Burdur-Salda Gölü güncel magnezyumlu çökellerin oluşumu

Abstract

Salda Gölü ve yakın çevresinde yapılmış olan bu çalışmada güncel magnezyum karbonat çökelimlerinin kökeni ve oluşum mekanizması ortaya konmaya çalışılmış, bu amaçla saha gözlemleri, alınan örnekler üzerinde petrografik incelemeler ve kimyasal analizler yapılmıştır. Arazi gözlemleri ile oluşumların çökelmeye hala devam etlikleri tespit edilmiştir. Ayrıca mineralojik ve kimyasal etüdler sonucunda çökelimlerde ana malzemenin kimyasal ayrışma kökenli olduğu ve ofiyolit kompleksinden türedigi, küçük ölçekli de olsa oluşan çökellerde metasomatik gelişim olduğu görülmüştür. Mikroskobik etüdler sonucunda hidromanyezit-manyezit dönüşümlerinin olduğu tespit edilmiştir. Ayrıca Salda Gölü 'nde güncel magnezyum karbonatların çok büyük oranda hidromanyezit bileşimli olduğu, ancak Kayadibi bölgesinde kireçtaşlannm yaygınlığı, ortama taşman Ca varlığı ve yerinde gelişen metasomatizma sonucu, sözkonusu bu çökelimlerde kısmi huntit oluşumunun varlığı da anlaşılmıştır. Göl suyu ve dip sedimanlarında yapılmış olan analizler sonucunda yüksek Mg elde edilmiştir ve bu durumun varlığı, belirtilen düşüncelerimizi destekler niteliktedir. Bölgede var olan tektonizmanın, mevcut oluşuma hızlandırıcı yönde bir etki yaptığı düşünülmektedir.

In this thesis, it is aimed to determine the formation mechanism and genesis of actual magnesium carbonate precipitations located around Salda lake. For this aim, the field studies have been done primarily, the collection of samples from the necessary rocks and sediments, the macro and micro studies on the samples using in-situ and laboratory techniques together with chemical measurements have been performed. Field and laboratory results were evaluated by taking into account the earlier investigations which had been held in and around the study area. The conclusions and the obtained informations are presented in the form of the eight chapters. Hydromagnesite is one of the rare forming mineral and it has been deposited in the form chemical precipitations in lacustrine basins where not only the evaporation process but also weathering and alteration steps are very effective in the formation and deposition periods. These basins are of lake-meromictic type and are favorable for multiperiodic and depositional hydrate and non-hydrate minerals bearing accumulations. Depending on the geology of the surrounding rocks and the tectonic positions of the basins, chemically different type of industrial mineral occurrences can be observed in these areas in all over the world. In Turkey, because of the very high active tectonism, especially in the western Anatolia, many small and large scaled basins have been created; and then many industrially importance deposits have been formed in these grabens including mainly boron minerals, coals, zeolites, natural sodium carbonate occurrences and magnesium bearing accumulations. These deposits have been mostly interbedded with sedimentary and volcano-sedimentary units most of which are tuff-tuffite, carbonated, clay-claystones generally. The simplified geological framework of The Salda Lake and its surrounding areas. It is regarded to the Salda lake is one of the current examples of the mentioned basins where actual hydromagnesite accumulations have been taken, the occasion of formation under the effect of both the active tectonism and the weathering process of the surrounding rocks. Mentioned occurrences called as Kocaadalar and Kayadibi occurrences are being studied in detail. Although the vicinity of the Salda lake comprises suitable places in terms of deposition of the actual sedimentary accumulations ranging in thickness from a few centimeters to hundreds of meters, due to tectonic contributions to the topographic positions, only in these two localities hydromagnesite accumulations have been formed. On the other hand, the change of the lake water level has resulted in the differences in thickness. The studies of the genesis were focused primarily on the surrounding ophiolitic rocks which are mainly consisted of dunite, harzburgite and serpentines and other ophiolitic units. All of these rocks are tectonically crushed and therefore sand to gravel sized xn particles of these rocks have been determined especially on the shore of the southern parts of the Kocaadalar Burnu location. In the district, the mentioned parts of the surrounding rocks were observed in the actually formed hydromagnesite and other hydrated magnesium bearing accumulations which are rich of clayey levels which contain high level of magnesium also. In the same localities, same weathering products were also observed as indicators of in-situ process ; from an ultrabasic rocks centers toward to the marginal parts, a seri of alteration steps such as weathering rock, Mg-nch clayey muddy zone, and hydrated Mg-nch accumulations were determined in the form of nodular structures in different series. These properties are the indicative parameter in term of the effects of surrounding rocks on the formation conditions. Figure 1 and 2. The actual sedimentary accumulations of Hydromagnesites observed in Kocaadalar Burnu (left) and of Kayadibi (right) On the other hand, tectonism is the other main factor which has been totally effected the occurrences not only beginning periods of the formations but also during the formation steps. These tectonic parameters have contributed the suitables places for continuation to precipitated and also possibly the ions which are necessary in order to form hydromagnesites depositions. On the other hand these tectonism, had resulted in a serie of paragenesis at the Kayadibi location where thick sedimentary sequences were observed. In these area, hydromagnesites were determined together with calcium carbonate minerals such as Glauberite, Dolomite together with rare forming other double carbonates like Huntite, Nesquehonite which have been formed generally because of the effect of Mg change in the solution from which the minerals have been precipitated or formed. Not only macroscopic studies but also microscopically these large intervals of minerals presences have reveal a wide and different paragenesis. " Xlll XRD and SEM analyses have also indicated some remarks in term of mineralogical impurities within Hydromagnesites, like magnesite, dolomite, aragonite, which are probably indicative to metasomatic reactions and also diagenetic enrichments. The presences of these minerals even if they are in a very little amount, carries a genetic importance depending on the places were determined. But, surprisingly, at the Kocaadalar location and its close surroundings hydromagnesites is the single mineral in general and it can not be observed a variety in the paragenesis except the presences of clay minerals. Another study we have undertaken is the lake-water analyses. Through two directions, the sampling have been done in the aim of making the correlation between two localities. Moreover, deep sediments have been collected from the same points. The results of both two types of sampling have indicated a difference between two localities the Kocaadalar occurrences and Kayadibi hydromagnesites from the view points of formation periods and shapes. These studies we have been undertaken have clearly revealed that the Salda Lake hydromagnesite occurrences have to be evaluated and scientifically considered under the concept of two formation periods and depositional environments. Therefore, the subject have been investigated from this approach and the current position have been discussed by taking into account earlier studies. As it is explained by the earlier studies, the occurrences have been forming under the effects of weathering process of surrounding rocks and possibly due to contributions of the lake waters. Furthermore, biologic contributions to the formations was also postulated. Although these observations and results can not be omitted in terms of their effects on the formation periods and steps, the results of this thesis are contributing the new approaches to the genesis of these occurrences, which are also indicative to the origin of the other sedimentary formations observed in and around the surrounding lakes such as Acıgöl, Burdur and possibly Yarışlı. As a results of the active tectonism, in Western Anatolia many small basins have been formed, which were very favorable areas particularly,in terms of sedimentary, volcanosedimentary depositions. Being one of these areas, in the earlier times it was postulated that there was a parent lake, a paleo lake, in the study area, which had covered on the lakes observed today around the Salda Lake. This lake had been subjected to enrichments in the favor of some ions, such as sodium, magnesium, carbonate and bicarbonate and etc. Under the effects of different chemical compositions of surrounding rocks and the various paths of evaporation ; and according to the paleotopographic conditions, tectonism had been responsible for the formations of some small basins from the same parent lake. Finally, around the study area, some lakes carrying partly similar properties have been occurred. It is regarded to the Salda lake as one of these basins. The waters of this lake had been subjected to concentrate in the favor of magnesium, carbonate and bicarbonate ions, because of the weathering processes of the rocks partly and also due to possibly hydrothermal inputs, coming from the main fault observed in the north-eastern part of the Lake, as a result of active tectonism. The fault system had been also contributed carbon dioxide to the lake. xiv Under the effects of these conditions Mg-bearing accumulations had been formed actually at the beginning periods. We assume that this was the first step of these actual Hydromagnesite depositons in the study area. And due to a new activation of the tectonism, the lake was deformed and subjected to an uplifting resulting in the occurrences of thick sedimentary levels as we see at the Kayadibi location. During this period hydrothermal solutions have been taken an occasion of entering to the environment and also contribute the necessary materials which are needed to the formation of Mg-bearing accumulations such as Huntite, nesquehonite and dolomite in addition to Hydromagnesite. During this period, on the other hand, the accumulations, formed in the first step, had been partly decomposed and dissoluted, especially in the north-eastern part of the Lake. The chemical structure of the Lake had been also changed. Under the effect of the second step of the tectonism, particularly at the contacts of limestones and ophıolıtes, carbon dioxide contribution, decarbonation may possibly provided. In other words, carbon dioxide source had been partly supplied by means of the trusting system observed around the Lake, which was the reason possibly of the decomposition of the limestones. The study which was performed for this purpose is supported our assumption and it is presented below. Furthermore, weathering processes had also controlled the formation in a similar manner that we have assumed in the first step. In this study, the formation conditions of the actual Mg-bearing accumulations were discussed and the possible steps which were subjected during its formations were evaluated as it is summarized below. 1) The actually forming Mg-bearing carbonates observed in and around the Salda Lake are determined as Hydromagnesites. 2) Hydromagnesite- magnesite transformations were determined as a results of microscopic studies. 3) Field observations have revealed that the formation are still going on in the studied area. 4) It is assumed that the origin of Mg and C02, which are the mam components in the formations, are the ophiolitic rocks and limestones together with the lake water which was enriched in the favor of these agents due to possible hydrothermal activity. 5) The chemical analyses have shown that the clayey materials, observed near to the main input to the lake, are contained slightly large amount of Mg ions, which is indicative in terms of the effects of the surrounding rocks to the formation of the occurrences. 6) It was determined dolomitic formations in the samples of limestones which are commonly observed around the Kayadibi occurrences. xv S18os k Koyakçı Manyezit 0 Yunak Manyezit -20 -1(1 13 C % Salda Hid. Salda Aragonit Denizli Hidrotermal * Kökenli Oluşumlar Pamukkale Traverten Oluşumları Figure 3. The diagram showing the probable sources of C02 in the investigated system 7) Because of the common calcium presence in the Kayadibi location, Huntite formations and depositions are expected in this area. 8) REE results are also supported the possible presence of other rare forming double carbonates around the area. 9) Because of the determination of sulfur presence in the samples, which were collected from the bottom the Lake, and also due to the thick levels of the occurrences seen in the lake ; it is regarded to the main fault, observed northwestern side of the Salda Lake, as the one of the main tectonic element that is responsible for the actual positions of the occurrences. 10) Tectonism was the principal factor which had controlled the mechanism in all periods. 11) It is postulated that the occurrences had been formed in a playa-sabhka like environment as a result of a chemical precipitation model under the effect of actual tectonism. In these periods metasomotism had possibly worked resulting in some very rare forming formations.