塔里木板块东南缘早二叠世角闪石岩的发现及大地构造意义

Discovery and tectonic significance of early Permian hornblendite in the southeastern margin of the Tarim Plate

甘肃大红山北角闪石岩体是塔里木板块东部新发现的一类镁铁质-超镁铁质岩体,通过野外观察、岩矿鉴定及地球化学研究,发现其岩浆分异不明显、岩石类型单一、组分为角闪石岩、全岩,w（SiO_2）=41.64%～50.83%、w（K_2O）/w（Na_2O）=0.45～0.66、w（K_2O）＋w（Na_2O）=1.02%～2.81%,属亚碱性拉斑玄武岩系列,具有岛弧环境地球化学特征.采用LA-ICP-MS锆石U-Pb法获得年龄为273.6土4.8Ma.反映早二叠世受北侧古亚洲洋的汇聚碰撞,塔里木板块东南缘处于汇聚碰撞的岛弧环境向相对稳定的后造山环境方向演化阶段.

Hornblendite pluton in northern Dahongshan,Gansu Province,is a newly discovered type of maficultramafic pluton in the eastern Tarim Plate.Combined with the field observation and analyses of rock-mineral identification,geochemical studies showed that the magmatic differentiation is not obvious,the type of rock is single,and the components are mainly amphibolite.The SiO_2 content of whole rock is 41.64%-50.83%,the ratio of w（K_2O）/w（Na_2O） is 0.45 to 0.66 and the value of w（K_2O）＋w（Na_2O） ranges from 1.02%to 2.81%.These characteristics showed that this type of rock belongs to the series of alkali tholeiite with the geochemical feature of an island arc environment.The age of the amphibole pluton achieved from the LA-ICP-MS U-Pb dating for zircons is 273.6±4.8 Ma,suggesting that the convergence collision island arc environment of the southeastern margin of Tarim Plate was transformed to relatively stable post- orogenic environment during the early Permian due to the convergence collision of the paleo-Asian ocean.