Slow mass movement in the Kangchenjunga area, eastern Nepal Himalaya     

Dhananjay  Regmi  Teiji  Watanabe 《Island Arc》2005,14(4):400-409

Abstract   The rates of the accumulated and continuous displacement of solifluction lobes in the Kangchenjunga area, eastern Nepal Himalaya, were determined using glass fiber tubes and a strain probe. Ground temperature, precipitation and soil moisture were monitored at two sites, whose altitude differed by approximately 100 m, to understand the solifluction process. The average movement rate of the glass fiber tubes on a 31° slope at altitudes of 5412–5414 m a.s.l. was approximately 11 mm/year, being almost threefold greater than that observed on a 22° slope at 5322–5325 ma.s.l. There was no significant difference in the depth of displacement at these sites. The continuous displacement measurement near the ground surface at 5414 m showed permanent downslope movement from early July. Such movement may be attributed to additional moisture supply during the monsoon season. The amplitude of the displacement cycle was highest at the ground surface, and decreased to virtually zero at and below 20 cm in depth. Probable factors leading to the relatively slow rates of downslope displacement at the surface and depth at the studied altitudes are the lack of concurrence of the freeze–thaw cycles and the high moisture condition in the soil, and the low moisture retention capacity of the soil because of steep slopes and superficial desiccation. The rate of displacement may be more pronounced at altitudes above 5600 m because of the freeze–thaw cycles during the summer season.  相似文献   

K-Ar Ages of Granitic Magmatism and Related Pegmatite Formation at the Umanotani-Shiroyama Mine, Shimane Prefecture, SW Japan and Their Bearings on Cooling History     

Shouji Kihara    Kenichi Hoshino    Makoto Watanabe    Hirotsugu Nishido  Shunso Ishihara 《Resource Geology》2005,55(2):123-129

Abstract. The Umanotani-Shiroyama pegmatite deposits, the largest producer of K-feldspar and quartz in Japan, are of typical granitic pegmatite. Ilmenite-series biotite granite and granite porphyry, hosting the ore deposits, and biotites separated from these rocks yielded K-Ar ages ranging from 89.0 to 81.4 Ma and 95.2 to 93.7 Ma, respectively. Muscovite and K-feldspar separated from the ore zone yielded K-Ar ages with the range of 96.2 to 93.1 Ma and 87.3 to 80.7 Ma, respectively. Muscovites from quartz-muscovite veins in the ore zone and in the granite porphyry yielded K-Ar ages of 90.4 and 76.3 Ma, respectively. K-feldspar is much younger in age than coexisting muscovite. It is noted that the K-Ar ages of biotite separates and the whole-rock ages are identical to those of muscovite and K-feldspar in the ore zone, respectively. These time relations, as well as field occurrence, indicate that the formation of the pegmatite deposits at the Umanotani-Shiroyama mine is closely related in space and time to a series of granitic magmatism of ilmenite-series nature. Using closure temperatures of the K-Ar system for biotite and K-feldspar (microcline), cooling rate of the pegmatite deposits is estimated to be about 82C/m.y. at the beginning, but slowed down to about 15C/m.y. in the later period.  相似文献   

Sorption behavior of the Pt(II) complex anion on manganese dioxide (δ-MnO2): a model reaction to elucidate the mechanism by which Pt is concentrated into a marine ferromanganese crust     

Mamiko Yamashita Maeno  Hironori Ohashi  Kotaro Yonezu  Akane Miyazaki  Yoshihiro Okaue  Koichiro Watanabe  Tamao Ishida  Makoto Tokunaga  Takushi Yokoyama 《Mineralium Deposita》2016,51(2):211-218

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Predominance of parallel‐ and cross‐predation in anglerfish          下载免费PDF全文

Masaki Yasugi  Michio Hori 《Marine Ecology》2016,37(3):576-587

Several studies in the last 20 years have revealed that morphological asymmetry in fish can be characterized as ‘antisymmetry’. Antisymmetry is a lateral dimorphism in which each population consists of individuals with well‐developed left sides (lefties) and well‐developed right sides (righties). This dimorphism influences predator–prey interactions. In some piscivorous fishes, it has been found that predators can catch more prey of the opposite morphological type to themselves (cross‐predation) than of the same morphological type (parallel‐predation). Our previous work clarified that the predominance of cross‐predation is caused by lateralized behaviors of predators and prey that correspond to their morphological antisymmetry. Moreover, based on the results of our behavioral observations, we hypothesized that parallel‐predation can predominate when predators encounter the potential prey frontally. To test this hypothesis, in the present study we investigated the relationship between lateral morphological types of anglerfish (Lophiomus setigerus) and those of the prey fishes found in their stomachs. Anglerfish attract potential prey using their first dorsal fin (illicium) as a lure, and their frontal encounters with potential prey fishes were photographed in situ and observed in an aquarium. The results of a stomach contents analysis indicated that parallel‐predation predominated in five benthopelagic prey fish species (perches and eels). By contrast, five benthic prey fishes (gobies and weevers) exhibited the predominance of cross‐predation. These results not only demonstrate the predominance of parallel‐predation in a natural fish community, but also suggest that the relationship between morphological types of predator and prey species can be reversed depending on the lifestyle of prey.  相似文献   

Different thermal preferences for brooding and larval dispersal of two neighboring shrimps in deep‐sea hydrothermal vent fields          下载免费PDF全文

Hiromi Watanabe  Takuya Yahagi  Yukiko Nagai  MiHye Seo  Shigeaki Kojima  Jun‐ichiro Ishibashi  Hiroyuki Yamamoto  Katsunori Fujikura  Satoshi Mitarai  Takashi Toyofuku 《Marine Ecology》2016,37(6):1282-1289

Temperature is an important factor affecting the distributions and life‐history traits of marine animals. Deep‐sea hydrothermal vents are suitable environments to examine ecologic differences related to temperature, due to the steep temperature gradients around the vents. Rearing experiments under various temperature conditions (5–30 °C) at atmospheric pressure demonstrated a difference in thermal effects on egg hatching and larva in two co‐occurring, vent‐associated alvinocaridid shrimps – the peripherally distributed Alvinocaris longirostris and the centrally distributed Shinkaicaris leurokolos. The duration before hatching became shorter as temperature increased, while the maximum hatching rate occurred at higher temperatures in S. leurokolos (10–20 °C) than in A. longirostris (10 °C). Hatched larvae of both species were negatively buoyant, and larva with normal abdominal length could actively swim and stay suspended in the mid‐ or surface water layers of the culture plates under our experimental conditions. However, no larvae settled or metamorphosed into juveniles under the rearing conditions used in this study. Larvae with shortened abdomens occurred under most of the experimental conditions, although they were less frequent at 10 °C in A. longirostris and 20 °C in S. leurokolos. The maximum survival periods at these temperatures were 88 days in A. longirostris and 30 days in S. leurokolos. These characteristics may cause differences in the distributional ranges of the two species. The present results indicate that temperature is an important factor controlling life‐history traits of vent shrimps.  相似文献   

Deep-sea meiofauna off the Pacific coast of Tohoku and other trench slopes around Japan: a comparative study before and after the 2011 off the Pacific coast of Tohoku Earthquake     

Tomo Kitahashi  Himiko Watanabe  Ken Ikehara  Robert G. Jenkins  Shigeaki Kojima  Motohiro Shimanaga 《Journal of Oceanography》2016,72(1):129-139

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Long-term monitoring of bottom environments of the continental slope off Otsuchi Bay,northeastern Japan     

Kazumasa Oguri  Yasuo Furushima  Takashi Toyofuku  Takafumi Kasaya  Masahide Wakita  Shuichi Watanabe  Katsunori Fujikura  Hiroshi Kitazato 《Journal of Oceanography》2016,72(1):151-166

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Gold deposits associated with the gabbroic rocks at Tirek area,western Hoggar,Algeria: fluid inclusion study     

Warda Saad  Djamal Eddine Aissa  Koichiro Watanabe  Sachihiro Taguchi 《Arabian Journal of Geosciences》2018,11(2):26

The Tirek gold deposit hosted in the Archean shield is one of the richest sources of mined gold for Algeria. The deposit is controlled by the East Ouzzal shear zone (EOSZ), a transcurrent N–S lithospheric fault. The EOSZ is a late Pan-African dextral-ductile shear zone separating two contrasting Precambrian domains: the Archean In Ouzzal block to the west (Orthogenesis with subordinate metasediments reworked and granulitized during the ca. 2 Ga Eburnean event) and a middle Proterozoic block to the east involved in the ca. 600 Ma Pan-African event. The auriferous quartz veins are mainly oriented in two directions, N–S veins hosted in mylonitic rocks and NE–SW veins hosted in gabbroic or gneissic bands. The NE–SW veins contain the richest ore. Gold ore is found in a system of veins and lenticular quartz veinlets arranged in anastomosing networks. The hydrothermal alteration associated with these veins is characteristically a carbonate-sericite-albite-pyrite assemblage. Gold is the main metal of economic importance; it is disseminated in the quartz as grains or fibers along microcracks and as microscopic grains in the host rocks. Microthermometric results and Raman laser data from fluid inclusions demonstrate that the ore-forming fluids contained H₂O-CO₂±CH₄ and were low salinity. Homogenization temperatures are commonly 250–310 °C. In the Tirek deposit, the role of the shear zone that hosts the mineralization was to drain the hydrothermal fluid. Interactions between the fluid and the mafic host rocks and CO₂ also contributed to the formation of the hydrothermal gold deposit at Tirek.  相似文献   

Mineral composition variation in Alpine Schist, Southern Alps, New Zealand: Implications for recrystallization and exhumation   总被引：1，自引：0，他引：1  

RodneyH.  Grapes Teruo  Watanabe 《Island Arc》1994,3(3):163-181

Abstract Compositional variation of silicates (plagioclase, K-feldspar, epidote, titanite, garnet, white mica, biotite, chlorite), ilmenite, carbonates (calcite, ankerite) and apatite, in quartzofeldspathic lithologies of the Alpine Schist, New Zealand, is discussed in terms of increasing metamorphic grade and possible isograd-producing reactions. The mineral data, in conjunction with geological considerations, are used to determine polychronous P-T arrays of an early high P/T event (c. 16°C/kb; 5°C/km) overprinted by a lower P/T event (c. 50°C/kb; 15°C/km) that provides an estimation of Mesozoic and Cenozoic exhumation of schist of 11 to 13 km and 19 to 22 km respectively. The effects of possible shear heating and recrystallization to form K-feldspar zone schist near the Alpine Fault is consistent with movement along a mid to lower crustal detachment surface during Cenozoic shortening, and near isothermal exhumation of the schists to form the Southern Alps.  相似文献   

Relation between chemical composition and particle-size distribution of ores in the profile of nickeliferous laterite deposits of the Rio Tuba Mine, Philippines   总被引：1，自引：0，他引：1  

Yoshio Ogura  Katsuyuki Murata  Michio Iwai 《Chemical Geology》1987,60(1-4):259-271

Lateritic Ni ore mined in the Rio Tuba Mine, Philippines, derived from ultramafic rock by tropical intense weathering, is generally composed of two accumulated zones, an upper laterite zone and a lower saprolite zone. These two zones are very different in appearance, mineral assemblage, chemical composition, and in other ways. A transitional zone may be seen between the upper and lower zones, but it does not develop to any appreciable thickness. Although serpentine and goethite are still predominant in the constituent minerals, other clay minerals are increasing.

The transitional zone may be subdivided into three groups based on chemical composition. The behaviour of the chemical composition in this horizon indicates a complicated process of component transportation under the weathering process.

In the ore, chemical components are closely related in particle size of constituent minerals. In the laterite - transitional - saprolite sequence, a common variation range and tendency in chemical composition for each particle size can be seen. However, taking samples with the same particle size the chemical composition obviously differed, representing the characteristics of the components for each zone.

Concerning the correlation coefficient of the chemical components of each zone, a somewhat different inter-component relationship can be seen in these zones. These differences of correlation suggest the different complicated lateritized conditions under which they are formed.  相似文献