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Journal ArticleDOI

Limestone assimilation and the origin of CO2 emissions at the Alban Hills (Central Italy): Constraints from experimental petrology

TL;DR: In this paper, the authors characterize the effect of carbonate assimilation on phase relationships at 200MPa and 1150-1050°C by experimental petrology and conclude that current CO 2 emissions in this region are the shallow manifestation of hot mafic magma intrusion in the carbonate-hosted reservoir at 5-6km depth.
About: This article is published in Journal of Volcanology and Geothermal Research.The article was published on 2007-10-01 and is currently open access. It has received 93 citations till now. The article focuses on the topics: Carbonate & Carbonate rock.

Summary (3 min read)

Introduction

  • The Alban Hills volcanic region (20 km south of Rome, in the Roman Province) emitted a large volume of potassic magmas (> 280 km3) during the Quaternary.
  • All magmas emitted in the Roman Magmatic Province are potassium rich (K2O/Na2O between 1 and 10), consistently with a metasomatized phlogopite-rich mantle source (Conticelli, 1998; Peccerillo, 1999; Elkins-Tanton and Grove, 2003; Peccerillo, 2005).
  • At first, an experimental study is presented to quantify the importance of the carbonate assimilation process at the Alban Hills, using phase relationships and liquid line of descent as an indicator of the degree of assimilation.
  • Then, the authors estimate the quantity of CO2 liberated by carbonate assimilation in the plumbing system of the Alban Hills and compare it to the measured current CO2 fluxes (Chiodini and Frondini, 2001; Gambardella et al., 2004).

2. Experimental Methods

  • In contrast to previous experimental studies on the petrology of the Alban Hills magmas (Trigila et al., 1995; Freda et al., 1997), which investigated the effect of gaseous CO2 on phase relationships, their experiments were performed on mixtures of a mafic end-member with carbonates and therefore also illustrate the effect of CaO and MgO addition to the magma.
  • The experimental temperatures were 1150, 1125, 1100 and 1075°C, nearly covering the entire course of magma crystallization from near-liquidus to near-solidus.
  • In order to maintain highly oxidizing conditions during the experiments, the autoclave was pressurized with pure Argon.
  • Selected samples were analyzed by Karl Fisher titration to determine their water content (Table 1) and then used as internal standards, together with the dry starting glass, to evaluate the water contents of the other samples from the total of the microprobe analysis (Devine et al., 1995, analytical error ~ 0.6 wt% H2O).
  • Therefore, to improve the estimation of H2O amounts dissolved in the glass and fluid phase abundances, the authors introduced in the mass balance calculations a relationship between H2O wt% in the glass and XH2O in the gas based on the solubility model of Newman & Lowernstern (2002).

3. Results: phase relationships and evolution of the residual liquid

  • Phase proportions and glass composition of each experimental sample are listed in Table 1, together with the experimental conditions and the composition of the starting glass.
  • In carbonate-free conditions, all the samples are water-undersaturated and no fluid phase is observed.
  • High temperature cpx is Si-Mg-rich and Al-Fe-poor.
  • Leucite and phlogopite appear at lower temperatures: 1100 and 1075°C, respectively.
  • The CaO contents of the residual liquids in near-liquidus experiments (#1150) strongly increase with calcite addition.

4.1. Mechanisms of carbonate assimilation

  • The added carbonates are completely consumed by reactions that modify the melt compositions, produce a CO2-rich fluid phase, and result in precipitation of cpx, and olivine (in dolomite-doped experiments).
  • Assimilation of dolomite involves both reactions (1) and (2) to produce cpx and olivine.
  • In both mechanisms (1) and (2), carbonate assimilation results in the diminution of magmatic SiO2 as the authors observed in their experimental charges (Table 1; Figure 2).
  • The desilication of the residual liquid is therefore the most important geochemical consequence of carbonate assimilation.

4.2. Carbonate vs. CO2 effect

  • In the literature on Alban Hills magmatic processes, high CO2 fugacity or high CO2/H2O ratio during magma formation and differentiation are often mentioned as responsible for the observed liquid line of descent (Freda et al., 1997; Palladino et al., 2001; Peccerillo, 2005).
  • Hereafter, the authors briefly clarify this crucial distinction.
  • In both cases, the experiments were performed at pressures of 1 atm, 200 and 400 MPa, with temperatures ranging between 1015 and 1230°C and fluid phase compositions varying from pure water to pure CO2.
  • The main effect of carbonate assimilation shown by their experiments is an important decrease in the silica content of the residual liquid, coupled with an increase in the alkali content during crystallization due to both reaction (1) and (2) (Fig.2a).
  • Hereafter the authors identify evidence of carbonate contamination in the magmatic product of the Alban Hills, essentially on the basis of the degree of silica-depletion during magmatic differentiation.

4.3. Quantitative assessment of limestone assimilation

  • Cpx and leucite, often accompanied by oxides, were the main crystallizing phases in the experimental charges, while plagioclase was never observed, in agreement with the reported mineralogical assemblages of Alban Hills lavas (Trigila et al., 1995).
  • In Figure 3, the same compositions as in Figure 2 are plotted in a CaO/Al2O3 vs. MgO diagram, which illustrates the chemical evolution of the residual liquids during crystallization and highlights Ca and Mg-enrichment due to carbonate assimilation.
  • This heterogeneity in the degree of assimilation is probably a feature of carbonate-magma interactions, as suggested by field studies.
  • In contrast, cpx compositions compatible with significant carbonate assimilation (~10 wt%) crystallized in silica-poor (<43 wt%), alkali-rich (Na2O+K2O > 9wt%) rocks, also compatible with high degrees of carbonate assimilation.
  • Altogether, it appears that important carbonate-magma exchanges are required to explain compositional and mineralogical variations at the Alban Hills.

4.4. Origin of CO2 emissions and volcanic hazard at the Alban Hills

  • Considering a maximum CO2 solubility in the melt of 0.5 wt% at 200 MPa from solubility data relevant to their compositions (Thibault and Holloway, 1994), 10wt% of carbonate assimilation would imply that ~ 5 wt% of the Alban Hills magma consisted of CO2-rich fluid phase.
  • Presently, the Alban Hills region is characterized by large CO2 emissions.
  • Considering such a rate of primitive magma replenishment within a carbonate hosted reservoir and an assimilation of 3-12 wt% carbonate, as deduced from their experimental data, the authors calculate an amount of produced CO2 of 0.8-6.2109 mol/year at depth.
  • The authors therefore suggest here, on the basis of the quantitative agreement between petrology, gas geochemistry and geophysics, that CO2 emissions at the Alban Hills mainly result from assimilation of sedimentary carbonate during the emplacement of a mafic magma at 5-6 km depth.

5. Concluding remarks

  • An experimental investigation has quantified the amount of sedimentary carbonate assimilated by the Alban Hills magmas in their crustal plumbing system.
  • Such assimilation explains the large variations in the degree of silica-undersaturation displayed by the magmatic products and corroborates previous geochemical studies revealing important contamination during magma ascent through, and storage within the carbonate crust.
  • Carbon dioxide degassing from the Albani Hills volcanic region, Central Italy.
  • Relationships between ultrapotassic and carbonate-rich volcanic rocks in central Italy: petrogenetic and geodynamic implications.
  • The starting composition AH7a used in the experiments is indicated by a filled square (a, c).

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Citations
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Journal ArticleDOI
TL;DR: In this article, an integrated petrological, geochemical, and geophysical model was proposed to explain the present-day anomalously high nonvolcanic deep (mantle derived) CO2 emission in the Tyrrhenian region.

142 citations


Additional excerpts

  • ...Interactions between magmas and carbonate rocks at walls of magma chambers locally contribute CO2 in some recent and active volcanic zones (e.g., Alban Hills, Mt. Ernici, Vesuvius; Federico and Peccerillo, 2002; Frezzotti et al., 2007; Iacono Marziano et al., 2007a, b)....

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Journal ArticleDOI
TL;DR: In this paper, the results of an experimental study of limestone assimilation by hydrated basaltic magmas in the range 1050-1150°C, 0.1-500 MPa are reported.
Abstract: The results of an experimental study of limestone assimilation by hydrated basaltic magmas in the range 1050-1150°C, 0.1–500 MPa are reported. Alkali basalts doped with up to 19 wt% of Ca,Mg-carbonates were equilibrated in internally heated pressure vessels and the resulting phase relationships are described. The major effects of carbonate incorporation are: 1) generation of CO2-rich fluid phases; 2) change in liquidus phase equilibria; the crystallization of Ca-rich clinopyroxene is favored and the other phases (e.g. olivine, plagioclase), present in the absence of carbonate assimilation, are consumed. As a consequence of the massive clinopyroxene crystallization, the residual melt is strongly silica-depleted and becomes nepheline-normative. Compositional and mineralogical evolutions observed in Mt.Vesuvius eruptive products match those documented in our experiments with added carbonates, suggesting the possibility that carbonate assimilation increased during the last 25ka of activity. In Central-Southern Italy, carbonate assimilation at shallow levels probably superimposes on deeper source heterogeneities.

136 citations


Cites background from "Limestone assimilation and the orig..."

  • ...…and dolostone in the sedimentary basement (5 to 20 km thick), the abundance of high temperature skarns in the eruptive products and the important CO2 emissions make carbonate assimilation a possible process occurring in the plumbing system of Italian volcanoes (Iacono Marziano et al. 2007)....

    [...]

  • ...If coexisting with the magma, its presence would undoubtedly affect the degassing behavior of the magma (Iacono Marziano et al. 2007) and both its density and viscosity: Assimilation of 9wt% carbonate would liberate a CO2-rich fluid (90% CO2 and 10% H2O) increasing by 20% the volume of the magma at…...

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  • ...Iacono Marziano et al. (2007) have shown that also Alban Hills volcanic rocks have most likely undergone important degrees of carbonate assimilation....

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  • ...…Ultimately, whenever the CO2-rich fluids produced by limestone assimilation are dissipated through the fault system of the surrounding rocks, CO2 emissions in volcanic areas (soil diffuse degassing, CO2 content in groundwaters, plume degassing) must be affected (Iacono Marziano et al. 2007)....

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Journal ArticleDOI
TL;DR: In this paper, the solubility of H2O-CO2 fluids in a synthetic analogue of a phono-tephritic lava composition from Alban Hills (Central Italy) was experimentally determined from 50 to 500 MPa, at 1200 and 1250 °C.
Abstract: The solubility of H2O-CO2 fluids in a synthetic analogue of a phono-tephritic lava composition from Alban Hills (Central Italy) was experimentally determined from 50 to 500 MPa, at 1200 and 1250 °C. Contents of H2O and CO2in experimental glasses were determined by bulk-analytical methods and FTIR spectroscopy. For the quantification of volatile concentrations by IR spectroscopy, we calibrated the absorption coefficients of water-related and carbon-related bands for phono-tephritic compositions. The determined absorption coefficients are 0.62 ± 0.06 L/(mol·cm) for the band at ~4500 cm−1 (OH groups) and 1.02 ± 0.03 L/(mol·cm) for the band at ~5200 cm−1 (H2O molecules). The coefficient for the fundamental OH-stretching vibration at 3550 cm−1 is 63.9 ± 5.4 L/(mol·cm). CO2 is bound in the phono-tephritic glass as CO32− exclusively; its concentration was quantified by the peak height of the doublet near the 1500 cm−1 band with the calibrated absorption coefficient of 308 ± 110 L/(mol·cm). Quench crystals were observed in glasses with water contents exceeding 6 wt% even when using a rapid-quench device, limiting the application of IR spectroscopy for water-rich glasses. H2O solubility in the ultrapotassic melts (7.52 wt% K2O) as a function of pressure is similar to the solubility in basaltic melts up to 400 MPa (~8 wt%) but is higher at 500 MPa (up to 10.71 wt%). At 500 MPa and 1200 °C, the CO2 capacity of the phono-tephritic melt is about 0.82 wt%. The high CO2 capacity is probably related to the high K2O content of the melt. At both 200 and 500 MPa, the H2O solubility shows a non linear dependence on XH2Of in the whole XH2Of range. The variation of CO2 solubility with XCO2f displays a pronounced convex shape especially at 500 MPa, implying that dissolved H2O promotes the solubility of CO2. Our experimental data on CO2 solubility indicate that the interaction between phono-tephritic magma and carbonate rocks occurring in the Alban Hills magmatic system may result in partial dissolution of CO2 from limestone into the magma. However, although the CO2 solubility in phono-tephritic melts is relatively high compared to that in silicic to basaltic melts, the capacity for assimilation of limestone without degassing is nevertheless limited to <1 wt% at the P - T conditions of the magma chamber below Alban Hills.

134 citations


Cites background from "Limestone assimilation and the orig..."

  • ...…H2O and CO2 between silicate melts and H2O-CO2 fluids (e.g., Eggler and Kadik 1979; Blank et al. 1993; Holloway and Blank 1994; Dixon et al. 1995; Jakobsson 1997; Tamic et al. 2001; King et al. 2002; Behrens et al. 2004a; Botcharnikov et al. 2005a, 2006), in a range of melt compositions,…...

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Journal ArticleDOI
TL;DR: In this paper, the authors proposed that CO2-rich fluids released during decarbonatization of sedimentary floor rocks passed up through the gabbroic magma led to the formation of the giantomagnetite deposit.
Abstract: In SW China, several large magmatic Fe-Ti-V oxide ore deposits are hosted by gabbroic intrusions associated with the Emeishan flood basalts. The Panzhihua gabbroic intrusion, a little deformed sill that contains a large titanomagnetite deposit at its base, concordantly intrudes late- Proterozoic dolostones. Mineralogical and chemical studies of the contact aureole in the footwall dolostones demonstrates that the metamorphism was largely isochemical, but for the release of large quantities of CO2 as the rocks were converted to marble and skarns during intrusion of the gabbroic magma. Petrological modelling of the crystallization of the intrusion, using H2O-poor Emeishan basalt as parent magma, shows that under normal conditions Fe-Ti-oxides crystallize at a late stage, after the crystallization of abundant olivine, clinopyroxene and plagioclase. In order for titanomagnetite to separate efficiently to form the ore deposit, this mineral must have crystallized earlier and close to the liquidus. We propose that CO2-rich fluids released during decarbonatization of sedimentary floor rocks passed up through the magma. Redox equilibria calculations show that when magma with the composition of Emeishan basalt is fluxed by a CO2-rich gas phase, its equilibrium oxygen fugacity (fO2) increases from FMQ to FMQ+1.5. From experimental constraints on magnetite saturation in basaltic magma under controlled fO2, such an oxidizing event would allow magnetite to crystallize near to the liquidus, leading to the formation of the deposit.

123 citations


Cites background from "Limestone assimilation and the orig..."

  • ...Due to the low CO2 solubility in the melt, all added CO2 is incorporated in the fluid phase (Iacono Marziano et al. 2007) which immediately leads to extremely high gas content in the system....

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  • ...We acknowledge that the presence of amphibole and biotite provides evidence for the presence of some water (or halogens) in the magma, but suggest that these minerals could have crystallized at a late stage from interstitial liquid within which water had become concentrated....

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  • ...Such high gas content in the magma is not gravitationally stable (Menand and Phillips 2007) and at relatively short timescales, the gas segregates and is expelled from the magma generating active hydrothermal systems at shallower depth (Iacono Marziano et al. 2007)....

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Journal ArticleDOI
TL;DR: The Colli Albani composite volcano is made up of strongly silica-understandably leucite-bearing rocks as mentioned in this paper, and the most alkali-rich magmas, restricted to the caldera-forming period (pre-caldera), are extremely enriched in incompatible trace elements and display more radiogenic Sr (87Sr/86Sr = 0.71006-0.71067), with slightly less radiogenic Pb with respect to those of the postaldera period.
Abstract: The “Colli Albani” composite volcano is made up of strongly silica-undersaturated leucite-bearing rocks. Magmas were erupted during three main periods, but a complex plumbing system dominated by regional tectonics channelled magmas into different reservoirs. The most alkali-rich magmas, restricted to the caldera-forming period (pre-caldera), are extremely enriched in incompatible trace elements and display more radiogenic Sr (87Sr/86Sr = 0.71057–0.71067), with slightly less radiogenic Pb with respect to those of the post-caldera period. Post-caldera volcanic activity was concentrated in three different volcanic environments: external to the caldera, along the caldera edge and within the caldera. The post-caldera magmas produced melilite- to leucitite-bearing, plagioclase-free leucitites. In contrast to the pre-caldera lavas, they are characterised by lower incompatible trace element abundances and less radiogenic Sr (87Sr/86Sr = 0.71006–0.71039). Magmas evolved through crystal fractionation plus minor crustal assimilation in a large magma chamber during the pre-caldera period. The multiple caldera collapses dissected and partially obliterated the early magma chamber. During the post-caldera stage, magmas were channelled through several pathways and multiple shallow-level magma reservoirs were established. A lithospheric mantle wedge previously depleted in the basaltic component and subsequently enriched by metasomatic slab-derived component is suggested as the mantle source of Colli Albani parental magmas. Two different parental magmas are recognised for the pre- and post-caldera stages. The differences may be related to the interplay between smaller degrees of melting for the pre-caldera magmas and more carbonate-rich recycled subducted lithologies in the post-caldera magmas.

115 citations

References
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Journal ArticleDOI
TL;DR: The VOLATILECALC solution models for the rhyolite-H2O-CO2 and basalt-H 2 O-CO 2 systems at magmatic temperatures and pressures below ∼ 5000 bar are presented in this paper.

856 citations

Journal ArticleDOI
TL;DR: Papale et al. as mentioned in this paper applied thermodynamic equilibrium between gaseous and liquid volatile components to model the volatile saturation surface in H 2 O−CO 2 -silicate melt systems.

491 citations


Additional excerpts

  • ...…of dissolved CO2 in carbonate-added glasses was arbitrarily fixed at 0.2 wt%, based on accepted solubility models (Newman and Lowernstern, 2002; Papale et al, 2006), considering that variations up to 0.6 wt% in the CO2 content of the glasses have been tested to have a negligible effect on the…...

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Journal ArticleDOI
TL;DR: In this paper, the authors present a regional map of CO2 Earth degassing from a large area (most of central and south Italy) derived from the carbon of deep provenance dissolved in the main springs of the region.
Abstract: [1] We present the first regional map of CO2 Earth degassing from a large area (most of central and south Italy) derived from the carbon of deep provenance dissolved in the main springs of the region. The investigation shows that a globally significant amount of deeply derived CO2 (10% of the estimated global CO2 emitted from subaerial volcanoes) is released by two large areas located in western Italy. The anomalous flux of CO2 suddenly disappears in the Apennine in correspondence to a narrow band where most of seismicity concentrates. Here, at depth, the gas accumulates in crustal traps generating CO2 overpressurized reservoirs which induce seismicity.

397 citations


"Limestone assimilation and the orig..." refers background or result in this paper

  • ...Moreover, the region is currently characterized by important CO2 emissions of deep origin (Chiodini and Frondini, 2001; Carapezza et al., 2003; Gambardella et al., 2004), as is most of CentralSouthern Italy (Gambardella et al., 2004; Chiodini et al., 2004)....

    [...]

  • ...CO2 origin is still debated in the absence of recent volcanic activity: deep magma degassing, metamorphic decarbonation of limestone and mantle degassing and have been proposed (Chiodini and Frondini, 2001; Gambardella et al., 2004; Chiodini et al., 2004)....

    [...]

  • ...Gas emissions in the CentralSouthern Italy are generally considered to derive from degassing of a mantle source (Chiodini et al., 2000, 2004) metasomatized by the addition of subducted crustal material (Peccerillo, 1999)....

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  • ...The carbon isotopic signature (δ13C between -3.5 and +0.9 ‰ vs. PDB) of the gases released by the vents (Chiodini and Frondini, 2001 and references therein) is consistent with an important contribution from marine carbonates (δ13C of Apenninic carbonates: 2.2 ± 0.66 ‰, Chiodini et al., 2004)....

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Journal ArticleDOI
TL;DR: In this article, three methods of estimating H20 contents of geologic glasses are compared: (1) ion microprobe analysis (secondary ion mass spectrometry), (2) Fourier-transform infrared spectroscopy (FTIR), and (3) electron micro-probe (EM) analysis using the Na decay-curve method.
Abstract: Three methods of estimating H20 contents of geologic glasses are compared: (1) ion microprobe analysis (secondary ion mass spectrometry), (2) Fourier-transform infrared spectroscopy(FTIR), and (3) electron microprobe analysis using the Na decay-curve method. Each analytical method has its own advantages under certain conditions, depending on the relative importance of analytical accuracy, precision, sensitivity, spatial resolution, and convenience, and each is capable of providing reasonably accurate estimates of the H20, or total volatile, content of geologicglasses.The accuracy of ion microprobe analyses depends critically on the availability of well-characterized hydrous standard glasses. Precision is often better than 0,2 wt% (10). The method provides good spatial resolution (-15 #m) and the capability to determine simultaneously the abundance of other volatile species of interest (e.g., F, B). FTIR spectroscopy provides excellent analytical sensitivity (-10 ppm), accuracy and precision «0.1 wt%),and the capability to determine the abundance of H20 and C02 species (H20, OH-, C02' eOj-) in analyzed glasses, although the spatial resolution (> 25-35 #m) is not as good as that of the ion microprobe. The main advantages of the estimation of H20 contents of hydrous glasses using the electron microprobe are excellent spatial resolution (- 10 #m) and analytical convenience. The disadvantages are that accuracy and precision (>0.5 wt%) are not as good as those associated with the other methods, but, for certain applications, these uncertainties may be acceptable for the estimation of H20 contents of H20-rich (> 1 wt%) samples.

393 citations


"Limestone assimilation and the orig..." refers methods in this paper

  • ...…by Karl Fisher titration to determine their water content (Table 1) and then used as internal standards, together with the dry starting glass, to evaluate the water contents of the other samples from the total of the microprobe analysis (Devine et al., 1995, analytical error ~ 0.6 wt% H2O)....

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Journal ArticleDOI
TL;DR: In this paper, the authors used the data on mantle xenoliths from basalts to support degassing models based on the assumption of limited indigenous carbon isotope variability within the mantle, nor the supposition that all 13 C depleted carbon is of surface origin.

360 citations


"Limestone assimilation and the orig..." refers background in this paper

  • ...The δ13C of the emitted CO2 ranges from -3.5 to +0.9 ‰ vs. PDB, strongly deviating from mantle signatures (δ13C: 4-7 ‰, Deines, 2002; Hekinian et al 2000 and references therein)....

    [...]

Frequently Asked Questions (13)
Q1. What contributions have the authors mentioned in the paper "Limestone assimilation and the origin of co2 emissions at the alban hills (central italy): constraints from experimental petrology" ?

In this paper the authors characterize the effect of carbonate assimilation on phase relationships at 200 MPa and 1150-1050°C by experimental petrology. Furthermore, carbonate assimilation liberates a large quantity of CO2rich fluid. A comparison of experimental versus natural mineral, glass and bulk rock compositions suggests large variations in the degree of carbonate assimilation for the different Alban Hills eruptions. A maximum of 15 wt % assimilation is suggested by some melt inclusion and clinopyroxene compositions ; however, most of the natural data indicate assimilation of between 3 and 12 wt % carbonate. Their results strongly suggest that present CO2 emissions in this region are the shallow manifestation of hot mafic magma intrusion in the carbonate-hosted reservoir at 5-6 km depth, with important consequences for the present-day volcanic hazard evaluation in this densely populated and historical area. 

The recycling of sedimentary limestone via the Adriatic subduction and subsequent thermal decomposition of carbonates in the mantle has been proposed as the mainmechanism responsible for the regional CO2 emissions in Italy. 

A kinematic model for the Plio-Quaternary evolution of theTyrrhenian-Apenninic system: implications for rifting processes and volcanism. 

The study showed that the liquid line of descent from the most primitive mafic composition recognized at Alban Hills requires 0 to 15wt% assimilation in order to explain the compositional range displayed by the eruptive products. 

the geochemical signature of released gases at the Alban Hills is also compatible with magmatic assimilation and decarbonation of limestone at crustal depth: the released gasses would inherit their helium isotopic signature from the parental magma, while their δ13C would be controlled by the assimilated limestone. 

The addition of extra water (1.5 wt%) reduces the degree of crystallization and, in particular, the leucite stability field (see #1100/5;1075/6;1125/3). 

The amount of dissolved CO2 in carbonate-added glasses was arbitrarily fixed at 0.2 wt%, based on accepted solubility models (Newman and Lowernstern, 2002; Papale et al, 2006), considering that variations up to 0.6 wt% in the CO2 content of the glasses have been tested to have a negligible effect on the mass balance calculations. 

Mass balance calculations were performed to compute phase proportions (glass, minerals and fluid phase) in the experimental charges, taking into account the compositions of the starting mixtures (including H2O and CO2), the residual melt (included dissolved H2O) and the mineral phases (Table 1 and 2). 

Bulk-rock and melt compositions consistent with the highest degree of assimilation in the TAS plots are also consistent with the highest degree of assimilation in the CaO/Al2O3 vs. MgO diagrams. 

Estimated CO2 production as a consequence of 3-12 wt% of sidewall assimilation has been shown to match present-day emissions of CO2 in this volcanic area. 

high CO2 content has been proposed to be at the originof the highly energetic eruptions at the Alban Hills (Palladino et al., 2001). 

According to Gaeta et al. (2006) it represents the most primitive magmatic liquid found at Alban Hills, on the basis of its high MgO content and low Na2O content. 

Geophysical and petrologicalmodelling of the structure and composition of the crust and upper mantle in complex geodynamic settings: The Tyrrhenian Sea and surroundings.