Denudation history of onshore central Vietnam: constraints on the Cenozoicevolution of the western margin of the South China Sea

Apatite fission track analysis is used to monitor the timing and rate of up per crustal cooling and denudation across central Vietnam in response to ri fting of the South China Sea. Results show regional denudation in the syn- and post-rift phases of the South China Sea occurred at a similar rate (sim ilar to 40 +/- 10 m/Myr), consistent with the sedimentation record in adjac ent offshore basins. This suggests that extension was not the dominant fact or controlling Cenozoic denudation, probably because the study area was suf ficiently distant from the actively rifted continental margin. A significan t change in regional cooling rate during the Upper Miocene (inferred denuda tion rates also shift from similar to 34 m/Myr to 390-500 m/Myr) is linked to enhanced erosion and deposition of prograding sediments in adjacent offs hore basins. This shift in denudation is associated, and contemporaneous, w ith initiation of regional basaltic magmatism and development of topography . (C) 2000 Elsevier Science B.V. All rights reserved.