I-Type magmatism in granitoids from e-ne Tafresh
Subject Areas :
Shiva
Ansari
1
(دانشجوی دکترای گرایش پترولوژی دانشگاه آزاد اسلامی واحد علوم و تحقیقات تهران)
Mohammad Hashem
Emami
2
(دانشیار گروه زمین شناسی دانشگاه آزاد اسلامی واحد اسلامشهر)
Majid
Ghaderi
3
(استادیار گروه زمین شناسی دانشگاه تربیت مدرس)
Khosro
Khosro-Tehrani
4
(استاد گروه زمین شناسی دانشگاه آزاد اسلامی واحد علوم و تحقیقات تهران)
Keywords: Tafresh, Petrography, Geochemistry, Nevis, enclave,
Abstract :
The polyphase Nevis granitoid pluton extends 70 km2, is located in Urmieh-Dokhtar zone, shows variationwhich in terms of emplacement depth is related to epizonal to mesozonal environments [16], and in range ofacidic to basic including tonalite, granodiorite, granite, monzonite, diorite and gabbro. The mentioned pluton isintruded to different units of volcano-sediments (according to the 1:250000 Geological Survey map) of Eocenesequences (E1, E2, E3, E4,E5, E6) and has imposed a contact metamorphism in Eocene [3]. Existance of maficenclaves in the main body could confirm the initial basic-intermediate magma replacement. According to thecoarse granular texture of these basic-intermediate rocks can be said that they have been replaced in crust middledepths (mesozonal) and in later stages, a large size of tonalitic magma intruded to the region shows variation intexture. Part of this tonalitic magma get to higher levels and show porphyry textures. Then they involved inmylonitic textures under tectonic stresses. Stress effects produced subgrain minerals and undulose extinction.The final phase of plutonism was made up leucocratic micro-granite and granophyres, comparing to tonalite theyhave limited volume and they are the most shallow plutonism in the area. Another pervasive process had beenthe effects of heat and fluid (hydrothermal process) caused by successive injections which had differentinfluences on the rocks, and created secondary mineral paragenesis of greenschist facies including epidote,chlorite, calcite, albite, sphene and opaque minerals, represent the geothermal system activities in differentphases and the formation history of polyphase Nevis pluton.Based on field surveys, lithology and geochemical, granitoids are I-type. These rocks are calc alkaline andmetaluminous.