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111.
Pumice flow from the 1883 Krakatau eruption significantly differs in both mineral and chemical compositions from any other volcanic rocks or ejecta of the Krakatau group, which belong to the tholeiitic series. Lithic fragments of granitic Rock, discovered in the pumice flow, are similar to West Malayan granitic rocks. No other granitic rock occurs throughout the Krakatau group, therefore, we consider that the granitic fragments came from the underlying complex at depths, where they were captured as foreign materials by the magma.It is possible that sialic crustal materials plunged into depths along a peculiar tectonic structure located at the Sunda Strait, which appears to be a sheared portion caused by deformation of the Sunda arc due to differential movement between the Indo-Australian oceanic plate and the Eurasian continental crust. The crustal materials were partially melted and produced a magma of granitic composition. The magma was mixed with or assimilated by an ascending basaltic magma originating probably from the upper mantle. This resulted in a dacitic magma distinctly dominant in silica, alkalis and volatile components, and the 1883 Krakatau eruption, characterized by the pumice flow of dacitic composition, took place. 相似文献
112.
Minoru Ozima Kazuo Saito Masahiko Honda Sigeo Aramaki 《Geochimica et cosmochimica acta》1977,41(4):453-461
K-Ar dating and 40Ar-39Ar step heating experiments have been done for successive zones from the surface to the interior in two, altered dredged submarine basalts (16-2-6 and Aries V-23). The K contents show a systematic decrease (surface to the interior), whereas the K-Ar ages show a similar decrease in one sample (16-2-6) and almost no change in the other (Aries V-23).A simple diffusion model suggests that the K content decreases systematically from the surface to the interior, whereas the K-Ar age decreases or remains almost constant, depending on whether the times of solidification and of commencement of K-diffusion are close to each other or differ significantly. Comparison of the observed K content and K-Ar age variations within the rocks with the theoretical model then suggests that the solidification age of the sample Aries V-23 is much older than the commencement of the potassium-diffusion, the latter age perhaps being represented by the Eocene planktonic foraminifera on this sample. The 40Ar-39Ar isochron age obtained for the freshest specimen of Aries V-23 is 86.6 ± 3.7 m.y., supporting the above conclusion.The mathematical simulation indicates that an apparent concordance of the K-Ar age observed in some submarine basalts may be an artifact, only reflecting the significant gap between the solidification age and the time of the commencement of the K-diffusion in the rocks. Microprobe examination reveals that the potassium enrichment in the outer margin, is mainly due to K feldspar, which is an alteration product of plagioclase. 相似文献
113.
Rare gas trapping during crystallization from vapor phases of (1) CdTe, (2) Zn, (3) Mg and (4) Fe3O4 has been studied. Samples were deposited as very fine crystals (about several hundred angströms) in ambient Ar atmospheres of various pressures. It was found that the amount of Ar trapped in the samples was proportional to the ambient Ar pressure. Stepheating degassing of the crystals showed that Ar was rather loosely trapped and released at relatively low temperatures. However, on a simple mechanical compaction of the crystal powder the retentivity of Ar was considerably enhanced. 相似文献
114.
Masahiko Takeda 《Geophysical Journal International》1985,80(3):649-659
Summary. UT variation of the internal part of S q currents is examined using the geomagnetic data during 1980 March 1–18, and the effect of the ocean is found. The ratio of the internal currents to the external increases when the external current vortex comes above the Atlantic and Pacific Oceans, and the internal current vortex shifts to the oceans when the external vortex approaches the edge of the oceans. The existence of the ocean increases the total induced current by about 30 per cent and this amount is consistent with model calculations for S q by previous workers. 相似文献
115.
A laser-heated diamond-anvil cell that is capable of operating up to a pressure of 63 GPa, with X-ray diffraction facilities using a synchrotron radiation source at the SPring-8, has been developed to observe the compressibility of a hexagonal aluminous phase, [K0.15Na1.66Ca0.11Mg1.29Fe2+ 0.86Al3.13Ti0.09Si1.98] Σ9.27O12. The hexagonal aluminous phase is a potassium host mineral from the subducted oceanic crust in the Earth's lower mantle. A sample was heated using a YAG laser at each pressure increment to relax the deviatoric stress in the sample. X-ray diffraction measurements were carried out at 300 K using an angle-dispersive technique. Pressure was measured using an internal platinum pressure calibrant. The observed unit-cell volumes were used to obtain a third-order Birch–Murnaghan equation of state: unit-cell volume V o=185.94(±16) Å3, density ρ o=4.145 g/cm3, and bulk modulus K o=198(±3) GPa when the first pressure is derivative of the bulk modulus K ′ o is fixed to 4. The density of hexagonal aluminous phase is lower than that of coexisting Mg-perovskite in the subducted oceanic crust. 相似文献
116.
Shigeaki Ono Tsuyoshi Iizuka Takumi Kikegawa 《Physics of the Earth and Planetary Interiors》2005,150(4):331-338
In situ X-ray diffraction measurements on a calcium aluminosilicate (CAS) phase have been carried out using a laser-heated diamond anvil cell up to a pressure of 44 GPa, employing a synchrotron radiation source. CAS is the major mineral formed from sediments subducted into the Earth's mantle. The sample was heated using a YAG laser after each pressure increment to relax the deviatoric stress in the sample. X-ray diffraction measurements were carried out at T = 300 K using an angle-dispersive technique. The pressure was calculated using an internal platinum metal pressure calibrant. The Birch–Murnaghan equation of state for the CAS phase obtained from the experimental unit cell parameters showed a density of ρ0 = 3.888 g/cm3 and a bulk modulus of K0 = 229 ± 9 GPa for K′0 = 4.7 ± 0.7. When the first pressure derivative of the bulk modulus was fixed at K′0 = 4, then the value of K0 = 239 ± 2 GPa. From the experimental compressibility, the density of the CAS phase was observed to be lower than the density of co-existing Al-bearing stishovite, calcium perovskite, calcium ferrite-type phases, and (Fe,Al)-bearing Mg-perovskite in subducted sediments in the lower mantle. Therefore, the density of subducted sediments in the lower mantle decreases with increasing mineral proportion of the CAS phase. 相似文献
117.
118.
S. Ono 《Journal of Geodesy》1985,59(3):275-288
In order to solve the problems of determining the shape of a part of the earth of national or continental extent, that is,
of rigorous constituting and computing of the astrogeodetic network, it is required to determine gravimetric deflections of
the vertical with an accuracy of, say, 0″.3. For this it is adequate to carry out additional gravity surveys in the neighborhoods
of computation points, in addition to a given uniform gravity survey (normal density gravity survey).
The study offers a method to determine the optimal distribution of gravity stations in such a gravity survey, which guarantees
a given accuracy of computed gravimetric deflections of the vertical for a given statistical condition which characterizes
the variation of the gravity field. The approach used here is based on the concept of the error of representation and the
error propagation of Vening Meinesz integrals. 相似文献
119.
We report trace element and Sr–Nd isotopic compositions of Early Miocene (22–18 Ma) basaltic rocks distributed along the back-arc margin of the NE Japan arc over 500 km. These rocks are divided into higher TiO2 (> 1.5 wt.%; referred to as HT) and lower TiO2 (< 1.5 wt.%; LT) basalts. HT basalt has higher Na2O + K2O, HFSE and LREE, Zr/Y, and La/Yb compared to LT basalt. Both suite rocks show a wide range in Sr and Nd isotopic compositions (initial 87Sr/86Sr (SrI) = 0.70389 to 0.70631, initial 143Nd/144Nd(NdI) = 0.51248 to 0.51285). There is no any systematic variation amongst the studied Early Miocene basaltic rocks in terms of Sr–Nd isotope or Na2O + K2O and K2O abundances, across three volcanic zones from the eastern through transitional to western volcanic zone, but we can identify gradual increases in SrI and decreases in NdI from north to south along the back-arc margin of the NE Japan arc. Based on high field strength element, REE, and Sr–Nd isotope data, Early Miocene basaltic rocks of the NE Japan back-arc margin represent mixing of the asthenospheric mantle-derived basalt magma with two types of basaltic magmas, HT and LT basaltic magmas, derived by different degrees of partial melting of the subcontinental lithospheric mantle composed of garnet-absent lherzolite, with a gradual decrease in the proportion of asthenospheric mantle-derived magma from north to south. These mantle events might have occurred in association with rifting of the Eurasian continental arc during the pre-opening stage of the Japan Sea. 相似文献
120.
Shigeaki Ono Miki Shirasaka Takumi Kikegawa Yasuo Ohishi 《Physics and Chemistry of Minerals》2005,32(1):8-12
High-pressure and high-temperature experiments conducted in a laser-heated diamond-anvil cell with a synchrotron X-ray diffraction method have revealed a phase transformation in the aragonite-type SrCO3 at pressures above 10 GPa. The new phase has an orthorhombic symmetry and was confirmed to remain stable to 32 GPa. The Birch-Murnaghan equation of state for new phase was determined from the experimental unit cell parameters, with K0 = 101 (± 16) GPa, K0 = 4 (constrained value), and V0 = 111.9 (± 2.2). This transformation in SrCO3 is different from that in BaCO3 as reported in previous studies. After decompression at ambient pressure, the high-pressure phase transforms to a metastable structure, which has an orthorhombic symmetry. This result should also resolve a dispute regarding the stable high-pressure phases in BaCO3, which is an analog material of CaCO3 and SrCO3.This revised version was published in February 2005 with corrections to the Introduction and to the References. 相似文献