Research Abstract
SUMMARY AND CONCLUSIONS:
The pressure-temperature conditions during metamorphism at Um Sheqila, Sikait, Um El Kheran and Um Tenadib based on garnet-biotite; garnet-plagioclase and alkali feldspar-plagioclase were estimated. The metamorphic conditions are obtained from the fourteen models of geothermobarometers. Schruers (1985) mentioned that the P-T estimates are 550-650 oC for the amphibolite facies and 700-825 oC for the granulite facies at 3-5 Kbar. The mineral parageneses suggest 525 oC, 440 oC, 555 oC and 727 oC for Um Sheqila, Sikait, Um El Kheran and Um Tenadib rocks respectively. All KD values determined for Um Sheqila, Sikait and Um El Kheran are consistent with the average values for the garnet and staurolite zones at Um Tenadib only; on which the data have been plotted in Fig. (4). The garnets show marked differences in composition from (72.26, 72.38, 56.59 and 69.11 alm.), (12.92 , 3.78, 8.15 and 13.39 pyr.), (10.55, 4.4, 11.92 and 11.74 sp.) and (4.27, 19.48, 23.38 and 5.39 gr.) at Um Sheqila, Sikait, Um El Kheran and Um Tenadib respectively. Um Sheqila and Um Tenadib garnets are notably rich in MgO and poor in CaO, in contrast to Um El Kheran and Sikait garnets; which are rich in MnO and poor in FeO. The lowest percentages of MnO and MgO and highest values of FeO are found in the Sikait garnets only.
