High-K volcanism in the Afyon region, western Turkey: from Si-oversaturated to Si-undersaturated volcanism

Volcanic rocks of the Afyon province (eastern part of western Anatolia) make up a multistage potassic and ultrapotassic alkaline series dated from 14 to 12 Ma. The early-stage Si-oversaturated volcanic rocks around the Afyon city and further southward are trachyandesitic volcanic activity (14.23 ± 0.09 Ma). Late-stage Si-undersaturated volcanism in the southernmost part of the Afyon volcanic province took place in three episodes inferred from their stratigraphic relationships and ages. Melilite– leucitites (11.50 ± 0.03 Ma), spotted rachyandesites, tephryphonolites and lamproites (11.91 ± 0.13 Ma) formed in the first episode; trachyandesites in the second episode and finally phonotephrites, phonolite, basaltic trachyandesites and nosean-bearing trachyandesites during the last episode. The parameter Q [normative q-(ne + lc + kls + ol)] of western Anatolia volcanism clearly decreased southward with time becoming zero in the time interval 10–15 Ma. The magmatism experienced a sudden change in the extent of Si saturation after 14 Ma, during late-stage volcanic activity of Afyon volcanic province at around 12 Ma, though there was some coexistence of Si-oversaturated and Si-undersaturated magmas during the whole life of Afyon volcanic province

Neogene Uplift and Magmatism of Anatolia: Insights from Drainage Analysis and Basaltic Geochemistry

It is generally agreed that mantle dynamics have played a significant role in generating and maintaining the elevated topography of Anatolia during Neogene times. However, there is much debate about the relative importance of subduction zone and asthenospheric processes. Key issues concern onset and cause of regional uplift, thickness of the lithospheric plate, and the presence or absence of temperature and/or compositional anomalies within the convecting mantle. Here, we tackle these interlinked issues by analyzing and modeling two disparate suites of observations. First, a drainage inventory of 1,844 longitudinal river profiles is assembled. This geomorphic database is inverted to calculate the variation of Neogene regional uplift through time and space by minimizing the misfit between observed and calculated river profiles subject to independent calibration. Our results suggest that regional uplift commenced in the east at 20 Ma and propagated westward. Secondly, we have assembled a database of geochemical analyses of basaltic rocks. Two different approaches have been used to quantitatively model this database with a view to determining the depth and degree of asthenospheric melting across Anatolia. Our results suggest that melting occurs at depths as shallow as 60 km in the presence of mantle potential temperatures as high as 1400°C. There is evidence that potential temperatures are higher in the east, consistent with the pattern of sub-plate shear wave velocity anomalies. Our combined results are consistent with isostatic and admittance analyses and suggest that elevated asthenospheric temperatures beneath thinned Anatolian lithosphere have played a first order role in generating and maintaining regional dynamic topography and basaltic magmatism

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