INVESTIGATING MINERALOGICAL AND PETROLOGICAL CHARACTERISTICS OF THE FLOOD BASALT ON THE ETHIOPIAN PLATEAU

The Ethiopian Plateau in East Africa has undergone a widespread flood basalt volcanic event around Oligocene time, covering an area of >500,000 km². This volcanic event was followed by numerous younger shield volcano building episodes in the Miocene and Pliocene times, as well as continental rifting.

Here, we investigated the spatial extent of this blood basalt by using ASTER multispectral satellite imagery and the petrographic analysis of the basalts using thin section petrography and scanning electron microscope (SEM).

The extent of the flood basalt was mapped using ASTER band combination for basalt spectral signature and basalt extraction index (BEI). Twelve basalt samples were collected from the plateau for thin sections to characterize their texture, mineralogical composition, and degree of chemical alteration. Petrographic and SEM results were combined with basalt extent map to visualize magma source and spatial variation of magma composition and nature.

Results of our thin section petrography indicate that these basalts are composed of plagioclase feldspar, olivine, and opaque minerals. The textures of the samples included porphyritic, glomeroporphyritic, flow-aligned, amygdaloidal, and poikilitic. Within the lava flows, vesicles and cavities have been observed. These vesicles have been filled with secondary minerals. We then analyzed these secondary minerals, including their field descriptions, optical, and SEM microscopy. The analysis of the mineral content will provide insights into the geologic conditions present at the time of these basalts’ crystallization. Based on the geographic distribution of the basalts, we can understand the conditions that caused the different textural and mineralogical properties. Results of this study will provide better insights into the volcanic eruption history of the Ethiopian Plateau flood basalts, which will be instrumental to understand past climatic changes.