Petrology of the Yamato nakhlites     

N. Imae  Y. Ikeda  H. Kojima 《Meteoritics & planetary science》2005,40(11):1581-1598

Abstract— The Yamato nakhlites, Y‐000593, Y‐000749, and Y‐000802, were recovered in 2000 from the bare icefield around the Yamato mountains in Antarctica, consisting of three independent specimens with black fusion crusts. They are paired cumulate clinopyroxenites. We obtained the intercumulus melt composition of the Yamato nakhlites and here call it the Yamato intercumulus melt (YIM). The YIM crystallized to form the augite rims, the olivine rims and the mesostasis phases in the cumulates. The augite rims consist of two layers: inner and outer. The crystallization of the inner rim drove the interstitial melt into the plagioclase liquidus field. Subsequently, the residual melt crystallized pigeonites and plagioclase to form the outer rims and the mesostasis. Three types of inclusions were identified in olivine phenocrysts: rounded vitrophyric, angular vitrophyric, and monomineralic augite inclusions. The monomineralic augite inclusions are common and may have been captured by growing olivine phenocrysts. The rounded vitrophyric inclusions are rare and may represent the composition of middle‐stage melts, whereas the angular vitrophyric inclusions seem to have been derived from fractionated late‐stage melts. Glass inclusions occur in close association with titanomagnetite and ferroan augite halo in phenocryst core augites and the assemblages may be magmatic inclusions in augites. We compared the YIM with compositions of magmatic inclusions in olivine and augite. The composition of magmatic inclusions in augite is similar to the YIM. Phenocrystic olivines contain exsolution lamellae, augite‐magnetite aggregates, and symplectites in the cores. The symplectites often occur at the boundaries between olivine and augite grains. The aggregates, symplectite and lamellae formed by exsolution from the host olivine at magmatic temperatures. We present a formational scenario for nakhlites as follows: (1) accumulation of augite, olivine, and titanomagnetite phenocrysts took place on the floor of a magma chamber; (2) olivine exsolved augite and magnetite as augite‐magnetite aggregates, symplectites and lamellae; (3) the overgrowth on olivine phenocrysts formed their rims, and the inner rims crystallized on augite phenocryst cores; and finally, (4) the outer rim formed surrounding the inner rims of augite phenocrysts, and plagioclase and minor minerals crystallized to form mesostasis under a rapid cooling condition, probably in a lava flow or a sill.  相似文献   

The X-ray Emission and the Magnetic Fields of Late-Type Stars     

J.R. Shi  G. Zhao  Y. Zhao 《Astrophysics and Space Science》2002,282(3):477-488

We present the results of X-ray luminosities of some active late-type stars, based on data primarily from the ROSAT position sensitive proportional counter (PSPC). According to the observations, we divide the stars into four groups: single, wide binary, binary and RS CVn. We investigated the correlation between the X-ray emission and the hardness ratio, coronal temperature, magnetic field strength, magnetic flux density. Our results suggest that the magnetic field plays a very important role in stellar X-ray emission.  相似文献   

Seismic moment distribution   总被引：1，自引：0，他引：1  

Y. Y. Kagan 《Geophysical Journal International》1991,106(1):123-134

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A procedure for tidal analysis with a Bayesian information criterion   总被引：16，自引：0，他引：16  

Y. Tamura  T. Sato  M. Ooe  M. Ishiguro 《Geophysical Journal International》1991,104(3):507-516

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An accurate interpolating scheme for semi-Lagrangian advection on an unstructured mesh for ocean modelling     

DANIEL Y. LE ROUX  CHARLES A. LIN  ANDREW STANIFORTH 《地球，A辑:动力气象学与海洋学》1997,49(1):119-138

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Aerosol spectral optical depths and typical size distributions at a coastal urban location in India     

K. NIRANJAN  Y. RAMESH BABU  G. V. SATYANARAYANA  S. THULASIRAMAN 《Tellus. Series B, Chemical and physical meteorology》1997,49(4):439-446

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Development of radiation-damage halos in low-quartz: cathodoluminescence measurement after He+ ion implantation     

K. Komuro  Y. Horikawa  S. Toyoda 《Mineralogy and Petrology》2002,76(3-4):261-266

Summary ?In cathodoluminescence (CL) images of synthetic low-quartz samples after He⁺ implantation at 4 MeV with a dose density over 1.14 × 10⁻⁴ C cm⁻², bright CL halos of about 14 μm in width from the implantation surface are recognized. These widths are consistent with the theoretical range. This confirms experimentally that the CL halos in low-quartz found in geological samples are formed by alpha radiation. It also shows that CL colour continuously changes with dose density, demonstrating that it is possible to use the CL halo as a new dosimeter that is useful for dating and analysis of radionuclide migration in natural geological media. Received December 3, 2001; revised version accepted February 27, 2002  相似文献   

Effects of topography on the spatial distribution of evapotranspiration over a complex terrain using two‐source energy balance model with ASTER data     

H. K. Kafle  Y. Yamaguchi 《水文研究》2009,23(16):2295-2306

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Black hole masses in narrow-line Seyfert 1 galaxies   总被引：1，自引：0，他引：1  

W. Bian  Y. Zhao 《Monthly notices of the Royal Astronomical Society》2004,352(3):823-827

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Wet and Dry Basalt Magma Evolution at Torishima Volcano, Izu Bonin Arc, Japan: the Possible Role of Phengite in the Downgoing Slab   总被引：1，自引：0，他引：1  

Tamura  Y.; Tani  K.; Chang  Q.; Shukuno  H.; Kawabata  H.; Ishizuka  O.; Fiske  R. S. 《Journal of Petrology》2007,48(10):1999-2031

The arc-front volcanoes of Sumisu (31·5°N, 140°E)and Torishima (30·5°N, 140·3°E) in thecentral Izu–Bonin arc are similar in size and rise asrelatively isolated edifices from the seafloor. Together theyprovide valuable along-arc information about magma generationprocesses. The volcanoes have erupted low-K basalts originatingfrom both wet and dry parental basaltic magmas (low-Zr basaltsand high-Zr basalts, respectively). Based on models involvingfluid-immobile incompatible element ratios (La/Sm), the parentalbasalts appear to result from different degrees of partial meltingof the same source mantle (20% and 10% for wet and dry basaltmagmas, respectively). Assuming that the wet basalts containgreater abundances of slab-derived components than their drycounterparts, geochemical comparison of these two basalt typespermits the identification of the specific elements involvedin fluid transport from the subducting slab. Using an extensiveset of new geochemical data from Torishima, where the top ofthe downgoing slab is about 100 km deep, we find that Cs, Pb,and Sr are variably enriched in the low-Zr basalts, which cannotbe accounted for by fractional crystallization or by differencesin the degree of mantle melting. These elements are interpretedto be selectively concentrated in slab-derived metasomatic fluids.Variations in K, high field strength element and rare earthelement concentrations are readily explained by variations inthe degree of melting between the low- and high-Zr basalts;these elements are not contained in the slab-derived fluids.Rb and Ba exhibit variable behaviour in the low-Zr basalts,ranging from immobile, similar to K, to mildly enriched in somelow-Zr basalts. We suggest that the K-rich mica, phengite, playsan important role in determining the composition of fluids releasedfrom the downgoing slab. In arc-front settings, where slab depthis 100 km, phengite is stable, and the fluids released fromthe slab contain little K. In back-arc settings, however, wherethe slab is at 100–140 km depth, phengite is unstable,and K-rich fluids are released. We conclude that cross-arc variationsin the K content of arc basalts are probably related to differingcompositions of released fluids or melts rather than the widelyheld view that such variations are controlled by the degreeof partial melting. KEY WORDS: arc volcano; degrees of melting; mantle wedge; water; wet and dry basalts  相似文献