Return to Rodinia? Moderate to high palaeolatitude of the São Francisco/Congo craton at 920 Ma

Summary, in English

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 Ilh»us 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.

• Author: 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
• Department/s: Department of Geology
• Publishing year: 2015-05-28
• Language: English
• Pages: 167-190
• Publication/Series: Geological Society Special Publication
• Volume: 424
• Issue: 1
• Links: http://dx.doi.org/10.1144/SP424.1
• Document type: Book chapter
• Publisher: Geological Society of London
• Topic: Geology
• Status: Published
• ISBN/ISSN/Other: ISSN: 03058719