Early Cretaceous magmatism archives crustal architecture of northern Lhasa Terrane, central Tibetan Plateau

Abstract

Identification of continental crustal architecture in orogenic belts is essential for understanding the geodynamic evolution of global continental collision systems. However, ongoing debates surrounding the crustal nature of the Lhasa Terrane in the central Tibetan Plateau impede our comprehension of its tectonic evolution. Mesozoic intermediate-felsic magmatism in the Lhasa Terrane offers key insights into the crustal architecture before the India-Asia collision. Here we report zircon U-Pb-Hf isotope, whole-rock element and SrNd isotope data from Early Cretaceous granitoids in the Baingoin batholith, northern Lhasa Terrane. These granitoids (127–115 Ma) exhibit variable SiO2 (62.99–73.86 wt%), K2O (1.15–4.74 wt%), and MgO (0.49–2.48 wt%) contents. They are classified as low- to high-K calc-alkaline and metaluminous to peraluminous series, enriched in large ion lithophile elements (e.g., Rb) and light rare earth elements ((La/Yb)N = 7.08–18.3), and depleted in high field strength elements (e.g., Nb, Ta, and Ti). These granitoids display geochemical affinities with I-type granitoid rocks and can be further subdivided into three groups. Group 1 granitoids exhibit the highest zircon εHf(t) (−1.57 to 5.85) and whole-rock εNd(t) (−3.37 to −2.45), and lowest (87Sr/86Sr)i (0.706018 to 0.706922) values, whereas Group 2 granitoids have wide ranges of zircon Hf (εHf(t) = −7.78 to 2.26) and enriched whole-rock SrNd isotope compositions ((87Sr/86Sr)i = 0.707214 to 0.707918; εNd(t) = −7.38 to −6.14). These suggest that Group 1 and Group 2 granitoids may be dominantly derived from the juvenile and ancient crustal sources, respectively. Group 3 granitoids are characterized by zircon Hf (εHf(t) = −2.85 to 3.52) and whole-rock SrNd isotope compositions ((87Sr/86Sr)i = 0.706473 to 0.707692; εNd(t) = −4.50 to −3.01) falling between the ranges of the previous two groups, likely represent a mixture of juvenile crustal-derived melt with 10–15% of reworked ancient crustal materials. Integrating previous research, we propose that the persistent ancient crustal basement beneath the northern Lhasa Terrane was concurrently undergoing significant modification through juvenile crustal materials during the Early Cretaceous. These Early Cretaceous Baingoin batholith preserves crucial records of crustal evolution and highlights the influence of upwelling asthenosphere during the transition from Bangong-Nujiang oceanic subduction to Lhasa-Qiangtang collision.