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ABRIDGED

 

ENGLISH VERSION

 

 

1. INTRODUCTION

 

In the framework of this Ph.D. thesis, the neotectonic evolution of the Central-western Peloponnessos was studied in detail (Fig. 1.1). The western Peloponnessos, being very close to the Hellenic Trench, is one of the most active areas in Greece. The targets of this Ph.D. thesis are the following: (i) compilation of the neotectonic map in scale 1:100.000, (ii) calculation of the rates of subsidence, and uplift during Quaternary, (iii) effort for understanding of the neotectonic evolution of Central-western Peloponnessos, and (iv) understanding of the regional stress field. In order to achieve the above mentioned, we studied the following: (i) The drainage networks of Zacharo, Neda, and Ano Messinia basins, (ii) The distribution of planation surfaces, (iii) The slope gradient as well as the erosion to the depth, (iv) The deformation of alpine structures during the neotectonic period. (v) Detail geological and tectonic mapping compiling the neotectonic map in scale 1/100.000. Based on this study the following new data and results came out, which are new evidences for the geological research of the area.

 

 

2. GEOLOGY

 

1.             A new occurrence of the Ionian geotectonic unit was mapped and studied in Lapithas Mt. (Kaiafas village) (Fig. 2.7, 2.8).

 

2.             The lithostratigraphy of the post alpine deposits resulted in the distinction of the following formations in the order from the older to younger in every basin:

 

a) Kyparissia – Kalo Nero basin (Fig. 2.13)

 

·         Raches formation (Early Miocene?) (Fig. 2.14)

·         Psili Rachi formation (Early  Pliocene ΝΝ-13) (Fig. 2.15, 2.16)

·         Peristera – Sidirokastron formation (Late Pliocene)

·         Myron formation (Early Pleistocene ΝΝ-19)

·         Mouriatada – Kakkava formation (Middle Pleistocene) (Fig. 2.19)

·         Σχηματισμός Κυπαρισσίας - Καλού Νερού (Τυρρήνιο?) (Fig. 2.20)

·         Kalo Nero formation (Latest Pleistocene)

 

 

b) Neda basin (Fig. 2.21)

 

·         Elaia formation (Late Pliocene)

·         Neda formation (Late - Middle Pleistocene, ΝΝ-19 ΝΝ-20) (Fig. 2.23, 2.24, 2.25)

·         Reddish Siliclastic formation (Late Pleistocene)

 

 

c) Zacharo basin(Fig. 2.29, 2.32)

 

i) Eastern sub-basin

 

·         Tsemberoula formation (Late Miocene – Early Pliocene?) (Fig. 2.30)

·         Loggo formation (Late Pliocene – Early Pleistocene?) (Fig. 2.31)

 

ii) Western sub-basin

 

·         Xirochorion formation (Late Pliocene) (Fig. 2.33)

·         Anydron formation (Late Pliocene – Middle Pleistocene ΝΝ-20) (Fig. 2.34)

·         Zacharo formation (Late – Middle Pleistocene)

·         Neochorion formation (Late Pleistocene?)

 

3.             Between the above mentioned formations many discordances were observed. In some cases, especially in Zacharo basin, lateral transition from one formation to the other was also observed.

 

4.             Sampling in many of the of the marine post alpine formations occurrences gave us the opportunity to define macro micro and nanno-fossils. They originate mainly from three stratigraphic horizons: i) Early Pliocene (ΝΝ-13), ii) Early Pleistocene (ΝΝ-19) and iii) Middle Pleistocene (ΝΝ-20).

 

5.             The origin of the pebbles that constitute the polymictic conglomerates of the Neda formation is of great interest, as some of them come from an area located far away from the nowadays watershed of the basin. The highest percent of the pebbles originate from the Pindos geotectonic unit (pelagic sediments), which is located in the nowadays basin , a lower percent comes from the carbonates of Tripolis geotectonic unit (Neritic carbonates) and a very small percent comes from metamorphic rocks (phyllites, quatzites) belonging in Arna geotectonic unit. The study of the pebble’s size shows that all this material came from east to west. The rocks occurring within the Neda basin watershed belong to Pindos unit. Thus, Neda basin should have communicated mostly periodically with Megalopolis basin, at the eastern margins of which, the Tripolis and Arna Geotectonic units occur.

 

6.             The marine – lagoonal sedimentation took place in very shallow environment in depths not surpassed the 20m and relatively in warm water.

 

7.             The lacustrine sedimentation of Tsemberoulas formation took place in warm climate conditions.

 

 

3. GEOMORPHOLOGY

 

1.       Six (6) self-sufficient morphological units occur in the Central-western Peloponnessos, most of them trending E-W, while the easternmost trends NNW-SSE. The six (6) morphological units are (Fig. 3.1, 3.2, 3.3):

 

1.       Lapithas Mt.

2.       Minthi Mt.

3.       Tetrazio Mt.

4.       Lykaeon Mt.

5.       Neda hills and

6.       Dorion – Kalo Nero hills

 

2.       The morphology of the above mentioned units shows an asymmetry related: (i) to the water divide, (ii) to the drainage basins distribution (iii) to the drainage network and (iv) to the slope gradient. (Drainage networks of a) Zacharo, b) Neda, γ) Ano Messinia, maps attached).

 

3.       The geomorphologic asymmetry is due to the neotectonic structure of the area.

 

4.       The drainage network is constituted by the following rivers:

 

·     Ano Messinia drainage network:

o        Amfitas and Mavrozoumenas drainage network.

o        Peristeras (Sellas) drainage network.

·     Neda drainage network.

·     Zacharo drainage network:

o        Tsemberoulas drainage network.

o        Anhydrous drainage network.

 

5.       The Peristeras drainage network is a 5th order drainage network, whereas the Amfitas and Mavrozoumenas one is 4th order and joining the form a 6th order stream that flows out south in the Gulf of Messinia. The 6th order Neda drainage network flows out west in the Gulf of Kyparissia. Within the Zacharo basin there are two drainage networks, the 4th order Anhydrous drainage network which flows out west in the Gulf of Kyparissia and the 5th order Tsemberoulas drainage network which joins the Alfios river system in the Olympia basin to the north.

 

6.       The main streams of the drainage network are controlled by the neotectonic fault zones and the faults trending E-W, while the smaller order streams are parallel to the alpine fold axes and thrusts trending according to the area location NE-SW, N-S or NNW-SSE and some special cases WNW-ESE (see also Tectonic Map, attached).

 

7.       The quantitative analysis of the Neda drainage network showed the following: (Tables 3-1, 3-2, 3-3):

 

a)       The asymmetric distribution of the 3rd order basins related to the main stream. (Fig. 3.4).

 

b)       The drainage network located north of the 6th. order stream is of dentritic type, while south more orthogonal and less dentritic type. Although there is intensive differentiation in the distribution of the stream number from basin to basin, it works in the framework of the HORTON’S law.

 

c)       The total stream number (ΣL) in every basin varies from 7 to 40. These deviations should be attributed mainly to the variety of the lithology (Fig. 3.5, 3.6).

 

d)       The 1st order streams developed on the post alpine (Pleistocene marine) deposits north of the 6th order stream are parallel to the faults trending NE-SW. Secondarily there are streams that have direction NNW-SSE or NW-SE.

 

e)       The 1st order streams, which are developed on the alpine formations of the Pindos geotectonic unit and occur north of the 6th order stream trend NW-SSE, N-S or NE-SW depending on the thrust and fold axes directions in the area. In cases the stream direction is Ε-W this direction is parallel to the fault direction.

 

f)        South of the 6th order stream, the 1st order streams trend N-S parallel to the thrusts and fold axes or they are parallel to the neotectonic faults trending E-W.

 

g)       The above mentioned for the 1st order streams are valid for the 2nd order streams.

 

h)       The 3rd order streams that are developed on the Pindos unit formations are parallel to alpine lineament, that is north of the 6th order stream they trend NE-SW and south N-S. In the east part they trend E-W.

 

i)         There is no deviation of the Bifurcation ratio Rb1,2 values from the expected values. The highest values must be related with the basin’s elongation, which is controlled by the tectonics mainly the alpine tectonics.

 

j)         There is intensive deviation of the Bifurcation ratio Rb2,3 values from the expected values. The highest values must be related with the basin’s elongation, which even in this case is controlled mainly by the alpine tectonics.

 

k)       It seems that there is no dependence of the Bifurcation ratio Rb1,2 values and the basin area as it seems to happen for the Bifurcation ratio Rb2,3 values (Fig. 3.6).

 

l)         The total stream length (ΣL) increases when the basin area increases (Fig. 3.7).

 

m)     The high deviation values of the mean stream length () are not depending of the area of the surficial occurrence of the geological formations. The high deviation values are observed in basins with high values of H (Z-z), which are located very close to the basin water divide (Fig. 3.8).

 

n)       The stream length ratios R1,2 and R3,2 are not depended by the lithostratigraphy of the formations on which the streams have been developed, but they mostly depend by the tectonics.

 

o)       The drainage density (D) depends on the mean altitude, the mean basin gradient, the relief energy and the tectonic structure of the major area.

 

p)       The stream frequency (F) depends on the lithology, the tectonics and the karstification.

 

q)       There is a strong relation between the 3rd order basin area and the geology of the basement. The larger basin areas have developed on alpine formations and the smaller on post alpine formations. Any deviation from this rule is due to the neotectonic deformation of the area.

 

r)        The 4th order stream that has been developed on the post alpine deposits trends NNW-SSE, parallel to the faults strike. On the contrary, the direction of the 4th order streams that have been developed on the alpine formations, have been affected so from the alpine tectonics as from the neotectonic deformation.

 

s)        The 5th order stream directions have been defined by the neotectonics (faults, fault zones).

 

8.       Two drainage networks have been developed within the Zacharo basin, the Tsemberoulas network to the east joining the Alfios river system and the Anhydrous network which flows out in the Gulf of Kyparissia. (See Drainage network of Zacharo basin map attached). The tectonics and mainly the neotectonics have affected all the directions of the streams of all orders.

 

9.       All the observed differentiation’s in the total stream number (ΣΝ) of the main drainage network related to the correspondingly basin area are due mainly to the neotectonic deformation of the area (Table 3-4).

 

10.   The geographical distribution of the planation surfaces that have been developed on the alpine formations indicate the existence of at least three blocks (Minthi, Lykaeon and Tetrazio). These three blocks behave as tectonic dipoles, which are rotated around an almost horizontal E-W axis southward (See Map of planation surfaces, Map of slope gradient attached).

 

11.   The geographical distribution of the planation surfaces created on the marine deposits of Early Pleistocene to Middle Pleistocene age, indicate a rotation around an almost horizontal E-W axis northward (See Map of planation surfaces, Map of slope gradient attached).

 

12.   The slope gradient of the valleys developed on the post alpine formations is depended from the dip and dip direction of the beds. We have low slope gradient when the slope gradient has the same dip direction as the beds and high slope gradient when the slope gradient has the opposite dip direction than the beds affecting proportionately the shape of the valleys (Map of slope gradient attached, Fig. 3.16).

 

13.   The morphological discontinuities strike mainly E-W and are related to the fault zones and faults of the same strike (Map of slope gradient attached).

 

14.   The incision is stronger transversal to the general strike of the morphological discontinuities, that is transversal to the big fault zones Kyparissia – Aetos, Neda, Lepreon – Figalia (Map of slope gradient attached).

 

15.   The karstification as well as the ground water flow in the carbonates of Gavrovo – Tripolis geotectonic unit, has been defined by the pre-flysch tectonics and mainly by the neotectonics and less by eustatic movements.

 

16.   In Lykaeon and Minthi Mts. the karstification, as well as the ground water flow, within the upper cretaceous limestones of Pindos unit, has been mostly defined by the tectonics and the neotectonic deformation that took place during the first stages of the neotectonic evolution of the area and less, and only locally, during the last stages.

 

17.   Karstification as well as ground water flow within the post alpine deposits has defined by the neotectonic deformation of the area during the last 1 Μa.

 

 

4. TECTONICS - NEOTECTONICS

 

1.       Based on the tectonic - neotectonic studies of the neotectonic macrostructures of the Central-western Peloponnessos in many scales of observation it was concluded that the main 1st order neotectonic mega-structure is the “Megalopolis – Lykaeon – Minthi - Tetrazio composite tectonic graben (MELYMITE CTG)”. Within MELYMITE CTG there are smaller order neotectonic macrostructures, (Zacharo, Neda, Megalopolis, and the northern part of Kalamata – Kyparissia tectonic grabens and tectonic horsts such as Minthi, Lykaeon and Tetrazio) (Fig. 4.2, 4.4).

 

2.       The MELYMITE CTG is a composite ductile-brittle type neotectonic structure, which can be characterized as a Mega-fold of syncline type if one takes into account the geotectonic units, and in the same time can be characterized as tectonic graben as big fault zones bound it.

 

3.       The MELYMITE CTG was not uniquely deformed during the neotectonic period. In the same time period, in it’s part (smaller order 2nd, 3rd, …neotectonic structure) conditions and environments of evolution can be recognize, which were totally different from the neighboring parts. This differentiation could be continued not only in one stage of evolution, but in more, and in some cases this differentiation was reversed. More simply, a mosaic of smaller fault-blocks, which can behave differentially each other during their evolution, constitutes the MELYMITE CTG composite tectonic graben.

 

4.       During the neotectonic period, the deformation is not limited only in the margins of the MELYMITE CTG composite tectonic graben, but it takes place within the MELYMITE CTG, which locally is very intensive. The intensity of the deformation is higher in the internal parts (especially during the last stages) than in some locations along the margins of the MELYMITE CTG, where the deformation during the last stages is not so intensive. In other words there is a migration of the intensity of the active deformation from the margins towards the internal part of the MELYMITE CTG. The same happens within the smaller (2nd, 3rd, …) order neotectonic macrostructures.

 

5.       The marginal fault zones of the neotectonic macrostructures strike mainly E-W in the western part and NNW-SSE in the eastern part. Their vertical throw is not constant along their whole length, but usually it increases from east to west concerning the E-W fault zones and from south to north concerning the NNW-SSE fault zones.

 

6.       The faults that constitute a fault zone have an enechelon arrangement.

 

7.       The faults occurring within the 2nd order neotectonic macrostructures, especially in areas between the fault zones may have different strikes but most likely they strike NNW-SSE and E-W in the west part and E-W and NNW-SSE in the east part (Fig. 4.6, 4.7, 4.8, 4.11, 4.13, 4.14, 4.15, 4.16).

 

8.       The striations observed on fault surfaces, almost always present a horizontal component once right lateral component of movement and once left lateral. Concerning the fault zones the left lateral component dominates during the older stages of evolution, while during the younger stages the right lateral component dominates.

 

9.       The neotectonic deformation is expressed not only by faults, but also with folds, structures that in some cases are principal and in other cases are not principal for the neotectonic deformation and evolution of the area. The folds and generally the ductile deformation, which is not easily observed on the surface because of the intense presence of the brittle tectonics. , The ductile deformation has played a very important role, so during the creation of the MELYMITE CTG composite tectonic graben (a mega-syncline in the scale of geotectonic units), as during its evolution, especially during the evolution of the 2nd, 3rd, … order neotectonic macrostructures. Furthermore, it has strongly affected the morphogenetic processes. The present morphology results from the above mentioned cases.

 

10.   Some remarks on the main faults and the major fault zones:

 

·  They set boundaries so between the 1st order neotectonic mega-structure MELYMITE CTG and the neighboring neotectonic macrostructures (for example Lapithas Mt., Kyparissia Mts.), as between the 2nd, 3rd order neotectonic macrostructures.

·  They set paleogeographic boundaries between the basins, as well as between the geological formations.

·  They displace the geological formations located on both sides.

·  They define the morphogenetic procedures creating morphological discontinuities, changing stream direction of the drainage network, or bounding terraces and planation surfaces.

·  Some faults may have been activated only in one stage of area evolution, other faults may have been activated in successive or not successive stages.

 

11.   Some of the faults activated during a certain stage are localized in a very well defined area. In many cases the reactivation of these faults is transferred in another area neighboring with the previous one, usually towards the internal part of the basins, (for example the transfer of the active part of the Kyparissia – Aetos fault zone to Peristeras fault zone and the North Lapithas f.z. to the Alfios river). In some cases this migration could be attributed to diapiric phenomena (for example, Lapithas Mt.).

 

12.   The kinematics of some faults and fault zones have changed during the neotectonic period, resulting the corresponding evidences depicted on the both sides’ blocks. A combination of such fault set bounds with blocks that behave in one stage as tectonic graben and in another stage as tectonic horst. It is very characteristic the case of the Neda fault zone, the north block worked as hangingwall and the south as footwall during the first period, while during the last stage the kinematic regime has shifted.

 

13.   This change in the kinematics of some faults doesn’t mean that in the same time the stress field of the major area changes. According to our opinion, the stress field should not have dramatically changed during the evolution of the MELYMITE CTG composite graben. That is the main characteristics in fault geometry and the presence of the horizontal component (small or large) is almost everywhere constant. The observed differentiation’s have a local character, and in some cases may be related to diapiric phenomena, as it has defined in the neighboring Olympia graben.

 

14.   Some of the blocks work continuously as grabens or horsts. Such examples are the Minthi, Tetrazio and Lykaeon horsts and the Kyparissia – Kalo Nero, Megalopolis grabens.

 

15.   The kinematics of most of the fault zones and faults results to rotations of the blocks they bound, while the combination of such fault zones causes rotations of blocks related with rotational couple stress field.

 

16.   The more recent fault zones and faults and more specifically the faults occurring in the NW part of the study area should be related with diapirs that occur in diper points.

 

17.   Neotectonic folds occur in the post alpine formations as well as in the alpine ones, in various scales. They can be characterized as open, closed or very closed folds. The general rule is the younger, the more open. Furthermore, it must be underlined that all these folds haven’t been created in conditions of considerable depth, (the theoretical area of ductile deformation) but, in surface conditions (the theoretical area of brittle deformation). In addition, it is impossible for anybody to suggest that these folds are synsedimentary structures, taking into account that the fold axes have a constant strike throughout all the beds of the formations (Fig. 4.52 through 4.66, Tables 4-1, 4-2, 4-3, 4-4).

 

18.   The study of deformation of the alpine tectonic structures within the MELYMITE CTG composite graben during the neotectonic period showed the following (See Tectonic map attached, and Fig. 4.69 to 4.93):

 

·          Within the Minthi horst, the main strike of the thrusts and fold axes is NE-SW.

·          Within the Tetrazio horst, the main strike of the thrusts and fold axes is N-S.

·          Within the Kyparissia Mts. Composite morphotectonic structure, the main strike of the thrusts and fold axes is ΝNW-SSE.

·          Within the above mentioned structures, the geometry of the thrust and the fold axes create a curved shape the convex part lies towards area of the Gulf of Kyparissia.

·          The projection of the fold axes plunge created in Pindos Unit in N-S cross section within the MELYMITE CTG composite graben, forms a mega anticline with an E-W axis located between Minthi Mt. and Tetrazio Mt. (Fig. 4.92).

 

 

5. SEISMOLOGY

 

Within the MELYMITE CTG area no destructive earthquake has been referred. On the contrary, many destructive earthquakes have referred in the surrounding area of Messinia, Olympia, and Megalopolis the last 3.000 years.

 

The geographical distribution of the epicenters for earthquakes with magnitude M>4.0 and for earthquakes with magnitude M<5.0, shows that they totally differ concerning the major area, while they coincide within the MELYMITE CTG composite graben (Fig. 5.4).

 

The map of Fig. 5.5 shows that there are accumulations of epicenters, with very good accuracy of epicentre location (5 – 10km), which can be identified with characteristic active morphotectonic structures of Western Peloponnessos (Alfios river, Neda river, Kyparissia – Aetos fault zone, Filiatra mega fold axis).

 

 

6. NEOTECTONIC EVOLUTION

 

6.1 Stages of the MELYMITE ctg neotectonic evolution

 

The neotectonic evolution of the Central-western Peloponnessos can be summarized in the stages depicted on the following Table:

 

TABLE

 

STAGE OF EVOLUTION

TIME PERIOD

EVENTS

A

(Fig. 6.1)

Latest Middle Miocene(?)–

Late Miocene

 

1.        The 1st order MELYMITE CTG composite graben starts it’s evolution

2.        The Kyparissia–Aetos, N. & S. Lapithas, and the E. margins of Megalopolis marginal fault zones started their evolution

3.        Probable start of creation and evolution of the mega-anticline structure of Pindos unit near the surface, and the mega-syncline structure at the surface of the tectonic contact between the Gavrovo-Tripolis and Pindos units in a certain depth

4.        The presence of intensive horizontal component during the fault zones activation causes dragging in the pre-existed alpine tectonic structures (fold axes, thrusts, etc)

5.        The creation of the 2nd order Zacharo and Kyparissia-Kalo Nero grabens started at the same time. The deposition of the Tsemperoulas formation (lacustrine facies) in the Zacharo basin and the Raches formation (marine facies) in the Kyparissia-Kalo Nero basin started, while the rest area was under erosional regime

6.        The morphotectonic procedures started (planation surfaces, drainage network)

 

B

(Fig. 6.2)

Late

Miocene

–

Lower

Late

Pliocene

(NN-12)

 

 

1.        The kinematic regime of the area is homogenized resulting everywhere uplift movements

2.        Partly the Kyparissia-Aetos, Minthi, N. & S. Lapithas, Pamissos, E. margins of Megalopolis, Taxiarches fault zones were activated

3.        The presence of intensive horizontal component during the fault zones activation continue causing dragging in the pre-existed alpine tectonic structures (fold axes, thrusts, etc) and rotation of blocks around vertical and horizontal axes

4.        The beds of the Zacharo basin deposits started folded with E-W axes, reverse and normal fault were created as well (synsedimentary tectonism)

5.        The mega-anticline structure of Pindos unit continue it’s evolution

 

C(Γ)

(Fig. 6.3)

Lower

Early

Pliocene

(ΝΝ-12)

–

Early

Pliocene

(ΝΝ-13)

 

 

 

1.        The creation and evolution of Melpia fault zone interrupts the MELYMITE CTG geometry and probably starts the creation of the Kalamata – Kyparissia graben

2.        The Taxiarches, Pamissos, Neda, Agaliani, Lykaeon, E. margins of Megalopolis fault zones were activated

3.        The presence of intensive horizontal component during the fault zones activation continue causing dragging in the pre-existed alpine tectonic structures (fold axes, thrusts, etc) and rotation of blocks around vertical and horizontal axes

4.        The asymmetric development of the Neda drainage network started. Probable communication with Elisson and Gionorrema drainage networks

5.        Marine sedimentation took place in the Kyparissia – Kalo Nero basin (Psili Rachi formation)

 

D(Δ)

(Fig. 6.4)

Early

Pliocene

(ΝΝ-13)

–

Late

Pliocene

 

1.        The activation of Melpia fault zone interrupts the MELYMITE CTG geometry and continue the evolution of Kalamata – Kyparissia graben

2.        The Kyparissia-Aetos, Melpia, Taxiarches, Pamissos, Neda, Lykaeon, E. margins of Megalopolis fault zones were activated

3.        The Megalopolis and Ano Messinia grabens started their creation. There is no evidence of sedimentation

4.        The presence of intensive horizontal component during the fault zones activation continue causing dragging in the pre-existed alpine tectonic structures (fold axes, thrusts, etc) and rotation of blocks around vertical and horizontal axes

5.        The Neda drainage network evolution continues. Probable communication with Elisson and Gionorrema drainage networks

6.        Folds with N-S axes and reverse NNW-SSE faults were created within thw Kyparissia - Kalo Nero basin

7.        The NW-SE Raches fault was activated

 

Ε

(Fig. 6.5)

Late

Pliocene

 

1.        The Kyparissia-Aetos, Melpia, Taxiarches, Pamissos, Neda, Lepreon-N Figalia, Lykaeon, Minthi, N. & S. Lapithas, Lykaeon, E. margins of Megalopolis fault zones were activated

2.        The creation of Neda graben starts

3.        The presence of intensive horizontal component during the fault zones activation continue causing dragging in the pre-existed alpine tectonic structures (fold axes, thrusts, etc) and rotation of blocks around vertical and horizontal axes

4.        The parallel evolution of the Kyparissia-Kalo Nero and Ano Messinia basins is interrupted

5.        The Megalopolis basin transforms to a closed geomorphological and hydrological system (lake) resulting the deposotion of Makrission formation. At the same time the Ano Messinia basin trasforms to a closed geomorphological system

6.        The Neda drainage network contiued it's evolution, probable periodical communication with Elisson and Ginorrema drainage network

7.        Deposition of the Peristeras-Sidirokastron formation (continental facies) in the Kyparissia-Kalo Nero basin, the Elaia formation (continental facies) in the Neda basin, the Loggo formation (lacustrine facies) in the E. Zacharo sub-basin and the Anhydrus formation (lagoonal facies) in the W. Zacharo sub-basin

8.        Synsedimentary tectonism in the Zacharo basin

 

F(ΣΤ)

(Fig. 6.6)

Early Pleistocene -

Middle

Pleistocene

(1.6 Μα

-

0.44 Μα)

 

1.        The Kyparissia-Aetos, Melpia, Pamissos, Neda, Lepreon-N Figalia, Lykaeon, Minthi, western part of N. & S. Lapithas, Lykaeon, E. margins of Megalopolis fault zones were activated

2.        Deposition of marine sediments under a subsiding tectonic regime in: (i) the Neda graben (Neda formation), (ii) a part of Kyparissia-Kalo Nero basin (Myron formation) and the western part of Zacharo basin (Zacharo formation). Synsedimentary tectonism

3.        The presence of intensive horizontal component during the fault zones activation continue causing dragging in the pre-existed alpine tectonic structures (fold axes, thrusts, etc) and rotation of blocks mainly around horizontal axes

4.        The parallel evolution of the Kyparissia-Kalo Nero and Ano Messinia basins is interrupted The Ano Messinia and Dorion basin have common evolution as they constitute a uniform closed geomorphologic system which filled in with continental deposits

5.        The activity of the E. margins Megalopolis fault zones is transferred westwards resulting the uplift of the Early Pliocene deposits (Makrision formation) at the E. margins. The Megalopolis basin continued to be a closed geomorphological and hydrological system (lake), which periodically communicates with the Neda basin. During this period the depositin of Dyrrachion and Apiditsa formation took place

6.        The asymmetric development of the Neda drainage network continues. Probable communication with Elisson and Gionorrema drainage networks

7.        There is no communication between the Megalopolis and Ano Messinia basins, while the Megalopolis basin was periodically communicated with the Neda basin

 

G(Η)

(Fig. 6.7)

0.44Μα

-

0.27Μα

 

1.        The Peristeras, Agaliani, Neda, Lepreon-N Figalia, Lykaeon, Minthi, western part of N. & S. Lapithas, Lykaeon, E. margins of Megalopolis fault zones were activated

2.        The depostion of marine sediments continues in the Neda basin (Neda formation) and the western patr of Zacharo basin (Zacharo formation). Synsedimentary tectonism. On the contrary, the Mouriatada-Kakkava formation (continental deposits) is deposited in the Kyparissia-Kalo Nero basin

3.        A regional uplift regime affects the area, but the uplift rates differ from place to place

4.        This differentiation of the uplift rates resulted the change of drain of Dorion and Ano Messinia basins

5.        The presence of intensive horizontal component during the fault zones activation continue causing dragging in the pre-existed alpine tectonic structures (fold axes, thrusts, etc) and rotation of blocks mainly around horizontal axes

6.        The activity of the E. margins Megalopolis fault zones is transferred westwards to the center of the basin resulting the subsidence of blocks creating smaller order basins, which fill in with younger lacustrine deposits. Uplif of the Early Pliocene deposits(Makrision formation) at the E. margins. The Megalopolis basin continued to be a closed geomorphological and hydrological system (lake), which periodically communicates with the Neda basin. The rates of sedimentation are higher than the rates of fault movements resulting the their cover

7.        The asymmetric development of the Neda drainage network continues. Probable communication with Elisson and Gionorrema drainage networks

 

H(Θ)

(Fig. 6.8)

0.27Μα

-

Present

 

1.        The MELYMITE CTG composite graben kinematically is homogenized as all the structure is under uplift regime with different rates from place to place

2.        The Peristeras (throw 100m), Agaliani, Neda (the uplift block shifted, throw >150m), Epitalion (throw >100m), western part of N. & S. Lapithas, Lykaeon (throw .250m), E. margins of Megalopolis fault zones were activated

3.        The younger neotectonic blocks are rotated around WSW-ENE axes. In the area of Neda basin, western part of Minthi & Lapithas Mts., the rotation direction is norhtwards, while the Lykaeon Mt. is rotated southwards

4.        The deposits within the Neda and Zacharo basins are macrofolded with folds of big radius curvature, whose axes strike E-W. The same happens at the western part of Alfios area.

 

 

 

6.2 Subsidence and uplift rates during Quaternary

 

One of the targets of the neotectonic study is to calculate the rates of block movements. Thus, in order to study, from the kinematic point of view, in large scale, geological bodies apart from the tectonic, geomorphologic, geodetic and other methods, the lithostratigraphic can also be used.

 

When in a geological structure (i.e. grabens) the following data is known:

 

             (i)           The time of birth of the structure (i.e. the time that starts the sedimentation)

           (ii)           The first location of the structure relatively to the sea level and

          (iii)           The present time location relatively to the sea level

 

Then, it is possible, under some presuppositions, to produce some conclusion of quantitative character for the rates of vertical movements, about the distinguished blocks of the lithosphere.

 

For the lithostratigraphic analysis most important are the following:

 

                i.             The sediment thickness

              ii.             The lithostratigraphy

             iii.             The continuity or not of the sedimentation

            iv.             The facies of the sedimentation

              v.             The present time altitudes of the Pleistocene marine deposits occurrence and

            vi.             The worldwide climatic changes during Quaternary

 

In order to calculate the mean subsidence and uplift rates except the above mentioned the following must be taken into account:

 

·             The visible thicknesses of the Pleistocene marine sediments in every basin is: 150m for the Kyparissia-Kalo Nero basin, approximately 400m for the Neda basin, and 250m for the Zacharo basin.

 

·             It is known, that 100m thickness of Early Pleistocene marine sediments have been eroded in other areas neighboring the study area (MARCOPOULOU-DIACANTONI et al., 1989). In our case we didn’t take into account this erosion, as the Early Pleistocene marine deposits have been covered by continental deposits in the Kyparissia–Kalo Nero basin, while the marine sedimentation continued in the other two basins up to the Middle Pleistocene (biozone NN-20).

 

·             In order to calculate the uplift rate, the higher elevations of occurrences of the sediments must be mapped. The Myron formation in Kyparissia-Kalo Nero has elevated to an altitude of 250m (Myron village, South of Peristeras river) and up to an altitude of 140m East of Kakkava village, North of Peristeras river. The Neda formation in Neda basin is located up to altitude of 400m at the northern margins of the basin (Lepreo, Faskomilia villages), 320m in the center part of the basin (Megavouni, Marathia hills) and 150m at the southern margins of the basin. The Zacharo formation in Zacharo basin is located up to an altitude of 400m at the northern margins of the basin (Koumouthekras village), 200m in the central part (Xirochori village) and 140m at the southwestern margin of the basin (Sxhinoi village).

 

·             Marine sediments, mainly of coastal facies, have deposited on a well - formed palaeorelief in the grabens. The sedimentation was continuous from the beging of Early Pleistocene up to the end of Early Pleistocene (biozone NN-19) in Kyparissia-Kalo Nero graben, while in the Zacharo and Neda grabens was continuous during the whole Early Pleistocene up to the Middle Pleistocene (biozone NN-20). The subsidence regime, therefore, should not have changed abruptly to an uplifting one, but this shift passed through a phase of relative constancy.

 

·             The disagreements about the timing of the Pliocene-Pleistocene boundary are well known. Some of the researchers accept that it is 2.4 Ma B.P. and others 1.6 Ma or in some intermediate timings. For our calculations we have accepted that the Pliocene-Pleistocene boundary is 1.6 Ma

 

·             The global climatic changes are well known during the transition from Pliocene to Pleistocene. Instead of the sea level decrease that could be attributed to a cold period, it is observed a transgression of the sea in the Early Pleistocene in the major area of Peloponnessos (MARCOPOULOU-DIACANTONI et al., 1990, FRYDAS 1990) which is due to the neotectonic deformation of the area.

 

The above mentioned data allows the calculation of the subsidence rates during the sedimentation (Early Pleistocene) and the uplift rates during the phase of uplift in every basin (Fig. 6.9).

 

 

i. Kyparissia – Kalo Nero basin

 

The subsidence rate (Vs) during the sedimentation was:

 

   Vs =150.000mm/1.200.000y = 0.125mm/y

 

The uplift rate (Vu) during the uplift movements is:

 

 

South of Peristeras river (Myron vil.)

 

Vu=250.000mm/400.000y= 0.625mm/y

 

North of Peristeras river (Kakkava vil.)

 

Vu=140.000mm/400.000y= 0.35mm/y

 

 

ii. Neda basin

 

The subsidence rate (Vs) during the sedimentation was:

 

Vs = 400.000mm / 1.330.000y = 0.30mm/y

 

The uplift rate (Vu) during the uplift movements is:

 

 

South margins Karyes village:

 

Vu=150.000mm/270.000y= 0.55mm/y

 

Central area (Megavouni-Marathia)

 

Vu=320.000mm/270.000y=1.18mm/y

 

North margin (Lepreo Faskomilia vil.)

 

Vu=400.000mm/270.000y=1.48mm/y

 

 

iii. Zacharo basin

 

The subsidence rate (Vs) during the sedimentation was:

 

   Vs = 280.000mm / 1.330.000y = 0.21mm/y

 

The uplift rate (Vu) during the uplift movements is:

 

 

South margin (Schinoi vil.)

 

Vu=140.000mm/270.000y= 0.52mm/y

 

Central-western part (Xirochori vil.)

 

Vu=280.000mm/270.000y= 1.03mm/y

 

North margin (Koumouthekras vil.)

 

Vu=360.000mm/270.000y= 1.33mm/y

 

In addition, taking into account that the Middle Pleistocene marine deposits occur at 300m altitude at the western part of the Lapithas North margin (Vrina village), the present days active neotectonic units are the western parts of: Lapithas, Minthi and Tetrazio Mts. These neotectonic units consist of the western part of each mountain and a part of the Pleistocene marine basin.

 

These neotectonic units, from the kinematic point of view, behave as tectonic dipoles rotating northwards around ENE-WSW rotational axis (Fig. 6.9).

 

6.3 The type of deformation of Central - Western Peloponnessos

 

In order to understand the stress field, which is responsible for the deformation of the Central - Western Peloponnessos during the neotectonic period, and more specifically during the last stages of its evolution, that is, after the end of the marine sedimentation in the Kyparissia - Kalo Nero, Neda and Zacharo basins, we have to take into account the following:

 

·       The form of the drainage network.

 

·       The differential intension of the incision, as well as its geographical distribution.

 

·       The geographical distribution of the planation surfaces developed on the alpine formations, which indicates a block rotation around E-W horizontal axes southwards.

 

·       The geographical distribution of the planation surfaces developed on the pleistocene marine deposits, which indicates a block rotation around E-W horizontal axes northwards.

 

·       The geographical distribution, as well as the elevation of the springs and the hydrablic gradient of the groundwater surface.

 

·       The geometry of the shorelines.

 

·       The geometry of the fault zones and the faults, all of which indicate a horizontal slip component, in other words, they are oblique or even strike slip.

 

·       The intense decrease or increase of the apparent vertical throw along the marginal fault zones combined with the en echelon arrangement of the faults that constitute the marginal fault zones of the neotectonic macrostructures, as well as the faults that occur within them.

 

·       The curvature of  the fault surfaces.

 

·       The presence of neotectonic folds in various scales with axes striking SWS - ENE.

 

·       The deformation of the alpine structures during the neotectonic period.

 

·       The curved shape of the Pindos unit thrust surface in some locations, combined with its syncline or anticline shape in regions neighbouring to the study area, that suggests similar deformation also within the study area, in spite the difficulties of constructing a contour map of that surface there.

 

·       The geographical distribution of the post-alpine sediments, combined with their facies, thickness and age.

 

·       The in situ stress field measurements, suggesting a horizontal domination of the area by compression or extension from one area to another. Of course, it is not clear whether these measurements correspond either to the σ1 or σ2 axis (the σΗmax), or the σ2 or σ3 axis (the σΗmin), nor is it clear what percentage of the axes they represent as their components on the horizontal plane. The fact that the results of the measurements are, in many cases, non - compatible (PAPANIKOLAOU et al., 1987), with the suggestions of the simplified extensional and compressional stress field based on the study of the neotectonic faults alone (PAQUIN et al., 1982, 1984), is very characteristic for the study area. If, on the other hand,  we take into account the more complicated stress fields (shear and rotational couple stress fields) instead of the simplified ones, all these measurements are compatible. The in situ stress field measurements taken in the Messinia province after the destructive Kalamata earthquake (13-9-1986) (PAPANIKOLAOU et al., 1987), combined with the PAQUIN et al., 1982 measurements in the Peloponnessos peninsula are shown in Fig. 6.10. It is evident that SW Peloponnessos is under compression in an E-W direction, with secondary either lower compression in N-S direction (Filiatra, Amfeia, Stoupa) or extension in N-S direction (Almyros). On the contrary, in the central Peloponnessos, extension dominates the area, in both the above mentioned directions. This general result of the E-W compression in in accordance with the overall active geodynamic conditions defining the Hellenic Arc. The partial variations are probably due to several causes (lithological, tectonical, accuracy of method, etc) and cannot lead to reliable conclusions, taking into account that the number of the measurements taken so far is very small. In any case, we have to remark that the in situ stress field measurements of 1987 largely agree with data from the fault plane solutions relating to Western Peloponnessos (DRAKOPOULOS & DELIBASIS 1982, PAPAZACHOS et al., 1984, HATZFELD et al., 1989), as well as with polarization data of the external Hellenic zone electrical field (LAZARIDOU - VAROTSOU & PAPANIKOLAOU, 1987) and the geometry of the WSW-ENE neotectonic macrofold axis at Filiatra (MARIOLAKOS & FOUNTOULIS 1991). PAPANIKOLAOU et al, 1987 remark that the values of the stress field measurements of 1987 are the highest ever measured within the Hellenic Arc,  and that they are at least double than measurements of any other area in Greece.

 

·       The distribution of the earthquake epicentres specified by the microseismic networks of PAPADOPOULOS 1985 and HATZFELD et al., 1990, in combination with the determined fault plane solutions which show co-existence of extension and strike slip and, moreover, in non-predictable directions for some cases.

 

According to all the above, it is evident that the deformation of Central Western Peloponnessos and, consequently, the deformation of the Hellenic Arc, is very complicated and greatly influences the intension of the seismic activity in several different areas. All these observations, characteristic for the neotectonic deformation, show that:

 

1.    The stress field of the greater area belongs to the rotational couple type, and

 

2.    The deformation is rather brittle-ductile, than clearly brittle.

 

Within this rotational stress field, local stress fields of different types may be generated and hosted (for example transextensional or transcompressional). Under the influence of such a stress field, all the previously mentioned neotectonic structures may be interpreted.

 

Normal faults may be developed either perpendicularly to the axis of extension, or parallely to the axis of compression. Through this point of view a great number of neotectonic normal type faults may be related to local compressional stress fields and, more specifically, to brittle-ductile type of deformation (MARIOLAKOS et al., 1988, MARIOLAKOS & FOUNTOULIS 1991, MARIOLAKOS et al., 1991) (Fig. 6.11).

 

 

6. CONCLUSIONS

 

The following paragraphs summarize the most important conclusions about the (Megalopolis-Lykaeon-Minthi-Tetrazio) MELYMITE CTG composite graben, according to the data presented in the past chapters and the stages of neotectonic evolution, as described previously.

 

·         The MELYMITE CTG composite graben is a composite brittle-ductile type neotectonic structure, that is, a mega structure, which can be seen as a syncline type mega-fold from the geotectonic units’ point of view, while it can also be considered as a tectonic graben, once it is bounded by great fault zones.

 

·         This composite structure has not had a uniform neotectonic deformation throughout its extent. For the same periods of time, totally different conditions of deformation and environment can be traced and distinguished in geographically neighboring parts of the area (2nd, 3rd, … order neotectonic structures). This differentiation can be last more than one stages of evolution and in some cases it goes opposite. In few words, the MELYMITE CTG composite graben consists of a faulted block mosaic that can differentiate their behavior during their evolution.

 

·         The deformation during the neotectonic period is not limited to the margins of MELYMITE CTG. On the contrary, it is traced and detected throughout the whole internal area, in parts of which it seems to be even more intense than near the margins (especially in the last stages of evolution). A migration of the activity from the margins to the internal areas is observed so in the MELYMITE CTG composite graben as in the 2nd, 3rd, … macrostructures.

 

·         The neotectonic deformation is not only expressed by faults, but also with folds, that is tectonic structures of which others are of major importance and others of minor importance for the neotectonic structure and evolution of the area. Thus, the major faults or fault zones:

 

 

1.    Delimitate the 1st order neotectonic macrostructure of MELYMITE CTG from the neighboring neotectonic macrostructures (i.e. Lapithas Mt., Kyparissia Mts., etc), as well as the internal 2nd, 3rd, …, order neotectonic macrostructures from each other.

 

2.    Set the geographic and paleogeographic boundaries of geological formations.

 

3.    Transpose very noticeably the geological formations on both sides.

 

4.    Don’t only interfere, but in fact determinate the morphogenetic procedures through the formation of morphological discontinuities, bends and turns of the streams of the drainage network and planation surfaces.

 

5.    May have been active during one or more subsequent or not subsequent stages.

 

Folds, and ductile deformation in general, which cannot be easily apprehended on the surface, due to the intense presence of brittle tectonics, has played a determinative in the formation, as well as the evolution of this composite tectonic structure as a mega-syncline considering the settings of the different geotectonic units in space. In addition, ductile deformation has affected considerably the morphogenetic procedures. The present scene is nothing more than a result of the above.

 

Some of the faults that have been active across their whole length during a certain stage, appear to have taken effect mainly in a limited area, while they have only rarely been active in other locations. In many cases, activation of faults in a next stage seems to be shifted to another neighboring area, usually towards the interior of the basins (i.e. transposition of the Kyparissia-Aetos fault zone towards Peristeras riverbed, and N. Lapithas fault zone towards Alfios riverbed). In some cases (i.e. N. Lapithas fault zone) this phenomenon could be related to phenomena of diapirism, the activity of which should have a respective duration.

 

·         The kinematic regime of some faults changes throughout neotectonic evolution during sequential or non-sequential stages, resulting to a respective reflection of the blocks of both sides of the faults. A combination of such cases of faults delimitates tectonic blocks that form a tectonic graben in one stage and a tectonic horst in the next stage. The case of the Neda fault zone is very representative. the fault zone originally contributed to the creation of the homonymous graben, when the north block submerged and the south uplifted, and in the final stage its kinematics reversed so that the south block submerged and the north one uplifted.

 

·         Nevertheless, the change of the kinematic regime of a number of faults does not correspond to a change of the stress regime of the whole area, which in the author’s opinion shouldn’t have changed importantly throughout the whole duration of the MELYMITE CTG evolution. That is, the main attributes of the geometry of faults and the presence of minor or major of a horizontal component of motion is almost everywhere changeless. The observed alternations are mainly of local interest, while in some cases they may reflect phenomena of diapirism (i.e. the neighboring Pyrgos – Olympia graben, LEKKAS et al., 1992).

 

·         Certain tectonic blocks continuously behave as grabens or horsts. Such cases are the Minthi, Tetrazio, Lykaeon horsts, the Megalopolis, Kyparissia-Kalo Nero grabens, etc.

 

·         Most of the tectonic blocks bounded by fault zones and faults rotate around horizontal or/ and a vertical rotation axes. Such a kinematic regime reveals an respective stress field.

 

·       The most recent faults and fault zones, especially the ones occurring in the NW part of the area have to be associated with the presence of evaporates in shallow, or greater depths. Such cases have been reported in the Kyllini peninsula (MARIOLAKOS et al., 1989), where activation of faults took place during the 16-8-88 earthquakes.

 

·       Folds occur in different scales and with varying angles of limbs. A general observation though is that the angle between the limbs is greater when the fold is more recent. In addition, the fact that these folds have not been formed in depth (the ductile type of deformation field theoretically) has to be pointed out. They have formed very close to the surface or at the surface, and of course none could propose that they are sedimentary structures considering that all the layers of the formations (i.e. Tsemberoulas formation) are deformed and that their geometry (strike of fold axes) is constant and very specific in every case.

 

Finally, it is easy to distinguish the non-active, probably active and active faults and fault zones in the study area taking into account the geological, geomorphological, tectonic, neotectonic and seismotectonic data, as well as the conclusions presented in the stages of the neotectonic evolution of the area. The categorization of the faults is presented on the Neotectonic map (attached).