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RENDICO~'l DELLA SOClET... IT.... LlA:"A Ol M1NER .... LOGIA E fETROLOCIA, 1985. Vol. 40, pp, 11I-J:H
Radiometric geochronology in Tuscany:results and problems
GIORGIO FERRARA, SONIA TONARINIIstiluto di Geocronologia e Geochimica IsolOpica del C.N.R., Via Cardinale Maffi 36, 56100 Pisa
Dipartimento di Sdenze della Terra dell'Universitil, Via S. Maria 53, 56100 Pisa
ABSTRACT. - All the age data up today publishedfor the Tusc:an rocks are presented, together withsome unpublished ones. Age results of the youngintrusive and effusive rocks of the tuscan anatecticprovince show often excess of ....Ar,. and strontiumisotopic disequilibrium among different minerals ofthe same rocks or isotopic disomogeneity amongrocks of the same intrusion. These facts easilyevident in very recent rocks, can be obscured byaging, but can be the source of errors also In
determining the age of old rocks of anatectic origin.
Key words: GCQChronology, Tuscany, Isotopicdisequilibrium. Anatexis.
RIASSUNTO. - Tuni i dati di eta sino ad oggi pubblicari sulle rocce della Toscana ed una serie didad inediri ven8ono prescntati e oommentati. Idati relativi alle vulcaniti e alle rocce intrusive dellaprovincia analenica toscana meltono in evidenzala presenza di "Ar'd in eccesso e l'esisrenza di dise·quilibrio isotopico tra fasi minerali e rocce lorali.Questi due fani, ben evidenti a causa delle eramolto basse (2,5-7,3 Ma} dei prodoni della provinciaanatenica toscana possono essere causa di erroreanche in rocce piu antiche aventi la stessa origin.:.
ParolI' chiave: Geocronologia, Toscana, Disequilibrio isotopioo, Analessi.
The Paleozoic basement
According to PUXEDDU (1984) the Palaeozoic complex of Tuscany is composed ofthe following informal suatigraphic units:1) Permian breccia and red sandstone;2) Carboniferous, slightly metamorphic lithicgreywake; 3) phyllite and quartzite of theButi Group, partly of Upper Silurian.LowerDevonian age; 4) quartzjte and phyllite ofthe Filladi Inferiori Group of probable Si·
lurian age; 5) micaschist of the MicaschistGroup and gneiss with thin interbeddedamphibolite levels of Lower Palaeozoic tothe Precambrian age. Another unit ofuncertain stratigraphic position is the Boccheggiano formation, of probable Silurianage showing petrologic and gcochemicalanalogies with formations of both the Budand Filladi Inferiori Groups (PUXEDDU et al.,1984). Radiometric age determinations areavailable for the phyllites and quartzites ofButi Group (BORSI et al., 1966) and fromsamples of micaschists, gneisses and amphibolites from deep wells in the LarderelloGeothermal Field (DEL MORO et al., 1982).In the first case the Rb/Sr method has beenused on total rock samples (table 3), in thesecond one both Rb/Sr and K/fu methodhave been applied on separate minerals(biotite, muscovite and hornblende, tables3 and 4). The total rocks isochron ageobtained on the Buti samples (285± 12 Ma)represents the age of the metamorphism ofthe sediments of Silurian-Devonian ages.Mineral ages obtained on the samples ofthe Larderello Deep Wells cluster in therange of 2.5-3.7 Ma revealing the existenceof a Pliocene thermal event to which theorigin of the field may be attributed; onlya muscovite yields an undisturbed Hercynianage (285± 11). .
Another series of Hercynian ages hasbeen obtained by EBERHARDT et aL (1962)on some samples of the allochtonous granitesof the «argille scagliose» complex (table3 and 4).
112 G. FERRAR .... , S. l'ON .... RINI
L.goTr.sime
M.Ami.t!
~"... "R.dieofani
On ~
"
SIENA
o
~ G.
4 • "F1RENZE rr:o. VR
0
§ ,....) ,~ n.
• no
0 "'Km0 ,
- "
"",,~'t.. i.<\Sgl
Roeeaslrada
M.Argen.tario
GROSSETOo
..,
Gigl~
~'Pisan;
prSAo
•Giannulri
•
,~
Monteeristo
LtVORNO
~"'., ..
:':. . .
<}Pi.nosa
Gorgonao
C.prai.
o
Fig. 1, - Map of Tuscany showing the localization of the considered major units.. Ca "" tuscan mCIl\.morph!c rocks; VT ~ tuscan mag~a~ic province: (vokanites); VR "" roman magmatic province; y "" gra·no,ltorncs and granites; ':lll "" aCIdIC sub-volcamc rocks; r.b = basic sub-volcanic rocks (from BARBERt et aI., 1971, slightly m<Xiified).
The ophiolitic complex
In Tuscany the ophiolitic complex can befound in the Toscana Marittima and in theElba island. The ophiolites consist of ultramafic rocks almost completely serpentinized,submarine tholeiitic basalts often spilitized,pillow lavas, hyaloclastites and minoramounts of gabbroic rocks and dykes. Inthis assemblage of rocks it is impossible
to use the Rb/Sr or (he V/Pb methodsbecause of the extremely low content of theradioactive isotopes of these rocks; it isalso difficult to apply the K/Ar methodbecause of the alteration and the metamorphism (l). The only possibility is to use
(') T<Xiay the Sm/Nd meth<Xi has been successful1yapplied in the age determination of ophioJiticcomplexes (DE PAOLO "" WASSI!RBURG, 1979) alsoof very young age (ZINDLER et al., 1982).
RADIOMETRIC GEOCHRONOLQGY IN TUSCANY: RESULTS AND PR08LEMS 113
the zircon that can be found in very smallamounts in some acidic differenciates thatare scarcely present in the gabbros of theApennines (MARINELLI, 1964; BARBERI etal., 1971). Zircons formed in this kind ofrocks must contain relatively small uraniumamounts, and are suitable to be used forthe fission track method of age determination.BIGAZZI et al. (1972,1973) have successfullyapplied this technique on some samples ofthe Northern Apennines obtaining results(table .5) in good agreement with thegeological knowledge.
Apuan Alp!!
The Tertiary metamorphic event that theApuan Alps have o:perienced has been datedby several authors (GJGLIA & RADICATI,1970; KLIGFIELD et al., 1977) using theK/Ar method on muscovites separated fromthe metamorphic rocks. The firSt quotedauthors have found two groups of ages(14 Md and 11 Ma, table 6) while KLlGFJELDet al. (1977), report also ages of 26 Ma.Unfortunately we did not find these resuhspublished anywhere, but only as abstract(V ECOG, Pisa 1977).
The rock.8 of the Tu.8can anateelieprovince
The problem of precise dating on veryyoung rocks is still a difficult goal for thegeochronology' because of the small amountsof radiogenic isotopes to be determined;besides this general fact, there are severalmore complications when dating anatecticrocks as those of the Tuscan province. Theanatecdc origin of the Tusean intrusivesand effusives has been proved on petrological(MARINELLl, 1961) and isotopic (FERRARA,1969; TAYLQR & TUll.I, 1976) grounds andthere is no doubt now that these rocks havebeen formed by (partial) melting of crustalmaterial (Tusean basement of Hercynianage). Theoretically the main causes of errorin applying the various methods of agedetermination can be briefly synthetized asfollowing:
I) K/AT m~thod. It is possible to findexcess of radiogenic .0Ar due to un-
complete outgassing during the mdtjngof the old Hercynian rocks. Also if theamounts of .0Arnl can be very smallthey are likely to influence young agevalues, expecially in low K minerals.
2) Rb/S, method. Partial melting of rocksof acidic composition can generatebatches of magma with disomogeneousSr isotopic composition thus ptecludingthe use of Rb/Sr for total rock isochrons.Besides this fact, the magma generatedby the partial melting can be a mixtureof minimum melt and different prOpOrtions of restite, sometimes representedby common mineral phases as plagioclase,biotite or cotdietite; this fact willproduce .rocks with isotopic disequilibrium among coexisting mineral phases(FERRARA, 1983) thus vanifying alsothe use of internal isochrons (FERRARAet al., 1977).
3) U/Pb m~thod. There is the risk, usingzircons (the only suitable material) thatold zircons not completely resettled tobe present, and also in very smallquantities, very young ages can beseriously affected. Fission tracks on glassand, when possible, on zircons, isprobably in such situation the besttechnique to use, but this method canbe sometimes not so precise as the abovequoted ones.
Concluding, extremely care most be takenin the interpretation of data obtained inthis kind of rocks and when possible different methods have to be applied in orderto have more meaningful results. Date up tonow obtained in the Tuscan anatectic rocksare presented together with 'some new ones,unpublished till today.
Vo/canit~s
The radiometric data up today availablefor the vokanites of Tuscany are reportedin tables 7, 8 and 9 according to the differentmethods used for the age determinations.Some samples have been measured with different techniques and it will be wonh tocompare and comment the obtained resultsin the light of what already written. For twosamples of Roccastrada and S. VincenzO wehave results by the K/Ar, Rb/Sr and Fission
114 G. FERRARA, S. TONARINI
SV 77- 3
--------------
"'Rb/"S'0.112 '--~----:~-~-~:---~~---:~-~----c:--~''--~
20 '0 210 230 250
Fig. 2. - Nicolaysen diagram relative to separated minerals of an acidic-volcanite sample from ~. Vinoccnzo. The existence of restidc phases with initial isotopic composition equal to 0.719 (PI = plagioclase;Co = cordiceilC and Bi = biodte) and phases with higher initial isotopic composition (0.725) whichrepresents th" analc:ctic liquid (Kj = K.fcldspars; RI = whole rock; VI = glass) have to be nOled. The(WO groups of minerals define two parallel isochrons }'ielding (in the error limit) two same ages, thatcorrespond 10 Ihe vokanitc cooling age (from FERRARA. 1983).
Track methods. For the sake of clarity resultsare compared in table 1.
For the Roccastrada samples the resultsby Rb/Sr and FT. methods are in agreementwithin the limits of the error (that is largein the case of Rh/Sr due to the very youngage of the sample). The K/ Ar result issignificantly lower hut we must point outthat a different sample has been used forthis measurement. It is important incomparing age results obtained by differentmethods to use the same sample. For S. Vincenzo there is a good agreement betweenthe K/Ar and F.T. methods, but Rb/Sr onbiotite is much lower than the other ones.In order to understand this difference aRb/Sr study on separated minerals was carried on (FERRARA et al., 1977) showing theexistence of a disequilibrium in the initialSr isotopic composition among the differentmineral phase, thus precluding the use of theRb/Sr method on biotitc-total rock (fig. 2).
Another comparison can be done with theM. Amiata samples that have been dated byK/ Ar and FT methods (tables 7 and 9);we cannor repeat here the comments onthese data, that can be found in the paperby BWAZZI et al. (1981), but we want tostress out the existence of excess of ~{\Arr"
in biotitcs; the isochron method in this case
gives good results showing also that ~\lAr<" isnot in excess in the sanidines, that represent,due to their high K content, an usefulmineral for dating very young volcanic rocksby the K/Ar method.
Volcanites from Capraia island do notbelong to the Tuscan anatectic provincebeing of subcrustal origin (FRANZINt, 1964;BoRsl, 1967) they can possibly be linked tothe calc-alkaline volcanic activity of Sardinia(BARBERI et al., 1971). The few K/Ar dataavailable (table 10) are from BORSI (1967)and PIERATTtNI (1978). The two authorsgive different ages for the onset of theCapraia volcanic activity (placed at 95 and8.26 Ma); the same discrepancy exists alsofor the end (4.8 and 2.65 Ma). Furtherdata are necessary in order to achieve abetter definition of the time span of theCapraia volcanic activity.
Intrusive rocks
The Elba granodiorite, which covers about42 per cent of the island surface, is the mostimportant stock among the intrusive rocksof Tuscan magmatic province. Numerous agedeterminations have been carried out on theElba samples by the K/Ar and Rh/Srmethods (table 11 and 12). We can start inanalyzing the K/Ar result beginning with the
RADIOMETRIC GEOCHRONOLOGY IN TUSCANY: RESULTS AND PROBLEMS 115
western Elba (M, Capanne granodiorite).Together with the already published resultsof EBERHARDT & FERRARA (1962), EVERNDEN& CURTlS (1965) and BoRSI et al. (1967)we report here the data that BORSI & FERRA RA presented at a congtess (1971) andwhich have been available, up today, onlyas a summary. If we put together all dataon the biotites of M. Capanne granodioritewc have ages between 7.0 and 7.6 Ma,except two low values of 6.4 and 6.7 Ma.A very large sample of M. Capanne biotite(ST£ 74) has been prep:ned and measuredseveral times in order to be used as aninternal laboratory standard (VILLA, 1978);the mean age value (on 24 runs) is 7.3 Ma.Taking also into account the data of table 11we can safely assume for the «apparent»K/ Ar age of M. Capanne biotite a value of7.2 : 7.3 M.l that we can use to comparewith the Rb/Sr data. Before doing that wewill also examine the data obtained on dykesof aplites of M. Capanne (table It). In thisC<lse the data show a big scatter rangingfrom 6.8 to 14.8 largely in excess with anypreviously published results. This scatter isinterpreted as due to ~OAr"j in excess. Tofurther testing such possibility BoRSl ""FERRAltA (1971) have carried on K/Ardcterminations on separate minerals of agranodiorite s<lmplc of M. C;lpanne.
The apparent age results (table 2) clearlydemonstrate an excess of ~oArrol. Due to thescarcity of suitable material, a minor numberof K/Ar data are available for the centraland eastern Elba. Some data have beenobtained by BORST & FERRARA (1971) andmore recently by SAUPE et al. (1982). Generally ages lower than M. Capanne oneshave been obtained: from 5.7 to 6.2 Ma(BORSI""FERRARA, 1971) from 5.1 to 6.1 Ma(SAUPE et aI., 1982).
In table 12 all the Rb/Sr data arc gatheredtogether ·including some writers' unpublishedresults. The 1961 and 1962 data representthe first age results obtained on Elbasamples by the Rb/Sr method and are tobe considered affa:ted by a larger error thanthe recent ones produced by VENZLAFF &
WALDECK (1971) and FERRARA & TONARINl(in press). The comparison of the Rb/Srresults obtained by the differe.'1t authorsfor the M. Capanne granodiorite is puzzling
because the mean value of 5.3 Ma (recalculated from VENZlAFF & \'(1ALDECK,1971, with = l.42· 10. 11
) Sltongly differsfrom the value for 6.73±0.04 and 6.88±0.04 obtained on two granodiorite samples(using the isochron method on separateminerals) by FERRARA & TONARINI (in press).In any case the Rb/Sr data are lower thanK/Ar ones, thus confirming the existence ofa ~tlArr'l excess.
Besides the Elba island, other intrusiverocks have been found In the Tuscanmagmatic province; the most important arethe granites of the Giglio and Montecristoislands and the Gavorrano granitic outcrop(fig. 1). A few kms from Gavorrano on alocality called Tor di Pierra a hidden graniticintrusion has been found (ARISl ROTA &
VlGHI, 1974). The few K/Ar data availablein literature are presented in table 13tOgether with some unpublished results. Thedata from Caste! di Pietra granite are quitediscordant and only one has a value doseto the nearby Gavorrano outcrop (which isvery likely coeval). The other two samples,showing higher apparent ages, can be affected by an excess of ~oArrd. Rb/Sr agedeterminations have been also carried on thesame rocks (table 14). In the case of Giglio,Montecrlsto and Gavorrano they agree withthe K/Ar ones; this is not the case forthe Caste! di Pietra samples, that give lowerages (BoRSI et al., 1979) close to the Ga·vorrano results.
Nothing more can be said from theseresults because they are very scarce, butagain we face with the existence of 4°Arrdexcess which seems to be a common featurefor [he Tuscan intrusive and effusive rocks.Rb/Sr data for Montecristo and Giglio showthe existence of an isotopic equilibrium forthe 81Sr/86Sr ratio among the coexistingminerals as reported for the granodioriteof M. Capanne (FERRARA &. TONARINI, inpress). This is not true for the Castel diPietra samples in which an isotopic disequilibrium has been found (FERRARA, 1983).Concluding this critical examination of theage data for the rocks of the Tuscan anatecticprovince, we can remark that both 40Arrdexcess on Sr isotopic disequilibrium havebeen frequently found. This finding, thatcan easily be evidenced on very recent rocks,
116 G. FERRARA, S. TONAR1NJ
can be obscured by aging and can be sourceof errors also in determining the age of oldrocks of anatectic origin.
Acknowlt!dgemt:/IIS. _" The authors would like topoint DUI that most of the unpublished aatll rq:>ortedin this paper were obtained by their colleagueand good friend Pro£. SERGIO BoRSI, whose researchcat.:et was abruptly ended by his untimdy departure.
R.occutrad.
s. Vlnc.nao
TABLE TABLE 2
"" Rb/St F.r. -- - .- n ''''-~~_ ...
2.3!-0.2 '-' !.C. S J.2J.:!:O.2J -- =" • '." 2.14,·tr • ,.,4.7!:O.14 3.26=0.15 4.U:!O.)7 • 'O.W J.563·,r n ,.,
" '.m 2.:Ill"'O'"' " 17.t
• 0." 7.~·,0"'l " 0.'
TABLE 3
RbjS, analytical data ~ Paleozoic basement
~_<'Q \"l',to • ,~ ••• •• .81$ .m '" !:16P~lo ~....lto
" on ... ~ 2.701 .m ,. , '"'.!luti g......, qu"W" 'n • '" 51.8 '.n .743
"lHt.!utt ;""'1' qu,rt>tto •• • '" '" 1./1 • 71' •7121It.50ti gr<I<Jp q...."tto
'" • 'n m ,. .715 .111Ht.aut1 q.....~ qu.",it. •• • '"
,.. '.55 .,. _711 ,..",-aut, ~""'p ..... '"it. ... • '" '" ,m · 71' .112Ht.Buti ~""'p qu"",.. •• • '" '" 10.l ... .712Ht.Bu" ~""'P ..... 'uit. •• • .. .. '.' ... .711
ss 10/1 • ... .., l.n .n6l
"!«,dll ... "", • ~ '" · 7<11 ,.~11
"",h... froo_ SA 15Cl • m '" 3. II .mlwell. ul"'Clorol1o • ,. .. •• .1l31 1•• S!. I
",. ,.. U8.1 .,,. ,
~ 0.8U. • .. '" • ./U8
",. ,. 351.8 .m, 6.1.0.7
SA lS:lO • ,. ,. Z.11 .nl1.. .., ,.. ,.., .716Z l.l:!. 0.2
",.."M,t< s.,.......no ..- • ,.. ,. 1.3' ./111.. W , 6ll.3 .,,. 3_l:!. O.l
$A '018 • '" '" I.SS .,,... '" U 509.1 .7"1 l.l~ 0.1
$A n'l • ,.'" ,. .7316.. 'n ,.. lSO.8 .73'1 .6~ C.l
TA8LE 4K/A, analytical data . Pafeo:;;oic basement
loc' tn. ~1. n. ""tr,,1 " 00..... r<l .1/, teAr rfl ... ",.
Ill. fr"co ... ,,,n' .. • ,. 8_13'IC-~ '/.8 n, ~1C •_CO , ...., .. • ,., lD.Dl·IC·S 9/ .• ,.. ~IC •
• .., '.".'0-S 9/.l ,.~IC •
PI'<'9OI. ,,,.10. .. ••• 6.U·W~ "., n," •.- • 8.10 11.Il·IC-/ "' 1.11~ .0 •.. ,." 8. JIl. 'C·/ "., 1.1I~ .•.
1Il"",M", ."" ?O"'" """ .. 1.16 '.78·W I SI., 3.50:!. .•.f_ ....p ..I" l."", ...110 ... .. 1.01"0.1 15./ 10.J~ .21 •
"- .. /.3S '.36·IC-7 .. 3-to.!. . '0 •
S5 12'1 .. 1.69 6.78.10.7 1/.1 1.fa:!: .06 •
<00""'" • 'I" ~.10·'0-'C,.T, '.. .~'IO"'O,.,",' '.96·W IC,·I '.. •~1·1O"1Oy-l, ~~. ,. 11·10"
RADIOMETRIC GEOCHRONOLQGY IN TUSCANY: RESULTS AND PROBLEMS 117
TA8LE ')
FISsion Iracler dala . OphiolillC complex
., .,• <V~
-~ ~l••. Illte.I.1 "och/'" tr"UlcJ ...'...,.,.,.! • ~.(t.ach) (,."to) ,_..
'I" ''9J10 C'proI\O
'" " ". IZ'S s.l-I01S lU,:."lll_)
L~I "-10 Co~ .. " '" •• S.l·10 a lU,:.ll(LI_J1»1 Ill. _11.
" '.l·1015 111:.U(U"J
~ l.l·1015 ,....10 .....11..
" 1.)01015 lM,:.n(_.....)
" l.l.l0IS 11.&:."
~ l.l·1015 "'.LOI S-1..
" -"'1015 111,:."(LI_)
lDI ••",llo ,. •. 1'1015 17O,:.n(_..)
lOI 11.,. 1
"1. )'1015 "l!.ll
LOT 51.... 11 " 1.3·IO"IS lts:.tI
1»1 • I..-,.Ill< I.......otlc ~I"_tl.te
_.,v..... f', ..,.o. ,t.ld.
,..•
TABLE 6K/ Ar analYlical dala . Apuan Alpr
~.~ ~1. ". IlIte.I.1 " 00,.,. r<I .11t .... ~ ~.
....1 ..1... _1. • •.n 1.11·1~ ., 11.0J.l1.lO""4 • 11.3
....1 >dIt<........1. • • 1.11 r.J1·1~ n n.rlit......1.....1_ .....1. ., • '.K 1....lr • IS.rM. ~.....1_ ....... .. • ,." 1.11'10"' " IS.JM. ...,10....I........1. ,0> • S.•S 1.61']0"' " "M ~h....1........1. ". • ,." S.t/·10·/ n ". SM. """I.....1...."~l. '" • >." I.SIo10·1 " 11.1., .....'1.....loH ...... 1• ". • '.0 1.11·JD"' " ""t. I""f.....I'" ...... ,. '" • '.10 1.8'10" " lS.lCI,.llt .. (Co....... ) "' • ••• 1.D·IO" " 10.'Sdltlt (5,",,_) 0> • 1." 5.10-10.1 .. 10.1
........ , ••••511·\0"10.,.-1•••••. n.lrIO.,·I,~•• 1.1'.lr'
118 l; FEltlI.ARA, S. TONAIl.INI
TA8l.E 7
K/Ar analytical dalo .. Volcanic rocks of TUrcUI1 anateetie province
-~s..l••, "'ten,1 u 00".. .....1/, .... ~ _.
1IIo<u...... "".110- ... " •. u 6._10-7
" U ~_7 0 •n. " ...... ...,.11.. " '.R I.US-lr • 0.' ,:..•1 •_,...,10\ .1_.. " ••• l,m.l0-6 • .., ,::.13
tooll.-"., •.....,....1\ " •. u J.(IlI.lr .. ." .:: 0 "".IIai... _t.. .., • •.U • .'lO!. 0 "11I.. IIoto.. Go-l,'I .. ''''1'1_1 • '.11 1.1»010-' .. .~_0CI'i' ",10.. f.ll .5~·W7 n .2130..011 •
" •.u ,nl'IO" • .~.110 •
" .. • UI.IO· I
" .~.1I' •lit. ,,"IoU DHoti.. ..11_11 • 10." 1.003· Hr' " .1'1,::.001 •
,10.. 1.11 .5".10.1 • .~.DI'.
" .... \.2"'10" " ,'13,::.041 •
" ." .1»'10"' " .611,::.0% •
~•. 1'"01' 0.·1011 .._..
• \O••J l.nl·lo· I
" .1M.:..OOS •
,10.. .." .6O!i·W' • .111':"~ •
" ,." 1.119·1C" " .3/].:..011 •
" ... .1W·W' • .'96.!..D1S •u. ...t,t> a.-lotl" Ml1-11 • 10•• .8lI1· 10'/ " .200.:..010.u. ....10.. 0.-1.. ,.. ""1/-10 • '.R .'0)'10-1 • .11<J:!..00l •
" ...1... 0'-1"'" "'11_11 • 10. l' .136.10-' " .~.O10.
u. 1rot1 ... 1).1_10"'.• *11_11 • •.u 1.111·lo-l " .~.Oll •
... ....1... 0<-1"1" *11·2. • 10.• 1.ln·10·l " .t8S~.01••
ott• .-1... or·I"I.. *11·ll • 1l.OJ 1.01(1-10-1 - .f"~,OO'i •_..", •• ~ 0 s.•. ,rllr', ' •• _.n·lo-'o,-I; ~l' l.lt.\r-••~. S.ll·lrll,.-l, '.' _."'·'rlo,-', OOK!lo 1.161·10'"
TABLE 8
Rh/Sr analytical da/a • Volcanic rocks 01 Tuscon ollouctic province
~1••. "'torlll "- .,.
". it""o",. o't\rOlt .. nn·l • ~ ,. '.5~ .l1S4.: I.l~~ "" ., 0.0/ ,.. .lJllI!:lO 1.Zti~.2S
Il>x<on,..,. "'¥OIl •• ., .. ... .. l/.l .1lM~ I ./~~~" •• .., •• .1St5.:'" 2.1 ~.S
KADIOMETRIC GEQCHRONOL<XiY IN TUSCANY: IlESULTS AND PROBLEMS 119
TABLE 9Fission /racks datll . Tuscan analecl;c provinu
" .,• "'~
~. ---.,.. S-I••. lIIun.1 _w'"' "'....". -'"' • ...1. ,.. ~.IV""") (vac") _. -- -* .. ,to1*
$O.ft_ ,1...,~ ..- D.Il·ID'S ••• ••• '.M !!l.ll ~ • '-' .._It.. (SUJ '~l-- •• ,t... ,- ,,- D.I:l·ID'S..,.,ltu (qlJ (rIMJ ••• ••• Ul !!l.n ,. x ..,
lit......n. 0> ,I... 'm .- r.ll·loIS ••• ••• O."l !!l.1lS00-1..1.. (11i) (IM) on .. '-'M. MI.u 11-1 ,I... on .- "o,,-I.'t .. (lOll) (Im) ••• 0.1" 0.1I7!!l.OU ,. x •••llt. lilt... 71_1,.1 ,I... ... -o,,·lottu ,m, (101.' ••• 0.11 O.U1!!l.OSl ,. .. •••M, ........ 77-1,..1 ,1... ... - •• O.J17 O.UO:!G.OS' ,.o,,-lutu '~I ('7lI1 .. •••lit, "'t... n·to ,,... ~ .- ••• O.lno·-latt.. POI) (Ino) O.I~.OZJ ,. X •••M., IIot ...
1/·11 !I"" '" - •••QJ-latn. (40) (Ull) O,l~ O.~,OZl '" .. •••Mt. "'t••• n-!!-I !I1... "' ..- ••• O. I.l .. 11O".on '-'QJ-l..IU POll (1001) ~ "M'. ",t.,. n_!!_! !I"" ~ ,,- ••• O.lllOI-l..n. POll) I~I
.. IIS!C.OZ~ '" " ..,",,"~It
,1... O.S9 !!l.0ll "~l ... t, .....
S'. ,t .......
" ... U1S 1.' "0"
u~.,rlIl'OltuElk , ...It.. " ~ 2101 1.2 " O'S " :.1.S
........11: r........ '.IS.l011,-1: 2~.•• S.er.IO-n..z, Ulu/2J5U.1]1_.
TABLE 10
KtAr analytical data - Capraia island
~, .,..
L.,tu
OI-l.,tt.
T..<~)'b "
'rocllyt> "Tr.<llyt> lt
....lttl< fl..
S-1••. .......tol .. so,.. nl .IIt-~
0" " S.Sl 1.1"'10"' •0" " S. ,. I.S:l6·wli X
on • ••• 1.13e.l0-1
"". • 1.10 J.2i4',0-1 ..on, • ,.• ,.,on • " ••• l7.'
~. •••
,. S :..1 • ..1. I :..l ••. , :._ 1 •• .• :..1 •r.6l:..IS, "•.~.ll.
.. ', ••. n·'lr 'O,-l"'. S.BS·W H,-l
SOIvl • 1. ,.·10-'
• '0 ••. n·1O"'Oy-1ll. S.•·lo- lI,-1
«lKfl.1.n-IO"'"
120 G. FERRARA, s. TONARII'II
TABLE 11
KfA, analytical data . Elba is/and
-~,,-1••. lllltoo1'"t,1 D iIOAr .. _UI "" ~ ~. ~.
*'~ ... (11)0
~ttU "5.>;. .• _ ..
Go""OOlt.dU .. 1.6;. •••
Go-.. tu " ". .. '.M " ••• • ,...... Ito .. ••• z.on-Io-' " P;' ... "",,_t••u. ( lOll .. 1.1. l.on.IW' 1.2;. •"'..... t.rlto [ 1011 .. 7.2. Z.!M·)O·' " ••• •Gr.... tanU •• .. '.D 2.111-10-' " • •_t...tu ." .. .." 1.""-10-' • •••" ....1...1... ." .. ... l.tJD.lcr' • ••• •"_Iw1"~ " .. ••• 1._·1cr' • ••• •ir_t.n..~ " .. •.n 1._.,0-' " ••• •..ltU
• q • .... 1.IWl-lcr' • n.' •"lIlt 'D • .." 1._·1,", • ..".t..~ .. .. .." I.•HO"" • ••• •.loIlttot M • '.0 1.tiloli·l~ .. IU •.11" ••• • .." l.m.1O"'6 .. \6.' •""lie. W. • Ul I.l4l·10" .. 12.' •c.,rol 11100,,_tt.~ ·" .. .." 1.looIIi·1l,..1 .. • •" ..tU ..".".,. ·... .. '.H 1...~·Hrl " .. •IinoIU _'I ••• .. ••• 1.911.10.1 • ••• •.... IiU [.~A • ••• 1.116·W' .. ••• •""11 t. " • l." .•'10"' .. .. •bU.... [It>o
0.--....1.. m .. .., )1;1'10"' • ••• •111--..·1.. [0 Zb .. ••• 1.'''·lIr' .. ••• •" ..tU ......,..,..,. ... .. .." 1.'10·1Irl " ... •_t..~ UD • 11." 2...·11)-4 " ... •Cnoot ..~ U. • 1I.1t U18'lcr' " ••• •,.11.. [11.1Ho • 2.1S
••__ 1.-1 II.S S,l;. .•• n,.ltl<> 111.156 • ••• l.lV·\O·1 " I. I!. ., •
""ltU '" • .., f.'ISt·HT' ".. 9,l::..' •,.11.. ". • '.0 1.-.1...1 • 4.1!..t.
!<OIl" ". • .." 1'.Cl .,,-1 M 5.1!. .f •
"'".. .. • .." ,.M·I...1 10.l 6.':.,1.....It.. ". • .." A.611.I... l ~4.~ • !..t.IloH.. ... • •.» A.lI1.10-' 16.6 i.i,!. .f •..........1... ". • t.rl 5.600'10'"' " 6.6!..t.
kOh' $ Ih • 1. II l.tet·l0-' " 6.'!..t.QO_,.,I.. f ~.I6b • '.0 B. '>111.10·' ,. S.,!. .6.
0'''''''''11. [ ~.11 • I. '1 '.111'10" " i.l!..' •0.-_,..11. [ 11.18 • l.17 B.1SI·W
''1.• S.'!. .1 •
0.--.... '. [ ~.I' • l. I. 1.1JI·llr'
.... S.'!. .l •QO,-.,.,l .. [ IS. III • •. n I.I<J·W
' ".. S.'!. ...fclolot [ 1I.13B,o. • .." l.ln·lO-' lS.3 U!. ...ldlln A 11.1_ • .." S.110·10-' 11.1 I.t:!. ., •SeIlh' AlI.ll1Q • ••• i ....·I... ' '.' l.'!..S •01-....1.. [ n.l. • 10.'1 1.1.·~ ••• S.A!.1.1 •.. .. " I.IV·I.... ".. ,.r!..f •
~.....' • 'l. S.I5·10-1I,..1; .. 0 f.JlI-llrlfy-l; OClr/lo 1.1I·1O"A& 'l 0 S." 10.11,..1; 'I 0 1.11.10.10,..1; CVl. l.lt·lr
·'loSII·l0·11,..1; '.' 0.M.10-lo,.-l, ~l 0 1.17-1....
RADIOMETRIC GEOCHRONOLOGY IN TUSCANY: RESULTS AND PROBLEMS
TABLE 12
Rh/Sr analytical data - Elba island
121
~ocl; tj'po ~1. n. ... ..d.1 ••• " ~ 81Fl1lI"sr (81$rl665r>. (31$rllllilr)j ••• _or.
...."m [I"
~'ft. .. ,~ '" ,~ .'0 . 11~ ... 18-~ •""~'1" .. 1~3' ,.. ~ .., . 11l ...~'1" " ,- 10.i ~5fl I . 111' .11~
,,~ti" " ,,~ ••• ,., 1.~li . Ill ••P_tito " II DI ,.. l516 •ili ./1~ "P_ii,. " ,,,. ,. •m ,•• ./1~ .,Gr.OO<Ii...1I. " 1\10 l.~O '00' m .111 10.lGroOO<llol'"ll. E. 15 • '" on ,.. ./151:. )
'''1" •• m '" .1If~ ~ .11<9 6.~.C4 "" ~ '" 1.91 .11\0:. 1 .110
" IlJI \.1~ ,," .i8f5:.)S .1109GroOO<ll0rit. ST[ 10 • '" '" 3.81 .1113:. • ".}" 00.' ". .., .I1S1:.f ./150 6.1):..04
" '",,, '.Il .1155:. 1 ,1150
" "OO I. f5 ,~ .9)5$:." .1151)Grani" • • 116.6 ~f~.6 1. ~19 .11fl ""} "Gr••l" " " ,~ i.6:1 3\8.) .Illl ,," 5.18Gronit. " " 'm 9.819 3Di.9 ,1)1l .IU8 S.)l~ti" " " - '.1:18 Olll \.Oll9 .11311 S,))P_,lt. 0 " 1111 I,m - 1.3iSl ./138 ,..~_'lto , " '0' 3.8fi S10) 1. I 1:1~ .Illl! ,ooChI"l El"....,,It. • • ~ll.6 Ill.8 6.136 ./151 "O}....,,1.. " " ~, 15.01 161.8 .Ilil ./1% 6,O~
6ro"ft. • " 17~.3 If.O~ l1l.i ,13D3 ./1% ••[.".m ElboQ.-.,.,.. lto Ell.16b • ., ", 5.81 .7101:. 3 .119~ 00
" 1JIl •• m .5 .15Jo1:. f ./19 ••c.__...I" [15,18 • '" '" ,.. .1104:. 5 .119~
" 1316 ., OD.) .15.5:. 9 ./19 •••Q•...,...lt. E15. l' • '" ,. 3./1 .1113:. I
"~" "' ll. f ,n .1l3ll!. 1 .111 ,C,·_·.. l .. [15.1lI • ,.. '" '0 . 1151:. 1 .Il~
" .. 11.5 '" .1l~3:, 1 ." ,..
TABLE 13
K/Ar analytical data - Minor intrusions
Ito<:t ,_SUpI. ". .....ri.1 " fD.,. r<l .1/i ODAr r<l: '".
_totr1"0 i ..nl .. " I. 18 ~.OZ5'1O"6 .. , :..l •Gigllo iconl .. " ,OO I "!loS.10-6 • • :..15 ..CoooJl,l1. ,r.ni" po",.,.,., • 8.10 \.019'10-6 " f. 3:.. I) ..ClIIl'l,lI. ""."ll ... lto " ••• 1.!t5ll,10-6 .. 5.1,;.16 ..CoooJlill. _.1.. ,
i.5~ 1.1(l4·1(r6 ", :..5
Iotcho9<J1."" ironlt. • '.00 6.\M-W I 00 l.J';.l •Ito<:<o"rod. ~,,"1'. ". " I. l' 9.1l0·W I • ).5:,,~ ·Go'O"''''' ,,,.Ito GlV»-1 " , .3f 1."3·\.,.6 " '.9:!:.15 •C.,,,I .i Pl.... ,,,nl" 5) Sil " ••• \.939· 10.6 " I.I;.!:_ ~ •eon.1 di ...... g....1t. " ~ " 6. ~5 1.3l)6.10-6 " 5,3:.. Tl •C.,tol dl >l.... i ... I.. S3 8il " 6.18 LiJ~'10-6 • 1.3:..1 •
,......", • ,~ " 5.8f·W\1y-l, '." •. It'1O"ICy-I, fDJIk • 1 19·10-f
• 'k " 5.81'10"11,·\, '6. 4.'16_10'10,-1, ~k" 1 Il'Wf
.,
"
122 G. FERRARA, S. TONARINI
TABLE
Rb/Sr analytical data14Minor intrusions
Roe. type S.... I. n. lI.I~d" .,. S, p~ &lr.b/86s. (&lS'/&OS"). (a1S,/SOs')1 ~. ..1IO<<o,t,,1Io 9"01'. R 101 " ". " '"' . 116 ./11 '-' •Ilo~,,,",, 9".1 to GAV /9-1 • ". ~ 3.91 . noli:!. 3 .11:l&J "
" '" ••• "' ./01.6.';11 .1I1S •.•.'; .6C..t.l 41 PI.t•• SI 119-1 • ,.
'" ••• ./151.'; • .1"9~9""""I.,lto
"' HO "" ,. Jll&:;ll • /l49 • ,.,C..t.l dl PI.". q"nl" " '" • ,.
'" ,." .11.7. 3 .ll.S!
"' '" , ". ./103.';10 .IUS '.3.'; """'tocrln" 9"nl" "" • "' '" 10.1 .1IS~ 3 "'} "" " " ."" ./157.';. 0 .1151
" '" '" " .116l!.'; 0 · J1517.3.'; .,
" 1916 ,., ,., 1.0111.';lIi · J1Sl
GI'lH" 9,onl" ". • ,. ". ••• ./116.'; °"'~" .., m " ./110.'; 0 · J17
" '",. ,. .IIS1! 0 .717 5.1.'; .1
" "",.. 161/ .8311!'2 .1l10
Table references
EHf.RHARDT et al.(1%2)
2 - BoRSI et al. ( 1982)3 - DEL MORO et al.
(I982)4 . BIGAZZI & FERRARA
(1971)5 _ BIGAZZI ctal. (J971)6 BIGAZZlctal.(1973)7 . GIGLlA & RADICATI (1970)8 - BoRSl Cl al. (196.5)9 - BoRStelal.(I971)
10· BARBERlelal.(I971)11 . EVERNDEN & (URTiS
(I96.5)12 BrCAZZt et al. (1981)
13 . FERRARA cr al. (1977)J4·I\RIAselal.(198la)J5 . ARIAS et al.{I98Jb)16 - BURsJ (1967)J7 PIERATTINr (1978)18 . EHERIIAll.DT &
FEll.RAll.A (1962)J9· BUkSI & FERRARA
(J97\)20· SAUPE"I al.(19H2l21 . FERRARA & TONARINI
(1985)22 V"NZJ.Aff &
\Xl ALDECK (1974)23 BoRSI el al. (1979)24 FERRARAeta!.(1961l
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RADIOMETRIC GEOCHRONOL(IGY IN TUSCANY: RESULTS AND PROBLEMS 123
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