Y

◙ Yellowknife: images of lithology and geomorphology of Slave Craton ◊ ◊

◊◊

alphabetic sections ◊ A ◊ B ◊ C ◊ D ◊ E ◊ F ◊ G ◊ H ◊ I ◊ J ◊ K ◊ L ◊ M ◊ N ◊ O ◊ P ◊ Q ◊ R ◊ S ◊ T ◊ U ◊ V ◊ W ◊ X ◊ Y ◊ Z ◊ elements of periodic table ◊ Mineral Index ◊ Rock Index

Yellowknife

The Slave Craton lies in Canada's Northwest Territories near Yellowknife, and forms a northwestern segment of the Canadian Shield (image at left) within the North American Craton (map, geological map, very simplified, maximum protolith age, cross-section, northern Slave mafic intrusions). The ASTER image (at left) of the Churchill District, which lies east of the Slave Craton, shows typical topography of the Canadian Shield. Introduction The Slave craton is a mere fragment of ancient crust, surrounded by Paleoproterozoic rifted margins. Cratons such as the Slave are remnants that preserve parts of the much larger, ancient pre-tectonic and tectonic systems in which they were generated. The Slave craton originated from the break-up of a much larger late Archean landmass and preserves a complex and spatially heterogeneous record of crustal growth that spans nearly 1.5 billion years. (garnets in subcontinental lithospheric mantle (SCLM)) The original landmass could have been the speculative late Archean supercontinent Kenorland or, perhaps more likely, a smaller landmass referred to as the supercraton Sclavia. Canadian Geology links : Geological Provinces Map : Age of Rocks Map : Major Rock Categories Map : Physiographic Regions Map : Shield Physiographic Regions Map : Surficial Materials Map : Relief Map : Comparative Cratonology in Canada: Slave against Buffalo : The upper crust sheds some crumbs: a top-down perspective of the Slave Craton : Slave Province Minerals & Geoscience: Mafic-Ultramafic Intrusions : Garnets: Key to the SCLM : The Deviant Archean

The Slave craton is a complex containing ancient collisional orogenic structures and accreted fragments, which now sits at the northeast of the North America craton. The Slave Province is "A" in the image at left - magnify - legend. The image above is located above the "I" on this geological map. Courtesy of USGS.

A. Cleaned exposures of the Acasta gneisses at their discovery site. Ancient tonalites (4.03 Ga) occur on left side of the picture, and are intruded by highly deformed younger granite sheets and mafic dykes. The Acasta Gneiss Complex dates from the Hadean at least 4.03-4.055 Ga, and is Earth's oldest known crustal rock outcrop. The complex comprises mostly Gray gneiss (granodioritic gneiss), White gneiss (tonalitic to granitic gneiss), younger foliated Granite (3.6 Ga), and many aplite and basaltic intrusions. (click to enlarge map of Slave Craton at right) Ancient Basement Complex

B. Basal quartzites of the Central Slave Cover Group overlying basement of the Central Slave Basement Complex (CSBC). Low foreground to the right are low-weathering basement gneisses; dark ridge in background are ca. 2.7 Ga basalts overlying the quartzites. The Cover Sequence : Ca. 2.73-2.70 Ga Tholeiitic Volcanism

B. Typical 2.95 Ga foliated tonalites of the Central Slave Basement Complex (CSBC) with transposed 2734 Ma mafic dikes. Ca. 2.73-2.70 Ga Tholeiitic Volcanism

C. Syn-Kam Group quartz-porphyritic tonalite intrusion (ca. 2713 Ma), silling into the northern part of the Yellowknife greenstone belt. This large sill-like body is cut by somewhat younger mafic dykes that likely fed the upper part of the greenstone belt. Inset: close-up of altered quartz-porphyritic tonalite. Ca. 2.73-2.70 Ga Tholeiitic Volcanism

G. Syn-Kam Group K-feldspar porphyritic granodiorite pluton in basement below greenstone belts.

D. Quartz porphyritic rhyolite breccia with carbonate matrix, typical for the uppermost part of 2690-2660 Ma felsic volcanic edifices. Ca. 2.73-2.70 Ga Tholeiitic Volcanism : Post-2.70 Ga Volcanism

E. Massive sulphide mineralization of the Sunrise deposit, associated with ca. 2670 Ma felsic volcanic rocks just below the interface with the Burwash Formation turbidites. Post-2.70 Ga Volcanism

F. Thickly bedded sandy turbidites typical of the Burwash Formation in its type area east of Yellowknife. The oblique areal photo shows an F1 syncline refolded by north-northwest trending F2 folds. Ca. 2.68-2.66 Ga Sedimentation : Ca. 2.65-2.63 Ga Closure Of The Burwash Basin : Post-2.63 Ga Turbidites :

K. Aerial photo of large scale, upright, fold structures in turbidites of the Yellowknife structural basin. Ca. 2.68-2.66 Ga Sedimentation : Post-2.63 Ga Turbidites

E. banded iron formation & D. fuchsitic* quartzite, & C. Basal quartz pebble conglomerate . . . all of the Central Slave Cover Group that overlies the basement complex. *Fuchsite is a green chromium rich variety of muscovite. The Cover Sequence : Ancient Basement Complex : Ca. 2.68-2.66 Ga Sedimentation :

I. Carbonate-cemented rhyolite breccia typical for the younger volcanic cycle. H. Polymict* conglomerate, including 10-30 cm granitoid cobbles, which occurs locally at the base of the younger, 2.69-2.66 Ga, volcanic cycle. *Depending on clast lithology, conglomerates are classified as oligomictic, petromictic, or polymictic. Ca. 2.73-2.70 Ga Tholeiitic Volcanism : Post-2.70 Ga Volcanism : Ca. 2.68-2.66 Ga Sedimentation : Post-2.63 Ga Turbidites

F. Variolitic* pillow basalts of the Kam Group, Yellowknife. *Variolites are a group of dark green basic igneous rocks that are most closely to basalts or diabases. On weathered surfaces, variolites appear pockmared due to pale colored spots, or spherules. The spots are typically grey, pale green, violet or yellowish, against dark green matrix of the rock.

G. Silicate facies iron formation interlayered with turbiditic greywackes, George Lake, northeastern Slave. This banded iron formation hosts significant epigenetic gold mineralization. Ca. 2.68-2.66 Ga Sedimentation : Post-2.63 Ga Turbidites

L. Late-tectonic conglomerates, less than 2600 Ma, unconformably overlying unroofed granitoid rocks, Point Lake.

M. Late-tectonic, 2585 Ma, K-feldspar megacrystic granite of the Morose Suite in the core of the domal Sleepy Dragon Complex; inset shows 1-2 cm-large K-feldspar megacrysts. 2.60-2.58 Ma, Final Orogenesis : Cratonization And Beyond

Natural Resources Canada > Earth Sciences Sector > Priorities > Geological Survey of Canada : Mineral Deposits of Canada : The Slave Craton: Geological and Metallogenic Evolution : Abstract : Introduction : Ancient Basement Complex : The Cover Sequence : Ca. 2.73-2.70 Ga Tholeiitic Volcanism : Post-2.70 Ga Volcanism : Ca. 2.68-2.66 Ga Sedimentation : Ca. 2.65-2.63 Ga Closure Of The Burwash Basin : Post-2.63 Ga Turbidites : 2.60-2.58 Ma, Final Orogenesis : Cratonization And Beyond : Summary : References : Table : Figures : Appendix : Mafic Dykes : Wecho River Outcrops : Diamonds/Kimberlites : Snare River Project : Southern Wopmay Orogen : Western Slave Study : Regional Metallogeny : Sekwi Mountain Project : Lac la Martre Aeromagnetic Survey :

satellite image courtesy of NASA, all images of geomorphologic features and lithology courtesy of Natural Resources Canada (source website)