Thermochronological Constraints from the Neoproterozoic to Mesozoic Exhumation of the Eastern Borborema Province, Northeastern Brazil
João M. Morais Neto1 and Paulo M. Vasconcelos2
1E&P/EXP, PETROBRAS, Rio de Janeiro, Brazil
2UQ-AGES, The University of Queensland, Brisbane, QLD, Australia
The denudation history of continents is registered in their thermal history and in the sedimentation record in marginal basins. In northeastern Brazil, the Borborema Province constitutes a major Precambrian shield formed during the assembly of Western Gondwana. It hosts an incomplete record of Paleozoic intracratonic basins, Mesozoic rifts and post-rift Phanerozoic covers. We combined 40Ar/39Ar geochronology, AFTT and apatite U-Th/He thermochronology to reconstruct the early uplift and erosional history of the source area for the sediments now stored in the marginal basins.
40Ar/39Ar cooling ages derived from amphibole, muscovite, biotite and K-feldspar for basement samples from distinct terranes amalgamated by the Brasiliano-Panafrican Orogeny (600-580 Ma) provide constraints on the thermochronological evolution. Inverse modeling of the K-feldspars results using the Arvert software (Zeitler, 2004), which incorporates the “multidomain diffusion model” concept (Lovera et al., 1989), yields thermal histories that fit the observed 40Ar/39Ar age spectra.
Cooling patterns record a relatively fast post-orogenic exhumation, implying the crystalline basement rose to a shallower crustal position (equivalent to <5 km depth) from late Cambrian-early Ordovician. Thermal modeling also reveals slow cooling during most of Paleozoic and Mesozoic, suggesting the whole region remained at mid- to low-temperatures (<200 oC) from 460±10 Ma until 200±10 Ma. By the early Jurassic cooling resumed, which we interpret as the effect of regional uplift preceding the fragmentation of Pangea. The thermochronological results also indicate that the Borborema Province cooled as a single block, indicating that continental-scale shear zones in the region played a minor role in controlling differential movement between distinct tectonic domains.
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