Tectonic delamination of the lower crust during Late Archean collision of the Abitibi—Opatica and Pontiac terranes, Superior Province, Canada

2006 ◽  
pp. 267-282 ◽  
Author(s):  
Keith Benn
Keyword(s):  
Lower Crust ◽  
Superior Province

The origin and history of the Kapuskasing structural zone, Ontario, Canada

1980 ◽  
Vol 17 (7) ◽  
pp. 866-875 ◽  
Author(s):  
Janet Watson
Keyword(s):  
Lower Crust ◽  
Bouguer Anomaly ◽  
Shear Zones ◽  
Superior Province ◽  
Dike Swarm ◽  
History Of ◽  
Dike Swarms ◽  
Relationship Of ◽  
The Relationship ◽  
Geochronological Evidence

Reexamination of geological, geophysical, and geochronological evidence suggests three principal conclusions. Firstly, the Kapuskasing line came into existence very shortly after the stabilization of the Superior Province. The upfaulting of strips of granulites and associated rocks, and probably the redistribution of densities in the lower crust responsible for the regional positive Bouguer anomaly, took place before the emplacement of the Matachewan dike swarm at ~2690 Ma. Secondly, relative movements along the line during this tectonic stage had an important sinistral transcurrent component and sinistral movements continued during the emplacement of the Matachewan swarm. Thirdly, displacements of various kinds took place on the Kapuskasing line during a number of later events spaced out over a period of more than 2000 Ma; some of their effects can be deduced from the relationship of regional dike swarms and of cratonic cover formations. These findings suggest that the Kapuskasing line did not originate as a rift structure. Analogies are seen with deep transcurrent shear zones of other continents.

scholarly journals The role of enigmatic deep crustal and upper mantle structures on Au and magmatic Ni-Cu-PGE-Cr mineralization in the Superior Province

2021 ◽  
Author(s):  
L B Harris ◽  
P Adiban ◽  
E Gloaguen
Keyword(s):  
Machine Learning ◽  
Fluid Flow ◽  
Lithospheric Mantle ◽  
Lower Crust ◽  
Numerical Models ◽  
Regional Metamorphism ◽  
Shear Zones ◽  
Superior Province ◽  
Upper Crust ◽  
Pge Mineralization

Aeromagnetic and ground gravity data for the Canadian Superior Province, filtered to extract long wavelength components and converted to pseudo-gravity, highlight deep, N-S trending regional-scale, rectilinear faults and margins to discrete, competent mafic or felsic granulite blocks (i.e. at high angles to most regional mapped structures and sub-province boundaries) with little to no surface expression that are spatially associated with lode ('orogenic') Au and Ni-Cu-PGE-Cr occurrences. Statistical and machine learning analysis of the Red Lake-Stormy Lake region in the W Superior Province confirms visual inspection for a greater correlation between Au deposits and these deep N-S structures than with mapped surface to upper crustal, generally E-W trending, faults and shear zones. Porphyry Au, Ni, Mo and U-Th showings are also located above these deep transverse faults. Several well defined concentric circular to elliptical structures identified in the Oxford Stull and Island Lake domains along the S boundary of the N Superior proto-craton, intersected by N- to NNW striking extensional fractures and/or faults that transect the W Superior Province, again with little to no direct surface or upper crustal expression, are spatially associated with magmatic Ni-Cu-PGE-Cr and related mineralization and Au occurrences. The McFaulds Lake greenstone belt, aka. 'Ring of Fire', constitutes only a small, crescent-shaped belt within one of these concentric features above which 2736-2733 Ma mafic-ultramafic intrusions bodies were intruded. The Big Trout Lake igneous complex that hosts Cr-Pt-Pd-Rh mineralization west of the Ring of Fire lies within a smaller concentrically ringed feature at depth and, near the Ontario-Manitoba border, the Lingman Lake Au deposit, numerous Au occurrences and minor Ni showings, are similarly located on concentric structures. Preliminary magnetotelluric (MT) interpretations suggest that these concentric structures appear to also have an expression in the subcontinental lithospheric mantle (SCLM) and that lithospheric mantle resistivity features trend N-S as well as E-W. With diameters between ca. 90 km to 185 km, elliptical structures are similar in size and internal geometry to coronae on Venus which geomorphological, radar, and gravity interpretations suggest formed above mantle upwellings. Emplacement of mafic-ultramafic bodies hosting Ni-Cr-PGE mineralization along these ringlike structures at their intersection with coeval deep transverse, ca. N-S faults (viz. phi structures), along with their location along the margin to the N Superior proto-craton, are consistent with secondary mantle upwellings portrayed in numerical models of a mantle plume beneath a craton with a deep lithospheric keel within a regional N-S compressional regime. Early, regional ca. N-S faults in the W Superior were reactivated as dilatational antithetic (secondary Riedel/R') sinistral shears during dextral transpression and as extensional fractures and/or normal faults during N-S shortening. The Kapuskasing structural zone or uplift likely represents Proterozoic reactivation of a similar deep transverse structure. Preservation of discrete faults in the deep crust beneath zones of distributed Neoarchean dextral transcurrent to transpressional shear zones in the present-day upper crust suggests a 'millefeuille' lithospheric strength profile, with competent SCLM, mid- to deep, and upper crustal layers. Mechanically strong deep crustal felsic and mafic granulite layers are attributed to dehydration and melt extraction. Intra-crustal decoupling along a ductile décollement in the W Superior led to the preservation of early-formed deep structures that acted as conduits for magma transport into the overlying crust and focussed hydrothermal fluid flow during regional deformation. Increase in the thickness of semi-brittle layers in the lower crust during regional metamorphism would result in an increase in fracturing and faulting in the lower crust, facilitating hydrothermal and carbonic fluid flow in pathways linking SCLM to the upper crust, a factor explaining the late timing for most orogenic Au. Results provide an important new dataset for regional prospectively mapping, especially with machine learning, and exploration targeting for Au and Ni-Cr-Cu-PGE mineralization. Results also furnish evidence for parautochthonous development of the S Superior Province during plume-related rifting and cannot be explained by conventional subduction and arc-accretion models.

Lateral crustal flow along discrete flat-lying lower crustal shear zones during Archean continent construction

2020 ◽  
Author(s):  
Graham Hill ◽  
Eric Roots ◽  
Ben Frieman ◽  
Jim Craven ◽  
Richard Smith ◽  
...  
Keyword(s):  
Gravitational Collapse ◽  
Lower Crust ◽  
Plate Tectonics ◽  
Shear Zones ◽  
Transitional Period ◽  
Superior Province ◽  
Near Surface ◽  
Low Resistivity ◽  
Crustal Shear Zones ◽  
Lower Crustal

<p>The nature of lithospheric evolution and style of the driving ‘tectonic’ processes occurring during Archean continent construction remain enigmatic. A significantly hotter thermal regime characterised the early Earth and was pervasive for much of the Archean. This resulted in construction of continents that were significantly weaker and unable to support the thick crustal sequences and topographies common to modern orogens. Gravitational collapse of these early continents may have occurred when deeper material became less dense by heating or partial melting and created a density contrast beyond the crustal competence and/or due to post-orogenic relaxation. Such a collapse could result in large scale horizontal spreading within the middle to lower crust and the development of lateral crustal flow along flat-lying shear zones producing fluid-deposited graphitic and metallic sulphide films at these depths, which, if preserved would produce broad scale quasi-horizontal mid-lower crustal low resistivity anomalies. Here we show 3D magnetotelluric resistivity models of the Archean Superior Province of Canada that reveal these types of anomalies that could represent lateral crustal flow in the middle to lower crust. Further, the magnetotelluric model shows narrow sub-vertical zones of low resistivity extending from the mid crust to the near surface, interpreted to represent remnant fluid pathways that potentially formed prior to gravitational collapse. These sub-vertical low resistivity features correlate spatially with crustal-scale deformation zones that potentially are host to hydrothermal ore deposits and abundant metasomatic mineral assemblages. The well preserved record of primary crustal amalgamation within the Superior Province of Canada with both features expected of autochthonous vertical ‘drip’ tectonics (sub-vertical fluid pathways) and allochthonous horizontal plate tectonics (flat-lying lower crustal shear zones) regimes, suggests a potential transitional period of tectonic evolution might have characterised the region during the late Archean.</p>

scholarly journals Lower-Crustal Xenoliths from Jurassic Kimberlite Diatremes, Upper Michigan (USA): Evidence for Proterozoic Orogenesis and Plume Magmatism in the Lower Crust of the Southern Superior Province

2012 ◽  
Vol 54 (3) ◽  
pp. 575-608 ◽  
Author(s):  
ROBERT E. ZARTMAN ◽  
PAMELA D. KEMPTON ◽  
JAMES B. PACES ◽  
HILARY DOWNES ◽  
IAN S. WILLIAMS ◽  
...  
Keyword(s):  
Lower Crust ◽  
Superior Province ◽  
Plume Magmatism ◽  
Crustal Xenoliths ◽  
Lower Crustal

Seismic properties of rock samples from the Pikwitonei granulite belt – God's Lake domain crustal cross section, Manitoba

1996 ◽  
Vol 33 (5) ◽  
pp. 757-768 ◽  
Author(s):  
David M. Fountain ◽  
Matthew H. Salisbury
Keyword(s):  
Cross Section ◽  
Wave Velocity ◽  
Acoustic Impedance ◽  
Lower Crust ◽  
Compressional Wave ◽  
Superior Province ◽  
Mafic Rocks ◽  
Wave Velocities ◽  
Granulite Belt ◽  
Felsic Rocks

Laboratory measurements of compressional and shear wave velocity to confining pressures of 600 MPa for a suite of representative samples collected from the Pikwitonei granulite belt and God's Lake domain, an Archean crustal cross section in the northwestern Superior Province, provide the basis of comparison of these terranes with the seismic characteristics of Archean lower crust. We found that felsic rocks in the Pikwitonei granulite belt and God's Lake domain, which make up the bulk of these terranes, have a similar average compressional wave velocity of 6.5 km/s at 600 MPa, indicating that felsic rocks show little velocity change across the amphibolite–granulite facies transition. Compressional wave velocities for mafic rocks from each terrane are between 7.1 and 7.3 km/s. Apparent Poisson's ratio ranges from 0.24 to 0.26 and 0.26 to 0.28 for felsic and mafic rocks, respectively. These velocity data compare favorably with data for similar lithologies from the Kapuskasing uplift. Using the relative abundances of the constituent lithologies, the weighted average compressional wave velocities of the God's Lake domain and Pikwitonei granulite belt at 600 MPa are 6.56 and 6.63 km/s, respectively. These values, coupled with velocity distribution functions based on the population statistics and relative abundance for each lithology, show that there is no correspondence between the seismic characteristics of the Pikwitonei granulite belt and typical Archean and Proterozoic lower crust. The average properties of the Pikwitonei granulite belt and God's Lake domain, however, correspond well with typical Archean and Proterozoic middle crust. This suggests that either the Pikwitonei granulite belt represents an extreme felsic end member of Archean lower crust or that the deepest levels of the Superior Province crust are not exposed in the Pikwitonei granulite belt. Similar distribution function diagrams for acoustic impedance show that the Pikwitonei granulite belt is characterized by high acoustic impedance contrasts, but the high-impedance component is low in abundance. If the strong reflections observed under the Pikwitonei granulite belt in recent Lithoprobe surveys are not due to other causes, such as favorably oriented bodies of metamorphosed banded iron formation, diabase, or rock units not exposed in this region but present at depth, then they are caused by surprisingly small volumes of mafic metavolcanic rocks.

Regional variation in paleomagnetic polarity of the Matachewan dyke swarm related to the Kapuskasing Structural Zone, Ontario

1990 ◽  
Vol 27 (2) ◽  
pp. 200-211 ◽  
Author(s):  
M. P. Bates ◽  
H. C. Halls
Keyword(s):  
Lower Crust ◽  
Regional Variation ◽  
Canadian Shield ◽  
Dyke Swarm ◽  
Published Data ◽  
Superior Province ◽  
The North ◽  
Paleomagnetic Pole ◽  
Abitibi Subprovince

The 2.45 Ga Matachewan dykes from the Abitibi Subprovince of the Canadian Shield yield a mean paleomagnetic pole of 42°N, 58°E (α95 = 3°; N (sites) = 36), which is a composite of new and previously published data. Domains of paleomagnetic polarity are defined: an area of dykes predominantly of reversed magnetization in the Abitibi Subprovince contrasts with an area of exclusively normal dykes to the north. The polarity domains are separated by faults related to the 1.95 Ga uplift and exposure of the lower crust in the Kapuskasing Structural Zone and therefore reflect Hudsonian age tectonics in the Archean Superior Province.

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