云南丽江苦橄岩Re-Os同位素地球化学初步研究

报导了云南丽江地区大具和仕满剖面12个苦橄岩和6个玄武岩的Re，Os含量和Os同位素组成。苦橄岩和玄武岩具有明显不同的Re-Os体系的特征。苦橄岩具有高的Os元素丰度［(1.5~3)×10-9］和低的Re元素丰度（<0.05×10-9）；共生的玄武岩具有低的Os元素丰度（<0.5×10-9）和相对高的Re元素丰度（<0.8×10-9）；苦橄岩具有低放射成因的 187Os/188Os 比值（0.123 3~0.126 6），而玄武岩具有高放射成因的187Os/188Os比值（0.133 8~0.157 7）。苦橄岩的Re-Os同位素特征与越南西北部二叠—三叠纪科马提岩具有低放射成因Os同位素特征相似，而玄武岩的Re-Os同位素特征与峨眉山大火成岩省（LIP）其他地区玄武岩的高放射成因的Os同位素特征相似。苦橄岩的Re-Os同位素特征表明，形成峨眉山LIP的地幔柱可能来自对流上地幔而不是深部的核-幔界面。换言之，峨眉山LIP的形成受控于岩石圈地幔过程而不是地幔柱过程。

Preliminary Study on Re-Os Isotope Geochemistry of Picrites from Lijiang Area, Yunnan Province

Here we present Re-Os abundances and Os isotopic compositions of 12 picrites and 6 associated basalts collected from Daju and Shiman sections, Lijiang area, western part of Emeishan large igneous province (ELIP Zhang et al, 2006). The results show that the picrites and associated basalts have distinctive Re-Os isotopic features. The picrites have higher Os abundances (1.5×10-9~3×10-9), and sligtly lower Re abundance (<0.05×10-9) than associated basalts (<0.5×10-9 and <0.8×10-9, respectively). However, the picrites have unradiogenic 187Os/188Os (0.1233~0.1266), but the basalts have supradiogenic 187Os/188Os (0.1338-0.1577). The Re-Os isotope geochemistry of ELIP lava may shed light on the mantle plume origin of ELIP. The mantle plume was derived from the asthenosphere rather than the deep core-mantle boundary. In other word, the ELIP eruption was controlled by interaction between lithosphere and asthenosphere (Saunders, 2005).