GEOCHEMISTRY OF SHANDERMAN ECLOGITES; CONSTRAINS ON NATURE OF PALEOTETHYS OCEANIC CRUST

Shanderman eclogites are exposed at west of Shanderman town, Talesh Mountains in the north of Iran. Shanderman eclogites have experienced blueschist facies condition on their prograde P-T path. Some hydrous phases such as glaucophane, zoisite and paragonite were stable at the peak of metamorphism. Amphibolite and Greenschist related minerals are formed during exhumation and subsequent fluid influx. Protolith of these rocks had basaltic composition. Geochemical studies indicate that most of the samples have tholeiitic features. Mg# versus Cr and Ni show that the original magma experienced olivine and clinopyroxene fractionation. Spider patterns show more fractionation of olivine compared to clinopyroxene. Behavior of relatively compatible trace elements versus major oxides show that major oxides had no significant (except for Na2O and to some extent FeO) variation during alteration and subsequent metamorphism. Based on REE, eclogite of the Shanderman can be divided into two groups. The first group shows PREE= 31.1 ppm and (La/Lu)N=0.6. The second group have PREE= 139.2 ppm and (La/Lu)N=2.3. Chondrite REE normalized patterns show that they are comparable with N-MORB and E-MORB. This indicate that either Shanderman eclogites parental magma source was not homogenous or it experienced melting with different degrees, indicating a change from low spreading to fast spreading oceanic crust.