Late Jurassic plutonic suites with diverse geochemical compositions are widespread in central Tibet, recording the evolution of the Bangong-Nujiang Tethyan Ocean. This paper presents new zircon U-Pb ages, whole-rock major- and trace-element compositions, and zircon Hf isotopic data for the intrusive plagiogranite body formed within the Labuco ophiolite complex of the Bangong-Nujiang suture zone. The Labuco plagiogranites yield a laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) zircon age of ca. 167 Ma, indicating a Late Jurassic age of crystallization. They are characterized by high Al2O3 and Na2O, and low K2O, TiO2, and MgO contents, with positive zircon εHf(t) values similar to those of high-Al plagiogranites. These features lead us to propose that partial melting of arc-type basalts at the base of the accretionary complex (at depths of >40 km) could be another petrogenetic explanation for the high-Al plagiogranites within the ophiolite complex. This study and earlier publications indicate that the Late Jurassic plutonic suites are characterized by diverse geochemical compositions and were formed in a subduction setting controlled by northward subduction of Bangong-Nujiang Tethyan oceanic lithosphere. Magmatic underplating, triggered by this subduction, played a key role in the vertical crustal growth in central Tibet.

Gold Open Access: This paper is published under the terms of the CC-BY-NC license.