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991.
东秦岭东段新发现的沙坡岭细脉浸染型钼矿地质特征、Re-Os同位素年龄及其地质意义 总被引:7,自引:0,他引:7
豫西洛宁沙坡岭钼矿床位于华北克拉通南缘东秦岭钼矿带东段,是新近发现的赋存于太古宙太华群变质岩中的细脉浸染型钼矿床。本文对其地质特征进行了研究,并初步测定了1个辉钼矿样品的Re-Os同位素年龄,获得模式年龄为126.8±1.7Ma,表明沙坡岭钼矿形成于燕山期,接近金堆城、雷门沟钼矿的形成时代,Re同位素含量显示其地幔来源的特征。沙坡岭钼矿形成机制错综复杂,有待进一步研究,特别是深部钻孔工程验证工作,对于验证深部是否隐伏着与成矿相关的斑岩体、储量更大的斑岩型钼矿有着重要作用,找矿潜力巨大。 相似文献
992.
Hongyan Geng Min Sun Chao Yuan Wenjiao Xiao Weisheng Xian Guochun Zhao Lifei Zhang Kenny Wong Fuyuan Wu 《Chemical Geology》2009,266(3-4):373-398
Voluminous granitic intrusions are distributed in the West Junggar, NW China, and they can be classified as the dioritic rocks, charnockite and alkali-feldspar granite groups. The dioritic rocks (SiO2 = 50.4–63.8 wt.%) are calc-alkaline and Mg enriched (average MgO = 4.54 wt.%, Mg# = 0.39–0.64), with high Sr/Y ratios (average = 21.2), weak negative Eu (average Eu/Eu = 0.80) and pronounced negative Nb–Ta anomalies. Their Sr–Nd and zircon Hf isotopic compositions ((87Sr/86Sr)i = 0.7035–0.7042, εNd(t) = 4.5–7.9, εHf(t) = 14.1–14.5) show a depleted mantle-like signature. These features are compatible with adakites derived from partial melting of subducted oceanic crust that interacted with mantle materials. The charnockites (SiO2 = 60.0–65.3 wt.%) show transitional geochemical characteristics from calc-alkaline to alkaline, with weak negative Eu (average Eu/Eu = 0.75) but pronounced negative Nb–Ta anomalies. Sr–Nd and zircon Hf isotopic compositions ((87Sr/86Sr)i = 0.7037–0.7039, εNd(t) = 5.2–8.0, εHf(t) = 13.9–14.7) also indicate a depleted source, suggesting melts from a hot, juvenile lower crust. Alkali-feldspar granites (SiO2 = 70.0–78.4 wt.%) are alkali and Fe-enriched, and have distinct negative Eu and Nb–Ta anomalies (average Eu/Eu = 0.26), low Sr/Y ratios (average = 2.11), and depleted Sr–Nd and zircon Hf isotopic compositions ((87Sr/86Sr)i = 0.7024–0.7045, εNd(t) = 5.1–8.9, εHf(t) = 13.7–14.2). These characteristics are also comparable with those of rocks derived from juvenile lower crust. Despite of the differences in petrology, geochemistry and possibly different origins, zircon ages indicate that these three groups of rocks were coevally emplaced at ~ 305 Ma.A ridge subduction model can account for the geochemical characteristics of these granitoids and coeval mafic rocks. As the “slab window” opened, upwelling asthenosphere provided enhanced heat flux and triggered voluminous magmatisms: partial melting of the subducting slab formed the dioritic rocks; partial melting of the hot juvenile lower crust produced charnockite and alkali-feldspar granite, and partial melting in the mantle wedge generated mafic rocks in the region. These results suggest that subduction was ongoing in the Late Carboniferous and, thus support that the accretion and collision in the Central Asian Orogenic Belt took place in North Xinjiang after 305 Ma, and possibly in the Permian. 相似文献
993.
994.
海拉尔盆地兴安岭群上库力组自下而上可分出5个重矿物组合:磁黄铁矿-锆石-白钛石-锐钛矿组合,黄铁矿高含量组合,黑云母-白钛石-锆石-钛铁矿组合,菱铁矿-白钛石-黑云母-电气石组合,白钛石-黑云母-菱铁矿-石榴子石组合.不稳定矿物含量高,不同层段呈现高低韵律性变化则与火山-沉积作用强弱交替变化的环境有关.较高的ATi指数反映母岩应为中-酸性火山岩.ZTR指数不高说明重矿物的成熟度较低.由下至上陆源重矿物变少,尤其是上库力组D段(凝灰岩段),自生黄铁矿占很高的百分比. 相似文献
995.
996.
本文讨论了SDSS的概念和基本理论,以决策支持为目标,面向半结构化和非结构化问题,用模型驱动的SDSS,是GIS未来的发展方向。在技术上用C语言实现了SDSS支撑软件的设计,并应用于国家科技攻关课题“三川河流域区域治理与开发信息系统”,取得了良好效果;同时对SDSS开发中存在问题作了讨论。 相似文献
997.
Y. Liu J. T. Hoeksema P. H. Scherrer J. Schou S. Couvidat R. I. Bush T. L. Duvall Jr K. Hayashi X. Sun X. Zhao 《Solar physics》2012,279(1):295-316
We compare line-of-sight magnetograms from the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO) and the Michelson Doppler Imager (MDI) onboard the Solar and Heliospheric Observatory (SOHO). The line-of-sight magnetic signal inferred from the calibrated MDI data is greater than that derived from the HMI data by a factor of 1.40. This factor varies somewhat with center-to-limb distance. An upper bound to the random noise for the 1′′ resolution HMI 720-second magnetograms is 6.3 Mx?cm?2, and 10.2 Mx?cm?2 for the 45-second magnetograms. Virtually no p-mode leakage is seen in the HMI magnetograms, but it is significant in the MDI magnetograms. 12-hour and 24-hour periodicities are detected in strong fields in the HMI magnetograms. The newly calibrated MDI full-disk magnetograms have been corrected for the zero-point offset and underestimation of the flux density. The noise is 26.4 Mx?cm?2 for the MDI one-minute full-disk magnetograms and 16.2 Mx?cm?2 for the five-minute full-disk magnetograms observed with four-arcsecond resolution. The variation of the noise over the Sun’s disk found in MDI magnetograms is likely due to the different optical distortions in the left- and right-circular analyzers, which allows the granulation and p-mode to leak in as noise. Saturation sometimes seen in sunspot umbrae in MDI magnetograms is caused by the low intensity and the limitation of the onboard computation. The noise in the HMI and MDI line-of-sight magnetic-field synoptic charts appears to be fairly uniform over the entire map. The noise is 2.3 Mx?cm?2 for HMI charts and 5.0 Mx?cm?2 for MDI charts. No evident periodicity is found in the HMI synoptic charts. 相似文献
998.
Chuiyu Lu Bo Zhang Xin He Guoliang Cao Qingyan Sun Lingjia Yan Tao Qin Tianchen Li Zepeng Li 《Ground water》2021,59(1):90-99
MODFLOW is one of the most popular groundwater simulation tools available; however, the development of lake modules that can be coupled with MODFLOW is lacking apart from the LAK3 package. This study proposes a new approach for simulating lake - groundwater interaction under steady-state flow, referred to as the sloping lakebed method (SLM). In this new approach, discretization of the lakebed in the vertical direction is independent of the spatial discretization of the aquifer system, which can potentially solve the problem that the lake and groundwater are usually simulated at different scales. The lakebed is generalized by a slant at the bottom of each lake grid cell, which can be classified as fully submerged, dry, and partly submerged. The SLM method accounts for all lake sources and sinks, establishing a governing equation that can be solved using Newton's method. A benchmarking case study was conducted using a modified model setup in the LAK3 user manual. It was found that when there is a sufficient number of layers at the top of the groundwater model, SLM simulates an almost identical groundwater head as the LAK3-based model; when the number of layers decreases, SLM is unaffected while LAK3 may be at a risk of giving unrealistic results. Additionally, the SLM can reflect the relationship between the simulated lake surface area and lake water depth more accurately. Therefore, the SLM method is a promising alternative to the LAK3 package when simulating lake - groundwater interaction. 相似文献
999.
A new formula for the concentration profile of nonuniform sediment is derived using the diffusion differential equation with equilibrium bed concentration.The interaction coefficient for nonuniform sediment particles as a function of both relative diameter and geometric standard deviation of nonuniform sediment is taken into account in the settling velocity.The diffusion coefficient is obtained from the logarithmic velocity profile.This new formula possesses several advantages as follows:(1)avoids theoretical defect of the Rouse formula,which states that the sediment concentration is infinite at the bottom and zero at the water surface.(2)suitable for an arbitrary fraction of nonuniform sediment,and(3)easy to apply with a simple form.The formula yields less difference among concentration profiles for various particles than that for uniform sediment and reveals the lawfor fractional concentration distribution of nonuniform sediment.The calculated concentration agrees well with the measured data from the Yangtze River. 相似文献
1000.
Chen Peixiong Sun Zhilin Zhou Xin Xia Yuezhang Li Li He Zhiguo Wang Rusheng Xie Haijian 《Ocean Dynamics》2021,71(3):323-341
Ocean Dynamics - Coastal reclamation projects have been extensively constructed along the coastline of the East China Sea over the past decades. To investigate the impact of reclamations on the... 相似文献