HR: 0800h
AN: T51D-0760    [Abstracts]
TI: Precambrian mylonitic belts and present-day stress field: the role played in the reactivation of the Pernambuco lineament, NE Brazil
AU: Ferreira, J M
EM: joaquim@dfte.ufrn.br
AF: Universidade Federal do RIo Grande do Norte, Departamento de Fisica, Natal, Rn 59078970, Brazil
AU: Bezerra, F H
EM: bezerrafh@geologia.ufrn.br
AF: Universidade Federal do RIo Grande do Norte, Departamento de Geologia, Natal, RN 59078970, Brazil
AU: Sousa, M O
EM: molucena@geologia.ufrn.br
AF: Universidade Federal do RIo Grande do Norte, Departamento de Geologia, Natal, RN 59078970, Brazil
AU: * do Nascimento, A F
EM: aderson@dfte.ufrn.br
AF: Universidade Federal do RIo Grande do Norte, Departamento de Fisica, Natal, Rn 59078970, Brazil
AU: Franca, G S
EM: georgesand@unb.br
AF: Universidade de Brasilia, Instituto de Geociàªncias/Observatà³rio Sismolà³gico, Brasila, DF 70910900, Brazil
AU: Assumpcao, M
EM: marcelo@iag.usp.br
AF: Universidade de Sao Paulo, Instituto de Astronomia, Geofisica e Ciencias Atmosfericas, Sao Paulo, SP 05508090, Brazil
AB: 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.
UR: http://www.dfte.ufrn.br
DE: 8100 TECTONOPHYSICS
DE: 8103 Continental cratons
DE: 8107 Continental neotectonics (8002)
DE: 8123 Dynamics: seismotectonics
DE: 8164 Stresses: crust and lithosphere
SC: Tectonophysics [T]
MN: 2007 Fall Meeting