Uplift, Deformation and Fluid Involvement Within an Active Normal Fault Zone in the Gulf of Corinth, Greece

Journal ofthe Geological Society, London, Vol. 151, 1994, pp. 531-541, 7 figs. Printed in Northern Ireland

Uplift, deformation and fluid involvement within an active normal fault zone in the Gulf of Corinth, Greece

GERALDROBERTS' & IAIN STEWART' 'Research School of Geological and Geophysical Sciences, Birkbeck College and University College London, Gower Street, London WClE 6BT, UK 'Division of Geography and Geology, West London Institute, College of Brunel University, Borough Road, Isleworth TW7 SOU, UK

Abstrart: The active Pisia Fault Zone is exposed close to the crest of a rotated carbonate fault-block that forms part of the southern margin to the Gulf of Corinth half-grabenin central Greece. The crest of the fault-block lies above sea-level whilstin the hanging-wall a marine basin exists. As a result, the diagenetic and structural characteristics of the fault zone record complexfluid involvement. Both early phreaticcarbonate syn-kinematic cements (characterized by drusyfabrics, baroque dolomites and crack-seal textures) and late vadose carbonate syn-kinematic cements (characterized by flowstones containing cave-collapse debris) exist in the uplifted footwall to the fault. Downward percolation of vadose meteoric waters and the upwelling of pore waters with elevated temperatures produced the diagenetic features observed within the fault zone. The co-existenceof early phreatic and late vadose cementswithin the fault zone is related to footwall uplift across the water-table and subsequent erosionalunroofing. The present-day elevation of phreaticcements to c. 650mabove current sea-level, providesa minimum estimate of footwall uplift along the fault. The wider implication is that temporal changes in deformation and fluid flow may typify fault-block evolution.

Recent studies have highlighted the uncertainty associated Diagenesis and footwall uplift in the crests of with predicting diagenetic and deformation features within carbonate fault-blocks the crests of fault-blocks. The poorly-understoodfactors that combine to limit prediction include the sources of pore Figure 1 summarizes the diageneticfeatures common in waters involved in diagenesis (Bjerlykke et al. 1989; Burley fault-controlled sea-cliffs composed of carbonates. It is well & MacQuaker 1992), the drivingmechanisms for fluid established that in such settingsthe water-table, which migration(Sibson et al. 1975; Carter et al. 1990;Sibson separatesthe vadose environment from the phreatic 1990), and the textural features associated with faults and environment, is generally at or slightly above sea-level due fracturesthat mayinfluence porosityand permeability tothe hydrodynamic head(Allan & Mathews 1982; (Knipe 1992). The preservation potential of structures and Humphrey 1988). Thus although after periods of heavy rain, diagenetic features at the crest of fault-block structures is the water-table may be higher than sea-level, out-pourings also uncertain, because uplift above sea-level may result in of freshwater from springs along the cliffswill return the erosion of the crest of the structure (Barr 1987;Yielding water-tableclose tothe level of sea-level. Similarly, the 1990). water-table cannot be belowsea-level as sea-water would Thispaper focuses on the diagenetic and deformation pour intothe air-filled fractures again restoringthe features within the crest of the carbonate fault-block that water-table close to sea-level. Phreatic cements, precipitated formsthe southern shores of the Gulf of Corinth below the water-table, are characterized by drusy fabrics half-graben, central Greece. Field and petrological observa- and dolomites and can be distinguished easily in the field tions from actively evolving fault zones, such as those in the fromvadose cements,precipitated above the water-table, Gulf of Corinth,permit the spatial relationships between which are commonly asymmetricand form stalactites, structuresand diagenetic features to beexamined more stalagmites and flowstoneswithin karstic cavities. This easily than can be achieved from studies of core material permits field geologists to distinguish deformation features from fault-block crests in the sub-surface. In the first part of developed close to surface from those formed at depth. In the paper, the idealized diagenesis of an active normal fault addition,the fluid sources within thestructure can be within carbonates is discussed. Following a brief outline of constrained. the regionalgeological setting, thepaper focuses onthe Withinactive normalfault zones vadose andphreatic deformation and diagenetic features of the Pisia Fault Zone, diagenetic products may, however,not show the simple an active normal fault zone in the eastern Gulf of Corinth. depth variationshown in Fig. 1. Field observations in Finally, the wider implications of this study in terms of the centralGreece haveshown that fault-block crests are not sources of fluid, the driving mechanisms for fluid flow, the stationary, but become uplifted relative to sea-level during nature of faults and fractures and the preservation potential earthquake episodes (Jackson et al. 1982; Vita-Finzi & King of features are discussed for other fault-block crests. 1985). If the level of the water-table stays close to sea-level

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i 1 DEPTH VARIATIONIN j CEMENT GEOMETRIES i DIAGENESIS i FAULT PLANE BOUNDING i j A ZONE OF CARBONATE .I.--_-- i 1) INFILTRATION ZONE i 1 Vertical caves, soils, 1 vegetation, collapse i B- Growth Hiatus breccias. fine-grained i showing speleothems. i dissolution and __-___-I.___-_._.- j 1 internal sediment 2) PERCOLATION ZONE 1 l C- Central hole CaCO, and H,CO, are in 1 i equilibrium, so that little D- Clean calcite i crystals grow dissolution or precipitation i i orthogonal to the occurs. Water descends i Flowstone growth zones through existing cavities. i i No Scale is Abundant speleothems in 1 implied the lower portion. i i .------3) CAPILLARY ZONE .li .------4) UPPER LENTICULAR ZONE aSmall crystals on i Sub-horizontal caves, hydraulic i the sides of the i cavity are erosion and corrosion due to i mixing of waters predominate. i overgrown by Some speleothems stch as i larger crystals cave pearls, calcite rafts. i whose growth Internal sediments and collapse i surfaces point i inwards from the INFLUX INTO breccias. Porosity is filled with 1 margins of the WATERSEA THE PHREATIC water resulting in drusy fabrics. cavity. Equant SYSTEM INTERNALSYSTEMSEDIMENT I 5) STAGNANT ZONE 1 crystals fill the 1 centre of the (Waters do not mix with Zone4 cavity. and this zone grades downwards1 -1cm SPELEOTHEMS i I m I into the deep conflate zone) i

Fig. 1. Illustration of the depth variationin diagenesis that may be expected within the crestsof carbonate fault-blocks lying closeto sea-level. The diagram is adaptatedfrom Gascoyne & Schwarcz (1982), Scholle et al. (1983) and Tucker& Wright (1990).

duringfootwall uplift then, presumably,phreatic cements at least 700 m of syn-rift stratigraphy (Brooks & Ferentinos will be over-grown by vadosecements and subjected to 1984; Higgs 1988). karstification as the rocks emerge above the water-table/sea- At the eastern end of this majorbasin-bounding fault level. With knowledge of eustaticsea-level changes, it is system, along thesouthern shores of the Gulf of possible to assess footwall uplift relativeto thewater- Alkyonides,faulting is expressedonshore as aseries of table/sea-level by examiningoverprinting relationships discontinuous fault strands that delimit the northern flanks between vadose and phreatic cements. Also, it is clear that of thecarbonate-dominated Gerania Mountains (Fig. 3). erosion accompanying footwall upliftwill progressively Some of these fault strands were ruptured during the 1981 strip-off theearliest-formed vadose portions of the Gulf of CorinthEarthquakes (M,<6.7) (Figs 2 & 3) fault-block,thereby unroofing the deeper-seated phreatic (Jackson et al. 1982; Taymaz et al. 1991). Well-located zone,and influencing thepreservation potential of hypocentrallocations for the 1981 earthquakes combined deformationfeatures in theuppermost levels of thefault with field studies of the surface-breaks indicate the geometry zone. of the fault to be moderately-dipping (40-50") and planar down to depths of c. 12 km (Jackson et al. 1982, Jackson & White 1989, Taymaz et al. 1991). The surface expression of Geological background to the Gulf of Corinth fault strands are topographic escarpments several hundred The Gulf of Corinth is a 120 km long, 30 km wide marine metres in height and delimited at their base by limestone basin that lies within the Aegean extensional province. This faultscarps and 1981 groundruptures. The fault zone province, characterized by north-south extension, separates studied in this paper, here termed the Pisia Fault Zone, lies plate convergence and subduction alongthe Hellenic Trench along the base of theescarpment between Pisia and from dextral strike-slip crustal motion along along the North Perachora (Fig. 3). Aegean Trough (Fig. 2) (Kelletat et al. 1976; Le Pichon & Raised beaches,uplifted coastal notches and incised Angelier 1979; Le Pichon 1982;Billiris et al. 1991). drainage basins along the southern margin of the Gulf of Seismological and structural studies indicate that extension Alkyonides indicate substantial uplift of the footwall to this is accommodated by movement on east-westtrending stretch of thebasin-bounding fault system (Leeder et al. normalfault systems, one ofwhich controlsthe southern 1991; Bentham et al. 1991). Furthermore,extensive margin of the Gulf of Corinth(Jackson et al. 1982; sediment cones, alluvial fans and fan deltas on the flanks of Vita-Finzi & King 1985; Taymaz et al. 1991). Seismic lines theGerania footwall block attestto prolonged erosion across the Gulf of Corinth suggest thatthis fault system (>3.6-4.0Ma) of the uplifted footwall crest (Leeder et al. bounds the southern edge of an asymmetric half-grabenwith 1991; Collier & Dart 1991). Absolutedating of raised

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escarpmentbetween Pisia andPerachora (Figs 2 & 3). Immediately tothe south of the village of Pisia, for example, the base of the fault escarpment is marked by a 50m high, fresh-looking fault plane (Figs 3 & Sa). Surface breaks up to 1 metre in height occurred at the foot of this faultplane in 1981 (Fig. Sa). However, the faultplane at Pisia merely forms a carapace to a fault zone that runs along the base of the Pisia Escarpment. A stream incised into the easternend of theexposure (Fig. Sa)allows asuite of deformed rocks underlying the fault plane to be examined (Fig. 5b). Although field observations of the structures that underlie this fault plane have been described by Stewart & Hancock(1988, 1990, 1991), no detailed microsructural or petrological observationswere reported. New field, petrological andmicrostructural observations of deformation and diagenetic features within thefault zone are presented below (Fig. 6), starting with the lowest exposed levels within the footwall to thefault zone and working towards the fault plane shown in Fig. 5a.

Fractures within thefootwall of the Pisia FaultZone .C 1981 SURFACE An intense fracture network exists within the footwall to the BREAKS Pisia Fault Zone (Fig. 5c, d & e). Bedding can be seen at outcrop,dipping gently to thesouth. Inthin section, the MAJOR NORMAL fracturesthat cut acrossbedding are filledwith calcite FAULTS cements andbaroque dolomite cements that contain thin stringers of material, petrographicallysimilar tothe PLIO- carbonates forming the wall-rocks to the fractures. Calcite I I PLEISTOCENE and dolomite cements are, in places, separated by stringers of carbonate. In other places, calcite crystals on either side of thecarbonate stringers are not in optical continuity, indicating that they are separate calcite crystals rather than a single calcite crystal with an inclusion of wall-rock. Between the stringers of carbonate, both the orientation of growth Fe. 2. Location map of the Gulf of Corinth. H, Hellenic Arc; NAF, North Anatolian Fault; PSP, Psatha-Skinos-Pisia Fault; LF, faces within the cements and crystal size are distributed in a Loutraki Fault; X-X', Line of section in Fig. 4. symmetrical pattern (Fig. 5d & e). Small crystals occur along thefracture margins andform a foundation upon whichlarger euhedral crystals havegrown. These larger marinedeposits of known elevation yieldsfootwall uplift crystals exhibit growth faces that consistently point inwards, rates for the late Quaternary of 0.2-0.8 mm a-' (Vita-Finzi away from the fracture margins. In some instances, crystal & King 1985; Collier 1990; Collier & Dart 1991; Leeder et size increases intothecentre of thefracture. In al. 1991). At least some of this uplift is likely to be produced cross-polarized light, the dolomite crystals exhibit undulose by recurrent co-seismic deformation,comparable in extinction. Undercathodoluminescence, both the calcite magnitude tothe c. 1 m surfacedisplacement recorded and dolomite are non-luminescent. following the 1981 earthquakes(Jackson et al. 1982; Vita-Finzi & King 1985). The active geological setting of the faults bordering the Interpretation GeraniaMountains provides a variety of potential fluid The petrographic characteristics of the cements within the sourceswhich may haveinteracted with the faultsduring footwall fractures suggests that they were precipitated in the theirstructural evolution (Fig. 4). Theseinclude deep- phreatic environment below the water-table. The symmetri- seated thermal waters emanating from fault lines along the cal distribution of crystal sizes suggests thatthe cements base of the Gerania Mountains, (Schroeder 1985; Fytikas & nucleated onboth sides of the fracturesand that the Kavouridis1985; Brehm 1985; Garagunis & Kollias1985) fractures werefilled with porewaters during cement vadose meteoricwater percolating downwards within the precipitation. The increase of crystal size into the centre of karst system of the Gerania Mountains and marine waters fractures is a feature of phreatic cements known as a drusy infiltrating from the adjacent Gulf of Corinth. fabric (Scholle et al. 1983; Tucker & Wright1990). The unduloseextinction within thedolomite crystals indicates that they are composed of baroque dolomite, precipitated at Deformation and diagenetic features within the Pisia elevated temperatures (>60"C) from magnesium-rich fluids Fault Zone (Tucker & Wright 1990). The source of the Mg may have The Pisia Fault Zone canbe examined in aseries of been from the influx of sea-water into the phreatic aquifer, exposuresalong thetrace of majora normal fault and the elevated temperatures may have been produced by

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,‘Psatha Gulf of Alkyonides PERACHORA Alepochori fl PENINSULA

GERANIA Fig. 3. Topographic map of the Gerania ‘f3 MOUNTAINS Mountains and the Perachora Peninsula Bay of Corinth _-- (see Fig. 2 for location) adapted from the _I: Area above 800 Loutraki ‘! 1 :50 OOO geological maps of the area ‘,-,--l metres produced by the Institute of Geology and N Normal faults Mineral Exploration, Athens (IGME 1 5 1984a, b, c, 1985). Notice that the t Pisia-Psatha Fault controls the high km Q Q Faultsruptured in thc 1981 earthquakes topography of the Gerania Mountains. L I

opening fractures during the pre-seismic stage of the seismic SW Gerania Mountains NE cycle and expelled when the fractures close during the phase Influx of meteoric watel of stress release produced by co-seismic fault slip. However, we seeno evidence to suggest thatfractures physically n closed. Indeed our observations suggest thecontrary, \\f because the euhedral crystals lining individual cracks are not broken or crushed, a feature which would be expected if the crackhad closed. We feel thatfracture closure occurred through the precipitation of crystals in the fracture porosity rather than by dynamic fracture closure. Although the influx of hot pore waters into phreatic aquifers has been observed during earthquakes along other faultsin Greece (e.g. M = Influxof marine waters ’ ‘ Ascending thermal waters Asteriadis & Livieratos 1989), it may bethat fractures Minimum thickness of syn-ritt within the fault-block crestwere simply conduitsfor 5km ascending fluids driven by the present-day hydrodynamic head, as is the casewith the nearby Loutraki hotsprings (Fig. 3) (Schroeder 1985; Fytikas & Kavouridis 1985; Brehm Fig. 4. Cross-section across the Perachora Peninsula showing 1985; Garagunis & Kollias1985). Thus, although evidence possible fluid sources for fault zone diagenesis. Location of section for seismicpumping along other faults isvery convincing shown on Fig. 2. Adapted from Perissoratis et al. (1986), with (Briggs & Troxell 1955; Stermitz 1964; Swensen 1964), not additional data from Collier & Dart (1991) and IGME (1984a, b, c, 1985). all crack-seal textures and phreatic cements close to faults may be diagnostic of seismically-drivenfluid motion, a process that may dominate the deeper portions of faults.

theentry of watersassociated with hot springs intothe phreatic system. Brecciated footwall carbonates The stringers of carbonate wall-rock within the fractures Overlying the footwall fracture belt is a zonewhere indicate crack-seala mechanism. The lack of optical brecciation is so intense that bedding cannot be seen (Fig. continuity across the stringers of wall-rockwithin calcite 5b). The breccia forms a zone running parallel to the fault veins confirms that different generations of calcite exist on plane that bounds the top of the outcrop. The thickness of eitherside of the stringer.Clearly cementation within this zone of breccia is difficult to determine as the top and fractures was episodicasdolomite and calcite were basehave not beenobserved in one locality, but, is precipitatedduring successivecrack events within one estimated to be in the range of 0.5-3m. Clast sizes within fracture. Individual cracks within thefracture became the breccia are<3 cm in diameter. Inthin-section, the completely infilled with cement before the next crack event larger clasts appear to be floating within a matrix of finer occurred. clasts (Fig. 5f). The larger clasts have angular shapes, but It is tempting to suggest that the rep,eated crack events rounding increases as the grain size decreases. The clasts are resulted in fluids being forced along the fault in the manner composed of Mesozoic carbonateand in placesoriginal envisaged by Sibson er al. (1975) in his model of seismic carbonategrains, bioclasts andinter-granular diagenetic pumping. This modelsuggests that fluids are drawninto cements are still visible within the clasts.

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Interpretation cavity collapse is a common feature of the higher parts of This breccia is interpretedto be a carbonate fault gouge karst systems where meteoric water is under-saturated with produced by grain-size reduction of the Mesozoic carbonates respect tocalcite and dissolution produces degradation of that form the footwall to the Pisia Fault Zone during fault the cavity walls. Presumably, the higher parts of the fault slip. The top of this carbonate faultgouge is a planar contact planethat bounds the base of the flowstone underwent dissolution and collapse so that fragments of carbonate fault with thelaminated calcite deposit reported by Stewart & Hancock (1988, 1990, 1991). For reasons that are discussed gouge fell downwards in to the vadose cavity and came to below, we believe this contact to be a second fault plane rest upon the growing flowstone. Further flowstone growth engulfed and covered the clasts of carbonate fault gouge. within the Pisia Fault Zone The fine-grained debris is interpretedhere as vadose silt composed of cementfragments that probably came from Laminated calcite deposits higher in the karst system where active dissolution degraded A laminated calcite deposit, termed a ‘layered marble’ by cavitywalls (see Tucker & Wright 1990). The cement Stewart & Hancock (1988, 1990, 1991) (Fig. 5b & g), trends fragmentswere carried by descendingmeteoric waters to parallel to and directly beneath the fault plane shown in Fig. come to rest upon the growth surface of the flowstone. The 5a. In thin-section the deposit can be seen to be composed air-filledinclusions andthe pitted nature of crystal of un-twinned, needle-like calcite crystals which are stacked terminations are interpreted as the product of dissolution on in layers (Fig. 5g). The euhedral crystals terminations that the growth surface ofthe flowstone caused by periodic influx bound the top of individual layers consistently point away of descending meteoricwaters that were undersaturated from thefootwall of thefault zone and are coated in with respect to calcite. fine-grainedcalcite debris. The crystalterminations are The flowstones at this locality are relict features, having pitted in placesand air-filled inclusionsexist within the been dated using a 23”T’h/234Utechnique at >350 ka by crystals.In the bottom 10mof the stream section, grey Roberts et al. (1993),who also discuss thepalaeoseis- clasts <15cm acrossoccur within thelaminated calcite mological implications of thesefeatures. Although no deposit (Fig. 5b & g). The clasts are composedof carbonate modern flowstones have been observed accumulating at this fault gouge (see above for description and interpretation). site, further to the east, at Psatha, intra-fault zone vadose The clasts areunderlain by laminations within the calcite meteoric cements and flowstones are forming today (Fig. 3). deposit, whilst higher laminations wrap around, enclose and Here, a large normal fault plane, interpreted as the along blanket the clasts. The lower levels of the laminated calcite strikecontinuation of thefault reactivated in the 1981 deposit rest directly on a planar surface which bounds the earthquakes (King et al. 1985; Leeder et al. 1991) is exposed top of azone of highly-brecciatedcarbonate interpreted in road cuttings. Roberts et al. (1993) describe open caverns above to be a carbonate fault gouge. Laminationswithin the within thefault zone containing vadose deposits, suchas calciteclose tothe plane bounding the underlyingfault flowstones thatare accumulating on fault planes and, in gouge are notintensely disrupted by fracturing or places, are cut by faults. After periods of heavy rain, water brecciation (Fig. 5h) and can be traced for several metres up can be seen pouring from the caverns which exist along the and down dip. The laminatedcalcite infillssmall-scale faults. Cave-collapse debris, composed of clasts of Mesozoic topography on the planar surface that bounds the top of the limestone,can be observed sticking out of growing carbonate fault gouge, and crystal size within the laminated flowstones, andare being engulfed by active vadose calcite increases away from the contact. cementation.

Interpretation Thislaminated calcite deposit is interpretedhere as a Fault plane that bounds the top of the laminated calcite flowstone; calcite a accumulation precipitated from deposit withinthe Pisia Fault Zone downward-percolating or flowing meteoric water within the vadose parts of karst systems (Gascoyne & Schwarcz 1982). Lineations in the form of corrugations and scratches exist It is envisaged that the flowstone grew within an air-filled upon the fault plane that forms a carapace to the Pisia Fault cavity thatexisted within the Pisia FaultZone, by the Zone (Fig. 5a & b). The material that comprises that fault precipitation of calcite from meteoric water flowingdown plane described by Stewart & Hancock (1988, 1990, 1991) as the lower wall of the cavity. The planar surface that bounds astylobreccia, is a breccia with clast sizes <3 cm in the top of the carbonate fault gouge and the base of the diameter. The breccia is similar to the brecciated footwall flowstone is interpreted here as a second fault plane within carbonates described above in that the larger clasts appear the Pisia FaultZone. The flowstone grew uponthis fault to be floating within a matrix of finer clasts. However, the plane which bounded the lower side of the vadose cavity. composition of the clasts is very different to those within the The cavitywas large (> severalmetres) as individual brecciated footwall carbonates. The clasts are composed of laminations can betraced for several metres up and crystalline calcite that is twinned (Fig. 5i). No bioclasts or down-dip of the flowstone before problems of access within sedimentarycarbonate grains exist within the clasts. In the stream section limit examination of the flowstone. The places, thin, fault zones 4cm wide emanate from the main crystals within theflowstone consistently point upwards, fault plane and cut down across the underlying laminated away from the underlying fault plane, which we interpret to flowstone (Fig.5b). Thin sections from these thin fault suggest that growth of the deposit occurred upwards into an zones show that they are lined with breccias with clasts of air-filled cavity. The clasts of carbonatefault gouge that crystallinecalcite thatare verysimilar tothe breccia exist within the flowstone are interpreted as the product of comprising the main faultplane. Examination of thin collapse of the higher parts of the vadose cavity. Cave and sections taken immediately above andbelow these thin fault

Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/151/3/531/4889927/gsjgs.151.3.0531.pdf by guest on 26 September 2021 Fig. 5. Photos of the Pisia Fault Zone.(a) View looking south east onto the fresh fault scarp that forms a carapace to the Pisia Fault A Zone. is location of the stream section shownin (b). (a) Field photo looking west across the stream section that cuts into the Pisia Fault Zone.A section across the Pisia Fault Zone is exposed in the wall side of the stream section.A, Fault gouge composedof comminuted bed-rock carbonate; B, contact between flowstone and underlying fault plane (see (h) for detail);C, clasts of 'bed-rock-derived gouge' within the flowstone (see (g) for detail); D, fault which cuts across and post-dates flowstone growth (see (i) for detail);E, fault plane shown in (a). (c) Field photo looking eastof fractures in the footwall to the Pisia Fault. The notebookis 30 cm across. This exposure existsc. 400 m to the west of the exposures shownin (a), within the thickly-vegetated area along the baseof the Pisia Escarpment.A-A is bedding. B-B is the orientation of fractures filled with phreatic carbonate cements.C is the baseof the zone of fault gouge composedof brecciated Mesozoic carbonate. (a) Photomicrograph (PPL) of fractures in the footwall to the Pisia Fault. The thin-section has been stainedusing Alizarin RedS. A is stringer of wall rock separating two generationsof baroque dolomite. B is a stringer of wall rock separating two generationsof calcite. C is a

Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/151/3/531/4889927/gsjgs.151.3.0531.pdf by guest on 26 September 2021 late cross-cutting fracturefilled with baroque dolomite. Thefield of view is 6 mm. (e) Photomicrograph in (PPL) of fractures in the footwall to the Pisia Fault. The thin-section has been stainedusing Alizarin Red S. A is an area of calcite cement. B is a stringer of wall rock separating two generations of baroque dolomite. In contrast to (d), Cis a late cross-cutting vein filled with calcite. The field of view is 6 mm. (f) Cataclastic fault gouge composedof comminuted bed-rock carbonate. A, carbonate grainswithin a large clast within the fault gouge; B. pre-deformation diagenetic cements between the carbonate grains. Field of view is 6 mm. (g) Photomicrograph (PPL) of the laminated flowstone located in (b). A, Clastof 'bed-rock-derived fault gouge' within the flowstone. The arrow points upwards. Fieldof view is 6 mm. (h) Photomicrograph (PPL) of contact between the flowstone and the underlying carbonate fault gouge (see (b) for location).Field of view is 6 mm. (i, j) Fault gouge derived from comminutionof the flowstone. Note the twinned natureof the calcite as compared with the precursor flowstone shown in (g). At least someof the deformation within the fault gouge has occurredby low-temperature twinning within the calcite grains. See (b) for location.Field of view is 6 mm. (i) PPL; (j) XPL.

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zones demonstrate that they are hosted completely within SKETCH AND EVOLUTION OF THE PlSlA FAULT ZONE the laminated flowstone. FLOWSTONECONTAINING 'SEDIMENTARY CLASTS OF UNDERLYING FAULT GOUGE DERIVED FROM BED-ROCK COLLUVIUM LAMINATIONS IN THE FLOWSTONEARE NOT DEFORMED BY Interpretation AN INTENSE FRACTURE NETWORK. The existence of lineations onthe faultsurface and the recent fault breaks reported from the base of the fault plane following the 1981Gulf of Corinth Earthquake Sequence (Jackson et al. 1982) indicate that this surface has been the site of co-seismic fault slip. We interpret the breccias that comprise the fault plane and thin breccia zones that cut the

flowstone asfault gouge. These fault gouges formed by FINE-GRAINED FOOTWA; BRECCIA FAULT GOUGE ZONE fracturing, disaggregation and grain-size reduction of the COMPOSED OF CLASTS flowstone that hosts thefault zones. Thus, the flowstone OFCOMMINUTED FINE-GRAINEDFAULT GOUGE COMPOSED OF FLOWSTONE COMMINUTEDBED-ROCK CARBONATESAND formed prior to the initiation of fault displacements along CONTAININGCLASTS OF FOOTWALLBRECCIA the main faultplane. Stewart & Hancock (1991)suggest fromtheir observations at outcrop,that stylolites and evidence for recrystallisation exist within these breccias. However,the existence of stylolites linedwith insoluble residue or fabrics that suggest growth of new minerals or recrystallisation hasnot been confirmedby petrographic studies. Twins exist within the calcite of the breccia clasts, whereasno twins exist within the flowstone calcite. The /WATER twinning hasbeen interpreted as the result of strain " accumulationwithin the clasts during slip within the fault gouge (Roberts et al. 1993). The factthat the uppermost portions of the flowstone have been faulted may explain why CAVE-COLLAPSEMATERIAL IS CAUGHT UP nopendant stalactite-like cements have been found. It is B AND ENVELOPED WITHIN THE FLOWSTONE suggested here that faulting and grain-size reductionhave destroyed anydownward-growing cementsprecipitated .. RENEWED FAULT DISPLACEMENTSPRODUCE upon the roof of the cave. A FAULT GOUGE COMPOSED OF COMMINUTED FLOWSTONE. THE LOW It is interesting tonote that despite the factthat the FRACTURE DENSITIES WITHIN THE FLOWSTONESUGGEST THAT SURFACE flowstone has hosted a fault plane that is known to undergo c FAULTING DOES NOT PRODUCEA DISTRIBUTEDNETWORK OF displacement during large magnitude earthquakes (Jackson EXTENSIONAL FRACTURES et al. 1982), (M,6.7-6.4 with c. 1m co-seismic fault slip at the surface), the flowstoneis comparativelyundeformed. Fig. 6. Summary of observations atPisia. A fault zone developed Fractures are relatively rare within the flowstone compared within bed-rock carbonates forms the substratum to flowstonea deposit which probably grew during a period of inactivityof fault tothe numberfractures within the Mesozoic limestones slip. Renewed fault activity has brecciated the flowstone. The 1981 within the footwall. In fact, fractures are rare within the so earthquake sequence produced a surface breakwithin the colluvium flowstone,that atoutcrop, individual cementlaminations which is shown at the northern endof the sketch. canbe traceddown-dip forseveral metres without disruption. likely that fluidadvection through passive fractures was driven by the hydrodynamic head in the area. Summary of the deformation and diagenetic history of the Pisia Fault Zone The petrological andmicrostructural evidence presented Stage 2. With prolonged fault activity, the phreatic portion above allows the following stages in the history of this part of the fault zone was uplifted across the water-table and into of the Pisia fault zone to be unravelled (Fig. 6). the vadose realm. Dissolutionprocesses produced cavities and caveswithin the fault zone. One of these cavescon- Stage 1. A fault zone developed within the Mesozoic lime- tained afault plane that delimited thetop of azone of stones producing a zone of carbonate fault gouge that was carbonatefault gouge. A flowstone precipitatedupon the underlain by, and probably contained within fractured Mes- fault plane from gravity-driven descending meteoric waters ozoic carbonates. It is as yet not cltar whether the fractures which at times carried vadose silts and also produced episo- close to the zone of carbonate fault gouge formed prior to dic dissolution of the flowstone. Debris produced by cave- the localization of the gouge zone, perhaps at the tip of the collapse became engulfed by the growing flowstone. Flow- juvenile fault, or, were produced during slip alongthe gouge stone precipitation seems to have beenun-interupted by zone. However,the existence of fracture-filling phreatic faulting events. cements indicates that the fractures openedbelow the water- table. Open fractures became infilled with phreatic cements Stage 3. A discrete fault surface developed within the flow- before renewed fracturing initiated further fracture porosity stone producing afault gouge composed of comminuted and pore water influx. Although the driving mechanism for flowstone. No fracture fillingvadose cements have been fluidflow may have been seismic pumping,it is equally found within the Mesozoic carbonates of the footwall, sug-

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gesting that faulting above the water-table did not produce MODEL OF FRACTURING AND FLUID FLOW WITHIN extensive fracture belts in the footwall. Extensive fracture ACTIVE FAULT ZONES

belts that exist in the footwall wereformed below the 1) NEARSURFACE SHATTER ZONE water-table and provide a record of the early history of the CONFINED TO ABOVE 500m VITA-FIN21 (L KING 1985 , HANCOCK 6 fault zone. BARW 1987, STEWART 6 HANCOCK

2) GREY ORNAMENT INDICATES TERS A :AULTZONE FRACTURING AT DEPTH OF A Stage 4. At present, the features described are relict struc- >500m BELOW THE PR€-RIFT TO tures preserved within the footwall of the currently active SYN-RIFT CONTACT / fault plane.Uplift of the footwall along this faultplane, VAWSE ZONE . together with erosion, has exposed these structures. PHREATIC ZONE 3) HANGING-WALLSUBSIDENCE ASSOCIATED WITH MARINE THEFOOTWALL WITHIN SEDIMENTATION VAWSE ZONE IS Upm in the footwd of the Pisia Fault Zone SUB-AERIALAND BECOMES ERODED Despite the factthat footwall uplift has been widely documentedfrom the Gulf of Corinth(e.g. Vita-Finzi &

King1985; Leeder et al. 1991; Bentham et al. 1991), to 6) NEAR SURFACE SHAnER ZON 7) ROCKSFOOTWALL IN THE date, it remains unclear how much uplift has occurred in the UPLlFEDTHE ACROSS UPLIFTEDDUE TO AREINTRA-FAUL ZONE HANGING-WALLCOLLAPSE footwalls of itsbordering faults. We suggest thatthe (STEWART 6 HANCOCK 1 S31 1 present-day elevation of fracture-filling phreaticcements provides an estimate of minimum amount of uplift relative to the present day sea-level/water-table for the Pisia fault . Zone. Baroque dolomite within the Pisia Fault Zone occurs 8) NEARSURFACE SHATTER 9) FRACTURESPRODUCED at an elevation of c. 650 m above sea-level. The baroque ZONE HAS A LOW PRESERVATION AT DEPTH REACHSURFACE POTENTIALDUE TO UPLIFTAND DUE TO UPLIFTAND dolomite musthave beenprecipitated below the water- EROSKJN. THE PRESERVED EROSON OF FOOTWALL VOLUME OF NEAR SU^-'--8WwRbC table,and it may bethat the source of magnesiumwas SHATTER ZONE DECF DURING TIMES A-TO-E 11) FLUID SOURCESFOR sea-water. Since sea-level has never been higher than a few CEMENTS WITHINTHE FAULT metres above its present level in the last 2.5 Ma (Imbrie et ZONEINCLUDE DESCENDING 10) NEAR-SURFACEFAULTING METEORIC WATERAND SEA al. 1984; Haq et al. 1987; Shackleton 1987) it is implied that DOES NOT INVOLVE WATER TOGETHER WITH BRECCIATON OF ROCKS IN THE THERMALASCENDING FOOTWALL TO THE SLIP PLANE WATERS FEEDING HOT baroque dolomites are most likely to have been uplifted by SPRINGS >650 m relative to present-day sea-levelby tectonic processes. Extrapolating late Quaternary uplift rates for the Fig. 7. Illustration of the evolution of deformation and diagenetic features within a carbonate fault-block that protrudes above southern shores of the Gulf of Alkyonides of 0.3 mm a-' sea-level, adapted from Vita-Finzi & King (1985), Hancock & (Collier 1990; Leeder et al. 1991), shows that uplift of 650 m Barka (1987) and Stewart & Hancock (1988, 1990, 1991). could be achieved in 2.2 Ma.

Discussion, conclusions and wider implications for diagenetic reactions, the study shows that fluid sources Figure 7 illustrates the evolution of the crest of the Pisia may change during the evolution of a fault zone, indicating Fault Block asinferred from diagenetic and structural that dynamic rather than static models are needed toexplain evidence presentedhere. According to thisscheme, the the hydrodynamics of fault-block crests. deep-seated phreatic fracture belts are lifted into the vadose (2) Widespreadfracture networks associatedwith the environment during footwall uplift and may be overprinted Pisia Fault Zoneare dominated by phreaticcements and by vadose features. The footwall is eroded as it rises above crack-seal textures. Such cementshave been precipitated sea-level, thereby progressivelyremoving theearly fault- from hotpore waters whosemigration may have been block crestthat hosted vadose diagenesis. Erosionand driven by seismicpumping atdepth, or equally by the further footwall uplift works to exhume the deeper parts of hydrodynamic head. The crack-seal textures indicate that thefault block crest which hasundergone fracturing and the connectivity of thefracture systemchanged during cementation within thephreatic realm below the water- progressive deformation and that much of the fracture belt table. was sealed by cementprecipitation early in its history. Although the abovescheme may beapplicable to Fractures formed during the phreatic history of a fault will carbonate fault-blockslying close to sea-level, fault-blocks notbe connected to fracturesformed when thefault has dominated by other lithologies (such as silici-clastic fault beenuplifted across the water-tableinto the vadose blocks or thosein crystalline basement),and fault-blocks environment. Our studyshows thatthe phreatic fracture developed in fully marine or fully continentalareas will belt does not have new fractures added to it during vadose show differentdiagenetic anddeformation features. faulting,but the influx of meteoricwater may induce However, a number of observations derived from this study textural modification such as dissolution. mayhave wider implications for reconstructingthe (3) It seemsthat during faulting in the vadose realm, structuraland diagenetic characteristics of other fault- largevolumes of rock surrounding the fault are not blocks. fractured, since no fracture-filling vadose cements have been (1) The Pisia Fault Zone containsthe products of foundin the footwall. Instead,fracturing is concentrated deformation and fluid flow that occurred above and below within the gouge zone of the active faultsurface. This is the water-table. Fluid sources include descending meteoric surprisinggiven that in recent times the faultzone waters, sea-water and watersascending from depth investigated hostedlarge normal faulting earthquakes (M, exhibiting elevatedtemperatures. In addition theto 6.4-6.7) and presumably contrasts with the situationat recognition that several sources of fluids may be available depth where widespread phreatic fracture belts may be the

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result of faulting. Thus there may exist a depth variation in HOUSEKNECHT,D.W. & PITMAN,E. D.(eds) Origin, diagenesis and faulting andfracturing whichmay becommon toother petrophysics of clay minerals in sandstones., SocietyofEconomic normal faults bounding tilted fault-blocks. Paleontologists and Mineralogists Special Publications, 47, 81-1 10. CARTER,N. L., KRONENBERG,A. K., Ross, J. V. & WILISCHKO.D. V. 1990. (4) The existence of phreatic cements at an elevation of Controls of fluids on deformation of rocks. In: KNIPE, R.J.& RUTIER,E. 650 m along the Pisia fault zone suggests that at least this H. (eds) Deformation, Mechanism Rheology and Tectonics. Geological amount of uplift hastaken place in the footwall.This Society, London, Special Publications, 54, 1-13. confirms that uplift of fault block crests can be substantial COLLIER,R. E. LL. 1990. Eustaticand tectonic controls upon Quaternary coastalsedimentation in the Corinth Basin, Greece. Journal of the (e.g. Barr 1987;Yielding 1991). Becauseerosion accom- Geological Society, London, 147,301-314. panies such uplift, the preservationpotential of features -& DART,C. J. 1991. Neogene to Quaternary rifting, sedimentation and within the crest of the fault-block, especially those affected uplift in the Corinth Basin, Greece. Journal of the Geological Society, by meteoric diagenesis, is low. Whether vadose or phreatic London, 148,1049-1065. FYTKAS,M. & KAVOURIDIS,T. 1985. Geothermal area of Sousaki-Loutraki. featuresdominate the crest of the upliftedfault-block is In: ROMIJN, E.,GROBA, E., LUE~IG,G. W., FIEDLER,K., LAUGIER,E., controlled by the extent of erosion and the rate of textural LOEHNERT,E. & GARAGUNIS,C. (eds) Geothermics, thermal-mineral modification produced by vadose diagenesis. waters and hydrogeology. Theophrastus, Athens. 19-34. These conclusions emphasize that deformationand GARAGUNIS,C. & KOLLIAS,P. 1985.Protection of an aquifer of the diagenesiswithin the crests of fault-blocks are likely to oligomineral water of Loutraki. In: ROMIJN,E., GROBA, E., LUEITIG, G. W.,FIEDLER, K., LAUGIER,E., LOEHNERT, E., GARAGUNIS, C. (eds) exhibit temporaland spatial variations. For this. reason, Geothermics thermal-mineral waters and hydrogeology . Theophrastus, more case studies of deformation and fluid flow within the Athens. 219-234. crests of fault-blocks areneeded to improvediagenetic GASCOYNE,M & SCHWARCZ,H.P. 1982. Carbonateand Sulphate models andreservoir predictions around ancient normal Precipitates. In: IVANOVICH,M. & HARMON,R. S. (eds) Uranium Series Disequilibrium: Applicationsto Environmental Problem. Clarendon faults in the subsurface. Press, Oxford. 268-301. HANCOCK,P. L. & BARKA,A. A. 1987.Kinematic indicators on active Thisstudy forms part of widera programme encompassing normalfaults in western Turkey. 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Received 8 April 1992; revised typescript accepted 7 September 1992

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