Geology and evolution of Precambrian rocks, Mt. Shelomo, Elat area

The Mt. Shelomo area (5 km NW of Elat, southern Israel) is composed of high-grade metamorphic, plutonic, sedimentary, and volcanic rocks, which are intruded by a younger dike swarm. The sedimentary section, mainly conglomerates, consists of pebbles and boulders derived from the crystalline country rocks. In north Mt. Shelomo, they are interbedded with the volcanic rocks, and both units unconformably overlie the basement. The young dike swarm, mostly composed of quartz-porphyritic rocks, represents the last magmatic phase in this area. The Mt. Shelomo area is divided into two parts by a major ENE-WSW-trending fault. Numerous dikes, sometimes comprising as much as 90% of the area, characterize the southern, topographically higher part. The northern, lower part, although intruded by similar dikes, is characterized by a smaller proportion of dikes, which comprise up to 15-20% of the area. The southern, uplifted block seems to include dikes that intruded the country rocks close to the roof of the magmatic chamber, whereas the northern downfaulted block consists of dikes that were emplaced in the same country rock but higher up above the roof of the magmatic chamber. The blocks, originally from different levels, have been juxtaposed by the displacement along the ENE-WSW fault. Two methods of Mg-Fe thermometry of coexisting garnet-biotite in migmatite resulted in two maximum temperatures, 702°C or 610°C, depending on the calculation model. Plagioclase-muscovite pairs reveal that the pressure during migmatization was 4.7 ± 1 kbar. The lower temperature estimate is felt to be the more realistic because of the lack of field evidence for melting. Rather, field and petrographic observations, such as the absence of alkali feldspar and similar plagioclase composition in adjacent leucosome and melanosome, support migmatization by metamorphic differentiation.