Paleocene rapid exhumation of Hong Kong: Implications for the Cenozoic rifting along the northern margin of the South China Sea

Unraveling the rifting history along the southeastern margin of the South China Block has important implications for establishing the origin and evolution of the South China Sea (SCS). However, the onset time of rifting associated with the opening of the SCS remains unclear. The Littoral Fault Zone is the largest boundary fault between the South China Block and the SCS, and its fault activity provides information about the evolutionary history of the SCS and crucial constraints on the opening of the SCS. Here we present new apatite (U-Th)/He (AHe) ages obtained from the Sunset Peak and Tai Mo Shan, Hong Kong, along the footwall of the extensional Littoral Fault Zone, to constrain the timing of fault activity. The AHe age-elevation relationships and thermal modeling results document an accelerated exhumation during similar to 60-55 Ma, which we interpret to be associated with extensional movement along the Littoral Fault Zone. The activity of this extensional fault at similar to 60-55 Ma is considered to be coeval with the initial deposition of conglomerate at the bottom of the Pearl River Mouth Basin in the hanging wall of the Littoral Fault Zone. Integration of thermochronological data, magmatic characteristics, and seismic and drilling data support that the Paleocene extension occurred widely in the southeastern margin of the South China Block, representing a prelude to the seafloor spreading in the SCS.