Abstract

Zircon fission track (ZFT), apatite fission track (AFT) and (U-Th)/He thermochronometric data are used to reconstruct the Cenozoic exhumation history of the South China continental margin. A south to north sample transect from coast to continental interior yielded ZFT ages between 116.6 +/- 4.7 Ma and 87.3 +/- 4.0, indicating that by the Late Cretaceous samples were at depths of 5-6 km in the upper crust. Apatite FT ages range between 60.9 +/- 3.6 and 37.3 +/- 2.3 Ma with mean track lengths between 13.26 +/- 0.16 mu m and 13.95 +/- 0.19 mu m whilst AHe ages are marginally younger 47.5 +/- 1.9-15.3 +/- 0.5 Ma. These results show the sampled rocks resided in the top 1-1.5 krn of the crust for most of the Cenozoic. Thermal history modeling of the combined FT and (U-Th)/He datasets reveal a common three stage cooling history which differed systematically in timing inland away from the rifted margin. 1) Initial phase of rapid cooling that youngs to the north, 2) a period of relative (but not perfect) thermal stasis at similar to 70-60 degrees C which increases in duration from the south to the north; 3) final-stage cooling to surface temperatures that initiated in all samples between 15 and 10 Ma. The timing and pattern of rock uplift and erosion does not fit with conventional passive margin landscape models that require youngest exhumation ages to be concentrated at or close to the rifted margin. The history of South China margin is more complex aided by weakened crust from the active margin period that immediately preceded rifting and opening of the South China Sea. This theological inheritance created a transition zone of steeply thinned crust that served as a flexural filter disconnecting the northern margin of the South China block and site of active rifting to the south. Consequently whilst the South China margin displays many features of a rifted continental margin its exhumation history does not conform to conventional images of a passive margin. (C) 2009 Elsevier B.V. All rights reserved.