almandine-rich and can be grouped according to grossular contents (10%). Rutile exhibits a wide range of Nb and Cr concentrations, most of them typical for a metapelitic origin. Zr-in-rutile formation temperatures range between ∼570 and 940 °C. Garnet and rutile geochemistry mainly correspond to amphibolite-to granulite-facies igneous and metasedimentary rocks, which exist in the Mesoarchean Karuma Group and the Neoarchean granitoid gneiss of the North Uganda Terrane. Both are part of the adjacent eastern rift flank of the Albertine Rift. A slight change of the heavy mineral composition at ∼4.5 Ma can be correlated with the onset of the synrift stage ∼0.5-1.0 Ma later than in the southern Albertine Rift. Sediment of Stage 2 (early Pleistocene ∼2.6-1.0 Ma) shows a higher quartz content of 82-93%, and lower contents of K-feldspar of 5-11%, plagioclase of 1-7%, and rock fragments of 1-2%. Stable heavy minerals (ZTR index: 19-63) and epidote dominate with minor amphibole and garnet. Rutile and garnet chemical compositions remain largely unchanged to Stage 1 pointing to the same primary source. Obviously, Pleistocene sediment was mainly recycled from sedimentary rocks of the Neoproterozoic Bunyoro

  7. Petrography and Geochemistry of the Zamora Batholith in the south of the sub-Andean zone (Ecuador) (United States)

    Villares, F. M.


    The Zamora Batholith is an intrusive complex that is located in the extreme south-east of Ecuador. It has dimensions of 200 x 50 km approximately. It is mainly located in the Zamora Chinchipe province from which it takes its name. This study consisted in the petrographic and geochemical characterization of the Zamora Batholith in the area covered by 1: 50,000 geological maps of Centro Shaime, Guayzimi, Paquisha, Los Encuentros and El Pangui. Fieldwork was done by the "Proyecto Mapeo Geológico escala 1:50.000 (zonas prospectivas mineras)" of the Instituto Nacional de Investigación Geológico, Minero, Metalúrgico of Ecuador. This research was performed with 59 thin sections and 10 whole - rock chemical analysis done in the C.I.C of the Granada University. The Zamora Batholith intrudes Triassic to Jurassic volcanic rocks. It is overlaid by sandstones of the Hollin Formation of the Upper Aptian age and shale and limestone from the Napo Formation. Post-cretaceous deposits of ash and lava flows of andesitic to rhyolitic compositions cover the batholith. The petrography of the Zamora Batholith ranges from tonalite to monzogranite with the same qualitative mineralogy. The rocks are composed by different proportions of plagioclase, amphibole, feldspar K, quartz, biotite, opaque, pyroxene and epidote, as accessory minerals has zircon, sphene and apatite. To the south of the Conguime and Guayzimi towns, the dominant petrography is medium to coarse grained amphibole granodiorite with tonalitic and monzogranitic subordinates. To the north monzogranites are dominant rocks and subordinate granodiorites. To the East of Santa Elena the sienogranites are associated with El Hito porphyritic granite that intrudes to Zamora Batholith. Frequently the batholith has propylitic alteration; which produces a primary association of chlorite, epidote, calcite and pyrite. The granitoids have dioritic to granitic compositions (60.09 to 73.6 wt.% SiO2) and are I - type, medium to high-K calc

  8. Lithospheric convective removal related post-collisional middle Eocene magmatism along the Izmir-Ankara-Erzincan suture zone (NE Turkey). (United States)

    Göçmengil, Gönenç; Karacık, Zekiye; Genç, Ş. Can


    Obliteration of the Mesozoic Neo-Tethyan Ocean and succeeding collision of the micro plates along the northern part of Turkey lead the development of the İzmir-Ankara-Erzincan suture zone (IAESZ). The suturing and collision stages terminate with the amalgamation of the three different crustal blocks (Pontides, Central Anatolian Crystalline Complex and Anatolide-Tauride Block) in the Paleocene-Early Eocene period. After the collisional stage; a new phase of extension and magmatism concomitantly developed at the both sides and as well as along the IAESZ during the Middle Eocene period. However, the origin, mechanism and driving force of the post-collisional magmatism is still enigmatic. To understand and better constrain the syn-to post collisional evolutionary stages, we have carried out volcano-stratigraphy and geochemistry based study on the middle Eocene magmatic associations along a transect ( 100 km) from Pontides to the Central Anatolian Crystalline Complex (CACC) at the NE part of the Turkey. Middle Eocene magmatic activity in the region has been represented by calc-alkaline, alkaline, shoshonitic volcanic and granitic rocks together with scarce gabbroic intrusions. We particularly focused on middle Eocene volcano-sedimentary successions (MEVSS) to constrain the tectono-magmatic evolution of the abovementioned transect. The volcano-sedimentary succsessions are coevally developed and cover the crustal blocks (Pontides and CACC) and the IAESZ with a region wide unconformity. We have differentiated three lava series (V1-V2-V3) and their sub-groups (V1a-V1b; V2a-V2b) in MEVSS. Generally, all lava series have middle-K to shoshonitic composition with distinct subduction characteristics. V1 series is marked by presence of hydrous phenocrysts such as amphibole+biotite. V1a sub-group constitute the first volcanic product and characterized by the high Mg# (42-69); alkaline basaltic andesite, and hawaiites. V1b sub-group is represented by calc-alkaline, low Mg# (24

  9. Behaviour of fluid mobile elements during subduction and exhumation of abyssal peridotites: Example of serpentinites from Cuba and Dominican Republic (United States)

    Deschamps, F.; Guillot, S.; Godard, M.; Chauvel, C.; Andreani, M.


    (Himalaya, Deschamps et al., in prep.). Other fluid mobile elements such As (up to 6.85 ppm), Sb (up to 0.84 ppm), Li (up to 2 ppm) or U (up to 0.62 ppm) present strong enrichment in serpentine from both groups (0.1 up to 50 times primitive mantle values). The occurrence of amphibole having REE signature close to oceanic amphiboles, in cumulates, are in favour of an hydration event, leading to the observed strong mobile element enrichment, at the ridge. Compositions of the oceanic derived samples - especially in fluid mobile elements - are relatively close to the abyssal peridotites from MARK Zone (Andreani et al., 2008), without evidence of mobility for trace element during prograde and retrograde metamorphism. It confirms that the observed enrichment result from sea-water/peridotites interactions at the ridge. Also it suggests that mobile element stored into serpentine minerals become immobile during subduction processes. Major consequence of this observation is that serpentine minerals (chrysotile and lizardite) are a good sink for mobile element (As, Sb and B) into subduction zones, until their dehydration.

  10. The crustal magma storage system of Volcán Quizapu, Chile, and the effects of magma mixing on magma diversity (United States)

    Bergantz, George W.; Cooper, Kari M.; Hildreth, Edward; Ruprecht, Phillipp


    Crystal zoning as well as temperature and pressure estimates from phenocryst phase equilibria are used to constrain the architecture of the intermediate-sized magmatic system (some tens of km3) of Volcán Quizapu, Chile, and to document the textural and compositional effects of magma mixing. In contrast to most arc magma systems, where multiple episodes of open-system behavior obscure the evidence of major magma chamber events (e.g. melt extraction, magma mixing), the Quizapu magma system shows limited petrographic complexity in two large historical eruptions (1846–1847 and 1932) that have contrasting eruptive styles. Quizapu magmas and peripheral mafic magmas exhibit a simple binary mixing relationship. At the mafic end, basaltic andesite to andesite recharge magmas complement the record from peripheral cones and show the same limited range of compositions. The silicic end-member composition is almost identical in both eruptions of Quizapu. The effusive 1846–1847 eruption records significant mixing between the mafic and silicic end-members, resulting in hybridized andesites and mingled dacites. These two compositionally simple eruptions at Volcán Quizapu present a rare opportunity to isolate particular aspects of magma evolution—formation of homogeneous dacite magma and late-stage magma mixing—from other magma chamber processes. Crystal zoning, trace element compositions, and crystal-size distributions provide evidence for spatial separation of the mafic and silicic magmas. Dacite-derived plagioclase phenocrysts (i.e. An25–40) show a narrow range in composition and limited zonation, suggesting growth from a compositionally restricted melt. Dacite-derived amphibole phenocrysts show similar restricted compositions and furthermore constrain, together with more mafic amphibole phenocrysts, the architecture of the magmatic system at Volcán Quizapu to be compositionally and thermally zoned, in which an andesitic mush is overlain by a homogeneous dacitic

  11. A common Pan-African Lithospheric Mantle (PALM) source for HIMU-like Pb-isotope signatures in circum-Mediterranean magmas (United States)

    Young, H. P.; Wang, Z.; Brandon, M. T.


    Isotopic compositions of widely distributed basaltic rocks of Europe and North Africa are clustered around a point that is displaced from modern MORB in 208Pb/204Pb vs. 206Pb/204Pb, pointing to the 'HIMU' component proposed by Zindler and Hart (1986). This observation was originally highlighted in an abstract by Cebria and Wilson (1995), who suggested that a reservoir of unknown origin exists in the convecting upper mantle of the Mediterranean and coin it the 'European asthenospheric reservoir' or EAR in order to distinguish it from the apparent influence of an additional 'lithospheric' component having a Sr-Nd isotope composition similar to continental crust that is observed in some, but not all, Cenozoic igneous rocks. While this study and most authors agree that the 'lithospheric' component in the model of Cebria and Wilson (1995) is crustal material associated with Cenozoic subduction, explanations for the origin of the HIMU-like EAR reservoir, however, are diverse, ranging from deep plumes to recently subducted slabs. These explanations are problematic. For example, neither plumes nor recent subduction are spatially broad enough to explain all of the EAR occurrences. Alternatively, we argue that both components (lithospheric and EAR) observed by Cebria and Wilson are lithospheric in origin. We propose that the origin of the HIMU-like Pb component is metasomatized sub-continental lithospheric mantle (SCLM). Comparison with synthetic evolution models of a veined mantle show the HIMU-like composition of European Cenozoic igneous rocks can be generated after ~500 Ma (Pilet et al., 2011). Major and trace element compositions of the European alkalic-basalts are similar to experimental melts of amphibole-pyroxenite veins in peridotite (a common feature of the SCLM) (Médard et al., 2006). A likely candidate for a veined 500 Ma SCLM in this region is the 'Pan-African' age terrane that is currently widely distributed from England to the Sahara as well as on the

  12. Nature of the magma storage system beneath the Damavand volcano (N. Iran): An integrated study (United States)

    Eskandari, Amir; Amini, Sadraddin; De Rosa, Rosanna; Donato, Paola


    Damavand intraplate stratovolcano constructed upon a moderately thick crust (58-67 km) over the last 2 Ma. The erupted products are dominantly trachyandesite-trachyte (TT) lavas and pyroclasts, with minor mafic magmas including tephrite-basanite-trachybasalt and alkali olivine basalts emplaced as cinder cones at the base of the stratovolcano. The TT products are characterized by a mineral assemblage of clinopyroxene (diopside-augite), orthopyroxene (clinoenstatite), feldspar (An2-58, Ab6-69, Or2-56), high Ti phlogopite, F-apatite, Fesbnd Ti oxides, and minor amounts of olivine (Fo73-80), amphibole and zircon, whereas olivine (Fo78-88), high Mg# (80-89) diopside, feldspar, apatite and Fesbnd Ti oxide occur in the mafic magmas. The presence of hydrous and anhydrous minerals, normal zonings, mafic cumulates, and the composition of magmatic inclusions in the TT products suggest evolutionary processes in polybaric conditions. In the same way, disequilibrium textures - including orthopyroxene mantled with clinopyroxene, reaction rim of phlogopite and amphibole, the coexistence of olivine and orthopyroxene, reverse, oscillatory and complex zonings of pyroxene and feldspar crystals - suggest magmatic evolutions in open systems with a varying temperature, oxygen fugacity, water as well as pressure and, to a lesser extent, melt chemistry. Mineral assemblages are used to model the physicochemical conditions and assess default parameters for the thermodynamic simulation of crystallization using MELTS software to track the P-T-H2O-ƒO2 evolution of the magma plumbing system. Thermobarometry and MELTS models estimated the initial nucleation depth at 16-17 kb (56-60 km) for olivine (Fo89) and high Al diopside crystals occurring in the mafic primary magma; it then stopped and underwent fractionation between 8 and 10 kb (28-35 km), corresponding with Moho depth, and continued to differentiate in the lower crust, in agreement with the geophysical models. The mafic rocks were formed

  13. An example of post-collisional mafic magmatism: the gabbro-anorthosite layered complex from the Tin Zebane area (western Hoggar, Algeria) (United States)

    Aı̈t-Djafer, Saı̈da; Ouzegane, Khadidja; Paul-Liégeois, Jean; Kienast, Jean Robert


    The Tin Zebane gabbro-anorthosite layered mafic intrusion represented by plagioclase-rich cumulates forms a set of small lenticular to round-shaped mainly undeformed bodies intruding the Pan-African high-pressure metamorphic rocks from western Hoggar (Tuareg shield, southwest Algeria). The coarse-grained anorthosites are mainly made of slightly zoned bytownite (An 86-74) with the higher anorthite content at the cores. Anorthosites are interlayered with leucogabbros and gabbros that show preserved magmatic structures and with olivine gabbros characterised by coronitic textures. The primary assemblage in gabbros includes plagioclase (An 93-70), olivine (Fo 77-70), zoned clinopyroxene (En 43-48Fs 05-13Wo 41-49 with Al 2O 3 up to 4.3 wt.%) and rare orthopyroxene (En 73-78). Pyroxenes and olivine are commonly surrounded by Ca-amphibole. The olivine-plagioclase contact is usually marked by a fine orthopyroxene-Cr-spinel-amphibole symplectite. A magnesian pigeonite (En 70-75Fs 19-20Wo 6-10) is also involved in corona. The coronitic minerals have equilibrated with the primary mineral rims at P- T- aH2O conditions of 797 ± 42 °C for aH2O=0.5 and 808 ± 44 °C for aH2O=0.6 at 6.2 ± 1.4 kbar. The Tin Zebane gabbroic rocks are depleted in REE with a positive Eu anomaly, high Sr (>10 ∗ chondrite) and Al 2O 3 concentrations (17-33%) that support plagioclase accumulation with the extreme case represented by the anorthosites. The REE patterns can be modelised using plagioclase, clinopyroxene and orthopyroxene REE signature, without any role played by accessory minerals. High MgO content points to olivine as a major cumulate phase. Anorthositic gabbros Sr and Nd isotopic initial ratios are typical of a depleted mantle source (Sr i=0.70257-0.70278; ɛNd=+5.9 to +7.8). This isotopic signature is identical to that of the 10-km wide 592 Ma old dyke complex composed of alkaline to peralkaline granites and tholeiitic gabbros and one single bimodal complex can be inferred. The source

  14. Temporal Constraints on Continental Rifting and the Exhumation of Pliocene Eclogites, SE Papua New Guinea (United States)

    Waggoner, A. G.; Baldwin, S. L.; Webb, L. E.; Little, T. A.; Fitzgerald, P. G.


    The youngest known HP-UHP rocks on Earth have been exhumed in the footwalls of the metamorphic core complexes (MCCs) of Goodenough and Fergusson Islands within the active Woodlark rift of southeast Papua New Guinea. What can the felsic and intermediate gneisses found in the lower plate of these metamorphic core complexes tell us about the thermal evolution of these HP-UHP rocks? Also, how does their exhumation during rifting temporally relate with the sea-floor spreading history of the Woodlark Basin? Ion-microprobe U-Pb zircon, 40Ar/39Ar amphibole, phengite, biotite, and K-feldspar analyses were performed on gneisses collected from the ductile shear zones of the MCCs of Goodenough and Fergusson Islands. The application of a broad range of thermochronometers permits the detailed determination of the thermal histories of these rocks from eclogite-facies conditions to their exhumation to middle and upper crustal levels. U-Pb zircon data from these lower plate gneisses indicate a period of zircon growth concordant with the timing of eclogite facies metamorphism as previously determined in mafic eclogites. This younger population of zircon occurs as rims on cores; the cores yield ages that range in age from Paleocene to Permian. These older ages indicate an inherited component likely reflecting the nature of the protolith of these gneisses. However, the abundance and degree of this inherited component is highly variable from sample to sample. New 40Ar/39Ar data from samples collected from the northern range-bounding Wakonai shear zone and the core of Goodenough Island MCC indicate rapid cooling of these rocks as recorded by Ar closure in amphibole, phengite, biotite, and K-feldspar (~500 to ~150 °C) at ~2-1.5 Ma. Samples from along the northern range front of the Goodenough MCC indicate a southeastward younging trend that parallels the active Wakonai normal fault from the northwest end of the island to the center of the island. However, no age gradient is apparent

  15. Structure and LA-ICP-MS zircon U-Pb dating of syntectonic plutons emplaced in the Pan-African Banyo-Tcholliré shear zone (central north Cameroon) (United States)

    Nomo, Emmanuel Negue; Tchameni, Rigobert; Vanderhaeghe, Olivier; Sun, Fenguye; Barbey, Pierre; Tekoum, Léontine; Tchunte, Periclex Martial Fosso; Eglinger, Aurélien; Fouotsa, Nicaise Alliance Saha


    The Tcholliré massif, in central north Cameroon, consists of elongated granite plutons that crop out along the Pan-African Tcholliré-Banyo shear zone (TBSZ), a potential suture zone within the Central Africa Orogenic Belt. New structural and geochronological data on these granites constrain the tectonic regime and timing of the TBSZ. The plutons consist of syntectonic granites and granodiorite containing dioritic mafic enclaves. They show an S2 sub-vertical foliation, that trends NE-SW to ENE-WSW. The related L2 lineation is subhorizontal to shallowly plunging to the SW or NE. Kinematic indicators such as asymmetric folds, sigmoidal-shape boudins, shear bands, imbricated feldspar phenocrysts along antithetic fractures point to a sinistral sense of shear. Microstructural analysis shows that structures are acquired from the submagmatic to the low temperature solid state suggesting progressive deformation of the magma during its emplacement, crystallization and cooling. U-Pb zircon dating on this massif yields emplacement ages of 719 ± 12 Ma for the biotite-amphibole granite and muscovite granite, 652.2 ± 5.4 Ma for the biotite-granite and 632 ± 13 Ma for the leucogranite. These geochronological data show in addition, Palaeoproterozoic inherited ages of 1631 ± 30 Ma on the leucogranites of this massif, and point to a Palaeoproterozoic contribution in their genesis. The range of ages (ca. 87 Ma) points to the timing of syntectonic emplacement of felsic magmas coeval with sinistral transpression along the TBSZ during the Pan-African orogeny. These results show that the TBSZ has recorded prolonged deformation associated with crustal magmatism between the Palaeoproterozoic Adamawa-Yadé domain to the southeast and the Sinassi-Mayo Kebbi Neoproterozoic magmatic arc to the Northwest.

  16. Slab-derived melt involvement in petrogenesis of the high-Nb basalts and magnesian andesites-dacites from NE Iran (United States)

    Ahmadi, Parham; Ghorbani, Mohammad Reza; Coltorti, Massimo; Kuritani, Takeshi; Cai, Yue; Fioretti, Anna Maria; Braschi, Eleonora; Giacomoni, Pier Paolo; Babazadeh, Shahrouz; Conticelli, Sandro


    Tertiary volcanic rocks in NW Firoozeh region, also known as Meshkan triangular structural unit, represent an episode of Tertiary post-collisional magmatism in NE Iran. The volcanic suite is made of Magnesian andesites to dacites associated with some high-Nb basalts. Despite a rather restricted range of emplacement age, variable from 24.1 to 21.7 Ma obtained on the basis of 40Ar-39Ar dating. Major and trace element data show that Firoozeh volcanic rocks were derived from two distinct parental magmas. The dominant high magnesian magmatic series constitutes a wide spectrum of volcanic rocks from andesite to dacite. The magnesian andesites-dacites are subalkaline and characterized by rather high MgO, Ni, Cr and Sr/Y ratio. High Sr/Y ratio of the magnesian andesites-dacites as well as their Sr-Nd isotopic composition support the notion that the magnesian andesites were originated by interaction of slab derived melts with overlying mantle wedge. Fractional crystallization of an amphibole and plagioclase mineral assemblage is found responsible for evolutionary path form the magnesian andesite to more evolved rocks. In contrast to the sabalkaline magnesian andesites- dacites, the high Nb basalts are sodic alkaline rocks and show silica-undersaturated degree. The high-Nb basalts are enriched in Nb, and a wide range of incompatible trace elements that include LILE, LREE. Almost identical Sr-Nd isotopic composition of the magnesian andesites-dacites and high-Nb basalts imply that the two magmatic series has probably shared a common mantle source. Generation of parental magmas of the two magmatic series are attributed to the asthenospheric upwelling and subsequent partial melting of mantle metasomatized by slab-derived melts. Key words: slab melt, High-Nb basalt, 40Ar/39Ar, High-Mg andesite

  17. Progressive enrichment of island arc mantle by melt-peridotite interaction inferred from Kamchatka xenoliths (United States)

    Kepezhinskas, Pavel; Defant, Marc J.; Drummond, Mark S.


    The Pliocene (7 Ma) Nb-enriched arc basalts of the Valovayam Volcanic Field (VVF) in the northern segment of Kamchatka arc (Russia) host abundant xenoliths of spinel peridotites and pyroxenites. Textural and microstructural evidence for the high-temperature, multistage creep-related deformations in spinel peridotites supports a sub-arc mantle derivation. Pyroxenites show re-equilibrated mosaic textures, indicating recrystallization during cooling under the ambient thermal conditions. Three textural groups of clinopyroxenes exhibit progressive enrichment in Na, Al, Sr, La, and Ce accompanied by increase in Sr/Y, La/Yb, and Zr/Sm. Trace elements in various mineral phases and from felsic veins obtained through ion microprobe analysis suggest that the xenoliths have interacted with a siliceous (dacitic) melt completely unlike the host basalt. The suite of xenoliths grade from examples that display little evidence of metasomatic reaction to those containing an assemblage of minerals that have been reproduced experimentally from the reaction of a felsic melt with ultramafic rock, e.g., pargasitic amphibole, albite-rich plagioclase, Al-rich augite, and garnet. The dacitic veins within spinel lherzolite display a strong enrichment in Sr and depletion in Y and the heavy rare earth elements (e.g., Yb). The dacites are comparable to adakites (melts derived from subducted metabasalt), and not typical arc melts. We believe that these potential slab melts were introduced into the mantle beneath this portion of Kamchatka subsequent to partial melting of a relatively young (and hot) subducted crust. Island arc metasomatism by peridotite-slab melt interaction is an important mantle hybridization process responsible for arc-related alkaline magma generation from a veined sub-arc mantle.

  18. Pleural mesothelioma in New Caledonia: associations with environmental risk factors. (United States)

    Baumann, Francine; Maurizot, Pierre; Mangeas, Morgan; Ambrosi, Jean-Paul; Douwes, Jeroen; Robineau, Bernard


    High incidences of malignant mesothelioma (MM) have been observed in New Caledonia. Previous work has shown an association between MM and soil containing serpentinite. We studied the spatial and temporal variation of MM and its association with environmental factors. We investigated the 109 MM cases recorded in the Cancer Registry of New Caledonia between 1984 and 2008 and performed spatial, temporal, and space-time cluster analyses. We conducted an ecological analysis involving 100 tribes over a large area including those with the highest incidence rates. Associations with environmental factors were assessed using logistic and Poisson regression analyses. The highest incidence was observed in the Houaïlou area with a world age-standardized rate of 128.7 per 100,000 person-years [95% confidence interval (CI), 70.41-137.84]. A significant spatial cluster grouped 18 tribes (31 observed cases vs. 8 expected cases; p = 0.001), but no significant temporal clusters were identified. The ecological analyses identified serpentinite on roads as the greatest environmental risk factor (odds ratio = 495.0; 95% CI, 46.2-4679.7; multivariate incidence rate ratio = 13.0; 95% CI, 10.2-16.6). The risk increased with serpentinite surface, proximity to serpentinite quarries and distance to the peridotite massif. The association with serpentines was stronger than with amphiboles. Living on a slope and close to dense vegetation appeared protective. The use of whitewash, previously suggested to be a risk factor, was not associated with MM incidence. Presence of serpentinite on roads is a major environmental risk factor for mesothelioma in New Caledonia.

  19. Chloritoid and barroisite-bearing pelitic schists from the eclogite unit in the Besshi district, Sanbagawa metamorphic belt (United States)

    Zaw Win Ko; Enami, M.; Aoya, M.


    The Sanbagawa metamorphic rocks in the Besshi district, central Shikoku, are grouped into eclogite and noneclogite units. Chloritoid and barroisite-bearing pelitic schists occur as interlayers within basic schist in an eclogite unit of the Seba area in the Sanbagawa metamorphic belt, central Shikoku, Japan. Major matrix phases of the schists are garnet, chlorite, barroisite, paragonite, phengite, and quartz. Eclogite facies phases including chloritoid and talc are preserved only as inclusions in garnet. P- T conditions for the eclogite facies stage estimated using equilibria among chloritoid, barroisite, chlorite, interlayered chlorite-talc, paragonite, and garnet are 1.8 GPa/520-550 °C. Zonal structures of garnet and matrix amphibole show discontinuous growth of minerals between their core and mantle parts, implying the following metamorphic stages: prograde eclogite facies stage→hydration reaction stage→prograde epidote-amphibolite stage. This metamorphic history suggests that the Seba eclogite lithologies were (1) juxtaposed with subducting noneclogite lithologies during exhumation and then (2) progressively recrystallized under the epidote-amphibolite facies together with the surrounding noneclogite lithologies. The pelitic schists in the Seba eclogite unit contain paragonite of two generations: prograde phase of the eclogite facies included in garnet and matrix phase produced by local reequilibration of sodic pyroxene-bearing eclogite facies assemblages during exhumation. Paragonite is absent in the common Sanbagawa basic and pelitic schists, and is, however, reported from restricted schists from several localities near the proposed eclogite unit in the Besshi district. These paragonite-bearing schists could be lower-pressure equivalents of the former eclogite facies rocks and are also members of the eclogite unit. This idea implies that the eclogite unit is more widely distributed in the Besshi district than previously thought.

  20. Defining asbestos: differences between the built and natural environments. (United States)

    Gunter, Mickey E


    Asbestos - while most think they know what this material is, few understand the current issues surrounding it. Few would also realize that asbestos is the form of a mineral, and even fewer would know that there are different types of asbestos, that not only had different industrial applications, but pose differing health risks when inhaled. Asbestos was in wide-spread use mid-last century in many consumer products, and no doubt saved thousands of lives, but by the latter part of last century concerns over its health risk caused its use to wane, to the point it was removed from many buildings. So in many ways the asbestos story was coming to an end in the 1990s, but two events in the USA - the vermiculite ore produced from Libby, Montana which contained amphibole asbestos and was used in a million homes in the USA as attic insulation and the concern for exposure to asbestos occurring in its natural setting in El Dorado Hills, California led to an increased concern of the potential for low-level environmental exposure to asbestos to the general public. The current dilemma we find ourselves in, especially in the USA, deals with the relationships between our knowledge of handling asbestos and an understanding of its risk potential in the built environment versus the natural environment. And one perfect metaphor for this is the term used by many non-geologists to differentiate asbestos in the built vs natural environment - 'naturally occurring asbestos'. Clearly a misstatement, but only one of many we must deal with as we struggle to understand the risk to humans of natural occurrences of asbestos. This paper will try and address some of these issues centering around those occurring in the USA.

  1. Origin of carbonatites of the Matcha alkaline pluton from Turkestan-Alai ridge, Kyrgyz Southern Tien Shan (United States)

    Vrublevskii, V. V.


    Postorogenic alkaline intrusions in the Turkestan-Alai segment of the Southern Tien Shan coexist with dikes and veins of carbonatites dated at ˜220 Ma. They are primarily composed of calcite and dolomite (60-85 %), as well as sodic amphibole, phlogopite, clinopyroxene, microcline, albite, apatite, and magnetite, with accessory niobate, ilmenite, Nb-rutile, titanite, zircon, baddeleyite, monazite-(Ce), barite, and sulfides. The rocks share mineralogical and geochemical similarity with carbonatites that originated by liquid immiscibility at high temperatures above 500°C. Silicate and salt-carbonate melts are derived from sources with mainly negative bulk ɛND(t) ˜ from -11 to 0 and high initial 87Sr/86Sr ratios (˜ 0.7061-0.7095) which may be due to mixing of PREMA and EM-type mantle material. Pb isotopic ratios in accessory pyrrhotite (206Pb/204Pb = 18.38; 207Pb/204Pb = 15.64; 208Pb/204Pb = 38.41) exhibit an EM 2 trend. The intrusions bear signatures of significant crustal contamination as a result of magma genesis by syntexis and hybridism. Concordant isotope composition changes of δ 13C (-6.5 to -1.9 ‰), δ 18O (9.2-23 %„), δD (-58 to -41 %„), and δ 34S (12.6-12.8 ‰) in minerals and rocks indicate inputs of crustal material at the stage of melting and effect of hot fluids released during dehydration of metamorphosed oceanic basalts or sediments. The observed HFSE patterns of the oldest alkaline gabbro may be due to interaction of the primary mafic magma with IAB-type material. The isotope similarity of alkaline rocks with spatially proximal basalts of the Tarim large igneous province does not contradict the evolution of the Turkestan-Alai Triassic magmatism as the «last echo» of the Tarim mantle plume.

  2. Silicate Veining Above an Ascending Mantle Plume - Evidence from New Ethiopian Xenolith Localities (United States)

    Rooney, T. O.; Furman, T.; Ayalew, D.; Yirgu, G.


    Quaternary basaltic eruptions in the Debre Zeyit (Bishoftu) and Butajira regions of the Main Ethiopian Rift host Al-augite, norite and rare lherzolite xenoliths, xenocrysts and megacrysts. These explosive basaltic eruptions are located 20 km to the west of the main rift axis and are characterized by cinder cones and maars. The host basalt was generated as a small degree partial melt of fertile peridotite between 15 and 25 kb and host abundant Al-augite (Type II) xenoliths derived from pressures up to 10 kb. The central Main Ethiopian Rift lies in a transitional zone between the continental rifting of East Africa and the sea floor spreading associated with the Red Sea. Lithospheric and sub-lithospheric processes that occur during the transition from continental to oceanic magmatism may be investigated using these xenolith-bearing basalts. Neither carbonatitic nor hydrous (amphibole + phlogopite) metasomatism is evident in either the xenoliths or host basalts, suggesting that infiltration of silicate melts that produced Al-augite veining dominates the regional lower crust and lithospheric mantle. These veins are significantly hotter (200 - 300 ° C) than the lherzolite wall rock they intrude suggesting the thermal influence of the Afar plume. Recent geophysical tomography indicates that this veining is pervasive and segmented, supporting the association of these Al-augite veins with the formation of a proto-ridge axis. Al-augite xenoliths and megacrysts have been observed in other continental rift settings such as Durango (Luhr, 2001) and Lake Baikal (Litasov, 2000), indicating Al-augite silicate melt metasomatism is a fundamental process associated with continental rift development.

  3. Geology and geochronology of Cardoso Island, in the southeastern coast of Sao Paulo State; Geologia e geocronologia da Ilha de Cardoso, sudeste do Estado de Sao Paulo

    Energy Technology Data Exchange (ETDEWEB)

    Weber, Werner


    This aim of work is the geological and geochronological study of rocks cropping out on Cardoso Island, on the southeastern coast of Sao Paulo States, close to be boundary with Parana State. The Island with an area of about 151 km{sup 2} is a protected area administered by the Forest Institute of Environment Secretariat of the State of Sao Paulo. It is mountanious, with a peak at 814 m, and is covered by dense Mata Atlantica vegetation. The terrains which compose the island are mainly an igneous complex with light grey leucocratic, inequigranular, medium - to coarse-grained syenites. The predominant Tres Irmaos Syenite (STI), composed of pyroxene, hornblende, and perthitic to mesoperthitic microcline, has a magmatic flow structures, and is cut by the Cambriu alkali-feldspar Granites (GC), which is pinkish grey, leucocratic and medium-grained. Geochemical analysis of STI and GC demonstrate their meta luminous alkaline nature and late-orogenic to an orogenic character. The geochronological results suggest that the bodies were formed between 620 and 570 My according to the U-Pb method in zircons, with cooling between 597 and 531 My (K-Ar in amphiboles). Whole rock Sm-Nd analysis yield T{sub DM} ages in the Meso and Paleoproterozoic (1.200 - 2.200 My). belt of low grade meta sedimentary rocks occurs in the northern part of the island. Quartz schist, quartz-mica schist and mica-quartz schist, often containing andaluzite and cordierite, predominate. The geochemical and geochronological data suggest that the sources of the metasediments were andesites of continental arc whose protolities separated from the mantle during the Paleoproterozoic, between 1.800 and 2.200 My. These metasediments probably continue on the continent in the Taquari region and extend southwards in narrow strips between the granitoids of the Paranagua Domain. Although quaternary deposits are expressive, they were not studied in details since they were not the objectives of this study. (author)

  4. Chrysotile effects on human lung cell carcinoma in culture: 3-D reconstruction and DNA quantification by image analysis

    International Nuclear Information System (INIS)

    Cortez, Beatriz A; Machado-Santelli, Glaucia M


    Chrysotile is considered less harmful to human health than other types of asbestos fibers. Its clearance from the lung is faster and, in comparison to amphibole forms of asbestos, chrysotile asbestos fail to accumulate in the lung tissue due to a mechanism involving fibers fragmentation in short pieces. Short exposure to chrysotile has not been associated with any histopathological alteration of lung tissue. The present work focuses on the association of small chrysotile fibers with interphasic and mitotic human lung cancer cells in culture, using for analyses confocal laser scanning microscopy and 3D reconstructions. The main goal was to perform the analysis of abnormalities in mitosis of fibers-containing cells as well as to quantify nuclear DNA content of treated cells during their recovery in fiber-free culture medium. HK2 cells treated with chrysotile for 48 h and recovered in additional periods of 24, 48 and 72 h in normal medium showed increased frequency of multinucleated and apoptotic cells. DNA ploidy of the cells submitted to the same chrysotile treatment schedules showed enhanced aneuploidy values. The results were consistent with the high frequency of multipolar spindles observed and with the presence of fibers in the intercellular bridge during cytokinesis. The present data show that 48 h chrysotile exposure can cause centrosome amplification, apoptosis and aneuploid cell formation even when long periods of recovery were provided. Internalized fibers seem to interact with the chromatin during mitosis, and they could also interfere in cytokinesis, leading to cytokinesis failure which forms aneuploid or multinucleated cells with centrosome amplification

  5. Uruguay geology contributions no. 4

    International Nuclear Information System (INIS)

    Preciozzi, F.


    Sedimentary facies: the metasiltites and mela sandstones develop granoblastic textures. The present lepidoblastic textures in flexured bands of seri cite and/or chlorite, a fine qranoblastic matrix made by quartz-feldespaths. The carbonates develop mosaic textures with big crystals of calcites and dolomite, generally elongated following metamorphic foliation (seri cite/chlorite). The quartzites develop qranoblastic textures, with few minerals. Volcanics facies: the basic volcanics presents doleritic intersect al textural, that exist saussuritized plagioclase and albitic diabasa with diopside-augite beaches. Usually the pyroxenes develop poiquilitic textural. Present amphiboles of the acti note series and frequently sphene. Others basic rocks are microlitio porfiric, in intersect al or fluidal matrix, with albite microliters in epi dote-chlorite-acti note criploerislalline ground.The stability relationships of the diferents types of basic metavulcanites show low metamorphic facies, with temperatures under 530-550 grades C, being the most Irequenl association: albite+actinote+chlorite+epidote+opaques- opaques.The clastic faciest are integrated by monogenic breccia with elements of varied vulcanites and porfiric rnicrolitic texture. The matrix is made of line quartz and epidote aggregate. The basic volcanism present hyalo-porfiric textures with saussuritized plagiodase pheno crystals, and quartz in a micro lo criptocrystalline ground. Were also defined rocks with porfiric texture in a piromeritic ground as well as rocks with vacuolar microlitic texture.The clastic facies are made by breccias with sharp elements, with rare cement, integrated by pyroclastic products, The volcanics rocks present retrometamorphism of the phenocrystals and devitrification. The plagioclase are traslormated in fine aggregates of albite epidote. The regional metamorphism minerals are represented by the para genesis: quartz+albite+chlorite+epidote+(seri cite-actinole), subfacies quartz albite

  6. Study of Arabian Red Sea coastal soils as potential mineral dust sources

    KAUST Repository

    Prakash, P. Jish


    Both Moderate Resolution Imaging Spectroradiometer (MODIS) and Spinning Enhanced Visible and InfraRed Imager (SEVIRI) satellite observations suggest that the narrow heterogeneous Red Sea coastal region is a frequent source of airborne dust that, because of its proximity, directly affects the Red Sea and coastal urban centers. The potential of soils to be suspended as airborne mineral dust depends largely on soil texture, moisture content, and particle size distributions. Airborne dust inevitably carries the mineralogical and chemical signature of a parent soil. The existing soil databases are too coarse to resolve the small but important coastal region. The purpose of this study is to better characterize the mineralogical, chemical and physical properties of soils from the Red Sea Arabian coastal plane, which in turn will help to improve assessment of dust effect on the Red Sea and land environmental systems and urban centers. Thirteen surface soils from the hot-spot areas of wind-blown mineral dust along the Red Sea coastal plain were sampled for analysis. Analytical methods included Optical Microscopy, X-ray diffraction (XRD), Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES), Ion Chromatography (IC), Scanning Electron Microscopy (SEM), and Laser Particle Size Analysis (LPSA). We found that the Red Sea coastal soils contain major components of quartz and feldspar, as well as lesser but variable amounts of amphibole, pyroxene, carbonate, clays, and micas, with traces of gypsum, halite, chlorite, epidote and oxides. The wide range of minerals in the soil samples was ascribed to the variety of igneous and metamorphic provenance rocks of the Arabian Shield forming the escarpment to the east of the Red Sea coastal plain. The analysis revealed that the samples contain compounds of nitrogen, phosphorus and iron that are essential nutrients to marine life. The analytical results from this study will provide a valuable input into dust emission models used

  7. Magma shearing and friction in the volcanic conduit: A crystal constraint (United States)

    Wallace, P. A.; Kendrick, J. E.; Henton De Angelis, S.; Ashworth, J. D.; Coats, R.; Miwa, T.; Mariani, E.; Lavallée, Y.


    Magma shearing and friction processes in the shallow volcanic conduit are typical manifestations of strain localisation, which in turn can have an influential role on magma ascent dynamics. The thermal consequences of such events could drive the destabilisation of magma and thus dictate the style of activity at the surface. Shear heating and fault friction are prime candidates for the generation of significant quantities of heat. Here we use a combination of field and experimental evidence to investigate how crystals can act as sensitive recorders of both physical and chemical processes occurring in the shallow volcanic conduit. Spine extrusion during the closing of the 1991-95 eruption at Unzen volcano, Japan, provided the unique opportunity to investigate marginal shear zone formation, which preserves a relic of the deformation during magma ascent. Our results show that crystals can effectively act as a deformation marker during magma ascent through the viscous-brittle transition by accommodating strain in the form of crystal plasticity before fracturing (comminution). Electron backscatter diffraction (EBSD) reveals up to 40° lattice distortion of biotite phenocrysts in zones of high shear, with negligible plasticity further away. Plagioclase microlites display a systematic plastic response to an increase in shear intensity, as recorded by an increase in lattice distortion towards the spine margin of up to 9°. This localisation of strain within the shear zone is also accompanied by the destabilisation of hydrous mineral phases (i.e. amphibole), compaction of pores (23-13% Φ), glass devitrification and magnetic anomalies. The narrow zone of disequilibrium textures suggests the likely effect of a thermal input due to strain localisation being the contributing factor. These observations are complimented by high-temperature high-velocity rotary shear experiments which simulate the deformation evolution during shear. Hence, understanding these shallow volcanic

  8. Petrogenesis and origin of the Upper Jurassic-Lower Cretaceous magmatism in Central High Atlas (Morocco): Major, trace element and isotopic (Sr-Nd) constraints (United States)

    Essaifi, Abderrahim; Zayane, Rachid


    During an uplift phase, which lasted ca. 40 Ma, from the Late Jurassic (165 Ma) to the Early Cretaceous (125 Ma), transitional to moderately alkaline magmatic series were emplaced in the Central High Atlas. The corresponding magmatic products include basaltic lava flows erupted within wide synclines and intrusive complexes composed of layered mafic intrusions and monzonitic to syenitic dykes emplaced along narrow anticlinal ridges. The igneous rock sequence within the intrusive complexes is composed of troctolites, olivine-gabbros, oxide-gabbros, monzonites and syenites. The chemical compositions of the various intrusive rocks can be accounted for by crystal accumulation, fractional crystallization and post-magmatic remobilization. The evolution from the troctolites to the syenites was mainly controlled by a fractional crystallization process marked by early fractionation of olivine, plagioclase and clinopyroxene, followed by separation of biotite, amphibole, apatite, and Ti-magnetite. Hydrothermal activity associated with emplacement of the intrusions within the Jurassic limestones modified the elemental and the Sr isotopic composition of the hydrothermally altered rocks In particular the monzonitic to syenitic dykes underwent an alkali metasomatism marked by depletion in K and Rb and enrichment in Na and Sr. As a result, their Sr isotopic composition was shifted towards higher initial Sr isotopic ratios (0.7067-0.7075) with respect to the associated gabbros (0.7036-0.7046). On the contrary, the Nd isotopic compositions were preserved from isotope exchange with the limestones and vary in a similar range to those of the gabbros (+1.6 High Atlas, the Middle Atlas and the eastern High Atlas domains during a period of relative tectonic quiescence.

  9. The 12.4 ka Upper Apoyeque Tephra, Nicaragua: stratigraphy, dispersal, composition, magma reservoir conditions and trigger of the plinian eruption (United States)

    Wehrmann, Heidi; Freundt, Armin; Kutterolf, Steffen


    Upper Apoyeque Tephra (UAq) was formed by a rhyodacitic plinian eruption in west-central Nicaragua at 12.4 ka BP. The fallout tephra was dispersed from a progressively rising plinian eruption column that became exposed to different wind speeds and directions at different heights in the stratosphere, leading to an asymmetric tephra fan with different facies in the western and southern sector. Tephra dispersal data integrated with geochemical compositions of lava flows in the area facilitate delimitation of the source vent to the south of Chiltepe Peninsula. UAq, Lower Apoyeque Tephra, Apoyeque Ignimbrite, and two lava lithic clasts in San Isidro Tephra together form a differentiation trend distinct from that of the younger tephras and lavas at Chiltepe Volcanic Complex in a TiO2 versus K2O diagram, compositionally precluding a genetic relationship of UAq with the present-day Apoyeque stratovolcano. Apoyeque Volcano in its present shape did not exist at the time of the UAq eruption. The surface expression of the UAq vent is now obscured by younger eruption products and lake water. Pressure-temperature constraints based on mineral-melt equilibria and fluid inclusions in plagioclase indicate at least two magma storage levels. Clinopyroxenes crystallised in a deep crustal reservoir at ˜24 km depth as inferred from clinopyroxene-melt inclusion pairs. Chemical disequilibrium between clinopyroxenes and matrix glasses indicates rapid magma ascent to the shallower reservoir at ˜5.4 km depth, where magnesiohornblendes and plagioclase fractionated at a temperature of ˜830 °C. Water concentrations were ˜5.5 wt.% as derived from congruent results of amphibole and plagioclase-melt hygrometry. The eruption was triggered by injection of a hotter, more primitive melt into a water-supersaturated reservoir.

  10. Magmatic (silicates/saline/sulfur-rich/CO2) immiscibility and zirconium and rare-earth element enrichment from alkaline magma chamber margins : Evidence from Ponza Island, Pontine Archipelago, Italy (United States)

    Belkin, H.E.; de Vivo, B.; Lima, A.; Torok, K.


    Fluid inclusions were measured from a feldspathoid-bearing syenite xenolith entrained in trachyte from Ponza, one of the islands of the Pontine Archipelago, located in the Gulf of Gaeta, Italy. The feldspathoid-bearing syenite consists mainly of potassium feldspar, clinopyroxene, amphibole, biotite, titanite, manganoan magnetite, apatite with minor nosean, Na-rich feldspar, pyrrhotite, and rare cheralite. Baddeleyite and zirkelite occur associated with manganoan magnetite. Detailed electron-microprobe analysis reveals enrichments in REE, Y, Nb, U, Th as well as Cl and F in appropriate phases. Fluid inclusions observed in potassium feldspar are either silicate-melt or aqueous inclusions. The aqueous inclusions can be further classified as. (1) one-phase vapor, (2) two-phase (V + L) inclusions, vapor-rich inclusions with a small amount of CO2 in most cases; homogenization of the inclusions always occurred in the vapor phase between 359 and 424??C, salinities vary from 2.9 to 8.5 wt. % NaCl equivalent; and. (3) three-phase and multiphase inclusions (hypersaline/sulfur-rich aqueous inclusions sometimes with up to 8 or more solid phases). Daughter minerals dissolve on heating before vapor/liquid homogenization. Standardless quantitative scanning electron microscope X-ray fluorescence analysis has tentatively identified the following chloride and sulfate daughter crystals; halite, sylvite, glauberite. arcanite, anhydrite, and thenardite. Melting of the daughter crystals occurs between 459 and 536??C (54 to 65 wt. % NaCI equivalent) whereas total homogenization is between 640 and 755??C. The occurrence of silicate-melt inclusions and high-temperature, solute-rich aqueous inclusions suggests that the druse or miarolitic texture of the xenolith is late-stage magmatic. The xenolith from Ponza represents a portion of the peripheral magma chamber wall that has recorded the magmatic/hydrothermal transition and the passage of high solute fluids enriched in chlorides, sulfur, and

  11. Chromite Composition and Accessory Minerals in Chromitites from Sulawesi, Indonesia: Their Genetic Significance

    Directory of Open Access Journals (Sweden)

    Federica Zaccarini


    Full Text Available Several chromite deposits located in the in the South and Southeast Arms of Sulawesi, Indonesia, have been investigated by electron microprobe. According to the variation of the Cr# = Cr/(Cr + Fe3+, the chromite composition varies from Cr-rich to Al-rich. Small platinum-group minerals (PGM, 1–10 μm in size, occur in the chromitites. The most abundant PGM is laurite, which has been found included in fresh chromite or in contact with chlorite along cracks in the chromite. Laurite forms polygonal crystals, and it occurs as a single phase or in association with amphibole, chlorite, Co-pentlandite and apatite. Small blebs of irarsite (less than 2 μm across have been found associated with grains of awaruite and Co-pentlandite in the chlorite gangue of the chromitites. Grains of olivine, occurring in the silicate matrix or included in fresh chromite, have been analyzed. They show a composition typical of mantle-hosted olivine. The bimodal composition and the slight enrichment in TiO2 observed in some chromitites suggest a vertical zonation due to the fractionation of a single batch magma with an initial boninitic composition during its ascent, in a supra-subduction zone. This observation implies the accumulation of Cr-rich chromitites at deep mantle levels and the formation of the Al-rich chromitites close or above the Moho-transition zone. All of the laurites are considered to be magmatic in origin, i.e., entrapped as solid phases during the crystallization of chromite at temperature of around 1200 °C and a sulfur fugacity below the sulfur saturation. Irarsite possibly represents a low temperature, less than 400 °C, exsolution product.

  12. Toxicological and epidemiological studies on effects of airborne fibers: coherence and public [corrected] health implications. (United States)

    Lippmann, Morton


    Airborne fibers, when sufficiently biopersistent, can cause chronic pleural diseases, as well as excess pulmonary fibrosis and lung cancers. Mesothelioma and pleural plaques are caused by biopersistent fibers thinner than ∼0.1 μm and longer than ∼5 μm. Excess lung cancer and pulmonary fibrosis are caused by biopersistent fibers that are longer than ∼20 μm. While biopersistence varies with fiber type, all amphibole and erionite fibers are sufficiently biopersistent to cause pathogenic effects, while the greater in vivo solubility of chrysotile fibers makes them somewhat less causal for the lung diseases, and much less causal for the pleural diseases. Most synthetic vitreous fibers are more soluble in vivo than chrysotile, and pose little, if any, health pulmonary or pleural health risk, but some specialty SVFs were sufficiently biopersistent to cause pathogenic effects in animal studies. My conclusions are based on the following: 1) epidemiologic studies that specified the origin of the fibers by type, and especially those that identified their fiber length and diameter distributions; 2) laboratory-based toxicologic studies involving fiber size characterization and/or dissolution rates and long-term observation of biological responses; and 3) the largely coherent findings of the epidemiology and the toxicology. The strong dependence of effects on fiber diameter, length, and biopersistence makes reliable routine quantitative exposure and risk assessment impractical in some cases, since it would require transmission electronic microscopic examination, of representative membrane filter samples, for determining statistically sufficient numbers of fibers longer than 5 and 20 μm, and those thinner than 0.1 μm, based on the fiber types.

  13. Accumulation of heavy metals in sediments of marine environments along the southwest coast of India

    International Nuclear Information System (INIS)

    Manjunatha, B.R.; Yeats, P.A.; Smith, J.N.; Shankar, R.; Narayana, A.C.; Prakash, T.N.


    In order to estimate the rate of excessive sediment accumulation that causes navigational problems and the impacts of urban and industrial development on sediment quality, concentrations of Cu, Ni, Zn, Cr, Mn, Fe and Ca, and radioactivity levels of 210 Pb and 137 Cs have been measured in nineteen sediment cores from estuarine, lagoonal, marsh, backwater and inner shelf areas along the southwest coast of India. Sediment accumulation rates in estuarine, lagoonal, marshy areas of the Karnataka coast (ELMKC) and Cochin Backwaters (CBw) are three to six times higher than those in the adjacent inner shelf areas, consistent with the deposition of terrigenous sediments in the river-sea interaction zones. Hydrogen sulphide was detected in most of the samples; sediment colour varied from shades of gray to dark green. Sediments have lower elemental concentrations and element enrichment factors (EFs) particularly for redox sensitive elements such as Mn due to prevalence of reducing conditions in the sedimentary column. Sediments of ELMKC and CBw have a predominantly terrigenous source. They contain low Ca contents, characteristic of tropical river sediments. In contrast, a higher Ca content of inner shelf sediments off both Karnataka State (ISKS-1) and Kerala State (ISKS-2) implies the importance of additional sediment (CaCO 3 ) flux from the marine biota. Measured Cu, Ni and Zn concentrations are generally low, perhaps reflecting the pristine nature of sediments. However, higher concentrations of Cr at all stations and of Zn at CBw indicate the input of Cr enriched minerals like amphibole and pyroxene from the catchment as well as Zn from anthropogenic sources. Heavy metal accumulation rates are high in estuarine, lagoonal, marsh and backwater areas along the southwest coast of India. This is not only due to the proximity of sources, but also due to high sediment accumulation rates because of the reduction of river flow in river-sea interaction zones owing to particle

  14. Antisana volcano: A representative andesitic volcano of the eastern cordillera of Ecuador: Petrography, chemistry, tephra and glacial stratigraphy (United States)

    Hall, Minard L.; Mothes, Patricia A.; Samaniego, Pablo; Militzer, Annemarie; Beate, Bernardo; Ramón, Patricio; Robin, Claude


    Antisana volcano is representative of many active andesitic strato-volcanoes of Pleistocene age in Ecuador's Eastern Cordillera. This study represents the first modern geological and volcanological investigation of Antisana since the late 1890's; it also summarizes the present geochemical understanding of its genesis. The volcano's development includes the formation and destruction of two older edifices (Antisana I and II) during some 400 + ka. Antisana II suffered a sector collapse about 15,000 years ago which was followed by the birth and growth of Antisana III. During its short life Antisana III has generated ≥50 eruptions of small to medium intensity, often associated with andesitic to dacitic lava flows and tephra, as well as with late Pleistocene and Holocene glacial advances. Throughout its long history Antisana's lavas have been characterized by a persistent mineral assemblage, consisting of 30-40 vol% phenocrysts of plagioclase, both clino- and orthopyroxene, and Fe-Ti oxides, with rare occurrences of olivine or amphibole, frequently in a microcrystalline to glassy matrix. This uniformity occurs despite the magma's progressive chemical evolution over ≥400 ka from early basic andesites (53-58 wt% SiO2) to intermediate and Si-rich andesites (58-62% SiO2), and recently to dacites (63-67% SiO2). Chemical diagrams suggest that crystal fractionation was the most likely magmatic process of evolution. The exception to this slowly evolving history was the short-lived emission at ∼210 ka of the Cuyuja lavas from Antisana II that generated a 73 km long andesitic lava flow. Contrasting with Antisana's general magmatic trend, Cuyuja lava (∼11 km3) is a high-Mg andesite with unusually high concentrations of incompatible elements. Antisana developed within the Chacana caldera complex, a large active siliceous center that began ∼3 Ma ago, however its lavas are chemically distinct from coeval lavas of Chacana.

  15. Determination of the geochemical weathering indices and trace elements content of new volcanic ash deposits from Mt. Talang (West Sumatra) Indonesia (United States)

    Fiantis, D.; Nelson, M.; Shamshuddin, J.; Goh, T. B.; van Ranst, E.


    Since the Indonesian archipelago is part of the very active and dynamic Pacific Ring of Fires, the volcanic eruptions occur from time to time. Immediately after the eruption of Mount Talang in West Sumatra (April 12, 2005), volcanic ashes, both unleached and leached were collected. The deposits from Mt. Talang were andesitic to basaltic in composition. The volcanic ash consisted of volcanic glass, plagioclase feldspar in various proportions, orthopyroxene, clinopyroxene, olivine, amphibole, titanomagnetite. We conducted the total elemental analysis of the bulk samples of the volcanic ash. The contents of major, trace and rare elements as well as heavy metals were determined by wet chemical methods and x-ray fluorescence (XRF) analyses. Although the volcanic ash of Mt. Talang are still very new, an evaluation of the geochemical weathering indices was performed with the objective of showing the volcanic ash condition at the early stage of weathering. Eight weathering indices were evaluated. The results showed that the unleached volcanic ash has higher Ruxton Ratio (R), Weathering Index of Parker (WIP), Product of Weathering Index (PWI) and Silica Titanium Index (STI) values compared to the leached ash, while the leached ash exhibited higher Chemical Index of Alteration (CIA), Chemical Index of Weathering (CIW), Vogt's Residual Index (VO), and Plagioclase Index of Alteration (PIA). These weathering indices can be used to quantify the condition of the volcanic ashes at the initial stage of weathering, to evaluate their fertility, to provide a better understanding of element mobility during weathering, and predict the source of soil nutrients as well as determine the products of primary minerals alteration.

  16. Volcanostratigraphic Sequences of Kebo-Butak Formation at Bayat Geological Field Complex, Central Java Province and Yogyakarta Special Province, Indonesia

    Directory of Open Access Journals (Sweden)

    Sri Mulyaningsih


    Full Text Available DOI:10.17014/ijog.3.2.77-94Bayat Complex is usually used as a work field for students of geology and other geosciences. The study area is located in the southern part of the Bayat Complex. Administratively, it belongs to Central Java Province and Yogyakarta Special Province. The lithology of Bayat is very complex, composed of various kinds of igneous, sedimentary, metamorphic, and volcanic rocks. Most of previous researchers interpreted Bayat as a melange complex constructed within a subduction zone. Kebo-Butak is one of formations that forms the Bayat field complex. The formation is composed of basalt, layers of pumice, tuff, shale, and carbonaceous tuff. Most of them are known as volcanic rocks. These imply that volcanic activities are more probable to construct the geology of Bayat rather than the subducted melange complex. The geological mapping, supported by geomorphology, petrology, stratigraphy, and geological structures, had been conducted in a comprehensive manner using the deduction-induction method. The research encounters basalt, black pumice, tuff with basaltic glasses fragments, zeolite, argilic clay, as well as feldspathic- and pumice tuff. Petrographically, the basalt is composed of labradorite, olivine, clinopyroxene, and volcanic glass. Black pumice and tuff contain prismatic clinopyroxene, granular olivine, and volcanic glasses. Feldspathic tuff and pumice tuff are crystal vitric tuff due to more abundant feldspar, quartz, and amphibole than volcanic glass. Zeolite comprises chlorite and altered glasses as deep sea altered volcanic rocks. The geologic structure is very complex, the major structures are normal faults with pyrite in it. There were two deep submarine paleovolcanoes namely Tegalrejo and Baturagung. The first paleovolcano erupted effusively producing basaltic sequence, while the second one erupted explosively ejecting feldspathic-rich pyroclastic material. The two paleovolcanoes erupted simultaneously and

  17. Evolution of the Archean continental crust in the nucleus of the Yangtze block: Evidence from geochemistry of 3.0 Ga TTG gneisses in the Kongling high-grade metamorphic terrane, South China (United States)

    Qiu, Xiao-Fei; Ling, Wen-Li; Liu, Xiao-Ming; Lu, Shan-Song; Jiang, Tuo; Wei, Yun-Xu; Peng, Lian-Hong; Tan, Juan-Juan


    Archean Tonalite-Trondhjemite-Granodiorite (TTG) rocks are scattered within the Kongling high-grade metamorphic terrane (KHMT) in the northern South China block. A comprehensive geochronological and geochemical study is carried out on the Taoyuan granitic gneisses, a newly recognized TTG suite in the northwestern KHMT. This suite has long been regarded as a Mesoproterozoic magmatic pluton, but U-Pb zircon ages of 2994 ± 22 Ma and 2970 ± 15 Ma are obtained by LA-ICP-MS method in this study. The Taoyuan gneiss suite is trondhjemitic in composition, and has high SiO2 (67.80-74.93 wt.%), Na2O (5.11-5.81 wt.%) contents with Na2O/K2O ratios greater than unity, and low Ni (2.56-7.61 ppm), Cr (1.26-7.67 ppm), Yb (0.32-0.82 ppm) and Y (4.48-11.5 ppm) contents. Plots show large variation in La/Yb and Sr/Y ratios and pronounced depletion in Nb, Ta and Ti in the primitive mantle-normalized spiderdiagram. The gneiss suite also displays two-stage Nd model ages close to its crystallization age with corresponding εNd(t) values of -2.5 to +3.5. It is thus suggested that the Taoyuan gneisses, in fact, is part of the Archean Kongling basement complex. Geochemical evidence implies that the TTG rocks may be derived from partial melting of subducted oceanic crust from a garnetiferous amphibolite source with residual assemblage of garnet + amphibole + plagioclase. Our study further indicates that the nucleus of the Yangtze block might experience a juvenile continental crustal growth during Mesoarchean. We also suggest that the Yangtze block may have its own crustal evolutionary history independent from the North China craton and the Tarim block before Paleoproterozoic.

  18. Evolving metasomatic agent in the North Andean subduction, deduced from magma composition of the long-lived Pichincha volcanic complex (Ecuador) (United States)

    Samaniego, P.; Robin, C.; Chazot, G.; Bourdon, E. P.; Jo, C.


    Geochemical studies of long-lived volcanic complexes are crucial for the understanding of the nature and composition of the subduction component of arc magmatism. The Pichincha Volcanic Complex (Northern Andean Volcanic Zone) consists of: (1) an older, highly eroded edifice, the Rucu Pichincha, whose lavas are mostly andesites, erupted from 1100 to 150 ka; and (2) a younger, essentially dacitic, Guagua Pichincha composite edifice, with three main construction phases (Basal Guagua Pichincha, Toaza and Cristal) which formed over the last 60 ka. This structural evolution was accompanied by a progressive increase of most incompatible trace element abundances and ratios, as well as by a sharp decrease of fluid-mobile to fluid-immobile element ratios. Geochemical data indicate that fractional crystallization of an amphibole-rich cumulate could account for the evolution from the Guagua Pichincha andesites to dacites. However, in order to explain the passage from the Rucu Pichincha andesites to Guagua Pichincha dacites, the mineralogical and geochemical data indicate the predominance of magma mixing processes between a mafic, trace-element depleted, mantle-derived end-member, and a siliceous, trace-element enriched, adakitic end-member. The systematic variation of trace element abundances and ratios in primitive samples of this volcanic complex leads us to propose that the Rucu Pichincha magmas came from a hydrous-fluid metasomatized mantle wedge, whereas Guagua Pichincha magmas are related to partial melting of a siliceous-melt metasomatized mantle. This temporal evolution implies a change from dehydration to partial melting of the slab, which may be associated with an increase in the geothermal gradient along the slab due to the presence of the subducted Carnegie Ridge at the subduction system. This work emphasizes the importance of studying arc-magma systems over long periods of time (of at least 1 million of years), in order to evaluate the potential variations of the

  19. Evolving metasomatic agent in the Northern Andean subduction zone, deduced from magma composition of the long-lived Pichincha volcanic complex (Ecuador) (United States)

    Samaniego, Pablo; Robin, Claude; Chazot, Gilles; Bourdon, Erwan; Cotten, Joseph


    Geochemical studies of long-lived volcanic complexes are crucial for the understanding of the nature and composition of the subduction component of arc magmatism. The Pichincha Volcanic Complex (Northern Andean Volcanic Zone) consists of: (1) an old, highly eroded edifice, the Rucu Pichincha, whose lavas are mostly andesites, erupted from 1,100 to 150 ka; and (2) a younger, essentially dacitic, Guagua Pichincha composite edifice, with three main construction phases (Basal Guagua Pichincha, Toaza, and Cristal) which developed over the last 60 ka. This structural evolution was accompanied by a progressive increase of most incompatible trace element abundances and ratios, as well as by a sharp decrease of fluid-mobile to fluid-immobile element ratios. Geochemical data indicate that fractional crystallization of an amphibole-rich cumulate may account for the evolution from the Guagua Pichincha andesites to dacites. However, in order to explain the transition between the Rucu Pichincha andesites and Guagua Pichincha dacites, the mineralogical and geochemical data indicate the predominance of magma mixing processes between a mafic, trace-element depleted, mantle-derived end-member, and a siliceous, trace-element enriched, adakitic end-member. The systematic variation of trace element abundances and ratios in primitive samples leads us to propose that the Rucu Pichincha magmas came from a hydrous-fluid metasomatized mantle wedge, whereas Guagua Pichincha magmas are related to partial melting of a siliceous-melt metasomatized mantle. This temporal evolution implies a change from dehydration to partial melting of the slab, which may be associated with an increase in the geothermal gradient along the slab due to the presence of the subducted Carnegie Ridge at the subduction system. This work emphasizes the importance of studying arc-magma systems over long periods of time (of at least 1 million of years), in order to evaluate the potential variations of the slab contribution

  20. Petrology of spinel lherzolite xenoliths from Youkou volcano, Adamawa Massif, Cameroon Volcanic Line: mineralogical and geochemical fingerprints of sub-rift mantle processes (United States)

    Njombie, Merlin Patrick Wagsong; Temdjim, Robert; Foley, Stephen F.


    The basaltic maar of Youkou, situated in the Adamawa Volcanic Massif in the eastern branch of the continental segment of the Cameroon Volcanic Line, contains mantle-derived xenoliths of various types in pyroclastites. Spinel-bearing lherzolite xenoliths from the Youkou volcano generally exhibit protogranular textures with olivine (Fo89.4-90.5), enstatite (En89 - 91Fs8.7-9.8Wo0.82-1.13), clinopyroxene, spinel (Cr#Sp = 9.4-13.8), and in some cases amphibole (Mg# = 88.5-89.1). Mineral equilibration temperatures in the lherzolite xenoliths have been estimated from three-two pyroxene thermometers and range between 835 and 937 °C at pressures of 10-18 kbar, consistent with shallow mantle depths of around 32-58 km. Trends displayed by bulk-rock MgO correlate with Al2O3, indicating that the xenoliths are refractory mantle residues after partial melting. The degree of partial melting estimated from spinel compositions is less than 10%: evidences for much higher degrees of depletion are preserved in one sample, but overprinted by refertilization in others. Trace element compositions of the xenoliths are enriched in highly incompatible elements (LREE, Sr, Ba, and U), indicating that the spinel lherzolites underwent later cryptic metasomatic enrichment induced by plume-related hydrous silicate melts. The extreme fertility (Al2O3 = 6.07-6.56 wt% in clinopyroxene) and the low CaO/Al2O3 ratios in the spinel lherzolites suggest that they could not be a simple residue of partial melting of primitive mantle and must have experienced refertilization processes driven by the infiltration of carbonatite or carbonated silicate melts.

  1. [Study on the FTIR spectra of OH in olivines from mengyin kimberlite]. (United States)

    Ai, Qun; Yang, Zhi-jun; Zeng, Xiang-qing; Zheng, Yun-long; Hu, Piao-ye


    The results of FTIR spectra study of OH in olivines from Mengyin kimberlite show that there are more than 60 OH absorption peaks in the range of 3800-3000 cm(-1). We identified four major spectral features in the OH absorption bands of kimberlitic olivines. One is with nuOH in the range of 3800-3700 cm(-1), which is caused by the vapour of the room circumstance, and can not be regarded as intrinsic or non-intrinsic nuOH of the olivines. Another one is with nuOH in the range of 3710-3620 cm(-1), which belongs to three "water"-bearing minerals including serpentine, talc and Mg-bearing amphiboles, which is the non-intrinsic nuOH of the olivines. There is the possibility that H in hydrous minerals mainly entered into olivines during post-emplacement processes of the kimberlite magma. The third one is with nuOH in the range of 3620-3425 cm(-1), which originated from H occupying the Si-defect in the olivine structure, forming humite-like defects, and/or the defects that H occupies (Mg,Fe)-depletion, which is certainly attributed to the intrinsic nuOH of the olivines. In this case, H possibly entered into olivines following its immersion in the high temperature and rich fluid kimberlite magma in the mantle circumstance. The last one is with nuOH in the range of 3425-3000 cm(-1). In this area, nuOH is assigned to fluid inclusions of the olivines, and is the non-intrinsic nuOH of olivines. Fluid inclusions can enter into the olivines either during post-emplacement processes of the kimberlite magma or during the periods that olivines were formed in the mantle.

  2. The Lost City Hydrothermal Field: A Spectroscopic and Astrobiological Analogue for Nili Fossae, Mars (United States)

    Amador, Elena S.; Bandfield, Joshua L.; Brazelton, William J.; Kelley, Deborah


    Low-temperature serpentinization is a critical process with respect to Earth's habitability and the Solar System. Exothermic serpentinization reactions commonly produce hydrogen as a direct by-product and typically produce short-chained organic compounds indirectly. Here, we present the spectral and mineralogical variability in rocks from the serpentine-driven Lost City Hydrothermal Field on Earth and the olivine-rich region of Nili Fossae on Mars. Near- and thermal-infrared spectral measurements were made from a suite of Lost City rocks at wavelengths similar to those for instruments collecting measurements of the martian surface. Results from Lost City show a spectrally distinguishable suite of Mg-rich serpentine, Ca carbonates, talc, and amphibole minerals. Aggregated detections of low-grade metamorphic minerals in rocks from Nili Fossae were mapped and yielded a previously undetected serpentine exposure in the region. Direct comparison of the two spectral suites indicates similar mineralogy at both Lost City and in the Noachian (4-3.7 Ga) bedrock of Nili Fossae, Mars. Based on mapping of these spectral phases, the implied mineralogical suite appears to be extensive across the region. These results suggest that serpentinization was once an active process, indicating that water and energy sources were available, as well as a means for prebiotic chemistry during a time period when life was first emerging on Earth. Although the mineralogical assemblages identified on Mars are unlikely to be directly analogous to rocks that underlie the Lost City Hydrothermal Field, related geochemical processes (and associated sources of biologically accessible energy) were once present in the subsurface, making Nili Fossae a compelling candidate for a once-habitable environment on Mars.

  3. Petrogenesis of coexisting SiO 2-undersaturated to SiO 2-oversaturated felsic igneous rocks: The alkaline complex of Itatiaia, southeastern Brazil (United States)

    Brotzu, P.; Gomes, C. B.; Melluso, L.; Morbidelli, L.; Morra, V.; Ruberti, E.


    The Itatiaia alkaline complex is a Late Cretaceous intrusion (72 Myr) made up of felsic differentiates, with syenitic rocks dominant throughout and with presence of both nepheline- and quartz-rich varieties. Dykes with phonolitic or trachytic composition cross-cut the coarse-grained facies. The rocks are arranged concentrically, with the core of the complex being formed by SiO 2-oversaturated syenites (with a small outcrop of granites), and are radially displaced by faults related to regional tectonic lineaments. The minerals show gradual but significant changes in composition (salitic and augitic to aegirine-rich pyroxenes, hastingsite and actinolite to richterite and arfvedsonite amphiboles, sodic plagioclase to orthoclase feldspars and so on) and the whole-rock trends are broadly consistent with fractional crystallization processes dominated by alkali feldspar removal. Sr-isotopic data indicate more radiogenic ratios for the SiO 2-oversaturated rocks (0.7062-0.7067 against 0.7048-0.7054 for the SiO 2-undersaturated syenites), consistent with small amounts of crustal input. The favored hypothesis for the petrogenesis of the different syenitic groups is the prolonged differentiation starting from differently SiO 2-undersaturated mafic parental magmas (potassic alkali basalts to ankaratrites, present in the Late Cretaceous dyke swarms of the area), accompanied by variable crustal contamination prior to the final emplacement. The lack of carbonatite as a significant lithotype, the potassic affinity of the Itatiaia complex, and the relatively high Sr-isotopic ratios match the characteristics of the other complexes of the Rio de Janeiro-Sa˜o Paulo states coastline and confirm the ultimate derivation of these differentiated rocks from an enriched lithospheric mantle source.

  4. Evaluation of the fate and pathological response in the lung and pleura of brake dust alone and in combination with added chrysotile compared to crocidolite asbestos following short-term inhalation exposure

    Energy Technology Data Exchange (ETDEWEB)

    Bernstein, D.M., E-mail: [Consultant in Toxicology, Geneva (Switzerland); Rogers, R.A., E-mail: [Rogers Imaging, Needham, MA (United States); Sepulveda, R. [Rogers Imaging, Needham, MA (United States); Kunzendorf, P., E-mail: [GSA Gesellschaft für Schadstoffanalytik mbH, Ratingen (Germany); Bellmann, B. [Fraunhofer Institute for Toxicology and Experimental Medicine, Hannover (Germany); Ernst, H., E-mail: [Fraunhofer Institute for Toxicology and Experimental Medicine, Hannover (Germany); Creutzenberg, O. [Fraunhofer Institute for Toxicology and Experimental Medicine, Hannover (Germany); Phillips, J.I., E-mail: [National Institute for Occupational Health, National Health Laboratory Service, Johannesburg South Africa and Department of Biomedical Technology, Faculty of Health Sciences, University of Johannesburg, Johannesburg (South Africa)


    This study was designed to provide an understanding of the biokinetics and potential toxicology in the lung and pleura following inhalation of brake dust following short term exposure in rats. The deposition, translocation and pathological response of brake-dust derived from brake pads manufactured with chrysotile were evaluated in comparison to the amphibole, crocidolite asbestos. Rats were exposed by inhalation 6 h/day for 5 days to either brake-dust obtained by sanding of brake-drums manufactured with chrysotile, a mixture of chrysotile and the brake-dust or crocidolite asbestos. The chrysotile fibers were relatively biosoluble whereas the crocidolite asbestos fibers persisted through the life-time of the animal. This was reflected in the lung and the pleura where no significant pathological response was observed at any time point in the brake dust or chrysotile/brake dust exposure groups through 365 days post exposure. In contrast, crocidolite asbestos produced a rapid inflammatory response in the lung parenchyma and the pleura, inducing a significant increase in fibrotic response in both of these compartments. Crocidolite fibers were observed embedded in the diaphragm with activated mesothelial cells immediately after cessation of exposure. While no chrysotile fibers were found in the mediastinal lymph nodes, crocidolite fibers of up to 35 μm were observed. These results provide support that brake-dust derived from chrysotile containing brake drums would not initiate a pathological response in the lung or the pleural cavity following short term inhalation. - Highlights: • Evaluated brake dust w/wo added chrysotile in comparison to crocidolite asbestos. • Persistence, translocation, pathological response in the lung and pleural cavity. • Chrysotile cleared rapidly from the lung while the crocidolite asbestos persisted. • No significant pathology in lung or pleural cavity observed at any time point in the brake-dust groups. • Crocidolite quickly

  5. Evaluation of the deposition, translocation and pathological response of brake dust with and without added chrysotile in comparison to crocidolite asbestos following short-term inhalation: Interim results

    Energy Technology Data Exchange (ETDEWEB)

    Bernstein, David M., E-mail: [Consultant in Toxicology, 1208 Geneva (Switzerland); Rogers, Rick, E-mail: [Rogers Imaging, Needham, MA 02494 (United States); Sepulveda, Rosalina [Rogers Imaging, Needham, MA 02494 (United States); Kunzendorf, Peter, E-mail: [GSA Gesellschaft für Schadstoffanalytik mbH, D-40882 Ratingen (Germany); Bellmann, Bernd [Fraunhofer Institute for Toxicology and Experimental Medicine, D-30625 Hannover (Germany); Ernst, Heinrich, E-mail: [Fraunhofer Institute for Toxicology and Experimental Medicine, D-30625 Hannover (Germany); Phillips, James I., E-mail: [National Institute for Occupational Health, National Health Laboratory Service (South Africa); Department of Biomedical Technology, Faculty of Health Sciences, University of Johannesburg (South Africa)


    Chrysotile has been frequently used in the past in manufacturing brakes and continues to be used in brakes in many countries. This study was designed to provide an understanding of the biokinetics and potential toxicology following inhalation of brake dust following short term exposure in rats. The deposition, translocation and pathological response of brake dust derived from brake pads manufactured with chrysotile were evaluated in comparison to the amphibole, crocidolite asbestos. Rats were exposed by inhalation 6 h/day for 5 days to either brake dust obtained by sanding of brake-drums manufactured with chrysotile, a mixture of chrysotile and the brake dust or crocidolite asbestos. No significant pathological response was observed at any time point in either the brake dust or chrysotile/brake dust exposure groups. The long chrysotile fibers (> 20 μm) cleared quickly with T{sub 1/2} estimated as 30 and 33 days, respectively in the brake dust and the chrysotile/brake dust exposure groups. In contrast, the long crocidolite fibers had a T{sub 1/2} > 1000 days and initiated a rapid inflammatory response in the lung following exposure resulting in a 5-fold increase in fibrotic response within 91 days. These results provide support that brake dust derived from chrysotile containing brake drums would not initiate a pathological response in the lung following short term inhalation. - Highlights: • We evaluated brake dust w/wo added chrysotile in comparison to crocidolite asbestos. • Persistence, translocation, pathological response in the lung and pleural cavity. • Chrysotile cleared rapidly from the lung while the crocidolite asbestos persisted. • No significant pathology observed at any time point in the brake-dust groups. • Crocidolite produced pathological response - Wagner 4 interstitial fibrosis by 32d.

  6. Asbestos in drinking water; Asbest im Trinkwasser

    Energy Technology Data Exchange (ETDEWEB)

    Spurny, K.R.


    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 10{sup 6} fibers/liter, and the fibers were thin and shorter than 5 {mu}m. Nevertheless, in some tap-water samples the asbestos fiber concentrations were higher than 10{sup 6} fibers/liter and/or the content of long fibers (longer than 5 {mu}m) was relatively high. It is recommended tapwater with asbestos fiber concentrations over 10{sup 6} fibers/liter and/or with greater content of long fibers should not be used for cooking or drinking unless filtered. (orig.) [Deutsch] Mehr als 100 Trinkwasser-Proben aus verschiedenen Bundeslaendern wurden untersucht und analysiert bei Anwendung eines standardisierten TEM-Verfahrens (ISO). Die Ergebnisse zeigten, dass Trinkwasser (alte Bundeslaender) mit feinen Asbestfasern, Chrysotil und Amphibolen, mehr oder weniger kontaminiert ist. In der Mehrheit der untersuchten Proben lagen die Asbestkonzentrationen im Bereich weniger als 10{sup 6} Fasern/Liter und die gemessenen Fasern waren duenn und kuerzer als 5 {mu}m. Nichtsdestoweniger, in einigen Wasserproben wurden Asbestfaser-Kontaminationen im Bereich ueber 10{sup 6} Fasern/Liter ermittelt. Diese Wasserproben enthielten auch hoeheren Anteil an langen Fasern. Es wird empfohlen, Wasser mit Asbestfaserkonzentrationen ueber 10{sup 6} Fasern/Liter oder mit einem hoeheren Anteil an langen Asbestfasern nicht ohne weitere Behandlung (Filtration) zu trinken und nicht zum Kochen zu verwenden. (orig.)

  7. Volcanic geology and geochemistry of Motuhora (Whale Island), Bay of Plenty, New Zealand

    International Nuclear Information System (INIS)

    Burt, R.M.; Cole, J.W.; Vroon, P.Z.


    Motuhora (Whale Island) lies c. 11 km offshore from Whakatane in the Bay of Plenty, New Zealand, and comprises tuffaceous marine sediments of the Camp Bay and Motuhora Formations separated by lavas, volcanic breccias, and slope-wash deposits of the Whale Volcanics. Whale Volcanics can be divided into East Dome, Central Dome Complex, and Pa Hill Dome. East Dome is a flow banded, chaotically jointed dacite that is probably extrusive. Central Dome comprises lava flows, and extensive volcanic breccias and tuffs which thicken into a local depression to the north of the central high, suggesting rapid growth and erosion of the dome. Pa Hill Dome is largely intrusive into Camp Bay Formation, although blocks of Pa Hill dacite in an upper slope-wash cobble bed suggest it was partially extrusive. The lavas are porphyritic with phenocrysts of plagioclase, orthopyroxene, and titanomagnetite with subordinate clinopyroxene and amphibole (particularly in Pa Hill Dome), and rare biotite. Rounded or broken and embayed quartz crystals are found in the Central Dome Complex and Pa Hill domes. Magmatic xenoliths are common in all lavas. Chemically the lavas are medium-K, calc-alkaline andesites and dacites, and show relative LILE enrichment and HFSE depletion typical of arc volcanics. Isotopically, samples tend to have more radiogenic Sr and less radiogenic Nd than volcanics from neighbouring White Island. It is likely that Motuhora lavas were formed by a multi-stage process involving partial melting of N-MORB-type mantle that had been fluxed by fluids rich in incompatible elements derived from the dehydrating downgoing slab and followed by crystal fractionation of the magma. As the magma rose through the lower continental crust it was contaminated, probably by Torlesse metasediment. Petrographic textures and mineral chemistry indicate that magma mixing, while in an upper crustal magma chamber, is the norm for Motuhora lavas. (author). 69 refs., 12 figs., 2 tabs

  8. Lacustrine sedimentation and facies model for the last 45,000 yr in Chalco basin. Central Mexico (United States)

    Ortega, B.; Lozano, S.; Caballero, M.; Herrera, D.


    Chalco basin in central Mexico (19° 15' N, 98° 58' W, 2200 m asl) is one of the most detailed lake sediment sequence analyzed in Mexico for paleoclimatic and paleoenvironmental studies. In this former lake, five drill cores up to 27 m depth were recovered in 1987-1989 by the UNAM team, and three cores covering most of the former sequence were obtained in 2008 and 2011. The upper 27 m of the Chalco lacustrine sequence contains the record of the last 45 kyr climate history in the northern American tropics. The active tectonic and volcanic setting of Chalco Lake in the Trans-Mexican Volcanic Belt, provides an opportunity to evaluate environmental (volcanic + tectonic vs. climatic) controls on lacustrine sedimentation. The establishment of a detailed time scale by 14C in pollen extracts provides an accurate chronological control. The stratigraphical and sedimentological analyses presented here provided the recognition of depositional environments and the architecture of the upper lacustrine succession. Sedimentary facies were defined on the basis of sedimentological descriptions, microscopic observation and compositional analyses. According to compositional criteria, facies were identified and groped into two main categories according to compositional criteria: 1) detrital and volcaniclastic, and 2) biogenic facies. The clastic facies includes massive to laminated, silty and clayey sediments composed of clay minerals, feldspars, amphiboles with minor amounts of quartz, opaque minerals and calcite. Diatoms are the most common biological remains in all the clastic facies. Most of the volcaniclastic deposits correspond to fall-out deposits, some of them of well documented eruptions of the nearby large stratovolcanoes Popocatepetl and Nevado de Toluca, which in turn serve as stratigraphical markers. The biogenic facies are massive to finely laminated diatom ooze and ostracod ooze layers. The sedimentary architecture of the lacustrine succession has been controlled by

  9. The Deccan tholeiite lavas and dykes of Ghatkopar-Powai area, Mumbai, Panvel flexure zone: Geochemistry, stratigraphic status, and tectonic significance (United States)

    Sheth, Hetu C.; Zellmer, Georg F.; Demonterova, Elena I.; Ivanov, Alexei V.; Kumar, Rohit; Patel, Rakesh Kumar


    Mumbai City, situated on the western Indian coast, is well known for exposures of late-stage Deccan pillow basalts and spilites, pyroclastic rocks, rhyolite lavas, and trachyte intrusions. These rock units, and a little-studied sequence of tholeiitic flows and dykes in the eastern part of Mumbai City, constitute the west-dipping limb of a regional tectonic structure called the Panvel flexure. Here we present field, petrographic, major and trace element and Sr-Nd isotopic data on these tholeiitic flows and dykes, best exposed in the Ghatkopar-Powai area. The flows closely resemble the Mahabaleshwar Formation of the thick Western Ghats sequence to the east, in Sr-Nd isotopic ratios and multielement patterns, but have other geochemical characteristics (e.g., incompatible trace element ratios) unlike the Mahabaleshwar or any other Formation. The flows may have originated from a nearby eruptive center, possibly offshore of Mumbai. Two dykes resemble the Ambenali Formation of the Western Ghats in all geochemical characteristics, though they may not represent feeders of the Ambenali Formation lavas. Most dykes are distinct from any of the Western Ghats stratigraphic units. Some show partial (e.g., Sr-Nd isotopic) similarities to the Mahabaleshwar Formation, and these include several dykes with unusual, concave-downward REE patterns suggesting residual amphibole and thus a lithospheric source. The flows and dykes are inferred to have undergone little or no contamination, by lower continental crust. Most dykes are almost vertical, suggesting emplacement after the formation of the Panvel flexure, and indicate considerable east-west lithospheric extension during this late but magmatically vigorous stage of Deccan volcanism.

  10. Cogenetic late Pleistocene rhyolite and cumulate diorites from Augustine Volcano revealed by SIMS 238U-230Th dating of zircon, and implications for silicic magma generation by extraction from mush (United States)

    Coombs, Michelle L.; Vazquez, Jorge A.


    Augustine Volcano, a frequently active andesitic island stratocone, erupted a late Pleistocene rhyolite pumice fall that is temporally linked through zircon geochronology to cumulate dioritic blocks brought to the surface in Augustine's 2006 eruption. Zircon from the rhyolite yield a 238U-230Th age of ∼25 ka for their unpolished rims, and their interiors yield a bimodal age populations at ∼26 ka and a minority at ∼41 ka. Zircon from dioritic blocks, ripped from Augustine's shallow magmatic plumbing system and ejected during the 2006 eruption, have interiors defining a ∼26 ka age population that is indistinguishable from that for the rhyolite; unpolished rims on the dioritic zircon are dominantly younger (≤12 ka) indicating subsequent crystallization. Zircon from rhyolite and diorite overlap in U, Hf, Ti, and REE concentrations although diorites also contain a second population of high-U, high temperature grains. Andesites that brought dioritic blocks to the surface in 2006 contain zircon with young (≤9 ka) rims and a scattering of older ages, but few zircon that crystallized during the 26 ka interval. Both the Pleistocene-age rhyolite and the 2006 dioritic inclusions plot along a whole-rock compositional trend distinct from mid-Holocene–present andesites and dacites, and the diorites, rhyolite, and two early Holocene dacites define linear unmixing trends often oblique to the main andesite array and consistent with melt (rhyolite) extraction from a mush (dacites), leaving behind a cumulate amphibole-bearing residue (diorites). Rare zircon antecrysts up to ∼300 ka from all rock types indicate that a Quaternary center has been present longer than preserved surficial deposits.

  11. Asbestos-associated mesothelial cell autoantibodies promote collagen deposition in vitro (United States)

    Serve, Kinta M.; Black, Brad; Szeinuk, Jaime; Pfau, Jean C.


    Fibrosis, characterized by excessive collagen protein deposition, is a progressive disease that can fatally inhibit organ function. Prolonged exposure to pathogens or environmental toxicants such as asbestos can lead to chronic inflammatory responses associated with fibrosis. Significant exposure to amphibole asbestos has been reported in and around Libby, Montana due to local mining of asbestos-contaminated vermiculite. These exposures have been implicated in a unique disease etiology characterized predominantly by pleural disorders, including fibrosis. We recently reported the discovery of mesothelial cell autoantibodies (MCAAs) in the sera of Libby residents and demonstrated a positive and significant correlation with pleural disease; however, a mechanistic link was not determined. Here we demonstrate that MCAAs induce pleural mesothelial cells to produce a collagen matrix but do not affect production of the pro-inflammatory cytokine tumor growth factor-β. While autoantibodies commonly induce a pro-fibrotic state by inducing epithelial–mesenchymal transition (EMT) of target cells, we found no evidence supporting EMT in cells exposed to MCAA positive human sera. Although implicated in other models of pulmonary fibrosis, activity of the protein SPARC (secreted protein, acidic and rich in cysteine) did not affect MCAA-induced collagen deposition. However, matrix formation was dependent on matrix metalloproteinase (MMP) activity, and we noted increased expression of MMP-8 and -9 in supernatants of mesothelial cells incubated with MCAA positive sera compared to control. These data suggest a mechanism by which MCAA binding leads to increased collagen deposition through altering MMP expression and provides an important mechanistic link between MCAAs and asbestos-related, autoimmune-induced pleural fibrosis. PMID:24304304

  12. Oxidative potential (OP) and mineralogy of iron ore particulate matter at the Gol-E-Gohar Mining and Industrial Facility (Iran). (United States)

    Soltani, Naghmeh; Keshavarzi, Behnam; Sorooshian, Armin; Moore, Farid; Dunster, Christina; Dominguez, Ana Oliete; Kelly, Frank J; Dhakal, Prakash; Ahmadi, Mohamad Reza; Asadi, Sina


    Concentrations of total suspended particulate matter, particulate matter with aerodynamic diameter Gol-E-Gohar Mining and Industrial Facility. Samples were characterized in terms of mineralogy, morphology, and oxidative potential. Results show that indoor samples exceeded the 24-h PM 2.5 and PM 10 mass concentration limits (35 and 150 µg m -3 , respectively) set by the US National Ambient Air Quality Standards. Calcite, magnetite, tremolite, pyrite, talc, and clay minerals such as kaolinite, vermiculite, and illite are the major phases of the iron ore PM. Accessory minerals are quartz, dolomite, hematite, actinolite, biotite, albite, nimite, laumontite, diopside, and muscovite. The scanning electron microscope structure of fibrous-elongated minerals revealed individual fibers in the range of 1.5 nm to 71.65 µm in length and 0.2 nm to 3.7 µm in diameter. The presence of minerals related to respiratory diseases, such as talc, crystalline silica, and needle-shaped minerals like amphibole asbestos (tremolite and actinolite), strongly suggests the need for detailed health-based studies in the region. The particulate samples show low to medium oxidative potential per unit of mass, in relation to an urban road side control, being more reactive with ascorbate than with glutathione or urate. However, the PM oxidative potential per volume of air is exceptionally high, confirming that the workers are exposed to a considerable oxidative environment. PM released by iron ore mining and processing activities should be considered a potential health risk to the mine workers and nearby employees, and strategies to combat the issue are suggested.

  13. Tectonic-and petrological interpretation of geochronological data on the basement at the Southeast border of the Quadrilatero Ferrifero, Minas Gerais, Brazil

    International Nuclear Information System (INIS)

    Cordani, U.G.; Kawashita, K.; Mueller, G.; Quade, H.; Reimer, V.; Roeser, H.


    In an attempt to elucidate the regional geological evolution of the Ouro Preto and Mariana Districts, SE Quadrilatero Ferrifero, Minas Gerais, the available petrographical and structural data were interpreted together with 5 Rb/Sr and 7 K/Ar age determinations. Various types of metamorphic rocks were identified, and four phases of regional petrographic evolution could be distinguished: a) pre-metamorphic phase indicated by relict sedimentary and other textures; b) pre-deformation metamorphic phase, manifested by several minerals, such as microcline; c) major syntectonic crystallization phase associated with the main regional diastrophism, presumaby the Minas orogeny; d) post-deformation phase, with retrograde metamorphic minerals. With one exception, the apparent K/Ar ages obtained on biotites and amphiboles were concordant, ranging between 480 and 540 m.y., and can be referred to the terminal episodes of cooling in the Brazilian cycle. The Rb/Sr data obtained from 3 whole-rock analyses, when plotted on a Sr 87 /Sr 86 - Rb 87 /Sr 86 diagram, indicated an age of approximately 2.000m.y., with an initial Sr 87 /Sr 86 ratio of 0.711. In this diagram, 2 other speciments from a single outerop plotted significantly above of the reference isochron of 2.000m.y. The apparent ages of about 2.700 m.y. are concordant with those for the Barbacena Group which occurs more toward the eastern side of the study area. From interpretation of petrographical and structural data, the following regional geological evolution can be inferred; a)2.700m.y. - Formation of rocks during the pre-Minas episode (diastrophism in Barbacena Series, or in the Bacao Complex; b) 2.000m.y. - Trans-Amazonian cycle - Main phase of syntectonic crystallization - Minas Series diastrophism; c) 500-600m.y. - Brazilian cycle - retrograde metamorphism, thrust tectonics and regional fracturing. (Author) [pt

  14. Geochemistry of Archean Mafic Amphibolites from the Amsaga Area, West African Craton, Mauritania: What Is the Message? (United States)

    El Atrassi, F.; Debaille, V.; Mattielli, N. D. C.; Berger, J.


    While Archean terrains are mainly composed of a TTG (Tonalite-trondhjemite-granodiorite) suite, more mafic lithologies such as amphibolites are also a typical component of those ancient terrains. Although mafic rocks represent only ~10% of the Archean cratons, they may provide key evidence of the role and nature of basaltic magmatism in the formation of the Archean crust as well as the evolution of the Archean mantle. This study focuses on the Archean crust from the West African Craton in Mauritania (Amsaga area). The Amsaga Archean Crust mainly consists of TTG and thrust-imbricated slices of mafic volcanic rocks, which have been affected by polymetamorphic events from the amphibolite to granulite facies. Our main objectives aim to the identification of the mafic lithology origin and a better understanding of their role in the continental crust emplacement. Our petrological observations show that these amphibolites have fine to medium granoblastic and nematoblastic textures. The amphibolites are dominated by amphibolite-facies mineral assemblages (mainly amphibole and plagioclase), but garnet and clinopyroxene occur in a few samples. Two groups are distinct in their geochemical characteristics (major and trace elements), although both have tholeiitic basalt composition. The first group show LREE-enriched patterns and negative Nb-Ta anomalies. The second group is characterized by near-flat LREE patterns and flat HREE patterns. This second group clearly shows no Nb-Ta anomalies. The first group could be related to arc-like basalts, as it is many similarities with some Archean amphibolites probably formed in a supra-subduction zone, for instance the volcanic rocks from the southern edge of the Isua Supracrustal Belt. On the contrary, the second group has a MORB-like signature which is more unusual during the Archean. Different scenarios will be discussed regards to the Archean geodynamics.

  15. Asbestos fibers in bronchoalveolar lavage and lung tissue of former asbestos workers. (United States)

    Teschler, H; Friedrichs, K H; Hoheisel, G B; Wick, G; Soltner, U; Thompson, A B; Konietzko, N; Costabel, U


    Bronchoalveolar lavage (BAL) provides a simple method of sampling inhaled particles deposited in the lower respiratory tract. We hypothesized that BAL could be used to measure the quantity and quality of lung asbestos burden. This would be true if BAL fluid asbestos fiber content reflected the total content as well as the size distribution of both uncoated and coated asbestos fibers in lung parenchyma. Therefore, we analyzed the asbestos fiber counts of 23 individual sample pairs in both BAL fluid and lung tissue samples obtained from 20 patients with occupational asbestos exposure using transmission electron microscopy (TEM). In addition, fiber type, fiber size, and aspect ratio were compared. Coated asbestos fibers were found in 10 of 23 BAL samples and 16 of 23 biopsies. The mean concentrations of coated asbestos fibers (i.e., asbestos bodies) in BAL and lung parenchyma showed a positive correlation (r = 0.75, p < 0.001). Likewise, the mean amphibole fiber concentrations correlated positively (r = 0.55, p < 0.01). However, there was no relationship between the mean chrysotile fiber counts in BAL and lung parenchyma (r = 0.18, p = 0.40). Asbestos fibers in lung tissue were significantly longer (8.2 +/- 0.5 versus 4.8 +/- 0.6 microns; p < 0.001) but had the same width (0.12 +/- 0.27 versus 0.11 +/- 0.15 microns; p = 0.24) when compared with those retrieved by BAL from the airspace compartment. The aspect ratio (dividing fiber length by width) was much higher in lung tissue than in BAL fluid (66.4 +/- 0.4 versus 42.9 +/- 0.5; p < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

  16. Mineral chemistry of monazite-(Nd, xenotime-(Y, apatite, fluorite and zircon hosting in lamprophyre dyke in Abu Rusheid area, South Eastern Desert, Egypt

    Directory of Open Access Journals (Sweden)

    Mohamed A. Ali


    Full Text Available The studied mineralized lamprophyre dyke in Abu Rusheid area is trending NNW-SSE, and occurs withinAbu Rusheid mineralized shear zone, measuring 0.2 - 1.0 m in width and 0.5 - 1.0 km in length. It was emplacedparallel with the Abu Rusheid shear zone. The dyke is mainly composed of plagioclases, amphiboles, mica (musco-vite and biotite, relics of pyroxenes with K-feldspars and quartz derived from surrounding country rocks asphenocrysts embedded in fine-grained groundmass. The lamprophyre dyke hosts REE-minerals monazite-(Nd,xenotime-(Y, and REE-bearing minerals apatite, fluorite, zircon-(Hf, rutile with inclusions of xenotime and ironoxides. The emplacement of lamprophyre dyke caused heating in the mineralized shear zone of Abu Rusheid area.The lamprophyre dyke was subsequently affected by hydrothermal alterations (e.g. chlorite-carbonate, muscovitization,fluoritization.The REE were remobilized from the mineralized shear zones by hydrothermal solutionsand re-precipitatedas REE-minerals xenotime-(Y and monazite-(Nd around flourapatite, fluorite, zircon andrutile. The solid solutions between monazite-(Nd and xenotime-(Y were formed as a product precipitation fromhydrothermal solutions. Also, the apatite mineral in the lamprophyre dyke was subjected to the heating duringthe emplacement, which lead to its alteration and breakdown with concominant precipitation of xenotime-(Yand monazite-(Nd. The chemistry of monazite-(Nd and xenotime-(Y obtained by scanning electron microscopy(SEM, and electron probe microanalysis (EPMA, showed that these minerals are enriched in U and Th. Themonazite-(Nd associated with fluorapatite in the studied dyke is poor in Th (0.02 ≤ Th ≤ 0.81 wt%, but usuallyrich in U (0.92 ≤ U ≤ 2.91 wt%, which indicates that monazite formed as a result of flourapatite metasomatism.

  17. New data on carbonatites of the Il'mensky-Vishnevogorsky alkaline complex, the southern Urals, Russia (United States)

    Nedosekova, I. L.


    Carbonatites that are hosted in metamorphosed ultramafic massifs in the roof of miaskite intrusions of the Il’mensky-Vishnevogorsky alkaline complex are considered. Carbonatites have been revealed in the Buldym, Khaldikha, Spirikha, and Kagan massifs. The geological setting, structure of carbonatite bodies, distribution of accessory rare-metal mineralization, typomorphism of rock-forming minerals, geochemistry, and Sr and Nd isotopic compositi