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越南西北部莱州地区出露的新生代煌斑岩岩脉对理解特提斯造山带东段的深部岩石圈特征和演化具有重要的地质意义。本文报道莱州地区煌斑岩的元素地球化学和Sr-Nd-Pb同位素组成特征,探讨其岩石成因。该地区煌斑岩属于钙碱性,钾质-超钾质煌斑岩特征。地球化学特征对比表明,莱州地区煌斑岩与哀牢山断裂带碱性岩具有相似的地球化学特征,但与海南和越南南部火山岩存在明显差异。分析结果表明,煌斑岩具有高的87Sr/86Sr比值、低143Nd/144Nd比值和高放射性成因Pb同位素组成特征。岩石的微量元素组成特征指示,形成煌斑岩的地幔源区可能经历过流体交代作用或沉积物组分的加入。低208Pb*/206Pb*比值暗示地幔源区富集事件是近期发生的,可能与晚古生代-早中生代印支地块向扬子地块俯冲事件有关。
The Cenozoic lamprophyre dykes exposed in the Laizhou area of northwestern Vietnam have important geological significance for understanding the characteristics and evolution of the deep lithosphere in the eastern segment of the Tethys orogenic belt. This paper reports the elemental geochemistry and Sr-Nd-Pb isotopic compositions of lamprophyres in Laizhou area and discusses their petrogenesis. Lamprophyre in this area belongs to calc-alkaline, potash-ultra-potash lamprophyre characteristics. The comparison of geochemical characteristics shows that the lamprophytes in Laizhou area and the Ailaoshan fault zone have similar geochemical characteristics, but have obvious differences with the volcanic rocks in Hainan and southern Vietnam. The results show that the lamprophyre has high 87Sr / 86Sr ratio, low 143Nd / 144Nd ratio and high Pb isotopic composition. The trace element compositional characteristics of the rock indicate that the mantle source zone forming the lamprophyre may have undergone fluid metasomatism or addition of sediment components. The low 208Pb * / 206Pb * ratio suggests that the mantle source enrichment event occurred recently and may be related to the Late Paleozoic-Early Mesozoic Indosinian subduction to the Yangtze block.