MAFIC PHYLLOSILICATES IN LOW-GRADE METABASITES - CHARACTERIZATION USING DECONVOLUTION ANALYSIS

The <2 mum clay fractions from low-grade metabasalts of eastern North Greenland are mixtures of mafic pbyllosilicates and celadonite that sh ow complex X-ray diffraction (XRD) patterns. Interpretation of such pa tterns is difficult and subjective using only visual examination of pe ak positions and shapes. Deconvolution analysis offers a less subjecti ve means of identifying peak positions for overlapping peaks and is ap plied to several composite peaks in a pattern; the peaks identified ar e then rationalized in terms of specific mixed-layer phases. Compariso n against NEWMOD patterns of the identified clay mixture provides an a dditional constraint on the phases identified. Three mafic phyllosilic ates, discrete chlorite and two chlorite-smectites with 60:40 and 80:2 0 proportions are demonstrated in the same XRD pattern. Modelling usin g NEWMOD of a mechanical mixture between these mineral shows an excell ent match to the observed XRD pattern. The recognition in low-grade me tabasalts of chlorite and random and different varieties of regular mi xed-layer chlorite-smectite offers support for the classical model of a tri-smectite to chlorite transition. This is in contrast to an alter native model proposing smectite and chlorite end-members with corrensi te as a discrete phase crystallizing directly without intervening mixe d-layer chlorite-smectite.