浙东南山门地区早白垩世同源岩浆活动的稀土元素制约

Early Cretaceous Comagmatic Activities of Shanmen Region,Southeastern Zhejiang Province,China:Constraints from Rare Earth Elements

对浙东南山门地区早白垩世中酸性火山-侵入杂岩进行了稀土元素含量的ICP-MS分析,对比研究了其稀土元素地球化学特征。不同类型岩浆岩的稀土元素除Eu外具有基本一致的轻稀土富集的右倾配分模式,以及稳定的Sm/Nd,La/Nd和La/Sm比值,表明它们具有一致的岩浆源区,只是分异演化程度不同。Eu/Sm比值(0.02～0.09和0.15～0.21)及一致的Nb/Ta比值(13.9～16.9),介于地壳和地幔值之间,表明其为壳幔岩浆混合作用的产物。稀土元素协变关系显示成岩过程可能以部分熔融作用为主。结合微量元素研究,山门地区早白垩世同源岩浆活动可能与古太平洋板块俯冲碰撞后岩石圈伸展引起的弧后引张构造有关。

REE content of early Cretaceous intermediate-acidic volcanic-intrusive complex in Shanmen region,southeast Zhejiang province,China,was analyzed by ICP-MS,REE geochemistry characteristics of which was studied comparatively.The REE distribution patterns for various rock types in the area were consistent with the exception of Eu and exhibit right-dipping patterns with LREE enrichment,and the stable Sm/Nd,La/Nd,La/Sm ratio,indicated that they had the same magma source,with different degree of differentiation and evolution.Eu/Sm ratio（0.02 to 0.09 and 0.15 to 0.21）and the consistent Nb/Ta ratio（13.9 to 16.9） between the values of the crust and mantle,indicated that they were products of the crust-mantle magma mixing.The covariant relation of REE suggested that partial melting may be the principal diagenetic process.Combined with trace elements geochemistry,early Cretaceous Comagmatic activities of Shanmen region may be related to back-arc extensional tectonic setting caused by lithospheric extension after subduction and collision of the ancient Pacific plate.