Petrología, fábrica estructural y geocronología U-Pb CA ID-TIMS en circón de las series de granitoides de la región de Namibe in the suroeste de Angola: un registro de la evolución tectonomagmática Eburneana en el Escudo del Congo Suroccidental

Javier Escuder-Viruete; Pablo Valverde-Vaquero; Aratz Beranoaguirre; Pilar Montero; José Manuel Plastov

doi:10.21701/bolgeomin/136.1/008

Authors

Javier Escuder-Viruete Instituto Geológico y Minero España, CSIC https://orcid.org/0000-0002-3108-9082
Pablo Valverde-Vaquero Instituto Geológico y Minero España, CSIC https://orcid.org/0000-0002-2184-0848
Aratz Beranoaguirre Institut für Geowissenschaften, Goethe-Universität Frankfurt https://orcid.org/0000-0002-1137-6498
Pilar Montero Laboratorio de Microsonda Iónica-IBERSIMS. Centro de Instrumentación Científica. Universidad de Granada https://orcid.org/0000-0002-3651-1473
José Manuel Plastov Instituto Geológico de Angola https://orcid.org/0000-0001-5509-5068

DOI:

https://doi.org/10.21701/bolgeomin/136.1/008

Keywords:

Southwestern Congo Shield, Eburnean orogeny, granitoid suites, Angola

Abstract

During the Orosirian to Statherian transition, a great textural and compositional variety of granitoids intruded the Namibe region of the Southwestern Congo Shield. This magmatic activity was contemporaneous with a regional Eburnean tectonometamorphic event dated 1.83-1.81 Ga ago, characterized by polyphase ductile deformation, crustal thickening, high-T/low-P regional metamorphism, partial melting and the formation of anatectic granites. Petrological and structural analyses, mainly at the outcrop scale, define three distinct granitoid suites. The planar-linear magmatic fabrics observed in the leucogranite sills of the G1 suite are aligned with the intrusive contact and the S2-L2 deformational fabrics in the enclosing gneisses. Consequently, the G1 suite granites are inferred to be syn- to late-kinematic with respect to the D2 deformation event. Granitoids of the gabbroic-dioritic and tonalitic-granodioritic associations within the G2 suite intruded the cores of D3 antiforms, forming elongated massifs parallel to the hinge zones. These intrusions exhibit a subvertical magmatic foliation and subhorizontal lineation, aligned with the S3-L3 fabrics of the host rocks, indicating emplacement of the G2 suite from syn- to late-D3. G3 suite granites form elliptical massifs that cut the D3 macrostructure and display a concentrically zoned textural organization. The orientation of the planar magmatic fabric and enclaves is subparallel to the S4 in the host rocks, suggesting the syn- to post-D4 intrusion of the G3 suite. U-Pb CA ID-TIMS zircon geochronology reveals that these suites intruded within a short time spam of ca. 10 Ma with distinctive pulses at 1808 Ma (G1-G2 suites) and 1803-1801 Ma (G2-G3 suites).

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