Search

Copyright of Canadian Journal of Earth Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This article presents a history of the development of U–Pb geochronology with emphasis on the role of Canadian researchers and some of its applications to Canadian geology. Modern U–Pb dating is the result of work by many individuals over the past 60 years, but the most important was Tom Krogh, who established methods that allowed determination of precise ages (<0.1% errors) on zircon using isotope dilution thermal ionization mass spectrometry. This was followed by the introduction of new analytical approaches by others, notably secondary ion mass spectrometry and laser ablation inductively coupled plasma mass spectrometry that allow intracrystal domains to be dated. U–Pb geochronology is now an indispensable tool for understanding the Earth. In collaboration with field mapping, it has vastly improved our understanding of the geological history of Canada as well as important geological events such as mass extinctions, secular changes in geological processes, and the birth of the solar system. [ABSTRACT FROM AUTHOR]

Anyox Pendant contains complexly deformed greenschist-facies volcanic strata overlain by a thick succession of turbidite sedimentary rocks. At the contact between the two are well-studied copper-rich volcanogenic massive sulphide deposits; however the age and correlation of the volcanic strata, including the ore horizon, are poorly known. New stratigraphic, structural, and geochronology studies elucidate the regional stratigraphic, tectonic, and metallogenic settings and significance of these strata. The thick turbidite succession is correlated with Bowser Lake Group and conformably overlies the volcanic succession. Volcanogenic units include pillowed basalt, volcaniclastic rocks, chlorite phyllite, tuffaceous siltstone, and abundant gabbroic sills and dykes. Strained leucocratic intrusions yielded U–Pb zircon crystallization ages of 176.9 ± 0.2 Ma and 185.6 ± 0.3 Ma. Volcaniclastic rocks yielded detrital zircons that constrain the maximum ages of the volcanic succession. The youngest zircon grains from four samples in different structural segments limit strata to younger than ca. 186 Ma, ca. 178 Ma, ca. 183 Ma, and ca. 186 Ma. The results, combined with the regional oldest age limit of Bowser Lake Group, constrain the volcanic succession to late Early Jurassic(?) and early Middle Jurassic age, and support correlation with Hazelton Group of Stikinia. Furthermore, they enable comparisons with the coeval Au-Ag-rich stratiform Eskay Creek deposit, expanding southward the zone of extension in western Stikinia, which tapped primitive mafic magmas and accompanied the last vestiges of Stikinian volcanism in the early Middle Jurassic.Le pendant Anyox contient des strates volcaniques au faciès des schistes verts, déformées de façon complexe et recouvertes d'une épaisse succession de roches turbidites sédimentaires. Au contact entre les deux, on retrouve des gisements d'origine volcanique de sulfures massifs, riches en cuivre, qui ont été étudiés en détail; toutefois, l'âge et la corrélation des strates volcaniques, incluant l'horizon contenant le minerai, sont mal connus. De nouvelles études stratigraphiques, structurales et géochronologiques définissent les contextes régionaux stratigraphiques, tectoniques et métallogéniques ainsi que l'importance de ces strates. L'épaisse succession de turbidites est corrélée au Groupe de Bowser Lake et repose en concordance sur la succession volcanique. Les unités d'origine volcanique comprennent des basaltes en coussins, des roches volcanoclastiques, de la phyllite chloriteuse, une siltite tufacée et un grand nombre de filons-couches et de dykes gabbroïques. Des intrusions leucocratiques sous contraintes ont donné des âges de cristallisation U–Pb sur zircon de 176,9 ± 0,2 Ma et 185,6 ± 0,3 Ma. Des roches volcanoclastiques ont fourni des zircons détritiques qui restreignent les âges maximums de la succession volcanique. Les grains de zircon les plus jeunes provenant de quatre échantillons dans des segments structuraux différents limitent les strates à plus jeunes que ~186 Ma, ~178 Ma, ~183 Ma et ~186 Ma. Les résultats, combinés à la limite d'âge régionale la plus vieille du Groupe de Bowser Lake, restreignent la succession volcanique au Jurassique précoce (?) et au Jurassique moyen précoce et appuient la corrélation avec le Groupe de Hazelton de Stikinia. De plus, ils permettent des comparaisons avec le gisement contemporain de Eskay Creek, riche en Au-Ag, qui étend vers le sud la zone d'extension dans le Stikinia occidental, laquelle a pénétré les magmas mafiques primitifs et a accompagné les derniers vestiges du volcanisme stikinien au Jurassique moyen précoce.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]