Stable Isotope Evaluation of Geothermal Gases from the Kızıldere and Tekke Hamam Geothermal Fields, Western Anatolia, Turkey
Volatiles transported from the Earth’s interior to the surface through permeable faults provide insights on the gas composition of deep reservoirs, mixing and migration processes, and can also be applied as gas-geothermometer. Here, we present carbon (δ<sup>13</sup>C), hydrogen (δ<sup...
| Main Authors: | , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
MDPI AG
2022-12-01
|
| Series: | Geosciences |
| Subjects: | |
| Online Access: | https://www.mdpi.com/2076-3263/12/12/452 |
| _version_ | 1827638723830874112 |
|---|---|
| author | Selin Süer Thomas Wiersberg Nilgün Güleç Fausto Grassa |
| author_facet | Selin Süer Thomas Wiersberg Nilgün Güleç Fausto Grassa |
| author_sort | Selin Süer |
| collection | DOAJ |
| description | Volatiles transported from the Earth’s interior to the surface through permeable faults provide insights on the gas composition of deep reservoirs, mixing and migration processes, and can also be applied as gas-geothermometer. Here, we present carbon (δ<sup>13</sup>C), hydrogen (δ<sup>2</sup>H) and nitrogen (δ<sup>15</sup>N) isotopic data of CO<sub>2</sub>, CH<sub>4</sub>, and N<sub>2</sub> from gas samples collected from the Kızıldere and Tekke Hamam geothermal fields, located along the eastern segment of the Büyük Menderes Graben, Turkey. The stable isotopic composition of carbon (δ<sup>13</sup>C) ranges from +0.30 to +0.99‰ (PDB) for CO<sub>2</sub> from Kızıldere and is slightly more variable (−0.95 to +1.3‰) in samples from Tekke Hamam. Carbon isotope data in combination with CO<sub>2</sub>/<sup>3</sup>He data reveal that ~97% (Tekke Hamam) to ~99% (Kızıldere) of CO<sub>2</sub> derives from limestone sources, with the residual CO<sub>2</sub> being magmatic in origin with no evidence for CO<sub>2</sub> from organic sources. The slightly higher contribution of limestone-derived CO<sub>2</sub> in Kızıldere, compared to Tekke Hamam can be attributed to the higher temperatures of the Kızıldere reservoir and resulting amplified fluid–limestone interaction, as well as helium depletion during phase separation for Kızıldere samples. In contrast to the carbon isotopic composition of CO<sub>2</sub>, the δ<sup>13</sup>C values of methane from Kızıldere and Tekke Hamam are clearly distinct and vary between −23.6 and −20.8‰ for Kızıldere and −34.4 and −31.7‰ for Tekke Hamam, respectively. The δ<sup>2</sup>H-CH<sub>4</sub> composition is also distinct, measured as −126.7‰ for Kızıldere and −143.3‰ for Tekke Hamam. CO<sub>2</sub>-CH<sub>4</sub> carbon isotope geothermometry calculations based on the isotopic fractionation of δ<sup>13</sup>C between the dominant component CO<sub>2</sub> and the minor component CH<sub>4</sub> reveals temperatures 20–40 °C and 100–160 °C higher than the bottom–hole temperatures measured for Tekke Hamam and Kızıldere, respectively. Based on the CO<sub>2</sub>-CH<sub>4</sub> carbon isotope disequilibrium, unusual high methane concentrations of ~0.3 to 0.4 vol.-% and CH<sub>4</sub>/<sup>3</sup>He-δ<sup>13</sup>C-CH<sub>4</sub> relationships we suggest thermal decomposition of late (Tekke Hamam) to over-mature (Kızıldere) organic matter and, to some extent, also abiogenic processes as principal source of methane. The N<sub>2</sub>/<sup>36</sup>Ar ratios of most samples reveal the existence of a non–atmospheric nitrogen component within the gas mixture issuing from both fields, in addition to a constant contribution of atmospheric derived nitrogen accompanied into the system via the meteoric recharge of the geothermal system. Based on the δ<sup>15</sup>N isotopic ratios (varying between −4.44‰ and 4.54‰), the non–atmospheric component seems to be a mixture of both sedimentary (crustal organic) and mantle nitrogen. The thick Pliocene sedimentary sequence covering the metamorphic basement is the likely major source for the thermogenic content of CH<sub>4</sub> and crustal N<sub>2</sub> gas content in the samples. |
| first_indexed | 2024-03-09T16:26:56Z |
| format | Article |
| id | doaj.art-d02037152d284f1fbf1b14d738ba1546 |
| institution | Directory Open Access Journal |
| issn | 2076-3263 |
| language | English |
| last_indexed | 2024-03-09T16:26:56Z |
| publishDate | 2022-12-01 |
| publisher | MDPI AG |
| record_format | Article |
| series | Geosciences |
| spelling | doaj.art-d02037152d284f1fbf1b14d738ba15462023-11-24T15:07:19ZengMDPI AGGeosciences2076-32632022-12-01121245210.3390/geosciences12120452Stable Isotope Evaluation of Geothermal Gases from the Kızıldere and Tekke Hamam Geothermal Fields, Western Anatolia, TurkeySelin Süer0Thomas Wiersberg1Nilgün Güleç2Fausto Grassa3Central Laboratory, Middle East Technical University, Ankara 06800, TurkeyHelmholtz Centre Potsdam, GFZ German Research Centre for Geosciences, 14473 Potsdam, GermanyGeological Engineering Department, Middle East Technical University, Ankara 06800, TurkeyIstituto Nazionale di Geofisica e Vulcanologia, Sezione di Palermo, 90146 Palermo, ItalyVolatiles transported from the Earth’s interior to the surface through permeable faults provide insights on the gas composition of deep reservoirs, mixing and migration processes, and can also be applied as gas-geothermometer. Here, we present carbon (δ<sup>13</sup>C), hydrogen (δ<sup>2</sup>H) and nitrogen (δ<sup>15</sup>N) isotopic data of CO<sub>2</sub>, CH<sub>4</sub>, and N<sub>2</sub> from gas samples collected from the Kızıldere and Tekke Hamam geothermal fields, located along the eastern segment of the Büyük Menderes Graben, Turkey. The stable isotopic composition of carbon (δ<sup>13</sup>C) ranges from +0.30 to +0.99‰ (PDB) for CO<sub>2</sub> from Kızıldere and is slightly more variable (−0.95 to +1.3‰) in samples from Tekke Hamam. Carbon isotope data in combination with CO<sub>2</sub>/<sup>3</sup>He data reveal that ~97% (Tekke Hamam) to ~99% (Kızıldere) of CO<sub>2</sub> derives from limestone sources, with the residual CO<sub>2</sub> being magmatic in origin with no evidence for CO<sub>2</sub> from organic sources. The slightly higher contribution of limestone-derived CO<sub>2</sub> in Kızıldere, compared to Tekke Hamam can be attributed to the higher temperatures of the Kızıldere reservoir and resulting amplified fluid–limestone interaction, as well as helium depletion during phase separation for Kızıldere samples. In contrast to the carbon isotopic composition of CO<sub>2</sub>, the δ<sup>13</sup>C values of methane from Kızıldere and Tekke Hamam are clearly distinct and vary between −23.6 and −20.8‰ for Kızıldere and −34.4 and −31.7‰ for Tekke Hamam, respectively. The δ<sup>2</sup>H-CH<sub>4</sub> composition is also distinct, measured as −126.7‰ for Kızıldere and −143.3‰ for Tekke Hamam. CO<sub>2</sub>-CH<sub>4</sub> carbon isotope geothermometry calculations based on the isotopic fractionation of δ<sup>13</sup>C between the dominant component CO<sub>2</sub> and the minor component CH<sub>4</sub> reveals temperatures 20–40 °C and 100–160 °C higher than the bottom–hole temperatures measured for Tekke Hamam and Kızıldere, respectively. Based on the CO<sub>2</sub>-CH<sub>4</sub> carbon isotope disequilibrium, unusual high methane concentrations of ~0.3 to 0.4 vol.-% and CH<sub>4</sub>/<sup>3</sup>He-δ<sup>13</sup>C-CH<sub>4</sub> relationships we suggest thermal decomposition of late (Tekke Hamam) to over-mature (Kızıldere) organic matter and, to some extent, also abiogenic processes as principal source of methane. The N<sub>2</sub>/<sup>36</sup>Ar ratios of most samples reveal the existence of a non–atmospheric nitrogen component within the gas mixture issuing from both fields, in addition to a constant contribution of atmospheric derived nitrogen accompanied into the system via the meteoric recharge of the geothermal system. Based on the δ<sup>15</sup>N isotopic ratios (varying between −4.44‰ and 4.54‰), the non–atmospheric component seems to be a mixture of both sedimentary (crustal organic) and mantle nitrogen. The thick Pliocene sedimentary sequence covering the metamorphic basement is the likely major source for the thermogenic content of CH<sub>4</sub> and crustal N<sub>2</sub> gas content in the samples.https://www.mdpi.com/2076-3263/12/12/452Kızıldere geothermal fieldTekke Hamam geothermal fieldsource of gasstable isotopesthermogenic methanenitrogen |
| spellingShingle | Selin Süer Thomas Wiersberg Nilgün Güleç Fausto Grassa Stable Isotope Evaluation of Geothermal Gases from the Kızıldere and Tekke Hamam Geothermal Fields, Western Anatolia, Turkey Geosciences Kızıldere geothermal field Tekke Hamam geothermal field source of gas stable isotopes thermogenic methane nitrogen |
| title | Stable Isotope Evaluation of Geothermal Gases from the Kızıldere and Tekke Hamam Geothermal Fields, Western Anatolia, Turkey |
| title_full | Stable Isotope Evaluation of Geothermal Gases from the Kızıldere and Tekke Hamam Geothermal Fields, Western Anatolia, Turkey |
| title_fullStr | Stable Isotope Evaluation of Geothermal Gases from the Kızıldere and Tekke Hamam Geothermal Fields, Western Anatolia, Turkey |
| title_full_unstemmed | Stable Isotope Evaluation of Geothermal Gases from the Kızıldere and Tekke Hamam Geothermal Fields, Western Anatolia, Turkey |
| title_short | Stable Isotope Evaluation of Geothermal Gases from the Kızıldere and Tekke Hamam Geothermal Fields, Western Anatolia, Turkey |
| title_sort | stable isotope evaluation of geothermal gases from the kizildere and tekke hamam geothermal fields western anatolia turkey |
| topic | Kızıldere geothermal field Tekke Hamam geothermal field source of gas stable isotopes thermogenic methane nitrogen |
| url | https://www.mdpi.com/2076-3263/12/12/452 |
| work_keys_str_mv | AT selinsuer stableisotopeevaluationofgeothermalgasesfromthekızıldereandtekkehamamgeothermalfieldswesternanatoliaturkey AT thomaswiersberg stableisotopeevaluationofgeothermalgasesfromthekızıldereandtekkehamamgeothermalfieldswesternanatoliaturkey AT nilgungulec stableisotopeevaluationofgeothermalgasesfromthekızıldereandtekkehamamgeothermalfieldswesternanatoliaturkey AT faustograssa stableisotopeevaluationofgeothermalgasesfromthekızıldereandtekkehamamgeothermalfieldswesternanatoliaturkey |