福建紫金山地区中生代构造环境转换的岩浆岩地球化学证据

紫金山地区的中生代岩浆岩主要由晚侏罗世花岗岩和早白垩世火山－侵入杂岩构成，其中后者与该地区大规模的铜金成矿作用有关。此外，该区的才溪二长花岗岩岩枝是在晚侏罗世紫金山花岗岩体定位之后，早白垩世火山－侵入杂岩形成之前侵位的。晚侏罗世花岗岩的元素地球化学特征显示，它是印支期－燕山早期陆内叠复造山过程中，陆壳岩石在相对低压条件下的熔融产物。早白垩世火山－侵入杂岩以高Al和Ti、富集轻稀土、Eu负异常不明显，相对富Sr,Cr,Ni,Zr,Cu,Au,Ag，以及较低的Sn,W,Rb/Sr值和较低的锶氧同位素初始比值，区别于晚侏罗世花岗岩；它们的Sr/Y-Y和Ni-Cr关系与残余10％榴闪岩或榴辉岩的MORB熔融曲线大致吻合，表明它们是地幔上隆、区域拉伸环境下洋壳物质部分熔融的岩浆产物。才溪二长花岗岩的元素地球化学介于晚侏罗世紫金山花岗岩与早白垩世火山－侵入杂岩之间，它是区域挤压向区域拉伸转换的标志性产物。岩浆岩地球化学证据显示，紫金山地区早白垩世大规模铜金成矿作用，形成于区域挤压转换到拉伸的构造环境。

Geochemistry of Mesozoic Magmatites in the Zijinshan Region and Implication on Regional Tectonic Inversion

Mesozoic magmatites in the Zijinshan region are composed of Late Jurassic granite pluton (157~140 Ma) and Early Cretaceous volcano-intrusive complexes (128~94 Ma), in which the latter is related to large-scale Cu-Au mineralizations of this region. In addition, the Caixi monzogranite with a zircon U-Pb age of 137 Ma was intruded after the granite pluton and before the volcano-intrusive complexes. Geochemistry of major and trace elements for Late Jurassic granites show that they were derived from continental crustal melting under lower pressure during the Indosinian to Early Yanshanian intracontinental orogeny. In comparison with the Late Jurassic granite, the Early Cretaceous volcano-intrusive complexes exhibit elevated Al, Ti, Sr, Cr, Ni, Zr, Cu, Au and Ag value, enrichment of LREE, lack of obviously negative europium anomaly, and lower Sn, W, Rb/Sr and Sr-O isotope ratio values. Their Sr/Y-Y and Ni-Cr relationship coincides with partial melting curves of MORE leaving a 10% garnet amphibolite or eclogite, that shows they were derived from partial melting of oceanic crustal under mantle upwelling and regional extension. Geochemistry of major and trace elements of the Caixi monzogranite lies between the Late Jurassic granite and the Early Cretaceous volcano-intrusive complexes giving a geochemical mark for regional tectonic inversion from compression to extension. Geochemistry of Mesozoic magmatites in the Zijinshan region provides an evidence for that large-scale Cu-Au mineralizations in this region formed under tectonic inversion environment from compression to extension.