Geophysical perspective on the structural interference zone along the Neoproterozoic Brasília and Ribeira fold belts in West Gondwana

João Gabriel Motta,Norberto Morales,Walter Malagutti Filho

doi:10.1590/2317-4889201720160144

João Gabriel Motta, Norberto Morales + Show 1 more

Open Access

https://doi.org/10.1590/2317-4889201720160144

Copy DOI

Abstract

ABSTRACT: The Brasília and Ribeira fold belts have been established in south-southwestern São Francisco Craton during the Brasiliano-Pan African orogeny (0.9-0.5 Ga - Tonian to Cambrian), and played an important role in West Gondwana continent assembly. The region is given by a complex regional fold and thrust belt superposed by shearing during the orogeny late times, with superposing stress fields forming a structural interference zone. These thrust sheets encompasses assemblies from lower- to upper-crust from different major tectonic blocks (Paranapanema, São Francisco), and newly created metamorphic rocks. Re-evaluation of ground gravity datasets in a geologically constrained approach including seismology (CRUST1 model) and magnetic data (EMAG2 model) unveiled details on the deep- crust settings, and the overall geometry of the structural interference zone. The Simple Bouguer Anomaly map shows heterogeneous density distribution in the area, highlighting the presence of high-density, high metamorphic grade rocks along the Alterosa suture zone in the Socorro-Guaxupé Nappe, lying amid a series of metasedimentary thrust scales in a regional nappe system with important verticalization along regional shear zones. Forward gravity modeling favors interpretations of structural interference up North into Guaxupé Nappe. Comparison to geotectonic models shows similarities with modern accretionary belts, renewing the discussion.

Highlights

Geophysical modeling is an approach to get an insight into Earth’s crust architecture based on indirect infor‐ mation by means of its physical properties, contribu‐ ting to classical structural geology evaluations (Jessell & Valenta 1996, Jessell & Jessell 2001)
Neoproterozoic collision and accretion tectonics resulted in a collage of several elements ageing from Archean to Mesoproterozoic due to diachronic basin formation, its deformation and closure (Brito Neves et al 1999, Cordani & Sato 1999, Strieder & Suita 1999, Campos Neto & Caby 2000)
394 Kilometers 0 20 40 km Results comprise qualitative interpretations over Bouguer Anomaly maps and forward models unveiling the geometry of the struc‐ tural interference zone

Summary

Introduction

Geophysical modeling is an approach to get an insight into Earth’s crust architecture based on indirect infor‐ mation by means of its physical properties, contribu‐ ting to classical structural geology evaluations (Jessell & Valenta 1996, Jessell & Jessell 2001). Most information derives from geoche‐ mistry and geochronology in a poorly developed scenario of integrative discussion of structural geology and geophysics. The later counts on contributions by Haralyi and Hasui (1982), Hasui et al (1993), Mantovani and Brito Neves (2005) and Mantovani et al (2005) dealing with tectonic elements outline such as cratonic blocks, regional suture zones and fold belts. Present knowledge on tec‐ tonic and structural development during this orogeny is under construction, several questions remain unanswered, mainly on geochronology and crust geometry — especially in the linking point between the two fold belts, which cons‐ titutes a structural interference zone (Trouw et al 2013). A point to stress is that the re‐evaluation of previous data, discussed with new evidences from different data sources, presents a good opportunity to settle past questions

Results

Discussion

Conclusion