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951.
Simon Nina S. C.; Carlson Richard W.; Pearson D. Graham; Davies Gareth R. 《Journal of Petrology》2007,48(3):589-625
A detailed petrological and geochemical study of low-temperatureperidotite xenoliths from Kimberley and northern Lesotho ispresented to constrain the processes that led to the magmaphileelement depletion of the Kaapvaal cratonic lithospheric mantleand its subsequent re-enrichment in Si and incompatible traceelements. Whole-rocks and minerals have been characterized forReOs isotope compositions, and major and trace elementconcentrations, and garnet and clinopyroxene for LuHfand SmNd isotope compositions. Most samples are characterizedby Archaean Os model ages, low Al, Fe and Ca contents, highMg/Fe, low Re/Os, very low (< 0·1 x chondrite) heavyrare earth element (HREE) concentrations and a decoupling betweenNd and Hf isotope ratios. These features are most consistentwith initial melting at 3·2 Ga followed by metasomatismby hydrous fluids, which may have also caused additional meltingto produce a harzburgitic residue. The low HREE abundances ofthe peridotites require that extensive melting occurred in thespinel stability field, possibly preceded by some melting inthe presence of garnet. Fractional melting models suggest that30% melting in the spinel field or 20% melting in the garnetfield followed by 20% spinel-facies melting are required toexplain the most melt-depleted samples. Garnet NdHf isotopecharacteristics indicate metasomatic trace element enrichmentduring the Archaean. We therefore suggest a model includingshallow ridge melting, followed by metasomatism of the Kaapvaalupper mantle in subduction zones surrounding cratonic nuclei,probably during amalgamation of smaller pre-existing terranesin the Late Archaean (2·9 Ga). The fluid-metasomatizedresidua have subsequently undergone localized silicate meltinfiltration that led to clinopyroxene ± garnet enrichment.Calculated equilibrium liquids for clinopyroxene and their HfNdisotope compositions suggest that most diopside in the xenolithscrystallized from an infiltrating kimberlite-like melt, eitherduring Group II kimberlite magmatism at 200110 Ma (Kimberley),or shortly prior to eruption of the host kimberlite around 90Ma (northern Lesotho). KEY WORDS: Kaapvaal craton; lithospheric mantle; metasomatism; NdHf isotopes; ReOs isotopes 相似文献
952.
Nitrogen loading to aquatic ecosystems from sewage is recognised worldwide as a growing problem. The use of nitrogen stable isotopes as a means of discerning sewage nitrogen in the environment has been used annually by the Ecosystem Health Monitoring Program in Moreton Bay (Australia) since 1997 when the technique was first developed. This ("sewage plume mapping") technique, which measures the delta(15)N isotopic signature of the red macroalga Catenella nipae after incubation in situ, has demonstrated a large reduction in the magnitude and spatial extent of sewage nitrogen within Moreton Bay over the past 5 years. This observed reduction coincides with considerable upgrades to the nitrogen removal efficacy at several sewage treatment plants within the region. This paper describes the observed changes and evaluates whether they can be attributed to the treatment upgrades. 相似文献
953.
Maxim Voronkov Andrej Sobolev Simon Ellingsen Andrei Ostrovskii Alexei Alakoz 《Astrophysics and Space Science》2005,295(1-2):217-223
We report the detection with the ATCA of 6.7 GHz methanol emission towards OMC-1. The source has a size between 40 and 90, is located to the south-east of Ori-KL and may coincide in position with the 25 GHz masers. The source may be an example of an interesting case recently predicted in theory where the transitions of traditionally different methanol maser classes show maser activity simultaneously. In addition, results of recent search for methanol masers from the 25 and 104.3 GHz transitions are reported. 相似文献
954.
Frank?McDermottEmail author Francisco?G.?Delfin?Jr. Marc?J.?Defant Simon?Turner Rene?Maury 《Contributions to Mineralogy and Petrology》2005,150(6):652-670
Pliocene to recent volcanic rocks from the Bulusan volcanic complex in the southern part of the Bicol arc (Philippines) exhibit
a wide compositional range (medium- to high-K basaltic-andesites, andesites and a dacite/rhyolite suite), but are characterised
by large ion lithophile element enrichments and HFS element depletions typical of subduction-related rocks. Field, petrographic
and geochemical data indicate that the more silicic syn- and post-caldera magmas have been influenced by intracrustal processes
such as magma mixing and fractional crystallisation. However, the available data indicate that the Bicol rocks as a group
exhibit relatively lower and less variable 87Sr/86Sr ratios (0.7036–0.7039) compared with many of the other subduction-related volcanics from the Philippine archipelago. The
Pb isotope ratios of the Bicol volcanics appear to be unlike those of other Philippine arc segments. They typically plot within
and below the data field for the Philippine Sea Basin on 207Pb/204Pb versus 206Pb/204Pb and 208Pb/204Pb versus 206Pb/204Pb diagrams, implying a pre-subduction mantle wedge similar to that sampled by the Palau Kyushu Ridge, east of the Philippine
Trench. 143Nd/144Nd ratios are moderately variable (0.51285–0.51300). Low silica (<55 wt%) samples that have lower 143Nd/144Nd tend to have high Th/Nd, high Th/Nb, and moderately low Ce/Ce* ratios. Unlike some other arc segments in the Philippines
(e.g. the Babuyan-Taiwan segment), there is little evidence for the involvement of subducted terrigenous sediment. Instead,
the moderately low 143Nd/144Nd ratios in some of the Bicol volcanics may result from subduction of pelagic sediment (low Ce/Ce*, high Th/Nd, and high
Th/Nb) and its incorporation into the mantle wedge via a slab-derived partial melt. 相似文献
955.
An integrated microtextural and chemical approach to zircon geochronology: refining the Archaean history of the Napier Complex,east Antarctica 总被引:9,自引:5,他引:4
Nigel?M.?KellyEmail author Simon?L.?Harley 《Contributions to Mineralogy and Petrology》2005,149(1):57-84
Integrated textural and chemical characterisation of zircon is used to refine the U–Pb geochronology of the Archaean, ultra-high temperature Napier Complex, east Antarctica. Scanning electron microscope characterisation of zircon and the rare earth element compositions of zircon, garnet and orthopyroxene are integrated to place zircon growth in an assemblage context, thereby providing tighter constraints on the timing of magmatic and metamorphic events. Data indicate that magmatism occurred in the central and northern Napier Complex at ca. 2,990 Ma. A regional, relatively low-pressure metamorphic event occurred at ca. 2,850–2,840 Ma. Mineral REE data from garnet-bearing orthogneiss indicate that ca. 2,490–2,485 Ma U–Pb zircon ages provide an absolute minimum age for the ultrahigh temperature (UHT) foliation preserved in this rock. Internal zircon zoning relationships and estimated zircon-garnet DREE values from paragneiss suggest that an absolute minimum age of ultra-high temperature metamorphism is ca. 2,510 Ma, but that it is more likely to be older than ca. 2,545 Ma. We suggest that the high proportion of published zircon U–Pb data with ages between ca. 2,490–2,450 Ma reflects late, post-peak zircon growth and does not date the timing of peak UHT metamorphism.Electronic Supplementary Material Supplementary material is available for this article at 相似文献
956.
A total of seven lithic clasts from the polymict eucrites ALHA76005 and ALHA77302 have been studied petrographically and analyzed with the electron microprobe. All clasts are composed predominantly of pyroxene and plagioclase, ± ilmenite, troilite, Fe-Ni metal, mesostasis, and silica. Pyroxene compositions in unequilibrated clasts and clast bulk compositions, calculated by modal recombination, indicate that the clasts originally crystallized under similar conditions and that they may be genetically related to each other by fractionation of pigeonite and plagioclase. 相似文献
957.
Little is known about the spatial and temporal distribution of blast fishing which hampers enforcement against this activity. We have demonstrated that a triangular array of hydrophones 1 m apart is capable of detecting blast events whilst effectively rejecting other sources of underwater noise such as snapping shrimp and nearby boat propellers. A total of 13 blasts were recorded in Sepangor bay, North of Kota Kinabalu, Sabah, Malaysia from 7th to 15th July 2002 at distances estimated to be up to 20 km, with a directional uncertainty of 0.2 degrees . With such precision, a network of similar hydrophone arrays has potential to locate individual blast events by triangulation to within 30 m at a range of 10 km. 相似文献
958.
A.?K.?SchmittEmail author J.?I.?Simon 《Contributions to Mineralogy and Petrology》2004,146(5):653-605
In this paper, we present boron isotope analyses of variably degassed rhyolitic glasses from Long Valley, California. The following results indicate that pre-eruptive boron isotopic signatures were preserved in degassed glasses: (1) averaged secondary ionization mass spectrometry (SIMS) measurements of H2O-rich (~3 wt%) melt inclusions from late erupted Bishop Tuff pumice are indistinguishable from positive thermal ionization mass spectrometry (PTIMS) analysis of vesiculated groundmass glass (11B=+5.0±0.9 and +5.4±5, respectively); (2) SIMS spot-analyses on H2O-poor obsidian (~0.15 wt% H2O) from younger Glass Mountain Dome YA (average 11B=+5.2±1.0) overlap with compositionally similar late Bishop Tuff melt inclusions; and (3) four variably degassed obsidian samples from the 0.6 ka Mono Craters (H2O between 0.74 and 0.10 wt%) are homogeneous with regard to boron (average 11B=+3.2±0.8, MSWD=0.4). Insignificant variations in 11B between early and late Bishop Tuff melt inclusion glasses agree with published experimental data that predict minor 11B depletion in hydrous melts undergoing gas-saturated fractional crystallization. Melt inclusions from two crystal-rich post-caldera lavas (Deer Mountain and South Deadman Dome) are comparatively boron-rich (max. 90 ppm B) and have lower 11B values (average 11B=+2.2±0.8 and –0.4±1.0 ) that are in strong contrast to the boron isotopic composition of post-caldera crystal-poor rhyolites (27 ppm B; 11B=+5.7±0.8). These variations in 11B are too large to be caused by pre-eruptive degassing. Instead, we favor assimilation of 11B depleted low-temperature hydrothermally altered intrusive rocks subsequent to fresh rhyolite recharge.Editorial responsibility: J. HoefsAn erratum to this article can be found at 相似文献
959.
Fluid-controlled quartz recovery in granulite as revealed by cathodoluminescence and trace element analysis (Bamble sector,Norway) 总被引:1,自引:0,他引:1
Alfons?M.?van den KerkhofEmail author Andreas?Kronz Klaus?Simon Torsten?Scherer 《Contributions to Mineralogy and Petrology》2004,146(5):637-652
Dispersed quartz veinlets in Proterozoic enderbitic charnockite from Tromøy, Bamble sector (southern Norway), with Ti-concentrations of mostly 80–180 ppm, produce bright blue cathodoluminescence (CL), against contrasting micro-textures of secondary pure quartz with low CL intensity. The textures comprise grain boundary alteration, healed micro-fractures, patches of secondary quartz, and euhedral quartz nuclei. The secondary quartz locally makes up 50% of the total quartz. Trace element analysis has been done by electron-probe micro-analysis (EPMA), laser-induced coupled plasma mass spectrometry (LA-ICPMS), and additional electron-paramagnetic resonance (EPR) spectroscopy. These studies testify systematic trace element reduction and extensive quartz recovery during retrograde metamorphism. We assume healing of a part of the aqueous fluid inclusions during a late thermal event, possible correlated with Paleozoic magmatic activity in the Oslo-Rift. During final cooling, aqueous fluids were largely retrapped in patches of secondary quartz associated with healed fractures, whereas carbonic inclusions (without secondary quartz) may have survived retrograde metamorphism. The variable but generally high salinity of fluid inclusions is assumed to be in part the result of quartz recovery by which ion concentrations were increased in the percentage range.Editorial Responsibility: J. Touret 相似文献
960.
Active regions were followed across the disk on OSO 4 spectroheliograms in the Lyman continuum (LC) and in Mg x 625. These observations indicate differential rotation with latitude, but not with height in the atmosphere. The measured equatorial sidereal rotation velocity is 14.7° ±0.2° per day in both chromospheric LC and coronal Mg x, where the quoted error is the standard deviation of a least-squares fit to the data. 相似文献