云南大理苦橄岩的Re-Os同位素特征:对峨眉山大火成岩省成因的制约

云南大理苦橄岩产出于峨眉山大火成岩省内带,位于峨眉山玄武岩系底部.岩石具斑状结构,斑晶占20％～40％左右,由自形-半自形的橄榄石和单斜辉石组成；基质约占60％ ～ 80％,主要由长条状斜长石和颗粒状单斜辉石组成,辉绿结构；含少量尖晶石.绝大部分样品全岩SiO2低于47％,为45.94％～46.37％(1个样品达47.35％),MgO大于18％,介于19.01％～23.77％之间,Na2O+ K2O低于2％,介于1.52％～1.97％之间,具典型苦橄岩的岩相学和岩石化学特征.全岩Re含量变化范围较小,介于0.349×10-9～0.424×10-9之间；Os含量变化范围较大,介于0.889×10-9～4.276×10-9之间；187Re/188Os=0.437±0.012 ～2.708±0.025,187Os/188Os =0.1283±0.0002～0.1354±0.0004;从中分选出的橄榄石的Re、Os含量分别为0.030×10-9～0.049×10-9、0.625×10-9～0.757×10-9,1s7Re/188Os =0.191±0.038 ～0.377±0.062,187Os/188 Os=0.1254±0.0005 ～ 0.1268±0.0005,均低于全岩；尖晶石的Os含量最高,为80.5×10-9,187Os/188 Os最低,为0.1252±0.0003.经质量平衡计算,基质的187Os/188Os比值介于0.1380 ～0.1415之间,与原始上地幔相比,基质的Re-Os同位素组成具有壳层熔岩的特点,而橄榄石和尖晶石具有熔融残留相的特点,基质的γOs大于0,介于+2.0～ +3.28之间,矿物的γOs均小于O,介于-2.01～-2.59之间,显示明显的亏损特征,无核-幔边界源区信息,而全岩的介于-1.11～ -3.24之间,为基质和斑晶及尖晶石的混合结果,推测峨眉山大火成岩省是壳-幔相互作用的产物.

Re-Os isotopes of Dali picrite(Yunnan):New constraints on the formation of Emeishan Large Igneous Province

Dali picrite in Yunnan Province occurs at the bottom of Emeishan basalt in the inner zone of Emeishan Large Igneous Province(ELIP).The picrite is highly porphyritic with 20%~40% euhedral-subhedral olivine and clinopyroxenite phenocrysts,and the groundmass with diabasic texture is composed of microcrystalline olivine,clinopyroxenite and plagioclase with minor spinel.SiO2 content of most picrites ranges from 45.94% to 46.37%,lower than 47%,except for one sample,whose SiO2 content is up to 47.35%.In all picrit...