Significance of age periodicity in the continental crust record: The São Francisco Craton and adjacent Neoproterozoic orogens as a case study

• Published in: Gondwana research 2020-10, Vol.86, p.144-163
• Main Authors: Marimon, Rodrigo S., Trouw, Rudolph A.J., Dantas, Elton L.
• Format: Article
• Language: English
• Subjects: Neoproterozoic orogens; Periodicity of the crustal age record; Regional and global tectonics; Secular isotopic variation; São Francisco Craton
• ISSN: 1342-937X; 1878-0571
• DOI: 10.1016/j.gr.2020.05.010

The São Francisco Craton, in Brazil, together with adjacent orogenic systems formed during Gondwana assemblage, are well-suited for the study of crustal growth processes. The region's geological history is marked by a series of complete tectono-metamorphic cycles, from the Archean to late Neoproterozoic, comprising arc-related magmatism followed by continental collisions and ultimately post-tectonic igneous events and rifting. In this contribution, a comprehensive isotopic database was compiled from the literature, composed mainly of high-quality U-Pb magmatic and metamorphic ages (ca. 1000), together with Lu-Hf (ca. 1300) and Sm-Nd (ca. 300) data. Using this database, combined with a tectonic/geochemical synthesized review of the region, it is possible to test which of the available contending models can better explain the apparent periodicity in the formation of the continental crustal. Some interpreted the peaks and troughs in the crustal age record as periods of increased magmatic production, controlled by periodic mantellic events. Another hypothesis is that subduction-related rocks are shielded from tectonic erosion after continental amalgamation, the peaks thus reflecting enhanced preservation potential. The latter hypothesis is favored, as the variability regarding the timing of arc-related peak magmatic production (U-Pb age peaks) from different tectonic provinces around the globe and in the considered regions, coupled to the fact that peak arc-production is always closely followed in time by major continental amalgamations (supercontinent formation), precludes a unified global causation effect, such as mantellic overturns or slab avalanches, and supports the preservation bias hypothesis. Furthermore, the worldwide (including the São Francisco Craton) occurrence of plume-related magmatism is concentrated during the periods of supercontinent break-up (i.e. after major collisions), which better relates to a top-down control on mantle convection and opposes most of the models that advocate for the primary periodicity of magmatic production, which predict enhanced plume activity slightly prior or concomitant to supercontinent formation events. [Display omitted] •Isotopic (U-Pb, Lu-Hf and Sm-Nd) compilation of the São Francisco Craton•Compiled data better fit the preservation bias model for the growth of continental crust.•Differences in age and crustal thickness during Neoproterozoic continental arc development