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Volume 101, Issue 3
Displaying 1-9 of 9 articles from this issue
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Approach to Mantle EvolutionYoshiyuki KOIDE1992 Volume 101 Issue 3 Pages 159-192
Published: June 25, 1992
Released on J-STAGE: November 12, 2009
JOURNAL FREE ACCESSThe isotopic descriptions of present-day mantle derived rocks reveal the regional and global heterogeneities of the Earth's mantle with systematic variations. The mantle heterogeneities and systematic variations include Dupal anomaly, mantle array, mantle plane, and LoNd array. They led to the hypotheses involving the mixing of some mantle components. The mantle components are identified as follows ; DMM (most depleted component in the Earth), EM II (enriched component derived from sediments and subducted oceanic crust), EM I (end-member of LoNd array), HIMU (end-member of LoNd array with high U/Pb ratio), and PREMA (common and major components in the Earth's mantle, synonymous with, PUM, CHUR, UR and BSE). These mantle components could be generated by the principal processes of chemical separation, time effect and component mixing. The chemical separation process changes the parent/daughter ratios, the time effect process varies the isotope ratios, and the component mixing process between mantle components resulted in isotopic variations of the magmas derived from mantles.
In the Earth's mantle evolution, two important global events occurred before about 3.8 Ga (1st event) and after 2 Ga (2nd event). The 1st event might be related to stratification of the early Earth, such as, the separation of the mantle and core, and/or the chemical stratification of mantle involving magma ocean. For a period of 3.8-2 Ga, the chemical structure of the mantle had been preserved. The second global event started at 2 Ga. This event might be related to the formation of the solid inner core from primitive liquid core, which might activate the mantle convection. The convection which mixed the mantle components should make the present isotopic variations of the mantle.View full abstractDownload PDF (5649K) -
Takayuki ISHII, Makoto KOBAYASHI, Hidekazu TSUJIMOTO1992 Volume 101 Issue 3 Pages 193-204
Published: June 25, 1992
Released on J-STAGE: November 12, 2009
JOURNAL FREE ACCESSThis paper is designed to examine the characteristics and formation processes of debris slopes on forested mountain sides. Two study areas were chosen. One is in the Mikouchi River Basin, Kanto District, Japan, and the other in the Muko River Basin, Kinki District, Japan. Both areas are composed of rhyolitic rocks overlayed by soil and tree growth.
The slopes studied are characterized by their concave profile and steep inclination which is comparable to or exceeds the angle of a talus slope. From a point of view of debris movement, the slope is, as a rule, split into five slope segments, from higer position to lower position : free face, debris-transported slope on which debris can not cease its motion due to steepness and small roughness, high-positioned steep clitter, talus and low-positioned gentle clitter. Two different processes are suggested to the cause of the reverse grading phenomena of debris deposits. One is the sieving process through the grain flow. The other is the removal of the surficial fines of weathered material to the inner coarser at upslope followed by their deposition at downslope in that order through one-at-a time movement such as rockfalls. The fact that the study areas are covered by a mantle of tree growth and soil is thought to suggest that the built-up material on the slopes in question might have been deposited over a relatively short period of time, although a small amount of deposition still continued at present.View full abstractDownload PDF (2412K) -
Yoko OTA, Akiko MIYAWAKI, Minako SHIOMI1992 Volume 101 Issue 3 Pages 205-224
Published: June 25, 1992
Released on J-STAGE: November 12, 2009
JOURNAL FREE ACCESSThis paper describes active faults which dislocate late Quaternary marine terraces of Sado Island and discusses a tectonic implication of these faults for the deformation of terraces. Sado Island is located on the tectonically active Sado Submarine Ridge in the Sea of Japan, off Niigata of central Japan, and consists of three major topographic units ; Osado Range, Kosado Range and Kuninaka Plain in-between, all of which trend nearly northeastward. Both Osado and Kosado are fringed by well-defined marine terraces up to 300m in altitude, and up to 130m for the last interglacial terrace, indicating the maximum uplift rate of 1 m/1, 000 yrs.
Two major active fault systems are recognised ; the Kuninaka-minami fault system on the west of Kosado and the Sotokaifu fault system on the west of Osado. They are striking parallel to the trend of the mountain ranges. The Kuninaka-minami fault system dislocates the last interglacial marine terrace and younger marine and fluvial terraces, and is composd of three segments, KM, KD and IT. These segments have two different surface expressions. One is an extremely convex terrace profile steeply dipping toward Kuninaka Plain (westward), and is interpreted as a flexural scarp (KM1, KD1 and IT1), and the other is a range-facing fault scarplet (KM2, KD2 and IT2). Vertical slip-rate is 0.1-0.3 m/1, 000 yrs for KM1, KD1 and IT1 and only 0.01-0.07 m/1, 000yr. for KM2, KD2 with an exception of 0.1 m/1, 000yr. for KD2. A progressive deformation is recognized in both types, which have been formed by repeated activities of reverse faulting. KM1, KD1 and IT1 are interpreted as the major synthetic faults with upthrown side on the east (mountain-side) and KM2, KD2 and IT2 are associated subsidiary antithetic faults.
The Sotokaifu fault system has two segments, KO and IG. No major synthetic flexural scarp is recognized and only range-facing fault scarps (KO2 and IG2) dislocate the last interglacial and younger marine terraces. KO2 and IG2 are regarded as the antithetic faults, judged by their similarity of the morphological characteristics and slip rate to those of KM2, KD2 and IT2, and the presence of exposure of reverse faults. Strong coastal erosion on the west coast of Osado, facing an open sea, is a reason for the absence of main synthetic fault on Osado. Kuninaka Plain is a fault angle depression bunded by the Kuninaka-minami fault system on the eastern side only.
These faults are responsible for the late Quaternary southeastward tilting, which is estimated from the height distribution of former shorelines on Osado and Kosado, but is opposite to the older deformation pattern expressed by generally steeper eastern slope than the western slope of mountainland of Osado and Kosado. It is, therefore, suggested that the faulting of these two systems have started sometime in middle to late Quaternary with the commencement of new tectonic regime.View full abstractDownload PDF (4638K) -
Yoshibumi TOMODA, Hiroshi MASUDA, Takeshi INABA, Chihiro MAEKAWA, Mina ...1992 Volume 101 Issue 3 Pages 225-232
Published: June 25, 1992
Released on J-STAGE: November 12, 2009
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1992 Volume 101 Issue 3 Pages 233
Published: June 25, 1992
Released on J-STAGE: November 12, 2009
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[in Japanese]1992 Volume 101 Issue 3 Pages 233a
Published: June 25, 1992
Released on J-STAGE: November 12, 2009
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[in Japanese]1992 Volume 101 Issue 3 Pages 233b-235
Published: June 25, 1992
Released on J-STAGE: November 12, 2009
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[in Japanese]1992 Volume 101 Issue 3 Pages 237
Published: June 25, 1992
Released on J-STAGE: November 12, 2009
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[in Japanese]1992 Volume 101 Issue 3 Pages Plate1-Plate2
Published: June 25, 1992
Released on J-STAGE: November 12, 2009
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