摘要:东天山巴里坤地区两个闪长岩体分别获得327 Ma 和333 Ma 的LA-ICP-MS 锆石U-Pb年龄，代表早石炭世一期岩浆活动。这些岩体具中等略高的SiO2（51.33%～62.48%）、高MgO（2.04%～11.16%）、高TiO2（0.67%～1.29%）、富钠（Na2O/K2O = 1.39～2.95），相对富集LILE和LREE、贫HFSE，亏损Nb、富集Pb，具中等略高的轻重稀土分馏，无或弱负铕异常的右倾谱型，与赞岐质高镁闪长岩相同。岩体基本没有受到陆壳物质混染，其锆石εHf（t）均为正值，且变化范围较大，指示来自受富集组分改造的亏损地幔。结合岩石中出现较多角闪石等含水矿物以及Pb富集，证明它们来自俯冲带之上有流体加入的地幔楔，高的TiO2和中等略高的轻重稀土分馏进一步表明，是俯冲消减板片部分熔融的长英质熔体与地幔橄榄岩相互作用后，交代改造地幔熔融岩浆侵位的产物。结合区域同期弧火山岩和花岗岩类的形成，以及于晚石炭世—二叠纪广泛出现碰撞/后碰撞高钾花岗岩、A 型花岗岩以及镁铁质—超镁铁质岩体和基性岩脉的研究认为，博格达—哈尔里克构造带在早石炭世处于与大洋俯冲消减有关的岛弧环境，此后于晚石炭世晚期—早二叠世开始转入后碰撞伸展的构造环境。
关键词: 高镁闪长岩/
锆石U-Pb定年/
地球化学/
岩石成因/
巴里坤地区
Abstract:The diorites exposed in Balikun area of the eastern Tianshan yield the formation ages of 327 Ma and 333 Ma, being an important period of magmatism during Early Carboniferous. They are characterized by moderate SiO2（51.33%～62.48%）, high but variable MgO（2.04%～11.16%）and high TiO2（0.67%～1.29%）, Na2O/K2O（1.39～2.95）. Geochemically, they have enrichment of LILE, poor HFSE and evident negative Nb anomalies, displaying the geochemical characteristics of subduction zone magmatism. Moreover, all rocks are moderately fractionated between LREE and HREE. They have no or weak negative Eu anomalies. These geochemical features are analogous to those of Sanukitic high-magnesian diorites. Their positive and variable εHf（t）values suggest that they are derived from a depleted mantle metasomatized by enriched components without any crustal contamination. In addition, their high TiO2 and moderate fractionation between LREE and HREE, together with enrichment of Pb and high amphibolites, indicating these high-magnesian diorites were derived from the partial melting of mantle metasomatized by the slab-derived melt under a hydrated condition. Combined with the occurrence of contemporary island arc-related volcanics and granites, as well as Late Carboniferous-Permian collision/post-collision granitoids, A-type granites, mafic-ultramafic rocks and mafic dykes in the Bogda-Harlik tectonic belt, we proposed that the Bogda-Harlik tectonic belt was involved in an island arc settings induced by plate subduction during Early Carboniferous, and then translated into the post-collision setting from Late Carboniferous to Permian.
Key words:High-magnesian diorites,/
U-Pb dating/
Geochemistry/
Petrogenesis/
Balikun areas
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