In 1984, Canada and the USSR entered into an Arctic Science Exchange agreement, an important theme of which is the comparison of the geological evolution of the Arctic regions of both countries. Before 1984, progress in understanding the geology of the Arctic was hindered by political and cultural barriers. Soviet and western scientists had not enjoyed easy access to each others' field areas, and this inhibited understanding and exchange of data. The 1984 agreement between Canada and the USSR 1 for scientific and technological exchange in the Arctic represents a major step forward in the pursuit of understanding the geology of the Arctic region. This report, on the geology of a remote and important Russian island, is a direct result of this exchange, and this cooperative effort will be a landmark in providing new constraints to regional plate tectonic models and in providing basic information to aid in exploration and evaluation of the resource potential of the Canada Basin region.
The Northern Canadian Cordilleran Miogeocline developed intermittently during the early Paleozoic and hosts alkalic and ultrapotassic volcanic rocks that are spatially restricted in thin beds and lenses and isolated volcanic piles. On the basis of geochemistry and geographic location, these volcanic rocks are subdivided into five main groups. Group I rocks (Porter Puddle and Macmillan rocks) are potassic basanites characterized by high Nb, Ce, and Nb/Y and low Zr/Nb. They are chemically similar to the Mountain Diatreme, indicating a genetic link. Group II rocks (Porter Puddle, Niddery, and Macmillan rocks) are also potassic but have lower abundances of Nb and Ce, higher Zr/Nb, and lower Nb/Y. Group III rocks (Vulcan and Itsi Lakes) are also potassic but are chemically variable, have lower contents of high field strength elements (HFSE) than the groups I and II rocks, and contain elevated Ba contents. Groups I–III are characterized by mica (biotite and phlogopite) phenocrysts, sanidine, augite, and Ba-feldspar, a mineral assemblage typical of ultrapotassic lavas. Group IV (Whale Mountain) alkali basalts are the least enriched in the large ion lithophile elements and have relatively low contents of HFSE compared with Groups I and II basalts. Groups I–III are consistent with partial melting of a previously metasomatized lithospheric mantle that was variably enriched in Ba, Nb, and Ce, whereas the group IV rocks are more typical of asthenospherically derived oceanic island basalt partial melts. The geochemistry of the volcanic rocks is consistent with paleotectonic models of the Selwyn Basin. The Selwyn Basin is a passive continental rift that underwent episodic extension and associated subsidence throughout the lower Paleozoic. Alkalic volcanism, and spatially and temporally associated Ba and base metal mineralization, is concentrated along rift-parallel normal faults, particularly where these faults are offset by transform faults.
Seventeen samples of stratiform barite hosted in Middle Cambrian to middle Mississippian marine sedimentary rocks of the western Canadian Cordillera were analyzed to determine their 6 3 4~ and 6180 values. Whereas some samples had isotopic values close to those for time-equivalent evaporites, others were clearly more enriched in the heavy oxygen and sulphur isotopes. Samples with isotopic values close to the evaporite curve were from very thick stratiform barites hosted mainly in organic-rich shales, and from thin and nodular beds hosted in organic-free sedimentary strata. All samples enriched in heavy isotopes were collected from thin or nodular deposits hosted in organic-rich sedimentary strata. Enrichment of barite in heavy isotopes can be achieved by a barite precipitation-dissolution process that cycles barium between oxygenated and reduced zones in either redox-stratified wet sediment, or sea water. This cycles requires barite to either settle from oxygenated sea water into more reducing water or to precipitate within or settle into wet sediment where Eh values are decreasing in situ during sediment buildup. Because all anomalously isotopically heavy barites are hosted in organic-rich strata, barite dissolution during this cycle likely occurs through the bacterial metabolism of organic matter and sulphate, during which sulphate with 1 6 0 and 3 2~ is preferentially broken down. The main products of this bacterial activity are C 0 2 and H2S, which can react to form carbonates or pyrite or can escape from the system, resulting in a depletion of light isotopes from the remaining aqueous sulphate. Because thick deposits of barite hosted in organic-rich shale, unlike smaller deposits hosted in the same strata, do not show heavy isotopic enrichment, the main factor controlling isotope fractionation is likely the rate of barite precipitation relative to barite dissolution and reduction.The 6 3 4~ versus 8180 values for six samples of Upper Devonian rocks plot fall on a line with a slope of 2. The data and observations presented here and in published reports indicate that alteration of the isotopic composition of stratiform barite strongly favours enrichment in heavy isotopes with respect to coeval sea-water sulphate. It should be possible then, to construct a barite sulphate isotopic composition age curve by averaging the lower 6180 and 634S values for samples of the same age.Dix-sept Cchantillons provenant d'un gite stratiforme de barite incorpork dans des roches skdimentaires marines d'bge cambrien moyen h mississippien moyen de la Cordillitre de l'ouest canadien furent analysCs pour determiner leurs valeurs de 634S et 6180. Bien que certains Cchantillons prksentaient des valeurs isotopiques se rapprochant d'kvaporites du m&me bge, d'autres Ctaient nettement plus enrichies en oxygkne lourd et en isotopes du soufre. Les tchantillons dont les valeurs isotopiques sont B proximitk de la courbe des Cvaporites proviennent de masses Cpaisses de barite stratiformes incluses principalement dans des schistes argileux rich...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.