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131.
Tetsuya Komabayashi Kei Hirose Emiko Sugimura Nagayoshi Sata Yasuo Ohishi Leonid S. Dubrovinsky 《Earth and Planetary Science Letters》2008,265(3-4):515-524
Simultaneous volume measurements of MgSiO3 post-perovskite (PPv) and perovskite (Pv) were performed in a diamond anvil cell (DAC) combined with synchrotron X-rays. An externally-heated DAC was used in addition to a laser-heated DAC for the volume measurement experiment at high temperatures. The volume data were collected in the stability field of post-perovskite from 115 to 130 GPa. The temperature generated in the externally-heated and the laser-heated DACs for the volume measurement were up to 832 and 2330 K, respectively. Using two different but complementary heating techniques, we collected the data at a wide temperature range from 300 to 2330 K. The obtained P-V-T data for PPv and Pv were fitted to a third-ordered Birch-Murnaghan equation of state (EOS). For a precise comparison of the volume between the two phases, the EOSs were constructed based on the same pressure scale of MgO. The simultaneous volume measurements and the volumes calculated from the determined EOSs demonstrate that the volume difference between PPv and Pv of about 1.5% is almost constant with increasing temperature to 4000 K at the transition. At the base of the mantle, this density difference corresponds to a temperature anomaly of 1300 K without the phase transition due to the very small thermal expansivity of minerals, which has a significant effect on mantle dynamics. The thermal expansivity contrast between the top and the bottom of the mantle is a factor of 3.6. From a mantle convection study, this value suggests that huge and hot plumes are formed at the core–mantle boundary. 相似文献
132.
Paleomagnetic studies and hotspot track analyses show that the Kula Plate was subducted dextrally with respect to the Eurasian Plate from the Coniacian to Campanian. However, geological evidence for dextral subduction of the Kula Plate has not been reported from Southwest Japan. Studies of the Coniacian to lower Campanian Miyama Formation of the Shimanto Belt reveal that the mélange fabrics show a dextral sense of shear both at outcrop and microscopic scales. In addition, thrust systems at map-scale also show dextral shearing. Restored shear directions in the mélange indicate dextral oblique subduction of an oceanic plate. This indicates that the Kula Plate subducted dextrally along the eastern margin of Asia during the Coniacian to early Campanian. Combinations with other published kinematic and age constraints suggest that Southwest Japan experienced a change from sinistral to dextral and back to sinistral shear between 89–76 Ma. This history is compatible with global-scale plate reconstructions and places good constraints on the timing of plate boundary interaction with the Cretaceous East Asian margin. 相似文献
133.
Hailong Lu Tatsuji Kawasaki Toshiyasu Ukita Igor Moudrakovski Tetsuya Fujii Satoshi Noguchi Tadaaki Shimada Masaru Nakamizu John Ripmeester Chris Ratcliffe 《Marine and Petroleum Geology》2011,28(10):1801-1805
Except for those occurring at seafloor, most of natural gas hydrate form in sediments and are subject to the influence of sediment. Among these factors, the particle size effect on hydrate saturation level in sediment have been studied with a series of silica sands with various sizes, and the results obtained clearly indicate that particle size does play an important role in affecting the saturation level of hydrate in sediments. The proton relaxation times of water confined in the same series of silica sands, which were determined with NMR measurement, show logarithmic relationship with particle size. By comprehensive consideration of the results of hydrate saturation and water proton relaxation times, the particle size effect observed is tentatively explained by the water availability for hydrate formation in sediments. 相似文献
134.
Takahiro Nakanishi Masanobu Yamamoto Tomohisa Irino Ryuji Tada 《Journal of Oceanography》2012,68(6):959-970
We investigated the spatial distribution of glycerol dialkyl glycerol tetraethers (GDGTs), alkenones, and polyunsaturated fatty acids in particulate organic matter collected at four sites along a depth transect from the continental shelf to the Okinawa Trough in the East China Sea during the spring bloom in 2008. The maximum alkenone concentration appeared in the top 25?m at all sites and the $ U_{37}^{{{\text{K}}'}} $ values were consistent with in situ water temperatures in the depth interval, suggesting that the alkenones were produced mainly in surface water. At the slope and shelf sites, GDGTs in the water column showed a concentration maximum at 74?C99?m depth, and the $ {\text{TEX}}_{86}^{\text{H}} $ agreed with in situ water temperatures, suggesting the in situ production of GDGTs in the depth interval. The low-salinity surface water above 20?m depth was characterized by low GDGT concentrations and low $ {\text{TEX}}_{86}^{\text{L}} $ -based temperatures, suggesting either the production of GDGTs in winter season or the lateral advection of GDGTs by an eastward current. At the slope and Okinawa Trough sites, TEX86-based temperatures were nearly constant in the water column deeper than 300?m and corresponded to temperatures at the surface and near-surface waters rather than in situ temperatures. This observation is consistent with a hypothesis that Thaumarchaeota cells produced in surface waters are delivered to deeper water and also indicates that the residence time of suspended GDGTs in the deep-water column is large enough to mix the GDGTs produced in different seasons. 相似文献
135.
Festus T. Aka Tetsuya Yokoyama Minoru Kusakabe Eizo Nakamura Gregory Tanyileke Bekoa Ateba Vincent Ngako Joseph Nnange Joseph Hell 《Journal of Volcanology and Geothermal Research》2008
From previously published 14C and K–Ar data, the age of formation of Lake Nyos maar in Cameroon is still in dispute. Lake Nyos exploded in 1986, releasing CO2 that killed 1750 people and over 3000 cattle. Here we report results of the first measurements of major elements, trace elements and U-series disequilibria in ten basanites/trachy-basalts and two olivine tholeiites from Lake Nyos. It is the first time tholeiites are described in Lake Nyos. But for the tholeiites which are in 238U–230Th equilibrium, all the other samples possess 238U–230Th disequilibrium with 15 to 28% enrichment of 230Th over 238U. The (226Ra/230Th) activity ratios of these samples indicate small (2 to 4%) but significant 226Ra excesses. U–Th systematics and evidence from oxygen isotopes of the basalts and Lake Nyos granitic quartz separates show that the U-series disequilibria in these samples are source-based and not due to crustal contamination or post-eruptive alteration. Enrichment of 230Th is strong prima facie evidence that Lake Nyos is younger than 350 ka. The 230Th–226Ra age of Nyos samples calculated with the (226Ra/230Th) ratio for zero-age Mt. Cameroon samples is 3.7 ± 0.5 ka, although this is a lower limit as the actual age is estimated to be older than 5 ka, based on the measured mean 230Th/238U activity ratio. The general stability of the Lake Nyos pyroclastic dam is a cause for concern, but judging from its 230Th–226Ra formation age, we do not think that in the absence of a big rock fall or landslide into the lake, a big earthquake or volcanic eruption close to the lake, collapse of the dam from erosion alone is as imminent and alarming as has been suggested. 相似文献
136.
Wang-jun Li Ming-chun Peng Motoki Higa Nobuyuki Tanaka Tetsuya Matsui Cindy Q. Tang Xiao-kun Ou Rui-wu Zhou Chong-yun Wang Hai-zhong Yan 《山地科学学报》2016,13(8):1411-1422
We built a classification tree(CT) model to estimate climatic factors controlling the cold temperate coniferous forest(CTCF) distributions in Yunnan province and to predict its potential habitats under the current and future climates, using seven climate change scenarios, projected over the years of 2070-2099. The accurate CT model on CTCFs showed that minimum temperature of coldest month(TMW) was the overwhelmingly potent factor among the six climate variables. The areas of TMW-4.05 were suitable habitats of CTCF, and the areas of -1.35 TMW were non-habitats, where temperate conifer and broad-leaved mixed forests(TCBLFs) were distribute in lower elevation, bordering on the CTCF. Dominant species of Abies, Picea, and Larix in the CTCFs, are more tolerant to winter coldness than Tsuga and broad-leaved trees including deciduous broad-leaved Acer and Betula, evergreen broadleaved Cyclobalanopsis and Lithocarpus in TCBLFs. Winter coldness may actually limit the cool-side distributions of TCBLFs in the areas between -1.35°C and -4.05°C, and the warm-side distributions of CTCFs may be controlled by competition to the species of TCBLFs. Under future climate scenarios, the vulnerable area, where current potential(suitable + marginal) habitats(80,749 km~2) shift to nonhabitats, was predicted to decrease to 55.91%(45,053 km~2) of the current area. Inferring from the current vegetation distribution pattern, TCBLFs will replace declining CTCFs. Vulnerable areas predicted by models are important in determining priority of ecosystem conservation. 相似文献
137.
138.
Ocean plate stratigraphy (OPS) within an ancient accretionary complex provides important information for understanding the history of an oceanic plate from its origin at a mid‐ocean ridge to its subduction at a trench. Here, we report a recently discovered chert–clastic sequence (CCS) that comprises a continuous succession from pelagic sediments to terrigenous clastics and which constitutes part of the OPS in the Akataki Complex within the Cretaceous Shimanto Accretionary Complex on the central Kii Peninsula, SW Japan. As well as describing this sequence, we present U–Pb ages of detrital zircons from terrigenous clastic rocks in the CCS, results for which show that the youngest single grain and youngest cluster ages belong to the Santonian–Campanian and are younger than the radiolarian age from the underlying pelagic sedimentary rock (late Albian–Cenomanian). Thus, the CCS records the movement history of the oceanic plate from pelagic sedimentation (until the late Albian–Cenomanian) to a terrigenous sediment supply (Santonian–Campanian). 相似文献
139.
Tetsuya Yokoyama Takeshi Kuritani Eizo Nakamura 《Geochimica et cosmochimica acta》2006,70(11):2885-2901
In order to unravel magma processes and the geochemical evolution of shallow plumbing systems beneath active volcanoes, we investigated U-series disequilibria of rocks erupted over the past 500 years (1469-2000 AD) from Miyakejima volcano, Izu arc, Japan. Miyakejima volcanic rocks show 238U-230Th-226Ra disequilibria with excess 238U and 226Ra, due to the addition of slab-derived fluids to the mantle wedge. Basaltic bombs of the 2000 AD eruption have the lowest (230Th/232Th) ratio compared to older Miyakejima eruptives, yielding the youngest 238U-230Th model age of 2 kyr. This reinforces our previous model that fluid release from the slab and subsequent magma generation in the mantle wedge beneath Miyakejima occur episodically on a several-kyr timescale. In the last 500 years, Miyakejima eruptives show: (1) a vertical trend in a (230Th/232Th)-(238U/232Th) diagram and (2) a positive linear correlation in a (226Ra/230Th)0 − 1/230Th diagram, which is also observed in lavas from some of the single eruptions (e.g., 1940, 1962, and 1983 AD). The variations cannot be produced by simple fractional crystallization in a magma chamber with radioactive decay of 230Th and 226Ra, but it is possibly produced by synchronous generation of melts in the mantle wedge with different upwelling rate or addition of multiple slab-derived fluids. A much more favorable scenario is that some basaltic magmas were intermittently supplied from deep in the mantle and injected into the crust, subsequently modifying the original magma composition and producing variations in (230Th/232Th) and (226Ra/230Th)0 ratios via assimilation and fractional crystallization (AFC). The assimilant of the AFC process would be a volcanic edifice of previous Miyakejima magmatism. Due to the relatively short timescales involved, the interaction between the assimilant and recent Miyakejima magmatism has not been recorded by the Sr-Nd-Pb isotopic systems. In such cases, Th isotopes and (226Ra/230Th) ratio are excellent geochemical tracers of magmatic evolution. 相似文献
140.
Joji Ishizaka Eko Siswanto Tetsuya Itoh Hiroshi Murakami Yukuya Yamaguchi Naho Horimoto Takashi Ishimaru Shinji Hashimoto Toshiro Saino 《Journal of Oceanography》2007,63(3):517-524
The Vertically Generalized Production Model (VGPM) was verified by the primary production data of the Sagami Bay, Japan. The
VGPM with open ocean parameters including P
B
opt
, maximum primary production per unit of chlorophyll a in the water column, explained only 40% of the variability of integrated primary production. Formulations of the open ocean
P
B
opt
showed no correlation with in situ
P
B
opt
. Adjustment of the parameters of chlorophyll a and temperature dependent P
B
opt
improved the estimation of integrated primary production to 47% of the variation. Vertical integration parameters of VGPM
also have to be adjusted to improve the estimation. Integrated primary production calculated with a stronger light dependency
and with the adjusted P
B
opt
model can explain 74% of the variation. This model was used to estimate primary production of the Sagami Bay during 2003
with satellite data. In situ measurements on cloudy days indicate that the use of satellite data from sunny days only overestimates primary production. 相似文献