Provenance of a Stenian succession in the eastern Jiangnan (Sibao) Orogen, South China: Implications on tectonic affinity and pre-Neoproterozoic crustal evolution

Abstract

The Lower Tieshajie Subgroup at the conjunction zone of the Yangzte and Cathaysia blocks represents the only Stenian sedimentary succession in the eastern Jiangnan (Sibao) Orogen of South China, bearing important clues on plate boundary and pre-Neoproterozoic crustal evolution. We report the first U-Pb and Hf isotopic data of detrital zircons from this succession to investigate the age and provenance characteristics. Age and Hf isotopic compositions of detrital zircons from the lower and upper parts of the metamorphosed Lower Tieshajie Subgroup are similar. They are exclusively of magmatic origins, showing youngest age peaks at ca. 1.17 Ga and ca. 1.15 Ga, respectively, but both with a rarity of 1.12–1.10 Ga ages from the nearby magmatic rocks. This constrains protolith deposition of the Lower Tieshajie Subgroup to be mainly at 1.17–1.12 Ga, while the timing of metamorphism is bracketed by the intruding unmetamorphosed granites to be 1.10–0.84 Ga, that is, related to Grenville-aged orogenesis at the Jiangnan Orogen. The detrital zircons yielded a broad age range of 3.28–1.03 Ga, dominated by a 1.20–1.10 Ga population interpreted to be sourced from coeval magmatic rocks within the Tieshajie Complex itself. The abundant Archean and Paleoproterozoic detrital zircons are well-matched with magmatic records from the Eastern Yangtze Block, suggesting a Yangtze Block affinity of the Lower Tieshajie Subgroup. This implies that the surface boundary between the Yangtze and Cathaysia blocks is located to the south of the Lower Tieshajie Subgroup, probably in between the two parts of the Tieshajie Group. Age peaks of detrital zircons at 2.85–2.78 Ga, 2.68 Ga, and 2.50 Ga, combined with regional data, suggest episodic magmatism involved both crustal growth and reworking during the late Archean in the Jiangnan Orogen and adjacent areas of the Eastern Yangtze Block, while the 2.10–1.80 Ga peak corresponds to significant reworking of pre-existing crust related to the early assembly of the Nuna (Columbia) Supercontinent. Regional correlations based on detrital zircon age spectra and tectono-magmatic histories show similarities between the Yangtze Block and North India, suggesting the two continents were likely in spatial proximity at least during the late Mesoproterozoic to Neoproterozoic time.