Cretaceous Episodic Extension in the South China Block, East Asia: Evidence From the Yuechengling Massif of Central South China

International audienceIn the Cretaceous, the subduction of the Izanagi/Paleo-Pacific plates beneath the South China Block (SCB) created a wide back-arc domain characterized by numerous extensional basins coeval with voluminous magmatism. The SCB witnessed the whole evolution by records of widespread extensional structures to accommodate the lithospheric stretching. In the interior of the SCB, the Yuechengling (YCL) Massif preserves a large, low-angle detachment fault, the Ziyuan Detachment (ZYD) at the western margin, and a high-angle ductile normal fault, the Tianhu Fault (THF), in the middle of the massif. Both faults display ductile shearing with top-to-the west kinematics but play different roles in two stages of extension. In the early stage at 140-120 Ma, the THF deformed the eastern YCL pluton at a temperature of 350 °C, but the ZYD shows limited movement at this time. On the contrary, the later stage (100-85 Ma) is characterized by pervasive middle- to high-temperature deformation ( 400-500 °C) and rapid exhumation along the ZYD, but the THF only underwent a near-surface brittle overprint. Across the SCB, the two-phase extension is widely recorded in other extensional structures and coincides with magmatic flare-ups at its eastern margin, suggesting episodic changes in the subduction dip. Combined with two compressional events that took place between the intervals of extension, the SCB experienced two cycles of compression-extension at 155-120 and 120-85 Ma. This periodicity is tentatively interpreted as a combined effect from the Izanagi/Paleo-Pacific subduction angle change and a thickening-foundering process in the arc region

Tectonostratigraphic history of the Ediacaran-Silurian Nanhua foreland basin in South China

This paper presents the tectonostratigraphic evolution of the Ediacaran-Silurian Nanhua Basin in South China and explores the relationship between clastic sedimentation in the basin and evolution of the adjacent Wuyi-Yunkai orogen. Sedimentary facies in the basin comprises, in an ascending order, turbiditic marine, shallow marine, and fluvial-dominated deltaic facies, featuring a lateral migration from southeast to northwest. We interpret the Ediacaran-Silurian Nanhua Basin as a foreland basin with a three-stage evolution history. Stage 1: the Ediacaran-Cambrian stage, recording the start of tectonic subsidence with turbiditic marine siliciclastic deposition, fed by exotic orogens outboard South China; Stage 2: the Ordovician to earliest-Silurian stage, characterized by a migrating depocenter with dominant shallow marine and deltaic siliciclastic deposition, fed by the local and northwestward propagating Wuyi-Yunkai orogen; Stage 3: the Silurian stage, showing the arrival of depocenter in the Yangtze Block during the waning stage of the orogeny with deltaic deposition in the remanent foreland basin. The Wuyi-Yunkai orogen remained the dominant sedimentary source region during Stage 3. Stage 1 was likely related to the collision of the South China Block toward northern India during the assembly of Gondwana, whereas Stages 2 and 3 recorded sedimentation during the northwestward propagation and subsequent orogenic root delamination/collapse of the Wuyi-Yunkai orogen, respectively. The Wuyi-Yunkai orogeny in South China is interpreted to have resulted from the far-field stress of the collision between South China and Indian Gondwana

Detrital provenance evolution of the Ediacaran–Silurian Nanhua foreland basin, South China

We report here in-situ U–Pb and Hf isotopic results of detrital zircons from sixteen Cambrian–Silurian siliciclastic samples across the Nanhua foreland basin, South China. Together with published data from Ediacaran–Silurian sandstones in the region, we establish the temporal and spatial provenance evolution across the basin. Except for samples from northeast Yangtze, all other Ediacaran–Silurian samples exhibit a prominent population of 1100–900 Ma, moderate populations of 850–700 Ma and 650–490 Ma, and minor populations of 2500 Ma and 2000–1300 Ma, grossly matching that of crystalline and sedimentary rocks in northern India. Zircon Hf isotopes further reveal four episodes of juvenile crustal growth at 2.5 Ga, 1.8 Ga, 1.4 Ga and 1.0 Ga in the source regions. Utilizing the basin history and late Neoproterozoic to early Paleozoic paleogeography of South China, we conclude that the Ediacaran–Cambrian sediments in the Nanhua foreland basin were mainly sourced from northern India and adjacent orogens, and the Ordovician–Silurian sediments were derived from both locally recycled Ediacaran–Cambrian rocks and eroded Cathaysian basement. The Wuyi–Yunkai late-orogenic magmatic rocks also contributed to the Silurian sediments in the basin. The upper-Ordovician to Silurian samples in northeast Yangtze received higher proportions of local Cryogenian (850–700 Ma) magmatic rocks which were uplifted during late-Ordovician to Silurian time. We speculate that there was an Ediacaran–Cambrian collisional orogen between South China and northern India, shedding sediments to the early Nanhua foreland basin. Far-field stress during the late stage of this collisional orogeny triggered the Ordovician–Silurian intraplate Wuyi–Yunkai orogeny in South China, and erosion of the local Wuyi–Yunkai orogen further provided detritus to the late Nanhua foreland basin