Rare earth abundances in chondritic phosphates and their implications for early stage chronologies     

Mitsuru Ebihara  Masatake Honda 《Earth and Planetary Science Letters》1983,63(3):433-445

The abundances of nine rare earth elements (REE) in phosphate separates from three ordinary chondrites, Saint Séverin (LL6), Bruderheim (L6) and Richardton (H5), were measured by instrumental neutron activation analysis. All REE except europium are enriched in the phosphate minerals (merrillite and chlorapatite) by factor of 200–300 relative to the chondritic average, whereas Eu is enriched by a factor of 40–50. Electron microprobe analysis showed no significant differences in phosphate mineral composition among the three chondrites studied, though the relative proportions of two minerals varied.According to our data, REE are enriched by almost the same factor in merrillite and chlorapatite in the Bruderheim and, with less certainty, in the other two chondrites. This behavior of REE contrast with that of the actinoid elements, Th, U and Pu, which are also enriched in phosphate but are fractionated between merrillite and chlorapatite. Since Pu and REE show different fractionation behavior in chondritic phosphates, it may be difficult to use REE as stand-ins for Pu in²⁴⁴Pu chronology.  相似文献   

Experimental studies of He and Ar degassing during rock fracturing     

M. Honda  K. Kurita  Y. Hamano  M. Ozima 《Earth and Planetary Science Letters》1982,59(2):429-436

We studied degassing of He and Ar from granite, basalt and volcanic tuff samples which were subjected to uniaxial compression. From the samples which were fractured in the dilatant region He was always degassed, while degassing of Ar dependent not only on the dilatancy, but also on the type of rock and the compressional conditions such as wet, room dry or vacuum conditions. It is concluded that degassing of rare gases from the compressed samples depends primarily on the generation of new surface area by dilatancy.  相似文献   

Cosmic-ray-produced⁴⁰K and⁵⁰V in the metal phase of chondrites     

Keiko Imamura  Masako Shima  Masatake Honda 《Earth and Planetary Science Letters》1975,26(1):54-60

Cosmic-ray-produced⁴⁰K in the metal phase of six chondrites and⁵⁰V in that of one chondrite were determined using a surface ionization mass spectrometer. The²²Ne_total/⁴⁰K_metal ratios of the chondrites are explained in part by shielding effects during cosmic-ray irradiation. The wide variation of this ratio in some groups of meteorites is explained in terms of partial loss of rare-gas nuclides. Radiation ages for the chondrites were determined using⁴⁰K measurements and production-rate estimates from thick target calculations.  相似文献   

Non‐iterative time integration scheme for non‐linear dynamic FEM analysis     

Riki Honda  Hisakazu Sakai  Sumio Sawada 《地震工程与结构动力学》2004,33(1):111-132

This paper proposes a non‐iterative time integration (NITI) scheme for non‐linear dynamic FEM analysis. The NITI scheme is constructed by combining explicit and implicit schemes, taking advantage of their merits, and enables stable computation without an iteration process for convergence even when used for non‐linear dynamic problems. Formulation of the NITI scheme is presented and its stability is studied. Although the NITI scheme is not unconditionally stable when applied to non‐linear problems, it is stable in most cases unless stiffness hardening occurs or the problem has a large velocity‐dependent term. The NITI scheme is applied to dynamic analysis of the non‐linear soil–structure system and computation results are compared with those by the central difference method (CDM). Comparison shows that the stability of the NITI scheme is superior to that of the CDM. Accuracy of the NITI scheme is verified because its results are identical with those by the CDM in which the time step is set as 1/10 of that for the NITI scheme. The application of the NITI scheme to the mesh‐partitioned FEM is also proposed. It is applied to dynamic analysis of the linear soil–structure system. It yields the same results as a conventional single‐domain FEM analysis using the Newmark β method. This result verifies the usability of mesh‐partitioned FEM analysis using the NITI scheme. Copyright © 2003 John Wiley& Sons, Ltd.  相似文献   

Small-scale mélange fabric between serpentinite block and matrix: Magnetic evidence from the Mitsuishi ultramafic rock body, Hokkaido, Japan     

Rie Morijiri  Mitsuru Nakagawa 《Tectonophysics》2005,398(1-2):33-44

The Mitsuishi ultramafic rock body in Hokkaido, Japan, consists mainly of serpentinized peridotites that originated from a depleted mantle. This study aims to show new evidence of small-scale mélange fabric of serpentinite matrix in the rock body. Each serpentinite block in the serpentine matrix shows large and stable intensities of natural remanent magnetization (NRM). However, the directions of serpentinite blocks' NRM in the matrix are randomly scattered. A Curie temperature (Tc) of 580 °C corresponding to pure magnetite was also observed. Additionally, there is no evidence of heating over 580 °C after serpentinization. The blocks in the matrix must have obtained crystallization remanent magnetization (CRM) during serpentinization. The directions of the blocks' characteristic remanent magnetization (ChRM) are also scattered. It shows that serpentinite blocks were magnetized prior to uplifting. The results of the study indicate that the magnetic carrier of the serpentinite blocks in the matrix is mainly composed of magnetite, and it can keep original magnetization before uplifting. The results also imply that the scattering directions of NRM indicate the presence of small-scale mélange fabric of serpentinite matrix.  相似文献   

Performance of regional distance centroid moment tensor inversion applied to the 2004 mid-Niigata prefecture earthquake, Japan     

Yoshihiro Ito  Shoji Sekiguchi  Tomomi Okada  Ryou Honda  Kazushige Obara  Sadaki Hori 《Geophysical Journal International》2006,167(3):1317-1331

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Small-scale convection under the back-arc occurring in the low viscosity wedge     

Satoru Honda  Mitsunobu Saito 《Earth and Planetary Science Letters》2003,216(4):703-715

Water released from subducting slabs through a dehydration reaction may lower the viscosity of the mantle significantly. Thus, we may expect a low viscosity wedge (LVW) above the subducting slabs. The LVW coupled with a large-scale flow induced by the subducting slabs may allow the existence of roll-like small-scale convection whose axis is normal to the strike of the plate boundary. Such a roll structure may explain the origin of along-arc variations of mantle temperature proposed recently in northeast Japan. We study this possibility using both 2D and 3D models with/without pressure- and temperature-dependent viscosity. 2D models without pressure and temperature dependence of viscosity show that, with a reasonable geometry of the LVW and subduction speed, small-scale convection is likely to occur when the viscosity of the LVW is less than 10¹⁹ Pa s. Corresponding 3D model studies reveal that the wavelength of rolls depends on the depth of the LVW. The inclusion of temperature-dependent viscosity requires the existence of further low viscosity in the LVW, since temperature dependence suppresses the instability of the cold thermal boundary layer. Pressure (i.e. depth) dependence coupled with temperature dependence of the viscosity promotes short wavelength instabilities. The model, which shows a relatively moderate viscosity decrease in the LVW (most of the LVW viscosity is 10¹⁸∼10¹⁹ Pa s) and a wavelength of roll ∼80 km, has a rather small activation energy and volume (∼130 kJ/mol and ∼4 cm³/mol) of the viscosity. This small activation energy and volume may be possible, if we regard them as an effective viscosity of non-linear rheology.  相似文献   

Effects of mirror reflection versus diffusion anisotropy on particle acceleration in oblique shocks     

Y. S. Honda  M. Honda 《Monthly notices of the Royal Astronomical Society》2005,362(3):833-837

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Preservation of near-solar neon isotopic ratios in Icelandic basalts     

Eleanor T. Dixon  Masahiko Honda  Ian McDougall  Ian H. Campbell  Ingvar Sigurdsson 《Earth and Planetary Science Letters》2000,180(3-4):309-324

Neon isotopic ratios measured in olivine and basaltic glass from Iceland are the most primitive observed so far in terrestrial mantle-derived samples. Ratios were measured in gas released from olivine and basaltic glass from a total of 10 samples from the Reykjanes Peninsula, Iceland, and one sample from central Iceland. The neon isotopic ratios include solar-like, mid-ocean ridge basalt (MORB)-like and atmospheric compositions. Neon isotopic ratios near the air–solar mixing line were obtained from the total gas released from glass separates from five samples. MORB-like neon isotopic compositions were measured in the total gas released from olivine and glass separates from four samples. Although there is clear evidence for a solar neon component in some of the Icelandic samples, there is no corresponding evidence for a solar helium ratio (320R_a>³He/⁴He>100R_a). Instead, ³He/⁴He ratios are mainly between 12±2(R_a) and 29±3(R_a), similar to the range observed in ocean island basalts, indicating that the He–Ne isotopic systematics are decoupled. The mantle source of Icelandic basalts is interpreted to be highly heterogeneous on a local scale to explain the range in observed helium and neon isotopic ratios. The identification of solar-like neon isotopic ratios in some Icelandic samples implies that solar neon trapped within the Earth has remained virtually unchanged over the past 4.5 Ga. Such preservation requires a source with a high [Ne_solar]/[U+Th] ratio so that the concentration of solar neon overwhelms the nucleogenic ²¹Ne* produced from the decay of U and Th in the mantle over time. High [Ne_solar]/[U+Th] ratios are unlikely to be preserved in the mantle if it has experienced substantial melting. An essentially undegassed primitive mantle component is postulated to be the host of the solar neon in the Icelandic plume source. Relatively small amounts of this primitive mantle component are likely to mix with more depleted and degassed mantle such that the primitive mantle composition is not evident in other isotopic systems (e.g. strontium and neodymium). The lower mantle plume source is inferred to be relatively heterogeneous owing to being more viscous and less well stirred than the upper mantle. This discovery of near-solar neon isotopic ratios suggests that relatively primitive mantle may be preserved in the Icelandic plume source.  相似文献   

The noble gas systematics of late-orogenic H₂O-CO₂ fluids, Mt Isa, Australia   总被引：2，自引：0，他引：2  

M.A. Kendrick  M. Honda  D. Phillips 《Geochimica et cosmochimica acta》2011,75(6):1428-1450

The noble gases (He, Ne, Ar, Kr and Xe) are powerful geochemical tracers because they have distinctive isotopic compositions in the atmosphere, crust and mantle. This study illustrates how noble gases can be used to trace fluid origins in high-temperature metamorphic and mineralising environments; and at the same time provides new information on the composition of noble gases in deeper parts of the crust than have been sampled previously.We report data for H₂O and CO₂ fluid inclusions trapped at greenschist to amphibolite facies metamorphic conditions associated with three different styles of mineralisation and alteration in the Proterozoic Mt Isa Inlier of Australia. Sulphide fluid inclusions are dominated by crustal ⁴He. However, co-variations in fluid inclusion ²⁰Ne/²²Ne, ²¹Ne/²²Ne, ⁴⁰Ar/³⁶Ar and ¹³⁶Xe/¹³⁰Xe indicate noble gases were derived from three or more reservoirs. In most cases, the fluid inclusions elemental noble gas ratios (e.g. Ne/Xe) are close to the ranges expected in sedimentary and crystalline rocks. However, the elemental ratios have been modified in some of the samples providing evidence for independent pulses of CO_2, and interaction of CO₂ with high-salinity aqueous fluids.Compositional variation is attributed to mixing of: (i) magmatic fluids (or deeply sourced metamorphic fluids) characterised by basement-derived noble gases with ²⁰Ne/²²Ne ∼ 8.4, ²¹Ne/²²Ne ∼ 0.4, ⁴⁰Ar/³⁶Ar ∼ 40,000 and ¹³⁶Xe/¹³⁰Xe ∼ 8; (ii) basinal-metamorphic fluids with a narrow range of compositions including near-atmospheric values and (iii) noble gases derived from the meta-sedimentary host-rocks with ²⁰Ne/²²Ne ∼ 8-9.8, ²¹Ne/²²Ne < 0.1, ⁴⁰Ar/³⁶Ar < 2500 and ¹³⁶Xe/¹³⁰Xe ∼ 2.2.These data provide the strongest geochemical evidence available for the involvement of fluids from two distinct geochemical reservoirs in Mt Isa’s largest ore deposits. In addition the data show how noble gases in fluid inclusions can provide information on fluid origins, the composition of the crust’s major lithologies, fluid-rock interactions and fluid-fluid mixing or immiscibility processes.  相似文献