Os, Nd and Sr isotope and trace element geochemistry of the Muli picrites: Insights into the mantle source of the Emeishan Large Igneous Province

A suite of picrites and basalts from the Mull area, in the northwestern part of the Emeishan continental flood basalt province, provides new and valuable information on the geochemistry of the Emeishan Large Igneous Province (LIP) and its source The Mull picrites can be classified as type-1 or type-2. The former shows ocean-island basalt-like trace element characteristics, with gamma os (260 Ma) values and epsilon(Nd) (260 Ma) values ranging from + 7 5 to +11 5 and from +6.0 to +7.8, respectively This is the first time that picrites with highly radiogenic Os and high Os contents (up to 3 3 ppb) have been recognized in the Emeishan LIP. These characteristics probably reflect a relatively enriched component in the Emeishan LIP source. The type-2 writes are characterized by non-radiogenic gamma os (260 Ma) values ranging from -42 to -0.3, and they may be further subdivided into type-2A and type-2B writes Type-2A planes contain moderate amounts of the light rare earth elements (LREEs), have low Ce-N/Yb-N values (1.1-20), and a relatively high initial epsilon(Nd) (+ 50 to + 66). In terms of Os and Nd isotopes, the Mull type-2A planes are similar to the Song Da komatiites of Vietnam and the Gorgona Island picrites, revealing the existence of a depleted mantle component in the Emeishan LIP source. In contrast with the type-2A writes. type-2B lavas exhibit a negative Nb anomaly and relatively lower initial eNd and gamma os values (Nb/La > 1.8: epsilon(Nd) (260 Ma) = -5.5 to +64, gamma os (260 Ma) = -4.2 to -1.9), suggesting that the type-2B lavas have a depleted mantle source, similar to type-2A, but that the type-2B lavas are also influenced by various degrees of mixing of depleted plume-derived melt, subcontinental lithospheric mantle, and/or continental crust. Given that the basalts in the Mull area show similar geochemical features to those of the type-2B picrites. their origins are Inferred to be similar (C) 2010 Elsevier B.V. All rights reserved