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Partial Melting and Counterclockwise P T Path of Subducted Oceanic Crust (Sierra del Convento Melange, Cuba) 总被引：1，自引：0，他引：1
Garcia-Casco Antonio; Lazaro Concepcion; Rojas-Agramonte Yamirka; Kroner Alfred; Torres-Roldan Rafael Luis; Nunez Kenya; Neubauer Franz; Millan Guillermo; Blanco-Quintero Idael 《Journal of Petrology》2008,49(1):129-161
Partial melting of subducted oceanic crust has been identifiedin the Sierra del Convento mélange (Cuba). This serpentinite-matrixmélange contains blocks of mid-ocean ridge basalt (MORB)-derivedplagioclase-lacking epidote ± garnet amphibolite intimatelyassociated with peraluminous trondhjemitic–tonalitic rocks.Field relations, major element bulk-rock compositions, mineralassemblages, peak metamorphic conditions (c. 750°C, 14–16kbar), experimental evidence, and theoretical phase relationssupport formation of the trondhjemitic–tonalitic rocksby wet melting of subducted amphibolites. Phase relations andmass-balance calculations indicate eutectic- and peritectic-likemelting reactions characterized by large stoichiometric coefficientsof reactant plagioclase and suggest that this phase was completelyconsumed upon melting. The magmatic assemblages of the trondhjemitic–tonaliticmelts, consisting of plagioclase, quartz, epidote, ±paragonite, ± pargasite, and ± kyanite, crystallizedat depth (14–15 kbar). The peraluminous composition ofthe melts is consistent with experimental evidence, explainsthe presence of magmatic paragonite and (relict) kyanite, andplaces important constraints on the interpretation of slab-derivedmagmatic rocks. Calculated P–T conditions indicate counterclockwiseP–T paths during exhumation, when retrograde blueschist-faciesoverprints, composed of combinations of omphacite, glaucophane,actinolite, tremolite, paragonite, lawsonite, albite, (clino)zoisite,chlorite, pumpellyite and phengite, were formed in the amphibolitesand trondhjemites. Partial melting of subducted oceanic crustin eastern Cuba is unique in the Caribbean realm and has importantconsequences for the plate-tectonic interpretation of the region,as it supports a scenario of onset of subduction of a youngoceanic lithosphere during the early Cretaceous (c. 120 Ma).The counterclockwise P–T paths were caused by ensuingexhumation during continued subduction. KEY WORDS: amphibolite; Cuba; exhumation; partial melting; trondhjemite; subduction 相似文献
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Ken?NiwaEmail author Takehiko?Yagi Kenya?Ohgushi 《Physics and Chemistry of Minerals》2011,38(1):21-31
Compression behaviors of CaIrO3 with perovskite (Pv) and post-perovskite (pPv) structures have been investigated up to 31.0(1.0) and 35.3(1) GPa at room
temperature, respectively, in a diamond-anvil cell with hydrostatic pressure media. CaIrO3 Pv and pPv phases were compressed with the axial compressibility of β
a > β
c > β
b and β
b > β
a > β
c, respectively and no phase transition was observed in both phases up to the highest pressure in the present study. The order
of axial compressibility for pPv phase is consistent with the crystallographic consideration for layer structured materials
and previous experimental results. On the other hand, Pv phase shows anomalous compression behavior in b axis, which exhibit constant or slightly expanded above 13 GPa, although the applied pressure remained hydrostatic. Volume
difference between Pv and pPv phases was gradually decreased with increasing pressure and this is consistent with the results
of theoretical study based on the ab initio calculation. Present results, combined with theoretical study, suggest that these
complicate compression behaviors in CaIrO3 under high pressure might be caused by the partially filled electron of Ir4+. Special attention must be paid in case of using CaIrO3 as analog materials to MgSiO3, although CaIrO3 exhibits interesting physical properties under high pressure. 相似文献
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Abstract: The present paper examines the changing climatic scenarios and associated effects on livestock farming (pastoralism) in the arid and semi arid lands (ASAL) of Kenya, which cover over 80% of the country. The study was carried out in the semi arid Mukogodo Division of Laikipia District in Kenya. This division received a mean annual rainfall of approximately 507.8?mm and the main source of livelihood was pastoralism. Questionnaire, structured interview, observation and literature review were the main methods of data collection. Rainfall was used in delineating changes in climate. Standardized precipitation index (SPI) and Markov process were used in analyzing drought severity and persistence, respectively. Approximately 38% of all droughts between 1975 and 2005 were prolonged and extremely severe, with cumulative severity indices ranging between ?2.54 and ?6.49. The probability that normal climatic conditions persisted for two or more consecutive years in Mukogodo Division remained constant at approximately 52%. However, the probability of wet years persisting for two or more years showed a declining trend, while persistence of dry years increased with duration. A drying climatic trend was established. This drying trend in the area led to increased land degradation and encroachment of invasive nonpalatable bushes. The net effect on pastoralism was large-scale livestock loss through starvation, disease and cattle rustling. Proper drought monitoring and accurate forecasts, community participation in all government interventions, infrastructural development in the ASAL and allocation of adequate resources for livestock development are some of the measures necessary for mitigating the dwindling pastoral economy in Kenya and other parts of the world. 相似文献
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Ken Niwa Takehiko Yagi Kenya Ohgushi Sébastien Merkel Nobuyoshi Miyajima Takumi Kikegawa 《Physics and Chemistry of Minerals》2007,34(9):679-686
Lattice preferred orientations (LPO) developed in perovskite and post-perovskite structured CaIrO3 were studied using the radial X-ray diffraction technique combined with a diamond anvil cell. Starting materials of each
phase were deformed from 0.1 MPa to 6 GPa at room temperature. Only weak LPO was formed in the perovskite phase, whereas strong
LPO was formed in the post-perovskite phase with an alignment of the (010) plane perpendicular to the compression axis. The
present result suggests that the (010) is a dominant slip plane in the post-perovskite phase and it is in good agreement with
the crystallographic prediction, dislocation observations via transmission electron microscopy, and a recent result of simple
shear deformation experiment at 1 GPa–1,173 K. However, the present result contrasts markedly from the results on MgGeO3 and (Mg,Fe)SiO3, which suggested that the (100) or (110) is a dominant slip plane with respect to the post-perovskite structure. Therefore
it is difficult to discuss the behavior of the post-perovskite phase in the Earth’s deep interior based on existing data of
MgGeO3, (Mg,Fe)SiO3 and CaIrO3. The possible sources of the differences between MgGeO3, (Mg,Fe)SiO3 and CaIrO3 are discussed. 相似文献
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Measurements of photosynthetically active radiation(PAR),which are indispensable for simulating plant growth and productivity,are generally very scarce.This study aimed to compare two extrapolation and one interpolation methods for estimating daily PAR reaching the earth surface within the Poyang Lake national nature reserve,China.The daily global solar radiation records at Nanchang meteorological station and daily sunshine duration measurements at nine meteorological stations around Poyang Lake were obtain... 相似文献
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Yasuhito Sekine Kenya Kodama Takamichi Kobayashi Seiji Obata Yu Chang Nanako O. Ogawa Yoshinori Takano Naohiko Ohkouchi Koichiro Saiki Toshimori Sekine 《Meteoritics & planetary science》2018,53(6):1267-1282
The present study systematically investigates shock-induced alteration of organic simulants of planetary bodies (OSPBs) as a function of peak shock pressure and temperature by impact experiments. Our results show that the composition and structure of OSPBs are unchanged upon impacts at peak pressures ≤~5 GPa and temperatures ≤~350 °C. On the other hand, these are dramatically changed upon impacts at >7–8 GPa and > ~400 °C, through loss of hydrogen-related bonds and concurrent carbonization, regardless of the initial compositions of OSPBs. Compared with previous results on static heating of organic matter, we suggest that shock-induced alteration cannot be distinguished from static heating only by Raman and infrared spectroscopy. Our experimental results would provide a proxy indicator for assessing degree of shock-induced alteration of organic matter contained in carbonaceous chondrites. We suggest that a remote-sensing signature of the 3.3–3.6 μm absorption due to hydrogen-related bonds on the surface of small bodies would be a promising indicator for the presence of less-thermally-altered (i.e., <350 °C) organic matter there, which will be a target for landing to collect primordial samples in sample-return spacecraft missions, such as Hayabusa2 and OSIRIS-REx. 相似文献
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Kenya Ohgushi Yoshitaka Matsushita Nobuyoshi Miyajima Yoshio Katsuya Masahiko Tanaka Fujio Izumi Hirotada Gotou Yutaka Ueda Takehiko Yagi 《Physics and Chemistry of Minerals》2008,35(4):189-195
Structural, morphological, magnetic, and thermal properties have been investigated for a novel post-perovskite oxide CaPtO3 synthesized under high pressure. By comparing obtained structural parameters with those for known post-perovskite compounds,
we argue that the chemical bond has a strong covalent character. Precise measurements of the Langevin susceptibility χ
0
= −9.6 × 10−5 emu/mol and Debye temperature θ ∼ 470 K provide a good opportunity to confirm the reliability of first-principle calculations on predicting physical properties
of the Earth’s D” layer. 相似文献
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