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91.
Takeshi Kuritani Takeyoshi Yoshida Jun-Ichi Kimura Yuka Hirahara Toshiro Takahashi 《Mineralogy and Petrology》2014,108(1):1-11
The water content of low-K tholeiitic basalt magma from Iwate volcano, which is located on the volcanic front of the NE Japan arc, was estimated using multi-component thermodynamic models. The Iwate lavas are moderately porphyritic, consisting of ~8 vol.% olivine and ~20 vol.% plagioclase phenocrysts. The olivine and plagioclase phenocrysts show significant compositional variations, and the Mg# of olivine phenocrysts (Mg#78–85) correlates positively with the An content of coexisting plagioclase phenocrysts (An85–92). The olivine phenocrysts with Mg# > ~82 do not form crystal aggregates with plagioclase phenocrysts. It is inferred from these observations that the phenocrysts with variable compositions were primarily derived from mushy boundary layers along the walls of a magma chamber. By using thermodynamic calculations with the observed petrological features of the lavas, the water content of the Iwate magma was estimated to be 4–5 wt.%. The high water content of the magma supports the recent consensus that frontal-arc magmas are remarkably hydrous. Using the estimated water content of the Iwate magma, the water content and temperature of the source mantle were estimated. Given that the Iwate magma was derived from a primary magma solely by olivine fractionation, the water content and temperature were estimated to be ~0.7 wt.% and ~1,310 °C, respectively. Differentiation mechanisms of low-K frontal-arc basalt magmas were also examined by application of a thermodynamics-based mass balance model to the Iwate magma. It is suggested that magmatic differentiation proceeds primarily through fractionation of crystals from the main molten part of a magma chamber when it is located at <~200 MPa, whereas magma evolves through a convective melt exchange between the main magma and mushy boundary layers when the magma body is located at >~200 MPa. 相似文献
92.
Yu. A. Martynov A. I. Khanchuk J. -I. Kimura A. V. Rybin A. Yu. Martynov 《Petrology》2010,18(5):489-513
Newly obtained precise analytical data on trace elements and radiogenic Sr, Nd, and Pb isotopes testify to anomalous geochemical
characteristics of mafic and intermediate Quaternary lavas in Paramushir (in the north of the Kuril arc), Kunashir and Iturup
(in the south) islands, which are the largest three islands of the Kuril island arc. The high K and LREE concentrations in
the volcanic products in Paramushir Island resulted from the southward expansion of the mantle thermal anomaly of the Kamchatka
Peninsula and the involvement of melts related to the melting of oceanic sediments in magma generation. The depleted characteristics
of the mafic volcanics are explained by the relatively young tectono-magmatic events during the opening of the Kuril backarc
basin. The Kuril island-arc system developed on a heterogeneous basement. The northern islands are a continuation of the volcanic
structures of southern Kamchatka, which were formed above an isotopically depleted and hot lithospheric mantle domain of composition
close to that of the Pacific MORB type. The southern islands were produced above an isotopically enriched and cold lithospheric
domain of the Indian-Ocean MORB type, which was modified in relation to relatively young backarc tectono-magmatic processes.
Although issues related to the genesis of the transverse geochemical zoning were beyond the originally formulated scope of
our research, the homogeneous enough isotopic composition of the rear-arc lavas in the absence of any mineralogical and geochemical
lines of evidence of crustal contamination suggests an independent magmatic source. 相似文献
93.
Binyam W. Woldemichael Jun-Ichi Kimura Daniel J. Dunkley Kenichiro Tani Hiroto Ohira 《International Journal of Earth Sciences》2010,99(8):1773-1790
The reworked Pre-Neoproterozoic and juvenile Neoproterozoic terrane of the Western Ethiopian Shield (WES) consists of three
N–S trending terranes. These are the western migmatitic gneissic terrane, the central metavolcano sedimentary terrane (CVST)
and the eastern migmatitic gneissic terrane. The eastern part of the CVST mostly consists of suture-related ultramafic-metasedimentary
complexes, whereas metavolcanics predominate in the western part. Gabbroic to granitic intrusions frequently occur in the
CVST and in adjacent areas. New zircon SHRIMP U–Pb ages for two gabbros and three diorites in the Ghimbi-Nedjo region of the
WES indicate magmatic crystallization ages. Two pulses of magmatism, at 860–850 and 795–785 Ma, are documented with the former
for the first time. The tholeiitic Kemashi diorite and Bikilal-Ghimbi gabbros have oceanic affinities and yield U/Pb zircon
ages of 856.3 ± 9.8 and 846.0 ± 7.6 Ma, respectively. The calc-alkaline Gebeya Kemisa pyroxene diorite, and the Senbet Dura
hornblende diorite plus the tholeiitic Wayu Meni gabbro, which collectively have arc-back arc characteristics are indistinguishable
at ages of 794.3 ± 9.4, 787.7 ± 8.8 and 778.1 ± 6.3 Ma, respectively. Positive εNd (4.5–7.0) and low initial 87Sr/86Sr (0.7029 ± 0.0002) and a mean T
DM model age of 0.95 Ga for the Ghimbi-Nedjo region (mean T
DM model age of 0.95 Ga for the WES overall) indicate that the magmas were generated from juvenile Neoproterozoic depleted mantle
sources, with no discernable involvement of pre-Neoproterozoic continental crust. The occurrence of gabbros and diorites with
oceanic tholeiite affinities combined with the new ages suggests that the intrusions were emplaced in the earliest stages
of the rifting of Rodinia. This event in the WES led to the development of a passive margin and associated plume-type magmatism
at ~855 Ma. The two intrusive groups with differing magma chemistry and ages suggest that the earliest magmatism was tholeiitic
and associated with the passive margin system followed by continental breakup to form the Mozambique Ocean. The combination
of tholeiitic and calc-alkaline magmatism was related to arc and back-arc basin formation and later terrane accretion (~830–690 Ma). 相似文献
94.
95.
T. Noguchi M. Kimura T. Hashimoto M. Konno T. Nakamura M. E. Zolensky A. Tsuchiyama T. Matsumoto J. Matsuno R. Okazaki M. Uesugi Y. Karouji T. Yada Y. Ishibashi K. Shirai M. Abe T. Okada 《Meteoritics & planetary science》2014,49(7):1305-1314
We observed cross sectional ultra‐thin sections near the surface of 12 particles recovered from the S‐type asteroid Itokawa by the Hayabusa spacecraft in 2010, using spherical aberration–corrected STEM and conventional TEM. Although their mineralogy is almost identical to the equilibrated LL chondrites and therefore basically anhydrous, micrometer‐to‐submicrometer‐sized sylvite was identified on the surface of Itokawa particle RA‐QD02‐0034. Separately, micrometer‐sized halite was also identified on the surface of Itokawa particle RA‐QD02‐0129. Detailed inspection of the sample processing procedures at the JAXA's Planetary Materials Sample Curation Facility and textural observation of the sylvite and halite indicate that they were clearly present on two Itokawa particles before they were removed from Clean Chamber #2 at JAXA. However, there is no direct evidence for their extraterrestrial origin at present. If the sylvite and halite are extraterrestrial, their presence suggests that they may be more abundant on the surface of S‐type asteroids than previously thought. 相似文献
96.
Tomoyuki Sato Keisuke Taniguchi Tomohiro Takagawa Fujio Masuda 《Geo-Marine Letters》2011,31(2):101-108
Flume experiments aimed to produce flaser bedding were conducted using fine sand and clay in a circular flume. The formation
process of mud drapes during the slack-water stage was revealed in detail. When the tidal current declines, a uniform mobile
mud layer initially settles from suspension and drapes the entire rippled sand bed (type A mud). When the remaining flow velocity
is very low, a more fluid mud begins to settle out (type B mud) that preferentially fills the ripple troughs, the ripples
and mud together forming a flat surface. At slack tide, the two-phase mud drape is temporarily stationary. After the onset
of the reversed flow phase, most of the type B mud is resuspended, while the type A mud is eroded from the crests, leaving
behind a remnant mud drape (flaser) in the troughs that is subsequently buried by migrating ripples. Type B mud generally
contains variable amounts of sand derived from eroded ripple crests, but does not show any visible internal sedimentary structures.
Type A mud represents the ‘mud drapes’ commonly described in the literature, the temporary existence of type B mud having
gone unnoticed because of its low preservation potential. When present, it can be recognized by its sand content and the occurrence
of flame structures in ripple troughs. Tidal deposits reflecting the existence and depositional characteristics of both type
A and type B mud are found in, for example, the macrotidal Oligocene Ashiya Group, Japan. 相似文献
97.
Ingrid Mann Melanie Köhler Hiroshi Kimura Andrzej Cechowski Tetsunori Minato 《Astronomy and Astrophysics Review》2006,13(3):159-228
Among the observed circumstellar dust envelopes a certain population, planetary debris disks, is ascribed to systems with
optically thin dust disks and low gas content. These systems contain planetesimals and possibly planets and are believed to
be systems that are most similar to our solar system in an early evolutionary stage. Planetary debris disks have been identified
in large numbers by a brightness excess in the near-infrared, mid-infrared and/or submillimetre range of their stellar spectral
energy distributions. In some cases, spatially resolved observations are possible and reveal complex spatial structures. Acting
forces and physical processes are similar to those in the solar system dust cloud, but the observational approach is obviously
quite different: overall spatial distributions for systems of different ages for the planetary debris disks, as opposed to
detailed local information in the case of the solar system. Comparison with the processes of dust formation and evolution
observed in the solar system therefore helps understand the planetary debris disks. In this paper, we review our present knowledge
of observations, acting forces, and major physical interactions of the dust in the solar system and in similar extra-solar
planetary systems. 相似文献
98.
A new method of producing pyrrhotite grains, which are most commonly found in cometary material and interplanetary dust particles, was developed. Pyrrhotite grains in the monophase having a 7C structure were predominately produced using a solid-solid reaction between iron and sulfur grains at room temperature. The characteristic infrared peaks were observed at 602, 563, and 397 cm−1 (16.6, 17.8, and 25.2 μm). 相似文献
99.
Yamato 792947, 793408 and 82038: The most primitive H chondrites,with abundant refractory inclusions
M. Kimura H. Hiyagon H. Palme B. Spettel D. Wolf R. N. Clayton T. K. Mayeda T. Sato A. Suzuki H. Kojima 《Meteoritics & planetary science》2002,37(10):1417-1434
Abstract— In this paper we report petrological and chemical data of the unusual chondritic meteorites Yamato (Y)‐792947, Y‐93408 and Y‐82038. The three meteorites are very similar in texture and chemical composition, suggesting that they are pieces of a single fall. The whole‐rock oxygen isotopes and the chemical compositions are indicative of H chondrites. In addition, the mineralogy, and the abundances of chondrule types, opaque minerals and matrices suggest that these meteorites are H3 chondrites. They were hardly affected by thermal and shock metamorphism. The degree of weathering is very low. We conclude that these are the most primitive H chondrites, H3.2–3.4 (S1), known to date. On the other hand, these chondrites contain extraordinarily high amounts of refractory inclusions, intermediate between those of ordinary and carbonaceous chondrites. The distribution of the inclusions may have been highly heterogeneous in the primitive solar nebula. The mineralogy, chemistry and oxygen isotopic compositions of inclusions studied here are similar to those in CO and E chondrites. 相似文献
100.