Mesozoic and Cenozoic accretionary orogenic processes in Borneo and their mechanisms.

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. [ABSTRACT FROM AUTHOR]