Morphologic Framework of the Ganos Region

The most prominent geomorphic structures in the Ganos area are the two topographic highs (white areas in Fig. 4.2) separated by a distinct linear narrow valley (Fig. 4.2, 4.3). In The northern high area, the Ganos Mt forms a 35-km-long elliptical-shape smooth high topography with an average 7-8 km width. The broad morphology of the mountain suggests that uplift occurred within a uniformly distributed deformation. The southern limb of the ridge is truncated by the Ganos fault, which is the origin of the linear narrow valley. The ridge axis of the Ganos Mt. is sub-parallel (~N65°E) to the Ganos Fault (N70°E).

Figure 4.2 : Classified elevation map of the Ganos region. The linear valley marks the N70°E trending Ganos fault, which is expressed in between two topographic highs; Ganos Mt. and Doluca H. The uniform structure of the Ganos Mt. and the drastic decrease in elevation from 924 to -1125 m on its eastern part is distinct (see text for detail).

The highest point of the Ganos Mt. (924 m) is located at the eastern part, nonetheless a few kilometre farther east the elevation decreases drastically about 2000 m. Steep slopes of 40-50° on the east plunge into the Marmara Sea where a depth of -1125 m is reached; at the Tekirdağ Basin (Fig. 4.2). The top of the Ganos Mt. is flat and the surface is slightly tilted to the SW. This plateau is a relic surface now uplifted to >

600 m. The western termination of the Ganos Mt is smoother, where it dies out in the

~100 m high Evreşe plain (Fig. 4.2). The topography south of the fault is significantly lower and more composite (Fig. 4.2). Three linear ridges are identical, which highest points are the Doluca Hill (689 m) on the east, Helva Hill (446 m) in the centre and Tahta Hill (280 m) on the west. The ridge axis of these three highs are oblique (N40-50°E) to the Ganos Fault. The northern limbs of the eastern two hills are truncated by the Ganos fault, too. Armijo et al., (1999) notes the difference in morphology among the three folds. The highest anticline is to the northeast (669 m), is very well preserved; has a nearly intact domal shape. The middle anticline is less elevated (444 m) and clearly more eroded.

Figure 4.3 : Topographic profiles taken sub-parallel to the Ganos fault on each side and along the fault itself. Grey line illustrates the topography of the northern highest points, whereas the black line corresponds to the southern highs. The filled area shows the elevation of the Ganos fault.

The depression formed by the fault is significant. The elevation on each side of the fault shows similar fluctuations. Comparable elevation changes are about 15-17 km apart on the NE, while they are parallel located on the SW. See Fig 4.2 for location of profiles.

The third anticline to the southwest, where the envelope of Miocene strata is the most eroded and almost entirely blanketed by younger alluvium and colluvium, is the lowest (280 m). Based on these observation Armijo et al., (1999) propose that the less eroded anticline (Helva Hill) is the youngest and currently the most active. For that reason south of the Ganos fault, folding activity decays south-westward along the trace of the North Anatolian Fault. As a result the oldest anticline located 70 km southwest on the Gelibolu peninsula represents the total offset of the North Anatolian Fault since the last 5 Ma (Armijo et al., 1999). The suggested age for the North Anatolian Fault in this region is disputed by Yaltırak et al., (2000). The 5 Ma age is constrained by an angular conformity between the Alçıtepe and Kirazlı formations that dates back to the Messinian crisis. However, Yaltırak et al., point out that the related units are conformably overlain and the correct age of the NAF is 3.7-3.4 Ma.

The debate still continues since recent investigation of calcareous nannoplankton content of the related showed that the Alçıtepe formation is a Pliocene unit postdating the Messinian crisis and that the Kirazlı formation is a Late Miocene unit predating the crisis (Melinte-Dobrinescu et al., 2009).

The southern land is formed of several smaller hills intersected by deep and wide

the north of the Ganos fault. The advanced erosion may be a result of two reasons: 1) a longer period of erosion or 2) due to the difference in lithology. Both interpretations may be valid. Zattin et al, (2005) applied apatite fission track analyses on sandstone samples on both sides of the Ganos fault and concluded that exhumation took place ~10 Ma earlier (Late Oligocene) on the southern part; hence erosion started at an earlier stage. Additionally, it also implies that a pre-existing structural discontinuity was present between the highs in Late Oligocene (Zattin et al; 2005; Yaltırak; 1996; Yaltırak & Alpar, 2002). As mentioned in the previous section the geology on two sides is also different. Lower Eocene to Lower Oligocene turbitides on the North are more resistive to erosion, while the Miocene fluvial and coastal deposits on the south are unconsolidated and erode easily. Hills in this region are associated with several landslides (Plate 1). For instance, the valley slopes of the Hoşköy river are regions were intense land sliding occurs. The south-eastern slopes of the Palamut H., Armutluk H., Bayrak H., and Panayır H. are also other areas were land-slides can be observed. Documents of the 1912 earthquake report land-slides triggered by tremor in these regions (Mihailovic, 1927).

The topography on both sides of the fault is highest on the east and decreases significantly down to sea level on their west with an important dissimilarity. The change in elevation is not proportional on the two sides. The decrease on the north is more drastic than on the south. In addition, the highest point along the fault and on the south is reached west of Yörgüç; after this locality the elevation is continuously higher on the south. The difference in elevation between the North and South is ~200 m. The Ganos fault shows also dissimilarity east and west of Yörgüç. On the east it runs along the southern limb of the Ganos Mt with an average trend of N70°E, while west of Yörgüç it strikes along the northern limb of Doluca Hill trending N67°E. The change occurs where the fault reaches its maximum elevation. The 3° anticlockwise rotation necessarily yields further compression in the region. Offshore and onland studies suggest that the Ganos fault dips to the north (85° - 50°) between the Tekirdağ basin and Mursallı (Yaltırak, 1996; Yaltırak & Alpar, 2002; Okay et al., 2004). West of this area, alterations of structure, geometry and dip may be associated. The morphology suggests that west of Yörgüç the compressional deformation is not anymore localized on the south. This is also consistent with geodetic observations where the GPS vectors strike parallel to the fault (see p. 44).