邯邢侵入体中幔源超镁铁质岩包体的发现及其矿物地球化学特征

THE DISCOVERY OF THE MANTLE-DERIVED ULTRAMAFIC XENOLITHS IN HANDAN XINGTAI INTRUSIVE COMPLEX AND THEIR MINERALOGICAL-GEOCHEMICAL CHARACTERISTICS

邯邢中基性侵入杂岩体中产有众多的岩石包体。作者在暗色闪长岩相中首次发现了超镁铁质岩包体,以方辉榄橄岩为主,由镁榄橄石(Fo=92±),顽火辉石(En=90±),铬透辉石和铬尖晶石组成,碎斑-平结构,发育扭折带。全岩SiO_2=41.02,MgO=42.24,∑EREE(3.95)甚低,稀土元素配分曲线显示特殊的向下凸的形状。δ^(18)O=6.5～7.0。辉石平衡温度约为1000℃,压力为20×10~8～22×10~8Pa。矿物-地球化学研究表明具上地幔岩特征,属A型包体,这在国内外文献中还未曾见过类似的报导。这个发现对探讨华北板块的地壳上地幔组成与演化,中生代构造岩浆活动的大地构造背景以及物质来源和邯邢式铁矿的成因将产生深远的影响。

There are many xenoliths in Handan-Xingtai intrusive complex, but the ultramafic xenoliths were discovered first time from the early petrographic rock facies, dark diorite. They contains large amount of harzburgite that consists of forsterite (Fo 92), enstatite (En 90), chromo-diopside and chromohercynite. Kink band occurred from forsterite with clastic-porphyry texture. They contain SiO_2 41.02％, MgO 42.24％, ∑REE 3.95ppm and δ^(18)O 6.5～7.0‰. The results evaluated from different geothermometers and geobarometers indicate the pressures of 20～22 GPa and the temperature of 1000℃. Besed on mineralogical and geochemical characteristics, we suggest that the harzburgite xenoliths are derived from upper-mantle,