Mechanism of Fe-Ti enrichment in the Haladala gabbros:Implication for the tectonic evolution of the western Tianshan orogenic belt
Mechanism of Fe-Ti enrichment in the Haladala gabbros:Implication for the tectonic evolution of the western Tianshan orogenic belt
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作者：
He‐Bo Peng
The Haladala gabbroic pluton at Tekex is the largest layered mafic-ultramafic intrusion in the northern margin of southwestern Tianshan orogenic belt,and contains abundant Fe-Ti oxides( up to 15%). The rocks were highly fractionated with low Fo( 64 ~75) olivine,low An plagioclase( mostly andesine-labradorite),and low Mg#( 0. 66 ~0. 87) clinopyroxene( salite or augite). Fe-Ti oxides consist mostly of V-Ti-magnetite( TiO 2 = 0. 8% ~ 20. 6%; V 2 O 3 = 0. 10% ~ 0. 83%) that always coexists with ilmenite or contains exsolution lamellae of ilmenite. The late-crystallizing micas on the periphery of anhedral Fe-Ti oxides are dominant phlogopites and minor biotites,and have relatively high F and Cl contents( "F + Cl"up to 3. 14%),indicating a water-poor source. The Haladala gabbros show wide range of major element concentrations( e. g.,Mg#= 0. 48 ~ 0. 73). The compositional variation of olivine-bearing gabbros was likely caused by fractional crystallization and / or accumulation of olivine and plagioclase,while that of olivine-free gabbros was mostly attributed to plagioclase and Fe-Ti oxides accumulation. Fe-Ti enrichment in the Haladala gabbros is the result of fractional crystallization of primary low oxygen fugacity and water-poor magma. The Haladala gabbros were derived from high degree partial melting of mantle source,which might record the early magmatism of the Tarim mantle plume expressing firstly in the pre-existing lithosphere weakness zones such as the Tianshan orogenic belt.
