辽宁宽甸新生代火山岩和地幔包体的稀有气体同位素组成及其演化意义

通过对宽甸新生代碱性玄武岩、地幔包体及辉石巨晶的稀有气体同位素组成的分析，认为不同岩性稀有气体含量的差异反映了岩浆作用过程中轻、重稀有气体的分馏特性，较轻的稀有气体(He、Ne)比较重的稀有气体(Kr、xe)具有更高的活动性和不相容性；该地区上地幔源区具有典型的MORB型源区特征，以辉石巨晶为代表；地幔包体的^3He／^4He值较低，可能是地幔流体交代作用造成的；大陆碱性玄武岩具有与大洋玄武岩截然不同的He同位素组成，反映了大陆区地幔岩浆上升过程中受到了陆壳物质混染。地幔源区^40Ar／^36Ar值为350左右，二辉橄榄岩和碱性火山岩的^40Ar／^36Ar值比大气略高，可能有大气组分的混合。部分样品中有^21Ne、^22Ne、^129Xe、^134Xe和^136Xe相对于大气的过剩现象，是核成因造成的。

Noble gas isotopic compositions of Cenozoic volcanics and mantle-derived xenoliths from Kuandian in Liaoning Province and their significance

The noble gas isotopic and compositional data of alkali basalt, lherzolite xenolith and megacryst clinopyroxene from Kuandian area confirm the opinion that fractionation of noble gases existed during magmatism, and that the lighter noble gases such as He and Ne have much higher mobility and incompatibility than heavier ones like Kr and Xe. Therefore, the lighter noble gases are relatively concentrated in volcanics, especially in volcanics with bubbles, whereas lherzolite xenoliths have quite abundant heavier noble gases. Megacryst clinopyroxene has the lowest abundance of noble gases, probably attributed to its highp-Tgeneration. Noble gas isotopic compositions reveal that the mantle source beneath Kuandian area has an MORB_like reservoir with 3He/4He being 10 Ra (atmospheric3He/4He value) and40Ar/36Ar being 350. Lherzolite xenoliths possess 3He/4He ratios of 2.59~4.53Ra, reflecting their highp_Tdeformation and metasomatism. Volcanics have very low3He/4He ratios (0.47~0.61 Ra), indicating the contribution of radiogenic4He due probably to crust contamination. Most samples show excesses of21Ne and22Ne compared with atmospheric neon, while Kr and Xe isotopic compositions are indistinguishable from atmospheric values with only a few samples showing excesses of129Xe,134Xe and136Xe.