THE PALEOGENE CONTINENTAL ADAKITES FROM THE MURES COULOIR, ROMANIA

摘要

The Paleogene adakites from the Mures Couloir or the Mures Rift occur in the Sarbi volcanic neck that consists of trachybasaltandesites of shoshonitic and mugearitic nature. Their most characteristic geochemical parameters are the following: Sr = 770 ppm; Ba = 620 ppm; Y = 12.6 ppm; Yb = 1.05 ppm; Sr/Y = 61; Ba/Y = 49; La/Yb = 27.5. Other occurrences of Paleogene volcanics from the Mures? Couloir are represented by necks and lavas of basaltandesites bearing arc and transitional-adakitic characteristics. All these rocks came from enriched magmas formed under tectonic settings determined by the genesis of the post-collision continental Mures Rift. These favoured a selective partial melting of the spinel lherzolitic mantle sources metasomatized during the Upper Cretaceous subduc-tion episode. The partial melting was of ca. 1 - 1.5 % in the case of the adakitic magma and of 3 - 4 % in that of the basaltandesitic magma.