Mid-Permian Luerma intraplate basalt in the southern Lhasa subterrane, Qinghai–Tibetan Plateau: Recording the initial breakup of the Lhasa terrane from northern Gondwana

Abstract

Among the numerous scientific questions concerning the evolution of the Tethys on the Qinghai–Xizang Plateau, the initial breakup of the Lhasa terrane from northern Gondwana remains disputed. This controversy stems primarily from the scarcity of intraplate magmatic records associated with this event and insufficient systematic research into its genetic mechanisms. However, the discovery of a Mid-Permian Luerma within-plate basalt in the Western part of the Lhasa Terrane provides new evidence for the exploration of this issue. Building on U–Pb dating of zircon via laser ablation–inductively coupled plasma–mass spectrometry (LA‒ICP‒MS), the estimated age of the basalt is approximately CA. 261 ± 1 Ma. Geochemically, the rock belongs to the shoshonite–latite series and contains high levels of iron (Fe₂O₃, 4.67–5.57 wt%; FeO, 3.51–5.59 wt%), magnesium (MgO, 3.86–6.58 wt%), total alkalis (K₂O + Na₂O, 4.43–8.07 wt%), and titanium (TiO₂, 2.00–3.78 wt%). Additionally, the basalt is enriched in large-ion lithophile elements and light and heavy rare-earth elements (LREEs/HREEs) whose ratios of the samples range from 9.92 to 16.92), with no apparent Eu or Ce anomalies (δEu, 0.88–1.07 and δCe, 0.81–1.22). Isotopically, the rock exhibits high ε_Nd(t) (0.77–2.76) and ε_Hf(t) (6.60–9.00) and low (⁸⁷Sr/⁸⁶Sr)_i (0.703248–0.705597) values. These findings indicate that the basaltic magma originated from the partial melting of the upper mantle within a plate. This study revealed that the Lhasa terrane separated from northern Gondwana by at least the Mid-Permian.