Juxtaposition of adakite, boninite, high-TiO₂ and low-TiO₂ basalts in the Devonian southern Altay, Xinjiang, NW China   总被引：1，自引：0，他引：1  

Hecai Niu  Hiroaki Sato  Haixiang Zhang  Jun'ichi Ito  Xueyuan Yu  Takashi Nagao  Kentaro Terada  Qi Zhang 《Journal of Asian Earth Sciences》2006,28(4-6):439-456

We present petrographic and geochemical data on representative samples of the Devonian adakite, boninite, low-TiO₂ and high-TiO₂ basalts and associated rocks in the southern Altay areas, Xinjiang, NW China. These volcanic rocks mostly occur as tectonic blocks within suture zones between the Siberian and Junggar plates. Adakite occurs in the Suoerkuduke area ca. 40 km south of Fuyun, and actually represents a poorly-sorted massive volcaniclastic deposit, mostly consisting of a suite of hornblende andesite to pyroxene andesite. The geochemical features of the adakite suggest its generation by melting of subducted oceanic crust. Boninite occurs in the Saerbulake area ca. 20 km southwest of Fuyun, as pillowed lava or pillowed breccia. It is associated with high-TiO₂ basalt/gabbro and low-TiO₂ basalt. The boninites are metamorphosed, but contain relict clinopyroxene with Mg# (=100*Mg/(Mg+Fe)) of 90–92, and Cr₂O₃ contents of 0.5–0.7 wt% and chromian spinel with Cr/(Cr+Al) ratio of 0.84. The bulk rock compositions of the boninites are characterized by low and U-shaped REE with variable La/Yb ratios. They are classified as high-Ca boninite. The Cr-rich cpx phenocryst and Chromian spinel suggests that the boninites were formed by melting of mildly refractory mantle peridotite fluxed by a slab-derived fluid component under normal mantle potential temperature conditions. Basaltic rocks occur as massive flows, pillowed lavas, tuff breccia, lapilli tuff and blocks in tectonic mélanges. Together with gabbros, the basaltic rocks are classified into high-TiO₂ (>1.7 wt%) and low-TiO₂ (<1.5 wt%) types. They show variable trace element compositions, from MORB-type through transitional back-arc basin basalt to arc tholeiite, or within plate alkalic basalt. A notable feature of the Devonian formations in the southern Altay is the juxtaposition of volcanic rocks of various origins even within a limited area; i.e. the adakite and the boninites are associated with high-TiO₂ and low-TiO₂ basalts and/or gabbros, respectively. This is most likely produced by complex accretion and tectonic processes during the convergence in the Devonian–Carboniferous paleo-Asian Ocean between the Siberian and Junggar plates.  相似文献   

Late Paleozoic adakites and Nb-enriched basalts from northern Xinjiang, northwest China: Evidence for the southward subduction of the Paleo-Asian Oceanic Plate   总被引：9，自引：0，他引：9  

Haixiang  Zhang  Hecai  Niu  Hiroaki  Sato  Xueyuan  Yu  Qiang  Shan  Boyou  Zhang  Jun'ichi  Ito  Takashi  Nagao 《Island Arc》2005,14(1):55-68

Abstract   Volcanic rocks consisting of adakite and Nb-enriched basalt are found in the early Devonian Tuoranggekuduke Group in the northern margin of the Kazakhstan-Junggar Plate, northern Xinjiang, northwest China. The geochemical characteristics of the andesitic and dacitic rocks in this area resemble that of adakites. The relatively high Al₂O₃, Na₂O and MgO content and Mg^♯ values indicate that the adakites were generated in relation to oceanic slab subduction rather than the partial melting of basaltic crust. A slightly higher SrI and a lower ɛ _Nd( t  = 375 Ma) compared to adakites of mid-oceanic ridge basalt (MORB) imply that slab sediments were incorporated into these adakites during slab melting. The Nb-enriched basalt lavas, which are intercalated in adakite lava suite, are silica saturated and are distinguished from the typical arc basalts by their higher Nb and Ti content (high field strength element enrichment). They are derived from the partial melting of the slab melt-metasomatized mantle wedge peridotite. Apparently, positive Sr anomalies and a slightly higher heavy rare earth element content in these adakites compared to their Cenozoic counterparts indicate that the geothermal gradient in the Paleo-Asian Oceanic subduction zone and the depth of the Paleo-Asian Oceanic slab melting are between those of their Archean and Cenozoic counterparts. The distribution of the adakites and Nb-enriched basalts in the northern margin of the Kazakhstan-Junggar Plate, northern Xinjiang, indicates that the Paleo-Asian Oceanic Plate subducted southward beneath the Kazakhstan-Junggar Plate in the early Devonian period.  相似文献   

Effective elastic thickness of island arc lithosphere under Japan   总被引：1，自引：0，他引：1  

Takeshi Kudo  Atsushi Yamaji  Muneyoshi Furumoto  Toshiyasu Nagao 《Island Arc》2001,10(2):135-144

Abstract Using topography and observed gravity anomalies, we have estimated the effective elastic thickness as a measure of strength of Japanese island arc lithosphere. The thickness is found to range from about 3 km to >20 km. The thickness seems to be controlled primarily by the thermal state of the lithosphere. The higher the heat flow, the thinner is the elastic plate. However, several areas show significant deviations. The smaller effective elastic thickness in the northern Ryukyu arc than that inferred from heat flow may be attributed to the stress regime. In Japan, extensional tectonics are going on only in the Ryukyu arc region. Shallow subducting slab under the south-western Japan frontal arc probably increases the effective thickness by several kilometers. The determined effective elastic thickness suggests that when we consider vertical movements in the volcanic arc, we should take account of topographic and subsurface loading over a few hundred kilometers. However, if the dip of the slab is shallow, the flexural responses of the underlying slab, not only that of the island arc lithosphere, should be taken into account for the compensation, as is the case of the south-western Japan frontal arc.  相似文献   

A possible case of SES selectivity at Kozu-shima Island, Japan     

Y. Orihara  Y. Noda  T. Nagao  S. Uyeda 《Journal of Geodynamics》2002,33(4-5)

Geoelectric potential difference monitoring has been conducted in Kozu-shima Island about 170 km south of Tokyo. During the monitoring period (14 May 1997–30 November 1999), there were 21 anomalous geoelectric changes that could have been VAN-type seismic electric signals (SES) and 26 M>3 earthquakes within about 20 km. Possible correspondence between the geoelectric changes and earthquakes has been examined. There seems to be some systematic tendency regarding the dependence of appearance/non-appearance of changes and their polarity on epicentral location. This observation, however, is preliminary and admittedly inconclusive because of small number of cases and non-uniqueness in signal-earthquake correlation.  相似文献   

Geomagnetic anomaly pattern of the Japan Sea     

Nobuhiro Isezaki  Seiya Uyeda 《Marine Geophysical Researches》1973,2(1):51-59

Using all available geomagnetic data, including those obtained in a detailed survey conducted by the authors in 1970, the geomagnetic anomaly pattern if the Japan Sea has been studied. It has been established that sublinear magnetic anomalies run subparallel to the general trend of the Japanese Islands. The peak to peak amplitudes of most of these anomalies are less than 300y, their wavelengths 20 to 40 km. The anomalies are much less distinct in linearity than those found in the northwestern corner of the Pacific basin off northeastern Honshu. The linear trend is better developed in the deeper basin areas and less recognizable in the Yamato- and Kitayamato-areas. The anomaly pattern appears to support the view that the Japan Sea floor evolved through a spreading process from numerous spreading centers. A definite conclusion about the genesis of the Japan Sea, however, must await further investigation.  相似文献   

Distribution and sources of organic matter in surficial sediments on the shelf and slope off Tokachi, western North Pacific, inferred from C and N stable isotopes and C / N ratios     

Toshihiro Usui  Seiya Nagao  Masanobu Yamamoto  Koji Suzuki  Isao Kudo  Shigeru Montani  Atsushi Noda  Masao Minagawa 《Marine Chemistry》2006,98(2-4):241-259

Organic carbon (C) and total nitrogen (N) contents and corresponding isotope ratios were determined in surficial sediment (0–3 cm) at 94 stations ranging from 21 to 1995 m water depth off Tokachi, Hokkaido, Japan, to elucidate the distribution and source of sedimentary organic matter. Suspended particulate organic matter (POM) in the seawater and suspended POM and sediment in the Tokachi River were also examined. δ¹³C, δ¹⁵N and C / N ratios of the samples in the Tokachi River suggest that the spring snowmelt is an important process for the transport of terrestrial organic matter to the coastal waters. δ¹³C values of suspended POM in the surface seawater were higher in May and November than in August, while δ¹⁵N values of the POM were higher in May and August than in November. These changes are attributed to seasonal changes in phytoplankton growth rate and nitrate availability. δ¹³C and δ¹⁵N values in the sediments off Tokachi were lowest near the Tokachi River mouth, and increased offshore to constant values that persisted from 134 to 1995 m water depth. The spatial variation in C / N ratios in the sediment mirrored those of δ¹³C and δ¹⁵N. Comparison of δ¹³C, δ¹⁵N and C / N ratios in the sediments off Tokachi with those in the Tokachi River and seawater indicates that about half of the organic matter in the sediment was of terrestrial origin near the Tokachi River mouth, and the sedimentary organic matter from 134 to 1995 m water depth was of marine origin. The organic C content in the sediment was high near the Tokachi River mouth, and also around 1000 m water depth. The C content was significantly correlated with silt plus clay content, with different regression lines for those stations shallower and deeper than 134 m, owing to several stations of higher C content with the elevated C / N ratio on the inner shelf. These results suggest that transport and deposition of organic-rich fine sediment particles by hydrodynamic processes were major factors controlling C content off Tokachi. In addition, the supply of a fraction of terrestrial organic matter with high C / N probably also affected C content on the inner shelf.  相似文献   

Possible effects of collisions on plate motions     

Makoto Yamano  Seiya Uyeda 《Tectonophysics》1985,119(1-4)

A large-scale collision at a plate boundary is expected to play an important role not only in the deformation at the boundary but also in the motion of the plate carrying the buoyant material to be accreted. Possible changes in rates and directions of such motions may be calculated provided that certain assumptions are made about the nature of the driving forces. In this model we shall assume basically that:

1. (1) an oceanic plate is driven by slab pull and ridge push, being resisted by basal asthenospheric drag and slab resistance; and

2. (2) because of detachment, slab pull is lost upon collision.

If, however, the calculated motion following collision has a convergent component at the boundary, a new subduction zone, with an increasing slab pull force, forms seaward of the accreting buoyant material.Calculations were first made on an idealized planar octagonal plate. Results indicated that, so long as the scale of collision is limited, changes in motion take place but the motion returns to the initial state. However, for large-scale collisions, the plate motion suffers a large directional change, which also changes the nature of some boundaries, and hence the motion approaches a new steady-state motion irreversibly. Calculations were then conducted on an idealized Philippine Sea plate on a spherical earth. For a sizable collision along the Taiwan-Philippine-Mindanao boundary, this boundary and perhaps the Bonin-Mariana boundary, may become a transform fault provided that slab pull-ridge push is the driving force. These results provide some support to Uyeda-McCabe model (1983) of episodic spreading of the Philippine Sea basins, as well as the predominance of strike-slip motion along collision boundaries. Finally, in agreement with prior studies, subduction of a ridge system, assumed to have been located along the southwestern rim of the Paleo-Pacific plate, was shown to be consistent with the change in direction of motion of that plate at 43 m.y.B.P.Calculations conducted in this study show that predicted changes are model dependent so that comparisons with observed or inferred motions may be useful as a means of estimating the relative importance of the various potential driving forces.  相似文献   

Seismotectonics and tectonic history of the andaman sea     

Takao Eguchi  Seiya Uyeda  Tadashi Maki 《Tectonophysics》1979,57(1):35-51

The Andaman Sea is considered as an actively spreading back-arc basin. Seismicity and newly determined focal-mechanism solutions in the Andaman Sea area support this view. The tectonic history of the region is inferred from magnetic lineations in the northeastern Indian Ocean and the northward motion of Greater India. The mid-oceanic ridge which migrated northward along the east side of the Ninetyeast Ridge collided with the western end of the “old Sunda Trench” in the Middle or Late Miocene (10–20 m.y. B.P.). This ridge—trench collision released much of the compressional stress in the back-arc area and the continued northward movement of India that collided with Eurasia exerted a drag on the back-arc region, causing the opening of the Andaman Sea. In appearance, the subducted ridge jumped to the back-arc area. Thus, the Andaman Sea is not an ordinary subduction-related back-arc basin, but probably a basin formed by oblique extensional rifting associated with both ridge subduction and deformation of the back-arc area caused by a nearby continental collision.  相似文献   

Terrestrial heat flow in Japan     

Ki-Iti Hôrai  Seiya Uyeda  Tsuneji Rikitake 《Bulletin of Volcanology》1964,27(1):191-193

Terrestrial heat flow, Q=K×ΔT/ΔZ cal/cm² sec has been determined at 51 localities (39 on land and 12 in the sea) in and around the Japanese Islands. The average values of observed heat flow in land and sea are 1.53µ cal/cm²sec and 1.48µcal/cm²sec respectively. These value do not differ greatly from the world’s averages. The outstanding features of the heat flow distribution are as follows:a) High heat flow region (Q>2.0µcal/cm²sec) exists in the Inner Zone of the Honshu Arc. This region of high heat flow is more distinct in the northeastern Japan than in the southwestern Japan.b) The High heat flow region seems to extend, through the Fossa Magna area, down to the Izu-Mariana Arc.c) It is also probable that a similar high heat flow zone exists in the inner side of the Kurile Arc.d) These zones of high heat flow precisely coincide with the zones of the Cenozoic orogeny in the area concerned.e) Far off the coast of the northeastern Japan, the area at about 150° E may be a high heat flow region.f) Low heat flow (Q<1.0µcal/cm²sec) prevails in the Pacific coast side of the northeastern Japan and in the oceanic area directly east of it, including the area of the Japan Trench.g) The region bounded by the above mentioned high and low heat flow regions has heat flow which is more or less normal. Based on these measurements, a « steady state ” temperature distribution in the crust has been calculated for each of the above regions of high, low and intermediate heat flow, and it was found that there is a large temperature differences between the bottom of the crust of the high and low heat flow regions: the temperature at the Moho boundary in the high heat flow regions should be as high as some 800～1000°C (d=27 km), whereas that under the low heat flow region should be only about 200°C (d=23 km). The high general temperature at the Moho under the high heat flow region seems to favor a production of magma in the upper mantle. Calculated Moho temperatures disfavor the hypothesis that the Moho boundary is due to phase transition.  相似文献   

Supercritical Fluid CO2 Technique for Destruction of Pathogenic Fungal Spores in Solid Clinical Wastes          下载免费PDF全文

Efaq A. Noman  Nik N. N. A. Rahman  Mohammad Shahadat  Hideyuki Nagao  Adel Al‐Gheethi  Tengku N. T. Lah.  Abdul K. M. Omar 《洁净——土壤、空气、水》2016,44(12):1700-1708

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