Cenozoic magmatism in the northern continental margin of the South China Sea: evidence from seismic profiles
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ORIGINAL RESEARCH PAPER
Cenozoic magmatism in the northern continental margin of the South China Sea: evidence from seismic profiles Qiao Zhang1,2,3 • Shiguo Wu1 • Dongdong Dong1
Received: 21 July 2015 / Accepted: 8 March 2016 Ó Springer Science+Business Media Dordrecht 2016
Abstract Igneous rocks in the northern margin of the South China Sea (SCS) have been identified via high resolution multi-channel seismic data in addition to other geophysical and drilling well data. This study identified intrusive and extrusive structures including seamounts and buried volcanoes, and their seismic characteristics. Intrusive features consist of piercement and implicit-piercement type structures, indicating different energy input associated with diapir formation. Extrusive structures are divided into flat-topped and conical-topped seamounts. Three main criteria (the overlying strata, the contact relationship and sills) were used to distinguish between intrusive rocks and buried volcanos. Three criteria are also used to estimate the timing of igneous rock formation: the contact relationship, the overlying sedimentary thickness and seismic reflection characteristics. These criteria are applied to recognize and distinguish between three periods of Cenozoic magmatism in the northern margin of the SCS: before seafloor spreading (Paleocene and Eocene), during seafloor spreading (Early Oligocene–Mid Miocene) and after cessation of seafloor spreading (Mid Miocene–Recent). Among them, greater attention is given to the extensive magmatism since 5.5 Ma, which is present throughout nearly all of the study area, making it a significant event in
& Dongdong Dong [email protected] 1
Key Laboratory of Marine Geology and Environment, Institute of Oceanology, CAS, Qingdao 266071, China
2
University of Chinese Academy of Sciences, Beijing 100049, China
3
Key Laboratory of Submarine Geosciences, Second Institute of Oceanography, State Oceanic Administration, Hangzhou 310012, China
the SCS. Almost all of the Cenozoic igneous rocks were located below the 1500 m bathymetric contour. In contrast with the wide distribution of igneous rocks in the volcanic rifted margin, igneous rocks in the syn-rift stage of the northern margin of the SCS are extremely sporadic, and they could only be found in the southern Pearl River Mouth basin and NW sub-sea basin. The ocean–continent transition of the northern SCS exhibits high-angle listric faults, concentrated on the seaward side of the magmatic zone, and a sharply decreased crust, with little influence from a mantle plume. These observations provide further evidence to suggest that the northern margin of the SCS is a magmapoor rifted margin. Keywords Igneous rock Seismic imaging Passive continental margin South China Sea
Introduction Magmatism plays an important role in plate reconstruction and regional tectonic evolution. Recently, considerable attention has been focused on magmatism in passive continental margins. Passive continental margins can be divided into magma-rich volcanic continen