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Hiroshi Yamamoto Natsumi Nakamori Masaru Terabayashi Hafiz Ur Rehman Masahiro Ishikawa Yoshiyuki Kaneko Takashi Matsui 《Island Arc》2010,19(3):458-469
Geological observations in the Horoman area, south‐central Hokkaido, show that the Horoman peridotite complex of the Hidaka metamorphic belt is a tectonic slice about 1200 m thick. The peridotite slab is intercalated into a gently east‐dipping structure. The underlying unit is a Cretaceous–Paleogene accretionary complex. Riedel shear planes in the sedimentary layers of the accretionary complex near the structural bottom of the peridotite slab indicate top‐to‐the‐west (thrust) displacement. The overlying unit is composed of felsic–pelitic gneisses and mafic–felsic intrusive rocks (the Hidaka metamorphic rocks). The boundary surface between the peridotite complex and metamorphic rocks forms a domal structure. Microstructures of sheared metamorphic rocks near the structural top of the peridotite slab indicate top‐to‐the‐east (normal) displacement. The results combined with previous studies suggest that the Horoman peridotite complex was emplaced onto the Asian margin (Northeast Japan) during the collision between the Asian margin and the Hidaka crustal block. 相似文献
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Graphitization of carbonaceous material in sedimentary rocks on short geologic time‐scales: An example from the Kinsho‐zan area,central Japan 
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下载免费PDF全文 Initially amorphous carbonaceous material becomes more crystalline with heating. The structural change depends not only on the maximum attained temperature but also the time‐scale of heating. Raman spectroscopy of natural samples that have been heated for time‐scales of 105 years or greater show that the degree of crystallinity has reached steady‐state. In contrast, laboratory studies show very little change in crystallinity of carbonaceous material (CM) after heating at 1000°C for a time of 3.5 weeks. Better constraints on the time‐scale for crystallization require experiments on time‐scales of years to thousands of years; such long time‐scales can only be derived from natural examples of CM‐bearing rocks that have been heated for a known length of time. Thermal modeling of contact metamorphism developed around a 13 m dike within the Akasaka Limestone in Gifu Prefecture shows the time‐scale of heating is of the order of 1–100 years. Raman spectroscopy reveals a significant increase in the crystallinity of the CM in a region within 3 m from the dike. A comparison between the temperature predicted for the contact aureole and the degree of crystallinity of the carbonaceous material shows that even close to the dike the CM has not reached steady‐state. This change began at over 550°C (modeled temperature) for a time‐scale of heating of a few years. Attaining steady‐state in the crystallization of CM under natural geological condition requires heating on time‐scales greater than about one hundred years. This study shows the utility of using natural laboratory studies to determine the kinetics of CM crystallization in rocks. 相似文献
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Late Olenekian assemblages in the western Panthalassa have been recovered from bedded radiolarian chert sequences of an accretionary complex, the Ashio belt. These faunas are documented and considered in terms of radiolarian diversity and faunal turnover during the latest Permian to Middle Triassic time. The fauna includes 30 radiolarians belonging to Spumellaria or Entactinaria, with two relicts from the Late Permian. This late Olenekian fauna is markedly different from Permian and Asisian faunas, respectively, and is herein named the Minowa fauna. Study of the literaure indicates that radiolarian provinces were significantly disconnected between the western Panthalassa and eastern Tethys during late Olenekian time. Furthermore, 121 of 143 species disappeared during late Olenekian time, and in turn 118 new species appeared in the western Panthalassa around the Olenekian-Anisian boundary. It is concluded that faunal turnover occurred at least three times between the latest Permian and Middle Triassic.The first turnover is the Poalaozoie-type radiolarian extinction at the Permain-Triassic boundary,the second is the diversification of spheroidal Spumellaria and Entactinaria between early and late Olenekian time, and the third is a faunal turnover from the Minowa fauna to the true Mesozoic-type radiolarian famas that are characterized by mulit0segmented Nassellaria. 相似文献
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