Hasandağ ve Keçı̇boyduran volkanları (Orta Anadolu) arasında yüzeyleyen volkanı̇k kayaçların volkanostratı̇grafı̇sı̇ ve petrolojı̇k özellı̇klerı̇nı̇n ı̇ncelenmesı̇
Volcanostratigraphic and petrologic features of volcanic rocks between Hasandagg and Keciboyduran volcano
Yazar: AYŞE ZEYNEP ÇALIŞKANOĞLU
Danışman: PROF. DR. ŞAFAK ALTUNKAYNAK
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Jeoloji Mühendisliği Ana Bilim Dalı
Derece: Yüksek Lisans, 2017
Konu: Jeoloji Mühendisliği = Geological Engineering

Özet:
İnceleme alanı Orta Anadolu Volkanik Kompleksi (OAVK) içerisinde yer alan Küçük Hasandağ ve Keçiboyduran volkanları arasında yer almaktadır. Çalışma alanı içerisinde her iki volkana ait ürünler mostra verir. Bu tez çalışması kapsamında volkanik kayalar üzerinde saha, petrografi ve jeokimya (ana-iz ve nadir toprak element ve Sr-Nd-Pb izotop) çalışmaları yapılmıştır. Ayrıca saha çalışmaları ve yüzey haritalamaları ile ortaya koyulan volkanostratigrafi, inceleme alanında 3S Kale Enerji Üretim A.Ş tarafından açılan Saadet 1 Sondaj'ından elde edilen Log verileri ile birlikte değerlendirilerek yaklaşık 2500 m kalınlığında bir volkanik istif incelenmiştir. Tüm bu verilerin ışığında bölgenin tabandan tavana volkanostratigrafisi, volkanizmanın kökeni, evrimi ve bölge jeodinamiği ile ilişkisine yaklaşımda bulunulmaya çalışılmıştır. 
Yüzey ve sondaj verilerine göre inceleme alanında istifin ulaşılabilen tabanını Oligo-Miyosen yaşlı sedimanter kayaçlar oluşturmaktadır. Sedimanter kayaçlar kumtaşı, kireçtaşı, marn ve çamurtaşından oluşmakta ve istifte üste doğru işlenmiş tüf-tüfitler ile temsil edilen epiklastik kayalara geçmektedir. Bunların üstünde Miyosen'den Kuvaterner'e kadar 4 farklı piroklastik/kırıntılı seviye ile birbirinden ayrılabilen 4 farklı lav fazından oluşan volkanik istif yer almaktadır.  Sondaj verilerine göre volcanik istif içerisinde; bazalt, andezit, bazaltik andezit ve dasit lavları gözlenmekte olup ara seviyeler halinde ignimbiritler gözlenmiştir. Bu ignimbiritler basılma göstermektedir. Volkanik istifte egemen olan Küçük Hasandağ volkanitleri bazalt, bazaltik andezit, andezit ve riyolit lavları ve ilişkili piroklastik (yağış, akma ve taşma) birimlerden oluşur. Keçiboyduran volkanı ise andezit ve dasit lavlarından oluşmaktadır. Her iki volkanda bölgedeki ana yapısal unsurlarına (Tuz Gölü Fayı vb.) paralel bir konumda yer almaktadır. Çıkış merkezleri KB-GD doğrultusunda uzanmaktadır.
Ana-iz element bileşimleri ve Sr-Nd-Pb izotop değerleri Küçük Hasandağ ve Keçiboyduran volkanitlerinin daha önceki dalma batma olay(lar)ı ile zenginleşmiş litosferik manto kaynağının %6-15 oranında kısmi ergimesi ile az oranda kabuksal kirlenmeye maruz kalmış melez bir bileşime sahip olduğuna işaret etmektedir. Küçük Hasandağ ve Keçiboyduran stratovolkanları Kuvaterner'de, çarpışma sonrası genişlemeli tektonik rejim altında, benzer bir kaynak alandan türemiş, eş kökenli ve eş zamanlı olarak gelişmiştir.

Abstract:
This study presents a detailed geological map, volcanic stratigraphy and major-trace element geochemistry (combined with Sr-Nd-Pb isotope compositions) of Small Mt. Hasan and Keçiboyduran volcanic rocks exposed around the Niğde with volcanic and sedimentary rocks of Saadet 1 Drilling Log at the study area.  
In the study area, volcano stratigraphy consists drilling and surface stratigraphy. This drilling data take to 3S Kale Enerji Üretim A.Ş. company an unpublished folder. Saadet 1 Drilling log contains both volcanic and sedimentary rocks. 
Saadet 1 well is located between the Mt. Small Hasan and Keçiboyduran stratovolcanoes to the north of the scoria cone (Kızıl Hill). The lithostratigraphic log has a thickness of 1612 meters and can be divided into two different units. The lower unit consist of sedimentary rocks (1612-1112m deep), while the upper unit consist of volcanic rocks (1112-0 m deep).
The lower sequence (sedimentary rocks) thickness reaches almost 500 meters. This sequence forming the most visible base for the study area is composed of conglomerate, siltstone, sandstone, mudstone and limestone units. Carbonate matrix and calcite veins are observed widely throughout the entire series. Also, mudstones exhibit different stratigraphic levels (such as 1315m deep) chlorite alternations. These levels are probably more sensitive, so they are more susceptible to alteration of hydrothermal fluids. Sedimentary rocks show the alternation in this sequence. Overlying these, there is a volcanic unit that is the upper sequence of the Saadet 1 log. 
The upper sequence is formed by volcanic rocks reaching approximately 1108 meters in thickness. These various types of volcanic rocks are made of a variety of lava flows and associated pyroclastic and volcanoclastic rocks. In these sequences are observed 4 different lava groups (basalt-andesite, andesite-dacite that is repeated itself in the sequence and basaltic andesite-andesite) that are separated by 4 different pyroclastic levels. There are volcanoclastic, debris flow and 2 different types of pyroclastic rocks (welded-unwelded ignimbrite and pyroclastic fall unit), showing the varied depth in the volcanic sequence. Pyroclastic fall unit is represented tuff with reddish pink into color. Pumices, quartz, feldispat and biotite with a small amount of lithic fragments into the ash matrix. Lithic fragments we complied from volcanic rocks that they are represented by acidic lavas. They are seen thin layer into the log, so we have been ignored them in stratigraphic column.  0-61 meters depth are observed ignimbrite that is reddish pink in color and unwelded, while 346-476 meters and 726-776 meters of ignimbrite is dark grey color with moderately to strongly welded. All ignimbrite levels contain pumices, lithic fragments and shards. Pumices is flattened into the welded ignimbrite and they show fiamme structure. In the unwelded ignimbrite, pumices show slightly elongation, they present ellipsoidal shapes. Lithic fragments into the both types of ignimbrite can be distinguished andesite, rhyolite, basaltic andesite, dacite in composition. Cracks and fracture into pyroclastic rocks are seen secondary calcite, chlorite and zeolite occurrences. The below part of this sequence includes varying from basalt to andesite lava series, reaching up to 130 meters thick, between 982 to 1112 meters. Basaltic lavas are very distinctive because they have a darker color and represent vesicular texture containing pyroxene and olivine crystals, while andesite lavas have red-brown color, porphyritic texture and comprise hornblend and biotite crystals. Also, felsic enclaves were founded within the basaltic lavas at the bottom of the volcanic units. The dominant rocks of the lava series are andesite-dacite lavas because they are observed 2 different levels into the volcanic sequence with almost 300 meters thick, among 406 to 846 meters depth. In generally, andesite-dacite lavas are represented porphyritic texture and are made up plagioclase, hornblend and biotite crystals. Andesite lavas contain pyroxene crystals in some levels of volcanic unit. The uppermost levels of lavas are represented basaltic andesite-andesite lava series. They are interfingering each other. They show intensive alternation of hematite and limonite into the varying layers. In some levels was observed an increase in vesicles. Carbonation were observed along these cracks and fracture. 
Early products of volcanism at the surface are ash, pumice and pumice-block tuffs and accretionary lapilli tuffs/breccia associated with explosive plinian-sub plinian eruptions.  These sequence thickness change place to place around the study area. Also, thin layers of reworked tuffs intercalated with sedimentary rocks (mudstone and marl) can be observed at the bottom of the volcanic sequence. Towards the upper part of the sequence they interfinger with pyroclastic flow deposits at the northern part of the study area. Pyroclastic flow deposit contains ignimbrite and ash-block flow units. Pyroclastic fall and flow deposits reach a maximum thickness of 600 m. Ignimbrite are pinkish colour and unwelded. Ash-block flow unit deform pyroclastic fall unit. Andesite and basaltic andesite of Small Mt. Hasan gradually passes each other and overlie the pyroclastic succession forming the most common lava phase in the region. Andesite is usually pink colour and basaltic andesite is black and dark grey color. Plagioclase and hornblend phenocrystals can be selected by easily. Their thicknesses vary from place to place at the study area. Dacitic and andesitic rocks of Keçiboyduran volcanoes cover the Small Mt. Hasan pyroclastic flow that is ignimbrite. Basaltic dykes and associated pyroclastic rocks of Small Mt. Hasan are observed at the upper parts of the volcanic succession. These basaltic dykes and associated pyroclastic rocks are black color and they are located middle of the study area. They do not cover the broad area.  The areal distribution of the volcanic rocks indicates that they were erupted from vents which set parallel to the NW-SE trending major fault systems (eg. Salt Lake Fault). 
Small Mt. Hasan have two main rock groups; andesite, basaltic andesite, rhyolite, basalt lavas and associated pyroclastic rocks; while Keçiboyduran has dacitic and andesitic lavas. Petrographically, they both display hemicrystalline porphyritic texture. While andesite, basaltic andesite, rhyolite, dacite and basalt group shows hyalopilitic, pilotaxitic, intersertal, glameroporphiric, trachytic texture; rhyolitic ignimbrite displays generally spherulitic texture, hyalopilitic and vitrophyric textures as a consequence of devitrification, and eutaxitic texture as a consequence of welding. 
All lava samples present disequilibrium textures such as clinopyroxene mantled by hornblende, hornblende surrounded by plagioclase, biotite mantled by hornblende, different stages of plagioclase, biotite and hornblende crystallization, sieve texture in plagioclases, reaction textures in hornblende and biotite, quartz crystals in olivine basalt mantled by pyroxene phenocrysts, plagioclase phenocrysts displaying patchy and oscillatory zoning, sieve and synensis textures, embayment structures in plagioclase phenocrysts. Also, basaltic samples include quartz ksenocrystals. 
Classification of the volcanic rocks in the area according to Le Bas et al., 1986 are basaltic andesite, andesite and rhyolite for Small Mt. Hasan; andesite and dacite for Keçiboyduran and Saadet 1 drilling samples. They are sub alkaline in nature (Ivrine and Baragar, 1971) and represented by mildly high-K calcalkaline rocks (Pecerillo and Taylor, 1976). The silica content of volcanic rocks of Small Mt. Hasan range from 52.21 to 72.49 wt % and Keçiboyduran samples range from 61.14 to 63.25 wt %. They display enrichment large ion lithophile elements (LILE: Rb, Ba, Sr and K) and LREE, and depletion in high field strange elements (HFSE: Th, Ta, and Ce) with significantly negative Nb, Ti, P and Y.  
Measured 87Sr/86Sr(m) ratios of Small Mt. Hasan vary between 0.70492 to 0.70519, 143Nd/144Nd ratios 0.51260-0.51270, 206Pb/204Pb ratios 18,869-18,855, 206Pb/204Pb ratios 38,864-38,882 and 207Pb/204Pb ratios 15,628-15,6402. Keçiboyduran stratovolcano has measured 87Sr/86Sr(m) ratio as 0.70514, 143Nd/144Nd ratio as 0.51265, 206Pb/204Pb ratio as 18,896, Pb/204Pb ratio as 38,896 and 207Pb/204Pb ratio as 15,641. Sr isotope and εNd values of 3 volcanic samples exhibit narrow changes. εNd values of Small Mt. Hasan and Keçiboyduran volcanic rocks change from 0.73 to 1.22. Small Mt. Hasan and Keçiboyduran volcanic rocks display similar La/Nb values; 2.20-2.86 and 2.53-2.84 respectively. Both La/Nb values and partial melting models of volcanic rocks indicate (6-15%) spinel lherzolite as possible source mineralogy. These rock samples show low Sr isotope values; therefore, they have low crustal contamination and AFC. 
The origin of the Cappadocian volcanism was possibly related to melting of a subduction-modified lithospheric mantle source, during the post collisional extension in Central Anatolia (Turkey).