Türkiye Jeoloji Bülteni

Abstract: Magma-water interaction is defined as one of the most important parameters determining the explosivity of volcanic eruptions. However, accurately quantifying the water content in volcanic products formed during syneruptive / post-eruptive processes remains a significant challenge. This study investigated the thermal expansion and decomposition behavior of obsidian sampled from the Nevşehir Acıgöl Maar, which was subjected to heat treatment without exhibiting perlitic texture development, in order to elucidate the underlying mechanisms and characteristics of the process. The physical and chemical changes that the banded obsidian experienced during its expansion were analyzed using various analytical methods. In this context, FT-IR analysis was used to observe modifications in water components. The mass loss in the sample was quantified using the TG-DTA method, while the textural changes occurring during the obsidian expansion experiment were determined through three-dimensional tomographic imaging technique. The results show that thermal decomposition of volcanic glass involves the releaseof volatiles and both primary and secondary water species across a range of temperatures. This study demonstrates experimentally that hydrous rhyolitic obsidian can generate vesicles that expand at varying rates, particularly inregions where water and volatiles are loosely bound within the glass structure.

Abstract: The southern margin of the Alaşehir Graben is bounded by the Alaşehir Detachment Fault (ADF),comprising ductile-brittle cataclastic rocks within the same extensional regime. This fault surface is exposed over~150 km from Turgutlu to Alaşehir and dips to the north at a low-angle (10°-30°). There are two main interpretations about the termination of tectonic activity on the ADF. The first is that recent movement of the fault ended in the late Miocene, based on the fact that it is cut by Plio-Quaternary high-angle normal faults. The second view suggests that tectonic activity continued until the Plio-Quaternary, based on the exhumation ages obtained from cataclastic rocks.We present measured stratigraphic logs of the Neogene sequence in the hanging wall of the ADF in the Salihli and Alaşehir areas to contribute to this discussion. The depositional evolution of the Alaşehir Graben can be described in three assemblages, including Miocene (Gerentaş, Kaypaktepe and Acıdere Formations), Late Miocene-Late Pliocene(Göbekli, Yenipazar and Erendalı Formations) and Plio-Quaternary sedimentary rocks (Asartepe Formation). The Miocene and Plio-Quaternary assemblages are represented by similar depocenters, including lacustrine, fluvial andalluvial-fan environments in the Alaşehir Graben. They are separated by the Late Miocene to Late Pliocene, which represents the depocenter of the flood plain. The flood plain deposits are a monotonous sequence that repeats itself andis not tectonically mobile after the first 140 meters from the stratigraphic bottom based on sub-rounded to rounded clasts from the cataclastic rocks belonging to the ADF. They represent a time of tectonic quiescence during the Late Miocene-Late Pliocene, indicating that tectonic activity on the ADF terminated in the Late Miocene. However, tectonic activity may have rejuvenated in the Plio-Quaternary as indicated by E-W oriented normal faults cutting through the Alaşehir Graben.

Abstract: In Lake Salda (Southwestern, Türkiye), modern microbialites containing hydrated Mg carbonates continueto form on the shoreline of the lake and at 15 m water depth in structures ranging from a few cm in size to about10 m in height with 3-4 m width. For the first time, these organo-sedimentary structures were classified and their morphotypes, sedimentological and textural characteristics along with their spatial distribution in the lake were identified. In this context, 5 different zones were identified in the lake. In the lake, stromatolitic thrombolites are themost dominant microbialite type, while stromatolites and thrombolites are restricted to certain parts of the lake. Stromatolitic thrombolites have a wide variety of morphologies, usually dome-shaped and cauliflower-like, while they are rarely tabular. On a meso-scale (cm), stromatolitic thrombolites exhibit finger-shaped (2-5 cm) laminatedmini-columns, and dendritic, and bulbous growth structures. Thrombolites with cauliflower morphology coalesce to form a large reef-like structure at depth (10-20 m). Thrombolites with stromatolitic laminae and dendritic internalstructure are limited to certain zones in the lake (Zone 2, 3). The macro-scale external morphology of the microbialitesis shaped primarily by the influence of the prevailing environmental conditions. Seasonal fluctuations in lake waterlevel, regional differences in sedimentation rates, prevailing winds and currents are the main factors controlling the depositional environment. The internal growth structure of microbialites depends on the microbial community structure and the conditions of the depositional environment. Mineralogical study of the microbial layer revealed adifferent hydrated Mg carbonate mineral, dypingite (Mg5(CO3)4. OH2.5H2O), for the first time. This mineral, closely related to extracellular polymeric matter (EPS), is the precursor of hydromagnesite. Petrographic investigations ofthe microbialites revealed the presence of abundant vertical and near-vertical filament (mineralised`)-like structures associated with carbonates, exhibiting a clotted texture containing peloids of various sizes in addition to a thin lamination. Nodular aragonites are generally associated with microbial layers, while fibres developed in void sand aragonite fans and isopach fringes formed by their aggregation indicate secondary and abiotic carbonate precipitation in the lake. Due to their structural, mineralogical and compositional diversity, Lake Salda microbialites are a potential modern analogue that may reveal the origin and formation processes of both Mg-carbonates inthe geological record and hydrated Mg-carbonates detected in a possible palaeolake in Jezero crater, one of the Martian craters. In this study, new data on Lake Salda microbialites is evaluated in terms of their origin, formation mechanism and potential for biosignatures.

Abstract: This paper presents the implications regarding earthquake behaviour through detailed fault mapping of the western segment of the Eskişehir Fault in light of paleoseismological observations and analytical age data. The stream beds are offset right-laterally by a few meters to a few hundred meters along the western extension of thefault, indicating that the current movement of the Eskişehir Fault is of right-lateral strike-slip character. Findings obtained from paleoseismological trenches in Erikli (Bilecik) and Kandilli (Eskişehir) villages reveal that recurrent surface ruptures occurred during the Holocene Period on the western segment of the Eskişehir Fault. Consideringthe possibility that the 1956 (M=6.5) Eskişehir earthquake may have originated from the central segments of the fault and transferred stress to adjacent segments, it is assessed that there is a high probability of a future earthquake (M ≈ 6.59) on the western segment, which could potentially produce surface faulting following a seismic quiescence period of approximately 1500 years in this segment.

Abstract: Gölcük (Koyulhisar-Sivas) Cu (Ag) mineralisation is hosted by Eocene basalt and andesite and pyroclastics with volcanic-volcano-sedimentary rocks. Ore minerals are bornite, chalcopyrite, covellite, chalcocite, malachite, magnetite and hematite. Alteration in the host rocks includes sericitization, argillisation, carbonation,iddingsitization and epidotization. Gangue minerals are limited to quartz and calcite. According to the analysis results for the drill core samples, 2.97% Cu and 37 g/t Ag grade was determined at an average depth of 9.7 m from the surface. Sulphur isotope values (δ34S ‰) range from -20.0 to +2.8 in surface samples and from -6.3 to +0.6 incore samples. Copper isotope values (δ65Cu ‰) range from -0.86 to +1.38 in surface samples and -1.41 to +2.69 incore samples. For Gölcük Cu (Ag) mineralization, ore mineral paragenesis, alteration mineralogy, deposit type, andisotope geochemistry values suggest that it may be a Manto-type deposit.

Abstract: Since the high-altitude regions of Türkiye`s mountainous areas were subjected to glaciation during the Quaternary glacial periods, glacial landforms are prominently developed and well-preserved in these landscapes.These landforms provide valuable insights in the paleoglacial conditions and environmental dynamics of pastglaciation events in mountainous terrains. This study investigates the morphometric characteristics of cirques and glacio-karstic dolines on Mount Geyik, one of the key karstic plateaus within the Central Taurus Mountains. Basedon the morphometric analyses, the spatial distribution of the paleo-Equilibrium Line Altitude (pELA) during the Quaternary glaciations was systematically reconstructed and interpreted. Mapping efforts identified 142 cirques and31 glacio-karstic dolines within the study area. Using the floor altitudes of these landforms, the average pELA forthe region was estimated at approximately 2185 m. However, this value does not represent a uniform level; rather,it varies as a function of several factors, including massif orientation, elevation, proximity to the sea, and total precipitation. Specifically, the pELA increases to ~2400 m in the north-facing sectors of the high karstic plateau, while it decreases to 2000 m / lower in the western and southwestern sections. These findings reveal a vertical difference of up to 630 m between the pELA levels of mountainous regions along the Black Sea and Mediterranean Sea coasts. Regarding cirque morphometry, the cirques of the Eastern Black Sea Mountains exhibit surface are as approximately twice as large as those of Mount Geyik, and display depths exceeding Mount Geyik`s cirques by anaverage of 75 m. Overall, the results underscore the significant influence of topographic and climatic variables on pELA variability and cirque morphometry across Türkiye`s coastal mountain ranges. 

Abstract: What distinguishes minerals grouped as gemstones (jewellery stones) from other metallic and industria  lminerals and building stones is that they do not require bulky reserves and production amounts. Even if they havelow reserves, if they are extracted with good quality, they are sought after for use in the jewellery industry, and when compared to other groups, these materials have very high economic value. Although gemstone science(gemmology) and the gemstone processing industry are not very developed in Türkiye and the potential of gemstones in our country has not yet been fully determined, gemstones represent high economic potential for our countrywhen mining is performed consciously and the products marketed well. Therefore, it is in our national interest thatnational mining, analysis and trade of gems in their raw and processed forms should be coordinated and disciplined.Differing and ignorant practices by the Ministry of Energy and Natural Resources and the Ministry of Treasuryand Finance regarding gemstones are contrary to our national interests and are in disorder. Managing gemstonesunder a single regulation has become a necessity due to logic and science. There is a definite need for new laws justabout mining, analysis, exchange and trading of gemstones. The content of this law should be specially preparedin accordance with equivalent laws from other countries in the world. A "Turkish Gemstone (Jewellery Stones(Gemmology) Application and Research Centre" should be established within the General Directorate of Miningand Petroleum Affairs (MAPEG) / General Directorate of Mineral Research and Exploration Institute (MTA).This centre should be able to organise mining, processing and marketing of gemstones and R&D activities, mostof which are still not active in our country. Today, the centres of gemstone trade in the world are places such asThailand (Bangkok), China (Hong Kong), and India (Jaipur, Bombay). The definition of precious stones in Article2/K of the Turkish Foreign Exchange legislation (Turkish Currency Protection Legislation No. 32) must be revisedand missing regulations must be updated. A similar revision should be made to standards TS-6173 and TS-6174regarding gemstones, which are currently enforced by the Turkish Standards Institute (TSE). When examined interms of the consumer, one of the main stakeholders in the jewellery industry in Türkiye and within the framework ofthe "Law on Consumer Protection No. 6502" in our general legal system, the current regulations and approachescannot respond with the penal effectiveness required for possible problems encountered in terms of gemstones. Basedon this determination, the law and the relevant regulations and related legislation need to be rearranged in order toprevent consumer grievance in relation to gemstones.