Introduction

Geological factors control the geomorphology of the terrains (Migoń and Vieira 2014). Especially, lithological properties of rocks led to the formation of different types and various sizes of landforms. For example, weathering of granitoids may form peculiar landforms owing to chemical and physical processes (Twidale 1986; Migoń 2006). Inselbergs, domes, bornhardts, and tors are significant topographical rises in plain areas, and major geomorphological features are observed in granitoids from different countries (Twidale 1986, 1995; Migoń 2006; Twidale and Bourne 2008). Weathering pits, tafoni, honeycomb weathering, polygonal cracks, spheroidal weathering, flared slopes, and blocks are the examples of other geomorphological structures identified in granitoid rocks (Twidale 1986, 1995; Migoń 2006; Twidale and Bourne 2008). Those structures can also be reported in different rocks (e.g., sandstone, and volcanic rocks) (Campbell and Twidale 1995) and are identified in the southern Submassif of the Menderes Massif in SW Turkey. Some of them present a good scene for sightseeing, trekking, and geopark tourism.

Type and ratio of weathering are mainly controlled by lithological properties, mineralogical compositions (Tuğrul and Zarif 1999); climatic conditions (Campbell and Twidale 1995; Twidale 1997); surface water, underground water, and structural properties (Migoń 2004a, b; Vidal Romani and Twidale 2010); hardness (Černa and Engel 2011); and textural properties and time (Twidale 1986; Migoń 2006). Some properties have great importance in the weathering of granitoids, such as denudation history (Erginal and Ertek 2008), subsurface weathering (Roqué et al. 2013), and magma emplacement (Twidale 1986; Migoń 1996, 2006). The weathering factors are variable depending on the geological history of the lithological unit and latitudes of the exposed rocks. However, metamorphism effects were not documented and discussed in detail within these studies. Moreover, the studies about granites in Turkey have mainly focused on their engineering properties (Tuğrul and Zarif 1999; Ceryan et al. 2008; Dağdelenler et al. 2011; Kilic et al. 2014), whereas the studies about their geomorphological features are limited (Erginal and Ertek 2008).

Both sides of the road among the Yatağan and Çine towns in SW Turkey contain peculiar geomorphological features (Fig. 1). This region has been considered as a geopark for a long time, because of two ancient cities, namely, Stratonikeia and Lagina, and those geomorphological features. The geopark was thought as an alternative tourism for Muğla Province, which is one of the most important summer tourism centers of Turkey. The Southern Submassif is part of the Menderes Massif (Figs. 1 and 2). Leucogranites and orthogneisses have been delineated and mapped under Southern Submassif in this region. Many studies, summarized in the regional geological setting section, were related to lithological properties, metamorphism history, and geological evolution of those units. The leucogranite and orthogneiss show some geomorphological features, which are reported widely in granitoids (Goudie 2004; Migoń 2006) and other rocks (Campbell and Twidale 1995). None of the studies on Menderes Massif has worked on those geomorphological features. Tafoni, polygonal cracks, flared slope, and several other geomorphological features can be identified in this region. Metamorphism history and related characteristics of the Southern Submassif are the diagnostic features compared to the other regions that have similar geomorphological features. The main aims of this study are to document the types and distributions of geomorphological features of the Southern Submassif and to discuss the metamorphism effects, such as foliation and mineral differentiation on the weathering and the evolution of the geomorphological features.

Fig. 1
figure 1

Location map of the study area. a General geological map and DEM view of the Southern Submassif and surrounding region (after Okay 2001; Whitney and Bozkurt 2002). Red rectangular area shows the location of the view in b. b Detailed DEM view of the study area

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Fig. 2
figure 2

General geological map of the study area (simplified and modified from MTA map). The leucogranite boundary is obtained from Bozkurt (2004)

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Material and method

This study is performed in the SE region of the Southern Submassif (Figs. 1 and 2). The geomorphological features of leucogranite and orthogneiss have been documented, noted, and photographed. Their dominant distributions and dimensions have been recorded. Metamorphic properties, mineral content, and alignment of them were researched. Foliations of the orthogneiss were measured. Thin sections of representative samples were analyzed by using polarizing microscopes in the general geology laboratory of Muğla Sıtkı Kocman University. Discontinuities of leucogranite and orthogneiss were measured, and dominant sets have been evaluated by using DIPS software. In order to determine the strength of the leucogranite and orthogneiss, the l-type Schmidt hammer has been used during the field studies. The hammer was applied in parallel and perpendicular directions to foliation.

Regional geology

The Menderes Massif (MM) is the largest (>40,000 km2) metamorphic core complex exposed in the Alpine orogenic belt (Fig. 1; Şengör et al. 1984; Bozkurt et al. 1995; Bozkurt and Oberhansli 2001; Whitney and Bozkurt 2002). The Southern Submassif is the southern part of the Menderes Massif. The central part of the Southern Submassif includes 700–750-m-high hills. The eastern and southern sides of these hills are cut by valleys (Fig. 2). The core of the Southern Submassif contains Upper Proterozoic metasediments, mica schist, orthogneiss, metagabbros, and metanorite intrusions (Figs. 1 and 2; Candan et al. 2001; Dora et al. 2001). The Massif is overlain by cover units including Paleozoic-Lower Tertiary platform carbonates, marl, clayey limestone, and marble (Figs. 1 and 2; Okay 2001; Özer et al. 2001).

A few studies have been performed on the detailed geology of the studied region (Mineral Research Institute-MTA; Bozkurt 2004; Koralay et al. 2012; Bozkurt et al. 2015). Precambrian migmatite, gneiss, augen gneiss, metagranitoid, Paleozoic augen gneiss, phyllite, schist, marble, and quartzite in the southern region were mapped in 1/25,000-scaled geologic maps prepared by MTA (Figs. 2 and 3). Bozkurt (2004) identified leucogranite including K-feldspar, plagioclase, quartz, muscovite, biotite, tourmaline, zircon, rutile, monazite, and opaque minerals around the Hacıaliler district (Fig. 2). Blastomylonitic orthogneisses with muscovite, biotite, quartz band and flattened feldspar (augen) are exposed in northern part of the metagranite (Bozkurt 2004). Semipelitic schist, marble lenses, psammitic schist crop out in southern part of the leucogranites (Bozkurt 2004). Bozkurt et al. (2015) reported that the leucogranite (late Middle Eocene) intruded to the orthogneisses and cover units of the Southern Submassif. However, Koralay et al. (2012) classified those rocks in and around the Hacıaliler district as leuco-tourmaline orthogneiss and biotite orthogneiss. These units intruded to southern garnet-mica schist and biotite-albite schist (Koralay et al. 2012).

Fig. 3
figure 3

a The orthogneisses form a bald hill north of the Memişler village. b Sketch diagram of the bald hill containing several pillar structures, corestones, and blocks. Some places have a rocky view, while some places are covered by thin regolith

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Metamorphism and tectonic history of southern Submassif

This massif was affected by two main metamorphisms that are regional HT/MP Barrovian-type in Eocene and subsequent greenschist retrograde metamorphism (Şengör and Yılmaz 1981; Şengör et al. 1984; Bozkurt and Satır 2000; Bozkurt and Oberhansli 2001; Rimmele et al. 2003; Bozkurt 2004). The southward transport of Lycian nappes (ophiolites, accretionary prisms, volcanosedimantary units, and Carboniferous-Permian-Upper Cretaceous sedimentary rocks) over the Menderes Massif has caused regional metamorphism (Şenel 1997; Robertson 2000; Bozkurt 2004). After the emplacement of Lycian Nappes to the south of the Southern Submassif, the E–W-trending Kale–Tavas Basin (ancestor of Gökova Graben in Fig. 1) was developed in Oligocene (Görür et al. 1995; Gürer and Yılmaz 2002). Later, NNW–SSE-directed Milas-Ören and Yatağan grabens were subjected to extensional periods in SW Anatolia during the Early–Middle Miocene (Gürer and Yılmaz 2002). The exhumation of the Southern Submassif led to an E–W-trending horst development in Late Miocene (Gürer and Yılmaz 2002) or Oligo-Miocene (Bozkurt 2004; Koralay et al. 2012). Bozkurt et al. (2015) reported the exhumation age of the massif as earliest Miocene based on the unconformable cover sediments. Then, recently active E–W Gökova Graben (Gökova Bay) cuts older units after Late Pliocene (Fig. 1; Görür et al. 1995; Gürer and Yılmaz 2002).

Gemorphological features, weathering profiles, and Grus development

The northern part of the study area includes a domed bald hill and high mountains (250–300 m higher from surroundings, e.g., Gökbel mountain) formed by orthogneiss (Fig. 1). The eastern and southern slopes of it rapidly decrease (Figs. 1, 3, and 4). The slope of the hill contains pillar structures (Figs. 3, 4, and 5). Moreover, other geomorphological features such as boulder, blocks, weathering pits, tafoni, honeycomb weatherings, and polygonal cracks are observed in the leucogranite and orthogneiss outcrops (Figs. 5 and 6). Table 1 summarizes properties and location of those geomorphological features.

Fig. 4
figure 4

a The orthogneisses form a bald hill southwest of the Memişler village (cow in circle for scale). b Sketch diagram of the bald hill. The skirt of the bald hill contains several pillar structures. Each pillar structure is fractured with NS- and EW-directed discontinuity sets. EW-directed exfoliation cracks have also affected these rocks. The crossing of joint sets forms several block–corestone formation

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Fig. 5
figure 5

a The pillar structure in orthogneiss (north of Hacıaliler District) is formed by the splitting of rocks along the fractures. Some large rock surface contains surface weathering and polygonal cracking. Some fractures (possibly younger structure) cut the spheoridal weathering (man in circle for scale: 1.75 m). b The pillar structure in leucogranite (south of Hacıaliler District) forms a dome-shaped ridge. The upper parts are sharpened as a result of the spheoridal weathering. Some fractures cut the spheoridal weathering. The tafoni is observed at the top of the pillar. Exfoliation crack is not observed in this type of structure (man in circle for scale, 1.75 m)

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Fig. 6
figure 6

Field view of the minor geomorphological structures that can be observed both in leucogranites and orthogneiss. a The weathering pit is formed as a result of the surface water flowing and selective erosion with various scales (in orthogneiss, SW Memişler village). The water flowing can create depressions with varying scales (hammer in circle for scale, 33 cm). b The polygonal crack or surface weathering is formed on the surface of boulder block (in orthogneiss, SW Memişler village; hammer in circle for scale, 33 cm). c Some blocks at the top of the rock contain tafoni with honeycomb weathering (in orthogneiss, N Hacıaliler District). d The close inside view of the tafoni includes honeycomb weathering (hammer in circle for scale, 33 cm). e A meter-scaled tafone includes honeycomb weathering and water trace. Two small depressions are observed at the left of the tafoni (in orthogneiss, N Hacıaliler District; hammer in circle for scale, 33 cm). f The selective weathering, tafone formation, and dome shape of the block can lead to the different view of the mushroom rock or corestone. A two to three-meter-scaled spoon-like mushroom rock is formed as a result of the breaking of the dome rock including tafoni (in orthogneiss, N Hacıaliler District). g Different types of geomorphological features can be observed in the same location. Fractures, exfoliation orientations, water, and subsurface weathering effect led to the formation of weathering pit, corestone, spheoridal weathering, and woolsack developments (in orthogneiss, N Hacıaliler District). h The surface weathering along the exfoliation or cracks led to the formation of spheoridal weathering and flared slope. The size of the flared slope can reach to a maximum of 2 m in height and 2.5 and 3 m in depth (in orthogneiss, N Hacıaliler District; man for scale, 1.75 m)

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Table 1 Geomorphological features, weathering profiles, and grus development in the Southern Submassif of Menderes Massif
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Pillar structures are relatively bigger geomorphological features in the study area (Table 1; Figs. 3, 4, and 5). Crossing of joints, subsequent water weathering followed by cracks, and stripping of disintegrated and decomposed products control their shape, size, and location. Dome-topped pillar structures are smaller than the flat-topped structures. Cracks, which cut the pillar structures, point out the younger structures that developed after weathering. Initially, flat-topped castellated-type pillar structures have been developed, and subsequent spheroidal weathering (possibly surface weathering) led to the development of dome-topped pillar structures.

Weathering pits are depression on the upper surface of the host rock (Table 1; Fig. 6a). These weathering pits like small channels are generally extended parallel to the foliation planes and carry surface water toward edges of rocks (Fig. 6e). They are rarely found at the bottom surface of rocks. Recent water traces have been observed in both upper and bottom surfaces of rocks.

Polygonal cracks are rectangular–pentagonal–hexagonal attached cracks, found on the sidewall of rocks in different sizes (Table 1; Figs. 5a and 6b). Their distributions are random in the study area, and only a few rock surfaces show these features.

Tafoni (tafone in singular) is the most common cavernous weathering type in the study area (Table 1; Figs. 5b and 6c–f). Their size and shape are highly variable (Table 1). Spheroidal weathering is observed at the top of it. Flared slopes are developed in the entrance of tafoni. Water traces and honeycomb weatherings have been found within the tafoni (Fig. 6d). The entrance of the tafoni is generally parallel to the mineral alignment and foliation. After the narrow entrance, tafoni are enlarged inside the upper layer.

Alveoli-honeycomb features are another cavernous but small features. They are developed inside the tafoni as several small chambers (Table 1; Fig. 6d). Water traces are also found in those small chambers.

The boulders and blocks can be found as attached to the host rock and detached blocks (Table 1; Figs. 6f, g). Crossing of joints and stripping of weathered parts led to the formation of attached blocks of various sizes on orthogneisses and leucogranites. Sometimes, blocks are detached from the rock body and transported downdip. Spheroidal weathering is observed on the upper surface of boulders and blocks. Weathering pit rarely causes wavy upper surfaces (Fig. 6g). Red color weathering is observed at the bottom of blocks due to weathering of iron-rich minerals. Generally, flared slopes are found at the lower edge of attached blocks (corestone; Fig. 6g). Sometimes, block separation led to the formation of woolsack (Fig. 6g).

The exfoliation cracks, sheeting (onion skin weathering), or pseudobedding are well observed in the orthogneiss than in the leucogranite. The exfoliation cracks of orthogneiss are parallel to foliation planes (Table 1; Figs. 4 and 5a). They are parallel to mineral alignment in leucogranite.

Spheroidal weathering is responsible for the roundness of boulders, blocks, and upper surfaces of pillar structures (Table 1; Figs. 5b, 6g, h). Flared slopes are another concave features developed at the base of blocks (Table 1; Fig. 6h). They are parallel to the other directional features such as foliation and mineral alignment (Fig. 6h).

Weathering profiles are different from the other features listed above. The weathering can cause a layered structure from surface to subsurface (I to VI grade, Thomas 2004; Turkington 2004; Migoń 2006; Heidari et al. 2013; Miśćević and Vlastelica 2014). Grade VI represents soil horizon at the surface and heavy weathering, while grade I represents the fractured fresh rock (Thomas 2004). The typical weathering profile is only observed in quartz quarry and several road cuts (Table 1; Fig. 7a). The thicknesses of V and VI grades are increased in downdip direction (Fig. 7a). The boundary between the grades is not regular due to their irregular growth along the fractures (Fig. 7a). The weathering profile is thicker in the quarry than in the road cut.

Fig. 7
figure 7

a The deep weathering is rarely observed in the study area. The thickest one is observed in the quartz quarry in leucogranite in W Seykel District (I fresh rock, II slightly weathered, III moderately weathered, V completely weathered, VI residual soil; man for scale, 1.75 m). b The grus including gravelly sand has a sharp contact with the unweathered orthogneiss rock in N Hacıaliler District (hammer for scale, 33 cm)

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Grus is weathered sediment derived from the upper part of the hill, transported in downdip direction and accumulated in lowland area among the hills (Table 1; Fig. 8b). The apparent thickness of quartz-rich sediment must be higher than 1–1.5.

Fig. 8
figure 8

DEM image of the detailed study area. Kinematic analyses of fractures measured from orthogneiss in N Hacıaliler District and W of the Memişler district. One location in S of Hacıaliler District has been chosen for fracture measurement in leucogranites

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Controlling factors for the development of gemorphological features

This section summarizes the controlling factors of geomorphological features observed within the study area. Fractures, exfoliation, climatic condition, rock strength, surface–underground water, biologic degradation, and subsurface weathering are the main controlling factors for the developments of geomorphological features in the granitoids (Twidale and Bourne 1975; Twidale 1986; Migoń 2004a, 2006; Twidale and Bourne 2008; Vidal Romani and Twidale 2010). Some of them are also important for the geomorphologic development and weathering of the Southern Submassif of Menderes Massif. These are listed below.

Structural alignments, pseudobedding (exfoliation cracks)

Migoń (2006) has reported cross, longitudinal, and diagonal fractures in granite blocks, and weathering along those cracks caused pillar structure formation. The orthogneiss has three joint sets in the eastern part (no. 29, dip/dip direction, 75°/185°, 69°/239°, 65°/270°; foliation 30°/284°), and two joint sets in the northern part (no. 29, dip/dip direction 69°/172°, 76°/88°; foliation 17°/323°). Four joint sets and randomly distributed joints were measured in leucogranite (no. 22, dip/dip direction, 68°/12°, 67°/272°, 52°/58°, 20°/192°; foliation 25°/223°) (Fig. 8). N–S-directed joints are evaluated as a cross joint, and E–W-directed joints are evaluated as longitudinal fractures in blocks. The exhumation of orthogneiss and leucogranite causes exfoliation cracks parallel to foliation. The exhumation of the massif, emplacement of Lycian nappes, and compressional and extensional forces caused these fractures. The southern side of the study area is located within the boundary between the massif and cover units. Thus, the density of fractures in the southern part is higher than that in the northern part.

The crossing of fractures led to host rock fragmentation and pillar and block formation. Moreover, abundant fractures cause easy circulation of underground water, so weathering effects diffuse through the rock interior. Some researchers, mentioned in Table 1, proposed that subsurface weathering is important in the development of several distinct geomorphological features (flared slope, polygonal cracks, etc.). Similarly, the underground water percolates into the orthogneiss and leucogranite via using discontinuities. When the rock is exhumed, those weathered parts are stripped, and the hard-resistant unweathered parts remain.

Foliation, mineralogical contents

The leucogranite consists of K-feldspar, plagioclase, quartz, muscovite, and biotite as primary minerals (Figs. 9a–c), whereas tourmaline, zircon, rutile, monazite, and opaques (e.g., magnetite) are accessory minerals (Bozkurt 2004). Quartz-tourmaline nodules reported by Bozkurt (2004) are also observed within the leucogranite. In addition, garnet minerals were determined under the microscope. The orthogneiss displays well-observed mylonitic foliation including parallel alignment of mica minerals (biotite and muscovite), quartz ribbons, and flattened feldspar porphyroclasts (Figs. 9d–f) and distinct NE-trending mineral lineation (Bozkurt 2004). Those bands can be easily followed during the field observations and petrographic analysis (Figs. 9e, f). Foliation of the orthogneiss is inclined to WNW. The flattened minerals are observed in leucogranite; however, they are not significant as in the case of orthogneiss. Mineral alignment of the leucogranite is inclined to SW. Wind and water (surface and underground water) are active along those features. Flared slopes and exfoliation cracks are parallel to foliation planes or mineral alignments in the study area. Red parts around the Fe-bearing minerals such as biotite exhibits the chemical weathering affects. Moreover, after the rapid weathering of less resistant minerals such as feldspar, durable minerals like quartz start to be transported via slope, surface water, wind, and gravity and form grus (Fig. 7b).

Fig. 9
figure 9

a A close view of the metamorphosed leucogranites that include large glassy quartz, pink K-feldspar, and black tourmaline. b Euhedral–subhedral grant is also found in the thin section of leucogranites (under normal light). c Granat is surrounded by large quartz and biotite minerals (under polarized light) (Tu tourmaline, Qu quartz, Bi biotite, Gr granat, Pl plagioclase). d Gneissic banding observed in orthogneiss including gray-colored glassy quartz and white-colored large and elongated plagioclase. e The elongated biotite mineral, quartz, and plagioclase are found in this rock (under polarized light). f Sometimes, large quartz creates an augen gneiss view in the rock (under polarized light)

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Climatic condition

Weathering caused by water, hydration, sapping, and halocasty are important processes in cavernous weathering (Strini et al. 2008; Twidale and Bourne 2008). When the rocks crop out, they will be under the effect of water attack, and this controls the weathering of rocks (Vidal Romani and Twidale 2010). Morever, tafoni enlargement is related to wind erosion, freezing, microclimatic conditions, and hydration (Twidale and Bourne 2008).

The leucogranite is exhumed after early Miocene (Bozkurt et al. 2015). Therefore, former and latter climatic conditions of exhumation are important. Akgün et al. (2007) reported that annual temperature varies (5.5–21.3 °C), as well as mean annual precipitation (1122–1520 mm) at Chattian and Aquitanian periods in western Anatolia. Mean annual temperature and precipitation were 1.1–20.8 °C and 1146–1322 mm, respectively, in the Early–Middle Serravallian–earliest Tortonian periods in Yatağan town, SW of the study area (Akgün et al. 2007). Lower precipitation was evaluated as 823 mm in the dry season during the middle–late Tortonian in this region (Akgün et al. 2007). Recently prevailing wind directions are S–E, N–E, and S–W in the study area (Haktanır et al. 2010; Ölgen and Gür 2011). The annual temperature of the Muğla region varies from −10.0 to 41.2 °C (56 years average; MGM 2013a, b); the annual average rainfall is 1130.5 mm (40 years average; MGM 2013a). These point out to the warmer climatic condition. Underground water percolation along the fracture is important in subsurface weathering. If recent climatic conditions were taken into consideration, wind weathering could have smoothened the sharp corner of the rock and promoted the spheroidal weathering and tafoni development and transportation of disintegrated rock fragments. The recent water leakages are particularly observed in the inner and outer parts of the rocks. Tafoni and honeycomb structures preserved inside into the tafoni have been developed within the rocks (Fig. 6e). The formation of weathering pits is also related to the movement of surface water on the rock surface (Fig. 6a).

Strength properties

The Schmidt Hammer test is one of the in situ tests used for determining the strength of rocks during field study (Özbek and Gül 2011). The higher rebound values of this hammer point out the more resistant rock. Anisotropy of the rock due to bedding and foliation may affect the strength of rock (Ulusay and Gökçeoğlu 1997; Özbek 2009). Thus, the Schmidt hammer is applied perpendicular and parallel to the foliation. The average Schmidt hammer rebound value is 45.8 perpendicular to the mineral alignment in leucogranite, and 38.6 parallel to the alignment. The average Schmidt hammer rebound value is 42.5 perpendicular to the foliation in orthogneiss, and 29 parallel to the foliation. The strength of both rocks is lower in the direction parallel to the mineral alignment. Therefore, weathering of rock firstly develops parallel to the exfoliation then intrudes and extends through the interior of the rock. Anisotropy of the orthogneiss is larger than the leucogranite due to metamorphic texture development.

Discussion

The leucogranite and orthogneiss in the Southern Submassif of Menderes Massif in SW Turkey show some geomorphological features that are typically reported in granitoids (Goudie 2004; Migoń 2006). Studies in the study area are mostly related to the general geological properties, deformation, and metamorphism history of the Menderes Massif (Bozkurt et al. 1995; Bozkurt and Satır 2000; Bozkurt and Oberhansli 2001; Whitney and Bozkurt 2002; Rimmele et al. 2003; Bozkurt 2004; Koralay et al. 2012; Bozkurt et al. 2015). These studies have not considered the geomorphological features of the Southern Submassif. Similarly, several studies about granitoids of Turkey have mainly focused on engineering properties of granitoids (Tuğrul and Zarif 1999; Ceryan et al. 2008; Dağdelenler et al. 2011; Kilic et al. 2014), whereas studies about their geomorphological features are limited (Erginal and Ertek 2008).

The inselbergs, domes, bornhardts, and tors are sharp hills surrounded by plain and macro landforms in granites (Ehlen 2004; Migoń 2004a, 2006; Twidale 2007). The domed bald hill and macro landforms of the study area (Figs. 1, 3, and 4) are surrounded by valleys. Exhumation of the massif led to its formation.

Pillar structures are pinnacle rockheads on low-lying host rock (Figs. 3, 4, and 5). The subsurface weathering during and after exhumation, surface weathering after exhumation, selective weathering along the fracture, and stripping of weathered units led to the formation of pillar structures, especially castellated-type pillar structures. Later surface weathering due to wind and water action may produce dome-topped pillar structures.

Migoń (2006) and Vidal Romani and Twidale (2010) emphasized that cross, longitudinal, and diagonal fractures or orthogonal structures in granite block increase the weathering effect. The orthogneiss has two and three joint sets, while leucogranite has four joint sets in the study area (Fig. 8). The southern part of the region has more discontinuity sets due to cover and core unit relations of the Southern Submassif. The exfoliation cracks act as another joint set at the upper part of units (Figs. 4 and 5a). Some joints are parallel to foliation of orthogneiss and mineral alignment of leucogranite, while some of them cut the foliation perpendicularly or obliquely. Those structures cause fragmentation of rocks and form a weakness zone for underground water action in subsurface environment. They led to the formation of attached and detached blocks (Figs. 3, 4, and 6f, g).

Mineral resistance and strength differentiation related to mineral alignment have significant effect on weathering. Migoń (2006) suggested that granular disintegration due to enlargement of mineral boundaries of granites promotes the weathering. The metamorphism of the studied units increases this effect. The metamorphism led to gneissic banding (Fig. 9), elongated and flattened alkali feldspar, quartz ribbons, and platy mica minerals (Bozkurt 2004). The resistances of those minerals are different. Mica minerals and feldspar can be easily eroded compared to the quartz.

Černa and Engel (2011) pointed out that the strength value of granite exposure is increased with depth based on the Schmidt hammer rebound values. The fracture density on surface and weathering led to low rebound values (Černa and Engel 2011). The granite has internal homogeneity in those applications, and the results are also valid for our study. However, the Schmidt hammer rebound values are variable in studied rock units due to mineral alignment and mineral content. The strength of orthogneiss is higher in perpendicular to the foliation than that parallel to the foliation. The leucogranite strength is relatively higher than that of orthogneiss in every direction because of mineral content and relatively low anisotropy. Thus, the weathering feature number of orthogneiss is relatively higher than that of leucogranite.

The fracture is splitted into several fragments of orthogneiss and leucogranite. Surface and underground water and wind action followed those weakness zones. They are especially acted at the crossing of joints, and the relatively low-resistant minerals start to weather. The weathering may cause a flared slope (Fig. 6h), spheroidal weathering (Figs. 5b and 6g, h), polygonal cracks (Figs. 5a and 6b), and weathering pits (Fig. 6a) on block surfaces (Fig. 7b). If the weathering affects the rock interior, cavernous type weathering such as tafoni (Figs. 5b and 6c–f) and honeycomb weathering (Fig. 6d) may develop.

In addition, Vidal Romani and Twidale (2010) reported that water caused the weathering of feldspar to clay, then led to the formation of quartz separation and grus. As a result of this process, similar quartz-rich grus filled the small valley of the study area (Fig. 7b).

Two stages of weathering are proposed for granitoid weathering, as the subsurface weathering (groundwater softening the main rock) and the stripping of regolith cover (Bourne and Twidale 2002; Vidal Romani and Twidale 2010). It is reported that the polygonal crack, boulder formation, pillar structure development, flared slopes, and grus formation are evaluated as a product of subsurface weathering by different researchers (Table 1). After the exposure of those structures, wind and surface water increase the weathering effect in the study area. Recent water traces in tafoni, honeycomb weathering, and weathering pit indicate the water effect.

All geomorphological landscapes listed above are determined in the Southern Submassif of Menderes Massif in SW Turkey, and they are observed in granitoids from different countries (USA, Ericson et al. 2005; Spain, Roqué et al. 2013; Portugal, Begonha and Sequeira Braga 2002; Ireland, Sweevers et al. 1995; Finland, Darmody et al. 2008; Central Europe, Migoń 1996; Iran, Heidari et al. 2013; Turkey, Erginal and Ertek 2008). Magma emplacement, tectonism, lithology, and fracture are proposed as main controlling factors for granitoid weathering (Migoń 2004a, 2006). In addition, tectonic and metamorphic history increases the weathering effect in the study area. Especially foliation, mineral alignment, mineral content, strength differences of minerals, and development of various discontinuity sets are offered for the weathering in the study area. Combination of all those factors led to the formation of a good scene for possible geotourism activity. It is necessary to take urgent measures by local and central authorities for protecting those geomorphological features, or at least those peculiar ones.

Conclusions

The results obtained in this study are listed below.

  • The study area includes orthogneiss and leucogranite that exhibit various geomorphological features of typical granitoid morphology. The larger features such as bald hill and pillar structures are well observed in the study area.

  • The weathering pits, polygonal cracks, tafoni and honeycomb weathering, spheoridal weathering, flared slopes, and blocks have been determined in this study. The weathering profile and grus are also found.

  • The tectonic alignments developed depending on the complex tectonic regime led to the fracturing of orthogneiss and leucogranite. Water follows these fractures in the subsurface. They initially control development of pillar structures, blocks, and boulders. The metamorphism of rocks caused foliation (i.e. gneissic banding and mineral alignment). Exhumation of these rocks formed exfoliation cracks. Strength differentiation of the foliated rocks and difference in mineral durability increase the weathering effect. Subsurface weathering led to formation of pillar structure, polygonal cracks, and flared slope. When weathered materials are stripped, they are exposed.

  • Under the effect of previous controlling factors, wind and water have initially attacked the weakest part—sharp corner of the rocks under surface weathering. Firstly, round-edged spheroidal weathering is formed, and then tafoni and honeycomb weatherings are developed depending on the advancing of weathering to the rock body.

These special geomorphologic landscapes primarily need to be preserved by both locals and public administrations in order to prevent them from the mining companies and establish a geopark to this area.