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PETROLOGY, MINERALOGY AND
GEOCHEMISTRY OF VOLCANIC ROCKS FROM
SAHAND VOLCANO (NW IRAN)
Pirmohammadi F.*, Amery A.**, Gahangiry A.**, Modjtahedy M.**
*Geology Department, Faculty
of science, Islamic Azad University/Shabestar Branch, Iran
petrofarhad@yahoo.com
**Geology Department,
Faculty of science, Tabriz University, Iran
Abstract
Volcanic
rocks of Sahand occur 40 km south of Tabriz. The volcanic rocks
comprise principally lava flow, domes and volcanic debris flow.
These rocks are basaltic andesite, andesite, dacite and rhyodacite.
Disequilibrium
texture, for example, dusty plagioclase, reaction rims, resorbed
mineral shapes are observed in some of these rocks. Textural and
geochemical characteristics of plagioclase phenocrysts from these
rocks record intrusion of basalt magma into dacitic host magma
chamber. Plagioclase phenocrysts in dacitic rocks are identified by
oscillatory zoning and low An content (An35-An50). These plagioclase
phenocrysts are engulfed, and resorption and dusty zone develops
during intrusion of basalt magma. Content increases toward rim of
these minerals. Chemical and textural zoning patterns that are
preserved in plagioclase phenocrysts provide useful information on
magma evolutions.
Key
word:
Tabriz,
Sahand, plagioclase,
basaltic
andesite,
dacite,
rhyodacite, magma.
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