Estimation of variation of mercury concentration in the oceans during the last several decades

Variation of mercury concentration in the oceans during the last several decades has been investigated by determining the mercury concentration in rock fishes caught recently andca. 20 years ago. From this result, it is concluded that there has been no variation of mercury concentration in the oceans during the last several decades.     

Direct PCR amplification of the 16S rRNA gene from single microbial cells isolated from an Antarctic iceberg using laser microdissection microscopy

Here, we describe a technique that allows the genetic linage analysis of 16S rRNA genes in bacteria observed under a microscope. The technique includes the isolation of microbial cells using a laser microdissection microscope, lysis of the cells, and amplification of the 16S rRNA genes in the isolated cells without interference by bacterial DNA contamination from the experimental environment or reagents. Using this technique, we successfully determined 15 16S rRNA gene sequences in cells isolated from an Antarctic iceberg. These sequences showed 94%–100% identity to their closest strains, which included bacteria that occur in aqueous, marine, and soil environments.     

Os, Pb, and Nd isotope geochemistry of the Permian Emeishan continental flood basalts: Insights into the source of a large igneous province

The nature of the source of continental flood basalts (CFB) is a highly debated topic. Proposed mantle sources for CFBs, including both high- and low-Ti basalts, include subcontinental lithospheric mantle (SCLM), asthenospheric mantle, and deep, plume-related mantle. Re-Os isotope systematics can offer important constraints on the sources of both ocean island basalts (OIB) and CFB, and may be applied to distinguish different possible melt sources. This paper reports the first Re-Os isotope data for the Late Permian Emeishan large igneous province (LIP) in Southwest China. Twenty one CFB samples including both low- and high-Ti basalts from five representative sites within the Emeishan LIP have been analyzed for Os, Nd, and Pb isotopic compositions. The obtained Os data demonstrate that crustal assimilation affected Os isotopic compositions of some Emeishan basalt samples with low Os concentrations but not all of the samples, and the Emeishan basalts with high Os contents likely experienced the least crustal contamination. The low and high-Ti basalts yield distinct Os signatures in terms of ¹⁸⁷Os/¹⁸⁸Os and Os content. The low-Ti basalt with the highest Os concentration (400 ppt) has a radiogenic Os isotopic composition (γOs(t), +6.5), similar to that of plume-derived OIB. Because the Os isotopic composition of basalts with relatively high Os concentrations (typically >50 ppt) likely represents that of their mantle source, this result implies a plume-derived origin for the low-Ti basalts. On the other hand, the high-Ti basalts with high Os concentration (over 50 ppt) have unradiogenic Os isotopic signatures (γOs(t) values range from −0.8 to −1.4), suggesting that a subcontinental lithosphere mantle (SCLM) component most likely contributed to the generation of these magmas. Combining Pb and Nd isotopic tracers with the Os data, we demonstrate that the low-Ti basaltic magmas in the Emeishan CFB were mainly sourced from a mantle plume reservoir, whereas the high-Ti basaltic magmas were most likely derived from a SCLM reservoir or were contaminated by a significant amount of lithospheric mantle material during plume-related magma ascent through the SCLM.     

Revision of the first order triangulation in the region disturbed by the Nankaido Earthquake of 1946

Zusammenfassung Nach dem Erdbeden von Nanka?do im Jahre 1946 hat man das Dreiecksnetz I. Ordnung in einem Gebiet von etwa 300 km Umkreis wiederbeobachtet, und zwar auf 47 Punkten insgeasamt 68 Winkel. Die letzte Triangulation fand in den Jahren 1885–96 statt.—Nach der Ausgleichung des Netzes wurden Punkverschiebungen bis zu 1,69 m festgestellt.

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Resumen Después del temblor de tierra de 1946, en Nanka?do, se ha vuelto a observar la red de triangulación de 1_H orden en un radio de 300 kilómetros aproximadamente. Los puntos de nuevo observados son 47 y los triángulos 68. La triangulaciín precedente se remontaba a los a?os 1885–96. Después de compensar la red, se han deducido los desplazamientos experimentados por los puntos sobre el terreno, que llegaron a ser de 1,69 metros.

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Résumé Après le tremblement de tèrre de 1946 à Nankaido, on a réobservé le réseau de triangulation de premier ordre dans un rayon de 300 km environ. Les points réobservés sont au nombre de 47, et les triangles en nombre de 68. La triangtlation précédente remontait aux années 1885–96. La compensation du réseau effectuée, on en a déduit les déplacements subis par les points sur le terrain, qui importent jusqu’à 1,69 m.

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Sommario Dopo il terremoto di Nankaido del 1946, è stata riosservata la rete di prim’ordine entro un raggio di circa 300 km. La precedente triangolazione risaliva agli anni 1885–96. Effettuata la compensazione, il confronto fra l’anticae la nuova triangolazione ha rivelato spostamenti nei vertici ammontanti fino a m 1,69.

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Communication présentée à l’Assemblée Générale de Bruxelles en 1951     

Re-Os geochronology of the Iimori Besshi-type massive sulfide deposit in the Sanbagawa metamorphic belt, Japan

Besshi-type Cu deposits are strata-bound volcanogenic massive sulfide deposits usually associated with mafic volcanic rocks or their metamorphic equivalents. Although there are numerous Besshi-type deposits in the Sanbagawa metamorphic belt, Japan, their tectonic settings and depositional environments remain controversial because of a lack of depositional age constraints. We report Re-Os data for the Iimori deposit, one of the largest Besshi-type deposits in western Kii Peninsula, in order to examine the robustness of the Re-Os isotope system for dating sulfide minerals in the high-P/T metamorphic belt and to elucidate the primary depositional environment of the Iimori sulfide ores. An 11-point Re-Os isochron plot yields an age of 156.8 ± 3.6 Ma. As this Re-Os isochron age is significantly older than the timing of the Sanbagawa peak metamorphism (110-120 or ∼90 Ma) and a well-defined isochron was obtained, the Re-Os age determined here is most likely the primary depositional age. Despite high-grade metamorphism at up to 520 ± 25 °C and 8-9.5 kbar, the Re-Os isotope system of the Iimori sulfides was not disturbed. Hence, we consider that the whole-rock Re-Os closure temperature for the Iimori sulfide ores was probably higher than 500 °C. As the accretion age of the Sanbagawa metamorphic belt is considered to be 120-130 or 65-90 Ma on the basis of radiolarian and radiometric ages, we estimated the time from the Iimori sulfide deposition on the paleo-seafloor to its accretion at the convergent plate boundary to be greater than 25 Myr. Consequently, the depositional environment of the Iimori sulfide ores was not in the marginal sea, but was truly pelagic.     

Elastoplastic deformation around underground openings under biaxial initial stress field

Estimation of elastoplastic deformation around an underground opening induced by the excavation of it, especially displacement and strain field in plastic region, is presented in this paper, as well as the formulation for calculating the displacement and strain in the plastic region around the underground opening by the coupled Boundary Element Method - Characteristics Method (BEM-CM). In this method, the non-associated flow rule is adopted to calculate the displacement and strain field in the plastic region, which is determined by the integration of the displacement along characteristics lines under the boundary condition of the elastic displacement on an elastoplastic interface analysed. It is shown that this method is one of the accurate and effective methods for estimating not only the shape and extent of the plastic region but also the state of the displacement and strain in the plastic region around the underground opening, comparing the theoretical solution with numerical results by this method for a circular opening under hydrostatic initial stress condition. Furthermore, this method is applied to rectangular and horse-shoe shaped openings and the characteristics of the strain field in the plastic region are discussed. © 1997 by John Wiley & Sons, Ltd.