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    STUDIA GEOLOGIA - Ediţia nr.3 din 2003  
         
  Articol:   TOWARDS AN IMPROVED MODEL OF THE LARAMIAN TRANSYLVANIDES.

Autori:  IOAN CORIOLAN BALINTONI.
 
       
         
  Rezumat:  The Transylvanides which represent the uppermost group of Alpine tectonic units of the Apuseni Mountains originated from a Mesozoic rift located between the Preapulian and Getic cratons (Rădulescu & Săndulescu, 1973; Săndulescu, 1984; Balintoni, 1997). The term “Foreapulian Block” (“Preapulian bloc” in Romanian translation), was used by Săndulescu (1994), for the continental mass from which the Northern Apusenides or Inner Dacides (the Codru and Biharia Nappe Systems) have been sheared. The name “Getic Craton” was proposed by Balintoni (1994a) for the continental fragment located between the Transylvanian Rift and the External Carpathian Flysch Basin, from which proceeded the Getic crystalline. The Transylvanides were emplaced antithetically, during the Austrian and Laramian orogenic phases. During the compressional (Early Cretaceous) period, the rift basin evolved towards a foreland retroarc type basin, because it was installed on the upper plate sheared margin. If the Austrian Transylvanides (ATS) and the Mediterranean Apusenides are described as “in-sequence” tectonic units, the Laramian Transylvanides (LTS) are “out of sequence”. In the Apuseni Mountains tectonic context, the Austrian orogenic phase is considered intra-Albian or around the Aptian-Albian boundary, the Mediterranean one as intra-Turonian (pre-Gosau) and the Laramian one as intra-Maastrichtian and close to the Maastrichtian end. This fact complicates the recognition of the Transylvanides, as well as their description and classification. Balintoni (1994, 1997) proposed a dual classification of the Transylvanides, with particular names for the Austrian and Laramian ones, because some parts of the ATS can be found again within several units of the LTS. According to latter classification of this author, the ATS include the Izvoarele, Valea Muntelui, Feneş, Colţul Trascăului, Bedeleu, Ardeu, Căbeşti, Căpâlnaş-Techereu and Bejan nappes, and the LTS comprise the Groşi, Crilş-Bucium, Vulcan, Frasin, Metalliferous Mountains, Curechiu-Stănija and Mureş nappes. Besides this, the Laramian Transylvanides transported also the post-Austrian sedimentary covers. Regarding the ATS and LTS many unsolved questions still persist, as it is for instance: the precise age for pre-Austrian and post-Austrian sedimentary formations; the correlation between the Austrian tectonic units enclosed by the Laramian nappes; the number of the LTS; the amplitude of the tectonic displacement; the relation between the Apuseni Mountains and the South Carpathians; the opening age of the Transylvanian Rift; the development of the magmatic component of the Transylvanides; the initial locale for the sedimentary and magmatic formations. In the following we will analyse some actual issues of the relation between the ATS and the LTS and present an improved model.  
         
     
         
         
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