Vhuhwavhohau Nengovhela 10th Inkaba yeAfrica/!Khure Africa (AEON) Conference/Workshop Lord Milner Hotel, Matjiesfontein - Karoo 29 September – 3 October 2014 A structural and geochemical analysis of Karoo sedimentary rocks along dolerite dike and sill contacts with implications on shale gas potential Vhuhwavhohau Nengovhela AEON (African Earth Observatory Network), and Department of Geosciences, Faculty of Science, Nelson Mandela Metropolitan University, South Africa, Email: vd.nengovhela@yahoo.com logo here…

Background Jurassic mass extinction Emplacement of Drakensberg Group 183Ma Svensen et al., 2006,2007,2008,2009,2012 linked magmatic activity to mass extinction Deposition of the Karoo sediments over a ± 125Myr time span

Study area

…Study area

Contact metamorphic model of low permeability sediments including shales. Baking of organic rich rocks leads to degassing of methane and carbon dioxide through breccia pipes/hydrothermal vents. After Svensen and Jamtveit (2010)

Contact metamorphism N Sandstone Dolerite sill Burial temperatures of the Karoo sediments 200ºC-300ºC Dolerite temperatures ± 1200ºC-1300ºC High temp. gradient results in contact metamorphism Dolerite sill Contact aureole size depends on the size of the magma body, lithification of sediments. 5cm

contact metamorphism in the Karoo Sandstone Dolerite sill-sandstone contact Almost sharp contact, with no visible effects of intrusive body on the host rocks. Dolerite sill 1.7m

contact metamorphism in the Karoo Weathered basaltic dike (50cm thick) within sandstones in Lady Grey 15cm

contact metamorphism in the Karoo Baking of Karoo sedimentary rocks particularly the organic rich lower Ecca formations led to outgasing of ±2000Gt of CO2. Devolitilization and metasomatism (CO2, H2O, and volatile elements) of the sedimentary strata occurred through hydrothermal vent complexes, breccia pipes, and contact metamorphic aureoles.

Aims and objectives To study the effect of dolerite intrusions on the Karoo sedimentary rocks To establish the relationship between fracture systems and dolerites within the contact aureole. To use geochemical analysis of minerals study thermal alteration within the contact aureole. To investigate the chemical composition, pressure-temperature (P/T) analysis of fluid inclusions using microthermometry.

Materials and Methods Materials Sandstones and shale’s collected within the contact aureole. Methods Field mapping Petrography Scanning electron microscopy Fluid inclusion microthermometry

Summary In summary, the study will shed light into the extent of contact metamorphism at different levels of the Karoo sedimentary strata by highlighting: Sill/dike thickness Size of contact aureole The mineralogy and chemical alteration of sediments within the aureole P/T conditions existing at the time of dolerite emplacement

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