Browsing by Author "Gal, Len P."

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    Metaphoric and structural geology of the northern Solitude Range, western Rocky Mountains, British Columbia
    (1989) Gal, Len P.; Ghent, Edward D.
    The northern Solitude Range of the Western Rocky Mountains comprises Hadrynian middle Miette Group strata, unconformably overlain by the lower Cambrian Gog Group, and succeeded by equivalents of the middle Cambrian lower Chancellor Group. In total some 2000m of strata are exposed . . The structural geology of the study area is dominated by the Porcupine Creek Anticlinorium (PCA), trending SE through the area. The core of the PCA is characterized by Miette and Gog Group strata in large, shallowly-plunging, upright folds (F2 ). A slaty cleavage (S2) is axial planar to these folds. Steep normal faults cut the limbs of F2 folds. The western flank of the PCA comprises mainly Chancellor Group rocks, in relatively tighter, and overturned F2 folds. Small isoclinal folds (F1) are locally apparent and refolded by F2 folds. An early layer parallel cleavage (S1) is crenulated by the later S2 cleavage. The 02 elements are correlative across the PCA, and 01 features are observed only in Chancellor Group lithologies, with the exception of Gog Group metasediments exposed in an anticline on the distal flank of the PCA. It is inferred that a detachment surface at the base of the Chancellor Group was active during 01 deformation, allowing the upper package of rock (Chancellor Group) to uncouple and deform above the relatively inert lower package (Gog and Miette Groups). Subsequent D2 deformation folded the entire package of rock, and was the major folding phase that formed structures of the PCA. The metamorphic grade increases toward the west, from a chloritoid + chlorite zone to a kyanite + staurolite zone. Geothermometry reflects the increasing grade, yielding estimates from ~450 ° C in the low garnet zone to ~540 ° C in the highest grade schists. Application of several geobarometers yield an average of 5.5-6.5 kbar. Pressure estimates from some pelitic assemblages, using measured mineral compositions and the thermodynamic data base of the GEO-CALC program (Berman et al., 1987) are ~ 7 kbar. Estimations of attendant fluid composition from mineral equilibria were water-rich, even for calcareous assemblages, suggesting infiltration and external buffering of fluid compositions. Petrographic analysis of pelitic samples indicates that peak metamorphic crystallization occured syn- . to post-D2. However, in the higher grade zones in the NW part of the study area, temperatures during D1 were at least sufficient to crystallize biotite. Isograds in the study area are subvertical, and there is little apparent disruption of the metamorphic field gradient across the Purcell Fault , in contrast to the Big Bend area (Craw, 1978). The lack of grade change across the fault may be due to post-thrusting heating and recrystallization in the footwall rocks (Solitude Range) under the relatively hotter rocks of the Selkirk Range.