74 research outputs found

    A mineral-scale investigation of the origin of the 2.6 Ma F√ľzes-t√≥ basalt, Bakony-Balaton Highland Volcanic Field (Pannonian Basin, Hungary)

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    Abstract The alkaline basalt of the F√ľzes-t√≥ 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‚Äď35) 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 F√ľzes-t√≥ 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 Hars√°ny ignimbrite, B√ľkkalja Volcanic Field, Northern Hungary: Syn-eruptive mingling of distinct rhyolitic magma batches?

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    Abstract The 13.5 Ma Hars√°ny ignimbrite, in the eastern part of the B√ľkkalja volcanic field, eastern-central Europe, provides a rare example of mingled rhyolite. It consists of two distinct pumice populations (‚ÄėA‚Äô- and ‚ÄėB‚Äô-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 ‚ÄėA‚Äô-type rhyolite magma from the ‚ÄėB‚Äô-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

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

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    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 (N√≥gr√°d-G√∂m√∂r) VF, PerŇüani Mts. (Pers√°nyi Mts.) VF and from the Lucaret-SanoviŇ£a (Luk√°cskŇĎ-Szikl√°s) 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

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    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‚ÄȬĪ‚ÄČ0¬∑73‚ÄČMa (2ŌÉ; full systematic uncertainties), around 20‚ÄČMyr after the high-K calc-alkaline to shoshonitic, short-lived, Ladinian (237‚Äď238‚ÄČMa) magmatic event of the Dolomitic Area. Their trace element and Sr‚ÄďNd isotopic signatures (87Sr/86Sri = 0¬∑7033‚Äď0¬∑7040; 143Nd/144Ndi = 0¬∑51260‚Äď0¬∑51265) are probably related to a garnet‚Äďamphibole-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‚Äďcarbonatitic magmatic event that intruded the mantle beneath the Southern Alps (e.g. Finero peridotite) between 190 and 225‚ÄČMa. 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 and geochemistry of trachy-basalts and basaltic trachy-andesites of Vulcanitas Corona Chico unit and the Barril Niyeu Volcanic Complex from the northwestern Meseta de Somuncurá, Río Negro province

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    En esta contribuci√≥n se documentan las caracter√≠sticas petrogr√°ficas y geoqu√≠micas de coladas l√°vicas expuestas en el sector noroeste de la Meseta de Somuncur√°, correspondientes a la unidad Vulcanitas Corona Chico y a la facies b√°sica del Complejo Volc√°nico Barril Niyeu (Superunidad Qui√Īelaf), ambas adjudicadas por varios autores al evento volc√°nico post-plateau. Las coladas l√°vicas estudiadas poseen predominantemente textura af√≠rica seriada a microporf√≠rica con microfenocristales de olivino y plagioclasa, en una pasta integrada por plagioclasa, olivino, clinopiroxeno, minerales opacos y apatito. Qu√≠micamente estas rocas se clasifican como traquibasaltos y traquiandesitas bas√°lticas de la suite alcalina s√≥dica, con se√Īal geoqu√≠mica similar a OIB y con anomal√≠a relativa positiva de Ba. Sobre la base de trabajos de relevamiento de campo, estudios petrogr√°ficos y los primeros datos geoqu√≠micos de roca total para la unidad Vulcanitas Corona Chico presentados en esta contribuci√≥n, se propone ampliar la caracterizaci√≥n de esta unidad informal, incorporando coladas de lava ampliamente distribuidas en el sector noroccidental de la meseta. Asimismo, se plantea homogeneizar y simplificar la nomenclatura de las unidades volc√°nicas referidas al evento post-plateau en el sector noroccidental de la meseta. De este modo, teniendo en cuenta que el evento post-plateau presenta variaciones composicionales, se recomienda hacer referencia a las unidades volc√°nicas utilizando nombres formacionales o de complejos volc√°nicos seg√ļn corresponda, limitando el uso de los t√©rminos plateau y post-plateau √ļnicamente para indicar la temporalidad de tales eventos volc√°nicos.The petrographic and geochemical characteristics of exposed lava flows in the northwest sector of Meseta de Somuncur√°, corresponding to the Vulcanitas Corona Chico unit and the basic facies of the Barril Niyeu Volcanic Complex (Qui√Īelaf Superunit), are presented in this contribution. Both, the Vulcanitas Corona Chico unit and the Barril Niyeu Complex, were attributed by several authors to the post-plateau volcanic event. Their dominant texture is aphyric seriate to microporphyric with olivine and plagioclase microphenocrysts in a groundmass of plagioclase, olivine, clinopyroxene, opaque minerals and apatite. Accordingly with their chemical features, these rocks classify as trachy-basalts and basaltic trachy-andesites of the sodic alkaline suite, with OIB-type geochemical signature and a relative positive anomaly in Ba. Based on field data, petrography and the first whole-rock geochemical data of the Vulcanitas Corona Chico presented in this contribution, it is proposed to expand the definition of this informal unit incorporating some of the lava flows from the northwestern part of Meseta de Somuncur√°. Likewise, it is proposed to homogenize and simplify the nomenclature of the post-plateau units in the northwestern sector of the Meseta. Therefore, considering that the post-plateau event shows compositional variations, it is recommended to refer to the volcanic units using their formational or volcanic complex names, limiting the use of plateau and post-plateau only to indicate the temporality of these volcanic events.Fil: Asiain, Lucia Montserrat. Consejo Nacional de Investigaciones Cient√≠ficas y T√©cnicas. Centro Cient√≠fico Tecnol√≥gico Conicet - Bah√≠a Blanca. Instituto Geol√≥gico del Sur. Universidad Nacional del Sur. Departamento de Geolog√≠a. Instituto Geol√≥gico del Sur; ArgentinaFil: Gargiulo, Maria Florencia. Consejo Nacional de Investigaciones Cient√≠ficas y T√©cnicas. Centro Cient√≠fico Tecnol√≥gico Conicet - Bah√≠a Blanca. Instituto Geol√≥gico del Sur. Universidad Nacional del Sur. Departamento de Geolog√≠a. Instituto Geol√≥gico del Sur; ArgentinaFil: Bjerg, Ernesto Alfredo. Consejo Nacional de Investigaciones Cient√≠ficas y T√©cnicas. Centro Cient√≠fico Tecnol√≥gico Conicet - Bah√≠a Blanca. Instituto Geol√≥gico del Sur. Universidad Nacional del Sur. Departamento de Geolog√≠a. Instituto Geol√≥gico del Sur; ArgentinaFil: Ntaflos, Theodoros. Universidad de Viena; AustriaFil: Reitinger, Johann. Universidad de Viena; Austri

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

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    Escuela Las Pircas es un cuerpo intrusivo m√°fico-ultram√°fico situado en el sector sur de la faja de rocas m√°ficas-ultram√°ficas La Jovita-Las √Āguilas, 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 m√°ficos-ultram√°ficos que constituyen esta faja son de gran inter√©s por ser intrusiones de tipo estratificadas portadoras de una mineralizaci√≥n de sulfuros de Fe-Ni-Cu-Co y minerales del grupo del platino. Las variaciones modales y geoqu√≠micas exhibidas por el cuerpo intrusivo Escuela Las Pircas, permiten definir en √©ste cuatro unidades estratigr√°ficas: unidad hornblend√≠tica pirox√©nica con plagioclasa, unidad ortopiroxen√≠tica hornblend√≠fera con plagioclasa, unidad nor√≠tica hornblend√≠fera inferior y unidad nor√≠tica hornblend√≠fera superior. Estas unidades constituyen una secuencia de niveles m√°ficos y ultram√°ficos intercalados, los cuales conforman la porci√≥n superior de la serie estratificada. Los resultados de los an√°lisis de qu√≠mica de roca total y mineral permitieron establecer que todas las unidades definidas corresponder√≠an a una misma secuencia magm√°tica, en la cual las diferencias mineral√≥gicas y geoqu√≠micas entre las distintas unidades habr√≠an sido controladas principalmente por variaciones en las tasas de nucleaci√≥n y crecimiento cristalino. Asimismo, los resultados de los an√°lisis petrogr√°ficos y qu√≠micos permitieron inferir que las unidades definidas en el cuerpo intrusivo Escuelas Las Pircas y las correspondientes a la Serie Estratificada del cuerpo intrusivo Virorco corresponder√≠an a una misma secuencia estratigr√°fica √≠gnea, donde las unidades del cuerpo intrusivo Escuela Las Pircas representan el mayor grado de evoluci√≥n.Escuela Las Pircas is a mafic-ultramafic intrusion located in the southern sector of La Jovita-Las √Āguilas 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 Cient√≠ficas y T√©cnicas. Centro Cient√≠fico Tecnol√≥gico Conicet - Bah√≠a Blanca. Instituto Geol√≥gico del Sur. Universidad Nacional del Sur. Departamento de Geolog√≠a. Instituto Geol√≥gico del Sur; ArgentinaFil: Ferracutti, Gabriela Roxana. Consejo Nacional de Investigaciones Cient√≠ficas y T√©cnicas. Centro Cient√≠fico Tecnol√≥gico Conicet - Bah√≠a Blanca. Instituto Geol√≥gico del Sur. Universidad Nacional del Sur. Departamento de Geolog√≠a. Instituto Geol√≥gico 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 Cient√≠ficas y T√©cnicas. Centro Cient√≠fico Tecnol√≥gico Conicet - Bah√≠a Blanca. Instituto Geol√≥gico del Sur. Universidad Nacional del Sur. Departamento de Geolog√≠a. Instituto Geol√≥gico del Sur; ArgentinaFil: Bjerg, Ernesto Alfredo. Consejo Nacional de Investigaciones Cient√≠ficas y T√©cnicas. Centro Cient√≠fico Tecnol√≥gico Conicet - Bah√≠a Blanca. Instituto Geol√≥gico del Sur. Universidad Nacional del Sur. Departamento de Geolog√≠a. Instituto Geol√≥gico del Sur; Argentin

    Olivine major and trace element compositions coupled with spinel chemistry to unravel the magmatic systems feeding monogenetic basaltic volcanoes

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    Monogenetic basaltic volcanic systems, despite their considerable smaller size and shorter lifetime compared to polygenetic volcanoes, can have complex pre-eruptive histories and composite volcanic facies architectures. Their source-to-surface investigation is essential for our better understanding of monogenetic volcanism and requires high-resolution mineral-scale analyses. In this study, we focus on diversely zoned olivine crystals and their spinel inclusions from alkaline basaltic volcanics that are the result of mixing of numerous magmas, crystals and fragments of various origins. The Fekete-hegy volcanic complex is one of the largest and most composite eruptive centers in the intracontinental monogenetic Bakony‚ÄďBalaton Highland Volcanic Field (western Pannonian Basin, Eastern Central Europe). It is a compound multi-vent system built up by multiple eruption episodes: initial maar-forming phreatomagmatic eruptions were followed by massive lava flows and magmatic explosive activity. We performed stratigraphically controlled sampling in order to reveal the history of the successively erupted magma batches represented by the distinct eruptive units, as well as to discover the petrogenetic processes that controlled the evolution of the magmatic system. The juvenile pyroclasts of the phreatomagmatic eruption products (unit 1) contain a remarkably diverse mineral assemblage including five different olivine types and three distinct spinel groups. In addition, they comprise various xenoliths. Based on detailed textural investigations combined with in situ electron microprobe analyses, high-resolution laser ablation ICP-MS trace element mapping and single spot measurements on the variably zoned olivines of unit 1 samples, eight distinct environments are inferred to have been involved in their formation. Four of these environments account for the significant compositional variation of the olivine-hosted spinel inclusions. A complex set of open- and closed-system petrogenetic processes operated during the evolution of the magmatic system: magma stalling, accumulation, storage, fractionation, mixing, replenishments, cumulate remobilization, incorporation of foreign fragments and crystals from the wall rocks. All these diverse environments and processes resulted in the mixed character of the erupted magmas during the initial phreatomagmatic eruptive phase. In contrast, the uniform petrological features and the small variations shown by the olivines and spinels from unit 2‚Äź‚Äď3 indicate that the later magmatic explosive ‚Äď effusive phase was preceded by a considerable change in the magmatic system; it experienced a simple evolution through olivine + spinel fractional crystallization without any of the complexities seen during the initial phase. The present study emphasizes the importance of high-resolution mineral-scale textural and chemical investigations to unravel the complexity of the sub-volcanic magmatic systems feeding monogenetic basaltic volcanoes. Compared to the application of whole-rock geochemistry alone, this approach enables a direct and more detailed insight into the architecture and evolution of these systems

    Origin of basaltic magmas of PerŇüani volcanic field, Romania: A combined whole 6 rock and mineral scale investigation

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    The PerŇüani volcanic field is a low-volume flux monogenetic volcanic field in the Carpathian‚ÄďPannonian region, 24 eastern-central Europe. Volcanic activity occurred intermittently from1200 ka to 600 ka, forming lava flow fields, 25 scoria cones andmaars. Selected basalts fromthe initial and younger active phaseswere investigated for major and 26 trace element contents and mineral compositions. Bulk compositions are close to those of the primitive magmas; 27 only 5‚Äď12% olivine and minor spinel fractionation occurred at 1300‚Äď1350 ¬įC, followed by clinopyroxenes at about 28 1250 ¬įC and 0.8‚Äď1.2 GPa. Melt generation occurred in the depth range from 85‚Äď90 km to 60 km. The estimated 29 mantle potential temperature, 1350‚Äď1420 ¬įC, is the lowest in the Pannonian Basin. It suggests that no thermal 30 anomaly exists in the uppermantle beneath the PerŇüani area and that themaficmagmas were formed by decom- 31 pressionmelting under relatively thin continental lithosphere. Themantle source of themagmas could be slightly 32 heterogeneous, but is dominantly variously depleted MORB-source peridotite, as suggested by the olivine and 33 spinel composition. Based on the Cr-numbers of the spinels, two coherent compositional groups (0.38‚Äď0.45 and 34 0.23‚Äď0.32, respectively) can be distinguished that correspond to the older and younger volcanic products. This in- 35 dicates a change in themantle source region during the volcanic activity as also inferred from the bulk rockmajor 36 and trace element data. The younger basaltic magmas were generated by lower degree of melting, from a deeper 37 and compositionally slightly different mantle source compared to the older ones. The mantle source character of 38 the PerŇüanimagmas is akin to that ofmany other alkaline basalt volcanic fields in theMediterranean close to oro- 39 genic areas. The magma ascent rate is estimated based on compositional traverses across olivine xenocrysts using 40 variations of Ca content. Two heating events are recognized; the first one lasted about 1.3 years implying heating 41 of the lower lithosphere by the uprisingmagma,whereas the second one lasted only 4‚Äď5 days,whichcorresponds 42 to the time of magma ascent through the continental crust. The alkaline mafic volcanismin the PerŇüani volcanic 43 field could have occurred as a response to the formation of a narrow rupture in the lower lithosphere, possibly 44 as a far-field effect of the dripping of dense continental lithospheric material beneath the Vrancea zone. Upper 45 crustal extensional stress-field with reactivation of normal faults at the eastern margin of the Transylvanian 46 basin could enhance the rapid ascent of the mafic magmas
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