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, Drilling sites (U1433 and U1434) of IODP Expedition 349 are indicated by 650 red dots, Bathymetric map of the Southwest Sub-basin, 2008.

, Southwest Sub-basin. The interpreted magnetic anomalies shown in thin black dashed lines are from

. Briais, The fossil spreading center is bounded by the white dashed lines, 1993.

, SWSB: the Southwest Sub-basin; ZNFZ: Zhongnan 655 Fracture Zone; XS Is.: Xisha Islands; ZS Is.: Zhongsha Islands; NS Is.: Nansha Islands; SWTB: 656 Southwest Taiwan basin; PRMB: Pearl River Mouth basin; QDNB: Qiongdongnan basin; ZJNB: 657 Zhongjiannan basin

. Qiu, The red lines present the coincident MCS sections 663 (NH973-1 and CFCST-MCS2013) we reprocessed. The black dots display the OBS positions of Line 664 OBS973, pp.973-976, 2011.

, Comparison of time-migrated section of profile 669 NH973-1 processed by CNOOC (d) and this study (e). The green lines indicate the location of CDP 670 8218

, OBS 24 (b) and OBS 25 (c) in the abyssal basin 674 show poor PmP arrivals

, CFCST-MCS2013 (b) over the Southwest sub-basin. The magnetic lineations interpreted 678 by Briais et al, 1993 are shown in red dashed lines. Letters indicated by arrows designate specific features discussed in the text. The black dashed 679 lines indicate the rift shoulders. The black boxes are further shown in Fig.6-9, Fig.5. Depth-converted MCS profiles NH973-1 (a)

, The uninterpreted (a) and interpreted (b) MCS section of profile NH973-1. See Fig.5a for location. Letters (B1-B2, H1) indicated with 683 arrows in (b) designate specific features discussed in the text. The magnetic anomalies interpreted by Briais et al, 1993 are shown in red dashed 684 lines (b). The red lines in (b) indicate normal faults. The corresponding velocity section from Fig

, interpreted (b) MCS section of profile NH973-1. See Fig.5a for location. Letters (B3-B5, H2-H4) indicated with 689 arrows in (b) designate specific features discussed in the text. The magnetic anomalies interpreted by Briais et al, 1993 are shown in red dashed 690 lines (b). The red lines in (b) indicate normal faults. The corresponding velocity section from Fig

, The uninterpreted (a) and interpreted (b) MCS section of profile CFCST-MCS2013. See Fig.5b for location. Letters (B1-B2, H1-H2) 694 indicated with arrows in (b) designate specific features discussed in the text. The magnetic anomalies interpreted by Briais et al, 1993 are shown 695 in red dashed lines (b). The red lines in (b) indicate normal faults

, The uninterpreted (a) and interpreted (b) MCS section of profile CFCST-MCS2013. See Fig.5b for location. Letters (B3-B8, H3-H9) 698 indicated with arrows in (b) designate specific features discussed in the text. The magnetic anomalies interpreted by Briais et al, 1993 are shown 699 in red dashed lines (b). The red lines in (b) indicate normal faults

, ray path (c) and final velocity model (d) 703 of line OBS973. The black and red dots in (b) represent the picked and modeled travel time, 704 respectively. Only one out of ten rays is shown in (c). The masked areas in (d) are not constrained by 705 rays. The magnetic anomalies interpreted by Briais et al, The initial velocity model (a), travel-time fitting (b), 1993.

, The 1-D 709 velocity profiles compared to the velocity envelope for Atlantic oceanic crust aged 0-127 Ma (White 710 et al, 1992). (b) The 1-D velocity profiles compared to the velocity envelope for thin oceanic crust 711 overlying serpentinized mantle from Whitmarsh et al, Fig.11. The 1-D velocity profiles through the final velocity model of OBS973 (Fig.9d). (a), 1996.

, A comparison of morphologic profiles of the Southwest Sub-basin (a), the Southwest Indian 715 Ridge at 15?30'E (b), the Mid-Atlantic Ridge at 14?30'N (c)

, Note the different scales. The values of full spreading rate (FSR) of the Southwest Sub-basin, the

, Southwest Indian Ridge, the Mid-Atlantic Ridge, and the East Pacific Rise are from Li et al, p.718, 2014.

. Dick, Grindlay et al, 1998, and Aghaei et al, 2003.