Low-temperature hydrothermal alteration of natural metamict zircons from the Eastern Desert, Egypt
Low-temperature hydrothermal alteration of natural metamict zircons from the Eastern Desert, Egypt
Mineralogical Magazine (June 2003) 67 (3): 485-508
- Africa
- age
- apatite
- crystal form
- dates
- Eastern Desert
- Egypt
- electron probe data
- fission tracks
- hydrothermal alteration
- infrared spectra
- ion probe data
- K/Ar
- low temperature
- mass spectra
- metals
- metamict minerals
- metamictization
- metasomatism
- nesosilicates
- North Africa
- orthosilicates
- phosphates
- Raman spectra
- rare earths
- SHRIMP data
- silicates
- spectra
- temperature
- U/Pb
- zircon
- zircon group
- zoning
Crystals of metamict zircon from a 619 + or - 17 m.y. post-tectonic granite in the S of the Eastern Desert show simple oscillatory growth zones with metamictization-induced fractures which provided pathways for fluid infiltration. Electron and ion microprobe analyses reveal areas rich in Th and U that are also heavily enriched in Ca, Al, Fe, Mn, LREE and water, but have lost Zr, Si and radiogenic Pb. These chemical changes are due to an intensive reaction with a low-T (120-200 degrees C) aqueous solution. A threshold degree of metamictization was necessary for the zircons to undergo hydrothermal alteration; at that point, aqueous domains start to form percolating clusters where bulk chemical diffusion is believed to increase dramatically. The time of this hydrothermal alteration (U-Pb SHRIMP 17 (super +6.9) (sub -4.8) m.y.) agrees with that of the main rifting event of the Red Sea and widespread low-T mineralizations along the Red Sea coast.
