Magmatic evolution in a sedimented margin and implications for lithospheric breakup: insights from high-resolution seismic data from the South China Sea

2020 ◽  
Author(s):  
Cuimei Zhang ◽  
Xiong Pang ◽  
Ming Su ◽  
Jinyun Zheng ◽  
Hongbo Li ◽  
...  
Keyword(s):  
High Resolution ◽  
South China Sea ◽  
Oceanic Crust ◽  
South China ◽  
Northern South China Sea ◽  
Magmatic Activity ◽  
Magmatic Evolution ◽  
Seismic Profiles ◽  
China Sea ◽  
Rifted Margins

<p>The interaction between magmatic and extensional processes related to the formation of rifted margins has been and still is highly debated. The interpretation of magmatic additions, timing of onset and budget of magma during rifting and lithospheric breakup remain controversial and poorly understood. In contrast, the emplacement of magmatic additions in rift systems with high sedimentation rates provides an exceptional perspective towards resolving some of these problems.</p><p>In this paper, we present two new high-resolution seismic profiles imaging the complete transition from the hyperextended crust to oceanic crust in the northern South China Sea (SCS). Based on the observation of magma-related structures and the interrelationship with the sedimentary sequence, we define forms and timing of magmatic additions. We show that magmatic activity initiated during necking and then propagated together with the seaward formation of “new” basement , as indicated by the occurrence of sills and laccoliths during hyperextension, and ENE striking cone-shaped volcanos during the final breakup stage before the establishment of an embryonic and then steady-state oceanic crust.</p><p>First order estimations of the magmatic budget in order to decipher the magmatic evolution show that it strikingly increased during final hyperextension and the breakup stage and lasted until 23.8 Ma. Thus, magmatic activity continued even after cessation of rifting. This study enables for the first time to provide a semi-quantitative estimate of when, where and how much magma formed during final rifting and breakup at a magma-intermediate margin.</p>

3D structures and sedimentary infill across the continent-ocean transition of the northern South China Sea: constraint by the drilling results from IODP Expeditions 367, 368 and 368X

2020 ◽  
Author(s):  
Chao Lei ◽  
Jianye Ren ◽  
Geoffroy Mohn ◽  
Michael Nirrengarten ◽  
Xiong Pang ◽  
...  
Keyword(s):  
South China Sea ◽  
Continental Crust ◽  
Oceanic Crust ◽  
South China ◽  
Lower Boundary ◽  
Seismic Survey ◽  
High Angle ◽  
Seismic Profiles ◽  
Continental Breakup ◽  
China Sea

<p>Apart from the Iberia-Newfoundland margins, the South China Sea (SCS) represents  another passive margin where continent-ocean transition basement was sampled by deep drilling. Drilling data from IODP Expedition 367-368 and 368X combined with seismic profiles revealed a narrow continent-ocean transition (COT) between the Distal High sampled at Site U1501 and the Ridge B sampled at Site U1500. Results suggested that major Eocene lithospheric thinning triggered Mid-Ocean Ridge type melt production which emplaced within hyperextended continental crust leading eventually to continental breakup.  </p><p>Because of available dense seismic survey consisting of deep-penetrated seismic data imaging as deep as 12 s TWT, as well as drilling results from IODP Expeditions 367-368 and 368X, the COT in the northern SCS enables us to investigate the 3D propagation of continental breakup and the interactions between tectonic extension and magmatism. The top of acoustic basement can be consistently interpreted through all of our seismic survey and reveal various types of reliefs and nature from hyperextended continental crust to oceanic crust. In the basement, deep-penetrated seismic profiles present series of densely sub-parallel high-amplitude reflections that occurred within the lower crust. The lower boundary of these reflections is often characterized by double continual and high reflections interpreted as the Moho. Across the COT, the basement structure is characterized by: 1) Series of tilted blocks bounded by high angle faults on the Distal High and filled by syn-tectonic sedimentary wedges, 2) Rounded mounds of the basement with chaotic seismic reflection and sedimentary onlaps on these structures, 3) Series of ridges delimited by high-angle normal faults with no sedimentary wedge on the first oceanic crust.</p><p>Based on the detail stratigraphic framework constraint by drilling results from IODP Expeditions, the nature and timing of formation of these basement highs can be investigated. Some of these highs are limited by extensional faults while the nature of mounded structures located on the thinnest continental crust remain mysterious.  Our detailed analyses emphasize the occurrence and local control of syn-rift magmatism in order to build such structures. At larger scale, the hyperextended continental crust is characterized by significant 3D morphological variations both observed on dip and strike profiles. In contrast, the initial oceanic crust is characterized by a more homogenous structure and consistently juxtaposed to continental crust over a sharp and narrow zone.</p><p> </p>

The high resolution sedimentary filling in Qiongdongnan Basin, Northern South China Sea

2015 ◽  
Vol 361 ◽  
pp. 11-24 ◽  
Author(s):  
Zhongxian Zhao ◽  
Zhen Sun ◽  
Zhenfeng Wang ◽  
Zhipeng Sun ◽  
Jianbao Liu ◽  
...  
Keyword(s):  
High Resolution ◽  
South China Sea ◽  
South China ◽  
Northern South China Sea ◽  
Qiongdongnan Basin ◽  
China Sea

Associated Interpretation of Sub-Bottom and Single-Channel Seismic Profiles from Shenhu Area in the North Slope of South China Sea - Characteristic of Gas Hydrate Sediment

2011 ◽  
Vol 217-218 ◽  
pp. 1430-1437
Author(s):  
Shou Jun Li ◽  
Feng You Chu ◽  
Yin Xia Fang ◽  
Zi Yin Wu
Keyword(s):  
South China Sea ◽  
South China ◽  
Gas Hydrate ◽  
Single Channel ◽  
Northern South China Sea ◽  
Seismic Profile ◽  
Seismic Profiles ◽  
Shenhu Area ◽  
Bottom Simulating Reflector ◽  
China Sea

Abstract：The study area of this paper is the slope of Shenhu Area in the northern South China Sea. We interpreted both sub-bottom and single-channel seismic profiles to describe the acoustic characteristic of gas hydrate sediment and to discuss the cause of its formation. We distinguished some abnormal physiognomy and geologic objects that are relative to gas hydrate in profiles. Protuberance, shallow fault, acoustic blank patch, partial enhanced reflection and acoustic blank zone were discovered in the legible sub-bottom profile. The shallow gassy belt locates under the seabed from 34 to 82 m. Contrasting the sub-bottom profile with the data of Chinese first gas hydrate expedition, we believed that the gas in the shallow gassy belt came from the decompounding of gas hydrate in deep stratum. Pockmark, seepage, fold and Bottom Simulating Reflector (BSR) were recognized in the single-channel seismic profile. The depth of BSR is slightly deeper than that of the samples of Chinese first gas hydrate expedition in the study area. We think the BSR in the seismic profile may be the bottom of gas hydrate. Based on the time-depth conversion, we plotted out Oligocene, early Miocene, middle Miocene and Pliocene in the seismic profile according to the sedimentary thickness, sedimentary rate and age of ODP site 1148 and set up the chronology of the gas hydrate sediment.

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