Romanian Journal of STRATIGR,APHY continuation of nÁRt nB sonuÁ ALE sEDINTDtoRINsTITUTUIUI DE,GEotoGIE $I GEoFIzlcÁ coMpTEs RENDUSDES SEANCES DE L'INSTITUTDE GEOTOGTEET GEOPHYSIQUE (4. Stratigrafie) Founded 1906by the Geologica|Instituüe of Romania Vol. 76 ISSN l,220-5664 Supplement No. 4 ElUElJFlEsTl.í995 IUGS, REGIONAL COMMITTEE ON MEDI'TERRANEAN NEOC]ENE STRATIGRAPHY 4 - 9 September GUIDE TO EXCURSIOAI 83 (POST_CONGNESS) TIME-SPACE EVOIUTTON OF NEOGENE-QUATERNARY VOTCANISM IN THE CALIMANI.GURGHIU-HARGHITA VOLCANIC CHAIN by Alexandru Szakács, Ioan Seghedi Institutul Geologic al Romániei Bucureqti - 1995 ?.j'E GEOLOGTCAL INSTITUTE OF ROMANIA The Geological Institutc of Romania is now publishing the following periodicals: Romanian Journal of Mineralogy Romanian Journal of Stratigraphy Romanian Journal of Petrology Romanian Journal of Tectonics and Regional Geology Romanian Journal of Mineral Deposits Romanian Journal of Geophysics Romanian Journal of Paleontology ''Dári ''Menrorii" ''Stu<lii Tbey supersede de Seamá ale $edin{elor'', and Tehnice qi Economice''' whose apparition goes back to 1910. Beside regular volumes, each series may occasionally contain Supplements (for abstracts and excursion guides to congresses and symposia held in Romania) and Special Issues (for larger papers of special interest). "Anuarul Institutului Geologic a] Romániei'' will appear also in a new form, containing both the annrral activity report and review papers. Editorial Board: Gheorghe Uduba5a (clrairman), Tudor Berza, Florian Marinescu, Marcel Márun(iu, Grigore Pop, VIad Roqca, Mircea Sándulescu Managing Editor: Anatol Rusu Executive Secretary: Felicia Istocescu Editorial Office: Geological lnstitute of Romania Str. Caransebeq No. I RO - 7967E Bucureqti - 32 Tel. (+40) I 665 66 25, 665 75 30 Fax (+40) 13128444 e-mail GIR BH [email protected]. RO The editor has changed the name as follows: Institutul Geologic al Romániei (1910_1952), Comitetul Geo|ogic (1953- l966), Comitetul de Stat al Geologiei (1967-1969),Institutul Geologic (1970_1974),Institutul de Geologie 9i Geofizicá (1975_1993),Institutul Geologic al Romániei (since l994). RoMANIAN JOURNAL oF STRATIGRAPHY supersedes "Dári de Seamá aJe $edin!elor'', Series 4/Stratigrafie * the Iast volume with this title being No. 74. Scientiffc Editor: Grigore Pop Advisory Board: Florian Marinescu Tlre manuscripts should be sent to the scieníific editor and/or executive secretary. Cortespondence concerning advertisments, announcements and subscriptions should be sent to the Managing Editor. @)GIR 1e95 ISSN 1220-5664 C.llassification index for libraries 55(058) Printed by the Geological Institute oÍ Ronlania Bucharest GUrDE TO EXCURSTON 83 (POST_CONGRESS) TIME.SPACE EVOIUTION OF NEOGENE.QUATERNARY ''8.tT'f; cÁr,ruANI-GU"xff Ü-ii[fT,B,.^NICCHAIN by Alexandru Szakács, Ioan Seglredi TRITA ^ : 2102oVf Pretrcsv . A L I M A N I MIS / ft,'*] TOPLITA ^__6qpan, T \--v-i--6 \J\ \ t Excursion IREA - AHf cruc itinerory \ BÁ| .{' CALIMANI-GURGHru-HARGHITA VOLCANIC CHAIN Introduction The Cálimani - Gurghiu - Harghita volcanic chain (CGH hereafter) forms the southernrnost portion and the largest occurrence area of the Carpathian Neogene/Quaternary rnostly calc- alkaline volcanic arc developed in Romania along the inner part of the Carpathian orogenic belt. Unlike other Neogene volcanic areas in Romania, much more eroded (oaq-Gutái and Apuseni Mts.), the fresh looking morphology of the CGH volcanic zone allowed the early recognition of individual volcanic edificesand prominent featuresincluding the unique crater lake Sf. Ana at the southern end of the chain. The chain display a roughly median position betweenthe East Carpattriansstructural units (Upper Cretaceousto Paleogene"Transcarpathian Flisch " Unit in the north, the "Crystalline- Mesozoic Zone" Unit in the east,the "CretaceousFlisch" Unit in the southeast)and the Neozoic Transylvanian basin molasses(fiS.1). Generalized structural models attempting to account for the broader-scaleconstitution of the CGH chain have been proposed by Rádulescu et al. (1964a, 1973). In this ''two compartment" model the lower part is constituted by a complex volcano-sedimentaryformation and the upper compartment by well preservedcomposite volcanic apparata. Increasing amount of geological data, achieved mainly in the last decade, suggest that the volcanic structures belonging to the CGH consist of a central volcanic zone with subvolcanic intrusive bodies in its infrastructure, an intermediate zone,corresponding to volcanic cone (mainly consisting of lava flows) and a peripheralmainly volcaniclasticzone. Effusive-explosivevolcanic activity prevailedat all stratovolcanicedifices building up a chain of adjoining arrdpartially overlapping composite edifices with well developedperipheral volcaniclasticaprons. Geotectonic setting Its general locabion with respect the major lithospheric tectonic units of the Carpathian system and the westernmargin of the Eurasian plate (i.e. behind the Carpathian accretionary prism) as well as its main geochemicalsignatures (i.e. their calc-alkalineaffinity) led the first applicants of the plate tectonic concept to the Romanian territory (Radulescu, Sándulescu, 1973,Bocaletti et al., 1973,Bleahu et al., 1973)to unanimouslyconsider the subduction-related character of the East Carpathian volcanic arc (fig.2). Westward subduction of the oceanic crust of an easterly "basin" or ocean, whose sparse,obducted remnants are discontinuously recorded within the inner flysch nappes of the East Carpathins, occurred beneath an inferred Transylvanian microplate or an assemblage of several microplates. Recently, the subducted crust involved in the generation of the Neogene volcanic arc is thought as belonging to a "marginal basin" of the Euroasian plate with thinned crust or a narrow oceanic-type crust (Rádulescu et al., 1994). There are, however,some problems with both timing and spatial relationships,especially along the CGH portion of the arc. L E 6t. N0 f+-r| lt l++ I -- l. ..1 | | 1...1 12 r"-:-;-'l rl l'""."."1 ffi r.----------t ll FTn rT'-i--r= t-T -t-H 5 t@l l5 r.T-T] o fTr-^:l t6 lxxl I -^{. I rr-l r.ffi:l t7 r---l 16 I t--r I l-^- | IA A AI l9 lL-r I l^ ^l l/- | f/'-,r \^l lL-r I I " I ?1 20Kn st(ults(/o - Fig. 2 Hypothetical block diagram showing the inffered present-day tectonic setting oÍ the CGH volcarric chailr Fig.r _ Volcanological map of Cálimani-Gurghiu.Harghita Morrntains (East Carpathians); 1. Quaternary swamp or lake deposits; 2. Tertiary postvolcanic and synvolcanic sediments; 3. Tertiary prevolcanic molasse sediments of Tralsylvanian basin; 4. Creüaceous.Tertiary sediments of the Flysch zone of East Carpathians; 5. Late Paleclzoic-Cretaceous sedinrents of East Carpathians; 6. Precambrian-Pa|eozoic metamorphic and plutonic rocks of Crysta||ing-IvÍ6sozoic Zone of East Carpathiarrs; 7. Nec.k; 8. Cratcr; 9. Caldera-like depressions; l0.Collapse calderas (caldera fault); ll.Porphyritic intrusive rocJrs; l2.Fine porp\yritic intrusive rock; l3.Volcanic core complexes; l4.Extrwive domes; l5.Lava flows; l6.Pyroclastic conel l7.Stratovolcanic co'e; lB.Efiusive cone; l9.Coarse pyroclastic rocksproximal facies; 20.Mudflow, debris avalanche, debris flow and ephemeral stream epiclastic volcauric rocks; 2l.Volcarr'ic edifices anrd areas: CÁLIMANI luTs..l' Drágoiasa; 2.Lucaciul; 3.Támául; 4.Rusca-Tihu; 5. Moldovanul; 6.CáIimani; 7. South Cfima.ni vocarric field; GURGHilJ MTS.- 8. Jirca; 9.obárqia; 10.Fáncel-Lápuqna; ll.Bacta; l2.Seaca- Tátarca; l3'Borzonü; l4.$umuleu; 15'Ciumani-Fierástraie; NORTH HÁRGHITA MTS.-16. Rác}ritig; l7.ostorog; l8.Ivo-Cocoizag; 19.Várghi9; soUTH HARGHITA MTS.-2o.$umuleu Ciuc; 21.Luci-Lazu; 22. Cucu; 23.Piligca; 24.Ciomadul; 25' Bicsa,d-Malrrag volcanic field. 'r flow deposits occurring on large surfaces in both soutlrern Cálimani a'nd northern Gurghitr Mts., including the intern caldera rim. No systematic investigation of this problem has yet been achieved. An andesiticdorne complex (Bacta) is adjoining to the southeasternpart of the caldera. In the western part an unnamed lava volca,nooverlies the peripheral volcaniclastics of northern Gurghiu Mts., but even its lava field extensionhas not been outlined accurately. Other composite volcanic structures in the southern part of Gurghiu Mts. include Seaca- ''caldera'' Tátarca with its surprisingly unifornr qtrasicircular rim and relatively simple (or poorly known?) structure and shape suggestingrather a shield, $umuleu with some "crater- rim" domes and well exposed core-complex and a large southern flank lava center, and the double cratered Ciumani-Fierastraieedifice. All of them are typically lava-built compositevol- canoeswith insignificantpyroclastics recorded in their cone structures. The5,are surroundedb5' coalescentvolcaniclastic aprons that, due to their similar ages,cannot be separatedaccording to their particular source volcanoes. The North Harghita volcanoesform a NNE tlending row of partially overlapping edifices. The northernnrostone (R,áchitiq)is a sinlple aphanitic dacitic dome volcano. ostor'oq,the next, is a rather small sized typical East Carpathian edifice rvith an obvious enlarged "crater", core- complex. rim domes, consistingof andesiticlavas, and vely tninor pyroclastics. Aphanitíc lava flows,similar to Ráchitiq rocks, are pt'esenton the rrort}ternflank arrd at the sorttlrea'sternfoot. It is uncertain whether this latter belongsto Ostoroqor the adjoining lvo-Cocoizaq structure. Ivo-Cocoizaqedifice is strongly eroded with a well exposed core cornplex, a morphologically not