Ancient crust-derived syenitic and A-type granitic intrusions in the Emeishan large igneous province, SW China

Abstract

Within the inner zone of the Emeishan large igneous province (ELIP), SW China, there are several small syenitic and A-type granitic intrusions not spatially related to giant Fe–Ti–V-deposit-bearing mafic–ultramafic layered intrusions. The representative Heime syenitic and Huili granitic intrusions as well as their spatially associated mafic dykes were developed at ca. 260 Ma, contemporaneous with the ELIP. The Heime metaluminous syenites are K-rich and have moderate SiO2 (60.1–61.4 wt%) and high total-alkali (Na2O + K2O = 9.68–10.7 wt%) contents with high K2O/Na2O ratios (1.18 to 1.74). The Huili metaluminous granites are K-rich A-type granites with moderate–high SiO2 (62.7–68.9 wt%), high total-alkali (7.96–8.62 wt%) and Zr (324–853 ppm) contents, and high 10,000 × Ga/Al ratios (2.68–3.22). Both of them are enriched in high-field-strength elements and light rare-earth elements, with significantly negative Nb–Ta–Sr–P–Ti anomalies. They also have highly evolved whole-rock SrNd isotopic compositions (Heime syenites, (87Sr/86Sr)i = 0.7092–0.7105, εNd(t) = −7.77 to −6.09; Huili granites, (87Sr/86Sr)i = 0.7116–0.7146, εNd(t) = −6.34 to −5.32). Zircon δ18O values of the Heime syenites (5.73‰–6.40‰) are slightly higher than those of the mantle zircons, and lower than those of the Huili granites (5.98‰–7.52‰). Zircon Hf 8isotopic compositions of the Huili granites (εHf(t) = −3.30 to +0.73) are higher than those of the Heime syenites (εHf(t) = −7.08 to −2.97), possibly indicating a more contribution of mantle component. In addition, the spatially associated mafic dykes display considerably higher εNd(t) values (Heime mafic dykes, −3.95 to −3.01; Heime mafic dykes, −0.58 to −0.51) than those of the Heime syenites and Huili granites. The parental magmas of both the Heime syenites and the Huili A-type granites show a close affinity to the K-rich, metaluminous syenitic magmas. Based on the Sr–Nd–O–Hf isotopic compositions of the Heime syenites, Huili granites, and spatially associated mafic dykes, we suggest that the K-rich syenitic magmas parental to the Heime syenites were produced mainly by remelting of Paleo–Mesoproterozoic mafic meta-igneous rocks, whereas those parental to the Huili A-type granites were generated by the remelting of Paleo–Mesoproterozoic basement rocks and mixing with small amounts of coeval mantle-derived basaltic melts.