西准噶尔晚泥盆世碱性玄武岩的地球化学特征及其与塔里木大火成岩省岩浆岩对比

西准噶尔是近年来中亚造山带的研究热点地区之一，发育多条蛇绿混杂岩带。随着研究的深入，蛇绿岩混杂岩带中不断有碱性洋岛玄武岩被识别出来。本文对克拉玛依及达尔布特蛇绿混杂岩中的晚泥盆世枕状玄武岩进行详细的岩石地球化学及Sr?Nd同位素组成研究。结果表明西准噶尔晚泥盆世枕状玄武岩属于碱性玄武岩系列，岩石具有高TiO₂ （2.3%～3.8%）及P₂O₅ （0.38%～0.91%），低MgO （2.41%～4.97%），轻、重稀土元素分异较为明显，(La/Yb)_N = 5.1～14.5，无明显Eu异常（Eu/Eu* = 0.96～1.1），相对富集Rb、Th、U，亏损Ba、K、Sr，没有明显Nb、Ta负异常，这些地球化学特征与洋岛玄武岩（OIB）极其相似。克拉玛依及达尔布特蛇绿混杂岩中枕状玄武岩具正ε_Nd(t)值（3.3～4.4）及年轻的模式年龄（0.83～0.72 Ga），表明其来源于亏损地幔源区，通过同位素及微量元素研究认为源区可能为富辉石的橄榄岩，或不含橄榄石的辉石岩和角闪石岩，克拉玛依及达尔布特蛇绿混杂岩中的晚泥盆世枕状玄武岩形成于大洋板内与地幔柱有关的海山/大洋岛屿环境。这些明显不同于大陆板内具有富集特征的塔里木大火成岩省，它们分别属于两个明显不同的同位素地球化学省，即以富集型地幔为同位素组成的南部省及以亏损型地幔为同位素组成的北部省。

Geochemical features of Late Devonian alkali basalts in West Junggar and compared with magmatic rocks in Tarim large igneous provinces

West Junggar is one of the hot study region in Central Asian Orogenic Belt （CAOB） in recent years，and have many ophiolitic mélange belts. With the deepening of the study，the alkali ocean island basalts （OIB） with different ages have been identified in ophiolitic mélanges. Studying on geochemical properties and Sr?Nd isotopic composition of Late Devonian pillow basalts within Karamay and Darbut ophiolitic mélanges，and the results show that the pillow basalts are characterized by alkaline affinity with high TiO₂ （2.3%～3.8%） and P₂O₅ （0.38%～0.91%），low MgO （2.41%～4.97%），clear differentiation of LREE and HREE，(La/Yb)_N = 5.1～14.5，no obvious Eu anomalies （Eu/Eu* = 0.96～1.1），Rb，Th and U enrichment and Ba，K，Sr depletion，and also no obvious Nb and Ta negative anomalies. Moreover，they have positive ε_Nd(t)（3.3～4.4），and young model age （0.83～0.72 Ga），derived from depleted mantle source with partial melting of pyroxene riched peridotite or free olivine pyroxenite and hornblendite in a plume-related intra-oceanic seamount/oceanic island settings. This is obvious different from Tarim large igneous province （TLIP） which is characterized by continental intraplate and enriched mantle features. They are belong to two distinct isotopic geochemistry province，the one is southern province with enriched mantle isotopic composition，and the other is northern province with depleted mantle isotopic composition.