【摘要】 江西彭山锡多金属矿集区位于钦行成矿带东段靠扬子板块一侧,是扬子板块东南缘重要的锡金属矿集区。彭山地区发育花岗岩底辟穹隆构造,而曾家垄岩体是穹隆构造核部的隐伏花岗岩体,由黑云母花岗岩和二云母花岗岩组成。对此岩体进行了详细的锆石U-Pb年代学、云母-长石-磷灰石矿物化学、全岩主元素、微量元素及Nd-Hf同位素研究,LA-ICP-MS锆石U-Pb定年结果表明黑云母花岗岩成岩年龄为(126.1±1.1)Ma,二云母花岗岩成岩年龄为(126.4±2.0)Ma,两者在误差范围内一致。岩相学和岩石地球化学表明黑云母花岗岩和二云母花岗岩均属于高分异花岗岩(均存在稀土四分组效应和异常的微量元素特征),但两者存在差异:二云母花岗岩相对高硅,富碱,为过铝质,具有较低的Ga/Al值,高Rb/Sr值,以及相对高的εNd(t)和εHf(t)值。曾家垄高分异花岗岩的形成模式为双桥山群变质沉积岩经部分熔融形成黑云母花岗岩之后留下的麻粒岩相残余体,在幔源高温玄武岩底侵作用下再次深熔,形成二云母花岗岩。玄武质岩浆的底侵不仅为麻粒岩相残余的部分熔融带来高温,同时也带来挥发分F和B等以及少量幔源物质(导致二云母花岗岩具有较高εNd(t)和εHf(t)值)。F和B的加入改变了岩浆体系的物理化学性质,显著降低了岩浆的黏度、密度和固相线温度,导致岩浆体系分离结晶过程延长和高度分离结晶;延长的岩浆演化过程活化了围岩中的水,导致强烈的熔-流体相互作用,形成高分异花岗岩的稀土四分组效应。同时,深部变质流体或/和围岩流体的活化也萃取了其中的成矿物质,这可能是成矿的原因,锡矿形成可能与岩体无关。更多还原

【Abstract】 The Pengshan Sn-polymetallic ore fields are located in De’an county,Jiangxi Province,which lies in the eastern part of the Qinzhou-Hangzhou metallogenic belt.There exists diaper structure in Pengshan district while the Zengjialong granite pluton occurs in the core part.It is composed of biotite granite and two-mica granite with tungsten mineralization.In this paper,we report detailed studies on LA-ICP-MS zircon U-Pb dating,Hf isotope,the whole rock major and trace elements,Nd isotopic compositions of the two rock types,and in-situ LA-ICP-MS trace element concentrations of mica,muscovite and apatite.The zircon U-Pb dating of the biotite granite and two-mica granite yields the ages of（126.1±1.1）Ma and（126.4±2.0）Ma,respectively.Petrography and geochemical data indicate that the biotite granite and two-mica granite are highly evolved granites（REE tetrad effect and modified behavior of trace elements）,while differences among them remain:two-mica granites have high silica and alkalis contents,low Ga/Al,high Rb/Sr ratios,weak LREE/HREE fractionation,pronounced negative Eu anomalies,and highε_Nd（t）andε_Hf（t）values.We suggest that the Zengjialong granites were derived from melting of the Shuangqiaoshan Group meta-sediments that left behind a granulitic residue in the lower crust.Further,the highly differentiated muscovite granite formed by re-melting of the residue,and triggered by the underplating of a new pulse of basaltic magma.Underplating of the basaltic magma provides not only the high temperature required for melting the residue but also the volatile（fluorine,boron）in the source of the granite.Addition of fluorine and boron lowered the solidus temperature and the viscosity of the granitic magma,thus prolonging the process of magma evolution.It appears to have resulted in extreme fractional crystallization and intense interaction between melt and the circulating waters from country rocks,forming the unusual geochemical features of the granite and subsequently extracting ore-forming metal from the country rocks,forming the polymetallic deposits.更多还原