排序方式： 共有7条查询结果，搜索用时 16 毫秒
1
1.
Abstract— A dark inclusion in the Vigarano CV3 carbonaceous chondrite consists almost exclusively of small (<5 μm in diameter) grains of Fe-rich olivine and is devoid of chondrules, Ca-Al-rich inclusions (CAIs) and their pseudomorphs. In backscattered electron images, this dark inclusion shows an unusual texture comprising a network of arcuate bands. Two or more bands occur roughly parallel, forming a set of succesive parallel bands, some crosscutting one another. The bands contain slightly higher amounts of relatively small (<1 μm) olivine grains and so are more densely packed than other areas. The olivine grains in the bands are slightly more Fe-rich than those in other areas. The bands commonly show gradation on the concave side due to a decrease in the abundance of the small Fe-rich olivine grains. Texturally, the arcuate bands closely resemble “dish structures” that are commonly observed in siltstones and sandstones on Earth. Dish structures are characterized by thin, dark-colored, subhorizontal to concave-upward laminations that are rich in relatively fine-grained material. On Earth, dish structures form during compaction and dewatering of unconsolidated fine-grained sediments; they are one of the characteristic sedimentary structures formed through fluidization of fine grains. The dark inclusion in Vigarano, therefore, provides the first evidence that sedimentary processes due to water migration may have taken place within planetesimals and further suggests that fluidization may have played a significant role in the formation of the carbonaceous chondrites. 相似文献
2.
Hiroshi NARAOKA Hajime MITA Masatoshi KOMIYA Shigekazu YONEDA Hideyasu KOJIMA Akira SHIMOYAMA 《Meteoritics & planetary science》2004,39(3):401-406
Abstract— A new organic parameter is proposed to show a chemical sequence of organic matter in carbonaceous chondrites, using carbon, hydrogen, and nitrogen concentrations of solvent‐insoluble and high‐molecular weight organic matter (macromolecules) and the molecular abundance of solvent‐extractable organic compounds. The H/C atomic ratio of the macromolecule purified from nine CM chondrites including the Murchison, Sayama, and seven Antarctic meteorites varies widely from 0.11 to 0.72. During the H/C change of ?0.7 to ?0.3, the N/C atomic ratio remains at ?0.04, followed by a sharp decline from ?0.040 to ?0.017 between H/C ratios from ?0.3 to ?0.1. The H/CN/C sequence shows different degrees of organic matter thermal alteration among these chondrites in which the smaller H/C‐N/C value implies higher alteration levels on the meteorite parent body. In addition, solvent‐extractable organic compounds such as amino acids, carboxylic acids, and polycyclic aromatic hydrocarbons are abundant only in chondrites with macromolecular H/C values >?0.5. These organic compounds were extremely depleted in the chondrites with a macromolecular H/C value of <?0.5. Possibly, most solvent‐extractable organic compounds could have been lost during the thermal alteration event that caused the H/C ratio of the macromolecule to fall below 0.4. 相似文献
3.
Naoya Imae Makoto Kimura Akira Yamaguchi Hideyasu Kojima 《Meteoritics & planetary science》2019,54(4):919-937
Using an X‐ray diffractometer, powder‐like diffraction patterns were acquired from in‐plane rotation of polished thin sections (PTSs) of 60 ordinary chondrites (23 H, 21 L, and 16 LL), in order to explore the thermal and shock metamorphism and its modifications of primordial features. The olivine (Ol) 130 peak position shown as Bragg indices clearly correlates with the chemical group for equilibrated ordinary chondrites (EOCs), while the peak is split or broad for unequilibrated ordinary chondrites (UOCs). The intensity ratio of kamacite may be useful for distinguishing the chemical group between H and L‐LL, but it is not definite because of heterogeneous terrestrial weathering of kamacite, especially in H chondrites. The summed intensities of the orthoenstatite (Oen) 511 and 421 peaks positively correlates with the metamorphic sequence from 3 to 6, while that of clinoenstatite (Cen) 22 is inversely correlated. The shock stage positively correlates with the summed full width of half maximum values of the Oen 511 and 421 peaks and the FWHM of Ol 130 peak for each class. Significant amount of Oen (Pbca) transformed through Cen (C2/c) finally to Cen (P21/c) is stable at high pressure for shock stage S6 (Tenham and NWA 4719). The shock melted LL chondrite is characterized by the occurrence of Cen and abundant homogeneous olivine. The effects of both thermal and shock metamorphism are thus incorporated into the bulk X‐ray diffraction (XRD) data. The bulk XRD method is useful for determining the bulk mineralogy, resulting in the classification of ordinary chondrites. The method is also applicable to samples other than PTS. 相似文献
4.
Takahiro Hiroi Hiroshi Kaiden Keiji Misawa Takafumi Niihara Hideyasu Kojima Sho Sasaki 《Polar Science》2011,5(3):337-344
Martian meteorite chip samples stored at the National Institute of Polar Research (NIPR) have been studied by a visible and near-infrared (VNIR) spectrometer. Measured spots are about 3 × 2 mm in size, which are clearly marked on photographs of the meteorite chips. Rock types and approximate mineral compositions of studied meteorites have been identified or obtained through this spectral survey with no sample preparation required. This study demonstrates that this kind of spectral survey is effective in classifying and describing Marian meteorites, and that such a VNIR spectrometer on a Mars rover would be useful for identifying these kinds of unaltered Mars rocks. Further studies which utilize a smaller spot size are desired for improving the accuracy of identifying the clasts and mineral phases in the rocks. 相似文献
5.
Fine-grained Ca-Al-rich inclusions (FGIs) in Yamato-81020 (CO3.0) and Kainsaz (CO3.1-CO3.2) chondrites have been studied by secondary ion mass spectrometry. The FGIs from Yamato-81020 consist of aggregates of hibonite, spinel, melilite, anorthite, diopside and olivine grains with no petrographic evidence of alteration. In contrast, the FGIs from Kainsaz commonly contain alteration products such as nepheline. From replacement textures and chemical compositions of altered and unaltered FGIs, we conclude that the alteration products formed by decomposition of melilite and anorthite. All phases in the Yamato-81020 FGIs are enriched in 16O, with δ17, 18O = ∼−40‰ except for one FGI that experienced melting. Oxygen isotopic compositions of melilite, anorthite, some spinel and diopside in Kainsaz FGIs changed from δ17, 18O = ∼−40‰ toward 0‰ by aqueous alteration. Alteration products in FGIs are depleted in 16O relative to primary phases, with δ17, 18O = ∼0‰. These results show that FGIs in CO chondrites commonly had 16O-rich compositions in the solar nebula. The original 16O-rich FGIs were modified to 16O-poor compositions during aqueous alteration in the parent body. 相似文献
6.
We studied the petrology and mineralogy of two types of shock-melted H chondrites: Yamato (Y)–791088 and LaPaz Ice Field (LAP) 02240. Y–791088, which consists of numerous coarse-grained relict phases (40%) and euhedral fine-grained minerals solidified from the shock melt (60%), experienced incomplete melting; a quiescent melt is indicated by the existence of abundant relict phases, pseudomorphed chondrules, and two types of glass. LAP 02240, which consists of small amounts of coarse-grained relict phases (～10%) and fine-grained minerals (～90%), experienced near-complete melting; a rapidly cooled mobilized melt is indicated by the homogeneous compositions of glass and opaque veins.The homogeneous compositions of relict olivines indicate that the precursors of both chondrites were equilibrated H chondrites. The melting features of Y–791088 and LAP 02240 are very similar to those of Y–790964 (LL) and the fine-grained lithology of Y–790519 (LL), respectively. These two types of shock-melted ordinary chondrites possibly formed in situ during dike formation. The quiescent melt is thought to have originated from the injection of shock-heated chondrite blocks into mobilized melt. These two types of melting could have occurred during dike formation on the H chondrite parent body. The textures of the two types of shock melts were not simply affected by the degree of shock melting: they were also controlled by the degree of shear stress. 相似文献
7.
Shoji KOJIMA 《Resource Geology》1999,49(3):175-181
Abstract: In Chile the principal gold deposits of the low- and high-sulfidation types occur in the middle Creataceous-early Eocene Precordillera and in the middle to late Miocene Andean Cordillera, respectively. In both areas their related magma-tism migrates south-east with time. This feature suggests that the metallogenic integrity is greatly affected by a change in the tectonic regime from a transpressive oblique subduction to a weakly-compressive normal subduction. Moreover, certain differences in the geologic setting, such as the structure of host rocks are recognized between the two types of Chilean epither-mal gold deposits. This data provide us not only with genetic implications regarding epithermal gold deposits, but also an important guide for gold exploration in the Chilean Cordillera. 相似文献
1