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

Chun Feng Li, Xing Xu, Jian Lin, Zhen Sun, Jian Zhu, Yongjian Yao, Xixi Zhao, Qingsong Liu, Denise K. Kulhanek, Jian Wang, Taoran Song, Junfeng Zhao, Ning Qiu, Yongxian Guan, Zhiyuan Zhou, Trevor Williams, Rui Bao, Anne Briais, Elizabeth A. Brown, Yifeng ChenPeter D. Clift, Frederick S. Colwell, Kelsie A. Dadd, Weiwei Ding, Iván Hernández Almeida, Xiao Long Huang, Sangmin Hyun, Tao Jiang, Anthony A.P. Koppers, Qianyu Li, Chuanlian Liu, Zhifei Liu, Renata H. Nagai, Alyssa Peleo-Alampay, Xin Su, Maria Luisa G. Tejada, Hai Son Trinh, Yi Ching Yeh, Chuanlun Zhang, Fan Zhang, Guo Liang Zhang

Research output: Contribution to journalArticlepeer-review

327 Scopus citations

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 uniform magnetization. The primary contribution to magnetic anomalies of the SCS is not in the top 100 m of the igneous basement.

Original languageEnglish
Pages (from-to)4958-4983
Number of pages26
JournalGeochemistry, Geophysics, Geosystems
Volume15
Issue number12
DOIs
StatePublished - 1 Dec 2014

Keywords

  • International Ocean Discovery Program Expedition 349
  • South China Sea tectonics
  • crustal evolution
  • deep tow magnetic survey
  • magnetic anomaly
  • modeling

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