The Hirabayashi borehole (Awaji Island, Japan) was drilled by the Geological Survey of Japan (GSJ) 1 year after the Hyogo-ken Nanbu (Kobe) earthquake (1995, MJMA=7.2). This has enabled scientists to study the complete sequence of deformation across the active Nojima fault, from undeformed granodiorite to the fault core. In the fault core, different types of gouge and fractures have been observed and can be interpreted in terms of a complex history of faulting and fluid circulation. Above the fault core and within the hanging wall, compacted cataclasites and gouge are cut by fractures which show high apparent porosity and are filled by 5–50 μm euhedral and zoned siderite and ankerite crystals. These carbonate-filled fractures have been observed within a 5.5-m-wide zone above the fault, but are especially abundant in the vicinity (1 m) of the fault. The log-normal crystal size distributions of the siderite and ankerite suggest that they originated by decaying-rate nucleation accompanied by surface-controlled growth in a fluid saturated with respect to these carbonates. These carbonate-filled fractures are interpreted as the result of co-seismic hydraulic fracturing and upward circulation of fluids in the hanging wall of the fault, with the fast nucleation of carbonates attributed to a sudden fluid or CO2 partial pressure drop due to fracturing. The fractures cut almost all visible structures at a thin section scale, although in some places, the original idiomorphic shape of carbonates is modified by a pressure-solution mechanism or the carbonate-filled fractures are cut and brecciated by very thin gouge zones; these features are attributed to low and high strain-rate mechanisms, respectively. The composition of the present-day groundwater is at near equilibrium or slightly oversaturated with respect to the siderite, calcite, dolomite and rhodochrosite. Taken together, this suggests that these fractures formed very late in the evolution of the fault zone, and may be induced by co-seismic hydraulic fracturing and circulation of a fluid with a similar composition to the present-day groundwater. They are therefore potentially related to recent earthquake activity (<1.2 Ma) on the Nojima fault. 相似文献
An analysis of the textures of pallasites has been made using data concerning the kinetic and rheological properties of silicates and metals. Pallasites containing rounded olivines (e.g., the Springwater and Brehnam pallasites) have been heated to above the solidus temperature of the metallic iron phases, ~ 1270 K. The rounded olivines of grain size 0.5–1.0 cm observed in the Springwater pallasites were formed between 1270 and 1370 K. On the other hand, those of grain size 0.5–1.0 mm as found in the Brehnam pallasites may have been heated to above 1370 K; however, the duration of heating at such high temperatures must have been less than 5 × 103 y. Pallasites containing angular olivines with microscopically rounded corners (e.g., the Eagle Station, Dora pallasites) have suffered shock events fracturing the olivine grains, which may correspond to collisions during the accretional stage of the parent body, and experienced successive annealing during cooling from a temperature between 1150 and 1270 K. 相似文献
Pressure effects on the lattice parameters of β- and γ-Mg2SiO4 have been measured at room temperature and at pressures up to 100 kbar using a multi-anvil high-pressure X-ray diffraction apparatus. The volume changes (ΔV/V0) at 90 kbar are 5.4 · 10?2 and 4.2 · 10?2 for β- and γ-Mg2SiO4, respectively. Isothermal bulk moduli at zero pressure have been calculated from least-square fits of the data to straight lines. They turn out to be 1.66 ± 0.4 and 2.13 ± 0.1 Mbar for β- and γ-Mg2SiO4, respectively. The α → γ transition obeys Wang's linear Vφ?ρ relation but the α → β transition does not. 相似文献
Melting relations of primitive peridotite were studied up to 25 GPa. The change of the liquidus phase from olivine to majorite occurs at 16 GPa. We confirmed the density crossover of the FeO-rich peridotite melt and the equilibrium olivine (Fo90) at 7 GPa. Sinking of equilibrium olivine (Fo95) in the primitive peridotite melt was observed up to 10 GPa. The compression curves of FeO-rich peridotitic and komatiite melts reported in this and earlier work suggest that the density crossover in the Earth's mantle will be located at 11–12 GPa at 2000°C, consistent with an previous estimation by C.B. Agee and D. Walker.
The density crossover can play a key role in the Moon and the terrestrial planets, such as the Earth, Venus and Mars. Majorite and some fraction of melt could have separated from the ascending diapir and sunk downwards at the depths below the density crossover. This process could have produced a garnet-rich transition zone in the Earth's mantle. The density crossover may exist in the FeO-rich lunar mantle at around the center of the Moon. The density crossover which exists at the depth of 600 km in the Martian mantle plays a key role in producing a fractionated mantle, which is the source the parent magmas of the SNC meteorites. 相似文献
Between late January and March of 1966, the western Subarctic region was widely investigated by MVArgo and MVG. B. Kelez. That is the first oceanographic measurement in this region during winter season. Oceanographic conditions and relative transports are discussed using these data. The Alaskan Stream which is closely related with the formation of the salmon fishing ground, is continuous as far west as long. 170°E and the westward transport of 8×106m3/sec occurs across long. 165°W. That are similar to the conditions in summer. The isolated warm water mass separated from the Alaskan Stream is more clearly defined as a clockwise gyre at the west of Komandorski Ridge. Transport of approximately 9×106m3/sec in the East Kamchatka Current reaches east of the Kurile Islands, where its water, mixing with the Okhotsk Sea water, forms the Oyashio Current having the volume transport of 7×106m3/sec. Generally, the circulation pattern in winter is similar to that in summer. Schematic diagram of relative transport and circulation in the Subarctic region in the North Pacific Ocean in winter is proposed. 相似文献
In 2006, we started construction of an observation network of 12 stations in and around Shikoku and the Kii Peninsula to conduct research for forecasting Tonankai and Nankai earthquakes. The purpose of the network is to clarify the mechanism of past preseismic groundwater changes and crustal deformation related to Tonankai and Nankai earthquakes. Construction of the network of 12 stations was completed in January 2009. Work on two stations, Hongu-Mikoshi (HGM) and Ichiura (ICU), was finished earlier and they began observations in 2007. These two stations detected strain changes caused by the slow-slip events on the plate boundary in June 2008, although related changes in groundwater levels were not clearly recognized. 相似文献
The structure of a single crystal hydrous ringwoodite, Mg1.89Si0.98H0.30O4 synthesized at conditions of 1300?°C and 20?GPa has been analyzed. Crystallographic data for hydrous ringwoodite obtained are; Cubic with Space group: Fd3m (no. 227). a= 8.0693(5)?Å, V=526.41(9)?Å3, Z=8, Dcalc= 3.48?g?cm?3. The results of site occupancy refinement using higher angle reflections showed the existence of a small degree of Mg2+-Si4+ disorder in the structure such as (Mg1.84Si0.05□0.11)(Si0.93Mg0.05□0.02)H0.30O4. The IR and Raman spectra were measured and OH vibration spectra were observed. A broad absorption band was observed in the IR spectrum and the maxima were observed at 3160?cm?1 in the IR and at 3165?cm?1 and 3685?cm?1 in relatively sharp Raman spectra, which suggest that locations between O-O pairs around the octahedral 16c and 16d sites are possible sites for hydrogen. 相似文献
A new phase of AlOOH (tentatively called δ-AlOOH) was synthesized at 21?GPa and 1000?°C and its crystal structure was identified by a powder X-ray diffraction method. Rietveld refinement revealed that this aluminum oxide hydroxide has an orthorhombic unit cell, a?=?4.7134(1) Å, b?=?4.2241(1) Å, c?=?2.83252(8) Å, V?=?56.395 (5) Å3, and Z?=?2 in the space group of P21?nm. A calculated density is 3.533?g?cm?3, which is about 4.48 and 15.04% denser than that of diaspore and boehmite, respectively. The δ-[Al0.86Mg0.07Si0.07]OOH is also stable at 21?GPa and 1000?°C, coexisting with majorite and phase egg, and its cell parameters are a?=?4.710(1) Å, b?=?4.215(1) Å, c?=?2.839(1) Å, and V?=?56.37(1) Å3. 相似文献