Post Gondwana Break-Up: Constraints from Apatite Fission Track Thermochronology in Sergipe and Alagoas Continental Margin, Brazil
Andréa R. Jelinek1, Farid Chemale1, José Antônio Cupertino2, and Adriano R. Viana3
1Isotope Geology Laboratory, UFRGS, Porto Alegre, Brazil
2Exploration Department, PETROBRAS, Rio de Janeiro, Brazil
3Research Center, PETROBRAS, Rio de Janeiro, Brazil
In an attempt to reconstruct the tectono-thermal history in the Sergipe and Alagoas continental margin, apatite fission track thermochronology was applied in a suite of fifteen outcrop samples in order to establish timing and intensity of the paleo-thermal events. The study area is included in the basement rocks between Jatobá Basin, at West, and Sergipe-Alagoas basins, at East. The sampling was accomplished along N-S profiles; throw the structural trend from the north of the São Francisco Craton to the Central-South part of the Pernambuco-Alagoas Massive.
The apparent fission track ages vary from 91 to 156 My and confined fission track lengths vary between 11.3 and 13.8 μm. Two groups of ages have been recognized: (i) The first one is that composed by closer samples to the coastal area. These samples present a small correlation between the ages and altitudes. In a general way, those closer of the coast line are the youngest observed ages and they compose most of the samples of this study. The ages vary around 100 My, and they register the rifting and rupture of the Atlantic Ocean in this region. (ii) The second group is that constituted by two samples of older ages, 156 and 140 My. These samples present a morph-tectonic register previous to the Gondwana rupture.
Based on fission track thermal history modeling, a slow and continuous denudation has recognized that begins in the Early Cretaceous, without great tectonic movements. But, in some cases, episodic denudation can be occur. In agreement with the denudation maps for thermal gradients in the order of 30°C/Km, it is observed that the denudation rates vary from 52 m/My to 126 m/My, being more accentuated in the close area to the São Francisco River.
AAPG International Conference and Exhibition, Cape Town, South Africa 2008 © AAPG Search and Discovery