U.S. DEPARTMENT OF THE INTERIOR 

U.S. GEOLOGICAL SURVEY

A geochemical and isotopic (Nd-Pb) comparison of volcanic rocks 

erupted during the last 3,550 yrs. B.P. of interplinian activity of SommaVesuvius volcano, Southern Italy

R. Somma 1 '2, R.A. Ayuso ! , B.De Vivo 2

1 U.S. Geological Survey, National Center, Mail Stop 954 Reston, VA 20192, USA 

Dipartimento di Geofisica e Vulcanologia , Via Mezzocannone 8, Napoli, 80134, Italy.

Open File Report 99-365

This report is preliminary and has not been reviewed for conformity with U.S.Geological Survey editorial 

standards or with the North American Stratigraphic code. Any use of trade, product or firm names is for 

descriptive purposed only and does not imply endorsement by the U.S. Government.
Abstract

Detailed stratigraphic sampling of formations from Somma-Vesuvius 

(Southern Italy) volcano complex erupted during the last 3550 years of inteplinian activity 

provide a framework for comprehensive chemical analyses and isotopic studies. The 

evolution of major- and trace-element abundances of these rocks suggest that fractional 

crystallization together with crustal assimilation are only a partial explanation of the 

complex processes occurring in the magma chamber. Our Nd and Pb isotopic data point to 

complex processes involving contributions from heterogeneus lithosphere, assimilation of 

continental crust, and magma mixing.

Introduction

This study is focused on establishing the geochemical and radiogenic isotope (Sr, 

Nd, Pb) signatures of magma sources of lavas and tephra erupted during Protohistoric 

(3550 yrs. BP.-79 A.D), Ancient Historic (A.D.79-472) and Medieval (472-1139 A.D.) 

interplinian activity of Somma-Vesuvius volcano (Fig.l). These data contribute to 

understanding the chemical evolution of the magmas during the interplinian activity at 

Mount Somma-Vesuvius and the relation between magma chemistry and its possible 

contribution to the mechanisms triggering explosive and effusive eruptions. We present 

here a progress report of the isotopic work done in the radiogenic lab of the U.S. 

Geological Survey, Reston VA.

The interplinian eruptions vary systematically in composition from tephri-phonolite 

to phono-tephrite (Fig.2). Radiogenic isotope compositions (143Nd/144Nd: 0.512504- 

0.512233; 206Pb/204Pb: 18.984-19.051; 207Pb/204Pb: 15.625-15.708; 208Pb/204Pb: 39.132- 

39.229) are similar to the overall Mount Somma-Vesuvius record for recent magmatic 

activity (Cortini and van Calstern, 1985; Ferrara et al., 1986; Civetta et al.1987; Cortini 

and Don Hermes, 1981;Civetta et al., 1991; Santacroce et al., 1993; Cioni et al., 1995; 

Caprarelli et al., 1993; D'Antonio et al. 1995; Ayuso et al., 1998) and the Roman 

Comagmatic Province in general (Vollmer, 1976; Vollemer and Hawkesworth, 1980;
Vollmer et al., 1981; Civetta et al., 1981; Rogers et al., 1985) and suggest the presence of 

enriched mantle sources. Chemical data obtained for the interplinian activity are compared 

to data for the plinian eruptions from the literature; the new geochemical database will be 

used to improve predictive models needed for evaluating the volcanic hazards associated 

with Mount Somma-Vesuvius.

Volcanolosical aspects of the interplinian activity at Mount Somma-Vesuvius.

Mitigation of volcanic hazards in densely inhabited areas is vital to ensure the 

welfare of people in the region about 800,000 people live on and around the flanks of 

Mount Somma-Vesuvius and there is a high potential for loss of lives and significant 

impact on the infrastructure of the region (Fig. 1). More than 15 cities are located on the 

flanks of Somma-Vesuvius - all are susceptible to destruction in the event of renewed 

explosive activity.

The Somma-Vesuvius volcanic complex is at the southern end of the Roman 

Comagmatic Province and is characterized by rocks belonging to the high potassium 

(HK) series. The volcanic material ranges from effusive lava to explosive tephra deposits. 

Recently, Ayuso et al. (1998) focused on three main cycles of activity, which reflect cycles 

identified by Arno' et al. (1987), and further defined by tephrostratigraphic and 

tephrocronologic studies by Rolandi et al. (1998). The first cycle of activity (>25-14 Ky 

B.P.) is characterized by several huge explosive eruptions (Codola, Sarno, Novelle, 

Seggiari, Lagno Amendolare) separated by small-scale effusive activity. The second cycle 

(8 Ky B.P.- 79 A.D.) is dominated by two plinian eruptions (Ottaviano and Avellino) and 

moderate strombolian-vulcanian activity. The third cycle of activity (79 A.D.-1944) is 

characterized by plinian ("Pompei") and subplinian eruptions ("Pollena", 1631) and 

"interplinian" strombolian-vulcanian activity.

Previous studies (Vollmer, 1976; Hawkesworth and Vollmer, 1979; Vollmer and 

Hawkesworth, 1980; Cortini and Don Hermes, 1981; Cortini and van Calstern, 1985; 

Santacroce et al., 1993; D'Antonio et al., 1995; Cioni et al., 1995, Aysuo et al., 1998)
focused on the geochemical and radiogenic composition of the magmas erupted during the 

plinian activity only limited data are now available for the interplinian activity.

Knowledge about the interplinian activity at Mount Somma-Vesuvius before the 

1631 A. D. interplinian eruption is incomplete due to the relatively small amount of 

magma erupted, relatively few scattered outcrops, and the difficulty of reconstructing valid 

stratigraphic sections for these deposits. Interplinian activity during the 25,000-14,500 yr 

B.P., predating the main Sarno plinian eruption, is found along the N and NE flanks of the 

volcano and mainly consists of lava flows and scoria fall layers emitted during 

strombolian-vulcanian activity. Successively different tephra outcrops belonging to the 

interplinian activity have also been recognized along the Mount Somma flanks. They 

mainly consist of scoria fall layers, lava flows and black nuee' ardent scoria deposits.

After the Avellino eruption ( 3,800 yr B.P.), well-defined interplinan activity has 

been identified on the N-NE to S-SE flanks of the volcano (Rolandi et al., 1998). 

Evidence for three main eruptions has been found intercalated with paleosoils rich in 

charcoal. The deposits consist of pumice layers of different grain-sizes and of conspicuous 

enrichment of lithic fragments and crystals in the finer fractions. The volume of magma 

erupted varies from 0.07 km3 dense rock equivalent (DRE) for the 1 st protohistroric 

eruption to 0.19 km3 DRE for the 3 rd protohistoric eruption.

The four strombolian-phreatomagmatic Medieval deposits were emplaced between 

the eruptive deposits of 472 A.D. and 1631 A.D. The volume of magma erupted for each

event ranges between 0.05-0.10 km DRE. Isopleth maps of selected interplinian layers 

show dispersion axes oriented toward the southeast except for tephra erupted during the 

1 st Medieval event which shows a dispersion axis toward the northeast. The data confirm 

that the eruptive columns which emplaced the interplinian layers had low energy and 

reached altitudes no higher than 10 km.

The activity at Somma-Vesuvius after the 1631 eruption is characterized by more 

than 300 years of nearly constant effusive eruptions with minor pyroclastic events usually 

occuring at the end of the eruptive cycles. This interplinian activity consists of a series of 

intermediate eruptions and of strombolian activity preceding the final eruption; Arno' et al. 

(1987) recognized 18 cycles of activity based on historic records.
Geochemical and isotopic (Nd-Pb) features of Protohistoric, Ancient Historic and 

Medieval interplinian activity at Mount Somma-Vesuvius

The geochemical analyses show that the products of the Medieval eruption vary 

from tephri-phonolite to phono-tephrite (Na20+K20: 8.1-11.4 wt %; Si02 49.9-46.8 wt 

%) (Fig.l). The radiogenic isotopic compositions (Table 1) for scoria ( 143Nd/144Nd: 

0.512422-0.512504; 206Pb/204Pb: 18.984-19.051; 207Pb/204Pb: 15.625-15.708; 208Pb/204Pb: 

39.132-39.229) show values similar to the recent Mount Somma-Vesuvius magmatic 

activity (Ayuso et al., 1998; Caprarelli et al., 1993). Fig.3a-b shows the lead isotopic 

compositions for Protohistoric, Ancient Historic and Medieval interplinian activities. The 

206Pb/204Pb isotopic compositions have distinct trends, from less radiogenic (Protohistoric) 

to more radiogenic (Ancient Historic), and than back to less radiogenic for the Medieval 

activity and ultimately to compositions that nearly match those of the Protohistoric rocks, 

suggesting the presence of heterogeneity in the sources involved during the interplinian 

activity.

Lavas and tephra erupted during the Recent 1631-1944 A.D. activity (Arno' et al., 

1987; Belkin et al., 1993 a, b; Trigila et De Benedetti, 1993) have a relatively narrow 

range for Si02, Ti02, FeO (total), MnO and P20s wt %', systematic variations exist 

between MgO, K20, Na20, A12O3 and CaO wt % that point to a relative depletion or 

accumulation of clinopyroxene from the magma. Isotopic compositions of Nd and Sr for 

the Recent activity (Hawkesworth and Vollmer, 1979; Cortini and Hermes, 1981; Civetta 

et al., 1991) show a slightly smaller range than values reported by Caprarelli et al. (1993) 

for the same units (143Nd/144Nd: 0.512379-0.512605; 87Sr/86Sr: 0.70716-0.70790). The 

143Nd/144Nd isotopic ratios for the interplinian Protohistoric, Ancient Historic and 

Medieval tephra analyzed in this study plot within the range determined for the Recent 

interplinan activity (Caprarelli et al., 1993; Ayuso et al., 1998).

We also note that the Nd isotopic compositions change systematically according to 

the stratighraphic position of the sample. From the Protohistoric ( 143Nd/144Nd: 0.512404- 

0.512470) to the Ancient Historic (143Nd/144Nd: 0.512449-0.512507), the values generally
increase. The opposite trend exists for the Medieval (143Nd/I44Nd: 0.512504-0.512406) 

interplinian activity (Fig.4). Our preliminary conclusion is that the isotopic variations of Pb 

and Nd could be explained by the progressive emptying of a zoned magma chamber 

containing isotopically heterogeneous magmas. The isotopically heterogeneous magmas 

could reflect the interaction of magmas derived from enriched-type mantle and the 

continental crust or continental mantle lithosphere (Stoltz et al., 1996; Ayuso et al., 1998). 

Heterogeneous sources may also result from melting of underplated subcontinental 

lithosphere in this area during crustal extension involved during the opening of the 

Tyrrhenian Sea (Lavecchia and Stoppa, 1996; Ayuso et al., 1998).

References

Arno' V., Principe C., Rosi M, Santacroce R., Sbrana A. & Sheridan M.F., 1987,

Eruptive history: Santacroce ed., CNR Quad. Ric. Sci. 114, p. 197-220 

Ayuso R., De Vivo B., Rolandi G., Seal II R.R. and Paone A, 1998, Geochemical and

isotopic (Nd-Pb-Sr-O) variations bearing on the genesis of volcanic rocks from

Vesuvius, Italy: Journal of Volcanological and Geothermal Research, v. 82, p. 53-

78.0 

Belkin H.E., Kilburn C.R.J., and De Vivo B., 1993a, Chemistry of the lavas and tephra

from the recent (AD. 1631-1944) Vesuvius (Italy) volcanic activity: U.S. Geological

Survey Open file report 93-399, p. 44 

Belkin H.E., Kilburn C.R.J., and De Vivo B.,1993b, Sampling and major element

chemistry of the recent (A.D. 1631-1944) Vesuvius activity; Journal of

Volcanological and Geothermal Research, v. 58, p. 273-290 

Caprarelli G., Togashi S. and De Vivo B., 1993, Preliminary Sr and Nd isotopic data for

recent laves from Vesuvius volcano: Journal of Volcanological and Geothermal

Research, v. 58, p 377-381. 

Cioni R., Civetta L., Marianelli P., Metrich N., Santacroce R. and Sbrana A., 1995,

Compositional layering and syn-eruptive mixing of a periodically rifilled shallow
magma chamber: the A.D. 79 plinian eruption of Vesuvius: J. of Petrology, v. 36, p.

739-776. 

Civetta L., Galati R. and Santacroce R., 1991, Magma mixing and convective

compositional layering within the Vesuvius magma chamber. Bull. Volcanol., v. 53, p.

287-300. 

Civetta L., D'Antonio M, Paone E., Santacroce R., 1987, Isotopic studies of the

products of the 472 A.D. Pollena eruption (Somma-Vesuvius): Bollettino GNV, 1987,

p. 263-271. 

Civetta L., Innocenti F., Manetti P., Peccerillo A. and Poli G., 1981,. Geochemical

characteristics of potassic volcanics form Mts. Ernici (Southern Latium, Italy): Contr.

Mineral. Petrol., v. 78, p. 37-47. 

Cortini M. and Don Hermes 0. ,1981, Sr isotopic evidence for a multi-source origin of

the potassic magmas in the Neapolitan Area (S. Italy): Contrib Mineral. Petrol., v. 77,

p. 47-55. 

Cortini M. and van Calstern W.C.,1985, Lead isotope differences between whole-rock and

phenocrysts in recent lavas from southern Italy: Nature, v. 314, p. 343-345. 

D'Antonio M., Tilton G.R. and Civetta L., 1995, Petrogenesis of Italian alkaline laves

deduced from Pb-Sr-Nd isotope relationships: American Geophysical Union Monogr.

Dedicated to M. Tatsumoto and G. R. Tilton, p. 253-267. 

De Vivo B., Torok K., Ayuso R.A., Lima A. and Lirer L., 1995, Fluid inclusion evidence

for magmatic silicate/saline /C02 immiscibility and geochemistry of alkaline xenoliths

from Ventotene Island, Italy: Geochim. Cosm. Chim. Acta, v. 59, p. 2941-2953. 

Ferrara G., Preite-Martinez M., Taylor H.P. Jr, Tonarini S. and Turi B., 1986, Evidence

for crustal assimilation, mixing of magmas, and a 87Sr-rich upper mantle: Contr.

Mineral. Petrol., v. 92, p. 269-280. 

Hawkesworth C.J. and Vollmer R., 1979, Crustal contamination versus enriched mantle:

143Nd/144Nd and 87Sr/86Sr evidence from the Italian volcanics: Contr. Mineral. Petrol.,

v. 69, p. 151-165. 

Lavecchia G. and Stoppa F., 1996, The tectonic significance of Italian magmatism: an

alternative view to popular interpretations: Terra Nova, v. 8, p. 435-446.
Rogers N.W., Hawkesworth C.J., Parker RJ: and Marsh J.S., 1985, The geochemistry of

potassic lavas form Vulsini, central Italy and implications form mantle enrichment

processes beneath the Roman region: Contrib. Mineral. Petrol., v. 90, p. 244-257. 

Rolandi G., Petrosino P. and Me Geehin J., 1998, The interplinian activity at SommaVesuvius in the last 3500 years: Journal of Volcanological and Geothermal Research.,

v. 82, p. 19-52. 

Santacroce R., Bertagnini A., Civetta L., Landi P. and Sbrana A., 1993, Eruptive

dynamics and petrogenetic processes in a very shallow magma resevoir: the 1906

Eruption of Vesuvius: J. of Petrology, v. 34, p. 383-425. 

Stoltz A.J., Jochum K.P., Spettel B., Hoffman A.W., 1996, Fluid- and melt-related

enrichment in the subarc mantle: evidence from Nb/Ta variations in island arc basalts:

Geology, v. 24, p. 587-590 

Trigila R. and De Benedetti A. A., 1993, Petrogenesis of Vesuvius historical lavas

constrained by Pearce element ratios analysis and experimental phase equilibria:

Journal of Volcanological and Geothermal Research., v. 58, p. 315-343. 

Vollmer R, 1976, Rb-Sr and U-Th-Pb systematics of alkaline rock: the alkaline rocks

from Italy: Geoch. Cosm. Acta, v. 40, p. 283-295. 

Vollmer R. and Hawkesworth C.J., 1980, Lead isotopic composition of potassic rocks

from Roccamonfina (South Italy): Earth Planet Sci. Lett., v. 47, p. 91-101. 

Vollmer R., Johnston K., Ghiara M.R., Lirer L. and Munno R., 1981, Sr isotope

geochemistry of megacrysts form continental rift and converging plate margin alkaline

volcanism in Southern Italy: Journal of Volcanological and Geothermal Research, v.

11, p. 317-327.

CAPTIONS

Tab.l. Lead and neodymium isotopic compositions for whole rocks form Protohistoric, 

Ancient Historic and Medieval interplinian activity.
Fig.l. Generalized geologic map of Somma-Vesuvius volcano and location of samples 

used in the comprehensive studies of this region (Ayuso et al., 1998). Samples used in this 

study shown in bold and underlined.

Fig.2. Silica/total alkali plot for Protohistoric, Ancient Historic and Medieval eruption 

glasses (Rolandi et al., 1998), and Recent (1631-1944 A. D.) interplinian activity (Belkin 

et al., 1993 a-b). Also shown for reference are the three compositional groups identified 

by Ayuso et al. (1998) and reported as insert the trend of Plinian Somma-Vesuvius activity 

in a silica/total alkali simplified plot.

Fig. 3. Pb isotope diagrams for interplinian Protohistoric, Ancient Historic and Medieval 

whole rocks: (a) 208Pb/204Pb vs 206Pb/204Pb, (b) 207Pb/204Pb vs 206Pb/204Pb. Ventotene 

xenoliths from De Vivo et al. (1995); Somma-Vesuvius cumulate from Cortini and van 

Calstern (1985); Recent (1631-1944 A. D.) interplinian activity from Caprarelli et al. 

(1993) and Ayuso et al. (1998). Arrows show possible mixing lines for Protohistoric, 

Ancient Historic and Medieval interplinian activity.

Fig.4. 143Nd/144Nd vs. Stratigraphic position for interplinian Protohistric, Ancient Historic 

and Medieval whole rocks. Also reported are results of the Recent interplinian activity 

(Caprarelli et al.,1993 and Ayuso et al.,1998).
Table 1

ID

R-1(1)Res

R-1(1)L1

R-1(1)L2

R-2(1) Res

R-2(1) L1

R-2(1) 12

R-3(1)ARes

R-3(1)AL1

R-3(1)A 12

R-3(1)B Res

R-3(1)B L1

R-3(1)BL2

R-3(1)C Res

R-3(1)C L1

R-3(1)CL2

R-3(1)D Res

R-3(1)D L1

R-3(1)D L2

R-3(1)ERes

R-3(1)EL1

R-3(1)E L2

R-3(1)F Res

R-3(1)F L1

R-3(1)FL2

R-4(1)A Res

R-4(1)AL1

R-4(1)AL2

R-4(1)B Res

R-4(1)B L1

R-4(1)BL2

S20(1) Res

S20(1) L1

S20(1) L2

S20(2) Res

S20(2) L1

S20(2) L2

S20(3) Res

S20(3) L1

S20(3) L2

S20(4) Res

S20(4) L1

S20(4) L2

S20(5) Res

S20(5) L1

S20(5) L2

S20(6) Res

S20(6) L1

S20(6) 12

206pb/204Pb 207Pb/204Pb 208Pb/204Pb

Medieval (472-1 631 A.D.)

19.0337

19.0532

19.0236

18.9827

19.0390

18.9726

18.9772

18.9733

18.9645

19.0142

18.9765

18.9998

19.0009

18.9932

19.0313

19.0409

19.0324

19.0199

19.0005

18.9897

19.0307

19.0334

18.9952

18.9923

18.9926

19.0239

18.9687

19.0053

18.9809

19.0434

15.6788

15.7090

15.6719

15.6429

15.7108

15.6282

15.6466

15.6413

15.6304

15.6704

15.6319

15.6561

15.6425

15.6332

15.6805

15.6875

15.6752

15.6622

15.6353

15.6209

15.6717

15.6664

15.6252

15.6316

15.6700

15.6952

15.6342

15.6626

15.6467

15.6398

Ancient Historic (A.D.

19.0488

19.0333

19.0433

19.0642

19.0530

19.0587

19.0615

19.0503

19.0440

19.0407

19.0444

19.0623

19.0438

19.0884

19.0601

19.0188

19.0319

19.0445

15.6554

15.6341

15.6492

15.6630

15.6456

15.6535

15.6601

15.6456

15.6401

15.6473

15.6427

15.6678

15.6462

15.6948

15.6662

15.6438

15.6383

15.6560

39.1414

39.2254

39.1107

39.0161

39.2413

38.9584

39.0054

38.9945

38.9595

39.1065

38.9868

39.0703

39.0321

38.9991

39.1587

39.1812

39.1421

39.1022

39.0121

38.9645

39.1351

38.7599

38.9772

39.0175

39.0854

39.1893

38.9716

39.0703

39.0131

39.0167

79-472)

39.0894

39.0186

39.0657

39.1092

39.0581

39.0836

39.1029

39.0581

39.0381

39.0504

39.0442

39.1238

39.0432

39.2193

39.1201

39.0188

39.0191

39.0740

143Nd/144Nd

0.512504

0.512472

0.512453

0.512440

0.512454

0.512436

0.512471

0.512463

0.512234

0.512406

0.512449

0.512481

0.512462

0.512477

0.512024

0.512467

L1= 1st leach (1.5N HBR+2N HCI) 2. 

L2= 2nd leach (9N HBr) 9 hrs on low 

Res.= Residue

5hrs on low hot plate 

hot plate

lo
Table 1

ID

S20(7) Res 

S20(7) L1 

S20(7)L2

S1 1(1) Res

S11(1)L1

S11(1)L2

S12(1) Res

S12(1)L1

S12(1)L2

S12(2) Res

S13(2)aRes

S13(2)bRes

S13(1)bRes

S13(1)bL1

S13(1)bL2

S14(1) Res

S14(1) L1

S14(1)L2wr

S14(2) Res

S15(1)bRes

S15(1)bL1

S15(1)bL2

S15(2)aRes

S15(2)aL1

S15(2)aL2

S16(1) Res

S1fiM^ I 1

S16(1) L2

S17(1)aRes

S17(1)aL1

S17(1)aL2

S17(1)bRes

S17(2)aRes

S17(2)bRes

S18(1)aRes

S18(1)aL1

S18(1)aL2

S1 8 bis Res

S18bisL1

S18bisL2

19.0811 

19.0406 

19.0451

Protohistoric

18.9779

18.9424

18.9668

18.9714

18.9657

18.9614

18.9501

18.9369

18.9434

18.9417

18.9572

18.9488

18.9497

18.9481

18.9331

18.9636

18.9560

18.9440

18.9633

18.9978

18.9767

18.9466

18.9558

18.9425

18.9549

18.9533

18.9542

18.9786

18.9292

18.9682

207Pb/204Pb 

15.7047 

15.6490 

15.6563

(3550 yrs.

15.6732

15.6218

15.6516

15.6524

15.6449

15.6413

15.6385

15.6305

15.6371

15.6339

15.6533

15.6326

15.6419

15.6367

15.6191

15.6543

15.6412

15.6393

15.6617

15.6920

15.6716

15.6325

15.6441

15.6305

15.6387

15.6378

15.6404

15.6496

15.6414

15.6311

208Pb/204Pb 

39.2364 

39.0541 

39.0754

B.P.- A.D. 79)

39.1036

38.9283

39.0286

39.0297

39.0049

38.9925

38.9876

38.9540

38.9777

38.9699

39.0301

38.9601

38.9951

38.9749

38.9167

39.0362

38.9900

38.9906

39.0584

39.1571

39.0887

38.9615

38.9970

38.9538

38.9805

38.9718

38.9807

39.0551

38.9628

38.9800

143Nd/144Nd 

0.512507

0.512405

0.512443

0.512434

0.512461

0.512404

0.512453

0.51247

0.51243

0.512445

0.512456

0.512462

0.512447

0.512246

0.512460

0.512469

L1= 1st leach (1.5N HBR+2N HCI) 2.5hrs on low hot plate 

L2= 2nd leach (9N HBr) 9 hrs on low hot plate 

Res.= Residue
Fig.1

Recent 

historic lavas

1631 A.D. 

Pyrodastic flows

Medieval lavas

79A.D. 

Pyrodastics

Pyrodastics

of explosive activity

(17000 y.b.p present)

Somma lavas

PALMA 

CAMPANIA

 

*S-2(3)

,S-3(3)

STRUNG

S*<1)

SARNO

\ C.S. Giorgio
12 

1416

--

10 --

8 --

Fig. 

2

X Recent wr 

Medieval 

A.D.1631

gl 

Protohistorjcgl. 

A.D.79A.D.472 

A Protqhistoric wr 

x 

Lagno 

Ottaviano

Avellino

Amendolare 

+ 

Sarno_______ Novelle-Seggiari

6 -

4 -

0

50 55 

Si02 wt.%
39.4

Fig. 3a

39.3 4-

39.2 4-39.1

39

38.9 +38.8 4-

38.6

38.7 2o

D

X RecentO MedievalO Ancient Historic

A ProtohistoricD Somma cumulate

AVentotene xenoliths

18.6 18.7 18.8 18.9 19 19.1 19.2

Pb
15.72

15.74

15.7 4-

£ 15.68 4-

15.6215.6415.66

I

2o

15.6

18.6

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