雷瓊地區新生代玄武岩地球化學分析及岩石成因

Abstract

雷瓊地區是位於東亞地區中國大陸的南端，其東為南海，其西為紅河-哀牢山剪切帶，在新生代時期是個火山活動活躍的地區。其主要元素、微量元素及稀土元素分析中，有著OIB的特徵及地函熱柱玄武岩環境特徵，共容元素的原始地函標準化作圖中，有著類似上部地函的特徵，有Ti的正異常及Cr、Ni的負異常。表示可能有橄欖石及斜輝石結晶沉降，造成Cr、Ni的濃度降低。Ti的正異常可能是金紅石參與部分熔融作用會使岩漿中Ti的成分增加。La/Ce、Ce/Nd、Th/La、Zr/Hf回歸曲線作圖。四條回歸曲線皆為回歸原點的直線，證明雷瓊地區新生代玄武岩的成分來源是均一的，屬同一地函源區。而岩漿演化過程，皆經歷上部地函的部分熔融及後期結晶分化作用，其中海南島結晶分化程度高於雷州半島。 前人同位素研究中，本區岩漿源區可能是來自DMM及EMII兩端成分源區。鄢全樹和石學法（2007）提出海南地熱柱模式，解釋南海海底新生代玄武岩中EMII來源的成因，也提供本研究區EMII來源的合理解釋。

Leiqiong area is located at the south of China in East Asia, South China Sea in the east, Red River - Ailaoshan shear zone in the west. During Cenozoic, it is active region of volcanic activity. The major elements, trace elements and REE distributions, indicate the same source for Leiqiong magma, with OIB and mantle plume characteristics. In the primitive mantle normalized compatible elements patterns there are positive Ti and negative Cr and Ni anomalies. The negative Cr and Ni anomalies may be related to the fractional crystallization of olivine and clinopyroxene while the positive Ti anomaly may be due to the involvment of rutile in the partial melting process.La/Ce, Ce/Nd, Th/La, Zr/Hf pairs have positive correlation and can be regressioned through the zero point indictating these magmas belong to the same source.Leiqiong magmatic evolution, have experienced partial melting of the upper mantle and crystallization differentiation. The degree of crystallization differentiation for Hainan Island basaltic magma is higher than the Leiqiong magma. Previous isotope studies suggest that this area may have DMM and EMII source composition. Hainan plume model was proposed to explain EMII source composition of Cenozoic basalts from the South China Sea, and it provided reasonable explanation of EMII source composition of Cenozoic basalts from the study area.