西天山哈拉达拉辉长岩的Fe-Ti富集机制及其构造意义  

Mechanism of Fe-Ti enrichment in the Haladala gabbros:Implication for the tectonic evolution of the western Tianshan orogenic belt

作　　者：贺鹏丽[1,2] 黄小龙[1] 李洪颜[1] 李洁[1,2] 于洋[1,2] 李武显[1] 

机构地区：[1]中国科学院广州地球化学研究所、同位素地球化学国家重点实验室,广州510640 [2]中国科学院大学,北京100049

出　　处：《岩石学报》2013年第10期3457-3472,共16页Acta Petrologica Sinica

基　　金：国家973计划项目(2011CB808906);国家自然科学基金项目(41130314、91214202)联合资助

摘　　要：特克斯哈拉达拉辉长岩体是西南天山出露规模最大的层状基性一超基性侵入杂岩体，其富含Fe—Ti氧化物（含量高达15％）。哈拉达拉辉长岩中的橄榄石具有较低的Fo值（64～75），斜长石主要为中-拉长石，单斜辉石相对低Mg^#（0．66～0．87），属于次透辉石或普通辉石，总体上显示出较高的岩浆演化程度。Fe-Ti氧化物以钒钛磁铁矿为主（TiO2=0．8％～20．6％；V2O3=0．10％～0．83％），常与钛铁矿呈矿物对共生或出溶钛铁矿。晚期的云母矿物均围绕他形的Fe-Ti氧化物生长，主要为富MgO的金云母，少量属于黑云母；大部分云母成分富含F、CI（F＋C1高达3．14％），指示岩浆形成于贫水环境。哈拉达拉辉长岩体的主量元素成分变化很大（Mg^#=0．48～0．73），橄榄辉长岩主要受橄榄石和斜长石的结晶分异／堆晶作用影响．而辉长岩的成分变化主要受控于斜长石和Fe—Ti氧化物的堆晶作用。哈拉达拉岩体的Fe—Ti氧化物主要为岩浆正常结晶分异作用的结果，该体系具有较低氧逸度、贫水的特点，其地幔源区的熔融程度较高，可能是塔里木地幔柱在天山造山带这一构造薄弱带的早期岩浆活动。The Haladala gabbroic pluton at Tekex is the largest layered mafic-uhramafic 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 （ TiO2 = O. 8% ～ 20. 6% ; V2 O3 = 0. 10%～ O. 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 hiotites, and have relatively high F and C1 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^# = O. 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.

关 键 词：辉长岩 磁铁矿 钛铁矿 结晶分异 地幔柱 天山造山带 

分 类 号：P588.124[天文地球—岩石学]