Early Cretaceous tectonic events implied in the time-lag between the age of radiolarian chert and its metamorphic basement in the Bantimala area, South Sulawesi, Indonesia     

Koji  Wakita  Munasri  Jan  Sopaheluwakan  Iskandar  Zulkarnain Kazuhiro  Mlyazaki 《Island Arc》1994,3(2):90-102

Abstract The Bantimala Complex of South Sulawesi consists mainly of mélange, chert, basalt, ultramafic rocks and high pressure type metamorphic rocks. Well-preserved radiolarians were extracted from 10 samples of chert, and K-Ar age dating was done for muscovite from five samples of schist of the Bantimala Complex. The radiolarian assemblage from chert is assigned middle Cretaceous (late Albian-early Cenomanian) age, while the K-Ar age data from schist range from 132 Ma to 114 Ma except for one sample with rare muscovite. The radiolarian chert is unconformably underlain by schist in the Bantimala Complex. The stratigraphie relationship and the time lag of these two kinds of age data from chert and underlying schist suggest short-time tectonic events immediately followed by a quick waning tectonism in this region during the Albian-Cenomanian transgression.  相似文献   

57Fe mössbauer study of clinopyroxenes in the join CaFe3+ AlSiO6 - CaTiAl2O6     

Masahide Akasaka 《Physics and Chemistry of Minerals》1983,9(5):205-211

Synthetic clinopyroxenes of compositions between CaFe³⁺AlSiO₆ and CaFe _0.85 ³⁺ Ti_0.15Al_1.15Si_0.85O₆ have been studied by ⁵⁷Fe Mössbauer spectroscopy. The spectra consist of two doublets assigned to Fe³⁺ in M1 and T sites. From the area ratios of the doublets the site occupancies of Fe³⁺ and Al were determined. Si decreases from 1.00 to 0.85 and Al+Fe³⁺ increases from 1.00 to 1.15 per formula unit with increasing CaTiAl₂O₆ component of the clinopyroxene. The atomic ratio of Fe³⁺(T)/Fe³⁺(total) is 0.11–0.16; 4.5–7.5 percent of the T sites are occupied by Fe³⁺. Thus the presence of Si-O-Fe³⁺, Al-O-Fe³⁺, and Fe³⁺-O-Fe³⁺ bonds is expected in addition to Si-O-Si, Si-O-Al and Al-O-Al bonds. However, the possibility of the former bonds being present would be small, because the amount of Fe³⁺(T) is far less than that of Si and Al. The isomer shift of Fe³⁺(T) is one of the largest in the values found previously for Fe³⁺(T) in silicates. It increases with increasing CaTiAl₂O₆ component and seems to be correlated to the ionic character of the cation — anion bonds calculated from electronegativity. The quadrupole splittings of Fe³⁺(M1) and Fe³⁺(T) decrease with the substitution of Fe³⁺?Ti⁴⁺ in the M1 and of Si?Al in the T sites.  相似文献   

Biological organic carbon export estimated from the annual carbon budget observed in the surface waters of the western subarctic and subtropical North Pacific Ocean from 2004 to 2013     

Masahide Wakita  Makio C. Honda  Kazuhiko Matsumoto  Tetsuichi Fujiki  Hajime Kawakami  Sayaka Yasunaka  Yoshikazu Sasai  Chiho Sukigara  Mario Uchimiya  Minoru Kitamura  Toru Kobari  Yoshihisa Mino  Akira Nagano  Shuichi Watanabe  Toshiro Saino 《Journal of Oceanography》2016,72(5):665-685

The annual flux of biologically produced organic carbon from surface waters is equivalent to annual net community production (NCP) at a steady state and equals the export of particulate and dissolved organic carbon (POC and DOC, respectively) to the ocean interior. NCP was estimated from carbon budgets of salinity-normalized dissolved inorganic carbon (nDIC) inventories at two time-series stations in the western subarctic (K2) and subtropical (S1) North Pacific Ocean. By using quasi-monthly biogeochemical observations from 2004 to 2013, monthly mean nDIC inventories were integrated from the surface to the annual maximum mixed layer depth and corrected for changes due to net air–sea CO₂ exchange, net CaCO₃ production, vertical diffusion from the upper thermocline, and horizontal advection. The annual organic carbon flux at K2 (1.49 ± 0.42 mol m^?2 year^?1) was lower than S1 (2.81 ± 0.53 mol m^?2 year^?1) (p < 0.001 based on t test). These fluxes consist of three components: vertically exported POC fluxes (K2: 1.43 mol m^?2 year^?1; S1: 2.49 mol m^?2 year^?1), vertical diffusive DOC fluxes (K2: 0.03 mol m^?2 year^?1; S1: 0.25 mol m^?2 year^?1), and suspended POC fluxes (K2: 0.03 mol m^?2 year^?1; S1: 0.07 mol m^?2 year^?1). The estimated POC export flux at K2 was comparable to the sum of the POC flux observed with drifting sediment traps and active carbon flux exported by migrating zooplankton. The export fluxes at both stations were higher than those reported at other time-series sites (ALOHA, the Bermuda Atlantic Time-series Study, and Ocean Station Papa).  相似文献   

Comparison of sinking particles in the upper 200 m between subarctic station K2 and subtropical station S1 based on drifting sediment trap experiments     

Makio C. Honda  Hajime Kawakami  Kazuhiko Matsumoto  Masahide Wakita  Tetsuichi Fujiki  Yoshihisa Mino  Chiho Sukigara  Toru Kobari  Mario Uchimiya  Ryo Kaneko  Toshiro Saino 《Journal of Oceanography》2016,72(3):373-386

Drifting sediment trap experiments were conducted during various seasons to elucidate the characteristics of particles sinking through the upper 200 m of the water column in the western Pacific at subarctic station K2 and subtropical station S1. The sinking particle flux increased when primary productivity was high at each station, during June–July at K2 and during February at S1. Biogenic opal (Opal) and CaCO₃ were the major components of the fluxes at K2 and S1, respectively. Contrary to the expectation of a high flux at the eutrophic station K2 and low flux at the oligotrophic station S1, the annual average organic carbon fluxes at 100 m were comparable at both stations: 62.7 mg C m^?2 day^?1 at K2 and 56.1 mg C m^?2 day^?1 at S1. The similarity of the fluxes was perhaps a reflection of the unexpectedly high primary production at S1. At K2, the organic carbon export ratio (organic carbon flux/primary productivity) was significantly and negatively correlated with primary production and tended to decrease with depth. The magnitude of the rate of attenuation of the organic carbon flux with depth was larger at S1 than at K2. This rate of attenuation tended to decrease and increase with primary production at K2 and S1, respectively. The explanation for these patterns may be that the flux of labile organic carbon at relatively shallow depths decreased with increasing primary production at K2, and zooplankton grazing pressure increased with increasing primary productivity at S1.  相似文献   

Insight into nitrous oxide production processes in the western North Pacific based on a marine ecosystem isotopomer model   总被引：2，自引：0，他引：2  

Chisato Yoshikawa  Hitomi Abe  Maki N. Aita  Florian Breider  Keichi Kuzunuki  Sakae Toyoda  Nanako O. Ogawa  Hisami Suga  Naohiko Ohkouchi  Sebastian O. Danielache  Masahide Wakita  Makio C. Honda  Naohiro Yoshida 《Journal of Oceanography》2016,72(3):491-508

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Seasonal variability of phytoplankton community structure in the subtropical western North Pacific     

Tetsuichi Fujiki  Kosei Sasaoka  Kazuhiko Matsumoto  Masahide Wakita  Yoshihisa Mino 《Journal of Oceanography》2016,72(3):343-358

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A review of Pacific salmon hatchery programmes on Hokkaido Island, Japan     

Morita  Kentaro; Saito  Toshihiko; Miyakoshi  Yasuyuki; Fukuwaka  Masa-aki; Nagasawa  Toru; Kaeriyama  Masahide 《ICES Journal of Marine Science》2006,63(7):1353-1363

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OPS mélange: a new term for mélanges of convergent margins of the world     

Koji Wakita 《International Geology Review》2015,57(5-8):529-539

Ocean plate stratigraphy (OPS) is essential to understanding accretionary wedges and complexes along convergent plate margins. Mélanges within accretionary wedges and complexes are the products of fragmentation and mixing processes during and following OPS accretion. A new term, ‘OPS mélange’, is proposed here for mélanges composed mostly of blocks of OPS with an argillaceous matrix, and for a mixture of mélanges of multiple origins with either broken or coherent formations. An OPS mélange results from the fragmentation and disruption of OPS, without admixing of other components. Three major types of OPS mélange can be distinguished on the basis of their components: turbidite type, chert–turbidite type, and limestone–basalt type. These three types potentially form similar mélanges, but they are derived from different parts of the OPS, depending on the level of the decollement surface. The concept of ‘OPS mélange’ can be applied to most of the mélanges in accretionary prisms and complexes worldwide. In addition, this proposal recognizes a distinction between processes of fragmentation and mixing of OPS components, and mixing of ophiolite components, the latter of which results in serpentinite mélanges, not OPS mélanges. Mélanges composed of OPS sequences occur worldwide. The recognition of OPS mélanges is a key aspect of understanding tectonic processes at convergent margins, which result in mélange formation in orogenic belts globally.  相似文献   

Mineralogy of the Boroo Gold Deposit in the North Khentei Gold Belt,Central Northern Mongolia          下载免费PDF全文

Chinbat Khishgee  Masahide Akasaka 《Resource Geology》2015,65(4):311-327

Mineral assemblages and chemical compositions of ore minerals from the Boroo gold deposit in the North Khentei gold belt of Mongolia were studied to characterize the gold mineralization, and to clarify crystallization processes of the ore minerals. The gold deposit consists of low‐grade disseminated and stockwork ores in granite, metasedimentary rocks and diorite dikes. Moderate to high‐grade auriferous quartz vein ores are present in the above lithological units. The ore grades of the former range from about 1 to 3 g/t, and those of the latter from 5 to 10 g/t, or more than 10 g/t Au. The main sulfide minerals in the ores are pyrite and arsenopyrite, both of which are divisible into two different stages (pyrite‐I and pyrite‐II; arsenopyrite‐I and arsenopyrite‐II). Sphalerite, galena, chalcopyrite, and tetrahedrite are minor associated minerals, with trace amounts of bournonite, boulangerite, geerite, alloclasite, native gold, and electrum. The ore minerals in the both types of ores are variable in distribution, abundance and grain size. Four modes of gold occurrence are recognized: (i) “invisible” gold in pyrite and arsenopyrite in the disseminated and stockwork ores, and in auriferous quartz vein ores; (ii) microscopic native gold, 3 to 100 µm in diameter, that occurs as fine grains or as an interstitial phase in sulfides in the disseminated and stockwork ores, and in auriferous quartz vein ores; (iii) visible native gold, up to 1 cm in diameter, in the auriferous quartz vein ores; and (iv) electrum in the auriferous quartz vein ores. The gold mineralization of the disseminated and stockwork ores consists of four stages characterized by the mineral assemblages of: (i) pyrite‐I + arsenopyrite‐I; (ii) pyrite‐II + arsenopyrite‐II; (iii) sphalerite + galena + chalcopyrite + tetrahedrite + bournonite + boulangerite + alloclasite + native gold; and (iv) native gold. In the auriferous quartz vein ores, five mineralization stages are defined by the following mineral assemblages: (i) pyrite‐I; (ii) pyrite‐II + arsenopyrite; (iii) sphalerite + galena + chalcopyrite; (iv) Ag‐rich tetrahedrite‐tennantite + bournonite + geerite + native gold; and (v) electrum. The As–Au relations in pyrite‐II and arsenopyrite suggest that gold detected as invisible gold is mostly attributed to Au⁺¹ in those minerals. By applying the arsenopyrite geothermometer to arsenopyrite‐II in the disseminated and stockwork ores, crystallization temperature and logfs₂ are estimated to be 365 to 300 °C and –7.5 to –10.1, respectively.  相似文献   

Stable isotope-guided analysis of congener-specific PCB concentrations in a Japanese coastal food web     

Hiroaki Matsuo  Masahide Kawano  Koji Omori  Kiyonori Nakajima  Ichiro Takeuchi   《Marine pollution bulletin》2009,58(11):1615-1623

Organisms collected from a coastal ecosystem in Japan were analyzed for concentrations of 205 polychlorinated biphenyls (PCBs) congeners; analyses were guided by δ¹³C and δ¹⁵N measurements. The regression slopes of log PCB concentration on δ¹⁵N value are regarded as indices of biomagnification in food webs. The slope (wet weight basis) of ΣPCBs was +0.104; the slope (lipid weight basis) was close to zero. Lipid content increased from 0.06% in a primary producer to 8.32% in the highest trophic level consumer. Hence, biomagnification of ΣPCBs (wet weight basis) can be attributed to increase of lipid content through the food web. For most of the congeners, the slopes (wet weight basis) exceeded those (lipid weight basis) by ca. 0.10. Slopes increased with increasing PCB chlorination levels between chlorine numbers 1–6; slopes decreased at higher chlorination levels. This decrease is likely caused by a decrease in membrane permeability with increasing molecular weight.  相似文献