R£:-Imcu-...:n UELLA !'oclt;TA 1TALl .... N.... DI MlNER.-\LOG1A E l'ETROLOGIA, 1985, Vu!. 40, pp. 73·106
Geochronology of volcanic rocks from Latium (Italy)
MARIO FORNASERl Istituto di Geochirnica dell'Universita, Citta Universit:nia, Piazza Aldo Moro, 0018.5 ROffia Centro di Studio per la Geocronologia e la Geochimica delle Formazioni Recenti del CN.R.
ABSTRACT. - The age determination data for A few reliable age measurements arc available volcanic rocks from Latium (haly) are reviewed. for the Sabatini volcanoes, rather uniformely scat· This paper reports the geochronological data obtained tert-d between 607 and 85 ka. The "tufo rosso a chefly by the Ar-K t~hnique, but also by Rb-Sr, scorie nere,. from the sabatian region, which is ""'rh, "C and fission tI"1lcks methods. the analogue of the ignimbrite C from Vico has a The Latium region comprises rocks belonging to firmly established age of 442 + 7 ka. This formation the acidic volcanic groups of Tolfa, Ceriti and Man. can be considered an impor-tant marker not only ziana districlS and to Mt. Cimino group, having for the tephrochronology but also, more generally, strong magmatic affinity with the Tuscan magmatic for the Quaternary deposits in Latium. province and the rocks of the Roman Comagmatic Taking into account all data in the literature Region. lbe last one encompasses the Vulsinian, the oldest known product of the Alban Hills show Vicoan, Sabatinian volcanoes, the Alban Hills and an age of 706 ka, but more recent measurements rhe volcanoes of the Valle del Sacco, often referred indicate for these pt RI"SSUN'TO. _ Vengono p2SS8te in rassegna le dei Colli Albani, le prime grandi effusioni Iilviche datazioni delle roctt vulC2niche del Lnio. QucstO dovrebbero avere un'ela di 706 kil, ma misure lavoro riporta i dlni onenuti prevalentemente con piu recenli indicano per questi prodoni un'eli piu il melodo polassio-arxon, ma anche con i rnetodi giavane: (400 k.). Una delle formazi.oni pirodastichc dd robidio-montio, dd C2rbonio-l4 e delle lracce dei Calli Albani, il «Iufo di Villa Senni .. ~ Slllta di fissione, datalll con grandc accuraloza e la sua eta di La regione lazi:l.le comprendc le f'OC'tt appane. JJ8 ± 8 k. C05tiluisce un imporl.missimo lermine: di riferimento per la crooologia di questo wlcano. nani .i &NPpi vulC2nici acidi dei complessi Tolfe. inferio~ tano, Cerile e Manzi.te ed al groppo cid M. ·G Un limite per l'attiviti: vuk:miCll nc:i Colli mino, nenli una pronuncialll affiniti magmalial Albani non si ~ .neon porulO stabili~ con preci sione. Vi sono pero chi.ri indizi di ;,m'ed abba con la proviocia Tosama e le I'lJn"t: deJla Provinci. (~.'O.OOO Comagmatica Romana. Quesl'ultima comprende i Stanxa recenle anni B.P.) per le ultime vulcani Vulsini, il vulamo di Vico, i vulcani Sal»· eruzioni frealomagtnltiche. Tuna la crooologi. deI tini, i Calli Albani ed i vulCllfli ddla Valle dd I'aniviti nei Calli Albani de"e essere revisKmata SICCO (o Valle Latin.), spesso denominali aoche a causa dell. 5Cana alleooibilita di moIli dati vulcani degli Ernici, lUui catlllleriuati TERN _/~- ... / ' \ I , '\, \ .... / RIET1 , ----. \ \ ,, ,,, / ," ( " , FiB. I. - The volcanic BrouPS of u{ium. encompasses the acidic volcanoes of Tolfa. activity (Roccamon6na, Phlegraean Fields, Ceriti and Manziate districts and of Mc Ci and Vesuvius). mino; the second the Vulsinian, Vicoao, Also the islands of the « Ardpelago Pon Sabatinian volcanoes, the volcanic region of tino.: Palmarola, Ponza, Ventotene. Santo the Alban Hills (often referred to as « Latian Stefano, belong to the Latium region. These Volcano.) and the volcan~ of the ValIe islands are located at the margins of del Sacco (also called Vulcani della Valle the Tyrrhenian trench and their magmatic Latina or Mts Ernici volcanoes). activity, developing from the Pliocene up The 6rst series has a strong petrographic to late Quaternary, evolved from an acidic affinity with the Tuscan magmatic proviott, to an alkaline potassic character. the anatectic nature of which has been widely BARBERI et al. (1967) pointed out that recognized. The second is characterized by a the 87S r/86S r ratios measured in the products pronounced albline-potassic character and is of the Pontine islands fall in a very narrow linked to the Campania alkaline magmatic range and cluster around an average value 76 M. FORNASERI TOLF..... C Fis. 2. - Tolfa, Cerili and M.lUiana diuriro. Samples loc.tion and 1ocaI.ity fillip. of 0.7073. thus suggesting a single magmatic some contradictory results are present, some source. On the other hand, the above ratio points are still open to discussion and some is significantly lower than the value normally times a more detailed work is needed. observed in materials of crustal origin, but higher as compared with typical values of The acidic volcanic group uncontaminated basalts. Two possible models are then considered Tal/a, Ceriti and Manziana district! for the origin of the rocks of the Pontine This district comprises the Tolfa and the islands: either they derive from a conta Cerile massifs and the minor volcanic nuclei minated basaltic magma or from partial of the Manziana sector such as Mt. Calvaria, melting of deep crust layers in which the Mt. San Vilo and others, and together with initial uSe/8lISc ratio is lower in comparison some of the producls of Ponza, represents with the uppermost surlicial zones. the mool ancien! occurrence of volcanic actio Some 180 age measurements are available vity in Lalium. for the different volcanic districts and we can The rocks of these massifs, although say that nonc of the most important volcanic showing topographically separated identities units was overlooked and that the framework are linked by similar structural and petro of the geochronology of the volcanic activity graphical features and are therefore referable in Latium is fairly well eslablished even if to a single genelic model. GEOCHRONOLOGY OF VOLCANIC ROCKS FROM LATlUM (ITALY) 77 Detailed research work by NEGRETTI biotite from a subvolcanite inclusion found (1963,1965 a, 1965 b), LAURO et al. (1965), in the chaotic tuffs of 'the Tol£a area (Mt. NEGRETTI et al. (1966), LAURO and NE Sassetto) showed an age of 6.4 ± 1 Ma. GRETTl (1969), FERRINI et al. (1970) build On the whole the present data do not up an exhaustive geological and petro give a clear image of the chronology of the graphical image of this volcanic complex. volcanic activity of the To1£a, Cerite and As for the geochronology, after a first K-Ar Manziana districts. Problems connected with dating by EVERNDEN and CURTIS (1965) on inheritance and loss of radiogenic argon a sanidine from the To1£a massif and a make it difficult to enter in chronological second one by BIGAZZI et al. (1979) on detail and need to be faced with adequate biotite crystals from the lava of Mt. Cucco techniques. dome (Cerveteri, Cerite district) a group of 20 K-Ar datings were obtained by LoMBARDI et al. (1974) of which eleven concern the To1£a sector, four the Cerite and five the Manziana sector. The results concerning lavas, ignimbrites and hypoabyssalites are presented in t::lble 1. From the televant data the following con Fig. 3. - Tolfa, Ceriti and Manziana districts: clusions may be drawn. frequency distribution of measured ages. a) Wide range variations are shown by the ages of the ignimbrites and lavas be The Cimino volcano longing to the same sector. In the To1£a The geology and petrology of Mt. Cimino massif, including some minor outcrops, the volcano are well known after the works of age of the lavas ranges from 2.4 to 3.7 Ma SABATlNl (1912), MATTIAS and VENTRIGLIA and the age of the ignimbrites from 2.1 to (1970), PUXEDDU (1971), MICHEWCCINI et 2.7 Ma. The age of 2.3 Ma determined by al. (1971) including an up to date biblio EVERNDEN and CURTIS (1965) approaches graphy. the lower limit found for the lavas and The geologic units forming the Cimino falls within the general age limits of the Tolfa products. volcano are fairly simple and may be sum marized as follows (PUXEDDU, 1971): Fot the Cerite massif the age limits are 2.4 and 4.1 Ma for the lavas and 2.4-4.0 Ma a) plateau ignimbrite of quarrzlatitic com for the ignimbrites. Such variations are position, often referred to as «peperino interpreted by the authors as due to inheri tipico» auct.; tance or to loss of radiogenic argon and b) lava domes of quarrzlatitic compo possibly to the so called «phenocryst effect». sition, often referred to as «peperino delle alture» auct.; b) The hypoabyssalites appear to have been emplaced during the first period of c) lava flows of latitic composition; activity of the To1£a volcanism, even if they d) lava Row of olivinlatitic composition, fit within the general variation limits of age. often referred to as « radial lava Rows» or «ciminites» (WASHINGTON, 1906). c) While field evidence shows that the lavas are older than the ignimbrites, K·Ar For the above-mentioned products a group dating do not allow to recognize a chrono of ten age estimations is available, enough logical order. At any rate these events must for locating the activity of the Cimino vol have occurred in a narrow interval of time. cano chronologically, even if some problems d) The magmatic activity in the To1£a, are still open (table 6). Cerite and Manziana sectors may be regarded As for the quarrz-Iatitic ignimbrite (pe as contemporary, belonging to the upper perino tipico lIuct.) the four measurements Pliocene and not to the lower Pliocene as available indicate ages varying from 1.19 ± stated by FAZZINI et a!. (1972). Only a 0.05 Ma to 1.3\ ± 0.008 Ma with an average 78 M. FORNASERl .!, ~ '" cltu-lti • ONTEIl'OSI Fig. 4. _ Cimino and Vioo volcanic groups: localities map. value of 1.27 Ma. Five measurement~ on 0.08 Ma) than the age of the lava domes lava domes from Mt. Cimino range from (1.066 ± 0.08 Ma). It is worth nOling, 0.975 ± 0.0.5 to Ll8 Ma with an average however, that at the lime of the measu value of 1.066 Ma. rements the «resolution. of these datings The only dating existing iD the literature was probably nOl shll1'p enough to settle the for the olivinlatitic lava flows (radial lavas, controversy about the priority of both for ciminites aucI.), of 0.94 ± 0.2 Ma, although mations (MITTEMPERCHER., TEDESCO, 1963; affected by a 100 large error, is consistent VENTRIGLIA, 1963; PUXEDDU, 1971); as a with the geological setting of these rocks. result more &Iailed measurements are re The latitic ignimbrite (pcperino tipico quired, taking also in account that, in mosl auc!.) thus appears somewhat older (1.27 ± cases, tongues of domt: lavas are ~n to flow GEQCHRONOLQGY OF VOLCANIC ROCKS FROM LATIUM (ITALY) 79 ovt:r the already consolidates ignimbritt: the Bolsena lIctivity (or at least not referable fPUXEDDU. 1971) but in Other cases the to the acLivity of Latera) are presented se ignimbrite covers are likely to be younger parately in tables 2, 3 in which they are than some domes IPUXEDDU, 1971). simply displayed in chronological order, distinguishing betw~n the lavas (table 2) and the ignimbrites (table 3). Comments will follow concerning their consistency with the geological situation. Table 4 conrains the data for the activity of Latera brocken down according to the respective volcanic phases following the evolmionary models proposed " by NAPPI (1969), SPARKS (1975). and METZELTIN and VEZ7..oLl (1983). " As regards the activity of Bolsena volcano , a few comments may be appropriate. a) The first products of [he activity of Bolsenll are fairly old. The dating obtained by NICOLET'fl et a!. (1969) on the lava flow IQ 00 of Torre Alfina (820 ± 40 ka) matches well with a dating recently performed by VILLA Fig. S. _ Cimino volcanic group: frequency (1984) on a phlogopite of a sample from a dimibution of measured ago. deep well drilled at Litera (862 ± 20 ka). The Torre Alfina lava flow was already considered coeval with the Radicofani rock The alkaline potll8sic volcanic group dated by EVERNDEN and CURTIS (196') at 880 ka (VAR.EKAMP. 1980). Th~ Vuhinian vokanoes Along with the most recent geological b) The youngest lava flow of the Bol. and petrographical works on the vulsinian sena volcano was dated at 40 ka. However, area (ScHNEIDER. 1965; MARINELLl and the latter figure, calculated by NICOLET71 er MITTEMPERGHER. 1966; NAPPI. 1969; TRI al. (1979) proved to be unacceptable as GILl.. 1966. 1969; TRlGlLA et al.. 1971; pointed out by METZELTIN and VEZZOLI VAREKAMP. 1980; METZELTIN and VEZZOLI. f 1983) because it is inconsistent with the 1983) over 50 radiometric datings on lavas geological record and not in agreement with and pyroclastic products have been performed the data first obtained by EVERNDEN and in the lasl few years. CURTlS (1965) of 328 ka, further confirmed at 3JJ ± 8 ka by METZELTIN and VEZZOLI To frame the results of these datings into (1983). The activity of Bolsena volcano is a definite and comprehensive pattern for the thus likely to cover a lime extent between evolution of the volcanism in the Vulsinian 860 and 150 ka. area is nOt an easy task, since most of the published data are affected by major errors c) As to [he Vulci lava flow there is and because some of the recently proposed disagreement between the value obtained by evolutionary patterns are based on radio NICOLETTI et al. (1981) of 180±40 ka and metric data, which in turn call for further that estimated by METZELTIN and VEZZOLI verification. (Ioc. cit.) of 322 ± 6 ka. The same holds We can assume as a~rtained that the for the Monte Calvo flow, dated at 410 ± volcanoes of Bolsena and Latera developed 150 ka (with large error) by NICOLETrI et indipendently (METZELTIN and VEZZOLl, a!. (1981) and at 316± 8 ka by METZELTIN 1983) and that the activity of the Bolsena and VEZZOLl. It should be noted that the cycle started before the beginning of the values determined by the latter authors with activity of Latera (NAPPI. 1969; METZELTIN refined techniques, affected by a minor error. and VEZZOLl. 1983). That being slated the are highly reproducible and are thus at radiometric data concerning the products of present the best available data· 80 M. FORNASERI T~re is also disagreement between the 01 A, 31 and 30 A) ydded isochrone (6g. 7) value obtained by NICOLETTI et 0.1. (1969) ages of 550 ka and this is the value recom for a lava flow of Buonviaggio, m:ar Porano mended by the authors for the ignimbrire (660 ± 30 ka) and the measurement of complex oulcropping near La Rocca along EVERNDEN and CURns (431 ka). the Trapon2o stream. Fig. 6. - TIle vulsinian vokanocs: localities map. ~ basal ignimbrites show ages ranging The ignimbrite oureropping along the Ar from 880 ± 40 ka to 400 ± 20 ka (NICo rone River dated at 880 ± 40 ka may well LElTl et al., 1981). 10 the opinion of these be the product of an older activity. authors, the youngest ages detennined (400 As for the Latent activity the available 450 ka) are less reliable. Three samples datings suggest ages ranging from 310 ± 10 GEQCHItONOl.OGY OF VOl.CA.-m; kOCKS FROM l.ATlUM (ITAU') 81 [055 ± 22 ka (Nlcou-:rn Cl 011.,1979) with two highly :lCcuratc values estimatL-o by ". ~'IETl.l:.l.T1N and Vt:zZOl.l (278 ± 8; 261 ± vs 31 I< 6.5 ka) (or the lower tr>lchytic ignimbrite IG-unill; an age of 190 ± 20 ka for the upper Irachytic ignimbrite (E-unit) and a ••• group of dating obtained by diff~r~nt authors and with different methods, ranging from ; 183 ± 4 to 117 ± 28 ka for the «complex .< Pitigliano volcanite ». The value &termincd '" VS30 I< by NtCOLE'IT1 et al. (1970) of 55 ± 20 ka vs 31 far 11 member of this complex neros further validation representing one of the youngest ages recordl.:d for the Latera activity and for ••• rhe ovcrall Vulsinian activity. Tbe Vico volcano • • Geology and petrology of the Vim volcano were throughly investigated and refcrence Fig. 7. _ The vulsinian volc.noes. lsochrone from should be ffillde to the works of WASHINGTON samples VS)I A, VS)() A llIld VS)1. (1906), SABATlNI (1912), LocAItOt (1965), MA'ITIAS and VENTkIGLlA (1970) in which ,. a complete bibliography is reported. - - For lhe Vico volcano the geochronological data are frankly scarce and need more detailed work and refinement. Only ~ven " age measurements have been performed on lavas and pyroclastic rocks. , One of the most important pyroclastic formations in the Vico district is the « tufo " - rossa a scorie nere» auct. (red tuff with black scoriae), which was interpteted b}' , LocAllOI (1965) as an ignimbrite sheet (ignimbrite C) extending 10 a maximum distance of 25 km from its emission cemer 1- and covering an are-d of about 1250 km::. 1000010'. South east and south west the ignimbrite ". C is in comact with the analogous formation Fig 8. _ 1be vulsinian volcanoes: frequency from the Sabatian district. For this reason distrlbutlon of measured ages. the ignimbrite C from Vim and its analogue belonging to the Sabatian district were often are reported ond the data for the similar considered as one single pyroclastk unit at· « tufo rosso a scorie nere ~ belonging to the tributed to the Vico volcano. According to Sabatini district are reported in tab. 8 and LocARDI (1965) however the ignimbrite C discussed in the next chapter. occurs always as a 6lling in the erosion In spite of its importance only two K-Ar valleys cut in the Sabatian formation. The measuremems are available for the vicoan question however is far to be settled, as ignimbrite. One of them (table 7, sample ALVAIlEZ et al. (1975) by determining the no. 9) is affected by a large error (520 ± elevation of the upper surface of the Tufa 120 ka); the second shows a more reliable Rosso concluded that all this unit is of Vico age of 420 ± 40 ka. This is clearly not enough origin. to assess precisely the age of the ignimbrite C. To avoid misunderstandings in table 7 onl}' Among the Others pyroc.lastic units from the age dala for the ignimbritc C from Vico Vico only a «black pozzolan» was considered. M. fOKNASt:1I1 Its age of 620± 220 ka, allhough :Iffectetl Onc of the effusive units of p:micular by such a large error is nOI in conflict with significance is the leucitilic lava flow of the age obtained for Ihe ignimbrite C since Monte Cucco, on the left side of Fosso della the pozzolan underlies lhe ignimbrile C and Mola in Cerveteri area, dated by B1GAZZI el may well represem one of the lerms of the al. (1973) at ·HO ± 20 ka. This lava flow i~nimbrite B of LocARDl (1965). is superimposeJ on a brown eanhy IUff and The remaining darings available indicare ;l white pumice luff refew.-d 10 ItS «lUfi an aClivity of the Vico volcano ranging from strati6C'ilti varicolori di Sacrofano (Sacrofano 820 to 95 ka. Ir is worth noting that rhe manycolored IUffs)>> (') and underlying a upper Hmir is affected by a vcry large error diatomitic layer, which in lurn underlies and needs further veri6cation ahhough ir is the «tufo rossa a scorie nere» auel, (~ consisreOl with rhe srraligraphic position of the chapter dealing with the Vico \'olcano rhe lava considered (NlCOLETTl, 1969). The :md below), rhe age of which is fairly well lower limit (95 ka) r~uhs from a measure established at -142 ka· The daling of the mem of EVERNDEN and CURTIS (1965) lava flow of Monte Cucco enabled the authors performed on a leueile-rieh lava from Ve to establish the age of the diiltomitic deposit tralla. and 10 stare the age of the Tarquinian period of marine sedimenliltion prt."Cisely. Moreover table 8 exhibilS the age data for the ... tufo rosso a scorie nere » from the Sa· batian region which, as alIe1tdy mentioned. is to be considered liS the analog of the ignimbrite C from Vico. The c tufo rossa II scorie nere I> is an important marker not only for the tephro chronology, but also for the chronology of Fig. 9. - 1be Vico yok..no: fn:tjl)eIKY Ji$uihuliun lhe Quaternary deposils in Lttium (AMBlto of masured aaa. SETTI et al., 1969; BoNAOQNNA and BrGAZZr, 1969, 1970; AMBROSET1'r et aI., 1972), The age of this formation may be regarded The Sabatin; volcanoes as one of the best known Ihrough Ihe nu· The aucntion of Ihe geochronologists in merous measuremcnls of [VEItNOEN :md the Sabatian disrrict was focused more on CURTIS (1965) including replicate measure· pyroclastic units than On lavas. This is partly ments on the same s'lmple llnd on differcnt a~ due to the nature of the Sabatian district, samples from dilferelll localities well, 10 which is characterized by a large number which one recent measurement by VILLA of eruptions with prevlliling explosive actio (1984) should be addl.-d, vity, as compared with the emission of lava In view of the d,lIa ltvailllble an age of flows. 442 ± 7 ka may be assigned to the «tufo Tables 8, 9 display the dating published rosso a scoric nere" from the Sab"lian re· up to this date, making reference to the gion, resulting from lhe lIver,tge of 8 succession of the pyroclastic units, as measurements, 'lfler nonmt!izing all values established bv MATTlAS and VENTRIGLlA to the new decay constllnts by STEIGEIl. and (1970). In tdble 8 the only twO available JAGER (1977). datings for lavas arc also shown taking into Although the published dala concerning account their stratigraphic position in re the ignimbrite C from Vico Fig. 10. - S.blUini volanic dimict: loca1itics map. The volcanic level interbedded in the resp.) are aHectc=d with large errors. For diatomitic deposit of Riano, for which two the same unit VILLA (1984 b) determined an quite concordant ages are reported. obtained age of 288 ± 6 kat which can be considered by different authors and with dilIerent the best value availablc=. owing to the 5maU mc=thods (AMBROSE'ITI et al., 1969; BoNA- associated error. In any case the time interval M. t'OIl.NAScKl between the deposition of the upper levels units not yet studied from the chronological of the « tu6 strad6cati varicolori de La Star viewpoint, such as the «tufo giatlo della ta» and of the « tufo giallo di Sacrofano» Via Tiberina », which represents also an appears to be rather small. important unit, llOd others. It turns out again that increasingly precise measurements are needed to better establish The Albafl Hills the chronological relationship between the two above-mentioned units. Even if the existing literature contains a As for the « tufo di Bracciano » which, in considerable amount of data, the present series, like the « tufo giallo di Sacrofano », state of the Alban Hills geochronology is overlies the «tu6 de La Storta », research far to be satisfactorv. work by BoNADONNA and BIGAZZI (1970) in To frame the existing data into a single the area of Monte Cucco (Cerveteri) showed evolutionary pattern reference will be made the existence of four levels; three of them to the chronostratigraphic sequence proposed were dated with the fission track technique by FORNASERI, SCHERILLO and VENTRIGLIA on biotite crystals, yielding ages of 177 ± (1963) of which use was made in drawing 30; 127 ± 13 and 90 ± 18 ka, respectively. up table 10. These data were used by the authors to For the lower terms of the series, the establish the correlation between erosive «6rst outcropping effusions» two datings phases and intratyrrhenian regressions of the are available, substantially concordant, by Quaternary in the surroundings of Rome. EVERNDEN and CURTIS (1965), at 706 ka and by GASPARtNl and ADAMS (1969) at 680 ± 50 ka, and two obtained more recently by VILLA (1984). The last ones, of 400 ± ID and 460 ± 6 ka, with which a very small error is associated would rejuvenate the age of those which were considered so far as the oldest lava flows of the Alban Hills, by , almost 300 ka. r- In the central area of this district, super I- f-I.---i imposed on the above mentioned first large lava effusions there is a significant pyroclastic 500 1000>10". complex referred to as the « complex of the lower tuffs» (complesso dei tufi inferiori). Fig. 11. - Sabatini vulcanic dis!rkl: frequency This complex includes the following terms, distribution of measured ages. from top to bottom, and omitting details, for which reference should be made to the An ejected block from the « tufo di Brac previously 'mentioned work by FORNASERI dano », considered as a fragment of a skarn et al. (I963), connected with an underlying plutonic body, a) Tufo di Villa Senni was dated by VILLA (private communica tion) with the potassium-argon method at b) Upper pozzolanas (grey pozzolanas) 334 ± 48 ka, a value which is obviously c) Tufo Iitoide della Campagna Romana, in line with the data previously reported. often referred to as «tufo Iionato da For the « tufo di Bracciano » which in the costruzione » stratigraphic sequence established by MAT d) Middle pozzolanas or pozzolane nere T1AS and VENTRIGLIA (1970) appears to e) Yellow conglomerate overlap the above described « tufo di Brac f) Lover pozzolanas often referred to as ciano», VILLA (1984 b) obtained a consistent «red pozzolanas» or «pozzolanas of age of 85 ± 9 ka. San Paolo ». Summing up, for the Sabatini volcanoes few reliable datings are available and more According the most recent papers (BER work has to be carried out la improve NARDI et aI., 1982; PECCERILLO et aI., 1984) previous data and to examine the pyrodastic the first activity phase of the Alban Hills GEOCHRONOLOGY OF VOLCANIC ROCKS FROM LATIUM (ITALY) 85 Fig. 12. ~ Alban Hills: localities map. was terminated by a big explosive episode, standpoint. For this formation, a wide age giving rise to the deposition of the Villa spectrum, extending from 620 ± 200 to Senni tuff, which is interpreted as due to 160 ± 30 ka can be inferred from the lite· empting of the magma chamber and suh rature (MASI et al., 1976; TADDEUCCI, 1969; sequent collapse of the caldeta. Following BIGAZZI et al., 1977; RADICATI DI BROZOLO this model the products of the activity of et al., 1981; VILLA, 1984). Fortunately to the Alban Hills are often referred to as make order in such a dispute an extremely «pre-caldera)~ and «post-caldera» depending accurate methodological study by RADICATT on their location with tespect to the « Villa DI BROZOLO et al., carried out with 4.0Ar_39Ar Senni» tuff. and with Rh-Sr methods was published in The « Villa Senni» tuff is also the best 1981, whose results may be summarized as known formation from the geochronological follows: 86 M. FORNASEIU ') .-::::-'-..../····1 ~===-v'~ : lOl'vw, ANAGNI Fig. 13. - Anagni and FOfllana Ranuecio archacoqical site: locality map. a) six leucite samples yielded de6ned mayor markers of the Alban Hills volnnic ·"Ar·:JllAr ages with an avernge value of districl. 338 ± 8 ka (Stt table 11). Out the previous datings of the same formation, only twO of the four obtained b) Rh-Sr measurements on leudte, bio with" the fission track technique are in fite and pyroxene allowed the determination agreement with the above value. Other values of internal isochrone ages ranging from 380 ± are to be considered as aberrant (tOO young 20 to 330 ± 20 ka, in good agreement with or too old) and arc to be rejected. [ht: previous ones. The situation for the lower terms in the c) The biorite ~oAr_aIlAr ages are in three complex of the « lower tuffs» is far from cases in agreement with the cagenetic leueites, being satisfactory. The only chronological although less preeise, but in the remaining information we have comes from a study on cases two discordant ages were obtained, the archaeological site of Fontana Ranuccio, suggesting that the biodtes must ~ con Anagni basin, conducted with the K/Ar siderro with cauLion for .oAr·!'Ar and K-Ar method by RADICATI DI BROZOLO and VILLA dating of Quaternary rocks. (in BlDDITTU et al., 1979). The stratigraphic profile of this site (fig. 14) includes different Nonetheless the study by RAOICATI et al. pyroclaslic uniu, among them the .. tufo allows 10 establish with certainty t~ age Iitoide della Campagna Romana. (3) is the of the« Tufo cli Villa Sc-nni. at 338±8 ka; upper limit of the Ranuccio site series, given its eXlension over an area of about which includes, proceeding dovnwards, the 1500 Km:! this IUff repre2nts one of the archaeological layer (6), a thin layer of leucite GEOCHRONOLOGY Of VOLCANIC ROCKS FROM LATlUM (lTALY) Si crystals (12), a thick layer of pozzolana (13), Senni », some problems arise as regards the and a tuffitic Iimnosol (14). thick pozzolana layer (13) which is, like The « tufo litoide» (3) was estimated to the «tufo litoide» (3) a product of the Alban be slightly younger than 366 ± 0.4 ka, this Hills (BJDDlTTU et al., 979). The age esti· being the age of a lapiIli tephra layer (4) mated for this pozzolana layer (between 428 found immediately below it. and 487 ka) is consistent with the expected The age of the thick pozzolana layer (13) age if one admits the value of 706 ±680 ka should be comprised between 528 ± 6 ka, for the oldest lava flows (EVERNDEN and which is the age of 14 and 487 ± 7.5 ka, CURTIS, 1965; GASPARINI and ADAMS, the age of 12· Incidentally, the age of the 1969) on which the pozzolana is super· palaeosol atchaeological layer (6) with imposed in the Rome area (Acquacerosa, industry of the lower Palaeolithic was Vallerano e[c). However this estimate is no measured at 458±5.7 ka. longer in agreement with the expected age if one accepts for these lavas the new values of VILLA (1984) (400 ± ID ka) and BER NARDl et a!. (1982) (460 ± 6 ka). Whether the pozzolana layer of Fome Ranuccio is to be considered as the same overlying the lava flows of Acquacetosa and VaIIerano or re presents an older pyrodastic unit is still an open is~ue, taking into account that the Fome Ranuccio series lies some 30 km away, eastward and on the opposite side of the volcanic complex. From the Tuscolano·Artemisio period, different lava flows were dated. One of them 5 is the well known lava flow of Capo di Bove (WASHINGTON, 1925; FORNASERl et al., 1963) for which GASPARINI and AOAMS obtained 520 ± 40 ka on leueite separates and 500 ± 50 ka on the whole rock. Nevertheless these concordant values are inconsistent with the stratigraphic position of the lava flow which overlaps the Villa Senni tuff of 338 ± 8 ka. For the same lava I flow [he dating of NrCOLETTI (360 ± 40 ka) I is more acceptable, but the best available A' B value was obtained by BERNARDI et al. (1982) L' 25m ~.: .- ._.._523.000.!l. 14 at 292 ± 6 ka. For the Divino Amore lava flow EVERNDEN Fig. 14. - Fontana Ranuccio site section. and CURTIS (1965) calculated 268 ka and Fig. 14. - 1: .. Terra rossa,. paleosol • 2; POOt:). genized layer. 3; .. Tufo litoide:,. - 4: Lapilli more recently BERNAROI et aI. (1982) 175± tephra . 5: Solifluclion and cryoturbatOO horiwn . 2 ka. For the Saponara lava flow, BERNARDl 6: Palaeosol archaeological layer. 7; Tephra from et al. give a consistent age of 260 ± 5 ka. Ernici Volcanoes with BUXUJ and Zelkovl1 flora The age obtained by the same authors for and Cydortomll elegllnJ . 8; Clayey Iimnosol . 9: Iron duticrust . 10; Tufitic current bedded sands a small lava outcrop east of Saponara poses . 11; Palaeosol - 12; Thin layer of leucile crystals some problems since this small lava flow 13; .. Poz7.01ana ,. - 14; Tuliitic limnosol. underlies the « tufo Iitoide» and, according '(From SEGRE and ASCENZI, 1984). to its stratigraphic position it should be « pre-caldera ». Now, while the age of the «mfo litoide» The large Java effusion of Laghetto (AI-12) is consistent with the expected age of this which represents a « post caldera» eruption, formation, which in the central area of the shows an age (365 ± 5 ka) slightly older Alban Hills underlies the «mfo di Villa than the expected one. 88 M. FORNASERI Even more serious problems are raised rounded by typical explosion products. One by the two lava flows which belong to of them is the well known «peperino .. of the Tuscolano-Artemisio rim and which, Albano. according to FORNASERl et al. (1963) a~ Many attempts were made to estimate la be considered • post caldera ». One of the age of this eruption. the2 lavas (AI-9) was dated by BERNARDI et al. (1982) at 477 ± 6 ka; the other a) The zircon found in the sands from (Al-38) at .524 ± 9 n. Both ages are older the Nettuno linoral with the fusion track than t~ obtained by the same authors and technique revealed an age of 59 ± 9 ka by VILLA (l984) for the lava £lows of Valle (BJGAZZI and FERRAIl.A, 1971); such sands raneUo (460± 6 ka) and Acquacetosa (4oo± are reasonably believed to have been fed hy 10 ka) underlying nOt only the «tufo di the «peperino .. of Albano (BIGAZZI and Villa Senni» but also the lower ponolana FERRARA, 1971). The same zircons (CERltAt formation, and consequently being «Plt et al., 1965) gave 43 ± 5 ka with the caldera» products. ~3l)Th method while TADDEUCCI (1969) If one considers the ages of Valleranel10 obtained an age of 67.5 ka, still working and of Acquacetosa lava flows and of « lUfo with disequilibrium methods on minerals di Villa Senni » as well established, the ages of the «peperino» groundmass. These re of AI·9 and of Al-38 samples are difficult ported data are to be considered as an upper to explain because they would represent the limit, since the afore mentioned minerals oldest lava products of the Alban Hills. can be older and not necessarily coeval with Furt~r 6eld work is needed to verify the the explosion. stl'lltigl'llphic position of both AI-9 and AI-38 hI Unhurned wood samples, embedded lavas and to give a satisfactory interpretation in the «peperino's .. layers were dated al C:). to such unexpected old ages 29.7 ± 0.4 ka with the lie method by Among t~ products of the lasr pe.riod of DE VRIES (1958). Pro£. DE VRlES (private the centl'lll activiry the ages measured range communication) pointed out that this date from 331 ± 7 (rhe lowesr of the: 7 lava flow had to be verified hut this did not unfortu outcropping at the north-east wall of the: nately happen owing his untimely death. cl'llter of Nemi) to 240 ± 3 ka for the lava Further unbumed wood samples collected in flow of Arcioni (Roaa di Papa) (BERNARDI the following years were repeatedly dlited et al., 1982) which is the youngest of the in Rome (ALESSIO et al., 1966; CoRTESl, prOOucts from the last period of the central 1984) but the obtained ages turned out activity. always higher than the local limit of the Coming back to the lava flow of Divino method 07-40 kal. Amore, until yet considered as a product of the Tuscolano-Artemisio period (FORNASERI et al., 1983), its younger age (In: ka) rises the question whether this flow belongs to the Tuscolano-Artemisi to, Attordill8 FUNICIELLO (prinle communicalion) 1000010'. lhe AI-9 J.v. flow .ppcan underlyill8 the • IUfo '" di Villa Senni ... Thi.\ rouId explain its unapcncd FIg. 15. - AJ1»n Hilb: frequency diSlfibulion old age. of ~ 118e$. (;EOCHIWNOLOGV OF VOLCANIC ROCKS FROM LAT!UM (ITALV) Fi~. 16. _ The lkrnkan disnicl: lo.:alititcs map. It is apparent Ihat there are clear signs Cl VE"fTA et al. (1981) in its geochcmiCal of ,I recent age for this eruption and further 'ISpectS. attempt are being made to obtain new infor The district involves different eruptive mation, At present it m,ly be reasonably centers, located near Patrica, Giuliano di assumed that the eruption of Albano rook Roma, Colle Castellone, Pofi, Roana and place about 40-50,000 years RP, others; ,their products may be considered as leudte tephrites and leucitites. The K/At ages obtained, shown in table Th" H",nicolI district 14, range between 700 ± 20 and 80 ± 40 ka The volcanoes of the valley of Sacco or and do not pose particular problems at Valle Latina, often referred to as Hernican present. volcanoes, are located about 50 Km east southeast of the Alban Hills and 70 Km northeast of the Auruncan district (Rocca " monfina), the latter one belonging to the Neapolitan area. " This district, well known after the studies • by VIOLA (1896, 1889), WASHINGTON (1906), $CHERILLO (1937), ACCORDI et al. (1967), FRANCO and DE GENNARO (1971), ANGE· LUCCI et al. (1974) was recently studied by '00 1000' 10'. BASILQNE and CIVETTA (1975), CIVETTA Fig. 17. - The Hcrniclln Jistrict: fr~llenLY dislri (1974) as regards the geochronology and by bution of measured ages. 90 M. FORNASERI A discussion concerning the chronological by SANTACROCE et a!. (1983) and SAVELt.I relation between the volcanic activity of the (1984). Hernian disukt and of the Alban Hills is The results obtained for the eastern group hard 10 undertake at present, owing the big (Ventotene and Santo Stefano) are displayed problems still open concerning the chrono in table 15. According 10 BARBEIU et al. logy of the Alban Hills. (1967) a quaternary volcanic activity pro I t may be considered as ascertained that duced trachybasaltic lava Rows at Ventotene both volcanic complexes were contempora and phonolithic ones at Santo Stefano. The neously active for a long period of ti~. ages measured range from 1.2 Ma for Santo Stefano to 1.7 Ma for Ventotene. New datings by SANTACROCE et al. (in press) for The Ponza archipelago the Punta dell'Arco lava Rows (Ventotene) The Ponza archipelago consists of two covering the entire pre-caldera sequence gave different groups of islands: the eastern group ages ranging from 0.81 to 0.48 Ma, in poor includes the islands of Ventotene and Santa agreement with the previous value of 1.7 Ma Srefanoj the western group the islands of obtained for the base of the same sequence. Ponza, Palmarola and Zannone. KtAr measurements on the Romanello lava The geology of the Pontine islands was flow and on pumices from different pyro· outlined in different works by DoELTER clastic units representing the products of a (1876), SABATlNI (1893, 1896, 1898), SEGRE post-caldera activity indicate 0.2 Ma as the 0954, 1956, 1960) and in a more recent lower age limit. paper by CAKMASSI et a1. (in press). Vol· Table 15 also displays the age deter canology and petrology were studied in minations for the volcanires of the western detail by BARBERI et al. (1967), METRICH islands (Ponza, Palmarola). According 10 and SANTACROCE (in press). BARBERl et al. (1967), the volcanic activity Age determinations have been performed in the western group started during the PHo by BARBERI et al. (1967) and more recently cene (5 Ma) with the emplacement of \., PAlMAROlA I, ZANNONE'- • ~,6J ,..tSl~ \ .. ~ 'P, ISOLA 01 PONZA I, VEN10TENE D rig. 18. - lnc Ponza archipelago: 100001i1ie$ IIUIp. GF.OCHRONOLOCY OF VOLCANIC ROCKS FROM LATIUM (ITALY) 91 rhyolitic volcanites. Approximately at the volcanic rocks of Latium, have been widely Quatcrnary-Pliocene boundary (1.9 Mal se used in discussing the Pliocene-Pleistoccne veral dykes intruded the brecciated lavas. limit in Latium. This problem however is A little later (1.7·1.6 Ma), an intrusion of a out of the scope of this work and will not sodalite lava dome took place at Palmarola. be discussed he~. The volcanic products, although of diffe~nt In table 17 the K/AI and fission track age and composition have a common magma results obtained up today are reponed. tic origin as shown by the concordant The provenance of the above mentioned "1Sr/MlSr initial ratio of 0.7073 (mean value). volcanic materials remains still an open On the basis of the new datings by question which deserves further attention in SAVELLI (1984) however, the above model the furure. was somehow modified in that the «rhyo litic dikes. display a K/Ar age substantially similar to that of the other acidic rocks Concluding remarkll and therefore they are not to be considered The data here reported represent the result as being separated by a significant inrerval of almost twenty years of activity in dating the of time. young VOlc~lOic rocks of Latium with various This result is in agreement with the techniques, among them the most widely model proposed by CARMASSI et al. for the used was the K·Ar method. From the first volcanic evolution of the island of Ponza in age measurements a significant improvement a shallow submarine environment. has been achieved due also to the availability The acidic volcanism of the Ponza archi of more sophisticated instruments and pelago is thus of pliocenic age. According to techniques, resulting in more precise data, SA VELL! (1984) during the lower Pleisto as shown by their small 115sociated error. cene, starting from 1.75 Ma, a pronounced Nevertheless the general situation con break in the volcanic activity occurred, not cerning the geochronology of volcaniC! of only in the Poma archipelago but also in Latium is still far to be satisfactory, due to the emerged volcanic a~as surrounding the the persistent difficulties in dating very Thyrrhenian Sea. The volcanic activity started young volcanic rocks. aJZ.ain at about 1.1-1.2 Ma with the em Many points a~ still open to discussion. placement of products of alkaline potassic Among them there a~ analytical problems affinity (Monte La Guardia trachytic lava connected with measurements near the limits flow, having an age of 1.1-1.2 Ma, according of the method. Moreover an accurate to BARBERI et al.. 1967). sampling. i.e. an accurate selection of samples with a precise location of the sampling point is of fundamental importance, and sometimes the significance of an age measurement is hard to evaluate and to be compared with " the results obtained in different laboratories owing to the lack of information on sampling localities and location. This remark is not so obvious because we have to take into Fill. 19. The Ponza archipdallO: frequency account the variability which is likely to distribution of measured ages. occur even in the same formation. As a matter of fact one of the possible Dating volcanic material interhedded in perturbing factor in dating young volcanics sedimentary (ormationll is the often invoked presence of excess argon. Such presence is now to be considered more A number of age measurements have been than a suspect after the 4°Ar/u Ar stepwise performed on volcanic levels interbedded in heathing experiments carried out by VILLA Neogene and Quaternary sediments, mostly (19&") on twO lcucites from the Alban Hills aimed to define a chronostratigraphic scale. (VS3 and AL43). revealing their contrasting These data, together with the al~ady behaviour with respect to AI geochemistry. reported and discussed age measurements on AL 43 is the first documented case of ~oAr 92 M. FORNASEKI excess in a leucite. VII.LA (198') considers A. + 1, 5.305 x 10 HI , ' as an attractive hypothesis the derivation of ~uK 0.01l9 atom% the excess argon from the man de. The experiment of VILLA indicates also SCHNEIDER, 1965, that such excess argon is nOI homogeneously .I, 0.583 X 101l'a l distributed in the Alban Hills products and, indirectly, that the results of the conven .I. 4.737 X 10-10 .' tional K-Ar dating should be considered with 1. + A, .'5.32 X IO- IU " , caution. In this respect the accuracy in me description of the sample location SttffiS to EVERNDEN and CURTIS, 1965: be appropriate and it is worth noting that an high analytical precision, even if desirable, .I. ~ 0.584 X lO+IO , ' is not necessarily a warranty that the ap .I, = 4.72 X 10.10 ,-' parem K-Ar age be a real age. 10 1 Taking this into account it seems advisable A. + A, = 5.304 X 10- a+ to recommend whenever possible, the use of the llIlAr.~oAr dating technique this one being BERNARDI et al., 1982; BtODI1IU et al., the specific method by which me eventual 1981; METZELTlN and VEZZOLI, 1983; NI p~ce of excess argon can be direcrly COUrTr el at., 1979, 1981; RAOICATI et revealed. al., 1981; VILLA, 1984 and private comm.; At present, to keep under control t~ VAREKAMP, 1979, 1980: conven!ional K-Ar dates, a comparison with ..1... 0..'581 x 10- 10 a-I diR'crent methOOs is advisable. RADICATI et al. (I98I) showw that t~ Rb-Sr methOO ..1., 4.962 x 10-10 a-I can Ix used as a cross cha:k criterion for A. + A, '5 ..'543 X 10.10 a-I rocks as young as l50 ka. An allempt to revive the K-Ca technique for high potas iOK 0.0167 atom% sium minerals (leucite, kaliophilite, kalsilire) should also Ix taken into consideration. Similarly fission track dating technique and Constants used by Rb-S, dating also the use of the 23O'fh disequilibrium melhod deserve particular attention as pos RAOICATI et al., 1981: sible alternative methods in estimating the ..1.. 1.42 x 10. 11 a-I age of Ihe very young volcanic rocks. Acknowlcdg",..nll. - This work was carried our in t~ frame of the research programme of Ihe Abbreviations used in the Tables Centra di Studio per la Gcocronologia e la Geo Anc Analcime chimka dc:lle Formuioni Re<:enli of the CN.R. The author thanks prof. S. METZELTlN, prof. Ap Apatite L. VF.ZZOll and Dr. r. VILLA who kindly allowed Aug Augite 10 make use of their unpublished data and prof. R. FUNICIP.LL() (or helpful discussion. Bi Biotite FT Fission tracks FS Feldspar separate Constants used by the K-Ar dating GM Groundmass ALVAREZ el al., 1976; BARBERI et al., l.L Leucite 1967; BAslLoNE and CIVETTA, 1975; BI 0/ Olivine GAZZl Cl al., 1979; CIVETTA, 1984 lInd pri Phi Phlogopire vate comm.; DISCENDENTl cl aI., 1978; GA SPARINI and AnAMs, 1969; LoMBAROl et Px Pyroxene aI., 1974; MASI et 1I1., 1976; NICOLETTI. Sa Sanidine 196'5: Tit Tilanile .4.. = 0..'58.'5 x 10 III a WR Whole rock ..1., = 4.72 x 10 I" a Zir Zircon GEOCHRONOLOGY OF VOLCANIC ROCKS FROM. LATIUM (ITALY) 93 TABLE 1 Tolla, Ceri/e, Manzia/e acidic volcanic group ~ _u ArrO 1 ," • e-at_I. o-Tu 1.tIo. .. ~ 7.1. 0.6677 2•. 3 2•• : 0.2 ~ 1 "- ...... f Tolf. ~ 10.~7 D dl ••• _co " ~ Tolf. LI.....I'" -... ~ '.03 1.0717 0'.3 ••• : 0.1 s'"" ...... _... c:..e""_to Tr"""",'" .. 3.93 ,.~ " 3.71°.12 s.n 1'TOdVUc U ...I ... .. ~ 1.11 0.71" 1~.3 2 •• : 0.2 ~ , -...:, I.U... U ~ ..~ q .• : 0.2 ~ , .' L.o 0I>0nI1. ..- '.' 0 L.o Golerooce Lt_I... .. D .. ~ ,.= ~.. 2.5: 0.2 ~ '" ~ .'_le LI.....I .. '" 0" D .." 1.3512 el.O '.0: 0.2 ,. Sele,te 0 D 0.7'19 3.2 : O.~ M'... """ollte .. '.I? 10.' ~ " _Ilon'er_ """ollte 0 ~ D ..'1 0.8U5 .. 2.3: 0.1 ." ! ,,",Icelo _. leU... D n., 3.8:0.1 ~ , " .. '.M .. <:elverlo L.otlte ~ - 12.2:0.1) ~ • ,. '" 0 '.M ,.- R.' ,. <:el ...... lo L.oUte 0 ~" ~ •.51 ~ 11 .• :0.1) ~ '" ,.- .. (1) ignimbrites; (2) hyflOlibyMlllite5; (3) inclusions. .§ , :sr;;:g~t>r;;~~ll::S:S ~ ~:ll:g ~ ~~IO:S:Sll: ~ :S:l:Slii~ -l! i :g ; •• • j · - '122~iiR2lil 51 i .... "! ...... , i ~ I': 22 la SI SI i la • ., .j .,., ., .,., a .,., .,., ., • ., •., • ., ., ., ., ., i' ~' ~' ~' ~' ~' ~' ~ " ~' ;';';";'; ·, §": i' ~~~~~~~ aa~R~ ~ I I III ;; ';:: , HUi i:~ l:l~:Slil::: 1iI ll; I? III r;; 8;.: ~~ ~:g :e .. o2lilo ... , !:I I I'! ! .;.;"':.;';~ l • ti ~ ~ ~ .; ~i ;: ~~;i"; :Ul:llnliliil~:2 ,.; ~ 2£ ri ~ ~Il g ~ ~ ~ . ~ , .'l! ';0 ,J if!'" ~ 2 !!::: Ill!! 'I " "" ~- I ~:s"!~"!~ ~ ~ l~ i .. ii1::: )Il;;; ;;; Ei ,I I U ~~ ~ ; ~~ ~ !i lG 1! • i f:: .~ ..!;, K .;,; <> <> <> cici ci .;,; 00 ~~ ,; .. .. ,.; ,.; .!,.;,.; ,.;,.; ';":ci .. oo .; ';N ,; ,; ,; ..: .. .= N ~ • ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ Iil ;! :g la ll! & 8 ~ ~ ~ ~ ~~ ~~ ~ ~ ~ ~ 1~la1ll2111 " • ";::::""'~2:!::!:::::';":';";'; ~"::e:e:!! ~ :e:e ...... :!: .. :!: ...;~~~~.;.; "~ " .~ ~ .1"j~lj.JjjjS lli;;;!li" li ,,;;; j , I j IS j j ~J I , 33.!llf > o .~ ~ !. " . , .- . ,. ,- :s fl~l:l~J2o:... •• ! i ! i i I ! ;g iE i i i i i ! 2 lliiS:J Cl , , , • ! , , 'l , , ••.~ 1 - - € ; ! I l ! } I E } ,.... , . ~ ,ill , , , ... . ~ -... i ~ ~ ~ , , ;: 3 :l :l ;: , , , 1 , -~ :l ....-- - .. , !"I ~ ~ , , i ' I 6 • • :• ~ ~ lliiil i , , i j j "i'l-l ..'I.. ::. j • • , I , . I I , ' :: ' ., ! , . , ! ! i J ! ~ i , ! j j • , , , • 1 i :l ! .'l • , 'i,Lt Jl ~•! J , < , -I ,. ! u.,• • j g ;;: di "" .. .3 "I.. H • ,, I • '*:1.,.;.; , !I! ; GEOCIIRONOLOGY OF VOLCANIC ROCKS FROM LATlUM (ITALY) 95 TABLE 3 Vulsiniol1 District - Boluna activity: basal ignimbrites K·Ar dlling .ooAT -.Ill .~ WClU.ITT -~ _. U'. nd .00ATrwI r. -~ u .. 3 ..,., • 10 a u_. _~u nu ~ 12.37 L_ 30.23 ~:.2O 0 " u_ T...... I ... phD. n .~ 12.la 2.0120 12.e11 QO :. «I ",,11... " n» . 10•• L_ 30<.81 ~: 20 nD 0 '.81 ».~ lIeO :. 20 " ro"'....II. ,.- 0 ~.~ " l_t... ft III '." L= 610 :. 20 0 " -'. n" 11. 211 1.1200 2:3.11 720 :. .00 " -" n- o 10.12 3.0101 ~.M 720 :. .00 " ,. ~ . 10.001 ].l!lOl «I n" D.M em :. " TABLE 4 Vulsinian District· LAtera activity ~ MT. ~, • 10 • 0.32l& 3.'"2 145.1: 9 ~, ,.~ .. - 0.3218 1.a7 la5.3: 9 ... Dopnoo O.26lI? 6.06 1511: 5 3 .1.laU... YIII. 12 GII 4.37 .__t----I-'~---'-'---'-t_------+--_t---I_--t_-'-.---.-_t--'-,_.R__+-'-"--,,-'-+-M-I 0.301 ,., " :22 3lI ••• • 117 : 211 311 12.05 ..~ .. ,~ .....1 nux unit 0.6.... ~.M ,~ 10.11 , ' "I!.he _I.,." 0.6195 ,~ ., 1l.29 0.1266 'M 1.1511 'lux unit wl'" 16.12 ~I_ ...Ided 1.155.l 171.7'" ., n_a 'R 1$<05:4 c.v. ~ nLl.OII LITIIOIO !I-'-'+~"'---+---+---+---+--t-+--+---+----+-I g.. u I _..... t_hJ". vs 66 Sa 9.15 O."qa 13.66 190:. 20 67 ::: E1--1I----I------+-'--'-'-'----_t-'--'-1--'--'-t_-'--'-+---'---I-----t_--.:.-+-, :: a • 10.71 O.lloI50 19.11 .:; 10 " ~ 11.93 LR X.X .:; 10 M H '" 10.01 I. '3 17.13 l.tppu n ... unH. 1.1163 .:; 6. ~I __Ie_ 11.03 1.12.5 .:; 6. _ n ... _It. , u 1.0151 , ...1... _le.. . 96 M. FQRNASERI TABLE 5 Vulsinian District - Latera activity -DJ dating SallPWI P~AS! UX:'~ITY ItlnR,AL ." R~r. ~ , "" .., • • . ... al... 146 :: ~ " Plti&l1ano ~ " ~~ .. . ~ . 190:: 30 . TABLE 6 M' Gmino acidic volcanic group K-Ar dating ~~ ,~" 1/ ~~ WC>Lln ROCX 1'YP! u,. rad- • ." "~P. .. • 3 ., ... 10 • " ." . ~.~7 1310 :: 80 .- -~, quact. 'u,tie ~ 10.0.0 " .. • ut I.,.l..,r'" • ~.51 ~.' 1390 !. 7'0 .- • l_clnr , ~ '.u 1190 ~ ~ .- of Vlurbo tlpieo .uet. I .." " , .. 8.18 ,.~ V 1190 ~ ~ .- U1l6. ~ 10.97 ,,~ Po.jIlonello ,a.,quoru__I_title .. " !lAUDl ~ 10.59 lISl .. CI.lr>o (..-porl"" '.~ " ,~ " (nor"" .....,.,1 dolle .lturo • ~ 10.44 " • .- .""t.) .-!n~ !. 25 '.~ " 9\lO !. ~ ~ Ollvlne laUto ~ ~ ,.~ .., 9<10!.200 .- lA> PI,,"" rod••l In. ne- • .. (Cl_1nl'" .\.<;t.) TABLE 7 Vieo volcanic District K-Ar dating .~" I.QCJ,UTY ~,~ 00.,...... 1 • oo.~ ~. ..nRUL .. / rood " .", " ..,., • 10 • L.""ltlc Iova 15.~2 , "o<,all. ~" " .. " • !l.a 2.... ~ 211 p.,IQ C•••ll.... Tr..,"'," •• 10. 7~ " .- " •" '.00 3-<1 :: 7~ ~. "<> ,... SorvoUI no<. po..o...... ~ .0.07 '.~~ , &40 !. .20 .- (IG111R8R.U 81) • .. , ~ ,~ San Roe<;O Le_P",,"ollte 10.15 2.8. 700 !. ••0 .. S.." "uU"" T...... ~ "« ~ 10.5(1 ,.~ 820 !. .~ pOonoI. • • .. GEOCHkONOLOGY OF VOLCANIC ROCKS FROM LATIUM (ITALY) 97 TABLE 8 MI. Sabatini volcanic District K-Ar dating ~ od/ ,~U rad • " .~ ~OC~~ITT roRIIAFIOll ""TDIIAL " " rad " g •. .. -, , " .., • " . _0- ~" BACC""" 1I W. " .. Il.~ '.~ ~.' M, • " 6o.ee""" IMCUJSIOII I. TOI"tI ., - 8.'3 L~ 17.3 3:1-< : 48 01 BRAceI""" (J.) ~ ... " Qu..'ry.""". Turo CULLO 01 L~ 10.12 , =, .. 10.:1-< 370 : 70 " .....,- .. &AC>l<'WAIIO (I) ~. .. 12. I 1.35 ~. -, Cale... rd • " .." Inc."", Vole...le 10.01 ,. , ,.- ,., 2SO : 80 lBl..,.,) dl...... ,_II)l2) , '-' 0.591 " ,., 200 : 80 • c...,. "" 'W, 15.75 ,.- '3.ll9 6.0 :"XI 80<1••_ STlllTIFlCAFI SAIl ID " , .~IIICOLORI,. " '.00 0.952 '.M 000 :200 1.593 '.~ !lOO :'00 ~ Sl'OllTA '.00 , Cop<> " ...11""" " 1.556 '.M '90 :200 (BASI) = " 18.7 23.6-0 '70 :! 50 , " ,.= For..., I~ Pt...... Turo 005S0 OM~ .. 12.18 '" ''" " "" ~ SCOllIE M"BB ",", .. " ." " "" .=. 1<>1185 12.07 .. I " '" " ea...... ""lIn. ("""'OIl'" of t ...... 1I.S3 '/V"-'>r'1o C of " '" " " .1<>1175 ll.'~ ." " - I.o<...dl) .. " " Ca.' dOl Cocco .. 1l.9 " '" " 0-- ..... s...... ,. 7 - .. 12.08 " '" .. So".,,,.., .-~, , ,;s.S _. .. ll.' ... -, • " .." "o"a IIola <.0",,1 ... " 1••89 '.M ".' -..0 :! 20 " Fr",,""'. ~, II.~ ,." "., S,. :! lIorl,- .. • " .. ~, Fr""",..... _ ILl 2.M ...... " " (I) Scc also dating with Fission Tracks and -rh, Table 9. (2) Average value 225 ± 60 X 10" a. TABLE 9 MI~ Sabatini volcanic District FT and """Th dating _u .00 LOC~LITT roRIIAllOll IIOTliRlAL U~ ~ , ." .m ... • ~ ,, 177 :! _Tt cucco , , " ~ " (Corv...r'l 12? :! 's "cr~" , , " " " go:! ,a SoB 7 .~ 200 :! 100 _YE GBUT(> TUf'O G1ALLO ... MO. ',"" (iIO• ....,) DJ SACROF""" ... SOB B >~ " .~. " VOLL£ VOLCAIIIC LBVBL DELL' IH,...RNO ~" IN OIOTOOllTliS - (Ri..,.,) "(oo TABLE 10 A/ban Hills K·Ar dating ~ ~~ _11, .~ ~" LOCALlrY SAMPU; U>. 'cc" rad" Rlr. ==. " ., 3 • " . 10 • P~uet. TlNAI. " ph,..,..lc e,plool""o '" .. Covo ..,,,,,1,,,,,,,,,,. K~4<)11 ~ 11.311 = &&11 .-<.... " " ' ~., '.""Iu .ophclU ~ 17.0 , u., , • • .. " • ." " , 17.8 -2~ ~ ~ ... ! phonol1t1c topnrlto .5.3 , ."""", " • ,." '.0 242 ~ "• " 01_ lake ~ 1~.9 , ~., , , "'phrltic ',""eltita " " .. -, " 101<., n_ > ".., '_phrltlc '.",cltlt. , '1.1 , ~ 19.7 , , I low••' Ion " " '" " , ,- Divino _c. "phrltle 'o""ltlt' ~ ,~ ~ 16.07 , " .. " ; ," Divino _. toohrHlc 16.2 1.13 92.' , , ,• '.""ltit. " " " ". " > 3.25 10.5 Co;><> dl 'e.hrHlc leu (1) See Table 13. (2) Average of two values. y-speclr. 1810%, at abs. 16.0} %. (3) Average of two values: y-spectr. 7.18 %; at. al». 6.29 %. (4) See Table 11. (5) Probably from ErnlCl volcanoes. but ovc:rlying a ... pozzolana .. layer from the Alban Hills. (6/ Tulfitic limnsol underlying the or po-t 2olana .. layer. GEOCHRONOLOGY OF VOLCANIC ROCKS FROM LATlUM (ITALY) 99 T,\BLF. II Alball Hills· Tu/o di Villa Senni (1) "'Ar·"'Ar dating SA~PLE SAllPtE MATERIAt !IF-F. ~ATE!lIAt REF. '"3 '", " x 10 • " x 10 • 342 .!. 16 336 =20 ~, " ~, " .. 348 !. 15 .. 278!. 15 343 1 333 !. 22 VS 4A " " ~, " .. 341 1 " .. 344 1 25 " ~ " .. 329 1 32 332 !. 17 " ~, " " 335 1 19 " m, " '" .. 380 1 22 344 1 ~" " " " 315 1 " Averaae value froJJ leucite ....ples ~', ~., VS4B. VS5, VS6. ~, 338 .!. 8·x ,,' • 'I) Sampk'S from different outcrops. TABLE 12 Alball Hills· Tu/o di Villa Senni (J) Rb-Sr dating ,~ fORMATION SAMPtE MAT • 87Rb/86 sr/86 (87Sr/815 REF. ..,~ SrJ1 '"3 "". " '" • x 10 a Co, 1177 12.89 218.2 0.71141 , , , ,,~ 13.00 216.6 0.711371 4 ~, 372 ! 2Q " ,,~ 0.71026 ! 3 .. m 297.4 0.71029 1 4 ~ ,0- m o,~ 0.71026 !. 4 0.7108.2 !. 6 1347 ~,' 107.0 0.71078 1 6 TUFO ~~ " 0.71031 337 1 50 , ' 0.71032 1 5 " 350.5 '.0- " .. '" 0.71038 1 7 VrttA 22.7 482.8 0.112 . 0.71032 !. 3 " 0.71095 ! 3 SENNI 18.4 122.6 " '" O.71IOO! 12 ~" 0.7103713 334 !. 2Q 0. 71041 1 3 ~, 278.9 '.W .. 0.71038! 4 •• 14.1 585.3 0.05 0. 71035 1 3 (I) Samples from different OUICropS. 100 M. FORNASERl TABLE 13 Alban Hills "C. Fission Tnc and -rh daling . LocALITY fO...... 'f!C'< ,. -,. 3 ... --.. -- • 10 • flnal «Uv'''' ~o--l'''' '19.7: 0.' " Pn> <>!>,..oUe R_13~ , 1 " , " , 0'0100'''''' R_13r.A !~i ", " -- (""....,"0 R_135S , " "_13~ , " 1]L i " .""--.. ) · ....&, '~Th 67 .': 5 M lI,to••l · '~Th 43 .': 5 Hott""" _. '" • · '" n ~:. 9 " , n 340 :. 70 M. , " n ,&0 :. 30 vUl." , " n • '"-, , " 300 :. "" " n =, " TABLE 14 Hernican District (Mt. Ernici) K-At dating -0...... 011• _~ ""... ~ . ~. ~~ _- "'",,'0' ='" • • • ,0-' • ,0" • ~". .~ 13.40 '.&!oII' """:.20 '" , " , l.vn "., ...... - ." " .. 400 -'- "" " lO." 2.~"" ~, Cl~li.... -.... ._, ~, • T...... '''. 1."""". •" ... a.ale' "• " " c" c...... , ••0.....« 1O",,"'t. .. • .." 0._' ... ~, • " 0.6_ c" Co"ot. T...... "le •.?l •• =. • 1.""it'" .. • o.~. •• 'iO ::: • " ".13 ' .•eo> """'-'- ch ""...ll...... "u. ,_,,It. 1'.' .., '" •" .." 1.719J oeCI:i!O '" " , C" ..,...... t ... 1.<_1...... 1< .. • •••• 0.2'51 , .010 .0:'00 " " 2.1. 0.111" ,. 2:'0 -'- !l0 c'O Spl.....' ...... ,...... " .. • ",<>tk_ ,. .. ,. 0.1= ,., '00 -,-'" (d.... 1 .. • " ~ ,.OO O.IOW ,. 0" ..'n....'... ""...,.."....." , • '100 -'- -0 " ~ !'Of!...... "'e ...., ...... """ '0 hi...... ,...,!tIt. , ,,,, ~ ZO .. .. d" ... o.?W ".. ". ~'Ut. ... • 5.lg ..~ '0.2 0'" :!. 20 " C,· vu.'1l O••n.- U 'XI:!. JO !.otic"it. 5.0' ,!'On) '" • 0.25'0 ,.. no :!. • " ",'""""Ho 0.'_ ,.. KI:!.40 .. , ••W -(Por!) """""' ..." ....a .. • ,.. "'o:!. 60 " ...... ,,_ ..- t.-Itle '.oolt". , 2.'- _:!.zo .. 1!'Or! ) ,,' " .... "." 2.~1 :t"1O:!. .., Cl..., , 0.0'" ,.. '''H•..,~.lt .. • ,., ._- .. • ,.. 0.'_ "o:!. eo " -o .§ ~ ~~r!r!r!r!r!tr!r! r! I ~~ttl :::::::::~~::::::1:1:1:I!I!I::::::~ I ~ .. ~ ~~~ ~ , ~ ~ :!:: !:; : S 3!l:!::~t:!:: ~ " "'''' , o 0 o 0 0 0 '" 000000 •••o 0 0 .~ ~ tl ~ ...... ,...,.,., -: -: ...... -: ~ -: ., ., . ., ., """""01 ., • t ., v~~, """" .. 4; ~ ~ -ll ...... ~ , , , to .. ! ... v .. :si • ~ ": "! !:!: g • ~ : 0 .. VVVV V o 0 .. ,.; ...... , .. & • ~ •• • •• • •• ~ i} ~ oi 5 ; Jl ::l ~ ~ ~ 1Il r.:: lC:~'i~::i~ !3 51 : . ., " .. 000 - •..... J g"L .,., 'j ,> ~ ::IlIl-c'': .. 1l1!l , , ~ ilil .. ~ ill 3 :!:: ;;: ilil I!' :::: I : ":'" ~ J : 00000000 , .. ..-: ~ .,; .,; .. .. -:.,;..:.:.: •.. •.. .. v v v v v 5 , c c . ~ ;;:;~!lll . ~ • lilQIl:'.~1!13 , , ~~~~~~~t'!·~~~~I~~ ~ c .. ~ .: ..: ..: .,; .; .0 , ,,; ,,; oi .,; ...... '" ...... • ...... • .. • i ,I ;: ' " ~• • " ~ • ~ " 11111;;;;;; I I .:! !Ii ;;llllj~jllllllll ~ ." i •• • '"-."" , ! • u ." " , ." ", ~ ~'" l' n.QUi § i I .... • ~ , . - , '~l!l~~!lii~I!~. ....~'" 1 ~ • i "'~"~lll~~" ! ... ~ N •N < , < C . o "o ~ ~ = I > ! i i I , '" ~ ~ ~ ~ • '" § ~ ~ i ~ ~ , ~ ~ ~ i ::: i i 5 tI t t ~ ~ ::: ; .f; ; I I..I ? j j j ~ n I II 11 1 Illl 1 H 1 ! HI i li i i i % ~ l • o ! . • I . 1 j I I I L i I : , I , I G ! ~ 0'1 ' ~ji!GG~ , 1, I . ;; ::: : ,I I ! l. I, :1:1 ! . , : , 1 I , , : j:I~jj , I • . , 1H I I _ , • ~~":oi~ . - ONUUS INUOJ.NilA ,,~ ¥10UII1Yd ~ 'I ~" 102 M. FORNASERI TABLE 17 Volcanic level interbedded in sedimentary Imits K-Ar and FT daling "",,-,n STRATICRAPHlC POSITION u=~ ~. """"" ""'." • . , Marco SI_ Quarry VolcanIc l,.."d 1nterbed Co..chl"no Volc..nlc level ove..lylna a l ...." 3.85.:.. 0.5 4,23 Viterbo Middle PlIce.,n" ch)'. " REFERENCES 1) ACCOl1ll B., ANGllUCCI A., SlllNA G. (1967) niSfflo p/~isloce"ico del14 MediI V.J/~ uli". Nou ,Jluslr.tiw ddt. Gut. Geolo,ic. d'lt.Ji•. (Luio). C.rillteristicht ~/rogr.fidx e ttolo Fodi U9-160, Frosinon~ ~ c.mno. 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III EUG Mcclinll, tera con riltrimtnto td modtllo tii di!trtnr.ia. SttllSbourg IAbsltaClJ. :iont pt, criSlaIliUiI:r;iOf/t! Irar.;onaltl. Pcriodico 9') VIOLA C. (1896) . OlItrvar.;oni gtolof,it:ht ItllIl" di Min., 38, 625-654. nrlla Vallt' dtl SattO in ProlJi"citl di Roma I" Ri) TRIGILA R. (1%9) - Sludio gtOpelrogrtlji(o dt/ studio pt'lro1.rajico di a/cunt rOttt. Boil. Com. crJmpltsso lJulcanita di Lltertl (Vu/cani Vulri· Gcvl. fhl1., 17, 4-3'. lIi). Nota l: Le lJulcaniti laliliche dd medio 96) VIOLA C. (1899) _ Mine,alogische /lnd petm· cor1O dt!! F, Olpeta. Periodioo di Min., 38, g,,,phischt Milftilungen aUI dem Hernilecnllln· 1"·220. de in der PrOlJin:r; Rom (lta/itn). Neocs }llhrb., ~R) TRIGIl.A H .• FERK(NI V., Co7.7.UPOLl D. (1971) 93·137. . Sludio g~~lrog'4e-o dt!! romp/tU/J vu/ami· 97) WASBlNGTON H$. (1906) . The Roman co ro JI Lltt'rll (V/lit"41ni Vulrinj). Nolo 11: Lt mtll-matic 't',,ion. Camegie ImailUtlOn, Publica· Urlt' pirQt;l"slica di Sununo Ira if f DIMI