Western Turkey has been dominated by N–S extension since the Early Miocene. The timing and cause of this N–S extension and related basin formation have been the subject of much debate, but new data from the Bigadic borate basin provide insights that may solve this controversy. The basin is located in the Bornova Flysch Zone, which is thought to have formed as a major NE-trending transform zone during Late Cretaceous-Palaeocene collisional Tethyan orogenesis and later reactivated as a transfer zone of weakness, and which separates two orogenic domains having different structural evolutions.



Volcanism in the Bigadic area is characterized by two rock units that are separated by an angular unconformity. These are: (1) the Kocaiskan volcanites that gives K/Ar ages of 23 Ma, and (2) the Bigadic volcano-sedimentary succession that yields ages of 20.6 to 17.8 Ma. Both units are unconformably overlain by Upper Miocene-Pliocene continental deposits. The Kocaiskan volcanites are related to the first episode of volcanic activity and comprise thick volcanogenic sedimentary rocks derived from subaerial andesitic intrusions, domes, lava flows and pyroclastic rocks. The second episode of volcanic activity, represented by basaltic to rhyolitic lavas and pyroclastic rocks, accompanied lacustrine–evaporitic sedimentation. Dacitic to rhyolitic volcanic rocks, called the Sindirgi volcanites, comprise NE-trending intrusions producing lava flows, ignimbrites, ash-fall deposits and associated volcanogenic sedimentary rocks. Other NE-trending olivine basaltic (Golcuk basalt) and trachyandesitic (Kayirlar volcanites) intrusions and lava flows were synchronously emplaced into the lacustrine sediments. The intrusions typically display peperitic rocks along their contacts with the sedimentary rocks. It is important to note that the Golcuk basalt described here is the first recorded Early Miocene alkali basalt in western Turkey.



The oldest volcanic episode occurred in the NE-trending zone when the region was still experiencing N–S compression. The angular unconformity between the two volcanic episodes marks an abrupt transition from N–S collision-related convergence to N–S extension related to retreat of the Aegean subduction zone to the south along an extensional detachment. Thrust faults with top-to-the-north sense of shear and a series of anticlines and synclines with subvertical NE-striking axial planes observed in the Bigadic volcano-sedimentary succession suggest that NW–SE compression was reactivated following sedimentation.



Geochemical data from the Bigadic area also support the validity of the extensional regime, which was characterized by a bimodal volcanism related to extrusion of coeval alkaline and calc-alkaline volcanic rocks during the second volcanic episode. The formation of alkaline volcanic rocks dated as 19.7 ± 0.4 Ma can be related directly to the onset of the N–S extensional regime in western Turkey. Copyright © 2005 John Wiley & Sons, Ltd.

Evidence for two episodes of volcanism in the Bigadiç borate basin and tectonic implications for western Turkey

In deep geological repositories for high-level nuclear wastes, interactions between steel canisters and clay-rich materials may lead to mineralogical transformations with a loss of the confining properties of the clays. Experiments simulating the conversion of smectite to Fe-rich clay phases in contact with Fe metal have been carried out to evaluate such a possibility by taking into account the effects of a series of critical parameters, including temperature, pH, and Fe/clay (Fe/C) and liquid/clay (L/C) ratios. The mineralogical and chemical transformations observed in these experiments have been compared with data from the literature, and subsequently used to propose a conceptual model for the main mineralogical transformations which can be expected in clay formations surrounding high-level nuclear waste repositories. In the presence of Fe metal and under low oxygen fugacity (<10−40) the main mineralogical sequences are as follows:



1. up to 150°C, under neutral pH, and L/C > 5: dioctahedral smectite (di-sm) → 7 A Fe-rich phase (berthierine, odinite–cronstedtite) for large Fe/C ratios (>0.5), or di-sm → Fe-rich di-sm + Fe-rich trioctahedral smectite (tri-sm) for small Fe/C ratios (0.1);

2. up to 150°C, under alkaline pH (10–12), and L/C > 5: di-sm → Fe di-sm (±palygorskite) for a small Fe/C ratio (0.1);

3. at 300°C, Fe/C = 0.1, and L/C > 5: di-sm → Fe-rich saponite → trioctahedral chlorite + feldspar + zeolite (near-neutral pH); di-sm → Fe-rich vermiculite + mordenite (pH 10–12).



Low temperatures (<150°C) and large L/C and Fe/C ratios seem to favor the crystallization of the serpentine group minerals instead of Fe-rich trioctahedral smectites or chlorites, the latter being favored by higher temperatures. The role of L/C and Fe/C ratios and the competition between them at different temperatures is a crucial point in understanding the transformation of smectite in contact with Fe metal.

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EFFECTS OF TEMPERATURE, pH, AND IRON/CLAY AND LIQUID/CLAY RATIOS ON EXPERIMENTAL CONVERSION OF DIOCTAHEDRAL SMECTITE TO BERTHIERINE, CHLORITE, VERMICULITE, OR SAPONITE

Zeolite-rich volcanic tuffs are widely distributed in almost every country of the world, where they are present in low-, medium-, or high-grade million-ton deposits. Even though the formation of the zeolite minerals may have followed different genetic paths, the zeolitic rocks have in common a matrix of finely crystalline zeolite that cements the other nonzeolitic particles and is responsible for the overall mechanical properties of the material. Zeolitic tuffs have been employed since pre-historic times in construction, mostly as dimension stone. This use is still the most common of natural zeolites in the building industry, although other applications have recently come to the forefront, such as lightweight aggregate or as additives for manufacturing blended cements.

Given the fact that much of this material is excavated and used locally and that the market demand is strongly affected by the trends of the building industry, estimates of the worldwide zeolitic tuff production for construction purposes are difficult to make. In Italy, where the use of zeolitic tuff as dimension stone is commonplace, about 75 quarries were reported in operation in 1992 with total production of about 3 x 106 tons per year (Aiello 1995). More recently, this production has decreased, due to the crisis of the building industry, and in 1998 it amounted to about 1.5 × 106 tons per year. In Japan, the production of tuff as dimension stone is currently about 4 × 105 tons per year (N. Kuchitsu, National Research Institute of Cultural Properties, Tokyo, Japan, pers. comm., 1996). Considering that zeolitic tuff is used as dimension stone in many other countries as well, e.g. Bulgaria, Cuba, Germany, Greece, Hungary, Mexico, Romania, and Turkey, the current worldwide zeolitic tuff consumption as dimension stone is about 3 × 106 tons per year.

Information is even more …

Use of Zeolitic Tuff in the Building Industry

Characterisation of archaeological mortars and plasters from kyme (Turkey)

Cappadocia is essentially covered by nine rhyolitic ignimbrite units, being the products of a multi-phase volcanism of Upper Miocene-Pliocene age. Around Urgup and the Kizilirmak River, these ignimbrites constitute a volcanic-sedimentary succession together with lacustrine sediments, called the Urgup formation. In the zeolite occurrences of Cappadocia that were found in the lacustrine parts of pyroclastics outcropping around the Tuzkoy, Sarihidir, Karain, Cokek, Ibrahim Pasa and Karadag areas, clinoptilolite is the most common mineral and is associated with chabazite, erionite and phillipsite in some areas. A gain of alkaline-earths from the lake water, which is compensated by a loss of alkalis from the glass, took place during the formation of the different zeolite assemblages, which were probably controlled by the composition of the parent glasses. The distribution of erionite confirms its relation with mesothelioma cases in Tuzkoy, Sarihidir and Karain villages that are located outside tourist areas. The high incidence of malignant mesothelioma in Karain may be explained by uncontrolled occupational exposure to erionite. The “fairy chimneys”, “canyons” and “underground cities”, which are situated in the unaltered or slightly altered parts of the Kavak, Zelve, Cemilkoy, Gordeles and Kizilkaya ignimbrites do not constitute any health risk for the inhabitants or for visitors.

Zeolite occurrences and the erionite-mesothelioma relationship in Cappadocia, central Anatolia, Turkey

The Bigadic, Emet and Kirka lacustrine basins of western Turkey may be considered as Tibet-type graben structures that were developed during the Miocene within the Izmir-Ankara suture zone complex. The volcanic-sedimentary successions of these basins are made up of mudstone, carbonate (limestone and dolomite) and detrital rocks, and also of crystal or vitric tuffs about 135 to 200 m thick. The Degirmenli (Bigadic), Emirler (Bigadic) Kopenez (Emet) and Karaoren (Kirka) tuffs constituting the zeolite deposits are situated beneath four borate deposits (colemanite, ulexite, borax). The most abundant diagenetic silicate minerals are K- and Ca-clinoptilolites in the zeolite deposits, and Li-rich trioctahedral smectites (stevensite, saponite and hectorite) and K-feldspar in the borate deposits. In the Degirmenli, Emirler. Kopenez and Karaoren deposits, the following diagenetic facies were developed from rhyolitic glasses rich in K and poor in Na: (glass + smectite), (K-clinoptilolite + opal-CT), (Caclinoptilolite + K-feldspar ± analcime ± quartz) and (K-feldspar+analcime+quartz). K-feldspar which is also rarely associated with phillipsite (Karaoren) and heulandite (Degirmenli and Karaoren), succeeds clinoptilolite and precedes analcime in these diagenetic facies where dioctahedral smectites, opal-CT and quartz are the latest minerals. No diagenetic transformations exist between clinoptilolite, K-feldspar and analcime that were formed directly from glass. The lateral facies distributions resulted from the differences in salinity and pH of pore water trapped during deposition of the tuffs, but vertical distributions in vitric tuffs seem to have been controlled by the glass/liquid ratio of the reacting system and the permeability or diffusion rate of alkali elements. The Bigadic, Emet and Kirka zeolite deposits which were formed in saline basins rich in Ca and Mg ions, show similar chemical changes, i.e. loss of alkalis and gain in alkaline-earth elements that have taken place during the diagenetic transformation of rhyolitic glasses to dioctahedral smectites or clinoptilolite. The absence of sodic zeolites such as mordenite, erionite, chabazite and silica-rich phillipsite is mainly due to the very high K/Na ratio of the starting materials rather than initial alkaline conditions or high Na content in lake waters.

Geological, mineralogical and geochemical characteristics of zeolite deposits associated with borates in the Bigadiç, Emet and Kirka Neogene lacustrine basins, western Turkey

N. Clauer

Papers

Geological, mineralogical and geochemical characteristics of zeolite deposits associated with borates in the Bigadiç, Emet and Kirka Neogene lacustrine basins, western Turkey