宁芜地区玢岩铁矿Pb同位素研究   总被引：16，自引：3，他引：13  

马芳  蒋少涌  姜耀辉  王汝成  凌洪飞  倪培 《地质学报》2006,80(2):279-288

本文对宁芜地区铁矿床中磷灰石和矿石进行了Pb同位素测定。磷灰石的208Pb-232Th等时线年龄为124Ma,与辉长闪长(玢)岩和钠长石岩的形成年龄均相吻合,为成矿时代与成岩时代相近提供了佐证。岩体长石Pb同位素显示,宁芜地区中生代火成岩的原始岩浆受到了大陆壳深部3.3Ga的古老岩系的混染。矿床中矿石铅主要来自赋矿母岩浆。成矿流体具有异常高的Th/U值,表明Th相对U的明显富集,这可能反映了流体中卤素为主要的矿物质迁移载体。  相似文献   

Oxygen isotope thermometry using quartz inclusions in garnet          下载免费PDF全文

R. J. Quinn  K. Kitajima  D. Nakashima  M. J. Spicuzza  J. W. Valley 《Journal of Metamorphic Geology》2017,35(2):231-252

Oxygen isotope ratios of quartz inclusions (QI) within garnet from granulite and amphibolite facies gneisses in the Adirondack Mountains, NY were analysed and used to determine metamorphic temperatures. Primary QI for eight of 12 samples have δ¹⁸O values significantly lower than matrix quartz (MQ). The primary QI retain δ¹⁸O values representative of thermal conditions during garnet crystallization, whereas the δ¹⁸O values of MQ were raised by diffusive exchange with other matrix minerals (e.g. mica and feldspar) during cooling. The δ¹⁸O differences between QI and MQ show that garnet (a mineral with slow diffusion of oxygen) can armour QI from isotopic exchange with surrounding matrix, even during slow cooling. These differences between δ¹⁸O in MQ and QI can further be used to test cooling rates by Fast Grain Boundary diffusion modelling. Criteria for identifying QI that preserve primary compositions and are suitable for thermometry were developed based on comparative tests. Relations between δ¹⁸O and inclusion size, distance of inclusion to host–garnet rim, core–rim zonation of individual inclusions, and presence or absence of petrological features (healed cracks in QI, inclusions in contact with garnet cracks lined by secondary minerals, and secondary minerals along the inclusion grain boundary) were investigated. In this study, 61% of QI preserve primary δ¹⁸O and 39% were associated with features that were linked to reset δ¹⁸O values. If δ¹⁸O in garnet is homogeneous and inclusions are removed, laser‐fluorination δ¹⁸O values of bulk garnet are more precise, more accurate, and best for thermometry. Intragrain δ¹⁸O(Grt) profiles measured in situ by ion microprobe show no δ¹⁸O zonation. Almandine–rich garnet (Alm_60–75) from each sample was measured by laser‐fluorination mass‐spectrometry (LF‐MS) for δ¹⁸O and compared with ion microprobe measurements of δ¹⁸O in QI for thermometry. The Δ¹⁸O(Qz–Grt) values for Adirondack samples range from 2.66 to 3.24‰, corresponding to temperatures of 640–740 °C (A[Qz–Alm] = 2.71). Out of 12 samples that were used for thermometry, nine are consistent with previous estimates of peak temperature (625–800 °C) based on petrological and carbon–isotope thermometry for regional granulite and upper amphibolite facies metamorphism. The three samples that disagree with independent thermometry for peak metamorphism are from the anorthosite–mangerite–charnockite–granite suite in the central Adirondacks and yield temperatures of 640–665 °C, ~100 °C lower than previous estimates. These low temperatures could be interpreted as thermal conditions during late (post‐peak) crystallization of garnet on the retrograde path.  相似文献   

ISRM Suggested Method for Monitoring Rock Displacements Using the Global Positioning System (GPS)     

Norikazu Shimizu  Shinichiro Nakashima  Tomohiro Masunari 《Rock Mechanics and Rock Engineering》2014,47(1):313-328

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Dehydration kinetics of muscovite by in situ infrared microspectroscopy   总被引：2，自引：0，他引：2  

Kazuyo Tokiwai  Satoru Nakashima 《Physics and Chemistry of Minerals》2010,37(2):91-101

Dehydration behavior of muscovite flake was investigated at 760–860°C by using in situ high-temperature IR microspectroscopy for the OH absorption band around 3,620 cm⁻¹. Isothermal kinetic heating experiments at each temperature gave detailed decrease curves of the OH band area with time. These curves have been simulated by the first and second order reactions or mono- and two-dimensional diffusion processes. The mono-dimensional diffusion was found to give the best fit to the experimental data and apparent diffusion coefficients D were determined at 760–860°C with the activation energy of 290 ± 20 kJ/mol. The apparent diffusion coefficients D varied with the sample thickness L. This variation can be explained by an m layers model with a unit length of L′ with a constant diffusion coefficient D′. Therefore, the dehydration process might be rate-limited by mono-dimensional diffusion through tetrahedral silicate sheet perpendicular to (001) planes of muscovite with a unit length of L′.  相似文献   

Dehydration kinetics of antigorite using in situ high-temperature infrared microspectroscopy     

Michiyo Sawai  Ikuo Katayama  Arisa Hamada  Makoto Maeda  Satoru Nakashima 《Physics and Chemistry of Minerals》2013,40(4):319-330

The dehydration kinetics of serpentine was investigated using in situ high-temperature infrared microspectroscopy. The analyzed antigorite samples at room temperature show relatively sharp bands at around 3,655–3,660 cm^?1 (band 1), 3,570–3,595 cm^?1 (band 2), and 3,450–3,510 cm^?1 (band 3). Band 1 corresponds to the Mg–OH bond, and bands 2 and 3 correspond to OH associated with the substitution of Al for Si. Isothermal kinetic heating experiments at temperatures ranging from 625 to 700 °C showed a systematic decrease of the OH band absorbance with heating duration. The one-dimensional diffusion was found to provide the best fit to the experimental data, and diffusion coefficients were determined with activation energies of 219 ± 37 kJ mol^?1 for the total water band area, 245 ± 46 kJ mol^?1 for band 1, 243 ± 57 kJ mol^?1 for band 2, and 256 ± 53 kJ mol^?1 for band 3. The results indicate that the dehydration process is controlled by one-dimensional diffusion through the tetrahedral geometry of serpentine. Fluid production rates during antigorite dehydration were calculated from kinetic data and range from 3 × 10^?4 to 3 × 10^?5  $ {\text{m}}_{\text{fluid}}^{ 3} \,{\text{m}}_{\text{rock}}^{ - 3} \,{\text{s}}^{ - 1} $ . The rates are high enough to provoke hydraulic rupture, since the relaxation rates of rocks are much lower than these values. The results suggest that the rapid dehydration of antigorite can trigger an intermediate-depth earthquake associated with a subducting slab.  相似文献   

The Tiger Sulfide Chimney,Yonaguni Knoll IV Hydrothermal Field,Southern Okinawa Trough,Japan: The First Reported Occurrence of Pt–Cu–Fe‐Bearing Bismuthinite and Sn‐Bearing Chalcopyrite in an Active Seafloor Hydrothermal System     

Kaul Gena  Hitoshi Chiba  Katsuo Kase  Kazuo Nakashima  Daizo Ishiyama 《Resource Geology》2013,63(4):360-370

A sulfide chimney ore sampled from the flank of the active Tiger vent area in the Yonaguni Knoll IV hydrothermal field, south Okinawa trough, consists of anhydrite, pyrite, sphalerite, galena, chalcopyrite and bismuthinite. Electron microprobe analysis indicates that the chalcopyrite contains up to 2.4 wt% Sn, whereas bismuthinite contains up to 1.7 wt% Pt, 0.8 wt% Cu and 0.5 wt% Fe. The Sn‐rich chalcopyrite and Pt–Cu–Fe‐bearing bismuthinite are the first reported occurrence of such minerals in an active submarine hydrothermal system. The results confirm that Sn enters the chalcopyrite as a solid solution towards stannite by the coupled substitution of Sn⁴⁺Fe²⁺ for Fe³⁺Fe³⁺, whereas Pt, Cu and Fe enter the bismuthinite structure as a solid solution during rapid nucleation. The fluid inclusions homogenization temperatures in anhydrite (220–310°C) and measured end‐member temperature of the vent fluids on‐site (325°C) indicate that Sn‐bearing chalcopyrite and Pt–Cu–Fe‐bearing bismuthinite express the original composition of the minerals that precipitated as metastable phases at a temperature above 300°C. The result observed in this study implies that sulfides in ancient volcanogenic massive sulfide deposits have similar trace element distribution during nucleation but it is remobilised during diagenesis, metamorphism or supergene enrichment processes.  相似文献   

Fall,classification, and exposure history of the Mifflin L5 chondrite     

Noriko T. Kita  Kees C. Welten  John W. Valley  Michael J. Spicuzza  Daisuke Nakashima  Travis J. Tenner  Takayuki Ushikubo  Glenn J. MacPherson  Linda Welzenbach  Philipp R. Heck  Andrew M. Davis  Matthias M. M. Meier  Rainer Wieler  Marc W. Caffee  Matthias Laubenstein  Kunihiko Nishiizumi 《Meteoritics & planetary science》2013,48(4):641-655

The Mifflin meteorite fell on the night of April 14, 2010, in southwestern Wisconsin. A bright fireball was observed throughout a wide area of the midwestern United States. The petrography, mineral compositions, and oxygen isotope ratios indicate that the meteorite is a L5 chondrite fragmental breccia with light/dark structure. The meteorite shows a low shock stage of S2, although some shock‐melted veins are present. The U,Th‐He age is 0.7 Ga, and the K‐Ar age is 1.8 Ga, indicating that Mifflin might have been heated at the time of the 470 Ma L‐chondrite parent body breakup and that U, Th‐He, and K‐Ar ages were partially reset. The cosmogenic radionuclide data indicate that Mifflin was exposed to cosmic rays while its radius was 30–65 cm. Assuming this exposure geometry, a cosmic‐ray exposure age of 25 ± 3 Ma is calculated from cosmogenic noble gas concentrations. The low ²²Ne/²¹Ne ratio may, however, indicate a two‐stage exposure with a longer first‐stage exposure at high shielding. Mifflin is unusual in having a low radiogenic gas content combined with a low shock stage and no evidence of late stage annealing; this inconsistency remains unexplained.  相似文献   

Cosmic‐ray exposure age and heliocentric distance of the parent body of the Rumuruti chondrite PRE 95410     

Tomoya Obase  Daisuke Nakashima  Tomoki Nakamura  Keisuke Nagao 《Meteoritics & planetary science》2020,55(5):1031-1047

We measured concentrations and isotopic ratios of noble gases in the Rumuruti (R) chondrite Mount Prestrud (PRE) 95410, a regolith breccia exhibiting dark/light structures. The meteorite contains solar and cosmogenic noble gases. Based on the solar and cosmogenic noble gas compositions, we calculated a heliocentric distance of its parent body, a cosmic‐ray exposure age on the parent body regolith (parent body exposure age), and a cosmic‐ray exposure age in interplanetary space (space exposure age) of the meteorite. Assuming a constant solar wind flux, the estimated heliocentric distance was smaller than 1.4 ± 0.3 au, suggesting inward migration from the asteroid belt regions where the parent body formed. The largest known Mars Trojan 5261 Eureka is a potential parent body of PRE 95410. Alternatively, it is possible that the solar wind flux at the time of the parent body exposure was higher by a factor of 2–3 compared to the lunar regolith exposure. In this case, the estimated heliocentric distance is within the asteroid belt region. The parent body exposure age is longer than 19.1 Ma. This result indicates frequent impact events on the parent body like that recorded for other solar‐gas‐rich meteorites. Assuming single‐stage exposure after an ejection event from the parent body, the space exposure age is 11.0 ± 1.1 Ma, which is close to the peak of ~10 Ma in the exposure age distribution for the solar‐gas‐free R chondrites.  相似文献   

Application of headed studs in steel fiber reinforced cementitious composite slab of steel beam-column connection     

Masayoshi Nakashima 《地震工程与工程振动(英文版)》2012,11(1):11-21

Steel fiber reinforced cementitous composites(SFRCC)is a promising material with high strength in both compression and tension compared with normal concrete.The ductility is also greatly improved because of 6%volume portion of straight steel fibers.A steel beam-column connection with Steel fiber reinforced cementitous composites(SFRCC) slab diaphragms is proposed to overcome the damage caused by the weld.The push-out test results suggested that the application of SFRCC promises larger shear forces transferred through headed studs allocated in a small area in the slab. Finite element models were developed to simulate the behavior of headed studs.The failure mechanism of the grouped arrangement is further discussed based on a series of parametric analysis.In the proposed connection,the SFRCC slab is designed as an exterior diaphragm to transfer the beam flange load to the column face.The headed studs are densely arranged on the beam flange to connect the SFRCC slab diaphragms and steel beams.The seismic performance and failure mechanism of the SFRCC slab diaphragm beam-column connection were investigated based on the cyclic loading test.Beam hinge mechanism was achieved at the end of the SFRCC slab diaphragm by using sufficient studs and appropriate rebars in the SFRCC slab.  相似文献   

Earthquake engineering research needs in light of lessons learned from the 2011 Tohoku earthquake     

Masayoshi Nakashima  Oren Lavan  Masahiro Kurata  Yunbiao Luo 《地震工程与工程振动(英文版)》2014,(Z1)

Earthquake engineering research and development have received much attention since the first half of the twentieth century. This valuable research presented a huge step forward in understanding earthquake hazard mitigation,which resulted in appreciable reduction of the effects of past earthquakes. Nevertheless,the 2011 Tohoku earthquake and the subsequent tsunami resulted in major damage. This paper presents the timeline of earthquake mitigation and recovery,as seen by the authors. Possible research directions where the authors think that many open questions still remain are identified. These are primarily based on the important lessons learned from the 2011 Tohoku earthquake.  相似文献