Petrology of the Volcanic Fields East and South-East of Ruwenzori, Uganda

Abstract

I. G eneral D escription of the V olcanic A reas U ntil 1891 the possibility was entertained that Ruwenzori, like the other high mountains of Central Africa, might be of volcanic origin. As a result of his explorations during that year, Dr. F. Stuhlmann (1894) showed that this preliminary suggestion was without foundation, adding that no signs of volcanic activity had been detected in the regions traversed. In 1894, however, G. F. Scott Elliot recognized three well-marked volcanic belts in the adjoining country east and southeast of Ruwenzori ( Elliot & Gregory, 1895, p. 674 ; Elliot, 1896, p. 168 ). He described the bedded tuffs, craters, and crater-lakes of Toro (fig. 1) as occurring in the Vijonga area (Lake Kijongo), north-west of Fort Portal; the Butanuka or Kyatwa area, south of Fort Portal, locally forming the boundary of the low Toro plains to the east; and the Katwe and Kaihura Straits area (north-west of the Kazinga Channel between Lakes George and Edward). It is remarkable that Stanley failed to recognize the volcanic origin of the famous salt-lake of the Katwe crater. He visited the locality in 1889 and commented on the deep depression and the salinity of the lake, and even recorded the occurrence of a spring of sulphurous water. Scott Elliot also indicated that Karimi Hill, south-west of Ruwenzori (now in Belgian territory), might be of volcanic origin, and suggested that the different belts of cones and craters were alined on fissures radiating outwards from the uplifted massif of Ruwenzori. The nature of Karimi Hill

The role of carbon from recycled sediments in the origin of ultrapotassic igneous rocks in the Central Mediterranean

“…1) (red diamonds in Fig. 3) are rare kalsilite-bearing melilitolites, named after those first described by Holmes and Harwood (1932) in Central Africa. They are strongly silica-undersaturated ultrapotassic rocks (i.e., larnite normative, see supplementary data; Table 1, Fig.…”

The Vesuvius and the other volcanoes of Central Italy

“…Lamproite-like rocks are invariably plagioclase-free, with forsteritic olivine, chromian spinel, Alpoor clinopyroxene, K-richterite, sanidine, and apatite; leucite may be present in silica-undersaturated lamproite-like rocks, which are missing in lamproite-like rocks from the Central Mediterranean (i.e., Corsica and Tuscany, Conticelli et al, 2010a). The kamafugite-like rocks are kalsilite-bearing melilitites (e.g., Holmes & Harwood, 1932;Sahama, 1974;Gallo et al, 1984;Peccerillo et al, 1988). Because of their extreme mineralogical variability the rocks were named from the locality of first discover.…”

Analysis of geophagy soils in Kibale Forest, Uganda

“…According to HOLMES and HARWOOD (1932) the Fort Portal lavas and pyroclastics range from carbonatites ( Fig. 4) with little silica and low alkali, to potash-rich ultrabasic lavas and lapilli comprised of such minerals as lucite, potash rich nepheline, kalsilite (KA1SiO4), pyroxenes, olivine, and mellilite.…”