How Did South China Connect to and Separate From Gondwana? New Paleomagnetic Constraints From the Middle Devonian Red Beds in South China

Abstract

The paleogeographic relationship between South China and Gondwana is critical for understanding the dispersion of Gondwana, accretion of Asia, and evolution of the Paleo‐Tethys. However, the lack of robust Devonian paleomagnetic data prevents a confirmative reconstruction of South China's connection to Gondwana and its subsequent separation during the Paleozoic. Here we report a new paleopole (33.6°N, 236.4°E; A95 = 3°) from the Givetian red beds (~385 Ma) in central South China. Fitting apparent polar wander paths between South China and Gondwana suggests that South China was connected to East Gondwana from the earliest Cambrian to Early Devonian, with its position closed to NW Australia. Thereafter, South China separated from Gondwana during ~400–385 Ma, as evidenced by their decoupled apparent polar wander paths. The paleomagnetic data suggest that the Paleo‐Tethys Ocean between South China and East Gondwana had been up to ~1,600 km latitudinally wide by ~360 Ma.

Paleomagnetic Constraint on the Carboniferous Paleoposition of Indochina and Its Implications for the Evolution of Eastern Paleo‐Tethys Ocean

“…As illustrated in Figure 6, a comprehensive rifting history of South China‐Indochina form Gondwana during the Devonian to Early Permian is shown. The separation of South China‐Indochina from eastern Gondwana (Figures 6a and 6b) is revised from Xian et al (2019) and Torsvik and Cocks (2017). The new paleomagnetic data in this study, combining with previous reported (Yan et al, 2019; Zhang et al, 2015, and references therein), indicate that the middle Carboniferous to Early Permian (Figures 6c and 6d) period is a tectonically quiet interval for the North Qiangtang‐Indochina‐South China blocks, because no significant drift occurred, which is also shown with paleolatitude variations in Figure 7.…”

“…The initial occurrence of pelagic radiolarian cherts and ophiolites in the Paleo‐Tethys suture zone suggest that the separation of South China‐Indochina‐North Qiangtang from Gondwana occurred since the Early‐Middle Devonian (Li et al, 1995, 2016; Metcalfe, 2013; Zhong, 1998). This interpretation is supported paleomagnetically through fitting apparent polar wander paths which indicated the rifting of South China‐Indochina from Gondwana occurred during ~400–385 Ma (Xian et al, 2019). Considering the Permian‐Triassic drifting history of the North Qiangtang and Indochina blocks has been schematically described (Ma et al, 2019; Song et al, 2017; Yan et al, 2018, 2019), reconstructing the Carboniferous configuration of eastern Gondwana blocks is essential to depict the evolution of the Paleo‐Tethys Ocean and provides clues for understanding the geodynamic mechanism of the dispersion.…”

“…During the late Paleozoic, because of the paucity of quantitative paleomagnetic data, the Indochina Block was supposed to wander across the paleo‐equator, back and forth, based on evidences of warm‐water fossils (Metcalfe, 2013; Scotese, 2004; Torsvik & Cocks, 2013). The South China Block was connected to Gondwana from the (pre‐)Cambrian to Late Devonian (Yang et al, 2004) and its separation from Gondwana was interpreted to be ~400–385 Ma through fitting apparent polar wander paths (Xian et al, 2019). Recently, Xian et al (2019) suggested that the South China‐Indochina had broken up with Gondwana by latest Devonian(~360 Ma), and the branch of Paleo‐Tethys Ocean between them was as wide as ~1,600 km latitudinally (Figures 6a and 6b).…”

“…The South China Block was connected to Gondwana from the (pre‐)Cambrian to Late Devonian (Yang et al, 2004) and its separation from Gondwana was interpreted to be ~400–385 Ma through fitting apparent polar wander paths (Xian et al, 2019). Recently, Xian et al (2019) suggested that the South China‐Indochina had broken up with Gondwana by latest Devonian(~360 Ma), and the branch of Paleo‐Tethys Ocean between them was as wide as ~1,600 km latitudinally (Figures 6a and 6b). Considering that the Late Devonian to Early Permian position of South China was constrained paleomagnetically to be at the equatorial area (Wu et al, 1998; Zhang et al, 2001, 2015), the ~180° clockwise rotation of South China during the Carboniferous which implies significant synchronal northward transition, as illustrated in Scotese (2004), is not consistent with these paleomagnetic studies.…”

“…We prefer that the Indochina Bock was located at 18.4 ± 4.0°S because of two reasons: first, its paleobiogeographic (Audley‐Charles, 1983) and lithofacies paleogeographic (Helmcke, 1985) relationships with North Qiangtang has long been documented (Li, 1987; Li et al, 1995; Metcalfe, 1996, 2013), and the Late Carboniferous‐Permian northward transition of North Qiangtang from the Southern Hemisphere to the Northern Hemisphere has been reconstructed paleomagnetically (Cheng et al, 2013; Ma et al, 2019; Song et al, 2017; Yang et al, 2016). Therefore, it is reasonable to consider that Late Carboniferous Indochina was located at the Southern Hemisphere; second, the breakup of the South China Block from Gondwana during the Middle‐Late Devonian was proved by paleomagnetic studies (Xian et al, 2019; Yang et al, 2004), which is consistent with the initial occurrence of pelagic radiolarian cherts and ophiolites in the Paleo‐Tethys suture zone (Li et al, 1995, 2016; Metcalfe, 2013; Zhong, 1998). Therefore, it is unlikely that the South China‐Indochina (or Annamia) blocks rifted from Gondwana during the Early Ordovician, transited to the Northern Hemisphere by the Late Ordovician and subsequently the Indochina moved back to the Southern Hemisphere by separating from South China during the Late Devonian to Late Carboniferous times, as illustrated in Torsvik and Cocks (2013).…”