Late Archaean mantle metasomatism below eastern Indian craton: Evidence from trace elements,REE geochemistry and Sr—Nd—O isotope systematics of ultramafic dykes     

A. Roy  A. Sarkar  S. Jeyakumar  S. K. Aggrawal  M. Ebihara  H. Satoh 《Journal of Earth System Science》2004,113(4):649-665

Trace, rare earth elements (REE), Rb-Sr, Sm-Nd and O isotope studies have been carried out on ultramafic (harzburgite and lherzolite) dykes belonging to the newer dolerite dyke swarms of eastern Indian craton. The dyke swarms were earlier considered to be the youngest mafic magmatic activity in this region having ages not older than middle to late Proterozoic. The study indicates that the ultramafic members of these swarms are in fact of late Archaean age (Rb-Sr isochron age 2613 ± 177 Ma, Sri ∼ 0.702 ± 0.004) which attests that out of all the cratonic blocks of India, eastern Indian craton experienced earliest stabilization event. Primitive mantle normalized trace element plots of these dykes display enrichment in large ion lithophile elements (LILE), pronounced Ba, Nb and Sr depletions but very high concentrations of Cr and Ni. Chondrite normalised REE plots exhibit light REE (LREE) enrichment with nearly flat heavy REE (HREE; (ΣHREE)_N ∼ 2–3 times chondrite, (Gd/Yb)_N ∼ 1). The ε^Nd(t) values vary from +1.23 to -3.27 whereas δ¹⁸O values vary from +3.16‰ to +5.29‰ (average +3.97‰±0.75‰) which is lighter than the average mantle value. Isotopic, trace and REE data together indicate that during 2.6 Ga the nearly primitive mantle below the eastern Indian Craton was metasomatised by the fluid (± silicate melt) coming out from the subducting early crust resulting in LILE and LREE enriched, Nb depleted, variable ε^Nd, low Sr_i(0.702) and low δ¹⁸O bearing EMI type mantle. Magmatic blobs of this metasomatised mantle were subsequently emplaced in deeper levels of the granitic crust which possibly originated due to the same thermal pulse.  相似文献   

A computational approach for the analysis of changes in polygon distributions     

Yukio Sadahiro  Mitsuru Umemura 《Journal of Geographical Systems》2001,3(2):137-154

 This paper develops a computational method for analyzing changes in polygon distributions. Unmovable polygons that change discontinuously without explicit functional linkage information are discussed. Six types of primitive events are used to describe the change: 1) generation, 2) disappearance, 3) expansion, 4) shrinkage, 5) union, and 6) division. The change of polygon distributions is decomposed into a combination of these events. A computational procedure for deducing a set of events from polygon distributions of two times is proposed. The method is applied to the analysis of the spatial competition between the major and small chains of convenience stores in Tokyo, Japan. Some empirical findings are shown. Received: 3 August 2000 / Accepted: 6 February 2001  相似文献   

Three topologically nontrivial choreographic motions of three bodies     

Milovan Šuvakov  Mitsuru Shibayama 《Celestial Mechanics and Dynamical Astronomy》2016,124(2):155-162

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Neutron capture effects on samarium,europium, and gadolinium in Apollo 15 deep drill‐core samples     

Hiroshi HIDAKA  Mitsuru EBIHARA  Shigekazu YONEDA 《Meteoritics & planetary science》2000,35(3):581-589

Abstract— The isotopic compositions of Sm and Gd in seven lunar samples from the Apollo 15 deep drill core were determined to discuss the effects of neutron capture near the lunar surface. Large isotopic deviations of ¹⁵⁰Sm/¹⁴⁹Sm, ¹⁵⁶Gd/¹⁵⁵Gd, and ¹⁵⁸Gd/¹⁵⁷Gd derived from neutron capture effects were observed in all samples. Although neutron capture products in lunar samples were investigated extensively in the 1970s, our precise isotopic measurements resulted in several new findings. The neutron fluence in the Apollo 15 drill core is a function of depth with a symmetric peak at 190 g/cm² depth from the surface, confirming the results of earlier investigations. Neutron fluence values calculated from the isotopic shifts by comparison to artificially irradiated standard reagents were (5.16–7.49) × 10¹⁶ n/cm². These values are 1.3 to 1.4x larger than those previously reported. Variations of ε_Sm/ε_Gd with depth are interpreted as being due to variations in the neutron energy spectrum. Here ε_Sm and ε_Gd are defined as in previous studies of lunar neutron stratigraphy. Our data suggest that the neutron is more thermalized at the lower layers than it is at the upper layers. In addition to large isotopic shifts for ¹⁴⁹Sm, ¹⁵⁰Sm, ¹⁵⁵Gd, ¹⁵⁶Gd, ¹⁵⁷Gd, and ¹⁵⁸Gd, isotopic enrichments of ¹⁵²Gd and ¹⁵⁴Gd derived from neutron capture for ¹⁵¹Eu and ¹⁵³Eu, respectively, were also observed in all samples.  相似文献   

A method for non-parametric damage detection through the use of neural networks     

Mitsuru Nakamura  Sami F. Masri  Anastassios G. Chassiakos  Thomas K. Caughey 《地震工程与结构动力学》1998,27(9):997-1010

A neural network-based approach is presented for the detection of changes in the characteristics of structure-unknown systems. The approach relies on the use of vibration measurements from a ‘healthy’ system to train a neural network for identification purposes. Subsequently, the trained network is fed comparable vibration measurements from the same structure under different episodes of response in order to monitor the health of the structure. The methodology is applied to actual data obtained from ambient vibration measurements on a steel building structure that was damaged under strong seismic motion during the Hyogo-Ken Nanbu Earthquake of 17 January 1995. The measurements were done before and after repairs to the damaged frame were made. A neural network is trained with data after the repairs, which represents ‘healthy’ condition of the building. The trained network, which is subsequently fed data before the repairs, successfully identified the difference between the damaged storey and the undamaged storey. Through this study, it is shown that the proposed approach has the potential of being a practical tool for a damage detection methodology applied to smart civil structures. © 1998 John Wiley & Sons, Ltd.  相似文献   

Historical Auroras in the 990s: Evidence of Great Magnetic Storms     

Hisashi Hayakawa  Harufumi Tamazawa  Yurina Uchiyama  Yusuke Ebihara  Hiroko Miyahara  Shunsuke Kosaka  Kiyomi Iwahashi  Hiroaki Isobe 《Solar physics》2017,292(1):12

A significant carbon-14 enhancement has recently been found in tree rings for the year 994, suggesting an extremely strong and brief cosmic ray flux event. The origin of this particular cosmic ray event has not been confirmed, but one possibility is that it might be of solar origin. Contemporary historical records of low-latitude auroras can be used as supporting evidence of intense solar activity around that time. We investigate previously reported as well as new records that have been found in contemporary observations from the 990s to determine potential auroras. Records of potential red auroras in late 992 and early 993 were found around the world, i.e. in the Korean Peninsula, Saxonian cities in modern Germany, and the Island of Ireland, suggesting the occurrence of an intense geomagnetic storm driven by solar activity.  相似文献   

Petrogenesis of the EET 92023 achondrite and implications for early impact events          下载免费PDF全文

A. Yamaguchi  N. Shirai  C. Okamoto  M. Ebihara 《Meteoritics & planetary science》2017,52(4):709-721

We report petrology and geochemistry of an achondrite EET 92023 and compare it with normal and anomalous eucrites. EET 92023 is an unbrecciated achondrite and shows a granular texture mainly composed of low‐Ca pyroxene and plagioclase, petrologically similar to normal cumulate eucrites such as Moore County. However, this rock contains a significant amount of kamacite and taenite not common in unbrecciated, crystalline eucrites. EET 92023 contains a significant amount of platinum group elements (PGEs) (ca. 10% of CI), several orders of magnitude higher than those of monomict eucrites. We suggest that the metallic phases carrying PGEs were incorporated by a projectile during or before igneous crystallization and thermal metamorphism. The projectile was likely to be an iron meteorite rather than chondritic materials, as indicated by the lack of olivine and the presence of free silica. Therefore, the oxygen isotopic signature is indigenous, rather than due to contamination of the projectile material with different oxygen isotopic compositions. A significant thermal event involving partial melting and metamorphism after the impact event indicates that EET 92023 records early impact events which took place shortly after the crust formation on a differentiated protoplanet when the crust was still hot.  相似文献   

A Transit of Venus Possibly Misinterpreted as an Unaided-Eye Sunspot Observation in China on 9 December 1874     

Hayakawa  Hisashi  Sôma  Mitsuru  Tanikawa  Kiyotaka  Willis  David M.  Wild  Matthew N.  Macdonald  Lee T.  Imada  Shinsuke  Hattori  Kentaro  Richard Stephenson  F. 《Solar physics》2019,294(9):1-13

Solar Physics - Large sunspots can be observed with the unaided eye under suitable atmospheric seeing conditions. Such observations are of particular value because the frequency of their appearance...  相似文献   

Families of symmetric relative periodic orbits originating from the circular Euler solution in the isosceles three-body problem     

Mitsuru Shibayama  Kazuyuki Yagasaki 《Celestial Mechanics and Dynamical Astronomy》2011,110(1):53-70

We study symmetric relative periodic orbits in the isosceles three-body problem using theoretical and numerical approaches. We first prove that another family of symmetric relative periodic orbits is born from the circular Euler solution besides the elliptic Euler solutions. Previous studies also showed that there exist infinitely many families of symmetric relative periodic orbits which are born from heteroclinic connections between triple collisions as well as planar periodic orbits with binary collisions. We carry out numerical continuation analyses of symmetric relative periodic orbits, and observe abundant families of symmetric relative periodic orbits bifurcating from the two families born from the circular Euler solution. As the angular momentum tends to zero, many of the numerically observed families converge to heteroclinic connections between triple collisions or planar periodic orbits with binary collisions described in the previous results, while some of them converge to “previously unknown” periodic orbits in the planar problem.  相似文献   

Trace element and isotopic studies of Permo-Carboniferous carbonate nodules from Talchir sediments of peninsular India: Environmental and provenance implications     

Prosenjit Ghosh  S. K. Bhattacharya  A. M. Dayal  J. R. Trivedi  M. Ebihara  M. M. Sarin  A. Chakrabarti 《Journal of Earth System Science》2002,111(2):87-93

Syngenetic carbonate nodules constitute an interesting feature of the glaciogene sediments of various Talchir basins in peninsular India. Petrographic, cathodoluminescence and sedimentary results suggest that many of these nodules contain primary carbonate precipitates whose geochemical signatures can be used for determining environment of deposition and provenance of the sediments and drainage source. Several nodules were collected from Gondwana basins of east-central India and analyzed for stable carbon and oxygen isotope ratios, REE and trace element composition, and Sr isotope ratio. The mean δ¹⁸O and δ¹³C values of the calcites in the nodules are — 19.5% and-9.7% (w.r.t. PDB) respectively suggesting a freshwater environment (probably lacustrine) for formation of these objects. Trace element ratios (Eu/Eu * and La/Yb) of the nodule samples show that the source of the sediments in the Damodar valley basin was the granites, gneisses and intrusives in the Chotanagpur region. The sediments in the Mahanadi valley were derived from granulites, charnockites and granites of the eastern ghat region. The Sr concentration of the carbonate phase of the nodules is low, ranging from 10–60 ng/g. The⁸⁷Sr/⁸⁶Sr ratios of the samples from the west Bokaro basin and Ramgarh basin vary from 0.735 to 0.748 (mean: 0.739) and from 0.726 to 0.733 (mean: 0.730) respectively. These values are consistent with our proposition that water of these basins drained through the granitic rocks of the Chotanagpur region. In contrast, the⁸⁷Sr/⁸⁶Sr ratios of the samples from the Talchir basin (Type area) of Mahanadi valley vary from 0.718 to 0.723 (mean: 0.719). These⁸⁷Sr/⁸⁶Sr ratios are close to those of the granulites in the adjoining eastern ghat belt suggesting that area as the drainage source.  相似文献