Tom succession Epidote Op 0] Chlorite AH Crenulation UN Garnet Biotite Muscovite Mylonite Downey succession Pyrite Tourmaline Calcite Wit i Chlorite as Plagioclase Muscovite’ ["— — — — — ——-] Mylonite Ramos succession Epidote Chlorite Crenulation Garnet Biotite Plagioclase|7Z ? 2? ? 41— Quartz JZIADSVISSIANGSLK ONS MUSCOVICG Ming — ne Mylonite Tregillus succession Calcite ape Chlorite KE YE Crenulation ful Garnet Biotite LILLY LLLL Plagioclase|] 7 QOH PII 7 Sphene Actinolite Epidote Chlorite Crenulation Biotite Plagioclase Quartz Muscovite Mylonite TIME Figure 52. Relative timing of the crystallization of meta- morphic minerals and the formation of cataclastic fabric and crenulations for rocks from units of the Snowshoe Group of the Barkerville Terrane. Old Young 1985 for documentation of Cretaceous strike-slip in northern British Columbia). Brittle shortening and extension, as indicated by cren- ulations, kinks, broad open small-scale folds, and exten- sional faults, overprint all other structures and mark a period of chlorite retrograde metamorphism. This is thought to be a response to uplift of the structural pack- age, at first remaining in a compressional environment and later changing to one of extension. The transition from compression to extension is inferred to be caused by the change from primarily Cretaceous transpressional tectonics to that of northerly-directed transtensional strike-slip (right-lateral). The initiation of the transten- sional strike-slip tectonics is assumed to coincide with that of the Fraser River Fault system and Tertiary extension and uplift of the southern Omineca Crystalline Belt (Price, 1979; Monger, 1985). ROCKS OF THE SLIDE MOUNTAIN TERRANE Antler Formation The Antler Formation as used in this report follows the definition of Sutherland Brown (1957,1963) and Camp- bell et al. (1973). It is included in the Slide Mountain Group. The Antler Formation consists predominantly of pillow basalt, cherty argillite, argillaceous chert, cherty siltite, chert and diabase. It also contains lesser amounts of agglomerate, volcanic breccia, gabbro, greywacke, black slate and ultramafic rock. The basalt, chert and mafic igneous rock characterize it from other units of the area. Pillow basalt of the Waverly Formation resembles that of the Antler Formation. The formation underlies the ridge system northward from Mount Tinsdale to Big Valley Creek. It has been mapped east, north, and west of the area by Sutherland Brown (1957,1963) and Campbell et al. (1973) in McBride map area, and Tipper (1961) in Prince George map area. Exposures at mounts Tinsdale and Murray and Slid- ing and Two Sisters mountains are representative of the formation. Its thickness is poorly known because the internal stratigraphy is difficult to trace. Sutherland Brown (1963) estimated the thickness to be 1100 m at Mount Murray and somewhat thicker in the Palmer Range. This estimate may be excessive because the for- mation is imbricated by thrusting (Struik and Orchard, 1985). The pillow basalt is dark grey green to grey, aphanitic to finely crystalline and is best developed on Mount Tinsdale and Mount Murray. Pillow structures in these areas range from 0.5 to 2 m across (Fig. 53). Matrix between the pillows is minor. Mineralogically the pillow basalt examined consists of: 73