Scientific Quarterly Journal of Geosciences

Scientific Quarterly Journal of Geosciences

Petrologic diversity and K-Ar datings of Shah Kuh pluton (South of Birjand)

Document Type : Original Research Paper

Authors
Daryoush Esmaeily 1
Mohammad Vali Valizadeh 2
Jamshid Hassanzadeh 2
Herve Bellon 3
1 Geology Department, Faculty of Science, Tarbiat Modarres University, Tehran, Iran
2 Geology Department, Faculty of Science. Tehran University, Tehran, Iran
3 IUEM. Universite de Bretagne Occidental, 29285 Brest Cedex, France
Abstract
Shah-Kuh granitic massif (South of Birjand) is mainly composed of monzogranite- granodiorite and syenogranite units which enclose large microgranitic bodies. Small outcrops of greisenized granites, occurred in the eastern part. The massif is cut by dacitic, andesitic, and aplitic dykes and mineralized quartz- tourmaline veins.
    The Presence of magnetite, magmatic allanite, amphibole and the lack of muscovite, aluminosilicates and pegmatitic veins attests to the I-type affiliation of these rocks. The monzogranite- granodiorite unit is distinct from syenogranites by the lack of amphibole, lower X mg of biotites and lower An% of plagioclase in the later.
     Based on thin section studies, four types of microstructures including magmatic, sub magmatic, high temperature subsolidus and low temperature subsolidus (mylonitic) are recognized.
Hydrothermal alteration effects on the pluton can be summarized as:
1-Formation of K-feldspar megacrysts; 2- Alteration of biotite to muscovite (or K-feldspar) + rutile + sulfides; 3- Formation of pale green biotite from magmatic biotite; 4 - Chloritization of biotite; and 5- Complete destruction of biotite and feldspar during greisenization.
     K-Ar dating was performed 13 biotite separates from main rock types. This gives an age of 165 ± 3.1 Ma (middle Jurassic) for the Shah- Kuh granite. With an average age of 168.3 ± 3.17 Ma, the microgranites represent the oldest unit among the dated samples. Monzogranite - grandiorite and syenogranite unites, which have been dated 165.2 ± 3.1 (Ma) and 161.6 + 2.5 (Ma), respectively, are somewhat younger unites. It can be concluded that all of the granitic rock types in the suite, formed in a very short period of time.
Keywords
Granitoid
Petrologic diversity
Radiometric dating
K-Ar
Shah-Kuh
South Birjand
Iran

Subjects

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Scientific Quarterly Journal of Geosciences
Volume 11, 41-42
Autumn & Winter 2002, Vol. 11, No. 41-42
Winter 2001
Pages 2-19