摘要
湘东北蕉溪岭富钠煌斑岩是产于陆内拉张环境的一组特殊的岩石类型 ,包括闪斜煌斑岩、棕闪煌斑岩、闪辉正煌岩等。在岩石化学组成上 ,Si O2 为 4 5 .78%～ 4 8.4 2 % ,K2 O+Na2 O为 5 .0 5 %～ 6 .5 6 % ,属于碱性玄武岩系列 ,岩石以富集Na2 O、Ti O2 、<Fe O>、Mg O,尤其以富钠为特征 ,K2 O/Na2 O平均值为 0 .4 1,在煌斑岩分类中属于钠质碱性煌斑岩。岩石Σ REE较高 ,富 L REE,不出现铕负异常 ,δEu平均值为 1.0 4。岩石 Rb- Sr等时线年龄为 136 .6 1Ma。岩石微量元素组成具有洋岛玄武岩 (OIB)型特征 ,HREE明显亏损 ,不出现 Ta、Nb、Ti的亏损以及 L IL E富集不明显 ,表明岩浆源区与岛弧环境无关 ,并且地壳物质混染程度很低。87Sr/86 Sr初始比值 0 .70 5 30 8～ 0 .70 5 36 6 ,εNd(t)为 +3.5～ +3.8,1 43Nd/1 44 Nd初始比值 0 .5 12 6 39～0 .5 12 6 5 4 ,具有较为均一的洋岛玄武岩 (OIB)地幔源区性质 ,并且位于地幔排列线附近。推测区内存在地幔柱构造环境 ,岩石的形成是在软流圈地幔上涌条件下导致深部地幔部分熔融产物 。
The lamprophyres occurring at Jiaoxiling area in northeastern Hunan Province are special types of lamprophyres within continental plate, which include kersantite, barkevite lamprophyre, spessartite and garganite. The contents of SiO2 are 45.78%similar to48.42%, K2O + Na2O are 5.054%similar to6.56%, they all belong to alkalic series. The characteristics of rocks are rich in Na2O, TiO2, <FeO>, MgO, especially in sodium, K2O/Na2O = 0.41, which show that the rocks belong to sodium-rich alkali lamprophyres (agpaitic lamprophyres) in lamprophyre classification. The whole-rock Rb-Sr isochron age of the lamprophyres in Jiaoxiling area is 136.61 Ma. The rocks have relatively high SigmaREE, no Eu negative anomalies (deltaEu = 1.04). Trace elements show that the rocks have characteristics of oceanic island basalt (OIB). HREE was depleted, but Ta, Nb, Ti were not depleted and LILE was very obviously not rich which shows that the magma source not occurred in island arc and the crustal assimilation was very limited. The initial Sr-87/Sr-86 isotope ratio of the lamprophyres is 0.705308similar to0.705366. The Initial Nd-143/Nd-144 isotope ratio is 0.512639similar to0.512654 and (epsilonNd)(t) + 3.5similar to + 3.8. Those accord with the nature of OIB magma source and locate near the mantle array,line. Geochemistry of the lamprophyres expresses the asthenosphere mantle diapirism and existing mantle plume. The agpaitic lamprophyre has special magma source. It was the product of part melting of mantle source controlled by asthenosphere mantle diapirism in the tectonic setting of mantle plume.
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2002年第4期459-467,共9页
Acta Petrologica Sinica
基金
中国科学院知识创新工程项目 ( KZCX2 -10 2 )
中国科学院矿床地球化学开放研究实验室基金项目 ( 2 0 0 0 )
中国科学院边缘海地质与古环境开放实验室基金项目 ( BYH0 1A0 2 )联合资助
关键词
富钠碱性煌斑岩
地球化学特征
洋岛玄武岩
蕉溪岭地区
岩石化学
地幔
sodium-rich alkalic lamprophyre (agpaitic lamprophyres)
geochemical characteristics
oceanic island basalt (OIB)
Jiaoxiling area
