Cüneyt Akal

Quantifying rates of detachment faulting and erosion in the central Menderes Massif (western Turkey) by thermochronology and cosmogenic 10Be

Exhumation of rocks in extensional tectonic settings results from a combination of normal faulting and erosion but the relative contribution of these processes has rarely been quantified. Here we present new low-temperature thermochronological data and the first 10Be-based catchment-wide erosion rates from the Boz Dağ region in the central Menderes Massif, which has experienced NNE–SSW extension since the Miocene. The slip rate of the shallow-dipping Gediz detachment fault, which defines the northern flank of the Boz Dağ block, is 4.3 (+3.0/−1.2) mm a−1, as constrained by zircon (U–Th)/He ages of c. 4–2 Ma in the footwall. Apatite and zircon (U–Th)/He and fission-track ages from the northern flank of the Boz Dağ block yield exhumation rates of 0.6–2 km Ma−1 beneath the Gediz detachment, whereas those on the southern flank are only 0.2–0.6 km Ma−1. Erosion of catchments on the northern and southern flanks proceeds at rates of 80–180 and 330–460 mm ka−1, respectively. This marked contrast is a combined effect of the topographic asymmetry of the Boz Dağ block and differences in rock erodibility. If these erosion rates persisted in the past, rock exhumation on the northern flank occurred predominantly by tectonic denudation, whereas rocks on the southern flank were mainly exhumed by erosion.

Orogenic vs anorogenic lamproites in a single volcanic province: Mediterranean-type lamproites from Turkey

Lamproites are mantle-derived ultrapotassic volcanic rocks, derived from phlogopite-bearing harzburgitic source. The origin of the metasomatism which enriched their mantle source is either an old event with a metasomatic component derived from the convecting mantle, or is a more recent introduction of an already aged metasomatic component. Together with different trace element signatures, this view serves for a general distinction between anorogenic and orogenic lamproites worldwide. In Turkey, lamproitic volcanism resulted from interplay of subduction/collisional and postcollisional/extensional regime since Miocene until Pliocene, in the Western Anatolia-Aegean and Kirka-Afyon-Isparta region. We present new set of Ar-Ar age data together with geochemical data, including Sr, Nd and Pb isotopes, of all Turkish lamproites. Our study revealed the most intriguing geochemical data: although the majority of lamproites have an orogenic affinity, with radiogenic 87Sr/86Sr, 207Pb/204Pb, and unradiogenic 143Nd/144Nd and 206Pb/204Pb, and high LILE/HFSE ratios, the lamproites from the most southern localities (Bucak area) exhibit geochemical features characteristic for anorogenic lamproites, with unradiogenic 87Sr/86Sr, 207Pb/204Pb, and radiogenic 143Nd/144Nd and 206Pb/204Pb, coupled with rather smooth incompatible trace element pattern with low LILE/HFSE ratios and high concentrations of Nb and Ti. The common and coeval occurrence of anorogenic and orogenic lamproites in a single volcanic province suggests that geodynamic distinction of lamproites based only on geochemistry may be questioned.

Radiological mapping in the granodiorite area of Bergama (Pergamon)-Kozak, Turkey

As higher radiation levels are associated with granodiorite area and the maps are more practical to interpret the results of radiological survey, the distributions of the specific activities of 226Ra, 232Th, 40K in soil-granite samples and indoor 222Rn activities throughout the granodiorite area of Bergama (Pergamon) were mapped in detail. Samples from the granites and soils underlying Kozak-Bergama (Pergamon) granodiorite area were collected and analyzed by HPGe gamma spectrometry system, while indoor radon levels in 20 dwellings of rural areas at this area were measured by the alpha track etch integrated method. This paper represents the baseline maps of natural radioactivity levels (226Ra, 232Th, 40K and 222Rn) and corresponding absorbed dose rates from outdoors terrestrial gamma radiation.

Indoor radon measurements in the granodiorite area of Bergama (Pergamon)-Kozak, Turkey

Indoor radon levels in 20 dwellings of rural areas at the Kozak-Bergama (Pergamon) granodiorite area in Turkey were measured by the alpha track etch integrated method. These dwellings were monitored for eight successive months. Results show that the radon levels varied widely in the area ranging from 11±1 to 727±11 Bq m(-3) and the geometric mean was found to be 63 Bq m(-3) with a geometric standard deviation of 2 Bq m(-3). A log-normal distribution of the radon concentration was obtained for the studied area. Estimated annual effective doses due to the indoor radon ranged from 0.27 to 18.34 mSv y(-1) with a mean value of 1.95 mSv y(-1), which is lower than the effective dose values 3-10 mSv given as the range of action levels recommended by International Commission on Radiation Protection. All dosimetric calculations were performed based on the guidance of the UNSCEAR 2000 report.

Kinematics and U-Pb zircon ages of the sole metamorphics of the Marmaris Ophiolite, Lycian Nappes, Southwest Turkey

ABSTRACT In the eastern Mediterranean, the Lycian Nappes are found in the structurally uppermost position in the Anatolide-Tauride belt related to the closure of the Neotethys. In Western Turkey, the Marmaris Ophiolite with the metamorphic sole occupies the uppermost tectonic position in the Lycian belt. The metamorphic sole is represented by discontinuous tectonic slices composed of amphibolites, phyllites, micashists and quartzo-feldspathic micaschists. Zircons from the micashists and quartzo-feldspathic micaschists display dark cores and rims. The cores yield ages between 229 and 175 Ma, inner rims yield ages between 153 and 143 Ma and the outer rims show a concordia age of 96.7 ± 0.79 Ma. In terms of their Th/U ratios, the cores and inner rims indicate igneous origin, whereas the outer rims indicate accretion during metamorphism. By dating of these zircons, the deposition time for the protolith of micaschists and quartzo-feldspathic micaschists could be constrained as the Early Cretaceous. Present-day orientation of the kinematic data from the sole metamorphics and the uppermost part of the Karabörtlen formation clearly suggest a top-to-the NE sense of shear. By taking into account the 25º–30º anticlockwise post-emplacement rotation of Southwest Turkey, it follows that the Lycian Nappes were emplaced eastward onto the Menderes Nappes. This tectonic model disagrees with the previous tectonic models suggesting northward or southward movement of the Lycian Nappes onto Menderes Nappes.

Constraints on Water Reservoir Lifetimes From Catchment‐Wide 10Be Erosion Rates—A Case Study From Western Turkey

The functionality and retention capacity of water reservoirs is generally impaired by upstream erosion and reservoir sedimentation, making a reliable assessment of erosion indispensable to estimate reservoir lifetimes. Widely used river gauging methods may underestimate sediment yield, because they do not record rare, high-magnitude events and may underestimate bedload transport. Hence, reservoir lifetimes calculated from short-term erosion rates should be regarded as maximum values. We propose that erosion rates from cosmogenic 10Be, which commonly integrate over hundreds to thousands of years are useful to complement short-term sediment yield estimates and should be employed to estimate minimum reservoir lifetimes. Here, we present 10Be erosion rates for the drainage basins of six water reservoirs in Western Turkey, which are located in a tectonically active region with easily erodible bedrock. Our 10Be erosion rates for these catchments are high, ranging from ∼170 to ∼1040 t/km2/yr. When linked to reservoir volumes, they yield minimum reservoir lifetimes between 25 ± 5 and 1650 ± 360 years until complete filling, with four reservoirs having minimum lifespans of ≤110 years. In a neighboring region with more resistant bedrock and less tectonic activity, we obtain much lower catchment-wide 10Be erosion rates of ∼33 to ∼95 t/km2/yr, illustrating that differences in lithology and tectonic boundary conditions can cause substantial variations in erosion even at a spatial scale of only ∼50 km. In conclusion, we suggest that both short-term sediment yield estimates and 10Be erosion rates should be employed to predict the lifetimes of reservoirs.