被动大陆边缘张-破裂过程与岩浆活动:南海的归属

The Rifting-Breakup Process of the Passive Continental Margin and Its Relationship with Magmatism: The Attribution of the South China Sea

岩浆在被动大陆边缘的张-破裂过程中起到决定性作用.南海东北部陆缘发育厚度达10 km的下地壳高速体,其成因机制长期存在争议,影响了对南海东北部陆缘构造归属的界定.为了分析南海共轭陆缘的张破裂机制,本文调研了国内外最新研究进展,系统分析了南海南北陆缘的地壳结构和岩浆活动特点,提出:南海陆缘和海盆中发育有大量岩浆活动,但东西陆缘存在较大差异,底侵高速体东厚西薄,推测为同张裂成因.根据地壳结构与底侵岩浆的量,将被动陆缘划分为5个子类,南海陆缘东侧为多岩浆型,向西变为少岩浆型.东西差异除与伸展速率有关,可能还与东侧陆缘发生了板缘破裂,而西侧陆缘发生了板内破裂有关.

Magma plays a key role in the rifting and breakup process of passive continental margin. Up to 10 km thick high velocity lower crust(HVLC) developed in the northeastern margin. Long term controversy toward its formation mechanism makes the margin classification difficult. In order to analyze the rifting and breakup mechanism of the SCS conjugate margins, this paper reviews the recent research progress of global margins, based on which the crustal structure and magmatic activity of the SCS are summarized. It is concluded that large amounts of magmatic activity occurred in the SCS with discrepancy between the eastern and western margins. The HVLC is thicker in the east and thinner or even absent in the west. It is speculated that the HVLC is of syn-rift underplating. According to the crustal structure and the amount of underplated magma, we suggest that the passive continental margin can be divided into 5 subclasses. The eastern continental margin of the SCS is of magma-robust type, and the middle and western margins are of magma-intermediate and magma-deficient types, respectively. In addition to the stretching rate, plate-edge rifting in the east and plate-interior rifting in the west continental margin may also contribute to the large difference in the amount of magmatic underplating.