Pb, Sr and Nd isotope study of two co-existing magmas in the Nizke Tatry Mountains, Western Carpathians (Slovakia)

摘要

Two co-existing plutonic rocks (diorite and granodiorite) were studied from an intrusion of Variscan age in the Raztocna Valley - Ni'zke Tatry Mountains, Western Carpathians. Geochemical analyses of major and trace elements constrain a volcanic arc as emplacement environment and give the first hints of a mixture of two magmatic end-members: the so-called Prasiva granodiorite and the Raztocna diorite. The ~(87)Sr/~(86)Sr(0) ratios vary between 0.7075 and 0.7118, the eNd_((0)) values range from -1.4 to --5.0. Common Pb isotopes reveal a dominant crustal source with minor influences from a mantle and a lower crustal source. Modelling based on Sr and Nd isotope data and using three component mixing calculations indicates that mixing of 2/3 of upper mantle material with. 1/3 upper crustal material can produce the isotopic composition of the Raztocna diorite. Very minor amounts of lower crust were incorporated in the diorite. For the Prasiva granodiorite, the mixing ratio of upper mantle and upper crust is similar, but a lower crustal reservoir contributed about 5-10 percent of the source material.