HISTORICAL EVOLUTION OF THE GEOLOGICAL RESEARCHES IN THE MENDERES MASSIF

Indexed In

Volume 142 / 2011

Authors:

O. Özcan DORA

Keywords:

Menderes Massif, Pan-African and Alpine metamorphism, young exhumation

Abstract:

The Pan-African basement of Menderes Massif is made up of homogenous paragneiss and schist units (metaclastic sequence) which are intruded by metagabbros and gneisses derived from different types of granites. The basement is unconformably overlain by Early Palaeozoic metaclastic series consisting of quartzite and metaconglomerate at the lowest level. They show a transition into schists, and the Palaeozoic sequence ends with Permo-Carboniferous black marbles of Göktepe formation. Both basement and Palaeozoic sequence are intruded by Early Triassic leucocratic granites which were converted into orthogneisses by Alpine metamorphism. The Mesozoic series of the Menderes Massif begins with Late Triassic meta-sandstone/metaconglomerate intercalation and continues with Jurassic to Cretaceous dolomites and massive marbles. Platform-type massive marbles with metabauxite lenses and well-preserved rudist fossils at the uppermost levels are conformably overlain by late Campanian - late Maastrichtian reddish pelagic marbles. Flysch-type middle Paleocene metaolistostrome forms the uppermost unit of cover series. The protoliths of clastic sediments of the Pan-African basement consisting of paragneiss and conformably overlying schist units were deposited on a passive continental margin. The zircon ages of the granitoids intersecting this clastic sequence are restricted to a time range between 570 and 520 Ma with an average of about 550 Ma. The polyphase metamorphic evolution of the basement under granulite (583 ±5,7 Ma), eclogite (529,9 ±22 Ma) and Barrowian-type medium-pressure conditions (average 540 Ma) are related with the Pan-African Orogeny. The isotopic data including the ages of detrital zircons (592-3229 Ma) of paragneiss and schist units, the intrusion ages of granitoids and the age of granulite facies metamorphism constrain an age for the deposition of protoliths of metaclastic sequence between 592-580 Ma, Lower Late Neoproterozoic. In Eocene time, Pan-African basement and cover series were affected by Barrowian-type Alpine metamorphism under greenschist, lower amphibolite facies conditions, traditionally called as the 'Main Menderes Metamorphism. However, new HP/LT evidence found in Mesozoic cover series reveals that this metamorphism is more complex than it was considered. It is generally accepted by many researchers that the exhumation of the Menderes Massif as a core complex is related with the extensional tectonic regime. It is assumed that there is a genetic relation between the intrusion of Eðrigöz - Koyunoba granites and the detachment fault in the northern part of the Menderes Massif. Furthermore; to the South of the Massif, it is suggested that the old thrust fault between the Menderes Massif and Lycian Nappes reworked as a detachment fault during the exhumation. The reason of extension in the region is the thermal weakness in the thickened crust made by the magmatism developed after the the collusion of Anatolide-Tauride platforms and the Sakarya continent. The intrusion ages of Eðrigöz and Koyunoba granitoids are 20-21 Ma and the detachment fault was active during 25-19 Ma. In addition, the symmetric core complex formation in the central submassif was carried out in the middle-late Miocene. Pliocene to recent active graben faults intersect the detachment faults.