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Post-volcanic activities in the Early Miocene Kırka-Phrigian caldera, western Anatolia – caldera basin filling and borate mineralization processes
No full textThe formation of large, economic borate deposits requires a boron-rich source, the means of transporting and concentrating the boron in a restricted environment, and mechanisms for the preservation of the deposit. There are several Miocene basins in western Turkey containing world-class borate reserves, with mineralization present as stratabound deposits in volcano-sedimentary successions. Although it is well-documented that the conditions required to form and preserve large borate deposits are most common in post-collisional tectonic settings (of which western Anatolia is a prime example), recent advances in the understanding of extensional tectonics and volcanism in this region, make it possible to gain fresh insights into their formation. Here, we suggest that formation of one of the largest borate deposits in the world was intimately related to the recently recognized Kırka-Phrigian caldera that lies in the northernmost part of the Miocene Eskişehir–Afyon volcanic field. Following caldera collapse, the basin filled with lacustrine sediments and volcaniclastic deposits with the boron mineralization concentrated in two main sub-basins: Sarıkaya and Göcenoluk. The close spatial and temporal relationship between borate deposition and the vast Early Miocene ignimbrite deposits that surround the caldera (and contain high levels of elements associated with mineralization) strongly suggest that the ignimbrites were the major source of boron. The boron was transported by geothermal fluids and post-volcanic gases that vented into warm water at the base of the caldera-paleolake system and was then concentrated during cycles of sedimentation and evaporation, with most of the mineralization concentrated along a N-S striking fault system
Origin and significance of tourmalinites and tourmaline-bearing rocks of Menderes Massif, western Anatolia, Turkey
No full textIn the western central portion of Anatolia lies the Menderes Massif — a large metamorphic crystalline complex made of Neoproterozoic to Precambrian basement rocks overlain by Palaeozoic to early Tertiary metasedimentary rocks, and with a multistage metamorphic evolution developed from the late Neo-Proterozoic to Eocene. We have undertaken a study of the petrology, geochemistry and boron isotope composition of these tourmaline occurrences aiming to constrain the processes responsible for the enrichment of boron and other fluid mobile elements in the Menderes Massif. The dispersed tourmaline has chemical and boron isotope compositions typical of a continental crust setting, but while some of the tourmalinites display similar signatures, others have heavier boron isotope compositions (up to + 7.5‰). We suggest that the tourmalinites with continental characteristics formed part of the original Pan African basement rocks, whereas those with heavier ?11B signatures formed by later metamorphism during the Alpine orogeny, possibly through interaction with subduction-like fluids. This proposed process may also have been coincident with metasomatism of the lithospheric mantle beneath the massif, which is known to have experienced multistage metasomatism and enrichment history up to Neogene time
Batı Anadolu Kırka (Eskişehir) Havzası Neojen Yüksek-K'lu Şoşonitik Volkanik Kayaçlar ve Boratlar Üzerine O- Ve H- İzotop Kısıtlamaları
No full textO, Sr and Nd isotopic constraints on Cenozoic granitoids of Northwestern Anatolia, Turkey: Enrichment by subduction zone fluids
No full textThe oxygen and strontium isotope compositions of Cenozoic granitoids cropping out in the Izmir-Ankara-Erzincan suture zone help constrain the petrological evolution of magmatism in northwest Anatolia. The magmatism was mostly widespread between late Eocene (similar to 37 Ma) and the middle Miocene (similar to 14-15 Ma), and is represented by volcanic and plutonic rocks of orogenic affinity, of which Ezine, Egrigbz, cataldag and Kozak are the largest Tertiary granitic plutons exposed in northwest Anatolia. They vary from granite to granodiorite, and are subalkaline, belonging to the high-K calc-alkaline I-type granite series. All these characteristics, combined with major, trace element geochemical data as well as mineralogical and textural evidence, reveal that the Oligocene-Miocene granitoids of NW Anatolia are comparable with volcanic arc granites, formed in a transitional oceanic to continental collisional tectonic setting, from a hybrid source, having crustal and mantle components that underwent further interaction with the upper crust. These plutons have initial Sr-87/Sr-86 ratios of 0.7072-0.7094, and epsilon Nd(t) values ranging from -3.48 to -1.20. These characteristics also indicate that a crustal component played an important role in the petrogenesis of NW Anatolian Oligocene-Miocene granitoids. The moderately evolved Ezine, Egrigoz, cataldag and Kozak granitoids, have delta O-18 values that are consistent with those of normal I-type granites (6-10 parts per thousand), but the delta O-18 relationships among minerals of samples collected from the intrusive contacts which are closest to mineralized zone, indicate a major influence of hydrothermal processes under subsolidus conditions. The oxygen isotope systematics of the samples from these plutons result from the activity of high-delta O-18 fluids (magmatic water), with major involvement of low-delta O-18 fluids (meteoric water) evident, near the edge zone of these plutons. This is most evident in delta O-18 quartz feldspar pairs from these granitoids, which commonly have values characteristic of open-system hydrothermal conditions, and is consistent with the presence of large scale base-metal mineralization around the NW Anatolian granitoids. (C) 2016 Elsevier Ltd. All rights reserved
O- and H- Isotope constraints on Neogene high-K calc-alkaline and shoshonitic volcanic rocks and borates in the Kırka (Eskişehir) basin, W Anatolia
No full textThe O and H isotopic ratios of borates, clay minerals, and volcanic rocks from the Kırka basin (south of Eskişehir, W Anatolia) have been analysed in order to better constrain the conditions that led to precipitation of the borates. The δ18Owr values of the volcanic rocks range from + 7.6 to + 15.9‰, but many samples are enriched in 18O by post-eruption hydration, as evidenced by the positive correlation between 18O and H2O (LOI up to 3.1 wt.%) contents. The δ18O values of the borate and clay minerals (smectite) range from 10.0 to 18.8‰, and 19.5 to 31.3‰, respectively. The large variation among the δ18O values of the borate minerals either is likely related to oxygen isotope fractionation during their formation and/or indicates that they formed at different stages of evaporation of the original brines over a range of temperatures. Considering that borax was a primary phase in the basin, decreasing δ18O values from borax to colemanite and ulexite is compatible with decreasing formation temperatures. The δD values of borate and clay minerals do not show significant differences (−64–−88‰, and −106–−125‰, respectively). The calculated δ18OH2O and δDH2O values of the fluid in equilibrium with the borate minerals (−11.6–5.93‰ and −85–−65‰, respectively) and in equilibrium with the smectite (14.4–17.0‰ and −126–−67‰, respectively) indicates that the basin brines were dominated by geothermal fluids. Overall, the oxygen isotope systematics of the borates and smectite in the Kırka basin are consistent with the smectite and borate minerals forming from brines that resulted from the ponding and evaporation of geothermal fluids that had undergone water-rock interaction with the local felsic volcanic rocks
Kırka (Eskişehir) Havzası Bor Minerallerinin Oksijen-Hidrojen İzotopSistematikleri ve Doğal İzotop Rezervuarları ile Karşılaştırılması
No full textGeochemical and mineralogical characteristics of calcic skarn in the Evciler district Kazdağ Çanakkale NW Anatolia
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