越南西北部莱州地区新生代煌斑岩地球化学特征及其成因  

Geochemical characteristics and origin of lamprophyre in the Laichau area,northwestern Vietnam

作　　者：杨一增[1] 龙群[1] 胡焕婷[1] HIEU Pham Trung NGUYEN Thi Bich Thuy 陈福坤[1] 

机构地区：[1]中国科学技术大学地球与空间科学学院壳幔物质与环境重点实验室,合肥230026 [2]Department of Geology, Hanoi University of Mining and Geology, Hanoi, Vietnam [3]Research Institute of Geology and Mineral RCesources, Hanoi, Vietnam

出　　处：《岩石学报》2013年第3期899-911,共13页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(41090372、40973042)资助

摘　　要：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。Cenozoic lamprophyre dykes exposed in the Laichau area of northwestern Vietnam hold geological significances for understanding geochemical features and evolution of deep lithosphere in the eastern part of the Tethyan orogenic belt. This study reports geochemical and Sr-Nd-Pb radiogenic isotopic composition of lamprophyre dykes from the Laichau area and discuss their petrogenesis and geological implications. Lamprophyre samples reported here are of eale-alkaline and potassic to uhra-potassie characteristics in major element contents. When compared with relating rocks in the neighbouring areas, lamprophyre dykes from the Laichau area are similar in geochemical composition with alkalic rocks in the Ailaoshan fault zone, but considerable different from volcanic rocks exposed in Hainan and southern Vietnam. The Laichau lamprophyre dykes show enriched isotopic feature of high s7 Sr/86 Sr ratios, low 143 Nd/ ~＊~ Nd ratios and high radiogenic Pb isotopic composition. Evidence of trace element contents from these lamprophyre samples indicates that the magma source of the lamprophyre dykes likely suffered metasomatic processes or input of sedimentary components before partial melting of the mantle. Low 2~sPb ＊/2~6Pb ＊ ratios of lamprophyre samples imply that enrichment of the mantle source producing the Laichau lamprophyre dykes took place recently, probably related to amalgamation of the Indoehina block to the Yangtze block during the Late Paleozoic to Early Mesozoic.

关 键 词：越南西北部 新生代 煌斑岩 地球化学 SR-ND-PB同位素 

分 类 号：P588.15[天文地球—岩石学]