Mctamorphic rocks of the St AnthonyComplex of north-western Newfoundland arc best interpreted in terms of a high-temperature shear zone formed between down-going continental margin rocks and overriding oceanic lithosphere in a subduction zone. High-grade rocks. immediately beneath the oceanic lithosphere pcridotite. display retrograde metamorphism in high-strain zones, whereas lower grade rocks, near the'base of the metamorphic complex. display prograde metamorphism in high-strain zones. Mylonite zones in metabnsitcs at all levels in the complex contain t he assemblage epidote-hornblende-albite-sodic oligoclase. These observations suggest that the 'inverted metamorphic gradient' within the St Anthony Complex results from the fortuitous preservation of residual metamorphic assemblages from different crustal levels within an epidote amphibolite facies shear zone. The degree of re-equilibration is strongly dependent on the degree of strain, and is best achieved in synmetamorphic mylonite zones. This interpretation of the St Anthony Complex can be extended to other sub-ophiolite metamorphic sheets, which show very similar relationships. It is proposed that most metamorphic sheets beneath ophiolites are high temperature shear zones. the P-T paths of which preserve records of burial and exhumation in subduction zones.
Key-work: metamorphic P-T paths, ophiolite emplacement. shear zone metamorphism Smyth. W. R. IY73. The stratigraphy and structure of the southern part of the Hare Bay Allochthou, northwestern Newfoundland. Unpubl. PhD thesis. Memorial Universiry of Newfoundland.
