Transcript Superior Province Projects: Synthesis

Crustal Thickness, variation
• 36-46 km (~42 km avg)
• paleothickness > by 6-20 km
• local Proterozoic (1.9 Ga) thickening
(Kapuskasing)
• local Proterozoic thinning (1.1 Ga)
• no correlation with surface tectonic
elements
• generally flat Moho
• local evidence for subduction scars at Moho
Crustal structure, velocity,
reflectivity
• Layered crust 6.9-7.5 km/s at base; >5.2
km/s at top
• low-dipping reflectivity below 10 km
• consistent gentle N dips
• steep faults sole into mid-crustal
subhorizontal reflectors
• Moho imbrication
Reflection Interpretation:
Western Superior Transect
Mantle lithosphere structure,
composition
• ca. 300 km-thick lithosphere
• high velocity (<8.8 km/s), anisotropic
shallow mantle
• depleted composition
• mantle domains recognized through
differences in seismic, electrical anisotropy
• NW Superior vs SW Superior
Magnetotelluric
Nature and age of
microcontinental fragments
• At least 7 independent Mesoarchean
fragments recognized
• variably reworked by Neoarchean (2.752.70 Ga) magmatism
• Nd isotopes (700 analyses), inherited
zircons (hundreds of observations)
Nature and style of Rifting
• thin quartz arenite, conglomerate, shale, carbonate,
BIF, volcanics (komatiite & tholeiite)
• local provenance
• tidal, platform, submarine fan
• some = rifting, ocean opening
• others = small platforms
Nature and Age of Accreted
Oceanic Rocks
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Plateau (rare MORB) basement
calc-alkaline edifices
arc-plume interactions
isotopically juvenile (εNd +5 to +2)
up to 25 km of section
juvenile tonalites
2745-2700 Ma
Nature and Age of Continental
Magmatic arcs
• N. Quebec: 2785-2700 Ma ton-gdi +/charnockitic vertical sheets ca. 5 kb
crystallization P
• W. Superior: multiple ca. 2745-2710 Ma
plutons, horizontal sheets ca. 4 kb
crystallization P
• prelude to continent-continent; oceancontinent collisions
Nature and Style of Postcollisional processes
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sanukitoid, alkaline, carbonatite magmatism
dextral transpression
granite “bloom” 2680-2660 Ma
deep crustal extension, metamorphism
peneplaned by 2480 Ma
Proterozoic dykes
local Laramide-style intracratonic uplifts
Keweenawan rift; alkaline magmatism