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1.
Attenuation of compressional waves in peridotite measured as a function of temperature at 200 MPa 总被引：3，自引：0，他引：3
Hiroki Sato I. Selwyn Sacks Tsutomu Murase Gregory Muncill Hiroyuki Fukuyama 《Pure and Applied Geophysics》1988,128(1-2):433-447
A technique has been developed to determine attenuation in rocks at high temperature using a gas-media, high-pressure apparatus. A pulse transmission technique and a spectral ratio method are used to study compressional seismic properties of rocks. Seismic waves are transmitted to and from the sample through buffer rods of mullite. The effect of seismic wave reflections within the sample assembly are cancelled out by taking ratios of the spectra measured at different temperatures. In order to obtain good signal-to-noise ratio for resolving the attenuation at high pressure and temperature, special care is taken in the sample assembly and the ultrasonic coupling between the sample, buffer rods and transducers. A very tight connection of the sample-buffer rod-transducer is essential for obtaining high frequency signals (>300 kHz) at high temperature. A small mass is attached to each outside end of the transducer to drive low frequency signals (<250 kHz) into the sample. Before attenuation measurements, the sample and the buffer rods are tightly compacted in a platinum tube at high pressure and room temperature to ensure pressure seal of the sample assembly. The frequency range of measurement covers 50 to 450 kHz for the sample. Attenuation is very small in the buffer rod compared to the sample for the entire temperature range of the study. Because of the small attenuation, a wide frequency band of 50 kHz to 3.2 MHz can be covered for investigating the attenuation in the buffer rod. The technique has been used to measure attenuation at high confining pressure, and temperatures including sub- and hyper-solidus of upper mantle rocks. Therefore, effects of partial melting on attenuation can be studied.The method is applied to the attenuation measurement in a peridotite as a function of temperature to 1225°C at 200 MPa confining pressure. At high temperature, signal amplitude decays more rapidly at high frequency than at low frequency, from which attenuation (andQ) can be determined using a spectral ratio method. No frequency dependence ofQ is resolved for both the sample and the buffer rod over the entire temperature and frequency ranges of the measurement. The results show thatQ decreases rapidly with increasing temperature even in the temperature range below the solidus of peridotites. Such temperature sensitivity ofQ is probably more useful to probe thermal structure in the upper mantle than that of conductivity at temperatures below the solidus. The results in this study are compared with available seismic velocity, electrical conductivity and solidus data for peridotites, suggesting that there is no discontinuous change in both mechanical and electrical properties of peridotites at the solidus temperature. Even at hypersolidus temperatures, it appears that velocity drops and conductivity increases continuously (not abruptly) with increasing melt fraction. This implies that mechanical and electrical properties of the upper mantle will gradually change at the boundary where the geotherm crosses the solidus. 相似文献
2.
A non-local theory is developed to study the Rayleigh–Taylor instability in an inhomogeneous dusty plasma in the presence of a uniform magnetic field. Using the fluid equations and the dynamics of charged dust grains, an eigenmode equation is derived to study the stability of the mode. Typical space parameters in the vicinity of Saturn are used to investigate the stability of the mode. The growth rate of the Rayleigh–Taylor is found to be drastically higher in a dusty plasma than in a pure plasma. This might have a wider consequence in explaining the origin of low-frequency modes in various situations in the space atmosphere. The effects of the dust charge, and the dust density on the growth rate of the instability are also studied. 相似文献
3.
Namık Aysal Marcel Guillong Tamara Bayanova Mayuko Fukuyama Nicole Leonard İsak Yılmaz Elif Varol Fatma Şişman Tükel Yusuf Kaan Kadıoğlu Nurullah Hanilçi Fulya Uzun Ersin Kaygısız 《Geostandards and Geoanalytical Research》2023,47(2):297-310
Gem quality andradite-rich garnet (IUC-1), obtained from the Miocene trachyte dome near Ankara city (Turkey), has been identified as a potential natural secondary reference material for U-Pb dating. In this study, U-Pb dating was performed in five different laboratories using isotope dilution TIMS and laser ablation ICP-MS to determine the homogeneity of euhedral garnet crystals. The U-Pb ID-TIMS data for IUC-1 yielded 207Pb/235U and 206Pb/238U ages of 20.9 ± 0.4 and 20.6 ± 0.8 Ma respectively, and these values are consistent with U-Pb LA-ICP-MS analyses, in which different garnet crystals yielded ages of 20.8 ± 0.1, 20.7 ± 0.1, 20.7 ± 0.2 and 20.2 ± 0.1 Ma. An andradite (IUC-2) from the Serçeören wollastonite skarn (Turkey) can be used as a secondary reference material provided detailed imaging of the crystals is undertaken. ID-TIMS data yielded 207Pb/235U and 206Pb/238U ages of 20.4 ± 0.4 and 20.9 ± 1.0 Ma respectively, and yielded U-Pb ages on different grains of 20.5 ± 0.1, 20.7 ± 1.0, 20.8 ± 1.7 and 20.9 ± 1.6 Ma. The assigned weighted mean age of IUC-1 (20.4 ± 0.5 Ma, 2s) is proposed as a 2023 reference value. IUC-1 garnet is expected to contribute significantly to rapidly developing garnet geochronology in the near future. 相似文献
4.
-- We have simulated a rupture transition from quasi-static growth to dynamic propagation using the boundary integral equation method. In order to make a physically reasonable model of earthquake cycle, we have to evaluate the dynamic rupture propagation in the context of quasi-static simulation. We used a snapshot of the stress distribution just before the earthquake in the quasi-static simulation. The resultant stress will be fed back to the quasi-static simulation. Since the quasi-static simulation used the slip-and time-dependent constitutive relation, the friction law itself evolves with time. Thus, we used the slip-weakening constitutive relation for dynamic rupture propagation consistent with that used for the quasi-static simulation. We modeled a San Andreas type strike-slip fault, in which two different size asperities existed. 相似文献
5.
K. Maki T‐F. Yui K. Miyazaki M. Fukuyama K‐L. Wang U. Martens M. Grove J. G. Liou 《Journal of Metamorphic Geology》2014,32(3):301-323
Metatexite and diatexite migmatites are widely distributed within the upper amphibolite and granulite facies zones of the Higo low‐P/high‐T metamorphic terrane. Here, we report data from an outcrop in the highest grade part of the granulite facies zone, in which diatexite occurs as a 3 m thick layer between 2 m thick layers of stromatic‐structured metatexite within pelitic gneiss. The migmatites and gneiss contain the same peak mineral assemblage of biotite + plagioclase + quartz + garnet + K‐feldspar with retrograde chlorite ± muscovite and some accessory minerals of ilmenite ± rutile ± titanite + apatite + zircon + monazite ± pyrite ± zinc sulphide ± calcite. Calculated metamorphic P–T conditions are 800–900 °C and 9–12 kbar. Zircon in the diatexite forms elongate euhedral crystals with oscillatory zoning, but no core–rim structure. Zircon from the gneiss and metatexite forms euhedral–subhedral grains comprising inherited cores overgrown by thin rims. The overgrowth rims in the metatexite have lower Th/U ratios than zircon in the diatexite and yield a 206Pb/238U age of 116.0 ± 1.6 Ma, which is older than the 110.1 ± 0.6 Ma 206Pb/238U age derived from zircon in the diatexite. Zircon from the diatexite has variable REE contents with convex upward patterns and flat normalized HREE, whereas the overgrowth rims in the metatexite and gneiss have steep HREE‐enriched patterns; however, both types have similar positive Ce and negative Eu anomalies. 176Hf/177Hf ratios in the overgrowth rims from the metatexite are more variable and generally lower than values from zircon in the diatexite. Based on U–Pb ages, trace element and Hf isotope data, the zircon rims in the metatexite are interpreted to have crystallized from a locally derived melt, following partial dissolution of inherited protolith zircon during anatexis, whereas the zircon in the diatexite is interpreted to have crystallized from a melt that included an externally derived component. By integrating zircon and petrographic data for the migmatites and pelitic gneiss, the metatexite migmatite is interpreted to have formed by in situ partial melting in which the melt did not migrate from the source, whereas the diatexite migmatite included an externally derived juvenile component. The Cretaceous high‐temperature metamorphism of the Higo metamorphic terrane is interpreted to reflect emplacement of mantle‐derived basalts under a volcanic arc along the eastern margin of the Eurasian continent and advection of heat via hybrid silicic melts from the lower crust. Post‐peak crystallization of anatectic melts in a high‐T region at mid‐crustal depths occurred in the interval c. 116–110 Ma, as indicated by the difference in zircon ages from the metatexite and diatexite migmatites. 相似文献
6.
SHRIMP U–Pb zircon dating of the Kinshozan Quartz Diorite from the Kanto Mountains,Japan: Implications for late Paleozoic granitic activity in Japanese Islands 
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下载免费PDF全文 The new result of SHRIMP U–Pb zircon dating of the Kinshozan Quartz Diorite from the Kanto Mountains, Japan, provides 281.5 ± 1.8 Ma. The age is 30 m.y. older than the available age of the Kinshozan Quartz Diorite obtained by hornblende K–Ar method. The new U–Pb zircon age represents the time of crystallization of the Kinshozan Quartz Diorite. The hornblende K–Ar age indicates the time that the Kinshozan Quartz Diorite cooled down to 500 °C which is the closure temperature of the systematics. Permian granites are found in small exposures in Japan, and frequently referred to as 250 Ma granites. The Kinshozan Quartz Diorite is considered as a type of the 250 Ma granites, and the age was influential in establishing a model of Paleozoic tectonic evolution for the Japanese Islands. The new age of the Kinshozan Quartz Diorite provides the opportunity to re‐examine the model. The Kinshozan Quartz Diorite and other Permian granites in the south of the Median Tectonic Line of Japan were constituents of the Paleo‐Ryoke Belt. The geochemical characteristics of the granitic rocks in the Paleo‐Ryoke Belt indicated that the granitic rocks were formed in a primitive island arc environment, and the new trace element data also support this interpretation. Examination of the available data and results of the present study suggests the late Paleozoic granitic activity in Japan as follows. At about 310–290 Ma, arc magmatism generated adakitic granites and other granites in the South Kitakami Belt. Quartz diorite and tonalites of primitive characteristic, such as the Kinshozan Quartz Diorite and granites in the Maizuru Belt appear to have been formed at the immature island arc, and accreted to the Japanese Islands at the end of Paleozoic or early Mesozoic era. During 260–240 Ma, granitic activity took place in the Hida and Maizuru Belts as a part of the Asian continent. 相似文献
7.
Eiichi Fukuyama Shiqing Xu Futoshi Yamashita Kazuo Mizoguchi 《Journal of Seismology》2016,20(4):1207-1215
We investigated the shear strain field ahead of a supershear rupture. The strain array data along the sliding fault surfaces were obtained during the large-scale biaxial friction experiments at the National Research Institute for Earth Science and Disaster Resilience. These friction experiments were done using a pair of meter-scale metagabbro rock specimens whose simulated fault area was 1.5 m?×?0.1 m. A 2.6-MPa normal stress was applied with loading velocity of 0.1 mm/s. Near-fault strain was measured by 32 two-component semiconductor strain gauges installed at an interval of 50 mm and 10 mm off the fault and recorded at an interval of 1 MHz. Many stick-slip events were observed in the experiments. We chose ten unilateral rupture events that propagated with supershear rupture velocity without preceding foreshocks. Focusing on the rupture front, stress concentration was observed and sharp stress drop occurred immediately inside the ruptured area. The temporal variation of strain array data is converted to the spatial variation of strain assuming a constant rupture velocity. We picked up the peak strain and zero-crossing strain locations to measure the cohesive zone length. By compiling the stick-slip event data, the cohesive zone length is about 50 mm although it scattered among the events. We could not see any systematic variation at the location but some dependence on the rupture velocity. The cohesive zone length decreases as the rupture velocity increases, especially larger than \( \sqrt{2} \) times the shear wave velocity. This feature is consistent with the theoretical prediction. 相似文献
8.
Shogo Aoki Kazumasa Aoki Mayuko Fukuyama Masatsugu Ogasawara Yuta Tsuchiya 《Island Arc》2021,30(1):e12420
In this study, the LA-ICP-MS zircon U–Pb dating of the Shimo-ondori diorites in the Shimanto accretionary complex of SW Japan provides ~130 Ma, representing the timing of their crystallization ages. Combined with the geological occurrence, that age clearly indicates that the diorites occur as blocks, not as intrusive rocks as suggested by previous studies. Moreover, the ages of the Shimo-ondori diorites are suggesstive that they could be influential for the estimate of the early-Cretaceous tectonic evolution for the eastern Asian margin. Their whole-rock chemical compositions show high MgO, Ni and Cr contents, and low total FeO/MgO ratios, indicating that they were crystallized from high magnesian andesite (HMA) magmas. Moreover, their TiO2 and REE compositions suggest that they were formed by the same processes as the sanukites. And, the zircon Hf isotopic ratios (εHf [~130 Ma] = +9.9 − +17.5), which is close to or slightly lower than that of the ~130 Ma depleted mantle, suggest that the wedge-mantle materials were predominantly involved in the formation of the dioritic magmas. Their geochronological and geochemical similarities of the Shimo-ondori diorites with the early Cretaceous adakites and HMAs in the eastern Asian margin suggest that they might have been formed possibly by the same slab rollback of the Izanagi plate at the early Cretaceous. After the crystallization of the Shimo-ondori diorites, they were delivered and deposited as blocks in a trench site with the surrounding sedimentary rocks of the Shimanto accretionary complex. 相似文献
9.
We estimated the stress fields of the aftershocks of the 2000 western Tottori earthquake (Mw 6.6) and the northern Hyogo swarm (max Mw 5.2) by a stress tensor inversion of moment tensor solutions reported from the National Research Institute for Earth Science and Disaster Prevention (Japan). The maximum principal stress direction of the western Tottori sequence was estimated as N107°E with a strike–slip regime. In the northern Hyogo swarm, the orientations of the principal stress directions could not be well constrained by the observed data, but after examining the detailed characteristics of the solution, we obtained a most probable solution of N113°E for the σ1 direction. These solutions are consistent with the maximum horizontal directions roughly estimated from the strike directions of large earthquakes occurring geographically between these two seismic activities. We measured the angle between each fault–slip direction and maximum principal stress direction to investigate the frictional properties of earthquakes. The distribution of the angles was forward modeled to estimate the coefficient of friction and the stress ratio, assuming uniformly distributed fault orientations. For the western Tottori sequence, a homogeneous stress field with a coefficient of friction less than 0.4 was estimated. A high stress level was also suggested because very little change occurred in the stress field during the mainshock. For the northern Hyogo sequence, the coefficient of friction was estimated to be between 0.5 and 1.0. 相似文献
10.