江西德兴银山中侏罗世火山岩年代学、岩石成因及构造背景  

Geochronology,petrogenesis and tectonic setting of Middle Jurassic volcanic rocks from Yinshan deposit in Dexing,Jiangxi Province

作　　者：余明刚[1] 洪文涛[1] 刘凯[1] 段政[1] 褚平利[1] 陈荣[1] YU Minggang;HONG Wentao;LIU Kai;DUAN Zheng;CHU Pingli;CHEN Rong(Nanjing Center,China Geological Survery,Nanjing 210016,Jiangsu,China)

机构地区：[1]中国地质调查局南京地质调查中心,江苏南京210016

出　　处：《华东地质》2022年第4期428-447,共20页East China Geology

基　　金：中国地质调查局“华东地区区域基础地质调查(编号:DD20221633)”项目资助。

摘　　要：江西德兴银山矿床是华南中侏罗世浅成低温热液型铜多金属矿床。德兴银山火山活动由早到晚可划分为流纹质、英安质和安山质3个火山喷发旋回,LA-ICP-MS锆石U-Pb定年结果表明,它们的年龄分别为168.6~169.9 Ma、168.5~171.4 Ma和166 Ma,与德兴斑岩铜矿含矿斑岩的时代(172~165 Ma)基本一致,均形成于中侏罗世。火山岩由早到晚从流纹英安岩到英安岩-安山岩的这种成分变化趋势主要受控于岩浆房在喷出前的成分分带。银山不同旋回的火山岩化学成分均具有低Ti、低Na、高K、相对富Al的特征,富集轻稀土元素、亏损重稀土元素,具高的Sr值、Sr/Y值和(La/Yb)_(N)值,无明显的Eu异常,表现出与赣东北地区同时代中酸性侵入岩类似的埃达克质岩石的特征;具有较亏损的ε_(Hf)(t)值(-1.98~+5.49),两阶段模式年龄(T_(DM2))为0.84~1.31 Ga,表明岩浆可能是继承于中元古代-新元古代江南造山带形成时期的洋-陆俯冲作用产生的初生地壳物质。德兴、银山中侏罗世埃达克质岩石可能是挤压背景下中元古代-新元古代岛弧岩浆岩经重熔作用形成;与此形成对照的是,南岭东段早侏罗世呈EW向分布的双峰式火山岩形成于后造山的强烈伸展环境,这说明上述赣东北与南岭中侏罗纪岩浆活动形成于明显不同的两种构造背景,暗示该时段是华南构造体制转折的关键时期。The Yinshan deposit is a typical hydrothermal copper polymetallic deposit in Dexing,Jiangxi Province.The Yinshan volcanic activities are composed of three volcanic eruption cycles,i.e.rhyolitic,dacitic and andesitic assemblages in sequence.LA-ICP-MS zircon U-Pb dating for the three volcanic cycle rocks indicate that they were formed at 168.6~169.9 Ma,168.5~171.4 Ma and 166 Ma,respectively,which is contemporary with the forming age of the ore-bearing porphyries in the Dexing copper mine,implying the metallogenic epoch of Middle Jurassic.The compositional variation of volcanic rocks from rhyodacite to dacitic and andesitic assemblages resulted from the compositional zonation within the magma chamber before eruption.The Yinshan volcanic rocks in different cycles show similar geochemical characteristics to the typical adakites in northeastern Jiangxi.All of them have high LREEs contents and depletion of HREEs,with low Ti,Na,high K,Al,Sr,Sr/Y and(La/Yb)_(N) ratios,and slightly negative Eu anomalies.Zircons from the samples haveε_(Hf)(t)values ranging from-1.98 to+5.49 and t_(DM2)model ages from 0.84 to 1.31 Ga,indicating that the magma possibly derived from Meso-to Neo-Proterozoic juvenile continental crust formed by the Neoproterozoic oceanic crust subduction along the Jiangnan Orogen.Based on the geochemical and Hf isotopic data in this study and previous studies,we suggested that the Middle Jurassic adakitic rocks in Dexing and Yinshan might originate from the remelting of Meso-to Neo-Proterozoic arc rocks in the compressional setting.Conversely,Early Jurassic EW direction bimodal volcanic rocks in east section of Nanling Mountains were formed in the strong extensional setting of post-collision,suggesting two distinct tectonic settings of Middle Jurassic magmatism between northeast Jianxi and Nanling,and Early-Middle Jurassic is the critical period to understand the tectonic transition in South China.

关 键 词：火山岩 LA-ICP-MS锆石U-PB定年 埃达克质岩石 构造体制转换 江西银山 

分 类 号：P58[天文地球—岩石学]