Geology of Ontario hiking trails takes you back in time.

Test Post Elliot Lake

-part of Southern Province, consisting of early Proterozoic rocks, mainly sedimentary rocks, some volcanics
-extend 450 km along north shore of Lake Huron to Sudbury, then north to Rouyn Noranda
-rocks are between 2.45 to 2.22 bya
-four groups from bottom to top (oldest to youngest) are Elliot, Hough, Quirke, Cobalt Groups
-cyclical lithologies in all but Serpent Formation (Quirke Lk Gr.)
-bottom is matrix supported conglomerate (diamictite)
-middle is mudstone, siltstone or limestone
-top is sandstone, usually thick and cross-bedded
-paleocurrents from S to SE (SE predominant)

-no diamictite-mudstone-sandstone sequence
-contains uranium and the only volcanic rocks in the Huronian Supergroup
Livingston Creek Fm – 400m thick in Sault Ste Marie, 300m at Thessalon, none east of Quirke Syncline
-bottom is clast-supported polymictic conglomerate
– cobble to boulder sized clasts
– clasts mainly pale grey granitic
– some clasts of mafic plutonic & metamorphic rocks
– deposition on alluvial fan
-top is grey sandstone, well sorted, fine to medium-grain
– well crossbedded with carbonate along forset beds
– no mudstone or pebbly units within sandstone
– deposition by median streams flowing in fault bounded valley
– walls of Archean rocks partly covered by alluvial fans
Thessalon Fm. – Huronian volcanics west of nose of Quirke Syncline correlatable with Thessalon area volcanics
-evidence suggests only period of Huronian volcanism in the area
-probably same age as Copper Cliff Fm (2.45 bya)
-up to 820 m thick at Sault Ste Marie, 670 m at Thessalon, 1080 m at Bass Lake (Aberdeen Township)
-interpreted as continental flood basalt sequence associated with continental rifting
-source of lavas was upper mantle rather than deeper mantle or plume component
-passive rifting led to multiple episodes of uplift & melting (not active rifting which is one uplifting & melting event)
-lithospheric stretching causes mantle upwelling, leading to episodic partial melting and volcanism
-stretching evidenced by syndepositional faults (subsidence) up to 400 m in sediments below volcanics
-amydules (epidote, chlorite, calcite) are common, often in complex zonal arrangements
-pillow structures rare but observed in most areas
-scoriaceous flow-tops filled with mixture of quartz & grey-red secondary albite (Na-plagioclase feldspar)
-lower unit is complex/mixed member/lower lava series
– includes basaltic andesite, tholeiitic andesite, mugearite, hawaiite, rhyolite, basalt, komatiites
– found in Dollberry Lk, Pecors Lk and Thessalon areas
– volcanics of Quirke Lk Syncline are geochemically similar to Thessalon lower lavas
– eruptions from central vents
– different batches of magma underwent crustal contamination within the lower and/or upper crust
– andesites in lower lava series are darker coloured
-upper unit is tholeiitic basalt
– probably part of continental flood basalt sequence, similar to island arc basalts
– magma derived from upper mantle during subduction in Kenoran orogeny
– no crustal contamination in this sequence
– greenish grey fine to medium grained
-some sediments associated with Thessalon Fm. represent early Huronian period of erosion
– in Duncan Township of Thessalon <1m pyritic quartz-pebble conglomerate found in lower lavas
– conglomerate overlain by few metres of coarse-grained arkose
– congromerate often lies directly on Livingstone Cr. Fm.
– where no Livingstone Fm., conglomerate lies directly on Archean basement
– conglomerate-arkose is disconformity between Thesalon Fm. volcanics and Livingstone Fm.
Matinenda Fm. – host rocks to area uranium deposits: arenites & intercalated quarts pebble conglomerate (QPC)
-lies on Huronian volcanics and Archean basement
-at Elliot Lk 800 m thick, at Thessalon & Sault Ste. Marie 50 m thick (mainly subarkose, subwacke)
-at Houghton Twp. Matinenda Fm. lies on grey sandstone of Livingston Fm.
-med-coarse subarkose, arkos & grit (poorly sorted quartz and feldspar in green sericite matrix)
-QPC is well sorted, rounded pebbles & cobbles of quartz & chert set in pyrite rich matrix
-pebbly subarkose scattered throughout coarse arkose units (more common near base)
-arkosic units have crossbedding, scour & fill structures
-NW source for Matinenda sediments
-deposited from shallow braided streams flowing south over SE dipping topography (tilted on deposition)
-formed by intense weathering of granitic source terrain
-two uranium ore zones both trending southeast, Nordic (1.6 x 5.6 km) and Quirke (3.2 x 9 km)
-paleographic features of basement determined position and orientation of zones
-uraniferous QPC is well developed at base of Fm. & 45m above base within arkose
-radioactive minerals are uraninite, brannerite, uranothorite
-represent modified paleoplacer origin when there wasn’t significant free oxygen in atmosphere -extensive weathering of granitic terrain released quartz, pyrite, uraniferous minerals -SE flowing streams carried the pebbles and minerals
-deposited as SE trending units following basement topography
McKim Fm. – turbidite sequence of dark grey subarkosic wakes, mudstones, subarkoses, lithwacke, litharenite
-extends from Blind River to the Grenville Front
-0-100m thick on south limb of Quirke Lk syncline and missing on the north limb
-deposition by submarine turbidity currents
-graded beds, parallel laminations, ripple marks, cross-laminations, Bouma cycles
-north of Murray Fault McKim rarely a few metres thick, south of fault up to 2400m at Sudbury
-in west distal facies: laminated silstone
-in east proximal facies: greywacke…..more tectonic activity, source for seds in east
-marine transgression that gradually drowned the Matinenda fluvial plain

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