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Structure, metamorphism, and geochronology of the Northern Wolverine complex near Chase Mountain, Aiken Lake map area, British Columbia Parrish, Randall Richardson

Abstract

The Wolverine Complex (Armstrong, 1949; Roots, 1954) and similar rocks to the northwest are of Precambrian age, correlate with Winderemere-type stratigraphy, and are poly-metamorphic and poly-deformational. Wolverine rocks near Chase Mountain have experienced two periods of tight to isoclinal folding (F1, F2) overprinted by one or more periods of northwest-trending large-scale open folding (F3), small-scale crenulation folding of various orientations, and minor faulting. The two earlier periods of folding were accompanied by metamorphism culminating in amphibolite facies at the close of F2. These early folds are recumbent to gently inclined, and the geometry of F2 is consistent with north-eastward transport of rocks in nappe-like fashion. An F3 large-scale fold deformed earlier foliations into an upright to steeply eastward inclined antiform which correlates with structures mapped to the north by Mansy (1972, 1974). Geochronometric data strongly suggest that metamorphic culmination occured in mid-Cretaceous or earlier time, and that many rocks in widespread areas south of 56½°N have experienced resetting of K-Ar and Rb-Sr dates during the Eocene. A stock of biotite quartz monzonite, termed the Blackpine Lake granitic stock, has a Rb-Sr whole rock isochron age of 62±7 m.y. @ 0.7052 ± .0002 Sr 87/86[sub i] and a mineral isochron age of 44.7±2 m.y., and it intrudes the Wolverine Complex. In surrounding schists, gneisses, pegmatites, and muscovite-bearing granitic rocks related to the metamorphism, Rb-Sr mineral dates (muscovite, plagioclase, K-feldspar, whole rock) range from 52-84 m.y. and reflect partial to complete resetting, whereas K-Ar dates are entirely reset to 43-47 m.y. Rb-Sr mineral dates on biotite from metamorphic rocks are anomalously younger than K-Ar dates, a problem which is not understood. Though Eocene volcanic rocks and sediments indicative of rapid uplift occur within or flanking the Omineca Crystalline Belt, their spatial distribution bears no relationship to the areas of resetting of K-Ar and Rb-Sr dates. Though an entirely satisfactory explanation remains elusive, the resetting of dates must in part be due to the thermal effect of intrusions of granitic rock similar to the Blackpine Lake granitic stock which is shown to have disturbed dates in surrounding metamorphic rocks.

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