Migration of protoplanets: Effects on terrestrial planet formation     

Takayuki Tanigawa 《Planetary and Space Science》2008,56(13):1758-1763

I review the role of planetary migration on the formation process of terrestrial planets. I first show a simple estimation for growth timescale of solid proto-planets and review a linear theory of disk-planet gravitational interaction to estimate the migration rate of proto-planets in a gas disk, and then discuss the difficulty of the formation of terrestrial planets in terms of comparison between migration timescale and growth timescale. Next I show recent studies which suggest possible mechanisms to solve the problem. I briefly discuss the formation process of Mercury in the context of terrestrial-planet formation.  相似文献   

Tectonics of an Early Carboniferous forearc inferred from a high-P/T schist-bearing conglomerate in the Nedamo Terrane, Northeast Japan     

Takayuki  Uchino  Makoto  Kawamura 《Island Arc》2010,19(1):177-191

The Nedamo Terrane, an Early Carboniferous accretionary complex, is the oldest biostratigraphically dated accretionary complex in Japan. The purpose of this study is to describe and interpret a conglomerate from the Nedamo Terrane that contains clasts of high-pressure/low-temperature (high- P/T ) schist (mainly garnet-bearing phengite schist) and ultramafic rock, and to infer the tectonics of an Early Carboniferous arc–trench system at the eastern margin of the paleo-Asian continent. Clasts of high- P/T schist and ultramafic rock within the conglomerate make up 8.4 and 6.7% of the total clasts, respectively, based on modal counts. These clasts are subangular to subrounded, whereas volcanic clasts are well rounded. The source of the schist clasts, which yield a radiometric age of 347–317 Ma, is considered to be the Renge Metamorphic Rocks of Southwest Japan or equivalent rocks. Based on the chemical composition of chromian spinel, the source of ultramafic clasts is inferred to be the island-arc-type Ordovician Miyamori and Hayachine ultramafic complexes in the Kitakami Massif. The conglomerate records multiple provenance regions, including an island arc (South Kitakami Terrane) and a forearc ridge; the high P/T schist and ultramafic rocks were exhumed in the forearc region. The duration of the interval from the early stages of exhumation of the schist to its deposition in the trench as clasts is estimated to have been less than 30 my.  相似文献   

PSDF: Particle Stream Data Format for N-body simulations     

Will M. Farr  Jeff AmesPiet Hut  Junichiro MakinoSteve McMillan  Takayuki MuranushiKoichi Nakamura  Keigo NitadoriSimon Portegies Zwart 《New Astronomy》2012,17(5):520-523

We present a data format for the output of general N-body simulations, allowing the presence of individual time steps. By specifying a standard, different N-body integrators and different visualization and analysis programs can all share the simulation data, independent of the type of programs used to produce the data. Our Particle Stream Data Format, PSDF, is specified in YAML, based on the same approach as XML but with a simpler syntax. Together with a specification of PSDF, we provide background and motivation, as well as specific examples in a variety of computer languages. We also offer a web site from which these examples can be retrieved, in order to make it easy to augment existing codes in order to give them the option to produce PSDF output.  相似文献   

Li isotopes and trace elements as a petrogenetic tracer in zircon: insights from Archean TTGs and sanukitoids   总被引：1，自引：0，他引：1  

Anne-Sophie Bouvier  Takayuki Ushikubo  Noriko T. Kita  Aaron J. Cavosie  Reinhard Kozdon  John W. Valley 《Contributions to Mineralogy and Petrology》2012,163(5):745-768

We report δ⁷Li, Li abundance ([Li]), and other trace elements measured by ion probe in igneous zircons from TTG (tonalite, trondhjemite, and granodiorite) and sanukitoid plutons from the Superior Province (Canada) in order to characterize Li in zircons from typical Archean continental crust. These data are compared with detrital zircons from the Jack Hills (Western Australia) with U–Pb ages greater than 3.9 Ga for which parent rock type is not known. Most of the TTG and sanukitoid zircon domains preserve typical igneous REE patterns and CL zoning. [Li] ranges from 0.5 to 79 ppm, typical of [Li] in continental zircons. Atomic ratios of (Y + REE)/(Li + P) average 1.0 ± 0.7 (2SD) for zircons with magmatic composition preserved, supporting the hypothesis that Li is interstitial and charge compensates substitution of trivalent cations. This substitution results in a relatively slow rate of Li diffusion. The δ⁷Li and trace element data constrain the genesis of TTGs and sanukitoids. [Li] in zircons from granitoids is significantly higher than from zircons in primitive magmas in oceanic crust. TTG zircons have δ⁷Li (3 ± 8‰) and δ¹⁸O in the range of primitive mantle-derived magmas. Sanukitoid zircons have average δ⁷Li (7 ± 8‰) and δ¹⁸O higher than those of TTGs supporting genesis by melting of fluid-metasomatized mantle wedge. The Li systematics in sanukitoid and TTG zircons indicate that high [Li] in pre-3.9-Ga Jack Hills detrital zircons is a primary igneous composition and suggests the growth in proto-continental crust in magmas similar to Archean granitoids.  相似文献   

High-pressure phase relations in the system TiO2–ZrO2 to 12?GPa: stability of αPbO2-type srilankite solid solutions of (Ti1?x , Zr x )O2 (0?≤?x?≤?0.6)     

Masaki Akaogi  Nanami Horiuchi  Takayuki Ishii  Hiroshi Kojitani 《Physics and Chemistry of Minerals》2012,39(10):797-802

Phase relations in the system TiO₂–ZrO₂ were examined in the pressure range of 3.5–12?GPa at 1,800?°C, using multianvil apparatus. At 1,800?°C, TiO₂ rutile transforms to αPbO₂ structure at 10?GPa, and the αPbO₂-type solid solution is stable in compositional range between TiO₂ and about (Ti_0.6, Zr_0.4)O₂ at 3.5–12?GPa. Combination of the present results with the published data at 0–3?GPa demonstrates that continuous solid solution with the αPbO₂-type structure is stable between TiO₂ and (Ti_1?x , Zr _x )O₂ (x?≈?0.6) at 0–12?GPa. This indicates that both the αPbO₂-type TiO₂ and srilankite Ti₂ZrO₆ with the same structure belong to the continuous solid solution system though the two phases have been regarded as different minerals. With increasing ZrO₂ content, lattice parameters of a- and c-axes of the αPbO₂-type solid solution increase, but b-axis is almost constant or slightly decreases. At higher pressure, the αPbO₂-type solid solution dissociates into two phases, αPbO₂-type phase and tetragonal zirconia. Srilankite with more TiO₂-rich composition than Ti₂ZrO₆ might be found in natural rocks derived from the deep upper mantle.  相似文献   

A Simulation Study of the Plasma Wave Enhancements in the Earth’s Equatorial Plasmasphere     

Mohammad Javad Kalaee  Yuto Katoh  Takayuki Ono 《Earth, Moon, and Planets》2013,110(3-4):131-141

In the equatorial plasmasphere, plasma waves are frequently observed. To improve our understanding of the mechanism generating plasma waves from instabilities, a comparison of observations, linear growth-rate calculations, and simulation results is presented. To start the numerical experiments from realistic initial plasma conditions, we use the initial parameters inferred from observational data obtained around the plasma-wave generation region by the Akebono satellite. The linear growth rates of waves of different modes are calculated under resonance conditions, and compared with simulation results and observations. By employing numerical experiments by a particle code, we first show that upper hybrid-, Z-, and whistler-mode waves are excited through instabilities driven by a ring-type velocity distribution. The simulation results suggest a possibility that energetic electrons with energies of some tens of keV confined around the geomagnetic equator are responsible for the observed enhancements of Z- and whistler-mode waves. While the comparison between linear growth-rate calculations and observations shows the different tendency of wave amplitude of Z-mode and whistler-mode waves, the wave amplitude of these wave modes in the simulation results is consistent with the observation.  相似文献   

Assessment of grain-scale homogeneity and equilibration of carbon and oxygen isotope compositions of minerals in carbonate-bearing metamorphic rocks by ion microprobe   总被引：1，自引：0，他引：1  

John M. Ferry  Takayuki Ushikubo  John W. Valley 《Geochimica et cosmochimica acta》2010,74(22):6517-6540

Nineteen samples of metamorphosed carbonate-bearing rocks were analyzed for carbon and oxygen isotope ratios by ion microprobe with a ∼5-15 μm spot, three from a regional terrain and 16 from five different contact aureoles. Contact metamorphic rocks further represent four groups: calc-silicate marble and hornfels (6), brucite marble (2), samples that contain a reaction front (4), and samples with a pervasive distribution of reactants and products of a decarbonation reaction (4). The average spot-to-spot reproducibility of standard calcite analyses is ±0.37‰ (2 standard deviations, SD) for δ¹⁸O and ±0.71‰ for δ¹³C. Ten or more measurements of a mineral in a sample that has uniform isotope composition within error of measurement can routinely return a weighted mean with a 95% confidence interval of 0.09-0.16‰ for δ¹⁸O and 0.10-0.29‰ for δ¹³C. Using a difference of >6SD as the criterion, only four of 19 analyzed samples exhibit significant intracrystalline and/or intercrystalline inhomogeneity in δ¹³C at the 100-500 μm scale, with differences within individual grains up to 3.7‰. Measurements are consistent with carbon isotope exchange equilibrium between calcite and dolomite in five of six analyzed samples at the same scale. Because of relatively slow carbon isotope diffusion in calcite and dolomite, differences in δ¹³C can survive intracrystalline homogenization by diffusion during cooling after peak metamorphism and likely represent the effects of prograde decarbonation and infiltration. All but 2 of 11 analyzed samples exhibit intracrystalline differences in δ¹⁸O (up to 9.4‰), intercrystalline inhomogeneity in δ¹⁸O (up to 12.5‰), and/or disequilibrium oxygen isotope fractionations among calcite-dolomite, calcite-quartz, and calcite-forsterite pairs at the 100-500 μm scale. Inhomogeneities in δ¹⁸O and δ¹³C are poorly correlated with only a single mineral (dolomite) in a single sample exhibiting both. Because of relatively rapid oxygen isotope diffusion in calcite, intracrystalline inhomogeneities in δ¹⁸O likely represent partial equilibration between calcite and fluid during retrograde metamorphism. Calcite is in oxygen isotope exchange equilibrium with forsterite in one of four analyzed samples, in equilibrium with dolomite in none of six analyzed samples, and in equilibrium with quartz in neither of two analyzed samples. There are no samples of contact metamorphic rock with analyzed reactants and products of an arrested metamorphic reaction that are in oxygen isotope equilibrium with each other. The degree of departure from equilibrium in analyzed samples is variable and is often related, at least in part, to alteration of δ¹⁸O of calcite during retrograde fluid-rock reaction. In situ sub-grain-scale carbon and oxygen isotope analyses of minerals are advisable in the common applications of stable isotope geochemistry to metamorphic petrology. Correlation of sub-mm scale stable isotope data with imaging will lead to improved understanding of reaction kinetics, reactive fluid flow, and thermal histories during metamorphism.  相似文献