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Christopher C. Olson1, Steven L. Dorobek2
(1) Texas A&M University, College Station, TX
(2) Texas A&M University

Abstract: Styles and significance of structural inversion across the Nam Con Son Basin, offshore SE Vietnam

Structural analysis of 2D regional seismic data indicates several styles of structural inversion and fault reactivation across the Nam Con Son Basin. Three distinct inversion styles are observed: 1) fault reactivated anticlines (fault-bend folds) with syn-inversion growth strata; 2) broad wavelength folding of basement hangingwall blocks bounded by faults with opposing dips; and 3) isolated pop-up structures associated with discrete transpressional shear zones or transfer zones between major normal fault systems with opposing dips. Within the Nam Con Son Basin fault reactivation is highly variable, resulting in inversion structures that involve either entire sub-basin fills (i.e., the main boundary fault to a sub-basin accommodates inversion) or isolated faults within the sub-basins. Reactivation along listric basin-bounding faults with shallow(?)-dipping detachments commonly exhibit the greatest magnitudes of inversion. For some sub-basins, almost all the Paleogene to middle Miocene extension was removed by reversal of syn-rift hangingwall displacements. This inversion style typically created fault-bend folds involving both syn-rift and early post-rift strata.

Erosional truncation at the crests of inversion folds is common and is at least partly related to major mid-Miocene and late Miocene- Pliocene lowstand events ("mid-Miocene" and "pre-Muda" unconformities, respectively). Inversion structures that affect entire sub-basins are prevalent only along the southwestern and northeastern ends of the Nam Con Son Basin. Limited post-inversion tectonic subsidence is associated with the fault-bend fold style of inversion. Accordingly, rethickening of the stretched subcrustal lithosphere must have occurred during inversion because there is no record of post-rift thermal subsidence in these parts of the basin.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana