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U-pb geochronology and lithogeochemistry of the Hope Bay greenstone belt, Slave structural province, Northwest Territories, Canada Hebel, Manfred U.


The Hope Bay greenstone belt (HBGB) is one of several Late Archean greenstone belts recognised within the Slave Structural Province (SSP) in the Northwest Territories, Canada. Unlike most other major greenstone belts in the SSP relatively little is known about the age and evolution of the HBGB. The main goal of this study was to construct a detailed chronostratigraphic and chemostratigraphic framework for the belt that would constrain the temporal and tectonic evolution and thus permit the HBGB to be placed in the regional geological context of the Slave Structural Province. A regional geochronological and lithogeochemical program was carried out in conjunction with geological mapping by BHP Minerals Canada Ltd. personnel. A total of 21 UPb age determinations, 174 major and trace element analyses, and 19 rare earth element analyses resulted from the study. U-Pb geochronology was selected as the critical tool for constraining the stratigraphic and temporal evolution of the belt because of its high blocking temperature and the precise ages that can be obtained using this method. Major, trace, and rare earth element data were employed to characterise the geochemistry of various igneous units and investigate the possible paleotectonic settings in which individual units were generated. The HBGB is characterised by a basal series of mafic dominated tholeiitic volcanic flows (Young Group), overlain by a sequence of calc-alkaline volcanic rocks (Westerberg Group), that are in turn overlain by sedimentary rocks of the Tweedy and Farrar group. These sequences were deposited over a period of at least 116 m.y. from ca. 2716 to ca. 2600 Ma. Chemical compositions of volcanic rocks are typified by low abundance of HFSE and depletions in Nb, Ti, Eu, and P relative to REE. The striking similarity between the overall lithologic assemblage and the geochemical signature of volcanic rocks in the HBGB with modern arc and back-arc systems (e.g. Mariana and Tonga-Kermadec regions) suggest the HBGB evolved in an arc-backarc geodynamic setting.

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