Cordilleran-type orogeny and episodic growth of continents: Insights from the circum-Pacific continental margins     

Takahiro Tagami  & Noriko Hasebe 《Island Arc》1999,8(2):206-217

A new material migration hypothesis for the plate subduction zone orogeny, so-called ‘the cordilleran-type orogeny’, is proposed on the basis of geological constraints as well as mechanics of accretionary wedges. The major tectonic processes of the hypothesis comprise: (i) episodic, extensive magmatism along the margin of an overriding plate; (ii) supply of voluminous igneous and eroded materials through forearc to trench, with an increase in the net sediment influx into trench; (iii) accelerated accretion of sediments beneath an overriding older accretionary wedge; and (iv) upward material migration within the wedge and resultant exhumation of high-P/T metamorphic rocks near the inland margin of the wedge. This hypothesis was validated by the test using available geo- and thermo-chronological data from two classical types of subduction-related orogens in Southwest Japan and California. The hypothesis, coupled with the thermochronologic point of view, requires the reconsideration of coevality of paired metamorphism. The temporal pairing is to be observed between the beginning of the regional high-T/P metamorphism and that of the uplift and exhumation of high-P/T metamorphism, with some time lag needed for material migration. Where the temporal pairing is examined therefore, the formation age of igneous rocks and related high-T/P metamorphic rocks should be compared to the exhumation age of high-P/T metamorphic rocks. The episodic, extensive magmatism that triggers the cordilleran-type orogeny shows a temporal correlation in the mid-Cretaceous for most circum-Pacific continental margins. The resultant widespread formation of accretionary complexes is also observed in the western part of the circum-Pacific margins. The deduced mid-Cretaceous circum-Pacific orogeny accompanied a gross increase in the continental crust production rate, and was approximately coeval with the Pangea breakup and the Central Pacific superplume episode, implying the orogeny as a part of the mid-Cretaceous pulsation of the Earth.  相似文献   

哈密盆地北缘活动断裂带微地貌     

柏美祥  罗福忠  李军  今泉俊文  宫内崇裕  原四强  麻勇 《内陆地震》1999,13(2):162-168

哈密盆地北线活动断裂带走向北西西,断续长180km。8条剖面的GPS测量结果显示,断坎坡度为15°～18°及31°～33°．单个断崖高3～10m。由年代学资料计算出该断裂带中全新世垂直活动速率为0．65±0．08mm／a,比晚更新世晚期垂直活动速率有所增大。  相似文献   

http://www.sciencedirect.com/science/article/pii/S1674987112000643   总被引：2，自引：1，他引：1  

Takahiro Endo  Toshiaki Tsunogae  M.Santosh  E.Shaji 《地学前缘(英文版)》2012,3(6):801-811

Incipient charnockites represent granulite formation on a mesoscopic scale and have received considerable attention in understanding fluid processes in the deep crust.Here we report new petrological data from an incipient charnockite locality at Rajapalaiyam in the Madurai Block,southern India,and discuss the petrogenesis based on mineral phase equilibrium modeling and pseudosection analysis. Rajapalaiyam is a key locality in southern India from where diagnostic mineral assemblages for ultrahigh-temperature（UHT） metamorphism have been reported.Proximal to the UHT rocks are patches and lenses of charnockite（Kfs + Qtz + Pl + Bt + Opx + Grt + Ilm） occurring within Opx-free Grt-Bt gneiss（Kfs + Pl + Qtz + Bt + Grt + Ilm + Mt） which we report in this study.The application of mineral equilibrium modeling on the charnockitic assemblage in NCKFMASHTO system yields a p-T range of～820℃and～9 kbar.Modeling of the charnockite assemblage in the MnNCKFMASHTO system indicates a slight shift of the equilibrium condition toward lower p and T（～760℃and～7.5 kbar）. which is consistent with the results obtained from geothermobarometry（710—760℃,6.7—7.5 kbar）. but significantly lower than the peak temperatures（>1000℃） recorded from the UHT rocks in this locality,suggesting that charnockitization is a post-peak event.The modeling of T versus molar H₂O content in the rock（M（H₂O）） demonstrates that the Opx-bearing assemblage in charnockite and Opxfree assemblage in Grt-Bt gneiss are both stable at M（H₂O） = 0.3 mol%-0.6 mol%.and there is no significant difference in water activity between the two domains.Our finding is in contrast to the previous petrogenetic model of incipient charnockite formation which envisages lowering of water activity and stabilization of orthopyroxene through breakdown of biotite by dehydration caused by the infiltration of CO₂-rich fluid.T-X_Fe³⁺（= Fe₂O₃/（FeO + Fe₂O₃） in mole） pseudosections suggest that the oxidation condition of the rocks played a major role on the stability of orthopyroxene:Opx is stable at X_Fe³⁺ <0.03 in charnockite.while Opx-free assemblage in Grt-Bt gneiss is stabilized at X_Fe³⁺ >0.12.Such low oxygen fugacity conditions of X_Fe³⁺ <0.03 in the charnockite compared to Grt-Bt gneiss might be related to the infiltration of a reduced fluid（e.g.,H₂O + CH₄） during the retrograde stage.  相似文献   

He+ ion implantation and electron irradiation effects on cathodoluminescence of plagioclase     

Masahiro Kayama  Hirotsugu Nishido  Shin Toyoda  Kosei Komuro  Adrian A. Finch  Martin R. Lee  Kiyotaka Ninagawa 《Physics and Chemistry of Minerals》2013,40(7):531-545

Cathodoluminescence (CL) spectra of unirradiated, He⁺ ion-implanted and electron-irradiated plagioclase minerals contain the following emission bands: (1) below 300 nm due to Pb²⁺, (2) at ~320 and ~350 nm to Ce³⁺, (3) at 380–420 nm to Eu²⁺, Ti⁴⁺ and/or Al–O^?–Al/Ti defects, (4) at 560–580 nm to Mn²⁺ and (5) at 720–760 nm to Fe³⁺. During the implantation of He⁺ ion, much of their energy may be dissipated by partial destruction and strain of the feldspar framework, resulting in quenching of CL. Deconvolution of CL spectra acquired from albite and oligoclase reveals an emission component at 1.86 eV (666 nm) assigned to a radiation-induced defect center associated with Na⁺ atoms. As its intensity increases with radiation dose, this emission component has potential for geodosimetry and geochronometry. Electron irradiation causes Na⁺ migration in plagioclase, and then a considerable reduction in intensity of emissions assigned to impurity centers, which is responsible for an alteration in the energy state or a decrease in luminescence efficiency following the change of activation energy. Emission intensity at 1.86 eV positively correlates with electron irradiation time for unimplanted and He⁺ ion-implanted albite and oligoclase, but negatively for the implanted albite above 1.07 × 10^?4 C/cm². It implies that radiation halo produced by α-particles should not be measured using CL spectroscopy to estimate β radiation dose on albite in the high radiation level.  相似文献   

Geometry of stress function surfaces for an asymmetric continuum     

Takahiro Yajima  Kazuhito Yamasaki  Hiroyuki Nagahama 《Acta Geophysica》2013,61(6):1703-1721

A two-dimensional stress field of dislocation or fault is geometrically studied for an asymmetric continuum. For geometric surfaces of the stress and couple-stress functions, the mean and Gaussian curvatures are derived. The mean curvature of couple-stress function surface is connected with the asymmetric of stress tensor. Moreover, the Gaussian curvature of stress function surface is characterized by both the stress and couple-stress. On the other hand, the mean curvature of stress function surface is not affected by the asymmetry of stress. Based on these geometric expressions, the Coulomb’s failure criterion and the friction coefficient are expressed by the curvatures of couple-stress function surface. Moreover, geometric structures of stress and couple stress function surfaces are shown for edge and wedge dislocations as faults. The curvatures of these surfaces show that the effect of couple-stress is constrained around the dislocations only.  相似文献   

Interannual variability of North Pacific eastern subtropical mode water formation in the 1990s derived from a 4-dimensional variational ocean data assimilation experiment     

T. Toyoda  T. Awaji  S. Masuda  N. Sugiura  H. Igarashi  T. Mochizuki  Y. Ishikawa 《Dynamics of Atmospheres and Oceans》2011,51(1-2):1-25

The interannual variability of eastern subtropical mode water (ESTMW) formation in the North Pacific is examined using a new ocean dataset constructed by a 4-dimensional variational data assimilation experiment covering the decade of the 1990s. The volume of newly formed ESTMW varies due to interannual variability in the following three physical processes taking place in the surface layer: (1) convergence in the transport of surface saline water induced by Ekman flow in the vicinity of the formation region, (2) thermal stratification in the preconditioning phase in association with the insolation anomaly induced largely by low-level cloud coverage, and (3) wintertime surface cooling in the eastern subtropics. We find that, in addition to the surface forcing, the properties of both the ESTMW and the upper mixed-layer water are broadly controlled by the volume of the new ESTMW component, and that the variations in the upper mixed-layer water affect the properties of ESTMW formed in the following winter. Due to the combined effect of these processes, the ESTMW subducts down to subsurface layers with a wide range of σ_θ values lying between 24.8 and 25.4 and with significant interannual variation in water mass formation.  相似文献   

The Maimai M8 experimental catchment database: Forty years of process-based research on steep,wet hillslopes     

Jeffrey J. McDonnell  Chris Gabrielli  Ali Ameli  Jagath Ekanayake  Fabrizio Fenicia  Jim Freer  Chris Graham  Brian McGlynn  Uwe Morgenstern  Alain Pietroniro  Takahiro Sayama  Jan Seibert  Mike Stewart  Kellie Vache  Markus Weiler  Ross Woods 《水文研究》2021,35(5):e14112

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Validation of TRMM Precipitation Radar satellite data over Indonesian region     

Rakhmat Prasetia  Abd. Rahman As-syakur  Takahiro Osawa 《Theoretical and Applied Climatology》2013,112(3-4):575-587

Research has been conducted to validate monthly and seasonal rain rates derived from the Tropical Rainfall Measuring Mission Precipitation Radar (PR) using rain gauge data analysis from 2004 to 2008. The study area employed 20 gauges across Indonesia to monitor three Indonesian regional rainfall types. The relationship of PR and rain gauge data statistical analysis included the linear correlation coefficient, the mean bias error (MBE), and the root mean square error (RMSE). Data validation was conducted with point-by-point analysis and spatial average analysis. The general results of point-by-point analysis indicated satellite data values of medium correlation, while values of MBE and RMSE tended to indicate underestimations with high square errors. The spatial average analysis indicated the PR data values are lower than gauge values of monsoonal and semi-monsoonal type rainfall, while anti-monsoonal type rainfall was overestimated. The validation analysis showed very good correlation with the gauge data of monsoonal type rainfall, high correlation for anti-monsoonal type rainfall, but medium correlation for semi-monsoonal type rainfall. In general, the statistical error level of monthly seasonal monsoonal type conditions is more stable compared to other rainfall types. Unstable correlations were observed in months of high rainfall for semi-monsoonal and anti-monsoonal type rainfall.  相似文献   

Millennial-scale oscillations of the westerly jet path during the last glacial period   总被引：1，自引：0，他引：1  

Kana Nagashima  Ryuji Tada  Atsushi Tani  Youbin Sun  Yuko Isozaki  Shin Toyoda  Hitoshi Hasegawa 《Journal of Asian Earth Sciences》2011,40(6):239-1220

It has been established that East Asian summer monsoon intensity varies with Dansgaard–Oeschger cycles, suggesting a connection between the climates of East Asia and the North Atlantic on a millennial timescale. However, the dynamics of such a connection are still unsolved. Here we demonstrate that temporal changes in the provenance of aeolian dust in Japan Sea sediments, which we interpret to reflect changes in the westerly jet path over East Asia, exhibit variations in harmony with Dansgaard–Oeschger cycles. The dominance of dust with a Mongolian Gobi provenance during stadials suggests a westerly jet axis located to the south of the Himalaya–Tibetan Plateau throughout most of the year, whereas the co-dominance of dust from both the Taklimakan Desert and the Mongolian Gobi during interstadials suggests that the westerly jet axis jumped to the north of the Tibetan Plateau at latest in summer. As the shift of the westerly jet axis to the north of the Tibetan Plateau is closely related to the onset of the East Asian summer monsoon, changes of the westerly jet path apparently critically affect the teleconnection between the climates of Asia and North Atlantic on a millennial timescale.  相似文献   

Decline in heavy metal contamination in marine sediments in Jakarta Bay,Indonesia due to increasing environmental regulations     

Takahiro Hosono  Chih-Chieh Su  Robert Delinom  Yu Umezawa  Tomoyo Toyota  Shinji Kaneko  Makoto Taniguchi 《Estuarine, Coastal and Shelf Science》2011

The ²¹⁰Pb geochronology, heavy metal concentrations (Zn, Cu, and Pb), and stable Pb isotope ratios (²⁰⁶Pb/²⁰⁷Pb) of three sediment cores collected from Jakarta Bay were analyzed to decipher the history of heavy metal contamination in the period 1900–2006. The chemical and isotopic analyses clearly suggest that anthropogenic metal accumulation in the sediments began in the 1920s and increased greatly from the 1970s until the end of the 1990s. From the end of the 1990s to 2006, accumulation rates were constant or decreased for Zn and Pb near the coastal industrialized area. Comparison of economic data and sociological information suggests that the decline in the concentrations of heavy metals could be attributed to the stricter environmental regulations which were enforced at the end of 1990s. However, metal contamination is currently still an important cause of concern in dealing with environmental preservation and protection in Jakarta Bay.  相似文献