Return to Rodinia? Moderate to high palaeolatitude of the São Francisco/Congo craton at 920 Ma
Published:January 01, 2016
D. A. D. Evans, R. I. F. Trindade, E. L. Catelani, M. S. D’Agrella-Filho, L. M. Heaman, E. P. Oliveira, U. Söderlund, R. E. Ernst, A. V. Smirnov, J. M. Salminen, 2016. "Return to Rodinia? Moderate to high palaeolatitude of the São Francisco/Congo craton at 920 Ma", Supercontinent Cycles Through Earth History, Z. X. Li, D. A. D. Evans, J. B. Murphy
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Moderate to high palaeolatitudes recorded in mafic dykes, exposed along the coast of Bahia, Brazil, are partly responsible for some interpretations that the São Francisco/Congo craton was separate from the low-latitude Rodinia supercontinent at about 1050 Ma. We report new palaeomagnetic data that replicate the previous results. However, we obtain substantially younger U–Pb baddeleyite ages from five dykes previously thought to be 1.02–1.01 Ga according to the 40Ar/39Ar method. Specifically, the so-called ‘A-normal’ remanence direction from Salvador is dated at 924.2±3.8 Ma, within error of the age for the ‘C’ remanence direction at 921.5±4.3 Ma. An ‘A-normal’ dyke at Ilhéus is dated at 926.1±4.6 Ma, and two ‘A-normal’ dykes at Olivença have indistinguishable ages with best estimate of emplacement at 918.2±6.7 Ma. We attribute the palaeomagnetic variance of the ‘A-normal’ and ‘C’ directions to lack of averaging of geomagnetic palaeosecular variation in some regions. Our results render previous 40Ar/39Ar ages from the dykes suspect, leaving late Mesoproterozoic palaeolatitudes of the São Francisco/Congo craton unconstrained. The combined ‘A-normal’ palaeomagnetic pole from coastal Bahia places the São Francisco/Congo craton in moderate to high palaeolatitudes at c. 920 Ma, allowing various possible positions of that block within Rodinia.
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Supercontinent Cycles Through Earth History
The supercontinent-cycle hypothesis attributes planetary-scale episodic tectonic events to an intrinsic self-organizing mode of mantle convection, governed by the buoyancy of continental lithosphere that resists subduction during the closure of old ocean basins, and the consequent reorganization of mantle convection cells leading to the opening of new ocean basins. Characteristic timescales of the cycle are typically 500 to 700 million years. Proposed spatial patterns of cyclicity range from hemispheric (introversion) to antipodal (extroversion), to precisely between those end members (orthoversion). Advances in our understanding can arise from theoretical or numerical modelling, primary data acquisition relevant to continental reconstructions, and spatiotemporal correlations between plate kinematics, geodynamic events and palaeoenvironmental history. The palaeogeographic record of supercontinental tectonics on Earth is still under development. The contributions in this Special Publication provide snapshots in time of these investigations and indicate that Earth’s palaeogeographic record incorporates elements of all three end-member spatial patterns.