Zircon SHRIMP chronology and geochemistry of the Haladala gabbro in south- western Tianshan Mountains
西南天山哈拉达拉岩体的锆石SHRIMP年代学及地球化学研究

The Haladala basic-ultrabasic pluton in southwest Tianshan Mountains consists of troctolite, olivine gabbro and gabbro. Typical cumulate textures occur in the troctolite and olivine gabbro. The cumulate minerals are mainly of olivine and plagioclase. The inter-cumulate minerals are mainly of pyroxene, amphibole and phlogopite. Gabbro shows typical gabbro-ophitic textures. Fractional crystallization played an important role in the formation of the Haladala intrusion. The zircon SHRIMP dating indicates that the gabbro crystallized at Late Carboniferous (308.3±1.8Ma, MSWD=0.86, n=15). The REE distribution patterns of the Haladala rocks are similar to that of the E-MORB. The studied samples with initial 87Sr/86Sr of 0.7040~0.7050 contain relatively abundant Rb, Cs, Ba and Sr. All these data suggest that the source of the Haladala magma was an enriched mantle. Based on their flat REE distribution patterns and geochemistry of other trace elements, we suggest that the rocks of mantle source are amphibole-bearing spinel lherzolite. The metasomatism caused by the subduction fluid of the Paleo- south Tianshan Ocean led to the formation of the enriched mantle. According to calculation, the primary magma of the Haladala pluton was formed by 10%~15% partial melting of amphibole-bearing spinel lherzolite.