HR: 0800h
AN: V21B-0601    [Abstracts]
TI: Peculiar Feldspar And Quartz Inclusions Within Zircons From Anorthosites, North Eastern Desert, Egypt
AU: * Eliwa, H A
EM: eliwa98@yahoo.com
AF: Minufiya University, EGYPT, Shibien El-Kom,, Minufiya,, 13613 Egypt
AU: Dawoud, M I
AF: Minufiya University, EGYPT, Shibien El-Kom,, Minufiya,, 13613 Egypt
AU: Khalaf, I M
EM: I_khalaf@yahoo.com
AF: Minufiya University, EGYPT, Shibien El-Kom,, Minufiya,, 13613 Egypt
AU: Negendank, J F
AF: Okayama university of Science, 1-1 Ridai-Cho,, Okayama, 700-0005 Japan
AU: Itaya, T
EM: Itaya@rins.ous.ac.jp
AF: GFZ, Potsdam, Berlin, 14473 Germany
AB: Zircons from three anorthosite outcrops along Wadi Dib area, north Eastern Desert of Egypt contain abundant and conspicuous inclusions of quartz, feldspar, amphibole and apatite. These anorthosites, as (50-100m thick) layers, represent the top of mafic-ultramafic intrusions exhibiting rhythmic layering visible by reputation of melanocratic and leucocratic layers. Field and microscopic studies exhibit that these anorthosites were affected by the action of residual magmatic solutions associated with the late stage crystallization of the younger granites, which modified their mineralogical composition. They are composed totally of plagioclase with subordinate amount of clinoenstatite, augite, amphibole, biotite, K-feldspar, and quartz. Accessories are magnetite, ilmenite, apatite and zircon. The abundance and the mode of occurrence of K-feldspar, quartz, and biotite with apatite and zircon among the megacrysts suggest their formation is ascribed to the interaction with the residual solutions. The microprobe data exhibit difference between feldspar and amphiboles contained herein zircons and those as anorthosite mineral constituents. The genetic relationship between zircons and their inclusions suggests later growth of zircons than inclusions and most probably at the final stage of rock modification. Zircons are magmatic and found in the interstitial feldspar and quartz among plagioclase megacrysts in aggregates or as individual grains. The microscopic and SEM images investigation exhibit that most zircons are subhedral to euhedral equant and prismatic crystals. Most zircons have same range of crystal morphologies and internal growth structures with predominance of prism /{100/} and pyramid /{101/} and occasionally prism /{110/} and pyramid /{111/}. No evidences for poly-faceted grains, inherited cores or later overgrowths were detected. CL images distinguished zircons with visible core-rim structures and others with regular and continuous growth zones contained herein various inclusions. The dark CL cores in the core-rim structured zircons are higher in U, Y and sometimes Hf relative to the CL bright rims. Microprobe data and x-ray chemical mapping of various zoned zircons suggest that U and Y with sometimes Hf have a negative correlation to the CL brightness, while Th doesn't exhibit any significant correlation.
DE: 3600 MINERALOGY AND PETROLOGY (replaces
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting