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Öğe Clay minerals in hydrothermally altered volcanic rocks, Eastern Pontides, Turkey(CLAY MINERALS SOC, 1999) Celik, M; Karakaya, N; Temel, AExtensive hydrothermal alteration is observed around volcanogenic massive sulfide deposits. These deposits are related to Late Cretaceous volcanism in various parts of the Eastern Pontide province. Mineral assemblages resulting from alteration consist of mostly clay minerals and silica polymorphs, some sulfate minerals, and scarce zeolite minerals. The clay minerals are kaolinite, illite, and smectite. These minerals were examined using X-ray diffraction (XRD), scanning electron microscopy (SEM)energy dispersive spectrometry (EDS), X-ray fluorescence spectroscopy (XRF), and differential thermal analysis (DTA)-thermal gravimetry (TG) techniques. The illite and the toseki deposits are a result of hydrothermal alteration of dacitic-andesitic volcanites. Two groups of bentonite deposits occur; the first mainly formed by hydrothermal solution whereas the second group resulted from halmyrolysis. The smectite in these alteration zones is generally montmorillonitic in composition and the interlayer cation is mostly Ca and lesser amounts of Na. The SiO2 and Fe2O3 contents of the hydrothermal bentonites are higher than those of the halmyrolysis smectites: however, the MgO content of both groups is similar. The Na2O and K2O contents of both groups are generally <0.5%. The hydrothermal bentonites are not plastic and have open honeycomb microtextures, although the halmyrolitic smectites are plastic with ultrafine and rod-shaped textures. Illite, which contains some smectite layers, is a 1M polymorph, and has an asymmetry to the low-angle side of the XRD peaks. The impure illite deposits contain various combinations of smectite, kaolinite and gypsum, galena, sphalerite, pyrite, goetite, and quartz. The illite has >35 wt. % Al2O3. The toseki raw material, which may be possibly useful as a porcelain raw material, is composed mainly of illite, kaolinite and quartz, or illite and quartz. The crystallinity of the kaolinite is poor.Öğe Fibrous foitite from Sebinkarahisar, Giresun Pb-Zn-Cu-(U) mineralized area, northern Turkey(MINERALOGICAL ASSOC CANADA, 1999) Yavuz, F; Celik, M; Karakaya, NFibrous foitite occurs in cavities in quartz Veins near Sebinkarahisar town, Giresun mineralized area [Pb-Zn-Cu-(U)], in northern Turkey. Veins of quartz + fibrous tourmaline generally cut monzonitic and syenitic rocks. Acicular and hairlike light gray crystals of foitite have a mean composition of square(0.43)Na(0.52)Ca(0.07), (Fe1.55Mn0.08Mg0.52Al0.67Ti0.01) Al-6 (BO3)(3) Si-6 O-18 (OH,O)(3) (OH)(1). The crystals of this low-temperature tourmaline radiate from irregular patches of schorl in cavities in quartz veins. Each fiber is zoned along its length with respect to Fe, Mn, Mg, Ca, Na, K, and P. The fibrous foitite from the Sebinkarahisar area contains higher Mg, Ca and Na contents than that from southern California and Elba.Öğe Metamorphic evolution of blueschists of the Altinekin Complex, Konya area, south central Turkey(WILEY-BLACKWELL, 2005) Droop, GTR; Karakaya, MQ; Eren, Y; Karakaya, NThe Altinekin Complex in south central Turkey forms part of the south-easterly extension of the Tavsanh Zone, a Cretaceous subduction complex formed during the closure of the Neo-Tethys ocean. The protoliths of metamorphic rocks within the Altmekin Complex include peridotites, chromitites, basalts, ferruginous cherts and flysch-facies impure carbonate sediments. Structurally, the complex consists of a stack of thrust slices, with massive ophiolite tectonically overlying a Cretaceous sediment-hosted ophiolitic melange, in turn overlying a sequence of Mesozoic sediments. Rocks within the two lower structural units have undergone blueschist-facies metamorphism. Petrographic, mineral-chemical and thermobarometric studies were undertaken on selected samples of metasedimentary and metabasic rock in order to establish the time relations of deformation and metamorphism and to constrain metamorphic conditions. Microstructures record two phases of plastic deformation, one predating the metamorphic peak, and one postdating it. Estimated peak metamorphic pressures mostly fall in the range 9-11 kbar, corresponding to burial depths of 31-38 km, equivalent to the base of a continental crust of normal thickness. Best-fit peak metamorphic temperatures range from 375 to 450 degrees C. Metamorphic fluids had high H2O:CO2 ratios. Peak metamorphic temperature/depth ratios (T/d values) were low (c. 10-14 degrees C/km), consistent with metamorphism in a subduction zone. Lawsonite-bearing rocks in the southern part of the ophiolitic melange record lower peak temperatures and T/d values than epidote blueschists elsewhere in the unit, hinting that the latter may consist of two or more thrust slices with different metamorphic histories. Differences in peak metamorphic conditions also exist between the ophiolitic melange and the underlying metasediments. Rocks of the Altinekin Complex were subducted to much shallower depths, and experienced higher geothermal gradients, than those of the NW Tavsanli Zone, possibly indicating dramatic lateral variation in subduction style. Retrograde P-T paths in the Altmekin Complex were strongly decompressive, resulting in localized overprinting of epidote blueschists by greenschist-facies assemblages, and of lawsonite blueschists by pumpellyite-facies assemblages. The observation that the second deformation was associated with decompression is consistent with, but not proof of, exhumation by a process that involved deformation of the hanging-wall wedge, such as gravitational spreading, corner flow or buoyancy-driven shallowing of the subduction zone. Copyright (c) 2005 John Wiley & Sons, Ltd.Öğe Mineralogical and chemical characterization of sepiolite occurrences at Karapinar (Konya Basin, Turkey)(CLAY MINERALS SOC, 2004) Karakaya, N; Karakaya, MC; Temel, A; Kupeli, S; Tunoglu, CThe Konya region in central Anatolia is covered by Pliocene-Late Pleistocene sediments and volcanites related to the sediments NNW of Karapinar, Turkey. In the area, the Upper Miocene-Quaternary Uzecek Dagi and Karacadag volcanites are generally of the same age and formed from magmas of similar composition. The Karapinar formation is brown to whitish-beige, partly fossiliferous and consists of limestone, marl, claystone and, locally, sandy layers. Silica-rich lenses, nodules and layers are observed in the upper strata which locally contain sepiolite-rich layers. The mineralogical composition of sepiolite samples taken from the area was determined by powder X-ray diffractometry, while the abundance of major-element oxides was measured by X-ray fluorescence spectrometry. The crystallographic and morphological properties of samples were determined by means of scanning electron microscopy and energy dispersive spectroscopy. Samples were taken from three sections and from random locations. Mineral assemblages in the same stratigraphic position are generally similar in the three sections, while the thickness of the individual beds varies between the sections. Dolomite and calcite are the main carbonate minerals in the sections. Sepiolite occurs primarily with dolomite and, locally, dolomite and calcite, and less commonly with just calcite. Generally, quartz, feldspar and mica are found, especially in the upper parts of the sections where tuff is abundant. CaO and MgO dominate the major-element oxides. The CaO content is between 1 and 30% while MgO is 3-21%. Al2O3 and SiO2 are generally higher in the sepiolitic and tuffitic layers. Al2O3 is <3% and SiO2 is between 15-18% in the sepiolitic layers. The average structural formula of sepiolite was calculated as: (Mg7.00Al0.44Fe0.18)(Si11.71Al0.29)O-30 (OH)(4)(OH2)(4)Ca0.13K0.09Na0.01. Sepiolite occurs as fibers and dolomite as subhedral or euhedral crystals. It is considered that sepiolite was formed either by conversion of dolomite or by direct precipitation from solution under alkaline and saline conditions in the Karapinar paleolake. The paleolake was saturated with respect to Mg, Ca and Si derived from groundwater that percolated along fracture systems.
