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Abstract— Olivine in the angritic meteorite Lewis Cliff (LEW) 86010 contains abundant exsolution lamellae of kirschsteinite. Compositional gradients adjacent to the interface in both host and lamellae were formed by diffusion of chemical components into and out of the lamellae during cooling and growth. We have compared these gradients with compositional profiles calculated from diffusion and heat flow equations to estimate the cooling rate and burial depth of the sample. The resulting values for cooling rate and burial depth depend on which values are used for the diffusion rate of Ca in olivine, and how measured diffusivities are extrapolated to the lower temperatures at which the lamellae grew. If the highest diffusion coefficients are used, the cooling rates obtained from seven different lamellae range from 30 to 52 °C/year, with an average of 42 °C/year, and burial depths (assuming an overburden with a thermal diffusivity typical of solid rock) range from 14 to 17 m, with an average of 15 m. If the lowest reasonable diffusion coefficients are used, the cooling rates range from 1.4 to 2.2 °C/year, with an average of 1.7 °C/year, and the depths range from 68 to 83 m, with an average of 75 m. For the highest Ca diffusivities, details of the compositional profiles near the olivine/kirschsteinite interface suggest that continuous cooling was greatly accelerated at a temperature near 600–700 °C. The simplest physical explanation for such an acceleration is excavation of the sample from its original burial depth by an impact event. If Ca diffusivities are lower, a two-stage cooling history is not required. 相似文献
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Toru YADA Akio FUJIMURA Masanao ABE Tomoki NAKAMURA Takaaki NOGUCHI Ryuji OKAZAKI Keisuke NAGAO Yukihiro ISHIBASHI Kei SHIRAI Michael E. ZOLENSKY Scott SANDFORD Tatsuaki OKADA Masayuki UESUGI Yuzuru KAROUJI Maho OGAWA Shogo YAKAME Munetaka UENO Toshifumi MUKAI Makoto YOSHIKAWA Junichiro KAWAGUCHI 《Meteoritics & planetary science》2014,49(2):135-153
Abstract– The Planetary Material Sample Curation Facility of JAXA (PMSCF/JAXA) was established in Sagamihara, Kanagawa, Japan, to curate planetary material samples returned from space in conditions of minimum terrestrial contaminants. The performances for the curation of Hayabusa‐returned samples had been checked with a series of comprehensive tests and rehearsals. After the Hayabusa spacecraft had accomplished a round‐trip flight to asteroid 25143 Itokawa and returned its reentry capsule to the Earth in June 2010, the reentry capsule was brought back to the PMSCF/JAXA and was put to a series of processes to extract recovered samples from Itokawa. The particles recovered from the sample catcher were analyzed by electron microscope, given their ID, grouped into four categories, and preserved in dimples on quartz slide glasses. Some fraction of them has been distributed for initial analyses at NASA, and will be distributed for international announcement of opportunity (AO), but a certain fraction of them will be preserved in vacuum for future analyses. 相似文献
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Sedimentary structures in the middle–late Miocene to early Pliocene Misaki Formation, Miura Group, Miura Peninsula, Central Japan, were studied, and paleocurrent data were interpreted as the result of deep-sea bottom-current flow. These current data were further compared with present-day bottom currents in the northwestern Pacific region. The Misaki Formation is thought to be a forearc deposit within the Izu oceanic arc, and is composed of thick volcaniclastic beds interbedded with siliceous biogenic clayey sediments. Sedimentary structures showing paleocurrent directions are involved in the upper part of the volcaniclastic beds, in the pumiceous beds just above the volcaniclastic beds, and in the pelagic sediments. Based on paleomagnetic data suggesting considerable rotation of the beds, all the current directions were reconstructed to their original orientation. The paleocurrents are summarized into the following three groups. The first group in the volcaniclastic beds indicates southeast-directed paleocurrent directions. The second group in the upper parts of volcaniclastic beds and in some pumiceous beds exhibits a southwest- and northeast-directed paleoflow. The third group usually observed in the pumiceous beds with parallel lamination displays a northwest- or southeast-directed paleocurrent. The origin of each group's paleoflow direction is attributed to turbidity current, internal tidal current, and contour current influences, respectively. Present-day observations of the deep-sea northwest Pacific suggest that most of the bottom-current indicators in the Misaki Formation are related to North Pacific Deep Water, possibly Antarctic Bottom Water as well as a combination of tidal and local effects. It is concluded that the beds of the Misaki Formation were deposited in the proto-Sagami basin ca 9 Ma and were formed under weak bottom currents in a wide and flat basin during colder climatic conditions, whereas the beds dated at ca 6 Ma were deposited under strong bottom-current flow, and were then accreted to the Honshu arc. 相似文献
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HIRONOBU SAKUMA RYUJI TADA MASAYUKI IKEDA YUICHIRO KASHIYAMA NAOHIKO OHKOUCHI NANAKO O. OGAWA SATOKO WATANABE EIICHI TAJIKA SHINJI YAMAMOTO 《Island Arc》2012,21(2):79-100
After the severest mass extinction event in the Phanerozoic, biotic recovery from the extinction at the Permian–Triassic boundary required approximately 5 my, which covers the entire Early Triassic. It is important to obtain information on the superocean Panthalassa, which occupied most of the world ocean, to explore paleoenvironmental changes during the Early Triassic at the global scale. In order to establish the continuous lithostratigraphy of pelagic sediments in Panthalassa during the Early Triassic, high‐resolution reconstruction of the Lower Triassic pelagic sequence in Japan was conducted for the first time based on detailed field mapping and lithostratigraphic correlation in the Inuyama area, central Japan. The reconstructed Early Triassic sequence is approximately 9.5 m thick, consists of five rock types, and is divided into eight lithological units. For the reconstructed continuous sequence, measurement of carbon isotopic composition of sedimentary organic matter (δ13Corg) was carried out. Stratigraphic variation of the δ13Corg value shows large‐amplitude fluctuations between ?34.4 and ?21.0‰ throughout the sequence. In order to establish a higher resolution age model for the reconstructed Lower Triassic pelagic sequence, we correlated δ13Corg records in the Inuyama area with high‐resolution isotopic profiles of carbonate carbon (δ13Ccarb) from shallow‐marine carbonate sequences in southern China based on the similarity in general variation patterns with age constraints by radiolarian and conodont biostratigraphy. The result provides a high‐resolution time scale for the pelagic sequence of Panthalassa during the Smithian and Spathian. The age model suggests a drastic increase in sedimentation rate during the late Smithian, which should have been caused by the increase in terrigenous input to this site. 相似文献
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MARI OGAWA AKIRA TAKEUCHI MUTSUO HATTORI MASAHARU OKANO MISUMI AOKI MAKIKO IMAMURA TOYOKI KSUBOI TOMONORI TSUBOI DAISUKE TANIMOTO TAKESHI NAGANUMA 《Island Arc》2002,11(4):274-286
Abstract The manned submersible Shinkai 2000 investigated yellow patches on the near-summit slope of Shiribeshi Seamount in the Japan Sea. Yellowish patches are often associated with seepage, and the possibility of seepage at Shiribeshi Seamount was tested by the following four lines of observation: (i) high subsurface temperature was measured at a ring-like patch, although no increase in subsurface temperature was observed at other patches; (ii) high gamma ray (γ-ray) intensity from the thorium series was recorded in the patch zone; (iii) the yellowish deposit was composed of calcite, quartz and amorphous iron compound, as seen at the yellowish patches in other seeps and volcanoes; (iv) lipid phosphate, a measure of microbial abundance, in sediments of the ring-like patch was determined, and the recorded microbial abundance was higher inside the patch than outside it. The four lines of observation are explained consistently by postulating that the seepage of warm fluid contained Fe and γ-ray sources. A hydrothermal origin of the yellow patches is not ruled out for the extinct but young (0.9 Ma) arc volcano. 相似文献
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Late Paleocene–middle Miocene pelagic limestone/chert sequences from the Mineoka Tectonic Belt, Boso Peninsula, central Japan, were biostratigraphically studied for planktic foraminifer fossils for the first time. The rock units are included as several isolated blocks tectonically within the ophiolitic mélange together with the Mio-Pliocene Honshu arc-derived terrigenous and Izu Arc-derived volcaniclastic materials. The pelagic sequences are grouped into the newly proposed Kamogawa Group which is subdivided into the Paleocene Nishi Formation, Eocene–Oligocene Heguri-Naka Limestone and early–middle Miocene Shirataki and Heguri Formations. This study of Kamogawa Group pelagic sequences throws new light on tectonic modeling of plate accretion to the unique trench–trench–trench (TTT)-type triple junction area off the Boso Peninsula. Different formations of the Kamogawa Group have different tectonic and paleogeographic significances for the oceanic plate with a seamount that was approaching the Izu and Honshu arcs during Pacific plate subduction, and that was accreted to the Honshu Arc during the middle Miocene. 相似文献
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