Structures, Deformation Mechanisms and Tectonic Phases, Recorded in Paleoproterozoic Granitoids of West African Craton, Southern Part: Example of Kan’s Complex (Central of Côte d’Ivoire)

The granito-gneissic complex of Kan is located in the central part of the Paleoproterozoic domain of Côte d’Ivoire. It consists essentially of migmatitic and mylonitic gneisses with basic intrusions and xenoliths. This Proterozoic domain belongs to the Man Leo shield, southern part of West African craton (WAC). The present study, essentially based on a structural analysis at outcrop scale, aims to identify deformation mechanisms and tectonic phasesrecorded in the granito-gneissic complex of Kan. Deformation mechanisms include: (1) flattening, (2) constriction, (3) simple shear (4), rotation (5), brittle shear, and (6) extension. The Kan complex deformation occurred during four major tectonic phases named D1, D2, D3 and D4. D1 corresponds to WNW-ESE compression. It led to the formation of NS to NNE-SSW foliation, of stretching lineation, and of folds with sub-horizontal axes. It is accompanied by N170° and N10° sinistral shear zones, which constitute globally a NS major transcurrent shear zone in the central part of Côte d’Ivoire. D1 is also marked by N90° dextral shear zones. Tectonic phase D2 is associated with EW compression. It is marked by N50° dextral and N110° sinistral transcurents shear zones. D3 corresponds to NNE-SSW compressive phase and is responsible of N110° crenulation cleavage formation. (D4) constitutes a brittle deformation phase. It correspondsto posteburnean deformation in the Proterozoic crust of Côte d'Ivoire. Generally, these deformation phases are similar to D2 and D3 reported in the Man-Leo shield and that are part of regional collisional phase referred to as Eburnean orogeny in the WAC

Chromite, mg-ilmenite and priderite as indicators minerals of diamondiferous cretaceous kimberlites and lamproites from Côte d'Ivoire (West Africa)

Seguela kimberlites are characterized by xenocrysts chromites with elevated contents of TiO2 (0.6-5%) due to reaction with the host rock and Magmatic. Chromites associated with diamonds have high levels of Cr 2O3 (usually > 55% wt), MgO (9-12%wt) and Al 2O3 (12% wt). The Cr content in xenocryst chromites is pressure dependent and thus indicative of diamond potential. Two groups characterized Seguela kimberlites chromites analyses. The first group is characterized by high contents of MgO (> 8.7 wt%) and Cr2O 3 (>57.8 wt.%). They contain more than 0.8 wt% TiO2. The Cr-Ti chromites are phenocrysts crystallized from TiO2-rich kimberlitic magmas derived from lithospheric mantle source. The second group present elevated contents of TiO2 (1-5%wt) intermediate Cr 2O3 (30%wt) and relatively low Al2O3 (<3%). The first group kimberlitic chromites are useful in diamond exploration. Chromites are associated with Mg-rich-ilmenite (Fe3+/Fe 2+ < 0.6), in kimberlite which is an important mineral indicator in diamond research. Priderite (TiO2 > 75%wt) with high K/(K+Ba > 0.8) ratio and jeppeyite with elevate BaO content (> 16%wt) and badeleyite (ZrO2> 75% wt) are characteristics minerals of Seguela olivine lamproite. These signatures allow to supose the geotectonic hypothesis of within plate continental Stratiform or Alpin (MORB) complex suggest by chromites Cr-spinels and spinels studies. Kimberlites contain diamonds with a large range in size, varying from microdiamonds (< 1 mm) weighting on average about 1 mg (0.005 carats) up to large diamonds 27 carats.29 page(s