U–Pb ages of some crystalline rocks from the Burlington Peninsula, Newfoundland, and implications for the age of Fleur de Lys metamorphism: Discussion

Abstract

In a recent paper, Mattinson (1977) reports some U-Pb zircon data from the Burlington Peninsula, Newfoundland, and proposes a synthesis of the isotopic data from this area. His synthesis, albeit tentative, is as follows (the geological units are shown in Fig. 1): (1) ophiolite formation -500-510 Ma ago (basal part of the Snooks Arm Group), followed by deposition of sediments in Arenig time; (2) emplacement of the Cape St. John Group and the Cape Brule porphyry -475 Ma; (3) intrusion of the Burlington granodiorite, Dunamagon granite, and Seal Island Bight syenite -440 Ma ago; and (4) resetting of some mineral ages in the Burlington granodiorite by an event -340 Ma ago. Since the Burlington granodiorite, Seal Island Bight s yenite, and Dunamagon granite are all either preor syn-kinematic intrusions, Mattinson also suggests that both deformation and metamorphism in the Burlington Peninsula had begun by -440 Ma, but not prior to 475 Ma. Mattinson's (1977) data represent a welcome , contribution to the understanding of the evolution I of the region, but we do wish to dispute some of his I findings. To begin with, we take strong exception to what we consider to be a misrepresentation by Mattinson of our Rb-Sr data, which we documented in a preliminary report to the Newfoundland Department of Mines and Energy (Bell and Blenkinsop 1975). Not only does the omission of our inferences give a distorted and unrealistic picture of our findings, but it denies us any credit for earlier drawing conclusions similar to Mattinson's regarding the Cape St. John volcanics. To set the record straight, we quote from our report (the quotation refers only to the Cape St. John volcanics):