Petrogenesis and metallogenic implications of Cretaceous magmatism in Central Lhasa, Tibetan Plateau: A case study from the Lunggar Fe skarn deposit and perspective review

Abstract

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.

Initial decratonization of the eastern North China Craton: New constraints from geochronology, geochemistry, and Hf isotopic compositions of Mesozoic igneous rocks in the Qingchengzi district

“…Thus, the Qingchengzi Mesozoic granitoids are primarily I, A, and S types. Further, the geochemical characteristics of A‐, I‐, and S‐type granites have been confirmed by numerous studies (Whalen et al, ; Eby, ; Chappell & White, ; Chappell, ; Clemens, ; Chappell, Bryant, & Wyborn, ; Ghani, Searle, Robb, & Chung, ; Pei et al, , Pei et al, ; H. W. Cao et al, ).…”

“…The major and trace element data of the Triassic–Middle Jurassic granitoids in the study area provide valuable information regarding the nature of their magma source. These granitoids contain high SiO 2 (68.94–77.07 wt.%) and low MgO (0.07–0.98 wt.%) concentrations and are depleted in Nb, Ta, P, and Ti and enriched in Rb, Th, and K, indicating that the formation of these rocks can be attributed to the partial melting of the crust (Gao et al, ; Chappell & White, ; Yang et al, ; H. W. Cao et al, ). The following points also prove this viewpoint: (a) the Ce/Pb and Nb/U ratios of the studied granitoids are 0.78–6.86 (average 2.94) and 2.70–10.76 (average 6.83), respectively, suggesting a continental crust source (Hofmann, Jochum, Seufert, & White, ); (b) these rocks have Rb/Sr ratios of 0.20–2.89 (an average of 0.86), Ti/Zr ratios of 3.40–13.46 (an average of 9.94), and Ti/Y ratios of 113.11–382.61 (an average of 265.49; Table ), which are consistent with the magma derived from the partial melting of crust (Pearce, ; Tischendorf & Paelchen, ; Wilson, ); and (c) the low concentrations of compatible elements (e.g., Cr, Co, and Ni) and low Mg # values (11–41) in these samples indicate that the primary magma of the granitic rocks in the Qingchengzi district was formed by the partial melting of the lower crustal materials (Rapp, Shimizu, Norman, & Applegate, ; Rapp & Watson, ).…”

“…These extensive magmatic activities can be used as an important clue to identify the initiation of the decratonization processes (Wu, Lin, Wilde, Zhang, & Yang, ; Y. G. Xu, Li, Pang, & He, ; Yang & Wu, ). Granitoids provide important information about the lithospheric processes and tectonic evolution, particularly with respect to their whole‐rock geochemistry and geochronology (Whalen, Currie, & Chappell, ; Eby, ; Pearce, ; Tang, Santosh, & Teng, ; Kaygusuz, Arslan, Sipahi, & Temizel, ; H. W. Cao et al, ). Therefore, the emplacement time and stage of these Mesozoic granitoids in the Qingchengzi district will help us understand the destruction of the eastern NCC and also provide important constraints with respect to the nature and evolution of the magmatic processes.…”

Sulphur and lead isotopic compositions of the Pb–Zn polymetallic deposits in the Linzizong volcanic area, Gangdese belt, Tibet: Implications for variation characteristics of ore‐forming material sources and exploration targeting

“…The Lhasa terrane has experienced a complex tectonic history, including the Triassic separation from Gondwanaland, the Early Jurassic subduction of the Neo‐Tethyan ocean, the Cenozoic India–Asian continental collision, and the E–W extension of the Lhasa terrane (Cao et al, , ; Chung et al, ; Yin & Harrison, ). The Gangdese magmatic belt within the Lhasa terrane formed by the northward subduction of Neo‐Tethyan slab in the Mesozoic–Early Cenozoic and the consequent India–Asia collision starting at ~55–50 Ma mainly consists of the Gangdese Batholith (predominantly of oxidized I‐type granitoids) and the large area of volcanism (Mo et al, , ; Zhu et al, , ).…”

Formation of Late Cretaceoushigh‐Mggranitoid porphyry in central Lhasa, Tibet: Implications for crustal thickening prior to India–Asia collision

“…The Tibetan Plateau is the world's highest and largest active collisional orogen (Dai, Dong, Li, et al, 2019; Hou, Zheng, Zeng, et al, 2012), and is central to investigations on continental collision processes and mountain building (Cao et al, 2019, 2020; Dai et al, 2019; Hou et al, 2015; Roberts & Searle, 2019; Yin & Harrison, 2000; Zhang, 2000). The broadly flat plateau has an average elevation of 5 km (Fielding, Isacks, Barazangi, & Duncan, 1994), and a crustal thickness up to 60 to 80 km, which is approximately twice that of the global average continental crust (Kind et al, 1996; Mo, Hou, Niu, et al, 2007; Zhang & Klemperer, 2005).…”