Hüseyin Yılmaz

Two-Stage Felsic Volcanism in the Western Part of the Southeastern Anatolian Orogen: Petrologic and Geodynamic Implications

We describe the petrogenesis of three phases of Late Oligocene to Middle Miocene felsic volcanism that occurred in the western part of the southeastern Anatolian orogen. All units are calcalkaline. The S-type character of these volcanic rocks is supported by their peraluminous natures (A/CNK 1.11-3.14) and high (up to 9.89%) normative corundum contents. Elevated Rb/Sr ratios and low MgO and Fe2O3total of the first phase suggest that it might represent melts lacking entrained Fe-Mg-rich crystals, and that the magma developed by muscovite-dehydration melting. Relatively lower Rb/Sr ratios and higher Ba, Sr and Eu concentrations, and high zircon-saturation temperatures of the last two phases, indicate that these melts formed by water-saturated melting. The felsic volcanism of Southeast Anatolia was initiated during continental collision as a result of convergence between the Eurasian and Arabian plates, and occurred during both collisional and post-collisional periods. During the former, volcanism (the first phase) occurred by anatexis of the muscovite-bearing Pütürge metamorphic rocks as a result of imbricate crustal thickening during the Late Oligocene-Early Miocene. In the Middle Miocene, continental exhumation and lithospheric fracturing caused partial fusion of the mantle beneath the Anatolian crust. Emplacement of hot, mantle-derived mafic melts in Anatolian lower crustal levels caused heating that led to partial melting, yielding felsic magmas of the second stage of volcanism (the last two phases).

Kinematics of the East Anatolian Fault Zone between Turkoglu (Kahramanmaras) and Celikhan (Adiyaman), eastern Turkey

In this study we determined the stress regime acting along the East Anatolian Fault Zone between Turkoglu (Kahramanmaras) and Celikhan (Adiyaman), from the Neocene to present-day, based on the inversion of striations measured on faults and on the focal mechanisms of earthquakes having magnitudes greater than 5.0. The inversions yield a strike-slip stress regime with a reverse component (i.e., transpression) operative in the Neocene to present with a consistent N-to NW-trending σ1 axis 156 ± 11° and an E- to NE-trending σ3 axis, 67 ± 9°σ3, producing left-lateral motion along the East Anatolian Fault Zone. The inversions of focal mechanisms yield a strike-slip stress deviator characterized by an approximately N-S (N89°W)-trending σ1 and an approximately E-W (N89°E)-trending σ3 axis. Both the kinematic analysis and structural observations indicate that the stress regime operating in the study area has had a transpressional character, giving rise to the Mio-Pliocene compressive structures (reverse faults, thrusts and folds) observed in the study area. Field observations allow estimation of a Pliocene age for the strike-slip East Anatolian Fault Zone.

The Nature of the Crustal Structure of the Eastern Anatolian Plateau, Turkey

The Eastern Anatolian Plateau (EAP) of Turkey, with an elevation ranging from 1700 to 2000 m, is located between the Eastern Pontide Arc to the north and the Arabian Platform to the south. In this region, pre-Maastrichtian tectonic units representing the crust crop out in only a few localities. As they are covered by Maastrichtian-Quaternary rock units, it is difficult to study the nature and mutual relationships of these pre-Maastrichtian tectonic units. The palaeotectonic units of the EAP comprise two different levels in the present study: (1) The lower level consists of platform-type carbonates and their metamorphic equivalents. These units may represent the Taurus Platform and its metamorphic equivalents. (2) The upper level consists of an ophiolitic-mélange prism which is made up mainly of oceanic crust; the prism comprises a complex of ophiolite, ophiolitic mélange, and fore-arc deposits. This upper unit represents a subduction-accretion prism and may have originated partly from the North Anatolian Suture to the north, and partly from the South-eastern Anatolian Suture to the south. Continental crustal rocks were thrust over by the ophiolitic mélange prism; thus outcrops of them are scarce in the region as they are exposed in tectonic windows through the ophiolitic thrust sheets. The pre-Maastrichtian tectonic units of the EAP are blanketed by Maastrichtian to Quaternary volcanic and sedimentary rock units; these sequences include successive transgressive and regressive intervals and overlie the palaeotectonic units along a pronounced unconformity. Olistostromal units are abundant in the Eocene sedimentary units and were derived from the ophiolites and ophiolitic mélange. The Maastrichtian-Quaternary cover is made up of collisional and post-collisional deposits across the whole region. Although the EAP has been experiencing considerable N-S compression, it has not been affected by significant crustal thickening because of the strike-slip tectonic regime that is dominant in the region.

Preliminary seismic microzonation of Sivas city (Turkey) using microtremor and refraction microtremor (ReMi) measurements

Sivas city, located in the inner east part of Anatolia (Turkey), is far from seismic sources. However, the city is under risk owing to strong earthquakes occurring around the area, and different soil conditions that can produce variation in the ground motion amplification. Microzonation of cities provides a basis for site-specific hazard analysis in urban settlements. In particular, seismic microzonation can be achieved by means of detailed seismic assessment of the area, including earthquake recordings and geological studies. In this paper, we propose a preliminary microzonation map for the city of Sivas, based on the variation in the dominant periods of the sediments covering the area. The periods are retrieved from microtremor measurements conducted at 114 sites, using the horizontal-to-vertical spectral ratio technique. The results of microtremor analysis were compared with those obtained from refraction microtremor measurements at two profiles crossing the studied area. According to the classification of dominant periods, Sivas area can be divided into four zones, probably prone to different levels of seismic hazard. However, specific studies including analysis of weak earthquakes are required in the future to validate our microzonation map.

Plio-Quaternary stress regime in Eşen Çay Basin, SW Turkey

Abstract The Plio-Quaternary Eşen Çay Basin is situated at the junction of Hellenic and Cyprus arcs in southwestern Turkey. The basin is important for understanding the tectonic evolution of the region in relation to the Hellenic and Cyprus arcs. Fault data from unconsolidated Pliocene and Quaternary deposits, as well as from pre-Pliocene lithologies, are analysed in order to reconstruct the evolution of the stress field evolution from Pliocene onwards. Inversion of measured fault slip vector data identifies two main stress states: extensional and strike-slip. Both states are characterized by a NE–SW-trending minimum horizontal stress axis (σHmin=σ3). The mean R value is 0.67, indicating a triaxial state of stress. The inversion also indicates the existence of extensional and strike-slip faulting characterized by a NW–SE-trending σ3 axis. This indicates a change in the direction of the minimum horizontal stress axis (σ3) from a NW–SE-trending σ3 that dominated prior to Quaternary to a NE–SW-trending σ3 that dominated during Quaternary up to actual time.

Fluid inclusion and LA-ICP-MS data on mineralising fluids of the Bizmisen Iron Deposit (Erzincan, Central Anatolia), Turkey

Current European manufacturing relies heavily on imports from China for unprocessed rare earth elements (REEs) and rare earth oxides (REOs). It has been suggested that the EU holds viable reserves of REEs that, with adequate research, could satisfy 10% of EU demand, by the recycling of mine waste from bauxite production (red muds) alone (Deady 2014). Focus has been turned to the potential for similar South China type laterite deposits being exploited in the EU, but limited exploration and understanding of EU laterite formations currently makes them unattractive to investment (Humphries 2013). Following early work by Bernard-Griffiths (BernardGriffiths 1996) into the REE content of the Cretaceous Serra deMonchiqueNepheline-Syenite intrusion, this project examines the clay mineralogy and geochemistry of a selection of pedogenic profiles, logging their variations in mineralogy, bulk chemistry and specific REE content and comparing them to currently producing regions in Southern China. Investigation is under way using a five stage sequential leach-ICP-MS method to identify REE hosting minerals and mineralogical hosting phases, supported byXRDanalysis ofmineralogy and clay structures. Initial results indicate similarities in clay hosted REE distributions through laterite profiles to other researched formations in Madagascar (Berger 2014) and China (Zhou 2013), where specific organic rich (acidic) soils and biogenic profiles of tropical (rainforest) environments were presented as a key factor for REE mobilisation during pedogenesis. Serra de Monchique has a unique climate, with similar seasonal rainfall and cycling, but is not a rainforest, nor in a tropical region. It is therefore hypothesised that classic REE distribution models may also be applied to non-classic environments for this deposit type, supporting the hypothesis of Herrington (Herrington 2007) that China-type REE hosting ionadsorption clay profiles could exist across Europe in novel and previously unresearched environments.