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991.
The petrology, geochemistry, geochronology, and Sr–Nd–Hf isotopes of the backarc granitoids from the central part of the Qilian block are studied in the present work. Both S- and I-type granitoids are present. In petrographic classification, they are granite, alkali feldspar granite, felsic granite, diorite, quartz diorite, granodiorite, and albite syenite. The SHRIMP ages are 402–447 Ma for the S-type and 419–451 Ma for the I-type granitoids. They are mostly high-K calc-alkaline granitoids. The S-type granitoids are weakly to strongly peraluminous and are characterized by negative Eu anomalies (Eu/Eu* = 0.18–0.79). The I-type granitoids are metaluminous to weakly peraluminous and are characterized mostly by small negative to small positive Eu anomalies (Eu/Eu* = 0.71–1.16). The initial (87Sr/86Sr) values are 0.708848–0.713651 for the S-type and 0.704230–0.718108 for the I-type granitoids. The εNd(450 Ma) values are − 8.9–−4.1 and − 9.7–+ 1.9 for the S-type and I-type granitoids, respectively. The TDM values are 1.5–2.4 Ga for the S-type and 1.0–2.3 Ga for the I-type granitoids. For the Qilian block, the backarc granitoid magmatism took place approximately 60 million years after the onset of the southward subduction of the north Qilian oceanic lithosphere and lasted approximately 50 million years. Partial melting of the source rocks consisting of the Neoproterozoic metasedimentary rocks of the Huangyuan Group and the intruding lower Paleozoic basaltic rocks could produce the S-type granitoid magmas. Partial melting of basaltic rocks mixed with lower continental crustal materials could produce the I-type granitoid magmas. Major crustal growth occurred in the late Archean and Meso-Paleoproterozoic time for the Qilian block. The magma generation was primarily remelting of the crustal rocks with only little addition of the mantle materials after 1.0 Ga for the Qilian block. 相似文献
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993.
通过粉煤灰与水6种不同比例的混合实验,利用质量平衡模型模拟分析混合静置0,1,3,7,14,21d后的水化学组分,以揭示粉煤灰浸出液中水化学组分的形成机制。研究结果表明:灞桥电厂粉煤灰浸出液为高pH值溶液,浸出液pH值急剧上升是粉煤灰中碱性氧化物CaO水解的结果;粉煤灰-水反应系统中,矿物的溶解沉淀作用和阳离子交换作用是主要的水文地球化学作用。 相似文献
994.
Osamu Seki Philip A. Meyers Kimitaka Kawamura Yanhong Zheng Weijian Zhou 《Organic Geochemistry》2009,40(6):671-677
Based on paleoclimatic reconstructions using various proxies, the Holocene Climate Optimum (10.5–6 ka) has been characterized as a warmer and wetter period in most of East Asia. The summer monsoons associated with the East Asian Monsoon evidently intensified and extended further inland from the Pacific Ocean, a source region of moisture. A notable exception to this general pattern exists in northeast China, where less wet conditions are recorded. We determined molecular compositions of individual plant wax hydrocarbons and their hydrogen isotope compositions (δD values) in a radiocarbon-dated peat core recovered from the Hani marsh in Jilin Province (China) and confirmed that the temperature-dependent effective precipitation in northeast China decreased during the Holocene Climate Optimum. A combination of Paq, an indicator of the relative contribution of aquatic to terrestrial plants, and the difference in δD between low (C23, C25 and C27) and high molecular weight (C31) n-alkanes in the Hani peat bog indicates a dramatic change in vegetation from the deglaciation to the Holocene. No significant differences were observed between the δD values of low and high molecular weight n-alkanes with relatively high δD values and low Paq during the early Holocene, indicating that all n-alkanes were produced by evapotranspiration-sensitive terrestrial plants during that time. However, lower δD values of mid-chain n-alkanes (C23, C25 and C27) relative to the long chain n-alkane (C31), together with higher Paq values during the deglaciation (14–11 ka), suggest an increase in the contribution of aquatic plants and a higher water level during the period. The study demonstrates that northeast China was under a markedly wetter climate condition during the late deglaciation. For the 16 kyr record in the Hani peat sequence, we infer that moisture delivery by the East Asian Monsoon was relatively invariable in northeast China, but increased evaporation during the warmer Holocene Climate Optimum reduced the effective precipitation, defined by the balance between precipitation and evaporation. 相似文献
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996.
建筑物模型是大规模数字城市建设的重要组成部分。本文主要讨论了大规模数字城市建设中建筑物的建模方法,包括批量建模方法和重点区域建筑物精细建模方法。文中介绍了建模的基本思想,使用AutoCAD二次开发的插件和OSG(Open Scene Graph)渲染引擎实现了基于DLG(Digital Line Graphic)的模型批量生成和精细模型生成。实验证明,该方法能够快速有效地进行大规模建筑物批量建模,并支持重点区域精细模型的编辑与生成,在最终的三维场景浏览中,模型美观,空间地理坐标精确,量测精度高,符合数字城市的建模要求。 相似文献
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利用单个基准站提供的改正信息对流动站的单频观测值数据进行改正,同时引入电离层参数进行实时电离层延迟估计,进行单频精密单点定位(PPP)计算。相比传统的单频PPP方法,本文方法对单频PPP的收敛速度和定位精度都有很大的提高,定位精度优于2cm,且受基准站距离的影响较小。 相似文献
1000.
基于中国地壳运动观测网络1999~2007年的GPS复测资料,建立起整体无净旋转基准,分析了山西地堑系内部地壳运动的细节特征,并利用图形单元法分析了其应变场的分布特征,深入剖析了地壳变形的动力学机制,得出山西地堑系现今构造应变场以NW-SE向拉张应变为主,与区域现代震源机制解及长期构造变形背景相一致;临汾、大同盆地是地堑内剪切应变高值区,现今地壳活动强烈。解释了地堑系内形变异常区的成因,由此揭示出连接临汾与太原盆地的构造隆起带两端的现今地壳活动十分强烈,并同时兼有拉张破裂趋势这一重要的构造事件。 相似文献