Simple determination of dimethylsulfide (DMS) and dimethylsulfoniopropionate (DMSP) using solid-phase microextraction and gas chromatography-mass spectrometry

Solid-phase microextraction (SPME) is a simple, sensitive and less destructive method for the determination of dimethylsulfide (DMS) in seawater. Combined with detection by gas chromatography-mass spectrometry (GC-MS), the method had sufficient sensitivity (minimum detectable concentration of DMS was 0.05 nM), and practical levels of reproducibility (relative standard deviation ≤7%) and linearity (r ² > 0.995) over a wide concentration range (0.5 to 910 nM). The protocol developed was applied to a Sagami Bay water sample to determine concentrations of DMS and DMSP, and in situ DMSP-lyase activity.     

Determination of the lithium and rubidium in sea water by double channel flame emission spectrophotometry

A precise and accurate technique for the determination of Li and Rb in sea water has been developed by using a double channel flame emission spectrophotometer. The advantage of this technique is that it is possible to correct the background emission by making use of the double channel system of the apparatus and to obtain constant intensity of emission even if there are large scale changes in the salinity of the sample. Sea water samples collected in the open sea and coastal areas of Japan were analyzed by this method. In one of the coastal areas, an extraordinarily high concentration of Li was found.     

Geochemistry and Origin of Ananai Stratiform Manganese Deposit in the Northern Chichibu Belt, Central Shikoku, Japan

Abstract. Major and trace element contents are reported for Permian manganese ore and associated greenstone from the Ananai manganese deposit in the Northern Chichibu Belt, central Shikoku, Japan. The manganese deposit occurs between greenstone and red chert, or among red chert beds. Chemical compositions of manganese ore are characterized by enrichments in Mn, Ca, P, Co, Ni, Zn, Sr and Ba, and negative Ce and positive Eu anomalies relative to post-Archean average Australian Shale (PAAS). Geochemical features of the manganese ore are similar to those of modern submarine hydrother-mal manganese deposits from volcanic arc or hotspot setting. In addition, geochemical characteristics of the greenstone closely associated with the Ananai manganese deposit are analogous to those of with-in plate alkaline basalt (WPA). Consequently, the Ananai manganese deposit was most likely formed by hydrothermal activity related to hotspot volcanism in the Panthalassa Ocean during the Middle Permian. This is the first report documenting the terrestrially-exposed manganese deposit that was a submarine precipitate at hotspot.     

Rare Earth, Major and Trace Elements in the Kunimiyama Ferromanganese Deposit in the Northern Chichibu Belt, Central Shikoku, Japan

Abstract. Rare earth, major and trace element geochemistry is reported for the Kunimiyama stratiform ferromanganese deposit in the Northern Chichibu Belt, central Shikoku, Japan. The deposit immediately overlies greenstones of mid-ocean ridge basalt (MORB) origin and underlies red chert. The ferromanganese ores exhibit remarkable enrichments in Fe, Mn, P, V, Co, Ni, Zn, Y and rare earth elements (excepting Ce) relative to continental crustal abundance. These enriched elements/ Fe ratios and Post-Archean Average Australian Shale-normalized REE patterns of the ferromanganese ores are generally analogous to those of modern hydrothermal ferromanganese plume fall-out precipitates deposited on MOR flanks. However in more detail, Mn and Ti enrichments in the ferromanganese ores are more striking than the modern counterpart, suggesting a significant contribution of hydrogenetic component in the Kunimiyama ores. Our results are consistent with the interpretation that the Kunimiyama ores were umber deposits that primarily formed by hydrothermal plume fall-out precipitation in the Panthalassa Ocean during the Early Permian and then accreted onto the proto-Japanese island arc during the Middle Jurassic. The presence of strong negative Ce anomaly in the Kunimiyama ores may indicate that the Early Permian Panthalassa seawater had a more striking negative Ce anomaly due to a more oxidizing oceanic condition than today.     

Geochemical Features and Tectonic Setting of Greenstones from Kunimiyama, Northern Chichibu Belt, Central Shikoku, Japan

Abstract. We report whole‐rock chemical data for the greenstones from the Kunimiyama area in the Northern Chichibu Belt and their implications on the tectonic setting of these rocks. The Kunimiyama greenstones are associated with stratiform fer‐romanganese deposits or bedded cherts in the northern part of the study area, but are closely associated with a thick limestone block or bedded cherts in the southern part. The constituent minerals of greenstones are albitized plagioclase, clinopy‐roxene, chlorite, calcite, epidote, pumpellyite, prehnite, quartz, celadonite, sericite and opaque minerals such as iron oxyhy‐droxide and hematite. These mineral assemblages, epidote + pumpellyite + chlorite and chlorite + pumpellyite + prehnite, suggest that the metamorphic grade of greenstones from the Kunimiyama area is prehnite‐pumpellyite facies. The whole‐rock chemical compositions of greenstones associated with ferromanganese deposits are generally similar to those of normal mid‐ocean ridge basalt (N‐MORB). In contrast, the chemical compositions of the greenstones associated with the limestone block are comparable to those of ocean island alkaline basalt. Greenstones associated with bedded cherts are of enriched MORB and ocean island basalt, as well as N‐MORB origins, suggesting they probably formed as a result of plume‐related MOR volcanism in the Panthalassa Ocean in Early Permian and by tectonic mixing of ocean island basalts with oceanic ridge crustal fragments during accretion/subduction processes. These geological and geochemical lines of evidence suggest that the Kunimiyama greenstones are allochthonous blocks of accreted oceanic crust and seamounts. The ferromanganese deposits are frequently accompanied by reddish greenstones. Compared to common greenish greenstones, the reddish greenstones are characterized by high MnO and rare earth element contents and distinct negative Ce anomalies, implying a slight contribution of hydro thermal component forming the ferromanganese deposits.     

Radiolarian Age of Red Chert from the Kunimiyama Ferromanganese Deposit in the Northern Chichibu Belt, Central Shikoku, Japan

Abstract. The radiolarian age of red chert from the Kunimiyama area of the Northern Chichibu Belt was determined in order to constrain the depositional age of the Kunimiyama deposit that is among the largest ferromanganese deposits in Japan. Pseudoalbaillella cf scalprata Holdsworth and Jones, Pseudoalbaillella cf longicornis Ishiga and Imoto and Pseudoalbaillella sp. belonging to the Ps. lomentaria Zone are found in the red chert, indicating an age of middle Early Permian (middle Wolfcampian). The red chert occurs immediately above the ferromanganese deposit, and the boundary between them is gradual. Based on their mode of occurrence and geochemical features, it is most likely that radiolarian chert and ferromanganese precipitate accumulated simultaneously to produce red chert during the waning stage of submarine hydrothermal activity that was responsible for the Kunimiyama deposit. Consequently, the age of Kunimiyama stratiform ferromanganese deposit is constrained as middle Early Permian (middle Wolfcampian).     

Radiolarian Age of Manganese Ore and Red Chert from the Ananai Stratiform Manganese Deposit in the Northern Chichibu Belt, Central Shikoku, Japan

Abstract. We obtain radiolarian fossils such as Follicucullus monacanthus, Pseudoalbaillella aff. globosa, Pseudoalbaillella cf fusiformis , and Pseudoalbaillella spp. belonging to the Pseudoalbaillella globosa and Follicucullus monacanthus Zones from manganese ore and associated red chert of the Ananai stratiform manganese deposit in the Northern Chichibu Belt, central Shikoku. The depositional age of the Ananai ore deposit is constrained as Guadalupian (Middle Permian) that is between 270.6 and 260.4 Ma in the updated geologic time scale.     

Origin of felsic volcanism in the Izu arc intra-arc rift

An intra-arc rift (IAR) is developed behind the volcanic front in the Izu arc, Japan. Bimodal volcanism, represented by basalt and rhyolite lavas and hydrothermal activity, is active in the IAR. The constituent minerals in the rhyolite lavas are mainly plagioclase and quartz, whereas mafic minerals are rare and are mainly orthopyroxene without any hydrous minerals such as amphibole and biotite. Both the phenocryst and groundmass minerals have felsic affinities with a narrow compositional range. The petrological and bulk chemical characteristics are similar to those of melts from some partial melting experiments that also yield dry rhyolite melts. The hydrous mineral-free narrow mineral compositions and low-Al₂O₃ affinities of the IAR rhyolites are produced from basaltic middle crust under anhydrous low-temperature melting conditions. The IAR basalt lavas display prominent across-arc variation, with depleted elemental compositions in the volcanic front side and enriched compositions in the rear-arc side. The across-arc variation reflects gradual change in the slab-derived components, as demonstrated by decreasing Ba/Zr and Th/Zr values to the rear-arc side. Rhyolite lavas exhibit different across-arc variations in either the fluid-mobile elements or the immobile elements, such as Nb/Zr, La/Yb, and chondrite-normalized rare earth element patterns, reflecting that the felsic magmas had different source. The preexisting arc crust formed during an earlier stage of arc evolution, most probably during the Oligocene prior to spreading of the Shikoku back-arc basin. The lack of systematic across-arc variation in the IAR rhyolites and their dry/shallow crustal melting origin combines to suggest re-melting of preexisting Oligocene middle crust by heat from the young basaltic magmatism.