Geochronological and geochemical evidence for the nature of the Dongling Complex in South China

• Sedimentary protolith of the Dongling Complex was deposited not earlier than 730 Ma.
• The sediments were primarily derived from Neoproterozoic and Paleoproterozoic rocks.
• The Dongling sediments were deposited in a failed continental rift basin in the Cryogenian.
• The rift basin was located at the boundary between the Yangtze craton and the Jiangnan orogen.
• The Dongling Complex is not a part of the ancient basement in the Yangtze craton.

The ancient basement of the Yangtze craton in South China is poorly exposed and its early evolution is loosely constrained yet. The Dongling Complex is usually advocated as the ancient basement of the Yangtze craton without an intensive study yet. Schist and gneiss from the Dongling Complex have high SiO2 and Al2O3 contents, low CIA values. Their REE and trace element distribution patterns are similar to PAAS and average upper crust. Their δ18O values are generally higher than 10‰ for quartz, demonstrating a sedimentary origin for their protolith. Detrital zircon U–Pb dating yields three distinct age populations for the Dongling metasediments: (1) >2.4 Ga with negative ɛHf(t) values, mostly on cores and unzoned grains; (2) ∼2.0 Ga with negative ɛHf(t) values on weak luminance and unzoned domains; (3) 730–830 Ma with ɛHf(t) values ranging from −24.8 to 4.9 on oscillatory zonings and fragmented euhedral grains. The zircons of different U–Pb ages exhibit similar REE patterns but different Ti-in-zircon temperatures. The zircon age populations are consistent with provenances from both the Yangtze craton and the Jiangnan orogen for the Dongling sediments. The youngest detrital zircon age of 731 ± 13 Ma provides an upper limit for the deposition age; the geological occurrence of overlying strata provides a lower limit of 635 Ma for the deposition age. In view of the extensional setting in South China during the middle Neoproterozoic, the most plausible tectonic environment for deposition of the Dongling sediments is a failed continental rift basin between the Yangtze craton and the Jiangnan orogen. Therefore, the Dongling Complex is not the ancient basement of the Yangtze craton despite the involvement of some basement materials in its protolith.

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