Zekiye Karacik

When Did the Western Anatolian Grabens Begin to Develop

Abstract To solve a long-lasting controversy on the timing and mechanism of generation of the western Anatolian graben system, new data have been collected from a mapping project in western Anatolia, which reveal that initially north-south trending graben basins were formed under an east-west extensional regime during Early Miocene times. The extensional openings associated with approximately north-south trending oblique slip faults provided access for calc-alkaline, hybrid magmas to reach the surface. A north-south extensional regime began during Late Miocene time. During this period a major breakaway fault was formed. Part of the lower plate was uplifted and cropped out later in the Bozdağ, Horst, and above the upper plate approximately north-south trending cross-grabens were developed. Along these fault systems, alkaline basalt lavas were extruded. The north-south extension was interrupted at the end of Late Miocene or Early Pliocene times, as evidenced by a regional horizontal erosional surface which developed across Neogene rocks, including Upper Miocene-Lower Pliocene strata. This erosion nearly obliterated the previously formed topographic irregularities, including the Bozdağ elevation. Later, the erosional surface was disrupted and the structures which controlled development of the Lower-Upper Miocene rocks were cut by approximately east-west trending normal faults formed by rejuvenated north-south extension. This has led to development of the present-day east-west trending grabens during Plio-Quaternary time.

Two contrasting magmatic associations of NW Anatolia and their tectonic significance

Abstract In northwestern Anatolia two magmatic episodes are distinguished. Initially an intermediate to felsic calc-alkaline association was formed during the Oligocene-Early Miocene. In this period, granitic plutons were intruded into shallow levels in the crust. They are associated with hypabyssal and volcanic rocks. This magmatic event is late/post collisional with respect to the Tethyan collision, which occurred during the Late Cretaceous-Eocene period. The magmatic activity occurred when the region was still suffering a N–S directed compression, which is the result of continuing convergence after the collision. Consequently the magmas passed through an excessively thickened continental crust and, therefore, were contaminated by the crustal materials. The magmatic rocks of this phase are commonly high-K calcalkaline and partly shoshonitic and hybrid. Their compositions reveal crystallization from mantle-derived magmas contaminated by a high amount of crustal components. This magmatic event may thus be regarded as a Tibetan type. The geological signature of the magmas is also similar to the arc-derived magmas. The reason for this is that the metasomatic mantle where the magmas formed was permanently enriched when the subduction and total consumption of the NeoTethyan ocean floor occurred. The second magmatic phase occurred during the Late Miocene-Pliocene. Sporadically developed alkaline basalts were formed during this period. They show geochemical affinities similar to rift-type basalts. This genetical implication is supported by the structural data, which reveal that the E–W trending grabens of the western Anatolia developed in this period under N–S extensional regime.

The Çubukludağ graben, south of İzmir: its tectonic significance in the Neogene geological evolution of the western Anatolia

Abstract Field studies on the Neogene successions in south of Izmir reveal that subsequent Neogene continental basins were developed in the region. Initially a vast lake basin was formed during the Early–Middle Miocene period. The lacustrine sediments underwent an approximately N–S shortening deformation to the end of Middle Miocene. A small portion of the basin fill was later trapped within the N–S-trending, fault-bounded graben basin, the Cubukludag graben, opened during the Late Miocene. Oblique-slip normal faults with minor sinistral displacement are formed possibly under N–S extensional regime, and controlled the sediment deposition. Following this the region suffered a phase of denudation which produced a regionwide erosional surface suggesting that the extension interrupted to the end of Late Miocene–Early Pliocene period. After this event the E–W-trending major grabens and horsts of western Anatolia began to form. The graben bounding faults cut across the Upper Miocene–Pliocene lacustrine sediments and fragmented the erosional surface. The Cubukludag graben began to work as a cross graben between the E–W grabens, since that period.

Geology of the northern side of the Gulf of Edremit and its tectonic significance for the development of the Aegean grabens

Abstract This paper describes the Neogene evolution of northwestern Anatolia based on geological data collected in the course of a new mapping program. The geological history of the region, as recorded by the Neogene sedimentary and magmatic rocks that overlie the Paleozoic–Triassic basement, began after a lake invasion during the Early Miocene period with the deposition of shale-dominated successions. They were accompanied by calc-alkaline intermediate lavas and pyroclastic rocks ejected through NNE trending fractures and faults. The Lower–Middle Miocene successions were deformed under a compressional regime at the end of the Middle Miocene. The deposition of the overlying Upper Miocene–Lower Pliocene successions was restricted to within NE–SW trending graben basins. The graben bounding faults are oblique with a major strike-slip displacement, formed under approximately the N–S extension. The morphological irregularities formed during the Miocene graben formations were obliterated during a severe erosional phase to the end of the deposition of this lacustrine succession. The present E–W graben system as exemplified from the well-developed Edremit graben, postdates the erosional phase, which has formed during the Plio-Quaternary period.

DIFFERENTIATING STYLES OF ALTERATION WITHIN KAOLIN-ALUNITE HYDROTHERMAL DEPOSITS OF ÇANAKKALE, NW TURKEY

The Biga Peninsula of NW Turkey is host to many kaolin and halloysite deposits with mineralization occurring at the intersections of fault zones in contact with Late Eocene.Miocene calc-alkaline volcanic rocks. Distinguishing between the relative overprinting of hypogene by supergene processes in these deposits is a challenge and important because they affect the physical-chemical properties of minerals and their potential for industrial applications. This study examines the Sarıbeyli-Sığırlı and Bodurlar kaolin deposits in NW Turkey, which were formed from similar volcanics as evidenced by 40Ar/39Ar. Late Eocene (34.2 ± 0.20 Ma) to Early Oligocene (32.7 ± 0.17 Ma) ages for both primary volcanic rocks and alunites are consistent with surrounding rocks in the Çanakkale region. Criteria used to distinguish hypogene alteration from supergene alteration processes come from X-ray diffraction (XRD), Fourier-transform infrared (FTIR) and Raman spectroscopies, thermal gravimetric analysis (TGA), scanning and transmission electron microscopy (SEM, TEM), and elemental analyses. Isotopic δ18O depletion and δD enrichment of the Sarıbeyli-Sığırlı deposit suggests that it was more influenced by magmatic waters than was the Bodurlar deposit. The Bodurlar deposit contains a paucity of dickite compared to the Sarıbeyli-Sığırlı deposit, which is evidenced by lower TGA endotherms, higher ratios of XRD intensities for reflections at 1.316 Å and 1.307 Å, distinctive FTIR absorbance bands at 3620 cm− 1 and 3652 cm−1, and relative Raman intensities of the γ1 and γ5 vibrational modes.A genetic model is proposed whereby these deposits are mainly formed through an acid-sulfate hydrothermal alteration, in what appears to be a volcanic-hydrothermal system. The extent of hydrothermal alteration was controlled by fault density and the initial texture of the volcanic rocks. These steam-heated environments included sulfide-enriched vapors and groundwater mixed to varying degrees in the vadose zone. The Sarıbeyli-Sığrlı and Bodurlar deposits, respectively, contain mineral assemblages that reflect both hypogene (kaolinite, alunite, dickite) and supergene (kaolinite, halloysite, jarosite) processes. These observations offer a basis for comparing and discriminating the relative influence of these two important alteration processes responsible for the formation of kaolin deposits in NW Turkey and around the world.

Volcano-stratigraphy of the extension-related silicic volcanism of the Çubukludağ Graben, western Turkey: an example of generation of pyroclastic density currents

Western Turkey9s extension-related Cumaovasi volcanic rocks (Lower Miocene, 17 Ma) are excellent examples of silicic eruptions. The sub-aerial silicic volcanism at Cubukludag Graben between Izmir and Kusadasi in west–central Anatolia is mainly in the form of rhyolite domes, lava flows and pyroclastic deposits. The initial features of volcanism derived from phreatomagmatic explosive eruptions from silicic magma that came into contact with lake waters during Neogene times. Most of the volcanic succession represents pyroclastic density currents (PDCs), known as the Kuner ignimbrite. The deposits are fine grained and laminated at the base and pass laterally and vertically into deposits displaying well-developed traction structures, soft sediment deformation and/or erosion channels in the NE part of the region. Alternate deposits of massive, diffusely stratified lapilli and ash are the main products of the later explosive stage. Massive lithic breccias forming the top of the sequences are the proximal facies of the PDCs. The lava phase mainly consists of rhyolite extruded as dome and fissure eruptions of lavas, aligned along NE–SW-trending faults as well as from extensional cracks that are nearly perpendicular to the main graben faults. Considering the tectono-stratigraphical aspects and geochemical nature of the study area, we propose that the Cumaovasi silicic volcanism was produced by extension-related crustal melting during the Late–Early Miocene period (17 Ma).