Evidence for change in crust formation process during the Paleoarchean in the São Francisco Craton (Gavião Block) : coupled zircon Lu-Hf and U-Pb isotopic analyses and tectonic implications.
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2022
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The continental crust growth/evolution processes and the tectonic regime through Eo- and Paleoarchean times
are enigmatic due to the scarcity of preserved crust. The Gaviao ̃ Block, S ̃
ao Francisco Craton (Brazil), contains
exposed and well-preserved Eo-Paleoarchean crust remnants, providing a rare opportunity to investigate these
issues. Here, we describe new U-Pb ages and Hf isotope data of 3.51–3.4 Ga tonalites and diorites from the
Gaviao ̃ Block and compare these with previously published Lu-Hf data from Hadean/Eo-Paleoarquean zircons
from the Gavi ̃
ao Block and other primitive cratons. The Eo- to Paleoarchean evolution of the Gaviao ̃ Block is
registered by ca. 360 Myr of continuous magmatic events from ca. 3.66 Ga to 3.30 Ga. From the available Hf
data, we interpret that each of the events younger than 3.6 Ga registers a new juvenile addition that assimilated
older crust, whereas the rocks older than 3.6 Ga are exclusively formed through the reworking of a Hadean, and
to a less extent early Eoarchean crust. The shift in the crust generation process with the input of juvenile material
into the Gavi ̃
ao Block has been documented within the ~ 3.8–3.5 Ga time in other primitive cratonic complexes
including the Wyoming, Pilbara, Kaapvaal, Slave, Singhbhum, and Yilgarn. As documented in these other cra-
tons, our data suggest that a shift in the Hf isotope record to rocks younger than 3.6 Ga reflects a transition from
stagnant-lid to mobile-lid tectonics in the crust formation process of the S ̃
ao Francisco Craton. This change in the
geodynamic regime appears to have been global at ca. ~ 3.8–3.5 Ga and facilitated the extraction of juvenile
melts, crustal reworking, evolved magmatism, and the production of stabilizing melt-depleted lithospheric
mantle.
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Hf-isotopes, Crustal evolution
Citação
SANTOS, C. dos. et al. Evidence for change in crust formation process during the Paleoarchean in the São Francisco Craton (Gavião Block) : coupled zircon Lu-Hf and U-Pb isotopic analyses and tectonic implications. Precambrian Research, v. 368, 2022. Disponível em: <https://www.sciencedirect.com/science/article/pii/S0301926821004009?via%3Dihub>. Acesso em: 29 abr. 2022.