Crustal architecture of Neoproterozoic terrains of western Gondwana revealed by integrated geophysical and structural data on the eastern Borborema Province, NE Brazil

Abstract

The deformation processes (e.g. accretionary or intraplate) occurring within the Borborema Province have been widely discussed, however the eastern part of the central subprovince lacks further investigation in such aspect. In this contribution, we present integrated airborne gamma ray and magnetometric geophysical data, as well as meso- and microstructural markers of the Archean-Paleoproterozoic Alto Moxotó and Neoproterozoic Rio Capibaribe terrains (central Borborema Province), providing evidence for hidden accretionary episodes in the region. Fourteen radiometric and ten magnetic domains were described and fitted with most of the geological units and mapped structures, suggesting geological contrasts between the studied terrains. For instance, the Alto Moxotó terrain presents high-to-medium eTh and eU radiometric signatures, spatially distributed along folded geometry, whereas the lithospheric record of the Rio Capibaribe terrain is characterized by K (%) enrichment and a dominant NE-SW sheared crust. In addition, the obtained Euler solutions show good correlations with the main structures and delineated shallow to intermediate sources of the Congo-Cruzeiro do Nordeste strike-slip shear zone system, the proposed structural boundary. This large set of shear zones are characterized by large mylonitic corridors with characteristic vertical foliation planes with moderately-plunging mineral lineations. Associated microstructures include bulging, subgrain rotation and recrystallization that, in association with the well-developed S–C fabrics and myrmekites indicate deformation at moderate temperature values (∼400–500 °C). Also, conspicuous fracture networks seen in plagioclase grains demonstrate that deformation also took place at the later developed brittle-ductile transition. Hence, the described contrasting rock ages and nature, geophysical signatures and deformational patterns is herein interpreted as the result of crustal agglutination during the Neoproterozoic, in which the Congo-Cruzeiro do Nordeste shear zone system would represent relics of a terrane boundary developed during the assembly of western Gondwana.