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Transitional Basalts and Eruptive Dynamisms around Nkoumelap Locality (West of the Bamoun Plateau, Cameroon Volcanic Line): Petrography and Volcanic Risks’ Evaluation

Luc Achille ZIEM A BIDIAS, Amidou MOUNDI, Jonas Didero TAKODJOU WAMBO

Journal of Geosciences and Geomatics. 2017, 5(2), 65-77 doi:10.12691/jgg-5-2-3
  • Figure 1. Location of the study area (green square) along the Cameroon Volcanic Line (adapted after [6]). Location of seamounts after [7]. Insert bottom right is after [8]
  • Figure 2. Simplified geological map of the Bamoun area (after [3])
  • Figure 3. Volcano-tectonic map and rosace of the lineamentary directions (below) of the sector Koutaba - Nkoumelap. The red arrow represents the mean lineamentary direction
  • Figure 4. Representative photomicrographs (a,b,c,d) showing some textures and the mineralogical associations. Microlitic texture averagely porphyric (a, sample TA9) and doleritic (b, sample ZB5) in a basalt; aphyric texture (c, sample ZB7); zoned phenocrysts (d, ZB59) and twinning (e,f. ZB2) in transitional basalts with porphyric texture
  • Figure 5. Chemical classification of pyroxenes in transitional basalts. (a) Position of pyroxenes in transitional basalt in the Q-J diagram of [22]; (b) Distribution of clinopyroxene of basalt in the Ti/(Ca + Na) diagram of [10]; (c) Mg-Ca-Fe2++Fe3++Mn diagram of pyroxenes [16]; (d) Position of clinopyroxenes in transitional basalts in the AlIV vs. AlIV diagram [23,24]. The domain limits are of [25]. RMC: fields of refractory mantle clinopyroxene [26]. HP=high pressure; LP=low pressure
  • Figure 6. TiO2 – FeO – Fe2O3 diagram giving the composition of the oxides of transitional basalts
  • Figure 7. Mg* vs. Al/Ti diagram of the clinopyroxenes. Mg*= Mg/Mg+Fe
  • Figure 8. Map of volcanic hazards on the west side of the Bamoun plateau. 0-20: negligible hazards; 20-40: low hazards; 40-60: mild hazards; 60-80: high hazards; 80-100: very high hazards. Combined field and remote sensing applications through the processing of the Landsat-7 Enhance Thematic Mapper Plus (ETM+) were used for the mapping of regional hazard map
  • Figure 9. Magmatic formations and associated risks to the west of Bamoun plateau. (a): Ignimbrites with a layered aspect; (b) huge rounded boulders suspended on the slopes of Njitet volcano in Bangourain; (c): feldsic lava dome in Nkan’yam; (d) and (e): volcanic product (ashes, lapilli and blocs) able to be mobilised on the flanks of hills in Nkoumelap. (f) basalt wall in Nkoumelap; (g) rhyolitic matrix of the lahar of Bangourain showing ignimbrite enclaves, basalts and rhyolites; (h) and (i): important extension of lahar of Bangourain respectively by flows in the surrounding valleys and revealed by areolar erosion; (j): “Bad lands” on the road linking the villages of Folap and Bangourain; (k) panoramic view grouping the villages directly exposed to the risks