The genesis of late alpine plutonic bodies of Rensen and Monte Alto (Eastern Alps): inferences from major and trace element data

Major element abundances and preliminary trace element data are reported for rock samples coming from the Late Alpine plutonic bodies of Rensen and Monte Alto, Eastern Alps (Italy). The rocks from Rensen range in composition between diorite and granite and display smooth variation of major element oxides against Differentiation Index. The abundances of Rb, Sr, Th and REE are variable and display a more or less well defined tendency to increase with D.I. with large scattering of values expecially in the granodiorites and tonalites. REE have variable degree of fractionation which tend to increase with D.I. The rocks from Mt. Alto have poorly variable composition being represented by predominant granodiorites and sporadic tonalites. Trace element Rb, Sr, Th and REE display again scattered values but generally significantly higher abundances with respect to the analogous rock-types from Rensen. REE are strongly fractionated with La/ Yb = 21-60 ca. The data obtained on the granodiorites from Mt. Alto suggest that these rocks are the product of partial melting of deep crustal rocks followed by small degree of crystal/ liquid fractionation at lower pressure. The data obtained on the Rensen suite do not allow to narrowly constraint any petrogenetic hypothesis although the field evidence suggests that this plutonic complex is the result of emplacement of different batches of magma possibly formed by distinct petrogenetic processes.