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91.
92.
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
93.
Makoto Taguchi Tetsuya Fukuhara Masahiko Futaguchi Mitsuteru Sato Takeshi Imamura Kazuaki Mitsuyama Masato Nakamura Munetaka Ueno Makoto Suzuki Naomoto Iwagami George L. Hashimoto 《Icarus》2012,219(1):502-504
Mid-infrared images of almost the entire Venus nightside hemisphere obtained by the Longwave Infrared Camera (LIR) onboard Akatsuki on December 9 and 10, 2010 reveal that the brightness temperature of the cloud-top ranges from 237 K in the cold polar collars to 243 K in the equatorial region, significantly higher than the values obtained by Venera 15. Other characteristic features of the temperature distributions observed are zonal belt structures seen in the middle and low latitudes and patchy temperature structures or quasi-periodic streaks extending in a north–south direction in the northern middle latitudes and southern low latitudes. 相似文献
94.
Toshiyuki Kurihara Kazuhiro Tsukada Shigeru Otoh Kenji Kashiwagi Minjin Chuluun Dorjsuren Byambadash Bujinlkham Boijir Sersmaa Gonchigdorj Manchuk Nuramkhan Masakazu Niwa Tetsuya Tokiwa Gen’ya Hikichi Takafumi Kozuka 《Journal of Asian Earth Sciences》2009,34(2):209-225
Recent mapping projects undertaken in Central Mongolia have revealed the widespread occurrence of radiolarian chert within a Paleozoic accretionary complex. We present the results of the first detailed tectonostratigraphic and radiolarian biostratigraphic investigations of the Gorkhi Formation in the Khangai–Khentei belt of the Central Asian Orogenic Belt.The Gorkhi Formation consists of sandstone shale, alternating sandstone and shale of turbidite affinity and chert with small amounts of siliceous shale, basalt, limestone, and clast-bearing mudstone. Radiolarian chert that is completely devoid of terrigenous clastic material is commonly associated with underlying basalt (sedimentary contact) and with conformably overlying siliceous shale and turbidite deposits. The tectonic stacking of basalt–chert and chert–turbidite successions is the most remarkable structural feature of the formation.The recovery of moderately well-preserved radiolarians and conodonts from red chert led to the recognition of four radiolarian assemblages that have a combined age range from the latest Silurian (Pridolian) to the Late Devonian (Frasnian). No age control exists for the siliceous shale, shale, and sandstone, although they are considered to be latest Devonian or slightly younger on the basis of stratigraphic relationships with underlying chert.The Gorkhi Formation has previously been interpreted as a thick sedimentary basin deposit overlying an unexposed Archean–Neoproterozoic basement; however, the stratigraphy within individual tectonic slices clearly corresponds to that of an ocean plate stratigraphy of an accretionary complex generated by the trenchward movement of an oceanic plate. From the lowermost to uppermost units, the stratigraphy comprises ocean floor basalt, pelagic deep-water radiolarian chert, hemipelagic siliceous shale, and terrigenous turbidite deposits. The biostratigraphic data obtained in the present study provide corroborating evidence for the existence of an extensive deep-water ocean that enabled the continuous sedimentation of pelagic chert over a period of nearly 50 million years. These data, together with structural data characterized by tectonic repetition of the stratigraphy, indicate that these rocks formed as an accretionary wedge along an active continental margin, possibly that of the Angara Craton. The mid-oceanic chert was probably deposited in the Northern Hemisphere portion of the Paleo–Pacific Ocean that faced the Angara Craton and the North China–Tarim blocks. Thus, we propose that subduction–accretion processes along the Paleo–Pacific rim played an important role in the accretionary growth of the active continental margin of the Angara Craton, directly influencing the evolution of the Central Asian Orogenic Belt. 相似文献
95.
Mathieu Hirtzig Tetsuya Tokano Sébastien Rodriguez Stéphane le Mouélic Christophe Sotin 《Astronomy and Astrophysics Review》2009,17(2):105-147
Saturn’s satellite Titan is a particularly interesting body in our solar system. It is the only satellite with a dense atmosphere,
which is primarily made of nitrogen and methane. It harbours an intricate photochemistry, that populates the atmosphere with
aerosols, but that should deplete irreversibly the methane. The observation that methane is not depleted led to the study
of Titan’s methane cycle, starting with its atmospheric part. The features that inhabit Titan’s atmosphere can last for timescales
varying from year to day. For instance, the reversal of the north–south asymmetry is linked to the 16-year seasonal cycle.
Diurnal phenomena have also been observed, like a stratospheric haze enhancement or a possible tropospheric drizzle. Furthermore,
clouds have been reported on Titan since 1993. From these first detections and up to now, with the recent inputs from the
Cassini–Huygens mission, clouds have displayed a large range of shapes, altitudes, and natures, from the flocky tropospheric
clouds at the south pole to the stratiform ones in the northern stratosphere. It is still difficult to compose a clear picture
of the physical processes governing these phenomena, even though of lot of different means of observation (spectroscopy, imaging)
are available now. We propose here an overview of the phenomena reported between 1993 and 2008 in the low atmosphere of Titan,
with indications on the location, altitude, and their characteristics in order to give a perspective of our up-to-date understanding
of Titan’s meteorological manifestations. We shall focus mainly on direct imaging observations, from both space- and ground-based
facilities. All of these observations, published in more than 30 different refereed papers to date, allow us to build a precise
chronology of Titan’s atmospheric changes (including the north–south asymmetry, diurnal and seasonal effects, etc). Since
the interpretation is at an early stage, we only briefly mention some of the current theories regarding the features’ nature. 相似文献
96.
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
97.
Tetsuya Yokoyama Festus T. Aka Minoru Kusakabe 《Geochimica et cosmochimica acta》2007,71(7):1835-1854
Precise measurements of 238U-230Th-226Ra disequilibria in lavas erupted within the last 100 yr on Mt. Cameroon are presented, together with major and trace elements, and Sr-Nd-Pb isotope ratios, to unravel the source and processes of basaltic magmatism at intraplate tectonic settings. All samples possess 238U-230Th-226Ra disequilibria with 230Th (18-24%) and 226Ra (9-21%) excesses, and there exists a positive correlation in a (226Ra/230Th)-(230Th/238U) diagram. The extent of 238U-230Th-226Ra disequilibria is markedly different in lavas of individual eruption ages, although the (230Th/232Th) ratio is constant irrespective of eruption age. When U-series results are combined with Pb isotope ratios, negative correlations are observed in the (230Th/238U)-(206Pb/204Pb) and (226Ra/230Th)-(206Pb/204Pb) diagrams. Shallow magma chamber processes like magma mixing, fractional crystallization and wall rock assimilation do not account for the correlations. Crustal contamination is not the cause of the observed isotopic variations because continental crust is considered to have extremely different Pb isotope compositions and U/Th ratios. Melting of a chemically heterogeneous mantle might explain the Mt. Cameroon data, but dynamic melting under conditions of high DU and DU/DTh, long magma ascent time, or disequilibrium mineral/melt partitioning, is required. The most plausible scenario to produce the geochemical characteristics of Mt. Cameroon samples is the interaction of melt derived from the asthenospheric mantle with overlying sub-continental lithospheric mantle which has elevated U/Pb (>0.75) and Pb isotope ratios (206Pb/204Pb > 20.47) due to late Mesozoic metasomatism. 相似文献
98.
Shoji Tetsuya Department of Environment Systems The University of Tokyo Tokyo - Japan 《中国地质大学学报(英文版)》2001,12(1)
I' Grade-tonnage diagrams are one of the most useful tools inthe resource assessment (e. g. St'nger, 1993). One' grade-tonnage diagram is well known as Laskys (1950) e\-7ation, whichdemonstrates the linear relation between average grade (x) andlOgarithms of cumulative ore tonnage (ac above a given gradex(0相似文献
99.
Noboru?KanekoEmail author Kazuhiko?Morita Tetsuya?Satoh Kimitake?Hayasaki 《Astrophysics and Space Science》2005,299(3):263-306
We study the fundamental modes of radiation hydrodynamic waves arising from one-dimensional small-amplitude initial fluctuations
with wave number k in a radiating and scattering grey medium using the Eddington approximation. The dispersion relation analyzed is the same
as that of Paper I (Kaneko et al., 2000), but is solved as a quintic in angular frequency ω while a quadratic in k
2 in Paper I. Numerical results reveal that wave patterns of five solutions are distinguished into three types of the radiation-dominated
and type 1 and type 2 matter-dominated cases. The following wave modes appear in our problem: radiation wave, conservative
radiation wave, entropy wave, Newtonian-cooling wave, opacity-damped and cooling-damped waves, constant-volume and constant-pressure
diffusion modes, adiabatic sound wave, cooling-damped and drag–force-damped isothermal sound waves, isentropic radiation-acoustic
wave, and gap mode. The radiation-dominated case is characterized by the gap between the isothermal sound and isentropic radiation-acoustic
speeds within which there is not any acoustic wave propagating with real phase speed. One of the differences between type
1 and type 2 matter-dominated cases is the connectivity of the constant-volume diffusion mode, which originates from the radiative
mode in the former case, while from the Newtonian-cooling wave in the latter case. Analytic solutions are derived for all
wave modes to discuss their physical significance. The criterion, which distinguishes between radiation-dominated and type
1 matter-dominated cases, is given by Γ0 = 9, where Γ0 = C
p
(tot)/C
V
(tot) is the ratio of total specific heats at constant pressure and constant volume. Waves in a scattering grey medium are also
analyzed, which provides us some hints for the effects of energy and momentum exchange between matter and radiation. 相似文献
100.
Takeshi Ohta Tetsuya Hiyama Hiroki Tanaka Takashi Kuwada Trofim C. Maximov Tetsuo Ohata Yoshihiro Fukushima 《水文研究》2001,15(8):1459-1476
The water and energy exchanges in forests form one of the most important hydro‐meteorological systems. There have been far fewer investigations of the water and heat exchange in high latitude forests than of those in warm, humid regions. There have been few observations of this system in Siberia for an entire growing season, including the snowmelt and leaf‐fall seasons. In this study, the characteristics of the energy and water budgets in an eastern Siberian larch forest were investigated from the snowmelt season to the leaf‐fall season. The latent heat flux was strongly affected by the transpiration activity of the larch trees and increased quickly as the larch stand began to foliate. The sensible heat dropped at that time, although the net all‐wave radiation increased. Consequently, the seasonal variation in the Bowen ratio was clearly ‘U’‐shaped, and the minimum value (1·0) occurred in June and July. The Bowen ratio was very high (10–25) in early spring, just before leaf opening. The canopy resistance for a big leaf model far exceeded the aerodynamic resistance and fluctuated over a much wider range. The canopy resistance was strongly restricted by the saturation deficit, and its minimum value was 100 s m?1 (10 mm s?1 in conductance). This minimum canopy resistance is higher than values obtained for forests in warm, humid regions, but is similar to those measured in other boreal conifer forests. It has been suggested that the senescence of leaves also affects the canopy resistance, which was higher in the leaf‐fall season than in the foliated season. The mean evapotranspiration rate from 21 April 1998 to 7 September 1998 was 1·16 mm day?1, and the maximum rate, 2·9 mm day?1, occurred at the beginning of July. For the growing season from 1 June to 31 August, this rate was 1·5 mm day?1. The total evapotranspiration from the forest (151 mm) exceeded the amount of precipitation (106 mm) and was equal to 73% of the total water input (211 mm), including the snow water equivalent. The understory evapotranspiration reached 35% of the total evapotranspiration, and the interception evaporation was 15% of the gross precipitation. The understory evapotranspiration was high and the interception evaporation was low because the canopy was sparse and the leaf area index was low. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献