Petrogenesis of Neoproterozoic Quartz Monzonite in Solwezi Region, Zambia: Constraint from Geochronology, Geochemistry and Sr–Nd–Hf Isotopes

The study of mafic–intermediate and felsic magmatism related to Neoproterozoic rift in the Lufilian Arc is of great significance for understanding the crustal growth and secular evolution of the region. Studies have shown that there are a large number of Neoproterozoic mafic rocks which are related to rifting in the Lufilan arc, but a few of related intermediate and felsic magmatism are discovered. A Neoproterozoic quartz monzonite with a zircon U–Pb age of 707.1±3.0 Ma was first discovered and reported in the Lufilian Arc. The pluton is characterized by relatively low MgO (0.46%～0.76%), CaO (1.63%～1.76%), K₂O (0.49%～0.56%), Mg^# values (8～13) and Sr/Y ratios (1.14～2.50), as well as high Al₂O₃ content (15.61%～16.02%). REE–normalized patterns show enrichment in LREE with (La/Yb)_N of 6.64～7.86 and their primitive mantle-normalized trace element patterns are characterized by depletion of LILEs (Rb, Ba, Sr, K) and P, Ti, Zr and enrichment of HFSEs (Nb, Ta, Hf). They have a low initial ⁸⁷Sr/⁸⁶Sr ratios (0.7058～0.7060) with positive ε_Nd(t) values (1.89～2.03) and their zircon ε_Hf(t) values range from 1.30 to 5.67, their isotopic data are similar to those of the Neoproterozoic mafic intrusions in the Solwezi region, suggesting that the quartz monzonite were generated by partial melting of newly emplaced mafic lower crust. In combination with the studies of geochronology and petrogenesis, it is concluded that the Lufilian Arc experienced a multi–stage crustal growth in the Neoproterozoic, the late intrusive mantle magma heated the mafic rocks emplaced in the lower crust at early stage, resulting in partial melting and reworking the early crust.