新疆坡北杂岩体西端镁铁-超镁铁质岩体成因的稀有气体同位素制约

新疆坡北镁铁-超镁铁质杂岩体由一个辉长岩体以及二十多个超镁铁质侵入体组成，其中坡一超镁铁质岩体稀有气体同位素组成揭示存在地幔柱的贡献。坡北杂岩体西端的坡一、坡四、坡十和坡十四等几个超镁铁质岩体的稀有气体同位素对比分析结果表明，岩浆矿物的³He/⁴He值（0.26~2.79Ra）分布于地壳与地幔值之间，较高的²⁰Ne/²²Ne和较低的²¹Ne/²²Ne值分布于Ne质量分馏线（MFL）和L-K线之间，⁴⁰Ar/³⁶Ar=295~598。³He/⁴He与⁴⁰Ar/³⁶Ar比值揭示坡北杂岩体西端不同超镁铁质岩体形成过程中地幔（柱）、地壳和大气组分的贡献不同，岩体成因也可能不同。其中，坡一岩体具有地幔柱作用的贡献，其他三个岩体的岩石圈地幔及地壳流体组分的贡献较大。岩浆地幔源区由深部地幔柱物质叠加俯冲流体交代的岩石圈地幔物质所组成，大气与地壳物质组分可能由俯冲再循环洋壳带入到岩浆地幔源区以及围岩物质的混入。

The noble gas isotopic constrains on the petrogenesis of mafic-ultramafic intrusions in the western end of the Pobei complex, Xinjiang, northwestern China

The large Pobei Permian layered mafic-ultramafic complex in the northeastern margin of the Tarim craton, western China is composed of a gabbro intrusion and more than 20 ultramafic intrusions. The isotopic compositions of noble gases in the Poyi (No.1) ultramafic intrusion revealed information of mantle plume. In present study the abundance and isotopic compositions of noble gases were analyzed for fresh minerals in mafic-ultramafic rock samples from No.1, 4, 10 and 14 ultramafic intrusions in the western end of Pobei complex. The results showed that olivine (Ol), pyroxene (Px) and plagioclase (Pl) magmatic minerals in the Pobei ^#1, 4, 10 and 14 ultramafic intrusions were in low values of ³He/⁴He ratios (0.26~2.79Ra). The ²¹Ne/²²Ne and ²⁰Ne/²²Ne were plotted and distributed between the Ne mass fraction line (MFL) and L-K line, the ⁴⁰Ar/³⁶Ar ratios ranged from 295 to 598. These isotopic compositions of noble gases indicated a mixture of different portion of mantle (plume), crust and air during the Pobei magmatic processes with different petrogenesis. The mantle plume was identified in the Poyi ultramafic intrusion, and more crustal fluid was added into lithospheric mantle in other three ultramafic intrusions. The magmatic source area of Pobei ultramafic intrusion was superimposed by deep mantle plume on lithospheric mantle that was reformed by subducted fluids.