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1.
TAKESHI NAKAGAWA ELISABETTA BRUGIAPAGLIA GUNNAR DIGERFELDT MAURICE REILLE JACQUES-LOUIS DE BEAULIEU YOSHINORI YASUDA 《Boreas: An International Journal of Quaternary Research》1998,27(1):15-24
Dense-media separation, frequently adopted as a standard pollen extraction method for use with minerogenic sediment samples, was adapted for use with organic-rich sediment and peat samples. A total of 15 organic-rich sediment samples, obtained from sites in Corsica and the Southern European Alps, was treated using both dense-media separation and the conventional preparation method in order to compare the relative efficiencies of the two methods. The dense-media separation method consistently achieved a remarkably higher purity of extracted pollen grains. This was especially true for the Corsican peat samples, the dense-media separations being quite pure, whereas the classical method produced samples that were so severely polluted with organic fragments that it was impossible to carry out a satisfactory pollen analysis. The percentage values of each taxon were generally similar using both methods, showing that the two methods are compatible for pollen analytical studies. Total pollen concentrations were generally higher with the dense-media separation method (especially for gyttja samples). In conclusion, dense-media separation is an efficient method for pollen extraction from organic as well as from minerogenic sediments and deposits. 相似文献
2.
This paper presents an experimental study on the local bed morphology and grain size characteristics around an impermeable spur dyke.A series of experiments are conducted with different types of sedime... 相似文献
3.
Masaharu NAKAGAWA 《地球学报》2012,33(S1):50-54
Bedded manganese ore deposits occur in many localities within the accretionary belts of the Shikoku region, SW Japan. The deposits occur mostly in bedded chert or its metamorphosed equivalent. These chert-hosted manganese deposits are considered to have been manganese nodule/crust-bearing siliceous sediments on deep-sea floor and have been converted to manganese ores by low-grade metamorphism through subduction-accretion process. The mineral assemblages of the ores reflect the metamorphic grade of the accretionary complexes. On the other hand, iron-manganese deposits and some manganese deposits occurring directly over basalt are considered to have been the hydrothermal precipitates associated with submarine volcanism. 相似文献
4.
Miyake-jima volcano has erupted at least 13 times during theperiod 1469–1983. To understand the historic magmaticprocesses, we focus on the mineral assemblage and chemical compositionsof crystal-clots in single samples from each of the eruptions.Most of the historic lavas consist of nearly aphyric to weaklyporphyritic basalt to andesite, but there also exist megacryst-bearingrocks. The megacrysts are considered to be xenocrysts from adeep-seated plutonic body. Many samples of each eruption containtwo types of clots beside megacrysts, termed here B-type andA-type. The B-type clots are composed of olivine, clinopyroxeneand plagioclase, whereas the A-type clots additionally containmagnetite and orthopyroxene. Compositional relationships betweenthese mafic minerals suggest that the minerals in the same typeof clots are in equilibrium. Comparing the chemical compositionsof the minerals in the two types of clots in each sample, theyare derived from distinct magmas: the B-type clots from basalticmagma and the A-type clots from andesitic magma. During thehistoric activity, the magma plumbing system appears to haveincluded two magma storage systems: a deep-seated basaltic anda shallower andesitic one. In many cases, basaltic magma hasinjected into shallower andesitic magma to form mixed magma;however, andesitic magma has sometimes erupted alone withoutextensive injections of basaltic magma. Temporal variationsof mineral compositions in the clots and estimated whole-rockcompositions of the end-member magmas suggest that the basalticmagma has differentiated gradually since 1469, and that itsmagmatic temperature has fallen from 1220 to 1180°C. Conversely,the andesitic magma has changed in a complex fashion to becomemore mafic (the magmatic temperature rose from 1050 to 1100°C).As a result of this study, it is estimated that the basalticmagma after the 1983 eruption was the least mafic, and the andesiticmagma the most mafic, of the historic eruptions. KEY WORDS: andesite; basalt; crystal-clots; evolution of magma; Miyake-jima volcano; magma mixing 相似文献
5.
Juvenile ejecta from the September and October 1995 eruptionsof Ruapehu volcano, New Zealand, indicate that mixing occurredbetween relatively higher- and lower-temperature (high-T andlow-T) andesitic magmas. Compositional zonations in clinopyroxenephenocrysts provide direct evidence for a pre-eruption crystal–meltmush chamber containing low-T magma, and elucidate the processesof magma mixing and eruption, following the injection of high-Tmagma. Many phenocrysts with Fe-rich cores derived from low-Tmagma have extremely reverse zoned mantles around slightly resorbedcores. Mg-value [100Mg/(Mg + Fe)] increases from 65–70to 相似文献
6.
Abstract: Southwest Hokkaido is largely covered by Late Miocene to Quaternary igneous rocks, and has a large number of gold veins and base-metal veins of the same age. Investigation of the silica-normalized concentration of elements has revealed regional petrochemical zoning; large ion lithophile elements (LILE) and K2O/(Na2O+K2O) of the rocks increase toward Japan Sea, whereas total FeO, CaO, and 87Sr/86Sr decrease. Mapped concentration isoplethes of these elements are not ideally parallel to the volcanic front, but protrude to the west at Funka Bay, and to the northwest at Matsumae Peninsula. Isoplethes of 87Sr/86Sr show similar patterns and two more northwestward protrusions in the northeast (Jozankei block) of southwest Hokkaido. Contrary to the general petrochemical trend, both high– and low-LILE volcanic rocks occur in the Jozankei block. The ore deposits are distributed in four metallogenic zones; manganese–base–metal zone on the Japan Sea side, pyrite-limonite zone mainly along the volcanic front, gold zone in the middle, and two units of gold–base–metal zone. The northern unit of this zone is in the Jozankei block, and seems a part of the gold zone overlapped by the manganese–base–metal zone. Thus, as a rule, pyrite–limonite, gold, and base-metal deposits accompany low–, intermediate–, and high-LILE igneous rocks, respectively. Individual deposits and volcanic rocks make chains oblique to the zones and the volcanic front. The majority of the ore deposits are distributed along ridges of Bouguer anomalies overlapped by the volcanic chains, which apparently control the patterns of the petrochemical isoplethes. This is typical for two volcanic chains to the north and south of Funka Bay, where the petrochemical isoplethes protrude to the west. This indicates that both the igneous activity and the mineralization have been under the control of tectonic fractures at the roots of the volcanic chains. The geological, petrochemical and metallogenic data support the idea that the chemical characteristics of the deposits are correlated mainly with the chemistry of the associated magmas, and partly with that of the host rocks. 相似文献
7.
This paper provides some additional evidence supporting the necessary (but insufficient) condition for the formation of stream meandering proposed by Nakagawa: where Me is a non-dimensional parameter, τs, and τb are the average bank and bed shear stress respectively, ps and pb are the average bank and bed wetted perimeter of a half-channel respectively, and K?0.2 is the critical value of the parameter estimated from experimental data. Provided the criterion is satisfied, the main thread of the stream meanders in the non-erodible channel, and the maximum amplitude amax, the angle a between the channel central axis and oblique crest line of the surface wave, and the mean wavelength L of the main thread decrease as the non-dimensional parameter Me increases. 相似文献
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9.
C. KOIKE H. CHIHARA K. KOIKE M. NAKAGAWA M. OKADA A. TSUCHIYAMA M. AOKI T. AWATA K. ATOBE 《Meteoritics & planetary science》2002,37(11):1591-1598
Abstract— We investigated thermoluminescence of silicates that are of interest in the interstellar and circumstellar medium after irradiation by γ‐rays and fast neutrons. The silicates are forsterite, orthoenstatite, olivine, quartz, and crystalline silicon. The irradiated enstatite shows weak and broad peaks at 545 and 760 nm. In contrast, irradiated bulk and powder samples of forsterite show strong and broad peaks at 640–660 nm. Although thermoluminescence of bulk forsterite is very similar to the extended red emission (ERE) of the Red Rectangle nebula, irradiated powdered forsterite did not reveal any sharp emission features over the broad band. Further, we investigated the possibility of thermoluminescence of crystalline silicon and found that luminescence scarcely appears. It is emphasized that the prominent carrier of ERE is forsterite and fused quartz. 相似文献
10.
TAKEO NAKAGAWA 《Sedimentology》1983,30(1):117-127
ABSTRACT An account of stream meandering and river morphology is given for five experiments, each having different conditions at the wetted perimeter of the channel.
On the basis of the present experiments, it is proposed that a necessary (but insufficient) condition for the formation of stream meandering is an appropriately small ratio of total bank shear force to total bed shear force, both per unit length downstream . In mathematical form, the criterion is expressed by τs and τs are an average bank stress and bed stress, respectively, and p s and p b b are an average bank wetted perimeter and bed wetted perimeter of a half-channel, respectively. The value of α is evaluated by Kinoshita's (1957) experiment and others.
It is also found that the flow pattern, channel morphology and sand waves on the bed are dependent upon the boundary conditions at the wetted perimeter. 相似文献
On the basis of the present experiments, it is proposed that a necessary (but insufficient) condition for the formation of stream meandering is an appropriately small ratio of total bank shear force to total bed shear force, both per unit length downstream . In mathematical form, the criterion is expressed by τ
It is also found that the flow pattern, channel morphology and sand waves on the bed are dependent upon the boundary conditions at the wetted perimeter. 相似文献