Tectonic history of the mandawa basin and the underlying basement in the coastal Tanzania: a window to the assembly, rifting and break-up of gondwana supercontinent
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Date
2016
Authors
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Publisher
University of Dar es Salaam
Abstract
Petrological, geochronological, and structural data of the Mandawa basement and sedimentary rocks in the Basin, demonstrate the Gondwana assembly in Neoproterozoic time and its subsequent break-up in Jurassic time. The basement rocks experienced peak metamorphic conditions at T = 630 - 751 °C and P = 5.8 - 8.7 kbar, indicating the amphibolite facies conditions. The metamorphic ages between ~600 and —590 Ma fall in the time window of the Kuungan Orogenic cycle (600 - 500 Ma), i.e. the final event of Gondwana amalgamation. The magmatic ages between 614 ± 18 Ma to 554 ±3.9 Ma suggest that metamorphism and magmatism were synchronous. The age of orthogneiss at 790 ± 8.7 Ma indicate Neoproterozoic protolith ages, similar to magmatism in the Eastern granulite of Tanzania and the Cabo Delgado Nappe complex of NE Mozambique. The oldest gneiss in the area has a Mesoproterozoic protolith age at 1050 ± 20 Ma similar to the records in the Unango/Marrupa Complex of NE Mozambique.nNew structural data from the field structural observations, digital elevation model (DEM), seismic and magnetic data from the Triassic-Jurassic Mandawa Basin of coastal Tanzania, suggest two major deformational events named D1 and D2 in this study. The D1 event generated the NNW-SSE trending deep-seated normal faults, and T-fractures. The geometry of these structures suggests that, the ENE-WSW extensional movements, probably associated with the rifting of Gondwanaland during Permo-Triassic time, generated them. The D2 event is related with the NNW dextral shear zone with NW-SE extensional movements, to generate the NNE-SSW, NNW-SSE and ENE-WSW Riedal shears, dextral strike slip faults, sinistral faults, normal faults and T-fractures. This event probably was associated with the drifting of Madagascar along the Davie transform fault during the Jurassic time. The geometry of Mandawa Basin suggests pull-apart origin, generated by transtensional event, followed by successive reactivation.
Description
Available in print form, East Africana Collection, Dr. Wilbert Chagula Library, Class mark ( THS EAF QE653.5.M7662)
Keywords
Geology, stratigraphic, Geology, Coastal area, Mandawa basin, Tanzania
Citation
Mtabazi, E G (2016), Tectonic history of the mandawa basin and the underlying basement in the coastal Tanzania: a window to the assembly, rifting and break-up of gondwana supercontinent, Master dissertation, University of Dar es Salaam. Dar es Salaam