Simon Hanmer - Academia.edu (original) (raw)

Papers by Simon Hanmer

Abstract: Localization of flow in natural quartzo-feldspathic shear zones at granulite-facies tem... more Abstract: Localization of flow in natural quartzo-feldspathic shear zones at granulite-facies temperatures does not occur purely by dislocation creep and dynamic recrystallization. From a review of some natural shear zones, initial faulting focused along a pre-existing shear zone, and/or the boundary of a volume of relatively strong crust or lithosphere, guides emplacement of hot mantle-derived melts into the base of the crust, lleading to extensive melting. When crystallized, the sub-solidus piu tons represent a focused zone of thermally softened material, capable of deforming readily and developing the full range of crystal-plastic microstructures and fabrics associated with mylonitcs, contrasting with the intrusion-free wall rocks.

Geoscience Canada, 1990

Preliminary precise age determinations of tectonic and metamorphic events across a transect of th... more Preliminary precise age determinations of tectonic and metamorphic events across a transect of the Torngat Orogen have shown a time-span of 80 million years between the oldest synmetamorphic intrusions and the latest uplift of the orogen. Two tectonothermal peaks have been determined at 1844 Ma (eastern and central part of the transect) and at 1826 Ma (western part of the transect). Resume Les premiers resultats d'une etude geochronologique de l'orogene de Torngat, axee sur la datation precise d'evenements tectoniques et metamorphiques, ont montre qu'une duree de 80 millions annees (entre 1860 Ma et 1780 Ma) separe les premieres intrusions synmetamorphes de la surrection finale de la chaine. Deux "pics" de deformation et de metamorphisme ont ete determines a 1844 Ma (au centre et a l'est de la chaine) et a 1826 Ma (a l'ouest).

Earth-Science Reviews

Endogenic and exogenic models have been developed over the past 25 years to explain the developme... more Endogenic and exogenic models have been developed over the past 25 years to explain the development of extensive, pervasive, high aspect ratio troughs and graben-like structures ("ribbons") and short-to long-wavelength folds in tessera terrains, commonly associated with crustal plateaus on Venus. Many of the models are complex, and appear to be both internally contradictory and inconsistent with well-established geological principles. They are based on what amount to assumptions regarding (i) the secular evolution of crustal thickness, (ii) crustal mechanical homogeneity and isotropy, (iii) the mechanics of ribbon formation, and (iv) the relative timing of ribbons in the structural geological sequence of tessera terrains. On the basis of both theoretical and observational considerations, this contribution will suggest that coupling the formation of tessera ribbons to the emplacement of dyke swarms relatively late in the structural development of tessera terrains may provide a resolution for the apparent inconsistencies in those published models.

Canadian Journal of Earth Sciences

The northwestern boundary zone of the Central Metasedimentary Belt (Grenville Province) in the Ha... more The northwestern boundary zone of the Central Metasedimentary Belt (Grenville Province) in the Haliburton area (Ontario) is a stack of alternating tonalitic and syenitic crystalline thrust sheets, transported toward the northwest on out-of-sequence, upper amphibolite facies, ductile thrust zones during the Grenvillian Orogeny, at 1060 Ma, approximately 100 Ma after the initiation of thrusting in the underlying Central Gneiss Belt. Kinematics of the deformation are complex. Predominant northwestward thrusting was, at least partly, coeval with subordinate northeastward thrusting. Late synmetamorphic extensional shears cut both thrusts and thrust sheets. Minor late thrusting on discrete ductile shear zones postdates the extensional structures. Belts of mechanically weak pelite(?) appear to have localised the thrust sheets. Highly mobile marble behaved as a relatively low viscosity fluid during transport, able to intrude and erode more competent wall rock.

European Journal of Mineralogy

The upper deck of the 3.2-2.6 Ga East Athabasca mylonite triangle, northem Saskatchewan, Canada c... more The upper deck of the 3.2-2.6 Ga East Athabasca mylonite triangle, northem Saskatchewan, Canada consists predominantly of crustal rocks metamorphosed at conditions exceeding 15 kbar and l000oC. Mylonitic quartzofeldspathic gneisses and gneiss-hosted metabasite alike record these conditions. Temperature is constrained to at least 1000'C by homogenization thermometry of temary feldspars in the felsic gneisses and by gamet-clinopyroxene exchange thermometry in mafic rocks. Minimum pressure of 15 kbar is indicated by the presence of matrix kyanite in association with the high-temperature feldspars. Primary corundum in certain gamet-clinopyroxenites also indicates pressure of at least 15 kbar. Unusual mineral compositions such as Ti-rich muscovite, Cr-bearing kyanite, and possible zircon exsolution from rutile are found in several locations. Oriented rutile needles in garnet, interpreted as exsolution, are pervasive. The upper deck is a discrete metamorphic terrane, 400 km' in area and l0 km in thickness. Elevation of this terrane into juxtaposition and fusion with granulite-facies lower crustal mylonites occurred within a 2.6 Ga intracontinental strike-slip shear zone. The upper deck is one of the very few high-pressure crustal metamorphic provinces known in the Americas and at 2.6 Ga it is among the oldest such, worldwide.

Geoscience Canada, Jun 1, 2005

Thirty-nine speakers prepared analyses, focusing on key points identified in discussions at CGC-s... more Thirty-nine speakers prepared analyses, focusing on key points identified in discussions at CGC-sponsored Council of Presidents meetings in November 2003 and May 2004, which concluded that we need to establish a better sense of community, awareness of activity and priorities, and a more unified 63

Tectonophysics, 1988

Hanmer, S., 1988. Great Slave Lake Shear Zone, Canadian Shield: reconstructed vertical profile of... more Hanmer, S., 1988. Great Slave Lake Shear Zone, Canadian Shield: reconstructed vertical profile of a crustal-scale fault mne. Tecionophysics, 149: 245-264. The Great Slave Lake Shear Zone (GSLSZ) of the northwestern Canadian Shield, a 25 km wide, early Proterozoic, transcurrent, dextral, mylonite zone, is a type example of a crustal-scale fault zone profile. With time: (1) the metamorphic grade decreased from granulite to greenschist facies; (2) the locus of high strain narrowed and jumped laterally, abandoning relatively older mylonites. Progressively younger mylonites represent both cooler temperatures and lower pressures; thus the sequence of narrowing mylonite belts represents a series of progressively shallower seated sections through the GSLSZ, (3) deformation evolved through the brittle-ductile transition, initially producing non~d~ation~ penetrative breecias, followed first by discrete non-rations faulting and subs~uently by dilational, quartz "stc=ckworks". Developing crustal-scale shear zones grow to an optimum width dictated by the requirement of minimum geologically reasonable strain rates for given conditions of wall rock rheology and displacement rate. Independent of variations in relative plate motion, mature shear zones change width and migrate laterally as a function of inferred thermally activated rheological changes witbin the wall rocks.

Tectonophysics, 2000

Seven accretionary sutures, formed between 1.16 and 1.03 Ga, have been identified by different au... more Seven accretionary sutures, formed between 1.16 and 1.03 Ga, have been identified by different authors in the Ontario-Quebec-Adirondack (OQA) segment of the Mesoproterozoic Grenville orogen in Canada. With one exception, the inferred accretionary terrane boundaries lie within, or at the margins of the Central Metasedimentary Belt (CMB), located between the Central Gneiss Belt and the Adirondack Highlands (Central Granulite Terrane). However, geological, geochronological, and petrological data suggest that the Grenville orogen on both sides of the proposed terrane boundaries (sutures) preserves a common 1.4-1.03 Ga tectonomagmatic history, inconsistent with its origin as a post-1.4 Ga collage of exotic tectonic blocks. Features which straddle the proposed 1.16-1.03 Ga 'sutures', from the Central Gneiss Belt, via the Adirondack Highlands, to the Mauricie area, include: (1) Mesoproterozoic continental crust (1.5-1.4 Ga) forming the host and/or basement to younger magmatic and supracrustal suites. (2) A 1.35-1.3 Ga continental arc, remnants of which occur from the CMB boundary zone (CMBBZ) in Ontario to the Appalachians in the United States, built on the 1.5-1.4 Ga continental crust. (3) Intrusions of 1.17-1.13 Ga age in the Central Gneiss Belt (mafic suite), and the Adirondack Highlands and their Quebec extension (AMCG suite, i.e. anorthosite massifs and related granitoids). (4) Relics of 1.18-1.14 Ga sedimentary basins in the northwestern CMB and the Mauricie area. We propose that an alternative model can adequately account for the observed geology of this part of the Grenville orogen wherein, the rocks of the OQA segment were part of an Andean-type margin between 1.4 and 1.2 Ga. At 1.35-1.3 Ga, a continental magmatic arc was built upon the southeastern margin of Laurentia represented by the 1.5-1.4 Ga Mesoproterozoic continental crust. The arc split at 1.3 Ga forming an ensialic back arc basin, relics of which now occur in the northwestern part of the CMB, and the back arc basin was flanked to the southeast by an active 1.28-1.25 Ga arc. Collision between the Laurentian margin and another continent (Amazonia?) occurred at 1.2 Ga, resulting in closure of the back arc basin and initiation of thrusting along the CMBBZ. Post-collisional lithospheric shortening led to convective removal of thickened subcontinental lithosphere, upper mantle melting, and extension of the overlying crust, resulting in widespread magmatic activity at 1.17-1.13 Ga, including emplacement of the AMCG massifs. Crustal extension generated sedimentary basins now represented by the St Boniface sediments in the Mauricie area (1.18 to between 1.15 and 1.09 Ga), and the penecontemporaneous Flinton Group in the northwestern CMB. Renewed, post-collisional, granulite facies shortening commenced at 1.12 Ga, manifested as

Precambrian Research, 2006

Rocks exposed in the MacQuoid-Gibson Lakes region, northwest Hearne subdomain, western Churchill ... more Rocks exposed in the MacQuoid-Gibson Lakes region, northwest Hearne subdomain, western Churchill Province, Canada comprise three major lithotectonic assemblages: the Principal volcanic belt; the metasedimentary MacQuoid homocline and; the Cross Bay plutonic complex. Neoarchaean supracrustal rocks of the belt range in age from <2745 to <2672 Ma and were intruded during the interval <2689 to 2655 Ma by diverse plutonic units ranging from gabbro through syenogranite, but greatly dominated by tonalite. Volcanic rocks occur only in the Principal volcanic belt and the MacQuoid homocline, are metamorphosed to amphibolite facies and vary from rare pillowed to common massive basalt and andesite, intercalated with less abundant, thin, dacitic to rhyolitic tuffs, lavas and volcaniclastic rocks. Basalt and andesite are dominated by subalkaline, FeO T-rich tholeiites with less common calc-alkaline rocks with higher SiO 2 contents and variable trace element contents. Felsic volcanic rocks exhibit calc-alkaline affinities and similarly diverse trace element abundances. The diverse trace element chemistry of the basalt and andesite supports their derivation from a heterogeneous mantle source(s) capable of generating MORB-, Arc-, BABB-and boninite-like rocks. Two geochemically distinct, arc-like suites were generated through contamination of the primary mantle-derived magmas either via assimilation of lower or middle tonalitic crust, or through contamination of their mantle source through subduction. Geochemical features of the felsic volcanic rocks indicate that these formed via both anatexis of crust in the amphibolite ± garnet stability field and via fractionation of more primitive progenitors in mid-upper crustal magma chambers. Nd t = 2680 Ma isotopic compositions cluster near depleted mantle, indicating that significant incorporation of older, >2700 Ma crust likely did not occur. Nd t = 2680 Ma values for three specimens, one from each of the Arc-like suites and one BABB-like basalt are slightly lower than the remainder, suggesting very minor incorporation of slightly older crust. These features imply that the processes that generated the MacQuoid supracrustal belt required simultaneous tapping of geochemically distinct mantle reservoirs with concomitant anatexis of sialic crust (garnet stability field) and fractionation of felsic magmas in upper crustal magma chambers. Shallow water deposition of abundant volcaniclastic rocks and semipelite along with minor conglomerate and quartzite was broadly contemporaneous with this magmatism. We envisage a geodynamic setting characterized by tectonomagmatic processes similar to those of modern supra-subduction zone back-arc marginal basins such as the Sea of Japan. Therein, an extensional, back-arc setting, likely proximal to continental crust, provides an explanation for a broad swath of diverse mantle-derived rocks intercalated with less common felsic rocks as well as an abundance of immature clastic metasedimentary rocks.

Precambrian Research, 2006

In the western Churchill Province, Canadian Shield, Neoarchean supracrustal and plutonic rocks, i... more In the western Churchill Province, Canadian Shield, Neoarchean supracrustal and plutonic rocks, intruded by Paleoproterozoic mafic dykes and granitic rocks, comprise the MacQuoid supracrustal belt and the structurally overlying Cross Bay plutonic complex. They form part of the northwestern Hearne subdomain that occupies an intermediate position between the continental Rae domain to the north and west, and the oceanic central Hearne subdomain to the south and east. New geological mapping and supporting geoscience are compatible with the presence of 2550-2500 Ma, southeast-directed, mid-crustal, thickskinned thrusting that juxtaposed the plutonic complex over the supracrustal belt. The structural contact between the MacQuoid supracrustal belt and the Cross Bay plutonic complex potentially represents a fundamental boundary between isotopically distinct crustal blocks. The ∼2190 Ma MacQuoid mafic dyke swarm cuts across Neoarchean deformation fabrics, but records ∼1.9 Ga, deep-crustal, regional metamorphism that affected both the supracrustal belt and the plutonic complex. Other Paleoproterozoic deformation events that occurred at ∼1850-1810 Ma are of local extent and appear to be relatively minor manifestations of more important events elsewhere, related to the Trans-Hudson orogen.

Abstract: Localization of flow in natural quartzo-feldspathic shear zones at granulite-facies tem... more Abstract: Localization of flow in natural quartzo-feldspathic shear zones at granulite-facies temperatures does not occur purely by dislocation creep and dynamic recrystallization. From a review of some natural shear zones, initial faulting focused along a pre-existing shear zone, and/or the boundary of a volume of relatively strong crust or lithosphere, guides emplacement of hot mantle-derived melts into the base of the crust, lleading to extensive melting. When crystallized, the sub-solidus piu tons represent a focused zone of thermally softened material, capable of deforming readily and developing the full range of crystal-plastic microstructures and fabrics associated with mylonitcs, contrasting with the intrusion-free wall rocks.

Geoscience Canada, 1990

Preliminary precise age determinations of tectonic and metamorphic events across a transect of th... more Preliminary precise age determinations of tectonic and metamorphic events across a transect of the Torngat Orogen have shown a time-span of 80 million years between the oldest synmetamorphic intrusions and the latest uplift of the orogen. Two tectonothermal peaks have been determined at 1844 Ma (eastern and central part of the transect) and at 1826 Ma (western part of the transect). Resume Les premiers resultats d'une etude geochronologique de l'orogene de Torngat, axee sur la datation precise d'evenements tectoniques et metamorphiques, ont montre qu'une duree de 80 millions annees (entre 1860 Ma et 1780 Ma) separe les premieres intrusions synmetamorphes de la surrection finale de la chaine. Deux "pics" de deformation et de metamorphisme ont ete determines a 1844 Ma (au centre et a l'est de la chaine) et a 1826 Ma (a l'ouest).

Earth-Science Reviews

Endogenic and exogenic models have been developed over the past 25 years to explain the developme... more Endogenic and exogenic models have been developed over the past 25 years to explain the development of extensive, pervasive, high aspect ratio troughs and graben-like structures ("ribbons") and short-to long-wavelength folds in tessera terrains, commonly associated with crustal plateaus on Venus. Many of the models are complex, and appear to be both internally contradictory and inconsistent with well-established geological principles. They are based on what amount to assumptions regarding (i) the secular evolution of crustal thickness, (ii) crustal mechanical homogeneity and isotropy, (iii) the mechanics of ribbon formation, and (iv) the relative timing of ribbons in the structural geological sequence of tessera terrains. On the basis of both theoretical and observational considerations, this contribution will suggest that coupling the formation of tessera ribbons to the emplacement of dyke swarms relatively late in the structural development of tessera terrains may provide a resolution for the apparent inconsistencies in those published models.

Canadian Journal of Earth Sciences

The northwestern boundary zone of the Central Metasedimentary Belt (Grenville Province) in the Ha... more The northwestern boundary zone of the Central Metasedimentary Belt (Grenville Province) in the Haliburton area (Ontario) is a stack of alternating tonalitic and syenitic crystalline thrust sheets, transported toward the northwest on out-of-sequence, upper amphibolite facies, ductile thrust zones during the Grenvillian Orogeny, at 1060 Ma, approximately 100 Ma after the initiation of thrusting in the underlying Central Gneiss Belt. Kinematics of the deformation are complex. Predominant northwestward thrusting was, at least partly, coeval with subordinate northeastward thrusting. Late synmetamorphic extensional shears cut both thrusts and thrust sheets. Minor late thrusting on discrete ductile shear zones postdates the extensional structures. Belts of mechanically weak pelite(?) appear to have localised the thrust sheets. Highly mobile marble behaved as a relatively low viscosity fluid during transport, able to intrude and erode more competent wall rock.

European Journal of Mineralogy

The upper deck of the 3.2-2.6 Ga East Athabasca mylonite triangle, northem Saskatchewan, Canada c... more The upper deck of the 3.2-2.6 Ga East Athabasca mylonite triangle, northem Saskatchewan, Canada consists predominantly of crustal rocks metamorphosed at conditions exceeding 15 kbar and l000oC. Mylonitic quartzofeldspathic gneisses and gneiss-hosted metabasite alike record these conditions. Temperature is constrained to at least 1000'C by homogenization thermometry of temary feldspars in the felsic gneisses and by gamet-clinopyroxene exchange thermometry in mafic rocks. Minimum pressure of 15 kbar is indicated by the presence of matrix kyanite in association with the high-temperature feldspars. Primary corundum in certain gamet-clinopyroxenites also indicates pressure of at least 15 kbar. Unusual mineral compositions such as Ti-rich muscovite, Cr-bearing kyanite, and possible zircon exsolution from rutile are found in several locations. Oriented rutile needles in garnet, interpreted as exsolution, are pervasive. The upper deck is a discrete metamorphic terrane, 400 km' in area and l0 km in thickness. Elevation of this terrane into juxtaposition and fusion with granulite-facies lower crustal mylonites occurred within a 2.6 Ga intracontinental strike-slip shear zone. The upper deck is one of the very few high-pressure crustal metamorphic provinces known in the Americas and at 2.6 Ga it is among the oldest such, worldwide.

Geoscience Canada, Jun 1, 2005

Thirty-nine speakers prepared analyses, focusing on key points identified in discussions at CGC-s... more Thirty-nine speakers prepared analyses, focusing on key points identified in discussions at CGC-sponsored Council of Presidents meetings in November 2003 and May 2004, which concluded that we need to establish a better sense of community, awareness of activity and priorities, and a more unified 63

Tectonophysics, 1988

Hanmer, S., 1988. Great Slave Lake Shear Zone, Canadian Shield: reconstructed vertical profile of... more Hanmer, S., 1988. Great Slave Lake Shear Zone, Canadian Shield: reconstructed vertical profile of a crustal-scale fault mne. Tecionophysics, 149: 245-264. The Great Slave Lake Shear Zone (GSLSZ) of the northwestern Canadian Shield, a 25 km wide, early Proterozoic, transcurrent, dextral, mylonite zone, is a type example of a crustal-scale fault zone profile. With time: (1) the metamorphic grade decreased from granulite to greenschist facies; (2) the locus of high strain narrowed and jumped laterally, abandoning relatively older mylonites. Progressively younger mylonites represent both cooler temperatures and lower pressures; thus the sequence of narrowing mylonite belts represents a series of progressively shallower seated sections through the GSLSZ, (3) deformation evolved through the brittle-ductile transition, initially producing non~d~ation~ penetrative breecias, followed first by discrete non-rations faulting and subs~uently by dilational, quartz "stc=ckworks". Developing crustal-scale shear zones grow to an optimum width dictated by the requirement of minimum geologically reasonable strain rates for given conditions of wall rock rheology and displacement rate. Independent of variations in relative plate motion, mature shear zones change width and migrate laterally as a function of inferred thermally activated rheological changes witbin the wall rocks.

Tectonophysics, 2000

Seven accretionary sutures, formed between 1.16 and 1.03 Ga, have been identified by different au... more Seven accretionary sutures, formed between 1.16 and 1.03 Ga, have been identified by different authors in the Ontario-Quebec-Adirondack (OQA) segment of the Mesoproterozoic Grenville orogen in Canada. With one exception, the inferred accretionary terrane boundaries lie within, or at the margins of the Central Metasedimentary Belt (CMB), located between the Central Gneiss Belt and the Adirondack Highlands (Central Granulite Terrane). However, geological, geochronological, and petrological data suggest that the Grenville orogen on both sides of the proposed terrane boundaries (sutures) preserves a common 1.4-1.03 Ga tectonomagmatic history, inconsistent with its origin as a post-1.4 Ga collage of exotic tectonic blocks. Features which straddle the proposed 1.16-1.03 Ga 'sutures', from the Central Gneiss Belt, via the Adirondack Highlands, to the Mauricie area, include: (1) Mesoproterozoic continental crust (1.5-1.4 Ga) forming the host and/or basement to younger magmatic and supracrustal suites. (2) A 1.35-1.3 Ga continental arc, remnants of which occur from the CMB boundary zone (CMBBZ) in Ontario to the Appalachians in the United States, built on the 1.5-1.4 Ga continental crust. (3) Intrusions of 1.17-1.13 Ga age in the Central Gneiss Belt (mafic suite), and the Adirondack Highlands and their Quebec extension (AMCG suite, i.e. anorthosite massifs and related granitoids). (4) Relics of 1.18-1.14 Ga sedimentary basins in the northwestern CMB and the Mauricie area. We propose that an alternative model can adequately account for the observed geology of this part of the Grenville orogen wherein, the rocks of the OQA segment were part of an Andean-type margin between 1.4 and 1.2 Ga. At 1.35-1.3 Ga, a continental magmatic arc was built upon the southeastern margin of Laurentia represented by the 1.5-1.4 Ga Mesoproterozoic continental crust. The arc split at 1.3 Ga forming an ensialic back arc basin, relics of which now occur in the northwestern part of the CMB, and the back arc basin was flanked to the southeast by an active 1.28-1.25 Ga arc. Collision between the Laurentian margin and another continent (Amazonia?) occurred at 1.2 Ga, resulting in closure of the back arc basin and initiation of thrusting along the CMBBZ. Post-collisional lithospheric shortening led to convective removal of thickened subcontinental lithosphere, upper mantle melting, and extension of the overlying crust, resulting in widespread magmatic activity at 1.17-1.13 Ga, including emplacement of the AMCG massifs. Crustal extension generated sedimentary basins now represented by the St Boniface sediments in the Mauricie area (1.18 to between 1.15 and 1.09 Ga), and the penecontemporaneous Flinton Group in the northwestern CMB. Renewed, post-collisional, granulite facies shortening commenced at 1.12 Ga, manifested as

Precambrian Research, 2006

Rocks exposed in the MacQuoid-Gibson Lakes region, northwest Hearne subdomain, western Churchill ... more Rocks exposed in the MacQuoid-Gibson Lakes region, northwest Hearne subdomain, western Churchill Province, Canada comprise three major lithotectonic assemblages: the Principal volcanic belt; the metasedimentary MacQuoid homocline and; the Cross Bay plutonic complex. Neoarchaean supracrustal rocks of the belt range in age from <2745 to <2672 Ma and were intruded during the interval <2689 to 2655 Ma by diverse plutonic units ranging from gabbro through syenogranite, but greatly dominated by tonalite. Volcanic rocks occur only in the Principal volcanic belt and the MacQuoid homocline, are metamorphosed to amphibolite facies and vary from rare pillowed to common massive basalt and andesite, intercalated with less abundant, thin, dacitic to rhyolitic tuffs, lavas and volcaniclastic rocks. Basalt and andesite are dominated by subalkaline, FeO T-rich tholeiites with less common calc-alkaline rocks with higher SiO 2 contents and variable trace element contents. Felsic volcanic rocks exhibit calc-alkaline affinities and similarly diverse trace element abundances. The diverse trace element chemistry of the basalt and andesite supports their derivation from a heterogeneous mantle source(s) capable of generating MORB-, Arc-, BABB-and boninite-like rocks. Two geochemically distinct, arc-like suites were generated through contamination of the primary mantle-derived magmas either via assimilation of lower or middle tonalitic crust, or through contamination of their mantle source through subduction. Geochemical features of the felsic volcanic rocks indicate that these formed via both anatexis of crust in the amphibolite ± garnet stability field and via fractionation of more primitive progenitors in mid-upper crustal magma chambers. Nd t = 2680 Ma isotopic compositions cluster near depleted mantle, indicating that significant incorporation of older, >2700 Ma crust likely did not occur. Nd t = 2680 Ma values for three specimens, one from each of the Arc-like suites and one BABB-like basalt are slightly lower than the remainder, suggesting very minor incorporation of slightly older crust. These features imply that the processes that generated the MacQuoid supracrustal belt required simultaneous tapping of geochemically distinct mantle reservoirs with concomitant anatexis of sialic crust (garnet stability field) and fractionation of felsic magmas in upper crustal magma chambers. Shallow water deposition of abundant volcaniclastic rocks and semipelite along with minor conglomerate and quartzite was broadly contemporaneous with this magmatism. We envisage a geodynamic setting characterized by tectonomagmatic processes similar to those of modern supra-subduction zone back-arc marginal basins such as the Sea of Japan. Therein, an extensional, back-arc setting, likely proximal to continental crust, provides an explanation for a broad swath of diverse mantle-derived rocks intercalated with less common felsic rocks as well as an abundance of immature clastic metasedimentary rocks.

Precambrian Research, 2006

In the western Churchill Province, Canadian Shield, Neoarchean supracrustal and plutonic rocks, i... more In the western Churchill Province, Canadian Shield, Neoarchean supracrustal and plutonic rocks, intruded by Paleoproterozoic mafic dykes and granitic rocks, comprise the MacQuoid supracrustal belt and the structurally overlying Cross Bay plutonic complex. They form part of the northwestern Hearne subdomain that occupies an intermediate position between the continental Rae domain to the north and west, and the oceanic central Hearne subdomain to the south and east. New geological mapping and supporting geoscience are compatible with the presence of 2550-2500 Ma, southeast-directed, mid-crustal, thickskinned thrusting that juxtaposed the plutonic complex over the supracrustal belt. The structural contact between the MacQuoid supracrustal belt and the Cross Bay plutonic complex potentially represents a fundamental boundary between isotopically distinct crustal blocks. The ∼2190 Ma MacQuoid mafic dyke swarm cuts across Neoarchean deformation fabrics, but records ∼1.9 Ga, deep-crustal, regional metamorphism that affected both the supracrustal belt and the plutonic complex. Other Paleoproterozoic deformation events that occurred at ∼1850-1810 Ma are of local extent and appear to be relatively minor manifestations of more important events elsewhere, related to the Trans-Hudson orogen.