tters 257 (2007) 450–462www.elsevier.com/locate/epsl

Earth and Planetary Science Le

U-series dating and geochemical tracing of late Quaternarytravertine in co-seismic fissures

I. Tonguç Uysal a,⁎, Yuexing Feng a, Jian-xin Zhao a, Erhan Altunel b,Dion Weatherley c, Volkan Karabacak b, Oya Cengiz d, Suzanne D. Golding a,

Michael G. Lawrence a, Kenneth D. Collerson a

a Earth Sciences and Centre for Microscopy and Microanalysis, University of Queensland, Brisbane QLD 4072, Australiab Department of Geological Engineering, Eskisehir Osmangazi University, Eskisehir, Turkey

c Earth Systems Science Computational Centre and Australian Computational Earth Systems Simulator, University of Queensland,Brisbane QLD, 4072, Australia

d Department of Geological Engineering, Süleyman Demirel University, Isparta, Turkey

Received 29 June 2006; received in revised form 28 February 2007; accepted 4 March 2007

Available onli

Editor: R.D. van der Hilst

ne 12 March 2007

Abstract

We present a method to constrain the timing of fissure generation related to late Quaternary seismic events using the uranium-seriestechnique. Dated samples were from travertine deposits precipitated in co-seismic extensional fissures along major active faults inWestern Turkey. Stable isotope andREE data indicate that the precipitation of the fissure travertineswas not controlled by the hydrologicregime that is responsible for the speolethem deposition in the same region. Moreover, the REE composition and concentration of thewater from which the fissure travertine precipitated were significantly different from those of the current geothermal waters in the studyarea. The carbonate generation in the co-seismic fissures is interpreted to be the product of rapid precipitation from deeply infiltrated andCO2-enriched surface water during seismic strain cycles. Results show that U-series dating of fracture-filling travertine deposits fromseismically active areas provide important temporal information relevant to establishing recurrence intervals of late Quaternary andprehistoric major earthquake events. Precise dating of prehistoric earthquakes may be of great value for seismic hazard studies andearthquake forecasting research, for which accurate estimates of recurrence intervals are critical.© 2007 Elsevier B.V. All rights reserved.

Keywords: earthquake; hydrothermal; travertine; Turkey; U-series dating

1. Introduction

The application of the 238U–234U–230Th disequilib-rium provides great opportunities for dating carbonatecrystallisation ages of less than 500,000 yr before

⁎ Corresponding author. Tel.: +61 7 33652166; fax: +61 7 33651277.E-mail address: t.uysal@earth.uq.edu.au (I.T. Uysal).

0012-821X/$ - see front matter © 2007 Elsevier B.V. All rights reserved.doi:10.1016/j.epsl.2007.03.004

present, especially since development of the thermalionization mass spectrometric (TIMS) technique [1].While U-series disequilibria have been applied routinelyto corals, speleothems and calcite veins for paleocli-matic studies [2–4], TIMS U/Th dating technique hasnot been used previously as a routine method for datingvein formations related to paleo-seismic events. Only afew attempts have been reported in the literature dealing

451I.T. Uysal et al. / Earth and Planetary Science Letters 257 (2007) 450–462

with dating of Pleistocene faults using U-series method[5,6]. These studies have used post-tectonic flowstoneson fault planes and syn-tectonic calcite mixed withbrecciated limestones. Some other studies have utilisedthe U-series dating technique to date displaced anddamaged cave deposits to constrain the recurrence pat-terns of paleo-seismic events [7,8]. In the current study,we examine fissure filling carbonate deposits in some ofthe most seismically active areas of Turkey that mayoffer a unique opportunity to constrain late Quaternaryfissure generation related to neotectonic processes andactive faulting. Although archaeological and historicalrecords indicate that a number of destructive earth-quakes that occurred between the 1st century B.C. and1900 A.D. were related to the activity of the PamukkaleRange-front Fault [9] (Fig. 1), no significant surfacerupturing or fissure generation and related travertinedeposition occurred during ancient times in the region.The only recent travertine deposits are the activeterraced mound travertines at Pamukkale precipitatingcurrently from spring waters that issue from pointsources [10]. The aim of this paper is to show that U-series age determination of travertine deposits in co-seismic fissures is an important geochronologicaltechnique to establish timing of fissure generationrelated to pre-historic late Quaternary seismic events.Although it is evident from structural geological contextthat the fissure formation is associated with faulting (seebelow), supporting geochemical data are needed toverify that the travertine deposition in the fissures wasseismically controlled rather than related to the nearsurface hydrologic regime. Therefore, we also con-ducted additional detailed trace element and C–O–Srisotopic studies of the travertine deposits and comparedthe chemical and isotopic compositions of the travertinewith those of some speleothem deposits in the sameregion.

2. Tectonic setting

The study area is situated in the Western AnatolianExtensional Province, which is one of the most rapidlyextending regions in the world with an extension rate of30–40 mm yr−1 [11,12]. The eastern limit of the WestAnatolian Extensional Province is composed of NW–SE and E–W-trending active faults that frame the Gedizand Menderes Grabens respectively (Fig. 1A). Thejunction of these grabens forms the Neogene–Quater-nary Denizli Basin that consists of terrigenous sedi-ments and massive limestones [13]. The MenderesMassif is the basement rock assemblage of the DenizliBasin, which is composed of gneisses, mica schist and

marble. The extensional fissures occur in close proxim-ity (within 500–2000 m) and subparallel to the activePamukkale Range-front Fault (Fig. 1B). Orientationsand the long axes of fissure-ridges coincide with thelocations of either step-over zones (relay ramps) or thelateral tips of fault segments [14–16]. Both these set-tings are the locations of earthquake rupture arrest wheredifferential stresses were insufficient to cause continuedMode II cracking (e.g., faulting), and resulted rather inthe development of out-of-plane Mode I fracture splays[17,18]. Such locations constitute a common site forvein networks and enhanced fluid migration that occursduring and after rupture events and may lead to sig-nificant mineral deposits [19]. In the study area, net-works of intersecting tensional fissures facilitatedsubsurface fluid flow leading to the deposition of thefissure-ridge travertines [14]. Sibson [20] reported tran-sitory surface effusions of hydrothermal fluids follow-ing some moderate to large recent earthquakes inconsolidated rocks and pointed out the association bet-ween such hydrothermal fluid flows and vein genera-tion. Based on observations of modern earthquakeactivity, Muir-Wood and King [21] also demonstratedthat earthquakes with normal fault movements expelsubstantial quantities of water to the surface or shallowenvironments. Examples from ancient tectonic regimesalso indicate that large amounts of hydrothermal fluidslead to significant mineral deposition following ruptureevents in brittle dilation sites along fault zones [22].

3. Sampling strategy and analytical procedures

Fissure-ridge travertine samples from the DenizliBasin (Fig. 1A) were collected from vertical fissuresconsisting of banded travertine, which are flanked bybedded travertines (see [10,23]). Travertine ridges areup to 1.5 km long and they contain vertically bandedfissure travertines along their central fissures, whichrange in width from 2 cm to 5 m [13]. Central fissuresconsist of two symmetrical parts formed synchronouslyand separated by a void at the mid-point. Samples werecollected along a cross-section of travertine depositsfrom the margins to the centre of the fissures. Sampleswere also taken along the lateral length of some fissures.Some vertically banded travertine (up to ∼10 cm thick,samples HCE and HB1) occurs on the fault scarp alongthe Pamukkale Range-front Fault (Fig. 1B), indicatingthat effusion of travertine precipitating fluids occurredalso along fault planes. Samples were taken from suchtravertine deposits hosted within the basement marbleon the Pamukkale Range-front Fault. In the Pamukkalearea, the travertine deposits (P samples) are hosted by

Fig. 1. (A) Simplified tectonic map of western Turkey. Heavy and light arrows indicate generalised regional motion and N–S extension, respectively[12]. Lines indicate active faults. NAFZ: North Anatolian Fault Zone. (B) Map of the distribution of fissure travertine and active normal faults in thePamukkale area. Modified from [10,11].

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the terrestrial Pliocene limestone–marl and the base-ment marble of Triassic–Cretaceous age [10,24]. Someother fissure travertine samples (Balkayasi or By sam-ples in Table 1) were collected from an eroded fissureridge travertine in the Gediz Graben (Fig. 1A), which islocated ca. 50 km to the northwest of Pamukkale andhosted by the basement gneiss and mica schist. SampleKemer 5 represents coarse (up to 1–2 cm) calcitecrystals that recrystallised from a brecciated limestoneon a fault scarp (Burdur–Fethiye Fault Zone, Fig. 1A,see [24]) near Burdur (Fig. 1A).

Stalagmite samples were collected from caves nearBurdur city (Fig. 1A). Sample In–A is from the Insuyucave, which is located ca. 10 km to the south of Burdurby the highway to Antalya. Samples BuI–A and BuK–U are from smaller caves exposed in a quarry nearBucak village in the same area (Fig. 1A). Sample In–Lstis the limestone of Middle Triassic to Jurassic age fromallochthonous Lycian nappes [25] that outcrops inInsuyu and represents the host rock of the speleothemand the recrystallised calcite samples.

The carbonates were reacted with orthophosphoricacid at 25 °C for 1 day to extract CO2 for carbon andoxygen isotope analysis [26]. An acid fractionationfactor of 1.01025 was used for the calculation of δ18Ovalues [27]. Analyses are reported in per mil relative toV-SMOW for oxygen and V-PDB for carbon withanalytical uncertainties of better than ±0.2‰ (2σ).

Table 1C, O and Sr isotope data

Sample name Sample type δ13 C (PDB) δ18

PamukkalePI-1 Fissure travertine 5.8 −1PII-1 Fissure travertine 4.7 −1PII-3 Fissure travertine 4.8 −1PIII-1 Fissure travertine 4.9 −1PIII-2 Fissure travertine 4.7 −1PIV-1 Fissure travertine 5.7 −1PIV-2 Fissure travertine 5.6 −1HB1 Fissure travertine 4.7 −1HCE Fissure travertine 5.1 −1

BalkayasiBy-1 Fissure travertine 6.0 −By-7 Fissure travertine 7.2 −By-9 Fissure travertine 5.2 −

Burdur–BucakIn–Lst Limestone 2.0 −In–A Speleothem −9.9 −BuK–U Speleothem −10.3 −BuI–A Speleothem −4.3 −Kemer 5 Recrystallised calcite 0.1 −1

Analytical precision was based on replicate analyses ofNBS-18 oxygen and carbon isotope compositions.

For Sr isotope analysis, carbonate was dissolved usingdistilled 7 N nitric acid. Samples were then centrifugedand the leachates were dried and converted to chlorideusing sub-boiling distilled HCl. Sr was separated bycation-exchange techniques. Sr isotopic ratios weremeasured on a VG Sector-54 thermal ionization massspectrometer and normalised to 86Sr/88Sr=0.1194. Rep-licate analyses of separate loads of NBS-987 yielded amean 87Sr/86Sr=0.710250±0.000010 (2σ).

Analytical procedures for U-series dating are similarto those described in Zhao et al. [3], except a 233U–236Udouble spike was used for mass fractionation correctionfor U isotopic ratio measurements.

For trace element analysis, the carbonates weredissolved in a 2% nitric acid solution with internalstandards added. The resulting solutions were analysedon a Thermo X-series ICP-MS in high performancemode with instrument conditions as described in [28].The raw data was corrected for the low, but detectableblank, internal and external drift, and for oxides anddoubly charged species [29]. Instrument response wascalibrated against two independent digests of the USGSreference material W-2, and confirmed by analysis ofother reference materials, treated as unknowns. Correc-tions were applied for oxides using formation ratesdetermined from pure single element REE standards.

O (PDB) δ18O (SMOW) 87Sr/86 Sr ±2σ

6.3 14.15.2 15.2 0.708083 0.0000044.4 16.0 0.708130 0.0000044.5 16.02.4 18.1 0.708157 0.0000044.3 16.1 0.708088 0.0000055.0 15.4 0.708037 0.0000054.6 15.8 0.708088 0.0000041.3 19.2 0.708153 0.000004

8.7 21.9 0.710424 0.0000048.6 22.0 0.711103 0.0000047.8 22.8 0.710423 0.000004

3.7 27.0 0.707457 0.0000069.1 21.4 0.705024 0.0000076.9 23.8 0.707472 0.0000043.4 27.4 0.706419 0.0000046.0 14.4 0.707929 0.000004

Fig. 2. Oxygen and carbon isotopic composition of the fissuretravertine (Pamukkale and Balkayasi) compared to that of speleothem,limestone and recrystallised calcite.

Fig. 3. 87Sr/86Sr versus δ18O (A) and δ13C (B) values for the fissuretravertine (Pamukkale and Balkayasi), speleothem, limestone andrecrystallised calcite.

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Apart from the dual BaO+ interferences on both Euisotopes, which significantly exceeded the Eu signal inmost samples, all other oxide corrections typicallyamounted to less than 5% of the raw count-rates of theanalyses, and did not exceed 10% even for the lowestconcentration samples. The extremely high ratio of Bato Eu concentrations and imperfect oxide correctionresult in unreliable Eu concentrations for the directdissolution method, such that Eu data are not reported.

4. Results

4.1. Petrography

Detailed thin-section petrography and XRD analysisshow that the fissure travertine used for U-series datingand geochemical analyses consist of pure aragonite(sample PI) or calcite (samples PIV, By, HCE and HB1)with no apparent depositional hiatus and no secondaryrecrystallisation. Samples from location PIV show evi-dence of repeated fracturing of a previously sealed cracksystem, and thus some secondary voids developed alongfracture surfaces. Samples from location PII and PIIIcontain both aragonite and calcite. The coexistence of twocarbonate minerals is unlikely to be the result ofsecondary diagenetic alteration, as aragonite and calcitelayers alternate regularlywith no petrographic evidence ofrecrystallisation and samples containing different carbon-ate minerals have similar and coherent REE pattern (seebelow). The presence of aragonite is favoured by rapidprecipitation rate, higher pCO2, and elevatedMg/Ca [30].

4.2. Oxygen and carbon isotopes

The oxygen and carbon isotope compositions of thefissure travertines are given in Table 1. As comparison,

the δ18O and δ13C values of the speleothem samples,recrystallised calcite on a fault scarp and the host lime-stone sample are also presented in Table 1. The fissuretravertines show a wide range in δ18O values from+14.1 to +22.8‰ (SMOW) and from −16.3 to −7.8‰(PDB), which are lower than those of the speleothemsamples (Fig. 2). The travertines have positive andnearly uniform δ13C values ranging between +4.7 and+7.2‰ (PDB) that are distinctively different from thenegative and much more variable δ13C values of thespeleothem samples (Fig. 2). The speleothems displaylower δ18O and δ13C values compared to the parentlimestone, whereas the δ18O value of the recrystallisedcalcite is significantly low, but with a similar δ13C valueto the limestone.

4.3. Sr isotopes

Sr isotopic compositions of the travertines, spe-leothems, recrystallised calcite and the parent limestoneare listed in Table 1 and plotted against δ18O and δ13Cvalues in Fig. 3A and B, respectively. Travertines fromeach area have relatively uniform but distinct 87Sr/86Srvalues, with those from Pamukkale (0.70804–0.70816)being slightly higher than that of the Triassic–Jurassiclimestone or marble (0.70746 for In–Lst in Table 1 or

Table 2Rare earth element data (in ppb)

PI-1 PII-1 PII-3 PIII-2 HCE HB1 By-1 By-7 By-9 Kem-5 BuI–A BuK–U In–Lst

La 2.28 17.3 13.1 5.61 4.20 2.49 39.3 10.1 35.4 1033 37.7 86.9 1168Ce 1.25 28.0 41.3 5.99 6.16 2.58 6.19 2.35 53.0 641 30.1 12.8 254Pr 0.17 3.35 3.46 1.14 0.90 0.30 7.32 0.53 9.66 183 5.19 18.6 165Nd 1.49 13.7 18.8 4.35 3.58 1.26 33.5 4.31 48.2 801 21.8 73.1 675Sm 1.25 4.14 3.53 1.31 1.33 0.73 8.08 2.46 12.6 167 4.37 13.9 124Eu 46.7 2.24 4.15 30.4Gd 2.50 3.77 3.49 1.27 0.56 0.49 11.4 3.30 16.3 244 6.14 14.7 156Tb 0.44 0.62 0.63 0.17 0.15 0.05 2.01 0.81 2.92 40.6 1.19 2.38 23.8Dy 4.05 3.61 4.34 1.73 0.76 0.39 18.5 8.32 22.1 281 9.08 14.9 152Ho 1.64 0.82 1.07 0.46 0.20 0.07 5.78 2.81 6.26 70.5 3.23 3.80 35.8Er 6.25 2.64 2.93 2.44 0.61 0.24 20.0 11.0 21.1 206 9.80 11.4 105Tm 1.13 0.37 0.43 0.58 0.09 0.04 3.40 1.80 3.27 30.6 1.52 1.70 15.5Yb 6.33 2.53 2.71 4.73 0.54 0.22 24.6 12.3 21.6 184 9.38 10.0 96.4Lu 1.03 0.43 0.35 0.97 0.12 0.04 3.50 1.80 3.08 27.3 1.43 1.54 15.1

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0.7068–0.7078 in [31]), whereas the 87Sr/86Sr forsamples from Balkayasi is well above the modernseawater value of 0.7092. Two speleothem samples have87Sr/86Sr ratios (0.70502–0.70642) significantly lowerthan Triassic–Jurassic marine limestone values in theregion together with negative δ13C values (Table 1;Fig. 3B).

Fig. 4. Chondrite-normalised REE patterns for (A) the fissure travertine (also sand mica schist of the same area, [32]); and (B) speleothem (BuI–A, BuK–

4.4. REE composition

Chondrite-normalised REE patterns of the fissuretravertines are displayed in Table 2 and Fig. 4A. Forcomparison, the REE patterns of the ubiquitous terracetravertine deposits (the terraced-mound travertine, [10])and the Pliocene limestone hosting all travertines in

hown for comparison are data for Pliocene limestone, terrace travertineU), recrystallised calcite (Kem 5) and limestone (In–Lst).

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Pamukkale area [32] are also shown in Fig. 4A. Thefissure travertines have significantly lower REE abun-dance (2–3 orders of magnitude) when compared to theterrace travertine and the hosting limestone. Fissuresamples PII-1 and PII-3 as well as HCE and HB1(travertine on the fault scarp) from the Pamukkale areashow REE patterns that are nearly parallel to that of thePliocene limestone. Some other fissure travertinesamples, PI-1 and PIII-2 from the Pamukkale area andBy-1, By-7 and By-9 from Balkayasi, display anenrichment of heavy REE (HREE) relative to middle(MREE) and light REE (LREE). Such a fractionation ofREEs may be related to carbonate complexationprocesses in shallow groundwater source for thesecarbonates [33,34]. In contrast to the fissure travertine,the terrace travertine show rather source rock-like REEpatterns, with significant LREE enrichment relative toMREE and HREE, as reflected by high (La/Lu)CN(Fig. 4A). The REE pattern of the terrace travertine isparallel to that of the mica schist that represents thebasement rocks in the area [32].

Chondrite-normalised REE patterns of the spe-leothems, recrystallised calcite and their parent lime-stone are presented in Fig. 4B. The speleothems have

Table 3U–Th isotopic data for fissure travertine samples and one recrystallised calc

Sample U 232Th (230Th/232Th) (234U/238U) ±2σ

(ppm) (ppb)

PI-1 0.075 0.030 2234 1.4547 0.0032PI-2 0.075 0.095 715 1.4634 0.0019PI-3 0.094 0.031 2651 1.4220 0.0024PII-1 0.538 0.495 1641 1.1845 0.0032PII-2 0.381 0.055 10590 1.1862 0.0015PII-3 0.383 0.248 2466 1.1982 0.0012PIII-1 0.548 0.041 23343 1.2074 0.0027PIII-2 0.475 0.128 6584 1.1983 0.0025PIV-1 0.110 0.124 51.4 1.4024 0.0036PIV-2 0.082 0.178 1269 1.3835 0.0024PIV-3 0.110 0.045 6416 1.3907 0.0025PIV-4a 0.083 0.088 2337 1.3521 0.0063PIV-4b 0.087 0.039 5580 1.3734 0.0021PIV-5 0.065 0.104 1758 1.3919 0.0019PIV-6 0.027 0.145 484 1.3914 0.0012PIV-7 0.071 1.520 140 1.4009 0.0021PIV-8a 0.057 0.137 1149 1.4116 0.0018PIV-8b 0.065 29.613 6.29 1.4295 0.0303PIV-9 0.082 0.058 3726 1.3591 0.0014PIV-10 0.088 0.132 1931 1.3883 0.0016HB1 0.098 1.314 106 1.1609 0.0029By-7 0.112 0.491 698 1.0146 0.0021Kem-5 0.130 2.587 149 0.9891 0.0013

Ratios in parentheses are activity ratios calculated from atomic ratios.The 230Th ages and initial 234U/238U ratios include a negligible to small correratio of 3.8±1.9.

similarly low REE abundance as the fissure travertine;however, unlike the fissure travertine, they inheritedtheir REE features largely from the parent limestone,which show parallel REE pattern. The recrystallisedcalcite also inherited its REE features from the parentlimestone, with both having same REE pattern andconcentration.

4.5. U-series dating

Samples of the first location (PI in Fig. 1B, samplesPI in Table 3) are from a banded fissure-ridge travertine,which represents an extensional fissure with a thicknessof ∼20 cm (Fig. 5A). The sampled part of the fissureshows no growth discontinuities (depositional hiatuses)and thus reflects continuous precipitation. Three sam-ples dispersed along the whole width of the vein werecollected from a fracture-filling travertine in this lo-cation. Samples PI-1 and PI-3 represent the travertinessituated on the margin (at the contact with wallindicating the earliest crystallisation phase) and thecentre point (the latest crystallisation phase), respec-tively, and sample PI-2 was located in the middlebetween PI-1 and PI-3 (Fig. 5A). Samples in this

ite from Western Anatolian

(230Th/238U) ±2σ 230Th/238U age ±2σ Initial234U/238U

(ka)

0.2985 0.0018 24.67 0.17 1.48770.2992 0.0023 24.55 0.21 1.49700.2925 0.0043 24.76 0.41 1.45270.4977 0.0014 58.31 0.30 1.21770.5001 0.0016 58.56 0.27 1.21980.5261 0.0015 61.71 0.25 1.23620.5743 0.0019 72.05 0.39 1.20740.5863 0.0026 75.01 0.52 1.19830.8960 0.0028 103.8 0.7 1.53991.3835 0.0024 107.9 0.8 1.52100.8759 0.0048 101.6 0.9 1.52100.8110 0.0031 94.6 0.9 1.46040.8293 0.0033 95.3 0.6 1.48920.9208 0.0040 109.9 0.8 1.53510.8603 0.0096 98.7 1.7 1.51770.9822 0.0095 121.0 2.0 1.56480.9106 0.0071 105.3 1.3 1.55460.9340 0.0063 107.2 4.2 1.58200.8734 0.0067 105.3 1.3 1.48390.9559 0.0027 117.4 0.6 1.54180.4686 0.0040 55.4 0.6 1.18891.0129 0.0068 N5000.9758 0.0038 N500

ction for non-radiogenic component with an average crustal 232Th/238U

Fig. 5. (A): Map and section illustrating the position of fissure travertine samples in location PI with the U/Th dates (ka). (B): Map showing theposition of fissure travertine samples in location PII with U/Th dates.

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location yield dates of 24.7±0.2, 24.5±0.2 and 24.8±0.4 ka (Table 3), which are identical within analyticaluncertainties and give a mean of 24.6±0.1 ka.

Samples from another location at Karakaya Hill weretaken near the tip (PII-1 and PII-2) and ∼200 m furthertowards the central part (PII-3) relative to length of a∼1000 m long fissure (PII in Figs. 1 and 5B). SamplePII-1 represents the initiation of the fissure travertinedeposition at the wall and sample PII-2 was taken 50 cmfurther towards the centre point of the fissure with a totalwidth of 115 cm. Samples of this location give U/Thdates of 58.3±0.3 and 58.6±0.3 ka, respectively(Table 3, Fig 5B). Further southeast towards the centralpart of the fissure, sample PII-3 that was collected nearthe margin yields a date of 61.7±0.25 ka (Fig. 5B).

Two samples were collected from another fissurelocated 500 m further to the east of location PII.

Both samples were taken near the margin (the earliestcrystallisation phase) of the fissure but at differentlocations along the lateral length of the fissure. SamplesPIII-1 and PIII-2 represent the tip and a location ∼20 mfurther towards the central part of the fissure, with U/Thdates of 72±0.4 and 75±0.5 ka, respectively.

Samples from location PIV (Fig. 1B) were collectedfrom a fracture zone with a thickness of 43 cm (Fig. 6A).Detailed field (macroscopic) examination of thislocation indicates that some secondary voids or veinshave developed within the original fissure travertine(Fig. 6A). Thin section analysis shows the presenceof small veinlets, which are not recognisable at themacroscopic scale (Fig. 6B, C). Crystal fibres growperpendicular to walls, reflecting a mode I opening.Microscopic observations provide evidence of repeatedfracturing of a previously sealed crack system followed

Fig. 6. (A): Block cut from an outcrop of fissure travertine in location PIV and the U/Th dates (numbers with arrows refer to U/Th dates in ka). Theinitial travertine growth occurred from the fissure margin to the right of the upper cuts towards the midpoint to the left of the bottom cuts. However,the initial sequence of the travertine growth has been obscured by repeated fracturing and multiple vein generations. Therefore, the cut block does notrepresent continuous travertine deposition. (B): Photomicrograph showing younger veinlets consisting of carbonate fibres and blocky crystals (white)within micritic carbonate material (black) of an earlier vein generation. Sample PIV-7 (121±2 ka) represents the micritic carbonate. Scale bar=1 mm.(C): Photomicrograph illustrating different carbonate vein generations. Note sharp contacts with abrupt termination of crystal growth and the radialalignment of new carbonate fibres on walls of earlier vein generations. Sample PIV-6 (98.7±1.7 ka) represents the new carbonate generation on theright. Scale bar=0.5 mm.

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by a new increment of veining. The U/Th dates rangefrom 94.6±0.9 to 121±2 ka (Fig. 6A, Table 3). The dateof 121±2 ka may represent the minimum age ofthe initial fissure generation and vein filling, afterwhich new cracks formed repeatedly, whereas the dateof 94.6±0.9 ka may reflect the timing of the latest veingeneration. The dates in between may indicate thetiming of individual vein formation events, which isconsistent with the petrographic observations; however,denser sampling and more U/Th data would constrainthe timing of discrete events more precisely.

Sample HB1, which is a vertically banded travertinedeposits along on the scarp of the Pamukkale Range-front Fault, yield an U/Th date of 55.4±0.6 ka.

Sample from Balkayasi (By samples) and onerecrystallised calcite on the fault scarp (Kem 5) yield

ages of N500 ka, which are beyond the limit of U-seriesdating technique.

5. Discussion

5.1. Oxygen, carbon and strontium isotopes

The stable isotope composition of the fissuretravertines is distinctively different from the composi-tion of speleothem deposits and the limestone in thesame region (near Burdur, Fig. 1A), although the hostrocks of the travertine (marble in Pamukkale) and thelimestone near Burdur represent a similar origin such asTethyan Mesozoic platform carbonates [24,25]. Theisotopic compositions of the speleothems reflect theinteraction of the groundwater with the soil material

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(including vegetation cover) and shallow rock forma-tions (particularly limestones) over a prolonged periodof time, as well as paleo-temperature and rainfallvariations. On the other hand, the lower and relativelywide-ranging δ18O values for the fissure travertine areindicative of precipitation from warmer spring waters atvariable temperatures. At a reasonable temperaturerange of 40–80 °C and using the equation from O'Neilet al. [35], the calculated δ18O values (δ18O=−0.2‰ to−11.4‰) of the thermal waters in Pamukkale areawould be similar to the oxygen isotope composition ofthe current meteoric water (−0.4‰ to −9.3‰ [36]), ifequilibrium was achieved with the travertines. Only thesamples from Balkayasi with higher δ18O values mayindicate the involvement of relatively evolved thermalwaters in the precipitation of the fissure travertines atthis location. The isotope systematics require moreintensive water–rock interaction with a larger contribu-tion from the metamorphic basement rocks to theoxygen isotope composition of the fissure carbonates inthis area, which is also consistent with slightly higherREE concentration of the Balkayasi samples comparedto those from the Pamukkale area (Fig. 4A). The Srisotopic composition with high 87Sr/86Sr ratios around0.710 for the Balkayasi fissure travertine indicatesinteraction of warm spring waters with the metamorphicbasement rocks (gneiss and phyllite) characterised byhigh Rb/Sr ratios [37]. In Pamukkale area, on the otherhand, nearly uniform and lower 87Sr/86Sr values ofabout 0.7080–0.7082 for the fissure travertine imply theinteraction of the local meteoric water with dominantlythe Triassic–Jurassic marble from the basement andsome Pliocene terrestrial limestone. The fact that HB1and HCE, which are hosted right within this Pamukkalemarble yield 87Sr/86Sr ratios nearly identical to the restof the ridge travertines also suggests that the marble isthe dominant source for Sr. In contrast, lower and morevariable 87Sr/86Sr values (0.7050–0.7064) in thespeleothems near Burdur are likely to be due to theeffect of the groundwater percolating through theorganic-rich soil material that contains less-radiogenicmafic components, mainly ophiolites, derived from theLycian nappes [25].

Based on the He and C isotope compositions,previous studies have suggested that the high pressureCO2 in the spring waters in seismically active regions ofTurkey, including the Pamukkale area, is related mainlyto a mantle source [38,39]. In the Pamukkale arealacking any volcanic activity, deep-seated extensionalstructures may have facilitated significant mantledegassing [38]. Alternatively, the CO2 in the springwaters may also have been derived from interaction with

Pamukkale marble and/or Pliocene terrestrial lime-stones. However, this scenario involving carbonates asa major CO2 source cannot account for samples fromBalkayasi (By samples) that are hosted by the basementgneiss and mica schist with a lack of occurrence of anycarbonate rocks or speleothem formation. This couldalso account for the significantly higher 87Sr/86Sr values(0.7104–0.7111) travertine samples from Balkayasi.

The fissure travertines are substantially enriched in13C and such remarkably positive (Fig. 2) δ13C valuesreflect most likely non-equilibrium isotope fractionationduring rapid CO2 degassing with preferential loss of

12Cfrom fluids during the precipitation of the fissuretravertine [40,41]. In contrast, δ13C values in spe-leothems are related to groundwater interaction with soilcover as well as isotope fractionation between theseepage water and carbonate deposition, and they areoften of negative and more variable values.

5.2. REE composition

Similar to the stable isotope results, REE features ofthe fissure travertines also suggest that the physico-chemical conditions during their precipitation wasdifferent from those of the speolethem deposition inthe same region. Furthermore, REE data provideevidence that the chemistry and trace element concen-trations of the water from which the fissure travertineprecipitated were different from those of the currentspring waters and the terraced-mound travertine in thePamukkale area. Based on a comprehensive hydro-chemical study, Möller et al. [32] showed that hotgeothermal waters as well as the currently precipitatingterrace travertine show REE patterns that were con-trolled by the basement Paleozoic mica schists, whilethe shallow spring waters have a limestone-like REEfeature. By contrast, the fissure travertines from thepresent study have remarkably low REE concentrationswith some pronounced HREE enrichment, which are notconsistent with the REE patterns of the source rocks.This suggests that the fissure travertine did notprecipitate from geothermal waters with a long resi-dence time in the source rocks and higher temperatures.The REE data rather indicate that the fissure travertinedeposited from a less mature and younger water in aclose proximity to the recharge area, i.e. at a base of themountain massif consisting of marble to the northeast ofthe Denizli Basin along which the Pamukkale Range-front Fault was developed (Fig. 1B).

The mechanism responsible for mobilisation of thesurface water and deposition of the travertine in co-seismicfissures and along the fault scarp can be explained by

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sudden dilation due to faulting (c.f. [21]). Such a process isnot only responsible for the creation of porosity-perme-ability but also generates a significant fluid pressuregradient that leads to fluid flow into the fissures and alongthe fault plane [42,43]. Substantial hydrological changes ofgroundwater level may occur following major earthquakes[21,44]. Fluctuations of groundwater potential may resultin infiltration of water into deep fault zone and outpouringalong surface rupture zone [42]. The meteoric water thathad been recharged from the high elevation area to thenortheast of Pamukkale Range-front and stored in karsticmarble and/or unconsolidated Neogene–Quaternary sedi-ments of the Denizli Basin may represent the source of thefluids from which the fissure travertine precipitated.Significant seismic strain cycles could have drawn downthe groundwater along the rupture zones by rapidgroundwater potential change [42] and facilitated thedeeply infiltrating surface water to be enriched in CO2 thatmigrated from depth. The fast ascent of deeply infiltratedgroundwater back to the surface along the fissures and faultplane would have resulted in a strong decrease in partialCO2 pressure and consequently rapid precipitation of thetravertine. Because of the transient nature of the water–rock interaction during this process, only a small amount ofREE could have been leached from the source rocks, whichis in contrast to the steady state conditions where the sourcerocks control the REE patterns of the geothermal waters[32].

5.3. Significance of U/Th dates

In the light of the above discussion, we propose thatthe fracturing and deposition of the fissure travertineswere initiated by seismic events related to active faultingin the Denizli Basin. Those fissures that contain nocarbonate deposits have been filled by debris because ofthe surface exposure of the fissures [13]. In somefissures, debris have been cemented by the carbonate,which commenced to precipitate relatively late after thefissure formation. The fissure travertine investigated inthe present study, by contrast, are completely free of anydetrital materials, as evidenced by petrographic and traceelement analyses. Non-radiogenic Th component in theU/Th dated samples is significantly low as reflected byvery low 232Th and very high 230Th/232Th activity ratios≫100 (see Table 3. Note that at 230Th/232ThN100, thecorrection for non-radiogenic 230Th contribution isminimal, b1%) ensuring the purity and suitability ofthese carbonates for precise U-series dating. This clearlyshows that the time between the fissure generation andthe commencement of the travertine crystallisation wasinsignificant, leaving virtually little chance for debris to

fall into the rupture zone. Thus, precise U/Th dating ofcarbonate-filled fissures provide important constraintson the late Quaternary fissure generation related to theneotectonic processes and active faulting.

Our U/Th dating results give significant informationon the time span during sealing of the extensional veins,as recorded by samples collected along the width of afissure generation. For example, 3 samples fromlocation PI (PI-1, PI-2 and PI-3, dated to 24.7±0.2,24.6±0.2 and 24.8±0.4 ka, respectively) representingthe margin (the earliest crystallisation phase), centrepoint (the latest crystallisation phase) and the middleportion between the margin and centre point (Fig. 5A)and two samples from location PII (PII-1 and PII-2,dated to 58.3±0.3 and 58.5±0.3 ka, respectively) takenat the margin and near the centre point of the fissure(Fig. 5B) yield statistically identical ages indicatingrapid vein growth within a few hundred yearsmaximum, confirming above field evidence for rapidvein formation. Much shorter time span of the carbonategrowth can be practically constrained for even youngersamples, given such low analytical uncertainties of ourU/Th dates. In addition, our results also confirm theprevious field observations and alpha-counting U-seriesdata that indicate growth of the fissures was a result ofseveral rupture events [23,45]. For example, U/Th datesof samples representing the planform midpoint of thefissures (sample PII-3 in Fig. 5B and sample PIII-2)constrain the timing of older events (i.e., initiation of thefissures), while those taken from the lateral tips (samplesPII-1, 2 in Fig. 5B and sample PIII-1) reflect the timingof propagation and dilation of the fissures.

This pilot study is the first attempt to precisely datetravertine deposits in co-seismic fissures using TIMStechnique, which shows promise to become a routinemethod for further studies of late Quaternary and pre-historic major earthquake events elsewhere in the world.The results of this study indicate that each fracturesystem was formed by discrete seismic events and thatthe geochemical system in each vein has remained closedsince its formation.

Paleo-seismic studies provide critical data to allowdetermination of recurrence intervals, augmentinghistorical and instrumental records. This new techniquemay offer the possibility of determining the recurrencestatistics of the largest fissure-forming earthquakes overintervals two or three orders of magnitude larger thanpreviously feasible. Although the uncertainties in theapproach yields relatively poorly constrained estimatesfor the timing of more ancient earthquakes, combinedwith records with more recent earthquakes recurrencestatistics may be estimated to higher accuracy.

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Recent advancements in earthquake simulationresearch provide the capacity to simulate long-termseismicity within topologically realistic fault models[46]. Historical and paleo-seismic records are vitallyimportant to verify the accuracy of these models and toconstrain the models for the purposes of simulation-based forecasting of future activity in a region. Turkey isa prime candidate for validating seismicity models, dueto the wealth of historical and instrumental dataavailable. A critical issue for simulation-based forecast-ing is whether simulations accurately reproduce theseismicity patterns of the region of interest. With theadditional data provided by U-series dating, this issuemay be addressed quantitatively. Modern seismicitydata may be used to constrain the parameters ofseismicity models and ancient data used to measurethe uncertainty in simulation-based forecasts. Improvedknowledge of the paleo-seismic history of faults usingthe U-series dating technique thus provides valuableadditional data with which to constrain and improvesimulations of earthquake fault system dynamics.

6. Conclusions

We conducted U-series dating of fissure-filled traver-tine to constrain fissure generation related to seismicevolution in prehistoric times. O–Sr isotope compositionsof the fissure travertines indicate that the fluids involvedin the precipitation of these carbonates originated from thelocal meteoric water, which interacted mainly with theshallow local rock formations. The stable isotope resultstogether with REE data suggest, however, that theprecipitation of the fissure travertines was not controlledby climate-related hydrologic regimes, which are respon-sible for the speolethem deposition in the same region.REE composition and concentration of the fissuretravertine is different from those of deeply circulated hotgeothermal waters interacting with metamorphic base-ment rocks under steady state conditions. The carbonategeneration in the co-seismic fissures can rather beexplained by rapid precipitation from surface water thatwas enriched in CO2 of deep origin and mobilised duringseismic strain cycles. Results show that U-series dating offissure-filling travertine deposits from seismically activeareas provide important temporal information relevant toestablishing recurrence intervals of late Quaternary andprehistoric major earthquake events.

Acknowledgements

The Australian Research Council (ARC), Universityof Queensland Early Career Researcher Grant (122 4119

56) and Deputy Vice-Chancellor for Research of theUniversity of Queensland provided financial support toUysal. Analytical costs and an ARC Research Associateposition to Feng were covered by ARC linkage projectsupport (LP0453664) to Zhao. The help of Mete Hançerin the fieldwork and sampling is gratefully acknowledged.We also appreciate the support from the OsmangaziUniversity, Turkey, for the equipment used for thesampling. The authors are grateful to Ken Ludwig andValérie Plagnes for their critical and constructive com-ments on an earlier version of this paper as well as to ananonymous journal reviewer for a very helpful review.

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