Permian flood basalts and mafic intrusions in the Jinping (SW China) Song Da (northern Vietnam) district: Mantle sources, crustal contamination and sulfide segregation

The similar to 260-Ma Emeishan large igneous province (ELIP) in SW China and northern Vietnam includes high-Ti and low-Ti volcanic rocks and coeval mafic-ultramafic plutons. In the Jinping (SW China)-Song Da (northern Vietnam) district, the southernmost part of the ELIP, basalts and gabbros of the high-Ti series displays a narrow range of epsilon Nd(t) values (+0.5 to + 1. 1) and low primitive in anti e-nonnal i zed Th/Nb ratios (similar to 1.4), similar to those of an 0113-like enriched mantle source. The rocks have chondrite-normalized R-EE patterns enriched in LREE and depleted in HREE. This feature, together with low A1203/TiO2 ratios (similar to 4), indicates that the primary melts were generated by small degrees of partial melting at garnet stable depths. The low-Ti series includes LREE-depleted and LREE-enriched picrites, basalts, olivine gabbros and gabbros. The LREE-depleted picrites have chondrite-normalized Ce/Yb ratios of 0.4-0.5, very positive epsilon Nd(t) values (+7.0), and very negative Th anomalies in primitive mantle-nonnalized trace element patterns. They were formed by high degrees of partial melting of a strongly depleted mantle source at relatively shallow mantle depths. The LREE-enriched picrites have very negative ENd(t) values (-7.8) that indicate a mantle source locally modified by subducted oceanic crust. Highly variable chemical compositions and epsilon Nd(t) values (+6.4 to - 10.2) of the low-Ti basalts and gabbros are attributed to variable degrees of upper crustal contamination of the picritic parental magmas. Therefore, the extrusive and intrusive rocks in this region clearly formed from heterogeneous mantle sources. Crustal contamination triggered S-saturation of some tow-Ti magmas and resulted in segregation of immiscible sulfide melts and generation of magmatic Ni-Cu-(PGE) sulfide deposits in this region. Eruption of magmas after sulfide segregation formed PGEdepleted low-Ti basalts. (c) 2007 Elsevier B.V. All rights reserved.