The Canadian Arctic Rift System is a major North American geological structure extending from the Labrador Sea in the southeast through Davis Strait, Baffin Bay and the Arctic Archipelago in the northwest. It consists of a series of interconnected rifts that formed during the Paleozoic, Mesozoic and Cenozoic eras. Extensional stresses along the entire length of the rift system have resulted in a variety of tectonic features, including grabens, half-grabens, basins and faults.
Development of the Canadian Arctic Rift System was accompanied by two plate tectonic episodes that originated on opposite sides of the North American plate and were propagated toward each other. Both were strongly controlled by pre-existing structures, which either guided the propagating faults or impeded their growth. The rift system is now inactive apart from minor adjustments that are indicated by occasional earthquakes in Baffin Bay and the Labrador Sea.
Geology The Canadian Arctic Rift System is a branch of the Mid-Atlantic Ridge that extends into the North American continent. It is an incipient structure that diminishes in degree of development northwestward, bifurcates at the head of Baffin Bay and disappears into the Arctic Archipelago. The rift system is mainly an extensional structure, which has allowed Greenland and Canada to rotate apart and form intervening seaways. The segment extending from the Labrador Sea to Baffin Bay is sometimes referred to as the Labrador Sea–Baffin Bay rift system or the North Atlantic–Labrador Sea rift system.
Tectonic evolution
Two rifting episodes created the Canadian Arctic Rift System. The first is referred to as the Boreal Rifting Episode which followed compression and exposure brought on by the Ellesmerian orogeny. The second is referred to as the Eurekan Rifting Episode and created most of the structures that comprise the Canadian Arctic Rift System. Both rifting episodes were active simultaneously from the Early Cretaceous to mid-Tertiary.
Boreal Rifting Episode The Boreal Rifting Episode began in the Late Devonian and emanated southeastward from the Canada Basin into the North American continent. It caused uplift of the Pearya Geanticline and Sverdrup Rim, as well as crustal extension which led to thinning and subsidence of the regional lithosphere. The rifting extended only into the area that would be occupied by the future central Queen Elizabeth Islands and was aborted there due to interfering structural trends. In the extreme west, in the Banks Island area, extension of the Boreal Rifting Episode continued uninterrupted until the mid-Tertiary.
Eurekan Rifting Episode The Eurekan Rifting Episode commenced in the Early Cretaceous as the Boreal Rifting Episode declined. Crustal stretching began at the south end of the rift system 130 million years ago, during which supercontinent Laurasia was in the process of breaking apart. Rifting began from the Atlantic Ocean then propagated northwest where the Labrador Sea started opening in the Late Cretaceous. Seafloor spreading commenced in the southern Labrador Sea 75–60 million years ago, during which Greenland moved north relative to mainland North America. This northward movement gave rise to compressive forces between northern Greenland and the Arctic Archipelago, setting the stage for the Eurekan orogeny. Seafloor spreading reached the northern Labrador Sea 60–40 million years ago and Greenland moved simultaneously past Ellesmere Island along the Nares Strait. Approximately of Paleocene separation occurred between Greenland and Baffin Island, producing oceanic crust within Baffin Bay.
With the commencement of active seafloor spreading in the Norwegian Sea during the Early Eocene, the direction of seafloor spreading changed in both the Labrador Sea and Baffin Bay. Continued spreading in the Norwegian Sea eventually separated Greenland from Eurasia, resulting in the creation of the Greenland plate and the South Greenland triple junction. By this time spreading within Baffin Bay and the Labrador Sea had slowed and became oblique, eventually ceasing between 45 and 36 million years ago.
The final phase of rifting was marked by continental extension in the mid-Tertiary. It breached the North American continent and reached the Arctic Ocean, resulting in the formation of the Parry and Nares submarine rift valleys, the Queen Elizabeth Islands and the Queen Elizabeth Islands Subplate. This rifting lasted until the Early Miocene or later.
The rift system today Little seismicity takes place on the Canadian Arctic Rift System, indicating it is now a nearly inactive structure and that the entire system is travelling as a part of the North American plate. Several earthquakes occur, but their patterns indicate tectonic forces characteristic of plate margins are not acting directly within the Canadian Arctic today. As a result, there are questions as to whether the Greenland plate should still be considered a separate plate. The present seismic activity may be mainly an expression of readjustment of existing rift structures to a regional stress field associated with post-glacial rebound.
The area between Greenland and Baffin Island is one of the most seismically active regions in eastern Canada. It was not known as a seismic zone until November 20, 1933, when an earthquake with a surface-wave magnitude of 7.3 occurred beneath Baffin Bay. This is the largest instrumentally recorded earthquake to have occurred along the passive margin of North America and possibly the largest passive-margin earthquake worldwide. Coincidentally, it is also the largest north of the Arctic Circle. In spite of its size, the 1933 Baffin Bay earthquake did not result in any damage due to its offshore location combined with the sparse population of the adjacent onshore areas. Analysis of seismograms indicate strike-slip faulting played a role in the occurrence of this earthquake. Earthquakes of magnitude 6.0 or greater have since been recorded in 1934, 1945, 1947 and 1957.
A linear belt of medium-amplitude earthquakes known as the Labrador Sea Seismic Zone is coincident with the extinct spreading axis of the Mid-Labrador Ridge. Earthquakes as large as magnitude 5.0 have been recorded along this zone since 1982.
Structure Faults The Ungava Fault Zone is a major tectonic feature of Davis Strait separating the failed Labrador Sea and Baffin Bay spreading centres. It was associated with leaky transform motion related to the northward motion of Greenland relative to mainland North America during the Paleogene. The fault zone has a length of roughly and an elongate north-northeast trend. A northern extension called the Ikermiut Fault Zone is dominated by Late Paleocene to Early Eocene thrust faults due to strike-slip movements between the Greenland and North American plates.
Situated on Bathurst Island is the Southeast Bathurst Fault Zone, a north–south trending system of normal faults forming a graben-like structure. It originally formed during the Boreal Rifting Episode, but was reactivated during a period of regional uplift and compression brought on by the Eurekan Rifting Episode. The South Cape Fault Zone to the northeast is a major east–west trending fault extending throughout much of the length of Jones Sound. It cuts across the peninsulas of southern Ellesmere Island.
Extending several hundred kilometres through Crozier Strait is the Crozier Strait Fault Zone. It lies within a north-trending anticline of the Cornwallis Fold Belt and appears to contain a lowered fault block. Bathymetric data suggest it is a possible graben structure with steep, linear, north–south margins that formed during the Eurekan Rifting Episode. The faults forming the supposed graben appear to have been guided in part by the structure of the Cornwallis Fold Belt, but probably were controlled ultimately by trends in the Precambrian crystalline basement.
The Kaltag Fault is a northeast trending structure extending along the continental margin northwest of the Queen Elizabeth Islands. It forms a boundary between the Canadian Arctic Rift System and other rifted structures to the northwest. The Kaltag acted as a transform fault with intermittent pulses of both extension and strike-slip displacement during three time intervals. Tectonism during the first time interval from Carboniferous to Permian was coeval with an early stage of the Boreal Rifting Episode. This was followed by a second time interval of tectonism from the latest Cretaceous to early Tertiary when the Boreal Rifting Episode was active and the Eurekan Rifting Episode was in an early stage of development. A third and final time interval of tectonism during the Miocene or Pliocene coincided with the final phase of the Eurekan Rifting Episode, during which the Kaltag Fault was the northwestern boundary of the Queen Elizabeth Islands Subplate.
Trending along the north side of Lancaster Sound is a major steeply dipping normal fault called the Parry Channel Fault. As much as of vertical displacement took place along this fault during the Eurekan Rifting Episode. The Northern Baffin and Admiralty faults trend along the south side of Lancaster Sound, the former of which is dominant. It extends from Admiralty Inlet in the west then trends eastward along the north coasts of Baffin and Bylot islands to Baffin Bay where it possibly connects with other rift structures.
The Prince Regent Fault is a major fault that trends along the east coast of Somerset Island. It forms the southwestern boundary of the Lancaster Aulacogen and is west of the inferred Brodeur Peninsula Fault, which presumably trends along the northwest coast of Baffin Island's Brodeur Peninsula. The main evidence of the Prince Regent Fault is the straightness of Somerset Island's east coast, but the southern end of this fault also connects with a lineament that is a known fault on land.
A series of fracture zones are present in the Labrador Sea. These include the northeasterly trending Julian Haab and Cartwright fracture zones, as well as the north-northeasterly trending Hudson, Snorri, Minna and Leif fracture zones. The change in trend corresponds with a more northerly spreading direction of the Mid-Labrador Ridge during the Eocene.
Basins Sverdrup Basin is a Carboniferous rift basin in the Queen Elizabeth Islands that formed during the Boreal Rifting Episode. It has a northeast–southwest axis of about and a width of up to , encompassing an area of .
Baffin Basin is a north-northwest trending geologic structure underlying much of central Baffin Bay. It formed as a result of seafloor spreading during the Tertiary opening of Baffin Bay around 56 million years ago. The northern extent of the basin is bounded by the Jones Sound, Lancaster Sound and Nares Strait aquatic sills below sea level while its southern extent is delimited by the Davis Strait aquatic sill roughly below sea level.
Lancaster Basin is a half-graben forming the eastern mouth of the larger Parry Submarine Rift Valley. It contains several block faulted structures and is filled with Mesozoic, Tertiary and Quaternary sediments.
Barrow Basin is a prominent topographic depression and, like Lancaster Basin to the east, represents a half-graben of the Parry Submarine Rift Valley bounded on the north by high-angle normal faults. Non-marine Tertiary sediments up to approximately thick exist in the Barrow Basin.
Lady Franklin Basin is one of the deepest basins offshore West Greenland. It was established during Early Cretaceous rifting and lies within a fault zone delimiting the northern end of the Labrador Sea. A thick succession of Cretaceous and Cenozoic sediments occupies the Lady Franklin Basin.