Rhyacian-Orosirian transitional arc-collisional magmatism in the Archean Piedade Microcontinent, southern São Francisco Paleocontinent, Brazil

Understanding of ancient accretionary orogenic systems through the correlation between pre-collisional assemblages described in different tectonostratigraphic terranes is not a straightforward task. The investigation of late-to-post collisional rocks, associated with the end-stage of convergent margin interactions, can be a reliable alternative due to a higher preservation bias. A typical rock assemblage in such settings is represented by C-type adakites chronologically associated with alkaline rocks and basic rocks with intraplate and MORB-like signatures.

The Piedade microcontinent, focus of the investigation, represents an important Archean crustal fragment enveloped by magmatic arc terranes, located in the southern segment of the Siderian to Orosirian Minas-Bahia orogenic system. In this work we present new petrographic, geochemical and isotopic (whole-rock Sm-Nd, and zircon U-Pb, and Lu-Hf) data for the bimodal rock association presently cropping out as metabasic and metagranitoid rocks intrusive within the Archean Piedade microcontinent. The timespan of ca. 2.07 Ga to 2.03 Ga represents the reworking of lower crustal lithologies plus the addition of mantle derived magmas during the late stages of the orogenic development. A comparison with similar assemblages of other orogenic systems from different ages demonstrates that the rock association of MORB- and intraplate mafic magmas with C-type adakites and alkaline granitoids is common throughout most of Earth eras, and records an event of lithospheric delamination, ie. slab break-off, followed by asthenospheric rise and partial melting of lithospheric mantle and lower crustal rocks.