ABSTRACT
The Riduo intermediate-felsic volcanic rocks are located in the eastern Lhasa terrane in southern Tibet. Zircon U–Pb dating, geochemical and Sr–Nd–Hf isotope analyses were carried out to constrain the age, petrogenesis and magma source of the Riduo magma suite, including andesite, dacitic tuff, and quartz diorite. Zircon U–Pb dating yielded Early Miocene ages of 19.5 ± 0.5 Ma (andesite), 17.6 ± 0.3 Ma (dacitic tuff), and 15.6 ± 0.5 Ma (quartz diorite). Geochemically, this early Miocene suite is adakitic with high SiO2 (55.76–69.46 wt.%), Al2O3 (15.21–16.61 wt.%), Na2O (3.82–4.83 wt.%), Sr (427–1033 ppm), and Sr/Y (24.5–145), but low Y (< 17.8 ppm) and Yb (< 1.82 ppm). The rocks also have low to high K2O (0.44–3.82 wt.%). They are enriched in light rare earth elements (LREEs), large ion lithophile elements (LILEs, e.g. K, Rb, Th and U), but depleted in high-field strength elements (e.g. Nb, Ta) and heavy rare earth elements (HREEs), and have weakly negative to positive Eu anomalies. Isotope analyses reveal that most samples have high whole-rock initial 87Sr/86Sr ratios (0.705611–0.708807), low εNd(t) (−2.25 to −1.15), and positive zircon εHf (t) (+1.29 to +6.49). We suggest that the early Miocene magmas in the eastern Lhasa terrane were likely sourced from post-collisional partial melting of the juvenile lower crust with minor mantle input. The magmas may have been crustal-contaminated during their ascent to the upper crust along the N-S-trending Cona-Riduo rift.
Highlights
The Miocene Riduo igneous suite in the Gangdese Copper Belt is investigated.
Intermediate-felsic volcanism was U-Pb dated to be Miocene (ca. 19.5–15.6 Ma).
The volcanic rocks have adakitic geochemical affinities.
Riduo adakitic magma likely derived from partial melting of juvenile lower crust.
Acknowledgments
We thank the editor and reviewer who have contributed to improve this work with their insightful comments and suggestions. We thank Fang-lin Han, Xin-lin Li, and Lian-dang Zhao for their field assistance, and Zhi Zhang for the insightful discussion.
Disclosure statement
No potential conflict of interest was reported by the author(s).
Supplementary material
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