CONTRIBUTIONS TO THE CHEMICAL MODELING OF SOME GRANITIC MASSES IN THE CENTRAL EASTERN DESERT, EGYPT

Gabal Delihimmi (140 km2), Gabal Abu Tiyur (30 km2) and Gabal Um Shaddad (17 km2) are three granitic masses located in the central Eastern Desert of Egypt, intruding older metavolcanics, granodiorite and metasediments. These three granitic masses were studied geochemically for petrogenetic modeling.
The modal mineralogic analysis shows that Gabal Delihimmi granites are composed of orthoclase perthites, quartz, plagioclase and biotites, whereas Gabal Abu Tiyur and Gabal Um Shaddad granites are composed of microcline perthites, quartz, plagioclase and minor biotites.
Fractional crystallization and mass balance modeling for the younger granites of Gabal Delihimmi granite, Gabal Um Shaddad granite and Gabal Abu Tiyur indicate their derivation from the parent mafic magma granodiorite, through fractional crystallization of plagioclase, hornblende, orthoclase, biotite, quartz and apatite with residual liquid ranging from 0.00% to 0.13%. The relatively small value ΣR2 (0.001) indicates a good fit of the resulting model.
Using REE petrogenetic modeling, Gabal Delihimmi granite can be produced from 40% non-modal partial melting for the bulk continental source materials followed by 35% crystal fractionation whereas Gabal Abu Tiyur (type 1) and Gabal Um Shaddad granites can be produced from 30% non-modal partial melting for the upper continental source materials followed by 40% crystal fractionation. On the other hand, Gabal Abu Tiyur granite (type 2) can be produced from granitic source materials by 50% modal partial melting followed by 60% crystal fractionation.
The tetrad effect was a feature of the magma-fluid system before magmatic crystallization or that the tetrad effect in the whole rock samples was inherited from an external fluid during or after the emplacement of the magma.