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The Tinjar-West Baram Line is a NW-trending trans-lithospheric fault in northern Kalimantan; its northwestern extension into the South China Sea (SCS) is the West Baram Line. In this paper, we propose that the geodynamic processes of the proto-South China Sea (PSCS) played a key role in the formation and evolution of the Tinjar-West Baram Line, based on previous studies of the strata, crustal thicknesses, gravity anomalies and other characteristics of the blocks adjacent to the Tinjar-West Baram Line and the palaeomagnetic-based plate reconstructions of the PSCS. The Tinjar-West Baram Line has a close link to the subduction of the PSCS. Structural restoration reveals that (1) before 35 Ma, the Tinjar-West Baram Line was a NE-trending transform fault, which is consistent with the NE-trending strike-slip faults widely distributed in the East Asian Continental Margin, in the PSCS. (2) From the perspective of tectonic evolution, the extinction of the PSCS and the spreading of the SCS drove the Luconia Block in the northern SCS to accrete to the western side of the Tinjar-West Baram Line. This process resulted in a contrast of crustal rocks adjacent to the Tinjar-West Baram Line; to the east of this line, the Nansha Trough is oceanic crust, whereas to the west of this line the Luconia Block has an affinity with continental crust. The velocity and thickness of the crust show great differences on either side of the Tinjar-West Baram Line. (3) The kinematic analysis of the Tinjar-West Baram Line reveals that the collisional orogeny between the Luconia and Kalimantan blocks happened at 45-37 Ma on the west of the Tinjar-West Baram Line; on its eastern side, the Nansha Trough was subducting south towards Kalimantan Island. During the interval 35-10 Ma, the kinematics of the Tinjar-West Baram Line shows a feature of dextral strike-slip faulting. (4) The earlier published palaeomagnetic data show that the Kalimantan Block experienced a counterclockwise rotation of about 50° during the period from 25 to 10 Ma. In addition, the exert counterclockwise rotation of about 20° of the Tinjar-West Baram Line happened due to the resistance of the Luconia Block. Therefore, the Tinjar-West Baram Line changed from an early NE-trending to late NW-trending structure which results in its present day tectonic framework. Thus, we suggest that the Tinjar-West Baram Line was originally a NE-trending transform fault of the PSCS extending to the continental crust. Subsequently, the Tinjar-West Baram Line became the western border of the PSCS, accompanying the collisional orogeny between the Luconia and Kalimantan blocks. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The probable N055°-oriented extinct spreading ridge of the East Sub-basin is cut across by the post-spreading volcanic ridge oriented approximately E-W in its western part and called the Zhenbei-Huangyan seamounts chain. A three-dimensional ocean bottom seismometer survey was conducted in 2011 and covered both the extinct spreading ridge and the Zhenbei-Huangyan seamounts chain in the East Sub-basin. The comprehensive seismic record sections of 39 ocean bottom seismometers underline the high-quality data with clear and reliable P-wave seismic first arrivals. The three-dimensional tomographic results show that the crust is oceanic on each side of the Zhenbei-Huangyan seamounts chain. The seafloor spreading lineaments and associated fracture zones pattern provide channels for magma migration and eruption. Based on the ratio of volcanic extrusive and intrusive materials and the shape of the upward convex 6.4 km/s iso-velocity curve beneath the Zhenbei and Huangyan seamounts, we conclude that the Zhenbei and Huangyan seamounts appear to be dominantly formed by intra-crustal intrusion. Combining previous geochemical studies of post-spreading volcanic ridge outcropping samples, the formation mechanism of the seamounts chain might be explained by a buoyancy-driven decompression melting mechanism occurring as separately evolving partial melting bodies beneath each seamount. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

As an important transition domain between the thinnest continental crust and the initial oceanic crust, the ocean-continent transition zone (OCT) preserves a wealth of information on the processes of lithospheric extension and breakup. The northern margin of the South China Sea (SCS) is a non-typical, magma-poor passive continental margin with a particular structural pattern and sedimentary formation. The OCT in the northern margin of the SCS was developed by a series of continental rifting and seafloor spreading. Based on several multi-channel seismic reflection profiles, crustal-scale structural profiles extracted from gravity data and ocean-bottom seismometers (OBS) data, this paper studies the deep crustal structures, deformation and geodynamics of the OCT to further understand the structural patterns and tectonic process from the lithospheric extension to its breakup. The OCT of the northern margin of the SCS is characterized by a crustal thinning and high-velocity layer (HVL) in the lower crust. The OCT has three structural units: rift depression, volcanic zone and tilted fault blocks. The HVL is mainly limited in the eastern portion of the northern SCS. The HVL is distributed essentially within the OCT but does not clearly develop everywhere in the OCT. We propose a hybrid model of rifting to fit characteristics of the northern margin of the SCS. A crustal-scale largely symmetric process predominated at the initial rifting stage. The basin-controlling faults subsequently penetrated the entire crust, resulting in asymmetric tectonic evolution. Then, the OCT occupied this asymmetric location. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]