TRACE ELEMENT AND SR-ND-PB-O ISOTOPIC SYSTEMS OF THE PANZHIHUA LAYERED GABBRO INTRUSION: CONSTRAINTS ON THE MANTLE SOURCE REGIONS AND ORIGIN OF V-TI-FE OXIDE DEPOSIT

Abstract

The Panzhihua intrusion, a part of the Emeishan large igneous province, is one of typical V - Ti magnetite ore-bearing layered gabbro intrusions. The Sr, Nd and Pb isotopic data overlap the field of the Emeishan basalts and oceanic island basalts, which suggests a genetic relationship to mantle plume. The high ratio of La/Nb values (> 1) and negative Nb anomalies on the primitive mantle-normalized trace element patterns characterize the contamination of lithospheric mantle or crustal materials. However, the low δ18OSMOW (‰) values (<6) suggest the absence of crustal contamination. Thus, the Panzhihua intrusion can be produced by a partial melting of mantle plume and lithospheric mantle, but not underwent crustal contamination. Positive correlation between Mg# and P2O5 and negative correlation between P2O5 and FeO suggest that addition of P is not the key role for the separation of immiscible oxide melts. In contrast, negative correlation between Mg# and Fe2 O3/FeO ratios implies that the increasing of oxygen fugacity is very likely the main factor to induce immiscibility of oxide melt.