Structures of the northeasternmost South China Sea continental margin and ocean basin: geophysical constraints and tectonic implications

Magnetic recording of the Cenozoic oceanic crustal accretion and evolution of the South China Sea basin

“…In early investigations on the geodynamics of the South China Sea (SCS), magnetic anomalies were essential to determining the ages and stages of seafloor spreading [8][9][10][11][12][13], seamount magnetism, and directions of plate movement [14], but these early studies were based primarily on a very limited number of magnetic tracks that were often far spaced, thus leaving a large margin of uncertainties in estimated oceanic crustal ages and seamount magnetism. In recent years, with the publication of the East Asia Magnetic Anomaly Dataset [15], high-resolution magnetic anomaly maps in the SCS are compiled [16][17][18][19], and high-resolution 3D analytical signal amplitudes and Curie point depths are calculated and mapped [17,20]. This magnetic anomaly dataset is based on measurements by multiple platforms at different time, with varying degrees of noise suppression, and no previous effort has been made in estimating the opening ages of the SCS based on this comprehensive database.…”

South China Sea Tectonics

“…For example, the opening of the East and Northwest Subbasins may have predated or been synchronous with that of the Southwest Subbasin ( Figure F5A) (Taylor and Hayes, 1983;Briais et al, 1993;Lee and Lawver, 1995;Tongkul, 1994;Honza, 1995;Zhou et al, 1995;Schlüter et al, 1996;Hall, 2002;Hall and Morley, 2004;Hayes and Nissen, 2005;Braitenberg et al, 2006;Sun et al, 2009). This model contrasts with others in which earlier opening of the Southwest Subbasin is preferred ( Figure F5B) (e.g., Ru and Pigott, 1986;Yao et al, 1994;Li et al, 2007a). This latter group of models considers the sharp contrasts between the East and Southwest Subbasins and the important role of the Zhongnan fault ( Figures F2, F4).…”

“…In particular, magnetic amplitudes and orientations in the Southwest Subbasin (Zone E) differ markedly from those in the East Subbasin (Zone D). These two subbasins are divided by a complex set of transform faults forming the Zhongnan fault zone (Figures F2, F4) (Yao, 1995;Jin et al, 2002;Li et al, 2007aLi et al, , 2008b. This magnetic contrast may support an episodic seafloor-spreading model (Ru and Pigott, 1986) or may be attributed to the different tectonic contexts within which the two subbasins evolved.…”

“…Recent heating from magmatic activity could have contributed to the high heat flow in the Southwest Subbasin (Ru and Pigott, 1986;Li and Song, 2012), but this hypothesis needs to be tested through drilling. A number of Cenozoic tectonic models have been proposed, but it remains uncertain as to whether the SCS basin experienced a single episode or multiple episodes of extension and seafloor spreading and, if multiple episodes, in what sequence the subbasins evolved (e.g., Taylor and Hayes, 1980;Pautot et al, 1986;Ru and Pigott, 1986;Briais et al, 1993;Yao et al, 1994;Hayes and Nissen, 2005;Li et al, 2007aLi et al, , 2008b. For example, the opening of the East and Northwest Subbasins may have predated or been synchronous with that of the Southwest Subbasin ( Figure F5A) (Taylor and Hayes, 1983;Briais et al, 1993;Lee and Lawver, 1995;Tongkul, 1994;Honza, 1995;Zhou et al, 1995;Schlüter et al, 1996;Hall, 2002;Hall and Morley, 2004;Hayes and Nissen, 2005;Braitenberg et al, 2006;Sun et al, 2009).…”

“…As a result of the marked contrast in magnetic anomaly amplitudes between the Southwest and East Subbasins of the SCS (Yao, 1995;Jin et al, 2002;Li et al, 2007aLi et al, , 2008b, it is questionable whether rifting and drifting within these two subbasins occurred synchronously and how these subbasins evolved in comparison to the Northwest Subbasin. Site U1433 is located in the Southwest Subbasin near the relict spreading center and magnetic Anomaly C5d identified by Briais et al (1993) (Figures F4, F8).…”