Scholarly record

CHARACTERISTICS OF THE ALANYA UNIT METAMORPHITES, ALANYA-ANTALYA, TURKEY

G. Kansun, H. Bas, K. Asan

Abstract

The Alanya unit consists of threeimbricate metamorphic nappes: These are Cambrian - Upper Permian aged The Mahmutlar group (the lower nappe), The Sugozu melange (middle nappe) (Late Cretaceous-Paleocene), and Lower Cambrian - Middle-Upper Triassic aged The Yumrudag group (upper nappe). The pelitic and semipelitic schists of the Alanya unit are shale and wacke in origin. These received material from acidic and probably medium compositional volcanic arc granites and deposited on the active continental margin and probably on the continental magmatic arc. In the Alanya unit the magmatic rocks such as eclogite, amphibolite and greenschists are basaltic in character; glaucophanites are of basaltic and andesitic/dasitic composition. These metamagmatic rocs are associated with a sub-alkaline magmatism of a subduction zone. The greenschists and the glaucop-hanites having intraplate basalt features show sub-alkaline rock characters of continental magmatic arc volcanism developed in the active continental margin. The amphibolites and eclogites reflect the oceanic plate origin in the subduction zone. The eclogites of the Sugozu melange with their very low pyrobe contents (Grpyrobe = 5.32 - 8.77 \%) belong to the “C-type (low temperature) eclogite” group. In these zoned garnets from center towards rim Ca (grossular) content decreases while Mg and Fe contents (pyrobe and almandine) increase. Related to the events During Late Cretaceous subduction and Late Maastrichtian- Paleocene thuristing of the Alanya unit over the Antalya unit the Alanya unit gained its fractured-folted structure, underwent multi-phased metamorp-hism and the nappes developped in the unit. During late Maastrichtian the lithologies of the middle nappe of the Alanya unit underwent eclogite and subsequently epidote blue schist facies metamorphism in the subduction zone. Eclogite facies metamorphism reflects ca. 50 km depth, max. 15,74  0,5 kb pressure and max. 476 C temperature conditions. Blue schist metamorphism reflects ca. 28 km depth, 7 kb pressure and 425-450 C temperature conditions. Following the HP-LT metamorphisms the Alanya unit underwent a progressive amphibolite facies metamorphism during the Paleocene, probably Early Paleocene. This metamorphism is like reactions progressing in the middle nappe from epidote-amphibolites facies to high temperature zones of Abukumatype cordierite-amphibolite facies, in the lower nappe from Abukuma-type green schist facies to high temperature zones of cordierite-amphibolite facies, in the upper nappe from Abukuma-type green schist facies to low temperature zones of cordieriteamphibolite facies. Occurring at 12-25 km depth this progressive metamorphism reflects, in the lower and middle nappes 3,5-6,5 kb pressure, 550-650 C conditions. During or following the nappe emplecemens in the Alanya unit, the whole unit underwent a retrograding metamorphism in a Barrovian-type greenschist facies. Occurring during the Late Paleocene-Early Eocene interval and obscuring the nappe contacts this metamorphism reflects 5-6 kb pressure, 425-450 C temperature conditions.

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