中国东部新生代玄武岩记录古太平洋俯冲带壳幔相互作用

大陆玄武岩通常具有与洋岛玄武岩相似的地球化学成分，其中含有显著的壳源组分.对于洋岛玄武岩来说，虽然其中的壳源组分归咎于深俯冲大洋板片的再循环，但是对板片俯冲过程中的壳幔相互作用缺乏研究.对于大陆玄武岩来说，由于其形成与特定大洋板片在大陆边缘之下的俯冲有关，可以用来确定古大洋板片俯冲的地壳物质再循环.本文总结了我们对中国东部新生代玄武岩所进行的一系列地球化学研究，结果记录了古太平洋板片俯冲析出流体对地幔楔的化学交代作用.这些大陆玄武岩普遍具有与洋岛玄武岩类似的地球化学成分，在微量元素组成上表现为富集LILE和LREE、亏损HREE，但是不亏损HFSE的分布特点，在放射成因同位素组成上表现为亏损至弱富集的Sr-Nd同位素组成.在排除地壳混染效应之后，这些玄武岩的地球化学特征可以由其地幔源区中壳源组分的性质来解释.俯冲大洋地壳部分熔融产生的熔体提供了地幔源区中的壳源组分，其中包括洋壳镁铁质火成岩、海底沉积物和大陆下地壳三种组分.华北和华南新生代大陆玄武岩在Pb同位素组成上存在显著差异，反映它们地幔源区中的壳源组分有所区别.中国东部新生代玄武岩的地幔源区是古太平洋板片于中生代俯冲至亚欧大陆东部之下时，在>200 km的俯冲带深度发生壳幔相互作用的产物.在新生代期间，随着俯冲太平洋板片的回卷引起的中国东部大陆岩石圈拉张和软流圈地幔上涌，那些交代成因的地幔源区发生部分熔融，形成了现今所见的新生代玄武岩. 

Crust-Mantle Interaction in the Paleo-Pacific Subduction Zone: Geochemical Evidence from Cenozoic Continental Basalts in Eastern China

Continental basalts,erupted in either rift or flood mode,usually show oceanic island basalt (OIB)-like geochemical compositions,with the presence of crustal components in the mantle sources of OIB. However,it is uncertain for OIB when and how the crustal components were incorporated into the mantle sources. In comparison,the formation of continental basalts is associated with specific settings for subduction of oceanic slabs and its interaction with the mantle. In this regard,a geochemical study of continental basalts can provide insights into the crust-mantle interaction in oceanic subduction channels. This is illustrated for the geochemistry of Cenozoic continental basalts in eastern China. These basalts are characterized by OIB-like trace element compositions and depleted to weakly enriched Sr-Nd isotope compositions. After precluding the effect of crustal contamination,the geochemical features of these basalts can be interpreted by recycling of crustal components into their mantle sources. The subducting oceanic crust is the major source of crustal components. In addition to both igneous oceanic crust and seafloor sediment,the lower continental crust of the overriding continental margin was offscrapped into the mantle sources. There are a series of differences in Pb isotope compositions between the Cenozoic basalts in North and South China,suggesting a difference in the nature of crustal components between these two areas. The mantle sources of Cenozoic continental basalts were produced by the crust-mantle interaction in the oceanic subduction zone during the Mesozoic subduction of paleo-Pacific slab beneath the Euroasian continent. Hydrous melts were produced by partial melting of the subducting oceanic crust at postarc depths. They were then reacted with the overlying mantle wedge to generate metasomatic domains,whose partial melting in the Cenozoic give rise to the continental basalts.