Geochemistry of the magmatic microgranular enclaves of Wadi Rahaba Area, Southern Sinia, Egypt
Reference:
Acta Mineralogica-Petrographica, Szeged 2008, Vol. 48, pp. 1-15.
Szerző:
Imbarak Sayed Hassen
Nabil Nasr El-Masry
Buda Györg
Abstract:
The study of the magmatic microgranular enclaves (MMEs) as relics of mafic magmas gives important information on the origin of parent magmas and their evolution. In the study area, MMEs are either concentrated at the margins of the I-type granodiorite pluton or within some parts of its interior. Most of the enclaves are either ellipsoidal or ovoid in shape and tend to have sharp contacts with the enclosing host rock. Sizeable enclaves, however, are less ellipsoidal and are characterized by curved boundaries. The contact is sometimes marked by a chilled margin with no sign of solid state deformation. MMEs exhibit classical features of mafic melts globules trapped in granitic magma. Swarms of MMEs are either related to convectioncurrents in magma chamber or to gravitational sorting of heterogeneous magmas. The enclaves contain the same mineral assemblages as the host rock though their proportions are different. They contain megacrysts ofplagioclase similar in composition to that of the host rock. The enclaves are composed mainly of plagioclase, K-feldspar, and hornblende in addition to minor amounts of clinopyroxene and orthopyroxene.
The MMEs are rather basic to intermediate in composition as their SiO2 content ranges between 46% and 58%. The composition of most MMEs clusters near the granodiorite trend line. Many trace elements do not show clear linear correlation with the SiO2 content and are scattered off the trends defined by related granodiorite. The petrographic and geochemical characteristics of the enclaves and their hosting granodiorite indicate that granodiorite is a product of partial melting and fractional crystallization of a basic magma, and that the enclaves are trapped blobs of basic to intermediate parental magma. Both major and trace elements contents of the investigated enclaves indicate that they were formed as a result of mingling and mixing during magma evolution.
acta2008-2009, chilled margin, granodiorite, I-type magmatic enclaves, Southern Sinai
