Alternating field-impressed AMS in rocks     

Bernard Henry  Diana Jordanova  Neli Jordanova  Jozef Hus  Jérôme Bascou  Minoru Funaki  Dimo Dimov 《Geophysical Journal International》2007,168(2):533-540

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Experimental study of a low-alkali tholeiite at 1–5 kbar: optimal condition for the crystallization of high-An plagioclase in hydrous arc tholeiite     

Daisuke?Takagi  Hiroaki?SatoEmail author  Mitsuhiro?Nakagawa 《Contributions to Mineralogy and Petrology》2005,149(5):527-540

We conducted melting experiments on a low-alkali tholeiite (SiO₂ ~52 wt%, MgO ~6.5 wt%, CaO/Na₂O~4.4, Al₂O₃/SiO₂ ~0.33) under both H₂O-undersaturated and H₂O-saturated conditions to investigate the effect of H₂O on the Ca–Na partitioning between plagioclase and melt. Experiments were performed in the temperature and pressure ranges of 1,000–1,300°C and 1–5 kbar, respectively, with varying H₂O contents of 0–12wt%. Redox condition was 0–2 log unit above NNO (nickel–nickel oxide) buffer. Temperature-bulk H₂O diagrams for the low-alkali tholeiite are constructed at 1, 2, and 5 kbar, and compositions of near-liquidus plagioclase and coexisting melt are determined. To exclude the effect of melt composition (CaO/Na₂O and Al₂O₃/SiO₂ ratios) on plagioclase composition and to reveal the effect of H₂O on An (=100×Ca/(Ca+Na)) content and (=(Ca/Na)_pl/(Ca/Na)_melt), we focused on the composition of near-liquidus plagioclases which crystallized from melts with nearly constant CaO/Na₂O and Al₂O₃/SiO₂ ratios. Our experimental results show that, at each experimental pressure, An content of the near-liquidus plagioclase and the K_D^Ca-Na almost linearly increases as H₂O content in melt increases. Each of the An content and the variations in a low-alkali tholeiitic system (CaO/Na₂O~4.0–4.5, Al₂O₃/SiO₂ ~0.27–0.33) can be described by one equation using temperature, pressure, and melt H₂O content as parameters. An content and of liquidus plagioclase increases with increasing melt H₂O and with decreasing pressure, elucidating that nearly H₂O-saturated conditions of 2–3 kbar is optimal for the crystallization of the most An-rich plagioclase (>An₈₈). We suggest this pressure condition of 2–3 kbar, corresponding to depth of 7–11 km, plays an important role for the origin of An-rich plagioclase in H₂O-rich low-alkali tholeiite. At pressures more than ca. 4 kbar, crystallization of liquidus Ca-rich clinopyroxene decreases the CaO/Na₂O ratio of liquid, thus prohibiting the crystallization of high-An plagioclase from hydrous tholeiite.  相似文献   

Field observation and numerical simulation of past and future storm surges in the Bay of Bengal: case study of cyclone Nargis     

Tasnim  Khandker Masuma  Shibayama  Tomoya  Esteban  Miguel  Takagi  Hiroshi  Ohira  Koichiro  Nakamura  Ryota 《Natural Hazards》2015,75(2):1619-1647

Natural Hazards - Storm surges are one of the most important risks to coastal communities around the Bay of Bengal, and it is feared that the threat they pose will increase with climate change in...  相似文献   

Restoration of Exotic Terranes Along the Median Tectonic Line, Japanese Islands: Overview     

Hideo Takagi  Hiroyoshi Arai 《Gondwana Research》2003,6(4):657-668

This paper reviews recent progress on the geotectonic evolution of exotic Paleozoic terranes in Southwest Japan, namely the Paleo-Ryoke and Kurosegawa terranes. The Paleo-Ryoke Terrane is composed mainly of Permian granitic rocks with hornfels, mid-Cretaceous high-grade metamorphic rocks associated with granitic rocks, and Upper Cretaceous sedimentary cover. They form nappe structures on the Sambagawa metamorphic rocks. The Permian granitic rocks are correlative with granitic clasts in Permian conglomerates in the South Kitakami Terrane, whereas the mid-Cretaceous rocks are correlative with those in the Abukuma Terrane. This correlation suggests that the elements of Northeast Japan to the northeast of the Tanakura Tectonic Line were connected in between the paired metamorphic belt along the Median Tectonic Line, Southwest Japan. The Kurosegawa Terrane is composed of various Paleozoic rocks with serpentinite and occurs as disrupted bodies bounded by faults in the middle part of the Jurassic Chichibu Terrane accretionary complex. It is correlated with the South Kitakami Terrane in Northeast Japan. The constituents of both terranes are considered to have been originally distributed more closely and overlay the Jurassic accretionary terrane as nappes. The current sporadic occurrence of these terranes can possibly be attributed to the difference in erosion level and later stage depression or transtension along strike-slip faults. The constituents of both exotic terranes, especially the Ordovician granite in the Kurosegawa-South Kitakami Terrane and the Permian granite in the Paleo-Ryoke Terrane provide a significant key to reconstructing these exotic terranes by correlating them with Paleozoic granitoids in the eastern Asia continent.  相似文献   

Structural controls on the 1998 volcanic unrest at Iwate volcano: Relationship between a shallow, electrically resistive body and the possible ascent route of magmatic fluid     

Koki Aizawa  Yasuo Ogawa  Masaaki Mishina  Kosuke Takahashi  Shintaro Nagaoka  Nobumasa Takagi  Shin'ya Sakanaka  Takuya Miura   《Journal of Volcanology and Geothermal Research》2009,187(1-2):131-139

Magnetotelluric (MT) measurements were conducted at Iwate volcano, across the entirety of the mountain, in 1997, 1999, 2003, 2006, and 2007. The survey line was 18 km in length and oriented E–W, comprising 38 measurements sites. Following 2D inversion, we obtained the resistivity structure to a depth of 4 km. The surface resistive layer (~ several hundreds of meters thick) is underlain by extensive highly conductive zones. Based on drilling data, the bottom of the highly conductive zone is interpreted to represent the 200 °C isotherm, below which (i.e., at higher temperatures) conductive clay minerals (smectite) are rare. The high conductivity is therefore mainly attributed to the presence of hydrothermally altered clay. The focus of this study is a resistive body beneath the Onigajo (West-Iwate) caldera at depths of 0.5–3 km. This body appears to have impeded magmatic fluid ascent during the 1998 volcanic unrest, as inferred from geodetic data. Both tectonic and low-frequency earthquakes are sparsely distributed throughout this resistive body. We interpret this resistive body as a zone of old, solidified intrusive magma with temperatures in excess of 200 °C. Given that a similar relationship between a resistive body and subsurface volcanic activity has been suggested for Asama volcano, structural controls on subsurface magmatic fluid movement may be a common phenomenon at shallow levels beneath volcanoes.  相似文献   

Petrology of a mantle-derived rhyolite, Hokkaido, Japan     

Tetsuichi Takagi  Yuji Orihashi  Kazuki Naito  Yasushi Watanabe 《Chemical Geology》1999,160(4):368-445

The Miocene Kitami rhyolite, consisting of orthopyroxene and plagioclase-phyric lavas and dikes, occurs on the back-arc side of the Kuril arc with coeval basalts and Fe-rich andesites. Temperatures estimated from orthopyroxene–ilmenite pairs exceed 900°C. Although the whole rock compositions of the Kitami rhyolite correspond to S-type granites (i.e., high K, Al, large ion lithophile elements, and low Ca and Sr), Sr–Nd isotope compositions are remarkably primitive, and similar to those of the coeval basalts and andesites. They are distinct from those of lower crustal metamorphic rocks exposed in the area. Comparison of chondrite-normalized rare earth element (REE) patterns between the rhyolite and the basalts and andesites show that the rhyolite is more light REE enriched, but has similar heavy REE contents than the basalts. All rhyolites show negative Eu anomalies. The geochemical data suggest that did not formed by simple dehydration melting of basaltic rocks or fractional crystallization of basaltic magmas. The features of slab-derived fluids expected from recent high pressure experimental studies indicates that mantle wedge is partly metasomatized with “rhyolitic” materials from subducted slabs; it is more likely that very low degree partial melting of the metasomatized mantle wedge formed the rhyolite magma.  相似文献   

A pollution history of Chesapeake Bay     

Edward D. Goldberg  Vern Hodge  Minoru Koide  John Griffin  Eric Gamble  Owen P. Bricker  Gerry Matisoff  George R. Holdren  Ruth Braun 《Geochimica et cosmochimica acta》1978,42(9):1413-1425

Present day anthropogenic fluxes of some heavy metals to central Chesapeake Bay appear to be intermediate to those of the southern California coastal region and those of Narragansett Bay. The natural fluxes, however, are in general higher. On the bases of Pb-210 and Pu-239 + 240 geochronologies and of the time changes in interstitial water compositions, there is a mixing of the upper 30 or so centimeters of the sediments in the mid-Chesapeake Bay area through bioturbation by burrowing mollusks and polychaetes. Coal, coke and charcoal levels reach one percent or more by dry weight in the deposits, primarily as a consequence of coal mining operations.  相似文献   

Distribution depth of the transforming stage larvae of myctophid fishes in the subtropical–tropical waters of the western North Pacific     

Chiyuki Sassa  Kouichi Kawaguchi  Yuichi Hirota  Minoru Ishida 《Deep Sea Research Part I: Oceanographic Research Papers》2007,54(12):2181-2193

We describe the day–night vertical distribution patterns of 18 species or types of myctophid fish larvae at the transforming stage based on discrete depth sampling from the surface down to 1000-m depth in the subtropical–tropical western North Pacific. A total of 551 transforming stage larvae were collected at the 19 sampling stations. Except for the Diaphus species and Notolychnus valdiviae, all of the transforming stage larvae (including genera Benthosema, Bolinichthys, Centrobranchus, Ceratoscopelus, Diogenichthys, Hygophum, Lampanyctus, Lobianchia, Myctophum, Symbolophorus, and Triphoturus) were collected in the lower mesopelagic zone from 600- to 900-m depth during both day and night, showing no diel vertical migration (DVM). On the contrary, the Diaphus species and N. valdiviae larvae undergo DVM during the transforming stage, occurring below 200-m layer during the daytime and migrating up to the upper 150-m layer at night, i.e., they show earlier adaptation to juvenile–adult behaviors. Most myctophid fish larvae are known to undertake substantial ontogenetic vertical migration (OVM) from the epipelagic to mesopelagic zones during their early life stage. Although considerable sampling effort was carried out in this study, transforming larvae, except for the above two migratory ones, were not collected in the epipelagic and upper mesopelagic zones, strongly suggesting that their sinking speed would be high. It would be advantageous for survival to spend their highly vulnerable transforming stage in the lower mesopelagic zone, where predation pressures are lower and physical conditions are more stable than in the upper layers.  相似文献   

Recent Occurrences of Dinophysis fortii (Dinophyceae) in the Okkirai Bay, Sanriku, Northern Japan, and Related Environmental Factors     

Kazuhiko Koike  Hirotaka Otobe  Minoru Takagi  Tadahisa Yoshida  Takehiko Ogata  Takashi Ishimaru 《Journal of Oceanography》2001,57(2):165-175

Occurrence of Dinophysis fortii, a causative organism of diarrhetic shellfish poisoning, in the Okkirai Bay, Sanriku was surveyed in 1995, 1996, 1998 and 1999. In each year, its major occurrence was detected from the late May or early June and continued until the late June or early July. Seawater temperature, salinity and nutrients measurements suggested that inflows of offshore water into the bay played key role on the first major occurrence of D. fortii. With an analysis of continuous temperature data in the Otsuchi Bay which locates north of the Okkirai Bay, this influent was considered to be intermittent inflow of the offshore water by internal tidal waves which propagated from north to south. First occurrence peak of D. fortii was synchronous with phycobilin containing microalgae, synechococcoid cyanobacteria and cryptomonad, in all years. In vivo fluorescence measurement of D. fortii cells in 1995 and 96 showed that the cells in these microalgal-rich water contained more phycobilin pigment than those in the microalgal-poor water. The result may support a hypothesis that D. fortii acquires phycobilin by an uptake of these microalgae. After the first major occurrence in the bay, D. fortii sometimes occurred in rather inshore waters where showed elevated ammonium level possibly due to increased heterotrophic activity. Together with another finding that D. fortii is mixotrophic, it could be assumed that the environment being suited to heterotrophic nutrition also stimulates D. fortii growth in the bay.  相似文献   

Aspects of rhodium marine chemistry     

Kathe K. Bertine  Minoru Koide  Edward D. Goldberg 《Marine Chemistry》1993,42(3-4)

Rhodium, one of the least abundant of the Pt-group elements in the earth's crust, has the second highest concentration in seawater. This may be a consequence of strong complexing, perhaps kinetically restrained with time constants of the order of centuries to millenia. The element shows a nutrient-like distribution in waters of the Pacific Ocean. Pelagic and coastal sediments have Rh concentrations close to crustal values. There is a remarkable enrichment of Rh in ferromanganese minerals that cannot be explained by oxidative capture. Unlike the other Pt-group elements, Rh is enriched in the high temperature hydrothermal sulfide deposits as well as phosphorites.  相似文献