| Summary: | The Cimmerian orogenic belt of North Dobrogea (East Romania) is located in the Carpathian foreland between the Moesian and Scythian Platforms. In the absence of reliable geochemical data on the different magmatic rock-types, various geodynamic models have been suggested for the Triassic-Jurassic evolution of this belt. Geochemical studies on mafic dykes emplaced in different Hercynian basement rocks, as well as on the Early-Middle Triassic Niculitel Formation basalts have been performed in order to provide new constraints for the geotectonic setting of this belt. A Permo-Triassic phase of crustal thinning of the Hercynian basement is suggested by the still poorly known alkaline magmatism. The Triassic magmatic history involves intrusion of tholeiitic dykes in the Hercynian basement of the Macin Zone, and extrusion of pillow basalts (Niculitel Formation) that most likely occurred above the carbonate compensation depth in a rifted basin with a thinned crust, as suggested by facies characteristics of carbonate rocks interbedded with basalts. This basin could have corresponded either to an aborted rift, or to a passive margin related to back-arc opening. Our data indicate that Macin and Niculitel basalts are derived from a MORB-type asthenospheric mantle source variably influenced by a plume-type component. The less enriched character of the Macin dykes reflects a lesser influence of plume source on magma composition with respect to the Niculitel basalts. Modern chemical analogues are found in the South West Indian and American-Antarctic Ridges, where composition of basalts range from pure plume-type ocean island basalts (OIBs) to pure MORBs, depending on the influence of the Bouvet mantle plume on MORB source. Regardless of the geochemical differences, which can reasonably be related to local variations of the plume component influence on the MORB source, a common geodynamic setting can be postulated for the origin of the two basaltic series. In the hypothesis of the aborted rift, an evolution of the mantle ...
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