Mineralogical and geochemical study of rodingites and associated serpentinized peridotite, Eastern Desert of Egypt, Arabian-Nubian Shield

We studied rodingite and rodingite-like rocks within a serpentinized ultramafic sequence and ophiolitic mélange at Um Rashid, in the Eastern Desert of Egypt. The Um Rashid ophiolite is strongly deformed, metamorphosed, and altered by serpentinization, carbonatization, listvenitization, rodingitization and silicification. The textures, whole-rock chemistry, and composition of fresh primary mineral relics show that the serpentinite protoliths were strongly melt-depleted harzburgite and minor dunite, typical of a supra-subduction zone fore-arc setting. The light-colored rocks replacing gabbro are divided on the basis of field relations, mineral assemblages and geochemical characteristics into typical rodingite and rodingite-like rock. Typical rodingite, found as blocks with chloritite blackwall rims within ophiolitic mélange, contains garnet, vesuvianite, diopside and chlorite with minor prehnite and opaque minerals. Rodingite-like rock, found as dykes in serpentinite, consists of hercynite, preiswerkite, margarite, corundum, prehnite, ferropargasite, albite, andesine, clinozoisite and diaspore. Some rodingite-like rock samples preserve relict gabbroic minerals and texture, whereas typical rodingite is fully replaced. Rodingite is highly enriched in CaO, Fe₂O₃, MgO, and compatible trace elements, whereas rodingite-like rock is strongly enriched in Al₂O₃ and incompatible trace elements. Based on geochemistry and petrographic evidence, both types of rodingitic rocks likely developed from mafic protoliths in immediate proximity to serpentinite but were affected by interaction with different fluids, most likely at different times. Typical rodingite development likely accompanied serpentinization and shows mineral assemblages characteristic of low-Si, high-Ca fluid infiltration at about 300 °C. Rodingite-like rock, on the other hand, likely developed from seawater infiltration

Mineralogical and geochemical study of rodingites and associated serpentinized peridotite, Eastern Desert of Egypt, Arabian-Nubian Shield

We studied rodingite and rodingite-like rocks within a serpentinized ultramafic sequence and ophiolitic mélange at Um Rashid, in the Eastern Desert of Egypt. The Um Rashid ophiolite is strongly deformed, metamorphosed, and altered by serpentinization, carbonatization, listvenitization, rodingitization and silicification. The textures, whole-rock chemistry, and composition of fresh primary mineral relics show that the serpentinite protoliths were strongly melt-depleted harzburgite and minor dunite, typical of a supra-subduction zone fore-arc setting. The light-colored rocks replacing gabbro are divided on the basis of field relations, mineral assemblages and geochemical characteristics into typical rodingite and rodingite-like rock. Typical rodingite, found as blocks with chloritite blackwall rims within ophiolitic mélange, contains garnet, vesuvianite, diopside and chlorite with minor prehnite and opaque minerals. Rodingite-like rock, found as dykes in serpentinite, consists of hercynite, preiswerkite, margarite, corundum, prehnite, ferropargasite, albite, andesine, clinozoisite and diaspore. Some rodingite-like rock samples preserve relict gabbroic minerals and texture, whereas typical rodingite is fully replaced. Rodingite is highly enriched in CaO, Fe₂O₃, MgO, and compatible trace elements, whereas rodingite-like rock is strongly enriched in Al₂O₃ and incompatible trace elements. Based on geochemistry and petrographic evidence, both types of rodingitic rocks likely developed from mafic protoliths in immediate proximity to serpentinite but were affected by interaction with different fluids, most likely at different times. Typical rodingite development likely accompanied serpentinization and shows mineral assemblages characteristic of low-Si, high-Ca fluid infiltration at about 300 °C. Rodingite-like rock, on the other hand, likely developed from seawater infiltration

Evolution and geochemical studies on a stromatic migmatite-amphibolite association in Hafafit area, Central Eastern Desert, Egypt

The infrastructural rocks exist in the form of the gneiss domes that constituting 7% of the surface outcrops of the basement rocks of the Eastern Desert of Egypt. This study is a closer look on the mesoscopic and microscopic characteristics and the chemical behaviour of typestromatic migmatites, associated with amphibolite bands and boudins that are exposed in the northeastern part of the Migif dome, Hafafit area. Therefore, the major oxides for the studied rocks were analyzed by using the wet chemical analysis technique, whereas the trace elements analyses were carried out by XRF technique.Microprobe analyses of the investigated minerals (amphiboles, plagioclase, biotite and muscovite) were carried out with a scanning microscope and wave length dispersive spectrometers.The paragenesis and microfabric evolution of these migmatites show that they are affected by three phases of deformation. These are associated with metamorphic differentiation, crystallization and segregation. Geochemical variation between mesosomes and leucosomes reflect original compositional variations, enhanced by metamorphic differentiation and short-range migration resulting in segregation of bands. This is followed by partial melting and in-situ formation of leucosomes. Geochemical data of the associated amphibolite show that they represent para- and ortho- amphibolites. Mineral chemistry show that hornblende of the migmatites is of ferro-tschermakitic, while from the amphibolites has magnesio-hornblende composition. Plagioclase of the amphibolite has An36-44, while of the migmatites has An25-32 in the leucosomes and An51-60 in the mesosomes and melanosomes. The amphibolites were formed at temperature ranges from 720-740ºC, whereas the migmatites at temperature ranges from 800-820ºC.The mineral chemistry support their formation in the upper amphibolite facies