湖南宝山矿区煌斑岩的地球化学特征及地质意义

Geochemical characteristics of lamprophyre and its geological significance in Baoshan deposit, Hunan province, China

最近在湖南宝山矿区发现了煌斑岩脉，岩石样品具有典型煌斑结构，斑晶矿物主要为辉石、长石、黑云母及石英。Si02含量为50．23％～51．29％，（Na2O＋K2O）为4．65％-5．63％，K20／Na20值为1．89～7．77。根据TAS图解和SiO2-NbfY图解投点，宝山煌斑岩为碱性系列钙碱性煌斑岩。煌斑岩过渡族元素配分型式为“w”形，相对富集Ti、Mn和Zn，明显亏损Cr、Co和Ni；微量元素表现为Th和LREE强烈富集并伴有K、Sr和Ba相对亏损的特征。煌斑岩中的锆石为岩浆锆石，U-Pb定年结果为（156±2）Ma，煌斑岩浆来源于受到俯冲组分改造的富集地幔。湖南宝山矿区煌斑岩的产出显示了燕山期深部岩浆活动的踪迹，反映燕山期区域陆内伸展的大地构造背景。

The lamprophyre vein from Baoshan minning area, southern Hunan Province, is a new discovery, the rock sample has typical lamprophyrie texture, the phenocryst minerals are pyroxene, feldspar, biotite and quartz. The contents of SiO2 range from 50.23% to 51.29%, the values of Na2O＋ K2O range from 4.65% to 5.63%, the values of K20/Na20 range from 1.89 to 7.77. According to figure of TAS and SiO2-Nb/Y, the samples belong to calc-alkaline lamprophyres of alkaline series. Distribution pattern for transitional-metal elements shows enrichment in Ti, Mn and Zn, obvious depletion in Cr, Co and Ni. The characteristics of trace elements show that strong enrichment in Th and LREE, relative depletion in K, Sr, Ba. The zircons collected from lamprophyre are magmatic zircons due to oscillatory zones, U-Pb dating results display the crystal average age of measured zircons is （156±2） Ma, the lamprophyre is derived from metasomatic enrichment lithospheric mantle. The discovery of lamprophyre from Baoshan suggests the trace of Yanhsanian deep basic magma activity, corresponding to regional intra-plate extensional tectonic background in Yanshanian stage.