琼中麻粒岩的成因:稀土元素地球化学制约

Genesis of Qiongzhong Granulite:Constraints of Rare Earth Element Geochemistry

稀土元素地球化学分析表明,琼中麻粒岩可以分为“高Ti”麻粒岩(TiO2含量大于1.0%)和“低Ti”麻粒岩(TiO2含量低于1.0%)两种化学类型。“高Ti”麻粒岩以稀土总量高,轻稀土高度富集,轻、重稀土强烈分馏为特征,稀土配分曲线呈右倾单斜型,与本区变基性火山岩的稀土分布特征相似;低“Ti”麻粒岩以稀土总量较低,轻稀土分馏强烈,但重稀土分馏不明显为特征,稀土配分曲线呈重稀土平坦的左高右低型,与许多浅成基性岩的稀土分布特征相似;认为琼中麻粒岩形成于晋宁期的可能性最大。两类麻粒岩的识别,有利于深化对琼中杂岩形成和演化过程的认识。

REE data for granulites in Qiongzhong complex reflect the two different chemical subtypes： （1） Samples with TiO2 contents greater than 1.0% （＂ high Ti＂ granulites） show rightward incline REE patterns, similar to the patterns of meta-basic volcanics in the complex, with high REE contents, and markedly LREE enrichments and HREE depletions. （2） Samples with TiO2 contents less than 1.0% （ ＂low Ti＂ granulites） show HREE flat patterns, comparable to many shallow basic rocks, with lower REE contents and modest LREE enrichments. Owing to rare-earth element geochemistry constrains on genesis, Qiongzhong granulites likely were formed in Jinning period. Identification of two granulites subtypes can contribute to re - know the process of formation and evolution of Qiongzhong complex.