GEOCHEMICAL JOURNAL
Online ISSN : 1880-5973
Print ISSN : 0016-7002
ISSN-L : 0016-7002
Volume 41 , Issue 5
Showing 1-7 articles out of 7 articles from the selected issue
  • JU-CHIN CHEN, C. Y. LO, Y. T. LEE, S. W. HUANG, P. C. CHOU, H. S. YU, ...
    2007 Volume 41 Issue 5 Pages 303-321
    Published: October 20, 2007
    Released: October 23, 2010
    JOURNAL FREE ACCESS
    The cored sediments sampled by R/V Marion Dufrense are mostly muds consisting mainly of quartz, feldspar, illite, chlorite + kaolinite and calcite. Authigenic carbonates mainly composed of aragonite, calcite, dolomite and associated with Fe-montmorillonite and pyrite occur in core samples collected from station MD-052911 (22°15.6'N, 119°51.0'E) at 2137-2140 cm and 2237-2240 cm depth which may be formed via sulfate reduction by CH4. In general Illite/Quartz intensity ratios of the sediments show little variation with core depth indicating the relatively constant abundance of illite in the source rock on Taiwan. The cored sediments have higher average Al2O3, ΣFeO and MgO but lower SiO2, Na2O, and CaO contents when compared with upper continental crust (UCC). High field strength elements (Zr, Hf, Y, Nb and Ta) are also depleted in the cored sediments. CaO, Sr, Mn and Pb in the core samples collected from station MD-052912 (22°21.5'N, 119°48.5'E) tend to decrease with depth which may be essentially related to the decrease of biogenic CaCO3 with core depth. The La/Th, La/Sc, Th/Sc ratios of the cored sediments are similar to those of UCC, however the (La/Yb)N ratios of the cored sediments are higher. The cored sediments display similar REE patterns with LREE enrichment and negative Eu anomaly reflecting a felsic nature of the source rock which can also be identified in the La-Th-Sc plot. The chemistry of the sediments can be deduced using a mixing model involved four end members i.e., shale, greywacke, quartzite and limestone.
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  • KHAN M. G. MOSTOFA, TAKAHITO YOSHIOKA, EIICHI KONOHIRA, EIICHIRO TANOU ...
    2007 Volume 41 Issue 5 Pages 323-331
    Published: October 20, 2007
    Released: October 23, 2010
    JOURNAL FREE ACCESS
    Photodegradation of dissolved organic matter (DOM), collected from two upstream and one downstream sites in the Lake Biwa watershed in Japan, was investigated using fluorescence properties of three-dimensional excitation emission matrix (3-D EEM). Solar irradiation caused a decrease in the dissolved organic carbon (DOC) concentration and in the fluorescence peak intensity (FI) of fulvic acid (FA)- and protein-like substances in DOM. Mineralization of DOC during an irradiation period (13 days) was observed to be higher in upstream samples (32-36%) compared to that in downstream sample (16%). DOC concentration in samples stored in the dark significantly decreased in the downstream sample (16%), while those in upstream samples hardly decreased (1-8%). The FI of FA-like substance decreased by 72-84% during 13-days irradiation (integrated solar intensity = 176 MJ m-2). The protein-like fluorescence was only observed in the downstream sample and the net decrease in the FI was 59% in the irradiated sample. The first-order reaction kinetics was applied to analyze the photodegradation of DOM. Two-step photodegradation was suggested for the fluorescent DOM (FDOM), while not for the DOC. Results obtained here suggested that FA-like FDOM is more susceptible to photodegradation compared with those of protein-like substances and DOC.
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  • SABER AL-ROUSAN, THOMAS FELIS, RIYAD MANASRAH, FUAD AL-HORANI
    2007 Volume 41 Issue 5 Pages 333-340
    Published: October 20, 2007
    Released: October 23, 2010
    JOURNAL FREE ACCESS
    An 18-year (1988-2005) stable oxygen isotopic composition (δ18O) of two coral colonies (Porites lutea and P. lobata) from two different sites in the northern end of the Gulf of Aqaba (Red Sea) successfully records the seasonal variability in sea surface temperature (SST). The mean annual SST record from the study sites ranges between 21.18°C to 26.32°C (1988-2005), whereas seawater salinity is close to 40.55 with annual variation less than 0.26 (1997-2005). Coral δ18O records from both corals showed consistent seasonal patterns of variations closely tracking the measured SST, with correlation coefficient (R2) of -0.67 to 0.72 at a monthly time scale. Results showed that the slopes of the δ18O-SST relation from both corals are similar (averaged 0.191‰/°C) and close to those reported earlier for Porites corals from other regions. The seasonal variations of coral δ18O (0.85-0.88‰) reveals 92-95% of the seasonal SST cycle indicating that large majority of the variations in coral δ18O data can be explained by variations in the SST, and only a small fraction (neglected) can be attributed to δ18O variations of seawater. Results from this study also indicates that splicing of isotopic transects in a single colony have no effect on its isotopic composition.
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  • YUPING SU, HONGFENG TANG, PAUL J. SYLVESTER, CONGQIANG LIU, WENJUN QU, ...
    2007 Volume 41 Issue 5 Pages 341-357
    Published: October 20, 2007
    Released: October 23, 2010
    JOURNAL FREE ACCESS
    Several types of granites including alkaline granites and alkali feldspar granites are distributed in the Karamaili tectonic belt of East Junggar, Xinjiang, China. Some medium-small tin deposits are located within or near the contact zones of the granitic intrusions. The alkaline granites share all the features commonly observed in peralkaline A-type granites. They contain alkalic mafic minerals such as riebeckite and aegirine; have high contents of SiO2, alkalis, Rb, Th, Zr, Hf, REE (except Eu), and high ratios of FeO*/MgO and Ga/Al; and show strong depletions in Ba, Sr, Eu in the spidergrams. Laser ablation-ICPMS U-Pb zircon geochronology indicates a crystallization age of ca. 305 Ma for the granites; TIMS analyses of the granites found high εNd(T) values of +5.9 to +6.5. Considering their geochemical features, alkaline granites most likely formed by fractional crystallization of granodioritic magmas, which were probably produced by partial melting of lower crustal basaltic to andesitic rocks formed from oceanic crustal materials that were deeply buried during late Paleozoic subduction and accretion. Six molybdenite samples from the Sareshike tin deposit in East Junggar yielded an isochron age of 307 ± 11 Ma (2σ) and a weighted mean model age of 306.5 ± 3.4 Ma, consistent with zircon U-Pb ages of the alkaline granites. Low Re contents (0.323-0.961 ppm) in the molybdenite suggest that they originated from crustal sources related to the alkaline granites. Considering their identical ages, close spatial distribution, and similar sources, we argue that the A-type granites have a genetic relationship with the tin mineralization, and that the same association may be important elsewhere.
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  • SHILIN LIU, GE LIN, YUNHUA LIU, YE ZHOU, FAXIONG GONG, YI YAN
    2007 Volume 41 Issue 5 Pages 359-378
    Published: October 20, 2007
    Released: October 23, 2010
    JOURNAL FREE ACCESS
    Petrographic and geochemical compositions of thirty-seven Middle Oligocene-Pliocene sandstone samples from the Nanpu Sag in Bohai Bay Basin were analyzed to evaluate their provenance, weathering, and tectonic setting. These sandstones comprise mainly arkoses and lithic arenites and a few graywackes, characterized by low to moderate quartz/total feldspar ratios (1.31-6.11, average 2.72 ± 0.98) and CIA values (45.87-70.13, 57.49 ± 5.93). The Middle-Upper Oligocene sandstones have average lower SiO2 (71.72 ± 5.16%), and higher Fe2O3 (3.06 ± 1.26%) and MgO (1.65 ± 0.39%), in contrast with the Miocene samples that generally have high SiO2 (76.46 ± 4.26%) and low Fe2O3 (3.04 ± 1.51%) and MgO (0.69 ± 0.32%) contents. Following the deposition, Fe2O3 (3.17 ± 1.00%) and MgO (1.07 ± 0.38%) contents increased again in the Pliocene samples. Such a compositional variation trend is interpreted as a change of tectonic activity in the sag from Middle Oligocene to Pliocene, i.e., stronger in the Middle Oligocene, weaker in the Miocene and to stronger again in the Pliocene. Qt-F-L plot, trace element provenance discrimination diagrams (e.g., Eu/Eu*, Co/Th, and La/Sc), and REE characteristics suggest that the source rocks were mainly derived from felsic igneous rocks, possibly from Mesozoic granitoids and felsic volcanic lavas in the Yanshan Fold Belt. Tectonic discrimination diagrams (e.g., SiO2-K2O/Na2O, Fe2O3* + MgO-TiO2, and Th-Sc-Zr/10) show that these sandstones were mainly deposited in an active continental margin setting, implying a remobilized intra-continental environment.
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  • Ö. TUNUSOGLU, T. SHAHWAN, A. E. EROGLU
    2007 Volume 41 Issue 5 Pages 379-389
    Published: October 20, 2007
    Released: October 23, 2010
    JOURNAL FREE ACCESS
    The uptake of aqueous Ba2+ ions by abiogenic calcite and aragonite was studied over a wide range of concentration; 1.0 × 101, 5.0 × 101, 1.0 × 102, 5.0 × 102, 1.0 × 103, 5.0 × 103, and 1.0 × 104 mg/L. The uptake process was characterized using ICP-AES, XRPD, SEM/EDS, and FTIR techniques. Up to the initial concentration of 5.0 × 102 mg/L, the uptake of Ba2+ ions was fast and obeyed Lagergren's kinetic model. The equilibrium data were adequately described using Freundlich isotherm model. The overgrowth of BaCO3 (witherite) took place at higher concentrations, in a kinetically slow process and enhanced the uptake of Ba2+ ions. Quantitative XRPD was used to evaluate the fractions of precipitated BaCO3 on calcite and aragonite minerals and monitor their variation with time. At all the studied concentrations, aragonite showed higher removal capacity of Ba2+ and faster uptake kinetics than did calcite. The precipitated crystals appeared to predominantly possess olivary-like morphology with an average particle size of 1-2 μm. EDS was used to reveal the elemental quantities of Ba and Ca after BaCO3 formation on calcite and aragonite surfaces. FTIR spectroscopy was employed to analyze the vibrational modes in carbonate mixtures upon incorporation of Ba2+ by sorption and precipitation mechanisms.
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