Mineralogy, zircon U–Pb–Hf isotopes, and whole‐rock geochemistry of Late Cretaceous–Eocene granites from the Tengchong terrane, western Yunnan, China: Record of the closure of the Neo‐Tethyan Ocean

Abstract

New data from mineralogy, geochemistry, zircon U–Pb dating, and Hf isotopes have revealed Late Cretaceous to Eocene magmatic intrusions in the Tengchong terrane and constrained the origin, tectonic setting, and characteristics of tin‐bearing and barren granitoids. We divide the studied granitoids into two groups: (a) the Late Cretaceous Zhinaxiang (70 Ma) and Early Paleocene Dazhupeng (65 Ma) S‐type barren granites and (b) the Eocene Lailishan A2‐type tin‐bearing granite (50 Ma). All these granitoids display Si‐ and K‐rich and calc‐alkaline characteristics and have similar chondrite‐normalized rare earth element patterns. However, geochemical differences do exist between the two groups of granites. The Zhinaxiang and Dazhupeng S‐type granites are slightly peraluminous, enriched in large‐ion lithophile elements (e.g., Rb and K), and depleted in high‐field‐strength elements (e.g., Nb, Ta, Zr, and Hf), whereas the Lailishan A2‐type granite has higher TFe2O3, high‐field‐strength element content, and Ga/Al ratios. The geochemical and Hf isotopic data indicate that the granites in this study were generated by partial melting of Paleoproterozoic metasedimentary rocks. Due to the subduction of the Neo‐Tethyan Ocean beneath the Eurasian plate, the Zhinaxiang and Dazhupeng S‐type granites were formed in a thickened‐crustal environment, whereas the Lailishan A2‐type granite was emplaced in a post‐collisional extensional setting attributed to slab break‐off. By comparison between tin‐bearing and barren granites, we propose that the Sn mineralization could be related to relatively high‐temperature and low‐pressure crystallization conditions.

A Late Cretaceous felsic magmatic suite from the Tengchong Block, western Yunnan: integrated geochemical and isotopic investigation and implications for Sn mineralization

“…The U-Pb ages of cassiterite (72-74 Ma) and 40 Ar-39 Ar ages of muscovite (72-73 Ma) from the Xiaolonghe tin deposit (Chen et al 2014;Cao et al 2016) indicate that the deposit formed simultaneously with the Guyong and Xiaolonghe plutons (Xu et al 2012;Chen, X. C. et al 2015;Qi et al 2015;Xie et al 2016), and this outcome implies a genetic relationship between the tin deposit and magmatism (Cao et al 2018). Previous studies regarded the XMS to be genetically related to the tin deposit from the perspective of formation age and stable isotopic (C-H-O-S-Pb-He-Ar) compositions (Cao et al 2016;Chen et al 2018); little attention was Fig.…”

“…The upwelling and underplating of mantle-derived magma induced by subduction of the Neo-Tethys provided the heat source for the partial melting of crustal rocks (Chen, X. C. et al 2015;Jiang et al 2017). The subduction of the Neo-Tethys beneath the Tengchong Block changed from flat to steep, and the convergence rate increased rapidly from c. 70 Ma (Cao et al 2018). Thus, we consider that the Late Cretaceous (∼75 Ma) magma in the central Tengchong Block was produced by the change in subduction angle, which resulted in the upwelling of the asthenosphere that provided heat for the melting of crustal rocks.…”

“…The large granitoids in the Tengchong Block define three N-S-trending belts from the Early Cretaceous eastern Donghe to Late Cretaceous central Guyong and Palaeogene western Binglangjiang granites (Fig. 1b) (Cao et al 2016(Cao et al , 2018Fang et al 2018). There are also abundant synchronous tin deposits, such as the Xiaolonghe and Lailishan in the Tengchong Block (Cao et al 2018).…”

“…1b) (Cao et al 2016(Cao et al , 2018Fang et al 2018). There are also abundant synchronous tin deposits, such as the Xiaolonghe and Lailishan in the Tengchong Block (Cao et al 2018). As the largest tin deposit in the Tengchong Block, the Xiaolonghe tin deposit located in the Guyong granite belt has been involved in several recent studies, which were mainly focused on the ore-forming processes and fluid evolution (Chen et al 2017(Chen et al , 2018Cui et al 2019), the geochronology of the deposit and related granites (Chen et al 2014;Zhang et al 2014;Cao et al 2016) and the genetic link between the metallogeny and magmatism (Cao et al 2016).…”

Cambrian magmatism in the Tethys Himalaya and implications for the evolution of the Proto‐Tethys along the northern Gondwana margin: A case study and overview

“…The trace element concentrations were analysed using a Perkin Elmer NexIon 300D ICP‐MS (Perkin Elmer, Branford, CT, USA) after the powdered samples were digested in an HF + HNO 3 mixture in high‐pressure Teflon bombs. Detailed procedures were described in Cao, Zhang, et al (). The analytical precision is generally higher than 1% for elements with concentrations of >200 ppm and 1–3% for elements with concentrations of less than 200 ppm.…”