安徽青阳—九华山复式岩体的成因及成矿潜力——来自锆石Hf同位素和微量元素的证据

Magmatic genesis and mineralization potential of Qingyang—Jiuhuashan complex pluton:Evidence from zircon Hf isotopes and trace elements

青阳—九华山复式岩体是安徽南部地区出露面积最大、最具代表性的复式岩体,该复式岩体的岩浆源区、演化过程和成矿联系等问题仍需要进一步查明。在前期对青阳—九华山复式岩体的地质、地球化学特征研究基础上,笔者等进一步开展了锆石微量元素与Hf同位素分析与研究。结果显示,青阳—九华山复式岩体4个阶段从早到晚(花岗闪长岩→二长花岗岩→正长花岗岩→细粒花岗斑岩),晚期(第三、第四阶段)比早期(第一、第二阶段)岩浆岩的锆石εHf(t)值呈显著增高趋势,岩浆形成温度升高(705.3℃→715.9℃→827.1℃→805.5℃),氧逸度降低(93.8→149.1→70.1→69.9)。进一步分析认为,青阳—九华山复式岩体源于同一具有壳幔混源的岩浆源区,随着时间的演化,岩浆房中幔源组分比例逐渐增高,幔源物质的加入,不仅提高了晚期岩浆形成温度,一定程度改变了源区组成。青阳—九华山复式岩体4个阶段花岗岩均经历了榍石、角闪石、金红石、斜长石等矿物的分离结晶,晚期(第三、第四阶段)花岗岩相比早期(第一、第二阶段)花岗岩具有更高的分异程度。青阳—九华山复式岩体中第一、第二阶段花岗岩具有较好的W—多金属矿床成矿潜力。

The Qingyang—Jiuhuashan complex pluton is the largest in outcrop and most representative among those complex plutons in southern Anhui provinces,but its magmatic genesis and mineralization potential are still waiting for further observation,including the magmatic sources,evolution and its metallogenic specificity.In this study,after geological characteristics observation and previous whole-rock geochemical summary,we systematically analyze the magmatic zircon trace elements and Hf isotopes from the four-stages intrusions of the Qingyang—Jiuhuashan complex pluton.The results show that,TheεHf(t)values of the 4 stages of intrusive rocks in the Qingyang—Jiuhuashan complex pluton(granodiorite→monzogranite→syenogranite→fine granite porphyry)consistently increasing from early to late.And the zircon forming temperatures of the early to late intrusions are gradually increasing(705.3℃→715.9℃→827.1℃→805.5℃),while gradually decreasing their Oxygen fugacity(93.8→149.1→70.1→69.9).it is suggested that the 4 stages melts were from the same crust—mantle mixed magmatic sources,where mantle ratios were gradually increased from early to late.The increasing mantle input resulted in the higher melting temperatures and compositions of the initial magma.During the evolution processes of the 4 stages of intrusive rocks in the Qingyang—Jiuhuashan complex pluton,all melts experienced distinct fractional crystallization of titanite,amphibole,rutile and plagioclase,and the later stages(stage III and IV)granite melts experienced higher FC degrees than the early ones(stage I and II).Compared with stage III and IV intrusions,The stage I and II intrusions of Qingyang—Jiuhuashan complex pluton have better metallogenic potential of the W—polymetallic deposit.