South China connected to north India in Gondwana: sedimentary basin and detrital provenance analyses

Abstract:

The paleoposition of South China during the Ediacaran–Silurian is important for understanding the assembly of Gondwana. We report here the tectonostratigraphic evolution of the Ediacaran–Silurian Nanhua foreland basin in South China, and discuss South China's connection with Gondwana and potential tectonic triggers for both the Wuyi-Yunkai orogeny in South China and the Bhimphedian orogeny in north India. The Nanhua basin was involved in a three-stage evolution, which are: Stage 1 (the Ediacaran–Cambrian) recording the start of tectonic subsidence with turbiditic marine clastic deposition, fed by exotic orogens outboard South China; Stage 2 (the Ordovician to earliest-Silurian) featured by migrating depocentres with dominant shallow marine to deltaic clastic deposition, fed by the local Wuyi–Yunkai orogen; and Stage 3 (the Silurian) showing the arrival of depocentre in the Yangtze Block during the waning stage of the Wuyi-Yunkai orogeny with deltaic deposition in the remanent foreland basin.

Detrital zircon analyses of the Ediacaran–Silurian sandstones across the Nanhua basin reveal a prominent age population of 1100–900 Ma (with a peak age at ~980 Ma) and moderate populations of Archean–Paleozoic ages, grossly matching that of crystalline and sedimentary rocks in northern India. Zircon isotopes of the Stage 1 samples suggest three Precambrian episodes of juvenile crustal growth at 3.0 Ga, 2.5 Ga and 1.0 Ga, and a major crustal reworking at 580–500 Ma for the source areas, which are constraint to be northwestern India and its surrounding orogens. Together with other evidence, we propose that South China likely collided with northwestern India during the Gondwana assembly, generated the Bhimphedian orogeny in north India and formed two foreland basins on both the north India and South China sides. Far-field stress of the collision triggered the Ordovician–Silurian Wuyi–Yunkai orogeny in South China. The Stage 2–3 samples in the Nanhua basin of South China were shed from the both locally recycled Ediacaran–Cambrian rocks and eroded Cathaysian basement within South China. The Wuyi–Yunkai late-orogenic magmatic rocks also contributed to the Stage 3 sediments in the Nanhua basin.