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1.
M. I. Holloway F. Bussy T. W. Vennemann 《Contributions to Mineralogy and Petrology》2008,155(1):111-121
Migmatites produced by low-pressure anatexis of basic dykes are found in a contact metamorphic aureole around a pyroxenite–gabbro
intrusion (PX2), on Fuerteventura. Dykes outside and inside the aureole record interaction with meteoric water, with low or
negative δ18O whole-rock values (+0.2 to −3.4‰), decreasing towards the contact. Recrystallised plagioclase, diopside, biotite and oxides,
from within the aureole, show a similar evolution with lowest δ18O values (−2.8, −4.2, −4.4 and −7.6‰, respectively) in the migmatite zone, close to the intrusion. Relict clinopyroxene phenocrysts
preserved in all dykes, retain typically magmatic δ18O values up to the anatectic zone, where the values are lower and more heterogeneous. Low δ18O values, decreasing towards the intrusion, can be ascribed to the advection of meteoric water during magma emplacement, with
increasing fluid/rock ratios (higher dyke intensities towards the intrusion acting as fluid-pathways) and higher temperatures
promoting increasing exchange during recrystallisation.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
2.
A reassessment of models for hydrocarbon generation in the Khibiny nepheline syenite complex, Kola Peninsula, Russia 总被引:2,自引:0,他引:2
Although hydrocarbon-bearing fluids have been known from the alkaline igneous rocks of the Khibiny intrusion for many years, their origin remains enigmatic. A recently proposed model of post-magmatic hydrocarbon (HC) generation through Fischer-Tropsch (FT) type reactions suggests the hydration of Fe-bearing phases and release of H2 which reacts with magmatically derived CO2 to form CH4 and higher HCs. However, new petrographic, microthermometric, laser Raman, bulk gas and isotope data are presented and discussed in the context of previously published work in order to reassess models of HC generation. The gas phase is dominated by CH4 with only minor proportions of higher hydrocarbons. No remnants of the proposed primary CO2-rich fluid are found in the complex. The majority of the fluid inclusions are of secondary nature and trapped in healed microfractures. This indicates a high fluid flux after magma crystallisation. Entrapment conditions for fluid inclusions are 450–550 °C at 2.8–4.5 kbar. These temperatures are too high for hydrocarbon gas generation through the FT reaction. Chemical analyses of rims of Fe-rich phases suggest that they are not the result of alteration but instead represent changes in magma composition during crystallisation. Furthermore, there is no clear relationship between the presence of Fe-rich minerals and the abundance of fluid inclusion planes (FIPs) as reported elsewhere. δ13C values for methane range from − 22.4‰ to − 5.4‰, confirming a largely abiogenic origin for the gas. The presence of primary CH4-dominated fluid inclusions and melt inclusions, which contain a methane-rich gas phase, indicates a magmatic origin of the HCs. An increase in methane content, together with a decrease in δ13C isotope values towards the intrusion margin suggests that magmatically derived abiogenic hydrocarbons may have mixed with biogenic hydrocarbons derived from the surrounding country rocks. 相似文献
3.
Crustal contamination and fluid/rock interaction in the carbonatites of Fuerteventura (Canary Islands, Spain): a C, O, H isotope study 总被引:7,自引:0,他引:7
Fuerteventura—the second largest of the Canary Islands consists of Mesozoic sediments, submarine volcanic rocks, dike swarms and plutons of the Basal Complex, and younger subaerial basaltic and trachytic series. Carbonatites are found in two Basal Complex exposures: the Betancuria Massif in the central part of the island and the Esquinzo area in the north.
values of the carbonatites increase progressively from south to north of the island. This phenomenon is attributed to different degrees of assimilation of sedimentary carbonate. Homogeneous, typically magmatic
values for carbonatites which have preserved primary igneous textures and minerals suggest a well-mixed reservoir where changes in
values result from the storage of carbonate magmas at different structural levels. The magma storage allowed assimilation of sediment to varying degrees before final emplacement of carbonatites. Shifts in
towards more positive and negative values from presumed primary compositions are observed in the carbonatites. On the basis of the oxygen isotope compositions of calcite, mica and K-feldspar, and the hydrogen isotope compositions of micas, the changes in the
values of the carbonatites can be related to fluid/rock interactions. 相似文献
4.
Jordana Borini Freire Rafael M. Sousa Karla Taufner Maria TW Carneiro Henrique R Filgueiras Dominik Lenz Paulo Dias Ferreira Denise C Endringer 《Marine Ecology》2021,42(1):e12633
Certain concentration of metal may influence survival in embryonic stages, reducing the birthrate and hatching emergence. This study aimed to evaluate concentration of metal in eggs and hatchlings of Dermochelys coriacea and correlate metal concentrations in eggs with hatching and emergence success. The samples were collected at Biological Reserve Station, ES, Brazil. At the nests' opening, unhatched eggs and stillborn hatchlings were collected to survey the successful hatching and emergence of D. coriacea. The eggs shell, egg content, and dead hatchlings metal concentrations were compared to hatching and emergence success. A positive correlation was found between the concentration of copper (Cu) in the hatchlings and the success of the emergence (r2 = .28, p < .05), and a moderate positive correlation between the concentrations of iron (Fe) and barium (Ba; r2 = .44, p < .05) and success hatching. The concentrations of metals in eggs and hatchlings of D. coriacea in the Espírito Santo are below the levels that could be considered harmful to the species. In summary, there is a positive correlation between metals levels and hatching and emergence success. 相似文献
5.
Guillaume Siron Lukas Baumgartner Anne‐Sophie Bouvier Benita Putlitz Torsten Vennemann 《Geostandards and Geoanalytical Research》2017,41(2):243-253
Five new biotite reference materials were calibrated at the SwissSIMS laboratory (University of Lausanne) for oxygen isotope determination by secondary ion mass spectrometry (SIMS) and are available to the scientific community. The oxygen isotope composition of the biotites, UNIL_B1 to B5, was determined by laser‐heating fluorination to be 11.4 ± 0.11‰, 8.6 ± 0.15‰, 6.1 ± 0.04‰, 7.1 ± 0.05‰ and 7.6 ± 0.04‰, respectively. SIMS analyses on spots smaller than 20 μm gave a measurement repeatability of 0.3‰ (2 standard deviation, 2s). The matrix effect due to solid solution in natural biotite could be expressed as a linear function of XMg and XF for biotite. No effect was found for different crystallographic orientations. SIMS analysis allows the oxygen isotope composition of biotite to be measured with a measurement uncertainty of 0.3–0.4‰ (2s) for biotites with similar major element compositions. A measurement uncertainty of 0.5‰ (2s) is realistic when F poor biotites (lower than 0.2% m/m oxides) within the compositional range of XMg of 0.3–0.9 were compared from different sessions. The linear correlation with F content offers a reasonable working curve for F‐rich biotites, but additional reference materials are needed to confirm the model. 相似文献
6.
Nejib Jemmali Fouad Souissi Emmanuel John M. Carranza Torsten W. Vennemann 《Resource Geology》2013,63(1):27-41
The Pb–Zn deposit at Jebel Ghozlane, in the Nappe zone (northern Tunisia), is hosted by Triassic dolostones and Eocene limestones and is located along faults and a thrust‐sheet boundary. The sulfide mineralization of the deposit consists mainly of galena and sphalerite and occurs as vein, stockwork, breccia, dissemination and replacement ores. Three hydrothermal stages are involved in the formation of the ores: stage I is dominated by celestite‐barite, hydrothermal dolomite DII, colloform sphalerite, and galena I; stage II consist of galena II; and stage III contains calcite. Galena in the deposit yielded average 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios of 18.705, 15.667 and 38.734, respectively, suggesting a single upper crustal source reservoir for metals. Trace element data indicate the presence of Zn‐ and As‐free galena and As‐rich galena (with 0.2–0.5% As). Sphalerite contains 0.4% As, 0.7–0.9% Cd and 0.1–1.5% Fe. Microthermometric analysis of fluid inclusions in celestite shows that the deposit formed from fluids composed of heterogeneous mixtures of saline (19.5 ± 1 wt% NaCl eq.) aqueous solutions sourced from basinal brines, and gaseous CO2‐rich phases bearing low amounts of CH4, N2 and/or H2S, at temperatures of 172 ± 5°C. 相似文献
7.
A. Demény L. Dallai M.-L. Frezzotti T.W. Vennemann A. Embey-Isztin G. Dobosi G. Nagy 《Lithos》2010,117(1-4):172-182
The origin and evolution of CO2 inclusions and calcite veins in peridotite xenoliths of the Pannonian Basin, Hungary, were investigated by means of petrographic investigation and stable isotope analyses. The fluid inclusions recovered in paragenetic olivine and clinopyroxene belong to distinct populations: type A (texturally early) inclusions with regular shapes (often with negative crystal forms) forming intragranular trails; type B (texturally late) inclusions defining randomly oriented trails that reach grain boundaries. Type B inclusions are often associated with silicate melt (type C) inclusions. Stable carbon isotope compositions in inclusion-hosted CO2 were obtained by vacuum crushing followed by conventional dual inlet as well as continuous flow mass spectrometry in order to eliminate possible lab artifacts. Olivines, clino- and orthopyroxenes of the host peridotite have oxygen isotope compositions from 5.3 to 6.0‰ (relative to V-SMOW), without any relationship with xenolith texture. Some of the xenoliths contained calcite in various forms: veins and infillings in silicate globules in veins, secondary carbonate veins filling cracks and metasomatic veins with diffuse margins. The former two carbonate types have δ13C values around –13‰ (relative to V-PDB) and low Sr contents (< 0.5 wt.%), whereas the third type,veins with high-temperature metasomatic features have a δ13C value of –5.0‰ and high Sr contents up to 3.4 wt.%. In spite of the mantle-like δ13C value and the unusually high Sr content typical for mantle-derived carbonate, trace element compositions have proven a crustal origin. This observation supports the conclusions of earlier studies that the carbonate melt droplets found on peridotite xenoliths in the alkaline basalts represent mobilized sedimentary carbonate. The large δ13C range and the 12C-enrichment in the carbonates can be attributed to devolatilization of the migrating carbonate or infiltration of surficial fluids containing 12C-rich dissolved carbon.Carbon isotope compositions of inclusion-hosted CO2 range from –17.8 to –4.8‰ (relative to V-PDB) with no relation to the amount of CO2 released by vacuum crushing. Low-δ13C values measured by stepwise heating under vacuum suggest that the carbon component is pristine and not related to surficial contamination, and that primary mantle fluids with δ13C values around –5‰ were at least partly preserved in the xenoliths. Tectonic reworking and heating by the basaltic magma resulted in partial CO2 release and local 13C-depletion. 相似文献
8.
Boron and Oxygen Isotope Composition of Certified Reference Materials NIST SRM 610/612 and Reference Materials JB-2 and JR-2 总被引:1,自引:0,他引:1
Simone Kasemann Anette Meixner Alexander Rocholl Torsten Vennemann Martin Rosner Axel K. Schmitt Michael Wiedenbeck 《Geostandards and Geoanalytical Research》2001,25(2-3):405-416
We present data on the concentration, the isotope composition and the homogeneity of boron in NIST silicate glass reference materials SRM 610 and SRM 612, and in powders and glasses of geological reference materials JB-2 (basalt) and JR-2 (rhyolite). Our data are intended to serve as references for both microanalytical and wet-chemical techniques. The δ11 B compositions determined by N-TIMS and P-TIMS agree within 0.5% and compare with SIMS data within 2.5%. SIMS profiles demonstrate boron isotope homogeneity to better than δ11 B = 2% for both NIST glasses, however a slight boron depletion was detected towards the outermost 200 μm of the rim of each sample wafer. The boron isotope compositions of SRM 610 and SRM 612 were indistinguishable. Glasses produced in this study by fusing JB-2 and JR-2 powder also showed good boron isotope homogeneity, both within and between different glass fragments. Their major element abundance as well as boron isotope compositions and concentrations were identical to those of the starting composition. Hence, reference materials (glasses) for the in situ measurement of boron isotopes can be produced from already well-studied volcanic samples without significant isotope fractionation. Oxygen isotope ratios, both within and between wafers, of NIST reference glasses SRM 610 and SRM 612 are uniform. In contrast to boron, significant differences in oxygen isotope compositions were found between the two glasses, which may be due to the different amounts of trace element oxides added at ten-fold different concentration levels to the silicate matrix. 相似文献
9.
The gold mineralization of the Hutti Mine is hosted by nine parallel, N–S trending, steeply dipping, 2–10 m wide shear zones, that transect Archaean amphibolites. The shear zones were formed after peak metamorphism during retrograde ductile D2 shearing in the lower amphibolite facies. They were reactivated in the lower to mid greenschist facies by brittle–ductile D3 shearing and intense quartz veining. The development of a S2–S3 crenulation cleavage facilitates the discrimination between the two deformation events and contemporaneous alteration and gold mineralization. Ductile D2 shearing is associated with a pervasively developed distal chlorite–sericite alteration assemblage in the outer parts of the shear zones and the proximal biotite–plagioclase alteration in the center of the shear zones. D3 is characterized by development of the inner chlorite-K-feldspar alteration, which forms a centimeter-scale alteration halo surrounding the laminated quartz veins and replaces earlier biotite along S3. The average size of the laminated vein systems is 30–50 m along strike as well as down-dip and 2–6 m in width.Mass balance calculations suggest strong metasomatic changes for the proximal biotite–plagioclase alteration yielding mass and volume increase of ca. 16% and 12%, respectively. The calculated mass and volume changes of the distal chlorite–sericite alteration (ca. 11%, ca. 8%) are lower. The decrease in δ18O values of the whole rock from around 7.5‰ for the host rocks to 6–7‰ for the distal chlorite–sericite and the proximal biotite–plagioclase alteration and around 5‰ for the inner chlorite-K-feldspar alteration suggests hydrothermal alteration during two-stage deformation and fluid flow.The ductile D2 deformation in the lower amphibolite facies has provided grain scale porosities by microfracturing. The pervasive, steady-state fluid flow resulted in a disseminated style of gold–sulfide mineralization and a penetrative alteration of the host rocks. Alternating ductile and brittle D3 deformation during lower to mid greenschist facies conditions followed the fault-valve process. Ductile creep in the shear zones resulted in a low permeability environment leading to fluid pressure build-up. Strongly episodic fluid advection and mass transfer was controlled by repeated seismic fracturing during the formation of laminated quartz(-gold) veins. The limitation of quartz veins to the extent of earlier shear zones indicate the importance of pre-existing anisotropies for fault-valve action and economic gold mineralization. 相似文献
10.
S. N. Feldstein Rebecca A. Lange Torsten Vennemann James R. O'Neil 《Contributions to Mineralogy and Petrology》1996,126(1-2):51-66
Complete chemical analyses, including ferric and ferrous iron, H2O contents and δD values for 16 phlogopite and biotite and 2 hornblende separates are presented. Samples were obtained from
volcanic rocks from four localities: (1) phlogopite phenocrysts from minette lavas from the western Mexico continental arc,
(2) biotite and hornblende phenocrysts from andesite lavas from Mono Basin, California, (3) phlogopite and biotite from clinopyroxenite
nodules entrained in potassic lavas from the East African Rift, Uganda, and (4) phlogopite phenocrysts from a wyomingite lava
in the Leucite Hills, Wyoming. The Fe2O3 contents in the micas range from 0.8 to 10.5 wt%, corresponding to 0.09 to 1.15 Fe3+ per formula unit (pfu). Water contents vary from 1.6 to 3.0 wt%, corresponding to 1.58 to 3.04 OH pfu, significantly less
than would be expected for a site fully occupied by hydroxyl. Cation- and anion-based normalization procedures provide accurate
mineral formulae with respect to most cations and anions, but are unable to generate accurate estimates of Fe3+/FeT, and overestimate OH at the expense of O on the hydroxyl site. These inaccuracies are present despite acceptable adjusted
totals and stoichiometric calculated site occupancies. The phlogopite and biotite phenocrysts in arc-related lavas from western
Mexico and eastern California have the highest Fe3+/FeT ratios (56–87%), reflecting high magmatic oxygen fugacities (ΔNNO = +2 to +5), in contrast to those from Uganda (25–40%)
and the Leucite Hills (23%). There is no correlation between the OH content and the Fe3+/FeT ratio in the micas. Values of KMg/Fe2+D (± 2σ errors) were calculated for three phlogopite-olivine pairs (0.12 ± 0.12, 0.26 ± 0.14, 0.09 ± 0.12), two biotite-hornblende
pairs (0.73 ± 0.08 and 1.22 ± 0.10) and a single phlogopite-augite pair (1.15 ± 0.12). Values of KF/OHD for two biotite and
hornblende pairs could not be determined without significant error because of the extremely low F contents (< 0.2 wt%) of
the four phases. The δD values obtained in this study encompass a large range (−137 to −43‰). The phlogopite and biotite separates
from Uganda have δD values of −70 to −49‰, which overlap those believed to represent “primary” mantle. There is a larger range
in δD values (−137 to −43‰) for phlogopite phenocrysts from western Mexico minette lavas, although their range in δ18O values (5.2–6.2‰) is consistent with “normal” mantle. It is unlikely, therefore, that the variable δD values reflect heterogeneity
in the mantle source region of the minette magmas. Nor can the extremely low δD values reflect degassing of H2 or H2O since almost 100% loss of dissolved water in the magma is required, an unrealistic scenario given the stability of the hydrous
phenocrysts. The very low δD values of the Mascota minette phlogopites require that the hydrogen be introduced from an external
source (e.g., meteoric water). Whatever the process responsible for the observed hydrogen isotope composition, it had no effect
on the δ18O value, f
O
2, a
H
2O or bulk composition of the host magmas.
Received: 5 January 1995 / Accepted: 19 March 1996 相似文献