Lithos 188 (2014) 97–112

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Lamprophyres of Italy: early Cretaceous alkaline lamprophyres ofSouthern Tuscany, Italy

Francesco Stoppa a,⁎, Alexei S. Rukhlov b,c, Keith Bell b, Mariangela Schiazza a, Giada Vichi d

a DiSPUTer, Università G. d'Annunzio, Campus Madonna delle Piane, Via dei Vestini, 66100 Chieti, Italyb Department of Earth Sciences, Carleton University, 1125 Colonel By Drive, Ottawa, Ontario K1S 5B6, Canadac British Columbia Geological Survey, PO Box 9333 Stn Prov Gov't, 5th Floor 1810 Blanshard St., Victoria, British Columbia V8W9N3, Canadad MV Geologia, v. Macera 8, Tivoli, Italy

⁎ Corresponding author. Tel.: +39 3487629637; fax: +E-mail address: fstoppa@unich.it (F. Stoppa).

0024-4937/$ – see front matter © 2013 Elsevier B.V. All rihttp://dx.doi.org/10.1016/j.lithos.2013.10.010

a b s t r a c t

a r t i c l e i n f o

Article history:Received 16 May 2013Accepted 9 October 2013Available online 18 October 2013

Keywords:Alkaline lamprophyresMantle isotopic end-membersPlumeEarly CretaceousTethys

Alkaline lamprophyres from southern Tuscany are early Cretaceous, ultrabasic, primary mantle melts that havenot undergone significant magmatic differentiation. Newmineralogical, geochemical and Sr, Pb and Nd isotopicevidence shows contrasting geochemistries with “crustal-like” and mantle geochemical features. High Mg#'s,however, coupled with high compatible elements, rule out any notable mantle melt dilution by bulk crustalcontamination. Variations of Zr/Hf and Ta/Nb indicate a source containing residual titanates while their REEgeochemistry suggests low degrees of partial melting and possible metasomatism of their source by carbonatiticmelts. Arrays in isotope ratio diagrams are consistent with mixing between two distinct mantle end members.One is FOZO-like in character, and supports the involvement of asthenosphere, while the second has 87Sr/86Srinitial values that are much higher than FOZO (N0.70641). High 87Sr/86Sr signatures are present in the otherItalian alkaline lamprophyres aswell as other potassic–ultrapotassic and carbonatitic rocks of Italy. Our preferredmodel involves melting of a two component, metasomatised mantle, which can be tied into plume-relatedmagmatism.

© 2013 Elsevier B.V. All rights reserved.

1. Introduction

Lamprophyres are genetically related to lamproites, kimberlitesand carbonatites which establish a firm link with deep-seated meltsderived from metasomatised mantle (Rock et al., 1991; Mitchell, 1994;Rock, 1987, Tappe et al., 2008). All of these rocks represent volatile-richmagmas rapidly emplaced at crustal levels during regional stages oflithospheric relaxation. Alkaline lamprophyres (AL) in Italy formdyke swarms that cut across different structural domainscommonly showing a large spatial and temporal distribution.There are eleven major early Cretaceous to Oligocene ALoccurrences reported from the Eastern and theWesternAlps, SouthernTuscany, Sardinia, and the Puglia Region (Fig. 1a). Similar repetitions areobserved in Africa (Bailey and Woolley, 1995), where four differentmagmatic cycles correspond with those found in the Mediterraneanarea: early Cretaceous (130–110 Ma), late Cretaceous (85 Ma), Eocene(40 Ma), and Miocene to Recent (b23 Ma). Their occurrence seems tobe independent of the geodynamic evolution of the Tethyan–Mediterranean area and none correlates with the main Tethyan tectonicevents (Dercourt et al., 1986).

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The lamprophyres found in Southern Tuscany mark one of theoldest events of K-alkaline magmatism in the history of the Italianmagmatism. Their present spatial distribution is shown in Fig. 1b.These rocks were known by the local name “selagite” and werepreviously considered to be mafic differentiates from granitic or syeniticmagmas (Debenedetti, 1958). Faraone and Stoppa (1990) classifiedthem as lamprophyres and linked their emplacement to within-plate continental extension during a mature stage of the Ligurianbasin development. In this paper we discuss the mineralogy andgeochemistry of the Southern Tuscany lamprophyres, including newNd, Sr and Pb isotopic data.

2. Geological setting

The Southern Tuscany alkaline lamprophyres (STALs) are Albian inage (ca. 110Ma) and occur in the Lower Cretaceous sequence of distalflysch that extends over an area of about 3000km2 in the provinces ofGrosseto and Siena, Central Italy (Fig. 1b). This flysch is located betweenthe subsiding margin of the Adria sector of the Africa plate and theLigurian branch of the Tethys Ocean. Even though they are not strictlyassociated with Jurassic ophiolites they were probably located onoceanic lithosphere (Fig. 1c). To the east lies the subsident Tuscanydomain marked by Triassic evaporites and Jurassic–Cretaceouslimestones overlying the Palaeozoic crystalline basement belonging tothe African sub-plate Adria (Brogi et al., 2000). To the north, the

Fig. 1. (a) Location of Italian alkaline lamprophyres; (b) geological map and location of the Southern Tuscany alkaline lamprophyres at Siena and Grosseto, Italy; (c) early Cretaceous(Aptian–Albian) palaeogeographic restoration of the Ligurian Branch of the Tethys Ocean with the location of the lamprophyres shown.

Table 1Modal compositions (vol.%) of the Southern Tuscany lamprophyres.

Location Sample name Lithology Olivinea Diopsideb Biotitec Kaersutited Alkali feldspare Calcite Apatite Accessorymineralsf

Senna River SF29 Dyke/sillSF30 Dyke/sill 3 20 12 4 46 6 2 7SF9 Dyke/sillSF11 Dyke/sillSF12 Dyke/sillSF23 Dyke/sill 3 20 15 – 38 18 2 4

Murci PMT3a Dyke/sillPMT7a Dyke/sill 4 18 20 – 35 16 2 5PMT2 Dyke/sillPMT4b Pillow-lava 14 63 – – – 15 2 6

Fosso Ripiglio FR5 Dyke/sillFR9 Pillow-lava 18 72 – – – 2 2 6FR1b Dyke/sillFR2b Dyke chilled margin 12 57 Total 12 9 – 2 8 + trevoriteFR6 Dyke/sillFR8 Dyke/sill

Castiglioncello del Trinoro S5 Dyke/sillS15 Pillow-lava 12 57 Total 12 9 – 2 8S16 Dyke/sillS4 Dyke/sill 3 16 12 4 42 15 3 5

a Phenocrysts pseudomorphed with pennite, chrysotile and carbonate.b Phenocrysts and euhedral groundmass grains (up to 6 wt.% TiO2, 9 wt.% Al2O3, and 0.9 wt.% Cr2O3, Mg#= 0.7–1.0) rimmed with aegirine–augite (up to 5 wt.% TiO2, b1wt.% Al2O3,

Mg#=0.1–0.2).c Zoned phenocrysts and euhedral groundmass crystals with eastonite–siderophyllite core and annite-rich rim (up to 10wt.% TiO2 and 3wt.% BaO, Mg#=0.7–0.5 and 0.5–0.2 for core

and rim, respectively). Unzoned biotite occurs in samples FR1b, FR2b, FR6, FR8, S5, S15, S16, and PMT2.d Phenocrysts with up to 7.7wt.% TiO2.e Interstitial, branched and spherulitic groundmass crystals of sanidine and subordinate anorthoclase and albite with b0.1wt.% SrO and b0.4 wt.% BaO.f Additional accessory phases found in all of the studied samples except PMT4b, FR5 and FR9 include: Ti–magnetite, chromite, rutile, ilmenite, pyrite, and chalcopyrite.

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internal ophiolitic Ligurian terrane underwent deformation andthrusting onto northern Corsica and the Briançonnaise margin ofthe European plate during the late Cretaceous phase of the AlpineOrogeny (Fig. 1c). The STALs were deformed during the Miocenewhen the host flysch of early Cretaceous age was thrust over theTuscany domain.

Mafic sills and lavas of Rapolano Terme within the Eocene Tuscanstratigraphic unit are the spatially closest igneous rocks to the STALs(Brogi et al., 2000). Brogi et al. (2000) assumed an early Cretaceousage for these rocks based on the sedimentological evidence andconsidered them to be petrologically similar to the STALs. However, inthis study we report considerable geochemical differences betweenthe two groups of rocks.

The STALs are found in a succession of pelagic, cherty micritesinterbedded in terrigenous turbidites represented by fine quartziticsandstones and silty–clay marls. Their contacts with the country rocksare either planar or irregular. Although there is evidence for the intrusionofmagma fingers in the soft sediments, the contacts are chilled and showsigns of slight re-crystallisation and oxidation (Brunacci et al., 1983).Dykes and sills, up to 2 m thick were emplaced en echelon and aretraceable for relatively short distances, due to later tectonic disturbances.Their textures are coarse-grained in the central parts and very fine-grained at the contacts which are also marked by the concentration ofcalcite ocelli. Pillow lavas have been found in several localities (Tables 1and 2). Pillows form small to relatively large accumulations with amaximum thickness of about 50m. They preserve typical features suchas porphyritic cores and aphanitic rims, radial cooling cracks, and vesiclesfilled by hydrothermal phases. They are embedded in a finely layered,grayish green to violet radiolarite, composed of mixtures of clastic micagrains, radiolarian chert and ore pigments. Hyaloclastic breccias indicatesmall undersea volcanoes and the down-slope rolling of the pillows.Although no feeders are seen, there is a close association between thedykes and lava flows.

3. Petrography and mineralogy

Table 1 summarises the main mineralogical and petrographicfeatures of the Southern Tuscany lamprophyres indicating the presenceof both sub-volcanic and effusive rocks (FR2b, PMT4b and FR9).The mineral compositions were analysed at The Natural HistoryMuseum, London, using a CAMECA SX50 wavelength-dispersivemicroprobe, operated at 15 kV, 10–15 nA and a 10–20 μm spot size(where possible), using a selection of mineral and synthetic standardsand the PAP matrix correction routine. Details of the mineralcompositions are given in Electronic supplements 1–7.

The presence of mica and amphibole is a necessary characteristicof lamprophyres. Further classification follows the InternationalUnion of Geological Sciences (IUGS) criteria and the more recentclassification proposed by Tappe et al. (2005). STALs containabundant euhedral mafic phenocrysts set in a microporphyritic orfelt-like groundmass. Coarser grained facies contain by volume: 35–46% of K-feldspar, 16–20% of diopside, 15–20% of mica andamphibole, 6–15% of carbonate, 4–7% of opaques, 3% olivine, and2% apatite. Carbonate-rich varieties contain up to 47% carbonate,up to 26% K-feldspar, 20% aegirine, 5% opaques, and 2% apatite.Skeletal clinopyroxene and amphibole are fresh; olivine and biotiteare partially altered (Fig. 2). Calcite is largely recrystallised. The finegrained varieties make up the chilled margins of the dykes and pillowsand contain in volume up to 9% of K-feldspar, 57–72% clinopyroxene,12–18% olivine, up to 12% mica and amphibole, up to 15% carbonate,6–8% opaques, and 2% apatite.

3.1. Carbonate ocelli

STALs contain spherical carbonate ocelli up to 2 mm in diameter(Fig. 2c, d). In some cases, they are concentrated at the contacts and

seem to have flowed following the thermal gradient from the hottestcentral part to the colder outer part of the dykes. Meniscus-shapedboundaries form ‘necks’ among the ocelli. The ocelli core containsintergrown calcite and analcime; small crystals of green aegirine grewperpendicular from the rim towards the centre of the structure(Fig. 2c, d). Apatite is also present and many crystals of strontianite upto 10 μm occur at the margins of calcite. There are no systematiccompositional differences in pyroxene (aegirine) and calcite in the ocelliand in the groundmass. SrO in the calcite varies between 0.46 and0.86wt.%. Four criteria indicate that ocelli may reflect liquid immiscibility(Rosatelli et al., 2010): (1) menisci among coalescent ocelli, (2) texturalassociation with high temperature silicate phases, (3) chemicalcompositions consistent with igneous carbonate, and (4) similarcomposition of silicate and carbonate phases in both ocelli andgroundmass (Vichi et al., 2005).

3.2. Phenocrysts–microphenocrysts

Euhedral olivine, diopside, biotite, and kaersutite form thephenocryst assemblage and all contain poikilitic inclusions ofoxides. Olivine phenocrysts are commonly pseudomorphed byaggregates of carbonates, penninite, and chrysotile (Fig. 2e, f). Chemicalcompositions of minerals and calculation details are given inelectronic supplements 1-7.

Clinopyroxene is diopside with 46 mol% enstatite, 51 mol%wollastonite, and 19 mol% ferrosilite (Fig. 3a). Na-rich clinopyroxeneranges from aegirine–augite to aegirine (Fig. 3b). The Cr2O3 ofclinopyroxene averages 0.2 wt.% Cr2O3 and is up to 0.9 wt.%. Itshows a positive correlation with the enstatite molar content andMg# (Fig. 3c). The Ca# is inversely correlated with Mg#. Diopsidegenerally has an undersaturated T-site (Fig. 3d). The aegirine molarproportion and TiO2 show an increase in the rims of the diopsidephenocrysts. SiO2/Al2O3 vs Mg# values all fall within the field reportedfor clinopyroxene in other ALs, but less evolved compositions overlapclinopyroxene found in calcalkaline lamprophyres (Fig. 3e).

Amphibole is euhedral and zoned, and can be classified as kaersutiteor ferrokaersutite having N0.5 Ti a.f.u. (Fig. 4a) (Leake et al., 1997). Al(a.f.u.) is sufficient to saturate the T-site (Fig. 4b). The Si (a.f.u.) variesfrom 5.58 to 6.02 and hence the amphiboles are sub-siliceous, a typicalfeature for ALs (Fig. 4b) (Rock et al., 1991). CaO/Na2O vs Al3O3/TiO2

fields are also typical of ultramafic lamprophyres and AL amphiboles(Fig. 4c). SrO and BaO are appreciable and make up to 0.39 wt.% and0.29wt.%, respectively, of the amphiboles.

Mica is normally skeletal and kink-banded (Fig. 2g, h). Corecompositions range fromphlogopite to biotite (Fig. 4d). Rims are anniticbiotite containing 50–80% siderophyllite (Fig. 4d). The TiO2 content isvery high, averaging 8 wt.% and reaching up to 10wt.%, a feature thatalso characterises ALs (Rock et al., 1991). BaO contents average0.7wt.% and can reach up to 2.7wt.%. Both Al and Ba positively correlatewith Ti# and are higher in the crystal core than the rim (Fig. 4e, f).

Hydroxy-fluorapatite forms up to 3mm-long prisms. SiO2 contentsrange from 0.3 to 2.9wt.% and positively correlate with SrO and LREEs.La2O3 and Ce2O3 contents are up to 0.95 and 0.72wt.%, respectively.

3.3. Groundmass

The groundmass is composed of variable proportions of K-feldspar,aegirine, mica and turbid calcite and/or dolomite. Quench, spheruliticand felty/branching textures of silicate minerals are typically observed(Fig. 2a, b). The feldspars are mostly K-feldspar. K-feldspar containshigh FeO up to 5.66 wt.%, SrO up to 1.4 wt.% and BaO up to 1.0 wt.%.Analcime occurs as rounded patches in the groundmass and as aninterstitial mineral. Aegirine contains 5 mol% Jd, 15–30 mol%Wo+En+Fs, and 70–100mol% Ae (Fig. 3b). The T site is saturated.Carbonates are either intergranular phases or form a microcrystallinegroundmass in the carbonate-rich STALs. The latter contain mostly

Table 2Bulk rock analyses of the Southern Tuscany lamprophyres.

Sample Senna River Murci Fosso Ripiglio Castiglioncello del Trinoro

Dyke/sill

Dyke/sill

Dyke/sill

Dyke/sill

Dyke/sill

Dyke/sill

Pillow-lava

Pillow-lava

Dyke/sill

Dyke/sill

Dyke/sill

Pillow-lava

Dyke-sill

Dyke/sill

Dyke/sill

Pillow-lava

Dyke/sill

Dyke/sill

Dyke/sill

Dyke/sill

Dyke/sill

SF12 SF30 SF29 SF23 SF9 SF11 PMT4brp PMT4b PMT7a PMT3a PMT2 FR9 FR5 FR8 FR6 FR2b FR1b S5 S16 S15 S4

SiO2wt.% 52.7 43.9 42.5 40.2 35.6 27.3 40.0 39.6 39.6 39.4 31.5 49.7 47.4 47.2 46.8 46.1 45.1 45.4 45.3 44.2 42.5TiO2 2.79 2.26 4.19 2.36 3.05 1.73 2.95 2.95 2.89 3.04 2.42 2.38 2.56 2.45 2.66 2.39 2.52 2.57 3.86 2.70 2.85Al2O3 11.5 13.3 13.8 11.7 11.9 9.4 11.0 11.1 11.6 11.8 11.2 11.0 12.6 12.5 13.0 10.7 11.8 12.3 11.5 10.5 11.8Fe2O3 2.76 4.12 4.88 2.58 4.32 1.82 4.13 4.29 2.79 3.92 5.84 5.24 6.55 6.14 6.81 5.03 6.25 6.07 5.27 4.98 3.63FeO 5.41 3.70 4.95 6.20 6.33 3.00 5.70 5.50 6.30 5.95 4.38 3.90 3.18 3.41 2.75 4.40 3.67 2.85 4.66 5.00 4.60MnO 0.07 0.09 0.11 0.17 0.11 0.28 0.09 0.09 0.10 0.14 0.18 0.14 0.14 0.13 0.12 0.14 0.17 0.11 0.19 0.14 0.10MgO 7.56 8.87 7.32 6.71 10.4 1.98 11.2 11.3 10.3 10.1 5.83 8.11 8.34 7.63 8.24 11.6 11.9 8.92 10.6 11.6 6.74CaO 5.62 6.07 7.49 11.1 10.6 26.9 8.16 7.99 8.62 9.29 18.2 9.36 9.99 9.90 9.80 7.45 8.86 10.0 7.41 9.00 9.60Na2O 2.18 3.47 3.72 2.06 1.55 3.25 1.55 1.56 2.11 1.38 1.87 1.94 2.92 1.70 1.79 1.35 1.66 3.44 1.08 0.88 2.36K2O 0.43 3.31 3.04 2.48 2.03 0.46 0.68 0.70 0.81 0.59 0.17 3.68 2.34 4.43 3.99 2.74 2.65 1.81 3.08 3.08 1.76P2O5 0.95 1.13 0.97 1.00 0.55 0.76 1.02 1.01 0.99 0.44 0.27 0.97 0.96 0.91 0.93 1.01 0.98 0.94 1.08 1.28 1.33CO2 2.54 2.55 1.64 7.72 6.67 20.3 5.78 5.79 6.60 6.24 13.14 0.73 0.57 0.30 0.60 0.16 0.26 1.79 0.62 0.06 6.24LOI 5.23 7.15 5.80 5.08 7.02 2.35 7.32 7.21 6.80 6.88 5.48 3.77 2.44 2.98 2.05 6.74 4.10 4.21 5.37 6.24 6.36Total 99.7 99.9 100.4 99.4 100.1 99.5 99.6 99.2 99.5 99.1 100.5 100.9 100.0 99.7 99.5 99.8 99.9 100.5 99.9 99.7 99.8A.I. 0.35 0.70 0.68 0.52 0.40 0.62 0.30 0.30 0.37 0.25 0.29 0.65 0.58 0.61 0.56 0.48 0.47 0.62 0.45 0.46 0.49Mg# 0.71 0.81 0.72 0.66 0.75 0.54 0.78 0.79 0.74 0.75 0.70 0.79 0.82 0.80 0.84 0.82 0.85 0.85 0.80 0.81 0.72ppm Ba 326 755 759 608 565 181 482 478 515 418 173 755 424 1254 1099 780 792 697 4527 3630 715Rb 11 41 50 35 25 9 16 16 18 10 2 27 17 36 33 33 33 31 39 40 36Sr 591 874 979 912 693 539 457 465 533 648 674 565 497 606 616 346 381 827 1118 1090 852Ta 5.5 5.3 6.5 4.9 5.2 3.4 4.9 5.2 5.4 6.1 5.3 4.5 5.7 5.6 5.2 4.6 5.1 6.3 5.9 5.9 6.3Nb 102 94 120 94 97 63 90 95 98 111 96 83 103 102 95 82 92 135 127 128 134Hf 8.2 7.9 10.2 7.0 7.9 5.2 7.0 6.9 7.3 8.3 7.8 5.8 7.2 7.2 7.0 5.4 6.5 9.0 8.1 7.3 7.9Zr 311 308 389 265 299 195 266 270 285 322 300 209 262 263 255 198 235 362 324 289 321

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Senna River Murci Fosso Ripiglio Castiglioncello del Trinoro

Dyke/sill

Dyke/sill

Dyke/sill

Dyke/sill

Dyke/sill

Dyke/sill

Pillow-lava

Pillow-lava

Dyke/sill Dyke/sill

Dyke/sill

Pillow-lava

Dyke-sill Dyke/sill

Dyke/sill

Pillow-lava

Dyke/sill Dyke/sill

Dyke/sill

Dyke/sill

Dyke/sill

SF12 SF30 SF29 SF23 SF9 SF11 PMT4brp PMT4b PMT7a PMT3a PMT2 FR9 FR5 FR8 FR6 FR2b FR1b S5 S16 S15 S4

Y 19 20 19 18 18 21 17 17 18 19 15 15 17 17 18 15 18 30 20 20 19Th 3.0 7.1 5.0 5.9 5.0 4.5 4.8 5.0 5.3 5.0 4.0 5.2 8.0 10.0 6.0 5.2 7.0 6.0 8.0 6.3 6.5U 1.0 2.1 1.6 2.0 1.5 1.4 1.5 1.4 1.6 1.5 1.2 1.7 2.5 3.1 1.9 1.6 2.2 1.9 2.5 2.0 2.0Cr 288 270 95 265 427 85 284 286 289 446 302 400 421 330 359 610 622 356 339 394 241Ni 190 278 96 220 406 59 314 314 285 509 442 400 411 263 290 562 577 289 408 326 165Co 33 53 51 34 59 25 43 44 40 71 56 61 67 92 62 83 80 50 171 40 57Sc 9.6 12.0 12.5 11.0 8.1 9.0 12.0 11.0 12.0 11.0 11.2 12.0 13.9 12.8 13.2 13.0 11.4 14.2 13.3 13.0 12.0V 193 132 199 137 210 107 150 154 151 257 203 154 219 210 195 152 186 253 226 165 157Cu 33 55 51 39 42 42 44 44 51 67 46 45 50 51 50 46 49 66 44 78 50Pb 9 2 6 3 4 16 9 8 2 6 10 2 2 7 11 6 4 9 2 2 2Zn 145 125 117 119 145 72 121 121 126 164 129 120 148 133 134 114 132 131 121 132 115Be n.a. 3 n.a. 3 n.a. 2 3 3 3 n.a. n.a. 2 n.a. n.a. n.a. 2 n.a. n.a. n.a. 3 3La 40 50 53 46 33 33 42 45 47 41 43 43 48 43 45 42 38 63 57 55 55Ce 97 114 111 104 82 65 99 103 106 99 95 96 99 103 94 98 93 136 130 122 127Pr 9.2 11.4 12.1 10.7 7.8 7.6 10.2 10.9 11.3 10.2 10.4 9.9 11.2 10.2 10.6 10.1 9.1 14.6 13.5 12.8 12.8Nd 39.9 52.0 55.4 47.8 36.6 34.8 47.3 49.2 51.8 48.9 45.9 44.9 47.9 48.7 46.3 45.1 41.7 63.4 63.8 57.0 58.2Sm 8.8 10.8 11.5 9.7 7.3 7.5 9.8 10.1 10.7 9.6 9.8 9.3 10.4 9.5 9.8 9.3 8.5 13.4 12.4 11.5 11.9Eu 2.9 3.6 3.8 3.1 2.4 2.5 3.1 3.2 3.4 3.0 3.1 3.1 3.4 3.1 3.2 3.0 2.8 4.3 3.7 3.8 3.7Gd 7.4 9.3 9.7 8.0 6.2 6.5 8.0 8.3 8.6 7.8 8.0 7.6 8.5 7.7 8.0 7.5 6.9 10.9 10.0 9.5 9.5Tb 0.9 1.2 1.2 1.0 0.8 0.9 1.0 1.0 1.1 1.0 1.0 0.9 1.1 1.0 1.0 1.0 0.9 1.3 1.2 1.2 1.2Dy 4.3 5.6 5.7 4.8 3.6 4.8 4.7 4.9 4.9 4.5 4.7 4.4 4.9 4.4 4.7 4.4 4.0 6.3 5.8 5.4 5.5Ho 0.7 0.8 0.9 0.7 0.5 0.8 0.7 0.7 0.7 0.7 0.7 0.7 0.7 0.7 0.7 0.7 0.6 0.9 0.9 0.8 0.8Er 1.7 2.1 2.2 1.9 1.4 2.3 1.7 1.8 1.8 1.7 1.7 1.6 1.8 1.6 1.7 1.6 1.5 2.2 2.0 2.0 1.9Tm 0.21 0.27 0.27 0.23 0.17 0.31 0.22 0.22 0.23 0.20 0.21 0.20 0.23 0.21 0.22 0.21 0.19 0.28 0.26 0.25 0.24Yb 1.1 1.5 1.5 1.3 0.9 1.7 1.2 1.2 1.3 1.1 1.2 1.1 1.3 1.2 1.2 1.2 1.0 1.5 1.4 1.3 1.4Lu 0.14 0.18 0.19 0.15 0.12 0.22 0.15 0.14 0.15 0.14 0.14 0.15 0.17 0.15 0.16 0.15 0.13 0.19 0.17 0.17 0.16

Notes: A.I.= atomic (Na+K)/Al; Mg#=atomic Mg/(Mg+Fe2+); n.a.=not analysed. The Multi-Method Multi-Element technique (method code: MELV) was employed that involved multi-acid (HF, HCl, HNO3, HClO4) digestion followed by thefusion of residue.Major elements were analysed by XRF, except CO2 (coulometry) and FeO (titration); trace elements by ICP-OES and ICP-MS. Concentrations are given in wt.% for oxides and ppm for trace elements.

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Fig. 2. (a) and (b) Quench, spherulitic and felty/branching textures of silicate minerals; (c) and (d) spherical carbonate ocelli and coalescent ocelli; (e) and (f) olivine and clinopyroxenephenocrysts pseudomorphed by aggregates of calcite, penninite, and carbonates; (g) and (h) skeletal and kink-banded micas.

102 F. Stoppa et al. / Lithos 188 (2014) 97–112

calcite with up to 1.2 wt.% MgO, with subordinate dolomite (up to15wt.% MgO) or ferroan dolomite (up to 9.8wt.% FeCO3). SrO averages0.2 wt.% and can reach up to 1.1 wt.%, MnO averages 0.2 wt.% and canbe up to 0.7 wt.%. LREE contents are up to 0.3 wt.%. Stable isotopesindicate an average, near-mantle values for δ13CPDB −3.80, and highaverage δ18OSMOW +22.17 (Table 3b, unpublished data courtesy of M.Brilli). This figure is typical of carbonates in extrusive carbonatites andhas been interpreted as due to sudden reaction of primary igneouscarbonate during eruption with the atmosphere (Zaitsev and Keller,2006).

Spinels are Fe–chromite with up to 35.5 Cr2O3 wt.%, ulvospineland Ti–magnetite solid solution with TiO2 up to 30.6 wt.%, and the rarespinel trevorite with NiO up to 41.9 wt.%. The ilmenite has variable but

high MnO contents, up to 12 wt.%, similar to values found in otherlamprophyric rocks (Rock et al., 1991). Other opaques are pyriteand chalcopyrite.

3.4. Modal classification

The STALs are difficult to classify on the basis of their modalmineralogy. Following the IUGS recommendations (Le Maitre,2002) they should be classified as minettes. However, their mineralassociation of kaersutite, groundmass aegirine and aegirine–augiterims of diopside phenocrysts, and the presence of analcime clearlyindicate that these rocks are more alkaline than minettes.The formation of aegirine and K-feldspar may be due to the

Fig. 3. (a) and (b) Conventional triangular diagrams for clinopyroxene showing diopside and aegirine in terms ofmolarWo–En–Fs andWEF–Jd–Ae; (c) Cr2O3 vsMg# (Mg/Mg+Fe2+) forSouthern Tuscany ALs; (d) Si (a.f.u.) vs Al (a.f.u.) showing undersaturation of clinopyroxene in STALs; (e) SiO2/Al2O3 vs Mg# showing diospide from STAL compared with clinopyroxenefrom worldwide lamprophyres (Rock et al., 1991).

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concentration of silica, alumina and alkalis in the silicate residuumduring carbonate precipitation or immiscible separation. Analcimeoccurs as a late-stage mineral, but because there is no clearindication that it replaces nepheline or other primary feldspathoids,it is probably a primary, groundmass phase co-precipitating withcalcite, K-feldspar, apatite, spinels and aegirine. Due to the presenceof ubiquitous analcime, the STALs are petrographically similar tosannaites with biotite being more abundant than the small kaersutitephenocrysts. The carbonate-rich STALs are clearly not ultramafic

lamprophyres (e.g., aillikites) because they contain abundant modalK-feldspar and lack perovskite or undersaturated phases.

4. Bulk rock geochemistry

4.1. Methodology

Major elementswere analysed byXRF, except CO2 (coulometry) andFeO (titration); trace elements by ICP-OES and ICP-MS. Concentrations

Fig. 4. (a) Classification of amphiboles in terms of Mg# vs Si (a.f.u.) (Leake et al., 1997); (b) Al (a.f.u.) vs Si (a.f.u.) showing saturation of the T site; (c) CaO/Na2O vs Al2O3/TiO2 comparingamphibole from STALs and worldwide lamprophyres (Rock et al., 1991); symbols as in (a); (d) Al–Mg–Fe2+ diagram for micas showing STAL mica composition in terms of molar content ofeastonite, phlogopite, siderophyllite and annite; (e) Al (a.f.u) vs Ti#; and (f) Ba (a.f.u.) vs Ti# for micas from STAL showing compositional variations from core to rim; symbols as in (d).LL=Lamproites , CAL=Calc-alKaline lamprophyres, UML=Ultramafic lamprophyres and AL=Alkaline lamprophyres.

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are given in wt.% for oxides and ppm for trace elements. Analyses werecarried out at XRAL Laboratories, North York, Ontario, Canada andActivation Laboratories (ACTLABS), Ancaster, Ontario, Canada. Most ofthe elements are reproducible within 6%, except for low concentrationsnear the detection levels which are reproducible within 20% of thequoted value. Electronic Supplements 8–10.

The 87Sr/86Sr, 143Nd/144Nd and 206Pb/204Pb, 207Pb/204Pb, 208Pb/204Pbisotopic ratios were analysed for fourteen bulk rock samples (Table 3a)using modified, conventional chemical separation techniques and amulti-collector Finnigan MAT 261 and Finnigan Triton TI massspectrometers operating in the static mode at Carleton University,Ottawa, Canada. Details of the analytical procedures are given in theElectronic Supplement 11–12. The Sr and Nd isotopic ratios werecorrected for mass fractionation by normalising the raw ratio

against the 88Sr/86Sr = 8.37500 and 143Nd/144Nd = 0.7219,respectively. The lead isotopic ratios were externally corrected formass fractionation against the double-spike corrected ‘true’ 208Pb/206Pbvalue for the NIST SRM 981 (Amelin and Davis, 2006). The meanfractionation correction factor per atomic mass unit (power law) was0.1519±0.0030% (n=29). The weighted mean results for the isotopicstandards run together with the Tuscan lamprophyres are as follows:NIST SRM 987 87Sr/86Sr = 0.710293 ± 74 (n = 5); Johnson andMatthey's NdStd in-house standard 143Nd/144Nd = 0.511847 ± 11(n = 3); NIST SRM 981 206Pb/204Pb = 16.950 ± 23, 207Pb/204Pb =15.506 ± 13, 208Pb/204Pb = 36.743 ± 33, 207Pb/206Pb = 0.91490 ± 6(n=4); USGS BCR-1 87Sr/86Sr=0.704992±6 (in-run 2σ error, n=1),143Nd/144Nd = 0.512636 ± 5 (in-run 2σ error, n = 1), 206Pb/204Pb =18.814 ± 4, 207Pb/204Pb = 15.631 ± 4, 208Pb/204Pb = 38.709 ± 13,

Table 3Section a. Atomic parent/daughter isotope abundance ratios, measured isotopic ratios and corrected for in-situ radioactive decay, initial isotopic ratios for the early Cretaceous alkalinelamprophyres of Southern Tuscany, Italy, assuming an age of 110Ma (Faraone and Stoppa, 1990). Section b. Stable isotopes.

Section a

Location Sample 87Rb 147Sm μa κb 87Sr 143Nd 206Pb 207Pb 208Pb 87Sr 143Nd εNd(110)c 206Pb 207Pb 208Pb

86Sr 144Nd 86Sr 144Nd 204Pb 204Pb 204Pb 86Sr 144Nd 204Pb 204Pb 204Pb

Measured Measured Measured Measured Measured Initial Initial Initial Initial Initiald

Senna River SF9 0.104 0.133 23.4 3.24 0.70653 0.51278 18.748 15.615 38.583 0.70635 0.51269 4.05 18.346 15.596 38.170SF9 rp. 0.11 0.133 0.51270 2.43SF11 0.045 0.129 7.8 3.31 0.70622 0.51267 18.794 15.683 38.870 0.70614 0.51258 1.92 18.654 15.676 38.718SF12 0.047 0.13 11 3.36 0.70493 0.51280 20.182 15.776 39.778 0.70486 0.51271 4.43 19.993 15.767 39.577SF30 0.12 0.128 17.6 3.34 0.70593 0.51279 18.724 15.610 38.501 0.70571 0.51270 4.32 18.344 15.592 38.077SF29 0.148 0.125 17.5 3.36 0.70527 0.51278 18.722 15.639 38.636 0.70505 0.51269 4.06 18.420 15.625 38.315

Murci PMT2 0.009 26.4d 0.70569 0.51274 18.660 15.645 38.589 0.70567 38.445PMT3a 0.045 0.121 12.7 3.54 0.70571 0.51275 18.673 15.623 38.526 0.70565 0.51266 3.46 18.455 15.612 38.281

Fosso Ripiglio FR1b 0.25 0.124 24.3 3.16 0.70518 0.51276 18.692 15.621 38.531 0.70481 0.51267 3.71 18.274 15.601 38.113FR5 0.099 0.121 59.1 3.42 0.70482 0.51277 19.652 15.650 39.301 0.70467 0.51269 4.03 18.635 15.601 38.199FR6 0.155 0.128 12.6 3.31 0.70466 0.51277 18.525 15.607 38.266 0.70439 0.51267 3.75 18.309 15.596 38.039FR8 0.172 0.129 12.9 3.32 0.70468 0.51274 18.529 15.595 38.252 0.70441 0.51265 3.33 18.308 15.584 38.019

Castiglioncello delTrinoro

S4 0.112 0.124 31.9 3.39 0.70531 0.51279 18.850 15.618 38.636 0.70511 0.51271 4.38 18.302 15.592 38.047S5 0.108 0.125 39 2.87 0.70527 0.51278 18.888 15.615 38.547 0.70508 0.51269 4.05 18.216 15.582 37.935S16 0.101 0.124 48 3.53 0.70584 0.51283 19.164 15.625 38.926 0.70567 0.51274 5.16 18.339 15.585 38.001S16 rp. 0.103 0.124 66.1 4.04 0.51275 19.182 15.635 38.968 3.56

Section b

Location Sample δ18O‰ (SMOW) δ13C‰ (PDB)

Senna River SF11 +22.02 −3.52SF11 +21.99 −3.56SF23 +22.43 −4.14SF23 +22.22 −4.01

Notes: The Sr andNd isotopic ratioswere corrected formass fractionation bynormalising the raw ratio against the 88Sr/86Sr=8.37500 and 146Nd/144Nd=0.7219, respectively. TheNBS987and La Jolla international standardsweremeasured as0.710250 ± 20 (2σ) and 0.511850±20 (2σ), respectively (over 7years). The Pb isotopic ratioswere corrected formass fractionationagainst the NBS 981 standard see Electronic Supplements 11-12. Themeasured Sr and Nd isotopic ratios are reproduciblewithin±0.02% of the quoted values at the 2σ level, whereas thereproducibility of the measured Pb isotopic ratios is within ±0.1% at the 2σ level based on replicate runs. The atomic parent/daughter isotope abundance ratios used for in-situ decaycorrection were calculated using both XRF (Rb, Sr, Th), and INAA and ICP-MS (Sr, Pb, Sm, Nd, U, Th) analyses from the same bulk rock powder samples.

a μ=atomic 238U/204Pb ratio.b κ=atomic 232Th/238U ratio.c εNd(110)=(143Nd/144Ndsample at 110Ma/143Nd/144NdCHUR at 110Ma−1)∗10000. Positive εNd values indicate depleted source relative to ‘ChondriticUniformReservoir’, whereas

negative values indicate a source enriched in the LREE.d Atomic 232Th/204Pb ratio.

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207Pb/206Pb = 0.83085 ± 6, 208Pb/206Pb = 2.0574 ± 3 (n = 3). Theuncertainties are at the 95% confidence level and apply to the lastsignificant digits of the respective mean values. The analyses of theduplicate samples indicate that the measured Sr and Nd isotopic ratioswere reproducible to within ±0.02% of the quoted values at the 2σlevel, and the reproducibility of the Pb isotopic ratios was ±0.1% atthe 2σ level. The effects of the procedural blanks were negligiblegiven the concentrations of Sr, Pb and Nd, and the size of the analysedsamples. Carbon and oxygen stable isotopes were analyzed at theMass Spectrometry Lab. of IGAG, CNR (Monterotondo, Rome).

4.2. Major elements

Geochemically the STALs are generally ultrabasic rocks (averageSiO2 b43wt.%), with a potassic character (Fig. 5a; Table 2). TiO2 rangesfrom 1.73 to 4.19wt.% and averages 2.73wt.%. Al2O3 is rather constantand averages 11.7wt.%. CaO is between 8 and 10wt.% in most samples.CaO strongly correlateswith CO2 that can reach up to 20.3wt.% (Fig. 5b).The Mg# (i.e. Mg/Mg + Fe2+) averages 0.76 and inversely correlateswith CO2 (Fig. 5c). There is no correlation between alkalinity indexandMg# as observed in other lamprophyres. High LOI and CO2 preventthe use of the TAS classification diagram. The STALs plot in an areabetween shoshonitic and alkaline lamprophyres in the normativetriangle (Ab + An+ Ne)–(Or + Lc)–(Ol + Di + Hy+Mt + Il) (Rock,1987). In ternary diagrams Al2O3–MgO–CaO and SiO2/10-CaO–TiO2x4(Rock et al., 1991), the data of STALs plot in the field of the ALs(Fig. 6a, b). The WIP (i.e. Weathering Index of Parker, Parker, 1970)

and CIA (i.e. Chemical Index of Alteration of Nesbitt and Young, 1982)are above 80 and below 55, respectively, indicating that most of thedyke rocks and lavas are fresh and have not suffered notable alterationor weathering (Fig. 5d, Bahlburg and Dobrzinski, 2011).

4.3. Minor and trace elements

Cr and Ni positively correlate with Mg# and average 341 and325 ppm respectively, and sum up to 1172 (Ni+Cr) ppm (Fig. 5c), afigure considerably higher than crustal sediments (Fig. 5c). Ba rangesfrom 173 to 4527 ppm and averages 973 ppm. Sr ranges from 346 to1118 ppm and averages 690 (Table 2). Tuscany ALs have a variableconcentration of LILEs (i.e. Large Ion Lithophile Elements), especiallyRb and K, and show a steepmantle-normalised pattern for incompatibleelements. LILEs are about 100 times higher than primitive mantle,HFSEs (i.e. High Field Strength Elements) are about 10 times higherand compatible elements are close to primitive mantle values (Fig. 7a,Table 2). LILEs are higher in the high Mg# and Cr+Ni-rich samples.The trace-element, mantle-normalised patterns generally overlap theaverage alkali lamprophyre composition, including the negative Kanomaly pointed out by Rock et al. (1991) on the basis of 310 analyses(Fig. 7a). LILEs show marked negative Pb and positive Ba spikeswith respect to GLOSS (GLobal Subducting Sediment, Planck andLangmuir, 1998) which in general has LILE abundances similarto average alkaline lamprophyre (Fig. 7a). We prefer GLOSS as arepresentative composition of subducting sediments than APS (AtlanticPelagic Sediments, Rollinson, 1993) because the central-north Atlantic

Fig. 5. (a) K2O vs Na2O showing the variation from high potassic to sodic character for Italian ALs and Southern Tuscany ALs; (b) CaO vs CO2; (c) (Cr + Ni) vs Mg# for STALs; and (d)Weathering Index of Parker (WIP): 100 × (Na/0.35 + Mg/0.9 + K/0.25 + Ca/0.7) vs Chemical Index of Alteration (CIA): 100 x (Al2O3/(Al2O3 + CaO + Na2O + K2O) (Bahlburg andDobrzinski, 2011) for Southern Tuscany Als and others from Italy. Shaded box for fresh rocks; symbols as in (c).

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has only passive margins. Alpine flysch is too young to be subductedbefore the early Cretaceous and there was no flysch in the JurassicTethys. Incompatible elements, normalised to primitive mantle, shownegative spikes of Sr, Hf, Ti,Yb, and U, similar to GLOSS. However,STALs have a much higher abundance of HFSEs with respect to theGLOSS and do not show negative spikes of Ta and Nb (Fig. 7a). Rapolanoalkali basalts show a similar LILE–HFSE distribution but at a lowerconcentration level (Fig. 7a).

Although the chondrite-normalised REE patterns do not have anegative Eu anomaly there is a small Ce positive anomaly, and theLREE/HREE ratios increase with increasing ΣREE (Fig. 7b). (La/Yb)cnand (Ce/Yb)cn are up to 30 and 26, respectively. The LREE and MREEdistribution in STALs is similar to that of the average worldwide AL(Rock, 1987; Rock et al., 1991), although the latter has slightly higherHREEs (Fig. 7b). The LREE/HREE ratios aremuchhigher in lamprophyresand especially in STALs with respect to GLOSS (Fig. 7b). NearbyRapolano igneous rocks have entirely different REE patterns, asexpected for basalts, with a LREE/MREE of about 1 and a very lowLREE/HREE of about 3 (Fig. 7b).

A plot of Sm/Y vs La/Sm can be used to model the degree of partialmelting of the mantle source (Mana et al., 2012). This plot suggeststhat the STALs formed by a 3–4% of partial melting of a variable,garnet-bearing peridotite (Fig. 8a). In addition, STALs have high Nband Sr vs La/Sm (Fig. 8b, c), considered a typical feature ofmelts derivedfrom amantlemesomatised by carbonatitic fluids (Downes et al., 2005).These results are consistent with the incompatible element distribution,where the STALs and other Italian ALs display considerably steeper REEpatterns and much higher abundances compared to the Rapolano.

STALs have high Nb/Ta (N20), Ce/Pb (N20), and Nb/U (N50), similarto those of the primitive mantle, and have high abundances of Nb andZr, and low abundances of Hf and Y, a signature considered typical ofwithin-plate basalts (Green, 1995). HFSE4+ and HFSE5+ ratios arethought to be ‘immobile’ during melt fractionation and able to reflectmantle source compositions (Wood, 1980). Because of high HFSEsolubility in AL these melts are capable of precipitating specific HFSE-rich mineral phases, unlike basalts (Chakhmouradian, 2006). The STALshave Zr/Hf and Nb/Ta ratios than those of crust and mantle suggestingthe presence of residual Hf+Ta-bearing titanates in their source(Lavecchia et al., 2006; Tappe et al, 2008) (Fig. 9a). Some Italian ALsshow a mantle composition and other a crust-like signature (Fig. 9b, c,d). However, the Nb/U and Ce/Pb ratios, Mg#s, and Cr and Ni contentsof the STALs are inconsistent with any bulk crustal involvement.

5. The Sr, Pb, and Nd isotopic data

Measured ratios have been back corrected assuming an age of110 Ma, the assumed emplacement age of the STALs (Faraone andStoppa, 1990). The initial ratios are quite variable and exceed the quotedanalytical uncertainties. The initial 87Sr/86Sr ratios show the greatestvariation and range from 0.70439 to 0.70635. The initial 143Nd/144Ndratios fall between 0.51258 to 0.51274. The initial 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios range from 18.22 to 19.99, from 15.58 to15.77 and from 37.94 to 39.58, respectively (Table 3a).

In the 143Nd/144Nd vs 87Sr/86Sr diagram (Fig. 10a) the STAL clusterclose to the CHUR–bulk Earth intersection. The initial 143Nd/144Nd ratiosare relatively constant compared to the relatively large variations in

Fig. 6. (a) and (b) Ternary diagramsAl2O3–MgO–CaO and SiO2/10–CaO–TiO2 x4 (Rock, 1987) for STALs andworldwide lamprophyres. Notemost of the STAL data fall in the field forworldwideALs.

Fig. 7. Multi-element diagrams for Rapolano alkali basalts, STALs, Italian ALs, worldwideALs (Rock et al., 1991), and GLOSS (Planck and Langmuir, 1998): (a) primordial mantle-normalised, incompatible-element patterns; Primordial mantle values are from Wankeet al. (1984), Taylor and McClennan (1985), McDonough and Sun (1995); (b) C1-chondrite-normalised REE patterns; C1-chondrite values are from McDonough and Sun(1995).

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87Sr/86Sr initial ratios. Such large variations in Sr isotopic ratios(0.70439 to 0.70635) can be attributed to several processes,including alteration, perhaps reflected by carbonates in the form ofveins and fracture infillings. However, the high SrO contents (0.15–0.97 wt.%, Vichi et al., 2005) of the carbonate ocelli is more in keepingwith a magmatic origin for at least some of the carbonates, perhapsinvolving a volatile CO2-rich melt and possible immiscible separationfrom a carbonated silicate parental liquid. Contamination of the originalmelt with continental crust or host limestone provides another way toincrease the 87Sr/86Sr ratios of the lamprophyres and because of this wehave plotted GLOSS and a data point “AIL” in several diagrams. AIL isAverage Italian Limestone based on analyses of limestones of differentages from along the length of Italy (Bell and Castorina, unpublisheddata). Although bulk continental crust or limestone contaminationmight well explain the variation in 87Sr/86Sr, such a mechanismis inconsistent with the Nd isotopic ratios and overall geochemistry ofthe lamprophyres. In the absence of any other ways of generating thevariable 87Sr/86Sr, the simplest explanation of the isotopic data fromSTALs involves mixing at mantle depths between two isotopicallydistinct end-members, either of two quite chemically differentsources (e.g., heterogeneous asthenosphere, or lithospheric and sub-lithospheric mantle) or melting and mixing of isotopically distinctminerals, such as those expected in old, metasomatised lithosphere(Meen et al., 1989; Ionov, 2002; Tappe et al., 2008). However, it seemsunlikely that lithosphere represents the actual source af the Italianlamprophyres since lithosphere is too cold to melt.

Except for one sample from Senna River (SF12), the STALs displayrelatively tight grouping of initial 206Pb/204Pb and 207Pb/204Pb ratioswhile the initial 208Pb/204Pb is more variable (Fig. 10d and e, Table 3a).Given its anomalous, radiogenic Pb isotopic composition, sample SF12is more likely to reflect a post-crystallisation disturbance in theU/Pb and Th/Pb systems and therefore is omitted from the followingdiscussion.

Because the lamprophyres are relatively young, direct comparisoncan be made with the present day isotopic components found in thesub-oceanic mantle (DMM, EM1, EM2, HIMU, PREMA, FOZO). DMMcharacterises the sources of MORBs and the remainder of thecomponents are based mainly on isotopic data from OIBs (Hart, 1988;Hart et al., 1992; Hauri et al., 1994; Zindler and Hart, 1986). The onlymantle end-members that show some resemblance to the data fromthe lamprophyres are FOZO and EM2, and in some of the isotope ratio

Fig. 8. (a) Sm/Y vs La/Sm for STALs showing models of partial melting for mantle peridotite with variable garnet proportion; tick marks indicate the degree of melting after Mana et al.(2012); (b) and (c) Nb vs La/Sm and Sr vs La/Sm diagrams showing the contrasting effects of mantle metasomatism by silicate and carbonatite melts after Downes et al. (2005).

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diagrams the data lie along, or on, a line drawn between these twocomponents. FOZO is of particular interest since it is considered amarker of deep-seated magmatism normally associated with plumes(e.g., Campbell and O'Neill, 2012).

On the Pb–Pb isotope ratio diagrams, the STALs, FOZO, AIL, and GLOSSall fall close to the end of the Stacey–Kramers growth curve, a curve thatshows the variation in Pb isotopic composition of average continentalcrust over time (Stacey and Kramers, 1975). The fact that the 207Pb/204Pb ratios for AIL and GLOSS are higher than those for both FOZO andmost of the STALs implies the Pb from the former was obtained frommuch older sources. Ruling out bulk contamination by either AIL orcontinental crust leads to the interpretation that the arrays might berelated to mixing lines involving two, isotopically distinct, mantlecomponents.

The following two points are worth noting:

(1) The first source with the highest 206Pb/204Pb ratio and the lowest87Sr/86Sr appears to be similar to FOZO (FOcus Zone), a com-ponent proposed by Hart and co-workers and based on thepoint of convergence of linear arrays from oceanic basalts andassociated rocks in three dimensional isotope ratio diagramsinvolving EM1, EM2, HIMU and DMM (Hart et al., 1992; Hauriet al., 1994). Bell et al. (2013) considered FOZO to be a common

component involved in the generation of Cenozoic magmatismin Italy and was part of the evidence used to argue for plumeactivity in Italy. The possible involvement of the FOZO end-member is better seen in the binary projection of the three-dimensional “mantle plane” defined by the DMM, HIMU andEMI end-members in the three-dimensional Sr–Pb–Nd isotopicspace (Fig. 10f).

(2) The second source has a similar 143Nd/144Nd ratio, but the 87Sr/86Srratio is much higher and the 206Pb/204Pb and 208Pb/204Pb ratiosare slightly lower than those of FOZO. Although 143Nd/144Nd vs87Sr/86Sr vs 206Pb/204Pb ratio diagrams may suggest the EM2mantle end-member as the second component, the Pb–Pb isotopicratio diagrams clearly rule out this possibility (Fig. 10).

The relatively uniform 143Nd/144Nd and Pb isotopic ratios of theSTALs, along with the large variations in the 87Sr/86Sr, suggest thatthe sources of the two end-members had quite different time-integrated Rb/Sr ratios, yet fairly similar time-integrated Sm/Nd, U/Pb and Th/Pb ratios. Variations in the Rb/Sr ratio accompanied byrelatively constant Sm/Nd and U/Pb ratios might suggest localenrichment of the mantle with a metasomatising agent rich in bothLILE and some HFSE. The elevated K, Ba and P abundances in thelamprophyres up to 10–100 times that of MORB (Faraone and

Fig. 9. Incompatible-element ratio diagrams for STALs showing Italian ALs, GLOSS, TC (total crust after Rudnick and Gao, 2003) for comparison and the effect of residual rutile in the bulksilicate Earth (BSE) source. Primordial mantle and chondrite C1 values after McDonough and Sun (1995).

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Stoppa, 1990) are consistent with a metasomatically modifiedmantle containing hydrous minerals.

The enormous variability shown by the isotopic data from all of theCenozoic volcanic rocks in Italy, including those from the classic RomanProvince, can be explained in terms of four, distinct, end-members,HIMU, EM1, FOZO, and ITEM (Lavecchia and Bell, 2012; Bell et al.,2013), withmost of the data falling along a binary mixing curve betweenthe latter two components (Bell et al., 2004, 2013). FOZO and ITEM thusform important and ubiquitous isotopic components in the mantleunderlying Italy. FOZO forms an end-member common to all, whereasITEM is a well-defined, highly radiogenic, end-member (87Sr/86Sr N 0.720) that is spatially more restricted and is related only tomagmatism that occurred along the eastern margin of the TyrrhenianSea and the length of Italy from Sicily to the Alps. ITEM has beenattributed either to widespread metasomatic activity associatedwith a plume of deep-seated origin or the involvement of sediments/upper continental crust/oceanic crust/metasomatised lithosphererecycled into a FOZO-like mantle prior to the Alpine Orogeny (forreviews see Owen, 2008; Bell et al., 2013).

The Italian alkaline lamprophyres shaded fields shown in all of theisotope ratio diagrams approximate the binary mixing curves betweenITEMand FOZOwhich is similar to theMIRT, theMain ItalianRadiogenicTrend of Bell et al., 2013). In all instances, data from the STALs lie on orclose to the curves implying that they belong to the MIRT of Bell et al.(2013) and to the general trend formed by the other Italian alkalinelamprophyres and with it the implication that both ITEM and FOZOcontributed to their sources. It should be noted that all of the Italianlamprophyres (alkaline, calcalkaline, and ultramafic) form part of MIRT,

with isotopic values that extend from ITEM (Western Alps, Owen, 2008)through to FOZO (Abruzzo, Stoppa, 2008). Low but different degrees ofpartial melting of a metasomatised mantle are consistent with thesefindings. It is interesting that ITEM shows Pb–Pb isotopic systematicscomparable to those of the EM2 mantle end-member. This suggests amuch older Pb source for ITEM than those for the present continentalcrust and the trench sediments, which have a much lower 207Pb/204Pbsignatures at a similar 206Pb/204Pb.

6. Discussion

STAL's mineralogy, geochemistry, and isotopic geochemistryindicate that these rocks are largely primitive magmas produced bypartial melting of a modified asthenospheric mantle source. STALsdisplay a clear positive correlation betweenMg#, Cr, Ni and LILE, rulingout simple magma differentiation. In addition, their high 87Sr/86Sr andmoderately radiogenic 143Nd/144Nd ratios are similar to many otherCenozoic mafic alkaline rocks of Italy. In particular, they exhibit similargeochemistry to other Italian ALs from Sardinia and in peninsular ItalyfromAbruzzo to the Alps, suggesting that they originated from a similarmantle source, despite the different emplacement ages and tectonicsettings (Bell et al., 2004, 2013; Lavecchia and Bell, 2012). Italian ALsshow specific isotopic features that can be described in terms of mixingof two mantle end-members. The high 87Sr/86Sr component is thoughtto reflect GLOSS or metasomatised lithosphere recycled into themantleat least 110 Ma ago, or LILE-rich metasomatic fluid/melt within theupwelling FOZO mantle. Our model excludes high-temperature, low-pressure, bulk assimilation of sedimentary rocks, limestones and/or

Fig. 10. Initial isotopic ratio diagrams: (a) 143Nd/144Nd vs 87Sr/86Sr; (b) and (c) 143Nd/144Nd and 87Sr/86Sr vs 206Pb/204Pb, respectively; (d) and (e) 207Pb/204Pb and 208Pb/204Pb vs 206Pb/204Pb,respectively. Geochron line plotted assuming the age of the Earth of 4.57Ga, and the initial terrestrial Pb isotopic composition after Tatsumoto et al. (1973). Curve shows isotopic evolutionof thecontinental crust after Stacey and Kramers (1975); (f) end-on projection of the three-dimensional ‘mantle plane’ based on the mantle components DMM, HIMU, and EM1. The coordinatesystem has been rotated about the initial 87Sr/86Sr abscissa so that the ‘mantle plane’ is normal to the page. The ordinate is a function of both initial 206Pb/204Pb and initial 143Nd/144Nd andis given by: ƒ(143Nd/144Nd, 206Pb/204Pb)=[(143Nd/144Nd)2+(206Pb/204Pb)2]1/2 sin[arctan{(143Nd/144Nd)/(206Pb/204Pb)}+0.000064] (Zindler et al., 1982). Shadedfield is for the Italian alkalinelamprophyres (unpublished data). The values we have chosen for FOZO are: 87Sr/86Sr=0.703–0.704, 143Nd/144Nd=0.5128–0.5130, 206Pb/204Pb=18.5–19.5, 207Pb/204Pb=15.55–15.65, and208Pb/204Pb=38.8–39.3 (Hauri et al., 1994). See text for discussion, the sources of the mantle end-member compositions, and other isotopic references.

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pelites. Limestone assimilation is ruled out on the basis of isotopes andalso because it is an auto-limiting phenomenon since the decompositionof carbonate would ultimately freeze the melt. We also see nopetrographic evidence for skarn formation which is expected when CaOcombines with silica in the melt. Chilled margins of STALs indicate rapidcooling of themeltmaking its dilution by contaminationwith the countryrocks unlikely. In addition, bulk contamination by crustal rocks would

lead to silica-saturation of themelt accompanied by an increase in alkaliescoupled with a decrease in Mg#, Cr, and Ni, none of which characterisethe STALs. Although initial 87Sr/86Sr ratios positively correlate with theelevated H2O contents of the STALs, the 87Sr enrichment is unlikely tobe due to the secondary alteration since 87Sr/86Sr does not correlate eitherwith WIP or CIA indices (Fig. 5d). Since a hydrous source is aprerequisite for lamprophyre magmas, it would seemmore plausible

Fig. 11. Binary diagrams of Nd and Sr isotopic ratios vs Ta/U ratio showing primordialmantle, C1 chondrite, ITEM, GLOSS and the Italian alkaline lamprophyres (shaded field).

111F. Stoppa et al. / Lithos 188 (2014) 97–112

that the correlation reflects mineralogy of the mantle source forSTALs, specifically the proportion of Rb-rich hydrous phases (e.g.,phlogopite, amphibole).

We conclude that the peculiar geochemistry of STALs and otherItalian ALs characterises primary melts generated by direct partialmelting of a FOZO-like asthenospheric mantle containing LILE- andvolatile-rich component (ITEM) as either metasomatic/magmaticveins or recycled GLOSS, continental crust, or metasomatisedlithospheric mantle, to cite some possibilities. Although the high 87Sr/86Sr ITEM component appears to have time-averaged Rb/Sr, Sm/Nd,Th/Pb and U/Pb ratios comparable to those of GLOSS, the former hasmuch higher 207Pb/206Pb at a similar 206Pb/204Pb, suggesting a mucholder source of Pb. The western Alps lamprophyres are much moreradiogenic than STALs and are considered to approach the proposedITEM mantle end-member (Owen, 2008).

STALs seem to have some similarity to GLOSS and this feature hasbeen attributed to the Eo-Alpine subduction of crustal material intothe mantle and then subsequent melting (Mattioli et al., 2011). It isdifficult to associate modern GLOSS directly to ITEM, which showsdistinct Pb-Pb isotopic signatures suggesting a much older source ofPb for the latter. ITEM has yet to be observed in active subductionzones, and STALs and many other Italian ALs pre-date the Eo-Alpinesubduction. Although we cannot rule out the involvement of ancient,recycled GLOSS or continental crust, we favour an alternative model.Correlations between radiogenic isotopes and HFSE ratios of STALs arenoteworthy (Fig. 11a, b). The data from STALs in Fig. 11 lie at the depletedextreme of the trend formed by Italian alkaline lamprophyreswhich doesnot overlapwith GLOSS,making the latter an unlikely candidate for ITEM.

The western Alps lamprophyres have extreme isotopic ratios and muchhigher Ce/Pb and much lower Nb/U than STAL. We have yet to formulatean acceptable model that can explain the extraction and transfer ofradiogenic components from a highly radiogenic source (e.g., continentalcrust) into the surrounding mantle while still preserving an ultrabasiccomposition during partial melting. The mafic characteristic coupledwith high alkalies is found in many alkaline ultrabasic rocks in cratonicareas, and has been attributed to very old metasomatised continentallithosphere (Meen et al., 1989; Tappe et al., 2008). However, the Tethyslithosphere is only Jurassic in age whereas Eo-Alpine subduction is lateCretaceous.

In our opinion, the STALs demonstrate the presence of a meta-somatised asthenospheric mantle, but we argue that the metasomaticagent is unrelated in time and space to Tethys subduction. Data suggestthat the metasomatic agent is not a silicate fluid or melt but probablyone that has a chemical composition similar to an alkaline carbonatite.Rosatelli et al. (2007) found melt veins and grain-boundary reactionin mantle nodules from Vulture Volcano suggesting percolation ofmetasomatising alkaline carbonatite melts characterised by high Rb/Srand low Sm/Nd ratios (Castorina et al., 2000). The findings ofCastorina et al. (2000) and Rosatelli et al. (2007) are consistent withthe general model of mantle metasomatism by an alkaline carbonatiticfluid (Meen et al., 1989). A C–H–O–K-rich fluid could be released fromthe mantle/core boundary during plume activity and could emerge atcrustal levels, in a relatively short time, triggered by core–mantleperturbations (Bell et al., 2013; Herzberg et al., 2013; Vidale andHedlin, 1998). Alternatively, ITEM, which perhaps first emerged in theMediterranean as early as 110Ma, could be an old recycled sediment,compositionally not unlike GLOSS, entrained in the upwelling FOZOmantle Bell et al. (2013).

7. Conclusions

On the basis of the new petrological, mineralogical and geochemicaldata from the Southern Tuscany lamprophyres the followingconclusions can be drawn:

1. The generation of the Tuscan lamprophyres involved two sources,one similar to FOZO and the other with similar 143Nd/144Nd butwith a much higher 87Sr/86Sr ratio and lower Pb isotopic ratios. The87Sr/86Sr ratios along with other geochemical characteristics cannotbe attributed to low pressure assimilation of crustal materials.

2. The isotopic data from STAL fall on the main isotope ratio trend forItalian alkaline lamprophyres and other alkaline igneous rocks ofItaly (MIRT of Bell et al., 2013) suggesting that both ITEM and FOZOare involved in their origin.

3. The positive correlation of Mg# with Cr+Ni and LILEs, plus high Nband Sr indicate potential carbonatite metasomatism of the mantlesource.

4. The origin of the lamprophyric melts is consistent with the model ofFaraone and Stoppa (1990) and Bell et al. (2013) in which the meltswere generated from a metasomatised source during the LigurianTethys extension, resulting from major transcurrent movementsthat occurred during migration of the European and African plates.

5. Our favoured model is very similar to the one of Meen et al. (1989),and is supported by the studies of mantle nodules in Italy (Rosatelliet al., 2007), which invokes mantle metasomatism by an LILE- andvolatile-rich agent (e.g., alkaline carbonatitic melts) associated witha mantle plume.

Supplementary data to this article can be found online at http://dx.doi.org/10.1016/j.lithos.2013.10.010.

Acknowledgements

The authors are grateful to S. Tappe and an anonymous reviewer fortheir critical and helpful reviews of this paper. Special thanks are due to

112 F. Stoppa et al. / Lithos 188 (2014) 97–112

A.Marzoli andDon Baker for their careful and constructive review of thefinal version. We would like to thank Frances Wall and the EMMA LabStaff (John Spratt, Terry Williams, Terry Greenwood, Anton Kearsleyand Tony Wighton) of the Natural History Museum in London fortheir assistance with the sample preparation and analytical facilities.Ineke de Jong, Carleton University, is thanked for help with the samplepreparation. We thank M. Brilli for having carried out the isotopicanalysis of carbon and oxygen. We thank Bernardo Cesare for the useof an optical microscope at Padua University. The research was partiallyfunded by the National Sciences and Engineering Research Council,Canada (Grant A7813 to K.B.), and NATO and Carleton University(fellowships to A.R.). Sampling, thin sections, bulk rock geochemicalanalyses and microprobe analyses were funded by G.d'AnnunzioUniversity grants awarded to G. Vichi, M. Schiazza and F. Stoppa.

References

Amelin, Y., Davis, W.J., 2006. Isotopic analysis of lead in sub-nanogram quantities by TIMSusing a 202Pb–205Pb spike. Journal of Analytical Atomic Spectrometry 21 (10),1053–1061.

Bahlburg, H., Dobrzinski, N., 2011. Chapter 6. A review of the chemical index of alteration(CIA) and its application to the study of Neoproterozoic glacial deposits and climatetransitions. In: Arnaud, E., Halverson, G.P., Shields, G.A. (Eds.), The Geological Recordof Neoproterozoic Glaciations. Geological Society, London, Memoir, 36, pp. 81–92.http://dx.doi.org/10.1144/M36.6.

Bailey, D.K., Woolley, A.R., 1995. Magnetic quiet periods and stable continentalmagmatism: can there be a plume? In: Anderson, D.L., Hart, S.R., Hofmann, A.W.,Lehnert, K. (Eds.), Plume 2: Alfred-Wegener-Conference extended abstracts, July17–21, Schloss Ringberg, Rottach-Egern, Germany. Terra Nostra, 3, pp. 15–19.

Bell, K., Castorina, F., Lavecchia, G., Rosatelli, G., Stoppa, F., 2004. Is there a mantle plumebelow Italy? Eos 85 (50), 541–547.

Bell, K., Lavecchia, G., Rosatelli, G., 2013. Cenozoic Italianmagmatism: isotope constraints forpossible plume-related activity. Journal of South American Earth Sciences 41, 22–40.

Brogi, A., Cornamusini, G., Costantini, A., Di Vincenzo, G., Lazzarotto, A., 2000. Cretaceousvolcanism of the Southern Tuscany: record of volcanic bodies from Tuscan successionof Rapolano Terme. Memorie della Societa Geologica Italiana 55, 329–337.

Brunacci, S., Donati, C., Farone, D., Manganelli, V., Stoppa, F., 1983. Vulcanismo alcalinocretaceo post-ofiolitico nell'alloctono liguride della Toscana meridionale. I: L'atreadel T. Senna (Siena-Grosseto). Ofioliti 8 (1), 47–76.

Campbell, Ian H., O'Neill, Hugh St C., 2012. Evidence against a chondritic Earth. Nature483, 553–558.

Castorina, F., Stoppa, F., Cundari, A., Barbieri, M., 2000. An enriched mantle source forItaly's melilitite–carbonatite association as inferred by its Nd–Sr isotope signature.Mineralogical Magazine 64 (4), 625–639.

Chakhmouradian, A.R., 2006. High-field-strength elements in carbonatitic rocks: geo-chemistry, crystal chemistry and significance for constraining the sources ofcarbonatites. Chemical Geology 235, 138–160.

Debenedetti, A., 1958. Sulle cosiddette “rocce ofiolitiche” della Valle della Senna (MonteAmiata). Rendiconti Società Italiana di Minineralogia e Petrologia 14, 157–164.

Dercourt, J., Zonenshain, L.P., Ricou, L.E., Kazmin, V.G., Le Pichon, X., Knipper, A.L.,Grandjacquet, C., Sbortshikov, I.M., Geyssant, J., Lepvrier, C., Pechersky, D.H., Boulin,J., Sibuet, J.-C., Savostin, L.A., Sorokhtin, O., Westphal, M., Bazhenov, M.L., Lauer, J.P.,Biju-Duval, B., 1986. Geological evolution of the Tethys belt from the Atlantic to thePamirs since the LIAS. Tectonophysics 123 (1–4), 241–315.

Downes, H., Balaganskaya, E., Beard, A., Liferovich, R., Demaiffe, D., 2005. Petrogeneticprocesses in the ultramafic, alkaline and carbonatitic magmatism in the Kola AlkalineProvince: a review. Lithos 85, 48–75.

Faraone, D., Stoppa, F., 1990. Petrology and regional implication of Early Cretaceousalkaline lamprophyres in the Ligure-Maremmano Group (Southern Tuscany, Italy):an outline. Ofioliti 15 (1), 45–59.

Green, T.H., 1995. Significance of Nb/Ta as an indicator of geochemical processes in thecrust–mantle system. Chemical Geology 120 (3–4), 347–359.

Hart, S.R., 1988. Heterogeneous mantle domains: signatures, genesis and mixingchronologies. Earth and Planetary Science Letters 90 (3), 273–296.

Hart, S.R., Hauri, E.H., Oschmann, L.A., Whitehead, J.A., 1992. Mantle plumes andentrainment: isotopic evidence. Science 256, 517–520.

Hauri, E.H., Whitehead, J.A., Hart, S.R., 1994. Fluid dynamic and geochemicalaspects of entrainment in mantle plumes. Journal of Geophysical Research 99 (B12),24275–24300.

Herzberg, C., Asimow, P.D., Ionov, D.A., Vidito, C., Jackson, M.G., Geist, D., 2013. Nickel andhelium evidence for melt above the core–mantle boundary. Nature 493, 393–397.http://dx.doi.org/10.1038/nature11771.

Ionov, D., 2002. Mantle structure and rifting processes in the Baikal–Mongolia region:geophysical data and evidence from xenoliths in volcanic rocks. Tectonophysics351, 41–60.

Lavecchia, G., Bell, K., 2012. Magmatotectonic zonation of Italy: a tool to understandingMediterranean geodynamics. In: Stoppa, F. (Ed.), Updates in Volcanology — AComprehensive Approach to Volcanological Problems. INTECH, pp. 153–178.

Lavecchia, G., Stoppa, F., Creati, N., 2006. Carbonatites and kamafugites in Italy: mantle-derived rocks that challenge subduction. Annals of Geophysics 49 (1), 389–402.

Le Maitre, R.W., 2002. Igneous Rocks: A Classification and Glossary of Terms, 2nd ed.Cambridge University Press, Cambridge.

Leake, B.E., Woolley, A.R., Arps, C.S.E., Birch,W.D., Gilbert, M.C., Grice, J.D., Hawthorne, F.C.,Kato, A., Kisch, H.J., Krivovichev, V.G., Linthout, K., Laird, J., Mandarino, J., Maresch,W.V., Nickel, E.H., Rock, N.M.S., Schumacher, J.C., Smith, D.C., Stephenson, N.C.N.,Ungaretti, L., Whittaker, J.W., Youzhi, G., 1997. Nomenclature of amphiboles: reportof the subcommittee on amphiboles of the International Mineralogical Association,Commission on New Minerals and Mineral Names. Mineralogical Magazine 61,295–321. http://dx.doi.org/10.1180/minmag.1997.061.405.13.

Mana, S., Furman, T., Carr, M.J., Mollel, G.F., Mortlock, R.A., Feigenson, M.D., Turrin, B.D.,Swisher III, C.C., 2012. Geochronology and geochemistry of the Essimingor volcano:melting of metasomatized lithospheric mantle beneath the North TanzanianDivergence zone (East African Rift). Lithos 155, 310–325.

Mattioli, M., Lustrino, M., Ronca, S., Bianchini, G., 2011. Alpine subduction imprint inApennine volcaniclastic rocks. Geochemical-petrographic constraints and geodynamicimplications from Early Oligocene Aveto–Petrignacola Formation (N Italy). Lithos 134,201–220.

McDonough, W.F., Sun, S.-S., 1995. The composition of the Earth. Chemical Geology 120,223–253.

Meen, J.K., Ayers, J.C., Fregeau, E.J., 1989. A model of mantle metasomatism by carbonatealkaline melts: trace-element and isotopic compositions of mantle source regions ofcarbonatites and other continental igneous rocks. In: Bell, K. (Ed.), Carbonatites:Genesis and Evolution. Unwin Hyman, London, pp. 464–499.

Mitchell, R.H., 1994. Suggestions for revisions to the terminology of kimberlites andlamprophyres from a genetic viewpoint. In: Meyer, H.O.A., Leonardos, O.H. (Eds.),Proc. Fifth Int. Kimberlite Conf. 1. Kimberlites and Related Rocks and MantleXenoliths. Spec. Publ., 1/A. Companhia de Pesquisa de Recursos Minerais, Brasilia,pp. 15–26.

Nesbitt, H.W., Young, G.M., 1982. Early Proterozoic climates and plate motions inferredfrom major element chemistry of lutites. Nature 299, 715–717.

Owen, J.P., 2008. Geochemistry of lamprophyres from the Western Alps, Italy:implications for the origin of an enriched isotopic component in the Italian mantle.Contribution to Mineralogy and Petrology 155, 341–362.

Parker, A., 1970. An index of weathering for silicate rocks. Geological Magazine 107,501–504.

Planck, T., Langmuir, C.H., 1998. The chemical composition of subducting sediment and itsconsequences for the crust and mantle. Chemical Geology 145, 325–394.

Rock, N.M.S., 1987. The nature and origin of lamprophyres: an overview. In: Fitton, J.G.,Upton, B.G.J. (Eds.), Alkaline Igneous Rocks. Geological Society Special Publications,30. Geological Society of London, United Kingdom, pp. 191–226.

Rock, N.M.S., Bowes, D.R., Wright, A.E. (Eds.), 1991. Lamprophyres. Blackie and Son,Glasgow-London, United Kingdom, p. 285.

Rosatelli, G., Wall, F., Stoppa, F., 2007. Calcio-carbonatite melts and metasomatism in themantle beneath Mt. Vulture (Southern Italy). Lithos 99, 229–248.

Rosatelli, G., Wall, F., Stoppa, F., Brilli, M., 2010. Geochemical distinctions betweenigneous carbonate, calcite cements, and limestone xenoliths (Polino carbonatite,Italy): spatially resolved LAICPMS analyses. Contributions to Mineralogy and Petrology160, 645–661.

Rudnick, R.L., Gao, S., 2003. Composition of the continental crust. In: Rudnick, R.L. (Ed.),The Crust. Treatise on Geochemistry, 3, pp. 1–64. http://dx.doi.org/10.1016/B0-08-043751-6/03016-4.

Stacey, J.S., Kramers, J.D., 1975. Approximation of terrestrial lead isotope evolution by atwo-stage model. Earth and Planetary Science Letters 26 (2), 207–221.

Stoppa, F., 2008. Alkaline and ultramafic lamprophyres in Italy: distribution, mineralphases and bulk rock data. In: Vladykin, N.V. (Ed.), Deep Seated Magmatism: Itssources and Plumes. Glazkovskaya Printing House, Irkutsk, pp. 209–238.

Tappe, S., Foley, S.F., Jenner, G.A., Kjarsgaard, B.A., 2005. Integrating ultramaficlamprophyres into the IUGS classification of igneous rocks: rationale and implications.Journal of Petrology 46 (9), 1893–1900. http://dx.doi.org/10.1093/petrology/egi039.

Tappe, S., Foley, S.F., Kjarsgaard, B.A., Romer, R.L., Heaman, L.M., Stracke, A., Jenner, G.A.,2008. Between carbonatite and lamproite. Diamondiferous Torngat ultramaficlamprophyres formed by carbonate-fluxedmelting of cratonicMARID-typemetasomes.Geochimica et Cosmochimica Acta, 72, pp. 3258–3286.

Tatsumoto, M., Knight, R.J., Allegre, C.J., 1973. Time differences in the formation ofmeteorites as determined from the ratio of lead-207 to lead-206. Science 180(4092), 1279–1283. http://dx.doi.org/10.1126/science.180.4092.1279.

Taylor, S.R., McClennan, S.M., 1985. The Continental Crust: Its Composition and Evolution.Blackwell, Oxford (312 pp.).

Vichi, G., Stoppa, F.,Wall, F., 2005. The carbonate fraction in carbonatitic Italian lamprophyres.Lithos 85 (1–4), 154–170.

Vidale, J.E., Hedlin, M.A.H., 1998. Evidence for partial melt at the core–mantle boundarynorth of Tonga from the strong scattering of seismic waves. Nature 391, 682–685.http://dx.doi.org/10.1038/35601.

Wanke, H., Dreibus, G., Jagoutz, E., 1984. Mantle chemistry and accretion history of theEarth. In: Kroner, A., Hanson, G.N., Goodwin, A.M. (Eds.), Archaean Geochem.Springer, New York, pp. 1–24.

Wood,D.A., 1980. The application of a Th–Hf–Ta diagram to problems of tectonomagmaticclassification and to establishing the nature of crustal contamination of basaltic lavasof the British Tertiary Volcanic Province. Earth and Planetary Science Letters 50 (1),11–30.

Zaitsev, A.N., Keller, J., 2006. Mineralogical and chemical transformation of OldoinyoLengai natrocarbonatites, Tanzania. Lithos 91, 191–207.

Zindler, A., Hart, S.R., 1986. Chemical geodynamics. Annual Review of Earth and PlanetarySciences 14, 493–571.

Zindler, A., Jagoutz, E., Goldstein, S., 1982. Nd, Sr and Pb isotopic systematics in a three-component mantle: a new perspective. Nature 298, 519–523.