Provenance study for the Paleozoic sedimentary rocks from the west Yangtze Block: Constraint on possible link of South China to the Gondwana supercontinent reconstruction

Abstract

The early Paleozoic and Devonian sedimentary rocks in the western part of the Yangtze Block were suggested to be derived from an exotic source that was once connected to South China. This conclusion was mainly based on that detrital zircons from these rocks give U-Pb age populations of 2400–2600Ma, 1750–1850Ma, 900–1000Ma, 750–870Ma and 500–680Ma, but corresponding magmatic rocks of such late Archean, Grenvillian and latest Neoproterozoic-Cambrian ages do not outcrop in this area or adjacent regions. Zircons from the Cambrian sedimentary rocks of this study show the youngest age peak at ca. 550Ma, and these zircons are mostly euhedral with positive εHf(t) values of +0.6 to +7.4. Because the unconformity between the Cambrian and Ordovician is evident in both west and south sides of South China, which is synchronous with its counterpart along the northern margin of the East Gondwana blocks (e.g. Himalaya region, Qiangtang, Western Australia), it is possible that these zircons were likely derived from a late Neoproterozoic-early Cambrian accretionary orogen (e.g. Bhimphedian orogeny) associated with the initial subduction of a proto-Tethys ocean beneath the margins of Gondwana continents. In contrast, the 500–680Ma zircon population of the Silurian-Devonian sedimentary rocks give an older age peak at ca. 650Ma and their εHf(t) values for the <540Ma grains are all negative (−27.8 to −0.3). These detrital zircons are rounded and could be possibly sourced from ‘Pan-African’ orogenic belts that formed during the amalgamation of the Gondwana, such as the East African and Prydz-Darling orogens between the segments of Gondwana. Early Neoproterozoic ages are dominant in the above sedimentary rocks of this study and correlate well with the large volume of 900–1000Ma magmatism in Grenville-age provinces (e.g. Rayner-Eastern Ghats belt in India-East Antarctica) formed from ocean closure and collision tectonics during the Rodinia assembly. Our Hf isotopic data for detrital zircons of above ages suggest different origins, i.e. crustal reworking and growth at episodes of ca. 2.5Ga, 0.9–1.0Ga, 0.75–0.87Ga and 0.6–0.68Ga. Coupled with the stratigraphic relationship, these age and Hf isotopic data support a South China-North India-Qiangtang continental margin system along the northern margin of the East Gondwana. The west portion of South China was possibly connected to the uplifted Himalaya region in the early Cambrian with continuous detrital inputs from India and surrounding orogenic belts.