Browsing by Author "Mutlu, Halim"

Now showing 1 - 3 of 3

Kuzeydoğu Anadolu Jeotermal Sistemlerin Hidrojeokimyasal ve İzotopik Yöntemler ile Araştırılması
(2016) Karakuş, Hüseyin; Aydın, Harun; Mutlu, Halim
Post-Earthquake Anomalies in He-Co2 Isotope and Relative Abundance Systematics of Thermal Waters: the Case of the 2011 Van Earthquake, Eastern Anatolia, Turkey
(Elsevier, 2015) Aydin, Harun; Hilton, David R.; Gulec, Nilgun; Mutlu, Halim
We report the helium and carbon isotope (He-3/He-4, delta C-13) and relative abundance (CO2/He-3) characteristics of hydrothermal gases from eastern Anatolia sampled similar to 1 month after the October 23, 2011 Van earthquake (Mw: 7.2, focal depth: 19 km). Seven sites were sampled which comprise three localities along the Caldiran Fault Zone, at a distance of 58-66 km to the epicenter (Group I), two localities north of the Caldiran Fault, about 90-113 km from the epicenter (Group II), and two localities in the vicinity of the historically-active Nemrut Caldera at a distance of 110-126 km from the epicenter (Group III). All sites were previously sampled for their He-CO2 systematics in 2009 (Mutlu et al., 2012) facilitating direct comparison with the post-earthquake dataset. The post-earthquake values cover a wide range of He-3/He-4, delta C-13 and CO2/He-3 ratios, from 0.84 to 6.37 RA (where RA = air He-3/He-4), -5.30 to + 0.49% (vs. VPDB), and 4.9 x 10(10) to 6.85 x 10(13), respectively. Group I samples show a consistent post-earthquake increase in He-3/He-4 whereas both Group II localities decreased in He-3/He-4. No change was recorded for the two Group III localities. He isotope variations are consistentwith simple changes in the proportions of mantle and crustal volatiles, with all Group I sites showing an increase in the mantle He contribution. We hypothesize that the enhanced mantle He signal is derived from asthenospheric melts intruded into the crust, with seismic perturbations responsible for bubble formation and growth leading to overpressure and gas loss. The strike-slip Caldiran Fault Zone provides the permeable pathway for the liberated volatiles to reach hydrothermal systems at shallow levels of the crust and the surface. Release of crustal He dominates the He mass balance of Group II samples as locations are further from the earthquake epicenter. Group III samples are even further away from the earthquake and show no perturbations in He isotopes. Whereas binary mixing dominates the He isotope systematics, CO2 shows additional effects involving the hydrothermal system. Consequently, changes in the balance between mantle and crustal CO2 are masked and more difficult to discern. The results emphasize the sensitivity of He isotopes to seismic perturbations in the crust and illustrate how location of sampling sites - on permeable segments of faults - and distance from seismic events influence resulting changes involving gas chemistry. (C) 2015 Elsevier B.V. All rights reserved.
Spatial Variations in Gas and Stable Isotope Compositions of Thermal Fluids Around Lake Van: Implications for Crust-Mantle Dynamics in Eastern Turkey
(Elsevier, 2012) Mutlu, Halim; Gulec, Nilgun; Hilton, David R.; Aydin, Harun; Halldorsson, Saemundur A.
We investigate the helium (He-3/He-4) and carbon (delta C-13) isotope compositions and relative abundance ratios (CO2/He-3) of gas samples together with the stable isotope compositions of dissolved carbon and sulfur and the oxygen and hydrogen isotopic compositions of the associated water phase from a number of geothermal fields located around Lake Van in eastern Anatolia, Turkey. The mantle-derived helium component, which is likely transferred to the crust beneath eastern Turkey by recent magmatism, is found to constitute up to 96% (e.g. Nemrut Caldera) of the total He content in fluids. As regards the spatial distribution of He, samples collected from areas of Pliocene-Quaternary volcanics are characterized by a wide and generally higher range of R/R-A ratios (0.93 to 7.76 R-A) compared to those of non-volcanic regions ((1.85 to 1.0 R-A). CO2/He-3 ratios vary over a wide range (2.4 x 10(5)-3.8 x 10(13)) but are mostly higher than that of the nominal upper mantle (similar to 2 x 10(9)). Oxygen-hydrogen isotope values of the waters are conformable with the Global Meteoric Water Line and indicate a local meteoric origin. Sulfate in waters is most probably derived from dissolution of marine carbonates and terrestrial evaporite units. Temperatures calculated by SO4-H2O isotope geothermometry lie between 40 and 199 degrees C, and are in poor agreement with reservoir temperatures estimated from silica geothermometers. Discordant temperatures may be due to either the relatively slow rate of isotopic equilibrium between water and sulfate or mixing of geothermal water with sulfate-bearing shallow waters which may modify the delta O-18 value. The delta C-13 (CO2) values of gas samples are consistently lower than those of their water counterparts, consistent with loss of CO2 from waters by degassing. Mixing between mantle and various crustal C-sources appears to be the main control on the C-isotope composition. The principal origin of CO2 in all samples is crustal lithologies, mainly limestone (similar to 85 to 98% of the total carbon inventory): thus, the crustal carbon flux is at least 10 times that from the mantle. There is a broad correlation between high He-3/He-4 values and thinner crust in the western part of the Lake Van region, where several historically-active volcanoes are located. This observation indicates that localized volcanic and magmatic activity exerts the primary control on the balance between mantle and crustally-derived volatiles in the region. (C) 2012 Elsevier B.V. All rights reserved.