内蒙古东北部激流河花岗岩中包体的特征及成因

Features and origin of inclusions in the Jiliuhe granite, northeastern Inner Mongolia,China

内蒙古东北部阿龙山地区,沿激流河两岸呈NE向分布的二长花岗岩、花岗闪长岩体中发育暗色微粒镁铁质包体。包体具典型的岩浆结构、淬火结构及针状磷灰石,部分包体中含寄主岩石的钾长石、石英巨晶。包体形态主要呈浑圆状,可见明显的塑性流变特点,与寄主岩石间常呈截然的接触关系,有时呈过渡状、雾迷状。寄主岩石富Si、K,并表现出岩浆演化的特点,包体富Mg、Fe、Ca,贫Si、Al,Na>K。寄主岩石和包体的稀土、微量元素曲线形态相近,均为左高右低的不对称右倾型、轻稀土富集型,包体Eu微弱亏损,寄主花岗岩的Eu中等—弱亏损。包体与寄主岩石在地球化学特征上既表现出了相似性,也表现出了明显的非同源性特点。这些特征表明早石炭世激流河花岗岩类中的暗色包体是岩浆混合的产物,部分代表了混合岩浆的基性端元。

Monzogranite and granodiorite are distributed in a NE direction along both banks of Jiliu River in the Along Mountains area, northeastern Inner Mongolia. Many dark-colored rnicrogranular mafic inclusions occur in these rocks. The inclusions have typical magmatic and quench textures and contain acicular apatite, and some inclusions contain K-feldspar and quartz megacrystals of host rocks. The inclusions are mainly rounded in shape, showing pronounced plastic rheological characters. They usually have a clear-cut contact relationship with the host rocks and sometimes transition or foggy contacts are also seen. The host rocks are rich in Si and K and exhibit the characteristics of magrnatic evolution. Inclusions are rich in Mg, Fe and Ca and poor in Si, Al, and Na with Na〉K. The rare earth element （REE） and trace element patterns for the inclusions and their host rocks are similar and both show an asymmetric, right-inclined LREE-enriched shape. Inclusions exhibit weak Eu depletion, while host rocks moderate-weak Eu depletion. Inclusions and host rocks display similarities in respect to geochemistry as well as non-cognate characters. These features indicate that dark inclusions in the Early Carboniferous Jiliuhe granites are the product of magma mixing and partly represent the basic end-member of mixed magma.