Abstract | Full Paper | PDF Reappraisal of Magmatic Origin for Euhedral Analcimes in Volcanic Rocks Roghieh Akbar Ashrafi (Presenter) Geological Survey of Iran (GSI), Meraj St., Azadi Sq., Tehran, Iran Tell: +98 21 6459281 Email: Rashrafi@khayam.ut.ac.ir Jamshid Hassanzadeh, Department of Geology, University of Tehran, PO Box 14155-6455, Phone: 61112985, Fax: +98 21 6491623 Email: jamshidh@khayam.ut.ac.ir Ali Mohammad Ghazi Georgia Department of Natural Resources, 2 Martin Luther King Jr., Suite 1154 Atlanta, GA 30334 Email: geoamg@langate.gsu.edu Abstract Analcime (NaAlSi2O6.H2O) occurs in various modes including hydrothermal, replacement, metamorphic and diagenetic. For the genesis of euhedral analcimes that occur as micro- to mega-phenocrysts in silica-undersaturated lavas, two different views exist: magmatic and hydrothermal replacement of leucites. Experimental data indicate that analcime is not stable in high T and low P. Other data supporting subsolidus origin of euhedral analcime include oxygen and hydrogen isotopes. Such data on lavas from Alberta indicate that analcimes have been equilibrated with meteoric water. Radiometric analcime ages younger than the host lavas for a tephrite-phonolite suite in Iran are presented as an independent argument against primary igneous view.