Mantle diapir-induced arc volcanism: The Ueno Basalts, Nomugi-Toge and Hida volcanic suites, central Japan   总被引：2，自引：0，他引：2  

Jun-Ichi Kimura  & Takeyoshi Yoshida 《Island Arc》1999,8(2):304-322

Stratigraphic and geochronological data show that the late Cenozoic Ueno Basalts and related Nomugi-Toge and Hida volcanic suites of the Norikura Volcanic Chain, Japan, were active for ~ 1 million years. Temporal and spatial variations of the volcanic activity and chemistry of the volcanic products suggest that it was induced by a common mantle diapir. The Ueno Basalts are small monogenetic volcanoes scattered over an area 50 km in diameter, and comprise a small volcanic province. The Ueno Basalts are almost all subalkalic basalt to basaltic andesite, erupted through the late Pliocene to the earliest Pleistocene (2.7–1.5 Ma). Andesite to dacite of the Nomugi-Toge volcanic rocks were concurrently active in the back arc side, and two eruption stages (2.6–2.2 and 2.1–1.7 Ma) are recognizable. Two voluminous dacite and rhyolite ignimbrites, the Hida Volcanic Rocks, were erupted deeper in the back-arc region, at ca 1.75 and 1.7 Ma. Both the Nomugi-Toge and Hida suites are also subalkalic, except for the last ignimbrite. In the Ueno Basalts, alkali olivine basalt was erupted in the earliest stage, and was followed by subalkalic basalt, showing that the magma segregation depth ascended with time. This coincided with uplift of the volcanic province and with quasi-concentric expansion of the eruption centers, suggesting that an upwelling mantle diapir was the cause of the volcanism. The Nomugi-Toge andesite–dacite lavas and the Hida dacite and rhyolite ignimbrites are considered to have originated from the same mantle diapir, because of their close proximity to the Ueno Basalts and their near-contemporaneous activity. Mantle diapirs have a significant role in the origin of subalkalic volcanic rocks in the island arcs.  相似文献   

Magma plumbing system beneath Ontake Volcano, central Japan   总被引：2，自引：0，他引：2  

Jun-Ichi Kimura  & Takeyoshi Yoshida 《Island Arc》1999,8(1):1-29

Ontake Volcano in central Japan was last active from ~ 100–35 Ka. The eruptions contained rhyodacite pumice and lavas in the first stage (stage O1, > 33 km³), followed by eruptions of andesite lavas and pyroclastics (stages O2 and O3, > 16 km³). Modeling of major and incompatible elements with Sr isotope ratios suggests that the primary magma was a high-alumina basalt. One andesite magma type appears to have evolved from the basalt in a closed system magma chamber, in part by fractional crystallization, and its generation included crustal assimilation. The other andesite magma type is considered to have evolved in an open system magma chamber in which repeated input of primary magma occurred together with wall-rock assimilation and fractional crystallization. The rhyodacite is inferred to have evolved in a closed system magma chamber by fractional crystallization of the second type of andesite. These genetic relationships require that the magma chamber functioned alternately as an open and a closed system. Geobarometry indicates that there may have been multiple magma chambers, located in the upper crust for the rhyodacite, near the upper–lower crust interface for the andesite and in the mid-lower crust for the basalt. These chambers were stacked to form the magma plumbing system of Ontake. Incompatible element compositions of the basalt are considered to have changed during the eruptions, suggesting that two different plumbing systems for stage O1 magma and for stages O2, O3 magmas existed during the 65 Ka of activity. Evolutionary history of the systems implies that the primary magma was introduced into the magma plumbing system each for ~ 17 500 years and that the life span of a magma plumbing system was shorter than 40 Ka.  相似文献   

Five Years' Activity of IGCP-368 “Proterozoic Events in East Gondwana”     

M. Yoshida  M. Santosh  C.B. Dissanayake 《Gondwana Research》1999,2(4):638-641

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The XUV Doppler Telescope (XDT)     

Sakao  T.  Tsuneta  S.  Hara  H.  Shimizu  T.  Kano  R.  Kumagai  K.  Yoshida  T.  Nagata  S.  Kobayashi  K. 《Solar physics》1999,187(2):303-333

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The 21-cm signature of early relic H ii regions     

Midori Tokutani  Naoki Yoshida  S. Peng Oh  Naoshi Sugiyama 《Monthly notices of the Royal Astronomical Society》2009,395(2):777-780

We calculate the spin temperature and 21-cm brightness of early H  ii regions around the first stars. We use outputs from cosmological radiation-hydrodynamics simulations of the formation and evolution of early H  ii regions. In the pre-re-ionization era, H  ii regions around massive primordial stars have diameters of a few kpc. The gas within the H  ii regions is almost fully ionized, but begins recombining after the central stars die off. The relic H  ii regions are then seen as bright emission sources in hydrogen 21 cm. We make brightness temperature maps of the H  ii regions, accounting for radiative coupling with Lyman α photons in a simplified manner. The spin temperature in the relic H  ii region is close to the gas kinetic temperature, generally several hundred to several thousand degrees. We show that the relic H  ii region can be as bright as  δ T _b∼ 100 mK  in differential temperature against the cosmic microwave background for an angular resolution of subarcseconds. While individual early H  ii patches will not be identified by currently planned radio telescopes, the collective fluctuations from early H  ii regions might imprint signatures in the 21-cm background.  相似文献   

Calcareous duricrust, Al Qasim Province, Saudi Arabia: Occurrence and origin     

M.A. Khalifa  Fujio Kumon  Kokhi Yoshida 《Quaternary International》2009,209(1-2):163

In Al Qasim Province, Saudi Arabia, calcareous pedogenic duricrust overlies the Upper Permian carbonates and clays of the Khuff Formation, and ranges in thickness from 60 cm to 2 m. It consists of white sandy duricrust capped by brown, nodular porous duricrust. Petrographic investigation led to recognition of three lithofacies that show spatial distribution: 1- structureless sandy calcareous mudstone, 2- brecciated-nodular calcareous mudstone, and 3- pisolitic calcareous mudstone. The diagenetic changes in duricrust are aggrading neomorphism and formation of calcite rims around quartz grains. Microprobe chemical analysis was performed on the diagenetically altered material. The development of the duricrust is controlled by four factors: the climate changes, the type of underlying rocks, source of carbonate and biological effects. The repeated changes from semi-arid climate with alternating wet and dry seasons are the main controlling factor, in generation of duricrust development. During humid periods, descending water carries the dissolved carbonates downward as bicarbonates, whereas dry and interpluvial period, the carbonate-rich solutions are carried upwards by capillary or evaporation. The claystone and sandstone interbeds possibly affect the development of calcareous duricrust, more than the sandstones and dolostones, because the former have the ability to attach calcium carbonate to form the duricrust. The development of calcareous duricrust is mainly attributed to the Pleistocene and Early Holocene alternating humid and arid periods that prevailed over the Arabian Peninsula during this time.  相似文献   

Genesis and Mixing/Mingling of Mafic and Felsic Magmas of Back-Arc Granite: Miocene Tsushima Pluton, Southwest Japan     

Ki-Cheol Shin    Masanori Kurosawa    Ryo Anma    Takanori Nakano 《Resource Geology》2009,59(1):25-50

The Middle Miocene Tsushima granite pluton is composed of leucocratic granites, gray granites and numerous mafic microgranular enclaves (MME). The granites have a metaluminous to slightly peraluminous composition and belong to the calc‐alkaline series, as do many other coeval granites of southwestern Japan, all of which formed in relation to the opening of the Sea of Japan. The Tsushima granites are unique in that they occur in the back‐arc area of the innermost Inner Zone of Southwest Japan, contain numerous miarolitic cavities, and show shallow crystallization (2–6 km deep), based on hornblende geobarometry. The leucocratic granite has higher initial ⁸⁷Sr/⁸⁶Sr ratios (0.7065–0.7085) and lower ε_Nd(t) (?7.70 to ?4.35) than the MME of basaltic–dacitic composition (0.7044–0.7061 and ?0.53 to ?5.24), whereas most gray granites have intermediate chemical and Sr–Nd isotopic compositions (0.7061–0.7072 and ?3.75 to ?6.17). Field, petrological, and geochemical data demonstrate that the Tsushima granites formed by the mingling and mixing of mafic and felsic magmas. The Sr–Nd–Pb isotope data strongly suggest that the mafic magma was derived from two mantle components with depleted mantle material and enriched mantle I (EMI) compositions, whereas the felsic magma formed by mixing of upper mantle magma of EMI composition with metabasic rocks in the overlying lower crust. Element data points deviating from the simple mixing line of the two magmas may indicate fractional crystallization of the felsic magma or chemical modification by hydrothermal fluid. The miarolitic cavities and enrichment of alkali elements in the MME suggest rapid cooling of the mingled magma accompanied by elemental transport by hydrothermal fluid. The inferred genesis of this magma–fluid system is as follows: (i) the mafic and felsic magmas were generated in the mantle and lower crust, respectively, by a large heat supply and pressure decrease under back‐arc conditions induced by mantle upwelling and crustal thinning; (ii) they mingled and crystallized rapidly at shallow depths in the upper crust without interaction during the ascent of the magmas from the middle to the upper crust, which (iii) led to fluid generation in the shallow crust. The upper mantle in southwest Japan thus has an EMI‐like composition, which plays an important role in the genesis of igneous rocks there.  相似文献   

Occurrence of water ponding on soil surfaces depending on infiltration rates on Mongolian rangeland          下载免费PDF全文

Katori Miyasaka  Sho Shiozawa  Kazuhiro Nishida  Siilegmaa Batsukh  Shuichiro Yoshida  Undarmaa Jamsran 《水文研究》2017,31(22):3996-4005

The occurrence of water ponding on soil surfaces during and after heavy rainfall produces surface run‐off or surface water accumulation in low‐lying areas, which might reduce the water supply to soils and result in a reduction of the soil water that plants can use, especially in arid climates. On Mongolian rangeland, we observed ponded water on the surface of a specific soil condition subjected to a heavy rainfall of 30 mm/hr. By contrast, ponded water was not observed for the same type of soil where livestock grazing had been removed for 6–8 years via a fence or for nearby soil containing less clay. We measured the infiltration rate (the saturated hydraulic conductivity of the surface soil, K_s) of the three sites by applying ponded water on the soil surface (an intake rate test). The results showed that K_s in the rangeland was lower than the rainfall intensity in the site where water ponded on the soil surface; however, K_s of the soil inside of the fence has recovered to 3 times that of the soil outside of the fence to exceed the rainfall intensity. Heavy rainfall that exceeds the infiltration rate occurs several times a year at the livestock grazing site where we observed ponded water. Slight water repellency of the soil reduces rain infiltration to increase the possibility of surface ponding for the soil.  相似文献   

Relationships between Kuroko volcanogenic massive sulfide (VMS) deposits, felsic volcanism, and island arc development in the northeast Honshu arc, Japan     

Ryoichi Yamada  Takeyoshi Yoshida 《Mineralium Deposita》2011,46(5-6):431-448

The northeast (NE) Honshu arc was formed by three major volcano-tectonic events resulting from Late Cenozoic orogenic movement: continental margin volcanism (before 21?Ma), seafloor basaltic lava flows and subsequent bimodal volcanism accompanied by back-arc rifting (21 to 14?Ma), and felsic volcanism related to island arc uplift (12 to 2?Ma). Eight petrotectonic domains, parallel to the NE Honshu arc, were formed as a result of the eastward migration of volcanic activity with time. Major Kuroko volcanogenic massive sulfide (VMS) deposits are located within the eastern marginal rift zone (Kuroko rift) that formed in the final period of back-arc rifting (16 to 14?Ma). Volcanic activity in the NE Honshu arc is divided into six volcanic stages. The eruption volumes of volcanic rocks have gradually decreased from 4,600?km³ (per 1?my for a 200-km-long section along the arc) of basaltic lava flows in the back-arc spreading stage to 1,000?C2,000?km³ of bimodal hyaloclastites in the back-arc rift stage, and about 200?km³ of felsic pumice eruptions in the island arc stage. The Kuroko VMS deposits were formed at the time of abrupt decrease in the eruption volume and change in the mode of occurrence of the volcanic rocks during the final period of back-arc rifting. In the area of the Kuroko rift, felsic volcanism changed from aphyric or weakly plagioclase phyric (before 14?Ma), to quartz and plagioclase phyric with minor clinopyroxene (12 to 8?Ma), to hornblende phyric (after 8?Ma), and hornblende and biotite phyric (after 4?Ma). The Kuroko VMS deposits are closely related to the aphyric rhyolitic activity before 14?Ma. The rhyolite was generated at a relatively high temperature from a highly differentiated part of felsic magma seated at a relatively great depth and contains higher Nb, Ce, and Y contents than the post-Kuroko felsic volcanism. The Kuroko VMS deposits were formed within a specific tectonic setting, at a specific period, and associated with a particular volcanism of the arc evolution process. Therefore, detailed study of the evolutional process from rift opening to island arc tectonics is very important for the exploration of Kuroko-type VMS deposits.  相似文献   

2011年日本东北近海地震震源上方的位移     

M.Sato  T.Ishikawa  N.Ujihara  S.Yoshida  M.Fujita  M.Mochizuki  A.Asada  万永革 《世界地震译丛》2011,(3)

2011年3月11日,一次大的板间地震(MW9.0)发生在日本东北宫城县附近的板块交界处。根据余震分布推测的震源区为约500km长、200km宽的近海区(Japan Meteo-rological Agency,2011)。  相似文献