塔里木东北缘二叠纪超镁铁质杂岩体群成因的气体同位素制约

A great amount of Permian layered mafic- ultramafic complexes are occurred as a cluster in the northeastern margin of Tarim Block, western China, with metallogenic potentials of Ni–Cu sulfide mineralization. Ubiquitous crustal assimilation veiled the information of deep mantle, sulfur saturation and ore-formation, but the type and proportion of crustal contamination and deep mantle are not accurately constrained. Helium and carbon isotopic compositions reveal that a mantle plume was involved during the formation of Pobei complex (Zhang et al., 2017 Chem. Geol.). The petrogenesis (type and proportion of crustal contamination) and geodynamic setting (mantle plume) of Permian mafic-ultramafic complexes in the the northeastern margin of Tarim Block, NW China will be research target. The chemical composition C-H-He-Ar isotopes of volatiles and integrated dating, treace elements, PGE, Nd-Sr-Hf isotopic approches will be used to reveal the type, proportion and processes of crustal contamination and mantle plume involved in the formation of the Beishan mafic- ultramafic complexe cluster, including Pobei, Luodong, Hongshishan, Xuanwoling and recently dicoveried Qixin etc. mafic-ultramafic complex. The intrusive temporal sequence, and the spatial variation of volatile of different type of rocks, cumulate rhythmic layers of magmatic minerals of each complex will bee established. The information of deep mantle will be descipered by deduction of radiogenic noble gas isotopes. The type, proportion and processes of crustal contamination will be revealed by C-H isotopic composition and distribution patterns of methane homologues. The proportions of mantle, crust and atmosphere etc. endmembers will be calculated using crust-mantle mixture model. All these data are integrated to reveal the contribution of mantle plume, type, proportion and processes of crustal contamination, stage of sulfur saturation and ore-formation during magma origination and envolution, and then to discuss the ore-forming geodynamic setting.

塔里木板块东北缘众多二叠纪超镁铁质杂岩体具有较大的铜镍铂族矿床成矿潜力，C-He同位素初步分析表明坡北岩体形成于后碰撞伸展环境叠加地幔柱作用(Zhang et al., 2017 Chem. Geol.)，因此这些杂岩体的成因联系与成矿动力学背景中的地幔柱贡献有待气体与固体同位素的综合制约。本项目以罗布泊-北山地区二叠纪超镁铁质杂岩体群的成因联系及成矿动力学背景为研究目标。对坡北、罗东、红石山、旋涡岭和新发现的启鑫等杂岩体开展流体化学、C-H-He-Ar同位素组成分析、及年代学和岩石地球化学补充配套研究，建立杂岩体形成的时间序列，确定不同韵律层流体组成空间变化特征，制约壳源混染物的类型及来源，扣除放射性稀有气体累积，揭示岩浆性质及深部地幔(柱)信息，采用壳-幔混合模型计算岩浆起源演化与动力学背景中地壳、地幔及大气端元组分的比例，探讨杂岩体成因联系、混染-硫饱和及成矿动力学背景。

对塔里木克拉通东北缘坡北、坡东、罗东、漩涡岭、启鑫等二叠纪大型镁铁–超镁铁质杂岩体进行野外考察及流体组成与C-S-He-Ar同位素组成分析，对比不同构造环境镍钴岩浆成矿岩体，塔里木东北缘二叠纪镁铁质岩浆活动形成大型镁铁-超镁铁质层状岩体年龄跨度大，主要分布于260~290 Ma，同时形成镍钴硫化物和铁钴氧化物矿床，Co主要富集在基性程度高的岩石中，镁铁-超镁铁质岩Ni与Co含量正相关，块状硫化物与磁铁矿矿石中Co与Ni相关性差，Co热液富集作用明显。塔里木东北缘二叠纪赋矿镁铁-超镁铁质岩地球化学特征相似，存在明显的成因联系和相似的动力学背景，岩浆源区为俯冲板片流体交代的亏损地幔，叠加地幔柱相关上涌软流圈，诱发岩石圈地幔发生部分熔融形成的高镁（铁）的母岩浆。高镁母岩浆经壳源混染、硫化物饱和富集镍钴形成铜镍钴硫化物矿床，富铁母岩浆氧逸度高、富水，岩浆分离结晶磁铁矿、叠加热液作用富集钴，形成铁钴氧化物矿床。流体组成和碳-氦同位素组成揭示不同岩体中地幔柱作用的贡献不同。