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A composite xenolith composed of a zircon-bearing, apatite-rich olivine-pyroxene hornblendite and an amphibole harzburgite part was found in an outcrop of Neogene alkali basalt at Szigliget, Bakony-Balaton Highland Volcanic Field, Western Hungary. The hornblendite is composed dominantly of amphibole that is strongly enriched in incompatible trace elements along with apatite, orthopyroxene and olivine. Zircon, rutile, ilmenite and sulphide occur as inclusions in the silicate minerals as accessory phases. On the basis of the chemical composition of the minerals, we estimate that the hornblendite crystallized at ~1000–1015 °C and 1.2–1.4 GPa pressure in the uppermost mantle under oxidising conditions (ΔlogfO2(FMQ)~ + 1.3). The hornblendite precipitated from a volatile and incompatible element-rich silicate melt with trachyte or phonolite composition, which might be derived from an alkali basalt melt by high-degree (>70%) fractional crystallisation.

Plio-Pleistocene alkali basalt hosted mafic garnet granulite xenoliths were studied from the Bakony-Balaton Highland Volcanic Field (BBHVF) to trace fluid-melt-rock interactions in the lower crust. Two unique mafic garnet granulite samples were selected for analyses (optical microscopy, microthermometry, electron microprobe, Raman and IR spectroscopy), which contain a clinopyroxene-plagioclase vein and patches with primary silicate melt inclusions (SMI). The samples have non-equilibrium microtexture in contrast with the overwhelming majority of previously studied mafic garnet granulite xenoliths. Primary silicate-melt inclusions were observed in plagioclase, clinopyroxene and ilmenite in both xenoliths. The SMI-bearing minerals located randomly in Mi26 and in a clinopyroxene-plagioclase vein on the edge of Sab38 granulites. Petrography and the fluid and melt inclusion study suggest that at least three fluid events occurred in the deep crust represented by these xenoliths. 1. Primary CO2-dominated ± CO ± H2S fluid inclusions were observed in the wall-rock part of Sab38 xenolith. 2. The crystallization of new clinopyroxene from melt, with CO2 + H2O fluid. 3. The crystallization of new plagioclase occurred in a heterogeneous fluid-melt system with additional N2 and CH4 during crystallization. A local reaction was observed between sphene and acidic melt, which formed ilmenite + clinopyroxene + plagioclase ± orthopyroxene. The ‘water’ content of the rock forming minerals was determined by infrared spectroscopy. The calculated bulk ‘water’ content of the Mi26 xenolith is 171 ± 51 ppm wt. %. The bulk wall rock part of the Sab38 granulite contains 55 ± 17 ppm wt. % of ‘water’, whereas the bulk plagioclase-clinopyroxene vein contains 278 ± 83 ppm wt. %. These results imply a very dry lower crust, locally hydrated by percolating fluids and melts.

Four fluid migration events were recorded during the Alpine metamorphism in the Sopron micaschist from the Grob gneiss series of the Lower Austroalpine Unit of the Eastern Alps near Sopron, using mineral chemistry data, geothermo-barometry and fluid inclusion studies.1. Tourmaline mineralisation in quartz veins and to some extent in the host rock. Similar mineral compositions in the quartz-tourmaline veins and in the host rock show equilibrium between fluid and the host rock. Geothermo-barometry gives 560-610oC temperature and 950-1230 MPa pressure for the formation of quartz-tourmaline veins which is the same as the determined P-T peak (T=560 and 600°C p= 840-1230 MPa).2. Fluids causing Mg-metasomatism in the shear zones. The result of this fluid invasion was the formation of leucophyllite in the shear zones and Mg-enrichment of some minerals (chlorite, muscovite, garnet) in the close vicinity of the shear zone. The effect of this fluid was confined to the shear zones and the neighbouring host rock.3. The rock was infiltrated along the shear zones and quartz veins with CO2-bearing hypersaline fluids during retrograde metamorphism. The presence of this fluid is evidenced by secondary CO2 inclusions and hypersaline aqueous fluid inclusions ± CO2. The aqueous fluid had high concentrations of Na, Ca, Fe, Al, Cl and contained moderate amounts of Mg, Zn, Ti, K, Mn, S and P. This fluid was the carrier of the REE and Th and locally precipitated florencite, monazite, allanite, apatite, thorite and thorianite in the shear zone. Traces of this mineralisation are found in quartz-tourmaline veins, postdating the tourmaline mineralisation.4. Late retrograde metamorphic fluid represented by two phase (liquid+vapor) aqueous inclusions of the NaCl-CaCl2-H2O system with total salinity between 25 and 28.5% and homogenisation temperatures between 229.6 and 322oC

Felsic to mafic granulite xenoliths from late Neogene basalt pyroclastics in four localities of the western Pannonian Basin (Beistein, Kapfenstein, Szigliget and Kaptalantoti (Sabar-hegy) were studied to find out their metamorphic and fluid history. The characteristic mineral assemblage of the granulites consists of Pl + Opx + Qtz ± Cpx ± Bt ± Grt ± Kfs. Based on abundant magmatic relic microstructural domains occurring in these rocks, the potential precursors might have been predominantly felsic igneous or high to ultrahigh temperature rocks. Ternary feldspar thermometry provides a rough estimate of temperatures of about 920–1070 °C. The first fluid invasion event, which is linked with this early high to ultrahigh temperature stage is characterised by primary pure CO2 inclusions in apatite and zircon. The densest primary CO2 inclusions indicate 0.52–0.64 GPa pressure at the estimated temperature range of crystallization. According to mineral equilibria and geothermobarometry, the high to ultrahigh temperature rock cooled and crystallized to granulite of predominantly felsic composition at about 750–870 °C and 0.50–0.75 GPa in the middle crust, between 20 and 29 km depths. The second fluid invasion event is recorded by primary CO2-rich fluid inclusions hosted in the granulitic mineral assemblage (plagioclase, quartz and orthopyroxene). In addition to CO2, Raman spectroscopy revealed the presence of minor N2, H2S, CO and H2O in these inclusions. Partial melting of biotite-bearing assemblages could be connected to the next fluid invasion shown by secondary CO2-rich fluids recorded along with healed fractures in plagioclase, clinopyroxene and orthopyroxene. This event could have happened at depths similar to the previous ones. The final step in the granulite evolution was the sampling in the middle crust and transportation to the surface in form of xenoliths by mafic melt. This event generated temperature increase and pressure decrease and thus, limited melting of the xenoliths. The youngest fluid inclusion generation, observed mostly in healed fractures of felsic minerals, could be associated with this event.

Silicate melt inclusions containing rhonite Ca2(Mg,Fe2+)4Fe3+Ti[Al3Si3O20] were studied in olivine phenocrysts from alkali basalts of six different volcanic regions: Udokan Plateau, North Minusa Depression, Tsagan-Khurtei Ridge (Russia), Bakony-Balaton Highland, Nograd-Gomor Region (Hungary) and Makhtesh Ramon (Israel). Rhonite-bearing silicate melt inclusions are relatively common phenomena in alkali basalts and usually coexist with inclusions containing no rhonite. Inclusions with rhonite generally occur in the core of the olivine phenocrysts. According to heating experiments and CO2 microthermometry, all the rhonite-bearing inclusions in core of the olivine phenocrysts were trapped as silicate melt at T > 1300 °C and P > 3–5 kbar. Rhonite crystallized in a narrow temperature range (1180–1260 °C) and P < 0.5 kbar. The petrography and thermometry of rhonite-bearing silicate melt inclusions show a general crystallization sequence: Al-spinel → rhonite → clinopyroxene → apatite → ± amphibole, Fe-Ti oxide (ilmenite or Ti-magnetite) → glass. Majority of rhonites from melt inclusions have Mg/(Mg + Fe2+) > 0.5 and belong to Mg-rich species Ca2Mg4Fe3+Ti[Al3Si3O20]. There are no essential differences in chemistry among rhonites from olivine-hosted silicate melt inclusions from phenocryst, from groundmass of alkali basalts, from alteration products of kaersutitic amphibole mega/xenocrysts and of kaersutite in deep-seated xenoliths in alkali basalts. The rare occurrence of rhonite as essential constituent in rocks may be explained from its microstructural peculiarities. This mineral is an intermediate member of the polysomatic spinel-pyroxene series. Possibly, the structural feature of rhonite does explain why it is an unstable mineral in under changing crystallization conditions. In general, the presence and chemistry of rhonite may be used for rough estimation of temperature, pressure and oxygen fugacity during crystallization of alkali basalts.

We investigate the effects of xenolith–host basalt interaction on lower crustal mafic granulite xenoliths from the Central Pannonian Basin. The xenoliths are devoid of any signs of melting, nevertheless various phenomena are identified, which indicate that the original mineralogy and chemistry of the xenoliths was modified during interaction with the host basalt. The rock-forming silicates are only slightly affected by alteration, but the Fe–Ti-oxides are overprinted to a significant extent. Complex chemical zoning patterns are detected using high-resolution element mapping in ilmenites and in lamellar titanomagnetite–ilmenite intergrowths. The chemical alteration of the Fe–Ti-oxides was diffusion-controlled and, hence, time and temperature dependent. On the basis of diffusion profiles in titanomagnetite we estimate the duration of xenolith–host basalt interaction to be at least 9–20 h. This is comparable to the time necessary for the ascent of the host basalt to the surface. It is too short to reflect alteration during granulite facies metamorphism in the deep crust. The chemical alteration of the titanomagnetite thus reflects the total duration of the xenolith–host basalt interaction.

Amphibole-bearing and amphibole-free garnet granulite xenoliths (clinopyroxene, plagioclase, garnet ± orthopyroxene, ± amphibole) from two localities of the Bakony–Balaton Highland Volcanic Field (Sabar-hegy and Szentbekkalla) were investigated by means of textural analysis, mineral chemistry, mineral equilibria, geothermobarometry and fluid inclusion studies. We have determined the P–T path of these lower crustal xenoliths, which begins at peak pressure between 0.9 and 1.4 GPa. The peak pressure was followed by temperature increase of about 200–300 °C and 0.3–0.7 GPa pressure decrease which is marked by breakdown reactions of garnet and pargasitic amphibole. Garnet broke down first to orthopyroxene–anorthite–spinel (type 1) then to olivine–plagioclase ± spinel (type 2) symplectite. Amphibole broke down to form clinopyroxene–plagioclase–Fe–Ti oxide-melt ± orthopyroxene ± olivine mineral assemblage. These changes in P–T conditions were caused by crustal thinning. The present day crustal thickness (max. 32 km) indicates that garnet granulites are no longer stable in the lower crust of the Pannonian Basin. The calculated crustal thinning factor is between 1.6 and 1.8 in accordance with the values calculated from tectonic methods. A unique CO2–CO–C fluid system—which has not been described from the lower crust so far—occurs in inclusions of the rock-forming minerals, mainly in plagioclase and clinopyroxene. A primary and two secondary fluid inclusion (FI) generations were identified on the basis of textural analyses and distribution of homogenization temperatures. Primary FIs are connected to the formation of garnet granulite. The older secondary generation was trapped after the main temperature increase and some pressure decrease during crustal thinning. The younger secondary generation trapped within the depth limits of the present lower crust at pressures between 0.6–0.7 GPa. The overall composition of the fluid system has not changed during crustal thinning. The calculated oxygen fugacity values are slightly above and under QFM (between 10–8.5 and 10–10.1 at 1200 °C).

This paper is devoted to the description of spessartine-almandine garnet (Sps: 39.8-60.2%; Alm: 29.1-56.76%; Grs

¶Fluid inclusions from two Mesoproterozoic, metamorphosed layered intrusive complexes, Niquelândia and Barro Alto, Goias State, Brazil record multiple fluid influx events from the magmatic to granulitic and retrograde metamorphic stages.

A partially molten buchite xenolith containing quartz, glass, mullite/sillimanite, corundum, Al-rich orthopyroxene, spinel, Mg-Al-bearing Fe-Ti oxides, ilmenite and rutile was found in the basaltic tuff of Szigliget (Balaton Highlands, Hungary). The pre-existing rock may have been a quartz-rich micaschist or phyllite from the wall of the magma vent. Minerals like mullite, Al-mullite and Al-rich orthopyroxene with Al2O3 between 7.62 to 11.54 wt% show ultrahigh-temperature (UHT) metamorphism of the xenolith with temperatures in excess of 1080 °C, which means that the temperature of metamorphism approached that of the enclosing alkaline basaltic melt. CO2 fluid inclusions with homogenization temperatures between +26.5 and +29.7 °C and mineral equilibria indicate pressure of buchitization between 310 and 390 MPa. Glass compositions are similar to a peraluminous leucogranite which is in accordance with melting experiments when metagreywackes, pelites and orthogneisses are involved. The presence of glass sugge...

Microthermometric investigations of silicate-melt inclusions and electron microprobe analyses were conducted on experimentally homogenized silicate-melt inclusions and on the host clinopyroxenes from 4 scoria samples of different layers from the Mt. Somma-Vesuvius medieval eruption (Formazione di Terzigno, 893 A.D.). The temperature of homogenization, considered the minimum trapping temperature, ranges from 1190 to 1260 ± 5 °C for all clinopyroxene-hosted silicate melt inclusions. The major and minor-element compositional trends shown by Terzigno scoria and matrix glass chemical analysis are largely compatible with fractional crystallization of clinopyroxene and Fe-Ti oxides. Sulfur contents of the homogenized silicate-melt inclusions in clinopyroxene phenocrysts compared with that in the host scoria show that S has been significantly degassed in the erupted products; whereas, Cl has about the same abundance in the inclusions and in host scoria. Fluorine is low (infrequently up to 800 ppm) in the silicate-melt inclusions compared to 2400 ppm in the bulk scoria. Electron microprobe analyses of silicate-melt inclusions show that they have primitive magma compositions (Mg# = 75-91). The composition of the host clinopyroxene phenocrysts varies from typical plinian-related (Mg#≥85) to non plinian related (Mg#≤85). The mixed source of the host clinopyroxenes and primitive nature of the silicate-melt inclusions implies that these phenocrysts, in part, may be residual and/or have a polygenetic origin. The similar variation trends of major and minor-elements between homogenized silicate-melt inclusions from the Terzigno scoria, and silicate-melt inclusions in olivine and diopside phenocrysts from plinian eruptions (Marianelli et al., 1995) suggest that the trapped inclusions represent melts similar to those that supplied the plinian and sub-plinian magma chambers. These geochemical characteristics suggest that the Vesuvius magmatic system retained a vestige of the most recent plinian event.

Nodules (coarse-grain “plutonic” rocks) were collected from the ca. 20 ka Pomici di Base (PB)-Sarno eruption of Mt. Somma-Vesuvius, Italy. The nodules are classified as monzonite-monzogabbro based on their modal composition. The nodules have porphyrogranular texture, and consist of An-rich plagioclase, K-feldspar, clinopyroxene (ferroan-diopside), mica (phlogopite-biotite) ± olivine and amphibole. Aggregates of irregular intergrowths of mostly alkali feldspar and plagioclase, along with mica, Fe-Ti-oxides and clinopyroxene, in the nodules are interpreted as crystallized melt pockets. Crystallized silicate melt inclusions (MI) are common in the nodules, especially in clinopyroxenes. Two types of MI have been identified. Type I consists of mica, Fe-Ti-oxides and/or dark green spinel, clinopyroxene, feldspar and a vapor bubble. Volatiles (CO2, H2O) could not be detected in the vapor bubbles by Raman spectroscopy. Type II inclusions are generally lighter in color and contain subhedral feldspar and/or glass and several opaque phases, most of which are confirmed to be oxide minerals by SEM analysis. Some of the opaque-appearing phases that are below the surface may be tiny vapor bubbles. The two types of MI have different chemical compositions. Type I MI are classified as phono-tephrite — tephri-phonolite — basaltic trachy-andesite, while Type II MI have basaltic composition. The petrography and MI geochemistry led us to conclude that the nodules represent samples of the crystal mush zone in the active plumbing system of Mt. Somma-Vesuvius that were entrained into the upwelling magma during the PB-Sarno eruption. PhD Programme (XXV Cycle, Coordinated by B. De Vivo) “Internal dynamics of volcanic systems and hydrogeological-environmental risks” of the University of Naples Federico II Virginia Tech Published version former journal title: Central European Journal of Geosciences

The complex microstructure of kelyphitic rims around garnet in lower crustal garnet granulite xenoliths from the Bakony–Balaton Highland Volcanic Field, Central Pannonian Basin has been studied in order to identify controls on garnet breakdown. Symplectites comprised of a vermicular intergrowth of submicron sized anorthite, orthopyroxene and spinel replace garnet at a sharp reaction front. Based on element distribution maps the transformation of garnet to symplectite is isochemical. Phase diagram calculations indicate that this reaction was induced by a pressure decrease and/or a temperature increase. In site-specific TEM foils prepared by focused ion beam technique and oriented parallel and perpendicular to the reaction front 200 nm wide rods of anorthite and 20 nm wide rods of spinel are identified. The rods are oriented approximately perpendicular to the replacement front and are embedded in an orthopyroxene matrix. The regular spacing of the symplectite phases along the reaction front suggests that their growth is controlled by diffusion. The kinetics of symplectite formation has been modelled based on irreversible thermodynamics. During interaction of the xenolith with the host basalt the microstructure and chemistry of the An–Opx–Spl symplectite was significantly modified and it was partially replaced by an olivine bearing symplectite. In contrast to primary symplectite formation, these processes were metasomatic in nature including addition of sodium, titanium and some trace elements from the basaltic melt and can clearly be discerned from the garnet breakdown. Based on these observations it is inferred that symplectite formation took place within the deep crust during the extension of the Pannonian Basin between 15 and 30 km depth at high temperature (850–1,050°C) prior to the volcanic transport to the surface.

Polymetamorphic cordierite andalusite-bearing micaschist from the Garabonc-1 borehole has been affected by three metamorphic episodes: Medium-pressure (800-900 Mpa), medium-grade (500-550 C ) Barrovian-type metamorphism occurred first, defined by the appearance of staurolite and kyanite. There are no geochronologic data concerning the age of this episode. Based on certain assumptions it is most probably related to the Caledonian or Early Hercynian orogenies. The second metamorphic episode was low-pressure/medium-grade in character (200-300 Mpa and 560 to 580 o C). Finally, contact metamorphism (100-150 Mpa and 600-640 o C) was caused by an intruding granitoid body. The characteristic minerals are andalusite, cordierite, fibrolite and spinel. The age of the granite intrusion is Carboniferous (Balogh et al., 1981). The most dense CO 2 ±CH 4 ±N e inclusions formed well after the peak P-T conditions. This inclusion type was sealed during all the three stages of metamorphism. There is no significant change in the fluid composition during the second phase. In addition to the pre-existing CO 2 ±CH 4 ±N 2 fluid hypersaline brine was trapped in connection with the third stage. The cooling and uplift of the terrain is recorded by low- to intermediate-salinity aqueous and gaseous CH 4 ±CO 2 inclusions