Paper No. 6
Presentation Time: 2:45 PM
PRESSURE-TEMPERATURE EVOLUTION AND GEOCHEMISTRY OF ECLOGITES IN THE BIGA PENINSULA, NORTHWEST TURKEY
High-P metamorphic rocks are common in the Alpine orogenic belt are principal indicators for the existence of former subduction zones. The Biga Peninsula in northwest Turkey contains high-pressure metabasic eclogite that occur in two localities; as lenses within a 2 km long, 500 m thick quartz-phengite schist slice that is in turn found in the greenschist-facies metasedimentary rocks of the Çamlıca metamorphics, and secondly in two north-south elongated eclogites occur as a tectonic slice between Kazdağ Massif and Çetmi Group. The P-T conditions under which these two exposures of eclogites formed are important to quantify the tectonic processes of subduction, exhumation and emplacement that high-pressure rocks of the Biga Peninsula record. New geochemical data suggest that both protoliths were N-type MORB basalt with high TiO2
O content and Nb/Y ratios. Most eclogite samples have tholeiitic signatures that formed in a volcanic arc setting. ∑REE abundances range from 47.55 to 107.4 ppm. Europium anomalies are slightly variable (Eu/Eu*= 0.9-1.1) and trace element contents are similar to typical MORB based on tectonic discrimination diagrams. All eclogites were probably derived from depleted mantle source, modified by fluids within the subduction zone.
The high-P mineral assemblage in eclogites from the Çamlıca region is omphacite + garnet + glaucophane + phengite + epidote + zoisite + quartz. The inclusions in garnet are glaucophane, quartz, phengite, Ca-amphibole, and rutile. However, the high-P mineral assemblage in eclogites from the Çetmi region is garnet + omphacite + glaucophane + epidote + phengite + quartz. P-T conditions are constrained at 550-675 oC and 16-22 kbar in eclogite from the Çamlıca region and 575-700 oC and 17-24 kbar in eclogite from the Çetmi region. Geochemical data and mineral chemistry indicate that the eclogites in the Biga Peninsula represent oceanic crust processed at significant depths (50-80 km) within the subduction channel and were juxtaposed with greenschist facies as a tectonic slice in the accretionary complex at higher structural levels.