ERKEN MİYOSEN ALAÇAMDAĞ (DURSUNBEY-BALIKESİR) MAGMATİK KOMPLEKSİNİN JEOLOJİSİ VE BATI ANADOLU GENLEŞME TEKTONİĞİNDEKİ KONUMU

Batı Anadolu'da genleşme rejimi, Geç Oligosen - Erken Miyosen'den günümüze kadar metamorfik çekirdek kompleksleri, KD/B-D doğrultulu tortul havzaların gelişimine ve magmatik kayaçların yerleşimine neden olmuştur. Erken Miyosen'de etkin olduğu bilinen Simav metamorfik çekirdek kompleksinin batı kenarında yer alan Alaçamdağ magmatik kompleksi, gerilme tektoniğini aydınlatacak veriler içerir. Kompleks, Erken Miyosen yaşlı granitik sokulumlar ile andezitten riyolite kadar bileşimdeki volkanik kayaçlardan oluşur. Menderes Masifi ve Izmir- Ankara Zonu kayaçlarını kesen granitik sokulumlar, litolojik ve dokusal özelliklerine göre Musalar ve Alaçam gra- nitleri olmak üzere iki farklı fasiyese ayrılmaktadır. Musalar graniti tipik holokristalin tanesel dokuya sahiptir. Alaçam graniti ise K-feldispat megakristalleri ile belirlenen porfiritik doku ile temsil edilir. Her iki granitik birim yer yer makaslama zonları boyunca milonitlere dönüşmüşlerdir. Volkanik kayaçlar ise Sağırlar volkanik birimi ve fel- sik volkanik kayaçlar olmak üzere iki birim olarak tanımlanmıştır. Sağırlar volkanik birimi, andezit ve dasit bileşim- li intrüzyonlar, domlar, lav akıntıları, dayklar ve volkanojenik tortul kayaçlardan oluşmaktadır. Sağırlar volkanik bi- rimi üzerine uyumsuz olarak gelen felsik volkanik kayaçlar ise ignimbrit, dasit ve riyolitlerden meydana gelir. Bu kayaçlar, alüvyal-gölsel tortul kayaçlarla yanal ve düşey girik dokanak ilişkileri gösterirler. Gerek sünümlü defor- masyon gösteren granitlerin varlığı gerekse tortul/volkanik istifler içerisinde yer alan havza içi açısal uyumsuzluk- lar ile sin-sedimanter deformasyon yapıları bölgenin Erken Miyosen'de etkin olarak genleşmeli tektonik rejime maruz kaldığını göstermektedir

Peperites associated with ultrapotassic lava flows, western Turkey

Peperites are recognised as a mixture of magma and sediment, which is generated by an interaction of partly emergent domes and lava flows with unconsolidated sediments. They commonly occur in back-arc and rift settings where progressive subsidence of basins occurs contemporaneously with magmatism. This presented research deals with peperites formed along the ephemeral lacustrine sediments and the overlying smallvolume ultrapotassic lava flows in western Turkey. Ultrapotassic rocks occur as domes, dykes and lava flows and include peperitic basal contact zones. The peperitic contact zone with lava flows is defined by up-to-a metre thick layer of magma and sediment mixture. Magma clasts display fluidal and blocky morphologies with variable sizes ranging from few mm to a few decimetres. Fluidal clasts predominate with respect to blocky varieties. They were locally in-situ fragmented into blocky clasts that form a typical jig-saw texture. Blocky clasts are variably shaped and include digitate margins. Tapered clasts also occur along foliation planes of lava flows. Peperitic textures related to ultrapotassic lava flows closely resemble those generated by olivine basalt flows. Clast morphologies suggest a progressive fragmentation due to decreasing temperature along with increasing viscosity during peperite formation. Sediment fluidisation and low viscosity are presumed to be major controlling factors for fluidal clast generation and non-explosive emplacement. Common occurrences of peperite-bearing volcanic edifices in western Turkey suggest that magmatism developed within a progressively subsiding basin, probably corresponding to rift or back-arc extensional/transtensional environment. © SGEM2012 All Rights Reserved by the International Multidisciplinary Scientific GeoConference SGEM Published by STEF92 Technology Ltd

An extensional and transtensional origin of elongated magmatic domes and localised transfer faults in the northern Menderes metamorphic core complex, western Turkey

The northern Menderes metamorphic core complex has complex exhumation history and is one of the key localities to investigate the spatial and temporal relationships of extensional and compressional structures. Detachment faults and syn-extensional plutons are linked to a series of antiforms and synforms and the denudation of the northern Menderes Massif occurred in three stages. The first stage is related to the development of detachment faults under the consistent NE–SW-directed extension. The second stage is represented by a series of elongated magmatic domes that were oriented parallel, oblique and perpendicular to the regional extension direction. Emplacement of these asymmetrical magmatic domes appears to have been controlled by heterogeneous extension and post-dates the extensional Simav detachment fault. On the third stage, progressive heterogeneous extension that led to updoming of plutons has been finally accommodated by a localised and short-lived transfer zone, which was described as the Gerni shear zone for the first time in this study. The transfer zone is formed by a NE-striking, dextral ductile/brittle shear zone that accommodated the propagation of folds, conjugated strike-slip faults and normal- and oblique-slip faults. Mylonites associated with the transfer zone are related to the localisation of strain along the thermally weakened strike-slip fault systems by short-lived intrusions rather than to the development of regional-scale detachment faults. These structures are consistent with a transtensional simple shear model, which properly explains the evolution of extensional and compressional structures exposed in the northern Menderes core complex. Structural setting of the Eğrigöz region is somewhat similar to that of the NE-trending gneiss domes in the northern Menderes Massif and updoming of magma during late stages of detachment faulting appears to have played an important role in the exhumation of lower and upper plate rocks