Paper No. 1
Presentation Time: 9:00 AM-6:00 PM
GEOCHEMISTRY AND PETROGENESIS OF PLAGIOGRANITES IN THE NEYRIZ OPHIOLITIC SEQUENCE, IRAN: CONSTRAINTS ON THEIR ORIGINS
Plagiogranite intrusives are found within gabbroic section of the Neyriz ophiolitic sequence which is located in southeast of Shiraz, Iran. Petrographically, the plagiogranite consists of tonalite and trondhjemite and keeps a sharp contact with the surrounding gabbro. All studied samples show well-preserved and distinctive hypidiomorphic inequigranular and miccrogrphic textures within which plagioclase, quartz, amphibole, pyroxene, sphene and zircon make the major minerals with magnetite as minor mineral. In many samples, epidote and chlorite are identified as secondary minerals. Field studies and microscopic analysis of plagiogranite intrusives suggest that these rocks have been altered by a low grade metamorphism (greenschist facies) due to hydrothermal alteration. The geochemical interpretation suggests a sub-alkaline type (calc-alkaline series) and metaluminous magma as the original magma for these intrusives. Typologically, the plagiogranite intrusives have the characteristics of the oceanic ridge granite (ORG) identical to I- type granites. Chonderite normalized REE patterns of Neyriz plagiogranites show a depletion in LREEs along with flat HREE patterns. The results of the geochemical studies in the context of the tectonic development of the Neyriz ophiolite indicate that these plagiogranites were formed in a suprasubduction zone environment and by partial melting of mafic rocks such as gabbro which in turn were formed by the anatexises of a previously depleted harzburgitic mantle.