冀北赤城红旗营子群中变质橄榄岩的岩石学与地球化学特征

PETROLOGY AND GEOCHEMISTRY OF THE METAMORPHIC PERIDOTITES FROM WITHIN THE HONGQIYINGZI GROUP IN CHICHENG,NORTH HEBEI PROVINVE,CHINA

冀北赤城红旗营子群中变质橄榄岩呈透镜状或团块状产于黑云斜长片麻岩之中，通过对其进行详细的岩石学和地球化学研究，结果显示：岩石类型为强烈蛇纹石化的方辉橄榄岩，具粒状变晶结构或鬣刺结构，变质橄榄岩富ω（MgO）（37．49％～38．91％），贫ω（CaO）（0．12％～1．17％），ω（Al2O3）（0．54％～1．54％）和ω（FeO^＊）（5．51％～9．06％），W（Ti02）介于0．01％～0．04％之间，REE含量低于原始地幔，过渡金属元素表现为不对称的“W”型配分型式，在Ti和Cu处形成明显的负异常“谷”。上述特征表明变质橄榄岩相当于SSZ型地幔橄榄岩，可能来自于消减带之下的上地幔，属于部分熔融程度很高的亏损地幔岩，因构造侵位而分布于红旗营子群之中，部分岩块则经历了俯冲-消减作用而形成鬣刺结构。

The metamorphic peridotites of harzburgitic composition in the Chicheng, North He- bei Province, China, occur as separate tectonic lenses or lumps within the biotite-plagioclase gneisses of the Late Paleozoic Hongqiyingzi Group, and they are divided, from textural point of view, into two main types. The first and more abundant type is granular textured rocks while the second shows a spinifex-like texture. They contain more ω（MgO） （37.49 % -38.91% ）, but less ω（CaO） （0.12%-1. 17%）,ω（Al2O3） （0. 54%-1. 54%） and ω（FeO^＊）（5.51%-9.06%）. Their ω（TiO2） ranges from 0.01% to 0.04 %. Total REE is less than the primitive pyrolite and the PM （primitive mantle）-normalized TME （Transitional metal element） distribution patterns are anisomerous W-type,and have remarkably negative Ti and Cu anomaly. Geochemical characteristics of the two metamorphic peridotites show that they are similar to SSZ-type pyrolite that came from upper mantle under subduction zone and might represent the depleted pyrolite which underwent higher partial melting. The metamorphic peridotites emplaced into the Hongqiyingzi Group by the faulting mainly,but some lumps underwent the subduction and resulted in the formation of metamorphic spinifex texture.