Rifting and magmatism in the northeastern South China Sea from wide‐angle tomography and seismic reflection imaging

Abstract

We present a new travel time tomography velocity model and seismic reflection images that delineate the rift architecture and magmatic features of the rifted margin in the northeastern South China Sea. These data reveal moderately stretched crust~25 km thick along the continental shelf and thin but laterally variable crustal thickness in the distal margin. Along the continental slope, crust rapidly thins tõ 4 km in a basin characterized by tilted fault blocks that sole into a low-angle detachment. Strain was localized to a degree within the highly stretched basin but failed to progress to breakup and seafloor spreading. Crust in the distal margin is~12-15 km thick. Few extensional structures are apparent in the distal margin, but seismic velocities are suggestive of highly thinned and magmatically intruded continental crust. The magmatic features we interpret include volcanic zones at the top of the basement that deform or disrupt overlying postrift strata, sills intruded into the postrift sedimentary section, and a high-velocity (~6.9-7.5 km/s) lower crustal layer that we take to be magmatic underplating or pervasive lower crustal intrusions. These features primarily occur in the distal margin and may have been emplaced during postrift seafloor spreading. The postrift magmatism may have been induced by convective removal of continental lithosphere following breakup and the onset of seafloor spreading in the South China Sea.

Magmatic evolution in the N-Gondwana margin related to the opening of the Rheic Ocean—evidence from the Upper Parautochthon of the Galicia-Trás-os-Montes Zone and from the Central Iberian Zone (NW Iberian Massif)

“…In a post-rift setting, convective removal of continental lithosphere (e.g., Platt and England 1994;Jull and Kelemen 2001) may provide the driving force for extension and partly sustain thermal anomalies created during rifting (e.g., Lester et al 2014). A thinned lithosphere favors partial melting as long as the lithospheric mantle is enriched and hydrated (Kelley et al 2006;Pin et al 2007).…”

Sedimentary facies and the rifting process during the late Cretaceous to early Oligocene in the northern continental margin, South China Sea

“…Many hydrocarbon fields have been found in this area, with a recent oil-equivalent production up to 2000 × 10 4 m 3 per year . Although some researchers have pointed out the episodes of the late Cretaceous to Oligocene rifting in separate basins or depressions of the margin (Ru and Pigott, 1986;Li, 1993;Gong and Li, 2004;Zhong et al, 2004;Clift and Sun, 2006;Ding et al, 2008;Zhu, 2008;Jiang et al, 2009;Shi et al, 2009;Cai et al, 2010;Cullen et al, 2010;Lee et al, 2010;Lei et al, 2011;Ren and Lei, 2011;Lester et al, 2014;Savva et al, 2014;Gao et al, 2015), our current understanding on the rifting history of the margin remains limited, possibly due to the lack of enough well controls and relative lower quality of seismic data for the deeply buried interval. The timing and episodes of the rifting process and the sedimentary filling characteristics of the associated rifted basins in the northern SCS margin are significant for understanding the regional geologic evolution of the margin, and further for petroleum exploration.…”

Structure and origin of the rifted margin of the northern Gulf of Mexico

“…Given that the GUMBO seismic-velocity images have good resolution (Fig. 7), we can make comparisons with the seismic-velocity structure of other rifted margins where the sediment cover is thinner and the basement morphology is better known (e.g., Dean et al, 2000;Lester et al, 2014).…”

“…other (e.g., Morgan et al, 1989;Dean et al, 2000;Lester et al, 2014). Likewise, the GUMBO marine seismic-refraction project benefitted from the existence of many regional marine seismic-reflection lines in the Gulf of Mexico that have been acquired by geophysical companies.…”