High temperature solvent growth of anorthite on the join CaAl2Si2O8-SiO2     

Jun Ito 《Contributions to Mineralogy and Petrology》1976,59(2):187-194

Stoichiometric anorthite, CaAl₂Si₂O₈, Pˉ1, with sharp a, b, c, and d diffractions was grown, using a CaV₂O₆ solvent, by cooling at 2 ° C per hour from 1450 to 750 ° C in air. Euhedral crystals up to 5 × 3× 0.5 mm, with prominent {010} and well-developed {110} and {001}, were obtained by spontaneous nucleation. Nonstoichiometric anorthite with excess SiO₂ (CaAl₂Si₂O₈+Si₂Si₂O₈) was grown on the join CaAl₂Si₂O₈-SiO₂. Chemical analysis of the synthetic anorthite, having the highest SiO₂ content, with maximum vacancies on M-site gave □_0.110 Na_0.006Ca_0.884Al_1.80Si_2.20O₈, and X-ray diffraction showed a trend from stoichiometric Pˉ1 through diffuse Pˉ1 to body-centered Iˉ1 probably reflecting increasing disorder caused by a higher Si/Al ratio in the T-sites and the positional disorder accompanied by M-site vancancies. Annealing of the nonstoichiometric diffuse Iˉ1 anorthite in air at 1050 ° C for 14 days resulted in exsolution of minute SiO₂ inclusions due to probable ordering in the T-sites and filling of M-sites by Ca. Stoichiometric Pˉ1 anorthite was not obtained by annealing at 1050 ° due to appreciable solubility of SiO₂ in CaAl₂Si₂O₈. Metastable hexagonal CaAl₂Si₂O₈ was found to be a twinned monoclinic crystal with cell dimensions: a = 10.24 (2), b = 17.74 (3), c= 14.99 (5) ?, β = 92.05 (5) °, space group C2.  相似文献   

准噶尔板块东北缘富铌玄武岩的发现及其地质意义   总被引：4，自引：0，他引：4       下载免费PDF全文

张海祥  牛贺才  于学元  单强  HiroakiSato  JunichiIto 《地质找矿论丛》2003,18(1):71-72

富铌玄武岩是硅过饱和,富Ｎａ2Ｏ,ＴｉＯ2,Ｐ2Ｏ5,同时富集高场强元素的一类岛弧玄武岩,这类玄武岩的ｗ(Ｎｂ)>7×10-6,(ｗ(Ｌａ)/ｗ(Ｎｂ))ＭＮ<2。它是由来源于70100ｋｍ深处、受ａｄａｋｉｔｅ熔体交代过的地幔楔橄榄岩部分熔融形成的,是大洋板块俯冲作用的产物。目前发现的富铌玄武岩大多分布在环太平洋新生代岛弧环境,与洋壳俯冲作用密切相关[1 5]。本研究在准噶尔板块东北缘富蕴县的索尔库都克附近首次发现了富铌玄武岩。它产于下泥盆统托让格库都克组中、上部。该地层自下而上的岩石组合为:玄武岩 火山凝灰角砾岩 火山集块岩 含…  相似文献   

Erratum to “Garnet-ilmenite-perovskite transitions in the system Mg₄Si₄O₁₂Mg₃Al₂Si₃O₁₂ at high pressures and high temperatures: phase equilibria, calorimetry and implications for mantle structure” [Phys. Earth Planet. Inter. 132 (2002) 303-324]     

Masaki Akaogi  Akira TanakaEiji Ito 《Physics of the Earth and Planetary Interiors》2003,135(4):291

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Authigenic calcium carbonate flux in groundwater-controlled lakes: Implications for lacustrine paleoclimate records     

M.D. Shapley  E. Ito 《Geochimica et cosmochimica acta》2005,69(10):2517-2533

Groundwater dominated lakes are an important feature of many landscapes. Their sediments are a particularly valuable source of paleoenvironmental information in semiarid regions where perennial lakes may otherwise be scarce. Where groundwater and lake composition are favorable, carbonate mineral precipitation, evaporative concentration of lake water, and microbial processes can combine to strongly deplete dissolved Ca relative to influent groundwaters. The authigenic carbonate flux (ACF) can then become limited by water column cation availability and thereby be coupled to groundwater inflow rates and aquifer recharge. Here we analyze sedimentary records from two marl-producing, groundwater-controlled lakes and demonstrate a link between one-dimensional ACF and the Palmer Drought Severity Index (PDSI), a measure of land surface wetness. In a restricted outflow lake with high-carbonate alkalinity, ACF is enhanced during historically wet climatic periods in response to increased aquifer recharge rates. ACF in this lake declines during droughts. A neighboring dilute lake with a high rate of groundwater outflow shows comparatively weak coupling between ACF and PDSI history. Ionic chemistry, carbonate mineral equilibria, and δ¹³C patterns of dissolved inorganic carbon show that the sensitivity of the ACF signal depends on the degree of evaporative evolution of lake water and the mineral saturation state of the water column under conditions of stratification and ice cover.  相似文献   

Field Workshop on Geology and Natural Hazards Along the Kaligandaki Valley, Central–West Nepal Himalaya     

M. Yoshida  Y. Konagaya  Y. Suganuma  T. Ito  B.N. Upreti 《Gondwana Research》2005,8(4):631-634

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Deep low-frequency earthquake swarm in the mid crust beneath Mount Fuji (Japan) in 2000 and 2001     

Motoo Ukawa 《Bulletin of Volcanology》2005,68(1):47-56

Beneath Mount Fuji, the highest active volcano in Japan, deep low-frequency (DLF) earthquake activity has been monitored since the early 1980s. The DLF earthquakes occurred in the mid-crustal depth range, and burst-type activity lasting from several minutes to 30 min was detected 10 to 20 times in an ordinary year. The DLF earthquake activity increased sharply in the period from October 2000 to May 2001, showing swarm-like activity. The occurrence rate during the DLF earthquake swarm was approximately 20 times higher than the usual activity, and the wave energy released during the swarm period was twice as high as the total wave energy during the past 20 years. The DLF earthquakes in the period from 1987 to 2001 were relocated by estimating station corrections in order to reduce the effect of the change of seismic station distribution. The epicenters of most DLF earthquakes occurred in an elongated region with a long axis of about 5 km, whose center is located 2–3 km NE from the summit. A few percent of the DLF earthquakes, however, occurred around the summit area, significantly apart from the main epicenter region. The focal depths of well-located DLF events range from 10 to 20 km. During the high activity period in 2000 and 2001, most DLF events occurred within this main hypocenter area. The sharp increase of DLF earthquake activity at Mount Fuji started immediately after magma discharge and intrusion events in the Miyake-jima and Kozu-shima regions in July and August 2000. The tectonic and volcanic activity changes around the area suggest that the DLF earthquake swarm at Mount Fuji was triggered by the change of state of the deep magmatic system around Mount Fuji.Editorial responsibility: J Stix  相似文献   

Planetary Boundary Layer over a Small Island as Observed by a Doppler Sodar     

Yoshiki Ito 《Boundary-Layer Meteorology》1997,85(3):379-390

Observations from a new five-beam phasedarray Doppler sodar located over a small islandrevealed the development of an internal boundary layer (IBL)from the edge of a cliff in strong windcases, and the presence of systematic convective motions in unstableconditions. The top of the IBL ischaracterized by a small wind maximum trailing fromthe strong wind area at the edge of the cliff, anddevelops with distance from the edge. In the presence ofcumulus clouds, an upwardvelocity region, surrounded by downward motion, wasobserved in the subcloud layer. Anupward convective pattern of organized motion following the passage of cumulus clouds may be young thermalsrising from a height of about 100 m.  相似文献   

Holocene Climate in the Northern Great Plains Inferred from Sediment Stratigraphy, Stable Isotopes, Carbonate Geochemistry, Diatoms, and Pollen at Moon Lake, North Dakota     

Blas L. Valero-Garcés  Kathleen R. Laird  Sherilyn C. Fritz  Kerry Kelts  Emi Ito  Eric C. Grimm 《Quaternary Research》1997,48(3):359-369

Seismic stratigraphy, sedimentary facies, pollen stratigraphy, diatom-inferred salinity, stable isotope (δ¹⁸O and δ¹³C), and chemical composition (Sr/Ca and Mg/Ca) of authigenic carbonates from Moon Lake cores provide a congruent Holocene record of effective moisture for the eastern Northern Great Plains. Between 11,700 and 9500¹⁴C yr B.P., the climate was cool and moist. A gradual decrease in effective moisture occurred between 9500 and 7100¹⁴C yr B.P. A change at about 7100¹⁴C yr B.P. inaugurated the most arid period during the Holocene. Between 7100 and 4000¹⁴C yr B.P., three arid phases occurred at 6600–6200¹⁴C yr B.P., 5400–5200¹⁴C yr B.P., and 4800–4600¹⁴C yr B.P. Effective moisture generally increased after 4000¹⁴C yr B.P., but periods of low effective moisture occurred between 2900–2800¹⁴C yr B.P. and 1200–800¹⁴C yr B.P. The data also suggest high climatic variability during the last few centuries. Despite the overall congruence, the biological (diatom), sedimentological, isotopic, and chemical proxies were occassionally out of phase. At these times the evaporative process was not the only control of lake-water chemical and isotopic composition.  相似文献   

Spatial distribution of shear wave anisotropy in the crust of the southern Hyogo region by borehole observations   总被引：2，自引：0，他引：2  

Takashi Mizuno  Kiyoshi Yomogida  Hisao Ito  Yasuto Kuwahara 《Geophysical Journal International》2001,147(3):528-542

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What can be learned from rotational motions excited by earthquakes?   总被引：1，自引：0，他引：1  

Minoru Takeo  Hidemi M. Ito 《Geophysical Journal International》1997,129(2):319-329

One answer to the question posed in the title is that we will have more accurate data for arrival times of SH waves, because the rotational component around the vertical axis is sensitive to SH waves although not to P-SV waves. Importantly, there is another answer related to seismic sources, which will be discussed in this paper.
Generally, not only dislocations commonly used in earthquake models but also other kind of defects could contribute to producing seismic waves. In particular, rotational strains at earthquake sources directly generate rotational components in seismic waves. Employing the geometrical theory of defects, we obtain a general expression for the rotational motion of seismic waves as a function of the parameters of source defects.
Using this expression, together with one for translational motion, we can estimate the rotational strain tensor and the spatial variation of slip velocity in the source area of earthquakes. These quantities will be large at the edges of a fault plane due to spatially rapid changes of slip on the fault and/or a formation of tensile fractures.  相似文献