Proterozoic Thermochronologic Implications from ⁴⁰Ar/³⁹Ar and K-Ar Dating of the Campo Belo Metamorphic Complex, Southern São Francisco Craton, Brazil

Four ⁴⁰Ar/³⁹Ar step-heating analyses, performed on Archean rocks of the Campo Belo complex, Minas Gerais state, yielded results in agreement with 24 K-Ar dates already available for the study area. Integrated interpretation of these results is compared with typical argon blocking temperatures of both biotites and amphiboles dated, as well as with the geologic scenario of the southern part of the São Francisco Craton and the adjacent Brasilia marginal belt, therefore providing better understanding of the regional thermal history. The resulting K-Ar and ⁴⁰Ar/³⁹Ar cooling patterns are diagnostic of a progressive isotopic rejuvenation of the Campo Belo complex during the Proterozoic. The oldest ⁴⁰Ar/³⁹Ar and K-Ar dates, in the range 2,100-1,900 Ma and 1,790-1,760Ma, are related to successive uplift of the basement structures due to evolution of the Transamazonian Mineiro belt and tectonism that originated the Espinhaço rift, respectively. The emplacement of plutonic rocks into the Archean Piumhi greenstone at ∼1,127, ∼726 and 635Ma (U-Pb ages) compares well with K-Ar dates on the basement rocks within the SW edge of the Craton, among 1,280 and 740 Ma. Although these radiometric data broadly support a Neoproterozoic age for the collision of the Brasilia belt, the oldest dates also suggest that a Mesoproterozoic tectonic reactivation may have occurred in the southern end of the São Francisco Craton.