Cent. Eur. J. Geosci. • 1(4) • 2009 • 377-392 DOI: 10.2478/v10085-009-0036-1

Central European Journal of Geosciences

Silicate-carbonate-salt liquid immiscibility and origin of the -haüyne rocks: study of melt inclusions in olivine foidite from Vulture volcano, S. Italy

Research Article

Liya I. Panina1∗, Francesco Stoppa2

1 Institute of Geology and Mineralogy: Siberian Branch, Russian Academy of Sciences, Koptyug pr. 3, Novosibirsk, 630090, Russia, 2 Dipartimento Scienze della Terra, Università G.d’Annunzio, via dei Vestini, 30, 66013 Chieti Scalo (CH), Italy

Received 27 June 2009; accepted 22 October2009

Abstract: Melt inclusions in clinopyroxenes of olivine foidite bombs from Serra di Constantinopoli pyroclastic flows of the Vulture volcano (Southern Italy) were studied in detail. The rocks contain abundant zoned phenocrysts and xenocrysts of clinopyroxene, scarce grains of olivine, leucite, haüyne, glass with microlites of plagioclase and K-feldspar. The composition of clinopyroxene in xenocrysts (Cpx I), cores (Cpx II), and in rims (Cpx III) of phenocrysts differs in the content of Mg, Fe, Ti, and Al. All clinopyroxenes contain two types of primary inclusion-pure silicate and of silicate-carbonate-salt composition. This fact suggests that the phenomena of silicate-carbonate immiscibility took place prior to crystallization of clinopyroxene. Homogenization of pure silicate inclusions proceeded at 1 225 – 1 190°C. The composition of conserved melts corresponded to that of olivine foidite in Cpx I, to tephrite-phonolite in Cpx II, and phonolite- trachyte in Cpx III. The amount of water in them was no more than 0.9 wt.%. Silicate-carbonate inclusions decrepitated on heating. Salt globules contained salts of alkali-sulphate, alkali-carbonate, and Ca-carbonate composition somewhat enriched in Ba and Sr. This composition is typical of carbonatite melts when decomposed into immiscible fractions. The formation of sodalite-haüyne rocks from Vulture is related to the presence of carbonate-salt melts in magma chamber. The melts conserved in clinopyroxenes were enriched in incompatible elements, especially in Cpx III. High ratios of La, Nb, and Ta in melts on crystallization of Cpx I and Cpx II suggest the influence of a carbonatite melt as carbonatites have extremely high La/Nb and Nb/Ta and this is confirmed by the appearance of carbonatite melts in magma chamber. Some anomalies in the concentrations and relatives values of Eu and especially Ga seems typical of Italian carbonatite related melts. The mantle source for initial melts was, most likely, rather uniform, undepleted and was characterized by a low degree of melting and probable presence of garnet in restite. Keywords: salt-silicate-carbonate inclusions • immiscibility • olivine foidite • plume metasomatism • Vulture-Italy © Versita Warsaw

∗E-mail: [email protected]

377 Silicate-carbonate-salt liquid immiscibility and origin of the sodalite-haüyne rocks: study of melt inclusions in olivine foidite from Vulture volcano, S. Italy

1. Introduction sulphate mineralization is represented by the haüyne- sodalite group rocks. Most of them are volcanic rocks Nowadays, most researchers favor the igneous origin of composed of haüynites and haüyne phonolites. The best carbonatite. Discussions focus mainly on the sources and known occurrences are in Western Germany (E.Eifel), mechanisms of formation of carbonatite melts, their initial Central and Southern Italy (Vulture volcano and Grotta composition, and character of transformation during crys- del Cervo), and Southern Armenia. Genesis of these rocks tallization. There are three most popular concepts on the is related by their very high crystallization temperature sources and mechanisms of carbonatite melt formation: a) and chemistry to primitive mantle magmas initially en- carbonatite melts are formed during melting of carbon- riched in alkali chlorides, sulphates and carbonates. A ate mantle; b) carbonatite melts appear owing to liquid classical example of spatial coexistence of carbonatites immiscibility in parental nephelinites or melilitite magma with the sodalite haüyne group of rocks is the Vulture during its high-temperature (> 800°C) evolution; c) car- volcano (Southern Italy). bonatite melts are residual low-temperature (< 800°C) Melt inclusions in the minerals of olivine foidite bomb from products of the crustal differentiation and fractionation of the Serra di Costantinopoli pyroclastic flows of the Vul- alkaline magmas. ture volcano can add a further piece of precious informa- Most of the previous authors are focused on melilitite- tion about concomitant genetic causes for haüyne-sodalite carbonatite association [1]. As to the origin of carbon- group appearance in carbonatite and alkaline- atites, most researchers think that two-phase silicate- mafic volcanoes. Inclusions have the unique property carbonate immiscibility plays a leading role in their for- to retain information about PT-parameters, compositions mation (see discussion in Stoppa et al. [2]). This assump- (initial and derivative), conditions of evolution (behavior tion is supported by numerous experimental data, results of some elements during the ascent and crystallization of studies of melt inclusions in , and geological of magma, evolution trend, crystallization differentiation observations. and fractionation processes, liquid immiscibility and mix- Experimental studies of synthetic and natural alkaline ing of melts), and degree of fluid saturation in mineral- systems [3–7] evidenced that liquid silicate-carbonate im- forming systems [25, 26]. Studies of melt inclusions in miscibility occurs in a wide range of temperatures and minerals provide us information about the reasons of ori- pressures, and depends on the composition of parental sil- gin of haüyne-sodalite group of minerals in carbonatites icate melt, degree of fluid saturation, and oxygen fugacity. and alkaline-mafic volcanic rocks.

An increase in the amount of alkalies and CO2 pressure expands the immiscibility field [8–11]. Volatiles cannot separate from the melt in the form of gas phase because 2. Geological background of the high activity of alkalies. This produces a structural change of the alkaline aluminosilicate melts and initiates Vulture is located on the Eastern side of the southern silicate-carbonate immiscibility. Moreover, experiments in Italian peninsula, in the Lucania region and is well sep- a carbonate-silicate system at critical concentrations of arated from the Recent leucititic volcanoes of the Roman alkalies, S, P, Cl, and F revealed that separated carbon- Region. The volcano lies on relatively thick lithosphere. ate melt contains immiscible portions of alkali-phosphate, This area is far away from the intermediate and deep alkali-chloride, alkali-fluoride composition [12]. seismicity of the southern Tyrrhenian Sea and is char- Abundant occurrences of silicate-carbonate and multi- acterized by a zone of intense, crustal, dip-slip earth- phase silicate-carbonate-salt immiscibility were detected quakes. Tectonic and volcano-tectonic processes have in thermometric experiments with melt inclusions in the produced a small horst and graben system within the minerals of different alkaline rocks [2, 13–23]. Of espe- pre-volcanic flysch substratum, and partially within the cial interest was multiphase carbonate-salt immiscibility volcano itself which presently reaches 1 326 m.s.l. Vul- in silicate-salt inclusions in perovskite of melilite rocks ture belongs to Province of kalsilite-bearing melilitites from the Krestovskaya intrusion (Polar Siberia). Here for and foidites (i.d. kamafugites), melilities and carbonatites the first time in thermometric experiments both silicate- named Intramountain Ultra-alkaline Province whose gen- carbonate and carbonate-salt immiscibility were observed. eral geological features are fully addressed in Lavecchia The latter was found in immiscible carbonate-salt glob- and Creati [27]. ules, which, on heating, separated into immiscible por- Vulture is a long-lived volcanic complex dating back to c. tions of alkali-sulphate, alkali-chloride, alkali-phosphate, 700 ka, formed during periods of relatively short activity and Mg, Ca, Fe-carbonate compositions [24]. separated by long resting periods. During the early pe- A very interesting association of carbonatites and alkali- riod, a phonolitic caldera, about 6×4.5 km in size filled

378 Liya I. Panina, Francesco Stoppa

with co-caldera deposits, domes and epiclastites were formed (710 and 750 ka). At the same time the sedimen- tary substratum was intruded by nepheline syenite dikes. At about 610 ka the Vulture-San Michele strato-volcano was formed by emission of foidite and phono-foidite pyro- clastics and lava flows with minor melilititic rocks forming a volcanic pile being approximately 600 m thick. The size of the volcano was then largely reduced by tectonic offset. A locally important strike-slip fault system was particu- larly active between 625 and 550 ka, and was likely re- sponsible for triggering a large sector collapse of the SSW flank of the volcano, associated with large pyroclastic flow emission. At approximately the same time, several satel- lite vents formed around the main volcano. A consider- able period of inactivity was terminated by a maar swarm which formed at 141±11 ka. The younger products are co- eruptive carbonatite and melilitite, which cover an area of approximately 15% of the volcano, although these rocks represent a small volume in comparison to the foidite- phonolite series. Additional varieties of igneous rocks, including ijolite, clinopyroxenite, soevite-alvikite, melilito- lite and uncompahgrite occur as ejecta. Mantle xenoliths, comprising of mostly spinel lherzolite and wehrlite-veined spinel lherzolites are frequently found [28, 29]. Some of the peridotite nodules carry Mg-garnet relicts and/or car- bonates and are important because they indicate the up- per mantle origin for the Vulture parental magma [30]. The studied samples come from an area (Figure 1) where the largest lava flow of the Vulture about 5 km long, 1 km wide and 3 m thick (lava flow of Piano di Croce) is lo- cated. It is a foiditic phonolite (haünyte) dated at about 560 ka [31]. Several slightly older lava flows (601 – 629 ka) are imbedded into voluminous pyroclastic deposits be- neath the Piano della Croce Lava flow and are mostly olivine (up to 8 vol%) foidite with subordinate phono- foidite, tephriphonolite and phonolite. The studied sam- ple is an olivine foidite fresh bomb in the pyroclastic flow which is well exposed in a quarry along the road between Figure 1. Geological map. Barile and Rapolla.

cooling. We used a microscope with a heating stage SiC 3. Methods for establishing the temperature of trapping of mineral- forming medium by host mineral, quenching of inclusion The major and trace element composition of rocks was content, and further determination of its composition on analyzed at the Institute of Geology and Mineralogy a microprobe. (Novosibirsk) using an X-ray fluorescent silicate method Microprobe analysis was used to determine the composi- on a VRA-20R analyzer and method of inductively con- tion of rock-forming minerals and composition of daugh- nected plasma mass spectrometry (ICP-MS) on a “Finni- ter/trapped phases and glasses in heated and unheated gan Element-1” mass spectrometer. melt inclusions. Analysis was performed on a “Camebax- To reconstruct the physicochemical conditions of forma- micro” microprobe at the Institute of Geology and Min- tion for olivine foidite, we studied primary and secondary eralogy, Siberian Branch of the RAS (Novosibirsk). The melt inclusions sealed in minerals during their growth and operating conditions were as follows: beam diameter of 1 –

379 Silicate-carbonate-salt liquid immiscibility and origin of the sodalite-haüyne rocks: study of melt inclusions in olivine foidite from Vulture volcano, S. Italy

2+ 2 μm, accelerating voltage of 20 kV and a beam current of amount of Cr2O3 and Mg# (Mg/Mg+Fe ) of clinopyrox- 15 – 30 nA, counting time of 10 s (for all elements). Data enes decreases from Cpx I (Mg#= 0.86 – 0.87) to Cpx reduction was performed using a PAP routine. Overlap II (Mg#= 0.73) and further to Cpx III (Mg#= 0.70 – corrections for Si(Kα)-Sr(Lα), Mn(Kβ)-Fe(Kα), Mn(Lα)- 0.69). All clinopyroxenes contain minor Cr – from 0.01 F(Kα), Fe(Lα)-F(Kα) were done. Precision for major ele- to 0.39 wt.% (see Table 4). ments was better than 2 rel.%. A total of 14 elements were The composition of K-feldspar varies substantially (Ta- sought using the following standards: orthoclase (K-Kα ble 1). Microlites of K-feldspar from groundmass are sim- and Al-Kα), diopside (Si-Kα, Ca-Kα and Mg-Kα), pyrope ilar in composition to orthoclase, contain to 2 wt.% CaO Kα Kα Kα (Fe- ), albite (Na- ), ilmenite (Ti- ), cloroapatite and 4 wt.% Na2O. Approximately the same composition (Cl-Kα), barite (BaLα,SKα), fluorapatite (PKα,F-Kα), was established for daughter phases from inclusions in Sr- rich, synthetic silicate glass (SrLα), Mn – garnet – Cpx I. K-feldspar from inclusions in Cpx II is higher mag- (MnKα). nesian, has the same composition as microcline, and con- The concentrations of trace elements, water and F in tains 0.6 wt.% BaO and 1.9 wt.% SrO. inclusions in the largest melt inclusions (> 20μm) were analyzed by Cpx III is hyalophan: they contain to 23.5 mole.% celsian secondary-ion mass spectroscopy (SIMS), using a Cameca component, 57.4 mole.% orthoclase component and 2.6 wt.% IMS-4f ion probe at the Yaroslavl’ Branch of the Physi- SrO. cotechnological Institute (YBPTI), Yaroslavl’, Russia. The Plagioclase occurs as idiomorphic and xenomorphic pris- − operating conditions were as follows: primary O2 beam matic grains ranging from medium sizes of phenocrysts of 20 μm, a beam current of 2 – 4 nA, energy offset of to microlites. Coarse or fine polysynthetic twinning is 100 eV and energy slit of 50 eV. Concentrations of ele- frequent. In chemical composition (Table 1) plagioclase ments were determined from the ratios of their isotopes grains correspond to bytownite and contain (wt.%): 0.6 to 30Si, using calibration curves for standard samples [32]. FeO, 0.96 SrO, and 0.16 BaO. < . Low background contents of H2O( 0 03 wt.%) were due Olivine is found mainly as small xenomorphic grains. It be-

to the 24 h high-vacuum exposure of the samples in the longs to Fo88−90 and contains 0.32 wt.% CaO and 0.25 wt.% mass spectrometer. The conditions for determination of MnO. fluorine were described by Portnyagin et al. [33]. Leucite is present as small euhedral grains, less fre- quently it fills interstices between clinopyroxene grains, and occurs as crystal inclusions in clinopyroxene phe- nocrysts. Leucite contains appreciable amounts of FeO 4. Mineralogy and petrography of (0.2 – 0.52 wt.%), Na2O (from 0.4 to 1.1 wt.%) and BaO (0.13 – 0.26 wt.%), reaching the maximum content in crys- olivine foidite tal inclusions (Table 1). Haüyne is represented by minute colourless or blue phe- Olivine foidite consists of numerous clinopyroxene phe- nocrysts. Often phenocrysts exhibit oscillatory zoning nocrysts, scarce grains of olivine, leucite haüyne and pla- with light and dark zones. Dark zones contain abundant gioclase immersed in brown glassy matrix which contains ore minerals. Haüyne contains 1.2 – 1.5 wt.% Cl (Table 1). microlites of K-feldspar and plagioclase. Among clinopy- The darker zones have more FeO (up to 0.4 – 0.55 wt.%) roxene we observed xenocrysts and zoned phenocrysts. and less Na2O (from 12 to 10.3 wt.%). The crystal inclu- Xenocrysts (Cpx I) are colourless or light-green fragments sions of haüyne in clinopyroxene are enriched in CaO (to ranging in size from a hundredth fractions of millimetre to 9.8 wt.%) and SrO (to 0.3 wt.%). one centimetre. Zoned phenocrysts are typically of hypid- Apatite and titanomagnetite occur mainly as crystal inclu- iomorphic or idiomorphic shape with zoning. Cores (Cpx II) sions in clinopyroxene. Apatite is somewhat enriched in are light- and yellow-green, and rims (Cpx III) are brown FeO (to 0.35 wt.%), SrO (1.2 – 1.3 wt.%), Cl (to 0.6 wt.%), and dark-green. Sometimes, colours have a reverse order. and SO (0.5 wt.%) (Table 1). Titanomagnetite contains Zoning of phenocrysts is marked by melt inclusions and 3 7.3 wt.% TiO , 10 wt.% Al O and to 5.3 wt.% MgO. crystal inclusions of apatite, haüyne, leucite, and plagio- 2 2 3 clase. The composition of xenocrysts, compared to that of zoned phenocrysts, has higher Si and Mg and contains lower amounts of Ti, Al and Fe (Table 1), and corresponds 5. Melt inclusions in clinopyrox- to fassaite composition. The cores of phenocrysts (Cpx II) enes and thermometric experiments have an intermediate composition (diopside-), and the rims (Cpx III) are enriched in Fe, Ti, and Al and de- In xenocrysts of Cpx I inclusions are scarce, randomly pleted in Si and Mg (salite-augite), respectively. The arranged, occur as clusters or, occasionally, in inner

380 Liya I. Panina, Francesco Stoppa

Table 1. Chemical composition of rock-forming minerals, microlites and daughter phases from melt inclusions, wt%.

Clinopyroxenea Leucite Haüyne 1(16) 2(14) 3(3) 4(18) 5(5) 6(2) 7(2) 8(1) 9(1) 10(1) 11(13) 12(2)

SiO2 50.60 47.55 45.70 44.59 44.61 54.78 55.05 55.74 34.65 33.86 31.44 32.61

TiO2 0.91 1.38 1.91 2.25 1.42 0.01 0.00 0.10 0.00 0.00 0.08 0.00

Al2O3 3.97 6.78 7.55 9.46 7.10 23.23 22.86 23.52 27.88 27.81 27.00 27.49 FeO 4.11 7.02 8.05 8.39 8.63 0.23 0.30 0.52 0.37 0.26 0.55 0.57 MnO 0.06 0.16 0.22 0.19 0.14 0.00 0.00 0.00 0.00 0.00 0.00 0.00 MgO 15.83 13.14 11.65 11.08 12.88 0.00 0.02 0.04 0.05 0.05 0.17 0.04 CaO 24.33 23.52 23.66 22.95 23.78 0.00 0.00 0.19 6.44 6.55 9.76 8.70

Na2O 0.27 0.46 0.58 0.54 0.57 0.53 0.42 1.06 12.76 13.62 10.30 9.07

K2O 0.00 0.00 0.00 0.00 0.00 20.58 20.78 18.86 4.41 1.40 3.57 2.26 BaO 0.00 0.00 0.00 0.00 0.00 0.15 0.16 0.26 0.00 0.00 0.00 0.00 SrO 0.00 0.00 0.01 0.00 0.00 0.00 0.00 0.00 0.07 0.08 0.28 0.28

P2O5 0.06 0.07 0.06 0.06 0.07 0.00 0.01 0.00 0.13 0.18 0.11 0.15 Cl 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 1.89 1.65 1.45 1.46

SO3 0.00 0.00 0.00 0.00 0.00 0.03 0.00 0.00 11.08 11.25 11.50 11.52 Total 100.14 100.08 99.39 99.51 99.20 99.54 99.60 100.29 99.73 96.71 96.21 94.15 O=Cl – – – – – – – – 0.47 0.41 0.36 0.32 Total 100.14 100.08 99.39 99.51 99.20 99.54 99.60 100.29 99.26 96.30 95.85 93.83

Ol Pl K-feldspar Apatite Magnetite Phl 13(2) 14(1) 15(1) 16(1) 17(2) 18(1) 19(4) 20(8) 21(1) 22(3) 23(5)

SiO2 40.78 47.22 53.13 62.70 63.09 63.27 0.67 0.97 0.04 0.03 34.99

TiO2 0.00 0.00 0.24 0.09 0.21 0.00 0.01 0.01 7.32 3.24 4.12

Al2O3 0.00 33.36 21.26 20.65 20.06 20.58 0.01 0.00 9.86 5.05 16.11 FeO 10.84 0.57 0.57 0.48 0.46 0.20 0.35 0.30 68.63 77.03 8.39 MnO 0.25 0.03 0.00 0.04 0.04 0.00 0.04 0.04 0.76 0.96 0.12 MgO 46.87 0.09 0.02 0.01 0.60 0.03 0.23 0.20 5.30 2.72 18.90 CaO 0.32 15.58 0.29 2.03 2.65 0.30 53.94 53.92 0.35 0.20 0.26

Na2O 0.00 1.89 1.04 4.06 3.33 0.69 0.19 0.25 0.09 0.06 0.67

K2O 0.00 0.22 8.83 9.14 7.95 13.71 0.02 0.04 0.00 0.03 9.14 BaO 0.00 0.16 11.72 0.01 0.13 0.63 0.00 0.01 0.00 0.00 1.50 SrO 0.00 0.96 2.59 0.00 0.12 1.87 1.26 1.17 0.05 0.04 0.01

P2O5 0.03 0.04 0.06 0.02 0.02 0.13 40.22 38.71 0.03 0.03 0.08 Cl 0.00 0.00 0.00 0.00 0.03 0.04 0.57 0.73 0.00 0.00 0.04

SO3 0.00 0.02 0.00 0.00 0.09 0.08 0.49 1.02 0.00 0.01 0.02 Total 99.09 100.14 99.75 99.23 98.78 101.53 98.00 97.37 92.43 89.40 94.35 O=Cl – – – – – 0.01 0.14 0.18 – – 0.01 Total 99.09 100.14 99.75 99.23 98.78 101.52 97.86 97.19 92.43 89.40 94.34 Clinopyroxene: 1 – xenocryst of Cpx I; 2 – core of zoned phenocryst of Cpx II; 3 – transitional zone between core and rim in zoned phenocryst of Cpx II-III; 4 – rim of zoned phenocryst of Cpx III; 5 – Cpx from melt inclusion. Leucite: 6 – idiomorphic grain, and 7 – xenomorphic grain, 8 – crystal inclusion in Cpx. Haüyne: zoned phenocryst: 9 – dark core and 10 rim; 11 – crystal inclusion in Cpx. 12 – phase from melt inclusion. Olivine (Ol): 13 – xenomorphic grain. Plagioclase (Pl): 14 – xenomorphic grain. K-feldspar: 15 – crystal inclusion in Cpx; 16 – microlite in glass; 17 – daughter phase from melt inclusion in Cpx I; 18 – the same in Cpx II. Apatite: 19 – crystal inclusion in Cpx; 20 – daughter phase from melt inclusions in Cpx. Magnetite: 21 – crystal inclusion in Cpx; 22 – daughter phase from inclusions in Cpx. Phlogopite (Phl): 23 – daughter phase from melt inclusion in Cpx. In parentheses is the number of analyses. a According to SIMS data, clinopyroxenes contains 0.01-0.39 wt.% Cr (see Table 4).

381 Silicate-carbonate-salt liquid immiscibility and origin of the sodalite-haüyne rocks: study of melt inclusions in olivine foidite from Vulture volcano, S. Italy

cracks. The inclusions are mainly large, at times attaining 30×30 mμ and even 100×60 micron. The inclusions are coarse crystallized and are irregularly shaped. Mineral phases in the inclusions are represented by clinopyrox- ene, phlogopite, K-feldspar, apatite, titanomagnetite, and, sometimes, by sulfides. Clinopyroxene typically occurs on inclusion walls and is hardly distinguishable from ma- trix mineral (Figure 2A). Some inclusions also contain fine crystallized salt aggregates. These form isolated segrega- tions of irregular, less often, of rounded shape (globules), occupying from 2 to 20% of inclusion volume. Some salt aggregates contain a poorly observable deformed gas bub- ble (Figure 2B,C). The presence of two types of inclusions (pure silicate and silicate-carbonate-salt) among primary inclusions evidences that these inclusions were conserved from heterogenous medium [25, 26, 34]. In zoned phe- Figure 3. Zoned phenocrysts of clinopyroxene with inclusions along its growth zones. nocrysts primary inclusions were found both in the core of Cpx II and in the rims of Cpx III, but mostly they oc- cur on the border of light and brownish zones (Figure 3). Their shape is prismatic, close to isometric, and some- an.5) has Mg#=0.70 – 0.65, is rich in Ti and Al, and is times irregular. Size is variable from minute to 50 mi- similar in composition to that of the transition zone of crons. Phase composition varies from glassy to partly or Cpx II-III. K-feldspar from melt inclusions in Cpx I, is or- completely crystalline. Glassy inclusions typically con- thoclase contains a minor anorthite component, and up to tain one or several small gas bubbles, occasionally with 0.5 wt.% FeO, 0.12 – 0.13 wt.% BaO, and SrO (Table 1, salt . The set of mineral phases in crystallized in- an.17). K-feldspar from inclusions in Cpx II has elevated clusions in Cpx II and Cpx III is nearly the same as in in- amount of BaO (0.63 wt.%) and SrO (1.87 wt.%) (Table 1, clusions from Cpx I, except haüyne which was absent from an.18). The composition of haüyne from melt inclusions Cpx I. Some inclusions also contained salt aggregates. is most similar to that of crystal inclusions in clinopyrox- ene but contains fewer alkalies (Table 1, an.12). Apatite unlike crystal inclusions in clinopyroxene is richer in Cl

(to 0.6 wt.%) and SO3 (1 wt.%). Titanomagnetite com- pared to crystal inclusions is more enriched in Fe, but contains less Ti, Mg, Al, and Ca (Table 1, an.22). Phl- ogopite (Table 1, an.23) contains appreciable amounts of

TiO2 (4.0 wt.%) and BaO (1.5 wt.%). Sulfides were found to contain 43.3 wt.% Fe and 31.25 wt.% S (analyses for other metals were not performed). Chemical composition of residual glass from unheated partly crystallized inclusions in Cpx II and Cpx III (Ta-

ble 2, an.5) is siliceous (56 – 58 wt.% SiO2), enriched in Al2O3 (21 – 24 wt.%) and alkalies (to 12 – 14 wt.% with predominance K over Na), contains to ∼0.3 wt.% Cl and

SO3 and is similar to that of alkaline trachyte. On heating, inclusions with or without salt aggregates be- have differently. In glassy and partly crystallized inclu- sions free from salt aggregates, silicate glass inclusions at 1 000°C become completely soft and gas bubbles in them Figure 2. Melt inclusions in the clinopyroxene b, c – silicate-salt sometimes begin to migrate. Above this temperature, most inclusions; a, d – silicate inclusions. mineral phases in inclusions melt and, at 1 150 – 1 200°C, the last crystals of apatite and clinopyroxene disappear The chemical composition of mineral phases from inclu- (Figure 2D). Gas bubbles in the silicate melt of inclusions sions with or without salt aggregates is the same (Ta- homogenize at 1 225 – 1 190°C in Cpx I, at 1 200 – 1 180°C ble 1). Clinopyroxene from inclusions in Cpx II (Table 1, in Cpx II, at 1 190 – 1 170°C in the rims of zoned phe-

382 Liya I. Panina, Francesco Stoppa

moves to the salt globule and merges with it. Further Table 2. Averaged chemical composition of glasses of melt in- increase in temperature results in complete melting of clusions in clinopyroxenes and the composition of glassy mineral phases in inclusion and appreciable decrease in matrix of rock, wt.%. the size of salt globule. Above 1 250°C, most inclusions 1(14) 2(20) 3(4) 4(19) 5(11) 6(1) decrepitate. Some inclusions after quenching in silicate

SiO2 46.66 48.87 50.15 55.83 57.00 54.46 glass preserve small salt globules with gas bubbles (Fig-

TiO2 1.35 1.22 0.99 0.80 0.34 0.21 ure 4).

Al2O3 13.24 17.03 18.59 22.19 23.53 25.29 FeO 5.89 4.67 4.67 1.60 0.61 3.60 MnO 0.16 0.14 0.14 0.07 0.01 0.11 MgO 7.60 5.03 4.79 0.79 0.04 2.10 CaO 13.64 8.48 8.73 3.04 0.65 11.59

Na2O 2.41 2.98 3.85 3.90 4.36 1.86

K2O 3.29 5.66 5.61 7.69 8.44 0.38 BaO 0.30 0.38 0.48 0.49 0.12 0.31 SrO 0.20 0.23 0.19 0.13 0.14 0.10

P2O5 1.46 0.52 0.42 0.25 0.31 0.14 Cl 0.39 0.47 0.27 0.39 0.50 0.01

SO3 1.07 0.53 0.18 0.11 0.35 0.00 Total 97.66 96.21 99.06 97.28 96.40 100.16 Figure 4. O=Cl 0.09 0.11 0.06 0.09 0.11 – Silicate-salt inclusion heated at 1 250°C and quenched, in zonal phenocryst of clinopyroxene: a – in transmitted, Total 97.57 96.10 99.00 97.29 96.29 100.16 b – reflected light. Note. 1-4 – experimentally heated and quenched glasses of melt Chemical composition of silicate and salt components of inclusions is given in Table 3, an.2; trace element inclusions: 1 – from Cpx I; 2 – from Cpx II; 3 – from intermediate zone composition of silicate glass is given in Table 4. between core of Cpx II and rim of Cpx III; 4 – from Cpx. 5 – residual glasses from unheated partly crystallized inclusions. 6 – glassy rock matrix. In parentheses is the number of analyses. The composition of silicate glass in them is the same as in melt inclusions free from salt globules: in the cores and in intermediate zones of phenocrysts (Table 3, an.1 and 2) nocrysts of Cpx III. it corresponds to that of tephriphonolite, and in the rims Microprobe analysis of quenched glasses from these inclu- (Table 3, an.3 and 4), it is similar to trachyphonolite. The sions (Table 2) shows that Cpx I formed from melts whose salt globules and segregations were found to contain (Ta- composition is similar to that of olivine foidite; cores of ble 3) varying amounts of CaO (20 to 49 wt.%), alkalies (2 zoned phenocrysts of Cpx II formed from tephriphonolitic to 14.5 wt.% with different ratios of K and Na), SO3 (5.5 to melts, whereas the rims of Cpx III result from a melt com- 43 wt.%), Cl (0.2 – 2.25 wt.%), SrO (5.0 – 10.2 wt.%), BaO (to positionally similar to phonolite or nepheline trachyte. All 4.5 wt.%). The CaO-richest salt aggregates (Table 3, an.1) generations of clinopyroxene seem to have crystallized contain minimum amounts of alkalies, Ba, Sr, Cl, SO3 and from a primitive alkaline-mafic magma, which was initially P2O5. Their normative composition is (mole %): 84 cal- rich in Mg, Ca and alkalies (with predominance of K over cite, ∼2 MgCO3, 0.8 SrCO3, 0.5 BaCO3, ∼5 CaSO4, 3.5 Na), as well as in Cl, CO2, and SO3. During differentiation K2SO4, 1.8 Na2SO4, and 0.3 apatite. Maximum contents and fractionation, the content of Si, Al, and alkalies in this of alkalies are typical of salt globules containing maximum magma increased, whereas that of cafemic components de- amount of SO3 (Table 3, an.2). Their normative composi- creased. During the growth of clinopyroxene (from Cpx I tion is dominated by sulphates of alkalies and Ca (mole to Cpx II and further to Cpx III) the contents of BaO and %): 57.3 CaSO4, 15.3 Na2SO4, 14.6 K2SO4, 4.7 CaCl2, SrO in the melt were 0.3 – 0.5 wt.% and 0.1 – 0.3 wt.%, re- 2.3 CaCO3, 2.1 BaCO3, 3.1 SrCO3, and 2.4 apatite. The spectively. The amount of SO3 drastically decreased from highest concentrations of Ba and Sr were found in salt 1.1 to 0.11 wt.% at nearly constant 0.4 wt.% content of Cl. globules containing moderate amounts of Ca and alkalies On heating, salts in silicate-carbonate-salt inclusion at (Table 3, an.3). Their normative composition is (mole %): 700 – 800°C, first become dark, then lighten, round, and 37 anhydrate, 17 thenardite, 11.5 calcite, 14.5 strontianite, at 870 – 900°C form globules with several gas bubbles. 4.5 arcanite, about 6 witherite, ∼2NaCl, 0.5 apatite and On further heating, gas bubbles in salt globules may both 0.5 siderite. appear or disappear. Bubbling stops at 1 060 – 1 100°C. Different compositions of carbonate-salt globules and seg- At these temperatures, the gas bubble in silicate melt regations suggest that the separated carbonate-salt melt

383 Silicate-carbonate-salt liquid immiscibility and origin of the sodalite-haüyne rocks: study of melt inclusions in olivine foidite from Vulture volcano, S. Italy

ments regularly increases from xenocrysts to cores of phe- Table 3. Chemical composition of glass and salt phase in individ- nocrysts, attaining maximum values in the rims of zoned ual melt silicate-salt inclusions from zoned phenocrysts of phenocrysts. An exception is the concentration of Cr, clinopyroxene, wt.%. which, on the contrary, decreases in the mentioned di- H. m.a Cpx II Cpx II-III CpxIII Cpx III rection from 3 980 to 110 ppm. The total content of REE Number 1 2 3 4 varies from 131 ppm in xenocrysts to 870 – 950 ppm in Incl. Si- Salt Si- Salt Si- Salt Si- Salt Fe-rich rims of phenocrysts. In general, REE are domi- glass glass glass glass nated by LREE. In the concentrations of REE xenocrysts

SiO2 49.97 1.13 48.67 0.56 56.28 0.09 55.91 10.57 and rims of zoned phenocrysts differ 4 times in HREE and

TiO2 1.29 0.07 0.95 0.09 0.57 0.00 0.25 0.28 5 – 10 times in LREE. The pattern of chondrite-normalized

Al2O3 17.66 0.22 19.03 0.39 23.85 0.00 23.50 5.05 concentrations of REE [38] has a negative slope (Figure 5) FeO 3.18 0.35 5.85 0.27 1.08 0.35 0.59 1.49 and high values of (La/Yb)n, which vary from 4.3 to 8.04. MnO 0.12 0.04 0.18 0.00 0.04 0.05 0.04 0.21 The pattern of REE displays positive Gd and negative MgO 5.75 0.94 3.79 0.42 0.02 0.00 0.02 0.22 Eu anomalies. The latter is especially high for Cpx III. CaO 6.75 49.29 8.74 29.91 0.69 23.12 0.59 19.63 It is worth noting that the positive Gd anomaly is typ-

Na2O 2.45 0.78 4.18 6.68 3.65 7.40 4.32 5.58 ical of all clinopyroxenes. Most likely, it reflects some

K2O 4.08 1.88 5.93 7.84 9.20 2.42 7.06 1.75 specific features of the melts. There are few examples of BaO 0.41 0.34 0.39 1.65 0.00 4.47 0.00 0.43 such anomalies in literature: in dunites from Blaschke Is- SrO 0.30 0.54 0.24 2.21 0.00 10.18 0.00 5.86 land in Canada [39], in komatiites from the Kostomusha

P2O5 2.35 0.13 0.39 0.98 0.26 0.22 0.28 0.32 and Khazovaar structures in the Baltic Shield in Rus- Cl 0.15 0.44 0.43 2.25 0.28 1.51 0.45 1.16 sia [40], and in clinopyroxenites of gabbro-dolerites from

SO3 0.76 5.49 0.25 49.80 0.10 33.36 0.05 17.62 the Naran (Mongolia) and Berezovskii (Sakhalin) mas- Total 95.22 61.64 99.02 103.05 96.02 83.17 93.06 70.17 sifs [41]. All clinopyroxenes reveal a noticeable deficiency ∗ O=Cl 0.03 0.10 0.10 0.51 0.06 0.34 0.10 0.26 of Eu: (Eu/Eu )n values, calculated from chondrite, are Total 95.19 61.54 98.92 102.54 95.96 82.83 94.96 69.91 low and vary from 0.5 – 0.6 in Cpx I and Cpx II to 0.44 – Note. Inclusions: 1 – heated to 1 160°C; 2 – heated to 1 250°C; 3,4 – 0.48 in Cpx III. unheated. Salt aggregates: 1 – in large globule, the rest – in the form of small round globules. Zoned phenocrysts of clinopyroxene: Cpx II – core; Cpx II-III – intermediate zone between core and rim; Cpx III – rim. a Host mineral.

evolved in its own way [35].

6. of the rock, clinopyroxenes, and melt inclusions

Figure 5. Distribution spectrum of chondrite-normalized contents of rare-earth elements [38] in clinopyroxenes of olivine foidite. Olivine foidite, clinopyroxene and their melt inclusions are Clinopyroxenes: 1 – xenocryst, 2-5 – zonal phenocrysts (2 – core, 3 – intermediate zone between core and rims, enriched in trace elements (Table 4). Clinopyroxene is one 4, 5 – rim). of the main concentrators of trace elements among rock- forming minerals. Its is rather favorable for the isomorphous incorporation of LILE and especially Xenocrysts and zoned phenocrysts of clinopyroxene also REE. The structure can host a wide set of cations of var- differ from each other in the values of Ti/Zr, Ce/Yb, Th/Yb, ious sizes and charges and can easily deform, providing and La/Yb: from xenocrysts to cores and rims of zoned a relatively easy compensation of heterovalent replace- phenocrysts the values of Ti/Zr decrease, whereas those ment of elements [36, 37]. of Ce, Th to La to Yb, on the contrary, increase (Table 4). The content of trace elements in studied clinopyroxenes To establish the degree of fractionation of elements dur- from olivine foidite, 1 – 2 orders of magnitude exceeds ing crystallization of clinopyroxene from melt, we esti- the chondrite norm (Table 4). The amount of trace ele- mated the partitioning coefficient of trace elements in the

384 Liya I. Panina, Francesco Stoppa

Table 4. Major (wt.%) and trace element (ppm) composition of olivine foidite, clinopyroxene and heated melt inclusions in them.

Rock Cpx I Cpx II Cpx II-III Cpx III Cpx III Incl I Incl I Incl II Incl II-III Incl III Incl III

SiO2 45.24 50.33 48.86 48.70 45.88 45.43 50.54 46.08 50.22 48.67 51.60 56.86

TiO2 1.38 0.98 1.33 1.23 2.00 2.08 0.80 1.29 1.08 0.95 0.89 0.41

Al2O3 17.38 4.61 6.17 5.96 8.39 9.28 15.47 12.82 15.86 19.03 19.38 23.25 FeO 8.32 4.31 5.74 6.22 9.67 8.74 3.58 5.32 4.50 5.85 4.65 0.80 MnO 0.17 0.07 0.08 0.11 0.18 0.17 0.08 0.11 0.13 0.18 0.17 0.08 MgO 4.98 15.52 14.04 13.76 10.60 11.18 6.09 7.86 6.06 3.79 2.02 1.07 CaO 11.78 24.47 24.66 24.26 22.67 22.52 9.14 13.77 9.58 8.74 6.10 3.97

Na2O 2.81 0.26 0.31 0.39 0.49 0.58 2.79 2.67 2.59 4.18 3.90 4.01

K2O 4.33 0.00 0.00 0.02 0.02 0.02 5.54 2.66 5.19 5.93 6.24 7.02 BaO – 0.00 0.00 0.00 0.00 0.00 0.28 0.21 0.27 0.39 0.22 0.36 SrO – 0.00 0.00 0.00 0.00 0.00 0.24 0.15 0.16 0.24 0.23 0.13

P2O5 0.62 0.07 0.07 0.07 0.05 0.07 0.55 0.89 0.53 0.39 0.19 0.35 Cl – 0.00 0.00 0.00 0.00 0.00 0.44 0.45 0.37 0.43 0.59 0.41

SO3 – 0.00 0.00 0.00 0.00 0.00 0.25 1.56 0.61 0.25 0.10 0.08 a H2O 2.04 – – – – – 0.562 0.876 0.494 0.018 0.340 0.180 F – – – – – – 0.30 0.55 0.41 0.40 1.04 0.40 Total 99.05 100.62 101.26 100.72 99.95 100.07 96.65 97.27 98.05 99.44 97.66 99.38 Rb 141 4.55 7.02 10.5 10.8 9.65 104 108 122 111 178 104 Ba 1 970 0.56 1.06 2.65 2.89 42.8 2 860 2 760 3 150 3 610 2 890 2 580 Th 44 0.31 0.642 6.67 2.94 4.71 55.9 28.4 32.3 75 94.3 67.4 U 13.4 0.016 0.04 0.38 0.28 0.6 19.1 8.98 9.85 25.6 32 23.9 Ta 3.8 0.43 0.84 3.21 2.33 2.31 3.7 2.7 3.6 5.59 7.44 7.61 K 35 945 12.6 21.9 18.6 3540 3340 44 900 40 500 46 300 55 800 73 700 42 500 Nb 63 0.5 0.86 13.7 9.16 11.5 106 54.3 61.7 148 186 148 La 178 12.4 29.7 119 104 117 116 133 137 200 213 168 Ce 325 41.4 104 352 320 333 174 263 255 357 425 423 Sr 23 50 225 362 791 993 854 1 980 2 300 2 340 3 190 3 720 2 300 Nd 147 38.5 88.8 248 194 220 44.6 94.1 84.1 108 118 179 Zr 308 81.7 221 797 767 775 14 205 208 307 418 758 Sm 27 10.5 24.4 57.3 45.8 44.9 7.65 16.7 14.2 19.7 18.5 37.9 Eu 6.1 2.61 5.2 12.9 10.1 11 19.5 20 26 31.9 28.4 30.5 Gd 15.8 16.6 40.2 108 102 101 21.6 42.6 46.8 64.7 79.2 101 Ti 8 273 6 080 6 350 18 200 13 000 13 800 4 670 8 140 7 140 6 170 5 780 12 100 Dy 9.6 4.88 11.2 24.8 20.5 20.9 3.54 7.03 6.33 8.71 9.38 17.1 Y 63 16.9 36.9 96.7 79.3 93.4 14 29.2 23.5 36.5 38.4 73.7 Er 3.8 2.21 4.88 12.8 10.6 10.7 2.29 4.41 3.56 5.5 6.03 10.2 Yb 2.9 2.18 5.43 12.7 11.2 11 1.89 4.04 3.07 5.13 5.24 9.95 Hf 7.8 4.08 8.06 21.8 16.1 16 3.26 5.5 5.27 6.72 6.25 14 V – 138 140 327 349 314 149 360 405 186 342 462 Cr – 3 980 345 146 110 111 1 250 1 440 392 48.2 21 74.1 Ti/Zr 26.8 74.42 28.73 22.83 16.95 17.81 32.89 39.7 34.33 20.1 13.83 15.96 Th/Yb 15.17 0.14 0.12 0.52 0.26 0.43 29.58 7.03 10.52 14.62 18 6.77 La/Nb 2.82 24.8 34.5 8.69 11.35 10.17 1.09 2.45 2.22 1.35 1.14 1.13 Zr/Y 4.89 4.83 5.99 8.24 9.67 8.3 10.1 7.02 8.85 8.4 10.9 10.3 Ba/Th 44.77 1.81 1.66 0.4 0.98 9.08 51.2 97.2 97.5 48.1 30.6 7.25 Eu/Eu∗ 0.83 0.6 0.5 0.49 0.44 0.48 4.32 2.17 2.79 2.47 1.93 1.42 Nb/Ta 16.58 1.16 1.02 4.27 3.93 4.93 28.6 20.1 17.1 26.5 25 19.4 Zr/Nb 4.89 163.4 256.98 58.7 83.73 67.39 1.34 3.77 3.37 2.07 2.25 5.12 Ti/Y 131.3 359.8 172.1 188.2 163.93 147.75 333.57 278.77 303.8 169.04 150.52 164.18 Note. Clinopyroxene: Cpx 1 – xenocryst; Cpx II – core and Cpx III – rim of zonal phenocrysts; Cpx II-III – intermediate zone between core and rim of zoned phenocryst. Inclusions: Incl I – in xenocrysts of Cpx I; 385 Incl II – in the core of zoned phenocryst of Cpx II; Incl II-III – in intermediate zone between core and rim of zoned phenocryst of Cpx II-III (inclusion with salt globule); Incl III – in the rim of Cpx III. aLOI. Determined on X-ray fluorescent analyzer URA-20R. Silicate-carbonate-salt liquid immiscibility and origin of the sodalite-haüyne rocks: study of melt inclusions in olivine foidite from Vulture volcano, S. Italy

Cpx−Liq system clinopyroxene-melt (KD ). The estimation was Cpx−Liq based on the partition of LILE and HFSE between inclu- Table 5. Clinopyroxene/melt partition coefficients (KD ). sion glasses and host mineral [42]. Element Cpx I Cpx II Cpx II-III Cpx III Cpx III The analysis showed (Table 5) that in xenocrysts of clinopyroxene the partitioning coefficient for all trace el- Rb 0.042 0.057 0.094 0.061 0.093 ements is always less than unit, whereas in zoned phe- Ba 0.0002 0.0003 0.0007 0.001 0.016 Cpx−Liq nocrysts (KD ) < 1 only for LILE, HFSE, La, Ce and Th 0.011 0.02 0.089 0.031 0.07 Eu. In zoned phenocrysts, the partitioning coefficient for U 0.001 0.0004 0.015 0.0088 0.025 Nd, Hf, Zr, Sm, Dy, Y, Er, and Yb is always > 1, no- Ta 0.159 0.233 0.574 0.31 0.3 ticeably increasing from cores to intermediate zones and K 0.003 0.0005 0.0003 0.048 0.078 Cpx−Liq rims. However, it is worth noting that (KD ) for Gd, Nb 0.009 0.014 0.092 0.049 0.078 Ti, V, and Cr in phenocryst cores is also < 1, whereas in La 0.09 0.217 0.595 0.446 0.62 the rims and especially in intermediate zones, it is > 1, Ce 0.157 0.408 0.986 0.753 0.878 i.e., the degree of accumulation of these elements some- Sr 0.098 0.155 0.248 0.267 0.37 what changed during crystallization of different zones of Nd 0.409 1.056 2.296 1.644 1.229 phenocrysts. On the diagram (Figure 6) the trends of KD Zr 0.398 1.062 2.596 1.835 1.022 values have a positive slope. Sm 0.629 1.718 2.908 2.476 1.185 Eu 0.13 0.2 0.404 0.356 0.36 Gd 0.39 0.859 1.669 1.288 1 Ti 0.747 0.889 2.95 2.249 1.14 Dy 0.694 1.769 2.847 2.186 1.22 Y 0.579 1.57 2.649 2.065 1.267 Er 0.501 1.371 2.327 1.758 1.049 Yb 0.54 1.769 2.476 2.137 1.106 Hf 0.043 1.529 3.244 2.576 1.143 V 0.383 0.346 1.758 1.02 0.68 Cr 2.764 0.88 3.029 5.238 1.498

Cpx−Liq because, as mentioned above, KD > 1 in the rims.

Figure 6. Pattern of partitioning of trace element between clinopy- Increase in the content of trace elements was, probably, roxene and melt. due to their supply with fluid or fresh melt. Coefficients of trace element distribution between melt The pattern for melt inclusions in clinopyroxenes, normal- and 1 – xenocrysts of clinopyroxene, 2-5 – zonal phe- nocrysts of clinopyroxene (2 – core, 3 – intermediate ized to MORB, has a negative slope owing to the high zone between core and rim, 4,5 – rims of phenocrysts). contents of LILE and Th, U and low concentrations of HREE as well as V and Cr (Figure 7). At general predom- Glasses of heated melt inclusions in clinopyroxenes are inance of LREE over HREE, (La/Yb)n values in inclusion the most enriched in trace elements: they one (HREE, Y, glasses from various clinopyroxenes vary from 41.4 in Cpx I Hf), two (most of other elements) and even three (Th, U) to 12.7 in Cpx III. On the pattern of incompatible elements orders of magnitude exceed the mantle norm (Table 4). The one can see minor Ta, Nb and Zr negative anomalies, es- trace element composition of melt during crystallization of pecially noticeable for inclusions in Cpx I and Cpx II, and xenocrysts and zoned phenocrysts of clinopyroxene varied appreciable Eu and Gd positive anomalies. considerably. The highest concentration of incompatible The intense positive Eu anomaly can be explained by elements was found in inclusion glasses from Cpx III, the the fact that the first to crystallize were femic miner- least – in xenocrysts of Cpx I. For example, melt inclusions als: olivine and clinopyroxene, which accumulated basi- in xenocrysts contain 405, cores of zoned phenocrysts 600, cally HREE. The initial amount of Eu in the melt pre- and rims 1 070 ppm REE. On crystallization of rims in served and increased during its evolution. The compo- zoned phenocrysts of Cpx III, compared to earlier crystal- sition of melt derivatives during differentiation and frac- lization of Cpx II cores, the melt was richer in Zr, Hf, Y, tionation was becoming similar to that of trachyte-syenite, Nd, Sm, Gd, Dy, Er, Yb, V, and Cr and was depleted in i.e. plagioclase-K-feldspar, which is a compatible element LILE, as well as in U, Th, Ta, Nb, La and Ce. Most likely, and concentrator of Eu. At this stage, the amount of Eu increase in the content of HREE and Ti in the melt dur- was maximum and it formed a positive anomaly. ing crystallization of Cpx III was much more appreciable The values of (Eu/Eu*)n, parameter calculated from prim-

386 Liya I. Panina, Francesco Stoppa

Figure 7. Primitive mantle-normalized [38] spidergram for olivine foidite and melt inclusions in xenocrysts and zonal phe- Figure 8. La/Nb–Nb/Ta diagram for olivine foidite (R) and nocrysts of clinopyroxens. heated and quenched silicate inclusions in xenocrysts Inclusions: 1,2 – in xenocrysts, 3 – in cores of zonal of clinopyroxene (I), core (II), intermediate zone be- phenocrysts, 4 – in intermediate zone between core and tween core and rim (II-III) and rim (III) of zonal phe- rim of phenocryst, 5, 6 – in the rim of zonal phenocrysts. nocrysts clinopyroxene. Fields of mantle and crystal Rock: 7 – olivine foidite. sources [38]: PM – primitive mantle, DM – depleted man- tle, ITACARB – Italian extrusive carbonatite, VUTCARB – vulture extrusive carbonatite, MR – “missing reservoir” (unknown reservoir with a high Nb/Ta ratio required for a balance in the silicate Earth). itive mantle [38] for inclusion glasses differ significantly depending on the location of inclusions in xenocrysts or zoned phenocrysts of clinopyroxenes: (Eu/Eu*)n=4.3 in different regions (Figure 8): in the region of carbonatite xenocrysts, 2.8 – 2.5 in the cores of zoned phenocrysts, influence in Cpx I and Cpx II, and in the region of primitive and it decreases to 1.9 – 1.4 in the rims. mantle in Cpx III. The rock under study also falls into the Ion microprobe analysis of the amount of water in inclusion region of the carbonatite influence. glasses shows a high dryness of conserved melts: maxi- mum water content was 0.88, and minimum was 0.02 wt.%. The highest contents of water were detected in inclusion 7. Discussion of results glasses from xenocrysts and cores of zoned phenocrysts, whereas the lowest, in the rims of phenocrysts. The The locations of melt inclusions from Cpx I and Cpx II in amount of dissolved F in inclusion glasses was nearly the the region of carbonatite influence Figure 8, can be ex- same (0.3 – 0.4 wt.%). plained by the fact that, during the intrusion, parental Olivine foidite is considerably enriched in incompatible magma segregated carbonatite melt. During crystalliza- elements, whose concentrations are two (Rb, Ba, Th, U, tion of xenocrysts and zoned phenocrysts of clinopyrox- Nb, La, Ce, and Sr) or one (other minor components) or- enes this matter was completely assimilated by magma. ders of magnitude higher than the mantle norm (Table 4). The localization of inclusions conserved in Cpx III, in the The highest concentrations are typical of LILE and LREE, region of primitive mantle suggests that a fresh inflow whereas the lowest, of Y and HREE. The pattern of trace was not differentiated. We note that the chemical com- elements in the rock, normalized to MORB [38], has a neg- position of intruded magma was considerably depleted in ative slope (Figure 7). The curve displays negative Ta, trace elements with slight chemical changes. The evidence Nd, Ti, Zr and Yb anomalies and minor Er and Tb maxi- for the changes comes from the smooth variations in the mums. Ba/Th in the rock is 44.8, which is 1.8 times lower composition of all clinopyroxenes and silicate melt inclu- than those in the primitive mantle (Ba/Th=79.7). The ra- sions. For example, in the composition of inclusions from tios of Nb, Ta, and La, reflecting the character of man- Cpx I to Cpx II and Cpx III the content of Si, Al, and al- tle sources in the rocks, are either close to mantle ratio kalies increases and the amount of Mg, Fe, Ca decreases, (Nb/Ta=16.6 against 14 in the mantle), or considerably i.e. the composition of melt evolved from olivine-foidite to higher (La/Nb=2.8 against 0.98 in the mantle). The rocks phonolite-nepheline trachyte. Appreciably lower amounts have high Ce/Yb=112, La/Yb=61.4, and low Zr/Y=4.9 val- of trace elements in Cpx I, Cpx II, and in trapped inclu- ues. sions compared to those in phenocryst rims can be also On the Nb/Ta – La/Nb diagram [43] the melts conserved due to separation of immiscible carbonatite melt enriched in different populations of clinopyroxene are localized in in these elements from the parental magma .

387 Silicate-carbonate-salt liquid immiscibility and origin of the sodalite-haüyne rocks: study of melt inclusions in olivine foidite from Vulture volcano, S. Italy

At the same time, the presence of both pure silicate in- is depleted in these components and becomes silicon over- clusions and those with varying ratios of carbonate-salt saturated. globules and segregations in melt inclusions suggests that Carbonate-salt melts spatially separated from silicate

the initial melt at the moment of crystallization of clinopy- parental magma are rich in Ca, alkalies, CO2, S, F, Cl, S, roxene was heterogeneous-silicate-carbonate-salt. Im- and P and are potential carbonatite melts. At significant miscible carbonate-salt globules had an alkali-sulphate, drops of temperature and pressure they become nonuni- alkali-sulphate-carbonate, and Ca-carbonate composition. form and separate into carbonate-salt immiscible frac- Most likely, the multiphase silicate-carbonate-salt im- tions [12]. The phenomena of multistage carbonate-salt miscibility of initial melt had occurred prior to crystal- immiscibility in carbonatite melts proceed in a wide tem- lization of clinopyroxenes, at high temperatures (higher perature range – from 1 250°C and higher to 800 – 600°C than 1 250°C). Primary silicate-carbonate inclusions with and dramatically increase in unstable physicochemical en- varying ratios of immiscible daughter phases such as cal- vironment. They start from separation of alkali-chloride, cite, dolomite, magnesite, and ankerite, were found in the alkali-sulphate , alkali fluoride, and alkali-phosphate liq- apatite from olivine phonolitic foidite bombs of the Vul- uids from the primary carbonatite melt (magma) and ter- ture volcano [44]. Primary silicate-carbonate inclusions minate in the formation of residual Ca-Fe-Mg carbonatite were also found in calcite from Vulture soëvites [45] where melts. dolomite is a predominant carbonate phase. Sharygin et The presence of alkali-sulphate, alkali-sulphate- al. [46], reports zoned phenocrysts of haüyne having pri- carbonate and Ca-carbonate (paralleled by Na- mary melt inclusions spatially associated with pyrrhotite carbonate) salt segregations and globules in silicate globules and crystal inclusions of apatite and clinopyrox- glass of inclusions in clinopyroxene of olivine foidite ene, less often with intergrowths of sulphides and halite. suggests that rocks with sodalite-haüyne group mineral Clinopyroxene phenocrysts show glass inclusions with sul- (including haüynite) in the Vulture volcanic complex are phide globules and crystal inclusions of apatite, haüyne, genetically related to carbonatite melts and decomposi- and magnetite. Particularly interesting is the occurrence tion into immiscible fractions. Probably, alkali-sulphate of extrusive carbonatite at Vallone Toppo del Lupo, where and alkali-sulphate-carbonate melts enriched in Cl, Ba, nyerereite inclusions were found in melilite [2]. Data from and Sr, are rapidly separated from carbonatite melts, carbonatite also show that immiscible Na-carbonate ex- and owing to their volatility and high mobility are isted in the magmatic system [2]. concentrated in cracks, voids, and apical parts of magma chamber and result in haüynite and haüyne phonolite. Most likely, carbonate-salt melts are immiscible compo- The occurrence of multiphase carbonate salt immiscibility nents of initial carbonatite melt. Some researchers, how- was found in carbonatite lavas of Oldoinyo Lengai [49] ever, believe [47] that the melt could result from remelting and Vallone Toppo del Lupo. Here amoeboid blisters of host carbonate rocks. But the fact of enrichment of and inclusion of alkali-carbonate, as well as Cl- and F- carbonate-salt globules in inclusions of K, Na, Ba, Sr, P, rich patches were found. These bodies were made up of Cl, S rules out this possibility, as it seems least likely that submicron-sized intergrowths of faceted minerals repre- host carbonate rocks could be enriched in such elements sented by: and in such high amounts. Analysis of literature data showed [35] that carbon dioxide, • alkali carbonates and alkali phosphates, alkalies, halogens, sulfur, and phosphorus primordially ex- • alkali carbonates and alkali Fe-sulphides. ist in all abyssal alkaline magmas and have a mantle ori- gin. Most likely, in the mantle they are distributed ir- These submicron-sized segregations are assumed to be regularly and are accumulated in deep-seated reservoirs, the result of rapid quenching of two types of alkali salt which appear during activation of mantle and develop- melts: sulfur-rich and phosphorus-rich, which separated ment of plumes [2, 48]. Here these fluids interact with from initial carbonatite magma. R. Mitchell [50] considers

mantle source and prompt highly SiO2-undersaturated, this to be evidence for the occurrence of liquid carbonate- Mg- and Ca- rich silicate magmas [29]. During the as- salt immiscibility. He suggests that halogen-rich melts

cent, primary magmas enriched in CO2, alkalies, SO3, accumulated in the upper parts of magma chamber and and halogens crystallize and fractionate, and at dras- during eruption were carried together with accumulated tic changes of temperatures and pressures the phenom- segregations of alkaline carbonates. A very interesting ena of liquid silicate-carbonate immiscibility take place phenomenon was described [51] in the zones of alter- in them. Immiscibility is accompanied by redistribution of ation in harzburgite nodules from the Montana-Clara vol- elements: most volatile components together with Ca pass cano (Canary archipelago) in association with II genera- into a carbonate-salt melt, and the silicate melt, naturally, tion minerals (olivine, clinopyroxene, and spinel) of syenite

388 Liya I. Panina, Francesco Stoppa

glass with globules of Fe-Ni-Cu monosulfides and glob- carbonatites and melilitites. Xenocrysts of Cpx I differ from ules of Ca-carbonates. Based on relationship of carbon- zoned phenocrysts also in partitioning coefficients of trace ates, alkaline silicate glass and sulphides, the authors elements in the system clinopyroxene-melt (Table 5, Fig- suggested that it is probable that three liquids coexist at ure 6). During crystallization of clinopyroxene xenocrysts reducing upper mantle conditions. all trace elements were preserved and accumulated in the Geochemical study showed that the primary magma from melt, and during crystallization of zoned phenocrysts Zr, which olivine foidite of the Vulture volcano crystallized Hf, Y, MREE and HREE (except Eu) partly concentrated was enriched in incompatible elements whose amount 1 – in clinopyroxenes with increasing level of accumulation in 2 orders of magnitude exceeded the mantle norm. Magma intermediate and peripheral zones. It is possible [53, 54], was considerably depleted in HREE relative to LREE. that crystallization of xenocrysts and zoned phenocrysts This suggests that the mantle source could contain sta- of clinopyroxene most likely, took place at different ther- ble garnet. On partial melting of this source, the amount modynamic parameters from melts with different degrees of LREE in primitive melts normally increases, whereas of enrichment in trace elements. HREE remains in garnet restite. The low degree of melt- ing of mantle substance in the rocks under study is evi- denced from the high absolute contents of Ti, Zr, and Y in 8. Conclusions clinopyroxenes, melt inclusions and in the rock (Table 4). Low Ti/Zr values in clinopyroxenes, which change from 1. Xenocrysts and zoned phenocrysts of clinopyrox- 74.4 in megacrysts to 28.7 in the cores, and 17 in the rims enes in olivine foidites crystallized at 1 225 – of zoned phenocrysts, most likely, suggest participation of 1 170°C. The composition of initial melt was het- unexhausted mantle in magma generation. It is consid- erogeneous, silicate-carbonate-salty. ered [52] that Ti/Zr for clinopyroxene of primitive mantle 2. The immiscible silicate melt during crystallization is estimated at 120. In the conditions of continental rifts, of clinopyroxenes was highly magnesian, alkaline in which magma generation is contributed by undepleted and evolved towards an increase in Si, Al, and al- mantle, this value decreases to below 100 at high concen- kalies and decrease in Mg, Fe, and Ca, altering trations of both elements. from olivine-foidite composition during formation of Rather constant values of Zr/Y, Ti/Y, Zr/Nb and Y/Nb in Cpx I to phonolite-trachyte during crystallization of melt inclusions (Table 4), which are used to characterize phenocryst rims. a magmatic source, suggest that the mantle source was uniform. The evidence for this also comes from close values 3. The immiscible carbonate-salt melt consisted of of Ta/Yb and Th/Yb in clinopyroxenes. alkali-sulphate, alkali-carbonate, Ca, Mg, Ba, and Sr-carbonate fractions separated from carbonatite The obtained results show that for olivine foidite the melt. The melt in the enrichment in alkalies, Sr, relative contents of Eu are close to that of chondrite ∗ Ba, P, S, and Cl was close to typical carbonatite (Eu/Eu = 0.83), whereas in melt inclusions in clinopy- melts, genetically related to alkaline magmatism, roxenes it is much higher (Table 4): 4.3 times in Cpx I and and did not show any features of participation of 2.8 to 1.4 times in Cpx II-III, appreciably decreasing from crustal matter. cores to rims. It is a common opinion [36] that for all man- tle magmas and primordial upper mantle a relative content 4. Haüynophyress and most minerals of sodalite- ± of Eu is within 20% from identical Eu concentrations in haüyne group are genetically related to carbon- ∗ chondrites. A higher Eu/Eu value is considered evidence atite melts and their decomposition into immisci- for fractional crystallization with participation of feldspars, ble fractions of alkali-sulphate and alkali-sulphate- leucite, and melilite. Indeed, in our case clinopyroxenes carbonate composition, which accumulated in the crystallized from differentiated melt after olivine, but prior upper part of magma column. to separation of feldspars. Perhaps for this reason, at the stage of formation of Cpx I, the Eu/Eu∗ in melt value was 5. Initial melts were enriched in incompatible el- maximum. During crystallization of zoned clinopyroxene ements, 1–3orders of magnitude exceeding phenocrysts, when microlites of foidite started to crystal- the mantle norm, with significant predominance of lize and accumulate Eu, this value began to decrease dras- LREE over HREE and were enriched in F, Cl, SO3, ∗ tically. It is worth noting that the Eu /Eu value and, espe- and CO2 and contained to 0.9 wt.% H2O. The man- cially, Gd value could be influenced by an unknown high tle source of melts was rather homogeneous, unde- Gd phase in the source and inherited by initial melt as pleted and was characterized by a low degree of similar positive anomaly has been observed in other Italian melting and probable presence of garnet in restite.

389 Silicate-carbonate-salt liquid immiscibility and origin of the sodalite-haüyne rocks: study of melt inclusions in olivine foidite from Vulture volcano, S. Italy

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