We used quantitative textural measurement, electron microprobe microanalysis and thermobarometry on clinopyroxene from a Cenozoic pyroxene-nephelinite flow located along the northern boundary of the West African craton to decipher magma differentiation processes in underlying magma chambers. The crystal size distributions of clinopyroxene phenocrysts show straight but also curved and kinked patterns and the clinopyroxene show large compositional variations in a single flow (Mg-number 48–88). These observations are strong evidence for magma mixing between a nephelinite magma and a more differentiated phonolitic melt at depth. Detailed thermobarometry on these clinopyroxene shows that at least three magma chambers are present below Saghro and that they are emplaced at the main physical interface within the lithosphere: (1) at the crust–mantle boundary, where the mantle-derived nephelinite has been mixed with a pre-existing phonolitic magma chamber; (2) at the lower–upper crust boundary; (3) close to the surface in a sub-volcanic magma chamber. Some high-pressure phenocrysts (up to 14 kbar) have also probably crystallized within the upper lithospheric mantle. The high clinopyroxene proportion in samples from the base of the flow is thought to reflect crystal settling during cooling of the nephelinite flow at the surface.
The study areas are located in the Katanga province to the South Eastern part of the Democratic Republic of Congo (DRC). It focuses on the Kolwezi and Tenke-Fungurume mining centers, located in the vicinity of the Basse-Kando reserve. The 3 study areas have faced large scale human induced the fragmentation of land cover. A combination of ancillary data and satellite imageries was interpreted to construct fragmentation dynamics over the last 30 years. This study is an initial step towards assessing the impact of fragmentation on sustainable land cover in the Katanga. The results bring out that large trends of fragmentation differently occurred over the last 30 years (1979 to 2011) in the three focused areas. The most dominant fragmentation processes were gains in barren soil and cities surface and a sharp reduction in burned areas. In Kolwezi, a close relationship is observed between growth and regression of barren soil and cities over vegetation. The Tenke-Fungurume site shows a growth during the 1980-1990 time slice and regression of vegetation during the following two decades. The Basse-Kando site analyze brings out growth of vegetation and regression of burned area due to vegetation conservation efforts. This is one of the studies in Katanga around mines activities that combine multi-source and spatio-temporal data on land cover to enable long-term quantification of land cover fragmentation.
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