D. Robinson et Re. Bevins, MAFIC PHYLLOSILICATES IN LOW-GRADE METABASITES - CHARACTERIZATION USING DECONVOLUTION ANALYSIS, Clay Minerals, 29(2), 1994, pp. 223-237
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.