福建北部近岸东台山岛火山岩形成时代、地球化学与古太平洋板块俯冲的响应

福建北部沿岸岛屿岩石组合以晚中生代火成岩为主，研究认为是古太平洋俯冲消减的产物，对反演洋盆构造演化具有重要的指示意义。本次对其中的福建北部海域东台山岛上广泛发育的酸性火山岩进行了锆石U-Pb定年以及全岩主微量地球化学分析工作。2件年代学样品分别获得了92 Ma和86 Ma的锆石U-Pb年龄，确定东台山岛火山岩形成于晚白垩世。全岩地球化学特征指示火山岩样品以酸性钙碱性岩石为主，整体富集Rb、Ba等元素，亏损Nb、Ta、Sr、Eu等元素，显示弧型岩浆岩的地球化学组成。研究认为东台山岛火山岩起源于古老下地壳变沉积岩熔融，并在浅层岩浆房内经历了不同程度的结晶分异过程。结合区域上晚中生代岩浆作用由陆向海的时空迁移特征，福建北部沿岸岛屿火山岩形成的深部动力学机制应该与古太平洋俯冲过程中的板片回转过程相关。

The age and geochemistry of volcanic rocks of Dongtaishan Island in northern Fujian and their response to the subduction of the Paleo-Pacific Plate

Coastal islands of northern Fujian are mainly composed of volcanic rocks, which were produced by the paleo-Pacific oceanic subduction. These volcanic rocks provide critical information about the geodynamic evolution of paleo-Pacific Ocean. In this paper, the authors report new zircon U-Pb ages and whole-rock major and trace element geochemistry of the felsic rocks from the Dongtaishan Island of northern Fujian. Two geochronological samples yielded zircon ages of ~92 Ma and ~84 Ma, indicating that the volcanic rocks in Dongtaishan Island were formed in Late Cretaceous. Geochemically, all these felsic samples are calcalkaline, enriched in Rb, Ba, and depleted in Nb, Ta, Sr and Eu, suggesting a geochemical affinity with arc volcanic rocks. It is thus concluded that these volcanic rocks were derived by partial melting of ancient crustal metasedimentary sources and followed by fractional crystallization in the shallow magma chamber. These new data, combined with the oceanward migration of late Mesozoic magmatic activity, have led the authors to propose that the coastal islands of northern Fujian were triggered by the slab rollback during oceanic subduction of paleo-Pacific Ocean.