Precambrian mylonitic belts and present-day stress field: the role played in the reactivation of the Pernambuco lineament, NE Brazil
Abstract
The Pernambuco lineament is a steeply dipping continental-scale ductile shear zone rooted within the Precambrian lithosphere of intraplate northeastern Brazil. It formed during the Brasiliano orogeny ~600 Ma and reactivated during the Pangea breakup in the Cretaceous, when it controlled fault propagation and sediment accumulation in several rift basins. The region is now under an ~E-W-trending horizontal compression and ~N-S- trending extension, and faulting occurs predominantly in a strike-slip regime. We investigated two aftershock sequences and the preexisting tectonic fabrics along the Pernambuco lineament in order to evaluate the role of these fabrics in the coseismic reactivation of continental-scale structures. In 1991 and 2002 coseismic reactivations nucleated along an ~E-W and NE striking mylonitic branchs. Both fault segments reactivated the mylonitic foliation and form part of a major system fuelled by an ~E-W-trending compression and ~N-S-trending extension. We conclude that the interplay between the present-day stress field and preexisting fabrics controls seismogenic fault location, attitude, and kinematics. The Pernambuco lineament is an example of a long-lived continental scale structure, where selective reactivation has occurred. Other shear zones in the region also show a long history of brittle reactivation and present similar orientation in relation to the present-day stress axes. We suggest they are dormant structures prone for reactivation under the present-day stress field.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2007
- Bibcode:
- 2007AGUFM.T51D0760F
- Keywords:
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- 8100 TECTONOPHYSICS;
- 8103 Continental cratons;
- 8107 Continental neotectonics (8002);
- 8123 Dynamics: seismotectonics;
- 8164 Stresses: crust and lithosphere