Paper Information

Journal:   GEOSCIENCES   SPRING 2016 , Volume 25 , Number 99; Page(s) 85 To 94.
 
Paper: 

DETERMINING TECTONOMAGMATIC ENVIRONMENT OF THE VOLCANIC ROCKS IN NORTHEAST OF THE GAVKHUNI PLAYA LAKE USING GEOCHEMICAL DATA

 
 
Author(s):  ABBASI GH., EBRAHIMI M.*, SHARIFI M., SHIRDASHTZADEH N., AHMADIAN J.
 
* DEPARTMENT OF GEOLOGY, FACULTY OF SCIENCES, UNIVERSITY OF ZANJAN, ZANJAN, IRAN
 
Abstract: 

The studied volcanic rocks to the northeast of the Gavkhuni playa lake are composed of rhyolite, trachydacite, trachyandesite and pyroclastic rocks including lithic tuff and volcanic breccia. Rhyolitic rocks have flow structure and hyalophyric texture with glassy to cryptocrystalline matrix in which quartz and feldspar crystal are present. The dominant texture in trachydacitic and trachyandesitic rocks in porphyritic texture in which plagioclase and rarely sanidine phynocrysts are set in a glassy to microcrystalline groundmass containing feldspar microlites. In trachydacites, quartz is present as small crystals and rarely as microphynocrysts. Plagioclase phynocrysts in trachydacitic and trachyandesitic rocks display sieve-texture. Amphibole and biotite are the mafic minerals of the volcanic rocks and they are partialy, at rims, or completely altered to Fe-Ti oxides. All of the studied rocks are high- K calc-alkaline in nature. According to the geochemical data, the volcanic rocks are depleted in high field strength elements such as Nb, Ti and Ta and enriched in large ion lithophile elements like Cs, K, Ba, Rb and Th which are characteristics of subduction related volcanic rocks. Nb negative anomaly is characteristic of continental rocks and indicates the continental crust involvement in the magmatic processes. The rocks are enriched in Cs, Rb, Ba and Pb indicating mantle metasomatism by fluids released from subducting oceanic lithosphere. Therefore, magma contamination and mantle metasomatism have affected the magma from which the volcanic rocks of the Gavkhuni playa lake have were generated. The calc-alkaline magmatism in the study area was associated with the closure of the Neotethyan Ocean.

 
Keyword(s): VOLCANIC ROCKS, GEOCHEMICAL DATA, TECTONIC SETTING, GAVKHUNI PLAYA LAKE
 
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