苏北盘石山、练山地幔捕虏体的PGE地球化学

Platinum group elements in mantle derived peridotitic xenoliths from North Jiangsu Province

通过锍镍火试金预富集法,分析了位于郯庐断裂带东侧的盘石山、练山地幔橄榄岩包体中铂族元素(PGE)和Au含量。不同于部分熔融残留成因地幔橄榄岩中通常所观察到的负斜率型或平坦型的分布模式,这两地的地幔橄榄岩以Pt、Pd、Ru相对富集,Ir、Rh相对亏损的"燕子型"分布模式为特征。Pt、Pd等不相容元素富集说明上地幔除经历过早期的部分熔融外,还经历了后期富Pt、Pd的高熔/岩比的熔(流)体的层析分离交代作用影响。盘石山地幔橄榄岩的PGE总量比练山高,Os的含量也比原始地幔值高;而练山地幔橄榄岩的Os含量比原始地幔值低,说明交代作用带走了练山地幔橄榄岩中的Os,却没有很大改变盘石山地幔橄榄岩中的Os含量,这可能与交代熔(流)体含硫量饱和程度有关。Rh的负异常可能与部分熔融过程中熔体较低的fO2有关。

The two main sampling areas, Lianshan and Panshishan are located in the east of the Tan-Lu fault zone in east China. The contents of platinum group elements （PGE） and Au in mantle derived peridotitic xenoliths from Lianshan and Panshishan were determined using a nickel, sulfide fire assay preconcentration method. The results indicated that the studied samples showed ＂M＂ -type PGE distribution patterns in condrite-normalized distribution pattern diagram, with Pt, Pd and Ru enrichments and Ir and Rh depletions, indicating that the studied upper mantle had not only experienced the early partial melting, but also intensive chromatographic fractionation of infiltrated metasomatic components processes. The total PGE concentrations in Panshishan were higher than those in Lianshan. The Os concentrations in Panshishan samples were higher, whereas those of Lianshan samples were lower than that of the primitive mantle, indicating that the percolation removed Os in Lianshan, while had no affect on Os abundances. That is related to saturation of sulfur in metasomatic melt （fluid） . The negative anomaly of Rh was probably relative to the lowfo2 in the partial melting.