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91.
Abyssal tholeiites from the Oceanographer Fracture Zone 总被引:17,自引:0,他引:17
David Walker Tsugio Shibata Stephen E. DeLong 《Contributions to Mineralogy and Petrology》1979,70(2):111-125
Unusual effects have been discovered in the major element phase relations of basalts from the Oceanographer Fracture Zone
(OFZ) which suggest that magma mixing of primitive basalt with the differentiation residue of a previous batch of primitive
magma has occurred. These effects include a reversal in mineral crystallization sequence which cannot happen during normal
differentiation processes or be explained by any plausible change in physical conditions. This unusual effect is encountered
as a result of curvature in composition space of the liquid-line-of-descent equilibria involving olivine, plagioclase, and
high-calcium clinopyroxene. Mixing of magmas at different stages of their evolution produces mixtures that do not lie on the
curved liquid-line-of-descent. Observation of such anomalous compositions in the OFZ suite supplements accumulating petrographic
and trace-element geochemistry evidence that magma mixing is an important petrogenetic process.
Mixing of fractionated residual liquids can produce mixtures which are either superheated or supercooled depending on the
sense of ‘thermal curvature’ of the liquid-line-of-descent. Both senses are encountered in the tholeiitic system, and this
effect may exert a qualitative control on the crystallization texture of the mixture.
A comparison of approximately 2,000 abyssal tholeiite compositions to the experimental liquid-line-of-descent reveals that
erupted differentiates which would be expected from advanced fractionation are scarce. Just this sort of phenomenon (the ‘perched’
steady state) was proposed by O'Hara (1977) as an earmark of the operation of a continuously fractionating magma chamber into
which fresh magma is periodically remixed. 相似文献
92.
Initial 87Sr/86Sr rations were determined for more than 80 plutonic rocks in Japan. The 87Sr/86Sr ratios of gabbroic and granitic rocks show no significant difference in plutonic terranes where both rocks occur closely associated, implying a genetic relationship between them (e.g., Green Tuff belt) or reequilibration at deep level (e.g., Ryoke belt). Wherever granitic rocks occur independently from gabbroic rocks, the granites have higher ratios than the gabbros.Initial 87Sr/86Sr ratios of the granitic rocks are low (<0.706) in Northeast Japan but high (<0.706) in Southwest Japan, the boundary being the Tanakura Tectonic Line. Within Southwest Japan, the ratios are low along the Japan Sea side of the southernmost area. This regional variation is generally correlated with thickness of the continental crust as deduced from the Bouguer anomaly.Initial 87Sr/86Sr ratios of the granitic rocks vary from 0.7037 to 0.7124. The low group (<0.706) is considered to consist of essentially mantle-derived magmas contaminated by crustal material in lesser but varying degree, because of its geological setting and initial 87Sr/86Sr values. The high group may have been formed by contamination of a deep-seated magmas by crustal material or by generation of the main part of the magmas within the continental crust. The ratios of individual belts reflect their own history depending upon age and Rb/Sr ratio of the crustal material.Initial 87Sr/86Sr ratios of granitic rocks are generally low for the magnetite-series but high for the ilmenite-series. Thus, a negative correlation is observed between initial ratios and 34S for most Cretaceous-Paleogene granites. However, Neogene ilmenite-series granites are low in both initial 87Sr/86Sr and 34S indicating interaction of the granitic magma with young sedimentary rocks enriched in 32S. 相似文献
93.
David Walker Stephen E. DeLong Tsugio Shibata 《Contributions to Mineralogy and Petrology》1980,74(1):1-6
Pillow basalt fragments from the Oceanographer Fracture Zone contain spherical microstructures seen in section as rings of equant microphenocrysts of olivine±plagioclase±augite. They are uniformly 1 mm in diameter and have the same vitreous or crystalline material on the inside and outside. These structures occur in the same sections as vesicles and segregation vesicles and are clearly distinguishable from them.The occurrence of these structures in pillow basalt fragments suggests a mode of formation resulting from pillow basalt extrusion. Mechanical disruption of the partially solidified inner surface of the pillow skin produces a dispersion of cool globules in the pillow interior. Crystals adhere to these tacky globules during continued pillow extrusion in a manner analogous to the formation of armored mud balls. 相似文献
94.
95.
We study the structure of a stationary and axisymmetric charge-deficient region (or a potential gap) in the outer magnetosphere of a spinning neutron star. A large electric field along the magnetic field lines is created in this potential gap and accelerates migratory electrons (e− ) and/or positrons (e+ ) to ultrarelativistic energies. Assuming that the gap is immersed in a dense soft photon field, these relativistic e± radiate γ -ray photons via inverse Compton (IC) scattering. These γ -rays, in turn, produce yet more radiating particles by colliding with ambient soft photons, leading to a pair-production cascade in the gap. The replenished charges partially screen the longitudinal electric field, which is self-consistently solved together with the distribution of e± and γ -ray photons. It is demonstrated that the voltage drop in the gap is not more than 1010 V when the background X-ray radiation is as luminous as 1037 erg s−1 . However, this value increases with decreasing X-ray luminosity and attains 1012 V when the X-ray radiation is 1036 erg s−1 . In addition, we find useful expressions of the spatial distribution of the particle fluxes and longitudinal electric field, together with the relationship between the voltage drop and the current density. Amazingly, these expressions are valid not only when IC scattering dominates but also when curvature radiation dominates. 相似文献
96.
Kohtaro Hosoda Hiroshi Murakami Akira Shibata Futoki Sakaida Hiroshi Kawamura 《Journal of Oceanography》2006,62(3):291-291
ADEOS-II Ocean: Advanced Earth Observing Satellite-II Ocean
Preface 相似文献97.
FOLEGA Fousseni ATAKPAMA Wouyo WALA Kperkouma MUKETE Beckline SHOZO Shibata AKIRA Osawa ZHAO Xiu-hai AKPAGANA Koffi 《山地科学学报》2019,(8)
The application of remote sensing in understanding tree species structural diversity and land use patterns relationship is imperative for reforestation and biodiversity conservation efforts. This study assesses land use patterns and tree species structural diversity in previously reforested hilly sandstone regions of northern Togo. The physical height, and diameter at breast height(DBH) more than 5 cm of all tree species in each given plot were measured in summer 2017. A total of 75 plots of 900 m~2 installed along the toposequence were recorded. In addition, a semi-supervised classification of Landsat 8 images in January of 2018, was also used to classify the land use patterns. 36 tree species and 19 families were recorded for the entire study area. Meanwhile, 19 tree species and 15 families were recorded for the previously afforested zones. The most abundant species included the Sterculiaceae, Zygophyllaceae, Meliaceae, and Mimosaceae. The trees stand structure represented 8.61 ± 0.57 m, 11.28 ± 1.76 cm, and 0.018 ± 0.009 m~2 per hectare for height, diameter and basal area respectively. Major land use patterns were tree and shrub savannahs, parklands and croplands which represented over 60% of the landscape. It is necessary to examine the regeneration and vegetative multiplication potentials of the most frequent and abundant tree species for any eventual future afforestation programs in these hilly sandstone regions of northern Togo. 相似文献
98.
Abstract: A total of 189 runs were completed to determine the rate of dissolved oxygen consumption in water by the reaction humic acid at 25°, 45°, and 65°C. Glass vial bottles were used as reaction vessels, and humic aicd and pure water of different intitial O2 concentration was loaded with humic acid/water weight of 0.008 and 0.009. Vials were opened periodically to measure O2 concentrations. The pH of the solution fluctuated in the early stages of the experiments and gradually decreased to a constant value. Dissolved oxygen concentration decreased, for example, from initial value of 12 mg/l to 9 mg/l at 25°C, to 5 mg/l at 45°C, and to 2 mg/l at 65°C after the reaction of 500 hours. Analyses of rates suggest that the reaction is first order, and rate constants are 8.42 × 10-9 at 25°C, 2.22 × 10-8 at 45°C, and 1.28 × 10-7 moles m-2 s-1 at 65°C. 相似文献
99.
Takashi Nakajima Teruo Shirahase Ken Shibata 《Contributions to Mineralogy and Petrology》1990,104(4):381-389
Cretaceous granitic rocks were emplaced over a distance of 700 km along arc in Southwest Japan. Rb–Sr and K–Ar ages of a major group of these granitic rocks, with ilmenite series ore mineralogy, were examined. Rb–Sr whole rock ages of 92.8±4.0 Ma and Rb–Sr and K–Ar biotite ages of 80–88 Ma were obtained on one group of these granitic rocks from Kamo-Sera area of central Hiroshima Prefecture. The K–Ar ages of various minerals, combined with the Rb–Sr whole-rock age, give a smooth cooling curve, which suggests a 5 to 10 Ma time-lag between intrusion and cooling at 300° C for the Cretaceous granitic rocks. The Rb–Sr whole-rock and Rb–Sr/K–Ar biotite ages of these granitic rocks become younger eastward along the Southwest Japan arc, and the time-lag between the two systems remains constant at 5 to 10 Ma over the entire area. The along-arc age variation does not support the genetical relationship of the Cretaceous granitoids with steady-state subduction. The Cretaceous granitic province at the eastern margin of Eurasian continent was, at least partly, formed by an episodic event such as ridge subduction. 相似文献
100.