A mineral-scale investigation of the origin of the 2.6 Ma Füzes-tó basalt, Bakony-Balaton Highland Volcanic Field (Pannonian Basin, Hungary)

Abstract The alkaline basalt of the Füzes-tó scoria cone is the youngest volcanic product of the Bakony-Balaton Highland Volcanic Field. The bombs and massive lava fragments are rich in various crystals, such as mantle-derived xenocrysts (olivine, orthopyroxene, clinopyroxene, spinel), high-pressure mineral phases (clinopyroxene) and phenocrysts (olivine, clinopyroxene). Peridotite xenoliths are also common. Ratios of incompatible trace elements (Zr/Nb and Nb/Y) suggest that the primary magma was formed in the transitional spinel-garnet stability field, at the uppermost part of the asthenosphere. Magmatic spinel inclusions with low-Cr# (22–35) in olivine phenocrysts can reflect a fertile peridotite source. The olivine, orthopyroxene, colourless clinopyroxene and spinel xenocrysts are derived from different depths of the subcontinental lithospheric mantle and their compositions resemble the mineral phases of the ultramafic xenoliths found in this region. The rarer green clinopyroxene cores of clinopyroxene phenocrysts could represent high-pressure products of crystallization from a more evolved melt than the host magma, or they could be derived from mafic lower crustal rocks. Crystallization of the basaltic magma resulted in olivine and clinopyroxene phenocrysts. Their compositions reflect polybaric crystallization with a final, strongly oxidized stage. The Füzes-tó basalt does not represent a certain magma composition, but a mixture of mineral phases having various origin and mantle-derived basaltic melt

Bimodal pumice populations in the 13.5 Ma Harsány ignimbrite, Bükkalja Volcanic Field, Northern Hungary: Syn-eruptive mingling of distinct rhyolitic magma batches?

Abstract The 13.5 Ma Harsány ignimbrite, in the eastern part of the Bükkalja volcanic field, eastern-central Europe, provides a rare example of mingled rhyolite. It consists of two distinct pumice populations (‘A’- and ‘B’-type) that can be recognized only by detailed geochemical work. The pumice and the host ignimbrite have a similar mineral assemblage involving quartz, plagioclase, biotite and sporadic Kfeldspar. Zircon, allanite, apatite and ilmenite occur as accessory minerals. The distinct pumice types are recognized by their different trace element compositions and the different CaO contents of their groundmass glasses. Plagioclase has an overlapping composition; however, biotite shows bimodal composition. Based on trace element and major element modeling, a derivation of ‘A’-type rhyolite magma from the ‘B’-type magma by fractional crystallization is excluded. Thus, the two pumice types represent two isolated rhyolite magma batches, possibly residing in the same crystal mush. Coeval remobilization of the felsic magmas might be initiated by intrusion of hot basaltic magma into the silicic magma reservoir The rapid ascent of the foaming rhyolite magmas enabled only a short-lived interaction and thus, a syn-eruptive mingling between the two magma batches

The lithospheric mantle and lower crust-mantle relationships under Scotland: a xenolithic perspective

In the British Isles the majority of volcanic rocks containing upper mantle and lower crustal xenoliths occur in Scotland. Most of the occurrences are of Carboniferous–Permian age. This paper presents new data on the mineral chemistry of spinel lherzolite xenoliths from the five principal Scottish tectonic terranes. Compositional variations among the minerals emphasize the broad lateral heterogeneity of the subcontinental lithospheric mantle across the region. The remarkable range of Al2O3 v. CaO exhibited by the clinopyroxenes compared with data from other ‘xenolith provinces' emphasizes the extremely complex tectonomagmatic history of the Scottish lithosphere. The generalized age increase from southern and central Scotland to the Northern Highland and Hebridean terranes of the north and NW, with concomitant complexity of geological history, is reflected also by trace element and isotopic studies. Reaction relationships in lherzolites from the Hebridean Terrane, owing to pervasive metasomatism, involve secondary growth of sodic feldspar. This, and light REE enrichment of clinopyroxenes, points to involvement of a natro-carbonatitic melt. Most pyroxenitic xenoliths are inferred to form a basal crustal layer with a generally sharp discontinuity above the underlying (dominantly lherzolitic) mantle. A second discontinuity is inferred to separate these ultramafic cumulates from overlying, broadly cognate metagabbroic cumulates

Modeling of Olivine and Clinopyroxene Fractionation in Intracontinental Alkaline Basalts: A Case Study from the Carpathian-Pannonian Region

Besides mantle peridotites primary basaltic melts are the best tool to investigate upper mantle petrology and geochemistry. However, de facto primitive melts are hard to found, as basaltic melts usually go through a fractionation process during their ascent towards the surface. Most primary melt calculators are based on the major or trace element compositions of olivine-phyric ocean island basalts and peridotites and are less accurate if clinopyroxene fractionation occurred. In this chapter a new fractionation modeling method of alkaline basalts will be introduced, which has been published earlier only in Hungarian. Olivine clinopyroxene fractionation of four basaltic volcanoes have been modeled from different Miocene- Quaternary volcanic fields from the Carpathian-Pannonian Region (Stiavnica (Selmec) VF, Novohrad-Gemer (Nógrád-Gömör) VF, Perşani Mts. (Persányi Mts.) VF and from the Lucaret-Sanoviţa (Lukácskő-Sziklás) volcano. Keywords: olivine, clinopyroxene, fractionation, intracontinental, monogenetic, alkaline basal

The alkaline lamprophyres of the Dolomitic Area (Southern Alps, Italy): markers of the Late Triassic change from orogenic-like to anorogenic magmatism

We present the first complete petrological, geochemical and geochronological characterization of the oldest lamprophyric rocks in Italy, which crop out around Predazzo (Dolomitic Area), with the aim of deciphering their relationship with Triassic magmatic events across the whole of the Southern Alps. Their Mg# of between 37 and 70, together with their trace element contents, suggests that fractional crystallization was the main process responsible for their differentiation, together with small-scale mixing, as evidenced by some complex amphibole textures. Moreover, the occurrence of primary carbonate ocelli suggests an intimate association between the alkaline lamprophyric magmas and a carbonatitic melt. 40Ar/39Ar data show that the lamprophyres were emplaced at 219·22 ± 0·73 Ma (2σ; full systematic uncertainties), around 20 Myr after the high-K calc-alkaline to shoshonitic, short-lived, Ladinian (237–238 Ma) magmatic event of the Dolomitic Area. Their trace element and Sr–Nd isotopic signatures (87Sr/86Sri = 0·7033–0·7040; 143Nd/144Ndi = 0·51260–0·51265) are probably related to a garnet–amphibole-bearing lithosphere interacting with an asthenospheric component, significantly more depleted than the mantle source of the high-K calc-alkaline to shoshonitic magmas. These features suggest that the Predazzo lamprophyres belong to the same alkaline–carbonatitic magmatic event that intruded the mantle beneath the Southern Alps (e.g. Finero peridotite) between 190 and 225 Ma. In this scenario, the Predazzo lamprophyres cannot be considered as a late-stage pulse of the orogenic-like Ladinian magmatism of the Dolomitic Area, but most probably represent a petrological bridge to the opening of the Alpine Tethys

Petrography, geochemistry and igneous stratigraphy of the Escuela Las Pircas intrusion, Sierra Grande de San Luis, Argentina

Escuela Las Pircas es un cuerpo intrusivo máfico-ultramáfico situado en el sector sur de la faja de rocas máficas-ultramáficas La Jovita-Las Águilas, la cual se extiende aproximadamente 100 km con rumbo NNE, con un ancho que oscila entre 3 y 5 km, y se halla emplazada en el faldeo oriental de la sierra Grande de San Luis. Los cuerpos máficos-ultramáficos que constituyen esta faja son de gran interés por ser intrusiones de tipo estratificadas portadoras de una mineralización de sulfuros de Fe-Ni-Cu-Co y minerales del grupo del platino. Las variaciones modales y geoquímicas exhibidas por el cuerpo intrusivo Escuela Las Pircas, permiten definir en éste cuatro unidades estratigráficas: unidad hornblendítica piroxénica con plagioclasa, unidad ortopiroxenítica hornblendífera con plagioclasa, unidad norítica hornblendífera inferior y unidad norítica hornblendífera superior. Estas unidades constituyen una secuencia de niveles máficos y ultramáficos intercalados, los cuales conforman la porción superior de la serie estratificada. Los resultados de los análisis de química de roca total y mineral permitieron establecer que todas las unidades definidas corresponderían a una misma secuencia magmática, en la cual las diferencias mineralógicas y geoquímicas entre las distintas unidades habrían sido controladas principalmente por variaciones en las tasas de nucleación y crecimiento cristalino. Asimismo, los resultados de los análisis petrográficos y químicos permitieron inferir que las unidades definidas en el cuerpo intrusivo Escuelas Las Pircas y las correspondientes a la Serie Estratificada del cuerpo intrusivo Virorco corresponderían a una misma secuencia estratigráfica ígnea, donde las unidades del cuerpo intrusivo Escuela Las Pircas representan el mayor grado de evolución.Escuela Las Pircas is a mafic-ultramafic intrusion located in the southern sector of La Jovita-Las Águilas mafic-ultramafic belt, which is a 3 to 5 km wide and 100 km long NNE trending belt located along the Eastern slope of the Sierra Grande de San Luis. The mafic-ultramafic bodies of this belt are of great interest since they are layered intrusions which carry an associated mineralization of Fe-Ni-Cu-Co sulfides and platinum group minerals. Modal and cryptic layering identified in Escuela Las Pircas intrusion allows the definition of four stratigraphic units: Plagioclase-bearing pyroxene hornblendite unit, plagioclase-bearing hornblende orthopyroxenite unit, lower hornblende norite unit and upper hornblende norite unit. Their petrographic features would suggest their belonging to the upper portion of the layered series. Bulk-rock and mineral chemistry results indicated that all the units of Escuela Las Pircas intrusion correspond to the same magmatic sequence, in which mineralogical and geochemical differences would have been mainly controlled by nucleation and crystal growth rate variations. Furthermore, petrographic and chemistry analysis indicate that the units defined in Escuela Las Pircas and in those from Virorco Layered Series respond to the same stratigraphic igneous sequence, being Escuela Las Pircas units those that represent the higher degree of evolution.Fil: Cacace, Francisco Esteban. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Geológico del Sur. Universidad Nacional del Sur. Departamento de Geología. Instituto Geológico del Sur; ArgentinaFil: Ferracutti, Gabriela Roxana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Geológico del Sur. Universidad Nacional del Sur. Departamento de Geología. Instituto Geológico del Sur; ArgentinaFil: Ntaflos, Theodoros. University of Vienna. Faculty of Earth Sciences, Geography and Astronomy. Department of Lithospheric Research; AustriaFil: Asiain, Lucia Montserrat. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Geológico del Sur. Universidad Nacional del Sur. Departamento de Geología. Instituto Geológico del Sur; ArgentinaFil: Bjerg, Ernesto Alfredo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Geológico del Sur. Universidad Nacional del Sur. Departamento de Geología. Instituto Geológico del Sur; Argentin

The Variscan subduction inheritance in the Southern Alps Sub-Continental Lithospheric Mantle: clues from the Middle Triassic shoshonitic magmatism of the Dolomites (NE Italy)

Although often speculated, the link between the Middle Triassic shoshonitic magmatism at the NE margin of the Adria plate and the subduction-related metasomatism of the Southern Alps Sub-Continental Lithospheric Mantle (SCLM) has never been constrained. In this paper, a detailed geochemical and petrological characterization of the lavas, dykes and ultramafic cumulates belonging to the shoshonitic magmatic event that shaped the Dolomites (Southern Alps) was used to model the composition and evolution of the underlying SCLM in the time comprised between the Variscan subduction and the opening of the Alpine Tethys. Geochemical models and numerical simulations enabled us to define that 5–7% partial melting of an amphibole + phlogopite-bearing spinel lherzolite, similar to the Finero phlogopite peridotite, can account for the composition of the primitive Mid-Triassic SiO2-saturated to -undersaturated melts with shoshonitic affinity (87Sr/86Sri = 0.7032–0.7058; 143Nd/144Ndi = 0.51219–0.51235; Mg # ~ 70; ~1.1 wt% H2O). By taking into account the H2O content documented in mineral phases from the Finero phlogopite peridotite, it is suggested that the Mid-Triassic SCLM source was able to preserve a significant enrichment and volatile content (600–800 ppm H2O) for more than 50 Ma, i.e. since the slab-related metasomatism connected to the Variscan subduction. The partial melting of a Finero-like SCLM represents the exhaustion of the subduction-related signature in the Southern Alps lithosphere that predated the Late Triassic-Early Jurassic asthenospheric upwelling related to the opening of the Alpine Tethys