Hearne Craton Research Articles

Structural history and granite emplacement in the Rottenstone Domain during closure of the Trans-Hudson Orogen, Davin Lake, northern Saskatchewan

The Rottenstone Domain at Davin Lake northern Saskatchewan, exhibits structural and granite-emplacement evidence for crustal thickening, and possible Himalayan-style extrusion, overprinted by transpressional strain increasing toward the contact with the Wathaman Batholith. Three discrete Rottenstone subdomains parallel the regional strike of the Trans-Hudson Orogen: (i) the southeast Rottenstone subdomain (SERSD) with gently northwest-dipping migmatitic straight gneiss (S1) and white granitoid rocks with pinch-and-swell structures parallel to the straight gneissosity; (ii) the central Rottenstone subdomain (CRSD), which partly preserves the same NW-dipping fabric (S1) but is overprinted at its margins by tight upright F2 folds and includes a stockwork of pink monzogranitic aplites and pegmatites; and (iii) the northwest Rottenstone subdomain (NWRSD) in which the F2 folds are generally tighter and penetrative and its network of narrow white granitoid rocks is deformed and transposed by the F2 folds; but in the northwestern part, a wide, syn-D2 complex of schlieric white tonalitic and diatexite sheets strikes parallel the orogen. The SERSD D1 straight zone may be a remnant of Himalayan-type extrusion zone although it could be the lowest member of a stack of ductile thrust sheets. The CRSD stockwork may represent fluid-assisted magma injection into extensional fractures above the postulated extrusion zone. The increasing transpressional strain northwestward expressed primarily by the F2 folds in CRSD and NWRSD defines the Davin Lake shear zone, into which the NWRSD granitoid dyke complex represents syntectonic magma injection. Both the postulated extrusion and transpression are related to oblique convergence of the Archean Sask craton with the Archean Rae–Hearne craton.

Provenance and tectonic setting of Paleoproterozoic metasedimentary rocks along the eastern margin of Hearne craton: Constraints from SHRIMP geochronology, Wollaston Group, Saskatchewan, Canada

Single detrital zircon grains from various parts of the Wollaston Group, a Paleoproterozoic metasedimentary succession deposited along the southeastern margin of the Hearne Province, northern Saskatchewan, Canada, were analyzed by SHRIMP U–Pb geochronological techniques. Zircon analyses are mostly concordant and yield ages ranging from ca. 2800 to 1780 Ma, although distinct age populations were detected in all samples. The stratigraphically oldest sample (Geoch 4) is dominated by a bimodal distribution of zircon ages (ca. 1.90 and 2.4–2.6 Ga), which is similar to that preserved in the sample (Geoch 2) from the middle portion of the Wollaston Group. The stratigraphically youngest sample (Geoch 9) contains ca. 2.1 Ga zircons, as well as zircons with the same ages as observed in Geoch 4 and Geoch 2. Zircon ages older than 2450 Ma appear to be consistent with the age of the Hearne Province basement, suggesting that part of the sedimentary detritus was locally derived. Zircons with ages in the 2430–2350 Ma range, found in all samples, may have been derived from a more distant source, such as Rae Province rocks that were affected by the recently identified Arrowsmith orogeny. Significant amounts of 1920–1880 Ma zircon grains are found in all samples; these are interpreted to represent sedimentary detritus derived from juvenile volcanic terranes. Zircons younger than 1860 Ma are interpreted to be the product of post-Wollaston Group thermal overprinting. Our data, together with field relationships and geochemical data, suggest that most of the preserved Wollaston Group was deposited in a back-arc to foreland basin environment. It received detritus from both Archean continental crust to the west and a juvenile continental magmatic arc, likely located to the east, as the youngest zircon ages are not consistent with the age of Taltson Orogen rocks to the west.

Lithospheric structure of the Trans-Hudson Orogen from seismic refraction - wide-angle reflection studies

The Trans-Hudson Orogen (THO) is the world's largest Paleoproterozoic orogenic belt. Data from three refraction profiles are used to investigate its lithospheric structure in Saskatchewan and Manitoba. R1 crosses the orogen from the Hearne craton on the west to the Superior craton on the east; R2 and R3 are along the orogen. P-wave velocity structural models are generated using a ray-based technique. On line R1, higher crustal velocities in its eastern part coincide with rocks of the Flin Flon – Namew gneiss complex. Depth to Moho is in the 40–45 km range and equates to that from the reflection data, including a small crustal root below the Sask minicontinent. Along lines R2 and R3, depth to Moho varies from about 40 km up to 55 km at the north end of R2 and south end of R3. In general, variations in crustal velocity and depth to Moho do not correlate with the location and extent of geological domains; they appear to reflect the complex deformation and metamorphic history of the crustal rocks. Mantle velocities are high, ~8.2 km/s. However a limited area shows prominent velocity anisotropy, with values of 8.6 km/s along R2 and R3 and 8.1 km/s along R1. We speculate that the observed anisotropy represents an ~100-km-wide mantle suture zone resulting from the collision of Archean plates. The suture zone accommodated limited extensional deformation, associated with a counterclockwise rotation of the Superior plate, to generate the anisotropy. In this model, the lithospheric mantle of the THO internal domains and Sask craton are detached.

Tectonic evolution of the Manitoba-Saskatchewan segment of the Paleoproterozoic Trans-Hudson Orogen, Canada

Time slices and schematic cross-sections that attempt to show the spatial and temporal relationship between geological entities within the Manitoba–Saskatchewan segment of the Trans-Hudson Orogen and that are consistent with the available geological, geophysical, geochemical, isotopic, and geochronological data are presented. The Trans-Hudson orogenic belt developed as a result of closure of the Manikewan Ocean, which initially opened at about 2.1 Ga by rifting of a possible Neoarchean supercontinent. The oldest oceanic arc rocks indicate that subduction was ongoing by 1.92 Ga, with the development of a complex Manikewan "Ring of Fire" that lasted for the next 100 Ma. Intraoceanic accretion of arc, ocean-floor, and ocean-island rocks within the Manikewan Ocean at 1.87 Ga formed the Flin Flon – Glennie complex, which then subsequently collided with the accreted terranes along the Hearne craton margin at ca. 1.85 Ga. These rocks were then deformed and metamorphosed over the next 75 Ma during collisions with the Sask craton and the Superior craton, both of which are interpreted to have been drifting generally northwards towards the Hearne craton. The generation of arc magmas in the orogen ceased at 1.83 Ga, an indication that continental collisions were well advanced at that stage. The present arrangement and erosion level of geological entities is related to structural reorganization after the peak of regional metamorphism at ca. 1.81. The schematic time slices and sections form part of ongoing efforts to better understand the geological evolution of the Paleoproterozoic of Canada.

Accretion history of the Trans-Hudson Orogen in Manitoba and Saskatchewan from paleomagnetism

Lithoprobe's sponsorship has led to the acquisition of paleomagnetic data from ~20 units throughout the Paleoproterozoic Trans-Hudson Orogen (THO) of Saskatchewan and Manitoba, essentially the first such data for the region. Discussed summarily in this paper, they provide an initial framework for the THO's tectonic evolution. They show that the Archean Hearne and Superior cratons were at subtropical and subpolar paleolatitudes, respectively, at ~1875 Ma, with the Lynn Lake – LaRonge arc midway between them in the Manikewan Ocean. By ~1855 Ma, this ocean was still ~5500 ± 700 km wide, and its seafloor was subducting northwestward under the Hearne craton and pericratonic Peter Lake domain margin with the coeval development of an Andean-type continental magmatic arc, the Wathaman–Chipewyan batholith. Between ~1855 and ~1810 Ma, coalescing apparent polar wander path (APWP) segments record closing of the ocean at a rate of ~12 cm/a, trapping and accreting the several separate intervening terranes (Flin Flon, Hanson Lake, Lynn Lake – LaRonge, Rottenstone, and presumably also other THO terranes). From ~1815 to ~1775 Ma, the assembled terranes drifted as a coherent craton, yielding a stillstand and hairpin in the APWP.

Origin of the Archean Sask craton and its extent within the Trans-Hudson orogen: evidence from Pb and Nd isotopic compositions of basement rocks and post-orogenic intrusions

U–Pb zircon ages from the exposed Sask craton are 2450–3100 Ma, from the Peter Lake Domain 2575–2640 Ma, and from rocks of the Trans-Hudson orogen 1840–1880 Ma. U–Pb monazite and zircon ages of post-orogenic pegmatites and aplites are 1770–1800 Ma. Common Pb and Sm–Nd isotopic compositions of post-orogenic intrusions, as probes of crust beneath the orogen, were compared to Sask craton rocks and ca. 1850 Ma orogenic rocks to infer the origin and subsurface distribution of the Sask craton within the internides of the Trans-Hudson orogen. Results show that post-orogenic intrusions within most of the Glennie Domain and Hanson Lake block were derived, at least in part, from Archean source materials, demonstrating that the Sask craton lies beneath Paleoproterozoic orogenic rocks present at the surface. In contrast, common Pb and Sm–Nd isotopic compositions from pegmatites and aplites of the La Ronge Domain are essentially identical with those of the Paleoproterozoic orogenic rocks into which they are intruded, indicating derivation by partial melting of similar rocks. Thus, if the Sask craton extended to the west beneath the La Ronge Domain, it was beneath the zone of melting that produced the post-orogenic intrusions, making it unlikely that the Sask craton is a detached part of the Hearne craton. Many samples from the Sask craton have elevated 208Pb/204Pb ratios, unlike Superior craton or Hearne craton rocks, suggesting that the Sask craton was derived from an exotic source, such as the Wyoming craton, which shares similar elevated 208Pb/204Pb ratios.

Electromagnetic image of the Trans-Hudson orogen — THO94 transect

The North American Central Plains (NACP) anomaly in enhanced electric conductivity and its relationship with the Paleoproterozoic Trans-Hudson orogen (THO) has been studied under the auspices of Lithoprobe for over a decade. The NACP anomaly was the first geophysical evidence of the existence of the THO beneath the Phanerozoic sediments of the Central Plains. This anomaly, detected geomagnetically in the late 1960s, has been the subject of a number magnetotelluric studies from the early 1980s. The PanCanadian and Geological Survey of Canada experiments in the 1980s and the Lithoprobe experiments in the 1990s together comprise four east–west and one north–south regional-scale profiles in Saskatchewan perpendicular to the strike of the orogen. In this paper, data from the northernmost line, coincident with seismic line S2B, are analysed and interpreted, and are shown to be key in determining the northern extension of the NACP anomaly. Dimensionality analysis confirms the rotation of deep crustal structures eastward to Hudson Bay, as earlier proposed on the basis of broad-scale geomagnetic studies. On this profile, as with the profile at the edge of the Paleozoic sediments, the NACP anomaly is imaged as lying within the La Ronge domain, in contact with the Rottenstone domain, and structurally above the Guncoat thrust, a late compressional feature. The location of the anomaly together with the surface geology suggests that the anomaly is caused either by sulphide mineralization concentrated in the hinges of folds, by graphite, or by a combination of both. Our interpretation of the data is consistent with that from other profiles, and suggests that the NACP anomaly was formed as a consequence of subduction and collisional processes involving northward subduction of the internides of the THO beneath the Hearne craton. On the southern part of this profile, a resistive structure is identified as the Sask craton, suggesting that Proterozoic rocks are above Archean rocks in the THO.

Tectonic implications of new SHRIMP and TIMS U–Pb geochronology of rocks from the Sask Craton, Peter Lake Domain, and Hearne margin, Trans-Hudson Orogen, Saskatchewan

This study reports new sensitive high-resolution ion microprobe (SHRIMP) and thermal ionization mass spectrometry (TIMS) U–Pb geochronological data for thirteen rocks from the Archean to Paleoproterozic Sask Craton, the Peter Lake Domain and Hearne margin, Saskatchewan. Seven samples from the exposed Sask Craton in both the Glennie Domain and Pelican Window record zircon growth between 2425 and 2525 Ma and at ~1800 Ma. Older precursor material has been identified, most notably a refined crystallization age of 3117 Ma for a sample of quartzofeldspatic gneiss ("Q-gneiss") in the Pelican Window, which also experienced ca. 2450 Ma zircon growth. Three samples from the Peter Lake Domain and a sample from the Linn Island inlier of the Wollaston Domain yield ages of ~2575 Ma. One sample from the Peter Lake Domain is distinctly older, yielding an age of 2640 Ma, but also displays zircon growth at 2575 Ma. The simplest interpretation of these data is that the Peter Lake Domain is likely a part of the Hearne margin, although the significance and distribution of 2575 Ma ages within the larger Hearne craton is unclear. Conversely, the age range of most samples from the Sask Craton is distinctly younger than those of the Peter Lake and Hearne margin rocks. We suggest that 2.45 Ga was a major episode of magmatic reworking of older material within the Sask Craton, which includes, but is not restricted to, 3.1 Ga precursors. These ages do not coincide with typical ages reported from the Superior craton and thus the data, although limited, support an exotic origin for the Sask Craton.

Structural controls on hypozonal orogenic gold mineralization in the La Ronge Domain, Trans-Hudson Orogen, Saskatchewan

The La Ronge Domain is a granite–greenstone belt in the Saskatchewan segment of the ca. 1.9–1.8 Ga Trans-Hudson Orogen. The La Ronge volcanic arc was accreted to the Archean Hearne craton from ca. 1.87 to 1.86 Ga. Subduction of oceanic lithosphere beneath the accreted La Ronge – Hearne margin produced a voluminous suite of continental-arc intrusions. In the Waddy Lake area, the 1852.6 ± 1.5 Ma Corner Lake stock and 1859 ± 4 Ma and 1861 ± 2 Ma feldspar porphyry dykes crystallized from magmas generated from melting of the subducted oceanic slab. During the ca. 1.83–1.80 Trans-Hudson collision of the Hearne craton with the Archean Sask and Superior cratons, a penetrative regional foliation and a steeply plunging lineation formed within the La Ronge Domain. During further contraction across the domain, the deformation became localized in dextral and oblique-slip shear zones that generally follow contacts between more competent and less competent rock units. Orogenic gold mineralization is associated with quartz veins that are surrounded by hypozonal potassic and sulfidic alteration zones. The Komis gold deposit, the only past-producing gold mine in the Waddy Lake area, formed in the strain shadow of the Round Lake stock during the development of the regional foliation and lineation. Mineralization is associated with quartz veins that cut through tonalite dykes that behaved more brittlely than the surrounding metavolcanic rocks. The Golden Heart and Corner Lake gold deposits are hosted by south-side-up oblique-slip shear zones, which belong to a regional system of structures that extend from Saskatchewan to Manitoba.

Nd isotope and geochemical constraints on the depositional setting of Paleoproterozoic metasedimentary rocks along the margin of the Archean Hearne craton, Saskatchewan, Canada

Abstract The Cree Lake Zone in the southwestern part of the Hearne craton, reworked during the Paleoproterozoic Trans-Hudson orogeny, includes the Wollaston Group, a sequence of Paleoproterozoic metasedimentary rocks. As these rocks have been multiply deformed and metamorphosed to high-grade, a geochemical and isotopic study was initiated to see through the overprinting events to better constrain the provenance and evolution of the Wollaston Group. The Wollaston Group consists of thick sedimentary successions representing different depositional and tectonic environments that can be subdivided into two subgroups. The Lower subgroup is represented by deep-water turbidite to shallow-water marine deposits. The Upper subgroup, separated from the Lower one by a regional unconformity, comprises molasse-type assemblages ranging from talus to shallow-marine/lacustrine, with subordinate volcanogenic rocks. Major and trace element data obtained from 31 psammopelitic rocks indicate that the clastic material was derived from sources consisting of both felsic and mafic material, although felsic sources are more important in the samples from the Lower subgroup. Sedimentary tectonic discrimination diagrams demonstrate that most of the Wollaston Group was deposited on an active continental margin rather than a passive margin. The e Nd values for the Wollaston Group psammopelites, calculated at 1.92 Ga, the approximate age of the boundary between the Lower and Upper subgroups, vary from −3.4 to −6.8, which yields an approximate 70:30 mixture between juvenile Paleoproterozoic detritus and Archean detritus from the Hearne craton. A secondary source of detritus may be 1.95–2.0 Ga rocks of the Taltson Orogen, which is exposed to the west of the Archean Rae–Hearne craton. The Wollaston Group records the complete evolution of the western margin of the Trans-Hudson Orogen during the Paleoproterozoic. The rifting of an Archean continent at ca. 2.1 Ga led to the deposition of the passive margin siliciclastic sediments comprising the lowermost, but poorly preserved part of Wollaston Group. The formation of a continental arc (Rottenstone) along the Hearne margin at ca. 1.92 Ga resulted in a change in tectonic environment from a passive margin to a back-arc basin, and detritus in most of the Lower subgroup was then derived from both basement and newly formed magmatic arc. Collision with the juvenile La Ronge arc led to uplift along the Hearne margin which transformed the back-arc basin into a retroarc foreland basin at ca. 1.88 Ga. Sedimentary starvation and shallowing of the basin led to widespread accumulation of carbonate and evaporite deposits in the west, whereas rapidly uplifted orogenic belts in the east provided sources of coarse-grained clastic detritus, forming the Wollaston Upper subgroup. Closure and inversion of the sedimentary basin occurred by ca. 1.86 Ga, coincident with the emplacement of mafic to felsic intrusive rocks in the Cree Lake Zone and the emplacement of the voluminous ca. 1860 Ma Andean-type Wathaman batholith into the continental margin. Closure was manifested by the onset of foreland-directed thrusting of the Wollaston Group.

Paleoproterozoic arc magmatism imposed on an older backarc basin: Implications for the tectonic evolution of the Trans-Hudson orogen, Canada

Compositional data from 72 granitoids and associated mafic rocks in the Paleoproterozoic Kisseynew domain, Trans-Hudson orogen, Canada, were used to evaluate the tectonic setting of magma generation between 1840 and 1820 Ma. These data thus provide insights into the development of the Trans-Hudson orogen just prior to amphibolite-grade metamorphism and the final stages of continental collision. The granitoid rocks are hornblende- or orthopyroxene-bearing, medium- to high-K calc-alkalic, and weakly peraluminous. The trends on Harker variation diagrams are consistent with crystal-fractionation processes, although the range in values is related to the temporal and spatial distribution of samples. The extent of LREE (light rare earth element) enrichment increases with increasing SiO 2 , as does variability in HREE (heavy rare earth element) fractionation and magnitude of Eu anomalies. Most samples have (Gd/Yb) n < 10 (suite Ia), although five have (Gd/Yb) n = 17-24, suggesting the presence of garnet residua (suite Ib). The range in rock types, calc-alkalic character, and negative Nb and Ti anomalies are all characteristic of arc environments. Magma generation within the Trans-Hudson orogen, including the Kisseynew domain, between 1.84 and 1.82 Ga was related to interaction between the Sask craton and the Flin Flon-Glennie complex. A decrease in subduction angle likely resulted from northward-directed subduction of more buoyant crust, with associated changes in thermal conditions leading to melting over a wide area. Most magmas formed in a slab-dehydration-dominated regime, although localized slab melts may have been generated. Ultimately subduction ceased, and the slab foundered into the mantle, potentially resulting in the generation of alkalic and potassic magmas within the Rae and Hearne cratons.

The 1830 Ma Trans-Hudson hairpin from paleomagnetism of the Wapisu gneiss dome, Kisseynew Domain, Manitoba

The Wapisu gneiss dome is located in the northeastern part of the Kisseynew Domain of the Trans-Hudson Orogen (THO) in north-central Manitoba. The dome is circular, about 6 km in diameter, with steeply-dipping flanks. It is composed of upper amphibolite-facies gneisses derived from turbiditic sediments, with leucogranitic sill-like intrusions that were metamorphosed, starting at about 1830 Ma. Alternating field and thermal step demagnetization of 153 specimens from 17 sites around the perimeter of the dome isolated a characteristic remanent magnetization (ChRM) direction of D = 346.6°, I = 78.9° (α95 = 5.3°, k = 46, N = 17) that gives a pole of 119.5° W, 75.8° N (dp = 9.5°, dm = 10.0°). Unblocking temperatures and saturation isothermal remanence analyses show that the ChRM resides mostly in single to pseudosingle domain magnetite or titanomagnetite, with minor hematite commonly present and with minor pyrrhotite present in the leucogranites. The ChRM is found to be postfolding with &gt;&gt;99.9% confidence, indicating acquisition on cooling from peak metamorphism at ~1810 ± 10 Ma. This Wapisu gneiss dome paleopole is the first from the Kisseynew Domain and the first from the 1830 to 1770 Ma interval in the THO. It indicates an ~90° bend or hairpin in the apparent polar wander path for the THO juvenile terranes and Superior craton. It is speculated that the hairpin marks the collisional impact of the Archean Sask craton and (or) Hearne craton, which drove the Paleoproterozoic Kisseynew Domain into the Archean Superior craton.

Geotectonics of the Hanson Lake block, Trans-Hudson orogen, central Canada: a preliminary paleomagnetic report

We present paleomagnetic results from the Sahli granite in the Hanson Lake block of the Trans-Hudson orogen. Evidence shows that the Sahli granite magnetization was acquired during a metamorphic event which probably peaked in the interval 1840–1800 Ma. The reset nature of the Sahli granite data is partly supported by a negative contact test from a cross-cutting mafic dyke. The Sahli granite results and those from the 1844±2 Ma Hanson Lake pluton and Jan Lake granite in the Hanson Lake block indicate high paleolatitudes compared with the low paleolatitudes found for the Wathaman batholith and other rocks of the Slave–Rae–Hearne cratons of similar ages to the north-west of the Trans-Hudson orogen. Estimates of the `north–south' width of about 4000 km for the Paleoproterozoic Manikewan ocean between the Archean Hearne and Superior cratons using the Hanson Lake pluton and Wathaman batholith poles, for example, are consistent with previous estimates. The angular difference between the Hanson Lake pluton and Sahli granite poles provides an apparent polar wander segment of the geomagnetic field for the Hanson Lake block to compare with the parallel segment given by the poles for the 1851 Ma Reynard Lake pluton and the 1838 Ma Boot Lake–Phantom Lake pluton for the adjacent Flin Flon domain. Both segments indicate a relative north–north-easterly path direction at an apparent polar wander rate within the range 4.3–0.4° per Ma, assuming no large-scale regional tilts of the plutons. The offset between the two apparent polar wander path segments indicates either an `east–west' component of closure of about 1000 km for the Manikewan ocean or vertical-axis counter-clockwise rotation of units within the Trans-Hudson orogen with respect to the Superior craton plus a possible north–south relative translation between the Hanson Lake block and Flin Flon domain.

LITHOPROBE reflection studies of Archean and Proterozoic crust in Canada

LITHOPROBE, Canada's national collaborative earth science research project established to develop a comprehensive understanding of the evolution of the North American continent, is a multidisciplinary program spearheaded by seismic reflection studies. Five recently recorded seismic lines, discussed in this paper, are located in Precambrian regions: the Mesoproterozoic Grenville Province, the Paleoproterozoic Trans-Hudson orogen (THO), the Paleoproterozoic/Archean basement of Alberta, and the Archean Superior Province. Data acquired across the Grenville orogen in eastern Quebec show strong reflectivity throughout the crust; upper crustal reflections can be correlated with exposed structural elements, including extensional shear zones and packages of deformed high-pressure rocks (eclogites). In a marine survey across the Grenville orogen off southeastern Labrador, seismic images show variably dipping reflections and a structural high associated with a major gravity anomaly. Data acquired across central Alberta show crustal-scale thrust stacking and imbrication of the Archean Hearne craton. To the east across the Trans-Hudson orogen, images of similar collisional features are observed. Geochronologic constraints indicate contemporaneity of tectonic activity between the two regions at 1.8 Ga, suggesting that collisional tectonic activity was coeval over a broad crustal region, ca. 1000 km across strike. In the Superior Province, seismic data across a collision zone involving the northern Abitibi greenstone belt and the arc-related Opatica plutonic belt show spectacular crustal reflectivity and dipping reflections that extend 8 s (∼30 km) into the mantle. The latter feature is interpreted as representing a relict 2.69-Ga-old suture associated with subduction, providing the first direct evidence that plate tectonics was active in the late Archean. These five examples, supported by other LITHOPROBE results, refute a number of generalizations about crustal reflectivity that have been made in the past and illustrate how reflection studies, combined with other geoscience studies, can lead to a better understanding of Precambrian tectonics. Reflectivity persists throughout the crust; there is no general separation into a poorly reflective upper crust and a reflective lower crust. Crustal reflectivity in Archean and Proterozoic regions is as pervasive as that in areas of more recent tectonism. The Precambrian reflection Moho is generally well defined but shows a range of characteristics. Relative ages of reflectors can be discerned and tectonic significance can be attached to characteristic features of the crustal reflectivity.

Structure of a Paleoproterozoic continent-continent collision zone: a LITHOPROBE seismic reflection profile across the Trans-Hudson Orogen, Canada

An ~ 800 km reflection seismic profile across the Trans-Hudson Orogen, northern Saskatchewan and Manitoba, images crustal-scale tectonic imbrication in an unprecedented picture of Paleoproterozoic crustal accretion and continent-continent collisional tectonism. The profile is crudely symmetric about a crustal-scale culmination in the western part of an accreted juvenile collage (Reindeer Zone). Geologic and isotopic data suggest that this culmination is cored by microcontinental Archean basement. West of the culmination, highly reflective juvenile crustal elements dip westward into the lower crust, beneath the Wathaman Batholith and Archean continental crust of Hearne craton. To the east, strong reflections in the juvenile Reindeer Zone crust and reworked Archean foreland of the Thompson belt have eastward dips persisting into the middle crust and extending beneath the Superior craton. A continuous reflection Moho, well-defined for > 500 km in the western part of the profile, shows marked relief (12- > 15 s), including a prominent root below the crustal culmination. These imaged structures give evidence of substantial crustal shortening and thickening via large-scale imbrication consistent with collisional orogeny. W-dipping structures below the Wathaman Batholith and reworked Hearne craton may reflect subduction polarity in this part of the orogen. However, geological evidence suggests that E-dipping structures below Superior craton are largely related to late/post-collisional deformation, rather than to prior oceanic subduction polarity.

Paleomagnetism of the Proterozoic Wathaman batholith and the suturing of the Trans-Hudson orogen in Saskatchewan

The Wathaman (Wathaman–Chipewyan) batholith is an 1854 ± 11 Ma, northeast-trending, homogenous, felsic pluton that is over 900 km long. It is thought to be a magmatic arc, with the Archean Hearne craton on its northwestern side as the hinterland and the remains of the Early Proterozoic Manikewan oceanic crust of the Trans-Hudson orogen on its southeastern side. Alternating-field and thermal step demagnetization methods isolate an A remanence component with a mean direction of D = 134.6°, I = 54.1° (α95 = 3.5°, k = 94, N = 19). Isothermal remanent magnetization tests confirm that this A magnetization component is preserved in pseudosingle to multidomain magnetite and in hematite. Contact tests with intruded older rocks of the Peter Lake domain, with younger crosscutting mafic dikes and with younger crosscutting shear zones, indicate that A is a primary remanence. Its pole position of 67°W, 9°N (dp = 3°, dm = 5°) confirms that it was formed along the margin of the Slave–Rae–Hearne craton, supporting tectonic models that it records a suture zone. It also indicates that the LaRonge – Lynn Lake domain, Flin Flon domain, and Superior Province were translated relatively northwestward into the suture by at least 11 ± 11°, 27 ± 12°, and 49° ± 16°, respectively, as the Manikewan Ocean closed.