ALBERT

Description: In Cambrian time, Laurentia was bounded on all sides by passive margins, providing an opportunity to establish a “Cambrian baseline” of detrital zircon provenance for the craton during a relatively quiescent tectonic stage. U-Pb detrital zircon ages from laser ablation–multicollector–inductively coupled plasma–mass spectrometry (LA-MC-ICP-MS) and sensitive high-resolution ion microprobe (SHRIMP) analysis of seven Cambrian sandstone samples from northern Northwest Territories are consistent with generally local provenance. Samples from Mackenzie Mountains were most likely derived from the Proterozoic Mackenzie Mountains Supergroup and are dominated by detrital zircon ages of ca. 1020–1516 Ma, but also contain populations of ca. 1615–1692 Ma and ca. 2699–2752 Ma. Cambrian sandstones from south of Great Bear Lake have a complementary set of detrital zircon age populations dominated by ca. 1810–2010 Ma, with smaller relative probability peaks at 2100 Ma, 2300 Ma, and 2600 Ma, which are consistent with derivation from the Hottah terrane, Great Bear magmatic zone, and Slave craton. Comparison of the signatures from Mackenzie Mountains and Great Bear Lake south suggests that there were two distinct sources of detrital zircon available to the northern Northwest Territories during the Cambrian. Detrital zircon ages from Cambrian strata of Victoria Island appear to be a mixture of Shaler Supergroup, Slave craton–like, Taltson-Thelon orogen, and Wopmay orogen sources.Following the dichotomy of detrital zircon age spectra presented by Cambrian samples from Mackenzie Mountains and Great Bear Lake south allows subdivision of other published detrital zircon ages from across northern Laurentia into two groups: Laurentia Cambrian type 1 suite reflects the Archean cratons and Paleoproterozoic orogens of the Precambrian Shield. Laurentia Cambrian type 2 suite is dominated by Grenvillian and older ages (1000–1500 Ma) and includes relative probability peaks at 1600–1700 Ma and 2700–2750 Ma. We find, therefore, that this Cambrian baseline mirrors the Precambrian tectonic fabric of Laurentia from Archean cratonization and Paleoproterozoic through Mesoproterozoic orogenesis, culminating in assembly of the supercontinent Rodinia. Furthermore, the Neoproterozoic breakup of Rodinia and establishment of passive margins surrounding Laurentia provided little new zircon available to the Cambrian sedimentary system. The detrital zircon spectra for the Cambrian of northern Laurentia are intended to provide a reference to test the affinity of suspect terranes and potentially exotic detrital zircon within Paleozoic foreland basins.

Description: The Neoproterozoic Franklin large igneous province on Victoria Island, Canada, is characterized by continental flood basalts and a sill-dominated feeder system. Field relationships indicate that fault-guided transfer zones allowed magma to jump up-section to form higher-level intrusions. Where sills connect to dikes and magmas moved up-section, roof and wall rocks are characterized by wide and intense contact-metamorphic haloes, consistent with throughflow of magma. The geometric constraints suggest that conduits may have opened episodically and then closed when magma pressure waned. The episodic nature of conduit opening events can explain the pulsed ascent of crystal slurries, and may also play a role in the deposition of Ni-sulfides.

Description: Detrital zircon provenance studies of Silurian flysch units that underlie the Hazen and Clements Markham fold belts of Ellesmere Island, Arctic Canada, were conducted to evaluate models for northern Caledonian palaeogeography and tectonics. Llandovery flysch was deposited along an active plate margin and yields detrital zircons that require northern derivation from the adjacent Pearya terrane. If Pearya originated near Svalbard and NE Greenland, it was transported by strike-slip faults to Ellesmere Island by the Early Silurian. Wenlock to Ludlow turbidites yield Palaeozoic–Archaean detrital zircons with dominant age-groupings c . 650, 970, 1150, 1450 and 1650 Ma. These turbidite systems did not fill a flexural foreland basin in front of the East Greenland Caledonides, but rather an east–west-trending trough that was probably related to sinistral strike-slip faulting along the northern Laurentian margin. The data support provenance connections with the Svalbard Caledonides, especially Baltican-affinity rocks of SW Spitsbergen that were proximal to NE Greenland during the Baltica–Laurentia collision. Pridoli flysch has sources that include Pearya, the East Greenland Caledonides and the Canadian Shield. Devonian–Carboniferous molasse in Arctic Canada has analogous detrital zircon signatures, which implies recycling of Silurian flysch during mid-Palaeozoic (Ellesmerian) collisional tectonism or that some collisional blocks were of similar Baltican–Laurentian crustal affinities. Supplementary material: Detrital zircon U–Pb age results, isotopic data and concordia diagrams of dated samples are available at http://www.geolsoc.org.uk/SUP18797 .

Description: 〈span〉Three tectonic events affected the northern margin of Laurentia between Early Ordovician and Early Devonian time. Each tectonic cycle started with an unconformity followed by rapid subsidence and an influx of clastic material, then decreasing sediment accumulation rates. The first cycle extends from the Tremadoc to late Katian (480−448 Ma), the second from late Katian to Ludlow (448−426 Ma), and the third from Ludlow to Lochkovian (426−410 Ma). A strong geodynamic link is interpreted between the first two sedimentary cycles and tectonic events on the composite Pearya terrane on northern Ellesmere Island, Nunavut, Canada. The first cycle is interpreted as a response to crustal thickening caused by the M’Clintock Orogeny on Pearya terrane and onset of subduction dipping under Laurentia. An extensive Middle Ordovician (Darriwillian) unconformity is not associated with a change in subsidence rate or a change of facies above and below, but is normally faulted. It is interpreted as a migrating forebulge or increase in crustal buoyancy due to breakoff of a subduction slab. The second cycle is synchronous with a Late Ordovician minor faulting event on Pearya terrane and volcanic units in the deep water basin between Pearya terrane and the carbonate platform. A major platform margin stepback, along with a positive ɛNd shift are associated with the late Katian Irene Bay Formation. The event also introduced numerous organisms of Siberian affinity into northern Laurentia. The third cycle, starting in Ludlow time is related to the onset of deformation in the Boothia foldbelt and is not recorded as a deformational event on Pearya terrane. The presence of aerially restricted intraplatform basins that are interpreted to be synchronous with, and caused by, tectonic events on Pearya terrane implies that it was close to its current location by Early Ordovician time. 〈/span〉

Description: Jurassic–Cretaceous sedimentary rocks of the Alberta foreland basin are a key record of the evolution of the Canadian Cordillera. We test a recent model for cyclical development of Cordilleran orogenic systems using detrital zircon analysis of the major sandstone units deposited between 145 and 80 Ma exposed in the Rocky Mountain Foothills near Grande Cache, Alberta. The basin history is well constrained by decades of study, and the stratigraphy has been previously subdivided into tectonostratigraphic wedges. U-Pb data from 14 detrital zircon samples are included in this study. All the major magmatic provinces of North America are represented in each sample, with the relative proportions varying between samples. The samples are assigned to five groups with the aid of multidimensional scaling. Groups 1–3 are interpreted to record recycling from specific passive-margin units of western North America with varying input from the Cordilleran magmatic arc. Group 4 is interpreted to record recycling from sedimentary strata in the United States and dispersal by basin-axial fluvial systems. Group 5 is dominated by Mesozoic zircon grains interpreted to have originated in the Cordilleran magmatic arc. Detrital zircon age spectra do not form groups based on the tectonostratigraphic wedges from which they were sampled; rather, within each tectonostratigraphic wedge, they exhibit evolution from diverse age spectra to a less-diverse distribution of detrital zircon ages. We constructed a proxy for magmatic flux of the Cordilleran magmatic arc using detrital zircon ages younger than 200 Ma; it shows three modes at ca. 165, 115, and 74 Ma. These ages are considered high-flux episodes of magmatism that are linked to cyclical uplift and plateau formation in the orogen. This cyclical process is interpreted to: (1) control sedimentation rates in the foreland; (2) account for evolving provenance by altering catchments; and (3) be a plausible mechanism for the deposition of the tectonostratigraphic wedges in the Alberta foreland basin.

Description: The tectonic setting of northern Laurentia prior to the opening of the Arctic Ocean is the subject of numerous tectonic models. By better understanding the provenance of detrital zircon in the Canadian Arctic prior to rifting, both the prerift tectonic setting and timing of rifting can be better elucidated. In the Sverdrup Basin, two distinct provenance assemblages are identified from new detrital-zircon U-Pb data from Lower Triassic to Lower Jurassic strata in combination with previously published detrital-zircon data. The first assemblage comprises an age spectrum identical to that of the Devonian clastic wedge in the Canadian Arctic and is termed the recycled source. In contrast, the second assemblage is dominated by a broad spectrum of near syndepositional Permian–Triassic ages derived from north of the basin and is termed the active margin source. Triassic strata of Yukon and Arctic Alaska exhibit a similar dual provenance signature, whereas in northeastern Russia, Chukotka contains only the active margin source. Complementary hafnium isotopic data on Permian–Triassic zircon have Hf values that are consistent with the common evolved crustal signature of the Devonian clastic wedge detrital-zircon grains and Neoproterozoic–Paleozoic basement rocks in the Arctic Alaska–Chukotka microcontinent. Furthermore, newly identified volcanic ash beds throughout the Triassic section from the northern part of the Sverdrup Basin, along with abundant Permian–Triassic detrital zircon, suggest a protracted history of magmatism to the north of the basin. We interpret that these zircons were sourced from a magmatically active region to the north of the Sverdrup Basin, and in the context of a rotational model for opening of Amerasia Basin, this was probably part of a convergent margin fringing northern Laurentia from the northern Cordillera along the outboard edge of Arctic Alaska and Chukotka terranes. In Early Jurassic strata, Permian–Triassic zircons decrease substantially, implying the diminution of the active margin as a sediment source as initial rifting isolated the Permian–Triassic source from the Sverdrup Basin.

Description: Keele Arch is a zone of anomalous structural, erosional, and depositional features along a corridor east of the Colville Hills and the northern Franklin Mountains, Northwest Territories, a region with significant economic potential. First described in 1975, it has since been found to have had a long history of uplift-to-sag reversals. This report presents a series of maps and sections, based largely on flattened reflection seismic lines that illustrate key stages of the arch’s development through time and space. In doing so it lays the foundation for future assessments of the arch’s influence on the surrounding stratigraphy. Preceded by a late Proterozoic syncline, it evolved through five major stages: 1) subsidence into a chain of Cambrian to mid-Ordovician grabens; 2) uplift of its central and southern zones to form a Late Silurian (pre-Devonian) arch; 3) renewed uplift into a pre-Cretaceous arch between the region east the Colville Hills and the Mackenzie River valley near Johnson River; 4) mid-Cretaceous reactivation of the pre-Cretaceous and southern pre-Devonian arches; and 5) subsidence of its central zone into Brackett Basin during the late-Campanian to Paleocene and inversion of the Cambrian McConnell Graben into the McConnell Range during late-Campanian to Paleocene time. The feature can be divided into four parts: 1) A northern segment between the Northern Franklin Mountains and the region east of the Colville Hills; 2) The north half of its central zone, where Cambro-Ordovician strata are exposed east of the northern Franklin Mountains; 3) The southern portion of the central zone between Brackett Lake and Keele River, where Tertiary rocks lie at the surface. This is the best documented and most tectonically active segment; and 4) a poorly understood segment under Mackenzie Valley, south of Keele River.

Description: New detrital zircon sensitive high-resolution ion microprobe (SHRIMP) geochronology and published framework geology of Neoproterozoic to Silurian strata are integrated to reexamine tectonic models of the Pearya terrane and the Franklinian margin at Ellesmere Island, Arctic Canada. Compared to Cambrian detrital zircon reference spectra, Neoproterozoic sandstones from the Pearya terrane contain Laurentian detrital zircon ages. In fact, they compare very well with Neoproterozoic strata of Greenland. Ultramafic, tholeiitic, and andesitic basalts of the Maskell Inlet complex, inferred to have an age of ca. 481 Ma, predate the M’Clintock orogeny at ca. 475 Ma. Ordovician granitoid ages within the Pearya terrane span ca. 475–463 Ma. A K-Ar cooling age of 452 Ma records post-tectonic exhumation. Deposited at ca. 450 Ma, new data show that the Cape Discovery Formation contains mainly ca. 500–450 Ma detrital zircon ages, but also older ages of 660–620 Ma. Upper Ordovician sandstones indicate that the Pearya terrane platform continued to receive near-syndepositional zircon. The Pearya terrane platform was submerged at ca. 435 Ma and overlain by Silurian flysch fed by sources similar to detrital zircon within Proterozoic to Ordovician strata of the Pearya terrane. Ties between the Pearya terrane and the Franklinian shelf include: similar Proterozoic-Cambrian stratigraphy; detrital zircon ages from the Lower Cambrian Grantland Formation that appear to be a combination of recycled Marinoan strata of Pearya terrane and Franklinian shelf strata; and profound unconformities on the Franklinian shelf that correlate temporally to the M’Clintock orogeny. A pericratonic model is a straightforward solution to the tectonic history of the Pearya terrane and the Franklinian shelf. We hypothesize that the Pearya terrane was part of the Franklinian margin in the Neoproterozoic and that the intervening deep water basin, or Hazen Trough, originated as a failed rift. The Maskell Inlet complex records ca. 481 Ma volcanism as a response to mantle upwelling beneath a subducting slab, shortly before or as the continent-ocean transition zone of the Franklinian margin was over-ridden. Continued convergence and crustal thickening during arc-continent collision drove the M’Clintock orogeny at ca. 475 Ma and resulted in the unconformities on the Franklinian shelf. After arc-continent collision, magmatism between ca. 475 and 438 Ma was related to subduction on the outboard margin, and the Pearya terrane was overlain by a low-accommodation retroarc foreland basin. A subsequent collisional event led to progressive drowning of the Pearya terrane and Franklinian platforms between 435 and 425 Ma. Silurian flysch then blanketed the Pearya terrane and entered the axis of the foreland basin, which also received sediment from cratonic sources of the flexural basin margin. Limited deformation at northern Axel Heiberg Island was associated with a ca. 390 Ma granitoid within the Pearya terrane. After a Devonian pulse of subsidence, infilling of the basin to form the Devonian clastic wedge overlapped in age with small ca. 368 Ma granitic intrusions within the Pearya terrane and was followed by extensive foreland deformation of the Late Devonian–Mississippian Ellesmerian orogeny.