1. 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,
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2. 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

3. Study area

4. …Study area

5. 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)

6. 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

7. 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

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

9. 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.

10. 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.

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

12. 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

13. Thank you