An ultramafic primary magma for a low Si, high Ti-Fe gabbro in the Panxi region of the Emeishan large igneous province, SW China

The Kelang gabbro (256±3Ma) is in contact with the peralkaline syenite of the Late Permian (~260Ma) Fe-Ti oxide-bearing Baima igneous complex and contains high contents of TiO₂ (~4.0wt.%) and Fe₂O₃t (~20wt.%) and low SiO₂ (~42wt.%) and Al₂O₃ (~11wt.%) content. The gabbros are primarily composed of plagioclase, clinopyroxene, olivine (Mg# ~50), ilmenite, magnetite, orthopyroxene (Mg# ~60), biotite and apatite. The Sr-Nd whole rock isotope data (I_Sr=0.7046, εNd_(T)=+2.5) and positive primitive mantle normalized anomalies of Ba, Sr and Ti and high Eu/Eu^* (~1.1) of the Kelang gabbro suggest a possible connection to the Baima cumulate gabbro (I_Sr=0.7047-0.7052, εNd_(T)=+1.6 to +4.2, Eu/Eu^*=1.5-3.6) but the bulk Cr content (~4ppm) and mineralogy are very different. Mass-balance, least-squares modeling suggests that the low Cr content of the Kelang gabbro is likely a result of fractionation of Cr-spinel from a picritic primary magma. After early fractionation of Mg-rich mafic silicates and Cr-spinel, the residual liquid will be enriched in Ti and Fe, depleted in Cr, have low Si and Al and resemble the bulk composition of the Kelang gabbro. Consequently, the Kelang gabbro may be the uppermost portion of a large mafic-ultramafic intrusion unrelated to the Baima igneous complex.