Features of the Tertiary Volcanism Around Sea of Marmara T

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Features of the tertiary volcanism around sea of Marmara T. Ercan, Ahmet Türkecan, Herve Guillou, M. Satir, D. Sevin, F. Saroglu

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T. Ercan, Ahmet Türkecan, Herve Guillou, M. Satir, D. Sevin, et al.. Features of the tertiary volcanism around sea of Marmara. Bulletin of The Mineral Research and Exploration, 1998, 120, pp.97-118. hal-03323404

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FEATURES OF THE TERTIARY VOLCANISM AROUND SEA OF MARMARA

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FEATURES OF THE TERTIARY VOLCANISM AROUND SEA OF MARMARA

Tuncay ERCAN*; Ahmet TÜRKECAN*; Herve GUILLOU"; Muharrem SATIR*"; Dilek SEVİN*** and Fuat SAROĞLU*****

ABSTRACT.- In the region around the sea of Marmara, limited by the boundaries of the 1:500 000 scale Istanbul Quadrangle, the volcanism starting in Upper Cretaceous and intermittently continuing through the end of Upper Miocene has been differentiated into five different stages, namely Upper Cretaceous, Eocene, Oligocene, Lower-Middle Miocene and Upper Miocene, and the volcanic outcrops situated in the region have been dated. Together with the detailed petrographic studies, nine samples from different areas and stages have been dated by K/Ar method, resulting in that the oldest and the youngest lava is of 74.3 ± 1.0 million years old (Upper Cretaceous) and 8.9±0.2 years old (Upper Miocene), respectively. Of these, belonging to the first four stages are mostly calcalkaline (some of the Eocene aged samples are tholeiitic) and are of basalt, basaltic andesite, trachyandesite, andesite, dacite, rhyolite type, whereas that of belonging to the fifth stage are alkaline and of basanite, basalt and trachybasalt types. The pyroclastics of various size and the tuffs of the first four volcanism stages crop out in a wide area. The Upper Cretaceous volcanics have completely formed beneath the sea. On the other hand, some of Eocene volcanics have formed beneath the sea which are seen intercalated with sediments while the others have formed on land. The lavas of Oligocene, Lower-Middle Miocene and Upper Miocene age have formed on land and are observed to be intercalated with lacustrine sediments, in places. Of the lavas stranded along the Black sea coast, the Upper Cretaceous aged ones have formed in a group of island arc volcanics and have been produced in a subduction zone and the Eocene, Oligocene and Lower-Middle Miocene aged ones have formed in an environment of compression during and after the collision and have been produced from a material of crust and mantle mixture. It is proposed that the Upper Miocene aged alcaline basaltic volcanics have formed in an environment of extension by the uplift of mantle after the change of tectonic regime in Middle Miocene.

INTRODUCTION THE FEATURES OF THE TERTIARY VOLCANISM

In the area around sea of (Marmara region, an in- The Tertiary volcanics around the sea of Marmara, tense volcanism has been effective starting from. Upper limited by the boundaries of the 1:500000 scale Istan- Cretaceous to the beginning of Pliocene displaying va- bul Quadrangle, and the Upper Cretaceous volcanics rious stages and forming widespread lavas and pyroc- cropping out along the Black sea coast have all toget- lastics having different petrographic and geochemical her been studied and differentiated into five different features. Although there have been many geological groups: studies in the region, there are no special and suffici- ent studies to reveal the Tertiary volcanism, the regi- Upper Cretaceous volcanics onal extension of the volcanic rocks, their ages, stages, petrochemical features and genetic explanations. Upper Cretaceous volcanics in the study area are This study intends to shed light on these questions to- situated in the north, along the Black sea coast in vici- gether with their relations with the adjacent sedimen- nity of Istanbul and in Igneada, close to Bulgarian-Tur- tary rocks and their datings. For this reason, samples kish State Boundary (Fig. 1). They generally are obser- from the Upper Cretaceous, Eocene, Oligocene, Lo- ved to intercalate with the sedimentary rocks of the sa- wer-Middle Miocene and Upper Miocene were taken me age. Upper Cretaceous aged sedimentary and vol- and dated by K/Ar method. canic rocks are widespread in the east of Istanbul, aro- 98 Tuncay ERCAN; Ahmet TÜRKECAN; Herve GUILLOU; Muharrem SATIR; Dilek SEVİN and Fuat ŞAROĞLU VOLCANISM AROUND SEA OF MARMARA 99

und Şile. Flysch type sediments, comprising an alter- rocks have completely formed during Upper Cretace- nation of conglomerate, sandstone, siltstone, marl, ous (Santonian - Campanian - Maastrichtian). claystone and limestone, bear various kinds of pyroclastics and lava flows in rather lesser amounts. These In the study area, the Upper Cretaceous volcanism are spilitic basalts, basalts, andesites, basaltic andesi- having small outcrops towards west (Akartuna 1953; tes, trachyandesites, dacites rhyolitic lavas, agglome- Erentöz,1953) is observed again in vicinity of lğneada. rates and tuffs, displaying typical submarine volca- These are basalts, basaltic andesites, spilitic basalts, nism. The most widespread of these is highly altered andesites, rhyodacites and rhyolitic lavas, tuffs and an- andesitic lava which contains plagioclase, rather less desites and are intercalated with Upper Cretaceous hornblende, biotite, augite and opaque minerals. The marine sediments. Pillow lavas are locally observed. argillization observed in these rocks is of large scale They are mostly andesites and basaltic andesites. An- and significant in industrial point of view. Besides, seri- desites are called "pyroxene andesites" since the citization, chloritization, carbonatization and zeolitizati- samples displaying porphyritic texture includes plagi- on are observed. Andesitic lavas are of porphyritic, oclase and pyroxene crystals. The plagioclases (ande- hyaloporphyritic, partly pylotaxitic texture. Plagioclase sine and oligoclase), crystallized as macro and microp- phenocrysts are hypidiomorph in places and its types henocrystals in hypidiomorph form, are generally seri- such as albite showing polysynthetic twinning and zo- citized, chloritized and epidotized. Some display glo- nal structure, andesine, oligoclase and labrador were meroporphyritic texture. Pyroxenes (clinopyroxene-au- determined (Yeniyol and Ercan, 1989/1990). Augites gite) form assemblages of glomeroporphyritic texture are partly idiomorphic and have uralitized and epidoti- as in xenomorph crystals. Some change into chlorite zed in places. Generally biotites have undergone mag- pseudomorphs including carbonates and carbonatiza- matic corrosion. In dacites and rare rhyolites, additi- tion. The matrix has intersertal texture and is formed by onal to the minerals listed above quartz crystals in va- the interfingering plagioclase microliths and the altered rious amounts can be seen. In trachyandesitic lavas pyroxene granules, chlorite and intercitial silica filling sanidine crystals are clearly visible. Spilitic lavas are in the space between. In the matrix, locally, concentric lesser amounts than intermediate lavas. Spilites comp- carbonatization, silicification and epidotization is obser- rise albite, augite and opaque minerals. Serpentinizati- ved. The andesitic lavas which are close to basalts in on, chloritization and carbonatization are seen in pla- texture, have been called as pyroxene andesite or ba- ces. Basaltic lavas display porphyritic, pylotaxitic, hya- saltic andesite in andesite-basalt transition. Tuffs are in loporphyritic and vitrophyric textures. They comprise many places have the appearance of lavas and are mainly of plagioclase and augite microliths together with plagioclase, augite, opaque mineral and olivine called as lapilli tuff and crystal tuff. Lapilli tuffs have a phenocrystals in a matrix of volcanic glass. Plagiocla- silicified, epidotized and prehritized matrix including ses display polysynthetic twinning and zonal structure volcanic rock fragments of andesitic nature and pyro- and are of andesine and labradorite type. Augites are xene andesite fragments, feldspat, amphibole (green observed to be partly twinned and altered. Basaltic la- hornblende) and pyroxene fragments. The fragments vas also show chloritization, zeolitization, carbonatiza- forming the samples are of angular, between 0.36 mm tion and argillization. Upper Cretaceous volcanism, in (coarse grained tuff) to 5.5 mm (lapilli) in length. vicinity of Istanbul, around Anadolukavağı and Rumeli- Crystal tuffs include fragments of plagioclase, quartz, kavağı at the northern end of the Bosphorus and Şile, amphibole (green hornblende), devitrified glass and is represented by agglomerates, sinerite, tuffs and la- chloritized volcanic rocks, and epidotized, carbonati- vas. Baykal (1943 and 1971) Baykal and Kaya (1966), zed and argillized fragments, sericite flakes and orga- Baykal and Önalan (1979), Okay (1948), Akartuna nic fragments. All these compounds mostly have been (1953) and Yeniyol and Ercan (1989/1990) who studi- bound with material changed into chlorite and/or clay ed fossiliferous sedimentary rocks intercalated with the minerals (most probably volcanic glass ashes and volcanic rocks representing the submarine volcanisift dusts). Crystal tuffs generally are composed of fine have concluded that both volcanic and sedimentary. grained materials of 0.01 mm grain size. 100 Tuncay ERCAN; Ahmet TÜRKECAN; Herve GUILLOU; Muharrem SATIR; Dilek SEVİN and Fuat ŞAROĞLU

In order to clarify the age problem of the Upper Cre- "Balıklıçeşme volcanics" and dated the unit as 37.3 ± taceous volcanics around the sea of Marmara a samp- 0.9 million years (Uppermost Eocene) based on the le was taken from a basaltic andesite lava in vicinity of K/Ar dating of the sample of andesitic lava with biotite iğneada which yielded 74.3 ± 3.1 million years (Cam- taken from the Balıklıçeşme village. The petrographic panian-Upper Cretaceous) by K/Ar method. studies on the Eocene volcanics situated in Biga peninsula result in that the andesitic lavas contain chloritized Eocene volcanics and argillized plagioclase microliths with porphyritic texture, plagioclase phenocrystals in a matrix conta- In the region around sea of Marmara Eocene vol- ining pyroxene and opaque minerals and also diopsitic canism has widespread outcrops in three different are- augite crystals whereas the dacitic lavas locally inclu- as: de quartz phenocrystals. Tuffs generally are of vitric and lithic but sometimes appear as ignimbritic in the fi- a) Eocene volcanics in Biga peninsula : Between eld. They are composed of, generally, sericitized, argil- Lapseki and Biga, to the north of Biga peninsula, most- lized plagioclase fragments, quartz fragments and vol- ly andesitic and locally dacitic lavas and tuffs which are canic rock fragments (andesite and dacite) and devitri- the first products of Eocene volcanism are observed. fied glass fragments. These are bound with a matrix They are underlain by the "Soğucak limestone" deter- composed of sericitized volcanic glass, ash and dust. mined to be of Middle Eocene age by Siyako et al., Grain sizes are varying between 3.2 mm (lapilli) and (1989). Lavas and tuffs are observed to be intercalated 0.02 mm (fine grained tuff). with conglomerates having thin coal seams, sandstones and shales, called "Fıçıtepe formation", which is b) Eocene volcanics in Gelibolu peninsula and defined to be delta plain -fluvial sediments (Siyako et southern thrace : Eocene volcanism in Gelibolu penin- al., 1989). These volcanics are supposed to be of Lo- sula and in southern Thrace has outcrops same as that wer-Middle Eocene age. On the other hand, there are seen in Biga peninsula. For example, in vicinity of Ge- some opinions about the volcanism to start in Paleoce- libolu town, mostly green and wine colored andesitic ne (Siyako et al., 1989; Ertürk et al., 1990). There is a and dacitic tuffs are observed as alternating with Midd- significant transgression in Middle Eocene resulting in le-Upper Eocene sediments and lavas are seen as the deposition of shallow marine "Soğucak limestone" small sills in places. Kopp (1964) has differentiated the in the region while the Eocene volcanism was still ef- Gelibolu volcanics as "Kömürtepe Andesite and tuffs", fective, forming lavas and tuffs of 1000 m in thickness. "Kavaklı Andesite", "Uçaktepe tuffite" and "Kocakuş Later on, the southern shelf of the basin has gradually tuffite". Onal and Yılmaz (1983) stating that the volca- deepened and Ceylan formation (Ünal,1967; Siyako et nics are of Upper Eocene, "Karaağaç member" of fly- al.,1989) comprising mainly of turbidites was deposi- sch type "Burgaz formation" includes tuff levels alternated. Two dacitic tuff levels (10-30 m thick), blue and ting with the other sedimentary units. Önal (1986) indi- green in color, which forms a marker bed in Ceylan for- cates that the Upper Eocene volcanic rocks, "Gelibolu mation (500 m thick) comprising turbiditic sandstone, volcanics" in his terminology, are andesites and daci- shale and marls in Biga peninsula, proves that the Eo- tes. Sumengen et al., (1987) have observed tuff levels cene volcanism was continuing in Upper Eocene. To- of Middle Eocene age in "Burgaz formation" which is a gether with the lavas and tuffs of andesitic and dacitic 600 m thick flysch unit. The same researchers have in- nature, there are ignimbritic tuffs that formed close to dicated the presence of tuff levels in the "Gaziköy for- the land. Despite the presence of all these data, it is mation" which is of shale-sandstone unit situated in the very difficult to differentiate and to map the members of upper levels. These thin bedded, light green colored si- the Eocene volcanism. Ercan et al., (1995) have na- licified tuffs are determined to be of Middle-Upper Eo- med all the Eocene volcanics in the Biga peninsula as cene age. Ceylan formation, observed in Gelibolu pe- VOLCANISM AROUND SEA OF MARMARA 101

ninsula, is a turbiditic sequence reaching up to 500 m macrophenocrystals to fine grained and microphe- in thickness and is an alternation of sandstone, cong- nocrystals in size and were crystallized in zonal struc- lomerate and limestone displaying Bouma sequences ture as hypidiomorph. Some of them display antiperthi- also includes tuff levels (Siyako et al., 1989) It is of Up- te formation. They have changed into chlorite and/or per Eocene age (Toker and Erkan, 1985). This forma- clay minerals due to alteration. Amphiboles (green tion can be seen in the inner sections of the Thrace ba- hornblende) were crystallized as idiomorphs in forms sin with increasing acidic tuff levels reaching up to 500 of medium to thin in size microphenocrystals. Some of m. The tuffs, observed as silicified locally, are quite wi- them form assemblages in glomeroporphyritic texture despread and can be correlated in well logs (Siyako et while some others display carbonatization. Together al.,1989). Burkan (1995) studied the distribution of the- with hornblende, sphene is also seen as secondary mi- se tuffs in Thrace basin making use of 11 different tuff neral. The matrix is probably formed by devitrification levels observed in 52 well logs and concluded that es- of volcanic glass and is of cryptocrystalline-felsitic tex- pecially along the Çorlu-Edirne line there lies a tuff la- ture. Along the fractures carbonate fillings are seen. yer of 450 m in thickness. They are of rhyolite, rhyoda- cite and dacite types and locally zeolitized (Özkanlı c) The Eocene volcanics in Armutlu peninsula and and Sonel.1995). around the the lake Apolyont : In Armutlu peninsula mostly andesitic lavas, tuffs and agglomerates of Midd- In Gelibolu peninsula, at the thalweg of the dam ne- le-Upper Eocene age spread over wide areas and are ar Tayfurköy, the green ignimbritic tuffs placed on the in primary relation with the sedimentary rocks of the sa- Eocene sandstones and the tuffs in vicinity of the Bak- me age. Akartuna (1968) who studied in the region in la burun to the west of Bolayır are typical outcrops. To detail for the first time, states that the volcanism starts the north, on the Keşan-Gelibolu roadcut near Evreşe, on the flysch with tuffs which is overlain by lava tuffs Eocene sandstones include volcanic materials and are and agglomerates of Paleocene-Eocene age which are cut by andesitic lavas. The small islands in gulf of Sa- later on called as "Sarısu volcanics" by Erendil et al., ros were formed by Eocene lavas (Ercan and Günay, (1991). They stated that this formation, comprising 1984). In vicinity of U9makdere village, to the south of pyroclastic and epiclastic rocks of 1000 m. thick, over- Tekirdağ, the siliceous tuffs of Eocene age are obser- lies the sedimentary units made up of conglomerate, ved together with the flysch of the same age. These sandstone, mudstone and limestone of 5-10 m situated tuffs, called "vitric tuffs", include devitrified glass frag- over the basement, metamorphic rocks. Pyroclastics ments, lesser plagioclase, biotite, sanidine, quartz in levels comprise fine or coarse grained tuffs displaying very few amount and volcanic rock fragments. They normal, reverse or symmetrical grading and andesitic have undergone intense chloritization and the traces of tuffs and lava fragments of various size in lapilli. Pyroc- glass chips are visible in them. Grain sizes are betwe- lastic flow deposits are alternated with lahar deposits of en rarely 4 mm (lapilli) and 0.08 mm (coarse grained generally symmetric graded and ill sorted. At some le- tuff) but the average grain size can be said to be 0.3 vels epiclastic deposits comprising large andesite mm (coarse grained tuff). Ertürk and Uygur (1994) blocks and pebbles, most probably of shore conglome- studying on the tuffs have differentiated products of. rate type are situated. In this sequence, lava flows at two different lithofacies formed in the marine environ- the upper levels, as 5 m thick layers, are alternated ment. These are well bedded, laminated green tuffs with pyroclastic rocks. Lava flows are andesitic volca- and locally carbonatized, siliceous white tuffs. They al- nics with plagioclase, pyroxene (augite) and hornblen- so state that the tuffs are mostly vitric and crystalline in de phenocrysts. Tuffs include plagioclase, glass and places. Lavas, on the other hand, are of andesitic type volcanic rock fragments having fluidal texture in a with porphyritic texture and include plagioclase and glassy matrix. All of this sequence, especially in the up- amphibole phenocrystals, Plagioclases range from per levels is cut by basaltic dykes. Basalts, with com- 102 Tuncay ERCAN; Ahmet TÜRKECAN; Herve GUILLOU; Muharrem SATIR; Dilek SEVİN and Fuat ŞAROĞLU

pounds such as olivine, augite and plagioclase, are ninsula, continue to appear southwestward, in the more fresh than andesites. In the limestones and north of lake Apolyont, along the ranges parallel to the sandstones situated at the lowest levels of the volcanic sjiore and in vicinity of Kemalpaşa displaying the same sequence fossils of. Lutetian age were found (Erendil et features. Lavas are hard, green in color, mostly ande- al., 1991) and it was concluded that the sequence star- sitic and basic and pillowed. Pyroxene andesitic lavas ted since then. The andesitic lava flow sample taken are of porphyritic and comprise plagioclase, pyroxene, from the north of İznik, between the villages Osmaniye- less hornblende and quartz as trace minerals. Plagioc- Sarısu yields 42.0±0.8 million years (Lutetian-Bartoni- lases are of various type and are crystallized as hypi- an) by K/Ar method and therefore the whole volcanism diomorph showing zonal structure. Pyroxenes (clinopy- can be said to be of Middle-Upper Eocene age. roxene-pidgeonite, augite and orthopyroxene-hyperst- henej are generally as hypidiomorph crystals. Matrix is Bargu and Sakınç (1987; 1989/1990) called the la- intergranular in places and pylotaxitic and includes pri- vas "Kızderbent andesite" and differentiated the pyroc- mary silica. Carbonatization and chloritization can be lastics as "Taşlıtepe formation" and "Geyikdere tuff seen locally. Brown and green hornblende crystals are member", "Tavşanlı tuff member" and "Handere tuff idiomorph with their surroundings opacitized. Basaltic member". They proposed that the depositional environ- andesite lavas contain idiomorph olivine crystals which ment is a gradually deepening shallow marine environ- are chloritized due to alteration. Basaltic lavas are cal- ment and the region emerged in Oligocene. led "olivine basalt", they are porphyritic and comprise plagioclase, olivine arid pyroxene phenocrysts. They The pyroclastic rocks which locally gets thicker of are generally hypidiomorph. They are as macro and this volcano- sedimentary sequence defined in Armut- microphenocrystals, some of them show zonal structu- lu peninsula have in some places undergone intense re. Mostly they form glomeroporphyritic assemblages. alteration. As a result of the diagenetic alteration of the- Some of them are poikilitic and have pyroxene inclusi- se andesitic, dacitic and rhyodacitic tuffs, hauylandite- ons. Olivines are chloritized, carbonatized due to alte- clinoptilolite group minerals from zeolites, mica, clay ration and their fractures are filled with iron oxide. Pyro- mixed layered minerals (seladonite, glokonite), opal- xenes (clinopyroxene-augite) are hypidiomorph and CT from silica group and calcite from carbonates have are in forms of macro and microphenocrystals. The authigenically formed (Uz et al., 1992; 1995). The tuffs matrix is intergranular and rather coarse grained and which are seen in white, dirty white, yellow-green in co- they are formed by the plagioclase microliths and mic- lor in the field display crystalline-glassy and lithic tran- rocrystals and by the granulated opaque minerals and sitions. Dusty tuff transitions as bands with binding ma- chloritized and carbonatized mafic mineral traces in terial which is in ash size can also be seen. The phe- between them. They have amygdaloidal structure in nocrystals are quartz, plagioclase (albite-orthoclase), places, filled by chlorite (at the sides) and calcite (in the sanidine and biotite in the acidic tuffs in which the alte- center). ration is higher. Intermediate (andesitic) tuffs include hornblende crystals. Lavas are mostly of andesitic, and Oligocene volcanics in places are of basaltic which cuts the andesitic lavas. Flow breccia structure and concentric alterations in The Oligocene volcanics situated around the sea of agglomerates are seen in places. Agglomerates are Marmara crop out at three different areas: observed from large block (a few meters) to lapilli size. All these coarse clastic volcanic materials are bound a) Oligocene volcanics in Biga peninsula : Biga pe- loosely with fine grained clay and tuff of volcanic origin. ninsula, starting from Lower Oligocene uplifted and emerged (Ercan et al., 1995) and first of all, the area The Eocene volcanics cropping out in Armutlu pe- between Çan and Çanakkale and the region around VOLCANISM AROUND SEA OF MARMARA 103

Manyas were effected from a volcanic stage expressed 28.0±0.9 and 22.4±0.8 million years. The first stages of by widespread lavas and tuffs of andesite, dacite, rhyo- Oligocene volcanism in Biga peninsula which is known dacite type. Many of them have been altered and silici- as "Çan volcanics" is very important in NW Anatolia fied. These are observed in white, yellow, red, brown, from the rich metallic mining point of view. Hydrother- green and blue colors and in different situations. Silici- mal alteration is very intense, in such areas, in silicified fied tuffs are hard and conchoidal. Unaltered lavas, zones Au, Ag, Pb, Cu, As, Fe, Mo, Zn and Hg deposi- which are quite rare, are mostly dark colored and inc- tion are seen which have been exploited since tho- lude brown plagioclase crystals, gray-black biotite and usands of years. dark gray pyroxene phenocrystals. Andesitic lavas are porphyritic and include plagioclase, amphibole and In the last stages of the Oligocene volcanism pro- pyroxene phenocrystals. Plagioclases (oligoclase-an- ducing outcrops of andesitic and locally dacitic lavas, desine-labrador) are hypidiomorph and display zonal tuffs and agglomerates the nature of the volcanism structure. Sometimes they show antiperthite formation was changed and instead the above listed generally and have poecilitic texture. They have changed into black dykes and black, small outcrops of trachyandesi- clay minerals in places due to alteration. tic and basaltic lava flows were produced. These which are called "Kirazlı volcanics" by Ercan et al., (1995) ha- Amphiboles (oxytiornblende) are as hypidiomorph ve yielded 27.6±0.6 and 31.1 ±0.7 million years by K/Ar macro and microphenocrystals. Some of them are opa- dating method. The texture of these trachyandesitic la- citized. Pyroxenes (clinopyroxene-augite) are as hypi- vas are microlitic porphyritic and hyalomicrolitic diomorph thin microphenocrystals. Dacitic lavas have porphyritic and they bear plagioclase (labrador and an- the same features. The quartz minerals they include desine), augite and lesser biotite and hornblende crystals in a glassy microcrystalline matrix. Plagioclases are as subautomorph crystals. The components of the which appear as phenocrystals and microliths have be- tuffs are sericitized, argillitized plagioclase fragments, en altered in places and have turned into minerals like quartz fragments, volcanic, rock fragments (andesite, sericite and zeolite. Basaltic lavas have intergranular quartz andesite and dacite) and devitrified glass frag- and microlitic porphyritic texture and bear plagioclase ments. These are bound with a matrix of volcanic (labrador and andesine), augite and olivine minerals in glass, ash and dust. Grain size is varying between 3.2 matrix of plagioclases and microliths of mafic minerals. mm (lapilli) and 0.04 mm (fine grained tuff) but generally considered as 0.30 mm (coarse tuff). Ignimbrites b) Oligocene volcanism in Gökçeada (Imroz) are observed with tuffs in places. Great part of the la- island : Gökçeada island is entirely made up of Tertiary vas are silisified, argillitized and pyritized locally. There rocks. At the basement there are two flysch deposits of are some hydrotermal quartz veins.in tuffs. In general, Eocene and Oligocene age (Akartuna, 1950; Okut, all of the mineral deposits in the region have formed in 1975). Lavas, tuffs and agglomerates of andesitic and relation with the Oligocene volcanism. The alteration of dacitic nature cut and overlie these rocks. Ercan et al., tuffs have resulted in formation of rich kaoline deposits. (1995) obtained 30.4±0.7 and 34.3±1.2 million years of age from the K/Ar dating of two different samples. The Oligocene volcanics are called "Can volcanics" by Ercan et al., (1995) during their study in which they c) Oligocene volcanism in Thrace : The Oligocene showed the distribution of the volcanics. An andesite volcanism in Biga peninsula and in Gökçeada island sample taken from, Lapseki-Umurbey village yielded spreads in Thrace and westward, in Greece and Bulga- 29.2±0.6 million years (between Chattian-Rupelian) ria. Ternek (1949) and Kopp et al., (1969) have stated based on K/Ar dating method. Dayal (1984) reached that the volcanism was effective during the whole Oli- almost the same result during his study in the area* with gocene. They also stated that andesitic and dacitic la- the samples taken from the east of Çan: 28.2±2, vas during both two volcanic stages and in Lower Oli- 104 Tuncay ERCAN; Ahmet TÜRKECAN; Herve GUILLOU; Muharrem SATIR; Dilek SEVİN,and:Fuat ŞAROĞLU

gocene and towards Upper Oligocene intense andesi- nic rocks start with, at the bottom, rhyodacitic tuffs, an- tic and dacitic and in places trachytic lavas were pro- desite, altered andesitic tuffs and reddish green tuffs duced. An andesitic sample collected near a quarry formed by the lahar flow. In the upper levels white around Keşan yielded 26.2±0.5 million years (Upper rhyolitic tuffs, rhyodacites, andesites, agglomerates Oligocene-Chattian) by K/Ar dating method. The phe- and ignimbrites are seen. Between Ipsala and Meriç nocrystals of the dated sample are mainly plagioclase andesitic and dacitic rocks of Oligocene age crops out. and lesser amphibole (hornblende) and pyroxene. Tuffs generally form thin layers between synsedimen- Opaque minerals and apatite are secondary minerals. tary deposits. Especially around Büyükaltıağaç village Plagioclases have turned into sericite and/or clay mi- ignimbritic tuffs with small obsidian fragments are ob- nerals and they appear as hypidomorph crystals in zo- served. Altered small dacitic lava outcrops in places nal structure. Some of them form glomeroporhyritic as- can also be seen. . semblages. Amphiboles (green hornblende) mostly observed as idiomorph crystals. Pyroxenes (augite) are In Central Thrace, on the other hand, tuff horizons seen in lesser amounts as microphenocrystals. The that have formed in a couple of stages having various matrix, having cryptocrystalline felsitic texture, is made thicknesses in between Oligo- Miocene deposits can up of crystalites. be seen spread in wide areas. These are the products of Oligocene volcanism (Lebküchner, 1974). These are Oligocene volcanism in Hisarlıdağ, in vicinity of generally weathered and kaolinitized andesitic and da- Enez, is being represented by lavas, tuffs and agglo- citic glassy tuffs and are difficult to differentiate from merates of mostly andesitic and dacitic nature. They, the sedimentary units (Ercan,1979). Some of them are which are called "Hisarlıdağ volcanics" by Saner reworked and some are air-fallen during the formation (1985) reach up to a thickness of 800 m. The same na- of deposits. For example, the Oligocene aged tuffs in me was used for the volcanics in the region by Sümen- vicinity of the Seğmenli and Selçuk villages to the west gen et al., (1987). A sample from this region yielded of Tekirdağ are observed have formed in lacustrine en- 35.0±0.9 million years (Lower Oligocene) by K/Ar da- vironment and are intercalated with the siltstone-clays- ting method. There are ignimbrites and tuffs in diffe- tone units. There are very thin coal seams in between. rent colors with large fiammes in Hisarlıdağ which for- The tuffs have come from a volcanic center in the vici- med at different stages, agglomerate levels and ande- nity, Kale tepe, and fallen into a lacustrine environment sitic lavas in places. The summit was formed by black to form layers. Gök (1990) named the tuffs as the "Fer- and pink colored ignimbrites. The components of the hadanlı tuff member" of the "Danişmen formation" of ignimbrites are plagioclase, biotite, devitrified glass Middle Oligocene age. They are white, dirty white, light fragments and volcanic rock fragments. They are sta- gray in color and bear agglomerate levels with a thick- ined by ironoxide hydroxides and volcanic glass flakes ness of maximum 25-30 m. They are processed and are lined up in flow structures. Andesitic lavas include used as trass in cement factories. They include abun- plagioclase, pyroxene and biotite phenocrystals. Pla- dant quartz, biotite, amphibole (green hornblende), gioclases (andesine) are hypidiomorph in zonal struc- plagioclase and volcanic rock fragments. Cement is ture. They range in a series from macrocrystals to mic- made up of volcanic glass, dust, ash, carbonate and roliths. Generally they are crystallized in zonal structu- clay. The lava samples taken from the Kale tepe are si- res as hypidiomorphs. Biotites are observed as hypidi- licified, carbonatized dacitic lavas and have amygdalo- omorph and xenomorph crystals whereas pyroxenes ids and totally chloritized mafic minerals, quartz and (clinopyroxene-augite) are crystallized as hypidi- plagioclases turned into clay minerals. omorphs. They are stained by the ironoxide hydroxides and due to intense corrosion around they are rounded. The Oligo-Miocene aged deposits spreading over The matrix is of cryptocrystalline felsitic texture and wide areas in Thrace overlies, in places, volcanic rocks margarite and globulite structures due to devitrication of Oligocene age. Ercan and Gedik (1986) studied the of volcanic glass can be observed. In Hisarlıdağ volca- core samples of Maltepe-1 well opened by Deilmann- VOLCANISM AROUND SEA OF MARMARA 105

Shell Oil Company in the north of Keşan (41 ° 01' 17" ge, medium to small sized phenocrystals as hypi- latitude and 26° 42' 3" longitude) and found out dacitic diomorphs and their outer boundaries are opatici- and rhyodacitic lavas of Oligocene age at 1850-1860 m zed. Pyroxenes (clinopyroxenes-augite) are as hypidi- depth. The same researchers also studied the core omorph and idiomorph microphenocrystals and their samples taken from inecik-1 well opened by Gulf Oil outer boundaries are stained with ironoxide hydroxi- Company in the east of Malkara (40° 55' 44" latitude des. They are observed either as single crystals or as and 27° 17' 16" longitude) and observed the existence glomeroporphyritic textured assemblages. The matrix of dacitic lavas of Oligocene age at 1488-1492 m is pylotaxitic and in places in cryptocrystalline felsitic depth. texture and made up of plagioclase microliths and cryst lites and cryoptcrystalline mezostas in between The Oligocene volcanism in Thrace is observed in them. Dacitic lavas, pinkish white, dirty white in color, wide areas both in Greece and Bulgaria. includes quartz and coarse plagioclase (andesine-oligoclase), biotite and hornblende phenocrystals. The Lower-Middle Miocene volcanics matrix is in spheroidal texture. This matrix, generally seen in acidic rocks has obtained this feature by the Lower-Middle Miocene volcanics around the sea of recrystallization of the glass already present. Rhyoda- Marmara takes place mainly in two places: citic lavas have more quartz phenocrystals than dacitic lavas and these phenocrystals are embedded in the a) Lower-Middle Miocene volcanics in Biga penin- matrix. As another difference from dacites, sanidine in sula and in Manyas : During Lower-Middle Miocene an less amount is also observed. Tuffs are generally inter- intense volcanism took place in Biga peninsula in diffe- fingered with andesitic lavas and agglomerates and rent stages and produced andesitic, dacitic, rhyodaci- include epidotized, chloritized and partly carbonatized tic, trachyandesitic and basaltic lavas, tuffs, agglome- mostly hornblende (idiomorph), biotite (hypidiomorph), rates and ignimbrites. These rocks are well known and epidot group minerals (pistasite), chlorite fragments, well studied with detailed investigations and the da- and argillized-sasuritized feldspat fragments. The mat- tings have yielded 21.5-16.8 million years (Ercan et rix is generally made up of biotite as microliths, less al.,1990; 1995). The volcanic rocks of Lower-Middle hornblende, plagioclase microliths (albite), pyroxene Miocene age in Biga peninsula and around Manyas ha- and quartz in lesser amounts. ve formed at the same time with deposits of Neogene age in a terrestrial environment. In places volcanic b) Lower-Middle Miocene volcanism in Thrace : Alt- products have formed and sometimes in depositi- hough there are widespread outcrops of Lower-Middle onal environments volcanic rocks and sedimentary Miocene volcanism in Biga peninsula, in Thrace, the rocks have mixed and formed volcano-sedimentary outcrops of this volcanism is observed in five small lo- units. Lavas are mainly of andesitic and in places of cations: dacitic and rarely rhyodacitic, trachyandesitic and basaltic. Andesitic lavas are generally pink, purple, dark /- Koyuntepe, to the east of Hisarlıdağ.- Lavas of gray or beige in color, with irregular and angular breaks pyroxene andesite type are very hard, black in color and rarely show flow structure. They mostly have hya- and have the appearance of basalt. Koyuntepe moun- locrystalline porphyric texture and include plagioclase, tain is made up of these lavas. They have plagioclase biotite, amphibole (hornblende) and pyroxene (augite) and pyroxene phenocrystals and amphibole (brown phenocrystals. Plagioclases are andesine and oligocla- hornblende) in lesser amounts. Plagioclases (andesi- se and crystallized as hypidiomorph in forms macro ne) display zonal structure and are generally hypidi- and microphenocrystals and display zonal structure. omorph. They include glassy matrix as inclusions and Amphiboles (brown hornblende) are generally hyptdi- are in various sizes as macro and microphenocrystals. omorph and opacitized mostly. Biotites are as lar- Pyroxenes (clinopyroxene-augite and orthopyroxene- 106 Tuncay ERCAN; Ahmet TÜRKECAN; Herve GUILLOU; Muharrem SATIR; Dilek SEVİN and Fuat ŞAROĞLU

hyphersthene) have crystallized as hypidiomorph. Cli- se and sanidine) displaying perthitic structure. Augites nopyroxenes are much more in amount whereas there are generally hypidiomorph and in glomeroporphyritic are very few amphiboles (brown hornblende), they are texture. Plagioclases are seen as thin spikes and mic- opacitized in their surroundings. The matrix is in pylo- roliths. They change into chlorite and/or clay minerals taxitic texture, the space between the crystals are filled in places. Biotites are crystallized as hypidiomorphs with volcanic glass. The samples yielded 17.3±0.4 mil- and opacitized. The trace minerals that changed into lion years (Burdigalian-Lower Miocene) by K/Ar met- chlorite + carbonate + opaque minerals are most pro- hod. bably olivines. The samples, according to Streckeisen 1976 classification, may be micromonzonites in syeni- //- Asar tepe, in the north of Korucuköy.- Asar tepe te-monzonite transition. The two samples collected in is composed of basaltic lavas. The lavas are in porphy- the area have yielded 21.27 + -0.24 and 18.47 + -0.20 ritic texture and include abundant olivine and pyroxene million years (Lower Miocene) by K/Ar method. Thus, and less plagioclase. Olivines are the most abundant by this work subvolcanic rocks of Miocene age in Thra- phenocrystals. and generally crystallized in hypidi- ce was found for the first time. omorph form as macro and microphenocrystals. Some of them form assemblages in glomeroporphyritic textu- IV- Karakaya tepe near Yenimuhacir village northe- re. Pyroxenes (basaltic augite) display zonal structure ast of Keşan.- At the basement marl of Oligocene age, and are observed as xenomorph crystals, as thin phe- sandstone, coal seams and tuffs are situated and the nocrystals forming assemblages in glomeroporphyritic magmatic rocks cutting these are similar to those sub- texture and microphenocrystals seen as hypidiomorph- volcanic hypabyssal rocks seen both in Kale tepe and single crystals. In these basaltic lavas having coarse Kartal tepe. They are of porphyritic texture, generally. grains, the matrix is intergranular in places (the space The main minerals are alkali feldspat, analcime, pyro- between plagioclase-labrador microliths filled with xene, biotite and olivine. Alkali feldspaths (orthoclase pyroxenes and opaque minerals) and intersertal in so- and less sanidine) are observed to include biotite and me places (chloritized mezostaz fill the space between pyroxene minerals as xenomorph crystals both in inter- plagioclase microliths). The lavas building Asar tepe citial and in poikilitic texture. Change into analcime and are similar with the Upper Miocene basaltic lavas. The clay minerals, in places, are seen. Analcimes are most- samples taken yielded 15.0±0.3 million years by K/Ar ly idiomorph and intercitial as xenomorphs and in pla- method (Lower-Middle Miocene, Burdigalian-Langhi- ces found together with zeolite minerals. Pyroxenes an). These are the first products of the alkali basaltic (clinopyroxene-diopside) are crystallized as idiomorph volcanism in Thrace. and hypidiomorph. Some of them are surrounded with a slight dark mantle (possibly a transition to aegirin au- Ill-Kale tepe and Kartal tepe near Harala village.- gite). They are observed as medium and thin microp- The volcanics forming the Kale tepe and Kartal tepe henocrystals. Biotites are generally crystallized as near Harala (Altınyazı) village are similar with the other hypidiomorph and are in reddish brown color (probably Lower-Middle Miocene aged basalts in their appearan- Ti biotite). They are observed as coarse phenocrystals. ce. On the other hand, the detailed petrographic and As secondary minerals apatite and opaque minerals geochemical studies have shown that these are sub- are seen. The samples are named "analcime syenite volcanic rocks crystallized in depth rather than the ba- porphyr", a vein rock, as attached to fold syenides ac- saltic lavas crystallized at the surface. The samples ge- cording to Streckeisen I.U.G.S.-1979 classification. nerally have poikilitic texture. They are composed of mainly pyroxene (clinopyroxene-augite) and plagiocla- V-Karamaden tepe, in the north of Keşan.- This is se (oligoclase-andesine) in decreasing amount, biotite, a small andesitic dyke. The phenocrystals of the samp- olivine, opaque minerals and apatite as secondary mi- les are plagioclase, amphibole and pyroxene. The tex- neral and all of them are in alkali feldspaths (orthocla- ture of the samples are porphyritic. Plagioclases (oli- VOLCANISM AROUND SEA OF MARMARA 107

goclase-andesine) have undergone magmatic corrosi- is generally glomeroprophyritic. Plagioclases are gene- on, they are seen as hypidiomorph crystals with zonal rally seen in the matrix rather than as phenocrystals. structures. Some of them are changed into chlorite and/or clay minerals. Amphiboles (green hornblende) The age of the young alkali basaltic volcanism in are mostly hypidiomorph as macro and microphe- Thrace has been under debate for long years. For nocrystals. Some of them are in glomeroporphyritic example, Umut et al., (1984) and Umut (1988) propo- texture. Pyroxenes (augite) are crystallized as hypidi- ses that they can be divided into two groups of Upper omorph. They are seen as macro and microphenocrys- Miocene-Pliocene age and of Pliocene-Quaternary age tals and are lesser than amphiboles. The primary tex- while Ercan (1992) states that the latest stage of the ture of the matrix is hyalopilitic and as a result of alte- basalts was effective towards the end of the Pliocene. ration chloritization and the formation of secondary si- Tapırdamaz and Yaltırak (1997) proposes that a part of lica can be seen. these basalts may be of Pliocene-Quaternary age. Sü- mengen et al., (1987), depending upon a radiometric Upper Miocene volcanics dating of a sample taken from Mahmutköy to the south of Keşan, states that the basalts are 6.7±0.7 million ye- The Upper Miocene volcanic rocks around the sea ars old (Upper Miocene). Besides, there are some other dating results from some outcrops such as of Marmara are seen as cutting the Tertiary sedimen- 4.88±2.19 million years and 6.47±0.43 million years tary rocks and forming single volcanic cones. They are (Upper Miocene) (Yücel Yılmaz, personal communica- seen in Thrace but now here else in the region, except tion). In order to shed light to the problem, during this for a small outcrop situated to east of lake Manyas. research, four different sample was dated by K/Ar met- They are completely of alkali olivine basalt type. They hod. The sample taken from Kara tepe (the basaltic co- have used the young opening fissures to reach to the ne appearing the youngest in the region) in vicinity of surface and have spread around them forming small Çorlu yielded 8.95±0.2 million years (Upper Miocene) flow outcrops and volcanic cones. In Thrace, some yo- and the samples taken from Karakaya tepe in the north ung basaltic volcanics crop but as scattered in betwe- of Tekirdağ yielded 8.9±0.2, 8.96±0.1, 8.92±0.1 million en Çorlu and Tekirdağ (Kara tepe, Çevrimkaya köyü, years (Upper Miocene). Therefore the age of the youn- Balabanlı köyü, Muratlı, Karakaya tepeleri, Osmanlı gest volcanism is determined as Upper Miocene. No köyü, Beşik tepe), in vicinity of Malkara (Karademir kö- volcanic rocks of Pliocene and Quaternary were found. yü, south of Ballıköy) and in vicinity of Keşan (Mahmut- köy, Kartal tepe, Sivri tepe, Küçükdoğanca köyü, Be- GEOCHEMICAL FEATURES OF THE TERTIARY ğendik köyü). The samples defined as olivine basalt VOLCANISM AROUND THE SEA OF MARMARA are in porphyritic texture and bear abundant olivine, less plagioclase, and lesser pyroxene as thin phe- During this study carried out around the sea of Mar- nocrystals. In some samples very few biotite is found. mara, other than the petrographic and geochronologic The matrix is of intergranular texture, the space betwe- studies on the volcanic rocks differentiated into five en interfingering plagioclase microliths are filled with groups according to their ages, chemical analyses on granulated pyroxene, less olivine and lesser opaque the representative samples were done and some geoc- minerals. In a very small area intersertal texture is se- hemical results were also obtained. Four samples from en. Olivines are the most abundant minerals and they Upper Cretaceous volcanics, 27 samples from Eocene are mostly crystallized as idiomorph. Some of them are volcanics, 21 samples from Oligocene volcanics, 9 observed as relicts changed into chlorite and calcite samples from Lower-Middle Miocene volcanics and 13 while the others are as less altered. They are surroun- samples from Upper Miocene volcanics (Fig.1) were ded by secondary, granulated opaque minerals (mag- collected and the total 74 samples were analized in netite?). Pyroxenes (clinopyroxene-augite) are seefl in MTA Chemical Laboratories to determine the major zonal structure as hypidiomorph crystals. The texture elements (Tables 1-2-3-4-5). Besides, 9 samples used 108 Tuncay ERCAN; Ahmet TÜRKECAN; Herve GUILLOU; Muharrem SATIR; Dilek SEVİN and Fuat ŞAROĞLU VOLCANISM AROUND SEA OF MARMARA 109 110 Tuncay ERCAN; Ahmet TÜRKECAN; Herve GUILLOU; Muharrem SATIR; Dilek SEVİN and-Fuat ŞAROĞLU VOLCANISM AROUND SEA OF MARMARA 111 114 Tuncay ERCAN; Ahmet TÜRKECAN; Herve GUILLOU; Muharrem SATIR; Dilek SEVİN and Fuat ŞAROĞLU

of calcalkaline and high potassium nature, and Eocene RESULTS volcanics have tholeiitic character. The same situation was observed on the FeO-(Na2O+K2O)-MgO diagram, By this research, the post-Upper Cretaceous volca- too (Fig.4). nic rocks around the sea of Marmara were differentiated in five groups and through detailed petrographic According to their chemical composition, when the and radiometric studies the "age" problem was clarified and some undated volcanics were dated. (Na2O+K2O) and SiO2 contents of the samples were plotted on the diagram prepared by Le Maitre et al., (1989), it can be said that the Upper Cretaceous volca- Especially in Thrace, some alkali basalts which we- nics are basaltic andesite, and trachyandesite, Eocene re claimed to be of Plio-Quaternary age by some pre- volcanics are basalt, trachybasalt, trachyandesite, ba- vious researchers by field observations were sampled saltic andesite, andesite, trachyandesite, trachyte, da- and dated -some of them were dated two times- to be cite and rhyolite, Lower-Middle Miocene volcanics are of Upper Miocene age. Besides that, the existence of trachyandesite, trachybasalt, andesite, dacite and Miocene aged subvolcanic rocks, which had not been rhyolite, Upper Miocene volcanics are basanite, basalt, observed before this study, was put forward. This study tracybasalt and trachyiandesite (Fig. 5). This result is aims only the dating, distribution and the petrographic concordant with the petrographic determinations. features of the volcanic rocks around the sea of Mar- VOLCANISM AROUND SEA OF MARMARA 115

mara but not the genesis of them. In fact, there are ted in Upper Cretaceous and ended in Lower Tertiary many research on the volcanic rocks in the region inc- (Şengör and Yılmaz, 1981; Yılmaz, 1995) but after the luding the major, trace and rare earth elements and the consumption of the oceanic material the convergence genesis of the volcanic rocks. For example, it was continued in Eocene. This convergence was taken up concluded that the Upper Cretaceous volcanic rocks with the shortening and thickening of the crust and ti- are generally produced from the crust and they belong tosphere which possibly continued until Middle Mioce- to a group of island arc volcanics produced from a sub- ne (Yılmaz, 1989). Therefore, post-Upper Cretaceous duction zone developed in a compressional regime Eocene, Oligocene, Lower-Middle Miocene volcanics due to the converging plates (Yeniyol and Er- are the last products of the subduction and collision, can, 1989/1990). post-collision type volcanics (Ercan et al., 1995; Er- can,1992). Polat et al., (1997) studying the Thrace vol- The major and trace element contents of the grani- canics in detail from the point of view of geochemistry tic rocks situated around İğneada together with the vol- proposes that andesitic volcanics of Eocene and Oligo- canics in Thrace and known to be of Upper Cretaceous cene age are from subcontinental lithospheric mantle age by K/Ar (Moore et al., 1980; Ohta et al., 1988) whereas alkali basalts of Upper Miocene age from ast- imply that they were formed in an island arc type sub- henospheric mantle. The alkali basalts of Upper Mioce- duction zone (Tokel and Akyol, 1987). It is stated that ne age must have formed due to the uplift of mantle ari- after the subduction of Sakarya continent and Rhodop- sing from an extensional system created by a new tec- Pontide block, the continent to continent collision star- tonic regime in the region after Middle Miocene. 116 Tuncay ERCAN; Ahmet TÜRKECAN; Herve GUILLOU; Muharrem SATIR; Dilek SEVİN and Fuat ŞAROĞLU

ACKNOWLEDGEMENTS Akartuna, M., 1953, Şile Şaryajının İstanbul Boğazı kuzey yakalarında devamı: MTA Derg., 61,14-20. The writers would like to thank İrfan Özcan and Kemal Yenigün for their invaluable help during the fi- , 1968, Armutlu yarımadasının jeolojisi: İst.Üniv. eldwork of this study which was realized in context of Fen Fak. Monog. 20, 12 s. the project "Map of Tertiary-Quaternary Volcanics of Bargu, S. and Sakınç, M., 1987, Armutlu yarımadasında Turkey" of MTA General Directorate Geological Rese- Kretase-Paleosen ilişkisi: Türkiye Jeol. Bült., 30, arch Department. 41-48.

Manuscript received July 28, 1997 and , 1989/1990, İzmit Körfezi ile İznik Gölü arasında kalan bölgenin jeolojisi ve yapısal özellik- leri: İstanbul Üniv. Müh.Fak. Yerbilimleri Derg., REFERENCES 6/1-2,45-76.

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