河南周庵铜镍矿锆石U-Pb年龄及地质意义

Zircon U-Pb age and geological significance of Zhou’an copper-nickel sulfide deposit in Henan province

通过对周庵岩体岩石化学、年代学和Sr,Nd同位素组成研究,获得以下认识:周庵岩体为贫硅、贫碱、铁质超镁铁岩,岩浆岩属亚碱性拉斑玄武岩系列;其轻、重稀土分馏明显,轻稀土富集,重稀土亏损;微量元素原始地幔标准化显示Rb,Th,U,La富集,Sm,Zr,Hf,Eu,Nd,Ta弱富集的板内拉斑玄武岩特征;同位素组成具有高w(87Sr)/w(86Sr)和低w(143Nd)/w(144Nd)的特点.综合w(Zr)/w(Nb),w(La)/w(Nb),w(Ba)/w(Nb),w(Rb)/w(Nb),w(Th)/w(Nb),w(Th)/w(La),w(Ba)/w(La)特征,周庵岩体岩浆源区为岩石圈地幔,岩浆曾受到地壳物质混染.获得周庵岩体LA-ICP-MS锆石U-Pb年龄为641.2±4.5Ma.岩石化学特征显示其形成的构造环境为大陆板内环境,据橄榄石F0计算和w(Pd)/w(Ir)–w(Ni)/w(Cu)图解推测原生岩浆可能为高镁玄武岩浆.由于周庵岩体位于秦岭与大别山造山带结合部,其构造背景及地幔性质的确认对揭示秦岭大别造山带地幔不均一性同样具有重要意义.

The major conclusions based on the lithochemistry, chronology and Sr, Nd isotopic compositions of Zhou＇an rock masses are： Zhou＇an rock masses are ferruginous ultramafic rock deficient in SiO2 and alkali; the magmatite is subalkali and belongs to tholeiitic basalt series; the lanthanon fractionation of the light and heavy is obvious because the LREE is concentrated and HREE is defective; trace element primitive mantle standardization shows the characteristics of volcanic arc basalt as being enriching in Rb; Th, U, La, hypoenriching in Sm, Zr, Hf, Eu and hypo-lean in Nd, Ta; the isotopic composition is high in w（87Sr）/w（86Sr） and low in w（143Nd）/w（144Nd）. From the proportionality of w（Zr）/w（Nb）, w（La）/w（Nb）, w（Ba）/w（Nb）, w（Rb）/w（Nb）, w（Th）/w（Nb）, w（Th）/w（La）, w（Ba）/w（La）, we could know that the magma of Zhou＇an rock masses comes from lithosphere mantle. The LA-ICP-MS zircon U-Pb age of Zhou＇an rock masses is 641.2±4.5 Ma, which is dated for the first time. Its petrochemical characteristics suggest an intraplate setting. From the F0 calculation of olivine and w（Pd）/w（Ir）w（Ni）/w（Cu） diagram, we inferred that primary magma might be high magnesia basalt magma. The Zhou＇an complex is located in the binding site of the Qinling and Dabie orogenic zones. And our confirmation of the character of its mantle source is very important in revealing the mantle inhomogeneity in the Qinling-Dabie orogenic zone.