Abstract

Rocks formerly mapped as Leech River Formation can be subdivided into two partly coeval rock units with completely different histories. The Upper Jurassic – Lower(?) Cretaceous Pandora Peak unit, which comprises black mudstone, terrigenous greywacke, radiolarian ribbon chert, green tuff, metabasaltic greenstone, minor pebbly mudstone, and a few blocks of limestone, was probably deposited in small basins on a continental margin. Local stratal disruption occurred before sediments were lithified. A static, high-pressure, low-temperature metamorphism produced lawsonite-bearing assemblages in metaclastic rocks. The Pandora Peak unit was originally coextensive with the Pacific Rim complex on western Vancouver Island and the Constitution formation in the San Juan Islands of Washington. The Leech River complex consists of foliated metasandstone, phyllite, and minor metabasalt of probable Jurassic–Cretaceous age. Multiple folding, transposition, and synkinematic greenschist- to amphibolite-facies metamorphism culminated about 40 Ma.The Pandora Peak unit is separated from crystalline rocks of the Wrangellia terrane by major faults. In southeast Victoria, partly retrograded amphibolites of the Wark–Colquitz complex overlie locally cataclastic lawsonite-bearing Pandora Peak rocks along the newly discovered Trial Islands thrust. A similar thrust separates the two units in Finlayson Arm, but near Port Renfrew the Pandora Peak terrane and crystalline West Coast complex are juxtaposed along the high-angle San Juan Fault. In each of these areas, emplacement of the Pandora Peak unit postdated the high-pressure (lawsonite-grade) metamorphism, which occurred between late Albian – early Cenomanian and Santonian–Campanian time (approximately 99–83 Ma). The Pandora Peak terrane was emplaced during a major Late Cretaceous or early Tertiary tectonic event that modified and probably truncated the southern margin of the Wrangellia terrane. Following this event the Leech River complex was faulted against the southern margin of the Pandora Peak terrane near Port Renfrew and in Goldstream Park in the Late Eocene or Early Oligocene.

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