PETROGENETIC FEATURES OF LATE NEOPROTEROZOIC ECLOGITES, META-GABBROIC AND GARNET AMPHIBOLITE DIKES IN THE MENDERES MASSIF, WESTERN TURKEY: IMPLICATIONS FOR CADOMIAN CRUSTAL EVOLUTION WITHIN THE PAN-AFRICAN MEGA-CYCLE

A recent study suggests that crystallization ages of the meta-gabbros in Tire and Birgi areas are about ~563 to 558 Ma with problematic rim age of zircons as ~535 Ma in the eclogitised meta-gabbros as interprating the age of the eclogite event. But no more radiogenetic age studies have not been reported from Alasehir, Kiraz and Cine areas yet. The goal of the study is to determine the petrogenetic features of the mafic rocks and propose a geodynamic model for their genesis. The eclogitic meta-gabbros in the Tire and Birgi areas were observed as small-scale (cm-m.). However, well-preserved larger bodies of eclogites and eclogitic gabbros have been reported from Kiraz area. The meta-gabbros in the MM have different (La/Yb)_N, (La/Sm)_N, (Gd/Yb)_N and (Eu/Eu)_N ratios as compared to the meta-gabbros in Birgi, Tire and Cine areas. The high Ti/Zr (>95)) and low Zr/Yb (<40) ratios of the meta-gabbros in the Alasehir area are compatible with melting of a depleted-mantle source. Conversely, low Ti/Zr (<65) and high Zr/Yb (>40) ratios and Nb, Th and Zr contents imply melting of a crustal source assimilated to depleted mantle for the meta-gabbros of the Birgi, Tire and Cine areas. Garnet amphibolites from these areas have high Ti, Y and Zr/Yb ratios and are highly enriched in LREE/HREE with negative (Eu/Eu)_N anomalies. Undated eclogitic rocks in Kiraz area have low Nb, Th and Zr (1.3, 0.2, 75 ppm, respectively) and high Y (28.9 ppm) with low LRE/HREE. The geochemical patterns of the garnet amphibolites show that they may have been metamorphic equivalents of the meta-gabbroic rocks in the Birgi, Tire and Cine areas but may have undergone Alpine HP-LT metamorphism. All meta-gabbroic dikes present back-arc geochemical affinity. We interpret that Andean-type subduction was followed by lithospheric thinning and resulted in opening of the initial stage of the back-arc basin in the peri-Gondwanan crustal part. The meta-gabbroic dikes (~ 563 to 558 Ma) may have been generated during this initial stage of this rifting. N-MORB type gabbroic stocks may then have been generated during the mature stage of continental rifting. This scenario can be correlated well with geodynamic models of the Late Neoproterozoic-Early Cambrian rocks of the other peri-Gondwanan terranes, which were affected by the Cadomian orogeny of the last phase of the Pan-African mega-cycle.