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21.
Daishido Tsuneaki Asuma Kuniyuki Ohkawa Tohru Obara Hirayoshi Komatsu Shinichi Nagane Kiyoshi 《Astrophysics and Space Science》1986,118(1-2):467-469
An FFT processor is being developed for the present pilot system of the large field radio patrol camera. A design of the processor is discussed.Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984. 相似文献
22.
A large volume of middle Miocene basaltic rocks is widely distributed across the back-arc region of Northeast Japan, including around the Dewa Mountains. Petrological research has shown that basaltic rocks of the Aosawa Formation around the Dewa Mountains were generated as a result of the opening of the Sea of Japan. To determine the precise ages of the middle Miocene basaltic magmatism, we conducted U–Pb and fission-track (FT) dating of a rhyolite lava that constitutes the uppermost part of the Aosawa Formation. In addition, we estimated the paleostress field of the volcanism using data from a basaltic dike swarm in the same formation. The rhyolite lava yields a U–Pb age of 10.73 ±0.22 Ma (2σ) and a FT age of 10.6 ±1.6 Ma (2σ), and the paleostress analysis suggests a normal-faulting stress regime with a NW–SE-trending σ3-axis, a relatively high stress ratio, and a relatively high magma pressure. Our results show that the late Aosawa magmatism occurred under NW–SE extensional stress and ended at ~ 11 Ma. 相似文献
23.
Radon concentrations in soil gas,considering radioactive equilibrium conditions with application to estimating fault-zone geometry 总被引:1,自引:0,他引:1
A calculation method for determining the amount of Rn isotopes and daughter products at the start of measurement (CRAS) is
proposed as a more accurate means of estimating the initial Rn concentration in soil gas. The CRAS utilizes the decay law
between 222Rn and 220Rn isotopes and the daughter products 218Po and 216Po, and is applicable to α-scintillation counter measurements. As Rn is both inert and chemically stable, it is useful for
fault investigation based on the soil gas geochemistry. However, the total number of α particles emitted by the decay of Rn
has generally been considered to be proportional to the initial Rn concentration, without considering the gas condition with
respect to radioactive equilibrium. The CRAS method is shown to be effective to derive Rn concentration for soil gases under
both nonequilibrium conditions, in which the total number of decays increases with time, and equilibrium conditions, which
are typical of normal soil under low gas flux. The CRAS method in conjunction with finite difference method simulation is
applied to the analysis of two active fault areas in Japan, and it is demonstrated that this combination could detect the
sharp rises in 222Rn concentrations associated with faults. The method also allows the determination of fault geometry near the surface based
on the asymmetry variation of the Rn concentration distribution when coupled with a numerical simulation of 222Rn transport. The results for the new method as applied to the two case studies are consistent with the data collected from
the geological survey. It implies that the CRAS method is suitable for investigating the fault system and interstitial gas
mobility through fractures. The present analyses have also demonstrated that high Rn concentrations require the recent and
repeated accumulation of 222Rn parents (230Th and 226Ra) in fault gouges through deep gas release during fault movement. 相似文献
24.
Detrital zircon multi‐chronology,provenance, and low‐grade metamorphism of the Cretaceous Shimanto accretionary complex,eastern Shikoku,Southwest Japan: Tectonic evolution in response to igneous activity within a subduction zone 下载免费PDF全文
Hidetoshi Hara Yoshihiro Nakamura Kousuke Hara Toshiyuki Kurihara Hiroshi Mori Hideki Iwano Tohru Danhara Shuhei Sakata Takafumi Hirata 《Island Arc》2017,26(6)
Detrital zircon multi‐chronology combined with provenance and low‐grade metamorphism analyses enables the reinterpretation of the tectonic evolution of the Cretaceous Shimanto accretionary complex in Southwest Japan. Detrital zircon U–Pb ages and provenance analysis defines the depositional age of trench‐fill turbidites associated with igneous activity in provenance. Periods of low igneous activity are recorded by youngest single grain zircon U–Pb ages (YSG) that approximate or are older than the depositional ages obtained from radiolarian fossil‐bearing mudstone. Periods of intensive igneous activity recorded by youngest cluster U–Pb ages (YC1σ) that correspond to the younger limits of radiolarian ages. The YC1σ U–Pb ages obtained from sandstones within mélange units provide more accurate younger depositional ages than radiolarian ages derived from mudstone. Determining true depositional ages requires a combination of fossil data, detrital zircon ages, and provenance information. Fission‐track ages using zircons estimated YC1σ U–Pb ages are useful for assessing depositional and annealing ages for the low‐grade metamorphosed accretionary complex. These new dating presented here indicates the following tectonic history of the accretionary wedge. Evolution of the Shimanto accretionary complex from the Albian to the Turonian was caused by the subduction of the Izanagi plate, a process that supplied sediments via the erosion of Permian and Triassic to Early Jurassic granitic rocks and the eruption of minor amounts of Early Cretaceous intermediate volcanic rocks. The complex subsequently underwent intensive igneous activity from the Coniacian to the early Paleocene as a result of the subduction of a hot and young oceanic slab, such as the Kula–Pacific plate. Finally, the major out‐of‐sequence thrusts of the Fukase Fault and the Aki Tectonic Line formed after the middle Eocene, and this reactivation of the Shimanto accretionary complex as a result of the subduction of the Pacific plate. 相似文献
25.
Harutaka Sakai Minoru Sawada Yutaka Takigami Yuji Orihashi Tohru Danhara Hideki Iwano Yoshihiro Kuwahara Qi Dong Huawei Cai Jianguo Li 《Island Arc》2005,14(4):297-310
Abstract Newly discovered peloidal limestone from the summit of Mount Qomolangma (Mount Everest) contains skeletal fragments of trilobites, ostracods and crinoids. They are small pebble-sized debris interbedded in micritic bedded limestone of the Qomolangma Formation, and are interpreted to have been derived from a bank margin and redeposited in peri-platform environments. An exposure of the Qomolangma detachment at the base of the first step (8520 m), on the northern slope of Mount Qomolangma was also found. Non-metamorphosed, strongly fractured Ordovician limestone is separated from underlying metamorphosed Yellow Band by a sharp fault with a breccia zone. The 40 Ar–39 Ar ages of muscovite from the Yellow Band show two-phase metamorphic events of approximately 33.3 and 24.5 Ma. The older age represents the peak of a Barrovian-type Eo-Himalayan metamorphic event and the younger age records a decompressional high-temperature Neo-Himalayan metamorphic event. A muscovite whole-rock 87 Rb–86 Sr isochron of the Yellow Band yielded 40.06 ± 0.81 Ma, which suggests a Pre-Himalayan metamorphism, probably caused by tectonic stacking of the Tibetan Tethys sediments in the leading margin of the Indian subcontinent. Zircon and apatite grains, separated from the Yellow Band, gave pooled fission-track ages of 14.4 ± 0.9 and 14.4 ± 1.4 Ma, respectively. These new chronologic data indicate rapid cooling of the hanging wall of the Qomolangma detachment from approximately 350°C to 130°C during a short period (15.5–14.4 Ma). 相似文献
26.
Zircon U–Pb ages of plutonic rocks in the southern Abukuma Mountains: Implications for Cretaceous geotectonic evolution of the Abukuma Belt 下载免费PDF全文
Yutaka Takahashi Masumi Mikoshiba Kazuya Kubo Hideki Iwano Tohru Danhara Takafumi Hirata 《Island Arc》2016,25(2):154-188
Plutonic rocks in the southern Abukuma Mountains include gabbro and diorite, fine‐grained diorite, hornblende–biotite granodiorite (Ishikawa, Samegawa, main part of Miyamoto and Tabito, Kamikimita and Irishiken Plutons), biotite granodiorite (the main part of Hanawa Pluton and the Torisone Pluton), medium‐ to coarse‐grained biotite granodiorite and leucogranite, based on the lithologies and geological relations. Zircon U–Pb ages of gabbroic rocks are 112.4 ±1.0 Ma (hornblende gabbro, Miyamoto Pluton), 109.0 ±1.1 Ma (hornblende gabbro, the Hanawa Pluton), 102.7 ±0.8 Ma (gabbronorite, Tabito Pluton) and 101.0 ±0.6 Ma (fine‐grained diorite). As for the hornblende–biotite granodiorite, zircon U–Pb ages are 104.2 ±0.7 Ma (Ishikawa Pluton), 112.6 ±1.0 Ma (Tabito Pluton), 105.2 ±0.8 Ma (Kamikimita Pluton) and 105.3±0.8 Ma (Irishiken Pluton). Also for the medium‐ to fine‐grained biotite granodiorite, zircon U–Pb ages are 106.5±0.9 Ma (Miyamoto Pluton), 105.1 ±1.0 Ma (Hanawa Pluton) and the medium‐ to coarse‐grained biotite granodiorite has zircon U–Pb age of 104.5 ±0.8 Ma. In the case of the leucogranite, U–Pb age of zircon is 100.6 ±0.9 Ma. These data indicate that the intrusion ages of gabbroic rocks and surrounding granitic rocks ranges from 113 to 101 Ma. Furthermore, K–Ar ages of biotite and or hornblende in the same rock samples were dated. Accordingly, it is clear that these rocks cooled down rapidly to 300 °C (Ar blocking temperature of biotite for K–Ar system) after their intrusion. These chronological data suggest that the Abukuma plutonic rocks in the southern Abukuma Mountains region uplifted rapidly around 107 to 100 Ma after their intrusion. 相似文献
27.
Kazuhiko Kano Toshiyuki Yoshikawa Yukio Yanagisawa Kenshiro Ogasawara Tohru Danhara 《Island Arc》2002,11(3):170-184
Abstract The present paper describes the newly discovered early Miocene unconformity in the northern Noto Peninsula, on the Japan Sea side, central Japan. The unconformity marks the boundary between an early Miocene non-marine to marine succession and a more extensive, late early to early middle Miocene marine succession, and contains a time gap of an order of 1 million years or less from 18 Ma or earlier to 17 Ma. The early Miocene succession likely represents an early phase of marine transgression and initial slow rifting. The overlying early to early middle Miocene succession records the climax of the opening of the Japan Sea at ca 16 Ma with widespread, rapid subsidence of the Japan Arc. The unconformity between the two transgressive successions may represent a global sealevel fall or, more likely, crustal uplifting because no upward-shallowing or regressive facies remains between the two successions. Early Miocene unconformities that are thought to be correlative with this unconformity in the northern Noto Peninsula occur in places along the Japan Sea coast of Sakhalin and Japan. They are likely to have been produced during rifting in response to upwelling of asthenospheric mantle, although more accurate age constraints are necessary to evaluate this idea. 相似文献
28.
Magnetic fluctuations observed in the magnetosheath and the outer magnetosphere with Ogo-5 during 6 months from November 1968, are analyzed to examine the resonance theory that monochromatic waves excited outside the magnetosphere are transmitted in the compressional mode into the magnetosphere, being transmitted further along the closed field lines in the torsional mode and are finally observed as long-period pcs on the Earth's surface. Ten observed results on the wave characteristics of the fluctuations including variance, spectrum, relation to the plasma stream, integrated power, longitudinal dependence are obtained and summarized. The fluctuations in the magnetosheath are found to be dominantly Alfvénic. Several pieces of evidence to support the resonance theory are found. 相似文献
29.
Seiji Maruyama Keiji Takemura Takafumi Hirata Tohru Yamashita Tohru Danhara 《第四纪科学杂志》2020,35(1-2):66-80
The major and trace element concentrations of volcanic glass shards from visible tephra layers in the SG93 and SG06 cores from Lake Suigetsu, central Japan, were determined by femtosecond laser ablation–inductively coupled plasma–mass spectrometry. The glass-shard analyses, together with the petrographic properties of the tephra samples, allow the Suigetsu tephra layers to be broadly classified into tephras derived from calderas on Kyushu Island, and from Daisen and Sambe volcanoes in the Chugoku district of southwest Japan. The layers correlated with tephras from Kuju caldera and Daisen volcano, and with the younger Sambe tephras, have adakitic elemental features. A Suigetsu tephra sample correlated with the Sambe−Kisuki tephra based on petrographic properties has an elemental pattern similar to that of the Toya tephra from Hokkaido Island, northeast Japan. This match implies that tephras from northeast Japan, as well as Kyushu–Chugoku tephras, are possible correlatives of the Suigetsu tephra layers. Both petrographic properties and major–trace element data of volcanic glass shards are essential for robust tephra correlations, and hierarchical cluster analysis proved additionally useful in statistically evaluating relationships among the tephras. 相似文献
30.