The nature and origin of Oshnavieh plutoniccompelex; application for origin of plutonic rocks in Sanandaj-Sirjan zone

Category Petrology
Group GSI.IR
Location 20th symposium on geosciences
Holding Date 16 April 2008

     The Oshnavieh Plutonic Complex (OPC), Northwestern of Sanandaj-Sirjan zone, consists mainly of three different suites as:
1- The oldest is Post Early Cretaceous — Pre Early Miocene diorite suite, 2- Granitic suite that is comagmatic with the diorite, and 3- Alkaline suite. Diorites have Si02 between 50-62 (wt%) and are characterized by relatively high CaO, Na20, low content of REE, They are homblande and Titanite bearing and Metaluminous and are xenolith Free. Chondrite—normalized (cn) REE patterns are relatively flat [(La/Yb)n =8.03(average)] and show small negative Eu anomalies [(Eu/Eu*) 0.9 (average)]. With these characteristics defenitely they are I type granite. The granite suite have Si02 between 65-69 (wt %) and in compare with diorite are characterized by high K20, Rb, Ba, and they are Peraluminous. The granites have Biotite as main mafic minerals, and Muscovite- Garnet (In Dourbeh granitic mass), also they contain restitic xenoliths. Chondrite — normalized (cn) REE patterns are different in compare with other suites, they enriched in LREE relative to HREE [(La/Yb)n =11.82 (average)] and show bigger negative Eu anomalies than diorites [Eu/Eu*0.5 (average)]. All these characteristics suggest the granite suite is S type. Compared with the diorite and granite suites, the Alkaline intrusive rocks have higher HFSE, REE and high ratios of Ga/Al and Fe/Mg , so, apparently they are A-type granite.