Crustal structure in the Mizuho Plateau, East Antarctica, by a two-dimensional ray approximation     

Akira Ikami  Kiyoshi Ito 《Journal of Geodynamics》1986,6(1-4)

Studies on the crustal and upper-mantle structure in Antarctica have been one of the major contributions to Antarctic research since the International Geophysical Year of 1957–1958. Many refraction surveys with small charge size have been conducted in Antarctica, but long-range experiments were also made in 5 regions on the margin of the Antarctic continent.In 1979–1981, the scientific program of the Japanese Antarctic Research Expedition was focused on the earth sciences, and in particular, an explosion seismic experiment along a long survey line was the major item during these years. An experiment along a 300 km-long line with three shots and 27 observation stations was successfully made in the northern Mizuho Plateau, East Antarctica.From the analysis of travel times and the amplitude study of synthetic seismograms, the crustal structure of the northern Mizuho Plateau was determined. The depths of the Conrad and the Moho discontinuties were determined as 31 km and 42 km, respectively. The P-wave velocity and depth relation was determined as 6.0 km/s on the surface of the bedrock, 6.3 km/s at a depth of 2 km, 6.8 km/s at the Conrad and 7.9 km/s at the Moho. The velocity in the crust increases gradually. The crustal structure obtained is representative of East Antarctica.  相似文献   

Submarine metamorphism of gabbros from the Mid-Cayman rise: An oxygen isotopic study     

Emi Ito  Robert N. Clayton 《Geochimica et cosmochimica acta》1983,47(3):535-546

Oxygen isotopic compositions of minerals in 22 samples of submarine gabbros were determined. The gabbros were collected using the submersible Alvin from the 700 m vertical section of the rift-valley wall of the Mid-Cayman spreading center. Our study indicates that in the Mid-Cayman Rise seawater barely reached the bottom of the plutonic layer. Abundant seawater penetration (water/rock mass ratio > 1) was limited to the upper part of the plutonic layer. From the observed oxygen isotopic compositions of coexisting minerals, and from the experimental and empirical determinations of equilibrium fractionation of oxygen isotopes for mineral-water, and mineral-mineral pairs, we show the following: (1) pyroxene and olivine did not exchange oxygen with seawater, (2) plagioclase is in isotopic disequilibrium with pyroxene; (3) the rate of oxygen exchange in plagioclase was not slowed by the absence of cation exchange; (4) plagioclase and amphibole have exchanged oxygen with seawater or isotopically modified seawater (δ¹⁸O ≤ 3%.); and (5) amphibole has exchanged or acquired (during formation) hydrogen from seawater at 380°C ≤ T ≤ 600°C. The decrease in extent of isotopic exchange of plagioclase and the decrease in amphibole abundance with depth indicate that seawater flux decreased rapidly with depth (water/rock mass ratio falling from 1.7 to 0.2 over a 300 m interval).  相似文献   

The effect of ferric iron on the electrical conductivity of olivine     

Al Duba  Jun Ito  John C. Jamieson 《Earth and Planetary Science Letters》1973,18(2):279-284

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Trace-element and isotopic constraints on the source of magmas in the active volcano and Mariana island arcs, Western Pacific     

Robert James Stern  Emi Ito   《Journal of Volcanology and Geothermal Research》1983,18(1-4)

Analytical results of the relative and absolute abundance of LIL-incompatible trace elements (K, Rb, Cs, Sr, and Ba) and isotopic compositions ( , , and ) are summarized for fresh samples from active and dormant volcanoes of the Volcano and Mariana island arcs. The presence of thickened oceanic crust (T 15–20 km) beneath the arc indicates that while hybridization processes resulting in the modification of primitive magmas by anatectic mixing at shallow crustal levels cannot be neglected, the extent and effects of these processes on this arc's magmas are minimized. All components of the subducted plate disappear at the trench. This observation is used to reconstruct the composition of the crust in the Wadati-Benioff zone by estimating proportions of various lithologies in the crust of the subducted plate coupled with analyses from DSDP sites. Over 90% of the mass of the subducted crust consists of basaltic Layers II and III. Sediments and seamounts, containing the bulk of the incompatible elements, make up the rest. Bulk Western Pacific seafloor has , δ ¹⁸O +7.2, K/Rb 510, K/Ba 46, and K/Cs 13,500. Consideration of trace-element data and combined systematics limits the participation of sediments in magmagenesis to less than 1%, in accord with the earlier results of Pb-isotopic studies. Combined data indicate little, if any, involvement of altered basaltic seafloor in magmagenesis. Perhaps more important than mean isotopic and LIL-element ratios is the restricted range for lavas from along over 1000 km of this arc. Mixtures of mantle with either the subducted crust or derivative fluids should result in strong heterogeneities in the sources of individual volcanoes along the arc. Such heterogeneities would be due to: (1) gross variations of crustal materials supplied to the subduction zone; and (2) lesser efficiency of mixing processes accompanying induced convection between arc segments (parallel to the arc) as compared to that perpendicular to the arc. The absence of these heterogeneities indicates that either some process exists for the efficient mixing of mantle and subducted material parallel to the arc or that subducted materials play a negligible role in the generation of Mariana-Volcano arc melts.Consideration of plausible sources in the mantle indicates that (1) an unmodified MORB-like mantle cannot have generated the observed trace-element and isotopic composition of this arc's magmas, while (2) a mantle similar to that which has produced alkali-olivine basalts (AOB) of north Pacific “hot spot” chains is indistinguishable in many respects spects from the source of these arc lavas.  相似文献   

Evaluation of spatial resolution and estimation error of seafloor displacement observation from vessel-based bathymetric survey by use of AUV-based bathymetric data     

Toshiya Fujiwara  Yuka Masaki  Fujio Yamamoto 《Marine Geophysical Researches》2015,36(1):45-60

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ISRM Suggested Methods for Determining the Creep Characteristics of Rock   总被引：4，自引：2，他引：2  

Ömer Aydan  Takashi Ito  Ugur Özbay  M. Kwasniewski  K. Shariar  T. Okuno  A. Özgenoğlu  D. F. Malan  T. Okada 《Rock Mechanics and Rock Engineering》2014,47(1):275-290

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Tropospheric delay correction with dense GPS network in L1-SAIF augmentation   总被引：2，自引：0，他引：2  

Noboru Takeichi  Takeyasu Sakai  Sounosuke Fukushima  Ken Ito 《GPS Solutions》2010,14(2):185-192

The L1-SAIF (L1 Submeter-class Augmentation with Integrity Function) signal is one of the Quasi-Zenith Satellite System (QZSS) navigation signals, which provides an augmentation function for mobile users in Japan. The tropospheric delay correction in the L1-SAIF augmentation is discussed in detail. Because the topographical features in Japan are complicated, the correction information is generated from GPS observation data collected at 200 GPS stations which are densely distributed over Japan. A total of 210 Tropospheric Grid Points (TGPs) are arranged to fully cover Japan. The TGPs that provide the correction information are selected adaptively to achieve the expected correction accuracy. This selection of TGPs is provided by the TGP mask message. Mobile users acquire the zenith tropospheric delay (ZTD) value at neighboring TGPs from the correction messages, and can estimate the local ZTD value accurately by using a suitable ZTD model. Only up to seven L1-SAIF messages are sufficient to provide the full correction information. Accuracy evaluations have proven that it is possible to achieve a correction accuracy of 13.4 mm RMS. The strategy presented here has been implemented into the augmentation system using the L1-SAIF signal, and its application guidance is presented in the QZSS interface specification.  相似文献