Giuseppe Piccarreta

Petrogenesis of Monte Vulture volcano (Italy): inferences from mineral chemistry, major and trace element data

The paper presents major and trace element data and mineral compositions for a series of foiditic-tephritic to phonolitic rocks coming from Monte Vulture, Southern Italy, and investigates their origin, evolution and relationship with the other centres of the Roman province.Major and trace element variation in the foiditic to tephritic suite agrees with a hypothesis of evolution by simple crystal/liquid fractionation, whereas the early erupted phonolitic trachytes and phonolites have geochemical characteristics which do not support their derivation from tephritic magma by crystal fractionation. Foiditic and phonolitic rocks have mineral compositions which are interpreted as indicating magma mixing. However geochemical evidence shows that this process did not play an important role during the magma evolution.The Vulture rocks have compositional peculiarities such as high abundance of Na2O, CaO, Cl and S, when compared with other Roman volcanics. Instead, the distribution of incompatible elements is similar to those of Roman rocks, except for a lower content of Rb and K, higher P and lower Th/Ta and Th/Nb ratios which are still close to the values of arc volcanics.The high contents of Na, Ca and of volatile components are tentatively attributed to the interaction of magma with aqueous solutions, rich in calcium sulphate and sodium chloride, related to the Miocene or Triassic evaporites occurring within the sedimentary sequence underlying the volcano. The distribution pattern of the incompatible elements is interpreted as indicative of magma-forming in a subduction modified upper mantle and of the peculiar location of M. Vulture.

Relationships between intermediate and acidic rocks in orogenic granitoid suites: petrological, geochemical and isotopic (Sr, Nd, Pb) data from Capo Vaticano (southern Calabria, Italy)

Abstract Major, trace element and isotopic data are reported for Hercynian granodiorites and tonalites from Capo Vaticano, Calabria, with the aim of clarifying the relationships between acidic and intermediate lithologies in orogenic intrusive suites. These granodiorites (SiO 2 = 70.5%–73.5%) are peraluminous, relatively depleted in Rb, U, Th, and Pb, and display a large variation in many geochemical and isotopic parameters. REE show fractionated, cross-cutting chondrite-normalized patterns with small but significant negative Eu anomalies. Initial (290 Ma) Sr and Nd, and present-day Pb isotope ratios are: ( 87 Sr 86 Sr ) 290 = 0.7105–0.7110 ; ( 143 Nd 144 Nd ) 290 = 0.51175–0.51221 ; 206 Pb 204 Pb = 18.35–18.50 ; 207 Pb 204 Pb = 15.64–15.76 ; 208 Pb 204 Pb = 38.51–39.03 . Pb isotope ratios determined for separated feldspars show similar 207 Pb 204 Pb and 208 Pb 204 Pb and higher 207 Pb 204 Pb ratios compared to the present-day values for the whole rock. The tonalites (SiO 2 = 57.6%–67.3%) are typically calc-alkaline in composition and most of them are weakly peraluminous. They display large heterogeneities in trace-element abundances, REE patterns and Nd and Pb isotope ratios, both between and within individual intrusive units. Sr, Nd and Pb isotopic compositions display a range of values close to that of the associated granodiorites ( 87 Sr 86 Sr ) 290 = 0.7099–0.7111 ; ( 143 Nd 144 Nd ) 290 = 0.51185–0.51224 ; 206 Pb 204 Pb = 18.31–18.56 ; 207 Pb 204 Pb = 15.65–15.72 ; 208 Pb 204 Pb = 38.41–39.59 . The obtained data indicate that the tonalites and granodiorites share many compositional features which point to a genetic linkage. Likewise, many petrological, geochemical and field data exclude the possibility that all the granodiorites derive from intermediate magmas by any common evolutionary process, such as crystal-liquid fractionation or assimilation-fractional crystallization (AFC), and point to a different genesis for the two rock types. An origin of the granodiorites by the mixing of two separate acidic melts, one of crustal anatectic origin and one probably derived from an intermediate magma by crystal/liquid fractionation or AFC, is suggested by the data presented. The tonalites appear to have been generated by interaction of a mafic magma with crustal end-member(s) with isotopic and geochemical signatures similar to those of the granodiorites. The large involvement of crustal material in the genesis of the Capo Vaticano granitoids is responsible for the many common compositional characteristics observed in the intermediate and acidic rocks. However, a contribution from mantle components is also indicated by petrological and geochemical data, as well as by the occurrence of mafic enclaves commonly present in the tonalites. Nevertheless, the geochemical and isotopic features of such a mantle component appear to be greatly diluted by a large quantity of crustal material involved in the genesis of the studied granitoids.

Petrogenesis of contrasting hercynian granitoids from the Calabrian Arc, southern Italy

Abstract The granitoids of the southern Calabrian Arc have been investigated for whole-rock and phase chemistry, zircon typology, REE, Sr and Nd isotopes. Two distinct granitoid associations, which are related in time and partly in space, are present: a calc-alkaline one and a peraluminous one. The prevailing calc-alkaline association is compositionally expanded (SiO2=48–70%) and biotite dominated, with tonalites and granodiorites as predominant rock types. The peraluminous association is compositionally restricted (SiO2=67–76%) and contains two-mica ± Al-silicates. Distinct peraluminous typologies occur also as core facies within the calc-alkaline types. All granitoids are ilmenite-bearing. The Cittanova (CN), Villa S. Giovanni (VSG) and Capo Rasocolmo (CR) peraluminous granites display zircon typology, REE patterns, ϵSrt- (+51 to +113) and ϵNdt-values (−8.5 to −4.6) at 290 Ma, suggesting a dominantly quartzofeldspathic metasedimentary source. In more detail, the CN types and the CR-VSG types require heterogeneous and different sources. The calc-alkaline granitoids display very variable REE patterns (CeN=25–227 and YbN=3.5–18.5 in the tonalites-granodiorites) and variable age-corrected ϵNdt-values (−8.5 to −0.25), whereas Sr values vary little (+82 to +93). Thus, in terms of ϵNdtϵSrt covariation, the data points define a vertical array, which is inconsistent with a model involving crustal contamination by mantle derivatives. A more viable mechanism seems to be the melting of hydrous and heterogeneous mafic lower crust (and/or basic underplate), producing distinct magma batches evolving independently. Crustal contamination, mingling and fractionation processes may all have contributed to the observed geochemical variations within the granitoids. The peraluminous granodiorites occurring within the Serre and Capo Vaticano multipulse calc-alkaline plutons exhibit isotopic ratios (ϵNdt = −6.11 to +0.33 and ϵSrt = +93 to +97) which are similar to those of the calc-alkaline host rocks, suggesting a possible genetic link. Geologic and geochemical data indicate a continental collision setting for this plutonic activity. The magmas were produced during late-thickening to exhumation phases following collision and moderate crustal overthickening, and were emplaced subsequently during a short time span. A mantle contribution should have favoured melting, which affected various sectors of the continental crust.

Tectonic structure and post-hercynian evolution of the Serre, Calabrian arc southern Italy: geological, petrological and radiometric evidences

Abstract Conflicting opinions exist concerning the structure and the post-Hercynian evolution of the Serre. The present paper deals with these topics on the basis of new geological, petrological and radiometric evidence. The composition of the so-called Stilo and Polia-Copanello units has been redefined. The above domains—former sections of upper and lower Palaeozoic continental crust respectively—came into contact, due to transcurrent movements 130–140 Ma ago. A significant vertical component during the transcurrent movements, probably, exhumed the former section of lower crust. The above domains, juxtaposed, were successively involved as a single kinematic body in the Alpine orogenesis. The results enable us to make inferences for the Calabrian Arc evolution and call attention to similarities between an Austro-Alpine element (Stilo + Polia-Copanello) of the Calabrian chain and a South-Alpine sector of the Alps (Ivrea + Ceneri zones).

Magma evolution at mount vulture (Southern Italy)

The Vulture complex is made up of foiditic, tephritic, phonolitic-trachytic and phonolitic products.New rock analyses have been performed in order to ascertain whether the various rock types derive from a unique parental magma and, if so, to define its nature.The data presented support that the Vulture suite originated from a foiditic melt which had differentiated at low pressures. The main process determining the foidite → → tephrite → phonolitic trachyte evolution seems to be the crystal fractionation of mainly clinopyroxenes, and opaques, with the contribution of plagioclases and haüyne too in the tephrite → trachyte evolution. Additionary role must have been played by a mixing of melts at different evolution stages occurred in a shallow seated magma chamber.

Granulite-amphibolite facies metasediments from the Serre (Calabria, Southern Italy): their protoliths and the processes controlling their chemistry

Abstract In the northwestern Serre, a near continuous section through the Palaeozoic lower continental crust crops out. This paper deals with granulite facies metasedimentary rocks of this section. Fifty-five chemical analyses (major elements, Sc, V, Cr, Co, Ni, Rb, Sr, Y, Nb and Ba) are given. Chemical data indicate that the original sedimentary sequence was made up of arenites in the lower part and mainly Fe and Mg rich pelites in the upper part. The metapelites experienced anatexis and removal of some melt, whereas the meta-arenites suffered only incipient anatexis and became dehydration granulites. The various rock types display an overall relatively low K/Rb ratio due mainly to the stability of K- and Rb-retaining phases. A weighted mean composition of the fragment of the lower continental crust outcropping in the Serre has been established by integrating the chemical data for metasediments (55 analyses), metabasites (92 analyses) and dioritic and tonalitic gneisses (10 analyses) with the field data. This composition compared to the compositions of the bulk continental crust and of other sections considered as belonging to the lower crust, confirms the hypothesis that (1) the lower crust is heterogeneous, and (2) it is more basic than the continental crust.

Petrological evidence for crustal thickening and extension in the Serre granulite terrane (Calabria, southern Italy)

The paper presents the metamorphic trajectory recorded by metapelitic migmatites of the upper part of the Hercynian lower continental crust of the Serre (southern Calabria, Italy). The relict minerals, reaction textures and phase equilibria define a clockwise P-T path. The prograde metamorphism from temperature of about 500 ◦ C and pressure of 4-5 kbar to T < 700 ◦ Ca nd P ∼ 8 kbar stabilized the assemblage Grt + Ky + Bt + Ms(Si/11ox =3.26-3.29) in the uppermost metapelites of the profile. Progressive heating led to H2O-fluxed and dehydration melting first of Ms, then of Bt at T < 700 ◦ C in the stability field of sillimanite. This process was followed by nearly isothermal decompression producing additional melt with a transition from Grt to a Grt + Crd stability field. Further decompression caused the formation of Crd-corona around garnet. Nearly isobaric cooling led to rehydration and retrogression across the stability field of andalusite up to the stability field of kyanite. The lowermost metapelites of the studied profile have lost most of the memory of the prograde P-T path; they record decompression and cooling. High-temperature mylonites occur in which boudinage, elongation and pull-aparts characterize the porphyroclasts. The pull-aparts in the high-T mylonites are filled with low-P minerals (Crd + Spl). The Hercynian metamorphic trajectory and the microtextures are consistent with crustal thickening and subsequent extensional regime. During extension, an important tectonic denudation probably caused the isothermal decompression. Extension also occurred in post-Hercynian times as documented by pull-aparts in sillimanite porphyroclasts filled with chloritoid within a low-grade mylonite.

Deep-rooted overthrusting and blueschistic metamorphism in compressive continental margins; an example from Calabria (southern Italy)

At the base of austroalpine nappes in Calabria alpine greenschist dynamometamorphism is overprinted by blueschist metamorphism. Tectonic overpressures and deep-rooted movements of upthrusting type in compressive regime are the key to generation of blueschistic conditions and to greenschist-bluecschist evolution of metamorphism. The tectonic overpressures are generated because the rocks at higher confining pressures and lower pore pressures have relatively higher resistance to deformation. The evolution from greenschist to blueschist conditions results from cooling during upward motion with overpressures remaining concentrated along the thrust zones.

Mineral Chemistry of Monte Vulture Volcanics: Petrological Implications

SummaryTwo distinct periods of volcanic activity are distinguishable at Monte Vulture volcanic complex: the first activity started with tephritic and foiditic volcanics, documented by xenoliths in the phonotrachytic (Ph-T) ignimbrites, lava blocks in a basal explosion breccia deposit beneath the Ph-T ignimbrites, sandy lenses rich in volcanic components in fluviatile conglomerates, and ended with emplacement of phonotrachytic deposits (Ph-T ignimbrites and lava domes); whereas subsequent activity produced deposits of foiditic and tephritic composition which built up the central volcano. The volcanics of the two periods do not fit a simple evolutionary model on the basis of geochemical signatures.New whole-rock and microprobe analyses of mafic minerals from volcanics of the first period are presented here, together with the published data on M. Vulture volcanics, to give a more comprehensive picture of the magma evolution.Principal features can be summarized as follows: (i) melanitic garnet occurs as a stable phase only in the volcanics of the first period of activity; (ii) olivine and diopside occur only in the cone building deposits; (iii) pyroxenes from the volcanics of the first stage crystallized under different physico-chemical conditions with respect to those occurring in volcanics of the central edifice; (iv) the analyzed lavas occurring as blocks in the explosion breccia deposit of the first stage display diversities with respect to the lavas of the central volcano, and it is likely that diverse parental magmas fed the first and the subsequent activities. During the first stage, crystal/liquid fractionation processes determined the evolution from the mafic parental magmas towards phonotrachytic compositions, as with the foidite-tephrtte sequence of the second stage (cone building deposits). Mineralogical evidence of mixing processes is present in the volcanics of the sequences of the two stages.ZusammenfassungZwei Stadien vulkanischer Aktivität sind im Monte Vulture Komplex zu unterscheiden. Das erste Stadium ist durch tephritische und foiditische Vulkanite, die als Xenolithe in den phonotrachytischen (Ph-T) Ignimbriten erhalten sind, durch Lava Blöcke in einer basalen Explosionsbrekkzie im Liegenden der Ph-T Ignimbrite und durch Sandlinsen in fluviatilen Konglomeraten, die reich an vulkanogenen Komponenten sind, gekennzeichnet. Es endet mit der Eruption der Phontrachyte (Ph-T Ignimbrite und Lava Kuppen). Während des zweiten Stadiums wurden vulkanogene Ablagerungen foiditischer und tephritischer Zusammensetzung, die heute den Zentralteil des Vulkans aufbauen, eruptiert. Die Geochemie der Vulkanite läßt sich nicht mit Hilfe eines einfachen Bildungsmodelles erklären. Neue Gesamtgesteins- und Mikrosondenanalysen von Vulkaniten des Erststadiums und deren mafischer Minerale werden gemeinsam mit bereits publizierten Daten über die Vulkanite des Monte Vulture präsentiert, um ein zusammenfassendes Bild seiner Magmenentwicklung zu geben.Grundsätzlich kann folgendes festgehalten werden: (i) Granat tritt als stabile Phase nur in den Vulkaniten des ersten Stadiums auf. (ii) Olivin und Diopsid sind auf die Vulkanschlote beschränkt. (iii) Die Pyroxene der Vulkanite des Frühstadiums kristallisierten unter anderem physikalisch-chemischen Bedingungen, als die im Zentralteil des Vulkans. (iv) Die untersuchten Laven, die als Blöcke in der basalen Explosionsbrekkzie auftreten, unterscheiden sich ebenfalls von denen des zentralen Teiles. Wahrscheinlich sind sie von unterschiedlichen Ausgangsmagmen abzuleiten. Durch Fraktionierung entstanden während des ersten Stadiums aus einem ursprünglich mafischen ein phonotrachytisches Magma und während des zweiten die foiditisch-tephritische Abfolge der Vulkanschlote. Hinweise auf Mischungsprozesse liegen vor.

Multi-stage dehydration–decompression in the metagabbros from the lower crustal rocks of the Serre (southern Calabria, Italy)

Porphyroblastic garnet-bearing metagabbros from the base of the lower crust section of the Serre (southern Italy) exhibit multi-stage dehydration and decompression after the Panafrican emplacement of their protoliths. The first dehydration event produced Am–Opx–Cpx–Pl–Grt as the peak assemblage. Two decompression stages are documented by: (1) coronas of Opx–Pl and Opx–Am, and symplectites of Opx–Am–Pl around clinopyroxene within the porphyroblastic garnet as well as in the matrix and (2) symplectites of Pl–Am–Opx–Grt having different textures around the porphyroblastic garnet. During the second decompression stage, a new local, somewhat intense, dehydration occurred and produced rims of Opx + Pl around the porphyroblastic amphibole, or lenses of Pl–Opx–Am–Spl ± Bt between layers of dominant amphibole. A deformation stage separates older from younger reaction textures. The porphyroblastic garnet, its inclusions and the matrix are affected by fractures, which have been overgrown by coronas and symplectites around the porphyroblastic garnet and the amphibole of the matrix. Preferred P–T estimates are: ~ 900 °C and ~ 1.1 GPa at the metamorphic peak; ~ 850 °C and 0.8–0.9 GPa during the formation of corona around clinopyroxene; 750–650 °C and 0.7–0.8 GPa during the formation of corona around garnet. All these textures formed under granulite-facies conditions. The subsequent metamorphic evolution consists of rehydration under amphibolite-facies conditions. The P–T–t path agrees with the path shown by the uppermost migmatites of the Serre section, and the P–T estimates at the top and the bottom of the section are consistent with the thickness (7–8 km) of the lower crustal segment. A contractional regime, which caused a crustal thickening of about 35 km, was followed by an extensional one producing significant crustal thinning; the change of tectonic regime probably occurred about 300 Ma ago when the emplacement of voluminous granitoids and the initial stages of exhumation of the lower crustal section had taken place.