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791.
Rainer?ThomasEmail author Hans-Jürgen?F?rster Karen?Rickers James?D.?Webster 《Contributions to Mineralogy and Petrology》2005,148(5):582-601
Quartz crystals from topaz–zinnwaldite–albite granites from Zinnwald (Erzgebirge, Germany) contain, in addition to primary and secondary fluid inclusions (FIs), abundant crystalline silicate-melt inclusions (MIs) with diameters up to 200 m. These MIs represent various stages of evolution of a highly evolved melt system that finally gave rise to granite-related Sn–W mineralization. The combination of special experimental techniques with confocal laser Raman-microprobe spectroscopy and EMPA permits precise measurement of elevated contents of H2O, F, and B in re-homogenized MIs. The contents of H2O and F were observed to increase from 3 to 30 and 1.9 to 6.4 wt%, respectively, during magma differentiation. However, there is a second MI group, very rich in H2O, with values up to 55 wt% H2O and an F concentration of approximately 3 wt%. Ongoing enrichment of volatiles H2O, F, B, and Cl and of Cs and Rb can be explained in terms of magma differentiation triggered by fractional crystallization and thus, is suggested to reflect elemental abundances in natural magmas, and not boundary-layer melts. Partitioning between melt and cogenetic fluids has further modified the magmatic concentrations of some elements, particularly Sn. The coexistence of two types of MIs with primary FIs indicates fluid saturation early in the history of magma crystallization, connected with a continuous sequestration of Sn, F, and B. The results of this study provide additional evidence for the extraordinary importance of the interplay of H2O, F, and B in the enrichment of Sn during magma differentiation by decreasing the viscosity of and increasing the diffusivity in the melts as well as by the formation of various stable fluoride complexes in the melt and coexisting fluid.
相似文献
Rainer ThomasEmail: Phone: +49-331-2881474 |
792.
Philip M. Scotney Stephen Roberts Richard J. Herrington Adrian J. Boyce Ray Burgess 《Mineralium Deposita》2005,40(1):76-99
Wetar Island is composed of Neogene volcanic rocks and minor oceanic sediments and forms part of the Inner Banda Arc. The island preserves precious metal-rich volcanogenic massive sulfide and barite deposits, which produced approximately 17 metric tonnes of gold. The polymetallic massive sulfides are dominantly pyrite (locally arsenian), with minor chalcopyrite which are cut by late fractures infilled with covellite, chalcocite, tennantite–tetrahedrite, enargite, bornite and Fe-poor sphalerite. Barite orebodies are developed on the flanks and locally overly the massive sulfides. These orebodies comprise friable barite and minor sulfides, cemented by a series of complex arsenates, oxides, hydroxides and sulfate, with gold present as <10 m free grains. Linear and pipe-like structures comprising barite and iron-oxides beneath the barite deposits are interpreted as feeder structures to the barite mineralization. Hydrothermal alteration around the orebodies is zoned and dominated by illite–kaolinite–smectite assemblages; however, local alunite and pyrophyllite are indicative of late acidic, oxidizing hydrothermal fluids proximal to mineralization. Altered footwall volcanic rocks give an illite K–Ar age of 4.7±0.16 Ma and a 40Ar/39Ar age of 4.93±0.21 Ma. Fluid inclusion data suggest that hydrothermal fluid temperatures were around 250–270°C, showed no evidence of boiling, with a mean salinity of 3.2 wt% equivalent NaCl. The 34S composition of sulfides ranges between +3.3 and +11.7 and suggests a significant contribution of sulfur from the underlying volcanic edifice. The 34S barite data vary between +22.4 and +31.0, close to Miocene seawater sulfate. Whole rock 87Sr/86Sr analyses of unaltered volcanic rocks (0.70748–0.71106) reflect contributions from subducted continental material in their source region. The 87Sr/86Sr barite data (0.7076–0.7088) indicate a dominant Miocene seawater component to the hydrothermal system. The mineral deposits formed on the flanks of a volcanic edifice at depths of ~2 km. Spectacular sulfide mounds showing talus textures are localized onto faults, which provided the main pathways for high-temperature hydrothermal fluids and the development of associated stockworks. The orebodies were covered and preserved by post-mineralization chert, gypsum, Globigerina-bearing limestone, lahars, subaqueous debris flows and pyroclastics rocks. 相似文献
793.
TBT contamination identified in Antarctic marine sediments 总被引:2,自引:0,他引:2
Negri AP Hales LT Battershill C Wolff C Webster NS 《Marine pollution bulletin》2004,48(11-12):1142-1144
We report for the first time butyltin contamination of near-shore sediments at six sites in the Ross Sea, Antarctica. A very high concentration of 2290 microg Sn kg(-1) sediment was recorded in one sample. The most likely source is abrasion of antifouling paint from the hulls of ice-breakers, but this pattern of contamination is also possible following ship groundings. Antifoulant biocides, such as TBT, have not been considered or detected in Antarctica previously and represent a new challenge to environmental managers and custodians. 相似文献
794.
Nicolas Deichmann Manfred Baer Jochen Braunmiller Cécile Cornou Donat Fäh Domenico Giardini Monika Gisler Sarah Huber Stephan Husen Philipp Kästli Urs Kradolfer Martin Mai Silvio Maraini Ivo Oprsal Thomas Schler Danijel Schorlemmer Stefan Wiemer Jochen Wössner Adrian Wyss 《Eclogae Geologicae Helvetiae》2004,97(3):447-458
795.
Adrian J. Brearley Ignacio Casanova Mark L. Miller Klaus Keil 《Meteoritics & planetary science》1991,26(4):287-300
Abstract— During a petrological study of the previously unclassified ordinary chondrite Los Martínez, we discovered a highly unusual Cr-rich inclusion which we believe is unique in both extraterrestrial and terrestrial mineralogy. The inclusion is highly zoned both compositionally and optically, with a Ca-Al rich, cloudy core and an opaque, Cr-Na-rich rim (up to 24 wt.% Cr2O3). Detailed SEM and TEM studies show that the inclusion now consists of a highly zoned, single crystal of plagioclase intergrown with chromium-rich spinel. The spinel has a well-developed crystallographic orientation relationship with the host plagioclase, which indicates that it is the product of exsolution. Although superficially similar to a plagioclase feldspar in composition, in detail the inclusion is Si-deficient and Al-enriched relative to a stoichiometric feldspar. We have not been able to identify a viable precursor mineral phase to the plagioclase-chromite intergrowth and suggest that it may be an unknown metastable phase. The Cr-rich precursors of the inclusion probably have close affinities to the chromite-plagioclase chondrules observed by Ramdohr (1967) in several ordinary chondrites. Based on the zoning in the inclusion, we suggest that it is the product of fractional crystallization from a melt, which may have formed as a liquid condensate, or by melting of solid condensates, in the solar nebula. Subsequent cooling of this melt condensate resulted in crystallization of the, as yet, unidentified phase. After crystallization, the inclusion was probably incorporated into a parent body where it underwent metamorphism and was probably shocked to some degree. During this period of parent body metamorphism, exsolution and decomposition of the unknown precursor occurred to produce the observed intergrowth of plagioclase and chromite. Finally, we have classified Los Martínez as an L6 ordinary chondrite breccia. 相似文献
796.
Emission (2 cm) from 15 Eunomia was detected on March 27, 1983, using the VLA. At this time, 15 Eunomia was 2.0 AU distant from Earth. A flux density of 687 ± 70 μJy was measured at 14.96 GHz (50-MHz bandwidth). If 246 km is adopted for the diameter, a disk temperature of184 ± 20°K results. This is consistent with a rapidly rotating, black sphere with 15 Eunomia's diameter and distance (171°K). 相似文献
797.
Adrian Gilli Flavio S. Anselmetti Daniel Ariztegui J. Platt Bradbury Kerry R. Kelts Vera Markgraf & Judith A. McKenzie 《地学学报》2001,13(6):443-448
Lake sediments from a closed basin in southern Patagonia (Argentina) provide a continental archive with which to reconstruct climate change and to test the interhemispheric synchroneity of abrupt events. High-resolution sub-bottom seismic profiles of Lago Cardiel indicate substantial lake-level changes since the late Pleistocene, which were identified and dated in a series of long piston cores. These data allow the reconstruction of the regional water balance at 49=" PSFT − BC "202S since the late glacial. The seismic stratigraphy reveals a dry late glacial climate with a desiccation of the basin around 11 220 yr BP (14 C). Lake level rapidly increased by 135 m at the Holocene transition. Following the early Holocene highstand at + 55 m, lake level never dropped significantly below modern level. The palaeoclimate changes implied by the Lago Cardiel record are out-of-phase with those implied by records from tropical South America and demonstrate considerable latitudinal asynchroneity in the climate evolution of this continent. 相似文献
798.
Ocean noise is characterized by both temporal and spectral properties. Time-domain statistics are often non-Gaussian, and spectra are typically non-white. Both attributes can be simulated at the same time by applying a spectral shaping filter to random numbers having a specified kurtosis. A method for generating random numbers with arbitrary kurtosis is presented 相似文献
799.
R. Howard J. M. Adkins J. E. Boyden T. A. Cragg T. S. Gregory B. J. Labonte S. P. Padilla L. Webster 《Solar physics》1983,83(2):321-338
We publish here rotation results from Doppler velocity measurements made at Mount Wilson over a period of more than 14 years. Altogether data from 188 rotations are presented. These results are displayed in various tables and figures. Measurements of scattered light along with its effect on the measured rotation rate are shown. 相似文献
800.