山东牟平—乳山金成矿带南段煌斑岩成因机制研究

Formation Mechanism of Lamprophyres in Southeast Part of the Muping–Rushan Gold Metallogenic Belt in Shandong Province

山东牟平—乳山金成矿带东南部发育大量的煌斑岩脉,主要为云斜煌岩和斜煌岩。本文选择牟乳带南段冯家镇地表出露的煌斑岩样品进行LA-ICP-MS锆石U-Pb年代学和全岩主微量元素研究。定年结果表明其成岩年龄为(150.6±6.1) Ma,属晚侏罗世。煌斑岩SiO_2=47.15%～58.91%,碱性岩系列,岩石为玄武质安山岩,属于太平洋型(钠质)火山岩。岩石具有富集大离子亲石元素(LILE)和轻稀土元素(LREE)、相对亏损高场强元素(HFSE)的特征。成岩过程中黑云母、角闪石、单斜辉石和少量的斜长石的分离结晶作用,研究认为该区的煌斑岩是来自于古太平洋板块的俯冲背景下幔源岩浆上侵,同时受到了壳源物质的混染。

There are lots of lamprophyre veins in the southeastern part of the Muping–Rushan gold metallogenic belt,which mainly comprise kersantite and fraidronite.In this paper,using geochemical and zircon LA-ICP-MS U-Pb dating methods,the authors selected the surface lamprophyres from Fengjia Town to do the study.The dating result shows that the petrogenetic age is(150.6±6.1)Ma,suggesting late Jurassic magmatic activity.Geochemical results show that the lamprophyres contain SiO2 47.15%~58.91%,and belong to alkaline rock series.The rocks are basaltic andesite,belonging to the Pacific type(sodium)volcanic rocks.The rocks are characterized by enrichment of large ion lithophile elements(LILE)and light rare earth elements(LREE),and relative depletion of high field strength elements(HFSE).The crystallization of biotite,amphibole,clinopyroxene and a small amount of plagioclase occurred during the rock-forming process.Lamprophyres were formed during the subduction of the paleo-Pacific plate,resulted from mantle-derived magma intrusion,and was contaminated by crustal source materials.