Ryoichi Yamada
Tohoku University
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Featured researches published by Ryoichi Yamada.
Geological Society, London, Special Publications | 2014
Takeyoshi Yoshida; Jun-Ichi Kimura; Ryoichi Yamada; Valerio Acocella; Hiroshi Sato; Dapeng Zhao; Junichi Nakajima; Akira Hasegawa; Tomomi Okada; Satoru Honda; Masahiro Ishikawa; Oky Dicky Ardiansyah Prima; Takeshi Kudo; Bunichiro Shibazaki; Akiko Tanaka; Toshifumi Imaizumi
Abstract We review the evolution of late Cenozoic magmatism in the NE Japan arc, and examine the relationship between the magmatism and the crust–mantle structure. Recent studies reveal secular changes in the mode of magmatic activity, the magma plumbing system, erupted volumes and magmatic composition associated with the evolution of crust–mantle structures related to the tectonic evolution of the arc. The evolution of Cenozoic magmatism in the arc can be divided into three periods: the continental margin (66–21 Ma), the back-arc basin (21–13.5 Ma) and the island-arc period (13.5–0 Ma). Magmatic evolution in the back-arc basin and the island-arc periods appears to be related to the 2D to 3D change in the convection pattern of the mantle wedge related to the asthenosphere upwelling and subsequent cooling of the mantle. Geodynamic changes in the mantle caused back-arc basin basalt eruptions during the back-arc basin opening (basalt phase) followed by crustal heating and re-melting, which generated many felsic plutons and calderas (rhyolite/granite phase) in the early stage of the island-arc period. This was followed by crustal cooling and strong compression, which ensured vent connections and mixing between deeper mafic and shallower felsic magmas, erupting large volumes of Quaternary andesites (andesite phase).
Scientific Reports | 2016
Tatsuo Nozaki; Jun-ichiro Ishibashi; Kazuhiko Shimada; Toshiro Nagase; Yutaro Takaya; Yasuhiro Kato; Shinsuke Kawagucci; Tomo-o Watsuji; Takazo Shibuya; Ryoichi Yamada; Tomokazu Saruhashi; Masanori Kyo; Ken Takai
Seafloor massive sulphide deposits are potential resources for base and precious metals (Cu-Pb-Zn ± Ag ± Au), but difficulties in estimating precise reserves and assessing environmental impacts hinder exploration and commercial mining. Here, we report petrological and geochemical properties of sulphide chimneys less than 2 years old that formed where scientific boreholes vented hydrothermal fluids in the Iheya-North field, Okinawa Trough, in East China Sea. One of these infant chimneys, dominated by Cu-Pb-Zn-rich sulphide minerals, grew a height of 15 m within 25 months. Portions of infant chimneys are dominated by sulphate minerals. Some infant chimneys are sulphide-rich similar to high-grade Cu-Pb-Zn bodies on land, albeit with relatively low As and Sb concentrations. The high growth rate reaching the 15 m height within 25 months is attributed to the large hydrothermal vent more than 50 cm in diameter created by the borehole, which induced slow mixing with the ambient seawater and enhanced efficiency of sulphide deposition. These observations suggest the possibility of cultivating seafloor sulphide deposits and even controlling their growth and grades through manipulations of how to mix and quench hydrothermal fluids with the ambient seawater.
Geochemistry Geophysics Geosystems | 2017
Arie Naftali Hawu Hede; Katsuaki Koike; Koki Kashiwaya; Shigeki Sakurai; Ryoichi Yamada; Donald A. Singer
The Hokuroku district, northern Japan, is globally recognized for rich ore deposits (kuroko and vein types), which have been thoroughly explored under thick vegetation cover. This situation is ideal to evaluate the effects of ore deposits on vegetation anomalies through geobotanical remote sensing. Here we present novel methods to detect vegetation anomalies caused by ore deposits and verify their usefulness by comparing the anomalies with a deposit potential map produced from multiple geological data. We use the reflectance spectra of Landsat ETM+ images acquired in summer and autumn to calculate a vegetation index for plant physiological activity. A key variable to detect the anomalies is a variation of vegetation index with time at each pixel. Difference in variation is enlarged by a sequence of image enhancement methods for the detection. We find that the vegetation anomalies, defined by the large ratios, correspond well to the high potential zones of ore deposits and known major deposits. Consequently, our methods can extend the applicability of remote sensing-based mineral exploration to the areas covered by thick vegetation, in addition to traditional arid and semi-arid areas. This article is protected by copyright. All rights reserved.
Transactions of Nonferrous Metals Society of China | 2014
Qing-qing Lu; Takuto Kanetsuki; Shin-ichi Yamasaki; Ryoichi Yamada; Takahiro Watanabe; Noriyoshi Tsuchiya
Abstract Focusing on the origin of the heavy metal, this study aims to build an imputed method to estimate the heavy metal content in river water by making a distinction between the heavy metal of natural origins and that caused by human activities. Supported by GIS, Kosaka watershed within the Hokuroku basin was divided into several sub-watershed polygons and the outflows of water and Cu were calculated for each polygon. Compared with the natural origin, the dominant Cu emissions affected the river water more significantly in local. Based on the mass balance closure, the heavy metal content of Cu in the Kosaka River was estimated by the conflux accumulation of tributaries and mine drainages. The estimated Cu concentrations were checked by comparing with the actually measured values at monitoring points along the Kosaka River and the results are coincidence with each other in general. It is revealed that the mainstream water quality could be estimated by seizing the water quality of upstream tributaries and human drainages.
Hydrometallurgy | 2009
Javier Vilcáez; Ryoichi Yamada; Chihiro Inoue
Tectonics | 2008
Valerio Acocella; Takeyoshi Yoshida; Ryoichi Yamada; Francesca Funiciello
Geochemical Journal | 2012
Takahiro Watanabe; Noriyoshi Tsuchiya; Y. Oura; Mitsuru Ebihara; Chihiro Inoue; Nobuo Hirano; Ryoichi Yamada; Shin-ichi Yamasaki; Atsushi Okamoto; Fumiko Watanabe Nara; Keishi Nunohara
Mineralium Deposita | 2011
Ryoichi Yamada; Takeyoshi Yoshida
Resource Geology | 2004
Ryoichi Yamada; Takeyoshi Yoshida
Mining geology | 1987
Ryoichi Yamada; Toshiaki Suyama; Nagashi Ogushi