ABSTRACT

The consumption of the Changning–Menglian Palaeo-Tethys ocean in the Triassic formed the Lincang granitic batholith in the southwestern China, once the oceanic supra-subduction zone. The batholith provides us a critical window to understand the nature of the crustal basements and the process of Palaeo-Tethyan termination. Here we report zircon U-Pb ages and Hf isotopes, and whole-rock elements and Sr-Nd isotopes of granitic samples from the central part of the Lincang batholith. The geochemical results reveal two genetic types of granites indicated by low-K and high-K affinities, respectively. The Group 1 low-K granitoids dated at 237–229 Ma are low-K calc-alkaline and metaluminous to peraluminous (A/CNK = 0.75–1.29), with K₂O contents of 0.13–1.33 wt%, K₂O/Na₂O ratios of 0.03–0.30, Rb/Sr ratios < 0.18, and initial ⁸⁷Sr/⁸⁶Sr = 0.71693 and ε_Nd(t) = −10.8. In contrast, the Group 2 high-K granitoids dated at 239–200 Ma are calc-alkaline and peraluminous (A/CNK = 1.02–1.20), with higher K₂O contents (3.15–4.7 wt%), K₂O/Na₂O ratios (1.15–2.00) and Rb/Sr ratios (0.77–2.62), and more enriched isotopic compositions (initial ⁸⁷Sr/⁸⁶Sr = 0.73129 to 0.74037, ε_Nd(t) = −13.1 to −11.0) as well as highly negative zircon ε_Hf(t) values of −16.8 to −6.7. The formation time of these granitoids is compatible with that of the post-collision of the Palaeo-Tethys, subsequently to the magmatic gap (250–240 Ma) coupling with the syn-collision stage. The magmatic source discriminations suggest that the low-K granitoids were derived from partial melting of the dehydrated low-K amphibolite source and the high-K granitoids were dominantly from the psammitic source with minor mantle-derived magma involvement. Using the geochemical variations of the granitic rocks related to the Palaeo-Tethyan closure, we reveal melting of multiple crustal sources rather than a sole source to construct the Lincang batholith.