Upper crustal podiform chromitite from the northern Oman ophiolite as the stratigraphically shallowest chromitite in ophiolite and its implication for Cr concentration   总被引：1，自引：0，他引：1  

Shoji?AraiEmail author  Jiro?Uesugi  Ahmed?H.?Ahmed 《Contributions to Mineralogy and Petrology》2004,147(2):145-154

A new type of podiform chromitite was found at Wadi Hilti in the northern Oman ophiolite. It is within a late-intrusive dunite body, possibly derived from olivine-rich crystal mush, between the sheeted dike complex and upper gabbro. This chromitite forms small (<30 cm in thickness) pods with irregular to lenticular shapes. Neither layering nor graded bedding is observed within the pods. The chromitite is in the upper crust, by far shallower in ophiolite stratigraphy than the other podiform chromitites that have ever been found in the Moho transition zone to the upper mantle. It is distributed along a small felsic to gabbroic melt pool within the dunite body, which was formed by melting of gabbroic blocks captured by the mush. Chromian spinel was precipitated due to mixing of two kinds of melt, a basaltic interstitial melt from the mush and an evolved, possibly felsic, melt formed by the melting of gabbro blocks. The podiform chromitite reported here is strikingly similar in petrography and spinel chemistry to the stratiform chromitite from layered intrusions. The former contains plagioclase and clinopyroxene as matrix silicates instead of olivine as well as includes euhedral and fine spinel with solid mineral inclusions. Chromian spinel of the upper crustal podiform chromitite from Oman has relatively low content of (Cr₂O₃ + Al₂O₃), the Cr/(Cr + Al) atomic ratio of around 0.6, and the relatively high TiO₂ content ranging from 1 to 3 wt%. We conclude that assimilation of relatively Si-rich materials (crustal rocks or mantle orthopyroxene) by olivine-spinel saturated melts can explain the genesis of any type of chromitite.Editorial responsibility: V. Trommsdorff  相似文献   

Altitudinal Distribution Of 20 Persistent Meteor Trains: Estimates Derived From Metro Campaign Archives     

Masa-Yuki Yamamoto  Masayuki Toda  Yoshihiro Higa  Kouji Maeda  Jun-Ichi Watanabe 《Earth, Moon, and Planets》2004,95(1-4):279-287

Observations of persistent meteor trains are limited because of the extreme rarity of the phenomenon. The altitudinal distribution of persistent trains has previously been investigated via limited instances of simultaneous observation from multiple sites, however, a statistical study of persistent trains has yet to be realized. The meteor train observation (METRO) campaign was established in Japan in 1998 to obtain images of persistent trains. From 1998 to 2002, the METRO campaign, involving Japanese amateur collaborators, captured more than 400 image sequences of persistent trains, resulting in 53 simultaneous multi-site observations. Several Japanese observers were involved in imaging persistent trains prior to the METRO campaign, producing 6 simultaneous observations over the period 1988–1997. In this paper, simultaneous multi-site observations of high spatial and temporal resolution are used to determine, via triangulation, the altitudinal distribution of persistent trains for 20 events. The altitudinal range of 2 Orionid trains was slightly higher than that of 18 Leonid trains. The Leonid train data reveal no clear dependence of upper and lower altitude on the brightness of the associated fireball. The upper altitude of the 18 observed Leonid trains were almost invariant with respect to local time (LT) of observation, however, a possible dependence of lower altitude on LT of observation was also found, indicating a near-constant penetrating path-length in the upper atmosphere for each train. The average upper altitude of persistent Leonid trains was 99.8 km, while the average central altitude was 93.0 km. These trends are probably determined by atmospheric conditions such as the abundance of O and O₃.  相似文献   

Local time asymmetries of the SSC-associated hydromagnetic variations at the geosynchronous altitude     

Masayuki Kuwashima  Hiroshi Fukunishi 《Planetary and Space Science》1985,33(6):711-720

167 SSC events have been studied by using the data observed at the multiple-satellites at the geosynchronous altitude. The strong local time asymmetry of the SSC amplitude which was found by Kokubun (1983) has been confirmed. The pronounced local time asymmetry has also been found with the direction of the initial movement of Psc magnetic pulsations. Those local time effects are interpreted by the intensification of the magnetopause surface current during a SSC event, and by the distance between the geosynchronous satellite and the surface current. It has also been clarified that the SSC signal propagates with a speed of 400–700 km s^?1 across the field lines in the magnetosphere as suggested by Wilken et al. (1982).  相似文献   

Simulating the carbon balance of a temperate larch forest under various meteorological conditions     

Motomu Toda  Masayuki Yokozawa  Akihiro Sumida  Tsutomu Watanabe  Toshihiko Hara 《Carbon balance and management》2007,2(1):6

Background  

Changes in the timing of phenological events may cause the annual carbon budget of deciduous forests to change. Therefore, one should take such events into account when evaluating the effects of global warming on deciduous forests. In this article, we report on the results of numerical experiments done with a model that includes a phenological module simulating the timing of bud burst and other phenological events and estimating maximum leaf area index.  相似文献   

Partitioning Eddy-Covariance Methane Fluxes from a Shallow Lake into Diffusive and Ebullitive Fluxes   总被引：1，自引：0，他引：1  

Hiroki Iwata  Ryuichi Hirata  Yoshiyuki Takahashi  Yuichi Miyabara  Masayuki Itoh  Kotaro Iizuka 《Boundary-Layer Meteorology》2018,169(3):413-428

Methane (\(\mathrm {CH}_{4}\)) is known to be emitted from lakes to the atmosphere via processes such as diffusion and ebullition (i.e., bubble emission). We developed a practical method for partitioning eddy-covariance \(\mathrm {CH}_{4}\) fluxes from a shallow lake into diffusive and ebullitive fluxes using a wavelet analysis based on local scalar similarity between the \(\mathrm {CH}_{4}\) concentration and other reference scalars, such as the air temperature or water vapour concentration, in the wavelet time-scale domain, with the hypothesis that similar and dissimilar fluctuation components are related to diffusive and ebullitive \(\mathrm {CH}_{4}\) fluxes, respectively. Our method is applied to approximately two weeks of data obtained at a shallow mid-latitude lake. The partitioned diffusive flux has a physically sound relationship with wind speed, supporting the validity of the method. The ratio of the diffusive flux to the total flux is typically 0.11 with flow from an area of steady bubble emission, but otherwise 0.36. Further validation is required using a larger dataset and data from other lakes. The proposed method can be easily applied to historical data because it requires only 10-Hz data of \(\mathrm {CH}_{4}\) concentration and other reference scalars, along with an empirical parameter.  相似文献   

Mineral chemistry of MUSES‐C Regio inferred from analysis of dust particles collected from the first‐ and second‐touchdown sites on asteroid Itokawa     

Tomoki Nakamura  Aiko Nakato  Hatsumi Ishida  Shigeru Wakita  Takaaki Noguchi  Michael E. Zolensky  Masahiko Tanaka  Makoto Kimura  Akira Tshuchiyama  Toshihiro Ogami  Takahito Hashimoto  Mitsuru Konno  Masayuki Uesugi  Toru Yada  Kei Shirai  Akio Fujimura  Ryuji Okazaki  Scott. A. Sandford  Yukihiro Ishibashi  Masanao Abe  Tatsuaki Okada  Munetaka Ueno  Junichiro Kawaguchi 《Meteoritics & planetary science》2014,49(2):215-227

The mineralogy and mineral chemistry of Itokawa dust particles captured during the first and second touchdowns on the MUSES‐C Regio were characterized by synchrotron‐radiation X‐ray diffraction and field‐emission electron microprobe analysis. Olivine and low‐ and high‐Ca pyroxene, plagioclase, and merrillite compositions of the first‐touchdown particles are similar to those of the second‐touchdown particles. The two touchdown sites are separated by approximately 100 meters and therefore the similarity suggests that MUSES‐C Regio is covered with dust particles of uniform mineral chemistry of LL chondrites. Quantitative compositional properties of 48 dust particles, including both first‐ and second‐touchdown samples, indicate that dust particles of MUSES‐C Regio have experienced prolonged thermal metamorphism, but they are not fully equilibrated in terms of chemical composition. This suggests that MUSES‐C particles were heated in a single asteroid at different temperatures. During slow cooling from a peak temperature of approximately 800 °C, chemical compositions of plagioclase and K‐feldspar seem to have been modified: Ab and Or contents changed during cooling, but An did not. This compositional modification is reproduced by a numerical simulation that modeled the cooling process of a 50 km sized Itokawa parent asteroid. After cooling, some particles have been heavily impacted and heated, which resulted in heterogeneous distributions of Na and K within plagioclase crystals. Impact‐induced chemical modification of plagioclase was verified by a comparison to a shock vein in the Kilabo LL6 ordinary chondrite where Na‐K distributions of plagioclase have been disturbed.  相似文献   

A Late Holocene geomagnetic secular variation record from Erhai Lake, southwest China   总被引：1，自引：0，他引：1  

Masayuki Hyodo  Arata Yoshihara  Kenji Kashiwaya  Takashi Okimura  Toshiyuki Masuzawa  Ryotaro Nomura  Shingo Tanaka  Tang Bang Xing  Liu Su Qing  & Liu Shi Jian 《Geophysical Journal International》1999,136(3):784-790

A secular variation record of the geomagnetic field direction for the last 6.5  kyr has been obtained from the magnetization of sediment cores from Erhai Lake, southwest China. In order to make a comparison with this record, secular variation in east-central China was investigated by combining available magnetic field data from historical records and archaeomagnetic measurements since about 350 bc . The secular variation in Erhai Lake shows features consistent with the combined record, except for the oldest three observed declination swings in Sian from 720 to 900 ad . Many features of declination and inclination in China also occur in Japan. From 500 to 1000 ad , declination was westerly ranging from about −20° to −5° in Erhai Lake, east-central China, and Japan.  相似文献   

Evapotranspiration and water source of a tropical rainforest in peninsular Malaysia          下载免费PDF全文

Marryanna Lion  Yoshiko Kosugi  Satoru Takanashi  Shoji Noguchi  Masayuki Itoh  Masanori Katsuyama  Naoko Matsuo  Siti‐Aisah Shamsuddin 《水文研究》2017,31(24):4338-4353

To evaluate water use and the supporting water source of a tropical rainforest, a 4‐year assessment of evapotranspiration (ET) was conducted in Pasoh Forest Reserve, a lowland dipterocarp forest in Peninsular Malaysia. The eddy covariance method and isotope signals of rain, plant, soil, and stream waters were used to determine forest water sources under different moisture conditions. Four sampling events were conducted to collect soil and plant twig samples in wet, moderate, dry, and very dry conditions for the identification of isotopic signals. Annual ET from 2012 to 2015 was quite stable with an average of 1,182 ± 26 mm, and a substantial daily ET was observed even during drought periods, although some decline was observed, corresponding with volumetric soil water content. During the wet period, water for ET was supplied from the surface soil layer between 0 and 0.5 m, whereas in the dry period, approximately 50% to 90% was supplied from the deeper soil layer below 0.5‐m depth, originating from water precipitated several months previously at this forest. Isotope signatures demonstrated that the water sources of the plants, soil, and stream were all different. Water in plants was often different from soil water, probably because plant water came from a different source than water that was strongly bound to the soil particles. Plants showed no preference for soil depth with their size, whereas the existence of storage water in the xylem was suggested. The evapotranspiration at this forest is balanced and maintained using most of the available water sources except for a proportion of rapid response run‐off.  相似文献   

Deep sea circulation of particulate organic carbon in the Japan Sea     

Shigeyoshi Otosaka  Takayuki Tanaka  Orihiko Togawa  Hikaru Amano  Eugeny V. Karasev  Masayuki Minakawa  Shinichiro Noriki 《Journal of Oceanography》2008,64(6):911-923

Seasonal and spatial variations of particulate organic carbon (POC) flux were observed with sediment traps at three sites in the Japan Sea (western and eastern Japan Basin and Yamato Basin). In order to investigate the transport processes of POC, radiocarbon (¹⁴C) measurements were also carried out. Annual mean POC flux at 1 km depth was 30.7 mg m⁻²day⁻¹ in the western Japan Basin, 12.0 mg m⁻²day⁻¹ in the eastern Japan Basin and 23.8 mg m⁻²day⁻¹ in the Yamato Basin. At all stations, notably higher POC flux was observed in spring (March–May), indicating biological production and rapid sinking of POC in this season. Sinking POC in the high flux season showed modern Δ¹⁴C values (>0‰) and aged POC (Δ¹⁴C < −40‰) was observed in winter (December–January). The Δ¹⁴C values in sinking POC were negatively correlated with aluminum concentration, indicating that Δ¹⁴C is strongly related to the lateral supply of lithogenic materials. The Δ¹⁴C values also showed correlations with excess manganese (Mn_xs) concentrations in sinking particles. The Δ¹⁴C-Mn_xs relationship suggested that (1) the majority of the aged POC was advected by bottom currents and incorporated into sinking particles, and (2) some of the aged POC might be supplied from the sea surface at the trap site as part of terrestrial POC. From the difference in the Δ¹⁴C-Mn_xs relationships between the Japan Basin and the Yamato Basin, we consider that basin-scale transport processes of POC occur in the Japan Sea.  相似文献   

临夏盆地新生代沉积物高分辨率岩石磁学记录与亚洲内陆干旱化过程及原因   总被引：4，自引：0，他引：4       下载免费PDF全文

方小敏  徐先海  宋春晖  韩文霞  孟庆泉  鸟居雅之 《第四纪研究》2007,27(6):989-1000

亚洲内陆干旱化是全球新生代大陆环境变化中最引人瞩目的重大事件,与新生代全球变冷和青藏高原隆升密切相关.文章通过对甘肃临夏盆地几乎连续的新生代沉积物系统岩石磁学性质研究,获取了高分辨率磁化率和非磁滞剩磁记录,揭示在29.0～8.6 Ma的漫长的以湖相粉砂岩和泥岩为主的渐新世晚期和中新世早、中期没有明显的长期变化,从8.6Ma开始持续增加,尤其从6.4Ma和5.3Ma开始表现出两次快速持续增加.同时,以8.6Ma为界磁性矿物相对含量发生明显变化,此前以赤铁矿为主,磁铁矿和磁赤铁矿次之,此后以磁铁矿和磁赤铁矿为主,赤铁矿次之,磁性矿物类型和性质类似于风成红粘土和黄土.因此,我们将这种沉积物中磁性矿物组合、性质和含量的长期变化解释为流域外风成物质的加入,指示我国西北内陆现代干旱气候可能从8.6Ma开始,7.4～6.4 Ma后急剧加速变干,5.3Ma后再次加速变干,并最终形成今天的干旱区的过程.9～8 Ma开始的青藏高原阶段性快速隆升和随后的全球变冷可能是驱动亚洲内陆干旱化进程的动力.  相似文献