LITHOS 476–477 (2024) 107594 Available online 4 April 2024 0024-4937/© 2024 Elsevier B.V. All rights reserved. Eocene rhyolites in the Shanglaxiu-Xialaxiu area of north-eastern Qiangtang Block, Tibet: Partial melting of juvenile crust? Yi-Wen Wei a, b , Jun Wang a , Qiang Wang a, b, * , Bing-Zhang Wang c , Andrew C. Kerr d , Wu-Fu Li c , Shan-Ping Li c , Jin-Heng Liu a , Chun-Tao Wang c , Zi-Long Wang a a State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China b College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing 100049, China c Qinghai Geological Survey Institute, Xining, Qinghai 810012, China d School of Earth and Environmental Sciences, Cardiff University, Cardiff CF10 3AT, UK A R T I C L E INFO Keywords: Rhyolites Juvenile crust Continental subduction Eocene Qiangtang Tibet ABSTRACT Many granitoids and their eruptive equivalents are substantially derived from the uppermost proportion of continental crust, and so their petrogenesis and source are significant in understanding the evolution and characteristics of continental crust. The Eocene felsic rocks in the Qiangtang block (central Tibet) commonly have enriched Nd isotope compositions and have been considered to be related to the recycling of ancient continental crustal material. In this paper we report new data on early Eocene felsic rocks with positive ε Nd (t) values in the northeastern Qiangtang block, which can be used to help understand Cenozoic evolution and characteristics of continental crust in the Qiangtang block. These rocks consist of rhyolites and occur in the Shanglaxiu and Xialaxiu areas in the north eastern Qiangtang block. Zircon U Pb dating yields ages of 47.8 ± 0.6 and 44.2 ± 0.7 Ma for the Shanglaxiu and Xialaxiu rhyolites, respectively, and so they represent the earliest record of Eocene magmatism in the Qiangtang block. The Shanglaxiu Xialaxiu rhyolites have relatively low calculated zircon saturation temperatures (719–819 ◦ C), along with high SiO 2 (74.8–83.3 wt%) and K 2 O (5.1–7.8 wt%) contents, and low MgO (0.2–0.3 wt%), Cr and Ni contents. They are enriched in light rare earth elements (LREEs), Rb, K, Th, Zr, and Hf, and are depleted in Nb, Ta, Ti, Sr, and P, with moderately negative Eu anomalies. The Shanglaxiu rhyolites have positive whole rock ε Nd (t) (0.3–0.4) and zircon ε Hf (t) (1.8–10.4), and variable zircon δ 18 O (6.3–7.3‰). The Xialaxiu rhyolites have slightly different whole rock ε Nd (t) ( 1.5 to  1.6), but similar zircon ε Hf (t) (2.2–7.7) and δ 18 O (6.7–7.2‰). We propose that the Shanglaxiu Xialaxiu rhyolites were most probably generated by partial melting of the pre existing juvenile crust with the addition of minor sedi- mentary material. This partial melting was possibly triggered by the south dipping continental subduction of the Songpan Ganzi block. The pre existing juvenile crust was probably formed during the subduction of Paleo-  Tethyan oceanic slab in Paleozoic Early Mesozoic. 1. Introduction The continental crust has long been a significant area of geological research (Niu et al., 2013; Rudnick, 1995). Incompatible trace element signatures of mantle derived island arc magmas (IAB) and the bulk continental crust are remarkably similar in that both are relatively enriched in “water soluble” elements (e.g., Ba, K and Pb) and depleted in “water insoluble” elements (e.g., Nb, Ta and Ti) (Niu et al., 2013; Rudnick and Gao, 2014). Consequently, it is widely accepted that the continental crust was principally generated through subduction zone magmatism (Rudnick, 1995). Nevertheless, this standard “island arc model” is not completely correct because bulk arc crust is too mafic and has a dominantly basaltic composition (Steven Holbrook et al., 1999) which is significantly different from the andesitic bulk composition of continental crust (Rudnick and Gao, 2014). Furthermore, it has been argued that arc crust does not contribute to net continental growth owing to the mass balance of subduction erosion, sediment recycling and arc crust production (Niu et al., 2013). * Corresponding author at: State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China. E-mail address: wqiang@gig.ac.cn (Q. Wang). Contents lists available at ScienceDirect LITHOS journal homepage: www.elsevier.com/locate/lithos https://doi.org/10.1016/j.lithos.2024.107594 Received 6 January 2024; Received in revised form 29 March 2024; Accepted 30 March 2024