山东胶州大西庄辉石巨晶Sr-Nd同位素组成及其源区性质

胶州大西庄玄武岩（73 Ma）中的辉石巨晶与寄主玄武岩具有几乎完全相同的同位素组成，其⁸⁷Sr/⁸⁶Sr（t）和ε_Nd（t）分别为0.703 3～0.704 1、+4.5～+6.5和0.703 5～0.703 8、+7.1～+7.6，暗示辉石巨晶和寄主岩具有相同的地幔源区，即辉石巨晶是玄武岩浆在高压下结晶的产物.亏损的同位素特征表明：在白垩世末期（～73 Ma），胶东地区的岩石圈地幔已经由富集转变为亏损，表现出类似于中国东部新生代地幔的同位素特征，即表明当时岩石圈减薄（或置换）已经完成.

Sr-Nd isotopic characteristics of the pyroxene megacrysts from Daxizhuang of Jiaozhou and their source significance

The pyroxene megacrysts hosted by basalt (73 Ma) at Daxizhuang, Jiaozhou and the host basalts showed uniform isotopic compositions,with ⁸⁷Sr/⁸⁶Sr(t)=0.703 3~0.704 1 and ε_Nd (t)= +4.5~+7.6,respectively,which suggested that they were derived from the same mantle source,and the megacrysts were crystallized from the host basaltic magma under high pressure.Moreover,the dating of 73 Ma of Daxizhuang basalts and hosted megacrysts showed the similar depleted isotopic characteristics with Cenozoic basalts from eastern China, implying that the transformation of the isotopic characters of the lithospheric mantle from enrichment to depletion in Jiaozhou, and also the lithosphere thinning was completed in Late Cretaceous (73 Ma).