Stratigraphic and geochronological characterization of the Mato Verde group, Central Espinhaço (Brazil) : an Eocalymmian rifting record in the western domain of the Congo-São Francisco paleocontinent.

Abstract

The Mato Verde Group comprises an important volcano-sedimentary record occurring in the eastern Congo-São Francisco paleocontinent along the western border of the Central Espinhaço. This succession is interpreted as a basin rift related to one of the stages of basin formation in the Espinhaço aulacogen at the northern end of the Araçuaí Orogen. The stratigraphic architecture and U-Pb data from the volcano-sedimentary succession, as well from the overlying succession, provide new insight into the evolution of Mato Verde rifting. The sedimentary pattern of this succession is interpreted as the basin infilling of an intracontinental rift that was compartmentalized in two half-grabens. The basal succession defined as the Panelas Formation contains entirely siliciclastic sedimentation, such as alluvial fan, delta fan and minor fluvial and lacustrine facies associations. Detrital zircon grains extracted from basal conglomerates show mainly Archean and Paleoproterozoic ages. The upper sequence is represented by the Riacho Seco Formation, which consists of volcanic lava beds and volcaniclastic rocks. At the top of the succession, a lapilli tuff is dated at 1586 ± 15 Ma, which is interpreted as the final age of the rift phase. The Vereda da Cruz Formation occurs in stratigraphic discontinuity above the Mato Verde succession and comprises exclusively aeolian sedimentation. The youngest grain defines a maximum sedimentation age of 1616 ± 30 Ma. This basin stage is interpreted as due to a thermal subsidence process that is related to Mato Verde rifting. The equivalent unit to the Mato Verde Group is only found in the Northern Espinhaço and is represented by the Pajeú Group. The basin-fill patterns and Calymmian ages suggest a direct link with the second rifting event within the São Francisco paleocontinent, which was responsible for the development of the Espinhaço basin.