Superior Province Research Articles

Correction to: Petrogenesis and Geodynamic Evolution of the Archean Shawmere Anorthosite Complex and Associated Gneisses, Kapuskasing Uplift, Superior Province, Canada

Correction to: Petrogenesis and Geodynamic Evolution of the Archean Shawmere Anorthosite Complex and Associated Gneisses, Kapuskasing Uplift, Superior Province, Canada

Crustal and uppermost mantle structures of the North American Midcontinent Rift revealed by joint full-waveform inversion of ambient-noise data and teleseismic P waves

Crustal and uppermost mantle structures of the North American Midcontinent Rift revealed by joint full-waveform inversion of ambient-noise data and teleseismic P waves

Testing the TTG–Metabasite Connection in the Southern Superior Province: an Integrated Geochemical, Isotopic, and Petrogenetic Modelling Approach

Abstract Archean cratons are dominated by tonalite–trondhjemite–granodiorite (TTG) suites, the products of crustal differentiation that formed early continental crust. These rocks may have been primarily generated by partial melting of hydrated basaltic crust in a variety of settings including subduction zones or the deep lithosphere. Sources are mainly inferred from examination of TTGs alone, as potential source rocks are rarely exposed. In the southern Superior Province, Canada, the Kapuskasing Uplift exposes an important crustal cross-section with upper- to middle-crustal TTGs and lower-crustal metabasites, which show evidence of having produced trondhjemitic anatectic melt. Here, we test the hypothesis that these metabasites were the source of the Mesoarchean to Neoarchean TTGs in the Kapuskasing Uplift by combining phase equilibrium and melt trace element modelling with whole-rock and zircon Lu–Hf isotope analysis and geochronology (garnet Lu–Hf and zircon U–Pb) of metabasic samples. By comparison of the results with existing data from TTGs in the Kapuskasing Uplift, we determined that the metabasites are plausible source rocks for the TTGs. The Lu–Hf systematics of the metabasites and TTGs are the most robust evidence of a genetic connection. Modelling results support an increase in TTG source depth over time. New geochronological data constrain partial melting of metabasite and crystallization of anatectic melt between ca. 2685 Ma and ca. 2600 Ma, coeval with crystallization of only the youngest TTGs. Overall, these results indicate a complex history of intracrustal differentiation in the Kapuskasing Uplift, with partial melting of two isotopically distinct lower-crustal metabasic sources at different times and depths.

Petrogenesis and Geodynamic Evolution of the Archean Shawmere Anorthosite Complex and Associated Gneisses, Kapuskasing Uplift, Superior Province, Canada

Abstract In this study, we integrated extensive field, petrographic, whole-rock major and trace element, and Nd–Pb–Sr–O isotope, and zircon U–Pb ages, trace element and Lu–Hf isotope data from the Neoarchean Shawmere Anorthosite Complex and surrounding gneisses to unravel their petrogenetic origin and tectonic history. The ~2765 Ma Shawmere Anorthosite Complex is interpreted to have been emplaced into a sequence of interlayered greywacke and basalt deposited in an intra-continental arc rift system above a north-dipping subduction zone. The complex consists mainly of anorthosite, leucogabbro, gabbro, and hornblendite that were emplaced as several batches of magmas and crystal mushes originating from sub-arc mantle sources. In contrast to the previous studies, our field and petrographic data suggest an igneous origin for the most hornblende in the complex, implying hydrous parental magmas. A hydrous magma origin is also consistent with the high-anorthite content (mostly 70–90%) of the plagioclase in the complex. Percolation of hydrous basaltic melts through gabbroic cumulates in crustal magma chambers led to extensive (>50%) replacement of igneous clinopyroxene by igneous hornblende. Continued subduction resulted in the closure of the intra-arc rift system and the intrusion of the complex by tonalite, granodiorite and diorite between 2765 and 2680 Ma in an Andean-type margin. The complex and surrounding gneisses underwent hornblende granulite-facies metamorphism mainly between 2680 and 2620 Ma, overlapping with mid-crustal east-west extension between 2660 and 2640 Ma. The granulite-facies metamorphism is recorded by the replacement of hornblende, plagioclase and clinopyroxene by garnet and the development of a garnet-orthopyroxene-plagioclase metamorphic assemblage with a granoblastic texture. Tectonic rebounding of mid-crustal rocks to upper crustal levels after 2620 Ma led to the formation of an extensive network of extensional fractures and retrograde metamorphism. Migration of CO2-rich hydrous fluids along the extensional fractures and grain boundaries resulted in the precipitation of many metasomatic minerals mainly at the expense of hornblende and plagioclase, including epidote, clinozoisite, tremolite, actinolite, paragonite, margarite, titanite, quartz, calcite, sillimanite, dolomite, and chlorite. Prevalent replacement of hornblende by garnet during prograde metamorphism and metasomatic replacement of hornblende and plagioclase by retrograde mineral assemblages disturbed the Sm–Nd, U–Th–Pb, and Rb–Sr isotope systems.

Quartz arenites as signatures of cratonisation: examples from the Archaean Stratigraphic Record, southern Africa

Abstract Holocene quartz-rich sands such as in the Orinoco River of Venezuela and Columbia, develop under a unique set of conditions including tectonic stability, intense weathering and long-term storage of sediment prior to burial. This review paper proposes that a similar set of conditions existed on the Mesoarchaean Earth by 3.0 Ga. Compositionally and texturally mature quartz arenites are present in the Mesoarchaean Hospital Hill Subgroup and correlative lower Mozaan Group, in the cover rocks of the Beitbridge Complex in the Limpopo Belt and at Buhwa in southern Zimbabwe as well as the Neoarchaean Manjeri Formation of Zimbabwe. These quartz arenites are interpreted as first-cycle and developed following the formation of stable cratons under conditions of slow subsidence (<10 cm/1 000 years), intense weathering in a hostile chemical environment related to the ambient carbon dioxide-rich atmosphere, long-distance intrabasinal transport by tides and/or waves and microbial processes that influenced the local chemical environment. Similar examples of Mesoarchaean quartz arenites are documented from the Yilgarn Block in Western Australia, the Slave and Superior provinces in Canada and the Dharwar and Singhbhum cratons in India. On a global scale, cratonisation was diachronous with the Kaapvaal Craton stabilised on a regional scale by 3.0 Ga whereas microcontinents existed over the remainder of Earth.

Characterization and Timing of Mineralization in the Garrison Gold District, Southern Abitibi Greenstone Belt, Canada

Abstract The decrease in gold discoveries is affecting the deployment of new technology and the general society demand, demonstrating the need for new gold exploration approaches. To date, gold exploration remains primarily focused in areas near well-known large gold districts. We demonstrate the potential for new discoveries and significant resource expansion in the Abitibi greenstone belt distal from the giant gold districts across the belt. Unlocking of additional resources in the Garrison district was accomplished by identification of zones of compentency contrast, which resulted in a variety of locally complex and unrecognized structural traps receptive to gold. Our approach is applicable to other little-explored areas in the Abitibi greenstone belt and other orogenic belts worldwide. The Garrison district, situated in the southern part of the Abitibi greenstone belt in the Superior province, lies along an ~3-km NE-trending segment of the gold-rich, Archean Porcupine-Destor deformation zone. The district contains several discoveries, which include the Buffonta deposit hosted in mafic volcanic rocks, the syenite-hosted 903 deposit, and the albitite dike-hosted Jonpol deposit. These deposits occur along high-strain zones developed in embayments and elongate, NE-trending domains of talc-chlorite-serpentine–altered ultramafic rocks, which localized strands and splays of the Porcupine-Destor deformation zone. In addition, the Garrcon deposit comprises northerly-trending gold-bearing quartz veins and lamprophyre dike swarms hosted in sedimentary host rocks that are bounded by high-strain zones. The intrusive rocks in all of these deposits were emplaced prior to gold deposition. They provided a competent substrate in areas of heterogeneous strain that localized gold mineralization. Initial alteration made the surrounding volcanic and sedimentary rocks also rheologically competent. This resulted in enhanced hydrofracturing and the formation of paragenetically late gold-bearing quartz veins. Widespread albite-pyrite-carbonate alteration in all of the gold deposits temporally overlapped with gold mineralization. New U-Pb zircon geochronology data reveal that ~2719 to 2712 Ma volcanism was followed by granitic magmatism and emplacement of a series of ~2683 to 2672 Ma dikes. One Re-Os analysis of a synmineralization molybdenite sample indicates that orogenic gold was deposited at 2671 ± 12 Ma. This is comparable to published ages of major orogenic gold deposits throughout the southern part of the Abitibi greenstone belt, indicating a broadly synchronous principal gold event across the belt.

New U-Pb zircon tuff ages and revised stratigraphic correlations in the Superior craton during the Great Oxidation Episode

New U-Pb zircon tuff ages and revised stratigraphic correlations in the Superior craton during the Great Oxidation Episode

Polyphase formation of a Neoarchean auriferous fault zone network in the Michipicoten greenstone belt, southern Superior craton

Correlating structurally distinctive fault zones for understanding an unknown deformation system at the regional scale remains a challenge for understanding orogenic evolution and gold endowment. The current study deals with this challenge in the southern Michipicoten greenstone belt (MGB) of the Superior craton focusing on a Neoarchean auriferous fault zone network. Three deformation events associated with episodic gold mineralization are revealed in the ca. 2745 Ma host granitoid: (1) northwest‒southeast shortening recorded by the subvertical Grace and Minto B fault zones and locally the inclined Jubilee and Hornblende fault zones; (2) top-to-north northeast strike–slip to oblique faulting indicated primarily by the dominant structures of the Jubilee and Hornblende fault zones; and (3) top-to-northeast extension demonstrated by the northeast-dipping Parkhill #4 and Cooper fault zones. Fault zone lithologies and mineral assemblages suggest that the localization of deformation for the formation of these fault zones was controlled by rheological heterogeneities and syn-deformation fluids. The first and second events are correlated with two shortening events in a gold-endowed, structurally, and kinematically distinctive deformation zone of the northern MGB. This correlation based on deformation processes suggests a larger footprint of gold mineralization associated with a regional deformation in the MGB and has implications for investigating structural evolution of orogens and orogenic gold mineralization in general.

Archean crustal growth and reworking in the Superior Province, Canada: Insights from whole-rock geochemistry and Nd isotopic data of the La Grande, Nemiscau and Opatica subprovinces

Archean crustal growth and reworking in the Superior Province, Canada: Insights from whole-rock geochemistry and Nd isotopic data of the La Grande, Nemiscau and Opatica subprovinces

Abundant 2480 Ma Detrital Zircons in ∼1740 Ma Vishnu Schist in Northwestern Arizona: Derivation From the Matachewan Large Igneous Province?

Detrital zircon grains in the ∼1740–1750 Ma Vishnu Schist and similar rock units in northwestern Arizona consist of up to 30% grains dated by U-Pb isotopic analysis at 2470–2490 Ma. These zircon grains are distributed over ∼40,000 km2 and define an age peak at 2480.0 ± 27.3 Ma (2SE). These grains have yielded unusually consistent 207Pb/206Pb dates, with generally smaller analytical uncertainty and greater concordance to ideal U-Pb evolution than grains of other ages. A weighted mean age of 2480 ± 0.9 Ma (2SE) for this zircon population reflects consistent analytical results and high analytical precision but not the accuracy of the age. The source of these zircons has not been identified. To better characterize the unidentified source, we analyzed 45 of these grains for trace and rare-earth elements by laser-ablation mass spectrometry and scanned 16 grains with an electron microprobe to identify mineral inclusions. Mass spectrometer determinations of Sc/Yb and Nb/Sc support derivation from an oceanic-island igneous source. Electron microprobe scans revealed quartz in 5 of 16 grains, indicating a felsic source. The low variability in 207Pb/206Pb dates and a generally linear relationship between U and Th support zircon derivation from a single igneous unit or closely related set of units without xenocrystic zircons. A literature search for other zircon populations with similar age and U/Th ratios identified ∼2480 Ma zircons in a Mesoproterozoic(?) metapsammite and conglomerate in southwestern Montana. This sandstone was deposited near the margin of the Wyoming craton and contains almost entirely 2400–3600 Ma zircons, unlike zircon grains in Vishnu Schist which include a large population of 1730–1900 Ma zircons. From this relationship we infer that the 2480 Ma zircons in both areas were derived from a source in the Wyoming craton. We conclude that the 2480 Ma Vishnu zircons were derived from a felsic batholith that formed above and from hotspot magma related to the ∼2450–2480 Ma Matachewan Large Igneous Province, that this batholith formed by mixing between a mantle-derived hotspot magma and assimilated Archean continental crust, and that the source rock was emplaced during initial rifting between the Wyoming craton and the Superior province.

Formation of a late-orogenic conglomeratic sequence in the Neoarchean western Wabigoon terrane, Superior craton

Formation of a late-orogenic conglomeratic sequence in the Neoarchean western Wabigoon terrane, Superior craton

Transpression or polyphase deformation along craton margins: Insights from the Archean–Proterozoic boundary near Sudbury, Canada

Transpression or polyphase deformation along craton margins: Insights from the Archean–Proterozoic boundary near Sudbury, Canada

Non-zero I/(Ca + Mg) recorded in Archean and Paleoproterozoic shallow marine Ca-carbonate sediments

Non-zero I/(Ca + Mg) recorded in Archean and Paleoproterozoic shallow marine Ca-carbonate sediments

Nitrogen isotope gradient on continental margins during the late Paleoproterozoic

Nitrogen isotope gradient on continental margins during the late Paleoproterozoic

The Snow Lake Deposits in Manitoba, Canada: Formation of Metamorphosed Amphibolite Facies Orogenic Gold Deposits During a Progressive and Prograde Orogenic Event

Abstract The Snow Lake camp is located in the ca. 1.89 Ga Flin Flon-Glennie Complex in the Paleoproterozoic Trans-Hudson orogen, Manitoba, Canada. The Flin Flon-Glennie Complex is bordered by the ca. 1.855 to 1.84 Ga metasedimentary Kisseynew domain to the north and by the Archean Superior craton to the east and is underlain by the Archean Sask microcraton. It hosts several orogenic gold deposits, including the No. 3 zone, Boundary zone, and New Britannia deposit (Toots, Dick, Hogg, Ruttan, and Mine East zones), which formed during thrusting of the Flin Flon-Glennie Complex and Kisseynew domain over the Sask microcraton. The New Britannia deposit produced 1.6 Moz Au and is the largest orogenic gold deposit in the Trans-Hudson orogen in Manitoba. The deposits consist of quartz ± carbonate veins surrounded by alteration zones of biotite, hornblende, plagioclase ± carbonate, diopside, orthoclase, and garnet. The veins and ore zones are folded within the hinge of the synthrusting Nor-Acme anticline, which has an axial plane cleavage defined by biotite and hornblende, but they also cut across the hinge of the anticline and contain foliated fragments of the wall rocks. These mutually overprinting relationships suggest that the veins and ore zones are synfolding. Garnet, diopside, and amphibole porphyroblasts grew during folding because they overgrow the foliation, which also wraps around them. Inclusions of gold and sulfide minerals within the porphyroblasts indicate that mineralization was emplaced early during folding at greenschist or lower amphibolite metamorphic conditions prior to the growth of the porphyroblasts at peak middle amphibolite metamorphic conditions. These observations are corroborated by laser ablation-inductively coupled plasma-mass spectrometry element maps of arsenopyrite grains. These maps reveal a primary internal enrichment of gold in arsenopyrite grains from the Toots, No. 3, and Boundary zones and a lack of primary lattice-bound gold in arsenopyrite grains of the Dick, Ruttan, and Mine East zones. The latter results from the deposition or remobilization of gold during a second hydrothermal event that occurred during shearing of these ore zones along a structure, the Howe Sound fault, which acted as a detachment surface during folding. The Snow Lake deposits are examples of orogenic gold deposits that formed early during a major thrusting and folding event and were later modified and metamorphosed at middle amphibolite facies conditions during the same progressive orogenic event.

Precambrian megacontinent NENA: stable configuration or Phanerozoic remagnetization?

We tested the coincidence of key poles, paleomagnetic poles, recalculated from the secondary different- age components of NRM and the reference Phanerozoic poles of the East European and Laurentia cratons. The main periods of such coincidences are highlighted. Based on the correlation of angular distances between pairs of the same-age poles of the East European and Superior cratons, three times poles (1.59–1.45 Ga, 580–550 Ma and 250–200 Ma) was found as a result of remagnetization during distroy of the supercontinent Pangaea. It is shown that the coincidence of the Precambrian pole with the Phanerozoic part of the APWP is not always a consequence of remagnetization, but may be due to the “repeatability” of the position of the same craton at the same position of the Globe as part of various Precambrian supercontinents. The potential “repeatability” of the position of the same tectonic block in the same area of the globe at different times in geologic history was carried out.. The results show that over a period of 2.5 Ga, the same block can be found more than twice in the same area of the Globe, which can explain the coincidence of poles of different ages. Distingsions between time of existences of NENA megacontinent and the Precambrian supercontinents Rodinia, Nuna/Columbia and Kenorland may be associated with introversal and extroversal mechanisms of supercontinent formation, respectively.

Strong Physical Contrasts Across Two Mid‐Lithosphere Discontinuities Beneath the Northwestern United States: Evidence for Cratonic Mantle Metasomatism

AbstractMid‐lithosphere discontinuities are seismic interfaces likely located within the lithospheric mantle of stable cratons, which typically represent velocities decreasing with depth. The origins of these interfaces are poorly understood due to the difficulties in both characterizing them seismically and reconciling the observations with thermal‐chemical models of cratons. Metasomatism of the cratonic lithosphere has been reported by numerous geochemical and petrological studies worldwide, yet its seismic signature remains elusive. Here, we identify two distinct mid‐lithosphere discontinuities at ∼87 and ∼117 km depth beneath the eastern Wyoming craton and the southwestern Superior craton by analyzing seismic data recorded by two longstanding stations. Our waveform modeling shows that the shallow and deep interfaces represent isotropic velocity drops of 2%–8% and 4%–9%, respectively, depending on the contributions from changes in radial anisotropy and density. By building a thermal‐chemical model including the regional xenolith thermobarometry constraints and the experimental phase‐equilibrium data of mantle metasomatism, we show that the shallow interface probably represents the metasomatic front, below which hydrous minerals such as amphibole and phlogopite are present, whereas the deep interface may be caused by the onset of carbonated partial melting. The hydrous minerals and melts are products of mantle metasomatism, with CO2‐H2O‐rich siliceous melt as a probable metasomatic reagent. Our results suggest that mantle metasomatism is probably an important cause of mid‐lithosphere discontinuities worldwide, especially near craton boundaries, where the mantle lithosphere may be intensely metasomatized by fluids and melts released by subducting slabs.

Joint Inversion of SPREE Receiver Functions and Surface Wave Dispersion Curves for 3‐D Crustal and Upper Mantle Structure Beneath the U.S. Midcontinent Rift

AbstractBroadband seismograms from the EarthScope Transportable Array and Superior Province Rifting EarthScope Experiment (SPREE) deployments are used to map the crust and uppermost mantle structures beneath the failed Midcontinent Rift (MCR) of Minnesota/Wisconsin, USA. The results suggest the existence of a variable zone of mafic underplating that is up to 20 km thick (40–60 deep). We jointly invert receiver functions and Rayleigh wave dispersion curves to quantify the region's crustal and mantle shear‐wave velocity structure. Basin sediment thicknesses are mildly asymmetric about the rift axis, with thickest regions immediately beneath the rift. 3‐D modeling shows anomalous lower crust and crust‐mantle transitions beneath the MCR. Sub‐MCR crustal thicknesses are generally >50 km with lower crust Vs of 4.0–4.2 km/s. Away from the MCR, the crust is typically ∼40 km thick. Strong variations in apparent crustal thickness are found along the MCR, increasing significantly in places. An additional layer of shear velocities intermediate between typical lower crust and upper mantle velocities (4.1–4.6 km/s) exists beneath most of the MCR which is thickest beneath the rift axis and pinches out away from the rift. This structure corroborates previous proposals of the presence of an underplated layer near the Moho. Results cannot distinguish between different mechanisms of emplacement (e.g., mafic interfingering within a subsequently down‐dropped lower crust vs. development of a high‐density pyroxenitic residuum at the top of the mantle). Also observed are anomalously high (>4.7 km/s) sub‐rift shear‐wave velocities at ∼70–90‐km depths, suggesting the presence of cold, depleted upper mantle material.

Development and application of feature engineered geological layers for ranking magmatic, volcanogenic, and orogenic system components in Archean greenstone belts

Development and application of feature engineered geological layers for ranking magmatic, volcanogenic, and orogenic system components in Archean greenstone belts

Deformation and paleopiezometry of auriferous quartz veins in Archean orogenic gold deposits of the Abitibi greenstone belt

Deformation and paleopiezometry of auriferous quartz veins in Archean orogenic gold deposits of the Abitibi greenstone belt