白银厂矿田石英钠长斑岩Sm-Nd, Rb-Sr 同位素特征及意义

摘要

Based on the previous studies of the volcanic rocks, the authorssampled 4 fresh quartz albitophyres from the well producing areas in Xiao Tieshan Mine to make up for the location not yet studied by previous workers. The isotopic analyses of the samp les are made. The results, together with previous information, show that the for mation of the quartz albitophyres has 2 episodes-the first at 502.5～539.46 Ma BP and the second at 395.8～402.97 Ma. According to the Sm-Nd isotopic model age f or the quartz albitophyres and the formation of the subvolcanic rocks synchronog enic with or a little later than the volcanic rocks in this area, it is well def ined that the volcanic rocks were formed in the Mid-Cambrian period. Their char acteristics indicate that the volcanic rocks could be generated from the variabl y enriched mantle source.%甘肃省白银厂矿田含矿火山岩中的石英钠长斑岩，对于该区火山岩的定年及形成物源区特征的研究具有十分重要的意义。作者在前人同位素分析数据稀疏的区域内，于现采区井下采集了4个新鲜无蚀变的石英钠长斑岩，进行了Sm-Nd,Rb-Sr同位素分析。结果表明，该区石英钠长斑岩形成时代有二期，第一期成岩年龄为502.50～539.46Ma，形成时代为中晚寒武世；第二期成岩年龄为395.80～402.97Ma，形成时代为早泥盆世，依据石英钠长斑岩的Sm-Nd模式年龄，并结合次火山岩的形成时代与该区火山岩同期或稍晚的关系，可确定该区火山岩的形成时代为中寒武世。同位素特征还表明，该区火山岩物质来源于经过一定富集作用的地幔，且地幔源区发生过部分熔融。