Tectonomagmatic evolution and green rock mineral chemistry of Jurassic Bonanza arc rocks at Pemberton Hills, Vancouver Island, British Columbia, Canada

Abstract

The Pemberton Hills study site is situated in northern Vancouver Island, British Columbia, and forms part of a northwest trending belt of porphyry deposits and prospects within the Wrangellia Terrane. The study site is underlain by late Triassic to middle Jurassic Bonanza Group volcanic rocks, with porphyry-related alteration and mineralization thought to be related to the emplacement of the Jurassic Island Plutonic Suite (181 – 141 Ma). Whole-rock geochemistry, high precision geochronology combined with trace element and Hf isotope analysis of zircons from various intrusive units has led to an improved understanding of the magmatic evolution of plutonic rocks at Pemberton Hills. The oldest unit is a granodiorite dated at 172.34 ± 0.11 Ma. Following this is a quartz diorite with an age of 172.01 ± 0.17 Ma, which overlaps with a tonalite dyke sample dated at 171.77 ± 0.13 Ma. A second quartz diorite sample yielded the youngest reported age at 171.44 ± 0.25 Ma. These results imply that felsic and intermediate plutonism were broadly synchronous at Pemberton Hills. [...]