Crustal structure across the extinct mid‐ocean ridge in South China Sea from OBS receiver functions: insights into the spreading rate and magma supply prior to the ridge cessation

<p>The characteristics of oceanic crust are dependent on the spreading rate of a Mid-Ocean Ridge (MOR). Crustal structure near an extinct MOR, therefore, provide unique constraints on how the magma supply and the crustal accretion respond to the reduced and ultimately ceased spreading. We present the crustal structure beneath 11 OBS sites near the extinct MOR in the central sub-basin of the South China Sea (SCS). We use the Receiver Function (RF) method to reveal the thickness and the Vp/Vs ratio of the crust based on the passive-source OBS data collected in this sub-basin. The thickness of the crust varies systematically with the distance to the ridge. &#160;The thinned crust near the ridge likely indicates that, in the late stage of spreading, the magma supply has diminished and the spreading rate has dropped to the ultra-slow range. While the Vp/Vs ratios at most sites fall into the normal range, there exist a few anomalously high Vp/Vs ratios (> 2.0) at sites very close to the ridge. These high Vp/Vs values can be explained by the serpentinization of the uppermost mantle beneath the sites. As the spreading rate and magma supply were reduced, fractures and fissures were easily developed at the frank of the crust accretion, allowing water enters the lowermost crust and serpentinizes the uppermost mantle.</p>

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Lithogeochemistry of the Mid-Ocean Ridge Basalts near the Fossil Ridge of the Southwest Sub-Basin, South China Sea

Minerals ◽

10.3390/min10050465 ◽

2020 ◽

Vol 10 (5) ◽

pp. 465 ◽

Cited By ~ 1

Author(s):

Kai Sun ◽

Tao Wu ◽

Xuesong Liu ◽

Xue-Gang Chen ◽

Chun-Feng Li

Keyword(s):

South China Sea ◽

Partial Melting ◽

Fractional Crystallization ◽

South China ◽

Spreading Rate ◽

Tholeiitic Basalt ◽

Spinel Peridotite ◽

China Sea ◽

Mid Ocean Ridge ◽

Ocean Ridge

Mid-ocean ridge basalts (MORB) in the South China Sea (SCS) record deep crust-mantle processes during seafloor spreading. We conducted a petrological and geochemical study on the MORBs obtained from the southwest sub-basin of the SCS at site U1433 and U1434 of the International Ocean Discovery Program (IODP) Expedition 349. Results show that MORBs at IODP site U1433 and U1434 are unaffected by seawater alteration, and all U1433 and the bulk of U1434 rocks belong to the sub-alkaline low-potassium tholeiitic basalt series. Samples collected from site U1433 and U1434 are enriched mid-ocean ridge basalts (E-MORBs), and the U1434 basalts are more enriched in incompatible elements than the U1433 samples. The SCS MORBs have mainly undergone the fractional crystallization of olivine, accompanied by the relatively weak fractional crystallization of plagioclase and clinopyroxene during magma evolution. The magma of both sites might be mainly produced by the high-degree partial melting of spinel peridotite at low pressures. The degree of partial melting at site U1434 was lower than at U1433, ascribed to the relatively lower spreading rate. The magmatic source of the southwest sub-basin basalts may be contaminated by lower continental crust and contributed by recycled oceanic crust component during the opening of the SCS.

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Jump event of mid-ocean ridge during the eastern subbasin evolution of the South China Sea

Interpretation ◽

10.1190/int-2015-0154.1 ◽

2016 ◽

Vol 4 (3) ◽

pp. SP67-SP77 ◽

Cited By ~ 1

Author(s):

Yan Qiu ◽

Yingmin Wang ◽

Wenkai Huang ◽

Weiguo Li ◽

Haiteng Zhuo ◽

...

Keyword(s):

South China Sea ◽

South China ◽

Seafloor Spreading ◽

The South China Sea ◽

Magnetic Data ◽

The South ◽

Tectonic Event ◽

China Sea ◽

Mid Ocean Ridge ◽

Ocean Ridge

The South China Sea is one of the largest marginal seas in the Western Pacific region, and it has been widely accepted that the evolution of the basin and the development of its oceanic crusts is closely linked to seafloor spreading. A great controversy, however, is around whether or not there was a jump of mid-ocean ridges during seafloor spreading, particularly in the eastern South China Sea subbasin. A tectonostratigraphic interpretation using high-resolution seismic data demonstrated that: (1) a southward jump event of the mid-ocean ridge took place in the eastern subbasin during the seafloor spreading; (2) the orientation of the mid-ocean ridge had dramatically changed after the event resulting in that the abandoned mid-ocean ridge is along an east–west direction, whereas the younger one is generally east–northeast/west–southwest oriented; (3) the corresponding surface caused by the jump tectonic event and the pre-event sequence can be traced throughout the earlier formed oceanic crust; and (4) paleo-magnetic data showed that the event occurred at approximately 25–23.8 Ma. The results of this study could be used to better understand the evolution and filling of the South China Sea and other associated marginal basins.

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