The East China Sea basins, located in the West Pacific Continental Margin (WPCM) since the late Mesozoic, mainly include the East China Sea Shelf Basin (ECSSB) and the Okinawa Trough (OT). The WPCM and its adjacent seas can be tectonically divided into five units from west to east, including the Min‐Zhe Uplift, ECSSB, the Taiwan–Sinzi Belt, OT, and the Ryukyu Island Arc, which record regional tectonic evolution and geodynamics. Among those tectonic units, the ECSSB and the OT are important composite sedimentary pull‐apart basins, which experienced two stages of strike‐slip pull‐apart processes. In seismic profiles, the ECSSB and the OT show a double‐layer architecture with an upper half‐graben overlapping on a lower graben. In planar view, the ECSSB and the OT are characterized by faulted blocks from south to north in the early Cenozoic and by a zonation from west to east in the late Cenozoic. The faulted blocks with planar zonation and two‐layer vertical architecture entirely jumped eastward from the Min‐Zhe Uplift to the OT during the late Cenozoic. In addition, the whole palaeogeomorphology of the ECSSB changed notably, from pre‐Cenozoic highland or mountain into a Late Eocene continental margin with east‐tilting topography caused by the eastward tectonic jumping. The OT opened to develop into a back‐arc basin until the Miocene. Synthetic surface geological studies in the China mainland reveal that the Mesozoic tectonic setting of the WPCM is an Andean‐type continental margin developing many sinistral strike‐slip faults and pull‐apart basins and the Cenozoic tectonic setting of the WPCM is a Japanese‐type continental margin developing dextral strike‐slip faults and pull‐apart basins. Thus, the WPCM underwent a transition from Andean‐type to Japanese‐type continental margins at about 80 Ma (Late Cretaceous) and a transition in topography from a Mesozoic highland to a Cenozoic lowland, and then to below sea‐level basins. Copyright © 2013 John Wiley & Sons, Ltd.
The Borneo Accretionary Orogen (BAO) is located in a central position of SE Asia, surrounded by the long‐lived westward subduction of the Pacific Plate, northward subduction of the Indian Plate beneath the Eurasian Plate and a passive continental margin of the South China Sea. Based on the previous studies in stratigraphy, structural geology and geophysics, a number of tectonic models on the BAO have been proposed, but these models do not perfectly match all of the geological facts. A field‐based structural analysis of the rocks of Sabah in Malaysia has recognized that the deformation in Sabah can be divided into four episodes (D1‐D4). The D1 deformation developed complete displacement foliation (S1) and NNE‐trending thrusts. Then D1 structures were reworked by the subsequent D2 deformation. D2 deformation resulted in WNW‐ or NW‐striking thrusts, followed by NNW–SSE‐trending thrusts and folds (D3). Some NNE‐trending sinistral strike‐slip faults and WNW‐trending dextral tension‐shear faults (D4) offset the D3 structures. D1 is related to the collisional event in the Sabah Orogeny during 23‐16 Ma, and D2 corresponds to the formation of the Deep Regional Uncomformity (DRU) at 16 Ma. D3 is related to the Shallow Regional Uncomformity (SRU) at 10 Ma. D4 is associated to the NW–SE‐trending extension after the multi‐stage collisional events. Analysis of the sedimentary and magmatic data reveals that the BAO is a Mesozoic and Cenozoic accretionary orogeny, represented by the intensely deformed Rajang‐Crocker Group Accretionary prism, ophiolites and calc‐alkaline igneous rocks. The accretionary orogen is related to the evolution of the Proto‐South China Sea Ocean (PSCS). The PSCS continuously subducted under the Borneo Block and closed in the Late Eocene–Early Miocene time. The subduction zone of the PSCS retreated to the north in the Mesozoic and Cenozoic and migrated to the present‐day Nansha Trough. The BAO is still active, as represented by a series of thrusting and subduction of the Dangerous Grounds under the Borneo Block. The NNE‐trending subduction‐related faults are considered as transform faults, rotating to the present‐day NW‐trending faults due to the anti‐clockwise rotation of the entire Borneo Block. In particular, the previous NNE‐trending Tinjar Fault is regarded as a major boundary in sedimentation and magmatism. To the NE of the fault, the strata and igneous rocks are Oligocene–Early Miocene, but to the SW of the fault, the strata and igneous rocks developed during the Cretaceous–Late Eocene interval. Copyright © 2016 John Wiley & Sons, Ltd.
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.
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