Mesoproterozoic to Paleozoic Nd isotope stratigraphy of the South China continental nucleus and its geological significance

Abstract

The Yangtze continental nucleus in South China is situated in the Huangling-Shennongjia area in western Hubei Province. It comprises the early Precambrian crystalline basement and generally successive Proterozoic to Phanerozoic sedimentary covers. This paper reports a comprehensive Nd isotope study of fine-grained sedimentary rocks from the regional Mesoproterozoic to early Paleozoic strata. The Nd model ages display a V-shaped variation from ∼2.5–2.8 Ga during the late Mesoproterozoic through ∼1.5–1.7 Ga during the Neoproterozoic Nanhua Period to ∼1.8–2.1 Ga during the Paleozoic Ordovician, with corresponding ɛ Nd(t) ranges of −11 to −14, −1.1 to −5.3, and −7.9 to −9.9, respectively. This evolutionary trend broadly resembles those documented in the sedimentary strata along the southeastern margin of the Yangtze Craton and within the Jiangnan orogenic belt, indicating that the whole South China block underwent a mantle-input related tectono-magmatic event at ∼0.8 Ga or earlier. However, the Huangling-Shennongjia area is discriminated from the other two regions by highly variable model ages (∼1.5–2.7 Ga) and ɛ Nd(t) values (1.38–−12.0) of the early Mesoproterozoic strata. Combined with the Archean model ages of the late Mesoproterozoic strata, it is suggested that the Mesoproterozoic sedimentary provenance of the Yangtze continental nucleus was distinct from that of the southeastern Yangtze Craton, likely indicative of an intervening aulacogen (or rift zone) or oceanic basin. In addition, the high comparability in Neoproterozoic to Paleozoic Nd isotope stratigraphy between the Yangtze Craton and the Jiangnan orogenic belt infers that the whole South China block had shared the same sedimentary basin and provenance since the Yangtze-Cathaysia welding at ∼0.9 Ga. Thus, it is proposed that the Yangtze Craton had comprised a collage of micro-continents during the pre-Neoproterozoic until the Rodinia assemblage when the primitive South China block was formed.