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排序方式: 共有139条查询结果,搜索用时 406 毫秒
1.
Paul McMillan Masaki Akaogi Eiji Ohtani Quentin Williams Ronald Nieman Robert Sato 《Physics and Chemistry of Minerals》1989,16(5):428-435
We have obtained infrared and Raman spectra for garnets synthesized at high (static) pressures and temperatures along the join Mg3Al2Si3O12 (pyrope) — Mg4Si4O12 (magnesium majorite). The vibrational spectra of Mg-majorite show a large number of additional weak peaks compared with the spectra of cubic pyrope garnet, consistent with tetragonal symmetry for the MgSiO3 garnet phase. The Raman bands for this phase show no evidence for line broadening, suggesting that Mg and Si are ordered on octahedral sites in the garnet. The bands for the intermediate garnet compositions are significantly broadened compared with the end-members pyrope and Mg-majorite, indicating cation disorder in the intermediate phases. Solid state 27Al NMR spectroscopy for pyrope and two intermediate compositions show that Al is present only on octahedral sites, so the cation disorder is most likely confined to Mg-Al-Si mixing on the octahedral sites. We have also obtained a Raman spectrum for a natural, shock-produced (Fe,Mg) majorite garnet. The sharp Raman peaks suggest little or no cation disorder in this sample. 相似文献
2.
Eiji Ohtani 《Earth and Planetary Science Letters》1984,67(2):261-272
The densities of silicate liquids with basic, picritic, and ultrabasic compositions have been estimated from the melting curves of minerals at high pressures. Silicate liquids generated by partial melting of the upper mantle are denser than olivine and pyroxenes at pressures higher than 70 kbar, and garnet is the only phase which is denser than the liquid at pressures from 70 kbar to at least 170 kbar. In this pressure range, garnet and some fraction of liquid separate from ascending partially molten diapirs. It is therefore suggested that aluminium-depleted komatiite with a high Ca/OAl2O3 ratio may be derived from diapirs which originated in the deep upper mantle at pressures from 70 kbar to at least 140 kbar (200–400 km in depth), where selective separation of pyropic garnet occurs effectively. On the other hand, aluminium-undepleted komatiite is probably derived from diapirs originating at shallower depths (< 200 km). Enrichment of pyropic garnet is expected at depths greater than 200 km by selective separation of garnet from ascending diapirs. The 200-km discontinuity in the seismic wave velocity profile may be explained by a relatively high concentration of pyropic garnet at depths greater than 200 km. 相似文献
3.
Experiments on the solubility of FeO in molten iron have been carried out at temperatures between 2100 and 2550°C. The results show that liquid FeO is extensively soluble in molten iron at 2500°C and indicate that they probably become completely miscible above 2800°C. Liquid iron in equilibrium with crystalline magnesiowüstite (Mg0.8Fe0.2)O which is believed to be an important mineral in the lower mantle, would dissolve about 14 mol.% of FeO at 2500°C and 40 mol.% of FeO at 2800°C. The geochemical implications of these results are discussed. It is concluded that the outer core probably contains a large amount of dissolved FeO and that oxygen is probably the principal light element in the outer core. 相似文献
4.
Tomoyuki Takahashi Takeyuki Takahashi Nobuo Shuto Fumihiko Imamura Modesto Ortiz 《Pure and Applied Geophysics》1995,144(3-4):747-767
A source model for the 1993 Hokkaido Nansei-Oki tsunami must satisfy certain conditions. Such conditions are presented in this paper, and two methods are used to determine the best source model for this event. A trial-and-error method selects DCRC-17a as the best among 24 different models. This model has three fault planes dipping westward. To reproduce well the tide gauge records at two locations, an inversion analysis is used to modify the dislocation of DCRC-17a. 相似文献
5.
6.
Japanese early-warning for debris flows and slope failures using rainfall indices with Radial Basis Function Network 总被引:3,自引:1,他引:2
Nobutomo Osanai Takeshi Shimizu Kazumasa Kuramoto Shinichi Kojima Tomoyuki Noro 《Landslides》2010,7(3):325-338
Early-warning systems for natural disasters are important tools for disaster risk reduction and for achieving sustainable
development and livelihoods. In 2005, the Japanese government initiated a new nationwide early-warning system for landslides
disasters. The main methodology of the system is to set a criterion for occurrences of debris flows and slope failures based
on several rainfall indices (60-min cumulative rainfall and soil–water index) in each 5-km grid mesh covering all of Japan.
Because many of the records of mass movements are lacking in scientific precision on timing and location, the system applies
Radial Basis Function Network methods to set the criterion based primarily on rainfall data recorded as not triggering disasters.
Since the end of March 2007, under torrential rainfall conditions, early-warning information has been disseminated as part
of weather news using TV, radio, and the Internet. Because of the increasing worldwide recognition of the importance of early-warning
systems for natural disaster reduction, the aim of this article is to introduce the new Japanese early-warning system to the
international landslide community. In this article, the method, the system, and the result of its application to landslide
disasters in 2009 are presented. 相似文献
7.
Origin of EL3 chondrites: Evidence for variable C/O ratios during their course of formation—A state of the art scrutiny 下载免费PDF全文
A. El Goresy Y. Lin M. Miyahara A. Gannoun M. Boyet E. Ohtani P. Gillet M. Trieloff A. Simionovici L. Feng L. Lemelle 《Meteoritics & planetary science》2017,52(5):781-806
Mineral inventories of enstatite chondrites; (EH and EL) are strictly dictated by combined parameters mainly very low dual oxygen (fO2) and sulfur (fS2) fugacities. They are best preserved in the Almahata Sitta MS‐17, MS‐177 fragments, and the ALHA 77295 and MAC 88136 Antarctic meteorites. These conditions induce a stark change of the geochemical behavior of nominally lithophile elements to chalcophile or even siderophile and changes in the elemental partitioning thus leading to formation of unusual mineral assemblages with high abundance of exotic sulfide species and enrichment in the metallic alloys, for example, silicides and phosphides. Origin and mode of formation of these exotic chondrites, and their parental source regions could be best scrutinized by multitask research experiments of the most primitive members covering mineralogical, petrological, cosmochemical, and indispensably short‐lived isotopic chronology. The magnitude of temperature and pressure prevailed during their formation in their source regions could eventually be reasonably estimated: pre‐ and postaccretionary could eventually be deduced. The dual low fugacities are regulated by the carbon to oxygen ratios estimated to be >0.83 and <1.03. These parameters not only induce unusual geochemical behavior of the elements inverting many nominally lithophile elements to chalcophile or even siderophile or anthracophile. Structure and mineral inventories in EL3 and EH3 chondrites are fundamentally different. Yet EH3 and EL3 members store crucial information relevant to eventual source regions and importantly possible variation in C/O ratio in the course of their evolution. EL3 and EH3 chondrites contain trichotomous lithologies (1) chondrules and their fragments, (2) polygonal enstatite‐dominated objects, and (3) multiphase metal‐rich nodules. Mineralogical and cosmochemical inventories of lithologies in the same EL3 indicate not only similarities (REE inventory and anomalies in oldhamite) but also distinct differences (sinoite‐enstatite‐graphite relationship). Oldhamite in chondrules and polygonal fragments in EL3 depict negative Eu anomaly attesting a common cosmochemical source. Metal‐dominated nodules in both EL3 and EH3 are conglomerates of metal clasts and sulfide fragments in EH3 and concentrically zoned C‐bearing metal micropebbles (≥25 μm ≤50 μm) in EL3 thus manifesting a frozen in unique primordial accretionary metal texture and composition. Sinoite‐enstatite‐diopside‐graphite textures reveal a nucleation and growth strongly suggestive of fluctuating C/O ratio during their nucleation and growth in the source regions. Mineral inventories, sulfide phase relations, sinoite‐enstatite‐graphite intergrowth, carbon and nitrogen isotopic compositions of graphite, spatial nitrogen abundance in graphite in metal nodules, and last but not least 129I/129Xe and 53Mn/53Cr systematics negate any previously suggested melting episode, pre‐accretionary or dynamic, in parental asteroids. 相似文献
8.
9.
Seismic observations have shown structural variation near the base of the mantle transition zone(MTZ)where subducted cold slabs,as visualized with high seismic speed anomalies(HSSAs),flatten to form stagnant slabs or sink further into the lower mantle.The different slab behaviors were also accompanied by variation of the "660 km" discontinuity depths and low viscosity layers(LVLs) beneath the MTZ that are suggested by geoid inversion studies.We address that deep water transport by subducted slabs and dehydration from hydrous slabs could affect the physical properties of mantle minerals and govern slab dynamics.A systematic series of three-dimensional numerical simulation has been conducted to examine the effects of viscosity reduction or contrast between slab materials on slab behaviors near the base of the MTZ.We found that the viscosity reduction of subducted crustal material leads to a separation of crustal material from the slab main body and its transient stagnation in the MTZ.The once trapped crustal materials in the MTZ eventually sink into the lower mantle within 20-30 My from the start of the plate subduction.The results suggest crustal material recycle in the whole mantle that is consistent with evidence from mantle geochemistry as opposed to a two-layer mantle convection model.Because of the smaller capacity of water content in lower mantle minerals than in MTZ minerals,dehydration should occur at the phase transformation depth,~660 km.The variation of the discontinuity depths and highly localized low seismic speed anomaly(LSSA) zones observed from seismic P waveforms in a relatively high frequency band(~1 Hz) support the hypothesis of dehydration from hydrous slabs at the phase boundary.The LSSAs which correspond to dehydration induced fluids are likely to be very local,given very small hydrogen(H~+) diffusivity associated with subducted slabs.The image of such local LSSA zones embedded in HSSAs may not be necessarily captured in tomography studies.The high electrical conductivity in the MTZ beneath the northwestern Pacific subduction zone does not necessarily require a broad range of high water content homogeneously. 相似文献
10.
Yangting Lin Ahmed El Goresy Sen Hu Jianchao Zhang Philippe Gillet Yuchen Xu Jialong Hao Masaaki Miyahara Ziyuan Ouyang Eiji Ohtani Lin Xu Wei Yang Lu Feng Xuchao Zhao Jing Yang Shin Ozawa 《Meteoritics & planetary science》2014,49(12):2201-2218
Two petrographic settings of carbonaceous components, mainly filling open fractures and occasionally enclosed in shock‐melt veins, were found in the recently fallen Tissint Martian meteorite. The presence in shock‐melt veins and the deuterium enrichments (δD up to +1183‰) of these components clearly indicate a pristine Martian origin. The carbonaceous components are kerogen‐like, based on micro‐Raman spectra and multielemental ratios, and were probably deposited from fluids in shock‐induced fractures in the parent rock of Tissint. After precipitation of the organic matter, the rock experienced another severe shock event, producing the melt veins that encapsulated a part of the organic matter. The C isotopic compositions of the organic matter (δ13C = ?12.8 to ?33.1‰) are significantly lighter than Martian atmospheric CO2 and carbonate, providing a tantalizing hint for a possible biotic process. Alternatively, the organic matter could be derived from carbonaceous chondrites, as insoluble organic matter from the latter has similar chemical and isotopic compositions. The presence of organic‐rich fluids that infiltrated rocks near the surface of Mars has significant implications for the study of Martian paleoenvironment and perhaps to search for possible ancient biological activities on Mars. 相似文献