阿尔金红柳沟斜长角闪岩的形成时代及其地球化学特征

Geochemistry and Geochronology of Amphibolite from the Hongliugou Area,Altyn Tagn,Northwestern China

阿尔金山北缘红柳沟蛇绿岩带南部发育一套斜长角闪岩,其Sm-Nd等时线年龄为(1 454±65)Ma,单颗粒锆石U-Pb年龄为(506±11)Ma稀土元素含量较低,具有平坦型和轻稀土元素微弱富集型两种稀土元素配分模式。微量元素经洋中脊玄武岩和岛弧玄武岩过渡类型的特征。各种岩石地球化学判别图解主要表现为洋中脊玄武岩,部分为岛弧玄武岩的特征,表明很可能形成于扩张的弧后盆地环境,结合与早古生代玄武岩地球化学特征的对比研究可以判断区内中元古代末至新元古代早期存在具有洋壳性质的基性火山活动。

A suit of amphibolite occurs at the south to Hongliugou ophiolite belt, in northern margin of the Altyn Tagn. Samples from the arnphibolite yielded a whole rock isochron Sm-Nd age of （1 454± 65）Ma and a single Zircon U-Pb age of （506 ± 11）Ma. The geological and geochemical evidences show that the former age is most likely interpreted as the form age and the latter age is almost consistent with the metarnophism in the early Paleozoic collision. Geochemical data suggest that the amphibolite mainly belongs to tholeiite series. Most of the samples have low REE with slightly enriched LREE or flat REE patterns. The spider diagrams of trace elements normalized by N-MORB are mainly similar to the transitional basalts between mid-ocean ridge basalts （MORB） and volcanic arc basalts （VAB）. In various discrimination diagrams, the samples also mostly plot in MORB field with minor in VAB field. Therefore, the amphibolite was probably formed in the tectonic setting of spreading basin-arc basin. The existing of oceanic basic volcanic activities is then deduced from the studies above.