Middle Oligocene oceanic crust of South China Sea jammed into Mindoro collision zone (Philippines)

1985 ◽  
Vol 32 (12) ◽  
pp. 1029
Keyword(s):  
South China Sea ◽  
Oceanic Crust ◽  
South China ◽  
China Sea ◽  
Collision Zone

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>

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>

Rapid transition from continental breakup to igneous oceanic crust in the South China Sea

2018 ◽  
Vol 11 (10) ◽  
pp. 782-789 ◽  
Author(s):  
H. C. Larsen ◽  
G. Mohn ◽  
M. Nirrengarten ◽  
Z. Sun ◽  
J. Stock ◽  
...  
Keyword(s):  
South China Sea ◽  
Oceanic Crust ◽  
South China ◽  
The South China Sea ◽  
The South ◽  
Continental Breakup ◽  
China Sea ◽  
Rapid Transition

scholarly journals Coexistence of Hainan Plume and Stagnant Slab in the Mantle Transition Zone beneath the South China Sea Spreading Ridge: Constraints from Volcanic Glasses and Seismic Tomography

Lithosphere ◽  
2021 ◽  
Vol 2021 (Special 2) ◽  
Author(s):  
Shuang-Shuang Chen ◽  
Rui Gao ◽  
Zewei Wang ◽  
Tong Hou ◽  
Jie Liao ◽  
...  
Keyword(s):  
South China Sea ◽  
Oceanic Crust ◽  
Mantle Plume ◽  
South China ◽  
The South China Sea ◽  
Spreading Ridge ◽  
The South ◽  
China Sea ◽  
Volcanic Glasses ◽  
Hainan Mantle Plume

Abstract The influence of Hainan mantle plume and subducting recycled oceanic crust beneath the spreading ridge of the South China Sea (SCS) have been widely proposed recently, but still controversial and ambiguous. Here, we present seismic tomographic evidence, new major and trace element, and Pb isotopic compositions of volcanic glasses from one International Ocean Drilling Program drill core (Site U1434) in the SCS spreading ridge. The volcanic glasses are relatively enriched in alkalis and light rare earth elements (LREEs) and depleted in heavy REEs (HREEs), exhibit slightly positive anomalies in Nb, Ta, Zr, and Hf as well as a positive Nb relative to La and Th, and show relatively high 207Pb/206Pb and 208Pb/206Pb isotopic ratios, suggesting ocean island basalt- (OIB-) type and enriched mantle 2- (EM2-) type geochemical features likely related to a mantle plume. These geochemical features are consistent with those of late Cenozoic volcanic rocks in Hainan and surrounding areas associated with a mantle plume, likely providing the influence of Hainan mantle plume beneath the spreading ridge of the SCS. The SCS primary-melt and volcanic glasses indicate that the source mantle involved 18.5% eclogite (dense, recycled oceanic crust from the stagnant subducted slab) and 46.1% garnet pyroxenite (produced by the reaction between the peridotite melt and recycled oceanic crust). The existence of Hainan mantle plume and stagnant subducted slab is further supported by geophysical evidence from a recent three-dimensional P-wave seismic tomographic model.

Chemical variations in hydrothermal systems recorded by epidote in altered oceanic crust of South China Sea

2020 ◽  
Author(s):  
Liyan Tian ◽  
Si-Yu Hu ◽  
Xuan-Ce Wang
Keyword(s):  
South China Sea ◽  
Oceanic Crust ◽  
South China ◽  
Subduction Zones ◽  
Biological Activities ◽  
Northern South China Sea ◽  
Hydrothermal Systems ◽  
China Sea ◽  
Calcite Veins ◽  
Hydrothermal Activities

<p>The circulation of seawater within the oceanic crust promotes the extensive chemical variations of the lithosphere prior to its entering subduction zones as well as the development of the biosphere. A good understanding of the chemical variations during hydrothermal circulation is essential to further decipher the biological activities in such extreme environments. Epidote is a common byproduct, but a good indicator for hydrothermal activities during the hydrothermal alteration of oceanic crust.</p><p>This study presents the petrographic and geochemical features of epidote from depth of 850-910 m (below the surface) in the northern South China Sea margin to provide insights into the possible chemical variations in hydrothermal systems in subsurface. Eight samples with obvious epidote veins were chosen from the altered basalts in Hole 1502B of IODP Expedition 368. They cover a range with different depth and occurrences, including epidote veins, composite epidote-calcite veins, and composite epidote-silica veins. Sulfide mineralization is widespread and dominated with pyrite, chalcopyrite and sphalerite. Scanning Electron Microscopy images show that the epidote-calcite vein samples display obvious zonation structure in epidote, and the others not. The major element concentrations of Fe also show variations with epidote zonation. We further carried out in situ trace element concentration measurement on epidote minerals by Laser Ablation-Induced Coupled Plasma-Mass Spectrometry. In Chondrite-normalized diagrams, all epidote mineral samples show flat patterns with significant positive Eu anomalies, which may relate to highly oxidized conditions maximising Eu<sup>3+ </sup>incorporation. We therefore propose that the zonation of epidote may reflect the pulse of hydrothermal activities, one of which is likely to be associated with the precipitation of chalcopyrite and sphalerite.</p>

The continent-ocean transition architecture and breakup mechanism at the mid-northern South China Sea

2021 ◽  
Author(s):  
Cuimei Zhang ◽  
Zhen Sun ◽  
Gianreto Manatschal ◽  
Xiong Pang ◽  
Sanzhong Li ◽  
...  
Keyword(s):  
South China Sea ◽  
Oceanic Crust ◽  
South China ◽  
Plate Tectonics ◽  
Gravity Data ◽  
Northern South China Sea ◽  
Plate Boundary ◽  
Drill Hole ◽  
China Sea ◽  
Breakup Mechanism

<p>Ocean Continent Transition (OCT) located between the edge of the continental and unequivocal oceanic crust is an ideal laboratory to understand one of the most fundamental processes of Plate Tectonics, namely the mechanism of formation of a new plate boundary, also referred to as lithospheric breakup. However, the location and architecture of the OCT and the processes governing the rupture of continental lithosphere and creation of new oceanic crust remain debated. In this paper, we present newly released high-resolution seismic reflection profiles that image the complete transition from unambiguous continental to oceanic crust in the mid-northern South China Sea (SCS), accompanied with IODP drill hole and gravity data, with the aim to map the OCT and explore where, when and how lithospheric breakup occur.</p><p>Based on observations and interpretations we define the limits of OCT. The results show that OCT corresponds to hybrid crust resulting from the complex interaction between crustal thinning along detachment systems and accretion of new syn-tectonic igneous materials. The observations suggest a sharp along strike transition in the OCT from a lower to an upper plate setting over a lateral distance of 25 km. The breakup in the northern SCS and the conjugate margin occurred asymmetrically and was accomplished by core-complex type structures related to a successive oceanward transition from tectonic to magma-controlled processes during plate separation. The along-strike variability in the basement architecture and the abrupt flip in detachment polarity in the OCT imply a sharp transfer fault to explain the segmentation of the margin. Such segmentation results from inherited pre-rift crustal and/or lithospheric heterogeneities. It is important to note that the segmentation did not control breakup and subsequent oceanic accretion.</p>

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