A study on Jurassic Granitic Rocks in the Inje-Hongcheon District, South Korea : I . trace and rare Earth Elements Geochemistry

International audienceInvestigating the trace element behavior, it is revealed that the granitic rocks from the Inje-Hongcheon district show both a systematic variation pattern with SiO2 content for some elements such as Rb, Sr, V, Sc, Ga, Pb and Zn, and a dispersed pattern for Ba, Y, Zr, Nb, TH, Cr and Ni. The systematic variation pattern is recognized in all of the granitic rocks (hornblende-biotite granodiorite, porphyritic biotite granite, equigranular biotite granite and two-mica granite, from center to margin). The dispersed pattern is characteristic in the granitic rocks which occur at the relatively marginal parts. Wether systematic or dispersed pattern in the trace element variation is controlled by the regularity of the weight fraction of the mineral phase containing the element and the supply degree of the element from the contaminant due to wallrock assimilation. The systematic variation pattern is caused by the regular variation of the weight fractions of the mineral phases containing the elements and low supply of elements due to wallrock assimilation. In contrast, the dispersed pattern indicates either dispersive weight fractions of the mineral phases containing the elements or considerable effect of the assimilation. The contents of eight rare eatrh elements (La, Ce, Nd, Sm, Eu, Gd, Dy, Yb) in the hornblende-biotie granodiorite, the porphyritic biotite granite and the equigranular biotite granite decrease with SiO2 content. However, those in the two-mica granite tend to increase with SiO2 content, indicating element enrichment during the solidification of the two-mica granite. The enrichment would be due either to the partitioning of the elements to liquid phase in the granitic system, or to wallrock assimilation.Although the resultant rare earth element (REE) pattern of the model calculation on the basis of Rayleigh fractionisation is similar to overall REE pattern of the granitic rocks, the behavior of the rare earth elements cannot be explained exclusively from simple fractionation. The possibility of wall rock assimilation must be considered