Zircon U–Pb geochronology and geochemistry of Late Cretaceous–early Eocene granodiorites in the southern Gangdese batholith of Tibet: petrogenesis and implications for geodynamics and Cu ± Au ± Mo mineralization

Abstract

Cu ± Au ± Mo mineralization is found in multiple intrusive suites in the Gangdese belt of southern Tibet (GBST). However, the petrogenesis of these ore-bearing intrusive rocks remains controversial. Here, we report on mineralization-related Late Cretaceous-early Eocene intrusive rocks in the Chikang-Jirong area, southern Gangdese. Zircon U-Pb analyses indicate that the mainly granodioritic Chikang and Jirong plutons were generated in the Late Cretaceous (ca. 92 Ma) and early Eocene (ca. 53 Ma), respectively. They are high-K calc-alkaline suites with high SiO 2 (64.8-68.3 wt.%) and Al 2 O 3 (15.1-15.7 wt.%) contents. Chikang granodiorites are characterized by high Sr (835-957 ppm), Sr/Y (118-140), Mg# (58-60), Cr (21.8-36.6 ppm), and Ni (14.3-22.9 ppm), and low Y (6.0-8.1 ppm), Yb (0.54-0.68 ppm) values with negligible Eu anomalies, which are similar to those of typical slab-derived adakites. The Jirong granodiorites have high SiO 2 (64.8-65.3 wt.%) and Na 2 O + K 2 O (7.19-7.59 wt.%), and low CaO (2.45-3.69 wt.%) contents, Mg# (47-53) and Sr/Y (14-16) values, along with negative Eu and Ba anomalies. Both Chikang and Jirong granodiorites have similar ε Hf (t) (7.6-13.1) values. The Chikang granodiorites were most probably produced by partial melting of subducted Neo-Tethyan oceanic crust, and the Jirong granodiorites were possibly generated by partial melting of Gangdese juvenile basaltic crust. In combination with the two peak ages (100-80 and 65-41 Ma) of Gangdese magmatism, we suggest that upwelling asthenosphere, triggered by the rollback and subsequent break-off of subducted Neo-Tethyan oceanic lithosphere, provided the heat for partial melting of subducted slab and arc juvenile crust. Taking into account the contemporaneous occurrence of Gangdese magmatism and Cu ± Au ± Mo mineralization, we conclude that the Late Cretaceous-early Eocene magmatic rocks in the GBST may have a significant potential for Cu ± Au ± Mo mineralization.

U–Pb zircon age and geochemistry of the Cuocun gabbro in the southern Lhasa Terrane: Implications for Early Cretaceous rollback of the Neo‐Tethyan oceanic slab

“…(a) Tectonic outline of the Lhasa Terrane showing the study area (modified after Zhu et al, 2011); (b) Simplified geological map showing the time‐space distributions of Mesozoic igneous rocks (after Zhu et al, 2013); (c) Simplified geological map of the Cuocun area (modified after Lang et al, 2014). Data sources: ages of Cretaceous magmatic rocks in the Lhasa Terrane are from Schärer, Xu, and Allègre (1984), McDermid, Aitchison, Davis, Harrison, and Grove (2002), Wen, Chung, et al, 2008, Wen, Liu, et al (2008), Zhou et al (2008), Ji et al (2009, 2014), Zhu, Zhao, et al (2009), Zhu, Mo, et al, 2009, Zhu et al (2011), Bedard et al (2009), Guillaume, Martinod, and Espurt (2009), Meng et al (2010), Zhang et al (2010), Liang, Wei, Xu, Hu, and Charllote (2010), Guan et al (2010), Guo (2011), Dai et al (2013), Ma, Wang, Li, et al (2013), Ma, Wang, Wyman, et al (2013), Ma et al (2015, 2013c), Zhang, Liu, Wu, Ji, and Wang (2014), Chen et al (2014), Jiang et al (2015), Ye et al (2015), Wang, Hu, Garzanti, An, and Liu (2017), Xie, Lang, Tang, Ma, and Zou (2018), and Li et al (2008) [Colour figure can be viewed at wileyonlinelibrary.com]…”

“…A consensus has been reached on the subduction of Late Triassic to Late Jurassic and Late Cretaceous. During the Late Triassic to Late Jurassic, the SLT was influenced by northward subduction of the Neo‐Tethyan slab and subsequent slab rollback of Neo‐Tethyan slab, forming the Bima Formation, Xiongcun Formation; Yeba Formation; Jiacha adakitic rocks (202–179 Ma; Shui et al, 2018), and Ruocuo adakitic rocks (182–170 Ma; Wang, Lang, Tang, Deng, & Cui, 2019; Lang, Wang, et al, 2019; Lang, Liu, et al, 2019; Lang et al, 2020; Liu et al, 2018; Ma, Meert, Xu, & Zhao, 2019; Pan et al, 2012; Wang, Ding, Liu, Zhang, & Yue, 2017; Zhu, Pan, et al, 2008; Zhu, Zhang, et al, 2008); In the Late Cretaceous, during 100–80 Ma, the SLT was influenced by northwards subduction of the Neo‐Tethyan oceanic ridge, forming gabbro, gabbro‐diorite, diorite, tonalite, granodiorite, and granite that are distributed along a narrow (~50 km wide) east‐west trending belt from Xietongmen to Milin (Guo, 2011; Jiang et al, 2015; Ma, Wang, Li, et al, 2013; Ma, Wang, Wyman, et al, 2013; Ma et al, 2015; Wen, Chung, et al, 2008; Wen, Liu, et al, 2008; Zhang et al, 2010, 2014). However, the geodynamic mechanism of the Early Cretaceous magmatism in SLT remains unclear.…”

“…During the Late Triassic to Late Jurassic, the SLT was influenced by northward subduction of the Neo-Tethyan slab and subsequent slab rollback of Neo-Tethyan slab, forming the Bima Formation, Xiongcun Formation; Yeba Formation; Jiacha adakitic rocks (202-179 Ma;Shui et al, 2018), and Ruocuo adakitic rocks (182-170 Ma;Wang, Lang, Tang, Deng, & Cui, 2019;Lang, Liu, et al, 2019;Lang et al, 2020;Liu et al, 2018;Ma, Meert, Xu, & Zhao, 2019;Pan et al, 2012;Wang, Ding, Liu, Zhang, & Yue, 2017;Zhu, Pan, et al, 2008; Zhu, Zhang, F I G U R E 1 (a) Tectonic outline of the Lhasa Terrane showing the study area (modified after Zhu et al, 2011); (b) Simplified geological map showing the time-space distributions of Mesozoic igneous rocks (after Zhu et al, 2013); (c) Simplified geological map of the Cuocun area (modified after Lang et al, 2014). Data sources: ages of Cretaceous magmatic rocks in the Lhasa Terrane are from Schärer, Xu, and Allègre (1984), McDermid, Aitchison, Davis, Harrison, and Grove (2002), , Wen, Liu, et al (2008, Zhou et al (2008), Ji et al (2009Ji et al ( , 2014, , Zhu, Mo, et al, 2009, Zhu et al (2011, Bedard et al (2009), Guillaume, Martinod, and Espurt (2009), Meng et al (2010), Zhang et al (2010), Liang, Wei, Xu, Hu, and Charllote (2010), Guan et al (2010), Guo (2011), , , , Ma et al (2015Ma et al ( , 2013c, Zhang, Liu, Wu, Ji, and Wang (2014), Chen et al (2014), Jiang et al (2015), Ye et al (2015), …”

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

“…Although a wealth of geochronological and geochemical data has been obtained from Southern Lhasa (Y. B. Hu, Liu, et al, ; Z. Q. Jiang et al, ; X. Sun, Zheng, Li, et al, ; S. Wu et al, ; B. Xu, Hou, et al, ; Zheng, Sun, et al, ), few studies have focused on Central Lhasa (Fu et al, ; L. Q. Wang, Tang, et al, ; Y. C. Zheng, Fu, et al, ).…”