New constraints on the Pan-African Orogeny in Central Zambia: A structural and geochronological study of the Hook Batholith and the Mwembeshi Zone

- Structural and geochronological study at the Lufilian Arc-Zambezi Belt junction
- Two orthogonal in shortening direction deformation events are described.
- Timing of granites emplacement and deformations is obtained by U-Pb geochronology.
- The role of the Mwembeshi Zone in the Pan-African Orogen is reconsidered.
- New model for the Pan-African tectonic evolution in Central Zambia is presented.

In Central Zambia, the Mwembeshi Zone (MwZ) separates two branches of the Pan-African Orogen: the Lufilian Arc and the Zambezi Belt. To the north of the MwZ, the Hook Batholith was emplaced within Neoproterozoic Katangan metasedimentary rocks. Field mapping and structural studies, microstructural observations, interpretation of airborne geophysical images and U-Pb zircon geochronology constrain a new model for the tectonic evolution of this poorly studied part of the orogen.Two temporarily separated and highly oblique orogenic contraction events are defined. D1 is characterised by a regional low-metamorphic grade E-W shortening that produced strain partitioning between N-S trending pure-shear-dominated and NW trending sinistral simple-shear dominated domains. The emplacement of the batholith between ca. 550 and 533 Ma (U-Pb zircon ages) is syn-tectonic to D1. The D2 N-S shortening event was active after ca. 530, which is indicated by the age of the newly dated, deformed molasse of the Hook Batholith. During D2, the MwZ developed as an E- to ENE-striking zone of pure-shear dominated deformation that localised to the south and within the already exhumed Hook Batholith.At the scale of the Pan-African Orogen in Southern Africa, the D1 is considered to be a far field expression of the E-W collision event in the Mozambique Belt. The following Early Cambrian D2 event corresponds to the high angle collision between the Congo and Kalahari Cratons and the stitching of the Lufilian and Zambezi belts along the MwZ. Therefore, in the Hook area, the MwZ cannot be regarded as a continental-scale wrench structure as widely discussed in the literature. The tectonic events in Central Zambia suggest that the amalgamation of Gondwana was accompanied by suturing along highly oblique orogenic belts during plate reorganization at around 530 Ma.