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31.
在鄂尔多斯地块西南缘的六盘山断裂带内出露铁马河辉绿岩。铁马河辉绿岩相对贫CaO、MgO和K_2O;富集FeOT、TiO_2和Na_2O。轻稀土相对富集,重稀土平坦,不显示Eu异常,稀土配分曲线显示右倾型;高场强元素无异常,大离子亲石元素K、Rb、Ba相对富集,显示富集地幔源的地球化学特征。对辉绿岩样品进行LA-ICP-MS锆石U-Pb测年,获得上交点年龄2018±16Ma,说明岩体形成于古元古代。样品具有低的(~(87)Sr/~(86)Sr)i值(07003~07064)和正的εNd(t)值(+514~+433),Nd同位素一阶段模式年龄(约20Ga)与LA-ICP-MS锆石U-Pb年龄基本一致,暗示其来源于软流圈地幔的部分熔融。结合区域地质资料的研究表明,华北克拉通西部地块(鄂尔多斯地块)在20Ga期间的伸展背景与东部陆块一致,暗示整个华北克拉通在20Ga左右存在广泛的裂解事件。 相似文献
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江西银山火山岩型铜、金多金属矿床成矿特点 总被引:4,自引:1,他引:3
江西银山铜、金多金属矿床的矿化紧紧围绕多个中心呈有规律地分布,成矿物质既由岩浆从地壳深部带来,又部分来自基底围岩;成矿作用既受燕山期火山机构控制,也受基底构造控制;矿化具有多个中心复合叠加分带的特点,是一个典型的地洼型多因复成矿床。 相似文献
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Xiao-chun Xu Jin-wei Lou Qiao-qin Xie Qiuxiang Xiao Jianfeng Liang San-ming Lu 《Ore Geology Reviews》2011,43(1):132-141
The Gaijing Pb–Zn–Mo deposit and Shapinggou Mo deposit in the Yinshan region, Jinzhai, Anhui province, China, are hosted in various granitic intrusions with 40Ar/39Ar ages obtained for biotite and hornblende of 136.8 ± 1.6 Ma (medium-grained monzogranite), 130.4 ± 1.2 Ma (fine-grained granite), and 125.4 ± 1.0 Ma (fine-grained diorite). The modes of occurrence and cross-cutting relationships among the igneous intrusions indicate that alkali quartz-syenite and quartz-syenite porphyry (cryptoexplosive breccia) formed later than the calc-alkali monzogranite, granite, and diorite. Molybdenum mineralization occurs in pipe-like bodies hosted in cryptoexplosive breccia (pipe), quartz-syenite (porphyry), monzogranite, and granite, whereas Pb–Zn mineralization occurs in veins distally from the Mo mineralization. The Re–Os isotopic model ages of molybdenite from the Gaijing Pb–Zn–Mo deposit are 112.6 ± 1.3 and 113.5 ± 1.3 Ma, consistent with the ages of other molybdenum deposits throughout the East Qinling–Dabie metallogenic belt. The geological characteristics and isotopic ages of the Gaijing Pb–Zn–Mo and Shapinggou Mo deposits indicate a genetic relationship to the emplacement of the quartz-syenite (porphyry) and to shallow-seated porphyry–cryptoexplosive breccia intrusions. The present results, combined with existing data, suggest that the Pb–Zn–Mo deposits and related igneous rocks were formed in a geodynamic setting of regional lithospheric thinning, delamination, and thermal erosion in East China. The deposits are part of the East Qinling–Dabie molybdenum belt, which in turn is part of a large-scale E–W-trending metallogenic belt in East China. 相似文献
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《International Geology Review》2012,54(13):1688-1704
The Yinshan Block, part of the Neoarchaean basement of the Western Block of the North China Craton, is composed of granite–greenstone and granulite–charnockite complexes. We report research on a suite of charnockites from the granulite–charnockite complex and characterize their geochemistry, zircon U–Pb geochronology, and Hf isotopic composition. The charnockites can be divided into intermediate (SiO2 = 59–63 wt.%) and silicic (SiO2 = 69–71 wt.%) groups. U–Pb zircon data yield protolith formation ages of 2524 ± 4 Ma, 2533 ± 15 Ma, followed by metamorphism at 2498 ± 3 Ma, 2490 ± 11 Ma, respectively, for these groups. Although the intermediate charnockites are characterized by higher Al2O3, TiO2, Fe2O3T, MnO, MgO, CaO, P2O5, K2O, Sr, and ΣREE content than the silicic charnockites, the ages and Hf isotopic composition of zircons and REE patterns of both intermediate and silicic charnockites are remarkably consistent, which indicates that they are genetically related. These charnockites are predominantly metaluminous to slightly peraluminous, calc-alkalic to calcic, and magnesian – characteristics generally related to a subduction setting. High-Sr + Ba granites with low K2O/Na2O characteristics, shown by these charnockites, imply a mixture of mafic and felsic magmas generated from an enriched mantle + lower crust. High MgO, Ni, Cr and Mg#, low K2O/Na2O, and metaluminous to slightly peraluminous natures imply that the source rocks most likely were amphibolites. Coeval calc-alkaline magmatism and high-T granulite-facies metamorphism under low-H2O activity in the area lead us to propose a model involving mid-ocean ridge subduction within a Neoarchaean convergent margin. The arc-related rocks accreted along the continent margin, and became a barrier when the lithospheric mantle ascended through the slab window. Melt derived from the decompressing mantle mixed with melt derived from the overlying, juvenile lower crust melt, which was warmed and metamorphosed by the ascending lithospheric mantle. 相似文献
35.
《International Geology Review》2012,54(7):895-913
ABSTRACTA comparative study was performed on the petrography, geochemistry and geochronology of charnockite and granulite in the Xiwulanbulang (XWLBL) area, northern margin of the North China Craton, NW China. Inclusions within garnet in the charnockite are used to identify the mineral assemblage in the granulite during peak metamorphism. The formation of charnockite is attributed to the anatectic of the protolith, as a result of granulite-facies metamorphism during the same tectono-thermal event. Anatexis occurred mainly during the post-peak isothermal depressurization stage (granulite and charnockite yield peak P–T conditions of 800–850°C and 1.0–1.2 GPa, and 750°C and 0.9–1.0 GPa, respectively), as inferred from the metamorphic evolution and P–T conditions derived from analyses of metamorphic minerals by electron microprobe (EMP). The garnets in the charnockite were a residual or peritectic mineral facies during anatexis, and the charnockite was the product of crystallization from melt with abundant residual minerals. Charnockite has similar geochemical characteristics to felsic granulite, although it differs in having 1) an uneven distribution of major and trace elements; 2) strong depletions in the large-ion lithophile element Cs, the heat-producing elements U and Th, and the high-field-strength elements Nb, Ta, P and Ti; and 3) both Eu-enriched and Eu-depleted patterns that are characteristic of granite formed by largely in situ anatectic. The geochemical data indicate that the XWLBL charnockite formed in a subduction-related volcanic arc setting. On the basis of our results, combined with geological data on the Neoarchean structural evolution of the Yinshan Block and εHf(t) values of 1.60–7.81, we propose that the anatectic of charnockite was related to slab break-off during mid-ocean-ridge subduction, which resulted in the ascent of mantle magma through the slab window. 相似文献
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银山地区火山岩-次火山岩由流纹岩、流纹英安斑岩、英安质熔岩、英安斑岩和粗面安山斑岩组成,喷发和侵入存在着反序特征.通过各种物理化学方法确定了岩浆房中存在的化学成分和温度、密度、粘度梯度.建立了以英安质岩浆为主,顶部有一层富SiO2、富K的流纹质岩浆,底部为少量粗面安山质岩浆的带状岩浆房.岩浆演化及带状岩浆房的形成是分离结晶、同化混染、岩浆对流和边界层机制共同作用的结果. 相似文献
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40.
阴山中生代地壳逆冲推覆与伸展变形作用 总被引:3,自引:0,他引:3
研究区属燕山—阴山中生代板内造山带西段的重要组成部分。依据变形特征和物质组成,可以分为北部构造活动带、中部隆起带和南部构造活动带3个不同的构造区。以中部隆起带为中心,在南北两侧的构造活动带中的构造样式和变形机制呈反向对称出现。逆冲构造和伸展构造在时间和空间上密切共生。在印支期—燕山早期地壳以逆冲挤压变形机制为主,形成了色尔腾山逆冲推覆体系和大青山逆冲推覆体系,而燕山晚期阶段在逆冲岩席上产生了背向伸展变形作用,形成了同构造的早白垩世呼和浩特—包头盆地和固阳盆地。 相似文献