High-Nb hawaiite–mugearite and high-Mg calc-alkaline lavas from northeastern Iran: Oligo-Miocene melts from modified mantle wedge     

Parham Ahmadi  Massimo Coltorti  Takeshi Kuritani  Yue Cai  Anna Maria Fioretti 《International Geology Review》2019,61(2):150-174

Tertiary volcanic rocks in northwestern Firoozeh, Iran (the Meshkan triangular structural unit), constitute vast outcrops (up to 250 km²) of high-Mg basaltic andesites to dacites that are associated with high-Nb hawaiites and mugearites. Whole-rock ⁴⁰Ar/³⁹Ar ages show a restricted range of 24.1 ± 0.4–22.9 ± 0.5 Ma for the volcanic rocks. The initial ratios of ⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd vary from 0.703800 to 0.704256 and 0.512681 to 0.512877, respectively, in the high-Mg basaltic andesites–dacites. High-Th contents (up to 11 ppm) and Sr/Y values (27–100) and the isotopic composition of the subalkaline high-Mg basaltic andesites–dacites indicate derivation from a mantle modified by slab and sediment partial melts. Evidence such as reverse zoning and resorbed textures and high Ni and Cr contents in the evolved samples indicate that magma mixing with mafic melts and concurrent fractional crystallization lead to the compositional evolution of this series. The high-Nb hawaiites and mugearites, by contrast, have a sodic alkaline affinity and are silica undersaturated; they are also enriched in Nb (up to 47 ppm) and a wide range of incompatible trace elements, including LILE, LREE, and HFSE. Geochemistry and Sr–Nd isotopic compositions of the high-Nb hawaiites and mugearites suggest derivation from a mantle source affected by lower degrees of slab melts. Post-orogenic slab break-off is suggested to have prompted the asthenospheric upwelling that triggered partial melting in mantle metasomatized by slab-derived melts.  相似文献   

Bayesian and Neural Network Approaches to Estimate Deep Temperature Distribution for Assessing a Supercritical Geothermal System: Evaluation Using a Numerical Model     

Ishitsuka  Kazuya  Kobayashi  Yosuke  Watanabe  Norihiro  Yamaya  Yusuke  Bjarkason  Elvar  Suzuki  Anna  Mogi  Toru  Asanuma  Hiroshi  Kajiwara  Tatsuya  Sugimoto  Takeshi  Saito  Ryoichi 《Natural Resources Research》2021,30(5):3289-3314

The temperature distribution at depth is a key variable when assessing the potential of a supercritical geothermal resource as well as a conventional geothermal resource. Data-driven estimation by a machine-learning approach is a promising way to estimate temperature distributions at depth in geothermal fields. In this study, we developed two methodologies—one based on Bayesian estimation and the other on neural networks—to estimate temperature distributions in geothermal fields. These methodologies can be used to supplement existing temperature logs, by estimating temperature distributions in unexplored regions of the subsurface, based on electrical resistivity data, observed geological/mineralogical boundaries, and microseismic observations. We evaluated the accuracy and characteristics of these methodologies using a numerical model of the Kakkonda geothermal field, Japan, where a temperature above 500 °C was observed below a depth of about 3.7 km. When using geological and geophysical knowledge as prior information for the machine learning methods, the results demonstrate that the approaches can provide subsurface temperature estimates that are consistent with the temperature distribution given by the numerical model. Using a numerical model as a benchmark helps to understand the characteristics of the machine learning approaches and may help to identify ways of improving these methods.

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Reducing global GHG emissions by replicating successful sector examples: the ‘good practice policies’ scenario     

Mark Roelfsema  Hanna Fekete  Niklas Höhne  Michel den Elzen  Nicklas Forsell  Takeshi Kuramochi 《Climate Policy》2018,18(9):1103-1113

This article shows the potential impact on global GHG emissions in 2030, if all countries were to implement sectoral climate policies similar to successful examples already implemented elsewhere. This assessment was represented in the IMAGE and GLOBIOM/G4M models by replicating the impact of successful national policies at the sector level in all world regions. The first step was to select successful policies in nine policy areas. In the second step, the impact on the energy and land-use systems or GHG emissions was identified and translated into model parameters, assuming that it would be possible to translate the impacts of the policies to other countries. As a result, projected annual GHG emission levels would be about 50 GtCO₂e by 2030 (2% above 2010 levels), compared to the 60 GtCO₂e in the ‘current policies’ scenario. Most reductions are achieved in the electricity sector through expanding renewable energy, followed by the reduction of fluorinated gases, reducing venting and flaring in oil and gas production, and improving industry efficiency. Materializing the calculated mitigation potential might not be as straightforward given different country priorities, policy preferences and circumstances.

Key policy insights

• Considerable emissions reductions globally would be possible, if a selection of successful policies were replicated and implemented in all countries worldwide.

• This would significantly reduce, but not close, the emissions gap with a 2°C pathway.

• From the selection of successful policies evaluated in this study, those implemented in the sector ‘electricity supply’ have the highest impact on global emissions compared to the ‘current policies’ scenario.

• Replicating the impact of these policies worldwide could lead to emission and energy trends in the renewable electricity, passenger transport, industry (including fluorinated gases) and buildings sector, that are close to those in a 2°C scenario.

• Using successful policies and translating these to policy impact per sector is a more reality-based alternative to most mitigation pathways, which need to make theoretical assumptions on policy cost-effectiveness.

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Synthesis of coda wave envelopes in randomly inhomogeneous elastic media in a half-space: single scattering model including Rayleigh waves     

Takuto Maeda  Haruo Sato  Takeshi Nishimura 《Geophysical Journal International》2008,172(1):130-154

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Internal differentiation of Kutsugata lava flow from Rishiri Volcano,Japan: Processes and timescales of segregation structures' formation     

Takeshi Kuritani  Takeyoshi Yoshida  Yoshitaka Nagahashi 《Journal of Volcanology and Geothermal Research》2010

Internal differentiation processes in a solidifying lava flow were investigated for the Kutsugata lava flow from Rishiri Volcano in northern Japan. In a representative 6-m thick lava flow that was investigated in detail in this study, segregation products darker than the host lavas manifested mainly in the form of pipes (vesicle cylinders) and layers (vesicle sheets), occurring around 0.5–2.3 m and 2.0–4.0 m above the base, respectively. Both the cylinders and sheets are significantly richer in incompatible elements such as TiO₂ and K₂O than the host lavas, which suggest that these products essentially represent residual melt produced during solidification of the lava flow. Field observation and the geochemical features of the lavas suggest that the vesicle cylinders grew upward from near the base of the flow by continuous feeding of residual melt from the neighboring host lavas to the heads of the cylinders. On the other hand, the vesicle sheets were produced in situ in the solidifying lava flow as fracture veins caused by horizontal compression. The vesicle cylinders have a remarkably higher MgO content (up to 8 wt.%) than the host lava (< 6 wt.%), whereas the vesicle sheets display MgO depletion (as low as 3.5 wt.%). The relatively high MgO content of the vesicle cylinders cannot be explained solely by the mechanical mixing of olivine phenocrysts with the residual melt. It is suggested that the vesicle cylinders were produced by the extraction of olivine-bearing interstitial melt from an augite-plagioclase network in the host lava, whereas the vesicle sheets were formed by the migration of the residual melt from a crystal network consisting of plagioclase, augite, and olivine in the host lava into platy fractures. We infer that this selective crystal fractionation for forming the vesicle cylinders resulted from processes in which abundant vesicles rejected from the upward-migrating floor solidification front prevented olivine crystals from being incorporated into the crystal network in the host lava. The vesicle cylinders are considered to have formed in ∼ 1 day after the lava flow came to rest, while relatively large vesicle sheets (> 1 cm thick) appeared much later (after ∼ 9 days). The formation of these segregation products was essentially complete within 20 days after the lava emplacement.  相似文献   

中国沿海及内陆地区长周期脉动特征分析     

车爱兰  于凯  冯少孔  杉山长志 《岩土力学》2011,32(Z2):166-171

地脉动台阵观测作为一种低成本的剪切波速度构造探测方法,预计将在中国地震灾害预防中起到重要作用。为了研究地脉动台阵观测中长周期信号的特征以及中国长周期地脉动的特点和适用性,开展了中国从沿海到内陆地区地脉动信号的观测和分析,探查由沿海到内陆地区地脉动的变化规律以及内陆地区广域的地脉动特征,发展适合于我国内陆地区的基于地脉动的地下构造勘探方法,在中国大陆上海市、西安市、天水市及兰州市进行了长周期地脉动观测。现场试验结果表明,上海地脉动特征与日本关东平原地区的观测结果类似,可以认为在海岸地区深部结构调查的地脉动台阵观测有良好的适用性。然而,西安、兰州、天水长周期地脉动能量只有上海的千分之一,因此需要进一步研究更加灵敏的仪器性能和更加稳定的观测方法。  相似文献   

Impact-induced phyllosilicate formation from olivine and water     

Yoshihiro Furukawa  Toshimori Sekine  Takeshi Kakegawa 《Geochimica et cosmochimica acta》2011,75(21):6461-6472

Shock-recovery experiments on mixtures of olivine and water with gas (air) were performed in a previous study to demonstrate water-mineral interactions during impact events (Furukawa et al., 2007). The products of these former experiments were investigated in the present study using transmission electron microscopy, scanning electron microscopy, and X-ray powder diffraction with the aim of finding evidence of aqueous alteration. Serpentine formed on the surface of shocked olivine with well-developed mosaicism. The yield of serpentine depended on the water/olivine ratio in the starting material, indicating progressive serpentinization under water-rich conditions. Comminution and mosaicism were developed in shocked olivine grains. The temperature and pressure changes of the samples during the experiments were estimated by constructing Hugoniots for mixtures of olivine and water, combined with the results of an additional fracturing experiment on a shocked container. Pressures and temperatures reached 4.6-7.2 GPa and at least 230-390 °C, respectively, for 0.7 μs during in-shock compression. Post-shock temperatures reached a maximum of ∼1300 °C, when the shock wave reached the gas in the sample cavity. The serpentine formed after the post-shock temperature maximum, most likely when temperatures dropped to between 200 and 400 °C. This is the first experiment to demonstrate the formation of phyllosilicates using heat supplied by an impact. The present results and estimations suggest that phyllosilicates could form as a result of impacts into oceans as well as by impacts on terrestrial and Martian crustal rocks, and on some asteroidal surfaces, where liquid or solid H₂O is available. A significant amount of phyllosilicates would have formed during the late heavy bombardment of meteorites on the Hadean Earth, and such phyllosilicates might have affected the prebiotic carbon cycle.  相似文献   

Eruptive history of the Barombi Mbo Maar, Cameroon Volcanic Line, Central Africa: Constraints from volcanic facies analysis     

Boris Chako Tchamabé  Dieudonné Youmen  Sébastien Owona  Issa  Takeshi Ohba  Károly Németh  Moussa Nsangou Ngapna  Asobo N. E. Asaah  Festus T. Aka  Gregory Tanyileke  Joseph V. Hell 《Central European Journal of Geosciences》2013,5(4):480-496

his study presents the first and detail field investigations of exposed deposits at proximal sections of the Barombi Mbo Maar (BMM), NE Mt Cameroon, with the aim of documenting its past activity, providing insight on the stratigraphic distribution, depositional process, and evolution of the eruptive sequences during its formation. Field evidence reveals that the BMM deposit is about 126m thick, of which about 20m is buried lowermost under the lake level and covered by vegetation. Based on variation in pyroclastic facies within the deposit, it can be divided into three main stratigraphic units: U₁, U₂ and U₃. Interpretation of these features indicates that U₁ consists of alternating lapilli-ash-lapilli beds series, in which fallout derived individual lapilli-rich beds are demarcated by surges deposits made up of thin, fine-grained and consolidated ash-beds that are well-defined, well-sorted and laterally continuous in outcrop scale. U₂, a pyroclastic fall-derived unit, shows crudely lenticular stratified scoriaceous layers, in which many fluidal and spindle bombs-rich lapilli-beds are separated by very thin, coarse-vesiculatedash-beds, overlain by a mantle xenolith- and accidental lithic-rich explosive breccia, and massive lapilli tuff and lapillistone. U3 displays a series of surges and pyroclastic fall layers. Emplacement processes were largely controlled by fallout deposition and turbulent diluted pyroclastic density currents under “dry” and “wet” conditions. The eruptive activity evolved in a series of initial phreatic eruptions, which gradually became phreatomagmatic, followed by a phreato-Strombolian and a violent phreatomagmatic fragmentation. A relatively long-time break, demonstrated by a paleosol between U₂ and U₃, would have permitted the feeding of the root zone or the prominent crater by the water that sustained the next eruptive episode, dominated by subsequent phreatomagmatic eruptions. These preliminary results require complementary studies, such as geochemistry, for a better understanding of the changes in the eruptive styles, and to develop more constraints on the maar’s polygenetic origin.  相似文献   

A Continuous and Mechanistic Representation of Calcite Reaction-Controlled Kinetics in Dilute Solutions at 25°C and 1 Atm Total Pressure     

Takeshi Arakaki  Alfonso Mucci 《Aquatic Geochemistry》1999,5(2):225-225

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The Optimal Design of TMD for Offshore Structures   总被引：15，自引：0，他引：15  

Sau Lon James HU  Tomotsuka TAKAYAMA 《中国海洋工程》1999,(2)

This paper presents the optimal design procedure of Tuned Mass Damper(TMD)for re-ducing vibration of an actual steel jacket offshore platform excited by random wave loading.In this study,a frequency domain is taken.The force on the structure is determined by use of the linearized Morisonequation for an input Power Spectral Density(PSD)of wave elevation.The sensitivity of optimum valuesof TMD to characteristic parameters of random wave spectrum is analyzed.An optimized TMD designfor the modeled platform is given based on design conditions and the findings of the study.  相似文献