8-12%

2C-F

4C-F 12-16% 16-20%

—

cleavage on outcrop scale is not well developed. Low seri- cite contents define the foliation. Dissolution surfaces are best developed when cleavage is parallel to bedding and, like the subgrain trains, are not usually detectable with the unaided eye.

Sandy conglomerate of the Guyet Formation, like the Yanks Peak Formation quartzite, has a poor cleavage expression in outcrops. As for the Yanks Peak Forma- tion, this poor expression is due to lack of abundant matrix micas, and because the conglomerate is essentially an L-tectonite; that is, a rock which has been deformed such that the strain ellipse is more cigar-like than pancake- like. Strain measured in eleven samples of Guyet Forma- tion conglomerate is mainly constrictional and records some 40% extension parallel to the regional fold axes. This extension formed during the period of ductile defor- mation and is unrelated to later brittle extension. Detailed descriptions of the strain measuring technique and the deformation characteristics of the conglomerate are given in Appendix B. Cleavage is poorly developed in the sandy conglomerate, not because it is much less deformed than the Cariboo Group, but because of its lithology and style of deformation. The polymictic nature of the conglom- erate has caused differential cleavage development between clasts.

Within the muddy conglomerate of the Guyet For- mation, cleavage relationships between clast and matrix are more obvious than in the sandy conglomerate. The shale matrix supports a well developed cleavage that pene- trates through both matrix and clasts of similar lithology. This contradicts the implication of Sutherland Brown (1957) that schistose clasts occur within an unfoliated matrix and agrees with the observation of Campbell et al. (1973, p. 58 and 79). The muddy conglomerate has a cleavage best described as intermediate between rough and smooth spaced, from the classification of Powell. (1979, Fig. 4, p. 27). Where there are pre-existing layers at angles to the cleavage it has the features of zonal and discrete crenulation cleavage as described by Gray (1977). The spacing of the cleavage is governed by the clast size.

Limestone displays various styles of cleavage, gener- ally poorly expressed. Best developed is bedding-parallel parting associated with dissolution surfaces. The parting surfaces have a 0.05 to 4 mm spacing and are quite smooth. Sericite flakes may occur along them when the limestone is moderately fine or more coarsely crystalline. Where there is a quartz-silt content, recrystallization localizes along the silt lenses and very thin planar disso- lution selvages border the zones of different crystal size.

Figure 24. Equal area net plots of the orientation of duc- tile style fold axes and the poles to cleavage for four structural domains of the Cariboo Terrane. Of the three characters in the labels, the first refers to the number of the domain (see Fig. 25), the second is a C for Cariboo Terrane and the third is either an S for cleavage surface or an F for fold axis.

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