ALBERT

Description: Ellesmere Island in Arctic Canada displays a complex geological evolution. The region was affected by two distinct orogenies, the Palaeozoic Ellesmerian orogeny (the Caledonian equivalent in Arctic Canada and Northern Greenland) and the Palaeogene Eurekan orogeny, related to the opening of Baffin Bay and the consequent convergence of the Greenland plate. The details of this complex evolution and the present-day deep structure are poorly constrained in this remote area and deep geophysical data are sparse. Receiver function analysis of seven temporary broad-band seismometers of the Ellesmere Island Lithosphere Experiment complemented by two permanent stations provides important data on the crustal velocity structure of Ellesmere Island. The crustal expression of the northernmost tectonic block of Ellesmere Island (~82°–83°N), Pearya, which was accreted during the Ellesmerian orogeny, is similar to that at the southernmost part, which is part of the Precambrian Laurentian (North America-Greenland) craton. Both segments have thick crystalline crust (~35–36 km) and comparable velocity–depth profiles. In contrast, crustal thickness in central Ellesmere Island decreases from ~24–30 km in the Eurekan fold and thrust belt (~79.7°–80.6°N) to ~16–20 km in the Hazen Stable Block (HSB; ~80.6°–81.4°N) and is covered by a thick succession of metasediments. A deep crustal root (~48 km) at ~79.6°N is interpreted as cratonic crust flexed beneath the Eurekan fold and thrust belt. The Carboniferous to Palaeogene sedimentary succession of the Sverdrup Basin is inferred to be up to 1–4 km thick, comparable to geologically-based estimates, near the western margin of the HSB.

Description: Saglek Basin is the more northerly of the two major sedimentary basins along the Labrador margin of the Canadian east coast in which exploration drilling was undertaken in the 1970s–early 1980s. Saglek Basin has an area of over 100,000 km 2 , and contains a clastic-dominated succession of late Cretaceous to Pleistocene age. Nine wells were drilled in Saglek Basin, with only one significant discovery. The Hekja O-71 well, drilled in the northern half of the basin just east of Frobisher Bay, flowed natural gas with condensates and has reserves estimated at approximately 6.51 x 10 11 m 3 (2.3 Tcf). A new interpretation of seismic and marine Bouguer gravity data shows the very strong influence of reactivated basement structures on the overlying section. Earthquake activity along the Labrador Sea seismic zone is proposed as a possible cause for episodic venting of thermogenic natural gas through pre-existing fracture networks. This may account for the observations of persistent oil slick features on the sea surface observed in satellite radar data. The presence of these oil seep indicators in the southern part of the basin implies the existence of a second petroleum system that is more oil prone. Source rock analysis indicates that three formations in the post-rift succession of the basin have petroleum source potential. Previous studies have raised the issue of inadequate thermal maturation of these rocks in downgrading the petroleum potential of the basin. An integrated 4-D basin modelling study, that shows significant natural gas generation, estimated that volumes of 2.83 x 10 9 m 3 (100 Tcf) could occur, along with a minor oil component, in self-sourced petroleum kitchens in some reservoirs and from sites deeper in the basin. Three separate prospect fairways are interpreted along the western side of the basin. Collectively, these observations suggest the petroleum potential of the Saglek Basin may be significantly higher than estimated previously.

Description: The crustal seismic velocity model (based on receiver functions) of Ellesmere Island and the structural geological cross-section of Ellesmere Island, both documented and discussed elsewhere in this volume, are here integrated into a crustal-scale transect crossing all the main tectonic domains. The velocity model satisfies much of the observed gravity field, but implies minor modifications with potentially important implications for characterizing the lower crust over the transect. The crust of the Pearya Terrane includes a high-velocity and high-density lower crustal body, suggested to represent a mafic underplate linked to the emplacement of the High Arctic Large Igneous Province. A similar body also lies directly beneath the Hazen Plateau, but this is more likely to be inherited from earlier tectonic stages than to be linked to the High Arctic Large Igneous Province. A large-scale basement-involving thrust, possibly linked to a deep detachment of Ellesmerian age, lies immediately south of the Pearya Terrane and forms the northern backdrop to a crustal-scale pop-up structure that accommodates Eurekan-aged shortening in northern Ellesmere Island. The thickest crust and deepest Moho along the transect are below the Central Ellesmerian fold belt, where the Moho is flexured downwards to the north to a depth of about 48 km beneath the load of the structurally thickened supracrustal strata of the fold belt.

Description: The Alpha–Mendeleev ridge complex is a prominent physiographic and geological feature of the Arctic Amerasia Basin. The Alpha and Mendeleev ridges are, respectively, the eastern and western components of a continuous seafloor high that is approximately 2000 km long and 200–400 km wide. A surge of interest in the tectonic evolution of Arctic submarine features has led to a wealth of new geophysical data collected from the Alpha Ridge. Current interpretations of its origin vary but there is compelling evidence that the Alpha Ridge may have formed as an oceanic plateau during the Late Cretaceous. Geological samples are rare but most samples recovered indicate a genetic link with the High Arctic Large Igneous Province (HALIP). In August 2016, Canada’s Extended Continental Margin-United Nations Convention on the Law of the Sea Program dredged approximately 100 kg of volcanic rocks from the Alpha Ridge. The large size and pristine state of the samples enabled the first comprehensive study of a single eruptive event in the volcanic record of the Alpha Ridge. The dredge sample is a lapilli tuff containing vitric and basaltic clasts. Textural evidence and the coexistence of juvenile and cognate clasts suggest a phreatomagmatic eruption. The vitric fragments consist of sideromelane glass with abundant plagioclase microlites. Texturally, these basaltic glass lapilli display a fresh glassy core surrounded by Fe- and Ti-rich zones and a palagonite rim. Major and trace element analyses of glassy cores indicate remarkably uniform, mildly alkaline basaltic compositions. The plagioclase-bearing glass yielded a 40Ar/39Ar plateau age of 90.40±0.26 Ma (2σ error) which included 89% of 39 Ar released. We interpret this result to represent the eruption age of the plagioclase microlites and consequently, of the host basaltic glass lapilli in the tuff. Volatile species analyses by infrared spectroscopy on the fresh basaltic glass suggests that the melt was effectively degassed to shallow level. Assuming equilibrium degassing, the homogeneous resulting values of H2O total in the range 0.1 to 0.19 wt.% (1σ error) indicate subaerial or shallow eruption (surface to 80 m). The new 40Ar/39Ar age for the sample is consistent with a 40 Ar/39Ar age of 89±1 Ma obtained for a sample of tholeiitic basalt dredged from the central part of the Alpha Ridge, and with the range of ages reported for HALIP igneous rocks exposed onshore in the Canadian Arctic Archipelago (130-80 Ma). Our new data provide evidence for local emergence of the Alpha Ridge in the Late Cretaceous. A comparison the Alpha Ridge and Kerguelen Plateau–Broken Ridge Large Igneous Province (LIP) provides new insights on the episodic nature of LIP magmatism and variations in eruptive style through time.

Description: Aeromagnetic data were collected over the Hall Basin and adjacentcoastal land areas of northern Nares Strait during the 2001 Canadian-GermanNares Strait Expedition to provide an improved onshore-offshore linkage ofgeological structures related to the Late Cretaceous Early PaleogeneEurekan Orogeny. The total field magnetic anomaly data are characterized bybroad long-wavelength anomalies compatible with thick sequences of nonmagneticSilurian and Devonian carbonate facies. On the Greenland side ofthe survey block, the magnetic anomalies are generally positive, possiblyreflecting the magnetic characteristics of deeply buried crystalline rocks of thePaleozoic platform. Over Ellesmere Island, the magnetic anomalies are low inamplitude, suggesting a different basement composition from Greenland. Twolinear northeast oriented positive magnetic anomalies are observed on JudgeDaly Promontory. One extends along the south coast between Carl Ritter Bayand the mouth of Daly River. The second occurs over the northern end of thepeninsula and extends offshore from Cape Baird to Robeson Channel. Fromfield samples, this anomaly has been correlated with thrust fault-boundedTertiary sedimentary basins, which have increased susceptibility valuescaused by the content of basalt clasts. The thrust fault, bounding the southernedge of these basins has been mapped as a continuous feature across JudgeDaly Promontory, however, the absence of a continuous magnetic anomaly islikely the result of complete erosion of the sedimentary wedge. The amplitudeof this anomaly decreases south of Carl Ritter Bay, as a result of decreasedcontent of basalt clasts. A small magnetic anomaly at 81.3 °N, 66.8 °W alsocoincides with an isolated outcrop of Tertiary rocks, associated with a differentfault. The offshore extension of these anomalies indicates a continuity ofthe Tertiary basins northeastward to Robeson Channel and to the LincolnSea. It does not follow a simple continuous line, but appears to be broken insubsections of slightly differing directions. Similar offsets are observed in aparallel magnetic anomaly in Hall Basin suggesting crosscutting NWSEtrending faults. The magnetic anomalies and onshore geological observationssuggest that the Wegener Fault is not a simple strike-slip fault, but a complexsystem of faults and a chain of blocks and basins.