The Lhasa terrane is one of the major segments of the Tibetan Plateau, with widespread Mesozoic to Cenozoic magmatic and metallogenic records. Here, we investigate timing and characteristics of magmatism associated with the Lunggar Fe skarn deposit in Central Lhasa. We also present Sr–Nd–Pb and Hf (zircon) isotopic data on three associated intrusions to gain insights on the tectonic and metallogenic evolution of the region. Our data reveal at least two magmatic pulses in Lunggar represented by Early Cretaceous I‐type granodiorite (112.9 ± 1.5 Ma) and granite porphyry (112.6 ± 1.3 Ma) with magma generation related to slab break‐off associated with the Bangong–Nujiang Ocean during closure of the Meso‐Tethyan ocean at ~113 Ma. Iron skarn mineralization at Lunggar was contemporaneous with local Early Cretaceous intrusive activity. Following this, Late Cretaceous adakitic diorite (90.5 ± 1.5 Ma) formed from delaminated thickened crust at ~91 Ma related to the northern subduction of the Yarlung‐Zangbo oceanic plate. We also provide a comprehensive review of the Cretaceous tectonic evolution of Central Lhasa, which trace the tectonic evolution as follows: (a) 145–120 Ma: southward subduction of the Bangong–Nujiang oceanic plate under the Lhasa terrane; (b) 120–115 Ma: Lhasa‐Qiangtang continental collision; (c) 115–110 Ma: slab break‐off of the Bangong–Nujiang Ocean; (d) 110–95 Ma: crustal thickening of the Central Lhasa lower crust; (e) 95–80 Ma: delamination of lithospheric mantle; and (f) 80–65 Ma: northward subduction of the Yarlung‐Zangbo oceanic plate and subsequent slab rollback. The related metallogenic events in Central Lhasa include (a) ~115–110 Ma skarn Fe mineralization associated with slab break‐off; (b) ~90–80 Ma porphyry Cu–Au mineralization formed in delaminated thickened crust of Central Lhasa; and (c) ~65 Ma skarn Pb–Zn mineralization produced from slab rollback of the Yarlung‐Zangbo Ocean.

The Cuonadong Dome in southern Tibet is a newly discovered gneiss dome in the Tethys Himalaya. Here, we investigate the Late Cambrian augen gneiss (orthogneiss) within the core of this dome to address the controversy surrounding early Palaeozoic tectonic evolution of the northern margin of eastern Gondwana. We report new zircon laser ablation multicollector inductively coupled plasma mass spectrometry (LA‐(MC‐)ICP‐MS) U‐Pb ages, Lu‐Hf isotopes, whole‐rock major and trace element geochemistry, and Sr‐Nd‐Pb data on representative samples from the granitic gneiss. The weighted mean of 116 analyses of zircon grains yields an age of 498.2 ± 1.5 Ma (mean square weighted deviation [MSWD] = 1.2). Forty‐one spots analyses on these grains show consistent εHf (t) values of −2 to +4 (average = +1.1), corresponding to Hf crustal model age (TDM2) of 1.3 to 1.6 Ga (average = 1.39 Ga). The orthogneiss (metagranite) is characterized by high Si and K contents, with low Al, Mg, and Ti, and A/CNK values ranging from 0.87 to 0.98 with an average of 0.92, indicating a metaluminous composition and I‐type granitoid affinity. The granitoid displays significant enrichment in light rare earth elements (LREEs) and relatively flat high rare earth element (HREE) patterns, with strong negative Eu anomalies (Eu/Eu* = 0.26–0.31). The primitive mantle‐normalized trace elements show a relative enrichment in large‐ion lithophile elements, such as Rb, and high‐field strength elements, such as Th, U, Zr, and Hf, with depletion in Ba, Nb, Ta, Sr, P, and Ti. The rocks show high initial 87Sr/86Sr ratios (0.7221–0.7248) and low εNd (t) values (−8.9 to −7.3) with Nd model ages (TDM) of 1.79–1.91 Ga. Their radiogenic Pb isotopic compositions show (206Pb/204Pb)t = 18.804–19.110, (207Pb/204Pb)t = 15.730–15.768, and (208Pb/204Pb)t = 38.409–39.054, indicating an ancient upper middle continental crustal origin. Our study shows that the protolith of the metagranite was most likely derived from the partial melting of upper continental crust with a minor contribution of depleted mantle materials. Through integration of the regional information on early Palaeozoic magmatism and metamorphic events, we contend that the protolith of the Cuonadong granitic gneiss formed in an accretionary setting associated with the early Palaeozoic Proto‐Tethys Oceanic plate subduction beneath the Gondwana continent.

Miocene postcollisional potassic and adakitic rocks are widely distributed in the southern Lhasa terrane and western central Lhasa terrane. However, coeval potassic and adakitic rocks in eastern central Lhasa terrane were rarely recognized, and their origins and formation mechanism remain controversial. In this paper, we provide new geochronological and geochemical data for the Miocene postcollisional potassic and adakitic intrusions exposed in the Qingdu area, eastern central Lhasa terrane, southern Tibet. The Qingdu Miocene intrusions consist of quartz monzonite porphyry and biotite granite with coeval zircon U–Pb ages of 14.1 Ma and 14.0 Ma, respectively. They have high SiO2 (67.98–75.32 wt.%), Al2O3 (14.13–14.78 wt.%), and K2O (4.06–6.18 wt.%) and low MgO (0.25–1.46 wt.%) contents. They are both enriched in light rare earth elements (LREEs) and depleted in heavy rare earth elements (HREEs), with high (La/Yb)N (25.37–42.32) ratios. The biotite granite samples have low Y (7.10–9.96 ppm) and Yb (0.61–0.85 ppm) contents, and high Sr (229–384 ppm) contents and high Sr/Y (30–41) ratios, which show adakitic geochemical characteristics, whereas the quartz monzonite porphyry samples show potassic geochemical characteristics. They display initial (87Sr/86Sr)i ratios of 0.7083–0.7103, εHf(t) values of −6.7 to −0.1, εNd(t) values of −8.96 to −7.44, (208Pb/204Pb)i ratios of 39.028–39.110, (207Pb/204Pb)i ratios of 15.662–15.684, and (206Pb/204Pb)i ratios of 18.541–18.577. These signatures indicate that both the potassic and adakitic intrusions are more likely to originate from partial melting of a thickened lower crust, which were mainly the products of the binary mixing between the juvenile and ancient crust components. Based on the spatial distributions and isotopic features of the postcollisional potassic and adakitic rocks in the Lhasa terrane, we suggest that the differences of the lower crustal composition played a crucial role in causing the geochemical variations of the Miocene postcollisional adakitic and potassic rocks in Lhasa terrane.