부산대학교 도서관

Concerning their provenance and age, the nappes of the Uppermost Unit of Crete are counted among the most enigmatic constituents of the Eastern Mediterranean. U–Pb dating of zircons separated from metavolcanic rocks of the Preveli nappe exposed near Lefkogia yielded Triassic emplacement ages at 237.3 ± 1.8, 241.5 ± 1.2 and 242.1 ± 1.2 Ma. U–Pb grandite dating of subvolcanic barren skarn of this area yielded the same age at 239.3 ± 2.3 Ma. The skarn is dominated by hydrous phases (ferri-actinolite, hydro-grandite, epidote), which developed at T = 400–450 °C in a marine extensional setting due to fluid-assisted metasomatic reactions between chert-bearing limestone and igneous veins. The fluids and their composition played a significant role for the complex oscillatory zoning of the grandite, which largely results from antithetic variations in Fe3+ and Al. The new U–Pb ages suggest that—similar to deep-seated skarns—U–Pb grandite dating of shallow-seated skarns allows dating the complementary record of hydrothermal activity related to the causative melt. Although the development of skarn is regarded as a short-lived process on geological time scales, the skarn formation of the Preveli nappe lasted for more than 20 m.y. as is indicated by additional U–Pb grandite ages obtained from skarn exposed near Kerames (232.7 ± 1.5 Ma) and near Gerakari (218.0 ± 3.5 Ma). The new ages and published data suggest the Uppermost Unit of Crete to be derived either from the peri-Rhodope domain of the Internal Hellenides or from the Pontides of northern Turkey. [ABSTRACT FROM AUTHOR]