Geochronology and geochemistry of the Dabure basalts, central Qiangtang, Tibet: evidence for ~550 Ma rifting of Gondwana

Abstract

Newly discovered basalts in the Dabure area (central Qiangtang block, northern Tibet) were subjected to laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U–Pb zircon dating, geochemical analyses, and zircon Hf isotope analyses. Dating of magmatic zircons from three basalt samples indicates that the Dabure basalts formed during the late Ediacaran (~550 Ma). Xenocrystic zircons yield ages of 700–1150 Ma, providing evidence of the Cryogenian crust in the Tibet block. The Dabure basalts are alkaline, rich in Ti and Fe, and are strongly enriched in light rare earth elements without Eu anomalies. The basalts are geochemically similar to within-plate basalts but are relatively depleted in Nb and Ta. Although the analysed zircons show differences in their Hf isotope compositions, the geochemical data suggest that the Dabure basalts were derived from enriched mantle and that the source magmas were contaminated by the continental crust. The basalts may have erupted during rifting at ~550 Ma (from the dating of magmatic zircons), and may have been a product of the initial breakup of Gondwanaland.

Keywords:

• Qinghai–Tibet plateau
• Qiangtang
• Gondwanaland
• basalt
• zircon LA-ICP-MS U–Pb dating

Acknowledgements

We thank the staff of the Geological Laboratory Centre of China, University of Geosciences (Beijing), for help with the LA-ICP-MS zircon U–Pb dating and the Institute of Physics, Peking University, for help with the CL image analysis. We also thank Ms Xu Feng, Dr Xie Chaoming, and Dr Zhai Qingguo for their help in the field.

Additional information

Funding

This research was funded by the National Science Foundation of China [grant numbers 41272240 and 41072166] and the China Geological Survey project [grant numbers 1212011221093 and 12120113036700].