Jennifer A. Elder Brady¹, Mark S. Baum¹

(1) Rutgers University, Piscataway, NJ

ABSTRACT: A Comparison of Inversion Structures in Passive-Margin Settings

Many rift basins on passive margins have undergone inversion. Our study compares inversion structures from the passive margins of southeastern Canada, northwestern Europe, and northwestern Australia. The inversion structures on these passive margins have striking similarities and notable differences in terms of relative timing and structural geometries.

Seismic data from all three areas and field observations from southeastern Canada indicate that one or more episodes of inversion, accompanied by uplift and erosion, affected these passive margins. In southeastern Canada, inversion occurred during and/or soon after the rift-drift transition. In northwestern Europe, inversion occurred before and after the rift-drift transition. In northwestern Australia, inversion occurred during and after the rift-drift transition.

Inversion structures on these passive margins include reactivated normal faults and contractional folds. Selective reactivation of normal faults as reverse faults occurred during inversion. Contractional hanging-wall folds range from narrow to broad and symmetric to asymmetric. Preliminary studies suggest that the orientation and geometry of the pre-existing normal faults strongly influenced the orientation and geometry of the inversion structures. In the Fundy rift basin of southeastern Canada, the strike of contractional folds is parallel to the strike of reactivated normal faults. Inversion-related folds are broader where associated with northeast-striking, lower-angle, predominantly dip-slip faults, and tighter where associated with east-striking, higher-angle, oblique-slip faults. Unlike the larger-scale folds, smaller-scale structures that are not associated with earlier extensional structures may give an unbiased measure of the maximum shortening direction.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado