OLSON, CHRISTOPHER C., Texas A&M University, Department of Geology and Geophysics, College Station, TX

ABSTRACT: Styles and Significance of Structural Inversion Across the Nam Con Son Basin, Offshore of SE Vietnam

The Nam Con Son Basin is part of a Tertiary rift basin complex located offshore of SE Vietnam. Early to middle Miocene regional contraction was accommodated along the eastern margin of the western Nam Con Son sub-basin through reactivation of west-dipping, N-S striking, extensional and transtensional faults. Inversion in the Western Nam Con Son subbasin occurred at the same time as the most intense phase of basin inversion in the West Natuna Basin to the southwest. Inverted faults in both basins closely follow the strike of the western side of the Natuna Arch, suggesting that the Natuna Arch served as a rigid buttress that concentrated stress and deflected strain.

The eastern and western Nam Con Son sub-basins are, separated by a N-S trending fault-bounded basement high that, apparently controlled structural differences between the subbasins. Basin inversion in the western sub-basin was accommodated through reactivation of the main basin-bounding faults which resulted in gentle asymmetric folding of the lower to, middle Miocene post-rift section. Inversion in the eastern sub-basin, however, is limited to middle Miocene time, and is characterized by highly selective reactivation of synthetic and antithetic faults that amplified pre-existing rollover in the hangingwall. The Vietnam Shear Zone defines the eastern margin of the Nam Con Son Basin and represents a major transpressional high that accommodated most of the strike-slip displacement associated with opening of the South China Sea, during middle Miocene time. In contrast, very little strike-slip deformation occurred in the eastern sub-basin during the middle, Miocene, and accordingly, only minor inversion structures developed.

AAPG Search and Discovery Article #90909©2000 AAPG Foundation Grants-in-Aid