Geochronology, petrogenesis and tectonic implications of the Jurassic Namco–Renco ophiolites, Tibet

Abstract

The nature of the Namco–Renco ophiolites in the northern Lhasa subterrane is widely disputed. To investigate their formation age, petrogenesis, and tectonic setting, the harzburgites, basalts, and metagabbros of the Namco ophiolite and the harzburgites, lherzolites, gabbros, and diabasic dikes of the Renco ophiolite were selected for whole-rock geochemical and zircon U-Pb dating and in situ Lu-Hf isotopic analyses. The geochemical and geochronological data indicate that the Namco metagabbros were generated at 178.0 ± 2.9 Ma, along with the Namco–Renco peridotites formed in the initial stage of a continental margin basin; whereas the Renco gabbros were developed at 149.7 ± 1.6 Ma, along with the Renco diabasic dikes and Namco basalts formed later in a mature back-arc basin. The Namco–Renco ophiolites were derived from a depleted mantle source with involvement of minor older crustal materials. Combined with the regional geological background, the Namco–Renco ophiolites were likely formed mainly associated with the southward subduction of the Bangong–Nujiang oceanic lithosphere beneath the Lhasa terrane. This study provides new constraints on the formation ages of the Namco–Renco ophiolites and the tectonic evolution of the Namco–Renco Ocean.

Keywords:

• Bangong–Nujiang suture zone
• Namco–Renco ophiolites
• back-arc basin
• geochemistry
• geochronology
• Lu-Hf isotope

Acknowledgements

We appreciate Hong-Fei Liu and Zhi-Xuan Li for their help in fieldwork, and Guo-Qing Zhou and Xiang-Lin Tu for their analytical assistance.

Additional information

Funding

This work was supported by the National Nature Science Foundation of China [grant number 41472054], [grant number 41372208]; China Geological Survey [grant number 1212011221105]; Open Research Foundation of the State Key Laboratory of Ore Deposit Geochemistry, Chinese Academy of Sciences [grant number 201304]; and the Fundamental Research Funds for the Central Universities, China [grant number 15lgpy21].