Transposition of structures in the Neoproterozoic Kaoko Belt (NW Namibia) and their absolute timing
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Three structural profiles across the Coastal Terrane, the Boundary Igneous Complex and the Orogen Core have been studied in the Kaoko Belt of northwestern Namibia. The oldest known Si fabric is inherited from an older tectono-metamorphic event. It occurs in the Coastal Terrane only and the extent of its reworking increases from south to north. The S1 foliation reactivates or folds Si fabric in the Coastal Terrane and appears as an early planar fabric in granitoids of the Boundary Igneous Complex and migmatites of the Orogen Core domain. Superimposed subvertical S2 fabric corresponds to axial plane cleavage of upright close to isoclinal folds and the extent of its development also increases from south to north. Active migration of partial melt during S2 development in the Orogen Core dates the onset of this deformation at ~550 Ma. Distribution of F2 fold axes and L2 stretching lineations suggests pure shear–dominated deformation associated with development of N–S trending S2 cleavage preserved in the central profile, followed by sinistral simple shear–dominated deformation on newly developed NW–SE trending pervasive cleavage in the northern part of the area. Such spatial variation in the deformation record is attributed to the irregular shape of the Congo Craton indenter that is reflected by heterogeneous development of the S2 cleavage front in the Coastal Terrane and the Boundary Igneous Complex. Common orientation of L1 and L2 stretching lineations and solid-state reworking on both S1 and S2 planes suggest single event of sinistral transpression since 550 Ma with strain partitioning into domains of oblique thrusting (reactivated S1) and transcurrent sinistral shearing (S2 and S3). Such succession of deformation structures suggests that major subvertical shear zones in the Kaoko Belt do not correspond to early crustal discontinuities, but rather reflect late strain localization during cooling.
KeywordsKaoko Belt Coastal Terrane Transpression Tectonics Gondwana
The authors express their great thanks to Dr. Charlie Hoffmann from Namibian Geological Survey for his support and numerous stimulating discussions as well as to Ewereth Muvangua and Aphary Muyongo for field assistance in the Hoanib profile. Dr. Ondrej Lexa is thanked for valuable discussions on numerous aspects of transpression tectonics. This study represents an output associated with fulfillment of the project no. 205/07/1409 of the Czech Science Foundation. The salary to PJ has been covered by the Ministry of Education, Youth and Sports of the Czech Republic Research Plan No. MSM0021620855. We greatly appreciate constructive reviews of C. Passchier and P. Oyhantcabal, which helped to improve the manuscript. The authors would like to thank S. Siegesmund for the opportunity to contribute to this volume as well as for editorial handling.
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