Hyperextended crustal structure of the Qiongdongnan Basin and subsequent magmatic influence from the Hainan mantle plume

Gravity-Seismic Joint Inversion of Lithospheric Density Structure in the Qiongdongnan Basin, Northwest South China Sea

“…In addition, the multichannel seismic profiles also suggest several 2 to 6-km-thick HVLs of >7.0 km/s beneath the two extremely thinned domains, which are almost widely distributed in the entire portion of the lower crust [26,30]. Confusingly, similar high-velocity anomalies are still not observed in the OBS profiles beneath QDNB, which are widely observed beneath the eastern part of the northwestern SCS, including the Pearl River Mouth Basin and Taixinan Basin [13,14,24,46,47]. HVLs are usually regarded as the result of partial melting caused by a synrift upwelling asthenosphere, as indicated by the mafic composition and high density of 2.90-3.05 g/cm 3 [6,9,16,29].…”

“…The lower crustal HVLs from OBS profiles are generally considered the most direct and important approaches to estimate the intensity of synrifting magmatic underplating [21][22][23]. However, probably limited by a small number of OBS profiles, there is still no conclusive evidence to support the lower crustal HVL beneath the QDNB for the present [13,14,24]. However, probably limited by a small number of OBS profiles, there is still no conclusive evidence that has yet been obtained to support the lower crustal HVL beneath the QDNB for the present, which could be attributed to the small number of OBS profiles.…”

“…In the case of the northern continental margin of SCS, the compositional or structural east-west heterogeneity has been observed by various geological and geophysical data, especially the prominent detachment faults, magmatic activity, middle crustal low-velocity layer, lower crustal high-velocity layers (HVLs), and partial serpentinization [1,7,[9][10][11]. Compared with the large amount of Ocean Bottom Seismograph (OBS) profiles and the International Ocean Discovery Program (IODP) seven sites programmed in the middle-east part of the northern continental margin, there are only a few OBS profiles carried out in the western part with limited resolution and reliability, including the Qiongdongnan Basin (QDNB) [12][13][14]. In spite of the well constraints for the sedimentary cover and fracture systems provided by the multichannel seismic profiles of petroleum companies, the study on deep crustal composition is still controversial, especially the magmatism anomaly [15][16][17][18].…”

“…The lithospheric structures of the QDNB have been studied in detail via multichannel seismic reflection profiles, OBS profiles, gravity inversion, seismic tomography, and surface heat flow [13,14,24,26,28,38,[40][41][42]. Numerous multichannel seismic reflection profiles revealed a gradually decreasing trend in the crust thickness from >22 km on the northern and southern parts to <10 km on the central depression, with two extremely thinned domains of <4 km [28,31,36,41].…”

Differences in Thermo-Rheological Structure between Qiongdongnan Basin and Pearl River Mouth Basin: Implications for the Extension Model in the Northwestern Margin of the South China Sea

“…The tectonic activities of the western QDNB and PRMB are strongly weakened at 32-30 Ma, but the detachment faults of Baiyun Sag, Liwan Sag, and Xisha Trough located in the eastern PRMB and QDNB are still active until 23 Ma and 16 Ma [50][51][52]. Characterized by detachment faults developing at the crust-mantle boundary, the Xisha Tough, Baiyun Sag, and Liwan Sag in the northwestern SCS are usually regarded as typical failed rifting basins, with a hyperextended continental crust of <10 km [21,26,53,54]. However, only the Baiyun Sag and Liwan Sag are recognized as the scope of COTZ along the northwestern SCS [22,23] (Figure 1).…”