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Volume 46 (2012)
- Issue 6 Pages 477-
- Issue 5 Pages 371-
- Issue 4 Pages 267-
- Issue 3 Pages 169-
- Issue 2 Pages 77-
- Issue 1 Pages 1-
Volume 46, Issue 6
Displaying 1-5 of 5 articles from this issue
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PIYALI SENGUPTA, ARIJIT RAY2012 Volume 46 Issue 6 Pages 477-491
Published: December 20, 2012
Released on J-STAGE: November 09, 2013
JOURNAL FREE ACCESSThe NE-SW, NW-SE and E-W trending Proterozoic Newer Dolerite dykes around Chaibasa, Jharkhand, India are found to intrude Singhbhum Granites of late Archean age. Clouded plagioclase, bastitised orthopyroxene and uralitized clinopyroxene, magnetite-ilmenite, quartz-feldspar granophyric intergrowth are the characteristic minerals present in the dolerite dykes which assign a low grade metamorphosed character to the dolerite. Both olivine normative and quartz normative varieties are observed in this suite of dykes. These dolerites have been classified into two groups on the basis of REE distribution patterns: one with LREE (Light Rare Earth Element) enriched pattern (Group I) and the other with flat REE pattern (Group II). A significant positive correlation among trace elements Nb, Zr, La, Ce for Group I dykes suggest variable degree of partial melting of the mantle source. In tectonic discrimination diagrams made with immobile incompatible trace elements Nb, Zr, Ti and Y, Group I dykes show arc-like geochemical signature while Group II dykes are similar to MORBs. Enrichment in some of the LILE and prominent depletion in Nb, P and Ti in Group I dykes suggest that the original melt was derived from a metasomatised mantle source. Group II dykes might derived from a MORB-type mantle source. Melting was triggered by volatiles in case of dykes of Group I while for the Group II dykes, melting was produced by thinning of the lithosphere and subsequent decompression.View full abstractDownload PDF (1331K) -
CAROLYNE PICKLER, DANIELE L. PINTI, BASSAM GHALEB, VICTOR-HUGO GARDU&N ...2012 Volume 46 Issue 6 Pages 493-504
Published: December 20, 2012
Released on J-STAGE: November 09, 2013
JOURNAL FREE ACCESSIn order to calculate the chronology of hydrothermal deposits precipitated from hot springs at Marítaro, Los Azufres geothermal field, Mexico, their 224Ra, 226Ra, 228Ra and 210Pb activities were measured. Hot springs contain large amounts of 226Ra which should be trapped in the lattice of precipitated minerals or be adsorbed on authigenic minerals. Since the time of deposition, a precise chronology can be obtained by measuring the daughter product 210Pb produced in situ, assuming a closed system. The final goal of the study was to test whether 210Pb-226Ra chronology could record past changes in the geothermal regime of the area. A 50-cm long sediment core was sampled but measured 226Ra, 228Ra and 210Pb activities were much lower than expected. The 226Ra activity ranges from 0.5 to 1.1 dpm/grock which contrast with the high 226Ra content measured in the geothermal wells and hot springs of the Los Azufres field (from 118 to 3098 dpm/gwater). This depleted content can be explained by the highly acidic conditions (pH < 3) of the Marítaro hot springs which have inhibited radium adsorption on secondary minerals. The absence of a clear trend in the 210Pb/226Ra activity ratio with depth might indicate that the system was not completely closed in the past to the exportation of 210Pb by acid leaching or 222Rn diffusion. Given these limitations, an average age of the bulk deposit was constrained at 20-50 yrs using the measured 210Pb/226Ra activity ratios.View full abstractDownload PDF (389K) -
TASUKU AKAGI, MISUZU HAYASHI, YURIKO HARA, RIE TAKADA, MARIKO EMOTO, S ...2012 Volume 46 Issue 6 Pages 505-515
Published: December 20, 2012
Released on J-STAGE: November 09, 2013
JOURNAL FREE ACCESSDissolved ion analyses of stream water were conducted monthly in three catchments of varying bamboo coverage of similar geological setting for one year. We found that the concentration of dissolved Si, non-sea salt Na, K, Mg, and alkalinity increased with the increase of bamboo coverage and we concluded that bamboo significantly contributes to chemical weathering. Based on the similar and constant Cl concentrations in stream water in the three catchments throughout the year, we simplified the system with respect to the evapotranspiration correction and basal runoff influence. Since calcite was not detected in the streambed sediment, non-sea salt Na and Ca are assumed to have originated from plagioclase, and thus the plagioclase weathering rate was calculated. The plagioclase weathering rate in bamboo forests was estimated to be more than 1000 mol ha-1 yr-1: twice as high as that in a control bamboo-free forest. The dissolved Si export rate of 0.11 mol/m2/yr from the two bamboo catchments is greater than that of bamboo-free catchment or reported data from rivers in other parts of the world. We discuss further the Si cycle in bamboo forests, comparing with that of bamboo-free forests.View full abstractDownload PDF (3081K)
Note
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YASUHIRO OBA, SIMON R. POULSON2012 Volume 46 Issue 6 Pages 517-520
Published: December 20, 2012
Released on J-STAGE: November 09, 2013
JOURNAL FREE ACCESSValues of the octanol-water partition coefficient (Kow) have been measured vs. pH for two fluorescent dyes (fluorescein, eosin Y) commonly used in hydrologic tracer tests. Values for both fluorescent dyes are similar, with slightly larger values for fluorescein vs. eosin Y at any given pH. Measured values of log Kow show a negative correlation vs. pH, and range from 2.78 for fluorescein (pH 4.29) to -1.22 for eosin Y (pH 7.63). Values of log Kow have been used to calculate example values of the organic matter-water partition coefficient (Kom) and the retardation coefficient (R), and suggest that fluorescein and eosin Y act as excellent hydrologic tracers at pH > 7, but become increasingly non-conservative at pH < 7. The results illustrate the importance of pH upon fluorescent dye speciation, and upon fluorescent dye adsorption behavior. Hence, measurement of pKa and the variation of log Kow vs. pH for other fluorescent dye tracers is recommended.View full abstractDownload PDF (112K)
Express Letter
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TAKAAKI ITAI, MICHIO KUMAGAI, YUIKA HYOBU, DAISUKE HAYASE, SAWAKO HORA ...2012 Volume 46 Issue 6 Pages e47-e52
Published: December 20, 2012
Released on J-STAGE: November 09, 2013
JOURNAL FREE ACCESSAn apparent temporal increase in Mn and As in a thin surface layer (ca. 2 cm) of sediments in Lake Biwa, Japan, was observed by comparing depth profile data from 1977 and 2009. By our estimation, several thousand tonnes of Mn and a few hundred tonnes of As newly accumulated during the 32 years to 2009. Given various methodological concerns and geochemical factors associated with Mn and As dynamics, this phenomenon is believed to have been caused by increased Mn and As influxes to the lake rather than by redistribution induced by the intra-annual decrease in the level of dissolved oxygen. Mass balance calculations indicated that it is unlikely that the recently accumulated quantities of Mn and As were supplied via rivers as dissolved phases; rather, ground-water is the more likely source of these quantities. Further monitoring surveys will be important for assessing the environmental impact of this temporal change.View full abstractDownload PDF (259K)
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