Deep CTD Casts in the Challenger Deep,Mariana Trench   总被引：1，自引：0，他引：1  

Keisuke?TairaEmail author  Daigo?Yanagimoto  Shoji?Kitagawa 《Journal of Oceanography》2005,61(3):447-454

On 1 December 1992, CTD (conductivity-temperature-depth profiler) casts were made at three stations in a north-south section of the Challenger Deep to examine temperature and salinity profiles. The station in the Challenger Deep was located at 11°22.78′ N and 142°34.95′ E, and the CTD cast was made down to 11197 db or 10877 m, 7 m above the bottom by reeling out titanium cable of 10980 m length. The southern station was located at 11° 14.19′ N and 142°34.79′ E, 16.1 km from the central station, where water depth is 9012 m. CTD was lowered to 7014 db or 6872 m. The northern station was located at 11°31.47′ N and 142° 35.30′ E, 15.9 km from the central station, and CTD was lowered to 8536 db or 8336 m, 10 m above the bottom. Below the thermocline, potential temperature decreased monotonously down to 7300–7500 db beyond a sill depth between 5500 m and 6000 m, or between 5597 db and 6112 db, of the trench. Potential temperature increased from 7500 db to the bottom at a constant rate of 0.9 m°C/1000 db. Salinity increased down to 6020–6320 db, and then stayed almost constant down to around 9000 db. From 9500 db to the bottom, salinity increased up to 34.703 psu at 11197 db. Potential density referred to 8000 db increased monotonously down to about 6200 db, and it was almost constant from 6500 db to 9500 db. Potential density increased from 9500 db in accordance with the salinity increase. Geostrophic flows were calculated from the CTD data at three stations. Below an adopted reference level of 3000 db, the flow was westward in the north of Challenger Deep and eastward in the south, which suggests a cyclonic circulation over the Challenger Deep. Sound speed in Challenger Deep was estimated from the CTD data, and a relation among readout depth of the sonic depth recorder, true depth, and pressure was examined.  相似文献   

Geological structure of the marginal plateau off Tottori,Southern-West of Honshu,Japan     

Tadahiko Katsura  Shoji Kitahara 《Journal of Oceanography》1977,33(5):259-266

A geological and geophysical survey off Tottori, southern-west of Honshu, Japan, was carried out by the Hydrographic Department of Japan during May and June (26 days) of 1974.In the survey area, there is marginal plateau which lies under the slope of the continental shelf adjacent to the Sanin district. By the closely-spaced surveying the marginal plateau was divided into two different zones based on differences of genesis and structure, which are identified in this paper as marginal plateaus A (west side) and marginal plateau B (east side). The tectonic boundary between marginal plateaus A and B, previously believed to exist near Tottori City, was not confirmed. An erosional plane, beneath the horizontally bedded upper layer was found to be 75 m lower than the submerged surface of marginal plateau A. Marginal plateau B is hypothesized to have been generated by the sliding of the upper layer. This is suggested by the presence of prominent slumping directed toward the bottom of the Oki Trough. This result implies that the submergence of the Oki Trough area and formation of the marginal plateau are closely related.  相似文献   

Investigation of the variation of the Kuroshio and daily mean sea levels     

Daitaro Shoji 《Journal of Oceanography》1978,34(6):310-315

In the past 30 years, I have been engaged in the study of the Kuroshio, especially of its time variations. In the course of the study I have tried to introduce various new methods such as GEK, mean sea level observation at island tide stations, multiple ship survey and temperature measurement by submarine cable and so on. In this report, some aspects of these studies are described and the usefulness of tide stations for the investigation of oceanic current is emphasized.  相似文献   

Distribution of gold and silver and its relation with hypogene ore minerals in the Esperanza porphyry deposit,Antofagasta Region,Chile     

Shoji Kojima  María Constanza San Martín  Toshiro Nagase  Daisuke Nakashima  Claudio Bisso  Andrew Menzies 《Resource Geology》2021,71(1):80-90

Modes of occurrence of Au‐ and Ag‐bearing phases and their relation with associated hypogene ore minerals were examined with the objective to elucidate Au‐Ag distribution at the Esperanza porphyry deposit in the Eocene Centinela copper belt, using ore‐microscope modal analysis, semi‐quantitative analyses by automated mineralogy, electron probe microanalysis, and secondary ion mass spectrometer. The Esperanza hypogene mineralization is characterized by early‐stage chalcopyrite‐rich veinlets in the potassic alteration zone and later polymetallic stage with tennantite and galena in the chlorite‐sericitic alteration zone. Only the early‐stage chalcopyrite contains fine‐grained electrum (Au₆₈Ag₃₂ ‐ Au₈₁Ag₁₉) and hessite (Ag₂Te), and thus yields positive correlations in Cu vs. Au and Cu vs. Ag grades that are clearly recognized in the hypogene sulfide zone. The early‐stage chalcopyrite grains frequently exhibit polysynthetic twinning suggestive of inversion from intermediate solid solution. These features suggest that the fine‐grained electrum and hessite are products exsolved in the cooling process with the intermediate solid solution to chalcopyrite inversion. In contrast, tennantite and galena of the later‐stage mineralization contain no detectable Ag, and it is thus proposed that the early‐stage inverted chalcopyrite is the principal storage of economically important precious metals.  相似文献   

Petrogenesis of ultramafic rocks and olivine-rich troctolites from the East Taiwan Ophiolite in the Lichi mélange     

Morishita  Tomoaki  Ghosh  Biswajit  Soda  Yusuke  Mizukami  Tomoyuki  Tani  Ken-ichiro  Ishizuka  Osamu  Tamura  Akihiro  Komaru  Chihiro  Aari  Shoji  Yang  Hsiao-Chin  Chen  Wen-Shan 《Mineralogy and Petrology》2018,112(4):521-534

Mineralogy and Petrology - We examine ultramafic and olivine-rich troctolite blocks of the East Taiwan Ophiolite (ETO) in the Lichi Mélange. Although ultramafic rocks are extensively...  相似文献   

Four lunar mare meteorites: Crystallization trends of pyroxenes and spinels     

Tomoko ARAI  Paul H. WARREN  Hiroshi TAKEDA 《Meteoritics & planetary science》1996,31(6):877-892

Abstract— We studied crystallization trends of pyroxene and spinel in four Antarctic meteorites known to be derived from mare regions of the Moon: Y-793169 and A-881757 (YA meteorites) are unbrecciated igneous basalts, EET 87521 is a fragmental breccia, and Y-793274 is a regolith breccia. All have relatively low bulkrock TiO₂ content, and the YA meteorites are uncommonly ancient. Our electron probe microanalysis (EPMA) data indicate that the YA meteorites and the dominant mare components of Y-793274 and EET 87521 conform to a general trend for Ti-poor (low-Ti and very low-Ti) mare basalts. Their pyroxenes show a strong correlation between Fe/(Fe + Mg) (Fe#) and Ti/(Ti + Cr) (Ti#), both ratios typically increasing from core to rim. These trends presumably reflect local crystallization differentiation of interstitial melt. Previous studies (M. J. Drake and coworkers) have suggested that the detailed configurations of such Fe# vs. Ti# trends may reflect the bulk TiO₂ contents of the parent magmas (basalts). As a more systematic approach to this problem, we plot bulk-rock TiO₂ as a function of the Fe# = 0.50 intercept of each rock's pyroxene Fe# vs. Ti# trend. We call this intercept the Fe#-normalized Ti#. Based on our data for EET 87521, the YA meteorites, and Apollo 12 basalts 12031 and 12064, plus literature data for several other Ti-poor mare basalts, we find a strong correlation between Fe#-normalized Ti# and the bulk TiO₂ content of the parent basalt. This correlation confirms that fragmental breccia EET 87521 is nearly pure very low-Ti (VLT) basalt and that the YA meteorites, for which bulk-rock TiO₂ results scatter due to unusually coarse grain size (A-881757) or scarcity of available sample (Y-793169), are pieces of an uncommonly Ti-poor, but not quite VLT, variety of low-Ti mare basalt. Extrapolating from this correlation, the dominant mare component of regolith breccia Y-793274 is probably of VLT affinity. Besides the normal mare pyroxene trend of strong correlation between Fe# and Ti#, Y-793274 includes two additional pyroxene compositional trends, both showing a wide range of Ti# despite relatively constant (and low, by mare standards) Fe#. The most magnesian of these trends consists of a single clast with a mode of orthopyroxene + MgO-rich ilmenite. These two trends are of uncertain origin. Possibly one or both represents the highland component of this regolith breccia, although, unlike most highland pyroxenes, these appear relatively unaltered by impact brecciation and metamorphism. Compositions of spinels in the coarse-grained A-881757 show an extraordinary distribution: chromite and ulvöspinel components vary among grains but are nearly constant within grains. Despite its old age and unusually coarse grain sizes, mineralogical evidence (i.e., heterogeneity within both pyroxene and spinel; typical pyroxene exsolution scale very coarse by mare standards but exceeded by the pyroxenes of EET 87521 and Y-793274) indicates that A-881757 was cooled only slightly more slowly than typical mare basalts and may have formed near the center of an uncommonly thick lava flow. Both of the VLT basaltic lunar meteorite breccias, EET 87521 and Y-793274, are composed dominantly of pyroxenes with exsolution coarser than normal for mare basalts. Possibly VLT basalt flows tend to be systematically thicker, and thus more slowly cooled, than more Ti-rich flows.  相似文献   

Compositional variations in spinel-hosted pargasite inclusions in the olivine-rich rock from the oceanic crust–mantle boundary zone     

Akihiro Tamura  Tomoaki Morishita  Satoko Ishimaru  Kaori Hara  Alessio Sanfilippo  Shoji Arai 《Contributions to Mineralogy and Petrology》2016,171(5):39

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Peridotite xenoliths from the Shiribeshi Seamount,Japan Sea: insights into mantle processes in a back-arc basin     

Yuji Ichiyama  Tomoaki Morishita  Akihiro Tamura  Shoji Arai 《Contributions to Mineralogy and Petrology》2016,171(10):86

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Magma mixing model for the genesis of middle crust in the Izu–Bonin–Mariana arc: evidence from plutonic rocks in the Mineoka-Setogawa ophiolitic mélange,central Japan     

Yuji Ichiyama  Hisatoshi Ito  Akihiro Tamura  Shoji Arai 《International Geology Review》2020,62(4):503-521

ABSTRACT

A Paleogene accretionary complex, the Mineoka–Setogawa belt is distributed adjacent to the northern portion of the collision zone between Honshu and Izu–Bonin–Mariana (IBM) arcs in central Japan, comprising a mélange of ophiolitic fragments of various sizes. The Eocene-Oligocene plutonic rocks in this belt (gabbro, diorite, and tonalite) have been interpreted as fragments brought from the deep crust beneath the IBM arc through tectonic collisions. The geochemical characteristics of the gabbro and associated basaltic dike are similar to those of the Eocene IBM tholeiitic basalt; thus, the gabbro was likely formed via the crystallization of the Eocene tholeiitic basaltic magmas, which was produced by the partial meltings of a depleted mantle wedge. A comparison with experimental results and geochemical modeling indicates that the tonalite was generated by 10–30% dehydration melting of the gabbro. Actually, Eocene–Oligocene felsic veins, which are coeval with the plutonic rocks, occur in the Mineoka–Setogawa gabbro. Plagioclase crystals in the diorite comprise Ca-rich and -poor parts in a single crystal. Their compositional characteristics are consistent with those of plagioclase in the gabbro and tonalite, respectively. The textures and chemical composition of plagioclase indicate that the diorite was formed by the mixing between mafic and silicic magmas. The whole-rock composition of the diorite also indicates the evidence for the mixing between basaltic magmas which were fractionated to variable degrees and homogeneous silicic magma. The mixing model proposed from the first direct observations of the IBM middle crust exposed on the Mineoka–Setogawa belt is applied to the genesis of the Eocene to present intermediate rocks in the IBM arc. If the continental crust were created at intra-oceanic arc settings such as the IBM arc, the magma mixing model would be one of the most likely mechanisms for the genesis of the continental crust.  相似文献   

Origin of fine‐grained peridotite xenoliths from Iraya volcano of Batan Island,Philippines: deserpentinization or metasomatism at the wedge mantle beneath an incipient arc?   总被引：7，自引：0，他引：7  

Shoji Arai  Megumi Kida 《Island Arc》2000,9(4):458-471

Abstract Peridotite xenoliths from the subarc mantle, which have been rarely documented, are described from Iraya volcano of the Luzon arc, the Philippines, and are discussed in the context of wedge-mantle processes. They are mainly harzburgite, with subordinate dunite, and show various textures from weakly porphyroclastic (C-type) to extremely fine-grained equigranular (F-type). Textural characteristics indicate a transition from the former to the latter by recrystallization. The F-type peridotite has inclusion-rich fine-grained olivine and radially aggregated orthopyroxene, being quite different in texture from ordinary mantle-derived peridotites previously documented. Despite their strong textural contrast, the two types do not show any systematic difference in modal composition. The harzburgite of C-type has ordinary mantle peridotite mineralogy; olivine is mostly Fo91–92 and chromian spinel mostly has Cr#s (= Cr/[Cr + Al] atomic ratios) from 0.3 to 0.6. Olivine is slightly more Fe-rich (Fo89–91) and spinel is more enriched in Cr (the Cr#, 0.4–0.8) and Fe³⁺ in F-type peridotites than in C-type harzburgite. Orthopyroxene in F-type peridotites is relatively low in CaO (<1 wt%), Al₂O₃ (<2 wt%) and Cr₂O₃ (<0.4 wt%). The F-type peridotite was possibly formed from the C-type one by recrystallization including local dissolution and precipitation of orthopyroxene assisted by fluid (or melt) of subduction origin. Textural characteristics, however, indicate a deserpentinization origin from abyssal serpentinite of which protolith was a C-type peridotite. In this scenario the initial abyssal serpentinite was possibly dehydrated due to an initiation of magmatic activity beneath an incipient oceanic arc like Batan Island. The F-type peridotite is characteristic of the upper mantle of island arc, especially of incipient arc.  相似文献