Joints and mineral veins during structural evolution: case study from the Outer Carpathians (Poland)

This paper focuses on mineral veins hosted in small-scale fractures within the Tertiary sandstones of the Magura nappe (Outer Carpathians). Joints, faults and tension gashes record three successive stages of the nappe structural evolution: (1) synsedimentary folding and thrusting, (2) regional rotation and (3) late-orogenic collapse. The flow of mineral-bearing fluids was channelized by small-scale fractures resulting in calcite and quartz-calcite veins. Folding: columnar calcite formed the most common filling of early joints and the joints-related tension gashes and strike-slip faults. The mineralisation was restricted to sandstones containing primary carbonates. Rotation: precipitation of columnar and fibrous calcite was largely restricted to joints reactivated as strike-slip faults. Collapse: the collapse-related mineralisation is the most abundant. Wide-spread fluid flow was channelized by normal faults resulting in fibrous calcite and quartz-calcite along these faults whereas several blocky and drusy calcite generation and single high temperature quartz-calcite assemblage precipitated in numerous adjoining joints

Ruin marble : a record of fracture-controlled fluid flow and precipitation

The ruin marble structure of the Cretaceous/Paleogene fine-grained marly limestone from the Outer Flysch Belt of the Western Carpathians has a non-tectonic origin, according to structural and sedimentological evidence. Distinctive offsets of coloured red-brownish ferric oxyhydroxide bands are not due to displacements along rock-cutting fractures, as they superficially appear to be. Evidences for shear movement along these pseudo-faults were not observed. Band offsets result from different velocities of pervasively diffusing fluids, precipitating ferric oxyhydroxides in corridors bounded by sets of mineralised systematic joints. During rock weathering, calcite-filled joints operated as barriers for lateral fluid diffusion, but enabled longitudinal diffusion along healed joints. Simple laboratory experiments have been performed to simulate the formation of natural ruin marble structure

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

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

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U-Pb-Th geochronology of monazite and zircon in albitite metasomatites of the Rožňava-Nadabula ore field (Western Carpathians, Slovakia): implications for the origin of hydrothermal polymetallic siderite veins

International audienceSodic metasomatites (albitites) occur around and within siderite veins in the southern part of the Gemeric tectonic unit of the Western Carpathians. Accessory minerals of the metasomatites represented by monazite, zircon, apatite, rutile, tourmaline and siderite are basically identical with the quartz-tourmaline stage of other siderite and stibnite veins of the tectonic unit. Statistical analysis of chemical Th-U(total)-Pb isochron method (CHIME) of monazite dating yielded Jurassic-Cretaceous ages subdivided into 3–4 modes, spreading over time interval between 78 and 185 Ma. In contrast, LA-ICPMS 206Pb/238U dating carried out on the same monazite grains revealed a narrow crystallization interval, showing ages of Th-poor cores with phengite inclusions identical within the error limit with Th-rich rims with cauliflower-like structure. The determined lower intercept at 139 ± 1 Ma overlapped the Vallanginian-Berriasian boundary, thus corroborating the model of formation of hydrothermal vein structures within an arcuate deformation front built up in the Variscan basement as a response to Early Cretaceous compression, folding and thrusting. In contrast, associated zircons are considerably older than the surrounding Early-Palaeozoic volcano-sedimentary rocks, showing Neoproterozoic ages. The zircon grains in albitite metasomatites are thus interpreted as fragments of Pan-African magmatic detritus incorporated in the vein structures by buoyant hydrothermal fluids

Combined U/Pb and (U-Th)/He geochronometry of basalt maars in Western Carpathians: implications for age of intraplate volcanism and origin of zircon metasomatism

International audienceThe age of intraplate volcanism in northern Pannonian Basin of Carpathians is revisited using a combination of zircon U/Pb, zircon (U-Th)/He and apatite (U-Th)/He dating techniques, complemented by electron microprobe (EMP) characterisation of dated minerals. A total of six maar structures and diatremes in the South-Slovakian Volcanic Field (SSVF) were dated and the obtained new ages yielded the following key findings: Two isolated maars in SE part indirectly dated by geomorphologic constraints to Late Pleistocene are actually of Pliocene (2.8 ± 0.2 Ma) and Late Miocene (5.5 ± 0.6 Ma) ages. In contrast, two maars in NW part of the study area are of Late Pliocene age (4.1 ± 0.4 and 5.2-5.4 Ma), younger than the Late Miocene age (~6.5 Ma) inferred previously from K/Ar data on the proximal basaltic lava flows. These maars therefore belong to the second volcanic phase that was previously identified only in SE part of the SSVF. In the light of the new geochronologic data, it seems likely that the Pliocene phreatomagmatic eruptions may have occurred along extension-related, NW- and NE-trending orthogonal faults. EMP analyses and imaging revealed an extensive syn- and post-growth metasomatic replacement by dissolution-reprecipitation in the majority of zircons. Abundant silicate melt inclusions in porous metasomatised parts of the zircons are diagnostic of magmatic rather than hydrothermal metasomatism. Consistent ages of the metasomatised and non-metasomatised zones do not indicate disturbance of the U-Pb system during the metasomatism. Enrichment in U and Th loss in the metasomatised zircons are diagnostic of an increasing oxygen fugacity triggered by degassing of the volatile residual melt during the final stages of alkali basalt fractionation. Rare zircon-to-baddeleyite transformation was probably connected with lowered silica activity in carbonated basaltic magmas in south-eastern part of the study area

High-density nitrogen inclusions in barite from a giant siderite vein: implications for Alpine evolution of the Variscan basement of Western Carpathians, Slovakia.

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