中文摘要：

扎河坝钾质火山岩位于准噶尔盆地的东北缘，下泥盆统托让格库都克组内。这些火山岩以玄武岩为主，具有较高的K20含量（1＋66％～4．63％）和K2O／Na2O值（O．36～1．65），并富Sr（665×10^-6～906×10^-6）、Ba（680×10^-6～1596×10^-6）等大离子亲石元素和轻稀土（La／YbPM〉8），显示出钾玄质岩石的特征。同时，这些岩石具有较高的TiO2（～1．7％），P2O5（～0．8％）和高场强元素含量，类似于高铌玄武岩。尽管具有较高的Nb含量（Nb=21×10^-6～23×10^-6），这些岩石仍呈现出明显的Nb～Ta亏损，显示了典型的岛弧特征。高的Nb／Yb（～5．9），Nb／Ta（19～21），Zr／Hf（46～51）值以及较高的钾含量表明这些岩石来自一个经交代作用富集的地幔源区。单纯的消减板块脱水难以造成高场强元素的富集，这些岩石较高的Ce／Th（47～50），Ce／Pb（13～19）和Ba／Th（341～777）值并缺乏明显的负铈异常等特征排除了消减沉积物熔体的加入。导致地幔富集的变质组份可能为来自消减板块的低程度熔体。扎河坝钾质玄武岩与稍早前报道的埃达克与富铌玄武岩一起，反映旱泥盆世曾经出现过洋壳的消减事件。准噶尔盆地中存在的特征岛弧岩浆表明热消减机制曾经广泛地出现在准噶尔板块演化的不同历史时期，而岛弧地体在准噶尔盆地基底的组成中可能占有较大的比例。

英文摘要：

Zhaheba potassic basaltic rocks outcrop within the Early Devonian Tuorangekuduke Group, NE margin of the Junggar Basin. The rocks exhibit dual geochemical characteristics of both potassic rocks and high-Nb basalts. On one hand, the rocks contain relatively high K2O（ 1.66 %～ 4.63 % ）and characterized by high K2O/ Na2O ratios （0.36～1.65）, high Sr （665 × 10^-6～906 × 10^-6）, Ba （680 × 10^-6～1596 × 10^-6） and highly fractionated REE （La/Yba 〉8）, displaying characteristics of shoshonitic rocks. On the other hand, these rocks possess relatively high TiO2 （ ～1.7 % ）, P2O5 （ ～0.8 % ）, Nb （21 × 10^-6～23 × 10^-6） and other HFSEs, which are quite analogous to those of high-Nb basalts. Although their high Nb contents, these rocks exhibit significant Nb-Ta depletion and show typical island-arc characteristics. The relatively high Nb/Yb （～5.9）, Nb/Ta （19～21）, Zr/Hf （46～51） ratios and K2O contents suggest that these potassic basaltic rocks were derived from a metasomatized, phlogopite- and/or amphibole-bearing mantle source. Aqueous fluid from dehydration of subducting slab cannot be the metasomatic agent because of the weak ability of transporting HFSEs to the mantle wedge. These rocks possess high Ce/Th （47～50）, Ce/Pb （13～19） and Ba/Th （341～777） ratios and do not show significant negative Ce anomaly, suggesting a negligible contribution from subducted sediments. We suggest that the metasomatic agent was probably the low-degree partial melt which, when interacted with the mantie wedge, could give rise to the relatively high K2O and enrichment of HFSEs and LILEs. The Zhaheba potassic basalts were most likely produced in an island arc environment which, in combination with typical Nb-enriched basalts in the center area of the Junggar basin, suggests that hot-subduction scheme could frequently occur during the evolution of the Junggar plate, and that arc-originated terranes could dominate the basement of the Junggar basin.