Ages and magnetic structures of the South China Sea constrained by deep tow magnetic surveys and IODP Expedition 349

Abstract

Combined analyses of deep tow magnetic anomalies and International Ocean Discovery Program Expedition 349 cores show that initial seafloor spreading started around 33 Ma in the northeastern South China Sea (SCS), but varied slightly by 1-2 Myr along the northern continent-ocean boundary (COB). A southward ridge jump of 20 km occurred around 23.6 Ma in the East Subbasin; this timing also slightly varied along the ridge and was coeval to the onset of seafloor spreading in the Southwest Subbasin, which propagated for about 400 km southwestward from 23.6 to 21.5 Ma. The terminal age of seafloor spreading is 15 Ma in the East Subbasin and 16 Ma in the Southwest Subbasin. The full spreading rate in the East Subbasin varied largely from 20 to 80 km/Myr, but mostly decreased with time except for the period between 26.0 Ma and the ridge jump (23.6 Ma), within which the rate was the fastest at 70 km/ Myr on average. The spreading rates are not correlated, in most cases, to magnetic anomaly amplitudes that reflect basement magnetization contrasts. Shipboard magnetic measurements reveal at least one magnetic reversal in the top 100 m of basaltic layers, in addition to large vertical intensity variations. These complexities are caused by late-stage lava flows that are magnetized in a different polarity from the primary basaltic layer emplaced during the main phase of crustal accretion. Deep tow magnetic modeling also reveals this smearing in basement magnetizations by incorporating a contamination coefficient of 0.5, which partly alleviates the problem of assuming a magnetic blocking model of constant thickness and

The role of rifting in the development of the continental margins of the southwest subbasin, South China Sea: Insights from an OBS experiment

“…3a and 3b), define the syn-rift units. Both are believed to be diachronous due to the overall southwestward propagation of rifting-drifting in the SCS (Briais et al 1993;Li et al 2014). Their diachronism along the margins has been addressed previously by several papers (Hutchison and Vijayan 2010;Franke et al 2011;Ding et al 2013;Steuer et al 2014;Song and Li 2015;Morley 2016).…”

“…This is closely followed by the spreading ridge-jump event around 23.6Ma in the Eastern SCS (Li et al 2014). With the bumpy spreading rate from 70mm/yr to 30mm/yr and the dominant faults trending from E-W to NE-SW ), a series dextral strike-slip fracture zone formed (Steuer et al 2014) resulting in a weakening of the rigid blocks.…”

“…Its southwestern tip indicates features of a failed rift (Li et al 2012b) where its fossil spreading center diminished, to the east it is bounded by the Zhongnan fault zone that separates it from the eastern subbasin. The SWSB formed ~23.6 Ma to ~16 Ma in the Cenozoic following a spreading ridge jump (Briais et al 1993;Barckhausen and Roeser 2004;Li et al 2014). …”

Intra- and intertrench variations in flexural bending of the Manila, Mariana and global trenches: implications on plate weakening in controlling trench dynamics

“…Briais et al 1993;Li et al 2014Li et al , 2015Sibuet et al 2016) with relatively small trench relief and width (Tables 2, and C1 and C2, Hayes & Lewis 1984;Rangin et al 1999;Galgana et al 2007;.…”

Mantle Potential Temperature Estimates of Basalt from the East Taiwan Ophiolite

“…Jahn (1986), Chung and Sun (1992), and Hsieh et al (2016), based on basalt geochemistry and Cr-spinel data from the peridotites, suggested that the ETO is likely representative of a midoceanic ridge. The nature of the ETO has direct implications on understanding the growth and development of the South China Sea (Taylor and Hayes 1980;Lee and Lawver 1995;Barckhausen and Roeser 2004;Barckhausen et al , 2015Li et al 2014;Chang et al 2015).…”