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21.
The detailed mapping of the blocks of the Pekul’ney complex revealed that cumulate ultramafics occur as separate tabular bodies among metamorphic rocks and are only fragmentarily observed in some of the blocks. Within these bodies, different types of ultramafics are regularly and multiply intercalated, forming banded structures, which supports their assignment to a single cumulate series. The tabular ultramafic bodies investigated in different blocks of the Pekul’ney complex are from 350 to 1100 m thick, and their internal structure is made up of intercalated regular rhythms of dunites-peridotites and olivine pyroxenites-olivine-free ultramafics (garnet, ceylonite, and clinozoisite clinopyroxenites, websterites, and hornblendites) and units of irregularly interlayered dunites, peridotites, and olivine pyroxenites. The thickness of individual regular rhythms ranges from 50 to 410 m. The cumulate ultramafics of the Pekul’ney complex were derived from a water-rich highly magnesian primary melt, which was equilibrated with mantle harzburgites, within a wide temperature range at pressures of 11–13 kbar in the geodynamic setting of the base of an ensialic arc. The Pekul’ney complex can be considered as a reference object for the petrological and geochemical investigation of the evolution of suprasubduction mantle melts during their high-pressure fractionation. 相似文献
22.
Shin-ichi Takehiro Masaki Ishiwatari Kensuke Nakajima Yoshi-Yuki Hayashi 《地球物理与天体物理流体动力学》2013,107(6):439-459
Linear stability of rotating thermal convection in a horizontal layer of Boussinesq fluid under the fixed heat flux boundary condition is examined by the use of a vertically truncated system up to wavenumber one. When the rotation axis is in the vertical direction, the asymptotic behavior of the critical convection for large rotation rates is almost the same as that under the fixed temperature boundary condition. However, when the rotation axis is horizontal and the lateral boundaries are inclined, the mode with zero horizontal wavenumber remains as the critical mode regardless of the rotation rate. The neutral curve has another local minimum at a nonzero horizontal wavenumber, whose asymptotic behavior coincides with the critical mode under the fixed temperature condition. The difference of the critical horizontal wavenumber between those two geometries is qualitatively understood by the difference of wave characteristics; inertial waves and Rossby waves, respectively. 相似文献
23.
Young kerogens isolated from seven freshwater lakes, six river mouths and four marine surface sediments were subjected to pyrolysis in vacuo. Their pyrolysates were trapped and separated subsequently for determination of hydrocarbons, fatty acids and alcohols. The abundances, carbon number distributions of long (C12) polymethylene chain lipid compounds and relative abundances of pristenes are proposed as possible indices applicable to discrimination between young kerogens from freshwater lacustrine and marine sediments. Some oil-shale kerogens of Eocene and Permian age were pyrolyzed in the same way, where the chain-length distributions of the pyrolysis products showed similar trends as those observed for the pyrolysis of young kerogens. 相似文献
24.
Igneous Petrogenesis of the Yakuno Ophiolite (Japan) in the context of the diversity of ophiolites 总被引:10,自引:0,他引:10
A. Ishiwatari 《Contributions to Mineralogy and Petrology》1985,89(2-3):155-167
An ophiolite complex includes three major members: basaltic volcanics, mafic-ultramafic cumulates, and residual peridotite. From the aspect of igneous petrology, three distinct types are recognized among the associations of the three members: (Liguria type) alkalic basalt, plagioclase-type cumulates, and lherzolite; (Yakuno type) high-alumina tholeiite, clinopyroxene-type cumulates, and clinopyroxene-bearing harzburgite; (Papua type) low-alumina tholeiite, orthopyroxene-type cumulates, and clinopyroxene-free harzburgite. In the light of recent experimental studies, the three types represent cogenetic, complementary products of low (<15%), moderate, and high (>30%) degrees of partial melting in the lherzolitic source mantle, respectively. The cumulates of the Yakuno ophiolite show structural and chemical continuity to the underlying residual peridotite, and were recrystallized at high pressures (5–10 kb). They originated in a deep, soft-floored magma chamber directly overlying the partially melted residual harzburgite, from which the magma was extracted. The three members of the Yakuno ophiolite were cogenetically formed through a magmatic event induced by a moderate degree of partial melting in the mantle. 相似文献
25.
Ryoshi Ishiwatari Shigeo Morinaga Bernd R.T. Simoneit 《Geochimica et cosmochimica acta》1985,49(8):1825-1835
Potassium permanganate oxidative degradations were conducted for kerogens isolated from Cretaceous black shales (DSDP Leg 41, Site 368), thermally altered during the Miocene by diabase intrusions and from unaltered samples heated under laboratory conditions (250–500°C).Degradation products of less altered kerogens are dominated by normal C4–C15 α,ω-dicarboxylic acids, with lesser amounts of n-C16 and n-C18 monocarboxylic acids, and benzene mono-to-tetracarboxylic acids. On the other hand, thermally altered kerogens show benzene di-to-tetracarboxylic acids as dominant degradation products, with lesser or no amounts (variable depending on the degree of thermal alteration) of α,ω-dicarboxylic acids. Essentially no differences between the oxidative degradation products of naturally- and artificially-altered kerogens are observed.As a result of this study, five indices of aromatization (total aromatic acids/kerogen; apparent aromaticity; benzenetetracarboxylic acids/total aromatic acids; benzene-1,2-dicarboxylic acid/benzenedicarboxylic acids; benzene-1,2,3-tricarboxylic acid/benzenetricarboxylic acids) and two indices of aliphatic character (Total aliphatic acids/kerogen; Aliphaticity) are proposed to characterize the degree of thermal alteration of kerogens.Furthermore, a good correlation is observed between apparent aromaticity estimated by the present KMnO4 oxidation method and that from the 13C NMR method (DENNIS et al., 1982). 相似文献
26.
A laboratory heating experiment was conducted in an attempt to evaluate the possible role of lipids as precursors for petroleum hydrocarbons. Lipids were extracted from a Recent lake sediment (Lake Haruna, Japan), and heated under N2 atmosphere, at 125–370°C, for 1–7 days. A significant amount of lipids was polymerized to kerogen-like matter (lipid-derived kerogen) at the low temperature of 175°C for 1 day. The polymerization follows first-order kinetics, and the half life of lipids is calculated to be 104–105 yr at 0–30°C. The lipid-derived kerogen generated a significant amount (62 mg/g) of n-alkanes (C14–C36) on heating at 350°C for 1 day.The results indicate a possible occurrence of lower temperature thermal polymerization of lipids in a relatively early stage of diagenesis as one of the formation pathways of kerogen with high hydrocarbon producing potential. 相似文献
27.
Alkaline potassium permanganate oxidation of a young kerogen (lacustrine) and 34 model compounds (saturated and unsaturated fatty acids, hydroxy acid, aliphatic dicarboxylic acids, aliphatic alcohols, normal hydrocarbon, β-carotene, phenolic acids, benzenecarboxylic acids, carbohydrates, amino acids and proteins) were conducted, followed by GC and GC-MS analysis of the degradation products. The stability of the degradation products of kerogen in permanganate solution and the relationship between degradation products and kerogen building blocks were determined.The results showed that aliphatic acids C12–C16 monocarboxylic acids and C6–C10 α,ω-dicarboxylic acids) were rather susceptible to oxidation compared with benzenecarboxylic acids and the former were degraded into lower molecular weight decarboxylic acids. It was concluded that oxidation at milder conditions (60° C, 1 hr) is appropriate for qualitative and quantitative characterization of the aliphatic structure of young kerogen. It was noteworthy that benzoic acid was produced in a significant amount by oxidation of amino acids (phenylalanine) and proteins, C18-isoprenoidal ketone from phytol, and C8 and C9 α,ω-dicarboxylic acids from unsaturated fatty acids, respectively; furthermore, 2,2-dimethyl succinic and 2,2-dimethyl glutaric acids were produced from β-carotene. 相似文献
28.
G. V. Ledneva B. A. Bazylev V. V. Lebedev N. N. Kononkova A. Ishiwatari 《Geochemistry International》2012,50(1):44-53
The Ust’-Belaya mafic-ultramafic massif is assigned to the Western Koryak fold belt and largely composed of residual spinel
peridotites, layered spinel and plagioclase peridotites, and gabbros. These rocks are crosscut by occasional plagiogranite
and diorite veins and exhibit locally a close spatial association with basalts and carbonate-sedimentary deposits of Late
Devonian and Early Carboniferous age. Based on this evidence, the massif was ascribed to the pre-Late Devonian ophiolite association.
Our study presents new U-Pb SHPIMP II zircon ages and petrographic and mineralogical data on samples of the layered amphibole
gabbro and vein diorite from the Ust’-Belaya massif. The approximate concordant U-Pb age corresponding to a timing of of amphibole
gabbro crystallization is 799 ± 15 Ma, and the concordant U-Pb age reflecting a timing of of vein diorite crystallization
is 575 ± 10 Ma. These ages coupled with geological studies of the massif, petrological and mineralogical investigations of
the dated samples, as well as literature data on the petrology of peridotites and the age of formed plagiogranites suggest
that the peridotites and layered gabbros of the Ust’-Belaya massif were formed by the Late Riphean, whereas the vein diorite
and plagiogranite were resulted from a later (Vendian-Cambrian) magmatic stage. The peridotites and gabbros of the massif
display no genetic relationship with spatially associated basalts and sedimentary rocks and, thus, they cannot be considered
as members the pre-Late Devonian ophiolitic association. The results of this study will inevitably lead to a significant revision
of geological and geodynamic interpretations of the Ust’-Belaya mafic-ultramafic massif. However, uneven study of the Precambrian
complexes of the Koryak and Chukchi areas, their evolution in different structures of the region cannot yet be described by
a single geodynamic scenario. 相似文献
29.
Tightly bound geolipids were separated from a 200 m sediment core of Lake Biwa by a second saponification of sediments from which unbound and bound lipids had been extracted. Tightly bound fatty acids, β-hydroxy acids, ω-hydroxy acids and α,ω-dicarboxylic acids were released; their concentrations ranged from 4.7–31.5, 5.6–60.5, 3.4–9.5 and 0.2–5.4 μg/g dry sediment, respectively. These geolipids were considered to be incorporated in humic substances.Tightly bound fatty acids showed a unimodal distriution with a peak at C16, suggesting that they originate from algae and bacteria and that they are more stable than unbound and bound fatty acids in the sediments. Most of the total β-hydroxy acids, which probably originate from bacteria, were found in the tightly bound fraction. This suggests that a large portion of tightly bound geolipids are formed in the water column and in surface sediments as a result of microbial alteration dead algae. Each class of tightly bound lipids showed higher concentrations between depths of 3 and 15 m in the sediments, where primary production was thought to be enhanced in the past. 相似文献
30.
We discuss the chemical compositions of rhyolites from three distinct tectonic settings: (i) the continental rift from Ethiopia (both Oligocene–Miocene and Quaternary rhyolites); (ii) the early Miocene continental arc of Japan (the Mt Wasso rhyolites related to the rifting of the Japan Sea); and (iii) the oceanic Izu–Bonin Island Arc. The comparison reveals that the oceanic island arc rhyolites have high contents of CaO, Al2O3, and Sr, and extremely low abundance of trace elements including K2O. In contrast, the Ethiopian continental rift rhyolites are characterized by low contents of CaO, Al2O3, and Sr, and high contents of K2O, and are enriched in the whole range of trace elements. The continental arc Mt Wasso rhyolites are apparently low in Nb content, although they display similar chemical trends to those of the Ethiopian rhyolites. This obvious difference in the chemical signatures of the rhyolites from the three tectonic settings is the consequence of their derivation from different sources. The implication of this result is that fractional crystallization processes were dominant in the rift‐related rhyolites both from continental rift and continental arc regardless of the prevailing tectonic setting and the nature of the crust (age, thickness, composition), whereas the oceanic island arc rhyolites may form through partial melting of young, mafic crust. 相似文献