Geology of the summit limestone of Mount Qomolangma (Everest) and cooling history of the Yellow Band under the Qomolangma detachment     

Harutaka  Sakai  Minoru  Sawada  Yutaka  Takigami  Yuji  Orihashi  Tohru  Danhara  Hideki  Iwano  Yoshihiro  Kuwahara  Qi  Dong  Huawei  Cai  Jianguo  Li 《Island Arc》2005,14(4):297-310

Abstract   Newly discovered peloidal limestone from the summit of Mount Qomolangma (Mount Everest) contains skeletal fragments of trilobites, ostracods and crinoids. They are small pebble-sized debris interbedded in micritic bedded limestone of the Qomolangma Formation, and are interpreted to have been derived from a bank margin and redeposited in peri-platform environments. An exposure of the Qomolangma detachment at the base of the first step (8520 m), on the northern slope of Mount Qomolangma was also found. Non-metamorphosed, strongly fractured Ordovician limestone is separated from underlying metamorphosed Yellow Band by a sharp fault with a breccia zone. The ⁴⁰Ar–³⁹Ar ages of muscovite from the Yellow Band show two-phase metamorphic events of approximately 33.3 and 24.5 Ma. The older age represents the peak of a Barrovian-type Eo-Himalayan metamorphic event and the younger age records a decompressional high-temperature Neo-Himalayan metamorphic event. A muscovite whole-rock ⁸⁷Rb–⁸⁶Sr isochron of the Yellow Band yielded 40.06 ± 0.81 Ma, which suggests a Pre-Himalayan metamorphism, probably caused by tectonic stacking of the Tibetan Tethys sediments in the leading margin of the Indian subcontinent. Zircon and apatite grains, separated from the Yellow Band, gave pooled fission-track ages of 14.4 ± 0.9 and 14.4 ± 1.4 Ma, respectively. These new chronologic data indicate rapid cooling of the hanging wall of the Qomolangma detachment from approximately 350°C to 130°C during a short period (15.5–14.4 Ma).  相似文献   

Geographical Distribution of 3He/4He Ratios in the Chugoku District, Southwestern Japan     

Yuji Sano  Naoto Takahata  Tetsuzo Seno 《Pure and Applied Geophysics》2006,163(4):745-757

We have collected 34 hot spring and mineral spring gases and waters in the Chugoku and Kansai districts, Southwestern Japan and measured the ³He/⁴He and ⁴He/²⁰Ne ratios by using a noble gas mass spectrometer. Observed ³He/⁴He and ⁴He/²⁰Ne ratios range from 0.054 R_atm to 5.04 R_atm (where R_atm is the atmospheric ³He/⁴He ratio of 1.39 × 10⁻⁶) and from 0.25 to 36.8, respectively. They are well explained by a mixing of three components, mantle-derived, radiogenic, and atmospheric helium dissolved in water. The ³He/⁴He ratios corrected for air contamination are low in the frontal arc and high in the volcanic arc regions, which are consistent with data of subduction zones in the literature. The geographical contrast may provide a constraint on the position of the volcanic front in the Chugoku district where it was not well defined by previous works. Taking into account the magma aging effect, we cannot explain the high ³He/⁴He ratios of the volcanic arc region by the slab melting of the subducting Philippine Sea plate. The other source with pristine mantle material may be required. More precisely, the highest and average ³He/⁴He ratios of 5.88 R_atm and 3.8±1.6 R_atm, respectively, in the narrow regions near the volcanic front of the Chugoku district are lower than those in Kyushu and Kinki Spot in Southwestern Japan, but close to those in NE Japan. This suggests that the magma source of the former may be related to the subduction of the Pacific plate, in addition to a slight component of melting of the Philippine Sea slab.  相似文献   

Geochemistry of the volcano-hydrothermal system of El Chichón Volcano, Chiapas, Mexico     

Yuri Taran  Tobias P. Fischer  Boris Pokrovsky  Yuji Sano  Maria Aurora Armienta  Jose Luis Macias 《Bulletin of Volcanology》1998,59(6):436-449

 The 1982 eruption of El Chichón volcano ejected more than 1 km³ of anhydrite-bearing trachyandesite pyroclastic material to form a new 1-km-wide and 300-m-deep crater and uncovered the upper 500 m of an active volcano-hydrothermal system. Instead of the weak boiling-point temperature fumaroles of the former lava dome, a vigorously boiling crater spring now discharges  / 20 kg/s of Cl-rich (∼15 000 mg/kg) and sulphur-poor ( / 200 mg/kg of SO₄), almost neutral (pH up to 6.7) water with an isotopic composition close to that of subduction-type magmatic water (δD=–15‰, δ¹⁸O=+6.5‰). This spring, as well as numerous Cl-free boiling springs discharging a mixture of meteoric water with fumarolic condensates, feed the crater lake, which, compared with values in 1983, is now much more diluted (∼3000 mg/kg of Cl vs 24 030 mg/kg), less acidic (pH=2.6 vs 0.56) and contains much lower amounts of S ( / 200 mg/kg of SO₄, vs 3550 mg/kg) with δ³⁴S=0.5–4.2‰ (+17‰ in 1983). Agua Caliente thermal waters, on the southeast slope of the volcano, have an outflow rate of approximately 100 kg/s of 71  °C Na–Ca–Cl water and are five times more concentrated than before the eruption (B. R. Molina, unpublished data). Relative N₂, Ar and He gas concentrations suggest extensional tectonics for the El Chichón volcanic centre. The ³He/⁴He and ⁴He/²⁰Ne ratios in gases from the crater fumaroles (7.3R_a, 2560) and Agua Caliente hot springs (5.3R_a, 44) indicate a strong magmatic contribution. However, relative concentrations of reactive species are typical of equilibrium in a two-phase boiling aquifer. Sulphur and C isotopic data indicate highly reducing conditions within the system, probably associated with the presence of buried vegetation resulting from the 1982 eruption. All Cl-rich waters at El Chichón have a common source. This water has the appearence of a "partially matured" magmatic fluid: condensed magmatic vapour neutralized by interaction with fresh volcaniclastic deposits and depleted in S due to anhydrite precipitation. Shallow ground waters emerging around the volcano from the thick cover of fresh pumice deposits (Red waters) are Ca–SO₄–rich and have a negative oxygen isotopic shift, probably due to ongoing formation of clay at low temperatures. Received: 21 July 1997 / Accepted: 4 December 1997  相似文献   

High-frequency earthquakes at White Island volcano, New Zealand: insights into the shallow structure of a volcano-hydrothermal system     

Yuji Nishi  Steven Sherburn  Bradley J. Scott  Mituhiko Sugihara 《Journal of Volcanology and Geothermal Research》1996,72(3-4)

Volcano-tectonic earthquakes at White Island are concentrated in a single seismically active zone, southeast of the active vents and at depths of less than 1 km. A few deeper earthquakes also occur beneath the active vents. A composite focal mechanism indicates that the stress regime in the shallow seismic zone is N-S extensional. Shallow seismicity occurs within the main volume of the volcano-hydrothermal system that underlies the Main Crater floor, and we interpret this as a region where the rocks have been weakened by past magmatic intrusions, elevated pore fluid pressure and physico-chemical effects of acid volcanic fluids, thereby allowing preferential seismic failure. Brittle seismic failure within this region requires a temperature less than about 400 °C, and implies high horizontal temperature gradients close to the active craters and fumaroles. Spasmodic bursts events are also a result of brittle failure, but occur close to zones of significant permeability in response to changes in local fluid pressure.  相似文献   

7th Annual Report on the International Status of Engineering Geology—Year 2001: Encompassing hydrogeology, environmental geology and the applied geosciences     

Allen W Hatheway  Yuji Kanaori 《Engineering Geology》2002,65(1):47-79

The year was marked by noteworthy advances in multinational consortia of commercial firms and of forward-looking universities. Again, the tenor of the practice of Engineering Geology has picked up. Not to be in the vanguard does indeed mean that one languishes in the dust raised by those on the move. Engineering geologists must understand an infinity of challenges stemming from land development, environmental protection and cleanup and resource development. This is a profession in which age can bring wisdom and increased competence.Most practitioners were busy in 2001; more than 80% of ASFE member companies report that business has increased or stayed the same for the past 6 months. Sixty percent of practitioners expect that their 2002 revenues will be stable or increase for Year 2002.  相似文献   

Decreases in turbidity during neap tides initiate late winter blooms of Eucampia zodiacus in a macrotidal embayment     

Yuji Ito  Toshiya Katano  Naoki Fujii  Masumi Koriyama  Kenji Yoshino  Yuichi Hayami 《Journal of Oceanography》2013,69(4):467-479

Eucampia zodiacus Ehrenberg is harmful, as it causes reduction in the quality of the aquacultured Porphyra thalli owing to nutrient depletions during dense blooms in the late winter in the macrotidal Ariake Sea, Japan. To understand the mechanism of bloom development, changes in the abundance of E. zodiacus during a bloom were investigated along vessel transects from February to April 2012. In addition, marine environmental variables were continuously monitored by the Ariake Sea Monitoring Tower, which revealed that turbidity periodically decreased during neap tides. During the 16 February neap tide, a high Secchi depth (4.3 m) was recorded at offshore stations and the Z _1% depth, at which the light intensity attenuates to 1 % of that at the sea surface, exceeded the water depth. On 16 February, the abundance of E. zodiacus was 52–732 cells mL^?1, peaking at 7.0 m depth offshore. Subsequently, abundance increased at all stations. During the 22 February spring tide, abundance became vertically uniform. On 19 March, abundance at the tower reached 3758 cells mL^?1 at the surface. We conclude that an improvement in light conditions in the deeper layer triggered the bloom, although the size and the duration of the bloom were determined by nutrient availability. Thus, decreases in turbidity during neap tides and subsequent strong vertical mixing during spring tides may be instrumental in the population dynamics of the large diatom E. zodiacus in macrotidal environments.  相似文献   

基于遥感的江苏省区域建设用海集约利用现状评价     

王玉洁  汤茹男  蔡雯沁  张慧铭  潘铄宇  张东 《海洋开发与管理》2019,36(11):15-22

区域建设用海是海域使用的一种重要方式。文章以土地与海域集约利用评价为参照,从"投入—产出"的角度出发构建了区域建设用海集约利用评价指标体系,利用遥感解译方法从2017年高分影像中提取并计算了江苏省12个区域建设用海的主要评价指标值,应用TOPSIS模型评价了江苏省沿海已建项目的集约用海现状。研究表明:①江苏省区域建设用海开发利用程度较低,53.2%的土地处于未利用状态,农渔业为面积占比最小的用地类型,江苏省对第二、第三产业的发展更为重视。②已有的开发活动中,人工设施面积较小,建筑与道路等面积占比远小于生态面积,区域生态健康状况良好。③根据指标计算,江苏省区域建设用海集约利用评价得分集中在0.4～0.6,集约利用程度整体较低,不同项目集约化利用程度差异较小,主要原因在于项目投资强度两极分化,道路等基础设施不够完善等。④从不同用海类型来看,交通运输用海集约利用程度最高,其用海结构布局最适宜,效率最高。文章所建指标具有指向性,应用TOPSIS模型进行无须赋予权重,因此更能客观真实地反映江苏省区域建设用海的集约利用情况。  相似文献   

强震区轻骨料混凝土桥梁地震响应研究          下载免费PDF全文

惠迎新  台玉吉  金宝宏  王海东 《世界地震工程》2019,35(1):193-200

为研究轻骨料混凝土桥梁的地震响应,以一座强震区典型连续梁桥为研究对象,在考虑轻骨料混凝土材料特性基础上建立桥梁结构有限元分析模型,采用非线性动力时程分析法进行结构地震响应分析,研究轻骨料混凝土材料布设位置对桥梁结构动力特性和地震响应的影响,并从内力和位移响应方面与普通混凝土桥梁进行对比。结果表明:与普通混凝土桥梁相比,仅上部结构或仅下部结构采用轻骨料混凝土对降低桥墩内力并不明显,而全桥采用轻骨料混凝土能够显著降低桥墩内力。轻骨料混凝土桥梁与普通混凝土桥梁地震内力和位移响应变化趋势不同,桥墩塑性发展程度和时间存在差异。采用轻骨料混凝土桥梁方案时,应综合考虑结构质量、刚度分布及材料塑性特性与普通混凝土桥梁的不同,合理确定抗震设计方案。  相似文献   

渔港防台风等级评估研究 ——以霞关一级渔港为例          下载免费PDF全文

韩小燕  梁连松  董宇佳  姚辰阳 《海洋开发与管理》2020,37(5):57-62

文章通过对历史上影响苍南近岸海域的24场风暴潮过程进行分析筛选,确定1323“菲特”为最危险台风路径基础,设计了8~17级的间距为22.5 km的18条构造台风路径,采用FVCOM浪、潮、流耦合模式分别计算潮位场、流场和浪场分布,通过分析渔港岸线是否淹没、锚泊地是否船只走锚、防波堤防浪能力3个指标确定单项防台评估能力,按“就低不就高”的原则最终确定霞关一级渔港的防台风等级为9级,并且渔船锚泊是渔港的薄弱环节,最后结合研究过程中发现的问题,提出渔港防台风建议。  相似文献   

The Southern Annular Mode and opposite-phased Basin Mode of the Southern Ocean circulation     

Yuji Iijima  Shigeru Aoki  Kunio Kutsuwada 《Journal of Oceanography》2009,65(1):53-60

Over the Southern Ocean the dominant modes of the atmospheric field are known as the Southern Annular Mode (SAM) or Antarctic Oscillation, and the Pacific South American (PSA) pattern. Statistical analysis of sea surface wind (SSW) from satellite observation revealed two leading modes of SAM-like and PSA patterns. In the high latitudes, the SAM-like pattern of the SSW had a large amplitude over the Bellingshausen Basin and Australian-Antarctic Basin, with opposite phase between the two basins. On the intraseasonal time scale, large-scale sea surface height (SSH) also had notable variability, showing a basin-scale anti-phase mode over the two basins. To explain the response of oceanic variations to these atmospheric modes, we analyzed the relationship between the dominant modes of wind stress and large-scale SSH on the intraseasonal time scale. The SAM-like pattern of wind stress was correlated with the SSH variation over the two basins. The SSH basin mode was most simply explained by a simple barotropic response to the SAM-like mode of wind stress, with the curl of opposite phase between the two basins. We conclude that the zonal asymmetry of the wind field of the SAM plays an important role in driving the antiphase SSH basin modes.  相似文献