A refined late-Cryogenian – Ediacaran earth history of South China: Phosphorous-rich marbles of the Dabie and Sulu orogens

Abstract

The late-Cryogenian-Ediacaran geological framework for South China is constructed principally from sedimentary successions preserved in the central and western regions of the Yangtze Block. New stratigraphic and carbonate-carbon isotope data allow us to extend that framework into the exhumed HP-UHP subduction complexes of the eastern Dabie and Sulu orogens that separate the South and North China cratons. Those data show that marble and phosphorous-rich (P-rich) units in those complexes were originally part of an Ediacaran shallow-marine shelf-carbonate platform. The basal pebbly schist (metadiamictite) and lowermost P-rich marble of the Jinping Formation (Haizhou Group) in the Sulu Orogen matches in both facies character and C-isotope profile that of the Marinoan-equivalent glacialcap carbonate couplet of the Nantuo and Doushantuo formations. The Daxinwu Formation (Susong Group) in the eastern Dabie Orogen contains a marble unit that has, for several hundreds of metres, a strikingly uniform C-isotope profile of low  13 C positive values and is overlain by a P-rich graphitic schist; these features match those of the late Ediacaran to early Cambrian Dengying Formation. These correlations establish that the HP-UHP metasedimentary rocks, many of which were once considered to be Palaeo-to Mesoproterozoic in age, are a Neoproterozoic-age cover sequence of the continental margin 2 of the Yangtze Block. Further, their widespread development limits their utility as indicators of offset across the Tan-Lu fault zone and, instead, favours tectonic models that interpret that feature as a continental-scale tear fault formed during the Mesozoic collision and suturing of the North and South China cratons.

Sedimentological Evidence for Pre‐Early Permian Continental Subduction in the Dabie Orogen, Central‐East China

“…The meta‐phosphorites are a distinguishing feature from the metamorphic belts to the north, and constitute the main industrial phosphate ore belt in China. The phosphate units were part of an Ediacaran shallow‐marine carbonate shelf and platform (Prave et al., 2018) and can be correlated with the Hong'an Group of the Hong'an orogen (H. Liu et al., 2023; X. Liu et al., 2023) and the Haizhou Group of the Sulu orogen (S. X. Li et al., 2022; H. Liu et al., 2023; X. Liu et al., 2023). Compiled detrital zircons from the metasedimentary rocks show major age peaks at c. 2.0 Ga and subordinate peaks at c. 2.5 Ga and c. 0.8 Ga ( n = 1,317, see Section 5.2 and Figure 10), with a SCB affinity.…”

Pre-UHP titanite archives pro- and retrograde episodes of fluid-marble-interaction (Dabie Shan UHP unit, China)

“…Frezotti et al, 2011). Wang and Rumble (1999), Rumble et al (2003), Zheng et al (2007), Liou et al (2012), and Zhang et al (2011) investigated crustal carbonate rocks in the Dabie and Sulu UHP units, originally formed in the Neoproterozoic (Rumble et al, 2000;Prave et al, 2018) and metamorphosed at UHP conditions during Triassic continental collision. They suggested minor internally buffered fluid-mineral interaction, and only insignificant infiltration of aqueous fluids and metasomatism in the deep subduction zone, until retrogression.…”