“吐哈天窗”卡拉塔格岩体的地球化学和岩石成因

Geochemistry and petrogenesis of the Kalatag intrusion in the "Tuha window"

卡拉塔格岩体是吐哈盆地南缘古生代天窗中唯一的一个岩体。主量元素特征表明卡拉塔格岩体属富钠的钙碱性系列;岩石富集轻稀土和Ba、K、La等大离子亲石元素,而亏损Th、Nb、P和Ti等高场强元素,具弱的Eu负异常,具有低的Sr同位素比值和高的εNd(t)值(+7.74～+9.13)。这些特征表明:(1)卡拉塔格岩体具有俯冲带幔源岩石的成分特点,反映其形成于岛弧环境。(2)卡拉塔格岩体来源于亏损地幔源区,且基本上未受到古老大陆地壳物质的污染,其形成与康古尔古大洋板块向北的俯冲分熔作用具有直接的成因关系。(3)该岩体的总体特征表明,吐哈盆地南缘在早古生代晚期为一活动的大陆边缘环境,卡拉塔格斑岩型金铜矿的形成与该区的古洋壳俯冲有成因联系。

The Kalatag intrusion is the unique intrusion in the Paleozoic inlier on the southern margin of the Tuha basin. The major element characteristics show that the intrusion belongs to the sodian calc-alkaline series. The rocks are enriched in light rare earth elements （LREE） and large ion lithophile elements （LILE） such as Ba, K and La but depleted in high field strength elements （HFSE） such as Th, Nb, P and Ti and have weak negative Eu anomalies and low Sr isotopic ratios and high eNd（t） values （＋7.74--＋9.13）. These characteristics indicate that： （1） the Kalatag intrusion has an affinity for mantle-derived rocks of a subduction zone and probably formed in an island-arc environment; （2）the intrusion was derived from a depleted mande source and in the main has not suffered from contamination with older continental crustal material and its formation have a direct generic relation to the fractional melting of the north-dipping subducted Kanggur paleo-oceanic plate;and （3）the intrusion can provide the evidence that the south margin of the Tuha basin was an active continental margin during the late part of the Early Paleozoic and that the Kalatag porphyry-type gold-copper deposit is related to the subduction of the paleo-oceanic crust in this area.