THE ORIGIN OF ZONED NEOPROTEROZOIC IGNEOUS SUITES, SOUTHWEST GABAL MEATIQ, CENTRAL EASTERN DESERT, EGYPT.IMPLICATIONS FROM PLAGIOCLASE-AMPHIBOLE CHEMISTRY AND REE GEOCHEMISTRY

Neoproterozoic rocks in the selected area are located southwest of GabalMeatiq, central Eastern Desert
of Egypt display compositional zoning including two distinctive rock suites, outer mafic (gabbro-diorite
suite) and inner felsic (tonalite- granitoid suite).The mafic suite has alkali -calcic affinity while the felsic
suite has calc-alkalic character. Both suites have formed under moderate oxygen fugacity (fO2) and
relatively low pressure. The chemical composition trends are functions of the mineralogical composition.
FeOt, CaO, MgO, Ni, Zr and La have well defined trend indicating predominance of fractional
crystallization processes. Trace elements abundance displays slight enrichment of the LILE (Rb, Ba) with
respect to HFSE (Zr and Y). The pattern of the felsic suite displays gradual decrease from Rb, Nb and to
positive Sr anomalies which consistent with accumulation of anorthite in this suite and fractionation of
mafic phases such as amphibole. The enrichment of LILE versus HFSE is a typical signature of
subduction related magmatic rocks. Chemical patterns display enrichment of Sr and marked depletion of
Ba and Nb which characterized magmatic rocks formed during subduction stages with accommodation of
crustal materials. Mafic suite has lower ΣREE values against higher ΣREE values of felsic suite. The
thermometric calculations indicated that the original magma has high temperature up to 864°C for mafic
suite and up to 963°C for felsic suite from apatite saturation temperature. The estimated zircon and
monazite temperatures are lower than those obtained by apatite saturation temperature and plagioclasehornblende
thermometer indicating that the original melt didn’t achieve zircon and monazite saturations.
Petrological and geochemical data postulated the same magmatic origin for the different rocks in the
zoned pluton. The geochemical data support the suggestion that the zoned pluton results in differentiation
of an original calc-alkaline magma. Field and geochemical data are consistent with a mixed fractional
crystallization/assimilation/multiple emplacement mechanisms for producing the diversity of rock types in
the study pluton.