Browsing by Author "Dampare, S. B."
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Item High-Pressure Granulites and Eclogites of the Dahomeyide Suture Zone (Adaklu, Southeastern Ghana): Petrogenetic Evolution and Tectonic Implications(University of Ghana, 2015-07) Amponsah, I.; Nude, P. M.; Dampare, S. B.; University of Ghana, College of Basic and Applied Sciences, School of Physical and Mathematical Sciences, Department of Earth ScienceThe Dahomeyide suture zone marks continental amalgamation between the Paleoproterozoic West African Craton (WAC) and the Sahara Metacraton (SMC). This suture zone of the Pan-African orogenic belt is encrusted by UHP/HP metamorphic rock bodies and associated ultramafic igneous plutonic rocks in SE Ghana through to Togo and Benin. The main identified rock types consist of mafic granulites (hornblende-garnet-pyroxene gneiss and pyroxenegarnet- hornblende gneiss), felsic gneiss, eclogite and pyroxenite. The petrography, structures and geochemistry of these rocks have been studied with the objective of inferring their petrogenesis and tectonic setting. Forty (40) thin sections were prepared and twenty-six samples were analyzed for major and trace elements using the Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES) and Inductively Coupled Plasma Mass Spectrometry (ICP-MS). Some garnet porphyroblasts observed in the mafic granulite of the suture zone have preserved an indicative microstructure of UHP and prograde-retrograde metamorphism. These were respectively attributed to the exsolved rutile rods in garnet and also disequilibrium textures (corona textures) of incomplete reactions observed within the granulites and eclogites. The area has been affected by three deformational events: D1, D2 and D3. The D1 event (characterized by dextral sense of deformation) was a transpressional event which produced the penetrative S1 foliations which are sub-parallel to the axial plane and axis of fold F1. D2 is marked by a dominant extensional event which resulted in the normal faults (Ft1 and Ft2) of the area and the stretched and rotated boudins in the pyroxene-garnethornblende gneiss. D2 is marked by sinistral sense of deformation and a subordinate compressional event which is evident by the thrusting of the boudins. D3 which is the last of the main phases of deformation (dextral sense) was a compressional event which is evident in the garnet-hornblende gneiss at Torkor. D3 resulted in the formation of the recumbent folds F2 which have over-printed F1. These three deformation events confirm with a typical convergent boundary deformation which starts with collision, extension and a final collision which are all represented by the D1, D2 and D3 respectively. The suture zone rocks at Adaklu consist largely of rocks with IAT affinities and also include suites of rocks with N-MORB (oceanic crust) and subordinate calc-alkaline geochemical signatures. These signatures are typical characteristics of an arc environment setting. There is also some crust contamination in the mafic rocks and hence the crust (lower crust) played an active role during the evolution of these rocks. In contrast the mafic/ultramafic rocks show very little crustal contamination as these rocks show negative Th, moderate U and almost flat Zr-Hf anomalies. Low Th/Yb and high Nb/Th ratios in the mafic/ultrmafic rocks are inconsistent with crustal contamination. However, comparably, the felsic gneiss has higher Th and Pb contents, higher Th/Yb and low Nb/Th ratios. Based on the geochemical data represented on the pyroxenites (high Ba/Nb, ~36-262; Ba/Zr, ~1.44-4.03; Ba/Th, ~144-524; and U/Th, ~0.5-1 relative to the primitive mantle and Mg# and Ni content), it is proposed that the primary melts of these ultramafic plutonic rocks in the area were derived from the normal lithospheric mantle wedge which had not been depleted by previous melt extractions and strongly modified by hydrous fluids.Item Petrography and Geochemistry of the Anyaboni Formation of Kwahu Group, Voltaian Supergroup, Ghana: Implications for Provenance and Uranium Exploration(University Of Ghana, 2015-07) Akontoh, F.A.; Asiedu D. K.; Dampare, S. B.; University Of Ghana, College of Basic and Applied Sciences, School of Physical and Mathematical Sciences, Department of Earth ScienceAn integrated petrographic and geochemical study of the Anyaboni Formation, Kwahu Group, Voltaian Supergroup in Ghana was carried out to infer the provenance, tectonic setting, paleoweathering and paleoclimate conditions and uranium mineralisation potential of the basin. Twenty representative rock samples were collected from the Anyaboni Formation in Asesewa and its surrounding areas for petrographic and whole rock geochemical studies. The major elements were analysed by ICP-OES and the trace elements/REEs by ICP-MS. Two main rock types were identified in the area based on field observations; feldspathic sandstones and quartz sandstones. The petrographic studies indicated that the sandstone type was quartz arenite with texturally and compositionally matured minerals. On the basis of petrography the provenance was defined as metamorphic source and the tectonic setting was revealed as that of craton interior (predominantly) and recycled orogen. The sedimentation also occurred in a low-relief and tropical (humid) climatic conditions. The geochemical studies indicated that the sandstone types are mainly subarkose with contributions of arkose, sublitharenite and quartz arenite. The parent lithology is a quartzose sedimentary igneous source with contributions from felsic source. The CIA and PIA values range from 66.05 to 80.77 and 66.67 to 98.34 respectively. These values indicate that the paleoweathering condition is moderate to high, leading to alteration of unstable minerals to stable, oxide/hydroxide and clay minerals. Tectonic setting discrimination diagrams based on the geochemistry confirmed a passive continental margin setting. Uranium concentration studied alongside with Th, Zr and V in the study area indicates generally low levels. However, there is a strong positive correlation between U and Th, Zr and V concentrations and can serve as pathfinders for U in the area.