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31.
《International Geology Review》2012,54(11):1332-1352
The Early Cretaceous Washan dioritic porphyry is spatially and temporally associated with Kiruna-type iron oxide deposits in the Ningwu basin, Middle-Lower Yangtze River Valley (MLYRV). We present new LA-ICP-MS U–Pb dating + zircon Lu–Hf isotopic studies, as well as bulk-rock major + trace element and Sr + Nd isotopic compositions of the porphyry. LA-ICP-MS U–Pb zircon analyses suggest that the pluton formed at 130.8?±?0.9 Ma. Analysed zircon ?Hf(t) values range from –7.0 to –4.1. The dioritic rocks are significantly enriched in Pb and light rare earth elements, relative to high-field strength elements (Nb + Ti), coupled in the absence of significant Eu anomalies. They exhibit age-corrected ?Nd(t) (t?=?130 million years) values of??3.5 to??3.9 and initial 87Sr/86Sr ratios of 0.70553–0.70653. The ore-bearing dioritic porphyry was derived from a parental basaltic liquid that was produced by partial melting of an enriched spinel-facies lherzolite in the Yangtze lithospheric mantle. This basaltic melt underwent a fractionation of plagioclase and clinopyroxene during ascent towards the surface, which led to the relative enrichment of iron in the residual melt. This type of magma was widespread in the MLYRV area but did not generate widespread Fe mineralization. In the Ningwu area, the dioritic magma was modified by minor assimilation of phosphorus-bearing rocks in the Yangtze upper crust. The special crustal characteristics of the Ningwu basin, i.e. phosphorus-rich strata, were likely a crucial factor controlling the formation of Kiruna-type iron oxide deposits. 相似文献
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长江中下游成矿带是我国东部重要的铁、铜多金属矿产资源基地,使用现代地球物理探测技术对该成矿带典型矿床深部结构进行探测,对认识深部矿床成因、总结找矿方法和深部找矿的实践具有重要意义。本文选取位于长江中下游成矿带庐枞矿集区内的泥河玢岩铁矿为实验区,开展了音频大地电磁(AMT)、可控源音频大地电磁(CSAMT)和瞬变电磁(TEM)等电磁法探测实验;通过对AMT、CSAMT和TEM数据的处理和反演,发现3者相同测线反演结果反映的控矿地质体电性特征基本一致,但细节上存在一定差异。综合3种电磁测深反演结果,电性特征刻画了砖桥组火山岩地层分布,分辨出闪长玢岩体的隆起部位和基本形态,揭示了矿体的赋存位置。认为在合理的数据采集、处理和反演条件下,电磁测深能有效地区分复杂地质构造条件下次火山岩与围岩的电性差异,找到控矿构造界面,从而推断出矿体的位置。 相似文献
33.
通过研究徐州塔山地区橄榄玄武玢岩的地球化学特征,对其岩石成因及构造环境进行判别,并进一步对其金刚石成矿前景进行探讨。结果表明,橄榄玄武玢岩属于大陆板内玄武岩,总体上略富集轻稀土元素,是在板内拉张构造背景下由石榴子石相的富集地幔经不同程度部分熔融形成的,且在岩浆结晶过程中存在一定程度的斜长石堆晶作用。其所含微粒金刚石与安徽栏杆金刚石相似,显示出金刚石生长初期的特点,应为幔源捕获成因。与金伯利岩相比,橄榄玄武玢岩在地球化学特征方面存在明显差异,整体表现为古近纪伸展期玄武岩浆的特征,不具备携带大量深源包体的条件,难以形成原生金刚石矿床。 相似文献
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甘肃天水地区长沟河闪长岩位于北祁连造山带东端,发育片麻状构造面理,长期以来被认为是形成于前寒武纪的侵入岩体。用LA-ICP-MS技术测得2组岩浆锆石的~(206)Pb/~(238)U年龄为463.3±2.3Ma(MSWD=0.52,n=11)和443.8±2.6Ma(MSWD=0.44,n=9)。锆石微量元素分析表明,2组年龄具有一致的微量元素组成,说明二者晶出于同源封闭的岩浆体系。t-Eu/Eu~*投图显示,约460Ma的岩浆锆石无Eu异常,与幔源岩浆锆石稀土元素特征一致。而约440Ma的岩浆锆石具有负Eu异常,指示母岩开始发生斜长石的结晶分离,与深熔作用过程一致。因此,约460Ma为长沟河闪长质片麻岩原岩的形成年龄,约440Ma为长沟河闪长质片麻岩深熔岩浆的结晶年龄。Hf同位素分析测试结果显示,约460Ma和约440Ma两组锆石的εHf(t)值分别为8.23~11.57和6.36~8.03,指示460Ma发育幔源新生地壳岩浆作用,而440Ma壳源再造活动增强。 相似文献
35.
铁格隆地区含矿岩石以闪长玢石及石英闪长玢岩为主,属钙碱性岩系和高钾钙碱性岩系,显示I型花岗岩的特点。岩体形成于早白垩世班公湖-怒江洋盆俯冲消减构造环境,成岩岩浆属氧化型岩浆,来源于壳幔结合部,并受到壳源物质的强烈混染。与玉龙、冈底斯斑岩矿带含矿岩石进行对比,该含矿玢岩在岩石类型、岩石化学、地球化学及成岩构造环境等方面均存在明显差异,指示其成矿动力学背景、成矿机理与"碰撞"及"碰撞后"的斑岩型矿床不同,属形成于"岛弧"环境的斑岩型铜金矿床。 相似文献
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37.
郯庐断裂带南段沙溪含铜斑岩体的40Ar/39Ar年代学研究及意义 总被引:8,自引:0,他引:8
对郯庐断裂南段沙溪含铜斑岩体中黑云母和斜长石单矿物的高精度40A r/39A r同位素测定,获得40A r/39A r平均坪年龄为132.62 M a±0.28 M a,40A r/39A r等时线平均年龄为132.59 M a±0.46 M a,而最小平均视年龄86 M a左右可能表示后期的一次热事件,可能对应于斑岩体与Cu-A u矿化有关的热液活动。这些年龄值比前人在该区及邻区获得的K-A r和R b-S r年龄更精确地代表沙溪含铜斑岩体的侵入时代。132.6M a左右的年龄代表着该区含铜(金)斑岩体的侵入时代,可以证实铜(金)斑岩型矿床是在稍后的大规模热液蚀变条件下所形成。 相似文献
38.
LIU Shuwen WANG Zongqi YAN Quanren LI Qiugen ZHANG Dehui WANG Jianguo YANG Bin GU Libing ZHAO Fengshan The Key Laboratory of Orogenic Belts Crustal Evolution Ministry of Education School of Earth Space Sciences Peking University Beijing 《《地质学报》英文版》2006,80(3):387-399
A mass of granitoid and dioritic intrusions are distributed in the southern Yidun Arc, among which the representative Indosinian intrusions include the Dongco and Maxionggou granitoid intrusions in Daocheng County and hypabyssal intrusions intruding into arc volcanic rocks near the Xiangcheng town. The Dongco and Maxionggou granitoid intrusions consist mainly of porphyraceous monzogranites, megacryst monzogranites and aplite granites. The Xiangcheng hypabyssal intrusions are composed dominantly of dioritic porphyries. SHRIMP zircon ages of 224±3 Ma and 222±3 Ma have been obtained for the Dongco granitoid intrusion and the Xiangcheng dioritic porphyries, respectively. The Xiongcheng dioritic porphyries show a cak-alkaline geochemical feature, and are characterized by higher Sr/Y ratios, depletive Nb, Ta, P and Ti, enriched LILEs, and lower εNd (t) (= -3.27), suggesting that they might be derived from mantle source magmas that were obviously contaminated by continent crustal materials. However, the Dongco and Maxionggou granitoids belong to high-potassium calc alkaline series with a per-metaluminous feature, and are characterized by higher CaO/(∑FeO+MgO) and Al2O3/(∑FeO+ MgO) ratios, lower (La/Yb)n and Sr/Y ratios, depletive Nb, Ta, Sr, P and Ti, enriched LILEs, and very low εNd (t) (= -8.10), indicating that the granitoids might be derived from partial melting of continental crust materials mainly of graywacke. Petrogenesis of Dongco and Maxionggou granitoids implies that there was an oceanic crust between the Zongza continental block (ZCB) and western margin of the Yangtze Craton (WMYZC). And the oceanic crust slab subducted westward during the Indosinian Epoch, producing an Andes-type continent marginal arc and a back arc basin at the WMSCC. Then the oceanic basin closed and a sinistrally lateral collision occurred at ca. 224 Ma-222 Ma between the ZCB and the WMYZC, causing partial melting of sediments in the back-arc basin to generate granitoid magmas of the Dongco and Maxionggou intrusions. 相似文献
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