Provenance study of detrital garnets and rutiles from basaltic pyroclastic rocks of Southern Slovakia (Western Carpathians)

Detrital garnets and rutiles have been recovered from basaltic pyroclastic rocks in the northern part of the Pannonian Basin and characterized using electron probe microanalysis and imaging. All garnets are dominated by the almandine component, except for one sample dominated by spessartine. A total of three garnet groups have been distinguished according to the increased contents of grossular (Group I), pyrope (Group II) and spessartine components (Group III). Compositions of the group I and II garnets with fluctuating Ca- and relatively low Mg contents are consistent with low- to medium-grade metasediments and/or metabasites. Locally increased Mg contents could indicate higher P–T metamorphic overprint. The dominantly metamorphic origin of the Group I and II garnets (composed of >99 % of samples) is also corroborated by chlorite, tourmaline, staurolite, ilmenite and andalusite inclusions. Spessartine-rich garnets (Group III composed of <1 % of samples) could be genetically linked with granitoids. Detrital rutiles invariably plot within the field of metasediments metamorphosed under amphibolite-facies conditions. Possible proximal (subjacent basement sampled by ascending lava) or distal sources (catchment sediments from uplifted Central Carpathian basement) of heavy mineral assemblages are discussed

REE Minerals as Geochemical Proxies of Late-Tertiary Alkalic Silicate ± Carbonatite Intrusions Beneath Carpathian Back-Arc Basin

The accessory mineral assemblage (AMA) of igneous cumulate xenoliths in volcanoclastic deposits and lava flows in the Carpathian back-arc basin testifies to the composition of intrusive complexes sampled by Upper Miocene-Pliocene basalt volcanoes. The magmatic reservoir beneath Pinciná maar is composed of gabbro, moderately alkalic to alkali-calcic syenite, and calcic orthopyroxene granite (pincinite). The intrusive complex beneath the wider area around Fiľakovo and Hajnáčka maars contains mafic cumulates, alkalic syenite, carbonatite, and calc-alkalic granite. Both reservoirs originated during the basaltic magma underplating, differentiation, and interaction with the surrounding mantle and crust. The AMA of syenites is characterized by yttrialite-Y, britholite-Y, britholite-Ce, chevkinite-Ce, monazite-Ce, and rhabdophane(?). Baddeleyite and REE-zirconolite are typical of alkalic syenite associated with carbonatite. Pyrochlore, columbite-Mn, and Ca-niobates occur in calc-alkalic granites with strong peralkalic affinity. Nb-rutile, niobian ilmenite, and fergusonite-Y are crystallized from mildly alkalic syenite and calc-alkalic granite. Zircons with increased Hf/Zr and Th/U ratios occur in all felsic-to-intermediate rock-types. If rock fragments are absent in the volcanic ejecta, the composition of the sub-volcanic reservoir can be reconstructed from the specific AMA and zircon xenocrysts–xenolith relics disintegrated during the basaltic magma fragmentation and explosion

Niobium Mineralogy of Pliocene A1-Type Granite of the Carpathian Back-Arc Basin, Central Europe

A1-type granite xenoliths occur in alkali basalts erupted during Pliocene–Pleistocene continental rifting of Carpathian back-arc basin (Central Europe). The Pliocene (5.2 Ma) peraluminous calc-alkalic granite contains unusually high concentrations of critical metals bound in Nb, Ta, REE, U, Th-oxides typical for silica-undersaturated alkalic granites, and syenites: columbite-Mn, fergusonite-Y, oxycalciopyrochlore, Nb-rutile, and Ca-niobate (fersmite or viggezite). In contrast, it does not contain allanite and monazite—the main REE-carriers in calc-alkalic granites. The crystallization of REE-bearing Nb-oxides instead of OH-silicates and phosphates was probably caused by strong water deficiency and low phosphorus content in the parental magma. Increased Nb and Ta concentrations have been inherited from the mafic parental magma derived from the metasomatized mantle. The strong Al- and Ca-enrichment probably reflects the specific composition of the mantle wedge modified by fluids, alkalic, and carbonatitic melts liberated from the subducted slab of oceanic crust prior to the Pliocene-Pleistocene rifting

Petrogenéza miocénno-pliocénnych granitoidov A-typu južného Slovenska: Petrogenesis of Miocene–Pliocene A-type granitoids of southern Slovakia

International audiencePetrogenetic association of post-orogenic A1-type granitoids genetically related to continental rifting and mantlederivedmafic magmas was recognized for the first time in the northern part of the Pannonian Basin. The variegated rocksuite comprises syenite, orthopyroxene-rich, charnockite-resembling granite (pincinite), and subalkalic granite stronglyenriched in Nb, Y and REE. Absence of rock-forming OH-bearing silicates in all rock types indicates water-deficient, hypersolvuscrystallization conditions and lacking overprint by deuteric hydrothermal alteration and/or subsequent metamorphic/metasomatic reactions. U-Pb-(Th) dating of monazite and zircon proved that all rocks crystallized within a narrow timeinterval between 5.2 and 5.8 Ma (Late Miocene – Early Pliocene boundary). The suite of A1-type granitoids is peraluminous,albeit individual rock types exhibit strongly fluctuating alkalis-to-calcium ratios: pincinite belongs to calcic rocks, granitesare calc-alkalic and syenites are alkalic. Except for magnesian pincinites, other rock types are ferroan. Syenites bear mostgeochemical features diagnostic of the A-type granites sensu stricto. They represent flotation cumulates from stronglydifferentiated alkalic basalt uncontaminated by the crustal material, as is indicated by the strontium and oxygen isotoperatios close to those in prevalent depleted mantle, strong enrichment in REE and Zr+Hf, moderate enrichment in Nb+Ta,and fluctuating distribution pattern of other elements. In contrast, a smoothed distribution pattern of trace elements inpincinites, enrichment in Ca, Ti, V, LREE, moderate depletion in Ba, Sr, absence of halogenides and siderophile elementsare interpreted as reflecting a high-degree dehydration melting of amphibole triggered by latent heat from alkali basaltunderplating the lower crust. The position within the field of OIB-like magmatic rocks rules out a substantial amount offelsic magmatic or sedimentary component in the zone of crustal anatexis. Sub-alkalic granites are provisionally interpretedas highly evolved residual melt originated by differentiation of alkalic basalt/trachybasalt modified by assimilation of aCa-rich contaminant, or as a low-degree partial melt from a mafic source similar to that in the case of pincinite. Position ofthe granites within the field for OIB-like magmatic rocks also excludes the substantial amount of felsic magmatic and/orsedimentary crustal component. In spite of the affinity to the A1-type subgroup, the sub-alkalic granites contain surprisinglyhigh concentrations of HFS elements, particularly Nb (up to 207 ppm). The coherent A1-subtype suite of early anorogenicgranitoids is different from the A2-subtype post-orogenic granitoids of the Western Carpathians formed dominantly bypartial melting of thin crust along continental margins during incipient Permian-Triassic rifting.Key words: A-type, granite, pincinite, syenite, xenolith, alkali basalt, Pannonian Basi

U-Pb geochronology of zircons from fossiliferous sediments of the Hajnáčka I maar(Slavakia) - type locality of the MN 16a biostratigraphic subzone

International audienc

Formation of Esseneite and Kushiroite in Tschermakite-Bearing Calc-Silicate Xenoliths Ejected in Alkali Basalt

Skarnoid calc-silicate xenoliths composed of anorthite, clinopyroxene and Mg-Al spinel occur in alkali basalts of the Pliocene-Pleistocene intra-plate magmatic province in the northern part of the Pannonian Basin. Randomly oriented and elongated pseudomorphs are tschermakite crystals replaced by olivine, spinel and plagioclase. The relict amphibole within the pseudomorphs is characterized by high VIAl, between 1.95 and 2.1, and very low occupancy of the A-site (3+Al)AlSiO6 endmember with an equal proportion of VIAl3+ and Fe3+. Concentrations of kushiroite CaAlAlSiO6 endmember, up to 47.5 mol%, are the highest recorded in terrestrial samples. The AlFe3+-rich pyroxenes originated at the expense of diopside-augite during the interaction with carbonate-aluminosilicate melt. Forsterite (Fo72–83) and hemoilmenite with up to 32 mol% geikielite (9.3 wt% MgO) also crystallized from the melt, leaving behind the residual calcic carbonate with minor MgO (1–3 wt%). Columnar habit of neoformed olivine growing across diopside-augite layers indicates rapid crystallization from eutectic liquid. Euhedral aragonite and apatite embedded in fine-grained calcite or aragonite groundmass indicate slow crystallization of the residual carbonatite around the calcite-aragonite stability boundary. Corundum exsolutions in rock-forming anorthite are products of superimposed low-pressure pyrometamorphic reworking during transport in alkali basalt. Concomitant alkali metasomatism produced neoformed interstitial sodalite, nepheline, sanidine, albite, biotite, Mg-poor ilmenite (10–18 mol% MgTiO3), Ti-magnetite and fluorapatite. Olivine-ilmenite-aragonite-calcite thermobarometry returned temperatures of 770–860 °C and pressures of 1.8–2.1 GPa, whereas plagioclase-amphibole thermobarometer yielded 781 ± 13 °C and 2.05 ± 0.03 GPa. The calculated pressures correspond to depths of 60–70 km. The calc-silicate xenoliths are most likely metamorphosed marbles; however, a magmatic protolith (metagabbro, metaanorthosite) cannot be ruled out owing to high Cr contents in spinels (up to 30 mol% chromite) and abundant Cu-sulfides

U–Th–Pb geochronology of zircon and monazite from syenite and pincinite xenoliths in Pliocene alkali basalts of the intra-Carpathian back-arc basin

International audienc