Földtörténeti kutatások és módszertani fejlesztések a K/Ar és Ar/Ar geokronológia területén = K/Ar and Ar/Ar geochronology: dating and methodical development

A lillafüredi nyírási zóna (LSZ) vizsgálata során egységesen kb. 76 M év kort állapítottunk meg a nyírási zónára és a befogadó metaandezitre. Ez vagy fluidális utóhatás, vagy pedig a nyírással egyidejű kiemelkedéshez kötődő lehűlés kora. A Rudabányai-hg-ben a Telekesoldal-takarót érintő, az anchi- és epizóna határára tehető metamorfózis korát a 137 – 117 M év kortartományban rögzítettük, továbbá kimutattunk egy fiatalabb (94 – 87 M év) fluidális hatást is. A Bükkium területén az epi- és anchizónás, valamint diagenetikusan átalakult kőzetek 4- 32µm-es ásványain rendre 117-100 M év, 140-120 M év és 184-173 M év mérhető az átalakulás korára. Mindhárom kőzetet a < 0,6 µm-es frakción kimutatható fluidális hatás érte rendre a harmadidőszak legelején, a felső-kréta kezdetén és 115-110 M éve. A Papukban a kis- és nagyon kisfokú metamorfózis nem nullázta teljesen a K/Ar kort. A kor csökkenése a szemcseméret csökkenésével hosszú idejű illitesedést mutat az alpi hegységképződés ausztriai és/vagy szubherciniai fázisában. Leucit tartalmú bazaltok K/Ar kora a ténylegesnél jóval fiatalabbnak adódhat az argonkivonó berendezés kályházásakor bekövetkező szerkezetváltozáshoz köthető argonleadás miatt. Csehország magmás kőzeteinek vizsgálata során az Ohre rift kialakulásához köthető melilites kőzetek kora 68-59 M év, a Moldanubikum gabbró intrúziói pedig korban a Cadomi extenzióhoz köthetők. | About 76 My age has been established for the Lillafüred Shear Zone (LSZ) and the metaandesite enclosing the LSZ. The age reflect the time of a fluidal effect after shearing and uplift, or the common time of shearing and uplift. The Telekesoldal-nappe in the Rudabánya hills has been affected by an epi-anchizonal metamorphism 137 – 117 My ago and thereafter by a fluidal effect 94 – 87 My ago. 117-100 My, 140-120 My and 184-173 My ages have been determined on 4-32 µm fractions of epi- and anchizonal metamorphics as well as diagenetically altered rocks in the Bükkium, respectively. < 0,6 µm fractions of all tree rock types show a younger fluidal overprint at the beginning of Cenozoic, in the earle Upper-Cretaceous and 115-110 My ago, respectively. In the Papuk low- and very low-grade metamorphism did not overprint fully the Variscan K/Ar ages. Deacrease of K/Ar ages with grain-size suggests a long-lasting illitization in the Austrian/Subhercynian phases of Alpine orogeny. K/Ar age of some leucite.bearing basalts may be much younger than the real age, since in the argon extraction line a part of radiogenic Ar may be removed at < 250 °C during baking, as a result of a structural change at this temperature. In the Czeh Republic melilitic rocks connected to the formation od Ohre rift intruded 68-59 My ago, and in the Moldanubicum intrusion of gabbros is connected to the Cadomian extension

Metamorfózis és tektonikai folyamatok korviszonyainak, a Tethys fejlődésének és a kapcsolódó magmás tevékenységnek a kutatása elsősorban a Kárpát-Balkán térségben. Fluidumok hatásának vizsgálata a K/Ar és Ar/Ar korokra. = Chronological studies of age relations of metamorphic and tectonic processes in the Carpatho-Balkan region and of the evolution of Tethys and related magmatic rocks. Effect of fluids on the K/Ar and Ar/Ar ages.

A Tihany vulkán első kitörése 7,92 +- 0,22 M év korú, ez a bazaltos vulkáni működés kezdete a Bakony - Balaton-felvidék területén, s jól közelíti a Congeria balatonica és Prosodacnomya zónák határát. A Hegyestű bazanitja Ar(rad) tartalmának 25-40 %-át leadja az Ar mérését megelőző előmelegítéskor. Az effektus a leucithoz és nefelinhez köthető, valószínűleg e két ásvány Hegyestűre jellemző szubmikroszkópikus szerkezetéhez. Csak 150 °C-on előmelegítve az effektus eltűnik, s a bazaniton megbízható kor, (7,56+-0,17 M év) mérnünk. Kimutattuk, hogy az Ar/Ar kor is lehet félrevezető, ha az "izokron" tk. keveredési vonal, ill. ha a többlet Ar és a K korrelál. A többlet Ar kimutatásával pontosabb kort (kb. 30 M év az 51 M év helyett) adtunk meg a Loucná-Oberwiesenthal vulkáni központra. Meghatároztuk a Roztoky Intrúzív Központ tinguaitjainak átlagos korát (29,3+-0,8 M év). A Bükkium és a Medvednica alacsony fokú metamorfitjain egy idősebb (alsó-kréta, júra) és egy fiatalabb, főleg felső kréta metamorf fázist sikerült elkülönítenünk. A szlovéniai metamorfitokon júrától miocénig terjedő kiemelkedési korokat határoztunk meg. | 7.92+-0.22 My has been determined for the first eruption of the Tihany volcano. This marks the start of basaltic volcanic activity in the Bakony - Balaton Highland and it is a good approximation for the boudary of Congeria balatonica and Prosodacnomya zones. It has been recognised that 25-40 % of Ar(rad) is released from the basanite of Hegyestű during baking the Ar line prior to degassing. This is an unusual phenomenon caused most likely by a special submicroscopic structure of leucite and nepheline in the basanite of Hegyestű. This effect disappears when baking temperature is reduced to about 150 °C and ages measured this way agree with the isochron age (7.56+-0.17 My) measured on leucite and nepheline free rock. It has been demonstrated that Ar/Ar method may give erroneous ages too, e.g. when mixing line is formed, or when Ar(ex) and K are correlated. It has been shown that old ages (~50 My) published for the Loucná-Oberwiesenthal volcanic centre are caused by excess Ar, the real age is ~30 My. An average age of 29.3+-0.8 My has been determined for the tinguaites of the Roztoky Intrusive Centre. By dating clay minerals of different grain sizes a Lower Cretaceous - Jurassic and a younger metamorphic phase has been distinguished for low-grade metamorphic rocks of the Bükkium and Medvednica. Uplift ages from Jurassic to Miocene have been detected on metamorphic rocks in Slovenia

40Ar/39Ar geochronology of Neogene phreatomagmatic volcanism 3 in the western Pannonian Basin, Hungary

Uncorrected proofNeogene alkaline basaltic volcanic fields in the western Pannonian Basin, Hungary, including the Bakony–Balaton Highland and the Little Hungarian Plain volcanic fields are the erosional remnants of clusters of small-volume, possibly monogenetic volcanoes. Moderately to strongly eroded maars, tuff rings, scoria cones, and associated lava flows span an age range of ca. 6 Myr as previously determined by the K/Ar method. High resolution 40Ar/39Ar plateau ages on 18 samples have been obtained to determine the age range for the western Pannonian Basin Neogene intracontinental volcanic province. The new 40Ar/39Ar age determinations confirm the previously obtained K/Ar ages in the sense that no systematic biases were found between the two data sets. However, our study also serves to illustrate the inherent advantages of the 40Ar/39Ar technique: greater analytical precision, and internal tests for reliability of the obtained results provide more stringent constraints on reconstructions of the magmatic evolution of the volcanic field. Periods of increased activity with multiple eruptions occurred at ca. 7.95 Ma, 4.10 Ma, 3.80 Ma and 3.00 Ma. These new results more precisely date remnants of lava lakes or flows that define geomorphological marker horizons, for which the age is significant for interpreting the erosion history of the landscape. The results also demonstrate that during short periods of more intense activity not only were new centers formed but pre-existing centers were rejuvenated

Revision of Scheumann’s classification of melilitic lamprophyres and related melilitic rocks in light of new analytical data

Dykes of the Late Cretaceous to Early Tertiary (79.5 ± 3.5 to 60.7 ± 2.4 Ma) melilitic rock series of the Osečná Com- plex and the Devil’s Walls dyke swarm, including ultramafic lamprophyres – polzenites – of Scheumann (1913) occur dispersed in the entire Upper Ploučnice River basin in northern Bohemia. Polzenites and associated melilitic rocks are characterized by the mineral association of olivine + melilite ± nephe- line, haüyne, monticellite, phlogopite, calcite, perovskite, spinels and apatite. New data on their mineral and chemical compositions from original Scheumann’s localities (the Vesec, Modlibohov, Luhov types) argue against the abolition of the group of ultramafic lamprophyres and the terms ‘polzenite’ and ‘alnöite’ by the Le Maitre (2002) classification. Marginal facies and numerous flat apophyses of the lopolith-like body known as the Osečná Complex show an olivine micro-melilitolite composition (lamprophyric facies). The porphyritic texture, chemical composition and the presence of characteristic minerals such as monticellite and phlogopite point to their affinity with ultramafic lamprophyres – polze- nites of the Vesec type. Melilite-bearing olivine nephelinites to olivine melilitites (olivine + clinopyroxene + nepheline + melilite ± haüyne and spinels with apatite) form a swarm of subparallel dykes known as the Devil’s Walls. The Scheumann’s non-melilite dyke rock “wesselite”, spatially associated with polzenites and often erroneously attributed to the polzenite group, is an alkaline lamprophyre of monchiquite to camptonite composition (kaersutite + phlogopite + diopside + olivine phenocrysts in groundmass containing clinopyroxene, phlogopite, haüyne, analcime, titanian mag- netite, apatite ± glass/plagioclase). First K–Ar data show Oligocene ages (30.9 ± 1.2 to 27.8 ± 1.1 Ma) and an affinity to the common tephrite–basanite rock series