Field observations and microstructural evidences of syntectonic emplacement of the Ngwi granitic plutons (central Cameroon domain).

Autor: Ludovic, Achu Megnemo, Maurice, Kwékam, Martial, Fozing Eric, Jules, Tcheumenak Kouémo, Julios, Efon Awoum, Cliff, Choumele Kana Styve, Belmien, Sobze Yemdji Robinson, Blandine, Kamgang Tchuifong Agnès, Lauraine, Azemekeu Folefack
Zdroj: Arabian Journal of Geosciences; Aug2021, Vol. 14 Issue 15, p1-20, 20p
Abstrakt: The NE-SW elongated Pan-African Ngwi granitic plutons (NGP) hosted in banded gneisses and biotite amphibolite country rocks belong to the central domain of the Central African Fold Belt (CAFB) in Cameroon. They consist of two-mica granite and amphibole-biotite granite both cross-cut by aplitic and pegmatitic veins. Two-mica garnet granite cross-cuts banded gneiss in Ngwi. Microstructural features recorded in granites reveal magmatic, submagmatic and high- to low-temperature solid-state deformations. Field structures testify that the investigated Ngwi area recorded three deformation phases: (1) D1 phase of WNW-ESE to NW-SE flattening deformation characterized by gently to moderately dipping S1 metamorphic foliation; (2) D2 phase of sinistral shear movement marked by low to steep dips (i) NNW-SSE to NE-SW strike of S2 metamorphic foliation in country rocks, parallel to C2 shear planes and B2 boudins; (ii) N-S to NE-SW strike of S2 magmatic foliation marked by the preferred orientation of biotite and feldspar crystals, locally disrupted by syn-magmatic shears (C2) in two-mica granite and (iii) low NNE plunges and low to steep SSW plunges stretching mineral lineations respectively in two-mica granite and banded gneiss, subparallel to the axes of NNW- to NE-trending "S"-shaped F2 folds; and (3) D3 phase of dextral shear motion characterized by NE- to NW-directed C3 shear planes, B3 boudins and "Z"-shaped F3 folds recorded in country rocks and the NGP. The NGP have recorded opposite sinistral (D2 Pan-African phase) to dextral senses of shear movements (D3 Pan-African phase). We propose that the emplacement and deformation of the NGP were initiated during regional D2 deformation, and they were completely achieved during the regional D3 deformation. The NGP are therefore syntectonic magmatic intrusions emplaced and deformed in a transpressive regime in relation to deformation along the Central Cameroon Shear Zone (CCSZ). [ABSTRACT FROM AUTHOR]
Databáze: Complementary Index
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