Ophiolites on the Southern Aegean islands Crete, Karpathos and Rhodes: composition, geochronology and position within the ophiolite belts of the Eastern Mediterranean

Abstract

Dismembered ophiolites on the Southern Aegean islands of Crete, Karpathos and Rhodes link the Jurassic ophiolites of the Hellenides (e.g., Pindos, Vourinos) and the Cretaceous ophiolites of the Taurides in southern Turkey (e.g., Antalya). The ophiolites of these islands do not form a continuous belt. There are significant differences in composition and age between the ophiolites of Crete in the west and those of Karpathos and Rhodes in the east. Crete: Peridotite relics in serpentinites are lherzolitic with high concentrations of Al 2O 3 and CaO (mean values of 2.7 and 2.0 wt.%, respectively). Spinels in these rocks are as rich in Al 2O 3 as those in fertile peridotites from orogenic lherzolite massifs. These rocks represent primitive, undepleted mantle material, indicating an origin at a slow-spreading ridge. The Cretan peridotites are intruded by gabbroic dikes ranging in composition from pyroxene gabbros to hornblende diorites and plagiogranites. The dominance of hornblende in these rocks and the geochemical signature indicate a subduction-related origin for these dikes. Hornblendites associated with the peridotites are regarded as metamorphic ferrogabbros, which were probably overprinted in high-temperature shear zones. K–Ar dating of hornblendites yielded ages around 160 Ma (Middle to Late Jurassic), indicating that these ophiolites are a part of the Jurassic ophiolite belt of the Balkan peninsula. Around 20 Ma younger K–Ar ages were derived for the gabbroic dikes within the peridotites. Karpathos and Rhodes: The peridotite relics in serpentinites from Karpathos and Rhodes are very low in Al 2O 3 and CaO and correspond to depleted harzburgites. The ultramafics are intruded by dolerite dikes which are very uniform in composition. The dikes show a trace element signature typical of island arc basalts. Both the depleted nature of the peridotites and the geochemistry of the dikes are typical of supra-subduction zone ophiolites. K–Ar dating of hornblendes from the dolerites yielded an early Late Cretaceous minimum age (around 90 Ma) for the ophiolites of the two islands. Both age and the remarkable similarity in composition and structure to ophiolite occurrences in southern Turkey demonstrate that the ophiolites of Karpathos and Rhodes belong to the Cretaceous ophiolite belt of the Eastern Mediterranean and the Middle East.