Geochemical evolution of historical lavas from Askja Volcano, Iceland: Implications for mechanisms and timescales of magmatic differentiation     

Takeshi Kuritani  Tetsuya Yokoyama  Hiroshi Kitagawa  Eizo Nakamura 《Geochimica et cosmochimica acta》2011,75(2):570-587

The mechanisms and the timescales of magmatic evolution were investigated for historical lavas from the Askja central volcano in the Dyngjufjöll volcanic massif, Iceland, using major and trace element and Sr, Nd, and Pb isotopic data, as well as ²³⁸U-²³⁰Th-²²⁶Ra systematics. Lavas from the volcano show marked compositional variation from magnesian basalt through ferrobasalt to rhyolite. In the magnesian basalt-ferrobasalt suite (5-10 wt% MgO), consisting of lavas older than 1875 A.D., ⁸⁷Sr/⁸⁶Sr increases systematically with increasing SiO₂ content; this suite is suggested to have evolved in a magma chamber located at ∼600 MPa through assimilation and fractional crystallization. On the other hand, in the ferrobasalt-rhyolite suite (1-5 wt% MgO), including 1875 A.D. basalt and rhyolite and 20th century lavas, ⁸⁷Sr/⁸⁶Sr tends to decrease slightly with increasing SiO₂ content. It is suggested that a relatively large magma chamber occupied by ferrobasalt magma was present at ∼100 MPa beneath the Öskjuvatn caldera, and that icelandite and rhyolite magmas were produced by extraction of the less and more evolved interstitial melt, respectively, from the mushy boundary layer along the margin of the ferrobasalt magma chamber, followed by accumulation of the melt to form separate magma bodies. Ferrobasalt and icelandite lavas in the ferrobasalt-rhyolite suite have a significant radioactive disequilibrium in terms of (²²⁶Ra/²³⁰Th), and its systematic decrease with magmatic evolution is considered to reflect aging, along with assimilation and fractional crystallization processes. Using a mass-balance model in which simultaneous fractional crystallization, crustal assimilation, and radioactive decay are taken into account, the timescale for the generation of icelandite magma from ferrobasalt was constrained to be <∼3 kyr which is largely dependent on Ra crystal-melt partition coefficients we used.  相似文献   

Infrared spectral energy distribution model for extremely young galaxies     

Tsutomu T. Takeuchi †  Hiroyuki Hirashita ‡  Takako T. Ishii  Leslie K. Hunt  Andrea Ferrara 《Monthly notices of the Royal Astronomical Society》2003,343(3):839-850

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Statistical distribution of building lot frontage: application for Tokyo downtown districts     

Hiroyuki Usui 《Journal of Geographical Systems》2018,20(3):295-316

The frontage of a building lot is the determinant factor of the residential environment. The statistical distribution of building lot frontages shows how the perimeters of urban blocks are shared by building lots for a given density of buildings and roads. For practitioners in urban planning, this is indispensable to identify potential districts which comprise a high percentage of building lots with narrow frontage after subdivision and to reconsider the appropriate criteria for the density of buildings and roads as residential environment indices. In the literature, however, the statistical distribution of building lot frontages and the density of buildings and roads has not been fully researched. In this paper, based on the empirical study in the downtown districts of Tokyo, it is found that (1) a log-normal distribution fits the observed distribution of building lot frontages better than a gamma distribution, which is the model of the size distribution of Poisson Voronoi cells on closed curves; (2) the statistical distribution of building lot frontages statistically follows a log-normal distribution, whose parameters are the gross building density, road density, average road width, the coefficient of variation of building lot frontage, and the ratio of the number of building lot frontages to the number of buildings; and (3) the values of the coefficient of variation of building lot frontages, and that of the ratio of the number of building lot frontages to that of buildings are approximately equal to 0.60 and 1.19, respectively.  相似文献   

Software Dedicated for the Curation of Geochemical Data Sets in Analytical Laboratories     

Yusuke Yachi  Hiroshi Kitagawa  Tak Kunihiro  Eizo Nakamura 《Geostandards and Geoanalytical Research》2014,38(1):95-102

Software designed for analytical laboratories to guarantee traceability and accessibility of rocks with their geochemical properties has been developed. The software documents the sample origin, current sample location and the location of any sample subsets (e.g., thin sections, solutions, etc.), and archives all associated geochemical data sets. The software can be installed on a personal computer so is available for use in any laboratory and allows curation before and after publication. The software will be of use in integrating and sharing geological reference materials within and among institutes. In this article, the system design and implementation are detailed. All source codes for the software are available at http://dream.misasa.okayama-u.ac.jp/ .  相似文献   

Rapid Alkalization in Lake Inawashiro, Fukushima, Japan: Implications for Future Changes in the Carbonate System of Terrestrial Waters     

Takuya Manaka  Hiroyuki Ushie  Daisuke Araoka  Akihiko Inamura  Atsushi Suzuki  Hodaka Kawahata 《Aquatic Geochemistry》2013,19(4):281-302

The global carbon cycle, one of the important biogeochemical cycles controlling the surface environment of the Earth, has been greatly affected by human activity. Anthropogenic nutrient loading from urban sewage and agricultural runoff has caused eutrophication of aquatic systems. The impact of this eutrophication and consequent photosynthetic activity on CO₂ exchange between freshwater systems and the atmosphere is unclear. In this study, we focused on how nutrient loading to lakes affects their carbonate system. Here, we report results of surveys of lakes in Japan at different stages of eutrophication. Alkalization due to photosynthetic activity and decreases in PCO₂ had occurred in eutrophic lakes (e.g., Lake Kasumigaura), whereas in an acidotrophic lake (Lake Inawashiro) that was impacted by volcanic hot springs, nutrient loading was changing the pH and carbon cycling. When the influence of volcanic activity was stronger in the past in Lake Inawashiro, precipitation of volcanic-derived iron and aluminum had removed nutrients by co-precipitation. During the last three decades, volcanic activity has weakened and the lake water has become alkalized. We inferred that this rapid alkalization did not result just from the reduction in acid inputs but was also strongly affected by increased photosynthetic activity during this period. Human activities affect many lakes in the world. These lakes may play an important part in the global carbon cycle through their influence on CO₂ exchange between freshwater and the atmosphere. Biogeochemical changes and processes in these systems have important implications for future changes in aquatic carbonate systems on land.  相似文献   

Fractional-order derivative and time-dependent viscoelastic behaviour of rocks and minerals     

Yusuke Kawada  Takahiro Yajima  Hiroyuki Nagahama 《Acta Geophysica》2013,61(6):1690-1702

A general constitutive equation for viscoelastic behaviour of rocks and minerals with fractional-order derivative is investigated. This constitutive law is derived based on differential geometry and thermodynamics of rheology, and the fractional order of derivative represents the degree of time delay. Analyzing some laboratory experimental data of high temperature deformation of rocks and minerals such as halite, marble and orthopyroxene, we propose how to determine the orders of fractional derivative for viscoelastic behaviours of rocks and minerals. The order is related to the exponents for the temporal scaling in the relaxation modulus and the stress power-law of strain rate, i.e., the non-Newtonian flow law, and considered as an indicator representing the macroscopic behaviour and microscopic dynamics of rocks.  相似文献   

Seasonal changes in camera-based indices from an open canopy black spruce forest in Alaska,and comparison with indices from a closed canopy evergreen coniferous forest in Japan     

Shin Nagai  Taro Nakai  Taku M. Saitoh  Robert C. Busey  Hideki Kobayashi  Rikie Suzuki  Hiroyuki Muraoka  Yongwon Kim 《Polar Science》2013,7(2):125-135

Evaluation of the carbon, water, and energy balances in evergreen coniferous forests requires accurate in situ and satellite data regarding their spatio-temporal dynamics. Daily digital camera images can be used to determine the relationships among phenology, gross primary productivity (GPP), and meteorological parameters, and to ground-truth satellite observations. In this study, we examine the relationship between seasonal variations in camera-based canopy surface indices and eddy-covariance-based GPP derived from field studies in an Alaskan open canopy black spruce forest and in a Japanese closed canopy cedar forest. The ratio of the green digital number to the total digital number, hue, and GPP showed a bell-shaped seasonal profile at both sites. Canopy surface images for the black spruce forest and cedar forest mainly detected seasonal changes in vegetation on the floor of the forest and in the tree canopy, respectively. In contrast, the seasonal cycles of the ratios of the red and blue digital numbers to the total digital numbers differed between the two sites, possibly due to differences in forest structure and leaf color. These results suggest that forest structural characteristics, such as canopy openness and seasonal forest-floor changes, should be considered during continuous observations of phenology in evergreen coniferous forests.  相似文献   

Galerkin boundary integral equation method for spontaneous rupture propagation problems: SH-case     

Hiroyuki Goto  Jacobo Bielak 《Geophysical Journal International》2008,172(3):1083-1103

We develop a Galerkin finite element boundary integral equation method (GaBIEM) for spontaneous rupture propagation problems for a planar fault embedded in a homogeneous full 2-D space. A 2-D antiplane rupture propagation problem, with a slip-weakening friction law, is simulated by the GaBIEM. This method allows one to eliminate the strong singularities from the integral representation of the traction, and to separate explicitly the expression for the traction into an instantaneous component; static and time-dependent components with weakly (logarithmic) singular kernels; and a dynamic component and a quasi-static component, with continuous, bounded, kernels. Simulated results throw light into the performance of the GaBIEM and highlight differences with respect to that of the traditional, collocation, boundary integral equation method (BIEM). Both methods converge with a power law with respect to grid size, with different exponents. There is no restriction on the CFL stability number for the GaBIEM since an implicit, unconditionally stable method is used for the time integration. The error of the approximation increases with the time step, as expected, and it can remain below that of the BIEM.  相似文献   

A ~30,000-year record of environmental changes inferred from Lake Chen Co,Southern Tibet     

Liping Zhu  Xiaolin Zhen  Junbo Wang  Houyuan Lü  Manping Xie  Hiroyki Kitagawa  Göran Possnert 《Journal of Paleolimnology》2009,42(3):343-358

Climatic and environmental changes since the last glacial period are important to our understanding of global environmental change. There are few records from Southern Tibet, one of the most climatically sensitive areas on earth. Here we present a study of the lake sediments (TC1 core) from Lake Chen Co, Southern Tibet. Two sediment cores were drilled using a hydraulic borer in Terrace 1 of Lake Chen Co. AMS ¹⁴C dating of the sediments showed that the sequence spanned >30,000 years. Analyses of present lake hydrology indicated that glacier melt water is very important to maintaining the lake level. Sediment variables such as grain size, TOC, TN, C/N, Fe/Mn, CaCO₃, and pollen were analyzed. Warm and moderately humid conditions dominated during the interval 30,000–26,500 cal year BP. From 26,500 to 20,000 cal year BP, chemical variables and pollen assemblages indicate a cold/dry environment, and pollen amounts and assemblages suggest a decline in vegetation. From 20,000 to 18,000 cal year BP, the environment shifted from cold/dry to warm/humid and vegetation rebounded. The environment transitioned to cold/humid during 16,500–10,500 cal year BP, with a cold/dry event around 14,500 cal year BP. After 10,500 cal year BP, the environment in this region tended to be warm/dry, but exhibited three stages. From 10,500 to 9,000 cal year BP, there was a short warm/humid period, but a shift to cold/dry conditions occurred around 9,000 cal year BP. Thereafter, from 9,000 to 6,000 cal year BP, there was a change from cold/dry to warm/humid conditions, with the warmest period around 6,000 cal year BP. After 6,000 cal year BP, the environment cooled rapidly, but then displayed a warming trend. Chemical variables indicate that a relatively warm/dry event occurred around 5,500–5,000 cal year BP, which is supported by time-lagged pollen assemblages around 4,800 cal year BP. Our lake sediment sequence exhibits environmental changes since 30,000 cal year BP, and most features agree with records from the Greenland GISP2 ice core and with other sequences from the Tibetan Plateau. This indicates that environmental changes inferred from Lake Chen Co, Southern Tibet were globally significant.  相似文献   

Surface mass balance on Glacier No. 31 in the Suntar–Khayata Range,eastern Siberia,from 1951 to 2014     

Yong Zhang  Hiroyuki Enomoto  Tetsuo Ohata  Tsutomu Kadota  Tatsuo Shirakawa  Nozomu Takeuchi 《山地科学学报》2017,14(3):501-512

This study presents a 64-year(1951–2014) reconstruction of the surface mass balance of Glacier No. 31, located in the Suntar-Khayata Range of the eastern Siberia, where the ablation zone is characterized by the extensive dark ice surface. We use a temperature index-based glacier mass-balance model, which computes all major components of glacier mass budget and is forced by daily air temperature and precipitation from a nearby meteorological station. The glacier shows a mean annual mass balance of –0.35 m w.e.a~(–1) during the past 64 years, with an acceleration of –0.50 m w.e. a~(–1) during the recent years. A cumulative mass loss of the glacier is ~22.3 m w.e. over the study period, about 56% of which is observed during 1991–2014. In addition to the contribution of temperature rise and precipitation decrease to recent mass loss of the glacier, an experimental analysis, in which the cleanand dark ice surfaces are respectively assumed to cover the entire ablation zone, indicates that dark ice surface, caused by insoluble impurities consisting of mineral dusts, cryoconite granules, and ice algae, plays a crucial role in the changing mass balance through enhancing melt rates in the ablation zone of the glacier.  相似文献