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    STUDIA GEOLOGIA - Issue no. 1 / 2002  
         
  Article:   TRANSPORT AND EMPLACEMENT OF THE 15.4 MA RHYOLITIC IGNIMBRITES FROM GUTAI MTS., EASTERN CARPATHIANS, ROMANIA.

Authors:  ALEXANDRINA FÜLÖP.
 
       
         
  Abstract:  The 15.4 Ma rhyolitic ignimbrites are the first volcanic products from Gutai Mts. The study of their sedimentary structures reflects the mechanisms involved in the transport and emplacement of the parental flows, essential to inffering the style of eruption and the source evolution and location. Primary sedimentary structures show massive deposits emplaced from mass flows, sequence of units showing the normal coarse-tail grading of the dense clasts and the reverse coarse-tail grading of the pumice clasts. They reflect concentrated laminar flows or dilute, subcritical flows emplaced by progressive aggradation. Secondary sedimentary structures are represented by the eutaxitic texture or welding, cooling textures (columnar jointings, spherulitic textures) and gas-escape pipes. They assess the hot state deposition with low degree of fluidization, low cooling rates and gas-retention regime. Ignimbrites are supposed to be emplaced as a single cooling unit, from the dense, bazal part of a maintained, stratified dilute pyroclastic current, in subcritical regime. This rheology, the temperature and volatiles regime is compatible with boiling-over eruptive style and caldera collapse. The source location is suggested within Gutai Mts area.  
         
     
         
         
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