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Recent quaternary tectonics in the hellenic arc: Examples of geological observations on land
~ec#Q~op~~§~e~*52 (1979) 267-275 @ Etsevier Scientific Pubfihing Company,
267 Amsterdam
-Printed
in The Netherlands
RECENT QUATERNARY TECTONICS IN THE HELLENIC ARC: EXAMPLES OF GEOLOGICAL OBSERVATIONS ON LAND
JACQUES
ANGE~I~R
Laboratoire de Tecfonique Cornpar&, LXpnrtement de Gefoiogie SWuciurale, Universite’ de Paris VI, 75230 Paris Cedex 05 (France) (Accepted
for publication
April 26, 1978)
ABSTRACT
Angelier, J., 1979. Recent Quaternary tectonics in the Hellenic Arc: examples of geological observations on land. In: C.A. Whitten, R. Green and B.K. Meade (Editors), Recent Crustal Movements, 1977. Tectonophysics, 52: 267-275. Upper Pleistocene and Holocene tectonic movements in the Aegean region are analyzed by geological means (deformation of shorelines, faults in Quaternary deposits, historical seismicity). Examples from Crete, Karpathos, Miles, Chios and Samos are presented. While subduction, indicated by geophysical data, occurs beneath the Hellenic AX, extensional tectonics (Le., normal faulting) takes place within and behind the arc, resulting in a slight expansion of the Aegean region towards the Eastern Mediterranean.
Numerous neotectonic studies have been carried out in the Aegean region during the last few years (Mercier et al,, 1972, 1976; Angelier, 1973,197?; Pechoux et al., 1973; Dufaure et al., 1975; Mercier, 1976; Philip, 1976). They are the complement of the geophysical data (not discussed here). The geology of the Aegean region has been summarized by Aubouin (1973). In this. paper we describe examples of Middie-Late Pleistocene and Holocene tectonic features. They are in the Hellenic (=Aegean) Arc (outer arc: Crete, Karpathos; inner, volcanic arc: Milos)~ or just behind it (Samos, Chios). A more general analysis of Late Miocene and Plio-Quaternary tectonics in the Aegean Arc has been proposed elsewhere (Angelier, 1977). Table I summarizes the main geological methods applied to neotectonic analysis. On each figure the localization is shown in (a); the stereograms are Schmidt’s projections of the lower hemisphere (where fault planes are shown as thin lines, normal striations as black dots, and directions of extension as large arrows).
268 TABLE
I
Main geological Evidence
methods
of recent
deformation
Altimetric variations shorelines Tectonic structures marine terraces dunes alluvia, fans slope deposits,
Morphological
Historical
TECTONIC
applied
of
(especially
screes
data
seismicity
ANALYSIS
to neotectonic
analysis
Examples
Particular
Fig. 1 Fig. 2
altimetric measurements paleontological and radiometrical dating, morphology
faults) in: Fig. 3 Fig. 4 Fig. 5 Fig. 6 Fig. 7
. .
techniques
stratigraphy of quaternary deposits (morphology, paleontology, radiochronology) tectonic analysis (especially fault mechanisms), including: separation of successive movements
Fig. 8
search of recent scarps, photogeology study of morphologies related to uplift or subsidence
see text
compilation of available descriptions; search and analysis of structures comparison with focal mechanisms of earthquakes
OF RECENT
DEFORMATIONS
Deformation of Qua ternary shorelines (1) Middle-Late Pleistocene shorelines: a comparison of their deformations in the Western Mediterranean (“arc” of Gibraltar and Alboran Sea) and the Eastern Mediterranean (Aegean Arc: Crete) was carried out in a collective study (Angelier et al., 1976). The greatest amplitudes were found in the Aegean Arc: marine terraces are strongly uplifted in Crete (up to 4 cm per century and more, for the last 125,000 years), and submerged in the Cyclads Archipelago (inner arc), Moreover, altimetric changes are sharp (Fig. 1) because of block faulting. (2) l+storical shorelines: a rapid recent uplift of the whole of western Crete is indicated by the elevation of ancient shorelines (Spratt, 1856) 2000 years old (14C: Hafemann, 1965), now up to 9 m at Elafonisi, 15 km west of Paleochora (Fig. 2). The rate of uplift is about 40-60 cm per century (average rate for the last 2000 years). Tectonic Wiirm)
structures
in Quaternary deposits (especially Riss, Tyrrhenian,
In addition to being deformed on a broad scale, marine terraces are cut by faults which are generally normal, as on Karpathos (Fig. 3). Consolidated
269
Fig. 1. Regional deformation of Quaternary shorelines on southeastern Crete. a. Location. b. Typical section of the three main marine terraces (7’1, 7’2, T3), with their shorelines (Sl, SZ, S’s), above Neogene deposits: approximate radiometric ages are given after Angelier et al., 1976. c. Altimetric changes of shorelines Si, Sz, S3 along the coast.
Fig. 2, Regional deformation of ancient historical shorelines, about 2000 years old, on western Crete. a. Location. b. Marine erosional levels near Paleochora: numerous nutches in addition to the main shoreline, complicate the pattern. c. Map of present elevations, in meters, of the main shoreline. It is emphasized that some heights may belong to slightly older or more recent levels - see (b): the ages indicated by Hafemann, at places shown as black dots, range from 1620 to 2375 years. In Gavdos the precise age is unknown, but the terrace contains remains of pottery. After observations of Spratt (1856), Hafemann (1965), Bonnefont (1971), Dermitzakis (1973), and the author. The heights of 1.22.2 m indicated in the northwestern peninsula (NW of Kastelli), after Dermitzakis (1973), are probably underestimated (P. Pirazzolli, pers. comm.).
270
Fig. 3. Normal faults in a Tyrrhenian marine terrace at the southern end of the island of Karpathos. a. Location. b. Section of a fault scarp: P = marine Pliocene; T = Tyrrhenian deposits with Strombus bubonius LMK; D = dunes. c. Zone of conjugate normal faults. d. Corresponding stereogram (see text).
Upper Pleistocene dunes are often faulted, for example on Karpathos, above the marine terrace, or on Milos (Fig. 4), where marine deposits are below sea level. On Milos (Fig. 4), Karpathos (Angelier, 1973), and in other places, the main Recent faulting is similar to the older faulting: (1) intense normal faulting during the Late Pliocene or Early Quaternary; (2) unconformable sedimentation during the Middle-Late Pleistocene; (3) reactivation of normal faults, cutting the latter deposits. Successive movements closely spaced in time have been observed: for example, on Samos, two consolidated conglomeratic fans are superposed: both are cut by normal faults, but a previous fracturation, which is mechanically similar, cuts only the lower fan (Fig. 5). In the same way the SW-facing scat-p of Mt. Kedhros, on Crete, is covered by screes, the older being consolidated but the younger unconsolidated. These screes are cut by the NW-SE normal fault on which discrete successive movements have occurred with different mechanisms (Fig. 6). In the vicinity, near Plakias, three successive tectonic movements are (Fig. 7): (1) large normal faulting at the end of the Pliocene or during Early Quaternary times; (2) slight compression generating small reverse faults; (3) extensional movements again, with probable reactivation of normal faults. Recent movements are also inferred from morphological data: some fault
-bfm
-
Fig. 4. Recent normal faults northeast of Adamas on the island of Milos. a. Location. b. Section of a fault: V = volcanic Pliocene; M = marine Pliocene; C and D = alluvia and dunes of Upper Pleistocene, Note (1) the curvature of the normal fault near the surface so that it resembles an open reverse fault; (2) the evidence of previous normal faulting: the unconformable deposits C and D overlie M on one side of the fault, V (older) on the other side. c. Section of a more important Recent fault. d. Corresponding stereogram, for both faults. Striae of the last movement were not observed, but other observations suggest that the movement is probably purely normal.
I
400m
4
b
Fig. 5. Fracturation and normal faulting in consolidated alluvial fans west of Marathokambos on the island of Samos. a. Location. b. Schematic section of the two superposed fans Ft and Fz, successively faulted, and details (note the curvature of one fault near the surface, as on Fig. 4b). c. Stereogram.
b
Fig. 6. Recent reactivation of a great normal fault near Spili (Crete), a. Location. h. Schematic section. c. Detailed view: large grooves indicating a normal-sinistral movement L, polished by thin recent striations; 2, purely normal, cutting unconsolidated screes (probably Wiirm). d. Stereogram: comparison of movements 1 and 2.
scarps give evidence of recent motion (Fig, 8), and particular are related to rapid uplift (see Bonnefont, 1971, for Crete).
morph~l~~es
An example may be described on Chios (Angelier and Tsoflias, 1976): an old N-S fault was reactivated during the ~ua~~a~, since consolidated screes are faulted; on this fault line, near Tholopotami, large open cracks
Fig. 7. Schematic section of sucdessive WSW of Spili (see Fig. 6a). explanation
movements in text.
in Plakias (Crete).
Localization:
13 km
Fig. 8. Morphological evidence of Recent normal faulting near Lastros (eastern Crete). a. Location. b. View of the almost constant height scarp, in homogeneous limestones. c. Detailed section of consolidated slope detritus cut by a similar fault near Mesa Mouliana. d. Stereograms of these faults.
probably originated during a 1546 earthquake, according to contemporaneous documents (note that landslides have also occurred there, some of which were caused by earthquakes, but they have no direct tectonic meaning). The direction of extension is close to WSW-ENE, and seems roughly compatible with focal mechanisms of recent earthquakes near Chios (1949,1969). No tectonic structure clearly caused by an earthquake with a known focal mechanism has been found in the islands we have studied. Detailed geophysical studies applied to present surface tectonics are poor or absent (i.e, precise geodetic levelling, strain and stress measurements, precise location of earthquake foci, including microseismicity). GENERALPATTERNOFRECENTAEGEANMOVEMENTS
Middle-Upper
Pleistocene
and Holocene
tectonic
~ec~Q~~~s
(1) Predo~~~unce of exte~sio~~Z movements (normal f~u~ting)~ on the emerging parts of the Aegean Arc and the Southern Aegean, most tectonic mechanisms observed by geological means are extensional. The AfricaEurasia convergence in the Mediterranean region occurs in two different ways: (i) westwards, near the Strait of Gibraltar - strike-slip faulting occurs (continental compression especially, see Bousquet’s paper in this volume); (ii) e~stwurds, in southern Greece - subduction of the Eastern Mediterra-
274
nean crust has been proposed on geophysical criteria (MacKenzie, 1970; Rabinowitz and Ryan, 1970; etc.); the Aegean Arc and the Aegean region, above the plunging lithospheric plate, are mainly affected by extensional tectonics (intense normal faulting). (2) Traces of compression on the outer margin of the arc: Recent compressional structures (reverse faults) have been clearly observed in the area of the Ionian Islands (Mercier et al., 1972). In addition, on Karpathos, some compressional structures exist but are extremely subdued (Angelier, 1973). The scarcity of compressional structures leads us to make the following hypotheses: (i) recent compression has occurred near the trenches - since even the submerged southern margin of the Cretan Arc is affected by normal faulting (Nesteroff et al., 1977), thrusts and transform faults can only be present in the Hellenic trenches and seaward: (ii) the apparently greater intensity of compression on the lonian Islands (Mercier et al., 1972) may be pr~cip~ly related to the closeness of the NW term~ation of the typical subduction zone beneath the arc (i.e., with the decrease of the mechanical decoupling of plates).
Subduction and the Aegean expansion Except for a small generalized compressional event during the Early Quaternary s.1. (Mercier et al., 1976), the Plio~uatem~ pattern of normal faults in the Aegean region (Aubouin, 1973) has not changed fundamentally since the Middle Pliocene. A neotectonic analysis including a comparison with available seismic data has been proposed elsewhere (Angelier, 1977). The extensional movements during Upper Pliocene and Early Quaternary times - and probably also during Recent times (with less numerous but roughly analogous observations) - have resulted in an expansion of the Aegean Arc and the Southern Aegean towards the Eastern Medite~ane~ Sea. This implies that, as Plio~uatern~y subduction processes were occurring beneath the Hellenic Arc, the Crete-Libya rate of convergence was slightly higher than that of the Middle Aegean-Libya. ACKNOWLEDGEMENTS
The research was supported by the French C.N.R.SJ1.N.A.G. (A.T.P. G~odynamique). We must add that without the help of the group “Californie” of this A.T.P., this paper could not have been presented by the author at the 1977 RCM Symposium; special thanks are due to Dr. Rend Blanchet. REFERENCES Angelier, J., 19’73. Sur la n6otectonique 6g6enne: failles ant&-tyrrhbniennes et posttyrrhbiennes dans I’fIe de Karpathos (Dodkanke, G&e). C.R. Somm. Sot. G&01. Fr., (7) 15: 105-109.
275 Angelier, J., 1977. Sur I’evolution tectonique depuis le Miocene superieur d’un arc insulaire mediterraneen: l’arc Ogden. Rev. Geogr. Phys. G&01. Dyn., (2), 19 (3): 271-274. Angelier, J. and Tsoflias, P., 1976. Sur les mouvements mio-plio-quaternaires et la sdismicite historique dans l’ile de Chios (Grece). CR. Acad. Sci. Paris, D, 283: 1389-1391. Angelier, J., Cadet, J.P., Delibrias, G., Fourniguet, J., Gigout, M., Guillemin, M., Hogrel, M.T., Lalou, C. and Pierre, G., 1976. Les deformations du Quaternaire marin, indicateurs neotectoniques. Quelques exemples mediterraneens. Rev. GBogr. Phys. Geol. Dyn., (2) 18: 427-448. Aubouin, J., 1973. Des tectoniques superposees et de leur signification par rapport aux modeles geophysiques: l’exemple des Dinarides: paleotectonique, tectonique, tarditectonique, neotectonique. Bull. Sot. Gbol. Fr., 15 (7): 426-460. Bonnefont, J.C., 1971. La Crete. Etude morphologique. These Geographic Universite Paris. University of Lille III, 1972, p. 845. Dermitzakis, M.D.. 1973. Recent tectonic movements and old strandlines along the coasts of Crete. Bull. Geol. Sot. Greece, 10 (1): 48-64. Dufaure, J.J., Kadjar, M.H., Keraudren, B., Mercier, J., Sauvage, J. and Sebrier, M., 1975. Les deformations plio-pleistocenes authour du golfe de Corinthe. CR. Somm. Sot. Geol. Fr., suppl. 17 (1): 18-20. Hafemann, D., 1965. Die Niveauanderungen an den Kiisten Kretas seit dem Altertum. Verlag Akad, Wiss. Lit. Mainz, Abh. Math. Naturwiss. Kl., 12: 709-788. MacKenzie, D.P., 1970. Plate tectonics of the Mediterranean region, Nature, 226: 239. Mercier, J., 1976. La neotectonique, ses methodes et ses buts. Un exemple: l’arc Bgeen (Mediterranee orientale). Rev. Gbogr. Phys. Geol. Dyn., (2), 18 (4): 323-346. Mercier, J,, Bousquet, B., Delibasis, N., Drakopoulos, I., Keraudren, B., Lemeille, F. and Sorel, D., 1972. Deformations en compression dans le Quaternaire des rivages ioniens (CQphalonie, G&e). Donnees neotectoniques et seismiques. CR. Acad. Sci. Paris, D, 275: 2307-2310. Mercier, J., Carey, E., Philip, H. and Sorel, D., 1976. La neotectonique plio-quaternaire de l’arc egeen externe et de la mer Egde et ses relations avec la seismicite. Bull. Sot. Geol. Fr. (7), 18 (2): 355-372. Nesteroff, W.D., Lort, J., Angelier, J., Bonneau, M. and Poisson, A., 1977. Esquisse structurale en Mediterranee orientale au front de l’arc egeen. In: B. Biju-Duval and L. Montadert (Editors), Int. Symp. Struct. Hist. Mediterr. Basins, Split, Oct. 1976. Editions Technip, Paris, 1977, pp. 241-256. Pechoix, P.Y., Pdgoraro, O., Philip, H. and Mercier, J., 1973. Deformations pliocenes et quaternaires en compression et en extension sur les rivages du golfe M~iaque et le canal d’Atalanti (Mer Egee, Grice). C.R. Acad. Sci. Paris, D, 76: 1813-1816. Philip, H., 1976. Un episode de deformation en compression B la base du Quaternaire en Grece centrale (Locride et Eubee nord-occidentale). Bull. Sot. Geol. Fr., (7), 18 (2): 287-292. Rabinowitz, P.D. and Ryan, W.B.F., 1970. Gravity anomalies and crustal shortening in the Eastern Mediterranean. Tectonophysics, 10: 585-608. Spratt, T.S., 1856. Travels and Researches in Crete, 2 ~01s. London, 387 pp. and 435 pp.
267 Amsterdam
-Printed
in The Netherlands
RECENT QUATERNARY TECTONICS IN THE HELLENIC ARC: EXAMPLES OF GEOLOGICAL OBSERVATIONS ON LAND
JACQUES
ANGE~I~R
Laboratoire de Tecfonique Cornpar&, LXpnrtement de Gefoiogie SWuciurale, Universite’ de Paris VI, 75230 Paris Cedex 05 (France) (Accepted
for publication
April 26, 1978)
ABSTRACT
Angelier, J., 1979. Recent Quaternary tectonics in the Hellenic Arc: examples of geological observations on land. In: C.A. Whitten, R. Green and B.K. Meade (Editors), Recent Crustal Movements, 1977. Tectonophysics, 52: 267-275. Upper Pleistocene and Holocene tectonic movements in the Aegean region are analyzed by geological means (deformation of shorelines, faults in Quaternary deposits, historical seismicity). Examples from Crete, Karpathos, Miles, Chios and Samos are presented. While subduction, indicated by geophysical data, occurs beneath the Hellenic AX, extensional tectonics (Le., normal faulting) takes place within and behind the arc, resulting in a slight expansion of the Aegean region towards the Eastern Mediterranean.
Numerous neotectonic studies have been carried out in the Aegean region during the last few years (Mercier et al,, 1972, 1976; Angelier, 1973,197?; Pechoux et al., 1973; Dufaure et al., 1975; Mercier, 1976; Philip, 1976). They are the complement of the geophysical data (not discussed here). The geology of the Aegean region has been summarized by Aubouin (1973). In this. paper we describe examples of Middie-Late Pleistocene and Holocene tectonic features. They are in the Hellenic (=Aegean) Arc (outer arc: Crete, Karpathos; inner, volcanic arc: Milos)~ or just behind it (Samos, Chios). A more general analysis of Late Miocene and Plio-Quaternary tectonics in the Aegean Arc has been proposed elsewhere (Angelier, 1977). Table I summarizes the main geological methods applied to neotectonic analysis. On each figure the localization is shown in (a); the stereograms are Schmidt’s projections of the lower hemisphere (where fault planes are shown as thin lines, normal striations as black dots, and directions of extension as large arrows).
268 TABLE
I
Main geological Evidence
methods
of recent
deformation
Altimetric variations shorelines Tectonic structures marine terraces dunes alluvia, fans slope deposits,
Morphological
Historical
TECTONIC
applied
of
(especially
screes
data
seismicity
ANALYSIS
to neotectonic
analysis
Examples
Particular
Fig. 1 Fig. 2
altimetric measurements paleontological and radiometrical dating, morphology
faults) in: Fig. 3 Fig. 4 Fig. 5 Fig. 6 Fig. 7
. .
techniques
stratigraphy of quaternary deposits (morphology, paleontology, radiochronology) tectonic analysis (especially fault mechanisms), including: separation of successive movements
Fig. 8
search of recent scarps, photogeology study of morphologies related to uplift or subsidence
see text
compilation of available descriptions; search and analysis of structures comparison with focal mechanisms of earthquakes
OF RECENT
DEFORMATIONS
Deformation of Qua ternary shorelines (1) Middle-Late Pleistocene shorelines: a comparison of their deformations in the Western Mediterranean (“arc” of Gibraltar and Alboran Sea) and the Eastern Mediterranean (Aegean Arc: Crete) was carried out in a collective study (Angelier et al., 1976). The greatest amplitudes were found in the Aegean Arc: marine terraces are strongly uplifted in Crete (up to 4 cm per century and more, for the last 125,000 years), and submerged in the Cyclads Archipelago (inner arc), Moreover, altimetric changes are sharp (Fig. 1) because of block faulting. (2) l+storical shorelines: a rapid recent uplift of the whole of western Crete is indicated by the elevation of ancient shorelines (Spratt, 1856) 2000 years old (14C: Hafemann, 1965), now up to 9 m at Elafonisi, 15 km west of Paleochora (Fig. 2). The rate of uplift is about 40-60 cm per century (average rate for the last 2000 years). Tectonic Wiirm)
structures
in Quaternary deposits (especially Riss, Tyrrhenian,
In addition to being deformed on a broad scale, marine terraces are cut by faults which are generally normal, as on Karpathos (Fig. 3). Consolidated
269
Fig. 1. Regional deformation of Quaternary shorelines on southeastern Crete. a. Location. b. Typical section of the three main marine terraces (7’1, 7’2, T3), with their shorelines (Sl, SZ, S’s), above Neogene deposits: approximate radiometric ages are given after Angelier et al., 1976. c. Altimetric changes of shorelines Si, Sz, S3 along the coast.
Fig. 2, Regional deformation of ancient historical shorelines, about 2000 years old, on western Crete. a. Location. b. Marine erosional levels near Paleochora: numerous nutches in addition to the main shoreline, complicate the pattern. c. Map of present elevations, in meters, of the main shoreline. It is emphasized that some heights may belong to slightly older or more recent levels - see (b): the ages indicated by Hafemann, at places shown as black dots, range from 1620 to 2375 years. In Gavdos the precise age is unknown, but the terrace contains remains of pottery. After observations of Spratt (1856), Hafemann (1965), Bonnefont (1971), Dermitzakis (1973), and the author. The heights of 1.22.2 m indicated in the northwestern peninsula (NW of Kastelli), after Dermitzakis (1973), are probably underestimated (P. Pirazzolli, pers. comm.).
270
Fig. 3. Normal faults in a Tyrrhenian marine terrace at the southern end of the island of Karpathos. a. Location. b. Section of a fault scarp: P = marine Pliocene; T = Tyrrhenian deposits with Strombus bubonius LMK; D = dunes. c. Zone of conjugate normal faults. d. Corresponding stereogram (see text).
Upper Pleistocene dunes are often faulted, for example on Karpathos, above the marine terrace, or on Milos (Fig. 4), where marine deposits are below sea level. On Milos (Fig. 4), Karpathos (Angelier, 1973), and in other places, the main Recent faulting is similar to the older faulting: (1) intense normal faulting during the Late Pliocene or Early Quaternary; (2) unconformable sedimentation during the Middle-Late Pleistocene; (3) reactivation of normal faults, cutting the latter deposits. Successive movements closely spaced in time have been observed: for example, on Samos, two consolidated conglomeratic fans are superposed: both are cut by normal faults, but a previous fracturation, which is mechanically similar, cuts only the lower fan (Fig. 5). In the same way the SW-facing scat-p of Mt. Kedhros, on Crete, is covered by screes, the older being consolidated but the younger unconsolidated. These screes are cut by the NW-SE normal fault on which discrete successive movements have occurred with different mechanisms (Fig. 6). In the vicinity, near Plakias, three successive tectonic movements are (Fig. 7): (1) large normal faulting at the end of the Pliocene or during Early Quaternary times; (2) slight compression generating small reverse faults; (3) extensional movements again, with probable reactivation of normal faults. Recent movements are also inferred from morphological data: some fault
-bfm
-
Fig. 4. Recent normal faults northeast of Adamas on the island of Milos. a. Location. b. Section of a fault: V = volcanic Pliocene; M = marine Pliocene; C and D = alluvia and dunes of Upper Pleistocene, Note (1) the curvature of the normal fault near the surface so that it resembles an open reverse fault; (2) the evidence of previous normal faulting: the unconformable deposits C and D overlie M on one side of the fault, V (older) on the other side. c. Section of a more important Recent fault. d. Corresponding stereogram, for both faults. Striae of the last movement were not observed, but other observations suggest that the movement is probably purely normal.
I
400m
4
b
Fig. 5. Fracturation and normal faulting in consolidated alluvial fans west of Marathokambos on the island of Samos. a. Location. b. Schematic section of the two superposed fans Ft and Fz, successively faulted, and details (note the curvature of one fault near the surface, as on Fig. 4b). c. Stereogram.
b
Fig. 6. Recent reactivation of a great normal fault near Spili (Crete), a. Location. h. Schematic section. c. Detailed view: large grooves indicating a normal-sinistral movement L, polished by thin recent striations; 2, purely normal, cutting unconsolidated screes (probably Wiirm). d. Stereogram: comparison of movements 1 and 2.
scarps give evidence of recent motion (Fig, 8), and particular are related to rapid uplift (see Bonnefont, 1971, for Crete).
morph~l~~es
An example may be described on Chios (Angelier and Tsoflias, 1976): an old N-S fault was reactivated during the ~ua~~a~, since consolidated screes are faulted; on this fault line, near Tholopotami, large open cracks
Fig. 7. Schematic section of sucdessive WSW of Spili (see Fig. 6a). explanation
movements in text.
in Plakias (Crete).
Localization:
13 km
Fig. 8. Morphological evidence of Recent normal faulting near Lastros (eastern Crete). a. Location. b. View of the almost constant height scarp, in homogeneous limestones. c. Detailed section of consolidated slope detritus cut by a similar fault near Mesa Mouliana. d. Stereograms of these faults.
probably originated during a 1546 earthquake, according to contemporaneous documents (note that landslides have also occurred there, some of which were caused by earthquakes, but they have no direct tectonic meaning). The direction of extension is close to WSW-ENE, and seems roughly compatible with focal mechanisms of recent earthquakes near Chios (1949,1969). No tectonic structure clearly caused by an earthquake with a known focal mechanism has been found in the islands we have studied. Detailed geophysical studies applied to present surface tectonics are poor or absent (i.e, precise geodetic levelling, strain and stress measurements, precise location of earthquake foci, including microseismicity). GENERALPATTERNOFRECENTAEGEANMOVEMENTS
Middle-Upper
Pleistocene
and Holocene
tectonic
~ec~Q~~~s
(1) Predo~~~unce of exte~sio~~Z movements (normal f~u~ting)~ on the emerging parts of the Aegean Arc and the Southern Aegean, most tectonic mechanisms observed by geological means are extensional. The AfricaEurasia convergence in the Mediterranean region occurs in two different ways: (i) westwards, near the Strait of Gibraltar - strike-slip faulting occurs (continental compression especially, see Bousquet’s paper in this volume); (ii) e~stwurds, in southern Greece - subduction of the Eastern Mediterra-
274
nean crust has been proposed on geophysical criteria (MacKenzie, 1970; Rabinowitz and Ryan, 1970; etc.); the Aegean Arc and the Aegean region, above the plunging lithospheric plate, are mainly affected by extensional tectonics (intense normal faulting). (2) Traces of compression on the outer margin of the arc: Recent compressional structures (reverse faults) have been clearly observed in the area of the Ionian Islands (Mercier et al., 1972). In addition, on Karpathos, some compressional structures exist but are extremely subdued (Angelier, 1973). The scarcity of compressional structures leads us to make the following hypotheses: (i) recent compression has occurred near the trenches - since even the submerged southern margin of the Cretan Arc is affected by normal faulting (Nesteroff et al., 1977), thrusts and transform faults can only be present in the Hellenic trenches and seaward: (ii) the apparently greater intensity of compression on the lonian Islands (Mercier et al., 1972) may be pr~cip~ly related to the closeness of the NW term~ation of the typical subduction zone beneath the arc (i.e., with the decrease of the mechanical decoupling of plates).
Subduction and the Aegean expansion Except for a small generalized compressional event during the Early Quaternary s.1. (Mercier et al., 1976), the Plio~uatem~ pattern of normal faults in the Aegean region (Aubouin, 1973) has not changed fundamentally since the Middle Pliocene. A neotectonic analysis including a comparison with available seismic data has been proposed elsewhere (Angelier, 1977). The extensional movements during Upper Pliocene and Early Quaternary times - and probably also during Recent times (with less numerous but roughly analogous observations) - have resulted in an expansion of the Aegean Arc and the Southern Aegean towards the Eastern Medite~ane~ Sea. This implies that, as Plio~uatern~y subduction processes were occurring beneath the Hellenic Arc, the Crete-Libya rate of convergence was slightly higher than that of the Middle Aegean-Libya. ACKNOWLEDGEMENTS
The research was supported by the French C.N.R.SJ1.N.A.G. (A.T.P. G~odynamique). We must add that without the help of the group “Californie” of this A.T.P., this paper could not have been presented by the author at the 1977 RCM Symposium; special thanks are due to Dr. Rend Blanchet. REFERENCES Angelier, J., 19’73. Sur la n6otectonique 6g6enne: failles ant&-tyrrhbniennes et posttyrrhbiennes dans I’fIe de Karpathos (Dodkanke, G&e). C.R. Somm. Sot. G&01. Fr., (7) 15: 105-109.
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