| 长江中下游宣城水东地区早白垩世酸性火山岩年代学、地球化学及岩石成因 |
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| 引用本文： | 王存智,黄志忠,赵希林,褚平利,黄文成,宋世明,陈志洪.长江中下游宣城水东地区早白垩世酸性火山岩年代学、地球化学及岩石成因[J].岩石矿物学杂志,2018,37(5):697-715. |
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| 作者姓名： | 王存智 黄志忠 赵希林 褚平利 黄文成 宋世明 陈志洪 |
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| 作者单位： | 中国地质调查局南京地质调查中心 |
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| 基金项目： | 中国地质调查局项目（DD20160036） |
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| 摘 要： | 位于长江中下游的宣城水东地区发育一套酸性火山岩,主要由流纹质角砾岩、流纹岩和珍珠岩组成。本文对该套火山岩进行了详细的锆石U-Pb年代学、主量元素、微量元素以及Nd-Hf同位素研究。LA-ICP MS锆石U-Pb定年结果显示3种岩性的火山岩年龄分别为133.2±0.8、133.4±0.8和131.5±0.9 Ma。主量元素组成上,这套酸性火山岩具高硅(72.51%~81.79%)、富钾(K_2O/Na_2O=2.04~14.93,平均6.72)、贫钙镁(Ca O=0.19%~1.57%,Mg O=0.06%~0.29%)的特征,属于弱过铝质(A/CNK=1.02~1.24)的高钾钙碱性-钾玄岩系列岩石。微量元素方面,轻重稀土元素分馏明显(La/Yb)_N=5.43~9.17],具明显的负铕异常(Eu/Eu~*=0.44~0.60),富集大离子亲石元素(LILE)Rb、Th、K和Pb等,亏损Ba、Sr、Nb、P和Ti等元素,表现出壳源的特征。全岩Sr-Nd和锆石Hf同位素组成变化范围相对较小,(~(87)Sr/~(86)Sr)_i为0.707 3~0.708 8,εNd(t)值为-7.05~-5.56,εHf(t)为-8.6~-1.3。结合区域地质研究成果,认为宣城水东地区酸性火山岩可能是在约135 Ma古太平洋板块俯冲作用之后的伸展-拉伸环境下,由新元古代早期新生地壳重熔而成。
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| 关 键 词： | 年代学 岩石成因 酸性火山岩 宣城 长江中下游 |
| 收稿时间： | 2017/10/26 0:00:00 |
Geochronology, geochemistry and petrogenesis of Early Cretaceous acid volcanic rocks in Shuidong area, Xuancheng City, in the middle-lower reaches of the Yangtze River |
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| WANG Cun-zhi,HUANG Zhi-zhong,ZHAO Xi-lin,CHU Ping-li,HUANG Wen-cheng,SONG Shi-ming and CHEN Zhi-hong.Geochronology, geochemistry and petrogenesis of Early Cretaceous acid volcanic rocks in Shuidong area, Xuancheng City, in the middle-lower reaches of the Yangtze River[J].Acta Petrologica Et Mineralogica,2018,37(5):697-715. |
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| Authors: | WANG Cun-zhi HUANG Zhi-zhong ZHAO Xi-lin CHU Ping-li HUANG Wen-cheng SONG Shi-ming and CHEN Zhi-hong |
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| Institution: | Nanjing Center, China Geological Survey, Nanjing 210016, China,Nanjing Center, China Geological Survey, Nanjing 210016, China,Nanjing Center, China Geological Survey, Nanjing 210016, China,Nanjing Center, China Geological Survey, Nanjing 210016, China,Nanjing Center, China Geological Survey, Nanjing 210016, China,Nanjing Center, China Geological Survey, Nanjing 210016, China and Nanjing Center, China Geological Survey, Nanjing 210016, China |
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| Abstract: | There is a suite of acid rocks consisting of rhyolitic breccia, rhyolite and perlite in Shuidong area, Xuancheng City, in the middle-lower reaches of the Yangtze River. In this paper, the authors reported detailed studies of the LA-ICP-MS zircon U-Pb dating, major elements, trace elements, whole-rock Nd isotopic compositions and zircon Hf isotopic compositions of the acid rocks. The results of zircon LA-ICPMS U-Pb dating are 133.2±0.8 Ma (rhyolitic breccia), 133.4±0.8 Ma (rhyolite) and 131.5±0.9 Ma (perlite), respectively. Geochemical researches indicate that the acid volcanic rocks are rich in silica (SiO2=72.51%~81.79%), K (K2O/Na2O=2.04~14.93, 6.72 on average) and poor in calcium (CaO=0.19%~1.57%) and magnesium (MgO=0.06%~0.29%), implying a typical high-K calc-alkaline to shoshonitic series with weakly peraluminous features (A/CNK=1.02~1.24). The rocks are enriched in LREE, LILEs (Rb, Ba, Th and K) but depleted in HFSE, especially Nb, Sr, P and Ti. The Eu/Eu* ratios vary from 0.44 to 0.60, with most rocks having prominent negative Eu anomalies. Based on integration of the geological characteristics of the study area, the authors proposed that the acid rocks were formed by anatexis of the Neoproterozoic middle and upper crust. The petrogenetic event probably occurred in an intraplate extensional environment after the subdutiion of the Pacific Plate at~135 Ma. |
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| Keywords: | geochronology petrogenesis acid volcanic rocks Xuancheng City middle-lower reaches of the Yangtze River |
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