Scientific Quarterly Journal of Geosciences

Scientific Quarterly Journal of Geosciences

Petrology and Petrogenesis of the Gatehdeh subvolcanic dome, Taleghan, Central Alborz, Iran

Document Type : Original Research Paper

Authors
Fereydun Sahabi
Amir Homayoun Saffarzadeh
Geology Department, Faculty of Science, University of Tehran., Tehran, Iran
Abstract
Gatehdeh subvolcanic dome has been intruded to the surface through a faulting network within the pyroclastics of the Karaj Formation (Eocene). The dome - forming rocks are alkali feldspar- microgranite in nature and characterized by fine-grained, aplitic texture and consisting of orthoclase (80- 85 percent), and quartz (10 percent). Phenocrysts of Plagioclase, Celsian, Biotite and Zircon are very few throughout the specimens. The orthoclase content of the rocks has been noticeably increased by formation of brown pigments during metasomatic alterations. Materials such as SiO2 о BaSO4, CaCO3 and Fe2O3 formed in the course of secondary mineralization as a cavity filling cement in the brecciated rocks and fractures. Richness of K2O (12-16 percent) and poorness of CaO, MgO, Na2O and TiO2 (totally less than 0.5 percent) are the most dominant geochemical characteristics of these rocks. However, they cannot be categorized as potassic or ultrapotassic rocks due to lack of minimum requirement of CaO and Na2O.
It is thought at this stage that the Gatehdeh subvolcanic mass was originated from a sialic crust, melted by conjugation of olivine- basaltic magma in the course of crustal melting process.
Keywords
subvolcanic dome, Taleghan, Central Alborz

Subjects

 
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Scientific Quarterly Journal of Geosciences
Volume 6, 21-22
Autumn & Winter 1997, vol. 6, No. 21-22
Winter 1997
Pages 32-39