| 安徽南陵—宣城地区岩浆岩锆石U-Pb年龄及元素地球化学特征 |
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| 引用本文： | 徐晓春,安昱华,许心悦,傅仲阳.安徽南陵—宣城地区岩浆岩锆石U-Pb年龄及元素地球化学特征[J].地球科学与环境学报,2020(1):15-35. |
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| 作者姓名： | 徐晓春 安昱华 许心悦 傅仲阳 |
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| 作者单位： | 合肥工业大学资源与环境工程学院 |
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| 基金项目： | 国家重点研发计划项目(2016YFC0600209) |
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| 摘 要： | 安徽南陵-宣城地区是一个中-新生代火山-沉积盆地,位于长江中下游构造-岩浆-成矿带东北段的东南翼。对该区发育的岩浆岩开展了较为系统的LA-ICP-MS锆石U-Pb定年及岩石主量、微量和稀土元素分析,并与长江中下游构造-岩浆-成矿带其他地区岩浆岩进行对比,旨在确定岩浆岩的成岩时代、探讨岩浆岩成因及其与成矿的关系。南陵-宣城地区岩浆岩一部分侵入于盆地基底中,另一部分喷发形成盆地盖层,还有一部分产于盆地之上的推覆构造(体)中。侵入岩的岩性主要为花岗岩、花岗闪长岩、石英闪长岩、辉石闪长岩等,火山岩主要为英安质火山碎屑岩和熔岩。获得的侵入岩锆石U-Pb年龄主要为138~135 Ma,火山岩年龄均小于134 Ma,表明岩浆作用发生于晚中生代(燕山晚期)早白垩世。岩浆岩主量元素显示高Si、K的特征,为亚碱性高钾钙碱性系列岩石;微量元素组成显示岩浆岩富集Rb、Th、U、K等大离子亲石元素,亏损Nb、Ta、Ti等高场强元素,火山岩比侵入岩较为亏损Sr和P;球粒陨石标准化稀土元素配分模式均表现为富集轻稀土元素的右倾模式和较弱的Eu负异常。元素地球化学特征指示区内岩浆岩具有壳幔混源且以幔源为主的特征。南陵-宣城地区既发育与长江中下游构造-岩浆-成矿带隆起区(如铜陵地区)同位素地质年龄和地球化学特征基本一致的侵入岩,又发育与凹陷区(如庐枞、宁芜等盆地)同位素地质年龄和地球化学特征基本一致的火山-次火山岩,显示该区晚中生代岩浆作用具有长江中下游构造-岩浆-成矿带隆起区和凹陷区的双重特征。岩浆作用的双重特征暗示与其有关的成矿作用也可能具有双重性,即既可能发育与隆起区侵入岩浆作用有关的斑岩型、矽卡岩型和脉型铜金等多金属矿床,也可能发育与凹陷区火山-次火山岩有关的玢岩型铁(硫)矿床。
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| 关 键 词： | 岩浆岩 锆石U-PB年龄 元素地球化学 岩石成因 火山岩 侵入岩 成岩成矿关系 安徽 |
Zircon U-Pb Ages and Element Geochemistry Characteristics of Magmatic Rocks in Nanling-Xuancheng Area of Anhui,China |
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| XU Xiao-chun,AN Yu-hua,XU Xin-yue,FU Zhong-yang.Zircon U-Pb Ages and Element Geochemistry Characteristics of Magmatic Rocks in Nanling-Xuancheng Area of Anhui,China[J].Journal of Earth Sciences and Environment,2020(1):15-35. |
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| Authors: | XU Xiao-chun AN Yu-hua XU Xin-yue FU Zhong-yang |
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| Institution: | (School of Resources and Environmental Engineering,Hefei University of Technology,Hefei 230009,Anhui,China) |
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| Abstract: | The Nanling-Xuancheng area of Anhui, which is a Meso-Cenozoic volcanic-sedimentary basin, is located in the southeastern limb of the northeastern part of middle-lower Yangtze river valley tectonic-magmatic-metallogenic belt. Zircon U-Pb dating, and major, trace and rare earth elements of the magmatic rocks in Nanling-Xuancheng area were focused, and compared with those of the magmatic rocks in other areas of middle-lower Yangtze river valley tectonic-magmatic-metallogenic belt, for determining the age, and discussing the petrogenesis of the magmatic rocks and the relationship between the magmatism and mineralization. In Nanling-Xuancheng area, a part of the magmatic rocks intruded into the basement of the basin or erupted as the cover rocks of the basin, and the other part of the magmatic rocks occurred in the nappe above the basin. The intrusive rocks are mainly granite, granodiorite, quartz diorite and pyroxene diorite, and the volcanic rocks are dacitic pyroclastic rocks and lavas. The results show that the zircon U-Pb ages of the intrusive rocks are between 138 Ma and 135 Ma, and the ages of the volcanic rocks are all less than 134 Ma, suggesting that the magmatism occurred in Early Cretaceous of Late Mesozoic(Late Yanshanian). The characteristics of major elements show that the magmatic rocks are high for Si and K, belonging to sub-alkaline and high-K calc-alkaline series;the characteristics of trace elements show that the magmatic rocks are rich in Rb, Th, U and K, and poor in Ti, Nb and Ta, the volcanic rocks are more deficient from intrusive rocks in Sr and P;the chondrite-normalized REE patterns show that the magmatic rocks are rich in LREE and have weak negative Eu anomalies. The element geochemical characteristics indicate that the magmatic rocks have the characteristics of crust-mantle mixed and mainly mantle-derived. Zircon U-Pb dating, and geological and geochemical characteristics of the magmatic rocks in Nanling-Xuancheng area indicate that the Late Mesozoic magmatism in the area has the dual characteristics of those in upwelling areas and depression areas of the middle-lower Yangtze river valley tectonic-magmatic-metallogenic belt, that is, the study area not only develops intrusive rocks in the upwelling area(such as Tongling area), but also develops volcanic rocks in the depression area(such as Luzong and Ningwu basins). The duality of magmatism may imply the duality of mineralization, that is, the study area may develop hydrothermal porphyry-type, skarn-type and vein-type Cu-Au and other polymetallic deposits related to intrusive magmatism, also porphyry-type Fe(S) deposits associated with volcanic-subvolcanic rocks. |
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| Keywords: | magmatic rock zircon U-Pb age element geochemistry petrogenesis volcanic rock intrusive rock relationship between magmatism and mineralization Anhui |
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