柴西南昆北地区花岗岩基岩地球化学特征及成因

研究区位于柴达木盆地和祁漫塔格-东昆仑造山带的过渡带的昆北断阶带。钻探揭示第三系盆地基底广泛分布花岗岩基岩。岩石学特征表明属二长花岗岩类,副矿物以锆石为主。化学成分分析结果表明,岩石具较高含量的SiO2和Al2O3,属过铝的钙碱性系列。岩石中强不相容元素Rb、Ba、Zr等强烈富集,Ta、Ce、Nb、Sr、Th等中等不相容元素富集中等;弱不相容元素Y富集。岩石稀土总含量大多在194.41～231.63μg/g之间;LREE/HREE比值为2.31～2.4;岩石属轻稀土富集型。岩石中Eu负异常明显,中等亏损;Ce略有亏损;Eu/Sm值在0.15～0.16间。地球化学特征显示岩石物质来源于下地壳物质的熔融,构造环境判别图解中样品投影于同碰撞期的区间,岩石是同碰撞构造环境下形成,为早古生代洋陆转换时的岩浆活动,属于加里东期造山旋回时期产物。

Geochemical Characteristics of Granite Matrix in Kunbei Area of Southwestern Qaidam Basin

The studied area was located in Kunbei Fault Terrace Belt,which was the transitional zone of Qaidam Basin and Qimantage Mountain in the Eastern Kunlun Orogenic Belt.The drilling results revealed that numerous granite matrixes were distributed in the basement of Tertiary sedimentary basins.Petrological characteristics suggested that the granites were monzogranites,and the accessory minerals were mainly zircons.Chemical composition analysis indicated that the granites belonged to the peraluminous calc alkaline series for their higher content of SiO2 and Al2O3.The highly incompatible elements(Rb,Ba,Zr) of the granites were strongly enriched while the moderately incompatible elements(Ta,Ce,Nb,Sr,Th) were enriched mildly and the weakly incompatible elements(Y) were enriched.ΣREE in the rock was mostly among 194.41~231.63(μg/g)with LREE/HREE ratio being 2.31~2.4 and belonged to type of LREE enrichment.The REE distribution patterns show that there exists obvious Eu anomaly and mediate Eu depletion,and Ce is slightly depleted.And Eu/Sm value generally ranges from 0.15 to 0.16.The geochemical characteristics reveal that its source materials are from the lower crust melting.On the identification diagram of tectonic setting,samples are plotted in the area at the syn-collision stage,the granites are formed during the syn-collision circumstances,they belong to the magma movement in the Early Paleozoic ocean-land transition,and they are considered as the products of Caledonian orogenic cycle.