| Summary: | The supercontinent Columbia existed from approximately 1.8 to 1.3 Ga. During this time, complex tectonic interactions occurred between northwestern Laurentia and Australia. This thesis concerns three geologic events on northwestern Laurentia. The first event is the development of a post-collisional sedimentary overlap assemblage at 1.6 Ga herein called the Wernecke-Ogilvie unlithified succession (WOUS). The second event is the formation of the Wernecke Breccia, a set of 1.60 Ga hydrothermal breccia zones. The third is the emplacement of the 1.38 Ga Hart River sills. The WOUS was a succession of sandstone and mudstone that was deposited after collision between Laurentia and Australia at ~1.6 Ga, and prior to the formation of the Wernecke Breccias at 1.60 Ga. The WOUS is contained as clasts within the Wernecke Breccia. On the basis of detrital zircon U-Pb ages, Lu-Hf model ages and neodymium isotope geochemistry, the WOUS is correlated to sedimentary units within the hydrothermal breccias of the Olympic Dam deposit on the Gawler Craton of Australia. The Wernecke Breccia occurs as zones that are metres to kilometres in size that are scattered over an area of 300 x 150 km. The breccia zones are post-orogenic and are hosted by the deformed and metamorphosed Wernecke Supergroup. The breccias formed from voluminous hydrothermal surges with a significant gaseous component. These surges vented, and overlying rock units foundered kilometres deep into the breccia zones. The Hart River sills extend from the eastern Ogilvie Mountains to the Wernecke Mountains. Individual sills are up to 200 km long and 500 m thick. The sills are mafic to intermediate, and tholeiitic. The sills are dated herein at 1382.15 ± 0.39 Ma and 1382.14 ± 0.36 Ma. The magma that formed the sills resulted from ~10% partial melting of spinel bearing mantle similar to a MORB source. Coeval and possibly related magmatism occurred farther south on Laurentia, and to the north on Siberia. These magmatic events occurred on a possible rift axis that extended along the western margin of Laurentia and may signify breakup of the supercontinent Columbia.
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