Rhyolite–dacite–trachyandesite association: a Mössbauer spectroscopy study

Abstract

Three volcanic dykes, rhyolite, dacite and trachyandesite cutting a radioactive granite, located between Latitudes 22° 47′ 396″–22° 47′ 884″ N and Longitudes 31° 54′ 883″–31° 54′ 894″ E in the south Western Desert of Egypt were sampled and analyzed by X-ray diffraction, 57Fe Mossbauer spectroscopy and chemical method. They are consisted of feldspar and quartz together with some paramagnetic minerals including aegirine plus minor riebeckite in the rhyolite; aegirine plus some riebeckite in the dacite; and riebeckite plus trace aegirine in the trachyandesite, respectively. The bulk content of iron in each dyke has characteristic ferric-quadrupole splitting and oxidation values: 0.29 millimeters per second (mm/s) and 100% for rhyolite; 0.31 mm/s and 82% for dacite; and 0.35 mm/s and 0.69% for trachyandesite. Variations in the quadrupole splitting have been attributed to changes from the local crystal chemistry, while the oxidation variations are source-related.