40ar/39ar isotopic dating of etna volcanic succession

ABSTRACT

Since the 1970’s, about 50 radio-isotopic ages have been deter-mined on Etna volcanics using different techniques: Th-U and K/Ar.Unfortunately, these ages cannot be readily used to constrain thenew stratigraphic setting of the volcano, because of the uncertaintyin sample locations or, sometimes, the large errors affecting the cal-culated ages. For this reason a program of radio-isotopic datingapplying the 40Ar/39Ar incremental heating technique to date thegroundmass of basaltic samples has been carried out from 2002.Forty samples (22 of which are of new publication) were collectedfrom key outcrops on Etna volcano, selected on the basis of theirstratigraphic position, while one sample was collected from theHyblean plateau volcanics. We have obtained reliable results fromall volcanics analysed from 542 ka up to 10 ka with the MSWD’s(Mean Square of Weighted Deviates) ranging from 0.03 up to 1.7excluding IS sample (MSWD = 6.28). These new results allow us to:i) assign an age to 19 of the 25 lithostratigraphic units defined in thenew geological map of Etna volcano; ii) clarify the uncertain strati-graphic position of isolated volcanic units; iii) constraint the tempo-ral hiatus that matches the main unconformities; iv) outline thelapse of time between the end of the Hyblean volcanism and thebeginning of eruptive activity in the Etna region.

KEY WORDS: Etna volcano, 40Ar/39Ar geochronology, vol-canic succession.

INTRODUCTION

The eruptive activity of Etna volcano has beenobserved since pre-historic times and was documented inhistorical sources from about the VIIth century BC (TAN-GUY, 1981, BRANCA & DEL CARLO, 2004). The first trulyscientific volcanological observations date back to the endof 17th century while searching explanations to the cata-strophic 1669 lava-flow eruption. During the 19th century,the geologists Charles Lyell, Sartorius von Waltershausenand Carlo Gemellaro tried to apply the stratigraphic prin-ciples as proposed a century before by James Hutton tothe Etna volcanic succession for reconstructing its geo-logical history. Unfortunately, the classic biostratigraphywas not available on a volcano and consequently the first

studies had no temporal constraints and only the geomet-rical relationship between the volcanic bodies was usedby Waltershausen for his geological map that was pub-lished between 1844 and 1857 (see BRANCA et alii, 2011aand b). Absolute age determination technique for volcanicrocks became available only in the 1950’s when massspectrometers began to be used in radio-isotopic dating.This technique is based on a comparison between theobserved abundance of a naturally occurring radioactiveisotope and its decay products, by using known decayrates. Radioactive decay immediately provided geologistswith key information for the chronostratigraphic recon-struction of the volcanic successions. In fact, about 50radio-isotopic ages have been determined on Etna vol-canics using different techniques since the 1970’s with theaim of constructing a time frame for the geological evolu-tion of the volcano. The first isotopic age determinationswere performed by CONDOMINES & TANGUY (1976) andby CONDOMINES et alii (1982) using 230Th-238U disequilib-rium techniques. ROMANO (1982) discussed these first agedeterminations on Etna volcanics, highlighting the dis-crepancies with the stratigraphy of the geological map ofMount Etna published in 1979 (ROMANO et alii, 1979).ROMANO (1982) argued that the main limitation for thegeological reconstruction of Etna volcano was the impos-sibility of achieving stratigraphic correlations usingradioisotopic data, except for 14C dating which has arange limited to less than ~50 ka. Only ten years later, thefour-phase geological evolution of Etna, as proposed byROMANO (1982), was constrained with radio-isotopic agesmeasured using the K/Ar technique by GILLOT et alii(1994). These authors dated 16 samples taken from differ-ent “structural sectors” (GILLOT et alii, 1994) of Etna,obtaining ages with typical accuracies ranging between103 and 104 years. GILLOT et alii (1994) used 5 samples toconstrain the oldest phase, Basal Subalkaline Lavas, fromabout 580 to 250 ka; 5 samples for the Ancient AlkalineCenters phase, from about 168 to 100 ka; 3 samples forthe Trifoglietto phase, from about 80 to 63 ka, and finally3 samples for the Ancient Mongibello, from about 34 to15 ka. Although these ages furnished the first accuratetime frame for Etna history, 16 age determinations arenot sufficient to fully clarify and constrain ROMANO’s(1982) stratigraphic reconstruction given the complexityof Etna volcanic succession. For example, the strati-graphic base of Mongibello Antico crops out along thenorthern wall of the Valle del Bove, but it was dated froman isolated lava flow located by the side of the Simetoriver at Barcavecchia locality. In the same year TRIC et alii

(*) Istituto Nazionale di Geofisica e Vulcanologia, Osser -vatorio Etneo, sezione Catania, Piazza Roma, 2 - 95123 Catania(Italy). Corresponding authors: phone: +390957165822; e_mail:[email protected]

(**) C.N.R - Istituto per la Dinamica dei Processi Ambientali-sezione di Milano, Via Mangiagalli, 34 - 20133 Milano (Italy).

(***) Faculty of Earth and Life Sciences, VU University, Am -sterdam (The Netherlands).

40Ar/39Ar isotopic dating of Etna volcanic succession

EMANUELA DE BENI (*), STEFANO BRANCA (*), MAURO COLTELLI (*), GIANLUCA GROPPELLI (**) & JAN R. WIJBRANS (***)

36-R2 – DE BENI

Ital.J.Geosci. (Boll.Soc.Geol.It.), Vol. 130, No. 3 (2011), pp. 292-305, 9 figs., 2 tabs. (DOI: 10.3301/IJG.2011.14)© Società Geologica Italiana, Roma 2011

Queste bozze, cor rette deb bo no es serere sti tuite im med i at a mente alla Se g re te riadel la Società Geo log i ca Ital i a nac/o Di par ti men to di Scienze del la Ter raPi az zale Aldo Moro, 5 – 00185 ROMA

36-DE BENI 292-305_GEOLOGIA 28/11/11 12.45 Pagina 292

(1994) published 17 additional K/Ar ages for Etna vol-canics. However, the value of this second data set forstratigraphic reconstructions was limited because theauthors did not present any adequate stratigraphic docu-mentation for the analysed samples. COLTELLI et alii(2000) reconstructed the Etna tephrostratigraphy of thepast 100 ka dating several pyroclastic marker bedsyounger than 50 ka with the 14C techniques. Moreover,BLARD et alii (2005) dated 6 samples with the K/Ar tech-nique with the aim of recording “fossil” cosmogenic pro-duction rates.

Even if all these earlier geochronological data repre-sented a good starting point for understanding the geolog-ical evolution of the volcano, several problems arose whenit was necessary to assign the time intervals to the phasesof the stratigraphic reconstruction proposed by BRANCA etalii (2004). In particular, samples of the same strati-graphic units yielded different ages, whether measured byTh-U or K/Ar methods. Furthermore, these age determina-tions sometimes presented large margins of uncertaintyup to 50% of the calculated age. Finally, many sampleslack of any precise geographical positions making impos-sible to use these ages to constrain the new stratigraphy.For this reason, during the drawing up of the new geologi-cal map of Etna volcano (BRANCA et alii, 2011a), we orga-nized a program of radio-isotopic dating. Our goal was tochronologically constrain the new stratigraphic setting ofthe volcano based on samples carefully located fromclearly defined lithostratigraphic and Unconformity-Bounded Units (BRANCA et alii, 2011a and b).

In the present paper, we briefly describe the method-ological approach applied to date Etna volcanics with theincremental heating 40Ar/39Ar technique and present theresults of 22 new age determinations that complete thechronostratigraphic framework of Etna volcanic succes-sion. In total, during our radio-isotopic dating program,we analysed 41 samples (22 of new publication) with theaim of: i) assigning an age to most of the lithostrati-graphic units defined in the new geological map of Etnavolcano (BRANCA et alii, 2011a); ii) clarifying the uncer-tain stratigraphic position of isolated volcanic bodieswith no or doubtful stratigraphic relationship; iii) defin-ing the temporal hiatus that matches the main unconfor-mities recognised in the Etna volcanic succession and iv) outlining the lapse of time between the end of theHyblean volcanism and the beginning of the eruptiveactivity in the Etna region.

METHODOLOGICAL APPROACH AND 40Ar/39Ar TECHNIQUE

The 40Ar/39Ar dating technique was applied to Etnabasalts for the first time by DALRYMPLE (1969) with theaim of constraining the effects of excess 40Ar in historicallava flows. Afterwards, FERRARI et alii (1989) tried to datesome volcanics outcropping at Mt Calanna, albeit unsuc-cessfully due to the presence of excess or inherited argonin the phenocrysts used for the experiments. In a first testthe incremental heating 40Ar/39Ar technique was appliedto the groundmass fraction of 10 Etna samples (DE BENI,2004; DE BENI et alii, 2005). The choice of this techniqueis a consequence of the fact that it generally producesmore precise and reliable ages when compared to theK/Ar and Th-U methods (WIJBRANS et alii, 1995). The40Ar/39Ar technique can be successfully applied to young

K-poor basalts, as was well shown by GUTMANN et alii(2000) and TURRIN et alii (2008) for the Pinacate vol-canics, SINGER (2008) and HORA (2009) also applied theincremental heating 40Ar/39Ar on very young basalts, inChile, obtaining noteworthy results. DE BENI et alii (2005)measured 5 samples from well-defined stratigraphic posi-tions to test the performance of incremental heating tech-nique on Etna’s volcanics. It was also possible to verifythe reliability of these results (DE BENI et alii, 2005) bycomparing them with the K/Ar dating performed byGILLOT et alii (1994). A sample (VP, DE BENI et alii, 2005)with an unequivocal geographic position (top of the VillaPapale section), was dated with both methods obtainingcomparable ages: 134 ka with Ar/Ar as well as 132 and138 ka with K/Ar (GILLOT et alii, 1994). After this test onEtna volcanics 9 more samples have been dated (BRANCAet alii, 2008 and 2009).

Our strategy for this dating program was to acquiresamples from well-studied geological sections, in closecollaboration between volcanologists and geochronolo-gists, using stratigraphical data to check the 40Ar/39Ar dating results (DE BENI et alii, 2005, DE BENI & GROP-PELLI, 2010).

Once each sample have been selected, we performedpetrographic observations of thin sections to verify theapplicability of the 40Ar/39Ar dating technique: samplesmust have a visibly defined groundmass with respect tophenocrysts. For a reliable radio-isotopic analysis, it isnecessary that the sample has a sufficient amount of K-derived 40Ar to be precisely measured by the mass spec-trometer. We analyzed the groundmass by a SEM-EDS toverify that its K2O content falls in the range 2-6% whichwas considered sufficient to perform a reliable analysis(DE BENI et alii, 2005). The samples were prepared forradioisotopic analyses by separating a groundmass frac-tion sized between 250 and 500 µm. After initial crushingof the rock, any particle containing phenocrysts (plagio-clase, olivine or clinopyroxene) was removed by liquiddensity separation. Finally, each sample was handpickedby using a microscope to remove those grains still includ-ing microphenocrysts, in order to obtain homogeneousgroundmass separates. Then 300-500 mg of each samplewas wrapped in aluminium foil and loaded into a quartztube together with standards for irradiation (duration: 1 hr) with fast neutrons in the Cd-lined RODEO facility ofthe EU/Petten HFR reactor (The Netherlands).

Three different heating techniques were used toextract argon from the prepared fractions: a defocusedcontinuous wave (CW) argon-ion laser beam for the firstset of samples; a furnace system installed in 2006(SCHNEIDER et alii, 2009) was used for the second set; andthe last set was measured in 2008 using a 50W CW CO2

laser as heating device. For the laser-heating, the samplewas spread out evenly in 15 mm diameter sample-holderpans on a copper tray that was moved following an x-yraster pattern that ensured even heating of the wholesample. The purified gas fractions, extracted using laser-heating, were analyzed with a MAP 215-50 mass spec-trometer (WIJBRANS et alii, 1995) to determine the inten-sities of 40Ar, 39Ar, 37Ar and 36Ar. The furnace extractionsystem fits into a cold trap that is used to catch anyvolatile components coming off the sample during stepheating. The gas purification section of the furnace line issimilar to that of the laser line in which a two-stage clean-ing strategy using Al-Zr alloy and Fe-V-Zr alloy as getter-

40AR/39AR ISOTOPIC DATING OF ETNA VOLCANIC SUCCESSION 293


ing materials is followed. Then the argon gas is admittedinto the mass spectrometer for isotopic analysis, a HidenHAL IV RC PIC-RGA quadrupole instrument (for moredetails see SCHNEIDER et alii, 2009). In the incrementalheating technique, the raw peak intensity data is regressedusing dedicated data reduction software (KOPPERS, 2002and http://earthref.org/tools/ararcalc/index.html) that pro-vides an easy-to-use graphical interface for calculatingplateau ages, total fusion ages and isochrones, followingthe regression of 40Ar/39Ar mass spectrometry data onintensity versus time diagrams.

SAMPLE DISTRIBUTION WITHIN ETNEAN VOLCANIC SUCCESSION

Table 1 summarizes the geographic and stratigraphicpositions, as well as the weighted plateau age and corre-sponding error (2σ) of the 41 samples. Table 2 reports thenew 22 results, contains the parameters used during theanalyses (i.e. total steps of incremental heating, numberof steps used during the calculation, %39Ar K-derivedused during the calculation and the standard) and addi-tional results (i.e. inverse isochron age and non radio -

294 E. DE BENI ET ALII

Fig. 1 -Mt. Etna shaded relief, stars indicate the samples location. Dashed black line indicates the area represented in fig. 2, dashed and solidwhite lines indicate the location of samples shown in figs. 3 and 4, respectively. The inset shows the location of Etna within Italy.



TABLE 1

Data table summarizing: the sample type, the location name, the geographic coordinates in UTM/WGS 84, the elevation in m a.s.l., the weighted plateau age in ka, the error in 2σ, MSWD, the stratigraphical position of the samplefrom BRANCA et alii (2011a) and the reference for the already published results. CV and CV2 are two age determina-tions of the same sample. Symbols located near the samples name indicate the heating techniques used to extract argon from the prepared fractions: °) defocused CW argon-ion laser beam, *) furnace system and ^) 50W CW CO2 laser.

The ArArCalc (KOPPERS, 2002) data tables of the samples are available as electronic supplementary material.

Supersynthem Synthem Lithosomatic UnitLithostratigraphic Unit

(Formation)

ED Lava flow Piedimonte 516734 4183968 220 10,4 2,6 1,13 Il Piano Mongibello Volcano Pietracannone This work

MC Lava flow Mt. Barca 4836714180231 595 28,7 12,6 0,27 Concazze Ellittico Volcano Piano Provenzana Branca et al.,

2009

ZT Lava flow VdB northern wall

(Serracozzo)504510 4178426 2005 29,1 10,6 0,58 Concazze Ellittico Volcano Pizzi Deneri This work

RZ Lava flow Randazzo 497730 4193894 655 30,8 21,2 0,08 Concazze Ellittico Volcano Piano Provenzana This work

LL Lava flow VdB northern wall

(Rocca della Valle)502214 4179327 2650 32,5 17,8 0,46 Concazze Ellittico Volcano Pizzi Deneri This work

DM Lava flowTimpa di Don Masi

top515258 4160691 80 32,9 10,6 0,28 Concazze Ellittico Volcano Piano Provenzana This work

BT Lava flow Bronte 482214 4179723 480 40,9 14,4 0,03 Concazze Ellittico Volcano Piano Provenzana Branca et al.,

2009

CS Lava flow Val Calanna top

(C.da Cassone)506435 4173683 1335 41,3 6,2 0,60 Concazze Ellittico Volcano Serra delle Concazze

Branca et al.,

2008

LN Lava flow Mt. La Nave 492456 4186445 1150 42,1 10,4 0,23 Concazze Ellittico Volcano Piano Provenzana This work

LB Lava flow VdB northern wall

(Rocca della Valle)502268 4179055 2520 56,6 15,4 0,47 Concazze Ellittico Volcano Serra delle Concazze This work

P1 Dyke VdB western wall 501995 4174171 2055 65,3 4,4 0,74 Zappini Cuvigghiuni Volcano Canalone della Montagnola De Beni. 2004

P2 Dyke VdB western wall 502044 4174251 2020 69,7 4,6 0,46 Zappini Cuvigghiuni Volcano Canalone della Montagnola De Beni. 2004

SH Lava flow VdB western wall 501071 4174799 2335 70,2 3,0 0,32 Zappini Cuvigghiuni Volcano Canalone della Montagnola This work

CV Lava flow VdB western wall 501947 4174028 2135 79,0 6,0 1,51 Zappini Cuvigghiuni Volcano Canalone della Montagnola De Beni. 2004

CV2 Lava flow VdB western wall 501947 4174028 2135 79,6 4,2 1,68 Zappini Cuvigghiuni Volcano Canalone della Montagnola This work

SVB199 NeckSerra Giannicola

Grande502342 4175685 2190 85,3 7,0 0,85 Zappini Giannicola Volcano Serra Giannicola Grande De Beni. 2004

SA 2 Lava flow VdB western wall 501952 4174083 2125 85,6 6,8 1,56 Zappini Salifizio Volcano Serra del Salifizio This work

FC Lava flow Val Calanna 506713 4173919 1100 93,0 6,0 0,38 Zappini Mt. Cerasa Volcano Mt. Fior di Cosimo Branca et al.,

2008

CGPumice

deposit VdB northern wall 506039 4177581 1368 99,1 10,6 0,59 Croce Menza Trifoglietto Volcano Cava Grande lithohorizon

De Beni et al.,

2005

CE Lava flow VdB northern wall

(Mt. Cerasa)506295 4177588 1380 99,9 8,6 0,20 Zappini Mt. Cerasa Volcano Mt. Scorsone This work

ER Lava flow VdB northern wall

(Mt. Cerasa)506202 4177796 1535 100,4 11,6 0,15 Zappini Mt. Cerasa Volcano Mt. Scorsone This work

ZB Lava flow VdB northern wall

(Serracozzo)504621 4177777 1730 101,8 14,6 0,20 Zappini Mt. Cerasa Volcano Mt. Scorsone This work

RC Lava flow VdB northern wall 505997 4177479 1397 101,9 7,6 0,30 Croce Menza Rocche Volcano Rocche De Beni et al.,

2005

TD Lava flow Tarderia 503950 4169253 1155 105,8 9,0 0,32 Croce Menza Tarderia Volcano Contrada Passo Cannelli Branca et al.,

2008

TR Lava flow VdB western wall 502181 4174615 1835 107,2 11,4 0,74 Croce Menza Trifoglietto Volcano Piano del Trifoglietto This work

NA Lava flow Acicatena Timpa 511920 4161735 250 111,9 9,2 0,50 Sant'Alfio Valverde This work

VS Lava flow Mt. D'Oro 510917 4158070 360 121,2 15,0 0,34 Sant'Alfio Valverde Branca et al.,

2008a

MT Lava flow Moscarello Timpa 511860 4176649 510 126,4 4,8 0,36 Sant'Alfio Moscarello De Beni et al.,

2005

CA Lava flow Val Calanna base 506614 4173960 1110 128,7 7,6 0,88 Sant'Alfio Calanna Branca et al.,

2008a

MB Lava flow Moscarello Timpa 512991 4174369 255 129,9 4,8 0,87 Acireale Timpa De Beni et al.,

2005

IN Lava flow Santa Caterina 515193 4161956 65 132,6 4,8 0,38 Acireale Timpa This work

VP Lava flow North of Catania 507793 4155037 207 134,2 6,6 0,83 Acireale Timpa De Beni et al.,

2005

TC Lava flow Olivo San Mauro 513351 4157774 195 145,8 14,0 0,20 Acireale Timpa Branca et al.,

2008a

PI Lava flow Ripa di Piscio 508863 4181057 1230 147,7 18,0 0,50 Acireale Timpa This work

AG Lava flow Acque Grandi 515314 4160791 5 154,9 17,0 0,49 Acireale Timpa This work

RN Lava flow Ripa della Naca 510155 4181172 920 180,2 19,2 0,37 Acireale Timpa di Don Masi This work

NK Neck Motta S. Anastasia 497494 4151650 290 320,0 48,4 0,87 Adrano S. Maria di Licodia This work

AD Lava flow Adrano 485412 4167395 510 332,4 43,4 0,25 Adrano S. Maria di Licodia This work

ACI Pillow lavaAcicastello Castel

cliff NE side513243 4156396 2 496,1 86,8 0,20 Aci Trezza Aci Castello

Branca et al.,

2008a

OW Pillow lava Acicastello 513120 4156972 30 542,2 85,8 0,83 Aci Trezza Aci Castello This work

IS Lava flowSpasa

(Catania plain)481836 4137499 10 1585,6 110,6 6,28 De Beni. 2004

SAMPLE TYPE LOCATIONCOORDINATE

UTM-WGS84 (m)

Hyblean Plateau volcanic succession

Ba

sa

l T

ho

leii

tic

Tim

pe

Va

lle

de

l B

ov

e

Reference

STRATIGRAPHIC POSITION (following Branca et alii, 2011a)

Str

ato

vo

lca

no

ELEVATION m

a.s.l.

WEIGHTED

PLATEAU AGE KaERROR 2! MSWD


genic 40Ar/36Ar intercepts from inverse isochrons) that areuseful to verify the reliability of the obtained age. Table 2also shows a brief petrographic description and the strati-graphic position following BRANCA et alii (2011a) (seealso figs. 1, 2, 3 and 4 for samples location).

The selection of the samples was guided by the aim ofdefining a chronological framework for the stratigraphicsetting of the new geological map of Etna volcano(BRANCA et alii, 2011a,b). The plateau age and K/Ca dia-gram of the new 22 samples, grouped in Supersynthems,are reported in figs. 5, 6, 7 and 8 and the fully regresseddata of all the samples are available as ArArCalc (KOP-PERS, 2002) summary data files as data repository.

On the basis of the stratigraphic reconstruction of theEtna volcanic succession proposed by BRANCA et alii(2011a), we selected some key samples to date the differ-ent steps of the geological evolution highlighted by therecognised Supersynthem, the highest rank units of the

Unconformity Bounded Unit stratigraphy. 4 samples wereselected from the Basal Tholeiitic Supersynthem, 11 sam-ples from the Timpe Supersyntem, 15 samples from theValle del Bove Supersynthem and 10 samples from theStratovolcano Supersynthem.

Regarding the Basal Tholeiitic Supersynthem, 2 sam-ples were taken from the lower SE flank of Etna to verifythe age of the earlier submarine product belonging to theAcitrezza Synthem (OW and ACI, fig. 2) and 2 samplesfrom the Adrano Synthem, on the lower W and S flanksof the volcano (AD and NK, fig. 1).

Concerning the Timpe Supersynthem, 7 samples wereanalysed for dating the Acireale Synthem (RN, AG, PI,TC, VP, IN and MB), and 4 samples to constrain the ageof the S. Alfio Synthem (CA, MT, VS and NA); all sampleswere collected from outcrops scattered over the easternflank of the volcano between 5 and 1230 m a.s.l. (figs. 1, 2and 3).


Fig. 2 - Shaded relief of the lower SE flank of Mt. Etna on which stars indicate sample locations. Inserts in clockwise direction: a) Mt. D’Oroand Gelso sections modified from BRANCA et alii (2008); b) Don Masi section modified from BRANCA et alii (2008); c) pillow lava cropping outclose to the cemetery of Acitrezza; d) aerial view of the Norman Acicastello castle rock.


Regarding the Valle del Bove Supersynthem, 4 sam-ples used to date the Croce Menza Synthem (TR, TD, RCand CG) were collected on the steep walls of the Valle delBove, between 1155 m and 1835 m a.s.l. (figs. 1, 3 and 4).Moreover, 11 samples were carefully chosen to constrainthe Zappini Synthem (FC, SA2, SVB199, CV, CV2, SH, P1and P2; see fig. 3), 3 of which belonging to the Mt. Scor-sone Formation (ZB, ER and CE; see fig. 4) came fromthe northern wall of the valley.

For dating the Stratovolcano Supersynthem, weanalysed 9 samples belonging to the Concazze Synthem(Ellittico volcano) that came from outcrops spread overthe whole volcano, between 80 and 2650 m a.s.l. (fig. 1).The proximal samples were collected along the inner-northern wall of the Valle del Bove (LB, LL and ZT seefig. 4), whereas the distal ones came from outcrops alongthe Alcantara and Simeto River valleys (LN, BT, MC andRZ see fig. 1) and from Acireale fault scarp (DM see fig. 2),one more sample came from the Val Calanna southernrim (CS see fig. 3). The youngest analysed sample (ED seefig. 1) belongs to a lava flow of the Il Piano Synthem(Mongibello volcano) that crops out close to Piedimontetown at 220 m a.s.l.

Finally, one sample was also collected from the vol-canic succession of Hyblean plateau, to constrain thelapse of time between the end of Hyblean volcanism(SCHMINCKE et alii, 1997) and the beginning of the erup-tive activity in the Etna region. The analysed samplebelongs to a rather weathered lava body cropping out atthe Spasa locality on the southern border of the Cataniaplain, one of the northernmost volcanic outcrops ofHyblean plateau (fig. 1).

DISCUSSION

The results of Etna radio-isotopic dating yielded,almost consistently, excellent plateau ages that allowedconstraining the geological evolution of the volcano (fig. 9)chronologically from the earliest erupted products, be -longing to the Basal Tholeiitic Supersynthem, up to theStratovolcano Supersynthem. All analysed samples pro-duced statistically meaningful plateau (tabs. 1 and 2),with initial isotopic ratios on average atmospheric withinerrors, moreover the MSWD value ranges from 0.03 up to1.7, excluding IS sample (MSWD 6.28) belonging to theHybelan plateau. The scatter in the result of this sampleas is borne out by its high MSWD value is probably due toits marked weathering caused by the contact withhydrothermal fluids. However, the resulting age is con-firmed by similar results (1.62 Ma; 1.47 Ma) obtainedwith the 40Ar/39Ar technique by TRUA et alii (1997) for vol-canics of the Vallone Loddiero (Hyblean plateau).

Generally K/Ca diagrams, of the new 22 results (figs. 5to 8), show a regular pattern, excluding samples NK (fig. 5) and RZ (fig. 8) that have anomalous high K/Caratios at the fifth step of incremental heating. Weattribute this behavior to incomplete removal of Ca-richphases (i.e. plagioclase or pyroxene microphenocrysts)from the groundmass during the sample preparation.

Sample LN was analyzed with 6 out of 12 steps ofincremental heating using 90.5% of 39Ar(K derived) andobtaining a regular plateau age, having an MSWD valueof 0.23 and a non-radiogenic 40Ar/36Ar intercept frominverse isochrons of 295.1±7.0. The obtained age of

42.1±10.4 ka is in accordance, within the error, with themean age of 32±4 ka (error is 1σ) calculated by BLARD etalii (2005) for sample SI 27b. This sample is located in thesame lava flow field (Mt. La Nave of BRANCA et alii,2011a) of our sample LN. SI 27b sample of BLARD et alii(2005) was dated with K/Ar technique and the resultingage was calculated as mean age between 37±4 ka and27±3 ka.

Dating the recent volcanics (<50 ka) we obtainedremarkable results in particular for the youngest ones(ED sample of 10.4±2.6 ka), considering the difficultygenerally encountered when dating K-poor basalt owingto both the low amount of radiogenic 40Ar (TURRIN et alii,2008) and the presence of excess and or extraneous argon(SNEEL, 2002). In fact, the amount of radiogenic Ar accu-mulated in ED sample was very low: total 40Ar extracted


Fig. 3 - Shaded relief of the Valle del Bove-Val Calanna, stars indi-cate sample locations within the southern wall. Val Calanna sectionmodified from BRANCA et alii (2008) and Serra Pirciata section (3-SP) modified from BRANCA et alii (2011a).



Fig. 4 - Shaded relief of the Valle del Bove area, stars indicate sample locations within the northern wall. Inserts in clockwise direction: Rocca dellaValle (8-RV) and Serracozzo (10-SC) sections modified from BRANCA et alii (2011a), Rocca Capra section modified from DE BENI et alii (2005).

Fig. 5 - Plateau ages and K/Ca diagrams of Basal Tholeiitic Supersynthem T.F. = Total Fusion age (Ka), N.I. = Normal Isochron age (Ka), I.I. = Inverse Isochron age (Ka), MSWD = Mean Square of Weighted Deviates; error in 2σ.


by incremental heating = 0.646830 V (sensitivity of massspectrometer: 3.3 * 10-15 moles/V, for more informationsee all dating parameters reported in the data repository).However, the perfect fit between the weighted plateau ageand total fusion age (10.5 ± 3.2 ka) and between normalisochron and inverse isochron age (14.1 ± 5.2 ka and 14.2 ± 4.8 ka,, respectively) confirms the reliability of thisresult.

We have obtained 40Ar/39Ar age determinations for 19out of a total of 25 lithostratigraphic volcanic units ofBRANCA et alii (2011a) (fig. 9). Among the 6 units notdated the Torre del Filosofo formation comprises histori-cal volcanics (<2 ka), conversely Pietracannone andPortella Giumenta formations were previously dated withthe radiocarbon method by COLTELLI et alii (2000). Theages of the other units can be assigned on the basis ofclear and robust stratigraphic evidence. In fact, the SerraCuvigghiuni, Acqua della Rocca and Valle degli Zappiniformations present direct stratigraphic relationships atthe base and/or at the top with chronologically well-con-strained lithostratigraphic units. For this reason it wasnot strategic to date them since we already had con-strained their time interval of emplacement. Finally, we

have tried to measure a lava flow of Monte Calvario for-mation (Ellittico Volcano, see fig. 9) an autoclastic lavabreccia, with hydrothermal alteration. Unfortunately, theobtained age was unreliable with respect to its strati-graphic position. Its anomalous old age 110.9 ± 86.6 ka isprobably due to the contact with hydrothermal fluids thatcaused the presence of extraneous Ar in the sample, asalso confirmed by the high MSWD value (10.12). In anycase, Monte Calvario formation is fortunately well con-strained at the top by the Biancavilla-Montalto Ign-imbrite, a member of the Portella Giumenta formationdated at about 15 ka by COLTELLI et alii (2000), and at thebase by the Piano Provenzana formation. In particular,Monte Calvario lava flows rest on a lava flow of PianoProvenzana formation that covers a paleosol dated at 18.0 ± 0.4 ka by KIEFFER (1975) with the 14C. Therefore,we can assert that the age of Monte Calvario formation isbetween 15 and 18 ka. In synthesis, we can now directlyestablish the emplacement age of more than 80% of thevolcanic lithostratigraphic units defined by BRANCA et alii(2011a), and the interval of deposition for the others.

Our data confirm a discontinuous volcanic activityduring the Basal Tholeiitic Supersynthem up to the


TABLE 2

Table of the new 22 samples with detail about the parameters used during the analyses: total number of steps of incremental heating, number of steps and % of 39Ar K-derived used during the calculation and the standard used tocalculate the irradiation constant J. In the brief petrographic description the abbreviations mean: P.I. porphyritic index; Plg plagioclase; Px pyroxene; Amph amphibole; Ol olivine; Ap apatite; Ox oxides. All the samples have a

porphyritic texture except for sample PI which is microcrystalline.

P.I. % Most abundant phenocrysts dimension in mm

Groundmass mineralogy

Groundmass texture

ED 10,4 2,6 1,13 11 9 97,14 25.260±0.288 14.2±4.8 292.3±3.8 10 plg 3-6 , px 1-2 , rare ol and apt 1 px, ol,plg intersertal

ZT 29,1 10,6 0,58 18 12 72,65 25.260±0.152 22.0±13.0 306.14±10.2 10 plg 2-3 , px 1-2 , rare ol 1 plg intersertal to hyalopytic

RZ 30,8 21,2 0,08 8 6 85,53 25.260±0.152 28.9±38.2 296.9±25.4 25 plg 2 -10 , px 3 , ol 2 plg, ol intersertal

LL 32,5 17,8 0,46 9 8 96,32 25.260±0.152 24.7±20.2 296.9±3.6 40 plg1-5 , px 1-3 , ol 1-2 plg, px, ol hyalopitic

DM 32,9 10,6 0,28 9 8 98,55 25.260±0.152 27.3±15.6 202.8±15.8 5 plg 2 , ol 1-2 , apt<1 plg, ol intersertal

LN 42,1 10,4 0,23 12 6 90,52 25.260±0.288 44.0 ±33.2 295.1±7.0 20 plg 1-7 , px 1-10 , ol 1-2 plg, ol intersertal

LB 56,6 15,4 0,47 7 5 82,69 25.260±0.152 52.1±23.4 297.2±6.8 35 plg 1-3 , px 2 , ol 1 px, plg ophitic

SH 70,2 3,0 0,32 11 8 93,04 25.260±0.288 71.1±9.6 294.9±5.0 10 plg 3 , px 1-10 , rare ol <1 plg, ol, ox intersertal to inergranular

CV2 79,6 4,2 1,68 12 8 95,37 25.260±0.152 75.6±8.0 300.1±7.9 20 plg 1-10 , px 2-4 , ol 2 , ox plg, ol, ox intersertal

SA 2 85,6 6,8 1,56 12 6 85,99 25.260±0.152 82.3±22.6 297.8±15.6 15 plg 1 gererally 3 up to 7 ,px 2-4 , ol 1-2 , ox plg, px, ox intergranular to

intersertal

CE 99,9 8,6 0,20 10 9 97,23 25.260±0.152 100.7±10.4 294.9±6.4 15 plg 1 gererally 2 up to 7 ,px 5 , ol 1-2 , rare apt plg, px, ol hyalopytic

ER 100,4 11,6 0,15 17 16 97,90 25.260±0.152 98.1±16.2 297.0±7.0 30 plg 1-3 , px 1-3 , rare ol<1 and apt 2 plg, px, ol intersertal

ZB 101,8 14,6 0,20 9 6 84,96 25.260±0.152 103.4±19.2 294.4±11.6 20 plg 1-3 , ol 1-4 , px 1-3 , rare px and apt <1 plg, ol hyalopytic

TR 107,2 11,4 0,74 12 7 84,89 25.260±0.152 117.7±36.2 292.7±9.6 25 plg 1-4 , px 1-4 , ol 2 , amph and apt 2 and ox plg, px, apt intergranular

NA 111,9 9,2 0,50 12 11 99,81 25.260±0.152 110.1±13.2 296.1±3.2 30 plg 3-6, px 1-3 , ol 1-2 and rare apt 3 plg, px, ol hyalopytic

IN 132,6 4,8 0,38 11 9 91,85 28.340±0.324 134.4±11.6 294.9±3.6 20 plg 1-3 , px 2-5 , ol 1-3 and rare apt 3 and ox plg, ol, px intersertal

PI 147,7 18,0 0,50 18 17 99,10 25.260±0.152 150.6±24.4 294.7±10.2 microlites: plg, ol ox plg, ol ox intersertal

AG 154,9 17,0 0,49 11 11 100,00 25.260±0.152 152.0±22.2 296.9±5.8 30 plg 1-3 , px 5 , ol 2-4 , rare apt 2 plg, px, ol intersertal

RN 180,2 19,2 0,37 8 5 81,50 25.260±0.152 182.2±70.6 294.5±47.2 30 plg 1-5 , px 2-4 , ol 2-4 , and apt 2 plg, px, ol and ox intersertal

NK 320,0 48,4 0,87 19 11 43,96 25.260±0.152 267.7±85.0 299.4±5.8 5 ol 1-2 , plg and px <1 plg, ol and ox ophitic

AD 332,4 43,4 0,25 9 6 87,92 25.260±0.152 328.7±112.2 296.6±28.2 10 ol 2-3 , plg 2 plg, ol intersertal

OW 542,2 85,8 0,8 10 9 96,10 25.260±0.152 476.3±140.0 296.4±1.6 5 ol 2-5 ol, plg intersertal or intergranular

Valle

del

Bov

e

Supersynthem (Branca et alii,

2011a)

Bas

al T

hole

iitic

Tim

pe

Petrography%39Ar (K) used

in plateau calculation

Standard Ma

Stra

tovo

lcan

o

SAMPLE

Non radiogenic 40Ar/36Ar intercepts

from inverse isochrons

Steps of incremental

heating

Steps used in the calculation

WEIGHTED PLATEAU AGE

KaERROR 2! Inverse

isochron age kaMSWD


beginning of the Timpe Supersynthem, thereafter theactivity became almost continuous. The lack of age deter-minations younger than 10 ka is due to the analyticallimit of 40Ar/39Ar dating method for young K-poorbasaltic rocks (TURRIN et alii, 2008), such as those of Etnavolcano.

In general, the obtained results are in agreement withthe stratigraphic setting of BRANCA et alii (2011a). Thestratigraphic sections located on the inner walls of theValle del Bove, and the fault scarps of Timpa diMoscarello and Timpa di Acireale (at Don Masi section atAcque Grandi locality), confirm the reliability of ourresults thanks to the good fit between the ages and strati-graphical positions (figs. 2, 3 and 4). The Rocca Caprasection, located in the northern wall of Valle del Bove,might seem an exception (fig. 4). However, consideringthe margins of uncertainty of these ages, we can assumethat they are still in agreement with the stratigraphy sincethe measured ages of the 4 samples are condensed in atime span of about 3 ka. For this reason we can assertthat the lava flows and the pyroclastic deposits wereemplaced in a quite short time interval, indistinguishableusing Ar/Ar technique.

The geochronological data, integrated with the strati-graphic data of BRANCA et alii (2011a), allow us to definethe temporal hiatus that matches the main unconformi-ties recognised in the volcanic succession and, therefore,their geological significance for detailing the temporalevolution of the eruptive activity in the Etna region (fig. 9). The age of IS sample of 1585.6±110.6 ka (DE

BENI, 2004), from the northernmost outcrop of Hybleanvolcanics, is in accordance with the radio-isotopic datesof TRUA et alii (1997) performed at the Vallone Loddierolocality (IB50 sample: 1470±20 ka and IB259 sample:1620±30 ka), where the youngest volcanics of the Hybleanplateau crop out. These data confirm a time gap of about1 Ma between the end of the Hyblean eruptive events and the emplacement of the oldest Etnean volcanics(542.2±85.8 ka, OW sample). However, the presence ofvolcanic bodies in the subsurface of the Catania plain(LONGARETTI et alii, 1991; GRASSO & BEN AVRAHAM,1992) could conceivably reduce this time gap.

Concerning the eruptive history of Etna (fig. 9), wefound evidence of a hiatus of about 160 ka between theoldest submarine volcanics of the Acitrezza Synthem andthe earliest subaerial lava flows of Adrano Synthem. Inthis time span the sedimentary deposition on the fore-deep basin ended as a consequence of the regional uplift(DI STEFANO & BRANCA, 2002). A hiatus of 140-100 kaoccurred between the Adrano Synthem and the followingAcireale Synthem. The calculated lapse of time is betweenthe youngest dating of Adrano Synthem (320.0±48.4 ka,NK sample) and the ages of the Acireale Synthem samples (180.2±19.2 ka RN sample; 225.0±15.0 and221.0±18.0 ka n.14 samples of GILLOT et alii, 1994). Thistime span is probably shorter than the calculated onebecause both the considered samples (RN and n. 14) arenot located at the base of the Acireale Synthem since theearliest products of this synthem rest below sea level(BRANCA et alii, 2011b). Therefore, the duration of the


Fig. 6 - Plateau ages and K/Ca diagrams of Timpe Supersynthem (for abbreviations see caption of fig. 5).


hiatus separating Basal Tholeiitic and Timpe Supersyn-thems is not well constrained yet. The early Acireale Syn-them samples suggest that the volcanism, extended overthe entire lower eastern flank of Etna’s present edificefrom the town of Acireale, at south-east, up to Ripa dellaNaca, at north-east tip. Toward the end of Acireale Syn-them, the eruptive activity became continuous for thefirst time and we find only local hiatus related to theshifting of the volcanic centres. In fact, the unconformitybetween Acireale and S. Alfio Synthems, occurringbetween 130 ka and 129 ka, is related to the different ori-gins of the products due to the shift of the volcanic feedersystem toward the central portion of Etna present edifice.Eruptive activity of the S. Alfio Synthem continued up toabout 112 ka from fissure systems located on the lowerSE flank of Etna.

We dated the products of each volcano belonging toValle del Bove Supersynthem (fig. 9). The most signifi-cant discovery is the evidence that the eruptive activitiesof Trifoglietto, Tarderia and Rocche volcanoes, belonging

to Croce Menza Synthem, are almost coeval. Even thoughthe age of the beginning of their activity is unknown,since the base of these volcanoes is not exposed, weobtained an age of 107.2±11.4 ka (TR sample) for themiddle-upper part of the Trifoglietto volcanic successionand ages of 105.8±9.0 ka (TD sample) and 101.9±7.6 ka(RC sample) for the top of Tarderia and Rocche volca-noes, respectively. Furthermore, we dated at 99.1±10.6 kathe pumice fall deposits (CG sample) that covers the Roc-che volcano; it represents the oldest tephra marker bedrecognized on Etna, spread along the Ionian coast (Unit Bof COLTELLI et alii, 2000). According to DEL CARLO et alii(2004) this tephra marker bed represents the pyroclasticdeposit related to a plinian eruption occurring at the endof Trifoglietto volcanic activity (Cava Grande lithohori-zon of BRANCA et alii, 2011). Therefore, considering thatthe youngest dating of S. Alfio Synthem (NA sample) is111.9±9.2 ka and the earliest sample of the Trifogliettovolcano has an age of 107.2±11.4 ka (TR sample) we canassert that no significant temporal hiatus separates the


Fig. 7 - Plateau ages and K/Ca diagrams of Valle del Bove Supersynthem (for abbreviations see caption of fig. 5).


Timpe Supersynthem from the Valle del Bove Supersyn-them. The volcanoes forming Zappini Synthem are almostcoeval and characterised by short periods of activity.Monte Cerasa volcano was active at least between about101.8±14.6 ka (ZB sample) and 93.0±6.0 ka (FC sample),and probably somewhat longer because we have no datingfor the top of its volcanic succession. Salifizio volcano wasactive 85.6±6.8 ka, in the same period in which the intru-sion of the large neck of Giannicola volcano occurred(SVB199 85.3±7.0 ka). Eruptive activity of Cuvigghiunivolcano started 79.6±4.2 ka (CV2 sample) and continued atleast up to 65.3±4.4 ka (P1 sample); although we have notdated its final volcanic products, the age of two Cuvigghi-uni dykes (P1 and P2: 69.7±4.6 ka) supports this inference.

Finally, the ages measured for the samples collectedalong the northern wall of the Valle del Bove allowed us toconstrain the eruptive activity of the Ellittico volcano (Con-cazze Synthem). In particular, the dating of LB sample,located close to the base of Ellittico volcano, shows that itwas already active around 56.6±15.4 ka. Therefore, consid-

ering that Cuvigghiuni volcano was active until 65.3±4.4 kaand shortly afterward, we can assert that the unconformitybetween Zappini and Concazze Synthems is only geomet-ric rather than temporal. At the same time, the dating ofthe samples collected on the lower flanks of Etna edificeindicates that the Ellittico volcano reached its maximumareal expansion at about 40 ka ago. Ellittico volcano activ-ity ended about 15 ka with a series of caldera-forming plin-ian eruptions (Unit D of COLTELLI et alii, 2000), in a similarway to end of Trifoglietto volcano activity.

CONCLUDING REMARKS

The stratigraphic succession of Etna volcano con-sists of 25 volcanic lithostratigraphic units defined byBRANCA et alii (2011a). Most of the units (19 on 25) havebeen directly and successfully dated with the 40Ar/39Arincremental heating technique. Firstly, we have verifiedthe consistency of this dating method (DE BENI et alii,


Fig. 8 - Plateau ages and K/Ca diagrams of Stratovolcano Supersynthem (for abbreviations see caption of fig. 5).


2005) by measuring 5 samples from units having well-known stratigraphic positions, one of which had beenpreviously dated with the K/Ar method (GILLOT et alii,1994). The obtained results have yielded excellentplateau ages in the range from 542 ka up 10 ka, covering98% of Etna’s geological history. The goodness of ourresults is testified by MSWD values ranging from 0.03up to 1.7, excluding IS sample (MSWD 6.28) which wasmarkedly weathering. Moreover, the age obtained forthe youngest analysed sample, 10.4±2.6 ka, is a remark-able result (see for comparison TURRIN et alii, 2008)considering the small amount of radiogenic Ar accumu-lated. In conclusion, Etna age determinations representa substantial step forward in the 40Ar/39Ar dating ofyoung basalts.

On the whole, the new 22 age data, together with the 19already published, allow constraining in time most of thevolcanic lithostratigraphic units recognized in the new geo-logical map of Etna volcano (BRANCA et alii, 2011a). Conse-quently the doubtful stratigraphic position of some units,such as the Calanna formation and the isolated lava flowscropping out on Ripa della Naca fault scarp, was clarify.Concerning the dating of the Unconformity Bounded Units,on the basis of which the stratigraphic reconstruction wascarried out, we are able to define the temporal hiatus andto infer the significance of the main unconformities andactivity phases recognised in the Etna volcanic succession,as summarized in the following points.

– In the oldest part of the eruptive history, during theBasal Tholeiitic Supersynthem, a hiatus of about 160 kaoccurred between the emplacement of the oldest subma-rine eruptions (Acitrezza Synthem) and the earliest sub-aerial lava flows (Adrano Synthem).

– The unconformity between the Basal Tholeiitic andTimpe Supersynthems is related to erosional processeswhose duration of 140-100 ka is considered a maximumestimate as the oldest portion of the Timpe Supersynthembase rests below the sea level.

– During the Timpe Supersynthem (towards the endof the Acireale Syntem), the eruptive activity in the Etnaregion became, for the first time, continuous startingfrom about 134 ka ago. After this time we find only shorthiatuses, consequently the observed unconformities havemainly geometric significance.

– The volcanoes of the Valle del Bove Supersynthem,which are partially coeval, are characterised by shortperiods of activity. They were active from at least 107 kaago up to about 65 ka ago. The superposition of 7 vol-canic centres during this time span produced the growthof the earliest polygenic central-type edifice at Etna dur-ing two main evolutionary stages: the Croce Menza andZappini Synthems.

– The Stratovolcano Supersynthem represents themain volcanic edifice. It began to build up through theEllittico volcano eruptions that were dated back toabout 57 ka ago. This edifice, stratigraphically the Con-


Fig. 9 - Schematic chronological reconstructionof Etna volcanic succession according to thestratigraphic setting proposed by BRANCA et alii(2011a and b). Only the volcanic units are reported in the lithostratigraphic column.


cazze Synthem, reached its maximum areal expansionabout 40 ka ago, proceeding up to 15 ka when a set ofplinian eruptions formed a large summit caldera, histori -cally named Ellittico Crater. The activity resumed insidethe caldera and expanded outside to cover the previousEllittico edifice, forming the volcanic succession of the Il Piano Synthem that is the present active volcaniccentre.

ACKNOWLEDGMENTS

We are very grateful to L. Miraglia from the Istituto Nazio -nale di Geofisica e Vulcanologia, Osservatorio Etneo, sezione di Catania (INGV-CT) for assistance with SEM–EDS analyses andto Karlijn de Groot, Mirek Groen, Cristel de Zwaan, and Bjoern Schneider from VU University for their support with theisotopic measurements at the Argon laboratory of the Vrije Uni-versiteit. Petrographic analyses were performed at the laboratoriesof the INGV-CT. The radio-isotopic datings were supported by:INGV-CT grants, CNR-IDPA grants and University of Cataniagrants (COFIN-2002 resp. F. Lentini). Finally, we are thankful toA. Bonaccorso (former director of INGV-CT) for promoting thisresearch.

We would like to thank the reviewers for the useful suggestionsto improve the text.

ELECTRONIC SUPPLEMENTARY MATERIAL

This article contains supplementary material, which is availableonline to authorized users (DOI: 10.3301/IJG.2011.14).

REFERENCES

BLARD P.H., LAVÉ J., PIK R., QUIDELLEUR X., BOURLÈS D. & KIEF-FER G. (2005) - Fossil cosmogenic 3He record from K-Ar datedbasaltic flows of Mount Etna volcano (Sicily, 38°N): Evaluationof a new paleoaltimeter. Earth and Planetary Science Letters,236, 3-4, 613-631, doi: 10.1016/j.epsl.2005.05.028.

BRANCA S., COLTELLI M. & GROPPELLI G. (2004) - Geological evolu-tion of Etna volcano. In: BONACCORSO A., CALVARI S., COLTELLIM., DEL NEGRO C. & FALSAPERLA S., eds., Mt. Etna VolcanoLaboratory. AGU (Geophysical Monograph series), WashingtonD.C., 143, 49-63.

BRANCA S. & DEL CARLO P. (2004) - Eruption of Mt. Etna during thepast 3,200 years: a revised compilation integrating the historicaland stratigraphical records. In: BONACCORSO A., CALVARI S.,COLTELLI M., DEL NEGRO C. & FALSAPERLA S., eds., Mt. EtnaVolcano Laboratory. AGU (Geophysical Monograph series),Washington D.C., 143, 1-29.

BRANCA S., COLTELLI M., DE BENI E. & WIJBRANS J.R. (2008) - Geo-logical evolution of Mount Etna volcano (Italy) from earliest products until the first central volcanism (between 500 and 100 kaago) inferred from geochronological and stratigraphic data. Int. J.Earth. Sci., 97, 135-152, doi: 10.1007/s00531-006-0152-0.

BRANCA S., DEL CARLO P., LO CASTRO M.D., DE BENI E. & WI-JBRANS J.R. (2009) - The occurrence of Mt Barca flank eruption inthe evolution of the NW periphery of Etna volcano (Italy). Bull.Volcanol., 71, 79-94, doi: 10.1007/s00445-008-0210-5.

BRANCA S., COLTELLI M., GROPPELLI G. & LENTINI F. (2011a) - Geo-logical map of Etna volcano, 1:50,000 scale. It. J. Geosci. (Boll.Soc. Geol. It.), 130 (3), 00-00 doi: 10.3301/IJG.2011.15.

BRANCA S., COLTELLI M. & GROPPELLI G. (2011b) - Geological evolutionof a complex basaltic stratovolcano: Mount Etna, Italy. It. J. Geosci.(Boll. Soc. Geol. It.), 130 (3), 00-00, doi: 10.3301/IJG.2011.13.

COLTELLI M., DEL CARLO P. & VEZZOLI L. (2000) - Stratigraphic con-straints for explosive activity in the past 100 ka at Etna Volcano,Italy. Int. J. Earth Sciences, 89, 665-677.

CONDOMINES M. & TANGUY J.C. (1976) - Age de l’Etna determine parla methode du dèsèquilibre radioactif 230Th-238U. C.R. Acad. Sci.Paris, D282, 1661-1664.

CONDOMINES M., TANGUY J.C., KIEFFER G. & ALLEGRE G.J. (1982) -Magmatic evolution of a volcano studied by 230Th-238U disequili -brium and trace elements systematics: the Etna case. Geochimicaand Cosmochimica Acta, 46, 1397-1416. Pergamon Press Ltd.U.S.A.

DALRYMPLE G.B. (1969) - 40Ar/36Ar Analyses of historic lava flows.Earth Planet. Science Letter, 6, 47-55.

DE BENI E. (2004) - Indagine stratigrafico-strutturale del basso ver-sante sud-orientale del Monte Etna ed applicazione del metododi datazione 40Ar/39Ar per la definizione delle principali fasievolutive del vulcano Etna. PhD tesis, University of Catania,151 pp.

DE BENI E., WIJBRANS J.R., BRANCA S., COLTELLI M. & GROPPELLIG. (2005) - New results of 40Ar/39Ar dating constrain the timing oftransition from fissure-type to central volcanism at Mount Etna(Italy). Terra Nova, 17 (3), 292-298.

DE BENI E. & GROPPELLI G. (2010) - 40Ar/39Ar radiometric dating toconstrain the volcanic stratigraphy: The Mt. Etna methodologicalcase. In: Groppelli G. & Viereck-Goette L., eds., Stratigraphy andGeology of Volcanic Areas. Geological Society of America SpecialPaper, 464, 241-248, doi: 10.1130/2010.2464(11).

DEL CARLO P., VEZZOLI L. & COLTELLI M. (2004) - Last 100 kaTephrostratigraphic record of Mount Etna. In: Bonaccorso A.,Calvari S., Coltelli M., Del Negro C. & Falsaperla S., eds., Mt. EtnaVolcano Laboratory. AGU (Geophysical Monograph series),Washington D.C., 143, 77-89.

DI STEFANO A. & BRANCA S. (2002) - Long-term uplift rate of the Etnavolcano basament (southern Italy) based on biochronologicaldata from Pleistocene sediments. Terra Nova, 14, 61-68.

FERRARI L., CALVARI S., COLTELLI M., INNOCENTI F., PASQUARÈ G.,POMPILIO M., VEZZOLI L. & VILLA I. (1989) - Nuovi dati geologicie strutturali sulla Valle di Calanna, Etna: implicazioni perl’evoluzione del vulcanismo Etneo. Boll. Gruppo Nazionale Vul-canologia, 2, 849-860.

GILLOT P.Y., KIEFFER G. & ROMANO R. (1994) - The evolution ofMount Etna in the light of potassium-argon dating. Acta Vul-canol., 5, 81-87.

GRASSO M. & BEN AVRAHAM Z. (1992) - Magnetic study of the northern margin of the Hyblean Plateau, southern Sicily: struc-tural implication. Ann. Tectonicae, 6, 202-213.

GUTMANN J.T., TURRIN B.D. & DOHRENWEND J.C. (2000) - Basalticrocks from the Pinacate volcanic field yield notably young40Ar/39Ar ages. Eos, Transactions American Geophysical Union,81 (4), 33.

HORA J.M., SINGER B.S. & WÖRNER G. (2009) - Volcano evolutionand eruptive flux on the thick crust of the Andean Central Vol-canic Zone: 40Ar/39Ar constraints from Volcán Parinacota, Chile.GSA Bulletin, 119 (3/4), 343-362, doi: 10.1130/B25954.1.

KIEFFER G. (1975) - Les dernières eruptions acides de L’Etna (Sicile).C.R. Acad. Sc. Paris, 280, 1349-1352.

KOPPERS A.A.P. (2002) - ArArCALC-software for 40Ar/39Ar age calcula-tions. Computers and Geosciences, 28, 605-619.

LONGARETTI G., RONCHI S. & FERRARI L. (1991) - Il magmatismodell’avampaese Ibleo (Sicilia Sud-Orientale) tra il Trias e il Qua-ternario: dati di sottosuolo della Piana di Catania dal Pleistoceneal Miocene Medio.Mem. Soc. Geol. It., 47, 537-555.

ROMANO R., LENTINI F. & STURIALE C. et alii (1979) - Carta geologicadel Monte Etna, scala 1:50.000. Progetto Finalizzato Geodinami-ca, Istituto Internazionale di Vulcanologia-C.N.R (Catania).Mem. Soc. Geol. It., 23 (1982).

ROMANO R. (1982) - Succession of the volcanic activity in the etneanarea.Mem. Soc. Geol. It., 23, 27-48.

SCHNEIDER B.S.H., KUIPER K.F., POSTMA O. & WIJBRANS J.R. (2009) -40Ar/39Ar geochronology using a quadrupole mass spectrometer.Quaternary Geochronology, 4 (6), 508-516

SCHMINKE H.U., BEHNCKE B., GRASSO M. & RAFFI S. (1997) - Evolu-tion of the northwestern Iblean Mountains, Sicily: uplift, Pliocene/Pleistocene sea-level changes, paleoenvironment, and volcanism.Geol. Rundsch., 86, 637-669.

SINGER B.S., BRIAN R.J., MELISSA A.H., NARANJO J.A., LUIS E.,MORENO-ROA L. & MORENO-ROA H. (2008) - Eruptive history,geochronology, and magmatic evolution of the Puyehue-Cordon




Caulle volcanic complex, Chile. GSA Bulletin, 120 (5-6), 599-618,doi: 10.1130/B26276.1.

SNEEL L.W. (2002) - Argon Thermochronology of Mineral Deposits. A Review of Analytical Methods, Formulations, and Selected Applications. U.S. Geological Survey Bulletin, 2194.

TANGUY J.C. (1981) - Les éruptions historiques de l’Etna: chronologieet localisation. Bull. of Volcanology, 44 (3), 585-640.

TRIC E., VALET J.P., GILLOT P.Y. & LEMEUR I. (1994) - Absolute pale-ointensities between 60 and 160 kyear from Mount Etna (Sicily).Phys. Earth Planet. Int., 85, 113-129.

TRUA T., LAURENZI M.A. & ODDONE M. (1997) - Geochronology of thePlio-Pleistocene Hyblean volcanism (SE Sicily): new 40Ar/39Ardata. Acta Vulcanologica, 9 (1/2), 167-176.

TURRIN B.D., GUTMANN J.T. & SWISHER C.C. (2008) - A 13±3 ka age determination of a tholeiite, Pinacate volcanic field, Mexicoand improved methods for 40Ar/39Ar dating of young basalticrocks. J. Volcanol. Geother. Res., 177, 848-856.

WIJBRANS J.R., PRINGLE M.S., KOPPERS A.A.P. & SCHEVEERS R.(1995) - Argon geochronology of small samples using the Vulcaanargon laser probe. Proc. K. Ned. Akad. Wet., 98, 185-218.

Manuscript received 20 December 2010; accepted 30 June 2011; editorial responsability and handling by R. Cioni.


40ar/39ar isotopic dating of etna volcanic succession

Documents