Fig. 3

Results of XRD analyses. a–c Representative diffractograms of untreated sample from 1.73 m (a), quartz and feldspars from 1.73 m (b), and quartz and feldspars from 14.92 m (c). Dashed lines represent reference diffraction patterns for quartz (a; RRUFFID = R110108), albite (b; RRUFFID = R040068), and sanidine (c; RUFFID = R060313) in arbitrary scale. Data are downloaded from RRUFF project (http://rruff.info/). d Depth variation of the diffractograms for quartz and feldspars showing changing contribution of potassium feldspar and plagioclase. Each diffractograms are normalized by the peak of quartz (qz). Some peak identifications were given for potassium feldspar (K-fds) and plagioclase (pl) on the top and bottom of the plot, respectively. e Blowup of diffractograms for plagioclase composition determination using the separations between \(\left( {111} \right)\) and \((1\bar{1}1)\) (left), and \((\bar{1}32)\) and \(\left( {131} \right)\) (right)