Szabados, Cs.

Árva-Sós, Erzsébet

English

MAURTTZ and CSAJÁGHY (1952) could not define exactly the data of consolidation and the genetic origins of the rocks found in the Mórágy granite and which was named "bostonite" by them. These questions have not been answered since that. K/Ar isotopic age of these rocks may reflects that the consolidation happened parallely to that of the rocks of the Early Cretaceous alkaline volcanism

Szabados Cs.

Árva-Sós Erzsébet

University of Szeged

Acta Mineralogica-Petrographica, Szeged, XXXVII, 129-141, 1996 THE AGE OF THE SO-CALLED "BOSTONITE" ROCKS OF MÓRÁGY HILL, S-HUNGARY C s . SZABADOS1 Department of Mineralogy, Geochemistry and Petrography Attila József University E . ÁRVA-SÓS 2 Institute of Nuclear Research of the Hungarian Academy of Sciences ABSTRACT MAURTTZ and CSAJÁGHY (1952) could not define exactly the data of consolidation and the genetic origins of the rocks found in the Mórágy granite and which was named "bostonite" by them. These questions have not been answered since that. K/Ar isotopic age of these rocks may reflects that the consolidation happened parallely to that of the rocks of the Early Cretaceous alkaline volcanism. INTRODUCTION The greenish coloured dyke rocks of Kismórágy quarries were mentioned firstly by RÓTH ( 1 8 7 6 ) and he named them as "diabas-diorite". They were perhaps "bostonites". This reddish-coloured dyke rocks which were characterized petrographically by MAURITZ and CSAJÁGHY ( 1 9 5 2 ) on the basis of their mineral composition and major element content were already regarded bostonites and the products of granitoid magmatism or the Early Cretaceous volcanism. The rocks which resemble the feldspar rich rocks described by MAURITZ ( 1 9 5 2 ) , and which are called "bostonites" are rendered by researches into three lithostratigraphic units, as follows: 1. The Mórágy Complex (Early Carboniferous) 2. The Gyűrűfű Rhyolite Formation (Early Permian) 3. The Mecsekjános Basalte Formation (Early Cretaceous) 1. Post-orogenetic rocks which are joint up to aplitic rocks: - On the basis of the rock-material of boreholes of the Mecsek Mts. and the petrographic characters of the dyke rocks of Mórágy Hill (GHANEM and RAVASZ-BARANYAI, 1 9 6 9 ; JÁRÁNYI, 1970 ; HETÉNYI a n d RAVASZ-BARANYAI, 1 9 7 3 ) . - On the basis of R E E content of these rock types (PANTÓ, 1 9 8 0 ) . 1 H-6701 Szeged, P. O. Box 651, Hungary 2 H-4001 Debrecen, P. O. Box 51, Hungary 161 2. These rock types have a Paleosoic age: BARABÁS and IMREH ( 1 9 5 6 ) found "bostonite" like pebbles in the Upper Permian and Upper Triassic sandstones. They raised the idea of two different genesis of bostonitic rock. VADÁSZ ( 1 9 6 0 ) admitted it. 3. These rocks of Mórágy Hill are products of the Early Cretaceous alkaline volcanism. - On the basis of petrographical-petrological researches (JANTKSY 1950, 1979; CSALAGOVITS 1964; FORGÓ et a l . 1966; SZEDERKÉNYI 1974 ; BLUK 1979 ; HARANGI 1990 , 1993; HUEMER 1993). - On the basis of Rb/Sr ages (142-143±20 Ma by SviNGOR and KOVACH 1978). - On the basis of K/Ar ages (108-110±5 Ma by ÁRVA-SÓS etal. 1979, 1987, 1992). RESULTS The investigated rocks occur as dykes in the granite. Therefore, determination of their lithostratigraphic age is impossible. The K/Ar isotopic age determination is the prepared and carried method in the ATOMKI, Debrecen, which is well aplicable in the igneous and methamorphic rocks. However, we usually get more exact K/Ar ages from the separated minerals of the fresh rock (e. g.: amphibole and micas) which keep the Ar well. The K/Ar isotopic ages of feldspathoid rocks reflect on the data of their consolidation or, since the feldspars have a low retaining capacity of the Ar, it reflects the date of the latest tectonic or thermal event which "rejuvenated" the rock. Three new K/Ar data of the whole rock and also on the separated feldspar minerals together with the three previous data clearly yield that the age of the reddish-coloured trachyte dyke rocks is between 106-118 million years. This may mean that the consolidation of these rocks happened parallely to that of the rocks of the Early Cretaceous alkaline volcanism. Since those rocks which were little altered only and had relatively high retaining capacity, they could not lose much Ar, therefore these ages are acceptable (Table 1.). Our research includes the first K/Ar data of the trachyandesites of Kismoragy. Both yielded a younger age than that of the trachytes. The average age (95 Ma) coincides with the Austrian orogen activity. It is possible that the K/Ar isotopic age shows the last tectonic effect. In this case the K/Ar isotopic data of the every rock type of this area should shows this the average (95 Ma). However, the K/Ar datum of the reddish-coloured trachyte dyke is 118 Ma in Kismoragy quarry No. 3. It is nearest to that of the trachyandesite rocks of Kismoragy quarry No. 5. Because we don't believe that different secondary effects happened in this territory, therefore the younger K/Ar data of trachyandesites as compared to trachytes may have been formed in two possible ways: - the trachyandesite rocks are product of a younger volcanic event, or - these younger data are the result of a strong decomposition and Ar-loss of the rock, therefore, the age of these rocks so to say grown younger again. Petrographical characteristics of trachyandesite rocks shows strongly altered features. Therefore this second hypothesis is acceptable. The K/Ar data of the trachytic and trachyandesitic rocks (so-called bostonitic rocks) are shown by Table 1. 162 TABLE 10 LOCALITY, ROCK TYPE FRACTION K-CONT % ATrad/g (ncm3/g) 4°Arrad • % AGE (Ma) Mórágy trachyte w. r. 4.83 2.1944x105 93.3 113.3±4.3 Kismórágy q. No. 3. trachyte w. r. 4.151 1.9655xl0's 65.9 118.0±4.7 Ofalu-Aranyos-v. trachyite K-feldspar M < 0.16 mm 4.62 2.0322x10'5 78.1 109.9±4.2 Kismórágy q. No. 5. trachyandesite w. r. acetous 5.07 1.8891xl0"5 73.6 93.5±3.6 Kismórágy q. No. 6. trachyandesite w. r. acetous 7.179 2.7904xl0"5 75.5 97.4±3.8 Previous measurement of K/Ar Ófalu "bostonite" w. r. w. r. 4.21 4.21 1.821 1.950x10"5 82.0 95.0 106+7 113+7 Mórágy "bostonite" w. r. 4.67 2.074x10"5 90.0 108+6 R E F E R E N C E S ÁRVA-SÓS E. (1979): K-AR módszeres kormeghatározások a Mecsek hegységből. Egyetemi doktori értekezés. Manuscript, Debrecen. ÁRVA-SÓS E., BALOGH K., RAVASZ-BARANYAI L., RAVASZ CS. (1987): Mezozóos magmás közetek K/Ar kora Magyarország egyes területein. MÁFI Évi Jel. az 1985. évről, 295-307. ÁRVA-SÓS E., RAVASZ-BARANYAI L. (1992): A Mecsek és Villányi hegység között feltárt kréta telérközetek K/Ar kora. MÁFI Évi Jel. az 1990. évről, 229-240. BARABÁS A. (1956): A mecseki perm időszaki képződmények. Kandidátusi értekezés. Manuscript, Budapest. BILIK I. (1979): A Mecsek hegység alsókréta tengeralatti vulkáni képződményei. Egyetemi doktori értekezés. Manuscript, Budapest. CSALAGOVIS J. I. (1964): De la palingenése calédonienne et des rapports de grandé tectonique du Massif de socle cristallin du Sud du Bassin Pannonién (Cisdanubie). Ann. Hist. Nat. Mus. Nat. Hung., Min.-Pal., 56,31-54. FORGÓ L., MOLDVAY L., STEFANOVITS P., WEIN GY. (1966): Magyarázó Magyarország 200000-es földtani térképsorozatához. L-34-XIII. Pécs. MÁFI GHANEM M. A. E. A., RAVASZ-BARANYAI L. (1969): Petrographic study of the crystalline basement rocks, Mecsek Mountains, Hungary. ActaGeol. Acad. Sci. Hung. 13, 191-219. HUEMER H. (1993): Geochemie und Petrogenese der kretazischen Vulkanite im östlichen Mecsek-Gebirge (Süd-Ungarn). PhD. thesis. Manuscript, Bécs. HARANGI Sz. (1990): A kelet-mecseki alsókréta vulkáni kőzetek geokémiai jellegei (Sokváltozós matematikai módszerek alkalmazása magmás geokémiai vizsgálatokban). Egyetemi doktori értekezés. Manuscript, Budapest. HARANGI SZ. (1993): A Mecsek hegység alsókréta vulkáni kőzetei. Kandidátusi Értekezés. Manuscript, Budapest. HETÉNYI R., RAVASZ-BARANYAI L. (1973): A baranyai antracittelepes felsőkarbon összlet a Siklósbodony 1. és a Bogádmindszent 1. sz. fúrás tükrében. MÁFI Évi Jel. 1973. évről. 323-361. IMREH L. (1956): A mecseki felsötriász homokkőöszlet felső részének kőzettani vizsgálata. MÁFI Évkönyve 45, 53-72. JANTSKY B. (1950): A mecseki kristályos alaphegység földtani viszonyai. MÁFI Évi Jel. az 1950. Évről, 65-77. JANTSKY B. (1979): A mecseki gránitosodott kristályos alaphegység földtana. MÁFI Évkönyv LX. 30, 147, 150. 163 JÁRÁNYi K. (1970): A Mórágy környéki gránitoid közetek vizsgálata, különös tekintettel a gránitosodás folyamatára. Szakdolgozat. Manuscript, ELTE, Budapest. Kiss J. (1962): A hydrothermal environment of Pb-Zn-Cu in the Erdősmecske granite. Annales U.S.B.d.R.E. Tomus V. MAURJTZ B„ CSAJÁGHY G. (1952): Alkáli telérközetek Mórágy környékéről. Földt. Közi. 82, 137-142. PANTÓ Gy. (1980): Rikafbldfémek geokémiája és néhány alkalmazási területe. Doktori értekezés. Manuscript,, MTA Könyvtár, Budapest 101-121. RÓTH S. (1876): Fazekasbodai-mórágyi hegylánc (Baranymegye) eruptív kőzetei. Magyar Kir. Földt. Int. Évkönyve IV/3. SZABADOS Cs. (1996): Bostonit-e a mórágyi bostonit. Földtani Közlöny, in press. SZABADOS CS. (1996): Penological characteristics of the so-called "bostonite" rocks of Mórágy Hill, Mecsek Mts., S-Hungary. Workshop "Magmatic Events in Rifted Basins" under the aegis IGCP Project No. 369., Budapest. In abstract. SZABADOS CS. (1996): Petrological characteristics of the so-called "bostonite" rocks of Mórágy Hill, Mecsek Mts., S-Hungary. Acta Geologica Hungarica. In press. SZAKMÁNY GY., JÓZSA S. (1994): Rare pebbles from the miocene conglomerate of Mecsek Mountains, Hungary. Acta Miner. Petr. Szeged XXXV, Supplementum, 53-64. SVINGOR É., KovÁCH Á. (1978): A Mecsek hegységi bosztonit kora Rb/Sr kormeghatározások alapján. Földt. Közi. 108, 94-96. SZEDERKÉNYI T. (1974): A délkelet-dunántúli ópaleozóos képződmények ritkaelem kutatása. Kandidátusi értekezés. Manuscript, MTA Könyvtár. VADÁSZ E. (1960): Magyarország földtana. Akadémiai Kiadó (2. kiadás) Budapest. Manuscript received 6. Sept. 1996. 164 

The age of the so-called "bostonite" rocks of Mórágy Hill, S-Hungary

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The age of the so-called "bostonite" rocks of Mórágy Hill, S-Hungary

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