Cenozoic structural development of the western flank of the Song Hong
Basin, Gulf of Tonkin, Vietnam: linking with onshore strike-slip
faulting and regional tectonics
Abstract
Cenozoic strike-slip deformation and associated basin formation in
Indochina provide critical clues on crustal response during India-Asia
collision. Typically, Indochina is considered a rigid block during
continental extrusion. We demonstrate that the Song Ca-Rao Nay Fault
System (SCRNFS) in north central Vietnam and its offshore extension, the
Hue Sub-basin, subdivided Indochina into discrete blocks. Using an
integrated dataset including topographic maps, geologic maps, onshore
fieldworks, and offshore seismic and well interpretation, the structural
evolution of the SCRNFS and Hue Sub-basin is investigated. During Late
Oligocene, the SCRNFS initiated with right-lateral motion, causing
pull-apart onshore and Hue Sub-basin opening offshore. The End-Oligocene
inversion affecting the northern Song Hong Basin also caused a major
NE–SW reverse fault in the Hue Sub-basin. In Early Miocene, rifting
resumed in the Hue Sub-basin with accelerated faulting and westward rift
migration in the south. This is distinct from the Song Hong Basin, where
the main rift period was Eocene(?) – Oligocene, and the Early Miocene
only features mild extension. During latest Early Miocene – earliest
Middle Miocene, the SCRNFS switched to left-lateral transpression. This
caused inversion and prolonged uplift in the northern-most Hue
Sub-basin. The inversion associated unconformity can be traced onshore
where it separates a compositionally immature conglomerate from an
overlying quartz conglomerate. Left-lateral transpression in the Hue
Sub-basin coincides with that in the Song Hong Basin and other inversion
events across SE Asia. This may have been caused by Australia-SE Asia
collision restricting escape movement of Indochina away from the
India-Asia collision zone.