Fig. 16

Photomicrographs of structures produced by D₄ deformation in the Yuli Belt along the Hongye River. Schematic in bottom left of each photograph illustrates the interaction of S₄ (red) with previous foliations or other structures. White arrow shows the coordinate direction, and plunge and trend indicate the view direction and pole to the plane of the thin section. See Fig. 15C for orientation data. a, b (XPL) show albite-rich (top) and albite-poor (bottom) domains defining the cleavage. c Quartz grains within microlithons that show grain shape preferred orientation, slight undulose extinction, and grain boundaries indicative of sub-grain rotation and grain boundary migration recrystallization. d Relationship between a relatively early formed lineation, defined by an aggregate shape preferred orientation (labeled L3-1, ASPO and a later lineation defined by a grain shape preferred orientation (labeled “L3, GSPO”). The early formed lineation is interpreted to represent D₂, whereas the later lineation is interpreted as L₄. Photograph is parallel to XY plane of S₄. e Albite porphyroblasts within a cleavage domain depicting an interior foliation and over-growth zoning. Acicular rutile with ilmenite coatings, tourmaline, and apatite inclusions are common, especially in grains with a deformed interior foliation. Locally, one coated ilmenite grain is isoclinally folded, while another depicts extension. f SEM-BSE image of image in e, depicting the variation in composition. Albite porphyroblasts contain ilmenite inclusions and are surrounded by chlorite and muscovite strain fringes. Different orientations of internal and external foliations indicate a top-to-the-right sense of shear, which in geographic coordinates is top-to-the-southwest. Orientation data are shown in Fig. 15