In situ small‐spot U‐Pb geochronology is essential for measuring zircon crystals containing micrometre‐scale heterogeneities, abundant inclusions, inevitable cracks and narrow growth zones, all of which are especially common in metamorphic zircons. We present a high spatial resolution (≤ 10 μm diameter) laser ablation‐multi‐collector‐inductively coupled plasma‐mass spectrometry (LA‐MC‐ICP‐MS) U‐Pb dating method using a Nu Plasma II mass spectrometer coupled with a GeoLas HD laser ablation system, which is capable of analysing zircon crystals with a wide range of U contents through two analytical modes (mixed‐mode for 10 μm ablation and IC‐mode for 5 μm ablation). We examined Pb/U down‐hole fractionation (DHF) as a function of different laser settings under small‐spot ablation, and how it controls the accuracy and precision of U‐Pb ages of zircon reference materials. After DHF correction using Iolite software (version 3.71), five measurement sessions (with different laser fluence and/or laser pulse settings) for the two analytical modes yielded accurate and precise U‐Pb ages for four zircon reference materials (Plešovice, 91500, GJ‐1 and Temora‐2). Further determinations of U‐Pb ages of three metamorphic zircon samples (~ 14 to 2000 Ma) from the Himalaya, North China Craton and North Qaidam were conducted, the results of which confirm the effectiveness and feasibility of this small‐spot ablation method for natural zircons with multiple growth zones.

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To investigate the evolution of the continental crust in the northern Tibetan Plateau, detrital zircon U–Pb geochronology and Hf isotopes analysis were performed on two fluvial sand samples from North Qaidam (the Yuka and Shaliu rivers). A total of 443 detrital zircon U–Pb ages and 244 Hf isotopic results were obtained and reveal that the South Qilian, North Qaidam, and East Kunlun terranes show affinity to the western Yangtze Block. Age distributions of detrital zircons from the Yuka River cluster mainly in two age intervals of 1,000–700 and 480–400 Ma. The corresponding εHf(t) values are mostly negative, with depleted two-stage Hf model ages (TDM2) of 2.1–1.6 Ga. In contrast, age data for the Shaliu River fall in the ranges of 1,000–700, 460–380, and 260–200 Ma, with TDM2 ages of 2.0–1.6 and 1.6–1.2 Ga. In addition, zircons with Neoproterozoic ages from both river samples possess common Paleoproterozoic TDM2 ages (2.0–1.6 Ga, with a peak of 1.8–1.7 Ga), indicating that the South Qilian, North Qaidam and East Kunlun terranes were probably part of the same Neoproterozoic continent. The East Kunlun and North Qaidam terranes are inferred to include Mesoproterozoic continental crust (1.6–1.0 Ga), suggesting differences in crustal evolution between the East Kunlun–North Qaidam and Qilian terranes. Phanerozoic magmatism in these three terranes was sourced mainly from the recycling of ancient continental crust with minor contributions from the juvenile crust.