Possible Spatial Distribution of the Mesozoic Volcanic Arc in the Present‐Day South China Sea Continental Margin and Its Tectonic Implications

Abstract

The distribution of the Late Mesozoic volcanic arc in the South China Sea (SCS) continental margin has long been a controversial topic due to its significance in understanding the transition mechanism of a margin from subduction to extension. Here a comprehensive analysis was conducted in the margin using reprocessed magnetic data, newly collected drilling/dredging samples, depositional environment, and deformation style inferred from multichannel seismic profiles to jointly constrain the possible distribution of the Mesozoic volcanic arc. From the map of reduced‐to‐the‐pole magnetic anomaly, several high‐positive magnetic anomaly belts can be discriminated, which cross the central Pearl River Mouth Basin, extend southwestward to the Zhongsha (Macclesfield Bank) and Xisha Islands (Paracel Islands), and distribute discontinuously around the southwest subbasin. Geophysical analysis shows that these belts have similar amplitudes and magnetic depths to known volcanic arcs, such as the Luzon, Cagayan, and Sulu arcs. Furthermore, the high‐amplitude positive magnetic anomaly belts coincide with the distribution of Late Mesozoic arc‐like granites, intermediate rocks, and agglomerates, suggesting that the belts possibly originated from the existence of Late Mesozoic volcanic arc. Accretion and compression environment located in front of the inferred arc provides independent supports to our interpretation. Results indicate that the southwest part of the arc is distributed on both sides of the southwest SCS subbasin, whereas the northeast part remains nearly in its original location, further suggesting that the breakup locations for the SCS margin might be the volcanic front/forearc in the northeast and the arc in the southwest during the opening of the SCS basin.

Cretaceous–Palaeogene sedimentary evolution of the South China Sea region: A preliminary synthesis

“…Li et al, ; C. Xu et al, ; Q. Yan et al, ). The termination of the Mesozoic massive continental arc system can be indirectly determined by the youngest emplacement ages of subduction‐related granitoids, and previous estimates from the South China Sea region largely constrained this transition at about 80–70 Ma (Jiang & Li, ; Knittel, ; F. C. Li, Sun, & Yang, ; Q. Yan et al, ). Detrital zircon geochronology of the Lower Cenozoic syn‐rift sediments also revealed a stage of magmatic quiescence during the latest Cretaceous (Shao et al, ; Shao, Cao, et al, ; W. Wang et al, ).…”

“…The pre‐Cenozoic rifting episode before the Proto‐South China Sea opening has been recognized by Ye et al () as ~100–72 Ma (though uncertain) when the largely ENE‐striking extensional fault systems and associated basins were gendered along the South China margin. During this period, the termination of the Izanagi subduction has been foreseen by the youngest emplacement of subduction‐related magmatism found in areas like Borneo (Breitfeld et al, ; Breitfeld & Hall, ), Palawan Continental Terrane (Knittel, ; Padrones, Tani, Tsutsumi, & Imai, ), Hainan Island (Jiang & Li, ), northern South China Sea (F. C. Li, Sun, & Yang, ; Q. Yan et al, ), and Taiwan (Chen et al, ; Yui et al, ). Subsequent Proto‐South China Sea spreading could probably be responsible for the development of compressional structure, represented by the ENE‐striking thrust system observed in the northern South China Sea by means of ridge push (Ye et al, ) or even for the Palaeocene regional unconformity (Morley, ).…”

“…For simplicity and wide acceptability, only the tectonic scenario before the Proto‐South China Sea opening is shown in Figure . During the Late Cretaceous, the northern South China Sea region could experience a large‐scale uplift and erosion because a number of boreholes penetrated the Cretaceous granitic basement without founding contemporary strata (F. C. Li, Sun, et al, ; Q. Yan et al, ). Limited boreholes have revealed that the Upper Cretaceous sequences of the Tainan Basin feature the transitional facies, whereas the occurrence of purplish gypsinate sandstones in the Upper Cretaceous of the Pearl River Mouth Basin (borehole LF35‐1‐1) marks a change from an early humid to a late arid terrestrial environment (Shao et al, ).…”

“…The pre-Cenozoic rifting episode before the Proto-South China Sea opening has been recognized by Ye et al (2018) as~100-72 Ma (though uncertain) when the largely ENE-striking extensional fault systems and associated basins were gendered along the South China margin. During this period, the termination of the Izanagi subduction has been foreseen by the youngest emplacement of subduction-related magmatism found in areas like Borneo Breitfeld & Hall, 2018), Palawan Continental Terrane (Knittel, 2011;Padrones, Tani, Tsutsumi, & Imai, 2017), Hainan Island (Jiang & Li, 2014), northern South China Sea (F. C. Li, Sun, & Yang, 2018;Q. Yan et al, 2014), and Taiwan Yui et al, 2012).…”

“…Li et al, 2012;Morley, 2012;von Hagke et al, 2016;Zahirovic et al, 2014), the formation of the Proto-South China Sea functioned directly as (Ru & Pigott, 1986;Savva et al, 2014), and the Late Cretaceous rifting along the South China margin was most likely linked to the opening of the Proto-South China Sea rather than the South China Sea (Ye et al, 2018). Magmatically, the Mesozoic-Cenozoic tectonic transition is also reflected in the evolution from the Basin and Range-style, broad magmatic province widely distributed in the Mesozoic South China to the bimodal volcanism sporadically distributed in the Early Cenozoic rift zone along the South China margin (F. C. Li, Sun, & Yang, 2018;Z.-X. Li & Li, 2007;Z.-X.…”