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931.
932.
M. Matsumoto S. Wallis M. Aoya M. Enami J. Kawano Y. Seto N. Shimobayashi 《Journal of Metamorphic Geology》2003,21(4):363-376
A largely undocumented region of eclogite associated with a thick blueschist unit occurs in the Kotsu area of the Sanbagawa belt. The composition of coexisting garnet and omphacite suggests that the Kotsu eclogite formed at peak temperatures of around 600 °C synchronous with a penetrative deformation (D1). There are local significant differences in oxygen fugacity of the eclogite reflected in mineral chemistries. The peak pressure is constrained to lie between 14 and 25 kbar by microstructural evidence for the stability of paragonite throughout the history recorded by the eclogite, and the composition of omphacite in associated eclogite facies pelitic schist. Application of garnet‐phengite‐omphacite geobarometry gives metamorphic pressures around 20 kbar. Retrograde metamorphism associated with penetrative deformation (D2) is in the greenschist facies. The composition of syn‐D2 amphibole in hematite‐bearing basic schist and the nature of the calcium carbonate phase suggest that the retrograde P–T path was not associated with a significant increase or decrease in the ratio of P–T conditions following the peak of metamorphism. This P–T path contrasts with the open clockwise path derived from eclogite of the Besshi area. The development of distinct P–T paths in different parts of the Sanbagawa belt shows the shape of the P–T path is not primarily controlled by tectonic setting, but by internal factors such as geometry of metamorphic units and exhumation rates. 相似文献
933.
Abstract— The Yamato nakhlites, Y‐000593, Y‐000749, and Y‐000802, were recovered in 2000 from the bare icefield around the Yamato mountains in Antarctica, consisting of three independent specimens with black fusion crusts. They are paired cumulate clinopyroxenites. We obtained the intercumulus melt composition of the Yamato nakhlites and here call it the Yamato intercumulus melt (YIM). The YIM crystallized to form the augite rims, the olivine rims and the mesostasis phases in the cumulates. The augite rims consist of two layers: inner and outer. The crystallization of the inner rim drove the interstitial melt into the plagioclase liquidus field. Subsequently, the residual melt crystallized pigeonites and plagioclase to form the outer rims and the mesostasis. Three types of inclusions were identified in olivine phenocrysts: rounded vitrophyric, angular vitrophyric, and monomineralic augite inclusions. The monomineralic augite inclusions are common and may have been captured by growing olivine phenocrysts. The rounded vitrophyric inclusions are rare and may represent the composition of middle‐stage melts, whereas the angular vitrophyric inclusions seem to have been derived from fractionated late‐stage melts. Glass inclusions occur in close association with titanomagnetite and ferroan augite halo in phenocryst core augites and the assemblages may be magmatic inclusions in augites. We compared the YIM with compositions of magmatic inclusions in olivine and augite. The composition of magmatic inclusions in augite is similar to the YIM. Phenocrystic olivines contain exsolution lamellae, augite‐magnetite aggregates, and symplectites in the cores. The symplectites often occur at the boundaries between olivine and augite grains. The aggregates, symplectite and lamellae formed by exsolution from the host olivine at magmatic temperatures. We present a formational scenario for nakhlites as follows: (1) accumulation of augite, olivine, and titanomagnetite phenocrysts took place on the floor of a magma chamber; (2) olivine exsolved augite and magnetite as augite‐magnetite aggregates, symplectites and lamellae; (3) the overgrowth on olivine phenocrysts formed their rims, and the inner rims crystallized on augite phenocryst cores; and finally, (4) the outer rim formed surrounding the inner rims of augite phenocrysts, and plagioclase and minor minerals crystallized to form mesostasis under a rapid cooling condition, probably in a lava flow or a sill. 相似文献
934.
We present the results of X-ray luminosities of some active late-type stars, based on data primarily from the ROSAT position
sensitive proportional counter (PSPC). According to the observations, we divide the stars into four groups: single, wide binary,
binary and RS CVn. We investigated the correlation between the X-ray emission and the hardness ratio, coronal temperature,
magnetic field strength, magnetic flux density. Our results suggest that the magnetic field plays a very important role in
stellar X-ray emission. 相似文献
935.
Seismic moment distribution 总被引:1,自引:0,他引:1
Y. Y. Kagan 《Geophysical Journal International》1991,106(1):123-134
936.
A procedure for tidal analysis with a Bayesian information criterion 总被引:16,自引:0,他引:16
937.
938.
939.
Summary ?In cathodoluminescence (CL) images of synthetic low-quartz samples after He+ implantation at 4 MeV with a dose density over 1.14 × 10−4 C cm−2, bright CL halos of about 14 μm in width from the implantation surface are recognized. These widths are consistent with the
theoretical range. This confirms experimentally that the CL halos in low-quartz found in geological samples are formed by
alpha radiation. It also shows that CL colour continuously changes with dose density, demonstrating that it is possible to
use the CL halo as a new dosimeter that is useful for dating and analysis of radionuclide migration in natural geological
media.
Received December 3, 2001; revised version accepted February 27, 2002 相似文献
940.